Optical inline inspection detecting 3D defects on complex free-form surfaces in harsh production environments
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Michael Strohmeier
M. Eng. Michael Strohmeier is a PhD student at BMW Group in Dingolfing since 2016 and works in cooperation with the Institute of Measurement and Automatic Control of the Leibniz University Hannover and the University of Applied Sciences Landshut. His research interests include optical sensor systems for metrology and inspection tasks as well as image processing in industrial fields of application.
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Matthias Schröder
Dipl. Wirt.Ing., MBA Matthias Schröder has been the head of the press shop production at the BMW Group located in Dingolfing in 2018. Since 2019 he supervises the technical planning of the body shop in Dingolfing. Prior to that he has been operating at several planning and operation management positions at the BMW Group based at the production plants Munich, Oxford, Leipzig as well as the Center of Research and Innovation in Munich.
Prof. Dr. rer. nat. Christian Faber holds the professorship for Sensor Technology and Image Processing at the University of Applied Sciences Landshut since 2012, after having worked in several positions in the private sector. Furthermore, he has been a member of the board of the German Society of Applied Optics (DGaO) for nine years. His research interests focus around optical metrology especially for 3D data acquisition and industrial image processing for automated optical inspection (AOI).
Abstract
In today’s industrial manufacturing, quality monitoring is one of the key elements to ensure continuous improvement and to trigger innovations. Especially inline inspection presents considerable challenges to the underlying measurement system. Besides the – in most cases – already not easily satisfiable demands concerning resolution, measurement uncertainty, and cycle time, the robustness of the chosen solution within the overall production environment is an essential requirement for a successful operation in the field. Furthermore, a sufficient ease of operation for the production staff plays a crucial role for the acceptance of the measurement technology. In sheet metal forming, for example, vibrations, ambient light variations and short cycle times as well as oiling and surface variations of the specimen under test challenge and simultaneously limit currently available measurement systems in their application. Especially in automotive manufacturing, visionary design concepts increase the complexity of components with respect to shape and forming capability, leading to critical areas on the object prone to constrictions and cracks. Varying geometry and surface defect characteristics call for an automated 3D inspection to maintain constant product quality for each single part. In this paper, an applied method for the inline inspection of free-form metal surfaces is presented, which allows for quality monitoring even in a harsh environment. So-called inverse fringe projection in combination with single-sideband demodulation facilitates the inspection of free-form metal surfaces in 3D, based on a single camera image (‘single-shot’), which allows for measurement even in a vibrating environment. Only one single camera and a projector are needed, simplifying the integration into series production considerably. Calibration-free, fast setup possibilities enable flexible handling and maintenance in a short-cycled production. First inline tests in a press shop at BMW proof the capability of this method. As an example, constrictions with a depth of about 80 microns could be detected automatically during series production within the press.
