Ring Laser Gyroscope

Abstract

To provide a ring laser gyroscope capable of reducing accumulation of accuracy deterioration of detection angular velocity due to lock-in phenomenon, which cannot be prevented even by dither vibration.SOLUTION: A ring laser gyroscope 100 includes: an optical block for generating a laser beam that counter-propagates a closed-loop optical path; a dither mechanism 200 for providing a dither vibration to the optical block to mitigate lock-in phenomenon; and a dither controller 300 for controlling the dither vibration. The dither controller 300 adds randomness to frequency of angular velocity of dither vibration.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to ring laser gyroscopes with dithering mechanisms that mitigate the lock-in phenomenon, and more particularly to the nature of the vibrations produced by the dithering mechanisms. [Background technology]

[0002] A ring laser gyroscope 900 known in the prior art will be outlined with reference to FIGS. 1 and 2. The ring laser gyroscope 900 includes an optical mechanism 910 and a signal processor 920. The optical mechanism 910 includes a glass optical block 11. A closed-loop optical path 12 (typically polygonal, and in the example shown in FIG. 1, triangular) is formed inside the optical block 11. Mirrors 13, 14, and 15 are located at each vertex of the optical path 12. The mirror 13 is a partially transmissive mirror, and the mirrors 14 and 15 are fully reflective mirrors. Anodes 16 and 17 and a cathode 18 are attached to each side of the optical path 12. A laser medium is sealed within the optical path 12. The laser medium is excited by applying a high voltage between the anodes 16 and 17 and the cathode 18. As a result, laser beams (clockwise and counterclockwise laser beams in the example shown in FIG. 1) propagate counter-propagatingly through the optical path 12. The clockwise laser light is reflected by mirrors 13, 14, and 15 in optical path 12 and travels clockwise in a triangular loop. The counterclockwise laser light is reflected by mirrors 13, 14, and 15 in optical path 12 and travels counterclockwise in a triangular loop. Hereinafter, the path of the laser light in optical path 12 will be referred to as the loop path.

[0003] When the optical block 11 rotates clockwise around the normal to the plane containing the loop path at a certain angular velocity (hereinafter referred to as the input angular velocity), the Sagnac effect causes the frequency of the clockwise laser light to decrease in proportion to the magnitude of the input angular velocity, and the frequency of the counterclockwise laser light to increase in proportion to the magnitude of the input angular velocity. When the optical block 11 rotates counterclockwise, the frequency of the clockwise laser light increases in proportion to the magnitude of the input angular velocity, and the frequency of the counterclockwise laser light decreases in proportion to the magnitude of the input angular velocity. The frequency difference between the frequencies of the clockwise and counterclockwise laser light corresponds to the number of movements of the optical interference fringes per unit time. Therefore, the magnitude and polarity of the input angular velocity can be detected by measuring the frequency difference and the movement direction of the optical interference fringes.

[0004] For this purpose, the laser light is extracted through mirror 13. In Fig. 1, reference numeral 22 denotes a prism for forming optical interference fringes between one laser light and the other laser light traveling in the same direction by refracting the path of one laser light, and reference numeral 21 denotes a photosensor for detecting the optical interference fringes (i.e., the interference light). Reference numeral 23 denotes a laser light intensity meter that measures the intensity of the extracted laser light in order to control the length of the loop-shaped path. Fig. 1 does not show a path length controller that controls the length of the loop-shaped path so as to keep the intensity of the laser light measured by laser light intensity meter 23 constant.

[0005] In FIG. 1, the photosensor 21, the prism 22 and the laser light intensity meter 23 are shown separated from the optical block 11, but the photosensor 21, the prism 22 and the laser light intensity meter 23 are attached to the optical block 11 or to a case to which the optical block 11 is fixed.

[0006] In a ring laser gyroscope, one of the undesirable phenomena from a practical standpoint is the lock-in phenomenon. The lock-in phenomenon occurs when the frequency difference between the clockwise and counterclockwise laser beams becomes zero, even though a non-zero input angular velocity is actually applied to the optical block 11. As a result, the angular velocity detected by the ring laser gyroscope becomes zero. The lock-in phenomenon arises from the synchronization of the counter-propagating laser beams and occurs when the optical block 11 rotates at a non-zero input angular velocity within a small range of angular velocities that includes zero (hereinafter referred to as the lock-in angular velocity range). Because the counter-propagating laser beams are subject to disturbances from various components that make up the ring laser gyroscope, it is impossible to completely prevent the lock-in phenomenon from occurring.

