Stereo Vision Controlled Variable Rate Sprayer for Specialty Crops: Part I. Controller Development

Abstract

Highlights Developed a stereo vision spray controller with a single board computer for precision sprayers. Developed algorithms to process stereo vision data, calculate spray volumes, and activate spray nozzles. Developed a graphical user interface to embed algorithms and operate the controller. Controller detected target volume and sprayed target in real time at various travel speeds before target was on spray area. The spray controller consumed 111 to 141 ms to acquire and process data and determine spray output. Abstract. Under laboratory conditions, a variable rate spray controller using stereo vision as a target detection sensor was developed and evaluated with moving spray targets at travel speeds ranging from 3.2 to 8.0 km h-1. The controller detected the target with a resolution of 480 pixels (vertical) × 640 pixels (horizontal) at a frame rate of 5 Hz and modulated spray nozzles at 10 Hz based on the analysis results of the stereo vision data. A customized graphical user interface was developed to operate the controller, display incoming data, and control other components. Evaluations of the controller with a flat, 3-dimensional box column and artificial tree targets with travel speeds ranging from 3.2 to 8.0 km h-1 showed that the controller consistently activated the nozzles 158.7 to 293.6 ms before the spray target arrived on the spray axis. The controller was also capable of repeatedly detecting the volume of the spray target with variations less than 12% for the same target at one travel speed, although it measured the volume generally higher than the manually calculated volume by as much as 33%, which resulted from duplicate target detection between detection cycles of the controller. These duplicated detections caused the overapplications of as much as 38%, although the controller repeatedly discharged spray volumes with variations less than 11% for the same target at the same travel speed. On average, the spray controller required 111.2 to 140.7 ms for data processing in one detection cycle, from image acquisition to activating spray nozzles for travel speeds ranging from 3.2 to 8.0 km h-1, with the potential to reduce this further. The developed controller would provide an economical and versatile platform for future variable rate sprayers with the benefits of stereo vision technology. Keywords: Automation, Crop protection, Precision Agriculture, Pesticide, RealSenseTM.