A Passivity-based Approach for Variable Stiffness Control with Dynamical Systems

TL;DR

This paper introduces a passivity-based control method for robots that combines motion generation and control, allowing variable stiffness and safe, reactive interactions with the environment in a unified closed-loop system.

Contribution

It proposes a novel control approach integrating motion planning with variable stiffness control, ensuring passivity and stability during interactions.

Findings

Successful simulation validation of the control approach.

Real robot experiments demonstrating safety and performance.

Effective energy tank implementation for passivity guarantees.

Abstract

In this paper, we present a controller that combines motion generation and control in one loop, to endow robots with reactivity and safety. In particular, we propose a control approach that enables to follow the motion plan of a first order Dynamical System (DS) with a variable stiffness profile, in a closed loop configuration where the controller is always aware of the current robot state. This allows the robot to follow a desired path with an interactive behavior dictated by the desired stiffness. We also present two solutions to enable a robot to follow the desired velocity profile, in a manner similar to trajectory tracking controllers, while maintaining the closed-loop configuration. Additionally, we exploit the concept of energy tanks in order to guarantee the passivity during interactions with the environment, as well as the asymptotic stability in free motion, of our closed-loop system. The developed approach is evaluated extensively in simulation, as well as in real robot experiments, in terms of performance and safety both in free motion and during the execution of physical interaction tasks.