Patent Publication Number: US-2007108693-A1

Title: De-stacking apparatus and method

Description:
BACKGROUND OF THE INVENTION  
      This application is directed to an apparatus and method for de-stacking relatively thin, flat items such as tortillas, egg roll skins, pizza blanks, pastry sheets, or similar products.  
      Many thin, flat food products such as tortillas, egg roll skins, and the like are packaged in stacks. When these products are to be used in a further food manufacturing process, they must be de-stacked one-by-one and placed onto a conveyor or other transportation device for further processing, such as filling, coating, wrapping, or the like. Currently, such products are normally de-stacked manually by a worker, which is relatively slow and labor-intensive, and can slow down an automated production line.  
      De-stacking of products such as tortillas and egg roll skins is a difficult task, because the product is not uniform in shape and thickness, is very fragile, and tends to be “sticky”, in other words, adjacent products or sheets in the stack have a tendency to stick together or adhere to one another. Attempts have been made to de-stack such products automatically, generally using suction cups or vacuum heads to lift the top product or sheet in a stack vertically upwards from the stack. In some cases, a single suction cup or vacuum head is applied at the leading edge of the stack, i.e. the edge closest to the location where a separated product is to be deposited after de-stacking. In other cases, multiple suction cups are applied around the periphery of the product.  
      The vacuum method of de-stacking is not consistent in lifting one product at a time from a stack. When such a method is used to de-stack tortillas, the tortillas at the top of the stack will lift off relatively easily. The bottom part of the stack has had the weight of the top part of the stack on top of it, so that the tortillas in the bottom part will tend to stick together, making them more difficult to lift off. This sometimes results in lifting of more than one tortilla at a time from the stack. Attempts to overcome this problem by increasing the vacuum applied at the bottom of the stack can sometimes cause damage by sucking holes in the tortillas. In general, machines using vacuum for de-stacking of thin food products have not been widely accepted in the industry due to their inconsistent operation and lack of production speed.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a new and improved apparatus and method for de-stacking relatively thin, flat items from a stack.  
      According to one aspect of the present invention, an apparatus for de-stacking flexible, planar products is provided, which comprises a support for supporting a stack of relatively flat products to be de-stacked in a de-stacking position, the support having a leading end, products in a stack in the de-stacking position having a forward edge closest to the leading end and a trailing edge remote from the leading end, a product exit adjacent the leading end of the support for receiving items as they are de-stacked from the stack, a picking head assembly movably mounted above the de-stacking position, a first drive device for moving the picking head assembly to a selected position between upper and lower end positions dependent on the height of the stack, the picking head assembly comprising a rotatable device and a series of spaced picking members projecting outwardly from the rotatable device, a second drive device for rotating the rotatable device, whereby picking members as they rotate engage successive products in the stack at the trailing edge of the stack and roll the product forwardly off the forward edge of the stack and into the product exit, and a controller for controlling operation of the first drive device so as to index the picking head assembly downwards into new product engaging positions as the height of stack is reduced.  
      The support may comprise a conveyor for conveying stacks of flexible, planar products one-by-one to a de-stacking position, and a collection device such as a conveyor or other processing equipment may be located beneath the product exit for collecting products one-by-one as they are de-stacked. The rotatable device may comprise a rotating drum of circular or other cross sectional shapes, but in an exemplary embodiment this device comprises an elongate conveyor having first and second end rollers and an endless chain or conveyor belt extending around the rollers, with the picking members projecting outwardly from the belt at predetermined intervals. The elongate picking conveyor is supported on one side by a support plate which in turn is mounted on the drive shaft of the first drive device. The second drive device is mounted on the support plate and rotates the first end roller. The roller and chain assembly has a longitudinal axis between the centers of the rollers and parallel to the travel paths of the lengths of chain or belt extending between the rollers, and this axis is oriented at a downward angle from the first end roller to the second end roller. In the operative position, the second end roller is located adjacent the trailing or rear edge of the upper most product of a stack in the de-stacking position. This means that picking members will engage the trailing edges of successive products in the stack as they pass around the second roller, peeling or rolling the engaged products forwardly towards the front edge of the stack until they roll completely off the stack and onto the collection device.  
