Simulation study of vibratory harvesting of Chinese winter jujube (Zizyphus jujuba Mill. cv. Dongzao)

doi:10.1016/j.compag.2017.09.036

Computers and Electronics in Agriculture

Volume 143, December 2017, Pages 57-65

https://doi.org/10.1016/j.compag.2017.09.036 Get rights and content

Highlights

•
Shaking of winter jujube trees at five frequencies were analyzed using finite element method.
•
Material properties of different parts of trees were determined experimentally.
•
Field experiments were conducted to compare with simulation.
•
Simulation methodology is possible to study interactions between shaker and tree.

Abstract

Chinese winter jujube is rich in nutrition, but its harvesting is labor-intensive. A feasible method for mechanical harvesting of Chinese winter jujube is vibration harvesting. Currently, harvesting shakers for jujube were designed and optimized mainly based on imperial method through field experiments which are complex, time-consuming and limited by time and environment. In order to improve the rationality in shaker design, a better understanding of the interaction between the shaker and the tree is necessary. The aim of this study was to develop a simulation framework for predicting the responses of trees under vibration excitation with a shaker using finite element methods, and find relationships between the responses and the excitation frequencies. Field experiments were conducted using a shaker at five frequencies (5, 10, 15, 20, and 25 Hz) with three replicated trees. The input force was measured by a tension sensor and the acceleration of trees was measured by tri-axial acceleration transducers. The trees were modeled using Autodesk Inventor 2014 and then simulated by finite element method in ANSYS 15.0. In simulation, the tree model was divided to two parts, including branches and trunk. For both parts, the wood’s mechanical properties were determined experimentally. Results show that the acceleration value of experiment is generally larger than that of simulation, and it increases from the bottom of branch to the top. The acceleration curves in both experimental and simulation conditions and the distribution nephograms indicated that the greater frequency of tree shaking generates greater acceleration. The mean correlation coefficients of acceleration between experiment and simulation is 0.62. The average resultant accelerations of measured and simulated showed a good alignment in changing trends. It can be concluded that the simulation is promising for studying the response of trees under the vibration excitation of the shaker.

Introduction

Chinese winter jujube (Ziziphus jujuba Mill.) is an indigenous tree to China and famous for its good taste and rich nutrition of fruit. Chinese jujube is one type of tree fruit crops belonging to Rhamnaceae group and has been cultivated since 4000 years ago. It is also a variety compatible with the present ecology and economy with the function of environmental reservation as an economic crop (Gao et al., 2011, Zhang et al., 2016). Chinese winter jujube is a kind of fresh jujube, which is deeply favored by people for its good taste and abundant nutrition, such as vitamin C, amino acids, cyclic AMP, carbohydrate, and minerals (Li et al., 2007, Sun et al., 2007). The jujube fruit are also used as some medicinal supplements, such as tonic medicine and health supplement for blood nourishment and sedation (Gao et al., 2013, Lam et al., 2016, Plastina et al., 2012).

Current methods in harvesting jujube fruits are labor intensive and time consuming, which needs develop an efficient and economical harvesting technologies to keep jujube industry sustainability. Previous researches showed that vibrating or shaking is one of the feasible methods of mechanical harvesting for jujube. Lee et al. (2003) developed a canopy jujube shaker which achieved a detachment rate of 95.8% at 6.7 Hz with 5 s. However, the high intensity of shaking impact of the shaker resulted in a high rate of fruit damage of 10.7%, most of which was caused by the direct contact between jujube fruits and the harvester during fruit separation. A jujube trunk shaking harvester prototype was developed by the Xinjiang Academy of Agricultural and Reclamation Science. The harvester is able to run at 9.0 or 16.7 Hz, and harvest 76 trees per hour with a detachment rate of 90% and fruit damaged less than 0.2% (Meng et al., 2013). Fu et al. (2014) designed a self-propelled canopy shaker for jujube, which works riding on trees and shakes branches to induce inertial force on the fruits by rods mounted on the shaker. The shaker was reported that it removed 96.2% fruit from trees when it was operated at a traveling speed of 0.3 m/s, amplitude of 9 mm, frequency of 15 Hz, and vibration duration of 17 s, while fruit and branches damage were reported as less than 2.8%. Although those shakers were significantly improved the harvesting efficiency, the development was dependent on imperial design and needs theoretical studies to identify relationships between jujube trees and vibration frequency.

