An electro-mechanical limb shaker for fruit thinning

Abstract

Mechanizing the fruit thinning operation will result in considerable cost savings for growers. This investigation has been conducted to improve mechanical thinning by exciting individual branches at a precise frequency and duration to achieve a superior distribution of fruit remaining on the tree. A unique and precise electromagnetic limb shaker that requires no branch clamping has been developed and evaluated under field conditions. Finite element analysis was performed on simulated limbs with the top free and restrained using Abaqus ® to evaluate solutions for improving fruit distribution and to explain field results. Extensive tests have been performed with this proposed limb shaker in nectarine, peach and prune orchards within Northern California. A force coupling manipulator allows our thinner to shake the branch without clamping to it, thus facilitating automation of the process. A powerful three-phase servo controlled linear motor drives a force coupler that shakes the tree branch. The size distribution of thinned fruit was determined for multiple shakes on the same limbs. This allowed quantification of the fruit thinning distribution. The innovative concept of holding the top of the limb avoided excessive removal of fruit from the tree top. High-speed video analysis enabled measurement of limb and fruit position as a function of time. Detachment accelerations were obtained in the video image plane. This precise limb shaker shows great potential for use in deciduous fruit orchards but further study is required in order to design a more automated prototype.