JPH06341809A - Mechelson interferometer - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a Michelson interferometer that can reduce the burden on a measurer and can measure the dimension of a piece to be measured with high accuracy without individual differences. [Structure] Base plate 1 in one optical path divided into two
In the Michelson type interferometer in which the block gauge BG having 1 and the optical wedge 9 are inserted, BG is present on the focal plane of the interference fringe.
Interference having a first light receiving point at a position corresponding to the interference fringes from the base plate and a second light receiving point at a position corresponding to the interference fringes from the base plate 11, and converting the light amount at each light receiving point into an electric amount. A fringe light amount photometric means is provided. The amount of light at each light receiving point is obtained as a function of the amount of movement of the optical wedge 9, the phase angle of each interference fringe is obtained based on this function, and the fractional value b of the interference fringe is calculated from this phase angle.
/ A is calculated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a Michelson interferometer. For example, the present invention relates to a Michelson-type interferometer that can measure the dimensions of a piece to be measured such as a block gauge with high accuracy without individual differences.

[0002]

BACKGROUND ART For example, as a measuring device for measuring the dimensions of a block gauge, a block gauge whose base plate is closely attached to a lower surface is inserted into one optical path of a Michelson interferometer, and the light reflected by the block gauge and the base plate is reflected. Is most widely used for measuring the size of the block gauge from the fractional value of the interference fringes, which interferes with the light from the other optical path.

Therefore, a conventional Michelson interferometer will be described with reference to FIG. In the figure, the light emitted from the He—Ne laser light source 1 passes through the optical isolator 2 and the lens 3 and is focused on the pinhole 4. After that, the beam is expanded by a beam expanding lens 5 into parallel rays of a size necessary for block gauge measurement, and then is deflected by 90 ° by a reflecting mirror 6, and is split into two by a beam splitter 7 into reflected light and transmitted light. . The reflected light is directed to the reference mirror 8, where it is reflected and returns to the beam splitter 7. The transmitted light passes through the optical wedge 9 toward the block gauge BG.

The optical wedge 9 is moved in a direction orthogonal to the transmitted light by the turning operation of the micrometer 10, and the movement amount can be read from the scale of the micrometer 10. The block gauge BG is set on a rotary table 12 which can be manually rotated in a state where a base plate 11 (a kind of reflecting mirror) is closely attached to the lower surface thereof. Although not shown, a plurality of block gauges BG can be set on the rotary table 12 at predetermined angles.

The light perpendicularly incident on the upper surface of the block gauge BG and the upper surface of the base plate 11 is reflected and transmitted through the optical wedge 9 again, and then reaches the beam splitter 7, where it returns from the reference mirror 8. Interferes with light. An observation telescope lens 13, a beam splitter 14, an autocollimation target 15, a pinhole 16 and an eyepiece 17 are provided in the observation optical system portion of the interference light.

Therefore, in the measurement, the base plate 11 is brought into close contact with the lower surface of the block gauge BG to be measured, and in this state, the base plate 11 is set downward and set at a predetermined position on the rotary table 12, and then the observation optical system is set. When observed through the eyepiece 17, interference fringes as shown in FIG. 8 are observed. Therefore, the fractional value b / a of the interference fringes of the block gauge BG and the interference fringes of the base plate 11
Is read, and the dimension of the block gauge BG is obtained from the fractional value b / a and an arithmetic expression based on the following measurement principle.

Therefore, the measurement principle of a block gauge using a Michelson interferometer will be described. When the measurement principle is mathematically expressed, it can be expressed by the following equation. L ₀ + ΔL ₀ + L ₀ αt = (λν / 2n) (N + b / a) (1) However, in the above formula (1), L ₀ : Nominal dimension of block gauge ΔL ₀ ; Manufacturing error of block gauge α Linear expansion coefficient of block gauge t; temperature difference of block gauge from 20 ° C. λν; vacuum wavelength of interference light n; air refractive index of interference optical path N; integer part of interference fringes b / a; fractional part of interference fringes is there.

