A low-cost, full-temperature calibration apparatus and method for fiber optic inertial measurement units.

Abstract

This invention relates to the field of inertial navigation technology, and more particularly to a low-cost, full-temperature calibration apparatus and method for fiber optic inertial measurement units (FIMs). The apparatus includes a temperature chamber for controlling the ambient temperature; an FIM including a quartz accelerometer and a fiber optic gyroscope; a precision indexing rotary table installed inside the temperature chamber for precisely rotating the FIM; a calibration fixture fixed on the precision indexing rotary table for fixing the FIM and ensuring its reference plane is aligned with the fixture's reference plane; and a high-precision inclinometer for calibrating the horizontal state of the precision indexing rotary table. This invention significantly reduces the cost of full-temperature calibration for similar FIMs by using a high-precision rotary table instead of the expensive temperature chamber turntable, and by fixing the FIM within the temperature chamber to achieve rotation. It also features ease of operation, wide applicability, and easy expansion.

Description

Technical Field

[0001] This invention relates to the field of inertial navigation technology, and in particular to a low-cost, full-temperature calibration apparatus and method for fiber optic inertial measurement units. Background Technology

[0002] A fiber optic inertial measurement unit (FIM) is a high-precision inertial sensor module that measures the linear acceleration and rotational angular increment of the module's own coordinate system relative to the inertial coordinate system. The linear acceleration is measured by a quartz accelerometer, and the rotational angular increment is measured by a fiber optic gyroscope. A complete FIM contains three quartz accelerometers and three fiber optic gyroscopes. Both types of sensors are fixed orthogonally along the X, Y, and Z axes according to the FIM's own coordinate system. The FIM also includes a temperature sensor and a power supply module to measure the temperature of each sensor. Its internal acquisition hardware outputs the various physical quantities (acceleration, angular increment, and temperature) as digital signals.

[0003] Due to limitations in mechanism and manufacturing, the feedback data from quartz accelerometers and fiber optic gyroscopes are affected by temperature, causing sensor errors. Common fiber optic inertial measurement unit (IFM) models include scaling factors, installation error matrices, and zero bias. The scaling factor and zero bias vary considerably with temperature over large temperature ranges, necessitating full-temperature calibration to improve the stability and accuracy of the IFM. Full-temperature calibration and compensation for IFM is defined as follows: based on the models of the quartz accelerometer and fiber optic gyroscope, using appropriate devices, equipment, and instruments, following a temperature testing procedure (with the temperature range covering the entire operating temperature range of the IFM), sensor data from the tested unit is collected, model parameters are calculated, and error compensation is performed based on these parameters to eliminate temperature effects and improve stability and accuracy.

[0004] Existing full-temperature calibration of fiber optic inertial measurement units (FIMs) requires the use of a temperature chamber turntable, such as a typical three-axis turntable. From the outside in, the turntable has azimuth, pitch, and roll degrees of freedom. A temperature chamber is fixed on the roll degree of freedom. During the temperature calibration process, the FIM is fixed inside the temperature chamber. The ambient temperature is controlled by the temperature chamber. The turntable drives the temperature chamber to rotate, forming different attitudes required for the calibration of the internal FIM. After collecting data at different temperatures and attitudes, the full-temperature model parameters of the sensor, including the zero bias and scaling factor, can be calculated using a calibration algorithm.

[0005] The temperature chamber turntable is a very expensive high-precision device, which makes the full-temperature calibration cost of fiber optic inertial measurement units very high. Full-temperature calibration of fiber optic inertial measurement units is an effective and necessary means to improve the full-temperature accuracy and stability of the final product. The high cost of the temperature chamber turntable has become a key factor hindering the reduction of the cost of fiber optic inertial measurement unit products.

[0006] Therefore, in view of the problem of excessively high cost of full-temperature calibration of fiber optic inertial measurement units, this invention proposes a low-cost device and method for full-temperature calibration of fiber optic inertial measurement units. Summary of the Invention

[0007] To address the issue of reducing the cost of full-temperature calibration for fiber optic inertial measurement units (FIMs), this invention proposes a low-cost device and method for full-temperature calibration of FIMs.

