JPH038593B2 - - Google Patents

Description

Detailed Description of the Invention "Industrial Application Field" This invention causes monochromatic light to travel in opposite directions as a clockwise traveling wave and a counterclockwise traveling wave in an annular optical path formed by a plurality of reflecting mirrors. The present invention relates to an optical angular velocity meter that measures the angular velocity of an annular optical path by detecting the frequency difference between these two traveling waves.

"Prior Art" In this type of conventional optical gyrometry, in the region of low angular velocity, the clockwise traveling wave and the counterclockwise traveling wave are scattered by the minute scattering source of the reflecting mirror, and mix with each other. The frequency of both traveling waves is the same, making it impossible to measure angular velocity. This phenomenon is called the lock-in phenomenon. Conventionally, various efforts have been made to reduce the highest frequency (referred to as lock-in frequency) at which this lock-in phenomenon occurs. How to reduce lock-in frequency in optical gyrometry
(1) Adding a bias as shown in the BODY-DITHER method; (2) As shown in Japanese Patent Application Laid-Open No. 57-20818, the scattered waves are considered to be phase-modulated carrier waves and side waves; Another method is to vibrate the reflecting mirror forming the annular optical path so that the modulation index becomes the root of the Betzel function, and the latter shifts to a frequency band sufficiently distant from the frequency exhibiting the lock-in phenomenon. As a method of JP-A-18397
As shown in the above publication, there is a method of adjusting the phase relationship of scattered waves of a reflecting mirror to reduce the total amount of scattered waves. This invention uses three methods.

Even if the reflecting mirror that forms the annular optical path is carefully manufactured, minute scattering sources remain on its mirror surface, and the scattered waves from these sources mix into the traveling wave, causing the lock-in phenomenon. There is a certain relationship in scattering intensity and phase between a traveling wave incident on a certain scattering source and its scattered wave, and the relationship between the traveling wave incident on a scattering source and the scattered wave can be expressed by a vector. Therefore, the scattered wave vectors from the respective scattering sources on the mirror surface of one reflecting mirror can be combined and treated as one representative scattered wave vector Er→. E is the traveling wave incident on the mirror surface, and r→ is the backscattering rate of the mirror surface. For an annular optical path consisting of three reflecting mirrors, the representative scattered wave vector by each reflecting mirror is E ₁ r→ ₁ ,
When E ₁ r→ ₂ and E ₁ r→ ₃ , for example, the scattered wave of the clockwise traveling wave is a vector combination of these three representative scattered wave vectors.

The method (3) above is to reduce the lock-in frequency from this point of view, and among the three mirrors forming the annular optical path, two reflecting mirrors are pushed in the normal direction of the mirrors to reduce the reflection. The phase relationship between each representative scattered wave of the mirror is changed so that the total size of the scattered waves is minimized. That is, the first
As shown in the figure, three reflecting mirrors 1, 2, and 3 are arranged at the vertices of an equilateral triangle, and these reflecting mirrors 1, 2, and 3 constitute a triangular annular optical path 4. When the reflector 1 is moved outward with respect to the annular optical path 4 in its normal direction as shown as 1', the reflector 2
is moved by an equal amount inside the annular optical path 4 in its normal direction, as shown by 2', so that the magnitude of the scattered waves of the reflecting mirrors 1, 2, and 3 is minimized. A dotted line 4' in FIG. 1 shows a change in the annular optical path 4 based on the movement of the reflecting mirrors 1 and 2. in this case,
The distance between the fixed mirror 3 and the two reflective mirrors 1 and 2 that are moved by the push pull changes, and for example, the difference in phase between which each of the scattering sources of the reflective mirrors 1 and 3 affects the traveling wave changes, That is, the phase relationship between the representative scattered waves of the reflecting mirrors 1 and 3 changes. However, as can be seen from Fig. 1, when reflector 1 moves by h ₁ , it moves by △x ₁ relative to reflector 2, and at this time, reflector 2 moves by h ₂ = h ₁
Because of the movement, the reflector 1 moves by △x ₂ = △x ₁ , and the optical distance between the two push-pull mirrors does not change, so the reflector 1,
The phase relationship between the two scattered waves cannot be adjusted. This method cannot truly minimize the lock-in area.

