Twofold Observer-Based Precise Force Control

Force sensor measurement noises and mechanical disturbances make realization of stable and robust force control systems challenging. With regard to this, a precise force control system that implements a combination of force and disturbance observers (DOBs) is proposed in this brief. The observers are a reduced-order multisensor-based force observer (RMFOB) to attenuate sensor measurement noises and a model-based force DOB (FDOB) to suppress the effects of mechanical disturbances. These are combined in a closed-loop setting to form a twofold observer-based precise force control system. A novel systematic tuning criterion for the RMFOB and FDOB cutoff frequencies utilizing sensor noise and force disturbance intensities derived from the proposed closed-loop system is developed. In addition, analysis of robust stability against nonlinearity and parameter variations of the proposed system is conducted using RMFOB cutoff frequency. Finally, effectiveness of the proposed method is verified by theoretical analyses, simulations, and experiments.