Design and Analysis of a Metamorphic Wrist Rehabilitation Parallel Mechanism

In order to improve the wrist rehabilitation training effect, a 3RPUPc-UPS metamorphic parallel mechanism is designed according to the physiological structure, motion characteristics and rehabilitation training requirements of the human wrist. Two motion modes of the mechanism, three-rotation and one-translation and two-rotation and one-translation, are obtained by locking or not locking the active joint of the metamorphic limb UPS. The motion output characteristics of the mechanism under two motion modes are analyzed based on the screw theory. The inverse kinematics solutions including the displacement, velocity and acceleration equations are derived. The singularity is discussed and all singular configurations are provided. The attitude workspace of the mechanism is analyzed using the Monte Carlo method. The structural optimization is performed based on the artificial bee colony algorithm. Research results show that the mechanism can fulfil all wrist rehabilitation training actions, such as the flexion/extension, ulnar/radial, traction/extrusion and pronation/supination motions.