A Variable Impedance Scheme for Flexible-Joint Robot Interaction and Tracking Control Based on Power-Shaping Signals and Minimal Modelling

Abstract

This work proposes a novel scheme, based on power-shaping control (PSC), that can endow flexible-joint robots with both tracking, and interactional, capabilities. In virtue of relying upon the PSC method, this approach entails minimal modelling requirements restricted to computation of the gravitational torque vector, and motor dynamics terms (available in manufacturer datasheets). Hence, it distinguishes itself by obviating the need for calculation of the more cumbersome link dynamics elements, such as the Coriolis and link inertia matrices. In contrast to analogous schemes, the highest-order term required by the proposed design is the third derivative of the motor position vector. Moreover, the propounded framework enables utilisation of non-collocated feedback for enhanced tracking accuracy, as well as variable impedance control (VIC) for interactional performance augmentation. The aforesaid features are effectuated without any reliance on coordinate transformations, thereby leaving the original dynamical model intact. Experimental results involving a flexible-joint robot (Baxter) corroborate the theoretical analyses, while demonstrating that interactional and tracking performance improvements can be achieved via the proposed scheme.