The aim of the project was to detect different types of defects on the surface of film encoder wheels such as impurities on the tracks, small scratches as well as imperfections occurred during the glass forming process.The goal was also to measure the dimensions of some features of the encoders like gaps, angles and incorrect distances. At Opto Engineering®, we found the detection of these problems very challenging. “We required high-resolution measurement and high-level scratch detection capabilities”, says Peters. “This system was intended to discover different types of scratches for individual disc sizes. The biggest challenge in this application is to be able to robustly detect the smallest defects within a large field of view. In order to achieve this, a careful choice of the illumination strategy was required”. Accuracy is critical for this kind of inspection, as Peters explains: “Our customers sell very precise encoder discs in different sizes from 1mm diameter to 100mm in diameter. Their function is to keep accuracy in some of the common machine vision applications, for example motion positioning and position detection: we have a huge responsibility because with a faulty disc these processes might fail!