Abstract:
This invention relates to a multi-purpose end effector for a robotic arm that moves a workpiece through an automated, multi-station, manufacturing operation. The end effector is particularly useful in a gear manufacturing operation in which a gear piece is annealed, ground and tested to ensure it meets desired specifications. The relatively lightweight and compact end effector securely grips the workpiece during multi-directional movements, and provides a degree of softness when loading the normally non-rotating workpiece onto a continuously rotating chuck or tool. The end effector is secured to the robotic arm by a cross-member equipped with three different gripping implements. A central gripping device extends from the middle of the cross-member, a loading arm extends from one end of the cross-member, and an unloading arm extends from the other end. Each gripping implement includes pneumatically controlled gripping fingers for holding the gear pieces. Each loading and unloading arm has a gripping cylinder and a rotatable sleeve for supporting its gripping mechanism. The loading arm has an extension cylinder for extending its gripping mechanism with a degree of softness or resiliency that helps prevent binding when the normally non-rotating workpiece engages the rotating chuck or tool.

Description:
BACKGROUND OF THE INVENTION 
     Multi-stage processes are commonly implemented in the manufacture of mechanical and electrical components such as gears, cams, pistons, rods, bolts, springs, fittings, circuit boards, capacitors, inductors, receivers, etc. For example, the process of manufacturing a gear from a gear blank may require the blank to pass through a drilling or boring stage where a central hole is rough bored through the flat face of the blank. The blank then passes through a stage where teeth are hobbed or otherwise formed along the outer radial perimeter of the blank. Some types of gears have hubs with threads. The gears are heat treated for hardness, and the threaded ends are annealed to relieve the stresses and brittleness caused by the heat treatment. The teeth and central hole are then precision ground so that the center of the pitch radius of the teeth coincides with the center of its hole. 
     Each manufacturing step or stage is performed by a separate machine or tool. For example, during a gear manufacturing operation, a gear blank is brought to a first station and loaded onto a first machine that performs a first task on the blank. The gear is then unloaded from the first machine, transported to a second station, and loaded on a second machine where another task is performed, and so on. This loading, machining, unloading and transporting process continues until each required task is complete. 
     One problem with multi-stage manufacturing operations is that they are often time consuming, labor intensive, and dangerous for the workers. The workers must walk by the machines when carrying heavy loads of workpiece, and load those parts into or onto the machines. Some machines contain fast moving and rotating parts. Other machines involve extremely hot temperatures or caustic acid baths. Hot shrapnel and caustic fluid is often thrown from the machines as the parts are drilled, sawed, ground, polished, and sprayed. Although shields are typically provided, they may not prevent all discharges, particularly if the shield is inadvertently left open. A worker that stands or walks in the wrong area, fails to put on proper safety attire, or accidentally slips, falls or leans against a machine can be severely hurt. Yet, safety precautions are inconvenient and frequently come at the expense of productivity. Workers may cut comers to meet or exceed desired productivity levels. 
     To speed up the manufacturing process and reduce labor requirements, stand-alone machines have been designed to hold a number of workpieces, and consecutively perform a single manufacturing process on those workpieces. For example, U.S. Pat. Nos. 2,329,301 and 3,728,829 disclose stand-alone, gear manufacturing machines that hold and dispense blanks through chutes to a position where a grinding or honing operation is performed to form the central bore of the gear. U.S. Pat. Nos. 3,533,258 and 4,106,632 disclose stand-alone machines that load gear blanks via chutes, and loading mechanisms that position the blanks into positions where a rolling operation is performed to form the teeth. In addition, U.S. Pat. No. 3,541,921 discloses an indexible, stand-alone, beveled gear cutting machine and control system that includes a three-armed turret. The turret picks up a gear piece from a first supply station, rotationally moves the piece to a first sequential station where a first finishing operation is performed, then move the piece to a second sequential station where a second finishing operation is performed, and finally return the gear piece to the supply station. 
     FIGS. 1-3 show a conventional gear grinding operation for gear pieces  5  having relatively flat side faces  6 , a generally circular outer surface or perimeter  7  with uniformly spaced, precision cut teeth  7   a,  and an inner surface  9  that forms a rough cut central opening  9   a.  The gear pieces  5  are ground via a grinding machine  10  with a continuously rotating chuck  12  of the type shown in FIG.  4 . The chuck  12  has three jaws or brackets  13 . Each jaw  13  has a dog  14  and a locator tooth  16 . As the dog  14  attempts to enter between the teeth  7   a  of the gear piece  5 , it imparts rotation to the gear piece and syncronizes that rotation with the chuck  12  as shown in FIG.  5 . Once the dog  14  has entered between two teeth  7   a,  the locator tooth  16  enters between two other teeth  7   a.  The jaws  13  then extend the locator teeth  16  to firmly grip the gear piece  5  as shown in FIG.  6 . Once gripped, the locator teeth  16  align the gear piece  5  so that the central axis of the pitch diameter of the gear teeth  7   a  are aligned with the central axis of the grinding tool. Conveyors  20  and  21  supply gear pieces  5  to and discharge them from this manufacturing operation. 
