On the Effects of Constraints on Bipedal Balance Control during Standing

The satisfaction of constraints between the foot-link and the ground is extremely important for balance control of bipedal standing. In this work, the effects of the gravity constraint, friction constraint and center of pressure constraint on balancing of bipedal standing are investigated. The regions in the state space are identified and divided into fully-actuated and underactuated regions based on whether the constraints are possible to be satisfied. The ranges of control torque are determined satisfying the constraints. More importantly, regions within which regardless of the controllers the constraints can not be satisfied are identified. The results also show the specific constraint causes the violation, and help us predict how the foot-link moves once the constraint is violated.