Torque-Bounded Task-Space Admittance Control for Redundant Manipulators

Abstract

This paper presents a task-space admittance controller applicable to redundant manipulators equipped with torque sensors. It extends Kikuuwe's (2019) torque-bounded admittance controller (TBAC), which allows for imposing explicit limits on the joint actuator torques without causing unsafe behaviors such as oscillation and overshoots. The proposed controller enforces the end-effector to follow predefined task-space dynamics as long as the joint torques are unsaturated and the configuration is away from singularities. The behavior in the nullspace, which arises from the redundant degrees of freedom and singular configurations, is governed by predefined joint-space dynamics. The task-space and joint-space dynamics are combined through a newly proposed continualized pseudoinverse, which employs the singular value decomposition. Results of experiments using a seven-degree-of-freedom Kinova Gen3 robot illustrate the validity of the proposed admittance controller in various scenarios, including the case where the robot is fully stretched.