JP3293666B2 - Non-contact optical type distance measuring device between two surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a possible change the wavelength Kohi
Measurement equipment using transparent measurement light,
Receives the interference light of each reflected light from the DUT
A pair of measurement optical systems, and receives interference light of the measurement light.
And a reference interference optical system for obtaining a known reference optical path difference.
The present invention relates to a non-contact optical type two-surface distance measuring device suitable for measuring a two-surface distance measuring device for an opaque material such as a thickness, a step, etc. , made of rubber, metal or other substance.

[0002]

2. Description of the Related Art A contact-type micrometer is conventionally known as a measuring device for measuring the thickness of an object. This micrometer measures the thickness, that is, the distance between two surfaces of an object, for example, an object to be measured, which is an opaque object such as a metal plate, by using a contact from both sides thereof. Further, as a non-contact optical type distance measuring apparatus between two surfaces, there is also known an apparatus which measures the thickness of an object to be measured which is a transparent body such as a plane parallel plate using an interferometer.

[0003]

However, since the conventional micrometer measures the thickness of the object to be measured across two surfaces thereof, the conventional micrometer is susceptible to deformation and is susceptible to flaws on the two surfaces. Undesirable to use for measuring. On the other hand, the conventional non-contact optical type distance measuring apparatus has a disadvantage that the thickness cannot be measured even when the object to be measured is an opaque body.

The present invention has been made in view of the above circumstances. Even if an opaque body made of rubber, metal or other material is used, the distance between two surfaces such as the thickness of the opaque body and a step is obtained without contact. It is an object of the present invention to provide a non-contact optical type distance measuring device capable of measuring the distance between two surfaces.

[0005]

A first aspect of the present invention.
In order to solve the above-mentioned problem, the non-contact optical type distance measurement device between two surfaces described in (1) measures the thickness of the measured object defined as the distance between one surface and the other surface of the measured object. Therefore, the object to be measured can be opposed and the wavelength can be changed.
A pair of opposing surface measurement optical systems for irradiating the respective surfaces with a functional coherent measurement light, and an interference light of the measurement light.
Reference interference optics for receiving and determining a known reference optical path difference
And a system, wherein the pair of opposing surfaces for measuring optical system which has a respective reference reflecting surface, and the reflected reference beam of the measuring beam from the reference reflecting surface and the reflected light beam of the measurement light from each surface of the object to be measured Each of which has a light receiver for receiving an interference light based on the reference light , wherein the reference interference optical system is based on the known reference optical path difference.
Has a light receiver for receiving Ku reference interference light, said each photodetector measuring process and circuit is connected to measure the thickness of the object to be measured based on the received light output, the measurement processing circuit
Is the reference obtained by changing the wavelength of the measurement light
Signal frequency of interference light from the light receiver of the interference optical system
The number of periods and the respective receivers of the pair of opposing surface measurement optical systems
The relationship between the ratio of the number of signal periods and the interference light
Calculating the thickness dimension using the reference optical path difference.
And features.

According to a second aspect of the present invention, there is provided a non-contact optical distance measuring apparatus between two surfaces, which is defined as a distance between one surface of an object to be measured and another surface. A pair of measurement optical systems for irradiating coherent measurement light having an optical axis parallel to each other and capable of changing the wavelength in order to measure a step of the measurement object, and interference light of the measurement light.
Reference interference light for detecting the known reference optical path difference
And a university system, which has a pair of measuring optical system reference reflecting surface respectively, based the on the reference reflected light of the measurement light beam from the reference reflecting surface and the reflected light beam of the measurement light beam from each surface of the object to be measured Each having a receiver for receiving the interference light,
The reference interference optical system is based on the known reference optical path difference.
Has a light receiver for receiving the quasi-interference light, wherein provided on each photodetector measurement processing circuit is connected to measure the thickness of the object to be measured based on the received light output, the measurement processing circuit, before
The reference interference light obtained by changing the wavelength of the measurement light
The number of signal periods for the interference light from the optical receiver
The interference light from each of the light receivers of the pair of measurement optical systems is
From the difference in the number of signal periods, the reference optical path
Calculating the step size of the measured object using the difference.
Features.

[0007]

According to a non-contact optical between dihedral distance measuring apparatus according to claim 1, 2 of the work for the present invention, a pair of measuring optical system is to be
One surface and the other surface of the measurement object are irradiated with measurement light.
Each light receiver of the pair of measurement optical systems receives interference light based on the reflected light from each of the surfaces and the reference reflected light from its reference reflecting surface. The reference interference optical system is based on the reference optical path difference
The reference interference light is received. The measurement processing circuit is configured to
The reference interference optical system obtained by changing the wavelength
The number of signal periods for the reference interference light from the
About the interference light from each of the receivers of the pair of measuring optics
From the ratio relationship with the difference in the number of signal periods, a known reference optical path difference is calculated.
To calculate the thickness or step of the measured object.
Therefore, it is not easy to accurately measure the wavelength of the measurement light.
Relatively easily measured without obtaining information about
The exact thickness or step of the constant object is measured.

[0008]

1 shows an optical diagram of a non-contact optical type two-surface distance measuring apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a single-wavelength coherent light emitted toward an object to be measured. A semiconductor laser 2 serving as a light source for performing the operation, a collimator lens 2 for converting a light beam emitted from the semiconductor laser 1 into a parallel light beam, and 3 an optical isolator. The semiconductor laser 1, the collimator lens 2, and the optical isolator 3 constitute a measurement light emission optical system. Collimator lens 2
Plays a role in turning the laser light emitted from the semiconductor laser 1 into a parallel light beam. The parallel light beam is used as measurement light. The optical isolator 3 prevents the measurement light from traveling backward to the semiconductor laser 1.

