METHOD OF TOLERANCE-BASED TRAJECTORY PLANNING

• US 20070046677A1
• Filed: 03/23/2006
• Published: 03/01/2007
• Est. Priority Date: 03/23/2005
• Status: Active Grant

• Current Assignee: Hurco Companies, Inc.
• Original Assignee: Hurco Companies, Inc.
• Inventors: Hong, Jiawei, Tan, Xiaonan
• Granted Patent: US 7,450,127 B2
• Time in Patent Office: Days
• US Class Current: 345/442
• CPC Class Codes: G05B 19/41 characterised by interpolation, e.g. the computation of intermediate points between programmed end points to define the path to be followed and the rate of travel along that path G05B19/25, G05B19/31, G05B19/37, G05B19/39, G05B19/40 take precedence
• CPC Class Codes: G05B 19/4103 Digital interpolation
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence
• CPC Class Codes: G05B 19/4163 Adaptive control of feed or cutting velocity without NC B23Q15/12
• CPC Class Codes: G05B 2219/34171 Generate polynomial fitting in tolerance zone around polygon
• CPC Class Codes: G05B 2219/34175 Overlap, between two blocks, continuous, smooth speed change, movement
• CPC Class Codes: G05B 2219/43057 Adjust acceleration, speed until maximum allowable moment for axis
• CPC Class Codes: G05B 2219/43199 Safety, limitation of feedrate
• CPC Class Codes: G05B 2219/43203 Limitation of speed, permissible, allowable, maximum speed
• CPC Class Codes: G05B 2219/50179 Dynamic tolerance, limit values as function of speed, type of command

Abstract

The present invention involves a method of operating a motive body, where a target path is identified. The motive body is commanded to follow the target path from an initial position. The first actual position is sensed of the motive body after the commanding step. A first target subpath is calculated from the first actual position to correct for predictive errors in movement of the motive body. The actual position of the motive body is determined along each of a plurality of axes, and a multi-dimensional position error between the actual position of the motive body in each of the axes and a multi-dimensional reference trajectory is calculated. A multi-dimensional position error signal dependent upon the calculating step is determined. At least one of a speed and a direction of the motive body is established dependent upon the multi-dimensional position error signal.

Claims

1. A method of operating a motive body, said method comprising the steps of:

identifying a target path;

commanding the motive body to follow the target path from an initial position;

sensing a first actual position of the motive body after the commanding step; and

calculating a first target subpath from the first actual position to correct for predictive errors in movement of the motive body.

2. The method of claim 1 comprising the further step of empirically determining the predictive errors in movement of the motive body, the empirically determining step occurring before the identifying step.

3. The method of claim 1 wherein the target subpath is calculated to compensate for random error in movement of the motive body from the initial position to the actual position.

4. The method of claim 1 wherein the calculating step is dependent upon a deviation of the first actual position of the motive body from the target path.

5. The method of claim 1 comprising the further steps of:

directing the motive body to follow the first target subpath;

sensing a second actual position of the motive body after the directing step; and

calculating a second target subpath to correct for errors in movement of the motive body.

6. The method of claim 1 comprising the further step of determining acceleration needed to complete the first target subpath within a desired period of time and at a desired final velocity.

7. The method of claim 1 comprising the further step of calculating desired acceleration levels along the first target subpath.

8. The method of claim 1 wherein the calculating step includes at least one of Centripetal Force Compensation for Arc Motion, Tangential Acceleration Compensation, Stick Friction Compensation, Leadscrew and Backlash Compensation, Spindle Softness Compensation, and System Delay Compensation.

9. The method of claim 1 wherein the motive body continues to move past the first actual position during the calculating step.

10. A method of operating a motive body, said method comprising the steps of:

empirically determining predictive errors in movement of the motive body;

monitoring actual movements of the motive body; and

controlling the actual movements of the motive body dependent upon;

the empirically determined predictive errors; and

random errors in the actual movements of the motive body.

11. The method of claim 10 comprising the further step of commanding the tool to follow a target path from an initial position, the monitoring step including sensing a first actual position of the motive body after the commanding step, the controlling step including calculating a first target subpath from the first actual position to correct for the predictive errors and the random errors in the movement of the motive body.

12. The method of claim 11 wherein the calculating of the first target subpath is dependent upon a deviation of the first actual position of the motive body from the target path.

13. The method of claim 11 comprising the further steps of:

directing the motive body to follow the first target subpath;

sensing a second actual position of the motive body after the directing step; and

calculating a second target subpath to correct for errors in movement of the motive body.

14. The method of claim 11 comprising the further step of determining acceleration needed to complete the first target subpath within a desired period of time and at a desired final velocity.

15. The method of claim 10 wherein the empirically determining step precedes the monitoring step and the controlling step.

16. The method of claim 10 wherein the controlling step includes compensating for the predictive errors and the random errors.

17. The method of claim 10 comprising the further step of calculating desired acceleration levels of the motive body.

18. The method of claim 10 wherein the controlling step includes at least one of Centripetal Force Compensation for Arc Motion, Tangential Acceleration Compensation, Stick Friction Compensation, Leadscrew and Backlash Compensation, Spindle Softness Compensation, and System Delay Compensation.

19. A method of operating a motive body having a plurality of sequential movements, said method comprising the steps of:

sensing an actual position of the motive body after a first of the movements of the motive body;

calculating a target position of the motive body based on the sensing step, the target position being calculated to compensate for predictive errors and random errors in the movements of the motive body; and

repeating the sensing and calculating steps for other ones of the movements of the motive body.

20. The method of claim 19 wherein the predictive errors are empirically determined.

21. The method of claim 19 wherein the predictive errors are empirically determined before the sensing and calculating steps.

22. The method of claim 19 wherein the target position is calculated to compensate for predictive errors in both the first movement and the other movements of the motive body.

23. The method of claim 19 comprising the further step of determining acceleration needed to reach the target position within a desired period of time and at a desired final velocity.

24. The method of claim 19 wherein the calculating step includes at least one of Centripetal Force Compensation for Arc Motion, Tangential Acceleration Compensation, Stick Friction Compensation, Leadscrew and Backlash Compensation, Spindle Softness Compensation, and System Delay Compensation.

25. The method of claim 19 wherein the motive body continues to move past the actual position during the calculating step.

26. A method of operating a motive body, said method comprising the steps of:

sensing an actual position of the motive body;

calculating a position error between the actual position of the motive body and a desired position of the motive body;

comparing the position error to a specified error tolerance; and

adjusting a speed of the motive body dependent upon the comparing step.

27. The method of claim 26 wherein the adjusting step includes increasing the speed of the motive body if the position error is below the specified error tolerance, and decreasing the speed of the motive body if the position error is above the specified error tolerance.

28. A method of operating a motive body, said method comprising the steps of:

sensing an actual position of the motive body along each of a plurality of axes;

calculating a multi-dimensional position error between the actual position of the motive body in each of the axes and a multi-dimensional reference trajectory;

producing a multi-dimensional position error signal dependent upon the calculating step; and

controlling at least one of a speed and a direction of the motive body dependent upon the multi-dimensional position error signal.

29. The method of claim 28 wherein the multi-dimensional position error is calculated as a vector.

30. The method of claim 28 wherein said controlling step includes using a tangential error feedback controller and a normal error feedback controller.

31. The method of claim 30 wherein said controlling step includes assigning more weight to an output of said normal error feedback controller than to an output of said tangential error feedback controller.

32. The method of claim 28 wherein the axes include an x-axis, a y-axis and a z-axis of a machine tool.