PAPER SET FEEDING

Abstract: A sheet set feeder (10) receives a stack of offset-jogged sheet sets (20). The feeder (10) separates individual sets from the stack (20) and provides them to a sheet set processor (512).

Description: PAPER SET FEEDING Background of the Invention The invention relates to feeding offset-jogged sets of sheets. Many devices for printing and/or processing sheets of paper, such as laser or other electronic printers, offset printers, photocopiers, and collating equipment, can be operated to produce plural "sheet sets," e.g., where each set of sheets is one copy of a multiple-page document. Successive sheet sets in the "stack" of sets are typically "offset-jogged" or "offset-stacked" with respect to one another. That is, each individual set is shifted or offset — either laterally, longitudinally, or radially — with respect to the immediately adjacent set or sets. After being printed and/or collated, individual sheet sets are often processed, such as by covering, trimming, folding, stitching, or otherwise binding them. Such processing can occur either "on-line" or "off-line." In on-line processing, individual sheet sets are removed and transported to the processor as they are outputted from the printer or collator. In off-line processing, the entire stack of sheet sets is transferred to the processor or processors after printing or collating is complete. The processor then identifies and processes individual sheet sets. Because processing equipment typically has a higher "throughput rate" (i.e., sheets per unit time) than printers or collators, the outputs of several printers and/or collators may be fed to a single processing unit. Summary of the Invention In one aspect of the invention, a shutter mechanism disposed beneath a hopper for a stack of offset-jogged sheet sets defines an aperture sized to admit individual sets from the stack. The shutter mechanism is driven so that the aperture moves from beneath one end of the bottommost sheet set — where a retainer supports the next-to-bottommost sheet set — to beneath the other end of the bottommost set. Another aspect of the invention is a method for feeding individual sets from a stack of offset-jogged sheet sets in a hopper. A shutter beneath the hopper is moved so that an aperture defined by the shutter moves from beneath one end of the bottommost sheet set to beneath the other end of the set. Among other advantages, the invention — which can be linked to the outputs of existing printing, copying, and/or collating equipment that produces offset-jogged sets — can be used to separate an individual sheet set as a whole from a stack of such sets for further processing, such as covering, trimming, or binding. Because it manipulates entire sheet sets, the invention can process a greater number of sheets per unit time than a device cycling at the same speed that manipulates every sheet within each set. Conversely, the invention can achieve the same overall sheet throughput rate as such a single-sheet manipulator while operating at lower cyclical speeds, thus reducing the likelihood of jamming and both the magnitude and rate of wear. The invention achieves these advantages by capitalizing on the offset-jogged nature of the stack of sheet sets. It is thus not necessary to, e.g., mark individual sheet sets, such as with bar codes or other optically readable markings that might remain on the final document and detract from its overall appearance. Nor is it necessary to, e.g., reformat or modify in any way the output from the printer or collator, such as by segregating individual sheet sets with physical markers, such as slip sheets or chip boards interleaved between adjacent sets. Because such markers need not be added to the stack as the sets are generated or separated out from the individual, separated sheet sets prior to processing, the overall complexity of the set-separating operation is reduced. Moreover, the invention can be used to separate sheet sets automatically, reducing or eliminating entirely the amount of human operator involvement necessary to process stacks of sets. Preferred embodiments of the invention include the following features. In a particularly useful embodiment, a sheet set conveyor (e.g., a rotator or a conveyor belt) is disposed beneath the aperture, and a door is disposed between the conveyor and the aperture. The door serves as a buffer to hold an individual sheet set after it passes through the aperture, and opens quickly to drop the set onto the conveyor below. The shutter defining the aperture includes a series of rollers extending, e.g., between flexible drive members such as link chains or the sides of a rigid planar frame. A sheet of urethane on a tensioning bar biased towards the rollers contacts at least some of the rollers, causing the rollers to spin as the aperture is moved with respect to the hopper by, e.g., a reversible motor or a linear actuator. Like the retainer supporting the next-to- bottommost sheet set, another retainer supports the bottommost sheet set. The retainers comprise shelves that extend from opposed sides of the hopper a distance approximately equal to the distance between the offset- jogged ends of the bottommost and next-to-bottommost sheet sets. The shelves are pivotally (or alternatively, slidably) mounted to the feeder housing, and include sheets of urethane located to contact the next-to- bottommost and bottommost sheet sets. The separation of adjacent sheet sets in the hopper is facilitated by wedges at the edges of the aperture, as well as by air jet passages in either the shelves or the wedges that provide timed air jet blasts. In another useful embodiment, the retainer for supporting the next-to-bottommost set comprises a portion of the shutter disposed adjacent the aperture. The aperture is defined by opposed edges of two shutter portions that can be moved with respect to one another. In another aspect of the invention, a sheet set processing system includes an offset-jogged sheet set feeder, a sheet set processor, and a mechanical conveyor that conveys sets from the feeder to the processor. Among other advantages in addition to those identified above, the processing system can be used to automatically separate and process individual sheet sets from a stack of such sets loaded into the feeder. In a particularly useful embodiment, the system includes a cover feeder, and the sheet set processor comprises one or more of the following: a stitcher, a folder, a face trimmer, a perfect binder, a mailing/inserting system, a shrink wrapper, or a collator. Other advantages and features will become apparent from the following description of the preferred embodiments and from the claims. Brief Description of the Drawings FIG. 1 is a cross-sectional side view of a sheet set feeder. FIG. 2 is a cross-sectional side view of the sheet set feeder shown in FIG. 1, with a stack of sheet sets placed into the feeder. FIG. 3 is a top view of the sheet set feeder shown in FIG. 1. FIGS. 4A, 4B, and 4C are cross-sectional side views of a mechanism for actuating a shelf of the sheet set feeder shown in FIG. 1. FIG. 5 is a cross-sectional side view of another sheet set feeder. FIG. 6 is a cross-sectional side view of the sheet set feeder shown in FIG. 5, with a stack of sheet sets placed into the feeder. FIG. 7 is a top view of the sheet set feeder shown in FIG. 5. FIGS. 8A, 8B, 8C, and 8D are schematic side views showing the sheet set feeder shown in FIG. 1 in operation. FIG. 9 is a perspective view of the sheet set feeder shown in FIG. 1 mated to a cover feeder. FIG. 10 is a perspective view of the sheet set feeder/cover feeder assembly shown in FIG. 9 mated to a stitcher/folder and a face trimmer. FIG. 11 is a perspective view of the sheet set feeder/cover feeder assembly shown in FIG. 9 mated to a perfect binder. FIG. 12 is a perspective view of two of the sheet set feeder/cover feeder assemblies shown in FIG. 9 mated in tandem to a mailing/inserting system. FIG. 13 is a perspective view of the sheet set feeder/cover feeder assembly shown in FIG. 9 mated to a shrink wrapper. FIG. 14 is a perspective view of the sheet set feeder/cover feeder assembly shown in FIG. 9 mated to a collator and finisher. FIG. 15 is a perspective view of the sheet set feeder/cover feeder assembly shown in FIG. 9 mated to a collator, a stitcher/folder, and a face trimmer. FIG. 16 is a perspective view of two of the sheet set feeder/cover feeder assemblies shown in FIG. 9 mated in tandem to a finisher. FIG. 17 is a perspective view of the sheet set feeder/cover feeder assembly shown in FIG. 9 with a rotator for rotating sheet sets. FIG. 18 is a side view of the rotator of the assembly shown in FIG. 17. FIG. 19 is a top view of the rotator of the assembly shown in FIG. 17. FIG. 20 is a cross-sectional side view of another sheet set feeder. FIG. 21 is a cross-sectional side view of the sheet set feeder shown in FIG. 20, with a stack of sheet sets placed into the feeder. FIG. 22 is a top view of the sheet set feeder shown in FIG. 20. FIG. 23 is a cross-sectional side view of a mechanism for actuating a shelf of the sheet set feeder shown in FIG. 20. FIGS. 24A, 24B, 24C, and 24D are schematic side views showing the sheet set feeder shown in FIG. 20 in operation. FIGS. 25A and 25B are side views of another sheet set feeder. FIGS. 26A, 26B, 26C, and 26D are schematic side views showing the sheet set feeder shown in FIGS. 25A and 25B in operation. FIGS. 27A, 27B, 27C, 27D, and 27E are schematic side views showing another sheet set feeder in operation. FIG. 28 is a side view of a shelf actuation mechanism for a sheet set feeder. FIGS. 29A, 29B, 29C, 29D, 29E, 29F, and 29G are sequential side views showing the shelf actuation mechanism of FIG. 28 in operation. FIG. 30 is a schematic side view of a hopper wall and shelf adjusting mechanism for a sheet set feeder. FIGS. 31 and 32 are perspective and schematic side views, respectively, of a shield mechanism for a sheet set feeder. FIG. 33 is a cross-sectional side view of a sheet set feeder with a stack of sheet sets placed into the feeder. FIGS. 34A is a cross-sectional side view of a gripper for grabbing the topmost set from the stack of sheet sets placed in the feeder shown in FIG. 33. FIGS. 34B is a cross-sectional side view of another gripper for grabbing the topmost set from the