Switching Control Method for Stable Landing by Legged Robot Based on Zero Moment Point

Abstract

This paper proposes a switching control method to achieve a smooth transition from an edge landing to a sole landing for a legged robot. When a biped robot walks, an undesirable condition at the moment of landing, such as hunting between the ground and the foot, may occur for several reasons. To avoid this condition, this paper focuses on a method that uses simple controllers to ensure a smooth transition from an edge landing to a sole landing. In the event of an edge landing, a force controller should be implemented for a smooth transition to a sole landing. This is because the force controller enables the foot to contact the ground softly. After the landing state is shifted to the sole landing, the control method should be changed to the position controller. Therefore, it is necessary to switch the control method according to the contact condition between the foot and the ground. To avoid the chattering of the controller switching, several hysteresis values are used for the zeromoment point (ZMP) position and ZMP velocity in the switching function. Simulations and experimental results confirmed the validity of the proposed method.