Abstract:
A system for forming a plurality of discrete objects into a stack is disclosed which system includes a frame having a top, a bottom and sides; a conveyor associated with the frame and having an end edge for dispensing discrete objects, a first support mounted on the frame near the end edge for receiving objects from the end edge and having an opening with a width smaller than the width of the objects, a first actuator operably connected to the first support for moving the first support between first and second positions relative to the end edge; a second actuator operably connected to the first support for moving the first support between upper and lower positions relative to the frame; a second support mounted on the frame beneath the first support having a width less than the width of the opening in the first support; a third actuator operatively connected to the second support for moving the second support between high and low positions, the second support high position being higher than the first support lower position; a third support mounted on the frame at a position higher than the second support low position and having an opening wider than the width of the second support; a fourth actuator operatively connected to the third support for moving the third support between a first position beneath the first support and a second position; a sensor for determining the number of discrete objects in a stack, the sensor being operatively coupled to the to the third actuator; and a controller for controlling the first, second, third and fourth actuators. A method of using the system is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
   The present application is a divisional application of U.S. application Ser. No. 10/143,845, filed May 14, 2002, now U.S. Pat. No. 6,918,736 which claims the benefit of U.S. provisional patent application Ser. No. 60/290,342 filed May 14, 2001, the disclosures of which are hereby incorporated by reference, and to which priority is claimed. 

   FIELD OF THE INVENTION 
   The present invention is directed to a method and apparatus for forming one or more rows of discrete, planar objects, into one or more stacks, and more specifically, toward a method and apparatus for continuously forming at least one moving stream of disk-like objects, such as frozen hamburger patties, into one or more stacks and moving the finished stacks to a station for further processing. 
   BACKGROUND OF THE INVENTION 
   Frozen hamburgers, chicken patties, sausage patties, and other disk-like food products typically are prepared by a manufacturer on one piece of equipment and then fed into a freezer. After leaving the freezer, they are screened by a metal detector, which causes contaminated patties to be ejected, and then conveyed to a stacker. Because the stacks formed by some stackers can vary in height, and because the number of stacks formed simultaneously by a stacker may be greater than the number of stacks that will fit in a case, the finished stacks are often manually removed from the stacker and loaded into cases. This manual loading step is labor-intensive, and, due to the presence of a human element, highly variable. 
   One known prior art patty stacking machine is disclosed in U.S. Pat. No. 6,052,969, assigned to the assignee of the present application, which is hereby incorporated by reference. That machine includes a conveyor for moving patties in a first direction and dropping them into helical coil. The patties fall between the loops of the coil, and as the coil is rotated, new loops are presented for receiving additional patties. The rotation of the coil advances the patties into a holder, and when the holder is filled, a mechanical jaw grips the stack and moves it to a packing station from which it is loaded into a packing machine. This machine serves its intended purpose adequately, but suffers from various problems such as being bulky. In addition, if patties are not accurately aligned with loops of the coil, they may hit the coil instead of falling between the loops which leads to stacks of varying heights and to product waste. 
   To maximize efficiency, it is preferable to have the entire process of stacking and packing patties automated, and to do so in a manner that allows for continuous production and that minimizes the likelihood of product jams. Furthermore, it is desirable that a patty stacking machine can easily be retrofitted to the end of a patty processing production line and that the machine be sufficiently compact so as not to interfere with other existing parts of the processing machinery. 
   SUMMARY OF THE INVENTION 
   These and other problems are addressed by the present invention which comprises a method and apparatus for receiving a plurality of disk-like objects, such as frozen hamburger patties, forming them into stacks, and transferring the stacks to a holding station from which they are packed into cartons. While the application is particularly well suited for use with frozen hamburger and related food patties, it may easily be adapted to process other food and non-food objects. Furthermore, nearly any symmetrical object can be processed according to the invention, and even non-symmetrical planar objects may be processed if they are properly oriented. Thus, while the invention will generally be described in the context of frozen, disk-like food patties, its application is in no manner limited to use with this type of product. 
