JP2940072B2 - Doppler speedometer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a Doppler velocimeter, which irradiates a moving object, a fluid, or the like (hereinafter, referred to as a “moving object”) with a laser beam, and applies a laser beam to the moving object. The present invention relates to a Doppler velocimeter that measures the moving speed of a moving object in a non-contact manner by detecting a shift in the frequency of scattered light that has undergone Doppler shift according to the moving speed.

(Prior 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 velocimeter irradiates a moving object with laser light, the frequency of scattered light from the moving object is
This is a device that measures the moving speed of a moving object using an effect (Doppler effect) that shifts in proportion to the moving speed of the moving object.

FIG. 3 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 converted into a parallel beam 3 by a collimator lens 2.
2 of transmitted light 5a and reflected light 5b by the beam splitter 4
After being split into luminous fluxes and reflected by the reflecting mirrors 6a and 6b, the incident angle θ from a different direction to the moving object 7 moving at the speed V
Are irradiated with two light beams. The scattered light from the moving object 7 is detected by the light detector 9 via the condenser lens 8. At this time, the frequency of the scattered light due to the two light beams undergoes a Doppler shift of + Δf and −Δf, respectively, in proportion to the moving speed V. here,
Assuming that the wavelength of the laser beam is λ, the frequency change Δf can be expressed by the following equation (1).

Δf = V · sin (θ) / λ ‥‥ (1) + Δf, −Δf
They interfere with each other to cause a change in brightness on the light receiving surface of the photodetector 9, and the frequency F is given by the following equation (2).

F = 2 · Δf = 2 · V · sin (θ) / λ ‥‥‥‥ (2) From equation (2), if the frequency F of the photodetector 9 (hereinafter referred to as “Doppler frequency”) is measured, it moves. The moving speed V of the object 7 is obtained.

In the conventional laser Doppler velocimeter, the Doppler frequency F is equal to the laser wavelength λ, as is apparent from equation (2).
Therefore, it was necessary to use a laser light source having a stable wavelength as a laser Doppler velocimeter.
As a laser light source with continuous oscillation and stable wavelength
A gas laser such as He-Ne is often used, but the laser oscillator is large and a high voltage is required for the power supply, so that the apparatus tends to be large and expensive.

Laser diodes (or semiconductor lasers) used in compact discs, video discs, optical fiber communications, and the like are very small and easy to drive, but have the problem of temperature dependence.

Fig. 4 ('87 Mitsubishi Semiconductor Data Book; quoted from Optical Semiconductor Device Edition) is an explanatory view of an example of the standard temperature dependence of a laser diode. This is due to the temperature change of the refractive index of the active layer of the diode, and is 0.05 to 0.06 nm / ° C. On the other hand, the portion where the wavelength changes discontinuously is called longitudinal mode hopping and is 0.2 to 0.3 nm / ° C.

In general, a method of controlling the laser diode to a constant temperature to stabilize the wavelength is adopted. In this method, it is necessary to mount a temperature control member such as a heater, a radiator, and a temperature sensor to the laser diode with a small thermal resistance to precisely control the temperature, so that the laser Doppler speed meter is relatively large and the cost is high. However, the instability due to the vertical mode hopping described above cannot be completely eliminated.

As a laser Doppler velocimeter that solves the above-mentioned problem, a laser beam is incident on a diffraction grating, and among the diffracted light obtained from the diffraction grating, + n-th order other than 0-th order and -n-th order (n is 1,
A method of irradiating a moving object with two diffracted lights of (2,...) At the same intersection angle as the angle formed by the two light beams, and detecting scattered light from the moving object with a photodetector (hereinafter, G-LDV) is known. It is proposed in Japanese Patent Application No. 1-83208.

Figure 5 shows the diffracted light when a laser beam I is incident perpendicular to the arrangement direction t of grating diffraction grating 10 of the transmission type comprising a grating pitch d, the diffraction angle theta ₀ at this time becomes the following equation.

sin θ ₀ = mλ / d where m is the diffraction order (0, 1, 2, ‥) and λ is the wavelength of the laser light.

