JPH09236701A - Fresnel lens and stamper manufacturing method used for molding the same - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a stamper (and Fresnel lens) for molding a Fresnel lens that requires a short working time for cutting. When cutting the surface of a plate-shaped workpiece that is mounted on a table and rotates in the horizontal direction using a cutting tool having a sharp-edged convex tip, the cutting depth of the cutting tool By continuously changing the sheath gradient by a predetermined amount and repeating the cutting process of linearly moving the cutting tool from the outside of the work material toward the center or from the center to the outside, the sawtooth unevenness becomes spiral. A stamper used for molding a Fresnel lens composed of continuous grooves is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fresnel lens applied to an optical product such as an OHP, a plate-making printer, a transmission type projection screen, etc., and particularly, a molding stamper (mold) that can be easily and quickly processed in a shorter time than ever before. And a Fresnel lens molded by the stamper.

[0002]

2. Description of the Related Art A Fresnel lens is a sheet-shaped lens in which an unnecessary portion of an optical lens main body is deleted so as to have optical characteristics equivalent to those of the lens. FIG. 1 (a)
1B is an original convex lens, FIG. 1B is a state in which the convex lens is divided into concentric circles at a predetermined pitch from the center, and FIG. 1C is a Fresnel lens exhibiting optical characteristics equivalent to those of the convex lens. FIG. 1D is a cross-sectional explanatory view showing a stamper used to mold the Fresnel lens. It should be noted that, in the figure, only the description regarding the convex lens is made conceptually, but it goes without saying that the Fresnel lens is not limited thereto and may be a concave lens.

The existing Fresnel lens has a structure in which serrated concavities and convexes (prisms) are arranged in a "concentric circle" for each wheel, and when cutting a molding stamper, it is an inverse type of the serrated concavity and convexity. Each groove must be cut independently.

In the above-mentioned cutting process, a "vertical lathe" is generally used.
Machine is used. When cutting the surface of a plate-shaped work piece that is mounted on a table and rotates in the horizontal direction using a cutting tool that has a sharp-edged convex cutting edge, a serrated concavo-convex pattern for one wheel When cutting a groove that is the reverse type, the Fresnel surface slope (Fresnel angle), the rise surface slope (rise angle), and the depth of cut (the Fresnel surface and the vertical depth of the rise surface) Therefore, the cutting tool is appropriately moved up and down and rotated with respect to the material to be cut. In order to form a groove for one wheel, two steps of cutting the Fresnel surface and cutting the rise surface are required. (See Fig. 2)

After the cutting of the groove of one wheel into a predetermined shape is completed, the cutting tool is moved, and the cutting of adjacent grooves is sequentially performed in the same manner to cut the stamper. The concentric cutting process is arbitrarily performed from the outside of the material to be cut toward the center or from the center to the outside.
In addition, when cutting one groove, Fresnel surface
The order of the rise surface does not matter.

In the above cutting process, the time spent for the movement of the cutting tool (vertical movement and rotation, movement to the adjacent groove) and the alignment of the cutting location is more than the time spent for the actual cutting itself. It is enormous, and as a result, there is a problem that the working time required for the entire cutting process of the stamper becomes enormous. In the working example by the applicant, the actual time required for the entire cutting process of the stamper of the Fresnel lens having a diameter of 40 inches is about 100 to 200 hours.

When cutting a Fresnel lens stamper having a diameter of 40 inches (1016 mm) and a groove pitch of 0.13 mm, the outermost radius R = 508 mm, and the number of grooves from the center to the outermost is 508/0. 13 ≒ 3900
Is a book.

As a groove of one wheel, when cutting the circumference at a position of R = 500 mm is assumed as exemplified below, the cutting process is completed and the cutting tool is moved to the adjacent groove (vertical movement and adjacent movement). In the case of (moving to the groove), the time required for cutting itself is about 30 seconds / circle, but the movement of the cutting tool requires about 1 minute 30 seconds.

Naturally, the cutting with a huge depth of cut exceeding the allowable load of the machine tool and the formability of the material to be cut is performed once (one round).
Since it cannot be performed in a gradual manner (several μm to several tens μ
The cutting depth is increased to m) so that the cutting depth becomes a predetermined amount over many times (how many times).

