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Mechanical Engineering
Ph.D Dissertation Defense


"Enhancing Mechanical Fruit Harvesting Machines Based on Vibration Analysis"

Taymaz Homayouni

Mechanical Engineering
University of California, Merced


Currently, fruit removal using multi-directional canopy and trunk shakers are the most widely used technique for harvesting nut trees. To develop an intelligent harvesting machine, a system needs to be developed to shake each tree optimally. Optimum mechanical harvesting machines aim to maximize fruit removal with minimum tree and fruit damage, using the least amount of energy. Maximum fruit removal requires the tree to be shaken around its natural frequency; however, the best shaking frequency is not the same for all trees.
In this work, vibration transmission in trees is studied to enhance mechanical harvesting machines while minimizing damage to the tree. Trunk shakers and canopy shakers are the most common commercial mass harvesting machines, each comes with a limitation. Further, a trunk shaker has more energy loss from tree trunk to its canopy compared to a canopy shaker.
The efficiency of the commercial harvesting machines is evaluated by quantifying the energy input to the trunk and the transferred kinetic energy throughout the tree canopy.  A set of wireless accelerometer sensor systems was developed and used to measure acceleration at different parts of the tree and the shaker machines. A mathematical model of vibration and force transmission throughout a pistachio tree is developed under different shaking conditions using a trunk shaker. A new method was developed to find proper shaking intensity as a function of the tree trunk size. Two canopy shakers were designed, fabricated and tested in the field for harvesting table olive trees. One design included an adjustable head, and one included a large canopy shaker for larger mature trees. It was found that a combination of canopy and trunk shaker results in the highest harvesting efficiency in olive trees.



Taymaz Homayouni is a Ph.D. candidate in Department of Mechanical Engineering at University of California Merced. He joined Professor Reza Ehsani’s group in 2017 and worked on vibration analysis in fruit harvesting machines. He received his B.Sc.  in Mechanical Engineering from Isfahan University of Technology, Iran (2013) and his M.Sc. In Mechanical Engineering and a minor in Robotics from Oregon State University, Corvallis, Oregon (2015).

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