EP0248752A1 - Automatic sheet feeder for a screen-printing machine having a mobile printing table - Google Patents

Abstract

- The invention relates to an automatic margin device for a screen printing machine with an outgoing plate, characterized in that it consists of a pre-margin plate (7) next to and integral with the printing plate (4 ), and comprising means (13) for front and side wedging, a device (11) for supplying printing material (10), provided at its upper part with guide rails (8) or the like in the extension those of the printing plate (4), a lifting device (12) to grab the material to be printed (14) in the feed device and deposit it on the pre-margin plate (7) when it is located on the guide rails (8) of the feed device, and of a lifting device (17) arranged above the printing plate (4) in the extended position of the latter and capable of transferring the material to print (18) from the pre-margin plate (7) on the print plate (4).

- Application to screen printing machines with outgoing plate.

Description

The present invention relates to automatic margin devices for screen printing machine of the type with horizontal displacement of the printing plate.

On these machines, the positioning of the material to be printed is generally done manually when the printing plate is in the extended position awaiting margin.

The operator is forced to wait for the return to the output position of the printing plate to bring the material to be printed in the locating position. When the material is, for example, a very thin or large sheet of paper, the operation is difficult, relatively long and therefore slows down the maximum possibilities of machine printing speed.

In order to overcome these drawbacks, the Applicant has designed a device for precise margin or automatic positioning making it possible to increase the rates of machines of the above type, such a device being described in French patent application No. 84 156352.

This device is made up in brief:
- a pre-margin plate arranged in the plane and next to the printing plate, integral with the latter and comprising an endless belt or bands enabling the material to be printed to be brought into frontal abutment against tabs of margin and a device making it possible to bring said material into abutment a lateral margin stop;
- a device for supplying material to be printed, provided at its upper part with guide rails in line with those of the printing plate;
a lifting device for gripping the material to be printed in the feed device and depositing it on the pre-margin plate when it is on the guide rails of the feed device, and
- a lifting device disposed above the printing plate in the extended position thereof and adapted to transfer the material to be printed from the pre-margin plate onto the printing plate.

The object of the present invention is to improve the above device in terms of the supply and positioning of the material on the printing plate of the machine, in order to improve the positioning accuracy and to lighten and reduce the size of the automatic margin device.

To this end, the subject of the invention is an automatic margin device for a screen printing machine with an outgoing tray, comprising a magazine for storing the printing sheets stacked flat, means associated with the printing tray of the machine and constituting a pre-margin support in the extension of the plane of said tray, means for gripping and transferring one by one of the sheets of said stack onto said pre-margin means, means for front and lateral wedging of the sheet placed on the pre-margin means and means for entering and transferring the sheet of the pre-margin means onto the printing plate, said device being characterized:
- In that said front wedging means consist of a transverse bar supported by the frame of the machine, provided, on the one hand, cleats or the like retaining the front edge of the sheet placed on said pre-margin means , on the other hand, means for detecting the presence of said front edge in abutment against said tabs, and, finally, means for gripping and lifting of said front edge, controlled by said detection means;
- And in that said lateral wedging means are constituted by means for moving said bar constituted by means for moving said transverse bar orthogonally to the direction of movement of the printing plate, controlled from said detection means and by detection means carried by the frame of the machine and capable, on the one hand, of detecting the lateral edge of the sheet placed on said pre-margin means and previously gripped by said gripping and lifting means, on the other hand, in stopping and holding in its position said bar and, finally, in controlling the exit from the tray printing in order to deposit said sheet therein.

Advantageously, with a view to reducing the bulk of the device and making it lighter, said pre-margin means are constituted by a tray-bar secured to the printing tray and by unrollable support bands driven by said tray-bar and interposed between the latter and the stack of sheets to be printed.

According to another remarkable characteristic of the device of the invention, with a view to ensuring absolutely rigorous placement of each sheet on the printing plate, the bar-means assembly for moving the latter is slidably mounted parallel to the direction movement of the printing plate by being resiliently recalled by spring or the like, said sliding being of small amplitude and caused by tabs or the like integral with the printing plate and acting, at the end of the output stroke of the latter, on end supports of said assembly.

