Robotic Tree-Fruit Harvesting With Telescoping Arms: A Study of Linear Fruit Reachability Under Geometric Constraints

Abstract

Modern commercial orchards are increasingly adopting trees of SNAP architectures (Simple, Narrow, Accessible, and Productive) as the fruits on such trees are, in general, more easily reachable by human or robotic harvesters. This article presents a methodology that utilizes three dimensional (3D) digitized computer models of high-density pear and cling-peach trees, and fruit positions to quantify the linear fruit reachability (LFR) of such trees, i.e., their reachability by telescoping robot arms. Robot-canopy non-interference geometric constraints were introduced in the simulator, to determine the closest position of the arms' base frames with respect to the trees, inside an orchard row. Also, design constraints for such arms, such as maximum reach, size and type of the gripper, and range of approach directions, were introduced to estimate the effect of each of these constraints on the LFR. Simulations results showed that 85.5% of pears were reachable after harvesting consecutively, at three different approach angles ('passes') with a gripper of size 11 cm and an arm extension of 150 cm. For peaches, after three passes, 83.5% were reachable with a gripper size of 11 cm and an arm extension of 200 cm. LFR increased as the gripper's size approached the maximum fruit size and decreased thereafter. Also, retractive grippers on linear arms yielded more fruit compared to vacuum-tube type grippers. Overall, the results suggested that telescoping arms can be used to harvest certain types of SNAP-style trees. Also, this methodology can be used to guide the design of robotic harvesters, as well as the canopy management practices of fruit trees.