Gradient Fresnel lens design
The current Fresnel lenses are flat-type or curved Fresnel lenses based on spherical surfaces. There is no Fresnel lens based on the free-form surface, and the free-form lens is combined with the Fresnel lens. A free-form Fresnel streetlight lens that produces uniform rectangular illumination is constructed. Since the surface of the free-form Fresnel lens is not a concentric circle, it is also called a gradient Fresnel lens.
Gradient Fresnel lens design idea: design the surface data of several free-form lens with the same light effect but different sizes, and import the adjacent size quarter-free surface lens surface data in Solidworks (as shown in Figure 1). Show, for the convenience of observation, here the display mode is changed to the wire frame diagram), and then the thickness method is used to cut the free-form surface into equal thickness. However, since the free-form surface type is special, it cannot be directly divided by the equal thickness method. Only by borrowing from its thoughts, the idea of the cutting method used in this paper is: firstly, according to the given light source characteristics and the illumination requirements of the target illumination surface, the lens design is designed to design ten free-form lenses with the same light-emitting effect but different sizes, but this The size is not set casually, but each lens is adjacent to its size. The lens is set at an initial point of a certain size. The given value differs by 0.5 mm, since each free-form lens is in accordance with the same light-emitting requirements and illumination distribution. Designed, so the same illuminance requirements can be achieved when they are used separately, so after stacking There is no big change in the final light output (as shown in Figure 2). First, import the quarter of the largest free-form lens, fit it into a surface, and import the second adjacent to the size. The lens data is also fitted as a curved surface. The outline of the lens is shown in Figure 1. By analyzing the length and width of the lens, the long side is cut by 1.5 mm and the wide side is cut by 0.4 mm for the first time. After cutting, the shape of the lens is as shown in Fig. 2. It is made into a whole by surface stitching. Then the same method is used to sequentially introduce the 8 free-form lenses into the rear and then cut to form a Fresnel surface (as shown in Figure 3). ), after cutting, through mirroring, surface stitching, etc., fit into a complete gradient Fresnel lens (as shown in Figure 4).
In the domestic theory of lens design and manufacturing, Shandong Yuying has half a century of experience in design and manufacturing.
Comparison of Gradient Fresnel Lens and Free-form Surface Lenses
The main reason for changing the free-form lens to the gradient Fresnel lens is to reduce the thickness of the lens and improve the transmittance, so as to solve the problem of poor heat dissipation of the LED free-form street lamp lens. This section is about the original free-form lens and the improved Fresnel lenses are structurally compared. As shown in Fig. 5, it is a schematic diagram of the outline of the original free-form surface lens. As can be seen from the figure, the half length of the bottom side is 19.085mm. Since the surface shape is an irregular free-form surface, the radius or length cannot be accurately labeled. Therefore, the point with the largest length is marked, and its value is 21.430 mm. Figure 6 shows that after the free-form surface lens is changed into a Fresnel lens, the corresponding bottom half has a length of 13.301 mm and a maximum length of 14.894 mm. This shows that the thickness is significantly reduced.
In order to more intuitively express the thickness reduction value after the free-form surface lens becomes a Fresnel lens, the two lenses are combined and observed, as shown in FIGS. 7 and 8, the shaded portion is the original free-form lens to be a Fresnel lens. Excess material removed later, it can be seen from the figure that after the free-form surface lens is changed into a Fresnel lens, the thickness is significantly thinned due to the deletion of many materials, so that the heat dissipation efficiency is improved, and the service life of the LED can be extended. The attenuation has been reduced.