[0007] To mitigate the lock-in phenomenon (i.e., to reduce the lock-in angular velocity range in which the frequency difference between the laser beams becomes zero), a dither mechanism 200 is attached to an opening 19 formed in the center of the optical block 11. The dither mechanism 200 vibrates the optical block 11 in the circumferential direction of the loop path, i.e., vibrates around the axis of the optical block 11 perpendicular to the plane containing the loop path. Hereinafter, this vibration will be referred to as dither vibration. For example, the angular frequency of the dither vibration is significantly larger (typically several hundred radians per second) than the upper limit (or absolute value of the lower limit) of the lock-in angular velocity range, and the angular amplitude of the dither vibration is less than 1 degree.

[0008] As shown in FIG. 2, the dither mechanism 200 includes a shaft 34 extending in one direction (i.e., perpendicular to the plane of the paper in FIG. 2), a cylindrical sidewall 32, and multiple (three in this example) connecting portions 33. The shaft 34 is located at the axis of the sidewall 32. The three connecting portions 33 extend radially from the shaft 34 to the sidewall 32. The three connecting portions 33 divide the space between the shaft 34 and the sidewall 32 at equal intervals. In this example, there are three spaces surrounded by the shaft 34, the sidewall 32, and two adjacent connecting portions 33, and one mounting portion 34a protrudes from the shaft 34 toward each of the three spaces. The mounting portions 34a have holes 34b for screws used when mounting the ring laser gyroscope 900 equipped with the dither mechanism 200, for example, by screwing it to a case. A piezoelectric element 35 is attached to each of both side surfaces of each connecting portion 33. The side wall portion 32 is in contact with the optical block 11.

[0009] 3 pieces Concatenation Of the three pairs (that is, six) of piezoelectric elements 35 attached to the section 33, two pairs are used to generate dither vibrations, and the remaining pair is used to detect the dither vibrations.

[0010] The dither mechanism 200 is a vibration generating mechanism and typically has a vibration frequency specific to the dither mechanism 200. Therefore, to efficiently drive the dither mechanism 200, it is desirable that the frequency of the dither vibration approximately matches the natural frequency of the dither mechanism 200. According to the prior art, to mitigate the lock-in phenomenon, a dither control unit 43 included in the signal processor 920 controls the dither vibration using an electrical signal (hereinafter referred to as a dither pick-off signal) obtained by a piezoelectric element used to detect the dither vibration so that the dither vibration has a frequency approximately matching the natural frequency of the dither mechanism 200 (see FIG. 3 of Patent Document 2). The piezoelectric element used to generate the dither vibration generates the dither vibration controlled by the dither control unit 43. The dither pick-off signal is also input to a bias signal removal unit 42 included in the signal processor 920.

[0011] Information about the optical interference fringes detected by the photosensor 21 (for example, the direction and speed of movement of the optical interference fringes) is input to a detection processing unit 41 included in the signal processor 920 and converted into angular velocity information. The angular velocity information output by the detection processing unit 41 is input to a bias signal removing unit 42.

[0012] The bias signal remover 42 uses the dither pickoff signal to remove the vibration angular velocity component corresponding to the dither vibration from the angular velocity information, and outputs the result as an angular velocity signal that represents the angular velocity of the motion of the device that includes the ring laser gyroscope 900.

[0013] Such ring laser gyroscopes are disclosed as prior art in, for example, Patent Documents 1, 2 and 3. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2014-055801 [Patent Document 2] Japanese Patent Publication No. 2013-024802 [Patent Document 3] U.S. Patent No. 6,683,692 Summary of the Invention [Problem to be solved by the invention]

[0015] As mentioned above, applying dither vibration to the optical block cannot completely prevent the occurrence of the lock-in phenomenon. This is because, each time the direction of the dither vibration changes, there is a time period during which the angular velocity of the optical block enters the lock-in angular velocity range. At this time, the lock-in phenomenon occurs. Therefore, for example, due to aging of the ring laser gyroscope or environmental temperature, sampling for digital processing in the signal processor may synchronize with the occurrence of the lock-in phenomenon, and this synchronization may cause accumulated degradation in the accuracy of the detected angular velocity. According to prior art, in order to reduce the accumulation of such accuracy degradation, randomness is imparted to the amplitude of the angular velocity of the dither vibration (i.e., random noise is added to the amplitude).

