Joerg Gerber’s research while affiliated with Fraunhofer Institute for Applied Optics and Precision Engineering and other places

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Publications (11)


Analysis of the measurement capability of optical fringe projection systems
  • Article

May 2003

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8 Reads

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2 Citations

Proceedings of SPIE - The International Society for Optical Engineering

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Joerg Gerber

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Matthias Heinze

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Quality control describes numerous methods for monitoring the quality of a production process. With respect to this it will be a growing requirement on optical 3D-measurement techniques to reach the demands of the measurement capability. Here the limitations to fulfill these demands under industrial conditions are discussed when using fringe-projection technique for 3D-measurement. The analysis is done while measuring an automotive stamping part and a 3D-gauge with a telecentric fringe projection system, as examples. In the analysis we determined some geometric features like diameter of hole and bending angles of parts of the object surface. The results demonstrate the possibility to achieve a standard deviation of lower than 1 mum within a measurement volume of 90 mm in diameter for the geometric features. Due to the low standard deviation a measurement capability has been reached like tactile measurement systems. To achieve this the influence of the locale choice of the geometric fitting procedure onto the point cloud has to be taken into account.


Von der Punktewolke zum Stichmaß

January 2000

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5 Reads

Digltalization of CAD models, complete manufacturing control and timely quality control of components are important tasks of modem industrial inspection. In many cases the 3-D object shape and its surface roughness are of special interest, whereas optical measurement techniques based on structured light are finding increasing application. Unfortunately, shadowing within the image field arises when those 3-D inspection systems are applied to objects having a strong surface tilt. Moreover, distortions appear if the detector is struck by light intensities too high for linear recording. These may be caused by specular reflection and diffraction at the object surface. Thus, within these parts of the images, one cannot obtain useful values during coordinate measurement. Using simple optical 3-D measurement systems with structured light, as a rule, only one part of the object surface is visible to the observation system and the projection system at the same time. As a result one gets one patch of the whole object surface. Only this part can be measured when observing the object with a matrix camera.


Industrial Lasers and Inspection (EUROPTO Series)

September 1999

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7 Reads

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1 Citation

Proceedings of SPIE - The International Society for Optical Engineering

Richard M. Kowarschik

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Joerg Gerber

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[...]

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The described 3D-measurement system with fringe projection applies the principle of uniform scale representation by the exclusive use of phase-measurement values for the coordinates of each point. The object under test is successively illuminated with a grating structure from at least 3 different directions with a telecentric system, whereas gray-code is combined with four or five 90 degs phase-shifts. A CCD-camera records the intensity distribution of the fringes that appear as intersection lines on the surface of the object. This gives the linearly independent absolute phase values which are necessary for the calculation of the coordinates. It should be pointed out that all coordinates (x, y, z) are determined with the same accuracy. To compensate the influence of specular reflections or shadow areas up to 15 directions of light projection can be used. Moreover, the object can be rotated around a second axis yielding other views of the object. So we get different patches of the object that are transformed into a global coordinate system without any interactive user help. During this procedure correlation methods or special points are not necessary. The calibration of the 3D-orientation of the second axis is realized with a special calibration body.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.


Adaptive optical 3D measurement with structured light

September 1999

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46 Reads

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94 Citations

Proceedings of SPIE - The International Society for Optical Engineering

The described 3D-measurement system with fringe projection applies the principle of uniform scale representation by the exclusive use of phase-measurement values for the coordinates of each point. The object under test is successively illuminated with a grating structure from at least 3 different directions with a telecentric system, whereas gray-code is combined with four or five 90 degs phase-shifts. A CCD-camera records the intensity distribution of the fringes that appear as intersection lines on the surface of the object. This gives the linearly independent absolute phase values which are necessary for the calculation of the coordinates. It should be pointed out that all coordinates (x, y, z) are determined with the same accuracy. To compensate the influence of specular reflections or shadow areas up to 15 directions of light projection can be used. Moreover, the object can be rotated around a second axis yielding other views of the object. So we get different patches of the object that are transformed into a global coordinate system without any interactive user help. During this procedure correlation methods or special points are not necessary. The calibration of the 3D-orientation of the second axis is realized with a special calibration body.


