CNC machine having interactive control of corner tolerance that is programmed to vary with the corner angle

• US 6,317,646 B1
• Filed: 03/17/1998
• Issued: 11/13/2001
• Est. Priority Date: 03/19/1997
• Status: Expired due to Fees

• Current Assignee: Fadal Engineering Company Incorporated
• Original Assignee: Fadal Machining Centers Incorporated
• Inventors: de Caussin, David Michael, de Caussin, Glenn F.
• Primary Examiner(s): Grant, William
• Assistant Examiner(s): Rapp, Chad
• Application Number:
  US09/040,116
• Time in Patent Office: 1,337 Days
• Field of Search: 700/172, 700/173, 700/175, 700/186, 700/187, 700/188, 700/193, 700/302, 700/303
• US Class Current: 700/173
• CPC Class Codes: G05B 19/40937 concerning programming of machining or material parameters, pocket machining
• CPC Class Codes: G05B 2219/36279 Machining parameter is strategy for making corners
• CPC Class Codes: G05B 2219/36281 Machining parameter is technology: surface roughness, corner, contour tolerance
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

Abstract

A CNC machine is programmed to redefine the corner tolerance as a function of the corner angle based on a recognition that corners having angles not equal to 90° have effective corner tolerances that are equal to the corner tolerance specified by the operator divided by the sine of the corner angle. An increase in machining speed is achieved, because, at corner angles not equal to 90°, the redefined corner tolerance is larger than the operator-specified corner tolerance and the CNC machine is permitted to machine the corner at an earlier time than conventional CNC machines. The CNC machine is also programmed to provide the operator with an interactive control of the parameters that control the speed and accuracy of machining. With this feature, the operator is able to observe the effects of changing the control parameters on the speed and accuracy of machining, and to customize the control parameters to a particular type of tool or application based on the observations.

Claims

1. In a positioning device, a method of moving a tool relative to a workpiece along a programmed path, the method comprising the steps of:

(a) specifying a tolerance;

(b) executing the programmed move to generate a sequence of move command signals, each move command signal indicating a desired position of the tool relative to the platform along the programmed path;

(c) moving the tool relative to the platform through a sequence of incremental moves in accordance with the move command signals, wherein, if the desired position indicated by a current move command signal is a corner on the programmed path, moving the tool relative to the platform along the programmed path until the position of the tool relative to the platform is within an allowable distance from the corner, and once the position of the tool relative to the platform is within the allowable distance from the corner, moving the tool relative to the platform towards a point on the programmed path beyond the corner in accordance with a next move command signal,

wherein the allowable distance is larger than the specified tolerance.

2. The method according to claim 1, wherein the allowable distance is derived as a function of the specified tolerance and an angle of the corner.

3. In a positioning device, a method of moving a tool relative to a workpiece along a programmed path, the method comprising the steps of:

(a) specifying a tolerance;

(b) executing the programmed move to generate a sequence of move command signals, each move command signal indicating a desired position of the tool relative to the platform along the programmed path;

(c) moving the tool relative to the platform through a sequence of incremental moves in accordance with the move command signals, wherein, if the desired position indicated by a current move command signal is a corner on the programmed path, moving the tool relative to the platform along the programmed path until the position of the tool relative to the platform is within an allowable distance from the corner, and once the position of the tool relative to the platform is within the allowable distance from the corner, moving the tool relative to the platform in accordance with a next move command signal; and

(d) interactively modifying the specified tolerance during the step of moving, wherein the allowable distance is larger than the specified tolerance, and

wherein the allowable distance is derived as a function of the specified tolerance and an angle of the corner.

4. In a positioning device, a method of moving a tool relative to a workpiece along a programmed path, the method comprising the steps of:

(a) specifying a tolerance;

(b) executing the programmed move to generate a sequence of move command signals, each move command signal indicating a desired position of the tool relative to the platform along the programmed path;

(c) moving the tool relative to the platform through a sequence of incremental moves in accordance with the move command signals, wherein, if the desired position indicated by a current move command signal is a corner on the programmed path, moving the tool relative to the platform along the programmed path until the position of the tool relative to the platform is within an allowable distance from the corner, and once the position of the tool relative to the platform is within the allowable distance from the corner, moving the tool relative to the platform in accordance with a next move command signal,

wherein the allowable distance is larger than the specified tolerance, and wherein each step of incremental moving includes the steps of producing a position correction signal based on a difference between a current position of the tool relative to the platform and the desired position indicated by the current move command, and moving the tool relative to the platform to a desired velocity based on the position correction signal.

5. The method according to claim 4, wherein each step of incremental moving further includes the steps of producing a velocity correction signal based on a difference between a current velocity signal of the tool relative to the platform and the position correction signal, and moving the tool relative to the platform based on the velocity correction signal.

6. The method according to claim 5, further comprising the step of interactively modifying a gain during the step of moving, wherein the gain represents sensitivity of the position correction signal to the difference between the current and desired positions of the tool relative to the platform.

7. In a positioning device, a method of moving a tool relative to a workpiece along a programmed path, the method comprising the steps of:

(a) specifying a tolerance;

(b) executing the programmed move to generate a sequence of move command signals, each move command signal indicating a desired position of the tool relative to the platform along the programmed path;

(c) moving the tool relative to the platform through a sequence of incremental moves in accordance with the move command signals, wherein, if the desired position indicated by a current move command signal is a corner on the programmed path, moving the tool relative to the platform along the programmed path until the position of the tool relative to the platform is within an allowable distance from the corner, and once the position of the tool relative to the platform is within the allowable distance from the corner, moving the tool relative to the platform in accordance with a next move command signal; and

(d) interactively modifying a programmed feed rate during the step of executing, wherein programmed feed rates are adjusted in accordance with the modified programmed feed rate and the adjusted programmed feed rates are employed during the step of executing,

wherein the allowable distance is larger than the specified tolerance.

8. In a CNC machine, a method of cutting a corner portion of a workpiece to a specified tolerance, the method comprising the steps of:

(a) cutting along a programmed cutting path toward a corner of the programmed cutting path; and

(b) when the cut specified in step (a) is within an allowable distance from the corner that is larger than the specified tolerance, cutting towards a point on the programmed path beyond the corner.

9. The method according to claim 8, wherein the allowable distance is equal to the specified tolerance divided by the sine of the angle of the corner.

10. The method according to claim 8, further comprising the step of programming the cutting path.

11. The method according to claim 8, wherein the step of cutting includes the steps of:

generating a desired position of the cut that is ahead of a current position of the cut;

determining a velocity of the cut based on a specified gain and a difference between the desired position and the current position; and

controlling an actual velocity of the cut to be equal to the determined velocity of the cut.

12. The method according to claim 11, further comprising the step of interactively modifying one of the specified tolerance and the specified gain during the step of cutting.

13. A CNC machine for cutting a corner portion of a workpiece, comprising:

a tool;

a platform;

a programmable control unit programmed to control the movement of the tool relative to the platform along a programmed path;

a drive assembly connected to at least one of the tool and the platform to move the tool relative to the platform along the programmed path,

wherein, once the drive assembly moves the tool relative to the platform to a position that is within an allowable distance from a corner of the programmed path, the tool is moved relative to the platform towards a point on the programmed path beyond the corner,

wherein the allowable distance varies with respect to an angle of the corner.

14. The CNC machine according to claim 13, wherein the allowable distance is derived as a function of a tolerance specified for corner cuts divided by the sine of the angle of the corner.

15. The CNC machine according to claim 13, wherein the programmable control unit generates a desired position of the tool relative to the platform at a location that is ahead of a current position thereof, and the drive assembly includes a servo controller which determines a velocity of the tool relative to the platform based on a difference between the desired position and the current position.

16. The CNC machine according to claim 15, wherein the drive assembly further includes an amplifier which controls an actual velocity of the tool relative to the platform to be equal the velocity determined by the servo controller.

17. The CNC machine according to claim 13, further comprising an interactive user interface permitting adjustments to a control parameter that affects the movement of the tool relative to the platform along the programmed path, and a handwheel for adjusting the control parameter in accordance with a rotation of the handwheel.

18. The CNC machine according to claim 17, wherein the control parameter includes a tolerance specified for corner cuts and the allowable distance is larger than the specified tolerance.

19. The CNC machine according to claim 18, wherein the drive assembly moves the tool relative to the platform with a velocity that is determined with respect to a specified gain of the drive assembly, and wherein the programmable control unit limits the programmed acceleration of the tool relative to the platform based on a specified ramp time.

20. The CNC machine according to claim 19, wherein the control parameter includes one of the specified tolerance, the specified gain, the specified ramp time, and the specified programmed feed rate, and the programmable control unit stores the values of the control parameters in a control parameters table at a position reserved for the tool currently mounted in the CNC machine.

21. A method of machining a workpiece within a specified tolerance by moving either a tool or a workpiece platform relative to each other along a programmed path, the method comprising the steps of:

(a) generating a sequence of move command signals, each move command signal indicating a desired position of the tool relative to the platform along the programmed path; and

(b) moving the either the tool or the platform relative to each other through a sequence of incremental moves in accordance with the move command signals, characterized in that,

if the programmed path includes a corner, following the current move command signal until the position of the tool relative to the platform is within an allowable distance from the corner, and then deviating from the programmed path in a linear direction towards a position on the programmed path beyond the corner to follow the next move command signal, wherein the allowable distance varies in accordance with the angle of the corner.