阅读说明：本技术 基于双向反馈网格法的led自由曲面透镜设计方法 (LED free-form surface lens design method based on bidirectional feedback grid method ) 是由 宋国华 杨超 范婷婷 缪建文 于 2021-09-13 设计创作，主要内容包括：本发明公开了一种基于双向反馈网格法的LED自由曲面透镜设计方法,其特征是：具体步骤为：对光源和目标照明平面进行网格划分,建立光源与目标面的映射关系,利用迭代的方式形成一个初始的自由曲面面型,根据扩展光源目标面的照度情况对每一条迭代曲线建立反馈系数,对网格点进行修正并建立新的映射关系,最终形成了均匀性良好、能量利用率高的目标面中心无光照度的自由曲面透镜。本发明设计的自由曲面透镜在照明区域内的均匀度良好、光能利用率较高,具有广阔的应用前景。(The invention discloses a method for designing an LED free-form surface lens based on a bidirectional feedback grid method, which is characterized by comprising the following steps of: the method comprises the following specific steps: the method comprises the steps of carrying out grid division on a light source and a target illumination plane, establishing a mapping relation between the light source and the target plane, forming an initial free-form surface type in an iteration mode, establishing a feedback coefficient for each iteration curve according to the illumination condition of the target plane of the extended light source, correcting grid points and establishing a new mapping relation, and finally forming the free-form surface lens with good uniformity and high energy utilization rate and without illumination in the center of the target plane. The free-form surface lens designed by the invention has good uniformity in an illumination area, high light energy utilization rate and wide application prospect.)

1. A method for designing an LED free-form surface lens based on a bidirectional feedback grid method is characterized by comprising the following steps: the method comprises the following specific steps: the method comprises the steps of carrying out grid division on a light source and a target illumination plane, establishing a mapping relation between the light source and the target plane, forming an initial free-form surface type in an iteration mode, establishing a feedback coefficient for each iteration curve according to the illumination condition of the target plane of the extended light source, correcting grid points, establishing a new mapping relation, and finally forming the free-form surface lens without illumination in the center of the target plane.

2. The method for designing the LED free-form surface lens based on the bidirectional feedback grid method as claimed in claim 1, wherein: simulation was also performed for light sources having dimensions of 1mm × 1mm, 2mm × 2mm, and 4mm × 4mm, respectively.

Technical Field

The invention relates to a design method of an LED free-form surface lens.

Background

The LED light source has the advantages of low carbon, environmental protection, low energy consumption, high luminous efficiency, long service life, good color rendering property and the like, the light intensity of the LED light source is approximately Lambert distribution, the LED light source is not suitable for being directly applied to illumination, and the illumination requirement can be met only by matching with a specific optical element. The secondary optical design is based on the non-imaging optical theory, so that the irradiated area has uniform illumination distribution and simultaneously obtains higher light energy utilization rate. Most of the current LED street lamps are lenses and reflectors which generate rectangular areas, for a design method of a free-form surface lens, Pablo et al provides an SMS synchronous multi-curved surface design method, and two refraction surfaces are designed simultaneously, so that conversion of two groups of incident wavefronts and emergent wavefronts can be realized, emergent rays of a light source can be controlled more accurately, the structure of the whole illumination system can be more compact, and the whole process is more complex. Wang et al propose an energy mapping method that establishes a mapping relationship between a point light source and a target surface, calculates normal vectors and discrete points to determine the surface of a lens, and thereby establishes a free-form surface lens that can control light well. However, the LED light source is an extended light source, and the illumination mode is greatly affected according to the increase of the size of the light source, so that the illumination condition is greatly deteriorated. How to solve the problem of uneven illumination distribution of a target area caused by the problem of light source expansion becomes a big problem in the aspect of secondary optical design of LEDs for researchers at home and abroad. To solve the above problem, Wangcai et al add feedback coefficients [18-20] to each mesh in the energy correspondence, establish a new correspondence and solve for the discrete points of the surface, and repeat this to finally achieve the desired design objective, but this method is very labor intensive and increases the difficulty due to the subdivision of the mesh.

