Research On Mechanism Design And Motion Planning Of Wheel-Legged Quadruped Robot

Wheel-legged quadruped robot refers to a combination of wheeled and legged quadruped robot,which has the advantages of strong terrain adaptability,fast speed and low energy consumption.It is mainly used in the fields of extraterrestrial detection,disaster rescue and pipe gallery detection.In this paper,a hip joint structure with high compact,orthogonal output and integration characteristics is proposed,which improves the ratio of height to leg length of a wheel-legged quadruped robot while avoiding obstacles.Firstly,a two-degree-of-freedom hip joint structure with both forward swing and abduction ability was designed based on the motion bionic mechanism,which was inspired by the swing trajectory of the athlete’s hip joint at the moment of hurdle jumping.By switching the two motor speed matching modes,the output of the differential transmission gear train with the orthogonal variation of the degree of freedom of the internal meshing helical gear train was realized,and the hip joint extension motion and the front swing motion were decoupled.Based on the hip joint structure,the leg topology was designed based on the joint freedom requirement in the obstacle crossing process,and the body structure was designed according to the robot size and structural constraints.Secondly,the kinematic model of the robot’s legs and whole body is established by the D-H method,and the leg motion Jacobi matrix is obtained.To analyze the leg flexibility,the reachable working space of the leg is calculated using Monte Carlo method to obtain the leg.The kinetic equations of the legs are derived according to the Lagrangian method,and the analytic formulas of the mass matrix,the Koch vector and the gravity matrix are obtained to provide inputs for achieving stable control of the joint motion.Then,based on the kinematic model,we propose a wheel-foot concordance gait planning method for robot overrunning.The mapping relationship between the robot’s overrun height and leg joint angle is optimized by genetic algorithm,and the Central of Gravity(COG)principle is used to constrain the gait of wheel-foot concordance to ensure the gait stability during the motion.The trajectory of the robot’s foot end is used to inverse the trajectory of the leg joint space,and the advantages and disadvantages of three planning algorithms,namely,variable trapezoidal acceleration curve trajectory,quintuple polynomial curve and S-curve trajectory,are compared and analyzed to ensure the soft contact between the robot’s foot end and the ground.Finally,a wheel-legged quadruped robot motion control simulation and experiment system is established.Firstly,we design the motion control algorithm of wheel-legged quadruped robot with high leg joints over obstacles,and verify the effectiveness of gait planning and motion control algorithm through simulation.The results show that the designed hip joint structure improves the obstacle crossing ability of the wheel-legged quadruped robot and ensures the stability of the body position during the obstacle crossing process.