   In a preferred embodiment, the invention comprises a continuous conveyor belt that is either part of a patty processing line or that is adjacent to a conveyor leading from a patty processing system and that receives patties therefrom. The subject invention can be used to stack a single row of patties, but for reasons of speed and efficiency, patties are usually arranged on a conveyor in multiple rows, frequently four, five or six rows. Therefore, the preferred embodiment of the invention is designed to process multiple rows by simultaneously forming multiple stacks and then transferring those stacks to a holding location, while another portion of the stacker continues to receive patties from the conveyor. In this manner, the stacker can process patties continuously, and there is no need to stop the conveyor to allow the stacks to be transferred from the stacker to the holding location. 
   The conveyor has an end edge over which the patties of each row fall onto a first holder, sometimes referred to as an upper support or shelf. The upper support preferably comprises a plurality of pairs of parallel pins that extend from a support toward the end edge of the conveyor so that individual patties in a given row drop one at a time off the end of the conveyor onto a pair of pins. Hereafter, the processing of a single stack of patties will sometimes be discussed, it being understood that other stacks are being formed substantially simultaneously on adjacent pairs of pins. The upper support is lowered as each new patty falls onto it in order to keep the top of the stack on the shelf about the same distance beneath the end edge of the conveyor. The height of the top of the stack varies somewhat during processing, but it preferably is maintained within a fairly narrow range to ensure that the patties drop consistently and form stacks. In the preferred embodiment, a counter adjacent the conveyor is used to count patties in a row just before they fall onto the upper support, and a cam is used to lower the shelf at a known rate. 
   A second holder comprising a plurality of fingers is positioned beneath the upper support, with each finger aligned with the opening between a pair of upper support pins. As the upper support drops, the pins eventually pass to each side of one of the fingers, and as the upper support drops further, the bottom of the stack contacts a finger on the second holder and is supported thereby. When the stack is completely supported by the fingers, the upper support pivots away from the stream of falling patties and returns to its starting position while the second holder continues to drop, keeping the top of the stack at a generally constant height. A transfer device is mounted beneath the second support, which device includes a plurality of openings aligned with each of the fingers on the second support. When a stack contains the correct number of patties, or is otherwise determined to be complete, the second holder drops so that the fingers pass through the openings in the transfer device, leaving the stacks supported by the transfer device. Preferably, as soon as the second shelf begins to drop, the end of the conveyor is moved to lengthen the conveyor and create a gap in the flow of patties; this delays the release of the next group of patties and allows the upper shelf to move into position to catch additional patties. The upper support thus supports a next group of falling patties, while the following processing steps are carried out on the first stack. 
   Once the stacks are supported on the transfer device and the fingers of the second support are located beneath the transfer device, the transfer device secures the stacks and moves sideways to transfer the stacks to a holder. As the transfer device is moving the stacks to the holder, the second support is free to return to its starting position beneath the upper support. Once the transfer of patties is complete, the transfer mechanism returns to its starting location beneath the second support, and the process is repeated. 
   It is therefore a principal object of the present invention to provide a stacking machine for forming a plurality of objects into one or more stacks. 
   It is another object of the invention to provide a method of forming a plurality of objects into one or more stacks of a fixed size in a continuous manner. 
   It is a further object of the present invention to provide a stacking machine having a transfer mechanism for transferring a first set of finished stacks to a holding area while a second set of stacks is being formed. 
   It is yet another object of the present invention to provide a stacking machine having first and second supports for supporting one or more stacks of planar objects. 
   It is yet a further object of the present invention to provide a stacking machine that is compact and easily retrofittable to existing equipment. 
   It is still another object of the present invention to provide a stacking machine for forming one or more stacks of planar disk-like objects that is reliable and not subject to jamming. 
   In furtherance of these objects, a method of forming a stream of discrete objects into a stack is disclosed that includes the steps of providing a frame having a top, a bottom and sides and providing a plurality of discrete objects each having a width. A first support is provided on the frame that has an opening smaller than the width of said objects, which support is movable vertically between upper and lower positions and movable horizontally between engaged and disengaged positions. The first support is held in said upper and engaged positions while said discrete objects are dropped onto said first support to form a stack having a top and a bottom. The first support is moved toward the lower position to maintain the top of said stack at a first level relative to said frame. A second support is provided beneath said first support which second support has a width less than the opening in said first support, and the second support is movable between a high position above said lower position and a low position. The first support is lowered toward the second support until said second support passes through said opening in said first support and contacts the bottom of said stack. Then the first support is moved to said disengaged position. The second support is lowered to maintain the top of said stack at said first level. A third support is provided that has an opening and is translatable between a first position beneath said second support and a second position. A sensor senses for the occurrence of a stack finished condition, and when that condition is detected, the second support is lowered until it passes thought the opening in said third support and said third support contacts the stack bottom. 