This is as shown in FIG.₀Nominal size of
Method ΔL₀There is a manufacturing error of ₀thermal expansion of αt
The block gauge BG in the open state with a scale of λν / 2n
When the scale is measured, the integer part of the scale scale is N
Meaning that the fractional value (fractional part) of the unit and scale is b / a
is doing.

In the above equation (1), the nominal dimension L ₀ , the linear expansion coefficient α, and the vacuum wavelength λν of the interference light are known in advance. In the case of Brockeck gauge GB,
It is known that the manufacturing error is very small, and the value of the manufacturing error ΔL ₀ is about 1/4 of the wavelength (≈0.15 μm) in the preliminary measurement before performing the interference measurement. The value of the temperature difference t from 20 ° C. is also actually measured with a resolution of about 0.001 ° C., for example.

The value of the air refractive index n is calculated by measuring atmospheric pressure, temperature and humidity and assuming carbon dioxide concentration, and calculating Δn / n≈
It can be determined with an accuracy of 3 to 5 × 10 ^-8 . Therefore, since the value of the integer part N of the interference fringes does not have a primary error, the manufacturing error ΔL ₀ can be calculated from the equation (1) by calculating the fractional value b / a of the interference fringes. That is, it is understood that obtaining the fractional value b / a of the interference fringe is most important in the measurement of the block gauge BG.

Conventionally, in measuring a block gauge, the fractional value b / a of interference fringes is obtained by the following method. B) When the optical wedge 9 is moved by rotating the micrometer 10 while observing the interference fringes through the eyepiece 17, the interference fringes are moved in parallel in the direction of arrow A in FIG. 8 as a group. Therefore, by this operation, as shown in FIG. 10 (A), the center of any interference fringe a ₀ of the block gauge BG is aligned with the reticle line of the eyepiece 17, and the value of the scale of the micrometer 10 at that time is set to the zero point. To do. (B) Next, as shown in FIG. 10 (B), the center of the interference fringe b ₀ of the base plate 11 adjacent to the interference fringe a ₀ is set to the eyepiece 1
Align the reticle line 7 and the micrometer 1 at that time
Read the value b on the 0 scale. C) Next, as shown in FIG. 10C, the center of the interference fringe a ₁ of the block gauge BG adjacent to the interference fringe a ₀ is set to the eyepiece 1
Align the reticle line 7 and the micrometer 1 at that time
Read the value a on the 0 scale. D) Finally, from the read values b and a, the fractional value b of the interference fringe
/ A is calculated.

[0012]

The conventional measurement has the following drawbacks. While the observer observes the interference fringes through the eyepiece 17, the center of the interference fringes is sequentially aligned with the reticle line of the eyepiece 17, and the scale value ba of the micrometer 10 at that time is read. When measuring with the reticle line or when reading the scale of the micrometer 10, individual differences easily occur depending on the measurer. Since the measurer must observe dark interference fringes through the eyepiece 17 and is obliged to make a close observation such as when adjusting to the reticle line, eye fatigue is great and it is not suitable for long-time measurement. Since the measurer faces the interferometer and works, the internal air temperature rises due to the influence of the human body heat source (100 to 150 W), and the influence also appears on the block gauge BG after 15 to 30 minutes. As a result, an error in the refractive index correction value and an error in the thermal expansion correction value are likely to occur.

The object of the present invention is to eliminate all such drawbacks of the prior art, reduce the burden on the measurer, and measure the dimensions of the piece to be measured with high accuracy and without individual differences. It is to provide a Michelson-type interferometer capable of performing the above.

[0014]

Therefore, according to the Michelson interferometer of the present invention, a piece to be measured, in which a base plate is closely attached, is inserted into the optical path of one of the two parallel light rays, and the measured piece is measured. The fractional value of the interference fringes is obtained by moving the interference fringes by moving the optical wedge inserted in one of the optical paths while causing the light reflected by the one and the base plate to interfere with the other light divided into two. In a Michelson interferometer for obtaining the dimension of a piece to be measured based on a fractional value, a first light receiving point arranged at a position corresponding to an interference fringe from the piece to be measured on a focal plane of the interference fringe, An interference fringes light quantity photometering means is provided which has a second light receiving point arranged at a position corresponding to the interference fringes from the base plate on the focal plane of the interference fringes and converts the light quantity at each light receiving point into an electric quantity. At the same time, the calculating means is provided for obtaining the electric quantity based on the light quantity at each light receiving point of the interference fringe light quantity photometric means as a function of the moving amount of the optical wedge, and calculating the fractional value of the interference fringe based on this function. , Is characterized.

