Surface inspection tool is widely customisable

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By eeNews Europe

Before mechanical precision parts leave the manufacturing hall, they get examined carefully: Even the smallest crack or dent can affect the reliability and lifetime of the final product. This is the case especially for parts to be used in safety-critical applications, for example in the automotive and aerospace industry. But also aesthetic aspects can play a role, for instance in products for use in interiors of cars or homes.

Those components typically are tested with image processing methods. Multiple cameras shoot images of the component from different perspectives, and a software algorithm scrutinises the images for irregularities. Each material has a specific surface structure; to assess the quality of the material, the test method needs to be tuned exactly to this respective material. Shape and size of the component as well as the desired resolution of the image are also factors. Systems currently available at the market are designed for specific materials and surface structures. No standard solution covers the entire spectrum of surface inspection tasks.

The Fraunhofer Institute for Business and Technology Mathematics (ITWM) has developed an alternative: A modular inspection system that can be adapted to customer-specific tasks. MASC – the acronym stands for Modular Algorithms for Surface InspeCtion – can be deployed in surface inspection applications for leather, metals, pater or even textiles. MASC embraces a wide spectrum of dimensions to be surveyed – from tiny components for medical applications to entire rawhides or roof plates. Two configurations are already in the productive service in the industry; one is MASC-STeX for the inspection of roof plates and MASC Dehnzelle for the inspection of expansion cells.

To conduct an inspection, the system first illuminates rasterises the surface of the device under test under different angles. “This is important to detect dents and ruptures that are visible from a specific side only”, says Markus Rauhut from Fraunhofer ITWM. In the case of free form surfaces, this procedure even captures data on areas covered by curvatures or corners. The more complex the geometry, the more cameras are required. “To keep the effort within reasonable limits, we focus on areas where a fault in practice would really have negative consequences”, says Rauhut. For the analysis of the images, the scientists assembled a comprehensive software library of processing algorithms. One algorithm, for instance, is designed to find edges or specific colour points on the surface. The basis version of the software alone already contains more than 300 algorithms which can be freely combined according to the needs of the respective test task.

A particular challenge bear those tasks that require very high resolution. No surface is entirely homogeneous; each exhibits minor brightness variations or other deviations. Conventional image-based surface inspection tools typically have a problem: The closer an inspection task comes to microscopic dimensions the more difficulties have designers to distinguish between acceptable surface irregularities and real faults. The undesired consequence: Perfect products receive a false rejection. Fraunhofer claims to have overcome this challenge. “We can refine the analysis with our methods that pseudo errors can virtually be ruled out”, says ITWM researcher Kai Taeubner.

Once all test parameters are set, the system is integrated into the customer’s production process. In this context, the cameras are installed either directly at the assembly line or handled by robots. Case an fault has been identified, the production process is halted and the machine operator gets notified. Faults can be classified, the devices under test can be assigned to quality categories.

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