JP6834116B2 - Distance measuring device and distance measuring method - Google Patents

Description

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

As a distance measuring device that measures the distance to a measurement object by utilizing the interference of light, a distance measuring device using a sinusoidal phase modulation method is known (see, for example, Patent Document 1). Such a distance measuring device generates a sinusoidal phase-modulated light wave by direct modulation of a laser light source or indirect modulation by an electro-optical element [EO (Electro-optical) element], and divides this light wave into measurement light and reference light. Then, the interference signal between the measurement light projected and reflected by the measurement object 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 having a phase difference of 90 ° at the lock-in amplifier.

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

Further, Patent Document 1 describes a two-wavelength sinusoidal phase modulation interferometer (distance measuring device) that performs distance measurement by a so-called two-color method as an application example of distance measurement by a sinusoidal phase modulation method.

JP-A-2015-075461

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

Further, in the distance measuring device using the conventional sinusoidal phase modulation method, when the position of the object to be measured is largely displaced along the path of the measurement light, the detection signal (interference signal) and the detection signal in the lock-in amplifier are detected. Since the phase shifts from the (reference signal), the signal strength of the two-phase sine wave signal output from the lock-in amplifier becomes weak, and distance measurement may not be possible.

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

The distance measuring device for achieving the object of the present invention divides a light wave generator that generates a sine wave phase-modulated light wave by a sine wave and a light wave generated by the light wave generator into measurement light and reference light. Detects the interference signal between the unit and the measurement light that is emitted to the measurement object that is displaced along the path of the measurement light divided by the division and reflected by the measurement object and the reference light that is divided by the division. Based on the interference signal detection unit, the sine wave signal detection unit that detects the two-phase sine wave signal from the interference signal detected by the interference signal detection unit, and the two-phase sine wave signal detected by the sine wave signal detection unit. , The amplitude that determines the amplitude of the AC component of the optical frequency of the light wave based on the distance difference calculation unit that calculates the optical distance difference between the measurement light and the reference light and the optical distance difference calculated by the distance difference calculation unit. Based on the determination result of the amplitude determination unit, which is the determination unit and determines the amplitude at which the modulation index that determines the aspect ratio of the lithage waveform formed by the two-phase sinusoidal signal is kept constant, and the determination result of the amplitude determination unit. It includes 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 object to be measured is displaced, so that the aspect ratio of the resage waveform formed by the two-phase sinusoidal signal is also kept constant. As a result, a two-phase correction signal that always forms a perfect circular Lissajous waveform is obtained when the aspect ratio of the Lissajous waveform is corrected. Therefore, the position of the measurement object is displaced based on these two-phase correction signals. Even in this case, the path difference between the measurement light and the reference light can be measured accurately. 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 apparatus 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 is represented by the product of the measurement object. It is equipped with an information acquisition unit that acquires the initial path difference, which is the path difference before the start of displacement, and the amplitude determination unit includes the initial path difference acquired by the information acquisition unit, the known refractive index, and the optics 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 geometric distance difference between the paths of the measurement light and the reference light.

In the distance measuring apparatus according to another aspect of the present invention, the center frequency of the optical frequency is f _c, the amplitude and Delta] f, the angular frequency and the frequency of the AC component of the optical frequency and omega _m and f _m, respectively, the time t The first-class k-th order Vessel function is J _k (m), the path difference is D, the initial path difference is D ₀ , the refractive index is n, the light velocity is C _0, and 2 × n × D / C. _{Let 0} be τ, 2π × f _c × τ be φ, the initial refractive index, which is the refractive index before the start of displacement, be n ₀ , the initial amplitude, which is the amplitude before the start of displacement, be Δf ₀ , and the modulation index be m. Then, the optical frequency f (t), the intensity I of the interference signal, the modulation index m, the two-phase sinusoidal signals S1 (φ) and S2 (φ), and the amplitude Δf are expressed by the following equations.

Is expressed using. Thereby, based on the optical distance difference calculated by the distance difference calculation unit, the amplitude of the optical frequency of the light wave can be determined and controlled with reference to each of the above mathematical formulas.

A distance measuring device for achieving the object of the present invention divides a light wave generator that generates a light wave phase-modulated by a sine wave and a light wave generated by the light wave generator into measurement light and reference light. Detects an interference signal between the unit and the measurement light emitted to the measurement object displaced along the path of the measurement light divided by the division unit and reflected by the measurement object, and the reference light divided by the division unit. And the sine wave signal detection unit that detects the two-phase sine wave signal 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. , The distance difference calculation unit that calculates the optical distance difference between the measurement light and the reference light based on the two-phase sine wave signal detected by the sine wave signal detection unit, and the optical distance calculated by the distance difference calculation unit. Based on the difference, the time delay detection unit that detects the time delay between the measurement light and the reference light, and the 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. It includes a detection control unit that causes the sine wave signal detection unit to detect a two-phase sine wave signal based on the corrected and phase-corrected first reference sine wave signal and second reference sine wave signal.

According to this distance measuring device, the phase delay between the interference signal and each reference sine wave signal is prevented, so that the signal strength of the two-phase sine wave signal may be weakened even if the position of the measurement object is displaced. Be prevented. As a result, it is prevented that the distance measurement (path difference measurement) cannot be performed.

In the distance measuring apparatus according to another aspect of the present invention, the optical distance difference is represented by the product of the path difference of the measurement light and the reference light and the refractive index of the path of the measurement light and the reference light, and the path difference is D. When the refractive index is n and the speed of light is C ₀ , the time delay detection unit sets the time delay τ as the following equation.

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

In the distance measuring apparatus according to another aspect of the present invention, the center frequency of the optical frequency of the sine wave phase-modulated light wave and f _c, of the AC component of the optical frequency amplitude and angular frequency were as Δf and omega _m, respectively, the time Is t, the first-class k-th order Vessel function is J _k (m), and 2π × f _c × τ is φ, the optical frequency f (t), the intensity I of the interference signal, and the first reference sine wave. 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 expressed using. As a result, 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 with reference to each of the above equations, and the sine wave signal detection unit performs. It is possible to control the detection of a two-phase sine wave 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 of the two-phase sine wave signal is 90 °, and the distance difference calculation unit sets the two-phase sine wave signal forming the elliptical lithage waveform to be true. The correction signal is corrected to a two-phase correction signal forming a circular sine wave, 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 target can be calculated, and at least one of the above-mentioned amplitude control and the two-phase sine wave signal detection control can be performed.

