EXPERIMENTAL VALIDATION OF A CONTROL METHOD FOR UNDERACTUATED BIPEDAL WALKING ON COMPLIANT GROUND

Daojin Yao, Yao Wu, Yang Wang, and Xiaohui Xiao

Keywords

Experimental validation, underactuated bipedal walking, compliantgroundNomenclaturewv robot walking speedxf horizontal displacement of CoMxfc horizontal displacement of CoM for control cycleuf horizontal velocity of CoM∗ School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China; email: {ydaojin, wuyao,wangyang.hf1987, xhxiao}@whu.edu.cnCorresponding author: Xiaohui XiaoRecommended by Prof. Enver Tatlicioglu(DOI:

Abstract

This paper presents the experimental validation of an adaptive feedforward control (AFC) method for underactuated bipedal walking on compliant ground using UBbot, a four-link planar robot prototype composed of two legs with knees and unactuated point feet. In previous studies, compliant ground was modelled as a springdamper system, and stable walking was achieved by adjusting the horizontal velocity of the biped’s centre of mass (CoM) to achieve a suggested value that has been proved available for realizing at least one walking cycle. This study introduces a control scheme to implement AFC in UBbot. First, the robot CoM position in the next cycle is calculated based on the CoM horizontal velocity variation in the current cycle using AFC. Then, the corresponding gait is obtained by the robot CoM position by using the method of virtual constraints. Finally, based on feedback linearization, underactuated bipedal walking is realized through torque control. Walking experiments were performed on ground made of three types of materials: concrete, particle board, and rubber. The results showed that AFC effectively suppressed the attenuation of walking speed caused by ground compliance, and dynamic walking with a step of 31% of the leg length was successfully realized on compliant ground.

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