Vacuum pallet type screen printing machine with registration means

Abstract

This disclosure is directed to a pallet type screen printing machine in which a pallet is indexed to a printing station when an article supported thereon is screen printed. A feed table with guides is cooperatively disposed relative to the pallet at a feed station to facilitate the accurate positioning of a work piece onto the pallet. The machine comprises an endless drive for effecting movement of one or more pallets to and from a printing station in an endless path whereby the face of the pallet is always maintained in a face up position. The pallet is formed to define a vacuum chamber which is operatively connected to a source for drawing a negative pressure thereon. A flexible coupling operatively connects the pallet to the endless drive to permit limited movement of the pallet so that the pallet may be brought into accurate registration with the printing head at the printing station. registration of the pallet in the printing station is effected by a locating cam and a cooperatively associated cam follower, which when activated, will effect the required alignment and registration of the pallet with the printing head.

Description

PROBLEM AND PRIOR ART

It is now known in the screen printing art that endless conveyor means in the form of an endless belt can be utilized for effecting the movement of an article to be printed to and from a printing section. Non-porous articles are maintained in position on such endless belts during movement by drawing a vacuum on the belt and the article supported thereon. Porous articles, e.g., cloth, are adhesively secured to the surface of the belt. However, in either event, i.e. whether the article was maintained in position either by vacuum or adhesive, accurate registration of the article supported on such endless belt with the printing head presented some difficulties because indexing of the belt would have to be effected over relatively long distances. The problem was particularly aggravated in multi-colored printing machines having lengths extending 50 feet or more depending on the number of color printing stations. Some of the registration difficulty resulted from the stretch induced in such belts over such long distances. Also when such endless belts were subjected to a vacuum, it was necessary to control the mode of operation (or function) of the vacuum acting on the belt and article supported thereon by changing from that of an article holding vacuum to that of an article indexing vacuum when the printing of an article at one location was completed. Consequently during the change of the vacuum function from holding to indexing, difficulty was sometimes encountered in prohibiting the article from shifting and thereby adversely affecting the registration of the article with a printing head. Also where long endless belts are employed it was frequently impossible to block out vacuum areas of the belt not utilized for either holding or indexing the article to be printed thereon. Consequently the holding ability of the vacuum would be diminished accordingly, which could effect the registration and/or holding of an article in position in place on the belt. Generally such conveyor belt type screen printing apparatus was particularly adapted for printing continuous webs, and are not particularly suitable for printing individual unit articles such as posters, and the like. Where such belt conveyors were required to be utilized in conjunction with heaters or dryers for effecting the rapid drying of the printing inks after each printing operation, it was noted that the temperatures resulting from the drying operation could adversely affect the belts. This was because the belts were generally formed of a material, e.g., a composition rubber, or leather-like material, which rendered the dissipation or conduction of heat difficult. For these reasons the dryers had to be operated at relative low temperatures to provide for the necessary dissipation of heat. This resulted in a slowing down of the machine operating time, which resulted in decreased production and increased cost.

OBJECTS

An object of this invention is to provide a screen printing machine having a movable pallet which a an elastic resilient material, as for example, rubber or the like, which may be provided with one or more bores, apertures or openings 48A (See FIG. 9) extending therethrough. Connected to the bearing 48 is a pin or link 49 which connects to the rollers 42A of the drive chains 42. In operation the flexible bearing defines the drive connection for the pallet, the functions as a cushion to permit relative limited movement of the pallet 35 relative to the drive chains 42, as will be hereinafter described in more detail. The arrangement is such that each pallet 35 is connected by opposed attachments 46--46 to the respective drive chains 42 to define a two-point attachment for the respective pallets and in to the driving chains 42.

As seen in FIGS. 6 to 8 the respective pallets 35 have connected to the opposed sides, front and rear rollers 40A and 40B by which the pallet 35 is disposed in rolling engagement with the rail members 36A, 36A, 37A, 37A. The arrangement is such that as the endless chains 42--42 are driven, the respective pallets 35 connected therebetween will be pulled along the length of the frame for movement from station to station.