"Purpose of the Invention" The present invention is intended to improve this point, and to obtain a true minimum lock-in frequency by configuring the annular optical path so that the phase relationship of each representative scattered wave by the reflecting mirror can be changed. The purpose is to provide an optical angular velocity meter that can perform

“Structure of the Invention” In this invention, n pieces (n is 3
At least (n-1) of the reflecting mirrors (an integer greater than or equal to)
The mirrors are movable in the tangential direction of the annular optical path.

Further, a means for generating a signal corresponding to the magnitude of the lock-in frequency from the light beam of the annular optical path, and a means for moving one of the above-mentioned reflecting mirrors in the tangential direction, and generating a signal corresponding to the magnitude of the lock-in frequency at that time, generate a signal corresponding to the magnitude of the lock-in frequency. Means for controlling the amount of movement of the reflecting mirror is provided so that the distance is minimized. With this configuration, for example, when a circular optical path is configured with three reflecting mirrors, the first reflecting mirror is moved in the tangential direction, and the amount of movement is adjusted so that the lock-in frequency is minimized. Next, the second reflecting mirror is moved in the tangential direction, and the amount of movement is controlled so that the lock-in frequency is minimized. The practical minimum lock-in frequency can be obtained by repeating the control alternately.

The above will be explained using FIG. 2. Vectors 1→, 2→, and 3→ in FIG. 2 are representative scattered waves E ₁ r→ ₁ , E ₁ r→ 2 , and E ₁ r→ 3 of reflecting mirrors 1, ₂ , and ₃ in FIG. 1, respectively.
It corresponds to

Now, the representative number waves 1→, 2→, and 3→ are in the state shown in Fig. 2A, and in this state, if the reflector 1 is moved in the tangential direction so that the lock-in frequency is minimized, the representative number waves 1 → becomes the state shown by vector 1′→,
In this state, the composite vector α→ of the three representative scattered waves is the minimum. Note that the conventional act of moving two reflecting mirrors by the same amount (because it is necessary to keep the optical path length constant) is basically equivalent to this, and changes the phase relationship of vectors 2→ and 3→ in the figure. It is not possible (if the reflecting mirrors 1 and 2 are moved in a push-pull manner, the vector 3→ will rotate, but they are essentially equivalent).

Next, if we move the reflector 2 in the tangential direction and rotate the vector 2→ so that the lock-in frequency is minimized, that is, when we obtain the minimum combined vector, the vector 2→ will become the 2'→ shown in Figure 2B. position, and the composite vector β→ at this time is smaller in magnitude than the composite vector α→. In the same way, if the reflector 1 is moved tangentially again and the vector 1'→ is rotated to obtain the minimum resultant vector, then this resultant vector γ→ becomes smaller than the resultant vector β→ as shown in Figure 2C. becomes even smaller. By repeating such operations, it is possible to obtain the practical minimum combined scattered wave amplitude.

As shown in Fig. 3, by moving the reflecting surface of the reflecting mirror in the tangential direction of the annular optical path (arrow 5 in the figure), the phase relationship between the representative scattering source 6 and the traveling plane wave can be changed. It is easy to understand what can be done. In addition, when the annular optical path 4 is an equilateral triangle, by moving the reflecting mirror by a distance twice the wavelength λ of the traveling wave, the representative scattered wave vector can be rotated by one rotation in the vector diagram, and this amount is determined by the phase adjustment. It's a sufficient amount. In other words, the reflecting mirror is moved in the tangential direction so as to minimize the lock-in frequency, but the amount of movement may be as small as 2λ or less.

Embodiment FIG. 4 shows an annular optical path portion in an embodiment of the optical angular velocity meter according to the present invention. This example is a case where an annular optical path is configured with three reflecting mirrors.

Passages 12, 13, and 14 are formed in the crystallized glass block 11, forming each side of a substantially equilateral triangle, and these passages 12, 13, and 14 constitute one continuous discharge space. Passage 12, 13,
Reflecting mirrors 15, 16, and 17 are arranged at each intersection position of 14. An anode 1 is provided at an intermediate position between the passages 13 and 14.
8 and 19 are provided, and a cathode 2 is provided in the middle of the passage 12.
1 is provided. A laser medium such as helium or neon is sealed in the discharge space, and the anodes 18, 1
9 and the cathode 21, the laser beam is sequentially reflected by the reflecting mirrors 15, 16, 17, 15, and a clockwise traveling wave traveling along the annular optical path 22 and the reflecting mirrors 15, 17, 16, 15 and are sequentially reflected,
A counterclockwise traveling wave traveling along the annular optical path 22 is generated. When an angular velocity around an axis 23 passing perpendicularly through the center of this annular optical path 22 is input, a difference occurs in the frequencies of the two traveling waves rotating in opposite directions.
For example, parts of the two traveling waves are taken out from a part of one reflecting mirror, these taken out traveling waves are caused to interfere with each other using a prism or a reflecting mirror, and the interference fringes are inputted based on the moving speed and direction of the interference fringes. The magnitude of the angular velocity and its direction are measured.

