Latitude-free north seeker north seeking method

Abstract

The invention discloses a latitude-free north seeking method of a north seeker, which comprises the following steps of: a) mounting a fiber-optic gyroscope on a rotatable turntable, enabling a sensitive shaft of the fiber-optic gyroscope to be vertical to a rotating shaft of the turntable, mounting two MEMS (Micro Electro Mechanical System) accelerometers on the turntable, enabling a measuring shaft of one MEMS accelerometer to be in the same direction as the sensitive shaft of the fiber-optic gyroscope, and enabling the measuring shaft of the other MEMS accelerometer to be vertical to the rotating shaft of the turntable; the measuring axis of the other MEMS accelerometer is perpendicular to the plane where the sensing axis of the fiber-optic gyroscope and the rotating shaft of the rotary table are located; b) respectively calculating an autorotation angular velocity component of the earth and attitude information of the rotary table by using measurement data of the fiber-optic gyroscope and the MEMS accelerometer when the rotary table rotates by 0 degree, 90 degrees, 180 degrees and 270 degrees, obtaining a three-dimensional attitude angle of the rotary table through simultaneous solution, and determining a north direction according to an azimuth angle in the three-dimensional attitude angle, according to the invention, north-seeking calculation can be completed without inputting external parameters, the precision is high, and the use is convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of inertial navigation devices, and particularly to a north-seeking method for a north-seeking instrument without latitude. Background Art

[0002] In modern society, the demand for precise navigation in fields such as aviation, aerospace, and national defense is increasing day by day. As a key navigation device, the north-seeking instrument has strict requirements for various indicators of the north-seeking instrument in specific usage scenarios such as different environments and different positions. Most existing north-seeking instrument design schemes can no longer meet the market demand. Currently, the traditional north-seeking instrument mainly has the following problems.

[0003] 1) When the base has an inclination angle, the local latitude needs to be input to find the north;

[0004] 2) It requires a signal acquisition and processing combination of FPGA + DSP;

[0005] 3) It has a large volume and high power consumption. Summary of the Invention

[0006] Aiming at the above deficiencies existing in the prior art, the purpose of the present invention is to provide a north-seeking method for a north-seeking instrument without latitude to solve the problem that in the prior art, the local latitude needs to be input to find the north when the base has an inclination angle.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A north-seeking method for a north-seeking instrument without latitude, including the following steps,

[0008] a) Install an optical fiber gyro on a rotatable turntable, with its sensitive axis perpendicular to the axis of rotation of the turntable. Two MEMS accelerometers are also installed on the turntable. The measurement axis of one MEMS accelerometer is in the same direction as the sensitive axis of the optical fiber gyro, and the measurement axis of the other MEMS accelerometer is perpendicular to the plane where the sensitive axis of the optical fiber gyro and the axis of rotation of the turntable are located;

[0009] b) Use the measurement data of the optical fiber gyro and the MEMS accelerometer when the turntable rotates at 0°, 90°, 180°, and 270° to calculate the component of the earth's angular velocity of rotation and the attitude information of the turntable respectively. By solving the equations simultaneously, the three-dimensional attitude angles of the turntable are obtained, and the north direction is determined through the azimuth angle in the three-dimensional attitude angles.

[0010] As an optimization, in step b, first establish a turntable coordinate system B. Define the sensitive axis of the optical fiber gyro as the X axis, and the Y axis is perpendicular to the plane where the X axis and the axis of rotation of the turntable are located; then, the component of the earth's angular velocity of rotation on the Y axis is:

[0011]

[0012] In the formula, ω iez, ω ieN are the components of the Earth's rotation speed ω ie on the celestial and north coordinate axes of the geographic coordinate system; θ is the pitch angle of the turntable, γ is the roll angle of the turntable, ψ is the azimuth angle of the turntable; ω T t is the rotation angle of the turntable;

[0013] Combined with the fiber optic gyro model, the measured data output by the Y-axis fiber optic gyro in the turntable coordinate system b is:

[0014]

[0015] In the formula, δ0 is the constant zero bias of the fiber optic gyro, K1 is the scale factor of the fiber optic gyro, δ i is the variable zero bias value of the fiber optic gyro at different positions.

