JPH10221020A - Length measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a length measuring system in which measuring precision is not influenced by air fluctuation. SOLUTION: An interferometer 4 is put as the position relation of a mirror 2 fixed on a moving object A is in accordance with Abbe's principle. An ultrasonic (b) transmitting and receiving device 5 is put adjacent to the interferometer 4. A wave processor 6 detects a time (t) when an ultrasonic wave (b) goes and comes back between the device 5 and the mirror 2, and a correction device 11 environmentally corrects wavelength of a laser beam a1 by output of sensors 8, 9, 10. After a processor 12 calculates the approximate value L' of the displacement amount of the moving object A by making the half value of the wavelength which the correction device 11 corrects one scale, the average absolute temperature TAVE of the atmosphere is calculated by the approximate value L' and the time (t) when a waveform processor 6 detects. The wavelength of the laser beam a1 is environmentally corrected again by means of the average absolute temperature TAVE of the atmosphere as Edlen type temperature parameter. Finally, the processor 12 calculates the normal displacement amount of the moving object A by making the half value of the wavelength in which it environmentally corrects a scale.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-precision positioning technology, and more particularly, to a laser length measuring system for measuring the amount of displacement of a moving object which is symmetrical in control.

[0002]

2. Description of the Related Art A laser interferometer capable of measuring a very high resolution of sub-nm is often used as a detection element of a positioning control system such as an XY stage of a super precision device such as a stepper used in semiconductor manufacturing. Used.

Hereinafter, an outline of a basic configuration of a length measuring system including the interferometer (hereinafter, referred to as a conventional length measuring system) will be described with reference to FIG.

After passing through a mirror interferometer 101, a laser beam 100a emitted from a laser oscillator 100 illuminates a mirror 102 mounted on a moving body A (for example, an XY table or the like) which is control-symmetric. The laser beam 100a reflected by the mirror 102 enters the mirror interferometer 101, and forms interference fringes with the reference beam (original laser beam). The output of the receiver 103 for detecting the intensity of the interference fringe is sinusoidal every time the moving body A moves by a distance corresponding to a half wavelength (λa / 2) of the laser light 100a along the optical path of the laser light 100a. To fluctuate. Therefore, the processing device 104
Counts the fluctuation of the output value of the receiver 103 every period. In some cases, the output of the receiver 103 is electrically divided in order to further improve the resolution.

On the other hand, in order to perform in-process measurement of environmental parameters T, P, and F required for calculating the refractive index n of the atmosphere, a temperature T in the atmosphere is detected near the optical path of the laser beam 100a. A temperature sensor 105, a barometric pressure sensor 106 for detecting atmospheric power P, and a humidity sensor 107 for detecting atmospheric humidity H are provided.

The correcting device 108 first calculates the refractive index n of the atmosphere from the following Edren's equation (1) using the environmental parameters T, P, and H detected by these sensors 105, 106, and 107. calculate.

[0007]

(Equation 1)

Subsequently, the correction device 108 uses the calculated refractive index n of the atmosphere and the following equation (2) to calculate the wavelength value λv (6.33) of the laser beam 100a in a vacuum.
nm), the laser beam 10 in the atmosphere can be corrected.
The wavelength value λa is 0a. Then, the wavelength value λa of the laser beam 100a in the atmosphere is input to the processing device 104.

Λa = λv / n (2) When the processing unit 104 receives the input of the wavelength value λa of the laser beam 100a, the processing unit 104 displaces the moving body A using the half value λa / 2 of the wavelength value as one scale. Calculate the quantity ΔL. Specifically, as the displacement amount ΔL of the moving body A, a distance corresponding to a scale corresponding to the count of output fluctuations of the receiver 103 is calculated. Thereafter, the calculation result ΔL is displayed on the display unit 104a, and is fed back as a main feedback signal to a servo amplifier (not shown) of the driving device of the moving body A.

