A method to regulate the torque of flexible-joint manipulators with velocity control inputs

Abstract

Nowadays, robotic systems make use of compliant joint actuation to provide safe human-robot physical interactions, and in general, to improve the friendliness of the mechanism. However, note that with the introduction of these passive flexible elements, the actuators (which input the control actions) can not explicitly set the driving torque of the joints; for these types of systems, the difference between the position of the motor and the position of the joint determines the driving elastic torque. To cope with this problem, in this paper we present a control method to indirectly regulate the driving torque of flexible-joint manipulators. For that we first propose a new mathematical model for manipulators with velocity control inputs; next we derive a servo-controller which can asymptotically regulate the driving torque while online estimating unknown parameters. We prove the stability of the numerical algorithm with Ljapunov theory. To validate the proposed method, we conduct an experimental study with a simple 1-DOF manipulator in a compliant force regulation task.