Mechanical Harvesting

Widespread interest in mechanical harvesting in the United States began in the early 1950s with the gradual decline in a readily available, qualified seasonal labor pool to hand harvest tree fruit. The majority of tree fruit mechanically harvested are destined for the processing market, especially tart cherries. Success in adapting mechanical harvesting

FIGURE H1.3. Mechanical harvest aids: (left) a one-person motorized tower and positioning aid, with forks for carrying a bulk container; (right) a self-propelled computerized harvesting aid with two pickers for inclined canopy trees

techniques to apple and other deciduous tree fruit crops has, however, been somewhat limited, especially for fresh-market-quality fruit. A major obstacle to mechanical harvesting has been excessive fruit damage. Since the 1980s, significant effort has been made to develop mechanical harvesters for fresh-market apples and to some extent peaches. However, with peaches, a lack of uniform maturity is a major problem. Recently, work has been directed toward harvesting fresh-market-quality sweet cherries. While progress has been made, a successful mechanical harvester for fresh-market apple, peach, and sweet cherry has not been developed.

Most commercial mechanical harvesters for tree crops operate on the shake-and-catch principle. A large clamp is attached to the tree trunk or to an individual limb. Fruit are detached, collected on a padded surface, and conveyed to a bulk container. The catching surface incorporates various deflectors, rollers, and positioning devices to reduce the impact of falling fruit and the damage from fruit-to-fruit contact. Various rotary inertial or recoil impacting devices built into the clamping head affect detachment. Most rotary shakers use a multidirectional action in the shaker device; impactors are unidirectional. Many commercial mechanical harvesters consist of two self-propelled units or halves, one on each side of the tree (Figure H1.4). One unit contains the shaking mechanism, a collecting surface, a conveyor system, and the bulk container. The other unit consists mainly of a collecting surface but may also have a conveying system. Some mechanical harvesters are single units with wraparound frames. These units resemble inverted umbrellas. In the United States, most tart cherries are mechanically harvested with two-half, inclined-plane, shake-and-catch harvesters. Canning peaches, and, to a lesser extent, apples for processing are also harvested with this type of equipment. The use of shake-and-catch mechanical harvesters for processing apples has declined since the 1990s, as processors have demanded higher-quality fruit for canning purposes. The shake-and-catch harvester principle has also been designed into over-the-row continuous moving units that can straddle small-stature trees. These units are more efficient, but fruit damage levels are similar to those obtained with the larger, two-half harvesters.

Skill is required to operate mechanical harvesters to avoid damage to trees as well as the harvested fruit. Trunk- or limb-shaking units place tremendous pressure on a tree's bark and cambium during the

FIGURE H1.4. A shake-and-catch mechanical harvester being used to harvest cling peaches. This unit employs a trunk shaker to detach fruit from the tree.

clamping and shaking operation. Irrigation should be halted several days prior to mechanical harvesting to reduce bark slipping. Clamping pads in the shaker heads must be lubricated periodically to avoid removing bark from a tree. Minimizing the duration of the shaking action is also important.

Compatible tree structures are considered necessary for successful mechanical harvesting. Smaller trees are more easily adapted to mechanical harvesters than large trees, but studies have shown that fruit damage may still be unacceptable with current state-of-the-art mechanical harvesters. Tree form can be adjusted to enhance fruit detachment and reduce fruit damage. With apple, recent work has concentrated on inclined trellis canopy forms that provide a more uniform, open canopy with easier access for the shaker or impacting mechanism and a clear path for fruit to the catching surface. When fruit are borne on long, slender branches, much of the energy applied to the tree is lost and fruit detachment is difficult. Pruning and training methods should encourage compact, stiff growth for easier fruit detachment. Spur-type apple trees are considered ideal for adapting to mechanical harvesting, since fruit are borne on short, stiff spurs.

Robotics has been incorporated into the latest experimental mechanical harvesters. In one such unit, television cameras mounted on the harvester feed information to an onboard computer, which then directs a robotic arm to the location of an individual fruit. Once the fruit is identified, a suction cup grasps the fruit; the arm rotates and removes the fruit, placing it into a conveyor. Another robotic bulk harvesting system designed for inclined trellis canopies uses sensors and intelligent adaptive technology along with a limb impactor (rapid displacement actuator) to locate and detach fruit and position the catching surface (Peterson et al., 1999). Although these units are still in developmental stages, the potential for mechanical harvesting of fresh-market-quality tree fruit appears promising.

Harvesting is the climax of the growing operation and a laborintensive step in bringing a tree fruit crop to market. Most tree fruit are still hand harvested to ensure the highest possible quality, but mechanical harvesters have been developed and are used for processing fruit, such as tart cherries and canning peaches. Research is ongoing to develop mechanical harvesters capable of harvesting fruit equal to the hand picker.



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