[0008] The technical solution of this invention is as follows: a low-cost, full-temperature calibration device for fiber optic inertial measurement units, comprising: a temperature chamber for controlling the ambient temperature; a fiber optic inertial measurement unit, including a quartz accelerometer and a fiber optic gyroscope; a precision indexing rotary table, installed inside the temperature chamber, for achieving precise rotation of the fiber optic inertial measurement unit; a calibration fixture, fixed on the precision indexing rotary table, for fixing the fiber optic inertial measurement unit and ensuring that its reference plane is aligned with the reference plane of the fixture; and a high-precision inclinometer for calibrating the horizontal state of the precision indexing rotary table.

[0009] As a preferred embodiment, a low-cost full-temperature calibration method for fiber optic inertial measurement units (FIMs) includes the following steps: installing a precision indexing rotary table inside a temperature chamber and calibrating its horizontal state; fixing the FIM on a calibration fixture, ensuring its coordinate system is aligned with the fixture's reference surface; controlling the temperature chamber to run a full-temperature calibration process covering the FIM's operating temperature range; rotating the FIM using the precision indexing rotary table to sequentially align each axis to the sky and ground, collecting sensor data under different attitudes; calculating the scaling factor and a temperature change trend model for the zero-bias error based on the collected data; and using the model to compensate for errors in the FIM.

[0010] Preferably, the measurement model of the quartz accelerometer is as follows: In this context, the subscript A represents the quartz accelerometer, and the superscripts X, Y, and Z represent the three coordinate axes of the fiber optic inertial measurement unit. The true acceleration vector acting on the triaxial quartz accelerometer; The pulse output vector acquired by the triaxial quartz accelerometer; This is the scale factor vector of the triaxial quartz accelerometer; This is the zero-bias error vector of the triaxial quartz accelerometer; This is the installation error matrix for a triaxial quartz accelerometer. All superscripts T are matrix transpose symbols.

[0011] Preferably, the measurement model of the fiber optic gyroscope is as follows: In this context, the subscript G represents a quartz accelerometer; This is the true vector of the angular velocity acting on the three-axis fiber optic gyroscope. The pulse output vector acquired by the three-axis fiber optic gyroscope; is the scaling factor vector of the three-axis fiber optic gyroscope; This is the zero-bias error vector of the three-axis fiber optic gyroscope; This is the installation error matrix for a three-axis fiber optic gyroscope.

[0012] As a preferred option, the measurement compensation model for the quartz accelerometer can be derived from the model of the fiber optic gyroscope and the measurement model of the quartz accelerometer as follows: ,in, It is the zero bias error vector of the quartz accelerometer expressed using pulses.

[0013] As a preferred approach, a continuous temperature variable symbol T is introduced into the measurement model of the quartz accelerometer, and the compensation model of the quartz accelerometer is rewritten as follows: If the scaling factor and zero-bias temperature model are obtained, and the installation error matrix is ​​obtained according to the room temperature calibration, then the fiber optic inertial measurement unit can be compensated according to equation (4), and the true value of the physical quantity can be calculated according to its output pulse.

[0014] Preferably, the Z-axis of the fiber optic inertial measurement unit pointing upwards is designated as ZU, and the Z-axis pointing downwards is designated as ZD; the X-axis of the fiber optic inertial measurement unit pointing upwards is designated as XU, and the X-axis pointing downwards is designated as XD; the Y-axis of the fiber optic inertial measurement unit pointing upwards is designated as YU, and the Y-axis pointing downwards is designated as YD.

[0015] During calibration, the recorded measurement data are all digital signal outputs from the fiber optic inertial measurement unit. The scaling factor and temperature variation patterns of zero bias are hidden within the output digital signal sequence. Based on the measurement model, when the three coordinate axes of the fiber optic inertial measurement unit point upwards and downwards respectively, the true values ​​measured by the triaxial quartz accelerometer are: , where the vector symbol subscript describes the attitude of the fiber optic inertial measurement unit, and g is the gravitational acceleration constant.

