Abstract:
A multi-spindle end effector is provided for a multiple axis robot. The multi-spindle end effector includes a plate housing having at least a pair of spaced-apart spindles mounted thereon. A servo-motor drivingly engages the spindles. A gear box steps down the RPMs of the motor to the desired RPM of the object to be rotated. A timing belt, which may be continuous, interlinks the first and second spindles so that the rotation of first spindle matches the rotation of the second spindle. An idler pulley may be employed to properly tension the belt.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/292,240 filed May 18, 2001. The disclosure of the above application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally relates to end effectors for robotic units and, more particularly, to a multi-spindle end effector for rotatably supporting multiple objects to be rotated. 
     2. Discussion 
     Many objects of manufacture require deburring, grinding, buffing and/or polishing prior to being deemed acceptable as a finished product. For example, many chrome parts, such as wheels for automotive vehicles, motorcycle parts, and plumbing and lock hardware, require such buffing and polishing. Manual performance of these tasks is difficult and labor intensive. 
     To expedite the processing of such articles of manufacture, automated polishing and buffing is sometimes employed. To date, the most successful technique for polishing and buffing through an automated mechanism involves the use of a six axis robot which positions the object of manufacture adjacent polishing and/or buffing wheels. A six axis robot is particularly well-suited for this purpose since it can be programmed to move from a staging area where a worker loads the object of manufacture onto the sixth axis mounting surface of the robot. Thereafter, the robot moves the object of manufacturer away from the staging area to a work area where buffing and polishing are performed. 
     While such six axis robots have provided a vast improvement over manual polishing and/or buffing, there is still room for improvement in the art. For example, conventional buffing and polishing robots are limited to manipulation of one object of manufacture at a time. This limits production capacity. 
     In view of the foregoing, it would be desirable to provide an automated mechanism for simultaneously processing a plurality of objects of manufacture. 
     SUMMARY OF THE INVENTION 
     The above and other objects are provided by a multi-spindle end effector for a six axis robot. The multi-spindle end effector includes a plate housing having at least a pair of spaced-apart spindles mounted thereon. A servo-motor drivingly engages the spindles. A gear box steps down the RPMs of the motor to the desired RPM of the object to be rotated. A timing belt, which may be continuous, interlinks the first and second spindles so that the rotation of first spindle matches the rotation of the second spindle. An idler pulley may be employed to properly tension the belt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to appreciate the manner in which the advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings only depict preferred embodiments of the present invention and are not therefore to be considered limiting in scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIG. 1 is a perspective view of a six axis robot suitable for working in conjunction with the multi-spindle end effector of the present invention; 
     FIG. 2 is a side view of the multiple spindle end effector of the present invention; 
     FIG. 3 is a plan view of a wheel mounting mechanism of the end effector of the present invention; 
     FIG. 4 is a plan view of the multi-spindle end effector of the present invention; 
     FIG. 5 is a front view of the sixth axis mounting surface of the robot illustrated in FIG. 1; 
     FIG. 6 is a side view of an idler pulley of the end effector of the present invention; 
     FIG. 7 is a side view of the end effector of the present invention coupled to the sixth axis mounting surface of the robot in FIG. 1; 
     FIG. 8 is a plan view of a second embodiment multi-spindle end effector of the present invention; 
     FIG. 9 is a side view of the multi-spindle end effector of FIG. 8; 
     FIG. 10 is a bottom view of the multi-spindle end effector of FIG. 8; 
     FIG. 11 is a side view of the multi-spindle end effector of FIG. 8 coupled to the sixth axis mounting surface of the robot in FIG. 1; 
     FIG. 12 is a plan view of a third embodiment multi-spindle end effector of the present invention; 
     FIG. 13 is a plan view of a fourth embodiment multi-spindle end effector of the present invention; 
     FIG. 14 is a plan view of a fifth embodiment multi-spindle end effector of the present invention; and 
     FIG. 15 is a plan view of a sixth embodiment multi-spindle end effector of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     The present invention is directed toward a multi-spindle end effector for a six axis robot. The multi-spindle end effector enables a plurality of objects of manufacture, such as wheels, motorcycle parts, plumbing fixtures, and builders and lock hardware to be simultaneously processed. For example, the multi-spindle end effector of the present invention is well suited to simultaneously rotate a pair of wheels for buffing and polishing. 
