An Electrorheological Fluid Actuator for Rehabilitation Robotics

Abstract

Transitioning rehabilitation robots from the clinic environment to the home could significantly increase the intensity and accessibility of therapy to stroke survivors. Home-based rehabilitation robots must become smaller and cheaper. In this paper, we consider a novel proof-of-concept actuator for human-machine interaction. The actuator incorporates a prototype electrorheological fluid developed to address issues previously reported in the literature. Two electrorheological fluid clutches are antagonistically arranged in a differential mechanism. The fluid clutches uncouple the output from the intrinsically high impedance of a geared dc motor. Mathematical modeling of predicted torque was compared with torque measurements. The clutches can transfer approximately 1.1 N·m at an electric field strength of 3 kV/mm. A testbed was also developed to study variable impedance control with the device where motion feedback was used to modulate the output impedance. An empirically derived model was used to program voltages/torques in response to perturbations in position. A benefit of the proposed design is the ability to statically coactivate both clutches to increase output impedance, which could potentially have benefits for training. We also discuss the advantages and disadvantages of electrorheological fluid actuators for human rehabilitation robotics.