Developing system

Abstract

A developing system is provided for a copying process such as an electrophotographic copying process in which a developer is supplied to the surface of a member which is formed with an electrostatic latent image to provide developing thereof. An electrode is disposed opposite the surface of the member with the developer interposed therebetween, and the induction potential of the electrode is maintained below a given value by means of a constant voltage element. The potential of the electrode is induced by either the image portion of the member's surface having the electrostatic latent image or by an unexposed, separate charged portion thereof.

Description

This is a continuation of application Ser. No. 435,270 filed Jan. 21, 1974 , now abandoned. below above a given value.

In another electrophotographic copying process, it is known that a photosensitive paper is entirely charged, followed by an imagewise exposure to form an electrostatic latent image, which is developed by a developing solution and finally fixed. The invention can be applied to such a process. Referring to FIG. 6, there is shown a vessel 37 of developing solution within which a guide member 38 is disposed, and a counter-electrode 39 is disposed above the guide member 38 with a given spacing therebetween. A photosensitive paper 40 having an electrostatic latent image formed thereon is passed between a pair of rollers 41 and 42 and is guided by the guide member 38 to advance through the developing solution within the vessel 37 in order to have its latent image developed. Subsequently the photosensitive paper is delivered to a fixing unit. The counter-electrode 39 is connected to the ground through a constant voltage element 43, and produces the similar electrode effect as mentioned above.

It should be understood that the invention can also be applied to an electrophotographic process using a powder developer rather than a developing solution, for example, a cascade developing process. Furthermore, the invention can equally be applied to an electrophotographic process in which the developing takes place by means of a magnetic brush, as shown in FIG. 7. In the developing system shown, a plurality of magnets 44 to 47 are fixed to an arbor 48 which is driven by suitable means, not shown, for rotation within a hollow cylinder 49. The hollow cylinder 49 is disposed at a position opposite to the drum 11 and is received within a container 50. A developer 51 comprising a mixture of carrier and toner is received within the container 50, and forms a magnetic brush 52 as a result of the attraction acting between the carrier and the magnets 44 to 47. As the magnets 44 to 47 rotate, the magnetic brush 52 also rotates around the cylinder 49 to carry the toner toward the surface of the drum 11 for the purpose of developing. In accordance with the invention, a plurality of counter-electrode segments 53-1, 53-2 . . . 53-n are secured on the inner surface of the cylinder 50 and function in the same manner as mentioned previously to provide an electrode effect. As shown, the container 50 is provided with a brush length adjusting member 54 and a scraper 55 which scrapes off the magnetic brush 52.

While in the above description, the invention has been illustrated with reference to an electrophotographic copying process, it should be understood that the invention can also be applied to copying processes other than the electrophotographic copying process in which a member having an electrostatic latent image formed thereon is to be developed with a developer. It will also be noted that the constant voltage element for maintaining the potential of the counter-electrode below a given value may comprise a plurality of such elements connected in series to provide any desired threshold value.

While the above embodiments relate to the induction of the potential of the developing electrode 19 from the image portion on the drum surface 11, it is also possible to induce a potential on the developing electrode 19 from a portion of the drum 11 which is charged to a constant potential and remains unexposed. In contrast to the electrophotographic copying process in which the drum surface 11 is entirely charged by the charger as mentioned previously, FIG. 8 shows a modified body with a surface of photosensitive material 11-2 having an area 11-1 which remains unexposed by the exposure unit 13. Such area may be provided at one end or both ends of the body and may be in the form of a band having a width in the range from 5 to 50 mm, for example. A potential of a given magnitude is induced on the developing electrode 19 by the charged potential on the area 11-1, and is maintained below the threshold value of the constant voltage element 23. The supply of a developing solution to the modified surface 11-2 produces a developing of the electrostatic latent image thereon in the usual manner, and the toner on the non-image portion is electrically attracted by the developing electrode 19 to prevent the background smearing and to improve the contrast in the image, thus producing the electrode effect. The potential of the developing electrode 19 is effectively induced by the potential of the blank area 11-1 to assure a high contrast in the image, and is held below the threshold value of the constant voltage element 23, so that the loss of an image area of reduced density is avoided. Such area 11-1 may comprise an insulating material such as an insulating film or the like. The area 11-1 is kept clear of contact with the transfer sheet, and this may result in overloading the cleaning unit 17. Such an overload can be avoided by providing the developing electrode 19 with a protective member 126 which comprises sponge or felt and is aligned with the area 11-1, as shown in FIG. 9(a), or by providing the developing electrode 19 with a blade 127 comprising an elastomer such as polyurethane rubber, as shown in FIG. 9(b), the member 126 or blade 127 cleaning the area 11-1 of the modified body.

