WO1998046400A1

WO1998046400A1 - Clamshell die cutting press having automatic sheet feeder

Info

Publication number: WO1998046400A1
Application number: PCT/US1998/007434
Authority: WO
Inventors: Robert G. Weidhaas, Sr.; Robert G. Weidhaas, Jr.; Matthew S. Amburg; John Shields
Original assignee: Preco Industries, Inc.
Priority date: 1997-04-14
Filing date: 1998-04-14
Publication date: 1998-10-22
Also published as: AU7115298A

Abstract

A sheet feeder (22, 220a) is provided for use with a clamshell-type die cutting press (24, 240a) having fixed and shiftable platens (36, 360, 38, 380). The feeder (22, 220a) includes an input assembly (44, 1020) for gripping a sheet to be processed, moving the latter to the shiftable platen (38, 380) and depositing the sheet to be processed onto the shiftable platen (38, 380) when the latter is in its open position. Additionally, the feeder (22, 220a) has a retrieval unit (94, 1320) operable to grip a processed unit on the shiftable platen (38, 380) in order to move the processed sheet away from the latter. A PLC-based control assembly (39, 370) is operably coupled with the sheet feeder (22, 220a) and the press (24, 240a) for concurrent operation of the input assembly (44, 1020) and retrieval unit (94, 1320) so that a sheet to be processed is moved toward the shiftable platen (38, 380) during at least a portion of the time that a processed sheet is moved away from the shiftable (38, 380).

Description

CLAMSHELL DIE CUTTING PRESS HAVING AUTOMATIC SHEET FEEDER

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is concerned with fully synchronized, preferably microprocessor-controlled, sheet feeder/clamshell die press apparatus which can attain operational speeds far in excess of prior devices of this type. More particularly, the invention pertains to such automated sheet feeder/die press apparatus having operational speeds limited only by the capacity of the die press, up to 3000 sheets per hour.

Description of the Prior Art

Large clamshell-type die cutting presses are well known in the printing and graphic arts industries. Generally speaking, such presses include a stationary die- supporting head together with a shiftable platen designed to support a sheet of stock to be cut. The platen is sequentially moved through a complex eccentric and cam drive from a lowered position where a previously cut sheet is removed from the platen and a fresh sheet is inserted, to a die cutting position in coacting relationship with the cutting die mounted on the stationary head. In many cases, sheet retrieval and insertion is done manually, i.e., an operator stands adjacent the press and as it opens, a cut sheet is removed, and a new sheet is inserted. Such operations are extremely slow and uneconomical.

Automatic sheet feeders have been proposed in the past for use with clamshell die presses. However, these prior sheet feeders utilize mechanical controls and linkages, and as a consequence are very complicated and difficult to accurately time. Furthermore, these feeders generally direct incoming sheets along a complex, non-linear path of travel and rely upon gravity to seat the incoming sheets within the press. As a consequence of these drawbacks, prior automatic sheet feeders cannot operate at speeds faster than approximately 1000 sheets per hour. While this is an improvement over manual sheet retrieval and insertion, the performance of such sheet feeders is still inadequate.

There is accordingly a need in the art for an improved sheet feeder/die press apparatus of simplified design which provides reliable, high speed die cutting on the order of from 1000-3000 sheets per hour, with complete and automatic, microprocessor- controlled synchronization between the sheet feeder and press units.

SUMMARY OF THE INVENTION The present invention overcomes the problems described and provides a greatly improved sheet feeder/die press apparatus. Broadly speaking, the preferred apparatus includes a PLC-controlled sheet feeder designed to operate with a PLC-controlled clamshell die press; the controllers are interconnected so as to insure automatic, high speed synchronization of the feeder and the press. Broadly speaking, the improved sheet feeders of the invention are adapted for feeding sheets to a clamshell-type die press for processing thereof, and for retrieving processed sheets from the press. Clamshell presses of this type are well known and include a fixed platen (normally supporting a die) and a shiftable platen movable between a closed die-cutting position adjacent the fixed platen and an open position. The sheet feeders of the invention include an input assembly for gripping a sheet to be processed, moving the sheet toward the shiftable platen and depositing the sheet to be processed onto the shiftable platen when the latter is in the open position; a retrieval unit for gripping a processed sheet on the shiftable platen and moving the processed sheet away from the shiftable platen; and a control operably coupled with the input assembly and the retrieval unit for operation thereof so that the sheet to be processed is moved toward the shiftable platen during at least a portion of the time that the processed sheet is moved away from the shiftable platen, i.e., the sheet movement is at least in part simultaneous.

The improved sheet feeders of the invention are preferably designed to feed sheets along a substantially horizontal, straight path from the pickup station to an endmost vacuum gripper device. This is done with full support along the path of travel of the sheet so as to avoid any droop or sag of the sheets which can reduce speeds and cause inaccuracies in registration. Furthermore, once the sheet is fully gripped, it is lowered onto the opened die platen and positively placed against the platen stops; this avoids the problem with prior art feeders of misregistration or slow feeding attendant upon dropping sheets by gravity into the press. The shiftable die press platen and the feeder are mechanically intercoupled so that, upon opening of the platen, the sheet- holding structure associated with the feeder is lowered to place the gripped sheet in position on the platen. Retrieval of cut sheets from the platen is achieved during the time that a fresh gripped sheet is lowered onto the platen. In one embodiment, a specialized cam and follower assembly assures that all potentially interfering apparatus is moved so as to allow a sheet retrieval vacuum device to remove a previously cut sheet from the platen before full placement of a fresh sheet thereon. The interconnection of the feeder and press PLCs makes it possible to properly time all components of the apparatus, and also greatly facilitates the makeready operation between runs of differing sizes, shapes and/or thicknesses of stock material.

The preferred sheet feeder/die press apparatus of the invention can attain operational speeds of up to 3000 sheets per hour, levels heretofore never obtainable.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic side view of a preferred die cutting assembly in accordance with a first embodiment of the invention shown in Figs. 1-8 and 22-24, showing the die platen closed and during the initial stages of delivery of a sheet to the clamshell die cutting apparatus; Fig. 2 is a schematic side view of the first embodiment similar to that of Fig. 1 , but illustrating the die platen partially open for retrieval of a previously die cut sheet and during the next stage of delivery of a fresh sheet to the die cutting apparatus;

Fig. 3 is a schematic side view of the first embodiment similar to that of Fig. 2, but depicting the die platen in its fully opened position with the delivery extension arms setting a fresh sheet in place on the platen;

Fig. 4 is a schematic top view of the first embodiment depicting the extension arm structure and die platen;

Fig. 5 is an enlarged, fragmentary side view of the first embodiment similar to that of Fig. 1 and showing the extension arm arrangement with the clamshell die in its closed position;

Fig. 6 is an enlarged, fragmentary side view similar to that of Fig. 2 and depicting the die platen of the first embodiment partially open during retrieval of a previously die cut sheet;

Fig. 7 is an enlarged schematic side view similar to that of Fig. 3 illustrating in more detail placement of a fresh sheet on the fully opened die platen in the first embodiment; and

