Presentation of the Secondary ImageMeasuring Instrument
Dr. B. Grubert
7.th International CTI-Forum ”Automotive Glazing“
October, 8th 2013
Overview
1 Introduction to MOLLER-WEDEL OPTICAL GmbH2 Causes and properties of the secondary image3 Presentation of the laser-based measurement method4 Comparison with the method according to ECE R43
Introduction to MOLLER-WEDEL OPTICAL GmbH
Established 2000 asindependent subsidiary ofMOLLER-WEDEL GmbHLocated: Wedel nearHamburgMid-size companyMember of the Swissbased HAAG-STREITHolding AGMain products: Opticalmeasuring and testinginstruments
Appearance of the Secondary Image
Double image with 6 arcmin secondary image angle separation.
Limits for Secondary Image Angle Separation
Investigations showed that a separation below 10 arcsecare not recognised as annoying.According to the regulation ECE R43 the largestpermissible value is 15 arcmin for area A and 25 arcmin forarea B.
Secondary Images in Windshields Caused by Wedge
The secondary images are caused by internal reflectionsin the windshield.
Secondary Images in Windshields Caused by Wedge
The secondary image angle is the angle between primaryand secondary image beam.
Calculation of the Secondary Image Angle Separationfor Wedges
ε ≈ 2α√
n2 − sin θ2
cos θ
The amount of secondary image angle εincreases with increasing internal wedge angle α of thewindshield,increases with increasing tilting angle θ of the windshield,increases with increasing refractive index n of thewindshield material.
Secondary Images in Windshields Caused byCurvature
Calculation of the Secondary Image Angle Separationfor Curvature
ε ≈ 2t tan arcsin sin θ
nR
3438 arcmin
The amount of secondary image angle εdecreases with increasing radius of curvature R of thewindshield,increases with increasing angle of incidence θ on thewindshield,increases with increasing thickness t of the windshield,decreases with increasing refractive index n of thewindshield material.
Measurement Principle of the Secondary Image AngleMeasuring Instrument
Image of Camera with Linear Sensitivity
Secondary image not visible.
Brightness Ratio Primary to Secondary Image
The primary image is usually 50 ∼ 100 times brighter than thesecondary for incidence angles 50◦ ∼70◦.→ for a camera with 8-bit resolution depth the brightness of
the secondary image is only 3 to 5, when the primaryimage has maximum brightness (255).
Image of Camera with Linear Sensitivity(Overmodulated)
Primary image is strongly overmodulated in order to makesecondary image visible
Image of Camera with Logarithmic Sensitivity
Primary and secondary image are visible.
Polarisation of the Secondary Image
The secondary image is predominantly linearly polarised inthe perpendicular plane for incidence angles ∼60◦ (∼Brewsterangle).→ The contrast between primary and secondary image can
be improved by a factor of 2 when using linearly polarisedillumination instead of non-polarised.
Illumination with linearly polarised light — paralleldirection
Secondary image not visible.
Secondary Image Angle Measuring Instrument
Features of the Secondary Image Angle Measurement(SIAM)-Instrument
Instrument is based on a proven set-up used at VW.No disturbance by local refractive index and powervariations due to small diameter of the test beam.Easy and fast set-up of the instrument.Laser is eyesafe (laser safety class 2).Measurement value is independent of the distancebetween laser, windshield and telescope.Measuring range: 68 arcmin × 50 arcmin.Measurement uncertainty: better than 0.5 arcminObjective measurement results due to PC-based imageevaluation software.
Features of the Evaluation Software
Real-time evaluation with 25 Hz frame rate.Automatic brightness control.Evaluation according to ECE R43.Display of the double image angle with magnitude (ε) anddirection (ϕ).Use of predefined customisable measurement templates.Generation of protocol (PDF or ODT).Export of measurement results to spreadsheet software(CSV-format).
Windshield View of the Software
Live-Image View of the Software
Protocol View of the Software
Sketch of the Set-Up for Conformity Check Accordingto ECE R43
Double3Collimator Telescope3with3Camera
Telescope3with3CameraFolding3MirrorLaser
120°
150°
210°
240° 300°
330°
30°
60°
10´
10´
20´
20´
30´
30´
10´
10´
20´
20´
30´
30´
12,6S33330°
Beam-SplitterCube
Beam-SplitterCube
TestWedge
Photograph of the Set-Up for Conformity CheckAccording to ECE R43
Camera Image from the Set-Up According to ECE R43
Results for Magnitude of Secondary Image Angle
Results for Direction of Secondary Image Angle
Summary
1 The secondary image is predominantly linearly polarised.2 By using a camera with logarithmic sensitivity and linear
polarised illumination the visibility of the secondary imageis strongly improved.
3 Automatic real-time evaluation allows objectivemeasurement of the secondary image angle separation.
4 Evaluation is according to ECE R43.