Abstract:
A spindle gripping device and method for use in a CNC machine for re-orienting a workpiece. The gripping device includes an attachment portion, a translational driver, and a gripping portion. The attachment portion mechanically attaches the gripping device to a spindle of the CNC machine, and allows a transfer of the rotation of the spindle to the gripping device. The translational driver translates the input rotational force into a linear movement. The gripping portion uses the linear movement to open and close claws of the gripping device. A controller monitors and controls the operation of the CNC machine, so as to control an exchange of the working tool with the gripping device, and to control actuation and subsequent movement of the gripping device to reposition the workpiece into a desired orientation.

Description:
BACKGROUND OF THE INVENTION 
     In a manufacturing setting, Computer Numerical Control (CNC) machines are commonly used to precisely work components. Specifically, a computer controller drives a machine tool to perform a cutting operation within a work envelope of the machine. The use of CNC machines has resulted in considerable improvements in the consistency and quality of machined parts. Further, CNC automation has reduced the time required to change the machine to produce different components. 
     CNC machines are generally used for drilling or tapping operations, such as an operation of drilling holes into an engine block. A typical CNC machine will have a work envelope within which the cutting operation is performed, a mounting block for holding the part to be operated upon, a spindle which generates a rotational force, a work tool for performing the drilling function, and a controller for instructing machine operation. In operation, a workpiece is placed in the mounting block, which is inside of the work envelope. The spindle, which has a drilling work tool attached, is then moved by a driver, which is directed by the controller, to drill holes in the workpiece in the correct locations along the workpiece. Generally, the spindle can be moved along the X, Y, and Z axes. A typical workpiece, such as an engine block, has six surfaces. As the workpiece must be held by the positioning block along at least one surface, the held surfaces are not available to the drilling work tool. As such, if a workpiece requires all six surfaces to be worked, the workpiece must be removed from the positioning block and reset such that the positioning block holds the workpiece along a different surface. Further, as the spindle is generally held from the top of the work envelope, the drilling is optimally carried out on the top surface of the workpiece. 
     In addition to improving the quality of manufactured components, improving the efficiency of the manufacturing process is also desirable. In this regard, the present CNC drilling machine has drawbacks. Placing the workpiece into the positioning block, repositioning the workpiece during operation, and removing the workpiece upon conclusion of the machining operation all reduce the efficiency of the system. Presently, the loading, unloading, and repositioning of the workpiece requires either: manpower, a separate robot, or a gantry loader. 
     Each of the alternatives has advantages and drawbacks. Manpower is flexible, however is also relatively expensive and can make errors in handling parts. Robots are accurate, but expensive. Gantry loaders are also expensive and must be custom designed. Further, all of the above options require the machine to be stopped and the safety doors to be opened, which in turn requires extra safety circuits and interlock programming to ensure safety. 
     Accordingly, a need exists in the art for an improvement in the loading, unloading, and/or repositioning of workpieces in a CNC drilling machine. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved device and method for loading, unloading, and/or repositioning a workpiece within a CNC machine so as to improve manufacturing efficiency while minimizing the drawbacks of the above described alternatives. 
     According to the present invention, the CNC machine includes a spindle, a part mounting block, a work tool, a gripper tool, and an automatic tool changer. The automatic tool changer allows for the work tool and the gripper tool to be interchangeably attached and detached from the spindle, so that the CNC machine can work a surface of a workpiece, can pick up and reposition the workpiece, and can then work a different surface of the workpiece. 
     According to the gripper tool of the present invention, the gripper tool includes an attachment portion, a translational driving portion, and a gripping portion. The attachment portion is connected with the spindle and is rotated by the spindle. The translational driving portion translates the rotation into linear movement. The gripping portion uses the linear movement to open and close claws disposed on the gripping portion. A controller associated with the CNC machine directs the gripper tool so as to position the gripper tool on the workpiece and to instruct the opening and closing of the gripper claws by controlling the rotational speed and direction of the spindle. 
     According to another aspect of the present invention, the gripper tool is used to facilitate the overall assembly process by receiving a workpiece into the CNC machine and outputting a machined workpiece from the CNC machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in conjunction with the embodiment shown in the drawings. The drawings are representative of the present invention and are not meant to limit the scope of the present invention. Reference to the drawings in describing the invention is only meant to simplify the description. 
