Abstract:
A CNC controlled rotating workpiece holding fixture is attached to a tombstone of a horizontal mill. The rotating workpiece holding fixture(s) allows workpieces to be independently rotated to allow milling of various surface of the workpiece thereby providing a five axis CNC capability. As many as eight rotating workpiece holding fixtures may be attached to a single tombstone. Each rotating workpiece holding fixture may be formed by a harmonic drive driven by a servo motor which provides a compact configuration and a very low gear ratio in the harmonic drive combined with the inherent braking of the servo motor provides stability. The rotating workpiece holding fixtures may be controlled using existing auxiliary outputs (e.g., M-Codes), present in CNC milling machines. The M-Codes are preferably created by an operator, multiplexed, sent to the tombstone, de-multiplexed, and used to control each rotating workpiece holding fixture.

Description:
The present application claims the priority of U.S. Provisional Patent Application Ser. No. 61/533,051 filed Sep. 9, 2011, which application is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to horizontal milling machines and in particular to rotating workpiece holding fixtures providing a fifth CNC controlled axis. 
     Known horizontal milling machines include four CNC controlled axes: a vertical spindle axis (Y); a horizontal spindle axis (X); a lateral depth workpiece fixture axis (Z); and a workpiece vertical rotational axis (B). While five axis vertical and horizontal milling machines are available, they are generally about three times the cost of a four axis horizontal milling machine. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing at least one CNC controlled rotating workpiece holding fixture which is attached to a tombstone of a horizontal mill. The CNC controlled rotating workpiece holding fixture(s) allows workpieces to be independently rotated to allow milling of various surface of the workpiece thereby providing a five axis CNC capability. A preferred embodiment includes as many as eight rotating workpiece holding fixtures to attached to a single tombstone. In one embodiment, each rotating workpiece holding fixture is formed by a harmonic drive driven by a servo motor. The novel combination of the harmonic drive and servo motor provides a compact stable configuration and a very low gear ratio in the harmonic drive combined with the inherent braking of the servo motor provides stability. The rotating workpiece holding fixtures may be controlled using existing auxiliary outputs (e.g., G-codes and M-Codes), present in CNC milling machines. The G-codes are preferably created by an operator, multiplexed, sent to the tombstone, de-multiplexed, and used to control each rotating workpiece holding fixture. 
     In accordance with one aspect of the invention, there is provided a CNC controlled rotating workpiece holding fixture comprising a harmonic drive and a servo motor. Known rotatable workpiece holders use large motors to position the workpiece and provide position holding. There is not sufficient space on a tombstone to mount more than one of these motors. The combination of a low ratio harmonic drive, for example at least 50 to one, and a servo motor provides the necessary position holding in a small envelope. 
     In accordance with one aspect of the invention, there is provided a CNC controlled rotating workpiece holding fixture receiving a multiplexed control signal. Servo motors required suitable for the present invention require as many as twelve wires. A tombstone with, for example, eight rotating workpiece holding fixtures, would this require a 96 conductor cable. There is insufficient space for such a cable rendering this approach impractical. Multiplexing reduces the wire requirement from 96 to four which is practical for a multiplicity of rotating workpiece holding fixtures mounted to a tombstone. 
     In accordance with one aspect of the invention, there is provided a method for controlling rotating workpiece holding fixtures. The method includes. attaching a tombstone to the horizontal mill, attaching between two and eight CNC controlled rotating workpiece holding fixture mounted to the tombstone, each rotating workpiece holding fixture including a harmonic drive and a servo motor; executing a CNC program including M-codes and G-codes generating rotating workpiece holding fixture commands for each rotating workpiece holding fixture, sending parallel DPRNT commands to a control box for each rotating workpiece holding fixture, the parallel DPRNT commands generated by the CNC controller based on instruction in the G-code and provided to the control box, multiplexing the parallel DPRNT commands to provide a multiplexed signal, sending activation signals from the CNC controller to an M-code relay, the sending triggered by the M-code, forwarding the activation signals to a control box, providing the multiplexed parallel DPRNT commands generated by the control box to the tombstone after receiving the activation signal from the M-code relay, receiving the multiplexed parallel DPRNT commands by a controller residing in the tombstone and de-multiplexing the multiplexed parallel DPRNT commands to obtain individual rotating workpiece holding fixtures commands, providing position signals to the rotating workpiece holding fixtures and providing rotating workpiece holding fixture position information back to the controller, communicating from the controller to the control box providing a first motion finished signal to the control box, communicating between the control box and the M-code relay providing a second motion finished signal to the M-code relay and communicating between the M-code relay and the CNC controller providing a third motion finished signal to the CNC controller. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  shows a prior art horizontal milling machine. 
