MEMS gyrocompass

Abstract

The present invention relates to the field of MEMS (Micro Electro Mechanical Systems) and, in particular, to the use of MEMS gyroscopes in a gyrocompass for finding a geographical heading. By including at least three MEM gyroscopes with offset sensing axes arranged in a known orientation, the gyrocompass of the present invention does not require precise mechanical rotation of the gyroscopes to determine the heading of the gyrocompass or to compensate for bias errors.

Description

Technical Field

[0001] This invention relates to the field of MEMS (Micro-Electro-Mechanical Systems), and more specifically, to the use of a MEMS gyroscope in a gyrocompass for finding a geographical heading. Background Technology

[0002] When determining geographic heading, the yaw direction, i.e., the orientation angle parallel to the Earth's surface, is most commonly found using a magnetic compass. However, both mechanical and electromagnetic compasses have significant drawbacks. The Earth's magnetic poles are quite far from the true geographic poles (where the Earth's axis of rotation intersects the Earth's surface), and furthermore, the North Magnetic Pole, in particular, is drifting at an increasing rate. Additionally, the Earth's magnetic field is weak and has been weakening (at an increasing rate) throughout its measurement history. Therefore, in many applications where magnetic materials are present, such as in cars and other vehicles with structural metals and currents that generate magnetic fields, and in indoor and urban areas with reinforced concrete or other metal-containing structures and objects, the weak field is practically unusable. Moreover, in applications requiring any kind of accuracy, even in good open outdoor conditions, the compass needs frequent calibration for reliable heading measurements.

[0003] Therefore, in applications requiring a high level of accuracy in determining geographical heading, such as marine navigation, other types of compasses, such as gyrocompasses, are used. A conventional gyrocompass is a mechanical gimbal that aligns its own axis of rotation with the Earth's axis. However, conventional gyrocompasses are large, expensive, and relatively unreliable devices that require regular maintenance.

[0004] To overcome the problems of conventional gyrocompasses, high-performance angular rate sensors, such as high-performance MEMS gyroscopes, have been used to directly measure the Earth's rotation relative to the device's heading. However, the static Earth rotation rate to be measured is typically at least three orders of magnitude smaller than the angular rate generated by the device's dynamic heading changes. Therefore, such a device must be essentially stationary during measurements used for heading determination.

[0005] The ability to measure very low rotational rates using MEMS gyroscopes is severely limited by the bias error of MEMS gyroscopes, which has historically been orders of magnitude larger than the Earth's rotational rate. Two methods, known as rotational and taggable methods, have been developed to attempt to counteract or eliminate bias error, thereby improving the performance of MEMS gyroscopes used in gyrocompasses. In the rotational method, the MEMS gyroscope rotates at a constant angular rate around the vertical yaw axis (i.e., the gravity axis), which alters the gyroscope's sensing axis relative to north. The gyroscope thus measures the changing component of the Earth's rotation, producing a sinusoidal waveform from which the direction of north can be determined as the peak amplitude (90°) of the sinusoidal waveform. Thus, the Earth's continuous rotation is modulated into an AC signal in this process, essentially eliminating the need for extreme offset accuracy. However, the higher the gyroscope's noise, the slower the rotation needs to be to average the readings and minimize the effects of noise. This results in very slow rotation, but at the same time, the rotational rate needs to be substantially constant for accurate heading determination. However, the mechanical systems required to generate such slow, continuous rotation are unreliable, bulky, complex, and expensive.

[0006] In the labelable configuration, the gyroscope rotates periodically by 180° to compensate for bias errors. However, because time needs to be allocated for the rotation and stabilization of the rate signal, the rotation of the gyroscope slows down the determination of the heading.

[0007] Patent application US2016 / 0047675A1 discloses an inertial measurement and navigation system having physically distinct sectors located in an orthogonally oriented array of angular rate sensors.

[0008] Patent application US2020 / 0033131A1 discloses an inertial navigation system with a three-axis MEMS gyroscope capable of rotating about a rotation axis.

[0009] Patent application US2006 / 0196269A1 discloses an inertial measurement system in which bias is eliminated by rotating the base about the input axis.

[0010] The publication "milli-HRG Inertial Navigation System" by ADMeyer and DM Rozelle discloses an inertial navigation system with a hemispherical resonant gyroscope that uses a 180-degree rotation to mitigate gyroscope bias error.

[0011] Patent application GB 2385078 A discloses a measurement-while-drilling assembly using two gyroscopes, which are rotated to remove bias. Summary of the Invention

[0012] According to a first aspect of the invention, a gyrocompass device is provided for determining a heading relative to the surface of the Earth or another rotating planetary body. The device comprises: one or more MEMS gyroscopes, wherein the one or more MEMS gyroscopes provide at least three sensing axes arranged such that the sensing axes lie in a first plane and each sensing axis is offset by a known offset angle relative to the other sensing axes; and electronic circuitry configured to receive rotation rates from the one or more MEMS gyroscopes and determine the heading of the device relative to the surface of the Earth or another rotating planetary body based on the rotation rates received from the one or more MEMS gyroscopes, and configured to fit the amplitude of a sine or cosine function to the received rotation rates and determine the latitude of the gyrocompass.

[0013] The angles of the sensing axes of the one or more MEMS gyroscopes can be spaced out in a regular 360 / N pattern, where N is the number of sensing axes.

[0014] N can be an even number, such that the sensing axes of the one or more MEMS gyroscopes are arranged in pairs, wherein the sensing axes in each pair are offset by 180 degrees.

[0015] The device can be configured to retrieve the value of the bias error for each sensing axis in the sensing axes of the one or more MEMS gyroscopes from a lookup table and subtract the bias error from the received rotation rate before determining the heading of the device.

[0016] The device can be configured to retrieve a value from a lookup table based on the sum of at least two of the received rotation rates, wherein the at least two received rotation rates are received from sensing axes arranged at regular intervals around 360 degrees, such that the Earth rotation component in the rate signal is canceled out in the sum of the at least two received rotation rates.

[0017] The device can be configured to retrieve a value from a lookup table based on the sum of the rotation rates received from all of the at least three sensing axes.

[0018] The device may also include a temperature sensor, and the device may be configured to retrieve a bias error value from a lookup table based on the temperature sensed by the temperature sensor, in addition to the sum of the received rotational rates.

[0019] The device circuitry can be configured to determine the device's heading by fitting a sine or cosine function to the received rotational rate. n+β) or C cos(α) n The form is α +β), where C is the amplitude of the sine function, which depends at least on the latitude of the device. n β is the offset angle of the nth sensing axis, and β is the phase offset, which has a fixed difference relative to true north. The heading of the device can be determined by changing the phase offset β to find the value with the minimum error in the fitting of the sine function to the received rotation rate. The sine or cosine function can be fitted to the received rotation rate using the least squares mean or other fitting methods.

