Design And Control Of The Hydraulic Actuated Biped Robot Motion System

With the achievement of Bigdog, LS3, Petman and Altas, the passion for the research of the hydraulic actuated legged robot has heated up all over the world. Legged robot actuated by hydraulic servo systems possess a number of advantages, such as faster dynamic ability, higher power-to-mass ratio, more compact in structure, stronger athletic ability in the field natural topography and better military application background. Many research institutions both at home and abroad have proposed their hydraulic actuated quadruped robots, but biped robots with load ability are difficult in technology and there isn’t hydraulic actuated biped robots with load ability been proposed till now. In this paper, the mechanism design of a hydraulic actuated biped robot lower-limb, the kinematics analysis, gait generation methods and stability control methods are researched. The main contents are shown as following:Firstly, based on the structure analysis of the traditional human-simulated biped robot lower-limb and the characteristics of the hydraulic actuated servo systems, an8-DOF hydraulic actuated biped robot motion system is designed; then the allowable maximum weight which could be imposed on the biped robot physical prototype is obtained by ADAMS simulation experiments.Secondly, based on the D-H method, the forward kinematics equations are built and the position parameters relative to the body fixed coordinate system of each joint are obtained. On this basis, the analysis solutions of the inverse kinematics equations are given based on the condition that the robot fits its feet closely to the terrain when landing on the ground; then the relationship between the trail of the foot end and the elongation of each cylinder is obtained; besides, the relationship between the squat distance and the step length of the biped robot is built.Thirdly, based on the cubic polynomial interpolation method, composed gaits of the feet relative to the body fixed coordinate system are proposed. With the position adjustments of the support feet relative to the body fixed coordinate system, the COP position is adjusted accordingly, and then the stability of the static walking of the biped robot is realized.Fourthly, the walking pattern generation method based on "LPDB" is proposed and the dynamical equilibrium of the biped robot in the lateral plane is realized; then the walking pattern generation method based on "FDCV" is proposed and the uniform straight motion of the biped robot is realized.Fifthly, Gaits for the biped robot climbing up and down stairs relative to the body fixed coordinate system are generated; then the constraint conditions for the biped robot walking system climbing up and down stairs dynamically and continuously are presented.Sixthly, for the situation that the impact force is variable in large range and lacking regularity when the legged robots walk dynamically, a series of stable control strategies based on the trunk posture information are proposed and the quick and stable walk of the8-DOF hydraulic actuated biped robot is realized.Seventhly, weight loading experiments in the MD.DAMS simulation environments and physical prototype empty load experiments in real word are used to verify the correctness and the effectiveness of the proposed walking pattern generation methods and control strategies.Innovative points of this paper:1. Based on the motion analysis of the traditional12-DOF human simulated biped robot, the first8-DOF hydraulic actuated biped robot of the nation is proposed, which is simple in structure, small in volume, good in practicability and economy in price. What’s more, the ratio of bear load and dead load is2.5.2. A new gait generation method based on the "LPDB-FDCV" is proposed, which avoids the huge impact caused by the discontinuous change of the COM acceleration. With the proposed walking generation method, the fast and stable dynamic movements of the hydraulic biped robot motion system are realized, such as walking forward, walking backward, stepping sideways, turning around, going up and down the slope and climbing up and down ladders dynamically and stable without double support phase.3. Focusing on the problems that the impact force is variable in large ranges and lacking regularity when the legged robots walk dynamically, a series of stable control strategies based on the trunk posture information are proposed and the quick and stable walk of the8-DOF hydraulic actuated biped robot is realized.