It all started with LW and SW in the early 1990s. BYK-Gardner´s well-known wave-scan analyzes waviness based on wavelength range and its intensity.
Picture 1: Waviness principle LW - SW
The LW value integrates waviness in the range of 1.2 - 12 mm and the SW value sums up fine textures in the range of 0.3 - 1.2 mm.
Picture 2: Sample measurements LW - SW
As material and process parameters changed, these integrated parameters were not always sufficient to differentiate various surface appearances.
Picture 3: Five new wavelength ranges
Folglich wurde im Jahr 2001 die nächste Generation vorgestellt: Das wave-scan DOI. Dieses Messgerät misst nun fünf Wellenlängenbereiche und bestimmt zusätzlich den sog. Distinct of Image (DOI). Diese sechs Messparameter werden grafisch dargestellt und als Strukturspektrum bezeichnet, was ein idealer Leitfaden für die Fehlersuche und Optimierung des Erscheinungsbildes - basierend auf Material- oder Applikationseinflüssen ist.
Bild 4: DOI-Prinzip des wave-scan und Strukture-Spectrum
Image 5: Film de construction et spectre de structure
Image 6: Rugosité du primaire - après ponçage
To keep it simple for QC control and management reports 1- or 2-dimensional scales are used. Additionally to LW and SW, OEM specific scales with different target values and tolerances were developed over the years.
Picture 7: Overview OEM scales - selection in smart-chart
In 2012, a new approach was initiated within the VW/Audi group and was first presented at our BYK-Gardner User Meeting in 2013.
Since then several visual studies were conducted and it became obvious that observers can distinguish samples based on its dominating wavelengths. In order to determine a specific waviness size, the optical profile of the wave-scan measurement needs to be analyzed with a so-called Fast Fourier Transformation, which is in simple words, a structure spectrum with much higher resolution.
The results are weighted according to the VW / Audi study to simulate an observation distance of 1.5 m.
Picture 8: Visual evaluation at Audi
Picture 9: FFT
Picture 10: CSF
Picture 11: FFT weighted
The result is up to four new scales:
- Dominant LW wavelength
and its maximum amplitude - Dominant SW wavelength
and its maximum amplitude
Highest intensity of dominant wavelenght > 2.4 mm:
- Dominant LW = 4.6 mm
- Dominant LW intensity = 25.1
Highest intensity of dominant wavelenght < 2.4 mm:
- Dominant SW = 1.3 mm
- Dominant SW intensity = 13.6
Two dominant wavelengths:
- Dominant LW = 4.4 mm
- Dominant LW intensity = 8.6
- Dominant SW = 1.3 mm
- Dominant SW intensity = 8.2
Curious? The new firmware is free of charge and available for download in the smart-chart package under:
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