In the distance measuring method for achieving the object of the present invention, a light wave generation step for generating a light wave whose sine wave phase is modulated by a sine wave and a light wave generated in the light wave generation step are divided into measurement light and reference light. After the step and the division step, an interference signal detection step of detecting an interference signal between the measurement light emitted from the measurement object displaced along the path of the measurement light and reflected by the measurement object and the reference light, Based on the sine wave signal detection step that detects the 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 It is a distance difference calculation step for calculating the optical distance difference between the two, and an amplitude determination step for 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 calculation step. Generated in the light wave generation step based on the amplitude determination step that determines the amplitude at which the modulation index that determines the aspect ratio of the lithage waveform formed by the two-phase sine wave signal is kept constant, and the determination result in the amplitude determination step. It has an amplitude control step for controlling the amplitude of a light wave.

In the distance measurement method for achieving the object of the present invention, a light wave generation step for generating a light wave phase-modulated with a sine wave by a sine wave and a light wave generated in the light wave generation step are divided into measurement light and reference light. After the step and the dividing step, an interference signal detection step for detecting an interference signal between the measurement light emitted from the measurement object displaced along the path of the measurement light and reflected by the measurement object and the reference light, In the sine wave signal detection step for detecting the two-phase sine wave signal corresponding to the first reference sine wave signal and the second reference sine wave signal from the interference signal detected in the interference signal detection step, and in the sine wave signal detection step. Based on the detected two-phase sine wave signal, the distance difference calculation step that calculates the optical distance difference between the measurement light and the reference light, and the measurement light based on the optical distance difference calculated in the distance difference calculation step. Based on the detection results of the time delay detection step that detects the time delay with the reference light and the time delay detection step, the phases of the first reference sine wave signal and the second reference sine wave signal are corrected, and after the phase correction. It has a detection control step for executing detection of a 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 object to be measured is displaced.

It is a block diagram which shows the structure of the distance measuring apparatus of 1st Embodiment. It is a functional block diagram which shows the function of the computer of 1st Embodiment. It is explanatory drawing for demonstrating the correction process by a correction part. It is a flowchart which shows the flow of the measurement process of the initial path difference D _0. It is explanatory drawing for _{demonstrating} the measurement process of the initial path difference D 0. It is a flowchart which shows the flow of the distance measurement processing by the distance measurement apparatus of 1st Embodiment. It is explanatory drawing for demonstrating the effect of the distance measuring apparatus of 1st Embodiment. It is a block diagram which shows the structure of the distance measuring apparatus of 2nd Embodiment. It is a functional block diagram which shows the function of the computer of 2nd Embodiment. It is a flowchart which shows the flow of the distance measurement processing by the distance measurement apparatus of 2nd Embodiment. It is explanatory drawing for demonstrating the effect of the distance measuring apparatus of 2nd Embodiment. It is a block diagram which shows the structure of the distance measuring apparatus of 3rd Embodiment. It is a functional block diagram which shows the function of the computer of 3rd Embodiment. It is a flowchart which shows the flow of the distance measurement processing by the distance measurement apparatus of 3rd Embodiment. It is a block diagram which shows the structure of the distance measuring apparatus 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 part and the 2nd correction part of 4th Embodiment. It is a block diagram which shows the structure of the distance measuring apparatus of 5th Embodiment. It is a flowchart which shows the flow of the distance measurement processing by the distance measurement apparatus of 6th Embodiment.

[Distance measuring device of the first embodiment]
FIG. 1 is a configuration diagram showing the configuration of the distance measuring device 10 of the first embodiment. The distance measuring device 10 measures a distance from a predetermined reference position (for example, a beam splitter 13) to a measurement optical side mirror 14 corresponding to a measurement object of the present invention by using a sinusoidal phase modulation method. The distance measuring device 10 includes a light wave generator 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, and the like. 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 equation [Equation 1] to the laser light source 23. _{Here, "I 0} " in the equation [Equation 1] is the signal strength (amplitude) of the sinusoidal signal S0 (t), and "ω _m " is the angular frequency of the sinusoidal signal S0 (t). "t" is the time.

For example, a semiconductor laser light source (LD: Laser Diode) is used as the laser light source 23, and the laser light source 23 is driven based on the sinusoidal 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, a sinusoidal phase shift occurs in the laser beam L. As a result, the laser beam L whose sine wave phase is modulated by the laser light source 23 is generated and is emitted to the beam splitter 13 via an optical fiber cable (not shown).

The method of generating the laser beam L with sinusoidal phase modulation is not limited to the method of utilizing the direct frequency modulation characteristic of the LD, and indirect modulation by a known electro-optical element (EO element) is used. May be good.

The sinusoidal phase-modulated laser beam L has an optical frequency f (t) represented by the following equation [Equation 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] amplitude. Further, the above-mentioned angular frequency “ω _m ” is the angular frequency (modulated 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 [sinusoidal phase] modulation of the optical frequency f (t).

The beam splitter 13 corresponds to the divided portion of the present invention, divides the laser light L incident from the laser light source 23 into the measurement light mL and the reference light rL, and divides the measurement light mL into the measurement light side mirror 14. It emits (transmits) toward and reflects the reference light rL toward the reference light side mirror 15. Further, the beam splitter 13 reflects the measurement light mL reflected by the measurement light side mirror 14 toward the detector 17, and also transmits the reference light rL reflected by the reference light side mirror 15 to the detector. It emits 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 the movement method (mechanism) is not particularly limited as long as _{the distance D m can be changed, and the stroke is further long.} A mechanism corresponding to the movement of is used. This 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 measurement 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 _Dr between the beam splitter 13 and the reference light side mirror 15 and the beam splitter 13 and the measurement light side mirror 14 The path difference D from the distance D _{m between them is measured.} The "distance measurement" in each embodiment of the present specification refers to the 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 light phase φ (t) is expressed by the following equation [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 formula [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) [ a sinusoidal phase] frequency modulation), satisfies "ω _m = 2πf _m." Further, "τ" in the equation [Equation 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 Time difference to return to the beam splitter 13). The refractive index of the time lag tau, the path difference of the measuring beam mL and the reference beam rL (the geometrical distance difference) and _{D (D = D m -D r} ), both the path for the measuring light mL and the reference light rL Is n and the speed of light is c ₀ , then 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 Equation 5 the following formula, the light intensity _E m, _{E r} is _{E m = Aexp (iφ m (} t)), is represented by _{E r = Bexp (iφ r (} t)), these Since the amplitudes A and B in the equation do not affect the following description, they are omitted.

