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To establish a profitable crop, it is not uncommon for the growers to thin one half parts or more of the developing fruits. Sensing the changing vibration characteristics of the tree limbs as fruit masses are incrementally removed from the limbs can provide a mechanism to monitor the amount of thinned fruit. The objective of this research is to correlate the changes in the vibration behavior of the branches with fruit removal by analyzing the response of accelerometers attached to the branches. Experiments were carried out in the laboratory with fresh cut branches and in the orchard on branches attached to the trees.

Samples were excited by hitting branch points with an impact hammer instrumented with a force transducer or by vertically displacing branch nodes from their original position and suddenly releasing it. Accelerometers were attached to the branch bark in order to measure the response acceleration at selected points in the direction perpendicular to the ground surface. Impact forces and accelerometer responses were input into a four channel storage oscilloscope. The oscilloscope recorded the time and the corresponding frequency domain signals. Different parameters were extracted from the frequency spectra. Output signals of the accelerometers were recorded and analyzed. Peaches were removed from the branch in steps. Clusters of fruit were removed in a random order. Some linear relationships have been found between the total energy contained in the spectra and the cumulative removed mass. The total energy has been computed as the sum of the energy content in the spectra of the accelerometers. Data indicated that the total energy contained in the spectra seems to correlate well with change in fruit mass removed from the branches.