[0010] Only by the configuration shown here, about ±
It is possible to realize a measurement accuracy of about 1.4 ppm (accurately, an accuracy of about ± 1.4 μm per 1 m of the measurement distance). However, if a compensator called a wavelength tracker is separately provided, about ± 0 ppm can be obtained. It is known that the measurement accuracy can be improved to about .14 ppm.

[0011]

In an actual measurement environment, there are few cases where the environmental parameters T, P, and H are uniformly distributed on the optical path of the laser beam 100a. Especially,
Due to the structure, a heat source (such as a motor for driving the moving body A) from near the optical path of the laser beam a cannot be removed, and the temperature unevenness T as shown in FIG.
₁ , T ₂ and T ₃ (however, T ₀ ≠ T ₁ ≠ T ₂ ≠ T ₃ ) occur very often. As a result, the refractive index distribution on the optical path of the laser beam a becomes non-uniform, that is, n ₀ {n ₁ }
Since n ₂ ≠ n ₃ , the wavelengths λ ₀ , λ ₁ ,
λ ₂ and λ ₃ usually cause aperiodic fluctuations as shown in FIG.

Since the temperature irregularities T ₁ , T ₂ and T ₃ change with time, the laser beam a
Also, the refractive index distribution on the optical path of the moving object A changes moment by moment, and even if the moving object A is stationary, it is as if the moving object A
As a result, a phenomenon in which the output value of the receiver 103 fluctuates minutely and randomly appears. The time-dependent state change of air that causes such a phenomenon is generally called air fluctuation. Depending on the stability of the state of the measurement environment, this air turbulence is sometimes sub-μm
Since there are cases where fluctuations reaching the order are given to the measurement values, they are considered to be a non-negligible error factor in an ultra-precision positioning control system that requires strict measurement accuracy of the detection element.

However, in the conventional length measuring system, the temperature T ₃ of the local space 300a detected by the temperature sensor 105 is used as the environmental parameter T indicating the temperature over the entire optical path of the laser beam 100a. As is clear from the above, the existence of the temperature variations T ₁ , T ₂ , and T ₃ on the optical path of the laser beam 100a is completely ignored. That is, no consideration is given to the correction of the measurement error caused by the air fluctuation. Therefore, in the conventional length measuring system, the measurement accuracy of the displacement ΔL of the moving object is naturally directly affected by the air fluctuation.

Accordingly, an object of the present invention is to provide a length measuring system in which measurement accuracy is not affected by air fluctuations in a measurement environment.

[0015]

In order to solve the above-mentioned problems, the present invention provides a laser light source for irradiating a laser beam having a known wavelength toward a measurement surface, a reference light and a laser reflected by the measurement surface. An interferometer that forms an interference fringe with light, and a processing device that calculates a distance according to a change in intensity of the interference fringe formed by the interferometer using a wavelength value of the laser light as a reference value. A system, comprising: an average temperature detecting unit that detects an average temperature of an atmosphere interposed between the laser light source and the measurement surface; a humidity detecting unit that detects a humidity of the atmosphere; and a pressure of the atmosphere. Pressure detection means,
The average temperature of the atmosphere detected by the average temperature detection means, the humidity of the atmosphere detected by the humidity detection means,
Using the pressure of the atmosphere detected by the pressure detecting means, in accordance with a predetermined known correction function, to environmentally correct a known wavelength value of the laser beam, and to use the processing apparatus as a reference value. And a length measuring system comprising:

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, the basic configuration of the length measuring system according to the present embodiment will be described with reference to FIG. 1 as an example in which the amount of displacement of the moving body A in the X direction is detected.

The displacement measuring surface A ₁ of the moving body A is
The reflector 2 is attached by the fixture 3. And
The interferometer 4, which is a displacement sensor, is arranged so that the positional relationship with the reflecting mirror 2 follows Abbe's principle. The laser beam a emitted from the laser oscillator 1 enters the interferometer 4 and is split by an internal beam splitter in two directions toward a reflecting mirror 2 and a reference mirror (not shown). Then, one laser beam a ₁ directed to the reflecting mirror 2 is reflected by the reflecting mirror 2, re-enters the interferometer 4, and interferes with the other laser beam reflected by the reference mirror (not shown). To form The intensity K of this interference fringe is detected by the receiver 7 in real time. Therefore, each time the moving body A moves in the X direction by a distance corresponding to a half wavelength (λ / 2) of the laser beam a ₁ , the output of the receiver 7 fluctuates sinusoidally.