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 detection unit of the present invention, and for example, a CCD (Charge Coupled Device) type or CMOS (complementary metal oxide semiconductor) type image sensor, a photodiode, or the like is used. 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 Sigma which is an electric signal. Then, the detector 17 outputs the detected interference signal Sigma to the first lock-in amplifier 18 and the second lock-in amplifier 19 via a signal line (not shown), respectively.

Here, the interference signal Sigma indicates the intensity I of the interference signal IL, and is represented by the following equation [Equation 6]. The "phase φ" in the equation [Equation 6] satisfies the following equation [Equation 7], and the "modulation index m" in the equation [Equation 6] satisfies the following equation [Equation 8]. Then, when the equation [Equation 6] is _{expanded into a series by the first-class k-order Bessel function Jk} (m), the equation [Equation 6] is represented by the following equation [Equation 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 refer to the first-referenced sine wave signals R1 (t) and the second, which will be described later, from the interference signal Sigma (intensity I of the interference signal IL) input from the detector 17. The two-phase sine wave signals S1 (φ) and S2 (φ) having a phase difference of 90 ° (including approximately 90 °) 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 drawing.

The first oscillator 25 is the first reference sine wave signal R1 (t) {corresponding to the _{second term "J 2} (m) cos {2ω _m (t-τ / 2)}" of the above equation [Equation 9]. Refer to the following [Equation 10] equation} to output to the first multiplier 26. The first multiplier 26 multiplies the interference signal Sig (intensity I) input from the detector 17 with the first reference sine wave signal R1 (t) input from the first oscillator 25, and obtains the multiplication signal. 1 Output to the low-pass filter 27.

The first low-pass filter 27 applies low-pass filter processing to the multiplication signal input from the first multiplier 26. As a result, in the interference signal Sig (intensity I), only the component equal to the frequency of the first reference sine wave signal R1 (t) becomes direct current, and the first sine wave signal S1 (φ) corresponding to this direct current component becomes the first direct current. 1 Passes through the low-pass filter 27. As a result, the first lock-in amplifier 18 has 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]. ] Expression reference} is detected.

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

The second oscillator 29 is a 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 equation [Equation 9]. Refer to the following [Equation 10] equation} to output to the second multiplier 30. The second multiplier 30 multiplies the interference signal Sig (intensity I) input from the detector 17 with the second reference sine wave signal R2 (t) input from the second oscillator 29, and obtains the multiplication signal. 2 Output to the low-pass filter 31. The second lock-in amplifier 19 applies a low-pass filter process to the multiplication signal input from the second multiplier 30. As a result, the second lock-in amplifier 19 has 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) {the following [Equation 11]. ] Expression reference} is detected.

As described above, the first lock-in amplifier 18 and the second lock-in amplifier 19 have a two-phase first sine wave signal S1 (φ) and a 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 the two-phase sinusoidal signals S1 (φ) and S2 (φ) have a phase difference of 90 °, they form an elliptical Lissajous waveform W1 (see FIG. 3) described later.

If the two-phase sinusoidal signals S1 (φ) and S2 (φ) have a phase difference of 90 °, that is, an elliptical resage waveform W1 (see FIG. 3) can be formed, the above equation [Equation 11] can be used. There is no limitation, and 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 two-phase sine wave signals S1 (φ) and S2 (φ) to be detected. change.

Further, in the present embodiment, the two-phase sine wave signal S1 (φ) at the start of the distance measurement by the distance measuring device 10, that is, in the state where the measurement optical side mirror 14 is at the measurement start position before the start of movement (before the start of displacement). ), S2 (φ) phase difference error (error from the ideal value 90 °) is corrected by phase difference correction of the two-phase sine wave signals S1 (φ) and S2 (φ). .. The phase difference correction is performed, for example, by the shifting mechanism 16 a measurement light side mirror 14 or move (changing the distance D _m), or to changing the center frequency f _c of the Equation 2 formula ..

If an offset error occurs in the two-phase sine wave signals S1 (φ) and S2 (φ), that is, if the center of the resage waveform W1 (see FIG. 3) deviates from the origin, the two-phase sine wave signal S1 Offset correction is also performed for (φ) and S2 (φ). Here, since offset correction is a known technique, the details thereof will be 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. Although the details will be described later, this computer 20 is 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, and the measurement light is mL. The optical distance difference nD from the reference light rL (see FIG. 2) is calculated. The optical distance difference nD is the path difference _D between the measuring beam mL and the reference light rL _(D m -D _r), represented by the product of the refractive index n of the path of the measuring beam mL and the reference light rL. Then, the computer 20 controls the amplitude Δf in the above equation [Equation 2] based on the calculated optical distance difference nD.

Although not shown, the computer 20 performs the entire operation of the distance measuring device 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. It may be controlled collectively.

[Computer Configuration 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) composed of various arithmetic units, a processing unit, and a storage unit. As shown in FIG. 2, the computer 20 executes a distance measurement program (not shown) read from a memory or the like (not shown) by the arithmetic processing circuit to obtain a signal acquisition unit 34, a correction unit 35, and a calculation unit 36. , The information acquisition unit 37, the amplitude determination unit 38, and the amplitude control unit 39.

The signal acquisition unit 34 acquires and acquires 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). The 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 process by the correction unit 35. As shown in FIG. 3, the resage waveform W1 formed by the two-phase sinusoidal signals S1 (φ) and S2 (φ) has the coefficients [J] of the two-phase sinusoidal signals S1 (φ) and S2 (φ). ₂ (m), J ₃ (m)] does not form 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 resage waveform W1 by multiplying the two-phase sinusoidal signals S1 (φ) and S2 (φ) by a “predetermined coefficient”, that is, centering on the origin. Correction is performed to generate two-phase correction signals V1 (φ) and V2 (φ) that form a perfect circular risage waveform W2. Hereinafter, this correction is referred to as amplitude correction.

