Portable Inertial Navigation System Calibration Device and Method

Abstract

This invention discloses a portable inertial navigation system (INS) calibration device and a portable INS calibration method. The device includes: a prism composed of a hexagonal hollow frame structure and six cover plates, with the INS to be calibrated placed inside the prism and connected to an internal mounting interface; a turntable including a base, a rotating shaft, a torque motor, a circular grating, and a fiber optic gyroscope, one end of the rotating shaft being rotatably connected to the base, and the other end forming a holding platform for placing the prism; a servo control drive module for controlling the torque motor according to control commands, and reading angle information detected by the circular grating via a synchronous serial port, and angular velocity information detected by the fiber optic gyroscope via an asynchronous serial port; and a host computer for generating control commands and obtaining angle and angular velocity information from the servo control drive module. This invention allows for the calibration of INS using a portable INS calibration device without relying on a north-pointing reference.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of calibration of inertial navigation systems, and in particular to a portable inertial navigation system calibration device and a portable inertial navigation system calibration method. BACKGROUND

[0002] Periodic detection and calibration of inertial navigation systems usually needs to be returned to the production factory, or completed by using secondary detection equipment of external laboratories. Due to important carriers being distributed in various places, even overseas on duty or exported to foreign countries, fixed laboratory calibration will greatly increase the number of spare parts of the inertial navigation system, as well as transportation and manpower costs, seriously restricting the attendance rate and combat effectiveness of the equipment system, and causing great difficulties for the use and maintenance of the equipment and the improvement of the technical and tactical level of future models.

[0003] There are mainly two kinds of existing strapdown inertial navigation system calibration equipment. One kind is to install a transition device on the carrier base, install a calibration device on the transition device, and then calibrate the real-time level and azimuth of the transition device; when the level and azimuth calibration reaches the requirement, the calibration device is removed; the inertial navigation system is installed on the transition device, and the calibration of the inertial navigation system is completed. The other kind is to install the required inertial navigation product on a bracket, start the power supply, and automatically run the calibration control; the computer sends a start inertial navigation instruction through the interface, controls the start, alignment and single-axis turntable north-seeking of the calibrated inertial navigation product; the interface receives the inertial navigation product data information and judges whether the performance of the inertial navigation product meets the requirement, and completes parameter compensation.

[0004] The existing inertial navigation system calibration equipment has a complex calibration process and cumbersome steps, and the calibration device has low structure performance, and in the specific implementation process, the north-seeking of the turntable is needed to complete the final calibration of the inertial navigation system. SUMMARY

[0005] The embodiments of the present application provide a portable inertial navigation system calibration device and a portable inertial navigation system calibration method, so as to more easily realize the field calibration of the inertial navigation system.

[0006] The portable inertial navigation system calibration device according to the embodiments of the present application comprises:

[0007] The prism comprises a regular hexagonal hollow frame structure and six cover plates, the six cover plates are adapted to be assembled to the six faces of the regular hexagonal hollow frame structure one by one, and the prism is internally provided with a mounting interface; the inertial navigation system to be calibrated is adapted to be placed in the prism and connected with the mounting interface.

[0008] The rotary table comprises a base, a rotating shaft, a torque motor, a circular grating and a fiber-optic gyroscope, one end of the rotating shaft is rotationally connected with the base, the other end of the rotating shaft is provided with a containing platform for placing the prism, the prism is adapted to be turned over on the containing platform, the torque motor is used for driving the rotating shaft to rotate, the circular grating is used for detecting the angle information of the rotating shaft, and the fiber-optic gyroscope is used for detecting the angular velocity information of the rotating shaft.

[0009] The servo control driving module is used for controlling the torque motor according to the control instruction, reading the angle information detected by the circular grating through a synchronous serial port and reading the angular velocity information detected by the fiber-optic gyroscope through an asynchronous serial port.

[0010] The upper computer is used for generating the control instruction and sending the control instruction to the servo control driving module and acquiring the angle information and the angular velocity information from the servo control driving module.

[0011] According to some embodiments of the present application, the servo control driving module is used for controlling the torque motor according to the control instruction in combination with the angle information and the angular velocity information.

[0012] According to some embodiments of the present application, the servo control driving module is used for collecting the current information of the torque motor through a current loop sensor and controlling the torque motor according to the control instruction in combination with the current information, the angle information and the angular velocity information.

[0013] According to some embodiments of the present application, the servo control driving module comprises a DSP and a CPLD, the DSP is used for generating a driving instruction for controlling the torque motor according to the control instruction, and the CPLD is used for completing bus signal decoding of the DSP and serial port communication with the circular grating and the fiber-optic gyroscope.

[0014] According to some embodiments of the present application, the cover plate is a hollow piece.

[0015] The positive hexahedral hollow frame structure is integrally machined by a high-precision numerical control machine tool, and the thickness of the structure is greater than or equal to 15 mm.