Further, the interference fringes light quantity photometric means is provided with an optical fiber having one end corresponding to each of the light receiving points, and light energy introduced into the optical fiber at a position distant from each of the light receiving points. And an optical sensor for converting into electric quantity.

[0016]

The piece to be measured, in which the base plate is in close contact, is inserted into the optical path of one of the two split parallel light rays, and the light reflected by the piece to be measured and the base plate interferes with the other half of the split light. Now, if the light intensity distribution of the interference fringes is measured with a physical quantity using the movement amount of the optical wedge as a parameter, it can be theoretically and experimentally approximated by a Sanui or Kosanui curve. That is, it can be approximated by the following equation.

Y = A cos (2πx / L + φ) + B (2) However, in the above formula (2), y: brightness of interference fringes A; amplitude of interference fringe brightness L; 1 fringe of interference fringes The amount of movement of the optical wedge necessary for movement x; the amount of movement of the optical wedge φ; the phase angle of the interference fringes B; the brightness bias.

In order to uniquely determine the above equation (2), it is necessary to obtain four constants A, L, φ and B. To do this, the movement amount x of the optical wedge is changed to x _1, x _2, x _3, x ₄ and the brightness y of the interference fringe corresponding to each x _1, x _2, x _3, x ₄ is changed.
_{If 1,} y _2, y _3, y ₄ are measured and the solution of the simultaneous equations is obtained, the four constants A, L, φ, B can be obtained. Therefore, if the phase angle φ ₁ of the interference fringes from the piece to be measured and the phase angle φ ₂ (or φ ₃ ) of the interference fringes from the base plate are obtained, the fractional value b / of the interference fringes is calculated from φ ₂ −φ ₁ / 2π. a can be obtained.

In the present invention, the moving amount x of the optical wedge is set to x _1, x _2,
Since it can be obtained by converting the light quantity at the first and second light receiving points into an electric quantity when changing to x _3, x ₄ , the electric quantity based on the light quantity obtained at each light receiving point and the optical wedge. Phase angle φ ₁ of the interference fringe from the measured piece and the phase angle φ ₂ (or φ ₃ ) of the interference fringe from the base plate based on the function of
Then, the fractional value b / a of the interference fringe is calculated from these phase angles φ ₁ and φ ₂ (or φ ₃ ).

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the Michelson interferometer according to the present invention will be described in detail below with reference to the drawings.
In the following description of the drawings, the same components as those in FIG. 7 described above will be designated by the same reference numerals, and the description thereof will be omitted or simplified. FIG. 1 shows the optical system of this embodiment. In the optical system of the present embodiment, the linear drive device 21 that automatically linearly moves the optical wedge 9, the length measurement unit 28 that measures the amount of movement, and the rotary drive device that automatically rotationally drives the rotary table 12. 31 and an interference fringe light amount photometric system 41 are newly added.

As shown in FIG. 2, the linear drive device 21 includes a base 22 and a feed screw shaft 23 rotatably supported by the base 22 at a right angle to the transmitted light.
Optical wedge moving motor 24 for rotating the feed screw shaft 23
A slider 26 which is movably guided to the base 22 via a bearing 25 in the same direction as the axial direction of the feed screw shaft 23 and has a base end portion screwed into the feed screw shaft 23; and a tip end of the slider 26. And a holding plate 27 that holds the optical wedge 9 inside.
In the present embodiment, when the optical wedge 9 is moved by 1 mm, the refractive index and the wedge angle of the optical wedge 9 are determined so that the interference fringes move in parallel by one stripe. Also, the length measurement unit 2
8 can detect the amount of movement of the holding plate 27, that is, the amount of movement of the optical wedge 9, mechanically, optically or electrically, and can output the detected value as an electric signal.