stack of sheet sets placed in the feeder shown in FIG. 33. FIG. 35 is a top view of the gripper shown in FIG. 34A. FIG. 36 is a cross sectional side view of the output of the feeder shown in FIG. 33 being fed into an accumulator. FIGS. 37A, 37B, 37C and 37D are schematic side views showing the sheet set feeder shown in FIG. 33 in operation. FIG. 38 is a schematic diagram showing the operation of a dual elevator stacking system. Description of Preferred Embodiments As shown in FIGS. 1, 2, and 3, a sheet set feeder 10 includes a housing 12. Two facing vertical walls of housing 12, left wall 14 and right wall 16, define a hopper 18 for receiving a stack 20 comprised of offset- jogged sheet sets 22a, 22b, 22c, 22d, each of which in turn comprises two or more sheets 24a, 24b, 24c, 24d of, e.g., paper. (Sheet set feeder 10 can also be used to feed offset-jogged sets of other types of substantially planar sheets, such as of film or fabric.) The distance between left wall 14 and right wall 16 of hopper 18 is approximately equal to the length of a single sheet set, plus the distance by which each set is offset-jogged with respect to adjacent sets. Right wall 16 can be moved toward and away from left wall 14 to adjust the dimensions of hopper 18 to accommodate sets of different lengths. A shutter 26 disposed beneath hopper 18 supports stack 20. Shutter 26 comprises a series of support rollers 28 disposed between a pair of link chains 30, 32. Rollers 28 are spaced at regular intervals along chains 30, 32, except for one region intermediate the ends of shutter 26 in which the rollers are separated to define an aperture 34. The top surface of shutter 26 defines a plane P as the top surface of aperture 34. A pair of wedges, left wedge 36 and right wedge 38, are attached, with their pointed ends directed toward one another, to opposite edges of aperture 34. Both the portion of shutter 26 that lies to the left of left wedge 36 and the portion of shutter 26 that lies to the right of right wedge 38 are approximately equal to the distance between left wall 14 and right wall 16 of hopper 18. The width of aperture 34 (i.e., the distance between chains 30, 32) is selected based on the width of sets 22a, 22b, 22c, 22d. The length of aperture 34 (i.e., the distance between the opposed edges of wedges 36, 38) is selected based on, among other things, the thickness of sets 22a, 22b, 22c, 22d, the thickness of the individual sheets of paper 24a, 24b, 24c, 24d in each set, and the width and length dimensions of the sheets. In general, as the thicknesses of the sets and sheets increase, so also should the length of aperture 34. The length of aperture 34 can be adjusted by, e.g., replacing wedges 36, 38 with wedges of different lengths. Alternatively, the length of aperture 34 could be adjusted automatically based on the dimensions of the sets and sheets placed into hopper 18. It has been found that an aperture length of about 4 in. (10.16 cm.) yields acceptable performance when feeding sets of standard 20 pound, 8 x 11 in. (21.6 x 27.9 cm.) sheets of paper, where the sets are between 2 sheets and 1 in. (2.54 cm., about 250 sheets) thick. Shutter 26, and thus also aperture 34, are reciprocatingly shuttled back and forth with respect to hopper 18 by the action of chains 30, 32. Other flexible drive members, such as belts, bands, or cables, could be used instead of chains 30, 32. Chains 30, 32 are continuous-loop chains that mesh with a pair of sprockets 40, 42 rotatably attached to housing 12. (Only those sprockets that mesh with chain 30 are shown. The sprockets that mesh with chain 32 are arranged in an identical fashion.) One of these sprockets, sprocket 40, is driven through a continuous-loop belt 54 by a reversible electric motor 56. Reversing the direction of rotation of motor 56 reverses also the direction of motion of aperture 34 with respect to hopper 18. In addition, the rotational speed of motor 56 may be controlled to vary the linear speed of chains 30, 32 and aperture 34. A door 44 is disposed directly beneath shutter 26, such that the space between door 44 and shutter 26 defines a primary set accumulator 43. Door 44 is comprised of left and right door halves 45, 46. A rack 47, 48 attached beneath each door half 45, 46 mates with a pinion gear 49, 50 driven by a respective motor 51 (only the motor 51 that drives right pinion gear 50 is shown) . Alternatively, a single motor can be used to drive both pinion gears. Motor 51 is a high-speed reversible electric motor, and the gear train is selected so that door halves 45, 46 open quickly when motor 51 is energized. A secondary set accumulator 52 is disposed beneath door 44. Secondary set accumulator 52 can include a conveyor belt 53 for carrying away individual sets 22a, 22b, 22c, 22d as they drop down from primary accumulator 43, and/or a rotator 540 (FIGS. 17, 18, 19) for rotating the individual sets, e.g., by 90°. Sheet set feeder 10 further includes a pair of shelves, left shelf 58 and right shelf 60, pivotally attached to housing 12. When they are horizontal, shelves 58, 60 extend away from walls 14, 16 a distance approximately equal to the distance between the ends of adjacent offset-jogged sheet sets 22a, 22b, 22c, 22d. Thus, left shelf 58 extends far enough into hopper 18 to support the left edge of sheet set 22a, but not far enough to support the left edge of sheet set 22b. Similarly, right shelf 60 extends far enough into hopper 18 to support the right edge of sheet set 22b, but not far enough to support the right edge of sheet set 22a. Sheets of urethane 57, 61 on the top surfaces of left and right shelves 58, 60 prevent the sets 22a, 22b, 22c, 22d from slipping off the shelves as shutter 26 moves back and forth. When aperture 34 shuttles toward and past left wall 14 of hopper 18, left shelf 58 rotates clockwise to the near-vertical orientation shown in FIG. 1. When aperture 34 shuttles back toward right wall 16, left shelf 58 rotates counter-clockwise to its original, horizontal orientation, as shown in FIG. 2. Similarly, when aperture 34 shuttles past right wall 16 of hopper 18, right shelf 58 rotates counter-clockwise to a near- vertical orientation, and rotates clockwise back to its horizontal orientation when aperture 34 shuttles back toward left wall 14. The mechanism 59 for actuating left shelf 58 is shown in detail in FIGS. 4A, 4B, and 4C. The mechanism for actuating right shelf 60 is identical in all material respects to mechanism 59. Left shelf 58 is attached to housing 12 by a pin hinge/torsion spring 98, which allows shelf 58 to rotate, and also biases it in a counterclockwise direction against left wall 14. Cam followers 99, 100 are rotatably attached to either end of left shelf 58 (see also FIG. 3). When left wedge 36 of aperture 34 moves to the left past left wall 14, cam followers 99, 100 engage channels 101, 102 in respective channel box cams 103, 104 located at the sides of aperture 34. Channels 101, 102 are shaped so that, as left wedge 36 continues to move to the left, left shelf 58 rotates clockwise to a near-vertical orientation, as shown in FIG. 4B. At this point, the left edge of channel box cam 103 passes a proximity switch 105, which reverses the direction of rotation of motor 56, and thus also the direction of movement of aperture 34. Channels 101, 102 are shaped so that, as channel box cams 103, 104 move to the right, left shelf 58 rotates counterclockwise back up to its original, horizontal, orientation. The path defined by this portion of channel 101 can be steeper than the portion of channel 101 that causes cam follower 99 to rotate shelf 58 clockwise to the vertical orientation. By making the path steeper in this manner, shelf 58 rotates back up to its horizontal orientation more rapidly than it rotated down to its vertical orientation. In short, because of the path of channel 101, shelf 58 drops relatively slowly as box cam 103 moves to the left (FIG. 4A) , and comes back up relatively rapidly as box cam 103 moves to the right (FIG. 4C) . By "snapping up" in this manner, shelf 58 is more rapidly positioned to support the left end of the next-to-bottommost sheet set, reducing the likelihood that the left end will "droop" down into aperture 34 (i.e., that the left end will cross the plane P of aperture 34, as defined by shutter 26). As shown in FIGS. 1 and 3, sheet set feeder 10 further includes a tensioning bar 70 that extends across hopper 18 between left wall 14 and right wall 16. (For clarity, tensioning bar 70 is not shown in FIG. 2.) Tensioning bar 70 is located between the edge of shutter 26 and the edge of stack 20 (set 22a is shown in phantom in FIG. 3), so as not to interfere with the motion of sets 22a, 22b, 22c, 22d as they pass through aperture 34. Springs 72, 74 are disposed between the ends 76, 78 of tensioning bar 70 and fingers 80, 82 projecting horizontally from the inside surfaces of walls 14, 16, biasing bar 70 downward toward shutter 26. A sheet of urethane 84 on the bottom surface of tensioning bar 70 contacts rollers 28 of shutter 26. Another sheet set feeder 110 is shown in FIGS. 5, 6, and 7. Sheet set feeder 110 is identical in many respects to sheet set feeder 10, except, whereas shelves 58, 60 in feeder 10 pivot, the shelves 112, 114 in feeder 110 retract into the left and right walls 116, 118 of the feeder. As in feeder 10, walls 116, 118, together with a shutter 120, define the hopper 122 of feeder 110, and drive chains 124, 126 move shutter 120 with respect to hopper 122. Shelves 112, 114 are slidably disposed between spaced-apart brackets 130, 132, 134, 136 attached to the housing 138 of feeder 110. A spring 140 attached between bracket 122 and a finger 142 projecting down from shelf 112 biases shelf 112 toward shelf 114, and a spring 144 attached between bracket 136 and a finger 146 projecting down from shelf 114 likewise biases shelf 114 toward shelf 116. Bearings 148, 150, 152, 154 are attached to drive chains 124, 126 near the corners of the aperture 155 in shutter 120. Thus, as shown in FIG. 5, when the left edge of aperture 155 moves past left wall 116, bearings 148, 150 engage the fingers 132 (only one finger 132 shown) projecting down from shelf 112, causing it to slide into left wall 116. Right shelf 114 behaves similarly when the right edge of aperture 155 moves past right wall 116. Shelves 112, 114 are