JP2013124871A - Magnetic measurement data calibration apparatus, azimuth angle measurement device, and buffer - Google Patents

Abstract

An object of the present invention is to provide a magnetic measurement data calibration apparatus for obtaining magnetic measurement data for calculating an offset closer to a true value as magnetic measurement data for determining offset calculation and validity.
An apparatus for calibrating magnetic measurement data according to the present invention is an apparatus for obtaining an offset of magnetic measurement data and correcting the magnetic measurement data, an inclination angle calculating unit for obtaining an inclination angle from acceleration data from an acceleration sensor, and an inclination A magnetic measurement data buffer provided with an area for storing magnetic measurement data for each combination with an angular range of angles, a magnetic measurement data determination unit for writing magnetic measurement data from a magnetic sensor in an area corresponding to an inclination angle, and The offset calculation unit that calculates the offset from the magnetic measurement data, and whether the calculated offset or the currently used set offset is likely is determined from the magnetic data stored in the magnetic measurement data buffer. An offset validity determination unit for setting a new set offset.
[Selection] Figure 1

Description

  The present invention relates to a magnetic measurement data calibration device, an azimuth measurement device, and a buffer for calibrating a magnetic sensor mounted on a portable device.

In recent years, a three-axis magnetic sensor (hereinafter simply referred to as a magnetic sensor) is mounted on a mobile device such as a mobile phone and is used for orientation measurement in the mobile device.
The magnetic sensor used for this azimuth measurement is usually adjusted with a zero magnetic field output value for each axis (hereinafter referred to as offset adjustment) using a triaxial Helmholtz coil before being mounted on a portable device.
In this specific adjustment procedure, geomagnetism is measured by a magnetic sensor calibrated in advance, and magnetic measurement data for each of the three axes output from the magnetic sensor calibrated in advance is used as reference magnetic measurement data for azimuth measurement. .

Next, a magnetic field in the direction opposite to the reference magnetic measurement data is applied to the target magnetic sensor that is the target of offset adjustment by the three-axis Helmholtz coil.
Here, when the target magnetic sensor has no offset, the magnetic measurement data to be output is 0 for all three axes, and when it has the offset, the magnetic measurement data to be output is not 0.
Here, the magnetic measurement data output from the target magnetic sensor is measured as an offset of the target magnetic sensor itself, and the offset of the magnetic measurement data output from the magnetic sensor is adjusted based on the magnetic measurement data.
That is, the offset measured by the 3-axis Helmholtz coil is subtracted from each magnetic measurement data from the magnetic measurement data output from the magnetic sensor, and the direction is detected as the measurement result of the magnetic sensor.

  However, even if the offset adjustment is performed with the magnetic sensor alone, many other parts are used in the portable device in addition to the magnetic sensor that detects the orientation, and the magnetic field generated by these other parts is applied to the magnetic sensor. It may have an effect on it. For example, a magnetic field is generated from a magnet mounted on a speaker, a magnet provided on an open / close switch, or nickel plating applied to a component of a portable device.

For this reason, an environmental offset due to the surrounding environment occurs with respect to the magnetic sensor provided inside the portable device, and magnetic measurement data in which the environmental offset is superimposed is output from the magnetic sensor alone that has performed the offset adjustment.
Therefore, after performing offset adjustment with a single magnetic sensor, the magnetic field generated by other components of the mobile device to be mounted is obtained from the actual orientation of the mobile device and the magnetic measurement data output by the magnetic sensor. A difference due to the environmental offset occurs in the bearing.

Further, it is conceivable to perform offset adjustment including environmental offset by a three-axis Helmholtz coil in a state where the magnetic sensor is mounted on a portable device together with other components.
However, the value of the environmental offset always fluctuates due to changes in the magnetic force of each component over time, changes in the temperature around the portable device, and the presence of an object that generates a strong magnetic field around the portable device. .

Therefore, even if the offset adjustment of the magnetic sensor including the environmental offset is performed after being mounted on the portable device by the three-axis Helmholtz coil, the environmental offset fluctuates every moment depending on the surrounding conditions. For this reason, the magnetic measurement data output from the magnetic sensor shifts from the true value due to the fluctuation of the environmental offset superimposed on the magnetic measurement data of the magnetic sensor.
For this reason, although it is necessary to perform offset again, the offset adjustment of the magnetic sensor mounted in the portable device cannot always be performed by the three-axis Helmholtz coil. Therefore, it is necessary to give the mobile device the function of adjusting the offset of the magnetic sensor without using the 3-axis Helmholtz coil.

For this reason, the offset adjustment unit mounted on the portable device measures a number of magnetic field strengths of each axis by the magnetic sensors of each of the three axes, temporarily stores the measured magnetic measurement data in the internal data buffer, and sets the offset. Calculation as a correct value is performed (see, for example, Patent Document 1).
That is, in Patent Document 1, a method is used in which the offset value is determined so that the distance between the magnetic measurement data stored in the data buffer and the offset is minimized.

However, the problem of the configuration of Patent Document 1 is that the magnetic measurement data stored in the data buffer is concentrated in the vicinity of a specific point, that is, the inclination angle composed of the pitch angle and the roll angle is the same. When there is a lot of magnetic measurement data at the position, the estimation accuracy of the offset is lowered.
That is, when calculating the offset that cancels the zero magnetic field output of the magnetic sensor in the zero magnetic field, if the magnetic measurement data is biased, the calculated offset is affected by the biased magnetic measurement data and becomes a true offset. In contrast, a shift occurs.

For this reason, after the magnetic measurement data is temporarily stored in the data buffer, the region of the stored magnetic measurement data is divided by the inclination angle to determine how much the acquired inclination angle of the magnetic measurement data varies. Here, the region division is, for example, a regular octahedron that divides the surface of a sphere centered on an offset into, for example, a regular octahedron and corresponds to the tilt angle at which each of the magnetic measurement data is measured (including the tilt angle). Group.
In this grouping result, the offset calculation is performed only when the number of regular octahedrons to which the magnetic measurement data is assigned is larger than the set value (exceeds a preset threshold value), and the true value determination for this offset (close to the true value) (For example, refer to Patent Document 2).

Japanese Patent No. 4391416 Japanese Patent No. 4448975

However, since Patent Document 2 stores magnetic measurement data in a time series in the data buffer, the following state may occur and processing for obtaining an accurate offset may not be performed.
a. All of the magnetic measurement data stored in the data buffer is concentrated on one of the regular octahedrons.
b. Most of the magnetic measurement data stored in the data buffer (for example, 80% or more) is concentrated on any one surface of the regular octahedron, and the remaining magnetic measurement data is distributed on the other surface.
c. When generating a regular octahedron that performs region division, the offset point that is the center of the sphere is shifted.

In other words, in the case of the above-described state a, when performing calibration, the orientation of the portable device is directed to any angle in order to acquire magnetic measurement data corresponding to a surface different from the currently distributed surface (like drawing a circle) Need to be rotated).
In addition, depending on the orientation of the mobile device, the number of the grouped surfaces of the magnetic measurement data does not exceed the threshold for calculating the offset. For this reason, the offset is not calculated and updated, the calibration time becomes long, the user needs to continue the operation of changing the orientation of the portable device, and the calibration becomes a troublesome work.

In the case of the state b, if the magnetic measurement data is already concentrated on one of the regular octahedrons even when the number of grouped surfaces of the magnetic measurement data exceeds the threshold for calculating the offset, As described above, it is not possible to calculate an accurate offset due to the influence of the magnetic measurement data of the concentrated surface.
That is, the surface on which the magnetic measurement data is concentrated has a higher weight when calculating the offset than the other surfaces, and an offset deviated from the true value is calculated.

In the case of the state c, when creating a regular octahedron for grouping the magnetic measurement data, it is necessary that the sphere that forms the regular octahedron is centered on an offset that is accurate to some extent. However, if the offset just before the regular octahedron is not calculated correctly, grouping into the regular octahedron will be associated with a surface that is different from the surface (inclination angle region) that should be determined.
For this reason, the grouping itself is unreliable, and when determining whether or not to perform offset calculation, an erroneous determination occurs, and an offset deviating from the true value may be calculated, or the true value offset In some cases, offset calculation is not performed even though

  The present invention has been made in view of such circumstances, and magnetic measurement data for calculating an offset closer to a true value as magnetic measurement data used for calculating an offset or determining the effectiveness of the calculated offset. An object of the present invention is to provide a magnetic measurement data calibration device, an azimuth angle measurement device, and a buffer that can obtain the above.

  The present invention has been made to solve the above-described problems, and a magnetic measurement data calibration apparatus according to the present invention has three measurement axes orthogonal to each other, and includes a magnetic sensor comprising an axis sensor that measures the geomagnetism in the measurement axis direction. A magnetic measurement data calibration device for obtaining an offset of magnetic measurement data that is a measurement result of geomagnetism for each measurement axis output from a sensor, and correcting the magnetic measurement data, wherein a roll angle is determined from acceleration data supplied from an acceleration sensor. And an inclination angle calculation unit for obtaining a pitch angle, and a magnetic measurement data buffer provided with an area for storing magnetic measurement data corresponding to each combination of the angle range of the roll angle and the angle range of the pitch angle And the magnetic measurement data supplied from the magnetic sensor to the roll angle and the pitch angle detected when measuring the magnetic measurement data. A magnetic measurement data determination unit that writes and stores the area to be stored, an offset calculation unit that obtains the offset from the magnetic measurement data by a predetermined calculation, a calculated offset that is an offset obtained by the offset calculation unit, and a current use The offset validity is determined by using the magnetic data stored in the magnetic measurement data buffer to determine which of the set offsets that are offset is likely, and using the offset determined to be likely as the new set offset. And a determination unit.

