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The kinematic equivalent model of the existing ankle rehabilitation robot is inconsistent with the anatomy structure of the human ankle, which will influence the rehabilitation effect . Therefore, this paper equivalent the human ankle to the UR model and proposes a novel 3-DOF generalized spherical parallel mechanism for ankle rehabilitation. The parallel mechanism has two spherical centers corresponding to the rotation center of the tibiotalar joint and subtalar joint. Via screw theory, the mobility of the parallel mechanism is analyzed, which meets the requirement of the human ankle. Its inverse kinematics is presented and singularities are identified based on the Jacobian matrix. The workspaces of the parallel mechanism are obtained by the search method and compared with the motion range of the human ankle, which shows that the parallel mechanism could meet the motion demand of ankle rehabilitation. In addition, on the basis of the motion/force transmissibility, the performance atlases are plotted in the parameter optimal design space and the optimum region is obtained according to the demands of practical application. The results show that the parallel mechanism can meet the motion requirements of ankle rehabilitation and have excellent kinematic performance in its rehabilitation range, which provides a theoretical basis for the prototype design and experiment verification.

The ability of ankle rehabilitation robots to accurately fit the actual human ankle motion is an important judgment basis for robot-assisted rehabilitation training. This paper proposes an evaluation index and mechanism parameter optimization method based on ankle-foot motion trajectory by exploring the human ankle-foot motion principle. First, the ankle UR equivalent model and a 3-DOF parallel ankle rehabilitation robot are described. Second, the ankle-foot motion data are measured by the body surface marker method, which proved the coupling of ankle-foot motion. Then, a new evaluation index, the ankle-foot motion comfort zone, is proposed, which is essentially the superimposed ankle-foot motion trajectory measured about 3-5 mm wide. Third, a mechanism parameter optimization method, is proposed in terms of the ankle-foot motion comfort zone as the evaluation index, which is applied to the 3-DOF parallel ankle rehabilitation robot, and the optimization results proved the feasibility of the method. Finally, the optimized rehabilitation robot is fitted with different ankle motions, and a prototype model is designed for kinematics simulation, which verifies the adaptability of the optimization method. The research results provide a theoretical basis for the configuration design of ankle rehabilitation robots, and provide a new direction for the optimization of the mechanism parameters.