Researchers have conducted field experiments to study the tree-shaker system, fruit-stem subsystems or tree systems using different types of shaker to harvest fruits. Savary et al. (2011) investigated the force and acceleration distribution on citrus tree branches and fruits. Du et al. (2012) studied sweet cherry tree acceleration responses under sinusoidal excitations, and quantified the distribution and dissipation of applied vibratory energy within the woody structure of cherry trees. Zhou et al. (2013) conducted a field experiment for identification of the suitable shaking frequency and duration in mechanical harvesting of sweet cherry. Wu et al. (2014) reconstructed a three-dimensional (3D) Chinese hickory tree and performed a dynamics analysis for the reconstructed tree using field experiment. However, these field experiment methods are complex, time-consuming and also limited by time and environment.

Another approach for optimizing shaker design is using finite element method to simulate fruit harvesting. Yung and Fridley (1975) developed a finite element model for an apple tree system. Upadhyaya et al. (1981) established a finite element model for the dynamics of branch based on linearized beam theory. Láng (2008) calculated the relationship between power consumption and trunk amplitude for all trunk cross-sections, and found the most efficient clamping heights of the shakers. Savary et al. (2010) simulated citrus tree canopy motion during harvesting using a canopy shaker. Tang et al. (2011) researched the vibration characteristics of wolfberry tree using the finite element method. Bentaher et al. (2013) studied the optimization of stem shaking conditions in the mechanical harvesting of olive fruits and the influence of different shakers on the dynamic response of olive tree by finite element analysis. Tinoco et al. (2014) used the finite element method to analyze mechanical properties of the fruit-peduncle of coffee. Fu et al. (2016) applied modal analysis and harmonic response analysis to determine the natural frequency and steady-state response of sea buckthorn tree to study the tree responses to shaking frequency and amplitude. In these studies, several assumptions were made to create the simulation models such as, ignoring the existence of leaves and fruits and assuming unified mechanical properties of the trunk and all branches. Although, these assumptions would cause differences between simulation results and pertinent practical application, they have been good indicators of how harvesting in reality might be.

In practice, branches of Chinese winter jujube are pruned every year to maintenance dwarf tree size, which makes differences in the mechanical properties between the trunk and branches. To our knowledge, there is no previous research considered this variation. In order to improve the simulation results toward further resembling of actual harvesting situation, the goal of this study was to develop simulation framework for evaluation of tree response to shaking excitation. The specific objectives included (1) measurement of the mechanical properties of the trunk and branches separately, (2) study of the acceleration and frequency response of jujube tree, and (3) establishment of 3D finite element models of jujube trees to develop and evaluate simulation framework. It aimed for studying the acceleration during vibration to predict the responses of trees under the vibration loading and find the relationship between the responses and frequencies of excitation.

Section snippets

Mechanical properties measurement

This study was conducted in a private fruit orchard (34°89′31″N, 109°92′53″E, and 366 m in altitude) at Xuzhuang Town, Dali County, Shaanxi Province, China. Three 6-year-old winter jujube trees (Tree 1, Tree 2, and Tree 3) were randomly selected from the orchard. The material properties of the trees were determined from fresh wood samples of trunk and branch which were selected randomly from the trees after the field experiment. Fig. 1 shows the different samples used for this experiment.

The

Mechanical properties of jujube tree

The properties of different parts in the trees are shown in Table 3. These values show a variability of mechanical characteristics between the trunk and branch. The density, moisture, and Poisson ratio of the branch are larger than that of the trunk, while the Young’s modulus and shear modulus of the branch are smaller than that of the trunk.

To our knowledge, very few work on the mechanical characteristics of jujube tree wood are published. In the harvesting season, the moisture of branch is

Conclusion

Chinese winter jujube trees were modeled using Autodesk Inventor 2014 and then simulated for vibration harvesting by finite element method in ANSYS 15.0 based on some assumptions. In simulation, the tree model was divided to two parts, including branches and trunk. For both parts, the wood’s mechanical properties were determined experimentally. Field experiments were conducted using a shaker at five frequencies (5, 10, 15, 20, and 25 Hz) on three trees.

