Personalized knee rehabilitation using a crank-adjustable four-bar mechanism with optimized ICR trajectories

Aging often leads to mobility issues from conditions like arthritis and stroke, causing knee pain and limiting daily activities. Effective rehabilitation is vital for restoring function and enhancing quality of life. However, most knee rehabilitation devices lack adaptability to individual knee joint kinematics, particularly the variable instantaneous center of rotation (ICR) during gait. This study proposes a crank-length adjustable four-bar mechanism device for knee rehabilitation in subjects of three different statures. The crank lengths are adjusted to correspond with the three distinct knee instantaneous center of rotation (ICR) trajectories. The planar four-bar linkage was synthesized using the Salp Swarm Algorithm (SSA) for optimal path generation. A two-phase optimization process was employed: first, determining parameters for the driving dyad to trace multiple desired paths, and second, using a least-squares circle-fitting method to finalize mechanism parameters, adhering to Grashof’s law. The mechanism supports three distinct ICR trajectories, ensuring precision and adaptability in replicating natural knee gait. Topology optimization was performed, incorporating position and static force analyses to determine orientations and reaction forces. Unlike previous approaches that assume a simplified center of gravity, this study incorporates the actual center of gravity, enabling more realistic computation of reaction forces based on the true positions of link centers of gravity during topology optimization. CAD models developed in Fusion 360 optimized the shape by removing material in low-force areas, achieving a 38.53% mass reduction and closely aligned actuation force compared to existing models. This lightweight, adaptable, and stable knee-support device is designed to minimize user strain and potentially enhance rehabilitation outcomes in simulation by supporting personalized knee motion during gait.