US3538846A

US3538846A - Sheet ejector system for a printing machine

Info

Publication number: US3538846A
Application number: US750950A
Authority: US
Inventors: Matthew L Jaffa; David Jaffa
Original assignee: Individual
Current assignee: PRECISION ACQUISITION Inc A DE CORP (NOW KNOWN AS PRECISION SCREEN MACHINES Inc
Priority date: 1968-08-07
Filing date: 1968-08-07
Publication date: 1970-11-10
Anticipated expiration: 1987-11-10

Description

United States [72] Inventors Matthew L.Jafta 2,335,064 11/1943 Kabel ..214/1(BS.2)UX 92 Clark nm he ford, NJ. 07070. 2,524,417 10/ 1950 Bamber ..214/ l (BS.2)UX and v 1 m, 318.; 2g r d Pl 2,959,412 1 1/1960 Sjostrom 271/84 Fairlm mwaefsey 0741 0 3,359,895 12/19'67 Forslund 101/123 2 Appl N 750,950 3,405,812 /1968 Kolbus ..214/1(BS.2)UX [22] Filed 8 Primary ExaminerRobert E. Pulfrey Patented 1970 Assistant Examiner-Alan E. Kopecki Attorney-Irving Seidman [54] SHEET EJECTOR SYSTEM FOR A PRINTING MACHINE ABSTRACT A h f i 10 Claims, 4 Drawing s eet e ector systern or a printing mac me 1neluding a conveyor having multiple, spaced-apart parallel [52] US. Cl 101/123, running endless n which carry Sheets from a table surface 2 1 37 1/631 18 of the printing machine to a point of deposit, and suction grip- Iut. e aligned the inter-belt paces and mcvablg along a car- B6511 riage which can be raised and lowered underneath the belts. Field of Search 101/123, The carriage is raised with the Suction grippers positioned 118, 2 6 1 toward the table to grip a sheet thereon, and with the carriage in the raised position, the suction grippers are moved between [56] References cued the belts and away from the table to drag the sheet onto the UNXTED STATES PATENTS belts. The carriage is then lowered to break the grip upon the 993,613 5/1911 Morrison... 101/316 sheet, thereby allowing it to be carried by the belts, and the 2,049,850 8/1936 Lytale et al.. ..214/1(B'S.2)UX suction grippers are repositioned toward the table in prepara- 2,120,679 6/1938 Pohle 101/316X tion for gripping the next sheet when the carriage is raised 2,169,739 8/1939 Owen ..214/1(BS.2)UX again.

f 1,31; SWITCHING AND I gfggg tg clgig LOGIC A a I 53A II ou n 4 I 1 55 521A; 54 3; F'" l I I I I I N (3) IO SOU T HYDRAULIC PRESSURE SOURCE Patented Nov. 10, 1970 v Sheet 3 0:34

Patented Nov. 10; 1970 Sheet Patented New. 10, 1970 3,538,846

Sheet 4 of4 FIG.4

SHEET EJECTOR SYSTEM FOR A PRINTING MACHINE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates in general to the printing art, and more particularly to a sheet ejector system for a printing machine.

In the printing of posters by silk screen printing machines, the poster sheet to be printed is laid upon a backing table and a printing head which is moveable relative to the table is brought down from a retracted position into a position of contact with the sheet to perform the printing operation. The printing head is then raised to allow removal of the printed sheet and placement of the next sheet on the table.

The production rate of the printing machine is inherently limited by the time which is needed to remove the printed sheets. It is therefore advantageous to provide a sheet ejector system that is capable of rapidly removing the printed sheets immediately after completion of each printing operation.

In the prior art, automatically operable sheet ejector systems employing various types of mechanical sheet grippers are known. However, such sheet ejector systems require that the printing head be raised clear of the table before any gripping of the sheet takes place.

The invention provides a sheet ejector system whereby the sheet can be gripped while the printing head is still in contact with it, so that the sheet can be pulled off the table as soon as the printing head begins to rise, without any waiting for the printing head to reach a predetermined clearance for insertion of any gripping means between the printing head and the sheet on the table.

