JP3977078B2 - Interfering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an interference length measuring device that detects a change in the position of an object without contact.
[0002]
[Prior art]
FIG. 5 shows a schematic diagram of an interferometer using a semiconductor laser as a conventional light source. The laser light beam 20 emitted from the semiconductor laser 1a is converted into parallel light by the collimator lens 2a, enters the polarization beam splitter 4, and is divided into measurement light 20a and 20b. The light beam 20 a passes through the ¼λ plate 5 b, becomes a condensed light beam by the condenser lens 6, and is condensed by the object 7 to be measured. On the other hand, the light beam 20b reflected by the polarization beam splitter 4 passes through the ¼λ plate 5a as reference light and is reflected by the reference mirror 8. The light beams reflected by the DUT 7 and the reference mirror 8 are again transmitted through the 1 / 4λ plate, and then the reference light is transmitted. The measurement light is reflected and becomes a combined light beam 21 and enters the 1 / 4λ plate 5c. . Since the light beam 21 is modulated only in the polarization information of the return light of the measurement light, the light beam that has passed through the ¼λ plate 5c becomes rotating linearly polarized light. Thereafter, the light beam enters the non-polarizing beam splitter 10 and is split into light beams 22 and 23. Thereafter, when the light beams pass through the polarizing plates 11a and 11b inclined by 45 degrees with respect to each other, sinusoidal signals having different phases by 90 degrees as shown in FIG. 6 (hereinafter referred to as A phase signal and B phase signal). It is detected by the sensors 12a and 12b. Since the direction of polarization of the light beam 21 is rotated by the displacement of the object to be measured, a sine signal of one cycle is obtained at λ / 2 according to the displacement of the object to be measured.
[0003]
[Problems to be solved by the invention]
The displacement meter using interference as shown in the conventional example measures, for example, a rotating shaft manufactured by machining . When laser light is irradiated on the scattering portion, a speckle pattern is generated due to the presence of light beams of various phases in the reflected light. The speckle pattern is a granular pattern of light, but when the speckle pattern and reference light interfere with each other, the interference signal of each speckle has a random phase, so the interference light signal on the sensor is averaged, so-called dropout It becomes a state. The A-phase B-phase sine wave signal from the sensor is calculated as a displacement based on the A-phase signal, the count value obtained by counting the B-phase signal with a counter, and the phase information of the A-phase B-phase. In other words, since the counter value required for calculating displacement information is not updated at the time of dropout, if the object to be detected is displaced more than the counter working distance when the signal is restored, an error is generated. In the rotating body, dropouts occur in the same part every week, and the shaft behavior is largely the same as the shaft shake synchronized with the rotation, so the shaft shows almost the same behavior at the time of dropout. Therefore, the error at the dropout every week is accumulated and deviates infinitely. As described above, the measurement of the rotating body has a problem that errors accumulate infinitely.
[0004]
[Means for Solving the Problems]
Interferometer as one aspect of the present invention, a multi-mode semiconductor laser light source, one of the light beam to divide the light beam into two light beams the multimode semiconductor laser light source is emitted by irradiating the reference mirror and the other light beam to the mobile A first light beam splitting unit that irradiates; a second light beam splitting unit that splits an interference light beam obtained by combining the reflected light beam from the reference mirror and the reflected light beam from the moving body into a plurality of light beams; and interferometer met and a light receiving means for receiving the respective light fluxes divided by said second beam splitting means, provided in said interference light beam optical path, a specific wavelength of the interference light beams obtained by the combined of the band-pass filter for guiding the light receiving element to extract only the light beam, the multi-mode semiconductor laser light the light beam from the light source to the first beam splitter And multi-mode fiber that, to have a.
