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Correction and Evaluation for Color Aberration on the Cut-off Line of a Vehicle Headlamp

차량용 헤드램프의 Cut-off Line에서 색수차 보정 및 평가

  • Received : 2018.12.11
  • Accepted : 2019.01.17
  • Published : 2019.02.25

Abstract

This paper presents methods to correct and evaluate the chromatic aberration occurring on the cut-off line of a headlamp without additional optical components and alignment process. To correct the chromatic aberration using a geometrical concept, the maximum differences in exit-ray angle between wavelengths are reduced by tilting the convex surface of an aspheric projection lens. To evaluate the chromatic aberration, the position and luminous intensity to be measured are suggested, and the criterion for chromatic aberration is presented through color coordinates. From the evaluation of an automotive headlamp designed using this geometrical method, it is found that the chromatic aberration of the cut-off line is significantly reduced.

본 논문에서는 추가적인 광학부품 및 조립공정 없이 차량용 헤드램프의 cut-off line에서 발생하는 색수차를 보정하는 방법과 이를 평가하는 방법을 제안한다. 기하학적인 방법으로 색수차를 보정하기 위해 비구면 프로젝션 렌즈의 볼록면에 tilt를 적용하여 파장별 최대 출사각도의 차이를 줄였으며, 색수차를 평가하기 위한 위치와 광도를 정하고 색 좌표를 통해 색수차 기준을 제시하였다. 이러한 기하학적인 방법을 이용하여 설계된 자동차용 헤드램프를 평가한 결과 cut-off line의 색수차가 상당히 감소되었음을 확인할 수 있었다.

Keywords

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Fig. 1. Test points for low beam in ECE R112 regulation.

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Fig. 3. Optical structure of a vehicle headlamp.

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Fig. 8. Comparison between spectrums: (a) LED source spectrum, (b) Projected beam spectrum on cut-off line.

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Fig. 9. Effects of difference and balance of the exit ray angle with wavelength.

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Fig. 10. Exit ray angles with wavelength at various tilted angles of aspheric lens surface.

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Fig. 11. Changes of ray bending by tilted surface of an aspheric lens.

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Fig. 12. Layouts of headlamp: (a) Conventional single lens of plano-convex, (b) New single lens of tilted plano-convex.

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Fig. 13. Measurement positions of cut-off line quality.

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Fig. 14. Simulation results for color aberration induced by each aspheric lens: (a) Conventional lens of plano-convex, (b) New lens of tilted plano-convex.

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Fig. 15. Positions having intensity more than 200 cd are marked as black dot points in CIE 1931 chromaticity diagram. Among them, color aberrations exist at the points outside the white light zone: (a) Conventional headlamp with plano-convex lens, (b) New headlamp with tilted plano-convex lens.

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Fig. 16. Comparison of color aberrations on cut-off line at various projected distances: (a) Conventional headlamp with plano-convex lens, (b) New headlamp with tilted plano-convex lens.

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Fig. 2. Various type headlamps: (a) Reflector type, (b) Projector type.

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Fig. 5. Layout for evaluation of color aberration in a headlamp.

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Fig. 6. (a) Layout of a headlamp with PC aspheric lens, (b) Exit ray angles with wavelength at exit pupil.

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Fig. 7. (a) Headlamp beam pattern, (b) Color aberration on cut-off line.

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Fig. 4. Color aberration on cut-off line, induced by upper and lower sections of the lens.

Table 1. Required intensity of ECE R112 regulation at several test points

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Table 2. Differences and balances of the exit ray angles at various tilted angles of aspheric lens surface (in degree)

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Table 3. Comparison of the angular positions having color aberrations between two headlamps

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Table 4. Simulated results in comparison with the requirements of the ECE R112 regulation

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References

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