| With the rapid development of the oil tea industry,it is important to achieve a high picking rate while ensuring that the tree is not damaged during mechanized harvesting of oil tea fruits.In this paper,by studying and analyzing the energy transfer law and strain response on branches and fruit shedding,the best operating parameters were obtained to achieve a high picking rate while ensuring that the tree branches are within the tolerable range,and to provide some reference for the vibration harvesting parameters of oil tea fruit canopy,and the main research results are as follows.(1)The biological parameters and inherent characteristics of the oil tea fruit and tree were obtained through preliminary research measurements.The bonding force of different varieties of oil tea fruits was measured and found that the tensile force of the fruit was greater than its shear and torsional force.Through force hammer test and threepoint bending test,the intrinsic frequency,damping coefficient and flexural elastic modulus of the tree branch were obtained,and the vibration frequencies selected for the tests in this paper were determined as 3Hz,5Hz,7Hz and 9Hz,and the expression of the relationship between the elastic limit bending strain of the branch and the diameter of the branch was established to provide a reference for the study of bending deformation during the vibration of the tree.(2)The double pendulum dynamics model of fruit and branch,branch mass-springdamping model and finite element model were established according to the tree structure.The acceleration condition of shedding fruit of Changlin 4 was analyzed to be 761.9 m/s2.The calibration test of the force between the tree and the branch at different frequencies and amplitudes of the picker was conducted by matrix inversion method to determine the magnitude of the force with the branch and found that the vibration effect was better at 50,60 and 70 mm amplitude.The ANSYS transient dynamics analysis revealed that the strain on the branch near the connection point between the secondary side branch and the primary side branch where the force was applied exceeded the elastic limit at a frequency of 9 Hz.(3)The tree energy transfer and harvesting effect during vibration harvesting were simulated and analyzed.The equations of motion of the fruit and branch double pendulum model and the equations of motion of the whole tree mass-spring-damping model were combined and simulated by simulink,and it was found that the energy on the branch increased continuously with the increase of the action frequency and with the increase of the action amplitude.The energy utilization rate is set as the proportion of the trunk energy to the action branch,and it is found that the energy utilization rate increases with the increase of frequency and amplitude.Most of the fruits on the action branches could be shed smoothly at the action frequency of 7Hz amplitude 50,60,70 mm and 9Hz amplitude 50,60,70 mm,but the other hanging branches were shed less effectively.(4)The accuracy of the model was verified by using a picking machine for forest vibration harvesting tests.The oil tea tree of Changlin 4 with high fruit maturity and clear branch structure was selected,and the operating parameters of frequencies 5,7and 9 Hz and amplitudes 50,60 and 70 mm were chosen for vibration tests according to the simulation results.The 16 measuring points on the tree were set up with sensors,the fruit shedding situation was counted and the relationship between the elastic limit bending strain and branch diameter was established,and it was found that the energy transfer law of the branch,the fruit shedding situation and the bending strain of the branch were consistent with the simulation results.The optimal vibration operation parameters of oil tea fruit canopy were obtained by combining the energy utilization efficiency,fruit shedding rate and branch strain,and the frequency of 7Hz and amplitude of 70 mm. |
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