The beam splitters 4, 5, and 6 are provided in front of the measuring light in the traveling direction. Beam splitter 4
Serves to reflect a part of the measuring light toward the reference interference optical system 7. The reference interference optical system 7 includes a beam splitter 8,
It consists of reflecting mirrors 9, 10 and a light receiver PD1. A part of the light beam reflected by the beam splitter 4 is reflected by the beam splitter 8 toward the reflecting mirror 9,
The rest is transmitted through the beam splitter 8 and guided to the reflecting mirror 10. The light beam guided to the reflecting mirror 9 and the light beam guided to the reflecting mirror 10 are reflected by the reflecting mirrors 9 and 10 to reverse the original optical path again, and the light beam reflected by the reflecting mirror 9 is converted to a beam slitter 8. Is transmitted to the photodetector PD1 and reflected by the reflection mirror 1
The light beam reflected by 0 is further reflected by the beam splitter 8 and guided to the photodetector PD1. The light beam reflected by the reflecting mirror 9 and the light beam reflected by the reflecting mirror 10 interfere in the optical path from the beam splitter 8 to the light receiver PD1, and become an interference light beam. Here, assuming that the optical distance from the point M1 of the beam splitter 8 to the point M2 of the reflecting mirror 9 is L2, and the optical distance from the point M1 of the reflecting mirror to the point M3 of the reflecting mirror 10 is L1, The optical path difference is (L1-L2). This optical path difference (L1-L2)
Is defined as a reference optical path difference, and is represented using a symbol Lbase. Interference fringes are formed on the photodetector PD1 according to the reference optical path difference Lbase.

The light beam transmitted through the beam splitter 4 is guided to the beam splitter 5. The beam splitter 5 plays a role of splitting this light beam. Part of the split light beam passes through the beam splitter 5 and is guided to one of the opposing surface measurement optical systems 12, and the remaining light beam is reflected by the beam splitter 5 and is guided to the other opposing surface measurement optical system 13. .
The measurement optical system 12 for the opposing surface has a reflection mirror 14, a condenser lens 15, a reference reflection surface 16, a condenser lens 17, a spatial filter 18, and a light receiver PD2 together with the beam splitter 6. The opposing surface measurement optical system 13 includes a reflection mirror 20, a beam splitter 21, a reflection mirror 22, a condenser lens 23, a reference reflection surface 24, a condenser lens 25, a spatial filter 26, and a light receiver PD3. Condensing lens 15 and condensing lens 23
Are arranged so that their optical axes O1 and O2 coincide with each other,
The object 2 to be measured is between the condenser lens 15 and the condenser lens 23.
8 is an installation space 29. Here, the measured object 28 is an opaque body, and the symbol P is one surface of the measured object 28, and the symbol Q is the other surface of the measured object 28.
The surfaces P and Q are finished, for example, in a mirror state, and the surfaces P and Q are substantially parallel.

The beam splitter 6 is a beam splitter 5
Is divided into a light beam going to the reference reflection surface 16 and a light beam going to the reflection mirror 14. The light beam traveling toward the reference reflection surface 16 is reflected again by the reference reflection surface 16 and travels backward along the original optical path toward the beam splitter 6. The light beam directed to the reflection mirror 14 is reflected by the reflection mirror 14 toward the condenser lens 15. The condenser lens 15 is moved back and forth in the direction of the optical axis O1, and the light flux is condensed by the condenser lens 15 and converged on the surface P. The light flux reflected by the surface P is condensed by the condensing lens 15 and travels back to the original optical path again toward the beam splitter 6. Then, the light beam reflected by the surface P interferes with the light beam reflected by the reference reflection surface 16, and this interference light beam is
7, guided to the spatial filter 18 and the light receiver PD2. The condenser lens 17 plays a role of converging the interference light beam on the spatial filter 18. The spatial filter 18 is located at a point conjugate to the point P1 of the spatial filter 18 (here, the plane P
Of the reflected light from the point P1 ′). Thereby, disturbance light is cut. Here, from the point M4 of the beam splitter 6 to the point P1 '
Assuming that the optical path length from the point M4 of the beam splitter 6 to the point M5 of the reference reflecting surface 16 is Lref1, the optical path length between the light beam reflected by the surface P and the light beam reflected by the reference reflecting surface 16 is Lp1. The difference is (Lref1-Lp). An interference fringe based on the interference light beam according to the optical path difference (Lref1−Lp) is formed on the photodetector PD2.

The light beam directed by the beam splitter 5 to the opposing surface measurement optical system 13 is reflected by a reflection mirror 20 and guided to a beam splitter 21. The light beam and the light beam traveling toward a reference reflection surface 24 are reflected by the beam splitter 21. The light beam is split into a light beam directed to the mirror 22. The light beam heading toward the reference reflection surface 24 is reflected by the reference reflection surface 24, travels backward in the original optical path, and returns to the beam splitter 21.
The light beam directed to the reflection mirror 22 is guided to the condenser lens 23. The condenser lens 23 is moved back and forth in the direction of the optical axis O2, and is focused on the surface Q of the measured object 28 by the condenser lens 23. The light beam reflected by the surface Q is collected by the condenser lens 2
The light is condensed by 3 and returns to the beam splitter 21 by traveling backward in the original optical path. The light beam reflected by the reference reflection surface 24 and the light beam reflected by the surface Q become an interference light beam at the beam splitter 21, and are guided to the condenser lens 25, the spatial filter 26, and the light receiver PD3. The condenser lens 25 plays a role of converging the interference light beam to the spatial filter 26, and the spatial filter 26
And plays the role of passing only the interference light beam based on the reflected light from the point conjugated to the point (here, the point Q1 'on the surface Q). Thereby, disturbance light is cut. Here, from the point M6 of the beam splitter 21 to the point M of the reference reflection surface 24.
The optical path length up to 7 is Lref2, and the point M of the beam splitter 21 is
Assuming that the optical path length from 6 to the point Q1 'is Lq', the optical path difference between the light beam reflected by the surface Q and the light beam reflected by the reference reflecting surface 24 is (Lref2-Lq '). Interference fringes based on the interference light beam according to the optical path difference (Lref2−Lq ′) are formed on the photodetector PD3.

