JPH0599639A - Inspection device for small unevenness of planar object - Google Patents

Abstract

PURPOSE:To provide an inspection device capable of recognizing defects with high accuracy and being easily controlled with a simple optical system and easily detecting unevenness defects of a large area even with a size in an order of millimeters. CONSTITUTION:An inspection device for small unevenness of planar objects comprises a laser light source 2, an optical fiber 6 of a core diameter (a), a convex lens 7 having a focal distance (f) of more than 100a, a cylindrical lens 8 for causing light to impinge on the surface of a planar subject for inspection, a screen 4 on which light reflected from the surface of the subject for inspection is projected, a CCD camera 5 for taking screen images, and an image processing portion 9. The convex lens 7 is disposed at a place separate by more than the focal distance from the end of the optical fiber and the cylindrical lens 8 forms light emitted from the convex lens 7 into rough slit light and causes the rough slit light to impinge on the surface of the planar subject for inspection at an angle of incidence phi from the diagonal direction, and light reflected at the surface in accordance with the surface configuration is projected onto the screen and the image processing portion 9 recognizes defective parts from image data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a synthetic resin or metal plate, a film, or an object to be inspected having a smooth surface with a laser beam, and from the reflected light from the surface, a gentle unevenness of the object to be inspected. , An inspection device for inspecting foreign matters and scratches.

[0002]

2. Description of the Related Art Conventionally, an inspection device which does not come into contact with an object to be inspected is laterally illuminated, and scattered light generated from a defect portion is photographed from directly above by a CCD camera so that sharp irregularities (cracks, protrusion foreign matters, fish eyes, etc.) can be obtained. ) Is inspected. On the other hand,
As a device for inspecting gentle unevenness, a device utilizing light interference has been proposed. Further, as a device for inspecting a large area such as a car body such as a dent on the order of several centimeters, a device for projecting a reflected light on a screen by irradiating it obliquely with a lamp light source has been proposed (Rodger
LR et al., Proc. SPIE Vol.954, P.208, 1990).

[0003]

SUMMARY OF THE INVENTION In a device that laterally illuminates and captures scattered light with a CCD camera, sharp irregularities (cracks, protruding foreign matter, fish eyes, etc.) that can obtain a sufficient scattered light intensity can be obtained. It is possible to inspect, but it is not possible to inspect mild irregularities. Further, in the device utilizing the interference of light, the optical system is complicated, the inclination and positioning accuracy of the object to be inspected are strict, and the image processing is also complicated, and as a simple inspection device that can be used in a factory production line or the like. I can't find anything remarkable. Furthermore, in a device that projects a lamp light source from a diagonal direction and projects it on a screen, a lamp is used as a light source, and conditions that can detect even weak uneven defects are not given, so that large-area uneven defects can be easily detected. When it comes to the millimeter order size, it becomes impossible.

The present invention has been made on the basis of the above background, and its object is to make it possible to inspect defects of gentle unevenness, to make the optical system simple and to operate easily, and to manufacture the factory. An object of the present invention is to provide a gentle unevenness inspection device that can be used as a simple inspection device that can be used in a line or the like, and that can easily detect a large-area unevenness defect and the like and also detect even a millimeter order size.

[0005]

The above-mentioned problems can be solved by the present invention described below. That is, the apparatus for inspecting gradual unevenness of a planar object according to the present invention includes a laser light source having a wavelength λ, an optical fiber having a core diameter a for guiding laser light, and a light beam emitted from the optical fiber. Distance f is 100
A convex lens of × a or more, a cylindrical lens that expands the laser light from the convex lens in one direction and makes it incident on the surface of the flat object to be inspected, a screen that reflects the light reflected from the surface of the object to be inspected, and an image on the screen. A gentle uneven defect surface having a defect width W and an average inclination angle of the defect surface of Δθ, which is composed of an area type or line type CCD camera for photographing and an image processing unit for processing image data from the CCD camera. An unevenness inspection device for an inspected object,
The convex lens is arranged at a distance more than the focal length from the end of the optical fiber, and the cylindrical lens has a slight divergence angle (2θ _L ) in the incident surface for the light emitted from the convex lens, which is required in the direction perpendicular to it. Form a slit light with a spread angle (2θ _T ) to obtain the inspection width, and let the slit light incident on the surface of the flat object at an angle of incidence φ, and reflect the surface reflected light reflecting the surface shape. It is characterized in that the image is projected on a screen, and the image processing unit processes the image data of the projected image on the screen and performs a density inspection to determine a defective portion.

In a preferred embodiment of the present invention, the shape of the uneven defect to be detected having a defect width of W and the average inclination angle of the defect surface is Δθ, and the distance L between the convex lens and the uneven defect of the object to be detected.
1. If the relationship between the unevenness defect to be detected and the inter-screen distance L2 is the incident angle φ between the incident light from the cylindrical lens and the normal to the surface of the object to be inspected, and the angle θ = 90 ° −φ,
{2L1L2 / (L1 + L2) sinθ}> {W / tan Δθ}
Is.

