Development of an Active Joint for Exoskeletons to Achieve Dynamic Transparency During Assistance

Abstract

Mechanical transparency during robot operation, known as dynamic transparency, would enhance the effectiveness of rehabilitation in human-assistive robots. Conventional dynamic transparency, which focuses on velocity, aims to reduce the interaction force between the robot and the user to zero, even at high motion speeds. Recognizing the limitations of conventional dynamic transparency, primarily discussed in terms of velocity, this paper proposes a novel concept of dynamic transparency during assistance. Accordingly, this paper introduces the concept of force-based dynamic transparency, defined as the ability to maintain the interaction force at the target value under motion disturbances. To conduct a feasibility study of the concept, we developed an active joint for exoskeleton robots powered by an integrated pneumatic-electromagnetic hybrid linear actuator (iPEHLA). The inertia force and kinetic friction of the actuator was considered in the dynamics model of this active joint, and its effect was discussed. The performance in dynamic transparency was evaluated.