Mr. Rüdiger Beermann Profile

Rüdiger Beermann

Research Associate at Leibniz Univ Hannover

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Publications (10)

SPIE Journal Paper | 2 June 2020 Open Access

Development of a reconstruction quality metric for optical three-dimensional measurement systems in use for hot-state measurement object

Lorenz Quentin, Rüdiger Beermann, Markus Kästner, Eduard Reithmeier

OE, Vol. 59, Issue 06, 064103, (June 2020) https://doi.org/10.1117/12.10.1117/1.OE.59.6.064103

KEYWORDS: Cameras, Refractive index, Projection systems, 3D metrology, Optical testing, 3D modeling, Calibration, Optical engineering, Algorithm development, Temperature metrology

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SPIE Journal Paper | 26 May 2020 Open Access

Calibration routine for a telecentric stereo vision system considering affine mirror ambiguity

Rüdiger Beermann, Lorenz Quentin, Markus Kästner, Eduard Reithmeier

OE, Vol. 59, Issue 05, 054104, (May 2020) https://doi.org/10.1117/12.10.1117/1.OE.59.5.054104

KEYWORDS: Cameras, Calibration, Sensors, Distortion, Mirrors, Stereo vision systems, 3D acquisition, Matrices, Projection systems, Clouds

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Proceedings Article | 1 April 2020 Presentation + Paper

Concept of a control system based on 3D geometry measurement for open die forging of large-scale components

Lorenz Quentin, Rüdiger Beermann, Kai Brunotte, Bernd-Arno Behrens, Markus Kästner, Eduard Reithmeier

Proceedings Volume 11352, 113520B (2020) https://doi.org/10.1117/12.2554720

KEYWORDS: 3D metrology, Control systems, Sensors, Optical testing

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Proceedings Article | 1 April 2020 Presentation + Paper

Affine structured light sensor for measurements through inspection windows: basic concept and direct calibration approach

Rüdiger Beermann, Lorenz Quentin, Markus Kästner, Eduard Reithmeier

Proceedings Volume 11352, 113520E (2020) https://doi.org/10.1117/12.2556081

KEYWORDS: Cameras, Sensors, Calibration, Refraction, 3D modeling, Inspection, Refractive index, Projection systems, Stereoscopic cameras, Matrices

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The realization of 3D triangulation measurements in inhomogeneous media is challenging, as the sensor light path is not necessarily rectilinear anymore and the triangulation principle is violated. An exemplary measurement scenario under inhomogeneous optical conditions is the geometry characterization through an inspection window. The discrete refractive index variation from air to inspection window and back to air (or even water) can require complicated light path modeling approaches in order to triangulate 3D surface data correctly. As commonly used entocentric lenses “fan out” the projected light rays, the rays’ incidence angles onto the refractive index interface are not constant, and the rays are individually deflected. In consequence, the typically used camera pinhole model does not apply anymore, or can only approximate the actual light path under refraction. In this paper, we present a structured light sensor concept for measurements through inspection windows, which does not require a special adaption of the light path model. The key is the application of a telecentric stereo camera pair and high-quality optical inspection windows. It can be shown theoretically, that no additional parameters are necessary to model light refraction induced by a plane-parallel plate – such as a window –, when used in combination with a telecentric lens. Next to the affine stereo camera pair, the sensor comprises an entocentric projector unit as feature generator. In previous work, the projector was calibrated with refraction model in order to provide a 3D point cloud basis for the affine camera calibration.¹ In the new approach, the projector is merely used as feature generator to solve the correspondence problem between the affine stereo camera pair. Besides the developed sensor hardware concept, we present an overview on the calibration strategy based on an affine self-calibration approach, the solving of the correspondence problem between the cameras, and first calibration and measurement results. In forthcoming work, the sensor is also meant to be used in three-media refraction scenarios.

Proceedings Article | 1 April 2020 Presentation + Paper

Model-based calibration routine for a triangulation sensor for inner radius measurements of cylindrical components

Rüdiger Beermann, Hagen Bossemeyer, Robin Diekmann, Markus Kästner, Eduard Reithmeier

Proceedings Volume 11352, 113520S (2020) https://doi.org/10.1117/12.2552729

KEYWORDS: Cameras, Calibration, Mirrors, Clouds, 3D modeling, Calculus, 3D metrology, Model-based design, Mathematical modeling

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None-tactile metrology systems for inner radius measurements of cylindrical objects with large diameters are often based on the triangulation principle, using a laser source as illumination unit and a camera as detection unit. Different approaches have been presented in the past in order to generate a complete profile section of the measurement object’s inner radius. A standard light-section sensor cannot provide a 360° view of the radius without sensor rotation around the cylinder axis. The additional rotation axis needs to be calibrated and the captured point clouds registered in the same coordinate frame. To spare the necessity of a rotational axis, we developed a prototype sensor based on the hardware approach suggested by Yoshizawa et al.,¹ using a cylinder cone mirror and a laser illumination unit in order to generate a line circle projected onto the inner radius. In combination with a wide-angle camera, the laser line can be captured in one shot. Unlike the approach by Yoshizawa et al. , we present a model-based calibration routine for the triangulation sensor by mathematically describing the laser light path. The cone mirror expands the laser light into a disc (plane) or into a cone – depending on the incidence angle between laser and mirror. In our model, the light cone is parametrized by the right circular cone equation to reduce the number of unknowns in regression calculus. The necessary 3D support points to approximate the model parameter are gained by recording planar calibration pattern poses with and without laser line. The intersection calculation between the camera’s line-of-sight and the projected laser light geometry is derived, and the mathematical ambiguity in the line-cone intersection successfully solved. We present first experimental calibration and measurement data of a cylinder. By intentionally misaligning sensor and cylinder axes with arbitrarily chosen angles, the robustness of the suggested procedure is demonstrated.

