| Developing unmanned agricultural equipment is an urgent need to solve the problem of agricultural employment and an inevitable trend of high-quality agricultural development in China.As the most widely used machine in agricultural production,the realization of tractor automatic driving is very important to the development of precision agriculture.Taking Dongfanghong LX954-C tractor as the research platform,this paper studied the path tracking algorithms and hardware.The main research contents are as follows:(1)Research on tractor path tracking algorithm.The two degree of freedom kinematic error model had been established.After summarized the shortcomings of the previous algorithm which depends on the accuracy of the model and is sensitive to nonlinear time-varying disturbances,the sliding mode controller was designed based on the idea of terminal sliding mode control for saturated and underactuated systems.The finite time disturbance observer was used to estimate the matched disturbance and unmatched disturbance in finite time.The chattering and antisaturation treatments were carried out.Then the stability of the control algorithm was proved.The simulation results showed that the algorithm can still make the lateral deviation and heading deviation converge rapidly in the presence of disturbances.(2)Research on tractor steering algorithm.The model identification experiment of the electric steering wheel steering system was carried out.The nonlinear PID algorithm was used to control the steering wheel speed.The parameters were optimized by the differential evolution algorithm.The square wave angle signal and sine wave angle signal are tracked by MATLAB simulation.The steering algorithm experiment was carried out in the field,and the effect is good.(3)Based on the need of automatic driving control,the tractor’s hardware is designed and refitted.Retrofitted the steering system with electric steering wheel and angle sensor.Refitted the reversing and throttle circuit by analyzing the original vehicle circuit.Installed the electric push rod on the hydraulic lifting,clutch and other actuators.Installed the navigation and positioning system and remote control system.Formulated the data transmission protocol.Designed and drawed the level signal PCB conditioning board.Compiled and debuged the bottom driver.The experiment proves that the hardware system can realize reversing,steering,throttle adjustment,hydraulic lifting and other actions,and the signal communication transmission can also meet the requirements of automatic tractor driving path tracking.(4)In order to verify the feasibility and superiority of the algorithm,the experimental verification of path tracking was carried out in the field with a large amount of ponding.The path tracking effects of different speeds and different algorithms are compared.The maximum lateral deviation is 0.09 m,and most of the data were within ± 0.06 m.The mean error was-0.0019 m,and the root mean square error was 0.0183 m.The accuracy and robustness of the path tracking algorithm meet the requirements. |
