Abstract
This research formulates an optimal control model that reproduces human sitting movements on a chair (stand-to-sit movements). The model switches its dynamics from a three-link and three-joint structure to a one-link and one-joint one at the time (switching time) when its thigh-link touches the seat of a chair, and optimizes its criterion function composed of three kinds of energy costs, a center-of-gravity cost, and an input cost. The research clarifies the model's performance in reproducing human stand-to-sit movements and discusses factors indispensable for sitting on a chair. Consequently, the following results are derived: (1) the model can produce various kinds of stand-to-sit movements by adjusting the switching time primarily and one of the input weights secondarily; (2) the energy costs and the center-of-gravity cost hardly affect the model's performance; (3) there exists the optimal switching time for the criterion function to take a minimum, and the stand-to-sit movements predicted using the optimal switching time agree well with the measured ones. These results suggest that the proposed model can be a plausible and effective model of the human stand-to-sit movement mechanism and that the switching time is a primary factor involved strongly in human sitting movements on a chair and the input weights can be secondary factors.
