Design and Testing of a Dual Air-Guiding Variable-Rate Spraying System Based on Vision Perception and Control

A dual air-guiding variable-rate spraying system based on vision perception and control was developed to address two limitations of conventional air-assisted sprayers in high-spindle, high-density apple orchards: insufficient airflow to the upper canopy, which results in poor spray retention and inadequate pest and disease control, and continuous spraying through canopy-free gaps above the trees, which wastes spray liquid. The structural parameters of the air-guiding system were optimized using computational fluid dynamics (CFD), single-factor tests, and a central composite design, while vision-based recognition was used to automatically shut off the uppermost nozzle in canopy-free areas. The results showed that the coefficient of determination between simulated and measured air velocities was 0.982, and the mean absolute percentage error was 3.15%. The optimized deflector split ratio was 0.4; the air-outlet length, height, and width were 115, 110, and 100 mm, respectively; and the diameter of the top air outlet was 100 mm. Field tests showed that the droplet deposition density in the inner canopy was 79 droplets/cm2. The deposition densities in the upper, middle, and lower canopies were 95, 94, and 92 droplets/cm2, respectively, with a coefficient of variation of 0.016, demonstrating good canopy penetration and vertical deposition uniformity. When the vision-based variable-rate spraying system was enabled, the arithmetic mean reduction in off-target ground deposition across the three monitoring rows was 43.7%. These results provide a technical reference for precise and uniform pesticide application and for reducing off-target spraying in high-spindle, high-density apple orchards.