JPH07287106A - Fresnel lens used for lighting optical system and its manufacture - Google Patents

Abstract

PURPOSE:To prevent an unnecessary light beam which exerts adverse influence on lighting characteristics from being generated by making the non-lens angle of a Fresnel lens surface satisfy a function shown by a specific equation within a range of height from the lens center to the lens height. CONSTITUTION:In the lighting optical system which guides the light from a light source of certain size to a lighted surface through the Fresnel lens to light the object surface, the functions theta1'', function sigma, and function theta-1' are defined by equations I-III respectively. Then the Fresnel lens surface is finished so that the non-lens angle phi of the Fresnel lens satisfies the function theta1'' within the range of height (h) from the zero to the lens height H0, where the height (h) where an equation IV holds is denoted as H0. In the equations I-III, (n) is the refractive index of the lens material constituting the Fresnel lens, (h) the height from the lens center, (d) the size of the light source, D the distance between the light source and Fresnel lens, and (f) the focal length of the Fresnel lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a Fresnel lens used in an illumination optical system applicable to a plate-making contact printer, a proximity exposure machine for liquid crystal display devices, etc., and a method of manufacturing the Fresnel lens.

[0002]

2. Description of the Related Art Illumination optical systems using Fresnel lenses are widely used in plate making contact printers and proximity exposure machines for liquid crystal display devices. In this illumination optical system, the Fresnel lens guides the light from the light source to the illuminated surface to illuminate the illuminated surface.

As shown in FIG. 16, a Fresnel lens surface 6 composed of a lens surface 2 and a non-lens surface 4 is formed on the Fresnel lens FL, and light rays are emitted from the plane 8 side of the Fresnel lens FL. When F is incident, the incident ray F is refracted by the plane 8 of the Fresnel lens FL, goes straight through the Fresnel lens FL, is refracted by the lens surface 2, and is guided to the illuminated surface. In this specification, the light ray F guided to the illuminated surface side as described above is referred to as a “normal light ray”.

However, when the incident light beam F is guided to the non-lens surface 4 in the Fresnel lens FL, it is totally reflected by the non-lens surface 4 and then emitted through the lens surface 2 as shown in FIG. Ray F _a ). In addition, as shown in FIG. 17, a light beam emitted from a certain lens surface 2 is
When incident on the non-lens surface 4 adjacent to
It is reflected by (light ray _Fb ), is incident on the Fresnel lens FL again, and is emitted again from the adjacent lens surface 2 to the illuminated surface side (light ray _Fc ).

Such light rays F _a , F _b and F _c are called "unnecessary light rays". This is not preferable in terms of illumination characteristics, and the presence of unnecessary light rays causes inconvenience in the proximity exposure machine. For example, if proximity exposure is performed using a Fresnel lens that generates unnecessary rays, it becomes difficult to accurately transfer the pattern formed on the mask or the like to the resist film. Further, there is a possibility that a plate-making printer incorporating the Fresnel lens may cause unevenness in halftone dot density, and that a liquid crystal exposure device may have a problem that a pattern dimension is out of order.

[0006]

By the way, when a point light source is used as the light source, in many cases, by setting the non-lens angle φ appropriately, the generation of the unnecessary light rays F _a , F _b , and F _c can be prevented. Can be prevented. However, when the light source has a certain size, for example, JP-A-62-175 is used.
As described in detail in Japanese Patent No. 087, there is no condition (setting of non-lens angle φ) that the unnecessary light rays reflected and refracted by the non-lens surface are not generated over the entire Fresnel lens. That is, even if the non-lens angle φ is set to any angle in a part of the Fresnel lens, unnecessary light rays are generated, and the above problem occurs.

Of these unnecessary light rays F _a , F _b , and F _c , it is the light ray F _c that has the most adverse effect on the illumination characteristics. Even if the generation of this light ray F _c is prevented, a great effect can be expected, and it is unnecessary. Although a Fresnel lens that suppresses the generation of the light ray F _c is demanded, conventionally, this type of Fresnel lens has not been present.

Further, even if such a Fresnel lens can be designed theoretically, if a complicated process is required to manufacture the lens, the Fresnel lens becomes expensive, so that the Fresnel lens is provided. At the same time, it is desired to provide a manufacturing method capable of manufacturing the lens in a simple process.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a Fresnel lens used in an illumination optical system capable of suppressing the generation of unnecessary light rays which adversely affect the illumination characteristics. The first purpose.

A second object of the present invention is to provide a method of manufacturing the Fresnel lens, which can manufacture the Fresnel lens by a simple process.

