Control system for manipulator apparatus with resolved compliant motion control

• US 4,603,284 A
• Filed: 06/05/1984
• Issued: 07/29/1986
• Est. Priority Date: 06/05/1984
• Status: Expired due to Term

• Current Assignee: Unimation Incorporated Shelter Rock Lane Danbury CT A Corporation
• Original Assignee: Unimation, Inc. (Stäubli Holding AG)
• Inventors: Perzley, William
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/617,363
• Time in Patent Office: 784 Days
• Field of Search: 318/632, 318/568, 318/568 M, 364/513, 901/9, 901/45
• US Class Current: 318/568.14
• CPC Class Codes: B25J 13/08 by means of sensing devices, e.g. viewing or touching devices
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: B25J 9/1638 compensation for arm bending/inertia, pay load weight/inertia

Abstract

A control system for manipulator apparatus having a manipulator arm movable in a plurality of axes utilizes resolved compliant motion control to improve servo response characteristics. The position and velocity of the manipulator arm are controlled using load modeling to account for compliance in the arm and to synthesize feedback signals representing movement of a remote point of the arm to provide a loop bandwidth greater than is possible using feedback signals from inner less remote points of the manipulator that are closer to the drive points. The feedback signals are derived using predetermined combinations of force related feedback signals from the axis drive arrangements and position and velocity feedback signals of the manipulator apparatus at points closer to the main drive and support structure of the manipulator and before certain compliant portions of the manipulator arm. To further enhance response and control of the manipulator arm, load modeling is also used to provide controlled deceleration before the manipulator arm is brought to a stop during work operation.

Claims

1. A control system for manipulator apparatus having a manipulator arm and a predetermined geometrical configuration and structure controllable in a plurality of axes, each controllable axis including drive arrangements for moving the manipulator structure in each of the respective axes, said manipulator structure including compliance intermediate outer portions of the manipulator arm and inner portions of the manipulator arm proximate the drive arrangements, said control system comprising:

means for a feedback signal representing the velocity of the manipulator arm in at least one controllable axis, said feedback signal being sensed at and representing velocity at a point between said compliance and said drive arrangement;

means for generating a drive signal representing the torque of the drive arrangement applied to the manipulator structure in said one controllable axis; and

means responsive to said feedback signal and said drive signal for generating a synthesized feedback signal representing the velocity of the manipulator arm in said one axis at a point after said compliance.

2. The control system of claim 1 further comprising means for providing command signals representing desired work movements of the manipulator arm and means responsive to said command signals and said synthesized feedback signals for moving said manipulator arm in accordance with said desired work movements and position represented by said command signals.

3. The control system of claim 2 wherein said command signals represent manipulator arm position and velocity in at least said one axis.

4. The control system of claim 2 wherein said command signal providing means further comprises means for providing predetermined controlled deceleration characteristic for the manipulator arm at the end of each arm movement.

5. The control system of claim 4 wherein said predetermined controlled deceleration characteristic is a constantly decreasing deceleration rate.

6. The control system of claim 2 further comprising means for storing and reading out program control signals, said command signal providing means being responsive to said program control signals.

7. A method for controlling a manipulator having a manipulator arm controllable in a plurality of axes and a driven support structure for the manipulator arm, the method comprising the steps of:

generating command signals representing at least the desired velocity of the manipulator arm in at least a first axis at a predetermined point on the manipulator structure, said manipulator structure including compliance intermediate said predetermined point and the driven point of the support structure;

synthesizing feedback signals corresponding to position and velocity of the manipulator arm in at least said first axis at said predetermined point on the manipulator structure in response to measured position and velocity signals from the manipulator structure derived from measurement at a point closer to the driven point of the support structure than said predetermined point and before said compliance; and

controlling movement of the manipulator arm in a servo loop in accordance with the synthesized feedback signals and the command signals.

8. A method for controlling a manipulator having a manipulator arm and drive means for moving said arm in a plurality of axes, said arm having support structure which includes compliance in at least one of said axes intermediate the outer end of said arm and the drive means for said one axis, which comprises the steps of:

generating a command signal representing at least the desired velocity of said arm in said one axis during movement to a predetermined location;

generating a velocity feedback signal corresponding to the actual velocity of said manipulator arm in said one axis at a point between said compliance and said drive means for said one axis;

developing a quantity corresponding to the component of velocity lost in said compliance during movement of said arm in said one axis;

utilizing said actual velocity feedback signal and said lost velocity quantity to provide a synthetic velocity feedback signal representing the actual velocity of said arm in said one axis at a point between said compliance and the outer end of said arm; and

controlling movement of said manipulator arm in said one axis in accordance with said command signal and said synthetic velocity feedback signal.

9. The method of claim 8, wherein said synthetic velocity feedback signal is equal to θ

₁ -1/K₁ (d/dt)(T), where θ

₁ is said actual velocity feedback signal, K₁ is the spring rate of said compliance, and T is the torque developed by said drive means for said one axis.

