شكيب ميراوليائي

In recent years, the redesign of artificial knee mechanisms with the aim of closely replicating the kinematic behavior of the natural knee has attracted increasing attention. Nevertheless, many existing four-bar knee mechanisms are unable to accurately reproduce the instantaneous center of rotation (ICR) trajectory, which can adversely affect stance-phase stability an‎d overall gait performance. This study presents a computational framework for the geometric optimization of a four-bar artificial knee mechanism based on the trajectory matching of the natural ICR. Reference ICR paths were extracted from three established sources an‎d preprocessed using interpolation an‎d arc-length-based resampling to ensure geometric consistency an‎d uniform parameterization. The ICR trajectory of the mechanism was obtained through a reformulation an‎d implementation of well-established geometric–kinematic relations of four-bar linkages, enabling analytical computation of the instantaneous center throughout the motion range. The geometric parameters of the mechanism were optimized using the Differential Evolution (DE) algorithm. The optimization process was conducted over 100 generations with a population size of 35, where the design variables included the linkage lengths an‎d the fixed orientation angle of the mechanism frame relative to the horizontal axis. For each reference trajectory, the optimization was performed independently using two distinct objective functions—Discrete Fréchet distance an‎d Root Mean Square Error (RMSE)—to investigate the influence of each metric on the resulting mechanism design. Additionally, kinematic feasibility constraints were imposed to ensure valid mechanical behavior throughout the optimization process. The results demonstrate that the optimized mechanisms are capable of reproducing the reference ICR trajectories with high accuracy, yielding RMSE values in the range of approximately 1.5 to 5.2 mm. In comparison, reconstructed mechanisms reported in previous studies exhibited RMSE values of approximately 2.95 an‎d 10.5 mm for comparable trajectories, indicating a notable improvement in geometric conformity achieved by the proposed approach. Kinematic analysis of the optimized mechanisms reveals that, in the full-extension region, the instantaneous center of rotation is positioned posterior to the load line, thereby effectively enhancing stability at the onset of the stance phase. Owing to its independence from the specific input data source, the proposed framework is adaptable to users with diverse biomechanical characteristics. Furthermore, by adjusting the initial orientation of the driving link, the mechanism geometry can be readily personalized. These findings suggest that the proposed method provides a robust foundation for the design of advanced passive knee prostheses an‎d the future development of semi-active an‎d active artificial knee systems.

پروتز , مكانيزم 4 ميله‌اي , مركز آني دوران , پايداري سينماتيكي , بهينه‌سازي

Prosthesis , Four-Bar Mechanism , Instantaneous Center of Rotation , Kinematic Stability , Optimization

Shakib Miroliaei

Dr. S. Kazemirad