JP2005265681A - Closed loop system optical fiber gyro - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a closed loop system optical fiber gyro in which the scale factor linearity is stabilized. <P>SOLUTION: A closed loop system optical fiber gyro comprising a light source 2, an optical fiber coil 5, a coupler 3 which branches and binds light from the light source 2 in the clockwise and counterclockwise directions around the optical fiber coil 5, a phase modular 4 which is arranged between the optical fiber coil 5 and the coupler 3 and modulates the phase of light passing therethrough, a light receiver 6 which converts the interference light intensity from the coupler 3 into an electric signal, an amplifier which amplifies the signal from the light receiver, and an A/D converter 8 which A/D converts the signal amplified by the amplifier 15, the optical fiber gyro executing signal processing of the output from the A/D converter in a digital manner, wherein the electric signal outputted from the light receiver 6 is branched into two, a feedback signal and a signal for automatic control of maximum phase shift, and signals amplified at mutually different amplification degrees are used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a closed loop optical fiber gyro, and more particularly, to a closed loop optical fiber gyro in which scale factor linearity is stabilized in a closed loop optical fiber gyro that uses a ramp-like waveform as a feedback signal.

A conventional example will be described with reference to FIG.
The closed-loop optical fiber gyro (hereinafter abbreviated as FOG) illustrated in FIG. 6 uses a digital phase ramp method that can expect the highest performance in terms of scale factor stability and linear performance as a feedback method. (See Patent Document 1). This FOG is disposed between the optical fiber coil 5 and the coupler 3, and the optical fiber coil 5, the coupler 3 for branching and coupling the light from the light source 2 around the optical fiber coil 5, and the optical fiber coil 5. An optical integrated circuit 4 that modulates the phase of light passing through the optical receiver, a light receiver 6 that converts the intensity of interference light from the coupler 3 into an electric signal, an amplifier 15 that amplifies the signal from the light receiver 6, and an amplifier 15 that amplifies the signal. An A / D converter 8 for A / D converting the electrical signal, and a synchronous detector 9, an integrator 10, a maximum phase shift automatic control circuit 13, a ramp generator 11, a timing pulse generating circuit 16, A phase modulation circuit 17 is provided for digital signal processing. The phase modulation signal generated and output from the phase modulation circuit 17 is applied to one phase modulator 40 included in the optical integrated circuit 4 to apply phase modulation to the bi-directional light. The output of the lamp generator 11 is applied as a step-like feedback signal to the other phase modulator 40 included in the optical integrated circuit 4 after D / A conversion and amplification, and phase modulation is applied to the bi-directional light.

This FOG has a maximum phase shift automatic control circuit 13 that holds the maximum phase shift at the time of applying a ramp voltage in the digital phase ramp system at an ideal value 2nπ [rad], and also outputs a rectangular wave phase modulation signal. The phase difference caused by the applied angular velocity is accurately detected as a control error signal. Deviation from the ideal value 2nπ of the maximum phase shift at the time of flyback of the digital phase ramp leads to degradation of the FOG scale factor linearity, and acts so that the time integration of the output of the synchronous detector 9 becomes zero. Conventionally, the moment when flyback occurs is detected, and the output of the synchronous detector 9 at that time corresponds to a control error signal, so that the Vnπ level is controlled automatically. When the maximum phase deviation deviates greatly from the true value, the maximum phase deviation automatic control circuit 13 is saturated and does not function normally. Here, the output of the synchronous detector 9 refers to the signal obtained by photoelectrically converting the intensity change of the interference light corresponding to the Sagnac phase difference generated in the optical part of the FOG in the light receiver 6 and amplified by the amplifier 15. This is the output detected by the reference signal synchronized with the phase modulation signal after A / D conversion in the D converter 8.
Here, when the maximum phase shift is deviated from 2nπ during flyback, the phase difference can be detected as a change in the intensity of the interference light. However, after photoelectric conversion in the light receiver, this is amplified at a predetermined magnification. If the maximum phase deviation is large, the output of the amplifier is saturated, and the detection output after AD conversion is not accurate.

More specifically, with reference to FIG. 7, this closed-loop FOG is a digital phased ramp system that gives a step-like phase shift as a feedback signal, and the width of the step is an optical fiber coil. Is set to the light propagation time τ. In addition, a rectangular wave (± π / 2) having a half period τ is also applied to the phase modulation.
In the phase modulation of the rectangular wave, a rectangular wave having a pulse width τ is applied to a phase modulator disposed on one side of the optical fiber coil, and the interference light propagating through the optical fiber coil is as shown in FIG. When there is no phase difference between the two lights (region I in FIG. 7), there is no intensity difference in the interference light for each τ. However, when an angular velocity is applied and a phase difference occurs (region II), an intensity difference occurs in the interference light for each τ.
Deviation from the maximum phase shift from 2nπ [rad] leads to degradation of scale factor linearity. FIG. 8 shows the relationship between the feedback phase difference and the interference light intensity. In the section indicated by a, when the maximum phase deviation is exactly 2π, the level is not reset and the feedback phase difference is continuously guaranteed without any level difference in the interference light intensity before and after the reset. When the maximum phase shift is smaller than 2π, a difference appears in the interference light intensity before and after the reset as shown in the section b. Similarly, a case where the maximum phase shift is given larger than 2π is indicated by an interval c. Thus, if a difference appears in the interference light intensity, it is demodulated as an error signal.

