Dynamics-Switching Optimal Control Model for Reproducing Human Rising Movements from a Chair

Abstract

This research formulates an optimal control model that reproduces human rising movements from a chair (sit-to-stand movements). The model switches its dynamics from a one-link and one-joint structure to a three-link and three-joint one at the time (switching time) when its body moves away from 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 sit-to-stand movements and discusses factors indispensable for rising from a chair. The following results are derived: (1) the model has the ability to produce various kinds of sit-to-stand movements by adjusting the weight of the input cost (input weight) and the switching time; (2) the input cost during sitting on the chair strongly affects the model's performance, whereas the energy costs and the center-of-gravity cost hardly do so; (3) there exists the optimal relation between the input weight and the switching time, and the sit-to-stand movements predicted according to the optimal relation agree well with the measured ones. These results suggest that the proposed model can be a plausible and effective model of the human sit-to-stand mechanism and that the input weight and the switching time can be factors indispensable for rising from a chair.

Keywords

• rising movements
• chair
• sit-to-stand movements
• optimal control model
• dynamics switching
• switching time
• input weight