Japanese Journal of Farm Work Research

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In order to design the fruit separation mechanism for a processing tomato harvester, fruit stem detachment forces and the natural frequencies of fruit clusters were measured, using for comparison cultivar Wasedaruma (round) and chico III (pear-shaped) tomatoes.
The results were summarized as follows:
1) Using fully matured Wasedaruma fruits, the average detachment forces were 1460gw (tensile force) at the calix, 980gw (tensile force) at the joint, and 330gw-cm (bending moment) at the peduncle. Using fully matured Chico III fruits, the average detachment forces were 1110gw, 630gw and 160gw respectively.
2) As fruits approached maturation, slight decrease in detachment forces were observed. However the differences between green and mature fruits were not great enough to suggest selective separation of matured fruits.
3) The natural frequency of Wasedaruma fruit clusters was found to lie in a range from 6.4 to 1.3Hz (median 2.8Hz.) There is a logalithmic correlation between lt1 (see Fig. 5.) and natural frequency of cluster.
4) The natural frequency of fruit clusters was less than that calculated from a cantilever model (with an attached mass equal to the average weight and position of fruit clusters) and greater than that of a simple pendulum model.
5) There are wide variations in natural fruit cluster configuration. Therefore it may be assumed that in the design of a fruit separation mechanism based on the resonance principle, forced vibration should be applied in a wide frequency range.

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