also provided with a number of air passages 160, 162 spaced at regular intervals along the lengths of the shelves. Air passages 160, 162 are angled slightly upwardly, and facilitate sheet separation during operation, as described in detail below. A manifold 164, 166 at the back of each shelf 112, 114 is in communication with all of the air passages in each shelf. A tube 168, 169 connects each manifold 164, 166 to a solenoid valve 170 (only tube 168 is shown connected to valve 170) , which is in turn connected to a source of pressurized gas 172. When solenoid valve 170 is energized, high pressure air is supplied to manifolds 164, 166, causing high-velocity air jets to issue from air passages 160, 162. In operation, stack 20 is placed into hopper 18 of sheet set feeder 10 so that bottommost set 22a rests on rollers 28, as shown in FIG. 8A. (The operation of feeder 110 is similar to that of feeder 10.) The right edge of aperture 34 is initially past right wall 16 of hopper 18, and so left and right shelves 58, 60 are oriented horizontally and vertically, respectively. Motor 56 is then energized to cause aperture 34 to move to the left. When the left wedge 36 of aperture 34 moves past the right edge of bottommost set 22a, gravity causes the end of set 22a to droop through the aperture (i.e., the end crosses plane P) , as shown in FIG. 8B. And when right wedge 38 moves past right wall 16, right shelf 60 rotates clockwise back to its horizontal orientation, thereby preventing the right edge of next-to-bottommost set 22b from drooping through aperture 34 (i.e., from crossing plane P) . Optionally, left and right wedges 36, 38 may each be provided with a manifold and a series of upwardly angled air passages, as in shelves 112, 114 of feeder 110. As shown in FIG. 8B, the passages 180 in right wedge 38 are supplied with air by a line 182 connected to a solenoid valve 184 and a source of pressurized air 186. When right wedge 38 moves to the left past right wall 16, solenoid 184 is activated and jets of air 189 issue from passages 180, further preventing next-to-bottommost set 22b from drooping through aperture 34 and facilitating the separation of set 22a from the bottom of stack 20. As aperture 34 continues to move to the left, left wedge 36 moves into the gap 188 between bottommost set 22a and next-to-bottommost set 22b, peeling off bottommost set 22a as shown in FIG. 8C. Urethane sheet 61 (FIGS. 1 and 2) on the top surface of right shelf 60 prevents set 22b from slipping to the left off shelf 60 as shutter 26 moves to the left. As shown in FIG. 8D, when left wedge 36 of aperture 34 moves past left wall 14 of hopper 18, left shelf 58 rotates clockwise to its vertical orientation, allowing set 22a to fall into primary set accumulator 43. When aperture 34 reaches its leftmost extent of travel, motor 56 reverses direction, causing the aperture to shuttle back towards right wall 16 of hopper 18. Left shelf 58 rotates counterclockwise back to its original, horizontal orientation to support set 22c (which is now the next-to-bottommost set) , and left wedge 36 peels set 22b (which is now the bottommost set) from the bottom of stack 20. While set 22b is being peeled off the bottom of stack 20, door 44 at the bottom of primary set accumulator 43 (FIG. 1) is quickly opened to allow set 22a to fall onto conveyor belt 53. Door 44 and primary accumulator 43 thus act as a buffer between set feeder 10 and conveyor belt 53, serving to synchronize the relatively slow rate at which individual sets are peeled off with the relatively high speed of conveyor belt 53. If primary accumulator 43 is not used, the drooping end of bottommost set 22a might come into contact with moving conveyor belt 53 before the set is completely stripped off stack 20. Should this occur, the relatively quickly moving belt 53 might, e.g., pull individual sheets 24a, 24b, 24c, 24d entirely or partially out of set 22a. If conveyor belt operates relatively slowly, primary accumulator 43 and door 44 may not be needed. When right wedge 38 of aperture 34 moves past right wall 16 of hopper 18, right shelf 60 again rotates to the vertical orientation shown in FIG. 8A, allowing set 22b to fall into primary set accumulator 43. The cycle repeats until all remaining sets 22c, 22d are fed into primary set accumulator 43, and from there onto conveyor belt 53. To provide for smooth motion of reciprocating shutter 26 throughout each cycle, motor 56 is initially controlled so that it ramps up from zero velocity to a constant speed. This speed is maintained until shutter 26 nears its leftmost or rightmost point of travel, at which point the motor speed is ramped back down to zero. The direction of rotation of motor 56 is then reversed, and the velocity profile repeated for the next cycle. When stack 20 consists of a number of sets, the weight of the sets is generally sufficient to cause rollers 28 to roll freely as shutter 26 shuttles back and forth. However, when stack 20 consists of only a few sets, the weight of the sets alone may in some circumstances be insufficient to cause rollers 28 to roll. If so, as it shuttles back and forth shutter 26 may move the entire stack laterally against left and right walls 14, 16, which can "de-jog" the sets (i.e., reduce or eliminate the offset between the ends of adjacent sets) . By pressing against rollers 28 with a constant force (as determined by springs 72, 74), tensioning bar 70 causes the rollers to roll irrespective of the weight of stack 20, preventing or reducing this de-jogging effect. Set feeder 10 thus allows individual sheet sets to be removed from the bottom of an offset-jogged stack of such sets. As shown in FIG. 9, set feeder 10 or 110 may be mated with a cover feeder 190, which typically feeds one or more covers 192 for each sheet set 22a, 22b, 22c, 22d fed by feeder 10. After the cover is placed on the top (and/or bottom) of the sheet set, the complete document 194 may then be sent (using conveyor belt 53, shown in phantom in FIG. 9) for further processing, e.g., by a stitcher/folder 196 (e.g., a Standard Horizon SPF-10 or SPF-20, available from Standard Duplicating Machines Corporation, 10 Connector Road, Andover, MA) and/or a face trimmer 197 (e.g., a Standard Horizon FC-10) , as shown in FIG. 10. Alternatively or additionally, the document may be processed by a perfect binder 198 (FIG. 11, e.g. a Standard Horizon BQ-440) , a mailing/inserting system 199 (FIG. 12, e.g., a Gunther DP 100), and/or a shrink wrapper 200 (FIG. 13, e.g., a Schaffer unit). Each offset-jogged sheet set in the stack placed into the hoppers of sheet set feeders 10, 110 is often a entire document, and each set is fed directly to one or more of the above processors or finishers after it is stripped off the bottom of the stack by the feeder. In some instances, however, particularly in the case of lengthy documents, each set is only a portion of a document, and it is necessary to combine multiple sets or add additional pages to a set to make a complete document prior to processing. For example, as shown in FIG. 14, sheet set feeder 10 is mated to, e.g., a Horizon MC-80 collator 510 and a finisher 512 (finisher 512, shown schematically in FIG. 14, generically represents one or more of the above- described processors) . Each of the individual sets 514 loaded into feeder 10 is only a portion of a document 516. The remaining eight pages of document 516 are loaded into the respective bins 518a-h of collator 510. As set 514 passes through collator 510, a single sheet is drawn from each bin 518a-h and placed onto set 514 in the proper order to complete document 516. The output of collator 510 is then sent to finisher 512 for further processing, such as by stitcher/folder 196 and face trimmer 197 as shown in FIG. 15. An alternative system 520 for combining sheet sets 522, 524 to make a single document 526 is shown in FIG. 16. In this system, two feeders 528, 530, each similar in construction to either feeder 10 or feeder 110, are connected in tandem, and the output of the second feeder 530 is supplied to a finisher 532. A stack 534 comprising sheet sets 522 is placed into feeder 528, and a stack 536 comprising sheet sets 524 is placed into feeder 530. Feeder 528 strips sheet set 522 off the bottom of stack 534 and sends it, via a conveyor 538, to feeder 530. As set 522 passes through feeder 530, set 524 is stripped off the bottom of stack 536 and placed on top of set 522 to complete document 526, which is then finished or processed as desired. In certain processing or finishing equipment, it is preferable that the set to be processed enter the processor "long-edge" first. However, because of the configuration of feeder 10 (as well as of feeder 110) , sets 22a, 22b, 22c, 22d absent some additional manipulation enter the processors "short-edge" first. To reorient the sets to accommodate such processing equipment, feeders 10, 110 can optionally be provided with a rotator 540 that rotates individual sets 542, e.g., by 90°, as shown in FIG. 17. The details of rotator 540 are shown in FIGS. 18 and 19. Rotator 540 includes a platter 544 disposed directly beneath door 44 (FIG. 1) of feeder 10. After a set 542 (shown in phantom) falls onto platter 544, the platter is rotated by a motor 546 and drive belt 548 assembly until set 542 is oriented as desired, as indicated by sensors 550, 552 that sense the rotational position of platter 544. Set 542 is then pushed off platter 544 and onto a main conveyor belt 553 by pusher pins 554, 556 that are driven by a secondary conveyor belt 557 so as to travel along slots 558, 560 in platter 544. Main conveyor belt 553 then, e.g., delivers set 545 to a finisher or processor. The specific implementation set forth above is only one illustration of an embodiment of the invention. Other embodiments are within the claims. For example, because it is flexible, the shutter of the paper set feeder need not run around an oval path as in feeders 10, 110, but can instead circulate through a variety of configurations to conform to packaging or other constraints. Thus, as shown in FIGS. 20, 21, and 22, a paper set feeder 210 can have a flexible shutter 212 (comprising chains 211, 213 driven by a reversible motor 215) that is routed behind the left and right walls 214, 216 of a hopper 218. As with feeders 10 and 110, left and right shelves 220, 222 