Daojin Yao, Yao Wu, Yang Wang, and Xiaohui Xiao
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 Uni-versity, Wuhan 430072, China; e-mail: {ydaojin, wuyao,wangyang.hf1987, xhxiao}@whu.edu.cnCorresponding author: Xiaohui XiaoRecommended by Prof. Enver Tatlicioglu(DOI:
This paper presents the experimental validation of an adaptive feed- forward control (AFC) method for underactuated bipedal walking on compliant ground using UBbot, a four-link planar robot proto- type composed of two legs with knees and unactuated point feet. In previous studies, compliant ground was modelled as a spring- damper 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 im- plement 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 experi- ments 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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