Joint-space impedance control for tendon-driven manipulators
View Patent ↗A system and method for controlling tendon-driven manipulators that provide a closed-loop control of joint torques or joint impedances without inducing dynamic coupling between joints. The method includes calculating tendon reference positions or motor commands by projecting a torque error into tendon position space using a single linear operation. The method calculates this torque error using sensed tendon tensions and a reference torque and internal tension. The method can be used to control joint impedance by calculating the reference torque based on a joint position error. The method limits minimum and maximum tendon tensions by projecting the torque error into the tendon tension space and then projecting ii back into joint space.
1. A method for providing torque control of a tendon-driven manipulator, said method comprising:
calculating by a processer, actuator reference positions or motor commands by projecting a torque error into a tendon position space using a single linear operation;
calculating the torque error using sensed tendon tensions, a reference torque and internal tension; and
limiting minimum and maximum tendon tensions by projecting the torque error into the tendon tension space and then projecting the torque error into a joint space.
2. The method according to claim 1 further comprising providing impedance control based on a joint position error.
3. The method according to claim 2 wherein positive joint stiffness is achieved by multiplying a joint space error by a stiffness constant.
4. The method according to claim 2 wherein positive joint damping is achieved by multiplying a joint space velocity error by a damping constant.
5. The method according to claim 4 wherein only a single velocity compensation term is used to provide torque controller stability and damping required by a desired impedance law.
6. The method according to claim 1 wherein limiting the tendon tensions includes converting a tendon limiting value from the joint space to the tendon space, limiting the tendon tensions, and converting the tendon tension back from the tendon space to the joint space.
7. The method according to claim 1 wherein a desired internal tendon tension is set by providing a torque reference signal to a torque controller.
8. The method according to claim 7 wherein the torque reference signal is provided to a torque controller that provides a difference between the torque reference signal and a torque feedback signal.
9. The method according to claim 1 wherein actuators are commanded by specifying a reference actuator position.
10. The method according to claim 1 wherein a proportional-integral controller is used to control torque and internal tension or joint space impedance.
11. The method according to claim 10 wherein a command actuator position is calculated by adding a velocity feedback term and a torque error term to a current actuator position.
12. The method according to claim 11 wherein a torque reference using the torque error is calculated by multiplying a joint error by a stiffness constant to realize a positive stiffness.
13. A method for providing torque control of a tendon-driven manipulator, said method comprising:
calculating by a processor, actuator reference positions or motor commands by projecting a torque error into a tendon position space using a single linear operation;
calculating the torque error using sensed tendon tensions, a reference torque and internal tension;
limiting minimum and maximum tendon tensions by projecting the torque error into the tendon tension space and then projecting the torque error into a joint space including converting a tendon limiting value from the joint space to the tendon space, limiting the tendon tensions, and converting the tendon tension back from the tendon space to the joint space;
providing a proportional-integral controller to control torque and internal tension or joint space impedance;
calculating a command actuator position by adding a velocity feedback term and a torque error term to a current actuator position; and
calculating a torque error reference using the torque error term by multiplying a joint error by a stiffness constant to realize a positive stiffness.
14. The method according to claim 13 further comprising providing impedance control based on a joint position error.
15. The method according to claim 14 wherein positive joint stiffness is achieved by multiplying a joint space error by a stiffness constant.
16. The method according to claim 14 wherein positive joint damping is achieved by multiplying a joint space velocity error by a damping constant.
17. The method according to claim 16 wherein only a single velocity compensation term is used to provide torque controller stability and damping required by a desired impedance law.
18. The method according to claim 13 wherein a desired internal tendon tension is set by providing a torque reference signal to a torque controller.
19. The method according to claim 18 wherein the torque reference signal is provided to a torque controller that provides a difference between the torque reference signal and a torque feedback signal.
20. The method according to claim 13 wherein actuators are commanded by specifying a reference actuator position.