[0016] As a preferred option, substituting equation (5) into the measurement equation that includes the temperature variable, the expansion can be written as:

[0017] ,in, The function of the X-axis quartz accelerometer output pulse measured under the Z-axis pointing to the sky as a function of temperature change can be understood as a polynomial model sequence of the collected temperature and sensor output sequence for the actual calibration process. It can be seen that the terms containing zero bias error have the same sign, while the terms containing scaling factor have opposite signs. Therefore, the linear combination of equations (6) to (11) can decompose and calculate the temperature trend of scaling factor and zero bias error.

[0018] As a preferred approach, the method for decomposing the temperature variation trend of the scaling factor and zero bias error is listed as follows:

[0019] The temperature trend of the zero bias error only includes the quartz accelerometer output pulses as a function of temperature under six attitudes; while the temperature trend of the scaling factor includes the gravitational acceleration constant g and the main diagonal elements of the installation error matrix. , and The gravitational acceleration constant can be calculated from the model or by querying the precise gravitational acceleration value at the calibration location. Since the installation error matrix does not change with temperature, the elements in the installation error matrix can be substituted into the calculation using the values ​​from the room temperature calibration.

[0020] As a preferred method, by rotating the precision rotary table inside the temperature chamber to obtain full-temperature calibration data for each axis pointing upwards and downwards, the scaling factor and zero bias error temperature trend of the fiber optic inertial measurement unit model can be obtained as a function of temperature. Based on this trend, a model with temperature as input and parameter values ​​as output is established, thereby completing the temperature calibration.

[0021] The beneficial effects of this invention are as follows: 1. This invention uses a high-precision rotary table to replace the expensive temperature chamber rotary table, fixing it in the temperature chamber to achieve the rotation of the fiber optic inertial measurement unit. This can significantly reduce the cost of full-temperature calibration of similar fiber optic inertial measurement units, while also being easy to operate, adaptable to a wide range, and easily expandable. 2. By collecting full-temperature data under each axis's pointing-to-the-sky and pointing-to-the-ground postures, and combining this with a mathematical model to decompose the scaling factor and the temperature change trend of zero bias, the full-temperature stability of the compensated sensor is significantly improved. Attached Figure Description

[0022] Figure 1 The diagram shown illustrates the installation and calibration of the precision indexing rotary table of the present invention. Figure 2 The diagram shown illustrates the fixing of the fiber optic inertial measurement unit of the present invention on a tooling fixture. Figure 3 The diagram shown is a schematic of the temperature calibration process for the fiber optic inertial measurement unit of the present invention. Figure 4 The diagram shows a comparison of the full-temperature calibration compensation effect of the X-axis quartz accelerometer of the present invention. Figure 5 The diagram shows a comparison of the full-temperature calibration compensation effect of the Y-axis quartz accelerometer of the present invention. Figure 6The diagram shows a comparison of the full-temperature calibration compensation effect of the Z-axis quartz accelerometer of the present invention. Figure 7 The diagram shows a comparison of the full-temperature calibration compensation effect of the X-axis fiber optic gyroscope of the present invention. Figure 8 The diagram shows a comparison of the full-temperature calibration compensation effect of the Y-axis fiber optic gyroscope of the present invention. Figure 9 The diagram shows a comparison of the full-temperature calibration compensation effect of the Z-axis fiber optic gyroscope of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides an embodiment of a low-cost, full-temperature calibration device for a fiber optic inertial measurement unit (FIM), comprising: a temperature chamber for controlling the ambient temperature; an FIM including a quartz accelerometer and a fiber optic gyroscope; a precision indexing rotary table installed inside the temperature chamber for precisely rotating the FIM; a calibration fixture fixed on the precision indexing rotary table for fixing the FIM and ensuring its reference plane is aligned with the fixture's reference plane; and a high-precision inclinometer for calibrating the horizontal state of the precision indexing rotary table.

[0025] Furthermore, in order to reduce the cost of full-temperature calibration of fiber optic inertial measurement units, it is necessary to avoid using expensive temperature chamber turntables. Temperature control of the temperature chamber is essential during the full-temperature calibration process. Therefore, in order to reduce costs, it is necessary to find a device to replace the turntable and achieve precise rotation and position control. This invention uses a precision indexing turntable to replace the turntable to achieve the flipping of the fiber optic inertial measurement unit being calibrated. The precision indexing turntable is a mature mechanical industrial product, which is often used in high-precision machining. Its manufacturing process is mature, its quality is reliable, and its price is low.

