Stable Gait Planning And Experiment Study Of Quadruped Robot

Quadruped robots not only possess simple structure with low control difficulty and good stability,but they also own strong ability in environment adaptation as they use mechanical legs moving on all kinds of terrain.This paper is to improve quadruped robots' ability in environment adaptation and to achieve their stable motions by focusing on quadruped robots' gait planning.A new gait planning method in which stability margin of robot and movement margin of mechanical legs are constraint conditions is proposed based on workspace of mechanical legs.Firstly,theory of gait and stability of quadruped robots is elaborated.Longitudinal stability margin is chosen for gait planning.A mathematical model of gait,that include stride sequence,support factor and trajectory of swing leg,is established.The trajectory of swing leg is planned by cubic spline curve equation.Secondly,kinematics model and inverse kinematics model of quadruped robot is established,founding a mapping relationship between foot's movement and joint variables.Based on the positions of supporting legs in the centroid coordinate system the mathematical model for calculating new foothold area for the swinging leg is proposed,in which longitudinal stability margin and kinematics margin of mechanical leg are constraints.Considering the effect of mechanical legs' workspace on calculating foothold area,workspaces of mechanical legs are analyzed and discretized to gain matrixes which could reflect characteristic of workspaces of mechanical legs.Those matrixes are used to complete gait planning of quadruped robot.Thirdly,simulation experiments for quadruped robot walking on flat and rugged terrain are carried out both in numerical calculation software and virtual prototyping software.The relationship between horizontal projection of footholds and COG would be analyzed in numerical calculation software to prove that the horizontal projection of the center of mass of the quadruped robot is always located in the support polygon formed by horizontal projection of footholds under the proposed gait planning method.Through analyzing rotation curves of all joint variables,continuity of mechanical legs' motions is proved and where mode of mechanical legs change isread.Kinematics Simulations of quadruped robot are conducted,in which motion charts of quadruped robot,curves of attitude angles,displacement curves and trajectories of mechanical legs are used to prove the correctness of gait planning.Lastly,a quadruped robot is built to conduct related experiments which include walking on flat and rugged terrain.The correctness of gait planning method is further proved through motion charts and curves of RPY attitude angles of the quadruped robot.