Industrial robot with servo

• US 5,581,166 A
• Filed: 03/30/1995
• Issued: 12/03/1996
• Est. Priority Date: 02/18/1986
• Status: Expired due to Term

• Current Assignee: Robotic Research LLC
• Original Assignee: Robotic Research LLC
• Inventors: Eismann, Paul H., Thompson, Jack M. Jr.
• Primary Examiner(s): Martin, David S.
• Application Number:
  US08/414,035
• Time in Patent Office: 614 Days
• Field of Search: 901/27-28, 901/34, 901/23, 901/24, 318/568, 318/572, 318/600-601, 318/615-618, 318/646, 318/432, 318/434, 318/560-563, 318/569, 318/621
• US Class Current: 318/568.22
• CPC Class Codes: B25J 17/02 Wrist joints
• CPC Class Codes: B25J 17/0241 One-dimensional joints
• CPC Class Codes: B25J 9/04 by rotating at least one arm, excluding the head movement itself, e.g. cylindrical coordinate type or polar coordinate type
• CPC Class Codes: B25J 9/046 Revolute coordinate type
• CPC Class Codes: B25J 9/08 characterised by modular constructions
• CPC Class Codes: B25J 9/1025 Harmonic drives in general: F16H49/001
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: B25J 9/1643 redundant control
• CPC Class Codes: G05B 2219/41116 Compensation for instability
• CPC Class Codes: G05B 2219/41203 Lead-phase compensation, lag-phase compensation servo
• CPC Class Codes: G05B 2219/42092 Position and force control loop together
• CPC Class Codes: G05B 2219/49292 Harmonic gear, transmission, strain wave gear
• CPC Class Codes: Y10T 74/20207 Multiple controlling elements for single controlled element

Abstract

In a device having a first member and a second member which are driven relative to one another by an actuator, a servocontrol derives feedback by sensing the torque applied on one of the members by the actuator. The actuator drive signal is modified by a compensation network in response to the torque measurement to provide stability across a bandwidth extending beyond the resonant frequency of the members, thereby providing smooth, accurate and precise motion.

Claims

1. A servocontrolled apparatus comprising:

a proximal member and a distal member, said members being driven relative to each other by an actuator;

means for supplying a velocity command signal;

means affixed to one of said members for sensing the relative velocity between said members, said sensing means providing a member velocity signal;

means for comparing said velocity command signal to said member velocity signal, said sensing means providing a velocity error signal; and

a velocity compensation network receiving said velocity error signal, said velocity compensation network providing a torque command signal;

means for sensing the torque exerted between said first and second members on said distal member by said actuator, said sensing means providing a member torque signal;

means for comparing said torque command signal to said member torque signal, said comparing means providing a torque error signal;

a torque compensation network receiving said torque error signal providing an output signal;

means for amplifying said output signal; and

means for supplying said amplified signal to said actuator whereby a force is produced in response thereto.

2. A servocontrolled apparatus according to claim 1 wherein said velocity command signal means comprises:

means for supplying a position command signal;

means for sensing the relative positions of said members, said sensing means providing a member position signal; and

means for comparing said position command signal to said member position signal, said sensing means providing a position error signal.

3. A servocontrolled apparatus according to claim 2 wherein said members comprise an arm joint of a manipulator.

4. A servocontrolled apparatus according to claim 3 wherein said actuator comprises a harmonic drive.

5. A servocontrolled apparatus according to claim 2 wherein said actuator comprises a harmonic drive.

6. A servocontrolled apparatus according to claim 1 wherein said velocity command signal means comprises:

a digital computer, said computer being operative to provide a digital position error signal by comparison of the relative positions of said members, sensed at a location on one of said members, to a computed position command, said position error signal being stepwise updated at time intervals designated by said computer; and

means for converting said digital position error signal to an analog velocity command signal.

7. A servocontrolled apparatus according to claim 6 herein said members comprise an arm joint of a manipulator.

8. A servocontrolled apparatus according to claim 7 wherein said actuator comprises a harmonic drive.

9. A servocontrolled apparatus according to claim 6 wherein said actuator comprises a harmonic drive.

10. A servocontrolled apparatus according to claim 1 wherein said members comprise an arm joint of a manipulator.

11. A servocontrolled apparatus according to claim 10 wherein said torque compensation network comprises a lead network.

12. A servocontrolled apparatus according to claim 10 wherein said actuator comprises a harmonic drive.

13. A servocontrolled apparatus according to claim 10 wherein said actuator comprises a harmonic drive.

14. A servocontrolled apparatus according to claim 1 wherein said torque compensation network comprises a lead network.

15. A servocontrolled apparatus according to claim 14 wherein said lead network is of the type comprising a lead-lag network.

16. A servocontrolled apparatus according to claim 1 wherein said actuator comprises a harmonic drive.

17. A servocontrolled apparatus according to claim 1 wherein said torque compensation network compensates to provide stability across a bandwidth extending beyond the resonant frequency of said members.

18. A method of position control in a structure having a first member and a second member connected by a drive system comprising the steps of:

a. determining the relative position between said first and second members and producing in response thereto an instantaneous position signal;

b. comparing said instantaneous position signal to a reference position signal and producing in response thereto a velocity goal signal;

c. determining the relative velocity between said first and second members and producing in response thereto an instantaneous velocity signal;

d. comparing said instantaneous velocity signal to said velocity goal signal and producing in response thereto an acceleration goal signal;

e. determining the motive force supplied by said drive system between said first and second members and producing in response thereto an instantaneous force signal; and

f. comparing said instantaneous force signal to said acceleration goal signal and producing in response thereto a drive system command signal.

19. A method of improved dynamic and static position control of a manipulator endpoint, the manipulator having a proximal structural member and a distal structural member driven relative to each other by a drive mechanism, comprising the steps of:

a. providing a position error signal indicative of the difference between the desired position of said distal member relative to said proximal member and the actual position of said distal member relative to said proximal member;

b. providing a velocity signal indicative of the actual velocity of said distal member relative to said proximal member;

c. combining said position error signal and velocity signal to produce an output signal;

d. providing a force signal indicative of the force between said distal member and said proximal member;

e. combining said output signal and said force signal to produce a drive signal whereby said drive signal corrects for nonideal mechanical properties or vibrations that otherwise would affect the position of said manipulator endpoint.