In order to make the designed ankle robotic system simpler, practical, and clinically oriented, we developed a novel $\underline{R}-2\underline{U}PS/RR$ ankle rehabilitation robot with a variety of training functions covering all the required ranges of motion of the ankle joint complex (AJC), where $U$ , $P$ , $S$ , and $R$ denote universal, prismatic, spherical, and revolute joints, respectively, and the underlined letter denotes the actuated joint. The robot was designed with three degrees of freedom (DOFs), with a series $R$ mechanism and a $2\underline{U}PS/RR$ parallel mechanism. The main advantage is that the height of the robot is very low, which is convenient for clinical use by patients. At first, the mechanism design and inverse solution of positions were introduced in detail. Then, the patient-passive exercise based on the predefined trajectory tracking and patient-active exercise based on the spring model were developed to satisfy different rehabilitation stages. Finally, experiments with healthy subjects were conducted to verify the effectiveness of the developed patient-passive and patient-active exercises of the developed ankle rehabilitation robot, with results compared with the existing ankle robotic system showing good trajectory tracking performance and interactive performance.

In the present work, the ankle rehabilitation robot (ARR) dynamic model that implements a new series of connection control strategies is introduced. The dynamic models are presented in this regard. This model analyzes the robot LuGre friction model and the nonlinear disturbance model. To improve the ARR system’s rapidity and robustness, a composite 2-degree of freedom (2-DOF) internal model control (IMC) controller is presented. The control performance of the compound 2-DOF IMC controller is simulated and analyzed in the present work. The simulation shows that the composite 2-DOF IMC controller has high following performance. For practical testing purposes, 1-DOF passive training and predetermined trajectory following have been completed for different swing amplitudes and frequencies. Moreover, the thrust and tension torque of the robotic dynamic and static loading characteristics are studied in active control mode. The experimental results show the effectiveness of passive training of the given trajectory and impedance training active control strategy. This paper gives the specific functions of ARR.