In the vicinity of the interferometer 4, various sensors 8, 9, 10 (in the present embodiment, absolute sensors of the atmosphere) for in-process measuring environmental parameters required for calculating the refractive index n of the atmosphere. A temperature sensor 8 for detecting the temperature T, a pressure sensor 9 for detecting the atmospheric pressure P, and a humidity sensor 10) for detecting the humidity H of the atmosphere are provided.

Further, next to the interferometer 4, an ultrasonic pulse b is transmitted toward the front reflecting mirror 2 in accordance with a control signal of a waveform processing device 6 to be described later, and its echo is received. A transmitter / receiver 5 is arranged. The reason why the interferometer 4 and the transducer 5 are adjacent to each other is that the optical path of the laser beam a ₁ emitted from the interferometer 4 and directed to the reflecting mirror 2 and the direction from the transducer 5 to the reflecting mirror 2 This is to make the path of the ultrasonic pulse b as close as possible.

Then, the processing unit 13 calculates the displacement ΔL of the moving body A based on the outputs of the detection elements 5, 7, 8, 9, and 10 described above. In order to execute an arithmetic process (to be described later) for this, the processing unit 13 includes a laser wavelength correction device 11 that calculates the wavelength λ of the laser beam in the atmosphere from the outputs T, P, and H of the sensors 8, 9, and 10. And the time t required for the ultrasonic pulse b from the output of the transducer 5 to reciprocate between the transducer 5 and the reflector 2 (hereinafter referred to as the reciprocating propagation time t of the ultrasonic pulse b). Processing device 6 that calculates
And a processing unit 12 for calculating the displacement amount ΔL of the moving body A from the output K of the laser wavelength correction device 11 and the output t of the waveform processing device 6. Hereinafter, the arithmetic processing performed by each of the devices 6, 11, and 12 of the processing unit 13 will be described along the flow of the entire measurement processing. However, in a ROM (not shown) of the laser wavelength correction device 11, a wavelength value λv (6.33 nm in the present embodiment) of the laser light a emitted from the laser oscillator 1 in a vacuum is stored in advance. Shall be. In addition, the formulas required for the following calculations are also:
It is assumed that the information is stored in the ROM of the laser wavelength correction device 11 in advance. Further, a distance L ₀ from the initial position of the reflecting mirror 2 to the interferometer 4 is stored in a ROMO (not shown) of the processing device 12.
It is assumed that the wavelength value λv of the laser beam a emitted from the laser oscillator 1 in a vacuum is stored in advance. In addition, other mathematical expressions required for the following calculations are also stored in the processing device 1 in advance.
2 is stored in the ROM.

The laser wavelength compensator 11 includes the sensors 8,
Environmental parameters T, P, 9 and 10 measured in process
First, using H, the refractive index n of the atmosphere is calculated from the experimental equation (1) of Edren described in the section of the related art. Subsequently, the refractive index n of the atmosphere and the equation (2) described in the section of the related art are used.
Is used to calculate the wavelength value λ of the laser beam a in the atmosphere by environmentally correcting the wavelength value λv of the laser beam a in the vacuum. Then, the wavelength value λ of the laser beam a in the atmosphere
Is input to the processing device 12. In addition, 3 used here
The pressure parameter P and the humidity parameter H of the three environmental parameters T, P, H are also input to the processing device 12.

On the other hand, the waveform processing device 6 periodically transmits the ultrasonic pulse b to the transmitter / receiver 5 to receive the reciprocating propagation time t of the ultrasonic pulse b in real time. Specifically, the time t from when the transmitter / receiver 5 transmits the ultrasonic pulse b toward the reflecting mirror 2 to when the echo is received is counted. Then, the round-trip propagation time t of the ultrasonic pulse b is sequentially input to the processing device 12.

