Low-cost full-temperature calibration device and method for optical fiber inertial measurement unit

Abstract

The invention relates to the technical field of inertial navigation, in particular to a low-cost full-temperature calibration device and method for an optical fiber inertial measurement unit, and the device comprises an incubator which is used for controlling the environment temperature; the optical fiber inertial measurement unit comprises a quartz accelerometer and an optical fiber gyroscope; the precise indexing rotary table is mounted in the incubator and is used for realizing precise overturning of the optical fiber inertial measurement unit; the calibration tool is fixed on the precise indexing rotary table and is used for fixing the optical fiber inertial measurement unit and ensuring that the reference surface of the optical fiber inertial measurement unit is aligned with the reference surface of the tool; the high-precision inclinometer is used for calibrating the horizontal state of the precise indexing rotary table; the high-precision rotary table is used for replacing an expensive incubator rotary table and is fixed in the incubator to realize overturning of the optical fiber inertial measurement unit, so that the cost of full-temperature calibration of similar optical fiber inertial measurement units can be greatly reduced, and meanwhile, the full-temperature calibration device has the characteristics of simplicity and convenience in operation, wide application range and convenience in expansion.

Description

Technical Field

[0001] The present invention relates to the field of inertial navigation technology, and in particular to a low-cost full-temperature calibration device and method for a fiber optic inertial measurement unit. Background Art

[0002] A fiber-optic inertial measurement unit (FIMU) 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. Linear acceleration is measured by a quartz accelerometer, and rotational angular increment is measured by a fiber-optic gyroscope. A complete FIMU contains three quartz accelerometers and three fiber-optic gyroscopes. Both sensors are fixed orthogonally along the X, Y, and Z axes according to the IMU's own coordinate system. The FIMU also contains a temperature sensor for measuring the temperature of each sensor and a power supply module. Its internal acquisition hardware outputs each physical quantity (acceleration, angular increment, and temperature) as a digital signal.

[0003] Due to mechanical and manufacturing limitations, the feedback data of quartz accelerometers and fiber optic gyroscopes is affected by temperature, which causes sensor errors. Common fiber optic inertial measurement unit models include scale factors, installation error matrices, and biases. The scale factors and biases vary with temperature, and this variation can be significant over a wide temperature range. Full-temperature calibration is required to improve the stability and accuracy of the fiber optic inertial measurement unit. Full-temperature calibration and compensation of a fiber optic inertial measurement unit is defined as: Based on the models of quartz accelerometers and fiber optic gyroscopes, using appropriate devices, equipment, and instruments, and following a temperature test process (the temperature range covers the entire operating temperature range of the fiber optic inertial measurement unit), sensor data from the test unit is collected, model parameters are calculated, and error compensation is performed based on the model parameters to eliminate temperature effects and improve stability and accuracy.

[0004] The existing fiber optic inertial measurement unit full-temperature calibration requires the use of a temperature chamber turntable. For example, a typical three-axis turntable has, from the outside to the inside, the azimuth, pitch, and roll degrees of freedom of the turntable. A temperature chamber is fixed on the roll degree of freedom. During the temperature calibration process, the fiber optic inertial measurement unit is fixed inside the temperature chamber. The ambient temperature is controlled by the temperature chamber, and the turntable drives the temperature chamber to rotate, forming the different postures required for the internal fiber optic inertial measurement unit calibration. After fully collecting data at different temperatures and different postures, the calibration algorithm can be used to calculate the full-temperature model parameters of the sensor, including the zero bias and scale factor.

[0005] The temperature chamber turntable is a very expensive high-precision device, which makes the full-temperature calibration cost of the fiber optic inertial measurement unit very high. The full-temperature calibration of the fiber optic inertial measurement unit 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, to address the problem of high cost of full-temperature calibration of the above-mentioned fiber optic inertial measurement unit, the present invention proposes a low-cost full-temperature calibration device and method for a fiber optic inertial measurement unit. Summary of the Invention

[0007] In order to reduce the cost of full-temperature calibration of a fiber optic inertial measurement unit, the present invention proposes a low-cost full-temperature calibration device and method for a fiber optic inertial measurement unit.