     Turning now to the drawing figures, FIG. 1 illustrates a six axis robot  10  suitable for use in conjunction with the multi-spindle end effector of the present invention. Although other multi-axis robots may be suitable for use herein, it is presently preferred to employ a FANUC Robotics S-430iW robot (165 Kg). This robot operates well in confined spaces and can handle the payload of the end effector. If a greater payload is required, other robots may be used such as FANUC Robotics R2000 (200 kg) or 5900 (400 kg). 
     The robot  10  includes a first axis of movement  12 , second axis of movement  14 , a third axis of movement  16 , a fourth axis of movement  18 , a fifth axis of movement  20 , and a sixth axis of movement  22 . The sixth axis of movement  22  enables a wrist  24  of the robot  10  to rotate while the fifth axis of movement  20  enables the wrist  24  to pivot. These ranges of motion are beneficial for manipulating the end effector as described below. 
     Turning now to FIG. 2, an end effector assembly  26  is illustrated coupled to the wrist  24  of the robot  10  illustrated in FIG.  1 . The end effector  26  includes a plate housing  28  which is preferably formed as an aluminum weldment to minimize weight without sacrificing strength. The plate housing  28  includes a base  30  surrounded by an integrally formed annular rib  32  (shown in phantom). The annular rib  32  stiffens the plate housing  28  while minimizing additional weight. 
     The base  30  includes a centralized recessed portion  34  where the end effector  26  is fixedly secured, e.g., bolted, to the wrist  24 . The recessed portion  34  positions the center of gravity of the end effector  26  axially away from the distal end of the wrist  24 . This saves wear and tear on the robot  10  (FIG.  1 ). 
     The plate housing  28  rotatably supports a laterally projecting first spindle  36  at one end and a laterally projecting second spindle  38  at an opposite end. Preferably, the first spindle  36  and second spindle  38  are formed of aluminum to minimize weight without sacrificing strength. The first and second spindles  36  and  38  preferably project parallel to one another and are spaced apart by a sufficient amount to ensure clearance of the objects of manufacture to be mounted thereto. For example, the preferred embodiment of the present invention can rotatably support a pair of vehicle wheels having diameters ranging from thirteen to twenty-six inches or a wide range of other parts such as motorcycle and plumbing fixtures. 
     The first spindle  36  is drivingly connected to one end of a gear box  40  mounted to the plate housing  28 . A second end of the gear box  40  is drivenly connected to a drive shaft of a servo-motor  42 . As such, rotation of the drive shaft of the servo-motor  42  is transferred through the gear box  40  to the first spindle  36 . 
     The servo-motor  42  provides a seventh axis of rotation for the robot  10  (FIG.  1 ). To minimize the weight extending beyond the end of the wrist  24 , the servo-motor  42  preferably extends opposite the first spindle  36  relative to the plate housing  28 . Although other motors may be suitable for use herein, it is presently preferred to employ a Fanuc Alpha 6/3000 motor. Larger motors may also be used. A 1.9 HP version of this motor preferably includes a straight drive shaft and a brake and has a speed of up to 3000 RPMs. The motor  42  is controllable to start and stop, index, “free wheel”, or reverse the objects coupled thereto. 
     The gear box  40  reduces the RPMs of the motor  42  transferred to the first spindle  36 . While different articles of manufacture require different RPMs depending on their final processing needs, it is presently preferred to reduce the RPMs of the first spindle  36  to a range of between 0 and 50 RPMs. Although other gear boxes may be suitable for use herein, it is presently preferred to employ an Alpha Gear TP 050 Gearhead reducer. Variant 1 of this two stage gearbox preferably has a reduction ratio of about 61:1. 
     The second spindle  38  is rotatably supported relative to the plate housing  28  by a spindle housing  44 . To minimize the weight extending beyond the end of the wrist  24 , the spindle housing  44  preferably extends opposite the second spindle  38  relative to the plate housing  28 . The spindle housing  44  includes a shroud  46  and a shaft  48  rotatably supported by a pair of steel bearings  50 . A driven pulley  52  (described below) is non-rotatably secured, e.g., splined, to the shaft  48 . 
