Design and Evaluation of a Sensor-Instrumented Clutch Mechanism for Quasi-Passive Back Exosuits.

Abstract

We designed, built, and evaluated a new sensor-instrumented clutch to expand the capabilities of quasi-passive back exos (exoskeletons and exosuits) to include force sensing, posture sensing, and versatile mode switching. Quasi-passive back exos provide workers with lifting assistance, which can reduce their back injury risk. Central to their design is a clutch mechanism that enables the exo to assist when engaged and be unobstructive when disengaged. However, current exo clutches can have limited sensing and control capabilities. We designed a new clutch that integrates an encoder, solenoid, inertial measurement unit, and microprocessor to estimate exo assistance, monitor posture, and switch between engaged and disengaged modes. To validate the new capabilities, 6 participants wore a back exo during stoop and squat tasks. Data from the clutch's encoder were used to estimate assistance and trunk-thigh flexion angle, then compared to motion analysis lab measurements. The prototype estimated exo assistance with an average error of 8.8 N (0.9 Nm of lumbar torque) and trunk-thigh angle with an average error of 6.7°. This prototype also maintained the core capabilities of a quasi-passive exo by withstanding 350 N of force when the clutch was engaged, exerting 7-20 N when disengaged, and switching between clutch modes in 0.1 seconds. We demonstrated an instrumented clutch that enabled exo assistance and posture monitoring, and more versatile control options, in addition to providing back relief. This clutch increases the capabilities of quasi-passive back exos, opening new opportunities for exo research and applications.