JPH10318760A - Optical interference angular speed meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an error from being generated in the input angular speed detection output when a ramp signal is mixed with the input to a synchronous detector and the input angular speed has has a specified magnitude, i.e., the ramp frequency fr=1/4nτ(τ is the light propagation time of an optical fiber coil). SOLUTION: Output Sd from a synchronous detector 9 is selected by an electronic switch (generally, a signal processing means) 21 during the interval of a ramp signal except the trailing edge reset time thereof and a specific signal, e.g. the output from the synchronous detector 9 at zero level or at the time of 2τ before, is delivered to an integrator 10 during the reset interval. Consequently, average value of unnecessary signals outputted from the synchronous detector 9 can be reduced extremely when a ramp signal Sr is mixed with an input to the synchronous detector 9. According to the arrangement, detection error of input angular speed can be reduced when the ramp frequency fr=1/4nτ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference gyro (also referred to as an optical fiber gyro, hereinafter referred to as an FOG), and more particularly to a signal processing technique of a closed loop type FOG having a good linearity of a scale factor.

[0002]

2. Description of the Related Art The structure of a closed loop type FOG is shown in FIG. In FIG. 5, light emitted from a light source 2 is split into two by an optical coupler 3, one of which is introduced into an optical IC 4. The optical IC 4 has a function of dividing light into two, a function of passing only a single polarized light, and a function of modulating light. Light I
Only a single polarization component is selected for the light input to C4,
The light is further divided into two, and the two divided lights are introduced into the optical fiber coil 5 as clockwise light and counterclockwise light, respectively.

The clockwise light and the counterclockwise light that have propagated through the optical fiber coil 5 encounter and interfere with each other at the optical IC 4. The interfering light includes information on the phase difference between the clockwise light and the counterclockwise light generated by the Sagnac effect, and the input angular velocity can be known by detecting the phase difference. Optical IC4
The light that has interfered in is introduced again into the optical coupler 3 and split into two,
One is introduced into the photodetector 6. In the photodetector 6, the optical signal is converted into an electric signal (including information on the input angular velocity). The optical unit 100 of the FOG is configured as described above.
The electric signal output from the photodetector 6 is input to the signal processing unit 200.

[0004] The signal processing unit 200 detects an input angular velocity (a phase difference between left and right circling lights) and a feedback signal (lamp signal) for canceling the phase difference between the left and right circulating lights caused by the input angular velocity. Is generated. The ramp signal Sr is a sawtooth wave, and the ramp signal Sr
Is added to the optical phase modulator 4b provided in the optical IC 4 so as to cancel the phase difference between the left and right surrounding lights caused by the input angular velocity (the phase difference caused by the input angular velocity and the phase difference caused by the input angular velocity). (A phase difference having opposite signs) can be generated between the left and right surrounding lights. In the signal processing unit 200, in order to detect the input angular velocity with high sensitivity, the phase modulator 4c in the optical IC 4 applies phase modulation to the left and right surrounding light propagating through the FOG optical fiber coil 5. . The signal processing unit 2 is provided in the phase modulator 4c.
A phase modulation signal is supplied from the phase modulation signal generator 7 of FIG.

[0005] The electric signal output from the photodetector 6 of the optical unit 100 is input to the synchronous detector 9 via the AD converter 8, where the same frequency component as the phase modulation frequency fe is detected. The detected phase modulation frequency component, that is, the synchronous detector output Sd contains information on the input angular velocity and is used as an error signal of the closed loop FOG. The synchronous detector output Sd is input to the integrator 10 and integrated. Then, based on the output of the integrator, a feedback signal for canceling the phase difference between the left and right surrounding lights generated by the angular velocity input, that is, a ramp (ram)
p) The ramp generator 11 generates the signal Sr. The lamp signal Sr generated by the lamp generator 11 is supplied to the optical IC
4 is applied to an optical phase modulator 4b provided therein. DA
The output of the converter 12 is a stepped waveform obtained by quantizing the sawtooth wave (see FIG. 7A).

[0006] The entire loop of the FOG including the signal processing section 200 works so that the output Sd of the synchronous detector 9 becomes zero. Note that the frequency fr of the ramp signal Sr generated by the ramp generator 11 is a component proportional to the angular velocity input to the FOG, and this is determined as the FOG output signal. The ramp signal Sr indicates that the direction of the input angular velocity is CW or CC.
It has a positive or negative polarity depending on W. Accordingly, the ramp generator 11 outputs a CW pulse or a CCW pulse having a frequency corresponding to the ramp signal frequency fr to the output terminals OUT1 and OUT2.