Full-hemisphere automatic optical 3D measurement system

September 1997

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9 Reads

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7 Citations

Proceedings of SPIE - The International Society for Optical Engineering

The measurement of 3D object shapes for the purpose of digitization of CAD-models and for the complete manufacturing control of components are important tasks of modern industrial inspection. The proposed 3D measurement system using structured-light illumination has the ability to avoid illumination-caused difficulties, like shadowing and excessive light intensities by light reflection and diffraction at the surface of the object, while measuring technical surfaces. For this purpose, the object under test is successively illuminated with a periodic grating structure from at least three different directions, using a telecentric projection system. At least three linearly independent phase-measurement values are measured by gray- code techniques to calculate the 3D coordinates of the object points. The experimental setup allows the determination of phase-measurement values with illuminations from up to 16 different directions. This is connected with a simultaneous variation of the intensity of the projected grating structures. Thus, areas of shadows are `shifted' across the object surface to spots where they have no influence on the result of the measurement, and also specular effects can be suppressed. Furthermore, in order to obtain the entire surface, the object to be digitized must be covered by many overlapping views taken from different directions. To view the entire surface, the object is moved into various measuring positions, using a second rotation axis. These views are merged within an object-centered coordinate system and are automatically rearranged into a uniform grid. For this purpose, a calibration procedure has been developed to measure absolute coordinates within a defined object coordinate system, so that the combination of the particular images is simple, because all measurements are performed within the same system of object coordinates. The power of this concept has been experimentally demonstrated, for example, by measuring the complete 3D shape and/or the roughness of specularly reflecting technical surfaces of different volumina.


Lasers, Optics, and Vision for Productivity in Manufacturing I

September 1996

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6 Reads

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8 Citations

Proceedings of SPIE - The International Society for Optical Engineering

The paper is aimed at the description of an optical shape measuring technique based on a consistent principle using fringe projection technique. We demonstrate a real 3D- coordinate measuring system where the sale of coordinates is given only by the illumination-structures. This method has the advantages that the aberration of the observing system and the depth-dependent imaging scale have no influence on the measuring accuracy and, moreover, the measurements are independent of the position of the camera with respect to the object under test. Furthermore, it is shown that the influence of specular effects of the surface on the measuring result can be eliminated. Moreover, we developed a very simple algorithm to calibrate the measuring system. The measuring examples show that a measuring accuracy of 10-4 (i.e. 10 micrometers ) within an object volume of 100 X 100 X 70 mm3 is achievable. Furthermore, it is demonstrated that the set of coordinate values can be processed in CNC- and CAD-systems.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.


Optical 3D coordinate-measuring system using structured light

September 1996

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23 Reads

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6 Citations

Proceedings of SPIE - The International Society for Optical Engineering

The paper is aimed at the description of an optical shape measuring technique based on a consistent principle using fringe projection technique. We demonstrate a real 3D- coordinate measuring system where the sale of coordinates is given only by the illumination-structures. This method has the advantages that the aberration of the observing system and the depth-dependent imaging scale have no influence on the measuring accuracy and, moreover, the measurements are independent of the position of the camera with respect to the object under test. Furthermore, it is shown that the influence of specular effects of the surface on the measuring result can be eliminated. Moreover, we developed a very simple algorithm to calibrate the measuring system. The measuring examples show that a measuring accuracy of 10-4 (i.e. 10 micrometers ) within an object volume of 100 X 100 X 70 mm3 is achievable. Furthermore, it is demonstrated that the set of coordinate values can be processed in CNC- and CAD-systems.




Three-coordinate measuring system with structured light

November 1994

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13 Reads

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16 Citations

Proceedings of SPIE - The International Society for Optical Engineering

The measurement of three-dimensional object shapes plays an important role in machine vision, solid modeling and other industrial applications. Well known optical methods for 3D- shape inspection are moire-techniques and contouring. Unfortunately, as a rule they are lacking because they measure only one coordinate, i.e., the height above a reference surface. The other coordinates in the reference plane have to be determined using the pixel distance of the observing CCD-camera or by other means. Here, we demonstrate a real 3D-coordinate measuring system using fringe projection techniques where the scale of coordinates is given by the illumination-structures. This method has the advantage that the aberration of the observing system and the depth-dependent imaging scale have no influence on the measuring accuracy. Moreover, the measurements are independent of the position of the camera with respect to the object under test.