The intensity I of the interference light observed at the photodetectors PD1, PD2, PD3 is represented by the following equation.

IPD1 = 2I ± 2√ (I × I) cos (4πLbase / λ) IPD2 = Ip + Iref1 ± 2√ (Ip × Iref1) cos ｛4π (Lref1-Lp) / λ｝ IPD3 = Iq + Iref2 ± 2√ (Iq × Iref2) cos {4π (Lref2-Lq ′) / λ} The meanings of the symbols used in the above formulas are as follows.

IPD1: the intensity of the interference light beam at the photodetector PD1; IPD2: the intensity of the interference light beam at the photodetector PD2; IPD3: the intensity of the interference light beam at the photodetector PD3; I: the reflected light beam reflected by the reference reflecting surfaces 9, 10 Are received by the photodetector PD1 alone, and the received light intensity of the reflected light beam reflected by the reference reflection surface 9 at the photodetector PD1 and the received light intensity of the reflected light beam reflected by the reference reflection surface 10 at the photodetector PD1 The received light intensity was assumed to be equal.

Ip: Received light intensity when the light beam reflected by the surface P of the object 28 to be measured is received by the photodetector PD2 alone; Iref1: Light beam reflected by the reference reflection surface 16 is received by the photoreceiver PD2 alone Iq: the received light intensity when the reflected light beam reflected by the surface Q of the measured object 28 is received by the photodetector PD3 alone; Iref2: the reflected light beam reflected by the reference reflecting surface 24 Received light intensity when received by the photodetector PD3 alone; λ: wavelength of measurement light π: pi Here, since the amplitude of the interference term is determined by the integration of the amplitude of the measurement light and the reference light, the reference light is increased. By doing so, the amplitude of the interference signal can be increased.

At this time, if the wavelength of the measurement light is changed by Δλ, the intensity of the interference light is omitted from the description of the DC component under the condition that the change Δλ is very small with respect to the wavelength λ. And changes according to the following equations.

[0018] IPD1 = 2√ (I × I) cos (4πLbase / λ-4πLbase × Δλ / λ 2) IPD2 = 2√ (Ip × Iref1) × cos {4π (Lref1-Lp) / λ-4π (Lref1- Lp) × Δλ / λ ² ＩIPD3 = 2√ (Iq × Iref2) × cos ｛4π (Lref2-Lq ′) / λ-4π (Lref2-Lq ′) × Δλ / λ ² ｝ Therefore, the wavelength is changed from λ to λ + Δλ. When the intensity of the interference light is continuously observed during the change, the value of 4πLbase × Δλ / λ ² , 4π (Lr
ef1−Lp) × Δλ / λ ² , 4π (Lref2-Lq ′) × Δ
A periodic intensity change can be observed only for the period based on λ / λ ² . The number of periods of this intensity change is proportional to the optical path difference and the wavelength change amount Δλ. That is, the photodetectors PD1, PD
2. The number of periods of the interference light signal obtained by the PD 3 is 2
Since π is one cycle, the number of cycles obtained by the photodetector PD1; 2Lbase × Δλ /
The number of periods obtained by the λ ² light receiver PD2; 2 (Lref1−L
p) The number of periods obtained by the Δλ / λ ² photodetector PD3; 2 (Lref2−Lq
') Δλ / λ ² .

Here, the optical path length Lp is fixed to an appropriate value,
When the thickness of the object to be measured 28 is “0”, an optical path length from the point M6 of the beam splitter 21 to the surface P is Lq, and a measuring optical system is configured so that Lref1−Lp = Lq−Lref2. The surface P is strictly matched with the position X, and the measured object 28 having the thickness d is moved to the facing surface measuring optical system 12.
13, the number of periods of the signal obtained by the photodetector PD3 is as follows.

The number of periods of the signal obtained by the photodetector PD3: 2 (Lq′−Lref2) × Δλ / λ ² = 2 {(Lq−d) −Lref2} × Δλ / λ ² The difference between the number of periods of the signal obtained with the device PD3 is as follows.

Difference in the number of signal periods = Number of signal periods obtained by PD2−Number of signal periods obtained by PD3 number = 2 (Lref1−Lp) Δλ / λ ² −2 (Lq−d) −Lref2} [Delta] [lambda] / [lambda] ² = 2d [Delta] [lambda] / [lambda] ² Therefore, if [Delta] [lambda] / [lambda] ² is known, the period number of the difference between the period number of the signal obtained by the photodetector PD2 and the period number of the signal obtained by the photodetector PD3 is determined. Thus, the thickness d of the measured object 28 can be calculated.

However, in practice, it is often difficult to determine the value of Δλ / λ ² . Therefore, if the period of the signal 2Lbase Δλ / λ ² obtained by the photodetector PD1 is simultaneously measured and the ratio Lbase is determined as a known value,
The thickness d can be determined by the following equation.