   Another aspect of the invention comprises a system for forming a plurality of discrete objects into a stack that includes a frame having a top, a bottom and sides and a conveyor associated with the frame that has an end edge for dispensing discrete objects. A first support is mounted on the frame near the end edge for receiving objects from the end edge and has an opening with a width smaller than the width of the objects. A first actuator is operably connected to the first support for moving the first support between first and second positions relative to the end edge and a second actuator is operably connected to the first support for moving the first support between upper and lower positions relative to the frame. A second support is mounted on the frame beneath the first support and has a width less than the width of the opening in the first support. A third actuator is operatively connected to the second support for moving the second support between high and low positions where the second support high position is higher than the first support lower position. A third support is mounted on the frame at a position higher than the second support low position, and the third support has an opening wider than the width of the second support. A fourth actuator is operatively connected to the third support for moving the third support between a first position beneath the first support and a second position, and a sensor is provided for determining the number of discrete objects in a stack, where the sensor is operatively coupled to the to the third actuator. A controller controls the first, second, third and fourth actuators. 
   Another aspect of the invention comprises a method of forming a stream of discrete disk-like objects into a stack that involves providing a frame having a top, a bottom and sides supporting a conveyor having an end edge. A plurality of discrete disk-like objects, each having a diameter, are placed on the conveyor. A first support is provided on the frame adjacent the end edge, which first support includes first and second spaced apart pins separated by a distance less than the diameter of the objects. The first support is movable vertically between upper and lower positions and pivotable between engaged and disengaged positions. The first support is held in the upper position and in the engaged position and the conveyor is operated to cause the objects to fall over the end edge of the conveyor and onto the first support to form a stack having a top and a bottom. A counter is incremented each time one of the disk-like objects passes a given location on the conveyor, and the first support is toward the lower position each time the counter is incremented. A second support is mounted beneath the first support that has a width less than the distance between the pins, the second support being movable between a high position above the lower position and a low position. The first support is lowered over the second support until the second support passes between the pins and contacts the bottom of the stack, then the first support is pivoted the disengaged position. The second support is lowered each time the counter is incremented when the stack is in contact with the second support. A third support is provided that has an opening wider than the second support and that is translatable between a first position beneath the second support and a second position. When the counter reaches a predetermined count, the second support is towered until it passes through the opening in the third support and the third support contacts the stack bottom. The first support is moved to the upper position and the engaged position after the top of the stack drops beneath the lower position, and the third support is moved to the second position and releases the stack into a stack holder after the third support contacts the stack bottom. Next, the second support is moved to the high position after the third support moves from the third support first position, and the third support is then returned to the third support first position after the stack has been released into the stack holder. 
   An additional aspect of the invention is a method of forming a plurality of rows of discrete objects into a plurality of stacks that involves providing a frame having a top, a bottom and sides and a plurality of discrete objects, each having a width, arranged in rows. A first support is provided on the frame that has a plurality of spaced apart openings smaller than the width of the objects, the first support being movable vertically between upper and lower positions and movable horizontally between engaged and disengaged positions where each of the plurality of openings is aligned with one of the plurality of rows. The first support is held in the upper and engaged positions and the discrete objects are dropped onto the first support over the plurality of openings to form a plurality of stacks each having a top and a bottom. Next, the first support is moved toward the lower position to maintain the tops of the stacks at a first level relative to the frame. A second support is provided beneath the first support comprising a plurality of fingers, each finger being aligned with and having a width less than the width of the openings in the first support. The second support is movable between a high position above the lower position and a low position. The first support is lowered over the second support until the plurality of fingers on the second support pass through the openings in the first support and contact the bottoms of the stacks. The first support is moved to the disengaged position and the second support is lowered to maintain the top of the stacks at the first level. A third support having a plurality of openings wider than and aligned with the plurality of fingers and translatable between a first position beneath the second support and a second position is provided. A sensor senses for the occurrence of a stack finished condition, and, when the condition is detected, the second support is lowered until the fingers pass thought the openings in the third support and the third support contacts the bottoms of the stacks. The stacks on the third support are covered and the third support is pivoted to invert the stacks on the third support while being translated toward a discharge location. 