Referring to FIG. 9, when the maximum phase shift at the time of flyback deviates from 2nπ [rad], the phase difference appears as the intensity of the interference light.
Referring to FIG. 10, the maximum phase shift automatic control circuit 13 detects a change in interference light intensity at the time of flyback (triggering the moment of flyback in the digital signal processing circuit section) and controls 2nπ. Is going. When this control is not performed, a scale factor linearity error of about 100 ppm occurs when the deviation from the maximum phase shift 2π is 2.5%.

Referring to FIG. 11, the interference waveform inputted from the coupler 3 to the light receiver 6 is photoelectrically converted here, amplified N times in the amplifier 15 and then digitally processed by the A / D converter 8. The Here, the gain (N times) of the amplifier 15 is determined by the phase difference corresponding to 1 LSB (Least Significant Bit) of the AD converter 8. When the intensity difference of the interference light exceeds the input range −FS to + FS of the AD converter 8, the deviation from the maximum phase shift from 2nπ (the intensity difference at the time of flyback) cannot be accurately detected.
Japanese Patent Laid-Open No. 11-295077

  According to the present invention, in order to eliminate the above inaccuracy, the output of the light receiver is divided into two, and separate amplifiers, AD converters, and synchronous detection circuits are prepared. The signal input to the first A / D converter is used for FOG control, while the signal input to the second A / D converter is used for maximum phase shift control. In the conventional means, when the deviation of the maximum phase deviation is large, the output of the amplifier is saturated. Therefore, the gain of the amplifier in the previous stage of the second A / D converter is the same as that in the previous stage of the first A / D converter. By making it smaller than the gain of the amplifier so as not to be saturated at the time of flyback, it becomes possible to accurately detect the phase shift.

Claim 1: A light source 2, an optical fiber coil 5, a coupler 3 for branching and coupling light from the light source 2 around both ends of the optical fiber coil 5, and disposed between the optical fiber coil 5 and the coupler 3. The phase modulator 4 that modulates the phase of the light passing through the optical receiver, the light receiver 6 that converts the interference light intensity from the coupler 3 into an electrical signal, the amplifier 15 that amplifies the signal from the light receiver 6, and the amplifier 15 In an A / D converter 8 that performs A / D conversion on the received signal and a closed loop optical fiber gyro that digitally processes the output of the A / D converter 8, the electrical signal output from the light receiver 6 is A closed-loop optical fiber gyroscope that uses two signals for feedback signals and maximum phase shift automatic control and that has been amplified with different amplification degrees was constructed.
According to a second aspect of the present invention, in the closed-loop optical fiber gyro described in the first aspect, the amplification factor is a closed-loop optical fiber gyro with a smaller maximum phase shift automatic control gain than the feedback signal gain. Configured.

  In the present invention, the gain of the amplifier in the first stage of the first A / D converter 80 and the second A / D converter 80 ′ is smaller than the gain of the first amplifier 150. By setting, by avoiding saturation of the output of the amplifier at the time of flyback, a phase cancellation error at the time of flyback can be accurately detected, and the maximum phase shift control is stabilized. Accordingly, it is possible to provide a closed-loop optical fiber gyro in which the scale factor linearity in the closed-loop optical fiber gyro that uses a ramp-like waveform as a feedback signal is stabilized.

The best mode for carrying out the invention will be described with reference to FIG. In FIG. 1, the same reference numerals are given to the members common to the members in FIG.
This FOG is disposed between the optical fiber coil 5 and the coupler 3, and the optical fiber coil 5, the coupler 3 for branching and coupling the light from the light source 2 around the optical fiber coil 5, and the optical fiber coil 5. And an optical integrated circuit 4 that modulates the phase of the light passing through the optical receiver 4 and a light receiver 6 that converts the intensity of interference light from the coupler 3 into an electrical signal. Then, the output of the light receiver 6 is branched into two, and a first amplifier 150, a first A / D converter 80, and a first synchronous detection circuit 90 are prepared separately, and a second amplifier 150 ' A second A / D converter 80 ′ and a second synchronous detection circuit 90 ′ were prepared. The first synchronous detection circuit 90 is connected to the first input terminal of the ramp generator 11 via the integrator 10, and the second synchronous detection circuit 90 ′ is connected via the maximum phase shift automatic control circuit 13. The signal is connected to the second input terminal of the lamp generator 11 and digitally processed. The signal input to the first A / D converter 80 is used for FOG control, while the signal input to the second A / D converter 80 ′ is used for maximum phase shift control. The first amplifier 150, the first A / D converter 80, the first synchronous detection circuit 90, and the integrator 10, a circuit for obtaining a signal used for FOG control, and the second amplifier 150 A circuit for obtaining a signal used for the maximum phase shift control comprising the ', the second A / D converter 80', the second synchronous detection circuit 90 'and the maximum phase shift automatic control circuit 13, A configuration in which the light-receiving device 6 is alternately switched and connected in a time-division manner via a switch (not shown) can be employed.

