JPH08292265A - Measuring device of displacement information - Google Patents

Abstract

PURPOSE: To prevent the effect of drop-out efficiently by integrating a photodetector receiving scattered light from an object with a light sensing changing means for changing a light sensing region of the photodetector. CONSTITUTION: Piezoelectric ceramic 25 is stuck on a vibrator 26, which is fixed as a cantilever by a vibrator fixing member 27. The vibrator 26 and a photodetector 9 are disposed integrally on a circuit board 30. Being driven by the resonance frequency fs of the vibrator 26, the ceramic 25 can make a vibratory displacement amount efficiently. When the vibrator 26 is disposed on an optical path of a converging optical system and made to vibrate, a direction and a region of light sensing are changed. When the optical path in the direction of the detector 9 is interrupted by the vibrator 26 at the time of occurrence of drop-out, the balance of light and shade of a speckle pattern on the detector 9 is lost and the state of drop-out can be eliminated. Even when an object moves at a low speed, accordingly, the drop-out for a long time can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement information measuring device. The present invention, for example, irradiates a moving object or fluid (hereinafter referred to as “moving object”) with laser light, and detects a frequency shift of scattered light that has undergone Doppler shift in accordance with the moving speed of the moving object. By doing so, the displacement information regarding the displacement of the moving object and the moving speed of the moving object can be favorably applied to the displacement information measuring device utilizing the Doppler effect so as to be measured in a non-contact manner.

[0002]

2. Description of the Related Art Conventionally, a laser Doppler velocimeter has been used as a device for measuring the moving speed of a moving object in a non-contact and highly accurate manner. Laser doppler speedometer
A moving object or fluid is irradiated with laser light, and the frequency of light scattered by the moving object or moving fluid shifts in proportion to the moving speed (Doppler effect). Alternatively, it is a device for measuring the moving speed of the moving fluid.

FIG. 1 is an explanatory view showing an example of a conventional laser Doppler velocimeter.

In FIG. 1, a laser beam emitted from a laser 1 is collimated by a collimator lens 2 into a parallel light beam 3
After being split into two light beams 5a and 5b by the beam splitter 4 and reflected by the mirrors 6a and 6b,
An object or fluid 7 moving at a velocity V is irradiated with two light beams at an incident angle θ. The light scattered by the moving object is detected by the photodetector 9 via the condenser lens 8. At this time, the frequency of the scattered light by the two light fluxes is proportional to the moving speed V and
It is subjected to Doppler shifts of Δf and −Δf. Here, if the wavelength of the laser light is λ, Δf can be expressed by the following equation (1).

Δf = Vsin θ / λ (1)

The scattered lights that have undergone the Doppler shifts of + Δf and −Δf interfere with each other to cause a change in brightness and darkness on the light receiving surface of the photodetector 9, and the frequency F thereof is given by the following equation (2). .

F = 2V sin θ / λ (2)

Therefore, if the frequency of the output signal of the photodetector 9 (hereinafter referred to as the Doppler frequency) is measured,
The velocity V of the moving object 7 can be calculated based on the equation (2).

FIG. 2 is a schematic diagram of an electrical processing section C for processing the signal from the photodetector 9.

The signal obtained from the photodetector 9 has its S / N improved by a bandpass filter (BPF) 12 and is output as a continuous signal by a phase locked loop (PLL) 13.

Now, the operation when dropout occurs as shown in FIG. 3 will be described. FIG. 3 is an example of a signal from the BPF 12 when dropout (A section) occurs. The dropout detector 18 constantly checks the A part signal, determines that dropout has occurred when the Doppler signal level is below a certain value as shown in FIG. 3, and turns off the switch (SW) 15 to make the phase comparator. 14 outputs and voltage controlled oscillator (VCO) 17
Separate the input of. The low pass filter (LPF) 16 holds the voltage immediately before the SW 15 is turned off, and the VCO 17 outputs a constant value. As a result, the PPL 13 does not cause the disturbance due to the dropout of the Doppler signal and maintains the frequency output immediately before the dropout. Then, when the Doppler signal level again exceeds a certain value, the dropout detector 1
8 turns on SW15 to perform normal PLL operation.