support the ends of alternate sets 224a, 224b, 224c, 224c stacked in hopper 218. The mechanism 226 for actuating the left shelf 220 of feeder 210 is shown in detail in FIG. 23. The mechanism for actuating right shelf 222 is identical in all material respects to mechanism 226. Left shelf 220 is attached to the right end of a pivot arm 228 pivotally attached by a pin hinge/torsion spring 230 to the housing 232 of feeder 210. A recess 234 in the left end of pivot arm 228 receives the outer race of a bearing 236 attached to one end of an actuating arm 238, such that pin hinge/torsional spring 230 biases pivot arm 228 in a clockwise direction against bearing 236. The other end of actuating arm 238 is attached to a cam 240 pivotally attached by a pin hinge 242 to housing 232. Cam 240 defines a pair of superimposed crescent-shaped recesses 244, 246 in its outer circumference. Recesses 244, 246 are sized to receive the outer race of a bearing 248 attached to link chain 211. When link chain 211 moves bearing 248 down past cam 240 (i.e., when the aperture 250 defined by shutter 212 moves past left wall 214), it engages recess 244, rotating cam 240 and actuating arm 238 in a counter- clockwise direction, to the position shown in phantom in FIG. 23. Because pivot arm 228 is no longer restrained from rotating by bearing 236, pin hinge/torsional spring 230 rotates it in a clockwise direction, to the position shown in phantom in FIG. 23, causing left shelf 220 to drop down. As bearing 248 continues to move down, it passes a proximity switch 252 mounted to housing 232, which reverses the direction of rotation of motor 215, and thus also the direction of movement of chains 211, 213 and aperture 250. When link chain 211 moves bearing 248 back up past cam 240, it engages recess 246, rotating cam 240 and actuating arm 238 in a clockwise direction back to its original vertical position. As actuating arm 238 rotates, bearing 236 engages the top surface of pivot arm 228, rotating it and left shelf 220 in a counter- clockwise direction back to their original horizontal positions. The operation of paper set feeder 210 is illustrated in FIGS. 24A, 24B, 24C, and 24D, and is similar in material respects to the operation of set feeders 10 and 110. Although making shutters 26, 120, 212 flexible so they can, e.g., wrap around the sides of hopper 218 (as in the case of feeder 210) or into other non-planar configurations may make feeders 10, 110, 210 more compact, the shutter can instead be relatively rigid and planar. For instance, as shown in FIGS. 25A and 25B, a set feeder 310 includes a shutter 312 comprised of individual rollers 314 disposed between the sides 315 (only one side shown) of a rectangular frame 316, e.g., of metal. As frame 316, and thus also the aperture 318 defined by shutter 312, shuttles back and forth with respect to the hopper 320, rollers 314 remain essentially coplanar. Frame 316 is shuttled back and forth by a pneumatic cylinder 321, but could instead be driven, e.g., manually, by a hydraulic cylinder, or by a drive chain arrangement similar to those employed in set feeders 10, 110, 210. Like set feeder 10, set feeder 310 includes left and right shelves 322, 324 and left and right wedges 326, 328 at the edges of aperture 318. Shelves 322, 324 can be actuated using any of the above-described or below- described mechanisms, or can instead be actuated by any other suitable mechanism, such as individual solenoids that are controlled based on the output of a sensor or sensors that determine the position of the aperture with respect to the hopper. In operation, set feeder 310 behaves in much the same manner as set feeders 10, 110, and 210 as shown in FIGS. 26A, 26B, 26C, and 26D. Although used in feeders 10, 110, 210, 310, the sheet set feeder need not have separate and discrete right and left shelves that support the edges of the bottommost and next-to-bottommost sheet sets. Such a feeder 410 is shown in operation in FIGS. 27A, 27B, 27C, 27D, 27E. (Although feeder 410 does not include right and left wedges at the edges of the aperture 412 in its shutter 414, they could be included if desired.) Shutter 414 of feeder 410 is relatively rigid and planar, like shutter 312 of feeder 310, but could instead be flexible if desired. Whereas the lengths of the apertures in set feeders 10, 110, 210, 310 remain fixed during operation, the length of aperture 412 varies as shutter 414 shuttles back and forth. As described below, this is accomplished by using two separate drive systems 432, 434 (shown schematically in FIG. 27A) that independently control, based on the outputs of a series of proximity sensors 436, 437, 438, 439, 440, 441, 442, 443 located to sense the position of shutter 414, the movement of the left and right halves 444, 446 of shutter 414. Drive systems 432, 434 comprise reversible motor and drive chain arrangements similar to those employed in set feeders 10, 110, 210, but could instead comprise, e.g., pneumatic or hydraulic cylinders as in set feeder 310. As shown in FIG. 27A, when the right edge 416 of aperture 412 is even with the right wall 418 of feeder 410 (as indicated by sensor 442) , the left edge 420 of aperture 412 is immediately adjacent right edge 416 (as indicated by sensor 438) . At this point, both halves 444, 446 of shutter 414 are moved so that both right edge 416 and left edge 420 move together to the left. When right edge 416 is even with the right edge of the bottommost set 424a in the stack 426 (as indicated by sensor 440) , as shown in FIG. 27B, right half 446 stops moving, and left half 444 continues to move to the left. As the length of aperture 412 increases, the right end of bottommost set 424a droops through the aperture, as shown in FIG. 27C. The portion of shutter 414 disposed immediately adjacent right edge 416 of aperture 412 supports next-to-bottommost set 424b, preventing it from also drooping through the aperture. When the length of aperture 412 has increased sufficiently (as indicated by sensor 441) , such that a gap 428 has formed between bottommost set 424a and next-to-bottommost set 424b, right half 446 of shutter 414 resumes moving to the left, at the same speed as left half 444. Right edge 416 then enters gap 428, stripping bottommost set 424a off the bottom of stack 426 as shown in FIG. 27D. When left edge 420 of aperture 412 reaches the left wall 430 of feeder 410 (as indicated by sensor 436) , left half 444 of shutter 414 stops moving. Right half 446 continues to move to the left until it is immediately adjacent left edge 420 (as indicated by sensor 439) , as shown in FIG. 27E. The process then reverses to strip off next-to- bottommost set 424b. An alternate shelf actuation mechanism 610 for, e.g., set feeder 10, is shown in FIG. 28. Shelf actuation mechanism 610 is similar to left shelf actuation mechanism 59 of set feeder 10, in that it is configured to cause the right paper support shelf 612 to rotate back up to the horizontal orientation more rapidly than it rotates down to the near-vertical orientation. Shelf 612 is rigidly attached to a pivot arm 614 in mechanism 610. The right end of pivot arm 614 is rotatably attached, via pivot 616, to the housing 618 of a set feeder similar in construction to set feeders 10, 110, 210, 310. The left end of pivot arm 614 carries a cam follower 620, which is configured to be received in a box cam 622. Box cam 622 is carried between the rollers 624 of a shutter mechanism similar in construction to the shutter mechanisms of set feeders 10, 110, 210, 310. Rollers 624, box cam 622, and another box cam (not shown) disposed on the other side of the shutter define an aperture in the shutter. The other box cam is similar in construction to box cam 622, but is configured to rotate a left paper support shelf (not shown) in the same manner that box cam 622 rotates right paper support shelf 612. Box cam 622 includes upper and lower pathways 626, 628 defined by a cam pivot arm 630 that pivots with respect to box cam 622 via a pivot 632. The left side of cam pivot arm 630 is overbalanced with respect to the right side of the arm, and thus the arm is biased by the force of gravity in the counterclockwise direction. Under the force of gravity alone, the left end of pivot arm 630 rests against the bottom wall of box cam 622. The operation of shelf actuation mechanism 610 is illustrated in sequential FIGS. 29A, 29B, 29C, 29D, 29E, 29F, and 29G. As shown in FIGS. 29A and 29B, when cam follower 620 first enters box cam 622, the right end of cam pivot arm 630 prevents the follower from entering upper path 626, forcing it instead into lower path 628. As box cam 622 continues to move to the right, cam follower 620 travels along lower path 628, causing shelf 612 to rotate downward in a counterclockwise direction, as shown in FIG. 29C. When it reaches the left side of pivot arm 630, follower 620 causes arm 630 to rotate clockwise. When cam follower 620 moves completely past the left end of pivot arm 630, gravity causes the overbalanced left side of the arm to rotate counterclockwise, until the left end of the arm again rests on the bottom wall of box cam 622, as shown in FIG. 29D. At this point, shelf 612 has rotated to a nearly vertical position, allowing the end of the bottommost paper set (not shown) to drop through the aperture. The shutter (and thus also box cam 622) then reverses 5 direction. As the box cam moves to the left, cam follower 620 comes into contact with the left end of cam pivot arm 630, as shown in FIG. 29E. Because of the steep profile of the left end the arm, cam follower 620 moves up very quickly, causing shelf 612 to rotate 10 rapidly up to the near-horizontal orientation. As explained above in connection with shelf actuating mechanism 59 of set feeder 10, by "snapping up" in this manner, shelf 612 is more rapidly positioned to support the free end of the next-to-bottommost sheet set, 15 reducing the likelihood that the free end will droop down into the aperture in the shutter. As box cam 622 continues to move to the left, cam follower 620 continues to traverse upper pathway 626, causing shelf 612 to return to its horizontal orientation, as shown in FIG. 20 29F. As shown in FIG. 29G, as cam follower 620 moves past the right end of cam pivot arm 630, the arm is caused to rotate in a clockwise direction. When the follower exits box cam 