[0011]

The invention according to claim 1 is used in an illumination optical system for guiding light from a light source having a certain size to a surface to be illuminated through a Fresnel lens and illuminating the surface to be illuminated. In order to achieve the above-mentioned first object, the Fresnel lens is provided with a function θ ₁ ″, a function σ and a function θ ₋₁ ′, respectively.

[0012]

[Equation 10]

[0013]

[Equation 11]

[0014]

[Equation 12]

Where n is the refractive index of the lens material forming the Fresnel lens, h is the height from the center of the lens,
d is the size of the light source, D is the distance between the light source and the Fresnel lens, and f is the focal length of the Fresnel lens.

[0016]

[Equation 13]

Assuming that the height h at which is satisfied is the lens height H ₀ , the non-lens angle φ of the Fresnel lens has a function θ ₁ ″ in the range from the height h of zero to the lens height H _0. The Fresnel lens surface is finished so as to be satisfied.

According to a second aspect of the present invention, the non-lens angle φ of the Fresnel lens has the following inequality when the height h from the lens center is in the range from the lens height H ₀ to the maximum lens height h _max.

[0019]

[Equation 14]

The Fresnel lens surface is finished so as to satisfy the above condition.

The invention of claim 3 is the method of manufacturing a Fresnel lens according to claim 1, wherein in order to achieve the second object, the step of preparing a mold block and the height h from the center of the lens are Letting the values of the function θ ₋₁ ′ and the function σ of claim 1 at the maximum lens height h _max be θ ₋₁ ′ (h _max ) and σ (h _max ), the cutting edge angle ψ is

[0022]

[Equation 15]

A step of preparing a cutting tool satisfying the following conditions,
The cutting tool is attached to one surface of the mold block so that the feed angle ω of the cutting tool satisfies the function θ ₁ ″ in a range corresponding to the lens height H ₀ from the center of the mold block. The process includes a step of forming a lens mold by feeding and cutting, and a step of forming a Fresnel lens by performing a lens forming process using the lens mold.

The invention of claim 4 is the method of manufacturing a Fresnel lens according to claim 2, wherein in order to achieve the second object, the step of preparing the mold block and the height h from the lens center are Letting the values of the function θ ₋₁ ′ and the function σ of claim 1 at the maximum lens height h _max be θ ₋₁ ′ (h _max ) and σ (h _max ), respectively, the cutting edge angle ψ is calculated by the formula (6) ) The step of preparing a cutting tool that satisfies

[0025]

[Equation 16]

When the height at which is satisfied is H ₀ ″, the feed angle ω of the cutting tool satisfies the function θ ₁ ″ in the range corresponding to the height H ₀ ″ from the center of the mold block. In addition, in the range corresponding to the maximum lens height h _max from the position corresponding to the height H ₀ ″, the feed angle ω of the cutting tool is

[0027]

[Equation 17]

Then, a step of feeding the cutting tool to one surface of the mold block to perform a cutting process to form a lens mold, and a lens forming process using the lens mold to form a Fresnel lens. And a step of performing.

[0029]

According to the first aspect of the invention, the non-lens angle φ on the Fresnel lens surface is a function θ ₁ ″ shown by the equation (1) in the range where the height h from the lens center is zero to the lens height H _0.
Therefore, it is possible to prevent the unnecessary light rays F _c (FIG. 17) that adversely affect the illumination characteristics from being generated, and also to prevent the unnecessary light rays F _b from being generated at the same time.

According to the second aspect of the invention, in the outer peripheral portion of the Fresnel lens, that is, in the range where the height h from the lens center is from the lens height H ₀ to the maximum lens height h _max , the non-lens angle φ Satisfies the inequality of the equation (5), the generation of unnecessary rays F _a , F _b , and F _{c in} the range is prevented.

According to the third aspect of the invention, a mold block and a cutting tool having a cutting edge angle ψ satisfying the expression (6) are prepared, and the feed angle ω of the cutting tool has a function θ ₁ ″. To satisfy, by sending the cutting tool to one surface of the mold block and performing a cutting process to form a lens mold, and then performing a lens forming process using the lens mold, The Fresnel lens of Item 1 is formed.

Further, in the invention of claim 4, a die block and a cutting tool having a cutting edge angle ψ satisfying the expression (6) are prepared, and the height H ₀ ″ is set from the center of the die block. In the corresponding range, the feed angle ω of the cutting tool satisfies the function θ ₁ ″, and in the range corresponding to the maximum lens height h _max from the position corresponding to the height H ₀ ″, the cutting tool is The feed angle ω is set within the range of the formula (8), and the cutting tool is fed to one surface of the mold block to perform cutting, thereby forming a lens mold, and then a lens using the lens mold. The Fresnel lens according to claim 2 is formed by performing the forming process.

