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Increasing demands for product quality and outsourcing of production in the automobile industry lead to in creasingly tight tolerances for the components. In the area of metal-mechanics these are largely dimensional and require frequently uncertainties in the micron region. For optical instruments this means microscopical resolu tion. Dimensional measurement with uncertainties of some microns is nothing new, state of the art equipment in fact goes far below. The task becomes difficult if the measurements have to be carried out in an industrial production environment - and deep inside a bore hole. This paper describes the development of an automatic measurement system for internal dimensions of brake master cylinders, specifically the development of endoscopes, illuminations for edge detection, and integration with other sensors, actuators and controllers. The most demanding part was the endoscope development, because, surprisingly, no commercial product for microscopic view and precision measurements was found on the market. As the market for such measurement machines is very small, and as the requirements were different for each endoscope, the budget allowed only the development of prototypes, using readily available optical components. Borders between faces with different orientation of metallic structures can be difficult do detect. A satisfactory metrological performance can be achieved only with carefully shaped illumination, even if the source is a simple LED (light emitting diode). The automation was responsible for the largest part of the overall cost, coming from the desire for a high throughput of the measurement machine, even when operated by not highly qualified personnel. With the safety requirements satisfied, such a device ends up as a pretty complex equipment. Nevertheless, these aspects will be mentioned only for completeness, because standard components and methods were applied.
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