[0016] However, even if randomness is imparted to the amplitude of the angular velocity of the dither oscillation, the frequency of the angular velocity of the dither oscillation is constant, so it is not possible to sufficiently prevent sampling for digital processing in the signal processor from synchronizing with the occurrence of the lock-in phenomenon.

[0017] In view of this background art, from another perspective, a ring laser gyroscope is provided that can reduce the accumulation of deterioration in accuracy of detected angular velocity caused by the lock-in phenomenon that cannot be prevented even by dither oscillation. [Means for solving the problem]

[0018] The technical matters described herein are not intended to explicitly or implicitly limit the invention described in the claims, nor to express the possibility of accepting such limitations by anyone other than those who benefit from the present invention (e.g., the applicant and the right holder), but are described simply to facilitate understanding of the gist of the present invention. The outline of the present invention from other perspectives can be understood, for example, from the claims at the time of filing of this patent application. According to the present invention, randomness is imparted to the frequency of the angular velocity of the dither oscillation, that is, random noise is added to the frequency of the angular velocity of the dither oscillation. [Effects of the Invention]

[0019] According to the present invention, it is possible to reduce the accumulation of deterioration in the accuracy of detected angular velocity caused by the lock-in phenomenon that cannot be prevented even by dither oscillation. [Brief explanation of the drawings]

[0020] [Figure 1] Prior art ring laser gyroscope configuration. [Figure 2] Dither mechanism configuration. [Figure 3] Block diagram of a feedback system. [Figure 4] Example of a first-order phase shifter. [Figure 5] 1 shows a configuration of a ring laser gyroscope according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Before describing the embodiments, a theoretical outline of the present invention will be described.

[0022] The lock-in phenomenon of a ring laser gyroscope originates from the synchronization phenomenon of counter-propagating laser beams. The time rate of change of the phase difference φ(t) between the counter-propagating laser beams is expressed as the Adler Equation (1), where t is the time, Ω is the input angular velocity, and Ω L is the upper limit (or absolute value of the lower limit) of the lock-in angular velocity range.

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[0023] To mitigate the lock-in phenomenon, equation (2) can be obtained by adding a sine wave, for example, representing the angular velocity of the dither oscillation, to equation (1). Ω d is the amplitude of the angular velocity of the dither oscillation, and ω d is the angular frequency of the angular velocity of the dither oscillation. The angular velocity of the dither oscillation is not limited to a sine wave, and may be expressed by, for example, a triangular wave.

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[0024] ω d When is sufficiently large (typically several hundred radians per second), equation (2) can be approximately rewritten as equation (3), where J0(x) is the zeroth-order Bessel function of the first kind and φ0 is the initial phase.

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[0025] According to the prior art, random noise is added to the amplitude of the angular velocity of the dither oscillation in order to reduce the accumulation of accuracy degradation of the detected angular velocity due to the lock-in phenomenon that cannot be prevented even by dither oscillation. This means that equation (4) shows that ξ(t) is random noise. In this specification, the terms "random" or "randomness" are used to mean having no regularity or periodicity, and do not necessarily require lack of determinism or lack of reproducibility.

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[0026] According to the prior art, ω d Since is constant, even if random noise is added to the amplitude of the angular velocity of the dither oscillation, it is not possible to sufficiently prevent the sampling for digital processing in the signal processor from synchronizing with the occurrence of the lock-in phenomenon. Therefore, in the present invention, random noise is added to the frequency of the angular velocity of the dither oscillation in order to reduce the accumulation of deterioration in the accuracy of the detected angular velocity caused by the lock-in phenomenon, which cannot be prevented even by dither oscillation. This means Equation (5).

