Contact transition control via joint acceleration feedback

Stable and controllable transition from free motion to constrained motion is of central importance for robots in contact with environment in many applications. In this paper, a joint acceleration feedback control of high bandwidth is employed to damp oscillations during the contact transition when the approaching speed does not vanish. In this control scheme, a classical integral force controller is refined by means of joint acceleration and velocity feedback. This is intended to achieve a stable contact transition without need of adjusting the controller parameters adaptive to the unknown or changing environments. Extensive experiments are conducted on the third joint of a three-link direct-drive robot to verify the proposed scheme for the environments of various stiffnesses, including elastic (sponge), less-elastic (cardboard), and hard (steel plate) surfaces. Results are also compared with those by the transition control without the acceleration feedback. The proposed scheme is shown to be promising in terms of robustness, stability, and adaptability.