         FIG. 1  schematically illustrates a CNC machine of the present invention. 
         FIG. 2  schematically illustrates a spindle of the present invention. 
         FIG. 3  schematically illustrates an automatic tool changer of the present invention. 
         FIG. 4A  schematically illustrates a gripper tool of the present invention. 
         FIG. 4B  is a perspective view of the gripper tool according to an alternate embodiment of the present invention. 
         FIG. 4C  schematically illustrates a sectional view of the gripper portion of the gripper tool of the present invention. 
         FIG. 5  illustrates a drill tool. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a CNC machine  100  includes a controller  102  and a work envelope  104 . The work envelope  104  has a top wall, a bottom wall, and two side walls cooperating to form a generally rectangular space that is accessible from at least one side via a selectively openable safety door  116 . The work envelope  104  receives a spindle  106 , a part mounting block  108 , an automatic tool changer  110 , a drill tool  112 , and a gripper tool  114 . As the CNC machine  100  described herein performs a cutting or drilling operation, it is important that the walls of the work envelope  104  and the safety door  116  are made of a strong material which will prevent any metal shards from escaping the work envelope  104  during machining. The work envelope  104  further defines a communication means to allow the controller  102  to connect with the CNC machine  100  components disposed within the work envelope  104 . 
     The controller  102  is connected with, and provides operating instructions to, the spindle  106 , the automatic tool changer  110 , and the part mounting block  108 . The spindle  106  is mounted to the top wall of the work envelope  104  so as to be movable in the X, Y, and Z directions, as is known in the art. The spindle  106  is generally conventional, and is adapted to receive rotary tools, and will be described hereinafter relative to the drill tool  112  and the gripper tool  114 . The part mounting block  108  is mounted generally centrally along the bottom wall of the work envelope  104 . The automatic tool changer  110  is disposed to a side of the spindle  106  along a side or back wall of the work envelope  104 . The automatic tool changer  110  is generally conventional, and is adapted to hold a plurality of rotary tools, including the drill tool  112  and the gripper tool  114 . As will be appreciated by those skilled in the art, the automatic tool changer  110  is adapted to install and remove rotary tools, such as the drill tool  112  and the gripper tool  114 , from the spindle  106 . 
     As mentioned above, the spindle  106  is movably mounted along a top wall of the work envelope  104 . As such, the spindle  106  can move so as to machine the top surface of the workpiece. The spindle  106  can be designed so as to have a swiveling head allowing the spindle  106  to work the side surfaces of the workpiece as well. However, it should be noted that since the workpiece must be mounted in the part mounting block  108 , some surface of the workpiece will always be inaccessible. 
     With reference to  FIG. 2 , the spindle  106  is shown in more detail. Specifically, the spindle  106  further includes a tool opening  118 , a connector  120 , and a driver  122 . The tool opening  118  is generally frustoconical in shape and extends laterally toward a center of the spindle  106 . The connector  120  is disposed at the inner or small end of the tool opening  118  and includes a retention notch  150  and lever arms  151 . The retention notch  150  is adapted to receive a retention knob  644 ,  144  associated with the work tools  112 ,  114 . The lever arms  151  secure the retention knob  644 ,  144  within the retention notch  150 . The secure reception of the retention knob  644 ,  144  within the retention notch  150  couples the work tool  112 ,  114  to the driver  122 , as will be explained in more detail below. 
     The driver  122  includes a motor  123  and a driver cone  99 . The motor  123  is drivingly attached to the driver cone  99 . The retention notch  150  is defined as an opening on a bottom end of the driver cone  99 , and the lever arms  151  extend through the driver cone  99 . Thus, the retention knob  644 ,  144  is coupled to the driver cone  99 , and is rotated by the rotation of the driver cone  99 . As will be described below, the retention knob  644 ,  144  is integrally formed with the work tool  112 ,  114 , such that as the retention knob  644 ,  144  is rotated, the work tool  112 ,  114  rotates integrally. It is noted that the spindle driving arrangement and the rotary connection between the spindle  106  and the work tool  112 ,  114 , briefly described herein, is conventional and well known in the art. 
