Acceleration feedback and friction compensation for improving the stability of admittance control

This paper proposes a position control scheme that is suitable for the use as the internal position servo of an admittance controller. The proposed controller is characterized by four points: (a) PDD
²
(proportional, derivative, and second derivative) feedback, (b) dither-based friction compensation, (c) sliding-mode-based noise filtering, and (d) variable D
²
gain. The PDD
²
structure and the friction compensation are theoretically expected to contribute the stability of the admittance control by expanding the bandwidth of the internal position control system. The sliding-mode-based filter is for smoothing the acceleration signals without producing a large phase lag. The variable D
²
gain is for reducing the effect of acceleration-measurement noise at low velocity. The proposed controller was tested with a 1-DOF device in contact with environments.