JPH02189412A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To improve measuring accuracy by outputting values within which the abso lute values of tangent and cotangent components are less than 1 as the rotation data in the direction of an optical fiber loop with a third operating means based on the results of the operations of first and second operating means. CONSTITUTION:This apparatus is composed of the following parts: a gyroscope part 10; a modulation control part 20 for driving a phase modulator 4; and a signal processing part 30 which processes the electric signal that is obtained by optoelectronic transducing operation through a photodiode 5. In the control part 20, not only the driving control of the modulator 4 is performed through an amplifier 24, but also synchronizing signals for the processing part 30 are formed through first and second 1/2 frequency dividers 22 and 23. In the processing parts 30, signal components cos2DELTAtheta and sin2DELTAtheta are taken out through first and second synchronizing detectors 33a and 33b. In a tan operator 35 and a cot operator 36, angular-speed values (absolute value is less than 1) having high linearity are computed through dividing operation. In an operating device 37, the measured angular speed value is specified through selecting operation taking reference to the signs of the obtained component signals of cos2DELTAtheta and sin2DELTAtheta.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an optical fiber gyro that uses the Sagnac effect to determine the rotational angle or rotational angular velocity of a moving object, and particularly relates to an optical fiber gyro that uses the Sagnac effect to determine the rotational angle or rotational angular velocity of a moving object, and particularly relates to an optical fiber gyro that uses the Sagnac effect to determine the rotational angle or rotational angular velocity of a moving object. The present invention relates to implementation of a processing circuit configuration suitable for both enlargement and improvement of measurement accuracy.

[Conventional technology]

As is well known, an optical fiber gyro is an interference system of an interferometric laser gyro that utilizes the Sagnac effect, which is constructed using optical fibers, and a light beam (laser light) that is split into two via a beam splitter is connected to an optical fiber loop. By making the light enter from both ends of the optical fiber loop and guiding the respective propagated lights of these incident lights through the optical fiber loop to the same optical path via the beam splitter again, optical interference based on the Sagnac effect is obtained. There is. This '1; tip is extracted as an electrical signal indicating rotational information (angular velocity) in the loop direction of the optical fiber loop through a suitable photodetector.

By the way, various techniques have been proposed to improve the sensitivity of these optical fiber gyros, among which:
The phase of the light propagating through the optical fiber loop is modulated as required, and the rotation information of the optical fiber loop is extracted as information phase-shifted by π/2, that is, sin function information (normally, the signal indicating the rotation information is (Output as cos function information indicating the maximum value when the loop is at rest)
This phase modulation method is attracting attention as a method that can improve one resolution and stabilize the zero point. In Figure 3,
An example of an optical fiber gyro that employs such a phase modulation method is shown below.

In other words, in the optical fiber gyro shown in FIG. 3, ■ is a laser beam generator, 2a and 2b are optical couplers that act as the beam splitters, 3 is an optical fiber loop (optical fiber coil), and 4 is a PZT (electrostrictive vibration generator). 5 is a photodiode used as the photodetector; 5 is an oscillator that generates an electric signal having a frequency f for driving the phase modulator 4; 1. A lock-in amplifier 8t that extracts and outputs a signal photo-electrically converted through a diode 5 by locking it in based on a signal with a frequency fo output from the oscillation 86, and normally from this lock-in amplifier 7, , light is emitted by the photodiode 5.
This is a modulation component of the fundamental frequency among the interference light components that are electrically converted.

Eo=KJt('1)2sin2Δ0-(
1) However, yl=2mfsin2ifoT, where K
: Constant Jl : Bessel function of the first kind - next term 2ΔO : Sagnac phase difference mf : Modulation index fo : Modulation frequency T : It is known that the component of light propagation time in an optical fiber is extracted as its output Eo . Incidentally, according to the Bessel function table, η=1.
Since it is known that the value of Jt (η) reaches its maximum at (determined by the applied voltage value), then s shown in the above equation (1)
The in-wave component is extracted.

