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.
This paper presents a procedure and the results of obstacle-avoidance control of a stationary strawberry-harvesting robot to be used with circulating-type movable bench cultivation. The stereovision unit detects mature and immature fruits from beneath the bench while being conveyed laterally. Based on the positional relation between them, the most appropriate direction for the end-effector approach is determined to avoid collision with immature fruits. The end-effector approaches along the calculated direction and controls its posture at 120 mm and 80 mm front of the target fruit, using visual feedback so as to match the roll angle of the end-effector with the peduncle angle, as estimated using a hand-eye camera. In the peduncle detection procedure, green LED lights are used to emphasize the calyx and peduncle. The proposed stereovision algorithm showed a success rate for detection of the appropriate approach angle of 89-93 . In the insertion test, the hand-eye camera was able to recognize the target peduncle at a success rate of 77-80 by facing the fruit from the most appropriate approach angle, and the end-effector was able to insert a peduncle at a success rate of 73-78 . The end-effector approach along the appropriate approach angle was confirmed to be the effective way to avoid collision with immature fruits, although several multiple insertions were observed. Our proposed procedure proved to work functionally together with the lateral movement of the movable bench.
To establish high plant density production of strawberry (Fragaria × ananassa Duch) using a movable bench which circulates the planting bed by longitudinal and lateral movement horizontally, three experiments were conducted. Subirrigation combined with supplementary surface irrigation was suitable as the nutrient solution supply method of the movable bench in experiment 1. For row spacing on the movable bench, we found that 0.50 m was the most efficient for fruit yield per m 2 in experiment 2. In experiment 3, based on the results from experiment 1 and 2, we designed and installed an experimental movable bench system of 9.6 m × 10.8 m. Three strawberry cultivars ('Akihime', 'Mouikko', 'Tochiotome') were grown using the movable bench system for forcing culture from September 2008 to May 2009. Marketable fruit yields of strawberries grown using the movable bench (MB) were compared to those grown using a conventional elevated bench (CB). In 'Akihime', the marketable fruit yield per plant of CB was higher than that of MB. In 'Mouikko' and 'Tochiotome', there was no significant difference in marketable fruit yield per plant between MB and CB. These results show that twice the number of strawberry plants per m 2 at CB can be grown at MB. They also show that MB can produce almost twice as much fruit yield per m 2 as CB.Key Words:elevated bed, subirrigation, surface irrigation
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