[0016] According to some embodiments of the present application, the rotary table further comprises two mutually perpendicular positioning plates, the positioning plates are arranged on the containing platform and are used for limiting the position and orientation of the prism.

[0017] According to some embodiments of the present application, the torque motor is connected with the rotary table through a cross roller bearing.

[0018] According to some embodiments of the present application, the rotary table further comprises a limiting device for limiting the rotation range of the rotating shaft.

[0019] The portable inertial navigation system calibration method according to the embodiments of the present application is implemented based on the portable inertial navigation system calibration device as described above;

[0020] The method comprises:

[0021] The turntable is leveled horizontally by means of a level.

[0022] The calibration of the inertial navigation system to be calibrated is performed by controlling the rotation of the turntable and combining the turning of the prism.

[0023] According to some embodiments of the present application, the calibration of the inertial navigation system to be calibrated is performed by controlling the rotation of the turntable and combining the turning of the prism, which comprises:

[0024] The zero bias repeatability and stability of the gyroscope and the accelerometer of the inertial navigation system to be calibrated are tested by means of the portable inertial navigation system calibration device.

[0025] The reference data are obtained by controlling the rotation of the turntable and combining the turning of the prism, the navigation solution of the inertial navigation system to be calibrated is compared with the reference data to obtain the calibration result, and at least part of the parameters of the calibration result are verified.

[0026] According to the embodiments of the present application, the calibration of the inertial navigation system can be performed by means of the portable inertial navigation system calibration device without relying on the north reference. The portable inertial navigation system calibration device is small in size, light in weight, simple in operation, and convenient to carry, which can greatly reduce the requirements for the external field conditions and the professional ability of the maintenance personnel, reduce the workload of the personnel, reduce the calibration cost, and improve the calibration efficiency.

[0027] The above description is only a summary of the technical solutions of the present application. In order to make the technical means of the present application more clearly understood, the specific embodiments of the present application can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0028] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description. The accompanying drawings are included to provide a description of preferred embodiments, and are not meant to limit the present application. In the drawings:

[0029] Figure 1 is a structural schematic diagram of a turntable in the embodiments of the present application;

[0030] Figure 2 is a longitudinal sectional schematic diagram of a turntable in the embodiments of the present application;

[0031] Figure 3is a structural schematic diagram of a prism in the embodiment of the present application;

[0032] Figure 4 is a structural schematic diagram of a prism in the embodiment of the present application;

[0033] Figure 5 is a structural schematic diagram of a prism in the embodiment of the present application;

[0034] Figure 6 is a structural schematic diagram of a prism in the embodiment of the present application;

[0035] Figure 7 is a structural schematic diagram of a prism in the embodiment of the present application;

[0036] Figure 8 is a structural schematic diagram of a prism in the embodiment of the present application; DETAILED DESCRIPTION

[0037] Exemplary embodiments of the present application will be described herein below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it is understood that the present application can be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. Additionally, in some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

[0038] The portable inertial navigation system calibration device according to the embodiment of the present application comprises:

[0039] The prism comprises a regular hexagonal hollow frame structure and six cover plates, and the six cover plates are adapted to be assembled to the six faces of the regular hexagonal hollow frame structure one by one. It can be understood that the prism itself is a regular hexagonal hollow structure. An installation interface is arranged inside the prism, and the inertial navigation system to be calibrated is adapted to be placed in the prism and connected with the installation interface.

[0040] The rotary table comprises a base, a rotary shaft, a torque motor, a circular grating and a fiber-optic gyroscope. One end of the rotary shaft is rotatably connected to the base. It can be understood that the other end of the rotary shaft is connected to the base, the base is used for supporting and fixing the rotary shaft, and the rotary shaft is rotatable relative to the base. The end face of the other end of the rotary shaft forms a horizontal holding platform for placing a prism. For example, in order to reduce the size of the rotary shaft, the cross-sectional size of the rotary shaft gradually increases from one end to the other end of the rotary shaft to form the holding platform at the other end. The prism is adapted to be turned over on the holding platform, so that the rotary table can provide different rotary positions for the to-be-calibrated inertial navigation system, so as to stimulate more errors of the to-be-calibrated inertial navigation system and improve the observability of the errors. The torque motor is used to drive the rotary shaft to rotate. The circular grating is used to detect the angle information of the rotary shaft. The fiber-optic gyroscope is used to detect the angular velocity information of the rotary shaft.

[0041] The servo control driving module is used to control the torque motor according to the control instruction, read the angle information detected by the circular grating through a synchronous serial port, and read the angular velocity information detected by the fiber-optic gyroscope through an asynchronous serial port.

[0042] The upper computer is used to generate the control instruction and send it to the servo control driving module, and obtain the angle information and the angular velocity information from the servo control driving module. The control instruction can control the torque motor to work in various working modes, such as a reach position mode, a step mode, a back-and-forth mode and the like.

