Force Allocation Control for Redundant-Torso Biomimetic Quadrupeds via Virtual Force and Fully Actuated System Approach

Abstract

Fully actuated system approach (FASA) provides a promising control framework for robots with redundant actuation, offering simplified controller design and increased design freedom. However, its application to legged robots remains challenging due to hybrid actuation from intermittent ground contact and redundant inputs. To address this, we propose Virtual Force-based FASA (VF-FASA), which introduces virtual forces as intermediaries to construct full-actuation conditions required by FASA. FASA generates virtual control laws based on a simplified torso dynamics model, and a matrix-weighted pseudoinverse optimization is employed to map these virtual inputs into actual torso joint torques and foot contact forces. This method achieves coordinated control of both the floating base and redundant torso, effectively leveraging joint redundancy for improved whole-body motion. Simulation results on a redundant-torso quadruped robot demonstrate robust trajectory tracking and effective whole-body coordination under dynamic locomotion. The framework expands FASA to legged systems, providing an effective approach for controlling quadruped robots.