   A further aspect of the invention comprises a system for forming a plurality of discrete objects arranged in rows into a plurality of stacks that includes a frame having a top and a bottom and a first side having an inner wall and a second side having an inner wall facing the first side inner wall. The first side inner wall and the second side inner wall each include a guide track. A first cam is mounted on the frame as is a drive for rotating the first cam and the second cam. A conveyor is associated with the frame and has an end edge for dispensing rows of discrete objects. A first support is mounted on the frame near the end edge, for receiving objects from the end edge, and has a plurality of rods spaced by a distance less than the width of the objects. A guide wheel is received in each of the guides on the frame first wall and the frame second wall, and a cam follower movable into engagement with the first cam is attached to the first support. A first actuator is operably connected to the first support for moving the first support between first and second positions relative to the end edge. A second actuator is operably connected to the first support for moving the first support between upper and lower positions. A second support is mounted on the frame beneath the first support and comprises a plurality of fingers each having a width less than the distance between the first support rods. A third actuator is operatively connected to the second support for moving the second support between high and low positions, the second support high position being higher than the first support lower position. A third support is mounted on the frame at a position higher than the second support low position and comprises a frame portion and a tray portion, the tray portion including a bottom wall having a plurality of openings wider than the width of the fingers. A fourth actuator is operatively connected to the third support for moving the third support between a first position beneath the second support and a second position, and a sensor is provided for counting the number of objects passing a point on the conveyor, the sensor being operatively connected to the drive for rotating the first cam and the second cam. A controller is also provided for controlling the first, second, third and fourth actuators and the drive. 
   Another aspect of the invention comprises a system for forming a plurality of discrete objects into a stack comprising a frame having a top, a bottom and sides, a conveyor associated with the frame and having an end edge for dispensing discrete objects, and a receiver mounted on the frame near the end edge for receiving objects from the end edge, the receiver having a first object-engaging portion adjacent the end edge and a second object-engaging portion located beneath the conveyor. 
   A further object of the invention comprises a stacker for forming a plurality of objects into stacks comprising a frame and a first support mounted on the frame having an opening with a width smaller than the width of the objects and being shiftable between an upper position and a lower position relative to the frame. A second support is also mounted on the frame beneath the first support and is aligned with the opening in the first support. The second support has a width less than the width of the opening in the first support and is shiftable between a first position above the first support lower position and a second position so that shifting the first support from the upper position to the lower position while the second support is in the first position causes the second support to pass through the opening. 
   An additional aspect of the invention comprises a transfer mechanism for receiving a stack of objects from a stacker and moving the stack to a location away from the stacker that includes a support having an opening wider than a stack-supporting element of the stacker, a wall normal to the support for engaging the side of the stack and a cover shiftable between a first position adjacent the top of the stack and a second position. The transfer mechanism also includes an actuating mechanism for moving the cover to the first position and the support toward the location while inverting the support to bring the stack bottom into a position above the stack top. 
   An additional aspect of the invention comprises a system for forming a plurality of discrete objects into a stack comprising a frame having a top, a bottom and sides and a conveyor associated with the frame, which conveyor has a generally horizontal surface movable in a first direction for moving a plurality of objects in the first direction toward and over an end edge. A movable receiver is mounted on the frame near the end edge for receiving objects from the end edge and is angled with respect to the surface, so that objects supported on the movable receiver move in a direction opposite to the first direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects will be better understood after a reading and understanding of the following detailed description of a preferred embodiment of the invention together with the following drawings of which: 
       FIG. 1  is a perspective view of a stacking device according to the present invention which device includes a conveyor, an upper support, a lower support and a transfer device. 
       FIG. 2  is an end elevational view of the stacking device of  FIG. 1 . 
       FIG. 3  is an assembly drawing of the stacking device of  FIG. 1 . 
       FIG. 4  is a perspective view of the upper support and lower support of  FIG. 1 . 
       FIG. 5  is a perspective view of the upper support of  FIG. 1 . 
       FIG. 6  is a perspective view of the lower support of  FIG. 1 . 
       FIG. 7  is a perspective view of the transfer device of  FIG. 1 . 
       FIG. 8  is a side elevational view of the transfer device of  FIG. 1 . 
