Effect of arm swinging and trunk twisting on bipedal locomotion It is expected that human locomotion, in which the trunk twists and arms swing, provides stability as well as compensation for the angular momentum because the trunk and arms are placed over legs and then their position and the acceleration influence the bipedal locomotion. This paper presents a bipedal robot equipped with a trunk, embedding a viscoelastic joint and two arms away from the midline of the trunk. Physical experiments show that a passive oscillation of the viscoelastic trunk joint around the yaw axis vertical to the ground and a swing of heavy arms provided an oscillation of zero moment point (ZMP) in the lateral direction and a small oscillation in the anteroposterior direction. This is despite the fact that the robot does not have a roll joint and the arm swings back and forth. Numerical analysis supports the results of the physical experiments through a simple model and by expressing ZMP trajectory, showing that the arm swinging facilitates antiphase locomotion in which right arm and left leg swings ahead and vice versa.

TIP Model: A Combination of Unstable Subsystems for Lateral Balance in Walking Balancing or postural stability is one of important locomotor subfunctions in bipedal gaits. The inverted pendulum and virtual pivot point (VPP) are common modeling approaches to analyze balance control in human and robot walking. In this paper, we employ the VPP concept to investigate posture control in the frontal plane. The outcomes demonstrate that unlike posture control in the sagittal plane, the VPP in the frontal plane is place below center of mass. This finding explains a novel hybrid strategy for lateral stability in human walking. The here proposed model shows that switching between unstable inverted virtual pendulums generate stable posture control in the frontal plane. This outcome is consistent within a group of seven human subjects walking at normal and slow speeds.