Design of a Parallel Wrist Rehabilitation Robot and Analysis of Physiological Effect on Training

Wrist impairments caused by stroke or long-term immobilization should be given more attention than the rehabilitation of proximal limb segments. In addition, the physiological effect of wrist exoskeletons on the training lacks sufficient research. According to the design requirements, a novel parallel wrist rehabilitation robot (PWRR) with two electric linear actuators and a passive prismatic joint was developed to achieve the training of the flexion/extension (F/E) and radial/ulnar deviation (R/U). The constraint forces caused by the axis misalignment were significantly reduced under the passive and active training by 0.75 +/- 0.22 N and 2.50 +/- 0.72 N, respectively. The total work of the active training increased with the velocity, whereas it was much smaller and had no obvious linear relationship with the velocity for the passive training. The sequence and degree of muscular activation of targeted muscles were measured and analyzed at three velocities to reveal the effects of the training mode and velocity on the physiological effects. PWRR could achieve the isometric training of wrist muscles at any angle of F/E and R/U validated by the comparative experiments of this device and weights. At each interactive force, the median frequency (MNF) of the EMG power spectrum and the average rectified value (ARV) of its amplitude decreased with increasing training time. The MNF slope increased with interactive thresholds, where the maximum slope was (-29.5 +/- 2.42) x10(-3)%/s at 15 N. Conversely, the ARV slope gradually decreased with the thresholds, where the maximum slope was (-61.0 +/- 8.55) x100(-3)%/s at 5 N.