JPS5944643A - Method for inspecting surface defect - Google Patents

Abstract

PURPOSE:To detect easily a surface defect of a surface to be inspected having processed stripes in a fixed direction by detecting the variation of a component of the reflected light quantity in the direction parallel to the processing stripes of the object to be inspected out of the reflected light from the object. CONSTITUTION:Luminous flux L is irradiated to an object 1 to be inspected having processed stripes 2 to detect the reflected light by a photodetector 3 such as television camera. The photodetector 3 is arranged to the direction perpendicular to the inspecting surface, and a sampling line 4 is made parallel to the direction of the stripes 2. Thus the variation N of the reflected light quantity due to the surface roughness can be decreased. Thereby, SN ratio of the variation S of the reflected light quantity level due to the defect part to the variation N of the reflected light quantity level at the normal part is increased, and the defect detection ability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-contact surface defect inspection method, and an object of the present invention is to provide an inspection method that can easily detect surface defects on a surface to be inspected that has processed lines in a certain direction. shall be.

BACKGROUND ART Conventionally, as a surface defect inspection method, a flying spot method and a flying image method, in which a spot light or the like is applied to a surface to be inspected and the reflected light is received, are widely known and put into practical use. In addition, as a special example, a polarized laser is used in place of the spot light, and a polarized filter is installed on the receiving side.
There are known methods that remove reflected light from normal surfaces and receive only scattered light from defective parts.The first two methods reduce specularly reflected light from defective parts, and the third method reduces scattered light. However, according to these methods, eliminating changes in the amount of reflected light in normal areas other than defective areas or keeping them extremely small is the key to improving defect detection ability. It is necessary. In other words, the spread and scattering of reflected light due to minute surface inclinations such as surface roughness inhibits defect detection, so it is suitable for detecting surface defects on objects with very smooth surfaces, such as hard disks. However, it is not necessarily suitable for inspecting ordinary workpieces that have a surface roughness of 1 μm or more.

Furthermore, in the case of the first and second methods described in 1jσ, since specularly reflected light is received, the permissible range of the optical axis is narrow, making it difficult to set conditions. This method has the disadvantage that the structure of the light receiving system to efficiently collect the scattered light is complicated, and each conventional method is not suitable when the inspection surface is curved. .

In view of the above-mentioned problems, the present invention proposes a method for detecting red-faced defects in ordinary workpieces, etc. The present invention proposes a method for detecting red-faced defects in ordinary workpieces, etc. The present invention is based on the spatial distribution shape of reflected light on a surface having regularity of surface roughness in a certain direction, such as machining lines. This makes it possible to detect defective areas by keeping changes in the reflected light in normal areas small.

In other words, the spatial distribution of reflected light from a normal part, which has regularity in a certain direction such as processed lines, has regularity in the same direction as the processed lines, and as shown in FIGS. The change (N) in the amount of reflected light in the normal part of 1) appears most significantly when sampling in the direction (θ = 90°) perpendicular to the processed line (2), and when sampled in the direction (θ = 90°) perpendicular to the processed line (2),
= 0°)/bling, so by paying attention to the amount of reflected light in the same direction as the processed line (2), it is possible to reduce the change in the amount of reflected light in the normal area. .

On the other hand, since the defective part has an irregular shape and is different from the regularity of the normal part, the level of reflected light from the defective part shows a considerable change regardless of the sampling direction. Therefore, the machining line (2
) by sampling parallel to (θ = 0°) and keeping the change in the level of reflected light in the normal area low, the change in the level of reflected light due to the defective area (S) and the change in the level of reflected light in the normal area (N ), the defect detection ability is improved, and defective parts can be easily detected.

