A Small-Gain Approach for Nonpassive Bilateral Telerobotic Rehabilitation: Stability Analysis and Controller Synthesis

In this paper, the design of a novel bilateral telerobotic architecture for rehabilitation purposes is proposed and the related feasibility, stability, and control challenges are studied. The objective is to incorporate the supervision of a local/remote human physiotherapist into haptics-enabled rehabilitation systems and allow the therapist to provide nonpassive nonlinear assistive/resistive forces in response to the patient's movements. This can address a challenge of conventional software-based rehabilitation systems, i.e., limited capability in adjusting the therapy. To guarantee human-robot interaction safety, a new design framework and a stabilizing controller are developed based on the small-gain approach. System stability and transparency are analyzed in the presence of the nonpassive, nonlinear, and nonautonomous behavior of the terminals (the therapist and the patient) and time-varying delays for the case of remote and cloud-based therapy. Several practical considerations have been taken into account to match the clinical needs and minimize the implementation cost. Simulation studies, practical implementation, and experimental evaluations are presented.