Mechanical Thumb Sensor for Fruit and Vegetable Sorting

Abstract

A 3-mm-diameter pin was used as a mechanical thumb to sense firmness of orange fruit and tomatoes. Two firm measuring devices were developed: one - based on the Go-No-Go Method to differentiate between firm and soft oranges, and the other - based on the Continuous Deformation Method to differentiate among hard-green, firm-red, and soft-red tomatoes. An online singulator-orientor machine, equipped with a firmness sensing device to distinguish between firm and soft orange fruits and to grade tomatoes in firmness groups, were built and tested. The machine stiffness-readings of tomatoes, as relates to manual grading, was discussed. The difference between firmness means was significant at the level of 1%. All of the red-firm tomatoes could easily distinguish from 100% of the green ones and from 52% of the turning-red tomatoes. A comparison between the machine firmness test and the manual test for Shamouti oranges was conducted. The machine test indicated a relatively high accuracy in firmness readings [coeff. of variation (CV) was found from 1.6% to 4.3%].