     The grinding machine  10  is combined with a conventional, stand-alone, loading/unloading machine  30 . The loading/unloading machine  30  has a frame  31  that supports a relatively large hydraulic or pneumatic expansion cylinder  32 . The cylinder  32  supports a bar  33  formed in the shape of a boomerang with an angle of about 120°. Each end of the bar  33  has a gripping arm  35  for gripping one gear piece  5 . One end of each gripping arm  35  is rigidly fixed to the bar  33 . The other end of the gripping arm  35  has a sleeve  36  that is free to rotate about its central axis. The central expansion cylinder  32  drives the bar  33  and both gripping arms  35  toward and away from the grinding machine  10 . The expansion cylinder  32 , rotatable bar  33  and two gripping arms  35  form a loader/unloader unit  39 . 
     A balloon-type gripping device  37  is situated around the outside of the rotatable sleeve  36  of each gripping arm  35  as shown in FIG.  3 . The fixed end of the bar  33  has a pneumatic or hydraulic line that controls the balloon-type gripping device  36 . The machine  30  inflates the balloon-type gripping device  36  to grip the inside surface of the central opening  9   a  of a gear piece  5 , and deflates the device to let go of the gear piece. In an alternate embodiment, the balloon-type gripping device  37  is replaced with a locking ball and a plunger device. 
     As best shown in FIG. 1, the machine  30  rotates the bar  33  gripping arms  35  of the loader/unloader unit  39  in a clockwise or counterclockwise direction about the central axis of the expansion cylinder  32 . The bar  33  rotates through a cycle in which each gripping arm  35  travels to a pick-up position, a load/unload position, and a discharge position. In the pickup position, one gripping arm  35  is aligned with a gear piece  5  on the supply conveyor  20 . In the load/unload position, one gripping arm  35  is aligned with the rotating chuck  12  of the grinding machining  10 . In the discharge position, one gripping arm  35  is aligned with the discharge conveyor  21 . 
     During operation, the expansion cylinder  32  is used to horizontally extend and retract the bar  33  and gripping arms  35  at each of the pick-up, load/unload, and discharge positions. To pick-up a gear piece  5 , one arm  35  of the gripping device  37  enters the central hole  9   a  of the gear piece  5  on the supply conveyor  20  and its balloon is inflated to grip that gear piece. The cylinder  32  is then retracted to pull the gripping arm  35  and gear piece away from the supply conveyor  20 . To load a gear piece  5  onto the rotating chuck  12 , the bar  33  rotates the gripping arm  35  and gear piece  5  into alignment with the rotating chuck  12 . The expansion cylinder  32  then extends the rotatable sleeve  36 , gripping device  37  and non-rotating gear piece  5  toward the chuck  12 . The dog  14  of the chuck enters between the teeth  7  of the gear  5  to impart rotational movement to the gear, and the locator teeth  16  then enter between the teeth  7   a.  After the locator teeth  16  firmly grip the gear piece  5 , the balloon is deflated to release that gear piece, and the cylinder  32  is retracted to pull the gripping arm  35  away from the chuck  12 . To unload a gear piece  5  from the rotating chuck  12 , the bar  33  rotates the empty gripping arm  35  into alignment with the rotating chuck  12  and gear piece  5 . The expansion cylinder  32  then extends the rotatable sleeve  36  and gripping device  37  into the central hole  9   a  of the gear piece  5 . The balloon type gripping device  37  is inflated to grip the gear piece  5 , and the cylinder  32  is retracted to pull the gripping arm  35  and gear piece away from the chuck  12 . 
     One problem with conventional stand-alone workpiece manufacturing machines is that each machine requires its own loading/unloading unit and supply and discharge conveyors. These loading/unloading units and conveyors are expensive, bulky and require a great deal of floor space. Each loading/unloading unit and conveyor also requires its own maintenance schedule. Should any part in the unit or conveyor jam or fail, the machine and the entire manufacturing operation may be shut down. Each time a worker goes near one of the loading/unloading units, the manufacturing operation must be shut down or the worker is exposed to possible injury. 
     Another problem with conventional, stand alone machines is that it is difficult to change over an assembly line using several machines to form a particular part. Each machine has to be set up to handle a workpiece of a particular size and shape. For example, in order to produce gears having a three-inch diameter, twenty-two teeth with a given pitch diameter and a one-inch diameter central hole, each stand-alone machine has to be adjusted to perform its specific task for this specific part. Then, the first machine in the assembly line must be loaded with specific gear blanks and processed. A substantial lag time can occur before the second and third machines in the process are ready to be filled with workpieces. In addition, many hours can be required to set up and test the accuracy of the machines. Manufacturing operations of this type are not conducive to small part runs, which are frequently required in the just-in-time manufacturing operations in use today. 
     A further problem associated with conventional, stand-alone, and indexible machines is that some manufacturing operations take longer than others. Indexible machines can only be incremented as quickly as it takes to complete the slowest machining operation. While only a few seconds may be needed to rough bore a hole in a gear piece, several minutes may be required to anneal that gear piece. 
