JPH03150502A - Aspherical plastic condensing lens - Google Patents

Abstract

PURPOSE:To improve the detection resolution for a surface flaw and defect of a plate material by constituting the condenser lens which satisfies specific conditions with a 1st aspherical surface which is close to a convex elliptic surface and a 2nd aspherical surface which has smaller curvature than the 1st surface and is close to a convex cylindrical surface. CONSTITUTION:Both the 1st aspherical surface 18 which approximates the convex elliptic surface and the 2nd aspherical surface 19 which has the curvature V2 smaller then the curvature C1 of the 1st surface and approximates the con vex cylindrical surface have positive refracting power and both the surfaces constitute the condenser lens 10. The requirements shown by inequalities I - III are met. In the inequalities I-III, (n) is the refractive index of plastic in use, (t) the thickness of the lens, (f) the focal length of the lens, and subscripts xz and yz components in an xz and yz plane of an (x), a (y), and a (z) orthogo nal coordinate axis while an optical axis is indicated on the (z) axis. Consequent ly, variation in the quantity of light of a diffraction pattern is made remarkable and the detection resolution for the surface flaw and defect can be improved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a surface inspection device that inspects flaws and defects on the surface of a plate material using diffracted light of a laser beam, and in particular, a surface inspection device that uses diffracted light to condense the diffracted light. This invention relates to a condensing lens that has the function of

(Prior Art) For example, in the surface inspection apparatus shown in FIG. 5, which is described in Japanese Patent Publication No. 52-21387, at the upper left of the plate material 2 to be inspected, which is moved in the direction of the arrow 1 by a drive mechanism (not shown), there is a An optical scanner 4 is provided which scans the surface of the plate 2 with a laser beam by moving in a direction 3 perpendicular to the movement direction 1 of the plate 2 and parallel to the plate 2 by a moving mechanism (not shown). A condenser lens 6 is provided perpendicularly to the reflected optical axis and parallel to the plate 2, and the light that has passed through the spatial filter 5 is The light is sent to a signal processing device (not shown) through the photomultiplier tube 7, and the diffraction pattern of the light diffracted by flaws and defects in the plate material 2 is detected.

(Problem to be Solved by the Invention) The function of the condensing lens 6 is to form a diffraction pattern on the spatial filter 5 corresponding to flaws and defects on the surface of the plate material 2. As shown in the figure, when the laser beam moves in the direction of arrow 3, the light diffracted in the same direction from each scanning point on the plate 2'' to the inspection surface (the surface of the plate 2) hits the same point on the spatial filter 5. We have to get together.

Now, the maximum diffraction angle of the diffracted light to be focused is θ, and the scanning surface (plate material 2
If the distance from the surface of the condenser lens 6 to the condenser lens 6 is g, the focal length of the condenser lens 6 is f, the scanning width is W, and the aperture of the condenser lens 6 is D, then f represents the brightness of the condenser lens 6. /D becomes f/D-f/ (W+2.9-tanθ), and in order to widen the scanning width W, a small and bright lens with f/D is required, but for this, f/D- There is a limit of 0.5, and the scanning width W is restricted. In addition, the condenser lens 6
For accuracy reasons, the scanning width cannot be widened, and the width is 200 to 300 mm.
is the limit.

As mentioned above, in order to inspect a wide plate material 2, it is necessary to arrange multiple sets of condensing lenses, spatial filters, and photomultiplier tubes in parallel, and in this case, the abrasiveness of the condensing lenses When glass is used, the weight of the condensing lens section becomes heavy.

The present invention was made in view of the above circumstances, and provides a condensing lens suitable for use in a condensing optical system of a surface inspection device capable of inspecting surface flaws and defects on a wide plate material. The purpose is to

[Structure of the Invention] (Means and Effects for Solving the Problems) In order to achieve the above object, the aspherical plastic condensing lens of the present invention is approximated by a convex ellipsoid and has a height of 10 mm from the optical axis of the lens. The first consists of an aspherical surface that includes terms proportional to the power of
a second surface having a curvature C2 smaller than the curvature C1 of the first surface and an aspherical surface approximated by a convex cylindrical surface or a toric surface; This is a single lens composed of surfaces both of which have positive refractive power, and is characterized by satisfying the following conditions.

