Integral force control with robustness enhancement

For robotic tasks involving contact between the robot end effector and the environment, force feedback is frequently used to maintain the required force of interaction. Among the many force control strategies proposed in the literature, integral force feedback has been found to be the most desirable algorithm due to its robustness with respect to the measurement time delay and its removal of steady state force error. However, there has not been any serious investigation of the controller performance under large force disturbances. We have experimentally observed that large force disturbances can cause bouncing instability of a nominally stable force control system. Motivated by this observation, we augment the standard integral force controller with three robustness enhancements: integral error scaling, force set-point scheduling, and integral windup saturation. Extensive experimentation on surfaces with different stiffness has shown the dramatic improvement of the modified controller.<
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