[0020] The device may also include a GNSS receiver or a connector for communicating with the GNSS receiver, and before performing a sine fit on the received rotation rate, the device may be configured to: receive the latitude of the device from the GNSS receiver; and calculate the amplitude of the sine function based on the received latitude.

[0021] The device circuitry can be configured to determine the device's heading when the received rotation rate value is below a threshold. The threshold can be at least 10 times the root mean square error of the received rotation rate.

[0022] The device may also include a GNSS receiver or a connector for communicating with the GNSS receiver and an inertial measurement unit, and the device may be configured to: calculate heading based on the outputs of the GNSS receiver and the inertial measurement unit; average the rotation rate of a sensing axis received from one or more MEMS gyroscopes over time; calculate the component of Earth rotation sensed by each sensing axis of the one or more MEMS gyroscopes based on the heading calculated according to the outputs of the GNSS receiver and the inertial measurement unit; and determine the bias error of each sensing axis of the one or more MEMS gyroscopes by subtracting the calculated component of Earth rotation for each sensing axis from the average rotation rate received from the sensing axes.

[0023] The device can be configured to calculate the heading based on the rotation rate received from one or more MEMS gyroscopes by subtracting a determined bias error for each sensing axis of one or more MEMS gyroscopes from the rotation rate received from the sensing axis before determining the heading of the device based on the received rotation rate.

[0024] The device may also include at least one of a yaw gyroscope and an inertial measurement unit, the yaw gyroscope being configured to measure the rotation of one or more MEMS gyroscopes about an axis perpendicular to the measurement axis of the one or more MEMS gyroscopes. The device may be configured to measure the motion of one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body while the rotation rate is measured by the one or more MEMS gyroscopes, and to stabilize the received rate by subtracting a calculated rate caused by the measured motion of the one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body from the received rotation rate before determining the device's heading.

[0025] The device can be configured to determine its heading by: receiving a first rotation rate from one or more MEMS gyroscopes at a first position; measuring the rotation of one or more MEMS gyroscopes from the first position to a second position; receiving a second rotation rate from one or more MEMS gyroscopes at the second position; calculating a differential rotation rate for each sensing axis of one or more MEMS gyroscopes by subtracting the second rotation rate from the first received rotation rate received from the sensing axis of the MEMS gyroscopes, or by subtracting the first received rotation rate from the second received rotation rate received from the sensing axis of the MEMS gyroscopes; and fitting the differential rotation rate to a sine or cosine function to determine a phase offset of the sine or cosine function, wherein the phase offset corresponds to the heading of the device.

[0026] The sine or cosine function can be [sin(β+α)] n )-sin(β+α n +θ)] or C[cos(β+α)] n )-cos(β+α n The form is α +θ), where C is the amplitude of the sine or cosine function, and α is the amplitude of the sine or cosine function. n θ is the offset angle of the nth sensing axis, θ is the measured rotation angle of one or more MEMS gyroscopes from the first position to the second position, and β is the phase offset, wherein the phase offset indicates the heading of the device.

[0027] The device can be configured to receive multiple first and second rotation rates for each sensing axis of one or more MEMS gyroscopes and to average the received rotation rates over time.

[0028] The device can also be configured to estimate the bias error of each sensing axis of one or more MEMS gyroscopes by comparing a first rotation rate and a second rotation rate with a calculated rotation rate caused by the rotation of the Earth or other rotating planetary body in the first and second positions. Estimating the bias error of each sensing axis of one or more MEMS gyroscopes may include calculating the bias error b of the nth sensing axis according to one of the following equations. n : or

[0029] Among them, R 1n It is the first received rotational rate of the nth sensing axis and R 2n is the second received rotation rate of the nth sensing axis, and C is the amplitude of a sine or cosine function.

[0030] The device can be configured to update the bias error lookup table using the calculated bias error. The device can also be configured to update the bias error lookup table based on the measured temperature.

[0031] The device can be configured to use at least one of a yaw gyroscope and an inertial measurement unit to measure the rotation of one or more MEMS gyroscopes from a first position to a second position, the yaw gyroscope being configured to measure the rotation of one or more MEMS gyroscopes about an axis perpendicular to the sensing axis of one or more MEMS gyroscopes.

[0032] The device can be configured to measure the rotation of one or more MEMS gyroscopes from the first position to the second position in response to detecting that one or more MEMS gyroscopes are rotating positively away from the first position.

[0033] The device can be configured to rotate one or more MEMS gyroscopes from a first position to a second position.

[0034] The differential rotation rate can be fitted to a sine or cosine function using the least squares mean or other fitting methods. The sum of the residuals or the sum of the squares of the residuals can be used as an indicator of the accuracy of heading determination. The device can be configured to increase the averaging time of the received rate signal and / or rotate one or more MEMS gyroscopes from a first position to a second or third position when the sum of the residuals or the sum of the squares of the residuals exceeds a threshold.

[0035] The device may also include an inclinometer or inertial measurement unit for determining the orientation of one or more MEMS gyroscopes relative to the Earth's gravitational field, and the circuitry may be configured to use the tilt measured by the inclinometer to correct heading and / or latitude calculations.

[0036] The device circuitry can be configured to calculate error correction based on the device's tilt after a heading determination based on the average inclinometer readings obtained during heading determination.

[0037] The device may include two MEMS gyroscopes, wherein each MEMS gyroscope includes at least two sensing axes that are perpendicular to each other and located in a first plane, and wherein the two MEMS gyroscopes are rotated 180 degrees relative to each other such that the sensing axes of the MEMS gyroscopes are arranged at 90-degree intervals.

[0038] According to a second aspect of the invention, a method is provided for determining a heading relative to the surface of the Earth or another rotating planetary body using a gyrocompass device. The method includes: receiving a rotation rate from one or more MEMS gyroscopes, wherein the one or more MEMS gyroscopes provide at least three sensing axes arranged such that the sensing axes lie in a first plane and each sensing axis is offset by a known offset angle relative to the other sensing axes; and determining the heading of the device relative to the surface of the Earth or another rotating planetary body based on the rotation rate received from the one or more MEMS gyroscopes. Determining the heading of the device includes fitting a sine or cosine function to the received rotation rate.

[0039] The angles of the sensing axes of one or more MEMS gyroscopes can be spaced in angles according to a regular 360 / N pattern, where N is the number of sensing axes. N can be an even number, such that the sensing axes are arranged in pairs, where the sensing axes in each pair are offset by 180 degrees.

[0040] The method may include retrieving the value of the bias error for each sensing axis in a lookup table for one or more sensing axes of a MEMS gyroscope and subtracting the bias error from the received rotation rate before determining the heading of the device.

[0041] The value retrieved from the lookup table can be based on the sum of at least two received rotation rates, wherein the at least two received rotation rates are received from sensing axes arranged at regular intervals around 360 degrees, such that the Earth rotation component in the rate signal is canceled out in the sum of the at least two received rotation rates.

[0042] The value retrieved from the lookup table can be based on the sum of the rotation rates received from all of the at least three sensing axes.