The invention provides a sheet ejector system for a printing machine including a conveyor positioned in adjacently extending relation to the table surface and having multiple, spaced-apart, parallel running endless belts which carry sheets from the table to a point of deposit, and a carriage which can be raised and lowered underneath the belts. On the carriage is provided a moveable suction gripper means having suction gripper elements aligned with the interbelt spaces. To remove a sheet, the carriage is raised with the suction gripper means positioned toward the table so that the gripper elements extend between the belts to grip the underside of the sheet, before the printing head begins to rise. With the carriage in the raised position, as soon as the printing head separates from the sheet, the suction grippers are moved between the belts and away from the table to drag the sheet onto the belts. The carriage is then lowered to break the grip on the sheet, thereby allowing it to be carried by the belts,.and the suction gripper means is repositioned toward the table in preparation for gripping the next sheet when the carriage is raised again.

For an automated ejector system, the movements of the carriage and gripper means can be controlled in accordance with the operation of the printing head. A switch responsive to the movement of the printing head can be employed to establish a signal indicating whether the printing head is down against the sheet or raised to permit removal thereof. Such signals are used to control the operation of motor devices that move the carriage and the gripper means, with the motions of said carriage and gripper means being limited by the action of other switches.

Starting with the printing head raised, the carriage in its down position and the gripper means at its inward position with respect to the table, upon occurrence of a printing head down signal, a motor is activated to raise the carriage to its up position where it is stopped by the activation of a limit switch, and in which position the suction elements of the gripper means establish contact with the underside of the sheet before the squeegee makes its pass to perform the printing operation. Upon occurrence of a printing head up signal, which occurs after completion of the printing operation, another motor is activated to move the gripper means away from the table towards an outward position thereby dragging the sheet onto the conveyor belts. During the movement of the gripper means from its inward position to its outward position, the carriage motor is haltedso that the carriage remains in its up position. The arrival of the gripper means at its outward position is detected by a limit switch that stops the gripper means motor and activates the carriage motor to lower the carriage so that the suction grip on the sheet is broken and the sheet is released onto the belts for transport thereby to the point of deposit. The arrival of the carriage atits down position is expediently detected by another limit switch that activates the gripper means motor to return the gripper means to its inward position so that it is ready to grip the next sheet as soon as the following printing head down signal causes the carriage to rise again.

If desired, a vacuum pump can be provided to supply the vacuum used for sheet gripping, in which case the connection of the gripper elements to the vacuum pump is preferably interrupted when the gripper means arrives at its outward position. The need for a vacuum pump and its associated controls can of course be eliminated by using resilient suction cups which are pressed against the sheet when the carriage is in the up position and are pulled away from the sheet with some assistance by the conveyor belts when the carriage is lowered.

One of the advantages afforded by the invention is that by gripping the sheet from underneath when the printing head is down, there is no problem in ejecting warped sheets since the printing head serves as a backing restraining any movement of the sheet away from the suction grippers when the carriage is raised. Thus, there cannot be any sheets bent upward because of the printing head, any sheet which happens to be bent downward will be pressed against the printing head by the gripper elements. To provide better support of the sheets and to prevent any warpage, the table is preferably provided with cut away indentations along the edge adjoining the conveyor. This allows the gripper elements to extend through the table indentations for contact with the sheet, and keeps the portions of the sheet between adjacent gripper elements flat.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing: FIG. 1 is a schematic elevation view, partly in section, of a printing machine equipped with a sheet ejector system according to a preferred embodiment of the invention.

FIG. 2 is a side elevation view illustrating in greater detail the printing machine shown in FIG. 1.

FIG. 3 is a side elevation view of the carriage and gripper means shown in FIG. 1.

FIG. 4 is a plan view of the sheet ejector system and adjoining portion of the printing machine shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION In FIGS. 1 and 2 there is shown a printing machine 10 having a generally horizontal table 11 that receives and holds sheets to be printed, and a printing head 12 which is moveable relative to table 11 by means of a motor 13 and cam and lever drive arrangement 14 mounted to the base 15 of table 11. Printing head 12 is moveable between a downward position as shown in FIG. 2 anc an upward or retracted position as shown in phantom in FIG. 1. In the downward position, a printing screen or stencil 16 carried by printing head 12 is pressed into contact with the upper side of the sheet to be printed and while in such sheet contact position, an ink spreading squeegee 17 also carried by printing head I! sweeps across stencil 16 to perform the printing operation. After the printing operation is completed, the printing head 12 is raised to its retracted position to allow removal of the printed sheet and permit the next sheet to be laid upon the table 11 for printing in the next cycle of operation.

While as in the prior art, the removal of printed sheets from the table l1 could be performed manually, the invention provides a sheet ejector system which automatically removes the printed sheets and conveys them to a depositing position immediately after each sheet is printed.