Here, the "predetermined coefficient" is a state in which the measurement light side mirror 14 is in the measurement start position before the start of movement, for example, the Least squares method or the like is used to approximate the lisage waveform W1 in an elliptical manner, or a two-phase sine wave signal. After detecting the amplitude ratio of S1 (φ) and S2 (φ) or _{measuring the initial path difference D 0} described later with a general-purpose measure to determine the modulation index m, the coefficients [J ₂ (m), J ₃ ( m)] is obtained by a known method such as calculation. Then, the correction unit 35 stores the "predetermined coefficient" obtained before the start of movement of the measurement light side mirror 14, and obtains the measurement light side mirror 14 from the measurement start position to the target position. The two-phase sine wave signals S1 (φ) and S2 (φ) to be obtained 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 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 amount of phase change of the phase difference φ (see FIG. 3) shown in the above equation [Equation 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. Further, the calculation unit 36 outputs the calculation result of the optical distance difference nD to the amplitude determination unit 38.

_{The information acquisition unit 37 has an initial path difference D 0} and an initial refractive index corresponding to the path difference D, the refractive index n, and the amplitude Δf at the start of the distance measurement, that is, when the measurement light side mirror 14 is at the measurement start position. The n ₀ and the initial amplitude Δf ₀ are acquired. The information acquisition unit 37 acquires angular frequency omega _m, center frequency _{f c,} and the distance _{D r.} Here, the initial refractive index n ₀ (n = n ₀ in this embodiment) is almost a constant, and the initial amplitude Δf ₀ , the angular frequency ω _m , the center frequency f _c, and the distance _Dr are set values. The information acquisition unit 37 acquires each value input in advance by the user.

Further, the initial path difference D ₀ (also referred to as dead path) can be obtained as a value measured by a general-purpose tape measure or a value measured by a distance measuring device 10. Hereinafter, an example of a method of measuring (calculating) the _{initial path difference D 0} with the distance measuring device 10 will be described. Here, the initial path difference _{D 0,} based on the [Equation 8] type and "ω _m = 2πf _m", represented by the following [Expression 12] expression.

In the above equation [Equation 12], the initial refractive index n ₀ , the initial amplitude Δf ₀ , and the angular frequency ω _m are constants or set values. Therefore, by obtaining the modulation index m, the initial path is obtained from the above equation [Equation 12]. The difference D ₀ can be obtained.

FIG. 4 is a flowchart showing the flow of the measurement process of the initial path difference D _0. Further, FIG. 5 is an explanatory diagram for explaining the measurement process _{of the initial path difference D 0.} As shown in FIGS. 4 and 5, the information acquisition unit 37 acquires the uncorrected two-phase sine wave signals S1 (φ) and S2 (φ) forming the resage waveform W1 from the signal acquisition unit 34 (step). S1).

Next, the information acquisition unit 37 performs elliptical approximation by the least squares method or the like on the Lissajous waveform W1 of the ellipse formed by the two-phase sinusoidal signals S1 (φ) and S2 (φ), thereby performing the following. The equation [Equation 13] is obtained (step S2).

The equation obtained by solving the above equation [Equation 13] with respect to "m" is represented by "m = F (x)". Then, as shown in the graph 41 in FIG. 5, the information acquisition unit 37 calculates the modulation index m by performing polynomial approximation with, for example, a ninth-order polynomial with respect to F (x) (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 . _{The initial path difference D 0} is calculated by substituting into the equation (Equation 12) (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 measurement result of the initial path difference D ₀ can be obtained in the distance measuring device 10.

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. As a result, 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} , the initial refractive index n ₀ , the initial amplitude Δf _0, and the 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 various information such as the optical distance difference nD input from the above-mentioned calculation unit 36 and 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 beam L (see the above equation [Equation 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 sinusoidal signals S1 (φ) and S2 (φ). Therefore, the amplitude determination unit 38 determines the amplitude Δf so as to keep the aspect ratio of the Lissajous waveform W1 constant.

Specifically, the amplitude Δf that keeps the modulation index m constant is expressed by the following equation [Equation 14] based on the equation [Equation 8]. Therefore, the amplitude determination unit 38 has an optical distance difference nD and an initial path difference D.
_By substituting various information such as 0 into the following equation [Equation 14], the amplitude Δf that keeps 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 is an oscillator so that the amplitude Δf of the optical frequency f (t) of the laser beam L generated by the light wave generation unit 12 matches the determination result of the amplitude Δf input from the amplitude determination unit 38. _{The angular frequency ω m} of the sine wave signal S0 (t) output from 22 is controlled. For example, a data table or an arithmetic expression showing the correspondence between the amplitude Δf of the optical frequency f (t) and the angular frequency ω _{m of the sinusoidal signal S0 (t) in which the amplitude Δf is realized is generated in advance. As a result, 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 calculation formula, and 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 process (distance measurement method) by the distance measurement device 10 of the first embodiment. Here, the distance measurement of the measurement optical 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 part of the distance measuring device 10, the laser light source 23 is driven by the light wave generation unit 12 based on the sine wave signal S0 (t) output from the oscillator 22, and the light frequency f (from the laser light source 23). The laser beam L of t) is emitted. The laser beam L is split into the measurement light mL and the reference light rL by the beam splitter 13. Then, the measurement light mL is emitted from the beam splitter 13 to the measurement light side mirror 14, reflected by the measurement light side mirror 14, and then incident on 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, reflected by the reference light side mirror 15, and then incident on the beam splitter 13.

The interference signal IL between the measurement light mL and the reference light rL incident on the beam splitter 13 is incident on the detector 17 and converted into an interference signal Sigma which is an electric signal by the detector 17. This 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. This completes the activation of the distance measuring device 10 (step S10).

Then, in a state where the measurement light side mirror 14 is in the measurement start position before the start of movement, the measurement of the initial path difference D ₀ (dead path) is started. _{Specifically, a method of inputting the measurement result of measuring the initial path difference D 0} using a general-purpose tape _{measure into the computer 20, or the initial path difference D 0} by the distance measuring device 10 described with reference to 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 on 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 _Dr to the computer 20 (information acquisition unit 37). Since these values are known, by inputting them into the memory or the like of the computer 20 in advance, the information acquisition unit 37 can acquire these values from the memory or the like without inputting by the user. it can. Thus, the information acquisition unit 37 outputs various kinds of information about the refractive index n and the center frequency f _c to the calculator 36, the initial path difference D ₀ and initial refractive index n ₀ and the initial amplitude Delta] f ₀ and the angular frequency omega _m Various information related to the above is output to the amplitude determination unit 38.

