Combined observer-based robotic force control with spatial payload inertia compensation

Accurate force sensing and robust disturbance rejection are fundamental to stable and precise robotic contact tasks. This paper proposes a combined observer-based framework for robotic force control that compensates for spatial payload inertia and rejects disturbances within the force loop. A spatial payload momentum observer (SPMO) is developed to decouple the inertial effects of the payload from the force/torque sensor. The observer leverages spatial dynamics and provides an explicitly characterized 1st-order low-pass filtered estimate of the contact wrench, avoiding noise from numerical differentiation. Integrated into a decoupled motion force control structure, a combined observer (CDOB) that accounts for force subspace dynamics and sensing filtering is designed to compensate for control disturbances. This design alleviates the inherent trade-off between transient response and control stability in existing force disturbance rejection approaches. Simulations and experiments under a 3.5kg payload and an electric sander validate the framework, including dual-axis force control that shows its spatial compensation capability. The SPMO achieves a favorable tradeoff between estimation delay and noise level compared to conventional methods, while the CDOB enables fast and robust disturbance rejection without compromising transient force control performance.