Abstract:
A pallet stacking assembly line having at least two pick-and-place robots are used. The first robot has a relatively low position. The second robot is in an elevated position. A pallet dispenser dispenses a first pallet onto a pallet conveyor The pallet conveyor moves the first pallet to a first build position in front of the first robot. The first robot picks products from a first pick position and stacks them on the first pallet. Once the stack of products on the first pallet reach approximately half the finished stack height, the pallet conveyor carries the first pallet to a second build position in front of the second robot. At the same time, the pallet dispenser dispenses a second pallet which is carried to the first build position. The second robot picks products from a second pick position and places them on the upper portion of the stack on the first pallet to complete the stack. Meanwhile, the first robot is picking and placing products on the lower portion of the second pallet. The process continues indexing, with both robots ideally being busy all the time. Each robot builds half the stack on the pallet,

Description:
RELATED APPLICATION 
       [0001]    This is a continuation application of U.S. patent application Ser. No. 11/036,921, filed Jan. 14, 2005, the entirety of which is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to the field of manufacturing. More specifically, the invention comprises an assembly line featuring two or more pick-and-place robots that are offset vertically (as well as horizontally) in order to increase the speed of the assembly line. 
         [0004]    2. Description of the Related Art 
         [0005]    It has long been known to assemble items on a pallet for shipping and storage. The pallet provides a base of support, as well as a convenient lifting point. Items are stacked on the pallet to a desired height. The completed assembly is then typically bound together using shrink wrapping, banding, or other known methods. 
         [0006]    Pick-and-place robots are used to automate the assembly of products on a pallet. Conveyors carry the products to the robot, which then picks the products up, orients them correctly, and places them correctly on the pallet. Such robots are quite versatile, in that they can handle a variety of product sizes, shapes, and masses. With the addition of suitable product identifying means (bar codes and the like) and controlling software, the robot can “nest” various products into a volumetrically efficient stack. Such a robot can also be used to handle a variety of products simply by changing the controlling software. 
         [0007]    However, those skilled in the art will know that such robots are limited in operational speed. The robot must typically swing over to a pick station, grab a product, reorient the product, swing the product over the pallet, and properly place the product in the nested stack. These operations take time, and ultimately limit the speed of such an assembly line. Thus, an assembly line having the versatility of pick-and-place robots, yet with faster speed, is desirable. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    The present invention, in one embodiment, comprises a new type of pallet stacking assembly line.  FIG. 1  shows the major components of the embodiment. Two pick-and-place robots are used. The first robot has a relatively low position. The second robot is in an elevated position. A pallet dispenser dispenses a first pallet onto a pallet conveyor, The pallet conveyor then moves the first pallet to a first build position in front of the first robot. The first robot then begins picking products from a first pick position and stacking them on the first pallet. 
         [0009]    Once the products on the first pallet reach approximately half the finished height, the pallet conveyor carries the first pallet over to a second build position in front of the second robot. At the same time, the pallet dispenser dispenses a second pallet which is carried to the first build position. The second robot picks products from a second pick position and places them on the upper portion of the first pallet in order to complete the stack. Meanwhile, the first robot is picking and placing products on the lower portion of the second pallet. The process continues indexing, with both robots ideally being busy all the time. Each robot only has to build half the pallet. Thus, overall line speed is increased. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is a perspective view, showing the proposed invention. 
           [0011]      FIG. 2  is a perspective view, showing a typical pick-and-place robot. 
           [0012]      FIG. 3A  is a detail view, showing a pick position. 
           [0013]      FIG. 3B  is a detail view, showing a pick position. 
           [0014]      FIG. 4  is a perspective view, showing the operation of the present invention. 
           [0015]      FIG. 5A  is a perspective view, showing the operation of the present invention. 
           [0016]      FIG. 5B  is a perspective view, showing the operation of the present invention. 
           [0017]      FIG. 6A  is a perspective view, showing the operation of the present invention. 
           [0018]      FIG. 6B  is a perspective view, showing the operation of the present invention. 
           [0019]      FIG. 7  is an elevation view, showing an alternate embodiment of the proposed invention. 
           [0020]      FIG. 8  is an elevation view, showing an alternate embodiment of the proposed invention. 
       
    
    
     REFERENCE NUMBERS IN THE DRAWINGS 
       [0021]      10  pallet stacking line 
         [0022]      12  product conveyor 
         [0023]      14  product 
         [0024]      16  pallet conveyor 
         [0025]      18  pallet dispenser 
         [0026]      20  pallet 
         [0027]      22  first pick position 
         [0028]      24  second pick position 
         [0029]      26  first build position 
         [0030]      28  second build position 
         [0031]      30  first robot 
         [0032]      32  second robot 
         [0033]      34  base 
         [0034]      36  first pivot 
         [0035]      38  second pivot 
         [0036]      40  third pivot 
         [0037]      42  fourth pivot 
         [0038]      44  fifth pivot 
         [0039]      46  lifting attachment 
         [0040]      48  turret 
         [0041]      50  first arm 
         [0042]      52  second arm 
         [0043]      54  first robot pedestal 
         [0044]      56  second robot pedestal 
         [0045]      58  inside feed belt 
         [0046]      60  outside feed belt 
         [0047]      64  through-feed gate 
         [0048]      66  ramp 
         [0049]      68  stop 
         [0050]      70  third pick 
         [0051]      72  third robot 
         [0052]      74  third robot pedestal 
         [0053]      76  alternate stacking line 
         [0054]      78  wrist 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0055]      FIG. 1  shows one embodiment of the present invention. Pallet stacking line  10  is built around pallet conveyor  16 . Pallet dispenser  18  dispenses single pallets onto pallet conveyor  16  at appropriate times. The pallets are then carried down the pallet conveyor to first build position  26  and second build position  28 . 
