JPS6329208A - Measuring method for flatness by moire fringe - Google Patents

Abstract

PURPOSE:To improve the accuracy of the measurement of the flatness of a surface to be inspected based on the order of moire fringes by providing a means for photographing the moire fringes at a position where the regularly reflected light beams of a light source from a surface to be inspected are not photodetected. CONSTITUTION:A camera 4 is equipped with a photographic lens L and a film F and the principal point H of the lens L is set at distance l from the light source O and at distance (b) from the surface to be inspected off a plane containing the center O of the light source 3 and a normal N to the center (c) of the body 1 to be inspected at a position of an angle theta to the center (c). The angle theta is so determined that the regularly reflected light beams R from the surface 1a to be inspected are not converged by the lens L. Consequently, no harmful light beams such as the regularly reflected light beams R from the body 1 to be inspected, diffracted light beams from a reference grating 2, and scattered light beams from the body 1 to be inspected are wade incident on the camera 4 and contour moire fringes formed on the surface 1a to be inspected are photographed sharply on a film F through the lens L.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention measures the flatness of a surface of an object by using moiré fringes formed by a reference grid and a deformed grid of an object. This invention relates to a method for measuring flatness based on moiré fringes.

(Prior Art) Conventionally, a contour line pattern measurement method, that is, a moire topography method, has been known as a measurement method using moire fringes. FIG. 3 shows a principle diagram of the lattice projecting moire topography method, which is one of the moire topography methods.

That is, according to this method, as shown in FIG. 3, a reference grid G, which is placed immediately in front of the subject and has transparent and opaque parts spaced at equal black and white intervals, is placed at a distance from this reference grid. When irradiated with a continuous point or line light source S, the light beam becomes a radial light beam with black and white brightness, forming a black and white pattern on the subject. This pattern is the reference grid G
When observed or photographed at a distance β from the light #S, it appears as a deformed lattice that has been deformed according to the shape of the surface of the subject. Then, the point sequence where the transparent part of the reference grid G and the white line part of the deformed grid on the subject intersect is
Contour line moiré fringes (also simply called moiré fringes) appear bright.

In this grating irradiation type moiré topography method, the pitch of the reference grating G is P. , where the order of the moire fringe is N, the distance hN from the reference grid G to the position where the Nth-order contour moire fringe is formed represents the amount of unevenness of the surface to be traversed, and is generally expressed by the following equation (a).

hN = bNPo / (fNPo) -- (a) In the previous equation, hN represents the measurement sensitivity, and the parameters b-1 and P. By appropriately selecting , the minimum measurement sensitivity can be up to about 10 μm.

FIG. 4 shows a conventional example constructed based on the grating irradiation type moiré topography method. In Figure 4, the reference grid 2 is placed just in front of the subject 1, and is illuminated by the light source 3 on the reference grid 2, which illuminates the subject 1.
A deformed lattice that is deformed due to the unevenness of the surface is formed on the surface. This deformed grid and the reference grid 2 overlap to produce contour moiré fringes. These contour moire fringes are
If the camera 4 is placed directly facing the reference grid 2 at a distance β from the light source 3 and a distance b from the light source 3, the flatness of the surface of the object 1 such as paper or wafer metal can be determined from the moire fringes. Easily measurable by contact.

(Problem to be Solved by the Invention) By the way, in the measurement method shown in Fig. 4, when 1 is a porous specimen such as ceramics, there are minute holes on the surface, so the illumination light is reflected. Produces light and scattered light. Therefore, since the reflected light and scattered light become flares, it is actually difficult to clearly and accurately observe or photograph the contour moiré fringes that occur on the surface of the subject. Therefore, the method shown in FIG. 5 can be considered as a method to improve this point.

FIG. 5 Tal shows a side view, and FIG. 5 fbl shows a plan view.

In FIG. 5, the camera 4 is positioned at a distance Mb from the reference grating 2 and a distance β from the light source 3 so that the specularly reflected light R of the light source 3 by the surface 1a to be examined of the object 1 enters the camera 4. It is provided within a plane that includes incident light 1 entering the subject 1 from the light source 3, a normal N erected on the subject surface Ta, and reflected light R corresponding to the incident light I.

According to the method shown in FIG. 5, the camera 4 can sufficiently collect the specularly reflected light R from the test surface 1a, so the contrast of the contour moiré fringes is improved. Also, diffracted light and diffracted light are incident and focused at the same time, and these become noise, deteriorating the flatness measurement accuracy.

(Means for Solving the Problems) In view of the above circumstances, the flatness measurement method using moire fringes of the present invention includes means for observing or photographing contour moire fringes caused by superimposing the reference grating and the deformed grating. It is arranged at a position where it does not receive the specularly reflected light of the light source reflected from the test surface of the test object.

(Function) The flatness measuring method using moiré fringes of the present invention is carried out as follows. A means for observing or photographing moiré fringes is provided at a position that does not receive specularly reflected light from a light source by the surface to be inspected.

By doing so, the specularly reflected light, the diffracted light by the reference grating, and furthermore the scattered light from the subject are prevented from entering the observation or photographing means. Since these lights and the contour moire fringes do not overlap, when the contour moire fringes that are observed or photographed are read, the flatness of the surface of the object to be examined can be measured from the fringe order of the moire fringes.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. FIG. 1 (al and fb) is, respectively,
1A and 1B show a plan view and a side view showing a flatness measurement method using moiré fringes according to the present invention. In the figure, reference numeral 1 is a test object made of a porous material such as ceramic, and la is a test surface of the test object. 2 is a reference grid, 3 is a light source, 4 is a camera,
O represents the center of the light source, C represents the center of the test surface 1, and H represents the principal point position of the photographing lens L provided in the camera.