Proceedings Article | 21 June 2019 Presentation + Paper

Structured light sensor with telecentric stereo camera pair for measurements through vacuum windows

Rüdiger Beermann, Lorenz Quentin, Markus Kästner, Eduard Reithmeier

Proceedings Volume 11056, 1105614 (2019) https://doi.org/10.1117/12.2526049

KEYWORDS: Projection systems, Calibration, Cameras, Sensors, Refraction, 3D modeling, Data modeling, Distortion, Structured light, Stereoscopic cameras

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Within the Collaborative Research Centre 1153 Tailored Forming a process chain is being developed to manufacture hybrid high performance components made from different materials. The optical geometry characterization of red-hot workpieces directly after the forming process yields diverse advantages, e.g., the documentation of workpiece distortion effects during cooling or the rejection of deficient components in an early manufacturing state. Challenges arise due to the high components temperature directly after forming (approximately 1000°C): The applied structured light method is based on the triangulation principle, which requires homogeneous measurement conditions and a rectilinear expansion of light. This essential precondition is violated when measuring hot objects, as the heat input into the surrounding air leads to an inhomogeneous refractive index field. The authors identified low pressure environments as a promising approach to reduce the magnitude and expansion of the heat induced optical inhomogeneity. To this end, a vacuum chamber has been developed at the Institute of Measurement and Automatic Control. One drawback of a measurement chamber is, that the geometry characterization has to be conducted through a chamber window. The sensors light path is therefore again affected - in this case by the window’s discrete increase of refractive index, and also due to the different air density states at sensor location (density at ambient pressure conditions) and measurement object location (density at low pressure conditions). Unlike the heat induced deflection effect, the light path manipulation by the window and the manipulated air density state in the chamber are non-dynamic and constant over time. The reconstruction of 3D geometry points based on a structured light sensor measurement directly depends on the mathematical model of detection and illumination unit. The calibration routine yields the necessary sensor model parameters. The window light refraction complicates this calibration procedure, as the standard pinhole camera model used for entocentric lenses does not comprise enough degrees of freedom to adequately parametrize the pixel-dependent light ray shift induced by thick vacuum windows. Telecentric lenses only map parallel light onto a sensor, therefore the window induced ray shift is constant for all sensor pixels and can be directly reproduced by the so-called affine camera model. In this paper, we present an experimental calibration method, and corresponding calibration data and measurement results for a structured light sensor with and without measurement window. The sensor comprises a telecentric stereo camera pair and an entocentric projector. The calibration of the telecentric cameras is conducted according to the well-known affine camera model. The projector is used as feature generator to solve the correspondence problem between the two cameras. The calibration data illustrates that the window refraction effect is fully reproduced by the affine camera model, allowing a precise geometry characterization of objects recorded through windows. The presented approach is meant to be used with the aforementioned vacuum chamber to enable a geometry characterization of hot objects at low pressure levels.

SPIE Journal Paper | 20 November 2018 Open Access

Full simulation model for laser triangulation measurement in an inhomogeneous refractive index field

Rüdiger Beermann, Lorenz Quentin, Gunnar Stein, Eduard Reithmeier, Markus Kästner

OE, Vol. 57, Issue 11, 114107, (November 2018) https://doi.org/10.1117/12.10.1117/1.OE.57.11.114107

KEYWORDS: Cameras, Sensors, Ray tracing, Optical simulations, Content addressable memory, Refractive index, Device simulation, 3D modeling, 3D metrology, Geometrical optics

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Proceedings Article | 2 November 2018 Paper

2D refractive index field measurements in air in different pressure scenarios

Rüdiger Beermann, Lorenz Quentin, Eduard Reithmeier, Markus Kästner

Proceedings Volume 10819, 108190E (2018) https://doi.org/10.1117/12.2500315

KEYWORDS: Refractive index, Cameras, Refraction, Optical testing, Sensors, Optical flow, 3D metrology, Vacuum equipment

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Proceedings Article | 26 June 2017 Paper

Light section measurement to quantify the accuracy loss induced by laser light deflection in an inhomogeneous refractive index field

Rüdiger Beermann, Lorenz Quentin, Andreas Pösch, Eduard Reithmeier, Markus Kästner

Proceedings Volume 10329, 103292T (2017) https://doi.org/10.1117/12.2269724

KEYWORDS: Refractive index, 3D metrology, Inspection, Laser optics, Bandpass filters, Manufacturing, Process control, Time metrology, Optical sensors, Visualization

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Proceedings Article | 26 June 2017 Paper

3D geometry measurement of hot cylindric specimen using structured light

Lorenz Quentin, Rüdiger Beermann, Andreas Pösch, Eduard Reithmeier, Markus Kästner

Proceedings Volume 10329, 103290U (2017) https://doi.org/10.1117/12.2269607

KEYWORDS: Projection systems, Process control, Data acquisition, Nondestructive evaluation, Structured light, Calibration, Optical testing, Digital Light Processing, Image resolution, Bandpass filters, Cameras, 3D metrology, Inspection

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