| Canopy shaking is currently the main mechanical harvesting method used for the large-scale continuous harvesting of fruits.The harvesting method is mainly applicable to the harvesting of vines or berries fruits used for the wine or juice industry,because the shaking system causes fruits bruises.For the mechanical harvesting of citrus in juice production,the existing canopy shaking harvesting machinery generated serious tree damage,which has a great influence on the next annual output of orchards.As a result,it is difficult to achieve large-scale popularization and application of mechanized harvesting of citrus.At present,manual picking for citrus harvesting is still the main method,which needs higher expenditure for the human labour cost,so that the mechanization of citrus harvesting is still low.Therefore,it is imperative to develop a novel canopy shaking system from the prospective of reducing tree damage.It is significant to promote the mechanization level for mechanical harvesting of citrus.On this research,‘Valencia’ orange was selected as the research object,which is widely planted in Florida(the largest citrus producing state in the United States)and used for the orange juice processing.Vibratory detachment mechanism of the citrus fruits in the vertical and horizontal direction was studied using a vibration experimental device and high-speed photography technology.The effective vibration mode of the shaking system was determined according to the shaking frequency and vibratory motion analysis of the citrus.Then,combined with the morphological characteristics of tree canopy,a kind of linked vibration mechanism based on the quick-return characteristics of crank-rocker mechanism was designed.After that,a two-section canopy shaking system was studied and developed.A virtual prototype modeling and simulation analysis of the shaking mechanism was made using virtual prototype technology.And the physical prototype was fabricated after determining the dimensions of the components.Finally,several performance experiments of the canopy shaking system under different conditions were carried out through laboratory tests and field tests,such as the vibration frequency,selection and distribution of the shaking rods,canopy vibration response,optimal frequency combination and so on.It provides a reference for the study and application of the canopy shaking harvesters.The main research contents and conclusions of this dissertation are as follows:(1)An advantageous horizontal vibratory mode for detaching citrus fruit was proposed.To explore the moving characteristics and vibratory detachment mechanism of citrus fruit along with the moving of branches made by external excitation in different direction,kinematic analysis of the citrus fruit along with branches in vertical and horizontal direction was conducted.Then,a vibratory device for simulating the citrus fruit vibration was constructed in accordance with the mode of the tree branches vibration.The acceleration and shaking frequency of the vibrating citrus fruit was tested and analysed by the acceleration measurement system.When the external excitation frequency was less than 5 Hz,the shaking frequency of citrus fruit generated by forced vibration in horizontal vibration was higher than the vertical direction,which produced higher shaking frequency under a lower externl excitation.And the vibration tracking of the citrus fruit was filmed by high speed camera,which presented the detachment process of the citrus vibration.It showed that the citrus fruit could produce more incentive vibration with external excitation frequency of 2.8 Hz in horizontal direction,which is beneficial for the detachment of citrus.(2)A two-section canopy shaking system based on crank-rocker mechanism was designed.The canopy actual height and fruit distribution thickness was measured through manual measurement,which was 1.89 m and 1.03 m,respectively.Then,on the basis of orchard investigation and canopy morphology characteristics,a novel two-section canopy shaking system was proposed.The shaking mechanism makes use of the quick-return characteristics of the crank-rocker mechanism to make the canopy shaker strike the tree canopy strongly,so as to improve the effectiveness of fruit vibration.After completing the design of the shaking mechanism,a virtual prototype model of the shaking system was established and simulated using SolidWorks and ADAMS software,respectively.Then,the physical prototype of the shaking system was manufactured according to the designed parameters.The height and width of the whole shaking system reached 2.54 m and 3 m,respectively,which satisfied the canopy adaptation and passing ability of the harvester platform.(3)The vibration performance of the shaking system was tested and analysed.The vibration acceleration and shaking frequency of the shaking system under different hydraulic motor speeds was tested and analyzed using the acceleration measurement system.Through analyzing the vibration acceleration,the adjustable shaking frequency range of the shaking system was obtained from 2.5 Hz to 6.8 Hz.In addition,bending deformation analysis and experimental studies of three kinds of shaking rod with different material or shape were conducted.The results showed that the bow-shaped flexible shaking rod had a good comprehensive performance.The amplitude of the shaking rod was from 578 mm to 630 mm when the external excitation frequency was 4.7 Hz.(4)The response relationship between tree canopy and shaking system was studied.The vibration model of main branch under external driving was established using the flexural vibration theory of beam.The deflection equation and shaking frequency formula of the main branch were deduced and analysed.Then,the acceleration change of the main branch under different external excitation was measured by the acceleration measurement system.When the main branch was driven under the external excitation frequencies gradually increased from 2.5 Hz to 4.7 Hz,the acceleration value of the smaller segment of the main branch was larger.When the external shaking frequency exceeded 4.7 Hz,the disturbance on the main branch in x,y,and z direction increased significantly and the acceleration value rose up obviously.On this moment,the fruit detachment percentage reached 86.5%.When the external excitation frequency reached 6.8 Hz,the larger external excitation has greater vibration intensity to the canopy.It indicated that the increase of shaking frequency would cause more tree damage.It means that the shaking frequency of this shaking system should not be more than 4.7 Hz during citrus harvesting.(5)Two kinds of shaking rod layout were proposed,namely staggered layout and parallel layout.The staggered layout of the shaking rod expanded the offset of 330 mm between the shaking rods,which improved the passing ability of the tree canopy during the vibration process,and obtained the fruit detachment percentage of 82.6% and tree damage rate of 5.4%.While the parallel layout of the shaking rod expanded the offset of 165 mm,which gained the fruit removal percentage of 83.5% and tree damage rate of 7.5%.It indicated that the shaking system could effectively reduce tree damage using 4&5 staggered layout and achieve higher fruit removal percentage.(6)The fruit removal percentage and tree damage rate under different shaking frequencies and driving speeds were evaluated through field trials.The results showed that the shaking system stroke the tree canopy with a lower vibration frequency range from 3.3 Hz to 3.6 Hz,which produced a similar low tree damage rate and fruit removal percentage.When the shaking system stroke the tree canopy at high shaking frequency of 6.8 Hz and low driving speed of 1 km/h,the high fruit removal percentage could be achieved,up to 89.3%,but it also caused higher tree damage rate about 15.3%.Analysing the fruit removal percentage and tree damage rate integrated with the shaking frequencies and driving speeds,the better harvest performance could be obtained when the shaking system was operating with driving speed of 3 km/h and shaking frequency of 4.7 Hz,the fruit removal percentage and tree damage rate were 82.6% and 5.4%,respectively.Its harvesting efficiency was up to 360 ~ 500 trees per hou.(7)The upper and lower shaking system employing different combined frequencies for canopy shaking harvesting was proposed.The harvesting tests with seven groups of shaking frequency combination was carried out.The results showed that the tree damage rate was relatively lower when the shaking frequency of the upper shaking system was higher than that of bottom shaking system.It indicated that the upper and lower shaking system with higher and lower combined frequencies could reduce tree damage.The optimal combined shaking frequency of this canopy shaking system was 4.7&4.1 Hz,and the corresponding fruit removal percentage and tree damage rate were 82.5% and 3.9%,respectively. |
PDF Full Text Request