     A still further problem with conventional stand-alone and indexible machines is that they do not incorporate gripping devices appropriate for a robotic application. Conventional machines impart specific types of movement on the workpieces they handle. For example, the above-noted conventional loader/unloader only imparts horizontal or rotational movement on the workpiece, but not at the same time. The gripping device only needs to grip the workpiece in such a way to avoid slipping from occurring during these specific movements. Accordingly, conventional loader/unloader units do not provide the secure grip needed when the parts are moved in a multi-directional path from one machine to another. 
     While robotics is well suited for some repetitious manufacturing operations, coordinating a robotic arm to go from machine to machine can be problematic. The robotic arms move quickly from one point to another, but have difficulty compensating when integrating tasks between different machines. For example, a machine that requires a degree of softness or compliance to load a workpiece onto a rotating tool or chuck is problematic for the rigid movements of the programmed robotic arm. 
     An additional problem associated with integrating a robot to work with several different machines is developing a practical end effector for such an activity. The speed and multi-directional movement of the robotic arm requires the end effector to be compact, balanced and light weight. An end effector that has excessive size or weight, or one that is unbalanced, will produce loads that will exceed the capacity of a given robotic arm. Accordingly, end effectors are typically designed to perform limited tasks and work with a specific machine. The robotic arm uses different end effectors to perform different tasks. 
     A further problem with both conventional robotic end effectors and conventional loader/unloaders is that they are not able to grip gear pieces having different sizes and shapes. The gripping mechanism on the loader/unloader has to be changed each time a different part run is made, which inhibits the ability to cost effectively produce smaller part runs. 
     The present invention is intended to solve these and other problems. 
     BRIEF DESCRIPTION OF THE INVENTION 
     This invention relates to a multi-purpose end effector for a robotic arm that moves a workpiece through an automated, multi-station, manufacturing operation. The end effector is particularly useful in a gear manufacturing operation in which a gear piece is annealed, ground and tested to ensure it meets desired specifications. The relatively lightweight and compact end effector securely grips the workpiece during multi-directional movements, and provides a degree of softness when loading the normally non-rotating workpiece onto a continuously rotating chuck or tool. The end effector is secured to the robotic arm by a cross-member equipped with three different gripping implements. A central gripping device extends from the middle of the cross-member, a loading arm extends from one end of the cross-member, and an unloading arm extends from the other end. Each gripping implement includes pneumatically controlled gripping fingers for holding the gear pieces. Each loading and unloading arm has a gripping cylinder and a rotatable sleeve for supporting its gripping mechanism. The loading arm has an extension cylinder for extending its gripping mechanism with a degree of softness or resiliency that helps prevent binding when the normally non-rotating workpiece engages the rotating chuck or tool. 
     One advantage of the present end effector invention is its versatility. The end effector is equipped with several different gripping implements that permit its use with a variety of machines. One implement or gripping device is capable of performing operations that require the robotic arm to pick up or place a workpiece on a stationary tool or rack. This gripping device is capable of gripping the inside or outside surface of a workpiece or object. The other two gripping implements have a rotating sleeve that allows them to unload a workpiece off a rotating tool or chuck. One of these two implement is also equipped with an extension cylinder that gives the otherwise rigid movement of the robotic arm a degree of softness or compliance. This allows the gripping implement to smoothly load a non-uniformly shaped workpiece, such as a gear with teeth on its perimeter, onto the jaws of a rotating chuck without binding. The versatility of the end effector allows the robotic arm to move quickly from machine to machine without slowing down to change end effectors, which greatly improves the overall speed of the robotic arm and the entire manufacturing operation. 
     Another advantage of the present end effector invention is that it allows the robotic arm to simultaneously handle the movements, and loading and unloading of workpieces as they proceed from machine-to-machine or operation-to-operation in a multi-station manufacturing process. This is accomplished even though different operations may take longer than others. One operation may be to pick up a first gear, move it to and align it with a rotating chuck of a grinding machine, and smoothly load the gear on the rotating chuck. While the grinding operation is being performed, the end effector can pick up a second gear on a holding rack and move it to another rack for a relatively long annealing operation, and then pick up a third gear. After the grinding operation is performed, the end effector can unload the first gear from the rotating chuck, and load the third gear on the rotating chuck. While the grinding and annealing operations are being performed, the end effector can move and load the first gear in another machine at another station. In this way, the end effector can simultaneously handle several gears at different stages of the manufacturing process, which greatly increases the speed and efficiency of the robotic arm and the automated manufacturing process. 
     A further advantage of the present end effector invention is its compact, lightweight and balanced design. The straddled, in-line arrangement of the gripping and extension cylinders in the loading arm produces a compact and balanced design that is well suited for robotic applications. The generally symmetrical layout of the three gripping implements provides a further degree of balance that reduces the stresses on the robotic arm. 
     A still further advantage of the present end effector invention is that it enables a multi-station manufacturing operation to be performed in a relatively small, organized area, and reduces the cost of maintaining the machines and their down time. Expensive, bulky, machine specific loading/unloading units are eliminated, as are the supply and discharge conveyors and numerous holding bins. This reduces the amount of maintenance time for the manufacturing operation, as well as down time and potential injury to workers. 
