Abstract:
The problem of potentially damaging a pallet layer that is gripped by clamps of a depalletizing tool is solved i) by detecting the real position of the layer using a pad on the tool that is movable with the clamps towards the pallet layer and whose detected stopping position determines the real position of the layer, and ii) while the layer is gripped by the clamp, by inserting under the layer curtains; the pressure on the layer by the clamps being adapted to the ease to go underneath the layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/001,676, filed on May 22, 2014, the contents of which are incorporated by reference herein. 
     
    
     FIELD 
       [0002]    The present disclosure relates to depalletizing, and more specifically to a tool for layer depalletizing. 
       BACKGROUND 
       [0003]    Distribution centers usually receive full pallets of goods from manufacturers. Those goods are stored in a warehouse section and are retrieved and palletized according to the retailers&#39; needs. Traditionally, the products were depalettized manually from the full pallets in the inbound area. This task is physically demanding and an automated approach is required for productivity and health &amp; safety reasons. 
         [0004]    U.S. Pat. No. 8,915,696 B2 issued on Dec. 23, 2014 to Baumann et al. and being titled “Device and Method for Depalletizing Stacked Bundles” describes a robotized system and method where stacked containers are depalettized. 
         [0005]    The depalletizing tool from Baumann possesses a base frame  1  and two underside support base parts  2   a  and  2   b  that can be moved towards and away from one another by means of slide bearings  3   a ,  3   b . Each support base part includes a roller as a leading edge. 
         [0006]    A drawback of the tool from Baumann is that the rollers tend to wear with time, are costly to replace and they have a minimal diameter that can cause a problem when small products have to be picked. Also, this approach relies solely on the friction action of the rollers to insert the movable support member underneath the products. Therefore, if the tool is not precisely positioned at the right height, the rollers could damage the products as they try to lift them with their rotating action. 
         [0007]    Also, the tool by Baumann includes light barriers as sensors to position the tool for the depalletizing process. This approach does work well when the products to be depalettized have a regular shape, do not have any open flap, and when all products are nicely stacked. If those conditions are not respected, the use of light barriers can cause false readings yielding a misguiding of the depalletizing device. 
         [0008]    Also, the method and tool by Baumann cannot handle the slip sheets that are often inserted between the layers for their separation. 
         [0009]    U.S. Pat. No. 7,934,759 B2, issued on May 3, 2011 to Weller and being titled “Packaging System Including Pallet De-Layering System” describes a system and method to handle a layer of multiple palletized products where an interior void is located in the product layer. The system includes void filling members carried by a gripper mechanism that is provided to improve holding the products for de-layering. 
         [0010]    The approach taken by Weller only works if there is at least one void in the layer of products, which is too restrictive. 
       SUMMARY 
       [0011]    The problem of potentially damaging a pallet layer that is gripped by clamps of a depalletizing tool is solved i) by detecting the real position of the layer using a pad that is movable with the clamps towards the pallet layer and whose detected stopping position determines the real position of the layer, and ii) while the layer is gripped by the clamp, when inserted under the layer curtains; the pressure on the layer by the clamps being adapted according to the front end ease to go underneath the products. 
         [0012]    According to an illustrative embodiment, there is provided a tool for layer depalletizing comprising:
       a frame for mounting the tool to a robot;   clamps movably mounted to the frame to grip a pallet layer;   curtains mounted to the frame below the clamps and being movable under the pallet layer while the pallet layer is gripped by the clamps; pressure on the clamps being adjusted depending on a movement resistance of the curtains when the curtains are inserted under the pallet layer.       
 
         [0016]    According to another illustrative embodiment, there is provided a tool for layer depalletizing comprising:
       a frame for mounting the tool to a robot;   clamps movably mounted to the frame to grip a pallet layer; and   a pad, mounted to the frame above the clamps, that is transversely movable towards and away a level defined by the clamps, and that defines a reference to determine a height of the pallet layer when the pad is moved towards the pallet layer.       
 
         [0020]    According to still another illustrative embodiment, there is provided a curtain assembly mounted to a layer depalletizing tool under clamps thereof comprising:
       two curtains, each defined by a plurality of rolls mounted in tracks so as to be slidably movable under a pallet layer while the pallet layer is gripped by the clamps; each of the plurality of rolls extending transversally to directions of movement of the curtains; each of the two curtains including a front end equipped with at least one rotatable friction element.       
