JPS58124285A - Angular velocity sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention provides an improvement for reducing the accumulation of gyro output angular error caused by the lock-in phenomenon by dithering or biasing a laser angular velocity sensor. 1. [Prior Art] In a simple laser angular velocity sensor, sometimes called a ring laser gyro, it is necessary to define an input axis around which the rotational speed is to be detected. Two monochromatic light beams are generated to travel in opposite directions generally along a closed loop path. Rotation of the ring laser gyro about the input axis lengthens the effective laser path length of one beam and shortens the effective laser path length of the other beam.

As a result, changing the path lengths of the two beams causes the frequency of each beam to change, making one higher and the other lower. The reason is that the frequency of the laser beam depends on the length of the laser path6, and the frequency of the two combined waves, and therefore the difference between the frequencies of the two waves, is a function of the rotation of the closed-loop path. , a phase relationship is established between the two waves that is a function of their rotation.

When two beams have different frequencies, the phase W between them changes at a rate proportional to the difference in frequency1,2
The total phase change ΔW between the two beams is proportional to the time integral of the frequency difference and proportional to the time integral of the input rotational speed about the input axis of the gyro. Therefore, the total phase change over time represents the total angular displacement about the input axis during the integration time, and the rate of change of phase between the two waves dF/d
t indicates the rotation speed around the input axis of the gyro.

However, at low rotational speeds, the frequency difference between the two beams is small, and the two beams tend to resonate with each other, i.e., to vibrate at only one frequency. Therefore, in a simple laser gyro, the frequency difference is zero at low rotational speeds, making it impossible to measure low rotational speeds.

The outer rotation speed is generally referred to as the 10-twin speed, below which the frequency difference between the two beams becomes zero. When the gyro is rotating below the lock-in speed and the beam is long-finned, the gyro's output angle error is zero.

Of course, if low rotational speeds cannot be accurately measured, the M characteristics of the laser angular velocity sensor in the navigation device will be reduced. Therefore, in order to use laser angular velocity sensors more effectively in navigation equipment, much development research is being conducted in the field of laser angular velocity sensors with the aim of reducing or eliminating the effect of the long fin 1.

``One way to reduce or eliminate the impact of long parakeets.''
No. 337,365 owned by the applicant
It is disclosed in No. 0. That patent discloses a laser angular rate sensor that is provided with an element for introducing a frequency bias into two light beams traveling in opposite directions. The applied frequency bias is such that a much higher frequency difference exists between the two light beams traveling in opposite directions for most of the time than the frequency difference that occurs just before Ronfin-1. . Furthermore, the sign or polarity of the introduced frequency difference is such that after one complete cycle of periodically reversing biases, the time-integrated frequency difference between the two optical biases is approximately zero.
be periodically reversed.

Near the time when the sign or direction of the bias reverses, the frequency difference ranges from the lock-in speed to zero, so there is a tendency for "long-finning". Bias is “
Since the time in which the gyro is finned is very short, the potential for gyro output angle errors to accumulate is greatly reduced as a result. However, errors still accumulate in the gyro output angle signal, and eventually the errors reach troublesome levels.1° This is especially true in navigation equipment.

An improvement to the biasing device shown in the aforementioned US patent is disclosed in commonly assigned US Pat. No. 3,467,472. This U.S. patent includes the aforementioned U.S. Pat.
In addition to periodically varying the bias as shown in No. 50, the bias can be changed so that the small gyro output angle errors that occur around the time when bias reversal are randomized, reducing the average cumulative error. A bias device that provides randomization is disclosed. Although this improvement is sufficient, in order to widely apply laser angular velocity sensors to inertial navigation systems, it is necessary to further reduce the Ronfin error.

Figure 1 is U.S. Patent Nos. 3,373,650 and 346,747.
2 shows a well-known typical ring laser gyro 100 shown in FIG. Two beams 11 in which the laser generating medium 10 has a substantially single frequency and travel in opposite directions
．． yields 12. Those beams are reflected by mirrors 13, 14 .
Proceed along the triangular closed loop path formed by 15.

This closed loop path is shown surrounding an orthogonal reference axis, herein referred to as the gyro input axis, 26.

Closed loop paths can be created in several ways. For example, the reflector 13 can be a concave spherical mirror 13' if desired. This concave mirror allows alignment of the optical path. The position of the reflecting mirror 14, which is a plane mirror, can be controlled by the transducer 14A1. In order to optimally perform laser oscillation, the reflecting mirror 14 is positioned so as to control the optical path lengths of the two light beams traveling in opposite directions. can be done.

Such a transducer is disclosed in commonly owned US Pat. No. 3,581,227. j Also, the optical path length control device is disclosed in U.S. Patent No. 41529 owned by the applicant.
It is disclosed in No. 71.

The combination of the reflecting mirror 15, combination prism 21, and detector 22 constitutes a laser gyro reader. Reflector 15 is shown as a semi-transparent plane mirror. A portion of the energy of the light beam 11.12 can therefore be transmitted through its reflector 15.

A portion of the energy of the beams 11, 12 transmitted through the reflector 15 is incident on the combination prism 21, so that the output light beams 11', 12' from the combination prism 21 are orthogonal to each other.

These light beams 11', 12' are uniquely related to the frequency and phase of the two light beams 11.12 traveling in opposite directions. The light beams 11', 12' are superimposed by a detector 22 to produce an interference stripe pattern consisting of alternating light and dark bands. This figure shows the behavior of the instantaneous phase relationship between two light beams traveling in opposite directions due to interference.

If the two light beams traveling in opposite directions have the same frequency, the instantaneous phase between the two light beams traveling in opposite directions is constant, and the interference pattern is constant. However, if two light beams traveling in opposite directions have different frequencies, their instantaneous phase relationship will change over time, and depending on which of the two beams has a higher frequency, they will interfere and cause interference. Hatan appears to move to the right or left.

Therefore, by monitoring the instantaneous phase relationship between the two light beams, the magnitude and direction of the rotational movement about the input @26 can be determined. The direction of its motion is determined by the direction of phase change, i.e. which beam has a higher frequency, and by the angle of rotation, i.e. the angular displacement of the closed loop path from a certain reference position, and the change in the number of fringes. and its portion passing through a fixed reference mark on the detector. Complete changes in interference stripes (from highest to lowest brightness,
from the lowest brightness to the highest brightness) is 2 between the two light beams.
Represents a phase change in π radians. The rate of change of the movement of the interference stripes indicates the rotational speed about the laser gyro input axis 26.

An example of an apparatus for detecting the laser gyro phase of two laser beams is shown in FIG. 1a.

This device consists of two detectors 22a, 22b placed on the output side of a combination prism 21, separated by about one-fourth (λ/4) of the spacing of the interference fringes. The physical dimensions of the device depend on the optical relationships in the device. Detector 2
2B, 22b can be comprised of a photodetector that generates an output signal indicative of the strength of the interference stripe pattern.

By separating the detectors 22a, 22b by about one-fourth the spacing of the interference stripes, the output of the photodetectors is phased such that the direction and magnitude of the movement of the interference stripes can be monitored. When the gyro is rotated clockwise, the interference fringe pattern moves in one direction, and when the gyro is rotated counterclockwise, the interference fringe pattern moves in the opposite direction. The rotation speed is determined by counting the number of maximum and minimum brightnesses resulting from interfering motions (light to dark) passing through one of the detectors, and the orientation of the two brightness signals provided by detectors 22a, 22b. The direction of rotation is determined by comparing the changes in 1, the brightness values detected by each detector indicating the instantaneous phase between the two light beams traveling in opposite directions. As explained later, each light beam is offset by a different offset angle β.

At each time each detector responds to a different brightness, as shown in Figure 1a. The output of each detector is directly related to the phase W between the beams, offset by some offset phase constant β that depends on the spatial location of the detector with respect to the brightness of the pattern and the instantaneous phase W. In the embodiment shown in FIG. 1a, the value of β is π/2 radians. If the detector is perfectly positioned, its value of β corresponds to λ,/4. In the following description, the value of β is indicated by an expression containing r.

Referring again to FIG. 1, the outputs of the detectors 22m, 22b are processed by a well-known signal processing circuit 2 for processing the outputs of those detectors to determine angular rotation, magnitude, orientation and rate of rotation.
given to 4. An example of this signal processing circuit 24 is disclosed in U.S. Pat. No. 3,373,650 and U.S. Pat.
No. 7425. The output of each detector is amplified and then used to trigger a digital cucumber that monitors relative outer plus and minus counts. Each count is 2π of two light beams traveling in opposite directions along a closed loop path about the input end 26.
Play with the phase change in radians. The relationship between each count and the angular displacement of the angular velocity sensor depends on the sensor's relationship between the input velocity and the bias frequency difference (ie, the scale factor). For example, 1 degree/hour (1/of the earth's rotation speed)
15) It is possible to make a laser gyro with an inertial input rotation speed relationship. This laser gyro causes the frequency difference between the two light beams in the laser gyro cavity to be IHz. 1 degree per hour is exactly 1 arc second per second of time6, so 1
An inertia angle η of 1 arc second is generated every second, resulting in a phase change of 2π radians between the two beams. The reason is that the frequency difference IHz over an integration time of 1 second
This is because the time integral of is 2π radians. Each count will then have a weight of one arc second, and a 360 degree rotation of the sensor about the input axis, or one revolution, will produce an output of 1296 otlO counts.

For rotations in one direction, those counts or culs are determined to be positive, and for rotations in the opposite direction, those culs are determined to be negative. J (logic similar to that used in digital incremental angle encoders) Typically, the closed loop path shown in FIG. 1 measures rotation about the gyro's input axis 26. for,
It is supported by a support element 25.

Although detector 22 is also shown supported by support element 25, detector 22 can be provided external to support element 25. Although the lasing medium is shown in FIG. 1 as being in the optical path of two light beams traveling in opposite directions, the invention is not limited to such a structure.5. so that the beam resonates in a closed loop path,
The lasing medium is only required to generate two light beams which travel in opposite directions along a closed loop path supported by the support element 25.

Next, the operation of the laser angular velocity sensor shown in FIG. 1 will be explained in detail. When there is no rotation about the input axis 26, the frequencies of the light beams 11 and 12 are equal and the light beam 1
The striped pattern created by 1', 12' on the detector 22 remains constant. When the support device 25 rotates about the axis 26, the frequency of one of the light beams increases and the frequency of the other light beam decreases depending on the direction of rotation. Correspondingly, the (7)l,t pattern on the detector 22 created by the beams 11', 12' moves with a speed proportional to the difference in frequency of the two beams 11.12, and the detection of either The brightness measured by the detectors 22a, 22b indicates the phase between the beams 11 and 12 traveling in opposite directions.

The rate of change in phase indicates rotation, and can be expressed mathematically by the following equation (1).

Here, F = instantaneous phase between the two original beams S - scale factor ωi of the gyro - input rotational speed ωL of the gyro = length/speed of the gyro.