Fig. 8 is an enlarged, fragmentary isometric view illustrating in detail the spring metal guides for the cut sheet vacuum retrieval bar, the latter extending along the side frames of the assembly and along the length of the intermediate arms in the first embodiment; Fig. 9 is a schematic side view of another preferred die cutting assembly in accordance with a second embodiment of the invention illustrated in Figs. 9-21, showing the die platen closed and with the sheet feeder in its position during initial stages of delivery of a sheet to the clamshell die cutting apparatus; Fig. 10 is an enlarged, fragmentary side view illustrating in greater detail portions of the sheet feeder of the second embodiment;

Fig. 11 is a fragmentary top view depicting the sheet feeder of the second embodiment;

Fig. 12 is a schematic side view in partial vertical section illustrating details of the overall die cutting assembly of the second embodiment;

Fig. 13 is an enlarged, fragmentary, schematic vertical sectional view illustrating the sheet feeder of the second embodiment during initial gripping of a sheet to be fed to the clamshell die cutting apparatus;

Fig. 14 is a view similar to that of Fig. 13 and illustrating the sheet feeder of the second embodiment where a sheet is being fed to the die cutting apparatus while a previously processed sheet is being retrieved;

Fig. 15 is a view similar to that of Figs. 13-14 and illustrating the sheet feeder of the second embodiment where a sheet to be processed is fed to the die cutting apparatus and the previously processed sheet is being retrieved; Fig. 16 is a vertical sectional view illustrating the preferred pickup head vacuum bar assembly forming a part of the second embodiment of the invention;

Fig. 17 is a fragmentary side view illustrating in detail the shifting unit used to move the pickup head vacuum bar in the second embodiment of the invention;

Fig. 18 is a fragmentary vertical sectional view depicting the construction of the retrieval vacuum bar unit of the second embodiment of the invention;

Fig. 19 is a fragmentary vertical sectional view illustrating the shifting assembly used to move the retrieval vacuum bar unit of the second embodiment of the invention;

Fig. 20 is a diagram illustrating the PLCs associated with the sheet feeder and clamshell die press of the second embodiment of the invention, with the respective inputs and outputs for each PLC;

Fig. 21 is a flow diagram illustrating the software used to control the clamshell die press in the second embodiment of the invention;

Figs. 22A and 22B are together a flow diagram illustrating the software used to control the clamshell die press in the first embodiment; Fig. 23 is a diagram illustrating the PLCs associated with the sheet feeder and clamshell die press of the first embodiment of the invention, with the respective inputs and outputs for each PLC; and

Figs. 24A and 24B are together a flow diagram illustrating the software used to control the sheet feeder in the first embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment-Figs. 1-8 and 22-24

Turning now to Figs. 1-8, a die cutting assembly 20 is depicted which includes an automated sheet feeder 22 operably coupled with a downstream clamshell-type die press 24. The feeder 22 has spaced side frames 25 and includes an input elevator unit 26 adapted to hold a stack of sheets to be die cut, a sheet pickup and conveying assembly 28 designed to sequentially pick up sheets from elevator unit 26 and convey such sheets rightwardly as viewed in Figs. 1-3, a shiftable extension arm assembly 30 for sequentially receiving sheets from assembly 28 and delivering these to the press 24, a shiftable cut sheet retrieval device 32 for removing cut sheets from the press 24, and an output collector/elevator unit 34. The press 24 includes a large stationary die- carrying head 36 and a shiftable platen 38 operatively coupled with head 36. Also, a PLC-based control assembly 39 forms a part of the assembly 20. The elevator unit 26 is conventional and includes primary and secondary sections controlled by motor and drives 40, 42, respectively. The two-stage elevator unit is designed to continuously provide a supply of sheets for processing, even during restocking of the primary section thereof.

The sheet pickup and conveyor assembly 28 includes an elongated laterally extending vacuum bar 44 having a motor and drive 46 operatively coupled thereto. The vacuum bar 44 has a plurality of laterally spaced suction cups 47 and is shiftable downwardly to grip the leading edge of a sheet to be processed, and for elevating the gripped sheet and moving it rightwardly as viewed in Figs. 1-3. The overall assembly 28 further includes an elongated conveyor belt 48 mounted on rollers as shown and powered by motor 50. A nip roller 52 is positioned adjacent the lefthand end of conveyor 48 and is selectively pivotal toward and away from the conveyor 48 by means of pneumatic piston and cylinder assemblies 54 and an intermediate crank mechanism 56. A short, stationary sheet-supporting plate 57 is also provided adjacent the forward end ofbelt 80 (see Fig. 5) The extension arm assembly 30 is positioned rightwardly as viewed in Figs. 1 -3 of the assembly 28 and includes a pair of laterally spaced apart, outermost elongated extension arms 58 each equipped with an elongated cam track 60 extending along the inner face thereof, as well as an upper surface 62. The extension arms 58 support a laterally extending front vacuum bar unit 64 provided with a series of selectively operable sheet-gripping suction cups 65, sheet stops 66 and a series of exhaust nozzles (not shown) for pressurized air (Fig. 4). The unit 64 is translatable fore and aft along the forward end of the extension arms 58; to this end, each arm 58 supports a rack 66 which are engaged by a suitable gear drive forming a part of the bar unit 64, allowing the latter to be selectively and accurately adjusted for different sheet sizes to be processed.

The overall assembly 30 also includes a pair of somewhat shorter intermediate arms 68 which are respectively inboard of the arms 58 and are likewise pivotally secured to the side frames 25. Each intermediate arm 68 includes a roller 70 which rides atop the upper surface 62 of the adjacent extension arm 58. The arms 68 are equipped with rotatable front chain sprockets 72 and supports 73 which are important for purposes to be described. Each intermediate arm 68 also supports a cam roller 74 as shown.

A secondary delivery belt unit 76 is positioned above the arms 58 and 68 and is mounted on a transversely extending pivotal shaft 78, the ends of the latter being supported by side frames 25. The unit 76 has spaced secondary conveyor belts 80 which are powered via an auxiliary power takeoff (not shown) from motor 50 as well as corresponding resilient sheet holddowns 82 for the belts 80 and rear nip roller 83. The pivotal shaft 78 carries a pair of arcuate cams 84 which coact with the cam rollers 74 on the intermediate arm 68.

The retrieval device 32 includes a pair of elongated chains 86 supported on endmost sprockets 88 mounted on side frames 25 and the front sprockets 72 mounted on the forward ends of the intermediate arms 68. A series of idler rollers 90 are also provided on each side frame 25 between the sprocket sets 88, 72. The chains 86 are driven via a servomotor 92 operatively coupled to the sprockets 88. An elongated, laterally extending sheet retrieval vacuum bar 94 is operatively attached to chains 86 and has a series of spaced vacuum cups 96 oriented to fit between the belts 80. The bar 94 is guided for fore and aft movement thereof by means of a pair of elongated spring metal guides 98 which extend along the inner face of each side frame 25 and also along the inner face of each intermediate arm 68. A pair of side frame-mounted supports 99 below conveyor belt 48 and support 73 on the arms 68 rigidify the guides 98. However, it will be observed that a mid-portion 100 of each guide 98 between the end of each support 99 and the adjacent rearward end of the proximal arm support 73 is unrestrained and therefore can bend and flex as necessary to accommodate pivotal movement of the intermediate arms 68. This arrangement is best shown in Fig. 8.