The ratio of the number of periods = (2dΔλ / λ ² ) / (2Lb
aseΔλ / λ ² ) = d / Lbase or thickness d = ratio of number of periods × Lbase This is the principle for measuring the thickness d. A more preferable measurement method based on this measurement principle will be described together with the measurement processing circuit. I do.

FIG. 2 is a diagram showing the measurement processing circuit. In FIG. 2, reference numeral 33 denotes a synchronization control circuit. The synchronization control circuit 33 outputs a synchronization signal to the clock circuit 34 and the wavelength control circuit 35. The wavelength control circuit 35 outputs to the drive circuit 36 and the wavelength control means 37.

Here, for the sake of simplicity, the wavelength control means 37 changes the wavelength λ of the coherent light linearly with respect to time, as shown in FIG.
It is assumed that the time tm required to change the wavelength by Δλ is 1 second.

The signal outputs obtained by the photodetectors PD1, PD2 and PD3 are amplified by amplifiers 38, 39 and 40 and input to DC component removing circuits 41, 42 and 43, and the DC output of the signals obtained by each photodetector is obtained. Each component is removed.

The number of periods of the change in the intensity of the signal obtained by the photodetectors PD2 and PD3 is represented by a frequency: fPD2 = 2 (Lref1-Lp) Δλ / λ ² (Hz) fPD3 = 2 ｛(Lq−d) − Lref2｝ Δλ / λ ² (Hz).

Here, (Lref1-Lp) = (Lq-Lref)
If the optical system is configured so as to satisfy the condition that (Lref1−Lp) is much larger than the thickness d using the equation (2),
The frequency fPD2 of the signal obtained by the photodetector PD2 and the frequency fPD3 of the signal obtained by the photodetector PD3 are substantially close to each other. When the amplitude of each signal is adjusted by the gain adjustment circuits 44 and 45 and mixed by the mixer 46, A beat signal. Here, the gain adjustment circuit 4
Reference numerals 4 and 45 are used for adjusting the contrast of the beat signal.

The difference frequency f between the frequency fPD2 and the frequency fPD3
bt becomes fbt = | fPD3−fPD2 | = 2d × (Δλ / λ ² ) (Hz). In this beat signal, the synthetic frequency (carrier signal frequency) f0 is f0 = (fpd2 + fpd3) / 2, and the beat signal S is S = Acos ｛2πd (Δλ / λ ² ) × t + (φ ₁ −φ ₂₎ ) /
2｝ · cos {2πf0 × t + (φ1−φ2) / 2}.

The beat signal S is shown in FIG.

In the above equation, the symbol A is the amplitude of the beat signal, and φ ₁ and φ ₂ are the initial phases of the signals output from the photodetectors PD2 and PD3.

The beat signal S is detected by the detection circuit 47, whereby the difference frequency fbt of the beat signal S is obtained. The detection signal S output from the detection circuit 47
'Is shown in (3) of FIG.

On the other hand, since the frequency of the reference interference signal obtained by PD1 is fPD1 = 2Lbase × Δλ / λ ² (Hz), the frequency ratio fb between the difference frequency fbt and the frequency fPD1 is fb.
When t / fPD1 is obtained, fbt / fPD1 = d / Lbase. Here, since Lbase is known, d = (fbt / f
The thickness d of the measured object 28 can be calculated by the equation PD1) × Lbase.

That is, the thickness d of the measured object 28 can be measured by changing the wavelength of the measurement light and performing the measurement while relating the frequency of the beat signal S to the frequency of the reference interference signal.

In order to relate the frequency of the beat signal S to the frequency of the reference interference signal, the measurement processing circuit sends the timing signal from the clock circuit 34 to the A / D conversion circuits 48 and 49 during the wavelength modulation period tm. Output. A /
The reference interference signal (see the signal waveform shown in (5) of FIG. 3) from which the DC component has been removed by the DC component removal circuit 41 is input to the D conversion circuit 48, and the detection circuit 47 is input to the A / D conversion circuit 49. Signal S ′ ((3) in FIG. 3)
(Refer to the signal waveform shown in Fig. 2). The A / D conversion circuit 49 A / D converts the detection signal S ′ based on the timing signal output from the clock circuit 34. A / D-converted detection signal S 'is stored in the waveform memory 50 (see the signal waveform of (4) in FIG. 3). A / D conversion circuit 4
Reference numeral 8 denotes a reference interference signal from which the DC component has been removed based on the timing signal output from the clock circuit 34.
/ D conversion. The A / D converted reference interference signal is stored in the waveform memory 51 (see the signal waveform of (6) in FIG. 3).

Here, the waveform memory 5 by A / D conversion
The fetch frequency of the data into 0 and 51 (clock frequency of A / D conversion; number of clock waveforms per second) is fad
Then, the number of data Ndata in one modulation period (tm)
Is Ndata = fad × tm. Therefore, the waveform memory 5
The signal frequency can be calculated by analyzing the period of the data taken in 0 and 51 and calculating the number of data constituting one period of the signal (determining the fraction). That is, assuming that one cycle of a signal is generally composed of nsignal data, the frequency fsignal of the signal is fsignal = fad / nsign
al (The number of data in one cycle is nsign
al, and if the frequency of the signal is fsignal, the total number of data per second is nsignal * fsignal, since this total number of data is equal to the data acquisition frequency fad).

Accordingly, if this processing is simultaneously performed on the reference interference signal from the reference interference optical system 7 and the output signal after detecting the beat signal by using the arithmetic circuit 52, even if the data fetch frequency fad is unknown. , Frequency ratio fbt /
fpd1 can be obtained (when calculating the frequency ratio,
The denominator and the fetching frequency fad of the data contained in the numerator are reduced approximately).