 Among these, ± n-th light other than the 0-th light is expressed by the following equation.

sinθ ₀ = ± nλ / d ‥‥ (3) (n is 1,2, ‥) FIG. 6 shows that the ± n-order diffracted light at this time is incident on the moving object 7 in different directions by mirrors 6a and 6b. FIG. 4 is an explanatory diagram of a Doppler velocimeter that irradiates two light beams so as to be θ ₀ .
From the equations (2) and (3), the Doppler frequency F of the photodetector 9 is given by F = 2V sin θ ₀ / λ = 2 nV / d (4) That is, regardless of the laser beam I, it is inversely proportional to the grating pitch d of the diffraction grating 10 and proportional to the moving speed of the moving object 7. Since the grating pitch d can be made sufficiently stable, the Doppler frequency F becomes a frequency proportional to only the moving speed of the moving object 7. The same applies to the diffraction grating 10 for a reflection type diffraction grating.

(Problems to be Solved by the Invention) The above-mentioned G-LDV type Doppler velocimeter was able to measure even if the moving speed was near 0 and to judge the moving direction. Further, although highly reliable detection that is hardly affected by environmental changes, particularly temperature changes, is possible, another problem related to the reliability of the Doppler velocimeter is dropout of a detection signal.

This is because the speed detection target of the Doppler velocimeter has random light scattering characteristics. The portion of the moving object irradiated with the diffracted light can be regarded as a collection of small particles that reflect the light, that is, a diffusing surface whose reflectivity fluctuates two-dimensionally. Since the light scattering characteristics of small particles are random and the distribution state of the set is constantly changing, the two-dimensional fluctuation period of the reflectance also changes to some extent randomly. The Doppler velocimeter detects the beat between the pitch of the interference fringes and the reflectance fluctuation period of the diffusing surface, which occurs when the two laser beams intersect at the predetermined intersection angle again. However, there is a problem that a no signal state, that is, dropout occurs.

In the conventional Doppler velocimeter, for detecting velocity information of a moving object, for example, as shown in FIG. 7, a photodetector 71 having a photodetector, an amplifier 72, and a band-pass filter (BPF) 7 are used.
Signal processing circuit 7 having 3 and phase locked loop 74
5 and using a wow and flutter meter 76 or the like.

However, after the Doppler signal has passed through the bandpass filter, dropout still occurs even though the S / N ratio is improved as shown in FIG. Further, even if a continuous signal can be obtained by the phase locked loop, there is a problem that the detection accuracy is still reduced when dropout occurs.

When the present invention detects the speed information of a moving object by an arithmetic unit having a signal processing unit using an output signal from the detecting unit,
By appropriately setting the circuit configuration of the signal processing unit,
It is an object of the present invention to provide a Doppler velocimeter capable of detecting velocity information with high accuracy without dropping detection accuracy even when dropout occurs.

(Means for Solving the Problems) The Doppler velocimeter of the present invention comprises: (1-1) irradiating an irradiation light beam on a moving object, and based on a shift of the frequency of scattered light from the moving object, In a Doppler speedometer that detects speed information, an optical system that causes the irradiation light beam to enter the moving object, and a light receiving system that detects scattered light from the moving object irradiated with the irradiation light beam,
A signal processing unit for calculating and detecting speed information of the moving object from a detection signal from the light receiving system, and the signal processing unit includes a phase locked loop for generating a periodic signal based on the detection signal; A drop-out detector for detecting a drop-out of the detection signal, a band-pass filter for filtering the detection signal, and a waveform shaper disposed next to the band-pass filter; The droop outputs a periodic signal and generates a signal for controlling the oscillator by comparing the phase of an output from the band-pass filter with an oscillator capable of controlling the oscillation state of the output periodic signal and the output periodic signal of the oscillator. And the dropout detector has a Doppler signal from the waveform shaper for a certain period of time. Between the input of the Fes-locked loop output and the oscillator of the phase comparator is characterized in that as cut switch means when there is no upper change.

