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

Objective: 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. Design and Methods: 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. Results: 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. Conclusion: We demonstrated an instrumented clutch that enabled exo assistance and posture monitoring, and more versatile control options, in addition to providing back relief. Significance: This clutch increases the capabilities of quasi-passive back exos, opening new opportunities for exo research and applications.