JPS6138401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that non-contactly and optically displays the uneven state of an object surface using contour lines.

Conventionally, to display the unevenness of an object's surface using contour lines, uniform illumination light is projected onto the object through a grating placed in front of the object, and the shadow of the grating is projected onto the object. In reality, these stripes are displayed as moiré stripes by observing them through a grating placed in front of them. However, if the uneven state of the object surface is to be displayed in this way, the projection fringes of the grating must be in front of the most protruding part of the object, so the projection fringes formed toward the back of the object surface are There is a drawback of obscurity due to the phenomenon of light diffraction. This drawback becomes particularly noticeable when the pitch of the grating is made small to reduce the height per uniform height stripe, but in order to eliminate this drawback, in addition to the above-mentioned method using moiré topography, It has also been considered to form an image of the image onto the object plane through a lens.
However, this method has not yet solved the essential problem. In other words, even if you project the grating onto the object plane, if you try to reduce the pitch of the grating to obtain contour lines for minute irregularities, the surface where the grating is imaged will be This is because the depth of the image is extremely shallow, and the stripes can only be projected onto the object within a very limited range.

An object of the present invention is to provide a contour line display device that enables the observation of clear contour lines with high contrast at a deep depth by projecting constant stripes onto the object surface regardless of the height of the object. It is about providing.

For this purpose, the present invention provides a light source that emits a coherent light beam, an optical system that divides the light beam emitted from the light source into two, and a light beam that is divided into two by the optical system. an optical system that generates interference fringes on a target object by superimposing them on the target object at an incident angle of , and an optical system that focuses the interference fringes generated on the target object on a desired imaging plane; An imaging optical system having an optical axis different from the incident angle is arranged on the imaging plane, and light transmitting parts and light blocking parts are arranged alternately at a predetermined pitch, and the width of the light transmitting part is
The value of (width of light transmitting part + width of light blocking part) is less than 0.05
This contour line display device is characterized in that it is equipped with a grating within a range of 0.35, and is capable of obtaining clear contour lines with high contrast.

The present invention will be explained below with reference to FIGS. 1 to 4.

First, referring to FIG. 1a, this shows an example of the configuration of the present invention in which grating is used as a means for obtaining contour lines. According to this, a light beam 3 emitted from a coherent light source 1 such as a laser oscillator is transmitted through beam expanding lenses 9, 10,
The light beam 3 is incident on the beam splitter 2 through the mirror 11, and the light beam 3 is split into two light beams 1 at this part.
It is separated into 3 and 14 parts. One of these light beams is directly irradiated onto the object 4 by the beam splitter 2, and the other is irradiated onto the object 4 through a mirror 12 so as to be superimposed on the other light beam. Each beam 13, 14 has a circular cross section. By superimposing the two light beams in this way, interference fringes 5 are formed on the object 4, but since these interference fringes 5 occur in all parts where the two divided light beams overlap, the fringe This can completely solve the conventional problem that the projected area is limited to a narrow range.

The interference fringes 5 formed on the surface of the object 4 are, for example, as shown in FIG. 1b. The interference fringes 5 are formed depending on the uneven state of the surface of the object 4 and the incident angle θ of the irradiation beam. According to the present invention, the interference fringes 5 formed in this manner on the object plane are imaged onto the imaging plane 7 by the imaging lens 6, and the grating 8 is formed on the imaging plane 7. Placed. The structure of this grating 8,
As shown in FIGS. 2a and 2b showing the front and plane sides, the shape is such that a light-shielding part 17 made of a light-shielding object is adhered to a glass substrate 18 at a predetermined pitch P, and the width of the light-shielding part 17 is A large number of light transmitting parts 19 having a width d are formed in parallel between the light shielding part 17 and the light shielding part 17. This grating 8
By observing the object image formed on the imaging plane 7 through the lens, moiré contour stripes 16 corresponding to the unevenness of the object can be observed in the object image 15, as shown in FIG. 1c. That's why.