[0026] A precision indexing rotary table is a mechanical platform that uses an adjustable, high-precision worm gear to drive the table's rotation. The rotary table surface is fixedly connected to the worm gear, and the control handle is fixedly connected to the worm. Through an adjustable mechanism, the backlash (the gap or idle stroke in the worm gear drive) between the worm gear and the worm is reduced to zero. The high-precision worm gear and the zero-backlash precision transmission ensure the angular control accuracy of the precision indexing rotary table.

[0027] Please see Figure 1The vertical precision indexing rotary table used in this method needs to be installed inside the temperature chamber and properly calibrated. The vertical precision indexing rotary table is installed on the temperature chamber platform with a separate foundation, and calibrated using a high-precision inclinometer to ensure that the normal line of the rotary table surface (the Y-axis of the coordinate system in the figure above, which is also the rotation axis of the table surface) is horizontal. A stop is fixed on the rotary table surface, and the baseline of the rotary table surface determined by this stop (the dotted line in the figure below) is calibrated to a horizontal line. The angular position of the rotary table at this time is defined as 0 degrees. At this time, the XOY plane of the coordinate system in the figure is the local horizontal plane (the letter O represents the origin of the coordinate system in the figure above), and the Z-axis of the coordinate system is the local plumb line.

[0028] Please see Figure 2 The fiber optic inertial measurement unit (IMU) to be calibrated is fixed on the calibration fixture. The fixture should be in the form of a cuboid, and its design should ensure that at least two mutually perpendicular reference planes on the outer surface of the cuboid can be used as mounting planes, defined as reference plane A and reference plane B. It should also ensure that after the fiber optic IMU is fixed, its two mutually orthogonal axes become the normals of reference plane A and reference plane B of the fixture.

[0029] For clarity, the fixture only shows three adjacent and perpendicular faces of the cuboid. The reference face A is filled with a horizontal line, and the reference face B is filled with a vertical line. The bottom face of the fiber optic inertial measurement unit is fixed on the reference face A, and the coordinate axis Z is perpendicular to the reference face A. The coordinate axis Y is perpendicular to the reference face B. The coordinate system of the fiber optic inertial measurement unit is defined in the manner of right (X), front (Y), and top (Z).

[0030] Furthermore, the sensor model and calibration parameters are explained as follows: the Z-axis of the fiber optic inertial measurement unit pointing upwards is designated ZU, and the Z-axis pointing downwards is designated ZD; the X-axis of the fiber optic inertial measurement unit pointing upwards is designated XU, and the X-axis pointing downwards is designated XD; the Y-axis of the fiber optic inertial measurement unit pointing upwards is designated YU, and the Y-axis pointing downwards is designated YD.

[0031] The measurement model for the quartz accelerometer is listed below: In this context, the subscript A represents the quartz accelerometer, and the superscripts X, Y, and Z represent the three coordinate axes of the fiber optic inertial measurement unit. The true acceleration vector acting on the triaxial quartz accelerometer; The pulse output vector acquired by the triaxial quartz accelerometer; This is the scale factor vector of the triaxial quartz accelerometer; This is the zero-bias error vector of the triaxial quartz accelerometer; This is the installation error matrix for a triaxial quartz accelerometer. All superscripts T are matrix transpose symbols.

[0032] The measurement model for the fiber optic gyroscope is listed below: In this context, the subscript G represents a quartz accelerometer; This is the true vector of the angular velocity acting on the three-axis fiber optic gyroscope. The pulse output vector acquired by the three-axis fiber optic gyroscope; is the scaling factor vector of the three-axis fiber optic gyroscope; This is the zero-bias error vector of the three-axis fiber optic gyroscope; This is the installation error matrix for a three-axis fiber optic gyroscope.

[0033] The model structure of the fiber optic gyroscope is exactly the same as that of the quartz accelerometer. The following discussion will only cover the data processing and calculation methods of the quartz accelerometer. The data processing methods of the fiber optic gyroscope are exactly the same. Based on the previous definitions, the measurement compensation model of the quartz accelerometer can be derived as follows: ,in, It is the zero bias error vector of the quartz accelerometer expressed using pulses.

