CN101738182A - Two-way constant speed frequency-offset laser gyro north finding method and two-way constant speed frequency-offset laser gyro north finder - Google Patents

Abstract

The invention relates to a two-way constant speed frequency-offset laser gyro north finder, and belongs to the technical field of inertial navigation equipment. The laser gyro north finder is provided with a two-way constant speed frequency-offset rotary table rotating around a vertical axis; the rotary table is provided with a laser gyro and an accelerometer; the sensing axis of the laser gyro deviates the rotary plane of the rotary table by a beta angle; and the input axis of the accelerometer is parallel to the rotary plane of the frequency-offset rotary table and is parallel to a projection of the sensing axis of the laser gyro on the rotary plane of the frequency-offset rotary table. The laser gyro north finder applies two-way constant speed frequency-offset technology, thoroughly eliminates influence of latchup effect on precision of the laser gyro, and performs rotation error modulation and filtering on the errors produced by the laser gyro due to other reasons to ensure that the precision of the laser gyro is greatly improved than that of other conventional frequency-offset technology so as to manufacture the arc-second high-precision laser gyro north finder.

Description

Northern instrument is sought in two-way constant speed offset frequency laser gyro north finding method and the laser gyro of two-way constant speed offset frequency

Technical field

The invention belongs to inertial navigation set technical field, particularly laser gyro and seek the improvement of northern instrument technology.

Background technology

The influence that the existing multiple offset frequency technology of laser gyro is used to solve the laser gyro latch up effect, its effect is also imperfect.Have only " constant speed offset frequency technology " can thoroughly eliminate the influence of " locking " effect in theory, but can't realize desired accurate constant speed on the engineering, so do not capture the technical barrier of " constant speed offset frequency technology " so far both at home and abroad yet.According to relevant bibliographical information, U.S. Li Deng company has taken the lead in using the laser gyro of " speed offset frequency technology " in the inertial navigation system of superhigh precision, this " speed offset frequency technology " allows the speed offset frequency turntable that loads laser gyro come and go the commutation rotation in the scope at 720 ° of angles, and commutation in per approximately two seconds is rotated once; It lacks a lot than " mechanical shaking offset frequency technology " (machine about about 400Hz is trembled frequency) commutation number of times, adopt special accurate commutation stop means, shorten speed offset frequency turntable commutation speed-change process as far as possible and cause the time of laser gyro, its navigation accuracy be significantly improved (about order of magnitude) through the lock district.This is the most advanced laser gyro offset frequency technology of using at present.Its principle is referring to Fig. 1, Fig. 2.

But the influence of speed offset frequency technology laser gyro " locking " effect remains the main error source of laser gyro.

Summary of the invention

The present invention seeks to seek employing " two-way constant speed offset frequency technology " in the northern instrument, reach and eliminate the error that laser gyro " locking " effect causes fully, thereby a high precision that produces the rad level is sought northern instrument in laser gyro.The technical barrier that need overcome mainly comprises: 1, design is greater than the commutation of two-way constant speed offset frequency turntable synchronous motor and the restraint device at 360 ° of angles; 2, accurately control laser gyro and accelerometer only enter the constant speed rotation at the offset frequency turntable whole 360 ° of angle segment sampling works, laser gyro and accelerometer are in off working state outside this section.

Specifically, the present invention realizes according to following steps:

1. on the two-way constant speed offset frequency turntable (2) of Z-axis (1) rotation, a laser gyro (3) and an accelerometer (4) are installed, the sensitive axes of laser gyro (3) is departed from two-way constant speed offset frequency turntable Plane of rotation β angle, the input shaft (5) of accelerometer (4) is parallel with offset frequency turntable Plane of rotation, and parallel in the projection of offset frequency turntable Plane of rotation with the laser gyro sensitive axes.

2. two-way constant speed offset frequency turntable (2) is rotated by the synchronous machine drives of band gear reducer, turning to driving lever of installing on a boss (6) and the pedestal (7) and optoelectronic switch (8) control synchronous motor on this turntable, the spacer pin (9) of restriction driving lever motion is simultaneously as the spacer pin of this turntable, and the corner of turntable is restricted to 360 °+2 γ; The size at γ angle will guarantee to reach synchronous rotational speed after the synchronous motor commutation.