[0033]

1 is a diagram showing an illumination optical system having a Fresnel lens according to the present invention. 2 is a partially enlarged view of the lens center portion of the Fresnel lens FL of FIG.
Further, FIG. 3 is a partially enlarged view of the lens outer peripheral portion of the Fresnel lens FL of FIG. In this embodiment, the non-lens angle φ at the Fresnel lens surface 6 satisfies the function θ ₁ ″ (equation (1)) at the central portion and the inequality of equation (5) at the outer peripheral portion, Since the Fresnel lens FL is finished, it is possible to effectively reduce unnecessary light rays that adversely affect the illumination characteristics.

Hereinafter, consideration will be given to the conditions under which unnecessary light rays are generated, specific examples, and the working effects of the examples will be described in detail. After the description of the Fresnel lens FL, the manufacturing method thereof will be described in detail.

[0035]

[Conditions for generating unnecessary light rays] As shown in FIG.
From the central part S ₀ and both ends S ₁ , S ₋₁ of the rays F ₀ , F ₁ ,
When each F ₋₁ is emitted, it enters a certain point P on the plane 8 of the Fresnel lens FL, is refracted at that point P, is refracted again at the lens surface 2, and then is irradiated from the Fresnel lens FL (the surface to be illuminated in FIG. Reach the right hand side).

FIG. 4 is an enlarged view near the point P. In the figure, the one-dot chain line is a virtual line parallel to the optical axis AX (FIG. 1), and the two-dot chain line is a virtual line orthogonal to the optical axis AX.
As shown in this figure, the light is emitted from the end S ₋₁ of the light source 10,
Rays F _-1 incident on the Fresnel lens FL at an incident angle theta _-1 is refracted at refraction angle theta _-1 'at the point P. This refraction angle θ ₋₁ ′ is given by equation (3) according to Snell's law. Then, the refracted ray travels in the Fresnel lens FL and is refracted again at the lens surface 2,
The lens surface 2 is tilted by the angle θ _-1 ″ with respect to the optical axis AX.
(Light ray F _-1 ″).

Further, light F ₁ emitted from the end portion S ₁ of the light source 10 is also the same analysis as above, light F ₁ incident at point P at the incident angle theta ₁ is refracted at the refraction angle theta ₁ ' , Refracts again on the lens surface 2 and forms an angle θ ₁ ″ with the optical axis AX (equation (1))
The light is emitted from the lens surface 2 in a tilted state (light ray F ₁ ″).

Further, the light ray F ₀ emitted from the central portion S ₀ of the light source 10 is also refracted by the flat surface 8 and the lens surface 2 of the Fresnel lens FL in the same manner as described above, and then, only by an angle θ ₀ ″ with respect to the optical axis AX. The light is emitted from the lens surface 2 in a tilted state (light ray F ₀ ″).

First, the relationship between the three light rays traveling in the Fresnel lens FL and the non-lens surface 4 will be considered.
Of the three light rays, the light ray F ₋₁ ′ emitted from the end S ₋₁ of the light source 10 and refracted at the point P has an inclination angle θ ₋₁ ′ with respect to the optical axis AX smaller than the non-lens angle φ. As shown in FIG. 16, this light ray F _-1 ′ is blocked by the non-lens surface 4, and an unnecessary light ray F _a is generated. Therefore,
The following relational expression

[0040]

[Equation 18]

If the condition is satisfied, it is possible to prevent the light ray traveling in the Fresnel lens FL from entering the non-lens surface 4.
As a result, it is possible to prevent generation of the unnecessary light beam F _a .

Next, the relationship between the three light rays emitted from the lens surface 2 and the non-lens surface 4 will be considered. If, when the "inclination angle theta ₁ of" emission light F ₁ and greater than non-lens angle phi, output light F ₁ "is, as shown in FIG. 17, it is incident on the non-lens surface 4, unnecessary light F _b , F _c is generated. in contrast, the non-lens angle φ and have the following formula "inclination theta ₁ of the" emitted light F ₁

[0043]

[Formula 19]

In the case of the relationship represented by, the incident light rays are prevented from entering the non-lens surface 4, and the unnecessary light rays F _b , F
It is possible to prevent the occurrence of _c .

