JP3168112B2 - Illumination optical system and method of manufacturing Fresnel lens used in the illumination optical system - Google Patents

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 for an illumination optical system applicable to a plate making printer, a proximity exposure machine for a liquid crystal display device, and the like, 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 close printers and proximity exposure machines for liquid crystal display devices. In this illumination optical system, light from a light source is guided to a surface to be illuminated by a Fresnel lens to illuminate the surface to be illuminated.

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. When F is incident, the incident light beam F is refracted by the plane 8 of the Fresnel lens FL, travels straight through the Fresnel lens FL, is refracted by the lens surface 2, and is guided to the surface to be illuminated. In this specification, the light ray F guided to the surface to be illuminated 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 as shown in FIG. Light ray F _a ) in the figure. Also, as shown in FIG. 17, light rays emitted from a certain lens surface 2
Incident on the non-lens surface 4 adjacent to the
(Light beam _Fb ), re-enters the Fresnel lens FL, and emerges again from the adjacent lens surface 2 to the illuminated surface side (light beam _Fc ).

[0005] Such rays F _a , F _b , and F _c are called “unnecessary rays”. It is not preferable in terms of illumination characteristics, and the presence of the unnecessary light beam causes a problem in the proximity exposure machine. For example, when proximity exposure is performed using a Fresnel lens that generates unnecessary light rays, it becomes difficult to accurately transfer a pattern formed on a mask or the like to a resist film. Further, a plate-making printer incorporating the Fresnel lens may cause halftone dot density unevenness, and a liquid crystal exposure apparatus may cause a problem that the pattern dimension is out of order.

[0006]

By the way, when a point light source is used as a light source, generation of unnecessary light rays F _a , F _b , and F _c is often performed by appropriately setting the non-lens angle φ. Can be prevented. However, when the light source has a certain size, for example, Japanese Patent Application Laid-Open No. 62-175
As described in detail in Japanese Patent Application Laid-Open No. 087, there is no condition (setting of the non-lens angle φ) over the entire surface of the Fresnel lens where unnecessary light rays reflected and refracted by the non-lens surface are not generated. 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.

[0007] exert the most adverse on the illumination characteristics of these unwanted rays F _a, F _b, F _c is the light F _c, can be expected a significant effect just to prevent the occurrence of light F _c, unnecessary Although a Fresnel lens which suppresses the occurrence of beam F _c is desired, a conventional Fresnel lens of this type did not exist.

Further, even if such a Fresnel lens can be theoretically designed, 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 also desired to provide a manufacturing method capable of manufacturing the lens in a simple process.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its first object to provide an illumination optical system capable of suppressing the generation of unnecessary light rays which adversely affect illumination characteristics. I do.

A second object of the present invention is to provide the illumination light
An object of the present invention is to provide a method of manufacturing a Fresnel lens used in the illumination optical system, which can manufacture a Fresnel lens used in a scientific system by a simple process.

[0011]

According to the first aspect of the present invention, light from a light source having a predetermined size is used for light from the light source.
An illumination optical system that guides a surface to be illuminated through a Fresnel lens having a Fresnel lens surface on a side opposite to a plane on which the light is incident and illuminates the surface to be illuminated, in order to achieve the first object. To the function θ ₁ ″, the function σ, and the function θ ₋₁ ′, respectively.

[0012]

(Equation 10)

[0013]

[Equation 11]

[0014]

(Equation 12)

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

[0016]

(Equation 13)

Assuming that the height h at which the above holds holds is the lens height H ₀ , the non-lens angle φ of the Fresnel lens is represented by the function θ ₁ ″ in the range from the height h of zero to the lens height H _0. The Fresnel lens surface is finished to satisfy.

According to a second aspect of the present invention, there is provided the illumination according to the first aspect.
In the optical system, the non-lens angle φ of the Fresnel lens
Is 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 following.

According to a third aspect of the present invention, there is provided the illumination according to the first aspect.
A method for producing a Fresnel lens used in an optical system, comprising: a step of preparing a mold block to achieve the second object; and a step of preparing a mold when the height h from the center of the lens is the maximum lens height h _max . Assuming that the values of the function θ ₋₁ ′ and the function σ of claim 1 are θ ₋₁ ′ (h _max ) and σ (h _max ), respectively,

[0022]

(Equation 15)

Preparing a cutting tool that satisfies
The cutting tool is placed on one side of the mold block so that the feed angle ω of the cutting tool satisfies the function θ ₁ ″ within a range corresponding to the lens height H ₀ from the center of the mold block. The method 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.