       FIG. 9  is a side elevational view of the stacking device of  FIG. 1  showing a stack of objects that has just been transferred from the second support to the transfer device. 
       FIG. 10  is a side elevational view of the stacking device of  FIG. 1  showing the transfer device in a position to release a stack at a discharge location while a second stack of objects on the upper support moves toward the lower support. 
       FIG. 11  is a side elevational view of the stacking device of  FIG. 1  showing a stack of objects supported on the lower support moving toward the transfer device which has returned to its starting location beneath the second support. 
       FIG. 12  is a side elevational view of the stacking device of  FIG. 1  showing the transfer device rotating and translating a stack of objects toward a discharge location while the upper support catches objects dropping off the conveyor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same, a general overview of the present device can be gained from viewing  FIGS. 1 and 3  which show a stacking device designated generally by the numeral  10 , with an adjacent conveyor  12  having an end edge  14 . A plurality of disk-shaped objects  16 , in this case, frozen hamburger patties, are arranged in rows on the conveyor  12  extending in the direction of movement of the conveyor. As conveyor  12  moves, it causes patties  16  to be advanced so as eventually to drop off end edge  14  onto an upper support  18 , as best shown in  FIG. 5 , to form stacks  20  of patties thereon as best shown in  FIG. 11 . Upper support  18  is downwardly movable in order to keep the top of stacks  20  at a generally constant level with respect to end edge  14  of the conveyor  12 . As upper support  18  descends, it transfers the stacks  16  to a lower support  22 , as best shown in  FIG. 3 , and moves laterally out of the falling streams of patties so that further patties  16  from the conveyor  12  fall directly onto the stacks  20  supported by lower support  22 . The lower support  22  is downwardly movable and continues to drop until a sensor  226  detects that the stacks  20  have reached their final size. At this point, lower support  22  transfers the stacks  20  to a stack transfer mechanism  24  that moves the stacks  20  laterally away from the conveyor  12  toward a discharge location. Additional falling patties  16  are caught by upper support  18  or lower support  22  as discussed above, and transfer device  24  returns to its starting position beneath the upper support  18  and the conveyor  12  before a subsequent set of stacks of patties  20  is complete. Controller  23 , as best shown in  FIG. 1 , controls the operation of the actuators and drives described herein, and is preferably a computer or PLC that controls the speed of the various drives and the operation of the actuators to carry out the steps of the process described herein. This arrangement allows for a continuous processing of patties  16  arriving at the end edge  14  of a conveyor  12  without the need to stop the conveyor each time a stack is completed. 
   Stacker  10  is installed on a fixed support  26 , such as a factory floor, and includes a fixed frame portion  28  fixed with respect to support  26  and a movable frame portion  30  that moves with respect to the fixed frame portion  28 , which fixed frame portion  28  and movable frame portion  30  for a frame for the stacker. Movable frame portion  30  includes four support wheels  32  resting on four platforms  34 , which in turn rest on the fixed support  26 . A motor  36  is operable connected to a shaft  38  which is rotatably supported by two bearings  40  that are supported by bearing supports  42 , one of which is shown in  FIG. 1 , mounted on floor  26 . Two arms  44  are fixed to shaft  38  and extend radially therefrom so that the ends of arms  44  describe an arc of a circle as the shaft  38  rotates. Tie rods  46  connect arms  44  to movable frame  30  so that, as motor  36  turns shaft  42  in a first direction, the movable frame portion  30  is pulled along platforms  34  toward motor  36 , and as motor  36  turns in a second direction, the movable frame portion  30  is pushed along platforms  34  away from motor  36 . The roller  48  supporting the end edge  14  of the conveyor  12  ( FIG. 3 ) is supported on the movable frame portion  30  while other portions of conveyor  12  are supported by the fixed frame portion  28 . Therefore, the conveyor  12  includes a slack take-up mechanism  50 , shown in  FIGS. 9–12 , which allows the effective length of the conveyor  12  to increase and decrease as the movable frame portion  30  moves away from and back towards the fixed frame portion  28 . When the effective length of the conveyor  12  is increased in this manner, the spacing is increased between rows of patties  16  arriving at end edge  14 , and this extra spacing or gap allows the upper support  18  to pivot back into the flow of falling patties to start a new stack. 