  In the magnetic measurement data calibration apparatus of the present invention, the offset calculation unit calculates an error function from the difference between the magnetic measurement data for each measurement axis of the measured magnetic measurement data and the previously obtained offset. An offset residual calculation unit for calculating an offset residual from the error function and the previously obtained covariance matrix, and adding the offset residual to the set offset set at the time of the previous measurement of the magnetic measurement data The offset update unit for calculating the calculated offset and the measured magnetic measurement data are used to update the covariance matrix of the magnetic measurement data using the previously measured magnetic measurement data as a population. And a covariance matrix updating unit that generates a new covariance matrix by adding the magnetic measurement data to the population.

  In the magnetic measurement data calibration apparatus according to the present invention, the offset calculation unit calculates the difference between the magnetic measurement data written in the area and the temporary offset for each measurement axis, squares it, and adds it for each area. Then, the addition result is added to all the areas where the magnetic measurement data is stored in the magnetic measurement data buffer, and the temporary offset that minimizes the addition result is used as the calculated offset.

  The magnetic measurement data calibration apparatus of the present invention is a standard deviation of a difference between the calculated offset calculated from the magnetic measurement data by the offset validity determination unit and the magnetic data stored in the magnetic measurement data buffer. A first standard deviation is obtained, and a second standard deviation which is a standard deviation of a difference between the set offset currently used and the magnetic data stored in the magnetic measurement data buffer is obtained, and the first standard deviation is obtained. The standard deviation is compared with the second standard deviation, and it is determined which of the calculated offset and the set offset is a new set offset based on the comparison result.

  The azimuth measuring device of the present invention has three measurement axes orthogonal to each other, and includes a magnetic sensor composed of an axis sensor for measuring geomagnetism in the measurement axis direction, and three measurement axes orthogonal to each other, and the measurement axis direction An acceleration sensor that measures the acceleration of the magnetic field, a magnetic measurement data calibration unit that obtains an offset of magnetic measurement data that is a measurement result of the geomagnetism for each measurement axis that is output from the magnetic sensor, and corrects the magnetic measurement data; An azimuth angle measurement unit that calculates an azimuth angle from magnetic calibration data obtained by calibrating the magnetic measurement data output from the magnetic measurement data calibration device, and determines a roll angle and a pitch angle from acceleration data supplied from an acceleration sensor. An area for storing magnetic measurement data corresponding to each combination of an inclination angle calculation unit and the roll angle angle range and the pitch angle angle range. The magnetic measurement data buffer provided and the magnetic measurement data supplied from the magnetic sensor are written and stored in the area corresponding to the roll angle and the pitch angle detected when measuring the magnetic measurement data. Any one of a measurement data determination unit, an offset calculation unit that obtains the offset from the magnetic measurement data by a predetermined calculation, a calculated offset that is an offset obtained by the offset calculation unit, and a set offset that is an offset currently used An offset validity determination unit that determines whether it is probable using the magnetic data stored in the magnetic measurement data buffer and uses the offset determined to be probable as a new set offset is provided.

  The buffer according to the present invention has three measurement axes orthogonal to each other, and outputs magnetic measurement data that is a measurement result of the geomagnetism for each measurement axis output from a magnetic sensor including an axis sensor that measures the geomagnetism in the measurement axis direction. An inclination angle calculation unit for obtaining an offset and correcting the magnetic measurement data, obtaining a roll angle and a pitch angle from acceleration data supplied from an acceleration sensor, and an offset calculation unit for obtaining the offset from the magnetic measurement data by a predetermined calculation And using the magnetic data stored in the magnetic measurement data buffer to determine which of the calculated offset that the offset calculation unit has obtained and the set offset that is currently used offset is likely, A magnetic measurement data determination unit that acquires magnetic measurement data from the magnetic sensor, and is determined to be probable. Is a buffer used in a magnetic measurement data calibration device comprising an offset validity determination unit that uses the offset as a new set offset, and for each combination of the roll angle angle range and the pitch angle angle range, the combination An area for storing magnetic measurement data corresponding to the magnetic measurement data is provided, and the roll angle and the pitch angle detected by the magnetic measurement data determination unit when the magnetic measurement data supplied from the magnetic sensor is measured. It is written in the area corresponding to.

According to the present invention, the pitch angle and the roll angle are set in a three-dimensional space within an angle range of a predetermined interval as magnetic measurement data used for calculating the offset or determining the effectiveness of the calculated offset. The spherical surface showing the omni-direction centered on the offset in the dimensional space is divided into regions designated by each of the pitch angle angle range and roll angle angle range, and each region in the magnetic measurement data buffer is set. Since the magnetic measurement data corresponding to the pitch angle and the roll angle is written in the storage area, the magnetic measurement data that varies in all directions can be accumulated.
As a result, according to the present invention, the magnetic measurement data accumulated in the dispersed region in the spherical shape can be used for calculating the offset or determining the effectiveness of the calculated offset, and weighting the magnetic measurement data in a specific direction. This makes it possible to calculate the offset closer to the true value as compared with the conventional case.

It is a schematic block diagram which shows the structural example of the azimuth angle measuring apparatus using the magnetic measurement data calibration apparatus by the 1st Embodiment of this invention. It is a figure explaining the shift | offset | difference of each axis | shaft of the absolute coordinate system calculated | required by a triaxial acceleration sensor, and the sensor coordinate system which the magnetic measuring device which is a triaxial magnetic sensor detects. It is a figure which shows the structural example of the magnetic measurement data table which stores the detected magnetic measurement data memorize | stored in the magnetic measurement data buffer. It is a figure explaining the area | region which divides | segments and produces | generates the sphere centering on an offset by an inclination angle. It is a flowchart which shows the operation example of the process which calibrates the magnetic measurement data M which the magnetic sensor 2 by 1st Embodiment detected. It is a figure which shows the other structural example of the magnetic measurement data table which stores the detected magnetic measurement data memorize | stored in the magnetic measurement data buffer. It is a schematic block diagram which shows the structural example of the azimuth measuring apparatus using the magnetic measurement data calibration apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the structural example of 14 A of offset calculation parts which perform the structure of the magnetic measurement data using RLS. It is a flowchart which shows the operation example of the process which calibrates the magnetic measurement data M which the magnetic sensor 2 by 2nd Embodiment detected. It is a flowchart which shows the operation example of the process which calculates | requires azimuth | direction angle (theta) of the azimuth | direction measuring device using the offset calculation part 1 of 1st Embodiment, or the offset calculation part 14A of 2nd Embodiment.

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram showing a configuration example of an azimuth measuring device using the magnetic measurement data calibration device according to the first embodiment of the present invention. This azimuth measuring device is mounted on a portable device or the like.
The azimuth measuring device of the present embodiment includes a magnetic measurement data calibration device 1, a magnetic sensor 2, an acceleration sensor 3, and an azimuth measuring unit 4.

The magnetic sensor 2 has three measurement axes that are orthogonal to each other, and is composed of an axis sensor that measures the geomagnetism corresponding to each of the measurement axes. The magnetic sensor 2 includes, for example, an X-axis direction magnetic detection unit 21 that measures magnetic measurement data M _x indicating the strength of the magnetic field in the measurement axis in the X-axis direction, and a magnetic measurement that indicates the magnetic field strength in the measurement axis in the Y-axis direction constructed from the Z-axis direction magnetic sensing portion 23 for measuring magnetic measurement data M _z indicating the strength of the magnetic field in the Y-axis direction magnetic detection unit 22, the Z-axis direction of the measuring axis for measuring data M _y, X-axis, This is a magnetic sensor having three measurement axes, Y-axis and Z-axis. Here, as the X-axis direction magnetic detection unit 21, the Y-axis direction magnetic detection unit 22, and the Z-axis direction magnetic detection unit 23, for example, a Hall element, a magnetoresistive element, a flux gate type magnetic element, or the like is used. The measurement axes of the X-axis direction magnetic detection unit 21, the Y-axis direction magnetic detection unit 22, and the Z-axis direction magnetic detection unit 23 are orthogonal to each other.

The acceleration sensor 3 has three measurement axes that are orthogonal to each other, and includes an axis sensor that measures acceleration corresponding to each of the measurement axes. The acceleration sensor 3 includes, for example, an X-axis acceleration detecting unit 31 that measures acceleration data S _x that indicates the intensity of acceleration in the measurement axis in the X-axis direction, and acceleration data S _y that indicates the intensity of acceleration in the measurement axis in the Y-axis direction. Of the X-axis, Y-axis, and Z-axis, comprising a Y-axis acceleration detection unit 32 that measures acceleration and a Z-axis acceleration detection unit 33 that measures acceleration data S _z indicating the intensity of acceleration in the measurement axis in the Z-axis direction. The acceleration sensor has three measurement axes. The measurement axes of the X-axis acceleration detection unit 31, the Y-axis acceleration detection unit 32, and the Z-axis acceleration detection unit 33 are orthogonal to each other.