Therefore, in order to completely prevent the generation of the unnecessary light rays F _a , F _b , and F _c , it is necessary to satisfy the expressions (9) and (10) at the same time. That is, the inequality of Expression (5) needs to hold.

However, in a general illumination optical system applied to a device such as a plate-making contact printer or a proximity exposure machine for liquid crystal display devices, it is impossible to satisfy the inequality of formula (5) over the entire Fresnel lens FL. It is impossible. Note that a specific example thereof will be described according to the embodiment described below.

[0047]

[First Embodiment] Next, the construction and working effects of the first embodiment will be described with reference to the first embodiment. For example, the refractive index of the material forming the Fresnel lens FL is n = 1.
5, the focal length f of the Fresnel lens FL = 1000 mm, the size d of the light source 10 = 140 mm, the distance D from the light source 10 to 700 mm, the size of the illuminated surface A = 1000 mm × 800 mm, The lens height h _max is half the diagonal of the illuminated surface and is 640 mm. Of the above parameters (n, f, d, D, A), other than f is the second
The values are the same in the three examples.

In this case, when the function θ ₁ ″ shown by the equation (1) and the function θ ₋₁ ′ shown by the equation (3) are plotted against the height h from the center of the lens, two lines shown in FIG. 5 are obtained. Curves C ″ and C ′ are obtained, and both curves C ″ and C ′ are h = H ₀ (2
81 mm). In addition, from the figure, the formula (5)
It can be seen that the above condition is satisfied only in the shaded region. That is, in the lens center portion, that is, in the range where the height h from the lens center is from zero to the lens height H ₀ , the formula (5)
There is no solution that satisfies. Therefore, it is impossible to completely prevent generation of unnecessary light rays over the entire Fresnel lens FL.

Therefore, in the first embodiment according to the present invention, the height h from the lens center is from zero to the lens height H _0.
In the range up to, the non-lens surface 4 is finished so that the non-lens angle φ satisfies the function θ ₁ ″ shown in the equation (1), so that the unnecessary light rays F _c (FIG.
Thereby preventing the occurrence of 7), thereby preventing simultaneously the generation of unnecessary light F _b. Also, Fresnel lens F
In the outer peripheral portion of L, that is, in the range where the height h from the lens center is from the lens height H ₀ to the maximum lens height h _max , the non-lens angle φ satisfies the inequality of Expression (5). 4 is finished, and unnecessary light rays F _a , F _b , and F within the range are finished.
The occurrence of _c is prevented.

FIG. 6 is a diagram showing unnecessary light rays generated when a light ray from the central portion S ₀ of the light source 10 is incident on the Fresnel lens FL according to the first embodiment. Also, FIG. 7 shows the first
The Fresnel lens FL according to the embodiment has an end portion S of the light source 10.
It is a figure which shows the unnecessary light beam which generate | occur | produces when the light beam from ₁ injects. In these drawings, reference numeral 12 indicates a surface to be illuminated, and line FF extending from the Fresnel lens FL to the surface to be illuminated 12 indicates an unnecessary ray. From these figures, light source 1
It can be seen that there is only an unnecessary ray having a small deviation angle with respect to the ordinary ray in both the rays from the central portion S ₀ and the edge portion S _{1 of 0} . Further, it can be seen that the unnecessary light rays are generated only in the central portion of the Fresnel lens FL, and the generation of the unnecessary light rays is suppressed.

[0051] Thus, according to the Fresnel lens FL according to the first embodiment, it is possible to suppress the generation of unnecessary light, unnecessary light F _c, in particular a material adverse effect on the illumination performance. Further, not only the unnecessary light rays F _c but also the unnecessary light rays F _b are prevented at the same time, and the amount of the unnecessary light rays can be greatly reduced. Therefore, by applying the illumination optical system (FIG. 1) having the Fresnel lens FL formed as described above to a device such as a plate-making contact printer or a proximity exposure machine for liquid crystal display devices, a mask pattern with excellent characteristics can be obtained. Can be transferred and images can be recorded.

[0052]

[Second Embodiment] Next, the configuration and operational effect of the Fresnel lens FL according to the second embodiment will be described. In the convergent illumination optical system having this Fresnel lens FL, the focal length f of the Fresnel lens FL is 600 mm.

FIG. 8 is a graph showing the function θ ₁ ″ and the function θ ₋₁ ′ with respect to the height h from the lens center, and the curves C ″ and C ′ in the figure are the function θ ₁ ″ and the function θ _{−1, respectively.} ′. Both of these curves C ″ and C ′ are h
= H ₀ (138 mm). The shaded area in the figure is an area that satisfies the expression (5).