      In this invention, no attempt is made to lift products vertically upwards and off the stack, which can lead to product damage and to products sticking together so that two or more products are lifted at once. Instead, the product is peeled or rolled over itself in a direction from the trailing edge forward, and then falls off the stack.  
      A sensor may be provided for detecting when a stack reaches the de-stacking position, and when there is no product left to be de-stacked, i.e. when the stack is depleted. This sensor is connected to the controller, which will turn off the drive to the stack conveyor when a stack reaches the de-stacking position. When the stack is completely de-stacked, the controller will actuate the first drive device to raise the picking head assembly to its uppermost position, then will actuate the drive to the stack conveyor to advance the next stack on the conveyor to the de-stacking position.  
      Each picking member may comprise a spaced pair of parallel picking feet, and the picking members are spaced apart at a distance less than the diameter of the product to be de-stacked. This distance may be of the order of one third of the product diameter.  
      According to another aspect of the present invention, a method of de-stacking flexible, planar products one-by-one from a stack is provided, which comprises the steps of:  
      positioning a stack of products in a de-stacking position below a picking head assembly, the stack having a leading edge and a trailing edge;  
      driving a picking head assembly to move a series of picking members along a path having a first end adjacent the trailing edge of an uppermost product in the stack and a second end spaced forwardly from the first end, the picking members moving from the first end to the second end and then back to the first end;  
      positioning the picking head assembly relative to the stack such that a picking member engages the trailing edge of an uppermost product and peels the product forwardly over itself as the picking member moves towards the second end of the path, until the product falls off the leading edge of the stack; and  
      continuing to engage successive products in the stack with successive picking members and peeling each product forwardly over itself and off the stack, while indexing the picking head assembly downwards as the stack height is reduced with removal of products from the top of the stack, until de-stacking is complete.  
      The method may also comprise the steps of detecting when all product has been de-stacked from a stack, and then raising the picking head assembly to a raised start position before moving another stack into the de-stacking position. The picking head assembly is then lowered until a picking member can engage the uppermost product in the new stack, and the procedure is repeated until the second stack is de-stacked. This process can be repeated for a plurality of stacks of products, providing an automatic and efficient de-stacking process. Product may be de-stacked one-by-one onto a conveyor positioned adjacent the leading edge of the stack for conveying the products to processing stations.  
      The picking head assembly may be a rotating head or may be a conveyor extending around spaced rollers defining first and second ends of the path. In the latter case, the conveyor may be inclined upwardly between the first and second ends to ensure that the picking members engage product only at its rear edge, so that it can be rolled forwardly.  
      The method and apparatus of this invention allows products to be more consistently taken off a stack one at a time and placed on another conveyor or another piece of process equipment for further processing. Because the product is peeled forwardly from its rear edge, rather than being lifted vertically upwardly off the stack, there is less risk of damage to the product and less tendency for adjacent products in the stack to stick together. This makes the apparatus and method ideal for de-stacking of relatively fragile, thin food products such as tortillas and egg roll skins. This invention reduces the expense incurred when a worker must lift product from a stack one-by-one and manually place such products individually on a conveyor or piece of equipment, and also produces more consistent and faster line speeds. There is currently no machine in the food industry that can de-stack product as consistently and rapidly as is possible with this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be better understood from the following detailed description of an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts, and in which:  
       FIG. 1  is a side elevation view of a de-stacking apparatus according to an exemplary embodiment of the invention, with the picking head assembly in a first position prior to engagement of a product such as a tortilla at the top of a stack;  
       FIG. 2  is a side elevation view similar to  FIG. 1  illustrating the picking head assembly at a subsequent position;  
