Equivariant Tracking Control for Fully Actuated Mechanical Systems on Matrix Lie Groups

TL;DR

This paper introduces a novel Lie group-based framework for trajectory tracking control of fully actuated mechanical systems, leveraging Lie-Poisson structures and energy shaping methods for improved control design.

Contribution

It presents a new representation of Lie-Poisson systems as left-invariant systems on semi-direct Lie groups, enabling the development of invariant tracking errors and control strategies.

Findings

Successful attitude tracking control demonstration

Invariant error dynamics with time-varying inertia

Novel Lie group-based control design methodology

Abstract

Mechanical control systems such as aerial, marine, space, and terrestrial robots often naturally admit a state-space that has the structure of a Lie group. The kinetic energy of such systems is commonly invariant to the induced action by the Lie group, and the system dynamics can be written as a coupled ordinary differential equation on the group and the dual space of its Lie algebra, termed a Lie-Poisson system. In this paper, we show that Lie-Poisson systems can also be written as a left-invariant system on a semi-direct Lie group structure placed on the trivialised cotangent bundle of the symmetry group. The authors do not know of a prior reference for this observation and we are confident the insight has never been exploited in the context of tracking control. We use this representation to build a right-invariant tracking error for the full state of a Lie-Poisson mechanical system and show that the error dynamics for this error are themselves of Lie-Poisson structure, albeit with time-varying inertia. This allows us to tackle the general trajectory tracking problem using an energy shaping design metholodology. To demonstrate the approach, we apply the proposed design methodology to a simple attitude tracking control.