[0043] The portable inertial navigation system calibration device in the embodiment of the present application can be used for calibration of the to-be-calibrated inertial navigation system. The motion of the rotary table and the prism provides real motion values for the to-be-calibrated inertial navigation system, the to-be-calibrated inertial navigation system performs navigation solution according to the output values of the gyroscope and the accelerometer, and compares the solution result with the real motion values provided by the portable inertial navigation system calibration device to obtain the measurement error of the to-be-calibrated inertial navigation system. The rotary table and the prism can provide different rotary positions, so as to stimulate more errors and improve the observability of the errors. The measurement error is taken as an observation variable of the to-be-calibrated inertial navigation system, and the error term to be calibrated of the inertial component is taken as a state variable, and an unbiased estimation is performed on the state variable.

[0044] The portable inertial navigation system calibration device in the embodiment of the present application can be used for testing whether the zero bias repeatability and stability of the gyroscope and the accelerometer are significantly reduced, so as to decide whether to recalibrate or return to the factory for maintenance.

[0045] By using the embodiment of the present application, the inertial navigation system can be calibrated without relying on the north reference. The portable inertial navigation system calibration device is small in size, light in weight, simple in operation and convenient to carry, and can greatly reduce the requirements for external field conditions and professional ability of maintenance personnel, reduce the workload of personnel, reduce the calibration cost and improve the calibration efficiency.

[0046] On the basis of the above-mentioned embodiments, further variant embodiments are proposed, and it should be noted that, in order to make the description brief, only the differences from the above-mentioned embodiments are described in the variant embodiments.

[0047] According to some embodiments of the present application, the servo control driving module is used to control the torque motor according to the control instruction in combination with the angle information and the angular velocity information.

[0048] According to some embodiments of the present application, the servo control driving module is used to collect the current information of the torque motor through the current loop sensor, and control the torque motor according to the control instruction in combination with the current information, the angle information and the angular velocity information.

[0049] For example, the servo control driving module adopts three-loop control of current loop, speed loop and position loop to control the torque motor. The control structure has decoupling control effect, and can complete the control of current, angular velocity and angular position in layers, as shown in Figure 5 .

[0050] According to some embodiments of the present application, the servo control driving module includes a DSP and a CPLD, the DSP is used to generate driving instructions for controlling the torque motor according to the control instruction, and the CPLD is used to complete the bus signal decoding of the DSP and the serial communication with the circular grating and the fiber-optic gyroscope. The principle block diagram of the controller circuit is shown in Figure 6 .

[0051] In some embodiments of the present application, the rigidity and perpendicularity of the prism are realized by the regular hexagonal hollow frame structure. The outer surface of the cover plate, i.e. the surface located outside the prism, is recessed relative to the corresponding regular hexagonal hollow frame structure. It can be understood that when the prism is placed on a flat plane, the regular hexagonal hollow frame structure is in contact with the plane, and the cover plate is spaced apart from the plane by the support of the regular hexagonal hollow frame structure. Therefore, as long as the perpendicularity and flatness of each surface of the regular hexagonal hollow frame structure are ensured, the perpendicularity and flatness of the prism can be ensured.

[0052] In some embodiments of the present application, the regular hexagonal hollow frame structure is integrally machined by a high-precision numerical control machine tool, and the structure thickness is greater than or equal to 15 mm.

[0053] According to some embodiments of the present application, the cover plate is a hollow piece. Therefore, the weight of the prism can be reduced to facilitate carrying and operation.

[0054] According to some embodiments of the present application, the rotary table further includes two mutually perpendicular positioning plates, which are arranged on the containing platform and used to limit the position and orientation of the prism.

[0055] According to some embodiments of the present application, the torque motor is connected with the rotary table through a cross roller bearing. Therefore, the axial size of the rotating shaft can be reduced.

[0056] According to some embodiments of the application, the rotary table further comprises a limiting device for limiting the rotation range of the rotary shaft.

[0057] The portable inertial navigation system calibration method according to the embodiments of the application is implemented based on the portable inertial navigation system calibration device as above;

[0058] The method comprises:

[0059] The rotary table is leveled by means of a leveler;

[0060] The inertial navigation system to be calibrated is calibrated by controlling the rotation of the rotary table and combining the turning of the prism.

[0061] According to some embodiments of the application, the inertial navigation system to be calibrated is calibrated by controlling the rotation of the rotary table and combining the turning of the prism, which comprises:

[0062] The zero bias repeatability and stability of the gyroscope and the accelerometer of the inertial navigation system to be calibrated are tested by using the portable inertial navigation system calibration device;

[0063] The reference data are obtained by controlling the rotation of the rotary table and combining the turning of the prism, the navigation solution of the inertial navigation system to be calibrated is compared with the reference data to obtain the calibration result, and at least part of the parameters of the calibration result are verified.