The sheet ejector system 20 comprises a multiple belt conveyor 21, a moveable carriage 22, and a moveable suction gripper assembly 23.

Conveyor 21 is expediently mounted to the table base 15 for support thereby in adjacently extending relation to table H and has a plurality of parallel spaced-apart endless belts 2 3 which pass over corresponding individual idler rollers A located adjacent to table 11, and over a common driving roller 25A located remotely from table 11, as can be seen more clearly in FIG. 4. Each of the idler rollers 25A is supported by a pair of brackets 25C for rotation relative thereto, and the brackets 25C are connected to a frame member 15A of base 15 for support thereby in fixed relation thereto. Thus, the space between each pair of adjacent belts 24 is unobstructed between frame member 15A and the outer roller 25B.

Roller 253 is rotatably driven by a motor 26 via a belt and pulley drive 27 so that all of the belts 24 move in unison for transporting sheets removed from table ll to a depositing position outboard of roller 25B.

As seen with greater detail in FIGS. 3 and 4, the carriage 22 is located in underlying relation to the conveyor 21 and is expediently supported by the table base 15 for movement relative to both the table ill and conveyor 21 along a path generally vertical and perpendicular to the straight length running portions of the conveyor belts 24. To guide the movement of carriage 22, it is provided with a pair of upright, parallel guide rods 28 each of which is slidably received through a pair of sleeve bearings 29 mounted to framing members of base 15. A hydraulic cylinder 30 mounted to base 15 by means of a bracket 31 serves as a motor meansfor moving carriage 22 up and down, and for such purpose, the piston rod 32 of cylinder 30 is connected to the center of a crossbar 33 which in turn is connected at each end to a guide rod 23. The guide rods 28, with the aid of a pair of braces 34 and a pair of plates 35, support a pair of elongated track members 36 in a generally horizontal attitude. Track members 36 are held in fixed spaced-apart parallel relation to each other by

crossbars

37 and 38.

To assure uniform movement of the carriage 22, a transversely extending shaft 61 is mounted between the plates and supported thereby for rotation relative thereto, and at the opposite end portions of shaft 61 are mounted a pair of pinions 62 that mesh with corresponding racks 63 fixedly supported by base 15 via stand off rods 64. During the movement of the carriage 22, should either side of the carriage 22 get slightly ahead of the other, this will cause a torque to be applied to shaft 61 and such torque will produce counterbalancing forces acting on plates 35 via the action of pinions 62 and racks 63.

The suction gripper assembly 23 extends transversely with respect to the tracks 36 and at each of its opposite ends, the assembly 23 engages a corresponding track as for support thereby in sliding contact therewith. A pair of shafts 39 are mounted to the carriage 22 for rotation relative thereto about axes located at the extremities of tracks 36 and generally perpendicular thereto. At the opposite ends of each of shafts 39 are mounted sprockets 40 which rotate with their respective shafts 39. Over one pair of sprockets 40 passes a chain 41A, the ends of which are connected to one end of the suction gripper assembly 23. Over the other pair of sprockets it passes a chain 418 the end of which are connected one to each end of the piston rod 42 of a double-acting hydraulic cylinder 43 fixedly mounted to the adjacent track 36.

Hydraulic cylinder 43, and the chain and sprocket arrangement defined by shafts 39, sprockets 40 and

chains

41A and 41B serve as a motor means which drives the suction gripper assembly 23 back and forth along the tracks 36 between an inward position X adjacent to table 11 and an outward position Y away from the table.

On the suction gripper assembly 23 are provided a plurality of suction gripper elements 44 which are positioned to travel along the spaces between belts 24 when the assembly 23 moves along tracks 36 with the carriage 22 in its upper position. Each suction gripper element M is provided with a suction cup 45 affixed to its free end, and this suction cup 35 can be either a resilient type which can exert a suction gripping force by merely being pressed against the surface of the sheet to be gripped, or can be operated by means of a vacuum pump 46 connected to assembly 23 by a flexible hose 47 with such hose 47 being connected to communicate with each suction cup 45 by suitable passage means (not shown).

in the operation of the sheet ejector system 20, the movements of the carriage 22 and the suction gripper assembly 23 are synchronized with the operation of the printing head 12.

