基于空间轨迹的行星轮系移栽机构设计方法研究

Design Method of Transplanting Mechanism of Planetary Gear Train Based on Spatial Trajectory

摘要:

为使行星轮系移栽机构能够实现复杂空间轨迹、更好地满足水稻宽窄行钵苗移栽的农艺要求，提出一种基于一般空间连续封闭轨迹的不等速行星轮系移栽机构逆向设计方法。首先，将行星轮系移栽机构简化为空间开链三杆二自由度（2R）机构，以3次非均匀B样条曲线拟合的理想轨迹曲线为约束，建立空间开链2R机构运动学模型，分析其末端轨迹形成机理，利用空间几何关系求解机构的杆长和输出轴的相对位置；然后，由输入与输出轴间的相对角位移关系得到轮系机构的总传动比，通过依附不等速齿轮副缩减开链机构自由度，并根据齿轮副组合类型进行传动比分配与非圆齿轮节曲线的设计。在应用实例中，基于空间“8”字形移栽轨迹设计了一种由平面非圆齿轮与圆锥齿轮组合传动的水稻钵苗宽窄行移栽机构，并进行了虚拟样机仿真与物理样机试验，结果表明：仿真轨迹、样机测试轨迹与拟合轨迹基本一致，验证了理论方法的正确性和可行性。

关键词:水稻钵苗;宽窄行移栽;行星轮系;逆向设计;空间轨迹

Abstract:

A reverse design method for transplanting mechanism of unequal speed planetary gear train based on general spatial continuous closed trajectory was proposed in order to make the planetary gear train transplanting mechanism achieve a complex spatial trajectory and better meet the agronomic requirements for transplanting rice seedlings in wide and narrow rows. First of all, the planetary gear train transplanting mechanism was simplified as a spatial three-bar two-degree-of-freedom (2R) open-loop mechanism, and the ideal transplanting trajectory curve fitted by the cubic non-uniform B-spline curve was used as a constraint to establish a spatial 2R mechanism kinematics model, the formation mechanism of the terminal trajectory was analyzed, the rod length and the relative position relationship between the rotation axis of the mechanism were solved by using the spatial geometric relationship. Secondly, the total transmission ratio of the planetary gear train mechanism was obtained from the relative angular displacement relationship between the input and output axes. The degrees of freedom of the spatial 2R mechanism were reduced by attaching to the unequal speed gear pair. The transmission ratio distribution and the pitch curve of the non-circular gear were designed according to the combination type of the gear pair. Finally, based on the spatial “8” shaped transplanting trajectory, a transplanting mechanism of rice seedling with wide and narrow rows driven by plane non-circular gear and bevel gear was designed in the application example, and the virtual prototype simulation and physical prototype test were carried out. The results showed that the simulation trajectory and test trajectory were basically consistent with the given trajectory, which verified the correctness and feasibility of the theoretical method.

Key words:rice pot seedling;wide-narrow-row transplanting;planetary gear train;reverse design;spatial trajectory