Biped robot reference generation with natural ZMP trajectories

Official URL: http://risc01.sabanciuniv.edu/record=b1161877 (Table of Contents)

Humanoid robotics attracted the attention of many researchers in the past 35 years. The motivation for research is the suitability of the biped structure for tasks in human environments. The control of humanoid robots is challenging due to its complex 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 and 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 LIPM based reference generation methods obtained by applying the ZMP Criterion are also reported. In these methods, the ZMP during a stepping motion is kept fixed in the middle of the supporting foot sole, which lacks naturalness. In fact, the ZMP in the human walk does not stay fixed, but it moves under the supporting foot. This thesis proposes a LIPM based reference generation algorithm that uses ZMP references which have double support phase and are also natural since moving ZMP references for single support phase are used. 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.