[0034] Furthermore, the calculation method for the model parameters is explained as follows: In the measurement model of the quartz accelerometer, the installation error matrix can be considered a constant (independent of time). However, the scaling factor and zero bias error change with temperature. The purpose of temperature calibration is to obtain a model of the temperature variation trend of the scaling factor and zero bias error. In the above compensation model, a continuous temperature variable symbol T is introduced (the symbol T in parentheses in the formula represents a continuous temperature variable, distinct from the matrix transpose symbol represented by the superscript T), and the quartz accelerometer compensation model is rewritten as follows: If the scaling factor and zero-bias temperature model are obtained, and the installation error matrix is ​​obtained according to the room temperature calibration, then the fiber optic inertial measurement unit can be compensated according to equation (4), and the true value of the physical quantity can be calculated according to its output pulse.

[0035] During calibration, the recorded measurement data are all digital signal outputs from the fiber optic inertial measurement unit (FIRST). The scaling factor and temperature variation patterns of the zero bias are hidden within the output digital signal sequence, and analysis is performed based on the measurement model. When the three coordinate axes of the FIRST point upwards and downwards respectively, the true values ​​measured by the triaxial quartz accelerometer are: In this equation, the vector symbol subscript describes the attitude of the fiber optic inertial measurement unit, and g is the gravitational acceleration constant. Substituting equation (5) into the measurement equation that includes the temperature variable, we can expand it to:

[0036] ,in, Let X be the function of the output pulse of the X-axis quartz accelerometer measured under Z-axis pointing upwards, which varies with temperature. For the actual calibration process, it can be understood as a polynomial model sequence of the collected temperature and sensor output sequence. It can be seen that the terms containing the zero bias error have the same sign, while the terms containing the scaling factor have opposite signs. Therefore, the linear combination of equations (6) to (11) can decompose and calculate the temperature trend of the scaling factor and the zero bias error. The decomposition method of the temperature change trend of the scaling factor and the zero bias error is listed as follows:

[0037] The temperature trend for zero bias error only includes the quartz accelerometer output pulses as a function of temperature under six attitudes; while the temperature trend for the scaling factor includes the gravitational acceleration constant g and the main diagonal elements of the installation error matrix. , and The gravitational acceleration constant can be calculated from the model or the precise gravitational acceleration value at the calibration location can be queried. Since the installation error matrix does not change with temperature, the elements in the installation error matrix can be substituted into the calculation using the results of the room temperature calibration (the room temperature calibration process does not require the use of a temperature chamber turntable).

[0038] In summary, by using the full-temperature calibration data obtained from the rotation of the precision rotary table inside the temperature chamber, the scaling factor and zero-bias error temperature trend of the fiber optic inertial measurement unit (including quartz accelerometers and fiber optic gyroscopes) can be obtained as a function of temperature. Establishing a model (such as a polynomial model) with temperature as input and parameter values ​​as output based on this trend completes the temperature calibration. It is important to note that every step mentioned in the flowchart is essential, and the data for each axis (pointing up and down) is required.

[0039] Please see Figure 3 Furthermore, the calibration method of the present invention is described as follows: First, the fiber optic inertial measurement unit to be calibrated is installed on a dedicated calibration fixture. The outer contour of the fixture is a cuboid, and the design ensures that there are at least two mutually perpendicular reference planes (A and B). During installation, the Z-axis of the fiber optic inertial measurement unit is perpendicular to the reference plane A of the fixture, and the Y-axis is perpendicular to the reference plane B. This installation method ensures that the coordinate system of the fiber optic inertial measurement unit is strictly aligned with the reference plane of the fixture, providing an accurate reference for subsequent attitude adjustment.

[0040] Place the reference surface B of the tooling tightly against the surface of the rotary table, and the reference surface A tightly against the stop block. Use a high-precision inclinometer to calibrate and ensure that the Y-axis of the rotary table surface is horizontal and the X-axis of the table surface determined by the stop block is also horizontal. At this time, define the angular position of the rotary table as 0 degrees, the XOY plane of the coordinate system as the local horizontal plane, and the Z-axis as the local vertical line.