The output collection/elevator unit 34 is designed to collect and stack, on a continuous basis, completed die cut sheets. The unit 34 has a pair of schematically depicted jog plates 102 (see Fig. 3, only one plate being shown) above the elevator 103, which are powered via motor 104. The jog plates 102 can be positioned at any convenient location, as will readily be understood. A selectively operable temporary curtain support 106 for die cut sheets is provided in order to allow removal of die cut sheets from the elevator 103, without stopping the operation of the overall assembly 20. Specifically, the curtain support 106 includes a pair of elongated continuous chains 108 supported on each side frame 25 and trained around drive and idler sprockets 110, 112. The chains 108 have, along a portion thereof, a series of spaced apart, transversely extending, axially rotatable sheet support rods (not shown) which, when moved in overlying relationship to elevator 103, temporarily support die cut sheets delivered to the unit 34 during unloading of the elevator 103. The curtain support 106 is operated via motor and drive 114. Elevator 103 is operated for up and down movement thereof by means of motor and drive 116.

The die press 24 is adjustably mounted on upstanding legs 118 permitting the entire press 24 to be moved up or down to a limited extent. The legs 118 thus support stationary head 36 as well as shiftable die platen 38, the latter including a stationary base 120. In detail, the head 36 is a heavy, massive unit presenting a flat die-supporting face 122 which holds cutting die 124. The head 36 also has a selectively operable air clutch 126, operated by conventional piston and cylinder assemblies, rotatable, geared drive wheels 128, gear encoder 130 operatively connected to the latter, and a home position sensor 131 (see Fig. 3) for resetting of encoder 130 during operation of the press. A Magnatek drive motor 132 is connected to clutch 126 via schematically illustrated coupling 134. The clutch 126 is interposed between motor 132 and drive wheels 128 and serves to selectively drive the latter when the clutch is engaged. A pair of pitman or crank arms 136 are pivotally connected to the drive wheels 128 to form an eccentric drive for the shiftable platen 38.

Die platen 38 includes a front die face 138 provided with front and side sheet stops 140 (Fig. 4) and is designed to coact with cutting die 124 mounted on face 122 of head 36. The platen 38 also has a rearward drive section 142 equipped with a roller 144 and a pair of cam plates 146 each having a cam slot 148 therein. The crank arms 136 are pivotally connected to drive section 142 as shown. The base 120 below drive section 142 includes a pair of cam rollers 150 respectively located for receipt within the adjacent cam slots 148. The upper margin of front die face 138 is provided with a transverse, pivotally mounted bar 152 having endmost cam rollers 154 respectively received within each cam track 60 of each extension arm 58. Thus, as the platen 38 shifts, the rollers 154 shift within the tracks 60, thereby determining the movement of the arms 58, 68 and related structure. Three spaced apart plate members 156 are operatively coupled to the transverse bar 152 and extend between end rollers 154 and pivot with the bar 152 in the manner to be described.

Although not shown in detail, those skilled in the art will appreciate that the assembly 20 is provided with the usual utilities in the form of electric power and pneumatics, the latter including a vacuum pump 158 (see Fig. 3) as well as selectively operable valves associated with pickup vacuum bar 44, cylinders 54, front vacuum bar unit 64 and retrieval vacuum bar 94.

OPERATION AND SOFTWARE CONTROL The sheet feeder 22 and die press 24 are both fully automated and electronically controlled. This permits an operator to quickly and easily select and adjust the feeder

22 and press 24 operating parameters such as the operating speed, sheet characteristics, press closing position, and dwell time "on-the-fly" with a minimum amount of makeready time.

As illustrated in Fig. 23, the feeder 22 is controlled by a programmable logic controller (PLC) or other control device that receives input signals from the press gear position encoder 130 and press Magnatek main drive motor 132 and provides output signals to the secondary elevator motor 42, primary elevator motor 40, output elevator motor 116, output curtain motor 114, conveyor motor 50, pickup servomotor 46, pickup head vacuum bar 44, retrieval servomotor 92, retrieval vacuum bar 94, nip roll cylinder 54, and front vacuum bar unit 64. Similarly, the press is controlled by a PLC or other control device that receives input signals from the press gear position encoder 130 and home sensor 131 and provides output signals to the sheet feeder PLC as well as the press Magnatek main drive motor 132 and air clutch 126. The PLCs are linked together by a communication link to synchronize the operation and timing of the sheet feeder 22 and die press 24 as described below. FEEDER CONTROL

The feeder PLC is programmed to control every function of the sheet feeder 22 and to keep the feeder in perfect synchronization with the die press 24 even after the feeder or press has been stopped as described in more detail below. The feeder PLC software is best understood with reference to the flow diagrams in Figs. 24 A and 24B.

In the ensuing discussion, it is assumed that the assembly 20 is in the Fig. 1 position, with die platen 38 having moved into coacting relationship with head 36 so as to normally die cut a sheet within the press 24 with little or no dwell or heating time.

In this orientation, the bar 152 is pivoted upwardly so that plates 156 assume a substantially horizontal orientation. Moreover, the motors 40, 42, 44, 50, 92, 114 and

116 are in an idle mode whereas motor 132 continues to operate with clutch 126 engaging wheels 128. The pneumatic systems associated with the assembly 20 are also idled.

The sheet feeder operation begins at step 160 when an operator activates the feeder PLC by operating an activation button or other input device on or interfaced with the feeder PLC. The feeder software then synchronizes the timing or positioning of the feeder 22 with the press 24 by directing the feeder PLC to send a signal to the press PLC to "home" the press in step 162. In response, the press PLC directs the Magnatek drive to run the press 24 for one cycle and position the press in its fully opened position as illustrated in Fig. 3. Similarly, step 164 directs the feeder PLC to "home" the sheet feeder 22.

The operator then activates a start button or other input device on or interfaced with the feeder PLC to begin the operation of both the feeder and the press in step 166. In response, step 1668 directs the press PLC to operate the press Magnatek main drive motor 132.

The program next directs the feeder PLC to read the speed of the Magnatek in step 170 to determine the speed of the press. To synchronize the speed of the feeder 22 with the press 24, the feeder PLC determines the speed at which its pickup and retrieval servomotors 46, 92 must operate. It does this by retrieving these corresponding speed values from a look-up table and storing the values in a memory register as depicted in step 172.

The PLC also includes controls that permit the operator to increase or decrease the speed of the feeder 22 and press 24. Since the feeder speed is determined by first measuring the press speed, the feeder and press always operate at the same speed even though they are not mechanically coupled. The feeder PLC next reads the press encoder 130 to determine the actual position of the press in step 174. When the feeder PLC determines that the press is in the appropriate position, it operates the pickup servomotor 46 and the pickup vacuum bar 44 in steps 176 and 178. This causes the bar 44 to descend as necessary and grip the topmost sheet within elevator unit 26. The PLC then directs the nip roll cylinders

54 to lift the nip roll 52 (step 180) so that the incoming sheet can be placed on the conveyor belt 48. The bar 54 is then moved rightwardly as shown in Fig. 1 to move the gripped sheet onto conveyor belt 48 (step 182).

