Universal adaptive machining chatter control fixture

• US 6,241,435 B1
• Filed: 03/25/1998
• Issued: 06/05/2001
• Est. Priority Date: 03/25/1998
• Status: Expired due to Fees

• Current Assignee: Vought Aircraft Industries, Inc. (Triumph Group, Inc.)
• Original Assignee: Vought Aircraft Industries, Inc. (Triumph Group, Inc.)
• Inventors: Van Nostrand, William C., Huang, Chien Y., Haas, Edwin G.
• Primary Examiner(s): BRIGGS, WILLIAM R
• Application Number:
  US09/048,403
• Time in Patent Office: 1,168 Days
• Field of Search: 29/565, 409/80, 409/131, 409/132, 409/141, 409/10, 821/58, 451/10, 451/9, 451/5, 451/11, 408/6, 408/143, 318/575, 318/571, 318/632, 318/649, 318/611, 364/474.19, 364/474.01, 269/305, 700/177
• US Class Current: 409/141
• CPC Class Codes: B23Q 17/0976 Detection or control of chatter B23Q15/12 takes precedence
• CPC Class Codes: B23Q 17/098 by measuring noise
• CPC Class Codes: B23Q 17/12 for indicating or measuring vibration
• CPC Class Codes: B23Q 5/225 not mechanically connected to the main drive, e.g. with separate motors connected to main drive through servomotors B23Q5/36
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence
• CPC Class Codes: G05B 2219/49048 Control of damping of vibration of machine base
• CPC Class Codes: Y10T 409/303752 Process
• CPC Class Codes: Y10T 409/304312 with means to dampen vibration

Abstract

A method for automatically minimizing an undesirable motion of a workpiece during a machining operation, and a universal adaptive machining chatter control fixture that operates in accordance with the method. The method comprises the steps of mounting the workpiece to an active, supporting structure, and then machining the workpiece. During the step of machining, an undesirable motion of the workpiece is sensed in the supporting structure. Thereafter, a compensating motion is applied to the supporting structure for minimizing the undesirable motion of the workpiece. The chatter control fixture can be attached to various types of machine tool devices, without requiring that the machine tool devices be retrofitted, and operates to minimize undesirable motions of the workpiece independently of the machine tool devices.

Claims

1. A method of minimizing an undesirable motion of a workpiece during a machining operation, comprising the steps of:

mounting the workpiece to a supporting structure;

machining the workpiece and, during the step of machining;

sensing, in the supporting structure an undesirable motion of the workpiece, said sensing step including a step of detecting an acceleration of the supporting structure and optionally also acoustic vibrations produced as a result of the undesirable motion, and wherein said step of sensing is performed by sensing accelerations of at least one of the workpiece and the supporting structure, along the x, y, and z axes; and

generating a compensating motion in the supporting structure for minimizing the undesirable motion of the workpiece, wherein the compensating motion is generated based on the detected acceleration and optionally also the acoustic vibrations.

2. A method of minimizing an undesirable motion of a workpiece during a machining operation as in claim 1, wherein, said undesirable movement of said workpiece, which is sensed, comprises machining chatter.

4. A method as set forth in claim 1, in which acoustic sensors are provided on the supporting structure and the method is performed to detect and minimize chatter-induced acoustic vibrations before they reach a level at which they become audible.

5. A method as set forth in claim 1, wherein the step of sensing is performed on a real-time basis and as dynamic changes occur to characteristics of the workpiece as a result of the step of machining.

6. A method as set forth in claim 1, wherein the step of sensing includes a step of producing, in response to sensing the undesirable motion of the workpiece, a signal corresponding to the undesirable motion of the workpiece;

and

wherein the step of generating includes steps of comparing the signal with a reference signal to produce an error signal, and generating the compensating motion so as to minimize a magnitude of the error signal.

7. A method as set forth in claim 1, wherein the supporting structure is secured to a separate machine tool structure, and wherein the steps of sensing and generating are performed independently of operations performed by a controller of said machine tool structure.

3. A universal adaptive machining chatter control process for minimizing workpiece chatter in a machine tool structure, said process comprising:

providing an active bed device comprising, an active bed for supporting a workpiece and a base for movably supporting said active bed for movement in at least x, y and z directions, said base being adapted to be secured to said bed of said machine tool structure;

securing a workpiece directly or indirectly to said active bed;

sensing any undesirable movement of said workpiece in at least the x, y and z directions during machining;

responsive to said sensing step, controlling the position of said active bed in the x, y or z directions, or any desired combination thereof, in a manner which will minimize any undesirable movement of said workpiece.