Equation (1,) describes the lock-in error relationship between the input velocity and the observable phase relationship. It should be noted that the rate of change of phase is directly related to the input velocity, but is modified by an error term that includes the gyro's linear velocity/velocity ωL'. When the input rotational speed is lower than ω■, the error term is very large. This error term is commonly referred to as the Ronfin error and is particularly troublesome when determining angular rotation.

The phase relationship between the beams can be observed by a photodetector with dimensions much smaller than the interference fringe spacing.

Rotational speed can be measured simply by recording the distance between the interference stripes, or the speed at which the highest brightness moves through the detector. The speed of movement is proportional to the difference in frequency. Each time a stripe spacing is recorded represents a phase change of 2π radians between the two beams. The integral of the frequency difference over time (counting the number of changes in the stripes) is, as mentioned above, proportional to the total phase change between the two beams, and therefore the integral time of the closed loop path about the gyro input axis. Proportional to the amount of full angle change in the middle. This is mathematically expressed by the following equation.

Here, △W has a frequency of f2. Beams 11 and 1 which are N
Total phase change (in radians) during the integration time of the phase between 2
The sign indicates the direction of rotation.

Each time at which one stripe interval is detected can be referred to as a "count." The total number of counts and the fraction of that total count multiplied by the scale factor indicates the angular displacement during the integration time, and the rate of change of the force 9t indicates the rotational speed.

Equation +1) can be expressed in various units using the output currant of the photodetector 22, and is shown by Equation (2).

Here, ■ - sensor input angular displacement expressed in counts, d I/d
t is the sensor input speed FL which is changed at a count of 7 seconds - the gyro's long fin speed C which is expressed at a count of 7 seconds - the angular displacement output of the gyro which is expressed at a count, and dC
/dt is the gyro output speed including lock-in error 1,10 Due to ink, the output C may not be equal to the actual input I. The output angle lock-in error of the gyro is (3
), it can be determined by the lock-in error variable E.

E = C-I (3
) (3), the output angular count of the gyro is equal to the input angular displacement plus a certain error based on the angular rotation about the gyro input axis.

c = I + E (4) By substituting equation (4) into equation (2), error equation (5) expressed by gyro output count is obtained.

Equation (5) is used for the type of ring shown in Figure 1.
This describes the lock-in error inherent in laser angular velocity sensors. The output of this sensor is a signal related to the inertial input angle measured by the sensor, the signal processing device 2
4. This sensor output includes a lock-in error approximately described by equation (5). In the following discussion, it is assumed that there is a sensor output signal that includes a lock-in error and is related to the inertial input to the sensor.

The objective of the invention is, of course, to minimize the lock-in errors that normally occur in sensor output signals. (5)
The utility of the formula will become clear from the following explanation.

As mentioned above, U.S. Pat. No. 3,373,650 teaches that two beams of light traveling in opposite directions are arranged such that there is a time-varying frequency difference of alternating sign between them most of the time. A laser gyro is disclosed in which a bias is applied that periodically reverses the frequency of the beam.

The reversing bias is of such a nature that the time-integrated frequency difference between the two light beams is approximately zero after a complete Ganni cycle of the periodically reversing bias. (The bias shown in U.S. Pat. No. 3,373,650 is either periodic or repeatable, or need not be periodic, just a sufficiently large number of flips per second. As disclosed in that U.S. patent, the periodic reversal of the bias mechanically
Alternatively, it can be done, for example, by directly changing the frequency difference between the two beams by acting directly on the lasing optical path, i.e. the lasing medium.3 The latter method is ``It's called something that gives 1 electrical bias.

In the mechanically biased method, the laser gyro is simply electromechanically driven forward and backward about the gyro's input axis so as to maintain an effective gyro input rotational speed that is higher than the lock-in speed most of the time, i.e. It is dithered and the input rotational speed only periodically reverses direction. The frequency of each beam is affected by the vibration, or dither movement, about the gyro's human power axis applied by this mechanical biasing method, so that vibrations in one direction will cause one frequency to be high, while the other vibration frequency will be higher. is low, and vibrations in the other direction change the frequency in the opposite direction. If the frequency of the oscillatory motion is high enough and the effective speed of rotation caused by the oscillation is high enough, there will be a varying frequency difference between the beams for most of the time;
Lock-in effects are largely avoided even when measuring low rotational speeds. Electrical biasing methods apply a frequency bias to two beams traveling in opposite directions by directly separating the frequencies of the laser beams by causing changes in the laser generation optical path. Electro-optical devices such as Faraday media are used in the optical path of these beams. In the mechanically biasing and electrically biasing methods disclosed in U.S. Pat. No. 3,373,650, the frequency of at least one of the beams is biased or changed to Allow a frequency difference between the beams to exist for most of the time. Since the bias seen by the blade periodically reverses, i.e. changes the sign of the frequency difference, the time integral of the frequency difference of the two beams is over one bias cycle, or dither cycle. is almost zero.

FIG. 1 shows a periodically reversing biasing device 30 for biasing the frequencies of two beams traveling in opposite directions. This device is coupled to the base 25 via electrical leads 31. In a mechanical bias device, the bias device 30 mechanically rotates the pace 25 in a positive direction and a reverse direction around the input shaft 26 of the gyro so as to change the frequency of at least one side. If it introduces a changing frequency bias that distorts the sign,
What kind of equipment can be used? In practice, in a fishing force sense, the biasing device 30 typically produces a frequency bias that reverses periodically, but periodicity is not necessarily required; i.e., the frequency bias is completely repeatable to provide useful lock-in error reduction. It doesn't have to be of a human nature.

The rotational movement caused by biasing device 30 will be referred to herein as dithering movement.

The actual rotation to be determined by the gyro is defined as an inertial motion input. Therefore, the gyro is connected to the gyro input shaft 2.
The sensor input motion that is actually measured around point 6 is the sum of the inertial input motion and the dither motion.33 Therefore, in order to obtain an output signal that indicates only the inertial input motion, it is necessary to combine the inertial input motion and the dither motion. A means must be provided to distinguish between Such discriminating means are well known and are not shown in FIG. An example of such a discrimination technique is shown in the above-mentioned U.S. Pat. No. 3,373,650; A bias is applied to maintain the frequency between the beams. Near the time when the mechanical bias reverses direction, the sign of the frequency difference changes and the corresponding rate of change dF/dt of the phase W between the beams becomes zero. These times are referred to here as zero velocity crossings and are important in describing the increase in Ronfin error. ;-zero velocity crossing] occurs.

Transcendental function of gyro output angular velocity Equation (1), (21) is a function of the instantaneous phase angle between two beams traveling in opposite directions, the sensor lock-in velocity, and the phase angle measurement offset.Lock To solve equation (1) to obtain the actual amount of in velocity, a time-varying equation for the value C or C is first obtained. It can be given by a varying bias of 1°. Then, the U.S. Pat. No. 3373
A device similar to the bias devices disclosed in the '650 and '3467,472 patents is described. In mechanical biasing devices, the ring laser gyro 100
The base 25 of the base 25 is periodically rotated in one direction and the other in the opposite direction, so that the difference in the frequencies of the two beams traveling in opposite directions is changed in a sinusoidal manner, and the sign thereof is periodically alternated. You will be forced to do so. In such a situation, as the base 25 rotates in one direction, the magnitude of the instantaneous phase angle between the beams increases continuously over time. When the direction of rotation of the base 25 is changed (zero speed crossing), the time-varying frequency difference tends to zero. Each zero speed false crossing is accompanied by a second derivative d"F/dt", and more importantly, the sign of the second derivative matches the direction of the u-turn angle.

FIG. 11 is a graph showing the error resulting from the relationship expressed by equation (5) for a dithered gyro in the zero speed crossing region where the direction of rotation is reversed.

A curve 412 is a graph showing the relationship between the gyro speed output and time, and shows a decrease in the frequency before the zero speed crossing at time T (1) and an increase in the frequency after that. The amplitude of a certain curve 412 depends on the lock-in speed ωI or FL (unit: count) of the sensor.The amplitude of a curve 412 depends on the gyro angle output error E
is obtained by integrating the curve 412. This error E oscillates with varying frequency and amplitude above the change in orientation and represents steps of increasing error angle E1 across the change in orientation. As can be seen from Fig. 11, the error given by equation (5) always exists, but has its most important effect on the zero speed crossing. In the case of a laser gyro, such changes occur twice each dither cycle, and such an error, shown in curve 413, occurs at each zero speed crossing. Unfortunately, in conventional biasing systems, their lock-in errors are not necessarily equal in magnitude and are not always opposite in sign, which often results in errors accumulating in the gyro's output. This is sometimes called random drift or random walk.

The above discussion concerns a mechanically dithered gyro. However, optical tubes or electrically dithered
Since the characteristics obtained are similar to those described above, their description will be omitted.

[Summary of the invention]

The present invention provides a dithering or biasing system for a laser angular velocity sensor to significantly reduce the effects of lock-in. The frequency bias introduced by this improved biasing device is varied so that the frequencies of the two opposing light beams and the phase between them are affected in a predetermined manner. The error accumulated during at least two successive bias periods or dither cycles is brought close to zero. Techniques for varying the amplitude of the frequency bias can be implemented with or without using the random bias principle.

A laser gyro assembly consists of a lasing medium that provides two waves of electromagnetic energy of approximately single frequency, here referred to as light beams, and a plurality of reflective mirrors that form a closed loop path or enclosed area. . The axis perpendicular to the enclosed area is generally defined as the gyro input axis. The two light beams travel in opposite directions along a closed loop path. .

That is, the beams are in opposite directions. A readout device is provided to monitor the frequency difference between the two light beams traveling in opposite directions. The readout device detects the instantaneous phase between two light beams traveling in opposite directions to each other, in order to distinguish between the corresponding clockwise and counterclockwise inertial rotations of the closed-loop path about the gyro input axis. Two detectors are used to distinguish between positive and negative phase changes. Note that the rate of change of phase between the two beams is indicative of the rotational speed, but its zero speed is indicative of lock-in or zero rotational speed.

〔Example〕

In the biasing apparatus of the present invention, the instantaneous phase between two beams traveling in opposite directions is varied during subsequent zero velocity crossings such that the error accumulated over a series of successive dither cycles is approximately zero. Frequency bias is controlled.

Next, the novel bias device NK of the present invention will be explained.

When the inertial input rotational speed is zero, only the sensor rotational speed is generated by dithering movement around the input shaft 26 of the laser gyro, and the laser gyro rotates in a positive sinusoidal manner around the input shaft 26. We will now explain a situation in which the dither is rotated in the opposite direction. FIG. 2 is a graph showing such a situation. Figure 2 shows the actual input dither angle, that is, the gyro input axis 2
The true gyro input angle I (count) centered at 6,
Figure 2 is a graph showing the relationship over time over several dither cycles when the dither movement is completely sinusoidal. It should be noted that "count" corresponds directly to a phase angle change of 2π radians. If there is no gyro lock-in speed, one full dither cycle
After the cycle, the gyro output angle C is zero, so no error or accumulation thereof occurs. Another way to express this is to calculate the dithering of the frequency difference between two beams of light traveling in opposite directions.
This means that the time integral over the period of the cycle is zero. However, as explained with reference to FIG. 11, a cumulative output angle error E occurs due to the long fin.