 
         [0022]    According to another illustrative embodiment, there is provided a method for layer depalletizing comprising:
       positioning clamps around at least one layer to depalletize;   using the clamps to grip and at least partially lift the at least one layer;   moving curtains under the at least one layer while monitoring a displacement speed thereof;   if the displacement of the curtains is indicative of a product blocking the movement of the curtains, then applying less pressure on the clamps;   moving the layer with the clamps to a selected area, while the curtains are maintained under the at least one layer; and   at the selected area, removing the curtains from under the at least one layer and the clamps releasing the at least one layer.       
 
         [0029]    According to a further illustrative embodiment, there is provided a method for layer depalletizing comprising:
       determining a real position of a layer by moving a pad towards a top surface of the layer;   positioning clamps around the layer using the real position of the layer;   using the clamps to grip and at least partially lift the layer;   moving curtains under the layer;   moving the layer with the clamps to a first area, while the curtains are maintained under the layer; and   at the first area, removing the curtains from under the layer and the clamps releasing the layer.       
 
         [0036]    Illustrative embodiments of the layer depalletizing tool include pressure adjustment of its side clamps to facilitate the gripping of the products located at the center of the layer (i.e. inside those located at the perimeter). 
         [0037]    In a layer depalletizing tool according to illustrative embodiments, the top pad allows measuring the height of the top surface of the layer to be picked for precise positioning of the tool. Such a top pad also prevents small products to “pop out” as curtains move underneath the products or when the curtains are opened when the products are placed. 
         [0038]    Other objects, advantages and features of the tool and method for depalletizing mixed load products will become more apparent upon reading the following non restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    In the appended drawings: 
           [0040]      FIG. 1  is a top perspective of a tool for layer depalletizing according to a first illustrative embodiment; the tool being shown attached to a robot arm; 
           [0041]      FIG. 2  is a top perspective of the tool from  FIG. 1 ; 
           [0042]      FIG. 3  is a top plan view of the tool from  FIG. 1 ; 
           [0043]      FIG. 4  is an exploded perspective of the tool from  FIG. 1 , the tool being shown without most of its frame; 
           [0044]      FIG. 5  is a top perspective of part of the frame and of the curtain actuating assembly; 
           [0045]      FIGS. 6A and 6B  are respectively top and bottom perspective view of the tool from  FIG. 1 , shown in position to grip a full pallet layer; 
           [0046]      FIGS. 7A and 7B  are perspective views similar to  FIGS. 6A and 6B  respectively, showing the clamps applying pressure on the pallet layer and the curtains being partially closed; 
           [0047]      FIGS. 8A and 8B  are perspective views similar to  FIGS. 6A and 6B  respectively, showing the clamps having released some of the pressure on the pallet layer and the curtains being completely closed; 
           [0048]      FIG. 9  is a flowchart of a method for layer depalletizing according to a first illustrative embodiment; and 
           [0049]      FIG. 10  is a perspective of a clamp assembly according to a second illustrative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    In the following description, similar features in the drawings have been given similar reference numerals, and in order not to weigh down the figures, some elements are not referred to in some figures if they were already identified in a precedent figure. 
         [0051]    The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more. 
         [0052]    As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements. 
         [0053]    A tool  10  for layer depalletizing according to a first illustrative embodiment will now be described with reference to  FIGS. 1 to 5 . 
         [0054]    As shown in  FIG. 1 , the tool  10  according to the first illustrative embodiment is operatively mounted to an industrial robot arm  12 , which is conventionally coupled to a robot controller  14 . 
         [0055]    The expression “controller” should be construed broadly as including one or more electronic devices, including for example one or more computers that are configured with components and/or programmed with instructions that produce one or more functionalities, including controlling both a robot and a tool attached to the robot. 
         [0056]    The robot  12  is in the form a standard industrial articulated robot arm suitable for the application. A conventional robot arm can be used, such as ABB&#39;s or IRB 760, FANUC&#39;s M410, or any similar robot arm offered by other manufacturers like Kuka or Motoman for example. 