A control system 50 responsive to the position of the printing head 12 and which senses the positions of both the carriage 22 and suction gripper assembly 23 provides for automatically controlled operation of the sheet ejector system 20. To implement such automatic control functions, the hydraulic cylinder 30 that moves the carriage 22 is controlled by a solenoid flow switching valve 51, and the hydraulic cylinder 43 that moves the suction gripper assembly 23 is controlled by another solenoid flow switching valve 52.

The position of the printing head 12 is sensed by switches 53A and 538. When the printing head 12 is down in the sheet contact position, switch 53A is activated, whereas when printing head 12 is up in the retracted position, switch 533 is activated. Similarly, the position of the carriage 22 is sensed by switches 54A and 54B, and the position of the suction gripper assembly 23 is sensed by switches 55A and 558. When carriage 22 is in its upper limit position, switch 54A is activated whereas when carriage 22 is in its lower limit position, switch Sd-B is activated. These upper and lower limit positions of the carriage 22 are of course established by the stroke length of hydraulic cylinder 30.

When suction gripper assembly 23 is in its inward limit position X switch 55A is activated whereas when suction gripper assembly 23 is in its outward limit position Y, switch 558 is activated. Here again, the inward and outward limit position X and Y of suction gripper assembly 23 are established by the stroke length of hydraulic cylinder 43.

The

switches

53A, 53B, 54A, 5148, 55A, 55B are connected to a switching and sequencing logic circuit 56 that controls the operator of the

solenoid valves

51 and 52.

To explain the operation of control systems 50, consider that at the start of a typical cycle of operation, the printing head 12 is raised and that the carriages 22 is in its lower limit position with the suction gripper assembly 23 being in its inward limit position X. A blank sheet (not shown) is laid upon table 11 and the printing head 12 is brought down into the sheet contact position to perform the printing operation upon the upper side of the sheet. When printing head 12 arrives at the sheet contact position, switch 538 is activated, and in response thereto, logic circuit 56 applies a control signal to the operating solenoid of valve 51 causing said valve 51 to assume a flow switching state activating hydraulic cylinder 30 to move carriage 22 from its lower limit position to its upper limit position. Upon arrival of carriage 22 at this upper limit position, switch 54A is activated. The suction gripper assembly 23 will remain at its inward limit position X and will rise with carriage 22 until the suction gripper members 44 extend through corresponding cutaway indentations 57 provided along the edge of table 11 adjoining conveyor 21 and are pressed into suction gripping contact with the underside of the sheet being printed. By providing such indentations 57, the sheet can be positively gripped from below when printing head 12 is pressing the sheet down against table 11, so that there is no chance of any warpage that might interfere with the intended gripping action.

After printing operation is completed, the printing head 12 is raised and upon arrival at an upward retracted position that allows free slide-out movement of the printed sheet, switch 53A is activated. Thus, at this point in the cycle, switches 53A, 54A and 55A are activated concurrently, to which concurrent activation of switches logic circuit 56 responds by applying a control signal to the operating solenoid of valve 52 causing said valve 52 to assume a flow switching state activating hydraulic cylinder 43 to move suction gripper assembly 23 from its inward limit position X to its outward limit position Y. During such movement, logic circuit 56 maintains the control signal previously applied to the solenoid of valve 51 so that carriage 22 is retained in its upper position as the gripper assembly 23 moves outward dragging the sheet off the table 11 and onto the belts 24.

Upon arrival of gripper assembly 23 at the outward limit position Y, switch 558 is activated, thereby causing logic circuit 56 to maintain the signal on the solenoid of valve 52 holding gripper assembly 23 at the outward position Y and concurrently to apply a control signal to the solenoid of valve 51 that causes said valve 51 to assume a flow-switching state activating hydraulic cylinder 30 to move carriage 22 from its upper position to its lower position. As carriage 22 moves downward, the suction gripper members 44 move downwardly away from the sheet which is retained by the belts 24 which is carried away thereby and ejected therefrom at the depositing position where belts 24 pass over roller 25B.

Arrival of the carriage 22 at the lower limit position activates switch 543 thereby causing logic circuit 56 to retain the signal on the solenoid of valve 51 so as to keep the carriage 22 at the lower position, and to apply a control signal to the solenoid of valve 52 causing said valve 52 to assume a flow switching state activating hydraulic cylinder 43 to move gripper assembly 23 from its outward position to its inward position. Thus, at the end of the sheet ejection cycle, both the carriage 22 and gripper assembly 23 will be in the proper positions for the start of the next sheet ejection cycle.

