Abstract:
Abstract: In order to study the transient response state and movement state of apricot fruit during different stages of exfoliation, a dynamic model of apricot fruit-fruit branch double pendulum hanging on a single long stem branch according to the actual growth of apricot fruit was established in this paper. The apricot fruit-stem separation conditions were analyzed theoretically, and the physical parameters of Kumai apricot fruit at ripening stage were measured. The whole forced vibration process of the target fruitS was recorded by using 2 high-speed cameras with same specifications perpendicular to the xoz plane and the yoz plane, and the relevant datas such as shedding time, speed, and acceleration were obtained. Theoretical analysis and experiments showed that the apricot fruit-fruit branch double pendulum system mainly shows 3 kinds of motion states: fruit branch drives fruit to swing, fruit branch drives fruit to twist and fruit swing. The average weight of the ripe fruit of Kumari apricot was 14.26 g, the average external dimensions were 28.84 mm in length, 27.93 mm in width, and 27.83 mm in thickness; the average surface hardness of mature fruit was 9.17 kg/cm2; and the average connection force of ripe fruit-stem is 2.923 N. Based on the measured spatial coordinates of the fruit in the xoz and yoz planes and Phantom Camera Control 3.1 high-speed video control software analysis, the whole spatial motion track of apricot fruit is nearly elliptical from vibration to shedding, the total time from vibration to shedding of target fruit was 0.322 s, and the maximum speed of the relative static origin of apricot fruit was 0.112 and 0.166 m/s when be dropped in spatial planes xoz and yoz. The instantaneous speed of the apricot fruit before shedding was 1.53 and 1.359 m/s, respectively, and the acceleration was 765 and 679.98 m/s2, respectively. Using MATLAB software, the velocity data of fruit in different planes xoz and yoz were compared with the Fourier fitting curves of velocity and time relative to stationary origin, and the fitting curve of the speed of apricot fruit during vibration shedding and the corresponding function were obtained. R2 value of the fitting function were 0.970 4 and 0.986. Through analyzing the speed function curve, the process of fruit vibration shedding could be divided into 3 periods: 0 to 0.148 s, 0.148 to 0.248 s, and 0.248 to 0.322 s. In the third stage, the fruit has already fallen off before it reaches the full cycle. To ensure the accuracy of the analysis, the analysis of the velocity function in the first 2 stages with complete vibration period showed that: in the xoz plane, the velocity fitting function R2 of the first 2 stages are 0.965 2 and 0.952 5, respectively, the speed change period is 0.15 s and the function amplitude is 0.021 m/s; the velocity fitting function R2 in the first 2 stages of the yoz plane is 0.954 5 and 0.981 1, respectively, and the speed change period is 0.13 s, the amplitude of the second stage function is twice that of the first stage, which is 0.054 and 0.027 m/s, respectively. The vibration cycle of the apricot fruit-fruit branch double pendulum system is close to the period of the excitation cycle. According to the calculation of the fruit weight of mature apricot, the shedding force components produced by acceleration on each plane were 11.22 and 9.7 N respectively, both of which were greater than the average connected force between mature apricot fruit and stalk. Based on the above characteristics of fruit vibratory shedding, this study can provide a theoretical basis for clarifying the shedding mechanism during fruit harvesting, optimizing the design parameters of apricot vibrating harvester, and improving the fruit recovery rate.