The ramp peak value control unit 13 in the signal processing unit 200 is for controlling the peak value of the ramp signal Sr output from the ramp generator 11, and here the peak value of the ramp signal Sr is controlled. The maximum phase shift of the resulting light is + 2mπ (m is an integer) (radian) or -2.
It has a function of controlling to be mπ (radian). The phase modulation signal generator 7 is for generating a phase modulation signal Sp necessary for detecting the input angular velocity with high sensitivity. Usually, this phase modulation signal Sp is
4 is set so as to apply a phase shift which alternately changes between + π / 2 (radian) and -π / 2 (radian) between the left and right light beams of the FOG via the optical phase modulator provided in the optical modulator 4.

Finally, the operation of the synchronous detector 9 in the signal processing section 200 will be described. FIG. 6 shows the configuration (block diagram) of the synchronous detector. In the synchronous detector 9, the input signal Sa is a signal S that alternates between +1 and -1.
The output obtained by multiplying by p 'is added by the adder 9c to the current value and the value before the time [tau] passed through the delay unit 9b by the adder 9c. Synchronous detection of the fetched signal Sa is achieved.

The phase modulation signal Sp has a duty ratio of 5
The frequency fe is a 0% rectangular wave, and the frequency fe is set to fe = １ ／ τ (1). τ is the time required for light to propagate through the optical fiber coil 5. From the equation (1), the phase modulation signal Sp
Is equal to 2τ.

[0010]

In the conventional closed-loop type FOG signal processing technique, the synchronous detector output Sd
When the ramp signal Sr is mixed in the synchronous detector input Sa, a signal near the specific angular velocity input, that is, when the ramp signal Sr is near the specific frequency given by the following equation (2), , An output error of the FOG occurs. This disadvantage is measured as a degradation in scale factor linearity during FOG performance. That is, when the input angular velocity is set to Ω = Kfr, the proportionality constant K deviates from a certain value near a specific frequency.

An object of the present invention is to provide a closed-loop type FOG in which the conventional disadvantages are eliminated and the above-mentioned scale factor linearity is improved. The cause of the incorporation of the ramp signal Sr in the synchronous detector input Sa is the coupling of the ramp signal Sr to the photodetector 6 and the signal transmission cable at the preceding stage of the synchronous detector 9. Further, the light intensity modulation by the ramp signal Sr in the optical phase modulator 4b provided on the optical IC 4 can also cause the lamp signal to be mixed.

The mechanism by which the FOG output error (deterioration of the scale factor linearity) in the prior art will be described below. Ramp signal frequency fr = 1 / T
(T is a cycle) fr = (1 / 2n) fe = (1 / 2n) (1 / 2τ) = 1 / 4nτ (2) fe: natural frequency of FOG, phase modulation signal frequency n: natural number ( n = 1, 2, 3,...): FIG. 7 shows waveforms at various parts of the synchronous detector when the stepped ramp signal Sr which satisfies the following equation is satisfied.

As shown in FIG. 7, when the ramp signal Sr satisfying the condition of the equation (2) is mixed into the synchronous detector 9, a signal appears at its output. This signal does not become zero even after long-time averaging, and shows a certain average value a. If the unnecessary signal output from the synchronous detector has an average value, a bias offset error Δf (or ΔΩ) occurs in the FOG output as shown in FIG. This bias offset error increases according to the average value a. Further, since a ramp signal Sr that satisfies the equation (2) is generated only when it is input to the synchronous detector 9, a bias offset error depending on the input angular velocity occurs. Therefore, this error is
When the OG is in a stationary state, the error is not detected at all, and is detected only when a specific angular velocity is input.
Despite the original bias error, it is apparently observed as a deterioration in the scale factor linearity of the FOG.

[0014]

According to the present invention, the integrator input signal is set to "zero" or "the synchronous detector output value before time 2τ" during the return period of the trailing edge of the ramp signal Sr which is the feedback signal of the FOG. In the period excluding the return period, a signal processing means for using the output of the synchronous detector itself as an integrator input signal is provided.

According to the present invention having such a configuration, a bias offset error depending on an input angular velocity caused by mixing of a ramp signal can be reduced or eliminated, and the scale factor linearity of the FOG is improved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a closed loop FO according to the present invention.
G is a first embodiment of the present invention. In this embodiment, the synchronous detector output Sd of the closed loop FOG is input to the electronic switch 21. The electronic switch 21 operates during the return period of the trailing edge of the ramp signal Sr.
It is operated by the flyback signal Sfb output from. The flyback signal Sfb is a signal that is at the H (high) level during the return period of the trailing edge of the sawtooth-shaped ramp signal (FIG. 2).
E) Yes. FIG. 2 shows a signal waveform of each part of the synchronous detector 9 of FIG.

In this embodiment, the electronic switch 21
When the flyback signal Sfb is at the L (low) level, the synchronous detector output Sd is input to the integrator 10, and when the flyback signal Sfb is at the H level, the zero level output from the zero signal generator 22 is integrated. Input to the container 10. By doing so, the ramp signal S
By mixing r into the synchronous detector 9, an average value of an unnecessary signal (a signal causing an FOG output error) appearing in the integrator input signal can be reduced.

That is, in FIG. 2, the output of the synchronous detector Sd (FIG. 2D) is input to the integrator 10 in the conventional embodiment, whereas the electronic switch output signal Se of FIG. Since the average value of the unnecessary signal is input to the integrator 10, the average value of the unnecessary signal is reduced from the average value a in FIG. As a result, it is possible to suppress the occurrence of a bias error due to the incorporation of a ramp signal, to perform highly accurate measurement for all input angular velocities, and to improve the scale factor linearity.

FIG. 3 shows a second embodiment according to the present invention. Also in this embodiment, the synchronous detector 9 and the integrator 10
And an electronic switch 21 provided between the electronic switch 2 and the flyback signal Sfb of the lamp generator 11.
1 is operating. FIG. 4 shows a signal waveform of each part of the synchronous detector 9 of FIG. In this embodiment, when the flyback signal Sfb is at the L level by the electronic switch 21, the synchronous detector output Sd is input to the integrator 10, and when the flyback signal Sfb is at the H level, the delay circuit 23 shown in FIG. , The synchronous detector output S before time 2τ
d is input to the integrator 10. Therefore, the output Se of the electronic switch has a waveform shown in FIG. 4F. By doing so, the average value of unnecessary signals appearing in the integrator input signal can be set to “zero” by mixing the ramp signal Sr into the synchronous detector 9. That is, in FIG. 4, in the present embodiment, the electronic switch output Se of FIG. F is input to the integrator 10, so that the average value of the unnecessary signal becomes zero.

[0020]

As described above, according to the present invention, the electronic switch 21 is inserted between the synchronous detector 9 and the integrator 10 of the closed loop type FOG, and the flyback signal Sfb
(H level when the ramp signal is in the recovery period)
Performs the signal processing of inputting the synchronous detector output Sd at zero or 2τ before to the integrator 10 during the period of the H level, so that the input angular velocity caused by the ramp signal Sr mixed into the input of the synchronous detector 9 is obtained. Is reduced or eliminated, and an effect of improving the scale factor linearity can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of a main part when a ramp signal is mixed into the input of the synchronous detector of FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a waveform diagram of a main part when a ramp signal is mixed in the input of the synchronous detector 9 of FIG. 3;

FIG. 5 is a block diagram of a conventional closed-loop optical interference gyro (FOG).

FIG. 6 is a block diagram of the synchronous detector 9 of FIG. 5;

7 is a waveform diagram of a main part when a ramp signal is mixed in the input of the synchronous detector 9 of FIG.

FIG. 8 is a graph showing a relationship between a bias offset error generated when a ramp signal is mixed into an input of the synchronous detector 9 and a ramp frequency fr in FIG. 5;

Claims (3)

[Claims] A light from a light source is incident on an optical coupler, an output light of the optical coupler is incident on a Y branch circuit, and one output light of the Y branch circuit is incident on a first phase modulator. Phase-modulated by a ramp signal having a frequency corresponding to the magnitude of the input angular velocity, the output light of the first phase modulator is incident on one end of the optical fiber coil, and the other branch output light of the Y branch circuit is the Incident on the two-phase modulator,
Modulated by the phase modulation signal, the output light of the second phase modulator is incident on the other end of the optical fiber coil, and the interference light between the left-handed light and the right-handed light of the optical fiber coil is branched by the optical coupler. Then, the light is incident on the photodetector and photoelectrically converted. The output of the photodetector is input to the synchronous detector, synchronously detected using the phase modulation signal as a synchronous signal, and the output of the synchronous detector is integrated by the integrator. The output of the integrator is input to a ramp generator, and the ramp signal is generated so as to cancel the phase difference between the left and right circling lights caused by the input angular velocity, and the ramp signal is subjected to the first phase modulation. A signal corresponding to the frequency of the lamp signal is output as a detection signal of the input angular velocity, and the signal is output as a detection signal of the input angular velocity. An optical interference gyro, wherein signal output means for selecting an output of the synchronous detector in between and selecting a specific signal during the return period and supplying the selected signal to the integrator is provided. 2. The optical interference gyro according to claim 1, wherein the specific signal is a signal having a magnitude of zero. 3. The method according to claim 1, wherein the specific signal is an output of the synchronous detector before a time 2τ (2τ is a period of the phase modulation signal, and τ is a light propagation time of the optical fiber coil). Characteristic optical interference gyro.