Involuntary movement during haptics-enabled robotic rehabilitation: Analysis and control design

In this paper, a safety concern arising from pathological tremors in patients interacting with haptics-enabled rehabilitation robots is analyzed and the issue of tremor amplification for assistive/coordinative robotic rehabilitation is investigated. In order to deal with this issue, a control architecture is proposed to dissipate the extra energy of the system and guarantee its stability and safety of the patient. For this purpose, (a) first, a multilayer adaptive filter is proposed to estimate high-frequency components of hand motions (corresponding to involuntary movements); (b) then a resistive force field is generated and applied by the robot to attenuate the tremor; and (c) simultaneously the residual low-frequency voluntary actions are amplified/coordinated to deliver appropriate therapy. Stability analysis and a stabilization scheme are developed to guarantee safe interaction regardless of variations in the patient's dynamics and tremor kinematics. The ultimate goal is to make it possible for patients with pathological tremors to take advantage of non-passive robotic assistive/coordinative therapy. This would not be possible using conventional systems due to the possibility of tremor amplification. Experimental results are presented.