An embodiment of the surface defect inspection method based on the principle of the present invention will be described below with reference to FIG. This example shows the machining lines (
2) When the inspection surface is the inspection object (1), and when a light receiving element (3) such as a television camera is arranged in a direction perpendicular to the inspection surface, the light receiving element (3) The amount of reflected light due to It is possible to reduce the change (N) in the reflected scene due to the

In addition, the change (N) in the amount of reflected light from the inspection surface having the processed streaks (2) varies greatly depending on the arrangement of the optical system such as the illumination direction, and the luminous flux (1,) is diffuse reflection illumination and the processed streaks (2) It is known that the change (N) in the amount of reflected light due to blush roughness is the smallest when the irradiation is from a direction parallel to the surface roughness. (oO) and the luminous flux (
Change in the level of reflected light amount with respect to the surface roughness of the surface to be inspected when irradiated with L) (N)
It can be seen that when the method of the present invention (grain direction sampling) is used for the x plane, the fluctuation coefficient (standard deviation of the amount of reflected light/average of the amount of reflected light) is reduced by 10% to 30 inches.

As a result, in the case of the method of the present invention, the above-mentioned S/N ratio was reduced to 10%.
~30% larger diameter means improved surface defect detection ability. In particular, when the illumination direction of the light beam (L) is made parallel to the direction of the processing lines (2),
The coefficient ((5'/Iave) is small, the change in the amount of reflected light in a normal area is the smallest, and it is less affected by surface roughness, making it easy to detect defective areas. Also, when actually detecting surface defects, The amount (threshold amount) for distinguishing a defective portion from a defective portion may be set using the above-mentioned motion coefficient.

Next, Fig. 5 shows an example in which the object to be inspected (1) has a ring shape, in which the cross-sectional view (,) is a plane, (4) is an inclined surface, and (c) is a convex cross-sectional view. This is the case when the surface becomes a curved surface. A light receiving element such as a camera (
3), and sample the reflection scene in the direction (4) perpendicular to the processed lines (2) of the object to be inspected (1).
) is rotated (arrow Y) to continuously inspect the entire circumferential surface υ, and the signal from the same element of the line camera (
Surface defects can be detected by continuously measuring the reflected light. In particular, even in this case, if the illumination is made into a light beam in the direction of diffuse reflection lines as described above, the light receiving element (
3) does not receive reflected light from normal parts, so even if the object to be inspected (1) is a curved surface, changes in the level of reflected light itself can be reduced, making it possible to easily detect defects. It is what it is.

As described above, according to the surface defect inspection method of the present invention,
It is possible to easily detect surface defects such as machined surfaces with normal surface roughness by reducing the influence of the surface roughness, and by combining the light beam with well-known diffuse reflection streak direction illumination, the surface to be inspected can be easily detected. The present invention is extremely useful because it has features such as being able to detect defects with extremely high accuracy even on curved and inclined surfaces.

[Brief explanation of the drawing]

The drawings show an embodiment of the surface defect inspection method of the present invention, and Fig. 8g1 is an explanatory diagram showing the sampling direction for the object to be inspected, and Fig. 2 shows the angle (θ) between the streak direction and the sampling direction in Fig. 1. Figure 3 is an explanatory diagram showing the measurement principle of the present invention, and Figure 4 shows the variation in the amount of reflected light with respect to the surface roughness (μmRmax) when the sampling direction is changed. Coefficient (σ/
FIG. 5 is an explanatory diagram showing an example in which the object to be inspected is ring-shaped. (1) Inspection object (2) Machining lines (3) Light receiving element (4) Light receiving line of reflected scene (5)
Light source seven,! , i1 Representative Patent Attorney Nomoto No. 1 1,
1 Le 11 Figure 1 Streak - Angle Rightward "sun 7" ring (b) 2nd [) Angle formed & (θ)

Claims (1)

[Claims] For inspection objects that have surface roughness with regularity such as processing lines, an appropriate irradiation light is projected onto the inspection object, and the reflected light from the object is parallel to the processing lines of the object. A non-contact optical surface defect inspection method that detects surface defects by changing the component of the amount of reflected light in different directions.