| China is the world’s largest producer of litchi,in which the planting area and output accounted for about 80% and 75% of the world.Since the orchard machinery research in C hina started late,the orchard mechanization level is low,and litchi picking operation is not well to achieve mechanization and automation operations.According to the existing problems of picking operation,a combing type litchi picking mechanism was designed to improve picking efficiency and reduce picking cost.1)The dynamic characteristics of vibrational harvesting for the litchi fruit trees were studied,and the transmission law of the vibration energy in the litchi branch was obtained,which provided the design basis for the excitation mode and structure selection of the picking machine.The experimental results show that the amplitude of vibration acceleration in X and Y directions increases with the increase of excitation frequency,and the amplitude of vibration acceleration in Y direction is less than that in X direction when the frequency is lower than 20 Hz.But when the frequencyis at 25~50Hz,the vibration acceleration amplitude in Y direction is greater than the X direction,and the maximum value is greater than that in X direction.The four transmission paths,the vibration transmission ratio in the X and Y directions of each measuring point increases first and then decreases along the direction of the transmission path,and the vibration acceleration ratio is smaller at the position closest to the end of the path.When the excitation point was in the trunk,it can be found that the energy delivered to the litchi crown is very small and it is difficult to achieve the separation force required for the separation of litchi.When the excitation point was near the branch of the canopy,the acceleration point of the branch near the crown position is larger,but the acceleration of the other points near the crown position is smaller.2)Based on the study of the mechanism of fruit vibration picking,the dynamic equation of excitation system is deduced,and the reference value of the amplitude and angular velocity of the exciter is obtained.According to the understanding of the present situation of litchi orchard cultivation,some design requirements of picking machine were put forward.According to the design requirements,the parameters of the eccentric mechanism of the core components and the arrangement of the comb mechanism were determined,and carried on the trial production to the machine.When the prototype was completed,use the high-speed camera on the litchi picking process to captured the statistical flow of litchi during the collision,analysis of the relationship between the location of fruit and the shedding time.3)The effects of vibration frequency,the distance between the upper comb row and the swing angle of the lower comb on the picking efficiency and damage rate of litchi were analyzed by single factor and orthogonal test,and the optimal combination parameters were determined.Through the analysis of the test results,found that when the eccentric wheel speed is at 23.33 Hz,the upper comb spacing is at 15 mm,the lower comb swing angle is at 30°,the litchi breaking rate is the lowest,and the row swing angle has a significant effect on the picking efficiency.When the eccentric wheel speed is at 26.67 Hz,the distance between the upper comb row is at 15 mm,the rotation angle of the lower comb is at 50°,the picking efficiency is the highest and the breakage rate of litchi is at 7.18%.4)The harvest quality test was conducted by p ut the mechanical vibration harvest and artificial picking litchi in the same test environment for 8 days,every two days to detect a litchi quality parameters to determine whether the mechanical picking have an impacton litchi quality.The results of the experimental analysis showed that there was no significant difference in the quality of litchi from mechanical picking group and artificial picking group,which satisfied the requirement of sales and transportation of litchi. |