• - Figure 1 est une vue générale schématique en élévation latérale d'un dispositif conforme à l'invention ;
• - Figure 2 est une vue de dessus du dispositif de la figu­re 1 ;
• - Figure 3 est une vue de détail en élévation latérale des moyens de calage frontal et latéral des feuilles sur les moyens de pré-marge ;
• - Figure 4 illustre le dispositif de la figure 3 à la fin de la course de rentrée du plateau d'impression ;
• - Figure 5 est une vue de dessus du dispositif de la figure 4 ;
• - Figure 6 preprésente le dispositif de la figure 1 avec le plateau d'impression en position rentrée, et
• - Figure 7 représente le dispositif de la figure 6 après que le plateau d'impression est ressorti.

Other characteristics and advantages will emerge from the description which follows of an embodiment of the device of the invention, description given by way of example only and with reference to the appended drawings in which:

• - Figure 1 is a schematic general view in side elevation of a device according to the invention;
• - Figure 2 is a top view of the device of Figure 1;
• - Figure 3 is a detail view in side elevation of means for front and side wedging of the sheets on the pre-margin means;
• - Figure 4 illustrates the device of Figure 3 at the end of the return stroke of the printing plate;
• - Figure 5 is a top view of the device of Figure 4;
• - Figure 6 shows the device of Figure 1 with the printing plate in the retracted position, and
• - Figure 7 shows the device of Figure 6 after the printing plate is out.

In Figure 1 is shown schematically in 1 a screen printing machine of the type with outgoing plate. Such a machine is perfectly known and does not need to be described in detail.

It comprises a frame 2 supporting a model-carrying frame 3, a printing plate 4 (in the extended position in FIG. 1) movable on horizontal rails symbolized at 5, arranged under the frame 3 and extended on the side of the machine while being supported by a console 6 itself carried by the frame 2.

In accordance with the invention, the printing plate 4 is extended, on its front side facing the stack 7 of printing sheets arranged flat on a lifting table in X 8, by a pre-margin plate 9 of very large dimensions. reduced since it consists, for example, of a simple flat bar of length equal to the width of the plate 4 and of sufficient width for mounting two retractable grippers 10 for gripping one by one of the sheets of the stack 7 brought in by a gripping system for example with suction cups 11.

The lifting table 8 is of a perfectly known type of jump elevation under the control of photoelectric cells so as to keep the top sheet of the stack 7 substantially at the same height, whatever the height of the stack on the table .

The tray-bar 9 is connected, on the side opposite to the tray 4, to a set of unrollable bands, symbolized at 12, wound around a rotary drum 13 of fixed horizontal axis.

These bands 12 are arranged side by side and intended to serve as a support for each sheet such as 14 taken from the stack 7 by the suction cup system 11 and brought by the latter above the tray-bar 9 so that the front edge of said sheet 14 is gripped by the clamps 10 .

In FIG. 1, the strips 12 are in the almost completely wound position on the drum 13, while in the retracted position of the plate 4 under the frame 3, the said strips 12 are almost completely unwound and form, by their upper faces in the extension of the upper face of the bar plate 9, a horizontal plane supporting and transporting the sheet 14 in the direction of the machine 1.

The system with unrollable support bands 12 is perfectly known and does not need to be described in detail. It includes, in addition to the bands themselves and the winding-unwinding drum, return bands for the support bands in their wound position and return rollers. The movement of unwinding of the bands 12 is ensured by the bar plate 9 integral with the plate 4.

The drum 13 is arranged as close as possible to the top of the stack 7 so as to ensure the continuity of the horizontal plane in which the sheet 14 moves between the top of the stack 7 and the printing plate 4.

The suction cup 11 and transfer system is conventional and comprises for example two vertical suction cups arranged at rest above the stack 7 at some distance from the edge facing the machine 1. The two suction cups are carried by a frame (not shown ) movable vertically and horizontally so as to grip the top sheet of the stack 7, near its edge facing the machine 1, lift it slightly, transfer it laterally in the direction of the clamps 10 (in the position shown in FIG. 1) ) to be retained.

The extreme position of the suction cups 11 has been shown in dashed lines in 11ʹ during their translation in the direction of the plate 4.

The means ensuring the movements of the suction cups 11 are completely conventional and do not need to be described in detail.

Once the suction cups 11 in their position 11ʹ, the vacuum is released, the suction cups release the sheet 14, held at this time by the clamps 10, and return to the initial rest position above the stack 7, ready for a new sheet capture and transfer cycle.

