In order to recover the motion ability of the patient's ankle joint, a practical 3DoF (degree of freedom) 2-UPS/RRR parallel mechanism with simple structure is presented, based on the analysis on the mechanisms of existing robots for ankle rehabilitation. The mechanism center of rotation matches accurately with the center of rotation of each patient's ankle, owing to the design of constraint branches and the moving platform in this paper. Inverse kinematics of the mechanism is solved using the analytical method by calculating the freedom of the mechanism, and thereby the velocity Jacobian matrix is established. Then, the workspace of the mechanism, which should meet all the training requirements, is solved by demarcating the driving parameters. Lastly, the kinematics performance of the mechanism is analyzed in simulation based on the Jacobian matrix. The results show that the mechanism is of favourable operability, flexibility and stiffness characteristics within the specified workspace. Moreover, the non-redundant electric motor is in simple structure, unnecessary interferences between the branches are effectively avoided, and the occupancy volume of the entire unit is distinctly reduced, which are superior to some existing ankle rehabilitation robots.
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