Magnetic measurement data correcting device 1 is supplied from the magnetic sensor 2, a magnetic measurement data _{M x,} magnetic measurements made of the magnetic measurement data _{M y} and magnetometric data _{M z} data _M (M _x, M y, _{M z)} of Magnetic calibration data M _f (M _fx , M _fy , M _fz ) in which the offset is calibrated based on the tilt angle (roll angle and pitch angle) output by the acceleration sensor 3 is output.
The azimuth measuring unit 4 uses the magnetic calibration data M _f (M _fx , M _fy , M _fz ) calibrated by the magnetic measurement data calibrating apparatus 1 and outputs the azimuth _directed by the azimuth measuring apparatus.

  Next, the magnetic measurement data calibration apparatus 1 includes an inclination angle calculation unit 11, a magnetic measurement data determination unit 12, a magnetic measurement data buffer 13, an offset calculation unit 14, a magnetic measurement data processing unit 15, an offset storage unit 16, and an offset validity. A determination unit 17 is provided.

The inclination angle calculation unit 11 calculates an inclination angle composed of a roll angle and a pitch angle, as will be described below.
That is, the inclination angle calculation unit 11 calculates its own inclination angle from the degree of gravity inclination detected by the acceleration sensor 3.
Next, FIG. 2 is a diagram for explaining the deviation of each axis between the absolute coordinate system obtained by the acceleration sensor 3 and the sensor coordinate system detected by the magnetic sensor 2.
In FIG. 2, an X axis, a Y axis, and a Z axis for calibrating a three-dimensional absolute coordinate system are defined. The rotation angle with the X axis as the rotation axis is the pitch angle (p), the rotation angle with the Y axis as the rotation axis is the roll angle (r), and the rotation angle with the Z axis as the rotation axis is the azimuth angle (θ ).

In the present embodiment, the absolute coordinate system means that the plane formed by the X axis and the Y axis is perpendicular to the gravity vector (vector quantity indicating the direction and magnitude of gravity), and the magnetic sensor 2 A coordinate system having the origin O as a point where all of the magnetic measurement data M (Mx, My, Mz) to be measured becomes zero.
The sensor coordinate system is a coordinate system formed by magnetic measurement data M (M _x , M _y , M _z ) measured by the magnetic sensor 2. For this reason, the sensor coordinate system is different for each measurement point at which the magnetic sensor 2 measures the magnetic measurement data M (M _x , M _y , M _z ).

However, the mobile device user portable, and form planes of X-axis and Y-axis of the absolute coordinate system, the measurement axis of the magnetic sensor, that is, the X axis in the sensor coordinate system (measurement axis of the M _x) and Y-axis (M _y It is difficult to make the plane formed by the measurement axis) parallel to each other.
Therefore, when the azimuth angle is estimated by the magnetic sensor 2, the measurement axis (X-axis detection magnetic field) in the X direction in the sensor coordinate system of the magnetic sensor 2 is always relative to the plane formed by the X axis and the Y axis in the absolute coordinate system. If the plane formed by the measurement axis in the Y direction (T-axis detection magnetic field) is parallel, the triaxial acceleration sensor used as the tilt sensor is always measured even if there is an influence of changes in the magnetic field due to the surrounding environment. The inclination angle of the magnetic sensor 2, that is, the azimuth measuring device can be accurately measured by the gravity vector.

At this time, when the azimuth measuring device (portable device) is in a horizontal state with respect to the ground surface, the acceleration measurement data output from the acceleration sensor 3 is the acceleration measurement data S (S _x , S _y , S _z ). . On the other hand, when the azimuth measuring device is tilted with respect to the ground surface, the acceleration measurement data output from the acceleration sensor 3 is assumed to be acceleration measurement data S ′ (S _x ′, S _y ′, S _z ′).
At this time, the relationship between the acceleration measurement data S (S _x , S _y , S _z ) and the acceleration measurement data S ′ (S _x ′, S _y ′, S _z ′) is expressed by the following equation (1). .

When the portable device carried by the user is in an inclined state, the output of the acceleration sensor 3 normalized by the gravitational acceleration in the inclined state is acceleration measurement data A (A _x , A _y , A _z ). When the azimuth measuring device is in a horizontal state with respect to the ground surface, since A (A _x , A _y , A _z ) = A (0, 0, 1), the above equation (1) is shown below (2 ).

Therefore, the tilt angle calculation unit 11 uses the acceleration measurement data A (A _x , A _y , A _z ) output from the acceleration sensor 3, and the pitch angle (p) from the following expression (3) The angle (r) is calculated by the following equation (4).

Next, FIG. 3 is a diagram showing a configuration example of a magnetic measurement data table that stores magnetic measurement data stored in the magnetic measurement data buffer 13. Here, the magnetic measurement data buffer 13 is a buffer in which a magnetic measurement data table for storing magnetic measurement data is stored.
In FIG. 3, the magnetic measurement data table includes an inclination angle of a combination of a roll angle and a pitch angle at a position where the magnetic measurement data is acquired, a flag indicating whether or not the magnetic measurement data is stored, and magnetic measurement data. Time information indicating the acquired time and measured magnetic measurement data are stored for each region.

Next, FIG. 4 is a diagram for explaining a region generated by dividing a sphere centered at an offset by an inclination angle.
The area indicates each range of the roll angle and the pitch angle including the position of the magnetic measurement data in the sphere with the offset as the center. That is, the number of regions in the magnetic measurement data buffer 13 is determined by the number obtained by dividing the measurement range of the tilt angle (roll angle and pitch angle) by a fixed angle. For example, in order to represent all directions with the offset O as the center, it is only necessary to measure a range where the pitch angle p is −90 ° to 90 ° and a roll angle r is −180 ° to 180 °.

At this time, when each of the pitch angle and the roll angle is divided at a constant angle of 30 °, the number of divisions of the pitch angle p is 6, and the number of divisions of the roll angle r is 12.
Therefore, the number of combinations of the angle ranges of these pitch angle p and roll angle r is 72, and there are 72 types of regions.
Returning to FIG. 3, the magnetic measurement data buffer 13 is configured so that the number of buffers proportional to the number of areas determined from the number of combinations of pitch angle and roll angle as described above is provided as the storage capacity.
Therefore, the magnetic measurement data having the same direction vector is not concentrated and accumulated as in the prior art, but when the magnetic measurement data having the same vector is supplied, the corresponding magnetic measurement data buffer 13 area is stored. , New magnetic measurement data of time is accumulated. For this reason, magnetic measurement data at different positions on the spherical surface indicating the directions in all directions in the three-dimensional space, that is, magnetic measurement data having vectors in the different directions are accumulated in the magnetic measurement data buffer 13.

Next, the reason why the magnetic measurement data in the magnetic measurement data buffer 13 approaches the spherical shape shown in FIG. 4 will be described below. FIG. 4 illustrates the trajectory of magnetic measurement data when the tilt angle changes.
In a state where the tilt angle is 0 (both the roll angle r and the pitch angle p are 0), when the portable device is rotated once around the circumference of a circle parallel to the ground plane, the magnetic measurement data M _z is As shown in FIG. 4, the trajectory is traced down on a certain spherical surface, that is, on the circumference of the lower surface of the sphere.
Further, when the roll angle r is 0 ° and the pitch angle p is 30 ° at the tilt angle, the magnetic measurement data M is obtained when the portable device is rotated once around the circle parallel to the ground plane. _As shown in FIG. 4, _z follows a locus on a circumference obtained by inclining the locus described above by 30 ° around the X axis.

The magnetic measurement data is stored in the magnetic measurement data buffer 13 as described above, for example, as shown in FIG. 3 or FIG. 6 to be described later, the angle range of the pitch angle p is 0 ° to 30 °, and the angle range of the roll angle r is 0. A combination from ° to 30 ° is set as the region R1. With respect to the address buffer of the region R1 in the magnetic measurement data buffer 13, the magnetic measurement data of the region sandwiched between the respective circumferences shown in FIG. 4 in the angle range of the roll angle r and the angle range of the pitch angle p is stored. May be written.
That is, by limiting the angle ranges of the roll angle r and the pitch angle p, it is possible to limit the range of magnetic measurement data that can be taken in the sphere of FIG. 4, and the range becomes a part of a spherical surface. In this way, the surface of the sphere is divided into regions (that is, all directions around the offset are divided into regions according to the angle range), and magnetic measurement data corresponding to each region is written into the magnetic measurement data buffer 13. By storing, the distribution of each magnetic measurement data M (M _x , M _y , M _z ) approaches a spherical surface.

The magnetic measurement data buffer 13 has an area set in advance, and the area R1 is set, for example, as a roll angle r ranging from 0 degrees to 30 degrees and a pitch angle p ranging from 0 degrees to 30 degrees.
Further, the region R2 is set so that the roll angle r is in the range of 0 to 30 degrees, and the pitch angle p is in the range of 31 to 60 degrees, and the other regions R3 to R72 are similarly set to the roll angle r and the pitch angle p. It is set with a range.

When setting the number of combinations by the angle range of the roll angle r and the angle range of the pitch angle p, that is, the number of regions, the smaller the region to be divided, the smaller the track of the magnetic measurement data (stored in the magnetic measurement data buffer 13). The position of the magnetic measurement data detected) approaches a spherical shape.
However, if the angle range becomes smaller than the measurement accuracy of the tilt angle, different buffer addresses are read out from the corresponding addresses by the combination of the roll angle r and the pitch angle p having measurement errors.
In other words, the magnetic measurement data buffer 13 cannot write to the buffer address that should be originally stored, and an incorrect result is obtained in the offset calculation process performed by the offset calculation unit 14 or the offset validity determination process performed by the offset validity determination unit 17. Will be output.

