JPH1137711A - Length measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a length measuring instrument that can make efficient measurement by automatically calculating correction data required for accurate length measurement. SOLUTION: The length measuring instrument is provided with an interferential optical system equipped with a beam splitter 4, which splits a laser beam from a light source 2 into two laser beams, a fixed reflecting surface 6a and a moving reflecting surface 8a, which reflect the two laser beams toward the splitter 4. The instrument is also provided with a detector 10, which detects the interferential state of the interferential optical system, a correction data calculating system which automatically calculates correction data for measurement, and a moving amount calculator 12 which calculates the moving distance of the moving reflecting surface 3 based on the correction data and the detected value of the detector 10. The correction data calculating system is provided with a refractive index detector 16 which detects the refractive index of the air based on the detected value of an environment detector 14 and a dead path calculator, which automatically calculates the value of a dead path based on the variation of the wave number of interference fringes detected by means of the detector 10 and the refractive index of the air when the oscillation wavelength of the light source 2 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, various length measuring instruments, precision machine tools, semiconductor manufacturing equipment, and the like. The present invention relates to a length measuring device capable of performing the following.

[0002]

2. Description of the Related Art Conventionally, as a length measuring device of this type, as disclosed in Japanese Patent Application Laid-Open No. 6-123607, for example, based on correction data (for example, a dead path value) set in advance.
2. Description of the Related Art A length measuring device capable of accurately obtaining various length measuring data is known (see FIG. 2).

As shown in FIG. 2, in the conventional length measuring apparatus, a laser beam emitted from a light source (for example, a semiconductor laser) 2 is divided by a beam splitter 4 into a reference laser beam and a length measuring laser beam. .

At this time, the reference laser beam is applied to the fixed reflecting surface 6a of the fixed body 6 fixed to the length measuring device, while the length measuring laser beam moves along the optical axis of the length measuring laser beam. Irradiation is performed on the movable reflection surface 8a of the movable body 8 that can be used. The light source 2, the beam splitter 4, the fixed reflecting surface 6
a and the movable reflecting surface 8a constitute an interference optical system.

In this state, by moving the movable reflecting surface 8a, the reference laser light reflected from the fixed reflecting surface 6a and the length measuring laser light reflected from the movable reflecting surface 8a interfere with each other. Then, based on the wave number of the interference fringe generated at this time, the amount of change in the optical path difference generated when the moving reflection surface 8a is moved is detected by the detector 10, and the detected value, that is, the wave number M is calculated by the movement amount calculation. Is output to the container 12.

In this case, since the wave number M changes in accordance with the moving distance of the movable reflecting surface 8a, the moving distance of the movable reflecting surface 8a can be detected by counting the wave number M.

The optical path difference means a difference between an optical path length until the reference laser beam reaches the detector 10 and an optical path length until the length measuring laser beam reaches the detector 10. The environment detector 14 is configured to be able to detect the temperature, pressure, and humidity of air near the moving reflection surface 8a of the interference optical system.

[0008] The refractive index calculator 16 is provided with the environment detector 1.
4, the refractive index difference (n) between the reference refractive index (refractive index of vacuum: 1) and the refractive index under the measurement environment (refractive index of air: n) based on the temperature, pressure, and humidity of the air detected by -1) is calculated in advance, and the calculated value is output to the movement amount calculator 12 as correction data used in a correction process described later.

The movement amount calculator 12 calculates the difference in refractive index of air (n
-1) Based on the correction data such as the dead path value DS and the like, the actual moving distance of the moving reflecting surface 8a from which the moving error has been removed is calculated.

Specifically, when measuring the length, the moving reflection surface 8a
Are located at an initial reference position A that is separated from the beam splitter 4 by a distance L, and the fixed reflection surface 6a
Is fixed at a position separated by a distance L ₀ from the beam splitter, the dead path value DS is defined by the relationship DS = L−L ₀ .