Two-way constant speed offset frequency turntable (2) is connected with the precision angle device, and the zero-bit of precision angle device should place in the middle of two extreme positions of offset frequency turntable, promptly in the centre position at 2 γ angles.

3. two-way constant speed offset frequency turntable angular velocity of rotation Component on the laser gyro sensitive axes

Be used for degating region is shifted out in the perform region of laser gyro; Angular velocity of rotation

Simultaneously the remainder error of laser gyro and the biasing and the alignment error of accelerometer are rotated modulation again.

4. each sampling period of computing machine is all gathered the angle [alpha] of two-way constant speed offset frequency turntable angle-measuring equipment output, when the laser gyro sampling work, with this angle [alpha] coordinate transform is carried out in the output of laser gyro and accelerometer.Angle [alpha] can also be calculated angle increment Δ α (Δ α _i=α _i-α _I-1), can eliminate offset frequency amount (± Δ α sin β) in the laser gyro output with it; When Δ α undergos mutation (i.e. 0 ° and 360 ° of forward and reverse saltus steps), promptly think the zero point of this turntable by angle-measuring equipment, send crossover point signal this moment, trigger the continuous sampling process of " startup " or " stopping " laser gyro and accelerometer, make the each continuous sampling process of computing machine all in whole 360 ° of scopes that offset frequency turntable constant speed is rotated, this has guaranteed that just laser gyro is to work under " two-way constant speed offset frequency " state.

5. the output of accelerometer can accurately calculate the attitude angle of seeking northern instrument through coordinate transform and error rotation modulation on the two-way constant speed offset frequency turntable.This attitude angle can be used for accurate leveling and seeks northern instrument (northern state is sought in leveling), carries out the attitude error compensation when perhaps seeking north under the attitude angle state is arranged.

Realize that the two-way constant speed offset frequency laser gyro of above-mentioned north finding method seeks northern instrument, it 1. has a two-way constant speed offset frequency turntable (2) around Z-axis (1) rotation, a laser gyro (3) and an accelerometer (4) and laser gyro (3) sensitive axes are installed on this turntable depart from this turntable Plane of rotation β angle, the input shaft (5) of accelerometer (4) is parallel with offset frequency turntable Plane of rotation, and parallel in the projection of offset frequency turntable Plane of rotation with the laser gyro sensitive axes.2. two-way constant speed offset frequency turntable (2) is rotated by the synchronous machine drives of band gear reducer, turning to driving lever of installing on a boss (6) and the pedestal (7) and optoelectronic switch (8) control synchronous motor on this turntable, the spacer pin (9) of restriction driving lever motion is simultaneously as the spacer pin of this turntable, and the corner of turntable is restricted to 360 °+2 γ.3. two-way constant speed offset frequency turntable (2) is connected with the precision angle device, and the zero-bit of precision angle device should place in the middle of two extreme positions of offset frequency turntable, promptly in the centre position at 2 γ angles.

Advantage of the present invention is:

1, realized that " constant speed offset frequency technology " seek application in the northern instrument in laser gyro, eliminated the influence of laser gyro " locking " effect fully, increased substantially the effective accuracy of laser gyro, made laser gyro seek the high precision that northern instrument also can reach the rad level.

2, seek and the laser gyro sensitive axes is departed from two-way constant speed offset frequency turntable Plane of rotation β angle in the northern instrument, drive, the constant speed offset frequency of laser gyro and laser gyro and accelerometer error rotation modulation are carried out simultaneously by this single axle table.

3, can be interrupted the characteristics of carrying out according to seeking northern instrument work, being chosen in two-way constant speed offset frequency turntable commutation speed change section inner laser gyro does not sample, when having only turntable to enter a turn over (the 360 ° of angles) section of constant speed rotation, sampling work is just carried out in laser gyro.Phase specific speed offset frequency turntable, positional precision, the physical strength of offset frequency turntable bridle of the present invention and reverse mechanism, and all reductions significantly of requirement that drive the synchronous motor margin of power.

Description of drawings

Fig. 1 is " machine is trembled offset frequency " method synoptic diagram in the existing offset frequency technology.

