JP2657906B2 - Non-contact light wave interferometry of block gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measurement method using an optical interferometer for accurately calibrating a block gauge based on the definition of a meter, and more particularly to a novel measurement method for quickly measuring a block gauge without bringing the block gauge into close contact with a base plate. .

[0002]

2. Description of the Related Art Recently, with the sophistication of products, a high-precision length standard is required even at a production site, and a block gauge is indispensable as a high-precision and simple standard. A measurement method using a light wave interferometer for accurately calibrating a block gauge based on the definition of a meter is mainly performed using a Michelson type interferometer. Although this interferometer has a simple structure and is easy to handle, it requires the block gauge to be in close contact with the base plate, and this operation requires skill, is poor in workability, and may cause measurement errors.

Further, as shown in FIGS. 2 to 4, an absolute measurement by a matching method using an interferometer without a block gauge being in close contact with a base plate is known. this is,
In FIGS. 2 and 3, first, the perforated blocks C and D are slightly moved right and left as indicated by an arrow A, and the beam splitter M shown in FIG.
Is adjusted so that the optical path length from the left and right beams becomes equal. When they are completely equal, a white interference fringe appears at a position 1 in FIG. Next, when the block gauge is slightly moved and the center plane of the block gauge coincides with the YY'Z plane, white interference fringes appear at the position 2 in FIG.

In this state, when the light source is switched to monochromatic light, monochromatic interference fringes appear at three points in FIG. By measuring the difference between the stripes of monochromatic light with respect to the line connecting the above white interference fringes 1-2, normal interference length measurement becomes possible,
This has the same effect as a measurement in which a base plate is provided on the YY'Z plane and a block gauge is closely attached to the base plate.

However, according to this method, it takes a long time to adjust white interference fringes, there is a rise in temperature due to the use of white light, and interference fringes appear only in one half of the surface of the block gauge. Therefore, when the flatness or parallelism of the block gauge is not good, there is a drawback that information over the entire surface cannot be obtained, and it has not been generally used recently.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides a new measuring method which can measure the length of a block gauge with almost the same accuracy as a conventional interferometer and greatly improves the measurement efficiency. To provide.

[0007]

A half mirror HMR for dividing light emitted from a light source LS into light directed to a block gauge BG and a light directed to a reference mirror MR via an optical wedge W, and a half for separating light directed to a block gauge again. LB using a mirror HM and two reflection mirrors M1 and M2 for directing light split by the half mirror HM to both end faces of the block gauge, respectively.
= .Lambda. / 2 {N + (. Epsilon.3-.epsilon.1) + (. Epsilon.3-.epsilon.2)}, which is a measuring method for obtaining the block gauge length LB, wherein (.epsilon.3-.epsilon.1) and (.epsilon.3-.epsilon.2) And measuring the length LB of the block gauge using known values of N and λ.

[0008]

FIG. 1 shows an optical system according to the measuring method of the present invention.
The light emitted from the light source LS is divided into light traveling toward the block gauge BG by the half mirror HMR and light traveling toward the reference mirror MR via the optical wedge W. The light heading for the block gauge is further divided by a half mirror HM, and a part of the light is reflected by the block gauge surface and returns along the same optical path as the going light, and the light passing through the side of the block gauge is HM-M1-M2-H.
M or HM-M2-M1-HM
Interferes with the reference light. Here, M1 and M2 are reflection mirrors.

In FIG. 1, the optical path length of HM-M1-BG is represented by L1, H
Assuming that the optical path length of MM2-BG is L2 and the optical path length of HM-M1-M2-HM is L3, the length LB of the block gauge is given by the following equation (1). LB = L3−L1−L2 (1) On the other hand, assuming that the wavelength of the incident light is λ, each optical path length L1, L2, L
3 is given by the following equation (2). 2L1 = λ (N1 + ε1) 2L2 = λ (N2 + ε2) L3 = λ (N3 + ε3) (2) where N1, N2 and N3 each represent an appropriate integer, and ε3 represents an appropriate decimal number.

From the equations (1) and (2), the length LB of the block gauge can be expressed by the equation (3). LB = λ / 2 {N + (ε3−ε1) + (ε3−ε2)} (3) where N = 2N3−N1−N2.

This equation shows that the length of the block gauge can be measured in the same manner as in the case of the normal light wave interference measurement. That is, (ε3−ε1) and (ε3−ε2) can be known from the deviation of the interference fringe from the light from the reference mirror MR. Therefore, if the approximate length of LB, that is, N and λ are known, the exact length of the block gauge can be known.

The optical system used in the present invention shown in FIG. 1 uses a He-Ne stabilized laser having a wavelength of 0.633 μm as a light source. The wavelength of this laser has been calibrated with an accuracy of 7 digits or more by comparing the frequency with the iodine stabilized laser. The optical wedge W can move in a direction perpendicular to the optical path crossing the optical wedge, and the amount of movement can be read by an electric micrometer. The interference fringes on the screen can be moved by this optical wedge, and (ε3−
ε1) and (ε3−ε2) can be measured.
S1 and S2 are shutters that block the same area as the block gauge surface. When measuring (ε3−ε1), S1 is opened and S2 is opened.
Is closed, so that interference between the optical paths L1 and L2 does not occur. These optical systems have a room temperature of 20 ± 0.2 ° C.
Install in a controlled temperature room.

