Image processing systems for evaluating glass and coating errors in lightbulbs
In order to ensure quality in the manufacture of lightbulbs, vosla GmbH runs optical testing stations in its production lines. The goal for a new station for a 360° final check was to automatically locate and measure the smallest of faults on the glass bulbs as well as in the application of color.
Fraunhofer IIS/EAS has developed a special optical set-up based on the customer-specific test software to achieve this. The optical set-up consists of four integrated imaging heads with a high resolution camera, beam splitter, and surface lighting which are arranged in a circle and equally spaced around the object to be measured. Eight different images of the test object are captured with the structures at a resolution of smaller than 30 µm, which allows for precise optical examination. Based on four reflected light and transmitted light images, a distinction is made between various degrees of transparency and the analysis of the image information is adjusted on that basis. Furthermore, color-controllable lighting allows for individual adjustment to the testing mechanism for the coatings, which vary in color depending on the type of lightbulb. Reflections and breakage in the glass bulbs are also detected and handled accordingly.
The analysis software allows for not only an extraction of characteristics, but also external geometric measurement of the test object and all relevant functional components. It detects production errors like scratches, cracks, air pockets, contaminants, splinters, and geometric deviations. The software uses the derived data and the programmable, permissible tolerances to conduct a quality assessment. The result of the test is a classification into user-defined levels of quality, based on which the test object is either further processed or sorted out.
The design and integration of the optical arrangement into the production line was done by a partner company, as was the preparation of a user interface.