不同激振方式下枸杞振动采摘仿真与试验

    Optimizing parameters for vibration harvesting of Lycium barbarum L. under various excitation modes

    • 摘要: 为实现枸杞摘熟留青,高效采收,根据枸杞无限花序特点和果-花-叶脱落加速度分布顺序,该研究提出一种无需直接接触果实的振动采摘方法,依靠果实惯性力完成熟果采摘。根据所述采摘方法提出上下同振、上静下振和上下反振的激振方式并设计相应的采摘机,得到振动头的运动学模型,同时建立枸杞枝条和枝-柄-果的仿真模型。通过有限元瞬态动力学分析与ADAMS动力学仿真方法,得到不同激振方式下枝条的振动响应,以及果实在激振下的振动响应,以此分析果实脱落机理。仿真结果表明,不同的激振方式会影响枝条的振动响应。为获得适宜枸杞采摘的激振方式和最佳振动参数,采用三因素三水平二次正交旋转组合试验,建立了以熟果采摘率、未熟果误采率、熟果损伤率为试验指标,以振动幅度、激振方式、振动频率为试验因素的数学模型,分析各因素对各指标的影响,获得最佳参数组合:振动幅度31.13 mm、激振方式上静下振、振动频率12.59 Hz。田间试验熟果采摘率为95.14%,未熟果误采率为4.61%,熟果损伤率为2.98%。研究结果可为后续机械化采收设备的设计和试验提供参考。

       

      Abstract: Lycium barbarum L.(L. barbarum) has been one of the most favorite fruits in recent years. However, manual harvesting cannot fully meet large-scale production, as the labor force decreases. It is urgent to realize efficient harvesting by picking ripe fruits rather than unripe ones. This study aims to optimize the parameters during vibration harvesting of L. barbarum under various excitation modes. The L. barbarum fruits were also selected and measured in Ningxia in western China. The normal distribution of the detachment force and detachment acceleration were plotted after measurement. It was found that the detachment force of ripe fruits was similar to that of flowers. There were overlapping areas among the unripe fruits and leaves. By contrast, the detachment acceleration was ranked in the ascending order of the ripe fruits, unripe fruits, leaves, and flowers. Ripe fruits also presented the lowest detachment acceleration without overlapping with the rest, suitable for the vibration to harvest L. barbarum. As such, the vibration-picking was employed without touching the fruits. Only the excitation area above the ripe fruit area of the branch was excited by vibration equipment, according to the characteristic of infinite inflorescence. Furthermore, the vibration head was closer to the ripe fruit area during harvesting, particularly without colliding with the ripe fruits for less damage. Three excitation modes were proposed for the branch in the corresponding vibration equipment. The upper and lower points vibrated in the same direction (simultaneous vibration); the upper point was fixed, and the lower point made a reciprocating vibration (pendulum vibration); the upper and lower points vibrated in the opposite direction (reverse vibration). The kinematics model of the clamping head was established to simulate the branch and branch-stalk fruit. The transient analysis was implemented to obtain the vibration responses of the branch under different excitation modes. The results show that the excitation modes dominated the vibration response of the branch. Moreover, the vibration response of the fruit under excitation was acquired via kinematics simulation of ADAMS. The mechanism of fruit shedding was analyzed after simulation. The results indicate that the vibration response gradually increased from the vibration head to the selection point of the branch, and then to the fruit. The verification test showed that the average relative error of branch amplitude and fruit velocity were 23.78% and 14.01%, respectively. The vibration response of L. barbarum branch, stalk, and fruit was verified after the test. The parameter experiment was taken by the Box-Behnken test. The mathematical models were then established for the picking rate of ripe fruit, picking rate of unripe fruit, damage rate of ripe fruit and vibration amplitude, excitation mode, and vibration frequency. The influences of various factors were analyzed to determine the optimal combination of parameters: the vibration amplitude was 31.13 mm; the excitation mode was pendulum vibration, and the vibration frequency was 12.59 Hz. The experiments with the optimal parameters show that the picking rates of ripe and unripe fruit were 95.14% and 4.61%, respectively, and the damage rate of ripe fruit was 3.83%. A better performance was achieved in the pendulum vibration as the optimal excitation mode. Fruit damage was minimized due to the high picking efficiency, particularly for ripe fruits. The findings can also provide valuable insights into the mechanized harvesting equipment for L. barbarum fruits.

       

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