   Movable frame portion  30  comprises a first vertical plate member  52  having an inner wall  54  and an outer wall  56 , and a second vertical plate member  58  having an inner wall  60  and an outer wall  62 . A guide  64  is formed on inner wall  54  of the first vertical plate member  52  by a pair of spaced rails  66 , while an upper guide is formed in the second vertical plate  58  by an upper slot  70 , and a lower guide is formed in second vertical plate  58  by a lower slot  74 . Rods  76  and  77  extend between the inner walls of the first and second vertical plates to maintain their spacing. 
   With reference to  FIGS. 3 and 5 , upper support  18  comprises a carrier  78  including a first side plate  80  having an inner side  82  and an arcuate slot  84 , and a second side plate  86  having an inner side  88 , an outer side  90  and an arcuate slot  92  aligned with arcuate slot  84  in the first side plate  80 . The second side plate  86  is parallel to the first side plate  80  and spaced therefrom by connecting rod  94 . Carrier  78  supports a pivoting member  96  comprising a first L-shaped member  98  having an outer wall  100  with a pin  102  (seen in  FIG. 3 ) projecting therefrom and an inner wall  104 , and a second L-shaped member  106  having an inner wall  108  facing inner wall  104  of the first L-shaped member  98  and an outer wall  110  from which a pin  112  projects. The outer wall  100  of first L-shaped member  98  overlies the inner side  82  of first side plate  80 , with pin  102  received in arcuate slot  84 , and extends beyond the first side plate  80 . The outer wall  110  of the second L-shaped member  106  overlies the inner side  88  of second side plate  86  with pin  112  received in arcuate slot  92  of the second side plate  16 . A first rod  114  extends between the middle portions of the inner walls  104 ,  108  of the first and second L-shaped members  98  and  106 , respectively, and a second rod  116  extends between the portions of the first and second L-shaped members  98  and  106 , respectively, that project beyond the first side plate  80  and second side plate  86 . A plurality of pins  118  arranged in pairs  120  spaced apart by a given distance extend radially from second rod  116  as best shown in  FIG. 5 . First L-shaped member  98  is pivotally connected to the inner wall  82  of first side plate  80  at a pivot point  122 , while second L-shaped member  106  is pivotally connected to the inner wall  108  of the second side plate  86  at a pivot point  124 . An actuator  126 , preferably a pneumatically actuated cylinder, is connected between first side plate  80  and an end  128  of first L-shaped member  98  on the opposite side of pivot point  122  from rod  114 , which actuator  126  causes first L-shaped member  98 , and hence carrier  78 , to pivot about pivot points  122  and  124 , while pins  102  and  112  in arcuate slots  84 ,  92  guide the movement of the pivoting member  96  with respect to the carrier  78 . Guide wheels  130  are mounted on the outer walls of the first side plate  80  and second side plate  86  which wheels are received in the guides  64 ,  70  of the vertical plates  52  and  58  of the movable frame portion  30 . A cam follower  132  also extends from the outer side  90  of the second side plate  86 . Plates  133  attached to rod  94  form a backstop against which patties impact as they form stacks on the pairs  120  of pins  118 . 
     FIG. 6  illustrates lower support  22 , which includes a first side plate  134  having an inner side  136  and an outer side  138 , and a second side plate  140  having an inner side  142  and an outer side  144 . A strut  146  connects the inner sides of the first and second side plates  134  and  140 , respectively, and a hexagonal rod  148  extends between the inner sides of the first and second plates parallel to strut  146 . Guide wheels  150  are attached to outer sides  138  and  144  of first side plate  134  and second side plate  140 , respectively, and the outer side  144  of second side plate  140  further includes a cam follower  152 . A plurality of fingers  154  are attached to hexagonal rod  148 , each of which includes at least one planar surface  156 . 
   Transfer mechanism  24 , best shown in  FIGS. 7 and 8 , comprises a first L-shaped plate member  158  and a second plate member  160  parallel to and spaced from first plate member  158  by a rod  162  extending between end portions of plate members  158  and  160  which rod  162  is supported at either end by bearings  164 . A tray assembly  166  includes two side plates  168  connected by a connecting rod  170 . A plurality of trays  172 , each having a bottom wall  174  having a slot  176  and side walls  178 , are pivotally attached to plate members  158 ,  160 . A hexagonal rod  180  is rotatably attached between side plates  168 , and a plurality of L-shaped covering fingers  182  are attached thereto. Actuator  184 , connected between the plate member  158  and hexagonal rod  180 , rotates the hexagonal rod  180  to move the L-shaped fingers  182  between a first position where a portion of the L-shaped fingers  182  overlies the trays  172  and a second position, as best shown in  FIG. 7 , where no portion of the L-shaped fingers  182  overlies the trays  172 . 
