Development of multi-orientation automatic spraying device for citrus orchards in hilly and mountainous areas

Abstract: In view of the poor adaptability of the existing automatic spraying device to citrus fruit trees with different crown size in hilly and mountainous areas, a bidirectional multi-mode automatic spraying device was development in this paper. The device was mainly composed of mechanical framework, high-pressure atomizing mechanism, air supply mechanism and automatic control system (which including power supply module, communication module, automatic target module, vehicle speed measurement module, motor drive module and solenoid valve). Changing the angle of spraying rod through the mode conversion mechanism, the vertical spraying mode, the 45° tilt spraying mode and the ground spraying mode were realized, which satisfied the adaptability requirements of the spraying device for citrus fruit trees of different sizes, and effectively improved the utilization of pesticides. Firstly, the canopy height of the fruit trees and the distance from the high pressure atomizing nozzle assembly to the crown surface were detected by the automatic target module composing of an ultrasonic sensor and a laser diode array, The ultrasonic sensor was responsible for detecting the top and bottom layers of the canopy, and guided the position adjustment of spraying rod and the on-off of solenoid value, so that the spraying rod could spray against the canopy; the laser diode array was responsible for detecting the distance between the spraying rod and the fruit trees, and guided the boom to adjust to the setting position. Secondly, the speed measuring module was used to detect the moving speed of the crawler-type walking tractors in real time. Thirdly, the collected datas were processed by the controller. The effects of the detection delay on the effect of the spraying were reduced by the cooperation of each module. The laboratory test results showed that the spray range and spray width of the device in 3 spray modes were in line with the quality requirements of plant protection machinery. The spray amount for one operation was 72-190 L/hm2, which met the requirements of the low dose spray. The ultrasonic sensor was arranged at 0.8m in front of the spraying rod, when the working speed of the crawler-type tractor was not more than 8 km/h, it effectively reduced the target error caused by the delay of signal detection and processing, and the target precision was 99.7%, which was in line with the design requirements. Orthogonal experimental design method was used in field experiments, the effects of vehicle speed, air supply intensity and sprinkler-to-canopy distance on spraying efficiency were investigated by establishing L9(34) orthogonal experimental design table. The results of spraying in vertical spraying mode and 45° tilt spraying mode showed that the average droplet coverage on the canopy surface was 82.5% and 78.7%, respectively, and the droplet deposition density was 109 and 106 droplets/cm2, respectively; the average droplet coverage in the canopy was 16.1% and 30.6%, respectively, and the droplet deposition density was 35 and 64 droplets/cm2, respectively. The spraying effects met the requirements of national standards.