Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the provisional patent application No. 60/244,517 for a Multiple Robotic Workstation With Multiple Fixtures, filed on Oct. 31, 2000. This claim is made under 35 U.S.C. §119(e) and 37 C.F.R. 1.53(c)(3). 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a workstation having multiple robots and multiple fixtures, and more specifically, the invention provides welding workstations for automotive assembly lines having multiple independently-working welding robots and multiple fixtures for holding workpieces. 
     BACKGROUND OF THE INVENTION 
     The efficiency of a welding workstation can be defined by the amount of time, normally a percentage, that a welding robot spends welding compared to the total time required for a particular repetitive cycle. The efficiency of the workstation relates to the amount of time that a welding robot takes to perform various welding operations compared to the total amount of time that the welding robot requires for a particular repetitive cycle. Idle time for a welding robot can occur when a new workpiece is loaded and prepared in a fixture. If the workstation has one welding robot and one fixture, the welding robot will stand idle as a completed part is unloaded from the fixture and a new workpiece is loaded onto the fixture. In the prior art, this problem was addressed by adding a second fixture at the workstation within reach of a single welding robot. In a workstation with two fixtures, the welding robot can complete welding operations at one fixture while workpieces are being loaded and unloaded at the second fixture. When the welding process is complete at the first fixture, the welding robot can move to the second fixture and immediately commence welding. 
     The amount of time that a workpiece is positioned in a fixture while work is being performed compared to the total amount of time that a workpiece is positioned in a fixture corresponds to workpiece efficiency. The amount of time that a workpiece sits idle in a fixture reduces the overall operating capacity of the workstation by reducing throughput, normally reported in parts per hour or similar units for the overall assembly process. In a workstation having one fixture and one welding robot, the amount of time that a workpiece sits idle in the fixture is minimized because the welding robot immediately commences welding operations as soon as a workpiece is loaded and any other setup procedures are completed. However, in a workstation that has two fixtures and one welding robot, a workpiece is loaded onto one fixture, is setup, and then sits idle until the welding robot completes welding operations at the second fixture. Therefore, in a workstation having one fixture and one welding robot, the workpiece efficiency is maximized while in a workstation having two fixtures and one welding robot the welding efficiency is maximized. It is desirable to provide a workstation wherein the welding efficiency and the workpiece efficiency are both enhanced. 
     SUMMARY OF THE INVENTION 
     The present invention includes a workstation having multiple robots and multiple fixtures. The workstation can perform processing operations on multiple workpieces sequentially or simultaneously. The robots performing processing operations on the workpieces are disposed between the fixtures and are independently movable relative to each other. The fixtures can be rotatable about a horizontal axis to position one of two or four major surfaces in a ready position for receiving workpieces. Each major surface has a separate workpiece rest for receiving workpieces of different configurations. 
     The present invention also includes a plurality of similar workstations positioned in sequence along an assembly line. A transfer robot can be disposed in between adjacent workstations for moving workpieces from one workstation to the next. The present invention can also include a robot for processing the workpieces while held by the transfer robot in between the adjacent workstations. 
     The present invention also provides an electronic control means for coordinating the movements of the processing robots. The electronic control means is programmable for processing any mix of workpieces of different configurations in any sequential order. The electronic control means presents the appropriate workpiece nest in the ready position to receive the workpiece to be processed next and operates the plurality of robots in programmable sequence to perform the necessary welding in an efficient manner for the particular workpiece. 
    
    
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like workpieces throughout the several views, and wherein: 
     FIG. 1 is an overhead view of a workstation according to the present invention; and 
     FIG. 2 is a schematic view of an electronic control means for the workstation according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A workstation  10  according to the present invention includes a multiple robotic workstation with multiple fixtures for processing multiple workpieces  12  and  14  of the same or different configurations sequentially or concurrently. The workstation  10  of the present invention has at least two fixtures, a first fixture  16  and a second fixture  18 . The workstation  10  includes multiple robots located interposed between the fixtures  16 ,  18 . In a preferred embodiment of the present invention, the workstation  10  has three robots  20 ,  22  and  24  positioned in between the two fixtures  16 ,  18  with overlapping areas of reach between adjacent robots. 
     The fixtures  16  and  18  are operable to hold workpieces  12  and  14 , respectively, in position for a processing operation. Preferably, the fixtures  16  and  18  located at workstation  10  are capable of positioning a plurality of workpiece nests corresponding to the desired body style and model to be processed through the workstation  10 . In the preferred configuration, each of the fixtures  16  and  18  include four different workpiece nests positioned on four major surfaces of a fixture having a rectangular or square cross-section and rotatable about a horizontal axis A to position one of the four major surfaces in an upright, ready position for receiving workpieces to be processed at the workstation  10 . 
