Impedance Adaptation by Reinforcement Learning with Contact Dynamic Movement Primitives

TL;DR

This paper introduces a reinforcement learning-based method to adapt robot impedance parameters online using DMPs for contact-rich tasks, enhancing robustness and performance in tasks like peg-in-hole and adhesive strip application.

Contribution

It combines DMPs with reinforcement learning to adapt impedance parameters online, enabling one-shot demonstrations and improved task robustness.

Findings

Enhanced robustness in contact tasks

Successful application to peg-in-hole and adhesive tasks

Effective impedance adaptation through RL

Abstract

Dynamic movement primitives (DMPs) allow complex position trajectories to be efficiently demonstrated to a robot. In contact-rich tasks, where position trajectories alone may not be safe or robust over variation in contact geometry, DMPs have been extended to include force trajectories. However, different task phases or degrees of freedom may require the tracking of either position or force -- e.g., once contact is made, it may be more important to track the force demonstration trajectory in the contact direction. The robot impedance balances between following a position or force reference trajectory, where a high stiffness tracks position and a low stiffness tracks force. This paper proposes using DMPs to learn position and force trajectories from demonstrations, then adapting the impedance parameters online with a higher-level control policy trained by reinforcement learning. This allows one-shot demonstration of the task with DMPs, and improved robustness and performance from the impedance adaptation. The approach is validated on peg-in-hole and adhesive strip application tasks.