[0008] The technical solution of the present invention is: a low-cost full-temperature calibration device for a fiber-optic inertial measurement unit, comprising: a temperature chamber for controlling the ambient temperature; a fiber-optic inertial measurement unit, comprising a quartz accelerometer and a fiber-optic gyroscope; a precision indexing turntable installed in the temperature chamber and used to achieve precise flipping of the fiber-optic inertial measurement unit; a calibration fixture fixed to the precision indexing turntable and used to fix the fiber-optic inertial measurement unit and ensure that its reference surface is aligned with the fixture reference surface; and a high-precision inclinometer for calibrating the horizontal state of the precision indexing turntable.

[0009] Preferably, a low-cost full-temperature calibration method for a fiber optic inertial measurement unit comprises the following steps: installing a precision indexing turntable in a temperature chamber and calibrating its horizontal state; fixing the fiber optic inertial measurement unit on a calibration fixture to ensure that its coordinate system is aligned with the fixture reference plane; controlling the temperature chamber to run a full-temperature calibration process to cover the operating temperature range of the fiber optic inertial measurement unit; flipping the fiber optic inertial measurement unit via the precision indexing turntable so that each axis points upward and downward in turn, and collecting sensor data in different postures; calculating a temperature variation trend model of the scale factor and zero bias error based on the collected data; and using the model to perform error compensation on the fiber optic inertial measurement unit.

[0010] Preferably, the measurement model of the quartz accelerometer is as follows: , Wherein, 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; is the true value vector of acceleration acting on the triaxial quartz accelerometer; It is the pulse output vector collected by the three-axis quartz accelerometer; is the scale factor vector of the triaxial quartz accelerometer; is the bias error vector of the tri-axis quartz accelerometer; is the installation error matrix of the tri-axis quartz accelerometer. All superscript Ts are matrix transpose symbols.

[0011] Preferably, the measurement model of the fiber optic gyroscope is as follows: , Wherein, the subscript G represents a quartz accelerometer; is the true value vector of the angular velocity acting on the three-axis fiber optic gyroscope; It is the pulse output vector collected by the three-axis fiber optic gyroscope; is the scale factor vector of the three-axis fiber optic gyroscope; is the bias error vector of the three-axis fiber optic gyroscope; is the installation error matrix of the three-axis fiber optic gyroscope.

[0012] Preferably, the measurement compensation model of 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, is the quartz accelerometer bias error vector expressed in pulses.

[0013] As a preference, 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 temperature model of the scale factor and zero bias is obtained, and the installation error matrix is obtained based on the normal temperature calibration, the fiber optic inertial measurement unit can be compensated according to formula (4), and the true value of the physical quantity can be calculated based on its output pulse.

[0014] As a preference, the Z-axis pointing upward of the fiber optic inertial measurement unit is set as ZU, and the Z-axis pointing ground of the fiber optic inertial measurement unit is set as ZD; the X-axis pointing upward of the fiber optic inertial measurement unit is set as XU, and the X-axis pointing ground of the fiber optic inertial measurement unit is set as XD; the Y-axis pointing upward of the fiber optic inertial measurement unit is set as YU, and the Y-axis pointing ground of the fiber optic inertial measurement unit is set as YD; During the calibration process, the recorded measurement data are all digital signal outputs of the fiber optic inertial measurement unit. The temperature variation patterns of the scale factor and zero bias are hidden in the output digital signal sequence. According to the measurement model, when the three coordinate axes of the fiber optic inertial measurement unit are pointing to the sky and the ground respectively, the true value measured by the triaxial quartz accelerometer is: , The vector symbol subscript describes the attitude of the fiber optic inertial measurement unit, and g is the gravitational acceleration constant.

[0015] As a preference, Equation (5) is brought into the measurement equation containing the temperature variable and expanded to be written as: , in, is the function of the X-axis quartz accelerometer output pulse measured under the Z-axis pointing sky condition with temperature variation. The actual calibration process 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 are of the same sign, while the terms containing the scale factor are of different signs. Therefore, the linear combination of equations (6) to (11) can decompose and calculate the temperature trend of the scale factor and zero bias error.

