Dahle is enthused about helping bring machine harvesting for cherries to fruition. “We have concerns about the reliability of the labor supply for hand harvest,” he says. Machines could “revolutionize the industry.”
Perfecting the machinery
Qin Zhang, director of WSU’s Center for Precision Agricultural Systems in Prosser, heads the harvester research, focusing first on problems in two existing shaking machines.
A handheld limb shaker using highfrequency vibrations “works perfectly under ideal conditions,” Zhang says. But those ideal conditions appear in at best only 10 percent of tree limbs.
That shaking frequency also is far higher than needed to achieve results on UFO trees, increasing the potential for limb damage, he says.
A larger tractor-driven shaker punches tree trunks to produce the needed force. “It works reasonably well, but it’s difficult to target the trunk,” Zhang says.
The impact can cause tree injuries that often lead to disease and ultimately replacing trees. “That’s a killer” for grower acceptance, he says.
This initial data will steer designs of a new prototype harvester for testing next year, Zhang says.
High-speed video shows fruit damage occurs mainly as cherries hit branches on their fall into the catch frame.
Positioning the catch frame directly under targeted branches should minimize damage, he says.
“With a simpler [tree] structure we can design simpler machines,” Zhang says. “More complexity means higher costs.”
Seattle area-based Picker Technologies is a project partner developing cherry prototypes of its mechanical-assist harvest platform. Randy Allard, vice president of research and development, says he anticipates integrating the company’s system with Zhang’s harvester for this year’s tests.
Ultimately Allard aims to field-sort culls, size harvested fruit before it leaves the orchard and field-pack high-value cherries into bags for immediate shipment.
“The packinghouse only has so much volume capacity” during harvest peaks, he says.
Variety selection is key
Another crucial factor to machine harvesting is variety selection. Shaking fruit off trees requires loosening the cherry from its stem—and the looser that connection, the softer the force needed.