This paper describes the development of a movable strawberry-harvesting robot that can be mounted on a travel platform, along with its practical operation in a greenhouse. The harvesting robot can traverse and enter an adjacent path and picking is performed with the travel platform halted on the travel path. Machine vision is used to detect a piece of red fruit and calculate its position in the three-dimensional space, whereupon its maturity level is assessed according to an area ratio determined by classifying the whole fruit into three areas: ripe, intermediate, and unripe area fractions. Sufficiently mature fruit are picked by the end-effector by cutting the peduncle. During operational tests in a greenhouse, our machine vision algorithm to assess maturity level showed a coefficient of determination of 0.84. Setting the maturity level parameter at 70 or 80% resulted in higher shippable fruit rates than the setting of 60%, because small unripe fruit positioned in front of larger ripe fruit were successfully skipped in the former case. Our results showed that a higher shippable fruit rate could be achieved later in the harvest season, reaching 97.3% in the test in June. The successful harvesting rate and work efficiency were 54.9% and 102.5 m h -1 , respectively.
One of the direct approaches for obtaining a high yield of strawberries is high-density cultivation. Such cultivation improves the efficiency of space utilization in a greenhouse; however, it requires the movement of planting benches. The aim of this study is to develop a circulating-type movable bench system for strawberry cultivation that realizes high-density cultivation and improves work efficiency. The developed system, which is 16.0 m long and 9.2 m wide, consists mainly of two longitudinal conveying units, two lateral conveying units, two nutrient supply units, a chemical sprayer, 62 planting benches, and a control unit. The design of the longitudinal conveying mechanism combining the rotating and sliding movements of rods for pulling the benches and a method of controlling the conveying units achieves effective circulation, resulting in a cycle time of 67.0 s during which the successive bench reaches the initial position. This cycle time could be shortened by increasing the speed of lateral conveying. The planting density obtained using this approach is 16.0 to 20.0 plants m -2 , which is roughly 2 to 2.5 times the plant density obtained in the conventional method of cultivation. Furthermore, the four cultivars used in this study showed vigorous growth, and the cultivars Akihime and Moikko showed a marketable yield twice as high as the conventional yield.
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