622, gravity causes the overbalanced left side of the arm to rotate 25 counterclockwise, until the left end of the arm again rests on the bottom wall of box cam 622. In some embodiments of set feeders 10, 110, 210, 310, 410, the offset-jogged stack of sheet sets completely fills the sheet set hopper, covering the 30 reciprocating shutter mechanism. For increased versatility, the hopper can instead be designed to handle sheets of various lengths and widths, e.g., 8^ in. x 11 in., 11 in. x 17 in., etc. For the reasons noted above, regardless of the paper size being processed, the stack 35 should just fit between the walls of the hopper, such that the offset-jogged ends of the stack are positioned over the paper support shelves. It is also desirable to cover any portion of the shutter mechanism that remains exposed on the sides of the stack, e.g., to prevent debris from entering and possible fouling the set feeder and to protect the operator of the feeder from the reciprocating shutter. A mechanism for automatically moving the hopper walls and paper support shelves to accommodate sheets of different lengths is shown in FIG. 30, and a shield mechanism for automatically covering the side portions of the shutter to accommodate sheets of different widths is shown in FIGS. 31 and 32. In the hopper wall and shelf adjusting mechanism 710 shown in FIG. 30, one hopper wall 712 (similar to hopper wall 16 of set feeder 10) and a paper set support shelf 723 are included in a movable housing assembly 714. Movable housing assembly 714 also includes a screw block 716 and a pair of linear bearings 718 that allow the entire housing assembly to be moved longitudinally, along rail 719, toward and away from the opposite wall 720 (and associated paper support shelf 721) of the hopper 722. Most components of adjusting mechanism 710 are positioned along the edge of the hopper, so as not to interfere with the feeding of paper sets. Rail 719 extends between a fixed left housing 724 (which carries hopper wall 720 and paper support shelf 721) and a fixed right housing 726. A motor 728 attached to left housing 724 drives a lead screw 730 threaded into screw block 716. When energized to rotate in one direction, motor 728 causes movable housing assembly 714, and thus also hopper wall 712 and shelf 723, to move closer to hopper wall 720 and shelf 721. When energized to rotate in the opposite direction, motor 728 causes the distance between the two hopper walls to increase. The control of motor 728 can be automated, e.g., to set the appropriate wall-to-wall hopper distance in response to a user's indication of the length of the paper to be processed. A similar mechanism is used to cover the portions of the shutter that lie alongside the stack of sheet sets. One side of a shield mechanism 810 is shown in FIGS. 31 and 32 (the other side of the shield mechanism is a mirror image of the this shield structure) . Mechanism 810 includes a series of overlapping slidable plates 812a, 812b, 812c, 812d, 812e. A movable side guide 814, a pair of linear bearings 816, and a screw block 818 are attached to the outermost plate 812e. Linear bearings 816 ride longitudinally along a linear rail 820 that extends between the sides of the set feeder hopper. A motor driver assembly 822 at one side of the hopper drives a pair of lead screws 824, one of which is threadably engaged with screw block 818, and the other of which is threadably engaged with the screw block (not shown) of the other half of the shield mechanism. The innermost plate 812a attaches to the housing 826 of the set feeder. All of the plates 812a, 812b, 812c, 812d, 812e ride on a support rail 828, such that the plates lie just above the shutter 830. In operation, if side guide 814 is located adjacent housing 826 (that is, if the shield mechanism 810 is "open") , motor 822 can be energized to rotate in one direction, drawing side guide 814 and outermost plate 812e toward the motor. When outermost plate 812e is almost fully exposed, a pair of tangs 832 at either end of plate 812e engage mating tangs 834 on next-to- outermost plate 812d, drawing plate 812d toward motor 822 as well. This process can be continued until all of plates 812a, 812b, 812c, 812d, 812e are fully extended, as illustrated in FIGS. 31 and 32. To "close" shield mechanism 810, motor 822 is energized to reverse the direction of rotation, until all of plates 812a, 812b, 812c, 812d, 812e are again adjacent to housing 826. As noted, shield mechanism includes two shield halves, each of which is driven by one of lead screws 824. Either or both shield halves can be independently decoupled from its associated lead screw 824, such that, e.g., only one shield half moves when motor 822 is energized. Thus, if the stack of sheet sets is placed in the center of the hopper, both shield halves are coupled to lead screws 824. When motor 822 is energized, both shields close at the same rate to cover the exposed shutter on both sides of the center-positioned (or "center-registered") stack. If the sheet stack is instead positioned against the left side of the hopper ("left registered"), the left shield half is decoupled from its associated lead screw 824. When motor 822 is energized, only the right shield half moves to cover the exposed shutter. Likewise, if the sheet stack is positioned against the right side of the hopper ("right registered") , the right shield half is decoupled from its associated lead screw 824. Like motor 728, the control of motor 822 can be automated, e.g., to close the shield by the appropriate amount in response to a user's indication of the width of the paper to be processed. So, in a set feeder that employs both shelf adjusting mechanism 710 and shield mechanism 810, the user could, e.g., press a button indicating the size of the paper to be processed (e.g., 8\ in. x. 11 in.), and the two mechanisms 710, 810 could automatically adjust the hopper size and cover any exposed portions of the shutter. The various features of the embodiments described herein, such as the air jet passages, the primary and secondary accumulator arrangement, the tensioning bar. the shelf-actuation mechanisms, and the drive mechanisms, may be interchanged among the various sheet set feeders as desired. Although in the above-described sheet set feeders 10, 110, 210, 310, 410, sheet sets are fed from the bottom of the stack, other feeder configurations are possible. For instance, in a sheet set feeder 1010 shown in FIG. 33, individual sets are fed from the top of the stack. Sheet set feeder 1010 includes a housing 1012. Two facing vertical walls of housing 1012, left wall 1014 and right wall 1016, define a hopper 1018 for receiving a stack 1020 comprised of offset-jogged sheet sets 1022a, 1022b, 1022c, 1022d, each of which in turn comprises two or more sheets 1024a, 1024b, 1024c, 1024d of, e.g., paper. (Sheet set feeder 1010 can also be used to feed offset-jogged sets of other types of substantially planar sheets, such as of film or fabric.) The distance between left wall 1014 and right wall 1016 of hopper 1018 is approximately equal to the length of a single sheet set, plus the distance by which each set is offset-jogged with respect to adjacent sets. Right wall 1016 can be moved toward and away from left wall 1014 to adjust the dimensions of hopper 1018 to accommodate sets of different lengths (e.g. by using mechanism 710) . An elevator 1026 disposed within hopper 1018 supports stack 1020. Elevator 1026 comprises a substantially flat surface that is moved up and down by an elevator mechanism 1028. Elevator mechanism 1028 may be driven by, e.g., a motor or a pneumatic pump, and may comprise, e.g. , a lead screw and screw block assembly, a chain drive arrangement, or a hydraulic or pneumatic piston. Pivoting fingers 1030, 1032 are located near the top opening of hopper 1018 on the left and right sides of hopper 1018, respectively. Pivoting fingers 1030, 1032 are pivotable about pivot points 1034, 1036 and are moved by pivoting mechanisms 1038, 1040, respectively. Pivoting mechanisms 1038, 1040 can be driven by, e.g., reversible electric motors, solenoids or pneumatic pumps. Pivoting mechanisms 1038, 1040 can be operated to pivot fingers 1030, 1032 around pivots 1034, 1036, and also to move pivots 1034, 1036 left and right along respective slots. Pivoting fingers 1030, 1032 hold topmost left- jogged and right-jogged sets 1022a and 1022b in place at their left and right ends, respectively. Pivoting finger 1030 can also be long enough to hold lower right-jogged set 1022b in place at its left end. Pivoting fingers 1030, 1032 depress respective ends of sets 1022a, 1022b slightly at the points of contact (which may cause respective opposite ends of sets 1022a, 1022b to be raised slightly, depending on the sheet material and the dimensions of the sheets) , facilitating the separation of sets 1022a, 1022b. A linear rail 1042 is disposed above hopper 1018. A gripper 1044 (shown in detail below in FIGS. 34A, 34B and 35) is attached to a carriage 1046, which moves back- and-forth along rail 1042 by, e.g., a reversible electric motor 1050. Reversing the direction of rotation of motor 1050 reverses the direction of motion of gripper 1044 along linear rail 1042. Gripper 1044 is moved left and right along linear rail 1042, and can be closed to grab the end of the topmost set, and opened to release the set. The rotational speed of motor 1050 may be controlled to vary the linear speed of gripper 1044 along linear rail 1042. To provide for smooth motion of gripper 1044, motor 1050 is initially controlled so that it ramps up from zero velocity to a constant speed. This speed is maintained until gripper 1044 nears its leftmost or rightmost point of travel, at which point the motor speed is ramped back down to zero. The direction of rotation of motor 1050 is then reversed, and the velocity profile repeated for the next cycle. A level sensor 1058 located near the top opening of hopper 1018 detects the height of stack 1020 within hopper 1018. Level sensor 1058 may be, e.g., an "electric eye" sensor (photosensor) or other type of sensing device. Level sensor 1058 determines when stack 1020 has been raised to a predetermined height by sensing the presence of the top of stack 1020 in the region of the top opening of hopper 1018. Level sensor 1058 communicates with elevator mechanism 1028 