[0043] The bias error value can be retrieved from the lookup table based not only on the sum of the received rotation rates, but also on the temperature sensed by the temperature sensor.

[0044] The sine function can be C sin(α)n +β) or C cos(α) n The form is α +β), where C is the amplitude of the sine function, which depends at least on the latitude of the device. n β is the offset angle of the nth sensing axis, and β is the phase offset, which has a fixed difference relative to true north, and the heading of the device can be determined by changing the phase offset β to find the value with the minimum error in the fitting of the sine function to the received rotation rate.

[0045] The sine or cosine function is fitted to the received rotation rate using the least squares mean or other fitting methods. The method may also include fitting the amplitude of the sine or cosine function to the received rotation rate to determine the latitude of the gyrocompass.

[0046] The method may also include: receiving the latitude of the device from a GNSS receiver; and calculating the amplitude of a sine function based on the received latitude.

[0047] When the received rotation rate value is below a threshold, the heading determination device can be executed. This threshold can be at least 10 times the root mean square error of the received rotation rate.

[0048] The method may further include: calculating the heading based on the outputs of the GNSS receiver and the inertial measurement unit; averaging the rotation rate of the search axis received from one or more MEMS gyroscopes over time; calculating the component of Earth rotation sensed by each sensing axis of the one or more MEMS gyroscopes based on the heading calculated according to the outputs of the GNSS receiver and the inertial measurement unit; and determining the bias error of each sensing axis of the one or more MEMS gyroscopes by subtracting the calculated component of Earth rotation for each sensing axis from the average received rotation rate from the sensing axes.

[0049] The method may also include calculating the heading based on the rotation rates received from one or more MEMS gyroscopes by subtracting a determined bias error for each sensing axis from the rotation rates received from the sensing axes before determining the heading based on the received rotation rates.

[0050] The method may further include: measuring the motion of one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body while measuring the rotation rate by one or more MEMS gyroscopes; and stabilizing the received rotation rate by subtracting a calculated rate caused by the measured motion of one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body from the received rotation rate before determining the heading of the device.

[0051] Determining the heading of the device may include: receiving a first rotation rate from one or more MEMS gyroscopes at a first position; measuring the rotation of one or more MEMS gyroscopes from the first position to a second position; receiving a second rotation rate from one or more MEMS gyroscopes at the second position; calculating a differential rotation rate for each sensing axis of one or more MEMS gyroscopes by subtracting the second rotation rate from the first received rotation rate received from the sensing axis of the MEMS gyroscopes, or by subtracting the first received rotation rate from the second received rotation rate from the sensing axis of the MEMS gyroscopes; and fitting the differential rotation rate to a sine or cosine function to determine a phase offset of the sine or cosine function, wherein the phase offset corresponds to the heading of the device.

[0052] The sine or cosine function can be C[sin(β+α)] n )-sin(β+α n +θ)] or C[cos(β+α)] n )-cos(β+α n The form is α +θ), where C is the amplitude of the sine or cosine function, and α is the amplitude of the sine or cosine function. n θ is the offset angle of the nth sensing axis, θ is the measured rotation angle of one or more MEMS gyroscopes from the first position to the second position, and β is the phase offset, wherein the phase offset indicates the heading of the device.

[0053] It can receive multiple first rotation rates and second rotation rates for each sensing axis of one or more MEMS gyroscopes and average them over time.

[0054] The method may also include estimating the bias error of each sensing axis of one or more MEMS gyroscopes by comparing a first rotation rate and a second rotation rate with a calculated rotation rate caused by the rotation of the Earth or other rotating planetary body in the first and second positions.

[0055] Estimating the bias error of each sensing axis of one or more MEMS gyroscopes may include calculating the bias error bn of the nth sensing axis according to one of the following equations: or

[0056] Among them, R 1n It is the first received rotational rate of the nth sensing axis and R 2n is the second received rotation rate of the nth sensing axis, and C is the amplitude of a sine or cosine function.

[0057] The method may further include updating the bias error value lookup table using the calculated bias error. The method may also further include updating the bias error value lookup table based on the measured temperature.

[0058] Measuring the rotation of one or more MEMS gyroscopes from a first position to a second position can be based on the output of at least one of a yaw gyroscope and an inertial measurement unit, wherein the yaw gyroscope is configured to measure the rotation of one or more MEMS gyroscopes about an axis perpendicular to the sensing axis of one or more MEMS gyroscopes.

[0059] Measuring the rotation of one or more MEMS gyroscopes from a first position to a second position can be performed in response to detecting that one or more MEMS gyroscopes are rotating away from the first position.

[0060] The method also includes rotating one or more MEMS gyroscopes from a first position to a second position.

[0061] The differential rotation rate can be fitted to a sine or cosine function using least-squares mean or other fitting methods. The sum of the residuals or the sum of the squares of the residuals is used as an indicator of the accuracy of the heading determination. The method may also include: increasing the averaging time of the received rate signal and / or rotating one or more MEMS gyroscopes from a first position to a second or third position when the sum of the residuals or the sum of the squares of the residuals exceeds a threshold.

[0062] The method may also include determining the orientation of the first plane relative to the Earth's gravitational field, and correcting the heading and / or latitude calculations based on the determined orientation.

[0063] This method may include calculating error correction based on the orientation of the device, based on the average orientation determination performed during the heading determination.

[0064] The one or more MEMS gyroscopes may include two MEMS gyroscopes, wherein each MEMS gyroscope includes at least two sensing axes that are perpendicular to each other and located in a first plane, and wherein the two MEMS gyroscopes are rotated 180 degrees relative to each other such that the sensing axes of the MEMS gyroscopes are arranged at 90-degree intervals. Attached Figure Description

[0065] Figure 1A and Figure 1B An example of the arrangement of MEMS gyroscopes in an embodiment of the MEMS gyroscope compass of the present invention is shown.

[0066] Figure 2 The first method for determining course is described.

[0067] Figure 3 A second method for determining heading is described.

[0068] Figure 4 A method for determining the heading and / or bias error of a MEMS gyroscope using its passive rotation is described.

[0069] Figure 5 A method for determining the heading and / or bias error of a MEMS gyroscope using its active rotation is described.

