Investigation of an experimental laser sensor-guided spray control system for greenhouse variable-rate applications

Authors: YAN, TINGTING - Nanjing Agricultural University; Zhu, Heping; SUN, LI - Jiangsu University; WANG, XIAOCHAN - Nanjing Agricultural University; LING, PETER - The Ohio State University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2019
Publication Date: 10/5/2019
Citation: Yan, T., Zhu, H., Sun, L., Wang, X., Ling, P. 2019. Investigation of an experimental laser sensor-guided spray control system for greenhouse variable-rate applications. Transactions of the ASABE. 62(4):899-911. https://doi.org/10.13031/trans.13366.
DOI: https://doi.org/10.13031/trans.13366

Interpretive Summary: The global greenhouse planting area is growing consistently every year and pesticide applications have ensured healthy and marketable crops. However, precision variable-rate spraying technology is lacking in this controlled environment plant production. During the short growing period, it is very common that small young plants are over sprayed, large plants are under sprayed, and empty areas are unnecessarily sprayed, causing significant chemical waste and environment contamination. In this research, an laser-guided variable-rate spray system was developed and tested in a laboratory before its integration with watering boom systems commonly used in greenhouses. Parameters in the spray system were configured according to the physical positions of the laser sensor and nozzles, and the sensor travel speed. The system accuracies were validated for synchronization of nozzle activation and laser sensor detection of objects and for desired spray volume discharged to the objects. Based on the laboratory evaluations, an experimental automatic laser-guided variable-rate spray boom system was developed and attached to a mobile watering boom in a commercial greenhouse. The system will be tested for its application accuracy, efficiency and efficacy under commercial greenhouse conditions and will be used to prevent greenhouse production from excessive chemical waste to the environment and protect workers from exposure to the harmful chemicals.

Technical Abstract: Precision variable-rate spraying technology is needed for controlled environment plant production in greenhouse. An experimental spray system for greenhouse applications was developed for real-time control of individual nozzle outputs. The system mainly consisted of a high-speed laser scanning sensor, 12 individual variable-rate nozzles, an embedded computer, a spray control unit, and a 3.6 m long mobile spray boom. Each nozzle was coupled with a pulse width modulated solenoid valve to discharge at variable rates based on object presence and plant canopy structures. Laboratory tests were conducted to evaluate the spray control system accuracy with regard to spray delay time, nozzle activation, and spray volume using four objects of different regular geometrical shapes and surface textures, and two artificial plants of different canopy structures. Other experimental variables included three laser detection heights from 0.5 to1.0 m and five constant travel speeds from 1.6 to 4.8 km h-1. A high-speed video camera was used to determine delay time and nozzle activation in discharging sprays on target objects after the laser sensor had detected the objects. The laser detection height and travel speed were found to have slight influence on the timing of the nozzle activation and operation. The nozzles started spraying in a range between 33 and 83 mm before reaching the target objects, and stopped spraying between 13 and 84 mm after passing the objects, ensuring the objects were fully covered by the spray. Spray volume corresponded to the object sizes well, and the spray control system performed with higher accuracy at lower boom travel speeds. Differences between the calculated spray volume based on the sensor detection and the actual spray volume ranged from 1.9 to 2.7 mL per target among all of the tested objects. The variable-rate spray control system reduced spray volume by 29.3% to 51.4% for all the objects compared with the conventional constant-rate spray mode. At the same time, the nozzles could be activated precisely by the object presence. Consequently, this experimental laser-guided system was implemented into a water-boom system in a commercial greenhouse for future investigations in its accuracy for discharging variable-rate sprays to save pesticides, water, and nutrients.