JP2510571B2 - Fiber optic gyro - Google Patents

Description

The present invention relates to an optical fiber gyro suitable for a position / orientation detection and route guidance system of a moving body.

[Conventional technology]

Conventionally, in a phase modulation type optical fiber gyro, an optical signal is photoelectrically converted and then directly processed through an AD converter.

[Problems to be solved by the invention] The conventional technology is compatible with a wide dynamic range by using a high-precision AD converter (14 to 16 bits) in one range. However, there are problems that the number of AD conversion bits is limited and the accuracy is remarkably deteriorated due to the quantization error of AD conversion for a small level input. An object of the present invention is to address such problems and ensure high accuracy over a wide range.

[Means for solving problems]

The above-mentioned object is a photoelectric conversion means for converting an optical signal of a phase modulation type optical fiber gyro into an electric signal, a fundamental wave detecting means for detecting a fundamental wave component of the electric signal, and a second harmonic component of the electric signal. In a fiber optic gyroscope equipped with a second harmonic detecting means for detecting and a fundamental wave amplifying means for amplifying the fundamental wave component, a fundamental wave level detecting means for detecting the magnitude of the fundamental wave component, and a detected Based on the magnitude of the fundamental wave component, an amplification gain computing means for computing the amplification gain of the fundamental wave amplifying means, the fundamental wave component amplified by the fundamental wave amplifying means, and the second harmonic component. A digital conversion means for inputting and digitally converting this, and a second harmonic component amplification means for amplifying the digitally converted second harmonic component with the amplification gain calculated by the amplification gain calculation means. Achieved by having.

[Action]

By varying the gain of the amplifier that amplifies the fundamental wave component, the quantization error due to A / D conversion can be reduced.

〔Example〕

FIG. 1 shows the principle of the phase modulation type optical fiber gyro system. FIG. 2 is an enlarged view of the input part of the electronic circuit system in the hardware configuration of FIG. In FIG. 3, the magnitude of the fundamental wave component (4) is detected, the level at which this is detected is determined at (5), and the magnification setting resistance of the programmable amplifier at (6) is adjusted according to that level. , AD conversion. The output of the gyro is expressed as follows.
E light traveling the full Ivor loop clockwise around _{cw = A · cos (ωt +} φ (t) + ψ cw) ... (1) counterclockwise _{E ccw = A · cos (ωt} + φ (t-τ) + ψ ccw) ... ( 2) Here, ω is the angular frequency of the light source φ (t) is the phase modulation signal by the phase modulator, and φ (t) = φ _m sinω _mt (3) Here, φ _m : degree of phase modulation ω _m : angular frequency.

(1), represented by signal output that is light detector after the light interference represented by (2) is the optical _{power, P = (E cw + E} ccw) 2 ... (4).

 This time is expanded and summarized as follows.

Where Ω is the angular velocity J _2n and J _{2n + 1} is the Bessel function, to be exact And if φ _m and ω _m τ are constant, J _2n and J _{2n + 1} are constants. Here, Ω is the angular velocity φ _m , the modulation factor of the phase modulator in FIG. 1, ω _m is the angular frequency of the phase modulator, τ is the time nL / c required for light to propagate through the fiber loop (c is the speed of light, L is the speed of light) Fiber length, n is a refractive index). A is a constant.

 From equation (5), Ω is obtained as follows.

Here, when the rotational angular velocity Ω is small, sin Ω is small, so F ₁ (that is, J ₁ sin Ω) becomes small and conversely F ₂ is cos Ω.
It is proportional to and becomes larger. As Ω increases, F ₂ decreases and Ω increases.

When F ₁ and F ₂ become small, the quantization error of AD conversion becomes relatively large and the error of equation (6) becomes large, so to avoid this, when F ₁ or F ₂ falls below a certain level, Quantization error can be reduced by increasing the gain of the amplifier and amplifying it several times, and performing AD conversion. At this time, if F ₁ is doubled and F ₂ is taken in without being amplified, it is necessary to double the value of F _{2 in} the processor after AD conversion and match the overall gain. is there.

Fig. 4 shows the relationship between range switching input and AD conversion output. When the range is one, the output ▲ ▼ is obtained with respect to the input ▲ ▼, and when the input is small, the output when the input is ▲ ▼ is shown as ▲ ▼. On the other hand, if the output is switched to ▲ ▼ when the input is ▲ ▼, or to ▲ ▼ for ▲ ▼, the output level for the input ▲ ▼ is ▲
It becomes a broken line like ▼ and ▲ in case of 1 range ▲
Since it is much higher than ▼, it can be expected that the relative error (= quantization error of AD conversion / input level × 100%) will be small.

The relative error curve is shown in FIG. Enter curve BGIL ▲
In the error curve for ▼, let X be the number of AD conversion bits,
Quantization error bit is a multiple of Y programmable gain M
Then, 2 ^X −1: Full scale (FUL) of AD conversion input = AD output bit: Input level of AD conversion (4) (4) Here, the PGA input is the input K of the programmable gain amplifier.

In Fig. 5, the input at point A is M = 1.0, PGA input = FUL, so the relative error Becomes

Also, if M is set so that C point and F point are also M · (PGA input) = (FUL), it is equal to the error at point B.

In the case of the input OA, since M = 1 in the equation (6), the error in the equation (6) increases in a hyperbolic manner when the PGA input becomes small.
Even when the range is switched to ▲ ▼, there is no change except that M has a certain value, and the same applies to ▲ ▼ input. The curves are CHK and FJ, respectively. From the above, when the range is switched to 3 steps, the error curve becomes BGCHFJ 1
It can be seen that it is much smaller than the range BGIL.

〔The invention's effect〕

According to the present invention, a relatively low bit (10-12 bits)
With the AD converter, a very wide dynamic range can be secured and a highly accurate gyro becomes possible.

[Brief description of drawings]

Figure 1 shows the principle of the phase modulation type optical fiber gyro.
2 is a hardware configuration diagram, FIG. 3 is an input circuit diagram, FIG. 4 is a diagram showing an input-output relationship of AD conversion by the range switching method, and FIG. 5 is a diagram showing a relative error due to range switching. . 1 ... Photodiode, 2 ... Fundamental wave detection circuit, 3 ... Second
Harmonic circuit, 4 ... Level detection circuit, 5 ... Level determination circuit,
6 ... Programmable amplifier, 7 ... Amplifier, 8 ... Multiplexer, 9 ... S4H, 10 ... A / D conversion, 11 ... Processing circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Matsumoto 4026 Kujimachi, Hitachi City Hitachi Ltd. Hitachi Research Laboratory (56) References JP-A 61-217718 (JP, A) JP-A 61 -155706 (JP, A)

Claims (1)

(57) [Claims] 1. A photoelectric conversion means for converting an optical signal of a phase modulation type optical fiber gyro into an electric signal, a fundamental wave detecting means for detecting a fundamental wave component of the electric signal, and a second harmonic component of the electric signal. In a fiber optic gyroscope equipped with a second harmonic detecting means for detecting the fundamental wave component and a fundamental wave amplifying means for amplifying the fundamental wave component, a fundamental wave level detecting means for detecting the magnitude of the fundamental wave component, Based on the magnitude of the fundamental wave component, an amplification gain computing means for computing the amplification gain of the fundamental wave amplifying means, the fundamental wave component and the second harmonic component amplified by the fundamental wave amplifying means. And a digital conversion means for digitally converting the same, and a second harmonic component amplifying means for amplifying the digitally converted second harmonic component with the amplification gain calculated by the amplification gain calculation means. Optical fiber gyro characterized by comprising and.