Focus distance modulated fibre-coupled confocal sensor for surface metrology

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Miniaturization and micro-structuring of complex components and accordingly even closer manufacturing tolerances put new challenges on dimensional metrology. Using special micro or nano coordinate measuring systems, it is already possible to realize highly accurate, three-dimensional relative motions between sensor and measuring object in range of a few millimetres and with resolutions in the nanometre or sub-nanometre range. However, there is still demand for high-precision sensors for probing of the measuring objects which are suitable for these challenging measuring tasks. The goal of this research project consists of investigations on the fundamentals, the development and evaluation of a robust, precise, high frequency focus distance modulated confocal point sensor and the integration and validation of this sensor into a nano coordinate measuring system. To achieve this, while maintaining the known advantages of the confocal measurement principle, an innovative combination of a fibre-coupled confocal illumination and detection, a tuneable, acoustically driven gradient-index fluid lens (TAG lens) for modulation of the focus distance and a novel signal processing, applying a lock-in amplifier, shall be used for the stage-scanning mode in a nano coordinate measuring system to significantly increase the accuracy and to reduce the measurement uncertainty and the measurement time.