Although the dither shown in FIG. 2 is sinusoidal, its role in the accumulation of the gyro output angle error E can be properly expressed by considering the dither as parabolic. That is, for a positive dither half cycle, the maximum dither
If we consider an upwardly convex parabola with an angle of 01 and a downwardly convex parabola with a maximum dither angle of 02 in the case of a negative dither half cycle, we can obtain a positive dither angle of 1. A parabola (that is, the gyro inertial input angle) can be expressed by the following equation, and a negative dither angle parabola can be expressed by the following equation. 1 Note that in the following discussion, the unit of the amplitude of the dither angle is 1 count υ, and therefore has the corresponding unit of the phase change between two beams traveling in opposite directions. The dither angle parabola corresponds to the first polarity of d"F/dt2' or d"C/dt", and the negative dither angle parabola corresponds to the second polarity, i.e., d2Vdt2" pole. 5° Corresponding to Opposite Polarity First, the positive dither angle parabola will be explained.

Substituting equation (6) into error equation (5) yields.

Unless the quality of the laser gyro is unacceptably low, the change in error E over several dither half cycles is very small. Therefore, (8)
E on the right side of the equation can be considered to be constant. Then, by time-integrating equation (8) from minus infinity to plus infinity, equation (9) representing the output angle error that increases for a positive dither angle parabola can be obtained.

The above integral is based on Fresnel integral properties.

Similarly, the increasing error expression for negative dither angle parabolas can be found in a similar manner.

For practical purposes, time and 吃2 are approximately equal to 42-, so they can simply be expressed as seconds. However, θl and θ2
Even a small difference between the two can make a big difference in trigonometric functions, so the difference between the two must be memorized.

The total error increment over one complete dither cycle can be expressed as the sum of the error accumulated during the positive dither angle parabola and the error accumulated during the negative dither angle parabola. The sum is ΔE2ΔE and ΔE. Here, (1) θi + − A2−02− is present in A. Using simple trigonometric formulas, equation (12) becomes as follows.

Assuming that the inertial rotation about the gyro input m26 is the only dither motion, equation (13) represents the total incremental gyro output angular error ΔE accumulated during a complete dither cycle.

Due to the error expressed by equation (13), a complete 1-dither
- When the angular displacement around the gyro input shaft 26 is zero during a cycle, the gyro output angle indicates that the gyro has rotated by a certain angle.

In navigation equipment this is indicated by a certain angular rotation. This is of course wrong. The reason for this is that when formula (13) was determined, it was assumed that there was no sensor movement other than dither movement. Each zero speed crossing in each dither cycle constitutes a clock-in error. Therefore, the gyro output angle error resulting from each dither half cycle will be cumulative. As a result, the accumulated (1
:3:) The error represented by the equation is an increasing contribution of the lock-in error, previously referred to as random drift or random 9-oak. If the cumulative error becomes too large when the laser gyro is operated continuously, it cannot be used as a precision navigation device, so it is necessary to minimize the cumulative error or
In the present invention, the cumulative gyro output error angle for each dither cycle, expressed by equation (12) or (13), is the sum of the two beams traveling in opposite directions. can be significantly reduced by changing the instantaneous phase difference between υ by a predetermined value at subsequent zero speed crossings. In the mechanically biased system described above, instantaneous phase differences can be handled by varying the maximum positive and negative dither amplitudes by a preselected amount at subsequent zero speed crossings.

FIG. 3 shows a block diagram of one embodiment of an error cancellation biasing device employing the principles of the present invention. ring·
A laser gyro 100 is coupled to a biasing device 30 via a coupling element 31 similar to that shown in FIG. The biasing device 30 can be constructed in either a mechanical or electrical manner. For convenience of explanation, the biasing device 30 and the coupling element 31 cause the ring laser gyro 100 to oscillate about its input axis 26, causing the vibrations of the two beams traveling in opposite directions within the ring laser gyro 100. Assume a mechanical configuration in which the number bias can be periodically reversed. This can be done, for example, using a motor coupled to the base 25. The bias device 30 is a bias control signal generator 3
It is controlled by a bias control signal given by 2.

The bias control signal applied from the bias control signal generator 32 to the connecting element 33 is applied to the first signal of the first signal generator 34, which produces an output of the form A*+(2πFdt'), where Fd is the desired dither frequency. The signal component and KsIn(2π
FXt) and the second signal component of the second signal generator 35 which yields an output of the form FXt).

36-digit adder 1st. The first . Adding the second signal component. Their combined signal output in summer 36 is a bias control signal that controls bias device 30. FX=Fd
/2, the bias control signal becomes a sine wave signal whose positive and negative maximum amplitudes are periodically changed. The periodic variation in the amplitude of the bias control signal is approximately determined by a second signal generator 35 having a selected amplitude and a selected frequency Fx. The frequency of the sinusoidal change is determined by Fd.

FIG. 4 is a graph illustrating the error-cancelling bias dithering motion of the present invention that significantly reduces lock-in errors in conventional sensor outputs. FIG. 4 shows a graph of the dither motion provided by the embodiment of the invention shown in FIG. is periodically varied by a preselected value determined by a bias control signal provided by . If Fx=Fd/2, the first sinusoidal dither angle shown in FIG. 1 has a positive maximum dither color amplitude θ1 and a maximum dither color amplitude θ
It has 2. The maximum positive and negative amplitudes of the second sinusoidal dither cycle are respectively θ:1. θ4. The third dither cycle is the same as the first dither cycle, and so on. The total incremental gyro output angle error resulting from two consecutive dither cycles is the sum of each incremental error in each half cycle of each dither cycle, equation (9).

(11) can be found by applying (11) to the two successive dither cycles shown in FIG.
4) It can be manipulated by formula.

△E (2 cycles) - △E (θl) + ΔE (θ2) + E
Jθ8)+ΔE(θ4)('14')The total incremental gyro output angle error described by equation (14) for two consecutive dither cycles is It can be reduced to zero.

sin (2π(θ2−E+−> )−−sin(2
yr(θ4−E+L)) (16)8 As before, it is assumed that E is small and approximately constant during the following few cycles. , (15), (16) The relationship shown in equations is θl-θ8=N±172 counts
(17) θ2-04=Ntl/2 counts (18) is always true. In these formulas, N is any integer 1.

Equations (17) and (18) are based on the maximum positive dither angle θ1. θ
3 differs by a partial difference of ±1/2 of the count, and the negative maximum dither thickness θ2. Assuming that the θ numbers differ by ±172 counts, the resulting increased gyro output angle error for two subsequent dither cycles with this relationship is approximately zero. That is, the lock-in error associated with the sensor output is reduced to approximately zero as described above.

It is important to emphasize that only the partial difference in counts between the maximum dither-negative amplitude is significant. The reason is,
This is because the integer part of the count corresponds to the integer 49 part of the 2π phase change between the two beams and has no effect on reducing the lock-in error (Equations (14), (15), (16) )).

Referring again to FIG. 3, the first signal generator 34, when operated independently of the second signal generator 35, causes the ring laser gyro 100 to generate maximum positive and negative dither color amplitudes A. The bias device 3° can be controlled so as to have the following characteristics. When the second signal generator 34 or the first (M) signal generator is operated independently, the laser gyro 100 produces maximum dither.
The amplitude of the output of the second signal generator 35 is selected such that the second signal generator 35 can control the biasing device 30 to have a color amplitude 1/2σ. The sum of the outputs of the first and second signal generators 34,35 constitutes the bias control signal of the bias control signal generator. Using this bias control signal, the amplitude A of the dither angle can be alternately increased or decreased by 1/4 of the count (π/2) by oscillating the rotation of the laser gyro 100 in the positive and reverse directions. to bring the difference between the maximum positive dither-negative amplitude and the maximum subsequent dither-negative amplitude to the desired value l/2(π) of counts, thereby giving equations (15), (1
The bias device 30 is controlled such that the equation shown in 6) is satisfied and the gyro output angle error accumulated over two subsequent dither cycles is approximately zero.

An example of biasing device 30 and coupling element 31 is a spring-mounted electromagnet as disclosed in US Pat. No. 3,373,650. When a pulse is given to the electromagnet, a torque is applied to the spring, which causes it to do ~ The Gyro 10
A dither operation or oscillation is performed in proportion to the magnitude and polarity of the pulse to which zero is applied. Since this spring-electromagnet system exhibits a high Q, a single applied pulse results in several cycles of dithering. Each pulse produces a very lightly damped sinusoidal ringing. When the pulse is combined with a sinusoidally dithered signal, the pulse produces a very lightly damped sinusoidally ringing dither angular amplitude at the dominant dither frequency. Such a system is shown in FIG. .

Another embodiment of the present invention is shown in FIG. 5, illustrating another error cancellation biasing device employing the principles of the present invention.

FIG. 5 is similar to the circuit shown in FIG. 3, except that bias signal generator 532 is used in place of bias signal generator 320 of FIG. Second signal generator 35
Bias signal generator 532 is similar to bias signal generator 3, except that pulse generator 537 is used instead of bias signal generator 3.
Similar to 2. As shown in FIG. 5a, pulse generator 537 provides alternating positive and negative pulses of amplitude P and in phase with the main dither signal generated by first signal generator 34. It can occur. In Figure 5a, curve 50
0 represents the dithering caused by the signal generated by the first signal generator 34 and curve 510 represents the dithering caused by the pulses generated by the pulse generator 537. . The dithering motion obtained by combining the two dithering motions is illustrated by the periodically intensified amplitude C. Second signal generator 537
By appropriately shaping the pulses generated by
A dither motion similar to that produced by the biasing device of FIG. 3 is produced. That is, the bias device #30 causes the laser gyro 100 to vibrate as shown in FIG. This oscillation causes the dither angle to alternately increase and decrease in amplitude by a quarter quanta. In such a situation, the desired difference of half a count between the maximum successive positive dither angle amplitude and the maximum successive negative dither angle amplitude is achieved and accumulated over two successive dither cycles. The gyro output angle error is reduced to almost zero.

The above analysis of equations (9) to (18) is intended to describe the conditions that reduce the accumulated gyro output angle error to almost zero for a cycle group consisting of M dither cycles. Can be generalized.

The mathematical expressions in equations (15') and (16) are expressed in general form by the expression shown in equation (19) for a group of M dither cycles.

In this equation (19), θp is the individual successive maximum positive dither angle amplitude (
count), θn are the respective maximum consecutive negative dither angle amplitudes rcount) in the same dither cycle group, and E is assumed to be small and approximately constant over M dither cycles. . .

