Extrusion International 3-2022

44 Extrusion International 3/2022 Measuring Technology Laser Measurement of Tubes and Extruder Bore Holes Using the Circular Triangulation Sensor (CiTriS, see picture 1), the inner geometry of bores, tubes, tanks, and other cavities can be measured. The radial laser beammeasures the inner geometry around 360° in 3600 angle steps. The result is a precise inner cross section, and a 3D-model of the inner surface profile can be generated from the data obtained. Using this technology, the verification of tolerances is possible. T he sensor, which has no rotating parts, projects a 360° radial laser beam on the target inner surface and measures the contour. The pro- jected laser line is imaged by a high- resolution image sensor. Using im- age analysis, the 2D contour of the cross section is created. In a single scan 3600 radii along the circumfer- ence are measured with a speed of up to 60 scans per second. The resul- tant radial resolution is 10µm. Operating at 60 scans per second, a 10 m tube can be inspected in 180 seconds with over 10000 cross sections. More than 38 million measure- ment points pro- vide a detailed surface in- spection. Operation in extruders Extruder bore holes are subject to wear and need regular inspection. The CiTriS scanner can be inserted at any required depth (Picture 2) and will measure the related cross section. Guiding sleeves or round guiding brushes are used to main- tain the aspect and centralise the sensor. The sensor should be easily moveable along the length of the tube. Exact centring is not required because of the wide radial measure- ment range of the sensor. The small- est sensor has a length of 169mm and measures a range of diameters from 60mm to 160mm. Larger sen- sors measure ranges up to 1000 mm. Smaller measurement ranges are in development. Depth determination To correlate the mea- sured cross sections with the distance of the scanner inside the extruder , a distance signal is used to trigger sensor mea- surement. The distance signal can be pro- duced by an encoder. Each move- ment of the sensor will trigger a cross sectional measurement. The integration of the encoder with the scanner is dependent upon the de- ployment method of the scanner. When mounting the CiTriS on a roll- er skid, the encoder can be mount- ed on a measuring wheel. In the case of small-bore holes and opera- tion with sliding sleeves, the cable length inserted into the bore hole will be measured for information on distance. A special cable guide with integrated encoder is available. Picture 1: Circular Triangulation Sensor (CiTriS) Picture 2: Operation in a double extruder Picture 3: 3D-Model of a bore in a double screw extruder showing significant wear. The depth of wear is shown in scaled colour