Fruit removal is the main aim of vibratory fruit-harvesting machines used on fruit-bearing trees. it is well known that fruits suddenly fall, especially within the transient and when frequency span technique is used, periodically accelerating and slowing down the shaker. The aim of this paper is to give some new and not yet investigated results about these machines, in particular clamp-trunk coupling and its effect on vibration transmission. A clamp-trunk coupling model was established for the separation of the different phenomena occurring when using shakers with two independently driven eccentric masses. First of all the acceleration can be broken up into two multiplicative factors representing the first one the main vibration mode, the second one the precession motion of the trajectory of the acceleration vector in XY plane. The second phenomenon highlighted in this paper is typical of clamp-trunk coupling: the phase modulation of the acceleration measured on the trunk.
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