Equation (19) shows that if the predetermined values of the maximum positive and negative dither angle amplitudes of a given dither cycle group satisfying Equation (19) are It may be the sum of incremental errors that are nearly zero. For example, if the maximum positive and negative dither angle amplitudes are monotonically and partially increased by one-fourth of a count on each subsequent dither cycle, the cumulative error will be zero over eight dither cycles. That's it. As before, this example uses 4 counts between subsequent maximum dither self-amplitudes.
Only fractional differences by a factor of one are important for trigonometric relationships. Of course, to achieve the above result, the eight positive maximum dither self-amplitudes and the eight negative maximum dither self-amplitudes at the zero speed crossing must satisfy the relationship shown in equation (19). Therefore, there is no need for it to increase monotonically. The eight positive and negative dither amplitudes that satisfy equation (19) can be found from the following equation.

Ai - A+ 1l - 1) count + n count where n = any integer A - some constant amplitude M determined by count - number of dither cycles in the selected group i 1st dither of a group M ~・It is a cycle. Therefore, many possibilities for varying the maximum dither cycle for successive groups of dither cycles are available in order to reduce the cumulative error to approximately zero for each successive group of dither cycles.

As described above, θp and θn in equation (19) are directly related to the instantaneous phase difference between the two beams traveling in opposite directions during positive and negative successive zero velocity crossings, as described above. Therefore, the above considerations also apply to the electrical biasing device, which provides a frequency bias without mechanical rotation.

It should also be noted that the amplitude used in the above equation is the maximum amplitude of the dither cycle. But more importantly, d? Gyro input at /dt or almost zero! 111
When corresponding to near zero sensor input speed centered around 26,
That is, the frequency difference is zero, and it is the dither self-amplitude when changing the sign. Sensor input velocity dVati dither motion plus inertial input motion.

The bias device shown in Figs. 3 and 5 and its corresponding analysis completely adjust the maximum positive and negative dither amplitudes so that equations (15), (16), and (19) are satisfied. to control. However, due to the very small perturbations in subsequent dither cycle pairs, other errors arise that are not included in the mathematical analysis described above. These perturbations may not be random and may be the result of selected biasing devices. To randomize their perturbations, a random signal generator similar to that shown in the aforementioned US Pat. No. 3,467,472 can be used. FIG. 6 depicts another embodiment of the present invention illustrating an error cancellation biasing device utilizing the principles of the present invention and that disclosed in U.S. Pat. No. 3,464,472.

FIG. 6 shows a biasing device similar to that shown in FIG. 3, except that a bias control signal generator 632 is used in place of the biasing signal generator 32 shown in FIG. signal generator 34 in Fig. 3.
Bias signal generator 632 is similar to bias signal generator 32, except that instead of , a first signal generator 634 is used that includes a random amplitude generator 634b and a sine function generator 634a. The first signal generator 634 produces a sine function similar to the first signal generator, except that the amplitude for successive dither cycle pairs varies randomly. The first signal generator 634 may similarly be used in place of the first signal generator 34 of the biasing device shown in FIG.

In operation, the dither device shown in FIG. 6 dithers the gyro for two dither cycles with some random maximum positive and negative dither amplitude. The dither amplitude is approximately constant except for the dithering performed by the second signal generator. The second signal generator varies the maximum dither self-amplitude such that two successive positive maximum dither self-amplitudes and two subsequent negative maximum dither self-amplitudes differ by one-half count. . Next, the amplitude of the first signal generator 634a is randomly varied and the next two
is held constant for two dither cycles, and so on. In this way, the errors resulting from perturbations in the biasing device are randomized so that their average value is greatly reduced.

In the above discussion, it was assumed that the laser gyro had only dither motion and zero inertial input motion. Here, the sensor input motion about the input axis of the laser gyro includes an inertial input motion with a constant rotational speed Ib, and the amplitude between two subsequent dither cycles is equal to 2 minutes of kacunto as described above. Let us consider a situation in which a laser gyro is subjected to dithering motions that differ by 1. This situation is illustrated graphically in FIG. In this graph, the base motion is a constant rotational speed Ib according to the following equation (20).

Ib=ix4Fd (21J) Here, Fd is the periodically inverted dither frequency, lit
is the angular increment of inertial input rotation in one quarter of the dither cycle.

In FIG. 7, the two consecutive maximum positive input angular amplitudes can be mathematically described by the following equation. .

Al=A+↓+l-31r21) where ■ is the angular rotation in the middle of the dither cycle and A is the normal input dither angular amplitude emphasized and canceled by the 1/4 count. Further, the subsequent maximum negative phase angle amplitude can be expressed by the following equation.

A2=A+--xis (Zri(2
1'), by substituting equation (22) into equation (13) and then adding the errors during the two successive dither cycles, we get the cumulative error (quant) resulting from the two successive dither cycles. The following formula is obtained for .

44n2π(A+'-I -E+ i) 15ln2π
(A--!-+x+E+t)+gln27r(A-
---I-E-31)), (23) From the trigonometry theorem, equation (23) becomes as follows.

Equation (24) shows that the error accumulated during two or more successive dither cycles when base motion is present is a function of the inertial input motion. When the speed of base movement is low, the biasing system shown in Figures 3,5-6 is far superior to conventional systems. On the other hand, when the velocity of the base motion is relatively high, the error cancellation biasing system of the present invention causes the total Ronfin error, which is the sum of all ΔE's, to increase as the inertial input velocity increases. This is undesirable at high inertial input speeds.

This is because it does not take into account the effect of inertial input velocity on the open loop control of the bias applied by the error canceller.

FIG. 8 shows a block diagram of another embodiment of the error cancellation biasing device of the present invention. This embodiment uses closed loop control 1. The apparatus shown in FIG. 8 provides the desired bias control taking into account the effects of inertial input speed. In FIG. 8, laser gyro 100 is coupled to biasing device 30 via coupling element 31. In FIG. Bias device 30 is controlled by a bias control signal provided by bias control signal generator 832. The laser gyro 100 includes a phase angle detector 800 and a coupling element 801.
and a phase angular velocity detector 802
are coupled via coupling element 803. This phase angle detector 802 produces an output signal whenever the phase angle between the light beams of the gyro 100 passes through zero (aVdt=o 2 ). Therefore, the output signal exhibits a "zero velocity crossing" or phase angle. This "zero speed crossing" is the same as described above.

The output signal of phase angle detector 800 is processed by error signal element 900. This error signal element 900 is a sample
6. Including hold circuit 804; The sample and hold circuit samples and holds the output value of the phase angle detector 800 at the zero velocity crossing indicated by the output signal of the phase angular velocity detector 802.

Phase angular rate detector 802 provides a gate signal to sample and hold circuit 804 via coupling element 805 .

Error signal element 900 includes a signal processor 875. The signal processor 875 is responsive to the output provided by the sample and hold circuit 804, and the output of the error signal element 900 is connected to the bias control signal generator 83 via a coupling element 810.
given to 2. Bias control signal generator 832 generates a bias control signal in response to a signal applied thereto.

Equations (12), (13), (2
4), the accumulated gyro output angular error is significantly smaller if the instantaneous phase angle between the second light beam at the zero velocity crossing differs by a selected value of plus or minus π radians. I said that it would be done. The closed-loop biasing device shown in FIG.
'17), (18) and (19), the values at successive zero crossings of the instantaneous phase angle between two beams traveling in opposite directions are The differential a'%tit'' has the same polarity as the polarity of the differential a'%tit'' and is chosen to have a lock-in error of plus or minus π radians such that the accumulated lock-in error over two subsequent dither cycles or bias reversal cycles is approximately zero. (the polarity of the second derivative corresponds to the same polarity of the dither angle in the mechanical embodiment).

Therefore, the lock-in error contained in the sensor output is substantially reduced to zero.1 The principle of closed-loop control for realizing the closed-loop biasing device shown in FIG. 8 is shown in the graph of FIG. 9. To explain this principle, we will again use a mechanical biasing device, but an electrical biasing device can be used as well.1 This biasing device is an electromechanically operated device. ,
Coupling element 31 comprises one or more leaf springs or other similar coupling elements to cause laser gyro 100 to oscillate about gyro input axis 26 in positive and negative directions and dither. Configure exercise. Such a system is assumed to be the high Q spring-mass system described above.

Assume that there is a certain input base motion rate and that there is a certain dither negative amplitude growth rate.

Let the input base motion rate be R counts per dither cycle and the amplitude growth rate be M counts per dither cycle. Then, as disclosed in U.S. Pat. No. 3,373,650, a fully sinusoidally dithered gyro has the following maximum and minimum dither negative amplitudes: Exist throughout.

AI = R-3/4 (, R+M') A 2 = N+ 1/4 (R-M) A8=P+1/
4 (R+M) A 4 =N+ 3/4 (M-R) where P, N represent the maximum positive and negative dither amplitudes (counts).

Here, it is assumed that pulses are applied as shown in FIG. The magnitudes of these pulses, X and Y, permanently increase the dither negative amplitude by X, Y. This is roughly similar to the situation when the biasing device is the high Q spring-mass system described above.

As shown in FIG. 9, pulses X, Y are applied synchronously with two dither cycles.

A pulse of amplitude 1'+x-1 is applied at point 1, i.e. at the start of a positive dither cycle, with amplitude I'-X
A pulse of l is provided at point 3, which is the start of the second subsequent positive dither cycle.

Furthermore, a pulse of amplitude 1+y-1 is applied at point 2, at the start of the negative portion of the first dither cycle;
At point 4, at the start of the negative portion of the second subsequent dither cycle, a pulse of amplitude 1-Y'' is applied. 3 In the high Q spring-mass system described above, in the absence of perturbations or random errors, the dither motion will alternate between values that differ by a selected value depending on the magnitude of the pulses X and Y. Indicates peak amplitude. If X and Y are chosen appropriately, the instantaneous phase angle between the two beams is given for two subsequent zero velocity crossings of the same polarity (same dither polarity) of d 2V/d t can be varied by the amount, for example, π radians.

The combination of the pulses X, Y with the four successive thicker amplitudes Al, A2, All, A4 at the four successive zero speed crossings specified above are expressed mathematically as follows.

A'l =P-3/4 (R+M)+Xλ22N+1/
4(RM)+X-Y 18 = P+1/4 (R+M)+X-Y-x=P+
1/4 (R+M)-Y6 = N+3/4 (M-R
)+(X-Y-X+Y)-N+3/4 (M-R)(2
5) Applying the principles of the invention, the accumulated gyro output angular error E will decrease significantly to zero for two subsequent dither cycles, given that their maximum amplitudes differ by 1/2 of a count. Can be made smaller. Maximum amplitude A'1.
The relationship between λz, A'a, and 7N4 is A'8 = 7(
+ -1/2 If the above conditions are true and equation (25) is solved for x and y, the following is obtained.