The moiré contour stripes formed in this way can be identified by the alternating appearance of bright stripes and dark stripes, and the larger the difference in brightness or intensity (contrast) between these stripes, the easier it is to identify them. This high contrast is advantageous in various ways. For example, when capturing moiré contour lines as an image and processing it electrically, the greater the contrast, the higher the signal-to-noise ratio (S/
This is because N) becomes large. Therefore, increasing contrast is generally important. How to increase this contrast will be explained below with reference to FIGS. 3a to 3c.

FIG. 3a shows the change in the intensity I with respect to the change in the position x of the interference fringes formed on the object surface, and it can be seen that the intensity changes in a sinusoidal shape as shown. In addition, Fig. 3b shows the transmittance t of the grating.
This is what is shown. When the grating is arranged so that the solid line display position is the position of the light transmitting part as shown in the figure, the intensity (t×I) of the interference fringe image passing through the light transmitting part of the grating is shown in Figure 3c. The maximum value (t×I)max is taken as follows. However, when the grating is arranged so that the light transmitting part is at the dotted line display position, the intensity of the light passing through the light transmitting part is the minimum, and therefore the minimum value (t×I)min. The ratio of these maximum value (t × I) max and minimum value (t × I) min (t × I) max / (t × I)
min is the contrast C that represents the clarity of moiré fringes
It is. FIG. 4 shows how this contrast C changes with respect to the ratio d/p between the width d of the light transmitting portion of the grating and the pitch p. Note that between contrast C and d/p, C=
The relationship is (πα+sinπα)/(πα−sinπα). However, α=d/p.

As is clear from FIG. 4, the contrast C increases as the width d of the light transmitting part becomes smaller compared to the pitch p, but the smaller d/p reduces the amount of light transmitted through the light transmitting part d. It can be seen that the relative intensity Im of the moiré contour image becomes low, contrary to the contrast C, because it decreases in proportion to /p. However, as shown in FIG. 4, the value of d/p is not arbitrarily determined, but should be determined within an appropriate range. In the present invention, this range is 0.05d/p0.35
The reason for this is as follows.

That is, since the illumination direction of the laser interference light for illuminating an object is from a certain limited direction, illumination unevenness occurs, and image intensity unevenness corresponding to this unevenness occurs on the image forming surface 7. . This is because it is desirable and necessary for the value of contrast C to be about 10 or more in order to observe contour lines as a continuous striped pattern even if such unevenness occurs. Based on this condition, the upper limit of d/p was determined to be 0.35. On the other hand, if the value of d/p is too small, the intensity of the moiré fringes becomes small, making it impossible to effectively utilize the power of the laser light source. Moreover, if the contrast of the moiré fringes is set to 500 or more, it will exceed the contrast limit caused by noise in the imaging system, so it becomes meaningless, and also due to the light diffraction phenomenon caused by the small d/p. Another disadvantage is that the light transmitted through the grating escapes to the outside of the imaging lens. Taking these circumstances into consideration, the upper limit of contrast is set at 500, and the lower limit of d/p is set at 0.05.

Finally, we will discuss concretely using numerical examples how many small-pitch interference fringes can be formed on the object plane according to the present invention.

In Figure 1a, the angle formed by the beams 13 and 14 is 2δ, and if they are incident on the object 4 in the figure at angles of θ + δ and θ - δ (the angle of incidence is on the x-z plane), then the interference between the two beams will be The light illuminates the object 4 with an intensity change I(x,z) expressed by the following equation.

I(x,z)=A[1+cos{2π・2sinδ/λ(c
os θ・x−sinθ・z)+φ] ...(1) However, Α: a constant proportional to the intensity of light, λ: wavelength of the laser beam, φ: a constant representing the phase. Here, the bright part of the interference light is 2n in Equation 1.
Since it is a part expressed by π (n; an integer), the bright stripes are a surface group that satisfies the following equation.

