Mr. Simon Schindwolf Profile

Simon Schindwolf

at Fraunhofer IOF

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Publications (3)

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Proceedings Article | 20 June 2021 Presentation + Paper

Irritation-free optical 3D-based measurement of tidal volume

Christoph Munkelt, Matthias Heinze, Simon Schindwolf, Stefan Heist, Gunther Notni

Proceedings Volume 11787, 117870A (2021) https://doi.org/10.1117/12.2592714

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The measurement of breathing biomechanics, such as tidal volume, can be used to assess both the breathing performance and the respiratory health of individuals. State-of-the-art methods like spirometry or body plethysmography require a mouthpiece or facemask., which can be uncomfortable to the test person. As an alternative, we propose to use the change of the geometric shape of the subject’s torso while breathing. By acquiring 3D point clouds of the person with a real-time near-infrared (NIR) 3D scanner, we measure those changes in a comfortable, irritation-free, and contact-free manner. Accordingly, two continuously measuring structured light 3D sensors, using a GOBO-based aperiodic sinusoidal pattern projector at a wavelength of 850 nm, simultaneously capture the upper front and side torso of the subject at a frame rate of 200 Hz. Both 3D scanners are calibrated and operated in a sensor network fashion, yielding a unified data stream within a global coordinate system. This results in increased coverage and reduced occlusion of the patient’s body shape, enabling robust measurements even in the presence of loose clothing and varying body figure. We collected data from 16 healthy participants in an upright sitting position, wearing everyday clothing during the measurements. For reference, we simultaneously recorded spirometry readings. An algorithm (“OpTidal”) tracks the volume of the subject’s torso from the 3D data. Comparison whith the reference data shows high correlation and low mean error for the absolute tidal volume readings. As such, our method is a viable, safe, and accurate alternative to spirometry and plethysmography.

Proceedings Article | 14 May 2018 Paper

3D shape measurement by thermal fringe projection: optimization of infrared (IR) projection parameters

Martin Landmann, Stefan Heist, Anika Brahm, Simon Schindwolf, Peter Kühmstedt, Gunther Notni

Proceedings Volume 10667, 1066704 (2018) https://doi.org/10.1117/12.2304761

KEYWORDS: 3D metrology, Cameras, 3D modeling, Thermography, Mid-IR, Infrared radiation

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Structured light projection techniques in the visible spectrum of light (VIS) are widely used for fast, contactless, and nondestructive optical three-dimensional (3D) shape measurements. For instance, 3D reconstruction can be performed with a stereo camera system combined with corresponding pixel search and triangulation. Recently, we increased the measurement speed significantly by GOBO projection of aperiodic sinusoidal fringes. Due to their optical properties, such as being glossy, transparent, absorbent, or translucent, some materials cannot be measured in VIS. Changing the spectral range from VIS to infrared (IR) allows measuring the 3D shape of some of these materials. Instead of diffuse reflection of structured light in VIS, the absorption of structured light in IR (e.g., CO₂ laser at 10.6 μm) combined with energy conversion and re-emission of light according to Planck’s law is used. Detection can be carried out at 3–5 μm. Depending on optical and thermal material properties (e.g., complex spectral refractive index, thermal conductivity, specific heat capacity, emissivity), the parameters of the projection unit have to be adjusted, e.g., intensity or illumination time. In this paper, we investigate the influence of material, geometry, and irradiation parameters on the temperature contrast. We present a simulation tool based on the Beer-Lambert law and heat diffusion equation for irradiation-induced thermal pattern on the object’s surface. It allows to determine optimized irradiation settings for well-known material and geometry parameters. We compare the simulation outputs with experimental results.

Proceedings Article | 14 May 2018 Paper

3D shape measurement of glass and transparent plastics with a thermal 3D system in the mid-wave infrared

A. Brahm, S. Schindwolf, M. Landmann, S. Heist, P. Kühmstedt, G. Notni

Proceedings Volume 10667, 106670D (2018) https://doi.org/10.1117/12.2304777

KEYWORDS: 3D metrology, Mid-IR, Cameras, Gas lasers, Glasses, 3D image processing, Thermography, Polymethylmethacrylate, 3D applications

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Structured light projection techniques are well established and an integral part of optical, accurate, and fast threedimensional (3D) measurements. Most problems occur when the projected patterns are not diffusely reflected at the objects’ surfaces. Therefore, we present a new optical 3D mid-wave infrared (MWIR) system based on a “shape from heating” approach with thermal pattern projection. Thus, the three-dimensional shape of materials that are transparent, translucent, or reflective in the visible wavelength range (e.g., glass, plastics, or carbon-fiber-reinforced material) can now be measured optically, contactless, and without a prior process of painting. The system operates with a stereo-vision setup of two cooled MWIR cameras (3-5 μm) and a CO₂ laser projection unit to heat up the objects’ surfaces with aperiodic patterns. A stack of thermal images can be used to find corresponding points in both MWIR cameras and to calculate the 3D information of the surface geometry. In this paper, we introduce the setup and measurement principle of the 3D MWIR system and show some relations between various system parameters (masks, temperature contrast, and material parameters) and the measurement accuracy. We demonstrate the capabilities of our sensor by presenting an impressive 3D result of a real object.

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