| A large amount of labor is being used in protected agriculture production,and their labor intensity is high.The temperature and humidity of working environment are very high.Mobile agricultural robots with autonomous operations needed to develop to make up for labor shortages and decrease labor cost,and has bigger market demand and the application prospect.Wheeled AGV system used in protected agriculture may be used as a kind of mobile carrying platform for fruit picking,carrying,spraying and information detection.It is a key technology of precision agriculture,and provides a kind of effective solution of reducing labor force and decreasing labor cost.Application-oriented need of target spraying,precision picking and carrying for fruit and vegetable in protected agriculture,practical wheeled AGV needs to be developed to use as a mobile platform,and realize obstacle avoidance navigation of AGV,which is a development trend of the production equipment of fruit and vegetable.It has important scientific research significance and application value to the production of fruit and vegetable.On the basis of summarizing the research status of AGV driving system and navigation technology at home and abroad,the paper integrated designs a wheeled AGV driving system used in protected agriculture under the funding of the fruit and vegetable picking robot project.Its main research contents are as follows:1.Application-oriented demand for greenhouse road or grassland,a kind of double crank steering system with changing length link was designed to eliminate wheel sideslip of the front wheel guided AGV,based on the steering principle of Ackermann.The correctness of the steering mechanism design was validated by using ADAMS simulation,and ANSYS software was applied to analyze the bearing capacity of connective structure of vertical steering axis of front wheel.The wheeled AGV system with pure rolling steering of front wheel and differential drive of rear-wheel was designed integrated,including total mechanical structure of AGV,sensor detection module,control module and communication module.2.By deducing steering dynamics models,closed loop control models of rotation angle of left and right front wheel were established in consideration of steering resisting moment.PID synchronous control algorithm of steering angle of left and right front wheel was proposed.The dynamic responses of steering control models were simulated by MATLAB,and relative control parameters were obtained.3.With Panasonic PLC as the core,a measurement and control system of AGV steering was built up,which consists of AC servo motor of left front wheel,AC servo motor of push rod,actuator and encoder.Synchronous closed loop control flow of front wheel steering system was designed.The AGV steering and driving control program was developed based on PLC,and realized pure rolling steering and drive of the AGV.4.Pivot steering tests on grassland roadway and turning travel test of AGV along S-type trajectory under hard roadway were carried out respectively.The results shown that the errors between expected turning angle and actual turning angle of left and right front wheel of steering system of front wheel guide AGV were no more than 0.1 degree,and AGV steering system can approximatively satisfy the movement condition of pure rolling and non-sideslip,which validates the correctness and effectiveness of pure rolling steering system design of wheeled AGV and steering control.The system can eliminate effectively the sideslip of front wheel guiding AGV,and may provide a reference for steering system design of front wheel guiding vehicle like wheeled tractor and application of wheeled AGV system in protected agriculture.5.Aiming at the problem of obstacles threat for wheeled AGV tracking along a linear ridge road,according to two kinds of traveling modes which are global presupposition path tracking and local trajectory anti-collision obstacle avoidance,the AGV lateral position deviation and heading deviation angle are used as inputs of fuzzy controller to obtain expected guidance angle of AGV front wheel.Obstacle-free navigation of the AGV along the preset straight ridge road was implemented.Based on the rolling optimization principle,the obstacle avoidance navigation strategies of adjusting heading deviation angle ?θ and vehicle speed ?v were proposed,and the AGV navigation algorithm of bypassing static obstacles,avoiding dynamic obstacles by deceleration or parking of AGV was designed.Based on the LabVIEW platform,the measurement and control programs of obstacle avoidance navigation of the AGV were developed.By real-time data acquisition of ultrasonic sensor,azimuth and attitude sensor and encoder,the model resolving of obstacle avoidance navigation was executed.The AGV obstacle avoidance drive was realized.6.Simulation experiments of obstacle avoidance navigation of wheeled AGV tracking along a linear ridge road were carried out.The results shown that the obstacle-free navigation algorithm can guide the AGV to track with the mode of deviation rectification along preset straight-line path of ridge road,and the anti-collision obstacle avoidance navigation algorithm can guide the AGV to avoid collision with obstacles on the ridge road,which verify the effectiveness of the navigation algorithms.It can provide a reference for anti-collision warning and obstacle avoidance technology of front-wheel guided vehicle like unmanned wheeled tractor to track along a straight-line ridge road.Finally,this paper summarizes the main innovations and research results of this paper,points out the difficult problems and directions that need to be further studied and solved for AGV for facility agriculture,and expects to be improved gradually in the future. |
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