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Vol. 226, Issue 10, October 2018, pp. 77-82




Autofocus in Two-Wavelength Contouring for Fast Inspection of Micro Parts

1, 2 Mostafa AGOUR, 1 Claas FALLDORF and 1, 3 Ralf B. BERGMANN

1 BIAS – Bremen Institute of Applied Beam Technology, Klagenfurter Straße 5, 28359 Bremen, Germany
2 Aswan s, Faculty of Science, Department of Physics, 81528 Aswan, Egypt
3 University of Bremen, Faculty 01: Physics and Electrical Engineering and MAPEX Center for Materials and Processes, 28359 Bremen, Germany

E-mail: agour@bias.de


Received: 25 June 2018 /Accepted: 31 August 2018 /Published: 31 October 2018

Digital Sensors and Sensor Sysstems


Abstract: We present a method for fast inspection of metallic micro parts. It is based on the combination of two-wavelength contouring and digital holographic microscopy (DHM). For fast evaluation, an autofocus algorithm to refocus the object digitally without the need for any external intervention is proposed. The method enhances the microscope objective’s depth of focus compared with imaging techniques by standard microscopy. Compared to standard DHM, an object side telecentric objective is utilized to overcome irreversible depth distortions caused by standard microscope objectives. The method is demonstrated by reconstructing the three- dimensional shape of a metallic deep drawn micro cup. Experimental results confirm the improved depth of focus of DHM.


Keywords: Digital holographic microscopy, Holographic contouring, Shape and deformation measurement, Depth of focus, Micro deep drawing parts.


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