         FIG. 2  shows a horizontal milling machine including rotating workpiece holding fixtures attached to a tombstone according to the present invention. 
         FIG. 3  is a functional diagram for the horizontal milling machine including rotating workpiece holding fixtures attached to a tombstone according to the present invention. 
         FIG. 4  shows electrical details of the tombstone according to the present invention. 
         FIG. 5A  is a front view of the tombstone according to the present invention having two rotating workpiece holding fixtures. 
         FIG. 5B  is a side view of the tombstone according to the present invention having two rotating workpiece holding fixtures. 
         FIG. 5C  is a top view of the tombstone according to the present invention having two rotating workpiece holding fixtures. 
         FIG. 6  is a perspective view of the tombstone according to the present invention having two rotating workpiece holding fixtures. 
         FIG. 7A  is a front view of the tombstone according to the present invention having four rotating workpiece holding fixtures. 
         FIG. 7B  is a side view of the tombstone according to the present invention having four rotating workpiece holding fixtures. 
         FIG. 7C  is a top view of the tombstone according to the present invention having four rotating workpiece holding fixtures. 
         FIG. 8A  is a first perspective view of the tombstone according to the present invention having four rotating workpiece holding fixtures. 
         FIG. 8B  is a second perspective view of the tombstone according to the present invention having four rotating workpiece holding fixtures. 
         FIG. 9A  is a front view of the tombstone according to the present invention having four rotating workpiece holding fixtures on the same face of the tombstone. 
         FIG. 9B  is a side view of the tombstone according to the present invention having four rotating workpiece holding fixtures on the same face of the tombstone. 
         FIG. 9C  is a top view of the tombstone according to the present invention having four rotating workpiece holding fixtures on the same face of the tombstone. 
         FIG. 10  is a perspective view of the tombstone according to the present invention having four rotating workpiece holding fixtures on the same face of the tombstone. 
         FIG. 11A  is a front view of the tombstone according to the present invention having eight rotating workpiece holding fixtures. 
         FIG. 11B  is a side view of the tombstone according to the present invention having eight rotating workpiece holding fixtures. 
         FIG. 11C  is a top view of the tombstone according to the present invention having eight rotating workpiece holding fixtures. 
         FIG. 12A  is a first perspective view of the tombstone according to the present invention having eight rotating workpiece holding fixtures. 
         FIG. 12B  is a second perspective view of the tombstone according to the present invention having eight rotating workpiece holding fixtures. 
         FIG. 13  is an exploded perspective view of the tombstone according to the present invention having four rotating workpiece holding fixtures. 
         FIG. 14  is a cross-sectional view of the tombstone according to the present invention having four rotating workpiece holding fixtures taken along line  14 - 14  of  FIG. 9A . 
         FIG. 15  is a cross-sectional perspective view of the tombstone according to the present invention having four rotating workpiece holding fixtures taken along line  14 - 14  of  FIG. 9A . 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A prior art horizontal milling machine  10  is shown in  FIG. 1 . The horizontal milling machine  10  includes vertical guide  14  carrying a spindle  12  and a horizontal table  16  carrying a tombstone  18 . The tombstone  18  moves laterally along the table  16  to position a workpiece attached to the tombstone  18  for milling by a cutter  20  carried by the spindle  12 . 
     A horizontal milling machine  11  according to the present invention including rotating workpiece holding fixtures  24  attached to the tombstone  22  is shown in  FIG. 2 . Four of the rotating workpiece holding fixtures  24  are shown built into a face of the tombstone  22 . Other embodiments of the present invention are shown in  FIGS. 5A-12B . 
