TORQUE CONTROL OF UNDERACTUATED TENDON-DRIVEN ROBOTIC FINGERS

• US 20100280662A1
• Filed: 03/10/2010
• Published: 11/04/2010
• Est. Priority Date: 04/30/2009
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company), 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: Wampler, Charles W. II, Diftler, Myron A., Abdallah, Muhammad E., Reiland, Matthew J., Ihrke, Chris A., Bridgwater, Lyndon, Platt, Robert J. JR.
• Granted Patent: US 8,565,918 B2
• Time in Patent Office: Days
• US Class Current: 700/261
• CPC Class Codes: H01R 13/052 co-operating with sockets having a circular transverse section
• CPC Class Codes: H01R 13/17 with spring member on the pin
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

A robotic system includes a robot having a total number of degrees of freedom (DOF) equal to at least n, an underactuated tendon-driven finger driven by n tendons and n DOF, the finger having at least two joints, being characterized by an asymmetrical joint radius in one embodiment. A controller is in communication with the robot, and controls actuation of the tendon-driven finger using force control. Operating the finger with force control on the tendons, rather than position control, eliminates the unconstrained slack-space that would have otherwise existed. The controller may utilize the asymmetrical joint radii to independently command joint torques. A method of controlling the finger includes commanding either independent or parameterized joint torques to the controller to actuate the fingers via force control on the tendons.

Claims

1. A robotic system comprising:

a robot having a total number of degrees of freedom (DOF) equal to at least n;

an underactuated tendon-driven finger driven by n or fewer tendons via at least one actuator, and having n DOF, the tendon-driven finger having at least two joints;

a plurality of sensors each adapted for measuring tension on a corresponding one of the tendons; and

a controller in electrical communication with the sensors and the robot, and adapted for receiving and processing the measured tensions from the sensors, as well as for controlling an actuation of the finger via the at least one actuator;

wherein the controller converts at least one of commanded joint torques and command joint behaviors into appropriate calculated tendon tensions, and controls the at least one actuator to achieve the calculated tendon tensions in the tendons, thereby eliminating an unconstrained slack space that would otherwise exist using only position control of the tendons.

2. The robotic system of claim 1, wherein the finger is characterized by an asymmetrical configuration in which at least one joint radius is different from the others, and wherein the controller utilizes the asymmetrical configuration in the force control of the tendons.

3. The robotic system of claim 2, wherein independent torque commands are provided by the controller to the at least two joints, as allowed by the asymmetric configuration

4. The robotic system of claim 2, wherein dependent or parameterized torque commands are provided by the controller to the at least two joints, as allowed by the asymmetric configuration.

5. The robotic system of claim 1, wherein the robot is a humanoid robot having at least 42 DOF as the total number of DOF.

6. The robotic system of claim 1, wherein a configuration of the tendons produces a tendon map, R, with at least one all-positive row and at least one all-negative row.

7. The robotic system of claim 6, wherein the controller parameterizes the space of allowable joint torques with a single DOF that either fully extends or fully flexes the finger, thereby providing a gripper finger that can fully open or fully close with a variable strength.

8. The robotic system of claim 1, further comprising a robotic hand having multiple fully-actuated fingers, wherein the underactuated finger is part of the robotic hand, and wherein the underactuated finger assists the fully-actuated fingers in the grasping of an object.

9. The robotic system of claim 1, further comprising a robotic hand having multiple underactuated fingers sharing the at least one actuator to provide shared actuation, wherein the controller commands joint torques as allowed by the shared actuation.

13. The finger of claim 8, wherein dependent or parameterized torque commands are provided by the controller to the at least two joints, as allowed by the asymmetric configuration.

14. The finger of claim 8, wherein a configuration of the tendons produces a tendon map, R, with at least one all-positive row and at least one all-negative row.

15. The finger of claim 8, wherein the controller parameterizes the space of allowable joint torques with a single DOF that either fully extends or fully flexes the finger, thereby providing a gripper finger that can fully open or fully close with a variable strength.

16. The finger of claim 8, wherein the finger is adapted for use as part of a robotic hand having fully-actuated fingers, and for assisting the fully-actuated fingers in the grasping of an object.

10. An underactuated tendon-driven finger for use within a robotic system having a total number of degrees of freedom (DOF) equal to at least n, and having a controller adapted for controlling an actuation of the tendon-driven finger via at least one actuator, the tendon-driven finger comprising:

n or fewer tendons and n DOF; and

at least two joints;

wherein the controller uses tension values of the tendons from a plurality of tension sensors to control the at least one actuator, and to convert commanded joint torques into appropriate calculated tendon tensions, thereby eliminating an unconstrained slack space that would otherwise exist in controlling only a position of the tendons.

11. The finger of claim 10, wherein the finger is characterized by an asymmetrical configuration in which at least one joint radius is different from the others, and wherein the controller utilizes the asymmetrical configuration in the force control of the tendons.

12. The finger of claim 11, wherein independent torque commands are provided by the controller to the at least two joints, as allowed by the asymmetric configuration

17. A method of controlling an underactuated tendon-driven finger within a robotic system having a total number of degrees of freedom (DOF) equal to at least n, the tendon-driven finger having at least two joints, n tendons, and n DOF, the method comprising:

measuring tension on each of the tendons using a plurality of tension sensors;

determining an appropriate calculated tension value for each tendon using the measured tension based on one of a desired joint behavior and a desired joint torque value; and

controlling the finger via at least one actuator using both the calculated and the measured tension values, thereby eliminating an unconstrained slack space that would otherwise exist in controlling only a position of the tendons.

18. The method of claim 17, wherein the at least two joints are characterized by an asymmetrical joint radius, and wherein the controller utilizes the asymmetrical joint radius to command independent joint torques.

19. The method of claim 17, further comprising:

using the tendon-driven finger as a secondary finger of a robotic hand to assist a primary finger of the robotic hand in the grasping of an object,