[0064] Further, the portable inertial navigation system calibration method according to the embodiments of the application adopts a discrete field calibration technology. The discrete field calibration technology performs the accelerometer calibration and the gyroscope calibration separately, and relies on the mechanical processing precision of the calibration device itself to ensure the coincidence degree between the coordinate axes. The calibration principle thereof is to perform navigation solution according to the output values of the gyroscope and the accelerometer, compare the solution result with the real value of the carrier provided by the rotary table, and obtain the measurement error of the system. The rotary table and the six-prism can provide different rotation positions, so as to stimulate more errors and improve the observability of the errors. The measurement error is taken as the system observation variable, the error term of the inertial component to be calibrated is taken as the state variable, and the state variable is unbiasedly estimated.

[0065] (1) Accelerometer component calibration:

[0066] A linear error model of the three-axis accelerometer component is established, and the calculation formula is: KA is a 3x3 scale factor matrix, and NA is the output pulse number of the accelerometer; is the accelerometer zero bias. The accelerometer component calibration needs to calibrate KA and Twelve error parameters are identified. The field calibration device provides different direction gravity reference input values for the accelerometer assembly by manually turning the polyhedral body to establish a linear equation set for each error parameter to be fitted and solved. According to the functional characteristics of the polyhedral body device, the twelve-position method is used to calibrate the accelerometer assembly. After the 12-position test is completed, a measurement equation set consisting of 12x3 equations can be established, and the least squares method is used for estimation, so that the accelerometer scale factor matrix KAand the calibration results of the zero offset .

[0067] (2) Gyroscope assembly calibration:

[0068] A linear error model of the three-axis gyroscope assembly is established, and the calculation formula is: ω b = K G N G - ε b . The 3x3 scale factor matrix KGis composed of scale factors and sensitive axis misalignment angles; NGis the gyroscope output pulse number; ε b is the gyroscope zero offset. Gyroscope assembly calibration requires identification of 12 error parameters of KGand ε b . Considering the angular position repeatability of the portable rotating platform, the angular position method is selected for gyroscope assembly calibration. In addition, if the forward and reverse rotation method is used, the error of the earth's rotation angular velocity can be offset, and the linear error model can be written in the integral form: Ω b = K G N ∑G - Θ b , where is the platform rotation angle, Ts is the sampling period, for example, the rotating platform rotates counterclockwise around the Z-axis of the inertial assembly for one revolution, then Ω b = [0 0 π] T ; N ∑G is the integral of the gyroscope output pulse, when the gyroscope uses the incremental output per cycle, N ΣG = ∑N G ; Θ b = ∑ε b T s is the integral of the gyroscope zero offset term.

[0069] The forward and reverse rotation process requires as much constant speed rotation as possible, so the automatic rotating platform and the manual polyhedral body turning are used to complete the calibration of all axes. After the 6 rotation processes are completed, the equation set is established according to the forward and reverse integral formula, and the scale factor matrix KGis analytically solved.

[0070] The main purpose of measurement uncertainty evaluation and performance verification is to evaluate and verify the device accuracy, calibration accuracy and comprehensive performance of the strapdown inertial device using the portable calibration device.

[0071] (1) Device accuracy evaluation

[0072] The purpose of device accuracy evaluation is to test whether the repeatability and stability of the zero bias of the gyro and accelerometer significantly decrease by using the portable off-site calibration device, so as to decide whether to recalibrate or return to the factory for repair.

[0073] ①Repeatability evaluation. Place the strapdown inertial system on the platform, collect data for a period of time after power-on and calculate the mean value. After power-off and static for a period of time, repeat the above test process several times at the same position, calculate the standard deviation of each mean value data, and compare and evaluate with the product specification.

[0074] ②Stability evaluation. Place the strapdown inertial system on the platform, collect data for a long enough time after power-on, calculate the zero bias stability and random walk coefficient of the inertial sensor by standard deviation or Allan variance method, and compare and evaluate with the product specification.

[0075] (2) Calibration result evaluation

[0076] Calibration result evaluation is to intuitively verify the main parameters in the calibration result after off-site calibration is completed.

[0077] ①Calibration repeatability verification. Calibrate the same strapdown inertial system for more than twice, and evaluate the calibration results by the repeatability of each calibration parameter.

[0078] ②Accelerometer residual error evaluation. This method is mainly suitable for verification of discrete calibration results. Record the accelerometer data collected at each static position, and calculate the specific force measurement residual error according to the formula: Take the statistical standard deviation as the evaluation basis. In the formula, fb is the reference input force ratio at each position.

[0079] ③Gyro residual error evaluation. Install the inertial level on the rotating platform, and sequentially stay at 0°, 90°, 180°, and 270° positions for 10 minutes. Collect the mean values of the gyro at each static position and calculate the formula:

[0080]

[0081] According to δω1 and δω2, evaluate the accuracy of the gyro zero bias calibration.

[0082] ④Gyro scale factor verification. After initial alignment with new parameters and entering navigation state, quickly rotate 360° around the Z-axis of the inertial navigation system. According to the heading difference before and after rotation, evaluate the accuracy of the Z-axis gyro scale factor. Use the same method to verify the accuracy of the X and Y axis gyro scale factors.

