JP2020079805A - Distance measurement device and distance measurement method - Google Patents

Abstract

To provide a distance measurement device and a distance measurement method capable of performing distance measurement even when a position of an object to be measured changes.SOLUTION: The distance measurement device includes: a time delay detection unit for detecting a time delay between measurement light and reference light on the basis of an optical distance difference calculated by a distance difference calculation unit; and a detection control unit for correcting phases of a first reference sine wave signal and a second reference sine wave signal on the basis of a detection result of the time delay detection unit, and for causing a sine wave signal detection unit to execute the detection of a two-phase sine wave signal on the basis of the first reference sine wave signal and the second reference sine wave signal after phase correction.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a distance measuring device and a distance measuring method using a sine wave phase modulation method.

A distance measuring device using a sine wave phase modulation method is known as a distance measuring device that measures the distance to a measurement target by utilizing light interference (for example, refer to Patent Document 1). Such a distance measuring device generates a light wave that is sine-wave phase-modulated by direct modulation of a laser light source or indirect modulation by an electro-optical element [EO (Electro-optical) element], and splits this light wave into measurement light and reference light. Then, the interference signal between the measurement light projected onto the measurement object and reflected and the reference light passing through the reference optical path is detected. Next, the distance measuring device inputs the detected interference signal to the lock-in amplifier and obtains a two-phase sine wave signal with a phase difference of 90° in the lock-in amplifier.

  Then, the distance measuring device corrects by multiplying the two-phase sine wave signal by a predetermined coefficient so that the Lissajous waveform formed by the two-phase sine wave signal output from the lock-in amplifier becomes a perfect circle. Then, the distance from the predetermined reference position to the measurement object is obtained based on the corrected two-phase correction signals.

  In addition, in Patent Document 1 described above, as an application example of the distance measurement by the sine wave phase modulation method, a two-wavelength sine wave phase modulation interferometer (distance measuring device) for performing distance measurement by a so-called two-color method is described.

Japanese Unexamined Patent Application Publication No. 2015-075461

  In recent years, not only the distance measurement of a measurement target object whose position is fixed, but also the distance measurement of a measurement target object that is displaced along the path (optical path) of the measurement light is performed by the distance measurement device. However, in the distance measuring device using the conventional sine wave phase modulation method including the above-mentioned Patent Document 1, when the position of the measurement object is largely displaced, it is formed by the two-phase sine wave signals output from the lock-in amplifier. The Lissajous waveform askect ratio changes. Therefore, even if the correction is performed by multiplying the two-phase sine wave signal after changing the aspect ratio by a predetermined coefficient corresponding to the two-phase sine wave signal before changing the aspect ratio, The formed Lissajous waveform does not become a perfect circle, and a large error occurs in the distance measurement result. Especially, when the distance measurement is performed by the two-color method described above, the error of the distance measurement result is expanded from several tens of times to one hundred and several tens of times. Further, the signal strength of the two-phase sine wave signal becomes weak, which may make distance measurement impossible.

  Further, in the distance measuring device using the conventional sine wave phase modulation method, when the position of the measuring object is largely displaced along the path of the measuring light, the detection signal (interference signal) and the detected signal in the lock-in amplifier are Since the phase is different from that of the (reference signal), the signal strength of the two-phase sine wave signals output from the lock-in amplifier becomes weak, which may make it impossible to measure the distance.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a distance measuring device and a distance measuring method capable of performing distance measurement even when the position of a measurement target is displaced.

  A distance measuring device for achieving an object of the present invention is a light wave generation unit that generates a light wave that is sine wave phase-modulated by a sine wave, and a division that divides the light wave generated by the light wave generation unit into measurement light and reference light. Section, detects the interference signal between the measurement light emitted to the measurement target that is displaced along the path of the measurement light split by the splitting unit and reflected by the measurement target, and the reference light split by the splitting unit Based on the sine wave signal detection unit that detects a two-phase sine wave signal from the interference signal detection unit that detects the interference signal detected by the interference signal detection unit, and the two-phase sine wave signal that the sine wave signal detection unit detects An amplitude that determines the amplitude of the AC component of the optical frequency of the light wave based on the distance difference calculator that calculates the optical distance difference between the measurement light and the reference light, and the optical distance difference that the distance difference calculator calculates. Based on the determination result of the determination unit, the amplitude determination unit that determines the amplitude at which the modulation index that determines the aspect ratio of the Lissajous waveform formed by the two-phase sine wave signal is kept constant, and the determination result of the amplitude determination unit, An amplitude control unit that controls the amplitude of the light wave generated by the light wave generation unit.

  According to this distance measuring device, the modulation index is kept constant even when the position of the measuring object is displaced, so that the aspect ratio of the Lissajous waveform formed by the two-phase sine wave signals is also kept constant. As a result, when the aspect ratio of the Lissajous waveform is corrected, a two-phase correction signal that always forms a perfect circular Lissajous waveform is obtained. Therefore, the position of the measuring object is displaced based on these two-phase correction signals. Even in the case of performing, the path difference between the measurement light and the reference light can be accurately measured. Further, it is prevented that the signal strength of the two-phase sine wave signal becomes weak and the distance measurement (path difference measurement) cannot be performed.

  In the distance measuring device according to another aspect of the present invention, the optical distance difference is represented by the product of the path difference between the measurement light and the reference light, and the refractive index of the path of the measurement light and the reference light, An information acquisition unit that acquires an initial path difference that is a path difference before the start of displacement, the amplitude determination unit, the initial path difference acquired by the information acquisition unit, a known refractive index, the optical calculated by the distance difference calculation unit. The amplitude is determined based on the target distance difference. Thereby, the amplitude of the optical frequency of the light wave generated by the light wave generation unit can be controlled based on the optical distance difference calculated by the distance difference calculation unit. The path difference referred to here is a geometrical distance difference between the paths of the measurement light and the reference light.

In a distance measuring device according to another aspect of the present invention, the center frequency of the optical frequency is f _c , the amplitude is Δf, the angular frequency and frequency of the AC component of the optical frequency are ω _m and f _m , respectively, and the time is t. And the first-order k-th order Bessel function is J _k (m), the path difference is D, the initial path difference is D ₀ , the refractive index is n, the speed of light is C _0, and 2×n×D/C Let ₀ be τ, 2π×f _c ×τ be φ, the initial refractive index that is the refractive index before displacement start be n ₀ , the initial amplitude that is the amplitude before displacement start be Δf ₀ , and the modulation index be m In this case, the optical frequency f(t), the intensity I of the interference signal, the modulation index m, the two-phase sine wave signals S1(φ) and S2(φ), and the amplitude Δf are expressed by the following equations:

  Is represented by. Accordingly, based on the optical distance difference calculated by the distance difference calculating unit, the amplitude of the optical frequency of the light wave can be determined and controlled by referring to the above-mentioned mathematical expressions.

  A distance measuring device for achieving an object of the present invention is a light wave generation unit that generates a light wave that is sine wave phase-modulated by a sine wave, and a division that divides the light wave generated by the light wave generation unit into measurement light and reference light. Section, detects the interference signal between the measurement light emitted to the measurement target that is displaced along the path of the measurement light split by the splitting unit and reflected by the measurement target, and the reference light split by the splitting unit And a sine wave signal detection unit that detects two-phase sine wave signals respectively corresponding to the first reference sine wave signal and the second reference sine wave signal from the interference signal detected by the interference signal detection unit. A distance difference calculation unit that calculates an optical distance difference between the measurement light and the reference light based on the two-phase sine wave signals detected by the sine wave signal detection unit, and an optical distance calculated by the distance difference calculation unit. Based on the difference, a time delay detection unit that detects a time delay between the measurement light and the reference light, and a phase of the first reference sine wave signal and the second reference sine wave signal based on the detection result of the time delay detection unit. A detection control unit that causes the sine wave signal detection unit to detect a two-phase sine wave signal based on the first reference sine wave signal and the second reference sine wave signal that have been corrected and have undergone phase correction.

  According to this distance measuring device, since the phase delay between the interference signal and each reference sine wave signal is prevented, the signal strength of the two-phase sine wave signal may be weak even when the position of the measurement object is displaced. To be prevented. As a result, it becomes possible to prevent the distance measurement (path difference measurement) from being disabled.

In the distance measuring device according to another aspect of the present invention, the optical distance difference is represented by the product of the path difference between the measurement light and the reference light and the refractive index of the path between the measurement light and the reference light, and the path difference is D And the refractive index is n and the speed of light is C ₀ , the time delay detection unit calculates the time delay τ as follows:

  Calculate using. As a result, the phases of the first reference sine wave signal and the second reference sine wave signal are corrected (the above-described phase delay is corrected) based on the optical distance difference calculated by the distance difference calculation unit, and the sine wave signal detection unit It is possible to control the detection of a two-phase sinusoidal signal.

In a distance measuring apparatus according to another aspect of the present invention, the center frequency of the optical frequency of the light wave phase-modulated by the sine wave is f _c , the amplitude and angular frequency of the alternating-current component of the optical frequency are Δf and ω _m , respectively, and was a t, the first kind k-th Bessel function and J _{k (m),} if the 2π × f _c × τ was phi, the optical frequency f (t), and the intensity I of the interference signal, a first reference sine The wave signal R1(t) and the second reference sine wave signal R2(t) and the two-phase sine wave signals S1(φ) and S2(φ) are expressed by the following equations:

  Is represented by. Thereby, based on the optical distance difference calculated by the distance difference calculation unit, the phases of the first reference sine wave signal and the second reference sine wave signal are corrected by referring to the above-mentioned mathematical expressions, and the sine wave signal detection unit It is possible to control the detection of a two-phase sinusoidal signal.

