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多子芋收获机柔性挡板式输送分离装置设计与试验

Design and experiment of the flexible baffle-type conveying and separating device for multiple taro harvesting machine

  • 摘要: 针对传统杆条式升运链输送多子芋时存在根土复合体翻滚回落、输送效率低和芋头破损率高的问题,该研究设计了一种柔性挡板式输送分离装置,通过分析柔性挡板对根土复合体的碰撞解聚特性与抛送作用,明确了影响输送分离性能的主要因素;采用离散元-有限元-多体动力学(DEM-FEM-MBD)三元耦合方法开展单因素仿真试验,结果表明柔性挡板可有效防止根土复合体翻滚回落,对芋头的最大冲击力较刚性挡板降低55.66%,结合根土复合体尺寸与输送稳定性需求,确定柔性挡板间距为300 mm,开展网格收敛性验证,确定柔性挡板网格尺寸为4 mm。通过Box-Behnken响应面台架试验,探究了输送筛面倾角、升运线速度和抖动轮频率对芋头平均输送时间与土壤筛分率的影响规律,经多目标优化得到最优参数组合为:输送筛面倾角18°、升运线速度0.62 m/s、抖动轮频率2 Hz时,土壤筛分率为88.76%,芋头输送时间为1.91 s,台架试验与仿真试验的土壤筛分率和芋头输送时间相对误差分别为0.20%和3.08%,验证了耦合模型的可靠性。田间验证结果显示,与传统杆条式输送分离装置相比,柔性挡板式输送分离装置土壤筛分率和输送成功率分别提升4.72和26.67个百分点,芋头破损率和收获损失率分别降低12.11和0.97个百分点,满足多子芋输送分离作业要求。研究结果可为芋头等根茎类作物高效低损收获装备优化设计提供参考。

     

    Abstract: Taro is one of the three major export specialty aquatic vegetables in China (along with lotus root and water chestnut). It can play an important role in the national strategy of rural revitalization. However, the current taro harvesting can rely mainly on manual labor, with the labor cost accounting for 40% to 50%. Mechanical harvesting has been confined to the conical spherical root-soil composite structure under a wet and sticky soil environment. The root system is also entangled and adheres to the soil during harvesting. It is then difficult to separate the taro from the soil. At the same time, it is prone to mechanical damage when subjected to impact, due mainly to the high moisture content (as high as 73.70%) of taro during harvesting. Therefore, it is urgent to explore the root-stem soil separation and the optimal separation mode of transportation in the current mechanical harvesting of taro. Particularly, the traditional rod-bar lifting chain can also be limited to the transport problems, such as the root-soil composite body rolling back and falling, low transportation efficiency, and high damage rate of taro. In this study, a flexible baffle-type device was designed for the taro transportation separation. The device was composed of rods, rubber baffles, vibrating wheels, frames, and chain drives. The collision dynamics were also analyzed on the disintegration and throwing of the flexible baffle on the root-soil composite body. The influencing factors on the transportation separation performance were identified as the height of the flexible baffle, the lifting line speed, the inclination angle of the screen surface, the vibration frequency, and the amplitude of the vibrating wheel. Discrete element method - finite element method - multi-body dynamics (DEM-FEM-MBD) were combined to determine the effects of the factors on the average transportation time and soil screening rate of taro. A series of experiments was finally carried out using a single-factor simulation. The results showed that the flexible baffle effectively prevented the root-soil composite body from rolling back. The maximum impact force of the flexible baffle on the taro was 55.66% lower than that of the rigid ones. The spacing of the flexible baffle was determined to be 300mm. The mesh size of the flexible baffle was determined to be 4mm using grid convergence. The relative error between the fitting curve and the physical experiment was 1.78%. A Box-Behnken response surface bench test was carried out to explore the influence of the transportation screen inclination angle, lifting line speed, and vibrating wheel frequency on the average transportation time and soil screening rate of taro. An optimal combination of the parameters was determined after multi-objective optimization: A transportation screen inclination angle of 18°, a lifting line speed of 0.62 m/s, and a vibrating wheel frequency of 2 Hz. The soil screening rate was 88.76%, and the taro transportation time was 1.91 s. The relative errors between the coupled simulation and the bench tests were 0.20% and 3.08%, respectively, which verified the reliability of the coupled model. Field verification showed that the soil screening rate and transportation success rate increased by 4.72 and 26.67 percentage points, respectively, in the flexible baffle-type transportation separation device. While the damage rate and harvest loss rate of taro were reduced by 12.11 and 0.97 percentage points, respectively. The separation and harvest quality of the flexible baffle-type transportation separation device were superior to those of the traditional rod-bar ones, fully meeting the requirements of the multi-sub-taro harvesting. The findings can also provide a strong reference to optimize the efficient and low-loss harvester for the taro, root, and tuber crops.

     

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