[0083] (3) Comparison and verification of new and old parameters

[0084] The new and old parameter comparison verification is to use the same original pulse number of the strapdown inertial assembly, respectively use the new / old parameter to perform alignment or navigation test, and verify the effectiveness of the parameter by comparing the navigation accuracy, and verify whether the inertial system meets the index requirement.

[0085] ① Static navigation verification. In the approximately north direction, the static base initial alignment and pure inertial navigation are performed, and the east-north direction velocity error of the navigation solution is used to evaluate the stability of the inertial device.

[0086] ② Four-position alignment verification. In the approximately north direction, self-alignment is performed, and after the alignment is completed, it is rotated approximately 90° around the azimuth axis to the next position B, and the heading ψ1 is recorded; the alignment is performed again at the position B, and the heading ψ2 is recorded, and whether δψ = ψ1- ψ2 meets the accuracy requirement is calculated. The alignment verification of the four positions is completed in sequence according to the above method, and the accuracy of the horizontal gyro zero offset and the Z-axis gyro scale factor can be evaluated.

[0087] ③ 180° rotation navigation verification. After the inertial system static base initial alignment is completed and enters the pure inertial navigation, it is rotated 180° around the azimuth axis, and the navigation accuracy of the system is evaluated through the navigation velocity error.

[0088] ④ Comprehensive rotation navigation verification. After the inertial system static base alignment is completed, the navigation accuracy of the system is evaluated through the navigation velocity error.

[0089] The portable inertial navigation system calibration device of the embodiments of the present application will be described in detail below with reference to the accompanying drawings in a specific embodiment. It should be understood that the following description is only exemplary and should not be construed as a specific limitation of the present application.

[0090] The purpose of the present application is to study a small volume, light weight, simple operation, convenient to carry field calibration equipment, which can greatly reduce the requirements for field conditions and the professional ability of maintenance personnel, reduce the workload of personnel, reduce the calibration cost, and improve the calibration efficiency.

[0091] The inertial navigation system calibration device of the present application meets the high structural performance, and studies a separate field calibration method which does not depend on the north reference, carries out measurement uncertainty and performance verification, and has strong universality and high automation degree, and is suitable for field calibration of various precision inertial navigation systems. The technical problem solved by the present application is how to calibrate the inertial navigation system by using a small-sized portable automatic control rotating platform and a multi-faceted prism device without relying on the north reference.

[0092] The portable inertial navigation system calibration device of the embodiment of the application is divided into two parts of structure design and servo control design according to functions. According to structure composition, the portable inertial navigation system calibration device is divided into two parts of a precision turntable and a multi-surface prism, and the specific design is as follows:

[0093] As shown in Figure 1 and Figure 2 , the turntable mainly comprises a base 4, a rotating shaft 1, a torque motor 5, a circular grating 8, a cross roller bearing 6, a fiber-optic gyroscope 7, a limiting device 3, a positioning plate 2 and the like. The transmission mode of the turntable adopts a direct shaft driving form of the torque motor, the position information is detected by the high-precision circular grating installed on the shaft, the rotation angle is fed back and the position is controlled, and the fiber-optic gyroscope detects the angular velocity information of the equipment. In order to reduce the axial size, the high-precision and large-load cross roller bearing is selected and installed in the inner circle of the motor. The stop of the limiting device is a floating stop structure, which can be the zero position of the turntable, so that the turntable can reach a position greater than ±180°. The positioning plate mainly limits the position and orientation of the prism to realize repeated positioning.

[0094] As shown in Figure 3 , the prism is a hollow structure of a regular hexagon, which is composed of a regular hexagon hollow frame 9 and a cover plate 10, and an installation interface is reserved in the inside, the inertial navigation system 11 to be calibrated is installed on the interface platform in the prism frame, and then placed on the turntable to perform related calibration work. The cover plates of each surface can be disassembled, which facilitates the installation of the tested equipment, and the height of the cover plate is lower than the surface height of the frame, which will not affect the flatness and perpendicularity of each surface. The frame is integrally machined by a high-precision numerical control machine tool, which can ensure the perpendicularity requirement of each plane. At the same time, in order to reduce the deformation in the later use process, the thickness of the frame is increased to 15 mm to ensure sufficient strength and rigidity; weight-reducing holes are processed in the middle of each cover plate to facilitate the observation of the tested equipment and reduce the weight of the prism, and the installation on the frame also increases the rigidity of the frame.

[0095] Servo control driving design: the servo system of the turntable is composed of a servo control driving module, a circular grating, a direct current torque motor and a fiber-optic gyroscope. The circular grating and the direct current torque motor are installed on the precision turntable and are installed on the shaft of the turntable, as shown in Figure 4 . The servo control driving module receives the control instructions from the upper computer and the status of the servo system through the serial port, determines the working mode of the turntable according to the instructions. The driving module provides accurate position and speed information for the measured object, reads the angle data of the circular grating through the synchronous serial port, reads the angular velocity data of the fiber-optic gyroscope through the asynchronous serial port, and then provides accurate input information for the inertial system.