[0041] The rotary table is zeroed and locked, and the temperature chamber runs the full-temperature calibration process. The Z-axis upward calibration data acquisition process is carried out, and the data ZU is collected. The rotary table is zeroed and locked, and the temperature chamber runs the full-temperature calibration process. During this process, the Z-axis of the fiber optic inertial measurement unit is perpendicular to the horizontal plane and points upward. The pulse data and temperature data output by the sensor are collected and recorded as ZU data.

[0042] After the temperature of the incubator returns to normal, the rotary table is rotated 90 degrees clockwise so that the X-axis of the fiber optic inertial measurement unit is perpendicular to the horizontal plane and points upward. The full-temperature calibration process of the incubator is run again, and the sensor output and temperature data under the X-axis pointing upward are collected and recorded as XU data.

[0043] After the temperature chamber returns to room temperature, control the rotary table to rotate 90 degrees clockwise again, so that the Z-axis is perpendicular to the horizontal plane and points downwards. Run the temperature chamber calibration process, collect data with the Z-axis pointing downwards, and record it as ZD data.

[0044] After the temperature chamber returns to room temperature, control the rotary table to continue rotating 90 degrees clockwise so that the X-axis is perpendicular to the horizontal plane and points downwards. Run the temperature chamber calibration process, collect data with the X-axis pointing to the ground, and record it as XD.

[0045] After the temperature chamber returns to room temperature, control the rotary table to zero, remove the fixture from the rotary table, and reinstall it so that reference surface A is in close contact with the rotary table surface and reference surface B is in close contact with the stop block. At this time, the Y-axis of the fiber optic inertial measurement unit is perpendicular to the horizontal plane and points upward. The rotary table is zeroed and locked, ready for Y-axis calibration data acquisition.

[0046] Run the full-temperature calibration process of the temperature chamber, collect the sensor output and temperature data under the Y-axis pointing upwards posture, and record it as YU.

[0047] After the temperature chamber returns to room temperature, control the rotary table to rotate 180 degrees so that the Y-axis is perpendicular to the horizontal plane and points downwards. Run the temperature chamber calibration process, collect data with the Y-axis pointing downwards, and record it as YD.

[0048] The calibration calculation was completed based on 6 sets of calibration data and the sensor measurement model.

[0049] Furthermore, this invention proposes an embodiment comparing temperature chamber turntable calibration with low-cost calibration: A certain type of fiber optic inertial measurement unit includes a three-axis quartz accelerometer and a three-axis fiber optic gyroscope. Without compensation, it is fixed in a temperature chamber and subjected to a uniform temperature change test from -40 to 60°C at a slope of 1°C / min. Pulse data is collected, and the pulse data is converted to acceleration and angular velocity units based on the constant scaling factor obtained from room temperature calibration. Combined with the temperature sequence, a 10-second segmented average processing (referred to as 10-second smoothing) is performed to obtain the uncompensated sensor full-temperature stability sequence. Then, the full-temperature zero-bias stability standard deviation index is calculated based on this sequence, i.e., the standard deviation of the 10-second smoothed data sequence relative to its own mean. The fiber optic inertial measurement unit (IMU) was calibrated at full temperature using the apparatus and method of this invention. The parameters and compensation model were written into the software. The calibrated IMU underwent repeated uniform temperature change tests, and the compensated physical quantity time series was collected. The temperature series was then smoothed for 10 seconds to obtain the compensated sensor full-temperature stability series. The full-temperature zero-bias stability standard deviation was calculated from this series using the same method. The same calibration process was performed using a temperature chamber turntable, and another full-temperature uniform temperature change test was conducted to obtain the compensated stability series and stability standard deviation.

[0050] The temperature trend curves of the 10s smoothed data are plotted below. The red curve is the uncompensated full-temperature stability sequence, the blue curve is the full-temperature stability sequence after low-cost full-temperature calibration compensation, and the green curve is the full-temperature stability sequence after full-temperature calibration compensation of the temperature chamber turntable.