An interferometer according to another aspect of the present invention includes a super luminescence diode and a light beam emitted from the super luminescence diode, which is divided into two light beams, which irradiates one of the light beams to a reference mirror and uses the other light beam as a moving body. A first light beam splitting unit that irradiates; a second light beam splitting unit that splits an interference light beam obtained by combining the reflected light beam from the reference mirror and the reflected light beam from the moving body into a plurality of light beams; and interferometer met and a light receiving means for receiving the respective light fluxes divided by said second beam splitting means, provided in said interference light beam optical path, a specific wavelength of the interference light beams obtained by the combined to be extracted only a light beam have a band-pass filter for guiding the light receiving element.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration of a small interferometer using a semiconductor laser according to an embodiment of the present invention. In the figure, the same reference numerals are given to the same members as in the conventional example.
[0006]
The laser beam 20a emitted from the multimode semiconductor laser 1a having the center wavelength λ becomes a condensed beam by the lens 2a, is guided to the multimode fiber 30, passes through the multimode fiber 30, and then enters the lens 2b. The light beam 20a is converted into a parallel light beam by the lens 2b, separated into a P wave and an S wave by the polarization beam splitter 3b, and one of the light beams becomes a reference light beam 21, which is transmitted through the ¼λ wavelength plate 5a and reflected by the reflection mirror 4. On the other hand, the light beam that has passed through the polarization beam splitter 3 b passes through the ¼λ wavelength plate 5 b as the measurement light beam 22, and becomes a condensed light beam by the condenser lens 6 and is irradiated onto the object 7 to be examined. At this time, the measurement light 22 is focused on the reflection surface 7 of the object to be examined. The light beam 22 reflected by the reflecting surface 7 passes through the original optical path again after being reflected and is reflected by the beam splitter 3b. On the other hand, the reference light beam 21 passes through the original optical path after reflection and then passes through the beam splitter 3b and is combined with the measurement light to become a light beam 23. Thereafter, the light beam 23 enters the non-polarizing beam splitter 8, and the reflected light becomes the light beam 24 and the transmitted light becomes the light beam 25.
[0007]
At this time, if the power of the condensing lens 6 is set so that the converging point of the light beam 22 becomes equal to the reflection surface 6 on which the reference light beam 21 is reflected and a wave optical equivalent optical path length, a low coherency light source is used. Demonstrates the maximum effect as an interferometer. In other words, considering the wavefront, the reflected light from the reflecting surface 7 of the object to be measured and the returning light from the reflecting surface 4 as the reference light are both combined as parallel light at the position of the contrast where the interference signal is maximum. Therefore, the maximum signal can be obtained in the photoelectric sensor that is configured later.
[0008]
The light beam 24 by passing through the band-pass filter 13a that transmits only wavelengths of lambda _1, to extract only the lambda ₁ information. The light beam having the wavelength λ ₁ becomes linearly polarized light by passing through the ¼λ plate 9 a, and the polarization direction of the polarization information is rotated based on the displacement of the test object 7. The rotating linearly polarized light beam 24 is split by the non-polarizing beam splitter 10a, the transmitted light is transmitted through the polarizing plate 11a, and the reflected light is transmitted through the polarizing plate 11b to be a light / dark signal, which is received by the photoelectric sensors 12a and 12b, respectively. the output signal Te is the electrical signal of the sine wave of one cycle with respect to 1/2 [lambda] ₁ moves along with the movement of the inspected object. The wave plates 12a and 12b are respectively installed with the polarization axes inclined by 45 degrees, and the sine signals from the photoelectric sensors 12a and 12b are signals having phases different from each other by 90 degrees (hereinafter, A phase and B phase. On the other hand, the non-polarizing beam splitter 8 light beam 25 that has passed through the extracts only the _second information lambda by passing through the band-pass filter 13b which passes only the wavelength of lambda _2. Thereafter transmitted through the 1 / 4.lamda plate 13b, similarly to the light beam 24 unpolarized light beam after being divided into two sections by splitter 10b, and enters the polarizing plate 11c, 11d and transmitted photoelectric sensor 12c, respectively, to 12d. 1 cycle with respect to this case, the electrical signal moves as 1/2 [lambda] ₂ to the movement of the object to be detected 11c and 11d are also installed with their polarization axes inclined by 45 degrees, so that the signs of the 90-degree phases of the A and B phases are also different. The No.. Performs where description of lambda ₁ and lambda ₂ to be extracted in FIG.