According to an interesting feature of the device of the invention, the deposition of the sheet 14 on the tray-bar 9 by the suction cups 11 is done slightly further than is necessary relative to the optimal and rigorous position of the sheet 14 relative to the support assembly 9-12, said optimal and rigorous position being that to which the suction cup transfer system 15 matches the exact placement of the sheet 14 on the printing plate 4.

This rigorous positioning of the sheet 14 on the assembly 9-12 will be carried out in a second step at the end of the reentry stroke of the printing plate 4, using the device generally designated by the general reference 16.

The device 16 is shown in more detail in FIGS. 3 to 5. It comprises a horizontal transverse bar 17 mounted axially movable along the double arrow 18 in two end guide pieces 19 themselves mounted movable along the double arrows 20 To this end, the bar 17 has at one end a guide pin 21 sliding in a bore formed in the guide piece 19 and, at its other end, a tapped hole in which meshes a screw 22 driven in rotation by a motor. electric 23 secured to the other guide piece 19. During the rotation of the screw 22, the bar 17 is prevented from rotating by the guide pieces 19 and moves in the direction of one or the other of the latter in a direction 18 perpendicular to that (20) of movement of the printing plate (4).

In its movements in the direction 20, the guide pieces 19 are guided by suitable members symbolized at 24 and integral with the frame 2 of the machine 1. The movement of the guide pieces 19 is controlled by two tabs 25 fixed to the plate impression 4 so as to come into contact with the internal sides of the parts 19 at the end of exit run from stage 4, for purposes which will be explained later. The guide pieces 19 are automatically returned to their initial position by suitable means such as springs 26 interposed between said pieces 19 and a part 27 of the frame of the machine 1.

Under the bar 17 are arranged two vertical tabs 28 known as the front setting of the sheet 14 (FIGS. 3 to 5) on the assembly 9-12.

Next to the cleats 28 are arranged two vertical suction cups 29 (device 15 of FIG. 1), turned downwards. The means of feeding these suction cups are not shown in the drawings for the sake of clarity.

The members 28 and 29 are arranged so that the assembly 4 and 9 can move freely under the crossbar 17.

Opposite the bar 17 are arranged, below the trajectory of the assembly 4-9, means such as fixed cams 30 cooperating with a pusher 30a integral with the clamps 10 to cause the retraction by rotation around a axis 30b of the grippers when these, in the last part of the re-entry stroke of the plate 4 in the machine 1, arrive near the bar 17. Thus, the sheet 14 is released, comes into contact (FIG. 4) with the cleats 28 for front chocking which make it move back a very small distance (of the order of 1 to 3 mm for example) on the assembly 9-12 and ensure precise frontal positioning.

Photoelectric reflection cells 31 fixed under the bar 17 are responsible for detecting the front edge 14a of the sheet 14 in abutment against the tabs 28.

The detection of the edge 14a by the cells 31 controls the putting into service of the suction cups 29 which then lift the opposite edge of the sheet 14 and maintain it, then the starting of the motor 23 so as, for example, to pull towards it the bar 17 until the lateral edge 14b of the sheet (FIG. 5) is detected by a photoelectric cell with reflection 32 secured to the guide part 19.

The signal emitted by this cell controls the stopping of the engine in its position thus maintaining the sheet 14 perfectly wedged frontally and laterally.

It then only remains to transfer the sheet 14 to the plate 4. For this purpose, the latter leaves the machine, the sheet 14 being retained perfectly maintained by the suction cups 29 of the bar 17 which remains frozen in its spatial position .

During the movement out of the assembly 4-9, the clamps 10 escape the cams 30 and return to the active position, ready to grip the edge of a new sheet presented by the system 11.

At the end of the exit stroke from the plate 4, the cleats 25 bear simultaneously against the guide pieces 19 and push them against the springs 26 by a very small distance (for example one tenth of a mm) sufficient to ensure remarkably precise positioning of the sheet 14 which is then released by the suction cups 29 (FIG. 7).

The tray 4 with its sheet can then return under the frame 3 for printing the sheet, during this new re-entry of the tray 4 into the machine, a new sheet being simultaneously brought from position 14 of FIG. 1 to the position 14 of figure 6.

The cycle is thus repeated automatically at the printing rate of the machine, that is to say without any loss of time and without any human intervention.

As soon as the sheet 14 is released by the suction cups 29 on the plate 4, the bar 17 is preferably returned to the initial transverse position, so as to transversely move the sheet 14 over the assembly 9-12 always in the same direction, in direction of cell 32.