In the meantime, the processing device 12 counts the output fluctuation of the receiver 7 for each cycle. Then, the wavelength value λ of the laser beam a _{1 in} the atmosphere from the laser wavelength correction device 11
When an input such as the above is received, first, the approximate value ΔL ′ of the displacement amount of the moving body A is calculated using the half-wavelength value λ / 2 of the laser beam a _{1 in} the atmosphere as one scale. Specifically, the receiver 7
Distance ΔL 'corresponding to the scale of the output fluctuation count value
Is calculated. Then, by adding this approximate value ΔL ′ to the distance L ₀ from the initial position of the reflecting mirror 2 to the interferometer 4, an approximate value L ′ of the distance from the current position of the reflecting mirror 2 to the interferometer 4 is calculated. I do. Further, when the input of the round-trip propagation time t of the ultrasonic pulse b is received from the waveform processing device 6, the round-trip propagation time t of the ultrasonic pulse b and the approximate value of the distance from the current position of the reflecting mirror 2 to the interferometer 4 are obtained. Using L ′, the following equation (3)
, The average absolute temperature T _Ave on the reciprocating path of the ultrasonic pulse b between the reflecting mirror 2 and the transducer 5 is calculated. That is, based on data input in real time from the laser wavelength correction device 11 and the waveform processing device 6, the average absolute temperature T on the reciprocating path of the ultrasonic pulse b between the reflecting mirror 2 and the transducer 5 is determined. Calculate _Av .

T _Ave = (2 × L ′ / (20.067 × t)) 2 (3) This equation (3) is derived according to the following process.

The propagation speed C of the ultrasonic wave in the air changes depending on the absolute temperature T of the air, the pressure P of the air, and the water vapor tension. If these values are limited to values near a normal state, the following formula is approximated. be able to.

C ≒ 20.067 × √T The propagation speed C of the ultrasonic wave in the air can be expressed by the following equation using the ultrasonic wave propagation distance L and the propagation time t.

C = 2 × L / t Therefore, if the parameter C is eliminated from the two equations representing the propagation velocity C of the ultrasonic wave in the air, the above-mentioned equation (3) can be obtained.
Can be led.

In this embodiment, since the exact distance from the reflector 2 to the interferometer 4 is unknown, the average value of the atmosphere is calculated using the approximate value L 'of the distance from the reflector 2 to the interferometer 4. While calculating the absolute temperature T _{a ve,} measurement error included in the approximate value L 'is the measurement error of the conventional measurement system (measurement long distance 1
(approximately ± 1.4 μm per m), the approximate value L ′ of the accurate distance from the reflecting mirror 2 to the interferometer 4 is used, and the atmospheric air calculated by Expression (3) is used. No extreme error occurs in the average absolute temperature T _Ave.

As described above, since the optical path of the laser beam a ₁ emitted from the interferometer 4 and the path of the ultrasonic pulse b transmitted from the transducer 5 are as close as possible, Ultrasonic pulse b between the reflector 2 and the transducer 5
Average absolute temperature T _A of the round-trip path can be assumed to remain unchanged almost the temperature distribution of the reciprocating optical path of the laser beam a ₁ between the interferometer 4 and the reflecting mirror 2. Under this assumption,
The average absolute temperature T _Ave on the reciprocating path of the ultrasonic pulse b between the transmitter / receiver 5 and the reflecting mirror 2 is calculated as the average absolute temperature on the reciprocating optical path of the laser beam a ₁ between the interferometer 4 and the reflecting mirror 2. It can be considered as temperature. Therefore, the processing device 12 calculates the average absolute temperature T _Ave calculated by the equation (3) as the temperature parameter T
, The average refractive index n _Ave on the reciprocating optical path of the laser beam a ₁ between the interferometer 4 and the reflecting mirror 2 is calculated from the empirical formula (1) described in the section of the related art. Note that the other two parameters P, H
Is input from the laser wavelength correction device 11 together with the wavelength value λ of the laser beam a ₁ in the atmosphere.