Further, as the area to be divided becomes finer, the number of areas in the magnetic measurement data buffer 13 increases as described above, and the offset calculation unit 14 calculates the offset coordinates O (O _x , O _y , O _z ). Time will increase.
Therefore, in the present embodiment, the number of divisions of the pitch angle p is 18, the number of divisions of the roll angle r is 36, and the number of combinations of the angle range of the pitch angle p and the angle range of the roll angle r is the number. The number of areas is 648. Here, the number of steps in the angle range is set every 10 °.

Returning to FIG. 1, the magnetic measurement data determination unit 12 synchronizes with acquisition of the magnetic measurement data M (M _x , M _y , M _z ) from the magnetic sensor 2, and the inclination angle data (roll angle r) from the inclination angle calculation unit 11. And the pitch angle p).
That is, the magnetic measurement data determination unit 12 calculates the magnetic measurement data M (M _x , M _y , M _z ) and the inclination angle of the position where the magnetic measurement data M (M _x , M _y , M _z ) is acquired. get.
Further, the magnetic measurement data determination unit 12 reads the time when the magnetic measurement data M is acquired from a timer that performs time measurement (not shown).
Thereby, the magnetic measurement data determination unit 12 extracts a region including the combination of the roll angle r and the pitch angle p in the tilt angle in the magnetic measurement data buffer 13.

Here, the magnetic measurement data determination unit 12 has a correspondence table in which the combination of the angle range of the roll angle r and the angle range of the pitch angle p is associated with the buffer address of the magnetic measurement data buffer 13 in the internal storage unit. Pre-written and stored.
Therefore, the magnetic measurement data determination unit 12 includes an angle range of the roll angle r including the pitch angle p and the roll angle r at the position where the acquired magnetic measurement data M (M _x , M _y , M _z ) is detected. A combination with the angle range of the pitch angle p is detected from the internal storage unit.
Then, the magnetic measurement data determination unit 12 stores the buffer address (address indicating the storage position for each area) stored in association with the combination of the angle range of the roll angle r and the angle range of the pitch angle p. Read from.

In the magnetic measurement data buffer 13, the magnetic measurement data determination unit 12 uses the acquired magnetic measurement data M (M _x , M _y , M _z ) for the buffer address read from the internal storage unit in the magnetic measurement data column ( Write to (write area) and store.
At this time, the magnetic measurement data determination unit 12 writes the magnetic measurement data M (M _x , M _y , M _z ) and rolls it in the column of the tilt angle corresponding to the buffer address read out of the magnetic measurement data buffer 13. The angle r and the pitch angle p are written, flag information indicating that the magnetic measurement data has been written is written in the flag column, and the magnetic measurement data M and the time at the time of acquisition are written in the time information column.

Here, when the magnetic measurement data is already written in the area in which the magnetic measurement data is written, the magnetic measurement data determination unit 12 determines which one of the magnetic measurement data to be written and the already written magnetic measurement data. Detection of new magnetic measurement data.
That is, the magnetic measurement data determination unit 12 compares the time information between the magnetic measurement data to be written and the already written magnetic measurement data, and determines that the magnetic measurement data with the later time is new.
Thereby, the magnetic measurement data determination unit 12 discards the magnetic measurement data to be written when the written magnetic measurement data is new, and if the written magnetic measurement data is old, the magnetic measurement data to be written is discarded. Overwrite.

The offset calculation unit 14 searches the flag column of each area from the magnetic measurement data table of the magnetic measurement data buffer 13, detects the area where flag information is set, reads the magnetic measurement data M from this area, Calculate the offset.
For example, the offset calculation unit 14 calculates the offset by the following equation (5).

In the equation (5), O _x , O _y , and O _z are offset values (offset coordinates O (O _x , O _y , O _z )), R is a constant, and each of Xi, Yi, and Zi Are the magnetic measurement data M _x , M _y , M _z in the respective regions.
Therefore, the offset calculation unit 14 uses the above-described equation (5), and subtracts the numerical values obtained by subtracting O _x , O _y , and O _z from the magnetic measurement data M _x , M _y , and M _z for each region. The squared numerical value is added, R2 is subtracted from the added numerical value, and this subtraction result is added in all areas to obtain the evaluation value G. At this time, the offset calculation unit 14 obtains a combination of O _x , O _y , and O _z that minimizes the evaluation value G while changing each of O _x , O _y , and O _z as provisional values. Are output as offset coordinates O (O _x , O _y , O _z ).

The offset validity determination unit 17 includes offset coordinates O (O _x , O _y , O _z ) stored in the offset storage unit 16 and magnetic measurement data M (M _x , The difference for each region with M _y , M _z ) is calculated, and the standard deviation σ1 of the difference in all regions is obtained.
The offset validity determination unit 17 also includes offset coordinate O (O _x , O _y , O _z ) that is a newly calculated offset, and magnetic measurement data that is a set offset stored in the magnetic measurement data buffer 13. A difference for each area with M (M _x , M _y , M _z ) is calculated, and a standard deviation σ2 of the difference in all areas is obtained.

Here, the offset validity determination unit 17 compares the standard deviation σ1 and the standard deviation σ2, and if the standard deviation σ1 is smaller than the standard deviation σ2, the offset storage unit 16 is not rewritten.
On the other hand, when the standard deviation σ2 is smaller than the standard deviation σ1, that is, when it is determined that the new offset is more likely than the offset coordinates already stored in the offset storage unit 16, the offset validity determination unit 17 stores the offset. The new offset coordinates O (O _x , O _y , O _z ) are overwritten on the part 16.
Since the standard deviation σ of the difference between the offset coordinate and the distance between the magnetic measurement data is calculated by using the above-described method using a large number of magnetic measurement data close to a spherical shape, the reliability of estimating the spherical surface is increased.

Further, instead of determining the above-described standard deviation σ and determining the effectiveness of the calculated offset coordinates O (O _x , O _y , O _z ), the calculated offset coordinates O (O _x , It is good also as a structure which determines the effectiveness of _Oy , _Oz ).
For example, the offset validity determination unit 17 uses the offset coordinates O (O _x , O _y , O _z ) stored in the offset storage unit 16 and the newly calculated offset coordinates O (O _x , O _y , O _It is good also as a structure which calculates | requires the difference with _z ) and uses this difference for determination of effectiveness.
That is, the offset validity determination unit 17 stores the threshold value in advance in the internal storage unit. This threshold value is set to the magnitude of geomagnetism, for example.

If the calculated difference exceeds the threshold value, the offset validity determination unit 17 is likely to have an error in the newly calculated offset coordinate O (O _x , O _y , O _z ). O _x , O _y , O _z ) are discarded, and the offset coordinates O (O _x , O _y , O _z ) stored in the offset storage unit 16 are left as they are.
On the other hand, when the calculated difference is equal to or smaller than the threshold value, the offset validity determination unit 17 has a high possibility that the newly calculated offset coordinate O (O _x , O _y , O _z ) is correct. O _x , O _y , O _z ) is overwritten on the offset coordinates O (O _x , O _y , O _z ) stored in the offset storage unit 16.

As another method for determining the validity, the offset validity determination unit 17 determines the distance between the offset coordinate O (O _x , O _y , O _z ) and the magnetic measurement data in each region of the magnetic measurement data buffer 13. Calculate for each area.
The offset validity determination unit 17 may be configured to use the difference between the maximum value and the minimum value as the determination value from the distances corresponding to each of the magnetic measurement data calculated for each region. The larger this judgment value is, the more the offset coordinate O (O _x , O _y , O _z ) is not equidistant from each of the magnetic measurement data in each region of the magnetic measurement data buffer 13, that is, not the center of the sphere. Means.

Here, the offset validity determination unit 17 determines the determination value D1 corresponding to the offset coordinate O (O _x , O _y , O _z ) stored in the offset storage unit 16 and the newly calculated offset coordinate O (O _x , O _y , O _z ) and a determination value D2.
When the determination value D1 is equal to or less than the determination value D2 (D1 ≦ D2), the offset validity determination unit 17 uses the offset coordinates O (O _x , O _y , O _z ) stored in the offset storage unit 16. It is determined that the offset coordinates O (O _x , O _y , O _z ) newly calculated are more effective.
Therefore, the offset validity judging unit 17, a new offset coordinates _{O (O x, O y,} O z) Destroys the offset coordinates stored in the offset storage unit _{16 O (O x, O y} , O z ) As it is.

On the other hand, when the determination value D1 is greater than or equal to the determination value D2 (D1> D2), the offset validity determination unit 17 currently uses the newly calculated offset coordinates O (O _x , O _y , O _z ). Is determined to be more effective than the offset coordinate O (O _x , O _y , O _z ) stored in the offset storage unit 16.
Therefore, the offset validity judging unit 17, a new offset coordinates _O (O _x, O y, _{O z),} and the offset coordinates _O stored in the offset storage unit _{16 (O x, O y,} O z) in Overwrite on the other hand.

In the offset storage unit 16, offset coordinates O (O _x , O _y , O _z ) are written and stored by the offset validity determination unit 17.
The magnetic measurement data processing unit 15 subtracts the offset coordinate from the magnetic measurement data M acquired from the magnetic sensor 2 and uses the subtraction result as corrected magnetic measurement data, and magnetic calibration data M _f (M _fx , M _fy). , M _fz ) and output to the azimuth measuring unit 4.
The azimuth measuring unit 4 uses the magnetic calibration data M _f (M _fx , M _fy , M _fz ) configured by the magnetic measurement data calibrating apparatus 1 and outputs the azimuth facing the azimuth measuring apparatus.

