Performance Analysis of Torque-sensorless Assist Control of a Powered Exoskeleton Using Highly Back-drivable Actuators

For human motion support, there is an active focus on research and development of powered exoskeletons. A powered exoskeleton is directly fitted to the human body; thus, it is necessary to consider the safety of the human-robot interaction, including improving the back-drivability. Toward this problem, a powered exoskeleton that uses a highly back-drivable reduction gearbox even at a high reduction ratio is proposed, and a user’s external force can be estimated without using a torque sensor even though the system has very high total gear ratio of 408.57:1. This paper investigated the apparent mechanical impedance of an exoskeleton during assist control execution and examined the performance and operability of the assist control. Finally, a questionnaire of participants was conducted and the mechanical impedance that resulted in a high operability was examined by implementing admittance control.