Switching control for tracking of a hybrid position-force trajectory

TL;DR

This paper introduces a switching control law for manipulators to achieve stable tracking of hybrid position-force trajectories in stiff environments, emphasizing the design of compliant wrists to improve performance and stability.

Contribution

It proposes a novel switching position-force control strategy with stability guarantees and guidelines for designing compliant wrists to enhance tracking in contact tasks.

Findings

The control law guarantees input-to-state stability under certain conditions.

Designing a compliant wrist improves tracking and reduces bouncing during contact.

Numerical simulations validate the effectiveness of the proposed approach.

Abstract

This work proposes a control law for a manipulator with the aim of realizing desired time-varying motion-force profiles in the presence of a stiff environment. In many cases, the interaction with the environment affects only one degree of freedom of the end-effector of the manipulator. Therefore, the focus is on this contact degree of freedom, and a switching position-force controller is proposed to perform the hybrid position-force tracking task. Sufficient conditions are presented to guarantee input-to-state stability of the switching closed-loop system with respect to perturbations related to the time-varying desired motion-force profile. The switching occurs when the manipulator makes or breaks contact with the environment. The analysis shows that to guarantee closed-loop stability while tracking arbitrary time-varying motion-force profiles, the controller should implement a considerable (and often unrealistic) amount of damping, resulting in inferior tracking performance. Therefore, we propose to redesign the manipulator with a compliant wrist. Guidelines are provided for the design of the compliant wrist while employing the designed switching control strategy, such that stable tracking of a motion-force reference trajectory can be achieved and bouncing of the manipulator while making contact with the stiff environment can be avoided. Finally, numerical simulations are presented to illustrate the effectiveness of the approach.