According to a fourth aspect of the present invention, there is provided the illumination according to the second aspect.
A method for producing a Fresnel lens used in an optical system, comprising: a step of preparing a mold block to achieve the second object; and a step of preparing a mold when the height h from the center of the lens is the maximum lens height h _max . Assuming that the values of the function θ ₋₁ ′ and the function σ in claim 1 are θ ₋₁ ′ (h _max ) and σ (h _max ), respectively, a cutting tool whose cutting edge angle 満 足 satisfies Expression (6) is prepared. The process of

[0025]

(Equation 16)

Assuming that the height at which H 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. As described above, the feed angle ω of the cutting tool is set within a range corresponding to the maximum lens height h _max from a position corresponding to the height H ₀ ″.

[0027]

[Equation 17]

Then, the cutting tool is fed into one surface of the mold block and cut to form a lens mold, and a lens forming process is performed using the lens mold to form a Fresnel lens. And a step of performing.

[0029]

According to the first aspect of the present invention, the non-lens angle φ on the Fresnel lens surface is the function θ ₁ ″ represented by the equation (1) when the height h from the center of the lens ranges from zero to the lens height H _0.
Is satisfied, the generation of the unnecessary light beam F _c (FIG. 17) which adversely affects the illumination characteristics is prevented, and the generation of the unnecessary light beam _Fb is also prevented at the same time.

Further, in the invention of claim 2, the outer peripheral portion of the Fresnel lens, i.e. in the height h in the range from the lens height H ₀ to a maximum lens height h _max from the center of the lens, the non-lens angle φ Satisfies the inequality expression (5), the generation of unnecessary light rays F _a , F _b , and F _c in this range is prevented.

According to the third aspect of the present invention, a mold block and a cutting tool whose cutting edge angle ψ satisfies the equation (6) are prepared, and the feed angle ω of the cutting tool has a function θ ₁ ″. In order to satisfy, by sending the cutting tool to one surface of the mold block and performing cutting, a lens mold is formed, and then a lens forming process using the lens mold is performed. A Fresnel lens used in the illumination optical system according to Item 1 is formed.

According to the fourth aspect of the present invention, a mold block and a cutting tool whose cutting edge angle ψ satisfies Expression (6) are prepared, and the height of the mold block is set to the height H ₀ ″ from the center of the mold 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 ω Is set in the range of Expression (8), and the cutting tool is fed into one surface of the mold block to perform cutting, thereby forming a lens mold, and then using the lens mold. 3. The lighting according to claim 2 , wherein the lighting is performed by performing a forming process.
A Fresnel lens used for the optical system is formed.

[0033]

FIG. 1 is a view showing an illumination optical system having a Fresnel lens according to the present invention. FIG. 2 is a partially enlarged view of the center of the Fresnel lens FL shown in FIG.
FIG. 3 is a partially enlarged view of the outer peripheral portion of the Fresnel lens FL of FIG. In this embodiment, the non-lens angle φ on the Fresnel lens surface 6 satisfies the function θ ₁ ″ (Equation (1)) at the center and the inequality of Equation (5) at the outer periphery. The Fresnel lens FL is finished, so that unnecessary light rays that adversely affect the illumination characteristics can be effectively reduced.

In the following, consideration of conditions for generating unnecessary light rays, specific embodiments, and the functions and effects of the embodiments will be described in detail. After the description of the Fresnel lens FL, its manufacturing method will be described in detail.

[0035]

[Conditions in which unnecessary light rays are generated] As shown in FIG.
From the central portion S ₀ and both ends S ₁ , S _-1 of the light beams F ₀ , F ₁ ,
When F _-1 is emitted, it is incident on a point P on the plane 8 of the Fresnel lens FL, is refracted at the point P, is refracted again on the lens surface 2, and then is transmitted from the Fresnel lens FL to the illuminated surface (see FIG. Right hand side).