  The operation of the FOG described above will be briefly described with reference to FIG. 2. To avoid saturation at the time of flyback (when the maximum phase deviation deviates from 2nπ), the output of the light receiver 6 is changed as described above. Branch into two. Here, A / D conversion is performed by the first A / D converter 80 during non-flyback, and A / D conversion is performed by the second A / D converter 80 'during flyback. The gain of the amplifier is set to N times for the first amplifier 150 and M times for the second amplifier 150 '. Here, the gain of the amplifier is set to a level at which saturation does not occur, with gain N ≧ gain M. By setting the gain of the amplifier to N ≧ M, saturation at the time of flyback can be avoided, a deviation from 2nπ can be accurately detected, and the scale factor can be stabilized. The signal AD-converted by the second A / D converter 80 'is used for maximum phase shift automatic control in the subsequent signal processing circuit.

Referring to FIG. 3, this is a waveform inputted to the A / D converter when the maximum phase shift at the time of flyback deviates from 2nπ [rad], that is, after photoelectrically converting the interference light. The signal amplified by the amplifier is shown. At the moment of flyback, the lower end is saturated.
Referring to FIG. 4, this shows the output after synchronous detection of the signal of FIG. Due to saturation, the phase cancellation error is smaller than the true value (detection limit).
Referring to FIG. 5, the present invention adopts the following configuration as a method of avoiding saturation of a phase cancellation error.

(1) The non-flyback signal is input from the first A / D converter 80, and the flyback signal is input from the second A / D converter 80 ′.
(2) In order to avoid saturation at the time of flyback, the gain of the amplifier in the first stage of the first A / D converter 80 and the second A / D converter 80 ′ is set to the gain of the second amplifier 150 ′. The gain is set smaller than the gain of the first amplifier 150.
(3) When the deviation of the maximum phase shift is large, the output of the amplifier is saturated. Therefore, the gain of the second amplifier 150 ′ is set smaller than the gain of the first amplifier 150 according to (2), By avoiding the saturation of the output of the amplifier, the phase cancellation error at the time of flyback can be accurately detected, and the maximum phase shift control is stabilized.

The figure explaining an Example. The figure explaining operation | movement of an Example. The figure which shows the signal input into an A / D converter in case the largest phase shift at the time of flyback has shifted | deviated from 2n (pi). The figure which shows the output after the synchronous detection of the signal of FIG. The figure explaining the method of the saturation avoidance of a phase cancellation error. The figure explaining a prior art example. The figure explaining operation | movement of a prior art example. The figure explaining the relationship between feedback phase difference and interference light intensity. The figure which shows the intensity | strength of the interference light of a phase difference in case the largest phase shift at the time of flyback has shifted | deviated from 2n (pi). The figure explaining the maximum phase shift automatic control circuit. The figure which shows the waveform photoelectrically converted in an optical receiver, amplified, and processed by an A / D converter.

Explanation of symbols

2 light source 3 coupler 4 optical integrated circuit 40 phase modulator 5 optical fiber coil 6 light receiver 8 A / D converter 80 first A / D converter 80 ′ second A / D converter 9 synchronous detector 90 first 1 synchronous detection circuit 90 'second synchronous detection circuit 10 integrator 11 ramp generator 13 maximum phase shift automatic control circuit 15 amplifier 150 first amplifier 150' second amplifier 16 timing pulse generation circuit 17 phase modulation circuit

Claims (2)

A light source, an optical fiber coil, a coupler that branches and couples light from the light source around both ends of the optical fiber coil, and a phase modulator that is arranged between the optical fiber coil and the coupler and modulates the phase of the light passing therethrough A receiver that converts interference light intensity from the coupler into an electrical signal, an amplifier that amplifies the signal from the receiver, an A / D converter that A / D converts the signal amplified by the amplifier, and A / In a closed loop optical fiber gyro that digitally processes the output of the D converter,
A closed-loop optical fiber gyro using a signal obtained by branching an electrical signal output from a light receiver into a feedback signal and a maximum phase shift automatic control and amplifying with different amplification degrees. In the closed loop optical fiber gyro described in claim 1,
A closed-loop optical fiber gyro with a gain that is smaller than the gain for feedback control and the maximum phase shift automatic control gain.

Images