In steps 184 and 186, the feeder PLC directs the nip roll cylinders 54 to lower the nip roll 52 onto the sheet and to turn on the conveyor motor 50, causing movement of the belts 48 and 80. The conveyor belt 48 then delivers the sheet rightwardly as viewed in Fig. 1 to belts 80 for continued motion of the sheet toward and into unit 64. In this connection, the essentially horizontal orientation of plates 156 provide the necessary support for the sheet in order to prevent drooping or sagging thereof. When the sheet is delivered to front vacuum bar unit 64, the conveyor is ramped to a stop and the feeder PLC activates the unit in step 188 to grip the sheet. In this orientation, the sheet is firmly gripped by the extension arms 58 and the related structure, between the front vacuum bar unit 64 and rear nip roller 83.

In the next operation, the gripped sheet is delivered to the press 24 while the previously cut sheet therein is retrieved. This is initiated by the rotating crank arms 136 which serve to open the shiftable platen 38 as illustrated in Figs. 2 and 3. As a consequence of this opening movement, the cam rollers 154 ride within the extension arm slots 60 begins lowering the extension arms with the gripped sheet toward the now opened die press 24, and also causes the intermediate arms 68 to move by virtue of the engagement of their supporting rollers 70 against the upper surfaces 62 of the extension arms 58. Such downward movement of the arms 58 causes the rear margin of the gripped sheet to move rightwardly as seen in Figs. 1 and 2 away from nip roller 83, so that such rear margin is now engaged by the holddown structures 82. At the same time, opening of the platen 38 causes the plates 156 to pivot downwardly to assume a somewhat vertical orientation as seen in Figs. 2 and 3.

During the described press opening sequence, the feeder PLC controls the retrieval servomotor 92 in step 190 to move the retrieval vacuum bar 94 to a position so that it is ready to remove the previously cut sheet from the opened press 24. This is accomplished by appropriate movement of the chains 86 causing the bar 94 to move rightwardly along the length of the spring steel guides 98, the latter extending along the length of the side frames 25 and also along the length of the intermediate arms 68 (Fig. 8). As described previously, the unrestrained mid-portions 100 of the guides 98 accommodate the downward shifting of the arms 58, 68. In order to permit passage of the vacuum cups 96 to the Fig. 2 position thereof for retrieval of a previously cut sheet, the secondary belt unit 76 is pivoted to a non-interfering position. This is accomplished because of the presence of the cams 84 on the rock shaft 78 supporting the unit 76. These cams cause the unit 76 to pivot appropriately so that the bar 94 and cups 96 may move to its Fig. 2 position adjacent the rearward end of a previously cut sheet on platen 38. The feeder PLC then activates the vacuum system associated with bar 94 in step 192 so that the cups 96 grips the cut sheet on the platen 38, and operates the retrieval servomotor 92 in step 194 to remove the cut sheet from the press and to withdraw bar 94 leftwardly.

In the next sequence best shown in Fig. 3, the platen 38 moves to its full opened position and, by virtue of continued downward movement of the arms 58, 68, the gripped sheet is positioned closely adjacent the stops 140. At this point, the PLC deactivates the front vacuum bar unit 64 in step 196 and causes a burst of positive pressure air through the exhaust nozzles, thereby freeing the sheet and allowing it to lay on the platen 38 against the stops 140. Continued rotation of the drive wheels 128 then serve to initiate closing of the die platen 38 (now loaded with a fresh sheet to be die cut) which begins elevation of the arms 58, 68 and their associated structures until the die platen 38 moves into coacting relationship with die 124 mounted on head 36.

During this time, the feeder PLC deactivates the vacuum bar 94 in step 198 so that the previously cut, gripped sheet is dropped and received on the stack of cut sheets in conveyor 103. The jogger motor 104 is operated during this time (step 200) to align the cut sheet with the other sheets in the stack.

The feeder PLC is also coupled with sensors (not shown) that monitor the height of the stack on elevators 103 to automatically position the elevators and sensors that detect misfeeds and faults. When the elevator 103 is essentially full, the curtain support apparatus 106 is activated through motor 114. This serves to shift the chains 108 so as to position the transverse rotatable support rods above the elevator 103. The stack of cut sheets on the elevator 103 can then be removed while the support rods receive cut sheets during continued operation of the assembly 20. Motor 114 is then activated, causing the support rods to pass beneath and clear the short stack of cut sheets generated during unloading of the elevator 103, until the support rods return to a non-interfering home position. In this fashion, die cut sheets can be continually removed from the assembly 20 without the need for slowing operation thereof.

PRESS CONTROL While the feeder PLC performs the steps described above, the press PLC simultaneously controls the operation of the press so that the sheet feeder 22 and press 24 are synchronized with one another. The press PLC is programmed to control every function of the press including its speed, stop and start positions, and dwell time. The press software also allows the press to be stopped or dwelled, restarted, and then quickly and automatically re-calibrated. This compensates for errors in the position of the press caused by factors such as clutch slippage and coasting of the press after the clutch has been disengaged.

The press-positioning portion of the software is best understood with reference to the flow diagrams in Fig. 22 A and 22B. The software begins at step 202 where it prompts the operator to enter an "open position value" that corresponds to the count of the encoder 130 when the press is in its fully opened position. For example, the encoder preferably includes 1300 counts for each rotation of the primary geared drive wheel 128 of the press. If an encoder count of 600 corresponds to the fully opened position of the press, the operator enters 600 in step 202. The program then stores 600 as the "open position value" in a memory register residing in or coupled with the PLC.

Step 204 then prompts the operator to enter a "closed position value" that corresponds to the count of the encoder when the press is in its fully closed position. For example, if an encoder count of 1200 corresponds to the fully closed position of the press, the operator enters 1200 in step 204. The program then stores 1200 as the "closed position value" in a memory register residing in or coupled with the PLC.

The program next moves to step 206 where it directs the press PLC to send an output signal to the air valves controlling the press clutch 126. In response, the air valves engage the clutch so that the press drive wheels 128 are rotated. Up to this point, the press was either completely stopped or was in a dwell condition but now begins to move.

In step 208, the press PLC verifies that the press is in fact operating by checking the status of the home sensor 131. The home sensor is coupled with the primary drive wheels 128 of the press and is tripped when the press begins to move. Step 208 asks whether the home sensor has been tripped. If the answer is yes, the program proceeds to step 210. However, if the answer is no, the program returns to step 208 and continues to loop until the home sensor 131 has been tripped. The press PLC then resets the encoder counter in step 210 to zero once the home sensor 131 has been tripped and then reads the encoder counter in step 212 to determine the actual position of the press. The program next moves to step 214 which attempts to stop the press in its fully opened position. Specifically, step 214 asks whether the encoder counter value read in step 212 equals the open position value entered in step 202 above. If the answer is no, the program loops back to step 212 until it does. However, if the answer is yes, the PLC sends an output signal to the clutch air valves in step 216 to direct the clutch to disengage the press drive wheels. At this point, the press coasts or is braked to a stop at or near its fully opened position.