Next, when the user performs a correction start operation of the aspect ratio of the Lissajous waveform W1, the correction unit 35 of the two phases 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 to a perfect circle by elliptical approximation of the Lissajous waveform W1 by the least squares method or the like, and stores the predetermined coefficient by 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 circular 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 the calculation of the optical distance difference nD. This completes the preparation for moving the measurement optical 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 S20 is started from step S15 described later. In addition, the user operates the measurement optical side mirror 14 with respect to the shift mechanism 16. 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 divides 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 Measurement processing including detection of the two-phase sine wave signals S1 (φ) and S2 (φ) by 19 is executed (step S15). The measurement process in 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 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 these 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 amplitude has been corrected are input from the correction unit 35 to the calculation unit 36.

Of 2-phase correction signal V1 (phi), calculator 36 which receives the input of V2 (phi) is to count a count value described above, and this count value, the center frequency f _c which is obtained from the information acquisition unit 37 And the known speed of light C ₀ , the optical distance difference nD is calculated from the above equation [Equation 7] (step S18, corresponding to the distance difference calculation 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.

The amplitude determination unit 38 that has received the input of the calculation result of the optical distance difference nD is based on the optical distance difference nD and various information such _{as the initial path difference D 0 previously input from the information acquisition unit 37.} Using the above equation [Equation 14], the amplitude Δf that keeps the modulation index m constant is determined (step S19, corresponding 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 sinusoidal signal S0 (t) corresponding to the determination result of the amplitude Δf by using the above-mentioned data table or calculation formula. _{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, corresponding to the amplitude control step of the present invention).

Hereinafter, the above-mentioned processes from step S15 to step S20 are repeatedly executed until the measurement light side mirror 14 reaches the target position (NO in step S21). As a result, the above-mentioned 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, by the processing from step S15 to step S18 described above, the optical distance difference nD in the state where the measurement optical side mirror 14 is stopped at the target position is calculated. Next, the calculation unit 36 determines the current path difference D (geometric distance) (at the target position) based on the calculation result of the optical distance difference nD and the information regarding the refractive index n input from the information acquisition unit 37. The difference) is calculated (step S22).

[Effect of the distance measuring device of the first embodiment]
FIG. 7 is an explanatory diagram for explaining the effect of the distance measuring device 10 of the first embodiment. In the figure, "J ₂ , J ₃ " is a value indicating the aspect ratio [J ₂ (m) / J ₃ (m)] of the resage waveform W1, and "distance (m)" is determined by the shift mechanism 16. It is the moving distance of the measured light side mirror 14 to be moved. In Comparative Example 44 and Example 45 in FIG. _7, obtained under the conditions _{f m = 10MHz, Δf 0 =} 200MHz, D 0 = 1m, a _{n 0 (n) ≒ 1,} C 0 and the velocity of light in vacuum It was done.

As shown in the upper part of FIG. 7, in Comparative Example 44 in which the amplitude Δf is not controlled, _{the aspect ratio of “J 2} and J ₃ ”, that is, the Lissajous waveform W1 changes as the measurement optical side mirror 14 moves. Therefore, when the two-phase sinusoidal signals S1 (φ) and S2 (φ) forming the lithage waveform W1 are multiplied by a predetermined coefficient obtained above, a perfect circular lisage waveform W2 is formed. Two-phase correction signals V1 (φ) and V2 (φ) cannot be obtained. Even if the path difference D (geometric distance difference) of the measurement optical side mirror 14 is obtained based on such two-phase correction signals V1 (φ) and V2 (φ), the measurement error becomes large.

Further, when the radius value of the Lissajous waveform W1 becomes small during the movement of the measurement optical side mirror 14, that is, when the signal strengths of the two-phase sine wave signals S1 (φ) and S2 (φ) become weak, the path There is a possibility that the difference D (geometric distance difference) cannot 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 measurements cannot be performed.

In contrast to such Comparative Example 44, as shown in the lower part of FIG. 7, in the present Example 45 in which the amplitude Δf is controlled, the modulation index m is kept constant regardless of the movement of the measurement optical side mirror 14. By doing so, _{the aspect ratio of "J 2} and J ₃ ", that is, 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 each position of the measurement optical side mirror 14 are multiplied by the predetermined coefficients obtained in advance, the lithage is always a perfect circle. Two-phase correction signals V1 (φ) and V2 (φ) forming the waveform W2 can be obtained. As a result, the path difference D (geometric distance difference) after stopping at the target position can be measured accurately.

[Distance measuring device of the second embodiment]
Next, the distance measuring device 10A of the second embodiment will be described with reference to FIG. FIG. 8 is a configuration diagram showing the configuration of the distance measuring device 10A of the second embodiment. The distance measuring device 10 of the first embodiment controls the amplitude Δf of the optical frequency f (t) based on the calculation result of the optical distance difference nD, but the distance measuring device 10A of the second embodiment is optical. The detection control of the two-phase sine wave signals S1 (φ) and S2 (φ) is performed by the first lock-in amplifier 18 and the second lock-in amplifier 19 based on the calculation result of the target distance difference nD.

As shown in FIG. 8, in the distance measuring device 10A of the second embodiment, the computer 20 is connected to the first oscillator 25 and the second oscillator 29 by wire or wirelessly instead of the oscillator 22. It has basically the same configuration as the distance measuring device 10 of the first embodiment. Therefore, those having the same function or configuration as 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, the arithmetic processing circuit (not shown) executes the above-mentioned distance measurement program (not shown), so that the signal acquisition unit 34 and the correction unit 35 described above are executed. , And functions as a time delay detection unit 50 and a detection control unit 51 in addition to the calculation unit 36 and the information acquisition unit 37.

Information acquisition unit 37 of the second embodiment obtains the initial refractive index n _{0 (refractive} index n) and center frequency f _c, 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 equation [Equation 7] as in the first embodiment, and detects the calculation result of the optical distance difference nD with a time delay. Output to 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.