In the prior art length measuring apparatus, the dead path value DS is measured in advance before the length measurement, and is input to the movement amount calculator 12 as correction data used for correction processing.
Now, the moving reflection surface 8a moves the distance L ₁ from the position A to the position B.
In this case, the wavelength of the laser light emitted from the light source 2 in vacuum is set to λ _0, and the moving reflection surface 8 a is set to “λ”.
_{When the} wave number M changes by “1” each time the light beam moves by “0/2”, the wavelength in the refractive index n becomes “λ ₀ / n”.

In this case, the moving error amount of the moving reflecting surface 8a based on the refractive index difference (n-1) of the air and the dead path value DS is (DS / λ ₀ ) × (n−1) × (λ ₀ / n). ) / 2 and it is possible to represent, by using the movement error amount as the correction data, actual travel distance L ₁ of the moving reflective surface 8a _{is, L 1 = M (λ 0} / 2n) - (DS / λ ₀ ) × (n−1) × (λ ₀ / n) / 2 = M (λ ₀ / 2n) − (DS / 2) × {1- (1 / n)}

[0013]

However, in the conventional length measuring device, it is necessary to input correction data necessary for the correction processing for obtaining the actual moving distance before the length measurement. That is, a troublesome initial setting such as setting a dead path value DS as correction data in advance before the length measurement and inputting the dead path value DS to the movement amount calculator 12 must be performed. For this reason, there is a problem that it takes time to start the length measurement.

In a system in which the dead path value changes each time the length measurement is performed, the dead path value DS is changed for each length measurement.
Must be set in advance, so that it takes time to start each length measurement, and there is a problem that it is difficult to perform the length measurement efficiently.

The present invention has been made in order to solve such a problem, and an object of the present invention is to automatically calculate correction data necessary for performing an accurate length measurement.
An object of the present invention is to provide a length measuring device capable of performing an efficient length measurement.

[0016]

In order to achieve such an object, a length measuring device according to the present invention comprises a dividing means for dividing light emitted from a light source into two lights, and a dividing means for dividing the light into two lights. A length measuring device comprising an interference optical system having a fixed reflecting means fixed at a fixed position and a movable reflecting means movable in a predetermined direction so as to reflect two lights toward the splitting means again. A detector that detects an interference state of the interference optical system, a correction data calculation system that automatically calculates correction data necessary for performing length measurement, and correction data calculated by the correction data calculation system and A moving amount calculator for calculating a moving distance of the moving reflecting means based on a detection value of the detector.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A length measuring apparatus according to one embodiment of the present invention will be described below with reference to FIG. In addition,
In the description of the present embodiment, the same components as those of the above-described related art (see FIG. 2) are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 1, a length measuring apparatus according to the present embodiment has an interference optical system (see FIG. 2) having the same configuration as the above-described conventional length measuring apparatus, and an interference state of the interference optical system. , A correction data calculation system for automatically calculating correction data required for length measurement, the correction data calculated by the correction data calculation system, and the detector 1
A movement amount calculator 12 for calculating the movement distance of the moving reflection surface 8a of the interference optical system based on the detected value of 0.

The correction data calculation system includes an environment detector 14 for detecting the temperature, pressure, and humidity of the air near the moving reflection surface 8a of the interference optical system, and the temperature, pressure, and air of the air detected by the environment detector 14. A refractive index detector 16 for detecting a refractive index of air under a length measuring environment based on humidity, and a wave number of an interference fringe detected by the detector 10 when the oscillation wavelength of the light source 2 of the interference optical system is changed. A correction data calculating means is provided for automatically calculating correction data necessary for length measurement based on the amount of change in M and the refractive index of air detected by the refractive index detector 16.

The correction data calculating means automatically calculates a dead path value indicating a difference between the optical path length from the beam splitter 4 to the fixed reflecting surface 6a and the optical path length from the beam splitter 4 to the moving reflecting surface 8a. Dead path calculator 1
8 are provided.

Specifically, when measuring the length, the moving reflection surface 8a
Are located at an initial reference position A that is separated from the beam splitter 4 by a distance L, and the fixed reflection surface 6a
Is fixed at a position separated by a distance L ₀ from the beam splitter, the dead path value DS is defined by the relationship DS = L−L ₀ .

