MEMS inertial measurement unit and methods for performing north finding and inclination measurement

Abstract

This invention discloses a MEMS inertial measurement unit (IMU) and a method for performing north-finding and inclination measurement. The IMU includes an IMU unit, a rotation mechanism, and a processing unit. The rotation mechanism is connected to the IMU unit and can drive the IMU unit to rotate around the azimuth axis. The processing unit is electrically connected to the IMU unit and the rotation mechanism. The processing unit is configured with a north-finding mode and an inclination measurement mode. When the processing unit executes the north-finding mode, the rotating IMU unit rotates and positions itself sequentially to two different angular positions. The processing unit collects relevant data from the IMU unit and calculates and outputs the azimuth angle using a two-position analytical algorithm. When the processing unit executes the inclination measurement mode, the rotation mechanism remains stationary. The processing unit collects relevant data from the IMU unit, performs attitude calculation, and outputs the azimuth angle, tilt angle, and tool face angle. This invention integrates north-finding and inclination measurement functions into a single device, achieving dual functionality and reducing the user's purchase, deployment, and maintenance costs.

Description

Technical Field

[0001] This invention relates to the field of inertial navigation and measurement technology, specifically to a MEMS inertial measurement device and a method for performing north finding and inclination measurement. Background Technology

[0002] Inertial measurement units (IMUs) are core components of inertial navigation and precision measurement systems, and their development trend is towards high precision, miniaturization, and multi-functional integration. Currently, high-precision north-finding instruments mostly employ fiber optic gyroscopes or laser gyroscopes. While these offer high accuracy, they suffer from drawbacks such as large size, heavy weight, high power consumption, and high cost, making them unsuitable for widespread application in portable, miniaturized platforms. In recent years, north-finding solutions based on MEMS gyroscopes have attracted attention due to their miniaturization potential. However, limitations imposed by the lower accuracy and poor zero-bias stability of MEMS gyroscopes prevent them from meeting the requirements for medium to high precision. Existing MEMS north-finding solutions often employ rotation modulation technology to suppress device errors, but their functionality is limited, typically only outputting azimuth information.

[0003] In addition, in fields such as oil drilling, geological exploration, and pipeline inspection, inclinometers are needed to measure and output the azimuth, inclination angle (tilt angle), and tool face angle of drilling tools or pipelines in real time. Existing inclinometers are mostly dedicated devices, typically employing a separate inertial measurement unit (IMU). These devices either rely on external reference signals or, while capable of autonomous orientation, also face a trade-off between accuracy and cost.

[0004] In practice, scenarios such as mining, oil exploration, and foundation pit monitoring often require knowing both the absolute orientation of the equipment (north-finding function) and its tilt attitude and rotation angle (inclination measurement function). This necessitates users carrying two independent systems, which not only significantly increases costs but also creates installation space conflicts. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a MEMS inertial measurement device that can achieve both high-precision north finding and static inclination measurement, and meet the needs of various complex application scenarios.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A MEMS inertial measurement unit includes an inertial measurement unit, a rotation mechanism, and a processing unit. The inertial measurement unit includes three MEMS gyroscopes and three MEMS accelerometers. The rotation mechanism is connected to the inertial measurement unit and can drive the inertial measurement unit to rotate around the azimuth axis. The processing unit is electrically connected to both the inertial measurement unit and the rotation mechanism. The processing unit is configured with a north-finding mode and an inclination mode. When the processing unit executes the north-finding mode, it controls the rotation mechanism to drive the inertial measurement unit to rotate and sequentially position it to two different angular positions. The processing unit collects data from the inertial measurement unit and calculates the heading angle of the carrier using a two-position analytical algorithm. When the processing unit executes the inclination mode, the rotation mechanism remains stationary and collects data from the inertial measurement unit to perform attitude calculation, outputting the azimuth angle, tilt angle, and tool face angle of the carrier.

[0008] As an optimization, when the processing unit executes the north-finding mode, the angles of the two different locations are 180° apart.

[0009] As an optimization, when the processing unit executes the north-finding mode, a filtering method is used to process the collected data to remove interfering data segments.

