抄録
The three-joint arm’s optimal control model has already been formulated which is characterized by a freezing-like mechanism in its hand joint and minimization of its consumed energy, and its effectiveness has been clarified in reproducing human reaching movement trajectories. This research clarifies the influence of the boundary conditions (fixed and free end point conditions) and the desired values (joint angles and visual coordinates) at the final point on the reaching movement trajectory predicted by the three-joint arm’s optimal control model. Consequently, the following results are obtained: (1) in the case of the desired values of joint angles, the difference in the boundary conditions at the final point has no influence on the predicted reaching movement trajectory; (2) the minimum-energy trajectory agrees well with the measured one, whereas the minimum torque-change trajectory disagrees with the measured one without a considerable increase in the three-joints’ viscous coefficients; (3) in the case of the desired values of visual x and y coordinates, the model can reproduce the measured reaching movement trajectory including the hand-joint freezing characteristics, though it requires an increase in the energy term’s weight of the model’s criterion function (i.e., enhancement of energy minimization) and an increase in the hand-joint freezing coefficient. These results suggest that human two-point reaching movements are likely to be executed in the basis of a rule that the arm posture including the hand changes as little as possible.
