JPH04369422A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To obtain a correct rotary angular velocity output without being influenced by the fly-back time by providing a plurality of integrators in a serrodyne wave generating circuit and switching means for alternately operating and using the integrators. CONSTITUTION:Two integrators 12A, 12B as serrodyne wave generating circuits are provided in the latter stage of an integrator 11 in parallel to each other. The outputs of the integrators 12A, 12B are added via switches 20A, 20B by an adder 21, and output to a serrodyne modulator 16 and a reset circuit 14. The output from the adder 21 is compared with a reference value from a 2pi reference device 15 by a 2pi comparator 22 and a -2pi comparator 23. The two integrators 12A, 12B are alternately driven by the switches 20A, 20B, so that one integrator 12B or 12A is completely reset while the other integrator 12A or 12B is operating. Accordingly, it becomes possible to generate serrodyne waves without the fly-back time.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to moving bodies, such as aircraft,
This invention relates to the rotation angle of ships, automobiles, etc., and to an optical fiber gyro for measuring the rotation angle thereof.

0002

[Prior art] Miniaturization in detection of rotational angular velocity, etc.
In order to achieve high reliability, optical fiber gyros that utilize the Sagnac effect of light have been developed in recent years, and are being put into practical use. Among these optical fiber gyros, the one that determines the rotational speed from the phase difference between clockwise and counterclockwise propagating light propagating in a long optical fiber loop is called an interference type optical fiber gyro. , development of the serodyne method is underway.

In the phase modulation method, as shown in FIG. 7, laser light output from a light source 1 such as a semiconductor laser or a light emitting diode is split by a coupler 5, one of which is incident on a polarizer 4, and the polarizer The light from 4 is split into clockwise light and counterclockwise light by coupler 6, and these lights enter from both ends of optical fiber loop 3 formed by winding one optical fiber multiple times, and each light is After passing through the fiber loop 3, it is emitted from the other end as an output light, is combined again by the coupler 6, passes through the polarizer 4, and enters the photoreceiver 2, which converts light to current. is output as In this configuration, when an angular velocity Ω is applied to the optical fiber loop 3, the Zagnac effect occurs in the lights traveling in the optical fiber loop 3 in mutually opposite directions, and a phase difference proportional to the angular velocity Ω is generated between the emitted lights. This phase difference Δθ is

[
0004

[Math 1]

It is expressed as 0005. Here, R is the radius of the optical fiber loop 3, L is the length of the optical fiber loop 3, λ is the wavelength of light emitted from the light source 1, and C is the speed of light. Furthermore, in this phase modulation method, a phase modulator 8 is provided at one end of the optical fiber loop, and this phase modulator 8 is driven by a signal from a signal oscillator 9 to add phase modulation to the light traveling in opposite directions. It will be done. If the angular frequency of the signal applied to the phase modulator 8, that is, the signal from the signal generator 9, is ωp, then the output I of the current-voltage converter 7 is:

[0006]

[Math 2]

[0007] Here, x is the phase modulation degree, J0
, J1, J2, . . . are Bessel functions, K is a proportionality constant, and t is time. Among the angular frequency components of the output I, the component of the angular frequency ωp is synchronously detected by the synchronous detector 10 using the signal of the angular frequency ωp from the signal generator 9 as a reference, thereby producing an output 2KJ1 (x )si
nΔθ can be obtained.

The serodyne method has been developed with the aim of achieving a wider dynamic range than the phase modulation method. A specific configuration of this Serodyne method is shown in FIG. In addition to the phase modulation method shown in FIG. 7, a serrodyne modulator 16 is provided at one end of the optical fiber loop 3 to superimpose a sawtooth wave (serodyne wave) on light traveling in opposite directions. 7, an integrator 11 that detects the phase difference between the clockwise light and the counterclockwise light using the synchronous detector 10 and integrates it, and an integrator 12 that integrates the output of the integrator 11, and generates a 2π reference signal. do 2
It includes a π reference device 15, a reset circuit 14 that compares this reference signal with the output of the integrator 12 and generates a reset signal to make the output of the integrator 12 into a sawtooth wave, and a counter 13 that counts this serrodyne wave. ing. Therefore,
The integrator 12, reset circuit 14, and 2π reference device 15 operate as a serrodyne wave generation circuit. To briefly explain the operation of this serrodyne method, the serrodyne modulator 16 is
Since it is provided at one end of the optical fiber loop 3, the phases of the left and right lights change at different timings. At this time, the phase difference between the left and right lights on the receiver is θS
Then,

[0009]

[Math 3]