     A driving pulley  56  is non-rotatably connected, e.g., splined, to the first spindle  36 . A synchronizer in the form of a timing belt  58  meshingly engages the driving pulley  56  and driven pulley  52  such that they are interconnected. The belt  58  preferably consists of rubber and includes teeth distributed thereabout. The belt  58  transfers the rotation of the first spindle  36  by the motor  42  (and gear box  40 ) to the second spindle  38  at a one-to-one ratio such that the rotation of the spindles  36  and  38 , as well as the objects of manufacture mounted thereto, is matched. To save weight, the driving pulley  56  and driven pulley  52  are preferably formed of aluminum. 
     A first object of manufacture in the form of an aluminum wheel  60  is non-rotatably connected to the first spindle  36  by a first pin  62 . The first pin  62  passes through a central orifice  64  in a locator plate  66  and frictionally wedges within an axial bore  68  of the first spindle  36 . A locating/indexing member  70  interengages the locator plate  66  and the wheel  60  to ensure that the wheel  60  adopts a pre-selected orientation when mounted to the end effector  26 . Preferably, different locator plates are employed depending upon the configuration of the object of manufacture to be secured to the end effector  26 . For example, complimentary bolt patterns should be ensured. 
     A wheel holder assembly  72  further secures the wheel  60  to the first spindle  36 . Referring now to FIG. 3, a detailed illustration of the wheel holder assembly  72  is illustrated. If another object of manufacture was to be supported on the end effector, the wheel holder assembly  72  may not be necessary. 
     The wheel holder assembly  72  includes a support arm  74  mounted to the locator plate  66 . The support arm  74  includes a support  76  slidably supporting a radially extending piston  78 . The piston  78  is biased in an outboard direction by a biasing member in the form of a spring  80 . A moveable arm  82  laterally extends from a free end of the piston  78 . In a first position, the distal end  86  of the arm abuttingly engages an edge of the wheel  60  to secure it in place while being processed. In a second position, the wheel  60  can be removed. 
     Referring again to FIG. 2, a second object of manufacture in the form of a wheel  90  is mounted to the second spindle  38 . A second pin  92  passes through a central orifice  94  in a locator plate  96  and frictionally wedges within an axial bore  98  of the second spindle  38 . A locating/indexing member  100  interengages the locator plate  96  and the wheel  90  to ensure that the wheel  90  adopts a pre-selected orientation (i.e., matching that of the first wheel  60 ) when mounted to the end effector  26 . A wheel holder assembly  102 , which is preferably identical to the wheel holder  72  described above, further supports the wheel  90  relative to the second spindle  38 . 
     Turning now to FIG. 4, a front view of the end effector  26  is illustrated. The plate housing  28  is generally shaped as an offset diamond and includes a plurality of elongated ribs  104  for added strength. The plate housing  28  also includes a plurality of mounting holes, generally shown at  106 , in the recessed portion  34  for accommodating fasteners such as bolts to secure the end effector  26  to the wrist  24  of the robot  10  (FIG.  1 ). 
     Referring to FIG. 5, the wrist  24  has a pre-selected bolt pattern  107  to which the mounting holes  106  (FIG. 4) are designed to match. 
     Referring again to FIG. 4, a pair of idler pulleys  108  and  110  are rotatably and slidably mounted to a pair of slots  112  and  114  formed in the base  30  of the end effector  26 . By selectively positioning the pair of idler pulleys  108  and  110  along their respective slots  112  and  114 , the tension of the belt  58 , which synchronizes the rotation of the first wheel  60  and second wheel  90 , is controlled. Maintaining proper tensioning on the belt  58  prevents belt slippage to ensure that the wheels  60  and  90  rotate in phase. 
     Turning to FIG. 6, the idler pulley  108  is illustrated in greater detail. Although only idler pulley  108  is illustrated, the idler pulley  110  (FIG. 4) is preferably identical thereto. The idler pulley  108  includes a sleeve  116  rotatably mounted on a shaft  118  of a jam nut  120 . An aluminum pulley wheel  122  is coupled to the sleeve  116  and accommodates the belt  58 . The jam nut  120  is selectively positionable along the slot  112  such that a desired tension can be placed on the belt  58  and then the idler pulley  108  can be locked in place. 
