The Effects of Shaking Frequency and Amplitude on Detachment of Lime Fruit

The aim of this study was to determine the most suitable shaking frequency and amplitude for shake harvesting lime fruit (C. aurantifolia). A tractor mounted limb shaker with adjustable shaking frequency and amplitude, powered by the tractor power-take-off shaft was designed and developed for this study. The rotating input power was transmitted to the shaker flywheel through a multiple sheave v-belt drive system where it was converted to reciprocating motion by a slider crank mechanism. The resulting vibrating motion could be transmitted to the tree limb through a telescoping boom and a special clamping device. A 3x3 factorial experiment arranged in a completely randomized design with three replications was conducted to investigate the effects of shaking frequency and amplitude on fruit detachment. Three levels of oscillating frequency (5, 7.5 and 10 Hz) and three levels of shaking amplitude (40, 80 and 120 mm) were investigated. Analysis of variance and mean comparison showed that the effect of shaking frequency on fruit detachment was significant. However, those of shaking amplitude and its interactions with frequency were not significant. The percentage of detached fruits significantly increased by increasing the shaking frequency, but the shaking frequency or amplitude had no significant effect on fruit damage. Complete fruit detachment (100%), was obtained by applying shaking amplitude of 120 mm at a frequency of 10 Hz, but considerable leaf removal at this combination of shaking frequency and amplitude was a limiting factor. Therefore, shaking the limbs at 80 mm amplitude and 10 Hz frequency with about 98.5% fruit detachment and negligible leaf shattering was found to be the most suitable combination. In order to determine the bonding strength of lime fruits, a series of tests were conducted in which, the average pulling force required for detaching ripe and unripe fruits as well as fruit mass and geometric mean diameter were measured. The average static force required for removing ripe fruits was found to be about 14.2% of that required for removing unripe fruits. The average ratio of tensile force required for removing a fruit to its weight (Fs/W) was measured as 6.9 and 61.8 for ripe and unripe fruits, respectively. The two indices suggest utilizing a limb shaker as a valuable approach for selective harvesting of ripe fruits. This is especially true for fruit varieties with non-uniform ripening characteristics.