Abstract
We already formulated a dynamics-switching three-link and three-joint (an upper body, two thighs, and two lower legs) optimal control model that reproduces human rising movements from a chair, and clarified its effectiveness and the existence of the optimal relation between two factors (input weight and dynamics-switching time t_1) indispensable for sit-to-stand movements. In order to quantitatively evaluate physical stress during rising movements from a chair, this research clarifies the relation between sit-to-stand movements and joint torques: the influence of the input weight and dynamics-switching time on the three-joint torques. Consequently, the following results are obtained: (1) as the degree of the upper body's forward tilt increases, i.e., the input weight becomes smaller and the switching time becomes larger, the magnitude of the joint torque changes from the tendency to decrease in the order of knee, ankle, and hip joints to the tendency to increase in the same order; (2) in an infinite number of optimal combinations of input weight and dynamics-switching time, there exists the optimum condition for the maximum of absolute torques in each joint to take a minimum value, and the sit-to-stand movements reproduced under the three optimum conditions for three joint torques are very close to measured movements. These results suggest that human rising movements from a chair can be quantitatively evaluated in terms of joint torques.
