多自由度振动气吸盘式水稻田间育秧精密播种机理研究

With the gradual increasing of planting area of high-yielding rice, the improvement of field seedling technology and the popularization of transplanters in our county, existing rice field seeders still can not meet the requirement of seed sowing accuracy of 1-2 seeds per hole. Based on the analysis of the field sowing conditions and the problems exposed during the preliminary tests, this project proposes to carry out the research on mechanism of precision seeder which is mainly composed of a multi-freedom vibration seeds tray and a vacuum plate for hybrid rice seedling in field. According to the structural of germinated rice seeds, a multi-layer composite model composed of glume, bud and brown rice, is developed. Considering the interference factors and the time-varying working status in field, the vibro-fluidization and discrete motion law of seeds under the excitation of a multi-freedom vibration seeds tray are anlyzed. By monitoring the motion state of seeds in real-time, a feedback control strategy for optimum adjustment the vibration parameters of tray is presented to promote seeds uniform movement in the tray. Then, the sowing dynamics process is calculated by considering the coupling effect of disrrete seeds and suction flow field. Taking the effect of seeds thickness, discrete distribution status and nozzle structure and operating differential pressure into comprehensive consideration, the sowing performance of seeder is analyzed, structure and operating parameters of the seeder are optimum designed. The research achievements are beneficial to provide a theoretical basis for the development of a precision seeder for rice field seedling, and also have important academic value and broad application prospect.

随着我国高产水稻种植的推广、田间育秧和机械化插秧技术的普及，现有的水稻育秧播种机尚不能满足1-2粒/穴的要求。分析田间播种工况的特点和前期工作所暴露的问题，本项目拟开展由多自由度振动种盘和负压吸盘构成的水稻田间育秧精密播种机构的工作机理研究。根据催芽后稻种的结构形态，建立由颖壳、糙米、嫩芽组成的多层复合结构种子力学模型；针对田间播种干扰因素多、工作状态时变的特点，研究种群在多自由度振动种盘激振下的流化和离散分层运动规律，并通过实时监测种群的运动状态，提出种盘振动参数的反馈控制策略，解决种群在种盘内均匀离散的难题；分析离散运动种群与气流场的耦合作用，计算吸排种动力学过程，从种群层厚、离散运动状态、吸孔结构和工作压差等多方面综合分析排种器作业性能，优化排种器结构和田间工作参数。研究成果可以为水稻田间育秧精密播种机的设计提供理论基础，具有重要的学术价值和应用前景。

项目针对实际工况时变、干扰因素多，现有排种器尚不能满足超级稻精密育秧播种的问题，提出从新机构设计、种群振动运动规律、分布状态监测、吸排种动力学过程等方面开展盘吸式排种器工作机理和作业性能研究。. 排种器种盘可以实现直线往复和两自由度水平转动合成的三自由度运动，吸盘可以水平、垂直移动和正负气压转换以完成吸排种过程。.根据水稻籽粒特性建立了三轴椭球体模型，采用离散元法模拟了种群在振动种盘内的运动过程。分析了种群冲击力特征，提出以悬臂梁称重传感器为测量器件，并设计了差动和均值两种信号处理电路，实现了振动状态下种群质量的实时监测，测量的非线性误差小于2.5%和5.5%；提出通过监测种盘底面不同区域的种群质量，平面拟合获取种群整体分布状态的方法，不同参数下的拟合面法向量角和转轴夹角与实际情况的平均误差小于5%；种群流动过程中的质心位移可以用指数函数表示，流动速度随振动频率、振幅和转角的增加而增大，随种群层厚的增加而减小。. 建立了排种器气流流道的三维模型，分析了压差、吸孔直径、内腔高度对气流速度和差异性的影响，计算了籽粒在吸种气流场中的受力，得到吸盘内腔高度大于50mm时，吸盘面板上的吸孔具有均匀的吸种能力，籽粒受力差异小于4%，有利于提高排种器的吸种精度。. 采用气固耦合法分析了吸排种动力学过程，得到吸孔直径2、2.5mm、负压差6、4kPa时，籽粒可以被有效吸附，控制合适的吸种位置是提高吸种性能的关键环节；籽粒在正压作用下的排种轨迹存在水平位移，为了保证籽粒准确落入相应的穴孔，排种口与育苗盘距离应控制在15mm以内。. 以种群分布拟合面法向量为输入参数，通过PLC模糊控制种盘振动方向角，可以促进种群在振动种盘内的均匀离散分布。对播种正交试验结果进行多目标优化，得到理想工作参数为：负压差4.2kPa、吸孔孔径2.5mm、振动频率10.4Hz、振幅4.0mm、吸种距离24mm，1-2粒/穴的播种率均超过97.5%，排种器对不同品种超级稻芽种具有很好的适应性。