A REVIEW OF CITRUS HARVESTING IN FLORIDA
by
Jodie D. Whitney, Ph.D.
Professor of Agricultural Engineering, P.E. University of Florida, IFAS Citrus Research and Education Center, Lake Alfred
ABSTRACT
The removal of Florida citrus from the tree for harvesting is still done by handpickers on ladders and requires a work force of 20,000 to 35,000 persons. Moving fruit from the grove and subsequent fruit handling has been mechanized in the last 40 years. Factors affecting harvesting are fruit type and utilization, grove characteristics, and harvest labor requirements and costs. Although mechanical harvesting research over the past 35 years has not developed a feasible machine to replace the picker, substantial design and field performance information has been developed to mechanize the har-vest of a significant portion of the crop if labor becomes unavailable or too costly. Some picking aids have been implemented to increase the productivity of pickers, but their feasibility is questionable under current conditions. Renewed attempts have been made to mechanize the harvest since 1993. A harvesting program administrator was employed by the Florida Department of Citrus in January 1995 to develop a program which will insure the harvest of future crops at a competitive cost. Record crops, low fruit prices, steadily increasing harvest costs, and more regulations are predicted for the next decade.
FACTORS AFFECTING HARVESTING
Fruit tvpe and utilization. Over the past 20 seasons, Florida citrus production has averaged 71% oranges, 23% grapefruit, and 6% specialty fruits (Citrus Summary, 1992-93). Since 1988, 83% of the citrus was processed, 93% of the orange, 55% of the grapefruit and specialty fruit. This left 17% of the citrus utilized as fresh, and with an average packout of 65%, 1710.65 or 26% of the crop was harvested destined for the fresh market. All fresh market fruit must be handled with care, especially the specialty varieties which have thin and fragile peels. All citrus harvested by hand is separated from the tree with a twisting, snapping motion except for tangerines which are often clipped to reduce peel damage. Productivity of the picker depends on the fruit type (size) and utilization (fresh generally lower than processed). A survey done during the 1967 season showed the productivity of the citrus picker in boxeslh averaged 11 in grapefruit, 7.3 in oranges, 4.9 in murcotts and tangelos, and 2.7 in tangerines (Florida Industrial Commission, 1967).
The harvest season for fresh fruit can last from/ September to July, whereas the main thrust of the processing season is usually Dece7ber to May. Valencia or late oranges have historically been slightly less than half the ,otal Florida orange production and is the only cultivar normally harvested after citrus trees bloom in the February-April period. Thus, Valencia has the mature and young (next years)fruit on the tree at harvest time. Selective harvest of the mature fruit presents no particular problems for hand harvest, but is a significant problem for mechanical removal devices and fruit-loosening abscission chemicals.
The need for tree topping has been alleviated somewhat by the increased acreage in bedded groves in which shallow root systems tend to limit tree height. Many factors must be considered in determining the appropriate tree height. Most of the citrus cultivar/rootstock combi-nations are relatively vigorous in nature and limiting tree height by tree topping can limit fruit yields. Growers tend to maximize tree growth for healthy-looking trees with the latest irrigation and fertilization techniques, and hope this will maximize fruit yields.
ROBOTIC HARVESTING RESEARCH
Research on robotic citrus harvesting began in Florida in 1983. When compared to previously researched mechanical harvesting systems, this approach offered some significant advantages. Abscission chemicals would not be needed. Mature Valencia oranges could be harvested selectively from the younger fruit. Fruit could be harvested for fresh or processed market. Harvesting could be accomplished any time of day or night and during inclement weather, unless handling of fresh fruit under these condi-tions were detrimental.
Harrell et al. (1985) developed a single arm system with machine vision that picked fruit with simple three-degree-of-freedom arms. A second generation arm (the Florida picking robot arm, Figure 17) designed by Harrell (1987) pivoted in a Hook-joint base about intersecting and perpendicular axes. A prismatic link, mounted on the Hook-joint, provided motion in and out of the citrus canopy. Arm actuation was accomplished with two rotary actuators and a hydraulic motor. A rack and pinion drive was used to obtain linear motion from the hydraulic motor. High performance servo valves, controlling actuator flow, were used to achieve the dynamic performance required for picking fruit.
Attached to the end of the sliding link was a rotating lip picking mechanism. A solid state color camera, ultrasonic range sensor, and incandescent lamp was incorporated into the picking mechanism for fruit identification and location. Color machine vision enabled the picking arm to rapidly distinguish between the various hues present in a citrus canopy.
When a fruit was detected by the vision system at the start of a pick cycle, angular velocities of the two rotational joints were regulated, maintaining the targeted fruits projection in the center of the image plane. The sliding link was actuated, extending the picking mechanism towards the targeted fruit until it was close enough to detach the fruit from the canopy. Once detached, the sliding link was retracted from the canopy and the fruit was dropped (intended for a fruit collection system), and the next pick
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