Abstract
Walking on rough terrains still remains a challenge that needs to be addressed for biped robots because the unevenness on the ground can easily disrupt the walking stability. This paper proposes a novel foot system with passively adjustable stiffness for biped robots which is adaptable to small-sized bumps on the ground. The robotic foot is developed by attaching eight pneumatic variable stiffness units to the sole separately and symmetrically. Each variable stiffness unit mainly consists of a pneumatic bladder and a mechanical reversing valve. When walking on rough ground, the pneumatic bladders in contact with bumps are compressed, and the corresponding reversing valves are triggered to expel out the air, enabling the pneumatic bladders to adapt to the bumps with low stiffness; while the other pneumatic bladders remain rigid and maintain stable contact with the ground, providing support to the biped robot. The performances of the proposed foot system, including the variable stiffness mechanism, the adaptability on the bumps of different heights, and the application on a biped robot prototype are demonstrated by various experiments.
Highlights
A two-legged mobile mechanism that can walk like a human is usually thought as the best suited locomotion method for robots aimed to coexist and collaborate with humans [1]
A stiffness adjustable foot system is developed for biped robot walking on the ground with small-sized bumps
The mathematical model of the variable stiffness mechanism is not studied in detail in this paper, considering that it is not the current focus
Summary
A two-legged mobile mechanism that can walk like a human is usually thought as the best suited locomotion method for robots aimed to coexist and collaborate with humans [1]. In order to realize stable walking, the majority of existing biped robots are equipped with rigid flat feet and controlled by a trajectory tracking control method based on the zero moment point (ZMP) theory [6,7,8,9]. The ZMP theory requires that the location on the ground about which the sum of all the moments of the active forces acting on the robot equals zero is strictly within the support polygon of the foot sole [10]. Effective for walking on flat and structured terrains, this method will cause some problems if the ground is uneven. When a biped robot walks on rough terrain, just a small bump under the sole can significantly reduce the contact area and disrupt the walking stability, causing the robot to fall [13]. If the bump is unforeseen for the control system of the biped robot, the sudden impact with the bump may cause
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