Of course, this cell 32 is adjustable in position transversely to the assembly 9-12. The same can be said of the members 11, 10, 28, 29, 31 which can be adjustable as to their spacing by an appropriate mounting on their respective supports.

The device of the invention can thus process sheets not only of various formats but also of various weights without any problem and without requiring intermediate adjustments.

Of course, the entire device is equipped with the usual means for controlling and linking the various phases of the operating cycle.

Finally, the invention is obviously not limited to the embodiment shown and described above, but on the contrary covers all variants thereof, in particular as regards the technology for producing certain subsystems such as the input means and transfer one by one of the sheets to be printed which, instead of the suction cups (11,29), can be replaced by any known system capable of ensuring the same functions.

Thus the suction cups 29 can advantageously be replaced by a system, of known type, with a partitionable suction slot to adapt to different formats.

Similarly, the retractable clamps 10, the photoelectric cell detectors 31, 32, or the means of transverse displacement of the bar 17 are also replaceable by means providing the same effects.

Furthermore, the major advantage of the unrollable strips 12 is to lighten the device for transferring the sheets between the stack 7 and the machine 1, but one could of course replace the assembly 9-12 with a rigid tray of the tray type. pre-margin described in the patent application mentioned at the beginning of this description.

Claims (9)

1. Automatic margin device for a screen printing machine with an outgoing plate, comprising a magazine for storing the printing sheets stacked flat (7), means associated with the printing plate (4) of the machine and constituting a support. of pre-margin in the extension of the plane of said tray, means for gripping and transferring one by one of the sheets of said stack onto said pre-margin means, means for front and lateral wedging of the sheet placed on the pre means margin and means for inputting and transferring the sheet of the pre-margin means onto the printing plate, said device being characterized:
- In that said front wedging means consist of a transverse bar (17) supported by the frame of the machine, provided, on the one hand, cleats or the like (28) retaining the front edge (14a) of the sheet placed on said pre-margin means (9, 12), on the other hand, means (31) for detecting the presence of said front edge (14a) in abutment against said tabs (28), and finally means (29) for gripping and lifting said front edge (14a), controlled by said detection means (31);
- And in that said lateral wedging means are constituted by means (23) for moving said transverse bar (17) orthogonally to the direction of movement of the printing plate (4), controlled from said detection means (31 ) and by detection means (32) carried by the frame of the machine and able, on the one hand, to detect the lateral edge (14b) of the sheet placed on said pre-margin means (9,12) and previously gripped by said gripping and lifting means (29), on the other hand, in stopping and holding in its position said bar (17) and, finally, in controlling the exit from the tray printing (4) in order to deposit said sheet thereon. 2. Device according to claim 1, characterized in that said pre-margin means are constituted by a bar plate (9) integral with the printing plate (4) and by unrollable support strips (12) driven by said bar tray (9) and interposed between the latter and the stack (7) of sheets to be printed. 3. Device according to claim 2, characterized in that said tray-bar (9) is provided with means for gripping and driving the front edge (14a) of the sheets transferred from said stack (7) by said means of capture and transfer one by one of the sheets. 4. Device according to claims 1 to 3, characterized in that said means for gripping the front edge consist of clamps (10) retractable during their passage under said crossbar (17). 5. Device according to one of claims 1 to 4, characterized in that said gripping means and transfer one by one of the sheets from said stack (7) as far as said pre-margin means (9-12) are constituted by a suction cup system (11) movable vertically and parallel to the direction of movement of the printing plate (4). 6. Device according to one of claims 1 to 5, characterized in that the bar (17) -means (23) movement assembly thereof is slidably mounted parallel to the direction of movement of the printing plate ( 4) by being resiliently recalled by spring or the like (26), said sliding being of small amplitude and caused by tabs or the like (25) integral with the printing plate (4) and acting, at the end of the output stroke of this last, on end supports (19) of said assembly 17-23. 7. Device according to claim 1, characterized in that said detection means (31 and 32) are photoelectric cells with reflection. 8. Device according to claim 1, characterized in that said gripping and lifting means (29) of the crossbar (17) are suction cups. 9. Device according to one of claims 1 to 8, characterized in that said front and lateral wedging means (28,31,32), said means for gripping and transferring sheets (11,29) and said means (10 ) gripping the front edge (14a) of the sheets on said pre-margin means (9,12) are adjustable in position orthogonally to the direction of movement of the printing plate (4).

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