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

The airflow of a sprayer is a primary component for successfully carrying spray droplets to the target trees. With the variation in orchard tree canopies, it is essential to control the airflow during spray operation. The study aimed to develop an automatic airflow control system for precision sprayers, considering the tree canopy densities for successful spray droplet depositions. The system was developed by retrofitting an iris damper at a three-point hitch airblast intelligent sprayer, which was installed at the sprayer's fans air inlet. A light detection and ranging (LiDAR) sensor was installed at the top of the sprayer. The LiDAR was used to acquire the tree canopy data, and a motor was employed to control the damper's opening with a micro-controller. To investigate the usefulness of the airflow control, a series of field tests was conducted at two different canopy density orchards with different varieties (GoldRush and Fuji). A total of eight trees (four trees from each variety) were randomly selected, and three different damper openings (full opening, intermediate opening, and full closing) were tested for each tree. Water sensitive papers (WSPs) were placed at five different locations of the tree (top, middle, bottom, back-left, and back-right). The airflows were measured at the back-side of the trees, and the spray performance was evaluated based on spray droplet depositions at the WSPs. A canopy density measurement algorithm scripted in MATLAB® was used to measure the canopy point density of individual trees. Two relationships (models) were built between 1) tree canopy points densities and airflows 2) canopy densities and damper openings. The combination of the two models was used to assess the amount of airflow required for a specific canopy density. Results of this study reported the system achieved good mean spray depositions of 37.4%, 36.09%, 51.01%, 23.0%, and 23.72% at the top, middle, bottom, back-left, and back-right positions, respectively for high-density trees using full damper opening. The intermediate opening provided some good insights for low-density trees, however, extensive investigations are needed to make the recommendation.