JPS60213815A - Optical interference angular velocity meter - Google Patents

Abstract

PURPOSE:To improve the linearity of the output, by inserting a phase modulator between an optical path and a light distributor, receiving the interference light of clockwise light and counterclockwise light, detecting the phase difference, and using the sine or cosine component as the gyroscope output in correspondence with the phase difference. CONSTITUTION:Light 12 from a light source 11 is distributed to clockwise light 14 and counterclockwise light 15 by a light distributor 13 and inputted to both ends of an optical path 16. Output light beams 17 and 18 are interfered by an light coupler 13. A phase modulator 22 is inserted between the light distributor coupler 13 and one end of the optical path 19. The interference light is detected by a light receiver 21 and supplied to synchronous detectors 24 and 27 having the same frequencies as the driving frequencies f0 and 2f0 of the modulator 22. The output voltage, which is outputted to a gyroscope output terminal 46 is compared with a reference voltage. When the phase difference is within the range of about + or -pi/4 with respect to + or -mx, the sine component outputted from a terminal 34 is guided to the terminal 46. When the phase difference is within the range of about + or -pi/4 with respect to + or -(2m+1)pi/2, the cosine component of a terminal 43 is guided to the terminal 46. The output has the excellent linearily over the entire range.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention, for example, allows right-handed light and left-handed light to be input from both ends of an optical path of an optical fiber configured in a loop shape, and to mutually combine the lights that have passed in opposite directions. The present invention relates to an optical interference angular velocity meter that detects the angular velocity given in the circumferential direction of an optical path from the intensity of the interference light.

Prior Art> As shown in FIG. 1, in a conventional optical interference gyrometer of this type, light 12 from a light source 11 such as a laser is split into a clockwise beam 14 and a counterclockwise beam 15 by an optical splitter/coupler 13. Output light 17.18
The output '/l, xr, and xs are coupled to the distribution coupler 13 and interfered with each other, resulting in interference light 19.
The light is received by the light receiver 21 as a light beam. The optical path 16 is composed of, for example, an optical fiber wound in a loop shape a plurality of times. When no angular velocity is applied to the optical path 16 in its circumferential direction, the phase difference between the emitted light beams 17 and 18 is zero; When an angular velocity Ω of Ω is applied, a so-called Sagnac effect occurs due to this angular velocity, and a phase difference Δφ occurs between the output lights 17 and 18 propagated through the optical path 16. This phase difference Δφ is Δφ=4"RLΩ...
・・・・・・・・・・・・・・・・・・・・・(1>λ
It is represented by C. Here, R is the radius of the loop-shaped optical path 16, L is the length of the loop-shaped optical path 16, λ is the wavelength of the light @ii, and C is the speed of the light. The light intensity of the interference light 19 [1゜1 is Io oc l-cogΔφ ・e・・・・・・・・・・・
・-1・-・misery・−・・・ (2) becomes. By measuring the intensity IO of the interference light beam 9, the angular velocity Ω can be detected. When the input angular velocity Ω is small, the phase difference Δφ is small and the change in CO8Δφ is small,
Sensitivity becomes extremely low.

In order to optimize the input sensitivity from this point of view, conventionally, as shown in FIG. Both lights propagating in opposite directions due to drive signals from 14. ．． In this case, the interference light 190 intensity Io is Io = C(1+ cogΔψ(Jo(#)+zJ寞(
”)cos2ωt′+・・・・・・+2 Jam (g
) cot 2mωt' +・−・) + sinΔψ
(2Jt (#) sinωt'+2Jm(g) ain3
ωt' +-・”・・+ 2 J * m-peek (s)
sin (2m-riωt'+・・・・・・・・・))
・・・・・・・・・(3)

Here C: Constant Jn: Bessel function of nth order (n = o r 1121
a...) g: 2Aainπfoτ A: modulation index, τ: propagation time of light through the optical path 16 fo: drive frequency t' of the phase modulator 22: -τ/2 Equation (as is clear from 3) The interference light 190 intensity IO includes a term proportional to coa Δφ and a term proportional to sin Δφ. Conventionally, in order to increase the sensitivity in the low input angular velocity range, the output of the optical receiver 21 is synchronously detected. Because of this, when the input angular velocity Ω increases and the phase difference Δφ between the right-handed P light 14 and the left-handed P light 15 approaches π/2, the sensitivity at the other end becomes poor and the dynamic range is limited. Ta.