     The robots  20 ,  22  and  24  are positioned between fixtures  16  and  18  with overlapping areas of reach between adjacent robots, preferably so that at least two robots can reach all areas of the workpiece to be processed. The robots  20 ,  22  and  24  are independently movable with respect to each other. Also, the processing robots  20 ,  22  and  24  are capable of performing various independent work cycles at each fixture. As used herein, “work cycle” refers to a particular quantity and configuration of processing operations on a part  12  or  14 . In a preferred embodiment of the workstation  10 , three robots  20 ,  22  and  24  are positioned between the fixtures  16 ,  18 . However, the present invention can be practiced with more than three robots. By way of example and not limitation, the robots  20 ,  22  and  24  can be welding robots. Each robot can perform welding operations at both fixtures  16  and  18 . The robots  20 ,  22  and  24  are disposed between fixtures  16  and  18  so that each robot can perform welding operations at programmed areas of the fixtures  16  and  18 . By way of example and not limitation, as shown in FIG. 1, robot  24  can be used to perform welding operations at one end of fixture  18  and one end of fixture  16 , while robot  20  can be performing welding operations at the other end of fixture  18  and the other end of fixture  16 . In such an embodiment of the present invention, robot  22  can be used to perform welding operations in the middle of fixture  16  and the middle of fixture  18 . Further, the robot  22  can also be used for welding operations at either end of fixture  16  and fixture  18 . By way of example and not limitation, if part  12  requires relatively numerous welding operations at end  26  and part  14  requires numerous welding operations at end  28 , robots  22  and  24  can each be responsible for a portion of the total number of welding operations required for both ends  26  and  28  of the parts  12  and  14 . The workstation  10  of the present invention provides flexibility in distributing the relative work loads among the robots  20 ,  22  and  24 . 
     It is desirable in the present invention to provide a workstation  10  for performing welding operations on multiple workpieces  12  and  14  by multiple robots  20 ,  22  and  24  while enhancing the overall efficiency of the workstation  10 . The workstation  10  is operable to perform welding operations on different components simultaneously or sequentially. By way of example and not limitation, part  14  can be an automotive floor pan (not shown) while part  12  can be an automotive body side assembly. These different styles of workpieces can be simultaneously processed at the workstation  10 . Furthermore, the operation of the robots  20 ,  22  and  24  can be synchronized to process different workpieces. The floor pan of this example generally requires a greater amount of time to load and setup for welding than a right hand body side assembly. However, the right hand body side assembly requires a greater number of welding operations than a floor pan. Workstation  10  according to the present invention, can begin welding the right hand body side assembly with the welding robots  20 ,  22  and  24  as soon as the right hand body side assembly is loaded onto fixture  16 , while the floor pan is being loaded into fixture  18  and set up for welding. One or more of the welding robots  20 ,  22  and  24  can be repositioned once the floor pan has been loaded onto the fixture  18  and setup to weld a first series of welds, such as to attach brackets to the floor pan. After welding the brackets to the floor pan, the one or more robots can return to welding the right hand body side assembly, while additional components are set up with respect to the floor pan prior to returning for a second series of welds. For workpieces that require additional loading after one or more welding operations, the welding robots  20 ,  22  and  24  can move between the fixtures while the additional loading occurs and return to the workpiece when loading is complete. 
     The workstation  10  can also be positioned adjacent to an identical workstation  10   a . As shown in FIG. 1, two workstations  10 ,  10   a  can be positioned adjacent to each other on an automotive assembly line. In such a configuration, transfer robots  30  and  32  can move workpieces from one fixture at one workstation  10  to the next workstation  10   a  for processing by robots  20   a ,  22   a , and  24   a . The transfer robots  30  and  32  can grasp the respective workpieces at appropriate locations for lifting the workpieces out of the fixtures  16 ,  18  at the first workstation  10  and positioning the workpieces at the fixtures  16   a ,  18   a  at the second workstation  10   a . The transferring of workpieces between workstations  10 ,  10   a  can also be set to perform a processing operation. Robot  38  shown in phantom in FIG. 1 can be positioned above and between the two workstation  10 ,  10   a  for applying a sealant or an adhesive to the workpiece while being held by one of the transfer robots  30 ,  32  during movement between fixtures  16 ,  16   a  and  18 ,  18   a  respectively. By way of example and not limitation, transfer robot  30  can grasp the part  12  from end  26 , lift the part  12  out of the fixture  16  at the first workstation  10 , hold the part  12  in an elevated position between the workstations  10 ,  10   a , and allow the robot  38  to apply a sealant or an adhesive to the part  12  before the part  12  is loaded onto the fixture  16   a  at the second workstation  10   a.    
     The workstation  10  of the present invention can also include an electronic control means  40 . The electronic control means  40  can control the position of the welding robots  20 ,  22  and  24  according to programmed repetitive movements. The electronic control means  40  can include a central processing unit  42 . The central processing unit  42  can receive a signal corresponding to the configuration of the respective workpieces to be worked on next, and the number and position of welds to be performed on the workpiece. 
     The central processing unit  42  is operable to receive a signal relating to the configuration of the workpieces to be loaded next onto fixtures  16  and  18 , respectively. This information is used to recall the programmed repetitive movement for the robots to accomplish the desired welding operations to be performed to control the position of the welding robots  20 ,  22  and  24  during the welding cycle. An infinite variety of workpieces can be processed with various loading times, preparation times, and welding times according to the present invention. The present invention provides a workstation  10  having multiple processing robots  20 ,  22 ,  24  and multiple fixtures  16 ,  18  for processing multiple workpieces  12 ,  14  sequentially or simultaneously at an improved rate of workstation efficiency. 
     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 embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

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