Time delay detection unit 50, an optical distance difference nD inputted from the calculating portion 36, the refractive index n inputted from the information acquisition unit 37 (if known input not required), to the known speed of light C ₀ Based on this, the above-mentioned time delay τ is calculated based on the following equation [Equation 15]. 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 outputs a first reference sine wave signal R1 (output by the first oscillator 25 of the first lock-in amplifier 18) based on the calculation result (detection result) of the time delay τ input from the time delay detection unit 50. The phase of t) and the phase of the second reference sine wave signal R2 (t) output by the second oscillator 29 of the second lock-in amplifier 19 are corrected (see the above equation [Equation 10]). Then, the detection control unit 51 sets the first lock-in amplifier 18 and the second lock-in amplifier 19 based on the first reference sine wave signal R1 (t) and the second reference sine wave signal R2 (t) after the phase correction. Detection control is performed to detect the two-phase sine wave signals S1 (φ) and S2 (φ).

[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 the flow of the distance measurement process (distance measurement method) by the distance measurement device 10A of the second embodiment.

Since the processes from step S10 to step S12 are basically the same as those in the first embodiment, specific description thereof will be omitted here. Then, when step S12 is completed, the user performs a control start operation for starting 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. (Step S13A). As a result, the detection control of the two-phase sine wave signals S1 (φ) and S2 (φ) shown in step S20A is started from step S15 described later.

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

At this time, the processes from step S15 to step S18 are executed in the same manner as in the first embodiment, and the calculation unit 36 calculates the optical distance difference nD corresponding to the current position of the measurement optical side mirror 14 and takes the time. Input to the delay detection unit 50.

Optical distance difference detection unit 50 delay time when receiving the input of nD, based on the the optical distance difference nD, a refractive index n which is inputted from the information acquisition unit 37, and the known speed of light C _0, the following equation The time delay τ is calculated (detected) using the equation 15], and the calculation result of the time delay τ is input to the detection control unit 51 (step S19A, corresponding 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 corrected and phase-corrected first reference sine wave signal R1 (t) and second reference sine wave signal R2 (t) 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 start from the interference signal Sig based on the first reference sine wave signal R1 (t) and the second reference sine wave signal R2 (t) after phase correction. Detection control for detecting the two-phase sine wave signals S1 (φ) and S2 (φ) is executed (step S20A, corresponding to the detection control step of the present invention).

By such detection control, the phase of the interference signal Sig [intensity I] represented by the above equation [Equation 9], and the first reference sine wave signal R1 (t) and the second reference sine wave represented by the above equation [Equation 10] The phase lag with and from the phase of the signal R2 (t) is corrected.

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

Then, 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, as in the first embodiment, the path difference D (geometric distance difference) after stopping at the target position is calculated by the calculation unit 36 through the processes from step S15 to step S18 (step S22).

[Effect of the distance measuring device of the 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, "x, y" in the following equation [Equation 16] is the x component and y component of the ideal Lissajous waveform W1 without phase delay, and "X, Y" is the actual Lissajous waveform with phase delay. It is an X component and a Y component of W1. Further, Comparative Example 44A and Example 45A in Figure _11, obtained under the conditions _{f m = 10MHz, Δf 0 =} 200MHz, D 0 = 1m, and _{n 0 (n) ≒ 1,} C 0 = velocity of light in vacuum It was done.

As shown in the upper part of FIG. 11, detection control of the two-phase sine wave signals S1 (φ) and S2 (φ), that is, the interference signal Sigma and the reference sine wave signals R1 (t) and R2 (t) In Comparative Example 44A in which the phase delay correction control is not executed, the coefficients a _x and a _y change in a sinusoidal shape. Therefore, the signal intensities of the two-phase sinusoidal signals S1 (φ) and S2 (φ) increase or decrease according to the change of the coefficients a _x and a _y. As a result, the signal intensities of the two-phase sinusoidal signals S1 (φ) and S2 (φ) are weakened, and the path difference D may not be measured.

As shown in the lower part of FIG. 11, with respect to such Comparative Example 44A, in the present Example 45A in which the detection control of the two-phase sine wave signals S1 (φ) and S2 (φ) is performed, the above-mentioned phase lag By being corrected, the coefficients a _x and a _y are kept constant. As a result, it is prevented that the signal intensities of the two-phase sinusoidal signals S1 (φ) and S2 (φ) are weakened as in Comparative Example 44A, so that the path difference D after stopping at the target position is reliably measured. can do.

[Distance measuring device of the 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 two-phase sine wave signals S1 (φ) and S2 (φ) are detected and controlled. However, in the distance measuring device 10B of the third embodiment, both the control of the amplitude Δf and the detection control of the two-phase sine wave signals S1 (φ) and S2 (φ) are performed.

FIG. 12 is a configuration diagram showing the configuration of the distance measuring device 10B of the third embodiment. FIG. 13 is a functional block diagram showing the functions of the computer 20 according to 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, it is different from each of the above embodiments. Those having the same function or configuration are designated by the same reference numerals and the 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 the functions of both the computers 20 of each of the above embodiments, the optical frequency f (t) is set based on the above-mentioned calculation result of the optical distance difference nD and the like. The amplitude Δf is controlled 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) is performed.

[Operation of the distance measuring device of the third embodiment]
FIG. 14 is a flowchart showing the flow of the distance measurement process (distance measurement method) by the distance measurement device 10B of the third embodiment. The flow of the distance measurement process of the third embodiment includes a point of performing a start operation (step S13B) in which the start operations (steps S13 and S13A) of the above-described embodiments shown in FIGS. 6 and 10 described above are combined. , Except for the fact that both the amplitude Δf control (steps S19 and S20) described in the first embodiment and the detection control (steps S19A and S20A) described in the second embodiment are performed in parallel. It is basically the same as the flow of the distance measurement process of the form.

[Effect of the distance measuring device of the third embodiment]
As described above, the distance measuring device 10B of 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 the detection control of φ) and S2 (φ) are executed, all the effects described in the above embodiments can be obtained.

[Distance measuring device of the fourth embodiment]
Next, the distance measuring device 10C of the fourth embodiment of the present invention will be described with reference to FIG. FIG. 15 is a configuration diagram showing the configuration of the distance measuring device 10C of the fourth embodiment. This distance measuring device 10C performs distance measurement by a so-called two-color method as an application example of distance measurement by a sinusoidal phase modulation method. Those having the same function or configuration as each of the above embodiments are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 15, the distance measuring device 10C of the fourth embodiment is a combination of the light wave generator 12, the distributor 60, and the harmonic generator 61 indicated by “SHG” (Second Harmonic Generation) in the figure. The wave device 62, the collimeter 63, the beam splitter 13, the measurement light side mirror 14, the reference light side mirror 15, the shift mechanism 16, the demultiplexer 64, the detectors 17A and 17B, and the 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 distributes the first laser light L1 to the combiner 62. The second laser beam L2 is emitted toward the harmonic generator 61.

