Development of a Variable-Rate Sprayer with Laser Scanning Sensor to Synchronize Spray Outputs to Tree Structures

Abstract

Efficient and effective precision spray equipment and strategies are in high demand to reduce pesticide use in tree crop production. An experimental variable-rate air-assisted sprayer implemented with a high-speed laser scanning sensor was developed to control the spray output of individual nozzles in real time. The sprayer consisted of a laser scanning sensor control system and an air and liquid delivery system. Each nozzle in the delivery system, coupled with a pulse width modulated (PWM) solenoid valve, achieved variable-rate delivery based on occurrence, height, and width of the target tree and its foliage density. Other components of the sensor control system included a unique algorithm for variable-rate control that instantaneously processed measurements of the canopy surfaces. To determine system delay time, a high-speed video camera was used to record the time period between sensor detection of the canopy and nozzle activation. Spray deposition uniformity inside canopies was verified by quantifying spray coverage inside four ornamental nursery trees of different sizes and canopy densities at 3.2 and 6.4 km h-1 travel speeds. Test results demonstrated that differences in spray coverage inside the canopies of these four trees in the spraying direction were not statistically significant, even though these trees had different structures, canopy volumes, and foliage densities. The canopy volume and foliage density measured with the algorithm developed for the laser sensor-controlled detection system exhibited little variation between the two travel speeds. Design criteria for the sensor-controlled system in the experimental sprayer were acceptable for variable-rate application, having great potential for spray volume and drift reduction, and thus reducing environmental impact.