| Automatic driving system of agricultural machinery is an important equipment in modern agriculture.It plays a more and more important role in increasing production and income of agriculture.The research on automatic driving of agricultural machinery mainly focuses on agricultural machinery intelligent navigation of agricultural kinematics model,navigation path tracking control and new algorithm of navigation and positioning.However,there are few researches on agricultural cruise control and less practical applications,more research is done on the cruise control systems of a car,and many achievements have been made in the dynamics system model and speed control algorithm.But the light load operation for large farm tractors,multifunctional harvester with cruise control system,it can greatly reduce the labor intensity of the driver,reducing harmful gas emissions,save fuel,improve production efficiency.Therefore,it is necessary to carry out in-depth research on the cruise control technology of agricultural machinery.Agricultural machinery cruise control system as an important part of automatic driving system of agricultural machinery,the system’s speed control effect on agricultural machinery navigation control and variable job control has a great impact.In this paper,practical application as the guide,with reference to research methods of car and truck automatic driving,designed agricultural speed cruise control system,and the hardware and software were implementation based on the LOVOL TA800 tractor.The main research work of this paper is as follows:(1)It is necessary to establish the longitudinal dynamic model of the tractor for the cruise control system to design a fixed speed control algorithm according to the characteristics of the model and the external disturbance characteristics.Aiming at the complexity of the longitudinal power transmission system of the tractor,this paper uses the modular mechanism modeling and the experimental data modeling to establish the longitudinal dynamic model of the tractor.Due to the nonlinearity of the longitudinal dynamics system,the inverse model method is used to linearize the model,which is convenient for the design of control structure and control algorithm of the standard cruise control system.The longitudinal dynamics model is simulated on Simulink,and the model is verified by real vehicle under driving condition.Comparing the simulation data with the experimental data,the results show that the model can accurately reflect the longitudinal dynamics characteristics of tractor,and can meet the requirements for the design of cruise control system.(2)The speed control system is designed according to the change of parameters under the working conditions of the tractor and the interference from the outside.The hierarchical control structure of the vehicle is introduced.The upper controller outputs the desired acceleration according to the set value of the traveling speed of the tractor,and the lower controller tracks the desired acceleration through the action of the actuator.Through the precise control of the tractor longitudinal acceleration to achieve system functions,this paper focuses on the design of the lower controller.The robustness of the control system becomes the focus of the design of the controller because of the nonlinearity of the longitudinal dynamics system,the gradient of the road,the change of the vehicle mass due to the tractor-mounted agricultural machinery,and the external disturbance factors such as wind resistance.Based on the dynamic cruise control system model of tractor,the upper layer PID controller is designed,and the transfer function of the lower layer system is identified by the frequency response experiment and the least square method.According to the transfer function and nonlinear characteristics of longitudinal acceleration response,a sliding mode variable structure controller is designed.Compared with the traditional PID control,the simulation results show that the controller effectively improves the robustness of the system to nonlinear characteristics and external disturbances.(3)Based on the above research results,the hardware and software of the cruise control system were designed based on the LOVOL TA800 tractor.In the hardware part,the anti-system power-off of the actuator and controller circuit of the system are designed,and the sensor is selected and installed;In the software part,the field computer software,sensor node software and controller software are developed based on the embedded operating system of μC/OS Ⅱ. |
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