Effects of constraints on bipedal balance control

The satisfaction of constraints between the feet and the ground is important during balance control of bipedal standing. In this work, the effects of such constraints on balance control of a simplified two-dimensional biped are studied. 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. It is also found that the angular velocity plays a crucial role in satisfying the constraints. For the biped under study, the friction constraint determines the critical angular velocity, above which the constraints are violated, but the center of pressure (COP) constraint dictates the bounds of the control torque in a large region around upright position