The second aspect of the present invention is based on the above analysis.
In the embodiment, in the range where the height h from the lens center is zero to the lens height H ₀ (= 138 mm), the non-lens angle φ satisfies the function θ ₁ ″ shown in the equation (1). The surface 4 is finished to prevent generation of the unnecessary light rays F _c (FIG. 17) and at the same time to prevent generation of the unnecessary light rays F _b . Further, the height from the outer peripheral portion of the Fresnel lens FL, that is, the lens center is increased. In the range where the height h is from the lens height H ₀ to the maximum lens height h _max , the non-lens surface 4 is set so that the non-lens angle φ satisfies the inequality of Expression (5).
By finishing the unnecessary light rays F _a , F _b , and
The generation of F _c is prevented. Thus, generation of unnecessary light rays is suppressed.

FIG. 9 is a diagram showing unnecessary light rays generated when a light ray from the central portion S ₀ of the light source 10 enters the Fresnel lens FL according to the second embodiment. FIG. 10 is a diagram showing unnecessary light rays generated when a light ray from the end S ₁ of the light source 10 is incident on the Fresnel lens FL according to the second example. As shown in these figures, both of the light rays from the central portion and the end portions of the light source 10 include only unnecessary rays having a small deviation angle with respect to the ordinary rays. Further, it can be seen that the unnecessary light rays are generated only in the central portion of the Fresnel lens FL, and the generation of the unnecessary light rays is suppressed.

As described above, according to the Fresnel lens FL according to the second example, the same effect as that of the first example can be obtained. That is, it is possible to suppress the generation of unnecessary light F _c and adversely affect the lighting characteristics, to prevent unwanted light F _b at the same time, it is possible to reduce the unnecessary light amount greatly. Therefore, by applying the illumination optical system (FIG. 1) having the Fresnel lens FL formed as described above to a device such as a plate-making contact printer or a proximity exposure machine for liquid crystal display devices, a mask pattern with excellent characteristics can be obtained. Can be transferred and images can be recorded.

[0057]

[Third Example] Next, the configuration and operational effect of the Fresnel lens FL according to the third example will be described. In the parallel illumination optical system having this Fresnel lens FL, the focal length f of the Fresnel lens FL is 700 mm.

[0058] Figure 11 is '"is a graph showing the curve C in FIG, C and functions theta _-1"' function theta ₁ to the height h from the center of the lens each function theta ₁ "and function theta _-1 Both curves C ″ and C ′ intersect at h = H ₀ (170 mm). The shaded area in the figure is an area that satisfies the expression (5).

Based on the above analysis, the third aspect of the present invention
In the embodiment, in the range where the height h from the lens center is zero to the lens height H ₀ (= 170 mm), the non-lens angle φ satisfies the function θ ₁ ″ shown in the equation (1). The surface 4 is finished to prevent generation of the unnecessary light rays F _c (FIG. 17) and at the same time to prevent generation of the unnecessary light rays F _b . Further, the height from the outer peripheral portion of the Fresnel lens FL, that is, the lens center is increased. In the range where the height h is from the lens height H ₀ to the maximum lens height h _max , the non-lens surface 4 is set so that the non-lens angle φ satisfies the inequality of Expression (5).
By finishing the unnecessary light rays F _a , F _b , and
The generation of F _c is prevented. Thus, generation of unnecessary light rays is suppressed.

FIG. 12 is a diagram showing unnecessary light rays generated when a light ray from the central portion S ₀ of the light source 10 enters the Fresnel lens FL according to the third embodiment. FIG. 13 is a diagram showing unnecessary light rays generated when a light ray from the end S ₁ of the light source 10 enters the Fresnel lens FL according to the third example. As shown in these figures, both of the light rays from the central portion and the end portions of the light source 10 include only unnecessary rays having a small deviation angle with respect to the ordinary rays.
Further, it can be seen that the unnecessary light rays are generated only in the central portion of the Fresnel lens FL, and the generation of the unnecessary light rays is suppressed.

As described above, according to the Fresnel lens FL according to the third example, the same effect as that of the first example can be obtained. That is, it is possible to suppress the generation of unnecessary light F _c and adversely affect the lighting characteristics, to prevent unwanted light F _b at the same time, it is possible to reduce the unnecessary light amount greatly. Therefore, by applying the illumination optical system (FIG. 1) having the Fresnel lens FL formed as described above to a device such as a plate-making contact printer or a proximity exposure machine for liquid crystal display devices, a mask pattern with excellent characteristics can be obtained. Can be transferred and images can be recorded.

