JPH0656299B2 - Flatness measurement method using moire fringes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is capable of measuring the flatness of the surface of a subject by using Moire fringes formed by a reference lattice and a deformed lattice on the subject. The present invention relates to a method of measuring flatness by moiré fringes.

(Prior Art) Conventionally, a contour 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 a lattice irradiation type moire topography method which is one of the moire topography methods.
That is, according to this method, as shown in FIG. 3, a reference grating G, which is placed immediately before the object and has transparent and non-transmissive parts formed at equal black and white intervals, is placed at a distance b from the reference grating. When illuminated by the point or line light source S that is lit, the light beam becomes a radial light flux with black and white brightness, forming a black and white pattern on the subject. This pattern is a reference grid G
When observed or photographed at a distance b from the light source S at a further distance b, it appears as a deformed lattice that is 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 modified grid on the subject intersect
Contour lines Moire fringes (also simply referred to as moire fringes) appear bright.

In this lattice irradiation type moire topography method, when the pitch of the reference lattice G is P _O and the moire fringe order is N, the distance h from the reference lattice G to the position where the contour moire fringes of the Nth order are formed. _N represents the amount of unevenness on the surface to be inspected, and is generally expressed by the following equation (a).

h _N = bNP _O / (l-NP _O ) ... (a) In the above equation, h _N represents the measurement sensitivity, and the minimum measurement sensitivity is about 10 μm by appropriately selecting the parameters b, l and P _O. It is possible up to.

FIG. 4 shows a conventional example constructed on the basis of the lattice irradiation type moire topography method. In FIG. 4, the reference grating 2 is arranged immediately in front of the subject 1 and is illuminated by the light source 3 on the reference grating 2 to form a deformed lattice on the surface of the subject 1 which is deformed by the unevenness of the surface. Form. The modified grid and the reference grid 2 overlap with each other to generate contour moire fringes. If the contour moire fringes are photographed by the camera 4 arranged so as to face the distance from the reference grating 2 to the distance b from the light source 3 by l, the moiré fringes of the object 1 such as paper or wafer metal are detected. The flatness of the surface can be easily measured without contact.

(Problems to be Solved by the Invention) By the way, in the measuring method shown in FIG. 4, when 1 is a porous object such as ceramics, since microscopic holes are present on the surface, it is reflected by illumination light. It produces light and scattered light. Therefore, since the reflected light and the scattered light become flares, it is practically difficult to clearly and accurately observe and photograph the contour moire fringes generated on the surface of the subject. Therefore, the method of FIG. 5 can be considered as a method of improving this point.
FIG. 5 (a) is a side view and FIG. 5 (b) is a plan view. In FIG. 5, the camera 4 has a distance b from the reference grating 2 and a distance from the light source 3 to 1 so that the specularly reflected light R of the light source 3 from the surface 1a of the subject 1 is incident on the camera 4. It is provided in a plane including the incident light I that is incident on the subject 1 from 3 and the normal line N standing on the subject surface 1a and the reflected light R corresponding to the incident light I. According to the method of FIG. 5, the camera 4 can sufficiently collect the specularly reflected light R from the surface to be inspected 1a, so that the contrast of the contour moire fringes can be improved, but the reflected light from the reference grating 2 and Diffracted light also enters at the same time and is condensed,
Since they become noise, the flatness measurement accuracy deteriorates.

(Means for Solving Problems) In view of the above circumstances, the flatness measuring method by moire fringes of the present invention is a means for observing or photographing contour moire fringes generated by superposition of the reference lattice and the deformable lattice,
In the vicinity of the specular reflection light of the light source reflected from the test surface of the subject,
It is provided at a position where the specularly reflected light is not received.

(Operation) The flatness measurement method using moire fringes of the present invention is performed as follows. A means for observing or photographing the moire fringes is provided at a position where the specular reflection light from the light source by the surface to be inspected is not received.
By doing so, the specularly reflected light, the diffracted light by the reference grating, and the scattered light from the subject are prevented from entering the observation or imaging means. Since the light and the contour moire fringes do not overlap with each other, if the observed or photographed contour moire fringes are read, the flatness of the surface to be inspected of the subject can be measured from the fringe order of the moiré fringes.

(Embodiment) An embodiment of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 (a) and 1 (b) are a plan view and a side view, respectively, showing a moire fringe flatness measuring method according to the present invention. In the figure, reference numeral 1 is a test object made of a porous material such as ceramics, and 1a is a test surface thereof. Reference numeral 2 is a reference grating, 3 is a light source, 4 is a camera, O is the center of the light source, C is the center of the surface 1 to be inspected, and H is the principal point position of the taking lens L provided in the camera.

As shown in FIG. 2, the reference grating 2 has transmissive portions 2a and non-transmissive portions 2b arranged at a pitch P _O , and the lattice is oriented in a direction perpendicular to the light rays from the center O of the light source 3, It is placed close to or in slight contact with the test surface 1a of the subject 1.