Subsequently, the processing unit 12 calculates the equation (2) described in the section of the prior art, the average refractive index n _Ave on the reciprocating optical path of the laser beam a ₁ between the interferometer 4 and the reflecting mirror 2, and Is used to environmentally correct the wavelength value λv of the laser beam a in a vacuum so that the laser beam a reciprocating between the interferometer 4 and the reflecting mirror 2 is corrected.
The average wavelength value λ _Ave of ₁ is calculated. If the average wavelength value λ _Ave of the laser beam a ₁ continues to fluctuate, at this stage,
The output fluctuation count value of the receiver 7 is corrected in accordance with the fluctuation rate of the average wavelength value λ _Ave of the laser beam a ₁ . Thereby, the count value corresponding to the output fluctuation of the receiver 7 due to the air fluctuation can be removed.

Thereafter, the processing device 12 uses the half value λ _Ave / 2 of the average wavelength value λ _Ave of the laser light a ₁ as a new scale, and uses the half value λ _Ave / 2 as a new scale, the distance corresponding to the scale corresponding to the count value of the output fluctuation of the receiver 7. Calculate ΔL. In the present embodiment,
This distance ΔL is used as a displacement amount of the moving body A as the display unit 12a.
Although only displayed above, the main feedback signal may be fed back to a servo amplifier (not shown) of the driving device of the moving body A in some cases.

As described above, according to the length measuring system, since the count value corresponding to the output fluctuation of the receiver 7 due to the air fluctuation is removed, the measurement error due to the air fluctuation does not appear. Further, instead of using the temperature (refractive index) of the local space on the optical path of the laser beam a ₁ , the laser beam a ₁ is produced using the average absolute temperature (average refractive index) over the entire optical path of the laser beam a _{1. Since} the wavelength of ₁ is environmentally corrected, the laser light a ₁
The measurement error caused by the uneven temperature (non-uniform refractive index distribution) generated on the optical path can be greatly reduced. Specifically, special measures to prevent air fluctuations (for example, providing a fan that blows air on the optical path of laser light, etc.)
It has already been confirmed by simulation and the like that the measurement accuracy of at least about ± 0.10 ppm can be achieved without performing the measurement. This value is used as the measurement accuracy (about ± 1.4 pp) of the conventional length measuring system under the same use condition.
Comparing with m), it is clear that the new adoption of the environmental correction of the laser wavelength using the average average refractive index of the atmosphere has achieved a significant elimination of measurement errors caused by air fluctuations in the measurement environment. Will be recognized.

It is needless to say that the measurement accuracy can be further improved by separately providing a wavelength tracker.

In this embodiment, the average temperature T _Ave on the optical path of the laser beam is calculated from the round-trip propagation time t of the ultrasonic pulse.
Is calculated, but this is not necessarily required. For example, if an ultrasonic transmitter and a receiver are separately arranged to detect a phase difference between transmitted and received signals, the average temperature T _Ave on the optical path of the laser beam can be obtained from the phase difference. Can also be calculated. With such a configuration, the frequency of the ultrasonic wave affects the resolution of the measurement, but practically no problem occurs if the use conditions and the like are limited.

Further, in the present embodiment, the interferometer 4 is calculated from the current position of the reflecting mirror 2 by using the count value of the output fluctuation of the receiver 7 and the wavelength value of the laser light whose environment has been corrected by the laser wavelength correcting device 11. The approximate value L 'of the distance to the interferometer 4 is calculated. However, if there is a simple measuring means capable of measuring the approximate distance from the current position of the reflecting mirror 2 to the interferometer 4 at the same level, Alternatively, it can be used.

Here, lastly, the reason why the ultrasonic pulse b is employed to detect the average temperature T _Ave on the optical path of the laser beam a ₁ in the present embodiment will be described.

