Design Optimization of a Variable Stiffness Actuator for Knee Exoskeleton Application

Abstract

The field of wearable devices and exoskeletons for rehabilitation and assistance is one of the main fields where variable stiffness actuators (VSAs) are continuously incorporated. This is due to the need for such devices to adapt to erratic environments and mimic human motions. Recently, a passive revolute joint design with controllable variable stiffness was proposed by the authors. However, the previous design was only introduced as a proof of concept, with no further investigation of the design stiffness change capabilities for application utilization. In this work, we introduce an extended analysis and comprehensive parametric study of the system’s main design parameters. Based on the performed analysis, we propose an optimization framework for this design concept that allows implementation in knee exoskeletons. The main design parameters that affect the stiffness performance are defined. The proposed method allows the identification of these design parameters, which enables the redesign of the system according to the predefined user requirements, such as size, desired stiffness range, and stiffness change rate. A bench-top experimental setup is constructed to validate the obtained optimal design parameters. Results show the ability to achieve the desired stiffness performance for the intended application.

Keywords

• Compliant joints and mechanisms
• design optimization
• knee exoskeletons
• variable stiffness actuators