Note that the amplitudes of pulses X and Y do not need to have a wide range of variation. The reason is that the strength of those pulses can be varied by any integer number of counts.64 It is only the fractional part of those counts that matters. Therefore, X,! : A range of 1 1/2 counts to +1/2 counts of the magnitude of Y is sufficient. .

Next, assume that the amplitudes of pulses X and Y are modulated such that equation (27) applies to any inertial input motion and/or any rate of dither angular amplitude change. It remains to determine the appropriate error signal to use to modulate the X and Y pulse generators. In particular, assuming that there is an error between X and Y by the amounts "x" and [y-1, (
28) The equation changes as follows.

Then, A"l=P+1/4 (M-3R)+1./2+x82N+3/4(,M-R) is obtained.

As a result, we get . Then, since modulation errors rXl and I-yJ are introduced, the equation expressed by equation (26) is no longer equal. Taking the sine on both sides of equation (31), sin 2π
(λ'a-A't)=a2π(x+y)
(32) sln2π():'4-4'z)-sIn2r
Since r(x-y)A=I or θ+1/8, (
4) Using the fact that the equations are equal, λ'1=C1-E+1/8 A''2=-C2+E+1/8 λ'8=CB-E+1/8 becomes '--C4+E+1/8. where CI, C2, Ca, C4 represent the instantaneous gyro output phase angles at four consecutive zero speed crossings. Substituting this into equation (32) yields the following equation.

5tn2π(C3-CI)=sfn2zrCx+y'
, ) (32a) sin2i(C4-C2)=
stn2π(y-X') (32b) Expanding the left side of these equations, we get (sb+2πC3)(cos2πC1) (cos2π
C3) (sln2πc1) = 龜2π(x+y) (dn2zrC4) (cos2πc2) − (cos
2πC4)(s1n2πC2)=mln2π(,y−x
) (33) is obtained.

According to equation (33), the error variables rx-+ and r, which depend on the sine and cosine values of the instantaneous gyro output phases between the light beams traveling in opposite directions at the four successive zero-velocity crossings,
A pair of simultaneous equations for determining y-1 is obtained.

The values of the trigonometric functions CI, C2, CB, and C4 are obtained at the output terminals of the detectors 22a, 22b, as shown in FIG. The detected quantities are separated by 1/4 of the interference stripe spacing. This spacing allows one detector to represent the sine value of the instantaneous gyro output phase angle between the light beams, and the other detector to represent the cosine value of that phase angle. Of course, there is a certain tolerance for the value of one-fourth of the interfering spacing, which will result in a small but negligible error.

Now assume that the output of detector 22& represents the sine of the phase angle between the two beams, and that the output of detector 22b represents the cosine of that same phase angle. Assume that the output is expressed by the following equation.

Un = A5 stone 2π(,Cn+α,)Vn =B
CO92ff(Cn+β) where n is the amplitude number 1 at the subsequent zero speed crossing,
2,3.4.

Nominally, input = -B and α = β. Here, A.

B represents the gain value of the detectors 22a and 22b, α and β are 1
/4 Represents the phase angle tolerance of interference fringe spacing. Here, the discriminant functions U8Vl −UIV8 and U4V2− U2V4
I will think about it. Since there is no limit on A, B, α, and β, 8k = UIIV■−UxVa=AB(sln2π(
C3+α) cos 2π(CI+β)−sin2ff(
C1+α) cos 2π(C3+β)) S2 = U4V2-UzV4=AB(sln2f (
C4+α) cos2π(C2+β) 5ln2π(C2
+α)cos2π(,C4+β)) From the trigonometric formula, the right sides of 31 and Sz are as follows.

S1=ABmn2π(C3-CI)cos2π(α-
β) 8! =ABsln2π(C4-C2') cos2π
(α−β) Therefore, the formula (32a', ), (32
b), 5l=ABcos2π(α+β'
)sln2yr(C3-C1)-A B cos 2π
(α-β')sIn2π(x+y)Sz=ABcos2
π(α-β)sIn2π(C4-C2)=ABcos2
π(α−β)! 11n2π(y-x). here,
Assuming that y and X are quite small, it can be written as Sl2K(x+y) S22K(y-X). Here, K=2πABcos2π
(It is α-th. Therefore, x = ('81-82)/2K y = (Sl+S2)/2.

Because X and y represent errors in To obtain the correct pulse amplitudes X and Y, x and y must be subtracted from X and Y, respectively. That is, X = X-x=X-(S 1-82
)/2KY'= Y-y=Y-(Sl-82)/2 This means that for a signal with zero error, X and Y are kept constant; otherwise, the error is This means that X, Y are modified by adding or subtracting increments x, y to modulate the Norculus amplitudes X, Y as commanded by the signal.

The error signals 31 and 82 are triangular multivalued ambiguities.
nometric multivalue ambig
Note that it has ``utility''. That is, the error signal has two amplitudes (C8 and C1 in the case of 81
In the case of S2, the error signal disappears not only when C4 and 02) differ by 1/2 count, but also when both amplitudes are equal. In other words, the zero error signal for X,.y is also returned when there is an error of 1/2 count.

Therefore, it is sometimes necessary to increase the error signal by 1/2 count. This ambiguity can be identified by performing another analog calculation.

That is, a = lUl+Ull IJ-IVl+Vll 1H
= lU2+U41+1v2+v+ If lG exceeds a certain threshold (for example, G'>1/2(1-B
)) Add 1/2 count to 81, and if H exceeds a certain threshold, add 1/2 count to 82.

FIG. 10 is a more detailed block diagram than FIG. 8 of a closed loop error cancellation biasing device employing the principles of the present invention. This closed loop error cancellation biasing device operates similarly to the biasing device shown in FIG. 8 and utilizes the control method described with reference to FIG. 9 and the control technique for equation (25). The closed loop biasing device shown in FIG.
, 8 assume an electromechanical biasing device exhibiting a high-Q, single-mass system similar to that shown in FIG. In FIG. 10, ring laser gyro 800 is mechanically biased via coupling element 31 from biasing device 30. In FIG. Bias device 30 is controlled by a bias control signal provided by bias control signal generator 832. Closed loop biasing device 10 of FIG. 10 includes an error signal generator 900.

The error signal generator 900 provides an error signal to the bias control signal generator 832 in response to the gyro output phase angle relationship between the two beams traveling in opposite directions. This completes the closed loop control system.

Bias control signal generator 832 includes an adder 836, an X-pulse generator 835, and an X-pulse generator 837. Adder 836 is similar to first signal generator 34 of FIG.
The output signals from signal generators 834 similar to . X pulse generator 835 and X pulse generator 837 generate pulse signals. Those pulse signals are sent to the adder 8
36 to the output signal of dither signal generator 834. The output of adder 836 is the bias control signal from bias control signal generator 832 and is provided to bias device 30.

Bias signal generator 832 receives an error signal from error signal generator 900. This error signal generator 900 includes a signal processor 875 and a sample/hold gate 804a.
, 804b, and signal storage devices 807a, 807b.

Signal processor 875 is responsive to the gyro output phase angle between two light beams traveling in opposite directions to determine the phase -/D.
- Process the angular data and generate an output error signal X that modulates the X-pulse generator 835 and an error signal y that modulates the X-pulse generator 837.

The biasing device of FIG. 10, like the biasing device shown in FIG. 8, requires the value of the phase angle W of two light beams traveling in opposite directions at the zero velocity crossing.

Furthermore, the control method used in the apparatus of FIG. 10 utilizes the sine and cosine values of the phase angle at the zero speed crossing. In FIG. 10, a laser gyro 800 similar to laser gyro 100 (FIG. 1) includes photodetectors 22a, 2.
2b is provided. The photodetectors 22a, 22b are separated from each other by a distance of 1/4 of the spacing of the interference fringe patterns and constitute a phase angle detector that generates signals indicative of the sine and cosine of the phase angle between the two beams. . The output terminal of the photodetector 22& is connected to a window comparator 841 via a time differentiation circuit 845a.
The output terminal of photodetector 22b is coupled to window comparator 843 via time differentiator circuit 845b. The output terminals of these window comparators are logically combined by an AND circuit 844. Window comparators 841 and 843, differential 77-76- dividers 845m and 845b, and AND gate circuit 8
44 performs the function of the phase angular velocity detector 8θ2 shown in FIG.

As shown in FIG. 10, an error signal generator 900
The sample and hold circuits 804a and 804b are gate-controlled by the output of an AND gate 844.

The output of the photodetector 220 is applied to the sample and hold circuit 804a, and the output of the photodetector 22b is applied to the sample and hold circuit 804b. The output of each sample and hold circuit 804a, 804b is provided to a temporary storage device 807m, 807b, respectively. These sample and hold circuits and temporary storage devices can be of analog type, digital type, or a combination thereof; however, for purposes of illustration, the sample and hold circuit 804m
, 804b are output to the photodetector 22a.

Let us consider this as a digital representation of 22b. Storage bag 98
It is assumed that 07m and 807b are normal digital memory circuits.

The outputs of temporary storage devices 807a, 807b are processed by signal processor 875 of the error signal generator. The signal processor 875 performs the calculation described above for equation (25) in order to extract the output control error signal indicating X and y in equation (25). The error signals x and y are generated by the X pulse generator 8.
35 and X pulse generator 837, respectively. The error signals x and y are generated by the X pulse generator 83 as described above.
5 and X pulse generator 837, respectively.

Since window comparators 841 and 843 are similar to each other, only window comparator 841 will be described. Illustrated in FIG. 10a is one embodiment for constructing a window comparator. 10th
Referring to figure a, window comparator 841 is connected to comparators 842a and 8
42b. Comparators 842a, 842b may be conventional operational amplifiers or other devices used as simple comparators to compare the levels of two signals. A differentiator 845a is connected to the positive input terminal of the comparator 842a.
output terminal is connected. The output of differentiator 845a is also connected to the inverting input terminal of comparator 842b. Comparator 84
The inverting input terminal of comparator 842b is connected to reference voltage [+1, and the non-inverting input terminal of comparator 842b is connected to reference voltage [-1. The outputs of the comparators 842m and 842b are the NOR gates 8
46.

Next, the operation of window comparator 841 will be explained. As long as there is a constantly changing phase of sufficient velocity (dF/dt) between the light beams, the output of phase differentiator 845a can be positive or negative, and its magnitude is a sufficiently small amount ε greater than a preselected value such as . In this situation, the output of one (but not both) of comparators 842a, 842b is at a high voltage level corresponding to a logic one (11'').

The output of NOR gate 846 is logic o in this situation.
('rOJ). On the other hand, zero speed crossing #/dt
is zero, the output of differentiator 845a falls to a value lower than the positive or negative value of ε, and comparators 842a and 842
The output of b becomes "0". In this situation, the output of NOR gate 210 becomes [1-1.