[0010] As an optimization, the filtering method is the moving mean square error filtering method.

[0011] As an optimization, the sliding mean square error filtering method includes setting a fixed-length time window and sliding the time window to calculate the mean square error of each data segment within the time window; setting a threshold and comparing the mean square error of each data segment with the threshold; if the mean square error of a data segment is less than the threshold, the data segment is retained for subsequent calculation; otherwise, the data segment is discarded.

[0012] A method for performing north-finding based on the above-mentioned device includes controlling the rotation mechanism to rotate the inertial measurement unit to a first position and holding it there, collecting static data of a first preset duration from the inertial measurement unit at the first position; controlling the rotation mechanism to rotate the inertial measurement unit to a second position and holding it there, the second position differing from the first position by a certain angle, collecting static data of a second preset duration from the inertial measurement unit at the second position; and calculating the heading angle of the carrier relative to true north using a two-position analytical algorithm based on the data collected at the first and second positions.

[0013] A method for performing inclination measurement based on the above-mentioned device, wherein the indexing mechanism remains stationary, static data of the inertial measurement unit is collected, and based on the collected data, the azimuth angle, tilt angle and tool face angle of the carrier are output through attitude calculation.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The north-finding and inclinometer functions are integrated into a single device, realizing dual-purpose functionality and reducing the user's purchase, deployment and maintenance costs;

[0016] (2) In the north-finding mode, the constant error of MEMS devices is effectively eliminated by the two-position analysis technology, and high-precision north-finding is achieved; in the inclination mode, high-precision full attitude measurement is achieved by fusing gyroscope and accelerometer data. Detailed Implementation

[0017] 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. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, but merely represent selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The MEMS inertial measurement device in this specific embodiment includes an inertial measurement unit, a shifting mechanism, and a processing unit. The inertial measurement unit includes three MEMS gyroscopes and three MEMS accelerometers. The shifting mechanism is connected to the inertial measurement unit and can drive the inertial measurement unit to rotate around the azimuth axis. The processing unit is electrically connected to both the inertial measurement unit and the shifting mechanism. The processing unit is configured with a north-finding mode and an inclination measurement mode. When the processing unit executes the north-finding mode, it controls the shifting mechanism to drive the inertial measurement unit to rotate and sequentially position it to two different angular positions. The processing unit collects data from the inertial measurement unit and calculates the heading angle of the carrier through a two-position analytical algorithm. When the processing unit executes the inclination measurement mode, the shifting mechanism remains stationary and collects data from the inertial measurement unit to perform attitude calculation, outputting the azimuth angle, tilt angle, and tool face angle of the carrier.

[0019] When the processing unit executes the north-finding mode, the angles of the two different locations are 180° apart.

[0020] When the processing unit executes the north-finding mode, it uses a filtering method to process the collected data to remove interfering data segments.

[0021] The filtering method described is a moving average error (MAO) filtering method. This method involves setting a fixed-length time window and sliding the window to calculate the MAO of each data segment within that window. A threshold is set, and the MAO of each data segment is compared to the threshold. If the MAO of a data segment is less than the threshold, that segment is retained for subsequent calculations; otherwise, it is discarded. This method of using MAO to improve the accuracy of the north-finding instrument assumes that the magnitude of the MAO of data segments reflects the degree of change in that segment; a larger MAO indicates more drastic changes. For stable gyroscope signals, large fluctuations indicate external interference and should be discarded before azimuth calculation.

[0022] A method for performing north-finding based on the above-mentioned device includes controlling the rotation mechanism to rotate the inertial measurement unit to a first position and holding it there, collecting static data of a first preset duration from the inertial measurement unit at the first position; controlling the rotation mechanism to rotate the inertial measurement unit to a second position and holding it there, the second position differing from the first position by a certain angle, collecting static data of a second preset duration from the inertial measurement unit at the second position; and calculating the heading angle of the carrier relative to true north using a two-position analytical algorithm based on the data collected at the first and second positions.