         [0057]    In the description and in the claim, the expressions ‘robot’ and ‘robot arm’ will be used interchangeably to mean a programmable system including articulated and/or movable members that can receive, control and move a tool. 
         [0058]    Since the operation of a robot and of a robot controller is believed to be well known in the art, it will not be described herein in more detail for concision purposes. 
         [0059]    As an input, a pallet (not shown), made of one or more layers  16  of products  18  (see  FIG. 6B  for example), is positioned in front of the robot  12 . Slip sheets (not shown) can be present between the layers  16  of products  18 . They can be removed with other means or left on the removed layer. The output includes one layer  16  removed from the pallet and placed for example on an outfeed conveyor (not shown). 
         [0060]    In some embodiments, the slip sheet positioned above the layer of products is removed at the same time. In this case, the layer  16  is placed for example on an outfeed conveyor and the slip sheet is dropped in a bin (not shown). 
         [0061]    Each layer  16  is made from a plurality of similar products  18  and each pallet is made of a plurality of layers  16 . The products  18  can be similar or different from one layer  16  to the other. Also, the layers  16  can be full or partial, i.e. products can cover the complete surface of the layer  16  or some free space or openings can be found on the surface of the layer  16 . 
         [0062]    The expression “product” should be construed herein as including any type of case, carton, tray, shrink wrapped bundle or tray, etc. Generally, the product is of a rectangular shape. They can contain bottles, cans, pouches, bags, etc. 
         [0063]    The product dimensions may vary greatly between each different type of product  18 . For example, their height can be between 2″ and 24″. 
         [0064]    The layer depalletizing tool  10  comprises a frame  20 , four side clamps  22 - 24  movably mounted to the frame  20  to grip and release a pallet layer  16 , two curtains  26  mounted to the frame under the clamps  22 - 24  to be inserted under a pallet layer  16  gripped by the clamps  22 - 24 , and a top pad  28 , mounted to the frame  20  above the clamps  22 - 24 . 
         [0065]    The frame  20  comprises two pairs of parallel walls  30 - 32  assembled so as to generally define a rectangular perimeter. Each wall  30  and  32  includes a bottom rectangular portion  34  and  36  respectively and an integral triangular portion  38  and  40  respectively. The two triangular portions  40  are slightly bent toward each other. 
         [0066]    The frame  20  further comprises two transversal rectangular hollow tubes  42  and  44 , extending respectively parallel to the walls  30  between the walls  32 , and parallel to the walls  32  between the walls  30 . Holes  45  (see  FIG. 6A ) are provided near the top of the triangular portions  38 - 40  of the walls  30 - 32 , where the hollow tubes  42  and  44  are secured, allowing passage for connectors and cables (not shown) through the walls  30 - 32  and then through the hollow tubes  42  and  44 . 
         [0067]    A mounting bracket  46  (see  FIG. 6A ) is secured to both hollow tubes  42  and  44 , at the intersection thereof and that allows attaching the tool  10  to the robot arm  12 . 
         [0068]    The frame components  30 - 44  are assembled using fasteners and/or welding and so are other parts of the tool  10  that are mounted to the frame  20 . 
         [0069]    The frame  20  is not limited to the above-described embodiment and other members can be provided to mount the tool  10  to the robot arm  12  and to operatively receive the other components thereof. 
         [0070]    As can be better seen in  FIG. 4 , each facing pair of side clamps  22  and  24  are slidably mounted to a respective track  43  and  45 , each fixed respectively underneath hollow tubes  42  and  44  for movement therealong via mounting assemblies  48  and  50  respectively. Since the mounting assemblies  48  and  50  are very similar, only the mounting of one of the clamp  22  to the frame  20  will be described herein in more detail. 
         [0071]    The mounting assembly  48  includes a bracket  52  that is slidably mounted to the hollow tube  42  via the track  43  thereunder, and attached to the distal ends of rods  60  of the two actuators  56 . The bar  54  fixedly connects the clamp  22  to the bracket  52 . The bar  54  is so mounted to the bracket  52  as to extend perpendicularly therefrom and to the clamp  22 . The clamp  22  is perpendicular to the hollow tube  42  in a plane that includes the bar  54 . 