In this way, according to the phase modulation type optical fiber gyro as illustrated in FIG. 3, when no phase modulation is applied, the interference light extracted as cos function information as shown in FIG. By the above phase modulation, the output is
sjn 15! as shown in FIG. 4(b)! It is possible to extract it as I number information. As is clear from comparing Figure 4 (i3) and (b), this means that the linearity of the Idemitsu fiber gyro in the low-speed rotation range has been improved, and the constant sensitivity of 41 in the same low-speed rotation range has also been significantly improved. It means to be improved.

[Problem to be solved by the invention]

As described above, the optical fiber gyro using the phase modulation method improves linearity in the low rotation speed range,
Although it is certainly effective in improving the sensitivity at Kaesong, the optical fiber gyro shown in Fig. 3 has a narrow measurement range and still poses a problem in practical use.

That is, as shown as range R in FIG. 4(b),
In the case of the optical fiber gyro, Sagnac phase shift 2
The rotational angular velocity could only be measured in the range of ±(π/2) with Δθ as a reference. For example, as noted in Figure 4(b), if we assume a value such as (π/2)±α, this means that both the value and sign are equal on the waveform of sin 2Δ0, and the value of 2Δ0 is (π/2) ) - α or (π/2) + α cannot be determined. Moreover, the value of this 2ΔO is ±(π/2
), s for the change in the value of 2Δθ
The change in the value of in 2ΔO becomes slow, and in the same region,
Since the ilQ constant accuracy is degraded, the practically usable 111Q constant range is narrower than the above range R (see FIG. 4(b)).

In addition, in the optical fiber gyro as shown in Fig. 3,
In addition to fluctuations in the laser power generated from the beam generator 1, losses in the optical system and optical coupler 2a
and when the branching ratio of 2b fluctuates due to temperature changes, etc.

The measurements will be directly influenced by these factors. In this case, even if it is possible to improve the al'l constant range, the reliability of the h+g constant value cannot be maintained.

The present invention has been made in view of these circumstances, and an object of the present invention is to provide an optical fiber gyro that can both expand the fixed range and improve the all-fixed accuracy.

[Means to solve the problem]

In this invention, the sJn wave component and the cos
Detection means for extracting wave component signals, first calculation means for calculating tan components from these extracted s i n wave component signals and cos wave component signals, and also these extracted s j n wave component signals. and a second calculation means for calculating a cot component from the cos wave component signal, and the absolute value of either the tan component or the cot component becomes 1 or less depending on the calculation results of the first and second calculation means. and a third calculating means for outputting the values of the range as loop direction rotation information of the optical fiber loop, to constitute an optical fiber gyro.

[Effect]

The sjn wave component signal and the cosine wave component signal extracted through the detection means commonly include various unstable element coefficients (noise coefficients) that are mainly a cause of amplitude fluctuations of the Sagnac interference light. Therefore, the tan component (=si
n-wave component/Co! II wave component) or cot component (=
By calculating cos wave component/sin wave component),
The above noise coefficients are canceled out, and only the signal component that purely corresponds to the Sagnac phase difference is extracted.

In addition, the values of these tan and cot components are continuous in the sagnac phase difference (2Δθ) direction with the absolute value of 1 as the apex in the range where the absolute values of each are less than or equal to 1. By selecting the appropriate value of these tan component or cot component within the range where the absolute value is 1 or less, as in the calculation means of 3, the measurement range will naturally be expanded. .

〔Example〕

FIG. 1 shows an embodiment of an optical fiber gyro according to the present invention. In FIG. 1, the same elements as those shown in FIG. 3 are designated by the same reference numerals.

First, in order to facilitate understanding of the embodiment,
With reference to FIG. 1, let us consider the angular velocity output by a single-phase modulation force type optical fiber gyro.

Now, when the radius of the optical fiber loop 3 is 1 (, the total length of the optical fibers constituting the loop 3 is Il, and the angular velocity when the loop 3 rotates in its loop direction is Ω), the interference light due to the Sagnac effect is It is well known that the phase difference 〇 is expressed as λC. Here, λ
is the wavelength of light propagating through the optical fiber loop 3,
Further, C is the speed of light at the same propagation destination.

