Research On Wheel-legged Quadruped Walking Robot Based On Series-parallel Mechanism

The wheel-legged hybrid robot is a kind of special service robot with high application prospects,because it can move quickly and efficiently by wheels and pass through the obstacles by legs.It has great movement flexibility and good adaptive capacity to environment.This paper is devoted to study on a wheel-legged hybrid robot with a serial-parallel hybrid mechanism as the leg structure,which has better flexibility,large carrying capacity,and good adaptive capacity to environment.It can be used to help humans to accomplish various tasks in dangerous and difficult environments.The main contents of this paper are as follows:Firstly,from the perspective of bionics,it is determined that the number of the robot's leg is 4,and the DOF of each leg is 3.On this basis,a wheel-legged hybrid mechanical leg configuration based on serial-parallel hybrid mechanism is proposed,and then the configuration design of the whole robot is completed.Through the DOF analysis,it is confirmed that the robot can meet the walking requirements.On the basis of the position analysis of the swinging leg,the workspace of the leg mechanism is solved,and the influence of various main parameters on workspace performance is analyzed.By solving the Jacobian matrix condition number of the leg mechanism,the kinematic performance of the leg is studied.Based on the above analysis,the dimensions parameters of each part of the robot are determined,and the structure design of the robot has been completed.Secondly,the Jacobian matrix between the foot end point of the leg mechanism and the driving units is deduced.The angular velocity and linear velocity of the center of mass of the upper leg,lower leg and three electric push rods,as well as the velocity and acceleration of the foot end point are solved.The simulation model of the leg mechanism is established by softwares,and its kinematics simulation is carried out.The dynamic model of the leg mechanism and the whole robot is established by using Lagrange equation method,then the numerical examples are solved and verified by software simulation.Thirdly,the foot-end trajectories without obstacles,considering obstacles and steps are planned.The theoretical basis for the stability of the robot is analyzed when it adopts static and dynamic gait,respectively.Based on trajectory planning and stability analysis,the intermittent walking gait,the coordinated walking gait,the diagonal trotting gait,the climbing step gait and the turning gait are planned,and the gait simulation is studied by software.Fourthly,the Hopf oscillator is selected as the Central Pattern Generator(CPG)gait control model,and the influence of each parameter in the mathematical model on the dynamic characteristics is analyzed.From two aspects of controlling the joint swing angle and the foot coordinate,the single-leg CPG model is established.Furthermore,the CPG control network of the robot is constructed,and the restraint weight matrix of each gait is obtained.The gait generation method based on CPG output signal is studied,the gait conversion between different gaits is analyzed,and the software simulation is carried out.The turning gait of the quadruped robot is analyzed concretely,and the CPG control model and the Simulink simulation model of the robot are established,then the data generated by the CPG are simulated and verified.Finally,the single-leg prototype of the wheel-legged quadruped walking robot is developed,and the debugging control program is programmed,then the single-leg prototype is debugged.The calibration experiment system of the single-leg prototype is built.Through the trajectory tracking experiment on the foot end,the position errors of the prototype in each coordinate direction are obtained.The main reasons for the error are analyzed,which provides the experimental basis for improving the motion accuracy of the robot prototype in the future.