     Turning now to FIG. 7, a side view of the end effector  26  is illustrated with the wrist  24  of the robot  10  (FIG.  1 ). By vertically pivoting the wrist  24  about the fifth axis of movement  20 , the end effector  26  can be moved in an arc. This is advantageous for positioning the objects of manufacture relative to buffing and/or polishing stations. Further, the end effector  26  can be rotated by rotating the wrist  24  about the sixth axis of movement  22 . 
     Referring now collectively to all the FIGS. 1-7, in operation, the robot  10  is programmed to position the end effector  26  at a loading station. An operator loads the wheels  60  and  90  onto the first and second spindles  36  and  38  respectively. By using the locating members  70  and  100 , the wheels  60  and  90  are commonly aligned. Thereafter, the robot  10  positions the wheels  60  and  90  adjacent select buffers. The servo-motor  42  rotates the first spindle  36  and wheel  60  by way of the gear box  40 . The rotation of the spindle  36  is transferred to the second spindle  38  by way of the driving pulley  56 , belt  58 , and driven pulley  52 . Since the first and second spindles  36  and  38  are interconnected by the belt  58 , the rotation of the wheels  60  and  90  is synchronized. After polishing and/or buffing, the wheels  60  and  90  are removed. 
     Turning now to FIGS. 8-10 a second embodiment end effector according to the present invention is illustrated. Whereas the first embodiment of FIGS. 2-7 is particularly tailored to accommodate two objects to be rotated, the second embodiment is particularly tailored to accommodate four objects to be rotated. 
     The second embodiment end effector assembly  226  includes a plate housing  228  which is preferably formed as an aluminum weldment to minimize weight without sacrificing strength. As most clearly illustrate in FIG. 9, the plate housing  228  includes a base  230  surrounded by an integrally formed annular rib  232 . The annular rib  232  stiffens the plate housing  228  while minimizing additional weight. 
     The base  230  includes a centralized portion  234  where the end effector  226  is fixedly secured, e.g., bolted, to the wrist  224 . If desired, the portion  234  may be recessed relative to the base  230  to position the center of gravity of the end effector  226  axially away from the distal end of the wrist  224 . This may save wear and tear on the robot  10  (FIG.  1 ). 
     The plate housing  228  rotatably supports a plurality of objects to be rotated (not shown) by way of a plurality of laterally projecting spindles  236   a-d . The spindles  236   a-d  are preferably distributed along a common edge of the plate housing  228 . The spindles  236   a-d  are preferably formed of aluminum to minimize weight without sacrificing strength. The spindles  236   a-d  preferably project parallel to one another and are spaced apart by a sufficient amount to ensure clearance of the objects of manufacture to be mounted thereto. For example, this embodiment of the present invention can rotatably support four of vehicle wheels having diameters ranging from fourteen to twenty-six inches. 
     A gear box  240  is mounted to the plate housing  228 . A servo-motor  242  is drivingly connected through a gear box  240  to a driving pulley  256 . Rotation of the drive shaft of the servo-motor  242  is transferred through the gear box  240  to the driving pulley  256 . The servo-motor  242  provides a seventh axis of rotation for the robot  10  (FIG.  1 ). 
     To minimize the weight extending beyond the end of the wrist  224 , the servo-motor  242  preferably extends opposite the driving pulley  256  relative to the plate housing  28 . Although other motors may be suitable for use in this embodiment, it is presently preferred to employ a Fanuc Alpha 6/3000 motor. A 1.9 HP version of this motor preferably includes a straight drive shaft and a brake and has a speed of up to 3000 RPMs. The motor  242  is controllable to start and stop, index, “free wheel”, or reverse the objects coupled thereto. 
     The gear box  240  reduces the RPMs of the motor  242  transferred to the driving pulley  256 . While different articles of manufacture require different RPMs depending on their final processing needs, it is presently preferred to reduce the RPMs of the driving pulley  256  to a range of between 0 and 50 RPMs. Although other gear boxes may be suitable for use herein, it is presently preferred to employ an Alpha Gear TP 050 Gearhead reducer. Variant 1 of this two stage gearbox preferably has a reduction ratio of about 61:1. 