[0051] Please see Figures 4-9 In the figure, 10s smoothing reduces the spikes in the quartz accelerometer curve. It can be clearly seen that the uncalibrated data curve has a significant trend with temperature change. Both compensation methods make the trend of the quartz accelerometer with temperature change less obvious. Since the 10s smoothing of the gyroscope still has a lot of spikes, the three time series graphs are drawn as dashed lines for easy observation. It can be seen that the red dashed line before calibration fluctuates a lot. After calibration using the low-cost method (blue dashed curve), the sensor output fluctuates less. The result of calibration using the temperature chamber turntable (green dashed line) is almost completely covered by the red and blue lines.

[0052] The standard deviation of the full-temperature zero-bias stability before and after compensation using the two methods is shown in the table below:

[0053] .

[0054] As shown in the numerical analysis in Table 1, both calibration and compensation methods can effectively compensate for the temperature trend of the fiber optic inertial measurement unit, especially for the full-temperature calibration and compensation of the quartz accelerometer, resulting in an order-of-magnitude improvement in full-temperature stability. The temperature chamber turntable method exhibits high compensation accuracy, an advantage derived from the high-precision control of the temperature chamber turntable. In terms of compensation accuracy, the low-cost method described in this invention is comparable to the full-temperature calibration and compensation method of the temperature chamber turntable, strongly demonstrating the effectiveness of the device and method described in this invention.

[0055] This invention uses a high-precision rotary table to replace an expensive rotary table. During the controlled temperature change test, the fiber optic inertial measurement unit is rotated inside the temperature chamber to record the data of each axis of the sensor pointing upwards and downwards. Based on the model and using the algorithm, the scaling factor and the zero bias temperature change trend are obtained by elimination, thus completing the full-temperature calibration of the fiber optic inertial measurement unit and achieving the goal of significantly reducing the full-temperature calibration cost of similar fiber optic inertial measurement units.

Claims

1. A low-cost, full-temperature calibration method for fiber optic inertial measurement units, characterized in that, The process includes the following steps: installing a precision indexing rotary table inside the temperature chamber and calibrating its level; fixing the fiber optic inertial measurement unit (IMU) on the calibration fixture, ensuring its coordinate system is aligned with the fixture's reference surface; controlling the temperature chamber to run a full-temperature calibration process, covering the IMU's operating temperature range; rotating the IMU using the precision indexing rotary table, sequentially pointing each axis upwards and downwards, and collecting sensor data under different attitudes; calculating the scaling factor and zero-bias error temperature change trend model based on the collected data; using the model to compensate for errors in the IMU; and listing the decomposition method of the scaling factor and zero-bias error temperature change trend as a formula as follows: ,in, The pulse output vector acquired by the triaxial quartz accelerometer; This is the scale factor vector of the triaxial quartz accelerometer; This is the zero-bias error vector of the quartz accelerometer expressed using pulses; the Z-axis of the fiber optic inertial measurement unit is set to ZU (pointing upwards), and the Z-axis of the fiber optic inertial measurement unit is set to ZD (pointing downwards); the X-axis of the fiber optic inertial measurement unit is set to XU (pointing upwards), and the X-axis of the fiber optic inertial measurement unit is set to XD (pointing downwards); the Y-axis of the fiber optic inertial measurement unit is set to YU (pointing upwards), and the Y-axis of the fiber optic inertial measurement unit is set to YD (pointing downwards). The temperature trend of the X-axis quartz accelerometer output pulse measured under the Z-axis pointing-up condition is a function of temperature; and so on. The temperature trend of the zero bias error only includes the function of the quartz accelerometer output pulse with respect to temperature under six attitudes; while the temperature trend of the scaling factor includes the gravitational acceleration constant g and the main diagonal elements of the installation error matrix. , and The gravitational acceleration constant can be calculated from the model or by querying the precise gravitational acceleration value at the calibration location. Since the installation error matrix does not change with temperature, the elements in the installation error matrix can be substituted into the calculation using the values ​​from the room temperature calibration.

