| The tractor automatic navigation technology is one of the hottest research fields of precision agriculture as well as a major means for realizing intelligent operating of agricultural vehicle in future. This paper presents a thorough research on key GPS automatic navigation technology of agricultural vehicle considering that working conditions and field conditions for the tractor are complex and that there is a high requirement on the precision of the driving path of the tractor. Major contents of the research are as follows:(1) The hydraulic control valve was selected by testing. A hydraulic control valve test platform specific to navigation was designed. The test platform can gather information about the flow and pressure of each measured hydraulic valve in a real-time manner, and can transmit the information to the PC software for analysis and processing by RS485bus. A method of evaluating the direction control valve based on both the dead zone and speed characteristics was put forward. Finally, the proportional valve KDG4V-3S-33C22A was selected as the direction control valve after evaluating the performance of the electromagnetic directional valve, electro-hydraulic servo valve and proportional direction valve.(2) A navigation valve block was developed. Using a variety of cartridge valves, a navigation valve block was designed with proportional direction valve as the core device. The valve group decides the driving status (manual or automatic) through MBS1250pressure sensor and adopts the Eaton DPS2-10logical cartridge valve to realize manual or automatic switching of oil circuits, using two SPC2-10check valves to prevent steering errors caused by leakage of the proportional valve. Finally, the navigation valve block was used in electro-hydraulic transformation of Foton Lovol M1004tractor, realizing the control of electrical signal in tractor steering.(3) A hardware platform for the automatic navigation system was built. A navigation controller based on PIC18F2580chip, the Trimble5700RTK-GPS positioning system, the AHRS-3000attitude sensor and MEMS gyroscope CRS03-02constitute the hardware platform of the autopilot system of the tractor. The hardware platform is the basis for realizing automatic navigation of the tractor. Compared with traditional means of encoder measuring, this method of using MEMS gyroscope to measure the turn angle of the front wheel helps reduce the use of connectors, decrease the difficulty in transforming the tractor and improve the working life of the system.(4) The PC software of tractor automatic navigation system is developed with the C#programming language at the environment of Microsoft Visual Studio2010, based on Windows XP operating system. The software has five functional modules of data communications, data collection and processing, path dependency, control decision and interface display, realizing the core functions of sensor data collection, information fusion, path planning, path tracking control, and system debugging.(5) The navigation control algorithm was studied. The fuzzy control, adaptive fuzzy neural network and pure pursuit model tracking algorithm were analyzed and compared; the navigation decision-making control system based on the pure pursuit model tracking algorithm was designed; the kinematics model of the tractor was established. The pure tracking model has been simulated by Matlab/Simulink software, and the simulation results show that the best visibility distance is2.06m and the system has good stability and sensitivity.(6) The experimental research on the automatic navigation system of the tractor was conducted. Based on the automatic navigation platform developed above, experiments on the control of the tractor walking straight at the flat road and in the fields have been done respectively. The experimental results are as follows:When the tractor walks on the flat road automatically at a speed of1m/s, the maximum lateral deviation is5.3cm, the average error is1.5cm, and the root-mean-square error is2.5cm. When the tractor walks in the fields at the same speed, the maximum lateral deviation is8cm, the average error is0.7cm, and the root-mean-square error is3.6cm. The results proved that the automatic navigation system has the capability of tracking the straight path of the tractor in a real-time and stable manner and meets the requirements of precision agriculture. |
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