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Institute for Measurement Technology
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Master Theses.

Design of a USB camera system with onboard image processing capabilities

Dominik Hofer

[Translate to Englisch:] Dominik Hofer

 

Strain measurement by laser-optical evaluation of laser speckle patterns on the test objects surface is a main research objective of the Institute for Measurement Technology of the Johannes Kepler University, Linz. Assuming that any movement of the speckle pattern occurs along its sensitive axis, recent projects used one or two line scan cameras to measure mechanical or thermal strain and the superposed rigid-body-motion in an uniaxial setup (see Fig. 1). This assumption may be proven invalid if the setup or the sample shows asymmetries. A new approach is to use 2D image sensors to measure or at least detect the movement of the speckles in the second dimension.

 

Abb. 1: Die bestehende Messanordnung im gemeinsamen Einsatz mit einer Zugprüfmaschine. Die Probe links im Bild wird mittig von einem Diodenlaser beleuchtet, beide  Zeilenkameras nehmen während der Belastung der Probe Bilder des auf der Oberfläche entstehenden Musters auf. Ein PC/104 Computersystems, rechts im Bild, wertet die  erfassten Daten aus und bestimmt die Verschiebung. Fig. 1: The existing measurement setup used to measure a tensile test specimen located left in this picture. Its surface is illuminated by a diode-laser and the scene is filmed by two line-scan cameras. A PC/104 computer system handles data processing and calculates the displacement of the speckle pattern induced by the laser on the rough surface of the specimen.

 

This diploma thesis is focused on the development of the camera shown in Fig. 2. It features a versatile interface to accommodate the system on the needs of the measurement task. Furthermore the camera is able to execute simple image processing algorithms besides basic data acquisition tasks. The final goal is to use two cameras of this kind to capture a `stereoscopic' view of the speckle field, to be able to render the system insensitive to out-of-plane deformation.

 

Fig. 2: The camera is controlled, read out and powered over USB. The SMB connectors either output, or accept as an input, a trigger signal. A push-button triggers a  frame, while the other resets the hardware. Furthermore the interface features two LEDs to show its status. Fig. 2: The camera is controlled, read out and powered over USB. The SMB connectors either output, or accept as an input, a trigger signal. A push-button triggers a frame, while the other resets the hardware. Furthermore the interface features two LEDs to show its status.

After a short introduction on laser speckles, the camera systems hard- and software and the application programming interfaces (APIs) of both the cameras firmware and the Windows application are depicted. Some sample images are shown and finally a small user guide demonstrates the use of this system as a stand-alone application (see Fig. 3) and in conjunction with Mathworks' Matlab.

 

[Translate to Englisch:] Abb. 3: Während sich die Registerkarte "Controls" mit dem Zugriff auf die Register der Hardware beschäftigt wird in der zweiten Karte "Camera" die Definition des  gewählten Bildausschnitts, der Belichtungszeit und der Datenrate vorgenommen. Das dargestellte Bild zeigt die Kameraplatine des zweiten Prototyps. [Translate to Englisch:] Abb. 3: Während sich die Registerkarte "Controls" mit dem Zugriff auf die Register der Hardware beschäftigt wird in der zweiten Karte "Camera" die Definition des gewählten Bildausschnitts, der Belichtungszeit und der Datenrate vorgenommen. Das dargestellte Bild zeigt die Kameraplatine des zweiten Prototyps.

August 11, 2009