Abstract: Based on the strong relationship between ultrasonic speed and properties of the propagation medium and the rapid response of ultrasonic speed to the medium properties,the theoretical and experimental analysis were made to conclude single valued correspondence of ultrasonic speed with density of polymer melt.Considering very short molding cycle for the injection process,an improved least square method by reducing the independent variable within the scope of 0 to 1 was proposed for the purpose of increasing computation speed.An online soft measurement model of polymer density according to single valued ultrasonic speed was established and the soft measurement model found application in precise control of injected weight of the article in the process of injection molding.Integrating the product of density of polymer melt determined by soft measurement model and cross-sectional area of the screw to stroke distance of injection,more precise control of the weight of molded article could be realized.The superiority of the weight control method based on soft measurement of melt density to the traditional volume control method was confirmed to the benefit of improving repeat weight accuracy of molded articles.

Key words: ultrasonic velocity, polymer melt density, weight repeatability precision, precision injection molding

摘要： 基于超声波传播速度与传播介质物性参数密切关联和快速响应的特性，通过实验和理论分析得到了超声波传播速度与聚合物熔体密度存在单值对应关系的重要结论；根据精密注塑制品成型周期短的特点，在实验的基础上采用改进最小二乘法，即缩小自变量使其在0～1的范围内可以有效降低拟合阶数，提高运算速度的方法，建立了基于超声波速度单值变量的熔体密度在线软测量模型，并将该软测量模型应用于注射成型过程中对聚合物熔体注射重量的控制；即由该软测量模型得到的在线熔体密度与螺杆截面积的乘积对螺杆注射行程进行积分，可以精确计算出聚合物熔体注射重量，以此实现对注射机成型制品重量的精密控制；理论和实验都验证了基于熔体密度在线软测量的注射量重量控制方法优于传统的体积控制方法，是提高注射成型过程制品重量重复精度的有效方法。

关键词: 超声波速度, 聚合物熔体密度, 重量重复度精度, 精密注塑成型