Objective Laser light source is a new type of automotive headlight light source that is efficient, compact, and long-lasting. It has attracted wide attention and research in recent years. It can provide longer and brighter illumination distance and brightness, as well as higher design freedom for heat dissipation and styling. Currently, some universities and research institutions have designed and optimized the freeform optical structure of laser headlights. However, most of the existing methods adopt sub-surface stitching or surface array to achieve the target illuminance distribution, which leads to discontinuity of the freeform surface and increases the production processing difficulty. In addition, the reflectors designed by the existing methods have low energy utilization rate. Aiming at the problems of difficult optical structure design and low energy utilization rate of laser headlights, a new freeform reflector design method based on spherical optimal transport theory is proposed, and a freeform reflector suitable for laser headlights (including low beam and high beam) is designed using this method.
Methods The algorithm flow chart of freeform reflector design is shown (Fig.1). First, according to the coordinates and illuminance of the test points and boundary vertices of the test area given by the regulation GB 25991—2010, the target illuminance on the target surface is obtained by using thin plate spline interpolation method. Then, different density Delaunay triangulation is performed on the target surface. A series of rotating ellipsoids are obtained with the origin and triangulation vertices as focal points (Fig.2), which are used to form the freeform surface. Then, the reflector design algorithm based on spherical optimal transport is used to iterate and obtain the eccentricity of these rotating ellipsoids. According to the size and luminous characteristics of the light source, the area of reflection light on the target surface is determined (Fig.5). If there is light irradiating to the dark area, the position of the sampling point is adjusted (Fig.7) until no reflected light can irradiate to the dark area. Finally, SolidWorks is used to model the reflection surface entity, fit it into a continuous freeform surface, and import it into Lighttools for optical simulation to verify the reliability of the algorithm.
Results and Discussions Simulation is carried out for low beam and high beam respectively. The light source used in simulation is a Lambert light source with a diameter of 1.2 mm and a divergence angle of 60° full angle. The simulation results show that the illuminance distribution on the distribution screen meets the regulation requirements, and the reflection surfaces are smooth and continuous. The illuminance of test points on low beam target surface is listed (Tab.3). The energy utilization rate of low beam system is 96.96%, and a clear bright-dark cutoff line is realized (Fig.12). The illuminance of test points on high beam target surface is listed (Tab.4). The high beam reflector is an array of three identical reflection surfaces. The energy utilization rate of high beam system is 97.80%.
Conclusions This paper proposes an improved reflector design method and designs a freeform reflector for laser headlights (including low beam and high beam). The reflector can not only form a distribution that meets the regulation GB25991—2010 requirements, but also has a smooth surface shape and high energy utilization rate. It can effectively reduce the power consumption of automotive headlights, improve the heat dissipation performance of automotive headlights, extend the service life of laser light sources, and facilitate equipment production and processing. It conforms to the new development trend of energy conservation, environmental protection and efficient use of energy in future automotive industry.
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