[0009]
Since the light source 1a is a multimode semiconductor laser, the wavelength spectrum has a width of about 3 nm with λ as the center as a collection of narrow spectral lines. By passing a multimode fiber having a dispersion effect as the light source light, the spectrum of the multimode laser, which is an assembly of emission line spectra, is converted into a gentle spectrum of Gaussian distribution as shown in FIG . By passing the interference light of this light beam through the filter 13a of the transmission spectrum λ1, only the interference information of the wavelength λ1 is extracted to be a light beam 24. Only the interference information of wavelength λ2 is extracted from the light beam 25 by the filter 13b having the transmission spectrum λ2. A light beam with a multi-mode laser as a light source passes through the multi-mode fiber so that a light beam with a dispersed spectrum can be obtained. And, it is known that extracting a specific emission line spectrum through a band-pass filter will yield a characteristic light beam close to a single mode laser. In this embodiment, interference can be obtained by using the same specific wavelength extraction method. It has succeeded in extending the interference distance as a total. Moreover, since the light source is a multimode laser, it is possible to perform stable measurement without being affected by noise due to mode hopping.
[0010]
For example, when measuring a φ4 mm shaft having a 20 μm shaft deflection and having a scratch of 0.5 mm width or a surface defect, when a signal dropout occurs due to a scratch of 0.5 mm width, The signal is lost at 25 portion. This means that there is a possibility of displacement of about 2 μm at the time of dropout. In other words, if a signal that does not have the same phase of the sine signal obtained from the two wavelengths λ ₁ λ _{2 in} the measurement range of 4 μm is output, even if dropout occurs, measurement is performed again with the correct value when recovered from dropout. You can start.
[0011]
That is, in the displacement meter of the present invention, if λ ₁ and λ ₂ are set so that the phases of the sine signals obtained from the light having the wavelengths of λ ₁ and λ _{2 in} the range of 4 μm in width are not overlapped, that is, λ ₁ × { If λ ₁ ÷ (λ ₂ −λ ₁ )} / 2 ≧ 4 μm, highly accurate rotation axis measurement can be easily performed. In the embodiment of the present invention, since two wavelengths are extracted from the spectral width of the multimode laser light, two adjacent wavelengths can be extracted.
[0012]
Specifically, when λ ₁ = 649 nm and λ ₂ = 651 nm, the outputs from the sensors 12a and 12b are sine wave signals of 649/2 = 324.5 nm. The outputs from the sensors 12c and 12d are 651/2 = 325.5 nm. Since both sine signals have the same phase about ± 105 μm ahead, the above equation is sufficiently satisfied, and it can be seen that a correct position signal can be output even if the signal is restored after dropout.
[0013]
Furthermore, if the temperature of the light source is adjusted by a Peltier element or the like, interference signals that can obtain stable wavelengths λ ₁ and λ ₂ can be maintained at the same level. Furthermore, if the signal levels of the photoelectric sensors 11a, 11b, 11c, and 11d are monitored and feedback is made to the Peltier elements so that the transmitted light amounts of the bandpass filters 13a and 13b are equal, stable wavelengths λ ₁ and λ ₂ can be obtained. Interference signals can be stabilized at the same level.
[0014]
The same effect can be obtained even if the light source is an SLED (super luminescence diode).
[0015]
Moreover, the same effect can be obtained even if the interference film filter is a filter using a fiber grating. Regarding the demultiplexing, the wavelength is extracted by a non-polarizing beam splitter and a band pass filter in this embodiment, but light having a wavelength of λ ₁ λ ₂ is similarly obtained using a well-known AWG (Arrayed Wave Guide). Can be extracted.
