Obstacle Crossing Stability Analysis And Path Offset Saturation Control Of A 2 DOF Vehicle With Articulated Bodies

It imposes strict requirements on the vehicle off-road performance due to complicated road conditions. The articulated wheeled vehicle is widely applied in complex terrain operations for its advantages of small turning radius, good maneuverability and strong adaptability of the terrain. This dissertation designs a 2 DOF vehicle with articulated bodies by referring to the structure of traditional articulated vehicles, military vehicles and theories of robots. The front body and the rear body of this vehicle are jointed by a hinge to make the vehicle large yaw angle and roll angle movement. The tyres contact with the ground well, which can provide sufficient traction and improve vehicle obstacle performance.This project is supported by the National Natural Science Foundation of China: “2 DOF articulated vehicle yawing control with actuator saturation and stability analysis based on interval method”(Serial number of the project: 51405187), and the National High Technology Research and Development Program 863: “Wheeled robot with 2 DOF articulated body for complex unstructured terrain”.In the obstacle negotiation experiments, it is found that the vehicle has large path offsets during surmounting the obstacle, which affects the maneuverability greatly. The steering wheel needs to be turned continuously to correct the direction, which can produce great lateral acceleration and lateral force. And when the vehicle is moving in complex terrains, the positional and posture of the front and the rear body are changing continuously, which makes the force of the vehicle very complex. These factors can produce great lateral acceleration and lateral force, reduce the stability, and even cause tipping accidents. In order to take full advantage of the 2 DOF vehicle with articulated bodies, make it work in more complex enviorment and overcome the limitations of manpower control, avoid the tipping accidents, it is necessary to design it as an unmanned vehicle. The obstacle negotiation stability anylysis and the yawing control are the key problems for unmanned technology.The obstacle negotiation performance is important for the 2 DOF vehicle with articulated bodies. In order to analyze the surmounting ability, an obstacle negotiation dynamic model is built as the basis of vehicle performance analysis. The 2 DOF vehicle with articulated bodies runs in complex terrain generally, therefore, a 7 DOF dynamic model is built in multi rigid body dynamic method to analyse the vehicle obstacle performance, the flexibility of the hydraulic steering mechanism and the tyre mechanical characteristics which affect the vehicle obstacle negotiation dynamic performance are considered also, which makes the 2 DOF vehicle with articulated bodies dynamic model more applicable and more accurately.According to the literature, more than 90% of the tipping accidents are caused by the motion and the operation in complex terrain, so it is significance to analyze the stability of 2 DOF vehicle with articulated bodies in the process of moving and operation, to avoid the serious security accidents and property loss. Based on the 7 DOF dynamic model, in which the lateral load transfer rate is considered as the decision foundation of stability, the obstacle negotiation stability is analyzed. First of all, when the vehicle is surmounting different obstacles, the numerical simulation method is used to analyze the influences of different slope angles and steering speed on the vehicle stability; secondly, experiments on the obstacle negotiation performance are carried out, when the vehicle is surmounting different obsatcles, the influences of the steering speed, the steering angle and the attitude angle on the vehicle stability are tested.; lastly, by comparing the vehicle obstacle negotiation experimental results with simulation analysis results, the 7 DOF dynamic model of 2 DOF vehicle with articulated bodies is verified to be accurate. By combining the dynamic model and the stability criterion, the vehicle obstacle negotiation could be analyzed and forecasted.When the 2 DOF vehicle with articulated bodies is excavating, the position of the vehicle mass center will change, which has great influence on the vehicle stability. Using the multi rigid body dynamics method, the vehicle dynamics model in operation has been built, the effects to the vehicle stability in different excavated material weight, different boom yaw angular velocity and different roll angle are reaserched by simulation and experiment.In order to analysis the obstacle negotiation yawing, firstly, the vehicle obstacle negotiation kinematics differential equations during obstacle negotiation are established with the multi rigid body kinematics method; secondly, according to the kinematic differential equations, the obstacle netotitation process is simulation analysed, the simulation results show that the motion direction is yawing in obstacle negoation course; lastly, the obstacle negotiation experiments are carried out, they are proved to be in good agreement with the simulation analysis results. By analyzing these differential equations, it is found that the torsional pendulum between front and the rear body is the main reason for deviation. In order to adapt the terrain, many articulated vehicles have the torsional pendulum between the front and the rear axle; therefore, it can be concluded that the 2 DOF articulated vehicle obstacle negotiation deviation analysis method and conclusion are suitable for oscillating axle vehicles.The remote control technology makes the vehicle possible to work in dangerous environment and precision motion path works. The motion path deviation control technology is a core technology for unmanned vehicle, therefore, the researches on it has important significance. The control input saturation problems are ubiquity in engineering applications, therefore, the control input saturation problem is considered in path following control. First of all, the kinematics model, dynamic model and the path deviation error dynamic model are built; secondly, the anti-saturation controller with the backstepping method is designed; lastly, by comparing the results of experiment and simulation, the anti-saturation control method is proved to inhibit the path deviation error effectively in circular motion and linear motion of the vehicle.