Method of controlling a robot arm based on adaptive friction
A method of controlling a robot arm with robot joints, where the joint motors of the joints are controlled based on a signal generated based on the friction torque (formula I) of at least one of the input/outside of the robot joint transmission and the robot joint transmission torque (formula II) between the input side and the output side of the transmission. The friction torque is determined based on: at least two of the angular position of the motor axle; the angular position of the output axle and/or the motor torque provided to the motor axle by the joint motor. The robot joint transmission torque is determined based on: at least one of the angular position of the output axle; the angular position of the output axle and/or the angular position of the motor axle; the angular position of the motor axle and the motor torque provided to the motor axle by the joint motor.
1. A method of controlling a robotic arm, where the robotic arm comprises joints connecting a base and a tool flange, where at least one of the joints is a rotational joint comprising a joint motor having a motor axle, where the motor axle is configured to rotate an output axle of the rotational joint via a joint transmission, the method comprising:
obtaining an angular position of the motor axle;
obtaining an angular position of the output axle;
obtaining a motor torque provided to the motor axle by the joint motor;
determining a friction torque of at least one of an input side of the joint transmission or and an output side of the joint transmission based on at least two of:
the angular position of the motor axle;
the angular position of the output axle; or
the motor torque provided to the motor axle by the joint motor;
determining a robot joint transmission torque between the input side and the output side of the joint transmission based on at least one of:
the angular position of the output axle;
the angular position of the output axle and the angular position of the motor axle; or
the angular position of the motor axle and the motor torque provided to the motor axle by the joint motor;
generating a motor control signal for the joint motor of the rotational joint based on:
the friction torque of at least one of the input side or the output side of the joint transmission; and
the robot joint transmission torque between the input side and the output side of the joint transmission.
2. The method of claim 1 , wherein the motor control signal is generated based also on at least one of:
the angular position of the motor axle;
the angular position of the output axle;
the motor torque provided to the motor axle by the joint motor;
a dynamic model of a robot comprising the robotic arm; or
at least one motion parameter corresponding to a desired motion of at least a part of the robotic arm.
3. The method of claim 1 , wherein the friction torque of at least one of the input side of the joint transmission or the output side of the joint transmission is obtained based on a deflection of the joint transmission, where the deflection of the joint transmission indicates a difference between the angular position of the motor axle and the angular position of the output axle.
4. The method of claim 1 , wherein:
obtaining the angular position of the motor axle comprises measuring the angular position of motor axle using a motor axle encoder; and
obtaining the angular position of the output axle comprises measuring the angular position of the output axle using an output axle encoder.
5. The method of claim 4 , wherein the friction torque of at least one of the input side of the joint transmission or the output side of the joint transmission is obtained based on the measured angular position of the motor axle and the measured angular position of the output axle.
6. The method of claim 1 , wherein determining the robot joint transmission torque is based on the friction torque of at least one of the input side of the joint transmission or the output side of the joint transmission.
7. The method of claim 1 , wherein generating the motor control signal comprises determining a desired transmission torque corresponding to a desired transmission torque of the joint transmission based on:
a dynamic model of a robot comprising the robotic arm;
at least one motion parameter indicating a desired motion of at least a part of the robotic arm; and
the friction torque of at least one of the input side or the output side of the joint transmission.
8. The method of claim 7 , wherein generating the motor control signal comprises determining a transmission torque error correction motor torque that minimizes a difference between the desired transmission torque and the robot joint transmission torque ({circumflex over (τ)} J ).
9. The method of claim 1 , wherein generating the motor control signal for the joint motor comprises determining a desired feed-forward motor torque indicating a desired motor torque of the joint motor based on:
a dynamic model of a robot comprising the robotic arm;
at least one motion parameter indicating a desired motion of at least a part of the robotic arm; and
the friction torque of at least one of the input side or the output side of the joint transmission.
10. The method of claim 1 , wherein generating the motor control signal comprises determining an error correction motor torque that minimizes errors associated with least one of:
a desired motion parameter of the robotic arm and an actual motion parameter of the robotic arm;
a desired angular position of the output axle and the angular position of the output axle;
a desired angular velocity of the output axle and an angular velocity of the output axle;
a desired angular acceleration of the output axle and an angular acceleration of the output axle;
a desired angular position of the motor axle and the angular position of the motor axle;
a desired angular velocity of the motor axle and an angular velocity of the motor axle;
a desired angular acceleration of the motor axle an angular acceleration of the motor axle; or
a desired torque provided to the motor axle by the joint motor and the motor torque provided to the motor axle by the joint motor.