     The spindles  236   a-d  are rotatably supported relative to the plate housing  228  by a plurality of spindle housings  244   a-d . To minimize the weight extending beyond the end of the wrist  224 , the spindle housings  244   a-d  preferably extend opposite the spindles  236  relative to the plate housing  228 . Each of the spindle housings  244   a-d  includes a shroud  246  and a shaft  248 . 
     A driven pulley  252  (described below) is non-rotatably secured, e.g., splined, to each of the shafts  248 . A driving pulley  256  is non-rotatably connected, e.g., splined, to the motor  242  by way of the gear box  240 . A synchronizer in the form of a timing belt  258  meshingly engages the driving pulley  256  and driven pulleys  252  such that they are interconnected. The belt  258  preferably consists of rubber and includes teeth distributed thereabout. 
     The belt  258  transfers the rotation of the driving pulley  256  by the motor  242  (and gear box  240 ) to the spindles  236   a-d  at a one-to-one ratio such that the rotation of the spindles  236   a-d,  as well as the objects of manufacture mounted thereto, is matched. To save weight, the driving pulley  256  and driven pulleys  252  are preferably formed of aluminum. 
     An object of manufacture such as the aluminum wheels of the first embodiment are non-rotatably connected to each of the spindles  236 . For clarity, these objects of manufacture are not illustrated in FIGS. 8-10. Nonetheless, one skilled in the art will readily appreciate that they are preferably coupled thereto as described above. When mounted, each wheel adopts a preselected orientation when mounted to the end effector  226 . 
     As best seen in FIG. 8, the plate housing  228  is generally shaped as a triangle and may include one or more elongated ribs  204  for added strength. The plate housing  228  also includes a plurality of mounting holes, generally shown at  206  in the portion  234  for accommodating fasteners such as bolts to secure the end effector  226  to the wrist  224 . The wrist  224  will generally have a pre-selected bolt pattern to which the mounting holes  206  are designed to match. 
     As shown in FIGS. 8-10, a plurality of idler pulleys  208   a  and  b  are rotatably and slidably separately mounted to a plurality of slots  212   a  and  b  formed in the base  230  of the end effector  226 . By selectively positioning the idler pulleys  208   a  and  b  along each respective slots  212   a  and  b,  the tension of the belt  258 , which synchronizes the rotation of the driven pulleys  252   a-d,  is controlled. Maintaining proper tensioning on the belt  258  prevents belt slippage to ensure that the objects to be rotated rotate in phase. As one skilled in the art will appreciate, the idler pulleys  108   a  and  b  are preferably constructed as described above. 
     Turning now to FIG. 11, a side view of the end effector  226  is illustrated with the wrist  224  of the robot  10  (FIG.  1 ). By vertically pivoting the wrist  224  about the fifth axis of movement  20 , the end effector  226  can be moved in an arc. This is advantageous for positioning the objects of manufacture relative to buffing and/or polishing stations. Further, the end effector  226  can be rotated by rotating the wrist  224  about the sixth axis of movement  22 . 
     Turning now to FIG. 12, a third embodiment of the present invention is illustrated. This embodiment is particularly tailored to accommodate three objects to be rotated. The third embodiment is similar in principle to the prior embodiments but includes three mounting positions for accommodating the objects to be rotated. 
     More particularly, the third embodiment end effector assembly  326  includes a plate housing  328  which is preferably formed as an aluminum weldment to minimize weight without sacrificing strength and may include ribs for added strength. The plate housing  328  includes a centralized portion  334  where the end effector  326  is fixedly secured, e.g., bolted, to the wrist  324 . If desired, the portion  334  may be recessed position the center of gravity of the end effector  326  axially away from the distal end of the wrist  324 . This may save wear and tear on the robot  10  (FIG.  1 ). 
     The plate housing  328  rotatably supports a plurality of objects to be rotated by way of a plurality of spindles  336   a-c . The spindles  336   a-d  are preferably distributed along a common edge of the plate housing  328  and are coupled to spindle housings as described above. The spindles  336   a-d  preferably project parallel to one another and are spaced apart by a sufficient amount to ensure clearance of the objects of manufacture to be mounted thereto. For example, this embodiment of the present invention can rotatably support three vehicle wheels having diameters ranging from fourteen to twenty-six inches. 
