Mr. Steffen Matthias Profile

Steffen Matthias

at Leibniz Univ Hannover

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Publications (4)

Proceedings Article | 20 February 2017 Paper

Fiber-optic fringe projection with crosstalk reduction by adaptive pattern masking

Steffen Matthias, Markus Kästner, Eduard Reithmeier

Proceedings Volume 10117, 101170A (2017) https://doi.org/10.1117/12.2254826

KEYWORDS: High dynamic range imaging, Reflection, Inspection, Sensors, Projection systems, Image quality, Fiber optics, Manufacturing, Measurement devices, Cameras, Deconvolution, Optical fibers, Point spread functions, Reflectivity, Spherical lenses

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Proceedings Article | 24 November 2016 Paper

Fast in-situ tool inspection based on inverse fringe projection and compact sensor heads

Steffen Matthias, Markus Kästner, Eduard Reithmeier

Proceedings Volume 10023, 100230K (2016) https://doi.org/10.1117/12.2247482

KEYWORDS: Inspection, Computer aided design, Image processing, Sensors, Head, Tolerancing, Projection systems, Cameras, Virtual reality, Distortion

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Inspection of machine elements is an important task in production processes in order to ensure the quality of produced parts and to gather feedback for the continuous improvement process. A new measuring system is presented, which is capable of performing the inspection of critical tool geometries, such as gearing elements, inside the forming machine. To meet the constraints on sensor head size and inspection time imposed by the limited space inside the machine and the cycle time of the process, the measuring device employs a combination of endoscopy techniques with the fringe projection principle. Compact gradient index lenses enable a compact design of the sensor head, which is connected to a CMOS camera and a flexible micro-mirror based projector via flexible fiber bundles. Using common fringe projection patterns, the system achieves measuring times of less than five seconds. To further reduce the time required for inspection, the generation of inverse fringe projection patterns has been implemented for the system. Inverse fringe projection speeds up the inspection process by employing object-adapted patterns, which enable the detection of geometry deviations in a single image. Two different approaches to generate object adapted patterns are presented. The first approach uses a reference measurement of a manufactured tool master to generate the inverse pattern. The second approach is based on a virtual master geometry in the form of a CAD file and a ray-tracing model of the measuring system. Virtual modeling of the measuring device and inspection setup allows for geometric tolerancing for free-form surfaces by the tool designer in the CAD-file. A new approach is presented, which uses virtual tolerance specifications and additional simulation steps to enable fast checking of metric tolerances. Following the description of the pattern generation process, the image processing steps required for inspection are demonstrated on captures of gearing geometries.

Proceedings Article | 29 April 2016 Paper

Comparison of LASER and LED illumination for fiber optic fringe projection

Steffen Matthias, Markus Kästner, Eduard Reithmeier

Proceedings Volume 9899, 989905 (2016) https://doi.org/10.1117/12.2225601

KEYWORDS: Endoscopy, LED lighting, Fiber optic components, Optical testing, Optical inspection, Light emitting diodes, Sensors, Fiber optic illuminators, Fiber optics, Fringe analysis, Phase measurement, Measurement devices, Projection systems, Cameras, Speckle pattern, Head

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The inspection of functional elements is a crucial part of modern production cycles. However, with higher integration of production machinery and products, the accessibility for measurement systems is more and more limited. A solution for this problem can be found in endoscopy techniques, which are able to transport the image information for optical measurement methods. In this paper, an optical inspection system based on the fringe projection proﬁlometry technique is presented. The ﬁber-optic fringe projection system uses two high-resolution image ﬁbers to connect a compact sensor head to the pattern generation and camera unit. In order to keep inspection times low, the system is developed with particular focus on fast projection times. This can be achieved by using a digital micro-mirror device, which is capable of projecting grey-scale patterns at a rate of more than 10 images per second. However, due to the low numerical aperture of the optical ﬁbers, a limiting factor for the pattern rate is the illumination path of the pattern generator. Two diﬀerent designs of the illumination path are presented, which are based on a LASER light source as well as a LED light source. Due to low beam divergence and high intensities LASERs are well suited for ﬁber coupling. Unfortunately, the coherent property of the light has negative eﬀects in certain measurement applications, as interference patterns, the so called speckle, appear on rough surfaces. Although speckle reducing methods are employed in the LASER beam path, the emergence of interference cannot be prevented completely. As an alternative, an illumination path based on a LED light source is demonstrated. To compare the eﬀects of the speckle, based on measurements on a planar calibration standard both designs are compared in terms of phase noise, which is directly related to the noise in the reconstructed 3-D point data. Additionally, optical power measurements of both methods are compared to give an estimation of coupling eﬃciency. Finally, the capabilities of the system are shown based on measurements of a micro-contour standard.

Proceedings Article | 22 June 2015 Paper

Endoscopic fringe projection for in-situ inspection of a sheet-bulk metal forming process

Steffen Matthias, Markus Kästner, Eduard Reithmeier

Proceedings Volume 9525, 952513 (2015) https://doi.org/10.1117/12.2184746

KEYWORDS: Sensors, Head, Inspection, Projection systems, Cameras, Endoscopy, Metals, Time metrology, Image sensors, Optical fibers

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Sheet-bulk metal forming is a new production process capable of performing deep-drawing and massive forming steps in a single operation. However, due to the high forming forces of the forming process, continuous process control is required in order to detect wear on the forming tool before production quality is impacted. To be able to measure the geometry of the forming tool in the limited space of forming presses, a new inspection system is being developed within the SFB/TR 73 collaborative research center. In addition to the limited space, the process restricts the amount of time available for inspection. Existing areal optical measurement systems suffer from shadowing when measuring the tool’s inner elements, as they cannot be placed in the limited space next to the tool, while tactile measurement systems cannot meet the time restrictions for measuring the areal geometries. The new inspection system uses the fringe projection optical measurement principle to capture areal geometry data from relevant parts of the forming tool in short time. Highresolution image fibers are used to connect the system’s compact sensor head to a base unit containing both camera and projector of the fringe projection system, which can be positioned outside of the moving parts of the press. To enable short measurement times, a high intensity laser source is used in the projector in combination with a digital micro-mirror device. Gradient index lenses are featured in the sensor head to allow for a very compact design that can be used in the narrow space above the forming tool inside the press. The sensor head is attached to an extended arm, which also guides the image fibers to the base unit. A rotation stage offers the possibility to capture measurements of different functional elements on the circular forming tool by changing the orientation of the sensor head next to the forming tool. During operation of the press, the arm can be travelled out of the moving parts of the forming press. To further reduce the measurement times of the fringe projection system, the inverse fringe projection principle has been adapted to the system to detect geometry deviations in a single camera image. Challenges arise from vibrations of both the forming machine and the positioning stages, which are transferred via the extended arm to the sensor head. Vibrations interfere with the analysis algorithms of both encoded and inverse fringe projection and thus impair measurement accuracy. To evaluate the impact of vibrations on the endoscopic system, results of measurements of simple geometries under the influence of vibrations are discussed. The effect of vibrations is imitated by displacing the measurement specimen during the measurement with a linear positioning stage. The concept of the new inspection system is presented within the scope of the TR 73 demonstrational sheet-bulk metal forming process. Finally, the capabilities of the endoscopic fringe projection system are shown by measurements of gearing structures on a forming tool compared to a CAD-reference.

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