[0070] Figure 6 A method for determining heading using stored bias error values ​​retrieved from a lookup table is described. Detailed Implementation

[0071] Figure 1A and Figure 1B An exemplary arrangement of the MEMS gyroscope in the MEMS gyroscope compass of the present invention is shown. Figure 1A Sixteen MEMS gyroscopes 101 to 116 are shown arranged on a substrate parallel to the plane of the page. In other words, the MEMS gyroscopes 101 to 116 are fixed on a planar substrate, such as a circuit board, with a known orientation. Although Figure 1A Sixteen MEMS gyroscopes are depicted, but the present invention can work with any number of MEMS gyroscopes, as long as the gyroscopes provide at least three sensing axes offset from each other. For example, two identical dual-axis MEMS gyroscopes can provide four offset sensing axes when the dual-axis MEMS gyroscopes rotate relative to each other (at any angle other than 90 degrees or 270 degrees). This is in Figure 1B Another arrangement depicted in the diagram shows a MEMS gyrocompass comprising two dual-axis MEMS gyroscopes 121 and 122 rotated 180 degrees relative to each other. This arrangement of the two MEMS gyroscopes provides four sensing axes spaced 90 degrees apart. Of course, it is possible to... Figure 1B Other gyroscopes, such as a three-axis gyroscope or a gyroscope as part of a 6-DOF inertial measurement unit, can be used in the same arrangement depicted, as long as there are at least three offset sensing axes provided by the two gyroscopes. In another embodiment (not shown), a single MEMS gyroscope can be fabricated and used in a gyrocompass that includes any number of offset measurement axes within a single package.

[0072] exist Figure 1A The image shows the X-axis and Y-axis (optionally also sensing axes) of the MEMS gyroscope 101. Figure 1AAs shown, the X-axis and Y-axis of each of the other gyroscopes 102 to 116 are oriented relative to the package of each gyroscope 102 to 116 in the same manner as the X-axis and Y-axis of gyroscope 101 are oriented relative to the package of gyroscope 101. The X-axis and Y-axis of each of the gyroscopes 101 to 116 are offset from each other by an offset angle α. Figure 1A An example of this offset angle α is shown for gyroscopes 103 and 106, where offset angle α represents the offset of the X-sensing axis of gyroscopes 103 and 106 relative to the X-sensing axis of gyroscope 101. Figure 1A In the arrangement of the sixteen MEMS gyroscopes shown, the gyroscopes are oriented with a regular rotation interval of 22.5 degrees, which is 360 degrees divided by the number of gyroscopes, 16. Therefore, the X-sensing axis of gyroscope 102 is rotated 22.5 degrees clockwise from the X-sensing axis of gyroscope 101. The X-sensing axis of gyroscope 103 is then rotated 22.5 degrees clockwise from the X-sensing axis of gyroscope 102, and so on.

[0073] Typically, but not necessarily, the sensing axes of the MEMS gyroscopes constituting the gyrocompass are arranged with a regular rotational interval relative to each other. Ideally, the interval α between the sensing axes is a multiple of 360 / N, where N is the number of sensing axes. Thus, when the MEMS gyroscopes, such as MEMS gyroscopes 101 to 116, are of the same type, i.e., when the sensing axes are oriented in the same direction relative to the gyroscope package, this can be considered as the assembly angle of each MEMS gyroscope corresponding to the interval α, which is preferably a multiple of 360 / N, where N is the number of gyroscopes.

[0074] In some implementations, it is not necessary for the sensing axes of the MEMS gyroscope to be equidistant around 360 degrees, as long as the orientation is precisely known and can be used later when determining the orientation of the device.

[0075] The Z-axis (optionally the sensing axis) of all MEMS gyroscopes 101 to 116 extends outward from the page toward the reader. The Z-axis of all gyroscopes are parallel to each other. However, it is not necessary for the MEMS gyroscopes forming the MEMS gyro compass to have a sensing axis in the Z direction. Each gyroscope in the MEMS gyroscope can be a single-axis gyroscope.

[0076] Figure 1A MEMS gyroscope 101 to 116 or Figure 1BEach sensing axis of the MEMS gyroscopes 121 and 122 measures a different contribution to the Earth's rotation, and when the substrate is parallel to the Earth's surface, i.e., when the Z-axis of the MEMS gyroscope is parallel to the direction of gravity, the component of Earth's rotation sensed by each gyroscope in degrees per hour follows the following equation:

[0077]

[0078] in, It is the latitude of the gyro compass, α n β is the offset angle of the nth sensing axis, and β is the phase offset. If the device is in a known heading (e.g., such that the X sensing axis of gyroscope 101 is aligned with true north), the rotational rate measured by MEMS gyroscopes 101 to 116 or 121 and 122 can be fitted to the expected measurement sine function by changing the phase value β. Therefore, the best-fit value of β indicates the difference between the orientation of the gyrocompass and the known heading, thus allowing the heading of the gyrocompass to be determined. The measured rotational rate can be fitted to a sine function using any suitable fitting technique, such as least squares fitting. It will be understood that the sine function in equation (1) can be simply replaced by a cosine function. This change only affects how the phase offset is interpreted, shifting it by 90 degrees.

[0079] If the latitude of the gyro compass With a certain degree of accuracy known, the heading determination process becomes simpler. Such determination can be made, for example, using GPS where available, or via geocoded user input if a rough location (e.g., city or state) is known. However, in the case of using high-performance MEMS gyroscopes 101 to 116 or 121 and 122 in a gyrocompass, the amplitude of a sine wave can also be determined from the measured data by fitting, and thus the latitude can be determined.

[0080] Equation (1) defines the amplitude components of a sine wave, i.e. The amplitude of 15 degrees per hour can vary depending on the tilt angle of MEMS gyroscopes 101 to 116 or 121 and 122. Furthermore, if the MEMS gyro compass is used on a planetary body other than Earth, the amplitude can also vary depending on the planetary body's rotation period. Therefore, in the project... In cases where the equations appear in the description herein, it will be understood that, without departing from the principles of the invention, the terms... The terms can be replaced with other terms depending on the tilt of the MEMS gyroscope and the rotation rate of the planetary body. For example, the more general term R cos(σ) can be used instead, where R corresponds to the rotation rate of the planetary body and σ is the angular difference between the plane of the sensing axis of MEMS gyroscopes 101 to 116 or 121 and 122 and the plane tangent to the surface of the planetary body at the same longitude at the equator.

[0081] In the first embodiment, heading determination should only be performed when the gyrocompass is substantially stationary relative to the Earth's surface. Thus, the rotational rates received from each gyroscope 101 to 116 or 121 and 122 essentially consist only of the Earth's rotational rate, bias error, and noise according to equation (1). The stationary state of the gyrocompass can be determined based on the range of samples collected from each gyroscope 101 to 116 or 121 and 122. Heading determination is performed when the sample range is less than a predetermined threshold. The data is evaluated for external disturbances before being used for further calculations to ensure that the compass is stationary and the results are not affected by motions not attributable to the Earth's rotation. A suitable value for the threshold is ten times the RMS noise of each gyroscope, although other thresholds may also be used. For a given type of MEMS gyroscope used in the gyrocompass, the threshold can be determined experimentally. Once the sample range drops below a threshold, the average (e.g., equal) received rotation rate can be determined for each MEMS gyroscope 101 to 116 or 121 and 122 on multiple received samples in order to minimize the effect of noise, and then the average received rotation rate can be used in heading determination, i.e., sine fitting.