11. The method of claim 8 , wherein generating the motor control signal comprises determining a resulting motor torque corresponding to a resulting motor torque to be applied by the joint motor, the resulting motor torque being based on at least one of:
the transmission torque error correction motor torque;
a desired feed-forward motor torque; or
an error correction motor torque;
where the motor control signal is generated based on the resulting motor torque.
12. A robot system comprising:
a controller;
a robotic arm controlled by the controller, the robotic robot arm comprising joints connecting a base and a tool flange, where at least one of the joints is a rotational joint comprising a joint motor having a motor axle, where the motor axle is configured to rotate an output axle of the rotational joint via a joint transmission;
wherein controller comprises:
an adaptive friction module configured to determine a friction torque of at least one of an input side of the joint transmission or an output side of the joint transmission based on at least two of:
an angular position of the motor axle;
an angular position of the output axle; or
a motor torque provided to the motor axle by the joint motor;
a transmission torque module configured to determine a robot joint transmission torque between the input side and the output side of the joint transmission based on at least one of:
the angular position of said output axle;
the angular position of the output axle and the angular position of the motor axle; or
the angular position of the motor axle and the motor torque provided to the motor axle by the joint motor; and
wherein the said controller is configured to generate a motor control signal based on the friction torque of at least one of the input side or the output side of the joint transmission and the robot joint transmission torque between the input side and the output side of the joint transmission, and (ii) to control the robotic arm by providing the motor control signal to the joint motor.
13. The robot system of claim 12 , wherein the adaptive friction module is configured to determine the friction torque of at least one of the input side of the joint transmission or the output side of the joint transmission based on a deflection of the joint transmission, where the deflection of the joint transmission corresponds to a difference between the angular position of the motor axle and the angular position of the output axle.
14. The robot system of claim 12 , further comprising:
a motor axle encoder configured to measure the angular position of the motor axle; and
an output encoder configured to measure the angular position of the output axle.
15. The robot system of claim 12 , further comprising:
a sensor configured to obtain the motor torque provided to the motor axle by the joint motor.
16. The robot system of claim 12 , wherein the controller comprises a feed-forward controller module configured to determine a desired transmission torque corresponding to a desired transmission torque of the joint transmission based on:
a dynamic model of a robot comprising the robotic arm;
at least one motion parameter indicating a desired motion of at least a part of the robotic arm; and
the friction torque of at least one of the input side or the output side of the joint transmission.
17. The robot system of claim 16 , wherein the controller comprises a torque Feed-back controller module configured to determine a transmission torque error correction motor torque that minimizes a difference between the desired transmission torque and the robot joint transmission torque.
18. The robot system of claim 12 , wherein the controller comprises a feed-forward controller configured to determine a desired feed-forward motor torque indicating a desired motor torque of the joint motor based on:
a dynamic model of a robot comprising the robotic arm;
at least one motion parameter corresponding to a desired motion of at least a part of the robotic arm; and
the friction torque of at least one of the input side or the output side of the joint transmission.
19. The robot system of claim 12 , wherein the controller comprises a feed-back controller configured to determine an error correction motor torque that minimizes errors associated with at least one of:
a desired motion parameter of the robotic arm and an actual motion parameter of the robotic arm;
a desired angular position of the output axle and the angular position of the output axle;
a desired angular velocity of the output axle and an angular velocity of the output axle;
a desired angular acceleration of the output axle and an angular acceleration of the output axle;
a desired angular position of the motor axle and the angular position of the motor axle;
a desired angular velocity of the motor axle and an angular velocity of the motor axle;
a desired angular acceleration ({umlaut over (Θ)} d ) of the motor axle and an angular acceleration of the motor axle;
a desired torque provided to the motor axle by the joint motor and the motor torque provided the motor axle by the joint motor.
20. The robot system of claim 16 , wherein the controller comprises a motor controller module configured to generate the motor control signal corresponding to a motor current for the at least one robot joint based on a resulting motor torque corresponding to a motor torque to be applied by the joint motor, where the resulting motor torque is determined based on at least one of:
a transmission torque error correction motor torque;
a desired feed-forward motor torque, or
an error correction motor torque.