When cutting the circumference at the position of R = 500 mm, the cutting depth is 109 μm, and the cutting depth is increased by 3 μm per rotation, and when the material to be cut rotates at 50 rpm, The material to be cut must be rotated about 36 times (= 109/3) until the desired cutting depth is reached, and the required cutting time is about 40 seconds (36/50).
= 0.73 minutes).

Further, it takes a long time to control the cutting tool (adjust the cutting depth and adjust the angle of the cutting surface) prior to the cutting, in addition to the time required for the cutting itself. Therefore, in order to cut all 3900 grooves (circumference), it takes 100 to 200 hours in total even if the cutting depth decreases toward the inner circumference.

Rather than a Fresnel lens in which sawtooth-shaped irregularities (prisms) are arranged in a "concentric circle" for each wheel,
Japanese Patent Publication No. 30-6223 and Japanese Patent Publication No. 52-4246 are known as proposals for manufacturing a stamper for a Fresnel lens, which is formed by grooves that are continuous in a "spiral shape".

In any of the above publications, a rotating cutting plate and a sliding body which can slide in the surface direction of the cutting plate are arranged, and a blade (which is rotatably mounted on the sliding body). (Bite) mounting base is arranged, and by continuously changing the angle of the cutting blade of the tool (bite) depending on the cutting position of the plate to be cut according to the movement of the sliding body,
It is disclosed that a spiral groove is cut.

However, it is difficult for the apparatus (method) disclosed in the above publication to actually manufacture a Fresnel lens (stamper) for practical use, and the reasons are as follows. This is only a disclosure relating to continuously changing the angle of the Fresnel surface, and does not consider cutting of the rise surface. For cutting with a huge depth of cut that exceeds the allowable load of the machine tool and the formability of the material to be cut, gradually increase the depth of cut (several μm to several tens of μm) and increase the depth of cut as many times as necessary. The fact that the cutting depth is set to a predetermined amount is not taken into consideration, and it is described that the manufacturing is completed by cutting once (continuously from the outermost periphery to the center).

[0015]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a stamper that requires a short working time for cutting the stamper, and a Fresnel lens molded by the stamper. In order to achieve the above object, the serrated irregularities are not concentrically arranged side by side for each wheel, but as shown in FIG. 3, the irregularities are continuous spirally from the center to the outermost periphery. Although the constitution is adopted, at that time, a method for actually manufacturing a Fresnel lens (stamper) practically used is provided by avoiding the above-mentioned reasons.

[0016]

That is, the invention according to claim 1 is a structure in which the unevenness forming the lens portion consisting of the Fresnel surface and the rise surface is spirally continuous from the center to the outermost periphery, The Fresnel lens is characterized in that the angle formed by each surface is desired with respect to the reference surface depending on the lens characteristics and the angle continuously changes from the center to the outermost periphery, depending on the position of the unevenness. Is.

According to a second aspect of the present invention, the surface of a plate-shaped material to be cut, which is mounted on a table and rotates in the horizontal direction,
When performing cutting using a cutting tool that has a convex cutting edge with an acute tip, while continuously changing the cutting depth and gradient of the cutting tool by a predetermined amount, from the outside of the work material to the center or from the center The method for manufacturing a stamper used for molding a Fresnel lens according to claim 1, characterized in that the cutting process is performed by linearly moving the cutting tool toward the outside.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 2 (a), the saw-toothed groove forming the Fresnel lens is composed of a Fresnel surface and a rise surface. For example, in the case of a Fresnel lens exhibiting the optical characteristics of a convex lens. The Fresnel angle θ ₁ increases by a predetermined amount from the center (0 °) of the lens toward the outer circumference. On the other hand, the rise angle θ ₂ is not necessarily required to change in angle according to the position of the lens like the Fresnel angle θ ₁ . 2B is a cross-sectional explanatory view of a stamper for molding the Fresnel lens shown in FIG. 2A, in which an inverted mold of the sawtooth groove of the Fresnel lens is formed. Hereinafter, for convenience of explanation, it is assumed that the rise angle θ ₂ is constant in all the grooves.