Here, the number of data Ndat in one modulation period tm
If a is fixed, nsignal is determined by the number of periods of the signal included in one modulation period tm. That is, the number of periods in one modulation period tm of the beat signal is Fbt, the number of data in one period of the beat signal is nb, the number of periods in one modulation period tm of the reference interference signal is Nbase, and the number of data in one period of the reference interference signal is Nbase. Number nba
se, then Ndata = Fbt × n for the beat signal
b, and Ndata = Nbase × nb for the reference interference signal
ase.

Therefore, Fbt × nb = Nbase × nbase, and Fbt / Nbase = nbase / nb.

Therefore, fbt / fPD1 = nbase / nb = (number of cycles of beat signal / number of cycles of reference interference signal) Therefore, fbt / fPD1, nbase / nb, number of cycles of beat signal / number of cycles of reference interference signal Of these, the one that is most easily obtained at the time of analysis may be calculated.

In the above description, the measurement object 28 is placed in the optical path with the surface P of the measurement object 28 exactly matching the position X.
It is not necessary that the surface P of the object 8 be exactly aligned with the position X and placed in the optical path. For example, the surface P of the measured object 28 may be shifted from the position X in the front-back direction of the optical axis.

For example, it is assumed that the surface P of the measured object 28 is shifted from the position X in a direction approaching the condenser lens 15;
Assuming that this shift amount is δ, it is considered that the surface P of the measured object 28 has been translated from the position X in a direction approaching the condenser lens 15 by δ, so that the frequency fPD2 of the signal obtained by the photodetector PD2 is fPD2 = 2 {Lref1- (Lp-δ )} becomes ^{Δλ / λ 2 = 2 {Lref1} -Lp + δ} Δλ / λ 2. Further, the frequency fPD3 of the signal obtained by the photodetector PD3 is fPD3 = 2 (Lq′−Lref2) Δλ / λ ² = 2λ (Lq−d + δ) −Lref2｝ Δλ / λ ² Therefore, the difference frequency fbt between the frequency fPD2 of the signal obtained by the photodetector PD2 and the frequency fPD3 of the signal obtained by the photodetector PD3 when the plane P2 is shifted by δ in the direction approaching the condenser lens 15 is fbt = | fPD3−fPD2 | = 2d × (Δλ / λ ² ) (Hz)

When the surface P is shifted from the position X by δ in the direction away from the condenser lens 15, the light receiving device P
Frequency FPD 2 of the signal obtained by D2 becomes fPD2 = 2 {Lref1- (Lp + δ)} Δλ / λ 2 = 2 {Lref1-Lp-δ}. Further, the photodetector PD3 frequency FPD 3 of the signal obtained by becomes fPD3 = 2 (Lq'-Lref2) Δλ / λ 2 = 2 {(Lq-d-δ) -Lref2} Δλ / λ 2. Therefore, the difference frequency fbt is as follows: fbt = | fPD3−fPD2 | = 2d × (Δλ / λ ² ) (Hz)

As is clear from the above equation, the thickness d of the measured object 28 can be measured even if the surface P of the measured object 28 is shifted from the reference position X. Since the condenser lens 15 is movable in the optical axis direction, even if the surface P of the measured object 28 is shifted from the reference position X,
The measuring light can be focused on its plane P.

In the above embodiment, the case where the wavelength of the coherent light of the semiconductor laser 1 is changed linearly with respect to time t has been described. However, it is difficult to control the wavelength of the coherent light to change linearly with respect to time t. Therefore, a more preferred embodiment will be described below.

In FIG. 4, reference numeral 52 denotes a clock circuit. The clock circuit 52 is controlled by the synchronization control circuit 33. In this embodiment, the semiconductor laser 1 is pulse-driven, and the wavelength of the coherent light is changed nonlinearly with respect to time t. The drive circuit 36 is controlled by the clock control circuit 52, and outputs a rectangular pulse current ((1) in FIG. 5).
) To drive the semiconductor laser 1. When the semiconductor laser 6 is turned on upon input of a rectangular signal, oscillation starts and the chip temperature T changes as shown in FIG. 5 (2). When the chip temperature of the semiconductor laser 1 changes, the oscillation wavelength changes. The relationship between the temperature and the wavelength has a one-to-one correspondence at positions other than the mode hop position. This temperature change is abrupt immediately after the start of oscillation, and gradually converges. After a certain time, the semiconductor laser 1 is turned off to return the temperature to the original state, and the irradiation of the coherent light is stopped. The width K of the rectangular pulse is determined in consideration of the wavelength change width Δλ. For example, a semiconductor laser 1 at a frequency of 1 kHz
When pulse driving is performed, the main characteristic portion of the wavelength change with respect to the temperature change can be used, and there is also reproducibility. A semiconductor laser 1 having a mode hop interval wider than the wavelength change width is used, and the reference temperature of the semiconductor laser 1 is set to a temperature control circuit 53 shown in FIG. Is controlled by The wavelength change corresponds to the temperature change. Like the temperature change, the wavelength change is not linear, but changes greatly at first, and the amount of change gradually decreases. Since the fluctuation of the oscillation output is very small, the fluctuation of the oscillation output within the pulse width K can be ignored.

Accordingly, the frequency fPD1 of the reference interference signal obtained by the photodetector PD1, the frequency fPD2 of the signal obtained by the photodetector PD2, the frequency fPD3 of the signal obtained by the photodetector PD3, and the frequency fbt of the beat signal initially have a frequency of High, gradually decreasing frequency.