     A still further advantage of the present end effector invention is that it reduces set up time and costs in an automated manufacturing operation, thereby enabling a smaller number of parts to be manufactured in a given part run such as in a just-in-time manufacturing operation. Each station in the operation does not need to be supplied with workpieces ready for that particular stage of processing. Instead, a small number of workpieces can be sent through the manufacturing operation by allowing the robotic arm and end effector to distribute the parts from station to station so that several workpieces are being simultaneously processed by different machines. 
     A still further advantage of the present end effector invention is that its gripping mechanisms are appropriate for a robotic application. The loading and unloading arms are each equipped with a pneumatic gripping cylinder that combines with a gripping mechanism with a mechanical lever to provide sufficient force to securely hold the workpiece as the robotic arm moves quickly through a variety of multi-directional movement patterns. This secure grip ensures the gear piece will remain in its desired gripped position on the end effector so that the robotic arm can accurately align the workpiece at the next station. 
     A further advantage of the present end effector invention is that it is able to grip and move a variety of gear pieces having different sizes and shapes. The gripping mechanisms on the end effector permit a wide range of motion of its gripping fingers. The same gripping mechanisms can be used in a variety of gear piece runs. This speeds up the time to change from one part run to another, and improves the machines ability to make the smaller part runs frequently found in a just-in-time manufacturing operation. 
     Other aspects and advantages of the invention will become apparent upon making reference to the specification, claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a conventional stand-alone loading/unloading machine equipped with an end effector having a central expansion cylinder that supports the middle of a bar with gripping arms at each end, one arm being at a discharge position. 
     FIG. 2 is a top view of the conventional stand-alone loading/unloading machine with one of the gripping arms at a loading/unloading position. 
     FIG. 3 is a cross sectional view of the gripping arm of the conventional loading/unloading device having a rotatable sleeve with a balloon-type gripping device. 
     FIG. 4 is a front view of a conventional, three jaw, rotating chuck, each jaw having a dog and a locator tooth for engaging a gear. 
     FIG. 5 is a front view showing a non-rotating gear as it is being loaded on the rotating chuck, the dog and locator tooth of the chuck being out of alignment with the teeth of the gear. 
     FIG. 6 is a front view of a gear loaded on the rotating chuck with the dog and locator tooth of the chuck aligned between the teeth of the gear. 
     FIG. 7 is an overhead view of an automated, multi-stage gear manufacturing station with a robot with its arm extended toward a grinding tool, and unloading arm aligned to remove a gear from the rotating chuck of the grinding tool. 
     FIG. 8 is an elevated, side view of the multi-station gear manufacturing operation showing the possible paths of travel of the robotic arm and end effector as they move from station-to-station. 
     FIG. 9 is a top view of the multi-purpose end effector having a cross-member that supports a central gripping device, a loading arm and an unloading arm, the unloading arm being in its extended position to grip the rotating gear piece held by the rotating chuck. 
     FIG. 10 is a front view of the multi-purpose end effector shown in FIG.  9 . 
     FIG. 11 is a side view of the loading arm showing its gripping cylinder in its gripping position and its extending cylinder in its retracted position. 
     FIG. 12 is a side view of the loading arm with its extension cylinder shown in an extended position. 
     FIG. 13 is a side view of the unloading arm showing the gripping cylinder and mechanism in their gripping position. 
     FIG. 14 is a flow chart showing the process of using the robot and end effector to load, unload and transport gear pieces through a multi-stage gear manufacturing operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiment in many different forms, the drawings show and the specification describes in detail a preferred embodiment of the invention. It should be understood that the drawings and specification are to be considered an exemplification of the principles of the invention. They are not intended to limit the broad aspects of the invention to the embodiment illustrated. 
     The present invention relates to a multi-station manufacturing operation  50 , such as the gear piece  5  annealing, grinding and testing operation shown in FIGS. 7 and 8. As noted above, each gear piece  5  has front and rear faces  6 , an outer surface or perimeter  7  with uniformly spaced teeth  7   a,  and an inner surface  9  forming a central opening  9   a.  A portion of the inner surface  9  of the gear pieces  5  may be threaded. The manufacturing operation  50  cycles the gear pieces  5  through a variety of stations. To protect workers from shrapnel, caustic fluid and moving equipment parts, a protective wall  51  is constructed around the restricted work area of the manufacturing operation  50 . 