[0016] Preferably, the temperature variation trend decomposition method of the scale factor and the zero bias error is listed as follows: , The temperature trend of the bias error only contains the function of the quartz accelerometer output pulse relative to temperature in the six attitudes; while the temperature trend of the scale factor contains the gravitational acceleration constant g and the main diagonal elements in the installation error matrix 、 and The gravitational acceleration constant can be calculated based on 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 result values of the normal temperature calibration.

[0017] Preferably, the full-temperature calibration data of each axis pointing to the sky and the ground is obtained by flipping the precision turntable in the temperature chamber, and the scale factor and zero bias error temperature trend with temperature change in the fiber optic inertial measurement unit model can be obtained. A model with temperature as input and parameter value as output is established for this trend, thereby completing the temperature calibration.

[0018] The beneficial effects of the present invention are as follows: 1. The present invention uses a high-precision turntable to replace the expensive temperature chamber turntable. This turntable is fixed in the temperature chamber to achieve the flipping of the fiber-optic inertial measurement unit, significantly reducing the cost of full-temperature calibration of similar fiber-optic inertial measurement units. It also features ease of operation, wide adaptability, and ease of expansion. 2. By collecting full-temperature data for each axis in both the sky-pointing and the earth-pointing postures and combining it with a mathematical model to decompose the temperature variation trend of the scale factor and zero bias, the full-temperature stability of the compensated sensor is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown is a schematic diagram of the installation and calibration of the precision indexing turntable of the present invention; Figure 2 Shown is a schematic diagram of fixing the fiber optic inertial measurement unit of the present invention on the tooling; Figure 3 Shown is a schematic diagram of the temperature calibration process of the fiber optic inertial measurement unit of the present invention; Figure 4Shown is a schematic diagram comparing the full-temperature calibration compensation effects of the X-axis quartz accelerometer of the present invention; Figure 5 Shown is a schematic diagram comparing the full-temperature calibration compensation effects of the Y-axis quartz accelerometer of the present invention; Figure 6 Shown is a schematic diagram comparing the full-temperature calibration compensation effects of the Z-axis quartz accelerometer of the present invention; Figure 7 Shown is a schematic diagram comparing the full-temperature calibration compensation effects of the X-axis fiber optic gyroscope of the present invention; Figure 8 Shown is a schematic diagram comparing the full-temperature calibration compensation effects of the Y-axis fiber optic gyroscope of the present invention; Figure 9 Shown is a schematic diagram comparing the full-temperature calibration compensation effects of the Z-axis fiber optic gyroscope of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, 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 part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0021] The present invention provides an embodiment: a low-cost full-temperature calibration device for a fiber-optic inertial measurement unit, comprising: a temperature chamber for controlling the ambient temperature; a fiber-optic inertial measurement unit comprising a quartz accelerometer and a fiber-optic gyroscope; a precision indexing turntable installed in the temperature chamber and used to achieve precise flipping of the fiber-optic inertial measurement unit; a calibration fixture fixed to the precision indexing turntable and used to fix the fiber-optic inertial measurement unit and ensure that its reference surface is aligned with the fixture reference surface; and a high-precision inclinometer for calibrating the horizontal state of the precision indexing turntable.

[0022] Furthermore, in order to reduce the cost of full-temperature calibration of the fiber optic inertial measurement unit, it is necessary to avoid using an expensive temperature chamber turntable. During the full-temperature calibration process, temperature control of the temperature chamber is essential. Therefore, in order to reduce costs, it is necessary to find a device to replace the turntable to achieve precise rotation and position control. The present invention uses a precision indexing turntable instead of a turntable to achieve the flipping of the calibrated fiber optic inertial measurement unit. The precision indexing turntable is a mature mechanical industry product, which is often used for high-precision machining. Its manufacturing process is mature, the quality is reliable, and the price is low.

[0023] The precision indexing rotary table is a mechanical platform that uses an adjustable, high-precision worm gear to drive the tabletop's rotation. The tabletop is rigidly connected to the worm gear, and the control handle is rigidly connected to the worm gear. An adjustable mechanism reduces backlash (the gap or idle travel in the worm gear drive) between the worm gear and the worm gear to zero. The high-precision worm gear and zero-backlash precision drive ensure the precision of the precision indexing rotary table's angular control.

