Presentation of the Secondary Image Measuring Instrument

Transcription

1 Presentation of the Secondary Image Measuring Instrument Dr. B. Grubert 7.th International CTI-Forum Automotive Glazing October, 8th 2013

2 Overview 1 Introduction to MÖLLER-WEDEL OPTICAL GmbH 2 Causes and properties of the secondary image 3 Presentation of the laser-based measurement method 4 Comparison with the method according to ECE R43

3 Introduction to MÖLLER-WEDEL OPTICAL GmbH Established 2000 as independent subsidiary of MÖLLER-WEDEL GmbH Located: Wedel near Hamburg Mid-size company Member of the Swiss based HAAG-STREIT Holding AG Main products: Optical measuring and testing instruments

4 Appearance of the Secondary Image Double image with 6 arcmin secondary image angle separation.

5 Limits for Secondary Image Angle Separation Investigations showed that a separation below 10 arcsec are not recognised as annoying. According to the regulation ECE R43 the largest permissible value is 15 arcmin for area A and 25 arcmin for area B.

6 Secondary Images in Windshields Caused by Wedge The secondary images are caused by internal reflections in the windshield.

7 Secondary Images in Windshields Caused by Wedge The secondary image angle is the angle between primary and secondary image beam.

8 Calculation of the Secondary Image Angle Separation for Wedges ɛ 2 α n 2 sin θ 2 cos θ The amount of secondary image angle ɛ increases with increasing internal wedge angle α of the windshield, increases with increasing tilting angle θ of the windshield, increases with increasing refractive index n of the windshield material.

9 Secondary Images in Windshields Caused by Curvature

10 Calculation of the Secondary Image Angle Separation for Curvature ɛ 2 t tan arcsin sin θ n R 3438 arcmin The amount of secondary image angle ɛ decreases with increasing radius of curvature R of the windshield, increases with increasing angle of incidence θ on the windshield, increases with increasing thickness t of the windshield, decreases with increasing refractive index n of the windshield material.

11 Measurement Principle of the Secondary Image Angle Measuring Instrument

12 Image of Camera with Linear Sensitivity Secondary image not visible.

13 Brightness Ratio Primary to Secondary Image The primary image is usually times brighter than the secondary for incidence angles for a camera with 8-bit resolution depth the brightness of the secondary image is only 3 to 5, when the primary image has maximum brightness (255).

14 Image of Camera with Linear Sensitivity (Overmodulated) Primary image is strongly overmodulated in order to make secondary image visible

15 Image of Camera with Logarithmic Sensitivity Primary and secondary image are visible.

16 Polarisation of the Secondary Image The secondary image is predominantly linearly polarised in the perpendicular plane for incidence angles 60 ( Brewster angle). The contrast between primary and secondary image can be improved by a factor of 2 when using linearly polarised illumination instead of non-polarised.

17 Illumination with linearly polarised light parallel direction Secondary image not visible.

18 Secondary Image Angle Measuring Instrument

19 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 power variations 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 distance between laser, windshield and telescope. Measuring range: 68 arcmin 50 arcmin. Measurement uncertainty: better than 0.5 arcmin Objective measurement results due to PC-based image evaluation software.

20 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 (ɛ) and direction (ϕ). Use of predefined customisable measurement templates. Generation of protocol (PDF or ODT). Export of measurement results to spreadsheet software (CSV-format).

21 Windshield View of the Software

22 Live-Image View of the Software

23 Protocol View of the Software

24 Sketch of the Set-Up for Conformity Check According to ECE R Laser Folding3Mirror Telescope3with3Camera Test Wedge 12,6S33330 Double3Collimator Beam- Splitter Cube Beam- Splitter Cube Telescope3with3Camera

25 Photograph of the Set-Up for Conformity Check According to ECE R43

26 Camera Image from the Set-Up According to ECE R43

27 Results for Magnitude of Secondary Image Angle

28 Results for Direction of Secondary Image Angle

29 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 image is strongly improved. 3 Automatic real-time evaluation allows objective measurement of the secondary image angle separation. 4 Evaluation is according to ECE R43.