     With further reference to  FIG. 1 , the part mounting block  108  is shown in detail. The part mounting block  108  can take several different forms. As shown, the part mounting block  108  is a vise-type mount, wherein arms  124  extend and retract, thereby locking the workpiece in place and then releasing the workpiece. The part mounting block  108  can be movably mounted within the work envelope  104 , so as to provide another axis of motion for the workpiece. As the part mounting block  108  is adapted to receive the workpiece, the part mounting block  108  may be specially fitted so as to receive a workpiece, or can be generally fitted to secure a broad variety of workpieces. It is believed that several mounting blocks are known in the art and may be used interchangeably with the present invention. 
     With reference to  FIG. 3 , the automatic tool changer  110  is shown in more detail. The automatic tool changer  110  includes a rotating leg  126  with a drill tool arm  128  and a gripper tool arm  130  disposed on either end of the rotating leg  126 . The rotating leg  126  rotates about a pivot post  132 , which runs through an opening in the center of the rotating leg  126 . The rotating leg  126  is driven by the automatic tool changer motor  134 . 
     As shown in  FIG. 3 , the automatic tool changer  110  has the rotating leg  126  situated generally horizontally and the pivot post  132  situated generally vertically, so that the rotating leg  126  and the pivot post  132  intersect each other in a generally perpendicular manner. The rotating leg  126  can rotate about the pivot post  132  and can also slide along the pivot post  132 . The changer motor  134  is adapted to move the rotating leg  126  up and down along the pivot post  132 , as well as rotate the rotating leg  126  about the pivot post  132 . 
     When idle, the rotating leg  126  is situated toward the top wall of the work envelope  104 , so as to remain out of the way of the spindle  106  and the work tool  112 ,  114 . When it is time for a tool change, the motor  134  drives the rotating leg  126  downward and rotates the empty arm  128 ,  130  toward the work tool  112 ,  114  attached to the spindle  106 . The arm  128 ,  130  grips the corresponding work tool  112 ,  114 . The controller  102  then instructs the lever arms  151  to release the retention knob  644 ,  144  of the work tool  112 ,  114 . The work tool  112 ,  114  is thereby released from the attachment to the spindle  106  and the motor  134  drives the rotating leg  126  further downward so as to remove the work tool  112 ,  114  from the spindle  106 . The motor  134  then rotates the rotating leg  126  so as to place the opposite arm  128 ,  130  below the spindle opening  118 . The motor  134  then drives the rotating leg  126  upward, so as to place the retention knob  644 ,  144  of the work tool  112 ,  114  into the retention notch  150  within the opening  118  of the spindle  106 . The controller  102  then directs the lever arms  151  to secure the retention knob  644 ,  144  to the retention notch  150 , thereby coupling the work tool  112 ,  114  to the driver cone  99 . The arm  128 ,  130  holding the tool  112 ,  114  then releases the tool  112 ,  114 , and the motor  134  drives the rotating leg  126  back to the idle position. The connection and disconnection of the work tools  112 ,  114  with the spindle  106  will be discussed in further detail below. 
     Automatic tool changers for CNC machines are well known and can take many different forms. The above description of an automatic tool changer  110  is merely one such example of an automatic tool change device and method. 
     With reference to  FIGS. 4A ,  4 B, and  5 , the work tools  112 ,  114  are shown in more detail.  FIG. 4A  shows a gripper tool  114  of the preferred embodiment, which includes an attachment portion  136 , a driving portion  138 , and a gripper portion  140 . 
     The attachment portion  136  is comprised of a frustoconical head  142  with the retention knob  144  integrally formed on the top portion thereof, a non-rotary housing  146 , and a positioning block  148 . The frustoconical head  142  is sized and shaped to fit in the spindle opening  118 . The retention knob  144 , as mentioned above, is adapted to be received within the retention notch  150  in the spindle opening  118 . The retention knob  144  fits through the opening of the retention notch  150 , and is secured within the retention notch  150  by the lever arms  151 . As described above, the retention notch  150  is the opening in the driver cone  99 , the driver cone  99  being operably connected to the motor  123 . Therefore, the connection of the retention knob  144  to the retention notch  150  defined in the driver cone  99 , couples the frustoconical head  142  to the motor  123 . As such, the rotation of the driver cone  99  is imparted to the frustoconical head  142 . 
     The housing  146  includes an opening  152  and an extension  154 . The opening  152  is adapted to receive the bottom portion of the frustoconical head  142  and the top portion of the gripper driving portion  138 . The frustoconical head  142  and the gripper driving portion  138  are integrally formed with one another and, as a singular unit, extend through the opening  152 . Therefore, the gripper driving portion  138  rotates with the frustoconical head  142 . 