Next, a process for calibrating magnetic measurement data in the magnetic measurement data calibration apparatus 1 of the present embodiment will be described with reference to FIGS. FIG. 5 is a flowchart showing an operation example of processing for calibrating the magnetic measurement data M detected by the magnetic sensor 2.
Step S1:
The magnetic measurement data determination unit 12 determines the number of regions based on the angle range of the pitch angle p and the roll angle r in all directions set by the user from the outside, and a buffer indicating each region in the magnetic measurement data buffer 13 A correspondence table is created in which addresses are associated with combinations of pitch angles r and roll angle r ranges in the region. The buffer address here indicates the address of each column of each area in the magnetic measurement data buffer 13 as described above.
Then, the magnetic measurement data determination unit 12 writes and stores the created correspondence table in the internal storage unit. That is, the magnetic measurement data determination unit 12 reserves an area for writing magnetic measurement data in the magnetic measurement data buffer 13.

Further, a buffer address indicating each area in the magnetic measurement data buffer 13 as a table fixed in advance with respect to the internal storage section of the magnetic measurement data determination section 12, and a combination of an angle range of the pitch angle r and the roll angle r in the area May be written and stored.
Then, the magnetic measurement data determination unit 12 initializes the flags of all the areas in the magnetic measurement data buffer 13. That is, the magnetic measurement data determination unit 12 deletes the flag information in all the flag fields in the magnetic measurement data buffer, and changes the state so that no magnetic measurement data is written.

Step S2:
The magnetic measurement data determination unit 12 reads the magnetic measurement data M (M _x , M _y , M _x ) from the magnetic sensor 2 and outputs a control signal for calculating the tilt angle to the tilt angle calculation unit 11. .
With this control signal, the tilt angle calculation unit 11 reads acceleration measurement data S (S _x , S _y , S _z ) from the acceleration sensor 3.
Then, as described above, the inclination angle calculation unit 11 calculates the roll angle r and the pitch angle p from the acceleration measurement data S, and determines the inclination angle data of the calculated roll angle r and pitch angle p as magnetic measurement data determination. Output to the unit 12.

Step S3:
The magnetic measurement data determination unit 12 searches the internal storage unit for a combination of the angle range of the roll angle r and the angle range of the pitch angle p including the roll angle r and the pitch angle p in the tilt angle data.
Next, the magnetic measurement data determination unit 12 reads the buffer address of the area in the magnetic measurement data buffer 13 corresponding to the combination of the searched angular range of the roll angle r and the angular range of the pitch angle p.

The magnetic measurement data determination unit 12 writes and stores the magnetic measurement data M (M _x , M _y , M _x ) in the buffer address read from the internal storage unit in the magnetic measurement data buffer 13. Write flag information in the flag column.
The magnetic measurement data determination unit 12 also includes time information indicating the time at which the magnetic measurement data M (M _x , M _y , M _x ) is read with respect to the buffer address in which the magnetic measurement data M is written, and an inclination angle calculation unit. Each of the 11 calculated tilt angle data is written and stored.

Step S4:
The offset calculation unit 14 extracts the area where the flag information is written from the magnetic measurement data buffer 13 and reads the magnetic measurement data of the extracted area.
Then, the offset calculation unit 14 calculates the offset coordinates O (O _x , O _y , O _z ) from the magnetic measurement data read from the magnetic measurement data buffer 13 as described above.
By performing the calculation by the statistical processing method using the equation (5), it is possible to obtain offset coordinates O (O _x , O _y , O _z ) with higher accuracy than other methods.
That is, since statistical estimation is performed using a lot of magnetic measurement data distributed evenly on the spherical surface, offset coordinates O (O _x , O _y , O _z ) closer to true values can be calculated.

Step S5:
The offset validity determination unit 17 uses the previously described offset coordinate O (O _x , O _y , O _z ) and the offset coordinate O (O _x , O _y , and O _z ) are determined to be effective.
Then, the offset validity judging unit 17, the offset coordinates _O newly calculated (O _x, O y, _{O z)} is the offset coordinates _O (O _x stored in the offset storage unit _16, O y, _{O z} ) If it is determined that there is more validity, the newly calculated offset coordinates O (O _x , O _y , O _z ) are written in the offset storage unit 16.

On the other hand, the offset validity determination unit 17 uses the offset coordinates O (O _x , O _y , O _z ) newly calculated as the offset coordinates O (O _x , O _y , O _z ) stored in the offset storage unit 16. ) If it is determined that there is more validity, the offset coordinates O (O _x , O _y , O _z ) of the offset storage unit 16 are not rewritten.
And the magnetic measurement data determination part 12 repeats the process of step S2 to step S5 mentioned above, and performs the update process of the offset coordinate O ( _Ox , _Oy , _Oz ) of the offset memory | storage part 16 periodically. .

According to the above-described embodiment, the sphere regions are divided, and the magnetic measurement data corresponding to the respective regions are written in the magnetic data measurement table of the magnetic measurement data buffer 13 and stored therein. The distribution of the magnetic measurement data M (M _x , M _y , M _z ) approaches a spherical surface.
For this reason, according to the present embodiment, the magnetic measurement data can be effectively written in the limited magnetic measurement data buffer 13 so as to surround the center coordinates of the sphere, and the offset calculation unit 14 stores these magnetic measurement data. It is possible to calculate offset coordinate coordinates O (O _x , O _y , O _z ) with high accuracy.

Next, FIG. 6 is a diagram showing another configuration example of the magnetic measurement data table stored in the magnetic measurement data buffer 13 and storing the detected magnetic measurement data.
Further, in the present embodiment, as shown in FIG. 3, the magnetic measurement data table has a configuration in which one magnetic measurement data is stored in each area.
However, as shown in FIG. 6, a configuration of a magnetic measurement data table that accumulates a plurality of magnetic measurement data in one area may be adopted.

At this time, the offset calculation unit 14 obtains the square of the difference from the offset for each magnetic measurement data in each region using the equation (5), finds the square sum in each region, and further sums this square sum in all regions. To obtain an evaluation value G.
In addition, when the magnetic measurement data is written in each area, the magnetic measurement data determination unit 12 overwrites the magnetic measurement data at the oldest time in the time information when the flag information is written in all the flags.
Thereby, in this embodiment, the data group of the magnetic measurement data which approaches a more spherical shape can be stored in the magnetic measurement data buffer 13.

<Second Embodiment>
The second embodiment of the present invention will be described below with reference to the drawings. FIG. 7 is a schematic block diagram showing a configuration example of an azimuth measuring device using the magnetic measurement data calibration device according to the second embodiment of the present invention. Each azimuth measuring device is mounted on a portable device or the like as in the first embodiment.
The azimuth measuring apparatus according to this embodiment includes a magnetic measurement data calibration apparatus 1A, a magnetic sensor 2, an acceleration sensor 3, and an azimuth measuring unit 4.
In FIG. 7, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

Magnetic measurement data correcting device 1A is supplied from the magnetic sensor 2, a magnetic measurement data _{M x,} magnetic measurements made of the magnetic measurement data _{M y} and magnetometric data _{M z} data _M (M _x, M y, _{M z)} of Magnetic calibration data M _f (M _fx , M _fy , M _fz ) in which the offset is calibrated based on the tilt angle (roll angle and pitch angle) output by the acceleration sensor 3 is output.
Only the configuration and operation different from the first embodiment will be described below.

In the present embodiment, an offset to be corrected is an offset O (O _x , O _y , O _z ). Here, O _x is an offset in the X-axis direction, O _y is an offset in the Y-axis direction, and O _z is an offset in the Z-axis direction.
The magnetic measurement data M _n (M _xn , M _yn , M _zn ) is the nth magnetic measurement data. The magnitude of the geomagnetic vector (hereinafter referred to as total magnetic force) is R.
Here, the total magnetic force is obtained by the following equation (6) using the magnetic measurement data M _n (M _xn , M _yn , M _zn ) and the offset O (O _x , O _y , O _z ).

The relationship of this equation (6) always holds. That is, when the user who carries the portable device moves, the magnetic measurement data in each measurement axis direction in the magnetic measurement data changes as the portable device rotates. However, as long as the total magnetic force detected from the magnetic measurement data does not change, when the magnetic measurement data is arranged as coordinate points in a three-dimensional space consisting of the X axis, the Y axis, and the Z axis, the magnetic measurement data consists of 3 measurement axes. It exists at any position on the same sphere in the dimensional space (this point is assumed to move on the same sphere as in the conventional example).
Therefore, if the total magnetic force is the same, the relationship of the above-described equation (6) always holds even if the magnetic measurement data in each measurement axis direction in the magnetic measurement data changes.

In the above formula (6), by using the four pieces of magnetic measurement data M, the offset components O _x , O _y , O _z and the total magnetic force R in each measurement axis of the offset O can be calculated.
Here, in order to modify the equation (1), a constant Q shown in the following equation (7) is defined.

  By using the above formula (6) and formulating the formula (5) as a matrix, the following formula (8) is transformed.