Window comparator 843 is connected to the output terminal of phase differentiator 845b. This window comparator 843 performs the same operation as described for window comparator 843 in response to the output of photodetector 22b. That is, when the rate of change of the phase angle between the light beams is higher than the threshold of the window comparator, the output of the window comparator 843 is always 1-0, and the rate of change of the phase angle is higher than the threshold ε. When it is lower, it is [1-1.

Next, the operation of the closed loop bias device shown in FIG. 10 will be explained. Photodetectors 22a and 22b are arranged at a distance of about 1/4 of the interval between the interference fringe patterns. The output of the photodetector 22a can be considered as the sine of the phase angle between the two light beams traveling in opposite directions, and the output of the photodetector 22b
The output of can be thought of as the cosine of the phase angle between the same beams of light.

At the zero speed crossing, the output of comparator 841.843 is "1". The reason for this is that since the time rate of change of the phase angle is zero, the value is between +ε and -ε. In this situation, since each output of window comparators 841 and 843 is [11], the output of AND gate 844 is "1".

However, in all other situations, the output of AND gate 44 is ``0-1'', providing a constantly applied dithering motion.
When it changes to 1, the sample and hold circuits 804a, 8
04b is gated and whatever is applied to its input terminal is sampled and held temporarily until the next gate, which occurs at the next zero speed crossing. Thus, the sample and hold circuit samples the outputs of photodetectors 22a, 22b, which represent the sine and cosine, respectively, of the phase angle between the light beams when each zero velocity crossing occurs. do. The outputs of the sample and hold circuits 804a and 804b are stored in a storage device 807a,
807b and then processed appropriately by signal processor 900.

Signal processor 900 combines the instantaneous phase angles from photodetectors 22a, 22b at subsequent zero velocity crossings to provide output control error signals X and y, as described with reference to equation (34). . The signal processor 875 uses the formula (3
The signal processing device 875 can be of either an analog type or a digital type, as long as it can perform arithmetic operations such as those described for solutions of simultaneous equations when explaining 3).

Continuing the discussion, it is important to identify the unipolarity of subsequent zero velocity crossings associated with the instantaneous phase angle during each portion of the dither cycle between two beams traveling in opposite directions. Hereinafter, we will refer to successive positive zero speed crossings as zero speed crossings where d 21F/d t '' is positive, and zero speed crossings where d 2F/d t 2 is negative. In a bias device, the positive and negative zero velocity crossings occur at the time the direction of rotation changes from the first direction to the second direction, and at the time the direction of rotation changes from the second direction to the first direction. Referring to FIG. 9, for example, successive positive zero velocity crossings correspond to dither negative amplitudes AI, A8, and successive negative zero velocity crossings correspond to dither negative amplitudes A2, A4.

Here, there is no inertial input motion, and bias control signal generator 832 provides a bias control signal to bias device 30 for each of two subsequent zero speed crossings of the same sign (i.e., positive or negative zero speed crossings). ) such that the instantaneous phase angles between the two beams at ) differ by exactly one-half count, or earth π radians. In this situation, the output signals x, y are zero, the X pulse generator 835 and the X pulse generator 837 remain constant, and the cumulative gyro output angle error is approximately zero, referring to FIG. The equations associated with FIG. 3 operate as described above.

We will now discuss the response of the closed loop biasing device shown in FIG. 10 in situations where there is some inertial input motion to the device shown in FIG. In this situation, the instantaneous phase angles between two consecutive zero velocity crossings of the same sign no longer differ by .pi. radians. In this situation, the signal processor 900 uses the X-pulse generator 835
The X value of the X pulse generator 837 and the Y value of the X pulse generator 837 are quickly given as appropriate X signal values and Y signal values.
The values of X and y are again set to zero. Therefore, the laser gyro is configured such that the phase angles between the light beams for subsequent zero velocity crossings of the same sign differ by π radians so that the total error accumulated over two dither cycles is approximately zero. X and y provide the closed loop error signal required for closed loop operation of the biasing device. Of course, this means that the lock-in error contained in the output of the sensor is also reduced to approximately zero.

The control technique described throughout by equation (25) and included in the embodiment shown in FIG. It should be noted that this is only one example of a control technique. In particular, the combination of error signal generator 90 and bias control signal generator 832 detects the instantaneous phase angle at the previously occurring clockwise peak phase angle and the instantaneous phase angle at the counterclockwise peak phase angle. Based on
Their instantaneous phase angles must be controlled.

The error signal generator 900 and the control strategy imposed thereon ensure that subsequent zero-velocity crossing values significantly reduce the lock-in error in the output signal typically associated with ring laser gyros, according to equation (19). Can be given a predetermined value. Additionally, although the embodiments described above use mechanical biasing techniques, electrical/optical techniques may also be used to reduce lock-in errors, as described above. Although the lock-in error reduction described above uses zero velocity cross phase angle information, other selected phase velocity points can also be selected. This is within the scope of the invention.

Briefly summarized, the lock-in error characteristic of a dithered or reverse biased ring laser angular rate sensor is the instantaneous phase difference between two oppositely traveling optical beams at subsequent zero velocity crossings. By controlling , it is canceled out. In particular, in the mechanically biased type, this can be handled by changing the amplitude of the clockwise and counterclockwise peaks, ie, the maximum amplitude, of the rotational vibration caused by the biasing mechanism. FIG. 8 shows a closed loop controller in which the actual phase angle at the zero speed crossing is detected and utilized for closed loop controller input and synchronization. FIG. 10 is a detailed block diagram of the control device shown in FIG. 8.

In this device, a biasing device for forward and reverse rotation of a ring laser angular velocity sensor is provided with a signal that causes a sinusoidal motion and a series of control pulses that control the phase angle as desired at the zero velocity crossing. .

Figure 12.13 shows a ring laser angular rate sensor arrangement that provides substantially the same closed loop control error cancellation biasing as is done by the arrangement shown in Figure 10.8. However, the apparatus shown in FIGS. 12-13 does not directly obtain phase angle information from a phase angle monitor, but instead utilizes a combination of velocity information and bias information signals.

FIG. 12 shows substantially the same as that shown in FIG. 1, except that the detector parts (FIG. 11), including detector 22 and combination prism 21, are separated from the ring laser portion of the sensor. The same ring laser angular velocity sensor 110
0 is shown. supplied by the laser medium 10;
A support mechanism 1101 supports waves 11 and 12 that propagate along a closed loop path composed of reflecting mirrors 13 and 14°15VC.
Supported by.

The base 1125 includes a combination prism 21' and a detector 22.
is fixed. The output of this detector 22 is transmitted to the signal processor 11
Given to 24. This signal processor supports ill 1
The 1° support mechanism 1101 and the base 1125 have a pivot axis substantially parallel to the input axis 26, which generates an output signal indicating the rotational speed of the entire angular velocity sensor device 1100, which is composed of the angular velocity sensor device 1100, which is composed of the angular velocity sensor device 101, the base 1125, and related parts. A rotary vibration mechanism 1130 is coupled to the support mechanism 1101 to vibrate the support mechanism 1101 in a rotational mode relative to the base 1125 approximately around a reference axis (not shown) that defines the base 1125 .

The device shown in FIG. 12 that has been described thus far is substantially similar to the device shown in U.S. Pat. No. 3,373,650, and is sometimes referred to as an in-case readout ring laser gyro device. In such devices, the signal processor 1124 generates a signal indicative of the rotational speed of the entire device 1100, but typically excludes the rotational motion caused by the rotary vibrator $1130. Devices of this type are well known in the art.

Also shown in FIG. 12 is a rotational vibration detector 1140.

The output signal of this rotational vibration detector 1140 is provided to a bias control signal generator 1150 via a connecting element 1141. The output signal of the signal processor 1124 is also provided to the bias control signal generator 1150 via a connection element 1142. A bias control signal generator 1150 connects a bias control signal to a rotary vibration mechanism 1130 through an element 1151.
Give through.

The rotational amplitude detector 1140 detects, in response to the rotational movement of the support mechanism 1101 relative to the base 1125, a clockwise rotational amplitude about a fixed reference axis that is arbitrarily defined as a non-moving reference, i.e., an uninduced rotational vibration. and a signal indicating the counterclockwise rotation amplitude is generated.

Bias control signal generator 115, as described below.
0, the signal processor controls the rotary oscillation mechanism 1130 to accurately control the subsequent zero velocity cross phase angle in a manner similar to that previously described to provide an error cancellation bias. A bias control signal is provided by combining the output of the rotational amplitude detector 1124 indicating speed information and the output of the rotational amplitude detector 1140 indicating rotational motion information. As explained in the explanations 1 to 1 above, 1 such as the rotary vibration mechanism 1130
Two types of biasing devices are generally shown in US Pat. No. 3,373,650. Support mechanism 1101 is attached to base 1125 via one or more springs 1131 or torsion elements such that sensor 1100 is essentially a high-Q spring-mass system. In such high Q devices, rotation is caused by a transducer 1132, such as a piezoelectric element attached to a spring and bending the spring. The transducer bends the spring in response to a control electrical signal to move the support mechanism 1101 to the base 11.
Rotate against 25. The pulses applied to the transducer 1132 of the rotary vibration mechanism 1130 effectively cause many cycles of rotational vibration since the device is a high Q spring-mass system. Each pulse produces a very lightly damped sinusoidal ringing. If the pulses are applied synchronously, the peak amplitude following the pulse can be controlled, which is approximately shown in the analysis of equations (24)-(28).

Let us now consider induced rotational vibrations similar to those shown in FIG. The signal applied to the rotary vibration mechanism is such that a first component of the control signal applied to the rotary vibration mechanism causes the sensor to dither sinusoidally at a first frequency. The second component of the applied control signal is applied alternately in combination with Y pulse trains, synchronized with a sinusoidal dither at the first frequency at points 1, 2, 3.4. is given by X pulse trains.

Next, the operation of the rotational vibration generated by the applied pulse train as described below will be explained.

(a) Randomize the amplitude of the pulse given to point 1 (Figure 9).

(b) Apply pulse +Y to point 2.

(C) Pulse-X7&: Add to point 3.

(di pulse-Y is added to point 4.

(,) Repeat steps (a) to (d).

The desired values of the magnitudes of X and Y for the Ronfin error cancellation bias are those described above in connection with equation (28).

X = M + 1/2 (28) and Y = R where M - dither - amplitude increase rate (clockwise and counterclockwise peak amplitude of induced rotational vibrations), R - rotation of the sensor device The speed is .

The above shows that the magnitudes of the X and Y pulses are adjusted for the dither period of the next two cycles based on the observed dither rotation and velocity induced during the previous two cycles. It can be expressed as an error correction control plan, such as This plan can be described mathematically as follows.