  In the distance measuring device according to another aspect of the present invention, the sine wave signal detection unit is a lock-in amplifier. As a result, a two-phase sine wave signal can be detected from the interference signal.

  In the distance measuring device according to another aspect of the present invention, the phase difference between the two-phase sine wave signals is 90°, and the distance difference calculation unit calculates the two-phase sine wave signals forming the elliptic Lissajous waveform as true The correction is made into a two-phase correction signal forming a Lissajous waveform of a circle, and the optical distance difference is calculated based on the two-phase correction signal. Thereby, the distance from the predetermined reference position to the measurement object can be calculated, and at least one of the amplitude control and the two-phase sine wave signal detection control described above can be performed.

  A distance measuring method for achieving the object of the present invention includes a light wave generation step of generating a light wave whose sine wave is phase-modulated by a sine wave, and a division method of dividing the light wave generated in the light wave generation step into a measurement light and a reference light. Step, after the dividing step, the measurement light emitted to the measurement object displaced along the path of the measurement light and reflected by the measurement object, the interference signal detection step of detecting the interference signal of the reference light, Based on the sine wave signal detection step of detecting a two-phase sine wave signal from the interference signal detected in the interference signal detection step and the two-phase sine wave signal detected in the sine wave signal detection step, the measurement light and the reference light are A distance difference calculating step of calculating an optical distance difference between, and an amplitude determining step of determining the amplitude of the AC component of the optical frequency of the light wave, based on the optical distance difference calculated in the distance difference calculating step, and Generated in the light wave generation step based on the amplitude determination step of determining the amplitude at which the modulation index that determines the aspect ratio of the Lissajous waveform formed by the two-phase sine wave signal is kept constant, and the determination result of the amplitude determination step An amplitude control step of controlling the amplitude of the light wave.

  A distance measuring method for achieving the object of the present invention includes a light wave generation step of generating a light wave whose sine wave is phase-modulated by a sine wave, and a division method of dividing the light wave generated in the light wave generation step into a measurement light and a reference light. Step, after the dividing step, the measurement light emitted to the measurement object displaced along the path of the measurement light and reflected by the measurement object, the interference signal detection step of detecting the interference signal of the reference light, A sine wave signal detecting step of detecting two-phase sine wave signals respectively corresponding to the first reference sine wave signal and the second reference sine wave signal from the interference signal detected in the interference signal detecting step, and a sine wave signal detecting step. Based on the detected two-phase sine wave signal, a distance difference calculation step for calculating an optical distance difference between the measurement light and the reference light, and a measurement light based on the optical distance difference calculated in the distance difference calculation step. A time delay detecting step of detecting a time delay with respect to the reference light, and the phases of the first reference sine wave signal and the second reference sine wave signal are corrected based on the detection result of the time delay detecting step. A detection control step of executing the detection of the two-phase sine wave signal in the sine wave signal detection step based on the first reference sine wave signal and the second reference sine wave signal.

  The distance measuring device and the distance measuring method of the present invention can measure the distance even when the position of the measuring object is displaced.

It is a block diagram which shows the structure of the distance measuring device of 1st Embodiment. It is a functional block diagram which shows the function of the computer of 1st Embodiment. It is an explanatory view for explaining a correction process by a correction part. It is a flowchart showing a flow of a measurement process of the initial path difference D _0. It is an explanatory diagram for explaining the measurement process of the initial path difference D _0. It is a flow chart which shows a flow of distance measurement processing by a distance measuring device of a 1st embodiment. It is explanatory drawing for demonstrating the effect of the distance measuring device of 1st Embodiment. It is a block diagram which shows the structure of the distance measuring device of 2nd Embodiment. It is a functional block diagram which shows the function of the computer of 2nd Embodiment. It is a flow chart which shows a flow of distance measurement processing by a distance measuring device of a 2nd embodiment. It is explanatory drawing for demonstrating the effect of the distance measuring device of 2nd Embodiment. It is a block diagram which shows the structure of the distance measuring device of 3rd Embodiment. It is a functional block diagram which shows the function of the computer of 3rd Embodiment. It is a flow chart which shows a flow of distance measurement processing by a distance measuring device of a 3rd embodiment. It is a block diagram which shows the structure of the distance measuring device of 4th Embodiment. It is a functional block diagram which shows the function of the computer of 4th Embodiment. It is explanatory drawing for demonstrating the correction process by the 1st correction|amendment part and 2nd correction|amendment part of 4th Embodiment. It is a block diagram which shows the structure of the distance measuring device of 5th Embodiment. It is a flow chart which shows a flow of distance measurement processing by a distance measuring device of a 6th embodiment.

[Distance Measuring Device of First Embodiment]
FIG. 1 is a configuration diagram showing a configuration of a distance measuring device 10 of the first embodiment. The distance measuring device 10 measures the distance from a predetermined reference position (for example, the beam splitter 13) to the measurement light side mirror 14 corresponding to the measurement object of the present invention by using the sine wave phase modulation method. The distance measuring device 10 includes a light wave generation unit 12, a beam splitter 13, a measurement light side mirror 14, a reference light side mirror 15, a shift mechanism 16, a detector 17, a first lock-in amplifier 18, A second lock-in amplifier 19 and a computer 20 are provided.

The light wave generation unit 12 includes an oscillator 22 and a laser light source 23. The oscillator 22 emits a sine wave signal S0(t) represented by the following [Formula 1] to the laser light source 23. Here, “I ₀ ”in the formula [1] is the signal strength (amplitude) of the sine wave signal S0(t), “ω _m ”is the angular frequency of the sine wave signal S0(t), and "t" is time.

  The laser light source 23 is, for example, a semiconductor laser light source (LD: Laser Diode), and is driven based on a sine wave signal S0(t) input from the oscillator 22. The oscillation wavelength of the laser light L (corresponding to the light wave of the present invention) emitted from the laser light source 23 shifts in a sinusoidal shape due to the direct frequency modulation characteristic of the LD. Therefore, the laser light L undergoes a sinusoidal phase shift. Thus, the laser light source 23 generates the laser light L that has been subjected to the sinusoidal phase modulation, and is emitted to the beam splitter 13 via an optical fiber cable (not shown).

  The method of generating the laser light L that is sine-wave phase modulated is not limited to the method of using the direct frequency modulation characteristic of the LD, but an indirect modulation by a known electro-optical element (EO element) is used. Good.

The sine wave phase-modulated laser light L has an optical frequency f(t) represented by the following [Formula 2]. Here, the center frequency of "f _c" is the optical frequency f in Equation 2] formula (t), "Δf" is the AC component of the optical frequency f varies with the sinusoidal phase modulation (t) [AC (Alternating current) component]. Further, the above-mentioned angular frequency “ω _m ”becomes the angular frequency (modulation angular frequency) of the AC component of the optical frequency f(t). In other words, “Δf” and “ω _m ” are the amplitude and angular frequency of the [sine wave phase] modulation of the optical frequency f(t).

  The beam splitter 13 corresponds to the splitting unit of the present invention, splits the laser light L incident from the laser light source 23 into the measurement light mL and the reference light rL, and transfers the measurement light mL to the measurement light side mirror 14. It emits (transmits) toward and reflects the reference light rL toward the reference light side mirror 15. In addition, the beam splitter 13 reflects the measurement light mL reflected by the measurement light side mirror 14 toward the detector 17, and transmits the reference light rL reflected by the reference light side mirror 15 to the detector. It is emitted toward 17.

The measurement light side mirror 14 reflects the measurement light mL incident from the beam splitter 13 toward the beam splitter 13. The measurement light side mirror 14 is moved (displaced) along the path (optical path) of the measurement light mL incident on the measurement light side mirror 14 by the shift mechanism 16. As a result, the distance D _m between the beam splitter 13 and the measurement light side mirror 14 is changed.

The shift mechanism 16 is a moving mechanism that moves the measurement light side mirror 14 along the path of the measurement light mL, and its movement method (mechanism) is not particularly limited as long as the distance D _m can be changed, and a longer stroke is possible. The mechanism corresponding to the movement of is used. The shift mechanism 16 moves the measurement light side mirror 14 from the measurement start position (initial position) to the target position (stop position) desired by the user along the path of the measurement light mL when the distance is measured by the distance measuring device 10. .. Then, in the present embodiment, after being moved from the measurement start position to the target position by the shift mechanism 16, the distance D _r between the beam splitter 13 and the reference light side mirror 15 and the distance between the beam splitter 13 and the measurement light side mirror 14 are reduced. The path difference D from the distance D _m between them is measured. In addition, "distance measurement" in each embodiment of the present specification refers to measurement of the path difference D.

Reference light side mirror 15 is provided spaced a distance D _r along the path of the reference light rL from the beam splitter 13, reflects the reference light rL incident from the beam splitter 13 to the beam splitter 13 .

Since the general form of the phase φ(t) of light is represented by the following [Equation 3], the phase φ _m (t) of the measurement light mL and the phase φ _r (t) of the reference light rL are as follows. It is expressed by the equation [4]. Where [Equation 3] "phi _0" in the formula and in [Equation 4] where is the initial phase, the "f _m" is the AC component of the optical frequency f (t) Frequency (optical frequency f (t) [ Sinusoidal phase] frequency of modulation), and satisfies “ω _m =2πf _m ”. Further, “τ” in the formula [4] is a time delay of the measurement light mL caused by the path difference between the measurement light mL and the reference light rL (the measurement light mL divided by the beam splitter 13 and the reference light rL are This is the time difference of returning to the beam splitter 13. This time delay τ is the refractive index of both paths for the measurement light mL and the reference light rL, where D (D=D _m −D _r ) is the path difference (geometric distance difference) between the measurement light mL and the reference light rL. Is n and the speed of light is c ₀ , τ=2×n×D/c ₀ (hereinafter, 2nD/c ₀ ) is satisfied. Then, a light intensity _{E m} of the measuring light mL, the light intensity _{E r} of the reference light rL are respectively represented by the following Equation 5 Equation. Here, in the following [Formula 5], the light intensities E _{m and} E _r are represented by E _m =Aexp(iφ _m (t)) and E _r =Bexp(iφ _r (t)). Amplitudes A and B in the equation are omitted because they do not affect the subsequent description.