[0016] When ω T t = 0°, 90°, 180° and 270°, there are:

[0017]

[0018] Then there are:

[0019]

[0020] Let:

[0021]

[0022] And it can be deduced that:

[0023]

[0024] Therefore, there are:

[0025]

[0026] Among them,

[0027] And θ and γ are calculated as follows,

[0028] In the turntable body coordinate system b, the component of the Earth's accelerometer on the y-axis is:

[0029]

[0030] In the formula, g represents the Earth's gravitational acceleration;

[0031] Combined with the accelerometer model, the measured data output by the y-axis accelerometer in the turntable body coordinate system b' is:

[0032]

[0033] When ω T t = 0°, 90°, 180°, 270°, there is

[0034]

[0035] Then there is

[0036]

[0037] Therefore, there is

[0038]

[0039] In the formula, ε a0 is the constant zero bias of the accelerometer, K a1 is the scale factor of the accelerometer, and δ a is the variable zero bias value of the accelerometer.

[0040] As an optimization, the zero bias stability of the fiber optic gyroscope ≤ 0.01° / h, and the zero bias stability of the accelerometer ≤ 50 μg.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] 1) It completely eliminates the need for external information to achieve north-seeking calculation;

[0043] 2) It uses a single computer chip to reduce the size and cost of the north-seeking instrument without sacrificing accuracy;

[0044] 3) It reduces the volume without affecting the north-seeking accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is the system block diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] The present invention will be further described below in conjunction with the drawings and embodiments.

[0047] To make the objectives, 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 only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, the detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0048] It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and should not be construed as indicating or implying relative importance. In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging vertically, but may be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined. In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged", "installed", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] Embodiment: Refer to Figure 1 , a north-seeking method for a north-seeking instrument without latitude, comprising the following steps,

[0050] a) Install an optical fiber gyro on a rotatable turntable, with its sensitive axis perpendicular to the axis of rotation of the turntable. Two MEMS accelerometers are also installed on the turntable. The measurement axis of one of the MEMS accelerometers is in the same direction as the sensitive axis of the optical fiber gyro, and the measurement axis of the other MEMS accelerometer is perpendicular to the plane where the sensitive axis of the optical fiber gyro and the axis of rotation of the turntable are located.

[0051] Specifically, the north-seeking device used in the present invention is composed of a fiber optic gyroscope with a zero bias stability of 0.01° / h, an accelerometer with a zero bias stability of 50ug, a transposition mechanism, a power supply system, and a navigation computer. The north-seeking device uses a fiber optic gyroscope to directly measure the angular velocity components of the earth's rotation in different directions, calculates the north direction using a corresponding formula, and completes the north-seeking compensation in an inclined state through the measurement value of the MEMS accelerometer. The present invention uses a gyroscope installed on a horizontal turntable of a transposition mechanism and a MEMS accelerometer installed on the turntable, and rotates the gyroscope to four positions of 0°, 90°, 180°, and 270° through a transposition mechanism, collects static data of the gyroscope at these positions for a period of time, and uses an analytical north-seeking algorithm to solve the azimuth.

[0052] This design needs to complete the functions of IMU raw data acquisition, indexing mechanism control, north-seeking solution and external communication. At the same time, it needs to reduce the volume, power consumption and localization requirements. The power supply system uses a 24V power supply DC / DC module to convert into 4 parallel power supplies, which respectively power the GD32 navigation computer, indexing mechanism, fiber optic gyroscope and MEMS accelerometer; after the navigation computer is started normally, the encoder in the indexing mechanism is used to perform 4-position north-seeking indexing control, and the IMU raw data is received through the IMU communication interface (RS422 is used in this design). The navigation computer solves the current heading and attitude information, and then outputs it through the user communication interface (RS422 and CAN are used in this design). The communication interface of this design meets the needs of most users.