Disclosure of Invention

The invention aims to provide a method for designing an LED free-form surface lens based on a bidirectional feedback grid method, wherein the designed free-form surface lens has good uniformity in an illumination area and high light energy utilization rate.

The technical solution of the invention is as follows:

a method for designing an LED free-form surface lens based on a bidirectional feedback grid method is characterized by comprising the following steps: the method comprises the following specific steps: the method comprises the steps of carrying out grid division on a light source and a target illumination plane, establishing a mapping relation between the light source and the target plane, forming an initial free-form surface type in an iteration mode, establishing a feedback coefficient for each iteration curve according to the illumination condition of the target plane of the extended light source, correcting grid points, establishing a new mapping relation, and finally forming the free-form surface lens without illumination in the center of the target plane.

Simulation was also performed for light sources having dimensions of 1mm × 1mm, 2mm × 2mm, and 4mm × 4mm, respectively.

The free-form surface lens designed by the invention has good uniformity in an illumination area, high light energy utilization rate and wide application prospect.

Drawings

The invention is further illustrated by the following figures and examples.

FIG. 1 is a schematic diagram of meshing of a light source with a target surface;

wherein: (a) a light source grid; (b) an annular target surface mesh; (c) dividing a grid of a square target surface;

FIG. 2 is a schematic diagram of an iterative building of a free-form surface;

wherein: (a) establishing a free curve; (b) establishing an initial free-form surface type;

fig. 3 is a flow chart of the invention of fig. 3.

Detailed Description

A method for designing an LED free-form surface lens based on a bidirectional feedback grid method comprises the following specific steps: the method comprises the steps of carrying out grid division on a light source and a target illumination plane, establishing a mapping relation between the light source and the target plane, forming an initial free-form surface type in an iteration mode, establishing a feedback coefficient for each iteration curve according to the illumination condition of the target plane of the extended light source, correcting grid points and establishing a new mapping relation, and finally forming the free-form surface lens with good uniformity and high energy utilization rate and without illumination in the center of the target plane.

Simulation was also performed for light sources having dimensions of 1mm × 1mm, 2mm × 2mm, and 4mm × 4mm, respectively.

The specific design method comprises the following steps:

1 design of

1.1 establishing a mapping relation between a light source and a target surface

Assuming that the light source is a point light source, the light source grid is unfolded along the meridian direction with two poles as the center, and corresponds to the radiation ring zone gradually unfolded from the high latitude to the low latitude, the area of each grid of the target surface is required to be equal, and the grid mapping relationship between the light source and the target surface is shown in fig. 1. The light source and the target illumination surface are divided into n parts according to the longitude direction (the included angle theta between the light and the z axis) and m parts according to the latitude direction (the included angle phi between the light and the x axis), the point light source is positioned at the origin of coordinates o, and the dotted line in (a) represents the light source grid after the condition of the extended light source is optimized.

For an LED light source, assuming that a designed free-form surface lens is an ideal optical element, the emergent light flux is as follows according to the principle of conservation of etendue in non-imaging optics:

in the formula E₀To illuminate a plane, I₀The intensity of the emergent light is shown, and S is the irradiation area of the target surface. Since the light source is axially symmetric to the target surface, taking 1/4 systems as an example, if the target surface achieves ideal uniform illumination, the luminous flux per grid of the target surface is:

wherein (i ═ 1,2, 3.., n).

