柑橘の機械収穫に関する基礎研究 (第2報)

振動中の果実-果梗系の力学と作用力について

抄録

For the purpose of inquiring into the shaking frequency that caused the citrus fruits to detach efficiently from the tree, the frequency response of it's fruit-stem system to forced vibration was, observed and simultaneously, the various forces applied to the stem ware measured, The mechanical models of the fruit-stem system were chosen for the numerical analyses of it's motions and the predicted motion was compared with the observed motion.
1) Motion picture analyses of the vibration characteristics of the fruit-stem system were made for Citrus Unshiu. The results of them are shown in Fig. 8 or Tab. 1.
2) The numerical analyses of the two mechanical models, double physical pendulum model and curved beam model, could make clear the vibration charcteristics of observed motions of Citrus Unshiu. Therefore, the motion characteristics of the fruits that bear in an orchard may be predicted from the investigation of their bearing conditions.
3) As the natural frequency of the first fundamental mode of double physical pendulum was under 2.5Hz, the inertial force due to the resonant motion of the fruit was too weak to detach the fruit from the tree. This mode, that induces the simple pendulum motion, should not be used to detach the fruit because the fruit damage of predetachment may be produced.
4) Twisting mode existed at the range of 5 to 7Hz and the torsinal moment due to the resonance was under 0.2kg-cm. If fruits are detached by only a tortional operation, the torsional moment of average 1.1kg-cm is required to shear the stem of Citrus Unshiu. Therefore, this mode cannot be used to detach the fruit.
5) When the second fundamental mode of double physical pendulum was induced, the ralative bending angle between the stem and fruit was maximized into approximately 70-80° and tensile and compressive force of the stem became larger, too. These natural frequencies were 6-8Hz in y-z coordinates and 8-10Hz in x-z coordinates. This mode is considered to be most suitable to detach the Citrus Unshiu's fruits from their sepals.
6) The second mode of trasverse vibration of the stem occurred at 14-15Hz in response to exciting displacement to have vertical component and the tensile and compressive force was increased rapidly at this time. If all the fruits, that bore in the orchard, could be shaken by the oscillating displecement to have vertical component, this mode would be used to detach the fruits. However, the more delaied experimental studies and field tests must be made, because the range of natural frequencies to induce this mode may be extended by the difference of physical property of each stem and the mature Citrus Unshiu's rinds are so tender and apt to float that a portion of their peels may be torn with the stem during detachment.