[0024] See also Figure 1 The vertical precision indexing turntable device used in this method needs to be installed in the incubator and properly calibrated. The vertical precision indexing turntable is installed on the incubator table with a separate foundation, and is calibrated using a high-precision inclinometer to ensure that the normal line of the turntable table (the Y axis of the coordinate system in the above figure, which is also the rotation axis of the table) is horizontal; a stopper is fixed on the turntable table, and the turntable table baseline determined by this stopper (the dotted line in the figure below) is calibrated to a horizontal line, and the angular position of the turntable 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 above figure), and the Z axis of the coordinate system is the local plumb line.

[0025] See also Figure 2 The Fiber Optic Inertial Measurement Unit (FIMU) to be calibrated is fixed to the calibration fixture. The fixture should have a rectangular outer contour. The design must ensure that at least two mutually perpendicular reference surfaces on the outer surface of the cuboid can be used as mounting planes, defined as reference plane A and reference plane B. It must also ensure that after the FIMU to be calibrated is fixed, its two mutually orthogonal axes become the normals of the fixture reference planes A and B.

[0026] For clarity, the tooling only draws three adjacent and perpendicular faces of the cuboid, of which reference face A is filled with horizontal lines, and reference face B is filled with vertical lines. The bottom face of the fiber optic inertial measurement unit is fixed on reference face A, and the coordinate axis Z is perpendicular to reference face A; the coordinate axis Y is perpendicular to reference face B. The coordinate system of the fiber optic inertial measurement unit is defined as right (X), front (Y), and top (Z).

[0027] Furthermore, the sensor model and calibration parameters are explained as follows: the Z-axis pointing upward of the fiber optic inertial measurement unit is set as ZU, and the Z-axis pointing ground of the fiber optic inertial measurement unit is set as ZD; the X-axis pointing upward of the fiber optic inertial measurement unit is set as XU, and the X-axis pointing ground of the fiber optic inertial measurement unit is set as XD; the Y-axis pointing upward of the fiber optic inertial measurement unit is set as YU, and the Y-axis pointing ground of the fiber optic inertial measurement unit is set as YD; The measurement model of the quartz accelerometer is listed as follows: , Wherein, 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; is the true value vector of acceleration acting on the triaxial quartz accelerometer; It is the pulse output vector collected by the three-axis quartz accelerometer; is the scale factor vector of the triaxial quartz accelerometer; is the bias error vector of the tri-axis quartz accelerometer; is the installation error matrix of the tri-axis quartz accelerometer. All superscript Ts are matrix transpose symbols.

[0028] The measurement model of the fiber optic gyroscope is listed as follows: , Wherein, the subscript G represents a quartz accelerometer; is the true value vector of the angular velocity acting on the three-axis fiber optic gyroscope; It is the pulse output vector collected by the three-axis fiber optic gyroscope; is the scale factor vector of the three-axis fiber optic gyroscope; is the bias error vector of the three-axis fiber optic gyroscope; is the installation error matrix of the three-axis fiber optic gyroscope.

[0029] The model structure of the fiber optic gyroscope is exactly the same as that of the quartz accelerometer. The following article only discusses 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 definition, the measurement compensation model of the quartz accelerometer can be derived as follows: , in, is the quartz accelerometer bias error vector expressed in pulses.

[0030] Furthermore, the model parameter calculation method is explained: In the measurement model of the quartz accelerometer, the installation error matrix can be considered a constant (independent of time). However, the scale factor and bias error will change with temperature. The purpose of temperature calibration is to obtain a temperature trend model for the scale factor and bias error. Introducing the continuous temperature variable symbol T into the above compensation model (the symbol T in brackets is the continuous temperature variable, different from the matrix transpose symbol represented by the superscript T), the quartz accelerometer compensation model is rewritten as follows: , If the temperature model of the scale factor and zero bias is obtained, and the installation error matrix is obtained based on the normal temperature calibration, the fiber optic inertial measurement unit can be compensated according to formula (4), and the true value of the physical quantity can be calculated based on its output pulse.

