Abstract:
A cutting machine is provided using two electric motors that are run simultaneously. A coupling assembly is interconnected between a tool holder and the drive motors to selectively engage the drive motors. One of the drive motors is used to move the tool holder in a forward direction, and the other drive motor is used to move the tool holder in a rearward direction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a cutting machine, and more particularly, the invention relates to a cutting machine suitable for use in tapping holes.  
         [0002]     Numerous machining operations require hole tapping to form threads. Typical tapping machines use a single motor that is driven in both forward and reverse rotational directions. The motor may be rotationally coupled to a lead screw, which supports a tool holder having the tapping tool. Rotation of the lead screw advances and retracts the tapping tool.  
         [0003]     To form the threads in a part, the tapping tool is rotationally driven in a forward direction. Once the tapping tool reaches the desired depth, the motor must be stopped so that the tapping tool may be rotationally driven in the reverse direction to retract the tapping tool from the part. Relatively large motors are used in the tapping machine so that a significant amount of kinetic energy must be overcome in stopping the motor. Moreover, the motors have special control packages relating to stopping and changing the rotational direction of the motor, and these control packages are expensive to operate and maintain. In addition to the special control packages, the motors themselves are typically specially constructed to perform such a tapping operation. For example, since the lead screw is directly coupled to the motor, the bearings of the motor must withstand the thrust loads during the tapping operation.  
         [0004]     As with any machining operation, it is desirable to use low cost equipment that has minimal set-up time and maintenance. Furthermore, it is desirable to have a fast cycle time to increase the through-put of the parts through the tapping operation.  
       SUMMARY OF THE INVENTION  
       [0005]     The inventive tapping machine provides a lead screw assembly having a tool holder. The lead screw assembly is supported on bearing blocks and, in one example, supports a pair of driven sprockets at an end opposite the tool holder. The lead screw assembly and first and second motors are supported on a machine support structure. The first and second motors are interconnected to the lead screw by drive belts. For the example shown, each of the first and second drive motors may include a clutch brake driven by the motors. The clutch brakes support a drive sprocket that is coupled to the driven sprockets by the drive belts.  
         [0006]     The first and second motors are driven simultaneously, and the clutch/brakes are manipulated to selectively rotationally couple the motors to the lead screw to advance and retract the tool holder. For example, the first motor brake/clutch is engaged while the second motor brake/clutch is disengaged to rotationally drive the lead screw in a first direction and advance the tool holder. The first motor clutch/brake is disengaged and the second motor clutch/brake is engaged to rotationally drive the lead screw in an opposite second direction to retract the tool holder. A controller is connected to various sensors, valves, and/or actuators to monitor and control the automated operation of the tapping machine.  
         [0007]     Accordingly, the above invention provides a low cost topping machine having a fast cycle time with minimal set-up time and maintenance.  
         [0008]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of one example of this invention with the controls and sensors depicted schematically.  
         [0010]      FIG. 2  is a flowchart of one of the inventive embodiments. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]     The inventive cutting machine  10  is shown in  FIG. 1 . The cutting machine  10  may be used for tapping holes in tapping plates used in oil filters. However, although the cutting machine  10  is described relative to tapping operations, one of ordinary skill in the art will appreciate that the inventive cutting machine  10  may be used for any number of machining operations.  
         [0012]     The cutting machine  10  includes a support structure  12  that comprises various plates and bracketry for supporting the components of the cutting machine  10 . First  14  and second  16  motors are mounted on the support structure  12 . In one example embodiment, the motors  14  and  16  may be standard 900 rpm 215T frames, which are one-fifth the cost of the tapping motors typically used in tapping machines. The motors  14  and  16  operate continuously in one direction, so there is no requirement for stopping and reversing the motors, which increases the motor life and extends cycle time. The motor  14  and  16  are controlled by standard AC inverter drives, which are one-tenth the cost of prior art controllers.  
         [0013]     The motors  14  and  16  are interconnected to a lead screw  24  by a coupling assembly  17 . The lead screw  24  is mounted on the support structure  12  using bearing blocks  26 . An end of the lead screw  24  includes a tool holder or chuck  28  supporting a tapping tool  30 . The bearing blocks  26  withstand the thrust load typically experienced by the prior art reversible motor.  
