A new shaker head design for reducing bark injuries on fruit trees

Abstract

To reduce bark damaging moments on the fruit tree trunk, a new shaker head arrangement is proposed. By applying two identical complete shaker units symmetrically on both sides of the trunk, the resulting shaking force will be normal to it and uniform in any direction. To prove the assumption, a theoretical model was set up and a laboratory model was built and tested. The theoretical model made the calculation of pure centrifugal forces of the eccentric shaker masses possible. Besides the new shaker head arrangement, the laboratory model enabled the study of the performance of present shaker heads. Test results lived up to the expectations: In case of the new shaker arrangement, the acceleration pattern was nearly uniform in all directions, both in the free and "tree" shake mode. In case of the usual shaker arrangements, asymmetric acceleration distributions were measured, which, besides injuring the bark, may result in lower fruit detachment rate.Keywords fruit harvest; inertial shaker; shaker head; bark injury IntroductionIn the mechanical stone fruit harvesting practice, both uni-and multidirectional inertial shaker machines are used. The unidirectional shakers cause theoretically only normal force to the trunk. In the praxis however there are other effects, which may damage the bark. Maximum displacements were found by Affeld et al.[1] to be 2,5 times greater during start-up and shutdown, than at steady-state. Relative displacements between the shaker and the trunk were also excessive and can exceed tolerable bark strength limits.According earlier experiments the effect of shaking direction influences the detachment rate [2]. By shaking the trees in multiple directions, nearly uniform acceleration acts on fruits in all directions. This results in higher detachment rate, compared to the uni-directional shaking. The phenomenon was also modelled and proved by FEM [3] [4].Multidirectional shakers produce forces not only in normal, but in tangential directions. The tangential forces tend to separate the bark from the cambium layer, which can cause long-lasting damage to the tree. In practice in order to reduce bark injuries, lubrication is applied between the sling surfaces of the shaker head [5] [6].In all cases, the shaker head is clamped to the trunk and is free to move, relative to the frame of the carrier machine. The present multidirectional shakers use a pair of counter-rotating eccentric masses to generate centrifugal forces changing in value and direction. The freedom of moving relative to the carrier is assured by the suspension of shaker head via 3 rubber isolators or chains (Figure 1).