     A driving pulley  356  is rotatably mounted to the plate housing  328  and is operably coupled to a gear box and servo motor as described above. A driven pulley  352  is non-rotatably secured, e.g., splined, to each of the spindles  336   a-c . A synchronizer in the form of a timing belt (not shown) meshingly engages the driving pulley  356  and driven pulleys  352  such that they are interconnected. 
     The belt transfers the rotation of the driving pulley  356  by the motor and gear box to the spindles  336   a-c  at a one-to-one ratio such that the rotation of the spindles  336   a-d,  as well as the objects of manufacture mounted thereto, is matched. An object of manufacture such as the aluminum wheels of the first embodiment are non-rotatably connected to each of the spindles  336 . For clarity, these objects of manufacture are not illustrated in FIG.  11 . 
     The plate housing  328  is generally shaped as a triangle and includes a plurality of mounting holes, generally shown at  306 , in the portion  334  for accommodating fasteners such as bolts to secure the end effector  326  to the wrist  324 . If desired, one or more idler pulleys (not shown) may be rotatably and slidably separately mounted to a the plate housing  328 . By selectively positioning such idler pulleys relative to the spindles  336   a-c,  the tension of the belt, which synchronizes the rotation of the driven pulleys  352 , is controlled. Maintaining proper tensioning on the belt prevents belt slippage to ensure that the objects to be rotated rotate in phase. 
     Turning now to FIG. 13, a fourth embodiment of the present invention is illustrated. This embodiment is particularly tailored to accommodate five objects to be rotated. The fourth embodiment is identical in principle to the prior embodiments but includes five mounting positions for accommodating the objects to be rotated. 
     More particularly, the fourth embodiment end effector assembly  426  includes a plate housing  428 . The plate housing  428  includes a centralized portion  434  where the end effector  426  is fixedly secured, e.g., bolted, to the wrist  424 . The plate housing  428  rotatably supports a plurality of objects to be rotated by way of a plurality of spindles  436   a-e.    
     The spindles  436   a-e  are preferably distributed along a common edge of the plate housing  428  and are coupled to spindle housings as described above. The spindles  436   a-e  preferably project parallel to one another and are spaced apart by a sufficient amount to ensure clearance of the objects of manufacture to be mounted thereto. For example, this embodiment of the present invention can rotatably support five vehicle wheels having diameters ranging from fourteen to twenty-six inches. 
     A driving pulley  456  is rotatably mounted to the plate housing  428  and is operably coupled to a gear box and servo motor as described above. A driven pulley  452  is non-rotatably secured, e.g., splined, to each of the spindles  436   a-e.  A synchronizer in the form of a timing belt (not shown) meshingly engages the driving pulley  456  and driven pulleys  452  such that they are interconnected. The belt transfers the rotation of the driving pulley  456  by the motor and gear box to the spindles  436   a-e  at a one-to-one ratio such that the rotation of the spindles  436   a-e,  as well as the objects of manufacture mounted thereto, is matched. 
     The plate housing  428  is generally shaped as a triangle and includes a plurality of mounting holes, generally shown at  406 , in the portion  434  for accommodating fasteners such as bolts to secure the end effector  426  to the wrist  424 . If desired, one or more idler pulleys (not shown) may be rotatably and slidably separately mounted to a the plate housing  428 . By selectively positioning such idler pulleys relative to the spindles  436   a-e,  the tension of the belt, which synchronizes the rotation of the driven pulleys  452 , is controlled. Maintaining proper tensioning on the belt prevents belt slippage to ensure that the objects to be rotated rotate in phase. 
     Turning now to FIG. 14, a fifth embodiment of the present invention is illustrated. This embodiment is particularly tailored to accommodate six objects to be rotated. The fifth embodiment is identical in principle to the prior embodiments but includes six mounting positions for accommodating the objects to be rotated. 
     More particularly, the fifth embodiment end effector assembly  526  includes a plate housing  528 . The plate housing  528  includes a centralized portion  534  where the end effector  526  is fixedly secured, e.g., bolted, to the wrist  524 . The plate housing  528  rotatably supports a plurality of objects to be rotated by way of a plurality of spindles  536   a-f.    