Cutting Tool (Bite) As shown in FIG. 2B, a cutting tool having a convex cutting edge with a sharp tip is used. In FIG. 2B, an angle θ ₃ formed between the surface a of the cutting tool for processing the Fresnel surface and the surface b of the cutting tool for processing the rise surface is formed by the Fresnel surface and the rise surface, which changes according to the groove to be processed. It must be an acute angle smaller than the minimum value of the angle θ ₄ .

Cutting Machine A vertical lathe is used to place a plate-shaped material to be cut (metal plate) on a table that rotates in the horizontal direction. (Not shown)

Cutting Conditions (Principle) The inclination and cutting depth of the cutting tool are changed based on the following principle. FIG. 4 illustrates the geometrical relationship of the lens surface to be obtained. The coordinates of the lens surface can be represented by a general formula as follows.

[0022]

[Equation 1]

In the above general formula, the required focal length of the lens
By substituting a specific coefficient corresponding to the diameter, etc., the coordinate Zmm of the lens surface at the position of radius Xmm from the center, the angle of the Fresnel surface divided into pitches, and the position where the Fresnel surface should exist (thickness of stamper) The cutting depth in the direction) can be obtained.

A curve representing the coordinates of the lens surface is z = f (x)
When the curve is divided at a constant pitch on the x-axis and the pitch is reduced, the curve of the lens surface can be approximated to be a straight line within the pitch. (See FIG. 4 (a)) When the above-mentioned constant pitch is made to correspond to each groove (circumference), the cutting depth and the Fresnel angle in the groove can be derived. (See Figure 4 (b))

Cutting There are various procedures for cutting the Fresnel lens molding stamper. An example of the cutting procedure will be described with reference to FIG. 2 in comparison with the cutting procedure according to the prior art.

<Invention> The reverse cutting of the saw-toothed groove forming the Fresnel lens is performed from the outermost periphery toward the center.

First, the Fresnel surface is cut.
Since the Fresnel angle and the cutting depth continuously change from the outermost circumference toward the center, the surface a of the cutting tool for processing the Fresnel surface is moved from the outermost circumference toward the center toward the predetermined Fresnel angle at that position. Cutting is performed so as to have a predetermined cutting depth at that position while matching with.

As described above, it is not possible to perform cutting with an enormous depth of cut at one time from the outermost circumference to the center. Therefore, the cutting tool is repositioned at the start position of cutting, and a similar spiral cutting is performed. The cutting depth of the Fresnel surface is set to a predetermined amount by gradually increasing the depth.

Next, the cutting tool is placed at a predetermined position where the cutting is started, and the rise surface is cut. Since the cutting depth continuously changes from the outermost periphery to the center, the surface b of the cutting tool for processing the rise surface is aligned with the predetermined rise angle at that position from the outermost periphery to the center. , Cut to a predetermined cutting depth at that position. Since the rise angle is assumed to be constant over the entire stamper, after the initial rotation adjustment, the rise angle is fixed and only the cutting depth is changed to proceed with the cutting.

<Prior Art> Since the sawtooth-shaped grooves forming the Fresnel lens are present in concentric circles independent of each other, when the reverse type of the grooves is cut, each wheel is independently cut. . That is, each groove has a constant Fresnel angle, rise angle, and cutting depth for each wheel.
The cutting procedure for each wheel will be described below.

The surface a of the cutting tool for processing the Fresnel surface is matched with the Fresnel angle of the groove and cut to a predetermined cutting depth.

Next, the tip of the cutting tool is placed at a predetermined position where the cutting is started, the surface b of the cutting tool is rotated so as to match the rise angle of the groove, and the cutting is performed to a predetermined cutting depth.

Both the Fresnel surface and the rise surface are processed by arranging the tip of an acute-angled cutting tool at a predetermined position, rotating the cutting tool so that the surface to be processed has a predetermined angle, and then cutting it vertically. Is carried out.