1.2 creating an initial free-form surface

The free surface is built up iteratively as shown in fig. 2, assuming that the refractive index of air is 1 and the refractive index of the lens material is n, according to the vector form of snell's law:

[1+n²-2n·(Out·In)]^1/2·N＝Out-n·In (3)

wherein Out is the unit vector of emergent light, and In is the unit vector of incident light. Determining In and Out of a point on the free curve according to the coordinates Q (j, i) (Qx, Qy, Qz) of the point and the coordinates corresponding to the point on the target surface, thereby determining a normal vector Nj, i corresponding to Q (j, i);

(N_x,N_y,N_z) Thereby obtaining a sum-normal vector N_j,iPerpendicular plane l_j,iIs shown as

N_x·(Q_x(j,i+1)-Q_x)+N_y·(Q_y(j,i+1)-Q_y)+N_z·(Q_z(j,i+1)-Q_z)＝0 (4)

The coordinates of the next point on the free curve can be obtained:

thereby obtaining a continuous free curve Q_jFinally, each free curve is obtained.

And (3) programming by using Matlab to calculate discrete point data of each curve, introducing the discrete point data into Solidworks to obtain an initial free-form surface type, and then setting material parameters to establish an initial curved lens model.

1.3 establishing feedback coefficients for optimization

In the curve solving process, except for the initial point of iteration, the data information of the next point is obtained from the previous point, although the Wangcai et al introduces the deviation angle theta_dThe error between the algorithm vector and the actual normal vector in the iteration process is normalized, but the error is inevitably generated and gradually increased in the iteration process; when the mapping relation between the light source and the target surface is established, the size of the free-form surface lens is far smaller than the distance from the light source to the target surface, and the distance from the free-form surface to the target surface is approximate to the distance from the light source to the target surface, so that errors can be generated; the free-form surface lens obtained by the lofting method also generates certain errors due to the number of the meridians, and the errors can be reduced by increasing the iterative meridians, namely, a method for subdividing the meshes; meanwhile, the LED light source is an extended light source, and the establishment of the free-form surface lens is based on the assumption of a point light source initially, so that the obtained illumination distribution is always greatly deviated from the expected illumination distribution, and the feedback is excellent according to the actual illumination conditionThe conversion is indispensable.

The influence of light on the illumination distribution on the target surface is continuous, and the influence always has a certain trend along the direction of an iteration curve, but for the condition that the center of the target surface has no illumination, the trend is not always developed towards a fixed direction, so that the uniform illumination distribution of an illumination area is realized by adopting a bidirectional feedback adjustment method. Taking a meridian on a free-form surface as an example, in the case of using an LED extended light source, a feedback coefficient a of a group of light source grids is introduced along the direction of the illuminance deviation of the meridian₁,...,a_k,...,a_nWherein a is₁,...,a_kIs a set of arithmetic progression of a_k,...,a_nAnd taking values of the feedback coefficients for a group of arithmetic series according to the real illumination distribution condition of the target surface. n is the number of the grids divided in the meridian direction. When p is less than or equal to k, the sum of the front p terms of the feedback coefficient is:

when n is more than p and more than k, from a_k+1Initially, the sum of the first p-k terms is:

the mesh of the target surface is divided, the area of each mesh of the target surface is required to be equal, and the optimization of the free-form surface lens is realized by changing the luminous flux of the light source mesh through a feedback coefficient, which can be expressed as:

φ_tol＝φ₁+φ₂ (9)

in the formulai＝1,...,k，φ_tolIs the total luminous flux of the target surface, phi₁Theta' is the angle of the emergent ray on the optimized free-form surface in the normal direction (z axis) of the light source for the total luminous flux of the adjusted grid.

Where i ═ k + 1., n, φ₂Theta' is the angle of the emergent ray on the optimized free-form surface in the normal direction (z axis) of the light source for the total luminous flux of the adjusted grid.