The first reason is that according to the current technology, the repetition period of the ultrasonic pulse b can be set to the order of msec or less, so that the average absolute temperature of the atmosphere is about 1K.
It is possible to measure with a response of about Hz. That is, according to the present technology, it is possible to sufficiently cope with the detection of the fluctuation of the average absolute temperature of the atmosphere (about 1 KHz) due to the air fluctuation.

The second reason is that, according to the present technology, the average absolute temperature of the atmosphere can be detected with a resolution enough to enable effective environmental correction.

A conventional length measuring system (measuring accuracy of about ± 1.4)
If the measurement error of (ppm) is due to air fluctuations alone, this is approximately ± 1.5% of the mean absolute temperature of the atmosphere.
This corresponds to a change of about K. Therefore, in order to perform effective environmental correction, it is necessary to detect the average absolute temperature of the atmosphere with at least a resolution of about 0.1K.

On the other hand, according to the table shown in FIG. 4, when the average temperature of the atmosphere fluctuates by about ± 0.1 K near normal temperature, the unit distance
The time t ₀ during which the ultrasonic pulse b propagates back and forth between (1 m) is
It can be seen that it changes by about ± 1.00 μsec. Therefore, in order to detect the average absolute temperature of the atmosphere with a resolution of about 0.1 K, it is necessary to detect the round trip propagation time of the ultrasonic pulse with a resolution of about 1.00 μsec.

However, at present, a technique for detecting the propagation time of ultrasonic waves in the atmosphere with a resolution of the order of 0.1 μsec has already been established. Therefore, according to the present technology, it is sufficiently possible to detect the average absolute temperature of the atmosphere with the resolution required in the present embodiment.

The third reason is that the sensitivity of the reciprocating propagation time of the ultrasonic pulse b to the variation of the absolute temperature of the atmosphere is extremely high, so that the average absolute temperature T _{Ave of the} atmosphere caused by air fluctuations.
Can be accurately calculated.

The reciprocating propagation time t of the ultrasonic pulse b depends not only on the fluctuation of the absolute average temperature of the atmosphere due to the air fluctuation, but also on the fluctuation of the propagation distance of the ultrasonic pulse b due to the vibration of the moving body A and the like. fluctuate. Therefore, the moving object A is included in the average absolute temperature T _{Ave of the} atmosphere calculated by Expression (3).
There is a high possibility that an error due to a change in the propagation distance of the ultrasonic pulse b due to vibrations of the subject is included.

However, considering that the measurement accuracy of the conventional length measuring system is about ± 1.4 ppm, the fluctuation of the propagation distance of the ultrasonic pulse b due to the vibration of the moving body A, etc. It is only about ± 1.4 ppm. That is, the time t during which the ultrasonic pulse b propagates back and forth between the unit distances
_{At 0} , only a small fluctuation of about ± 8.2 nsec appears.

On the other hand, when the average temperature of the atmosphere fluctuates by about ± 0.1 K near normal temperature, the time t ₀ during which the ultrasonic pulse b propagates back and forth between the unit distances (1 m) is about ± 1.00 μs.
As described above, a variation that reaches ec appears.

As described above, the fluctuation of the propagation distance of the ultrasonic pulse b due to the vibration of the moving body A or the like hardly causes an error in the average absolute temperature T _Ave of the atmosphere calculated by the equation (3). . Therefore, it is possible to accurately calculate the fluctuation of the average absolute temperature T _Ave of the atmosphere due to the air fluctuation.

[0048]

According to the length measuring system of the present invention, the displacement of the moving body can be measured with high accuracy without being affected by the fluctuation of the air in the measuring environment.

Therefore, when the heat source (for example, a motor or the like) that causes air fluctuations cannot be removed from the vicinity of the optical path of the laser beam due to the structure, a particularly advantageous effect is exhibited. You can expect.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a length measuring system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a basic configuration of a conventional length measuring system.

