Modeling and Evaluation of Soft Gears for Wearable Robots

With global aging, the incidence of motor dysfunc- tion is increasing. Especially, the upper limb motor dysfunc- tion requires assistance and rehabilitation to involve in daily activities such as eating and brushing one’s teeth. In recent decades, wearable robots have made remarkable progress, with a wide variety of upper limb assistive robots being developed and commercialized. However, it relies on a control system using sensors and software, and there is a possibility that a sudden collision could damage the wearable robots or the users. Therefore, to further improve safety, it is desirable to add mechanical safety devices such as torque limiters. In previous studies, we proposed a new torque limiter with a soft gear transmission mechanism and verified its feasibility. On the other hand, to apply this torque limiter to wearable robots, it is necessary to model the deformation behavior of the soft gear and establish a design methodology. In this study, we proposed a modeling method for soft gears and conducted the evaluation experiments using a finite element analysis and a prototype. The proposed model predicted slip torque values of 0.78 Nm (forward) and 1.54 Nm (reverse), with an error rate of approximately 13% from the experimental values. Wearable robots equipped with the soft gears have the potential to improve safety and be used in daily life.