         [0072]    Two pneumatic actuators  56  are provided between the hollow tube  42  and the bracket  52  to cause movement thereof, and therefore also the movement of the clamp  22  along the hollow tube  42 . More specifically, the body  58  of each actuator  56  is secured to the hollow tube  42  on respective lateral side thereof and the distal end of the rod  60  of the actuator is fixedly mounted to the bracket  52 . 
         [0073]    The clamps  22  and  24  are moved in parallel pair to grip a pallet layer from two opposite sides thereof and then from the other sides. The actuators  56  are therefore operated four (4) at first (secured on a same hollow tube  42  or  44 ), and then the other four simultaneously. According to another embodiment, all clamps  22  and  24  are actuated simultaneously. 
         [0074]    Providing the nominal dimension of a pallet layer  16 , each pair of clamps  22  and  24  are movable between an extended position to a retracted position where the clamps  22  or  24  apply a pressure onto the layer  16  from corresponding opposite sides. 
         [0075]    While the clamps  22  and  24  have different widths, clamps according to another embodiment may have the same width. 
         [0076]    Clamps according to another embodiment (not shown) are pivotally mounted to the frame. According to other embodiment (not shown), the clamps have other configuration than those illustrated herein, and are mounted to the frame so as to be differently movable relative to the frame. 
         [0077]    With reference to  FIGS. 5 ,  7 A and  8 B, both curtains  26  are defined by a series or metallic rolls  62  that are both slidably and rotatably mounted to the rectangular portions  34  of the frame  20  therebetween. Together, both curtains  26  extend along the full length of the portions  34 , each spanning half the length. 
         [0078]    More specifically, each roll  62  is provided at its longitudinal ends with hub portions  63  (see  FIG. 8B ) that are received in parallel tracks  64  mounted to the inner face of the frame  10 . Each of the four (4) tracks extends along the bottom edge  66  of the rectangular portion  34 , from the center thereof to the end of an accurate portion  68  of the tracks  64  that raises towards the triangular portion  38  near the longitudinal end side of the wall  30 . The arcuate portions  68  defines a curtain receiving portion when the curtains  26  are opened. 
         [0079]    It is to be noted that, in some Figures, some of the rolls  62  are not shown to alleviate the views. 
         [0080]    Each curtain  26  includes at its front end a rotating head  70 , which is slidably mounted in the tracks  64  along with the rolls  62  and also rotatably mounted to the tracks  64 . 
         [0081]    The rolls  62 , along with the head  70  of each curtain  26 , are moved along their respective tracks  64  by an actuator  72 . The body  74  of the actuator  72  is secured to the rectangular portion  34  of one of the wall  30  on the outer face thereof, and its rod  76  is fixedly mounted to the head  70  via a mounting bracket  78  ( FIG. 7B ) for translation of the head  70  in unison with the rod  76  along the track  79 , which is attached to the outer face of the rectangular portion  34 . 
         [0082]    When the curtains  26  open, the actuators  72  pushes the heads  70  along the tracks  64  forces the rolls  62  in the same direction. When the curtains  26  close, the actuators  72  pulls the heads  70  along the tracks  64  in the same direction. 
         [0083]    The heads  70  are in the form of a plurality of rotatable friction elements  80  extending along the front edge of each curtain  26 . The friction elements  80  are in the form of rubber O-rings mounted onto two parallel rolls  82  for rotation thereon in an endless manner. The two rolls  82  are rotatably mounted to the mounting brackets  78  therebetween. 
         [0084]    As can be better seen in  FIGS. 5 and 7B , the two rolls  82  of each curtain  26  are driven by a drive assembly including i) one side chain  84  extending along the straight portion of respective tracks  64 , and being mounted to a driving sprocket  86  and a driven sprocket  87 , the later fixed at the end of each roll  82 , ii) a drive  90  secured to the wall portion  34  and operatively coupled to one of the two chains  84  via a respective one of the driving sprockets  86 . The chains  84  are so positioned relative to the two rolls  82  via the sprockets  87  so that rolls  82  and associated chains  84  rotate in unison. Rotation of each drive  90  therefore causes the rotation of the O-rings  80 . A person skilled in the art will now appreciate that the head  70  can both rotate and slide along the tracks  64  at the same time and independently. 
