JPS63218847A - Inspection of surface flaw - Google Patents

Abstract

PURPOSE:To identify the kind of a flaw part on the basis of a pattern, by preliminarily calculating the patterns due to the illumination conditions of detection signals different at every kinds of the flaw parts and using different illumination conditions. CONSTITUTION:The samples of flaws A, B, C are irradiated with light while the illumination angle theta of a light projecting part 1 is changed to preliminarily measure S/N ratios. There is clear difference between each of three patterns. By a simple method utilizing the difference between the S/N ratio patterns due to the kinds of flaw parts, plural kinds of the flaw parts can be discriminated and identified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a non-contact optical surface defect inspection method.

[Conventional technology]

In general, reflected illumination means are used to detect surface defects on products made of materials that do not transmit light, and in particular, in non-contact optical surface defect inspection methods, illumination means that match the surface texture of the surface to be inspected are used. This is important for improving defect detection ability.

Conventionally, when inspecting extremely smooth flat surfaces such as magnetic disks, spot light is applied to the surface to be inspected.

The specularly reflected light is received by an image sensor of a television camera, and the defective part is detected by the decrease in the specularly reflected light at the defective part. Inspection methods using specular reflection methods, such as the flying spot method, have been put into practical use.

However, with this method, it is necessary to eliminate or keep the change in the amount of reflected light in normal areas other than defective areas to be extremely small in order to improve the defect detection ability. It is difficult to apply this method to the inspection of objects to be inspected that have curved surfaces and may also include curved surfaces, as the spread and scattering of reflected light due to surface roughness impedes defect detection. A diffuse reflection method has been devised.

In this diffuse reflection method, the optical system is configured so that it does not receive specularly reflected light from normal parts of the surface to be inspected, and defects are detected by the presence or absence of specularly reflected light from defective parts or by the increase or decrease in diffusely reflected light. It is something. According to this method, the permissible range of the optical axis is expanded, making it easier to set conditions, the configuration of the light receiving system is simplified, and the amount of reflected light is greatly reduced due to surface roughness in areas other than the defective area. Effects such as reduction in size are also observed.

[Problem that the invention seeks to solve]

In surface defect inspection using diffuse reflection method.

It is important to set lighting conditions that match the reflection characteristics of the defect so that the best amount of reflected light can be obtained from the defect. It is difficult to accurately detect defects and identify the type of defects using only this method.

In view of these problems, the present invention provides a surface defect inspection method that can easily identify the types of "multiple types of defective parts having different reflection characteristics."

[Means for solving the problem and their effects] For different types of defective samples, the illumination conditions are changed to determine the reflected light from the defective sample -i s t -m, and the amount of reflected light from the normal surface is determined. When determining the ratio to N, that is, the S/N ratio, it is found that the pattern differs depending on the type. This is because the uneven shape, surface roughness, reflectance, etc. of the defective portion differ depending on the type of the defective portion.

Therefore, in the surface defect inspection method according to the present invention, in advance,
After obtaining a pattern based on the illumination conditions of a detection signal that differs for each type of defective part, the type of defective part is identified based on the pattern using a plurality of different illumination conditions.

The principle of the method of the present invention will be explained with reference to FIGS. 1 and 2. First, in FIG. 1, (W) is the object to be inspected, (1)
(2) is a light projecting unit that irradiates light onto the surface to be inspected (Wo) of the object to be inspected (W); (2) is a camera that receives reflected light from a defective portion existing on the surface to be inspected (WO); (3) is camera (2)
This is a processing device that processes image information from. Light projecting section (1
) is the illumination angle (incident angle) θ with respect to the surface to be inspected (wo)
The light reflected from the normal portion of the surface to be inspected (−゛) is mainly reflected in the specular reflection direction θ゛ (θ=θ゛). The camera (2) is arranged so as not to receive specularly reflected light from the normal part (in the figure, it is arranged in a direction perpendicular to the surface to be inspected (-°)).

Figure 2 shows 3
type of surface defect, i.e. defect area (A).

The results of measuring the S/N ratio for each sample in (B) and (C) are shown, that is, the defective part shown in (A) in the same figure (
The S/N ratio of A) is the maximum in the upper left pattern when the illumination angle θ is 20° or less.
The N ratio is maximum in the vicinity of 40° to 60@ in an upwardly convex pattern, and the S/N ratio of the defective part (C) shown in the same figure (C) is 60
It can be seen that there is a clear difference between the three types, showing an upward-sloping pattern that reaches its maximum when the temperature is greater than or equal to °. Therefore, it is possible to identify a plurality of types of defective parts based on such pattern differences.

〔Example〕

Examples of the surface defect inspection method of the present invention will be described below.