<Object of the Invention> The object of the invention is to provide an optical interference gyrometer that has a wide dynamic range, can perform measurements with high accuracy and good linearity over the entire range, and can maintain constant input sensitivity over the entire operating temperature range. It is in the interest of providing.

<Summary of the Invention> According to the present invention, a phase modulator is inserted between the optical path and the optical distribution coupler, the interference light between the clockwise beam and the counterclockwise beam is received by a light receiver, and the light receiver The output of the optical receiver is synchronously detected in a first synchronous detector at the driving frequency of the phase modulator, and synchronously detected in a second synchronous detector at a frequency that is 02 times the driving frequency of the output tube of the light receiver. The phase difference between the clockwise and counterclockwise lights is mπ (m++=0+1e2...)
The detection output is used to send the output of the first synchronous detector to the gyro output terminal, and calculate the position of the clockwise light and counterclockwise light. The phase difference is ±(2m
1) Detect that the range is within π/4 for 2 (m=o+it2...), and send the output of the second synchronous detector to the gyro output terminal. .

Furthermore, if necessary, each output of the first synchronous detector and the second synchronous detector is squared and added, and the driving voltage of the phase modulator or the light receiving voltage is adjusted so that the output becomes constant according to the added output. feedback control of the output of the device.

<Embodiment> FIG. 3 shows an embodiment of the present invention, and parts corresponding to those in FIG. 2 are given the same reference numerals. The output of the photoreceiver 21 is supplied to the synchronous detectors 24 and 27 through bandpass f-wave devices 25 and 26 whose pass frequency bands are the lIAwJ frequencies fo and 2fo of the phase modulator 22, respectively. The output of the 1d signal source 28 having a frequency twice the drive frequency fo is supplied to a 1/2 frequency divider as a modulation signal source 23, and its output is supplied to voltage regulators 31 and 32. Voltage regulator 31.3
One of the two outputs is selected by a switch 33 and supplied to the phase modulator 32 as a drive signal. Further, the output of the branching device 23 is directly supplied to the switch 34, and the output of the branching device 23 is directly supplied to the switch 34.
5, and the switch 34 uses the output of one of the branching device 23 and the inverter 35 as a reference signal to the synchronous detector 24.
supply to The output of signal source 28 is fed directly to switch 37 through phase shifter 36 and through inverter 38 . The switch 37 supplies the output of one of the phase shifter 36 and the inverter 38 to the synchronous detector 27 as a reference signal.

The output of the synchronous detector 24 is supplied to the terminal 39 and also to the switch 41, and the output of the synchronous detector 27 is supplied to the switch 41 and the terminal 43 through the gain adjuster 42. The switch 41 supplies the output of the terminal 39 or 43 to the low-pass single-wave generator 44 , and the output of the low-pass f-wave generator 44 is supplied to the gyro output terminal 46 through the linearity correction circuit 45 .

The output of the gyro output terminal 46 is supplied to the non-inverting input side and the inverting input side of comparators 48 and 49 in the control circuit 47, and is compared with the reference voltage +Vr-Vr of the reference power supply 51 and 52, respectively. The outputs of the comparators 48 and 49 are respectively supplied to an up count/to terminal UP and a down count terminal Do of a reversible counter 53, and are counted up and down, respectively. The output of the output terminal with a weight of 2° of the reversible force 9 and 53 is supplied to the switch 33 and 41 as a switching control signal, and the output of the output terminal with a weight of 21 is supplied to the switch 3.
4.37 as a switching control signal. The switches 33, 34, 37, and 41 are connected to the terminal NC side, the rim stain pressure regulator 31, the frequency divider 23, the phase shifter 36, and the terminal 39 side in the initial state (switching control signal is logic 10''), respectively. , the switching control signal is logic @l-, respectively on the terminal NO side,
Toe stain pressure regulator 32, inverter 35, inverter 3
8, connected to terminal 43. The count value of the reversible counter 53 can be output from the output terminal 54.

