Balance Control Strategy of Biped Walking Robot SUBO-1 Based on Force-Position Hybrid Control
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International Journal of Precision Engineering and Manufacturing https://doi.org/10.1007/s12541-020-00438-1
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Balance Control Strategy of Biped Walking Robot SUBO‑1 Based on Force‑Position Hybrid Control Hyo‑Joon Lee1 · Jung‑Yup Kim1 Received: 1 May 2020 / Revised: 24 August 2020 / Accepted: 3 November 2020 © Korean Society for Precision Engineering 2020
Abstract This paper deals with a balance control strategy based on a force-position hybrid control of biped walking robot, SUBO-1 for stable walking on irregular terrain environments. Walking robots basically require the position control of the leg to accurately land the swing foot on the correct position. Also, they need a force-based balance control to prevent them from falling over on irregular terrain. This study derives the location of the Zero Moment Point (ZMP) to control the Capture Point (CP) for keeping balance of the robot, and additionally obtains the total vertical force required for both feet to maintain the desired height of the Center of Mass (CoM). The vertical force, roll and pitch moments of each foot that optimally satisfies the derived ZMP and the total vertical force of the both feet, are calculated through the Quadratic Programming (QP). To realize the vertical force, roll and pitch moments of each foot, a feedforward control using Jacobian and a PI control using a force/torque sensor at the foot are used simultaneously, and the horizontal forces and yaw moment of each foot are used in Task-Space PD control for positioning of foot. Finally, the proposed method is verified through balance control experiments in double support and single support phases using the biped walking robot, SUBO-1 in the presence of external force and varying ground slope Keywords Balance control · Biped walking robot · Force-position hybrid control
1 Introduction Biped walking robots were expected to handle dangerous tasks on behalf of people in disaster circumstances where people cannot enter. However, when a nuclear power plant accident in Fukushima occurred in 2011, biped walking robots were not able to replace humans. One of the reasons why biped walking robots have failed to replace human is that walking stability is not guaranteed in irregular terrain environments. In the meantime, many researchers have proposed various balance control strategies to ensure walking stability of biped walking robots. Hun-ok Lim et al. proposed a balance control strategy that compensates for the movements of the torso and waist to eliminate the instantaneous instability during biped walking, and adopted the position-based impedance * Jung‑Yup Kim [email protected] 1
Department of Mechanical System Design Engineering, Seoul National University of Science & Technology, Seoul 01811, South Korea
control that absorbs the impact and contact force between the ground and landing feet to improve walking stability [1]. Koichi Nishiwaki et al. developed a method that combines three strategies: changing the reference ZMP inside the sole of the foot, changing the posit
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