Tension distribution in a tendon-driven robotic finger
A method is provided for distributing tension among tendons of a tendon-driven finger in a robotic system, wherein the finger characterized by n degrees of freedom and n+1 tendons. The method includes determining a maximum functional tension and a minimum functional tension of each tendon of the finger, and then using a controller to distribute tension among the tendons, such that each tendon is assigned a tension value less than the maximum functional tension and greater than or equal to the minimum functional tension. The method satisfies the minimum functional tension while minimizing the internal tension in the robotic system, and satisfies the maximum functional tension without introducing a coupled disturbance to the joint torques. A robotic system includes a robot having at least one tendon-driven finger characterized by n degrees of freedom and n+1 tendons, and a controller having an algorithm for controlling the tendons as set forth above.
1. A method for distributing tension among n+1 tendons of a tendon-driven finger in a robotic system, the finger being characterized by n degrees of freedom, the method comprising:
determining a maximum functional tension and a minimum functional tension; and
using a controller to automatically distribute tension among the n+1 tendons using a tendon map containing moment arm data mapping tendon tensions to joint torques within the tendon-driven finger, such that each tendon is assigned a tension value that is less than the maximum functional tension and greater than or equal to the minimum functional tension.
2. The method of claim 1 , wherein using a controller to automatically distribute tension includes: calculating, using the controller, a linear scaling of joint torques of each of a plurality of joints of the tendon-driven finger in order to find a scaled solution.
3. The method of claim 2 , further comprising:
iterating the scaled solution if any of the tension values of a given tendon exceeds the corresponding maximum functional tension for that tendon.
4. The method of claim 1 , wherein n=3.
5. The method of claim 1 , wherein the minimum functional tension is greater than zero, and wherein internal tension of the tendon-driven finger is minimized by ensuring that a lowest assigned tension value equals the minimum functional tension.
6. The method of claim 1 , wherein the maximum functional tension is satisfied without introducing a coupled disturbance to joint torques of each of a plurality of joints of the tendon-driven finger.
7. A robotic system comprising:
a robot having at least one tendon-driven finger characterized by n degrees of freedom and n+1 tendons; and
a controller having an algorithm for controlling the n+1 tendons;
wherein the algorithm is adapted for:
determining a maximum functional tension and a minimum functional tension of the tendon-driven finger; and
automatically distributing tension among the n+1 tendons, such that each tendon is assigned a tension value that is less than the maximum functional tension and greater than or equal to the minimum functional tension; and
wherein the controller includes a tendon map containing moment arm data mapping tendon tensions to joint torques within the tendon-driven finger, and wherein the algorithm is further adapted to automatically distribute tension using the tendon map.
8. The robotic system of claim 7 , wherein the robot is a humanoid robot having at least 42 degrees of freedom.
9. The robotic system of claim 7 , wherein the algorithm is adapted to automatically distribute tension by: calculating a linear scaling of joint torques of each of a plurality of joints of the tendon-driven finger in order to find a scaled solution.
10. The robotic system of claim 9 , further comprising: iterating the scaled solution if any of the tension values of a given tendon exceeds the corresponding maximum functional tension for that tendon.
11. The robotic system of claim 7 , wherein n=3.
12. A controller for a tendon-driven robotic finger having n degrees of freedom, the tendon-driven finger comprising n+1 tendons, wherein the controller includes an algorithm adapted for:
determining a maximum functional tension and a minimum functional tension of the tendon-driven finger; and
automatically distributing tension among the n+1 tendons, such that each tendon is assigned a tension value that is less than the maximum functional tension and greater than or equal to the minimum functional tensions;
wherein the controller includes a tendon map containing moment arm data mapping tendon tensions to joint torques within the tendon-driven finger; and
wherein the algorithm is further adapted to automatically distribute tension using the tendon map.
13. The controller of claim 12 , wherein the algorithm is adapted to automatically distribute tension by: calculating a linear scaling of joint torques of each of a plurality of joints of the tendon-driven finger to find a scaled solution.
14. The controller of claim 13 , further comprising: iterating the scaled solution if the tension value exceeds the maximum functional tension.
15. The robotic system of claim 12 , wherein n=3.