High-speed 3D shape measurement of transparent objects by sequential thermal fringe projection and image acquisition in the long-wave infrared. - In: Thermosense: Thermal Infrared Applications XLV, (2023), 125360P, S. 125360P-1-125360P-11
Recently, we have successfully tackled the challenge of measuring the 3D shape of uncooperative materials, i.e., materials with optical properties such as being glossy, transparent, absorbent, or translucent. By projecting sequential thermal fringes in the long-wave infrared (LWIR) combined with a stereo camera setup in the midwave infrared (MWIR), we were able to three-dimensionally record object shapes within one second. However, in many applications, e.g., for 100 % quality assurance, even shorter measurement times are required. To achieve camera frame rates higher than 125 fps at room temperature, Max Planck’s law of thermal emission teaches us a change in the camera spectral range from MWIR to LWIR. If irradiation and image acquisition have to run in parallel, the camera chips must therefore be protected against the radiation projected by the CO2 laser at a wavelength of 10.6 µm. Appropriate filters have been available only recently. In this contribution, we present our high-speed LWIR 3D sensor. The work includes a characterization of our setup regarding its measurement accuracy and speed. The results are compared to the performance of previous thermal 3D sensors. We show 3D measurement results of static objects as well as of a dynamic measurement situation of a transparent object. Furthermore, we demonstrate that our setup enables us to extend the measurability of material classes towards objects with high thermal conductivities.
https://doi.org/10.1117/12.2663331
Underwater 3D scanning system for cultural heritage documentation. - In: Remote sensing, ISSN 2072-4292, Bd. 15 (2023), 7, 1864, S. 1-14
Three-dimensional capturing of underwater archeological sites or sunken shipwrecks can support important documentation purposes. In this study, a novel 3D scanning system based on structured illumination is introduced, which supports cultural heritage documentation and measurement tasks in underwater environments. The newly developed system consists of two monochrome measurement cameras, a projection unit that produces aperiodic sinusoidal fringe patterns, two flashlights, a color camera, an inertial measurement unit (IMU), and an electronic control box. The opportunities and limitations of the measurement principles of the 3D scanning system are discussed and compared to other 3D recording methods such as laser scanning, ultrasound, and photogrammetry, in the context of underwater applications. Some possible operational scenarios concerning cultural heritage documentation are introduced and discussed. A report on application activities in water basins and offshore environments including measurement examples and results of the accuracy measurements is given. The study shows that the new 3D scanning system can be used for both the topographic documentation of underwater sites and to generate detailed true-scale 3D models including the texture and color information of objects that must remain under water.
https://doi.org/10.3390/rs15071864
Interactive robot teaching based on finger trajectory using multimodal RGB-D-T-data. - In: Frontiers in robotics and AI, ISSN 2296-9144, Bd. 10 (2023), 1120357, S. 01-13
The concept of Industry 4.0 brings the change of industry manufacturing patterns that become more efficient and more flexible. In response to this tendency, an efficient robot teaching approach without complex programming has become a popular research direction. Therefore, we propose an interactive finger-touch based robot teaching schema using a multimodal 3D image (color (RGB), thermal (T) and point cloud (3D)) processing. Here, the resulting heat trace touching the object surface will be analyzed on multimodal data, in order to precisely identify the true hand/object contact points. These identified contact points are used to calculate the robot path directly. To optimize the identification of the contact points we propose a calculation scheme using a number of anchor points which are first predicted by hand/object point cloud segmentation. Subsequently a probability density function is defined to calculate the prior probability distribution of true finger trace. The temperature in the neighborhood of each anchor point is then dynamically analyzed to calculate the likelihood. Experiments show that the trajectories estimated by our multimodal method have significantly better accuracy and smoothness than only by analyzing point cloud and static temperature distribution.