FIG. 3A is a conceptual diagram of air fluctuation, and FIG.
FIG. 7 is a diagram for explaining wavelength fluctuation of laser light due to air fluctuation.

FIG. 4 is a table showing the relationship between the propagation speed and propagation time of ultrasonic waves and the temperature of the atmosphere.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser oscillator 2 ... Reflecting mirror 3 ... Fixture 4 ... Interferometer 5 ... Transceiver 6 ... Waveform processing device 7 ... Receiver 8 ... Temperature sensor 9 ... Barometric pressure sensor 10 ... Humidity sensor 11 ... Laser wavelength correction device 12 ... Processing Device 13 ... Processing unit

Claims (3)

[Claims] 1. A laser light source for irradiating a laser beam having a known wavelength toward a measurement surface, an interferometer for forming an interference fringe between a reference beam and the laser beam reflected on the measurement surface, and A processing device that calculates a distance in accordance with a change in the intensity of the interference fringes formed by the interferometer using a wavelength value as a reference value, wherein a distance between the laser light source and the measurement surface is provided. Average temperature detecting means for detecting the average temperature of the intervening atmosphere; humidity detecting means for detecting the humidity of the atmosphere; pressure detecting means for detecting the pressure of the atmosphere; and the temperature of the atmosphere detected by the average temperature detecting means. Average temperature, and the humidity of the atmosphere detected by the humidity detecting means,
Using the pressure of the atmosphere detected by the pressure detecting means, in accordance with a predetermined known correction function, to environmentally correct a known wavelength value of the laser beam, and to use the processing apparatus as a reference value. And a length measuring system comprising: 2. A laser light source for irradiating a laser beam having a known wavelength toward a measurement surface, an interferometer for forming interference fringes between reference light and the laser beam reflected by the measurement surface, and A processing device for calculating a distance corresponding to a change in the intensity of the interference fringes formed by the interferometer using a wavelength value as a reference value, wherein the measurement surface is measured from a position near the laser light source. Toward
Along with transmitting an ultrasonic wave propagating in an atmosphere interposed between the laser light source and the measurement surface along an optical path of the laser light emitted from the laser light source, an echo of the ultrasonic wave from the measurement surface A transmitter / receiver for receiving the ultrasonic wave, as a reciprocating propagation time in which the ultrasonic wave reciprocates in the atmosphere, from the time the transmitter / receiver transmits the ultrasonic wave until the reflected wave of the ultrasonic wave is received Reciprocating propagation time detecting means for detecting the time of the laser light; a humidity sensor disposed at a position near the optical path of the laser light, and detecting the humidity of the atmosphere at the position; and a humidity sensor disposed at a position near the optical path of the laser light. A pressure sensor that detects the pressure of the atmosphere at the position, a rough distance measuring unit that measures a rough distance from the laser light source to the measurement surface, a round-trip propagation time detected by the round-trip propagation time detecting unit,
Using the approximate distance measured by the approximate distance measuring means,
Average temperature calculating means for calculating an average temperature of the atmosphere, an average temperature of the atmosphere calculated by the average temperature calculating means, a humidity of the atmosphere detected by the humidity sensor, and a temperature of the atmosphere detected by the pressure sensor. Using pressure and
A length measuring system comprising: a first environment correction unit configured to environmentally correct a wavelength value of the laser light used as a reference value by the processing device according to a predetermined known correction function. 3. A length measuring system according to claim 2, wherein said approximate distance measuring means is disposed at a position near an optical path of said laser beam, and detects a temperature of said atmosphere at said position. The temperature of the atmosphere detected by the temperature sensor, the humidity of the atmosphere detected by the humidity sensor, and the pressure of the atmosphere detected by the pressure sensor, according to a predetermined known correction function, Second environment correction means for environmentally correcting the wavelength value of the laser light, and as the approximate distance, the interference fringes formed by the interferometer with the wavelength value of the laser light environment corrected by the second environment correction means as a reference value A length measuring system comprising: a calculating unit that calculates a distance according to a change in intensity.