[0096] The servo control system adopts three-loop control of current loop, speed loop and position loop:

[0097] The current loop sensor adopts resistance sampling, the angle sensor selects a circular grating, the control system adopts asynchronous serial port to read the angular velocity data of the fiber optic gyroscope, and the angle differential and loop correction are realized by the servo software. The control structure has decoupling control effect, and can complete the control of current, angular velocity and angular position of the servo system in layers. The control servo loop diagram of the turntable is shown in Figure 5 .

[0098] The servo control driving module controller circuit design:

[0099] The controller adopts a DSP+CPLD control scheme, the DSP mainly completes loop correction and turntable operation control, and the CPLD mainly completes DSP bus signal decoding and BISS serial port communication with the circular grating. The controller circuit principle diagram is shown in Figure 6 .

[0100] The servo control driving module power conversion circuit:

[0101] The power conversion circuit mainly consists of AC-DC (AC to DC) circuit and DC-DC (DC to DC) circuit. The input is 220V / 50Hz mains, which is converted to 28VDC after AC-DC and filtering, and is provided to the bus voltage of the azimuth torque motor. 28VDC is converted by a DC-DC converter to obtain +5V as control power, and the voltage required for the operation of related chips is obtained through a power conversion chip. The power conversion circuit is shown in Figure 7 .

[0102] The turntable software includes turntable control DSP software and turntable control CPLD software:

[0103] (1) The main function of the turntable control DSP software is to complete receiving the host computer command and controlling the turntable to realize the motion of reaching position, step mode and back and forth mode with the turntable control hardware instrument. The software consists of state initialization subroutine, system control subroutine, timer interrupt service subroutine, ADC (analog to digital conversion) interrupt service subroutine. The servo system software flow chart is shown in Figure 8 .

[0104] The state initialization subroutine completes the system register setting, interrupt logic setting, XINTF (external interface) register setting, PWM (pulse width modulation) module setting, SCI (asynchronous serial port) module initialization, ADC (analog to digital conversion) module initialization and DAC (digital to analog conversion) module initialization. The setting of the system control register mainly includes PLL system clock setting, watchdog setting, high and low speed peripheral clock scaling register and peripheral clock control register setting, etc.

[0105] The running period of the turntable system control module is 2ms, so the timing interrupt is a 2ms interrupt, and the function of the service subprogram thereof is mainly to provide a timing mark for the system control module.

[0106] The ADC (analog-digital conversion) interrupt is triggered by a PWM (pulse width modulation) period, and the ADC (analog-digital conversion) interrupt service subprogram mainly accomplishes: reading in the azimuth conversion data converted by the ADC (analog-digital conversion) module and performing data processing, performing current loop correction according to the power amplifier current setting value calculated by the system control subprogram, obtaining the pulse width value of the required PWM (pulse width modulation) control signal, and updating the same.

[0107] The turntable control CPLD software:

[0108] The software functions mainly include: parallel bus read-write timing control; DAC (digital-analog conversion) conversion timing control; circular grating BISS serial communication; local address decoding and IO (input-output port) control.

[0109] The portable inertial navigation system calibration device of the embodiment of the application can realize a discrete field calibration method independent of a north reference, comprising the following steps:

[0110] Before use, the automatic control rotating platform should be leveled by means of a level. The discrete calibration method performs accelerometer calibration and gyroscope calibration separately, and relies on the machining precision of the calibration device itself to ensure the coincidence degree between coordinate axes. The calibration principle thereof is to perform navigation solution according to the output values of the gyroscope and the accelerometer, and compare the solution result with the actual value of the carrier provided by the turntable to obtain the measurement error of the system. The turntable and the six-pyramid can provide different rotating positions, so as to stimulate more errors and improve the observability of the errors. The measurement error is taken as a system observation variable, and the error item of the inertial component to be calibrated is taken as a state variable, and an unbiased estimation is performed on the same.

[0111] (1) Accelerometer component calibration:

[0112] A linear error model of the three-axis accelerometer component is established, and the calculation formula is: KA is a 3*3 scale factor matrix, and NA is the number of pulses output by the accelerometer; is the zero offset of the accelerometer. The calibration of the accelerometer component needs to calculate KA and Twelve error parameters are identified. The field calibration device provides different direction gravity reference input values for the accelerometer assembly by manually turning the polyhedral body to establish a linear equation set for each error parameter to be fitted and solved. According to the functional characteristics of the polyhedral body device, the twelve position method is used to calibrate the accelerometer assembly. After the 12 position test is completed, a measurement equation set consisting of 12x3 equations is established, and the least squares method is used for estimation, so that the accelerometer scale factor matrix KAand the calibration results of the zero offset

[0113] (2) Gyroscope assembly calibration:

[0114] A linear error model of the three-axis gyroscope assembly is established, and the calculation formula is: ω b = K G N G - ε b . The 3x3 scale factor matrix KGis composed of scale factors and sensitive axis misalignment angles; NGis the gyroscope output pulse number; ε b is the gyroscope zero offset. Gyroscope assembly calibration requires identification of 12 error parameters of KGand ε b . The angular position method is selected for gyroscope assembly calibration, considering that the angular position repeatability of the portable rotating platform is easier to ensure. In addition, if the forward and reverse rotation method is used, the error of the earth's rotation angular rate can also be offset, and the linear error model can be written in the integral form: Ω b = K G N ∑G - Θ b , where is the platform rotation angle, Ts is the sampling period, for example, the rotating platform rotates counterclockwise around the Z axis of the inertial assembly for one revolution, then Ω b = [0 0 π] T ; N ∑G is the integral of the gyroscope output pulse, when the gyroscope uses the incremental output per cycle, N ΣG = ∑N G ; Θ b = ∑ε b T s is the integral of the gyroscope zero offset term.

[0115] The forward and reverse rotation process requires as constant speed rotation as possible, so it is necessary to complete the calibration of all axes by cooperating the automatic rotating platform and the manual turning of the polyhedral body. After the 6 rotation processes are completed, the equation set is established according to the forward and reverse integral formula, and the scale factor matrix KGis analytically solved.

[0116] Measurement uncertainty evaluation and performance verification:

[0117] ​The main purpose of measurement uncertainty evaluation and performance verification is to evaluate and verify the precision, calibration accuracy and overall performance of the inertial device using a portable calibration device.

[0118] (1) Device precision evaluation

[0119] The purpose of device precision evaluation is to test whether the zero repeatability and stability of the gyro and accelerometer have significantly decreased using a portable field calibration device, so as to decide whether to recalibrate or return to the factory for repair.

[0120] ① Repeatability evaluation. Place the strapdown inertial system on the platform, collect data for a period of time after power on and calculate the mean value. After power off and static for a period of time, repeat the above test process several times in the same position, calculate the standard deviation of each mean value data, and compare with the product specification for evaluation.

[0121] ② Stability evaluation. Place the strapdown inertial system on the platform, collect data for a long enough time after power on, calculate the zero stability and random walk coefficient of the inertial sensor by standard deviation or Allan variance method, and compare with the product specification for evaluation.

[0122] (2) Calibration result evaluation

[0123] Calibration result evaluation is to intuitively verify the main parameters in the calibration result after field calibration is completed using a portable field calibration device.

[0124] ① Calibration repeatability verification. Calibrate the same strapdown inertial system more than twice, and evaluate the calibration results by the repeatability of each calibration parameter.

[0125] ② Accelerometer residual error evaluation. This method is mainly suitable for verification of discrete calibration results. Record the accelerometer data collected at each static position, and calculate the specific force measurement residual error according to the formula: Take the statistical standard deviation as the evaluation basis. In the formula, fb is the reference input force ratio at each position.

[0126] ③ Gyro residual error evaluation. Install the inertial level on the rotating platform, and sequentially static at 0°, 90°, 180° and 270° positions for 10 minutes, collect the mean value of the gyro at each static position and calculate the formula:

[0127]

[0128] According to δω1 and δω2, evaluate the accuracy of the gyro zero calibration.

[0129] ④ Gyro scale factor verification. After initial alignment using the new parameters and entering navigation mode, the system is rapidly rotated strictly 360° around the Z-axis of the inertial navigation system. The accuracy of the Z-axis gyro scale factor is evaluated based on the difference in heading before and after the rotation. The accuracy of the X and Y-axis gyro scale factors is verified using the same method.

[0130] (3) Comparison and verification of new and old parameters

[0131] The comparison and verification of new and old parameters involves using the same original pulse count of the strapdown inertial component and conducting alignment or navigation tests with both new and old parameters. The effectiveness of the parameters is verified by comparing the navigation accuracy, and whether the inertial system meets the performance requirements. This method is primarily aimed at inertial systems with self-alignment and pure inertial navigation capabilities.

[0132] ① Static navigation verification. Initial alignment of the static base and pure inertial navigation were performed in a roughly due north direction. The stability of the inertial devices was evaluated by the northeast velocity error calculated from the navigation.

[0133] ② Four-position alignment verification. Perform self-alignment in approximately due north. After alignment, rotate approximately 90° around the azimuth axis to the next position B and record the heading ψ1. Realign at position B and record the heading ψ2. Calculate whether δψ = ψ1 - ψ2 meets the accuracy requirements. Complete the alignment verification at four positions sequentially using the above method to evaluate the accuracy of the horizontal gyroscope zero bias and the Z-axis gyroscope scaling factor.

[0134] ③ 180° rotation navigation verification. After the initial alignment of the inertial system's static base is completed and it enters pure inertial navigation, it rotates 180° around the azimuth axis, and the navigation accuracy of the system is evaluated by the navigation speed error.

[0135] ④ Comprehensive navigation verification. After the static base of the inertial system is aligned, the navigation accuracy of the system is evaluated by the navigation speed error.

