Research on spray delay control of a variable-rate orchard sprayer based on a laser-scanning system

Abstract. Spray delay control is a key technology for variable-rate orchard sprayer to realize precision spray. A variable-rate trailed sprayer, which integrated with a laser-scanning system and a variable-rate spray control system, was developed to verify the accuracy of the spray delay control. The laser-scanning system, which mainly included a 270° wide-range laser-scanning sensor, a speed measuring device mounted on the sprayer wheel, a microcontroller and a variable-rate control program run on an onboard computer, was applied to detect bilateral trees to obtain canopy gridding volumes and create spray data in real time. The variable-rate spray control system which mainly included flow rate control units and solenoid valves communicated with the laser-scanning system via CAN bus. Each nozzle in the variable-rate spray control system, coupled with a solenoid valve, could achieve variable-rate spray according to the canopy gridding volumes and the sprayer travel speed. In order to test the performance of the spray delay control method, a toward-target spray experiment was conducted to record the distance between the laser sensor detection position and the nozzle activation position by using a video camera under different travel speeds and canopy grid sizes. The results showed that each of the detection positions and the corresponding nozzles activation positions at different speeds were close, with the distance error range of 0 to 0.03 m, 0.01 to 0.07 m and 0.08 to 0.14 m at gird width of 0.07 m, 0.14 m and 0.21 m respectively, which indicated that the spray delay control method was practical to control spray outputs to match detected target positions.