Achim Gesierich

Würth Elektronik (Germany)

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Thorsten Bothe

Bremen Institute for Applied Beam Technology

Ralf B. Bergmann

Bremen Institute for Applied Beam Technology

Wansong Li

Sichuan Agricultural University

Claas Falldorf

Bremen Institute for Applied Beam Technology

Werner P. O. Jueptner

Bremen Institute for Applied Beam Technology

Fabian Thiemicke

Bremen Institute for Applied Beam Technology

Christoph von Kopylow

Bremen Institute for Applied Beam Technology

Wolfgang Osten

University of Stuttgart

Jan Burke

Fraunhofer Institute of Optronics, System Technologies and Image Exploitation

Annika Bohlen

Bremen Institute for Applied Beam Technology

Cooperative Institutions

Bremen Institute for Applied Beam Technology

Optica

University of Bremen

Institute for Applied Systems Technology Bremen

Gesellschaft zur Förderung angewandter Informatik

Aswan University

University of Stuttgart

ORCID

Bellingham Technical College

Carl von Ossietzky Universität Oldenburg

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Absolute optical surface measurement with deflectometry

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2012)

Wansong Li Marc Sandner Achim Gesierich Jan Burke

Deflectometry utilises the deformation and displacement of a sample pattern after reflection from a test surface to infer the surface slopes. Differentiation of the measurement data leads to a curvature map, which is very useful for surface quality checks with sensitivity down to the nanometre range. Integration of the data allows reconstruction of the absolute surface shape, but the procedure is very error-prone because systematic errors may add up to large shape deviations. In addition, there are infinitely many combinations for slope and object distance that satisfy a given observation. One solution for this ambiguity is to include information on the object's distance. It must be known very accurately. Two laser pointers can be used for positioning the object, and we also show how a confocal chromatic distance sensor can be used to define a reference point on a smooth surface from which the integration can be started. The used integration algorithm works without symmetry constraints and is therefore suitable for free-form surfaces as well. Unlike null testing, deflectometry also determines radius of curvature (ROC) or focal lengths as a direct result of the 3D surface reconstruction. This is shown by the example of a 200 mm diameter telescope mirror, whose ROC measurements by coordinate measurement machine and deflectometry coincide to within 0.27 mm (or a sag error of 1.3μm). By the example of a diamond-turned off-axis parabolic mirror, we demonstrate that the figure measurement uncertainty comes close to a well-calibrated Fizeau interferometer.

Fizeau interferometer

Radius of curvature

Surface reconstruction

10.1117/12.928690

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Citations (35)

Three-dimensional camera

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2003)

Thorsten Bothe Achim Gesierich Ricardo Legarda-Sáenz Werner P. O. Jueptner

Industrial- and multimedia applications need cost effective, compact and flexible 3D profiling instruments. In the talk we will show the principle of, applications for and results from a new miniaturized 3-D profiling system for macroscopic scenes. The system uses a compact housing and is usable like a camera with minimum stabilization like a tripod. The system is based on common fringe projection technique. Camera and projector are assembled with parallel optical axes having coplanar projection and imaging plane. Their axes distance is comparable to the human eyes distance altogether giving a complete system of 21x20x11 cm size and allowing to measure high gradient objects like the interior of tubes. The fringe projector uses a LCD which enables fast and flexible pattern projection. Camera and projector have a short focal length and a high system aperture as well as a large depth of focus. Thus, objects can be measured from a shorter distance compared to common systems (e.g. 1 m sized objects in 80 cm distance). Actually, objects with diameters up to 4 m can be profiled because the set-up allows working with completely opened aperture combined with bright lamps giving a big amount of available light and a high Signal to Noise Ratio. Normally a small basis has the disadvantage of reduced sensitivity. We investigated in methods to compensate the reduced sensitivity via setup and enhanced evaluation methods. For measurement we use synthetic wavelengths. The developed algorithms are completely adaptable concerning the users needs of speed and accuracy. The 3D camera is built from low cost components, robust, nearly handheld and delivers insights also into difficult technical objects like tubes and inside volumes. Besides the realized high resolution phase measurement the system calibration is an important task for usability. While calibrating with common photogrammetric models (which are typically used for actual fringe projection systems) problems were found that originate from the short focal length and the extreme opening angle of the system as well as the large depth of focus. The actual calibration method is outlined and current problems are shown. An improved calibration of the system is discussed for improved results in future.

USable

Digital Light Processing

Structured-light 3D scanner

Tripod (photography)

Camera lens

10.1117/12.501959

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Citations (4)

Lateral Shearing Interferometer based on a Spatial Light Modulator in the Fourier Plane

Springer eBooks (2009)

Claas Falldorf Reiner Klattenhoff Achim Gesierich Christoph von Kopylow Ralf B. Bergmann

Shearing (physics)

Spatial light modulator

Spatial frequency

Shearing interferometer

10.1007/978-3-642-03051-2_13

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Citations (9)

Contents: PhotonicsViews S1/2021

PhotonicsViews (2021)

Christoph Halisch Tim Radel Dieter Tyralla Thomas Seefeld Fabian Thiemicke

10.1002/phvs.202170124

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Citations (0)

Digital Holographic Measurement System

PhotonicsViews (2021)

Fabian Thiemicke Achim Gesierich Wansong Li Claas Falldorf Ralf B. Bergmann

10.1002/phvs.202100007

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3D-Camera for Scene Capturing and Augmented Reality Applications

Thorsten Bothe Achim Gesierich W. Li Christoph von Kopylow N. Kopp

Coordinate based 3D multimedia applications benefit from cost effective, compact and easy-to-use profilers like the miniaturized 3D-Camera that works on basis of the fringe projection technique. The system uses a compact housing and is usable like a video camera with minimum stabilization like a tripod. Camera and projector are assembled with parallel optical axes having coplanar projection and imaging planes. Their axes distance is comparable to the human eyes' distance, giving a compact system of shoebox-size and allow measuring high gradient objects like the interior of tubes and delivering captured scenes with minimum loss by shadowing. Additionally, the 3D-Camera can be used for the Inverse Projection technique, allowing single-frame video rate capture and to virtually place information like virtual labels or defect maps onto the surface of objects, thus, allowing augmented reality applications. In this paper, the concept and realization of the 3D-Camera is described and an overview of possible applications is given.

USable

Tripod (photography)

Frame rate

10.1109/3dtv.2007.4379467

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Citations (9)

Compact 3D camera

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2002)

Thorsten Bothe Wolfgang Osten Achim Gesierich Werner P. O. Jueptner

A new, miniaturized fringe projection system is presented which has a size and handling that approximates to common 2D cameras. The system is based on the fringe projection technique. A miniaturized fringe projector and camera are assembled into a housing of 21x20x11 cm size with a triangulation basis of 10 cm. The advantage of the small triangulation basis is the possibility to measure difficult objects with high gradients. Normally a small basis has the disadvantage of reduced sensitivity. We investigated in methods to compensate the reduced sensitivity via setup and enhanced evaluation methods. Special hardware issues are a high quality, bright light source (and components to handle the high luminous flux) as well as adapted optics to gain a large aperture angle and a focus scan unit to increase the usable measurement volume. Adaptable synthetic wavelengths and integration times were used to increase the measurement quality and allow robust measurements that are adaptable to the desired speed and accuracy. Algorithms were developed to generate automatic focus positions to completely cover extended measurement volumes. Principles, setup, measurement examples and applications are shown.

USable

Aperture (computer memory)

Structured Light

Structured-light 3D scanner

10.1117/12.473573

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Citations (11)