       FIG. 3  is a side elevation view similar to  FIGS. 1 and 2  illustrating engagement of the picking head assembly with a trailing edge of a product at the top of the stack;  
       FIG. 4  is a side elevation view similar to FIGS.  1  to  3  illustrating the product being peeled or rolled forwardly by picking feet of the picking head assembly, subsequent to the position of  FIG. 3 ;  
       FIG. 5  is a side elevation view similar to  FIG. 4  illustrating a subsequent stage when the product drops off the forward edge of the stack;  
       FIG. 6  is a side elevation view similar to FIGS.  1  to  5  but illustrating the position of the picking head assembly when the height of the stack has been reduced and the picking feet engage the trailing edge of a product at the top of the reduced height stack;  
       FIG. 7  is a side elevation view of the apparatus of FIGS.  1  to  6  with an optional vacuum head for assisting in raising the trailing edge of an upper product so that it can be more readily engaged by the picking feet;  
       FIG. 8  is a rear end elevation view of the apparatus of  FIG. 7 ;  
       FIG. 9  is a schematic top plan view of the apparatus of FIGS.  1  to  6 ;  
       FIG. 10  is a schematic front elevation view of the apparatus of  FIG. 9 , with the picking head assembly in its lower position;  
       FIG. 11  is an enlarged front elevation view of the picking head assembly of FIGS.  1  to  6 ,  9  and  10 , illustrating the drive system in more detail;  
       FIG. 12  is a view similar to  FIG. 10 , illustrating the picking head assembly in its upper position;  
       FIG. 13  is a schematic block diagram of the control system for the various drive motors of the apparatus of FIGS.  1  to  12 ; and  
       FIG. 14  is a flow diagram of the steps carried out by the system in automatically de-stacking products from successive stacks. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      The drawings illustrate a de-stacking apparatus and method according to an exemplary embodiment of the present invention. The apparatus is particularly designed for de-stacking of relatively thin, flexible, flat or sheet-like food products such as tortillas, egg roll skins, pizza bases, pastry, and the like. However, it will be understood that this apparatus may be used to de-stack any relatively flat product from a stack, whether food or non-food.  
      FIGS.  1  to  6  and  9  to  12  illustrate a de-stacking apparatus  10  according to an exemplary embodiment of the present invention. The apparatus  10  basically comprises a frame  12  on which a stack support comprising a first, horizontal conveyor  14  is mounted for conveying flat, flexible products in stacks  15  to a de-stacking position, and a picking head assembly  16  adjustably mounted above the de-stacking position for movement between lower and upper end positions, the lower position being illustrated in  FIGS. 10 and 11 , and the upper position being illustrated in  FIG. 12 . A second conveyor  18  is positioned below and in front of the forward end of the conveyor  14  for receiving products de-stacked from the stack  15  and falling through an exit opening in front of the forward end of conveyor  14  (see  FIG. 5 ) and onto conveyor  18 . Conveyor  18  then conveys products one-by-one to further processing stations. It will be understood that conveyor  18  need not be part of the apparatus  10  but the apparatus may simply positioned to drop de-stacked products onto this conveyor or onto any other adjacent piece of processing equipment. Stack feed conveyor  14  may be made longer than illustrated in the drawings or may receive stacks fed onto it from an adjacent conveyor positioned end-to-end with conveyor  14  so that stacks can be continuously fed to the de-stacking position after each stack is completely de-stacked. Conveyor  14  is driven by conveyor motor  17  (see  FIGS. 10 and 13 ). The conveyor and picking head assemblies may be mounted on separate frames, as indicated in  FIGS. 9 and 10 , if desired.  FIGS. 11 and 12  illustrate the picking head assembly  16  alone.  
      In the illustrated embodiment, the picking head assembly  16  comprises an elongate, endless loop belt, conveyor or chain device having a first, drive wheel or sprocket  20  at one end of the looped path, a second, driven wheel or sprocket  22  at its trailing end, and a continuous belt or chain  24  extending around the two end wheels. The picking head assembly has an outer frame comprising spaced, elongate side plates  25  secured together by a central bolt  26  and a pin  28  extending between the plates at the trailing end, on which sprocket  22  is rotatably mounted. The frame is mounted at its leading end on mounting plate  30 , as best illustrated in FIGS.  9  to  12 , such that the conveyor device is inclined downwardly from its leading end to its trailing end, as best illustrated in  FIG. 1 . The angle of the conveyor device is adjustable by means of an angle adjustment screw  31  ( FIG. 11 ) and will be adjusted based on the diameter of the product to be de-stacked. In the case of 12 inch diameter tortillas, an angle of around 22 degrees has been found to be appropriate.  
