Mr. Daniel Härter Profile

Daniel Härter

at Univ of Freiburg

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Publications (4)

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SPIE Journal Paper | 1 July 2011

Active triangulation metrology system with high dynamic range

Daniel Härter, Claas Müller, Holger Reinecke

JM3, Vol. 10, Issue 03, 033007, (July 2011) https://doi.org/10.1117/12.10.1117/1.3610168

KEYWORDS: High dynamic range imaging, 3D metrology, Digital micromirror devices, Cameras, Metrology, Dynamical systems, Light emitting diodes, Mirrors, Collimation, Prisms

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We build up an active triangulative metrology system with a high dynamic range for measuring the three-dimensional shape of microstructures and for reverse engineering. The triangulation is done using a stereomicroscope to project dot shaped measurement labels through one port. The second port is used to locate their positions. In a calibrated system, three-dimensional coordinates are allocated to the measured positions. Using a digital mirror device (DMD) the generation of user definable patterns is very quick and flexible. Furthermore, the DMD features high brightness and contrasts values. This is important to recognize and distinguish projected measurement labels. The illumination is done by a white high power light-emitting diode, which is collimated and coupled to the DMD with a total internal reflection prism. The acquisition of measurement data from bright and dark surface areas results in a high change in brightness of measurement labels. To measure bright and dark surfaces in one measurement, a high dynamic range imaging technique is required. To identify measurement labels a temporal coding is used. Identification enables the adaption of the brightness of each projected measurement label. This results in a homogeneous brightness distribution of measurement labels, which enables their measurement in a second step. As a result, the dynamic of the measurement system is expanded by the dynamic of the projection device.

Proceedings Article | 11 February 2011 Paper

3D metrology system using an active triangulation with high dynamic range

D. Härter, C. Müller, H. Reinecke

Proceedings Volume 7932, 79320E (2011) https://doi.org/10.1117/12.873998

KEYWORDS: 3D metrology, Cameras, High dynamic range imaging, Digital micromirror devices, Projection devices, Light emitting diodes, Mirrors, Collimation, Optical testing, Reverse engineering

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We build up a new type of 3D metrology system for measuring the 3D shape of micro-structures and for reverse engineering techniques. The measurement principle is an active triangulation with a high dynamic range. The optical imaging is realized with a stereomicroscope. This features a field of view from square-centimeters down to square-millimeters at a constant triangulation angle. One port of the stereomicroscope is used to project measurement labels onto a measurement object and the second port to observe them by a camera. A calibration enables the assignment of 3D coordinates to the position of a measurement label in the camera image. To generate measurement labels we use a projection device that consists of a collimated, white light power LED illuminating a digital mirror device (DMD). The use of a DMD features the quick generation of user definable measurement labels with high brightness and contrast. Due to working with different magnifications and examining surfaces with different properties, the size and the spacing of projected measurement labels has to be adaptable. During a measurement as many measurement labels as possible should be visible in the camera image. Therefore the acquisition of measurement data from bright and dark surface areas requires a high dynamic range. The measurement labels in the camera image are distinguished with a temporal coding. This identification enables the adaption of the brightness of each measurement label in the projection pattern. As a result the dynamic of the measurement system is expanded by the dynamic of the projection device.

SPIE Journal Paper | 1 January 2011

3-D metrology system with internal calibration

Daniel Härter, Claas Müller, Holger Reinecke

OE, Vol. 50, Issue 01, 013604, (January 2011) https://doi.org/10.1117/12.10.1117/1.3530130

KEYWORDS: Calibration, Cameras, 3D metrology, Metrology, Imaging systems, Mirrors, Optical testing, Binary data, 3D image processing, Digital micromirror devices

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3-D metrology systems are used from examination and qualification of micro manufacturing techniques to reverse engineering of microstructures. For this purpose, the generation of capable and reliable 3-D coordinates in large numbers is essential. Combining classical triangulation with a new technique of calibrating measurement labels results in high rates of reliable 3-D metrology data. The triangulation setup consists of a stereomicroscope mounted on a 5-axis-gantry to generate all necessary points of view. Measurement labels are projected through one port of the stereomicroscope while their positions are localized through the second port. Providing a calibration rule is defined, the measurement system assigns each localized position to an absolute coordinate. For registration purposes, measurement labels are projected on a semitransparent mirror. Localizing measurement labels simultaneously with an observation and a calibration camera in connection with the working distance defines the calibration rule. By modifying the working distance between calibration camera and stereomicroscope, the measurement volume is scanned. The grid of the calibration camera chip acts as a measurement standard for the measurement labels. This approach features the spatial registration of a huge amount of measurement labels, covering the measurement volume, without building up the optical model of the imaging in a short time.

Proceedings Article | 24 August 2010 Paper

3D metrology system with internal calibration

D. Härter, C. Müller, H. Reinecke

Proceedings Volume 7767, 77670O (2010) https://doi.org/10.1117/12.863599

KEYWORDS: Calibration, Cameras, 3D metrology, Imaging systems, Mirrors, Binary data, CCD cameras, Data acquisition, Image registration, 3D modeling

Read Abstract +

3D metrology systems are used to examine and qualify micro- and nano-manufacturing techniques and further for reverse engineering of micro- and nanostructures. For this purpose the generation of capable and reliable 3D-coordinates in large numbers is essential. Combining classical triangulation with a new technique of calibrating measurement labels results in high rates of reliable 3D metrology data. The triangulation setup consists of a stereomicroscope mounted on a 5-axis-gantry to generate all necessary points of view. Measurement labels are projected through one stereomicroscopeport and their positions are localized through the second port. Providing the calibration rule is determined, the measurement system assigns each localized position to an absolute coordinate. For registration purposes measurement labels are projected on a semitransparent mirror. Localizing measurement labels simultaneously with an observation and a calibration camera in connection with the working distance, defines the calibration rule. By modifying the working distance between calibration camera and stereomicroscope, the measurement volume is scanned. The grid of the calibration camera chip acts as a measurement standard for the measurement labels. This approach features the spatial registration of a huge amount of measurement labels covering the measurement volume in short time without building up the optical model of the imaging.

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