         [0056]    First robot  30  is mounted atop first robot pedestal  54 . It is positioned next to first build position  26 . Second robot  32  is mounted atop second robot pedestal  56 , alongside second build position  28 . 
         [0057]    The assembly line is configured to stack products  14  onto pallets. Product conveyor  12  conveys the products to the robots. Those skilled in the art will know that such a conveyor can assume many forms. The version shown in  FIG. 1  may actually be two conveyors placed side by side in order to increase the delivery of products. The drawing view shows a simplified rendition of this product conveyor. The reader should bear in mind that many other types could be substituted for the belt-type shown. These would include simple gravity feeders, vibratory feeders, and the like. 
         [0058]    Two separate pick positions are provided, with the term “pick position” meaning a location where the products are stationary for a period sufficient to allow them to be grabbed by a robot. The product conveyor in  FIG. 1  feeds initially to second pick position  24 , under second robot  32 , down ramp  66 , under first robot  30 , and from there to first pick position  22 .  FIG. 3A  shows a detail view of second pick position  24 . The products are fed in from the left side of the view. Inside feed belt  58  and outside feed belt  60  independently feed products along. These belts preferably feed products along in such a manner that any product picked by a robot from pick position  24  is rapidly replaced. Two through-feed gates  64  regulate the flow of products out of the second pick position and down ramp  66 . These through feed gates can be lowered flush with or below the level of the conveyor belts, so that products can pass over them. 
         [0059]      FIG. 3B  shows a detail view of first pick position  22 . It features stops  68 , which prevent any product going beyond the first pick position. Such conveyors and controlling gates are well known to those in the art. However, a brief description may be helpful. Still referring to  FIG. 3B , when first robot  30  removes a product from the first pick position, the appropriate conveyor is activated to feed a new product into position. 
         [0060]    Of course, those products reaching the first pick position must first pass through the second pick position. Looking at  FIG. 3A , if the second robot picks a product off inside feed belt  58 , the appropriate conveyor is activated to feed a new product to the void. If additional products are needed down at first pick position  22 , the far through-feed gate  64  can be opened for a period to pass products through the second pick position, down the ramp, and over to the first pick position, while the second robot is placing the product just picked. Using this approach, product conveyor  12  keeps a steady supply of products at the two pick positions. 
         [0061]      FIG. 2  shows a typical pick-and-place robot (in this case; second robot  32  from the line shown previously). Base  34  attaches the robot to its mount. First pivot  36  allows turret  48  to rotate with respect to base  34 . Second pivot  38  allows first arm  50  to pitch with respect to turret  48 . Third pivot  40  allows second arm  52  to pitch with respect to first arm  50 . Fourth pivot  42  allows wrist  78  to pitch with respect to second arm  52 . Fifth pivot  44  allows lifting attachment  46  to rotate with respect to wrist  78 . The lifting attachment also includes devices for lifting a product, such as plates which pinch together, suction points, or similar devices. 
         [0062]    Robots such as shown in  FIG. 2  are very flexible. They can handle a variety of different products placed in a variety of different ways. Because of these facts a single assembly line can be used to handle a variety of products—such as cardboard boxes one day and soda bottles the next. However, those skilled in the art will know that such flexible robots are often not as fast as custom-configured machinery. The present invention seeks to ameliorate this speed limitation. 
         [0063]      FIGS. 4 through 6B  illustrate the proposed assembly line in operation. In  FIG. 4 , pallet dispenser  18  has dispensed a pallet  20  onto pallet conveyor  16 . The pallet is then moved down the line and brought to rest at first build position  26 . First robot  30  is then activated. It picks products from first pick position  22  and stacks them on the pallet. 
         [0064]    In  FIG. 5A , the stack of products  14  on pallet  20  is approaching one half the total specified height of the completed pallet.  FIG. 5B  shows the operation just after the first half of the stack has been completed. At this point, the first robot has paused. Pallet conveyor  16  is activated to move the first pallet from first build position  26  to second build position  28  (moving from left to right in the view). The pallet dispenser is activated while this move is ongoing in order to place a second pallet on the pallet conveyor.  FIG. 5B  shows this second pallet approaching first build position  26 . This second pallet is dispensed so that as the first pallet reaches the second build position, the second pallet reaches the first build position. 