(1) 1.45<n<1.60(2)
1.1<C1xz/C2xz<1.6(3) 0
．． 15<t/fyZ<0.25.0.10<
t/f Each xz, yz in the x, y, z orthogonal coordinate axes
Represents in-plane components.

By adopting the above structure, the present invention realizes a lens that is light in weight and has a small aperture ratio f/D (D is the aperture of the lens in the scanning direction) of about 1.5 to 2, making it bright. When the aspherical plastic condensing lens of the invention is applied to a surface inspection device, the change in the light amount of the diffraction pattern becomes noticeable, and the detection resolution of surface flaws and defects can be improved.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an aspherical plastic condenser lens according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example in which the plastic condenser lens of the present invention is applied to a surface inspection device.

An aspherical plastic condenser lens (hereinafter referred to as a condenser lens) 10 is applied to a surface inspection device as shown in FIG. That is, a moving mechanism (not shown) is located at the upper left of the plate material 12 to be inspected, which is moved in the direction of arrow 11 by a driving mechanism (not shown).
(not shown) is provided with an optical scanner 14 that scans the surface of the plate 12 with a laser beam by moving in the X-direction, in the X-direction, at right angles to the moving direction 11 of the plate 12, and parallel to the plate 12, and scans the surface of the plate 12 with a laser beam. A predetermined number (three in this embodiment) of condensing lenses IO for receiving the reflected and diffracted light of the scanned light are arranged perpendicular to the reflected optical axis and parallel to the plate material 12. A light guide rod 15 is provided horizontally on the upper part of the condensing lens 1O so that the upper part almost becomes the focal plane, and a light diffusing part 15a is provided only in the part indicated by diagonal lines where the desired diffracted light component reaches. The diffused light is guided to photomultiplier tubes 16a and 1.6b disposed on the left and right sides of the light guide rod 15, equivalently forming a bandpass filter. Furthermore, between the row of condensing lenses 10 and the light guide rod 15, partition plates 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 30, 30, 40, 40, 40, 40, 40, 40, 50, 50, 50, 50, 40, 40, reflected and diffracted light are prevented from being vertically reflected and transmitted are provided at both ends of each condensing lens 10 between the row of condensing lenses 10 and the light guide rod 15.・・・
・ is provided.

The condensing lens IO has two optical axes, the first of the condensing lenses 10
In the XYZ orthogonal coordinates with the vertices of the surface 1B and the second I9 as vertices, 1+J1- (1+K)C2h2 +dh' +eh6+f h8+gh10, where h: height from the optical axis (=Jx2+y") C: curvature of the aspherical surface (-1/R, R: radius of curvature) K: conic constant d, e, f, g: 4th, 6th, 8th, respectively
It is composed of a single lens consisting of the first and second surfaces of an axially symmetric aspherical surface shape expressed by the following aspherical coefficients: n: refractive index of lens material C1: curvature of first surface C2 : Curvature of the second surface t : Thickness of the lens f : Focal length The lens is characterized by satisfying the following conditions.

(1) 1.45<n<1.6(1(2)
1.1<CIXZ/C2XZ<1.8(3) 0
．． 15<t/f yz<0.25.0, 10<
t/f xz< 0.20 above condition (1), (
2) , (1) will be explained.

Condition (1) is a condition regarding the refractive index of the lens material used, and indicates the range of materials that can be used with existing plastic materials, and is a precondition for conditions (2) and (3), which express the lens shape.

Condition (2) is a condition regarding the surface shape of the condensing lens 10, and the diffraction angle of the reflected diffracted light of the laser beam is θ.

When condensing diffracted light in the range of ~25°, this has the effect of forming a diffraction pattern in a good condition on the light diffusing portion 15a.

Condition (3) is a condition regarding the thickness of the condensing lens 10,
This has the effect that the thickness of the end portion 2o of the lens, called the edge thickness, does not become negative, that is, the lens does not become impossible to manufacture, and that the lens thickness does not become too large and the light weight of the lens is maintained.

Furthermore, in order to collect diffracted light having a wide range of diffraction angles and form a diffraction pattern, it is desirable that both surfaces of the condensing lens 10 be aspherical. That is, the first surface 18 is preferably an aspherical surface approximated by an ellipsoid (-1<K<0), and the second surface 19 is preferably an aspherical surface approximated by a cylindrical or toric surface. desirable.

