Printer with face-down delivery of collated printed sheets at the top, and a manually removable PC/developer cartridge

Abstract

A compact printer has a sheet feeder positioned at its front wall and electrophotographic components arranged along a sheet moving path for receiving a sheet from the sheet feeder and for exposing, developing, then transferring a toner image onto the sheet. At its rear side, the printer has an image fixing unit and a discharge portion for discharging the sheet to a side output tray or onto the top wall of the printer. The discharge portion is provided with a detachably hinged, sheet turning apparatus when it is desired to discharge sheets onto the top wall, or with a detachably hinged cover with a rear opening to discharge sheets onto a rear side output tray.

Description

This or frame 35 which supports the record unit 23 and has a rib 35a that can facilitate grasping by hand. The receiver 35 includes a pair of side plates 36, in which a groove 37 is formed adjacent to the sleeve 34 and extend in a direction perpendicular to the length of the receiver. The shaft 38 which carries the driver roller 13 of the record unit 23 is received in the groove 37, thus positioning the record 11 with respect to the developing sleeve 34. It will be seen that the record unit 23 is merely placed on top of the bottom plate 39 of the receiver 35, with the shaft 38 being received in the groove 37, and hence is freely movable in the vettical vertical direction even though its movement in the lateral direction is constrained. When the record unit 23 is placed on top of the bottom plate 39, only the bottom projections 29, 30 extending from the support plates 26 of the record unit 23 bear against the bottom plate 39, thus avoiding any damaging effect upon the record 11. In its free end, the receiver 35 is formed with a horizontal groove 40, which serves positioning the developing unit 31 on the body of the printer. As shown in FIGS. 2 and 4, the rear ends of the side plates 36 are interconnected by a stay 73 for strengthening purpose.

FIG. 7 shows the record unit 23 and the developing unit 31 assembled together. In FIG. 7, it will be seen that the bearing 41 is shown as mounted on the shaft 38 of the drive roller 13 and engages the groove 37 formed in the receiver 35 of the developing unit 31. It will be understood that the use of such bearings is conventional and is available anywhere in the arrangement.

When placing the record unit 23 on the receiver 35, a touch of a finger of an operator with the surface of the record will modify the photosensitive response of the record in the region where the finger is touched. Hence, the unit 23 must be carried by fingers which are inserted into the slots 26a. To permit such mounting, notches 36a are formed in the side plates 36 to provide relieved areas for the fingers.

Referring to FIGS. 11, 12 and 19, the side plates 36 of the receiver 35 are provided with a first member 49 and a second member 50, respectively. The first member 49 is secured to the side plate 36 by set screws 51, and is L-shaped in section as indicated in FIG. 19 and carries a pair of spacers 52 having a control surface 52a on its opposite ends. The upper end portion of the control surface is bevelled to provide a guide surface 52b which is utilized when mounting the record unit 23.

In the example shown, the second member 50 is similarly shaped as the first member 49, and is secured to the other side plate 36 by set screws 53. It comprises a guide member 54 carrying a pair of guides 54a on its opposite ends which are located opposite to the spacers 52, and a resilient member 55 which is clamped together with the guide member 54 to the other side plate 36. In the arrangement shown, a pair of resilient members 55 are provided. At least the resilient member 55 is formed of an electrically conductive material for electrical contact with the receiver 35, which is in turn connected to the electrical ground of the printer through a leader 56 (see FIG. 9). In the example shown, the resilient member 55 comprises a metal leaf spring, but may also be formed by a coiled metal spring.

The position of the record unit 23 relative to the receiver 35 is determined by the width Wc of the spacer 52 which is in turn determined in consideration of other devices disposed around the record 11. The projection length of the resilient member 55 is chosen such that the width Wa of the record unit 23, as measured across the support plate 26, is greater than the distance Wb between the control surface 52a and the distal end 55a of the resilient member in its free condition. It will be seen that the distance between the control surface 52a and the guide 54a is greater than the width Wa by a clearance Wd, the magnitude of which is chosen to permit an easy attachement or detachment of the record unit 23 with respect to the receiver 35.

When the record unit 23 is allowed to fall down over the receiver 35 as shown in FIG. 11, the pair of support plates 26 move down between the guide surfaces 52b and the guides 54a, and one of the support plates 26 is resiliently urged by the resilient member 55 to cause the other support plate 26 to abut against the control surface 52a, as shown in FIG. 12. Thus, the record unit 23 is positioned by moving down while flexing the resilient member 55 to cause the opposite support plate 26 to be resiliently urged against the control surface 52a until the projections 29, 30 (see FIG. 5) bear against the bottom plate 39. At the same time, the conductive member 55 achieves an electrical connection with the receiver 35. It will be seen that when removing the record unit from the receiver 35 of the developing unit which serves as a support unit, the resilient members 55 are again flexed, thus facilitating the removal.

In the embodiment shown in FIGS. 11 and 12, two spacers are used, one being the spacer 52 which is fixed and having the control surfaces 52a and another or guide member 54 having guides and which is associated with the resilient members 55. However, the second spacer or guide member 54 may be omitted, using only the resilient member 55 to form the second member. In this instance, the resilient member 55 may be electrically conductive, and it is desirable that it is located to bear against the central portion of the support plate 26, as viewed in the direction of movement of the record 11. Even such a simplified arrangement properly positions the record crosswise as a result of the support plates 26 being controlled by a pair of control surfaces 52a and a single resilient member while simultaneously achieving an electrical connection with the receiver.

The record in the form of the endless belt has its upper run 11a disposed to be guided by the top plate 28 of the support plate, and the rubbing action therebetween gives rise to static electricity, which is reflected by adhering of the record to the top plate 28 to cause an increased loading on the drive. Even a non-uniform feed rate of the record may result as a result of a slip occurring between the record and the drive roller 13. Consequently, it is essential that the support plates for the record be securely connected to the ground.

The record 11 comprises a base layer formed by flexible rubber or synthetic resin, a conductive layer formed by a thin aluminium film which is evaporated thereon, and a record layer or a photoconductive layer formed on top of the conductive layer. Additionally, it may include an insulating layer which occurs the photoconductive layer.

Accordingly, one lateral edge of the record 11 is stipped to expose the conductive layer, which is disposed for contact with a brush which is in turn connected to the ground. Such exposed portion may be applied with a reinforcing agent.

In FIG. 8, it will be noted that one lateral edge of the record 11 is formed with an exposed portion 68 where the conductive layer is exposed. The exposed portion 68 is disposed for contact with the free end of a brush 69 which is formed by conductive fibers. The brush 69 is supported by the side plate 67 in an electrically conductive manner, through a bracket 70. Referring to FIG. 2, it will be seen that the location of the brush 69, as viewed in the direction of movement of the record 11, is chosen to be on the tensioning side of the record 11 and in a region close to the drive roller 13 where the record travels straightforward. The choice of such location is a result of the recognition of the following problems: When the brush is disposed for contact with the endless belt or record 11 on the free or relaxing side thereof, undulations in the running belt cause a change in the condition of contact with time, resulting in a variation in the contact resistance and hence the impedance of the conductive path. The record assumes a most stable condition around the belt roller, but if the brush is disposed around the curved portion of the belt, the individual fibers which form the brush contact the record at mutually different angles, preventing an electrically effective contact from being achieved in a stable manner. Because the record unit 23 is detachable with respect to the printer and is assembled integrally with the developing unit 31, the belt portion around the follower roller 12 is left for utilization. However, the roller 12 is displaceable in order to permit a tensioning of the record, so that there is not obtained a fixed distance between the brush and the record, again preventing a stabilized conductive path from being formed.

As a result, it will be seen that the only location left for the record to assume a stable position will be close to the drive roller 13 having its shaft 38 fixedly mounted and on the tensioning side 11a where the belt assumes a straight configuration and where oscillations caused by the movement of the belt is minimized. In this manner, the relative position of the record 11 with respect to the brush is maintained constant, allowing a stabilized conductive path to be maintained.

As shown in FIG. 8, the other lateral edge of the record 11 is formed with a sub-scan sync mark 71, the significance of which

be described later. As shown in FIG. 8, a sub-scan sync detector 72 is fixedly mounted on the side plate 60, so as to read the mark 71.

Record/Developing Unit

The developing unit 31 which carries the record unit 23 in this manner is mounted so as to permit its insertion into or withdrawal from the printer. As shown in FIG. 9, the printer is provided with a guide plate 57 which cooperates with the top of the vessel 33, and with another guide plate 56 which cooperates with the bottom plate 39 of the vessel 33 of the developing unit 31, and the developing unit 31 is inserted into the printer within a space confined by these guide plates. As shown in FIG. 10, the printer is provided with a pair of guide plates 58 which cooperate with the opposite sides of the developing unit 31 to locate it crosswise or the record, with respect to the body of the printer. The printer also includes a side plate 60 carrying a pin 59 which is used to position the developing unit 51 as it is inserted. The pin 59 is adapted to engage the groove 40 (FIGS. 5 and 7) formed in the free end of the developing unit for positioning it. Brackets 61, 62 are suitably located on the side plates 60, 67 (FIG. 8) of the printer for supporting the bearings on the rotary shaft 38 of the drive roller 13 and bearings 42 on the rotary shaft 12a of the follower roller 12 of the record unit as the latter is inserted. These brackets cooperate with the respective rollers to position the record 11 in the vertical direction. In this manner, both of the rollers 12, 13 and the developing sleeve 34 are substantially aligned with each other in the horizontal direction and parallel to the direction of insertion. While the brackets 62 may be fixed to the side plates 60, 67 (FIG. 4), it is necessary that at least that bracket 62 which is mounted on the side plate 60 be rockably mounted where a belt offset correcting mechanism is to be provided.

It will be seen that the supporting arrangement described above is provided with a variety of positioning means, so that when the record/developing unit 5 (FIG. 7) including the record unit 23 and the developing unit 31 is inserted into the printer to a given location therein, a desired relative position of the unit 5 with respect to other members and devices disposed within the printer can be reliably and easily assured. Also, by withdrawing the developing unit 31 out of the printer as required, a replenishment of toner into the vessel 31 or a replacement of the record 11 is greatly facilitated.

As mentioned previously, the record/developing unit 5 comprises a unitary construction including the developing unit 31 and the record unit 23 which is supported therein. It is necessary to remove the unit out of the printer at regular or irregular intervals for a routine maintenance purpose such as the replenishment of developer or a change of the endless belt or record, for example.

Accordingly, in accordance with the invention, the degree of withdrawal of the record/developing unit 5 is selectively varied depending on the kind of maintenance work to be performed.

Referring to FIG. 40, intermediate its length, the guide plate 56 is formed with a slot 56a in which a detent piece 121a of a stop 121 is disposed. As shown in FIG. 4, the stop 121 is fixedly mounted on a shaft 122 which extends across the side plates 60, 67. One end of the stop 121 is engaged with a spring 123, whereby it is urged to rock in a direction to cause the detent piece 121a to project into the slot 56a. Fixedly mounted on one end of the shaft 122 is one end 124a of an operating arm, the other end of which fixedly carries an operating knob 125, which extends externally of the printer as shown in FIG. 1. It is to be noted that the bottom plate 39 of the unit is formed with an engagement slot 39a.

When the record/developing unit 5 is mounted in place within the printer as shown in FIG. 40, the stop 121 bears against the lower surface of the bottom plate 39. As the unit 5 is pulled in the direction of an arrow from this position, the detent piece 121a slides along the lower surface of the bottom plate 39 until it engages the slot 39a, as shown in FIG. 41, whereupon a further withdrawal is prevented. In the position shown in FIG. 41, the vessel 33 is pulled out the printer, and the top cover 33a thereof can be either opened or closed, thus enabling a replenishment of developer. It will be noted that the record unit 23 remains within the printer at this time, thus preventing the record 11 from being exposed to the indoor illumination to cause a degradation of the response thereof.

When the record 11 is to be changed, the unit 5 is pulled to the position shown in FIG. 41, whereupon the operating knob 125 is pushed to cause the operating arm 124 to rock so that the detent piece 121a on the step 121 is retracted out of the engagement slot 39a. Subsequently, the unit may be pulled out of the printer. When replacing the unit in which the record is changed, into the printer, the tapered portion of the stop 121 is urged by the front edge 39b (FIG. 12) of the bottom plate 39 to move angularly, thus allowing a mounting operation without presenting any resistance thereto.

In the arrangement of FIG. 40, the stop 121 is engaged with or disengaged from the bottom plate 39 of the unit 5. Alternatively, the stop may cooperate with the side plate 36 as shown in FIG. 42. In this instance, a stop 36 is mounted on a shaft 126 adjacent to the side plate 36. The stop 36 is urged by a spring 128 to cause its detent piece 127a into abutment against the side plate 36. The stop 127 includes an arm, the end 127b of which is disposed in abutment against one end of an operating slider 129. The slider 129 is formed with guide slots 129a in which stationary pins 130 are loosely fitted to permit a sliding movement thereof. The side plate 36 is formed with an engagement slot 36b (FIG. 43). As the unit 5 is pulled in a direction indicated by an arrow (FIG. 42) until the detent piece 127a moves into the slot 36b, a further withdrawal of the unit 5 is prevented at such position shown in FIG. 43. This position of the unit corresponds to the replenishment position illustrated in FIG. 41. As the stop 127 locks the unit, it simultaneously drives the operating slider 29 to cause an operating knob 129b to project externally of the printer. When it is desired to withdraw the unit completely out of the printer, the knob 129b may be pushed inward, as viewed in FIG. 43, causing the stop 127 to be disengaged from the slot 36b, whereupon a further withdrawal of the unit is enabled.

It will be seen that since a change of a record is performed by a user who is unskilled with such operation, it is hazardous to start the operation of a printer before it is confirmed that the record is properly loaded. It is frequently possible that only the support member may be loaded without mounting the record in place or the support member may be loaded at an improper position.

A loading operation of the record by the use means that a shakedown run is inhibited. In other words, a satisfactory image must be formed from the beginning after the record has been loaded. However, fine dirt may be deposited on a fresh record during its storage, or the record may bear static electricity. As a result, a first copy obtained may be disturbed in its image quality. In consideration of this, the invention provides an arrangement which allows a confirmation to be made that a change of the record has been properly done, thus assuring the formation of a satisfactory image from the beginning.

In FIG. 7, the developing vessel 33 is partly formed with a plate-shaped piece 33c, and a photo-sensor 400 of transmission type is disposed within the printer. The sensor is located so as to be engaged by the piece 33c whenever the record/developing unit 5 is properly inserted within the printer as indicated in FIG. 2.

A photo-sensor 401 of reflection type is disposed within the printer for detecting the presence or absence of the record 11 when the record/developing unit 5 is properly loaded. Since the sensor 401 detects light reflected from the record 11, it is located immediately behind the cleaning station as indicated in FIG. 2, thus operating in a region where a contamination of the record is minimized.

As indicated in FIG. 92, the photo-sensor 401 of reflection has its output connected to the input of AND gate A6 while the photo-sensor 400 of transmission type is connected through inverter INV3 to the input of the AND gate A6, the output of which is connected to an associated control circuit. When the record/developing unit is loaded into the printer, the sensor 401 detects the presence of the record 11 and produces a signal. When the record is properly loaded, the piece 33c engages the sensor 400 to cause the latter to produce a signal. The signal from the sensor 400 indicates that the unit 5 has been properly loaded and hence such signal can be applied to the control circuit to condition the operation of the printer in accordance with the presence of this signal. When the record unit 23 is not mounted or when the unit 5 is mounted without properly placing the record 11 therein, the printer is inoperable, thus preventing a malfunctioning. The same applies when the unit 5 is not properly loaded.

When the unit 5 which carries the record 11 is properly loaded, the control circuit produces a signal which allows the record unit 23 to be driven for a given time interval in preparation to the formation of an image, thus performing a neutralization and a cleaning operation of the record 11 to assure that a satisfactory image may be formed from the very first copy.

In other words, a change of the record can be simply performed by any one who has no skill or knowledge. Alslo, whenever a fresh record is loaded into the printer, the control circuit produces a signal which instructs the printer to perform a series of given operations in preparation to the formation of an image during a given time interval. Thus, it is assured that a satisfactory image is formed for the very first copy.

Developing Unit

The printer according to the invention adopts a magnetic brush developing process in which a magnetic developer is used to convert an electrostatic latent image into a visual image.

The printer of the invention includes a developing unit incorporating a developing process which prevents such white streaking form occurring. In this developing process, an electrostatic latent image is developed while establishing a distribution of magnetic field which prevents the existence of the developer in a region between a location where a magnetic developer is supplied to the sleeve and the developing station and extending parallel to the axis of the sleeve whenever the sleeve remains stationary. Also, in this developing process, during the development of an electrostatic latent image, a distribution of magnetic field is established so that the developer does not exist in a region between a location where the thickness of the developer on the sleeve is controlled by a control member and the developing station and extending parallel to axis of the sleeve whenever the sleeve remains stationary.

When the sleeve remains at rest, the configuration of the magnet or magnets disposed internally therein may be changed to cause the configuration of the magnetic brush formed on the sleeve to be varied under the influence of the magnetic force from the magnets. Magnets fixedly mounted within the sleeve are normally arranged so that adjacent magnets present poles of dissimilar polarities. However, in certain instances, two adjacent magnets are arranged to present poles of similar polarity to produce a crowd of developer by driving the magnetic developer which has been adhering to the sleeve surface toward the record.

To achieve the object of the invention, of the magnets which are disposed within the sleeve for use as means for generating a magnetic field, adjacent magnets located between a location where the developer is supplied and the developing station are disposed to present poles of similar polarity. The purpose of such disposition is not to drive the developer on the sleeve outwardly or to produce a crowd of developer. Driving the developer is undesirable in causing the problem of dispersion of the developer. In accordance with the invention, a distribution of magnetic field is produced to create a region extending parallel to the axis of the sleeve where the developer is absent whenever the sleeve remains at rest, by providing magnetic poles of similar polarity between the developer supply location and the developing station or between the location where the thickness of the developer layer on the sleeve is controlled and the developing station, without causing the developer to be driven.

