Design and Fabrication of Force Augmenting Exoskeleton using Motion Intention Detection

Abstract

The design, fabrication and performance evaluation of the knee exoskeleton to assist sit-to-stand (STS) motion are presented. The mathematical, CAD and Simscape/MATLAB modeling for the estimation of exoskeleton torque, the factor of safety (FOS) and controller gains are also included. The knee exoskeleton is equipped with two motion sensors. One sensor is meant to detect the intention of motion. This signal is used as a reference trajectory to derive the actuation system. The 2nd sensor is to measure the actual knee joint position which is used as a feedback element to carry out the control mechanism. The exoskeleton is primarily meant for force augmentation by supplementing up to 20% of knee joint torque required, specifically for elderlies and those under rehabilitation. To reduce the total mass to approximately 7 kg, the device frame is made of light-weight aluminum alloy and a worm-gear DC motor is used as the sole actuator. As against commercially available lower limb exoskeletons, our design is simpler, low-cost and easy to use and maintain. It has been tested on able-bodied subjects and has shown the reliability of operation and user comfort. It is expected that its performance for target users, i.e., people with limited sit-to-stand motion capability will produce good results as well. This device can be modified to carry out support for gait and running tasks.