[0010] Here, TS is the period of the serrodyne wave, and τ is the time difference determined by the fiber length. At this time,
The output I of the current-voltage converter 7 is Δθ of the equation 2 (Δθ+θ
S), and the interference output of the synchronous detector 10 becomes 2KJ1(x)sin(Δθ+θS). This is integrated by integrators 11 and 12 and fed back to the serrodyne modulator 16 so that the phases of the emitted lights match, that is, sin(Δθ+θS)=
The period of the serrodyne wave is changed so that it becomes 0 (Δθ=-θS). Since θS is proportional to the serrodyne period, Δθ is also proportional to the serrodyne period, and by counting the frequency of this serrodyne wave with the counter 13, the rotational angular velocity Ω can be output. In other words, if the frequency of the serrodyne wave is fS = 1/TS.

[0011]

[Math 4]

[0012]

[0013]

[Problems to be Solved by the Invention] However, in such conventional optical fiber gyros, the reset time (referred to as flyback time) of the serrodyne wave from 2π limits the performance of the optical fiber gyro, and the scale factor error of the gyro There is a problem of increasing the That is, if there is a flyback time, Δθ+θS
Since =0 does not hold, there is a problem that the output from the synchronous detector 10 does not become 0 and an error occurs. In order to eliminate the flyback time, it is necessary to rapidly discharge the charge by reducing the time constant of the integrator 12 circuit that generates the serrodyne wave. However, the actual circuit configuration is extremely difficult. Therefore, there is a limit to how close the flyback time can be to zero. SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an optical fiber gyro that can obtain a correct rotational angular velocity output without being affected by flyback time.

[0014]

[Means for Solving the Problems] The optical fiber gyro according to the present invention includes a light source 1, an optical fiber loop 3, and a first propagating light and a second propagating light from the light source 1, as shown in FIGS. 1 and 8, for example. an optical splitter 6 for distributing the propagating light into the optical fiber loop 3 and propagating both in opposite directions to each other;
A serrodyne modulator 16 that causes a phase shift in the first propagating light and the second propagating light, and a serrodyne modulator 16 that causes a phase shift in the first propagating light and the second propagating light, and a device that connects the first propagating light and the second propagating light that have propagated through the optical fiber loop 3 to the same waveguide. a photodetector 2 for guiding and detecting the serrodyne wave, and a serrodyne for generating a serrodyne wave having a period corresponding to the phase difference between the first propagating light and the second propagating light and driving the serrodyne modulator 16. In an optical fiber gyro which has a wave generation circuit and calculates rotational angular velocity from this phase difference, a plurality of integrators 12A and 12B are provided in the serrodyne wave generation circuit, and these integrators 12A and 12B are operated alternately and alternately. Switching means 20A, 20B to be used, adder 21,
A reset circuit 14 and a 2π reference device 15 are provided.

[0015]

[Operation] Means 2 for switching multiple integrators 12A, 12B
0A and 20B are operated alternately, and one integrator 1
While 2A or 12B is operating, the other integrator 12B or 12
By completely resetting A, it is possible to generate a serrodyne wave with no flyback time.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical fiber gyro according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of the main parts of an optical fiber gyro according to the present invention. In FIG. 1, parts corresponding to those in FIGS. 7 and 8 are given the same reference numerals. In this embodiment, the serrodyne wave generation circuit shown in FIG. 8 is configured as shown in FIG. That is, two integrators 12A and 12B are provided in parallel after the integrator 11 as a serrodyne wave generation circuit. Furthermore, each integrator 12A,
The output of 12B passes through each switch 20A, 20B, and the adder 21 adds the two signals together, and outputs the resultant signal to the serrodyne modulator 16 and the reset circuit 14. In FIG. 1, 10a indicates an input terminal to which the output from the synchronous detector 10 is supplied.

The reset circuit 14 includes a 2π comparator 2
2, -2π comparator 23, exclusive OR (XOR) circuit 24, and flip-flop circuit 25. The output from the adder 21 is sent to the 2π comparator 22 and the -2π comparator 23 and then to the 2π reference unit 15.
compared with the reference value from The output from adder 21 is 2
When it reaches π, the output of the 2π comparator 22 becomes high level, and the output of the XOR circuit 24 becomes high level. Similarly, when the output from the adder 21 becomes -2π, the output from the -2π comparator 23 becomes high level, and the XOR circuit 2
The output of No. 4 becomes high level. flip-flop circuit 2
5 outputs a rectangular wave in which the signal from the XOR circuit 24 repeats rising and falling at the input timing to the Q terminal. At the same time, a rectangular wave with an inverted phase is output to the Q terminal.