In FIG. 34, the developing unit 16 comprises a non-magnetic cylindrical developing sleeve 34 which is disposed for rotation in the counterclockwise direction, and a plurality of magnets 111, 112, 113, 114, 115 and 116 which are arranged within the sleeve 34 and forming together means for generating a magnetic field. The sleeve 34 is disposed in the opening of the developer vessel 33 which contains a supply of developer. The developer used comprises a one-component developer formed by magnetic toner alone. The vessel 33 has a side wall 33b on the developer discharge side on which a developer control member 117 is mounted. The control member 117 is located opposite to the magnet 116. The magnet 111 presents main developing poles, and is centrally recessed as shown. The magnet 111 is disposed at a location which is slightly upstream, as viewed in the direction of rotation of the sleeve, 34, of a point on the sleeve which is closest to the record 11. Other magnets are disposed so that they present N- and S-poles alternately. As the sleeve 34 rotates, the developer is carried out of the vessel 33 in the direction of rotation of the sleeve 34. The provision of the control member 117 in the outlet opening removes an excessive amount of developer on the sleeve, thereby forming a developer layer of a given thickness. In this manner, a magnetic brush having a tuft of a given height is formed on the sleeve.

As mentioned previously, the main developing magnet 111 is centrally recessed. In terms of the magnetic strength at the surface of the sleeve 34, the magnitude of the flux corresponding to the opposite edges of the magnet will be approximately 1,200 Gauss while the magnitude of the flux corresponding to the central recess will be about 800 Gauss. The use of such a magnet enables the developer to be absent in a region of the sleeve 34 which corresponds to the central recess of the magnet when the sleeve 34 ceases to rotate. As indicated in FIG. 35, a region 118 is defined where the developer is absent and which extends parallel to the axis of the sleeve 34. The region 118 must be located within an extent R shown in FIG. 34. Specifically, such region must be located intermediate the location where the developer is supplied onto the sleeve and the developing station. As will be noted from FIG. 35, the region 118 where the developer is absent is slightly offset on the upstream side, as viewed in the direction of rotation of the sleeve, with respect to the developing station which is shown by reference character T in this figure.

Assuming that the space between the control member 117 and the sleeve 34 is plugged with foreign particles, the developer fails to be supplied to such area of the sleeve. Accordingly, an area 119 is formed on the sleeve 34 where the developer fails to be supplied, as shown in FIG. 35. However, the existence of the region 118 where the developer is absent before the arrival of the developer at the developing station T substantially avoids the insufficient supply caused by the control member 117 as a result of the absence of the developer axially all over the sleeve in a defined region. This is attributable to the facilitated migration of the developer to most stable position. As a result, any significant degree of insufficient supply of the developer is removed all over the full width of the developing station T.

When such developing unit is used to convert an electrostatic latent image on the record 11 into a visual image to thereby produce a copy, it is found that the occurrence of white streakings which result from the insufficient supply of developer is substantially eliminated and any remaining influence is minimal.

In the described magnetic brush developing unit, the main magnet 111 is replaced by a pair of magnets 111A, 111B of similar polarity and disposed close to each other, as shown in FIG. 36. As before, the developer is absent in a region on the surface of the sleeve 34 which corresponds to the spacing between the magnets 111A, 111B when the sleeve 34 ceases to rotate. The region where the developer is absent is indicated by broken line circle. A similar result is ottained as before when using this developing unit for the developing step.

In the arrangement of FIG. 36, a group of magnets disposed within the sleeve 34 is rotated through about 60° clockwise, as indicated in FIG. 37. The pair of adjacent magnets 111A, 111B of similar polarity are then located opposite to the control member 117. It is found that a similar result as before is obtained so long as the region where the developer is absent on the sleeve 34 is situated between the developing station and the developer control member.

In an example shown in FIG. 38, a developing unit is provided for developing an electrostatic latent image in which two regions are formed between the developer control member 117 and the developing station where the developer is absent. At this end, three magnets 111A, 111B and 111C presenting magnetic poles of similar polarity are disposed at an equal spacing intermediate the developer control member 117 and the developing station. The occurrence of any area on the sleeve where the toner is insufficiently supplied in the region of the developer control member 117 cannot cause a white streaking, since as the developer is carried through the two regions where the developer are absent, such area is replenished with toner.

Another example is shown in FIG. 39 which is similar in principle of operation to the arrangement of FIG. 36, but in which a cylindrical magnet 120 presenting N- and S-poles alternately around its periphey is substituted for the rod magnets to serve as means for generating a magnetic field. The cylindrical magnet 120 affords advantages that the location of magnetization can be arbitrarily chosen and that the unit can be assembled to establish a spacing of high precision between the sleeve 34 and the surface of the magnet.

In one practical implementation, a magnetic toner having an average particle diameter of 10 to 13 microns is used, and linear speed of the records is 111 is chosen to be 70 mm/sec and the linear speed of the non-magnetic sleeve is chosen to be equal to 210 mm/sec, whereby a developed image of good quality is obtained which is free from any white streaking. Representing the linear speed of the record by Vp and that of the sleeve by Vs, good results are obtained in a range of the ratio Vs/Vp=1.5 to 4∅ It is found that good results are obtained when Vs has a value from 50 to 300 mm/sec, preferably from 150 to 300 mm/sec.

In the above description, the use of a single developer control member has been assumed. Where a plurality of such control members is used, it is only necessary that at least one region be magnetically formed where the developer is absent between the developing station and one of the control members which is closest to the developing station.

The printer of the invention is provided with a developing unit which overcomes described disadvantages and which is capable of removing any residual toner on the sleeve without contact therewith while preventing a damage to the sleeve and an agglomeration of toner, thus enabling an image of a stabilized, good quality to be obtained.

Referring to FIGS. 2 and 34, there are disposed within the developer vessel 33 a first agitating member 190 mounted on an agitator shaft 189, and a second agitating member 191 which is disposed out of contact with the developing sleeve, but extending parallel thereto. The second agitating member 191 is formed by a magnetic material and is in the form of a screw shaft having a thread 192, as shown in FIG. 58.

A mechanism 193 for reciprocately rotating the second agitating member 191 and for reciprocately translating it relative to the developing sleeve 34 is interposed between the agitator shaft 189 and the second agitating member 191. As shown in FIG. 59, the mechanism 193 comprises a circular flange 194 fixedly mounted on the end of the shaft 189, a pin 195 fixedly mounted on the flange 194, and a forked lever 196 having its one end fixedly mounted on one end of the second agitating member 191 and having its fork disposed in slidable fitting engagement with the pin 195. As the shaft 189 rotates in one direction, such rotating motion is converted by the lever 196 into a reciprocately angular motion of the second agitating member 191, which rotates through an equal angle in the forward and the reverse direction.

In the developing unit mentioned above the magnetic line of force from the second agitating member 191 is concentrated into a narrow space between the thread 192 and the sleeve 34 where part of the toner is retained, causing another portion of the toner which is subsequently fed to such space to be laterally displaced, as indicated by an arrow d in FIG. 58, thus achieving a lateral agitating effect. The angular motion of the second agitating member 191 causes a movement of the toner in a direction indicated by an arrow e, whereby the toner retained between the sleeve 34 and the agitating member 191 is gradually replaced by another portion of the toner, removing any residual toner from the sleeve 34 and agitating it with a remainder of the toner. It is to be noted that if the second agitating member 191 is caused to rotate in only one direction, the toner will be offset to one side within the vessel 33, producing an adverse influence upon the developing step. In addition, such rotation would urge the toner, promoting an agglomeration thereof. The reciprocately angular movement of the second agitating member 191 avoids the likelihood that the same toner may be maintained retained between the member 191 and the sleeve 34, and an angular motion at a low rate which is equal to or less than several revolutions per minute prevents the occurrence of any agglomeration of tone, thus assuring a removal of toner from the sleeve 34 and agitation thereof.

It should be understood that the configuration of the second agitating member 191 is not limited to that of a screw shaft as indicated in FIG. 58, but may be constructed as shown at 191A in FIG. 60. In this instance, the second agitating member 191A includes a shank 191Aa carrying a plurality of axially spaced circular flanges 192A. In this instance, it is necessary that the member 191A be subject to a reciprocately translation relative to the developing sleeve 34 at a low rate. In this instance, the shank 191Aa need not be rotated. As a further alternative, the second agitating member may be configured with chevronshaped projections in an array parallel to the axis of the developing sleeve 34 and disposed for axial translation in a reciprocately manner. It need not be rotated is in the embodiment shown in FIGS. 58 and 59. Thus, the only requirement is that the toner be retained between the chevron-shaped projections and the sleeve so as to produce the similar functioning as described in the above embodiment.

It will be appreciated that the provision of the second agitating member which is located close to but out of contact with the developing sleeve and disposed for relative reciprocately motion with respect to the developing sleeve assures a removal of any residual toner from the developing sleeve and a subsequent agitation without accompanying a contact with the sleeve, thus preventing a damage to the sleeve and an agglomeration of toner while maintaining the printer in a condition which is capable of producing an image of good,stabilized quality.

Offset Detecting Means

The invention avoids the described difficulty by providing a belt offset compensating mechanism including offset detecting means and offset control means which provides a correction for the offset of the belt. The offset detecting means can be constructed according to a first and a second approach. Considering the first approach initially, the offset detecting means according to the first approach comprises a combination of a photo-interrupter including a light source and a light receiving element, and a light shield member which is movable to intercept the light path between the source and the element, thus allowing an offset in the record to be detected.

FIG. 20 shows a first embodiment of the offset detecting means according to the first approach. As indicated by numeral 74 in FIGS. 2 and 4, the detecting means 74 is disposed in opposing relationship with a region of the record 11 which extends around the roller 12, such region being hereafter referred to as a curved region.

In FIG. 20, the offset detecting means 74 comprises a support member 76 attached to a bracket 75 which is disposed in front of the record 11. The support member 76 includes a pivot 76a which rotatably carries a detection feeler 77. The detection feeler 77 includes a contact finger 77a which is located on one side of the support member 76 that is nearer the record 11, and the other side of the feeler is formed as a light shield 77b. The feeler is disposed so that the free endof the contact finger 77a can abut against the edge of the record 11. A photo-interrupter 78 is disposed on the path of angular movement of the light shield 77b.

FIG. 21 is a cross section taken along the line X--X shown in FIG. 20, illustrating the arrangement of the photo-interrupter 78. As shown, the photo-interrupter 78 includes a light source 79 and light receiving element 80, and produces an output signal in accordance with the amount of light from the source 79 which is received by the element 80. As shown, the light shield 77b is angularly movable so as to intercept the light path between the source 79 and the element 80.

In a region below the support member shown in FIG. 20, an L-shaped stop 81 is mounted on the bracket 75 in order to limit the rotation of the contact finger 77a in the counterclockwise direction. While not shown, tension means such as a coiled torsion spring or leaf spring is mounted on the detection feeler 77 to urge it to rotate in the counterclockwise direction, as viewed in FIG. 20. Consequently, the contact finger 77a is urged against the stop 81 unless it is engaged by the edge 11c of the record 11.

The operation of the offset detecting means 74 will be described. During a normal record operation, the record 11 travels in a direction indicated by an arrow A, with its edge indicated by a line d in FIG. 20. There occurs no contact between the contact finger 77a and the edge 11c under this condition, and hence the light shield 77b cannot intercept the light path from the light source 79 to the light receiving element 80 of the photo-interrupter 78. Accordingly, the photo-interrupter 78 produces an output signal, the magnitude of which depends on the amount of light passing through such path. However, the record 11 is offset in a direction by an arrow C, and the edge of the record 11 reaches a position e shown in FIG. 20, the edge 11c initially bears against the contact finger 77a at a position I (shown in solid line), whereupon the finger 77a moves clockwise about the pivot 76a asas the record 11 continues to shift in the direction C, with consequence that the finger 77a reaches its position II shown in broken lines in FIG. 20. Simultaneously with the angular movement of the contact finger 77a, the light shield 77b also moves angularly from its solid line position I' to its broken line position II', thus intercepting the light path between the source 79 and the element 80 of the photo-interrupter 78. When the light path is thus interrupted, a change occurs in the output signal from the photo-interrupter. In this manner, an offset occurring in the record 11 in the direction C is indicated by a change in the output signal from the photo-interrupter 78.

On the other hand, if the record is offset in the opposite direction or in a direction indicated by an arrow D shown in FIG. 20, such offset can be detected by another detecting means (FIG. 4) which is identical with the offset detecting means 74 mentioned above and which is disposed to cooperate with the other edge 11d (FIG. 4) of the record 11.

A change occurring in the output signal from the photo-interruptercontained in both of the offset detecting means is transmitted through a control circuit, to be described later, and which provides a suitable correction for the offset of the record 11.

The offset detecting means is disposed so as to be opposite to the curved region of the record 11, and the reason herefor will now be described with reference to the drawings. FIG. 22 shows the record 11 in the form of an endless belt, and rollers 12, 13 around which the record extends. In FIG. 22, the the curved region of the belt mentioned above is indicated by a both-ended arrow E. There is another curved region E₁ corresponding to the other roller 13. In regions located between these curved regions and which are indicated by bothended arrows G, G₁, the record is linear. Accordingly, regions G, G₁ will be referred to as linear regions. Assuming that a force is externally applied to the edge of the record 11 in a direction to cause an offset thereof in a direction perpendicular to the direction of drive A, it will be seen that the record 11 is easily susceptible to deformation in the linear regions G, G₁ but is less susceptible to deformation in the curved region E. Accordingly, it is preferred to choose the curved region E where the susceptibility to deformation is reduced as compared with the linear regions G, G₁ for bringing a contact finger into contact therewith. In this manner, the angular movement of the contact finger is stabilized while minimizing deformation of the edge of the record 11.

FIG. 23 shows offset detecting means according to a second embodiment which is based on the first approach initially mentioned. A amjor difference over the first embodiment shown in FIG. 20 resides in the fact that offset detecting means 82 shown includes a pair of photo-interrupters 83a, 83b which are suitably spaced in a region of angular movement of the light shield 77b, and the stop 81 shwwn in the first embodiment is removed. In this arrangement, resilient means, not shown, urges the contact finger 77a so that it is maintained in abutment against the edge of the record 11 and moves angularly as the edge shifts. By way of example, if the edge of the record 11 shifts from its solid line position d to its broken line position e, the contact finger 77a moves angularly from its solid line position I to its broken line position II. Conversely, when the edge of the record 11 shifts to a position indicated by phantom lines f, the contact finger 77a moves angularly to phantom line position III. As the contact finger 77a moves angularly to either position II or position III, the light shield 77b moves angularly to either position II' or position III', respectively. The photo-interrupters 83a, 83b are arranged such that the light path of the phot-interrupter 83a is intercepted when the light shield 77b reaches the position II' while the light path of the photo-interrupter 83b is intercepted when the light shield 77b reaches the position III'. In other respects, the arrangement is similar to that of the first embodiment shown in FIG. 20, and accordingly corresponding parts are designated by like numerals and will not be described.

In this embodiment, the record 11 normally travels in the direction of the arrow A with its edge aligned with the line d during the normal record operation. Under this condition, the light shield 77b intercepts the light path of neither photo-interrupter 83a nor 83b, which therefore produces an output signal depending on the amount of light passing through the light path thereof. However, if the record 11 is offset in the direction C and the edge thereof shifts to the position e, the contact finger 77a moves angularly to its position II and the light shield 77b simultaneously moves angularly to its position II'. In this position, the light shield intercepts the light path of the photo-interrupter 83a, producing a change in the output signal therefrom. On the other hand, if the record 11 is offset in the direction D and its edge shifts to to the position f, the contact finger 77a moves angularly to its position III and the light shield 77b simultaneously moves angularly to its position III'. In this position, the light shield 77b intercepts the light path of the photo-interrupter 83b, causing a change in the output signal therefrom. In this manner, the single offset detecting means 82 may be utilized to detect either offset of the record 11 in the direction C or D, in terms of a change in the output signal fom either photo-interrupter 83a or 83b. As before, such change in the output signal from the photo-interrupter 83a or 83b is transmitted to belt offset control means to be described later.

FIG. 24 shows a third embodiment of offset detecting means. In this embodiment, offset detecting means 84 comprises a slide bar 85 disposed in opposing relationship with or in front of (or to the left, as viewed in FIG. 24) of the roller 12 associated with the record 11 and extending in the axial direction of the roller 12 and having a length which slightly exceeds the width of the record 11. The slide bar 85 is centrally formed with a light shield 86 which projects forwardly, or to the left as viewed in FIG. 24, and is also provided with a pair of contact fingers 87a, 87b on its opposite ends which extends rearwardly or to the right as viewed in FIG. 24. The slide bar 85 is formed with a pair of spaced, axially elongate slots 85a, 85b, which are fitted over stationary pins 88a, 88b, respectively. The cooperation between the pins 88a, 88b and the slots 85a, 85b provide a guiding action which allows the slide bar 85 to move in a direction parallel to the roller 12 and through a stroke corresponding to the length of each slot 85a, 85b. The direction of such movement is indicated in FIG. 24 by arrows C' and D'. The projection length of the contact fingers 87a, 87b is chosen to permit the abutment of either edge 11c or 11d of the record 11 against such fingers as the record 1 shifts in a direction indicated by arrow C or D. It will be seen that the light shield 86 moves simultaneously with the slide bar 85 as the latter moves in either direction C' or D'. A pair of photo-interrupters 89a, 89b are juxtaposed along a direction parallel to the direction of movement of the light shield 86 so as to be located within along a direction parallel to the direction of movement of the light sheild 86 so as to be located within the extent of movement of the light shield 86.

