JPH02201112A - Surface inspection method for frp product - Google Patents

Abstract

PURPOSE:To allow the well conduction of the surface inspection of an FRP product by Fresnel diffraction by adjusting the distance between a spot light source and an inspection surface and maximizing the S/N of an ordinary surface pattern and the pattern of a true defect. CONSTITUTION:Rays of the light source 1, such as ultra-high pressure mercury lamp, are imaged at a focus by a lens system 2 to form the spot light source 3. The surface 4 of the FRP product is irradiated with the ray thereof and the annular pattern is generated on a screen 5 by the Fresnel diffraction of the reflected light. The difference between the patterns is made distinct if the S/N of the annular pattern occurring in the undulation of the ordinary surface and the annular pattern occurring in the product defect is maximized by adjusting the distance (a) between the spot light source 3 and the inspection surface 4. A recessed part P is thus easily detected. The contrast is maximized near the distance a=50mm in this case.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an inspection method that utilizes Fresnel diffraction and is suitable for finding surface pinholes, which are defects specific to FRP molded products.

[Conventional technology and its issues]

In FRP products, small holes (pinholes) often occur on the surface after molding due to air bubbles contained between reinforcing materials such as glass fibers mixed into the material, so it is important to inspect the appearance of the finished product. . Traditionally, this inspection has been performed visually by holding the product up to light or immersing it in a penetrating liquid.

However, with this inspection method, there are many oversights, and
Secondary problems arise such as discoloration of the product due to penetrating liquid. Therefore, there is a need for objective inspection using an optical inspection device instead of using the naked eye.

Conventionally, surface inspection methods have been known that utilize ring-shaped patterns generated by Fresnel diffraction based on surface defects. However, this inspection method was developed for inspection targets with high reflectivity such as iron plates, and FRP
It was difficult to directly apply this method to inspection objects with relatively low surface reflection, such as products. Moreover, in the case of FRP products, there are relatively large undulations with a period of around 1 cm even on the normal surface due to the manufacturing characteristics, so Fresnel diffraction occurs even based on this, and inspection There was a problem in that the difference from the target pinhole was not clear.

In view of the problems of the prior art, it is an object of the present invention to provide suitable conditions for applying a surface inspection method using Fresnel diffraction to the inspection of FRP products.

[Means to solve the problem]

The purpose of this is to irradiate light from a point light source onto the surface of the FRP product to be inspected, and observe the ring-shaped pattern generated on the screen by Fresnel diffraction of the reflected light to recognize the presence or absence of surface defects. The feature is that the distance i1a from the light source to the surface of the FRP product is adjusted to maximize the S/N ratio between the ring-shaped pattern caused by the waviness of the normal surface and the ring-shaped pattern caused by the true defect. This is achieved by a surface inspection method that

Hereinafter, the present invention will be explained in more detail based on preferred embodiments shown in the drawings.

[Example] First, the principle of Fresnel diffraction pattern projection method will be explained based on FIG.

When the light emitted from the point light source Q is irradiated onto the surface of the sample where the depression P exists, the reflected light is projected onto the screen S,
Due to the recesses P, a ring-shaped pattern is produced with a dark center and bright surroundings. The outer diameter of this ring-shaped pattern is (where λ is the wavelength of light, and a is the distance M between the point light source and the sample surface.
, b is the distance between the sample surface and the screen.

d is the diameter of the recess) It is expressed as

That is, the size of the dent P, which is a defect, is enlarged to D/d and projected in the form of a screen, so that it can be easily discovered.

Figures 2 (a) and (b) represent charts obtained by measuring the normal surface area of the FRP product and the area containing defective pinholes using a surface roughness meter, respectively. In the case of products, even on normal surfaces, approx.
There are irregularities with a period of about 81 undulations. on the other hand,
The pinhole is a deep hole with a diameter of about 200 to 400 μm. Therefore, the former also causes a ring-shaped pattern due to Fresnel diffraction to be formed on the screen, which may be mistaken for a pattern based on the latter true defect.

As a result of measuring a large number of FRP products based on the above-mentioned principle, the inventor found that the distance a between the point light source and the sample surface was
It has been found that as the pattern becomes smaller, the magnification of the pattern projected onto the screen increases, and the contrast decreases and becomes blurred.

Based on this, we conducted various studies and found that, near a = 50M, the contrast of the ring-shaped pattern based on the undulations of the normal surface becomes the minimum, while the contrast of the pattern based on the pinhole becomes the maximum. It has been found that the S/N ratio of patterns with true defects is maximized.

Figure 3 shows an outline of an inspection device constructed based on such a principle. An ultra-high pressure mercury lamp or a short arc xenon lamp is used as the light source l, and this is focused through the lens system 2. It is configured to form an image to form a point light source 3 and to irradiate the surface 4 of the FRP product to be inspected. Furthermore, a screen 5 made of non-reflective white paper or frosted glass is set so as to be substantially perpendicular to the reflected light.

As mentioned above, depending on the surface condition of the object to be inspected, the point light source 3
The distance M a y! between and the inspection surface 4! :In order to be able to adjust the S/N ratio as appropriate to maximize it, this device was attached via a vertically movable hinge 12 to a pillar 11 fixed to a pedestal 10, as shown in Fig. 4. It is mounted on the rod 13 by a rotatable hinge 14 so that it can face the FRP product to be inspected at a predetermined angle and distance.

Contrary to pinholes, for small protruding defects, by setting the distance a to a negative value as shown in Figure 5, a similar ring-shaped pattern due to diffraction can be created on the screen. It is possible to form Since the surface defects of FRP products often have complicated shapes, it is desirable to adjust the distance a within a positive or negative range to determine the position where the contrast is best.

Note that it is also possible to use a laser beam as the light source, and thereby a clearer ring-shaped pattern can be obtained.

[Brief explanation of the drawing]

Figure 1 is a principle diagram for explaining the formation of a ring-shaped pattern by Fresnel diffraction used in the present invention. Figures 2 (a) and (b) are surface states of FRP products that are the subject of the present invention. 3 is a schematic diagram illustrating the outline of the device used in the present invention, 4 is an external view of the same, and 5 is a diagram showing a case where the distance a is negative. It is a schematic diagram. ■...Light source, 2--Lens system, 3--Point light source, 4--Surface of FRP product, 5--Screen, 10- Frame, 11--Pillar 12.14--Hinge, 13- -・Rod.

Claims (1)

[Claims] 1. When recognizing the presence or absence of surface defects by irradiating light from a point light source onto the surface of the FRP product to be inspected and observing the ring-shaped pattern generated on the screen by Fresnel diffraction of the reflected light, By adjusting the distance to the surface of the FRP product, the S/S ratio between the ring-shaped pattern caused by the waviness of the normal surface and the ring-shaped pattern caused by the true defect is determined.
A surface inspection method characterized by setting the N ratio to the maximum.