Stitched open-loop measurements with a focal-distance-modulated confocal sensor
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Janik Schaude
Janik Schaude has been a research associate at the Institute of Manufacturing Metrology since 2017. Since 2020, he is head of the institute’s calibration laboratory. His main fields of research are nanometrology, atomic force microscopy and optical metrology.
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Andreas Christian Gröschl
Andreas Christian Gröschl has been a research associate at the Institute of Manufacturing Metrology since 2012. From 2015 to 2020, he was head of the institute’s calibration laboratory. His main fields of research are optical and nano metrology.
and
Tino Hausotte
Tino Hausotte is professor and head of the Institute of Manufacturing Metrology. His areas of research are X-ray computed tomography in dimensional metrology, coordinate and surface metrology, micro- and nanometrology, photogrammetry and numerical measurement uncertainty evaluation.
Abstract
The article presents measurements with a high-speed focal-distance modulated fibre-coupled confocal sensor integrated into a nano measuring machine (NMM-1). Combined with an appropriate signal processing, this axial beam modulating sensor yields a linear characteristic curve within a range of about 600 nm. This characteristic curve enables scans in closed-loop constant distance mode, where the controller of the NMM-1 keeps the distance between the measured surface and the sensor constant. Therefore, only one lateral scan is necessary to measure a given topography. Nevertheless, it is also possible to conduct open-loop constant height measurements on discrete heights. The axial offset between the heights needs to be only slightly less than the measuring range of the sensor, leading to a great reduction of the number of needed lateral scans to measure a given topography compared to a conventional confocal sensor, where the axial offset for a similar optical system is typically about 50 nm. To combine the scans taken at different heights, it is possible to stitch them using overlapping measuring points taken at two adjacent heights. Within this article, measurements are conducted on a roughness standard in closed-loop constant distance and in open-loop constant height mode, where the latter are evaluated with and without the application of the stitching algorithm.
Zusammenfassung
In diesem Artikel werden Messungen mit einem hochfrequent fokusabstandsmodulierten, fasergekoppelten Konfokalsensor, welcher in eine Nanomessmaschine (NMM-1) integriert ist, vorgestellt. Kombiniert mit einer geeigneten Signalauswertung liefert dieser Sensor eine lineare Kennlinie innerhalb eines Bereichs von ca. 600 nm. Durch diese werden axial geregelte Scans ermöglicht, bei welchen der Controller der NMM-1 den Abstand zwischen der Messobjektoberfläche und dem Sensor konstant hält. Somit genügt ein lateraler Scan, um eine gegebene Oberfläche zu messen. Weiterhin können ungeregelte laterale Scans auf diskreten Höhen durchgeführt werden, wobei der axiale Offset nur geringfügig kleiner als der Messbereich des Sensors zu sein braucht. Hierdurch reduziert sich die Anzahl notwendiger lateraler Scans zur Messung einer gegebenen Topografie im Vergleich zu einem konventionellen Konfokalsensor, bei welchem der axiale Offset bei einem vergleichbaren optischen System typischerweise etwa 50 nm berägt, ganz erheblich. Um die auf unterschiedlichen Höhen aufgenommenen Scans miteinander zu kombinieren, können wiederum überlappende Messpunkte, welche auf zwei benachbarten Höhen gemessen wurden, für ein Stitching herangezogen werden. In diesem Artikel werden Messungen auf einem Raunormal in beiden Betriebsmodi durchgeführt. Die ungeregelten Messungen werden mit und ohne die Anwendung des Stitching-Algorithmus ausgewertet.
Funding statement: The authors wish to thank the German Research Foundation (DFG) for funding the project “Focus distance modulated fibre-coupled confocal sensor for surface metrology” (HA 5915/10-1).
About the authors
Janik Schaude has been a research associate at the Institute of Manufacturing Metrology since 2017. Since 2020, he is head of the institute’s calibration laboratory. His main fields of research are nanometrology, atomic force microscopy and optical metrology.
Andreas Christian Gröschl has been a research associate at the Institute of Manufacturing Metrology since 2012. From 2015 to 2020, he was head of the institute’s calibration laboratory. His main fields of research are optical and nano metrology.
Tino Hausotte is professor and head of the Institute of Manufacturing Metrology. His areas of research are X-ray computed tomography in dimensional metrology, coordinate and surface metrology, micro- and nanometrology, photogrammetry and numerical measurement uncertainty evaluation.
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Author contributions: JS led the editing and review process and contributed data curation, formal analysis, investigation, methodology, supervision, validation, visualisation and writing of the original draft. AG contributed to formal analysis, investigation, methodology, visualisation and the review process. TH had the project administration and was responsible for the conceptualisation, methodology, funding acquisition, and the idea for the focal-distance-modulated confocal sensor. Additionally TH supported the review process.
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© 2021 Walter de Gruyter GmbH, Berlin/Boston
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Articles in the same Issue
- Frontmatter
- Beiträge
- Qualifizierung von Gleichstrom-Elektrizitätszählern für Schnellladestationen
- Flow distortion effect on electromagnetic flowmeter and mitigation using magnetic flux manipulation
- Dynamic water fill level measurement using a phantom-dependent adaptive electrical capacitance tomography (ECT) method
- Kombinierte Abstands- und Materialerkennung mit induktiven Näherungssensoren
- Stitched open-loop measurements with a focal-distance-modulated confocal sensor
- Eigenerwärmung von Widerstandsthermometern für Lufttemperaturmessungen bei Impulstromspeisung
- Linear, spatio-temporally resolved ultrasound measurement of the liquid fraction distribution in froth
- NMR spectroscopy threshold signal-to-noise ratio
- Investigations on the positioning accuracy of the Nano Fabrication Machine (NFM-100)
