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To ensure boom sprayer safety and spraying efficiency, the sprayer boom height must be adjusted during pesticide application. The field variation characteristics of the sprayer boom height are the basis of the boom balance adjustment. A boom height detection system based on ultrasonic sensors was designed. Field tests were performed in 2.0 ha of vacant fields and 13.44 ha of wheat stubble fields. A signal processing method based on the K-means clustering algorithm was used to preprocess the ultrasonic sensor data. The results showed that the K-means clustering algorithm could effectively improve the detection accuracy of an ultrasonic sensor. The boom height variation was greatest at the sides of the boom, and the primary frequencies of the boom height variation were concentrated within a low-frequency band from 0 Hz to 1 Hz. The U-turn operation was more likely to cause the boom to contact the crop canopy or the ground than row operation. As the spraying speed increased, the maximum boom height variation and maximum roll angle increased; these primary components decreased in frequency, and the amplitude clearly increased. The maximum boom height variation exceeded 50 cm, and the maximum roll angle exceeded 3°, which not only aggravated the droplet drift but also caused damage to the boom and nozzles due to contact with the ground or the crop canopy. These findings can provide a theoretical basis for use in the development of an automatic boom height adjustment system.

Orchard pesticide off-target deposition and drift cause substantial soil and water pollution, and other environmental pollution. Orchard target-oriented spraying technologies have been used to reduce the deposition and drift caused by off-target spraying and control environmental pollution to within an acceptable range. Two target-oriented spraying systems based on photoelectric sensors or ultrasonic sensors were developed. Three spraying treatments of young cherry trees and adult apple trees were conducted using a commercial sprayer with a photoelectric-based target-oriented spraying system, an ultrasonic-based target-oriented spraying system or no target-oriented spraying system. A rhodamine tracer was used instead of pesticide. Filter papers were fixed in the trees and on the ground. The tracer on the filter papers was washed off to calculate the deposition distribution in the trees and on the ground. The deposition data were used to evaluate the systems and pesticide off-target deposition achieved with orchard target-oriented sprayers. The results showed that the two target-oriented spraying systems greatly reduced the ground deposition compared to that caused by off-target spraying. Compared with that from off-target spraying, the ground deposition from photoelectric-based (trunk-based) and ultrasonic-based (canopy-based) target-oriented spraying decreased by 50.63% and 38.74%, respectively, for the young fruit trees and by 21.66% and 29.87%, respectively, for the adult fruit trees. The trunk-based target-oriented detection method can be considered more suitable for young trees, whereas the canopy-based target-oriented detection method can be considered more suitable for adult trees. The maximum ground deposition occurred 1.5 m from the tree trunk at the back of the tree canopy and was caused by the high airflow at the air outlet of the sprayer. A suitable air speed and air volume at the air outlet of the sprayer can reduce pesticide deposition on the ground.

Sprayer boom height (Hb) variations affect the deposition and distribution of droplets. An Hb control system is used to adjust Hb to maintain an optimum distance between the boom and the crop canopy, and an Hb detection sensor is a key component of the Hb control system. This study presents a new, low-cost light detection and ranging (LiDAR) sensor for Hb detection developed based on the principle of single-point ranging. To examine the detection performance of the LiDAR sensor, a step height detection experiment, a field ground detection experiment, and a wheat stubble (WS) height detection experiment as well as a comparison with an ultrasonic sensor were performed. The results showed that the LiDAR sensor could be used to detect Hb. When used to detect the WS height (HWS), the LiDAR sensor primarily detected the WS roots and the inside of the WS canopy. HWS and movement speed of the LiDAR sensor (VLiDAR) has a greater impact on the detection performance of the LiDAR sensor for the WS canopy than that for the WS roots. The detection error of the LiDAR sensor for the WS roots is less than 5.00%, and the detection error of the LiDAR sensor for the WS canopy is greater than 8.00%. The detection value from the LiDAR sensor to the WS root multiplied by 1.05 can be used as a reference basis for adjusting Hb, and after the WS canopy height is added to the basis, the value can be used as an index for adjusting Hb in WS field spraying. The results of this study will promote research on the boom height detection method and autonomous Hb control system.

Pesticide application rate and airflow supply rate are the two manipulated outputs of an orchard sprayer control system. The distribution of pesticide deposits inside and outside the canopy of fruit trees depends largely on the airflow supply rate supply. The pesticide application rate and airflow supply rate should be simultaneously controlled precisely to realize the orchard precision spraying. Based on the axial flow fan, this paper designs an orchard airflow adjustment test bench that can independently control the fan speed, the air inlet area and the angle of deflector in the bellows. The fan speed is adjusted by DC motor. The air inlet adopts a louver structure to change the air inlet area by adjusting the inclination angle of the louvers. The air outlet adopts a tower structure, the deflectors at different nozzle positions of the air outlet are controlled by 22 steering gears to independently adjust the angle of the deflector. The independent adjustment tests of fan speed, air inlet area and angle of deflectors in the air outlet was carried out based on the test bench. The results showed that the air speed and air volume at different positions of the fruit tree canopy can be regulated by adjusting the fan speed and the inclination angle of the deflector or the air inlet area and the inclination angle of the deflector. This research provides a new method for the airflow online on-demand adjustment based on changes in the volume and density of the fruit tree canopy.