Operatively associated with each of the pallets 35 is an electrically operated vacuum pump 52 which is suitably secured to the underside of the pallet 35, and is carried therewith as the pallet is moved along 4th the length of the frame in its endless path. The outlet of the pump 52 is suitably connected in communication with the interior or the vacuum chamber 38 of the associated pallet 35 through a connecting conduit 53. Each pallet 35 is thus provided with its own independent pump for drawing a vacuum pressure on the chamber 38 of the pallet means 35.

The vacuum pump is activated by an electric motor means 52A. The operation is such that the vacuum, when utilized, is maintained continuously operative as the pallet 35 is advanced from station to station. The operation of the vacuum pump is rendered continuously operative by an electric commutating track 55, see FIG. 13, extending along the frame. The electric track 55 (See FIGS. 3 and 13) is provided with suitable electric rails or conductors 55A which are operatively wired in an electric circuit to a source of electrical energy. (Not shown.) Connected to the underside of each pallet is an electric trolley means 56 which is adapted to ride in electrical contact with the electric rails or conductors 55A. The trolley 56 in turn is electrically connected to the motor 52A of the vacuum pump so that when trolley 56 is electrically connected to electrical rails 55A, the motor 52A and vacuum pump is energized; and it is maintained energized as long as trolley 56 is maintained in sliding contact with electric rail 55A.

As best seen in FIG. 4, the electric track 55 comprises two sections 55B and 55C, each supporting electrical conducting rails 55A. The main portion 55B of the electric track 55 extends beyond the feed station FS and continues along the remaining length of the frame 26. The arrangement is such that when the pallet trolleys 56 ride this portion 55B of track 55, the vacuum pump 52 is activated if current is flowing through conductors track 55 55A or B. Thus once the electric trolley 56 of the pallets 35 engages track section 55B, the vacuum pump 52 is maintained constantly activated as the pallets 35 advance from station to station. A second portion 55C of the track 55 which forms the continuation of the first track portion 55B, but with the conducting rails electrically insulated from those of sections 55B, is disposed at the feed station FS. This second track portion 55C is operatively connected to a suitable switch (not shown) so that the current flowing through the conducting rails of this section of the track 55C is controlled independently of track section 55B. The switch controlling the current to track section 55C can be actuated by an operator at the will of the operator to facilitate the positioning of an article on the pallet 35 associated with track section 55C, without affecting the vacuum operating on the other pallets 35. In operation, an operator feeding the articles to be printed on the pallet 35 in the feed station FS will normally deactivate the vacuum pump 52 operating on the pallet in the feed station when placing the article to be printed thereon. When the article has been properly orientated into its proper position on the pallet 35 in the feed station FS, the operator then will energize the vacuum pump 52 to draw the vacuum on the pallet in the feed station to maintain the article orientated in position thereon. Thus at the feed end of the machine the vacuum pump can be operated between an on and off position. As the pallet in the feed station FS advances to the first printing station, the trolley 56 connected thereto slides off portion 55C and onto portion 55B of the electric track. In doing so the vacuum pump 52 of the pallet 35 is brought under the influence of the current flowing through track portion 55B whereby it functions to maintain the vacuum pump 52 actuated throughout the movement of the pallet 35 through the succeeding printing stations. As the trolley 56 of the pallet 35 is moved beyond the end of track section 55B, the current flow to the vacuum pump motor is interrupted, thereby releasing the vacuum on chamber 38. When this occurs the article which has been printed can be removed from the pallet 35.

Each pallet 35 is provided with independent means for effecting registration of the pallet 35 with respect to an associated printing head 30 when the pallet 35 has been advanced to a printing station. The arrangement is such that the pallet 35 can be accurately registered to accommodate or compensate for any slack or play in the flexible drive 42. As the respective pallets 35 are connected to the respective endless drives 42 by a two-point connection, each containing a flexible bearing or coupling 48, the pallets 35 may be moved or shifted relative to the chain 42 an amount sufficient to bring the respective pallets 35 in accurate registration with the printing head 30. The means for effecting the registration of the pallet 35 at the printing station comprises a an angled member 60 connected to the undersurface of the pallet 35. As best seen in FIGS. 6 and 7, the horizontal flange 60A of the angled member 60 is suitably secured to the bottom plate 35B of the pallet 35. The dependent flange 60B extends downwardly from the pallet and transversely thereof. Mounted to the frame at each printing station is a bracket 61 (see FIG. 11) on which a pair of spaced apart stop rollers 62 are positioned. The stop rollers 62 function as a lateral stop to limit lateral displacement of the pallet 35 as the pallet is moved into registration. The arrangement is such that when the pallet 35 is laterally displaced to effect registration, lateral movement is limited by engagement of flange 60B with stop rollers 62. When the pallet is laterally displaced for registration, the pallet 35 is squared relative to the printing station as the flange 60B engages stop rollers 62.

