Design and performance analysis of a parallel wrist rehabilitation robot (PWRR)

Wrist rehabilitation robots are essential for assisting patients with stoke or wrist injuries. Such devices compensate for deficiencies in manual rehabilitation training, and reduce the workload of rehabilitation physicians. A parallel wrist rehabilitation robot (PWRR) driven by two pneumatic actuators is developed in this paper, consisting of two rotational degrees of freedom for the movements of flexion/extension (F/E) and radial/ulnar deviation (R/U). All components connected to the forearm or the wrist adopt an open structure to improve the wearable convenience, and the PWRR is suitable for most patients, especially those with hypertonia. To determine the PWRR range of motion, the physiological motion space (PMS) of the wrist joint in autonomous and boundary elliptical movements is measured with the help of a VICON motion capture system. The PMS in boundary motions processes an elliptical shape, and the ulnar deviations occupy the most range of motion. The theoretical workspace (TWS) of PWRR is then calculated and designed based on the kinematic model and the distribution characteristics of PMS. In addition, two indices are introduced to evaluate the kinematic performance of PWRR. A PWRR prototype is developed based on the optimal geometrical parameters and detailed structures. Its effective workspace (EWS), which has more clinical significance, is acquired by measuring the F/E and R/U movements during autonomic movements. The EWS, is smaller than TWS due to the physical structure, volume, and interference of mechanical elements. Besides, EWS can nearly encircle PMS, and satisfies all single-axis rehabilitations and compound motions of the wrist complex. The two indices, motion isotropy da and condition number κ, within TWS change smoothly with no mutation, suggesting that PWRR is sufficiently kinematically isotropic, and has no singularity configuration. The analysis shows that the developed PWRR can be applied widely in the wrist rehabilitation.