Minimized two-wavelengths interferometer with sinusoidally phase modulation using an oscillating mirror

Fig. 1: a) Photograph of the miniaturized interferometric high-speed sensor with additive manufactured sensor housing and b) schematic illustration of the sensor with expansion by a second wavelength

Increasing demands on the dimensional accuracy and form deviation of manufactured products as well as its fast and cost-effective quality inspection increases the requirements with respect to the measuring equipment too. The optical and tactile measuring instruments currently used fulfill the requirements for measurement accuracy, but are not very flexible in terms of their applicability, are relatively expensive and require low measuring speeds. To meet the requirements mentioned above, a fiber-coupled interferometric high-speed point sensor is developed in the measurement technology group at the University of Kassel, see Fig. 1.

Fig. 2: Comparison of measured profiles of a chirp structure using the optical sensor (a-c) and a tactile stylus instrument (d). Here, the results are additionally related to different scan velocity: 80 mm/s, b) 50 mm/s, c) 1mm/s and d) 0.5 mm/s.

Besides miniaturized geometrical dimensions and high lateral scan velocities (see comparison measurements in Fig. 2) the unambiguous range of adjacent height values are increased by using two wavelengths instead of one. This enables height measurement up to 9.5 µm. Due to the usage of mass products for the most components of the optical sensor the costs are relatively low.

Funded by:

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Dr.-Ing. Sebastian Hagemeier

S. Hagemeier, K. Bittner, F. Depiereux, P. Lehmann
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