Linear Reachability of Fruits in Orchard Trees with Actuator Constraints

Abstract. Fruits in modern, high-density orchard trees are much more accessible than those in traditional trees. Hence, simpler telescopic arms may suffice for harvesting. In a previous study, linear fruit reachability was defined as the total number of linearly reachable fruits on a number of trees along a particular approach direction divided over the total number of trees. Cumulative linear fruit reachability was also defined as the total number of fruits that were linearly reachable after a number of consecutive harvesting passes. This work extends the concept of linear reachability by introducing physical constraints for the harvesting actuator, such as gripper cross-section, as well as a minimum distance constraint of the machine from the canopy, due to branches extending in the row. A case study for high-density Bartlett pear trees was considered. For this variety the minimum marketable fruit diameter was 2.15 inches (5.5 cm) and minimum length to diameter ratio was 1.1 and the maximum marketable fruit diameter was 3.25 inches (8.3 cm) and maximum length to diameter ratio was 1.54. Using the data collected in the commercial orchards, the position of the farthest rigid branch that extends into the orchard row was identified and its distance from the tree centerline was computed which was 1.5 m. Results showed that the cumulative linear fruit reachability after 3 harvesting passes dropped from 93% to 77% as the gripper diameter increased from 6.5 cm to 13.75 cm for an arm extension of 2 m.