The rotary drive device 31 has a table drive motor 32, a rotary shaft 33 rotated by the table drive motor 32, a worm 34 fixed to the tip of the rotary shaft 33, and a mesh with the worm 34. The worm wheel 36 is fixed to the rotary shaft 35 of the rotary table 12. The table drive motor 32 of the rotary drive device 31 and the optical wedge movement motor 24 of the linear drive device 21 are mounted outside the optical chamber 18 whose outer wall is made of a material containing a heat insulating material.

The interference fringes light amount photometric system 41 is an optical path switching mirror 42 that is insertable into the optical path between the observing telephoto lens 13 and the beam splitter 14 and is retractable from the optical path, and this optical path switching mirror 42. Three optical fibers 43 for introducing the interference light whose optical path is switched by 42
_1, 43 _{2 and} 43 ₃ are included. Each end face of each of the optical fibers 43 _1, 43 _2, 43 ₃ is arranged corresponding to three light receiving points arranged in a straight line at equal intervals on the focal plane of the interference fringes. That is, as shown in FIG. 3, the central light receiving point J ₁ is arranged at a position corresponding to the interference fringe from the block gauge BG, and the two light receiving points J _2, J outside thereof are provided.
Reference numeral ₃ is provided at a position corresponding to interference fringes from the left and right sides of the base plate 11.

The optical energy introduced into each of the optical fibers 43 _1, 43 _2, 43 ₃ is, as shown in FIG. 4, optical sensors 44 _1, 44 _2, 44 provided at positions apart from the light receiving point.
Converted to electricity by ₃ and then the optical power meter 4
5 _1, 45 _2, 45 ₃ after being read by the W units by, is sent to the data processing unit 51 as an arithmetic unit through a cable 50 (such as a personal computer.). Here, these optical power meters 45 _1, 4
5 _2, 45 _3, the optical sensor 44 _1, 44 _2, 44 ₃ and the interference fringe light intensity measuring system 41, an interference fringe light intensity measuring means 46 is formed. Further, the information on the moving amount of the optical wedge 9 measured by the length measuring unit 28 is also converted into a digital amount and then sent to the data arithmetic processing unit 51 through the cable 50.

In addition to the above, in the data processing unit 51, the temperature information of the block gauge BG detected by the temperature sensor 56 attached to the side surface of the block gauge BG and the atmospheric pressure information detected by the atmospheric pressure sensor 57 are also stored. Humidity information detected by the humidity sensor 58 is sent through the hygrometer 55 while being sent through the thermometer 53, the barometer 54, and the digital voltmeter 52.

The data processing unit 51 controls the drive of the motors 24, 32 via the motor drive circuits 24A, 32A, and at the same time, information on the amount of movement of the optical wedge 9 from the length measuring unit 28 and the optical power. Meter 45
The fractional value b / a of the interference fringes is calculated based on the information on the brightness of the interference fringes from _1, 45 _2, 45 ₃ . The x _1, x _2, x _3, x ₄ are sent from the length measuring unit 28, and the y _1, y _2, y _3, y ₄ are sent from the optical power meters 45 _1, 45 _2, 45 ₃ respectively. Therefore, the data processing unit 51 calculates the equation (2) based on these pieces of information, and calculates the phase angle φ ₁ of the interference fringes from the block gauge BG and the base plate 11
The phase angles φ _{2 and} φ ₃ of the interference fringes from the left and right sides of are obtained. FIG. 5 shows the relationship between the phase angles φ ₁ , φ _{2, and} φ ₃ of each interference fringe.

By the way, the three optical fibers 43 _1, 432 _,
Although 43 ₃ are arranged on a straight line, the direction of the interference fringes may be inclined with respect to this straight line as shown in FIG. This is due to the inclination of the reference mirror 8 and the rotary table 12 due to the fact that the direction of the wedge angle of the equal thickness interference deviates from the originally correct direction. Therefore, the data processing device 5
1 is obtained by taking the average value of φ ₂ and φ ₃ as φ _4.
4 is used as the phase angle of the base plate 11 in the calculation, and the value of b / a is determined from (φ ₄ −φ ₁ ) / 2π = b / a (3).

