Development of a Safety-Oriented Interaction Strategy and Compliant Limb Sensor System for a Gait Rehabilitation Robot

Robots are expanding into new fields through human-robot interaction, however this has created safety concerns due to collisions. This research develops the Safety-Oriented Interaction Strategy (SOIS) that detects collisions by measuring deformation of a compliant limb sensor (CLS) and yields using a zero force controller that directly feeds back CLS deformation. Using a 1DoF LTI model, controller stability was proven and the reduction of impedance and CLS deformation was analyzed. The effect of nonlinearities on the controller was simulated. Stiction was found to generate oscillations that could be eliminated by thresholding CLS feedback. The proposed controller displayed similar deformation and force reduction as admittance control during experiments while remaining stable. Potentiometer and optical based planar CLSs were prototyped and the potentiometer based CLS was more accurate (average errors <1mm/0.5 degrees). However, the potentially lightweight optical based sensor can follow general motion, and with refinement can be used in future designs.