Passive Variable Impedance For Shared Control

TL;DR

This paper presents a holistic framework for stabilizing variable impedance and arbitration in shared robotic control, ensuring passivity and enabling flexible, adaptive manipulation strategies validated through simulations and real experiments.

Contribution

It introduces methods to passivate systems with variable stiffness and arbitration, allowing for stable, flexible shared control without constraining stiffness or arbitration design.

Findings

The approach stabilizes impedance controllers with variable parameters.

Methods are validated in simulation and real robot experiments.

The framework enables flexible, adaptive shared control strategies.

Abstract

Shared Control methods often use impedance control to track target poses in a robotic manipulator. The guidance behavior of such controllers is shaped by the used stiffness gains, which can be varying over time to achieve an adaptive guiding. When multiple target poses are tracked at the same time with varying importance, the corresponding output wrenches have to be arbitrated with weightings changing over time. In this work, we study the stabilization of both variable stiffness in impedance control as well as the arbitration of different controllers through a scaled addition of their output wrenches, reformulating both into a holistic framework. We identify passivity violations in the closed loop system and provide methods to passivate the system. The resulting approach can be used to stabilize standard impedance controllers, allowing for the development of novel and flexible shared control methods. We do not constrain the design of stiffness matrices or arbitration factors; both can be matrix-valued including off-diagonal elements and change arbitrarily over time. The proposed methods are furthermore validated in simulation as well as in real robot experiments on different systems, proving their effectiveness and showcasing different behaviors which can be utilized depending on the requirements of the shared control approach.