Torque-position transformer for task control of position controlled robots
View Patent ↗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/(I eff s 2 +b eff s), where I eff is an effective moment of inertia and b eff is an effective damping coefficient.
1. 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 Q in (s) to an actual joint position Q out (s) via Q out (s)=T(s)Q in (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 τ des (s) of the selected joint; and
e) determining Q in (s) of the selected joint corresponding to τ des (s) via Q in (s)=τ des (s)/(E(s)(1−T(s)).
2. The method of claim 1 , wherein said transfer function H(s) is a physical transfer function of said selected joint.
3. The method of claim 1 , wherein said transfer function H(s) is an idealized transfer function of said selected joint.
4. The method of claim 3 , wherein H(s) is given by H(s)=1/(I eff s 2 +b eff s), where I eff is an effective moment of inertia of said selected joint, and b eff is an effective damping coefficient of said selected joint.
5. The method of claim 4 , wherein said transfer function H(s) differs substantially from a physical transfer function G(s) of said selected joint.
6. A robotic control method for a position controlled robot, the method comprising:
selecting two or more joints of the robot; and
providing desired torque inputs to each of the selected joints as corresponding position inputs according to the method of claim 1 .
7. 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 Q in (s) to an actual joint position Q out (s) via Q out (s)=T(s)Q in (s);
b) a processor including a torque to position converter, wherein said torque to position converter is capable of providing Q in (s) corresponding to a desired dynamic torque τ des (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 Q in (s) of the selected joint corresponding to τ des (s) via Q in (s)=τ des (s)/(E(s)(1−T(s)).
8. The system of claim 7 , wherein said transfer function H(s) is a physical transfer function of said selected joint.
9. The system of claim 7 , wherein said transfer function H(s) is an idealized transfer function of said selected joint.
10. The system of claim 9 , wherein H(s) is given by H(s)=1/(I eff s 2 +b eff s), where I eff is an effective moment of inertia of said selected joint, and b eff is an effective damping coefficient of said selected joint.
11. The system of claim 10 , wherein said transfer function H(s) differs substantially from a physical transfer function G(s) of said selected joint.