Variable Stiffness Control with Strict Frequency Domain Constraints for Physical Human-Robot Interaction

TL;DR

This paper introduces a gain-scheduled variable stiffness control method for physical human-robot interaction that enforces strict frequency domain constraints, enhancing safety and performance.

Contribution

It proposes a novel gain-scheduling approach with frequency-specific constraints, reducing conservativeness and improving impedance control in human-robot interaction.

Findings

Effective frequency-specific impedance control demonstrated

Enhanced safety and adaptability in experiments

Outperforms fixed-gain passivity-based methods

Abstract

Variable impedance control is advantageous for physical human-robot interaction to improve safety, adaptability and many other aspects. This paper presents a gain-scheduled variable stiffness control approach under strict frequency-domain constraints. Firstly, to reduce conservativeness, we characterize and constrain the impedance rendering, actuator saturation, disturbance/noise rejection and passivity requirements into their specific frequency bands. This relaxation makes sense because of the restricted frequency properties of the interactive robots. Secondly, a gain-scheduled method is taken to regulate the controller gains with respect to the desired stiffness. Thirdly, the scheduling function is parameterized via a nonsmooth optimization method. Finally, the proposed approach is validated by simulations, experiments and comparisons with a gain-fixed passivity-based PID method.