It was observed that the acceleration value

Acknowledgements

The work was supported by the Key Research and Development Program in Shaanxi Province of China (Project No. 2017NY-164), and the National Natural Science Foundation of China (Grant No. 31301242), and the China Postdoctoral Science Foundation (Grant No. 2015M572602), and the International Scientific and Technological Cooperation Foundation of Northwest A&F University (A213021505). The authors would like to express our great thanks Dr. Jianfeng Zhou from University of Missouri and Dr. Ahmad

References (29)

X. Du et al.
Dynamic responses of sweet cherry trees under vibratory excitations
Biosys. Eng.
(2012)
L. Fu et al.
Simulation of vibration harvesting mechanism for sea buckthorn
Eng. Agri. Environ. Food
(2016)
Q. Gao et al.
Physico-chemical properties and antioxidant capacity of different jujube (Ziziphus jujuba Mill.) cultivars grown in loess plateau of China
Sci. Hortic.
(2011)
C.T.W. Lam et al.
Chemical and biological assessment of Jujube (Ziziphus jujuba)-containing herbal decoctions: Induction of erythropoietin expression in cultures
J. Chromatogr.
(2016)
J. Li et al.
Nutritional composition of five cultivars of Chinese jujube
Food Chem.
(2007)
P. Plastina et al.
Identification of bioactive constituents of Ziziphus jujube fruit extracts exerting antiproliferative and apoptotic effects in human breast cancer cells
J. Ethnopharmacol.
(2012)
S.K.J.U. Savary et al.
Study of force distribution in the citrus tree canopy during harvest using a continuous canopy shaker
Comput. Electron. Agric.
(2011)
L. Sun et al.
Effect of nitric oxide on alcoholic fermentation and qualities of Chinese winter jujube during storage
Agric. Sci. China
(2007)
H.A. Tinoco et al.
Finite element modal analysis of the fruit-peduncle of Coffea arabica L. var. Colombia estimating its geometrical and mechanical properties
Comput. Electron. Agric.
(2014)
C. Wu et al.
3D reconstruction of Chinese hickory tree for dynamics analysis
Biosys. Eng.
(2014)

L. Zhang et al.

Tea polyphenols incorporated into alginate-based edible coating for quality maintenance of Chinese winter jujube under ambient temperature

LWT - Food Sci. Technol.

(2016)

H. Bentaher et al.

Finite elements modeling of olive tree mechanical harvesting using different shakers

Trees

(2013)

W. Fu et al.

Design of self-propelled dwarf and close planting jujube harvester

J. Agric. Mech. Res.

(2014)

Q. Gao et al.

The jujube (Ziziphus jujuba Mill.) fruit: a review of current knowledge of fruit composition and health benefits

J. Agric. Food Chem.

(2013)

Cited by (27)

