【作者】 许红；

【导师】 朱群雄； 吴大鸣；

【作者基本信息】 北京化工大学 ， 控制理论及控制工程， 2012， 博士

【摘要】 在聚合物精密注塑成型过程中，由喷嘴注射出的聚合物熔体重量能否实现精确可控，是影响精密注塑制品的重量重复精度的直接因素。基于注射过程中聚合物熔体密度随着过程状态变量压力、温度变化的特性，传统体积控制方法无法实现注射重量的一致性控制，而基于熔体密度在线测量的注射重量控制是解决这一问题的较好方法。本文对聚合物熔体关键参数，熔体密度及熔体体积弹性模量的软测量方法进行了研究；提出了基于超声波速度单值变量的熔体密度软测量模型，利用超声波传播速度对介质密度的依赖性及快速响应性，较好地满足了成型周期短、注射压力多级变化的聚合物熔体密度的在线测量。主要工作内容如下：1、在综合分析国内外超声波技术在液体介质、固体介质密度在线测量及聚合物加工领域应用基础上，对基于透射模式超声波实时测量聚合物熔体密度存在的单值性和快速响应性进行系统的理论研究，提出了应用超声波技术实现聚合物熔体注射成型过程中熔体密度的在线测量。2、对影响聚合物熔体密度变量的相关易测变量的测量响应速度进行了研究，从机理建模和统计建模两方面，确定适应于聚合物熔体密度及聚合物熔体体积弹性模量的软测量建模方法。3、构建了基于超声波速度的熔体密度软测量模型所需的实验装置，研制能够模拟注射过程聚合物熔体过程状态变化的实验装置，对聚合物熔体物性关键参数－聚合物熔体密度及熔体体积弹性模量进行了测量方法的研究，同时通过改进的组合数字滤波方法剔除超声波透射传播过程中多次回波干扰及环境噪声干扰对超声波传播速度测量精度的影响。4、基于神经网络建立了以状态变量温度、压力为输入变量的聚合物熔体体积弹性模量的软测量模型，并采用基于最佳部分网络的神经网络集成技术有效地提高了聚合物熔体体积弹性模量软测量模型的测量精度。5、基于最小二乘拟合多项式法建立了超声波速度单值变量的熔体密度在线软测量模型，并将该模型应用于注射过程中，通过实验验证用基于熔体密度在线测量的注射量重量控制方法替代体积控制方法，可以有效地提高注塑制品的重量重复精度。更多还原

【Abstract】 During the precision injection molding process of polymer, whetherthe weight of polymer melt injected from nozzles can be preciselycontrolled, is the direct factor which affects the weight repeatabilityprecision of accurate injection molding parts.As in the processing of injection, the density of polymer melt varieswith the state variables like pressure and temperature, traditional volumecontrolling method cannot realize consistency control of injection weight.While on the other hand, injection weight controlling method based ononline measurement of melt density is the best solution to solve thisproblem.This paper is going to study a soft measurement method of polymermelt key parameter, namely, the melt bulk modulus; it puts forward a softmeasurement model of melt density based on single value variable ofultrasonic velocity; then, the dependence and quick response to mediumdensity of ultrasonic propagation velocity is used to meet the onlinedensity measurement of polymer melt, which has injection molding cycle and multi-level infection pressure. The paper devotes to the followingtasks:1. Based on the comprehensive analysis of successful applications ofultrasonic technology in online measurement of liquid and solid mediadensity and in polymer processing, the single-valuedness and quickresponse existing in the ultrasonic real-time measurement of polymermelt density based on the transmission mode is studied theoretically andsystematically, Furthermore, online measurement of melt densityachieved by ultrasonic technology during the injection molding processof polymer melt is put forward.2. The response speed of easily-measured variables related to thepolymer melt density variables is studied, and the soft-measurementmodeling method adapted to melt density and volumetric elastic modulusof polymer melt is decided from both mechanism modeling and statisticalmodeling.3. Necessary experimental equipments are researched and developedfor online measurement of melt density based on ultrasonic technology,including the experimental device which could imitate pressure variationin injection process. A study of the measurement methods for the keyphysical parameters of polymer melt, such as active density and bulkmodulus is further performed. Then influences on the measuring accuracyof ultrasonic propagation velocity by the interferences of multiple echoes and environment noises during the ultrasonic transmission propagationare removed by adopting the combined digital filtering method.4. A soft measurement model of the the bulk modulus of polymermelt with the state variables of temperature and pressure as inputvariables is established on the basis of neural network. Meanwhile, themeasurement accuracy of such soft measurement model of bulk modulusof polymer melt is significantly improved through the application ofneural network integration technonology based on the optimal parts of thenetwork.5. The online soft measurement model of melt density based onultrasonic velocity is established by improved least squares binarypolynomial fitting, and used in the injection process. It is certified in theexperiment that the weight control method of injection weight based onthe melt density online measurement is better than the volume controlmethod in the improvement of the weight repeatability precision ofinjection molding parts.更多还原