Further, the optical signal e generated from the beam generator 1 shown in FIG. 1 is as follows: 8L: Ksinωt
-(3) K: Constant ωL: When expressed by the above angular frequency, the optical signal ec which is divided into two by the optical coupler 2a or 2b and input into the optical fiber tube 3 in the CW force direction (clockwise direction) is as follows: e c = K15inωt K1: Optical path constant ... (4)
The optical signal eQQ which is also divided into two and input into the same optical fiber loop 3 in the CCW direction (counterclockwise direction) is e c c
= K15inωt = (5)K
2: The optical path constant becomes the optical path constant, and these optical signals ec and QQQ are further phase modulated by the phase modulator 4, undergo a sagnac phase shift through the optical fiber loop 3, and are returned from the optical fiber loop 3 to the optical coupler 2b. optical signal e
crn and ecc, m are each ecm=Ktsin(ωt+α+Δf)) ・(
6) e c c m = K2sin(ω
− β −Δ θ ) (7). Here, α and β indicate the amounts of modulation given to the optical signals ec and QQQ by the phase modulator 4, respectively, and a=m fsin(p L+γ) −(
8) β = m f 5in (p - γ)... (9) m
f: modulation index (value indicating depth of modulation) I; yen: modulating angular frequency γ: phase difference with respect to the angular frequency.

Now, such an optical fiber gyro (gyro part 1.0
), optical signals a crn and Q (2CIn) shown as equations (6) and (7) are guided to the same optical path via optical couplers 2b and 2a, and are sent to photodiode 5. It is considered that the combined light (input) is input.Here, when this combined light (interference light) is P+, the interference light PL is given by the following equation.

PL: ecm+eccm”: KIKZ(1
−cos(2(11t + α+β)) (1−cos
(2ΔO+β−α)]...(10) On the other hand, from equations (8) and (9), α+β= m
f (sin(p t +7) 15in(P t
'/))=2mfsinptcosy °・
= (11) α − β = m f (sin(p
t + y )−sin(p ty
))=-2m f cos p t sinγ
-(12), so these equations (11) and (
Substituting equation 12) into equation (lO) above, PL=KtKz(1-Cog(2(11t +2m f
sinp t, cosγ)]X(1+cos(2Δθ−
2m fcosp tsiny)): KIKZ(1-c
os2 (1) tcoS(2m fcosYsinp
t)-sin2ω and 5in(2m f cos y
sin p t ))X(1+cos2ΔOcos(2
mfsinycosp t) + sin 2ΔO5in
(2m f sin γ cospt)) (13) The interference light PL thus provided is converted into a current signal (photo-electrical conversion) through the photodiode 5. On this occasion,
Since the photodiode 5 does not respond to the angular frequency ω of light, this converted current is expressed as
The term that does not include cosωt and sinω in equation (13) above, that is, IL=KzKz(1+cos2Δθc
os(2m fsinycosp t)+5in2Δθ
sin(2mfsinycosp L)) −(14
) will be expressed in the form. This (14)
If we expand the formula into a series, we get IL=KtKz(1+cos2Δ(J o(2rn f
sinγ)Xcos(2n+1)pt)) =KtKz(1+cos2ΔθJo(2mfsiny)
+2sLn2ΔθJt(2mfsiny)cosp t
−2cos2ΔθJ z(2m f 5iny )co
s2 p t-2sin 2ΔOJs(2mfsiny
)cos3p t+2cos2ΔθJa(2mfsin
γ) cos4 p t+ 2 sin 2ΔOJa(
2mfsinY)cos5p t] (15) It can be seen that the current IL is formed by combining harmonic components of each order. In a phase modulation optical fiber gyro, the fundamental wave component in equation (15), that is, r2sir+2ΔθJ t(2m f 5iny) co
sp t 4 terms are extracted and used as the angular velocity output (formula (]) above, where sin γ in formula (15)
Let's consider the value of .

Above r2sin2ΔOJ 1(2m f 5iny)c
In order to maximize the extraction output in osp t J, it is necessary to maximize r J t(2m f 5iny)4. The optimal method for this is si
The goal is to maximize nγ and minimize the value of rnf, so that 2mfsiny=1.84. At this time, Jl (1, 84) becomes maximum. In addition, on the contrary, if sinγ is made small,
Increasing mf to Jt (1,84) means increasing the voltage applied to the phase modulator (PZT) 4, which increases unnecessary mode vibration of the modulator and increases modulation noise. do.