8. A chatter control device for a machining structure, comprising:

means for securely supporting a workpiece;

sensing means located in said support means, said sensing means for sensing, in said supporting means, an undesirable motion of said workpiece during a machining operation of said workpiece, said sensing means also for outputting a detection signal in response to sensing the undesirable motion of said workpiece, said detection signal corresponding to the undesired motion of said workpiece, said sensing means comprising at least one accelerometer for sensing accelerations of said workpiece along the x, y, and z axes; and

motion generating means, coupled to an output of said sensing means, said motion generating means for generating, in response to receiving said detection signal, a compensating motion in said supporting means to minimize the undesirable motion of said workpiece.

9. A universal adaptive machining chatter control fixture as in claim 8 wherein, said undesirable movement of said workpiece, which is sensed, comprises machining chatter.

10. A chatter control device as set forth in claim 8, wherein said sensing means further comprises means for sensing acoustic vibrations resulting from said undesirable motion of said workpiece.

11. A chatter control device as set forth in claim 8, wherein said supporting means further comprises at least three corner edges, and wherein said chatter control device further comprises at least three accelerometers, each of said accelerometers being located at a respective one of the corner edges for sensing accelerations of at least one of said supporting means and said workpiece along a respective one of the x, y, and z axes.

12. A chatter control device as set forth in claim 8, wherein said supporting means comprises an active bed having an upper surface for securely supporting said workpiece, and wherein said motion generating means includes:

a control processor, coupled to the output of said sensing means, said control processor being responsive to said detection signal for generating information representative of a position of the active bed, said control processor also for comparing the information to a predetermined reference parameter, and for generating a control signal in response to determining that said information does not equal said predetermined reference parameter, wherein said control signal specifies that said compensating motion be applied to said supporting means;

a base portion; and

actuating means, said actuating means including a first portion supported in said base portion and a second portion extending from said base portion and supporting said active bed, said second portion of said actuating means for applying said compensating motion to said active bed in response to said actuating means receiving said control signal.

13. A chatter control device as set forth in claim 8, wherein said motion generating means includes a closed-loop control system having an input coupled to the output of said sensing means, said closed-loop control system being responsive to said detection signal for controlling at least one of an amplitude, phase, and frequency of said compensating motion, based on a comparison of said detection signal to a predetermined reference parameter, and wherein an output of said closed-loop control system provides information relating to said machining operation.

14. A chatter control device as set forth in claim 8, wherein said supporting means comprises means for securing said supporting means to a machine bed of a machine tool structure.

15. A chatter control device as set forth in claim 14, wherein said securing means includes at least one slot for receiving a bolt for engaging with said machine bed for securing said supporting means to said machine bed.

16. A universal adaptive machining chatter control fixture for attachment to a bed of a machine tool structure, said fixture comprising:

an active bed for supporting a workpiece and a base for movably supporting said active bed for movement in at least x, y and z directions, said base being adapted to be secured to the bed of said machine tool structure;

means for securing a workpiece directly or indirectly to said active bed;

means for sensing any undesirable movement of said workpiece in at least the x, y and z directions during machining;

actuating means for adjusting the position of said active bed in the x, y or z directions or any desired combination thereof; and

control means responsive to said sensing means for controlling said actuating means in a manner which will minimize any undesirable movement of said workpiece.

17. A universal adaptive machining chatter control fixture as in claim 16 wherein, said sensing means comprises means for sensing movement of said active bed in said at least x, y and z directions.

18. A universal adaptive machining chatter control fixture as in claim 17 wherein, said control means comprises:

a control processor coupled to the output of said sensing means, said control processor responsive to said sensing means, generating a signal representative of a position of said active bed, comparing said signal to a predetermined reference parameter, generating a control signal in response to the difference between said position signal and said reference parameter for application to said actuating means to provide a compensating motion to said active bed to minimize chatter of said workpiece.

19. A universal adaptive machining chatter control fixture as in claim 18 wherein, said base has an open box like shape comprising a base portion for securing to said bed of said machine structure and a wall portion arranged about a periphery of said base portion and wherein said active bed includes a first portion which is adapted to extend over said wall portion and a second portion which is adapted to extend into the opening in said base so that it is surrounded by said wall portion and wherein said actuating means are supported by said base portion and said wall portion of said base and are adapted to engage said second portion of said active bed to adjust the position of said active bed.

20. A universal adaptive machining chatter control fixture as in claim 19 wherein said wall has a rectilinear shape and said actuating means comprises means for providing a directional force responsive to an applied electrical signal from said control means.

21. A universal adaptive machining chatter control process as in claim 20 wherein, said undesirable movement of said workpiece, which is sensed, comprises machining chatter.

22. A universal adaptive machining chatter control process as in claim 20 wherein, said sensing step comprises sensing movement of said active bed in said at least x, y and z directions.

23. A universal adaptive machining chatter control fixture as in claim 16 wherein, said undesirable movement of said workpiece, which is sensed, comprises machining chatter.