Therefore, when the reference interference signal and the beat signal are A / D-converted using the A / D conversion circuit 54 using a trigger circuit having a fixed frequency, data having a high frequency at the initial stage and a temporarily lowering the frequency are obtained. This is recorded in the waveform memory, and the cycle of the signal cannot be calculated as it is.

Therefore, between the frequency fbt of the beat signal and the frequency fPD1 of the reference interference signal, fbt = fPD1 × d / L
Focusing on the relation of base, since the thickness d and the reference optical path difference Lbase are constant, the frequency fbt is equal to the frequency fPD1.
It can be seen that this is a constant multiple of. Therefore, the waveform of the reference interference signal shown in (6) of FIG. 5 is sliced by a predetermined threshold value V of the trigger circuit 52 ', and the trigger circuit 53' is sliced.
Then, a trigger signal G shown in (7) of FIG. 5 is generated. The trigger signal G is used as a conversion timing signal of the A / D converter 54. Further, the trigger signal G is input to the analog switch circuit 56 via the frequency divider 55.
The analog switch drive circuit 56 is used for switching a cutoff frequency of a variable frequency low-pass filter 58 described later.

The variable frequency low-pass filter 58 forms a detection circuit 47 together with the squaring circuit 57. The frequency variable low-pass filter 58 is such that the frequency fbt of the beat signal at the beginning of the one modulation period tm (period immediately after the rise of the rectangular pulse) is higher than the composite frequency f0 at the end (period immediately before the fall of the rectangular pulse). If the filter is configured to pass the initial beat signal of the one-wavelength modulation period tm, the carrier signal itself at the frequency f0 will be transmitted at the end, and the detection cannot be performed reliably. Because. The cut-off frequency of the variable frequency low-pass filter 58 is changed in synchronization with the frequency change. For example, as shown in FIG. 6, the frequency variable filter 58 is connected in parallel to a series body of resistors R1, R2,..., R6 having different resistance values and resistors R1, R2,. R
Analog switch S for shorting 1, R2, ..., R6
, S6,..., S6 and a capacitor C. The analog switch driving circuit 56 includes the analog switch S1,
S2,..., S6 are turned on / off. As an example, when the ratio of the resistance values of the resistors R1, R2,..., R6 is set to 1, 2, 4, 8, 16, and 32 and the configuration is 6 bits, the cutoff frequency fcut is: fcut = constant × ｛1 / (C · R)｝ where C is the capacitance of the capacitor and R is the combined resistance value.

Therefore, the cutoff frequency is set to a high frequency initially, and as the frequency of the reference interference signal decreases,
Decrease cutoff frequency. Only the resistance value corresponding to the numerical value “1” is turned off, and the maximum set value of fcut is set to “1”.
The cutoff frequency fcut can be changed from the maximum set value “1” to the set value “1/63” when all the analog switches are turned off. As shown in FIG. When output from the frequency divider 55, the cutoff frequency can be changed as shown in FIG.

The signal passing through the detection circuit 47 (see the waveform (4) in FIG. 5) is input to the A / D converter 54.
The A / D converter 54 receives the trigger signal G shown in (7) of FIG.
Is used as a timing signal to capture data. The generation interval of the trigger signal G changes as the frequency changes, as shown in FIG. The frequency of the beat signal A / D-converted by the A / D converter 54 also changes in the same manner as the frequency of the reference interference signal, and the ratio is constant. Is a signal having a constant period apparently. Therefore, the waveform shown in (5) of FIG. 5 is stored in the memory 50. When the number of data in one cycle of the obtained signal is measured, it is fPD1 / fbt.

Therefore, the thickness d can be obtained from the equation d = (fbt / fPD1) × Lbase.

FIG. 9 shows a second embodiment of the non-contact optical type distance measuring apparatus according to the present invention, in which one surface P and the other surface Q of the object 28 to be measured are observed and condensed. Lens 15,
The focus adjustment of 23 is facilitated.

In the second embodiment, a dichroic mirror 63 constituting a part of the observation optical system is provided between the reflection mirror 14 and the condenser lens 15, and between the reflection mirror 22 and the condenser lens 23. A dichroic mirror 64 is provided. The dichroic mirrors 63 and 64 have a characteristic of transmitting measurement light and reflecting other light. The direction of reflection of the dichroic mirror 63 is
5, an image sensor 66 is provided, and a dichroic mirror 6 is provided.
An imaging lens 67 and an image sensor 68 are provided in front of the reflection direction 4. According to this configuration, while observing the surfaces of one surface P and the other surface Q of the measured object 28, the condenser lens 15,
Twenty-three adjustments can be made.

FIG. 10 shows a third embodiment of the non-contact optical type distance measuring apparatus according to the present invention. In the first and second embodiments, it has been described that the measured object 28 is an opaque body, and the front surface P and the back surface Q are completely separated. However, the non-contact optical type distance measuring apparatus according to the present invention can also be applied to an isotropic transparent body. In the case of this transparent body, the measurement light applied to one surface P passes through the inside of the transparent body and is emitted from the other surface Q, and the measurement light applied to the other surface Q is applied to the inside of the transparent body. , And is emitted from one surface P, and there is a possibility that the measurement light of the one opposing surface measuring optical system and the measuring light of the other opposing surface measuring optical system are mixed, albeit slightly.

