Extrusion International 4-2019

34 Extrusion International 4/2019 MEASUREMENT TECHNOLOGY Manual light tables are commonly used in the industry for a visual sample testing and incoming goods inspection of plastic material. The material to be inspected is illuminat- ed on a table and manually inspected for contamination by an operator. This time-consuming method depends on the respective auditor. The respective form on the day, ex- perience and amount of time the operator is investing in the inspection of the material are just a few factors that influence the quality of the test result, hence, only a lim- ited repeatability is given. Reflective and highly transpar- ent pellets further complicate themanual visual inspection. Further limits are detectable sizes of contamination for the human eye as well as their classification into size classes. Alternative optical inspection devices available on the market feed the test material through a hopper and a channel into the inspection area. Thereby, pictures of the material are taken successively. Distinct allocations of contamination to the graphic material as well as a follow- up inspection are not possible. Optical sample testing with automatic light table system and evaluation The combination of visual light table and an automatic sample testing is an innovative technology. The opera- tor places the test material on a sample tray. The auto- matic light table transports the tray with the material through the inspection area, which is equipped with a CMOS line scan color camera. The inspection takes place automatically and within seconds: A projector marks contaminated material directly on the sample tray. Si- multaneously, it is displayed and marked on the monitor including information on size and area of the contami- nation (picture 1). By analyzing the images, contamina- tion like black specks starting from 50 μm (2 mil) and dis- colorations are automatically detected, visualized and analyzed in transparent as well as colored or diffuse ma- terial. As an alternative to optical technology, a system with X-ray technology is available for the detection of metallic contamination inside as well as on the surface of nontransparent, colored and transparent plastic materi- als. Individual contaminated pellets can be selected and zoomed in. At the same time, they are optically visual- ized on the sample tray by cross hairs (picture 2). A clear allocation of the contamination and follow-up inspec- tion are always possible and permit new insights regard- ing the production process. Statistical evaluation and storage of the measuring values The presented optical inspection and analysis system con- tains a specially developed analysis software for the detec- tion, visualization and evaluation of contamination. The software includes an image gallery of detected contami- nation as well as statistics regarding their size, area and number. Furthermore, previously recorded image material can be imported for follow-up analysis. The inspection and analysis system can be integrated into the company net- work via a LAN interface in order to export and process collected data. The data provides the users with compre- hensive information about the process and the material quality. For example, by establishing a central and con- Picture 2: Sample traywithpellet sample: Detected contamination is highlighted in color. Pellets that are selectedon themonitor are visualized on the sample tray by cross hairs Picture 3: Examples of detected contamination by optical technology: Discoloration inflakes Picture 4: Examples of detected contamination by optical technology: Foreignbody infilm Picture 5: Examples of detected contamination by optical technology: Black speck inpellet