[0031] During the calibration process, the recorded measurement data are all digital signal outputs of the fiber optic inertial measurement unit. The temperature variation patterns of the scale factor and zero bias are hidden in the output digital signal sequence and analyzed according to the measurement model. When the three coordinate axes of the fiber optic inertial measurement unit are pointing to the sky and the ground respectively, the true value measured by the triaxial quartz accelerometer is: , Wherein, the vector symbol subscript describes the attitude of the fiber optic inertial measurement unit, g is the gravitational acceleration constant, and Equation (5) is substituted into the measurement equation containing the temperature variable, which can be expanded to: , in, is the function of the X-axis quartz accelerometer output pulse measured under the Z-axis pointing sky condition with temperature variation. The actual calibration process 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 are all of the same sign, while the terms containing the scale factor are of different signs. Therefore, the linear combination of equations (6) to (11) can decompose and calculate the temperature trend of the scale factor and the zero bias error. The decomposition method of the temperature variation trend of the scale factor and the zero bias error is listed as follows: , The temperature trend of the bias error only contains the function of the quartz accelerometer output pulse relative to temperature in the six attitudes; while the temperature trend of the scale factor contains the gravitational acceleration constant g and the main diagonal elements in the installation error matrix 、 and The gravitational acceleration constant can be calculated based on 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 result values of the normal temperature calibration (the normal temperature calibration process does not require the use of a temperature chamber turntable).

[0032] In summary, by flipping the precision turntable in the temperature chamber to obtain the full-temperature calibration data of each axis pointing to the sky and the ground, the scale factor and zero bias error temperature trend of the fiber optic inertial measurement unit (including quartz accelerometers and fiber optic gyroscopes) model that changes with temperature can be obtained. Based on this trend, a model with temperature as input and parameter values as output (such as a polynomial model) is established to complete the temperature calibration. It should be noted that each step mentioned in the flowchart is indispensable, and the data for each axis pointing to the sky and the ground are required.

[0033] See also 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 rectangular parallelepiped, and the design ensures that there are at least two mutually perpendicular reference surfaces (A and B). During installation, the Z axis of the fiber optic inertial measurement unit is perpendicular to the reference surface A of the fixture, and the Y axis is perpendicular to the reference surface B. This installation method ensures that the coordinate system of the fiber optic inertial measurement unit is strictly aligned with the reference surface of the fixture, providing an accurate reference for subsequent posture adjustment.

[0034] Place the reference surface B of the fixture close to the table of the turntable, and the reference surface A close to the block. Use a high-precision inclinometer to calibrate to ensure that the Y-axis of the turntable is horizontal and the X-axis of the table determined by the block is also horizontal. At this time, the angular position of the turntable is defined as 0 degrees, the XOY plane of the coordinate system is the local horizontal plane, and the Z axis is the local plumb line.

[0035] The turntable is reset to zero and locked, the temperature chamber runs the full-temperature calibration process, and the Z-axis pointing-up calibration data collection process is carried out. The data ZU is collected, the turntable is reset to zero and locked, and the temperature chamber is started to run 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.

[0036] After the incubator returns to room temperature, control the turntable to rotate 90 degrees clockwise so that the X-axis of the fiber optic inertial measurement unit is perpendicular to the horizontal plane and points upward. Run the incubator's full-temperature calibration process again to collect sensor output and temperature data in the X-axis pointing upward attitude and record them as XU data.

[0037] After the incubator returns to room temperature, control the turntable to rotate 90 degrees clockwise again so that the Z axis is perpendicular to the horizontal plane and points downward. Run the incubator calibration process and collect data with the Z axis pointing to the ground, which is recorded as ZD data.

[0038] After the incubator returns to room temperature, control the turntable to continue rotating 90 degrees clockwise so that the X-axis is perpendicular to the horizontal plane and points downward. Run the incubator calibration process and collect data with the X-axis pointing to the ground, which is recorded as XD.

[0039] After the incubator returns to room temperature, control the turntable to zero, remove the tooling from the turntable, and reinstall it so that reference surface A is close to the turntable surface and reference surface B is close to the block. At this time, the Y-axis of the fiber optic inertial measurement unit is perpendicular to the horizontal plane and points upward. The turntable is zeroed and locked, and preparation is made for Y-axis calibration data collection.

[0040] Run the full-temperature calibration process in the temperature chamber to collect the sensor output and temperature data in the Y-axis pointing upward posture, and record them as YU.