FIG. 4 is an enlarged view near 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, 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. The refraction angle θ ₋₁ ′ is given by Expression (3) from Snell's law. Then, the refracted light travels through the Fresnel lens FL and is refracted again at the lens surface 2,
The lens surface 2 is tilted at an 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 ' Is refracted by the lens surface 2 again, and the angle θ ₁ ″ with respect to the optical axis AX (formula (1))
The light exits from the lens surface 2 in a state of being tilted only (light ray F ₁ ″).

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

First, the relationship between the three light beams traveling in the Fresnel lens FL and the non-lens surface 4 will be considered.
Of these 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 is such that the inclination angle θ ₋₁ ′ with respect to the optical axis AX becomes smaller than the non-lens angle φ. As shown in FIG. 16, this light beam F _-1 ′ is blocked by the non-lens surface 4, and an unnecessary light beam _Fa is generated. Therefore,
The next relation

[0040]

(Equation 18)

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

Next, the relationship between the three light beams 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]

[Equation 19]

In the case of having the relationship shown by the following expression, the outgoing light beam is prevented from entering the non-lens surface 4, and the unnecessary light beams F _b , F _b
The occurrence of _c can be prevented.

Therefore, in order to completely prevent the generation of the unnecessary light rays F _a , F _b , and F _c , it is necessary to simultaneously satisfy the equations (9) and (10). That is, the inequality expression (5) needs to be satisfied.

However, in a general illumination optical system applied to a device such as a plate making contact printer or a proximity exposure device for a liquid crystal display element, it is not possible to satisfy the inequality expression (5) over the entire surface of the Fresnel lens FL. Impossible. A specific example will be described with reference to an embodiment described below.

[0047]

[First Embodiment] Next, the structure and operation and effect of the first embodiment will be described with reference to the first embodiment. For example, the refractive index n of the material constituting the Fresnel lens FL = 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 the lens D = 700 mm, and the size A of the illuminated surface = 1000 mm × 800 mm. The lens height h _max is half the diagonal line of the surface to be illuminated, and is 640 mm. Of the above parameters (n, f, d, D, A), except for f, the second and
The values are the same in the three embodiments.

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 with respect to the height h from the lens center, the two shown in FIG. Curves C ″ and C ′ are obtained, and both curves C ″ and C ′ are h = H ₀ (2
81 mm). Also, from FIG.
It can be seen that satisfying is limited to the region indicated by the oblique lines. That is, when the height h from the lens center, that is, the center of the lens is in the range of zero to the lens height H ₀ , the equation (5) is obtained.
There is no solution that satisfies. Therefore, it is impossible to completely prevent the generation of unnecessary light beams over the entire Fresnel lens FL.

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

[0050] FIG. 6 is a diagram showing the unnecessary light generated when the 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. FIG. 7 shows the first
The end S of the light source 10 is attached to the Fresnel lens FL according to the embodiment.
FIG. 4 is a diagram showing unnecessary light rays generated when light rays from ₁ enter. In these figures, reference numeral 12 denotes an illuminated surface, and a line FF extending from the Fresnel lens FL to the illuminated surface 12 indicates an unnecessary light beam. From these figures, the light source 1
By any of the rays from the central portion S ₀ and the end S ₁ of 0., only a small unnecessary rays of polarization angle it can be seen that absent the normal light. Further, it can be seen that the unnecessary light is generated only at the center of the Fresnel lens FL, and the generation of the unnecessary light 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 beam _Fc but also the unnecessary light beam _Fb is prevented at the same time, and the amount of the unnecessary light beam can be greatly reduced. Therefore, by applying the illumination optical system (FIG. 1) having the Fresnel lens FL formed as described above to an apparatus such as a plate making contact printer or a proximity exposure machine for a liquid crystal display element, a mask pattern with excellent characteristics can be obtained. Transfer, image recording, and the like.

[0052]

[Second Embodiment] Next, the structure, operation and effect of a Fresnel lens FL according to a second embodiment will be described. In the convergent illumination optical system having the 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 center of the lens. The curves C ″ and C ′ in FIG. 8 show the function θ ₁ ″ and the function θ _{−1, respectively.} These curves C ″ and C ′ correspond to h
= H ₀ (138 mm). The hatched area in the figure is an area that satisfies Expression (5).

Based on the above analysis, the second embodiment 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 (= 138 mm), the non-lens is adjusted so that the non-lens angle φ satisfies the function θ ₁ ″ represented by the equation (1). finish surface 4, thereby preventing the generation of unnecessary light F _c (FIG. 17), thereby preventing simultaneously the generation of unnecessary light F _b. the outer peripheral portion of the Fresnel lens FL, that is high from the center of the lens In the range from the lens height H ₀ to the maximum lens height h _max , the non-lens surface 4 is adjusted so that the non-lens angle φ satisfies the inequality expression (5).
By finishing unnecessary light rays F _a , F _b ,
Thereby preventing the occurrence of F _c. Thus, the generation of unnecessary light is suppressed.

[0055] FIG. 9 is a diagram showing the unnecessary light generated when the light ray from the central portion S ₀ of the light source 10 is incident on the Fresnel lens FL according to the second embodiment. Further, FIG. 10 is a diagram showing the unnecessary light generated when the light beam from the end S ₁ of the light source 10 is incident on the Fresnel lens FL according to the second embodiment. As shown in these figures, there is only an unnecessary light beam having a small deflection angle with respect to a normal light beam in any of the light beams from the central portion and the end portion of the light source 10. Further, it can be seen that the unnecessary light is generated only at the center of the Fresnel lens FL, and the generation of the unnecessary light is suppressed.

As described above, according to the Fresnel lens FL of the second embodiment, the same effects as those of the first embodiment 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 an apparatus such as a plate making contact printer or a proximity exposure machine for a liquid crystal display element, a mask pattern with excellent characteristics can be obtained. Transfer, image recording, and the like.

[0057]

[Third Embodiment] Next, the structure, operation and effect of a Fresnel lens FL according to a third embodiment will be described. In the parallel illumination optical system having the Fresnel lens FL, the focal length f of the Fresnel lens FL is 700 mm.

FIG. 11 is a graph showing the function θ ₁ ″ and the function θ ₋₁ ′ with respect to the height h from the center of the lens. The curves C ″ and C ′ in FIG. 11 show the function θ ₁ ″ and the function θ _{−1, respectively.} These curves C ″ and C ′ intersect at h = H ₀ (170 mm). The hatched area in the figure is an area that satisfies 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 is adjusted so that the non-lens angle φ satisfies the function θ ₁ ″ represented by the equation (1). finish surface 4, thereby preventing the generation of unnecessary light F _c (FIG. 17), thereby preventing simultaneously the generation of unnecessary light F _b. the outer peripheral portion of the Fresnel lens FL, that is high from the center of the lens In the range from the lens height H ₀ to the maximum lens height h _max , the non-lens surface 4 is adjusted so that the non-lens angle φ satisfies the inequality expression (5).
By finishing unnecessary light rays F _a , F _b ,
Thereby preventing the occurrence of F _c. Thus, the generation of unnecessary light is suppressed.

[0060] FIG. 12 is a diagram showing the unnecessary light generated when the light ray from the central portion S ₀ of the light source 10 is incident on the Fresnel lens FL according to the third embodiment. Further, FIG. 13 is a diagram showing the unnecessary light generated when the light beam from the end S ₁ of the light source 10 is incident on the Fresnel lens FL according to the third embodiment. As shown in these figures, there is only an unnecessary light beam having a small deflection angle with respect to a normal light beam in any of the light beams from the central portion and the end portion of the light source 10.
Further, it can be seen that the unnecessary light is generated only at the center of the Fresnel lens FL, and the generation of the unnecessary light is suppressed.

As described above, according to the Fresnel lens FL of the third embodiment, the same effects as those of the first embodiment 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 an apparatus such as a plate making contact printer or a proximity exposure machine for a liquid crystal display element, a mask pattern with excellent characteristics can be obtained. Transfer, image recording, and the like.

In the first to third embodiments, the non-lens surface 4 is adjusted so that the non-lens angle φ satisfies the function θ ₁ ″ at the center and satisfies the expression (5) at the outer periphery. When 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 effects as those of the above embodiment can be obtained.