     The spindles  536   a-f  are preferably distributed along a common edge of the plate housing  528  and are coupled to spindle housings as described above. The spindles  536   a-f  preferably project parallel to one another and are spaced apart by a sufficient amount to ensure clearance of the objects of manufacture to be mounted thereto. For example, this embodiment of the present invention can rotatably support six vehicle wheels having diameters ranging from fourteen to twenty-six inches. 
     A driving pulley  556  is rotatably mounted to the plate housing  528  and is operably coupled to a gear box and servo motor as described above. A driven pulley  552  is non-rotatably secured, e.g., splined, to each of the spindles  536   a-f . A synchronizer in the form of a timing belt (not shown) meshingly engages the driving pulley  556  and driven pulleys  552  such that they are interconnected. The belt transfers the rotation of the driving pulley  556  by the motor and gear box to the spindles  536   a-f  at a one-to-one ratio such that the rotation of the spindles  536   a-f , as well as the objects of manufacture mounted thereto, is matched. 
     The plate housing  528  is generally shaped as a triangle and includes a plurality of mounting holes, generally shown at  506 , in the portion  534  for accommodating fasteners such as bolts to secure the end effector  526  to the wrist  524 . If desired, one or more idler pulleys (not shown) may be rotatably and slidably separately mounted to a the plate housing  528 . By selectively positioning such idler pulleys relative to the spindles  536   a-f , the tension of the belt, which synchronizes the rotation of the driven pulleys  552 , is controlled. Maintaining proper tensioning on the belt prevents belt slippage to ensure that the objects to be rotated rotate in phase. 
     Turning now to FIG. 15, a sixth embodiment of the present invention is illustrated. This embodiment is particularly tailored to accommodate seven objects to be rotated. The sixth embodiment is identical in principle to the prior embodiments but includes seven mounting positions for accommodating the objects to be rotated. 
     More particularly, the sixth embodiment end effector assembly  626  includes a plate housing  628 . The plate housing  628  includes a centralized portion  634  where the end effector  626  is fixedly secured, e.g., bolted, to the wrist  624 . The plate housing  628  rotatably supports a plurality of objects to be rotated by way of a plurality of spindles  636   a-g.    
     The spindles  636   a-g  are preferably distributed along a common edge of the plate housing  628  and are coupled to spindle housings as described above. The spindles  636   a-g  preferably project parallel to one another and are spaced apart by a sufficient amount to ensure clearance of the objects of manufacture to be mounted thereto. For example, this embodiment of the present invention can rotatably support seven vehicle wheels having diameters ranging from fourteen to twenty-six inches. 
     A driving pulley  656  is rotatably mounted to the plate housing  628  and is operably coupled to a gear box and servo motor as described above. A driven pulley  652  is non-rotatably secured, e.g., splined, to each of the spindles  636   a-g . A synchronizer in the form of a timing belt (not shown) meshingly engages the driving pulley  656  and driven pulleys  652  such that they are interconnected. The belt transfers the rotation of the driving pulley  656  by the motor and gear box to the spindles  636   a-g  at a one-to-one ratio such that the rotation of the spindles  636   a-g , as well as the objects of manufacture mounted thereto, is matched. 
     The plate housing  628  is generally shaped as a triangle and includes a plurality of mounting holes, generally shown at  606 , in the portion  634  for accommodating fasteners such as bolts to secure the end effector  626  to the wrist  624 . If desired, one or more idler pulleys (not shown) may be rotatably and slidably separately mounted to a the plate housing  628 . By selectively positioning such idler pulleys relative to the spindles  636   a-g , the tension of the belt, which synchronizes the rotation of the driven pulleys  652 , is controlled. Maintaining proper tensioning on the belt prevents belt slippage to ensure that the objects to be rotated rotate in phase. 
     Thus, an end effector is provided for a six axis robot which accommodates a plurality of objects to be rotated. The end effector interconnects each object to be rotated such that they are synchronized and indexable as a unit. Advantageously, multiple objects of manufacture can be simultaneously processed with the end effector of the present invention. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. For example, the particular geometry of the mounting plate can be varied to accommodate the objects to be rotated in a modified distribution.