Spectral Sensors by Carl Zeiss

Headlight coating

INTRODUCTION

On most automobile models, the protective window ofheadlights is made of plastic.
To protect the surface against scratches and yellowing
by UV light, it is coated externally in the production
process with a protective coating.
The coating is applied by spraying. Subsequently it isdried and cured by IR and UV irradiation.
To keep the reject rate low , it is important to check thethickness of the coating in the production process.
If the coating is too thick, there is the risk of peelingand cracking. If the coating is too thin, it will notprovide sufficient protection. The entire process can be
fully automated.

Figure 1: Headlight coating process

THE METHODE
The coating thickness measuring system determines
the coating thickness and transfers the results to aprocess computer for evaluation. It is possible to selectrejects and record the trend of the batch. In general,
there are two decisive reasons for the in-line use of themeasuring system:a) Optimisation and inspection of coating parameters,such as spraying density , curing time and UV
illuminance

LabCoatm ea su ring h ea ddiffusing p latesb) Quality certification to ISO 9000 standards forautomobile subsuppliers

Figure 2: Thickness measuring system〒164‑0011
東京都中野区中央4‑4‑5第一小林ビル
Tel: 03‑5328‑2858 Fax: 03‑5328‑2859

Spectral Sensors by Carl Zeiss

THE SYSTEM
Coating thickness measurement is based on the principle of white light interference.
A halogen lamp (CLH 500) illuminates the sample through optical fibres and subsequently arranged optical elements.
The light reflections from top and bottom side of the protective coating interfere with each other.
The interference spectrum is detected by a fast diode array spectrometer and evaluated. The method allow themeasuring of double coatings.
The spectra are transmitted to the PC through a serial interface (RS 422). The PC calculates the coating thickness(FFT). Additionally, status data is transmitted informing of plausibility and current system parameters.
An open-end terminal program provides easy integration of the system in existing processes.
THE SOFTWARE
Manual measurement programThis program module serves for manual thickness measurement using the hand-held measuring head (reflection).
Integration time and averaging are selectable. The program measures dark current, reference and sample individually.
The interference curve is displayed. As result of measurement, the thickness appears along with information whether
the result is in or outside the tolerance range.
Flat plate measurement
This program module measures one thickness per diffusing screen (reflection measurement). The measurement isreleased through a switching contact on the measuring head. Thickness,inrange status and measurement standby state are displayed and output through a port.

THE BENEFITS
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Analysis and response time greatly reduced
Fast and continuous monitoring
Established and proved system and method
High reliability, low maintananceEasy to use software
Fiber optics allow flexibility in installation and location of the system

SYSTEM SPECIFICATIONS
Spectral range
Measuring range
Measuring reproducibility
Measuring time/data point
Size of measuring spot

Carl Zeiss
Spectral Sensors

400 ... 1020 nm (optional changeable)
0.6 ... 80 µm (polymer coating)< 0.1 µm
< 300 ms
approx. 3 mm

D-07740 Jena
Telephon:++49 364164 33 85
Telefax:++49 364164 33 11
E-Mail:info.spektralsensorik@zeiss.de
Internet:
http:\\www.zeiss.de