[0053] In the present invention, the entire IMU assembly and navigation computer board are placed in the center of the device, the power module is embedded in the back of the gyroscope, adjacent to the navigation computer board, and a large capacitor is placed in the center of the rotating disk to prevent the gyroscope from interfering with the motor when rotating. Larger modules such as the motor and power filter are placed at the four corners of the device, and the internal layout of the device is reasonably arranged, and the overall structure meets the requirements of miniaturization. The sealing of the entire product is carried out in the form of a cover, and the center of gravity of the product is near the central axis.

[0054] The IMU assembly consists of a fiber optic gyroscope, two MEMS accelerometers, and a gyroscope mounting bracket. During the design, the center of gravity of the platform's rotating mechanism is theoretically guaranteed to coincide with the central axis of rotation through careful design and layout of parts, material selection of parts and standard parts, weighing of gyroscopes and other purchased parts, and their placement. Even if there is a deviation, the deviation value is quite small. The truss hollow box structure is adopted to improve the rigidity and anti-deformation ability, while also reducing the weight.

[0055] The indexing mechanism mainly consists of a brushed DC motor, a gear transmission device, and a support ring (frame). At the initial power-on moment of the north-seeking instrument, the brushed DC motor drives the IMU turntable to rotate. Using the angle information feedback by the electric encoder in real time, the mechanical zero position ensures that the turntable returns to zero. After the turntable returns to zero and reaches the target position, the navigation computer controls the brushed DC motor in sequence to rotate to the next target position according to the analytical north-seeking algorithm program.

[0056] To reduce the volume of the device, the output shaft of the motor drives the rotation plane of the gyro through a transmission device. The transmission device consists of a gearbox composed of a small gear and a large gear. The transmission ratio of this gearbox is 1:7. The advantage of this scheme is that the high speed of the brushed DC motor is further reduced through the transmission device, and the torque is increased, realizing the advantages of low speed, high torque, stopping immediately when power is off, small volume, and low power consumption.

[0057] The navigation computer is designed based on the ARM chip GD32H737 of GigaDevice, and mainly completes data processing, storage, and external communication. This chip has the following advantages:

[0058] 1) The single core supports a main frequency of 600MHz and supports floating-point operation;

[0059] 2) Flash capacity: 2048K;

[0060] 3) SRAM capacity: 1024K;

[0061] The reference clock selects the 25MHz active crystal oscillator of Beijing Chenjing Company to provide the working clock for GD32H737VIT6. Through the internal integrated clock multiplier and PLL of ARM, the core working frequency can reach 600MHz.

[0062] The communication circuit adopts 1-way RS422 and 1-way CAN communication, and all chips in the circuit adopt domestic solutions.

[0063] The power supply system of the north-seeking instrument consists of a power filter and a DC / DC. The power supply system is an important part of the north-seeking instrument. To prevent the product from being interfered by large-current devices on the carrier and ensure the internal power quality of the product, according to the externally provided input power, it is filtered and then DC-DC converted to provide to the input end of the secondary power module, and the secondary power module converts it into the secondary power required by the system.

[0064] Among them, the north-seeking instrument software runs in the navigation computer to realize data calculation.

[0065] Specifically,

[0066] b) Calculate the component of the Earth's angular velocity of rotation and the attitude information of the turntable using the measurement data of the fiber optic gyroscope and the MEMS accelerometer when the turntable rotates at 0°, 90°, 180°, and 270°. Solve the equations simultaneously to obtain the three-dimensional attitude angles of the turntable, and determine the north direction through the azimuth angle in the three-dimensional attitude angles.

[0067] The present invention adopts an analytical north-seeking algorithm. The analytical north-seeking algorithm calculates the north direction by using the measured values of the rate gyroscope for the horizontal components of the Earth's rotation speed in different azimuths. It uses the rate gyroscope as an angular velocity measurement tool, so the measurement accuracy requirements for the gyroscope in the small speed range are relatively high. This solution adopts the analytical north-seeking algorithm. Since the MEMS accelerometer is used to measure the horizontal attitude, north-seeking can be realized in the tilted state, but the north-seeking accuracy is slightly reduced compared with that in the horizontal state.

[0068] Since, the Earth's rotation speed ω ie and the components of the gravitational acceleration g on the three coordinate axes of east (E), north (N), and sky (Z) in the geographic coordinate system (t system) are:

[0069]

[0070] In the formula, L is the local latitude.