According to the configuration shown in FIG. 3, the driving frequency afo component is extracted from the bandpass f-wave generator 25, and therefore, as shown in equation (3) and equation (4), ' ・Listen/Song (4) A component proportional to sin Δφ is extracted. This is detected by the synchronous detector 24, and an output proportional to sin Δφ is obtained at the terminal 39. In equation (4), J+ ( x)
Since the sensitivity is maximum when = 0.53, 5 = 2Asi
It is preferable to drive the phase modulator 22 so that nxf□τ=1.84. Therefore, in this embodiment, the drive frequency fot is selected to an appropriate value, and the voltage regulator 31 is set to #I.
This is the case where the modulation index A't is adjusted to maximize the sensitivity.

As mentioned above, the output of the terminal 39 is proportional to sin Δφ, and changes by sin Δφ with respect to the phase difference Δφ between the clockwise light and the counterclockwise light, as shown in the song 1M65 in Figure A of #G4.

On the other hand, a component twice the drive frequency fo is extracted from the bandpass P-wave device 26, and this is a quadratic component proportional to eollΔφ as shown in equations 3 and 5.

1! oc ((BB Δφ・J proverb (scog 2 (
act' =---------=(5) In this case, J's C
In this example, the voltage regulator 32 is adjusted to adjust the modulation index A to obtain the maximum sensitivity.

The gain of the gain adjustment amplifier 42 is set to #I so that both outputs of the terminal 39t43 are at the same level with a phase difference Δφ=π/4.
4 will be adjusted. The output of the terminal 43 is W, which is proportional to 008Δφ with respect to the phase difference Δφ, as shown by a curve 56 in FIG. 4A.

If the phase difference Δφ is within the range of 0/π/4, switch 3
3.34 and 38.41 are in the condition shown in FIG. In the comparator 48, the output of the manual output terminal 46 is the reference ridge pressure vrt.
-If exceeded, a pulse as shown in FIG. 4 is generated. This pulse is added and counted by a reversible counter 53. On the other hand, when the output of the gyro output terminal 46 becomes larger than -Vr in the negative direction, the comparator 49 generates a voltage pulse as shown in FIG. The output with a weight of 2° of the reversible counter 53 changes as shown in Figure 4, and the output with a weight of 2' changes as shown in Figure 4E.
When the output of ° is high level (logic "L"), the switch 33,
41 is switched, and an output proportional to the signal at the terminal 43, ie, cooΔφ, is output to the gyro output terminal 46. Conversely, when the output of the gyro output terminal 46 becomes larger in the negative direction than the reference voltage -Vr, a signal is obtained from the comparator 49, and the reversible counter 53 performs subtraction counting, so that the output with a weight of 2c becomes a high level. Then, the switches 33 and 41 are activated and the signal at the terminal 43, that is, cogΔ, is activated as in the previous case.
An output proportional to φ is output to the gyro output terminal 46.

From the above state, the phase difference Δφ further increases as an absolute amount,
The output proportional to CO8Δφ is the reference voltage +Vr or -Vr
When the absolute value of si becomes larger, the comparator 48 or 49 obtains the si signal, the reversible counter 53 adds or subtracts, and the switch 33.41 returns to return the signal at the terminal 39, that is, si.
An output proportional to nΔφ can now be obtained at the gyro output terminal 46. At the same time, a signal polarity inversion command (switching control signal) is output by the output of the reversible counter 53 with a weight of 2' so that the output proportional to sin Δφ and cos Δφ has a positive characteristic with respect to the phase Δφ, and the switch 34.3
7 is switched. As a result, the polarity of the reference signal of the synchronous detector 24.27 is inverted, and the polarity of the output of the synchronous detector 24.27 is inverted. In the above, the phase difference Δφ is π/
If the gyro output voltage proportional to sin Δφ and cog Δφ in 4 is set to a slightly smaller absolute value than the reference voltage Vr, sin Δφ and coo Δ shown in FIG.
A signal 55,56 proportional to φ can be obtained as a sawtooth output as shown in FIG. 4G by control of the control circuit 47. Katsu sin.

It is possible to provide hysteresis in the switching of the signals proportional to Δφ and cogΔφ, thereby allowing stable operation. In this way, the phase difference Δφ is equal to mπ,
4, the sinΔφ component is taken out as the gyro output, and for ±(2m+1)i, the balance π/
4, the cogΔφ component is extracted as a gyro output, and an output is obtained with the most preferable linearity over the entire range.

This output can be determined by the following equation: angular velocity fti.