Fig. 2 is " speed offset frequency " method synoptic diagram in the existing offset frequency technology.

Fig. 3 and Fig. 4 are " two-way constant speed offset frequency " of the present invention method synoptic diagram.

Fig. 5 is northern instrument " two-way constant speed offset frequency " structural representation for the present invention seeks.

Fig. 6 is commutation of driving lever photoelectricity and stop means synoptic diagram in the present invention the seeks northern instrument.

Fig. 7 seeks northern coordinate system for leveling.

Embodiment

As shown in Figure 5, " two-way constant speed offset frequency " laser gyro north searching instrument method, it is to realize according to following steps: (1) is departed from two-way constant speed offset frequency turntable Plane of rotation β angle with the laser gyro sensitive axes and is installed, by this turntable driven rotary, the constant speed offset frequency of laser gyro and error rotation modulation are carried out simultaneously; When (2) being chosen in turntable and entering a turn over section of constant speed rotation, sampling work is carried out in laser gyro.

Seek the two-way constant speed offset frequency turntable that has to rotate in the northern instrument around Z-axis, a laser gyro and an accelerometer are installed on this turntable, the laser gyro sensitive axes departs from this turntable Plane of rotation β angle, the input shaft of accelerometer is parallel with offset frequency turntable Plane of rotation, and parallel with the laser gyro sensitive axes in the projection of offset frequency turntable Plane of rotation, referring to Fig. 5.The rotation of two-way constant speed offset frequency turntable realizes two purposes: one is the component of this turntable angular velocity of rotation on the laser gyro sensitive axes, realizes laser gyro constant speed offset frequency; Its two, be that other remainder error of laser gyro and the biasing and the alignment error of accelerometer are rotated modulation, make these constant errors be modulated into the alternation error of zero-mean, eliminated through integral filtering.Accelerometer just can accurately be measured the attitude angle of seeking northern instrument through the error modulated filter, seeks north having under the situation of attitude angle, and this attitude angle can fine compensation be sought northern error owing to what attitude angle produced; Seeking under the northern state this attitude angle in leveling can be used for accurate leveling and seeks northern instrument.Two-way constant speed offset frequency turntable is rotated by the synchronous machine drives of band gear reducer, turning to driving lever of installing on a boss and the pedestal and optoelectronic switch control synchronous motor thereof on this turntable, referring to Fig. 6, the spacer pin of restriction driving lever motion also is the spacer pin of this turntable simultaneously, and the corner of turntable is restricted to 360 °+2 γ.The size at γ angle will guarantee to reach synchronous rotational speed (its angle is determined according to actual conditions) after the synchronous motor commutation.Be the condition that guarantees that the laser gyro sampling work carries out when constant speed is rotated, turntable α zero point angle position should be in centre position, 2 γ angle.Each sampling period of computing machine is all gathered the angle [alpha] of two-way constant speed offset frequency turntable angle-measuring equipment output, when the laser gyro sampling work, with this angle [alpha] coordinate transform is carried out in the output of laser gyro and accelerometer.Angle [alpha] can also be calculated angle increment Δ α (Δ α _i=α _i-α _I-1), when Δ α undergos mutation, promptly think the zero point of this turntable by angle-measuring equipment, send crossover point signal this moment, trigger the continuous sampling process of " startup " or " stopping " laser gyro and accelerometer, make each continuous sampling process all in whole 360 ° of scopes that the positive and negative constant speed of offset frequency turntable is rotated.This error that is rotated modulation for the biasing of other remainder error of laser gyro and accelerometer and alignment error and offsets turntable angle-measuring equipment and synchronous motor rotating speed is the condition of necessity.The two-way constant speed offset frequency turntable corner of seeking in the northern instrument is limited, can adopt the flexible cable transmission of electricity, avoids using the contact power transmitting device.

Northern computing method are sought in the present invention's " two-way constant speed offset frequency " laser gyro, and to seek north with leveling be example.X ' axle laser gyro quiet (no offset frequency component) output angle increment.

ΔΩ _X′＝ΔΩ′ _X′μΔαsinβ

Annotate: in offset frequency turntable inhour rotation up-to-date style with "-" number; In the offset frequency turntable turns clockwise up-to-date style with "+" number.

The projection of X ' shaft angle increment on offset frequency turntable coordinate system

The angle increment that navigation coordinate is fastened

$\left[\begin{array}{c}{\mathrm{\&Delta;\&Omega;}}_{{\mathrm{<figure-callout\; id="1"\; label="X"\; filenames="H2009102544841E00014.png,H2009102544841E00021.png"\; state="\{\{state\}\}">X</figure-callout>}}_1}\\ {\mathrm{\&Delta;\&Omega;}}_{{\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="H2009102544841E00014.png,H2009102544841E00021.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1}\\ {\mathrm{\&Delta;\&Omega;}}_{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="H2009102544841E00011.png,H2009102544841E00013.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}\end{array}\right]=\left[\begin{array}{ccc}\cos \mathrm{\&alpha;}& \sin \mathrm{\&alpha;}& 0\\ -\sin \mathrm{\&alpha;}& \cos \mathrm{\&alpha;}& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;\&Omega;}}_X\\ {\mathrm{\&Delta;\&Omega;}}_Y\\ {\mathrm{\&Delta;\&Omega;}}_{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="H2009102544841E00011.png,H2009102544841E00013.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0}\end{array}\right]=$

$=\left[\begin{array}{ccc}\cos \mathrm{\&alpha;}& \sin \mathrm{\&alpha;}& 0\\ -\sin \mathrm{\&alpha;}& \cos \mathrm{\&alpha;}& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{c}\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}}^{\&prime;}\mathrm{\&mu;\&Delta;\&alpha;}\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\\ 0\\ \left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}}^{\&prime;}\mathrm{\&mu;\&Delta;\&alpha;}\sin \mathrm{\&beta;}\right)\sin \mathrm{\&beta;}\end{array}\right]=$

$=\left[\begin{array}{c}\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}}^{\&prime;}\mathrm{\&mu;\&Delta;\&alpha;}\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\cos \mathrm{\&alpha;}\\ -\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}}^{\&prime;}\mathrm{\&mu;\&Delta;\&alpha;}\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\sin \mathrm{\&alpha;}\\ \left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}}^{\&prime;}\mathrm{\&mu;\&Delta;\&alpha;}\sin \mathrm{\&beta;}\right)\sin \mathrm{\&beta;}\end{array}\right]$

X ₁Y ₁The integration of shaft angle increment

${\mathrm{\&Omega;}}_{{\mathrm{<figure-callout\; id="1"\; label="X"\; filenames="H2009102544841E00014.png,H2009102544841E00021.png"\; state="\{\{state\}\}">X</figure-callout>}}_1}=\underset{j=1}{\overset{j=m}{\mathrm{\&Sigma;}}}{\left[\underset{i=1}{\overset{i=n}{\mathrm{\&Sigma;}}}\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}i}^{\&prime;}{\mathrm{\&mu;\&Delta;\&alpha;}}_i\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\cos {\mathrm{\&alpha;}}_i\right]}_j$

${\mathrm{\&Omega;}}_{{\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="H2009102544841E00014.png,H2009102544841E00021.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1}=-\underset{j=1}{\overset{j=m}{\mathrm{\&Sigma;}}}{\left[\underset{i=1}{\overset{i=n}{\mathrm{\&Sigma;}}}\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}i}^{\&prime;}{\mathrm{\&mu;\&Delta;\&alpha;}}_i\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\cos {\mathrm{\&alpha;}}_i\right]}_j$

Calculate at the position angle

$\mathrm{\&psi;}=\mathrm{arctg}\frac{{\mathrm{\&Omega;}}_{{\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="H2009102544841E00014.png,H2009102544841E00021.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1}}{{\mathrm{\&Omega;}}_{{\mathrm{<figure-callout\; id="1"\; label="X"\; filenames="H2009102544841E00014.png,H2009102544841E00021.png"\; state="\{\{state\}\}">X</figure-callout>}}_1}}=\mathrm{arctg}\frac{-\underset{j=1}{\overset{j=m}{\mathrm{\&Sigma;}}}{\left[\underset{i=1}{\overset{i=n}{\mathrm{\&Sigma;}}}\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}i}^{\&prime;}{\mathrm{\&mu;\&Delta;\&alpha;}}_i\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\sin {\mathrm{\&alpha;}}_i\right]}_j}{\underset{j=1}{\overset{j=m}{\mathrm{\&Sigma;}}}{\left[\stackrel{i=n}{\underset{i=1}{\mathrm{\&Sigma;}}}\left({\mathrm{\&Delta;\&Omega;}}_{X^{\&prime;}i}^{\&prime;}{\mathrm{\&mu;\&Delta;\&alpha;}}_i\sin \mathrm{\&beta;}\right)\cos \mathrm{\&beta;}\cos {\mathrm{\&alpha;}}_i\right]}_j}$

Explain:

1.X '-laser gyro sensitive axes;

2. Δ Ω ' _{X '}-one total output angle increment of adopting laser gyro one number time;

3. Δ Ω _{X '}-one quiet (no offset frequency component) output angle increment of adopting laser gyro one number time;

4. the position, angle of α-offset frequency turntable;

5. Δ α-corner (angle increment) of adopting offset frequency turntable one number time;

6.n-turn over of offset frequency turntable (360 °) adopt number for several times;

7.m-seek the turn over number of northern process offset frequency turntable.

The implication of several angles and definite principle among the present invention:

α-offset frequency turntable corner (position, angle in a certain moment);

-offset frequency turntable angular velocity of rotation;

Δ α-one of offset frequency turntable is adopted the corner (angle increment) of one number time;

β-laser gyro established angle;

γ-offset frequency turntable restraint angle respectively is provided with a commutation (counter-rotating) speed change buffering angle at the two ends of 360 ° of turn overs.

Offset frequency turntable angular velocity of rotation

Be that the needs that rotation is modulated according to error are provided with in seeking northern instrument.

Laser gyro established angle β is in order to make the laser gyro measurement axis can obtain offset frequency turntable angular velocity of rotation

A suitable projection components, when β=0, offset frequency turntable turning axle vertical with the laser gyro measurement axis (90 °), projection components

The offset frequency turntable just can not provide offset frequency angular velocity to laser gyro.When the size to fit of β angle, projection components

Just can make the degating region of the workspace disengaging laser gyro of laser gyro.So the size at β angle is by laser gyro degating region (being decided by the laser gyro quality), measured angle speed (rotational-angular velocity of the earth) maximal value and offset frequency turntable angular velocity of rotation

Size determine.

Claims (9)

1. two-way constant speed offset frequency laser gyro north finding method is characterized in that implementing according to following steps:

(1). on the two-way constant speed offset frequency turntable (2) of Z-axis (1) rotation, a laser gyro (3) and an accelerometer (4) are installed, the sensitive axes of laser gyro (3) is departed from two-way constant speed offset frequency turntable Plane of rotation β angle, the input shaft (5) of accelerometer (4) is parallel with offset frequency turntable Plane of rotation, and parallel in the projection of offset frequency turntable Plane of rotation with the laser gyro sensitive axes;

(2). two-way constant speed offset frequency turntable (2) is rotated by the synchronous machine drives of band gear reducer, control turning to of synchronous motor with driving lever of installing on a boss (6) and the pedestal (7) and optoelectronic switch (8) on this turntable simultaneously, the spacer pin (9) of restriction driving lever motion is simultaneously as the spacer pin of this turntable, and the corner of turntable is restricted to 360 °+2 γ; The size at γ angle will guarantee to reach synchronous rotational speed after the synchronous motor commutation; Two-way constant speed offset frequency turntable (2) is connected with the precision angle device, and the zero-bit of precision angle device should place in the middle of two extreme positions of offset frequency turntable, promptly in the centre position at 2 γ angles;

(3). two-way constant speed offset frequency turntable angular velocity of rotation

Component on the laser gyro sensitive axes

Be used for degating region is shifted out in the perform region of laser gyro; Angular velocity of rotation

Simultaneously the remainder error of laser gyro and the biasing and the alignment error of accelerometer are rotated modulation again;

(4). each sampling period of computing machine is all gathered the angle [alpha] of two-way constant speed offset frequency turntable angle-measuring equipment output, when the laser gyro sampling work, with this angle [alpha] coordinate transform is carried out in the output of laser gyro and accelerometer;

(5). the output of accelerometer is through coordinate transform and error rotation modulation on the two-way constant speed offset frequency turntable, accurately calculate the attitude angle of seeking northern instrument, this attitude angle is sought in leveling and is used for accurate leveling under the northern state and seeks northern instrument, carries out the attitude error compensation when perhaps seeking north under the attitude angle state is arranged.

2. laser gyro north finding method according to claim 1 is characterized in that angle [alpha] can also be calculated angle increment Δ α (Δ α in step (4) _i=α _i-β _I-1), can eliminate offset frequency amount (± Δ α sin β) in the laser gyro output with it; α undergos mutation when Δ, that is: 0 ° during with 360 ° of forward and reverse saltus steps, promptly think the zero point of this turntable by angle-measuring equipment, send crossover point signal this moment, trigger the continuous sampling process of " startup " or " stopping " laser gyro and accelerometer, making the each continuous sampling process of computing machine all in whole 360 ° of scopes that offset frequency turntable constant speed is rotated, is to work under " two-way constant speed offset frequency " state to guarantee laser gyro.

3. realize that the two-way constant speed offset frequency laser gyro of above-mentioned north finding method seeks northern instrument, it is characterized in that having a two-way constant speed offset frequency turntable (2) around Z-axis (1) rotation, a laser gyro (3) and an accelerometer (4) and laser gyro (3) sensitive axes are installed on this turntable depart from this turntable Plane of rotation β angle, the input shaft (5) of accelerometer (4) is parallel with offset frequency turntable Plane of rotation, and parallel in the projection of offset frequency turntable Plane of rotation with the laser gyro sensitive axes.

4. northern instrument is sought in laser gyro according to claim 3, it is characterized in that the laser gyro sensitive axes is departed from two-way constant speed offset frequency turntable Plane of rotation β angle installs by this turntable driven rotary, angular velocity of rotation

Component on the laser gyro sensitive axes

Be enough to degating region is shifted out in the perform region of laser gyro, the constant speed offset frequency of laser gyro and the error rotation modulation of laser gyro and accelerometer are carried out simultaneously.

5. northern instrument is sought in laser gyro according to claim 3, it is characterized in that two-way constant speed offset frequency turntable (2) is rotated by the synchronous machine drives of band gear reducer, turning to driving lever of installing on a boss (6) and the pedestal (7) and optoelectronic switch (8) control synchronous motor thereof on this turntable, the spacer pin (9) of restriction driving lever motion is simultaneously as the spacer pin of this turntable, and the corner of turntable is restricted to 360 °+2 γ; The size at γ angle will guarantee to reach synchronous rotational speed after the synchronous motor commutation.

6. northern instrument is sought in laser gyro according to claim 3, it is characterized in that two-way constant speed offset frequency turntable (2) is connected with the precision angle device, and the zero-bit of precision angle device should place the centre of two extreme positions of offset frequency turntable, promptly in the centre position at 2 γ angles.

7. northern instrument is sought in laser gyro according to claim 3, it is characterized in that each sampling period of computing machine all gathers the angle [alpha] of two-way constant speed offset frequency turntable angle-measuring equipment output, when laser gyro and accelerometer sampling work, coordinate transform is carried out in the output of laser gyro and accelerometer with this angle [alpha].

8. northern instrument is sought in laser gyro according to claim 3, and the output that it is characterized in that accelerometer on the two-way constant speed offset frequency turntable can accurately calculate the attitude angle of seeking northern instrument through coordinate transform and error rotation modulation.This attitude angle is sought in leveling and be can be used for accurate leveling under the northern state and seek northern instrument, carries out the attitude angle compensation when perhaps seeking north under the attitude angle state is arranged.

9. northern instrument is sought in laser gyro according to claim 7, it is characterized in that the process that computing machine carries out continuous sampling to laser gyro and accelerometer at every turn, all in whole 360 ° of scopes that the positive and negative constant speed of offset frequency turntable is rotated.

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