Humanoid Walking Robot Control with Natural ZMP References

Abstract

Humanoid robotics attracted the attention of many researchers in the past 35 years. The motivation of research is the suitability of the biped structure for tasks in the human environment. The control of a biped humanoid is a challenging task due to the hard-to-stabilize dynamics. Walking reference trajectory generation is one of the key problems. The zero moment point (ZMP) criterion is widely employed in the stability analysis of biped robot walk. Linear inverted pendulum model (LIPM) based reference generation obtained by applying the ZMP criterion are reported in the literature. In these methods, generally, the ZMP during a stepping motion is kept fixed in the middle of the supporting foot sole. This paper employs a reference generation algorithm based on the linear inverted pendulum model (LIPM) and moving support foot ZMP references. This kind of reference generation possesses naturalness, in that, the ZMP in the human walk does not stay fixed, but it moves forward, under the supporting foot. The application of Fourier series approximation simplifies the solution and it generates a smooth ZMP reference. A suitable swing foot reference is employed too. A number of modes of trajectory and force control methods for locomotion are devised and applied. The developed techniques are tested through simulation with a 12 DOF biped robot model. The results obtained are promising for implementations