Q terminal and Q of the flip-flop circuit 25
Outputs from the terminals become a reset signal A and a reset signal B, which reset the integrator 12A and the integrator 12B, respectively, and at the same time cause the switch 20A and the switch 20B to perform switching operations. The integrators 12A and 12B are in operation when the reset signal is at a high level, and are in a reset state when the reset signal is at a low level. Further, the switches 20A and 20B are connected to the integrator 12 when the reset signal is at a high level.
A and 12B are connected to the adder 21, and the ground is connected to the adder 21 when the signal from the flip-flop circuit 25 is at a low level. Since the integrator 12A and the integrator 12B and the switch 20A and the switch 20B are configured to be operated by the Q terminal of the flip-flop circuit 25 and the Q terminal from which an inverted signal is obtained, respectively,
The integrator 12A and the integrator 12B are alternately reset and alternately connected to the adder 21.

FIG. 2 shows a timing chart according to this embodiment. As shown in FIGS. 2(a) and 2(b), the output of the integrator 12A and the output of the integrator 12B are alternately operated and reset in response to the output of the XOR circuit 24 (see FIG. 2(f)). That is, the switches 20A and 20B and the integrators 12A and 12B are switched by reset signals A and B as shown in FIGS. 2(g) and 2(h) obtained at the Q terminal and Q terminal of the flip-flop circuit 25. This switch 2
Since 0A and switch 20B conduct signals to adder 21 when integrator 12A and integrator 12B are in the operating state (FIGS. 2(c) and 2d), the output of adder 21 is continuous. This results in a sawtooth waveform (Fig. 2(e)). Here, since there is an operating time ts of the switch, a flyback time occurs in the output of the adder 21, but this flyback time is about 10 ns, and the flyback caused by the time required for the discharging time of the conventional integrator. It is a much shorter time compared to In this example, the other components are configured as shown in FIG.

Since this example is constructed as described above, the two integrators 12A and 12B are connected to the switches 20A and 20B.
By operating the integrator 12A or 12B alternately and completely resetting the other integrator 12B or 12A while one integrator 12A or 12B is operating, a serrodyne wave with no flyback time can be generated. can be obtained.

Next, a second embodiment of this serrodyne wave generating circuit is shown in FIG. (This example in FIG. 3) In the example shown in FIG. Therefore, the voltage does not reach 0V instantly, but it takes a finite amount of time to reach 0V. Therefore, by superimposing the signals from the integrator 12A and the integrator 12B for the time ts, the adder 21
An offset occurs in the serrodyne wave output from the serrodyne wave. In order to improve this point, the example in FIG.
By delaying the operation start times of A and integrator 12B by a predetermined period of time, overlapping is avoided as much as possible.

Therefore, in this embodiment, an AND circuit 26 and a delay circuit 27 are newly inserted after the Q terminal of the flip-flop circuit 25, and an AND circuit 28 and a delay circuit 29 are newly inserted after the Q terminal. There is. A signal output from the Q terminal of the flip-flop circuit 25 is sent to a delay circuit 27 and an AND circuit 26. The signal input to the delay circuit 27 is input to the AND circuit 26 with a delay of a delay time td. Therefore, the reset signal A output from the AND circuit 26 becomes a rectangular wave whose rise is delayed with respect to the output of the XOR circuit 24 by the delay time td determined by the delay circuit, as shown in FIG. 4(g). Similarly, the signal output from the Q terminal of the flip-flop circuit 25 is also shown in FIG.
As shown in FIG. 2, the waveform becomes a rectangular wave whose rise is delayed with respect to the output of the XOR circuit 24 by the delay time td. Others are shown in Figure 1.
Configure in the same way as .

With such a configuration, this delay time td
Since the operation start time of the integrator 12A and the integrator 12B can be delayed by the amount of the integrator 12A and the integrator 12B, if this delay time td is set to a value approximately equal to the operating time ts of the switches 20A and 20B, the integrator 12A and the integrator 12B It is possible to eliminate the offset due to the overlap with (Fig. 4(e)
). 4(a) and (b) are the outputs of the integrators 12A and 12B, respectively, and FIG. 4(c) and (d) are the outputs of the switch 20A.
and 20B, and FIG. 4(f) is the output of the XOR circuit 24.

Next, a third embodiment of this serrodyne wave generating circuit is shown in FIG. To explain this example in Figure 5, Figure 1
, parts corresponding to those in FIG. 3 are given the same reference numerals, and their explanations will be omitted. In the example of FIG. 1, since the integrators 12A and 12B are amplifiers with small gains in the reset state, offsets occur in each integrator, as shown in FIGS. 2(a) and 2(b). This embodiment is an improvement on this point, and prevents the occurrence of offset by cutting off the input signal to the integrators when the integrators 12A and 12B are in the reset state. Therefore, in this embodiment, in addition to the example shown in FIG. 3, switches 30A and 30B are newly provided at the front stage of the integrators 12A and 12B. switch 30A,
30B performs a switching operation in response to reset signals A and B (FIG. 6(g) and (h)) sent from the reset circuit 14, and when the reset signal is at a high level, the integrator 11 and integrators 12A and 12B are switched. is connected, and when the reset signal is at a low level, the ground and the integrators 12A, 12B are connected to cut off the input to the integrators 12A, 12B.

With this configuration, the integrator 1
Integrator 12A when 2A and 12B are in the reset state
, 12B can always be set to 0, and integration can be started from 0 without offset when the operating state is reached. FIG. 6 shows a timing chart according to this embodiment. By eliminating each offset between the integrator 12A and the integrator 12B (see FIGS. 6(a) and 6(b), the switch 20
The outputs of A and 20B become as shown in FIGS. 6(c) and 6(d), and the offset can be eliminated from the output of the adder 21 (FIG. 6(e)). FIG. 6(f) shows the output of the XOR circuit 24, and FIGS. 6(g) and (h) show the reset signals A and B.

In each of the embodiments of the serrodyne wave generating circuit described above, each integrator 12A, 12B only needs to be reset from the start of reset to the start of the next operation. In other words, it only needs to be completed during the maximum usable frequency of the serrodyne wave, so the reset time required for the conventional serrodyne wave generation circuit is much slower (about 10-3 times). can get. Incidentally, in the above embodiment, an example was described in which two serrodyne wave generating circuits were provided, but it goes without saying that three or more serrodyne wave generating circuits may be provided in the same manner as described above. Furthermore, it goes without saying that the present invention is not limited to the above-described embodiments, and can take various other configurations without departing from the gist of the present invention.

[0027]

[Effects of the Invention] According to the present invention, a plurality of integrators are provided in the serrodyne wave generation circuit, and a switching means is provided for alternately operating and using these integrators, thereby reducing the flyback time. can be made small regardless of the reset time of the serrodyne wave generation circuit itself, resulting in a highly accurate optical fiber gyro, and has the excellent effect that the configuration of the serrodyne wave generation circuit can be simplified.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of essential parts of an optical fiber gyro according to the present invention.

FIG. 2 is a waveform diagram for explaining FIG. 1;

FIG. 3 is a configuration diagram showing another example of the essential parts of the optical fiber gyro of the present invention.

FIG. 4 is a waveform diagram for explaining FIG. 3;

FIG. 5 is a configuration diagram showing another example of the essential parts of the optical fiber gyro of the present invention.

FIG. 6 is a waveform diagram for explaining FIG. 5;

FIG. 7 is a configuration diagram showing an example of a phase modulation method of a conventional optical fiber gyro.

FIG. 8 is a configuration diagram showing an example of a conventional serrodyne type optical fiber gyro.

[Explanation of symbols]

1. Light source 2 Photo receiver 3 Optical fiber loop 4 Polarizer 5,6 Coupler 7 Current-voltage converter 8 Phase modulator 9 Signal generator 10 Synchronous detector 11, 12A, 12B Integrator 13 Counter 15 2π standard 16 Serodyne modulator 20A, 20B switch 21 Adder 22 2π comparator 23 −2π comparator 24 XOR circuit 25 Flip-flop circuit

Claims (1)

[Claims] 1. A light source, an optical fiber loop, and an optical splitter that distributes light from the light source into first propagation light and second propagation light and propagates both to the optical fiber loop in mutually opposite directions. a serrodyne modulator that causes a phase shift in the first propagating light and the second propagating light; and a Serrodyne modulator that causes the first propagating light and the second propagating light that have propagated in the optical fiber loop to be connected to the same waveguide. a photodetector for guiding and detecting the serrodyne wave, and a serrodyne wave generator for generating a serrodyne wave having a period corresponding to the phase difference between the first propagating light and the second propagating light and driving the serrodyne modulator. In the optical fiber gyro which has a circuit and calculates the rotational angular velocity from the phase difference,
An optical fiber gyro characterized in that a serrodyne wave generation circuit is provided with a plurality of integrators, and a switching means is provided for alternately operating and using these integrators alternately.