  The measurement light mL reflected by the measurement light side mirror 14 and the reference light rL reflected by the reference light side mirror 15 are combined by the beam splitter 13. As a result, the interference signal IL, which is an optical interference signal between the measurement light mL and the reference light rL, is emitted from the beam splitter 13 to the detector 17 via an optical fiber cable (not shown).

  The detector 17 corresponds to the interference signal detector of the present invention, and is, for example, a CCD (Charge Coupled Device) type or CMOS (complementary metal oxide semiconductor) type image sensor, or a photodiode. The detector 17 detects (receives) the interference signal IL incident from the beam splitter 13, and converts the interference signal IL into an interference signal Sig which is an electric signal. Then, the detector 17 outputs the detected interference signal Sig to the first lock-in amplifier 18 and the second lock-in amplifier 19, respectively, via a signal line (not shown).

Here, the interference signal Sig indicates the intensity I of the interference signal IL and is represented by the following [Equation 6]. The “phase φ” in the formula [6] satisfies the formula [7] below, and the “modulation index m” in the formula 6 satisfies the formula [8] below. Then, when the formula [6] is series-expanded by the first-order kth-order Bessel function J _k (m), the formula [6] is represented by the following formula [9].

  The first lock-in amplifier 18 and the second lock-in amplifier 19 correspond to the sine wave signal detection unit of the present invention. The first lock-in amplifier 18 and the second lock-in amplifier 19 use a first reference sine wave signal R1(t) and a second reference sine wave signal R1 (t), which will be described later, from the interference signal Sig (intensity I of the interference signal IL) input from the detector 17. Two-phase sine wave signals S1(φ) and S2(φ) having a phase difference of 90° (including approximately 90°) respectively corresponding to the reference sine wave signal R2(t) are detected.

  The first lock-in amplifier 18 includes a first oscillator 25, a first multiplier 26, and a first low-pass filter 27 indicated by “LPF” (Low-pass filter) in the figure.

The first oscillator 25 uses the first reference sine wave signal R1(t){ corresponding to “J ₂ (m)cos{2ω _m (t−τ/2)}” in the second term of the above [Formula 9]. The following [Formula 10] reference} is output to the first multiplier 26. The first multiplier 26 multiplies the interference signal Sig (intensity I) input from the detector 17 by the first reference sine wave signal R1(t) input from the first oscillator 25, and outputs the multiplication signal as the first signal. 1 to the low-pass filter 27.

  The first low-pass filter 27 performs low-pass filter processing on the multiplication signal input from the first multiplier 26. As a result, only the component of the interference signal Sig (intensity I) that is equal to the frequency of the first reference sine wave signal R1(t) becomes DC, and the first sine wave signal S1(φ) corresponding to this DC component becomes It passes through the 1 low-pass filter 27. As a result, the first lock-in amplifier 18 causes the first sine wave signal S1(φ) of the frequency component corresponding to the first reference sine wave signal R1(t) from the interference signal Sig (intensity I) {the following [Equation 11] ] Reference expression} is detected.

  The second lock-in amplifier 19 includes a second oscillator 29, a second multiplier 30, and a second low-pass filter 31 indicated by “LPF” in the figure.

The second oscillator 29 uses the second reference sine wave signal R2(t){ corresponding to “J ₃ (m)sin{3ω _m (t−τ/2)}” in the third term of the above [Formula 9]. The following [Equation 10] reference} is output to the second multiplier 30. The second multiplier 30 multiplies the interference signal Sig (intensity I) input from the detector 17 by the second reference sine wave signal R2(t) input from the second oscillator 29, and outputs the multiplication signal as the first signal. 2 Output to the low pass filter 31. The second lock-in amplifier 19 performs low-pass filter processing on the multiplication signal input from the second multiplier 30. As a result, the second lock-in amplifier 19 causes the second sine wave signal S2(φ) of the frequency component corresponding to the second reference sine wave signal R2(t) from the interference signal Sig (intensity I) to ] Reference expression} is detected.

  As described above, the first lock-in amplifier 18 and the second lock-in amplifier 19 have the two-phase first sine wave signal S1 (φ) and the second sine wave signal S2 having a phase difference of 90° from the interference signal Sig (intensity I). (Φ) [hereinafter, abbreviated as two-phase sine wave signals S1(φ) and S2(φ)] is detected, and these two-phase sine wave signals S1(φ) and S2(φ) are output to the computer 20. To do. Since these two-phase sine wave signals S1(φ) and S2(φ) have a phase difference of 90°, they form an elliptic Lissajous waveform W1 (see FIG. 3) described later.

  The two-phase sine wave signals S1(φ) and S2(φ) have a phase difference of 90°, that is, if an elliptical Lissajous waveform W1 (see FIG. 3) can be formed, the equation [11] is used. The present invention is not limited to this. In this case, the first reference sine wave signal R1(t) and the second reference sine wave signal R2(t) are generated according to the detected two-phase sine wave signals S1(φ) and S2(φ). change.

Further, in the present embodiment, when the distance measurement is started by the distance measuring device 10, that is, when the measurement light side mirror 14 is at the measurement start position before the movement start (before the displacement start), the two-phase sine wave signal S1 (φ ), S2(φ) phase difference error (error from ideal value 90°) is corrected so that the two-phase sine wave signals S1(φ) and S2(φ) are phase difference corrected. .. This phase difference correction is performed, for example, by moving the measurement light side mirror 14 (changing the distance D _m ) by the shift mechanism 16 or changing the center frequency f _c of the above [Formula 2]. ..

  When an offset error occurs in the two-phase sine wave signals S1(φ) and S2(φ), that is, when the center of the Lissajous waveform W1 (see FIG. 3) deviates from the origin, the two-phase sine wave signal S1 is generated. Offset correction is also performed on (φ) and S2(φ). Here, since the offset correction is a known technique, its details are omitted.

The computer 20 is wired or wirelessly connected to the oscillator 22, the first low pass filter 27, and the second low pass filter 31. As will be described later in detail, the computer 20 uses the measurement light mL based on the two-phase sine wave signals S1(φ) and S2(φ) input from the first lock-in amplifier 18 and the second lock-in amplifier 19. An optical distance difference nD from the reference light rL (see FIG. 2) is calculated. This optical distance difference nD is represented by the product of the path difference D(D _m −D _r ) between the measurement light mL and the reference light rL and the refractive index n of the paths of the measurement light mL and the reference light rL. Then, the computer 20 controls the amplitude Δf in the above [Formula 2] based on the calculated optical distance difference nD.

  Although not shown, the computer 20 operates the entire distance measuring apparatus 10 including the light wave generation unit 12, the shift mechanism 16, the detector 17, the first lock-in amplifier 18, and the second lock-in amplifier 19. You may perform integrated control.

[Configuration of Computer of First Embodiment]
FIG. 2 is a functional block diagram showing the functions of the computer 20 of the first embodiment. The computer 20 has an arithmetic processing circuit (not shown) including various arithmetic units, processing units, and storage units. As shown in FIG. 2, the computer 20 executes a distance measurement program (not shown) read out from a memory or the like (not shown) by the arithmetic processing circuit, so that the signal acquisition unit 34, the correction unit 35, and the calculation unit 36. And functions as the information acquisition unit 37, the amplitude determination unit 38, and the amplitude control unit 39.

  The signal acquisition unit 34 acquires and acquires the two-phase sine wave signals S1(φ) and S2(φ) from the first lock-in amplifier 18 and the second lock-in amplifier 19 via a communication interface (not shown). Two-phase sine wave signals S1(φ) and S2(φ) are output to the correction unit 35.

FIG. 3 is an explanatory diagram for explaining the correction processing by the correction unit 35. As shown in FIG. 3, the Lissajous waveform W1 formed by the two-phase sine wave signals S1(φ) and S2(φ) is a coefficient [J of the two-phase sine wave signals S1(φ) and S2(φ). ₂ (m), J ₃ (m)], it is not a perfect circle centered on the origin but an ellipse centered on the origin. Therefore, the correction unit 35 corrects the aspect ratio of the Lissajous waveform W1 by multiplying the two-phase sine wave signals S1(φ) and S2(φ) by a “predetermined coefficient”, that is, centering on the origin. The correction is performed to generate the two-phase correction signals V1(φ) and V2(φ) so as to form the perfect circular Lissajous waveform W2. Hereinafter, this correction is referred to as amplitude correction.

Here, the "predetermined coefficient" means that the Lissajous waveform W1 is approximated to an ellipse by the method of least squares, or a two-phase sine wave signal in a state where the measurement light side mirror 14 is at the measurement start position before the movement start. After detecting the amplitude ratio of S1 (φ) and S2 (φ) or determining the modulation index m by measuring an initial path difference D ₀ described later with a general-purpose measure, the coefficients [J ₂ (m), J ₃ ( m)] is calculated by a known method. Then, the correction unit 35 stores the “predetermined coefficient” obtained before the movement of the measurement light side mirror 14 is started, and obtains it until the measurement light side mirror 14 reaches the target position from the measurement start position. The two-phase sine wave signals S1(φ) and S2(φ) thus generated are multiplied by a predetermined coefficient stored in advance to perform amplitude correction. The two-phase correction signals V1(φ) and V2(φ) corrected by the correction unit 35 are output to the calculation unit 36 (see FIG. 2).