via a controller (not shown) to activate elevator mechanism 1028 to move elevator 1026 upward so that top set 1022a is positioned at the proper height to be grabbed by gripper 1044. A rubber-tipped push rod or snubber 1148 resides within left wall 1014 of housing 1012 and is actuatable to move horizontally back and forth. Snubber 1048 is capable of pushing a right-jogged set, e.g., next-to- topmost set 1022b, to the right a short distance so that gripper 1044 may easily grab the right end of set 1022b. Air jets 1150, 1160 are disposed on housing 1012. Air passages 1151, 1162 connected to air jets 1150, 1160, respectively, pass through housing 1012 and are angled slightly downwardly. Air passages 1151, 1162 are directed toward the left and right ends of topmost set 1022a and next-to-topmost set 1022b. Air jets 1150, 1160 may be controlled to issue air blasts, or slower, more steady streams of air, through air passages 1151, 1162. Air jets 1150, 1160 comprise manifolds 1152, 1164 and solenoid valves 1154, 1166, respectively, which are in turn connected to a source or sources of pressurized gas. When solenoid valves 1154, 1166 are energized, air from the gas source is supplied to manifolds 1152, 1164, causing air to issue from air passages 1151, 1162. Valves 1154, 1166 can be operated to deliver low-velocity to high-velocity air flow. Air jet 1150 may be activated to produce a stream of air directed downwardly toward the right end of next-to-topmost set 1022b, to facilitate set separation during operation, as described in detail below. Similarly, air jet 1160 may be activated to produce a stream of air directed downwardly toward the left end of next-to-topmost set 1022b. As shown in greater detail in FIGS. 34A, 34B and 35, gripper 1044 is comprised of substantially planar jaws 1052, 1054 which, in their open position, are spaced apart by a distance at least slightly greater than the thickness of the set which is to be grabbed. The interior surfaces of jaws 1152, 1054 are lined with thin rubber pads 1053, 1055, which, when in contact with the sheets of the grabbed set, provide a friction force to assist in holding the set within jaws 1152, 1054. Jaw 1152 is fixedly connected to gripper arm 1045. Jaw 1054 is connected to a movable rod 1056 that may be activated to move up and down by, e.g., a solenoid or a motor/lead screw/screw block arrangement (such as used in hopper wall and shelf adjusting mechanism 710) . Rod 1056 is telescoped within gripper arm 1045 to be movable therein. Rod 1056 may be moved upward, bringing jaw 1054 closer to jaw 1152 to grab topmost set 1022a. Rod 1056 may also be moved downward, increasing the separation between jaws 1152, 1054 to release the grabbed set. Alternatively, jaws 1052, 1054 may be pivotally connected for grabbing topmost set 1022a, as shown in FIG. 34B. Instead of the single-pivot arrangement shown in FIG. 34B, the jaw assembly could be a multi-pivot linkage, such as a parallelogram linkage. A leading edge sensor 1060, disposed on jaw 1052 near the opening formed by jaws 1052, 1054, detects when the right edge of topmost set 1022a has entered jaws 1052, 1054. A trailing edge sensor 1062 disposed on jaw 1052 near rod 1056 detects when gripper 1044 has fully captured the right edge of topmost set 1022a. When this occurs, set 1022a is grabbed by closing jaws 1052, 1054. Leading edge sensor 1060 and trailing edge sensor 1062 may be, e.g., electric eye sensors, similar to level sensor 1058 described above. As shown in FIG. 36 (not to scale) , an accumulator 1076 is located adjacent to hopper 1018. A substantially planar surface 1077 runs along the length of accumulator 1076 from hopper 1018. Planar surface 1077 is positioned at a height so that topmost set 1022a remains substantially horizontal when set 1022a is pulled off the top of stack 1020 and through accumulator 1076. When gripper 1044 releases grabbed set 1022a within accumulator 1076, it will fall without substantially disturbing the organization of the sheets of set 1022a, since set 1022a remains in a nearly horizontal orientation as it is pulled into accumulator 1076 until it is dropped. Accumulator 1076 includes a conveyor belt 1080. Accumulator 1076 can include other means for carrying away sets 1022a, 1022b, 1022c, 1022d, and/or a rotator 246 (FIGS. 17, 18, 19) for rotating the individual sets, e.g. , by 90°. The bottom of gripper 1044 is spaced above conveyor belt 1080 by a distance greater than the thickness of a typical large set 1022a, e.g., about two inches. Two solenoid-actuated pins 1078 (only one shown in FIG. 36) project from the top surface of conveyor belt 1080 when the solenoids are energized, and are recessed below the surface of the conveyor belt when deenergized. An indicator switch 1200 (such as a proximity switch) lies directly above pins 1078, such that when a finger 1079 on gripper 1044 moves past the switch, it sends a signal to the controller to open the jaws of the gripper. The pins 1078 are spaced apart (in the direction perpendicular to the plane of FIG. 36) to allow gripper 1044 to move between them. The operation of this subassembly of accumulator 1076 is described in detail below. Like bottom set feeder 10, top set feeder 1010 is configured to interface with finishing and processing equipment, such that the conveyor belt 1080 supplies individual sets, in sequence to, e.g., a cover feeder 190 (FIG. 9) , a stitcher/folder 196 and/or a face trimmer 197 (FIG. 10) , a perfect binder 198 (FIG. 11) , a mailing/inserting system 199 (FIG. 12) , and/or a shrink wrapper 200 (FIG. 13) . In operation, stack 1020 is placed into hopper 1018 of sheet set feeder 1010 so that bottommost set 1022d rests on elevator 1026, as shown in FIG. 33. When stack 1020 is placed in hopper 1018, level sensor 1058 may not detect that set 1022a is at the proper height to be grabbed by gripper 1044. If so, level sensor 1058 will send a signal to the controller (not shown) to activate elevator mechanism 1028 to raise elevator 1026. When level sensor 1058 detects that set 1022a is at the proper height to be grabbed by gripper 1044, level sensor 1058 sends a signal to the controller (not shown) to activate elevator mechanism 1028 to cease upward movement of elevator 1026. As shown in FIG. 33, gripper 1044 moves along linear rail 1042 from right to left to grab the right end of topmost set 1022a. Two different cycles are used to remove the offset-jogged sets 1022a, 1022b, 1022c, 1022d from the top of stack 1020. In the first cycle, left-jogged set 1022a is removed from the top of stack 1020. As shown in FIG. 37A, carriage 1046 moves along linear rail 1042 from the right until leading edge sensor 1060 detects the right edge of set 1022a. When it does, sensor 1060 sends a signal to the controller to activate air jet 1150, producing a blast of air through air passage 1151 to slightly raise the right end of set 1022a and slightly lower the right end of set 1022b, facilitating separation of sets 1022a, 1022b. The blast of air from jet 1150, in conjunction with the effect of pivoting finger 1030, which pushes down on the left side of set 1022a and consequently may raise the right side of set 1022a, facilitates separation of the right ends of sets 1022a, 1022b so that the jaws 1052, 1054 of gripper 1044 may easily slide around the right end of set 1022a. When trailing edge sensor 1062 detects that the jaws 1052, 1054 of gripper 1044 have fully encompassed the right edge of topmost set 1022a, jaws 1052, 1054 clamp shut to firmly grasp topmost set 1022a. Pivoting mechanism 1038 is activated by, e.g., a timer or a stepper mechanism (not shown) , to rotate finger 1030 to release the left edge of set 1022a to allow set 1022a to be pulled off the top of stack 1020. Once gripper 1044 has grabbed set 1022a, carriage 1046 reverses direction and moves to the right to pull set 1022a off the top of stack 1020. The timer or stepper mechanism that activates pivoting mechanism 1038 may also activate air jets 1150, 1160 to issue air blasts, or slower, more steady steams of air, through air passages 1151, 1162 to facilitate separation of sets 1022a, 1022b so that set 1022a may easily slide across the top of set 1022b. After gripper 1044 pulls set 1022a to the right a short distance, e.g., one inch, pivoting finger 1030 is activated by the timer or stepper mechanism to contact the left end of next-to-topmost set 1022b to help prevent set 1022b from being pulled to the right by gripper 1044 along with topmost set 1022a. As shown in FIG. 37B, gripper 1044 pulls set 1022a to the right. At this point, conveyor belt 1080 is stopped, and the solenoids that drive pins 1078 are energized to extend the pins. When finger 1079 passes switch 1200, the controller opens jaws 1052, 1054 of gripper 1044. As gripper 1044 continues to move to the right between the pins, set 1022a is stopped by pins 1078. When the jaws of the gripper slide completely out from underneath the set, set 1022a falls onto conveyor belt 1080. The lower jaw 1054 of gripper 1044 is then closed, the solenoids that drive pins 1078 are deenergized to retract them, and conveyor belt 1080 is switched on to deliver set 1022a to, e.g., the associated processing equipment. Once topmost set 1022a has been removed from stack 1020, level sensor 1058 detects that the topmost set 1022b of stack 1020 is not at the required level to be grabbed by gripper 1044. Level sensor 1058 sends a signal to the controller (not shown) to activate elevator mechanism 1028 to raise elevator 1026 until topmost set 1022b is at the proper height to be grabbed by gripper 1044. When level sensor 1058 detects that topmost set 1022b has reached the proper level to be grabbed by gripper 1044, level sensor 1058 sends a signal to the controller (not shown) to cause elevator mechanism 1028 to cease the upward movement of elevator 1026. In the second cycle, right-jogged set 1022b is removed from the top of stack 1020. As shown in FIG. 37C, carriage 1046 moves along linear rail 1042 from the right so that the open jaws 1052, 1054 of gripper 1044 will easily slide around the right edge of topmost set 1022b. Before gripper 1044 reaches hopper 1018, the controller (not shown) activates pivoting mechanism 1034, 1036 to rotate fingers 1030, 1032, respectively, upward and out of the path of gripper 1044. When leading edge sensor 1060 detects the