JP3358426B2 - Fresnel lens and method of manufacturing stamper used for molding the same - Google Patents

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 optical products such as OHPs, plate making printers, and transmission type projection screens, and more particularly, to a molding stamper (die) which is easier and shorter than 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 unnecessary portions in an optical lens main body are removed so as to exhibit optical characteristics equivalent to those of the lens. FIG. 1 (a)
FIG. 1 (b) shows a state in which the convex lens is concentrically divided at a predetermined pitch from the center, and FIG. 1 (c) shows a Fresnel lens which has optical characteristics equivalent to those of the convex lens. FIG. 1D is a sectional explanatory view showing a stamper used to mold the Fresnel lens. Although FIG. 2 conceptually describes only the convex lens, the Fresnel lens is not limited to this, and it goes without saying that a concave lens may be used.

[0003] The existing Fresnel lens has a configuration in which saw-toothed irregularities (prisms) are arranged in a "concentric" shape for each wheel. A certain groove must be cut one by one independently.

[0004] In the above-mentioned cutting, a "vertical lathe" is generally used.
A machine called is used. When cutting the surface of a plate-shaped workpiece to be mounted on a table and rotating in the horizontal direction using a cutting tool having a sharp-edged, convex-shaped cutting edge, a single sawtooth-shaped unevenness is formed. When cutting a groove which is the inverse of the above, the slope of the Fresnel surface (Fresnel angle), the slope of the rise surface (rise angle), the depth of cut (the depth in the vertical direction of the Fresnel surface and the rise surface) The cutting is performed while appropriately moving the cutting tool up and down and rotating with respect to the material to be cut so as to satisfy (1). 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)

[0005] After the cutting of the groove of one wheel into a predetermined shape is completed, the cutting tool is moved, and similarly, the cutting of the adjacent groove is sequentially performed to cut the stamper. The concentric cutting is performed arbitrarily regardless of whether the material is to be cut from the outside to the center or from the center to the outside.
When cutting one groove, the Fresnel surface
The order of the rise surfaces does not matter.

[0006] In the above-mentioned cutting, the time spent for the movement of the cutting tool (vertical movement and rotation, movement to the next groove) and the alignment of the cut portion 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 work of the stamper becomes enormous. In fact, it takes about 100 to 200 hours in the work example by the applicant as the time required for the entire cutting of the 40-inch diameter Fresnel lens stamper.

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

[0008] Assuming that the circumference of one wheel groove is to be cut at a position of R = 500 mm as illustrated below, the cutting process is completed, and the cutting tool is moved to the next groove (up and down movement and adjacent movement). In this case, the time required for the cutting itself is about 30 seconds / 1 round, but the movement of the cutting tool alone takes about 1 minute and 30 seconds.

As a matter of course, the cutting with an enormous cutting depth exceeding the allowable load of the machine tool and the formability of the workpiece is performed once (one round).
Because it cannot be performed in
In step m), the cutting depth is increased so that the cutting depth reaches a predetermined amount over and over (number of rounds).

In the case of cutting the circumference at the position of R = 500 mm, the cutting depth is 109 μm, and the cutting bit increases the cutting depth by 3 μm per rotation. When the material to be cut rotates 50 times per minute, It is necessary to rotate the workpiece approximately 36 times (= 109/3) until the desired cutting depth is reached, and the required cutting time is approximately 40 seconds (36/50).
= 0.73 min).

In addition, it takes an enormous amount of time to control the cutting tool (adjustment of the cutting depth and rotation of the angle of the cut surface) prior to cutting, in addition to the time required for cutting itself. Therefore, it takes 100 to 200 hours in total to cut all 3,900 grooves (circumference), even if the cutting depth decreases toward the inner circumference.

Instead of a Fresnel lens having a configuration in which saw-toothed irregularities (prisms) are arranged concentrically for each wheel,
Japanese Patent Publication No. Sho 30-6223 and Japanese Patent Laying-Open No. 52-4246 are known as proposals relating to the manufacture of a stamper for a Fresnel lens having grooves that are “spirally” continuous.

In any of the above publications, a rotating plate to be cut and a sliding member slidable in the surface direction of the plate to be cut are arranged, and a blade (rotary) is rotatably mounted on the sliding member. It is a configuration in which a mounting table is arranged, and by continuously changing the angle of the cutting blade of the cutting tool (bite) depending on the cutting position of the plate to be cut in accordance with the movement of the sliding body,
It is disclosed that a spiral groove is cut.

