Mechanical Design of an Active Hip and Knee Orthosis for Rehabilitation Applications

Abstract

This paper presents the mechanical design of an active hip and knee orthosis for rehabilitation applications. The exoskeleton device consists of two motorized joints providing 2 DOF per leg and can support a non-standard critical user (1.90 m in height and 100 kg in weight) in rehabilitation gait conditions (gait speed ≈ 0.3 m/s). The work’s methodology is firstly established with literature review to explore relevant orthotic projects already developed. Then, project requirements are defined, including critical user conditions, joint restrictions and rehabilitation gait torques and angular motion. The exoskeleton’s structure is modelled following critical static and dynamic conditions and solved analytically for static failure and stiffness criteria. The actuation drive components are designed based in numerical modelling and also solved for static failure and stiffness criteria. The project’s mechanical components are then designed following the results once they reached acceptable safety levels. The mechanical components can be subdivided into three main groups: lumbar support, limb structural links and actuation drives. Those groups a integrated to construct a prototype of the orthotic device. The assembled prototype presented the aimed robustness when tested for basic motion control associated with a equivalent rehabilitation gait pattern with artificial loads. The test trials showed low levels of induced deflection and the actuation drive was able to replicate the torques required, therefore, making the orthosis to meet successfully the intended mechanical prerequisites.