A Safe Torque Limiter Design Applied to An Assistive Walking Device against Unexpected Load

Abstract

Considering the practical situations of the assistive device, user regularly encounters unbalance postures which induce unexpected load to break the elements of the servo motor. This study aims to design a torque limiter for protecting the assistive walking device against the unexpected load and extending the service lives. We applied sandwich structure design which arranged the material sheet between the output shaft and final gear. When the surface forces of the material sheet over the limit friction load, the output shaft slipped and protected the device simultaneously. Hence, the properties of material sheet play a key role in this torque limiter. We have developed two types (with/ without groove), and experimentally validate the friction torque performance of NBR and PVC materials by using these torque limiters. Finally, by assembling this torque limiter into our developed assistive walking device that can conduct the same actuating motions as the unmodified motor, and prevent the equipped motor broken from the unexpected load.