Next, the length measuring operation for measuring the moving distance of the moving reflecting surface 8a will be described. In this measurement operation, the case of moving the moving reflective surface 8a positioned at the initial reference position A at a distance L ₁ by a position spaced B.

First, the operation of calculating the dead path value DS automatically performed at the time of length measurement will be described. At the time of length measurement, in a state where the movable reflecting surface 8a is positioned at the initial reference position A, based on the temperature, pressure and humidity of the air detected by the environment detector 14, the refractive index detector 16 is used.
Detects the refractive index n of air under the length measurement environment.

The refractive index n of the air is determined by the refractive index detector 16.
Is detected, the dead path calculator 18 changes the oscillation wavelength of the light source 2 of the interference optical system. Specifically, the oscillation wavelength of the light source 2 is swept by continuously changing the injection current injected into, for example, a semiconductor laser provided in the light source 2 (for example, continuously changing over ± 1 mA). In this case, the oscillation wavelength of the light source (semiconductor laser) 2 is
Since the oscillation wavelength changes in proportion to the injection current, when the oscillation wavelength is changed by a certain amount, the injection current may be changed by a certain amount.

While such wavelength sweep is performed electrically, the refractive index n of air changes according to changes in temperature, pressure and humidity of air. Therefore, the time required for the wavelength sweep is very short as compared with the change time of the refractive index n of air. Therefore, it is considered that the refractive index n of the air during the wavelength sweep does not always change stably.

The refractive index n of the air is input to the dead path calculator 18 together with the change amount ΔP of the wave number M of the interference fringe detected by the detector 10 from the start of the sweep to the end of the sweep.

Here, an operation in which the dead path calculator 18 automatically calculates the dead path value DS based on the relationship between the variation ΔP and the wavelength sweep will be described. Even if the refractive index n of air is always constant, if the oscillation wavelength is changed by a fixed amount Δλ, the wave number M of the interference fringe detected by the detector 10 changes correspondingly.

Specifically, when the wavelength of the laser light emitted from the light source 2 in vacuum is λ ₀ , the wave number Pb of the laser light included in the dead path value DS is changed to Pb before changing the oscillation wavelength. = DS × (2n / λ ₀ ).

When the oscillation wavelength is changed by Δλ, the wave number Pa of the laser beam included in the dead path value DS is Pa = DS × {2n / (λ ₀ + Δλ)}.

Therefore, from the start of the sweep to the end of the sweep, the variation ΔP of the wave number M of the interference fringes detected by the detector 10 is as follows: ΔP = Pa−Pb = DS × 2n × [｛1 / (λ ₀ + Δλ)｝ − (1 / λ ₀ )] = DS × 2n × (−Δλ) / {λ ₀ × (λ ₀ + Δλ)}.

Therefore, the dead path value DS is given by: DS = (− ΔP / 2n) × {λ ₀ × (λ ₀ + Δλ)} /
Δλ is calculated.

Next, based on the dead path value DS automatically calculated by the dead path calculator 18 and the refractive index n of the air detected by the refractive index detector 16, the moving amount calculator 12 calculates the moving reflection surface 8a. The operation for calculating the moving distance of the camera will be described.

Now, when the movable reflecting surface 8a is moved from the initial reference position A to the position B by a distance L ₁ ,
The dead path value DS as correction data is automatically input from the dead path calculator 18 to the movement amount calculator 12.

Further, the refractive index calculator 16 includes the environment detector 1
4, the refractive index difference (n) between the reference refractive index (refractive index of vacuum: 1) and the refractive index under the measurement environment (refractive index of air: n) based on the temperature, pressure, and humidity of the air detected by -1) is calculated in advance, and the calculated value is output to the movement amount calculator 12 as correction data used in a correction process described later.

The movement amount calculator 12 calculates the difference in the refractive index of air (n
-1) Based on the correction data such as the dead path value DS and the like, the actual moving distance of the moving reflecting surface 8a from which the moving error has been removed is calculated.