Furthermore, in a preferred embodiment, the relationship between the resolution Res and the beam divergence angle θL of the CCD camera, is ^{_{Res> {λ / 2θ L 2}} }.

[0008]

According to the present invention having the above-mentioned structure, the following operations and operations are performed. As shown in FIG. 1 exemplifying the device according to the present invention, a laser beam is used as a light source, the laser beam is guided to an inspection position by an optical fiber, and a convex lens and a cylindrical lens are used to spread an angle of divergence in a direction perpendicular to and parallel to an incident surface. Respectively form slit lights of θ _T and θ _L (θ _T > θ _L ) and are oblique to the plane inspection object at an angle θ (incident angle φ is θ = 90 ° −φ). It is made incident, and a slight difference in reflection angle between the site of gentle unevenness and the site of smoothness is projected on a screen arranged at a distance L2 from the position of the inspection object and converted into position information. Therefore, when the surface to be inspected is a completely flat surface, the light density is macroscopically uniform on the screen, but if there is a defective portion,
As illustrated in FIG. 2, the density of light rays becomes uneven, and a light intensity distribution 10 corresponding to the undulating state of the surface is obtained.

The divergence angle θT in the direction perpendicular to the incident surface is selected in accordance with the required inspection range of the object to be inspected, and is formed by using a concave or convex cylindrical lens. Now, when the surface to be inspected is a completely flat surface, if an optical system is formed so that the light rays emitted from the convex lens do not intersect at all up to the screen surface, there will be minute defects on the surface to be inspected. Also,
The image will be projected faithfully without blurring. In order to achieve this condition, the distance between the exit end of the optical fiber and the convex lens only needs to be in the Fraunhofer region, which is 100 times or more the core diameter a. When the distance between the convex lens and the inspection object is L1, that is, it is necessary to satisfy the relationship of L1 ≧ f ≧ 100 × a (1).

The principle of the inspection apparatus according to the preferred embodiment of the present invention will be described with reference to FIG. 3 schematically showing the inspection of the surface of the object to be inspected. The light ray reflected from the defect portion having the inclination Δθ as shown in FIG. 3 shifts by S1 = L2tan (Δθ) (2) as compared with the case where the position projected on the screen is flat. If this shift amount is the projection width MW from the defect area W, MW = {(L1 + L2) / L1 × Wsinθ} (3) or more, the rays are added to increase the ray density,
Since it becomes bright on the screen and a dark portion is generated within the projection width MW, the contrast reflecting the defect shape is enhanced. That is, if L1, L2, and θ are set so as to satisfy the condition of S1> MW / 2, the defect width W or less and the inclination Δθ are set.
The above unevenness defects can be detected. Rewriting this condition gives the following equation. {2L1L2 / (L1 + L2) sinθ}> {W / tanΔθ} (4) As shown by the formula (4), the contrast between the defective portion and the normal portion can be made clear by placing the screen sufficiently far away. .. If the screen cannot be placed far away, it is possible to increase the magnification by placing a concave cylindrical lens or the like between the screen and the object to be inspected.

Next, the function of the inspection apparatus of the preferred embodiment of the present invention for removing speckle noise will be described. Since the image is enlarged, the resolution of the CCD camera can be increased, and speckle noise that occurs when a light source with high coherency such as a laser is used can be removed. The average diameter of the speckle is λ /, using the wavelength λ and the spread angle θ _L of the light beam.
Since it is represented by (4θ _L ² ), the resolution (R
If es) satisfies the relationship of the expression (5), it is possible to remove the influence of speckle noise of the image. Res> {λ / 2θ _L ² } (5) In this mode, not only the change in shape but also the change in the reflectance on the surface of the inspection object, for example, even if there is a foreign matter defect or a scratch defect, on the screen. Can be captured as a change in the intensity distribution of.

[0012]

EXAMPLES The present invention will be described based on examples. Figure 1
It is a figure which shows an example of the apparatus structure of this invention. H of wavelength 633 nm
Light emitted from the e-Ne laser light source 2 is guided to a light projecting portion using an optical fiber 6 (core diameter a = 50 μm), and a convex lens 7
(Focal length 20 mm) is used to form a slightly divergent bundle of rays. In this example, the beam divergence angle was θ _L = 1.7 degrees. This divergent ray bundle is converted into a plano-concave cylindrical lens 8
Was used to set the divergence angle in the direction perpendicular to the incident surface to the inspection object 1 to θ _T = 66 degrees. The slit-shaped spread light beam 3 is made incident on the inspection object 1 at an incident angle of 86.2 degrees (θ = 3.8 °), and the surface reflected light is projected on the white screen 4. The distances between the cylindrical lens 8 and the inspection object 1 and between the inspection object 1 and the screen 4 are L1 = 270 mm and L2, respectively.
= 1310 mm. The positional relationship between them is (1) and (4) above.
I am satisfied with the formula.

