Study On Dynamic Characteristics Of Wheel-legged Vehicle Under Typical Working Conditions

Wheel-legged vehicle is essentially a multi-mode robot,which combines the characteristics of wheeled vehicles and legged robots,it can complete tasks in complex environments preferably.Therefore,the research on wheel-legged vehicle has important practical significance.This thesis mainly studies the kinematics and dynamics modeling process of wheeled-legged vehicle,as well as its gait motion characteristics and attitude control method.Firstly,the model of the wheel-legged vehicle is established to determine the overall structure and parameters.For wheeled vehicle mode,a 10-DOF dynamics model is constructed to analyze its differential steering process.For quadruped robot mode,the motion coordinate system of body and leg are defined by the standard D-H method to deduce the pose transformation matrix of the foot end relative to the reference coordinate system,from which we get the kinematics solution.Besides,the inverse solution is got by analytic method.The dynamic equations of one single-leg are built due to Lagrange theory,from which the relation between joint torque and its motion is gained.In addition,the model of the wheel-legged vehicle is built by Simscape Multibody to verify its accuracy.Then,gait and gait parameters of quadruped robot mode are defined from the biological point of view,and its optimal step sequence is determined according to the value of static stability margin.The gait control methods based on foot trajectory planning and central pattern generator are proposed.Considering the working characteristics of the wheel-legged vehicle,four typical working conditions are set:straight-line walking,turning,uphill and downhill,up and down the steps.Finally,The CPG network control model is constructed by coupling four Hopf oscillators,and the simulation of straight-line walking is completed by combining the virtual model control method.The simulation results show that the body attitude can maintain stability.Based on the CPG network control model,the signal of side swing joint is devised for the simulation of turning condition.The results show the wheellegged vehicle can realize rapid and smooth turning with small turning radius,which means it has remarkable steering ability and flexibility.According to the trajectory planning method and the parameters of the ramp and step,the compound cycloid trajectory is designed.The simulation of uphill and downhill,up and down the steps are completed to verify the obstacle climbing ability of the wheel-legged vehicle and the effectiveness of virtual model control method.In this thesis,foot trajectory planning and CPG network control are introduced into the gait control of the wheel-legged vehicle.Furthermore,the body attitude control is considered,and desired results are obtained.