     A functional diagram for the horizontal milling machine  11  including the rotating workpiece holding fixtures  24  attached to the tombstone  22  is shown in  FIG. 3 . A CNC controller  30  includes CNC programs having, among other code, M-codes and G-codes. M-codes are activate commands and G-codes are operations. The operations described by the G-codes are executed only after the corresponding M-code is executed. The G-codes used by the present invention produce a set of parallel CNC position commands  32  sent to a control box  34  describing a set of positions for the rotating workpiece holding fixtures  24 , and the corresponding M-code produces an activate signal  31   a  sent to the M-code relay  33  to initiate a motion of the rotating workpiece holding fixtures  24  described by the parallel CNC position commands  32 . The parallel CNC position commands  32  are preferably carried over an RS232 cable from the CNC controller  30  to the control box  34 . After receiving the activate signal  31   a , the M-code relay  33  provides a initiate motion signal  35   a  to the control box  34 . The M-code relay  33  also provides a control signal  37  to the horizontal mill  11  to prevent machining while workpiece holders are in motion. 
     The control box  34  multiplexes the multiplicity of parallel CNC commands  32  which may be stored in the control box  34  for future use. After receiving the initiate motion signal  35   a  indicating that the rotating workpiece holding fixtures  24  can be moved (i.e., when machining has stopped), the control box  34  sends a multiplexed signal over data signal interface  36  to the tombstone  22  to control positions each of the rotating workpiece holding fixtures  24 . The tombstone  22  receives a power signal  39  from the control box  34  to power the rotating workpiece holding fixtures  24 . 
     The control box  34  receives position information back over the signal interface  36  and when the rotating workpiece holding fixtures  24  have reached the commanded positions, the control box  34  sends a motion complete signal  35   b  back to the M-code relay  33 , which forwards a motion complete signal (e.g., an M-fin signal)  31   b  to the CNC controller  30 , and the CNC controller  30  executes the next command in the CNC program. 
     Signal details of the tombstone  22  are shown in  FIG. 4 . A controller  38  receives and de-multiplexes the multiplexed CNC position commands  32  received over signal interface  36  for each of the rotating workpiece holding fixtures  24 . Individual rotating workpiece holding fixtures  24  receive commands over interface  40  between the controller  38  and each of the each rotating workpiece holding fixture  24 , and the signal interface  40  carries position information for each of the rotating workpiece holding fixtures  24  back to the controller  38 . When all of the CNC position commands  32  have been completed, a motion complete signal is sent to the control box  34  over the interface  36 . 
     A front view of the tombstone  22   a  according to the present invention having two rotating workpiece holding fixtures  24  is shown in  FIG. 5A , a side view of the tombstone  22   a  according to the present invention having two rotating workpiece holding fixtures  24  is shown in  FIG. 5B , a top view of the tombstone  22   a  according to the present invention having two rotating workpiece holding fixtures  24  is shown in  FIG. 5C , and a perspective view of the tombstone  22   a  according to the present invention having two rotating workpiece holding fixtures  24  is shown in  FIG. 6 . The tombstone  22   a  has two rotating workpiece holding fixtures  24  vertically separated on a first face  42   a  of the tombstone  22   a . The rotating workpiece holding fixtures  24  could be horizontally separated or diagonally separated, or on opposite faces  42   a  and  42   b  of the tombstone  22   a . The rotating workpiece holding fixtures  24  may be centered on one or both faces  42   a  and  42   b  for carrying large workpieces. 
     A front view of the tombstone  22   b  according to the present invention having four rotating workpiece holding fixtures  24  is shown in  FIG. 7A , a side view of the tombstone  22   b  according to the present invention having four rotating workpiece holding fixtures  24  is shown in  FIG. 7B , a top view of the tombstone  22   b  according to the present invention having four rotating workpiece holding fixtures  24  is shown in  FIG. 7C , a first perspective view of the tombstone  22   b  according to the present invention having four rotating workpiece holding fixtures  24  is shown in  FIG. 8A , and a second perspective view of the tombstone  22   b  according to the present invention having four rotating workpiece holding fixtures  24  is shown in  FIG. 8B . The tombstone  22   b  has two rotating workpiece holding fixtures  24  vertically separated on the first face  42   a  of the tombstone  22   b  and two rotating workpiece holding fixtures  24  vertically separated on the second face  42   b.    
     A front view of a tombstone  22   c  according to the present invention having four rotating workpiece holding fixtures  24  on the first face  42   a  of the tombstone  22   c  is shown in  FIG. 9A , a side view of the tombstone  22   c  having four rotating workpiece holding fixtures  24  on the first face  42   a  of the tombstone  22   c  is shown in  FIG. 9B , a top view of the tombstone  22   c  having four rotating workpiece holding fixtures  24  on the first face  42   a  of the tombstone  22   c  is shown in  FIG. 9B , and a perspective view of the tombstone  22   c  having four rotating workpiece holding fixtures  24  on the first face  42   a  of the tombstone  22   c  is shown in  FIG. 10 . 