The means for effecting the squaring or registration of the pallet relative to its printing head comprises a locator 63 having a V notch 63A formed therein. The locator 63 is connected to the depending flange 60B of member 60. Cooperatively associated with the locator 63 is a follower in the form of a roller 64 connected to the end of a push rod 65 of a piston and cylinder activating means 66. The piston and cylinder assembly 66 is suitably supported on a supporting bracket 67 connected to the machine frame 26 in each printing station. The arrangement is such that the push rod 65 of the roller 64 is operatively connected to the piston rod 66A of the piston and cylinder assembly 66. Accordingly, whenever the piston and cylinder assembly 66 is actuated the push rod 65 advances the roller 64 towards the notch 63A of the locator 63, and as the roller 64 is seated into the V-notch 63A, the pallet 35 is displaced or squared accordingly as the depending flange 60B of the member 60 is moved into abutment against the stops 62. The pallet 35 is thus squared in registration with the printing head 30 so that the article to be printed, supported thereon, can be located in accurate registration with the stencilled portion of the printing screen 32 supported on the printing head 31. As the electric trolley 56 is operatively connected in circuit to the vacuum pump 52 carried on the pallet 35 by engagement in electrical contact with the supply of the electric track 55B, the vacuum is maintained on the pallet as it is brought into registration. Where the apparatus 25 is provided with a plurality of printing stations, the arrangement is such that the pallets 35 are individually capable of being brought into registration at each printing station while the vacuum is maintained thereon.

As best seen in FIGS. 14 and 15 the drive means for the endless drive or chain 42 comprises a motor means. In the illustrated form of the invention a fluid actuated or hydraulic motor 70 is employed. The hydraulic motor 70 is operatively connected to a control valve 71 for controlling the fluid flow to motor 70 by which the speed of the motor 70 is regulated. The output shaft 72 of the fluid motor 70 has connected thereto a sprocket 73 which is connected in driving relationship to a drive sprocket 74 by means of a chain drive 75 interconnected therebetween. The drive sprocket 74 is connected to the main drive shaft 76. Journalled to the main drive shaft 76 is the driving sprocket 43 of the endless chain drive 42. As best seen in FIG. 1 the drive sprocket 43 of the drive chain 42 is connected adjacent the feed end FS of the machine. The other end of the chain drive 42 is threaded over end idle sprocket 44.

Connected to the main drive shaft 76 is a drive sprocket 77 for effecting the indexing or advancing of the pallets 35 toward and away the respective printing stations. As shown in FIGS. 14 and 15 the drive indexing sprocket 77 is connected in driving relationship to an indexing sprocket 78 by means of a connected driving chain 79. Operatively connected to the shaft 80 of the indexing sprocket 78 is a rotating ram 81 and ram roller 81A which function to control the fluid flow to the motor 70. An actuating lever 82 is pivoted about pivot 83 for movement toward and away from the valve 71 controlling the flow of fluid to motor 70. The arrangement is such that rotation of the ram 81 and roller 81A as the indexing shaft 80 is rotated effects displacement of the lever 82 to control the actuation of valve 71. To limit the rotation of the ram 81 there is provided a ram stop 84 which is actuated between operative and inoperative position by means of a piston and cylinder assembly 85. As viewed in FIG. 14 when the ram stop 84 is raised to its upper position, as indicated in the dotted line showing thereof, the shaft 80 containing the ram 81 and ram roller 81A is permitted to rotate thereby causing the ram roller 81A to engage the actuating lever 82. The engagement between the ram roller 81A and the actuating lever 82 is such that as the displacement of the actuating lever 82 activates the control valve 71 controlling the flow of fluid to the motor to effect the speed thereof, the arrangement is such that as the pallet 35 approaches the printing position, the speed of the motor is gradually reduced due to the reduction in flow of fluid thereto and thereby resulting in the controlled deceleration of the pallet as it reaches printing position. By effecting controlled deceleration of the pallets 35 as they reach printing position, excessive banging and machine vibration is minimized.