By solving the above equation (8), the offset components O _x , O _y , O _z , and the total magnetic force R can be obtained. At this time, it is necessary that an inverse matrix on the left side of the equation (8) exists.
However, magnetic noise from each part of the portable device or from the outside is superimposed on the actual magnetic measurement data M.
For this reason, the offset components O _x , O _y , O _z and the total magnetic force R calculated from the equation (8) may not be able to obtain accurate values.
Therefore, by using a statistical method, that is, RLS (Recursive Least Square) method, by reducing the magnetic noise, the most true value of the offset components O _x , O _y , O _z , the total magnetic force R is obtained. An estimated value considered to be close to (hereinafter, maximum likelihood estimated value) is calculated. The description that the maximum likelihood estimated value can be calculated will be described later. Hereinafter, calibration of magnetic measurement data using the RLS method in the present embodiment will be described.

As shown in FIG. 7, the magnetic measurement data calibration apparatus 1A includes a measurement data input unit 10, an inclination angle calculation unit 11, a magnetic measurement data determination unit 12, a magnetic measurement data buffer 13, an offset calculation unit 14A, and magnetic measurement data processing. Unit 15, offset storage unit 16, and offset validity determination unit 17.
The measurement data input unit 10 converts an analog axis sensor measurement value input from each of the X-axis direction magnetic detection unit 21, the Y-axis direction magnetic detection unit 22, and the Z-axis direction magnetic detection unit 23 into a digital value. Output. Here, each of the X-axis direction magnetic detection unit 21, the Y-axis direction magnetic detection unit 22, and the Z-axis direction magnetic detection unit 23 magnetizes a voltage value that is an analog value corresponding to the magnetic field detected in its own sensing direction. Output as measurement data.
The measurement data input unit 10, when converting magnetometric data _M analog values (M _x, M y, _{M z)} and magnetic measurement data _M digital value (M _x, M y, _{M z)} in, In order to remove the offset value contained in the magnetic measurement data of the analog value, the offset adjustment with the magnetic sensor alone may be performed.

FIG. 8 is a block diagram illustrating a configuration example of the offset calculation unit 14A that performs configuration of magnetic measurement data using the RLS described above.
The offset calculation unit 14A includes a covariance matrix calculation unit 14A_1, a covariance matrix update unit 14A_2, an error function calculation unit 14A_3, an offset residual calculation unit 14A_4, an offset update unit 14A_5, and a storage unit 14A_6.
The covariance matrix calculation unit 14A_2 sets the initial value of the covariance matrix P used in the offset residual calculation unit 14A_4 described later as shown in the following equation (9).

In equation (9), the covariance matrix calculator 14A_1 sets the constant α in a range from 1.000 to 100.000, for example.
In addition, a column matrix indicating magnetic measurement data in a matrix of 4 rows × 4 columns on the left side in the equation (9) is defined as a vector z _{n in} the following equation (10).

Further, a matrix of 4 rows × 1 column on the left side in the equation (9) is defined as an offset vector x _n in the following equation (11).

The above equation (11) is a matrix indicating a vector composed of an offset O _n (O _xn , O _yn , O _zn ) and constant Q _n calculated from the total magnetic force when updated using the n-th magnetic measurement data. It is.

Error function calculation unit 14A_3, using the following equation (12) calculates an error function _{e n.}

That is, the error function calculation unit 14A_3 uses the n-th measured magnetic measurement data M _n and the previously calculated offset On _-1 (the offset obtained using the (n-1) th magnetic measurement data M _n-1 ). If, because the _(total magnetic force were determined using _n-1 th magnetic measurement data M _n-1) total force R _n-1 previously calculated, to calculate the error function e _n.
Here, the error function calculator 14A_3, the distance and the square of the distance between the magnetic measurement data _{M n} and the offset _{O n,} calculates the square of the total magnetic _{R n-1,} a magnetic measurement data _{M n} and the offset _{O n} from square, subtracting the square of the total magnetic R _n-1, the subtraction result and the error function e _n. Here, the distance between the magnetic measurement data M _n and the offset O _n, X-axis is the measurement axis, in 3-dimensional space consisting of Y-axis and Z-axis, and the offset O _n-1 magnetometric data M _n This is the distance between the coordinate points of the magnetic measurement data M _n and the offset On _-1 when arranged.

Offset residual calculator 14A_4 includes error function _{e n} obtained error function calculator 14A_3, using a covariance matrix _{P n-1} obtained at the previous measurement, the following equation (13), offset residual η Is calculated.

  In this equation (13), the forgetting factor ρ is a constant used in the RLS method. Generally, it is set in the range of 0.95 <ρ <1.

The covariance matrix updating unit 14A_2 uses the covariance matrix P _n when the magnetic measurement data M _n is included in the covariance matrix population as the matrix z _{n in the} equation (10) and the transposed matrix z in the equation (10). and _n ^T, the covariance matrix _{P n-1} to a population of _{M n-1} from the magnetic measurement data _{M 0,} using the forgetting factor [rho, is calculated by the following shown (14). That is, the covariance matrix updating unit 14A_2 uses the measured magnetic measurement data M _n to update the covariance matrix P _n−1 of the magnetic measurement data whose population is the previously measured magnetic measurement data, and performs measurement. The obtained magnetic measurement data M _n is added to the population to generate a new covariance matrix P _n .

Offset updating unit 14A_5 is offset vector _{x n-1} obtained from the magnetometric data _{M n-1} immediately preceding, from the offset residual eta, the offset vector _{x n} corresponding to the magnetic measurement data _{M n,} the following ( 15) Calculated by the equation.

The magnetic measurement data processing unit 15 in FIG. 7 subtracts O _xn , O _yn , and O _zn in the offset vector X _n from each of the magnetic measurement data M _xn , M _yn , and M _zn of the magnetic measurement data M _n , Magnetic calibration data M _f (M _fx , M _fy , M _fz ) is calculated.
The offset update unit 14A_5 stores the covariance matrix P corresponding to the valid offset vector Xn, the offset vector x, and the total magnetic force R in the storage unit 14A_6 according to the control signal of the offset validity determination unit 17 described later. Write and store. Each of the covariance matrix P, the offset vector x, and the total magnetic force R is the data immediately before being used in the next calculation when written, respectively, the covariance matrix P _n−1 , the offset vector X _n−1 and the total magnetic force R. It is written as a magnetic force Rn _-1 . Similarly, the offset update unit 14A_5 writes and stores the offset vector X _n−1 and the total magnetic force R _n−1 in the offset storage unit 16 in accordance with a control signal from the offset validity determination unit 17 described later. .
In addition, the initial value of the covariance matrix P, the forgetting coefficient ρ, the expressions (10), (11), (12), (13), (14), and (15) are stored in the storage unit 14_A. Pre-written and stored.

In the present embodiment, the offset validity judging section 17 performs the offset O _n is valid for determining whether or not obtained from the magnetic measurement data M _n read from the magnetic sensor 2, it is determined that the offset O _n is not valid If, using the offset _{O n-1} previously determined as a new offset _{O n.}
At this time, the offset validity determination unit 17 reads and uses the magnetic measurement data used when determining the validity from the magnetic measurement data buffer 13.
That is, as already described, the magnetic measurement data buffer 13 is provided with a data buffer corresponding to the number of combinations of the angle range of the pitch angle p of the inclination angle and the angle range of the roll angle r. Here, in the magnetic measurement data buffer 13, the magnetic measurement data in the area where the flag information is written in the flag is used for the validity determination process of the offset validity determination unit 17. For example, as in the first embodiment, 648 areas are provided, and when flag information is written in a flag of an area corresponding to 200 magnetic measurement data M, the 200 magnetic measurements The data is read from the magnetic measurement data buffer 13 by the offset validity determination unit 17 and used as magnetic measurement data from the magnetic measurement data M ₁ to M ₂₀₀ .

Here, the magnetic measurement data determination unit 12 searches the correspondence table of the internal storage unit for an area corresponding to the angle range including the combination of the detected roll angle r and pitch angle p from which the magnetic measurement data M _n is measured, Magnetic measurement data M _n is written and stored in the searched area of the magnetic measurement data buffer 13.
At this time, when a plurality of magnetic measurement data are stored in one area (in the configuration of the magnetic measurement data table in FIG. 6), the offset validity determination unit 17 in the searched area of the magnetic measurement data buffer 13 The newest magnetic measurement data _Mn is overwritten on the oldest magnetic measurement data. That is, the offset validity determination unit 17 writes and stores only the magnetic measurement data determined to be updated by the magnetic measurement data determination unit 12 by calculating the offset.

Further, the offset validity judging unit 17, the offset _{O n-1} from the offset storage unit 16 reads out the total magnetic _{R n-1,} the vector of the offset _{O 1 (O 1x, O 1y} , O 1z) and The total magnetic force is R ₁ .
The offset validity determination unit 17 stores each of the magnetic measurement data M ₁ to M _n stored in the magnetic measurement data buffer 13 and flag information described in the flag, and the offset vector O according to the following equation (16). ₁ and the distance _{d 1n} the calculated respectively.

That is, for each magnetic measurement data M, the offset validity determination unit 17 squares the result of subtracting the offset O _1x from the magnetic measurement data M _x and squares the result of subtracting the offset O _1y from the magnetic measurement data _My . The result of subtracting the offset O _1z from the magnetic measurement data M _z is squared.
And the offset effectiveness determination part 17 calculates _| requires the distance _d1n by adding the squared result, and calculating the square root of an addition result. Here, the offset validity judging section 17 corresponds to each of Mn from the magnetic measurement data M1, obtains each _{d 1n} from the distance _{d 11.}
Moreover, the offset validity determination part 17 calculates the evaluation value G1 by the following (17) Formula.

