Torque-position transformer for task control of position controlled robots
AssigneeThe Broad of Trustees of the Leland Stanford Junior University
InventorsOussama Khatib, Peter Thaulad, Jaehoung Park
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Abstract
Torque control capability is provided to a position controlled robot by calculating joint position inputs from transformation of the desired joint torques. This is based on calculating the transfer function 1/E(s), which relates the desired joint torque to joint position. Here E(s) is a servo transfer function D(s) or an effective servo transfer function D*(s). The use of an effective servo transfer function D*s) is helpful in cases where joint nonlinearities are significant. The effective servo transfer function D*(s) is defined with respect to an ideal joint transfer function G*(s)=1/(Ieffs2+beffs), where Ieff is an effective moment of inertia and beff is an effective damping coefficient.
Claims11
A robotic control method for a position controlled robot, the method comprising:
- a) determining a closed loop position transfer function T(s) of a selected joint of the robot relating a commanded input joint position Qin(s) to an actual joint position Qout(s) via Qout(s)=T(s)Qin(s);
- b) selecting a dynamic open loop joint torque to position transfer function H(s) relating to the selected joint;
- c) determining a corresponding effective servo transfer function E(s) of the selected joint according to E(s)=T(s)/(H(s)−T(s)H(s));
- d) providing a desired dynamic torque τdes(s) of the selected joint;
- and
- e) determining Qin(s) of the selected joint corresponding to τdes(s) via Qin(s)=τdes(s)/(E(s)(1−T(s)).
A robotic control system comprising:
- a) a position controlled robot having a closed loop position transfer function T(s) of a selected joint of the robot relating a commanded input joint position Qin(s) to an actual joint position Qout(s) via Qout(s)=T(s)Qin(s);
- b) a processor including a torque to position converter, wherein said torque to position converter is capable of providing Qin(s) corresponding to a desired dynamic torque τdes(s) of the selected joint according to a method comprising:
- selecting a dynamic open loop joint torque to position transfer function H(s) relating to the selected joint;
- determining a corresponding effective servo transfer function E(s) of the selected joint according to E(s)=T(s)/(H(s)−T(s)H(s));
- and
- determining Qin(s) of the selected joint corresponding to τdes(s) via Qin(s)=τdes(s)/(E(s)(1−T(s)).
Dependencies are inferred from the claim text.