The Key Technology Research Of Path Following Control On Tractor

In agricultural production in our country,has always been based on manual operation,low operating efficiency,high cost,labor demand and other problems have long troubled people.With the continuous progress of the society,when people have higher requirements for operation quality and efficiency,agricultural mechanization technology has brought greatly changes in agricultural production mode.As one of the main agricultural tools,tractor can realize the functions of sowing,tillage,ridding,harvesting,transportation,fertilization and pesticide spraying,etc.The tractor equipped with automatic navigation system can not only reduce labor intensity,but also improve operating efficiency,so tractor automatic navigation system is particularly important.The key technologies of tractor automatic navigation system mainly include positioning technology,sensor technology,path planning,navigation control technology,automatic steering technology and communication technology and so on.The main content of this paper is the path tracking control technology in the tractor automatic navigation system,which mainly includes the navigation system and the automatic steering system.The main research work as follows:1.The test platform of tractor automatic navigation system is set,including Shuang Li SL704 tractor,Bei Dou dual-antenna positioning system and signal receiving device.According to the need of autonomous steering system,the advantages of automatic steering system based on power motor are analyzed,and the steering motor,torque sensor and angle sensor are selected,the tractor automatic steering system hardware of based on motor is modified.Finally,the whole structure of the path tracking control system is determined.The slide-mode control method is adopted on navigation control system,and the PID control method based on the modified Smith prediction structure is used on automatic steering system.2.In order to obtain the desired front wheel angle of the tractor,a two-degreefreedom model is established considering the actual working environment of the tractor.A navigation controller is designed based on the advantages of sliding mode,with lateral deviation error as the input of the controller,the front wheel angle as the output of the controller.To solve the inherent shake in sliding mode control and improve the service life of steering motor,a navigation controller with adaptive approach law is designed based on sliding mode control theory and Matlab/Simulink simulation software is used for the experiment.3.In order to enable the tractor to quickly track the desired front wheel angle,the working principle based on motor is analyzed and the mathematic model is established.The designed hardware system includes MCU circuit,torque detection circuit,relay control circuit,drive circuit,current detection circuit,communication circuit,angle detection circuit,and the PCB is designed.The automatic steering controller based on the improved Smith prediction structure is designed,including steering tracking controller and anti-interference controller with the internal model PID form.In order to verify the performance of the designed controller,the Matlab/Simulink simulation platform is used to build the model of controller.Sinusoidal signal and square wave signal are used as the input of the controller respectively to analyze the tracking,anti-interference and robustness of the controller.As for the simulation results,it can be seen that the designed automatic steering controller can make the tractor to track the desired steering angle of the front wheel,and the designed automatic steering controller can meet the accuracy requirements of the tractor’s automatic navigation for steering control.As two key techniques in navigation system,navigation control system and automatic steering system has the vital role for path tracking of tractor working process.A great number of simulation tests are carried out on the two systems in this article.The simulation results suggest that the navigation controller based on the adaptive approach law and the steering controller based on PID form can ensure the tractor to run in accordance with the desired trajectory,with the maximum lateral deviation not more than 0.005 m and the maximum heading angle not more than 0.3°.