Development of an automatic airflow control system for precision sprayers based on tree canopy density

Authors: MAHMUD, MD SULTAN - Pennsylvania State University; ZAHID, AZLAN - Pennsylvania State University; HE, LONG - Pennsylvania State University; Zhu, Heping; CHOI, DAEUN - Pennsylvania State University; KRAWCZYK, GRZEGORZ - Pennsylvania State University; HEINEMANN, PAUL - Pennsylvania State University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2023
Publication Date: 4/28/2023
Citation: Mahmud, M., Zahid, A., He, L., Zhu, H., Choi, D., Krawczyk, G., Heinemann, P. 2023. Development of an automatic airflow control system for precision sprayers based on tree canopy density. Journal of the ASABE. 65(6): 1225-1240. https://doi.org/10.13031/ja.14972.
DOI: https://doi.org/10.13031/ja.14972

Interpretive Summary: current intelligent air-assisted sprayers can provide improved spray penetration and deposition uniformity with significant reductions in pesticide use, they are only able to adjust liquid flow rates as needed to match crop canopy architectures. To further improve their spray application efficiency, the air volume released from the sprayers should be also controlled to match the crop foliage density. In this research, an automatic control system was developed and tested to control spray air volume to simultaneously match the foliage density measurements using a laser sensor under apple orchard conditions. The air flow was regulated by manipulating air inlet diameters using an iris damper. Airflow penetrations to carry spray droplets into apple trees and spray deposition quality were investigated with different tree densities and five damper opening diameters. Models were established for foliage densities, airflow penetration and damper diameters. The airflow control system was able to perform the air volume regulation with slow electro-mechanical motions based on average tree canopy density for uniform spray coverage and reduced drift in real time. Thus, this system would have great benefits to potentially improve intelligent sprayers with precision variable rates of both liquid and air to further reduce pesticide waste in specialty crop production.

Technical Abstract: The airflow discharged from orchard airblast sprayers is a primary component for successfully carrying spray droplets to the target trees. Because of the variation in orchard tree canopies, control of the airflow to minimize off-target loss during spray application is essential. An automatic airflow control system for precision sprayers was developed to maximize spray droplet coverage on targets and minimize off-target loss while considering the tree canopy densities. The primary component of the system was an iris damper, which was designed as a retrofit attachment on the fan inlet of a threepoint airblast intelligent sprayer. A 3D light detection and ranging (LiDAR) sensor was installed at the top of the sprayer to acquire the tree canopy data. A motor was employed to control the damper opening with a micro-controller. To develop the models required for automatic airflow control, field experiments were conducted at three canopy density orchards with different cultivars (GoldRush, Gala, and Fuji). A total of 15 trees (five trees from each cultivar) were randomly selected, and five different damper openings (openings 1, 2, 3, 4, and 5) were tested for each tree. Opening 1 represented the same air inlet as a traditional precision airblast sprayer, while openings 2, 3, 4, and 5 were the sequentially reduced air inlets of the sprayer. A canopy density measurement algorithm was scripted to measure the canopy point density of individual trees. Three models were built to show relationships between (1) tree canopy point densities and airflows; (2) canopy densities and damper openings; and (3) damper opening and motor steps. The combination of the two models (2 & 3) was used to assess the amount of airflow required for a specific canopy density. Field validations for medium and high-density trees showed that the system achieved adequate spray penetration at the top, middle, bottom, back-left, and back-right positions of the tree sections and reduced off-target loss at the ground and edge of next row sections using openings 4 and 2, respectively. However, the mechanical motion of the damper required 3 s to move from minimum to maximum opening, so the average canopy density was recommended to control the airflow. The overall results suggested that the automatic airflow control system could reduce spray drift and off-target losses and improve spray application efficiency in orchards.