[0023] A method for performing inclination measurement based on the above-mentioned device, wherein the indexing mechanism remains stationary, static data of the inertial measurement unit is collected, and based on the collected data, the azimuth angle, tilt angle and tool face angle of the carrier are output through attitude calculation.

[0024] The calculation process of the two-position parsing algorithm is as follows:

[0025] Based on the mounting platform, when the inertial measurement unit is in the first position, the MEMS gyroscope measures the horizontal component of the Earth's rotation angular velocity as follows:

[0026] ;

[0027] ;

[0028] ;

[0029] ;

[0030] When the inertial measurement unit is in the second position, the MEMS gyroscope measures the horizontal component of the Earth's rotational angular velocity as follows:

[0031] ;

[0032] ;

[0033] ;

[0034] ;

[0035] Based on the two-position analytical algorithm, the heading angle relative to true north is calculated. :

[0036]

[0037] In the formula This is the Earth's rotational angular velocity. It is the acceleration due to gravity. The latitude of the carrier For the pitch angle of the carrier, For the roll angle of the carrier, This refers to the constant error of the MEMS gyroscope.

[0038] The components of the Earth's rotational angular velocity and gravitational acceleration on the East (E), North (N), and Sky (Z) axes of the geographic coordinate system (t-frame) are as follows:

[0039] ;

[0040] Right now

[0041] ;

[0042] Therefore, the components of the Earth's rotational angular velocity and gravitational acceleration in the carrier coordinate system can be calculated as follows:

[0043] ;

[0044] Using MEMS gyroscopes and MEMS accelerometers in the carrier coordinate system , Axial measurement value The pitch and roll angles of the carrier were calculated:

[0045] .

[0046] When executing the north-finding mode, the processing unit receives the north-finding command, then controls the indexing mechanism to precisely position itself at 0° (first position) and remain stationary, continuously collecting raw data from the inertial measurement unit for a duration of t1; the processing unit then controls the indexing mechanism to rotate 180°, precisely position itself at the second position and remain stationary, again collecting raw data from the inertial measurement unit for a duration of t2; the collected data is subjected to moving average error filtering, if the average error of a certain data segment exceeds a preset threshold, the data segment is considered to be disturbed and is discarded, retaining the stable data segment and calculating the average value; the above average value is substituted into the two-position analytical algorithm for calculation to obtain the heading angle relative to the true north reference.

[0047] The calculation process for the inclinometer mode is as follows:

[0048] Based on the current pitch angle of the carrier Roll angle and heading angle This yields the rotation matrix of the carrier coordinates relative to the inertial coordinates. :

[0049] ;

[0050] In the formula, trigonometric functions , , The azimuth angle of the carrier was calculated. Inclination angle and tool face angle :

[0051] .

[0052] When executing the inclination measurement mode, the processing unit receives the inclination measurement command, and then the processing unit controls the indexing mechanism to lock the current or a certain position, keeping the entire device stationary; it collects the raw data from the inertial measurement unit to perform full attitude calculation, and obtains the azimuth angle, tilt angle and tool face angle.

[0053] The IMU consists of three MEMS gyroscopes, three MEMS accelerometers, a mounting bracket, and related circuitry. The three MEMS gyroscopes are orthogonally mounted on the bracket, and the three MEMS accelerometers are also fixed to the IMU mounting bracket. The centers of the three gyroscopes and three accelerometers are aligned as much as possible, and the accelerometers are positioned as close as possible to the IMU's rotation center to minimize size effect errors. A truss hollow box structure is used, which improves rigidity and resistance to deformation while also reducing weight.

[0054] The indexing mechanism mainly consists of a brushless DC motor, encoder, gearbox, and support ring (frame). The indexing mechanism's orientation shaft system is characterized by the motor rotor and shaft being integrated, reducing the shaft diameter; the nested structure reduces the shaft height and rotation radius, thereby reducing the overall size and weight of the equipment.

[0055] The brushless DC motor combined with the gearbox design increases the torque and achieves the advantages of low speed, high torque, automatic stop upon power failure, small size, and low power consumption.