First, the first embodiment shown in FIG. 3 is 1. In normal surface defect inspection, it is difficult to measure the SN ratio pattern by continuously changing the illumination angle, so the first embodiment shown in FIG. From each pattern, for example, the illumination angle 0a = 15''' suitable for detecting the defective part (A), the illuminating angle 0b = 45° suitable for detecting the defective part (B), and the suitable illuminating angle 0b = 45° for detecting the defective part (G). A suitable illumination angle 0c = 70° is set, and the light projecting parts (1a), (tb), and (lc) are arranged at these angles.Figure 4 shows the defect area (A), and Figure 5 shows the defect area. Part (B) and Figure 6 show images of the defective part (C) detected separately using the three illumination angles mentioned above. From these images, it is possible to detect the defective part (C) by illuminating at the three set angles mentioned above. There is a clear difference in the reflection characteristic pattern (it can be seen that the amount of reflected light is significant at the illumination angle of 15° for defective part (A), 45° for (B), and 70° for (C)), and therefore This makes it possible to identify the type of detected defect.

The second embodiment shown in FIG. 7 has illumination angles Oa and θ, respectively.
Light projector (fa) (Ib) (Ic) with b and θC set
This system has cameras (2aH2b) (2c) arranged to receive the reflected light from each illumination separately, and the processing device (3) is slightly complicated, but it can detect parallel defects due to three illumination conditions. Detection can be performed.

Furthermore, as in the third embodiment shown in FIG.
When W) is a continuous sheet, the roll part (R
By utilizing the curvature of ), the method of the present invention can be carried out using only one light projector (1) 8 and camera (2). In other words, when the object to be inspected (the buttocks) moves due to the rotation of the roller (4), within the field of view of the camera (2), the illumination angle for any part of the surface of the object to be inspected (the ladle) changes as the object moves. For example, if a television camera is used as the camera (2), as shown in FIG. Line (gl), (slb),
When measuring the S/N ratio for specific scanning lines such as (slc), we found that the defective areas (A) (B
) and (C), different patterns were obtained for both, as shown in the following table.

If the output is binarized with an SN ratio of 3, identification using 3 bits becomes possible.

In actual quality determination, for example, for the defective portion (A), the determination standard may be set at an illumination angle of 0a=75°, and the quality may be determined based on this.

In addition, in each of the above-mentioned Examples.

Three illumination conditions were used to identify the three types of defective parts, but depending on the pattern of the reflection characteristics of each defective part, the types can be identified even under two illumination conditions as shown in the following table.

In general, depending on n types of illumination conditions, it is possible to identify two types, including non-defective products (normal), that is, 2”-
This makes it possible to identify the type of one type of defective part.

〔Effect of the invention〕

As described above, the surface defect inspection method according to the present invention includes:
This method identifies the type of defect by focusing on the difference in reflection characteristics depending on the type of defect.It uses a simple method that uses different patterns of defect detection signals to identify multiple types of defects using multiple lighting conditions. This has an excellent effect of enabling identification.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the principle of the method of the present invention, and Figure 2 is (A
) CB) (C) are SN ratio pattern diagrams of various defective parts, and FIG. 3 is an explanatory diagram showing the first embodiment of the method of the present invention.
4 to 6 are images detected using a plurality of illumination horn layers for each of various defective parts according to the same embodiment, FIG. 7 is an explanatory diagram showing the second embodiment, and FIG. 8 is an explanatory diagram showing the third embodiment. FIG. 9 is a front view of a television screen according to the embodiment, and FIG. 1O is a pattern diagram of various defective parts according to the embodiment. (1) (la) (IN (lc) Emitter (2) (2a) (2b) (2c) Camera (3) Processing device (W) Object to be inspected (wo) Inspection target surface agent Masuji No Wood Yang - 1 Figure 1 Figure 2 Figure 3 W Figure 7 Figure 8 Figure 9 Figure 1 (5) Procedure Amendment Old (voluntary) March 1, 1985 Commissioner of the Patent Office Small Kunio Kawa 1, Indication of the case Patent Application No. 51895 of 1988 2, Name of the invention Surface defect inspection method 3, Person making the amendment Relationship with the case Patent applicant 4, Agent
Person 1055, “3. Column B of Detailed Description of the Invention J” of the specification subject to amendment, Contents of amendment

Claims (1)

[Claims] In a non-contact optical surface defect inspection method, a defective part is detected by irradiating a surface to be inspected of an object to be inspected with light and electrically detecting the amount of light reflected from the surface to be inspected using an image sensor, Different types of defects are prepared in advance.
A surface defect inspection method comprising: determining a pattern based on illumination conditions of a detection signal, and then identifying the type of defective portion based on the pattern using a plurality of different illumination conditions.