CN103257381A - Solar spotlight Fresnel lens and its designing method - Google Patents

Abstract

The invention relates to a solar concentrating Fresnel lens and a design method thereof. Based on the principle of optical refraction, it calculates the derivatives of the Fresnel mirror surface point by point, and then integrates the derivatives to obtain the vector height of the lens surface. The design method of the invention can simply and quickly complete the design of the Fresnel lens by means of modern computer technology. Compared with the pure optical design method, the technical solution of the present invention has the characteristics of simplicity and ease; compared with the current traditional Fresnel lens design method, the lens provided by the design method of the present invention has small spot diameter, uniform energy distribution, etc. Advantages, can effectively improve the light energy conversion efficiency of solar concentrating lenses, especially for large-diameter Fresnel lenses, the advantages and effects are more obvious.

Description

A solar concentrating Fresnel lens and its design method

technical field

The invention relates to a concentrating lens and a design method thereof, in particular to a Fresnel lens and a design method for concentrating solar energy.

Background technique

Fresnel lens is a kind of lens invented by French physicist Augustin Jean Fresnel in 1822. Compared with traditional spherical or aspherical lenses, Fresnel lens adopts multiple coaxial or parallel prism sequences The discontinuous curved surface replaces the continuous spherical surface of the general lens. Therefore, the Fresnel lens has a simple structure, is easy to manufacture, is lighter and thinner than the general lens in terms of weight and volume, and can obtain a larger aperture to focal length ratio in design. . Although Fresnel lenses were originally designed for lighthouse searchlights, Fresnel lenses are currently used in many fields such as projectors, large-screen rear projection TVs, portable magnifying glasses, solar water heaters, solar power plants, and solar panels for space vehicles. Wide range of applications.

The original Fresnel lens used a prism sequence due to the limitations of the manufacturing process, optical design and processing technology at that time. However, from an optical point of view, the prism sequence cannot focus light on one point, so that the spot of this type of Fresnel mirror is large, the temperature of the spot cannot be very high, and the energy of the spot is not uniform.

Before the present invention was made, the literature "Fresnel lens unified design method" ([J]. Solar Energy Sinica, 1991, 12 (4): 423-426.) and "General design method and efficiency of Fresnel concentrating lens Analysis” ([J]. Journal of Wuhan University of Technology, 2010,3(6):62-66), some improved methods were proposed on the basis of prism sequence design. The development of modern computer technology and the improvement of processing technology have made it possible to design and process more complex Fresnel lenses. Another Fresnel lens design method based on aspheric surfaces uses a series of spherical surfaces for design. From the principle of optics, it can be seen that the spherical mirror can focus on the paraxial light well at one point. The farther away from the axis, the more the focus will be out of focus. Therefore, the above design is not suitable for making large-diameter Fresnel lenses.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a solar concentrating Fresnel lens with a small diameter of the concentrating diffusion circle, uniform distribution of light energy, high spot temperature, and effective improvement of light energy conversion efficiency. design method.

The technical scheme that realizes the object of the present invention is to provide a kind of design method of solar concentrating Fresnel lens, comprises the steps:

1. Take the positive direction of the busbar of the Fresnel mirror as the X-axis, and divide it into n equal parts according to the equal distance dx on the X-axis, and the coordinates of each node are X ₁ , X ₂ ... X _n ;

处，设定母线矢高

及母线在该处的导数

为0；  2. In

, set the busbar vector height

and the derivative of the bus at that point

is 0;

，估算

处的矢高，再根据光学折射原理确定

处的导数

，按式

,确定下一坐标处的矢高

；重复本步骤，得到任意位置处的矢高

； 3. Press

, estimated

The sagittal height at the place is determined according to the principle of optical refraction

derivative at

, press

, determine the next coordinate Yataka

;Repeat this step to get any position Yataka

;

是否大于等于指定宽度；若是，则当前环带设计完成，执行步骤5；反之，返回步骤3； 4. Judgment Whether it is greater than or equal to the specified depth, or judge

Whether it is greater than or equal to the specified width; if so, the current ring design is completed, and step 5 is performed; otherwise, return to step 3;

所对应的

和

设定为0，对剩余节点的坐标x，重复步骤3～4进行下一环带的设计，依次完成全部环带的设计，得到一种太阳能聚光菲涅尔透镜。 5. Put the next

Corresponding

and

Set it to 0, repeat steps 3-4 for the next ring design for the coordinate x of the remaining nodes, complete the design of all rings in turn, and obtain a solar concentrating Fresnel lens.

The technical solution of the present invention also includes a solar concentrating Fresnel lens obtained by the above design method.

Due to the utilization of the above-mentioned design scheme, the present invention has the following advantages compared with the prior art:

1. The design method provided by the present invention is different from the traditional design method to directly calculate the vector height of the curved surface, but by calculating the derivative at each point of the curve, and then integrating the numerical value of the derivative at each point to obtain the vector height of the curve. In the design, only need Given the refractive index of the material, aperture, focal length and allowable depth or width, the required Fresnel surface can be obtained, the design method is simple, the adjustment is flexible, and the design cycle is short and the cost is low.

2. Compared with the traditional design method, because the surface shape designed by the present invention can theoretically focus sunlight on one point, the light energy distribution of the obtained concentrating circle of confusion is uniform; also because the designed Fresnel lens circle of confusion The diameter is small, so under the same aperture conditions, the temperature that the spot can reach is much higher than that of the traditional design, which can greatly improve the conversion efficiency of light energy.

