EFFECTS OF CONSTRAINTS ON BIPEDAL BALANCE CONTROL DURING STANDING

Abstract

In this work, the effects of the gravity constraint, friction constraint, center of pressure (COP) constraint, and tip-over constraint on balance control of a simplified two-dimensional biped during standing are investigated. The bounds imposed on the control torque due to the constraints are first determined. Such control bounds have significant effects on designing balance control laws and can be used to predict the type of falls if the constraint is violated. It is found that there exists a critical angular velocity, above which, regardless of the control torque, the constraints will be violated. It is also found that the gravity constraint is the least important since it is always satisfied when the friction constraint is satisfied. For the biped under study, the friction constraint determines the critical angular velocity in most of the region around the upright position, while the COP constraint dictates the bounds of the control torque. Since the tip-over constraint is equivalent to the COP constraint as both feet are on the same level ground, it is concluded that the tip-over constraint is the most important when the magnitude of the angular velocity is below the critical value.