In operation, when the record 11 is offset in the direction C, its edge 11c bears against the contact finger 87a to urge it, thus causing the slide bar 85 to move in the direction C'. Simultaneously, the light shield 86 moves in the direction C', with the light shield intercepting the light path of the photo-interrupter 89a, whereupon a change is produced in the output signal therefrom. In this manner, an offset of the record 11 in the direction C is indicated by a change in the output signal from the photo-interrupter 89a. On the other hand, an offset of the record 11 in the direction D is indicated by a change in the output signal from the photointerrupter 89b.

FIG. 25 shows a fourth embodiment of offset detecting means which is constructed on the basis of the first approach. In FIG. 25, offset detecting means 90 shown comprises an angularly movable arm 91 disposed in front, or to the left, as viewed in FIG. 25, of, the curged region of the record 11 corresponding to the roller 12 and extending in a direction parallel to the axis of the roller 12 and having a length which slightly exceeds the width of the record 11. At its center, the arm 91 is pivotally mounted on a pin 92. On its opposite ends, the arm 91 carries a pair of contact fingers 93a, 93b which extend rearwardly, or to the right, as viewed in FIG. 25. The projection length of the contact fingers 93a, 93b is chosen to permit the abutment of either edge 11c or 11d of the record 11 against a corresponding one of the contact fingers whenever the record 11 is offset in a direction indicated by either arrow C or D. A pair of photointerrupters 94a, 94b are disposed forwardly, or to the left, as viewed in FIG. 25, of the arm 91, generally in alignment with the opposite ends thereof. These photo-interrupters 94a, 94b, are constructed in the same manner as the photo-interrupter 78 shown in FIG. 21. It is to be understood that the opposite ends of the arm 91 are formed to function as light shields 91a, 91b having a thickness wihich is less than the lenght of optical path in respective photo-interrupters 94a, 94b. Accordingly, as the arm 91 moves angularly through a given stroke, the light shield 91a or 91b is capable of intercepting the light path of the associated photo-interrupter, in the same manner as illustrated in FIG. 21.

In operation, when the record 11 is offset in the direction C, its edge 11c bears against the contact finger 93a to urge it to cause a clockwise movement of the arm 91. Consequently, the arm 91 reaches a condition which is indicated by phantom lines. In this position,the light shield 91a intercepts the light path within the photo-interrupter 94a, thus producing a change in the output signal therefrom. In this manner, an offset of the record 11 in the direction C is indicated by a change in the output signal from the photo-interrupter 94a. Similarly, an offset of the record 11 in the direction D is indicated by a change in the output signal from the other photo-interrupter 94b.

In each of the embodiments described above, the combination of a photo-interrupter and a light shield may be replaced by a combination of a microswitch and a contact finger or a combination of a reed switch and a magnet or any other known detecting elements.

In contrast to the offset detecting means based on the first approach, the second approach initially mentioned is based on detecting an offset of the record by the combination of a photo-sensor or reflection type which is disposed adjacent to an edge of the record, and a detection patter having an optical reflectivity which is different from the optical reflectivity of the record and movable into a zone detectable by the photo-sensor whenever the edge of the record shifts in a direction perpendicular to the direction in which it is normally driven.

FIG. 26 shows a first embodiment of offset detecting means which is based on the second approach. In FIG. 26, the record 11 in the form of an endless belt extends around belt rollers 12, 13 so as to be driven in a direction indicated by arrows A. Both lateral edges of the record 11 are formed with detection patterns 95a, 95b along their full length. These patterns are formed by using a material which exhibits an optical reflectivity different from the optical reflectivity of the record 11. A pair of photo-sensors 96a, 96b of reflection type are disposed above the opposite edges of the record 11 in the planar or straight region thereof, namely, in a region of the record 11 other than those disposed around the rollers 13, 12.

FIG. 27 is a front elevation of the arrangement shown in FIG. 26, illustrating the relative position of the photo-sensors 96a, 96b. In FIG. 27, the record 11 is shown as being driven in a normal manner, and hence, there is no offset of the control 11 in either direction C or D, which is perpendicular to the direction in which the record 11 is driven. Under this condition, it will be noted that the photo-sensors 96a, 96b are located above the record 11 in zones which are offset inwardly from the detection patterns 95a, 95b, as viewed in the lateral direction. Thus, the record 11 is present in the detectable zones of the sensors 96a, 96b. Accordingly, the sensors 96a, 96b produce output signals which corresponds to the optical reflectivity of the record 11. It is to be understood that devices disposed around the record 11 as shown in FIG. 2 are omitted from illustration in FIGS. 26 and 27 for purpose of clarity.

If an offset of the record 11 occurs in the direction C as it is driven in the direction A, the detection pattern 95b also shifts in the direction C. After the detection pattern 95b has travelled through a suitable distance, it moves into the detectable zone of the photo-sensor 96b, whereupon a change beings to occur in the output signal from the latter since the optical reflectivity of the detection pattern 95b is different from that of the record 11. Accordingly, an offset of the record 11 in the direction C is indicated by a change in the output signal from the photo-sensor 96b. Similarly, an offset of the record 11 in the direction D is indicated by a change in the output signal from the photo-sensor 96a.

FIG. 28 shows timing charts which illustrate a change occurring in the output signal from either photo-sensor 96a or 96b as a result of an offset of the record 11. The graph (c) illustrates an offset of the record 11 in the direction C while the graph (d) illustrates an offset of the record 11 in the direction D. In the graph (c), the record 11 is present in the detectable zones of both sensors 96a, 96b from the instant (t=0) when an offset of the record 11 occurs in the direction C until the detection pattern 95b moves into detectable zone of the sensor 96b (t=t₁), and hence an output signal We from the sensor 96a and an output signal Wf from the sensor 96b both assumes an H level. After time T₁, the record 11 is present in the detectable zone of the sensor 96a while the detection pattern 95b is present in the detectable zone of the sensor 96b, and hence the signal We assumes an H level while the signal Wf assumes an L level. It is understood that the H and the L level depend upon the optical reflectivity of the record 11 and the detection pattern 95b. For example, if the optical reflectivity of the record 11 is greater than that of the detection pattern 95b, the H level will be a high level and the L level will be a low level.

Similarly, referring to the graph (d), both output signals We, Wf assume an H level as in the graph (c) from the instant (t=0) when an offset of the record 11 begins to occur in the direction D until the detection pattern 95a, moves into the detectable zone of the sensor 96a (t=t₂). After time t₂, the detection pattern 95a is present in the detectable zone of the sensor 96a while the record 11 is present in the detectable zone of the sensor 96b, and hence the signal We assumes an L level while the signal Wf assumes an H level.

FIG. 29 shows a second embodiment of offset detecting means which is based on the second approach. The record 11 is shown as supported by the roller 12, and is formed with a detection pattern 97 on only its one edge, which pattern exhibits a different optical reflectivity from the record 11. In FIG. 29, the record 11 is shown is being normally driven. Hence, no offset occurs in a direction perpendicular to the direction in which the record 11 is driven, namely, in a direction C or D shown. A photo-sensor 98a of reflection type is disposed directly above the detection pattern 97 under this condition of the record, and another photo-sensor 98b of reflection type is aligned with the sensor 98a laterally, or in a direction perpendicular to the direction in which the record 11 is driven and located inwardly offset from the detection pattern 97. Un the condition shown, the detection pattern 97 is present in the detectable zone of the sensor 98a while the record 11 is present in the detectable zone of the sensor 98b. Accordingly, the sensor 98a produces an output signal which corresponds to the optical reflectivity of the detection pattern 97 while the sensor 98b produces an output signal which corresponds to the optical reflectivity of the record 11.

If an offset of the record 11 occurs in the direction C, the detection pattern 97 also shifts in the direction C. After the detection pattern 97 has travelled through a suitable distance, it moves into the detectable zone of the photo-sensor 98b, whereupon a change begins to occur in the output signal therefrom. It will be noted that no change occurs in the output signal from the sensor 98a since the detection pattern 97 continues to be present within the detectable zone thereof. Accordingly, an offset of the record 11 in the direction C is indicated by a change in the output signal from the sensor 98b.

Similarly, an offset of the record 11 in the direction D is indicated by a change in the output signal from the sensor 98a since the record 11 moves into the detectable zone of the sensor 98a. The record 11 continues to be present within the detectable zone of the sensor 98b during such offset, and there occurs no change in the output signal from the sensor 98b.

FIG. 30 shows timing charts illustrating a change occurring in the output signal from either sensor 98a or 98b shown in FIG. 29. Graph (c) illustrates an offset of the record 11 in the direction D. In the graph (c), the detection pattern 97 is present in the detectable zone of the sensor 98a from the instant (t=0) when an offset of the record 11 begins to occur in the direction C until the pattern 97 moves into the detectable zone of the sensor 98b (t=t₃). During such interval, the record 11 continues to be present in the detectable zone of the sensor 98b. Accordingly, the sensor 98a produces an output signal We' of an L level while the sensor 98b produces an output signal Wf' of an H level. After the time t₃, the detection pattern 97 is present in the detectable zone of both sensors 98a, 98b, so that both of the signals We' and Wf' assume an L level. The significane of the H or L level remains the same as before.

In the graph (d), the detection pattern 97 is present in the detectable zone of the sensor 98a from the instant (t=0) when an offset of the record 11 begins to occur in the direction D until the record 11 moves into the detectable zone of the sensor 98a. At this time, the record 11 continues to be present in the detectable zone of the sensor 98b. Accordingly, the signal We' assumes an L level while the signal Wf' assumes an H level. After time t₄, the record 11 is present in the detectable zones of both sensors 98a, 98b, which therefore produce signals We' and Wf' of an H level.

FIG. 31 shows a third embodiment of offset detecting means which is based on the second approach. A series of detection patterns 99, which are spaced apart in a direction perpendicular to the direction in which the record 11 is driven are formed on the surface of part of the top plate 28 of the support plate 26 which is located adjacent to the roller 13. As before, the detection patterns 99 exhibit an optical reflectivity which is different from that of the record 11. A photo-sensor 372 of reflection type is disposed above the detection patterns 99 so as to be aligned with the edge of the record 11. If an offset of the record 11 occurs in the direction D as viewed in FIG. 31, the detection patterns 99 on the top plate 28 are sequentially exposed. When the exposed detection pattern 99 enters the detectable zone of the sensor 372, a change occurs in the output signal therefrom, thus indicating the occurrence of an offset of the record 11.

Belt Offset Control Means

FIG. 26 illustrates the principle of operation of offset control means. In FIG. 26, the record 11 is carried by the belt rollers 12, 13 so as to be driven in directions indicated by arrows A. As mentioned previously, the drive roller 13 has its rotary shaft 38 fixedly mounted while the other roller 12 is disposed so that it is tiltable about the axis thereof which lines in a plane including the rollers 12, 13, as indicated by arrows I, J. If the opposite axial ends of the roller 12 are tilted in the direction of the arrow I, and offset of the record 11 in the direction D. Conversely, if the opposite axial ends of the roller 12 are tilted in the direction of the arrow J, an offset of the record 11 occurs in the direction C. Such phenomenon is remarkable when the record 11 is formed of a material such as polyester terephthalate which has a low elastic modulus.

FIG. 32 shows one form of offset control means. Specifically, one axial end 12c of the roller 12 which carries the record 11 is received in a notch 62a formed in the bracket 62 which is fixedly mounted on the side plate 67 (FIG. 8) of the printer by set screws 100. The other axial end 12b the roller is received in a notch 102 formed in a control piece 101a which is formed on one end of a generally L-shaped control arm 101.

At its bend, the control arm 101 is rotatably mounted on a pin 104 which is secured to the side plate 60 (FIG. 4) by set screw 103. The opposite end of the control arm 101 which is remote from the control piece 101a is connected with one end of a tension spring 106 and also with a rod 105 of a solenoid 105. When the solenoid 105 is deenergized, the spring 106 urges the control piece 101a to move in the direction of an arrow P, thus tilting the roller 12 in the same direction about the end 12c. However, when the solenoid 105 is energized, the rod 105a is retracted, thus urging the control piece 101a to move in the direction of an arrow Q, thus tilting the roller 12 in the same direction about the end 12c.

When the solenoid 105 is deenergized during the movement of the record 11 in the direction of the arrow A, the roller 12 is urged by the spring 106 to be tilted in the direction of the arrow P. Consequently, the record 11 has a tendency to produce an offset in the direction of the arrow D. If an offset of the record 11 in the direction D exceeds an allowable limit, the solenoid 105 is energized to tilt the roller 12 in the direction of the arrow Q. The resulting tilting prevents a further offset of the record 11 in the direction of the arrow D, and the record 11 then tends to shift in the direction C, thus compensating for an offset in the direction D. If an offset of the record 11 in the direction C which occurs as a result of energization of the solenoid 105 exceeds an allowable limit, the solenoid 105 may be deenergized, thus compensating for an offset in the direction C.

In the arrangement described above, it is necessary to provide a tilting motion of the roller of a magnitude which is greater than necessary to provide an offset control. Accordingly, stops, not shown, may be suitably located on the path of movement of the control arm 101, thus preventing greater movement of the control arm than necessary.

In the offset control means shown in FIG. 32, the follower roller 12 is disposed so as to be tiltable about its one end which serves as a fulcrum point while permitting a vertical movement of the other end to compensate for an offset of the belt. However, an offset of the belt may also be compensated for by changing the distance between the opposite axial ends of the follower roller 12 and the opposite axial ends of the drive roller 13. As mentioned previously, a tension is maintained in the record 11 by the spring 27 (FIGS. 5 and 6). If the spring force FL and FR (FIG. 26) applied to the opposite axial ends of the follower roller 12 is chosen such that FL>FR, for example, the record 11 is biased to be offset in the direction of the arrow D. On the other hand, the axial end (shown at 12b in FIG. 32) of the follower roller 12 to which the spring force FL is applied may be engaged with the control arm so that when the sensor 96a produces an offset detection signal, the control arm is rocked to change the forces applied to the opposite sides of the record 11 such that FL>FR. As a result, the record 11 will be displaced in the direction of the arrow C. Such displacement in the direction of the arrow C can be stopped when the sensor 26a detects the detection pattern 95a.

Alternatively, the opposite ends of the follower roller 12 may be engaged with separate control arms so that the roller may be tilted either vertically or horizontally in response to an offset detection signal from offset detecting means.

While a combination of solenoid and tension spring is used as drive means associated with the control arm in the described arrangement, it should be understood that such drive means is not limited thereto, but may utilize a motor,the rotation of which is transmitted through an electromagnetic clutch and a cam or gear to drive the control arm.

The offset detecting means and the offset control means are effectively used in a combination. A specific example will be described with reference to FIG. 33, which represents a block diagram of an arrangement to drive the offset control means in response to a signal from the offset detecting means. Specifically, offset detecting means 107 produces a signal which indicates an offset of the record. The detection signal is fed to a decision circuit 108, which determines the direction in which and the time when the control is to occur. Such information is supplied to control signal generator 109, which in turn produces a control signal fed to offset control means 110 in order to drive or stop drive means such as solenoid contained in the offset control means 110.

The belt offset control means is located adjacent to the follower roller 12. However, as mentioned previously, the transfer charger 19 is located below the follower roller 12. In other words, the space below the follower roller 12 represents a transfer region where the toner image is transferred onto a record sheet.

FIGS. 88 and 89 show an arrangement including a pair of offset detectors (R) and (L) which are disposed adjacent to the opposite lateral edges of the record to detect an offset thereof, and also including solenoids SOL(R) and SOL(L) which cause either end of the follower roller 12 to be tilted. FIG. 89 is a series of timing charts which illustrate the operation thereof.

Specifically, an offset detection signal which is detected by a detection feeler (shown at 77 in FIG. 20) is supplied to AND gates A4, A5 together with a main motor control signal and the inversion of a transfer charger control signal, both of which are produced by a control circuit, thus driving either solenoid SOL(R, L) such as that shown at 105 in FIG. 32, for example, through a driver. To prevent the solenoids from being energized simultaneously as a result of noises, the inversion of one of the output signals is utilized as a gate signal to the other gate. It will be apparent from FIG. 88 that the solenoid can be energized or the offset control can take place only when the main motor is driving and the transfer charger is not in operation. In this manner, the offset control occurs when no transfer operation takes place, thus voiding adverse influences upon the image being formed. This also minimizes the power dissipation since the solenoid ceases to be energized whenever the main motor is at rest.

It will be understood from the foregoing description that a deformation of the record is avoided since no force is applied to the edge of the record which constrains a movement thereof. The provision of offset detecting means and the offset control means associated with the roller which operate in response to the detection signal avoids the need for a high accuracy in the construction of the record and the rollers. It will be appreciated that both the offset detecting means and the offset control means are simple in construction, preventing a complication, an increased size and an increased cost of the printer.

Drive System

FIG. 13 shows a drive system used in the support arrangement mentioned above. The rollers 12, 13 which support and drive the record 11 and the developing sleeve 34 are substantially aligned with each other in a direction parallel to the direction in which the developing unit 31 is inserted or withdrawn. A power transmission gear 63 is disposed so as to be offset in a direction substantially normal to the direction of alignment, and is connected to a drive source associated with the printer. The gear 63 meshes with a drive gear 64 which is fixedly mounted on the rotary shaft 38 of the drive roller 13. In the example shown, the power transmission gear 63 meshes with the drive gear 64 in the lower part thereof, but it may be disposed to mesh with the gear 64 in the upper region thereof. The drive gear 64 in turn meshes with a driven gear 66 fixedly mounted on the rotary shaft 65 of the developing sleeve 34. In this manner, the power from the drive source of the printer is transmitted through the gears 63, 64 and 66. FIG. 14 is a perspective view illustrating this arrangement. This arrangement of the drive system facilitates the insertion or withdrawal of the developing unit 31 while assuring a positive power transmission when the unit 31 is inserted. As discussed above, since the record unit and the developing unit are assembled as separate unitary construction, they can be easily mounted on or dismounted from the printer while allowing a positive control of positioning. It will be understood that the clearance between the record and the developing sleeve and the individual chargers must be very closely maintained, but that according to the invention, these clearances are easily achieved to a high accuracy by the provision of a variety of positioning means even though the record/developing unit is detachable from the remainder of the printer, thus dispensing with a position adjustment while avoiding any likelihood of misalignment. It will also be noted that a large opening need not be provided as required in prior arrangements, but instead a small opening and simple guide means allow a replacement or repair of the record as well as the replenishment of a developer. The unitary construction of the record and the developing unit results in a compact and simple arrangement, and enables a facilitated replacement of the entire record, thus eliminating the likelihood that the surface of the record may be damaged or marred by the developer during the replacement. The drive system is constructed in a manner to facilitate the mounting or dismounting of these units while assuring a positive power transmission, thus preventing undue stresses from being produced during the mounting or dismounting of these units.

Referring to FIG. 3, a drive system used in the printer of the invention will be described. A motor 273 is utilized as a drive source, and a pair of pulleys 274, 275 are integrally mounted on its rotary shaft. An endless timing belt 280 extends around the pulley 274 as well as pulleys 276, 277, 278 and a tension pulley 279. The pulleys 276, 277, 278 are fixedly mounted on their respective shafts 281, 282, 283, respectively, Which are in turn rotatably mounted in the side plate 67 (FIGS. 4 and 8).

The gear 63 is fixedly mounted on the shaft 281, and meshes with the gear 64 which is substantially integral with the drive roller 13, as shown in FIGS. 8 and 13. The gear 64 meshes with the gear 66 on the developing sleeve 34.

The gear 284 is fixedly mounted on the shaft 282 associated with the pulley 277, and meshes with a gear 286 which is fixedly mounted on the shaft 285 associated with the cleaning roller 256.

A gear 287 is fixedly mounted on the shaft 283 associated with the pulley 278, and meshes with a gear 289 which is fixedly mounted on the shaft 288 associated with the fixing roller 197. The gear 289 meshes with a gear 290 which is integral with the shaft 291 associated with the pressure roller 198. Thus, the rollers 197, 198 rotate without relative slip therebetween. As shown in FIG. 62, a gear 235 is fixedly mounted on the shaft 234 associated with the delivery roller 206, and a pair of idle gears 292, 293 are interposed between gears 235, 289 in meshing engagement therewith. A one-way clutch 294 is provided between the gear 289 and the shaft 288 so that the drive is transmitted only in a direction from the gear 289 to the shaft 288. Consequently, when the drive system is at rest, the fixing roller 197 is freely rotatable in the conveying direction of the record sheet.

A timing belt 296 extends around the other pulley 275 on the shaft of the motor 273 and around a pulley 295. As shown in FIG. 4, the pulley 295 is mounted on the shaft 297 associated with the lower roller 18b of the conveyor roller pair 18, with a conveyor clutch 299 interposed therebetween which comprises a solenoid clutch. When the conveyor clutch 299 is energized, the pulley 295 and the shaft 297 are coupled together for integral rotation. This condition is referred to as an on-condition of the clutch. A gear 298 is fixedly mounted on the shaft 297 associated with the lower roller 18b, and meshes with a gear 301 fixedly mounted on one end of the shaft 300 associated with the upper roller 18a. As shown in FIG. 4, a gear 302 is fixedly mounted on the other end of the shaft 300, and meshes with a gear 303 which is in turn mounted on the shaft 305 associated with the feed roller 17, with a feed clutch 304 interposed therebetween which comprises a solenoid clutch. When the feed clutch 304 is energized, the rotation of the gear 303 is transmitted to the shaft 305, causing the feed roller 17 to rotate in the feed direction. The feed roller 17 is mounted on the shaft 305 with a one-way rotary clutch 306 interposed therebetween as shown in FIG. 2, and is freely rotatable when the shaft 305 does not rotate. It will be seen from the above description that the single motor is utilized as the sole drive source in the printer of the invention. The drive from the motor as well as the operation of various sensors and solenoid clutches will be described later.

Exposure/Charging Unit

Referring back to FIG. 22, it was mentioned that the record 11 is divided into four regions which are differentiated from each other in respects of the planarity and the speed response. Of these four regions, a variation in the relative position of the record surface with respect to other devices or units is minimized in the tensioned, linear region G and the driven, curved region E₁. The feed rate of the record is stabilized in the driven, curved region E₁ and the tensioned, linear region G₁ in the proximity of the region E₁. The other or slackened linear region G is subject to a variation in the position and the feed rate of the record surface as a result of undulations while the other or follower, curved region E is subject to a variation in the feed rate.

In consideration of the varying responses of the individual regions of the record 11 as mentioned above, it is found that it is desirable to perform the charging, exposure and developing steps, all of which are most significant in the formation of an image, during a movement of the record 11 from the tensioned, linear region G₁ toward the driven, curved region E₁.

More specifically, the above requirement can be satisfied by choosing the exposure station at a location within the linear region G₁ which is immediately before the point where a contact between the record 11 and the drive roller 13 occurs and where a variation in the record surface is minimal and a variation in the speed is minimized. Similarly, the developing station is chosen in the curved region E₁ where the record 11 is in contact with the drive roller 13 to minimize a change in the developing gap and the running speed. Finally, the charger 14 is disposed in the tension region G₁ where the record extends rectilinearly and a variation of the record surface is minimized.

The exposure unit 15 comprises a gas laser such as He-Ne laser or a semiconductor laser as a light source, the beam of which is modulated and deflected to scan the record surface with a beam spot having a varying light intensity (sub-scan). However, it should be understood that the printer of the invention is not limited to this type of exposure. By disposing the exposure unit so that it irradiates the record 11 in its planar region (or linear region) before the planar region turns into a curved region, the adjustment of the parallelism of the scan beam crosswise of the record is facilitated.

Specifically, referring to FIG. 2, it will be seen that the charger 14 is disposed in the tension, linear region of the record 11, the exposure unit 15 is disposed to direct its imagewise radiation toward the linear region of the record immediately before the linear region enters the curved region. It is to be noted that the charger 14 is of Scorotron type.

The charger 14 is of Scorotron type as shown in FIG. 2, and includes a discharge electrode 249 and a grid 250 connected to respective voltage sources, not shown, and which are encased within a shielded casing 251. The charger 14 is also detachably mounted on the printer and is movable in the same direction as the transfer charger 19. It will be recognized that both the charger 14 and the transfer charger 19 radiate a corona discharge of the same polarity toward the record 11 and the rear surface of the record sheet.

Sheet Feeder

In accordance with the invention, when the top cover of a tray is opened, a bottom plate is automatically lowered to permit a replenishment of record sheets.in to the tray. When the top cover is closed, the bottom plate is resiliently urged upward in an automatic manner, thus enabling a sheet feeding operation. Thus, with this sheet feeder, a simple operation of opening or closing the top cover is all that is required to perform a replenishment of record sheets. Also, in this sheet feeder, the printer need not be provided with a raising member, thus simplifying the construction of the printer.

The printer of the invention includes a detector assembly in which a single sensor is capable of detecting the presence or absence of record sheets and also capable of detecting whether the bottom plate urges the record sheets against the feed roller to enable a normal feed operation whenever the top cover is closed. In addition, the printer is provided with a paper reset mechanism which positively returns those record sheets which are held between the feed roller and the friction pad into the tray as the bottom plate is lowered during a replenishment of record sheets.

In FIG. 2, a sheet feeder is generally shown by numeral 130. Record sheets contained in the sheet feeder can be fed, one by one, beginning with the uppermost one, by the cooperation between the feed roller 17 and a friction pad 131 to move along a guide plate 132 into the nip between a pair of conveyor rollers 18. The presence or absence of a record sheet or sheets in the sheet feeder 130 is detected by a paper end sensor 133.

The sheet feeder 130 includes a tray 3 in the form of a box having an open top. A rear portion of the bottom of the tray 3 is defined by a fixed bottom plate 134 while a front portion is formed by a movable bottom plate 135. The movable bottom plate 135 is in effect pivotally mounted on the tray 3 at its rear end 136 so as to be tiltable in a vertical plane about the rear end. A coiled compression spring 137 urges the movable bottom plate 135 upward, as viewed in FIG. 2. A top cover 4 is pivotally mounted on a pin 138 at its one end and is adapted to cover the top of the tray 3.

Referring to FIG. 44, it will be noted that the front end of the top cover 4 is provided with a pair of bearing pieces 139 on the opposite sides thereof. The pin 138 is fixedly mounted on side plates (not shown) of the tray 3. The bearing piece 139 includes a stub shaft 142 on which a roller 141 is mounted. It is to be understood that a pair of rollers 141 are provided in opposing relationship with each other on the opposite lateral sides of the movable bottom plate 135. A detent pin 143 is fixedly mounted on the bearing piece 139.

At the front end, the side plate of the tray fixedly carries a pivot pin 144 on which a friction arm 145 is rockably mounted. On its one end, the friction arm carries a friction pad 131 formed by a material such as rubber or the like and secured to a support 146. The friction pad 131 is maintained in abutment against the feed roller 17 under the resilience of a coiled tension spring 147 which has its one end engaged with the arm 145. It is to be understood that a pair of friction arms 145 are pivotally mounted on the opposite side plates of the tray and are connected with each other so that the friction pad 131 is located substantially midway therebetween. The other end of the spring 147 is anchored to a pin 149 which is fixedly mounted on the side plate, not shown, of the tray. An interlock lever 148 is rockably mounted on the pin, and includes one end 148a which is folded to be located opposite to one end 145a of the arm 145. The other end 148b of the interlock lever 148 extends to a location below the stub shaft 142 on which the roller 141 is mounted. It is to be understood that the shaft 142 extends long enough to be engageable with the other end 148b of the lever.

At the front end of the tray 3, both of the side plates are formed with a pair of arms 150 (only one being shown), across which a support shaft 151 extends. As shown in FIG. 46, a rocking lever 152 is fixedly mounted on one end of the support shaft 151, and fixedly carries a pin 153 on its free end, to which one end of a connecting rod 154 is connected. The other end of the connecting rod being secured to the detent pin 143. A pair of paper reset levers 155 are fixedly mounted on the support shaft 151, and are spaced apart to locate the feed roller 17 therebetween, as shown in FIG. 46. It is to be noted that the free end of the paper reset levers 155 is located above the upper edge of a front plate 156 of the tray (FIGS. 44 and 45). The front plate 156 is formed with notches 156 to receive the levers 155 as they rock, and are also formed with a notch 156b which is adapted to receive the friction pad 131.

As shown in FIG. 44, when the top cover 4 is closed, the friction pad 131 bears against the feed roller 17 while the paper reset levers 155 are removed from the front plate 156. The compression spring 137 urges the movable bottom plate 135 upward against the lower periphery of the feed roller 17. If a stack of record sheets is placed on the bottom plate 135, an uppermost one of the record sheets will be held against the lower periphery of the feed roller 17.

A loading operation of record sheets will now be described.

The top cover 4 which assumes its closed position in FIG. 44 may be opened by turning it counterclockwise about the pin 138, whereupon the rollers 141 mounted on the bearing pieces 139 bear against the movable bottom plate 135 to move it down against the resilience of the spring 137, as shown in FIG. 45. Subsequently, a stack of record sheets may be inserted between the top cover 4 which assumes an open position and the movable bottom plate 135 and moved forward until their leading edge bears against the front plate 156. Subsequently, the top cover 4 may be closed as shown in FIG. 44, whereupon the spring 137 urges the bottom plate 135 upward, whereby an uppermost one of the record sheets in the stack is held against the peripheral surface of the feed roller 17.

It will be appreciated that the record sheets may be replenished when the paper end sensor 133, to be described later, detects the absence of record sheets and provides a corresponding indication to an operator, and also when it is desired to add record sheets to the remaining supply of record sheets within the tray. In the latter instance, a plurality of record sheets have their leading end held between the feed roller 17 and the friction pad 131, and hence, these record sheets must be returned into the tray.

When the record sheets are added to the remaining supply of record sheets within the tray, as the top cover 44 which is closed as shown in FIG. 44 is moved to its open position shown in FIG. 45, a corresponding movement of the connecting rod 154 acts through the rocking lever 152 and the support shaft 151 to rock the paper reset levers 155 clockwise. Simultaneously, the shaft 142 engages the end 148b of the interlock lever 148 to cause it to rock clockwise, whereby the other end 148a of the lever causes the friction arm 145 to rock counterclockwise. Thus, the friction pad 131 moves way from the feed roller 17 to release the leading end of any record sheet held between the pad 131 and the feed roller 17, as the top cover 4 is opened. Simultaneously, the paper reset levers 155 rock into abutment against the leading end of the record sheets which are thus released, thus returning them into the tray. In this manner, when record sheets are added to the remaining record sheets within the tray, there is no record sheet which is held between the feed roller 17 and the friction pad 131, and the added record sheets are placed on top of record sheet which are properly oriented on top of the movable bottom plate 135 which then assumes a lowered position.

In the arrangement shown in FIG. 44, the paper reset levers are caused to be moved in direct association with a movement of the top cover 4, but may be driven in association with a rocking motion of the movable bottom plate 135 which is interlocked with the top cover 4. Referring to FIGS. 47 to 49 which illustrate such an arrangement, a paper reset lever 158 is fixedly mounted on the support shaft 151, and is engaged by a spring 159, which urges it in a direction away from the front plate 156. The lever 158 is formed with an engaging piece 158a, which projects through a slot 156c formed in the front plate into the tray so as to be engageable with the front edge of the movable bottom plate 135.

In FIG. 47, as the top cover 4 is opened (FIG. 44), the movable bottom plate 135 is lowered as shown in FIG. 48. At the same time, the friction pad 131 moves away from the periphery of the feed roller 17, releasing the leading edges 24a of any record sheets 24 held therebetween. As the bottom plate 135 moves down, its front edge engages the engaging piece 158a to cause the paper reset lever 158 to rock to an angular position shown in FIG. 48. As the lever 158 rocks in this manner, record sheet which is located above the upper edge of the front plate 156 is urged, at its leading edge, by the lever 158 to be returned onto the remainder of record sheets which move down together with the bottom plate. After replenishment of fresh record sheets, closing the top cover allows the movable bottom plate 135 to move upward, whereby the paper reset lever 158 is returned to the position shown in FIG. 47 under the resilience of the spring 159.

Returning to FIG. 44, a bracket 160 is fixedly mounted above the bottom plate 135, as viewed in FIG. 44. As shown in more detail in FIGS. 50 to 52, the bracket 160 rotatably carries the shank 162 of a feeler 161 having an active end 163 which is aligned with an opening 135a formed in the movable bottom plate 135. If any record sheet 24 is present in the bottom plate 135, it rests thereon to assume an angular position shown in solid line in FIG. 51. However, when there is no record sheet on the bottom plate, it falls into there opening 135a by gravity, and assumes an angular position shown in phantom line in FIG. 51. A detector plate 164 is integral with a hub 165 which is secured to the end of the shank 162 by means of a screw 166, and carries a shutter blade 167 on its free end which is disposed for selective movement into a gap 169 formed in a photoelectric switch 168 comprising oppositely disposed light emitting element and light receiving element, thus selectively intercepting the optical path between these elements. The detector plate 164 is positioned so that the shutter blade 167 is disposed within the gap 169 whenever the feeler 161 assumes the angular position shown in solid line in FIG. 51 while the shutter blade 167 is disposed within the gap 169 whenever the feeler 161 assumes the angular position shown in solid line in FIG. 51 while the shutter blade 167 is located out of the gap 169 whenever the feeler 161 assumes the angular position shown in phantom line in FIG. 51. Accordingly, the photoelectric switch 168 produces a signal when the optical path is intercepted, which is different from a signal produced when the optical path is not intercepted. This signal is fed to a control unit. Such control may enable a record operation for the sheet feeder only when the optical path is intercepted. It will be noted that an interlock wing 170 having a hub 171 is secured to the shank 162 of the feeler 161 by means of a screw 172. Another feeler 173 is pivotally mounted on a pin 174 which is secured to the side plate of the tray 3 and includes an active end 175 which is adapted to selectively engage the lower surface of the top cover 4. When the top cover 4 is in its normally closed position, the feeler assumes an angular position spaced from a stop pin 177 against the resilience of a bias spring 176, as indicated in solid line in FIG. 51. When the top cover 4 is swung more than a given angle in the opening direction from its closed position shown, the feeler 173 moves angularly into abutment against the stop pin 177 under the resilience of the spring 176, as shown in FIG. 52. The other end 178 of the feeler 173 is adapted to engage the interlock wing 170 selectively. When the top cover 4 assumes its closed position, it permits a free movement of the active end 163, detector plate 164 and interlock wing 170 between their solid line positions as indicated in FIG. 51. However, when the top cover 4 is swung from its closed position and the feeler is caused by the spring 176 to move counterclockwise, the end 178 of the feeler 173 engages the interlock wing 170 to thereby drive the detector plate 164 until the shutter blade 167 thereof moves out of the gap 169.

Accordingly, the shutter blade 167 of the detector plage 164 can be placed within the gap 169 of the photoelectric switch 168 when at least one record sheet 24 is present on the movable plate 153 and the top cover 4 is in its normal closed position, as shown in solid line in FIG. 51. When no record sheet 24 is present on the bottom plate 135, the active end 163 of the feeler 161 falls into the opening 135a, as indicated in phantom line in FIG. 51, whereby the detector plate 164 moves counterclockwise, as viewed in FIG. 51, causing the shutter blade 167 to move downwardly and out of the gap 169. When the top cover 4 is not in its normal closed position, the combination of the feeler 173 and the interlockwing 170 causes the detector plate 164 to move clockwise, as viewed in FIG. 52, thus moving the shutter blade upwardly and out of the gap 169. At this time, the feeler 163 is raised upward above the bottom plate 135, thus facilitating a replenishment of record sheets. It will be seen that the single photoelectric switch allows the detection of the presence or absence of a record sheet or sheets on the bottom plate and the detection of open or closed position of the top cover.

The feed roller 17 is located above the front plate 156 of the tray 4, and is substantially centered crosswise of the tray (FIGS. 2 and 4). As will be evident from FIG. 4, the feed roller 17 is in staggered relationship with the peripheral surface of the upper roller 18a in the roller pair 18. The upper roller 18a and the lower roller 18b are disposed in abutment against each other. The drive to these rollers will be described later.

A register sensor 179 is disposed downstream of the roller pair 18, as viewed in the direction in which the record sheet 24 is conveyed (FIG. 2). The purpose of the register sensor is to detect a record sheet from the tray 4 which is held between the roller pair 18. When it detects a record sheet, it produces a signal to interrupt the rotating drive to the roller pair 18 and the feed roller 17, as will be further described later.

A mechanism which prevents the sheet feeder from being contaminated will now be described. Referring to FIG. 2, a record sheet guide cover 180 is disposed below the record/developing unit 5, and extends over a region which is sufficient to protect the record sheet and its conveying path from any falling developer. The guide cover 180 is disposed intermediate the side plates 60, 67 by having positioning pieces 181, 182 formed on their opposite sides (only one each of them being shown) engaged with positioning pins 183, 184, which are fixedly mounted on the guide plates 56, FIGS. 8 and 54 showing only one of them.

The guide cover 180 comprises a cover body 180a on which the positioning pieces 181, 182 are formed, and a front guide 180b which is shaped by folding the front edge of the body 180a. The guide cover 180 is detachably mounted on the positioning pins 183, 184 in a space which is left after the record/developing unit 5 has been removed out of the printer. The cooperation between the positioning pins 183, 184 and the positioning pieces 181, 182 allows the location of the guide cover to be adjusted in the fore-and-aft direction. FIG. 54 illustrates that the guide cover extends over a region which is greater in lateral width than the roller pair 18 and a record sheet 24. After the record/developing unit 5 is loaded into the printer when the guide cover 180 is mounted in place, the bottom plate 39 of the receiver 35 prevents an upward movement of the cover.

When mounted in place within the printer, the front guide 180b of the guide cover 180 defines a record sheet passage 186 by cooperating with a guide plate 185 which is fixedly mounted within the printer. It will be seen that the guide cover 180 provides an isolation between an image forming region inclusive of the record 11 and the cleaning unit 22 on one hand and the record sheet and its passage on the other hand even though the unit 5 is either entirely or partly withdrawn from the printer for replacing the record or replenishing the developer, thus preventing a contamination which is attributable to a falling developer or floating developer.

In addition, the front guide 180b of the cover 180 defines a passage for the record sheet so as to maintain a proper orientation of the record sheet as it is being conveyed to the transfer station. An advantage can be obtained by avoiding the fixed mounting of the cover on the printer. Specifically, the feed roller 17 must be cleaned periodically since a reduction in the coefficient of friction of the peripheral surface of the roller prevents a normal feed operation. During such cleaning operation, the unit 5 may be withdrawn and then the guide cover 180 can be dismounted from the positioning pins 183, 184 by shifting it upwardly, whereupon an access through the opening of the printer is obtained to perform a maintenance work.

In the above description, the guide plate 185 which defines the passage 186 is mounted on ths printer, but a guide plate 185A which is substantially integral with the front guide 180b may be provided as illustrated in FIG. 55.

FIGS. 56 and 57 show different forms of guide cover 180. Specifically, leaf springs 187 or a strip of foam material 188 may be secured to the upper surface of the cover body 180a to prevent any unintended movement or rattling between the bottom plate 39 of the unit 5 and the upper surface of the cover.

Transfer Unit

The transfer charger 19 comprises a discharge electrode 247 connected to a high tension voltage source, not shown, encased within a shielded casing 248. By opening the side plate 8 of the printer (FIG. 1), the transfer charger 19 can be withdrawn in a direction indicated by the arrow.

Fixing Unit

The printer of the invention employs a fixing unit of roller type.

In the fixing unit of the invention, a delivery roller is driven at a peripheral speed which is greater than that of the fixing roller so that a tension is maintained in the record sheet as it is being conveyed by both of the rollers, and acts as a drive source, which cooperates with a member projecting into a path of movement of the record sheet to cause an angular movement of the separation claw so that it is removed from the roller. In this manner, the separation claw can be moved into contact with or away from the fixing roller in a simple arrangement.

Referring to FIG. 61, the fixing unit includes a pair of fixing roller 197 and pressure roller 198 which are disposed in abutment against each other. Either heat or pressure fixing technique may be employed. For example, when heat fixing technique is employed, there is provided one-revolution clutch or slip friction mechanism which operates to apply a required magntitude of pressure between the rollers only during the time when the record sheet 24 passes therebetween. The fixing roller 197 is associated with a separation claw 201 which is rotatably mounted on a shaft 199 and urged to rotate counterclockwise by a spring 200 and having its free end 201a disposed in contact with the surface of the fixing roller 197, and a cleaning mechanism 202 which operates to wipe off any toner which may be deposited on the roller surface. A delivery roller pair 25 including a pair of rollers 204, 205 are disposed on the exit side of the fixing roller pair, with a guide plate 203 interposed therebetween. In this manner, a coveying path 206 for the record sheet is defined as shown in phantom line in FIG. 61. A delivered sheet sensor 272 is disposed along the path 206 to detect the presence of any record sheet which moves along the path. In FIG. 61, only the feeler of the sensor 272 is shown, with its free end 272a located on the path 206.

It is to be noted that the peripheral speed of the fixing roller 197 is chosen to be less than the peripheral speed of the roller pair 25. The separation claw 201 is also formed with a protuberrance 201b which is located on the opposite site from the free end 201a and which projects onto the path 206 when the free 201a is maintained in contact with the fixing roller 197.

In operation, the record sheet 24 bearing an unfixed toner image thereon is fed between the fixing roller 197 and the pressure roller 198 for purpose of fixing. The leading end of the record sheet 24 is separated from the fixing roller 197 by the free end 201a of the claw 201 which is maintained in contact with the roller 197 under the resilience of the spring 200, and moves along the guide plate 203 toward the delivery roller pair 25. When the leading end of the record sheet 24 reaches the nip between the roller pair 25, it is fed while it is being held between the pair of fixing roller 197 and pressure roller 198 and between the roller pair 25. Since the peripheral speed of the roller pair 25 is greater than the peripheral speed of the fixing roller 197/pressure roller 198, it will be seen that a tension is produced in the record sheet 24 located on the path 206, and the sheet is pulled toward the roller pair 25. However, the pressure acting between the fixing roller 197 and the pressure roller 198 is greater in magnitude, thereby avoiding any interference with the fixing operation. It will be seen that the protuberance 201b projects into the conveying path 206, and is urged by the tensioned record sheet 24 to cause a clockwise movement of the claw 201 as shown in FIG. 62, whereby the free end 201a moves away from the fixing roller 197. At this end, the resilience of the spring 200 which brings the claw 201 into contact with the fixing roller 197 is chosen to be less than the magnitude of the tension. As the trailing end of the record sheet 24 moves out of the nip between the fixing roller 197 and the pressure roller 198, no tension is maintained in the sheet, whereby the claw 201 returns to its initial position under the resilience of the spring 200, thus returning the free end 201a into contact with the fixing roller 197.

Accordingly, the claw 201 can be maintained removed from the fixing roller 197 during the time the record sheet 24 is being conveyed by both the pair of fixing roller 197 and pressure roller 198 and the delivery roller par 25. The free end 201a is otherwise maintained in contact with the fixing roller 197 so as to be effective in its original functioning to separate the record sheet 24 while allowing a standby mode to be available. The use of the tension in the record sheet 24 as a drive source avoids any need for the provision of a separate drive source or member to move the claw 201 into contact or away from the fixing roller, thus allowing a cost reduction in a simple manner. A difference in the peripheral speed between the fixing roller 197 and the delivery roller pair 25, which is designed to produce a tension in the record sheet 24 which is effective to serve as a drive source to move the separation claw 201, also enables a paper jamming to be prevented as a result of conveying the sheet in its taut condition. In this manner, any damage to the fixing roller 197 when the separation claw 201 is maintained in contact therewith or a reduced reliability in separating the record sheet which is attributable to the toner deposition on the free end 201a is both eliminated in a simple manner while increasing the useful life of the fixing roller 197 and the separation claw 201 to improve the separation performance, avoiding the occurrence of a jamming and increasing the operational reliability.

It will be recognized that the peripheral surface of the fixing roller must be maintained clean in connection with the reliability of the fixing unit. In FIGS. 61 and 63, in a region opposite from the region which is contacted by the record sheet, the fixing roller 197 is contacted by the a thermistor TH which provides a temperature control of a heater 207 disposed within the roller 197. The cleaning unit 202 is disposed on the entrance or advance side of the fixing roller 197. A pad 209 formed of beat resistant felt has its one end held between a bracket 210 and an aluminium holder 211, which are secured together by a screw 212, and has its other end disposed in abutment against the peripheral surface of the fixing roller 197. A cushion 213 formed of soft, heat resistant material such as foamed silicone rubber is disposed inside the pad 209 to urge it gently against the fixing roller, thus preventing the roller 197 from being damaged by contact with the pad. As shown in FIG. 64, the opposite ends of the brabket 210 are secured to tabs 214a, folded from a frame 214, by stepped screws 215. It is to be noted that the axis of the screws 215 is downwardly offset from the center of the fixing roller 197 by a distance l. The height of the stopped screw 215 is chosen to be greater than the thickness of the sheet of the bracket 210, with a difference between the height of the step and the thickness of the bracket 210 being suitably chosen so that it is available to the restoring effect of the pad 209 and the cushion 213. A magnetic member 216 is secured on top of the bracket 210 by a securing bracket 217, and is located close to the fixing roller 197.

In operation, since the bracket 210 is urged by the stepped screws 215 at a point which is by a distance l below the center of the fixing roller 197, it tilts outwardly about the fulcrum defined by the lower end of the tab 214a extending from the frame 214. As a consequence, the pad 209 is most strongly urged against the peripheral surface of the fixing roller 197 in its bottom region, and such bias gradually decreases toward the top region of the pad 209. Consequently, any toner deposited on the fixing roller 197 is partly removed by an upper region of the pad 209 while the remainder is completely cleaned off by the lower region of the pad. In this manner, an efficient cleaning operation takes over the entire surface of the pad 209, minimizing the deposition or accumulation of toner on the top of the pad 209. Any accumulation of toner 218 on the top portion of the pad 209 is attracted by the magnetic member 216, thus preventing such pad from creeping under the abutting surface of the pad 209.

Delivery Unit

The cover 9 of the printer (FIG. 1) is partly movable by being connected with a hinge 219 which is mounted on a bracket 225 of the printer, as shown in FIG. 61. The fixing unit 20 includes a top cover 220 which can be opened and closed by its being connected to a hinge 221 which is mounted on a stay 222. Secured to the top cover a bracket 223 which supports the shaft 199 and a holder 224 which supports the paper delivery roller 205. When the top cover 220 is moved to is open position; an access is available to the conveying path 206 within the fixing unit, thus facilitating the removal of any jammed paper or the inspection of the internal construction.

As shown in FIG. 1, the printer of the invention is provided with the sheet abutment 10 which is located farthest from a user's position. Hence an operator must extend his hand to get the recorded sheets or copies. Accordingly, it is convenient to construct the delivery means in a manner such that the recorded sheets are accessible to an operator while he sits on his chair.

In FIG. 61, the cover 9 is disengaged from the hinge 219, which is then replaced by a hinge 226 shown in FIG. 62. A delivery unit 227 includes a pair of side plates 228 (only one being shown), the lower end 228a of which is connected to the hinge 226. The side plate 228 includes folded portions 228b, 228c, to which a unit cover 229 is secured by set screws, with fastener plates 230, 231 interposed therebetween. As shown in FIGS. 62 and 65, one of the side plates 228 rotatably carries a pulley 232 and a gear 233 which are disposed in coaxial relationship. The gear 233 meshes with a gear 235 integrally mounted on a shaft 234 for delivery roller 206. The delivery roller 206 represents a drive roller, the drive system of which will be described later. A delivery roller 236 is mounted on a shaft 237 which is rotatably journalled in both the side plates 228 (only one being shown). A pulley 238 is fixedly mounted on one end of the shaft 237, and a belt 239 extends around the pulleys 238, 232.

The unit cover 229 is formed with a delivery port 240, and the delivery roller 236 is located inwardly of the delivery port. The roller 236 is formed of an elastic material such as foamed polyurethane rubber, and is disposed so that its upper peripheral surface is held in abutment against a keep plate 241. A record sheet is conveyed by being held between the rotating roller 236 and the keep plate 241. However, it should be noted that the roller 236 and the plate 241 may be spaced apart from each other as illustrated in FIG. 66. In this instance, the keep plate 241 is formed with a pair of projections 241a in it on the opposite sides of the roller 236 so that the peripheral surface of the roller and these projections are staggered with respect to each other, as viewed in the axial direction even though there is no direct contact between thekeep plate and the roller.

Curved guide members 242, 243 are disposed between the delivery roller pair 25 and the delivery roller 236 to define a record sheet turning path 244. In FIG. 62, the record sheet is conveyed along the conveying path 206 and the turning path 244 and through the delivery port 240 onto the top cover of the printer, generally in a direction indicated by an arrow. An operator, sitting on a chair, is easily accessible to the record sheet which is delivered onto the top cover of the printer.

It will be seen that the hinge 226 permits the delivery unit 227 to be opened and closed with respect to the rest of the printer. It can be opened to open the top region of the fixing unit, generally in the same manner as described above in connection with the cover 9 shown in FIG. 61. A magnet 245 is attached to one end 228d of the side plate 228 so as to be magnetically anchored to an abutment plate 246 which is secured to the hinge 221, thus assuring a positive meshing engagement between the gears 233 and 235.

Neutralizer

In the arrangement shown in FIG. 2, the neutralizer 21 comprises a discharge electrode 252 which produces an a.c. corona or a.c. corona which is d.c. biased to the opposite polarity from the polarity to which the record is charged, and a neutralizing lamp 253, both of which are housed within a shielded casing 254. The arrangement shown is designed to neutralize the record sheet as well as the record, and at this end, its charge is offset to the left, and the left-hand side of the shielded casing 254, as viewed in FIG. 2, is left open in order to avoid a jamming of the record sheet. In conjunction with the separation which takes place at the curvature, the disposition of the neutralizer for cooperation with the curved region of the record 11 disposed around the roller 12 improves the separation of the record sheet from the record.

Cleaning Unit

Referring to FIG. 2, the arrangement of the cleaning unit 22 will now be described. The cleaning unit essentially comprises a casing 255 which is detachably mounted on the printer so as to be movable in the same direction as the charger, and a cleaning roller 256, a magnetic roller 257 and a recovering shaft 258, all of which are rotatably supported by the casing in parallel spaced relationship with each other. The cleaning roller 256 comprises a non-magnetic sleeve 259 having fibers of short lengths implanted on its surface and a plurality of magnets 260, 261, 262, which are three in the example shown, and which are disposed inside the sleeve. The sleeve 259 is driven for rotation in a clockwise direction, by a drive system to be described later. The non-magnetic sleeve may be formed of aluminium, for example, on the surface of which are applied fibers having lengths on the order of 0.3 to 1 mm, formed from materials such as synthetic fibers of nylon and rayon, natural fibers such as cotton or wool, or conductive fibers of carbon and metals. It is maintained at a spacing from the record surface which is on the order of 0.2 to 0.5 mm. Thus, lengths on the order of 0.1 to 0.5 mm of the fibers implanted on the sleeve surface are maintained in contact with the record surface while the sleeve rotates, thus removing any residual magnetic toner on the record surface. Any residual magnetic toner on the record is mechanically separated therefrom by the fibers implanted on the sleeve surface, and is also attracted to the sleeve surface under the influence of the magnetic force from the magnets disposed therein. The toner removed is conveyed away as the sleeve rotates.

The cleaning unit 22 used in the printer of the invention comprises a cleaning roller capable of producing a magnetic field on its surface which is effective to remove any residual magnetic toner on the record surface, and a magnetic member which is located opposite to the cleaning roller with the record interposed therebetween, the arrangement being such that at least one of the cleaning roller or the magnetic member is disposed in virtually freely movable manner to permit the record to be held between the cleaning roller and that the magnetic member under the influence of the magnetic force from the cleaning roller. This assures a uniform contact between the cleaning roller and the record surface to enable a satisfactory cleaning effect, with a simple construction which is simple and easy to manufacture and assemble.

The magnetic roller 257 has its peripheral surface disposed in contact with the cleaning roller 256 for magnetically transferring any developer removed from the record surface by the roller 256. A blade 263 is disposed in abutment against the peripheral surface of the magnetic roller 257 to scrape off any developera that has been transferred. The scraped developer calls down onto the recovering shaft 258, which is peripherally formed with a helical groove or provided with a coiled spring so that the developer can be conveyed in the axial direction into a vessel which is provided externally of the casing during the rotation of the shaft in one direction.

