Contact transition control via joint acceleration feedback

Stable and controllable transition from free motion to constrained motion i s of central importance for robots in contact with environment in many appl ications. In this paper, a joint acceleration feedback control of high band width is employed to damp oscillations during the contact transition when t he approaching speed does not vanish, In this control scheme, a classical i ntegral force controller is refined by means of joint acceleration and velo city feedback. This is intended to achieve a stable contact transition with out need of adjusting the controller parameters adaptive to the unknown or changing environments. Extensive experiments are conducted on the third joi nt of a three-link direct-drive robot to verify the proposed scheme for the environments of various stiffnesses, including elastic (sponge), less-elas tic (cardboard), and hard (steel plate) surfaces. Results are also compared with those by the transition control without the acceleration feedback. Th e proposed scheme is shown to be promising in terms of robustness, stabilit y, and adaptability.