The Doppler frequency F obtained as a continuous signal by the above operation is measured by calculating the moving speed V of the moving object 7 by the calculating means 19 based on the equation (2).

[0013]

[Problems to be solved by the invention] However,
When the dropout occurs for a long time, an error occurs between the signal captured by the PLL 13 and the signal that should be output when the object actually moves, and the measurement accuracy deteriorates. In particular, when measuring the same object, the dropout time is longer and the measurement accuracy tends to be worse at low speeds.

On the other hand, there is a method (frequency shifter) for making a frequency difference before irradiating the object to be measured with two light fluxes as a technique capable of measuring from the stationary state including the velocity direction.

In this case, assuming that the shift amount due to the frequency shifter is fR, the equation (2) becomes F = 2Vsin (θ) / λ + fR (3) In such a case, if the dropout occurs in the stationary state, the dropout state continues during the stationary state.

In general, if the dropout state continues for a long time, it is determined that the measurement is impossible and a detection error state occurs. Therefore, it may not be possible to measure as a continuous signal.

The dropout of this Doppler signal is
It occurs when the AC component of the photoelectric signal accidentally disappears due to the averaging effect when a plurality of speckles having various phases are collected by the sensor.

FIG. 4 is a block diagram of speckle pattern observation, and 10 is a two-beam spot irradiated on the object 7 to be measured. FIG. 5 shows a speckle pattern from the spot 10 on the CCD camera 11.

When the DUT 7 moves in the direction of the arrow in FIG. 4, the intensity of the speckle pattern in FIG.
It is modulated with a period of / 2 sin θ. Dropout is a phenomenon in which the beat signal amplitude of the total light intensity decreases when the light and dark distributions of the speckle pattern are almost the same.

It is an object of the present invention to provide a displacement information measuring device capable of preventing such an undetectable state due to dropout and continuously detecting displacement information.

It is a first object of the present invention to provide a displacement information measuring device capable of more accurately preventing the influence of dropout in such a device capable of continuously and continuously detecting displacement information.

A second object of the present invention is to provide a displacement information measuring device capable of more efficiently preventing the influence of dropout in such a device capable of continuously detecting displacement information.

[0023]

A first aspect of the present invention for achieving the above object is to allow a light beam from a light source means to enter an object,
In a displacement information measuring device that receives scattered light from the object by a photodetector and measures relative displacement information with the object based on the frequency shift of the scattered light, scattering from the object A displacement information measuring device having a lighting changing means for changing a lighting area or a lighting direction of a photodetector for collecting light, wherein the photodetector and the lighting changing means are integrally configured. Is.

A second invention for achieving the above object is as follows:
Displacement information in which a light beam from the light source means is incident on an object, scattered light from the object is received by a photodetector, and relative displacement information with the object is measured based on a frequency shift of the scattered light. In the measuring device, there is provided a lighting changing means for changing a lighting area or a lighting direction of a photodetector for collecting scattered light from the object, and the light changing means means an optical path for blocking at least a part of a light receiving optical path. It is a displacement information measuring device having a shielding member and vibrating the optical path shielding member according to the resonance frequency of the optical path shielding member.

A third aspect of the invention is characterized in that, in the above-mentioned structure, the optical path blocking member is constituted by a tuning fork type vibration member.

A fourth aspect of the invention is characterized in that, in the above structure, scattered light from the object is guided to the photodetector via a lens system.

A fifth aspect of the present invention is characterized in that, in the above structure, the luminous flux incident on the object is two luminous fluxes, and the photodetector and the lighting changing means are arranged outside the plane formed by the optical paths of the two luminous fluxes. To do.

A sixth aspect of the invention is characterized in that, in the above structure, it further has a phase-locked loop that forms a periodic signal based on the output signal from the photodetector.

A seventh aspect of the invention is characterized in that, in the above structure, the lighting changing means vibrates the vibrating portion with a piezoelectric material.

[0030]

EXAMPLE FIG. 6 is a schematic view of the essential portions of a laser Doppler velocimeter according to Example 1 of the present invention.

In the housing 100, the laser light emitted from the laser diode 1 is arranged so as to be linearly polarized on the Z axis, and becomes a parallel light flux 3 by the collimator lens 2. The parallel light flux 3 is divided into two light fluxes 5a and 5 by the diffraction grating 40 having a grating arrangement direction of Y axis and a grating pitch of d.
It is divided into b at the diffraction angle θ.

