Repeated and intensive gait training can improve muscle strength and movement coordination of patients with neurological or orthopedic impairments. However, conventional physical therapy by a physiotherapist is laborious and expensive. Therefore, this therapy is not accessible for the majority of patients. This paper presents a six-bar linkage mechanism for human gait rehabilitation with a natural ankle trajectory. Firstly, a six-bar linkage mechanism is selected as the original mechanism to construct a gait rehabilitation device. Then the ankle trajectory is formulated as a function of the crank angle. And the rotation angle of the crank is set as a linear function of time. Therefore, constant speed motor is sufficient to control the mechanism. For the dimensional synthesis, the precise point distances of the gait trajectory and the coupler curve are set as objective functions, with the kinematic constraints including in the optimization procedure. To obtain the optimal structure design parameters, a cooperative dual particle swarm optimization algorithm is developed. The results show that the coupler curve matches well with the gait trajectory. The average distance between the 60 precision points is 3.5 mm.
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