Biped robot reference generation with natural ZMP trajectories

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 a key problem. A criterion used for the reference generation is that the reference trajectory should be suitable to be followed by the robot with its natural dynamics with minimal control intervention. Reference generation techniques with the so-called linear inverted pendulum model (LIPM) are based on this idea. The zero moment point (ZMP) criterion is widely employed in the stability analysis of biped robot walk. Improved versions of the LIPM based reference generation obtained by applying the ZMP criterion are reported too. In these methods, the ZMP during a stepping motion is kept fixed in the middle of the supporting foot sole. This kind of reference generation lacks naturalness, in that, the ZMP in the human walk does not stay fixed, but it moves forward, under the supporting foot. This paper proposes a reference generation algorithm based on the LIPM and moving support foot ZMP references. The application of Fourier series approximation simplifies the solution and it generates a smooth ZMP reference. Trajectory and force control methods for locomotion are devised and applied too. The developed techniques are tested through simulation with a 12 DOF biped robot model. The results obtained are promising for implementations