Citations (7)


... A 3D reconstruction can be achieved using fringe projections [17][18][19][20][21][22][23][24][25][26]. Nevertheless, a grating with sinusoidal transparency [27][28][29] delivers a higher accuracy [30]. However, it is cumbersome to manufacture an accurate sinusoidal grating, and the T. Yang and F. Gu The advent of digital light processing (DLP) technology has changed the modulation paradigm of structured-light, in which the spatial light field is programmable. ...

Reference:

Overview of modulation techniques for spatially structured-light 3D imaging
Three-coordinate measuring system with structured light
  • Citing Article
  • November 1994

Proceedings of SPIE - The International Society for Optical Engineering

... Various researchers have proposed different registration approaches, including using an iterative closest point algorithm [8,9], a photogrammetric technique [10], a self-calibration method [11], and moving objects in multiple overlapping measurement positions together with a special 3D calibration [12,13]. However, reliable, rapid, general purpose 3D registration is still a difficult and open problem. ...

Full-hemisphere automatic optical 3D measurement system
  • Citing Article
  • September 1997

Proceedings of SPIE - The International Society for Optical Engineering

... A colored light source is assigned to illuminate the part, multiple cameras are assigned to photograph different areas, and each camera is viewed through an appropriate colored filter so that only the particular colored light is visible. Kowarschik [169] et al. used the projection orientations of as many as 15 fringe patterns to offset the impact of specular reflections or dark areas. In addition, the target object can be revolved and the camera captured images from different viewing angles and converts them to local coordinates, which are eventually synthesized into global coordinates. ...

Adaptive optical 3D measurement with structured light
  • Citing Article
  • September 1999

Proceedings of SPIE - The International Society for Optical Engineering

... As most technical surfaces show hybrid (i.e. locally mixed) specularly reflective and scattering behavior [Sch96], choosing the correct GOP technique usually requires test measurements with both techniques and measurement parameter optimization. For the areal shape measurement of objects with spatially varying reflective behavior, neither of the techniques can be used. ...

Optical 3D-Measurements of Objects with Technical Surfaces
  • Citing Article
  • January 1996

Proceedings of SPIE - The International Society for Optical Engineering

... The advantage of this setup is the constancy of magnification connected with a simple linear mathematics for a 3D triangulation system. 10 In using such telecentric systems one has to correct the deviation of the scaling factor for different object distances. The change in the image size ⌽ , ͑corr͒ is dependent on the image size itself and on the distance ⌽ of the object from the image plane ...

Optical 3D coordinate-measuring system using structured light
  • Citing Article
  • September 1996

Proceedings of SPIE - The International Society for Optical Engineering

... In order to solve the problem of variable measurement distance, some scholars have proposed monocular vision measurement methods using telecentric lenses [19][20][21][22] or a 3D measurement method based on binocular stereo vision [23][24][25] or fringe projection [26][27][28][29][30]. For example, Quan et al. adopted the object telecentric optical path to avoid the measurement error caused by the change of working distance in the measurement process and measured the hole of the tube support plate of the steam generator with high precision [23], but its field of view of each measurement is only about 38 mm × 32 mm, which is not suitable for large-size workpieces. ...

Analysis of the measurement capability of optical fringe projection systems
  • Citing Article
  • May 2003

Proceedings of SPIE - The International Society for Optical Engineering

... However, the DFP system is derived from the stereo vision (SV) system based on the principle of triangulation [9], meaning that the viewpoint of the camera is different from that of the projector. For an SV system, the shadow induced by triangulation is difficult to completely eliminate [10,11,12]. Therefore, the extraction of an accurate phase map in DFP could be challenging when the camera captures fringe images with shadows. ...

Lasers, Optics, and Vision for Productivity in Manufacturing I
  • Citing Article
  • September 1996

Proceedings of SPIE - The International Society for Optical Engineering