   As best shown in  FIG. 7 , a belt drive  186  is located in housing  188  (seen in  FIG. 2 ) attached to plate member  160 , and includes a first flanged wheel  190  mounted on the outer side of plate member  160 , which flanged wheel is coupled to a member  192  having an extending lever arm  193  connected to an actuator  194 . A second flanged wheel  196  is operably coupled to connecting rod  170  and rotationally coupled to first flanged wheel  190  by a belt  198 . When actuator  194  presses against lever arm  164 , it rotates the first flanged wheel  180  which rotation moves belt  198  and causes the second flanged wheel  196  and hence connecting rod  170  to rotate; this tilts tray assembly  166  with respect to plates  158 ,  160 . Actuator  200  attached to second plate member  160  causes the entire tray assembly  166  to pivot about the axis of rod  162 , while actuator  202  moves the tray assembly  166  away from the conveyor  12  toward a stack discharge location and return the tray assembly  166  to its starting position after the patties have been discharged. 
   Referring now to  FIG. 1 , a motor support  204  is mounted on the outer wall  62  of vertical support plate  58 , and a motor  206  is mounted on the support. The motor  206  turns a shaft connected to vertical plate  58  and two cams—an inner cam  208  adjacent plate  58  and an outer cam  210  between the inner cam and the motor  206 . 
   The mounting of upper support  18  between first vertical plate  52  and second vertical plate  58  is apparent in  FIG. 3  which illustrates the guide wheels  130  of second L-shaped member  106  received between rails  66  of guide  64  and guide wheels  130  of first L-shaped member  98  extending toward upper slot  70  of second vertical plate member  58 . Cam follower  132  rides along the outer surface of inner cam  208  and the downward movement of the upper support  18  is limited by the bottom end of slot  70 . The mechanism for holding the upper support  18  against cam  208  is best seen in  FIG. 3 , and comprises an actuator  212  mounted on the outer wall  56  of first vertical plate  52  which moves a lever arm  214  attached to a rotatable shaft  216  mounted between first vertical plate  52 , and second vertical plate  58  at an upper edge thereof. From shaft  216  extend first and second angled arms  218  which overlie connecting rod  94  of the upper support. By moving lever arm  214 , actuator  212  raises and lowers angled arms  218  to press down upon the upper support or to move the arms  218  away from the upper support. 
   Lower support  22 , as best seen in  FIG. 3 , is mounted between first vertical plate  52  and second vertical plate  58  with the guide wheels  150  of the outer sides  138  of first plate  134  received between rails  66  of guide  64  and the set of guide wheels  150  on the outer side  144  of second plate  140  extending through lower slot  74  of second vertical plate  58 . Cam follower  152  is biased upwardly against outer cam  210  by a mechanism that includes an actuator  220  mounted on the outer wall of  56  of the first vertical plate  52  connected to a lever arm  222  which in turn is connected to a shaft  224  rotatably mounted between the first and second vertical plates  52 ,  58  on the edge of the plates beneath the conveyor  12 . Two arms  223  connect shaft  224  to first side plate  134  and second side plate  140  of lower support  22  so that, when actuator  220  moves lever arm  222  and turns shaft  224  in a first direction, cam follower  152  of the lower support  22  is pressed upwardly against outer cam  210  and pulled away from outer cam  210  when shaft  224  is turned in the opposite direction. 