  Returning to FIG. 2, the calculation unit 36 functions as the distance difference calculation unit of the present invention together with the correction unit 35 described above. The calculation unit 36 draws the Lissajous waveform W2 shown in FIG. 3 described above based on the two-phase correction signals V1(φ) and V2(φ) input from the correction unit 35 from the start of measurement to the present time. The number of rotations (real number) rotated around the origin is counted as a count value. This count value is a value indicating the magnitude of the phase change amount of the phase difference φ (see FIG. 3) shown in the above [Formula 7].

Then, calculating unit 36, the count value obtained by counting, based on the known center frequency f _c and the velocity of light C _0, to calculate the optical distance difference nD from the [Equation 7] expression. Then, the calculation unit 36 calculates the path difference D based on the calculated optical distance difference nD and the known refractive index n. The calculation unit 36 also outputs the calculation result of the optical distance difference nD to the amplitude determination unit 38.

The information acquisition unit 37 starts the distance measurement, that is, when the measurement light side mirror 14 is at the measurement start position, the path difference D, the refractive index n, and the initial path difference D ₀ and the initial refractive index respectively corresponding to the amplitude Δf. Obtain n ₀ and the initial amplitude Δf ₀ . Further, the information acquisition unit 37 acquires the angular frequency ω _m , the center frequency f _c , and the distance D _r . Here, since the initial refractive index n ₀ (n=n ₀ in this embodiment) is almost constant, and the initial amplitude Δf ₀ , the angular frequency ω _m , the center frequency f _c, and the distance D _r are set values, The information acquisition unit 37 acquires each value input by the user in advance.

As the initial path difference D ₀ (also referred to as dead path), a value measured by a general-purpose measure or a value measured by the distance measuring device 10 can be acquired. Hereinafter, an example of a method of measuring (calculating) the initial path difference D ₀ by the distance measuring device 10 will be described. Here, the initial path difference D ₀ is represented by the following [Equation 12] based on the above [Equation 8] and “ω _m =2πf _m ”.

In the above [Formula 12], since the initial refractive index n ₀ , the initial amplitude Δf ₀ , and the angular frequency ω _m are constants or set values, the modulation index m is calculated to obtain the initial path from the above [Formula 12]. The difference D ₀ can be determined.

FIG. 4 is a flowchart showing the flow of the measurement process of the initial path difference D ₀ . In addition, FIG. 5 is an explanatory diagram for explaining the measurement processing of the initial path difference D ₀ . As shown in FIGS. 4 and 5, the information acquisition unit 37 acquires from the signal acquisition unit 34 the two-phase uncorrected sine wave signals S1(φ) and S2(φ) that form the Lissajous waveform W1 (step). S1).

  Next, the information acquisition unit 37 performs ellipse approximation by the least-squares method or the like on the elliptic Lissajous waveform W1 formed by the two-phase sine wave signals S1(φ) and S2(φ). The formula [13] is obtained (step S2).

  An equation obtained by solving the equation [13] for "m" is represented by "m=F(x)". Then, the information acquisition unit 37 calculates the modulation index m by performing polynomial approximation on F(x) by, for example, a 9th-order polynomial, as shown by a graph 41 in FIG. 5 (step S3).

Next, the information acquisition unit 37 sets the previously acquired initial refractive index n ₀ , initial amplitude Δf _0, and angular frequency ω _m , the modulation index m calculated in step S3, and the known speed of light C ₀ to the above [ Equation 12] is substituted into the equation to calculate the initial path difference D ₀ (step S4). According to this method, the modulation index m can be calculated with a calculation accuracy of ±0.02, and as a result, the initial path difference D ₀ can be calculated with a calculation accuracy of ±450 μm. As a result, the distance measuring device 10 can obtain the measurement result of the initial path difference D ₀ .

Returning to FIG. 2, the information acquisition unit 37 outputs various information including the refractive index n and the center frequency f _c to the calculator 36 described above. Thereby, the calculation unit 36 can calculate the above-mentioned optical distance difference nD. Further, the information acquisition unit 37 outputs various information including the acquired initial path difference D ₀ , initial refractive index n ₀ , initial amplitude Δf _0, and angular frequency ω _m to the amplitude determination unit 38.

The amplitude determination unit 38 is generated by the light wave generation unit 12 based on the optical distance difference nD input from the calculation unit 36 and various information such as the initial path difference D ₀ input from the information acquisition unit 37. The amplitude Δf of the optical frequency f(t) of the laser light L to be generated (see the above [Formula 2]) is determined. At this time, the amplitude determining unit 38 determines the amplitude Δf so as to keep the above-mentioned modulation index m constant. In other words, the modulation index m is a value that determines the aspect ratio [J ₂ (m)/J ₃ (m)] of the Lissajous waveform W1 formed by the two-phase sine wave signals S1(φ) and S2(φ). Therefore, the amplitude determination unit 38 determines the amplitude Δf that keeps the aspect ratio of the Lissajous waveform W1 constant.

Specifically, the amplitude Δf that keeps the modulation index m constant is represented by the following [Formula 14] based on the above [Formula 8]. Therefore, the amplitude determining unit 38 determines that the optical distance difference nD and the initial path difference D
_By substituting various information such as ₀ into the following [Formula 14], the amplitude Δf for keeping the modulation index m constant is determined. Then, the amplitude determination unit 38 outputs the determination result of the amplitude Δf to the amplitude control unit 39.

The amplitude control unit 39 sets the oscillator so that the amplitude Δf of the optical frequency f(t) of the laser light L generated by the light wave generation unit 12 matches the determination result of the amplitude Δf input from the amplitude determination unit 38. 22 controls the angular frequency ω _m of the sine wave signal S0(t). For example, a data table or an arithmetic expression showing the correspondence relationship between the amplitude Δf of the optical frequency f(t) and the angular frequency ω _m of the sine wave signal S0(t) at which the amplitude Δf is realized is generated in advance. Thereby, the amplitude control unit 39 determines the angular frequency ω _m of the sine wave signal S0(t) corresponding to the determination result of the amplitude Δf based on the data table or the arithmetic expression, and outputs the sine wave output from the oscillator 22. The angular frequency ω _m of the signal S0(t) can be controlled.

[Operation of the distance measuring device of the first embodiment]
Next, the operation of the distance measuring device 10 having the above configuration will be described with reference to FIG. Here, FIG. 6 is a flowchart showing the flow of the distance measurement processing (distance measurement method) by the distance measurement device 10 of the first embodiment. Here, the distance measurement of the measurement light side mirror 14 moved from the measurement start position to the target position by the shift mechanism 16 will be described.

  When the user turns on the power of each unit of the distance measuring device 10, the laser light source 23 is driven based on the sine wave signal S0(t) output from the oscillator 22 in the light wave generation unit 12, and the optical frequency f( The laser light L of t) is emitted. The laser light L is split by the beam splitter 13 into measurement light mL and reference light rL. Then, the measurement light mL is emitted from the beam splitter 13 to the measurement light side mirror 14, is reflected by the measurement light side mirror 14, and then enters the beam splitter 13. On the other hand, the reference light rL is emitted from the beam splitter 13 to the reference light side mirror 15, is reflected by the reference light side mirror 15, and then enters the beam splitter 13.

  The interference signal IL between the measurement light mL and the reference light rL that has entered the beam splitter 13 enters the detector 17 and is converted by the detector 17 into an interference signal Sig that is an electrical signal. The interference signal IL is output from the detector 17 to the first lock-in amplifier 18 and the second lock-in amplifier 19, respectively.

  Next, in the first lock-in amplifier 18 and the second lock-in amplifier 19, the interference signal Sig (intensity I) corresponds to the first reference sine wave signal R1(t) and the second reference sine wave signal R2(t), respectively. The two-phase sine wave signals S1(φ) and S2(φ) are detected, and these two-phase sine wave signals S1(φ) and S2(φ) are output to the computer 20. With the above, the activation of the distance measuring device 10 is completed (step S10).

Then, the measurement of the initial path difference D ₀ (dead path) is started in the state where the measurement light side mirror 14 is at the measurement start position before the start of movement. Specifically, a method of inputting the measurement result obtained by measuring the initial path difference D ₀ using a general-purpose measure, or the initial path difference D ₀ by the distance measuring device 10 described in FIGS. 4 and 5 described above. Select the measurement method of. As a result, the information acquisition unit 37 of the computer 20 acquires the initial path difference D ₀ (step S11).

Further, the user inputs information regarding the initial refractive index n ₀ (refractive index n), the initial amplitude Δf ₀ , the angular frequency ω _m , the center frequency f _c , and the distance D _r to the computer 20 (information acquisition unit 37). Since these values are already known, the information acquisition unit 37 can acquire these values from the memory or the like by inputting them in the memory or the like of the computer 20 in advance, without the user having to input them. it can. Accordingly, the information acquisition unit 37 outputs various information regarding the refractive index n and the center frequency f _c to the calculation unit 36, and the initial path difference D ₀ , the initial refractive index n ₀ , the initial amplitude Δf _0, and the angular frequency ω _m . It outputs various kinds of information on the amplitude determining unit 38.

Next, when the user performs a correction start operation for correcting the aspect ratio of the Lissajous waveform W1, the correction unit 35 receives the two-phase signals acquired from the first lock-in amplifier 18 and the second lock-in amplifier 19 via the signal acquisition unit 34 and the like. The sine wave signals S1(φ) and S2(φ) are analyzed. Incidentally, in this case, above the offset correction, and a phase difference correction to rotate the Lissajous waveform W1 by changing the movement or center frequency f _c of the measurement light side mirror 14, and as needed.

