基于恒力机构的香蕉落梳装置设计与自适应性分析
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国家自然科学基金项目(51675189)、现代农业产业技术体系建设专项资金项目(CARS-31)和广东省现代农业产业技术体系创新团队项目(2017LM2153)


Design and Analysis of Self-adaptability in Banana Crown-cutting Device Based on Constant-force Mechanism
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    摘要:

    针对香蕉机械化落梳过程中出现的自适应性差的问题,设计了基于恒力机构的可自适应环抱蕉茎插切式香蕉落梳装置,并对落梳装置的径向自适应性和转动自适应性进行了分析。采用两斜置压缩弹簧的结构,引入负刚度,再与正刚度的水平压缩弹簧并联组成恒力机构,提高了落梳刀具组对果轴粗细的径向自适应性,对恒力机构的力-位移特性曲线和刚度-位移特性曲线进行分析,并优选关键参数,得出斜置压缩弹簧的刚度系数k1=12N/mm,水平压缩弹簧的刚度系数k2=3N/mm,初始状态斜置压簧的倾斜角θ0=36.87°,恒力行程对应的落梳刀组包络圆直径范围为80~100mm,对应的恒力f=180N。在加载有扭簧的虎克铰链基础上设计了可释放两个转动自由度的落梳刀盘,根据测定的香蕉果轴弯曲度设置刀盘旋转角范围为±10°,根据建立的三维模型中的几何参数得出,落梳刀具末端的工作空间是一个半径为300mm的球面。对落梳刀具末端的柔度矩阵进行分析,结果显示,落梳刀盘旋转角为0°,即刀盘与机架上底面平行时线柔度最大,最大值为0.8182mm/N,落梳刀盘旋转角为10°时线柔度最小,最小值为0.77mm/N,说明落梳刀具末端的线柔度随刀盘旋转角的增大而减小。试验结果表明,梳柄切口符合试验指标的蕉梳占所有样本的81.25%,切口质量良好,该装置设计合理,且满足实际落梳作业的要求。

    Abstract:

    Aiming to solve the problem of poor adaptability in the process of mechanized banana crown-cutting, an adaptable banana crown-cutting device by stalk-surrounding and insert-cutting was designed, which was based on constant-force mechanism, and the radial adaptability and rotational adaptability of banana crown-cutting device were analyzed. A constant-force mechanism was introduced in the device, including two oblique compression springs provided negative stiffness and one horizontal compression spring provided positive stiffness, which enhanced the radial adaptability of the device. The force-displacement characteristic curves and stiffness-displacement characteristic curves of the constant-force mechanism were analyzed and the key parameters were also optimized. The stiffness coefficient of oblique spring in the constant-force mechanism was 12N/mm and the stiffness coefficient of horizontal spring was 3N/mm. In the initial state, the inclination angle of the oblique spring was 36.87°. The diameter of the enveloping circle was 80~100mm when the device was in constant force state, meanwhile, the constant force was 180N. Based on the Hooke hinge, reversible cutting platforms that can release two free rotational degrees were designed. The cutting platforms’ rotational angle was set as ±10°, according to the curvature of banana stalks. According to the geometric parameters of the established 3D model, the working space at the end of the cutter was a spherical surface with a radius of 300mm. The flexibility matrix of the cutter-end was analyzed. The result showed that when the rotational angle of the cutting platform was 0°, the flexibility of the cutter-end was the largest and the maximum value was 0.8182mm/N,and when the rotational angle of the cutting platform was 10°, the flexibility of the cutter-end was the smallest and the minimum value was 0.77mm/N. The results showed that the flexibility of the cutter-end was decreased gradually when the cutting platforms’ reversal angle became bigger. The tests showed that 81.25% of samples fulfilled requirements, the quality of the incisions were good. The machine, which was reasonably designed, fulfilled the requirements of banana crown-cutting.

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杨洲,郭杰,金莫辉,段洁利,付函,许泽宇.基于恒力机构的香蕉落梳装置设计与自适应性分析[J].农业机械学报,2019,50(6):148-155.

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  • 收稿日期:2018-11-19
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  • 在线发布日期: 2019-06-10
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