Freeform Lens Design For Illumination Of Vehicle-mounted Head Up Display Projector

Due to the advantage of small packaging size,high conversion efficiency,low power consumption,long life and environment-friendly,LED become the fourth generation source which gradually taking place of the traditional light source such as incandescent and halogen.Now LED is gradually applied to the field of illumination system of projectors with the improvement of the luminous efficiency.However,compared with the conventional light source,the beam divergence angle of the LED light source is relatively large.The LED without secondary optical design will fail to meet the prescribed irradiance distribution,and also cause a large amount of energy loss.Therefore,we need to design LED secondary lens to redistribute the light in order to increase the light efficiency and meet the specific lighting standard.In this paper,three LED free-form lenses are designed according to the non-imaging optical theory,which can be used to realize uniform rectangular illumination of LCD display chips in vehicle-mounted Head Up Display projectors.Compared with the conventional projection lighting system based on the principle of imaging optics,it has more compact structure with fewer optical elements.The designed lenses satisfy the requirements of the illumination system of the vehicle-mounted Head Up Display projectors: To obtain a rectangular light spot with the uniformity of above 90% on the LCD within the distance of 50 mm from the LED,and the size of the rectangular light spot is the same as the size of the LCD.The application of the free-form light distribution element can further realize the miniaturization of the illumination system.And all the designed lenses in this paper can be processed to get the actual product.First of all,this paper describes the characteristics of LED light source,traditional lighting system,free-form surface design method in light distribution and non-imaging optical theory in detail.Secondly,three kinds of LED freeform lenses are designed based on non-imaging optical theory.The compact LED freeform lens,the outer surface of witch uses a step-by-step design method combined with a tangential iteration method.Firstly,we derive the relationship of the points on the lens profile based on energy conservation law.And then,we get the freeform lens profile by programming in MATLAB.The inner freeform surface is designed by using optimization method.Finally,a rectangular light spot with the uniformity of 92% and optical efficiency of 85% is obtained on the receiving surface 20 mm away from LED.Then,in order to further improve the optical efficiency of the illumination system of vehicle-mounted HUD projector,an LED free-form lens based on uniform illumination TIR structure is designed in this paper.The lens uses step-by-step design method combined with trial-and-error method.Firstly,the equation about the profile of TIR is obtained by ODE method.The profile of TIR is obtained by solving the equation.Finally,a rectangular light spot with the uniformity of 92% and optical efficiency of 88% is obtained on the receiving surface 40 mm away from LED.Finally,in order to reduce the deviation between the actual product and the theoretical model,an LED free-form lens based on collimated TIR structure is designed.The lens consists of a collimated TIR lens and the micro-texture on the exit surface.The micro-texture structure can simultaneously realize the transformation of the spot from circular to rectangular and the increase of the uniformity.Firstly,the relationship of the points on the profile of the collimated TIR lens is deduced,then we get the collimated TIR lens profile by programming in MATLAB.And the micro-texture structure is adjusted with trial-and-error method.Finally,a rectangular light spot with the uniformity of 91% and optical efficiency of 89% is obtained on the receiving surface 45 mm away from LED.