[0082] exist Figure 2 The method of the first embodiment is described in the figure. At step 201, the MEMS gyrocompass determines whether it is stationary relative to the Earth's surface, for example, using the thresholding method described above. At step 202, the rotational rates of MEMS gyroscopes 101 to 116 or 121 and 122 are read and averaged, and at step 203, the read rotational rates are fitted to a sine function of equation (1) based on the known offset angle of each sensing axis of the sensing axes of MEMS gyroscopes 101 to 116 or 121 and 122. The phase offset β is determined based on the sine function fitting. At step 204, the heading of the device is determined based on the phase offset β. If the phase offset β is measured to be such that zero indicates true north, this step may be negligible (or even skipped), in which case the phase offset β may be directly output as the determined heading at step 205. If another compass direction besides north corresponds to β = 0, a simple calculation can be performed to provide an indication of the heading angle. In other applications requiring lower precision, the phase offset β can be converted to compass direction, such as north, northeast, east, etc., and output in this form.

[0083] Following step 203 above, the sum of the residuals or the sum of the squares of the residuals can be used as an indication of the accuracy of the heading determination. The sum of the residuals or the sum of the squares of the residuals can be compared to a threshold, and if the sum exceeds the threshold, the averaging time of the rates received from MEMS gyroscopes 101 to 116 or 121 and 122 can be increased to reduce the impact of noise on the measurement. Furthermore, if the sum exceeds the same or different thresholds, the gyrocompass can perform rotation determination and / or bias error estimation, as described below regarding... Figure 4 or Figure 5 As described.

[0084] In a second embodiment, the gyrocompass need not be stationary, provided that all significant angular motions of the gyrocompass are known to affect the measured rate of Earth rotation obtained by the gyroscope. Therefore, in a second embodiment, the gyrocompass may further include an inertial measurement unit (IMU) for measuring the motion of the gyrocompass relative to the Earth, and this measured motion can be subtracted from the gyroscope data to stabilize the reading. Alternatively, one or more of the MEMS gyroscopes 101 to 116 or 121 and 122 may further include a sensing axis perpendicular to the Earth's surface in the vertical direction, i.e., when the sensing axis (or axis) used to measure Earth rotation is parallel to the surface. The rate of rotation measured by the vertical sensing axis or the overall motion measured by the IMU can be used to compensate for the rotation of the gyrocompass during heading determination. In this case, an accelerometer may also be provided to provide more information about the motion of the MEMS gyrocompass. In another alternative, one or more of the MEMS gyroscopes 101 to 116 or 121 and 122 may be an IMU, for example, including a three-axis gyroscope and a three-axis accelerometer.

[0085] exist Figure 3 The method of the second embodiment is illustrated. At step 301, the rotation rate is read from MEMS gyroscopes 101 to 116 or 121 and 122, while the motion of the MEMS gyrocompass relative to the Earth's surface is simultaneously measured. At step 302, the rotation rate read from MEMS gyroscopes 101 to 116 or 121 and 122 is stabilized by subtracting the calculated rate from the measured relative motion of the gyrocompass. The resulting rotation rate is then used in heading determination at steps 303 to 305. Steps 303 to 305 are performed as described above regarding steps 203 to 205.

[0086] In the third embodiment, the MEMS gyrocompass can utilize passive rotation of the device to determine the bias error of each gyroscope 101 to 116 or 121 and 122, or, in the case of a multi-axis gyroscope, the bias error of each axis of each gyroscope, which affects the heading determination calculation. In this case, "passive rotation" refers to the gyrocompass rotating about the yaw axis, i.e., perpendicular to... Figure 1A or Figure 1B The gyroscope depicted in the diagram rotates or fully rotates any portion of the axes of all sensing axes, subjecting the gyrocompass device to "passive rotation" due to externally applied forces. For example, if the gyrocompass device is deployed in a vehicle, the gyrocompass rotates as the vehicle rotates, and this rotation can be used in the methods described below. To utilize this passive rotation, the MEMS gyrocompass also includes at least one yaw gyroscope having a sensing axis arranged perpendicular to the sensing axes of MEMS gyroscopes 101 to 116 or 121 and 122. Therefore, this gyroscope is capable of measuring the rotation of the MEMS gyrocompass relative to the Earth's surface. This gyroscope can be one of the MEMS gyroscopes 101 to 116 or 121 and 122 used in heading determination itself, or it can be a separate gyroscope, such as part of an inertial measurement unit. Alternatively, in another alternative, one or more of the MEMS gyroscopes 101 to 116 or 121 and 122 may be an IMU, such as including a three-axis gyroscope and a three-axis accelerometer.

[0087] exist Figure 4 The method is described in [the document]. At step 401, at a first stationary position (relative to the Earth's surface) before the detection of passive rotation, the measured rotational rate of each MEMS gyroscope 101 to 116 or 121 and 122 is recorded and averaged over time to minimize the influence of noise on the received rotational rate. Therefore, after step 401, the rotational rate R of each sensing axis in the sensing axes is known. 1n Among them, each rate R 1n =γ 1n +b n γ 1n It is assumed to be the static angular velocity measured by the nth sensing axis at the first position, which is mainly composed of the Earth's rotation, and b n It is the bias error of the nth sensing axis.

[0088] At step 402, the rotation of the MEMS gyro compass around the yaw axis is detected. After rotation is detected, time integration of the yaw rate signal (or other measurement of rotation) begins at step 403. When rotation is detected to have stopped at step 404, time integration of the yaw rate signal stops at step 405. The integrated yaw rate signal (or other measurement of rotation) displays the rotation angle θ.

[0089] Alternatively, sensor fusion, such as Kalman filtering, can be used instead of time integration of the yaw rate signal to estimate the rotation angle θ. Preferably, a 6-DOF inertial measurement unit is provided instead of a yaw gyroscope. This method significantly improves the accuracy of heading change estimation and also takes into account the true 3D orientation rather than just the in-plane component. Furthermore, when using advanced sensor fusion algorithms such as Kalman filtering, the system benefits from using a tilt axis, i.e., the substrate on which the MEMS gyroscopes 101 to 116 or 121 and 122 are located is tilted relative to the horizontal plane. In this arrangement, the yaw angle and Earth rotation measurements are a linear combination of the gyroscope readings and the tilt angle data, and the gyroscope bias error estimation can be significantly improved.

[0090] After the rotation, at step 405, the measured rotational rate of each sensing axis is recorded again at the second rest position (relative to the Earth's surface) and averaged over time as in step 401 to provide a second set of rotational rates R. 2n , where R 2n =γ 2n +b 2n γ 2n It is assumed to be the static angular rate measured by the nth gyroscope at the second position, which is mainly composed of the Earth's rotation, and b n This is the bias error of the nth sensing axis. Due to the rate of change R of the bias error... 1n and R 2n The time between measurements is relatively short, so it can be assumed that the bias error b n The results were the same in both measurements.

