Gait planning of biped robot based on feed-forward compensation of gravity moment

Abstract

To improve the walking stability of biped robot, the adjusting angle is added to the ankle joint for eliminating the lateral disequilibrium. Three dimensional linear inverted pendulum model(3D-LIPM) is applied for depicting the motion of the biped robot. The motions of the stance and swing leg have an influence on the height of center of mass(COM), which is verified by the computer simulation. The model of the pendulum is also established for analyzing key factors which lead to the unbalance of the biped robot in the lateral plane, and analyzing results can be used to optimize the gait data. The motion trajectory of the each joint of the biped robot is generated by using the cosine and cycloid functions. The landing velocity of the swing leg is set to zero, and the impact is effectively reduced. Based on the inertial measure unit(IMU), the horizontal posture of the foot is kept by adjusting the ankle motors of the stance leg, and the walk stability of the biped robot is greatly improved. The inverse solution for discrete points of the walking trajectory is obtained by a numerical iterative means, which can satisfy the requirement of the control cycle of 10ms. The walking test is implemented on the flat ground, and the biped robot can steady walk with the single stance phase of 3s, the double-stance phase of 2s and the step-length of 200mm. the experiment results prove that compensation means of the gravity moment is available for the walking gait of biped robot.