Decoupling Control for Heavy Quadruped Robot: A Hip-Based Optimal Virtual Force Distribution and Control Framework

The high self-weight and complex operating environment make implementing force sensor-based motion control of Heavy Quadruped Robots (HQR) challenging. In addition, for such robots, the mass of the heavy leg significantly impacts the ground reaction force (GRF) distribution and observation in the traditional control framework. This paper presents a GRF-Iess locomotion control framework for HQR based on five individual floating-base dynamics, fully considering the mass of legs and the coupled influence between the body and legs. We disassemble the full dynamics of the HQR into five spatially rigid parts with floating bases. The interaction effect between the body and legs is assumed to be a virtual spatial force (VSF), performing as the body's driving force and the loading force of the legs, which is obtained through the Nonlinear Disturbances Observer (NDOB). To realize the spatial trajectory control of the body, we utilize Quadratic Programming (QP) to solve the optimal VSF distribution on the body's hip joints. Furthermore, we employ Position-based Impedance Controllers (PIC) to build a VSF control loop to ensure that each grounded leg provides sufficient VSF to drive the body without slippage. Verification results show the promising locomotion control ability of the proposed framework for HQR.