[0091] At step 406, the two sets of received rotation rates R are used. 1n and R 2n The gyrocompass's heading is determined by the measured rotation angle θ. Using equation (1) above, the rotation rate R... 1n With R 2n The difference between them can be expressed as:

[0092]

[0093] Therefore, the unknown phase offset β, corresponding to the heading of the gyrocompass in its initial position before rotation, can be determined by fitting equation (2) to the data. After rotation, the current heading of the gyrocompass can be determined by adding the measured rotation angle θ to the heading determined in the first position before rotation. The differential rotation rate, i.e., R, is then calculated using least squares or other fitting methods. 1n -R 2n Fit to a sine or cosine function. The sum of the residuals or the sum of the squares of the residuals can be used as an indicator of the accuracy of the heading determination.

[0094] This method of determining the course is particularly advantageous because even when the offset error b n Even when the error is large, this method can still provide an accurate heading indication. However, passive rotation can also be advantageously used to determine the offset error b. n Therefore, passive rotations, which may not always align with the needs of course determination, can be primarily used to determine the bias error, which can then be calculated by subtracting the determined bias error b from the received rotation rate before sinusoidal fitting. n And respectively used in the description above and in Figure 2 and Figure 3 In the method of the first or second embodiment shown.

[0095] To determine the bias error b n , Figure 4 The method includes an additional step 407 after determining the initial phase offset β in the first position, wherein the bias error b of each sensing axis is calculated according to equation (3) (or an equivalent equation if equation (1) uses a cosine function instead of a sine function). n .

[0096]

[0097] At step 407, the bias error b of each sensing axis of gyroscopes 101 to 116 or 121 and 122 has been determined. n Subsequently, the bias error can be stored in the memory of the gyrocompass device, so as described above according to... Figure 2 or Figure 3 The method is accessed during the heading determination period. Whenever an opportunity arises or after the minimum elapsed time since the last update, the gyrocompass can continuously update the stored bias error based on the passive rotation of the gyrocompass.

[0098] Among alternative methods for determining gyroscope bias error, for example, a process similar to maytagging can be used... Figure 1A or Figure 1BIt is used in conjunction with the MEMS gyroscope compass depicted herein. The rotational rate R of the sensing axes of MEMS gyroscopes 101 to 116 or 121 and 122 is read at the first position. 1n Then, all MEMS gyroscopes 101 to 116 or 121 and 122 are rotated 180 degrees to a second position, and the rotation rate R of MEMS gyroscopes 101 to 116 or 121 and 122 is read again at the second position. 2n For a given phase offset β, when the MEMS gyroscope and therefore the sensing axis rotate 180 degrees, the rotation rate measured by the gyroscope after the rotation is:

[0099]

[0100]

[0101]

[0102] Therefore, by using the first measured value R 1n Subtract the second measured value R from the middle 2n The result was halved to offset the bias error b. n And the true rotation rate is preserved. As mentioned above, once this step has been repeated for all MEMS gyroscopes 101 to 116 or 121 and 122, the obtained values ​​can be fitted to equation (1) again. Similarly, by using the first measured value R 1n Second measured value R 2n Adding the results and halving them cancels out the static rotation rate caused by the Earth's rotation, leaving only the bias error b. n .

[0103] However, compared to MEMS gyrocompasses that include at most one or two sensing axes and use repeated 180-degree rotations to determine the heading of the device, the gyrocompass of the present invention requires only a single rotation because the heading of the device can be determined by sinusoidal fitting of the rate signals from three or more sensing axes of gyroscopes 101 to 116 or 121 and 122.

[0104] Furthermore, in a MEMS gyro compass that includes at most one or two sensing axes, this rotation must be an accurate 180-degree rotation in order to account for the aforementioned bias error b. n The calculation cancels out the component of the rate signal caused by the Earth's rotation; however, in the device of the present invention comprising MEMS gyroscopes 101 to 116 or 121 and 122 having at least three sensing axes, the rotation angle is not necessarily 180 degrees, and the rotation mechanism does not necessarily provide a precise rotation angle. Specifically, the above regarding Figure 4The described method can be used with active rotation of gyroscopes 101 to 116 or 121 and 122, rather than passive rotation dependent on chance. Active rotation of gyroscopes 101 to 116 or 121 and 122 can be provided by an actuator that is part of the gyrocompass device itself, or by prompting rotation of a device or system on which the gyrocompass is mounted. For example, gyroscopes 101 to 116 or 121 and 122 can be arranged on a rotatable platform, and the actuator can cause the platform to rotate relative to the rest of the device. Alternatively, if the gyrocompass is mounted in a smartphone, the user of the smartphone can be prompted to rotate the smartphone before heading determination. (See reference...) Figure 5 The method is described in more detail.

[0105] At step 501, the rotation rate of each sensing axis of the measured MEMS gyroscopes 101 to 116 or 121 and 122 is recorded and averaged over time to minimize the influence of noise on the received rotation rate. At step 502, the MEMS gyroscopes 101 to 116 or 121 and 122 are rotated by an arbitrary angle to a second position. This rotation is measured, for example, by integrating the rate signal from the yaw axis gyroscope or using IMU and sensor fusion, as described above. Figure 4 As described in step 403. At step 503, the rotation of MEMS gyroscopes 101 to 116 or 121 and 122 is stopped and the measurement of rotation is terminated. At step 504, the measured rotation rate of each sensing axis of the MEMS gyroscopes 101 to 116 or 121 and 122 is recorded at a second position and averaged over time. At step 505, according to the above... Figure 4 The initial phase offset β in the first position is determined using the same method described in step 406. Additionally, the sum of the residuals or the sum of the squares of the residuals can be used as an indicator of the accuracy of the heading determination. At step 506, the bias error of each sensing axis of the MEMS gyroscope is determined by comparing the measured rotation with the difference between the determined headings at the first and second positions.

[0106] In another method for compensating for bias errors, the MEMS gyro compass can use a lookup table with known bias error values ​​for each MEMS gyroscope or each sensing axis, which can be used to correct the received rotation rate.

[0107] The bias error of each MEMS gyroscope 101 to 116 or 121 and 122 and their sensing axes varies over time and based on the temperature of the MEMS gyroscope. Therefore, the measurement of the bias error according to one of the methods described above may need to be repeated periodically with changes in time and temperature conditions.

[0108] Bias error can be considered as a function of time and temperature. When MEMS gyroscopes 101 to 116 or 121 and 122 are arranged such that their sensing axes are separated at regular intervals of 360 / N degrees, where N is the number of sensing axes, the component of the received rotational rate caused by the Earth's rotation is canceled out in the sum of the received rotational rates. Therefore, the simple sum of the received rates provides the sum of the bias error at the time of measurement, which itself corresponds to the point in time since the device was powered on, and can therefore be used to look up the bias error value for each MEMS gyroscope 101 to 116 or 121 and 122 in a lookup table. A temperature sensor may also be included in the MEMS gyrocompass to provide temperature measurement.

[0109] Subsequently, the bias error value can be retrieved from a lookup table stored in the memory of the MEMS gyroscope compass or elsewhere based on the sum of the bias errors and optionally the temperature, and said bias error value is subtracted from the received rotational rate before fitting the rate to a sine function according to equation (1), as mentioned above regarding Figure 2 and Figure 3 The method described is shown in the figure.