[0071] That is,

[0072]

[0073] g t =[0 0 -g] T

[0074] Thus, the components of the Earth's rotation speed ω ie and the gravitational acceleration g in the carrier coordinate system can be obtained as:

[0075]

[0076] Analytical north-seeking generally completes the north-seeking process on a stationary base. Using the measured values of the gyroscope and the accelerometer on the o xb 、o yb axial directions of the carrier coordinate system The pitch angle, roll angle, and azimuth angle of the vehicle can be calculated using the above formula.

[0077] Pitch angle:

[0078]

[0079] Roll angle:

[0080]

[0081] Azimuth angle:

[0082]

[0083] Both the accelerometer and the gyroscope have certain bias and scale factor instability errors, so their measured values are all with errors. To explore the accuracy potential of inertial instruments, in this solution, we install the gyroscope on the indexing mechanism, with its sensitive axis parallel to the turntable tabletop, and the MEMS accelerometer is installed on the base. We use the gyroscope and the MEMS accelerometer to measure the component of the earth's angular velocity of rotation and the attitude information of the current device, and then obtain the three-dimensional attitude angles of the carrier through simultaneous solution. The advantage of this multi-position north-seeking method is that during the static north-seeking process, the gyroscope (i.e., the constant drift) can be accurately measured and compensated, thus significantly improving the north-seeking accuracy.

[0084] To achieve the purpose of rapid north-seeking at any location, the four-position north-seeking scheme in the tilted state is very important. In the tilted state, the accelerometer must be involved. By calculating the measured results of the accelerometer, the current tilt angle of the carrier is obtained, and the tilt angle is used to project and decompose the gyro data to calculate the azimuth angle ψ in the tilted state. When the pitch angle and roll angle of the carrier are not zero, first establish the turntable coordinate system b' system, define the sensitive axis of the fiber optic gyroscope as the x-axis, and the y-axis is perpendicular to the plane where the x-axis and the turntable rotation axis are located; then, the component of the earth's angular velocity of rotation on the y-axis is:

[0085]

[0086] In the formula, ω ieZ and ω ieN are the components of the earth's rotation speed ω ie on the celestial and north coordinate axes of the geographical coordinate system respectively; θ is the pitch angle of the turntable, r is the roll angle of the turntable, ψ is the azimuth angle of the turntable; ω T t is the rotation angle of the turntable;

[0087] Combined with the fiber optic gyroscope model, the measured data output by the y-axis fiber optic gyroscope in the turntable coordinate system b' system is:

[0088]

[0089] In the formula, δ0 is the constant bias of the gyroscope, K1 is the scale factor of the gyroscope, and δ i is the variable bias value of the gyroscope at different positions.

[0090] When ω T t = 0°, 90°, 180° and 270°, there are:

[0091]

[0092]

[0093] Then there is:

[0094]

[0095] Let:

[0096]

[0097] And it can be deduced that:

[0098]

[0099] Therefore, there is:

[0100]

[0101] Among them, and θ and γ are calculated as follows. In the b - coordinate system of the turntable body, the component of the earth gravity accelerometer on the y - axis is:

[0102]

[0103] In the formula, g represents the gravity acceleration of the earth;

[0104] Combined with the accelerometer model, the measured data output by the accelerometer on the y - axis in the b - coordinate system of the turntable body is:

[0105]

[0106] When ω T t = 0°, 90°, 180°, 270°, there is

[0107]

[0108] Then there is

[0109]

[0110] Therefore, there is:

[0111]

[0112] In the formula, ε a0 is the constant zero bias of the accelerometer, K a1 is the scale factor of the accelerometer, and δ a is the variable zero bias value of the accelerometer.

[0113] It can be seen that the four - position north - seeking method in the inclined state can cancel the influence of the gyroscope, but it requires a prior value of the gyroscope scale factor, and its north - seeking accuracy is correspondingly lower than that in the horizontal state.