[0063]

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

A flat mold block as a raw material of a lens mold for forming the Fresnel lens FL is prepared, and the cutting edge angle ψ of a cutting tool as a cutting tool for cutting the mold block is determined. I do. In particular,
The cutting edge angle ψ is determined in a range in which the inequality expression (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 cut in accordance with the required non-lens angle φ by adjusting the feed angle ω of the cutting bit 14, but the lens block is formed on the outer peripheral portion (FIG. 15). Since the angle σ is relatively large, the portion corresponding to the lens surface of the mold block is cut, and the inclined surface 16a corresponding to the non-lens surface is simultaneously cut by the side surface 14a of the cutting bit 14, so that the inclination 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)

Can be represented by Therefore, if
When the tip angle ψ is set to a predetermined angle or more, the cutting tool 1
The mold block 16 is unnecessarily scraped off at the side surface 14a of the fourth member 4, and as a result, the angle φ ′ becomes larger than the desired non-lens angle φ. In order to prevent this, the maximum value of the non-lens angle φ, that is, the value θ ₋₁ ′ (h _max ) of the function θ ₋₁ ′ at the maximum height h _max , as can be seen from the equation (9), The angle φ ′ (h _max ) at the height h _max is the following relational expression.

[0067]

(Equation 21)

It is necessary to satisfy the following. Also, the tip angle ψ
Is larger than 0 ゜, and by rearranging equation (12), equation (6) is obtained. As can be seen from the above analysis,
In order to manufacture the Fresnel lens FL according to the present invention, the cutting edge angle of the cutting tool 14 must be within the range shown by the equation (6).
Need to decide.

When the cutting edge angle ψ of the cutting tool 14 is determined, the height H ₀ ″ is determined next. The height H ₀ ″ is determined by the mold block 1.
6 indicates the position from which the feed angle ω should be set within the range of Expression (8), and the height from the center of the mold block 16 when Expression (7) holds. 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 ″. 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 satisfying the expression (8), and the cutting tool 14 is fed to the upper surface of the mold block 16. To form a lens mold.

Subsequently, a lens forming process is performed using this lens mold. For example, the lens mold is heated and compressed to 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 of the lens mold.

As described above, according to the method of manufacturing a 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 adjusted 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 height according to the height, the Fresnel lens FL can be manufactured by a simple process.

When the Fresnel lenses FL of the first to third embodiments are manufactured by the above manufacturing method, the basic manufacturing steps are all 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
Is manufactured, the maximum value of the cutting edge angle ψ is 61.3 °. For example, when the cutting edge angle ψ is set to 60 °, the equation (11) is obtained.
Is changed as shown by a curve C in FIG. 5 according to the height h from the center. The height H ₀ ′ when the angle φ ′ becomes zero is 286 mm. The height H ₀ ″ is 452 mm. Therefore, in this embodiment, the height H ₀ ″ (= 452) from the center of the mold block 16.
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 the feed angle ω to, for example, zero, and a desired Fresnel lens FL is manufactured using the lens mold. I have.

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 ′ represented by Expression (11) changes as shown by a curve C in FIG. 8 according to the height h from the center. Note that the height H ₀ ′ when the angle φ ′ becomes zero is 291 mm. 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.
While the cutting tool 14 is cut at a feed angle ω that satisfies the function θ ₁ ″, 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
Is manufactured, the maximum value of the cutting edge angle ψ is 51.5 °. For example, when the cutting edge angle 設定 is set to 50 °, the equation (11) is obtained.
The angle φ ′ shown in FIG. 11 depends on the height h from the center in FIG.
Changes as shown by the curve C in FIG. The height H ₀ ′ when the angle φ ′ becomes zero is 287 mm. The height H ₀ ″ is 339 mm. Therefore, in this embodiment, the height H ₀ ″ (= 33) from the center of the mold block 16.
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 the feed angle ω to, for example, zero, and a desired Fresnel lens FL is manufactured using the lens mold. I have.

[0077]

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

[0078] According to the invention of claim 2, the outer peripheral portion of the further lens, the range of height h from the words lens center from the lens height H ₀ to a maximum lens height h _max is non-lens Since the angle φ satisfies the inequality 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 third aspect of the present invention, a mold block and a cutting tool whose cutting edge angle ψ satisfies Expression (6) are prepared, and the height H ₀ from the center of the mold block is prepared. "The cutting tool is fed into one surface of the mold block and cut to form a lens mold so that the feed angle ω of the cutting tool satisfies the function θ ₁ ” within the corresponding range. because there, irradiation of claim 1 by using the lens mold
A Fresnel lens used for a bright optical system can be manufactured.

