Synchronization of a class of cyclic discrete-event systems describing legged locomotion

TL;DR

This paper applies max-plus linear systems to model and analyze the synchronization of multi-legged robot gaits, providing explicit formulas for system eigenstructure and demonstrating robustness and rapid gait switching.

Contribution

It introduces a max-plus framework for modeling legged locomotion, deriving closed-form eigenstructure expressions, and enabling robust, fast gait transitions.

Findings

Closed-form max-plus eigenvalue and eigenvector expressions

Guaranteed robustness to perturbations and gait switching

Systematic methodology for gait controller synthesis

Abstract

It has been shown that max-plus linear systems are well suited for applications in synchronization and scheduling, such as the generation of train timetables, manufacturing, or traffic. In this paper we show that the same is true for multi-legged locomotion. In this framework, the max-plus eigenvalue of the system matrix represents the total cycle time, whereas the max-plus eigenvector dictates the steady-state behavior. Uniqueness of the eigenstructure also indicates uniqueness of the resulting behavior. For the particular case of legged locomotion, the movement of each leg is abstracted to two-state circuits: swing and stance (leg in flight and on the ground, respectively). The generation of a gait (a manner of walking) for a multiple legged robot is then achieved by synchronizing the multiple discrete-event cycles via the max-plus framework. By construction, different gaits and gait parameters can be safely interleaved by using different system matrices. In this paper we address both the transient and steady-state behavior for a class of gaits by presenting closed-form expressions for the max-plus eigenvalue and max-plus eigenvector of the system matrix and the coupling time. The significance of this result is in showing guaranteed robustness to perturbations and gait switching, and also a systematic methodology for synthesizing controllers that allow for legged robots to change rhythms fast.