[0056] The encoder selection requirements are based on a positioning accuracy controlled within 0.02 degrees, requiring an encoder accuracy of 0.01 degrees, a resolution of 17 bits or higher, and multi-turn accuracy. Due to size limitations, the encoders that can be selected are basically limited to magnetic encoders or capacitive encoders.

[0057] The inertial measurement unit contains three single-axis gyroscopes and three accelerometers, which can be referred to as the gyroscope assembly and the accelerometer assembly, respectively.

[0058] Three-axis gyroscope calibration model

[0059] ;

[0060] in: .

[0061] These represent the gyroscope's sampled output, scale factor, ideal angular rate input along the input axis, and zero-point drift error, respectively.

[0062] Triaxial accelerometer calibration model

[0063] ;

[0064] in,

[0065] ;

[0066] These represent the accelerometer's sampling output, scale factor, ideal acceleration input along the input axis, and zero-point offset error, respectively.

[0067] The device of this embodiment was tested, and the results show that:

[0068] North-finding mode: North-finding time ≤ 5 min; North-finding accuracy ≤ 0.5°*sec (Lat) (1σ); Horizontal accuracy ≤ 0.1° (1σ);

[0069] Inclination measurement mode: Azimuth: ±2° (1σ) (3°≤ inclination angle≤60°); ±3° (1σ) (60°< inclination angle≤85°); Inclination angle: ±0.1° (1σ) (0°≤ inclination angle≤60°); ±0.25° (1σ) (60°< inclination angle<90°); Tool face angle: ±1° (1σ).

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A MEMS inertial measurement device, characterized in that: The system includes an inertial measurement unit (IMU), a shifting mechanism, and a processing unit. The IMU comprises three MEMS gyroscopes and three MEMS accelerometers. The shifting mechanism is connected to the IMU and can rotate the IMU around its azimuth axis. The processing unit is electrically connected to both the IMU and the shifting mechanism. The processing unit is configured with a north-finding mode and an inclination-measuring mode. When the processing unit executes the north-finding mode, it controls the shifting mechanism to rotate the IMU and position it sequentially to two different angular positions. The processing unit collects data from the IMU and calculates the heading angle of the carrier using a two-position analytical algorithm. When the processing unit executes the inclination-measuring mode, the shifting mechanism remains stationary and collects data from the IMU to perform attitude calculations, outputting the carrier's azimuth angle, tilt angle, and tool face angle.

2. The MEMS inertial measurement device according to claim 1, characterized in that: When the processing unit executes the north-finding mode, the angles of the two different locations are 180° apart.

3. The MEMS inertial measurement device according to claim 1, characterized in that: When the processing unit executes the north-finding mode, it uses a filtering method to process the collected data to remove interfering data segments.

4. The MEMS inertial measurement device according to claim 3, characterized in that: The filtering method is the moving mean square error filtering method.

5. The MEMS inertial measurement device according to claim 4, characterized in that: The sliding mean square error filtering method includes setting a fixed-length time window and sliding the time window to calculate the mean square error of each data segment within the time window; setting a threshold and comparing the mean square error of each data segment with the threshold. If the mean square error of a data segment is less than the threshold, the data segment is retained for subsequent calculation; otherwise, the data segment is discarded.

6. A method for performing north-finding based on the apparatus of any one of claims 1 to 5, characterized in that: The system controls the indexing mechanism to rotate the inertial measurement unit to a first position and hold it there. At the first position, static data of a first preset duration is collected from the inertial measurement unit. The system also controls the indexing mechanism to rotate the inertial measurement unit to a second position and hold it there. The second position is at a certain angle different from the first position. At the second position, static data of a second preset duration is collected from the inertial measurement unit. Based on the data collected at the first and second positions, the heading angle of the carrier relative to true north is calculated using a two-position analytical algorithm.

7. A method for performing inclinometer measurement based on the device according to any one of claims 1 to 5, characterized in that: The indexing mechanism remains stationary, collects static data from the inertial measurement unit, and outputs the azimuth angle, tilt angle, and tool face angle of the carrier through attitude calculation based on the collected data.

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