In this way, unless sin γ is maximized, that is, γ
= (π/2), otherwise the S/N ratio will be poor.

Therefore, in practice, it is necessary to set the above equations (8) and (9) as follows. This means that the modulation phase moves symmetrically during the time that the light beam propagates within the optical fiber loop 3. Finally, let us consider the optimum value of the modulation frequency fo based on these conditions.

Now, the light propagation time T in the optical fiber loop 3 is T=
n L/C-(16) n: Core refractive index L: Total length of optical fiber C: Assuming that it is determined as the speed of light, the condition for the above modulation phase to move symmetrically is T/2 N = n L/C −(17)N=1.2,
3. ... becomes.

On the other hand, if the modulation frequency is f, then this is f=1/T
...(18).

Therefore, by substituting the above equation (17) into this equation (18).

f = C/2 N n L
=・(19), and the minimum modulation frequency fa that can satisfy the above γ=(π/2) is i o= C/ 2 n L
”・(20).

Next, with reference to FIG. 2, we will first explain the principle of the embodiment shown in FIG.
15) r2sin of the angular velocity output obtained as in the formula
2ΔθJ 1(2m f sin y )cos p
t 4 term and r2cos2ΔOJz(2mfsiny)c
os2p tJ terms, or more generally, the 5in2Δ0 component and the cos2Δθ component are respectively extracted and used. These components are extracted.

As shown in FIG. 2(a), the value changes periodically depending on the value of 2ΔO. In addition, in the above consideration, assuming that only 51 terms are extracted, selecting the value of (2mfsiny) as (1, 84) is
As explained above, it is preferable to maximize the amplitude, but when using two components, the Jt term and the 52 term, as in the example here, the value of (2mfsiny) for each is set to (2, 4 ) is effective in making the respective amplitude values the same and minimizing the DC component (Jo term). All of these are clear from the Bessel function of the first kind.

In addition, in this example, the component of sin 2Δθ and c
By mutually dividing the components of os 2Δθ, the components of tan 2Δ0 (=sin2ΔO/CO52
Δθ) and the component of cot 2ΔO (=cos2ΔO/5i
n2ΔO) is newly determined, and as shown in FIG. 2(b), (c) and (e), the value of 2ΔO is -1≦≦2.
In each range of 80≦π, the value of tan 2ΔO is adopted as the angular velocity output of the optical fiber gyro of this embodiment, and the value of cot 2ΔO is adopted as the angular velocity output of -1 π≦2ΔO. adopt. Incidentally, each of these points adopted under these conditions has a mutual absolute value of 1 or less, and high linearity is maintained over all these ranges.

In this embodiment, the extracted values of each component of 5in2ΔO or cos 2Δθ are further used as reference information for specifying the 71ill constant area of the angular velocity output.

That is, specifying the value of 5in2ΔO shown by the broken line in FIG. 2(b) and specifying the value of tan 2ΔO shown by the solid line in FIG. 2(b).
As is clear from comparing the characteristics of values of 0 and cot2ΔO in the range adopted above, for example, in Fig. 2(d)
In 41 regular job 1 and measurement area 1■, the output values adopted are in the range of 0≦tan2ΔO≦1,
With this value alone, it is impossible to determine which of these measurement ranges the value is in, but as shown in Figure 2(b), the above sin
By referring to the value of 2ΔO, these ill! It becomes possible to judge the fixed area. In the illustrated range of −π≦280≦π, the output value is in the range of 0≦tan 2Δθ≦1, and 5jn
2Δ1) has a positive sign (shaded area in FIG. 2(b)), there is no constant area other than measurement area 1 shown in FIG. 2(d). This means that cos as shown in Figure 2(C)
This also applies mutatis mutandis to the relationship with the value (sign) of 2ΔO. The following table shows each 711! shown in FIG. 2(d). By I constant area,
This is a list of these identified relationships.