For a circularly symmetric system, good illumination distribution can be achieved in a target area by optimizing theta according to the marginal ray theory. For non-circularly symmetric systems, the gradient invariance in the conversion from two dimensions to three dimensions can cause errors in the illumination distribution of the target area, and the errors can be solved by subdividing the mesh and adjusting the mesh of the target surface. For rectangular illumination patterns, "hot spots" appear at the diagonal "^[22]This is improved by increasing the illumination area near the target face diagonal line, adjusting the target face grid area with phi, and adding a set of feedback coefficients a 'for the target face grid area to each warp line'₁,...,a′_k,...,a′_nTo perform the optimization. By performing feedback optimization on each meridian on the free-form surface, a free-form surface lens which is suitable for an LED extended light source and can generate a uniform illumination area is obtained, and a design flow is shown in FIG. 3.

According to the method, Matlab software is used for programming calculation to obtain the surface type data of the free-form surface before and after optimization, then the data is led into Solidworks software for modeling, and then Tracepro software is used for respectively performing ray tracing on the free-form surface lens before and after optimization to obtain the illumination conditions of the target surface with different sizes. A free-form lens that achieves a uniform annular area and a non-axial "box" shaped free-form lens are contemplated. The designed free-form surface lens is made of PMMA (polymethyl methacrylate), the refractive index n of the material is 1.49, the inner surface of the free-form surface lens is designed to be a hemispherical surface so as to simplify the design, the radius of the inner spherical surface of the free-form surface lens is 5mm, the center of the free-form surface lens is 10mm, the height of the free-form surface lens is 11.16mm and 12.68mm respectively, and the width of the free-form surface lens is 20.82mm and 22.66mm respectively. The light source used is a square LED light source with the side length of 2mm, the emergent half angle of the light source is 60 degrees, the total luminous flux is 100lm, and the target surface is 10m away from the light source.

2 simulation

And respectively guiding the free-form surface lenses before and after optimization into optical simulation software for tracking, and setting a light source to be an LED light source with the size of 2mm multiplied by 2mm, wherein the number of the tracked light rays is 500 ten thousand. In order to better evaluate the uniformity and energy utilization rate in the target area, the uniformity in the target area is defined as E ═ U_min/E_maxIn which E_min、E_maxMinimum and maximum illumination values within the target region, respectively; light energy utilization rate N ═ phi_target/φ_totalWherein phi_target、φ_totalRespectively the luminous flux received in the target area and the total luminous flux emitted by the light source. Simulation results show that the uniformity of the target area of the optimized annular lens is improved to 92.5% from 85%, and the light energy utilization rate is improved to 91.2% from 84.9%; the uniformity of the target area of the square lens is improved from 64.3% to 90.9%, and the energy utilization rate is improved from 66.2% to 92.6%. After the feedback coefficient is optimized, the uniformity and the energy utilization rate of the free-form surface lens are improved.

Light sources with dimensions of 1mm × 1mm and 4mm × 4mm were simulated. Simulation results show that the free-form surface lens after feedback optimization can be well suitable for an LED extended light source, and a uniform illumination area is generated on a target plane. For the LED extended light source with the size not more than 4mm multiplied by 4mm, the uniformity and the energy utilization rate of the free-form surface lens obtained through feedback optimization in a target illumination area reach over 90.5 percent, and the LED extended light source has a good illumination effect.

3 conclusion

And meshing the light source and the target surface, establishing a corresponding mapping relation, and establishing an initial free-form surface type through iteration. And according to the condition of the LED extended light source, an optimization method of bidirectional feedback adjustment is provided and adopted, and two free-form surface lenses without illumination in the center of an illumination area are designed. The simulation results of the extended light sources with the sizes of 1mm multiplied by 1mm, 2mm multiplied by 2mm and 4mm multiplied by 4mm are respectively carried out, and the simulation results show that the uniformity and the light energy utilization rate of the target illumination areas of the two free-form surface lenses can reach more than 90% for the LED extended light sources with the sizes not more than 4mm multiplied by 4 mm. The condition of the LED extended light source can be effectively responded, and the designed free-form surface lens has a good far-field illumination effect and is suitable for occasions such as road illumination.