     Gear pieces  5  are initially brought to the manufacturing operation  50  on steel trays  52  or plastic racks  53 . Each tray  52  or rack  53  has an array of uniformly spaced posts  54 . Each gear is placed on the tray  52  so that one post  54  extends through the center opening  9   a  of a gear piece  5  to hold it in place. The trays  52  are brought to a supply station  55  with a bin or magazine  56  that is accessible from outside the protective wall  51 . The magazine  56  moves the tray  52  inside the manufacturing operation  50  and orients the tray so that each post  54  and gear piece  5  is located at specific coordinates. The gear pieces  5  are then moved to an annealing station  60  and placed on the posts of the rack  53  at the annealing machine  61 . After annealing, the gear pieces  5  are moved to a cooling station  65 , and placed at a specific location on a cooling rack  66 . Once cooled, the gear pieces  5  are brought to a grinding station  70  with a conventional center hole grinding machine  10  as shown in FIGS. 1-3. The gear pieces  5  are loaded onto the continuously rotating chuck  12  of the machine  10 . After grinding, the gear pieces  5  are unloaded from the grinding machine  10  and brought to a testing station  75  where they are placed on a testing machine  76 . If the gear piece  5  tests satisfactory, it is brought to a completion station  80 , and placed on a rack  53  of a cart  81 . After the racks  53  in the cart  81  are full, the cart  81  and gear pieces  5  are then removed for further processing or shipment. A regripping station  85  may also be provided to allow the robot  100  to move the gear piece  5  from one of its three implements to the other, as discussed below. 
     A robot  100  cycles the gear pieces  5  through the multi-station manufacturing operation  50 . The robot is preferably mounted to the floor via its base or platform  101 , and includes a multi-piece arm  105  with an end  106 . The end  106  includes a cylindrically shaped, rotatable mount  108  for securing a tool or attachment. The mount  108  includes electrical connections and pneumatic lines (not shown) for connecting to the tool or attachment. The pneumatic lines typically supply about 80 to 100 pounds per square inch of pressure. The base  101 , multi-piece arm  105  and mount  108  are conventional in nature. The robot  100  is located toward the middle of the operation  50  with the various stations being located around the robot in a generally circular pattern at a distance that allows its end  106  to reach each station. The robotic arm  105  is capable of moving in multi-directional paths of travel  109 . The robot  100  is programmed to simultaneously cycle several gear pieces  5  through the operation  50  as discussed below. 
     Multi-Purpose End Effector 
     The robot  100  is equipped with a multi-purpose end effector  120 . The end effector  120  includes three different implements for gripping and handling the gear pieces  5  and plastic racks  53 . As discussed below, the gripping implements include a gripping device  150 , a loading arm  200 , and an unloading arm  300 . 
     As best shown in FIGS. 9 and 10, an elongated cross-member or spacing bracket  130  supports and spaces the gripping implements  150 ,  200  and  300  apart so that each is capable of moving to a particular station and engaging a gear piece  5  without interference from the others. The cross-member  130  is bolted or otherwise rigidly secured to the mounting bracket  108  of the robotic arm  105  via a circular mounting plate  132 . The cross-member  130  is robustly sized to support the implements  150 ,  200  and  300 , and is wider towards its middle section  135  and tapers towards its ends  136  and  137 . The cross-member  130  is made of aluminum, and trapezoidal openings are formed in the wings of the cross-member  130  to reduce its mass and weight. A circular hole is formed in the middle  135  of the cross-member  130 . One circular hole is also formed toward each end  136  and  137  of the cross-member  130 . The end holes are equidistant from middle  135  of the cross-member  130 . 
     The central gripping device  150  is a conventional three jaw parallel gripper driven by a dual action cylinder, such as that made by CCMOP of Paris, France. The gripping device  150  has a generally cylindrical housing  152  with front and rear ends  154  and  155 . The housing  152  forms an internal cylinder. The rear end  155  of the housing  152  is snuggly received by the hole in the middle  135  of the cross-member  130 , and is bolted or otherwise rigidly secured to the cross-member  130  and mounting plate  132 . The central axis of the gripping device  150  is linearly aligned with the central axis of the cylindrical mounting bracket  108  of the robot  100 . The front end  154  of the housing  152  includes a gripping mechanism  160  with three movable fingers  165 . The fingers have a 25 millimeter stroke that gives them a great amount of versatility. The fingers  165  can be extended to an outer gripping position  170  to grip the outside surface  7  of the gear pieces as in FIG. 9, or they can be retracted to an inner gripping position  175  for gripping the inside surfaces  9  of the holes in the gear pieces  5  or the racks  53  as in FIG.  8 . The robot  100  includes a regulator (not shown) that controls the amount of pressure supplied to the chambers of the gripping device  150  to regulate the gripping force of the fingers  165 . 
     The gripping device  150  includes a piston and rod assembly (not shown) that divides its internal cylinder into a front and a rear chamber. The pneumatic lines of the robot  100  are in controlled communication with the chambers. A switch (not shown) opens and closes the flow of air to the chambers. When one chamber is pressurized its release valve is closed and the release valve for the other chamber is opened. The pressurization of the rear chamber advances the piston toward the front of the housing  152 . The pressurization of the front chamber pushes the piston back toward the rear of the housing  152 . The piston rod is pivotally linked to the jaws or base portions  166  of the fingers  165 . Forward advancement of the rod pushes the jaws  166  outwardly through lateral slots and spreads the fingers  165  apart. Backward movement of the rod pulls the jaws  166  inwardly through the lateral slots to close the fingers  165  together. 