[0041] After the incubator returns to room temperature, control the turntable to rotate 180 degrees so that the Y-axis is perpendicular to the horizontal plane and points downward. Run the incubator calibration process and collect data with the Y-axis pointing to the ground, which is recorded as YD.

[0042] The calibration calculation is completed based on 6 sets of calibration data and sensor measurement model.

[0043] Furthermore, the present invention proposes an embodiment for 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, which are fixed in a temperature chamber without compensation and subjected to a uniform temperature change test from -40~60℃ with a slope of 1℃ / min. Pulse data is collected and converted into acceleration and angular velocity units based on the constant scale factor obtained from the normal temperature calibration. The temperature sequence is combined with a 10s segmented averaging process for the data (referred to as 10s smoothing) to obtain the uncompensated sensor full-temperature stability sequence. The full-temperature zero-bias stability standard deviation index is then calculated based on this sequence, that is, the standard deviation of the 10s smoothed data sequence relative to its own mean is calculated. The fiber-optic inertial measurement unit (FIMU) was calibrated over full temperature using the device and method of the present invention. The parameters and compensation model were written into the software. The calibrated FIMU was then subjected to repeated uniform temperature change tests. The compensated physical quantity time series was collected and, combined with the temperature series, smoothed for 10 seconds. This was the compensated sensor's full-temperature stability series. The full-temperature zero-bias stability standard deviation index was calculated for this series using the same method. The same calibration was performed using a temperature chamber turntable, and the full-temperature uniform temperature change test was repeated to obtain the compensated stability series and stability standard deviation index.

[0044] The temperature trend curve of the 10-second smoothed data is plotted as follows, where 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 and compensation, and the green curve is the full-temperature stability sequence after full-temperature calibration and compensation using the incubator turntable.

[0045] See also Figure 4-Figure 9 In the figure, 10s smoothing reduces the burrs on the quartz accelerometer curve. It can be clearly seen that the calibration data curve has a significant trend with temperature. Both compensation methods make the temperature trend of the quartz accelerometer less obvious. Because the 10s smoothing of the gyroscope still has large burrs, for ease of observation, the three time series graphs are drawn in dotted form. It can be seen that the red dotted line before calibration has large fluctuations. After calibration using the low-cost method (blue dotted curve), the sensor output fluctuations are even smaller. The result of calibration using the incubator turntable (green dotted line) is almost completely covered by the red and blue lines.

[0046] The full temperature zero bias stability standard deviation indicators before compensation and after compensation using the two methods are shown in the following table: .

[0047] The numerical analysis in Table 1 demonstrates that both calibration and compensation methods effectively compensate for the temperature trends of the fiber-optic inertial measurement unit, particularly the full-temperature calibration and compensation of the quartz accelerometer. The full-temperature stability after compensation is improved by an order of magnitude. The compensation accuracy of the temperature chamber turntable method is very high, a benefit brought about by 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 using the temperature chamber turntable. This result strongly demonstrates the effectiveness of the device and method described in this invention.

[0048] The present invention uses a high-precision turntable instead of an expensive one. During a controlled temperature change test, the fiber-optic inertial measurement unit (FIMU) is flipped inside a temperature chamber, and the upward and downward pointing data of each sensor axis are recorded. Using an algorithm based on a model, the scale factor and zero bias temperature variation trend are decomposed and decomposed to complete the full-temperature calibration of the FIMU, significantly reducing the full-temperature calibration cost of similar FIMUs.

Claims

1. A low-cost full-temperature calibration device for a fiber-optic inertial measurement unit, characterized in that: It includes: a temperature chamber for controlling the ambient temperature; a fiber optic inertial measurement unit (FIMU) containing a quartz accelerometer and a fiber optic gyroscope; a precision indexing turntable installed in the temperature chamber for precise flipping of the FIMU; and a calibration fixture fixed on the precision indexing turntable for fixing the FIMU and ensuring that its reference surface is aligned with the fixture reference surface. High-precision inclinometer, used to calibrate the horizontal state of the precision indexing turntable.