Next, the data processing unit 51 uses the b / a
The equation (1) is calculated using the value of. First, the temperature information from the temperature sensor 56, the atmospheric pressure information from the atmospheric pressure sensor 57, and the humidity information from the humidity sensor 58 are sent to the data processing unit 51, respectively, and in advance,
Since the carbon dioxide concentration information has been input, the air refractive index n is calculated from these information.

Subsequently, the nominal dimension L ₀ of the block gauge BG to be measured and the manufacturing error ΔL ₀ ′ obtained by preliminary measurement are input to the data processing unit 51. Then, the data arithmetic processing unit 51 has already known the linear expansion coefficient α, the temperature difference t, the vacuum wavelength λν of the interference light, and the air refractive index n. Therefore, the integer part N of the interference fringe is determined based on these data. To do. Finally, by substituting the value of b / a obtained from the measurement result into the equation (1), the manufacturing error ΔL of the block gauge BG.
_Ask for ₀ .

Therefore, according to this embodiment, the first light receiving point J ₁ arranged at the position corresponding to the interference fringe from the block gauge BG on the focal plane of the interference fringe and the base plate on the focal plane of the interference fringe. An interference fringe light quantity photometric means 46 is provided which has _{second and third} light receiving points J _{2 and} J ₃ arranged at positions corresponding to the interference fringes from 11, and converts the light quantity at each light receiving point into an electric quantity. At the same time, the light quantity at each light receiving point of the interference fringe light quantity photometric means 46 is obtained as a function of the movement amount of the optical wedge 9, and the fractional value b / a of the interference fringe is calculated based on this function. It is possible to eliminate all the disadvantages of.

That is, the light quantity of the interference fringes from the block gauge BG and the interference fringes from the base plate 11 is converted into an electric quantity, and the electric quantity is obtained as a function of the moving amount of the optical wedge 9. Based on this function, each interference is obtained. The phase angles φ ₁ , φ ₂ , φ ₃ of the stripes are calculated, and the fractional value b / a is calculated based on the phase angles φ ₁ , φ ₂ , φ ₃ , that is, all measurement processing is performed by the measurer. Since it can be automatically performed without relying on it, there is no individual difference depending on the measurer, and the burden on the measurer (eye fatigue) can be reduced. Therefore, there is no problem even in long-time measurement. Moreover, since there is no influence of the human body heat source, the error in the refractive index correction value and the error in the thermal expansion correction value can be eliminated.

The interference fringe light quantity photometric means 46 has optical fibers 43 _1, 4 arranged at one end corresponding to each of the light receiving points.
3 _2, 43 ₃ and optical sensors 44 _1, 44 _2, 44 provided at positions distant from the respective light receiving points and converting the light energy introduced into the optical fibers 43 _1, 43 _2, 43 ₃ into an electric quantity. _Since it is configured to include ₃ and ₃ , the accuracy can be further improved.
That is, since the optical sensors 44 _1, 44 _{2, and} 44 ₃ can be arranged at positions apart from the respective light receiving points by the optical fibers 43 _1, 43 _{2, and} 43 ₃ , the optical sensors 44 _1, 44 _{2, and} 44 ₃ heating sources can be separated to thermally safe distance, it is possible to eliminate the influence of heat generated from the light sensor 44 _1, 44 _2, a preamplifier incorporated in the 44 _3.

A linear driving device 2 including a motor 24 for automatically moving the optical wedge 9 in a direction perpendicular to the transmitted light.
1, the rotary drive device 31 including the motor 32 for automatically rotating the rotary table 12 is provided, so that all the drives can be remotely controlled. Therefore, also from this point, the influence of the human body heat source can be eliminated. Moreover,
As for the motors 24 and 32 of the respective drive devices 21 and 31,
Since it is attached to the outside of the optical chamber 18 formed of a heat insulating material, it is possible to eliminate the influence of heat generation from the motors 24 and 32.