X(new) = X('1ist) + x
(101)Y(new) 2Y('1ast)
+ y (102) Here, ! -(1/2) (1+D3+D4-DI-02)
(103)y=-R+(1/2)(D2+D3-DI
-04) (104) DI and D3 indicate the magnitude of two consecutive peak clockwise amplitudes, D2. D4 indicates the magnitude of two consecutive peak counterclockwise amplitudes. Their amplitude magnitudes were those detected by rotational amplitude detector 1140 during the previous two dither cycles. R indicates the input velocity determined from the normal stripe pattern reader provided by detector 2z and signal processor 1140. The error term x+7 is similar to the error term shown in equation (31), which is a function of the magnitude of the input angle, and can be equal to the zero velocity crossing C.

As shown in the mathematical analysis of equation (24), the device provides an error cancellation bias. As indicated earlier in this specification, the application of an error cancellation bias is achieved by varying the phase angle between the optical beams for successive zero-velocity crossing pairs of the same sign by plus or minus π radians, so that the two dither 1, which, of course, means that the lock-in error associated with the output of the sensor is reduced to approximately zero. When the inertial input rotation to the sensor device 1100 is large and R is zero, following a random pulse < Generates a phase angle difference. The dither amplitude fluctuations that occur according to the control plan are corrected by "x" which is based on the response of the system to past values of the X pulse. On the other hand, sensor 11
00 ノ[lEThe perturbation of the system including the presence of rotation is (2
8) Compensated by the value of the X pulse determined by the formula.

A more detailed embodiment of the bias control signal generator of the apparatus shown in FIG. 12 is shown in FIG.

The bias control signal generator 115o is connected to the amplitude storage device 131.
0, dither speed detector 132o, rX,j error calculator 1325, ryJ error calculator 1326, X pulse calculator 1330, X pulse calculator 1331, storage device 1340, synchronizer 135o, , random pulse generator 1360, and digital-to-analog ('D/A)
It consists of a converter 1370, a sine function generator 138o, and an adder 1390. As is well known in the art, many parts of the block shown in FIG. This can be achieved with just one step.

The output of the rotational amplitude detector 1140 is
This is a signal indicating the angular displacement between the base 1125 and the rotation reference axis. This signal represents the magnitude and sign around a zero or steady state reference axis.

This information can be provided by various transducers coupled to device 1100 via coupler 1135. The output of rotational amplitude detector 1140 is provided to amplitude storage 1310. The output of this dither speed detector is provided to a synchronizer 1350 and an amplitude store 1310. Dither rate detector 1320 is essentially a differentiator circuit responsive to amplitude detector 1140. In operation, the dither speed detector 1320 detects zero speed, the speed at the turning point of the dither motion, ie, the point at which the dither rotation changes direction. At the instant when the direction of the dither rotation changes, the amplitude storage device appropriately stores the value of the angular displacement at the time of the rotation and stores four successive values, namely two peak clockwise amplitude values and two counterclockwise peak amplitude values. memorize the value. At the same time, the output of dither speed detector 1320 is provided to synchronizer 135o so that pulses X and Y are synchronized at the dither rotations. More specifically, 1 is given intermediately between the occurrence of a peak amplitude and the subsequent occurrence of another peak amplitude of a different sign.
The output of the amplitude storage device 1310 is [x] error calculator 13
25 and 1°[y
-1 error calculator 1326 also receives speed information, which is a signal indicating speed R, from signal processor 1124. The IX1 error calculator 1325 and the 1-y-l error calculator 1326 are calculated using the formula (10
3,).

Perform the mathematical calculation approximately described by (1Oa). 1-x'' error calculator 1325 is provided to an X-pulse calculator 1331. This X pulse calculator is (101
) performs the mathematical function described by the formula. 1-yj
The output of error calculator 1326 is provided to X-pulse calculator 133°. Y pulse calculator id: (102)
Perform the mathematical function described by the formula. The outputs of the X-pulse calculator 1331 and the X-pulse calculator 1330 provide storage for storing the values of X and Y (hereinafter referred to as Each is stored in the device 1340.

To the synchronizer 1350, the X pulse calculation,
An input representing a random pulse value provided by a random pulse generator 1360 is provided.

Synchronizer 1350 converts the values determined by X-pulse calculator 1331, X-pulse calculator 1331, and random pulse generator 136 into digital-to-analog converter 137.
0 and its digital-to-analog converter 13
The output of the TO is applied to the rotary vibration mechanism 1130 via an adder 1390 as a component of a bias control signal. Adder 1390 adds the pulses provided by digital-to-analog converter 1370 to the signal provided by sine function generator 1380 to move support mechanism 1101 to base 1.
125, it is dithered sinusoidally with approximately constant amplitude and a first frequency. The first frequency is approximately the resonant frequency of the spring-oscillation system. .

Note that the output of the sinusoidal function generator 1380 represents a sinusoidal drive signal that is part of the bias control signal to maintain the oscillatory rotation of the spring-oscillator system that makes up the sensor 1100. The plotter 1380 can be comprised of a variety of devices for causing such motion. In particular, in order to maintain such oscillations, it is well known to take the output of a rotational amplitude detector through a closed-loop feedback controller so as to amplify and phase shift the output of the rotational amplitude detector. .

The operation of the closed loop error cancellation bias provided by the apparatus shown in Figure 12.13 will now be described. Two dithers with a pulse train approximately shown in Figure 9.
Explain how the cycle works.

The first pulse in the two dither cycles is random and the device is running at times. The synchronizer causes the laser gyro device 1100 to dither with the value provided by the random pulse generator 1360, i.e.
In combination with an oscillating sinusoidal signal, it can be applied at point 1.

Before applying the "10Y pulse" at point 2, the amplitude memory stores the information of the previous two peak clockwise dither amplitudes represented by Dl and D2 and the previous two peaks represented by D2 and D4. Contains counterclockwise dither amplitude information. Their amplitude values were determined when the dither rate detector determined the turning point (dither rate -0) in the previous two dither cycles. 1-X1
An error calculator can perform that calculation, similarly, l
-y-1 error calculator can perform calculations of velocity information values. Next, the Y pulse calculator 1330 adds together the previously added magnitude of Y, the value of Y (list). The Y(list) is the value added to the y error calculation during the previous two dither cycles. This pulse magnitude is applied at points 2 and 4, except for the opposite polarity shown in FIG.

In a similar manner, the X-pulse calculator 1331 calculates the value of the next X-pulse and returns the result at point 3, obtained in the previous two dither cycles and stored in Based on the previous value of X given, add it to the value determined by the X error calculation. The values determined by Y pulse calculator 1330 and X pulse calculator 1331 are then stored in storage 71340 (denoted by Y(1ast) and - prepare for the next determination of the pulse in the cycle 13 This process repeats itself continuously.

Although not shown in FIG. 13, a well-known central processing block is provided which controls the transfer of information from the plurality of calculation blocks and storage blocks shown in FIG.

Synchronizer 1350 receives input from dither speed detector 1320 indicating when the dither motion turns. Synchronizer 1350
One example is the time between successive turns, i.e. the clockwise peak amplitude or turn point, so that the appropriate pulse X or YA pulse generator or random pulse generator determines the time after the turn point to apply. and the counterclockwise peak amplitude or turning point. Note that the sign function generator can equally be used as a means to synchronize the input via synchronizer 1350 in place of the input provided by the dither speed detector. In this case, the sine function generator 138
Zero output from 0 indicates the point in time during which the peak rotational amplitude is induced when a pulse should be applied. Of course, there are many possibilities to synchronize those pulses to the turn times.

In some situations, it may be desirable to offset the times at which pulses X, Y and the random pulses are applied to a time midway between the turn times as shown in FIG. This has the advantage that losses and time delays in the entire device can be compensated for.

The embodiment shown in Figure 12.13 allows subsequent zero velocity crossings of the same sign to differ by a predetermined value so that the instantaneous phase angle between the two light beams is not directly measured.
Figure 2 shows how a closed loop error cancellation biasing device can be constructed to control the phase angle of a light beam so that the total error accumulated between two dither cycles is approximately zero. . That is, the apparatus shown in FIG. 12 can combine velocity information normally available in most ring laser gyros with information about the rotational vibrations caused by the dither mechanism. Of course, one group of dithers with more than two cycles
It is possible to modify the error cancellation bias system of the present invention to vary the successive values of the zero speed crossing of a cycle such that the total error accumulated over a selected group of cycles is approximately zero. It is. Of course, this device requires various control signals to provide the appropriate bias to achieve the desired results. In the illustrated pulse device, different numbers of pulses are of course required.

The error cancellation bias system of the present invention controls the phase angle between the waves traveling along the ring laser closed loop path in combination with the bias normally applied to reduce long-fin errors in the gyro. Phase angle control may also be performed in other ways without departing from the scope of the invention.

[Brief explanation of the drawing]

Fig. 1 is a diagram of a conventional ring laser angular velocity sensor, Fig. 1a is a diagram of an example of a phase angle detector used in the sensor of Fig. 1, and Fig. 2 is a diagram of a dithered senna dither angle. FIG. 3 is a block diagram of an embodiment of the present invention; FIG. 4 is a graph illustrating the principle of the present invention; FIG. 6 is a block diagram of another embodiment of the invention; FIG. 7 is a graph of dither angle versus time plus inertial input motion; FIG. 8 is a graph of the invention. A block diagram of a closed loop feedback bias device using the principle of FIG. 9 is a graph of the synchronous bias control signal pulse and dither movement,
Figure 0 is a detailed block diagram of the device shown in Figure 8, Figure 10a.
Figure 11 is a detailed diagram of the window comparator, Figure 11 is a graph of the Ronfin error inherent in the type of sensor shown in Figure 1, Figure 12 is
13 is a block diagram showing another embodiment of the closed loop feedback bias device according to the present invention, and FIG. 13 is a diagram showing details of the bias control signal generator of FIG. 12. 30...Bias device, 32, 532 .632,832...bias control signal generator, 34.35...signal generator,
537... Pulse generation a, 634... Random amplitude generator, 800... Phase angle detector, 802...
...Phase angular velocity detector, 804...Sample/hold circuit, 875...Signal processor, 841, 84
3...Window comparator. Patent applicant: Honeywell Inc. Sub-Agent: Masaki Yamakawa (e.g., 1 person) F”tcp, 5 Fto, 6 Ficy-9 Fta, fj

Claims (1)

