基于高速摄影的冬枣果实振动脱落规律分析

为研究冬枣振动采收过程中果实的运动规律和脱落轨迹,采用改装的电动往复锯连接自制振动采摘头对树枝进行高速振动,用高速相机记录不同振动频率(15、20、25 Hz)下冬枣果实的运动轨迹,对高速视频进行分析,计算在振动过程中的枣果脱落类型、脱落时间和运动轨迹,以及果实脱落时的速度、加速度和惯性力。结果表明:1)冬枣果实的主要脱落类型是旋倾型,15、20和25Hz时,旋倾型脱落的果实个数比例分别为81%、66%和78%,参考已有研究经验,冬枣机械收获宜选用连续式振动设备;2)随着振动频率的增大,果实的平均脱落时间减小,3个频率的果实脱落时间分别为1.71、0.54和0.43s,15Hz时果实脱落时间与20和25Hz时的果实脱落时间存在显著性差异,而20与25Hz时的果实脱落时间无显著性差异;3)果实的速度和加速度随着振动频率的增大而增大,但不同频率的果实平均脱落惯性力不存在显著性差异,3个频率下分别为0.48、0.43和0.49N。本研究结果可为机械收获装备的设计选型与研发提供理论依据。

Analysis of winter jujube fruit motion in vibration harvesting based on high-speed videos

Winter jujube fruit (WJF) is rich in nutrition,but its harvesting is labor-intensive.Therefore,it is necessary to study the mechanical harvesting of WJF.This study focused on the evaluation of the effect of different vibration frequencies on fruit motion,detaching time and detachment force during mechanical WJF harvesting with a shaker.The shaker was modified from a jigsaw by replacing its saw with a vibrating head.A high-speed camera in 750 fps was used to capture the fruit trajectory on 15 branches excited at the frequencies of 15,20 and 25 Hz.The fruit detaching time,motion patterns,acceleration and inertial force of fruit detaching from limbs were extracted from the high-speed videos.The results showed that the majority of the three identified motion patterns were tilting,column,and beam-column.The tilting motion were accounting for 81%,66% and 78% of all the motion patterns at 15,20 and 25 Hz,respectively.A continuous shaker thus could be used for mechanical harvesting of WJF.Fruit detaching times were significantly affected by the vibration frequency with fruits being fast detached at high frequencies,and their values at the three frequencies were 1.71,0.54 and 0.43 s,respectively.The fruit detaching time at 15 Hz was significantly different from that those at 20 Hz and 25 Hz,whereas there was no significant difference in fruit detaching time between 20 Hz and 25 Hz.The velocity and acceleration of WJF were increased with the increasing of vibration frequency,but the average inertial force of fruit detachment changed less.The detaching force of white ripe WJF was less than that of crisp ripe WJF.In conclusion,higher frequency generates high harvest efficiency,but when the frequency reached a certain value,the increase of frequency had less effect on the detaching time of fruit,and frequency also has little effect on inertia force of fruit detachment.Overall,the results indicate that 20 Hz might be the optimal vibrating frequency and it was possible to selectively harvest the crisp ripe fruit.