Uddhav Bhattarai, Manoj Karkee. Washington State University, Center for Precision and Automated Agricultural Systems, Prosser WA, 99350. May 13, 2024
The tree fruit production industry around the world relies heavily on a semi-skilled seasonal workforce for critical field operations such as training, pruning, blossom and fruitlet thinning, and harvesting. Blossom thinning is an essential crop-load management technique dependent upon an arduous and labor-intensive manual operation to achieve the desired result. Large-scale chemical and mechanical thinning approaches are available, but chemical thinning results can be unpredictable, and mechanical thinning can be indiscriminate and may damage a significant part of the tree canopy. These challenges compel the development of an efficient system that can perform precise blossom thinning in the target canopy regions with high accuracy, effectiveness, and reliability.
At Washington State University #AgRobotics lab, we developed and field-tested a robotic system for precision blossom thinning in apples. Similar to how humans use their hands, fingers, eyes, and knowledge to locate and remove flowers, the robotic system utilizes a vision system with a depth camera, a mechanical arm (UR5e industrial robotic manipulator), and a cutting tool (end-effector) that is similar to a weed cutter with a string attached to a center spindle. Once the camera captures the canopy, robust programming optimized for apple flower identification recognizes and delineates apple flower clusters. The manipulator carrying the end-effector then navigates to the target flower clusters. When the target is reached, the end-effector is triggered and performs the thinning.
The system was tested in a commercial apple orchard growing the EnvyTM apple variety in a V-trellised architecture. Two thinning methods were investigated to assess performance in selectively thinning flower clusters in target canopy regions: boundary thinning, removing flowers along the exterior of a flower cluster; and center thinning, actuating the end-effector at the center of the target cluster. The field evaluation results demonstrated that the integrated system could thin varying proportions of blossoms from targeted clusters based on the chosen thinning strategy. The boundary thinning approach achieved a 67.2% thinning with a cycle time of 9.0 seconds, whereas the center thinning approach thinned 59.4% of flowers with a cycle time of 7.2 seconds per cluster. While the system requires improvement in terms of thinning decisions, speed, and scalability, the proposed system is one of the first robotic systems tested for blossom thinning in commercial orchards and could be a crucial advancement for developing a multipurpose robotic system for orchards.
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Funding and acknowledgements
This research is partially funded by the Washington Tree Fruit Research Commission, and National Science Foundation and United States Department of Agriculture, National Institute of Food and Agriculture through “AI Institute for Agriculture” program. Grant Number: 2021-67021-35344
Additional information
Bhattarai, U., Zhang, Q., & Karkee, M. (2024). Design, Integration, and Field Evaluation of a Robotic Blossom Thinning System for Tree Fruit Crops. Journal of field Robotics. 1-20, DOI: .
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