Effects of joint torque constraints on humanoid robot balance recovery in the presence of external disturbance

A humanoid robot should be able to keep balance under unexpected disturbance, and can take three strategies, i.e. ankle strategy, hip strategy and step strategy, to recover balance from biomechanics research. In this paper, the relationship between limited joint torque and balance recovery strategy is analyzed using Zero moment Point Manipulability Ellipsoid. Furthermore, during balance control, the constraints between the feet and the ground must be maintained. The satisfaction of these constraints, namely the gravity constraints, the friction constraints and the CoP constraints, imposed bounds on the control torque are investigated. Such control bounds have significant effects on designing balance recovery strategies and can be used to predict the type of falls.