At this time, the diffraction angle θ is the laser wavelength λ
Then, dsin θ = λ (5) The two light beams 5a and 5b have an angle θ,
Electro-optic crystals 22a, 22 having a c-axis (optical axis) in the Z-axis
b. The electrode 23a is attached to the electro-optic crystal 22a,
A voltage is applied by 23b, so that an electric field is applied only to the light beam 5a. Electro-optic crystal 22a, 22b
If the thickness is de = 1 mm, the length is l = 20 mm, the laser wavelength is λ = 780 nm, and the grating pitch is d = 1.6 μm, the substantial length l through which the light beams 5a and 5b pass through the electro-optic crystals 22a and 22b. ′ Is l ′ = 1 / cos (θ ′) (6) where θ ′ is the angle of the light beam inside the electro-optic crystal,
When the extraordinary light refractive index of the electro-optic crystal is Ne, it becomes as follows.

Sin (θ) = Ne · sin (θ ′) (7)

From the equation (5), since θ≈29.18 degrees, l ′ = 2
With an extraordinary light refractive index Ne = 2.2 and a Pockels constant γ = 32.2 × 10 ^-9 (mm / V), the voltage amplitude is V ≈ 224V.
Then, the phase difference between the two light beams becomes 2π. When serrodyne driving at frequency fR, two light fluxes 5c and 5d having a frequency difference of fR
Is obtained. The two light beams 5c and 5d are reflected by the mirrors 21a and 21.
Two beams are irradiated at the incident angle θ to the DUT 7 which is deflected at b and is moving at the velocity V. Light scattered by the object is reflected by the reflecting prism 24 via the condenser lens 8 so that the optical axis of the condenser optical system is turned back and is integrated with the circuit board 30 (FIG. 6).
(Not shown) is detected by the photodetector 9.

In this way, the photodetector 9 and the vibrator 2 which will be described later are provided at the positions where the luminous flux reflected by the reflecting prism 24 is received.
The circuit board 30 provided with 6 is arranged.
The photodetector 9 and the oscillator 26 can be arranged outside the plane formed by the optical paths of the two light beams 5c and 5d, and the optical system portion can be downsized.

The Doppler frequency of the detected scattered light is
According to the frequency difference fR between the two light fluxes, the following is obtained as in the equation (3).

F = 2V sin (θ) / λ + fR (8)

From the equation (5), the equation (8) becomes F = 2V / d + fR (9), and it becomes possible to detect a signal having no wavelength dependence of the laser. That is, when the wavelength changes, the diffraction angle changes according to the equation (5), whereby the frequency fluctuation due to the wavelength fluctuation of the Doppler signal is canceled and the wavelength dependence is eliminated. Further, the incident angle on the electro-optic crystals 22a and 22b also changes, but the polarization direction is changed to the electro-optic crystals 22a and 22b.
Since it coincides with the c-axis of b, the electro-optic crystals 22a, 22b
The polarization direction is maintained after transmission. Further, although the substantial length l'changes and the voltage amplitude changes from the equation (6), the amount of change can be almost ignored. Therefore, a highly accurate signal can be detected even if the wavelength changes.

The detection signal from the photodetector 9 that receives the scattered light from the object in the above-described manner is the same electric processing unit as that shown in FIG. 2 including the BPF, the PLL and the dropout detector. The signal is processed to obtain a continuous signal, and the speed is measured from the frequency F obtained from this continuous signal by an arithmetic unit (not shown) based on the equation (9).

In this structure, since the electro-optical crystals 22a and 22b are arranged in the two-beam optical paths, the electro-optical crystals 22a and 22b can be introduced without changing the optical positional relationship such as the two-beam optical path length. Be seen.

