Input Decoupling of Lagrangian Systems via Coordinate Transformation: General Characterization and its Application to Soft Robotics

TL;DR

This paper characterizes when a coordinate transformation can decouple actuators in Lagrangian systems, providing conditions for collocated systems, and applies these results to control soft robotic systems effectively.

Contribution

It offers a general characterization and necessary conditions for input decoupling via coordinate transformation in Lagrangian systems, with applications to soft robotics.

Findings

Identifies conditions for coordinate transformations that decouple inputs in Lagrangian systems.

Provides a simple test to verify if a system is collocated.

Derives novel controllers for damped underactuated systems.

Abstract

Suitable representations of dynamical systems can simplify their analysis and control. On this line of thought, this paper aims to answer the following question: Can a transformation of the generalized coordinates under which the actuators directly perform work on a subset of the configuration variables be found? Not only we show that the answer to this question is yes, but we also provide necessary and sufficient conditions. More specifically, we look for a representation of the configuration space such that the right-hand side of the dynamics in Euler-Lagrange form becomes $[\boldsymbol{I} \; \boldsymbol{O}]^{T}\boldsymbol{u}$, being $u$ the system input. We identify a class of systems, called collocated, for which this problem is solvable. Under mild conditions on the input matrix, a simple test is presented to verify whether a system is collocated or not. By exploiting power invariance, we provide necessary and sufficient conditions that a change of coordinates decouples the input channels if and only if the dynamics is collocated. In addition, we use the collocated form to derive novel controllers for damped underactuated mechanical systems. To demonstrate the theoretical findings, we consider several Lagrangian systems with a focus on continuum soft robots.