Therefore, in the third embodiment, instead of the beam splitters 6 and 21, the polarization beam splitter 6 ',
21 ', a quarter-wave plate 70 is provided between the reference reflection surface 16 and the polarization beam splitter 6'.
波長 wavelength plate 7 between the light beam and the polarizing beam splitter 21 ′
1 is provided. Further, a 波長 wavelength plate 72 is provided between the condenser lens 15 and one surface P of the measured object 28, and the condenser lens 2
１ ／ wavelength plate 73 between the third surface Q and the other surface Q of the measured object 28
Is provided. The optical axes of the quarter-wave plate 72 and the quarter-wave plate 73 are orthogonally arranged. Polarizing beam splitter 6
'And 21' transmit P-polarized coherent light and reflect S-polarized coherent light. Further, a polarizing plate 74 is provided between the condenser lens 17 and the polarization beam splitter 6 ′ so as to make an angle of 45 degrees with respect to the P-polarized light and the S-polarized light. A polarizing plate 75 that forms an angle of 45 degrees with respect to P-polarized light and S-polarized light is provided.

First, the measurement light beam guided to one of the opposing surface measurement optical systems 12 will be described.

When the polarization direction of the coherent light from the semiconductor laser 1 is maintained at an angle of 45 degrees with respect to the polarization beam splitters 6 'and 21', the polarization beam splitter 6
The measurement light of the P-polarized component among the measurement light guided to ′ passes through the polarization beam splitter 6 ′, and the P-polarized component is guided to the 波長 wavelength plate 72 via the condenser lens 15. On the other hand, the measurement light of the S-polarized component is reflected by the polarization beam splitter 6 ′ and guided to the １ ／ wavelength plate 70. Then, the measurement light of the P-polarized light component is converted into circularly polarized light by the 波長 wavelength plate 72. The plane P of the measured object 28 is illuminated by the circularly polarized measurement light. A part of the circularly polarized measurement light is reflected by the surface P, but a part thereof is
And leaks out of the other surface Q. The circularly polarized measurement light reflected by the surface P is guided to the 波長 wavelength plate 72 to become S-polarized light orthogonal to the P-polarized light, and the polarization beam splitter 6 ′
And is guided to the condenser lens 17. The S-polarized measurement light reflected by the polarization beam splitter 6 ′ becomes circularly polarized light by the １ ／ wavelength plate 70, is reflected by the reference reflection surface 16, and is again guided to the 波長 wavelength plate 70.
Polarizing beam splitter 6 as P polarized light orthogonal to S polarized light
′, Passes through the polarization beam splitter 6 ′, and is guided to the condenser lens 17. Since the polarizing plate 74 is disposed between the condenser lens 17 and the polarizing beam splitter 6 ′, the polarization directions of the S-polarized measurement reflected light and the P-polarized reference reflected light partially match, Interference occurs in the light receiver PD2.

Next, the measurement light beam guided to the other opposing surface measurement optical system 13 will be described.

The measurement light of the P-polarized light component of the measurement light reflected by the beam splitter 5 passes through the polarization beam splitter 21 ′, and the P-polarized light component is transmitted to the 波長 wavelength plate 73 via the condenser lens 23. Be guided. On the other hand, the measurement light of the S polarization component is reflected by the polarization beam splitter 21 ′ and guided to the 導 か wavelength plate 71. Then, the measurement light of the P-polarized light component is converted into circularly-polarized light by the 板 wavelength plate 73.
The surface Q of the measured object 28 is illuminated with the circularly polarized measurement light. A part of the circularly polarized measurement light is reflected by the surface Q, but a part of the light is transmitted through the object to be measured 28 and the surface P
Leaks from The circularly polarized measurement light reflected by the surface Q is guided to the 波長 wavelength plate 73 to become S-polarized light orthogonal to the P-polarized light, and is reflected by the polarization beam splitter 21 ′ to be guided to the condenser lens 25. The S-polarized measurement light reflected by the polarization beam splitter 21 ′ becomes circularly polarized light by the 波長 wavelength plate 71, is reflected by the reference reflection surface 24, is again guided to the 波長 wavelength plate 71, and becomes S-polarized light. The light is guided to the polarizing beam splitter 21 ′ as orthogonal P-polarized light, passes through the polarizing beam splitter 21 ′, and is guided to the condenser lens 25. Since the polarizing plate 75 is disposed between the condenser lens 25 and the polarizing beam splitter 21 ′, the polarization directions of the S-polarized measurement reflected light and the P-polarized reference reflected light are partially changed to the light receiver PD3. Interfere at

Next, the circularly polarized measurement light incident from the surface P and transmitted through the object to be measured 28 and leaked from the surface Q, and the incident light from the surface Q and transmitted through the object to be measured 28 and leaked from the surface P The emitted circularly polarized measurement light will be described.

The circularly polarized measurement light that has entered from the surface P, transmitted through the object to be measured 28 and leaked from the surface Q is a 波長 wavelength plate 72.
Since the optical axes of the light and the quarter-wave plate 73 are orthogonal to each other, the circularly-polarized measurement light that has passed through the surface P and leaked out of the surface Q passes through the quarter-wave plate 73 to become P-polarized light. Becomes
The measurement light of the P-polarized light is guided to the polarization beam splitter 21 ′ by the reflection mirror 22. However, the polarization beam splitter 21 ′ has a property of transmitting the P-polarized light. Measurement optical system 13
Interference with the measurement light beam is prevented. For the same reason, the light enters from the surface Q, passes through the measured object 28, and
The measurement light of the circularly polarized light leaked from the measurement light beam is prevented from interfering with the measurement light flux of the measurement optical system 12 for one of the opposed surfaces.