The press PLC once again reads the encoder counter in step 218 to determine the actual position of the press. The program then moves to step 220 where it asks whether the encoder count read in step 218 equals the known encoder count correspond- ing to the fully opened position for the press (600 using the example above). If the answer is yes, this indicates that the press stopped at the desired opening position. The program then proceeds to step 222 where the PLC directs the press to dwell for a predetermined amount of time.

However, if the encoder count read in step 218 does not equal the known encoder count corresponding to the fully opened position, this indicates that the press is not in its proper open position and is therefore out of calibration. Since the press continues to coast after the clutch disengages the press drive wheel in step 216, this is usually the case during the first few cycles of the press because the actual position of the press is typically beyond the fully opened position. The program then moves to step 224 which subtracts the open position value entered in step 202 from the encoder count read in step 218 to determine the error.

Step 226 then adds or subtracts the error from the open position value depending upon whether the press stopped short or advanced beyond the fully opened position. For example, if the press stopped short of the fully opened position so that it is in a position corresponding to an encoder count of 590, step 224 arrives at an error of +10 steps. Step 2-24 then adds this error to the open position value and stores this new open position value in the register described in step 202. However, if the press advanced beyond the fully opened position so that it is in a position corresponding to an encoder count of 610, step 224 arrives at an error of -10 steps. Step 226 then subtracts this error from the open position value and stores this new open position value in the register described in step 202. This new open position value is used during the next press cycle to stop the press in steps 214 and 216. These steps are repeated during each cycle of the press until the press opens in the desired position.

Thus, steps 218, 220, 224 and 226 of the program automatically correct for any errors in the opening position of the press by reading the encoder when the PLC first attempts to stop the press in its opened position, calculating the error between the desired opened position and the actual opened position, and then compensating for this error by adjusting the activation of the clutch during the next cycle of the press. This positioning and calibration sequence typically achieves an actual opened position that is within one encoder count of the desired opened position within two cycles of the press.

Once the dwell period for the press expires, the program moves to step 228 which once again directs the press PLC to send an output signal to the clutch air valves to direct the clutch to engage the press drive wheels so that the press once again begins to move. The press PLC then reads the encoder counter in step 230 to once again determine the actual position of the press.

The press PLC then attempts to stop the press in its fully closed position in step 232. Specifically, step 232 asks whether the encoder counter value read in step 230 equals the closed position value entered and stored in step 204. If the answer is no, the program loops back to step 230 until it does. However, if the answer is yes, step 234 directs the press PLC to send an output signal to the clutch air valves to direct the clutch to disengage the press drive wheels. At this point, the press coasts or is braked to a stop at or near its fully closed position.

The press PLC then once again reads the encoder counter in step 236 to determine the actual position of the press. The program then moves to step 238 where it asks whether the encoder count read in step 236 equals the known encoder count corresponding to the fully closed position for the press ( 1200 using the example above) . If the answer is yes, this indicates that the press has stopped in its desired position. The program then proceeds to step 240 where the PLC directs the press to dwell for a pre- determined amount of time.

However, if the encoder count read in step 230 does not equal the known encoder count corresponding to the fully closed position, this indicates that the press is not in its proper position and is therefore out of calibration. Since the press continues to coast after the clutch disengages the press drive wheel in step 234, this is usually the case during the first few cycles of the press because the actual position of the press is typically beyond the fully closed position. The program therefore moves to step 242 which subtracts the closed position value from the encoder count read in step 236 to determine the error.

Step 244 then adds or subtracts the error from the closed position value depending upon whether the press stopped short or advanced beyond the fully closed position. For example, if the press stopped short of the fully closed position so that it is in a position corresponding to an encoder count of 1190, step 242 arrives at an error of +10 steps. Step 244 then adds this error to the closed position value and stores this new closed position value in the register described in step 204. However, if the press advanced beyond the fully closed position so that it is in a position corresponding to an encoder count of 1210, step 240 arrives at an error of - 10 steps. Step 242 then subtracts this error from the closed position value and stores this new closed position value in the register described in step 204. This new closed position value is then used during the next press cycle to stop the press in steps 232 and 234. These steps are repeated during each cycle of the press until the press closes in the desired position.

Thus, the program automatically corrects for any errors in the closing position of the press by reading the encoder when the PLC first attempts to stop the press in its closed position, calculating the error between the desired closed position and the actual closed position, and then compensating for this error by adjusting the activation of the clutch during the next cycle of the press. This positioning and calibration sequence typically achieves an actual closed position that is within one encoder count of the desired closed position within two cycles of the press.

Once the dwell period for the press expires, the program then moves to step 246 which repeats the described press cycle.

Second Embodiment-Figs. 9-21

Turning next to Figs. 9-19, a die cutting assembly 200a is depicted which includes an automated sheet feeder 220a and an operably coupled downstream clamshell-type press 240a. The feeder 220a includes a pair of spaced side frames 250 along with input elevator unit 260 adapted to hold a stack of sheets to be die cut, a pickup and conveying assembly 280 (see Fig. 12) designed to sequentially pick up sheets from elevator unit 260 and convey the sheets rightwardly as viewed in Fig. 9, a shiftable extension arm assembly 300 for sequentially receiving sheets from assembly 280 and delivering these to press 240a, a shiftable die cut sheet retrieval device 320 for removing cut sheets from the press 240a, and an output collector/elevator unit 340. The press 240a includes a large stationary die-carrying head 360 and a shiftable platen 380 operatively coupled with head 360. Finally, a PLC-based control assembly 370 forms a part of the assembly 200a.

The elevator unit 260 is conventional and includes primary and secondary sections controlled by motor and drives 400, 420, respectively. The two-stage elevator unit 260 is designed to continuously supply sheets for processing, even during restocking of the primary section thereof.

The sheet pickup and conveyor assembly 280 (Fig. 12) includes an elongated, laterally extending vacuum bar 440 having a motor and drive 460 operatively coupled thereto. The vacuum bar 440 has a plurality of laterally spaced apart suction cups 470 and is shiftable downwardly to grip the leading edge of a sheet to be processed, and for elevating the gripped sheet and moving it leftwardly as viewed in Fig. 12. The overall assembly 280 further includes a plurality of elongated, laterally spaced apart, endless conveyor belts 480 mounted on rollers 482, 484 powered by motor 500 via drive chain 502 (Fig.9). A nip roller 520 is positioned adjacent the righthand end of conveyor belts

480 above roller 482 and is selectively pivotal toward and away from the belts 480 by means of a pair of piston and cylinder assemblies 540 and intermediate crank mechanisms 560.

The extension arm assembly 300 broadly includes apair of elongated, outermost main arms 580, a pair of inboard secondary arms 600 and a registration table 620. The arms 580, 600 and table 620 are each pivotally supported on the side frames 250.