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[0027] Below, ω d Here, for simplicity, an explanation based on an analog circuit will be provided. dThe mechanism for applying random noise to the torque u can be constructed using a digital circuit. d The equation of motion of the rotational motion of the optical block by the dither mechanism that applies t to the optical block is expressed by equation (6). d represents the displacement angle of the optical block due to the dither vibration, J represents the moment of inertia of the optical block, C represents the viscous damping coefficient, K represents the spring constant, and M represents the amplitude of the sinusoidal torque. d is a function of time t.

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[0028] The homogeneous equation when the right-hand side of equation (6) is 0, i.e., the solution of damped free vibration, decays over time, so after a sufficient amount of time has passed, only the steady vibration, which is the particular solution to the sinusoidal torque, remains. Therefore, we will only examine the steady vibration. Assuming that the particular solution is given by equation (7), we will find the relationship between the angular amplitude Θ and the phase angle φ.

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[0029] By substituting equation (7) into equation (6), equations (8) and (9) are obtained, where η = ω d / ω n is the frequency ratio, ζ=C / C C is the damping ratio, and ω n =√(K / J) is the undamped natural angular frequency, and C C =2√(JK)=2Jω n is the critical damping coefficient and Θ0=M / K.

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[0030] When the vibration system consisting of the optical block and the dither mechanism resonates, the frequency ratio η that gives the maximum response magnification ris called the resonance point and is given by equation (10). The phase angle at the resonance point is given by equation (11). Note that the viscous damping coefficient C of an actual optical block is sufficiently small, so φ r is approximately 90 degrees.

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[0031] In this way, ω d =η r ω n By applying a sinusoidal torque u to the optical block at an angular frequency of , the vibration system resonates, and the φ r With a phase delay equivalent to the displacement angle θ d Therefore, the displacement angle θ d Consider a feedback system 800 that feedback controls the sinusoidal torque u based on the above. The feedback system 800 is connected to the vibration system 810 and the displacement angle θ d and a first-order phase shifter 830, and the displacement angle θ detected by the sensor 820 d The phase of the signal representing r By driving the dither mechanism with a signal advanced by , and applying a sinusoidal torque u to the optical block, we can create an oscillatory system that oscillates at the resonant frequency. A block diagram of this feedback system 800 is shown in Figure 3.

[0032] The transfer function of the vibration system 810, that is, equation (6), is given by equation (12). Since the numerator of equation (12) is simply a gain, in the following explanation, equation (13), which is the transfer function of a general second-order lag system, will be considered.

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[0033] The closed-loop transfer function W of the feedback system 800 shown in FIG. c is expressed by equation (14). L is the gain of the sensor 820. τ is the time constant of the primary phase shifter 830, and when the primary phase shifter 830 has the configuration shown in FIG. 4 as an example, τ=CR.

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[0034] W c The second term in the denominator of the formula (15) is the open-loop transfer function W0, and it is known that the feedback system exhibits resonance characteristics in a band where the gain |W0| (see formula (15)) of the open-loop transfer function W0 is approximately 1.

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[0035] W c is expanded to equation (16).

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[0036] By expanding equation (16) into partial fractions, W c can be expressed by equation (17).

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[0037] Since a vibration system is designed so that vibrations are expanded or sustained, that is, the system is unstable or at the stability limit, if we obtain sustained vibrations at the stability limit, then c = a. Therefore, by comparing equations (16) and (17), we can obtain equation (23) from equation (18). However, ω d >0,L<0,τ>0.

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[0038] Equation (24) is obtained from equations (22) and (23). As is well known, the gain of the first-order phase shifter 830 is 1 regardless of the frequency, and the gain of the transfer function of the second-order lag system is given by equation (25), as is well known. Therefore, when the frequency of the second-order lag system is ω dWhen it matches (ω=ω d ), the gain |W0| of the open-loop transfer function W0 is 1, and it can be seen that the feedback system 800 exhibits a resonance characteristic.

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[0039] Furthermore, equation (26) can be obtained from equation (24) and equation (8). Therefore, by controlling the angular amplitude of the optical block to be constant, L and ω d At this time, by randomly changing τ at a speed that is sufficiently slower than the response speed of the control, ω d It can be seen that it is possible to randomly change the phase shift amount by the phase shifter around the resonance point. d can be given random noise.