Claims

1. A developing system for electrophotographic copying apparatus for the type comprising:

a member having a surface of photosensitive material; and

means for forming an electrostatic latent image on said photosensitive surface by successive charging and exposure steps;

wherein the improvement comprises:

developing means for supplying a developer to said member to develop the latent image, said developing means comprising an electrode disposed in opposing relationship with the surface of said member with the developer interposed therebetween; and

means for permitting enabling the induced potential on the electrode from said electrostatic latent image to float below a given value, said permitting enabling means comprising constant voltage means connected between said electrode and ground for preventing said induced potential from exceeding said given value.

2. A developing system as in claim 1 further comprising means for charging an area on at least one end portion of said member adjacent said image surface during the charging step and for keeping said area unexposed during the exposure step, such that said area on the end portion of said member induces a potential on said electrode.

3. A developing system according to claim 1 wherein said electrode comprises a plurality of electode electrode elements disposed along a direction of travel of the member relative to said developing means, the plurality of electrode elements having a unidirectional conductive characteristic in a direction opposite to said direction of travel of said member.

4. A developing system according to claim 3 further comprising a plurality of diodes respectively connected between adjacent electrode elements to provide the unidirectional conducting characteristic.

5. A developing system according to claim 2 wherein said electrode comprises a plurality of electrode elements, each arranged along the direction of travel of the member of photosensitive material, the plurality of electrode elements having a unidirectionally conducting characteristic in a direction opposite to the travel of the member.

6. A developing system according to claim 5 in which diodes are connected between the adjacent electrode elements of the plurality to provide the unidirectionally conducting characteristic.

7. A developing system according to claim 1 wherein said constant voltage means comprises a constant voltage diode having a threshold value corresponding to said given value.

8. A developing system for an electrophotographic copying apparatus of the type comprising:

a member having a photosensitive surface;

means for forming an electrostatic latent image on said photosensitive surface by successive charging and exposure steps;

wherein the improvement comprises:

developing means for supplying a developer to said surface while moving relative thereto to develop said latent image, said developing means comprising:

an electrode disposed in opposing relationship with said surface with the developer interposed therebetween, said electrode comprising:

a plurality of electrode elements disposed along the direction of travel of said member relative to said developing means and having a unidirectional conducting characteristic in a direction opposite to said direction of travel of said member; and

the foremost element of said plurality of electrode elements in said direction of travel of said member having its potential additionally increased.

9. A developing system for electrophotographic copying apparatus of the type comprising:

a member having a surface of photosensitive material;

means for charging said photosensitive surface; and

means for exposing said charged photosensitive surface to form an electrostatic latent image thereon;

wherein the improvement comprises:

developing means for supplying a developer to said photosensitive surface while it is moving relative thereto to develop the latent image, said developing means comprising:

an electrode disposed in opposing relationship with said photosensitive surface with the developer interposed therebetween, said electrode comprising a plurality of electrode elements, each arranged along the direction of travel of the member relative to said developing means, said elements having a unidirectionally conducting characteristic in a direction opposite to said direction of travel of said member;

a plurality of diodes respectively connected between adjacent electrode elements for providing the unidirectionally conducting characteristic; and

the electrode element which is foremost in said direction of travel of said member having its potential additionally increased;

means for maintaining the induced potential on the electrode from said electrostatic latent image below a given value, said maintaining means comprising:

a constant voltage element connected between said electrode and ground and having a threshold value corresponding to said given value; and means for charging an area on at least one end portion of said member adjacent said image surface during the operation of said charging means and for maintaining said area unexposed during the operation of said exposure means such that said area on the end portion of said member induces a potential on said electrode.

10. A developing system for electrophotographic copying apparatus of the type comprising:

a member having a surface of photosensitive material;

means for charging said photosensitive surface; and

means for forming an electrostatic latent image on said charged photosensitive surface;

wherein the improvement comprises:

developing means for supplying a developer to said photosensitive surface to develop said latent image, and said developing means comprising:

an electrode disposed in opposing relationship with said photosensitive surface with the developer interposed therebetween; and

means for maintaining the induced potential on the electrode from said electrostatic latent image below above a given value, said maintaining means comprising:

a constant voltage element operatively connected to both said electrode and said means for charging said photosensitive surface and connected between said electrode and ground and having a threshold value corresponding to said given value.