That is, the offset validity determination unit 17 subtracts the total magnetic force R ₁ from each of the distances d ₁₁ to d _1n and squares each subtraction result to obtain the sum of the squares of the subtraction results. The results are added, and the sum of the squares as the addition result is set as the evaluation value G1.
Further, the offset validity determination unit 17 sets the offset vector of the offset On obtained from the magnetic measurement data Mn read from the magnetic sensor 2 as O ₂ (O _2x , O _2y , O _2z ), and this vector O ₂ (O _2x , O _2y , O _2z ) and the magnetic measurement data Mn, the total magnetic force R2 is newly obtained.
Then, the offset validity determination unit 17 calculates the distance d _2n corresponding to each of the magnetic measurement data M ₁ to M _n stored in the data buffer by the following equation (18).

That is, the offset validity judging unit 17, for each magnetic measuring data M, squares the result of subtracting the offset O _2x from magnetometric data M _x, the offset O _2y squares the result of subtracting from the magnetometric data M _y The result of subtracting the offset O _2z from the magnetic measurement data M _z is squared.
And the offset effectiveness determination part 17 calculates _| requires distance _d2n by adding the squared result, and calculating the square root of an addition result. Here, the offset validity judging section 17 corresponds to each of Mn from the magnetic measurement data M1, obtains each _{d 2n} from the distance _{d 21.}
Further, the offset validity determination unit 17 calculates the evaluation value G2 by the following equation (19).

That is, the offset validity determination unit 17 subtracts the total magnetic force R ₂ from each of the distances d ₂₁ to d _2n and squares each subtraction result to obtain the sum of the squares of the subtraction results. The results are added, and the sum of squares as the addition result is set as an evaluation value G2.
When the evaluation values G1 and G2 are calculated, the offset validity determination unit 17 compares the evaluation value G1 with the evaluation value G2.
At this time, when the offset O ₁ and the total magnetic force R ₁ are true values, the evaluation value G 1 is a true value, and when the offset O ₂ and the total magnetic force R ₂ are true values, the evaluation value G2 is a true value. That is, it is considered that the evaluation value G1 becomes smaller as the offset O ₁ and the total magnetic force R ₁ become closer to the true value, and the evaluation value G2 becomes smaller as the offset O ₂ and the total magnetic force R ₂ become closer to the true value.

Therefore, the offset validity judging unit 17 compares the evaluation values G1 and G2, evaluation value G2 is smaller than the evaluation value G1 (G2 <G1) when the offset _{O n} and total magnetic _{R n} newly calculated It is determined that the value is closer to the true value than the previously calculated offset On _-1 and total magnetic force Rn _-1 .
On the other hand, when the evaluation value G2 is equal to or greater than the evaluation value G1 (G2 ≧ G1), the offset effectiveness determination unit 17 determines the offset O _n−1 calculated previously and the offset O newly calculated as the total magnetic force R _n−1. determining from the _n and the total force R _n or close to the true value, or similar to.

Here, the offset validity judging unit 17, when the G2 <G1, the offset O _n and the total force R _n are newly calculated, and outputs to the magnetic measurement data processing unit 15, indicating that updating the offset The control signal is output to the offset update unit 14A_5.
Offset updating unit 14A_5, when the control information indicating that updating the offset O _n-1 previously calculated is supplied, the offset O _n-1 for that is stored in the offset storage unit 16 and the storage unit 14A_6, new overwrite offset O _n calculated for. Thus, the latest offset _{O n} is held in the storage unit 14_6.
Further, when G2 ≧ G1, the offset validity determination unit 17 outputs the offset value and the total magnetic force R stored in the offset storage unit 16 and the storage unit 14A_6 to the magnetic measurement data processing unit 15, and A control signal indicating that the offset is not updated is output to the offset update unit 14A_5.
Offset updating unit 14A_5, when the control information indicating that no update the offset is supplied, without overwriting the offset O _n-1 calculated last time is stored in the storage unit 14_6, the offset O _n-1 previously calculated Do not update the value of. Thus, in the offset storage unit 16 and the storage unit 14A_6 as latest offset, the offset O _n of the same value is maintained offset O _n-1 previously calculated.
Also in the second embodiment, the same processing as the offset validity determination by the offset validity determination unit 17 in the first embodiment is performed, and the validity of the offset stored in the offset storage unit 16 and the storage unit 14A_6 is increased. You may judge.

Next, processing for calibrating magnetic measurement data in the magnetic measurement data calibration apparatus 1A of the present embodiment will be described with reference to FIGS. FIG. 9 is a flowchart showing an operation example of processing for calibrating the magnetic measurement data M detected by the magnetic sensor 2.
Step S11:
When the power of the portable device is turned on, the magnetic measurement data determination unit 12 counts the number of combinations of the angle range of the pitch angle p and the angle range of the roll angle r in the tilt angle, as in step S1 in the first embodiment. An area corresponding to is secured for the magnetic measurement data buffer 13.
In addition, the magnetic measurement data determination unit 12 initializes all the flag fields in the secured area, sets the magnetic measurement data not written, and advances the process to step S12.

Step S12:
The covariance matrix calculator 14A_1 initializes the offset O and the total magnetic force R.
At this time, for example, as the initialization value of the offset O, the offset value measured by the triaxial Helmholtz coil of the single magnetic sensor 2 is written and stored in advance in the storage unit 14_6. In addition, as a value for initializing the total magnetic force R, geomagnetic reference values in a plurality of areas are written and stored in advance in the storage unit 14_6.

Next, after powering on the portable device, the user selects a region including his / her residence from a plurality of regions displayed on the display unit of the portable device.
As a result, the covariance matrix calculation unit 14A_1 reads the initial value of the offset O from the storage unit 14_6, and reads the geomagnetic reference value stored corresponding to the area selected by the user as the initial value of the total magnetic force R. .
In addition, when a GPS (Global Positioning System) function is mounted on a portable device, the covariance matrix calculation unit 14A_1 includes an area including latitude and longitude information obtained from GPS (an area defined by a range of latitude and longitude information). Alternatively, the geomagnetic reference value stored corresponding to may be read as the initial value of the total magnetic force R.
And covariance matrix calculation part 14A_1 advances a process to step S13.

Step S13:
Next, the covariance matrix calculation unit 14A_1 initializes the covariance matrix P. That is, the covariance matrix calculation unit 14A_1 reads the equation (9) that is written and stored in advance in the storage unit 14A_6, and sets the read equation (4) as the initial value of the covariance matrix.
And covariance matrix calculation part 14A_1 advances a process to step S14.

Step S14:
The measurement data input unit 10 includes magnetic measurement data M _xn as magnetic measurement data M _n from each of the X-axis direction magnetic detection unit 21, the Y-axis direction magnetic detection unit 22, and the Z-axis direction magnetic detection unit 23 of the magnetic sensor 2. _Read M _yn and M _zn .
Then, the measurement data input unit 10 outputs the read magnetic measurement data M _n to the magnetic measurement data determination unit 12, the offset calculation unit 14A, and the magnetic measurement data processing unit 15.
After reading the magnetic measurement data M _n , the magnetic measurement data determination unit 12 retrieves the buffer address of the area including the pitch angle p and the roll angle r supplied from the tilt angle calculation unit 11 from the correspondence table of the internal storage unit. To do.
Then, the magnetic measurement data determination unit 12 writes the magnetic measurement data Mn to the searched area in the magnetic measurement data buffer 13.

The error function calculation unit 14A_3 is read from the storage unit 14A_6 to (12), magnetic measurement data _M xn read from the magnetic sensor _2, and _{M yn} and _{M zn,} offset _{O n} read from the storage unit 14A_6 _{-1 (O xn-1, O} yn-1, O zn-1) substituted and, to calculate the error function _{e n.}
That is, the error function calculator 14A_3 squares the result of subtracting the offset O _xn-1 from the magnetic measurement data M _xn , squares the result of subtracting the offset O _yn-1 from the magnetic measurement data M _yn , and generates the magnetic measurement data. The result of subtracting the offset O _zn−1 from M _zn is squared.
The error function calculation unit 14A_3 adds the result of each subtraction, from the addition result, by subtracting the square of the total magnetic R _n-1, obtaining an error function e _n.
After calculating the error function _{e n,} error function calculation unit 14A_3 advances the process to step S15.
Further, in the loop (repetitive processing) from step S14 to step S18 in the flowchart of FIG. 9, in the first loop after the portable device is turned on, the offset On _-1 is the numerical value of the offset in initialization. Similarly, the numerical value of the total magnetic force in initialization is used as the total magnetic force R _n−1 .

Step S15:
The offset residual calculation unit 14A_4 reads the expression (10), the expression (13), the forgetting factor ρ, and the covariance matrix P _n−1 obtained last time from the storage unit 14A_6.
Next, the offset residual calculation unit 14A_4 generates a matrix of the vector z _n by substituting the magnetic measurement data M _n into the equation (10), and generates a transposed matrix z _n ^T of the generated matrix of the vector z _n. To do.
Then, the offset residual calculation unit 14A_4 substitutes each of the forgetting coefficient ρ, the covariance matrix P _n−1 , the vector z _n, and the transposed matrix z _n ^{T into} the equation (13) to calculate the offset residual η, The offset residual η is output to the offset update unit 14A_5.
After calculating the offset residual η, the offset residual calculation unit 14A_4 advances the process to step S16.