Next, the measurement results will be shown. Amplitude of about 5μ on the surface
m (= H), width about 1mm (= W), angle about 0.2 degree (= Δθ) wrinkle-like gentle unevenness of 20mm urethane rubber was used as the object to be inspected, and the above optical system was used on the surface. An image obtained by irradiating light and capturing the surface reflection image projected on the screen by the CCD camera 5 in the area is shown in FIG. Since the resolution of the CCD camera is Res = 500 μm and the above expression (5) is satisfied, the effect of speckle noise was not seen at all in the image.

When the image of FIG. 4 is binarized by the image processing device, an image as shown in FIG. 5 is obtained, and the convex portion can be recognized as a white defect. No white defect was observed in the binarization of the reflection projection image in the inspected object having a completely smooth surface and no irregularity defect. In the present embodiment, the image taken in by the camera is binarized by the image processing device 9, but the image may be recognized by using a method such as a defect determination method based on the amount of change in light intensity with the adjacent pixel of the CCD.

In the present embodiment, the above-mentioned values are used to obtain a magnifying power of 5.9 times the magnified projected image. The magnification is the distance between the screen and the inspection object, the distance between the inspection object and the lens, the incident angle,
It can be arbitrarily selected by changing the divergence angle of the light beam. The brightness of the image was determined by the incident angle, and the surface reflectance of about 70% was obtained at the above-mentioned incident angle. This reflectance is obtained from the Fresnel reflection coefficient. For example, in order to obtain a reflectance of 50% or more, the incident angle φ must be 10 degrees or less. When applying an actual production line, if the reflectance is 50% or more, an image can be sufficiently observed even under normal illumination.

[0016]

INDUSTRIAL APPLICABILITY The present invention is a gradual unevenness inspection device for a flat object, and by using a slit-shaped laser beam having a slight divergence angle, it is possible to inspect gradual unevenness, foreign matter, and flaw defects. Therefore, if the minimum shape of the defect that needs to be detected is given, the defect can be recognized with high accuracy, the optical system can be easily and easily operated, and it can be used as a simple inspection device that can be used in factory production lines. In addition, it is possible to easily detect irregularities and defects having a large area, and it is possible to detect even a millimeter order size.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an inspection apparatus according to the present invention.

FIG. 2 is an explanatory diagram of the principle of the present invention.

FIG. 3 is an enlarged view of a concavo-convex defect for explaining the action of the surface of the inspection object.

FIG. 4 is an image diagram of enlarged projection of a defect portion.

FIG. 5 is an image diagram obtained by performing binarized image processing on an enlarged projection image.

[Explanation of symbols]

 1 Inspected object 2 He-Ne laser light source 3 Slit-shaped divergent light beam bundle 4 Screen 5 CCD camera 6 Optical fiber 7 Convex lens 8 Cylindrical lens 9 Image processor 10 Intensity distribution

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Suga 3816 Noborito, Tama-ku, Kawasaki-shi, Kanagawa Mitsubishi Rayon Co., Ltd. Tokyo Research Laboratory

Claims (3)

[Claims] 1. A convex lens having a focal length f of 100 × a or more, which makes a laser light source having a wavelength λ, an optical fiber having a core diameter a for guiding the laser light, and light emitted from the optical fiber substantially parallel to each other. And a cylindrical lens that expands the laser light from the convex lens in one direction and makes it incident on the surface of the flat object to be inspected, a screen that reflects light reflected from the surface of the object to be inspected, and an image on the screen is captured. It has a gentle uneven defect surface having a defect width W and an average inclination angle of the defect surface of Δθ, which is composed of an area-type or line-type CCD camera and an image processing unit that processes image data from the CCD camera. In an unevenness inspection device for an object to be inspected, the convex lens is arranged at a position separated by a focal length or more from an optical fiber end, and the cylindrical lens emits light emitted from the convex lens. Morphism plane a slight divergence angle (2 [Theta] _L) has, it spread angle to obtain a test width required in a direction perpendicular (2 [Theta] _T)
To form a rough slit light having an angle of incidence, and the rough slit light is obliquely incident on the surface of the flat inspection object at an incident angle φ, and the surface-reflected light reflecting the surface shape is projected on a screen, and the image processing is performed. A part is a device for inspecting gradual unevenness of a planar object which processes image data of a projected image on a screen and performs a density inspection to determine a defective portion. 2. The defect width is W and the average inclination angle of the defect surface is Δθ.
The relationship between the shape of the unevenness defect of the detection target, the distance L1 between the convex lens and the unevenness defect of the detection target, and the relationship between the unevenness defect of the detection target and the distance L2 between the screens are the incident light from the cylindrical lens and the normal line to the surface of the inspection object. Angle of incidence φ and angle θ
= 90 ° −φ, {2L1L2 / (L1 + L2) sinθ}> {W / tanΔθ}. The gradual unevenness inspection device for a flat object according to claim 1, characterized in that: 3. The planar shape according to claim 1, wherein the relationship between the resolution Res of the CCD camera and the beam divergence angle θ _L is Res> {λ / 2θ _L ² }. Concavity and convexity inspection device for objects.