Each of the main arms 580 includes an elongated rail 640 pivotally secured to a corresponding side frame 250 via coupler 660, with the inner surface of each rail 640 presenting an elongated track 680. An upstanding track member 700 is affixed to each rail640 and presents an elongated track slot 720 therethrough. The outboard face of each rail 640 is equipped with an elongated bearing rail 740 which supports a bearing block 760 for fore and aft movement along rail 740. Each block 760 carries a gusseted, upstanding support 780, the latter receiving an elongated bearing rail 800. Each bearing rail 800 is slidably received by a bearing block 820, the latter being pivotally connected to a fixture assembly 840 as best seen in Fig. 10. Each block 760 and associated structure is shiftable along the length of the associated rail 640 by means of a driven timing belt 860 supported on fore and aft pulleys 880, 900. The aft pulleys 880 are mounted on cross shaft 920, the latter being driven by stepper motor 940 and drive assembly 960. The forward pulleys are mounted on the ends of the rails 640 as shown. A pair of gripping plates 980, 1000 respectively coupled to support 780 and bearing block 760 cooperatively grip the adjacent belt 860 so that, upon actuation of stepper motor 940, the belt 860 is moved, thereby moving bearing block 760 and its associated structure along the bearing track 74.

A shiftable front vacuum bar unit 1020 extends laterally between the track members 700 and is operatively coupled with the fixture assemblies 840. As best seen in Fig. 16, each of the assemblies 840 includes a pair of plates 1040 on opposite sides of the associate track member 700 which support two cam followers 1060; the latter are located within slot 720, for travel therealong. A somewhat U-shaped connector 1080 is coupled between each of the ends of the vacuum bar 1020 and the adjacent inboard plate 1040 so as to accommodate movement of the pitman arms of press 240a.

The main arms 580 are powered for up and down pivotal movement thereof through the medium of an elongated, transversely extending bar 1100 which is affixed to the uppermost end of shiftable platen 380. The ends of bar 1100 are equipped with rollers 1120 which are respectively received within the inboard track 680 of each arm 580. Thus, as the platen 380 pivots during operation of press 240a, motion is transmitted to the arms 580 for corresponding up and down pivotal movement thereof.

The secondary arms 600 are each pivoted to side frame 520 and extend generally along the length of the associated arms 580. Each of the arms 600 carries a spring block

1140 supporting a roller 1160; each roller 1160 rides upon the upper surface of a corresponding main arm 580. The forward end of each of the arms 600 carries a pulley

1180, and a support roller 1200 is located midway between the ends of each arm 600 (Fig. 15).

The registration table 620 is in the form of a substantially planar, laterally extending member pivotally supported on roller 484. A pair of generally wedge-shaped followers 1220 are affixed to the underside of the sides of table 620 and ride upon the rollers 1200. As best seen in Fig. 11, the plate 620 is equipped with a registration unit 1228 including apair of elongated slots 1230 each receiving a corresponding, elongated vacuum bar segments 1232, 1234. As shown, each of the bar segments 1232, 1234, is slightly shorter in length than the associated opening 1230 thereby permitting lateral movement of the bar segments 1232, 1234. Each of the segments has a series of vacuum apertures 1240 therein which are operatively coupled with a vacuum source (not shown). Also, the bar segments 1232, 1234 are mounted to a selectively operable motive unit such as an air cylinder to effect lateral movement thereof; one or more sensors (not shown) are provided in the table 620 to sense the margin of sheets fed to the table, and the controller for the feeder actuates the registration unit to laterally adjust the sheets as needed.

The retrieval device 320 includes a retrieval vacuum bar unit 1260 which is shiftable fore and aft on a track assembly 1280 and is driven by belt drive 1300. The unit 1260 includes an elongated, transversely extending sucker or vacuum bar 1320 having trailing extension plates 1340 interconnected via cross shaft 1342, each plate 1340 supporting a multiple-roller track follower 1360 (Fig. 19). The track assembly 1280 comprises a pair of elongated metallic tracks 1380 respectively secured to each side frame 250 through the medium of inwardly projecting intermediate angles 1400 (Fig. 18). As illustrated in Fig. 14, however, the forward end of each track 1380 is free of the supporting angle 1400 and is secured to connectors 1420 affixed to the underside of each arm 600. Thus, the forward ends of the tracks are flexible and move up and down with the main arms 580 and secondary arms 600 as will be described.

The belt drive 1300 includes a cross shaft 1440 extending between the side frames 250 and supporting a pair of pulleys 1460. The shaft 1440 is powered for rotation by motor unit 1480. In addition, the drive 1300 includes a pair of drive belts 1500 respectively trained around the rearmost pulleys 1460 and the pulleys 1180 previously described. In order to facilitate movement of the belts 1500, a tensioning pulley 1520 is affixed to each side frame as best seen in Fig. 12. Upper and lower guide pulleys 1520, 1540 are likewise mounted to the ends of roller 484 and side frame 250 respectively for guiding the movement of the upper and lower stretches of each belt 1500. Finally, a pair of idler pulleys 1560 are mounted to side frames 250 as best seen in Fig. 15. As illustrated in Fig. 19, each of the belts 1500 is gripped by the corresponding track follower 1360 affixed to each plate 1340, so that upon movement of the belts 1500, the retrieval vacuum bar 1320 is shifted.

The output collection/elevator unit 340 is designed to collect and stack, on a continuous basis, completed die cut sheets. The unit 340 has a stationary front plate 1580 and a rearward jog plate 1600 above a vertically movable elevator plate 1620 (powered by output elevator motor 1680). A conventional cam-type actuator 1640 is used to jog the plate 1600 and impart movement to the side plates 1660. The purpose of the jog assembly is to even up a stack of output sheets processed in the die cutting assembly 200a. Finally, the unit 340 has a translatable roller-type curtain 1700 which is selectively shiftable to a horizontal, temporary hold position illustrated in Fig. 12 in order to receive processed sheets while the elevator 1620 is unloaded. The motion of curtain 1700 is controlled by output curtain motor 1720 and conventional drive 1740. The die press 240a is adjustably mounted on upstanding legs 1760 permitting the entire press 240a to be moved up or down to a limited extent. The legs 1760 thus support stationary head 360 as well as shiftable die platen 380, the latter including a stationary base 1780. In detail, the head 360 is a heavy, massive unit presenting a flat die-supporting face 1800 which holds cutting die 1820. The head 360 also has a selectively operable air clutch 1840, operated by conventional piston and cylinder assemblies, rotatable, geared drive wheels 1860, gear encoder 1880 operatively connected to the latter, and a home position sensor (not shown) for resetting of encoder 1880 during operation of the press. A Magnatek motor 1900 is drivingly connected to a main drive wheel 1920 for the press as shown. A pair of pitman arms 1940 are pivotally connected to the drive wheels 1920 to form an eccentric drive for the shiftable platen 380.