To effect the transfer of the respective pallets 35 between the upper and lower flights of the chain drive as the pallets move in the endless path of travel, transfer means 87 and 88 are provided at each end of the machine. See FIGS. 1 and 2. The transfer means 87 and 88 cooperate with the drive means 42 to maintain the respective pallets 35 horizontal and face up as they round the end sprockets 43 and 44. At the feed end of the machine the transfer means 87 includes a lifting sprocket 89 rotatably journalled about a suitable shaft 90 to which a driving sprocket 91 is journalled. As shown in FIG. 1 the periphery of the lifting or transfer sprocket 89 is provided with a series of circumferentially spaced notches 89A which are adapted to engage the rear or lead rollers 40A of the pallets advancing or moving toward the sprocket 89 along the lower flight. The rotation of the lifting sprocket 89 is timed so that the notches will engage with rollers 40A of the approaching pallet 35 as the chain attachment or housing 47 rounds sprocket 43. Timing of the lifting sprocket 89 is attained by driving it from the main drive shaft 76 by an auxiliary chain drive 92.

As best seen in FIG. 1, the auxiliary drive 92 comprises a drive sprocket 93 journalled to the main shaft 76. A complementary sprocket 91 journalled to shaft 90 to which the lifting sprocket 89 connected, and sprockets 93 and 91 are connected in driving relationship by a drive chain 92. The rotation of the lifting sprocket 89 is thus timed to the speed of the main chain drive 42 through appropriate gearing ratios of the respective sprockets.

The arrangement is such that as pallet 35 advances beyond its end sprocket 43, the lead roller 40A engages one of the notches 89A on the lifting sprocket 89 causing the associated end of the pallet to raise as the chain attachment housing 47 rides up on the chain sprocket 43. In this manner both ends of the leading pallet in the lower flight are raised simultaneously as the pallets 35 are advanced from station to station; the top of the pallet being always maintained in a face up position.

At the discharge or other end of the machine 25, the transfer means 88 is defined as a curved guide or channelway for accommodating the end rollers 40B of the respective pallets 35, as they approach the end of the upper flight of drive means 42. As shown in FIG. 2, the transfer means 88 includes a curved rail section 88A which defines an extension of rail 36A. A companion guide rail 88B is spaced from rail section 88A to guide and confine the rollers 40B of pallet 35 as the pallet is transferred from the upper to lower flight of the chain drive 42. As the other end of the pallet is supported by the chain attachment 47, the co-action between the transfer means 88 and end sprocket 44 effect the transfer of the endmost pallet between the upper and lower flights. The curve of rail section 88A and its complementary rail 88B prohibits any vertical drop of the pallet, and as the chain attachment end 46 is guided around end sprocket 44, the following end or rollers 40B are similarly guided by the transfer means 88 resulting in that the pallet is maintained substantially horizontal and face up as it rounds the end of the chain drive 42.

To assist in positioning an article to be printed on the pallet 35 at the feed end of the machine, a feed table 95 is provided. As best seen in FIG. 4, the feed table 95 has an end portion which overlies a portion of the pallet. Guides 95A are provided on the table 95 to facilitate the positioning of the article on the pallet so as to be in proper registration with the screen when the pallet 35 is advanced to a printing station. By locating the guides on the table rather than the pallet the entire surface of the pallet is available for printing. When an operator or an automatic feeder has located the article with respect to the guides 95A on table 95, a portion of the article is supported on the pallet. By actuating the vacuum of the pallet at the feed station, the article is secured thereto, and as the pallet is advanced through the feed station, it will slide the remainder of the article off the feed table and onto the underlying portion of the pallet 35.