According to the fourth aspect of the present invention, a mold block and a cutting tool whose cutting edge angle ψ satisfies Expression (6) are prepared, and the height H ₀ from the center of the mold block is prepared. In the range corresponding to ″, the feed angle of the cutting tool is a function θ ₁ ″
And in a 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);
The illumination optics according to claim 2, wherein a lens mold is formed by feeding the cutting tool to one surface of the mold block and performing a cutting process. 3.
Fresnel lenses used in the system can be manufactured.

[Brief description of the 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 center part of the Fresnel lens of FIG. 1;

FIG. 3 is a partially enlarged view of a lens outer peripheral portion of the Fresnel lens of FIG. 1;

FIG. 4 is an enlarged view near point P in FIG. 1;

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

FIG. 6 is a diagram illustrating unnecessary light rays generated when light rays from the central part of the light source enter the Fresnel lens according to the first example.

FIG. 7 is a diagram illustrating unnecessary light rays generated when light rays from the end of the light source enter the Fresnel lens according to the first example.

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

FIG. 9 is a diagram illustrating unnecessary light rays generated when light rays from the central part of the light source enter the Fresnel lens according to the second example.

FIG. 10 is a diagram illustrating unnecessary light rays generated when light rays from the end of the light source enter the Fresnel lens according to the second example.

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

FIG. 12 is a diagram illustrating unnecessary light rays generated when light rays from the center of the light source enter the Fresnel lens according to the third example.

FIG. 13 is a diagram illustrating unnecessary light rays generated when light rays from the end of the light source enter the Fresnel lens according to the third example.

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

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

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

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

[Explanation of symbols]

 2 lens surface 4 non-lens surface 6 Fresnel lens surface 10 light source FL Fresnel lens

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomohiro Moriwaki 4-chome Tenjinchi, Horikawa-dori-Terauchi, Kamigyo-ku, Kyoto 1 Daikoku Screen Manufacturing Co., Ltd. .Cl. ⁷ , DB name) G02B 3/08

Claims (4)

(57) [Claims] 1. A light from a light source having a predetermined size,
On the opposite side of the plane where the light from the light source
The function θ ₁ ″, the function σ, and the function θ ₋₁ ′ are respectively expressed by the following formulas in an illumination optical system for guiding the illumination target surface through a Fresnel lens having a lens surface. (Equation 2) (Equation 3) Here, n: refractive index of the lens material constituting the Fresnel lens, h: height from the center of the lens, d: size of the light source, D: distance between the light source and the Fresnel lens, f: the Fresnel lens The focal length of is defined as 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. An illumination optical system , wherein the Fresnel lens surface is finished. 2. The illumination optical system according to claim 1, wherein the non-lens angle φ of the Fresnel lens is such that the height h from the lens center is the maximum lens height h _max from the lens height H _0.
The following inequality in the range up to The illumination optical system , wherein the Fresnel lens surface is finished so as to satisfy the following . 3. The illumination optical system according to claim 1 ,
A method for preparing a Fresnel lens, comprising: a step of preparing a mold block; and a value of the function θ _-1 ′ and the function σ according to claim 1, wherein the height h from the lens center is the maximum lens height h _max. To θ
_-1 '(h _max ) and σ (h _max ), the cutting edge angle ψ is given by the following equation: And a step of preparing a cutting tool that satisfies the following: so that the feed angle ω of the cutting tool satisfies the function θ ₁ ″ within a range corresponding to the lens height H ₀ from the center of the mold block. Sending a cutting tool to one surface of the mold block to perform a cutting process to form a lens mold; and performing a lens forming process using the lens mold to form a Fresnel lens. and method for producing a full <br/> Renerurenzu used in an illumination optical system according to claim 1. 4. An illumination optical system according to claim 2 , wherein
A method for preparing a Fresnel lens, comprising: a step of preparing a mold block; and a value of the function θ _-1 ′ and the function σ according to claim 1, wherein the height h from the lens center is the maximum lens height h _max. To θ
_-1 '(h _max ) and σ (h _max ), the cutting edge angle ψ is given by the following equation: A step of preparing a cutting tool that satisfies 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 given by Sending the cutting tool to one surface of the mold block and performing cutting to form a lens mold; and performing a lens forming process using the lens mold to form a Fresnel lens. , with a method for producing a full <br/> Renerurenzu used in an illumination optical system according to claim 2.