In this embodiment, the two reflecting mirrors 15 and 16 are plane mirrors, and the other reflecting mirror 17 is a concave mirror with a radius of curvature sufficiently long compared to the annular optical path length. One reflecting mirror 15 is attached to the movable part of the piezoelectric driver 24 in order to control the laser oscillation wavelength λ to be constant as in the conventional case. The piezoelectric driver 24 is driven and controlled by a control circuit,
The reflector 15 can be reciprocated in its normal direction, that is, in the radial direction with respect to the input shaft 23. By this reciprocating movement, the oscillation wavelength is controlled so as to be at the dots-place center of the laser medium value.

Both plane reflecting mirrors 15 and 16 form an annular optical path 22.
can be moved in the tangential direction. For this purpose, reflecting mirrors 15 and 16 are provided on piezoelectric actuators 25 and 26, respectively, which utilize the thickness sliding phenomenon of, for example, Y-cut crystal plates.
It is movable in the tangential direction with respect to the annular optical path 22. These three drive units 24, 25, and 26 are connected to a control circuit (not shown) through lead wires 27, 28, and 29, respectively.

FIG. 5 shows an example of a control system for controlling each of the above-mentioned driving sections in the optical angular velocity meter of the present invention to minimize scattered waves.

A driving unit 24 that moves the reflecting mirror 15 in the normal direction is connected to the output side of the optical path length controller 30, and the driving unit 24 moves the reflecting mirror 15 in the normal direction.
Drive unit 2 that moves 5 and 16 in the tangential direction, respectively.
5 and 26 are connected to the output sides of servo amplifiers 31 and 32, respectively, and oscillators 33 and 3 are connected to the optical path length controller 30 and each servo amplifier 31 and 32, respectively.
4 and 35 supply small amplitude signals of mutually different frequencies.

On the other hand, either a clockwise traveling wave or a counterclockwise traveling wave is taken out from the reflecting mirror 17 and sent to the light receiving element 36.
and is converted into an electrical signal. This electrical signal is amplified by an amplifier 37 and distributed to first, second, and third demodulators 38, 39, and 40. Each demodulator 3
8, 39, 40 are the oscillators 33, 3, respectively.
4 and 35 are supplied and their input signals are synchronously detected, the demodulated signal of the first demodulator 38 is sent to the optical path length controller 30, and the demodulated signals of the second and third demodulators 39, 40 are sent to the lock-in instruction. Each is input to the control output device 41. From the lock-in instruction control output device 41, the servo amplifier 31 of the tangential drive section of the reflecting mirror,
A control signal is input to 32.

In this control system, the optical path length controller 30 drives the piezoelectric driver 24 with a signal obtained by superimposing the signal from the oscillator 33 on the DC control signal, and
The optical path length of the annular optical path 22 is changed by moving the annular optical path 22 in its normal direction. At this time, the laser oscillation state is detected from the demodulated output of the demodulator 38, and based on the detection, the controller 30 is controlled to control the magnitude and polarity of the DC control signal output from the controller 30, thereby achieving the optimum oscillation state. The optical path length is controlled as follows.

On the other hand, although not shown in the figure, the ring laser section is oscillated by an external device, and the angular velocity around its central axis repeatedly passes through the lock-in band as it oscillates. In this way, the intensity of the extracted laser light changes when passing through the lock-in band. This change is called the winking phenomenon. The magnitude of the winking phenomenon corresponds to the height of the lock-in frequency, as shown in Japanese Patent Laid-Open No. 18397/1983.

