Servo controller and method

• US 6,744,233 B1
• Filed: 06/26/2002
• Issued: 06/01/2004
• Est. Priority Date: 11/01/2000
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Tsutsui, Kazuhiko
• Primary Examiner(s): Duda, Rina I
• Application Number:
  US10/169,015
• Time in Patent Office: 706 Days
• Field of Search: 318/560, 318/567, 318/569, 318/572, 318/600, 318/609, 318/610, 318/632, 318/671
• US Class Current: 318/560
• 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 2219/41163 Adapt gain to friction, weight, inertia
• CPC Class Codes: H02P 23/06 Controlling the motor in four quadrants
• CPC Class Codes: H02P 23/18 Controlling the angular speed together with angular position or phase

Abstract

An ideal position is calculated based on an ideal servo system model, the difference between the calculated ideal position and the actual position feedback is multiplied by a predetermined gain only for a predetermined time from the direction reversing time of the ideal position, and the result is added to the speed command as the correction amount, so that variations in the correction effect, caused by the effect of a secular variation of the friction amount and the work condition difference is suppressed and even in a machine system with large elastic change in torsion of a ball screw, a seal material, etc., undercut caused by torsion restoration after the correction, etc., is suppressed and a servo system is prevented from becoming unstable.

Claims

1. A servo control method comprising the steps of generating a speed command based on a difference between a position command and actual position feedback, generating a current command based on a difference between the speed command and actual speed feedback, and controlling a servomotor based on the current command;

wherein an ideal position is calculated based on an ideal servo system model, and a difference between the calculated ideal position and the actual position feedback is multiplied by a predetermined gain only for a predetermined time from a direction reversing time of the ideal position, and the result of this multiplication is added to the speed command as a correction amount.

2. The servo control method as claimed in claim 1 wherein the above-mentioned gain is attenuated over a predetermined time from a maximum value at or after the direction reversing time of the ideal position.

3. The servo control method as claimed in claim 1 or 2 wherein the difference between the ideal position and the actual position feedback at the direction reversing time of the ideal position is stored as an offset value, the offset value is subtracted from the difference, and the subtraction result is multiplied by the gain.

7. The servo control method as claimed in claim 1, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

8. The servo control method as claimed in claim 2, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

9. The servo control method as claimed in claim 3, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

4. A servo control method comprising the steps of generating a speed command based on a difference between a position command and actual position feedback, generating a current command based on a difference between the speed command and actual speed feedback, and controlling a servomotor based on the current command;

wherein an ideal position is calculated based on an ideal servo system model, and the position feedback or a cumulative position of the ideal servo system model is multiplied by a predetermined gain only for a predetermined time from a direction reversing time of the calculated ideal position, and the result of the multiplication is added to the current command as a correction amount.

5. The servo control method as claimed in claim 4 wherein the speed feedback or speed of the ideal servo system model is multiplied by a second predetermined gain only for a predetermined time from the direction reversing time of the ideal position and the result is added to the current command as the correction amount.

6. The servo control method as claimed in claim 4 or 5 wherein a coefficient proportional to the difference between the ideal position and the actual feedback position is used as the gain.

10. The servo control method as claimed in claim 4, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

11. The servo control method as claimed in claim 5, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

12. The servo control method as claimed in claim 6, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

13. A servo control apparatus comprising means for detecting a position and speed of a servomotor, a position control section for generating a speed command based on a difference between a position command and actual position feedback, a speed control section for generating a current command based on a difference between the speed command and actual speed feedback, and a current control section for controlling an electric current allowed to flow into the servomotor based on the current command for controlling the above-mentioned servomotor;

the servo control apparatus further comprising an ideal servo system model, subtraction means for outputting a difference signal between an ideal position calculated by the model and the actual position feedback, and means for multiplying the difference signal output by the subtraction means by a predetermined gain only for a predetermined time from a direction reversing time of the ideal position and adding the result to the speed command as a correction amount.

14. The servo control apparatus as claimed in claim 13 wherein the gain is attenuated over a predetermined time from a maximum value at or after the direction reversing time of the ideal position.

15. The servo control apparatus as claimed in claim 13 or 14 comprising storage means for storing the difference between the ideal position and the actual position feedback at the direction reversing time of the ideal position as an offset value and subtraction means for subtracting the offset value stored in the storage means from the difference, wherein the subtraction result provided by the subtraction means is multiplied by the gain.

19. The servo control apparatus as claimed in claim 13, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

20. The servo control apparatus as claimed in claim 14, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

21. The servo control apparatus as claimed in claim 15, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

16. A servo control apparatus comprising means for detecting a position and speed of a servomotor, a position control section for generating a speed command based on a difference between a position command and actual position feedback, a speed control section for generating a current command based on a difference between the speed command and actual speed feedback, and a current control section for controlling an electric current allowed to flow into the servomotor based on the above-mentioned current command for controlling the servomotor;

the servo control apparatus further comprising an ideal servo system model and means for multiplying the above-mentioned position feedback or a cumulative position of the ideal servo system model by a predetermined gain only for a predetermined time from a direction reversing time of the ideal position of the model and adding the result of the multiplication to the current command as a correction amount.

17. The servo control apparatus as claimed in claim 16 comprising means for multiplying the speed feedback or speed of the ideal servo system model by a second predetermined gain only for a predetermined time from the direction reversing time of the ideal position of the model and adding the result to the current command as the correction amount.

18. The servo apparatus as claimed in claim 16 or 17 wherein a coefficient proportional to the difference between the ideal position and the actual feedback position is used as the gain.

22. The servo control apparatus as claimed in claim 16, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

23. The servo control apparatus as claimed in claim 17, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.

24. The servo control apparatus as claimed in claim 18, wherein the ideal servo system model is a model considering a delay of a position loop system from the position command to the position feedback and a mechanical delay of an object to be controlled.