         [0065]    Once the first pallet reaches second build position  28  and the second pallet reaches first build position  26 , second robot  32  begins picking products from the second pick position and stacking them on the first pallet in order to build the upper half of the stack. At the same time, first robot  30  is starting anew stack on the second pallet.  FIG. 6A  shows this step in the process, with both robots in operation ( FIG. 6A  shows the two pallets after the robots have completed about 70% of their respective stacking tasks). 
         [0066]    Once the stack on the first pallet is completed, the entire process indexes one position (The pallet at the second build position is completed and moved down the line; the pallet at the first build position moves to the second build position; and a fresh pallet is placed on the first build position).  FIG. 6B  shows this step in the process. The reader will note that the leading pallet  20  supports a completed stack of products and is moving down the line (from left to right in the view). The next pallet  20  supports one half of a completed stack and is moving to second build position  28 . The pallet dispenser is also dispensing a new (empty pallet), which is moving toward first build position  26 . 
         [0067]    The reader will thereby realize that the two robots are in nearly continuous operation, with the first robot building the lower half of each pallet stack and the second robot building the upper half of each pallet stack. The line&#39;s productivity is nearly doubled, since during most of the cycle two pallets are being loaded instead of only one. This productivity enhancement can be easily understood by contemplating the rate at which completed pallets pass down the pallet conveyor. In the conventional approach—using only one robot—a completely stacked pallet rolls down the line at a time interval equal to the time needed for a single robot to stack all the products on the pallet. 
         [0068]    Using the approach shown in  FIG. 6B , a completed pallet moves away from the second build position every time the line “indexes” (moves a pallet from build position to build position). This indexing occurs at a time interval equal to the time needed for a single robot to stack one half of the products on the pallet. Thus, the production rate is nearly doubled. It is not exactly doubled, since some time is lost moving the pallets from station to station, but this time loss is minimal. 
         [0069]    The approach shown has other advantages as well. A robot having a range of motion encompassing the entire pallet stack is no longer needed. The placing of the second robot at a higher elevation allows the use of a relatively small robot having a relatively limited range of motion. This fact means that the same type of robot can be used for both build positions. 
         [0070]    Of course, those skilled in the art will realize that the approach just described is not limited to the use of two robots. A two-robot approach implies dividing the pallet stack into a lower half and an upper half. If three robots are used, then the pallet stack can be divided into a lower third, a middle third, and an upper third.  FIG. 7  shows such an embodiment, employing first robot  30 , second robot  32 , and third robot  72 . 
         [0071]    Third robot  72  sits atop third robot pedestal  74 . A product conveyor is used as before, but the version shown in this embodiment has three pick positions, including the addition of third pick position  70  proximate third robot  72 . The robots are vertically staggered so that the first robot&#39;s range of motion encompasses the lower third of the pallet stack, the second robot&#39;s range of motion encompasses the middle third of the pallet stack, and the third robot&#39;s range of motion encompasses the upper third of the pallet stack. 
         [0072]    The line shown in  FIG. 7  allows simultaneous operations on three pallets, with one being proximate each robot. While the first robot is stacking the lower third, the second robot will be stacking the middle third and the third robot will be stacking the upper third. This configuration nearly triples the output speed of the assembly line. Of course, the approach can be expanded to use four or more robots in such a vertically staggered arrangement. 
         [0073]    A linear assembly line has been illustrated thus far, but those skilled in the art will know that many line configurations can be developed using the present invention.  FIG. 8  shows one such approach, designated as alternate stacking line  76 . This version uses a pallet conveyor with a ninety degree bend. Two adjoining belts are used, along with a stop gate and various control features. All these assembly line components are conventional and—as they do not form a novel portion of the present invention—they will not be described in further detail. The reader will observe that the pallets pass through first build position  26  and second build position  28 , then change direction to travel further down the line. 
         [0074]    First robot  30  and second robot  32  are vertically staggered as before, with second robot pedestal  56  being significantly taller. A differed type of product conveyor is used. The product conveyor  12  shown in  FIG. 8  approaches the build position from a perpendicular direction. Rather than feeding the products through one pick position to reach the next, it simply feeds the two pick positions simultaneously. Short inclined sections are used in order to place second pick position  24  at a higher elevation than first pick position  22 . This elevation offset places each respective pick position closer to its respective robot. 
         [0075]    Of course, a single pick position can be used for both robots. Such a pick position can be placed at an intermediate elevation. However, line speed is generally enhanced by providing a dedicated pick position for each robot. It also generally allows the use of a robot with a smaller range of motion. 
         [0076]      FIG. 8  shows only one example of many of the line configurations which can be conceived. Line layouts are often dictated by the available floor space and the placement of other components in the overall assembly process. The reader will understand that the novel features of the present invention could be incorporated into literally hundreds of different assembly lines having different appearances. 
         [0077]    Although the preceding descriptions contain significant detail they should not be viewed as limiting the invention but rather as providing examples of the preferred embodiments of the invention. As one example, many types of robots can be substituted for the conventional “arm” units shown in the illustrations. Gantry-type robots can function just as well using the vertically-staggered approach. Accordingly, the scope of the invention should be determined by the following claims, rather than the examples given. 
         [0078]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.