(1-2) A light beam from a light source is incident on a diffraction grating, and two diffracted lights from the diffraction grating are incident so that the two diffracted lights intersect each other near the moving object. The shifted scattered light is detected by the detecting means,
In a Doppler speedometer that detects speed information of the moving object by a signal processing unit using an output signal from the detection unit,
The signal processing unit includes a phase locked loop for generating a periodic signal based on the detection signal of the detection unit, a dropout detector for detecting a dropout of the detection signal of the detection unit, and further filtering the detection signal. And a waveform shaper arranged next to the band-pass filter, wherein the phase-locked loop outputs a periodic signal, and an oscillator capable of controlling an oscillation state of the output periodic signal, and the oscillator A phase comparator that generates a signal for controlling the oscillator by comparing the phase of the output from the band-pass filter with the output periodic signal of the oscillator, and the drop-out detector includes: When the Doppler signal has not changed for a certain period of time, Between the output of and input of the oscillator is characterized in that as cut with the switching means.

In particular, in the Doppler velocimeter of the above configuration (1-1) or (1-2), (a-1) the dropout detector turns on the switch means when the dropout ends.

(A-2) The optical system causes an irradiation light beam having a wavelength λ to be incident on a moving object at a predetermined incident angle θ, and the incident angle θ changes according to a change in the wavelength λ of the irradiation light beam. Making the irradiation light beam incident on the moving object so as to be substantially constant.

(A-3) Two diffraction lights of ± n order (n = 1, 2,...) From the diffraction grating are applied to a moving object and are substantially equal to the intersection angle of the diffraction angles of the two diffraction lights from the diffraction grating. Incident at an angle such that the two diffracted lights intersect each other near the moving object.

And so on.

(Embodiment) FIG. 1 is a schematic view of a main part of an optical system according to an embodiment of the present invention. In the figure, reference numeral 101 denotes a Doppler speedometer. Reference numeral 1 denotes a light source, which comprises, for example, a laser diode, a semiconductor laser, or the like (hereinafter, referred to as "laser"). Reference numeral 2 denotes a collimator lens, which converts a light beam from the laser 1 into a parallel light beam 3. 10 is a diffraction grating, and the ± 1-order diffracted light of the reflective grating pitch d is set so as to diffract the diffraction angle theta _1. 6a and 6b are reflecting mirrors, respectively, which are arranged to face each other. Reference numeral 7 denotes a moving object or a moving fluid (hereinafter, referred to as a “moving object”), which is moving at a moving speed V in the direction of the arrow 7a. A condensing lens 8 condenses scattered light having undergone Doppler shift from the moving object 7 on a detection surface 9a of a photodetector 9 serving as a detection unit.

Numeral 14 denotes a calculating means, which has a signal processing unit described later, and calculates and calculates the moving speed V of the moving object 7 using the Doppler signal obtained by the photodetector 9.

In this embodiment, a laser beam emitted from a laser 1 is collimated by a collimator lens 2 into a parallel beam 3 having a diameter of about 2 mm.
As a result, the light is incident on the diffraction grating 10 having a reflective grating pitch d of about 1.6 μm in a direction perpendicular to the grating arrangement direction t. The diffracted light 5a of ± n order diffracted by the diffraction angle theta ₁ by the diffraction grating 10 (in this example n = 1), 5b reflecting mirror 6a which is disposed perpendicular to the grating arrangement direction, are respectively reflected by 6b, Moving object 7
Is incident to cross each other so that the spot diameter is overlapped from each said were direction on the moving object 7 side at the same incidence angle theta ₁ to.

