| In the development of precision agriculture at home and abroad,automatic navigation of agricultural machinery is one of the key and basic technologies,and its in-depth study has important scientific research and application value.The auto-navigation technology of developed countries such as the United States is relatively mature,which is mainly manifested in the following aspects: stable and reliable products;good speed adaptability;diversified products with complete functions;and basically all foreign brand products in our market before 2015.Domestic agricultural machinery navigation research started late.In view of the situation that large-scale farmland in China urgently needs navigation products and foreign products are expensive,it is urgent to improve the overall performance of agricultural machinery automatic navigation system in China,and to conduct in-depth research on key technologies.At present,there are the following problems in the research of agricultural machinery automatic navigation in China: 1.The main research and development abroad is based on single antenna GNSS/INS integrated navigation products,whose core components are expensive in our market,especially high-precision inertial navigation sensors.(2)The application of integrated navigation core technology in agricultural machinery automatic navigation is still immature,especially the high precision positioning and orientation technology of single antenna GNSS/INS integrated navigation under static and different speeds.(3)Accurate steering control,including steering control system modeling,time-varying and control problems.(4)The adaptability of path tracking control algorithm,especially the adaptive problem of path tracking control in different road conditions,different speeds,different planning paths(straight lines and arbitrary curves)and different vehicle states.The application of system integration,agricultural machinery automatic navigation system should be integrated with agricultural machinery CAN bus intelligent control terminal,in order to promote the development of agricultural machinery navigation to the direction of more autonomous operation ability of unmanned operation.(1)In view of the high price of single antenna GNSS/INS integrated navigation core components and the immature application of domestic agricultural machinery navigation technology,this paper uses dual antenna GNSS for high-precision positioning and attitude determination.Firstly,a test platform for positioning and attitude determination accuracy of dual-antenna GNSS receivers is built.The dynamic and static positioning and attitude determination accuracy of representative dual-antenna GNSS board cards at home and abroad are tested.The test results show that the dynamic and static positioning and attitude determination accuracy of dual-antenna GNSS board cards at home and abroad can meet the requirements of navigation accuracy of agricultural machinery.The dual antenna GNSS positioning and attitude measurement equipment is installed on the agricultural machinery vehicle,and the coordinate information of the agricultural machinery navigation control point in the navigation plane coordinate system is obtained through the conversion of the Gauss projection and Euler angle coordinate transformation matrix.The simulation and comparative test results show that the scheme based on dual antenna GNSS can meet the positioning and attitude accuracy requirements of agricultural machinery navigation system in a more open environment.Based on dual-antenna GNSS positioning and attitude determination,the price of navigation system can be greatly reduced,but it is vulnerable to the failure of positioning information caused by differential unlocking.In this paper,a differential unlocking method based on dual-antenna GNSS and dead reckoning is studied,which can maintain the positioning accuracy within 23 S or about 5 cm after differential unlocking.(2)The steering control process is complex and the steering control is rough.In this paper,the working principle of the full hydraulic steering system is studied,and the electronically controlled hydraulic steering system is reformed.Based on the working principle and process of the electronically controlled hydraulic steering system,the parametric model of the electronically controlled hydraulic steering system is established.Because the parameters of each component are difficult to determine,based on the off-line test identification method,an accurate mathematical model of the steering system piecewise function is established in this paper.Based on the model of steering system,a fuzzy PID controller with dead-time compensation and saturation limit is designed to control steering and improve the steering control effect.In view of the fact that navigation is in line tracking state most of the time and steering angle is small,a variable universe fuzzy PID controller is designed,which further improves the control quality of small angle steering control.(3)Aiming at the adaptability of the path tracking control algorithm,this paper uses preview tracking model path tracking control method to improve the method of small-angle linear pole optimal placement based on kinematics model.There are some shortcomings of approximate conditions in the small-angle linearization algorithm of agricultural machinery kinematics model.This method avoids the approximate conditions by previewing and tracking auxiliary straight lines to guide the agricultural machinery to track the planning path quickly and steadily.In order to find the best forward-looking distance of preview tracking model method at different velocities,the parameters of the best forward-looking distance at different velocities are tuned by the method of multi-objective optimization based on particle swarm optimization,and the functional relationship between the velocity and the best forward-looking distance is regressed.The simulation results show that the improved forward-looking distance adaptive preview tracking model path tracking control method has good upper linearity performance,anti-jamming performance and speed adaptive performance for linear navigation path tracking control under medium speed(4m/s).(4)Aiming at the problem of system integration,based on the AGCS-I Agro-machinery automatic navigation system developed jointly by South China Agricultural University and Revo Heavy Industry Co.,Ltd.,the rear-loading of the Agro-machinery automatic navigation system for Revo Tx1104 tractor and GE80 grain combine harvester and the transformation of the CAN bus intelligent control terminal are carried out.The Agro-machinery automatic navigation system is used as the bus vehicle intelligent control terminal.On the basis of automatic navigation function of agricultural machinery,the integrated cooperative electronic control of two agricultural machinery CAN node intelligent terminal engine ECU(EECU),shift ECU(power shift TECU or CVT)and machinery is realized.Furthermore,the automatic driving,rotary tillage and harvesting operations are realized.On the basis of the single-machine automatic driving operation,the integration of the two-machine master-slave navigation cooperative operation system is carried out,and the dual-machine cooperative automatic driving operation is explored and realized.Based on the above research results,the whole machine was tested.Including on-line test of tractor automatic navigation system,straight track test of bumpy complex road surface,speed adaptive test,ground turning control accuracy test and master-slave navigation speed tracking accuracy test.The experimental results further verify the feasibility and validity of the research results in this paper. |
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