[0016]
【The invention's effect】
As described above, the interferometer proposed by the present invention uses a low-coherency light source as a light source, divides a light beam into two light beams in a light transmission member, and uses one light beam (measurement light beam) as an optical head. Irradiate with a fixed reference mirror, irradiate the object to be moved or displaced with the other light beam, combine the reflected light beams in the transmitting member to obtain an interference light beam, and only a specific wavelength light A configuration is adopted in which light of a specific wavelength is extracted by a wavelength selection filter through which light is transmitted and detected by a light receiving element. By adopting this configuration, a multimode semiconductor laser can be used as the light source, so light source means that are not affected by noise caused by so-called mode hops can be used, and even if a dropout occurs due to scratches on the measurement surface, etc. An interferometer that can output a correct position at the time of revival can be realized. Further, by extracting a specific emission line spectrum through a wavelength selection filter, a measurement light beam having characteristics close to that of a single mode laser can be obtained, and the interference distance as an interferometer can be greatly extended. Further, by controlling the temperature of the light source, a plurality of wavelengths can always be output at the same level.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an interferometer of an example embodiment according to the present invention. FIG. 2 is a schematic diagram showing an output signal of the interferometer of the example embodiment according to the present invention. Fig. 4 is a diagram illustrating the emission wavelength spectrum of the light source used. Fig. 4 is a transmission characteristic diagram of a bandpass filter used in the interferometer of the embodiment according to the present invention. Fig. 5 is a schematic diagram of a conventional interferometer. Schematic diagram showing the output signal of the interferometer of the [Sign Explanation]
DESCRIPTION OF SYMBOLS 1a Semiconductor laser 2a, 2b Collimator lens 3b, 4 Polarization beam splitters 5a, 5b, 5c, 9a, 9b 1/4 (lambda) board 6 Condensing lens 7 Measured object 8, 10, 10a, 10b Non-polarization beam splitters 11a, 11b 11c, 11d Polarizing plates 12a, 12b, 12c, 12d Photoelectric sensors 20a, 20b, 20, 21, 22, 23, 24, 25 Luminous flux 30 Multimode fiber

Claims (5)

And a multimode semiconductor laser light source, a first light beam splitting means for irradiating one of the light beam to divide the light beam into two light beams the multimode semiconductor laser light source is emitted by irradiating the reference mirror and the other light beam to the mobile, the A second light beam splitting unit that splits an interference light beam obtained by combining the reflected light beam from the reference mirror and the reflected light beam from the moving body into a plurality of light beams and the second light beam splitting unit. each of the light flux met interferometer and a light receiving means for receiving,
A bandpass filter provided in the interference light beam path, for extracting only the light beam having a specific wavelength from the interference light beam obtained by combining and guiding the light beam to the light receiving element;
Interference device which have a a multi-mode fiber for guiding the light beam from the multimode semiconductor laser light source into the first beam splitter. A superluminescent diode, and a first beam splitter for irradiating one of the light beam to divide the light beam into two beams said superluminescent diode is emitted by irradiating the reference mirror and the other light beam to the mobile, from the reference mirror A second light beam splitting unit that splits an interference light beam obtained by combining the reflected light beam and the reflected light beam from the moving body into a plurality of light beams; and the respective light beams split by the second light beam splitting unit. met interferometer and a light receiving means for receiving,
The provided interference light beam light path, the multiplexed interferometric device which have a band-pass filter for guiding the light receiving element to extract only the light beam of a specific wavelength of the interference light beams obtained. Interference device according to claim 1, characterized in that a light source temperature control means to said multi-mode semiconductor laser light source. The light source temperature adjustment means interference device according to claim 3, characterized in that the Peltier element. 3. The interference apparatus according to claim 1, wherein the band pass filter is provided in an optical path from the second light beam splitting unit to the light receiving unit.

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