https://doi.org/10.3389/frobt.2023.1120357
3D-Formvermessung transparenter Objekte mit thermischer Streifenprojektion. - In: Leitfaden zur Wärmefluss-Thermographie, (2022), S. 66-69
Miniaturisiertes, ortsaufgelöstes, multispektrales, echtzeitfähiges Bildverarbeitungssystem für industrielle und biomedizinische Anwendungen (MINIMIZE); Teilvorhaben: MINIMIZE-Processing : Schlussbericht zum Teilvorhaben MINIMIZE-Processing : Laufzeit des Vorhabens: 01.06.2018-31.12.2021. - Ilmenau : Technische Universiät Ilmenau, Fachgebiet Qualitätssicherung und Industrielle Bildverarbeitung. - 1 Online-Ressource (20 Seiten, 6,49 MB)Förderkennzeichen BMBF 13N14835
https://doi.org/10.2314/KXP:1852350644
Kontaktlose Überwachung der Vitalparameter Neu- und Frühgeborener durch multispektrale 3D-Messung in Echtzeit - NeoVital; TP3: Entwicklung eines Multispektral-3D-Sensors für die kontaktlose Vitalparametermessung - MeVa : Schlussbericht im Programm Zwanzig20 - Allianz 3Dsensation. - Ilmenau : [Technische Universität Ilmenau]. - 1 Online-Ressource (26 Seiten, 2,67 MB)Förderkennzeichen BMBF 03ZZ0482C
https://doi.org/10.2314/KXP:1852296879
Training program for the metric specification of imaging sensors. - In: Acta IMEKO, ISSN 2221-870X, Bd. 11 (2022), 4, S. 1-6
Measurement systems in industrial practice are becoming increasingly complex and the system-technical integration levels are increasing. Nevertheless, the functionalities can in principle always be traced back to proven basic functions and basic technologies, which should, however, be understood and developed. For this very reason, the teaching of elementary basics in engineering education is unavoidable. The present paper presents a concept to implement a contemporary training program within the practical engineering education on university level in the special subject area of optical coordinate measuring technology. The students learn to deal with the subject area in a fundamentally oriented way and to understand the system-technical integration in detail from the basic idea to the actual solution, which represents the common practice in the industrial environment. The training program is designed in such a way that the basics have to be worked out at the beginning, gaps in knowledge are closed by the aspect of group work and the targeted intervention of a supervisor. After the technology has been fully developed theoretically, the system is put into operation and applied with regard to a characterizing measurement. The measurement data are then evaluated using standardized procedures. A special part of the training program, which is to promote the own creativity and the comprehensible understanding, represents the evaluation of the modulation transfer function (MTF) of the system by a self-developed algorithmic program section in the script-oriented development environment MALTAB, whereby students can supportively fall back on predefined functions for the evaluation, whose implementation however still must be accomplished.
https://doi.org/10.21014/actaimeko.v11i4.1361
Inline process monitoring of hairpin welding using optical and acoustic quality metrics. - In: 2022 12th International Electric Drives Production Conference (EDPC), (2022), insges. 8 S.
Due to the electrification of the drive train, hairpin technology for stators has established itself in the automotive industry. Hairpins are rectangular copper wires connected to full stator coils using laser beam welding. The welding results depend on the preliminary processes and tolerances of the welding system. The quality of the connection is defined by its cross-sectional area that is influenced by porosity. Another quality characteristic are spatters. The quantification of the cross-sectional area and porosity of the welding seams is usually carried out post-process using X-Ray computed tomography (CT). This paper investigates spatters using high-speed camera-based image processing and airborne sound using an optical microphone. By varying influencing factors of the welding result (position deviations, maximum laser power, focal position shift, stripping quality), different quality levels of the welding joints are generated. With the developed method for in-process evaluation of high-speed camera images, a spatter detection and quantification of their number and size is enabled. The method shows an accuracy of 84%. In addition, the characteristics of the recorded airborne sound during the process allows conclusions to be drawn about the welding results. Deviations in maximum laser power, height offset, focal position shift and stripping quality can be detected. Both methods provide a reliable inline monitoring of the welding process as well as its quantitative quality assessment.
https://doi.org/10.1109/EDPC56367.2022.10019745
Process control of laser ablated coated surface applying an adapted image processing system. - In: 12th CIRP Conference on Photonic Technologies, (2022), S. 584-587
The aim of the work was the implementation of a control system for laser ablation processes of optical coatings. Therefore, a glass substrate with metal-based coating was ablated using picosecond laser radiation. Depending on the laser fluence and scanning parameters (pulse and line distance) the removal of the layer has been investigated. With the help of an adapted image processing system a global characterization of the transmissive properties of the surfaces where the optical coating was ablated has been performed. After the ablation process, the surfaces were scanned and the resulting areas where the transmissive properties are OK or not OK have been detected. Due to the generated transformation of the image data to x- and y-coordinates a subsequent laser ablation corrects the detected areas which are not OK in a control loop. The developed approach can help to reuse expensive optics and masks in industrial and scientific applications.
https://doi.org/10.1016/j.procir.2022.08.155
Efficient freeform-based pattern projection system for 3D measurements. - In: Optics express, ISSN 1094-4087, Bd. 30 (2022), 22, S. 39534-39543
For three-dimensional (3D) measurement of object surface and shape by pattern projection systems, we used a hybrid projection system, i.e., a combination of a projection lens and a transmissive freeform to generate an aperiodic sinusoidal fringe pattern. Such a freeform effects a light redistribution, thus leading to an effective and low-loss pattern projection, as it increases the total transmission intensity of the system and has less power dissipation than classical projection systems. In this paper, we present the conception and realization of the measurement setup of a transmissive fringe projection system. We compare the characteristics of the generated intensity distribution with the classical system based on GOBO (GOes Before Optics) projection and show measurement results of different surface shapes, recorded with the new system.
https://doi.org/10.1364/OE.470564