US 12,330,306 B2
Obtaining the gear stiffness of a robot joint gear of a robot arm
Emil Madsen, Aarhus C (DK)
Assigned to Universal Robots A/S, Odense S (DK)
Appl. No. 17/275,726
Filed by UNIVERSAL ROBOTS A/S, Odense S (DK)
PCT Filed Sep. 10, 2019, PCT No. PCT/EP2019/074075
§ 371(c)(1), (2) Date Mar. 12, 2021,
PCT Pub. No. WO2020/053195, PCT Pub. Date Mar. 19, 2020.
Claims priority of application No. 18194683 (EP), filed on Sep. 14, 2018.
Prior Publication US 2022/0105628 A1, Apr. 7, 2022
Int. Cl. B25J 9/16 (2006.01); B25J 13/08 (2006.01); G05B 19/4155 (2006.01)
CPC B25J 9/1653 (2013.01) [B25J 9/1633 (2013.01); B25J 9/1674 (2013.01); B25J 13/088 (2013.01); G05B 19/4155 (2013.01); G05B 2219/40269 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A method of obtaining a stiffness of a gear of a joint on a robotic arm, where the joint is connectable to at least one other joint on the robotic arm, where the joint comprises a motor having a motor axle, where the motor axle is configured to rotate an output axle through the gear, and where the method comprises:
applying torque to the motor axle using the motor;
obtaining an angular position of the motor axle;
obtaining an angular position of the output axle,
obtaining a deflection of the gear based on the angular position of the motor axle and the angular position of the output axle;
obtaining a flexibility torque of the gear at the deflection of the gear based on at least the angular position of the motor axle, the angular position of the output axle, and a dynamic model of the robotic arm, where the dynamic model defines a relationship between forces acting on the robotic arm and resulting accelerations of the robotic arm;
performing operations repetitively, the operations comprising:
applying a new torque to the motor axle using the motor;
obtaining a new angular position of the motor axle;
obtaining a new angular position of the output axle;
obtaining a new deflection of the gear based on the new angular position of the motor axle and the new angular position of the output axle; and
obtaining a new flexibility torque of the gear at the new deflection of the gear based on at least the new angular position of the motor axle, the new angular position of the output axle, and the dynamic model;
storing each deflection of the gear and each flexibility torque of the gear at a corresponding deflection of the gear;
fitting, to a mathematical function, the flexibility torques and deflections of the gear that were stored, where the mathematical function comprises a polynomial function that is based on a recursive least squares estimation; and
determining the stiffness of the gear based on the mathematical function.