     The loading arm  200  is securely bolted to the cross-member  130  via a donut shaped mounting collar  205  that is bolted around the front of the hole toward the end  136  of the cross-member as shown in FIGS. 11 and 12. A pair of pneumatic cylinders  210  and  240  straddles the cross-member  130 . The cylinders are conventional pneumatic cylinders with a three inch bore and a one inch stroke, such as those made by Compact Air Products, Inc. of Westminster, S.C. The centerlines of the arm  200  and cylinder  210  and  240  pass through the center of the hole. This straddled, in-line arrangement produces a compact arm  200  that is relatively lightweight and balanced on the cross-member  130 . The loading and unloading arms  200  and  300  are equidistant from the middle  135  of the cross-member  130  to further improve the balance of the end effector  120 . This lightweight and balanced design reduces the torque and other forces on the robotic arm  105 . 
     The extension cylinder  210  is formed by a cylindrical housing  211  with front and rear ends and a hollow interior. The housing  211  is securely bolted to the mounting collar  205 . The interior is divided into front and rear chambers  212  and  213  by a piston  215 . The pneumatic line of the robot  100  is in controlled communication with both chambers  212  and  213 . A switch (not shown) opens and closes the pneumatic line to the chambers. When chamber  212  is pressurized, its release valve is closed and the release valve of chamber  213  is open. Alternately, when chamber  213  is pressurized, its release valve is closed and the release valve of chamber  212  is open. The pressurization of the rear chamber  213  pushes the piston  215  toward the front of the housing  211 . The pressurization of the front chamber  212  pushes the piston back toward the rear of the housing  211 . The robot  100  has a separate regulator for controlling the pressurization of chamber  213  to produce a relatively slow and soft extension of the gripping piston  215 . 
     The piston  215  has an integrally molded sleeve  216  that extends axially from both the front and rear sides of the piston. The sleeve  216  passes through the front and rear walls of the cylindrical housing  211 . Seals prevent air leakage between the housing  211  and the sleeve  216 . The front portion of the sleeve  216  is covered by a cap  218 . The cap  218  is securely bolted to the end of the sleeve  216 . The piston  215 , sleeve  216  and cap  218  form a central tubular opening for receiving a hollow shaft  220 . The front end of the hollow shaft  220  passes through and extends out of the cap  218 . A pair of spaced axial bearings  221  and  222  is secured to the front end of the hollow shaft  220 . The hollow shaft  220  is pinned or otherwise rigidly secured to the cap  218 . The piston  215  is movable between a forward or extended position  225  as shown in FIG. 11, and a rearward or retracted position  226  as shown in FIG.  12 . The hollow shaft  220  moves with the piston  215 . 
     An interior or middle hub  230  is pinned or otherwise rigidly secured to the rear end of the hollow shaft  220 , so that it also moves with the piston  215 . The middle hub  230  is received inside and is slidingly supported by the donut shaped collar  205  via a bushing. A torque or anti-rotational plate  235  is securely bolted to the rear end of the middle hub  230 . The plate  235  has a notch for slidingly receiving a pin  236  extending from the rear of the cross-member  130 . The anti-rotational plate  235  and pin  236  prevent the rotation of the piston  215 , hollow shaft  220  and middle hub  230 . 
     The gripping cylinder  240  is similar in construction and operation to the extension cylinder  210 . The gripping cylinder  240  has a cylindrical housing  241  with a hollow interior. The housing  241  is securely bolted to and supported by the middle hub  230  so that it moves with the piston  215  of the extension cylinder  210 . The interior of the cylinder  240  is divided into front and rear chambers  242  and  243  by a piston  245 . The pneumatic line of the robot  100  is in controlled communication with both chambers  242  and  243 . A switch (not shown) is activated by the robot to open and close the pneumatic line to these chambers  242  and  243 . When chamber  242  is pressurized by the pneumatic line, its release valve is closed and the release valve of chamber  243  is open. Alternately, when chamber  243  is pressurized by the pneumatic line, its release valve is closed, and the release valve of chamber  242  is open. The pressurization of rear chamber  243  pushes the piston  245  toward the front of the housing  241 . The pressurization of the front chamber  242  pushes the piston  245  back toward the rear of the housing  241 . The piston  245  has an integrally molded sleeve  246  that extends from both the front and rear of the piston. The sleeve  246  passes through the front and rear walls of the housing  241 . Seals prevent air leakage between the housing  241  and the sleeve  246 . The rear portion of the sleeve  246  is covered by a cap  248  that is securely bolted to the sleeve  246 . The piston  245 , sleeve  246  and cap  248  form a central tubular opening for receiving a solid shaft  250 . The rear end of the shaft  250  is pinned or otherwise rigidly secured to the cap  248 . The front end of the solid shaft  250  passes through and extends from the hollow shaft  220 . The front end of the shaft  250  is supported by an axial thrust bearing  251 . 
     A rotatable sleeve  260  and a gripping mechanism  270  are secured to the front end of the loading arm  200 . The rotatable sleeve  260  has a housing formed by upper and lower hubs  261  and  265  and a cap  267  that are securely bolted together. The lower hub  261  is supported by spaced, axial bearings  221  and  222  fixed to the outside of hollow shaft  220 . The axial bearings  221  and  222  and a spacer  263  are sandwiched between an inner rim  262  of the lower hub  261  and a lip  266  formed by the slightly smaller inside diameter of the upper hub  265 . This sandwiched construction secures the rotatable sleeve  260  to the hollow shaft  220 , while permitting free axial rotation of the sleeve. 