If the 411 constant of the angular velocity is carried out based on this principle, at least in the range of change of 2ΔO and the range corresponding to 2π radians, it will be possible to track the angular velocity continuously under any circumstances, that is, in the range corresponding to 2π radians. At the very least, you can quickly and accurately grasp the measurement range, and
Highly sensitive angular velocity measurement with rich linearity can be achieved at any part within the same region. In addition, by calculating the < tan component and cot component as described above, the constant KIK2 in the above equation (15) is canceled out, and therefore the angular velocity measured above is The output is not adversely affected.

Now, the embodiment shown in FIG. 1 is constructed based on this principle, and as shown in FIG. The modulation control section 20 for driving the modulator 4 and the photodiode 5 (usually a pin photodiode is used) of the gyro section 10 process the electrical signal photo-electrically converted as required to output angular velocity or angle. The signal processing unit 30 is configured to have roughly three parts: a signal processing unit 30 for obtaining an output;

Among these, the modulation control unit 20 generates a signal 4 having a frequency four times the optimum modulation frequency fO as shown by the above equation (zO).
The oscillator 21 that oscillates and outputs fo, this 9! A first frequency divider 2 receives the waveformed signal 4Jo and divides the frequency by 1/2.
2. A second frequency divider 23 which receives this 1/2 frequency-divided signal 2fo and further divides it by 1/2, and the frequency division by this second frequency divider 23 results in the frequency f o . For example, as described in Principle 1,
γ) = (2, 4), and the gyro unit 10
An amplifier 24 . It is composed of each of the following. This modulation control section 20 not only controls the drive of the phase modulator 4 through the amplifier 24, but also forms a synchronization signal 43 for the signal processing section 30 through the first and second frequency dividers 22 and 23. It is supposed to be done.

The signal processing unit 30 also includes a /V (current/voltage) converter 31 that converts the current IL (see equation (15) above) photo-electrically converted through the photodiode 5 of the gyro unit 10 into a voltage 4i; An AC amplifier 32 amplifies this converted voltage signal as required, and from this amplified signal, based on the frequency divided output 2fo from the first frequency divider 22 of the modulation control section 20, its second harmonic bottom, That is, r2cos2ΔOdz(2mfsi
nγ) cos2p(1 term amplitude value KIKz2cmos
a first synchronous detector 33a that extracts (synchronous detection) a signal corresponding to 2ΔθJ 2 (21Tl f sin y );
A first A/D (analog/digital) converter 34a that converts this synchronously detected signal (analog signal) into a digital signal with appropriate resolution, and the AC amplifier 32.
From the signal amplified in
That is, r 2 sin 2ΔOJl(2mfsiny)cos in the above formula (15)
Amplitude value of p tJ term K IK 22 sin 2Δθ
A second synchronous detector 33b extracts (synchronously detects) a signal corresponding to J t (2rn f sin y ), and converts this synchronously detected signal into a digital signal in the same way as the first Δ/D converter 34a. The second A/D converter 34b, the output of these A/D converters 34-a (cos 2ΔO component), and the A/D converter 34
By accepting the output of b (sin2ΔO component), the component of tan 2Δ0 (=sin2ΔO component) described in the above principle is obtained.
tan calculator 35 that calculates and outputs Δ0/cos2ΔO)
, similarly receives the outputs of these A/D converters 34a and 34b, and converts the cos as described in the above principle.
A cot calculator 36 that calculates and outputs the component of 2ΔO (=cos2ΔO/5in2Δ0). Then, while referring to the output of the A/D converter 34a or 34b, the gyro calculates a value within a range whose absolute value is 1 or less according to the calculation results of the tan calculation unit 35 and the cot calculation unit 36. They each include a computing device 37 that computes and outputs the angular velocity information of the section 10 or the time-integrated angular velocity information as angle information.

That is, in this signal processing unit 30, the first and second synchronous detectors 33a and 33b extract two types of signal components cos 2Δθ and sin 2Δθ as shown in FIG. The tan calculation unit 35 and the cot calculation unit 36 calculate the angular velocity value with high linearity based on the above-mentioned principle (see FIG. 2(b) or (Q)) and calculate the error value through their respective division operations. The constant K IK 2 including the stability element is canceled, and the arithmetic unit 37 calculates the value while referring to the sign of the extracted cos 280 component or sin 2ΔO component signal of each calculated angular velocity value. Through the selection operation, the measured angular velocity value is specified based on the above-mentioned principle.

