Extended Capture Point and Optimization-based Control for Quadrupedal Robot Walking on Dynamic Rigid Surfaces

TL;DR

This paper extends the capture point concept and develops an optimization-based control method enabling quadrupedal robots to walk stably on dynamic rigid surfaces, addressing complex nonlinear dynamics and surface movement.

Contribution

It introduces a novel extension of the capture point for dynamic surfaces and a QP-based feedback controller explicitly considering surface motion.

Findings

Successful simulation of quadrupedal walking on rocking surfaces

Improved walking performance over previous offline planning methods

Validated stability and robustness of the control approach

Abstract

Stabilizing legged robot locomotion on a dynamic rigid surface (DRS) (i.e., rigid surface that moves in the inertial frame) is a complex planning and control problem. The complexity arises due to the hybrid nonlinear walking dynamics subject to explicitly time-varying holonomic constraints caused by the surface movement. The first main contribution of this study is the extension of the capture point from walking on a static surface to locomotion on a DRS as well as the use of the resulting capture point for online motion planning. The second main contribution is a quadratic-programming (QP) based feedback controller design that explicitly considers the DRS movement. The stability and robustness of the proposed control approach are validated through simulations of a quadrupedal robot walking on a DRS with a rocking motion. The simulation results also demonstrate the improved walking performance compared with our previous approach based on offline planning and input-output linearizing control that does not explicitly guarantee the feasibility of ground contact constraints.