right edge of set 1022b, it sends a signal to the controller (not shown) to stop carriage 1046. The controller then activates snubber 1048 to push set 1022b to the right a short distance so that gripper 1044 may easily grab the right end of set 1022b. When trailing edge sensor 1062 detects that the jaws 1052, 1054 of gripper 1044 have fully encompassed the right edge of topmost set 1022b, jaws 1052, 1054 clamp shut to firmly grasp topmost set 1022b. Once gripper 1044 has grabbed set 1022b, carriage 1046 reverses direction and moves to the right to pull set 1022b off the top of stack 1020. The timer or stepper mechanism may also activate air jets 1150, 1160 to issue air blasts, or slower, more steady streams of air, through air passages 1151, 1162 to facilitate separation of sets 1022b, 1022c so that set 1022b may easily slide across the top of set 1022c. As shown in FIG. 37D, gripper 1044 pulls set 1022b to the right, and the set is disengaged from the gripper in the manner described above in connection with set 1022a. Pivoting fingers 1030, 1032 are reset to their original positions, and the first and second cycles are repeated until all remaining sets 1022c, 1022d are fed onto conveyor belt 1080. An additional feature of the invention is a stacker 1100 for loading offset-jogged sets onto elevator 1026. As shown in FIG. 38 (schematic diagram), a second elevator 1082 may be loaded while individual sets are removed from elevator 1026 according to the procedure described above. Elevators 1026 and 1082 are driven independently by, e.g., separate belt systems (not shown) . While stack 1020 on elevator 1026 is being processed on the left portion of the system shown in FIG. 38, elevator 1082 is at the right of the system and at its lowest position, or an intermediate position, and a new stack of sets may be loaded onto elevator 1082. Alternatively or additionally, elevator 1082 may rest at the lowest position so that a dockable cart 1084 may be locked onto elevator 1082, e.g., using mechanical guides and couplings, to transfer a stack of sets 1083 onto elevator 1082. Alternatively or additionally, elevator 1082 may be lowered in incremental steps, as determined by a sensor or sensors 1088, so that stacks of sets may be loaded manually at a height convenient for the operator. Sensor 1088 may be, e.g., an electric eye sensor. When processing on elevator 1026 is complete, elevator 1026 is moved to the right portion of the system shown in FIG. 38 and lowered to be loaded, elevator 1082 (loaded with a stack 1083 of sets) simultaneously moves to the left for processing of stack 1083. What is claimed is:

Claims: 1. A sheet set feeder comprising: a housing including a hopper for receiving a stack of sheet sets comprising a bottommost sheet set having a first end and a second end and a next-to-bottommost sheet set having a first end and a second end, the first end of the bottommost sheet set being offset-jogged with respect to the first end of the next-to-bottommost sheet set; and a shutter mechanism supported by said housing and disposed at least in part beneath said hopper, said shutter mechanism defining an aperture sized to admit the bottommost sheet set and the next-to-bottommost sheet set, and a surface of said shutter mechanism and said aperture defining a plane, said shutter mechanism including: a driver for moving at least a portion of said shutter mechanism with respect to said hopper from a first position wherein said aperture is disposed beneath the first end of the bottommost sheet set to a second position wherein said aperture is disposed beneath the second end of the bottommost sheet set, and a first support for preventing the first end of the next-to-bottommost sheet set from crossing said plane when said aperture is disposed beneath the first end of the bottommost sheet set. 2. The sheet set feeder as recited in claim 1 wherein said first support comprises a first shelf. 3. The sheet set feeder as recited in claim 2 wherein said first shelf extends from a wall of said hopper a distance approximately equal to the distance between the first end of the bottommost sheet set and the first end of the next-to-bottommost sheet set. 4. The sheet set feeder as recited in claim 2 wherein said first shelf is pivotally mounted with respect to said housing. 5. The sheet set feeder as recited in claim 4 wherein said support includes a mechanism for pivoting said first shelf between a substantially horizontal orientation and a substantially vertical orientation. 6. The sheet set feeder as recited in claim 5 wherein said mechanism for pivoting pivots said first shelf from said substantially vertical orientation to said substantially horizontal orientation faster than said mechanism for pivoting pivots said first shelf from said substantially horizontal orientation to said substantially vertical orientation. 7. The sheet set feeder as recited in claim 5 wherein said mechanism for pivoting comprises a box cam. 8. The sheet set feeder as recited in claim 2 wherein said first shelf is slidably mounted with respect to said housing. 9. The sheet set feeder as recited in claim 1 wherein said first support comprises a portion of said shutter mechanism disposed adjacent said aperture. 10. The sheet set feeder as recited in claim 1 wherein said shutter mechanism further includes a second support for preventing the second end of the bottommost sheet set from crossing said plane when said aperture is disposed beneath the second end of the bottommost sheet set. 11. A sheet set feeder comprising: a housing including a hopper for receiving a stack of sheet sets comprising a bottommost sheet set having a first end and a second end and a next-to-bottommost sheet set having a first end and a second end, the first end of the bottommost sheet set being offset-jogged with respect to the first end of the next-to-bottommost sheet set; a shutter supported by said housing and disposed at least in part beneath said hopper, said shutter defining an aperture sized to admit the bottommost sheet set and the next-to-bottommost sheet set; a driver for moving said aperture with respect to said hopper from a first position wherein said aperture is disposed beneath the first end of the bottommost sheet set to a second position wherein said aperture is disposed beneath the second end of the bottommost sheet set, and a first shelf pivotally mounted with respect to said housing for supporting the first end of the next-to- bottommost sheet set when said aperture is disposed beneath the first end of the bottommost sheet set. 12. The sheet set feeder as recited in claim 11 wherein said first shelf extends from a wall of said hopper a distance approximately equal to the distance between the first end of the bottommost sheet set and the first end of the next-to-bottommost sheet set. 13. The sheet set feeder as recited in claim 11 further comprising a mechanism for pivoting said first shelf between a substantially horizontal orientation and a substantially vertical orientation. 14. The sheet set feeder as recited in claim 13 wherein said mechanism for pivoting pivots said first shelf from said substantially vertical orientation to said substantially horizontal orientation faster than said mechanism for pivoting pivots said first shelf from said substantially horizontal orientation to said substantially vertical orientation. 15. The sheet set feeder as recited in claim 14 wherein said mechanism for pivoting comprises a box cam. 16. The sheet set feeder as recited in claim 11 further comprising a second support for preventing the second end of the bottommost sheet set from crossing said plane when said aperture is disposed beneath the second end of the bottommost sheet set. 17. A feeder comprising: a housing including a hopper; a shutter supported by said housing and disposed at least in part beneath said hopper; a driver supported by said housing for moving said shutter with respect to said hopper; and a shield supported by said housing that can be selectively positioned to cover at least a portion of said shutter. 18. The feeder as recited in claim 17 wherein said shutter defines an aperture. 19. The feeder as recited in claim 17 wherein said shield comprises a plurality of overlapping plates. 20. The feeder as recited in claim 17 further comprising a motor for selectively positioning said shield. 21. A feeder comprising: a housing including at least two opposed hopper walls for defining a hopper; a shutter supported by said housing and disposed at least in part beneath said hopper; a driver supported by said housing for moving said shutter with respect to said hopper; and a hopper adjustment mechanism for changing the spacing between said two opposed hopper walls. 22. The feeder as recited in claim 21 wherein said shutter defines an aperture. 23. The feeder as recited in claim 21 wherein said hopper adjustment mechanism includes a motor. 24. A sheet set feeder comprising: a housing including a hopper for receiving a stack of sheet sets comprising a topmost sheet set having an end and a next-to-topmost sheet set having an end, the end of the topmost sheet set being offset-jogged with respect to the end of the next-to-topmost sheet set; and a set snatcher movably mounted in said housing, said set snatcher including a gripper, said set snatcher configured to bring said gripper into engagement with the end of the topmost sheet set and to operate said gripper to grasp the end of the topmost sheet set. 25. The sheet set feeder as recited in claim 24 wherein said set snatcher is configured to move said gripper while said gripper is operated to grasp the end of the topmost sheet set. 26. The sheet set feeder as recited in claim 25 further comprising a finger mechanism for holding the next-to-topmost set on the stack of sheet sets while said set snatcher moves said gripper while said gripper is operated to grasp the end of the topmost sheet set. 27. The sheet set feeder as recited in claim 25, further comprising a conveyor to receive the topmost sheet set. 28. The sheet set feeder as recited in claim 27, wherein said conveyor includes an actuator to operate said gripper to release the topmost sheet set onto said conveyor. 