Diagonal walk reference generator based on Fourier approximation of ZMP trajectory

Humanoid robots should be capable of adjusting their walking speed and walking direction. Due to the huge design space of the controller, it is very difficult to control the balance of humanoids walk. The position of the Zero Moment Point (ZMP) is widely used for dynamic stability measurement in biped locomotion. The reference trajectory of the Center of Mass (CoM) of a humanoid can be computed from a predefined ZMP trajectory. In order to generate the CoM trajectory, many researchers represent the ZMP equation using the motion equations of simple physical system, e.g. the cart-table model. A Fourier series approximation based method, which generates the CoM trajectory, was previously proposed for straight and curve walking. This paper extends these techniques to generate side and diagonal walking. In order to generate diagonal walking, straight and side walking are combined. The proposed CoM generation approach was tested on a simulated NAO robot. Experiments indicate that the method is successful in generating stable side and diagonal walking. Comparison results of the proposed method with ZMP preview control method show the benefits of the proposed technique.