         [0085]    An end roll  92  is provided between the two driven sprockets  88  of each curtain  26  to further ease the displacement of the heads  70  along the tracks  64  by linking the chains  85  located at each end of the heads  70  therefore assuring that the heads  70  remain perpendicular to the tracks  64 . 
         [0086]    It is to be noted that elements of the drive assembly, including the belts  84  have been omitted in some drawings to alleviate the views. 
         [0087]    With reference more specifically to  FIGS. 2-4 , the top pad  28  and its actuating mechanism will now be described. 
         [0088]    The top pad  28  is in the form of a plate that is movable towards and away a pallet layer  16  gripped by the clamps  22 - 24 . The top pad  28  is made movable by its mounting to the frame  10  via a pad actuating assembly  100 . The plate is made of a soft resilient material, such as rubber or plastic, which is reinforced on its non-contacting face with metal tubes. According to other embodiments, the pad  28  is made of another material and/or is not reinforced. 
         [0089]    The pad actuating assembly  100  includes four pad holder shafts  102 - 108  that are rotatably mounted to the frame  20 , eight pad holder wheels  110  mounted in parallel pairs on each shafts  102 - 108 , four link elements  112 , each secured to both the top pad  28  and the wheels  110  of a respective shaft  102 - 108  therebetween, four shaft pulleys  114 - 120 , each one secured near one end of each shaft  102 - 108 , a top pad linear actuator  122  secured to the frame  20 , a pulley assembly  124  fixedly mounted to the frame  20 , and four cables  126 - 132 , each one operatively coupling a respective shaft pulley  114 - 120  to the movable end of the actuator  122 . 
         [0090]    The four pad holder shafts  102 - 108  are rotatably mounted to the hollow tubes  42 - 44  via four support brackets  134 . Together the four shafts  102 - 108  are relatively positioned end to end in a square configuration. 
         [0091]    Each link elements  112  is secured to a respective pair of wheels  110  for partial winding thereon and fixedly to the plate  28  via an attachment  136 . 
         [0092]    The pulley assembly  124  includes a support  138 , secured to the hollow tube  42  so as to be positioned at the movable end of the actuator  122 , and three (3) intermediary pulleys  140 - 144  rotatably mounted to the support  138  thereunder. 
         [0093]    As can be better seen in  FIG. 3 , the intermediary pulleys  140 - 144  and the position and orientation of the actuator allows connecting the four shaft pulleys  114 - 120  to the actuator&#39;s rod  146  using the cables  126 - 132 . 
         [0094]    In operation, the top pad  28  is raised by causing the actuator  122  to retract its rod  146 , thereby simultaneously pulling onto the cables  126 - 132 . This causes the shafts  102 - 108  to simultaneously rotates, yielding a pulling force onto the link elements  112  that raises the top pad  28 . The reverse effect is obtained by extending the actuator rod  146 . 
         [0095]    The operation of the tool  10  will now be described with reference to  FIGS. 6A-8B  and to  FIG. 9 , which describes a full layer depalletizing method  200  according to an illustrative embodiment. 
         [0096]    When the robot controller  14  receives a signal indicative that a pallet layer  16  is ready to be picked (step  202 ), the controller  14  uses a received nominal position of the layer to be picked to command the robot  12  to position the tool  10  so that the clamps  22  and  24  surround the layer  16  (step  204 ) (see  FIGS. 6A and 6B ). 
         [0097]    It is to be noted that, for most layer depalletizing tools, systems and methods from the prior art, the positioning of the tool relies solely on the nominal vertical position of the layer. 
         [0098]    It is however known in the material handling industry that products  18  are often crushed within a pallet by the weight of the layer  16  or layers located above. This is of course particularly true for the last layers sitting directly on the pallet to be depalettized. Therefore, the nominal position of each layer  16 , used in the initial programming of the robot  12 , can lead to a wrong positioning of the tool, limiting the capacity of the system to adequately depalletize the layers  16 . 
         [0099]    The top pad  28  is coupled with a sensor (not shown) allowing to evaluate the real height/position of the top surface  148  of the layer  16  being picked, therefore enabling the tool  10  to be positioned more precisely. This added precision enables the depalletizing system, including the robot  12  and tool  10 , to be more efficient and reduces the probability of product damages or even avoid cases where the bad positioning prevents the products  18  of being depalettized. 