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

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

The collimator 63 parallelizes the first laser beam L1 and the second laser beam L2 incident from the combiner 62 and emits them 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 divides the first laser beam L1 incident from the collimator 63 into the first measurement light mL1 and the first reference light rL1, and the second laser beam L2 is combined with 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 exit.

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 combined by the beam splitter 13, and the first measurement light mL1 and the first reference are made. 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 is combined. The second interference signal IL2 between mL2 and the second reference light rL2 is emitted to the demultiplexer 64.

The demultiplexer 64 (for example, a dichroic mirror) has a property of transmitting light corresponding to the wavelength range of the first laser beam L1 and reflecting light corresponding to the wavelength range of the second laser beam 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 is incident on the detector 17A, and the second interference signal IL2 reflected by the beam splitter 13 is incident on the detector 17B.

The detectors 17A and 17B (corresponding to the interference signal detection unit of the present invention) are the same as the detectors 17 of each of the above embodiments. The detector 17A detects the first interference signal IL1 incident from the demultiplexer 64, and outputs the first interference signal Sigma1 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 Sigma2 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 each of the above embodiments, respectively. It has basically the same configuration as.

The first lock-in amplifier 18A and the second lock-in amplifier 19A are a two-phase sine wave signal S1 having a phase difference of 90 ° represented by the following equation [Equation 17] from the first interference signal Sigma1 input from the detector 17A. (Φ1) and S2 (φ1) are detected. Incidentally, both for the phase φ1 and the modulation index m1 in Equation 17] where the path difference corresponding to the measurement light mL1 and the reference beam rL1 (the geometrical distance difference) and _{D 1,} the measurement light mL1 and the reference light rL1 When the refractive index of the path of is n ₁ , it is expressed by the following equation [Equation 18]. These 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 are two-phase sine waves having a phase difference of 90 ° represented by the following equation [Equation 19] from the second interference signal Sigma2 input from the detector 17B. The signals S1 (φ2) and S2 (φ2) are detected. Incidentally, both for the phase φ2 and the modulation index m2 in [Expression 19] where the path difference corresponding to the measurement light mL2 and the reference beam rL2 the (geometrical distance difference) and _{D 2,} the measurement light mL2 and reference light rL2 When the refractive index of the path of is n ₂ , it is expressed by the following equation [Equation 20]. These 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. This computer 20 controls the amplitude Δf of the optical frequency f (t), detects and controls the two-phase sine wave signals S1 (φ1) and S2 (φ1), and the two-phase sine wave signals S1 (φ2) and S2 ( The detection control of φ2) is performed.

FIG. 16 is a functional block diagram showing the functions of the computer 20 according to the fourth embodiment. As shown in FIG. 16, in the computer 20 of the fourth embodiment, the arithmetic processing circuit (not shown) executes the above-mentioned distance measurement program (not shown) to acquire the first signal acquisition unit 34A and the second signal. Section 34B, first correction section 35A and second correction section 35B, first calculation section 36A and second calculation section 36B, information acquisition section 37, amplitude determination section 38, amplitude control section 39, and time delay. It functions as a detection unit 50, a detection control unit 51, and a 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 the acquired two-phase sine wave signal S1. (Φ1) and S2 (φ1) are output to the first correction unit 35A. Further, the second signal acquisition unit 34B acquires 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 two-phase sine wave. The signals S1 (φ2) and S2 (φ2) are output to the second correction unit 35B.

FIG. 17 is an explanatory diagram for explaining the correction process 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 second. The correction unit 35B corrects the amplitude of 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 sinusoidal signals S1 (φ1) and S2 (φ1) forming the elliptical Lissajous waveform W1A by a predetermined coefficient to obtain a perfect circular Lissajous. Two-phase correction signals V1 (φ1) and V2 (φ1) forming the waveform W2A are generated. Further, the second correction unit 35B multiplies the two-phase sinusoidal signals S1 (φ2) and S2 (φ2) forming the elliptical Lissajous waveform W1B by a predetermined coefficient to form a perfect circular Lissajous waveform W2B. The two-phase correction signals V1 (φ2) and V2 (φ2) forming the above are generated.

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 embodiments. _{The optical distance difference n 1} D ₁ is calculated from the above equation [Equation 7] based on the center frequency f _c and the known speed of light C _0. The second calculation unit 36B, the second correction unit corrects the signal of the 2-phase input from 35B V1 (φ2), V2 and (.phi.2), based on the center frequency _{f c} and light speed _{C 0} described above, the [ _{The optical distance difference n 2} D ₂ is calculated from the equation [Equation 7].

Then, the first calculation unit 36A outputs the calculated optical distance difference n ₁ D ₁ to the amplitude determination unit 38, the time delay detection unit 50, and the third calculation unit 66, respectively. Further, the second calculation unit 36B outputs the calculated optical distance difference n ₂ D ₂ to the third calculation unit 66.

The amplitude determination unit 38 is based on various information such _{as the optical distance difference n 1} D ₁ input from the first calculation unit 36A _{and the initial path difference D 0} previously input from the information acquisition unit 37. Similar to the first embodiment, the above equation [Equation 14] is used to determine the amplitude Δf that keeps the modulation index m constant. _{As a result, the amplitude control unit 39 controls the angular frequency ω m} of the sinusoidal signal S0 (t) based on the determination result of the amplitude Δf by the amplitude determination unit 38, thereby adjusting the amplitude Δf of the optical frequency f (t). 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. , The time delay τ is calculated using the above equation [Equation 15] as in the second embodiment. Then, the detection control unit 51 includes 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 lock-in amplifier 18A, 18B, 19A, 19B, 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) ) Is detected and controlled.

The third calculation unit 66 is known based _{on the optical distance difference n 1} D ₁ input from the first calculation unit 36A _{and the optical distance difference n 2} D ₂ input from the second calculation unit 36B. The path difference D (geometric distance difference) is calculated using the following equation [Equation 21] based on the color method principle. In addition, "A" in the formula [Equation 21] is a constant.