C is the speed of light, λ is the wavelength of light from the light source 11, and R is the optical path 160
radius, L is the length of the optical path 16, K is the proportionality constant (rad/
V), Vo is the voltage of the gyro output terminal 46, m is the difference between the total number of angle addition pulses and the total number of angle subtraction pulses,
The contents of the count value of the Tsumashi Town reverse counter 53 are taken out from the terminal 54.

The polarity of this angular velocity Ω is determined using the output of the most significant bit of the reversible counter 53.

The dynamic range in this example is the phase difference Δψ
This is a range corresponding to 64π, that is, about 32 wavelengths. This dynamic range can be widened by increasing the number of bits of the reversible counter 53. The control circuit 47 can be configured not only by a logic circuit like this, but also by converting the output of the gyro output terminal 46 into a digital signal, comparing it with a reference value, and calculating the corresponding counting operation with the reversible counter 53. As before, sinΔφ and cog are calculated according to each range of phase difference.
It is also possible to extract a gyro output proportional to Δψ.

As solved from equation (4-5), the input sensitivity is X (=2A
ainπfoτ). The value of X is the driving frequency fo of the modulation index A1 phase modulator 22 and the optical path 16.
is determined by the propagation time τ of light through . Drive frequency fO
and the propagation time τ are relatively less affected by temperature, but the modulation index A is easily affected by temperature. Phase modulator 2
2, for example, wraps one end of the optical path 16 around an electrostrictive vibrator, applies a driving voltage of frequency fo to the electrostrictive vibrator, causes it to vibrate, expands and contracts the optical path 16, and transmits clockwise light passing through it. and the left-handed light are phase-modulated. The drive frequency fo is generally set to match the resonance point of the electrostrictive vibrator in order to efficiently expand and contract the electrostrictive vibrator. Since this resonant frequency changes depending on temperature, the modulation index A is more influenced by the temperature as the mechanical Q (which refers to the "suddenness" of mechanical vibration at the resonant frequency) of the electrostrictive vibrator is higher.

As a result, the X value changes, and the human power sensitivity fluctuates.

For example, you can solve this problem as follows.

That is, the output after synchronous detection proportional to sinΔφ is vl, C
If the output after synchronous detection proportional to O8Δψ is Vx, then Ml = Ks sinΔφ, Vx = Kg cog
Δφ can be expressed as (7). Here, K r −K * is a proportionality constant.

Suppose that K * = 'K snow = K, and vl and V spirit t-
When squared and added together, the value takes a constant value as shown in the following formula.

(8) Therefore, if the modulation index A or the output voltage from the photoreceptor 21 is controlled so that the value of Vf is always constant, the input sensitivity can be reduced. can be kept constant. FIG. 5 shows an example of a configuration in which the modulation index A is changed by controlling the drive voltage of frequency fo applied to the phase modulator 22 to keep the input sensitivity constant.

First, the output of terminal 39 proportional to sinΔφ and cogΔ
The output of the terminal 43 proportional to φ is the output of the switch 57.
．． 58 and a gain adjustment amplifier 61.
62. The weight of the reversible counter 53 is 2
The output of the switch 57.58.64 through the terminal 63
is supplied as a control signal to

Reference power sources 65 and 66 are connected to the switch 64. When the control signal of terminal 63 is 01, switch 57.58
．． 64 is at the position of contact NC. Therefore, the signal layer input to the terminal 39 is supplied as is to the 2-east circuit 67, and the signal input to the terminal 43 is amplified by the amplifier 62 so that the proportionality constant Km is equal to 1.
is supplied to The two signals squared by the two east circuits 67 and 68 are added by an adder circuit 69, the added output is compared with the reference voltage of the reference power supply 65 by a differential amplifier 71, and the error signal is amplified. Ru. The amplified error signal is supplied to the automatic gain 414 rectifying circuit 72,
The amplitude of the drive voltage of frequency fo input to the terminal 73 is controlled, and its output is sent from the terminal 74 to the phase modulator 22 (j
Figure I3).