      A series of spaced picking feet or pins  32  project outwardly from the belt or chain  24  at spaced intervals. The picking feet in the exemplary embodiment are arranged in pairs (i.e. two spaced pins at each picking position on the belt), as best illustrated in  FIG. 11 . The picking feet may be provided on two separate chains secured together by a central belt section, as indicated in  FIG. 8 . However, single picking feet on a single chain may be used instead of two feet at each picking location, or additional conveyor chains may be used if three or more spaced feet at each picking location are desired. The picking feet in this embodiment comprise generally spaced, flat ended or blunt pins. However, picking feet of other shapes may be used in other embodiments, such as picking feet with bent ends. The picking feet should not have pointed ends which could potentially cause damage to the product being de-stacked, which is generally relatively fragile. The longitudinal spacing between the picking feet and thus the total number of picking feet will be dependent on the dimensions of the product to be de-stacked. For twelve inch flour tortillas, for example, nine pairs of equally spaced picking feet may be provided, at four inch center to center spacings. The picking feet will be closer together for smaller diameter products.  
      The picking head assembly  16  is supported via a rigid support frame  34 , as best illustrated in FIGS.  9  to  12 . The support frame  34  has an upper support plate  35  with a central opening (not visible in the drawing). A drive or locator motor  36  is mounted beneath the support plate via mounting bolts  38 , with a drive shaft  40  projecting upwardly through the opening in plate  35  and secured to the mounting plate  30  by Allen screw  42 . The motor  36  is a linear servomotor and operates to drive the picking head assembly up and down between the lowermost or down position illustrated in  FIG. 11  and the uppermost or raised position of  FIG. 12 . Frame  34  may be supported on caster wheels  44  as indicated in  FIG. 9 , for easy transport from one position to another. FIGS.  1  to  8  illustrate a sheet metal safety shield  37  which may be bolted onto the machine frame in order to surround the picking head drive assembly. The safety shield is omitted in FIGS.  9  to  12  in order to reveal the drive assembly in more detail.  
      A second drive motor or rotator motor  45  is mounted on the picking head assembly mounting plate  30  via support flange  46 , and the drive of motor  45  is connected via shaft coupling  47  to a rotating drive shaft  48 . Motor  45  is a rotary servomotor. Shaft  48  extends through a series of shaft bearings  50 , through the plate  25 , and is connected to the drive wheel or sprocket  20  so as to rotate the wheel and thereby move the chain or belt  24  around both end wheels or sprockets  20 ,  22 . The outer end of shaft  48  is rotatably secured to the outer side plate  25  of the support frame of the picking head assembly via bearing  52  and collar  54 . Motor  45  will rotate wheel  20 , causing picking feet to travel along a lower de-stacking path facing stack  15  and having a first end at drive wheel  22  and a second end at drive wheel  20 .  FIG. 1  illustrates the operative position of the picking head where the first end of the de-stacking path is adjacent the rear or trailing edge of an uppermost product  69  in the stack  15 .  
      A photo sensor or detector  55  is mounted on the outer surface of frame  34  facing the conveyor  14  so as to detect when a stack of product reaches the de-stacking position, as best illustrated in  FIG. 10 . A programmable control unit  56  is mounted on the opposite outer surface of the frame and has an outer control panel  57  for user control of the operation of the various motors, as generally illustrated in FIGS.  9  to  12 . The control unit contains various motor controllers and wiring for the system. As illustrated in  FIG. 13 , the control unit has three programmable drive controllers,  58 ,  60  and  62  for controlling the operation of the locator motor  36 , the rotator motor  45  which moves the picking head belt  24 , and the conveyor motor  17  which moves the stacks of product to be de-stacked, respectively. Any suitable programmable motor controllers may be used, such as Allen-Bradley Ultra 3000™ Digital Servo Drives, as manufactured by Rockwell Automation of Milwaukee, Wis. The motor controllers may be set up to operate in the desired sequence using a lap top computer programmed using Ultraware™, which is off-the-shelf software available from Rockwell Automation for control of the Ultra 3000 motor controllers or drives. The system set up will determine the sequence of operation of the three motors to de-stack tortillas, as best illustrated in  FIG. 14 . Alternatively, the control unit may have a computer or central processing unit used to control operation of the three drive motors according to program instructions and operator input.  
      The control panel or user input  57  allows an operator to start and stop the de-stacking process and also to vary several parameters. The input device or panel  57  has a start button, an emergency stop button, an off button, a selector switch for selecting the incremental step spacing of the locator motor, i.e., the down and up indexing distance of the picking head assembly, and a controller for varying the rotator motor speed. A pilot light is also provided to indicate when the apparatus is turned on. The locator step spacing switch will be connected to controller  58 , and the speed control switch will be connected to controller  60 . Photosensor  55  is connected to the rotator motor controller  60  and to the conveyor motor controller  62 .  
      As indicated above,  FIG. 14  indicates the programmed sequence of the system to de-stack a series of products, such as tortillas or the like, from a stack. Prior to operation, the operator will select the desired indexing steps of the controller, based on product thickness. There are unlimited adjustments for changing the amount of drop of the picking head assembly after each cycle based on the thickness of the product, as controlled by the motor drive or controller  58  which controls the locator motor  36 . The operator will also select the desired rotator motor speed, in other words the time for each complete revolution of the picking belt or chain in order to de-stack one product from the stack. The apparatus can be set up to de-stack products at a rate between 15 and 300 products per minute, depending on the speed desired and the time required for subsequent processing operations.  
      Once the system has been properly set up, the operator presses the start button in step  60 , which in turn switches on the photosensor  55  and starts the stack conveyor motor  17  (step  62 ). The locator motor  36  is also actuated to raise the picking head assembly into the upper position of  FIG. 12  (step  64 ). When the photosensor  55  detects the arrival of a stack  15  of product such as tortillas at the de-stacking position beneath the picking head assembly (step  65 ), the stack conveyor motor  17  is turned off (step  66 ).  
      The rotator motor  45  is then turned on (step  68 ) so as to de-stack product one at a time from the stack. FIGS.  1  to  5  illustrate the sequence of operation to de-stack one product from the stack. In  FIG. 1 , the stack  15  has arrived at the de-stacking position, the conveyor motor has been turned off, and the picking head assembly is in the raised position ready to engage and de-stack a product from the stack. In  FIG. 2 , the rear most picking foot, or picking foot pair  32   a , has moved forwardly to a location close to the rear edge of the stack  15 . In  FIG. 3 , picking foot  32   a  has engaged the upper tortilla or other product  69  in the stack and has started to roll the rear edge  70  forwards. In  FIG. 4 , the picking foot  32   a  has advanced further forwards towards the leading or drive roller  20 , and has also peeled the top tortilla forwards as indicated. Finally, in  FIG. 5 , the picking foot  32   a  has rolled the upper tortilla  69  completely off the stack, so that it falls onto the product conveyor  18  beneath. It therefore takes approximately half of one complete revolution of the conveyor belt or chain  24  in order to de-stack one product from stack  15 .  
      Once controller  60  determines that the rotator motor  45  has rotated the conveyor belt through about one half rotation or cycle (step  72 ), it will signal the controller  58  to index the picking head  16  down by a distance equal to the approximate thickness of one product (step  74 ), and the next tortilla in the stack will then be engaged at its rear edge by the closest picking head  32 , and rolled off the stack in exactly the same way as illustrated in FIGS.  1  to  5 . The product thickness selected may be between thirty five and sixty five thousandths of an inch, or more. This process continues until the entire stack is de-stacked.  FIG. 6  illustrates a point in the sequence in which only a few tortillas are left in the stack  15  and the picking head assembly is approaching its lower position, and the upper tortilla  75  has just been engaged by one of the picking feet  32  and rolled forward a short distance. When the photosensor  55  detects that the last product has been removed from the stack (step  76 ), the rotator motor  45  will be turned off (step  77 ). If there are more product stacks remaining to be de-stacked ( 78 ), the stack conveyor motor will be turned on again, and the process will be repeated until the next stack of product is de-stacked. When a processing operation is complete, the operator turns off the machine and the sequence ends ( 79 ).  