     The gripping mechanism  270  is formed by a glide  271  and gripping fingers  280 . The glide is snuggly received inside upper hub  261 , and is free to slide axially in the hub via a bushing. The axial thrust bearing  251  of the solid shaft  250  engages and rotatably supports the glide  271 . The glide  271  is firmly pinned to a draw bar  272 . The thrust bearing  251  of the solid shaft  250  is sandwiched between the draw bar  272  and a rim  273  of the glide  272 , so that the glide  271  and draw bar  272  move in unison with the solid shaft  250 . The draw bar  272  has four longitudinal channels, each of which receives one finger  280 . Two pins  275  extend from the draw bar  272  into each channel. Each channel is shaped to snuggly receive a longitudinal portion  281  of one gripping finger  280 . Each longitudinal portion  281  has two angled slots  282  for receiving the two pins  275  associated with the channel in which it fits. A lateral portion  285  of the gripping fingers  280  is restricted from longitudinal movement by the cap  267  of the rotatable sleeve  260 . The slots are sloped about ten degrees from the centerline of the loading arm  200  to produce a mechanical lever that accentuates the gripping force of the fingers due to the pressure exerted on the gripping piston  215 . 
     When the piston  245  of the gripping cylinder  240  moves forward to its extended position  255 , the solid shaft  250  pushes the draw bar  272  forward while the gripping fingers  280  are held longitudinally fixed by the cap  267  of the rotatable sleeve  260 . This causes the slots of the gripping fingers  280  to ride up the pins  275  of the draw bar  272 , thus spreading the finger apart so that the outside surface  283  of the fingers  280  grips the inside surface  9  of the gear piece  5 . When the piston  245  of the gripping cylinder  240  moves back to its retracted position  256 , the solid shaft  250  pulls the draw bar  272  back while the gripping fingers  280  are again held longitudinally fixed by the lip  266  of lower hub  265  of the rotatable sleeve  260 . This causes the slots of the gripping fingers  280  to ride down the pins  275  of the draw bar  272 , thus moving the fingers together to release the grip on the inside surface  9  of the gear piece  5 . 
     The unloading arm  300  differs from loading arm  200  in some respects as shown in FIGS. 9 and 13. A spacing tube  310  and a hollow tube  320  replace the mounting collar  205 , extension cylinder  210 , middle hub  230  and anti-rotation plate  235 . The spacing tube  310  is securely bolted around the front of the hole of the cross-member  130  at end  137 . The front end of the spacing tube  310  extends the same distance forward from the cross-member  130  as the cap  218  of the piston  215  of the extension cylinder  210 . The hollow tube  320  is dimensionally equivalent to the hollow shaft  220 , and is securely pinned or otherwise rigidly attached to the inside of the spacing tube  310 . Axial bearings  321  and  322  are secured to the outside of the hollow tube  320 . These bearings  321  and  322  are equivalent to axial bearings  221  and  222 . 
     The gripping cylinder  340  is structurally and operationally equivalent to the gripping cylinder  240  of the loading arm  200 . The gripping cylinder  340  has a cylindrical housing  341  that is securely bolted around the rear of the hole in the cross-member  130  at end  137 . The interior of the cylinder  340  is divided into front and rear chambers  342  and  343  by a piston  345 . The pneumatic line of the robot  100  is in controlled communication with both chambers  342  and  343 . A switch (not shown) is activated by the robot to open and close the pneumatic line to these chambers. When chamber  342  is pressurized by the pneumatic line, its release valve is closed and the release valve of chamber  343  is open. Alternately, when chamber  343  is pressurized by the pneumatic line, its release valve is closed, and the release valve of chamber  342  is open. The pressurization of rear chamber  343  pushes the piston  345  toward the front of the housing  341 . The pressurization of the front chamber  342  pushes the piston  345  back toward the rear of the housing  341 . The piston  345  has an integrally molded sleeve  346  that extends from both the front and rear of the piston. The sleeve  346  passes through the front and rear walls of the housing  341 . Seals prevent air leakage between the housing  341  and the sleeve  346 . The rear portion of the sleeve  346  is covered by a cap  348  that is securely bolted to the sleeve. The piston  345 , sleeve  346  and cap  348  form a central tubular opening for receiving a solid shaft  350 . The rear end of the shaft  350  is pinned or otherwise rigidly secured to the cap  348 . The front end of the solid shaft  350  passes through and extends from the hollow tube  320 . The front end of the shaft  350  is supported by an axial thrust bearing  351 . 
