Dynamics of Fruit Tree Trunk Impact

ABSTRACT THE theory of colliding bodies is applied to the prob-lem of impact harvesting of tree fruits. We found for the impaction of a pendulum or a spring loaded mass with a tree trunk: 1 that a simple one degree of freedom model is an adequate representation of the impact response of the tree, 2 that multiple impacts are shown to exist, in agree-ment with experimental studies, 3 that certain physical properties of a tree relevant to the design of impact harvesting equipment (e.g., dynamic mass, damping coefficient, spring stiffness and Young's modulus) can be obtained from a pendulum test, and 4 that the energy transferred from the pendulum to the tree is not simply the difference between the initial and final potential energy of the pendulum or the spring loaded mass when at zero velocity. The error due to neglecting the loss in mechanical energy may be as high as 40 to 50 percent, which is a significant portion of the energy input. Therefore, it is necessary to take into ac-count the mechanical energy lost due to impact in such studies.