ROBUST OPERATION OF TENDON-DRIVEN ROBOT FINGERS USING FORCE AND POSITION-BASED CONTROL LAWS

• US 20120109379A1
• Filed: 11/01/2010
• Published: 05/03/2012
• Est. Priority Date: 11/01/2010
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust), U.S.A. as represented by the Administrator of the National Aeronautics and Space Administration
• Inventors: Abdallah, Muhammad E., Reiland, Matthew J., Hargrave, Brian, Diftler, Myron A., Strawser, Philip A., Ihrke, Chris A., Platt, Robert J. Jr.
• Granted Patent: US 8,489,239 B2
• Time in Patent Office: Days
• US Class Current: 700/260
• CPC Class Codes: B25J 15/0009 comprising multi-articulated fingers, e.g. resembling a human hand
• CPC Class Codes: B25J 9/1045 comprising tensioning means

Abstract

A robotic system includes a tendon-driven finger and a control system. The system controls the finger via a force-based control law when a tension sensor is available, and via a position-based control law when a sensor is not available. Multiple tendons may each have a corresponding sensor. The system selectively injects a compliance value into the position-based control law when only some sensors are available. A control system includes a host machine and a non-transitory computer-readable medium having a control process, which is executed by the host machine to control the finger via the force- or position-based control law. A method for controlling the finger includes determining the availability of a tension sensor(s), and selectively controlling the finger, using the control system, via the force or position-based control law. The position control law allows the control system to resist disturbances while nominally maintaining the initial state of internal tendon tensions.

Claims

1. A robotic system comprising:

a robotic finger driven by a tendon; and

a control system configured for determining whether a tension sensor is available in the finger, for selectively controlling the finger via a force-based control law when a tension sensor is available in the finger to measure the tension value, and via position-based control law when the tension sensor is not available in the finger to measure the tension value.

2. The robotic system of claim 1, further comprising a plurality of the tendons, each tendon having a corresponding tension sensor, wherein the control system is configured for selectively controlling the finger via the force-based control law when all of the tension sensors are available, and via the position-based control law when none of the tension sensors are available.

3. The robotic system of claim 2, wherein the control system is further configured for selectively injecting a compliance value to the position-based control law when only some of the tension sensors are available.

4. The robotic system of claim 3, wherein the compliance value is a function of a tension error determined as a difference between a desired tension and an actual tension of one of the tendons.

5. The robotic system of claim 1, further comprising an actuator for moving the tendon, wherein the control system uses a two-tier architecture or hierarchy in which a joint controller forms an upper control loop and an actuator controller forms a lower control loop in the two-tier architecture, and wherein:

the joint controller is configured for executing the force-based control law and the position-based control law to thereby respectively control the force and position of the joints of the robotic finger; and

the actuator controller being configured for executing only the position-based control law to thereby control the position of the actuator.

6. The robotic system of claim 5, where any commanded actuator positions for the actuator that are sent down to the actuator controller are constrained to the range-space of the finger.

7. The robotic system of claim 1, further comprising a hand having a plurality of the fingers, with each finger having a plurality of the tendons, and with each tendon having a corresponding tension sensor, wherein each finger is independently controllable with respect to the other fingers in a manner dependent on the number of available tension sensors in the finger that is being independently controlled.

8. The robotic system of claim 1, further comprising an actuator for moving the tendon, wherein the control system uses a two-tier architecture having a lower and an upper control loop, and wherein the lower control loop actively servos to an actuator position of the finger to allow the finger to resist motion in the null-space of a tendon map matrix for the finger, while also nominally maintaining an initial internal tension on the tendon.

9. A control system for a robotic finger driven by a tendon, the control system comprising:

a host machine; and

a non-transitory computer-readable medium on which is recorded a control process providing a two-tier control architecture for controlling the finger;

wherein the host machine is configured for executing the control process to thereby determine the availability of a tension sensor in the finger suitable for measuring a tension value, and for selectively controlling the finger;

via a force-based control law when the tension sensor is available to measure the tension value; and

via a position-based control law when the tension sensor is not available to measure the tension value.

10. The control system of claim 9, wherein the finger includes a plurality of the tendons each having a corresponding tension sensor, and wherein the host machine is configured for selectively controlling the finger via the force-based control law when all of the plurality of tension sensors are available in the finger, and via the position-based control law when none of the plurality of tension sensors are available.

11. The control system of claim 10, wherein the host machine is further configured for selectively injecting a compliance value to the position-based control law when only some of the tension sensors are available.

12. The control system of claim 11, wherein the compliance value is a function of a tension error determined by the host machine as a difference between a desired tension and an actual tension of one of the tendons.

13. The control system of claim 9, further comprising:

an actuator for moving the tendon, wherein the host machine includes each of a joint controller and an actuator controller in a two-tier architecture or hierarchy, and wherein;

the joint controller is configured for executing the force-based control law and the position-based control law in an upper control loop of the two-tier architecture to thereby respectively control the force and position of the joints of the robotic finger; and

the actuator controller is configured for executing only the position-based control law in a lower control loop of the two-tier architecture to thereby control the position of the actuator.

14. The control system of claim 9, further comprising:

a hand having a plurality of the fingers, with each finger having a plurality of tendons, and with each tendon having a corresponding tension sensor, wherein each finger is independently controllable with respect to the other fingers in a manner dependent on the number of available tension sensors in the finger that is being independently controlled.

15. A method for controlling a tendon-driven finger in a robotic system, the method comprising:

determining the availability of a tension sensor for measuring a tension value of the tendon; and

selectively controlling the finger, via a control system, using a force-based control law when the tension sensor is available to measure the tension value, and using a position-based control law when the tension sensor is not available to measure the tension value.

16. The method of claim 15, wherein the finger has a plurality of the tendons each having a corresponding tension sensor, the method further comprising:

selectively controlling the finger via the force-based control law when all of the tension sensors are available, and via the position-based control law when none of the tension sensors are available.

17. The method of claim 16, further comprising:

selectively injecting a compliance value to the position-based control law when only some of the tension sensors are available.

18. The method of claim 17, further comprising:

calculating the compliance as a function of a tension error, wherein the tension error is determined as a difference between a desired tension and an actual tension of one of the tendons.

19. The method of claim 16, wherein the robotic system includes an actuator configured for moving the tendon, the method further comprising:

using a joint controller to execute the force-based control law and the position-based control law to thereby respectively control a force and a position of a joint in the finger in an upper control loop of a two-tier architecture or hierarchy; and

using an actuator controller to execute only the position-based control law to thereby control a position of the actuator in a lower control loop of the two-tier architecture.

20. The method of claim 19, further comprising an actuator for moving the tendon, wherein the control system uses a two-tier architecture or hierarchy in which a joint controller forms an upper control loop and an actuator controller forms a lower control loop in the two-tier architecture, and wherein:

the joint controller is configured for executing the force-based control law and the position-based control law to thereby respectively control the force and position of the joints of the robotic finger; and

the actuator controller being configured for executing only the position-based control law to thereby control the position of the actuator, and wherein any commanded actuator positions for the actuator that are sent down to the actuator controller are constrained to the range-space of the finger.