As mentioned previously, the record 11 extends around the pair of belt rollers 12, 13, which are in turn supported by the support plates 26 (FIG. 7). It has also been mentioned previously that the position of the follower roller 12 is not fixed in order to allow a correction of the belt offset and that the arbor of the drive roller 13 is fixed to secure the location of the exposure station and to provide the ground connection

It is to be noted that there is a certain clearance between the bearing 43 on the follower roller 12 and the groove 40 (FIG. 6). In other words, when the record unit 23 is mounted in place, the support plate 26 is slightly rockable about the shaft 38 of the drive roller 13.

Referring to FIG. 67, it will be noted that an opposing member 264 formed of a magnetic material is secured to the lower surface of the top plate 28 extending from the support plate 26, over the entire axial length of the cleaning roller 256. Any suitable fastening means such as the use of adhesive, adhesive tape or screw may be employed at this end. Accordingly, the opposing member 264 is substantially disposed so as to be freely movable, and moves upwardly under the attraction exerted by the magnet within the non-magnetic sleeve 259 and is held attracted to the surface of the non-magnetic sleeve with the record 11 and the top plate 28 interposed therebetween. As a result, if a perfect parallelism is not maintained between the surfaces of the non-magnetic sleeve 259 and the record 11, the record 11 is caused to contact the surface of the sleeve 259 in a uniform manner, thus uniformly cleaning any residual magnetic toner on the record 11.

The magnetic toner deposited on the surface of the non-magnetic sleeve 259 is conveyed as it rotates, to be transferred onto the magnetic roller 257 and thence scraped off by the blade 263 to be carried by the recovering shaft 258 to the exterior of the cleaning unit. In this embodiment, if the rotary shafts of the belt rollers 12, 13 are parallel the rotary shaft of the sleeve 259, and the top plate 28 is parallel to the surface of the sleeve 259, it is not always necessary to provide a clearance between the rotary shafts of the rollers 12, 13 and their support members 26.

In the example mentioned above, the record unit inclusive of the record 11 is adapted to be lifted. FIG. 68 diagrammatically illustrates another example in which an opposing member 264 is simply placed in a depression formed in the top plate 28 of the support member 26. In this instance, only the opposing member 264 is lifted to bring the record 11 into uniform contact with the surface of the cleaning roller 256. Accordingly, it is unnecessary to provide a clearance between the rotary shaft of the belt roller 12 and the support member 26, the only requirement being that a given gap be provided between the opposing member 264 and the surface of the cleaning roller 256 so that the opposing member 264 can be lifted.

Another modification is illustrated in FIG. 69 in which the top plate 28 of the support member 26 is formed with an opening to receive the opposing member 264 therein and in which the opposing member 264 is placed on a receiver plate 267 which is carried by the top plate 28 by means of pins 265, 266. Again, only the opposing member 264 is held attracted to the surface of the cleaning roller 256 together with the record 11. Where the opposing member 264 is secured to the receiver plate 267, the pins 265, 266 may be loose fit with the receiver plate 267 so that the opposing member 264 can be lifted together with the plate 267.

In an arrangement in which the opposing member 264 directly contacts the moving record 11, the surface of the opposing member 264 which faces the record 11 can be formed in various profiles as illustrated in FIG. 70, in order to minimize the resistance of contact to reduce the loading effect or to increase the area of contact with the sleeve 259 as much as possible to thereby enhance the cleaning efficiency. Thus, the surface of the opposing member which engages the record 11 may be formed with rounded corners or with convex or concave surface. The purpose of the opposing member in such cleaning unit is not only bringing the record surface into uniform contact with the cleaning roller in a so-called "confirming" manner as a result of magnetic attraction from the cleaning roller, but is to produce an effective movement of any residual toner on the record under the influence of the magnetic field formed thereon to enhance the cleaning effect. However, in respect of the latter, variations during the manufacturing process or the aging effect may make it difficult to form a magnetic field which is effective to move the residual magnetic toner from the record surface. To cope with this problem, in the cleaning unit of the invention, an arrangement is made such that the relative position between the opposing member and the cleaning roller can be changed. Either the cleaning roller or the opposing member may be shifted in position, but it is preferable to adjust the location of the opposing member in consideration of the power transmission system.

Various means may be employed to adjust the location of the opposing member. For example, the opposing member 264 may be formed with a slot which is elongate in a direction parallel to the direction of movement of the record 11 and which is engaged by a set screw, extending therethrough, so as to position and clamp it to the top plate 28.

As mentioned previously, the unit is characterized in that at least one of the cleaning roller or the opposing member is disposed in substantially displaceable manner. It will be apparent from the foregoing description that the term "substantially" is used to connote not only that the cleaning roller or opposing member itself is disposed in a displaceable manner, but also that it is fixedly mounted on another member which is disposed in a displaceable manner. The term "displaceable" refers to a "movable condition" which is allowed by a "play" or "rattling" provided. Since "at least one of the cleaning roller or the opposing member" must be displaceable, it will be seen that the cleaning roller may be disposed to be displaceable or both the cleaning roller and the opposing member may be disposed in a displaceable manner, in contradistinction to the embodiments described above.

Disposing the opposing member 264, formed of a magnetic material, on the rear surface of the record 11 as means which brings the record 11 into contact with the cleaning roller 256 brings forth another advantage. It will be understood that the cleaning effect can be improved by determining their relative position so that a sliding contact between the record 11 and the cleaning roller 256 is achieved. However, in the printer of the invention, the record 11 is movable, as it is contained in the record unit, in a direction perpendicular to the axial direction of the cleaning roller 256. Hence,if the record and the cleaning roller are maintained in contactact with each other regardless of the position assumed by the record unit during its withdrawal, a sliding contact between them will occur to damage the record surface when the unit is mounted or dismounted. However, in the present unit, the use of the opposing member 264 which is disposed to be attracted by the magnet 260 internally housed within the cleaning roller 256 minimizes such likelihood of damaging the record. Specifically, it is only after the record/developing unit 5 has been inserted to a given position within the printer that the opposing member 264 is subject to attraction by the magnet 260 (FIG. 67) to bring the record 11 into contact with the cleaning roller 256. Accordingly, the record 11 will be disengaged from the peripheral surface of the roller 256 if the opposing member 264 has been moved to a point where it is not suficiently ifluenced by the magnet 260 to bring the record into contact with the peripheral surface of the roller 256.

Alternative means, which is a substitute for the opposing member 264 formed of a magnetic material and which brings the record 11 into contact with the cleaning roller 256, will now be described. Such means represent an example which causes the record 11 to contact the cleaning roller 256 with a force which is uniform, as viewed in the axial direction of the roller 256. In FIG. 71, there is shown a non-magnetic sleeve 259, and an opposing member 268 formed of a pliable material and having substantially the same length as the sleeve 259 is secured to the top plate 28 at a point directly opposite to the sleeve 259. Such a pliable material may comprise rubber, sponge, felt, brush hair, or an enclosure containing a material such a jelly or liquid. Even though a pliable material having flexibility is sufficient for the purpose of the invention, a pliable material having elasticity is more preferred. Since it is only necessary that the pliable material be present in at least region of the opposing member 268 which contacts the record 11, the opposing member 268 may comprise a rigid material to which the pliable material is applied. However, it is necessary in such instance that the pliable material has a sufficient thickness to allow a sufficient shrinkage when constricted.

Since the top plate 28 is inherently designed to support and guide the upper run of the record 11, the surface of the top plate 28 is in contact with or very close to the rear surface of the record 11, and the surface of the cleaning roller 256 is in contact with or very close to the surface of the record 11. When the opposing member 268 of a given thickness is interposed between the cleaning roller 256 and the top plate 28 which are located in this manner, the pliable material, which forms the opposing member 268, shrinks "in conformity to" the sleeve surface when contricted, thus urging the record 11 to contact the sleeve surface gently and uniformly. As a consequence, any residual magnetic toner on the record 11 is uniformly cleaned.

To bring the opposing member 268 into abutment against the cleaning roller 256 with the record 11 interposed therebetween, a spring 269 may be used as illustrated in FIG. 72. Specifically, the top plate 28 may be formed with a recess in a region opposite to the cleaning roller 256 in which to receive the spring 269, on top of which the opposing member 268 is placed. Consequently, the opposing member 268 is urged upward to bring the record 11 into abutment against the cleaning roller 256. The spring 269 can be omitted if the opposing member 268 has a thickness greater than the depth of the recess. A single spring 169 may be disposed centrally, as viewed in a direction perpendicular to the plane of the drawing, or a pair of springs may be disposed at the opposite ends of the top plate 28. Since the opposing member 268 is merely placed on top of the spring 269, it is capable of moving in either direction, that is, displaceable, assuring that the record 11 contacts the surface of the cleaning roller 256 uniformly and "in confirmity" thereto if the parallelism between the cleaning roller 256 and the record 11 is not perfectly attained.

In the arrangement described above, the upper surface of the opposing member 268 is maintained in contact with the rear surface of the record 11, and hence in order to minimize the resistance of contact therebetween to reduce the loading effect or to increase the area of contact between the record 11 and the cleaning roller 256 to thereby enhance the cleaning effect, the upper surface of the opposing member 268 can be profiled in various manners as illustrated in FIG. 70. Thus, the surface of the opposing member 268 which contacts the record 11 may be formed with rounded corners or as convex or concave surfaces.

In the various embodiments described above, the cleaning member comprises the non-magnetic sleeve 259 in which magnets are housed. Accordingly, a magnetizable material or a magnet 270 of the opposite polarity from that of the opposing magnet within the sleeve may be applied to the underside of the opposing member 268, as shown in FIG. 73. The magnetizable material or the magnet 270 is attracted by the magnet disposed within the sleeve, and hence the opposing member can be urged into abutment against the cleaning roller, with the record interposed, without utilising any mechanical bias. Examples of such an arrangement are shown in FIGS. 74 and 75.

In FIG. 74, an opposing member 264, which is constructed in a manner illustrated in FIG. 68, is provided with a cushion 271 of a pliable material such as that mentioned previously, on its surface located opposite to the record 11 for contact with the rear surface thereof.

In FIG. 75, an arrangement as shown in FIG. 67 is utilized, and a cushion 271 is formed on the top plate 28 in opposing relationship with the cleaning roller 256 so that it may contact the rear surface of the record.

When the cushion is brought into contact with the rear surface of the record 11 as shown in FIGS. 74 and 75, the pressure, which is produced as the opposing member 264 urges the record 11 into abutment against the cleaning roller 256 under the influence of magnetic force from the roller 256, is made uniform in the direction of generatrices of the roller. In other words, the record 11 uniformly contacts the cleaning roller 256 as viewed crosswise, thus assuring a uniform cleaning of the record.

Sequence Control

FIG. 76 is a block diagram of a sequence control unit of the printer of the invention. As shown, the control unit includes a central processing unit CPU, a read only memory ROM, a random access memory RAM and an input/output port I/O, all of which constitute together a microcomputer. A double pole main switch 2 is connected to an a.c. source, and is also connected to a main relay 307 and a relay source 308. The relay switch 307 is connected to an a.c. drive system 309 and a control system power source 310. A pair of power switches 311 have their one end connected to the ground, and the other end if one of the swiches is conneceted through a resistor 312 to the positive output of the power source 310 while the other end of the other power switch is connected to the collector of a transistor 313 and also connected through the solenoid coil of the relay 307 to the positive output of the source 308. The transistor 313 has its emitter connected to the ground and the base connected to the central processing unit. A timing pulse generator 314 (FIG. 8) comprises a slitted disc 315 fixedly mounted on the shaft 281 of the gear 63 which rotates the drive shaft for the record 11, and a photointerrupter 316 or reflection sensor which is operable to detect a slit or slits in the disc 315. An operating panel 317 includes ten keys. A display 318 (FIG. 1) provides a variety of indications. A circuit 319 drives the motor and neutralizing charger 19; a circuit 320 operates the charger 14, the exposure unit 15 and the transfer charger 19; a circuit 321 drives the feed roller 17 and the conveyor roller pair 18 which convey a record sheet; a jamming detection circuit 322 detects the occurrence of a jamming of a record sheet; a circuit 323 control the fixing unit 20, and a circuit 324 detects an error in the sub-scan synchronization and the timing pulse. A circuit 325 detects the exhaustion of toner in the developing unit is and the absence of record sheet in the sheet feeder 130.

In accordance with a selected one of programs stored in the memory ROM, the central processing unit CPU processes the signals which are received from the panel 317 and the circuits 322 to 325 through the input/output port I/O, and also performs an interrupt operation in response to a sub-scan sync signal and the timing pulse from the sub-scan sync detector 72 and the timing pulse generator 314 to effect a sequence control by outputting signals to the various units and circuits 318 to 321 and 323, in a manner to be described below.

1. From power-on to warm-up of heater (see FIG. 77 (1))

When the main switch 2 is turned on, the main relay power source 308 is energized. Subsequently when the power switches 311 are turned on, the source 308 energizes the main relay 307, whereby both the a.c. drive system 309 and the control power source 310 are energized. It is to be noted that when no power is supplied, the record 11 remains at rest at a position indicated in FIG. 78 (1), and the non-record area x (junction) of the record 11 is located such that the record region may be adversely influenced. In the example shown, the non-record area x is located below the charger 14 which is outside the curved region when it remains at rest. This is because during the formation of an image, an ozone may be produced by the charger 14 and may adversely influence the adjacent region if the record 11 remains at rest for a prolonged period of time. Positions y and z shown in FIG. 78 indicate the leading end of an image on the record 11 or the point where the record is initiated and the location of the sub-scan mark 71 (FIG. 8).

When the power source 310 is energized, the central processing unit CPU begins to operate, initially clearing the memory RAM, resetting input/output circuits of the input/output port I/O and determining a stack pointer SP. Various flip-flops F/F, timing pulse counter TPCOU, set counter SETCOU (presetting the number of copies to be printed) and the like are previously programmed within the memory RAM. Heater F/F is then set to cause the fixing unit control circuit 323 to turn the heater 207 of the fixing unit 20 on. TPCOU is cleared, and the mask for an interrupt INT1 (an interrupt in response to a timing pulse) is reset while setting a mark for an interrupt INT2 (an interrupt in response to the detection of a sub-scan sync mark). When the heater 207 warms up to a given temperature, it is then turned off by the control circuit 323. In response to a signal from the control circuit 323, the central processing unit CPU recognizes that the heater 207 is turned off, and then turns the motor and the neutralizer 21 on. When the motor 273 is set in motion, a timing pulse TP causes TPCOU to count up. When the count reaches a given number N, both the motor 273 and the neutralizer 21 are turned off, and the heater F/F is reset and the mask for INT1 is set. When the motor stops, the record 11 has moved to a position shown in FIG. 78 (2) where the non-record area x is located upstream of the neutralizer 21 and immediately before the follower roller 12. The mask for INT2 is set to avoid the possibility that noises may be fed to the input system which receives the sub-scan sync mark detection signal during the rotation of the motor.

2. Main Routine

While not shown in detail in FIG. 77 (2), the main routine executes programs relating to the display of the number of copies, record enablement (ready/busy), the exhaustion of record sheet, the exhaustion of toner, the occurrence of a jamming in the feeding and conveying system, an error of the sub-scan synchronization, an error in the timing pulse, the breakage of a thermistor and the recovery of tone, all by the display 318.

An error in the sub-scan synchronization and the timing pulse is checked during the time the record 11 is in motion. The sub-scan sync mark z on the record 11 is detected by the detector 72, and unless the sub-scan sync mark is detected for the next time within a time interval which is slightly longer than the time required for the record 11 to complete its one revolution, it is determined that an error has occurred in the sub-scan synchronization. The timing pulse generator 314 produces a timing pulse in response to the movement of the record 11, and there is provided a timer having a duration which is greater than the normal pulse interval to enable a determination that an error in the timing pulse has occurred in the event the timing pulses are not produced within the duration of the timer. If a breakage of the thermistor occurs when the printer is in its mode, the fixing unit control circuit 323 immediately displays the breakage by establishing a busy condition. However, if the breakage occurs in the process of the record operation, the busy condition is established upon completion of the process being executed.

Part of the fixing unit control circuit 323 is shown in FIG. 79 where TH represent a thermistor, TP a thermal fuse disposed within the fixing unit 20, TR1 a transistor, OP1 a comparator and R1 to R7 resistors. The purpose of the thermistor TH is to detect the temperature of the fixing unit 20, and has a characteristic such that it exhibits a high resistance at low temperatures and a low resistance at elevated temperatures.

A thermal fuse TP, resistor R₂, thermistor TH, and another resistor R₃ are connected in series, and a constant voltage V is applied across the series circuit. Both the thermal fuse TP and the thermistor TH are disposed in a region adjacent to the heater of the fixing unit 20. The junction B between the resistor R₂ and the thermistor TH is connected to the inverting input of an operational amplifier OP1, operating as a comparator, and the junction between the thermistor TH and resistor R₃ is connected to the base of a transistor Tr1. A reference voltage, produced by a division of the constant voltage V, is applied to the non-inverting input of the amplifier OP1. The comparator OP1 compares the potentials at the points A and B against each other, and responds to the temperature detected by the thermistor mistor by providing an low level or "0" whenever the heater temperature is below a given value and providing a high level or "1" whenever the heater temperature exceeds the given value, such output being applied to the input port of RAM. The breakage of the thermistor TH causes the transistor Tr1 to be turned off, whereby an abnormality signal of a high level or "1" is applied to the input port RAM. In the event of blowout of the thermal fuse TP, the transistor Tr1 is similarly turned off, applying an abnormality signal of high level or "1" to the input port of RAM. In either instance, the single line is utilized to signal to CPU the occurrence of high level "1" which represents an abnormality. CPU responds to the high level by interrupting the sequence of printing operation according to a given schedule and alerts the occurrence of an abnormality.

