UBC Theses and Dissertations

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UBC Theses and Dissertations

Development of an Electronic size and colour grader for tomatoes Von Beckmann, Joerg Walter


The greenhouse tomato industry in British Columbia requires that tomatoes be colour graded into four categories, and size graded, based on diameter, into four categories. Automatic colour graders for only two category classifications have been developed, while a size grader based on weight is commercially available. To meet industry demands, automatic size and colour grading of greenhouse tomatoes for the fresh market is necessary. The development of an automatic size and colour grader, which fulfills industry grading requirements is needed to reduce production costs and to accelerate the implementation of complete mechanization in tomato handling. This thesis outlines the design, fabrication and testing of a grading machine capable of simultaneously size and colour grading tomatoes into fourteen different size and colour categories at a rate of five tomatoes per second. The number of categories may be increased or decreased to meet individual needs. Tomatoes are randomly fed onto a conveyor with one inch (2.5 cm) minimum spacing and passed single file under a fibre optic illuminating and sensing head. Size and colour of individual tomatoes are measured electronically and the information stored in a memory until each tomato reaches an appropriate eject location, where the tomato is pneumatically ejected into a storage bin. The memory and eject mechanisms are synchronized with the conveyor belt so that changes in belt speed do not affect grading. The grading rate is strictly a function of mechanical handling operations, and is limited by the ability of the pneumatic eject system to supply enough air to remove tomatoes from the conveyor in the allotted time. Colour grading is based on the ratio of light reflected from the tomato surface in two narrow bands of the visible spectrum. Size grading is based on a diameter measurement of the tomato, as it passes under the sensing head, with a grading resolution of approximately 3/64 inch (0.12 cm). Misclassification of oversized or undersized tomatoes in a given size category was less than 10%.

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