As described above, even in the distance measuring device 10C that measures the distance 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 that of each of the above embodiments can be obtained.

[Distance measuring device of the fifth embodiment]
Next, the distance measuring device 10D of the fifth embodiment will be described with reference to FIG. FIG. 18 is a configuration diagram showing the configuration of the distance measuring device 10D of the fifth 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 those having the same function or configuration as the first embodiment. The description thereof will be omitted.

Due to its non-linearity, the optical frequency f (t) of the laser beam L emitted from the light wave generation unit 12 of each of the above embodiments is a second harmonic and a third harmonic as shown in the following equation [Equation 22]. May have second harmonics. In this case, _{the signals of 2 ω m} and 3 ω _m of the laser beam L become an error factor of the distance measurement.

Therefore, in the distance measuring device 10D of the fifth embodiment, the following [Equation 23] is applied to the laser light source 23 from the oscillator 22 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 of distance measurement caused by the second harmonic and the third harmonic of the optical frequency f (t).

Similarly, in the distance measuring devices 10A to 10C of the second to fourth embodiments, the sine wave signal SD (t) may be output from the oscillator 22.

[Distance measuring device of the sixth embodiment]
Next, the 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 (step S13) of the amplitude Δf is performed, the measurement light side mirror 14 is directed 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 also between steps S13 and S14.

Since the distance measuring device of the sixth embodiment has basically the same configuration as the distance measuring device 10 of the first embodiment, the same reference numerals are given to those having the same function or configuration as the first embodiment. The description thereof will be omitted.

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

As shown in FIG. 19, after the control start operation of the amplitude Δf (step S13), the correction unit 35 is based on the two-phase sine wave signals S1 (φ) and S2 (φ), and the two-phase sine wave signal S1 ( The number of rotations (real number) at which the point drawing the resage waveform W1 formed by φ) and S2 (φ) rotates around the origin is counted as the rotation number of the resage waveform W1 (step SA1).

Then, when the rotation speed of the Lissajous waveform W1 reaches a predetermined number of times (step SA2), the correction unit 35 corrects the aspect ratio of the Lissajous waveform W1 by elliptical approximation, that is, the two-phase sine wave signals S1 (φ), S2. Multiply (φ) by the coefficient determined by ellipse approximation (step SA3). Next, the correction unit 35 performs a count reset to return the count value of the rotation speed of the Lissajous waveform W1 to zero (step SA4).

Hereinafter, the processes from step SA1 to step SA4 are repeatedly executed until the measurement optical side mirror 14 is moved from the measurement start position to the target position (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, so that even if the aspect ratio correction in step S12 is not effective, the Lissajous The aspect ratio of the waveform W1 can be corrected with high accuracy.

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

[Other]
In each of the above embodiments, the laser beam L is described as an example of the light wave of the present invention, but various light waves that can be used for distance measurement using the sinusoidal 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, but the present invention is used for distance measurement of various measurement objects capable of reflecting at least a part of the measurement light mL. 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 both may be integrated. Further, 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 and the like of each of the above-described embodiments, the computer 20 may be provided at a different location. In this case, the computer 20 uses the two-phase sine wave signal S1 (φ), via the Internet or the like. Acquisition of S2 (φ) and the like, 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 ... Measurement light side mirror, 15 ... Reference light side mirror, 17, 17A, 17B ... Detector, 18, 18A, 18B ... 1st lock-in amplifier, 19, 19A, 19B ... 2nd lock-in amplifier, 20 ... computer, 22 ... oscillator, 23 ... laser light source, 25, 25A, 25B ... 1st 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 generator that generates a light wave with sine wave phase modulation by a sine wave,
A dividing unit that divides the light wave generated by the light wave generating unit into measurement light and reference light, and
Interference between the measurement light that is emitted to the measurement object that is displaced along the path of the measurement light divided by the division and reflected by the measurement object and the reference light that is divided by the division. Interference signal detector that detects signals and
A sine wave signal detection unit that detects a two-phase sine wave signal corresponding to a first reference sine wave signal and a 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 signal detected by the sine wave signal detection unit.
A time delay detection unit that detects a time delay between the measurement light and the reference light based on the optical distance difference calculated by the distance difference calculation unit.
Based on the detection result of the time delay detection unit, the phases of the first reference sine wave signal and the second reference sine wave signal are corrected, and the phase-corrected first reference sine wave signal and the second reference sine wave are corrected. A detection control unit that causes the sine wave signal detection unit to detect the two-phase sine wave signal based on the signal.
A distance measuring device including. 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.
When the path difference is D, the refractive index is n, and the speed of light is C ₀ , the time delay detection unit sets the time delay τ as 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 sinusoidal phase modulated light wave and f _c, the amplitude and angular frequency of the AC component of the optical frequency and Δf and omega _m, respectively, and the time t, the first kind k Bessel 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), the second reference sine wave signal R2 (t), and the two-phase sine wave signal S1. (Φ) and S2 (φ) are the following formulas,

The distance measuring device according to claim 2, which is represented by 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 sinusoidal signals is 90 °.
The distance difference calculation unit corrects the two-phase sine wave signal forming an elliptical Lissajous waveform into a two-phase correction signal forming a perfect circular Lissajous waveform, and the optical based on the two-phase correction signal. The distance measuring device according to any one of claims 1 to 4, which calculates a target distance difference. A light wave generation step that generates a light wave with sine wave phase modulation by a sine wave,
A division step of dividing the light wave generated in the light wave generation step into measurement light and reference light, and
After the division step, an interference signal detection step of detecting an interference signal between the measurement light emitted from 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 detection step for detecting a two-phase sine wave signal corresponding to a first reference sine wave signal and a second reference sine wave signal from the interference signal detected in the interference signal detection step.
A distance difference calculation step for calculating an optical distance difference between the measurement light and the reference light based on the two-phase sine wave signal detected in the sine wave signal detection step.
A time delay detection step for detecting a time delay between the measurement light and the reference light based on the optical distance difference calculated in the distance difference calculation step, and a time delay detection step.
Based on the detection result of the time delay detection step, the phases of the first reference sine wave signal and the second reference sine wave signal are corrected, and the phase-corrected first reference sine wave signal and the second reference sine wave are corrected. A detection control step for executing the detection of the two-phase sine wave signal in the sine wave signal detection step based on the signal, and a detection control step.
Distance measuring method having.

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