4. The design method is applicable to any type of Fresnel lens.

Description of drawings

Fig. 1 is the design schematic diagram of a kind of solar concentrating Fresnel lens provided by the present invention;

Fig. 2 is the result schematic diagram of the Fresnel annulus that obtains by the design method that the embodiment of the present invention provides;

Fig. 3 is the light spot figure of the Fresnel lens manufactured by traditional design method;

Fig. 4 is a light spot diagram of a Fresnel lens provided by an embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be further elaborated below in conjunction with the accompanying drawings and embodiments.

Example 1:

Utilize the present invention to design a Fresnel lens with the following requirements: material refractive index n=1.499, aperture D=120mm, focal length f=120, specified depth h=1mm.

The specific implementation steps of the Fresnel mirror design method provided in this embodiment are as follows:

，该点处的导数为

，把菲涅尔镜的母线沿X轴正方向按等间距dx分成N等分，第1点的坐标为

，该点处的导数为

，

为平行光线在

处的入射角。 1, referring to accompanying drawing 1, it is the schematic diagram of the Fresnel mirror design method that the present invention provides, suppose the center point coordinate of Fresnel lens is

, the derivative at this point is

, divide the generatrix of the Fresnel mirror into N equal parts along the positive direction of the X-axis at equal intervals dx, and the coordinates of the first point are

, the derivative at this point is

,

for parallel rays in

angle of incidence at .

，在中心处： Center point coordinates of Fresnel lens The derivative at is

, at the center:

。

.

。这时对应的z暂时以估算值：

 近似表达。 2. Take dx=0.1,

. At this time, the corresponding z is temporarily estimated:

approximate expression.

According to the principle of optical refraction, the equation can be derived as shown in formula (1):

                （1） ；

(1) ;

，则对应的

。在求出后，将实际对应的z值确定为：

。 In the formula, f is the focal length, n is the refractive index of the material, in this embodiment, f=120, n=1.499; from the equation (1) to solve

, then the corresponding

. in seeking After that, the actual corresponding z value is determined as:

.

3. Repeat step 2 to calculate in turn:

 

 

...

 

The calculation of the first ring is completed. A simple calculation program can be written with computer software to complete the above calculations.

。重新设定起始点（

）： 4. The end x-coordinate of the first ring is

. Reset the starting point (

):

,

。 Calculate the corresponding according to the principle of optical refraction:

.

5. Repeat steps 2 and 3 to complete the design of the second ring.

 

 

...

 

 

6. Repeat steps 4 and 5 to complete the design of any rings, thereby completing the design of the entire Fresnel lens.

The last ring designed in this embodiment is the 26th ring, X ₂₆ =59.500000000001

 

 

...

 

See accompanying drawing 2, which is a schematic diagram of the annular zone results of the Fresnel lens obtained according to the above steps (the coordinate units in the figure are all in mm).

Referring to accompanying drawing 3 and Fig. 4, they are respectively the spot pattern of the Fresnel lens designed by traditional method and the spot pattern of the Fresnel lens that adopts the present embodiment design method to design; Contrast the result of Fig. 3 and Fig. 4 and can see It can be seen that the spot diameter of the Fresnel lens designed by the traditional method is about 50 mm, which is a diffuse spot; the spot diameter of the Fresnel lens provided by this embodiment is reduced to about 10 mm. Under certain conditions, the temperature that the light spot can reach is much higher than that of the traditionally designed lens, which can greatly improve the conversion efficiency of light energy.

There are generally two criteria for the design of Fresnel lenses: equal width and equal depth. Considering that in practical applications, the light in the central area is the main light energy, it should be ensured that the annular zone in the central area is as wide as possible. Therefore, a Fresnel lens with a constant depth design is more practical, and the steps in this embodiment are based on the constant depth design. It is also applicable to the equal width design, only need to change the standard of ring belt transformation to equal width. The design method of the invention is relatively simple, and the sagittal height data of the Fresnel lens can be quickly calculated only by giving the refractive index n of the material, the focal length f of the lens, the aperture D of the lens, and the depth h or width w of the lens.

Claims (2)

1. the method for designing of a Salar light-gathering Fresnel Lenses is characterized in that comprising the steps:

(1) the bus positive dirction with the Fresnel mirror is X-axis, is divided into the n five equilibrium by equidistant dx on X-axis, and the coordinate of each node is respectively X ₁, X ₂X _n

(2) exist

The place sets the bus rise

And bus is at the derivative at this place

Be 0;

(3) press

, estimation

The rise at place is determined according to the light refraction principle again

The derivative at place

, by formula

, determine next coordinate

The rise at place

Repeat this step, obtain the optional position

The rise at place

(4) judge

Whether more than or equal to designated depth, or judge

Whether more than or equal to specified width, which width; If then execution in step (5) is finished in current endless belt design; Otherwise, return step (3);

(5) with the next one

Corresponding

With

Be set at 0, to the coordinate x of residue node, the design of next endless belt is carried out in repeating step (3)～(4), finishes the design of whole endless belt successively, obtains a kind of Salar light-gathering Fresnel Lenses.

2. a kind of Salar light-gathering Fresnel Lenses that obtains by the described method for designing of claim 1.

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