2. The low-cost full-temperature calibration method for fiber optic inertial measurement units according to claim 1, characterized in that: The measurement model of the quartz accelerometer is as follows: In this context, the subscript A represents the quartz accelerometer, and the superscripts X, Y, and Z represent the three coordinate axes of the fiber optic inertial measurement unit. The true acceleration vector acting on the triaxial quartz accelerometer; The pulse output vector acquired by the triaxial quartz accelerometer; This is the scale factor vector of the triaxial quartz accelerometer; This is the zero-bias error vector of the triaxial quartz accelerometer; This is the installation error matrix for a triaxial quartz accelerometer. All superscripts T are matrix transpose symbols.

3. The low-cost full-temperature calibration method for fiber optic inertial measurement units according to claim 2, characterized in that, The measurement model for a fiber optic gyroscope is as follows: In this context, the subscript G represents a quartz accelerometer; This is the true vector of the angular velocity acting on the three-axis fiber optic gyroscope. Pulse output vector acquired by a three-axis fiber optic gyroscope; is the scaling factor vector of the three-axis fiber optic gyroscope; This is the zero-bias error vector of the three-axis fiber optic gyroscope; This is the installation error matrix for a three-axis fiber optic gyroscope.

4. A low-cost, full-temperature calibration method for fiber optic inertial measurement units according to claim 3, characterized in that: The measurement compensation model for the quartz accelerometer can be derived from the model of the fiber optic gyroscope and the measurement model of the quartz accelerometer as follows: ,in, It is the zero bias error vector of the quartz accelerometer expressed using pulses.

5. A low-cost, full-temperature calibration method for fiber optic inertial measurement units according to claim 4, characterized in that: By introducing the continuous temperature variable symbol T into the measurement model of the quartz accelerometer, the compensation model of the quartz accelerometer is rewritten as follows: If the scaling factor and zero-bias temperature model are obtained, and the installation error matrix is ​​obtained according to the room temperature calibration, then the fiber optic inertial measurement unit can be compensated according to equation (4), and the true value of the physical quantity can be calculated according to its output pulse.

6. A low-cost, full-temperature calibration method for fiber optic inertial measurement units according to claim 5, characterized in that: During calibration, the recorded measurement data are all digital signal outputs from the fiber optic inertial measurement unit. The scaling factor and temperature variation patterns of zero bias are hidden within the output digital signal sequence. Based on the measurement model, when the three coordinate axes of the fiber optic inertial measurement unit point upwards and downwards respectively, the true values ​​measured by the triaxial quartz accelerometer are: , where the vector symbol subscript describes the attitude of the fiber optic inertial measurement unit, and g is the gravitational acceleration constant.

7. A low-cost, full-temperature calibration method for fiber optic inertial measurement units according to claim 6, characterized in that: Substituting equation (5) into the measurement equation that includes the temperature variable, we can expand it to: ,in, The function of the X-axis quartz accelerometer output pulse measured under the Z-axis pointing to the sky as a function of temperature change can be understood as a polynomial model sequence of the collected temperature and sensor output sequence for the actual calibration process. It can be seen that the terms containing zero bias error have the same sign, while the terms containing scaling factor have opposite signs. Therefore, the linear combination of equations (6) to (11) can decompose and calculate the temperature trend of scaling factor and zero bias error.

8. A low-cost, full-temperature calibration method for fiber optic inertial measurement units according to any one of claims 1-7, characterized in that: By using the full-temperature calibration data obtained by rotating the precision rotary table inside the temperature chamber, which points to the sky and to the ground along each axis, the scaling factor and zero bias error temperature trend of the fiber optic inertial measurement unit model can be obtained. Based on this trend, a model with temperature as input and parameter values ​​as output is established, thereby completing the temperature calibration.

9. A device for low-cost full-temperature calibration of fiber optic inertial measurement units, characterized in that, The method described in any one of claims 1-8 includes: a temperature chamber for controlling the ambient temperature; a fiber optic inertial measurement unit including a quartz accelerometer and a fiber optic gyroscope; a precision indexing rotary table installed in the temperature chamber for achieving precise rotation of the fiber optic inertial measurement unit; and a calibration fixture fixed on the precision indexing rotary table for fixing the fiber optic inertial measurement unit and ensuring that its reference surface is aligned with the reference surface of the fixture. A high-precision inclinometer is used to calibrate the horizontal state of a precision indexing rotary table.

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