2. A low-cost full-temperature calibration method for a fiber-optic inertial measurement unit, using the low-cost full-temperature calibration device for a fiber-optic inertial measurement unit according to claim 1, characterized in that: The process includes the following steps: installing a precision indexing turntable in a temperature chamber and calibrating its horizontal state; fixing a fiber optic inertial measurement unit on a calibration fixture to ensure that its coordinate system is aligned with the fixture reference plane; controlling the temperature chamber to run a full-temperature calibration process to cover the operating temperature range of the fiber optic inertial measurement unit; flipping the fiber optic inertial measurement unit using the precision indexing turntable, so that each axis points upward and downward in turn, and collecting sensor data in different postures; calculating a temperature change trend model of the scale factor and zero bias error based on the collected data; and using the model to compensate for the fiber optic inertial measurement unit.

3. The low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to claim 2, characterized in that: The measurement model of the quartz accelerometer is as follows: ， Wherein, 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; is the true value vector of acceleration acting on the triaxial quartz accelerometer; It is the pulse output vector collected by the three-axis quartz accelerometer; is the scale factor vector of the triaxial quartz accelerometer; is the bias error vector of the tri-axis quartz accelerometer; is the installation error matrix of the tri-axis quartz accelerometer. All superscript Ts are matrix transpose symbols.

4. The low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to claim 3, characterized in that: The measurement model of the fiber optic gyroscope is as follows: ， Wherein, the subscript G represents a quartz accelerometer; is the true value vector of the angular velocity acting on the three-axis fiber optic gyroscope; It is the pulse output vector collected by the three-axis fiber optic gyroscope; is the scale factor vector of the three-axis fiber optic gyroscope; is the bias error vector of the three-axis fiber optic gyroscope; is the installation error matrix of the three-axis fiber optic gyroscope.

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

6. The low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to claim 5, characterized in that: Introducing the continuous temperature variable symbol T into the measurement model of the quartz accelerometer, the quartz accelerometer compensation model is rewritten as follows: ， If the temperature model of the scale factor and zero bias is obtained, and the installation error matrix is obtained based on the normal temperature calibration, the fiber optic inertial measurement unit can be compensated according to formula (4), and the true value of the physical quantity can be calculated based on its output pulse.

7. The low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to claim 6, characterized in that: Set the Z-axis pointing upward to ZU and the Z-axis pointing ground to ZD. Set the X-axis pointing upward to XU and the X-axis pointing ground to XD. Set the Y-axis pointing upward to YU and the Y-axis pointing ground to YD. During the calibration process, the recorded measurement data are all digital signal outputs of the fiber-optic inertial measurement unit. The temperature variation of the scale factor and zero bias is hidden in the output digital signal sequence. According to the measurement model, when the three coordinate axes of the fiber-optic inertial measurement unit point to the sky and the ground, the true value of the three-axis quartz accelerometer is: ， The vector symbol subscript describes the attitude of the fiber optic inertial measurement unit, and g is the gravitational acceleration constant.

8. The low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to claim 7, characterized in that: Substituting Equation (5) into the measurement equation containing the temperature variable, it can be expanded to: ， in, is the function of the X-axis quartz accelerometer output pulse measured under the Z-axis pointing sky condition with temperature variation. The actual calibration process 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 are of the same sign, while the terms containing the scale factor are of different signs. Therefore, the linear combination of equations (6) to (11) can decompose and calculate the temperature trend of the scale factor and zero bias error.

9. The low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to claim 8, characterized in that: The temperature variation trend decomposition method of the scale factor and zero bias error is listed as follows: ， The temperature trend of the bias error only contains the function of the quartz accelerometer output pulse relative to temperature in the six attitudes; while the temperature trend of the scale factor contains the gravitational acceleration constant g and the main diagonal elements in the installation error matrix 、 and The gravitational acceleration constant can be calculated based on 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 result values of the normal temperature calibration.

10. A low-cost full-temperature calibration method for a fiber-optic inertial measurement unit according to any one of claims 1 to 9, characterized in that: By flipping the precision turntable in the temperature chamber to obtain the full-temperature calibration data of each axis pointing to the sky and the ground, the temperature trend of the scale factor and zero bias error in the fiber optic inertial measurement unit model that changes with temperature can be obtained. Based on this trend, a model with temperature as input and parameter value as output is established to complete the temperature calibration.

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