OPERATION OF THE MACHINE

The article to be printed is loaded onto the respective pallets 35 as the pallet 35 is moved into the feeding station FS at the feed end of the machine. The article registration onto its respective pallet 35 in the feed station FS is facilitated by means of a feeding table 95 which has a marginal portion overlapping or overlying a portion of the pallet 35 in the feed station. The orientation means or guides 95A provided on the feed table assist in orientating or locating the article to be printed properly upon its respective pallet. When the material or article to be printed is properly orientated on the pallet 35 in the feed station, a switch (not shown) for activating the vacuum pump 52 is energized to draw a vacuum on chamber 43 38 of pallet 35. The pallet is then advanced to the first printing station whereby the vacuum being drawn on the chamber causes the article to be printed to be adherred adhered thereto and to advance therewith to the printing station. As the pallet 35 approaches the first printing station, the pallet is decelerated by actuation of the deceleration means described and brought to a standstill at the printing station. To effect accurate registration of the pallet 35 and the article supported thereon and to compensate for any slack in the drive chains 42, the piston and cylinder assembly 66 of the registration means is activated. When actuated the push rod 35 65 advances the connected cam follower 64 to engage the V-notch of the cam locator which will effect displacement of the guide 60 with the guide followers or stops 62 to effect the alignment of the pallet with the printing head. The flexible coupling or bearing 48 between the pallet and drive chains permits the pallet to be displaced. As the trolley 56 of the pallet is engaged in electrical contact with the conducting rail 55A of the electrified track 55, the vacuum pump is maintained activated to maintain a continuous vacuum on the pallet 35 during a printing operation.

With the pallet 35 registered in position at the printing station, the printing head 30 is lowered whereby the screen 32 is properly positioned in registration on the work piece or article to be printed. The actuation of the squeegee 33 in a conventional manner will effect the printing stroke forcing the inks or dyestuff through the design of the stencilled screen and onto the article to be printed. Upon completion of the printing stroke the printing head 30 is raised to an inoperative or non-printing position. As the printing head is being raised to a non-printing position, the piston and cylinder assembly 66 of the registration means is deactivated causing the cam follower 64 to be withdrawn freeing the pallet for advancement to the next station. Then the piston and cylinder assembly 85 is actuated to index the pallet to the next station. In a multiple color printing machine the next station may comprise a second printing station wherein a second color may be printed onto the article. In the event that a means is required for effecting the drying of the ink on the article before a second color may be applied, it will be understood that a heater or drying oven may be interposed between successive printing stations. In this manner the printed article may be dried as it advances to the next printing station. However, it will be understood that the utilization of a heater or dryer with the apparatus as described is optional depending upon the nature and type of screen printing operation being performed.

To advance or index the respective pallets 35 to the next station, piston and cylinder assembly 85 is energized to release the ram stop and effect the movement of the indexing means and associated drive means 42.

In doing so, the actuation of the ram 81 on the decleration lever 82 controlls control the flow of fluid to the fluid drive motor accordingly to effect the acceleration and/or the deceleration of the pallet driving means.

The construction of the pallets described is such that it constitutes a good heat conductor and when used in conjunction with a dryer or heater, will function to effect the rapid dissipation of the heat therefrom. For this reason dryers may be operated at higher heat temperatures to promote faster drying, and thereby increase the machine output, or conversely reduce the cycling time of the apparatus. Also the pallets are not adversely affected by the heat output of such heating means when utilized in conjunction therewith.

It will be noted that the apparatus described is particularly applicable for use in printing non-porous material. However, it will be understood that porous type material can also be screen printed by the apparatus described. This can be attained either by coating the top of the pallets 35 with a suitable adhesive by which the porous material may then be secured thereto without the intervention of the vacuum means, or optionally the porous material to be printed may be suitably secured to a non-porous backing sheet by suitable adhesive, which backing sheet in turn is maintained in position on the respective pallets through the interaction of the vacuum means.

While the instant invention has been described with respect to a particular embodiment thereof it will be readily appreciated and understood that variations and modifications may be made without departing from the spirit or scope of the invention.