In the present embodiment, with this configuration, the ± n-order diffraction angle (of the diffracted light) from the diffraction grating 10 changes according to the change in the wavelength λ, and the incident angle θ to the moving object changes. An optical system having a diffraction grating, a mirror, and the like is configured so that the ratio sin θ / λ at that time is substantially constant.

The condenser lens 8 condenses the scattered light having the frequency subjected to the Doppler shift Δf, −Δf shown in the equation (1) in proportion to the moving speed V of the moving object 7 on the detection surface 9a of the photodetector 9. . At this time, the two scattered lights having received the Doppler shifts Δf and −Δf interfere with each other on the detection surface 9a. The photodetector 9 detects the amount of light based on the brightness of the interference fringe at this time. That is, the photodetector 9 moves at the moving speed V where n = 1 in the equation (4).
A Doppler signal that does not depend on the oscillation wavelength λ of the laser 1 and has a Doppler frequency F proportional to F = 2V / d2 (5) is detected. Then, the moving speed V is obtained from the equation (5) by the arithmetic means 14 using the output signal from the photodetector 9.

FIG. 2 (A) is a block diagram of a first embodiment of a signal processing unit constituting one element of the calculating means 14 of FIG. In the figure, reference numeral 102 denotes a signal processing unit. Reference numeral 21 denotes a bandpass filter (BPF) to which the Doppler signal S from the photodetector 9 in FIG. 1 is input. Reference numeral 22 denotes a dropout detector, and reference numeral 23 denotes a phase locked loop (PLL), which performs signal interpolation at the time of dropout as described later.
The phase locked loop 23 has a phase comparator 24, a switch means (SW) 25, a low pass filter (LPF) 26, and a voltage controlled oscillator (VCO) 27. In the figure, the Doppler signal S is improved in S / N ratio by the band pass filter 21 and the phase locked loop 23
Is input to The phase locked loop 23 outputs a Doppler signal as a continuous signal.

Now, it is assumed that the Doppler signal has caused a dropout in a no-signal state as shown in FIG. 8, and the operation at this time will be described.

Dropout detector 22 is always a bandpass filter
The output state of the Doppler signal output from 21 is checked. When the level of the Doppler signal falls below a certain value as shown in FIG. 8, it is detected that dropout has occurred. Then, the switch means 25 is turned off, and the system between the output signal of the phase comparator 24 and the input signal to the voltage controlled oscillator 27 is separated. At this time, the low-pass filter (LPF) 26 holds the voltage immediately before the switch means 25 is turned off, and the voltage-controlled oscillator 27 outputs a signal of a constant value.

Thus, the phase locked loop 23 corrects only the output signal due to the dropout of the Doppler signal and maintains the output of the Doppler signal of the frequency before the dropout. When the dropout detector 22 detects that the level of the Doppler signal from the band-pow filter (BPF) 21 has exceeded a certain value, the switch means 25 is turned on, and the normal operation of the phase locked loop 23 is performed. Return to.

In the present embodiment, signal interpolation is performed when a dropout occurs in this way to prevent a decrease in detection accuracy.

FIG. 2 (B) is a block diagram of a second embodiment of the signal processing unit constituting one element of the calculating means 14 of FIG.

In the present embodiment, a waveform shaper 28 is provided next to the band pass filter (BPF) 21 in comparison with the first embodiment of FIG. 1A, and the waveform of the Doppler signal is shaped, and then input to the phase locked loop 23. The points are different, and the other configuration is basically the same as the first embodiment. The waveform shaper 28 is composed of a comparator having a hysteresis and a logic.

The signal processing method of the Doppler signal in this embodiment will be described with reference to FIG. The S / N ratio of the Doppler signal detected by the photodetector is improved by a band pass filter (BPF) 21, but a dropout as shown in FIG. 9A may occur. At this time, the output signal from the waveform shaper 28 is the ninth
The output signal is interrupted as shown in FIG. Therefore, the dropout detector 22 checks the rising timing T of the output signal from the waveform shaper 28. The dropout detector 22 is compared to a predetermined time T ₃ with the timing T T
<Off when of T _3, also T> when of T ₃ to be turned on. In FIGS. 9 (B) and 9 (C), T ₁ <T ₃ and off, T ₂
It is turned on at> T _3. The output of the dropout detector 22 is turned off at the rising edge of the output signal from the FIG. 9 (C) after the timing T ₂ as shown in the next waveform shaper 28.