[0110] Figure 6 A method for determining the heading of a MEMS gyroscope compass using the lookup table mentioned above is described. At step 601, the rotational rate of MEMS gyroscopes 101 to 116 or 121 and 122 is measured / read. Optionally, the temperature of the device / MEMS gyroscopes 101 to 116 or 121 and 122 is also measured simultaneously.

[0111] At step 602, the measured rotation rates are summed. As mentioned above, since the sensing axes of MEMS gyroscopes 101 to 116 or 121 and 122 are arranged in a regular pattern with intervals of 360 / N degrees, the Earth's rotation is canceled out in the sum of the received rotation rates, leaving only the sum of the bias error. Alternatively, instead of determining and using the sum of all received rotation rates to find the bias error value, the sum of other combinations of sensing axes can be used for this purpose, as long as the Earth's rotation rate is canceled out in the sum. In practice, this means that the bias can be found using the rates of any subset of sensing axes arranged in a regular pattern around 360 degrees.

[0112] At step 603, based on the sum of bias errors and, if available, based on temperature, the individual bias error values ​​for each axis of MEMS gyroscopes 101 to 116 or 121 and 122 are retrieved from a lookup table.

[0113] At step 604, the retrieved bias error is subtracted from the measured rotational rate to provide a corrected rotational rate. At step 605, the corrected rotational rate is used to perform the above-mentioned... Figure 2 or Figure 3 A sinusoidal fitting method is described for determining the heading of a MEMS gyroscope.

[0114] The bias error lookup table can be initialized by measuring the reported rotation rate over time, for example, a 24-hour period, of each MEMS gyroscope 101 to 116 or 121 and 122. Preferably, this is performed after the MEMS gyrocompass has been manufactured, rather than before it is assembled into the gyrocompass based on the individual MEMS gyroscopes. The measured rotation rate and temperature are measured within the initialization time period while the device is stationary. The bias error lookup table is filled at least with the individual bias error of each sensing axis of the MEMS gyroscopes 101 to 116 or 121 and 122 at discrete time steps and optionally at different temperature steps or ranges.

[0115] During the use of a MEMS gyrocompass, the bias error lookup table can be updated after initialization or instead of initialization. When the MEMS gyrocompass includes or is combined with an IMU that detects any changes in position when the system is powered on, the bias error lookup table can be updated during operation when the device is stationary.

[0116] The above about Figure 4 and Figure 5 Any method described for identifying bias errors using passive or active rotation of MEMS gyroscopes 101 to 116 or 121 and 122 can be used to populate the lookup table.

[0117] To conserve the memory required for the bias error lookup table, bias error data can be measured at extended, i.e., non-uniform intervals, as the drift rate decreases over time. The number of cells in the bias error lookup table is approximately m×n×(x+2), where m is the number of temperature points, for example 10, x is the number of sensing axes of the MEMS gyroscope 101 to 116 or 121 and 122, and +2 refers to the optional stored sum and time value. Therefore, the size of the lookup table can be kept below a few thousand cells. It is not necessary to store the sum or time of the bias error in the bias error table, as the sum used to look up individual bias error values ​​can be calculated from the individual bias error values, and the time value is not essential for the basic functionality of the lookup table. However, pre-calculating and storing the sum value speeds up the lookup time when accessing the lookup table in operation. While not strictly necessary, the time value allows for the calculation of the drift rate. The drift rate can be used when the bias error drift is not monotonic. The drift rate decreases significantly with increasing operating time, thus allowing the identification of corrective portions of the table by dividing the table into two or more monotonic sections.

[0118] In all the embodiments described above, the MEMS gyrocompass may further include one or more accelerometers for determining the tilt of the MEMS gyroscope relative to the direction of gravity. When the MEMS gyrocompass includes an inertial measurement unit (IMU), the tilt of the MEMS gyroscope can be determined by the IMU instead of another separate accelerometer. Samples from one or more accelerometers are collected simultaneously with the rotation rate from the MEMS gyroscope for heading determination relative to true north. The tilt of the MEMS gyroscope affects both the latitude and heading determination results; therefore, error correction due to the tilt of the MEMS gyroscope can be calculated after heading calculation based on the average accelerometer readings within the rotation rate sampling period.

[0119] When the gyrocompass includes a GPS receiver (or any other GNSS receiver or connector for communicating with a GNSS receiver) and an inertial measurement unit (IMU), alternative methods for determining the bias error can be used to replace or supplement the methods described above. The heading of the device can be calculated based on GPS and IMU measurements. The component of Earth rotation sensed by each MEMS gyroscope / sensing axis is calculated based on the heading determined from the GPS and IMU measurements, and then the component of Earth rotation is subtracted from the average received rotation rate received from the corresponding sensing axes of MEMS gyroscopes 101 to 116 or 121 and 122. The motion of the gyrocompass is averaged in the average received rotation rate, so after the subtraction, only the bias error of each MEMS gyroscope is retained. The bias error can then be used in subsequent heading determination based on the received rotation rate from the MEMS gyroscopes.

[0120] Although the invention has been described above with respect to determining the heading of a MEMS gyro compass relative to the Earth's surface, it will be understood that the invention will function in the same manner on any rotating planetary body, and therefore can also be used in environments outside Earth, such as the surface of Mars. Therefore, the fact that the description refers to Earth should not be considered a limitation of the invention.

Claims

1. A gyrocompass device for determining heading relative to the surface of the Earth or another rotating planetary body, the device comprising: One or more MEMS gyroscopes, each fixed in a known orientation on a substrate parallel to a first plane, wherein the one or more MEMS gyroscopes provide at least three sensing axes, the at least three sensing axes being arranged such that the sensing axes lie within the first plane and each sensing axis is offset by a known offset angle relative to the other sensing axes; and Electronic circuitry configured to receive rotational rates from at least three sensing axes of the one or more MEMS gyroscopes and determine the heading of the device relative to the surface of the Earth or another rotating planetary body based on the rotational rates received from the one or more MEMS gyroscopes. The circuit is configured to determine the heading of the device by fitting a sine or cosine function to the received rotation rate.

2. The gyrocompass device according to claim 1, wherein, The angles of the sensing axes of the one or more MEMS gyroscopes are spaced out in a regular 360 / N pattern, where N is the number of the sensing axes.

3. The gyrocompass device according to claim 1 or 2, wherein, The device is configured to retrieve the value of the bias error for each of the sensing axes of the one or more MEMS gyroscopes in a lookup table and subtract the bias error from the received rotation rate before determining the heading of the device.

4. The gyrocompass device according to claim 1 or 2, wherein, The sine function is C sin(α n+ β) or C cos(α) n+ β) in the form of, where C is the amplitude of the sine function, the amplitude depending at least on the latitude of the device, α n β is the offset angle of the nth sensing axis, and β is the phase offset, which has a fixed difference relative to true north, and wherein the heading of the device is determined by changing the phase offset β to find a value with the minimum error in the fitting of the sine function to the received rotation rate.