Die platen 380 includes a front plate face 1960 provided with front and side sheet stops similar to those described in connection with the first embodiment. The platen face 1960 is designed to coact with cutting die 1820 mounted on face 1800 of head 360. The platen 380 also has a rearward, conventional drive section 1980 of the type described in the first embodiment.

Although not shown in detail, those skilled in the art will appreciate that the assembly 200a is provided with the usual utilities in the form of electric power and pneumatics, the latter including a vacuum pump (not shown) as well as selectively operable valves associated with pickup vacuum bar 440, cylinders 540, front vacuum bar unit 1020 and retrieval vacuum bar 1320.

OPERATION AND SOFTWARE CONTROL The sheet feeder 220a and die press 240a are both fully automated and electronically controlled. This permits an operator to quickly and easily select and adjust the feeder 220a and press 240a operating parameters such as the operating speed, sheet characteristics, press closing position, and dwell time "on-the-fly" with a minimum amount of make-ready time. As illustrated in Fig.20, the feeder 220a is controlled by a programmable logic controller (PLC) or other control device that receives input signals from the press PLC and Magnatek main drive motor 1900 and provides output signals to the secondary elevator motor 420, primary elevator motor 400, output elevator motor 1680, output curtain motor 1720, feeder conveyor motor 500, pickup bar motor 460, input servomotor 940, pickup head vacuum bar 440, retrieval servomotor 1480, retrieval vacuum bar unit 1260, nip roll cylinder 540, and front vacuum bar unit 1020. Similarly, the press is controlled by a PLC or other control device that receives input signals from the press gear position encoder 1880 and the home sensor and provides output signals to the sheet feeder PLC as well as the press Magnatek main drive motor 1900 and air clutch 1840. The PLCs are linked together by a communication link to synchronize the operation and timing of the sheet feeder 220a and die press 240 as described below.

FEEDER CONTROL The feeder PLC is programmed to control every function of the sheet feeder 220a and to keep the feeder in perfect synchronization with the die press 240a even after the feeder or press has been stopped as described in more detail below. The feeder PLC software is similar to that described with reference to the first embodiment, and is further understood from a consideration of the flow diagram of Fig. 21.

In the ensuing discussion, it is assumed that the assembly 200a is in the Fig. 9 position, with die platen 380 having moved into coacting relationship with head 360 so as to normally die cut a sheet within the press 240a with little or no dwell or heating time. The motors 400, 420, 460, 500, 1480, 1720 and 1680 are in an idle mode whereas motor 1900 continues to operate with clutch 1840 engaging wheel 1920. The pneumatic systems associated with the assembly 200a are also idled. The sheet feeder operation begins at step 2000 when an operator activates the feeder PLC by operating an activation button or other input device on or interfaced with the feeder PLC. The feeder software then synchronizes the timing or positioning of the feeder 220a with the press 240a by directing the feeder PLC to send a signal to the press PLC to "home" the press in step 2020. In response, the press PLC directs the Magnatek drive to run the press 240a for one cycle and position the press in its fully opened position as illustrated in Fig. 15. Similarly, step 2040 directs the feeder PLC to "home" the sheet feeder 220a.

The operator then activates a start button or other input device on or interfaced with the feeder PLC to begin the operation of both the feeder and the press in step 2060. In response, step 2080 directs the press PLC to operate the press Magnatek main drive motor 1900.

The program next directs the feeder PLC to read the speed of the Magnatek in step 2100 to determine the speed of the press. To synchronize the speed of the feeder 220a with the press 240a, the feeder PLC determines the speed at which its pickup and retrieval motors 460, 1480 must operate. It does this by retrieving these corresponding speed values from a look-up table and storing the values in a memory register as depicted in step 2120.

The PLC also includes controls that permit the operator to increase or decrease the speed of the feeder 220a and press 240a. Since the feeder speed is determined by first measuring the press speed, the feeder and press always operate at the same speed even though they are not mechanically coupled.

The feeder PLC next reads the press encoder 1880 to determine the actual position of the press in step 2140. When the feeder PLC determines that the press is in the appropriate position, it operates the pickup bar motor 460 and creates a vacuum in vacuum bar 440 in steps 2160 and 2180. This causes the bar 440 to descend as necessary and grip the topmost sheet within elevator unit 260. The PLC then directs the nip roll cylinders 540 to lift the nip roll 520 (step 2200) so that the incoming sheet can be placed on the conveyor belt 480. The bar 540 is then moved leftwardly as shown in Fig. 12 to move the gripped sheet onto conveyor belts 480 (step 2220). In steps 2240 and 2260, the feeder PLC directs the nip roll cylinders 540 to lower the nip roll 520 onto the sheet and to turn on the conveyor motor 500, causing movement of the belts 480. The conveyor belts 480 then deliver the sheet leftwardly as viewed in Fig. 12 to registration table 620, and a vacuum is drawn at the vacuum apertures 1240 of the vacuum bars 1232, 1234. In step 2270, the registration unit 1228 is activated as necessary to laterally adjust the gripped sheet for registration purposes.

Next, an input vacuum is drawn through input vacuum bar 1020 (which is in its starting position illustrated in Fig. 12) in step 2280, causing the leading edge of the sheet to rise and become firmly gripped.

In step 2300, the input servomotor 940 is activated to shift the input vacuum bar 1020 along the length of the main arms 580. As a consequence, the vacuum bar unit

1020 traverses the lengths of the track slots 720 so that the leading edge of the gripped sheet is moved leftwardly and downwardly towards the face 1960 of movable platen 380, as shown in Fig. 15.

In the next operation, the gripped sheet is delivered to the press 240a while the previously cut sheet therein is retrieved. This is initiated by the rotating pitman arms

1940 which serve to open the shiftable platen 380 as illustrated in Figs. 13-15. As a consequence of this opening movement, the rollers 1120 ride within the main arm tracks 680 so as to lower the main arms 580 with the gripped sheet toward the now opened die press 240a, and also causes the secondary arms 600 to move by virtue of the engagement of their supporting rollers 1 160 against the upper surfaces of the main arms 580. Such downward movement of the arms 580 causes the trailing margin of the gripped sheet to move leftwardly as seen in Figs. 13 and 14.

During the described press opening sequence, the feeder PLC controls the retrieval motor 1480 in step 2320 to move the retrieval vacuum bar 1320 to a position so that it is ready to remove the previously cut sheet from the opened press 240a. This is accomplished by appropriate movement of the belts 1500 causing the sucker bar 1320 to move rightwardly as shown in Fig. 11 along the lengths of the tracks 1380. As described previously, the forward ends of the tracks 1380 are designed to accommodate the downward shifting of the arms 580, 600. When the retrieval vacuum bar 1320 reaches the end of its travel (Fig. 14), the feeder PLC then activates the vacuum system associated with bar 130 in step 2340 so that the vacuum bar cups grip the cut sheet on the platen 380. Next, in step 2360, the servomotor 1480 is activated to shift the vacuum bar 1320 so as to withdraw the previously cut sheet from platen 380 rightwardly as viewed in Fig. 15 for ultimate placement within collector/elevator unit 340, whereupon the vacuum bar 1320 is returned to its ready position illustrated in Fig. 13.

