Abstract:In order to meet the requirements of fourbar bionic knee joint to realize characteristics of natural gait, considering the flexibility of leg swing phase, optimization mathematical model for size parameters of four-bar knee joint was presented with the goal of minimizing the root mean square error of the ankle joint center point trajectory and the target trajectory of a man. Parameters of the four-bar knee were optimized using Sequential Quadratic Programming method, which was realized by Medium-Scale Algorithms in Matlab. By kinematics simulation, it was verified that the center point trajectory curve of the optimized four-bar knee well matched with the target one, and natural gait of a man was able obtained. What's more, the ‘J’ shape curve of the instantaneous center trajectory for this mechanism was plot, by which good motion bionic characteristics were fully verified. Finally position of the instantaneous center at support time is analyzed, and the scheme of loading self-locking structure of smart Magneto rheological (MR) damper is suggested for its better stabilities by aimed at support time.