Claims

1. A screen printing machine comprising

a frame,

a printing head defining a printing station mounted on said frame,

a track means on said frame extending along the length of said frame,

a pallet means movably mounted on said track,

said pallet means including spaced apart upper and lower plates and connected end walls defining therebetween a vacuum chamber,

said upper plate having a series of apertures formed therein,

means connected to said pallet means for drawing a vacuum on said chamber,

spaced apart roller means connected to said pallet means disposed in rolling contact with said track means,

a flexible endless drive disposed along each side of said frame,

said endless drive including an upper flight and a lower flight,

a flexible coupling connecting said pallet means to each of said endless drivers,

motor drive means connected to said endless drive to effect the actuation thereof for moving the connected pallet toward and away from said printing station,

means for effecting registration of said pallet means with said printing head when in the printing station,

and transfer means adjacent each end of said endless drives for effecting movement of said pallet means between said upper and lower flights, said transfer means always maintaining said pallet means face up.

2. The invention as defined in claim 1 and including an electric track,

and a sliding contact engaging said electric track,

said contact being connected in circuit to said vacuum drawing means, whereby said latter means is energized when said sliding contact is disposed in electrical contact with said track.

3. The invention as defined in claim 1 wherein said registration means includes a locator having a notch carried on said pallet means,

and a cooperating follower positioned on the frame to engage said locator notch,

and means for activating said follower.

4. The invention as defined in claim 1 wherein said transfer means includes a transfer sprocket adjacent one end of said machine,

and a transfer guide means at the other end of the machine,

means formed on the periphery of said transfer sprocket for receiving said rollers whereby said sprocket when engaged by said rollers functions to transfer said pallet means, face up, between said flights.

5. The invention as defined in claim 1 and including indexing means connected to said motor drive means to limit the movement of said pallet means to said printing station.

6. The invention as defined in claim 1 and including means for decelerating the speed of said motor drive means as said pallet means approaches said printing station.

7. The invention as defined in claim 1 wherein said pallet means includes roller means, and said transfer means at one end of said flight comprising:

a transfer sprocket,

means for driving said transfer sprocket in unison with said drive means,

said transfer sprocket having means formed about the periphery thereof for engaging the roller means connected to said pallets, whereby said transfer sprocket co-acts with said drive means to lift said pallets from the lower flight to the upper flight.

8. In a screen printing machine including a frame having a feed end, and a screen printing head mounted on said frame for movement between printing and non-printing position positions, the improvement comprising:

pallet means, said pallet means having an upper and lower member defining a chamber therebetween, said upper member having apertures formed therein,

a drive means for effecting the movement of said pallet means toward and away from a printing station located below said printing head,

said drive means comprising an endless flexible drive moving in an endless path along spaced apart upper and lower flights,

means connecting said pallet means to said endless flexible drive to be driven along said endless path,

transfer means disposed adjacent the opposed ends of said endless path for effecting the transfer of said pallets between said flights, said transfer means maintaining said pallets in a face-up position throughout the travel thereof along said endless path,

a vacuum producing means connected to the chamber of said pallet means for drawing a negative pressure on said chamber as said pallet means moves along said endless path,

a registration means operatively associated with said pallet means for effecting registration of said pallet means with said printing head when in the printing position beneath said printing head.

9. The invention as defined in claim 8 wherein said pallet connecting means includes a resilient coupling means to provide for limited relative movement between said pallet means and its said flexible drive.

10. The invention as defined in claim 9 wherein said drive means includes:

a pair of spaced apart endless flexible driving means extending along the longitudinal sides of said frame,

said resilient coupling means comprising opposed connecting links disposed to on opposed sides of said pallet,

one end of said link being connected to the adjacent flexible drive means,

a resilient bearing member connected to the other end of said link, and

and a bearing housing connected to the sides of said pallet means for receiving said resilient bearing member.

11. The invention as defined in claim 9 wherein said drive means including include a pair of opposed endless flexible drives, said pallet means being disposed between said flexible drives,

said resilient coupling means are being oppositely disposed on said pallet means to form a connection with the respective endless drives whereby said flexible drives pull said pallet means therebetween to and from a printing station when actuated,

and said registration means comprising a locating means connected to said pallet and,

a complementary follower positioned on the frame to engage said locating means, and

and means for activating said follower to effect registration of said pallet means in the printing station.

12. The invention as defined in claim 8 and including a feed table disposed to one side of the pallet means at the feed end of said machine,

said feed table extending slightly over the side of said pallet means in overlying relationship thereto, and

and means on said table for properly orientating a work piece on said pallet means whereby the work piece is partly supported on said feed table and partly on said pallet means at the feed end.

