Whole-Body Admittance Control of Anti-Saturation for Quadruped Manipulators with Impact Force Observer

Quadruped manipulators require precise detection of external impact forces to ensure safe and compliant responses during environmental interactions. However, these systems often lack tactile sensors on their body surfaces or force/torque sensors at critical joints. This study introduces a whole-body admittance control framework for quadruped manipulators, utilizing a novel external impact force observer that estimates impact forces acting on the manipulator or the quadruped's base without relying on dedicated force sensors. The observer leverages the robustness of a super-twisting algorithm (STA) based on the momentum model of quadruped manipulators. Model uncertainties are mitigated using a low-pass filter (LPF) and compensated by ground reaction forces, significantly reducing estimation oscillations during dynamic gaits. By integrating these estimated impact forces, the whole-body admittance control framework enables compliant interactions with the environment and mitigates unsafe behaviors caused by torque saturation through a set-valued feedback loop that constrains command torques within actuation limits, including joint torque boundaries and friction cone constraints of the ground reaction force. Experimental validation across diverse scenarios confirms the effectiveness of this approach in facilitating safe and adaptive interactions between quadruped manipulators and external forces.