[0136] Key points and protected aspects of this invention: 1. Optimized structural design. The rotating shaft and adapter plate are designed as a single component, which not only improves the natural frequency of the turntable but also reduces the system's installation error. Simultaneously, the motor brush holder is designed as a separate unit, allowing for reasonable assembly. Each component has undergone optimized weight reduction design, with strict weight control. 2. Dual reading head technology. The installation requirements for the grating are very high; adjusting the adjusting screws on the circular grating ensures that its circumferential runout does not exceed 5μm. Dual reading heads combined with internal signals from the controller are used to eliminate the grating's dimensional installation eccentricity error. 3. Discrete on-site calibration technology independent of north-pointing reference. Traditional calibration methods have incomplete error modeling, leading to pseudo-equilibrium between various coupling parameters and decreased calibration accuracy. This invention establishes a complete error model including the calibration of accelerometer and gyroscope components, identifies error parameters, and provides rotational excitation by manually rotating a polygonal prism, improving calibration accuracy and efficiency in the field without relying on the turntable's north-finding capability.

[0137] Advantages of this invention: 1. The miniaturized portable automatic control rotary platform and the field calibration equipment composed of a multi-faceted prism are small in size, light in weight, simple to use, and easy to transport and install. This reduces the requirements for field conditions and the professional skills of maintenance personnel, reduces the workload of personnel, lowers calibration costs, and improves calibration efficiency, which is of great significance for improving the availability rate, mission performance capability, and combat effectiveness of military equipment; 2. The turntable integrates high-precision servo hardware and software control components; 3. Based on the portable field calibration equipment, a discrete field calibration method that does not rely on a north reference, i.e., does not require the turntable to find north, is studied. Measurement uncertainty and performance verification are carried out. It has strong versatility, a high degree of automation, and is suitable for field calibration of inertial navigation systems of various precision.

[0138] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0139] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A portable inertial navigation system calibration device, characterized in that, include: The prism comprises a regular hexagonal hollow frame structure and six cover plates. The six cover plates are adapted to be assembled one-to-one with the six faces of the regular hexagonal hollow frame structure. The prism has an internal mounting interface, and the inertial navigation system to be calibrated is adapted to be placed inside the prism and connected to the mounting interface. The cover plates are hollow parts. The regular hexagonal hollow frame structure is integrally CNC machined using a high-precision CNC machine tool, and its structural thickness is greater than or equal to 15mm. A turntable includes a base, a rotating shaft, a torque motor, a circular grating, and a fiber optic gyroscope. One end of the rotating shaft is rotatably connected to the base, and the other end face of the rotating shaft forms a holding platform for placing the prism. The prism is adapted to rotate on the holding platform. The torque motor drives the rotating shaft to rotate, the circular grating detects the angle information of the rotating shaft, and the fiber optic gyroscope detects the angular velocity information of the rotating shaft. The turntable also includes two mutually perpendicular positioning plates disposed on the holding platform to define the position and orientation of the prism. The servo control drive module is used to control the torque motor according to the control command, and read the angle information detected by the circular grating through the synchronous serial port, and read the angular velocity information detected by the fiber optic gyroscope through the asynchronous serial port. The servo control drive module includes a DSP and a CPLD. The DSP is used to generate drive instructions for controlling the torque motor according to the control instructions. The CPLD is used to decode the bus signals of the DSP and to communicate with the circular grating and the fiber optic gyroscope via serial port. The host computer is used to generate control commands and send them to the servo control drive module, and to obtain the angle information and the angular velocity information from the servo control drive module.

2. The portable inertial navigation system calibration apparatus of claim 1, wherein, The servo control drive module is used to control the torque motor according to the control command, combined with the angle information and the angular velocity information.

3. The portable inertial navigation system calibration apparatus of claim 2, wherein, The servo control drive module is used to collect the current information of the torque motor through the current loop sensor, and control the torque motor according to the control command, combining the current information, the angle information and the angular velocity information.

4. The portable inertial navigation system calibration apparatus of claim 1, wherein, The turntable also includes a limiting device for limiting the rotation range of the rotating shaft.

5. A method of calibrating a portable inertial navigation system, characterized by, The portable inertial navigation system calibration method is implemented based on the portable inertial navigation system calibration device as described in any one of claims 1-4; The method includes: The turntable was leveled using a spirit level. By controlling the rotation of the turntable and combining it with the flipping of the prism, the inertial navigation system to be calibrated is calibrated.

6. The method of claim 5, wherein, The calibration of the inertial navigation system to be calibrated by controlling the rotation of the turntable and in conjunction with the flipping of the prism includes: The zero-bias repeatability and stability of the gyroscope and accelerometer of the inertial navigation system to be calibrated were tested using a portable inertial navigation system calibration device. By controlling the rotation of the turntable and combining it with the flipping of the prism, reference data is obtained. The navigation calculation results of the inertial navigation system to be calibrated are compared with the reference data to obtain the calibration results, and at least some parameters of the calibration results are verified.

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