When examining the exhaustion of record sheet, the paper end sensor 133 contained in the circuit 325 detects the presence or absence of record sheet in the tray 3. It produces a sheet exhausted signal when the record sheet is exhausted. In response thereto, the central processing unit CPU resets print F/F (P F/F) to 0, sets a last paper F/F (RP F/F) to 0 and sets an end F/F (E F/F) to 1, thereby allowing the display 318 to indicate the exhaustion of record sheet. The record operation is terminated when the last record sheet has been delivered to the abutment 10.

The occurence of a jamming in the feeding and the conveyor system is checked at a given count of timing pulses, as will be noted from the timing chart of FIG. 81 and the flow chart of FIG. 77 (6). Upon occurrence of a feed mistake, the heater and the process are turned off, bringing a write enable signal WRE to 0. Because the motor is not stopped, its motion is stopped after completion of the sheet delivery during the preceding step. Upon occurrence of a jamming in the course of conveying the record sheet, the motor, the heater and the process are immediately turned off in response to the detection of a jamming since the record sheet may be entangled into the fixing unit 20 or the conveyor system. The display 318 obviously indicates the occurrence of such a feed mistake and jamming. The detection of a feed mistake and jamming will be described in detail later.

A key input is checked by examining a print input or a count of copies input from the operating panel 317.

In the main routine, the operations described above are repeated except when an interrupt operation takes place.

3. Power off (see FIG. 77 (3))

This operation is included as part of an error check routine.

Initially a check is made to see if the motor is turned off, and if the power switches 311 are turned off when the motor is off. The central processing unit CPU receives a low level input when the power switches 311 are turned on, and receives a high level input when the power switches 311 are turned off. When the power switches are turned off, the timing pulse counter TPCOU is cleared to turn the heater off and to turn the motor on while resetting the mask for INT1 and setting the mask for INT2. When the motor is set in motion, the timing pulse TP is counted by TPCOU, and when the count reaches a given value M, the motor is turned off, followed by turning the transistor 313 off with a certain time delay. The main relay 307 is turned off, thus deenergizing the a.c. drive system 309 and the control system power source 310. The record 11 then comes to a stop at the position shown in FIG. 78 (1).

4. Print start (FIG. 77 (4))

When a print key on the operating panel 317 is turned on, a key input check routine responds thereto by setting P F/F and resetting RP F/F and E F/F to 0. SETCOU is then checked to see if any number is present. If the preset number is found to be equal to 0, SETCOU is set to 1. The mask for INT1 is then set while the mask for INT2 is reset. Finally, the motor 273 and the neutralizer 21 are turned on.

5. INT2 operation in response to sub-scan sync signal (FIG. 77 (5))

When a sub-scan sync signal is supplied from the detector 72, INT2 routine is executed. Initially the mask for INT1 is set to inhibit an interrupt operation in response to a timing pulse, and after a certain time delay, a check is made to see if there still occurs the sub-scan sync signal. If no sub-scan sync signal is detected, the mask for INT1 is reset, returning the program to the start. The prupose of checking the sub-scan sync signal is to assure against the presence of any flaw or dust at a location other than the mark on the record 11. Accordingly, if a mark is once detected by the detector 72, unless it is detected during the next check, a decision is rendered that it is not a normal mark, thus preventing a malfunctioning. When a mark is determined to be normal, TPCOU is reset to 0 and it is checked whether RP F/F is set. If RP F/F is not set, SETCOU is checked. If RP F/F is set, E F/F is set, thus setting the mask for INT2. If a check of SETCOU reveals that its count is not 0, the operation goes to a routine which sets the mask for INT2. If SETCOU is found to be 0, RP F/F is set, thus setting the mask for INT2. After setting the mask for INT2, the mask for INT1 is reset, returning to the routine from which an interrupt has occurred. The detection circuit which detects the sync signal is shown in FIG. 82 and will be described later.

6. INT1 operation in response to timing pulse (FIGS. 77 (6) and 81)

When the timing pulse is supplied, it is counted by TPCOU, which controls various operations.

(1) When a print signal from a print key on the operating panel 317 is inputted, the mask for INT1 remains set until the sub-scan sync mark is detected by the detector 72, and hence TOCOU does not operate (as mentioned previously in connection with the print start). P F/F assumes a value of 1.

(2), When the motor is set in motion and the sub-scan sync mark is detected by the detector 72, TPCOU is reset to 0 and the mask for INT2 is set while resetting the mask for INT1. Accordingly, TPCOU counts up for each timing pulse which is applied subsequently. The mask for INT2 is left in its set condition until TPCOU reaches a given value L, thus inhbiting an interrupt operation in response to a mark detection signal from the detector 72 in order to prevent the occurrence of a mark detection signal in response to the presence of flaw or dust on the record 11.

(3) The timing pulse is counted by TPCOU, and a check is made to see if heater F/F is equal to 0. If it is 0, the charger 14 is turned off at the time when the count of TPCOU reaches a present value A. If the heater F/F assumes a value of 1, the operation enters the power on routine.

(4) When the count of TPCOU reaches a preset value B, WRE is reset to 0, but without effect since WRE is not originally set at the print start.

(5) The charger is turned on when TPCOU assumes a value of 1.

(6) When TPCOU assumes a preset value of J, WRE is set 1, allowing an external timer TM to start. As shown in FIG. 80, the timer TM receives the input WRE through an inverter N1 and a differentiator including capacitor C1 and resistor R8.

Referring to FIG. 80, there are shown flipflops F1 to F4, inverters N1 to N5, capacitors C1 to C7, resistors R8 to R14, gates A1 to A3, drivers DR1, DR2, conveyor clutch MC1 (shown by numeral 299 in FIG. 4) which drives the conveyor system, and feed clutch MC2 (shown by numeral 304 in FIG. 4) which drives the feed roller 6a. The flipflop F1 is set by WRE, and is reset by a detection signal from the resistor sensor 179 (FIG. 2). The flipflop F2 is set by a detection signal from the register sensor 179, and is reset by a detection signal from the delivery sensor 272 (FIG. 61). The register sensor 179 detects a record sheet at the location of the conveyor roller pair 18 while the delivery sensor 272 detects a record sheet at the location of the delivery port. The central processing unit CPU checks outputs from the flipflops F1 and F2 at a given timing to render a determination concerning a feed mistake and a jamming.

(7) (a) When TPCOU reaches a present value of C, FSYNC, a signal externally supplied and indicative of the width of an image, is checked and if it is equal to 1 and there is no conveyor jamming, the operation returns to the start.

(b) If FSYNC is not equal to 1, WRE is reset to 0, turning the charger 14 off.

(c) When a conveyor jamming is checked during the step (a) or (b), the occurrence of a conveyor jamming is determined to be present if the sheet does not reach the delivery sensor 272 and the flipflop F2 is set. The conveyror jamming F/F is then set to 1, turning the charger 14 and the transfer charger 19 off, with the display 318 providing an indication to this effect.

(8) (a) If SETCOU is not equal to 0 and RP F/F is equal to 0 when TPCOU reaches a present value of D, a feed signal and a conveyor signal are outputted to set the filiflops F3 and F4, thus turning the convoyor clutch MC1 and the feed clutch MC2 on while decrementing SETCOU by one. If SETCOU is not equal to 0 and RP F/F is equal to 0, the operation returns to the start.

(b) If SETCOU is not equal to 0 and RP F/F is equal to 1 after decrementing SETCOU by one in the step (a), P F/F is reset to 0, returning the operation to the start.

(c) If SETCOU is equal to 0 after decrementing SETCOU by one in the step (a), P F/F is reset to 0, returning the operation to the start.

(d) If SETCOU is not equal to 0 and RP F/F is equal to 1, P F/F is reset to 0, returning the operation to the start.

(e) If SETCOU is equal to 0, the charger 14 is turned off. RP F/F is set to 1 while P F/F is reset to 0, returning the operation to the start.

(9) When the sheet reaches the location of the register sensor 179, both flipflops F3 and F4 are reset, turning the feed clutch MC2 and the conveyor clutch MC1 off.

(10) When TPCOU reaches a present count of E, the feed signal is turned off to supply a reset signal to the flipflop F4, thus turning the feed clutch MC2 off.

(11) When TOCOU reaches a present count of F, a jamming is checked, and if the sheet does not reach the register sensor and the flipflop F1 is set, it is determined that there occurred a feed mistake, setting the feed jamming F/F to 1 to turn the charger 14, the transfer charger 19, the feed clutch MC2 and the conveyor clutch MC1 off. The display 318 displays the occurrence of a jamming.

(12) When TPCOU reaches a preset count of G, the transfer charger 19 is turned off.

(13) When TPCOU reaches a preset count of K, the transfer charger 19 is turned on.

(14) When TPCOU reaches a preset count of L, the mask for INT2 is reset.

(15) When TPCOU reaches a preset count of H, and if RP F/F and E F/F are equal to 1's, the entire process including the rotation of the motor 273 is turned off, setting the masks for INT1 and INT2. The record 11 now comes to a stop at the same position as it assumed at the print start.

A. "1" in P F/F allows the operations mentioned above under the sub-paragraphs (1) to (14) to be performed, but "1" in RP F/F prevents the feed clutch MC2, the conveyor clutch MC1, the charger 14 and the transfer charger 19 from being turned on.

B. If both RP F/F and E F/F are set to 1, only the operation under the sub-paragraph (15) takes place.

It should be understood that during the operation A or B takes place, other items may be checked or other components may be turned off without causing any difficulty. In the example shown, the record 11 moves through three revolutions when a single copy is to be produced.

As discussed above, in accordance with the invention, the position where the record stops after a record operation is located upstream of re-usable step (neutralizing and claning step) as close thereto as possible. In this manner, the time spent until the record operation is initiated is reduced, as is the movement of the record upon completion of the record operation. Because the re-usable step is not entered intermediate its length, it is possible to use the record repeatedly under identical conditions, assuring the formation of a good image.

The junction x in the record 11 located in the non-record area is contrasted to the remainder of the record in that it is uneven in profile, has a reduced strength and is liable to cause an exfoliation of photoconductive layer. Accordingly, it is undesirable that the junction be located around the curved regions E, E1 (FIG. 22) when the record comes to a stop. In this respect, it will be seen that according to the invention, the junction is located on a linear zone, preventing any force from acting upon the junction which tends to weaken it, thus assuring that the mechanical strength of the record be maintained over a prolonged period of time.

One technique to detect a sync signal will now be described with reference to FIGS. 82 and 83. FIG. 82 shows a sync signal detector circuit SDA where A₁, A₂ represent AND circuits, MM₁, MM₂ monostable multivibrators, INV₁ INV₂ inverters. The operation of the detector circuit SDA will be apparent by reference to waveforms of signals shown in FIGS. 83(a) to (f), but will be briefly described below.

The output signal from the detector 72, FIG. 83(a), is applied to ttone input of AND circuit A₁, the other input of which is connected to receive a high level signal from the inverter IV₂. When the signal from the inverter INV₂ is high, AND circuit A₁ produces an output in the form of a pulse Ps. The monostable multivibrator MM₁ is triggered by the leading edge of the pulse Ps to produce an output pulse Pm1. FIG. 83(b), having a pulse width τ_m which is less than the pulse width τ of the normal sync signal.

The pulse Pm1 is inverted into a pulse Pn1, FIG. 83(c), by the inverter INV₁, which pulse is then supplied to one input of AND circuit A₂. The other input of AND circuit A₂ is fed from the output of AND circuit A₁ has a greater pulse width than the output pulse τ_m from the monostable multivibrator MM₁, there is produced on the output side of AND circuit A₂ a pulse Pst shown in FIG. 83(d).

When the signal supplied from the detector 72 is not the sync signal Ps, but is a noise, the pulse width of the noise which is greatly reduced as compared with the pulse width τ of the sync signal prevents such noise pulse from being outputted by AND circuit A₂. In this manner, the output pulse Pst from AND circuit A₂ is supplied to CPU as a true sync signal.

It Will be seen that when the printer is performing a continuous record operation, the record 11 is moving at a uniform speed so that the prevailing sync signal will appear at a given time interval T₁. Accordingly, when a true sync signal is detected by AND circuit A₂, a gate signal may be formed having a pulse width T₂ which is slightly less than the period T₁ of the sync signal and referred to the time of occurrence thereof and applied to AND circuit A₁, thus enabling a more reliable detection of the sync signal.

In FIG. 82, the output pulse Pst from AND circuit A₂ is applied to the monostable multivibrator MM₂, which is triggered by the trailing edge of the output pulse Pst to produce a pulse Pm2, FIG. 83(e), of a pulse width T₂ which is slightly less than the period T₁ of the sync signal on its output side. The pulse Pm2 is fed through the inverter INV₂, which converts it into a gate pulse Pn2. FIG. 83(f), to be applied to AND circuit A₁.

It will be appreciated that the described techhique allows a true sync signal to be detected from among output signals of the detector 72 and to supply the sync signal to the control unit.

The printer of the invention is provided with safeguard means, the control of which is simplified, to assure against the occurrence of a trouble in conveying the record sheet, such as a feed mistake or paper jamming. Such safeguard means include the paper end sensor 133 which detects the presence or absence of record sheet or sheets in the tray 3, a write enable circuit which is enabled when "sheet present" signal is produced to supply a signal which permits a supply of the record sheet, the register sensor 179 disposed rearwardly of the conveyor roller pair 18 for detecting whether or not a record sheet fed by the feed roller 17 is present at the location of the sensor, the register sensor 272 (FIG. 61) disposed in the region of the delivery roller 25 for detecting the presence or absence of the record sheet, register failure detection means responsive to the write enable signal for producing a "feed success" signal if the record sheet is detected by the register sensor 179 and for producing a "feed success" signal regardless of the register sensor 179 in the event the write enable signal is not produced, and jamming detection means for producing a "no jamming" signal if the presence of the record sheet is detected by the delivery sensor 272 after the presence of the record sheet has been detected by the register sensor 179, a "jamming" signal if the delivery sensor 272 fails to detect the presence of the record sheet, and a "n jamming" signal regadless of the delivery sensor 272 in the event the register sensor 179 has detected the absence of the record sheet. Independently from the status of the paper end sensor 133, register failure detection means and jamming detection means, a sampling operation is maintained at suitable timings as the process proceeds.

Referring to FIG. 84, when the motor is set in motion, FIG. 84(a), and the sync signal is supplied, FIG. 84(b), the process control proceeds on the basis of the sync signal. After the occurrence of the sync signal, an output from the paper end sensor is sampled. FIG. 84(m), at a time t₁, and an output from the jamming detection means is sampled at a time t₂, FIG. 84(l), and a feed mistake is sampled at a time t₃, FIG. 84(k), all under the control of CPU (FIG. 76). The write enable is outputted, FIG. 84(c), after it has been determined that the record sheet has not exhausted, and subsequently the feed drive system is activated. A flipflop circuit F1 is set, FIG. 84(i), by the leading edge of the write enable, and is reset, FIG. 84(i) by the leading edge of the register sensor 179, FIG. 84(g) Thus, the write enable output is construed as a feed success in the event an output from the register sensor 179 has a leading edge until t₃, and is construed as a feed failure in the event such output has no leading edge until time t₃. In the latter instance, the feed drive system is stopped, the heater 207 (FIG. 61) is turned off, and after the preceding record sheet is delivered out of the printer, the motor is stopped, providing a display of a feed failure or mistake. In the event the write enable is not outputted, the flipflop circuit F1 is not set, and this is construed as a feed success. A flipflop circuit F2 is set, FIG 84(j), by the leading edge of the register sensor 179, and is reset, FIG. 84(j), by the trailing edge, FIG. 84(h), of the delivery sensor 272 (FIG. 61). Specifically, after a successful feed operation, if there is a leading edge from the delivery sensor 272 until time t₂ of the next cycle, no jamming is determined. However, if there is a leading edge, the occurrence of jamming is determined, the heater 207 is turned off, and the entire drive system is stopped with a display of jamming. In the event of a feed failure, the flipflop circuit F2 is not set, and hence a jamming is not detected during the delivery operation of the preceding record sheet.

FIG. 85 shows a series of timing charts which are applicable when the paper end or exhaustion is detected. In the example, shown, the paper end is detected during the second cycle. When the paper end is detected (see T₁ in FIG. 85), no write enable is outputted, and the feed drive system does not operate. Consequently, the flipflop circuit F1 is not set, and accordingly if a signal is sampled in order to detect a feed failure, a feed success results. Since no transfer sheet is supplied to the register sensor 179, the flipflop circuit F2 is not set, and hence any operation to detect a jamming results in the determination of no jamming. While in the above description, the paper end is detected at a given timing, it is only necessary that it be detected before a signal is outputted which indicates that a feed operation is going to take plate. In the example shown, such signal corresponds to the write enable.

FIG. 86 graphically illustrates a series of timing charts for the occurrence of a feed mistake, which is assumed to occur during a second cycle. Upon occurrence of a feed mistake (see T₂ of FIG. 86), the heater 207 is turned off in order to prevent any danger, but the preceding record sheet on which the image is properly formed is fixed by utilizing waste heat of the heater 207 and is delivered externally of the printer. The motor comes to a stop when the record reaches a given position. In the meantime, a jamming detection is made, but the failure of the flipflop F2 to be set as a result of the feed mistake allows a determination to be rendered that no jamming has occurred, whereby a safeguard operation takes place alone reliably as a result of feed mistake.

FIG. 87 is a flow chart for the described operations which may be carried out by using a microcomputer or the like. The least significant bit at address X performs the same function as the flipflop F1, and the status of the register sensor is fed to the least significant bit of N-th I/O, which status represents "0" when the record sheet is "present" and is equal to "1" when it is absent. The least significant bit at address Y performs the same function as the flipflop F2 and the status of the delivery sensor 272 is fed to the least significant bit of M-th I/O, which status represents "0" when the record sheet is "present" and represents "1" when it is absent.