  Then, the correction unit 35 obtains and stores a predetermined coefficient for correcting the Lissajous waveform W1 into a perfect circle by elliptic approximation of the Lissajous waveform W1 by the method of least squares or the like, and the predetermined coefficient is 2 Amplitude correction is performed by multiplying the phase sine wave signals S1(φ) and S2(φ). As a result, the aspect ratio of the Lissajous waveform W1 is corrected, and the two-phase correction signals V1(φ) and V2(φ) forming the perfect circle Lissajous waveform W2 are generated by the correction unit 35 (step S12). These two-phase correction signals V1(φ) and V2(φ) are input from the correction unit 35 to the calculation unit 36, and the calculation unit 36 starts calculation of the optical distance difference nD. This completes the preparation for moving the measurement light side mirror 14.

  Next, the user performs a control start operation of the amplitude Δf (step S13). As a result, the control of the amplitude Δf shown in step S15 to step S20 described later is started. Further, the user operates the shift mechanism 16 to move the measurement light side mirror 14. As a result, the shift mechanism 16 moves the measurement light side mirror 14 from the measurement start position to the target position along the path of the measurement light mL (step S14).

  At this time, the light wave generation unit 12 generates the laser light L, the beam splitter 13 splits the laser light L, the detector 17 detects the interference signal Sig, and the first lock-in amplifier 18 and the second lock-in amplifier. A measurement process including detection of the two-phase sine wave signals S1(φ) and S2(φ) by 19 is executed (step S15). The measurement process of step S15 corresponds to the light wave generation step, the division step, the interference signal detection step, and the sine wave signal detection step of the present invention.

  The signal acquisition unit 34 of the computer 20 acquires the two-phase sine wave signals S1(φ) and S2(φ) from the first lock-in amplifier 18 and the second lock-in amplifier 19, and the two-phase sine wave signals S1. (Φ) and S2(φ) are input to the correction unit 35 (step S16). The two-phase sine wave signals S1(φ) and S2(φ) input to the correction unit 35 are subjected to amplitude correction or the like by multiplying the predetermined coefficient previously obtained by the correction unit 35 (step S17). As a result, the two-phase correction signals V1(φ) and V2(φ) whose amplitudes have been corrected are input from the correction unit 35 to the calculation unit 36.

The calculation unit 36, which receives the two-phase correction signals V1(φ) and V2(φ), counts the count value described above, and the center frequency f _c acquired from the information acquisition unit 37. And the known speed of light C ₀ , the optical distance difference nD is calculated from the equation [7] (step S18, which corresponds to the distance difference calculating step of the present invention). The calculation result of the optical distance difference nD is input from the calculation unit 36 to the amplitude determination unit 38. Further, the calculation unit 36 calculates the current path difference D (geometric distance difference) based on the calculation result of the optical distance difference nD and the information of the refractive index n input from the information acquisition unit 37.

Upon receiving the input of the calculation result of the optical distance difference nD, the amplitude determining unit 38, based on the optical distance difference nD and various information such as the initial path difference D ₀ previously input from the information acquiring unit 37, An amplitude Δf that keeps the modulation index m constant is determined using the equation [14] (step S19, which corresponds to the amplitude determination step of the present invention). The determination result of the amplitude Δf is input from the amplitude determination unit 38 to the amplitude control unit 39.

Upon receiving the input of the determination result of the amplitude Δf, the amplitude control unit 39 determines the angular frequency ω _m of the sine wave signal S0(t) corresponding to the determination result of the amplitude Δf by using the above-described data table or arithmetic expression. By doing so, the angular frequency ω _m of the sine wave signal S0(t) output from the oscillator 22 is controlled. As a result, the amplitude Δf is controlled so as to keep the modulation index m constant (step S20, which corresponds to the amplitude control step of the present invention).

  Hereinafter, the processes from step S15 to step S20 described above are repeatedly executed until the measurement light side mirror 14 reaches the target position (NO in step S21). As a result, the above-described control of the amplitude Δf is continuously performed.

  When the measurement light side mirror 14 reaches the target position (YES in step S21), the movement by the shift mechanism 16 is completed and the measurement light side mirror 14 stops at the target position. Then, the optical distance difference nD in the state where the measurement light side mirror 14 is stopped at the target position is calculated by the processing from step S15 to step S18 described above. Then, the calculation unit 36 calculates the current path difference D (at the target position) D (geometric distance) based on the calculation result of the optical distance difference nD and the information about the refractive index n input from the information acquisition unit 37. The difference) is calculated (step S22).

[Effects of Distance Measuring Device of First Embodiment]
FIG. 7 is an explanatory diagram for explaining the effect of the distance measuring device 10 of the first embodiment. Note that “J ₂ , J ₃ ”in the figure is a value indicating the aspect ratio [J ₂ (m)/J ₃ (m)] of the Lissajous waveform W 1, and “distance (m)” is determined by the shift mechanism 16. It is a moving distance of the measuring light side mirror 14 to be moved. Further, Comparative Example 44 and Example 45 in FIG. 7 were obtained under the conditions that f _m =10 MHz, Δf ₀ =200 MHz, D ₀ =1 m, n ₀ (n)≈1, and C ₀ were the light speed in vacuum. It has been done.

As shown in the upper part of FIG. 7, in Comparative Example 44 in which the control of the amplitude Δf is not performed, “J ₂ and J ₃ ”, that is, the aspect ratio of the Lissajous waveform W1 changes with the movement of the measurement light side mirror 14. Therefore, when the two-phase sine wave signals S1(φ) and S2(φ) forming the Lissajous waveform W1 are multiplied by the predetermined coefficient obtained previously, a perfect circular Lissajous waveform W2 is formed. Two-phase correction signals V1(φ) and V2(φ) cannot be obtained. Even if the path difference D (geometrical distance difference) of the measurement light side mirror 14 is obtained based on the two-phase correction signals V1(φ) and V2(φ), the measurement error will be large.

  Further, when the radius value of the Lissajous waveform W1 becomes small during the movement of the measurement light side mirror 14, that is, when the signal strengths of the two-phase sine wave signals S1(φ) and S2(φ) become weak, The difference D (geometrical distance difference) may not be measured. In particular, since the distance measurement by the distance measuring device 10 is a relative measurement, once the radius value of the Lissajous waveform W1 becomes zero (that is, once the Lissajous waveform W1 disappears), subsequent measurement cannot be performed.

In contrast to the comparative example 44, as shown in the lower part of FIG. 7, in the present example 45 in which the control of the amplitude Δf is executed, the modulation index m is kept constant regardless of the movement of the measurement light side mirror 14. As a result, “J ₂ and J ₃ ”, that is, the aspect ratio of the Lissajous waveform W1 is kept constant,
The radius value of the Lissajous waveform W1 never becomes zero. As a result, when the two-phase sine wave signals S1(φ) and S2(φ) acquired at the respective positions of the measurement light side mirror 14 are multiplied by the respective predetermined coefficients, the Lissajous circle is always a perfect circle. Two-phase correction signals V1(φ) and V2(φ) forming the waveform W2 are obtained. As a result, the path difference D (geometric distance difference) after stopping at the target position can be accurately measured.

[Distance Measuring Device of Second Embodiment]
Next, the distance measuring device 10A of the second embodiment will be described with reference to FIG. FIG. 8: is a block diagram which shows the structure of 10 A of distance measuring apparatuses of 2nd Embodiment. In the distance measuring device 10 of the first embodiment, the amplitude Δf of the optical frequency f(t) is controlled based on the calculation result of the optical distance difference nD and the like, but in the distance measuring device 10A of the second embodiment, The detection control of the two-phase sine wave signals S1(φ) and S2(φ) by the first lock-in amplifier 18 and the second lock-in amplifier 19 is performed based on the calculation result of the physical distance difference nD.

  As shown in FIG. 8, in the distance measuring apparatus 10A of the second embodiment, the computer 20 is connected to the first oscillator 25 and the second oscillator 29 in place of the oscillator 22 in a wired or wireless manner, except for the above-mentioned first embodiment. It has basically the same configuration as the distance measuring device 10 of the one embodiment. Therefore, the same functions or configurations as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

  FIG. 9 is a functional block diagram showing the functions of the computer 20 of the second embodiment. As shown in FIG. 9, in the computer 20 of the second embodiment, an arithmetic processing circuit (not shown) executes the distance measurement program (not shown) described above, so that the signal acquisition unit 34 and the correction unit 35 described above. , And the calculation unit 36 and the information acquisition unit 37, and also functions as the time delay detection unit 50 and the detection control unit 51.

The information acquisition unit 37 of the second embodiment acquires the initial refractive index n ₀ (refractive index n), the center frequency f _{c, and the} like, and outputs these various types of information to the calculation unit 36. As a result, the calculation unit 36 of the second embodiment calculates the optical distance difference nD from the above [Formula 7] as in the first embodiment, and detects the calculation result of the optical distance difference nD as a time delay. Output to the unit 50. Further, the information acquisition unit 37 of the second embodiment outputs information regarding the refractive index n to the time delay detection unit 50.

The time delay detection unit 50 sets the optical distance difference nD input from the calculation unit 36, the refractive index n (input is not necessary if known) input from the information acquisition unit 37, and the known speed of light C ₀ . Based on the following [Equation 15], the above-mentioned time delay τ is calculated. Then, the time delay detection unit 50 outputs the calculation result of the time delay τ to the detection control unit 51.

  The detection control unit 51, based on the calculation result (detection result) of the time delay τ input from the time delay detection unit 50, outputs the first reference sine wave signal R1( output by the first oscillator 25 of the first lock-in amplifier 18). The phase of t) and the phase of the second reference sine wave signal R2(t) output from the second oscillator 29 of the second lock-in amplifier 19 are corrected (see the formula [Equation 10] above). Then, the detection control unit 51 causes the first lock-in amplifier 18 and the second lock-in amplifier 19 to operate based on the phase-corrected first reference sine wave signal R1(t) and second reference sine wave signal R2(t). Detection control for detecting the two-phase sine wave signals S1(φ) and S2(φ) is performed.

[Operation of the distance measuring device of the second embodiment]
Next, the operation of the distance measuring device 10A having the above configuration will be described with reference to FIG. Here, FIG. 10 is a flowchart showing a flow of a distance measuring process (distance measuring method) by the distance measuring device 10A of the second embodiment.

  Since the processing from step S10 to step S12 is basically the same as that of the first embodiment, a detailed description is omitted here. Then, when step S12 is completed, the user performs a control start operation for starting the detection control of the two-phase sine wave signals S1(φ) and S2(φ) by the first lock-in amplifier 18 and the second lock-in amplifier 19. Perform (step S13A). As a result, the detection control of the two-phase sine wave signals S1(φ) and S2(φ) shown in step S15 to step S20A described later is started.

  Then, the user moves the measurement light side mirror 14 toward the target position from the measurement start position by the shift mechanism 16 as in the first embodiment (step S14).

  At this time, the processing from step S15 to step S18 is executed as in the first embodiment, and the calculation unit 36 calculates the optical distance difference nD corresponding to the position of the measurement light side mirror 14 at the present time and the time. Input to the delay detection unit 50.

The time delay detection unit 50 that has received the input of the optical distance difference nD, based on the optical distance difference nD, the refractive index n input from the information acquisition unit 37, and the known speed of light C ₀ , calculates 15] is used to calculate (detect) the time delay τ, and the calculation result of the time delay τ is input to the detection control unit 51 (step S19A, which corresponds to the time delay detection step of the present invention).

  Upon receiving the input of the calculation result of the time delay τ, the detection control unit 51 determines the phases of the first reference sine wave signal R1(t) and the second reference sine wave signal R2(t) based on the calculation result of the time delay τ. The first reference sine wave signal R1(t) and the second reference sine wave signal R2(t), which have been corrected and phase-corrected, are output from the first oscillator 25 and the second oscillator 29. As a result, the first lock-in amplifier 18 and the second lock-in amplifier 19 output the interference signal Sig based on the phase-corrected first reference sine wave signal R1(t) and second reference sine wave signal R2(t). Detection control for detecting the two-phase sine wave signals S1(φ) and S2(φ) is executed (step S20A, which corresponds to the detection control step of the present invention).

  By such detection control, the phase of the interference signal Sig [strength I] represented by the above [Formula 9] and the first reference sine wave signal R1(t) and the second reference sine wave represented by the above [Formula 10] The phase delay with respect to the phase of the signal R2(t) is corrected.

  Hereinafter, the processes from step S15 to step S20A described above are repeatedly executed until the measurement light side mirror 14 reaches the target position (NO in step S21). Thereby, the above-mentioned detection control is continuously performed.

  When the measurement light side mirror 14 reaches the target position (YES in step S21), the movement by the shift mechanism 16 is completed and the measurement light side mirror 14 stops at the target position. Hereinafter, similar to the first embodiment, the calculation unit 36 calculates the path difference D (geometrical distance difference) after stopping at the target position through the processing from step S15 to step S18 (step S22).

[Effects of Distance Measuring Device of Second Embodiment]
FIG. 11 is an explanatory diagram for explaining the effect of the distance measuring device 10A of the second embodiment. Incidentally, _"a x, _{a y"} in the drawing is a coefficient included in the number 16 the following formula. Further, in the following [Formula 16], "x, y" are the x and y components of the ideal Lissajous waveform W1 with no phase delay, and "X, Y" are the actual Lissajous waveform with phase delay. It is the X component and the Y component of W1. Further, Comparative Example 44A and Example 45A in FIG. 11 were obtained under the conditions of f _m =10 MHz, Δf ₀ =200 MHz, D ₀ =1 m, n ₀ (n)≈1, and C ₀ =light speed in vacuum. It has been done.

As shown in the upper part of FIG. 11, the detection control of the two-phase sine wave signals S1(φ) and S2(φ), that is, the interference signal Sig and the reference sine wave signals R1(t) and R2(t) are performed. In the comparative example 44A in which the phase delay correction control is not executed, the coefficients a _x and a _y change in a sine wave shape. Therefore, the signal strengths of the two-phase sine wave signals S1(φ) and S2(φ) increase/decrease according to changes in the coefficients a _x and a _y . As a result, the signal strength of the two-phase sine wave signals S1(φ) and S2(φ) becomes weak, and the path difference D may not be measured.

In contrast to the comparative example 44A, in the present embodiment 45A in which the detection control of the two-phase sine wave signals S1(φ) and S2(φ) is performed as shown in the lower part of FIG. The correction keeps the coefficients a _x and a _y constant. As a result, the signal strength of the two-phase sine wave signals S1(φ) and S2(φ) as in Comparative Example 44A is prevented from being weakened, so that the path difference D after stopping at the target position can be reliably measured. can do.

[Distance Measuring Device of Third Embodiment]
Next, the distance measuring device 10B of the third embodiment will be described with reference to FIGS. 12 and 13. In the first embodiment, the amplitude Δf of the optical frequency f(t) is controlled, and in the second embodiment, the detection control of the two-phase sine wave signals S1(φ) and S2(φ) is performed. However, the distance measuring device 10B of the third embodiment performs both the control of the amplitude Δf and the detection control of the two-phase sine wave signals S1(φ) and S2(φ).

  FIG. 12: is a block diagram which shows the structure of the distance measuring device 10B of 3rd Embodiment. FIG. 13 is a functional block diagram showing the functions of the computer 20 of the third embodiment. As shown in FIGS. 12 and 13, since the distance measuring device 10B is a device in which the distance measuring device 10 of the first embodiment and the distance measuring device 10A of the second embodiment are combined, The same functions or configurations are designated by the same reference numerals, and description thereof will be omitted.

  The computer 20 of the third embodiment is wired or wirelessly connected to the oscillator 22, the first oscillator 25 and the first low pass filter 27, and the second oscillator 29 and the second low pass filter 31, respectively. Since the computer 20 of the third embodiment has both functions of the computer 20 of each of the above embodiments, the optical frequency f(t) of the optical frequency f(t) is calculated based on the calculation result of the optical distance difference nD. The control of the amplitude Δf and the phase correction of the reference sine wave signals R1(t) and R2(t), that is, the detection control of the two-phase sine wave signals S1(φ) and S2(φ) are performed.

[Operation of Distance Measuring Device of Third Embodiment]
FIG. 14 is a flowchart showing a flow of a distance measuring process (distance measuring method) by the distance measuring device 10B of the third embodiment. The flow of the distance measurement processing of the third embodiment is that a start operation (step S13B) that is a combination of the start operations (steps S13 and S13A) of the above-described embodiments shown in FIGS. 6 and 10 is performed. , Each of the above embodiments except that the control of the amplitude Δf (steps S19 and S20) described in the first embodiment and the detection control (steps S19A and S20A) described in the second embodiment are both performed in parallel. This is basically the same as the flow of the distance measurement processing of the form.

[Effects of Distance Measuring Device of Third Embodiment]
As described above, the distance measuring device 10B according to the third embodiment controls the amplitude Δf of the optical frequency f(t) described in the first embodiment and the two-phase sine wave signal S1(described in the second embodiment. Since both φ) and S2(φ) detection control are executed, all the effects described in the above embodiments can be obtained.

[Distance Measuring Device of Fourth Embodiment]
Next, a distance measuring device 10C according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 15: is a block diagram which shows the structure of 10 C of distance measuring apparatuses of 4th Embodiment. The distance measuring device 10C performs distance measurement by a so-called two-color method as an application example of distance measurement by a sine wave phase modulation method. It should be noted that parts that are the same in function or configuration as those of the above-described respective embodiments are given the same reference numerals, and description thereof will be omitted.

  As shown in FIG. 15, the distance measuring device 10C of the fourth embodiment includes a light wave generation unit 12, a distributor 60, a harmonic wave generator 61 represented by “SHG” (Second Harmonic Generation) in the figure, and a combination. Wave device 62, collimator 63, beam splitter 13, measurement light side mirror 14, reference light side mirror 15, shift mechanism 16, demultiplexer 64, detectors 17A and 17B, and first lock-in. It includes amplifiers 18A and 18B, second lock-in amplifiers 19A and 19B, and a computer 20.

  The distributor 60 (for example, a coupler) distributes the laser light L emitted from the light wave generation unit 12 into the first laser light L1 and the second laser light L2, and the first laser light L1 to the multiplexer 62. The second laser light L2 is emitted toward the harmonic generator 61.

  The harmonic generator 61 wavelength-converts the second laser light L2 incident from the distributor 60 and has a second laser light L2 having an optical frequency [2×f(t)] twice as high as that of the first laser light L1. Is generated and the second laser light L2 is emitted to the multiplexer 62.

  The multiplexer 62 multiplexes the first laser light L1 incident from the distributor 60 and the second laser light L2 incident from the harmonic generator 61, and combines the first laser light L1 and the second laser light L2. The light L2 is emitted to the collimator 63.