The light source 3 is a point or linear light source that uses a halogen lamp, a mercury lamp, or the like as a light emitting source, and illuminates the reference grid 2. The illuminated reference grating 2 forms a deformed grating which is deformed by the irregularities of the surface 1a to be inspected, on the surface 1a to be inspected of the object 1 in proximity to or in contact with it. The modified grid and the reference grid 2 overlap to produce contour moire fringes. Light source 3
The center O is at a distance b from the surface 1a of the subject 1 to be examined in the height direction.

The camera 4 includes a taking lens L and a film F.
The principal point H of the photographing lens is a plane including a center 0 of the light source 3 and a normal line N standing on the center C of the surface 1 at a distance of 1 from the light source O and a distance of the surface 1a to b. It is placed outside at a position of an angle θ = 10 ° toward the center C of the surface to be inspected 1. The angle θ is determined in consideration of the size of the subject 1 and the angle of view of the lens L so that the specularly reflected light R from the test surface 1a is not condensed by the lens L. When the camera 4 is placed at the position described above, the specular reflection light of the light source by the subject 1 and the diffracted light by the reference grating 2 and the harmful light such as the scattered light from the subject will not enter the camera 4. ,
The contour moire fringes generated on the surface 1a of the subject 1 are clearly photographed on the film F through the photographing lens L.
In this case, since the camera 4 obliquely captures the contour moire fringes, the pitch of the moire fringes is not P _O but P ′ = P _O.
The value is represented by / cos θ. In the formula (a), P _O
If P ′, the distances b and l, and the photographed moire fringe order N are substituted instead, the amount of unevenness h of the test surface 1a of the subject 1
_N is required. As an example, P _O = 0.1 mm, b = 2
When 35 mm, l = 1200 mm, N = 1, and θ = 10 °, the unevenness amount h _{N = 1} of the surface 1a to be tested becomes 0.0199 mm. Sixth
The figure shows a ceramic surface as a surface to be inspected P _O = 0.1 mm, b = 235 by the method of FIGS.
It is a photograph taken with a lens L having a focal length of 50 mm with mm, l = 1200 mm and θ = 10 ° set. In the photograph of FIG. 6, one moire fringe represents an uneven amount of 0.02 mm. FIG. 7 shows the surface of the ceramic with P 2 _O = 0.1 mm, b = 250 mm, and l = by the conventional method shown in FIG.
Lens L with a focal length of 50 mm set to 1000 mm
It is a picture taken in. In the photograph of FIG. 7, one moire fringe represents an unevenness amount of 0.025 mm. Comparing the above two figures, it is known that the photograph of FIG. 6 according to the present invention records much more clearly the moire fringes showing the concave and convex state of the ceramic surface as compared with the photograph of FIG. 7 of the conventional example.

The following method is also available as another practical use of the flatness measuring method based on the moire fringes. As can be seen from the equation (a), the pitch P _{O of the} moire fringes, the distances b and l, and the allowable unevenness h _{N of the} surface to be inspected are determined in advance, and the order No of the moire fringes is determined from these values. Ask. With this No as a limit value, the order N of the moire fringes photographed by the camera is
If it is within the range, it is determined that the unevenness amount h _N of the surface to be inspected 1a is within the allowable value.

If a television camera or a projection screen is used instead of the camera, the moire fringes can be read instantly, so that the work can be performed efficiently. The selection of the moire fringe observation means and the imaging means is determined in consideration of the work content and the size of the work space.

(Effects of the Invention) As described above, according to the flatness measuring method using moire fringes of the present invention, the means for observing or photographing the moiré fringes emits the specularly reflected light from the light source that is reflected from the test surface of the subject. Since it is provided at a position where it does not receive light, the flatness of a porous material such as a ceramic as an object to be measured can be accurately measured without being affected by harmful light such as the specular reflection light.

[Brief description of drawings]

1 (a) and 1 (b) are a plan view and a side view, respectively, showing a flatness measuring method by moire fringes according to the present invention, and FIG. 2 is an explanatory view for explaining a reference lattice which is a constituent element of the present invention. , FIG. 3 is an explanatory view for explaining the principle of the lattice irradiation type moire topography method, FIG. 4 is a conventional example constructed based on the principle of FIG. 3, and FIGS. 5 (a) and 5 (b) are respectively. It is a side view and a top view showing other prior art examples constituted based on the principle of Drawing 3. FIG. 6 is a photograph of moire fringes on the ceramic surface taken by the method of FIG. 1 of the present invention. FIG. 7 is a photograph of the moire fringes on the ceramic surface taken by the method of FIG. 4 of the conventional example. 1 ... Subject, 1a ... Test surface, 2 ... Reference grating, 3 ... Light source, 4 ... Camera, C ... Center of test surface, θ ... Camera looks at center of test surface Depression angle.

Claims (1)

[Claims] 1. Contour line moire fringes formed by superimposing a reference grating illuminated by a light source that emits visible light and a deformed grating generated on a test surface of a subject close to or in contact with the reference grating. In the method of observing or photographing, the means for observing or photographing is provided in the vicinity of the specularly reflected light of the light source reflected from the surface to be inspected and at a position where the specularly reflected light is not received. measuring device.