29. The sheet set feeder as recited in claim 24 further comprising a gas jet carried by said housing, said gas jet oriented to direct a stream of gas between the end of the topmost set and the end of the next-to- topmost set. 30. The sheet set feeder as recited in claim 24 wherein said gas jet is operable to produce a steam of gas to raise the end of the topmost sheet set with respect to the end of the next-to-topmost set. 31. The sheet set feeder as recited in claim 30 wherein said gripper grasps the raised end of the topmost sheet set. 32. The sheet set feeder as recited in claim 24 further comprising a snubber carried by said housing, said snubber operable to engage a second end of the topmost set and extent along a path directed towards the end of the topmost set. 33. The sheet set feeder as recited in claim 24 wherein said gripper grasps the topmost sheet set at a predetermined level with respect to said hopper. 34. The sheet set feeder as recited in claim 33 further comprising a sensor carried by said housing to detect the presence of the topmost sheet set at said predetermined level. 35. The sheet set feeder as recited in claim 34 further comprising an elevator to raise the stack of sheet sets responsive to an output of said sensor so that the topmost sheet set is at said predetermined level. 36. The sheet set feeder as recited in claim 24 wherein said set snatcher moves linearly. 37. The sheet set feeder as recited in claim 36 wherein said set snatcher moves along a rail carried by said housing. 38. The sheet set feeder as recited in claim 37 wherein said gripper comprises a first jaw and a second jaw, said second jaw being movable with respect to said first jaw to grasp the end of the topmost sheet set. 39. A method for feeding sheet sets comprising: loading a hopper with a stack of sheet sets comprising a topmost sheet and a next-to-topmost sheet set, said sheet sets having corresponding ends, the end of the topmost sheet set being offset-jogged with respect to the corresponding end of the next-to-topmost sheet set; and grasping the end of the topmost sheet set at a predetermined level. 40. The sheet set feeder as recited in claim 39 further comprising detecting the presence of the topmost sheet set at said predetermined level. 41. The method as recited in claim 40 further comprising moving the next-to-topmost sheet set to said predetermined level after the topmost sheet set has been moved off the stack of sheet sets by said set snatcher. 42. An stack loading system for use with a sheet set feeder, comprising: a first elevator for supporting a first stack of offset-jogged sheet sets to be processed by the sheet set feeder; and a second elevator for loading a second stack of offset-jogged sheet sets while the first stack of offset- jogged sheet said is being processed by the sheet set feeder; said first elevator and said second elevator being driven independently. 43. A sheet set feeder comprising: a housing including a hopper for receiving a stack of sheet sets comprising a bottommost sheet set having a first end and a second end and a next-to-bottommost sheet set having a first end and a second end, the first end of the bottommost sheet set being offset-jogged with respect to the first end of the next-to-bottommost sheet set; and a shutter mechanism supported by said housing and disposed at least in part beneath said hopper, said shutter mechanism defining an aperture sized to admit the bottommost sheet set and the next-to-bottommost sheet set, said shutter mechanism including a driver for moving at least a portion of said shutter mechanism with respect to said hopper from a first position wherein said aperture is disposed beneath the first end of the bottommost sheet set to a second position wherein said aperture is disposed beneath the second end of the bottommost sheet set, said shutter mechanism including a first retainer for supporting the next-to-bottommost sheet set when said aperture is disposed beneath the first end of the bottommost sheet set. 44. A sheet set feeder as recited in claim 43 further comprising a sheet set conveyor disposed beneath said aperture. 45. A sheet set feeder as recited in claim 44 further comprising a door disposed between said aperture and said conveyor. 46. A sheet set feeder as recited in claim 43 further comprising a sheet set rotator disposed beneath said aperture. 47. A sheet set feeder as recited in claim 43 wherein said first retainer comprises a first shelf. 48. A sheet set feeder as recited in claim 47 wherein said first shelf extends from a wall of said hopper a distance approximately equal to the distance between the first end of the bottommost sheet set and the first end of the next-to-bottommost sheet set. 49. A sheet set feeder as recited in claim 47 wherein said first shelf is pivotally mounted with respect to said housing. 50. A sheet set feeder as recited in claim 47 wherein said first shelf is slidably mounted with respect to said housing. 51. A sheet set feeder as recited in claim 47 wherein said first shelf includes a sheet of urethane disposed to contact the next-to-bottommost sheet set. 52. A sheet set feeder as recited in claim 43 wherein said first retainer comprises an air jet passage. 53. A sheet set feeder as recited in claim 52 wherein said shutter mechanism includes a member attached to an edge of said aperture, said member defining said air jet passage. 54. A sheet set feeder as recited in claim 53 wherein said member is a wedge. 55. A sheet set feeder as recited in claim 52 wherein said first retainer comprises a first shelf, said first shelf defining said air jet passage. 56. A sheet set feeder as recited in claim 43 wherein said first retainer comprises a portion of said shutter mechanism disposed adjacent said aperture. 57. A sheet set feeder as recited in claim 56 wherein said aperture is defined by opposed edges of a first shutter portion and a second shutter portion. 58. A sheet set feeder as recited in claim 57 wherein said driver is configured to move said first shutter portion with respect to said second shutter portion. 59. A sheet set feeder as recited in claim 43 wherein said shutter mechanism further includes a second retainer for supporting the bottommost sheet set. 60. A sheet set feeder as recited in claim 43 wherein said shutter mechanism comprises a series of rollers. 61. A sheet set feeder as recited in claim 60 further comprising a tensioning bar biased against at least some of said rollers. 62. A sheet set feeder as recited in claim 61 wherein said tensioning bar includes a sheet of urethane in contact with said at least some rollers. 63. A sheet set feeder as recited in claim 60 wherein said rollers extend between flexible drive members. 64. A sheet set feeder as recited in claim 63 wherein said flexible drive members comprise link chains. 65. A sheet set feeder as recited in claim 60 wherein said rollers extend between sides of a relatively rigid planar frame. 66. A sheet set feeder as recited in claim 43 wherein said driver comprises a reversible motor. 67. A sheet set feeder as recited in claim 43 wherein said driver comprises a linear actuator. 68. A sheet set processing system comprising: an offset-jogged sheet set feeder for receiving a stack of sheet sets comprising a bottommost sheet set having opposed first and second ends and a next-to- bottommost sheet set having opposed first and second ends, the first and second ends of the bottommost sheet set between offset-jogged relative to the respective first and second ends of the next-to-bottommost sheet set, said offset-jogged sheet set feeder being operable to sequentially provide in series at an output the bottommost sheet set and the next-to-bottommost sheet set; a sheet set processor for processing sheet sets; and a sheet set conveyor disposed to mechanically convey sheet sets from said offset-jogged sheet set feeder to said sheet set processor. 69. A sheet set processing system as recited in claim 68 wherein said sheet set conveyor comprises a sheet set rotator. 70. A sheet set processing system as recited in claim 68 wherein said offset-jogged sheet set feeder comprises a shutter defining an aperture sized to admit the bottommost sheet set and the next-to-bottommost sheet set. 71. A sheet set processing system as recited in claim 70 wherein said offset-jogged sheet set feeder comprises a driver for moving said shutter from a first position wherein said aperture is disposed beneath the first end of the bottommost sheet set to a second position wherein said aperture is disposed beneath the second end of the bottommost sheet set. 72. A sheet set processing system as recited in claim 68 further comprising a cover feeder. 73. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a stitcher. 74. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a folder. 75. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a face trimmer. 76. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a perfect binder. 77. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a mailing/inserting system. 78. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a shrink wrapper. 79. A sheet set processing system as recited in claim 68 wherein said sheet set processor comprises a collator. 80. A method for feeding sheet sets comprising: providing a sheet set feeder including: a hopper for receiving a stack of sheet sets; and a shutter disposed at least in part beneath said hopper, said shutter defining an aperture sized to admit individual sheet sets; loading said hopper with a stack of sheet sets comprising a bottommost sheet set having a first end and a second end and a next-to-bottommost sheet set having a first end and a second end, the first end of the bottommost sheet set being offset-jogged with respect to the first end of the next-to-bottommost sheet set; moving said shutter with respect to said hopper from a first position wherein said aperture is disposed beneath the first end of the bottommost sheet set to a second position wherein said aperture is disposed beneath the second end of the bottommost sheet set; and supporting the first end of the next-to-bottommost sheet set with a retainer, included within said shutter, when said shutter is in said first position.

Inventors: DARCY JAMES A, FRYKLUND GILBERT G, WEEKS THOMAS E, DARCY, JAMES, A., FRYKLUND, GILBERT, G., WEEKS, THOMAS, E.
Applicants: STANDARD DUPLICATING MACHINES, STANDARD DUPLICATING MACHINES CORPORATION
Application year: 1996
Main classification: B65G59
IPC codes: B65H3