  The collimator 63 collimates the first laser light L1 and the second laser light L2 incident from the multiplexer 62 and outputs the parallel light to the beam splitter 13. A parabolic mirror or the like may be used instead of the collimator 63.

  The beam splitter 13 of the third embodiment splits the first laser light L1 incident from the collimator 63 into the first measurement light mL1 and the first reference light rL1 and also converts the second laser light L2 into the second measurement light mL2. It is split into the second reference light rL2. Then, the beam splitter 13 emits the first measurement light mL1 and the second measurement light mL2 toward the measurement light side mirror 14 and directs the first reference light rL1 and the second reference light rL2 toward the reference light side mirror 15. And emit.

  The first measurement light mL1 reflected by the measurement light side mirror 14 and the first reference light rL1 reflected by the reference light side mirror 15 are multiplexed by the beam splitter 13, and the first measurement light mL1 and the first reference light rL1 are combined. The first interference signal IL1 with the light rL1 is emitted to the demultiplexer 64. Further, the second measurement light mL2 reflected by the measurement light side mirror 14 and the second reference light rL2 reflected by the reference light side mirror 15 are also combined by the beam splitter 13 in the same manner, and the second measurement light The second interference signal IL2 of mL2 and the second reference light rL2 is emitted to the demultiplexer 64.

  The demultiplexer 64 (for example, a dichroic mirror) has a characteristic of transmitting light corresponding to the wavelength range of the first laser light L1 and reflecting light corresponding to the wavelength range of the second laser light L2. As a result, the demultiplexer 64 transmits the first interference signal IL1 incident from the beam splitter 13 and reflects the second interference signal IL2 incident from the beam splitter 13. Then, the first interference signal IL1 transmitted through the beam splitter 13 enters the detector 17A, and the second interference signal IL2 reflected by the beam splitter 13 enters the detector 17B.

  The detectors 17A and 17B (corresponding to the interference signal detector of the present invention) are the same as the detector 17 of each of the above-described embodiments. The detector 17A detects the first interference signal IL1 incident from the demultiplexer 64 and outputs the first interference signal Sig1 to the first lock-in amplifier 18A and the second lock-in amplifier 19A, respectively. On the other hand, the detector 17B detects the second interference signal IL2 incident from the demultiplexer 64 and outputs the second interference signal Sig2 to the first lock-in amplifier 18B and the second lock-in amplifier 19B, respectively.

  The first lock-in amplifier 18A and the second lock-in amplifier 19A, and the first lock-in amplifier 18B and the second lock-in amplifier 19B are the first lock-in amplifier 18 and the second lock-in amplifier 19 of the above-described embodiments, respectively. It has basically the same configuration as.

The first lock-in amplifier 18A and the second lock-in amplifier 19A use the first interference signal Sig1 input from the detector 17A to calculate a two-phase sine wave signal S1 with a phase difference of 90° expressed by the following [Formula 17]. (Φ1) and S2 (φ1) are detected. Note that the phase φ1 and the modulation index m1 in the equation [17] are both for the measurement light mL1 and the reference light rL1 with the path difference (geometric distance difference) corresponding to the measurement light mL1 and the reference light rL1 being D _1. When the refractive index of the path of is set to n ₁ , it is represented by the following [Formula 18]. The two-phase sine wave signals S1(φ1) and S2(φ1) are input to the computer 20.

On the other hand, the first lock-in amplifier 18B and the second lock-in amplifier 19B use the second interference signal Sig2 input from the detector 17B to generate a two-phase sine wave having a phase difference of 90° represented by the following [Formula 19]. The signals S1(φ2) and S2(φ2) are detected. Note that the phase φ2 and the modulation index m2 in the equation [19] are set to D _{2 which} is the path difference (geometric distance difference) corresponding to the measurement light mL2 and the reference light rL2, and both the measurement light mL2 and the reference light rL2. When the refractive index of the path of is set to n ₂ , it is represented by the following [Formula 20]. The two-phase sine wave signals S1 (φ2) and S2 (φ2) are also input to the computer 20.

  The computer 20 of the fourth embodiment is wired or wirelessly connected to the oscillator 22, the first lock-in amplifiers 18A and 18B, and the second lock-in amplifiers 19A and 19B, respectively. The computer 20 controls the amplitude Δf of the optical frequency f(t), the detection control of the two-phase sine wave signals S1(φ1) and S2(φ1), and the two-phase sine wave signals S1(φ2) and S2( φ2) detection control is performed.

  FIG. 16 is a functional block diagram showing the functions of the computer 20 of the fourth embodiment. As shown in FIG. 16, in the computer 20 of the fourth embodiment, an arithmetic processing circuit (not shown) executes the above distance measurement program (not shown), so that the first signal acquisition unit 34A and the second signal acquisition are performed. Unit 34B, first correction unit 35A and second correction unit 35B, first calculation unit 36A and second calculation unit 36B, information acquisition unit 37, amplitude determination unit 38, amplitude control unit 39, and time delay. It functions as the detection unit 50, the detection control unit 51, and the third calculation unit 66.

  The first signal acquisition unit 34A acquires the two-phase sine wave signals S1(φ1) and S2(φ1) from the first lock-in amplifier 18A and the second lock-in amplifier 19A, and acquires the acquired two-phase sine wave signal S1. (Φ1) and S2 (φ1) are output to the first correction unit 35A. The second signal acquisition unit 34B acquires the two-phase sine wave signals S1(φ2) and S2(φ2) from the first lock-in amplifier 18B and the second lock-in amplifier 19B, and acquires the acquired two-phase sine wave. The signals S1(φ2) and S2(φ2) are output to the second correction section 35B.

  FIG. 17 is an explanatory diagram for explaining the correction processing by the first correction unit 35A and the second correction unit 35B of the fourth embodiment. As shown in FIG. 17, the first correction unit 35A performs amplitude correction and the like on the two-phase sine wave signals S1(φ1) and S2(φ1) input from the first signal acquisition unit 34A, and then performs the second correction. The correction unit 35B performs amplitude correction and the like on the two-phase sine wave signals S1 (φ2) and S2 (φ2) input from the second signal acquisition unit 34B.

  Specifically, the first correction unit 35A multiplies the two-phase sine wave signals S1(φ1) and S2(φ1) that form the elliptical Lissajous waveform W1A by a predetermined coefficient to generate a perfect circle Lissajous. Two-phase correction signals V1(φ1) and V2(φ1) forming the waveform W2A are generated. In addition, the second correction unit 35B multiplies the two-phase sine wave signals S1(φ2) and S2(φ2) forming the elliptical Lissajous waveform W1B by a predetermined coefficient, so that the Lissajous waveform W2B is a perfect circle. Two-phase correction signals V1(φ2) and V2(φ2) that form

  Returning to FIG. 16, the first correction unit 35A outputs the generated two-phase correction signals V1(φ1) and V2(φ1) to the first calculation unit 36A. Further, the second correction unit 35B outputs the generated two-phase correction signals V1(φ2) and V2(φ2) to the second calculation unit 36B.

The first calculation unit 36A and the second calculation unit 36B function as the distance difference calculation unit of the present invention together with the first correction unit 35A and the second correction unit 35B described above. The first calculation unit 36A acquires the two-phase correction signals V1(φ1) and V2(φ1) input from the first correction unit 35A and the information acquisition unit 37, similarly to the calculation unit 36 of each of the above-described embodiments. Based on the center frequency f _c and the known speed of light C ₀ , the optical distance difference n ₁ D ₁ is calculated from the equation [7]. In addition, the second calculation unit 36B, based on the two-phase correction signals V1 (φ2) and V2 (φ2) input from the second correction unit 35B, and the above-described center frequency f _c and light speed C ₀ , the above [ The optical distance difference n ₂ D ₂ is calculated from the equation [7].

Then, the first calculating unit 36A outputs the calculated optical distance difference n ₁ D ₁ to the amplitude determining unit 38, the time delay detecting unit 50, and the third calculating unit 66, respectively. The second calculation unit 36B also outputs the calculated optical distance difference n ₂ D ₂ to the third calculation unit 66.

The amplitude determination unit 38, based on the optical distance difference n ₁ D ₁ input from the first calculation unit 36A and various information such as the initial path difference D ₀ previously input from the information acquisition unit 37, the above As in the case of the first embodiment, the amplitude Δf that keeps the modulation index m constant is determined by using the above [Formula 14]. Accordingly, the amplitude control unit 39 controls the angular frequency ω _m of the sine wave signal S0(t) based on the determination result of the amplitude Δf by the amplitude determination unit 38, so that the amplitude Δf of the optical frequency f(t) is changed. Control.

Further, the time delay detection unit 50 is based on the optical distance difference n ₁ D ₁ input from the first calculation unit 36A, the refractive index n ₁ input from the information acquisition unit 37, and the known speed of light C _0. As in the second embodiment, the time delay τ is calculated using the equation [15]. Then, the detection control unit 51 determines the first oscillators 25A and 25B of the first lock-in amplifiers 18A and 18B and the second oscillators 29A and 29B of the second lock-in amplifiers 19A and 19B based on the calculation result of the time delay τ. The phase of each reference sine wave signal (not shown) oscillated from is corrected. As a result, in each of the lock-in amplifiers 18A, 18B, 19A, 19B, detection control of the two-phase sine wave signals S1(φ1), S2(φ1) and two-phase sine wave signals S1(φ2), S2(φ2) are performed. ) Detection control is performed.

The third calculating unit 66 uses the known distance 2 based on the optical distance difference n ₁ D ₁ input from the first calculating unit 36A and the optical distance difference n ₂ D ₂ input from the second calculating unit 36B. The path difference D (geometrical distance difference) is calculated using the following [Equation 21] based on the color method principle. Note that “A” in the formula [21] is a constant.