FIG. 7 is a diagram showing the configuration of the photodetector 9 and the vibrator 26 integrally formed on the circuit board 30 of FIG. 6, and FIG. 7A is a side view of the circuit board 30 of FIG. In the figure,
6B is a view of the circuit board 30 as seen from the bottom of FIG. 6. Piezoelectric ceramics 25 is attached to the vibrator 26, and is fixed as a cantilever by a vibrator fixing member 27.
The resonance frequency fs (Hz) of the vibrator 26 is fs = (1.875 ² / 2πl ² ) √ (EI / ρA) (10) l: length (m), E: longitudinal elastic modulus (Pa), I: the second moment (m ⁴⁾ ρ: specific gravity ^{(kg / m 3), A} : is calculated by the cross-sectional area (m ^2). Piezoelectric ceramics 25 and vibrator 26
By vibrating the vibrator 26 by driving it at the same frequency as the resonance frequency fs, the amount of vibration displacement of the vibrator 26 can be obtained with a small voltage.

With such a configuration, it is possible to change the lighting direction and the lighting region by vibrating the vibrator 26 provided on the optical path of the condensing optical system. If the piezoelectric vibration actuator blocks the optical path in the specific lighting direction toward the sensor when a dropout occurs, the light-dark balance of the speckle pattern on the sensor is upset, and the dropout state disappears. Therefore, long-time dropout can be avoided even when the moving object is moving at a low speed.

For this purpose, the light-receiving surface 9 of the photodetector 9 is
The a and the oscillator 26 must be accurately aligned. As can be seen from FIG. 7B, alignment of the light receiving surface 9a (0.6 mmφ) of the photodetector 9 and the vibrator 26 (width 0.3 mm) requires accuracy, but in the present embodiment, the photodetector is used. Since both the oscillator 9 and the oscillator 26 are integrally formed on the circuit board 30, alignment is facilitated. Further, with the configuration shown in FIG. 7, if the optical axis of the condensing optical system shown in FIG. 6 is adjusted, the vibrator 26 directly exhibits the effect as a blocking member.

FIG. 8 shows an example of the detection signal from the photodetector 9, and FIG. 8A shows vibration when the dropout occurs in the stationary state, and FIG. 8B shows vibration from the state shown in FIG. This is the case where the child 26 is driven. In the signal state shown in FIG. 8A, even if the signal processing described in FIG. 2 is performed, a detection error occurs and a continuous signal is not output. In the configuration of the present invention, FIG.
As can be seen from (b), the dropout state and the non-dropout state are repeated in the cycle of the resonance frequency fs, and the continuous dropout state is prevented. In such a periodic signal detection state, continuous signal output is possible by performing the signal processing described in FIG.

In this embodiment, as described above, the position of the blocking member and the light receiving surface of the photodetector 9 is made by integrally forming the photodetector and the means for changing the light collection area of the photodetector. The alignment becomes easy, and the positional deviation due to the change with time of the both becomes less likely to occur.

Further, in this embodiment, as described above, the vibrator 2 is used.
By driving 6 at the same frequency as the resonance frequency fs, the vibration displacement amount of the vibrator 26 can be efficiently obtained with a small voltage.

FIG. 9 shows the structure of the circuit board 30 in the laser Doppler velocimeter of the second embodiment of the present invention. The configuration of the other parts of this embodiment is the same as that of the first embodiment, and therefore the explanation is omitted. 6A is a view of the circuit board 30 viewed from the side of FIG. 6, and FIG. 6B is a view of the circuit board 30 viewed from the bottom of FIG. In the present embodiment, the blocking member is constituted by the tuning fork type vibrator 28 as shown in the figure, and the piezoelectric ceramics 25 is attached to one of the tuning forks to form the piezoelectric ceramics 2.
5 is driven at the same frequency as the resonance frequency fs of the vibrator 26 to vibrate the tuning fork. Tuning fork vibrator 2
The circuit board 8 is soldered to the circuit board 30 to form an integrated structure. In the tuning fork type vibrator 28 of FIG. 9, the left and right vibrators vibrate in opposite directions and torque is applied in opposite directions at the nodes, but the two torques cancel each other out at the mounting portion to the circuit board 30. ing. For this reason, an unnecessary vibration mode is not generated in the vicinity of the mounting portion due to the torque at the time of vibration, resulting in a more stable state.

FIG. 10 shows the result of simulating the resonance mode of the tuning fork type vibrator 28. The dotted line shows the position before vibration. From this, it can be seen that there is no vibration at the mounting portion on the circuit board 30.

[0049]

As described above, according to the present invention,
The undetectable state due to dropout is prevented, and displacement information can always be detected continuously.