A DC control signal is supplied from the lock-in instruction control output device 41 to the servo amplifier 31, a weak AC signal from the oscillator 34 is superimposed on this DC control signal, and the signal is supplied to the drive unit 25. It moves according to the magnitude and polarity of the control signal. The demodulated output of the demodulator 39 at this time corresponds to the intensity of the laser beam at that time, that is, it corresponds to the magnitude of the lock-in frequency. In response to this demodulated output, the lock-in instruction control output device 41 outputs the servo amplifier 31.
The DC control signal for the demodulator 39 is controlled so that the demodulated output (lock-in frequency) of the demodulator 39 becomes small. Through this feedback control, the movement of the reflecting mirror 15 is stopped when the lock-in frequency becomes the minimum.

Next, the DC control signal from the lock-in instruction control output device 41 is supplied to the servo amplifier 32, and the DC control signal is superimposed with a weak AC signal from the oscillator 35 and supplied to the drive section 26. Reflector 16
moves in the tangential direction. The demodulated output of the demodulator 40 at this time corresponds to the intensity of the laser beam at that time, and therefore corresponds to the magnitude of the lock-in frequency. Lock-in instruction control output device 41 according to this demodulated output
controls the DC control signal to the servo amplifier 32 so that the demodulated output (lock-in frequency) of the demodulator 40 becomes small. As a result, the movement of the reflecting mirror 16 is stopped at the point where the lock-in frequency becomes the minimum. Thereafter, the above-described drive control for the drive units 25 and 26 is repeated alternately until a practical minimum lock-in frequency is obtained.

Note that when the backscattering rates of the reflectors 15, 16, and 17 are equal (|r ₁ |=|r ₂ |=|r ₃ |), the lock-in frequency is minimized by moving the reflector 15 in the tangential direction. After this, the lock-in frequency may be minimized by simultaneously moving the reflecting mirrors 15 and 16 and by doubling the moving amount of the reflecting mirror 16 with respect to the moving amount of the reflecting mirror 15. Furthermore, when the amount of backscattering of each reflecting mirror is known, it is possible to execute a program to determine how to move the reflecting mirror in the tangential direction.

"Effects of the Invention" As explained above, there is no need to make efforts to improve the mirror surface quality of the reflecting mirror, which is difficult to do, and the lock-in frequency can be achieved using a simple structure without using a particularly complicated structure by using a reflecting mirror of the current quality. It is possible to significantly reduce the Along with this, the random drift error proportional to the lock-in frequency decreases,
It also helps to improve the linearity of the scale factor, which is also related to the magnitude of the lock-in frequency, and has a great effect on improving the performance of the optical gyrometer.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the annular optical path formed by three reflecting mirrors, Fig. 2 is a diagram showing the phase relationship of representative scattered waves of each reflecting mirror, and Fig. 3 is a diagram showing the phase relationship of representative scattered waves of each reflecting mirror. A diagram showing the change in the phase position of the scattering source when the reflecting mirror is moved in the tangential direction, FIG. 4 is a diagram showing the annular optical path section in the embodiment of this invention, and FIG. 5 is a diagram showing the control system in the embodiment of this invention. FIG. 11: Crystallized glass, 12, 13, 14: Traveling wave path, 15, 16: Planar reflecting mirror, 17: Concave reflecting mirror, 18, 19: Anode, 21: Cathode, 22:
Annular optical path, 23: rotation center of annular optical path, 24: normal direction drive section, 25, 26: tangential direction drive section, 2
7, 28, 29: Lead wire from the drive unit, 30:
Optical path length controller, 31, 32: Servo amplifier, 3
3, 34, 35: Oscillator, 36: Photodetector, 3
7: Amplifier, 38, 39, 40: Demodulator, 41:
Lock-in control instruction output device.

Claims (1)

[Claims] 1 An annular optical path is formed by n reflecting mirrors (n is an integer of 3 or more), and two almost monochromatic light beams are rotated through the annular optical path in opposite directions, and there is a gap between these two optical beams. In an optical angular velocity meter that detects the frequency difference between the two optical beams and determines the angular velocity about the axis of the annular optical path, means for generating a signal corresponding to the magnitude of the lock-in frequency of the optical beam;
means for individually moving at least (n-1) of the reflecting mirrors in the tangential direction of the annular optical path; and moving one of the reflecting mirrors in the tangential direction, and adjusting the magnitude of the lock-in frequency at that time. means for controlling the amount of movement of the reflector so as to minimize the lock-in frequency in response to a signal representing the optical angular velocity.