南疆落地红枣捡拾机构的机理分析及参数优化研究

Jujube is the second largest crop in Xinjiang, and its harvesting method relies on artificially picking up those knocked and naturally fallen jujubes. A parallel-type crank-rocker pick-up mechanism was proposed in this research, which can implement the action of picking up the jujubes on the ground and retroject them continuously. Moreover, the mechanism of picking up will be studied and the parameters of the mechanism will be optimized. Establishing the equation of similar trochoidal trajectory (composite trajectory of connecting rod working point motion and machine forward motion ) to explore the influence law of parameters of the crank rocker mechanism and the speed of the machine on similar trochoidal trajectory. The ideal working curve segment of single mechanism will be obtained in order to ensure the picking up and tossing back effect of the landing jujubes. To study the conditions of continuous tossing back for jujubes in a parallel crank rocker mechanism, and analyze the influence law of the number of single mechanisms, the phase difference, and the hinge position of the rocker arm and the frame on the complementary characteristics of the working curve. Obtaining the working curve of the parallel mechanism and determining the its parameters, and ensuring that the movement trajectory of the working point of each connecting rod is consistent with the ideal working curve to achieve continuous tossing back of the materials. Moreover, studying the dynamic characteristics of the parallel mechanism and its coupled system with jujubes to improve the dynamic characteristics of the mechanism, and to optimize the connecting rod configuration and the working parameters of the mechanism. The model will be revised based on experimental studies. This research results will lay theoretical basis for pickup mechanization of the landing jujubes, and also can provide a reference for the study of citrus, walnuts and other similar material pick up mechanism.

红枣是新疆第二大农作物，其采收方式是将自然脱落或敲落的红枣依靠人工进行捡拾。项目提出一种可实现对落地枣挑起并持续后抛的并联式曲柄摇杆捡拾机构，并开展捡拾机理研究与机构参数优化。首先建立类余摆线轨迹（连杆工作点运动与机具前进运动的复合轨迹）方程，探索曲柄摇杆机构参数、机具前进速度对类余摆线轨迹的影响规律，获取单组机构工作行程理想曲线段，确保落地枣的挑起与后抛效果；研究并联式曲柄摇杆机构持续后抛的条件，分析单组机构组数、相位差及摇杆与机架的铰接位置对工作曲线互补特性的影响规律，获取并联机构工作曲线，确定并联机构参数，确保各连杆工作点运动轨迹与理想工作曲线吻合，实现物料的持续后抛动作；研究并联机构及其与红枣耦合系统的动力学特性，改善机构动态特性，优化连杆构型与机构工作参数，进行试验研究并修正模型。研究成果可为落地枣机械化捡拾奠定理论基础，还可为核桃、柑橘等类似物料捡拾机构的研究提供参考。

红枣是药食同源食物，营养丰富还具有医疗和保健作用。我国是红枣的主产区。新疆南部塔克拉玛干沙漠周边已成为我国红枣主要种植区域。目前，红枣主要采取人工捡拾收获，劳动强度大，效率低，且收获期劳力紧张，雇工成本高，亟需实现红枣的机械化采收。本研究搭建了曲柄摇杆式落地枣挑抛捡拾机构高速摄像试验平台，分析了曲柄摇杆式红枣挑抛捡拾机理及红枣机械损伤机理，确定了捡拾机构最优参数。.项目组分析了落地红枣与作业园区表层土壤物料特性，分别获取了基本物理特性参数，同时研究了物料颗粒间及其与接触材料间的力学特性，并构建了响应关系模型，最终构建了红枣及土壤的离散元仿真模型。.项目组建立了挑抛捡拾机构工作轨迹运动学模型，研究了机构参数对轨迹的影响规律。建立了机构参数优化数学模型，利用MATLAB软件优化获得较优参数组合，并利用高速摄像台架试验进行轨迹验证。结果表明，曲柄转速为60 r/min、机具前进速度为150 mm/s时，能实现红枣捡拾的捡起和抛送。.项目组搭建了挑抛式落地枣捡拾高速摄像试验平台并进行了挑抛捡拾试验，分析了红枣挑抛捡拾过程及红枣运动特性。明确了捡拾过程分为入土、捡拾升运、抛送及返回四个工作行程段，建立了捡拾过程红枣运动模型，分析确定各行程段起始位置及运动学特性。分析了关键因素对红枣水平、数值位移及抛离速度的影响规律。.项目组基于能量平衡原理对挑果杆与红枣的接触碰撞进行了分析，明确红枣挑抛捡拾损伤机理。对红枣整果进行静态压缩试验，得到红枣损伤的临界受载力为204.5N、114.9N。基于Hertz理论对红枣与捡拾齿接触碰撞力学特性进行分析，得到红枣损伤临界速度值约为5.48 m/s。.项目组利用多体动力学软件ADAMS与离散元软件EDEM联合仿真，构建了机构-土壤-红枣系统仿真模型，对并联式捡拾装置工作过程进行了仿真分析，获取了不同构型的捡拾齿作用下红枣与土壤的运移规律，结果表明，该装置可实现落地枣的连续捡拾与交替后抛输送。