     The housing extension  154  extends horizontally from the portion of the housing  146  defining the opening  152 , and supports the positioning block  148 . The positioning block  148  extends upward from the housing extension  154  so as to connect to the spindle  106 . The positioning block  148  connects to a non-rotary portion of the spindle  106 , and through the connection, stabilizes and prevents rotation of the housing  146 . Therefore, the housing  146  remains stationary as the frustoconical head  142  and the gripper driving portion  138  rotate within the opening  152 . 
     The gripper driving portion  138  is integrally formed with a bottom end of the frustoconical head  142 . The gripper driving portion  138  includes a driver  156 , a frame  158 , and a ball screw  160 . The driver  156  is the gripper driving portion  138  component that is integrally formed with the bottom end of the frustoconical head  142  and extends through the opening  152  in the housing  146 . The driver  156  rotates integrally with the frustoconical head  142 . The ball screw  160  is integrally attached to a bottom end of the driver  156 . 
     The ball screw  160  includes a threaded rod  162 , a housing  164 , an adapter  166 , and a piston  168 . The threaded rod  162  is attached to the driver  156  such that the threaded rod  162  rotates integrally with the driver  156 . The housing  164  defines a threaded opening sized to threadably receive the threaded rod  162 . The adapter  166  is connected to and extends horizontally from the housing  164  to support the piston  168 . The piston  168  is supported by the adapter  166  so as to be generally perpendicular to the adapter  166  and is generally parallel with the axis of the driver  156 . 
     The frame  158  includes a vertical support plate  170 , an upper support plate  172 , and a lower support plate  174 . An upper end of the vertical support plate  170  is attached to the housing  146  and is thereby held in a stationary, non-rotary position. The upper support plate  172  and the lower support plate  174  are disposed horizontally and are attached to the vertical support plate  170 . Thus, the arrangement of the frame  158  generally resembles an upside-down letter “F”. 
     The upper support plate  172  and the lower support plate  174  each define circular openings with bearings disposed therein, the circular openings/bearings adapted to fit the threaded rod  162 . The housing  164  is received between the upper and lower support plates  172 ,  174 , which are spaced a distance from one another to allow the housing  164  a range of vertical movement so as to drive the gripper portion  140 , as will be described in more detail below. 
     Further, the vertical support plate  170  defines an opening  176  that is positioned and sized so as to fit the adapter  166 . Specifically, the adapter  166  is slidably received within the opening  176  so as to be movable only in the vertical direction as rotation of the threaded rod  162  moves the housing  164  vertically. 
     The gripper portion  140  is attached to a bottom end of the vertical support plate  170  of the frame  158 , and is operably connected to the piston  168 . With reference to  FIG. 4C , the gripper portion  140  includes a gripper base  178 , a gripper actuator  180 , and gripper claws  182 . The gripper base  178  is attached to the vertical support plate  170  and houses the gripper actuator  180 . 
     A top end of the gripper base  178  defines a cylindrical opening  184  adapted to receive the piston  168 . The gripper actuator  180  is disposed at a bottom end of the cylindrical opening  184  and is operably attached to the piston  168 . 
     The gripper actuator  180  includes a pivot pin  186  and two elbows  188 . The gripper actuator  180  is adapted to convert the linear motion of the piston  168  into transverse motion opening and closing the gripper claws  182 . The pivot pin  186  is disposed along a central axis of the piston  168  and the cylindrical opening  184 . Each of the elbows  188  has a bent portion, such that the elbows are generally L-shaped. Each elbow  188  connects with the pivot pin  186  at one end, with the far end connecting to one of the gripper claws  182 . At the end of the elbows  188  which connects with the pivot pin  186 , each elbow  188  is operably connected to the piston  168 . In this regard, it is noted that the end of the elbows  188  connecting with the pivot pin  186  extends beyond the pivot pin  186  toward the piston  168 . The piston  168  defines an inverted U-shaped end  164 , so that each projection of the U shaped end  164  connects with one of the elbows  188 . 
     As the piston  168  moves downwardly, the inverted U-shaped end  164  engages the upper ends of the elbows  188  such that the lower elbow ends, and the claws  182  secured thereto, move toward one another. Similarly, when the piston  168  moves upwardly, the elbows  188  rotate in an opposite direction whereby the claws  182  move away from one another. 