Zusammenfassung
In der heutigen industriellen Fertigung nimmt die Qualitätsüberwachung eine zentrale Rolle ein, um nachhaltige Verbesserungen zu schaffen und Innovationen zu initiieren. Besonders für den Inline-Einsatz von Messsystemen zur Bauteilinspektion sind beträchtliche Herausforderungen zu bewältigen. Neben den – in vielen Fällen bereits nicht leicht zu realisierenden – Anforderungen hinsichtlich Auflösung, Messunsicherheit und Taktzeit muss das Verfahren in unkooperativen Produktionsumgebungen oftmals stark schwankenden Messbedingungen und Störeinflüssen robust standhalten. Zusätzlich ist zur Sicherstellung der Akzeptanz der Messtechnik in der Produktion eine einfache Bedienbarkeit durch das Personal von entscheidender Bedeutung. In der Blechumformung beispielsweise begrenzen Vibrationen, schwankendes Umgebungslicht und kurze Taktzeiten sowie die erforderliche Bauteilbeölung und variierende Oberflächenausprägungen die Einsatzmöglichkeit bestehender Messverfahren. Besonders im Automobilbau erhöhen visionäre Designansprüche immer weiter die Komplexität in Form und Oberfläche, was an umformkritischen Bauteilbereichen zu Einschnürungen und Rissen führen kann. Solche variierenden Geometrie- und Oberflächendefekte erfordern eine automatisierte 3D-Inspektion, um eine konstante Produktqualität zu gewährleisten. In diesem Beitrag wird eine angewandte Messmethodik im Bereich der Umformtechnik vorgestellt, welche eine Qualitätsüberwachung auch in harter Produktionsumgebung erlaubt. Die Kombination aus sog. inverser Streifenprojektion und Einseitenbanddemodulation ermöglicht die 3D-Inspektion von metallischen Freiformflächen basierend auf einer einzelnen Kameraaufnahme („Single-Shot“), wodurch die Messung auch in stark vibrierender Umgebung möglich wird. Bestehend aus nur einer Kamera und einem Projektor lässt sich das System leicht in die Serienproduktion integrieren. Kalibrierfreie, schnell zu installierende Aufbauten erlauben eine flexible Handhabung und Wartung in einer streng taktzeitgesteuerten Produktion. Erste Inline-Versuche in einem Presswerk bei BMW belegen die grundlegende Fähigkeit der Messmethodik – so konnten beispielsweise Einschnürungen mit einer Tiefe von 80 µm während der Serienfertigung im Inline-Einsatz erfolgreich automatisiert detektiert werden.
About the authors
M. Eng. Michael Strohmeier is a PhD student at BMW Group in Dingolfing since 2016 and works in cooperation with the Institute of Measurement and Automatic Control of the Leibniz University Hannover and the University of Applied Sciences Landshut. His research interests include optical sensor systems for metrology and inspection tasks as well as image processing in industrial fields of application.
Dipl. Wirt.Ing., MBA Matthias Schröder has been the head of the press shop production at the BMW Group located in Dingolfing in 2018. Since 2019 he supervises the technical planning of the body shop in Dingolfing. Prior to that he has been operating at several planning and operation management positions at the BMW Group based at the production plants Munich, Oxford, Leipzig as well as the Center of Research and Innovation in Munich.
Prof. Dr. rer. nat. Christian Faber holds the professorship for Sensor Technology and Image Processing at the University of Applied Sciences Landshut since 2012, after having worked in several positions in the private sector. Furthermore, he has been a member of the board of the German Society of Applied Optics (DGaO) for nine years. His research interests focus around optical metrology especially for 3D data acquisition and industrial image processing for automated optical inspection (AOI).
References
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© 2019 Walter de Gruyter GmbH, Berlin/Boston
Artikel in diesem Heft
- Frontmatter
- Editorial
- 119. Jahrestagung der Deutschen Gesellschaft für angewandte Optik in Aalen
- Beiträge
- Topografiemessung an verkapselten mikroelektromechanischen Systemen mittels Kurzkohärenz-Interferometrie
- Photogrammetric determination of the refractive properties of liquid crystal displays
- Messen von asphärischen Linsenformen mittels räumlicher Kohärenz
- Reguläre Beiträge
- Optical inline inspection detecting 3D defects on complex free-form surfaces in harsh production environments
- Dickenbestimmung transparenter Schichten mit einem chromatisch-konfokalen Sensor
Artikel in diesem Heft
- Frontmatter
- Editorial
- 119. Jahrestagung der Deutschen Gesellschaft für angewandte Optik in Aalen
- Beiträge
- Topografiemessung an verkapselten mikroelektromechanischen Systemen mittels Kurzkohärenz-Interferometrie
- Photogrammetric determination of the refractive properties of liquid crystal displays
- Messen von asphärischen Linsenformen mittels räumlicher Kohärenz
- Reguläre Beiträge
- Optical inline inspection detecting 3D defects on complex free-form surfaces in harsh production environments
- Dickenbestimmung transparenter Schichten mit einem chromatisch-konfokalen Sensor
