In many industrial production plants, 100 percent control of the manufactured goods is a mandatory requirement in the area of quality assurance. In order to be able to guarantee this even at high production rates, specially adapted customer-specific measuring systems are necessary.
For Johnson Matthey Catalysts GmbH, a fully automatic measuring cell for the optical inspection of cylindrical honeycomb catalysts was developed. Due to their special manufacturing process, ceramic fully active catalysts are more effective than conventional catalysts but are subject to greater geometric fluctuations. They are used for exhaust gas purification in passenger cars, trucks, ships, and power plants. As a result of the large number of different application scenarios, there is a large range of types with diameters from 140 mm to 330 mm and lengths from 100 mm to 300 mm. The entire range of types must be tested in large quantities in a three-shift operation. On one hand, the system must guarantee high reliability, and, on the other, it must react flexibly to increasing on-demand production with changeover times of just a few minutes. The two-stage inspection process begins with the all-round measurement of the shell surface. The catalytic converters are lifted out of the conveyor section by a specially designed mechanical system and rotated around the cylinder axis. Parallel to the 3D measurement, the outer surface is examined with a high-resolution camera for cracks from 100 μm width. The specially designed reconstruction and calibration algorithm allows the calculation of a multitude of geometric dimensions such as different diameters, cylindricity, angularity, or barrel shape. The full-surface measurement also allows local deformations, defects, and break-outs to be detected and interpreted simultaneously. In the second inspection stage, up to 50,000 individual channels are inspected for web breaks, cell closure, and cracks using two 28 MPixel cameras. The results of the 2D image evaluation are differentiated by a complex classification into different crack groups and defect clusters. The measuring cell was integrated into the production finishing line and is characterized by optimized handling for the highest possible cycle rate. The measured data obtained is fed back to the customer's main system and the Manufacturing Execution System and provides the basis for classifying the test specimens for the subsequent sorting robot. The measuring cell and the coupled evaluation unit communicate with each other and with the higher-level end line via industrially standardized communication protocols of the automation technology.
The customer-specific, fully automatic inspection system represents the process coordinated by Fraunhofer IOF for a new development suitable for industrial use, starting with a feasibility study, through the coordination of the interfaces, assembly, commissioning, and up to the final system optimization.
Authors: Peter Lutzke, Peter Kühmstedt, Gunther Notni