(A) soft variable stiffness band based on electroadhesive clutch for wearable robot

Abstract

Recently, an exoskeleton has been developed to apply additional torque to the joints or adjust the stiffness of the human body to assist human performance. The suit needs to be designed with two primary goals to achieve optimal form and function for safe and dynamic interaction. The first is to minimize the kinematic restrictions on the user's natural degrees of freedom. It is necessary to increase the user's safety with high backdrivability. Second, minimize the wearable robot weight to put a slight burden on the user. An exoskeleton with quasi-passive actuation is an attractive solution. It has been studied as simple structures using elastic springs and clutches. The spring stores elastic energy during the calf muscle relaxes and returns the stored energy with muscle contraction. The clutches control the energy storage timing to prevent interference of the elastic body during tension This study developed a variable stiffness band that can change the stiffness according to the motion by embedding a clutch in the elastic body. Unlike existing quasi-passive actuation, which can provide a fixed auxiliary torque trajectory, it releases energy separately through a clutch at the desired timing and provides adjustable assistive torque. The electro-adhesive clutch made it possible to provide a high brake force capable of actuating different stiffness with a small volume. Adjust the stacking clutch layers number to reduce the required voltage and contact area. Also, the developed variable stiffness band is customizable according to the target joint. Developed variable stiffness band performed 0.96 Nm/rad in dorsiflexion and 3.22 Nm/rad in plantarflexion. In a dynamic situation, VSB performs stiffness of 1.66 Nm/rad in the dorsiflexion and 4.05 Nm/rad in the plantarflexion. The energy consumption rate in PF is about twice that of energy storage in DF. And it shows high repeatability more than 1000 times.