Design and performance evaluation of a variable-rate orchard sprayer based on a laser-scanning sensor

Jichen Cai,Chunjiang Zhao,Shuo Yang,Xiu Wang,Yuanyuan Gao

doi:10.25165/j.ijabe.20191206.4174

Abstract

To improve the precision spraying strategy and reduce excessive pesticide application in orchards, an air-assisted sprayer integrated with a laser-scanning system was developed to realize the toward-target variable-rate spraying. In the spray control system, a method of calculating canopy gridding volumes was designed to ensure the canopy was divided into a uniform grid size, a variable-rate spray model was used in the flow rate decision software to control the spray output according to the canopy gridding volumes and travel speed, and a method of saving and accessing spray data was used to control the spray delay. The effects of different grid sizes and travel speeds on the spray performance were evaluated by quantifying spray coverage uniformity inside tree canopies. The results showed that spray coverage uniformity declined with increasing grid width from 0.14 to 0.28 m although the mean spray coverage on each target location showed no significant differences. Additionally, there were no significant variations in mean spray coverage at speeds of 1.0, 1.2 and 1.4 m/s for a tested tree of 1.6 m width and at any experimental speeds for a tested tree of 1.3 m width, which indicated that the variable-rate sprayer could provide good spray coverage uniformity under various travel speeds with a canopy size limitation. Compared with the same sprayer without the variable-rate spray function, the intelligent sprayer prototype realized effective toward-target spraying and avoided overspraying while providing sufficient spray coverage. Keywords: laser-scanning sensor, variable-rate spray, orchard, precision sprayer, pesticide application efficiency DOI: 10.25165/j.ijabe.20191206.4174 Citation: Cai J C, Wang X, Gao Y Y, Yang S, Zhao C J. Design and performance evaluation of a variable-rate orchard sprayer based on a laser-scanning sensor. Int J Agric & Biol Eng, 2019; 12(6): 51–57.

Highlights

Excessive pesticide usage in orchards caused by overspraying[1,2,3] increases production costs and environmental pollution
The mean spray coverage on the front, middle and back target locations of the tree were reduced because the front target location was closest to the nozzles and the branches and leaves of the tree blocked some of the spray droplets from reaching the middle and back locations[20]
The mean spray coverage on all target locations was less than with constant-rate application, especially in the spaces between trees, demonstrating that the use of the laser sensor was an effective way to avoid overspraying while providing sufficient spray coverage and to realize on-target spraying[11] with high accuracy

Summary

Introduction

Excessive pesticide usage in orchards caused by overspraying[1,2,3] increases production costs and environmental pollution. Several variable-rate sprayer prototypes[9,10,11] integrated with laser-scanning sensors have been developed and evaluated in orchard experiments. With the improvement of the sprayer, a large number of orchard experiments comparing against conventional spray application were conducted by Zhu et al.[16] The results showed that the laser-guided sprayer used less pesticide than conventional constant-rate sprayers and still achieved comparable levels of pest control, which demonstrated the practicability of variable-rate spraying based on laser sensor detection. The experiment was conducted under a 0.8 m/s travel speed and the results showed that the control of air volume improved the spray coverage uniformity on the backs of trees, and the minimum number of droplets was 46.2 per cm. The influence of variable travel speed on the spray deposition[13] or droplet density was not mentioned

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Conclusion