It will be evident from the foregoing description that in accordance with the invention, a simple arrangement utilizing a pair of flipflop permits a sampling of individual outputs at times t₁, t₂ and t₃ in each of blocks A1, A2, B and C, thus facilitating a simplified control. In addition, the paper end or feed mistake removes the necessity to prevent a subsequent detecting operation, further simplifying the control in an advantageous manner.

In accordance with the invention, there is provided means which turn off the power supplies after desired processings have been completed within the printer and after the region of the record where an image to be formed was moved out of the region of the charger.

Said means comprises a power connection apparatus connected between a commercial a.c. source and a receiving end including the power supply unit, in combination with power turn-on means which allows the receiving end to be fed from the a.c. source. When the turn-on means is closed, the connection apparatus is brought to its "connected" condition, and when the turn-on means is disconnected, the connection apparatus is brought to its "interrupted" condition after completion of necessary processings within the printer.

In the printer of the invention, an error in the timing can be reliably detected with a reduced cost arrangement, while avoiding the use of time limit circuit or elements which are analog in nature. Specifically, in accordance with the invention, the count of timing timing pulse which has occurred since the detection of the mark is monitored, and an error in the timing is detected when such count exceeds a given value which is slightly greater than the magnitude of a count which would be reached during the movement of the record between successive detections of the mark. In this manner, the central control unit which effects the primary timing control can be utilized to detect an error by digital processing of the timing pulses. This avoids the need for any external timer, and enables an error detection which is substantially free from the influence of tolerances in the values of C and R components or temperature fluctuations.

In accordance with the invention, a variation in the offset which results from the initialization of the timing pulse count is avoided. Specifically, in accordance with the invention, a count C_T of timing pulse is compared against a standard value Q at the time when the mark is detected, and a deviation C_T -Q therebetween is chosen as an initial count. By way of example, if the count C_T at the time the mark is detected is equal to A-1, it is determined that the timing pulse occurred immediately after the detection of the mark during the previous initialization or that the control timing during the previous cycle has been advanced by one timing pulse, relative to the position of the record. Consequently, the initial count is now preset to -1, thus delaying the control timing to be used during the current cycle by one timing pulse relative to the position of the record. If C_T =Q+1 at the time when the mark is detected, it is determined that the timing pulse has occurred immediately before the detection of the mark during the previous initialization or that the control timing used during the previous cycle has been lagging by one timing pulse relative to the position of the record. Accordingly, the initial count during the current cycle is preset to +1, thus delaying the control timing during the current cycle by one timing pulse as compared with the previous cycle. If C_T =Q, the initial count of 0 is chosen, assuming that the control timing matches the position of the record.

In the prior art practice, any timing pulse which occurs during the time the mask INT1 is being set is neglected, resulting in a non-uniform image width (in the sub-scan direction). An actual image width is determined in accordance with a preset number of timing pulses (count J→B in the timing chart). If TP.COU is reset to 0 during such time, there occurs an error of 0±1 in the number of counts from J to B. Accordingly, in the present embodiment, above situation is taken into consideration by comparing the prevailing count of TP.COU with a number of timing pulses (count Q) required for the record 11 to complete one revolution, and by setting TP.COU equal to FF, to 1 to 0, respectively, if it is equal to Q-1, Q+1 or other than Q±1, respectively (It is that TP.COU comprises 8 bits and provides a hexadecimal code.) Hence, if the sum of the delay time and the number of instructions executed by INT2 is substantially equal to the duration of the width of the timing pulse, there results a substantially uniform image (print) width. Any deviation can be held within two-third the usual value. Since TP.COU is equal to 0 at the start, there is no change in the content of TP.COU. While the initial count of 0 is used, it should be understood that the initial count need not be limited to 0. While it is assumed that the timing pulse has an error in a range of 0±1, it is also possible to use an error of 0±5, for processing by a program.

In the flow chart which controls the print operation, a slip may occur between the drive roller or follower roller and the record 11 during the time the belt is driven. Any slip may cause a disturbance in the image as a result of an exposure onto the non-record area or lagging operations in various steps. For this reason, a number (P) which is slightly greater than the number of timing pulses required for one revolution of the record is preset in the program which is used to execute the flow chart. There is no problem whatsoever if the record 11 is maintained in close contact with the roller since the sub-scan sync signal has been sensed (INT2). On the contrary, if dust, toner or the like becomes interposed therebetween during use to cause a slip so that a greater number of timing pulse than normal are counted and the preset value P is reached, the sub-scan error flipflop is set to 1. Under the normal driving condition, the counter is initialized by the detection of the mark until the preset value P is reached, and hence the sub-scan error flipflop cannot be set. If the sub-scan error flipflop is set to 1 by reaching the preset value P, the flip-flop is set in the error check flow chart shown in FIG. 77 (3), whereby various mechanism are deenergized and an error display is given.

FIGS. 90 and 91 show different forms of the power supply unit. In the arrangement of FIG. 90, the power turn-on means comprises an NPN power transistor circuit 322, which is connected to the coil of a main relay 307. In this manner, the circuit 322 is turned on in response to an external power on signal, thereby closing the main relay 307. The external power on signal is fed to the input port of ROM, which is monitored by CPU, which controls the printing operation and the opening/closing of the main relay 307 in the manner mentioned above. When the power supply is to be turned on in response to an operation by an operator, the circuits 313 and 332 are shunted by a power switch 311. In the arrangement of FIG. 91, in order to eliminate the power dissipation in the a.c.-to-d.c. conversion circuit 308 during the time the power supply is turned off, the circuit 308 is eliminated, and is replaced by a double-pole power switch 333 which is connected in shut with the relay 307. In this manner, the power dissipation is entirely eliminated when the power switch 333 is open, there is no external power on signal and CPU turns the switching circuit 313 off.

Claims

1. A compact, electrophotographic printer comprising:

a housing having a front wall and a rear wall, side walls, a top wall, and a bottom wall, said walls defining an interior space;

a sheet feeder for feeding a sheet in said housing;

sheet moving means defining a sheet moving path for moving a sheet fed from said sheet feeder;

electrophotographic components positioned in said interior space along the sheet moving path;

fixing means disposed at an end of the sheet moving path for fixing an image on the sheet;

a sheet delivery unit for receiving the sheet discharged from a sheet discharging port in said printer and having a delivery port for delivering the sheet on said top wall;

a delivery roller disposed in said delivery port;

guide members for guiding the sheet discharged from the printer to said delivery roller;

delivery roller driving means engageable to a rotating member disposed at said sheet discharging port for rotating said delivery roller; and

a cover which is a portion of said top wall, covering an upper portion of said fixing means, wherein said cover is attached to said printer so as to be openable;

wherein said rotating member disengages from said delivery roller driving means when said cover is opened; and

wherein said sheet delivery unit deposits the sheet on said top wall substantially over said electrophotographic components.

2. A compact, electrophotographic printer according to claim 1, wherein said top wall has an opening formed therein through which said fixing means is accessible, and said sheet delivery unit is hinged on said rear wall so as to be pivotable from an operating position covering said opening to a service position exposing said opening.

3. A compact, electrophotographic printer according to claim 1, wherein said sheet delivery unit is detachably hinged to said rear wall so as to be detachably removable therefrom, and wherein said printer further comprises a cover which is hingably mounted to said rear wall to pivotably cover and expose said sheet discharging port, in place of said sheet delivery unit, said cover having a rear opening exposing said sheet discharging port through said rear wall for allowing sheets to be discharged out a rear side of said housing, and a receiving tray mounted at the rear side of said rear wall for receiving the discharged sheets thereon.

4. A compact, electrophotographic printer according to claim 1, further comprising a photosensitive member and means for forming a latent image on said photosensitive member wherein said latent image forming means includes means for receiving image data from an external device corresponding to an image to be recorded, and exposure means for optically exposing said photosensitive member to a light beam.

5. A compact, electrophotographic printer according to claim 4, wherein said external device is a computer.

6. A compact, electrophotographic printer according to claim 4, wherein said exposure means includes a laser beam exposure unit.

7. A compact, electrophotographic printer as in claim 4, wherein said exposure means comprises an optical scanning means.

8. A compact, electrophotographic printer according to claim 1, further comprising a photosensitive member and developing means, both of which are removable from said printer as a unit.

9. A compact, electrophotographic printer as in claim 1, including side plates for guiding said sheets delivered on said top wall.

10. An image forming apparatus comprising:

a photosensitive member and a first gear secured thereto for rotation about a first axis, a charger electrostatically charging the photosensitive member, an exposure device forming latent images at said photosensitive member, a developing device developing said latent images into developed images and a second gear secured thereto for rotation about a second axis, a paper supply device, an image transfer device transferring said developed images to paper supplied from the paper supply device, a fixing device fixing the images transferred to said paper, and a paper discharging device discharging paper with images fixed thereon;

a single unit comprising a frame supporting at least said photosensitive member and said developing device, said frame supporting said first and second gears for rotation, with the first and second axes substantially parallel to each other and spaced from each other by a selected distance, and with the first and second gears meshed with each other to rotate in synchronism;

said apparatus including a housing having a mounting structure defining an insertion/removal path for said single unit along which said single unit is inserted into the housing to an operative position and is manually removed from the housing;

wherein said insertion/removal path is substantially perpendicular to said first and second axes;

a selectively rotating driving gear in said housing;

one of said first and second gears meshing with said driving gear to be driven thereby when said single unit is inserted into the housing to said operative position;

whereby when the single unit is at its operative position in the housing, the driving gear drives one of said first and second gears, and the driven gear in turn drives the other one of said first and second gears to ensure a positive power transmission from the driving gear to the first and second gears, and wherein the single unit can be inserted into or removed from the printer while allowing a positive control of positioning.

11. An image forming apparatus as in claim 10, wherein said apparatus is a printer.

12. An image forming apparatus as in claim 11, including a face-down output portion formed at a top surface of said printer, wherein said paper discharging device discharges paper with images fixed thereon onto said output portion.

13. An image forming apparatus as in claim 11, in which said housing has side walls extending along said insertion/removal path and a front, and wherein said single unit is inserted/removed from in front of the printer.

14. An image forming device as in claim 11, in which said housing has side walls extending along said insertion/removal path and a front, and said housing includes a mounting structure defining another insertion/removal path along which said sheet supply device is inserted into and removed from the housing from in front of the printer.

15. An image forming device as in claim 11, in which said housing has side walls extending along said insertion/removal path and a front, and said printer includes a display and a control panel visible to and directly accessible by a user directly from in front of the printer.

16. An image forming apparatus comprising:

a photosensitive member, a charger electrostatically charging the photosensitive member, an exposure device forming latent images at said photosensitive member, a developing device developing said latent images into developed images, a paper supply device, an image transfer device transferring said developed images to paper supplied from the paper supply device, a fixing device fixing the images transferred to said paper, and a paper discharging device discharging paper with images fixed thereon;

a single unit comprising a frame supporting at least said photosensitive member and said developing device;

said apparatus including a housing having a mounting structure defining an insertion/removal path for said single unit along which said single unit is inserted into the housing to an operative position and is manually removed from the housing;

wherein said insertion/removal path is substantially perpendicular to a longitudinal rotational axis of said photosensitive member;

a selectively rotating driving gear in said housing;

a driven gear mounted for rotation at said frame and meshing with said driving gear to be driven thereby when said single unit is inserted into the housing to said operative position;

wherein said frame has a sidewall transverse to said rotational axis, and said driven gear is mounted in a position substantially inside said side wall, thereby facilitating insertion/removal of the single unit.

17. An image forming apparatus as in claim 16, wherein said apparatus is a printer.

18. An image forming apparatus as in claim 17, including a face-down output portion formed at a top surface of said printer, wherein said paper discharging device discharges paper with images fixed thereon onto said output portion.

19. An image forming apparatus as in claim 17, in which said housing has side walls extending along said insertion/removal path and a front, and wherein said single unit is inserted/removed from in front of the printer.

20. An image forming device as in claim 17, in which said housing has side walls extending along said insertion/removal path and a front, and said housing includes a mounting structure defining another insertion/removal path along which said sheet supply device is inserted into and removed from the housing from in front of the printer.

21. An image forming device as in claim 17, in which said housing has side walls extending along said insertion/removal path and a front, and said printer includes a display and a control panel visible to and directly accessible by a user directly from in front of the printer.

22. A compact electrophotographic printer delivering printed sheets stacked face-down at the top of the printer in the order of printing so that the sheets are collated as delivered, said printer having a control panel and a display directly accessible to the user for viewing and operation from in front of the printer and said printer being configured for the manual insertion/removal by the user, from in front of the printer, of both a sheet supply and a single unit carrying at least a photosensitive member and a developing unit in directions generally parallel to the side walls of the printer so that the printer need not be accessible from other sides for that purpose and can reduce the use of office space in operation, comprising:

a printer housing having a front and a back, a top, left and right side walls, and an input for externally generated digital signals representing matter to be printed;

said top comprising an output portion for face-down delivery of printed sheets stacked in an order of printing, said output portion being directly user-accessible from in front of the printer;

a display and a control panel mounted at printer locations comprising areas spaced from said left and right walls and directly visible and accessible by a user from in front of the printer;

a sheet supply manually inserted into the printer directly from in front of the printer, in a direction generally parallel to the left and right side walls, and removable manually from the printer in an opposite direction;

internal components defining a sheet path generally parallel to said left and right side walls and extending from said sheet supply to said output portion and changing direction at an intermediate portion of the path;

a sheet feeder feeding sheets in succession from said sheet supply into said path;

electrophotographic components including at least a photosensitive member having an axis of rotation extending in a direction from one to the other of said left and right side walls, an exposure unit receiving digital signals from said input and in response forming latent images at said photosensitive member, a developing unit developing latent images formed at the photosensitive member, and a transfer unit transferring developed images from said photosensitive member to sheets fed along said path, wherein at least said photosensitive member and said developing unit are joined into a single removable unit;

a mounting structure for said removable unit defining an insertion/removal path generally parallel to said left and right side walls along which a user manually inserts the removable unit in the printer and manually removes the removable unit from the printer; and

a printed sheet ejector receiving sheets with images transferred thereto and delivering the received sheets face-down onto said output portion stacked in the order of printing so the sheets are collated as delivered.

23. An electrophotographic printer as in claim 22, in which said insertion/removal path extends generally toward the back of the printer for insertion and toward the front of the printer for removal of the removable unit.

24. An electrophotographic printer as in claim 23, in which the sheet path extends generally from the front toward the back of the printer and then from the back toward the front of the printer.

25. An electrophotographic printer as in claim 24, in which the display and control panels are at the front of the printer.

26. An electrophotographic printer as in claim 25, including a power on/off switch mounted at the front of the printer.

27. An electrophotographic printer as in claim 22, in which at least a portion of the output portion is vertically aligned with and overlies the photosensitive member.

28. An electrophotographic printer as in claim 22, including at least one rib at a front portion of said removable unit to facilitate grasping by the user for removal of the unit from the printer.

29. An electrophotographic printer as in claim 28, in which said rib has a side visible from in front of the printer after the unit has been inserted in the printer in an operational position.

30. An electrophotographic printer as in claim 22, in which said printing sheet ejector is positioned to eject sheets at a level higher than that of at least a portion of said output portion facing the back of the printer.

31. An electrophotographic printer as in claim 22, in which the back of the printer includes a hinged cover manually movable to an open position to allow access to a portion of said sheet path.

32. A method of printing matter represented by externally generated digital signals supplied to a printer, comprising the steps of:

receiving digital signals supplied from an external source and representing matter to be printed at a printer having left and right sides, a front and a top;

electronically processing said digital signals into optical printing signals and exposing therewith a photosensitive member in the printer to thereby form latent images thereon and developing the latent images;

guiding sheets along a sheet path generally parallel to the left and right sides of the printer and extending within the printer from a sheet supply to an output portion at the top of the printer;

transferring developed images from the photosensitive member to sheets moving along said sheet path;

delivering sheets with images transferred thereto from said sheet path onto said output portion in a direction generally parallel to said left and right side of the printer, stacked face-down, with each successively printed sheet over the sheet printed last and with the printed sheets collated as delivered to the output portion;

manually inserting a sheet supply into the printer within a first guiding structure for insertion/removal of the sheet supply and manually removing the sheet supply from the printer within said first guiding structure in directions generally parallel to said left and right sides of the printer;

manually inserting a photosensitive member and a developing unit formed as a single unit into the printer within a second guiding structure and manually removing said unit from printer within said second guiding structure along directions generally parallel to the left and right sides of the printer; and

displaying printer function and manually inputting printer commands at printer locations that are spaced from the left and right sides of the printer;

whereby a user services the printer by inserting/removing the paper supply and the unit containing the photosensitive member and the developing unit, and observes the display and operates the control panel, from in front of the printer without needing access to other sides of the printer for that purpose and thereby said method reduces office space requirements for the operation and user servicing of said printer.

33. A method as in claim 32, in which said guiding comprises guiding said sheets along a path that initially extends from the front toward the back of the printer and then turns up toward the top of the printer.

34. A method as in claim 33, in which the user gains access to at least the portion of the path that turns up toward the top of the printer by manually pivoting at least a hinged portion of a back wall of the printer about a hinge axis extending in a direction from one to the other of the left and right sides of the printer.

35. A method as in claim 33, in which the direction in which the user manually inserts said unit into the printer is toward the back of the printer.

36. A method as in claim 35, in which the user inserts said sheet supply into the printer is toward the back of the printer.

37. A method as in claim 33, in which the user turns the printer off and on by manually operating a switch at the front of the printer.

38. A method as in claim 33, in which the user removes said unit by grasping a rib formed therein and pulling in a direction away from the back of the printer.