Impedance Control for Manipulators Handling Heavy Payloads

TL;DR

This paper introduces a novel impedance control scheme for manipulators handling heavy payloads, effectively shaping force responses without acceleration measurements and ensuring stability despite payload uncertainties.

Contribution

The proposed control method enables accurate impedance shaping for heavy payloads without requiring acceleration data or dynamic estimators, and it handles nonlinear impedance models.

Findings

Effective impedance shaping demonstrated in experiments.

Controller remains stable with payload inertia differences.

No need for wrist accelerometers or dynamic estimators.

Abstract

Attaching a heavy payload to the wrist force/moment (F/M) sensor of a manipulator can cause conventional impedance controllers to fail in establishing the desired impedance due to the presence of non-contact forces; namely, the inertial and gravitational forces of the payload. This paper presents an impedance control scheme designed to accurately shape the force-response of such a manipulator without requiring acceleration measurements. As a result, neither wrist accelerometers nor dynamic estimators for compensating inertial load forces are necessary. The proposed controller employs an inner-outer loop feedback structure, which not only addresses uncertainties in the robot's dynamics but also enables the specification of a general target impedance model, including nonlinear models. Stability and convergence of the controller are analytically proven, with results showing that the control input remains bounded as long as the desired inertia differs from the payload inertia. Experimental results confirm that the proposed impedance controller effectively shapes the impedance of a manipulator carrying a heavy load according to the desired impedance model.