3-Dimension analysis of human arm stiffness in reaching movement using arm robot

In rehabilitation, a robot is useful and effective for repetitive trainings. However, few rehabilitation robots have adaptability to personal difference. Therefore, an index for quantitative assessment of the difference is required to achieve the adaptability. In conventional research, a hand stiffness is used as one of the indeces, and a dynamic hand stiffness is measured only in 2 dimensions. Then, in this paper the dynamic hand stiffness of reaching motions is measured in 3 dimensions by using an arm robot. The experimental results are represented as stiffness ellipsoids. Moreover, the results are compared with the ellipsoids in 2 dimensions. From these results, it is revealed that the characteristics of the dynamic hand stiffness in 3 dimensions is different from that in 2 dimensions. The fact implicits that a human controlls his/her arm stiffness not in work space but in joint space.