     The Rotatable sleeve  260  and gripping mechanism  270  of the loading and unloading arms  200  and  300  are interchangeable. When the piston  345  of the gripping cylinder  340  moves forward to its extended position  355 , the solid shaft  350  pushes the draw bar  272  forward while the gripping fingers  280  are held longitudinally fixed by the cap  267  of the rotatable sleeve  260 . This causes the slots  282  of the gripping fingers  280  to ride up the pins  275  of the draw bar  272 , thus spreading the finger apart so that the outside surface  283  of the fingers  280  grips the inside surface  9  of the gear piece  5 . When the piston  345  of the gripping cylinder  340  moves back to its retracted position  356 , the solid shaft  350  pulls the draw bar  272  back while the gripping fingers  280  are again held longitudinally fixed by the lip  266  of lower hub  265  of the rotatable sleeve  260 . This causes the slots  282  of the gripping fingers  280  to ride down the pins  275  of the draw bar  272 , thus moving the fingers together to release the grip on the inside surface  9  of the gear piece  5 . 
     Operation of Robotic Arm and Multi-Purpose End Effector 
     Although the following should be understood given the above discussion, the following is provided to assist the reader in understanding the operation of the robotic arm and end effector in the preferred embodiment. The process of annealing, grinding and testing gear pieces  400  is shown in FIG.  14 . As noted above, the first step  410  is to provide a multi-station manufacturing operation  50  with several stations  55 ,  60 ,  65 ,  70 ,  75 ,  80  and  85  and racks or machines  56 ,  61 ,  66 ,  71 ,  76 ,  81  and  86 . Unprocessed gear pieces  5  are initially brought in on steel trays  52  or plastic racks  53  as in step  415 . The trays  52  are brought to the supply station  55  and placed in the magazine  56  that automatically moves the tray inside the restricted work area. Magazine  56  orients the tray  52  and its posts  54  so that each gear piece  5  is located at specific coordinates known to the robot  100 . 
     The next steps  420  and  425  are to use the robot  100  and gripping device  150  to pick up one of the unprocessed gear pieces  5  from the tray  52  at the supply station  55 , and move the gear piece  5  to the annealing station  60 . At the annealing station  60 , the robot  100  uses unload arm  300  to pick up a previously annealed gear piece  5  from one of the posts  54  on the rack  53  at that station, and places the unannealed gear piece on one of the posts of that rack. While the unannealed gear piece  5  is being processed in step  430 , the robot  100  moves the annealed gear piece to a cooling station  65 , uses the gripping device  150  to pick up a previously cooled gear piece  5  from one of the posts of the rack  66  at that station, and places the uncooled gear piece on one of the posts of that rack as in step  435 . While the uncooled gear piece  5  is cooling in step  440 , the robot  100  takes the cooled gear piece  5  to the regripping station  85  where it transfers the gear piece to its loading arm  200  in steps  445  and  450 . 
     The robotic arm  105  then proceeds to the grinding station  70  in step  455 . The grinding station  70  includes a conventional center hole grinding machine  10 , less the conveyors  20  and  21  and stand-alone loader/unloader  30  shown in FIGS. 1-3. As noted above, the grinding machine  10  includes a continuously rotating chuck  12  that grips the teeth  7   a  of the gear piece  5  during the grinding operation. The robot  100  aligns the unloading arm  300  in front of the rotating chuck  12 , and moves the end effector  120  forward to insert its retracted gripping mechanism  270  into the center hole  9   a  of the gear piece  5  rotating on chuck  12 . The robot  100  then pressurizes the rear chamber of the gripping cylinder  340  to grip the gear piece  5 . This causes the gripping fingers  280  to firmly engage the rotating gear  5 , which results in the rotation of its sleeve  260 . After the chuck  12  releases the gear piece  5 , the robot  100  moves the entire end effector  120  and arm  300  a short linear distance away from the chuck  12  while still maintaining its alignment with the chuck. The robot  100  then rotates the mount  108  180° to position the loading arm  200  in front of the chuck  12  as in step  460 , and pressurizes the rear chamber of the extension cylinder  210  to move its gear piece  5  into engagement with the chuck as in step  465 . After the gear piece  5  is loaded on the chuck  12 , the robot  100  pressurizes the front chambers of the gripping cylinder  240  to release its grip on the gear piece  5 . The robot then pressurizes front chamber of the extension cylinder  210  to move the gripping mechanism  270  away from the rotating gear piece  5  and chuck  12 . 
     While the grinding machine  10  grinds the gear piece on its chuck  12  as in step  470 , the robot  100  moves the ground gear piece to a testing station  75  as in step  475 , uses the gripping device  150  to pick up a previously tested gear piece, and places the untested gear piece at that station. While the ground gear piece  5  is being tested in step  480 , the final step  485  to complete the manufacturing cycle is to move the tested gear piece  5  to a completion station  80 , and places the gear piece on a rack  53  of a cart  81 . When one rack  53  becomes full of finished gear pieces  5 , the robot  100  picks up another rack  53  and places it on the cart. 
     The above manufacturing operation  50  enables processing stations  60 ,  65 ,  70  and  75  to perform their functions while other gear pieces  5  are being simultaneously picked up, moved and placed at other stations. The manufacturing operation  50  is able to anneal, grind and test about 120 gear pieces an hour. After a period of time, the cart  81  and its racks  53  of gear pieces  5  are removed for further processing or shipment. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the broader aspects of the invention.