DRS-LIP: Linear Inverted Pendulum Model for Legged Locomotion on Dynamic Rigid Surfaces

TL;DR

This paper extends the linear inverted pendulum model to dynamic rigid surfaces, providing an analytical solution and a hierarchical planning framework for legged robots on moving surfaces, validated through simulations and experiments.

Contribution

It introduces the DRS-LIP model for dynamic surfaces and develops an efficient analytical solution and planning framework for legged robot locomotion.

Findings

The DRS-LIP model accurately predicts robot dynamics on moving surfaces.

The analytical solution enables real-time trajectory generation.

Experimental results confirm the effectiveness of the proposed approach.

Abstract

Legged robot locomotion on a dynamic rigid surface (i.e., a rigid surface moving in the inertial frame) involves complex full-order dynamics that is high-dimensional, nonlinear, and time-varying. Towards deriving an analytically tractable dynamic model, this study theoretically extends the reduced-order linear inverted pendulum (LIP) model from legged locomotion on a stationary surface to locomotion on a dynamic rigid surface (DRS). The resulting model is herein termed as DRS-LIP. Furthermore, this study introduces an approximate analytical solution of the proposed DRS-LIP that is computationally efficient with high accuracy. To illustrate the practical uses of the analytical results, they are used to develop a hierarchical planning framework that efficiently generates physically feasible trajectories for DRS locomotion. The effectiveness of the proposed theoretical results and motion planner is demonstrated both through simulations and experimentally on a Laikago quadrupedal robot that walks on a rocking treadmill.