The major drawbacks of current lower limb rehabilitation robots are high cost and complex structure which make them inappropriate to be applied in the community and family. In this paper, we design an 1-degree-of-freedom (DOF) robot with humanoid gait for lower limb rehabilitation based on Watt-I six-bar mechanism. Let the normal gait trajectory be target trajectory, the dimensions of the mechanism are calculated by path synthesis. First, the objective function to reflect the accuracy of trajectory reproduction and relevant constraints are established. Then GA-BFGS hybrid algorithm is used to minimize the objective function. After that, the optimized mechanism is analyzed by trajectory comparison, velocity / acceleration analysis and joint angle detection. Further, the kinematic simulation of the mechanism is also completed. The results show that while the crank is rotating at a constant speed, the mechanism can reproduce the time sequence and the shape of target trajectory approximately to realize walk training for patients with lower limb disorders whose legs are 810.0–860.0mm long (the corresponding heights are about 1650.0–1750.0mm). Finally, the specific structure of lower limb rehabilitation robot based on this mechanism is designed and the principle prototype model is given.

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