13. The invention as defined in claim 8 wherein said pallet means includes roller means, and said transfer means at one end of said flight comprises a transfer guide means positioned to receive the roller means of said pallet, and to cooperate with said drive means for effecting transfer of said pallet means between the upper and lower flight in said face-up position.

14. The invention as defined in claim 8 and including means for maintaining said vacuum producing means actuated as said pallet means is moved toward and away from said printing station.

15. In a screen printing machine having a frame and a plurality of printing heads mounted on said frame to define a plurality of printing stations, each of said printing heads being adapted to support a printing screen and an associated squeegee, the improvement comprising,

a plurality of pallet means supported on said frame by drive means having endless vertically spaced aparts apart flights,

said endless drive means for effecting the movement of said pallet means from station to station along said flights in an endless path,

means for flexibly coupling each of said pallet means to said endless drive means at spaced intervals along said endless drive means,

means for effecting the registration of said pallet means with its respective printing head when disposed in said printing stations,

each of said pallet means including spaced apart upper and lower members defining a chamber therebetween, said upper member having apertures formed therein,

a vacuum producing means connected to each of said pallet means for drawing a negative pressure on the associated pallet chamber,

means for maintaining said vacuum producing means activated as said pallet means advances through the respective printing stations, and

and transfer means adjacent each end of said endless path for maintaining said pallet means in a face-up position through the entire travel thereof about said endless path.

16. The invention as defined in claim 15 wherein said endless drive means comprises:

opposed flexible endless drives extending along the adjacent longitudinal sides of said frame, and

said flexible coupling means including oppositely disposed links,

a resilient bearing connected to one end of each of said links, said resilient bearing being coupled to said pallet means,

and said registration means including a locator on each of said pallet means and an associated follower located on said frame at each printing station, and

means for activating said follower to effect registration of said follower with said locator on said pallet means in a printing station.

17. The invention as defined in claim 16 wherein the direction of movement of said follower is substantially normal to said locator on said pallet means.

18. In a screen printing machine having a frame, a screen printing head defining a printing station and mounted on said frame for movement between printing and non-printing positions, pallet means, drive means and means for operatively connecting said pallet means to said drive means to effectuate substantially concomitant movement of said pallet means with said drive means,

said improvement comprising,

means operatively connected with said drive means for indexing said pallet means with respect to said printing station,

means for effecting registration of said pallet means with said printing head after said pallet means have been indexed to said printing station,

said means connecting said pallet means to said drive means includes elastic resilient coupling means,

said resilient coupling means comprising at least one link interconnected between said pallet means and said drive means,

said link comprising a bearing housing connected to said pallet means and an elastic resilient bearing member, and

said resilient bearing member being disposed within said bearing housing and being connected to said drive means.

19. A screen printing machine in accordance with claim 18, wherein

said pallet means includes a pair of opposed sides, and

said bearing housing is connected to one of the sides of said pallet means.

20. A screen printing machine in accordance with claim 18, wherein

said pallet means includes a pair of opposed sides,

said drive means includes a pair of opposed endless flexible drives, and

said resilient coupling means being disposed on the opposed sides of said pallet means and forming a connection with the respective endless drives whereby said flexible drives move said pallet means to and from said printing station when actuated.

21. A screen printing machine in accordance with claim 20, wherein

said pallet means is positioned between said endless drives.

22. A screen printing machine in accordance with claim 18, wherein

said registration means comprises

locating means carried by said pallet means, and

a cooperating follower positioned on the frame, and

means for activating said follower to cause the same to engage said locator means to effect registration of said pallet means with respect to said printing head.

23. A screen printing machine in accordance with claim 22, wherein

said locator means comprises a locating notch of predetermined geometrical configuration, and

said cooperating follower is engageable within said locating notch.

24. A screen printing machine in accordance with claim 23, wherein

said locating notch is disposed on the underside of said pallet means.

25. A screen printing machine in accordance with claim 18, wherein

said resilient member is fabricated of a resilient material having a predetermined geometrical configuration, and

said resilient material has a plurality of apertures formed therein for increasing the resiliency of said member.