On the kinematics of human wrist during pointing tasks with application to motor rehabilitation

In this work, the kinematics of the human wrist during pointing tasks is assessed and discussed, especially in relation to the use of wrist robots. First, the existence of intrinsic kinematics constraints (or Donders' law, similarly to oculomotor system) for the human wrist during pointing tasks is verified. To this end, a novel approach based on a hand-held device is presented which allow assessing wrist movements without any mechanical loading. Second, similar pointing tasks are assessed by means of a state-of-the-art wrist robot, typically used in robot-mediated therapy as well as assessment tool. By comparing experimental results relative to the pointing task performed by healthy subjects with the hand-held device and with the robot, a loading effect on the performance due to the mechanisms of the robot is remarked. A functional requirement for the next generation of rehabilitation robots is thus provided.