5. The gyrocompass device according to claim 1 or 2, wherein, The circuit is configured to determine the heading of the device when the received rotation rate value is below a threshold.

6. The gyrocompass device according to claim 1 or 2, wherein, The device further includes a GNSS receiver or a connector for communicating with the GNSS receiver and an inertial measurement unit, wherein the device is configured as follows: The heading is calculated based on the output of the GNSS receiver and the inertial measurement unit; The received rotation rate for each sensing axis is averaged over time; Based on the heading calculated according to the output of the GNSS receiver and the inertial measurement unit, calculate the component of Earth's rotation sensed by each sensing axis of the one or more MEMS gyroscopes; and The bias error of each sensing axis of the one or more MEMS gyroscopes is determined by subtracting the calculated component of the Earth's rotation for each sensing axis from the average received rotation rate of the respective sensing axis.

7. The gyrocompass device according to claim 1 or 2, wherein, The device further includes at least one of the following: A yaw gyroscope configured to measure the rotation of one or more MEMS gyroscopes about an axis perpendicular to the measurement axis of the one or more MEMS gyroscopes; as well as Inertial measurement unit; The device is configured to measure the motion of the one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body while the rotation rate is being measured by the one or more MEMS gyroscopes, and to stabilize the received rotation rate by subtracting a calculated rate caused by the measured motion of the one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body from the received rotation rate before determining the heading of the device.

8. The gyrocompass device according to claim 1 or 2, wherein, The device is configured to determine its course in the following manner: Receive a first rotation rate from one or more MEMS gyroscopes at a first position; Measure the rotation of the one or more MEMS gyroscopes from the first position to the second position; At the second position, a second rotation rate is received from one or more MEMS gyroscopes; The differential rotation rate for each sensing axis of the one or more MEMS gyroscopes is calculated by subtracting the second received rotation rate of the sensing axis from the first received rotation rate received from the MEMS gyroscope, or by subtracting the first received rotation rate of the sensing axis from the second received rotation rate received from the MEMS gyroscope. The differential rotation rate is fitted to a sine or cosine function to determine the phase shift of the sine or cosine function, wherein the phase shift corresponds to the heading of the device.

9. The gyrocompass device according to claim 1 or 2, further comprising an inclinometer or inertial measurement unit for determining the orientation of the one or more MEMS gyroscopes relative to the Earth's gravitational field, wherein, The circuit is configured to use the tilt measured by the inclinometer to correct heading and / or latitude calculations.

10. The gyrocompass device according to claim 1 or 2, wherein, The device includes two MEMS gyroscopes, wherein each MEMS gyroscope includes at least two sensing axes that are perpendicular to each other and located in the first plane, and wherein the two MEMS gyroscopes are rotated 180 degrees relative to each other such that the sensing axes of the MEMS gyroscopes are arranged at 90-degree intervals.

11. A method for determining a heading relative to the surface of the Earth or another rotating planetary body using a gyrocompass device, the method comprising: Receiving rotation rates from one or more MEMS gyroscopes, wherein the one or more MEMS gyroscopes are fixed in a known orientation on a substrate parallel to a first plane and provide at least three sensing axes, the at least three sensing axes being arranged such that the sensing axes lie within the first plane and each sensing axis is offset by a known offset angle relative to the other sensing axes; and The heading of the device relative to the surface of the Earth or other rotating planetary body is determined based on the rotation rate of the at least three sensing axes received from the one or more MEMS gyroscopes, wherein determining the heading of the device includes fitting a sine or cosine function to the received rotation rate.

12. The method according to claim 11, wherein, The angles of the sensing axes of the one or more MEMS gyroscopes are spaced out in a regular 360 / N pattern, where N is the number of the sensing axes.

13. The method according to claim 11 or 12, wherein, The method includes retrieving the value of the bias error for each of the sensing axes of the one or more MEMS gyroscopes from a lookup table and subtracting the bias error from the received rotation rate before determining the heading of the device.

14. The method according to claim 11 or 12, wherein, The sine function is C sin(α) n+ β) or C cos(α) n+ β) in the form of, where C is the amplitude of the sine function, the amplitude depending at least on the latitude of the device, α n β is the offset angle of the nth sensing axis, and β is the phase offset, which has a fixed difference relative to true north, and wherein the heading of the device is determined by changing the phase offset β to find a value with the minimum error in the fitting of the sine function to the received rotation rate.

15. The method according to claim 11 or 12, wherein when the value of the received rotation rate is below a threshold, the heading of the device is determined.

16. The method according to claim 11 or 12, wherein, The method further includes: Heading is calculated based on the output of the GNSS receiver and inertial measurement unit; The received rotation rate for each corresponding rotation axis is averaged over time; Based on the heading calculated according to the output of the GNSS receiver and the inertial measurement unit, calculate the component of Earth's rotation sensed by each sensing axis of the one or more MEMS gyroscopes; and The bias error of each sensing axis of the one or more MEMS gyroscopes is determined by subtracting the calculated component of the Earth's rotation for each sensing axis from the average received rotation rate of the respective sensing axis.

17. The method according to claim 11 or 12, wherein, The method further includes: While measuring the rotation rate by the one or more MEMS gyroscopes, the motion of the one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body is also measured; and The received rotation rate is stabilized by subtracting a calculated rate caused by the measured motion of the one or more MEMS gyroscopes relative to the surface of the Earth or other planetary body from the received rotation rate before determining the heading of the device.

18. The method according to claim 11 or 12, wherein determining the heading of the device comprises: Receive a first rotation rate from one or more MEMS gyroscopes at a first position; Measure the rotation of the one or more MEMS gyroscopes from the first position to the second position; At the second position, a second rotation rate is received from one or more MEMS gyroscopes; The differential rotation rate for each sensing axis of the one or more MEMS gyroscopes is calculated by subtracting a second rotation rate of the sensing axis from a first received rotation rate received from the MEMS gyroscope, or by subtracting the first received rotation rate of the sensing axis from the second rotation rate received from the MEMS gyroscope. The differential rotation rate is fitted to a sine or cosine function to determine the phase shift of the sine or cosine function, wherein the phase shift corresponds to the heading of the device.

19. The method according to claim 11 or 12, wherein, The method further includes: Determine the orientation of the first plane relative to the Earth's gravitational field, and The heading and / or latitude calculations are corrected based on the determined orientation.

20. The method according to claim 11 or 12, wherein, The one or more MEMS gyroscopes include two MEMS gyroscopes, wherein each MEMS gyroscope includes at least two sensing axes that are perpendicular to each other and located in the first plane, and wherein the two MEMS gyroscopes are rotated 180 degrees relative to each other such that the sensing axes of the MEMS gyroscopes are arranged at 90-degree intervals.

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