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 armsrsquo; 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 (rsquo;passesrsquo;) 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 gripperrsquo;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.