Design of the Compliant Mechanism of an Assistive Device for the Knee

Compliant mechanisms are designed to deform in a controlled manner in response to external forces, using the flexibility of their components to store potential elastic energy during deformation, gradually releasing it upon returning to their original form. This article examines a knee orthosis designed to assist users during the stand-up motion, utilizing a compliant mechanism to balance the user's weight and minimize strain on leg muscles during this motion. The design process for the semi-rigid knee orthosis involved selecting materials and developing a numerical model for the compliant mechanism, which is represented as a spring. Geometric properties are obtained through the numerical modeling of the spring once the desired stiffness and safety factor values have been reached. Subsequently, a 3D finite element analysis was conducted. The study reveals a strong correlation between the maximum stress in the mathematical model (250.22 MPa) and the simulation (239.8 MPa), with an error of 4.16%. Both analyses of safety factors yielded results of 1.02 for the mathematical approach and 1.1 for the simulation, with a consistent margin of error of 7.84%. The spring's stiffness exhibits a 5.62% difference when analytically calculated at 90.82 Nm/rad and 85.71 Nm/rad in the simulation. These results suggest significant potential for the proposed device in helping patients with knee orthopedic restrictions, contributing to ongoing efforts in advancing the understanding and treatment of knee osteoarthritis.