This study developed and experimentally evaluated an automatic boom-height control system for boom sprayers for large-scale field crop farming by integrating a compact position-sensitive detector (PSD)-based boom-height detection device with a hydraulic control mechanism. The detection device, equipped with three PSDs arranged at a 6° outward tilt in a three-dimensional configuration, suppressed optical interference and contributed to system miniaturization. A two-step signal processing algorithm combining minimum-value selection and median filtering enabled stable measurement of crop canopy height, with detection errors within ±5 cm for potato, soybean, and sugar beet. Larger errors (+7.4 cm) were observed for wheat, indicating the need for crop-specific correction. Step response experiments of the hydraulic control system were conducted using a container 65 cm high as a reference object. The results showed rise and fall times of 0.95 and 2.41 s, respectively, demonstrating stable operation without overshoot. These findings highlight both the effectiveness of PSD-based sensing for boom-height detection and the necessity of implementing more sophisticated control strategies to achieve accurate regulation in long, flexible agricultural booms.

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