Research On Dynamic Walking Of The Hydraulic Actuated Biped Robot

Biped robot has strong ability to surmount obstacles and performs great movement flexibility. Due to high power-to mass-ratio and the fast dynamic ability of hydraulic actuator, the combination of the robot and the hydraulic actuator has a stronger dynamic performance. With multi-degree of freedom joints and complex structure, Biped robot is a multi-variable, strong coupling system. How to achieve high dynamic stability comparable to human walking has always been one of the most challenging and attractive problem. With the advent of a new generation of robots Atlas, the hydraulically driven biped robot will attract more attention in the world. The paper focuses on the hydraulically driven biped robot. The dynamic stable walking gait algorithm of bipedal robot with load-bearing ability is analyzed.From the perspective of bionics, the human body structure and motion mechanism of lower limbs is researched. DOF configuration, dimensional parameter and the hydraulically driven system are determined. Knee and hip are designed by the four-bar mechanism. The parallel form is used in the ankle. The hydraulic cylinder and valve is separated in the actuator, which ensure the compact structure and lightweight. The relationship between the angle of joint and the elongation of hydraulic cylinder is analyzed by the direct and inverse kinematics, which facilitate the robotic control.In the low-dimensional model space, centroid trajectory planning is researched from two aspects: one is based on the Linear Inverted Pendulum Model(LIPM), the other Spring-Loaded Inverted Pendulum(SLIP). Off-line and on-line methods based on LIPM are proposed. Due to the influence from the reaction forces generated by the collisions against the ground and the inertial forces generated by the acceleration of foot, the optimized bezier curve is regard as the trajectory of swing leg. The centroid trajectory is mapped into the joint trajectory in the high-dimensional robot space by inverse kinematics. Based on the structure of robot, kinematics simulation has been accomplished by Matlab, which validates the rationality of the algorithm.The experiment prototype is completed; afterwards experiment of single cylinder position servo is conducted, in order to research the effect of pressure and servo valve gain and frequency on the accuracy. Combination of theory and simulation results, experiments have been done, including mark time, dynamic walking, walking on the uneven ground, walking bearing weight. Through data analysis, dynamic walking and stability control algorithms have been demonstrated available.