         [0100]    The sensor can be in the form of an analog laser distance sensor or any other similar means. 
         [0101]    In step  206 , the top pad  28  is lowered and positioned over the top layer on the pallet. 
         [0102]    The robot  12  positions the tool  10  to the theoretical height of the layer  16  to be picked. Knowing that the top pad  28  contacts the upper surface of the layer  16 , the sensor measures its position. The controller  14  then computes the real height of the layer  16  with the theoretical height and, if necessary, adjusts the tool  10  position accordingly. 
         [0103]    Using the top pad  28  to determine the real height of the top surface of the pallet represents a robust way to achieve this task. For example, even if a flap of a product  18  is lifted or a product  18  is not well positioned, the top pad&#39;s overall position is not affected and will therefore provide a valuable and precise information about the real height of the layer  16 . When needed, the robot  12  adjusts the height of the tool  10  (step  210 ). 
         [0104]    Considering that each layer  16  can be composed of a plurality of products  18 , it often happens that some products  18  have no side facing the exterior of the layer. According to the first illustrative embodiment, a combination of mechanisms is provided that allows the clamps to grip them adequately. 
         [0105]    First, the four clamps ( 22 - 24 ) are used to compress the whole layer on each side without horizontally moving the layer (step  212 ) by activating and controlling the pneumatic actuators  56 . 
         [0106]    The robot  12  then slightly lifts the tool  10  to create a gap mainly between the lower surfaces  150  of the products  18  located on the perimeter of the layer  16  and the top surface of the products  18  of the layer  16  just underneath (step  214 ). 
         [0107]    The closing of the horizontal curtains  26  is then initiated so that they are inserted under the layer  16  (step  216 ). This step is illustrated in  FIGS. 7A and 7B . 
         [0108]    The rotating friction heads  70  of the curtains  26  contribute to move the products  18  from the gripped layer  16  over the horizontal curtains  26 . This more specifically allows the products  18  that are not located on the perimeter of the layer  16  and that are generally only partially lifted by the side clamps  22 - 24  or sometimes not lifted at all to move over the horizontal curtains  26 . 
         [0109]    The friction created on the vertical faces of the products  18  by the pressure of the clamps  22 - 24  sometimes prevents the products  18  to move upward to enable the horizontal curtains  26  to close underneath without damaging the products  18 . When this happens, the pressure is automatically reduced on the side clamps  22 - 24  so the above mentioned friction is also reduced, therefore facilitating the movement of the curtains  26  to lift and pick the remaining products  18  of the layer  16  to be picked. 
         [0110]    Variation on the pressure of the clamps  22 - 24  is adjusted, in step  218 , by monitoring the linear movement of the horizontal curtains  26 . If a product  18  prevents this movement, the horizontal curtains  26  cannot move forward. When this happens, it is concluded that at least one product  18  is blocking the movement. Therefore, the pressure is reduced on the clamps  22 - 24  by the actuators  56  (step  220 ) to continue with the process of picking all the products  18  on the layer  16 . 
         [0111]    According to another embodiment, the linear movement of the curtains  26  is monitored so as to detect a movement resistance thereof even when the curtains continue to move. 
         [0112]    When the curtains  26  are completely closed (see  FIGS. 8A-8B ), the layer is completely gripped by the tool  10  (step  222 ), and the robot  12  moves the tool  10  with the gripped layer  16  and transfers the layer  16  to an outfeed location and the method continues with step  204 . 
         [0113]    In addition to the above-described function of allowing a precise assessment of the position of the top layer  16  of the pallet, the top pad  28  also prevents that small products  18  ““pop out” of the layer  16  as the horizontal curtains  26  move underneath. Such movement of products  18  would occur for example when the layer  16  is composed of small products  18 , i.e. products  18  with reduced height. The weight of the top pad  28  is sufficient to prevent the “pop out” effect of small products without limiting the capacity of the horizontal curtains  26  to go underneath them. Similarly, the top pad  28  prevents the small products  18  to “pop out” when the horizontal curtains  26  are removed from underneath the products  18 . 