However, with the apparatus (method) disclosed in the above publication, it is difficult to actually manufacture a practically used Fresnel lens (stamper) for the following two reasons. This is only 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 cutting depth exceeding the allowable load of the machine tool and the formability of the workpiece, the cutting depth is gradually increased (several μm to several tens of μm), It is not considered that a predetermined depth of cut is provided over the entire surface, but it is described as if manufacturing is completed by one continuous cutting operation (from the outermost periphery to the center).

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a stamper which 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 saw-toothed unevenness is not concentrically arranged for each wheel, but is continuous in a spiral shape from the center to the outermost periphery as shown in FIG. In this case, there is provided a method of actually manufacturing a Fresnel lens (stamper) practically used, avoiding the above-mentioned reasons.

[0016]

[0017]

According to a first aspect of the present invention, there is provided a lens unit comprising a Fresnel surface and a rise surface.
Is uneven in a spiral pattern from the center to the outermost periphery.
And each surface forms depending on the position of the irregularities.
If the angle is desired with respect to the reference plane according to the lens characteristics
In both cases, the angle changes continuously from the center to the outermost periphery
Of stampers used for molding Fresnel lenses
A method for cutting a surface of a plate-shaped workpiece to be mounted on a staple and rotating in a horizontal direction by an NC machine tool using a cutting tool having a sharp-edged, convex-shaped cutting edge. When cutting the Fresnel surface, the cutting is performed by moving the cutting tool linearly from the outside to the center or from the center to the outside while continuously changing the cutting depth and gradient of the cutting tool by a predetermined amount. Processing is repeated to obtain irregularities of a predetermined depth , and when cutting the rise surface
The center from the outside of the cutting material or from the center outward, repeats the row cutting linearly moving the byte
A method for manufacturing a stamper used for molding a Fresnel lens, characterized in that irregularities having a predetermined depth are obtained .

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 2A, a serrated groove constituting a Fresnel lens has 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 periphery. On the other hand, rise angle theta ₂ are not necessarily required angular change in accordance with the position of the lens as a Fresnel angle theta _1. FIG. 2B is a cross-sectional explanatory view of a stamper for molding the Fresnel lens of FIG. 2A, in which a reverse shape of the serrated groove of the Fresnel lens is formed. For convenience of explanation, rise angle theta ₂ is an advancing talk as constant in all the grooves.

Cutting tool (bite) A bite having an acute-angled, convex-shaped cutting edge as shown in FIG. 2 (b) is used. In FIG. 2B, the 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 between the Fresnel surface and the rise surface which change according to the groove to be processed. It must be less acute than the minimum value of the angle theta _4.

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

Cutting conditions (principle) The gradient of the cutting tool and the cutting depth are changed based on the following principle. FIG. 4 illustrates the geometric relationship of the lens surfaces to be obtained. The coordinates of the lens surface can be represented by the following general formula.

[0022]

(Equation 1)

In the above general formula, the focal length of the lens to be obtained
By substituting specific coefficients corresponding to the diameter and the like, the coordinates Zmm of the lens surface at the position of the radius Xmm from the center, the angle of the pitch-divided Fresnel surface, and the position where the Fresnel surface should exist (thickness of the stamper) Depth of cut in the direction).

The curve representing the coordinates of the lens surface is represented by z = f (x)
In the case where the curve is divided at a constant pitch on the x-axis, if the pitch is reduced, the curve of the lens surface can be approximated as a straight line within the pitch. (See FIG. 4 (a).) If the above-mentioned constant pitch corresponds to each groove (circumference), the cut depth and the Fresnel angle in the groove can be derived. (See Fig. 4 (b))

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

<Invention> The reverse cutting of the sawtooth-shaped groove constituting 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 periphery toward the center, the surface a of the cutting tool for processing the Fresnel surface is moved from the outermost periphery toward the center at a predetermined Fresnel angle at that position. While cutting so as to have a predetermined cutting depth at that position.

As described above, it is impossible to cut the enormous depth of cut from the outermost periphery to the center at one time. Therefore, the cutting tool is disposed again at the starting position of cutting, and the same spiral cutting is performed at the same depth of cut. The depth of cut of the Fresnel surface is adjusted to a predetermined amount while gradually increasing the depth.

Next, the cutting tool is arranged at a predetermined position where cutting is started, and the rise surface is cut. Since the cutting depth continuously changes from the outermost periphery toward the center, the surface b of the cutting tool for machining the rise surface is aligned with a predetermined rise angle at that position from the outermost periphery toward the center. The cutting is performed until a predetermined cutting depth at the position is reached. Since it is assumed that the rise angle is constant over the entire area of the stamper, after the first rotation adjustment, cutting is advanced by changing only the cutting depth while keeping the rise angle fixed.