The optical system is adjusted so that the deviation of the optical axis or the like becomes sufficiently small, and the block gauge is measured after the system has reached thermal equilibrium. To measure interference fringes, first use shutter S1
Is opened, S2 is closed, (ε3−ε1) is measured, and then (ε3−ε2) is measured by reversing the opening and closing of the shutter. The temperature of the block gauge during measurement is measured with a thermistor thermometer, and the measured block gauge length is corrected. Also, at room temperature,
By measuring the atmospheric pressure and the humidity, correction based on the refractive index of air is performed.

Assuming that the phase change that occurs when light is reflected on the surface of the block gauge is constant irrespective of the gauge, the phase change is corrected experimentally by making close contact with the base plate and comparing with a measured value. In experiments, the dimensions were 1.0
Several measurements were made on each of 1, 1.5, 8, 24.5 and 90 mm block gauges.

[0015]

[Effects] Table 1 shows a comparison between the measured values of the dimensions of the block gauge obtained by the measurement of the embodiment and the measured values of the NRLM-tsugami light wave interferometer (Michelson type interferometer). Than this,
The difference between the measured value and the NRLM-tsugami light wave interferometer is ± 0.0
It can be seen that it is within 3 μm.

In the alignment of the optical system, in the optical system in the embodiment, the counterclockwise optical path of L3 and the clockwise optical path must be parallel. If the angle between the two optical paths is δθ, the length of the measured block gauge is − (LBδθ ² ) / 8 by approximation to the second order of δθ.
Error occurs. When L3 and the reflected light from the block gauge are not parallel and the angle between the two optical paths is δψ, the approximation of δψ to the second order is (L3δψ ² ) /
4 errors occur.

In the optical system of the present invention, for the former, δθ is adjusted to about 7 × 10 ^-4 rad by adjusting the directions of the reflecting mirrors M1 and M2, and for the latter, δψ is adjusted by adjusting the direction of the block gauge. It can be about 10 ^-4 rad. Than this, if L3 measures the block gauge 100mm at ^{1m, - (LBδθ 2) /} 8 = -
An error of 5 × 10 ⁻⁹ m, (L3δψ ² ) / 4 = 3 × 10 ⁻⁹ m occurs. This value is sufficiently small as an error in the dimension measurement of a normal block gauge.

According to the experimental results of the embodiment, the difference between the measured value of the present invention and the measured value of the NRLM-tsugami interferometer is relatively large in a 90 mm block gauge. This is because the accuracy of the thermometer used for temperature correction in the embodiment was ± 0.0
It is about 3 ° C, which seems to be mainly due to it.
This may be improved by improving the adiabaticity and temperature measurement accuracy of the experimental device. With respect to the block gauge of 1.01 to 24.5 mm, the difference from the NRLM-tsugami interferometer is within ± 0.01 μm, which is very good agreement.

The optical system used in the embodiment of the present invention does not require close contact between the block gauge and the base plate, but requires twice the number of measurements as in the conventional interferometer. This can be a burden on the measurer and can also cause measurement errors. However, in recent years, with the spread of inexpensive and high-performance optoelectronic devices, the technology for automatically measuring interference fringes has also been advanced. The use of such a technique also eliminates the disadvantage of increasing the number of measurements. Further, since laser light can be used as observation light, it is possible to greatly improve the S / N ratio.

[0020]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical system used in the measurement method of the present invention.

FIG. 2 is a schematic view of a conventional interferometer for measuring a block gauge, which is used for an absolute measurement by a matching method.

FIG. 3 is an enlarged explanatory view of two special block gauge portions used in the conventional example shown in FIG. 2;

FIG. 4 is a diagram showing the relationship between interference fringes in the case of absolute measurement by a matching method in a conventional example.

[Explanation of symbols]

 LS light source HMR half mirror HM half mirror MR reference mirror W optical wedge SC screen BG block gauge M1, M2 reflection mirror C, D block gauge C1, D1 adhesion surface G1, G2 block gauge end surface

Claims (1)

(57) [Claims] 1. A light emitted from a light source LS is supplied to a block gauge B.
A half mirror HMR for splitting light toward G and a light toward the reference mirror MR via an optical wedge, a half mirror HM for splitting light again toward the block gauge, and the half mirror HM
LB = λ / 2 ｛N using two reflection mirrors M 1 and M 2 for directing the light divided by the above to both end faces of the block gauge, respectively.
+ (Ε3−ε1) + (ε3−ε2)｝ This is a measuring method for obtaining the block gauge length LB, where (ε3−ε1) and (ε3−ε2) are the light from the reference mirror MR and the block gauge. Measurement is performed by moving the interference fringes of the screen with the optical wedge W from the deviation of the interference fringes from the reflected light from the end face, and the length LB of the block gauge is measured using known N and λ. Non-contact light wave interferometry. Here, λ is the wavelength of the used light, N is an integer part of a quotient obtained by dividing the gauge dimension by λ / 2, and ε represents a fractional part thereof.