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[0040] From the viewpoint of efficient driving of the dither mechanism, the upper limit of the phase shift is the natural frequency ω d It is preferable that the phase shift does not exceed, for example, 1% of the natural frequency of the dither mechanism. In other words, it is preferable that the fluctuation range of the frequency to which randomness is imparted does not exceed 2% of the natural frequency of the dither mechanism. The lower limit of the phase shift amount can be determined depending on the degree of change in the natural frequency of the dither mechanism due to, for example, changes in the environmental temperature or aging. d This is the amount of phase shift that can give a change of, for example, 0.25 Hz to the

[0041] A ring laser gyroscope 100 according to an embodiment will be described with reference to FIG. 5. The ring laser gyroscope 100 has the same configuration as the ring laser gyroscope 900, except that it includes a dither controller 300 instead of the dither control unit 43 of the ring laser gyroscope 900. Therefore, by clearly stating that the description of the ring laser gyroscope 900 excluding the dither control unit 43 is incorporated herein, duplicate descriptions of the same components will be omitted. In FIG. 5, components other than the dither control unit 43 included in the signal processor 920 are not shown.

[0042] The dither controller 300 includes an A / D converter 302, an amplitude control circuit 304, a first random noise generator 306, a phase shifter 308, a second random noise generator 310, a multiplier 312, a D / A converter 314, and an amplifier circuit 316.

[0043] The A / D converter 302 converts the dither pick-off signal into a digital signal. The amplitude control circuit 304 compares the amplitude of the digital dither pick-off signal, obtained by passing the digital dither pick-off signal through a low-pass filter and a square root calculator, with a reference amplitude and performs PID control on the amplitude so that the amplitude of the digital dither pick-off signal remains constant. Methods for imparting randomness to the amplitude of the digital dither pick-off signal include changing the reference amplitude based on pseudo-random numbers generated by a first random noise generator 306, or adding an amplitude based on pseudo-random numbers generated by the first random noise generator 306 to the amplitude of the digital dither pick-off signal obtained by PID control.

[0044] The phase shifter 308 is, for example, a voltage-controlled digital phase shifter, and controls the phase of the digital dither pickoff signal so as to generate stable self-oscillation, as described above. To impart randomness to the phase of the digital dither pickoff signal, for example, a method of varying the phase amount based on pseudorandom numbers generated by the second random noise generator 310 can be used.

[0045] A multiplier 312 multiplies the output of the amplitude control circuit 304 by the output of the phase shifter 308. A D / A converter 314 converts the output of the multiplier 312 into an analog signal. An amplifier circuit 316 power-amplifies the output of the D / A converter 314. The power-amplified output of the D / A converter 314 is supplied to a piezoelectric element that generates dither vibration. Note that a PWM converter may be used instead of the D / A converter 314.

[0046] The input to the A / D converter 302 is not limited to the dither pick-off signal, but may be, for example, a signal obtained by passing a signal representing the phase difference φ(t) between the laser beams through a high-pass filter.

[0047] Without being limited to the above embodiment, a configuration in which the dither controller 300 does not include the first random noise generator 306 is also acceptable.

[0048] Random noise may be constantly applied to the frequency of the angular velocity of the dither vibration, or may be applied to the frequency of the angular velocity of the dither vibration when the strength of the output signal of the amplitude control circuit 304 falls below a predetermined threshold. Random noise may be constantly applied to the amplitude of the angular velocity of the dither vibration, or may be applied to the amplitude of the angular velocity of the dither vibration when the strength of the output signal of the amplitude control circuit 304 falls below a predetermined threshold.

[0049] The second random noise generator 310 may generate pseudo-random values ​​at regular time intervals or at random time intervals.

[0050] Whether or not randomness is imparted to the frequency of the angular velocity of the dither vibration can be easily determined by, for example, performing FFT analysis on the sound of the dither vibration.

[0051] <Addendum> While the present invention has been described with reference to exemplary embodiments, those skilled in the art will recognize that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. Furthermore, many modifications can be made to adapt a particular system, device, or component thereof to the teachings of the present invention without departing from the essential scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.