[0036] More specifically, when the moving reflective surface 8a is moved to the position B from the position A, by the detector 10, the detected value corresponding to the moving distance L ₁ i.e. wavenumber M is detected, the detected value i.e. wavenumber M is input to the movement amount calculator 12.

In this case, the wavelength of the laser light emitted from the light source 2 in vacuum is λ ₀ , and the movable reflection surface 8 a is “λ ₀
When the wave number M changes by “1” each time the light beam moves by “/ 2”, the wavelength in the refractive index n becomes “λ ₀ / n”.

In the moving amount calculator 12, the moving error amount of the moving reflecting surface 8a based on the refractive index difference (n-1) of the air and the dead path value DS is expressed as (DS / λ ₀ ) × (n-1). × (λ ₀ / n) / 2, and by using this movement error amount as correction data, the actual movement distance L _{1 of the} movement reflection surface 8a is calculated.
L ₁ = M (λ ₀ / 2n) − (DS / λ ₀ ) × (n−1) × (λ ₀ / n) / 2 = M (λ ₀ / 2n) − (DS / 2) × ｛ 1− (1 / n)｝.

As described above, according to the present embodiment, it is possible to automatically calculate correction data necessary for performing accurate length measurement at the time of length measurement, thereby enabling efficient length measurement. It is possible to provide a simple length measuring device.

The present invention is not limited to the above-described embodiment, but can be variously modified without adding new matters. For example, when the refractive index of the air is detected by the refractive index detector 16, the humidity of the air in the vicinity of the moving reflection surface 8a does not necessarily have to be considered because the influence on the change in the refractive index of the air is small.

For example, every time the movable reflecting surface 8a is positioned at the initial reference position A, a reset signal for resetting the detection value of the detector 10, ie, the wave number M, is output to the detector 10, and the output timing of this reset signal is Synchronously, the dead path calculator 18 calculates the dead path value D as described above.
A series of operations for calculating S may be automatically started. In this case, since the operation of calculating the dead path value DS is performed in synchronization with the output timing of the reset signal, the latest dead path value DS can be automatically calculated for each length measurement.

[0042]

According to the present invention, by automatically calculating correction data necessary for performing accurate length measurement,
A length measuring device capable of performing efficient length measurement can be provided.

[Brief description of the drawings]

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

FIG. 2 is a diagram schematically showing a configuration of a conventional length measuring device.

[Explanation of symbols]

 Reference Signs List 2 light source 4 beam splitter 6a fixed reflecting surface 8a moving reflecting surface 10 detector 12 moving amount calculator 14 environment detector 16 refractive index detector 18 dead path calculator

Claims (3)

[Claims] 1. A splitting means for splitting light emitted from a light source into two lights, and fixed at a fixed position so that the two lights split by the splitting means are reflected again toward the splitting means. What is claimed is: 1. A length measuring apparatus comprising an interference optical system having a fixed reflecting unit and a moving reflecting unit movable in a predetermined direction, comprising: a detector for detecting an interference state of the interference optical system; A correction data calculation system for automatically calculating the correction data, and a movement amount calculation for calculating a movement distance of the movement reflection means based on the correction data calculated by the correction data calculation system and a detection value of the detector. A length measuring device comprising a measuring device. 2. The correction data calculation system according to claim 1, wherein said environment detector detects at least a temperature and a pressure of the air in the vicinity of said moving reflection means, and based on the detection value of said environment detector, Refractive index detector for detecting the refractive index, the interference state detected by the detector when changing the oscillation wavelength of the light source of the interference optical system and the refractive index of the air detected by the refractive index detector 2. The length measuring apparatus according to claim 1, further comprising: a correction data calculating unit that automatically calculates correction data necessary for performing the length measurement based on the length measurement. 3. The correction data calculating means automatically calculates a dead path value indicating a difference between an optical path length from the dividing means to the fixed reflecting means and an optical path length from the dividing means to the moving reflecting means. 3. The length measuring apparatus according to claim 2, further comprising a dead path calculator for calculating the dead path.