After finishing the machining of the rise surface, the surface b of the cutting tool is rotated so as to escape from the processed rise surface (of course, the surface a of the cutting tool does not come into contact with the processed Fresnel surface), Allow the cutting tool to escape vertically from the work material.

After the predetermined cutting process for one groove is completed, the cutting tool is moved to the cutting position of the next groove, and the cutting process according to the condition (Fresnel angle / cutting depth) of the next groove is similarly performed. To do.

As described above, the fundamental difference between the present invention and the prior art is that the present invention has one continuous groove and the prior art has a predetermined number of grooves. Therefore, in the present invention, the entire area from the outermost periphery to the center can be continuously cut at once, and the cutting tool is separated from the material to be cut each time the next groove is cut to interrupt the cutting operation.
There is no need to set the angle and depth of cut again. Therefore, it is obvious that the time required for the entire cutting process of the stamper is dramatically reduced.

Other cutting procedures (cutting from the center to the outermost circumference, cutting the rise surface first, changing the rise angle according to the lens position,
Etc.), the advantages of the present invention also apply, but the description thereof will be omitted.

[0038]

EXAMPLE An example of the above cutting procedure will be described.
As a Fresnel lens, focal length f = 151 mm, diameter 2
In order to fabricate a film having a diameter of 00 mm, the following coefficients are substituted into the above equation 1. It should be noted that although the coefficient to be substituted varies depending on the design specifications of the lens, the description of the procedure for leading is omitted here.

C = + 0.0134720 1 + k = 0 A ₄ = -0.2125440E-7

Here, the radius from the center X = 51.61 mm
The movement of the tip of the cutting tool at the time of cutting will be specifically described.

When the above formula 1 is converted into a formula for obtaining the angle of the Fresnel surface and the Fresnel angle is obtained, as shown in FIG. 6, X =
The Fresnel angle θ _{1 at} a position of 51.61 mm is 39.0.
82 °, next to the center side (X = 51.48 mm position)
The Fresnel angle θ ₁ of the groove is 38.991 °.

Therefore, the bite gradient is 0.0 while the position of X = 51.61 mm of the work material makes one rotation on the table and the bite moves to the position of X = 51.48 mm.
It changes by 91 °.

In such cutting, the strict control of the bite gradient and cutting depth depends on the NC accuracy of the machine tool (vertical lathe). Further, when the cutting depth is repeated until it reaches a predetermined amount, it is necessary to strictly perform the alignment accuracy between the cutting tool and the cutting portion of the workpiece, but the alignment also depends on the NC accuracy of the machine tool. It will be.

[0044]

EFFECTS OF THE INVENTION By performing the cutting of the stamper in a spiral shape, the time required for the entire cutting process is drastically shortened as compared with the concentric cutting, and when the Fresnel lens is press-molded by the stamper, a resin is used. The releasability of the stamper is also improved, and the Fresnel lens molded by the stamper has the same optical characteristics as the existing Fresnel lens that has been put into practical use (has concentric grooves). is there.

[0045]

[Brief description of drawings]

FIG. 1 is a sectional view conceptually showing a Fresnel lens.

FIG. 2 is a cross-sectional view showing a Fresnel lens, a stamper, and a cutting processing state thereof.

FIG. 3 is a plan view conceptually showing a Fresnel lens.

FIG. 4 is an explanatory diagram showing a geometrical relationship of lens surfaces.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yasuhiro Kikuchi 1-5-1 Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd.

Claims (2)

[Claims] 1. An unevenness forming a lens portion composed of a Fresnel surface and a rise surface is spirally continuous from the center to the outermost circumference, and the angle formed by each surface depends on the position of the unevenness. A Fresnel lens which is desired with respect to a reference surface in accordance with lens characteristics and whose angle changes continuously from the center to the outermost periphery. 2. A cutting tool for cutting a surface of a plate-shaped workpiece that is mounted on a table and rotates in a horizontal direction by using a cutting tool having a sharp-edged convex cutting edge. 2. A cutting process in which a cutting tool is linearly moved from the outside to the center of the material to be cut or from the center to the outside while continuously changing the depth and the gradient by a predetermined amount. A method for manufacturing a stamper used for molding the Fresnel lens according to 1.