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Calibration of the incident beam in a reflective topography measurement from an unknown surface
Author(s): Tobias Binkele; David Hilbig; Friedrich Fleischmann; Thomas Henning
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Paper Abstract

The precision of measurements as well as the need for precise measurements are increasing more and more. Thus, the importance of a good calibration of a setup is increasing, too. In the world of topography measurement a huge variety of techniques are available. Some of these techniques are using known shadow patterns reflected by the device under test (DUT). The reflected patterns are recorded using a camera with imaging optics. From the changes of the patterns, the topography can be resolved. Other measurement techniques are using a tactile sensing head, which is in contact with the surface to determine its topography. However, these techniques need a reference surface to calibrate movements. If this reference surface presents deviations from its expected form, errors are introduced.
We have developed a calibration method for reflective surface measurements based on experimental ray tracing (ERT) without the need of a reference surface. In our measurement setup, a narrow laser beam introduced in the measurement under a certain angle is reflected by the device under test. After the reflection the position and the direction of the ray in terms of the coordinate system of the camera is detected. Thus, no errors are introduced by using an additional imaging optic. To calibrate position and direction of the incident ray in respect to the coordinate system of the camera, the reflected rays from the measurement are used only. From these rays, the incident ray is determined by detecting the line, all reflected rays are intersecting with. This leads to two major advantages. First, there is no calibration run needed, since the measurement data can be used directly for the calibration. Second, for the calibration no well-known reference surface is needed. However, some regulations have to be considered for a stable process of this calibration method. In terms of peak-to-valley values of the sag of the surface as well as of the change of the surface slope, the surface has to show values deviating from zero. If a surface like this is measured, a separate measurement run can be performed using another surface fulfilling these requirements. Since the DUT is scanned by moving the DUT itself, the position and the direction of the incident ray is not changed from one measurement to another and can be reused. We describe the newly introduced calibration method for the incident ray in detail and present the necessary boundary conditions. The calibration has been tested using simulations and has been implemented in a measurement setup. Within this measurement setup, the expected performance resulting from the simulations has been examined.

Paper Details

Date Published: 26 June 2017
PDF: 7 pages
Proc. SPIE 10329, Optical Measurement Systems for Industrial Inspection X, 103291S (26 June 2017); doi: 10.1117/12.2270291
Show Author Affiliations
Tobias Binkele, Hochschule Bremen Univ. of Applied Sciences (Germany)
David Hilbig, Hochschule Bremen Univ. of Applied Sciences (Germany)
Friedrich Fleischmann, Hochschule Bremen Univ. of Applied Sciences (Germany)
Thomas Henning, Hochschule Bremen Univ. of Applied Sciences (Germany)


Published in SPIE Proceedings Vol. 10329:
Optical Measurement Systems for Industrial Inspection X
Peter Lehmann; Wolfgang Osten; Armando Albertazzi Gonçalves, Editor(s)

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