Performance analysis and trajectory planning of multi-locomotion mode ankle rehabilitation robot

A multi-locomotion mode ankle rehabilitation robot (MLMARR) based on the 2-UPU/RPU (U: universal; P: prismatic; R: revolute) parallel mechanism with actuators above the end effector is proposed. In addition to the rehabilitation training of the basic motion orientation of the ankle, the MLMARR enables up/down or back/forth traction rehabilitation training, ensuring the training of muscle groups and ligaments related to the ankle motion. First, degrees-of-freedom analysis is conducted based on the screw theory. Subsequently, using the closed-loop vector method and coordinate system rotation transformation, inverse position analysis is performed and the Jacobian matrix is described. In addition, three types of kinematic singularities are identified by analyzing the Jacobian matrix. Moreover, the workspace is determined by the limit boundary method. Three rehabilitation training modes are set and dynamic simulations are performed according to the ankle rehabilitation requirements; on this basis, the linear actuators can be selected reasonably. Finally, the effectiveness and accuracy of rehabilitation training are evaluated based on experimental data obtained using an MLMARR prototype. This research reveals the characteristics and superiority of the proposed MLMARR and offers the basis for the future improvement of the device. •An multi-locomotion mode ankle rehabilitation robot based on the 2-UPU/RPU parallel mechanism with actuators above the end effector has been proposed. The actuators are located above the end effector, which is similar to the motion driving direction of the ankle. •The rotation center of the moving platform coincides with the actual physiological center of the ankle, ensuring that secondary injuries of the ankle during the rehabilitation training process will be avoided.•The multi-locomotion mode ankle rehabilitation robot can realize a variety of rehabilitation locomotion modes of the ankle. Thus, it can accurately mimic the manual treatments and ensure the training of muscle groups and ligaments related to the ankle motion.