Development of a Selective Automated Blossom Thinning System for Peaches

Abstract

The objective of this investigation was to develop and test an automated selective fruit-thinning system for blossom removal in peach tree orchards. The proposed system needed to visualize the tree fruit canopy, discriminate targets (blossoms), mechanically reach the canopy from a stable platform, and remove unwanted targets. The system consisted of kinematic targeting and heuristic programming, a robotic arm, and a pomologically designed end-effector. A quarter-scale robotic arm based on a Fanuc M-16iL manipulator model and rotating brush end-effector were designed and constructed for this study. The normal and tangential force requirements to remove a peach blossom from a shoot were also evaluated. The resultant blossom force tests yielded a range of 0.44 to 0.57 N for the normal force and 0.49 to 0.71 N for the tangential force. The precision and accuracy of the robotic arm and end-effector placement were then examined. A kinematic positioning test for the robotic arm consisting of 120 repetitions fell within the first standard deviation of a proposed ±2.54 cm precision standard. With a confidence level of 95% and a margin of error of ±8.96%, the robotic arm had a consistent range of -1.26 cm to +1.57 cm vector magnitude per target location. For the end-effector positioning test, the brushes reached the proposed ±2.54 cm target area 100% of the time. The deviation from the target to the center of the brushes was within the first standard deviation with a confidence level of 95% and a margin of error of ±10.33%, and the end-effector brushes had a consistent range of -2.97 cm to +3.04 cm per target location. The selective spatial thinning heuristic algorithm was also tested. The heuristic test consisted of a series of branches that varied in length from 10, 15, and 20 cm spanwise across the branch, with three artificial blossoms placed every 5 cm. The end-effector successfully removed the unwanted blossom in each case.