Design of 1-DOF Robot With Humanoid Gait for Lower Limb Rehabilitation Based on Watt-I Six-Bar Mechanism

At present, the global population is stepping into aging stage. Rehabilitation training for patients with lower limb disorders by medical equipment has become a prominent social demand. In view of the complex structure, difficult control and expensive cost of current lower limb rehabilitation robots, an 1-degree-of-freedom (DOF) robot with humanoid gait for lower limb rehabilitation based on Watt-I six-bar mechanism was designed. Let the normal ankle gait trajectory of human be target trajectory, the mechanism was synthesized in scale. First, the ankle gait trajectory was acquired by joint angles and kinematic model of human lower limb. Then, the objective function to reflect the accuracy of trajectory reproduction and relevant constraints were established according to existing kinematic model of Watt-I six-bar mechanism. After that, GA-BFGS hybrid algorithm which combines respective advantages of genetic algorithm (GA) and BFGS (a kind of Quasi-Newton method) was used to minimize the objective function. According to optimization result, the dimension of this Watt-I six-bar mechanism was defined and the corresponding diagram was showed. Next, the optimized mechanism was analyzed by trajectory comparison in terms of shape and time sequence, velocity and acceleration analysis and joint angle detection. Further, the kinematic simulation of the mechanism was also completed.

The results show that when the crank rotates at a constant speed, the mechanism can reproduce the time sequence and the shape of target trajectory approximately to realize lower limb rehabilitation training for patients with lower limb disorders whose legs are 810.0-860.0mm long (the corresponding heights are about 1650.0-1750.0mm), which theoretically proved the rationality of the mechanism. Finally, the specific structure of lower limb rehabilitation robot based on this mechanism was designed. Its overall structure was showed by 3D model and its pivots as well as one of connecting rods were illustrated in detail. The robot consists of constant speed motors, belt drive devices, speed governors and Watt-I six-bar mechanisms which are arranged symmetrically on both sides and there is also a weight reduction system. According to 3D model, the corresponding principle prototype model was also given. Compared with the present lower limb rehabilitation robots with multi-DOF on the market, it have simpler structure, lower cost and it is easier to control and more convenient to operate, so it is suitable to be popularized into neighborhood and family.

The works in this paper provide some references for the structure design of generalized preferential robot for lower limb rehabilitation with humanoid gaits.