Next, when the output of the dropout detector 22 is turned on, the switch means 25 is turned off as shown in FIG. 9 (D), and the system of the output signal of the phase comparator 24 and the input signal of the voltage controlled oscillator 27 is separated. You. At this time, the low-pass filter (LPF) 26 holds the voltage immediately before the switch means 25 is turned off, and holds the voltage controlled oscillator 27
Outputs a signal of a constant value.

As a result, the phase locked loop 23 corrects only the output signal due to the dropout of the Doppler signal and maintains the output of the Doppler signal of the frequency before the dropout as shown in FIG. 9 (E).

When the output signal of the dropout detector 22 is turned off, the switch means 25 is turned on and the operation returns to the normal operation of the phase locked loop 23.

In the present embodiment, signal interpolation is performed when a dropout occurs in this way to prevent a decrease in detection accuracy.

Although the reflection type diffraction grating is used in the embodiment shown in FIG. 1, the present invention can be similarly applied to a transmission type diffraction grating. As the diffracted light, diffracted light of second or higher order may be used in addition to the ± 1st order diffracted light.

In addition, the angle of incidence of the laser beam 3 on the diffraction grating 10 may not be perpendicular but may be incident at a fixed angle. At this time, the two diffraction lights of the ± n-order diffraction light may be incident on the moving object while maintaining the same intersection angle as the intersection angle of the two diffraction lights of the ± n-order diffraction light generated by the diffraction grating 10.

If a light beam emitted from the same light source is used, at least two of the two diffracted lights incident on the moving object are used.
If one diffracted light is the n-th order diffracted light, the other diffracted light may be any other than the n-th order, for example, 0 order, n + 1 order, n + 2 order.

In addition, two radiations emitted from the same light
One of the two light beams is made into an n-th order diffracted light and is incident on the moving object, and the other light beam is directly incident on the light receiving element without passing through the moving object, and interferes with the scattered light from the moving object to generate a Doppler signal. You may get it.

According to the present invention, a phase-locked loop is provided with a dropout detector, a band-pass filter and a waveform shaper are provided for a detection signal, and the phase-locked loop outputs a periodic signal. And an oscillator capable of controlling the oscillation state of the output periodic signal and a phase comparator for generating a signal for controlling the oscillator by comparing the phase of the output from the band-pass filter with the output periodic signal of the oscillator. Since the output detector is configured to switch between the output of the phase comparator of the phase locked loop and the input of the oscillator by a switch when the Doppler signal from the waveform shaper does not change for a certain period of time, the Doppler When a signal has a dropout, it can be accurately detected and the state of the signal from the oscillator can be properly maintained. As a result, the speed information of the moving object can be detected with high accuracy.

In particular, if the configuration is further restored, the disturbance of the output signal from the phase locked loop due to the dropout of the Doppler signal during the measurement is automatically corrected, and the speed information of the moving object can be detected with high accuracy.