In the third embodiment, the optical axes of the quarter-wave plate 72 and the quarter-wave plate 73 are arranged orthogonal to each other. Are arranged in parallel, and the polarization beam splitter 21 'has a configuration equivalent to transmitting S-polarized light and reflecting P-polarized light.
The circularly polarized measurement light incident from the surface P and transmitted through the object to be measured 28 and leaked to the surface Q is converted into S-polarized light by transmitting through the quarter-wave plate 73. Since the light passes through the polarization beam splitter 21 ′, the measurement light of the circularly polarized light which enters from the surface P, passes through the object to be measured 28, and leaks from the surface Q is measured by the measurement optical system 13 for the other opposing surface. Interference with the light beam is prevented. The circularly polarized measurement light incident from the surface Q and transmitted through the object to be measured 28 and leaked to the surface P is transmitted through the 波長 wavelength plate 72 to generate P.
Since the P-polarized measurement light is transmitted through the polarization beam splitter 6 ′, the circularly-polarized measurement light that enters from the surface Q, transmits through the object to be measured 28, and leaks from the surface P is polarized. Is prevented from interfering with the measurement light beam of the measurement optical system 12 for one facing surface.

FIG. 11 shows a fourth embodiment of the non-contact optical type distance measuring apparatus according to the present invention, which shows an optical configuration for measuring a step d 'of an object 28 to be measured. The optical axis O1 of the measuring optical system 12 for the opposite surface and the optical axis O2 of the measuring optical system 13 for the other opposite surface are arranged in parallel, and other configurations are substantially the same as those of the first embodiment. Therefore, the detailed description is omitted.

Although the embodiment has been described above, one surface P and the other surface Q of the measured object 28 are optically clean and smooth surfaces, and the parallelism between the one surface P and the other surface Q is sufficiently good. In such a case, the thickness d and the step d ′ of the measured object 28 can be measured without using the condenser lenses 15 and 23.

[0067]

According to the first aspect of the present invention, since the non-contact optical type distance measuring apparatus according to the first aspect is constructed as described above, even if it is an opaque body made of rubber, metal or other substance. The thickness of the opaque body can be measured without contact.

According to the non-contact optical type distance measuring apparatus according to the second aspect of the present invention, it is possible to measure a step of an object to be measured.

[Brief description of the drawings]

FIG. 1 is a view showing an optical system of a non-contact optical type distance measuring apparatus according to the present invention.

FIG. 2 is a measurement processing circuit diagram for obtaining a step using the optical system shown in FIG. 1;

3 is an explanatory diagram of signal waveforms of the measurement processing circuit shown in FIG.

FIG. 4 is a diagram showing another embodiment of the measurement processing circuit.

FIG. 5 is an explanatory diagram of signal waveforms of the processing circuit shown in FIG.

FIG. 6 is an explanatory diagram of a frequency low-pass filter.

FIG. 7 is a timing chart for explaining the operation of the frequency divider.

FIG. 8 is a graph showing a change in cutoff frequency.

FIG. 9 is a diagram showing an optical system of a second embodiment of the non-contact optical type distance measuring apparatus according to the present invention.

FIG. 10 is a view showing an optical system of a third embodiment of the non-contact optical type distance measuring apparatus according to the present invention.

FIG. 11 is a diagram showing an optical system of a fourth embodiment of the non-contact optical distance measuring apparatus between two surfaces according to the present invention.

[Explanation of symbols]

 7 Reference interference optical system 12, 13 Opposing surface measurement optical system 16, 24 Reference reflection surface 28 Object to be measured P One surface Q Other surface PD1, PD2, PD3 Receiver

Claims (2)

(57) [Claims] 1. A device for measuring the thickness of an object to be measured, which is defined as the distance between one surface of the object to be measured and the other surface thereof, and having a wavelength that can be opposed to the object to be measured. age
A pair of opposing surface measurement optical systems for irradiating each surface with coherent measurement light, and receiving interference light of the measurement light.
And a known reference path difference reference interference optical system for obtaining the Te, the which has a pair of opposing surfaces for measuring optical system reference reflecting surface respectively, the reflected light beam of the measurement light from each surface of the object to be measured receiving an interference light based on the reference reflected light of the measurement light beam from the reference reflecting surface and has the light receiver, respectively, before
The reference interference optical system is a reference based on the known reference optical path difference.
It has a light receiver for receiving the interference light, a measurement processing circuit for measuring the thickness of the object to be measured based on the light reception output of each of the light receivers, the measurement processing circuit,
The reference interference optics determined by changing the wavelength of the measurement light
The number of signal periods for interference light from the
Interference from each of the photodetectors of the pair of opposed surface measurement optical systems
From the relationship of the ratio with the difference in the number of signal periods for light,
A non-contact optical type distance measuring apparatus between two surfaces, wherein the thickness dimension is calculated using a quasi-optical path difference . 2. A coherent device having optical axes parallel to each other and having a variable wavelength for measuring a step of an object to be measured, which is defined as a distance between one surface of the object to be measured and another surface thereof. br /> and a pair of measuring optical system for irradiating the cement measurement light, the measurement
To obtain a known reference optical path difference by receiving the light interference light
And a reference interference optical system, the pair of measuring optical system which has a respective reference reflecting surface, and the reflected reference beam of the measuring beam from the reference reflecting surface and the reflected light beam of the measurement light from each surface of the object to be measured Each having a light receiver for receiving an interference light based on the reference interference optical system , the reference interference optical system
A light receiving device for receiving a reference interference light based on the light beam, and each light receiving device is connected to a measurement processing circuit for measuring a step of the object to be measured based on a light receiving output thereof;
The path is determined by changing the wavelength of the measurement light.
The signal about the interference light from the receiver of the quasi-interference optical system
The number of periods and the amount of light from each of the receivers of the pair of measurement optical systems.
From the relationship between the ratio of the difference between the number of signal periods and the
Calculating the step size of the measured object using a reference optical path difference
Non-contact optical dihedral distance measuring apparatus characterized by that.