In particular, according to the first aspect of the invention, in such a device capable of constantly and continuously detecting displacement information, the photodetector and the lighting change means are integrally formed, so that the positions of the both can be easily aligned. As a result, positional deviation due to changes over time is less likely to occur, and the effect of dropout can be more accurately prevented.

According to the second aspect of the invention, in such a device capable of constantly and continuously detecting displacement information, the optical path shield member included in the lighting changing means is vibrated in accordance with its resonance frequency, so that the optical path is reduced with a small voltage. The vibration displacement amount of the blocking member can be obtained, and the influence of dropout can be more efficiently prevented.

According to the third aspect of the invention, since the optical path blocking member is composed of the tuning fork type vibration member, it is possible to resonate without generating an unnecessary vibration mode.

According to the fourth aspect of the invention, by guiding the scattered light to the photodetector through the lens system, the light receiving efficiency of the scattered light including the signal can be increased and the S / N can be improved.

According to the fifth aspect of the invention, by disposing the photodetector and the lighting change means outside the plane formed by the optical paths of the two light fluxes, it becomes possible to downsize the entire apparatus.

According to the sixth aspect of the invention, in a device using a phase-locked loop, it becomes possible to prevent the undetectable state due to dropout and always detect displacement information continuously.

According to the seventh aspect of the invention, the lighting changing means can be made more compact, and the apparatus can be made compact.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of a conventional laser Doppler velocity meter.

FIG. 2 is a diagram illustrating a signal processing system of a laser Doppler speedometer.

FIG. 3 is a diagram illustrating dropout of a Doppler signal.

[Figure 4] Speckle pattern observation block diagram

FIG. 5 is a diagram showing a speckle pattern.

FIG. 6 is a schematic diagram of a laser Doppler speedometer according to the first embodiment of the present invention.

FIG. 7 is a circuit board configuration diagram of the present embodiment.

FIG. 8 is a diagram illustrating a Doppler signal.

FIG. 9 is a circuit board configuration diagram of a laser Doppler speedometer according to a second embodiment of the present invention.

FIG. 10 is a diagram showing a result of resonance simulation of a tuning fork vibrator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source means 2 collimator lens 4 beam splitters 6a, 6b mirror 7 moving object 8 condensing lens 9 photodetector 13 PLL 19 computing means 20 diaphragm member or vibrating member 21a, 21b mirrors 22a, 22b electro-optic crystal 23 electrode 24 reflection Prism 25 Piezoelectric ceramics 26 Vibrator 27 Vibrator fixing member 28 Tuning fork vibrator 30 Circuit board 40 Diffraction grating

Claims (7)

[Claims] 1. A light flux from a light source means is incident on an object,
In a displacement information measuring device that receives scattered light from the object by a photodetector and measures relative displacement information with the object based on the frequency shift of the scattered light, scattering from the object A displacement information measuring device having a lighting changing means for changing a lighting area or a lighting direction of a photodetector for collecting light, wherein the photodetector and the lighting changing means are integrally configured. . 2. A light beam from a light source means is incident on an object,
In a displacement information measuring device that receives scattered light from the object by a photodetector and measures relative displacement information with the object based on the frequency shift of the scattered light, scattering from the object A light detector that has a light collecting area for changing a light collecting area or a light collecting direction of the light detector, and the light collecting changing means has a light path blocking member for blocking at least a part of a light receiving light path; A displacement information measuring device, characterized in that the optical path blocking member is vibrated in accordance with a resonance frequency. 3. The displacement information measuring device according to claim 2, wherein the optical path blocking member is composed of a tuning fork type vibration member. 4. The displacement information measuring device according to claim 1, wherein scattered light from the object is guided to the photodetector via a lens system. 5. A light beam incident on the object is defined as two light beams,
The displacement information measuring device according to any one of claims 1 to 4, wherein the photodetector and the lighting change means are arranged outside a plane formed by the optical paths of the two light fluxes. 6. The displacement information measuring device according to claim 1, further comprising a phase-locked loop that forms a periodic signal based on an output signal from the photodetector. 7. The lighting changing means has a structure in which a vibrating portion is vibrated by a piezoelectric material.
Displacement information measuring device according to any one of ~ 6.