In this series of closed loops, the error signal is always zero. Therefore, the human sensitivity is always kept constant. When the control signal with a weight of 2 degrees at the other terminal 63 becomes "1", the switch 57.58*64 is switched to the NO contact. As a result, the signal input to the terminal 39 is transmitted to the amplifier 61.
The signal is supplied to the 2-east circuit 67 after being amplified so that the number KI becomes equal to Km. The signal input to the terminal 43 is directly supplied to the square circuit 68. The two squared signals are added by an adder circuit 69, and compared with a reference voltage of a reference power supply 66 by a differential amplifier 71.
The error signal is amplified. 1. The amplified error signal is supplied to an automatic gain adjustment circuit 72, which controls the amplitude of the driving voltage of frequency fo input to a terminal 74.
The signal is supplied to the phase modulator 22 through.

As a result, the input sensitivity is kept constant as described above.

Note that the reference power supply 65 outputs a reference voltage set so that the input sensitivity proportional to sinΔφ in equation (4) is maximized, while the reference power supply 66 outputs a reference voltage set so that the input sensitivity proportional to sinΔφ in equation (4) is
It is set so that the input sensitivity proportional to is maximum and outputs nine reference voltages. Although the voltage of the excitation signal is controlled by the output of the differential amplifier 71 in FIG. 5, the output of the photodetector 21 may be automatically controlled by the output of the differential amplifier 71.

Effect> In the conventional method shown in Figure 2, when the phase difference between the far right-handed beam and the left 1-gram I beam approaches π/2, the sensitivity becomes extremely poor and the dynamic range is limited. However, according to the present invention, in equation (6) shown above, m
Even if the value of changes, the linearity when m is 0 is shown in Figure 4 G.
As shown in Figure 3, they are the same, and the deviation value does not increase in the high range. By providing the linearity correction circuit 45, high linearity can be obtained over the entire measurement range. Further, in this invention, the dynamic range can theoretically be expanded without any limit.

Further, by controlling the drive voltage of the phase modulator 22 or the output of the photodetector 21 by a signal proportional to eoaΔφ and a signal proportional to sinΔφ, the input sensitivity can be kept constant over the operating temperature range.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams showing a conventional optical interference angular velocity meter, FIG. 3 is a block diagram showing an example of an optical interference angular velocity meter according to the present invention, and FIG. 4 is an explanation of the operation of step 7. FIG. 5 is a block diagram showing a part of the optical interference gyrometer according to the present invention. 1: light source, 13: optical distribution coupler, 16: optical path, 221
: Photoreceiver, 22: Phase modulator, 24.27: Synchronous detection circuit, 25.26: Bandpass P-wave device. 42+61+62: gain adjustment amplifier, 28: value signal source, 23: V2 frequency divider, 31.32: voltage regulator. 36; Phase shifter, 44: Low-pass f'lHL unit, 45: Linearity correction circuit, 35.38: Inverter, 46: JAI 4 output terminal, 47: Control circuit, 48.49 = Comparator, 51 .52, 65.66: Reference power supply, 53: Reversible counter, 67.68: Square circuit, 69: Addition circuit, 72: Automatic gain adjustment circuit. Patent issuer: Japan Aviation Electronics Industry, Ltd. Agent Kusano
table

Claims (2)

[Claims] (1) an optical path that goes around at least once; a means for passing clockwise light and counterclockwise light on the optical path; and an interference means for interfering with the clockwise light and counterclockwise light that have propagated through the optical path; A phase modulator is disposed in series between the interference means and one end of the optical path to change the phase of the clockwise light and the counterclockwise light, and the optical intensity of the interference light is detected as an electrical signal. a first synchronous detector that synchronously detects the output of the optical receiver at a frequency that is the same as the driving frequency of the phase modulator; The second synchronous detector performs synchronous detection based on the frequency, and the phase difference between the right-handed beam and the left-handed beam is ±mπ (m=o+i+
a first range detection means for detecting that the range is within the range of π/4 with respect to (m=0.1.2...
), the output of the first synchronous detector is connected to a gyro output terminal. and means for guiding the output of the g2 synchronous detector to the gyro output terminal according to the detection output of the second range detection means. (2) a first squaring circuit that squares the output of the first synchronous detector; and a second squaring circuit that squares the output of the second synchronous detector.
The outputs of the multiplication circuit and the first and I@2 square circuits are set to 〃0
Claim 1, further comprising an adding means for adjusting the amount of time, and means for controlling the drive voltage of the phase modulator or the output of the photodetector so that the output of the receiver becomes constant depending on the output of the adding means. The optical interference gyrometer described.