In the first to third embodiments, the non-lens angle φ satisfies the function θ ₁ ″ at the central portion and the expression (5) at the outer peripheral portion so that the non-lens surface 4 is If the maximum lens height h _max is smaller than the lens height H ₀ , the entire Fresnel lens surface 6 may be finished so that the non-lens angle φ satisfies the function θ ₁ ″. The same effect as in the above embodiment can be obtained.

[0063]

[Manufacturing Method of Fresnel Lens] Next, a manufacturing method of the Fresnel lens FL will be described.

A flat plate-shaped mold block, which is a raw material of a lens mold for forming the Fresnel lens FL, is prepared, and a cutting edge angle ψ of a cutting tool as a cutting tool for cutting the mold block is determined. To do. In particular,
The cutting edge angle ψ is determined within a range in which the inequality shown in the equation (6) is satisfied. The reason is as follows. That is,
At the center of the Fresnel lens FL (FIG. 14), the lens angle σ
Is relatively small, the die block 16 can be machined in accordance with the required non-lens angle φ by adjusting the feed angle ω of the cutting tool 14, but at the outer peripheral part (FIG. 15), Since the angle σ is relatively large, in addition to cutting the portion corresponding to the lens surface of the mold block, the side surface 14a of the cutting tool 14 also cuts the inclined surface 16a corresponding to the non-lens surface at the same time. The angle φ'of the surface 16a with respect to the perpendicular 18 is determined regardless of the feed angle ω. Where the angle φ ′ is

[0065]

[Equation 20]

It can be expressed as Therefore, if
When the cutting edge angle ψ is set to a predetermined angle or more, the cutting tool 1
The mold block 16 is scraped off more than necessary on the side surface 14a of No. 4, so that the angle φ ′ becomes larger than the desired non-lens angle φ. To prevent this, the maximum value of the non-lens angle phi, the clogging formula (9) maximum function theta _-1 at a height h _max 'values of theta _-1' as can be seen from (h _max), maximum The angle φ '(h _max ) at the height h _max is

[0067]

[Equation 21]

It is necessary to satisfy Also, the cutting edge angle ψ
Is larger than 0 °, the formula (6) is obtained by rearranging the formula (12). As you can see from the above analysis,
In order to manufacture the Fresnel lens FL according to the present invention, the cutting edge angle ψ of the cutting tool 14 is within the range shown by the formula (6).
Need to decide.

When the cutting edge angle ψ of the cutting tool 14 is determined, the height H ₀ ″ is next obtained. This height H ₀ ″ is the mold block 1
6 shows the position from which the feed angle ω is set within the range of Expression (8) by the distance from the center of 6, and the height from the center of the mold block 16 when Expression (7) is established. It is h. That is, the height H ₀ ″ indicates the position where the die block 16 starts to be cut by the side surface 14 a of the cutting tool 14.

When the height H ₀ ″ is obtained as described above, the feed angle ω of the cutting tool 14 satisfies the function θ ₁ ″ in the range from the center of the mold block 16 to the height H ₀ ″. Further, in the range from the height H ₀ ″ to the maximum height h _max , the feed angle ω of the cutting tool 14 is set to an arbitrary value that satisfies the expression (8), and the cutting tool 14 is fed to the upper surface of the mold block 16. The lens mold is formed by cutting with.

Subsequently, a lens forming process is performed using this lens mold. For example, the lens mold is heated and compressed with a lens material such as an acrylic resin which is a material of the Fresnel lens FL (lens forming process). Finally, the Fresnel lens FL thus formed is taken out from the lens mold.

As described above, according to the method of manufacturing the Fresnel lens according to this embodiment, after the cutting edge angle ψ of the cutting tool 14 is determined, the feed angle ω of the cutting tool 14 is set from the center of the mold block 16. Since the lens mold corresponding to the Fresnel lens FL can be easily formed by setting the Fresnel lens FL in accordance with the height of the Fresnel lens FL, the Fresnel lens FL can be manufactured by a simple process.

When the Fresnel lens FL of the first to third embodiments is manufactured by the above manufacturing method, the basic manufacturing steps are the same, but the cutting edge angle ψ,
The angle φ ′ and the height H ₀ ″ are different from each other.

For example, the Fresnel lens FL of the first embodiment.
When manufacturing, the maximum value of the blade edge angle ψ is 61.3 °. For example, when the blade edge angle ψ is set to 60 °, the formula (11)
The angle φ'shown changes with the height h from the center as shown by the curve C in FIG. The height H ₀ ′ when the angle φ ′ becomes zero is 286 mm. Further, the height H ₀ ″ is 452 mm. Therefore, in this embodiment, the height H ₀ ″ (= 452) from the center of the mold block 16.
up to mm), the cutting tool 14 is cut at a feed angle ω satisfying the function θ ₁ ″, while the height H ₀ ″ (= 45
In the range from 2 mm) to the maximum height h _max (= 640 mm), a lens mold is formed by cutting with a feed angle ω of zero, for example, and a desired Fresnel lens FL is manufactured by this lens mold. There is.

When the Fresnel lens FL of the second embodiment is manufactured, the maximum value of the cutting edge angle ψ is 47.9 °,
For example, when the cutting edge angle ψ is set to 45 °, the angle φ'shown in the equation (11) changes as shown by the curve C in FIG. 8 according to the height h from the center. The height H ₀ ′ when the angle φ ′ becomes zero is 291 mm. Also, the height H ₀ ″
Is 304 mm. Therefore, in this embodiment, the height H ₀ ″ (= 304 mm) from the center of the mold block 16 is set.
In the range up to, the cutting tool 14 is cut at the feed angle ω satisfying the function θ ₁ ″, while the height H ₀ ″ (= 304 m
maximum height h _{m ax} (= 640mm) to the extent of forming a lens mold by cutting a feed angle ω example as zero from m), to produce the desired Fresnel lens FL further by the lens mold ing.

Further, the Fresnel lens FL of the third embodiment.
When manufacturing, the maximum value of the blade edge angle ψ is 51.5 °. For example, if the blade edge angle ψ is set to 50 °, the formula (11)
The angle φ ′ indicated by is shown in FIG. 11 according to the height h from the center.
Changes as shown by the curve C in FIG. The height H ₀ ′ when the angle φ ′ becomes zero is 287 mm. Further, the height H ₀ ″ is 339 mm. Therefore, in this embodiment, the height H ₀ ″ (= 33) from the center of the mold block 16.
In the range up to 9 mm, the cutting tool 14 is cut at a feed angle ω that satisfies the function θ ₁ ″, while the height H ₀ ″ (= 3
In the range from 39 mm) to the maximum height h _max (= 640 mm), a lens mold is formed by cutting with a feed angle ω of zero, and a desired Fresnel lens FL is manufactured by this lens mold. There is.

[0077]

As described above, according to the first aspect of the invention, the non-lens angle φ on the Fresnel lens surface is expressed in the range from the height h from the lens center to zero to the lens height H _0. Since the function θ ₁ ″ shown in (1) is satisfied, it is possible to suppress the generation of unnecessary light rays that adversely affect the illumination characteristics.

Further, according to the invention of claim 2, in the range of the outer peripheral portion of the lens, that is, the height h from the lens center from the lens height H ₀ to the maximum lens height h _max , the non-lens Since the angle φ satisfies the inequality of the expression (5), it is possible to prevent the generation of unnecessary light rays in the range and suppress the generation of unnecessary light rays.

According to the invention of claim 3, a mold block and a cutting tool having a cutting edge angle ψ satisfying the expression (6) are prepared, and the height H ₀ from the center of the mold block. In order to form a lens mold, the cutting tool is fed into one surface of the mold block for cutting so that the feed angle ω of the cutting tool satisfies the function θ ₁ ″ in the corresponding range. Therefore, the Fresnel lens according to claim 1 can be manufactured using the lens mold.

Further, according to the invention of claim 4, a die block and a cutting tool having a cutting edge angle ψ satisfying the expression (6) are prepared, and the height H ₀ from the center of the die block. In the range corresponding to ″, the feed angle of the cutting tool is the function θ ₁ ″
To satisfy the above condition, and within the range corresponding to the maximum lens height h _max from the position corresponding to the height H ₀ ″, the feed angle ω of the cutting tool is set to an arbitrary value that satisfies the expression (8),
Since the lens mold is formed by feeding the cutting tool to one surface of the mold block and performing the cutting process, the Fresnel lens according to claim 2 can be manufactured using this lens mold. .

[Brief description of drawings]

FIG. 1 is a diagram showing an illumination optical system having a Fresnel lens according to the present invention.

FIG. 2 is a partially enlarged view of a lens central portion of the Fresnel lens shown in FIG.

FIG. 3 is a partially enlarged view of a lens outer peripheral portion of the Fresnel lens shown in FIG.

FIG. 4 is an enlarged view near a point P in FIG.

FIG. 5 is a graph of each function with respect to the height h from the lens center in the first example.

FIG. 6 is a diagram showing unnecessary light rays generated when a light ray from the central portion of the light source is incident on the Fresnel lens according to the first example.

FIG. 7 is a diagram showing unnecessary light rays generated when a light ray from the end of the light source is incident on the Fresnel lens according to the first example.

FIG. 8 is a graph of each function with respect to the height h from the lens center in the second example.

FIG. 9 is a diagram showing unnecessary light rays generated when a light ray from the center of the light source is incident on the Fresnel lens according to the second example.

FIG. 10 is a diagram showing unnecessary light rays generated when a light ray from an end portion of a light source is incident on the Fresnel lens according to the second example.

FIG. 11 is a height h from the lens center in the third embodiment.
Is a graph of each function with respect to.

FIG. 12 is a diagram showing unnecessary light rays generated when a light ray from the center of the light source is incident on the Fresnel lens according to the third example.

FIG. 13 is a diagram showing unnecessary light rays generated when a light ray from an end portion of a light source is incident on the Fresnel lens according to the third example.

FIG. 14 is a diagram showing an embodiment of a method of manufacturing a Fresnel lens according to the present invention.

FIG. 15 is a diagram showing an embodiment of a method of manufacturing a Fresnel lens according to the present invention.

FIG. 16 is a diagram showing a mechanism of generating unnecessary light rays in a Fresnel lens.

FIG. 17 is a diagram showing a mechanism of generating unnecessary light rays in a Fresnel lens.

[Explanation of symbols]

 2 Lens surface 4 Non-lens surface 6 Fresnel lens surface 10 Light source FL Fresnel lens

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Moriwaki 1 Horikawa-dori Teranouchi, Kamigyo-ku, Kyoto 1-chome, 1 Tenjin Kitamachi, Tenjin Kitamachi Dai Nippon Screen Manufacturing Co., Ltd.

Claims (4)

[Claims] _{1. A} function θ ₁ ″, a function σ and a function θ _{− in} an illumination optical system that guides light from a light source having a certain size to a surface to be illuminated through a Fresnel lens and illuminates the surface to be illuminated. each [number 1] ₁ ' [Equation 2] [Equation 3] However, n: refractive index of the lens material which comprises the said Fresnel lens, h: height from the lens center, d: size of the said light source, D: distance between the said light source and the above Fresnel lens, f: the above Fresnel lens The focal length of is defined as When the height h at which is satisfied is the lens height H ₀ , the non-lens angle φ of the Fresnel lens satisfies the function θ ₁ ″ in the range from the height h of zero to the lens height H _0. A Fresnel lens used in an illumination optical system, characterized in that the Fresnel lens surface is finished. 2. The non-lens angle φ, when the height h from the lens center is in the range from the lens height H ₀ to the maximum lens height h _max , the following inequality: The Fresnel lens used in the illumination optical system according to claim 1, which is finished so as to satisfy. 3. The Fresnel lens manufacturing method according to claim 1, wherein the mold block is prepared, and the function θ of claim 1 when the height h from the lens center is the maximum lens height h _{max. -1} ′ and the value of the function σ are θ
_-1 '(h _max ) and σ (h _max ), the cutting edge angle ψ is And a step of preparing a cutting tool satisfying the above condition, so that the feed angle ω of the cutting tool satisfies the function θ ₁ ″ in a range corresponding to the lens height H ₀ from the center of the mold block. A step of feeding a cutting tool to one surface of the mold block to perform a cutting process to form a lens mold; and a step of performing a lens forming process using the lens mold to form a Fresnel lens. A method of manufacturing a Fresnel lens according to claim 1. 4. The Fresnel lens manufacturing method according to claim 2, wherein the mold block is prepared, and the function θ of claim 1 when the height h from the lens center is the maximum lens height h _{max. -1} ′ and the value of the function σ are θ
_-1 '(h _max ) and σ (h _max ), the cutting edge angle ψ is And a step of preparing a cutting tool satisfying There "when a, the height H ₀ from the center of the mold block" the height which satisfies H ₀ as in the range corresponding to the feed angle ω of the cutting tool meets the function theta ₁ ", The maximum lens height h _max from the position corresponding to the height H ₀ ″.
In the range corresponding to, the feed angle ω of the cutting tool is A step of feeding the cutting tool to one surface of the mold block to perform a cutting process to form a lens mold; and a step of forming a Fresnel lens by performing a lens forming process using the lens mold. The method of manufacturing a Fresnel lens according to claim 2, further comprising: