JP4996559B2 - Ring laser gyro optical path length control circuit and ring laser gyro - Google Patents

Description

  The present invention relates to a ring laser gyro, and more particularly to an optical path length control circuit for controlling an optical path length in a glass block.

  A ring laser gyro oscillates a pair of laser beams propagating in opposite directions (clockwise and counterclockwise) in a ring-shaped optical path formed in a glass block (laser oscillation tube). An oscillation frequency difference is generated between the laser beams, and the input angular velocity is detected from interference fringes formed by superimposing these two laser beams.

  In the ring laser gyro configured as described above, when the glass block expands or contracts due to a temperature change, the optical path length changes, and a rotation error (scale factor error) occurs in the ring laser gyro output, so the laser light amount is kept at the maximum light amount. Thus, optical path length control is performed to keep the optical path length constant. FIG. 4 shows a conventional configuration example of an optical path length control circuit together with a glass block.

  Although the glass block 11 is schematically shown in FIG. 4, an optical path that forms a triangle is formed inside, and mirrors 12 to 14 are arranged at the apexes of the triangle. In the figure, 15 indicates a mirror transducer that displaces the mirror 14 to control the optical path length, and 16 indicates laser light propagating in two directions (clockwise and counterclockwise).

  The mirror transducer 15 is driven by the carrier (carrier wave) generated by the carrier generation circuit 21, whereby the mirror (movable mirror) 14 vibrates and the optical path length changes, and the light quantity of the laser beam 16 changes. The amount of laser light is detected by the photodiode 22, and the amplifier 23 converts the output current of the photodiode 22 into a voltage and amplifies it. The amplified detection output of the laser light quantity is input to the multiplier 24 and multiplied by the carrier, that is, synchronous detection is performed using the carrier. The output of the multiplier 24 is integrated by an integrator 25, and the output of the integrator 25 is added to a carrier for driving the mirror transducer 15 by an adder 26. With such a circuit configuration, the mirror transducer 15 is added. Is controlled to a position that maximizes the amount of laser light.

  FIGS. 5 and 6 show the principle of such optical path length control. FIG. 5 shows the relationship between the displacement amount of the mirror transducer 15 and the laser light amount, and the change in the laser light amount due to carrier application. This shows four points d. FIG. 6 shows the output after synchronous detection (output of the multiplier 24) and the output after smoothing (output of the integrator 25) when positioned at points a to d. When the optical path length fluctuates and the laser light quantity decreases to a position such as point a or point c, the photodiode 22 detects the decrease in the laser light quantity, and the output voltage of the integrator 25 causes the mirror transducer 15 to move to the position b. Voltage.

  When the laser light quantity is maximum at the point b, the light quantity change of the laser light quantity detected by the photodiode 22 is twice the frequency of the carrier, and becomes 0 when synchronous detection is performed. It is to do. In FIG. 5, the change in the amplitude of the laser light quantity at points b and d is exaggerated.

  Incidentally, the laser oscillation tube formed on the glass block 11 has a higher-order laser oscillation mode. Therefore, when the light amount of laser oscillation is minimized, high-order mode laser oscillation may occur as shown in FIG. Even if the higher order mode occurs, the optical path length control is not normally performed at the position where the higher order mode is generated. However, for example, when the power is turned on or the mirror position is reset (the mirror position is returned to the initial state). In other words, a situation may occur in which the high-order mode peak is controlled by noise that causes the mirror transducer 15 to be displaced. If it is controlled at the peak part of the higher mode, the ring laser gyro does not operate normally, which is a big problem.

  On the other hand, it is originally desirable that the laser light has a maximum light amount and a constant state, and it is desirable that there be no carrier that drives the mirror transducer and vibrates the mirror for optical path length control. For this reason, it is preferable to reduce the carrier amplitude as much as possible. However, if the carrier amplitude is reduced, the signal-to-noise ratio becomes smaller. The smaller the carrier amplitude, the higher the mode is controlled by the noise. This is likely to occur.

In order to cope with such a problem, Patent Document 1 describes that the carrier amplitude is increased at power-on and reset, and then the carrier amplitude is gradually decreased to be constant at a certain size. ing.
Japanese Patent No. 2626897

  According to the method described in Patent Document 1, when the power is turned on and at the time of reset, the amplitude of the carrier exceeds the region of the higher mode and the mirror is vibrated greatly. Control can be avoided.

  However, in the method described in Patent Document 1, the carrier amplitude decreases with time. Therefore, when the carrier amplitude is reduced and a transition is made from the peak of the fundamental mode to the peak of the higher mode due to noise, the carrier amplitude remains small in this case, so it is not possible to return to the peak of the basic mode. Instead, it will be controlled by a higher mode mountain.

  In view of such problems, an object of the present invention is to provide an optical path length control circuit capable of always appropriately controlling an optical path length so as not to be controlled by a high-order mode mountain. .

  According to the first aspect of the present invention, an optical path length control circuit of a ring laser gyro in which a pair of laser beams propagates in opposite directions through an optical path in a glass block is detected by a carrier generating circuit that generates carriers and a photodiode. A first multiplier that multiplies the detection output of the laser light quantity and the carrier, a first integrator that integrates the output of the first multiplier, a control means that outputs a control output, a carrier and a control output And a first adder for adding the output of the second multiplier and the output of the first integrator. The control means includes a first reference voltage generation circuit that generates the first reference voltage, a subtracter that subtracts the first reference voltage from the laser light amount detection output, and an inverting type that integrates the output of the subtractor. A second integrator, a second reference voltage generating circuit for generating a second reference voltage, and a second reference voltage added to the second integrator to obtain the control output. An adder is used, and a mirror transducer that controls the optical path length is driven by the output of the first adder.

  According to the invention of claim 2, an optical path length control circuit of a ring laser gyro in which a pair of laser beams propagate in opposite directions through an optical path in a glass block includes an oscillator that outputs a signal having a frequency twice that of a carrier, A frequency divider that divides the output of the oscillator to generate a carrier, a first multiplier that multiplies the detection output of the laser light amount detected by the photodiode and the carrier, and an output of the first multiplier A first integrator for integrating; a control means for outputting a control output; a second multiplier for multiplying the carrier and the control output; an output of the second multiplier and an output of the first integrator; And a first adder for adding. The control means includes a third multiplier that multiplies the detection output of the laser light amount and the output of the oscillator, a first reference voltage generation circuit that generates a first reference voltage, and an output from the third multiplier. A subtractor that subtracts one reference voltage; an inverting second integrator that integrates an output of the subtractor; a second reference voltage generation circuit that generates a second reference voltage; and a second integration And a second adder that adds the output of the detector and the second reference voltage to obtain the control output, and drives the mirror transducer that controls the optical path length by the output of the first adder. .

  According to a third aspect of the present invention, a ring laser gyro is provided with the optical path length control circuit according to the first or second aspect.

  According to the present invention, the carrier amplitude is always controlled, and the carrier amplitude can be increased when the laser light amount is small, and the carrier amplitude can be decreased when the laser light amount is large. Therefore, it is possible to eliminate the problem of being controlled at the peak portion, and to always appropriately control the optical path length.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of a first embodiment of an optical path length control circuit according to the present invention. Parts corresponding to those in FIG. 4 are denoted by the same reference numerals.

  In this example, the optical path length control circuit is obtained by adding a control means 30 and a multiplier 41 to the conventional configuration shown in FIG. 4, and the control means 30 generates a first reference voltage. The generating circuit 31 includes a reference voltage generating circuit 32 that generates a second reference voltage, a subtractor 33, an integrator 34, and an adder 35.

  The amount of laser light is detected by the photodiode 22, and the current is converted into a voltage by the amplifier 23 and amplified. The detection output (detection voltage) of the laser light amount amplified by the amplifier 23 is a signal in which the carrier signal component is superimposed on the DC voltage, but the amplitude of the carrier signal component is very small compared to the DC voltage. Further, the control means 30 does not use the carrier signal component for control. Therefore, the output of the amplifier 23 input to the control means 30 will be described as a DC voltage.

  The output of the amplifier 23 (the detection output of the amplified laser light amount) is input to the subtracter 33 of the control means 30. The first reference voltage is input from the reference voltage generation circuit 31 to the subtractor 33, and the subtracter 33 subtracts the first reference voltage from the output of the amplifier 23, and the difference obtained by the subtraction is input to the integrator 34. input. The integrator 34 integrates the inputted difference. The adder 35 receives the output of the integrator 34 and the second reference voltage generated by the reference voltage generation circuit 32, and the adder 35 adds them. The output of the adder 35 is a control output, and the control means 30 outputs this control output to the multiplier 41.

  The multiplier 41 multiplies the input control output by the carrier generated by the carrier generation circuit 21 (hereinafter referred to as carrier (1)), and the multiplier 41 obtained by multiplying the carrier (1) by the control output. (Hereinafter referred to as carrier (2)) is input to the adder 26.

  In the above, the first reference voltage generated by the reference voltage generation circuit 31 is a voltage smaller than the output of the amplifier 23 when the laser light quantity is the maximum value (point b in FIG. 5), for example, when the laser light quantity is the maximum value. The voltage is half of the output of the amplifier 23. For example, if the output of the amplifier 23 is +1 V when the laser light amount is the maximum value, the first reference voltage is +0.5 V, which is half of that.

  The input voltage of the integrator 34 becomes positive when the output of the amplifier 23 is larger than the first reference voltage, in other words, when the laser light amount detected by the photodiode 22 is larger than the reference value, and becomes negative when the output is small. The integrator 34 is an inverting integrator, and the polarity of the output of the integrator 34 is inverted. When the input is positive, the output is negative. For example, when an integrator having a saturation voltage of ± 5V is used as the integrator 34, the negative output when the input is positive is at least -5V.

  The second reference voltage generated by the reference voltage generation circuit 32 is set to a voltage (for example, +10 V) larger than the output of the integrator 34 and is added to the output of the integrator 34 by the adder 35.

  Assuming that the second reference voltage is + 10V, when the output of the amplifier 23 (laser light amount detection output) is larger than the first reference voltage, the sum of the output of the integrator 34 and the second reference voltage is, for example, + 5V. The multiplier 41 outputs the carrier (2) with an amplitude of 5V. On the other hand, when the output of the amplifier 23 is smaller than the first reference voltage, the output of the integrator 34 is positive (for example, maximum + 5V), and the sum of the output of the integrator 34 and the second reference voltage is The value becomes larger than the second reference voltage (for example, + 15V), and the multiplier 41 outputs the carrier (2) with an amplitude of 15V.

  On the other hand, the output of the amplifier 23 is input to the multiplier 24, multiplied by the carrier (1), and synchronously detected. Thus, when the laser light quantity is the maximum value (point b in FIG. 5), the output of the integrator 25 is 0, and at this time, the output of the multiplier 41 becomes the carrier (2) with the minimum amplitude, and the adder 26 performs integration. The mirror transducer 15 is driven by being added to the output of the detector 25.

  That is, in this example, the amplitude of the carrier (2) for driving and controlling the mirror transducer 15 by adding to the output of the integrator 25 is always controlled, and a laser light quantity larger than a predetermined laser light quantity is obtained. The output of the integrator 25 is added to the carrier (2) having the minimum amplitude, and the mirror transducer 15 is driven and controlled so that the amount of laser light becomes the maximum (basic mode peak).

  When the laser light amount is smaller than the predetermined laser light amount, there is a possibility of being in the vicinity of the high-order mode mountain, so that the amplitude of the carrier (2) is increased so that it does not stay at the high-order mode mountain. 15 is displaced greatly.

  Therefore, even if the signal-to-noise ratio decreases due to a decrease in the amount of laser light or an increase in the noise voltage, the control is not performed in a higher-order mode peak due to the influence of noise.

Next, a second embodiment of the optical path length control circuit according to the present invention shown in FIG. 2 will be described.
In this example, the configuration of the control means is different from that of the first embodiment, and instead of the carrier generation circuit 21 of FIG. 1, an oscillator 61 that outputs a signal having a frequency twice that of the carrier (1), and the output of the oscillator 61 And a frequency divider 62 that generates a carrier (1) by dividing the frequency into 1/2, and the frequency divider 62 outputs the carrier (1). In this example, the control means 50 includes a reference voltage generation circuit 51 that generates a first reference voltage, a reference voltage generation circuit 52 that generates a second reference voltage, a multiplier 53, a subtractor 54, an integrator 55, and an adder 56. And is composed of. Note that the output of the oscillator 61 is hereinafter referred to as 2f carrier.

  The output of the amplifier 23 is input to the multiplier 53 of the control means 50. The multiplier 53 receives the 2f carrier from the oscillator 61, and the multiplier 53 multiplies the output of the amplifier 23 and the 2f carrier. FIG. 3 shows the output waveform of the multiplier 53 when the amount of laser light is the respective points a to d in FIG. 5 and the average value thereof. As shown in FIG. In the portion (point b), the average value of the output of the multiplier 53 is a positive voltage. The first reference voltage generated by the reference voltage generation circuit 51 is set to a value slightly smaller than the average value of the outputs of the multiplier 53 when the laser light quantity is b point (maximum value).

  The output of the multiplier 53 and the first reference voltage are input to the subtractor 54, and the subtractor 54 subtracts the first reference voltage from the output of the multiplier 53. The output of the subtractor 54 is input to the integrator 55 and integrated. The integrator 55 is an inverting integrator, and when the average value of the output of the subtractor 54 is positive, the output is negative.

  As in the first embodiment, the second reference voltage generated by the reference voltage generation circuit 52 is set to a voltage higher than the maximum output voltage (saturation voltage) of the integrator 55 and is added to the output of the integrator 55 by the adder 56. Is done. The output of the adder 56 is a control output, and the control means 50 outputs this control output to the multiplier 41.

  The multiplier 41 multiplies the input control output by the carrier (1) generated by the frequency divider 62. The output of the multiplier 41 becomes the carrier (2) in which the amplitude of the carrier (1) is controlled, and is input to the adder 26. Similarly to the first embodiment, the adder 26 adds the output of the integrator 25 and the carrier (2), and drives the mirror transducer 15 by the output of the adder 26.

  In this example, the value (average value) after the multiplication of the output of the amplifier 23 and the 2f carrier becomes maximum when the laser light amount is maximum, and when the laser light amount is maximum, the amplitude of the carrier (2) is minimum. It is controlled to become.

  On the other hand, when the laser light quantity decreases beyond the maximum value of the laser light quantity (basic mode peak), the value of the first reference voltage becomes larger than the average value of the output of the multiplier 53, and the negative input is reduced. Since the signal is input to the integrator 55, the polarity is inverted by the integrator 55 and the output becomes positive, thereby increasing the amplitude of the carrier (2). Therefore, the mirror transducer 15 can be displaced greatly, and the situation where it is controlled at the peak portion of the higher-order mode can be avoided.

  The first and second embodiments of the present invention have been described above. Since the first embodiment shown in FIG. 1 looks at the absolute value of the laser light amount, the configuration is simple, but the laser light amount is Since changes due to temperature and changes with time occur, this change becomes a problem. For example, when the first reference voltage or the carrier size is set, there is a problem that the degree of freedom in design is reduced.

  On the other hand, although the configuration of the second embodiment is more complicated than that of the first embodiment, it does not look at the absolute value of the laser light amount, but looks at the light amount change according to the magnitude of the carrier signal component. The laser light quantity that appears as fluctuations in the DC voltage is not affected by changes in temperature or aging. In this respect, the degree of freedom in designing the first reference voltage and the carrier size is increased, and it becomes easy to realize desired performance.

The block diagram which shows the structure of the 1st Example of the optical path length control circuit by this invention. The block diagram which shows the structure of the 2nd Example of the optical path length control circuit by this invention. The figure which shows the output waveform of the multiplier of the control means in FIG. 2, and its average value. The block diagram which shows the example of a conventional structure of an optical path length control circuit. The figure for demonstrating the principle of optical path length control. The figure which shows the output after the synchronous detection in FIG. 4, and the output after smoothing. The figure which shows the state in which the peak of the high-order mode has generate | occur | produced in the laser light quantity.

Claims (3)

An optical path length control circuit of a ring laser gyro in which a pair of laser beams propagate in opposite directions through the optical path in the glass block,
A carrier generation circuit for generating carriers;
A first multiplier that multiplies the detection output of the laser light amount detected by the photodiode and the carrier;
A first integrator for integrating the output of the first multiplier;
Control means for outputting a control output;
A second multiplier for multiplying the carrier and the control output;
A first adder for adding the output of the second multiplier and the output of the first integrator;
The control means includes
A first reference voltage generation circuit for generating a first reference voltage;
A subtracter for subtracting the first reference voltage from the detection output of the laser light amount;
An inverting second integrator for integrating the output of the subtractor;
A second reference voltage generation circuit for generating a second reference voltage;
A second adder that adds the output of the second integrator and the second reference voltage to form the control output;
An optical path length control circuit for a ring laser gyro, wherein a mirror transducer for controlling an optical path length is driven by an output of the first adder. An optical path length control circuit of a ring laser gyro in which a pair of laser beams propagate in opposite directions through the optical path in the glass block,
An oscillator that outputs a signal having a frequency twice that of the carrier;
A frequency divider that divides the output of the oscillator to generate carriers;
A first multiplier that multiplies the detection output of the laser light amount detected by the photodiode and the carrier;
A first integrator for integrating the output of the first multiplier;
Control means for outputting a control output;
A second multiplier for multiplying the carrier and the control output;
A first adder for adding the output of the second multiplier and the output of the first integrator;
The control means includes
A third multiplier for multiplying the detection output of the laser light amount and the output of the oscillator;
A first reference voltage generation circuit for generating a first reference voltage;
A subtractor for subtracting the first reference voltage from the output of the third multiplier;
An inverting second integrator for integrating the output of the subtractor;
A second reference voltage generation circuit for generating a second reference voltage;
A second adder that adds the output of the second integrator and the second reference voltage to form the control output;
An optical path length control circuit for a ring laser gyro, wherein a mirror transducer for controlling an optical path length is driven by an output of the first adder.   A ring laser gyro comprising the optical path length control circuit according to claim 1.

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