Integrated Disturbance Observer-Based Robust Force Control

For robotic tasks that involve combined transmitting and contact force control, achieving the high-performance motion control while ensuring stable environment contact is difficult. Among the factors that affect the quality of this force control, in this article, we may account vibrations due to misalignment in the mechanical components, actuator inaccuracies, nonlinear effects of friction, and backlash. All the above mentioned factors can be collectively considered as force disturbances. Toward high-performance motion control and contact stability, a novel integrated disturbance observer (DOB) (IDOB) is proposed. The IDOB uses force sensor measurements with position measurements and a plant model to isolate and robustly suppress the effects of force disturbances within the plant without compromising contact stability. This is applied here to a force control system to demonstrate the enhanced force control performance in free space and in contact. The passivity, robust stability, and disturbance rejection of the proposed IDOB are compared with those of existing force controllers, with and without force-based DOBs. Finally, actual experiments are conducted in free space and contact under various interaction conditions, showing that the IDOB improves transmitting force control and disturbance suppression performances. Moreover, peak collision force is reduced while maintaining contact stability with stiff environments.