Control of a Quadruped Robot with Bionic Springy Legs in Trotting Gait

Legged robots have better performance on discontinuous terrain than that of wheeled robots. However, the dynamic trotting and balance control of a quadruped robot is still a challenging problem, especially when the robot has multi-joint legs. This paper presents a three-dimensional model of a quadruped robot which has 6 Degrees of Freedom （DOF） on torso and 5 DOF on each leg. On the basis of the Spring-Loaded Inverted Pendulum （SLIP） model, body control algorithm is discussed in the first place to figure out how legs work in 3D trotting. Then, motivated by the principle of joint function separation and introducing certain biological characteristics, two joint coordination approaches are developed to produce the trot and provide balance. The robot reaches the highest speed of 2.0 m.s-1, and keeps balance under 250 Kg.m.s-1 lateral disturbance in the simulations. The effectiveness of these approaches is also verified on a prototype robot which runs to 0.83 m.s-1 on the treadmill, The simulations and experiments show that legged robots have good biological properties, such as the ground reaction force, and spring-like leg behavior.     

Rolling dynamics of a neutrophil with redistributed L-selectin

The most common white blood cell is the neutrophil, which slowly rolls along the walls of blood vessels due to the coordinated formation and breakage of chemical selectin-carbohydrate bonds. We show that L-selectin receptors are rapidly redistributed to form a cap at one end of the cell membrane during rolling via selectins or chemotactic stimulation. This topography significantly alters the adhesive dynamics as demonstrated by computer simulations of neutrophils rolling on a carbohydrate selectin-ligand substrate under flow. It was found that neutrophils with a redistributed L-selectin cap roll on sialyl Lewis-x with a quasi-periodic motion, as characterized by relatively low velocity intervals interspersed with regular jumps in the rolling velocity. On average, neutrophils with redistributed L-selectin rolled at a lower velocity when compared with cells having a uniform L-selectin distribution of equal average density. We speculate on the possible biological implications that these differences in adhesion dynamics will have during the inflammatory response.