Further, the focal length f of the condensing lens 10 is 1/f=(n
1) ((+ −C2) 10 CI C2・t ・(n−
1) 2/n... (4) Also, the thickness of the end 2o of the condenser lens 1o (
The edge thickness) tc is determined by the following, where D is the aperture of the condenser lens 10 in the scanning direction of the optical scanner 14. Therefore, the aperture ratio f of the condenser lens 10
/D can be made smaller by decreasing the focal length f and increasing the aperture, but if you try to increase the aperture, the edge thickness tc will become smaller and negative according to equation (5), and the edge thickness Since it is impossible to manufacture a lens with a negative tc, there is an upper limit to the aperture size. On the other hand, if an attempt is made to reduce the focal length f, it is necessary to increase the lens thickness t according to equation (4), but if the lens thickness t increases, the lens weight increases, which is not preferable.

Therefore, if the lens shape satisfies the above conditions (1) to (3), by calculating equations (4) and (5),
While keeping the edge thickness tc at about 1 degree, the aperture ratio f/D is set to 1.
About 5 to 2 lenses can be obtained.

Next, specific examples will be shown below.

0 (Example 1) Laser beam wavelength λ-632, 8 nm, f yz = 1
12.5 III, f xz-200mm.

C1xz-8,818Xl0-3, C1yz-8,81
8xlO-3t = 21.0mm.

n = 1.5[i7, C2xz-7,353Xl0-
32yz-0 [First side] K--0,552325 d--7,71869x 1O-10e--2,3
1228X 1.0"'f --1,08247X t
o" g =-5,68660x 10-" An optical path diagram of the condenser lens lOa of Example 1 is shown in FIG.

(Example 2) Laser beam wavelength λ-632, 8ro++ sf y
z=113.711m5f xz-200l1m.

C1xz-1,022Xl0-2, C1yz-1,02
2Xl0-3t -25,0 關, n -1,489, C2xz-8,475X10=1 2yz-0 [First side] K--0,491353 d = -8,32041, -6,
60132X 10"' f --3,25582X 10-17g --3,1
328Bx 10'' FIG. 4 shows an optical path diagram of the condenser lens 10b of Example 2.

In addition, in the above example, an example is shown in which PC (polycarbonate) with a refractive index of 1.567 and PMMA (polymethyl methacrylate) with a refractive index of 1.489 is used as the lens material. Lenses with comparable performance can be realized using other plastic materials of about .60.

Furthermore, in the first embodiment, the aspherical surface of the lens surface is a rotationally symmetrical aspherical surface or a cylindrical surface, but other aspherical surfaces other than those mentioned above can also be used.

[Effects of the Invention] As detailed above, according to the aspherical plastic condenser lens of the present invention, a bright lens with a small aperture ratio f/D of about 1.52 to 2 can be realized. When the aspherical plastic condensing lens of the invention is applied to a surface inspection device, changes in the amount of light in a diffraction pattern can be made noticeable, and the detection resolution of surface flaws and defects is improved.

In addition, since plastic is used for the lens material,
Compared to a glass lens of the same volume, the lens weight is approximately 1/3, making it significantly lighter.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an aspherical plastic condensing lens according to an embodiment of the present invention, Fig. 2 is a diagram showing an example of application of the plastic condensing lens of the present invention to a surface inspection device, and Fig. 3 is an embodiment. 1, FIG. 4 is an optical path diagram of Example 2, and FIG. 5 is a diagram showing a conventional surface inspection apparatus.

Claims (1)

[Scope of Claims] A first surface consisting of an aspherical surface approximated by a convex ellipsoidal surface and including a term proportional to the tenth power of the height from the optical axis of the lens;
and a second surface made of an aspherical surface approximated by a convex cylindrical surface or a toric surface having a curvature C2 smaller than the curvature C1 of the surface, and both the first surface and the second surface have positive refractive power. An aspherical plastic condenser lens, which is a single lens constituted by a surface, and is characterized by satisfying the following conditions. (1) 1.45<n<1.60 (2) 1.1<C1xz/C2xz<1.6 (3) 0.
15<t/fyz<0.25, 0.10<t/fxz<0.20 where n is the refractive index of the plastic used, t is the thickness of the lens, f is the focal length of the lens, and , subscript x
z and yz represent components in the xz and yz planes of the x, y, and z orthogonal coordinate axes with the optical axis as the z axis.