   The operation of the stacker will now be described with reference primarily to  FIGS. 9  though  12  which show the stacker in various stages of forming a plurality of hamburger patties into stacks and transferring those stacks from a stacking location toward a discharge location. Beginning with  FIG. 9 , patties  16  move along conveyor  12  and fall over the end edge  14  of the conveyor onto fingers  118  of upper support  18 .  FIG. 9  shows one patty  16  already supported by the fingers  118  with another about to fall onto the first patty to begin to form a stack. Beneficially, the upper support  18  and the lower support  22  are located generally beneath the end edge  14  of the conveyor  12 , and thus the stacks that form on the upper and lower supports are also formed generally beneath the conveyor  12 . This formation of stacks beneath the end of the conveyor advantageously contributes to the compact size of this stacking device because the stacks are formed against the direction of movement of conveyor  12 . Actuator  212  rotates lever arm  214  to turn shaft  216  to press arms  218  against the upper support to hold the upper support cam follower  132  against inner cam  208 , and, as the radius of cam  132  decreases while it rotates counterclockwise as viewed in  FIGS. 9–12 , the upper support  18  moves downwardly toward the lower support  22 . The rotation of the inner cam  208  is based on the rate that the stack is forming as detected by optical detector  226 , best shown in  FIG. 1 , so that the top of stack  20  remains approximately the same distance below conveyor end edge  14  and ensures that each patty drops a similar distance in a similar manner to form consistent stacks. 
     FIG. 10  shows stack  20  on fingers  118  has grown in size and moved closer to the finger elements  154  of lower support  22 . As the upper support  18  continues its descent, the pair of fingers  118  of the upper support  18  supporting the stack will pass to either side of one of the fingers  154  of the lower support  22  so that, as the upper support  18  continues to drop past the lower support  22 , the stack  16  will be deposited on the lower support  22 , and actuator  126  will pivot the upper support  18  away from the conveyor  12  so that additional patties  16  will fall onto the stack on the lower support  22 . 
   In  FIG. 11 , the stack has grown to its finished size, at which point actuator  220  pivots shaft  224  to drop the lower support  22  to cause lower support finger  154  to pass through the slot  176  in bottom wall  174  of one of the trays  172  of the transfer mechanism  24 , to leave the stack supported on the transfer mechanism  24 . In this figure too, the pins  118  of the upper support  18  can be seen moving back toward conveyor  12  to catch the next patty falling therefrom in order to start a second stack rather than allowing it to fall on to the completed stack on the transfer mechanism. At this point, motor  36  rotates shaft  38  to pull movable frame  30  away from fixed frame  28  to lengthen the conveyor (effectively moving end edge  14  away from the next row of patties) and delay the passage of additional patties over end edge. This second stack will be processed in the same manner as was the first stack. 
     FIG. 12  shows the transfer mechanism  24  has rotated and translated away from the conveyor  12  toward a discharge location  228  on which the stacks will be deposited. To accomplish this movement, actuator  200  first pulls and then pushes against lever arm  201  to rotate lever arm  201  in a counterclockwise direction as seen in  FIG. 8  which, through a gearing mechanism, rotates tray assembly  166  to the inverted orientation seen in  FIG. 12 . Actuator  194  presses against lever arm  193  to pivot the tray assembly  166  relative to the transfer mechanism wall  158  to fully invert the stack  20  of patties and deposit them onto holder  228 , which holder has a slot in a bottom support wall to allow covering fingers  182  to pass therethrough when actuator  184  moves the covering fingers  182  away from the stack prior to returning to its starting location beneath the conveyor  12  in time to receive the next stack of patties from the lower support  22 . 
   During the foregoing process, drive  36  rotates shaft  38  to move movable frame  30  along supports  34  on fixed frame  28  to position the movable frame portion  30  and hence the transfer mechanism  24  for optimal operation. As seen in  FIG. 11 , where stack  20  is transferred from the lower support  22  to the transfer mechanism  24 , movable frame portion  30  is closest to fixed frame portion  30 , and wheels  32  are positioned near the right edges of supports  34  as viewed in  FIGS. 9–12 .  FIG. 9  shows the transfer mechanism  24  has moved to a point approximately halfway between the conveyor  12  and discharge location  228 , and movable frame portion  30  has also moved in this direction as can be seen from the positions of wheels  32  on the supports. In  FIG. 12 , transfer mechanism  24  has reached discharge location  228 , and the movable frame portion  30  has also moved closer to the discharge location as can be seen from the positions of wheels  32  on the supports  34 . As discussed above, this motion provides for lengthening and shortening the conveyor as needed to vary the spacing between advancing rows of patties to give the upper support time to move into a stream of falling patties. 
   The subject invention has been described above in terms of a preferred embodiment. However, numerous obvious additions and modifications will become apparent to those skilled in the art upon a reading of the foregoing description. It is intended that all such additions and modifications form a part of the present invention to the extent that fall within the scope of the several claims appended hereto.