Torque-Bounded Task-Space Admittance Control for Redundant Manipulators
Ryo Kikuuwe
AI summary
Problem
Standard admittance control cannot easily impose explicit actuator torque limits without causing unsafe snapping or overshooting, and extending it to task-space for redundant manipulators requires careful handling of singularities and null-space dynamics.
Approach
The method extends a 1-D torque-bounded controller to task-space by combining task and joint proxy dynamics through a novel continualized pseudoinverse, using a normal-cone operator to enforce torque bounds while maintaining stability.
Key results
- Formulates a task-space admittance controller with explicit joint torque bounds
- Introduces a continualized pseudoinverse to safely handle singular configurations
- Enables null-space admittance control without explicit basis computation
- Validates safe operation near singularities on a 7-DOF Kinova Gen3 robot
Why it matters
Enables safer physical human-robot interaction and assembly tasks by guaranteeing torque limits without compromising task-space compliance or stability.
Abstract
This article presents a task-space admittance con- troller applicable to redundant manipulators equipped with torque sensors. It extends Kikuuwe’s (2019) torque-bounded admittance controller, which allows for imposing explicit limits on the joint actuator torques without causing unsafe behaviors, such as oscil- lation and overshoots. The proposed controller enforces that the end-effector follows 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 admittancecontrollerinvariousscenarios,includingthecasewhere the robot is fully stretched.