In the next sequence best shown in Fig. 15, the platen 380 moves to its full opened position and, by virtue of continued downward movement of the arms 580, 600, the incoming gripped sheet is positioned closely adjacent the platen stops. At this point, the PLC deactivates the front vacuum bar unit 1020 (step 2400) and causes a burst of positive pressure air to be directed through the bar thereby freeing the sheet and allowing it to lay on the platen 380 against the stops. Continued rotation of the drive wheel 1920 then serves to initiate closing of the die platen 380 (now loaded with a fresh sheet to be die cut) which begins elevation of the arms 580, 600 and their associated structures until the die platen 380 moves into coacting relationship with die 240a mounted on head 360.

During this time, the feeder PLC deactivates servomotor 940 to return it to its zero or home position (step 2420) and the vacuum to retrieval vacuum bar 1320 is terminated (step 2440). In step 2460, the previously cut, gripped sheet is dropped and received on the stack of cut sheets in collector/elevator unit 340, and the jog plate 1600 is actuated to align the cut sheet with the other sheets in the stack.

The feeder PLC is also coupled with sensors (not shown) that monitor the height of the stack on elevator 340 to automatically position the elevator, and additional sensors that detect misfeeds and faults. When the elevator 340 is essentially full, the curtain 1700 is activated through motor 1720. This serves to shift the curtain 1700 so as to position it above the elevator 340. The stack of cut sheets on the elevator 340 can then be removed while the curtain 1700 receives cut sheets during continued operation of the assembly 200a. Motor 1720 is again activated, causing the curtain 1700 to pass beneath and clear the short stack of cut sheets generated during unloading of the elevator 340, until the curtain returns to a non-interfering home position. In this fashion, die cut sheets can be continually removed from the assembly 200a without the need for slowing operation thereof.

PRESS CONTROL The press PLC of the second embodiment is controlled via the same software and logic control described in detail in connection with the first embodiment.

Therefore, attention is directed to this discussion, with the understanding that different reference numerals have been used for the press encoder and other components in the second embodiment, and that appropriate correction of that discussion is required when applied to the second embodiment. The controllers of the embodiments discussed herein make use of a pair of

PLCs. Those skilled in the art will appreciate that, in alternate forms, use can be made of a single PLC or other types of motion-controlling devices.

As used herein, "die press" and "cutting die" and similar terms should be understood in a broad sense to embrace traditional cutting dies as well as all other types of sheet processing which may be carried out in presses such as embossing or other forming operations.

Claims

Claims:

1. A sheet feeder adapted for feeding sheets to a clamshell-type die press for processing thereof, and for retrieving processed sheets from the press, said die press including a fixed platen and a shiftable platen movable between a closed position adjacent the fixed platen and an open position, said sheet feeder comprising: an input assembly for gripping a sheet to be processed, moving the sheet toward the shiftable platen and depositing the sheet to be processed onto the shiftable platen when the latter is in said open position; a retrieval unit for gripping a processed sheet on said shiftable platen and moving the processed sheet away from the shiftable platen; and a control operably coupled with said input assembly and said retrieval unit for operation thereof so that said sheet to be processed is moved toward the shiftable platen during at least a portion of the time that the processed sheet is moved away from the shiftable platen.

2. The sheet feeder of claim 1, said input assembly comprising a pair of pivotally movable main arms, an input vacuum gripper carried by said main arms and shiftable along the length thereof.

3. The sheet feeder of claim 2, said retrieval assembly comprising a movable retrieval vacuum gripper disposed generally below said input vacuum gripper.

4. The sheet feeder of claim 2, each of said arms including an upstanding plate having a track formed therein, said input vacuum gripper extending between said plates, there being fixtures operatively coupled to the opposed ends of said input vacuum gripper and riding in said plate tracks for guiding the movement of the input vacuum gripper.

5. The sheet feeder of claim 1, said retrieval assembly comprising a movable retrieval vacuum gripper.

6. The sheet feeder of claim 1 , including an input elevator unit for holding a stack of sheets to be processed, said input assembly operable for successively gripping sheets from said stack and individually moving gripped sheets towards said shiftable platen.

7. The sheet feeder of claim 1 , including an output elevator unit for holding a stack of processed sheets, said retrieval unit including structure for successively delivering processed sheets to said output elevator, and for depositing said processed sheets onto said output elevator.

8. A method of feeding sheets to a clamshell-type die press for processing thereof, and for retrieving processed sheets from the press, said die press including a fixed platen and a shiftable platen movable between a closed position adjacent the fixed platen and an open position, said method feeder comprising the steps of: gripping a sheet to be processed, moving the sheet toward the shiftable platen and depositing the sheet to be processed onto the shiftable platen when the latter is in said open position; gripping a processed sheet on said shiftable platen and moving the processed sheet away from the shiftable platen; and operating said input assembly and said retrieval unit so that said sheet to be processed is moved toward the shiftable platen during at least a portion of the time that the processed sheet is moved away from the shiftable platen.

9. The method of claim 8, including the steps of moving said sheet to be processed along a path of travel above said processed sheet, and moving the processed sheet from the shiftable platen prior to deposition of the sheet to be processed on the shiftable platen.

10. The method of claim 8, each of said gripping unit steps comprising the steps of providing a vacuum-operated gripping device, and creating vacuum conditions therein.

11. A cutting die assembly comprising: a clamshell -type die press for processing of sheets including a fixed platen and a shiftable platen movable between a closed position adjacent the fixed platen and an open position; a sheet feeder operably coupled with said press for feeding sheets to the press for processing thereof, and for retrieving processed sheets from the press, said sheet feeder including-- an input assembly for gripping a sheet to be processed, moving the sheet toward the shiftable platen and depositing the sheet to be processed onto the shiftable platen when the latter is in said open position; a retrieval unit for gripping a processed sheet on said shiftable platen and moving the processed sheet away from the shiftable platen; and a control operably coupled with said input assembly and said retrieval unit for operation thereof so that said sheet to be processed is moved toward the shiftable platen during at least a portion of the time that the processed sheet is moved away from the shiftable platen.

12. The press of claim 11 , said input assembly comprising a pair of pivotally movable main arms, an input vacuum gripper carried by said main arms and shiftable along the length thereof.

13. The press of claim 12, said retrieval assembly comprising a movable retrieval vacuum gripper disposed generally below said input vacuum gripper.

14. The press of claim 12, each of said arms including an upstanding plate having a track formed therein, said input vacuum gripper extending between said plates, there being fixtures operatively coupled to the opposed ends of said input vacuum gripper and riding in said plate tracks for guiding the movement of the input vacuum gripper.

15. The press of claim 11, said retrieval assembly comprising a movable retrieval vacuum gripper.

16. The press of claim 11, including an input elevator unit for holding a stack of sheets to be processed, said input assembly operable for successively gripping sheets from said stack and individually moving gripped sheets towards said shiftable platen.

17. The press of claim 11, including an output elevator unit for holding a stack of processed sheets, said retrieval unit including structure for successively delivering processed sheets to said output elevator, and for depositing said processed sheets onto said output elevator.