As described above, according to the embodiment shown in FIG. 1, the range in which the angular velocity can be measured with high precision as an optical fiber gyro is achieved based on the above-mentioned principle.
The value of 2ΔO can be expanded to at least the range of −π≦2Δθ≦π, and the gyro unit 1
By canceling the constant KIK2 that occurs during light propagation at 0,
This measured value can be made even more reliable.

Note that the above range of -π≦2Δθ≦π is a range in which the angular velocity value can be immediately specified even if it is discontinuous in time. When the same measurement is performed, the measurable range is also ±ψ (infinity). In this case, there is no need to refer to the cos 2Δ0 component or the sin 2 to component signal for specifying the measurement range, and the calculation unit 37 uses the tan calculation unit 35 and the cot calculation unit 36 to calculate the It is sufficient for each member to have the function of selecting each time a range whose absolute value is 1 or less.6 Incidentally, the above-mentioned "temporally discontinuous" means that the gyro unit 10 (optical fiber loop 3) This refers to a situation where a power source (not shown) is turned on after rotation, or where the power source is switched or turned off during measurement.

In addition, the above-mentioned canceled constant KxKz means that factors such as fluctuations in the output of the optical beam generated from the beam generator 1, fluctuations in the branching ratio of the optical couplers 2a and 2b, fluctuations in the loss of the optical fiber loop 3, etc. It is a constant that is aggregated. Therefore, the fact that this constant K I K z is canceled out means that all the adverse effects caused by these variable factors on the angular velocity output of the gyro unit 10 are eliminated.

By the way, in the above embodiment, the principle and configuration example were shown for the case where the present invention is applied to a phase modulation type optical fiber gyro as shown in FIG. 1 or 3, but interference due to the Sagnac effect The present invention can be applied to any other type of optical fiber gyro as long as both the above-mentioned sine wave component and cosine wave component can be extracted from the optical output.

〔Effect of the invention〕

As explained above, according to the optical fiber gyro according to the present invention, high sensitivity measurement with excellent linearity is realized over a wide angular velocity or angular range, and the stability and reliability of measured values are also maintained at a high level. It becomes like this.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the optical fiber gyro according to the present invention, Fig. 2 is a diagram showing the operating principle and operating characteristics of this embodiment of the optical fiber gyro, and Fig. 3 is a diagram showing the conventional phase modulation method. FIG. 4 is a block diagram showing an example of an optical fiber gyro, and is a graph showing a comparison of the operating characteristics of the optical fiber gyro when phase modulation is not applied and when phase modulation is applied. 1... Beam generator, 2a, 2b... Optical coupler, 3
...Optical fiber loop, 4...Phase modulator, 5...
・F1・Diode, 21...Oscillator, 22.23
...172 Frequency divider, 33a, 33b... Synchronous detector, 35... Tan operator, 36... Cot operator,
37... Arithmetic device.

Claims (1)

[Claims] 1. A light beam split into two via a beam splitter is made to enter from both ends of an optical fiber loop, and the respective propagated lights of these incident lights through the optical fiber loop are routed again via the beam splitter to the same optical path. In an optical fiber gyroscope, interference light based on the Sagnac effect of the guided light is extracted through a photodetector through photodetector as loop direction rotation information of the optical fiber loop.
detection means for extracting wave component and cosine wave component signals, respectively; first calculation means for calculating a tan component from the extracted sine wave component signal and cosine wave component signal; and the extracted sine wave component signal. and a second calculation means for calculating a cot component from the cos wave component signal; and according to the calculation results of the first and second calculation means, the absolute value of either the tan component or the cot component is 1 or less. an optical fiber gyro, comprising: third calculation means for outputting a value in a range as loop direction rotation information of the optical fiber loop. 2. The third calculation means calculates the positive value of the sine wave component signal or the cosine wave component signal extracted by the detection means,
The optical fiber gyro according to claim 1, wherein the measurement range of the value to be output as the rotation information is specified by referring to a negative sign.