       FIGS. 7 and 8  illustrate an optional vacuum head  80  which may be added for de-stacking of more “sticky” products or products which are non-uniform so that they are more difficult to pick up. The apparatus of  FIGS. 7 and 8  is otherwise identical to that of FIGS.  1  to  6  and  9  to  12 , and like reference numerals have been used for like parts as appropriate. A vacuum supply pipe  82  extends from the rear of the picking head assembly through an opening provided for this purpose in the side plate  25  and into the space between the upper and lower runs of the conveyor belt  34 , at a location adjacent the rear or driven roller  22 . The pipe is bent down to provide vacuum head  80  facing the product stack  15 , but not actually contacting the uppermost product in the stack. An on-off valve  84  is provided for turning the vacuum supply on and off. When the vacuum is on, the suction at vacuum head  80  will tend to lift the top product  85  at its trailing edge  86  so that the trailing edge can be more easily engaged by the picking feet  32 , as indicated in  FIG. 8 . The vacuum head  80  can be turned on or off by the operator based on whether or not the picking feet are successful in picking up and separating product from the stack on their own.  
      Although the picking head assembly in FIGS.  1  to  12  is a conveyor belt carrying a series of spaced picking feet, it may alternatively comprise a rotating cylindrical drum or head which may carry a user specified number of spaced picking feet, depending on the type and size of product to be de-stacked. The picking feet project radially outwardly from the outer surface of the drum. Other parts of the apparatus in this embodiment will be identical to the previous embodiment, with the locator motor  36  directly rotating the drum or head and the locator motor indexing it up and down based on product thickness.  
      The de-stacking apparatus and method of this invention is an improvement over the prior art techniques of manually de-stacking, or methods using suction cups which were subject to many disadvantages. The apparatus of this invention is easy to use, reliable, and efficient, and provides much more consistent de-stacking than previously proposed automated de-stackers. It is suitable for use in de-stacking many types of relatively thin and flat, flexible products, including food products such as any type or size of tortilla, egg roll skins, pizza blanks, and the like. The apparatus may be readily modified for de-stacking of any products typically packaged in stacks, whether food or non-food. In the case of relatively thin, flexible products, the product is lifted relatively gently at its rear edge and peeled forward over the top of itself until it rolls off the forward end of the stack. This reduces the risk of damaging the product or lifting more than one product when two products are stuck together, as can happen with relatively sticky products, particularly towards the bottom of a stack. The picking apparatus is automatically indexed down after each product is removed from the stack. When a stack is depleted, a new stack is automatically positioned for de-stacking.  
      The main difference between the apparatus of this invention and prior art de-stacking proposals using vacuum is that this apparatus does not use vacuum to try and lift the top product directly upwards from the stack. Instead, the product is gently peeled forward from its rear edge and off the stack. The picking head can be of various designs, from a conveyor with picking feet to a rotating head with picking feet, and can be customized for specific products to be de-stacked. The number, spacing, and shape of the picking feet can also be varied based on the size and type of product to be de-stacked. This apparatus takes one product at a time from the stack substantially consistently and at a constant speed, and places the product on another conveyor or another piece of process equipment. The de-stacking speed does not vary unless manually altered by the controller. The apparatus is particularly suitable for the food processing industry where thin, flat food products are typically provided initially in stacks that must be de-stacked one by one for further processing.  
      Although some exemplary embodiments of the invention have been described above by way of example only, it will be understood by those skilled in the field that modifications may be made to the disclosed embodiments without departing from the scope of the invention, which is defined by the appended claims.