  As described above, also in the distance measuring device 10C that performs distance measurement by the two-color method, the amplitude Δf of the optical frequency f(t) is controlled and the two-phase sine wave signals S1(φ1) and S2(φ1) are detected. By performing the control and the detection control of the two-phase sine wave signals S1(φ2) and S2(φ2), the same effect as each of the above-described embodiments can be obtained.

[Distance Measuring Device of Fifth Embodiment]
Next, the distance measuring device 10D of the fifth embodiment will be described with reference to FIG. FIG. 18: is a block diagram which shows the structure of the distance measuring device 10D of 5th Embodiment. Since the distance measuring device 10D has basically the same configuration as the distance measuring device 10 of the first embodiment, the same reference numerals are given to the same functions or configurations as those of the first embodiment. The description is omitted.

Due to the nonlinearity, the optical frequency f(t) of the laser light L emitted from the light wave generation unit 12 of each of the above-described embodiments is the second harmonic and the third harmonic as shown in the following [Equation 22]. It may have a second harmonic. In this case, the signals of 2ω _m and 3ω _m of the laser beam L become error factors in the distance measurement.

  Therefore, in the distance measuring device 10D according to the fifth embodiment, the following [Equation 23] is applied from the oscillator 22 to the laser light source 23 so as to cancel the second harmonic and the third harmonic of the optical frequency f(t). ] The sine wave signal SD(t) represented by the equation is output with an appropriate intensity. As a result, it is possible to reduce the error in the distance measurement due to the second harmonic wave and the third harmonic wave of the optical frequency f(t).

  Note that the sine wave signal SD(t) may be output from the oscillator 22 in the distance measuring devices 10A to 10C according to the second to fourth embodiments as well.

[Distance Measuring Device of Sixth Embodiment]
Next, a distance measuring device (not shown) of the sixth embodiment will be described. For example, in the distance measuring device 10 of the first embodiment, as shown in FIG. 6 described above, when the control start operation of the amplitude Δf (step S13) is performed, the measurement light side mirror 14 is turned to the target position. It is being moved (step S14). On the other hand, in the distance measuring device of the sixth embodiment, the aspect ratio of the Lissajous waveform W1 is corrected even between step S13 and step S14.

  The distance measuring device according to the sixth embodiment has basically the same configuration as the distance measuring device 10 according to the first embodiment. Therefore, the same reference numerals are used for the same functions or configurations as those of the first embodiment. Is attached and its description is omitted.

  FIG. 19 is a flowchart showing the flow of distance measurement processing (distance measurement method) by the distance measurement device of the sixth embodiment, and in particular, the correction of the aspect ratio of the Lissajous waveform W1 after step S13. Note that the processing up to step S13 is the same as that of the above-described first embodiment shown in FIG. 6, and therefore description thereof will be omitted here.

  As illustrated in FIG. 19, after the control start operation of the amplitude Δf (step S13), the correction unit 35 uses the two-phase sine wave signal S1(S1(φ), S2(φ) based on the two-phase sine wave signals S1(φ) and S2(φ). φ) and S2(φ) form a Lissajous waveform W1 at which the number of revolutions (real number) rotated around the origin is counted as the number of revolutions of the Lissajous waveform W1 (step SA1).

  Then, when the number of rotations of the Lissajous waveform W1 reaches a predetermined number (step SA2), the correcting unit 35 corrects the aspect ratio of the Lissajous waveform W1 by elliptic approximation, that is, the two-phase sine wave signals S1(φ), S2. (Φ) is multiplied by the coefficient determined by elliptic approximation (step SA3). Next, the correction unit 35 resets the count value of the rotation number of the Lissajous waveform W1 to zero (step SA4).

  Hereinafter, until the measurement light side mirror 14 is moved from the measurement start position toward the target position, the processing from step SA1 to step SA4 is repeatedly executed (step SA5). Since the subsequent processing is the same as that of the first embodiment shown in FIG. 6, description thereof will be omitted here.

  As described above, in the distance measuring device of the sixth embodiment, the aspect ratio of the Lissajous waveform W1 is corrected even between steps S13 and S14. Therefore, even if the aspect ratio correction in step S12 is not effective, the Lissajous The aspect ratio of the waveform W1 can be accurately corrected.

  The distance measuring devices 10A to 10D according to the second to fifth embodiments may also correct the aspect ratio of the Lissajous waveform W1 as in the sixth embodiment.

[Other]
In each of the above embodiments, the laser light L is described as an example of the light wave of the present invention, but various light waves that can be used in distance measurement using the sine wave phase modulation method may be used.

  In each of the above embodiments, the measurement light side mirror 14 is described as an example of the measurement object of the present invention. The invention can be applied.

  In each of the above embodiments, the first lock-in amplifier 18 and the second lock-in amplifier 19 are provided separately, but they may be integrated. The sine wave signal detection unit of the present invention is not limited to the lock-in amplifier, and is not particularly limited as long as it can detect the two-phase sine wave signals S1(φ) and S2(φ).

  In the distance measuring device 10 or the like of each of the above-described embodiments, the computer 20 may be provided in another place, and in this case, the computer 20 may use the two-phase sine wave signal S1(φ), Acquisition of S2(φ) and the like, and control of amplitude Δf and detection control (or one of both controls) are performed.

  10, 10A, 10B, 10C, 10D... Distance measuring device, 12... Light wave generator, 13... Beam splitter, 14... Measuring light side mirror, 15... Reference light side mirror, 17, 17A, 17B... Detector, 18, 18A, 18B... First lock-in amplifier, 19, 19A, 19B... Second lock-in amplifier, 20... Computer, 22... Oscillator, 23... Laser light source, 25, 25A, 25B... First oscillator, 29, 29A, 29B Second oscillator, 35... Correction unit, 35A... First correction unit, 35B... Second correction unit, 36... Calculation unit, 36A... First calculation unit, 36B... Second calculation unit, 37... Information acquisition unit, 38 ... Amplitude determination unit, 39... Amplitude control unit, 50... Time delay detection unit, 51... Detection control unit

Claims (6)

A light wave generation unit that generates a light wave that is sine wave phase-modulated by a sine wave,
A division unit that divides the light wave generated by the light wave generation unit into measurement light and reference light,
Interference between the measurement light emitted to the measurement target that is displaced along the path of the measurement light divided by the division unit and reflected by the measurement target, and the reference light divided by the division unit. An interference signal detection unit for detecting a signal,
A sine wave signal detection unit that detects two-phase sine wave signals corresponding to the first reference sine wave signal and the second reference sine wave signal from the interference signal detected by the interference signal detection unit,
A distance difference calculator that calculates an optical distance difference between the measurement light and the reference light based on the two-phase sine wave signals detected by the sine wave signal detector,
Based on the optical distance difference calculated by the distance difference calculation unit, a time delay detection unit that detects a time delay between the measurement light and the reference light,
The phase of the first reference sine wave signal and the second reference sine wave signal is corrected based on the detection result of the time delay detection unit, and the phase-corrected first reference sine wave signal and the second reference sine wave signal are corrected. A detection control unit that causes the sine wave signal detection unit to detect the two-phase sine wave signal based on a signal;
A distance measuring device. The optical distance difference is represented by the product of the path difference between the measurement light and the reference light and the refractive index of the path of the measurement light and the reference light,
When the path difference is D, the refractive index is n, and the speed of light is C ₀ , the time delay detection unit calculates the time delay τ by the following equation:

The distance measuring device according to claim 1, which is obtained by using. The center frequency of the optical frequency of the sine wave phase-modulated light wave is f _c , the amplitude and angular frequency of the AC component of the optical frequency are Δf and ω _m , respectively, and the time is t. When the function is J _k (m) and 2π×f _c ×τ is φ,
The optical frequency f(t), the intensity I of the interference signal, the first reference sine wave signal R1(t) and the second reference sine wave signal R2(t), and the two-phase sine wave signal S1. (Φ) and S2(φ) are the following equations,

The distance measuring device according to claim 2, which is expressed using.   The distance measuring device according to any one of claims 1 to 3, wherein the sine wave signal detection unit is a lock-in amplifier. The phase difference between the two-phase sine wave signals is 90°,
The distance difference calculation unit corrects the two-phase sine wave signal forming an elliptic Lissajous waveform into a two-phase correction signal forming a perfect circle Lissajous waveform, and based on the two-phase correction signal, the optical difference is calculated. The distance measuring device according to claim 1, wherein the distance difference is calculated. A light wave generation step of generating a light wave whose sine wave is phase-modulated with a sine wave;
A division step of dividing the light wave generated in the light wave generation step into a measurement light and a reference light,
After the dividing step, an interference signal detection step of detecting an interference signal between the measurement light emitted to the measurement object displaced along the path of the measurement light and reflected by the measurement object and the reference light. When,
A sine wave signal detecting step of detecting two-phase sine wave signals respectively corresponding to the first reference sine wave signal and the second reference sine wave signal from the interference signal detected in the interference signal detecting step;
A distance difference calculating step of calculating an optical distance difference between the measurement light and the reference light based on the two-phase sine wave signals detected in the sine wave signal detecting step,
Based on the optical distance difference calculated in the distance difference calculating step, a time delay detecting step of detecting a time delay between the measurement light and the reference light,
The phase of the first reference sine wave signal and the second reference sine wave signal is corrected based on the detection result of the time delay detection step, and the phase-corrected first reference sine wave signal and the second reference sine wave signal are corrected. A detection control step of executing detection of the two-phase sine wave signals in the sine wave signal detection step based on a signal;
A method for measuring distance.

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