| In recent years,agricultural UAV,especially multi-rotor UAV,has made great progress in agricultural information acquisition,aerial pesticide spraying,sowing,fertilization,forest fire fighting and so on because of its high efficiency and flexibility.Spraying UAV with pesticide can effectively avoid the contaction of operators and pesticides,reduce the harm of pesticides to operators.However,due to the limitation of single dose and endurance of UAV,it is necessary to return to the fixed landing point to replace the liquid or battery,which greatly affects the operation efficiency.If the moving operation platform loaded with UAV,medicine tank and battery can move within a certain range according to the operation position of UAV,and the UAV will automatically land on the platform to replenish medicine,the flight distance of replenishing medicine and replacing battery can be shortened,and the operation efficiency can be improved.Based on this idea,the research takes the Quadrotor UAV as the object,combine Beidou System with Machine vision system to study autonomous precision moving platform landing technology for agricultural UAV,so as to realize autonomous precision landing on the moving drug storage vehicle for agricultural UAV,and provide effective technical support for the agricultural UAV to realize automatic,intelligent and efficient operation.The main work and conclusions are as follows:(1)The landing scheme of UAV autonomous precision platform was proposed.Through analysis,the landing process of UAV autonomous precision moving platform was divided into three stages:higher to platform,closer to platform and about to land.Different control strategies were adopted to improve the accuracy of autonomous landing.When the UAV was high above the ground,the flight controller received the position data of the platform and UAV respectively,calculated the relative position between UAV and platform to adjust the flight attitude and made it close to the moving platform.When the UAV was close to the platform,visual positioning was used to detect the relative position information between the landing mark of the moving platform and UAV,so as to adjust the flight attitude of UAV close to the moving platform;When landing,the distance between UAV and platform was measured in real time by ultrasonic module.When the ranging value was less than 16cm,the electromagnet loop on the landing leg of UAV was triggered to make electromagnet live and platform iron plate absorb,so as to realize stable landing of UAV.(2)The positioning method of moving platform based on Beidou satellite were designed.BN-880 and BD-357 modules were selected as the positioning modules of Beidou satellite of UAV and moving platform respectively.Two data receiving,wireless data transmission and flight control algorithms were designed for Beidou satellite positioning module.When the UAV was higher from the moving platform,the UAV flight controller detected the position of the platform and made the UAV approach the ground mobile platform according to the relative position.At the same time,the dynamic mean method was used to update the position data in real time to improve the positioning accuracy.The results of data analysis showed that the positioning accuracy of the relative positioning method was within 1.5 m,which meets the requirements of the system.(3)This paper implemented a method of moving target accurate detection and positioning based on machine vision.In order to improve the landing accuracy of UAV when it was close to the mobile platform,a kind of UAV landing sign with nested features was studied and designed.The actual distance model between the landing sign and UAV was constructed,and the sign was identified and located by using the visual processing module of openmv.The results showed that in the X,Y and Z directions,the determination coefficients R~2 between the predicted value and the actual value of the distance model were0.991,0.989,0.939 and 0.996,0.998,0.973 respectively,and the recognition rate of the landing mark algorithm was 97.5%,which had high measurement accuracy.(4)A kind of adsorption fixing device and damping structure for UAV anti drop landing were designed.The mobile platform was made of magnetic material,and the spring was installed below it to play the role of shock absorption.When the UAV lands,it triggered the relay through the distance measurement value to make the electromagnet electrified,so as to realize the reliable,safe and stable landing of the UAV to the mobile platform,and avoid the UAV from sliding from the platform.(5)The hardware construction and software design of UAV landing system were completed.Using Ubuntu to build UAV flight control development environment,the main program and data communication program of UAV autonomous precision landing process were designed.In the open environment,the system was tested by fixed-point landing and mobile landing.The test results showed that the average landing error of UAV system was6.78 cm when it landed to the mobile apron at a fixed point.When the apron moved at 3km/h,the average mobile landing error of UAV system was 13.29 cm. |