[0114] In summary, the present invention integrates a fiber optic gyroscope, a MEMS accelerometer, a indexing mechanism, a navigation computer, and a power supply system into one device, achieving a full-attitude north-seeking function, and reserving one RS422 serial port and one CAN port for external communication to meet the interaction requirements between the north-seeking instrument and external devices. This north-seeking instrument can achieve full-attitude north-seeking without external input of latitude information, and the north-seeking accuracy can reach 0.06*secL°. When the north-seeking instrument device is working properly, the power supply is connected to the power supply circuit of the navigation computer board through a connector, and the power supply circuit performs DC / DC conversion on the input voltage and outputs it to the remaining functional modules, and the power-on of the north-seeking instrument is completed; after the power-on is completed, the navigation computer board controls the indexing mechanism to return to the zero position first, and then rotates to four positions of 0°, 90°, 180°, and 270° relative to the zero position respectively to collect data of the gyroscope and accelerometer. After the data collection is completed, the navigation computer performs north-seeking calculation, and the obtained attitude and heading information is output through the communication interface; after receiving the north-seeking instruction, it quickly repeats returning to the zero position, rotating, collecting, calculating, and outputting the current heading and attitude information of the device.

[0115] Therefore, the present invention completely realizes north-seeking calculation without external information; uses a single computer chip to reduce the size and cost of the north-seeking instrument on the premise of unchanged accuracy; reduces the volume without affecting the north-seeking accuracy.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solution shall be covered by the scope of the claims of the present invention.

Claims

1. A method for finding the north by a north finder without latitude, characterized in that: The following steps are included: a) A fiber optic gyroscope is mounted on a rotatable turntable, with its sensitive axis perpendicular to the rotation axis of the turntable. Two MEMS accelerometers are also mounted on the turntable, with the measuring axis of one MEMS accelerometer being in the same direction as the sensitive axis of the fiber optic gyroscope, and the measuring axis of the other MEMS accelerometer being perpendicular to the plane where the sensitive axis of the fiber optic gyroscope and the rotation axis of the turntable are located; b) The measurement data of the fiber optic gyroscope and MEMS accelerometer when the turntable rotates 0°, 90°, 180° and 270° are used to calculate the earth's rotation angular velocity component and the turntable's attitude information respectively. The three-dimensional attitude angle of the turntable is obtained by simultaneous solution, and the north direction is determined by the azimuth angle in the three-dimensional attitude angle.

2. A method for finding the north without latitude using a north finder according to claim 1, characterized in that: In step b, firstly, the turntable coordinate system b′ is established, and the sensitive axis of the fiber optic gyroscope is defined as the X-axis, and the Y-axis is perpendicular to the plane where the X-axis and the turntable axis are located; then, the component of the earth's rotation angular velocity on the Y-axis is: In the formula, ω ieZ ,ω ieN The Earth's rotation speed ω ie The component on the celestial and north axes of the geographic coordinate system; θ is the pitch angle of the turntable, γ is the roll angle of the turntable, and ψ is the azimuth angle of the turntable; ω T t is the rotation angle of the turntable; Combined with the fiber optic gyroscope model, the measured data of the Y-axis fiber optic gyroscope output in the turntable coordinate system b′ is: Where δ0 is the constant zero bias of the fiber optic gyroscope, K1 is the scale factor of the fiber optic gyroscope, and δ i is the changing zero bias value of the fiber optic gyroscope at different positions. When T When t=0°, 90°, 180° and 270°, we have: Then we have: set up: And it can be deduced that: So we have: in, and where θ and γ are calculated as follows, In the turntable body coordinate system b′, the component of the earth gravity accelerometer on the y-axis is: In the formula, g represents the gravitational acceleration of the earth; Combined with the accelerometer model, the measurement data output by the y-axis accelerometer in the turntable body coordinate system b′ is: When T When t=0°, 90°, 180°, 270°, Then there is Therefore, there are: In the formula, ε a0 is the constant zero bias of the accelerometer, K a1 is the scale factor of the accelerometer, δ a is the changing zero bias value of the accelerometer.

3. The method for finding the north by a north finder without latitude according to claim 2, characterized in that: The zero bias stability of the fiber optic gyroscope is ≤0.01° / h, and the zero bias stability of the accelerometer is ≤50ug.

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