<Prior Art> Since the serrated grooves constituting the Fresnel lens exist in concentric circles independent of each other, when cutting the reverse mold of the grooves, cutting is performed independently for each wheel. . That is, in each groove, the Fresnel angle, the rise angle, and the cutting depth are constant 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 made coincident with the Fresnel angle of the groove, and cut to a predetermined cutting depth.

Next, the tip of the cutting tool is arranged at a predetermined position where cutting is started, and the surface b of the cutting tool is rotated so as to coincide with the rise angle of the groove, and cutting is performed until a predetermined cutting depth is reached.

For both the Fresnel surface and the rise surface, the sharp tip of the tool is arranged at a predetermined position, the tool is rotated so that the surface to be machined is at a predetermined angle, and then cut vertically to process. Is performed.

After the machining of the rise surface is completed, 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 contact the processed Fresnel surface). Release the cutting tool vertically from the workpiece.

After the predetermined cutting operation for one groove is completed, the cutting tool is moved to the cutting position of the next groove, and the cutting operation according to the conditions (Fresnel angle and cutting depth) of the next groove is similarly performed. Do.

As described above, a fundamental difference between the present invention and the prior art is that the present invention has one continuous groove, and the conventional art has a predetermined number of grooves. Therefore, in the present invention, the entire region from the outermost periphery to the center can be continuously cut at once, and the cutting process is interrupted by separating the cutting tool from the material to be cut each time the next groove is cut.
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 drastically reduced.

Other cutting procedures (cutting from the center to the outermost periphery, cutting the rise surface first, changing the rise angle according to the position of the lens,
Etc.), the advantages of the present invention apply as well, but their description is omitted.

[0038]

EXAMPLE An example in the above cutting procedure will be described.
As a Fresnel lens, focal length f = 151 mm, diameter 2
In order to manufacture a wafer having a thickness of 00 mm, the following coefficients are substituted into the above equation (1). Although the coefficient to be substituted changes according to the design specification of the lens, the description of the procedure for deriving the coefficient is omitted here.

C = + 0.01347720 1 + k = 0 A ₄ = −0.2125440E-7

Here, the radius X from the center is 51.61 mm.
The movement of the tip of the cutting tool at the time of cutting at the position is described in detail.

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

Accordingly, the gradient of the cutting tool is 0.0 until the position of X = 51.61 mm of the material to be cut makes one rotation on the table and the cutting tool moves to the position of X = 51.48 mm.
It changes by 91 °.

In such cutting, the strict control of the inclination of the cutting tool and the cutting depth depends on the NC accuracy of the machine tool (vertical lathe). Further, in repeating the cutting depth until the cutting depth reaches a predetermined amount, the positioning accuracy between the cutting tool and the cutting portion of the workpiece must be strictly performed, but the positioning also depends on the NC accuracy of the machine tool. Will be.

[0044]

According to the present invention, the time required for the entire cutting process is drastically reduced as compared with the concentric cutting by performing the cutting of the stamper in a spiral shape. The releasability of the stamper from is improved, and the Fresnel lens molded by the stamper has the same optical characteristics as the existing Fresnel lens (having concentric grooves) that has been put into practical use. is there.

[0045]

[Brief description of the 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 state thereof.

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

FIG. 4 is an explanatory diagram showing a geometric relationship between lens surfaces.

Continuation of the front page (56) References JP-A-7-287106 (JP, A) JP-A-7-241918 (JP, A) JP-A-4-281443 (JP, A) JP-A 52-4246 (JP) , A) Shokai Sho 57-28402 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 3/08

Claims (1)

(57) [Claims] 1. A lens portion comprising a Fresnel surface and a rise surface
Are formed spirally from the center to the outermost periphery.
The angle between each surface is based on the position of the unevenness.
Depending on the lens characteristics for the surface desired and center
From above to the outermost circumference
Manufacturing method of stamper used for molding lens
When cutting the surface of a plate-shaped material to be cut mounted on a staple and rotating in the horizontal direction with an NC machine tool using a cutting tool having a sharp-edged, convex-shaped cutting edge, the Fresnel surface In the case of cutting, while continuously changing the cutting depth and gradient of the cutting tool by a predetermined amount, the cutting process of linearly moving the cutting tool from the outside of the workpiece to the center or from the center to the outside is repeated. Done and of a given depth
Obtain irregularities, and when cutting the rise surface, repeat the cutting process of linearly moving the cutting tool from the outside of the workpiece to the center, or from the center to the outside, to obtain irregularities with a predetermined depth. A method of manufacturing a stamper used for molding a characteristic Fresnel lens.