         [0014]     The inventive cutting machine  10  may be configured in any number of arrangements. For the example shown, the first  14  and second  16  motors are mounted with their rotational axes parallel to one another in the example shown. In that example, the motor axes are offset from the axis of the lead screw  24  and parallel to the lead screw  24 .  
         [0015]     The coupling assembly  17  comprises components transferring rotation from the motors  14  and  16  to the tool holder  28 . The first motor  14  rotationally drives a clutch/brake  18 . The clutch/brake  18  supports a drive sprocket  20  that is coupled to a driven sprocket  22 , which is supported on the end of the lead screw  24  opposite the chuck  28 , by a drive belt  23 . Similarly, the second motor  16  rotationally driven a clutch/brake  32  having a drive sprocket  34 . The drive sprocket  34  is coupled to a driven sprocket  36  on the lead screw  24  by the belt  38 . The driver sprockets  22  and  36  are supported on a jackshaft coupled to the lead screw.  
         [0016]     For the example shown, the clutch/brakes  18  and  32  may be double acting piston units available from the Carlson Company, PowerFlo Model No. 1375CAB-CS. Air from an air source  40  is coupled to the clutch/brakes  18  and  32  using pneumatic lines and valves  44 . The valves  44  and air source  40  are shown schematically and may be arranged in any suitable manner. When air is applied to a clutch port, the piston moves to engage the clutch and release the brake. When air is supplied to a brake port, the piston disengaged the clutch and engages the brake. More detail of the operation of the clutch/brakes  18  and  32  will be described below.  
         [0017]     A controller  46  is connected to the valves  44  and other sensing devices and actuators to control and monitor the automated operation of the cutting machine  10 . The lead screw  24  includes a feature  48  used in detecting the longitudinal position of the tapping tool  30 . A forward  50  and rearward  52  stroke sensor may be mounted on a plate near the feature  48 . The feature  48  is aligned with the forward stroke sensor  50  when the tapping tool reaches its forward-most desired position. Similarly, the feature  48  is aligned with the rearward stroke sensor  52  when the tapping tool  30  reaches its rearward-most desired position. The cutting machine  10  may also include an overrun sensor  54  that is aligned with the feature  48  when the tapping tool  30  is in an undesired position. The sensors  50 ,  52 , and  54  are connected to the controller  46 .  
         [0018]     A machine  56  moves and holds a part  58  to be machined in a desired manner near the tapping tool  30 . The machine  56  may include a part position sensor  60  that is connected to the controller  46  to coordinate the operation of the clutch/brakes  18  and  32 .  
         [0019]     One example of the inventive cutting process  62  is shown in  FIG. 2 . The first  14  and second  16  motors are simultaneously driven, as indicated at  64 . For the example shown, the motors  14  and  16  are driven in opposite directions relative to one another. During start-up, both brakes of the clutch/brakes  18  and  32  may be engaged. Once the part position sensor  60  detects a part  58  in a desired position, the clutch port of the clutch/brake  18  of the first motor  14  is pressurized to engage the clutch and release the brake. Once the clutch is engaged, as indicated at  66 , the lead screw assembly is rotationally driven by the belt  23  to advance the tapping tool, as indicated at  68 . The hole in the part  58  is tapped to form the threads.  
         [0020]     Once the forward stroke sensor  50  detects the feature  48 , the brake port of the clutch/brake  18  is pressurized to disengage the clutch and engage the brake, which stops the forward rotation of the lead screw  24 , as indicated at  70 . The clutch/brake  32  of the second motor  16  is manipulated to rotationally drive the lead screw  20  in reverse. Specifically, the clutch port of the clutch/brake  32  is pressurized to engage the clutch and release the brake which rotationally drives the lead screw  24  rearward through belt  38 , as indicated at  72 . The tapping tool  30  is retracted as indicated at block  74 . The machine  56  moves the next part  58  into the desired position. Once the part position sensor  60  detects the part  58  and the rearward stroke sensor  52  detects the feature  48 , the tapping operation is repeated.  
         [0021]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.