2 sin δ/λ (cos θ・x−sin θ・z)+c ₀ = n...
(2) However, C ₀ =φ/2π. On the other hand, the height h of the surface of the object, that is, the z-like shape is expressed by the following equation.

z=h(x,y)...(3) Therefore, the equation of the bright part of the interference fringes projected onto the object plane is expressed as follows using equations 1 and 2.

h (x, y) = 1/sin θ {cos θ x + ( ₀ − λn/2 sin δ)} ...(4) However, ₀ is a constant. When these fringes are imaged on a grating using an imaging lens with a magnification of 1, the image becomes exactly as shown in Equation 4. Further, the equation for the center of the light transmitting portion of the grating can be expressed as follows using pitch p.

x=mp+ ₁ ...(5) However, m and ₁ are integers and constants, respectively.
Since the brightest fringe of the image observed through the grating simultaneously satisfies equations 4 and 5, this fringe also satisfies the following equation.

h (x, y) = 1/sin θ (cos θ・mp−p′n+c)
… …(6) p′≡λ/2sinδ …(7) However, C= ₀ + cosθ・₁ . p' is the pitch of the laser interference fringe plane group. Moiré contour lines are observed as m=n+N+k (N; constant integer, k;
When h(x, y) is n
This is when it is possible to express it in a way that does not depend on it. Therefore, it is necessary to adjust the optical system so that the condition expressed by the following equation is satisfied.

pcosθ=p′ (8) At this time, from equation 6, the k-th contour line is expressed by the following equation.

h(x,y)=p'k+c'/sinθ...(9) However, C' is a constant and C'=C+Np. Also,
The height difference Δh between the contour lines is obtained from the above equation as follows.

Δh=p′/sin (=λ/2sinθsinδ)...
…(10) As a result, for example, He−Ne can be used as a laser light source.
If a (helium ion) laser (λ = 0.63 μm) is used and 2δ = 14° and θ = 30°, Δh is 5 μm.
m. Also, if 2δ=0.36°, Δh is
It becomes 100μm. That is, according to the present invention, contour lines with small height changes between contour lines can be displayed with a simple configuration.

As explained above, according to the present invention, it is not only possible to form interference fringes with a deep depth of focus on the object plane, but also to form interference fringes with a small pitch of several μm to several hundred μm on the object plane. Therefore, it is possible to display contour lines with small height changes between contour lines with a simple configuration without being subject to spatial constraints.
The value of (width of light transmitting part + width of light blocking part) is less than 0.05
The grating within the range of 0.35 not only allows for free observation, but also provides the effect of obtaining clear contour lines with high contrast.

[Brief explanation of the drawing]

1A to 1C are diagrams showing an example of the configuration of a contour line display device according to the present invention, an example of interference fringes formed on an object plane, an example of moiré contour lines observed through grating, and a second diagram, respectively. Figures a and b are the first
Figure a is a front view and a plan view showing the configuration of the grating, Figures 3 a to c are diagrams for explaining the relationship between the arrangement of the grating and the intensity of moiré fringes, and Figure 4 is FIG. 3 is a diagram showing how the contrast and relative intensity change depending on the ratio of the width of the light transmitting part to the pitch. 1... Coherent light source, 2... Beam splitter, 6... Imaging lens, 7... Image forming surface, 8... Grating.

Claims (1)

[Claims] 1. A light source that emits a coherent light beam, an optical system that splits the light beam emitted from the light source into two, and a light beam that is split into two by the optical system and is directed onto a target object at a desired angle of incidence. an optical system that generates interference fringes on the object in a superimposed manner; and an optical system that focuses the interference fringes generated on the target object on a desired imaging plane, and has an optical axis that is different from the incident angle. The imaging optical system is arranged on the image forming surface, and light transmitting parts and light shielding parts are arranged alternately at a predetermined pitch, and the width of the light transmitting part / (width of the light transmitting part + width of the light shielding part). A contour line display device comprising: a grating having a value within a range of 0.05 to 0.35.