In the above embodiment, from the above equation (2),
When determining the phase angle φ, let x be x_1,x _2,x_3,x_FourAnd change
Each x_1,x_2,x_3,x_FourCorresponding to y_1,y_2,y_3,y
_FourThe phase is calculated by measuring and solving the simultaneous equations.
The angle φ was determined, but noise, fluctuations, and
Due to movement, etc., with one calculated value of φ from the above 4 data,
There is a risk of large error. So, for example,
B) Provide 8x32 = 32 light receiving points in one cycle of the curve
If φ is determined by the average value of the
You can Regarding the number of light receiving points, 8 is 4
Or may be 10 and limited to 8
Not a thing. The point is that accuracy is improved by the averaging effect.
It should be possible.

In the above embodiment, the equation (2) is used as the basis.
, The phase angle φ of the interference fringes from the block gauge BG₁And
Phase angle of interference fringes from the left and right sides of the base plate 11
φ_2,φ₃, And φ₂And φ₃And the average value of φ
_FourAnd obtain this φ_FourAnd φ ₁And the fractional value b of the interference fringe
/ A was decided, but from the base plate 11
For the phase angle of the interference fringe of₂Or φ₃One of
Only one may be used. For example, φ₂If only φ₂-Φ
₁The fractional value b / a of the interference fringes may be determined from / 2π.

Further, in the above embodiment, the block gauge B
Although an example of measuring the dimension of G has been described, the present invention
The present invention is not limited to this, and can be applied to all measured pieces whose dimensions are to be measured with high accuracy.

[0037]

As described above, according to the Michelson interferometer of the present invention, the burden on the measurer can be reduced, and the dimension of the piece to be measured can be measured with high accuracy without individual differences. It has the effect that

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system showing an embodiment of the present invention.

FIG. 2 is a diagram showing a linear drive device and a length measurement unit in the same embodiment.

FIG. 3 is a diagram showing light receiving points in the above embodiment.

FIG. 4 is a block diagram showing an electrical system in the embodiment.

FIG. 5 is a diagram showing phase angles of the interference fringes from the block gauge and the interference fringes from the base plate in the same example.

FIG. 6 is a diagram showing a state in which the directions of interference fringes are inclined.

FIG. 7 is a schematic diagram showing a conventional Michelson interferometer.

8 is a diagram showing a state of interference fringes observed by the interferometer of FIG.

FIG. 9 is a diagram showing a relationship among nominal dimensions of a block gauge, manufacturing errors, and thermal expansion.

FIG. 10 is a diagram showing a method for measuring the phase angle of interference fringes in a conventional Michelson interferometer.

[Explanation of symbols]

7 Beam splitter 9 Optical wedge 11 Base plate 43 _1, 43 _2, 43 ₃ Optical fiber 44 _1, 44 _2, 44 ₃ Optical sensor 46 Interference fringe light quantity photometric means 51 Data arithmetic processing unit (arithmetic means) BG block gauge (measured piece) )

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuya Narumi 1-20-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Mitsutoyo Co., Ltd.

Claims (2)

[Claims] 1. A measurement piece having a base plate in close contact is inserted into the optical path of one of the two split parallel light beams, and the light reflected by the measurement piece and the base plate interferes with the other split light. In addition, the fractional value of the interference fringe is obtained while moving the interference fringe by moving the optical wedge inserted in one of the optical paths, and the dimension of the measured piece is obtained based on this fractional value Michelson interferometry In the apparatus, a first light receiving point arranged at a position corresponding to an interference fringe from the measured piece on the focal plane of the interference fringe, and a position corresponding to the interference fringe from the base plate on the focal plane of the interference fringe. An interference fringe light quantity photometric means for converting the light quantity at each light reception point into an electric quantity is provided, and an electric quantity based on the light quantity at each light reception point of the interference fringe light quantity photometric means is provided. amount The determined as a function of the amount of movement of the optical wedge, a calculating means for calculating the fractional values of interference fringes based on this function is provided, Michelson-type interferometric measuring device, characterized in that. 2. The Michelson interferometer according to claim 1, wherein the interference fringes light quantity photometric means is an optical fiber having one end arranged corresponding to each of the light receiving points, and is separated from each of the light receiving points. A Michelson interferometer, comprising: an optical sensor provided at a position for converting the light energy introduced into the optical fiber into an electric quantity.