[0052] Furthermore, the use of terms such as "first" and "second" does not denote order or importance, and terms such as "first" and "second" are used to distinguish elements. The terms used herein are for the purpose of describing embodiments and are not intended to limit the present invention in any way. The term "comprises" and its conjugations, when used in this specification and / or the appended claims, reveal the presence of the mentioned features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The term "and / or" includes any and all combinations of one or more of the associated listed elements, if any. In the claims and the specification, unless otherwise specified, the use of words such as "connected," "coupled," "joined," "connected," or their equivalents, and all forms thereof, does not necessarily negate the presence of one or more intermediate elements between two elements that are, for example, "connected" or "coupled" to each other or "coupled" to each other. In the claims and the specification, the term "optional," if any, should be understood as a term that represents the same meaning as the universal symbol ∀, unless otherwise specified. For example, the phrase "for any X" has the same meaning as "for all X" or "for each X."

[0053] Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Furthermore, terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art and this disclosure, and should not be interpreted ideally or excessively formally unless explicitly defined.

[0054] It will be understood that in describing the present invention, many techniques and steps are disclosed. Each of these has distinct advantages, and each can be used in combination with one or more, or in some cases all, of the other disclosed techniques. Therefore, to avoid cluttering, this specification will refrain from describing every possible combination of individual techniques or steps. Nevertheless, the specification and claims should be read with the understanding that such combinations are fully within the scope of the present invention and claims.

[0055] The corresponding structure, material, acts, and equivalents of all functional elements combined with means or steps in the following claims are intended to include the structure, material, or acts, if any, that perform the function in combination with other elements.

[0056] Although the present invention has been described above with reference to exemplary embodiments, it is not limited to these embodiments. Various modifications and variations are possible without departing from the spirit of the present invention. The selected and described embodiments are intended to illustrate the principles of the present invention and its practical application. The present invention may be used in various embodiments with various modifications and variations, which are determined according to the expected use. All such modifications and variations are intended to be included within the scope of the present invention, as defined by the appended claims, and are intended to be accorded the same protection when interpreted in accordance with the breadth that is fairly, legally, and equitably to be given. [Explanation of symbols]

[0057] 11 Optical Block 12 Optical path 13. Mirror 14. Mirror 16 Anode 18 Cathode 19 Opening 21 Photo sensor 22 Prism 23 Laser light intensity measuring device 32 Side wall 33 Consolidated Department 3 4 Shaft 34a Mounting part 34b hole 35 Piezoelectric element 41 Detection processing section 42 Bias signal removal section 43 Dither control section 100 Ring Laser Gyroscope 200 Dithering mechanism 300 Dither Controller 302 A / D converter 304 Amplitude control circuit 306 First Random Noise Generator 308 Phase shifter 310 Second Random Noise Generator 312 Multiplier 314 D / A converter 316 Amplifier Circuit 800 Feedback System 810 Vibration System 820 Sensors 830 1st order phase shifter 900 Ring Laser Gyroscope 910 Optical mechanism 920 Signal Processor

Claims

1. A ring laser gyroscope, an optical block configured to generate laser beams that counter-propagate through a closed-loop optical path; a dither mechanism configured to apply a dither vibration to the optical block to mitigate the lock-in phenomenon; a sensor for detecting a displacement angle of the optical block; a dither controller including a phase shifter and a random noise generator that generates random noise, wherein the phase shifter drives the dither mechanism with a signal obtained by shifting the phase of a signal representing the displacement angle of the optical block by a time-varying phase shift amount obtained by varying a constant phase shift amount required to oscillate the dither mechanism at the natural frequency of the dither mechanism in response to the random noise, thereby providing randomness so that the frequency of the angular velocity of the dither oscillation is not constant; Including, Ring laser gyroscope.

2. 2. The ring laser gyroscope according to claim 1, The frequency fluctuation range of the angular velocity of the dither vibration does not exceed 2% of the natural frequency of the dither mechanism. A ring laser gyroscope characterized by:

3. 3. The ring laser gyroscope according to claim 1, the random noise generator generates the random noise at regular or random time intervals; While the random noise generator is not generating the random noise, the dither controller drives the dither mechanism with a signal obtained by shifting the phase of the signal representing the displacement angle of the optical block by the constant phase shift amount required to cause the dither mechanism to oscillate at the natural frequency of the dither mechanism. A ring laser gyroscope characterized by:

4. 4. The ring laser gyroscope according to claim 1, The dither controller is configured to further impart randomness to the amplitude of the angular velocity of the dither oscillation. A ring laser gyroscope characterized by:

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