[Scope of Claims] (1) An angular velocity sensor in which two waves travel in opposite directions along a closed loop path, wherein the frequency of each wave is a function of the rotational speed of the closed loop path, and There is a corresponding phase relationship between the waves that is a function of the rotational speed of the closed-loop path, and the sensor has a first In the angular velocity sensor that generates a sensor signal of
The phase W of the phase relationship between the waves is d (/'/d
The lock-in error in the first sensor signal is made sufficiently small by alternating the first and second values when a selected time occurs at which a selected value of t occurs. An angular velocity sensor, characterized in that it comprises a biasing device capable of altering at least one of said waves. (2) An angular velocity sensor in which two waves propagate in opposite directions along a closed loop path, the frequency of each wave being a function of the rotational speed of the closed loop path, and a distance between the waves. There is a corresponding phase relationship that is a function of the rotational speed of the closed loop path, and the sensor generates a first sensor signal that is related to the rotational angle of the sensor but includes a lock-in error that is specific to the sensor. in the angular velocity sensor, the frequency of each of the waves and the corresponding phase relationship between the waves is varied in such a way that the sign of the frequency difference between the waves is periodically alternated. a biasing device capable of rotationally oscillating the closed loop path relative to a fixed reference axis in response to a control signal; and a dF having a predetermined relationship that reduces the lock-in error in the first sensor signal. said bias control directing said bias such that said phase W of said phase relationship between said waves takes a selected phase value at a time selected to occur at which a selected value of /dt occurs; a bias control signal generator that generates a signal, wherein the bias control signal is (1
) causing the rotational vibration at a first frequency;
(ii) the clockwise peak amplitude value of the rotational oscillation about the fixed reference axis so as to change the phase of the phase relationship between the waves at approximately the time when a selected value of dvrya t occurs; An angular velocity sensor characterized by being capable of controlling a counterclockwise peak amplitude value. (3) An angular velocity sensor in which two waves propagate in opposite directions along a closed loop path, wherein the frequency of the waves is a function of the rotation speed of the closed loop path, and the frequency between the waves is a function of the rotational speed of the closed loop path; a first sensor signal, wherein there is a corresponding phase relationship that is a function of the rotational speed of the closed loop path, the first sensor signal being related to the true rotation angle of the sensor, but including a lock-in error inherent to the sensor; The frequencies of the six waves and the corresponding phase relationships between them are determined in the angular velocity sensor that generates a a biasing device capable of rotationally oscillating the closed loop path relative to a fixed reference axis in response to a control signal such that the phase ψ of the phase relationship between the waves is such that dlJ:/dt At zero, d
a bias for generating said bias control signal which directs said biasing device to assume a selected phase value in the case of successive groups of successive occurrences of time such that the values of lF/dt have the same polarity; a control signal generator;
The bias control signal includes (1) causing the rotational vibration at approximately a first frequency, and (iD dv,
peak amplitude values of said rotational oscillations clockwise about said fixed reference axis and counterclockwise so as to change the phase of said phase relationship between said waves approximately when a selected value of yat occurs. angular velocity sensor, wherein the selected phase value of each group has a predetermined phase relationship that reduces the lock-in error in the first sensor signal. . (4) An angular velocity sensor in which two waves propagate in opposite directions along a closed loop path, the frequencies of the six waves being a function of the rotational speed of the closed loop path, and between the waves There is a corresponding phase relationship that is a function of the rotational speed of the closed loop path, and the sensor generates a first sensor signal that is related to the true rotation angle of the sensor but includes a lock-in error that is specific to the sensor. in the angular velocity sensor, the frequencies of the six waves and the corresponding phase relationships between the waves are varied in such a way that the sign of the frequency difference between the waves is periodically alternated. a biasing device capable of rotationally oscillating the closed loop path relative to a fixed reference axis in response to a control signal; Take the clockwise amplitude or the selected amplitude value and (
11) successive peak counterclockwise amplitudes of successive groups of successive peak counterclockwise amplitudes take on selected amplitude values such that said lock-in error in said first sensor signal is reduced; a bias control signal generator that generates the bias control signal that directs the bias device, the bias control signal comprising: (1) approximately the first bias control signal;
causing the rotational vibration at a frequency of 0i) dF
the peak amplitude value of said rotational oscillations clockwise about said fixed reference axis and counterclockwise so as to change the phase W of said phase relationship between said waves approximately at the time when a selected value of /at occurs; angular velocity sensor, wherein each peak amplitude has a corresponding instantaneous value of the phase relationship associated therewith. (5) An improved angular velocity sensor in which two waves travel in opposite directions along a closed loop path, comprising:
the frequency of the wave is a function of the rotational speed of the closed loop path;
There is a corresponding phase relationship between the waves that is a function of the rotation speed of the closed-loop path, and the sensor has a phase relationship that is related to the true rotation angle of the sensor, but which includes a lock-in error inherent in the sensor. the improved angular rate sensor that generates one sensor signal; a biasing device that changes the frequency of at least one of the waves and the corresponding phase relationship between the waves in response to a bias control signal; a bias control signal generator for generating the bias control signal, wherein the bias control signal is such that the phase γ of the phase relationship between the waves has a value of dW/dt of zero and a correspondence of dF/dt. The biasing device can be controlled to alternate between at least a first value and a second value when the values to be applied are of the same polarity, and the bias control signal generator is configured to control providing a first signal component of the bias control signal to periodically vary the frequency of at least one of the waves such that the difference varies periodically by a selected value at the first frequency; The difference in frequency between the first element and the wave is the second
a second signal component of the bias control signal that periodically varies the frequency of at least one of the waves by a selected value in the frequency of the wave;
and an element of the bias control signal such that the phase takes at least a first value and a second value when a time when d(/'/dt is zero selectively occurs). An improved angular velocity sensor characterized in that the first signal component and the second signal component have selected magnitudes that affect the phase. a support element supporting two forward single frequency electromagnetic radiation;
an element responsive to said waves for providing a sensor signal related to the true angle of rotation of said closed loop path; and at least one element responsive to said waves related to the instantaneous phase W of said phase relationship between said waves. a phase angle detector that generates one output signal; and at least one of the wave frequencies in response to a bias control signal;
a biasing device that alters the corresponding phase relationship between the waves and when the selected value of dV/dt is selected in response to at least one output signal of the phase angle detector; , a bias control signal generator that generates the bias control signal that directs the bias device so that the phase takes a selected value that satisfies a selected relationship, and the frequency of the combined wave is a corresponding phase relationship exists between the waves that is a function of the rotational speed of the closed-loop path, and a corresponding phase relationship exists between the waves that is a function of the rotational speed of the closed-loop path; A ring laser angular velocity sensor characterized in that the biasing device can be controlled such that the phase dream takes a selected phase i when (An angular velocity sensor in which two waves propagate in opposite directions along a closed loop path, the frequency of the combined wave is a function of the rotational speed of the closed loop path, and there is a There is a corresponding phase relationship that is a function of the rotational speed of the closed loop path, and the sensor generates a first sensor signal that is related to the true rotation angle of the sensor, but that includes a Ronfin error that is specific to the sensor. In the angular velocity sensor, a bias device capable of rotationally vibrating the closed loop path with respect to a fixed reference axis so as to change the frequency of the combined waves and periodically alternate the sign of the frequency difference between the waves. and an output signal indicative of successive peak clockwise amplitudes and successive peak counterclockwise amplitudes about the fixed reference axis in response to rotational movement of the sensor about the fixed reference axis. a rotational amplitude detector capable of generating a rotational amplitude detector; a speed indicator responsive to the propagating wave to generate an output signal indicative of the rotational speed of the closed loop path; The output signal of the speed indicator is configured to take a selected phase value that satisfies a certain predetermined relationship such that the Ronfin error in the first sensor signal is reduced when the time at which the speed indicator occurs is selected. and a bias control signal generator responsive to the output signal of the amplitude detector to generate the bias control signal directing the peak clockwise amplitude and the peak counterclockwise amplitude, the bias device comprising: (11) controlling the peak clockwise amplitude and the peak counterclockwise amplitude of the rotational vibration about the fixed reference axis; angular velocity sensor, wherein each peak amplitude has a corresponding instantaneous phase value of the phase relationship associated with them. such that the frequency of the combined wave is a function of the rotational speed of the closed-loop path, and there is a corresponding phase between the waves that is a function of the rotational speed of the closed-loop path. a relationship exists, the sensor generates a first sensor signal related to the true rotation angle of the sensor, but including a lock-in error inherent in the sensor, and the frequency of the combined wave is varied to A method for reducing a lock-in error in the angular velocity sensor, the method comprising: a bias device capable of rotationally vibrating the closed loop path so as to periodically alternate the sign of a frequency difference between the angular velocity sensors; a step of measuring the phase value for the phase relationship when dv//dt which is approximately zero occurs, and dF/dt which is approximately zero;
of the rotational oscillation such that when selected and generated, the phase of the phase relationship takes on a selected value that satisfies a predetermined relationship that reduces the lock-in difference in the first sensor signal. A method for reducing a lock-in error in an angular velocity sensor, comprising: changing a clockwise peak amplitude and a counterclockwise peak amplitude. (9) An angular velocity sensor in which two waves propagate in opposite directions along a closed loop path, wherein the frequency of the combined wave is a function of the rotational speed of the closed loop path, and there is a distance between the waves. There is a corresponding phase relationship that is a function of the rotational speed of the closed loop path, and the sensor generates a first sensor signal that is related to the true rotation angle of the sensor but includes a lock-in error that is specific to the sensor. and a bias device capable of rotationally oscillating the closed loop path so as to vary the frequency of the combined waves and periodically alternating the sign of the frequency difference between the waves. A method for reducing lock-in error in an angular velocity sensor, the method comprising: measuring the rotational speed of the sensor; measuring clockwise peak amplitude and counterclockwise peak amplitude of the rotational vibration; the rotational speed of the sensor and the clockwise peak amplitude and counterclockwise peak amplitude of the rotational vibration so that the phase W of the phase relationship takes the selected value when a certain time is selected and occurs. a method for reducing lock-in error in an angular velocity sensor, comprising: measuring subsequent clockwise peak amplitude values and counterclockwise peak amplitude values in response to the selected past values; 1 (10) A dithered angular velocity sensor in which two waves travel in opposite directions along a closed loop path, the frequency of the combined wave being a function of the rotational speed of the closed loop path, and the frequency of the combined wave being a function of the rotation speed of the closed loop path; There is a corresponding phase relationship between the waves that is a function of the rotation speed of the closed-loop path, and a first phase relationship that is related to the true rotation angle of the sensor, but includes a lock-in error inherent to that sensor. The dithered angular velocity sensor generates a sensor signal of
The phase of the phase relationship is such that the phase values that occur when a pair of dF/dt, which is zero, and dV/dt, which has the same polarity, occur consecutively are such that the phase values differ by π radians. A dithered angular velocity sensor, characterized in that it comprises a biasing device capable of varying the dithered angular velocity sensor. Ql) An angular velocity sensor in which two waves travel in opposite directions along a closed loop path, the frequency of the combined wave being a function of the rotational speed of the closed loop path, and between the waves there is There is a corresponding phase relationship that is a function of the rotational speed of the closed loop path, and the sensor generates a first sensor signal that is related to the true rotation angle of the sensor, but that includes a lock-in error that is specific to the sensor. The angular velocity sensor is provided with a dither mechanism capable of vibrating the sensor in a rotational mode about a reference axis such that a pair of consecutive peak amplitudes of the same sign differ by a selected difference value. An angular velocity sensor featuring: