Calibration method for inertial measurement unit of hemispherical resonator gyroscope

Abstract

The invention provides a hemispherical resonator gyroscope inertial measurement unit calibration method which comprises the following steps: step 1, mounting a hemispherical resonator gyroscope inertial measurement unit on a rotary table, and after the rotary table returns to zero, enabling the inertial measurement unit to point to the east-north-sky direction to finish initial alignment; 2, the hemispherical resonator gyroscope inertial measurement unit navigates at the current calibration position to set time; step 3, rotating the rotary table to a next calibration position, continuously rotating the rotary table for a plurality of circles and then rotating the rotary table to the next calibration position in the rotating process, and obtaining the output of the spinning top in rotation; step 4, repeating the step 2 to the step 3 until all calibration positions are traversed; and step 5, calibrating various errors of the inertial measurement unit by adopting a Kalman filter according to the obtained gyroscope output. By applying the technical scheme of the invention, the technical problem of insufficient error estimation precision of the inertial measurement unit caused by the fact that the rotary table rotates to drive standing wave precession in the prior art can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of inertial measurement, and in particular relates to a calibration method for a hemispherical resonant gyro inertial measurement unit. Background Art

[0002] The rate-integrating hemispherical resonator gyroscope is a solid wave gyroscope that uses the precession of the standing wave of the hemispherical resonator vibration along the circumferential direction to sense the angular motion of the base. It adopts a "two-piece" structure of a resonator and a flat electrode. While having high precision, the structure is simpler and more suitable for low-cost mass production. It can directly measure the rotation angle of the carrier, and the standing wave precession coefficient of the resonator is only determined by the resonator structure. The scale factor is extremely stable. It has the unique advantages of high precision, radiation resistance, low power consumption, small size, high reliability, long life and full life maintenance-free, meeting the development needs of a new generation of weapons and equipment.

[0003] The hemispherical resonant gyro inertial measurement unit is composed of three hemispherical resonant gyros and three accelerometers. In order to achieve high-precision navigation solution, it is necessary to calibrate the inertial measurement unit and perform error estimation and compensation on the hemispherical resonant gyro and accelerometer.

[0004] In the traditional inertial measurement unit calibration process, the inertial measurement unit is generally controlled to point in different directions through a turntable, and the local earth's rotation angular velocity component and gravity acceleration component are used as a reference to estimate the zero bias and installation deflection of the gyroscope and accelerometer; or the speed, position and other errors calculated by the inertial measurement unit in different orientations are observed, and the Kalman filter is used to achieve the above error estimation.

[0005] Since the errors of the hemispherical resonant gyro's zero bias, scale factor and other errors are related to the position of the standing wave, when the traditional multi-position stop-turn calibration method is adopted, the rotation of the turntable will drive the standing wave to precess, causing the gyro to present different error characteristics at different calibration positions, thus affecting the estimation accuracy of the gyro's zero bias and scale factor errors. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0007] The present invention provides a hemispherical resonator gyro inertial measurement unit calibration method, the hemispherical resonator gyro inertial measurement unit calibration method comprising:

[0008] Step 1: Install the hemispherical resonant gyro inertial measurement unit on the turntable. After the turntable returns to zero, the inertial measurement unit points to the northeast sky direction to complete the initial alignment.

[0009] Step 2: The hemispherical resonant gyro inertial measurement unit navigates and sets the time at the current calibration position;

[0010] Step 3: The turntable rotates to the next calibration position. During the rotation process, the turntable first rotates continuously for several circles and then rotates to the next calibration position to obtain the output of the rotating gyroscope;

[0011] Step 4: Repeat steps 2 to 3 until all calibration positions are traversed;

[0012] Step 5: Based on the obtained gyro output, a Kalman filter is used to calibrate the various errors of the inertial measurement unit.

[0013] Furthermore, in step three, the turntable first rotates continuously for at least three revolutions and then rotates to the next calibration position.

[0014] Furthermore, in step 5, the state quantity X of the filter is set to X=[δv 3×1 φ 3×1 δk g3×1 A g6×1 δk a3× 1A a6×1 ε g3×1 ε a3×1 ] T , where X is the state variable, δv is the velocity error, φ is the misalignment angle, δk g is the gyro scale factor error, A g is the gyro installation deflection angle, δk a is the accelerometer scale factor error, A a is the installation deflection angle between accelerometers, ε g is the gyro bias, ε a is the accelerometer bias.

[0015] Furthermore, the gyro scale factor error δk g Expressed as δk g =δk c +δk θ , where δk c is the scale factor error constant term, δk θ is the term of scale factor error varying with standing wave.

[0016] Furthermore, the gyro bias ε g Denoted as ε g =ε c +ε θ , where ε c is the gyro zero bias constant term, ε θ is the term of gyro zero bias changing with standing wave.

[0017] Furthermore, in step five, the speed error is used as a measurement for filtering estimation.

[0018] The technical solution of the present invention provides a calibration method for a hemispherical resonant gyro inertial measurement unit, which is a calibration method combining turntable indexing and continuous rotation. The error associated with the standing wave is identified by the change in the gyro output during rotation, and a high-precision error calibration is achieved by using the Kalman filter method. Compared with the prior art, the technical solution of the present invention can solve the technical problem in the prior art that the error estimation accuracy of the inertial measurement unit is insufficient due to the precession of the standing wave driven by the rotation of the turntable. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A schematic diagram of the process of calibrating a hemispherical resonant gyro inertial measurement unit provided according to a specific embodiment of the present invention is shown;

[0021] Figure 2 A schematic diagram showing the change of gyro zero bias during the rotation of the turntable by ninety degrees according to a specific embodiment of the present invention is shown;

[0022] Figure 3 A schematic diagram showing the change in the rotation angle of a turntable between two calibrated positions according to a specific embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0025] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to actual proportional relationships. The technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0026] like Figure 1 As shown, according to a specific embodiment of the present invention, a hemispherical resonant gyro inertial measurement unit calibration method is provided, the method comprising:

[0027] Step 1: Install the hemispherical resonant gyro inertial measurement unit on the turntable. After the turntable returns to zero, the inertial measurement unit points to the northeast sky direction to complete the initial alignment.

[0028] Step 2: The hemispherical resonant gyro inertial measurement unit navigates and sets the time at the current calibration position;

[0029] Step 3: The turntable rotates to the next calibration position. During the rotation process, the turntable first rotates continuously for several circles and then rotates to the next calibration position to obtain the output of the rotating gyroscope;

[0030] Step 4: Repeat steps 2 to 3 until all calibration positions are traversed;

[0031] Step 5: Based on the obtained gyro output, a Kalman filter is used to calibrate the various errors of the inertial measurement unit.

[0032] By applying this configuration, a calibration method for a hemispherical resonant gyro inertial measurement unit is provided. The method is a calibration method that combines turntable rotation and continuous rotation. The error associated with the standing wave is identified by the change in the gyro output during rotation, and the Kalman filter method is used to achieve high-precision error calibration.

[0033] Due to the influence of error factors such as manufacturing, circuit, and control, the hemispherical resonant gyroscope has zero bias and scale factor errors, and its error characteristics are related to the standing wave azimuth.

[0034] The relationship between the hemispherical resonant gyro zero bias and the standing wave azimuth is as follows:

[0035]

[0036] Among them, ε is the gyro zero bias, θ is the standing wave azimuth, is the damping unevenness, θ t is the angle corresponding to the damping axis, Δω is the frequency difference, θ ω is the angle corresponding to the rigid axis, Q is the energy corresponding to the orthogonal component, and E is the energy corresponding to the standing wave amplitude.

[0037] The relationship between the hemispherical resonant gyro scale factor error and the standing wave azimuth is as follows:

[0038] δk(θ)=Δlsin4θ+Δθcos4θ (2)

[0039] Among them, δk is the scale factor error, Δl is the gain error, and Δθ is the electrode non-orthogonality error.

[0040] It can be seen that the hemispherical resonant gyro error is related to the standing wave angle θ and shows periodic changes within a week.

[0041] Furthermore, the azimuth precession angle of the hemispherical resonant gyro standing wave is proportional to the external rotation angle.

[0042] θ=k b η (3)

[0043] Among them, k b is the Blaine coefficient, which indicates the proportional relationship between the standing wave azimuth and the external rotation angle, and η is the external rotation angle.

[0044] During the calibration of the HRG IMU, the turntable needs to be rotated to make the IMU point in different directions. When the turntable rotates, it will drive the gyro standing wave to precess, causing the gyro zero bias and scale factor to change. At this time, the above error is no longer a constant. See the schematic diagram of the zero bias change during the turntable rotation. Figure 2 .

[0045] Now we take two positions for analysis. Assuming that the platform body moves from the "northeast sky" to the "northwest sky", for the hemispherical resonant gyroscope, its celestial gyroscope output is as follows:

[0046] ωz=ωe U +εc+ε θ (kbΩt)+(δkc+δk θ (kbΩt))Ω

[0047] Among them, ω z is the z gyro output, ε c is the gyro constant bias, ε θ is the gyro bias associated with the standing wave azimuth, ω eU is the celestial component of the Earth's rotation angular velocity, δk c is the scale factor error constant term, δk θ is the scale factor error varying with standing wave, Ω is the turntable speed, and t is time.

[0048] For a conventional gyroscope, there is no ε θ and δk θ During the rotation, Ω changes from 0 to the set value and then to 0, δk c The term Ω is a variable value and is related to the turntable speed, thus achieving decoupling from the constant input and constant zero bias.

[0049] However, for the hemispherical resonant gyroscope, due to the existence of δk θ , during the rotation process δk θ Ω and δk c Ω coupling, resulting in an inability to accurately estimate δk c .

[0050] Similarly, during conventional rotation calibration, the gyro sensitive axis can be pointed in different directions to separate the constant drift and the earth's rotation component. θ , resulting in gyro bias (ε c +ε θ ) and cannot be decoupled from the Earth’s rotation.

[0051] In summary, it can be seen that changes in gyro bias and scale factor will lead to a decrease in the calibration accuracy of the inertial measurement unit. For this reason, a turntable rotation scheme needs to be designed to excite the above errors and separate the constant error from the error that changes with the standing wave azimuth angle.

[0052] Considering ε θ and δk θ is related to the standing wave position, while the gyro constant zero bias ε c and the scale factor error constant term δk c Regardless of the position of the standing wave, the present invention designs the following rotation scheme: when the turntable rotates from the previous position to the next target position, the turntable first rotates continuously for multiple circles and then rotates to the target position.

[0053] As a specific embodiment of the present invention, in order to further ensure the error identification accuracy, the turntable can be set to rotate continuously for no less than 3 circles. During the rotation process, the change of the turntable angle between the two calibration positions is shown in FIG. Figure 3 .

[0054] Through multiple rotations, the standing wave azimuth θ changes continuously within a large range. c and δk c It shows a constant characteristic, and according to formulas (1) and (2), the rotation of ε θ and δk θ It exhibits sine and cosine characteristics, which can achieve error excitation and separation.

[0055] As a specific embodiment of the present invention, the three sensitive axes of the inertial measurement unit can be set to point in sequence: northeast, northwest, southwest, southeast, northeast, northwest, southwest and southeast. The above calibration position sequence is not unique and can be modified according to actual calibration needs.

[0056] After obtaining the output of the gyro during the rotation of the turntable, the present invention uses a Kalman filter to calibrate the various errors of the inertial measurement unit. The state quantity X of the filter is set as follows:

[0057] X=[δv 3×1 φ 3×1 δk g3×1 A g6×1 δk a3×1 A a6×1 ε g3×1 ε a3×1 ] T (4)

[0058] Among them, X is the state quantity, δv is the velocity error, φ is the misalignment angle, δk g is the gyro scale factor error, A g is the gyro installation deflection angle, δk a is the accelerometer scale factor error, A a is the installation deflection angle between accelerometers, ε g is the gyro bias, ε a is the accelerometer bias.

[0059] In the Kalman filter calculation process, the speed error is used as a measurement for filter estimation.

[0060] In order to accurately estimate and identify the zero bias and scale factor of the hemispherical resonant gyro, it is necessary to split the gyro zero bias and calibration factor errors into constant terms and terms that vary with the standing wave. g and ε g It is expressed as follows

[0061]

[0062] In order to achieve linear estimation, ε can be replaced by θ and δk θIt is expressed as a linear combination of sin4θ and cos4θ. The coefficients are estimated during the filtering process, thereby achieving error separation and identification, and realizing high-precision calibration of the errors of the inertial measurement unit.

[0063] According to the relationship between the zero bias and the scale factor of the hemispherical resonant gyro and the azimuth angle of the standing wave, the present invention increases the continuous rotation steps of the turntable and designs a corresponding Kalman filter during the calibration process to separate the errors related to the standing wave, thereby realizing the excitation and identification of the above errors, avoiding the influence of the errors on the estimation of parameters such as the constant zero bias and the installation deflection angle, and improving the calibration accuracy of the hemispherical resonant gyro inertial measurement unit.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calibrating a hemispherical resonator gyro inertial measurement unit, characterized in that: The hemispherical resonant gyro inertial measurement unit calibration method comprises: Step 1: Install the hemispherical resonant gyro inertial measurement unit on the turntable. After the turntable returns to zero, the inertial measurement unit points to the northeast sky direction to complete the initial alignment. Step 2: The hemispherical resonant gyro inertial measurement unit navigates and sets the time at the current calibration position; Step 3: The turntable rotates to the next calibration position. During the rotation process, the turntable first rotates continuously for several circles and then rotates to the next calibration position to obtain the output of the rotating gyroscope; Step 4: Repeat steps 2 to 3 until all calibration positions are traversed; Step 5: Based on the obtained gyro output, a Kalman filter is used to calibrate the various errors of the inertial measurement unit.

2. The hemispherical resonator gyro inertial measurement unit calibration method according to claim 1, characterized in that: In step three, the turntable first rotates continuously for at least three revolutions and then rotates to the next calibration position.

3. The hemispherical resonator gyro inertial measurement unit calibration method according to claim 1, characterized in that: In step 5, the state quantity X of the filter is set to X = [δv 3×1 φ 3×1 δk g3×1 A g6×1 δk a3×1 A a6×1 ε g3×1 ε a3×1 ] T , where X is the state variable, δv is the velocity error, φ is the misalignment angle, δk g is the gyro scale factor error, A g is the gyro installation deflection angle, δk a is the accelerometer scale factor error, A a is the installation deflection angle between accelerometers, ε g is the gyro bias, ε a is the accelerometer bias.

4. The hemispherical resonator gyro inertial measurement unit calibration method according to claim 3, characterized in that: Gyro scale factor error δk g Expressed as δk g =δk c +δk θ , where δk c is the scale factor error constant term, δk θ is the term of scale factor error varying with standing wave.

5. The hemispherical resonator gyro inertial measurement unit calibration method according to claim 4, characterized in that: Gyro bias ε g Denoted as ε g =ε c +ε θ , where ε c is the gyro zero bias constant term, ε θ is the term of gyro zero bias changing with standing wave.

6. The hemispherical resonator gyro inertial measurement unit calibration method according to claim 1, characterized in that: In step five, the velocity error is used as a measurement for filter estimation.

Images