10. The method of claim 8, wherein said command signal includes a component representing a desired position to which said arm is to be moved, said method including the steps of:

generating a position feedback signal corresponding to the actual position of said arm in said one axis at a point between said compliance and said drive means for said one axis;

developing a quantity corresponding to the component of position lost in said compliance during movement of said arm in said one axis;

utilizing said actual position feedback signal and said said lost position quantity to provide a synthetic position feedback signal representing the actual position of said arm in said one axis at a point between said compliance and the outer end of said arm; and

controlling movement of said manipulator arm in said one axis in accordance with said position component of said command signal and said synthetic position feedback signal.

11. The method of claim 10, wherein said synthetic position feedback signal is equal to θ

₁ -T/K₁, where θ

₁ is said actual position feedback signal, K₁ is the spring rate of said compliance, and T is the torque developed by said drive means for said one axis.

12. The method of claim 8, wherein said command signal includes a controlled deceleration characteristic portion as the arm approaches said predetermined location so that most of the energy stored in said compliance is dissipated before the arm reaches said predetermined location.

13. The method of claim 12, wherein said controlled deceleration characteristic causes said arm to decrease at a constant rate of deceleration.

14. The method of claim 8, wherein said command signal comprises a velocity profile representing a desired variation in the velocity of said arm in said one axis during movement to said predetermined location.

15. The method of claim 14, wherein said velocity profile includes a controlled deceleration portion as the arm approaches said predetermined location so that most of the energy stored in said compliance is dissipated before the arm reaches said predetermined location.

16. The method of claim 15, wherein said controlled deceleration portion produces a linear decrease in the rate of deceleration of said arm as said arm approaches said predetermined location.

17. A control system for a programmable manipulator having a manipulator arm and drive means for moving said arm in a plurality of axes, said arm having support structure which includes compliance in at least one of said axes intermediate the outer end of said arm and the drive means for said one axis, comprising:

means for generating a velocity feedback signal corresponding to the actual velocity of said manipulator arm in said one axis at a point between said compliance and said drive means for said one axis,

means for devloping a quantity representing the portion of said actual velocity which is lost in said compliance during movement of said arm in said one axis; and

means responsive to said velocity feedback signal and said quantity representing said lost velocity for developing a synthetic velocity feedback signal representing the velocity of said manipulator arm in said one axis at a point between said compliance and the outer end of said arm.

18. The control system of claim 17, which includes means for providing a command signal representing a desired velocity of movement of said arm, and servo loop means responsive to said command signal and said synthetic velocity feedback signal for controlling said drive means.

19. The control system of claim 18, wherein said command signal comprises a velocity profile representing a desired variation in the velocity of said arm in said one axis during movement to a predetermined location.

20. The control system of claim 19, wherein said velocity profile includes a controlled deceleration portion as the arm approaches said predetermined location so that most of the energy stored in said compliance is dissipated at the time said arm reaches said predetermined location.

21. The control system of claim 20, wherein said controlled deceleration portion of said velocity profile produces a linear decrease in the rate of deceleration of said arm as said arm approaches said predetermined location.

22. A control system for a programmable manipulator having a manipulator arm and drive means for moving said arm in a plurality of axes, said arm having support structure which includes compliance in at least one of said axes intermediate the outer end of said arm and the drive means for said one axis, said support structure having a relatively low first anti-resonant frequency due to said compliance, comprising:

means for generating a velocity feedback signal corresponding to the actual velocity of said manipulator arm in said one axis at a point between said compliance and said drive means for said one axis,

means responsive to said actual velocity feedback signal for developing a quantity representing the actual velocity of said arm in said one axis at a point between said compliance and the outer end of said arm, and

servo-loop means for controlling said drive means for said one axis in accordance with an input command signal and employing said quantity as a synthetic velocity feedback signal, whereby the bandwidth of said servo loop means may be increased above said first anti-resonant frequency of said support structure.

23. The control system of claim 22, which includes means for generating a drive signal corresponding to the torque developed by said drive means for said one axis, and means jointly responsive to said actual velocity feedback signal and said drive signal for devloping said quantity.

24. The control system of claim 23 wherein said quantity is proportional to θ

₁ -1/K₁ (d/dt)(T), where θ

₁ is said actual velocity feedback signal, K₁ is the spring rate of said compliance, and T is the torque developed by said drive means for said one axis.

25. The control system of claim 22, wherein said command signal includes a component representing a desired position to which said arm is to be moved, means for generating a position feedback signal corresponding to the actual position of said arm in said one axis at a point between said compliance and said drive means for said one axis, means responsive to said actual position signal for developing a further quantity representing the actual position of said arm in said axis at a point between said compliance and the outer end of said arm, and means utilizing said further quantity in said servo loop means as a synthetic position feedback signal.

26. The control system of claim 25, wherein said further quantity is equal to θ

₁ -T/K₁, where θ

₁ is said actual position feedback signal, K₁ is the spring rate of said compliance, and T is the torque developed by said drive means for said one axis.