     A front view of a tombstone  22   d  according to the present invention having eight rotating workpiece holding fixtures  24  is shown in  FIG. 11A , a side view of the tombstone  22   d  having eight rotating workpiece holding fixtures  24  is shown in  FIG. 11B , a top view of the tombstone  22   d  having eight rotating workpiece holding fixtures  24  is shown in  FIG. 11C , a first perspective view of the tombstone  22   d  having eight rotating workpiece holding fixtures  24  is shown in  FIG. 12A , and a second perspective view of the tombstone  22   d  having eight rotating workpiece holding fixtures  24  is shown in  FIG. 12B . 
     An exploded perspective view of the tombstone  22   c  having four rotating workpiece holding fixtures  24  is shown in  FIG. 13 , a cross-sectional view of the tombstone  22   c  taken along line  14 - 14  of  FIG. 9A  is shown in  FIG. 14 , and a cross-sectional perspective view of the tombstone  22   c  taken along line  14 - 14  of  FIG. 9A  is shown in  FIG. 15 . The rotating workpiece holding fixtures  24  are preferably harmonic drives  44  driven by servo motors  46 , for example, the Harmonic Systems model number CSG-32-160-2UH-SPxxx harmonic drive. The commonly used rotating workpiece holders (or indexers) for milling machines uses a screw drive. Unfortunately, a screw drive is to big and bulky to fit into a tombstone. Additionally, the harmonic drive provides a gear ratio (a reduction) of at least 50 to 1, and preferably about 160 to 1, which combined with the braking of the servo motor has an important benefit of preventing the workpiece from rotating during milling. The preferred harmonic drive and servo motor provides about 250 Mn of torque. 
     Standard horizontal milling machines use CNC programs which include G-Code and M-Code to control the machine. M-Codes may be used to trigger auxiliary outputs (e.g., activate and de-activate signals sent to external devices) which enable users to control and monitor the external devices. The CNC controllers  30  also have an RS232 output port configured to communicate with the external devices to describe operations. To use the RS232 port, special commands called DPRNT commands are used to send information from the RS232 port. The present invention uses the M-Codes activate signals and RS232 port to control the rotating workpiece holding fixtures  24 . The DPRNT commands contain information about the angle to which each rotating workpiece holding fixtures  24  is commanded to rotate, and the M-Code triggers the rotating workpiece holding fixtures  24  to start rotating. 
     When the CNC controller  30  encounters an M-Code, the CNC controller  30  sends the activate signal to turn on the low voltage M-code relay  33  and waits for conformation (e. g., the M-fin signal). The activate signal is forwarded to the control box  34  and initiates rotation the rotating workpiece holding fixtures  24  on the tombstone  22  to the proper angle(s). Once the movement is completed, the control box  34  sends back a completed signal  35   b  to the M-code relay  33  which sends the M-fin signal  31   b  to the CNC controller  30  allowing the CNC machine to continue with the next operation. Using this DPRNT command along with the M-Code allows each indexer to move simultaneously or independently. 
     Examples of sample codes are: 
     Sample programming for Tombstone and Turnnion (independent movements on drives): 
     DPRNT[C1*90.]; (Moves top left side drive clockwise to 90°) 
     M21; (or user defined M-Code) 
     DPRNT[C2*180.]; (Moves top right side drive clockwise to 180°) 
     M21; (or user defined M-Code) 
     DPRNT[C3*-180.] (Moves bottom left side drive clockwise to −180°) 
     M21; (or user defined M-Code) 
     DPRNT[C4*25.] (Moves bottom left side drive clockwise to 25°)) 
     M21; (or user defined M-Code); and 
     Sample programming for Tombstone and Turnnion (simultaneous movements on drives): 
     DPRNT[C1*90.]; (Moves top left side drive clockwise to 90°) 
     DPRNT[C2*180.]; (Moves top right side drive clockwise to 180°) 
     DPRNT[C3*-180.] (Moves bottom left side drive clockwise to −180°) 
     DPRNT[C4*25.] (Moves bottom left side drive clockwise to 25°) 
     M21; (or user defined M-Code) 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.