     In operation, rotation of the driver  156  causes the threaded rod  162  to rotate. Since the housing  164  threadably engages the rod  162  but cannot rotate, rotation of the threaded rod  162  within the housing  164  causes the housing  164  to move linearly (up or down). As the housing  164  moves vertically, the adapter  166  and the piston  168  move integrally with the housing  164 . Thus, spindle rotation is translated into linear motion of the piston  168 . Linear movement of the piston  168  drives the claws  182  to open and close, as described above. 
     With reference to  FIG. 5 , the drill tool  112  includes an attachment portion  636 , a driving portion  638 , and a drill  640 . The attachment portion  636  has a frustoconical head  642  and a retention knob  644 , and is attached to the spindle  106  in the same manner as the gripper tool  114 . The drill tool  112  also includes a non-rotary housing  646  having an extension  654  supporting a positioning block  648 , and is attached to the spindle  106  in the same manner as the corresponding components of the gripper tool  114 . The non-rotary housing  646  defines a housing opening  652 , through which the frustoconical head  642  is connected to a drill driving portion  638 . The drill  640  is attached to a bottom end of the drill driving portion  638 . As the spindle  106  rotates the frustoconical head  642 , the drill driving portion  638  and the drill  640  rotate integrally with the frustoconical head  642  of the attachment portion  638 . It is noted that the drill tool  112  is conventional and well known in the art. 
     Operation of the CNC machine  100  as a whole will now be explained with reference to the gripper tool  114  shown in  FIG. 4A . Initially, the safety door  116  of the work envelope  104  is opened. The safety door  116  can be opened manually or by a separate automatic means, where the separate automatic means can be the controller  102  directing a motor (not shown) to open and close the safety door  116 . Once the safety door  116  is open, a workpiece (not shown) is placed on the part mounting block  108 . The workpiece can be placed on the part mounting block  108  manually, by the gripper tool  114  (the operation of the gripper tool  114  will be described in further detail below), or by an automated loader external to the CNC machine  100 . Once the workpiece is placed on the part mounting block  108 , the safety door  116  is closed. The controller  102  then instructs the mount arms  124  to extend and thereby securely grip the workpiece in the part mounting block  108 . 
     Assuming the drill tool  112  is attached to the spindle  106 , once the workpiece is secured in the part mounting block  108 , the machining of the workpiece can begin. As mentioned above, the spindle  106  is movable in the X, Y, and Z directions. Thus, with the present embodiment, the drill tool  112  can drill anywhere on the two-dimensional top surface of the workpiece. The drill tool  112  is moved in the X and Y direction to the proper drilling locations, and then lowered in the Z direction toward and into the workpiece so as to drill a hole at the correct position to the correct depth. The spindle  106  movement is controlled by the controller  102 . 
     The drill tool  112  can be utilized to drill as many holes as is necessary in the workpiece, with the instructions coming from the controller  102 . Once the drill tool  112  has completed drilling the holes in the top surface of the workpiece, the workpiece must be repositioned prior to the drill tool  112  being able to drill holes on any other workpiece surface. It should be noted that with advancements in drill technology, modern drilling tools have heads which can pivot, and therefore operate on surfaces other than the top surface of the workpiece. However, so long as the workpiece is clamped in the work envelope  104 , certain surfaces of the workpiece cannot be reachable by the drill tool  112 . For the purpose of the present description, the drill tool  112  will be described as only operating on the top surface of the workpiece. 
     Once the drill tool  112  has completed the drilling operations, assuming it is necessary to drill holes on another surface of the workpiece, the workpiece must be reoriented in the part mounting block  108 . This operation is performed by the gripper tool  114 . To utilize the gripper tool  114 , the automatic tool changer  110  must remove the drill tool  112  from the spindle  106  and install the gripper tool  114  in the spindle  106 . 
     Upon completion of the drilling operations, the spindle  106  moves the drill tool  112  to the uppermost, central position within the work envelope  104 . The controller  102  then instructs the automatic tool changer  110  to initiate the tool change. First, the rotating leg  126  is lowered along the pivot post  132  by the automatic tool changer motor  134  until the rotating leg  126  is in a vertical line with the drill tool  112 . Then, the motor  134  rotates the drill tool arm  128  toward the drill tool  112  until the drill tool arm  128  contacts the drill tool  112 . It is noted that, as the rotating leg  126  is divided in half by the pivot post  132 , each half of the rotating leg  126  with the respective tool arm  128 ,  130  disposed thereon, should be a length allowing the arm  128 ,  130  to operably receive the corresponding tool when the rotating leg  126  rotates the arm  128 ,  130  toward the work tool. As such, the work tool  112 ,  114  and spindle  106  need not be disposed centrally within the work envelope  104  so long as the work tool is within the reach of one half of the length of the rotating leg  126 . 
     When the drill tool arm  128  contacts the drill tool  112 , the drill tool arm  128  securely grips the drill tool  112 . At this point, the controller  102  instructs the lever arms  151  to release the retention knob  644 . Then, the drill tool arm  128 , together with the rotating leg  126 , are moved in a downward direction by the automatic tool changer motor  134 , releasing the drill tool  112  from the spindle  106 . Specifically, the retention knob  644  is released from the retention notch  150  of the spindle  106 . The drill tool  112  is then lowered by the rotating leg  126  so that the retention knob  644  is below the spindle opening  118 . 
     The controller  102  then instructs the motor  134  to rotate the rotating leg  126  as to move the drill tool arm  128  away from the spindle  106 , and move the gripper tool arm  130  to a position below the spindle  106  so that the retention knob  144  of the gripper tool  114  is directly below the retention notch  150  of the spindle  106 . The motor  134  then moves the rotating leg  126  upward so that the frustoconical head  142  of the gripper tool  114  fits in the opening  118  of the spindle  106 , until the retention knob  144  is received in the retention notch  150 . The lever arms  151  are then instructed to secure the retention knob  144  in the retention notch  150 , thereby connecting the gripper tool  114  with the driver cone  99 . As such, the gripper tool  114  is installed and ready for gripping operation. 
     The controller  102  then directs the gripper tool  114  to grip the workpiece. Initially, the spindle  106  is instructed to rotate so as to rotate the threaded rod  162  to cause the ball screw housing  164  and the piston  168  to move upward relative to the gripper claws  182 , opening the gripper claws  182 . The controller  102  then instructs the gripper tool  114  to move to a gripping location on the workpiece by moving the spindle  106  to the corresponding point on the X, Y, and Z axes. 
     Once the gripper tool  114  is in position, the spindle  106  rotates the threaded rod  162 , moving the ball screw housing  164  downwardly, causing the piston  168  to move downwardly, and forcing the gripper claws  182  to close to grip the workpiece. Once the workpiece is securely gripped by the gripper claws  182 , the controller  102  instructs the mount arms  124  to release the workpiece and then instructs the spindle  106  to raise the gripper tool  114  and the workpiece. The spindle  106  then moves the gripper tool  114 , which is holding the workpiece, and lowers the gripper tool  114 , so as to flip the workpiece and thereby place the workpiece in the part mounting block  108  with a different surface exposed to be worked on. In many CNC machines  100 , the part mounting block  108  is adapted to be movable along a fourth or fifth axis. When this is the case, the motion of the part mounting block  108  cooperates with the gripper tool  114  to assist in repositioning the workpiece. The mount arms  124  are then extended to lock the workpiece in position. The spindle  106  rotates the threaded rod  162  so as to move the ball screw housing  164  and the piston  168  upwardly, opening the claws  182 , and thereby releasing the workpiece. 
     Then, to machine the newly exposed surface, the operation of exchanging the gripper tool  114  with the drill tool  112  is performed. The operation for this exchange is the same as for replacing the drill tool  112  with the gripper tool  114 , except that the opposite arm  128 ,  130  of the rotating leg  126  is used to remove the gripper tool  114  and to install the drill tool  112 . Once the drill tool  112  is installed, the controller  102  instructs the drilling operation on the newly exposed surface. The process of drilling, tool exchange, and manipulating the workpiece is repeated until work on all surfaces of the workpiece is completed. Each iteration follows the same general method described above. At the completion of the operations, the mount arms  124  retract, thereby allowing the workpiece to be removed from the work envelope  104 . 
     With reference to  FIG. 4B , an alternate embodiment for a gripper tool  190  is shown. Specifically, the gripper tool  190  includes a frame  192 , a wedge  194 , a threaded rod  196 , and gripper claws  198 . The frame  192  is attached to the non-rotary housing  146 . 
     The frame  192  comprises two vertical plates  200 , a horizontal plate  202 , a spring mount  204 , and biasing springs  206 . The vertical plates  200  extend downwardly from the housing  146  so that broad faces of the vertical plates  200  face one another. The threaded rod  196  is connected with the attachment portion  136  in the same manner as the driver portion  138  is connected to the attachment portion  136  in the gripper tool  114  shown in  FIG. 4A . The threaded rod  196  is disposed between the vertical plates  200  and extends parallel to the vertical plates  200 , which connect to the horizontal plate  202 . The horizontal plate  202  defines an opening  208  lined with bearings that rotatably receive the threaded rod  196 . The spring mount  204  is attached to a bottom surface of the horizontal plate  202 . A biasing spring  206  extends between each lateral face of the spring mount  204  and an associated claw  198 . 
     The horizontal plate  202  also defines tabs  210  adapted to receive and support the claws  198  through a full range of claw  198  motion. The claws  198  are connected to the frame  192  via the spring mount  204  and the springs  206 . The springs  206  bias the claws  198  toward a closed position. 
     The wedge  194  has tapered sides and defines a threaded opening through its center, so that the wedge  194  threadably receives the threaded rod  196 . The wedge  194  is slidably received between the vertical plates  200 , so that as the threaded rod  196  rotates, the wedge  194  moves in linearly, up or down. The wedge  194  is positioned so that as the wedge  194  is lowered, the tapered sides of the wedge  194  progressively engage and slide down the inner surface of the claws  198 , driving the claws  198  open. As the wedge  194  is raised, the wedge  194  no longer forces the claws  198  away from one another, so that the biasing effect of the springs  206  causes the claws  198  to close. 
     It should be understood that other gripper variations can be used with the present invention. The gripping tools can take many different forms, and any gripping tool which is driven to perform the gripping function by the spindle rotation is considered to be within the scope of the present invention. Further, it should be understood that the gripper need not grip the workpiece by closing claws about a part of the workpiece. The gripper claws can also grip by entering a hole while together and then expanding to grip the workpiece by engaging the inner walls of the hole of the workpiece. 
     The gripper tool  114  defined in the present invention, in addition to manipulating the workpiece during operations, can be used in other ways to help improve overall system efficiency as well. Specifically, the gripper tool  114  can be integrated into a larger material flow operation. For the gripper tool  114  to facilitate such an operation, the gripper tool  114  is to be attached to the spindle  106  at the beginning of the operation and at the close of the operation. Specifically, the workpiece is to be delivered to the CNC machine  100  at the beginning of the operation. The controller  102  then instructs the opening of the safety door  116  and directs the spindle  106  to move the gripper tool  114  to the workpiece. The gripper tool  114  then grips the workpiece and carries the workpiece to the part mounting block  108 . The workpiece is set in the part mounting block  108  so as to have the initial surface of the workpiece operated on by the drill tool  112 . At the conclusion of working all surfaces of the workpiece, the gripper tool  114  is attached to the spindle  106 . The gripper tool  114  then picks up the workpiece, the controller instructs the opening of the safety door  116 , and the gripper tool  114  places the workpiece in an output carrier. 
     The carrier for bringing the workpiece to the CNC machine  100  and carrying the workpiece away from the CNC machine  100  can be of any variety typically used in an assembly operation. One such example is a conveyor system, wherein the workpiece rides along a conveyor before being picked up and then set back down by the gripper tool  114 . 
     It should be understood that the description of the embodiment provided above is to provide a simplified explanation of the present invention. Accordingly, several components associated with the invention were defined in a simple form. It is considered apparent that one skilled in the art would recognize variations and modifications which are considered to be in the scope of the present invention. Specifically, while the present invention is described as utilizing a drill tool  112 , any rotary tool could be substituted for the drill tool. 
     Further, there are many different kinds of CNC machines amenable for use with the present invention. While a vertical CNC machine has been described, the invention is also amenable for use with a horizontal CNC machine by moving the location of the components. Further, CNC machines commonly have part mounting blocks mounted on movable tables. The tables are adapted to move along fourth and/or fifth axes. This motion facilitates the repositioning of the workpiece.