         [0114]    In some applications, slip sheets (not shown) are provided between some layers  16  of products  18  in a pallet. A standard approach is to have an independent device that automatically removes the slip sheets between each layer depalletizing sequence. This approach works well but is quite expensive considering the addition of the independent device. 
         [0115]    According to a further embodiment (not shown), the tool for layer depalletizing is provided with a component that retrieves a slip sheet (not shown) located over the layer  16  of products  18  at the same time the layer  16  is depalettized. 
         [0116]    Since such a tool is similar to the tool  10 , and since this further method is similar to the method  200 , for concision purposes, only the differences therebetween will be described with reference to  FIG. 9 . 
         [0117]    The tool includes a top pad including suction cups (not shown) to remove any slip sheet over the layer  16  at the same time the layer  16  is depalettized. When the layer  16  is completely gripped by the tool (step  222 ), the suction cups are activated (step  224 ). Another laser sensor (not shown), which is facing downward towards the gripped pallet, or the same referred to hereinabove, is used to determine if there is a slip sheet attached to the top pad  28 . As the robot  12  lifts and transfers the layer  16 , the top pad  28  is slightly lifted (step  226 ). If the laser sensor still detects the presence of an object (step  228 ), this means that there is a slip sheet over the layer  16  being depalettized (step  229 ) and the vacuum is kept on the suction cups (step  230 ). The robot  12  then drops the slip sheet in a bin ( 236 ) after the layer  16  is placed on the outfeed conveyor (step  232 ) or somewhere else. In the contrary, if the sensor does not detect anything, this means that there is no slip sheet over the layer being depalettized. When such is the case, the vacuum is removed from the suction cups and the robot  12  directly moves back to pick the next layer  16  on the pallet once the previous layer  16  is placed on the outfeed conveyor (step  238 ). 
         [0118]    Turning now to  FIG. 10 , a further embodiment of the clamps  322  and  324  will now be described briefly. The clamps  322 - 324  are adapted for at least two different lengths and at least two different widths of pallet layers  16 . According to this embodiment, the lateral side portions of the clamps  322  and  324  are provided with respective fingers  326  and  328  that allows a first positioning of the clamps  322 - 324  for smaller pallet layers, wherein the fingers  326  and  328  are completely interlaced, i.e. two adjacent clamps  322  and  324  intersect near the proximate ends of their fingers  326  and  328 . A second positioning of the clamps  322 - 324  is further allowed for bigger pallet layers (not shown), wherein there is no interlacing between two adjacent clamps  322  and  324 . The clamps  322 - 324  can also take intermediary positions wherein there is partial interlacing between two adjacent clamps  322  and  324 . 
         [0119]    In such an embodiment of the clamps  322 - 324 , double stroke actuators (not shown) are used instead of the single stroke actuators  56 . When a smaller size pallet is depalettized, one stroke action of the double stroke actuator is kept retracted and only the other stroke action is used to open or closed the clamps. Such a shorter stroke movement reduces the travel of the clamps  322 - 324 , and thus the cycle time. 
         [0120]    When a larger size pallet is depalettized, one stroke action of the double stroke actuator is kept extended and only the other stroke action is used to open or closed the clamps. 
         [0121]    According to another embodiment, the layer depalletizing tool can grip more than one layer, depending of the products&#39; height and weight and the size of the clamps. 
         [0122]    It is to be noted that many other modifications could be made to the depalletizing tools and methods described hereinabove and illustrated in the appended drawings. For example:
       the robot arm can be replaced by a gantry type equipment or any other similar means;   the layer can be placed on an output conveyor, a pallet, a table, a platform, an AGV or any other means that can accept the layer;   in some applications, the tool is provided with only one pair of facing clamps;   the shape and length of the clamps may be different than those illustrated;   other friction reducing elements than the rotating heads  70  can be used in the front end of the horizontal curtains;   the mechanism to move the top pad towards and away the gripped pallet can be different than illustrated and so is the pad;   the various actuators to move the top pad, the side clamps and the curtains can be pneumatic, electric, servo driven or any other way;   other devices than a laser sensor can be used to confirm the presence of a slip sheet when a layer is being depalettized.       
 
         [0131]    It is to be understood that embodiments of the layer depalletizing tool are not limited in their application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. Other embodiments can be foreseen and practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation.