Biped Robot Reference Generation with Natural ZMP Trajectories
Erbatur, Kemalettin and Kurt, Okan (2007) Biped Robot Reference Generation with Natural ZMP Trajectories. (Submitted)
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— Humanoid robotics attracted the attention of many researchers in the last four decades. The motivation of the 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. Improved versions of the LIPM based reference generation obtained by applying the Zero Moment Point (ZMP) Criterion, widely employed in the stability analysis of biped robot walk, are reported too. In these methods, generally, the ZMP reference 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. A simple inverse kinematics based joint space controller is used for the tests of the developed reference trajectory through full-dynamics 3D simulation. A 12 DOF biped robot model is used in the simulations. Simulation studies suggest that the moving ZMP references are more energy efficient than the ones with fixed ZMP under the supporting foot. The results are promising for implementations.
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