Vibration response characteristics of Jujube trees based on finite element method and structure-from-motion
2024, Scientia Horticulturae
It is an indispensable step to choose optimal vibration parameters in jujube fruits vibration harvesting. Excessive vibration frequency will cause jujube tree damage, otherwise, the separation of fruit and fruit stalk cannot be achieved, resulting in harvesting failure. In our work, finite element method and vibration tests are applied to find optimal vibration parameters. To improve the accuracy of finite element method, a low-cost 3D reconstruction method is proposed to build jujube tree model. Experimental result showed that the phenotypic information of the reconstructed jujube tree and the real jujube tree have a high similarity, and their determination coefficient R² reach to 0.984. Moreover, the natural frequencies of jujube tree are analyzed by modal analysis, transient analysis is applied to analyze vibration transfer characteristics. The simulation and experimental results show that the optimal vibration frequency range of jujube tree is 25∼30 Hz, the optimal vibration excitation location is on the main trunk and as high as possible close to the secondary branches, which can obtain maximum vibration response for optimum harvesting efficiency. The average determination coefficient is 0.66 between test and simulation results at different frequencies. This study can provide references for accurate 3D modeling of jujube trees, selection of appropriate vibration parameter range and the development of jujube harvesting machinery.
Natural frequency identification model based on BP neural network for Camellia oleifera fruit harvesting
2024, Biosystems Engineering
Vibratory harvesting is an important means of mechanically harvesting tree fruit. The optimal excitation parameters are usually experimentally determined under complex conditions with different environments and machine configurations. Optimisation methods include tree modelling and dynamic analysis but experimental validation can take much time due to the complexity of tree structure and properties. A simple and appropriate identification model that could identify the natural frequencies of trees might simplify the process and promote the technology. A natural frequency identification model is proposed based on back propagation (BP) neural network to identifying the natural frequency of the tree based on its structure. Taking Camellia oleifera tree with its upright canopy as an example, the excitation parameters that can achieve better harvesting of fruit was determined here by orthogonal test. A dynamic model was established, and the tree structure variables were derived as the input layer of the model. The dataset of tree dynamics was established by finite element analysis and the effective natural frequency region was set as the model output layer. A natural frequency identification model was established based on TensorFlow, where the input and output parameters are fitted using a BP neural network. Application of the model was carried out after substantial training and testing. In the range of natural frequencies 6-7Hz, the mean square error between the natural frequency identification value and the measured value was only 0.0408, which verified the reliability of the model.
Experiment and analysis on walnut (Juglans regia L.) shedding force based on low-frequency vibration response
2023, Industrial Crops and Products
Walnut (Juglans regia L.) is a highly valuable crop and is widely used as a food, medicine, and industrial product. Studying walnut detachment force is an important prerequisite for bed harvesting through low-frequency shaking. In this study, the stalk–branch and stalk–fruit kinetic models were analyzed under different vibration modes by establishing a local vibration model. A platform was built to conduct tests of static separation force separately for different modes. The inertial force and static separation force of the vibration response were analyzed by combining each vibration parameter with the local fruit–stalk–branch vibration model, and the separation ratios were derived under different vibration parameters. In the vibration response with a frequency of 10 Hz and amplitude of 80 mm, the maximum separation ratios of inertial tensions at connection points between the branch and stalk, stalk and tail fruit, and stalk and side fruit were 0, 25.5%, and 26.3%, respectively; the maximum separation ratios of the inertial bending moment were 86.4%, 96%, and 83%, respectively; and the detachment difficulty coefficient of the motion mode generating inertial bending moments was much lower than that of the mode generating inertial tensions. The relationship between the separation force and biological characteristics was analyzed, and field vibration tests were conducted to verify the separation force tests. The results of the study can guide development and adjustment of vibration parameters of a vibrating device for harvesting and help further study of the effect of excitation mode on fruit shedding.
Effect of leaves in the dynamic response of olive tree branches and their computational model
2022, Computers and Electronics in Agriculture
Citation Excerpt :
However, these techniques consider the global volume of the canopies and introduce a lot of information in the point clouds obtained, making it difficult to distinguish between tree structure and foliage mass. To this end, techniques based on obtaining the points on Cartesian coordinates have reported good results (Peng et al., 2017). The method used in our work, based on trilateration, allows simplification of the modelling as desired, because it takes the desired number of points and can focus exclusively on the tree structure, in this case, the branches.