Such a configuration is particularly effective in a device in which a frequency error due to wavelength fluctuation is optically prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an optical system according to one embodiment of the present invention, and FIG.
FIGS. 7A and 7B respectively show the first and the first signal processing units according to the present invention.
FIG. 3 is a block diagram of a second embodiment, FIG. 3 is a schematic diagram of a conventional Doppler velocimeter, FIG. 4 is an explanatory diagram showing the temperature dependence of the oscillation wavelength of a laser diode, and FIG. FIG. 6 is a schematic diagram of a Doppler velocimeter using G-LDV, FIG. 7 is a block diagram of a conventional Doppler signal processing method, and FIG. 8 is a dropout of a Doppler signal. FIG. 9 is an explanatory diagram of the signal processing in FIG. 2 (B). In the figure, 1 is a laser, 2 is a collimator lens, 5a, 5b
Is a diffracted light, 6a and 6b are reflecting mirrors, 7 is a moving object, 8 is a condenser lens, 9 is a photodetector, 10 is a diffraction grating, 14 is arithmetic means, 10
2 is a signal processing unit, 21 is a band pass filter, 22 is a dropout detector, 23 is a phase locked loop, 24 is a phase comparator, 25 is a switch means, 26 is a low pass filter, 27 is a voltage controlled oscillator, 28 is It is a waveform shaper.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shujiro Kadowaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-61-56986 (JP, A) JP-A-1 JP-A-4-1419 (JP, A) JP-A-59-89037 (JP, A) JP-A-63-131092 (JP, A) JP-A-62-80574 (JP, A) JP-A-4-25787 (JP, A) Japanese Patent Application Laid-Open No. Hei 4-25788 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01S 7/00-17/95

Claims (5)

(57) [Claims] A Doppler velocimeter for irradiating an illuminating light beam on a moving object and detecting speed information of the moving object based on a shift in the frequency of scattered light from the moving object; An optical system for causing the light beam to enter, a light receiving system for detecting scattered light from a moving object irradiated with the irradiation light beam, and a signal processing unit for calculating and detecting speed information of the moving object from a detection signal from the light receiving system The signal processing unit has a phase locked loop for generating a periodic signal based on the detection signal, a dropout detector for detecting a dropout of the detection signal, and further filters the detection signal. A band-pass filter; and a waveform shaper disposed next to the band-pass filter, wherein the phase-locked loop outputs a periodic signal and generates an output periodic signal. An oscillator whose state can be controlled, and a phase comparator for comparing a phase of an output from the band-pass filter with an output periodic signal of the oscillator to generate a signal for controlling the oscillator, and detecting the dropout. The device is configured to switch between the output of the phase comparator of the fez-locked loop and the input of the oscillator by a switch when the Doppler signal from the waveform shaper has not changed for a certain period of time or longer. Features Doppler speedometer. 2. A light beam from a light source is incident on a diffraction grating, and two diffracted lights from the diffraction grating are incident so that the two diffracted lights intersect each other near the moving object. A Doppler velocimeter that detects the shifted scattered light by a detection unit and detects speed information of the moving object by a signal processing unit using an output signal from the detection unit. A phase locked loop for generating a periodic signal based on the detection signal, a dropout detector for detecting a dropout of the detection signal of the detection means, a bandpass filter for filtering the detection signal, A phase shaper disposed next to the filter, wherein the phase-locked loop outputs a periodic signal, and controls an oscillation state of the output periodic signal. A phase comparator that generates a signal for controlling the oscillator by comparing the phase of the output from the oscillator and the output periodic signal of the oscillator with the output from the bandpass filter, and the dropout detector, When the Doppler signal from the waveform shaper has not changed for a certain period of time or more, the output from the phase comparator of the phase-locked loop and the input to the oscillator are switched by switch means. Doppler speedometer. 3. The Doppler velocimeter according to claim 1, wherein said dropout detector turns on said switch means when the dropout is completed. 4. An optical system according to claim 1, wherein the irradiating light beam having a wavelength λ is incident on a moving object at a predetermined incident angle θ, and the incident angle θ changes according to a change in the wavelength λ of the irradiating light beam. 2. A Doppler velocimeter according to claim 1, wherein said illuminating light beam is incident on said moving object so as to be substantially constant. 5. The ± n order (n = 1, 2,...) From said diffraction grating
The two diffracted lights are incident on a moving object at an angle substantially equal to the intersection angle of the diffraction angles of the two diffracted lights from the diffraction grating so that the two diffracted lights intersect each other near the moving object. The Doppler velocimeter according to claim 2, characterized in that: