Extrusion Asia Edition 3-2016

33 Extrusion Asia Edition 3/2016 图 3：CCD 线阵传感器检测原理及衍射分析 Image 3: CCD line sensor measuring principle and analysis by diffraction analysis without optics and moving parts “ 扫描式测量系统” 在旋转棱镜和光电传感器之间有两个平行放置的透镜，激光 束通过旋转棱镜对测量区域进行扫描。第一道透镜通过测量 区域发出平行光束，而第二道透镜则会将光束折射到光电传 感器上。当对被测物体进行扫描的时候，位于两个透镜之间 的被测物将对激光束造成阻断。因此，产品外径的测量是通 过比较激光束通过整个测量区域以及整个产品表面的时间来 计算的。在这种情况下，时间就等于外径（图1）。检测速率 取决于棱镜的旋转速度。棱镜的面越多检测频率越高，这也 意味着对棱镜镜面的清洁度有着较高要求。通常需要更多的 测量值进行平均，从而得到相对准确的数值。 “ CCD线阵传感器测量系统” 目前有两种常用的CCD线阵传感器技术测量方法。第一种方 法是通过使用光学原理（透镜）将激光束聚焦到线阵传感器 上。通过被遮挡的阴影区域计算被测物的外径。这种方法的 优点是没有机械运动部件，但透镜的成本相对较高。 第二种方法采用高精度CCD线阵传感器直接针对激光在物体 两侧产生的衍射波纹进行成像，由衍射波纹计算物体外径。 其检测速率非常高,只受限于所选的CCD传感器。这种方法的 优点是无需昂贵的镜片并且没有机械运动部件。 扫描和线阵传感器技术的主要区别是CCD线阵传感器技术是 完全数字化工作，无需运动部件。因此，其准确性、复检精 度及检测速率都更高并且无需校准。采用线阵传感器技术可 以使用双轴或是三轴的测量头测量物体的外径。它能够测量 从0.05到500 mm，透明和非透明的各种材料的产品外径。此 外，还有一些型号可提供高达5000次/每轴/每秒的测量，因 此，该技术也可用于可靠检测产品的鼓包或凹陷。 用于测量产品外径、壁厚及偏心的技术 对于某些应用领域来说，仅仅测量产品的外径是不够的，管 材制造商往往还需要运用检测设备进一步测量产品的壁厚与 偏心。 此外，除了质量控制和工艺优化之外，对塑料材料的 节省和生产成本的降低也是不可或缺的考虑因素。 对于管材 的壁厚测量来说，传统的技术手段是采用超声波测量技术。 该方法适用于单层结构产品的壁厚测量，但是其应用受限于 材料性质、塑料温度和耦合介质。现在可以通过 X 射线技术 对所有产品参数进行精确的测量，不受环境或材料的影响。 超声波技术 超声技术仅适用于部分管材的在线品质控制。例如，超声波 不能穿透复合管中用以隔绝水气的铝层，因此不适用于该类 产品的检测。当测量橡胶软管时，超声信号在很大程度上被 橡胶的气孔及橡胶材料所吸收，因此他们也不能进行可靠的 测量。不仅如此，含有传统编织加强层的多层橡胶软管，由 am that is focused on one line sensor using optics (lenses). By counting the darkened diodes from the shadow image of the object, the diameter is determined. The advantage of this me- thod is the omission of moving parts, but the costs for the lens are high ( ). The second approach is an intelligent method for which a high- resolution CCD line is directly illuminated by a laser and the dia- meter is calculated from the diffraction fringe. The measuring rate is extremely high and only limited by the chosen CCD line sensor. The advantages of this second method are the omission of the expensive lenses as well as moving parts. The main difference between scanning and the line sensor technology is that the CCD line sensor technology works solely digitally and does not need moving components. Therefore, ac- curacy, repeatability and measuring rate are higher and a cali- bration is not necessary. Gauge heads that work with the line sensor technology measure the diameter in two or three planes. They are capable of measuring opaque as well as trans- parent products from all kinds of material with a diameter from 0.05 to 500 mm. In addition, some models offer up to 5,000 measurements/per axis/ per second and therefore, as well a re- liable detection of lumps and neckdowns. Technologies for the measurement of diameter, wall thickness and eccentricity For applications where a diameter measurement is not suffi- cient, manufacturers of hoses and tubes use measuring systems that additionally measure the wall thickness and the eccentrici- ty of the products. Thereby, in addition to the quality control and process optimization, the saving of plastic material and cost reduction play an essential role. Conventionally available technologies are, for example, based on ultrasound technology. This method is suitable for the basic measurement of the wall thickness of single layer products but reaches its limits due to its function and dependence on material properties, the plastics temperature and the coupling medium. A precise measurement of all product parameter without the dependence on environ- mental or material influences is nowadays ensured by the X-ray technology. Ultrasound technology The ultrasound technology is only partly suitable for online qua- lity control of hoses and tubes. For example, the ultrasound is not able to penetrate the aluminum layer that is used as a va- por barrier in composite pipes and is therefore not applicable for this application. Measuring rubber hoses, the ultrasound signals are largely absorbed by the porosity and absorption of the rubber so that they are also not reliably measurable. Fur- thermore, multi-layer rubber hoses contain typical fabric rein- forcements, which divert the ultrasound echo and make a mea- surement impossible. The ultrasound measurement is usually realized in a water bath as the water is used as a coupling me- dium for the transmission of the sound. A precise temperature compensation is necessary as the propagation speed of the ul- trasound, which is used for the calculation of the eccentricity, depends on temperature and material. This technology requires a calibration. Further, an estimation of the wall thickness is