The application of vibration in the mechanical harvesting of fruit trees is a determining factor to achieve fruit detachment. The acceleration required to do so is experimentally determined in expensive tests using different machines and configurations. A simple, appropriate model that could predict the vibration response of plant matter might facilitate these simulations of different conditions and optimise the process. Several mathematical and computational models exist that employ great simplifications and produce uncertain results. We propose a computational model for simulating the dynamic response of branches with and without foliage under forced vibration, applied to the case of the olive tree. We also present a method for characterising the mechanical properties necessary to conduct the simulation using commercial software, Ansys, and the experimental determination of the properties. To do so, we propose some simplifications in the modelling. Next, computational simulations replicate the same conditions as the real vibration tests conducted in the laboratory, and the accelerations produced at the origin and ends of the branches are determined. The results offer a good degree of similarity between the calculated and experimental values in terms of natural frequencies, although some dispersion of transmissibility exits between the origin and ends of the branches, above all for larger branches and when considering their foliage. Branches without leaves had lower natural frequencies. The damping coefficient of branches with leaves was almost twice than ones without although the acceleration transmissibility is much bigger.
Analysis and experimental study on vibration response characteristics of mechanical harvesting of jujube
2022, Computers and Electronics in Agriculture
Citation Excerpt :
Fig. 12 shows that the first six natural frequencies of the lateral branch and the jujube basal branch are the largest in the sections of 6 ∼ 7 Hz, 12 ∼ 13 Hz, 14 ∼ 15 Hz, 17 ∼ 18 Hz, 18 ∼ 19 Hz and 22 ∼ 23 Hz. Compared with the method of modal analysis in simulation software(Peng et al., 2017), the frequency sweep test does not need to obtain the material characteristics of jujube tree (such as stiffness parameters, mass parameters, etc) to establish an accurate simulation model, so it is simple and easy to operate. A total of 17 experimental points are estimated according to the field experiment scheme, and the error is shown in Table 5.
To explore the vibration energy transmission characteristics of mechanical harvesting of jujube and improve the effectiveness of vibration harvesting, the vibration response characteristics of small and densely planted Jun jujube branches were experimentally studied and evaluated. According to the agronomic requirements of mechanical harvesting of jujube, first, this paper analyzes the vibration harvesting mechanism of jujube, establishes the transverse bending vibration mechanical model of jujube branches, and obtains the sixth-order natural frequency of jujube branches through vibration frequency sweep experiments. Based on the slope scoring principle and response surface method, the impact of different excitation parameters on the jujube branch vibration effect evaluation index P_z was characterized through field experiments, and an optimized vibration effect score was obtained. The results showed that the low-order natural frequencies of small and densely planted jujube branches were mainly concentrated in the range of 6 ∼ 22 Hz, and the vibration response was the most intense at 17.5, 18.0 and 22.5 Hz, which was more conducive to vibration harvesting. By optimizing the relationship between the excitation parameters and evaluation index P_z, a better jujube branch vibration effect score of P_z = 85.63 is obtained, which provides a reference for the design and development of high-efficiency jujube vibration harvesting devices.
Optimal vibration parameters for olive harvesting from finite element analysis and vibration tests
2022, Biosystems Engineering
Citation Excerpt :
Several researchers used finite element method (FEM) to simulate and optimise harvesting systems and to identify the effect of harvest parameters on the actual harvest by iterating a large number of designs in less time(Hoshyarmanesh, Dastgerdi, Ghodsi, Khandan, & Zareinia, 2017; Láng, 2008; Savary, Ehsani, Schueller, & Rajaraman, 2010; Yung & Fridley, 1975). Fu et al. (2016) analysed the vibration harvesting mechanism of sea buckthorns using the FEM while Peng, Xie, et al. (2017) analysed the response of Chinese winter jujube trees to vibration excitation using FEM and studied the relationship between these responses and the excitation frequencies in the range 5–25 Hz. Moreover, Liu, Gang, Ehsani, Toudeshki, and Wang (2018) simulated the vibration harvest of a citrus canopy using ANSYS and studied the effects of vibration frequency and penetration depth on fruit shedding.
Several vibration harvesting parameters must be obtained through experiments due to the complexity of olive branches. However, the pure test method significantly reduces the efficiency of equipment development. Therefore, in this study, we proposes a research method based on a combination of finite element simulation and vibration tests to address this problem. SolidWorks was used to establish a three-dimensional model of an olive tree including some smaller branches, The natural frequency and modal vibration modes of olive trees were determined by modal analysis. Furthermore, the vibration parameters were determined by harmonic response analysis. Then, the vibration motor was tested at five frequencies (10, 15, 20, 25, and 30 Hz), and the results were compared with the transient analysis results. The results show that the vibration response is more intense in the medium frequency range (18.66–28.96 Hz). It is inefficient and uneconomical to harvest all olives by applying force to the trunk. It is more effective to apply vibration force to the lateral branch to lessen the damage inflicted to the tree. An excitation force of 5220 N at 25 Hz to the left branch is suitable for harvesting the olive fruit. The average correlation coefficient of the maximum resultant acceleration observed in the tests and its simulated value was 0.63, indicating that the model can predict the vibration response reliably. Finally, the results of the harmonic response analysis were verified by transient analysis. This study can serve as a reference for the design of vibration harvesters.

View all citing articles on Scopus

View full text

Original papersSimulation study of vibratory harvesting of Chinese winter jujube (Zizyphus jujuba Mill. cv. Dongzao)

Highlights

Abstract

Introduction

Section snippets

Mechanical properties measurement

Mechanical properties of jujube tree

Conclusion

Acknowledgements

Biosys. Eng.

Eng. Agri. Environ. Food

Sci. Hortic.

J. Chromatogr.

Food Chem.

J. Ethnopharmacol.

Comput. Electron. Agric.

Agric. Sci. China