As shown in FIG. 2, the reference grating 2 has a transparent portion 2a and a non-transparent portion 2b at a pitch P. The grating is oriented perpendicularly to the light beam from the center O of the light source 3, and is placed close to or in slight contact with the surface 1a to be examined of the subject 1.

The light source 3 consists of a point or linear light source using a halogen lamp, a mercury lamp, or the like as a light source, and illuminates the reference grating 2. The illuminated reference grid 2 forms a deformed grid on the test surface Ta of the test subject 1 that is close to or in contact with it, which is deformed by the unevenness of the test surface 1a. This deformed lattice and the base lattice 2 overlap to produce equal-height pure moiré fringes. light source 3
The center O of is located at a distance b from the surface 1a to be examined of the subject 1 in the height direction.

The camera 4 is equipped with one film F on the photographing lens.

The principal point H of the photographing lens is a distance l from the light source O, a distance from the test surface 1a to b, and is placed on the center O of the light source 3 and the center C of the test surface l, and is the modulus L? Test surface 1 outside the plane including IN
It is placed at an angle θ-10° toward the center C of . This angle θ is determined by considering the size of the subject 1 and the angle of view of the lens I, so that the specularly reflected light R from the subject surface 1a is
− The angle is determined so that no light buildup occurs. When the camera 4 is placed in the position described above, harmful light such as specularly reflected light from the light source by the subject 1, diffracted light by the reference grating 2, and even scattered light from the subject will not enter the camera 4. , a thousand contour fringes on the surface to be examined 1a of the object 1 are clearly photographed on a film Fl through a photographing lens L. In this case, since the camera 4 captures the pure moire fringes obliquely, the pitch of the moire fringes is determined by the pitch of the moire fringes described above. Dena(P'-p.

/cosθ. In the above formula (A), P
, by substituting P', distance Mb, 1, and the photographed moiré fringe order N, the unevenness of the surface 1a to be examined 1a of the object 1 can be found. As an example, Po −0,
] mm X b = 235 1, 7! =120
When 0 m++ Figure 6 shows the surface of the ceramic as the surface to be inspected at P, -0, 1 m by the method of Figure 1 +a+, (bl) of the present invention.
s, b=235mm, ff-1200mm, θ-1O°
This photo was taken with a lens I with a focal length of H50mvs. In this photograph of Fig. 6, moire fringes 1
The book represents the amount of unevenness of 0.02 ms. FIG. 7 shows the surface of the ceramic coated with P by the conventional method shown in FIG.

-0,111,b-25f)mn,,#=1000m-
This photo was taken using the lens L with the focal length set to 50. In this photo in Figure 7, Senryoshi stripes 1
The book represents an unevenness of 0.025 mm. Comparing the above two figures, the photograph in Figure 6 according to the present invention is compared to the photograph in Figure 7 in the conventional example.
It can be seen that the moiré fringes, which indicate the unevenness of the ceramic surface, are much more clearly recorded than in the photograph shown in the figure.

Another practical method of measuring flatness using moiré fringes is the following method. As shown in (A) above, first the pitch P of the moiré fringes. , the distance L, and the permissible unevenness Wk h N of the surface to be inspected are determined, and the order No. of the moiré fringes is determined from these values. With this No as a limit value, if the order N of the moire fringes photographed by the camera is within the above-mentioned No, it is determined that the amount of unevenness hN of the surface to be inspected 1a is within the allowable value.

Note that if a television camera or a projection screen is used instead of the camera, moire fringes can be read instantaneously, making the work more efficient.

The selection of means for observing and photographing moiré fringes is determined by taking into consideration the nature of the work, the size of the workplace, and other factors.

(Effects of the Invention) As explained above, according to the flatness measurement method using moire fringes of the present invention, the means for observing or photographing moire fringes is used to detect specularly reflected light from a light source that is reflected from the test surface of an object. Since it is installed at the 0 position where no light is received, flatness measurements of multi-JLtT materials such as ceramic and porcelain can be accurately performed without being affected by harmful light such as the specularly reflected light.

[Brief explanation of the drawing]

FIG. 1 (al and fbl are a plan view and a side view, respectively, showing the flatness measurement method using moiré fringes according to the present invention, FIG. The figure is an explanatory diagram explaining the principle of the grating irradiation type moire topography method, Figure 4 is a conventional example constructed based on the principle of 3M, and Figure 5 (al and (bl are respectively based on the principle of Figure 3). FIG. 7 is a side view and a plan view showing another conventional example constructed based on the above-described method. FIG. 6M is a photograph of moiré fringes on a ceramic surface taken by the method shown in FIG. This is a photograph of moire fringes on the ceramic surface taken by the method shown in Fig. 4. 1... Subject, 1a... Test surface, 2... Base Y1!! grating, 3... Light source, 4 ...Camera, C...Center of the surface to be inspected, θ...Angle at which the camera looks at the center of the surface to be inspected. Atsushi figure 5 (α) Mei y figure (b)

Claims (1)

[Claims] A method of observing or photographing contour moiré fringes formed by the superposition of a reference grating illuminated by a light source that emits visible light and a deformed grating generated on the test surface of a subject that is close to or in contact with the reference grating. A flatness measuring method using moiré fringes, characterized in that the observing or photographing means is provided at a position where it does not receive specularly reflected light from a light source reflected from the test surface.