The switching and sequencing logic circuit 56 can be any one of several known types adapted to perform the foregoing specified valve switching functions. In cases where automated operation of the carriage 22 and gripper assembly 23 is not desired, the

switches

53A, 5313, 54A, 54B, 55A, 5513 can be connected instead to corresponding indicator devices, such as signal lamps (not shown) and the

valves

51 and 52 can be operated manually by an operator monitoring such indicators.

in cases where the suction cups 45 are aspirated by means of the vacuum pump 46, it is advantageous to shut off the vacuum to the cups 45 when the carriage 22 is lowered to release the sheet onto the belts 24. This can be done conveniently by means of a solenoid operated valve 71 flow connected in series between vacuum pump 46 and the hose 47. The solenoid of valve 71 is expediently activated by logic circuit 56 to shut off the vacuum to suction cups 45 whenever valve 51 is operated to lower carriage 22.

By providing for shutting off the vacuum to suction cups 4S, somewhat thinner sheets can be handled without any danger of tearing because smaller pulling forces are required to break the grip of the suction cups 45.

It should be noted that the conveyor 21 can be omitted if desired, in which case the carriage 22 and suction gripper assembly 23 are operated merely to pull sheets off the table 11, with the sheets thus removed being taken off the carriage 22 by an operator or by some other means (not shown).

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodi ment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

We claim:

1. In a printing apparatus having a table for receiving sheets to be printed and a printing head moveable relative to the table from a sheet contact position in which the printing operation is performed to a retracted position that allows removal of the printed sheet from the table, a sheet ejector system which comprises a conveyor means positioned in adjacently extending relation to said table and including a plurality of spaced-apart endless belts running along parallel paths to transport sheets removed from said table to a depositing position; a carriage means disposed in underlying relation to said conveyor means and moveable relative to said conveyor means and table between a first position remote therefrom and a second position adjacent thereto; and a suction gripper means supported by said carriage means for movement relative thereto along a path parallel to the running paths of said belts, said suction gripper means including a plurality of suction gripper members disposed for extension between said belts when the carriage means is in said second position to grip a sheet on the table, said suction gripper means being moveable away from said table to drag the sheet onto said belts, and said carriage means being moveable from said second position to said first position when the suction gripper means is away from the table to break the grip of the suction gripper members on the sheet and thereby release same onto said belts for transport thereby to said depositing position.

2. A sheet ejector system according to claim 1 wherein the suction gripper elements of said suction gripper means are positioned for gripping contact with the side of the sheet under that which is contacted by the printing head.

3. A sheet ejector system according to claim 2 including motor means, supported by said carriage means for movement therewith and connected to said suction gripper means to move same relative to said carriage means back and forth between an inward position adjacent to said table and an outward position further away from said table.

4. A sheet ejector system according to claim 3 including means defining a plurality of cut-away indentation along that edge of the table adjoining said conveyor means, said indentations being disposed to accommodate extension therethrough of corresponding gripper elements for gripping contact with said underside of the sheet.

5. A sheet ejector system according to claim 4 wherein the second position of said carriage means is elevated above the first position of said carriage means and including a motor means connected to said carriage means for raising and lowering same between said first and second positions.

6. A sheet ejector system according to claim 5 including control means responsive to the position of said printing head and connected to the motor means for said carriage means to activate said motor means to move said carriage means from said first position to said second position when the printing head arrives at said sheet contact position.

7. A sheet ejector system according to claim 6 wherein said control means is responsive to the movement of said printing head from the sheet contact position to said retracted position and is connected to the motor means for said suction gripper means to activate said motor means to move the suction gripper means from said inward position to said outward position when the carriage means is in said second position and the printing head is in said retracted position.

8. A sheet ejector system according to claim 7 wherein said control means activates the motor means for said suction gripper means to move the suction gripper means from said outward position to said inward position when the carriage means is in said first position.

9. A sheet ejector system according to claim 7 including a vacuum source means connected to said suction gripper means to aspirate the suction gripper member thereof for gripping said sheet, and wherein said control means is connected to said vacuum source means to interrupt the aspiration thereby of said suction gripper members when the suction gripper means arrives at said outward position.

10. A sheet ejector system according to claim 7 wherein the motor means for said suction gripper means includes an endless chain drive means connected to said suction gripper and having a reciprocable output member connected to said means and a linear motor connected to said carriage means chain drive means.