Step S16:
The covariance matrix updating unit 14A_2 reads the expression (10), the expression (14), the forgetting factor ρ, and the covariance matrix P _n−1 from the storage unit 14A_6.
Next, the covariance matrix update unit 14A_2 generates a matrix of the vector z _n by substituting the magnetic measurement data M _n into the equation (10), and generates a transposed matrix z _n ^T of the generated matrix of the vector z _n. To do.
Then, the covariance matrix updating unit 14A_2 substitutes the forgetting factor ρ, the covariance matrix P _n−1 , the vector z _n, and the transposed matrix z _n ^T into the equation (14), and creates a new covariance matrix. _Pn is generated and written and stored in the storage unit 14A_6. The covariance matrix P _n written by the covariance matrix updating unit 14A_2 in the storage unit 14A_6 is used as the covariance matrix P _n−1 in the magnetic field loop.
Including this magnetic measurement data M _n, after all of the magnetic measurement data M to generate the covariance matrix P _n to the population that was used to generate the covariance matrix P ever, the covariance matrix update unit 14A_2 advances the process to step S17.

Step S17:
The offset update unit 14A_5 reads the expressions (11) and (15) from the storage unit 14A_6.
Next, the offset updating unit 14A_5 is (11) with respect to formula, and substituting the offset _{O n-1} calculated last time and the total force _{R n-1,} obtaining the vector _{x n-1} of the offset.
Then, the offset update unit 14A_5 substitutes the offset residual η supplied from the offset residual calculation unit 14A_4 and the obtained vector into the equation (15), and measures the magnetic measurement data M _n (ie, the current time). An offset vector x _n indicating the offset at is calculated. That is, the offset update unit 14A_5 calculates a vector _xn indicating a new offset by adding the offset residual η to the vector _xn-1 .
After calculating the vector _{x n,} offset updating unit 14A_5 advances the process to step S18.

Step S18:
Next, the offset validity determination unit 17 searches the magnetic measurement data buffer 13 for an area (inclination angle) in which flag information is described in the flag (flag field), and corresponds to the inclination angle in which the flag information is described. The magnetic measurement data M ₁ to M _n stored in the above are read out from the magnetic measurement data buffer 13, and the offset O _n−1 (O ₁ ) calculated and stored in the previous time is read out from the offset storage unit 16 to be magnetic. For each measurement data M, the distance d _1n is calculated by the above-described equation (16).
Then, the offset validity judging unit 17 reads a magnetic measurement data M _n-1 are stored in the offset storage unit 16 and the offset O _n-1, calculates the total magnetic R ₁ (6) below.
Thereby, the offset validity determination unit 17 calculates the evaluation value G1 from the calculated distance d _1n for each magnetic measurement data and the total magnetic force R _{1 according} to the equation (17).

Next, the offset validity judging unit 17 searches the area flag information is described in the flag, a M _n from magnetometric data M ₁ to the flag information is stored in correspondence with the inclination angle described, Read from the magnetic measurement data buffer 13.
Then, the offset validity judging unit 17, and each of the M _n from magnetometric data M _1, in the currently calculated by the stored offset O _{n (O 2),} for each magnetic measuring data M, the above-described (18 ) To calculate the distance d _2n .
Further, the offset validity judging unit 17, using the magnetic measurement data M _n, and the offset O _n read from the offset storage unit 16, calculates the total magnetic R ₂ by (6).
Thereby, the offset validity determination unit 17 calculates the evaluation value G2 by the equation (19) from the calculated distance d _2n for each magnetic measurement data and the total magnetic force R ₂ .

Next, the offset validity determination unit 17 compares the calculated evaluation values G1 and G2, and determines whether or not the evaluation value G2 is less than the evaluation value G1.
At this time, when the evaluation value G2 is less than the evaluation value G1, the offset validity determination unit 17 stores the offset O _n obtained this time as an offset in the previous offset storage unit 16 and storage unit 14A_6 and stored. since than _n-1 close to the true value determines not to update the offset O _n that currently obtained.
Then, the offset validity determination unit 17 outputs a control signal indicating that the offset value stored in the offset storage unit 16 and the storage unit 14A_6 is updated to the offset update unit 14A_5.
When the control information indicating that performing this update is supplied, the offset updating unit 14A_5, compared offset stored in the storage unit 14A_6 and offset storage unit 16 overwrites the offset O _n determined now, the offset Update the value.

On the other hand, the offset updating unit 14A_5, when evaluation value G2 is rated value G1 or more, with respect to the offset _{O n} found this time, the offset O, which is stored is written as an offset to the previous offset storage unit 16 and the storage unit 14A_6 _{Since n-1} is closer to the true value, a control signal indicating that updating is performed while maintaining the previously written offset value is output to the offset update unit 14A_5.
When the control information indicating that this update is not performed is supplied, the offset update unit 14A_5 maintains the values of the offset O and the previous offset On _-1 stored in the offset storage unit 16 and the storage unit 14A_6. Overwrite as is and update the offset value.

As described above, according to this embodiment, an offset O _n-1 previously obtained, using a magnetic measurement data M _n measured at the present time, so that the error function e _n is minimized, offset residual η calculates, this in order to calculate the offset O _n and offset residual η using the offset O _n-1 previously obtained, it is possible to minimize magnetic noise that is superimposed on the magnetic measurement data M _n, conventional it is the higher accuracy compared to determine the offset O _n of the magnetic measurement data M _n measured thing.

Further, according to this embodiment, since the current of the magnetic measurement data M _n seek offset O _n, when determining the offset residual η to be added to the offset O _n-1 previously obtained, to what extent reflects the error function Is set by the covariance matrix P _n−1 having the previous measured values as the population, the current magnetic measurement data M _n, and the forgetting factor ρ, the move because there is no need to measure a plurality of magnetometric data M, each time measuring the new magnetic measurement data M _n, to obtain the offset O _n-1 easily offset O _n the current from up to the previous time It becomes possible to improve the compliance with the fluctuation of the environmental offset.

According to the present embodiment, every time the magnetic measurement data M which has been determined to be used for the calculation of the offset O is supplied, it is determined to calculate the offset On, the offset O _n and the previous valid that the calculated offset Which one of the offset On-1 stored in the storage unit 16 is closer to the true value is compared with the evaluation values G1 and G2 calculated using the magnetic measurement data buffer 13, and an offset closer to the true value is obtained. Since the selected offset is stored in the storage unit 14_6, the offset O that is always estimated to be closest to the true value can be used for the calibration of the magnetic measurement data M, and the magnetic measurement data can be calibrated with high accuracy. It will be.
Here, in the magnetic measurement data buffer 13, the magnetic measurement data in which the flag information is described in the flag column is obtained by dividing a sphere centered at the offset by a combination of the pitch angle p and the roll angle r. The magnetic measurement data supplied to the area is stored. For this reason, according to the present embodiment, evaluation values G1 and G2 for determining whether or not a true value is calculated from magnetic measurement data distributed all over the sphere centered on the offset. There is no bias in the value, and the effectiveness can be judged with high accuracy.

Further, the measurement data input unit 10 may be configured to perform the following data processing. The measurement data input unit 10 calculates the distance d between the magnetic measurement data M _{n −1 for} which the previous offset On _n−1 was calculated and the magnetic measurement data M _n measured at the present time. As described above, the distance d is obtained by measuring the magnetic measurement data M _n in a three-dimensional space (three-dimensional space indicating a magnetic field) constituted by the measurement axes in the X-axis, Y-axis, and Z-axis directions of the magnetic sensor 2. And M _n−1 are the distances of the respective coordinate values.
The measurement data input unit 10, if the calculated distance d does not exceed the threshold value d _s set in advance, the magnetic measurement data correcting device 1A, does not perform the calculation of the offset O _n by new magnetometric data M _n control I do. In this case, as the data stored in the storage unit 14_6, the numerical value calculated in the magnetic measurement data M _n-1 is stored as it is without being rewritten.

Here, the threshold value d _s is set as follows. That is, the threshold value d _s is determined by a numerical value corresponding to the measurement noise in the measurement of the magnetic sensor 2. When the measurement noise of each measurement axis in the X-axis, Y-axis, and Z-axis directions for measuring magnetic measurement data is measurement noise v _x , v _y , z _v , the magnetic sensor 2 in time series even in a stationary state. The distance between the measured magnetic measurement data is not zero.
With the azimuth measuring device in a stationary state, the fluctuation width of the magnetic measurement data of each measurement axis in the X-axis, Y-axis, and Z-axis directions is measured in advance, and the range including this fluctuation width is measured as noises v _x , v _y , z _v And

Therefore, the measurement data input unit 10 obtains the threshold value d _s by the following equation (20). This threshold value d _s is written and stored in the storage unit 14_6 in advance. Here, the threshold value d _s is the length of the measurement noise vector (v _x , v _y , z _v ), that is, the origin of the three-dimensional space constituted by the measurement axes of the magnetic sensor 2, and the measurement noise v _x , v _y, is set at a distance between the coordinate values of z _v.
For example, when a magnetic sensor having a standard deviation of measurement noise of 1 μT on each measurement axis in the X-axis, Y-axis, and Z-axis directions is used, the fluctuation range obtained by the equation (20) is 4.5 μT at the maximum. In this case, the threshold value ds is set as 5 μT.
The measurement data input unit 10, after the offset O _n is determined, the magnetic measurement data M _n in magnetometric data buffer 13, and stores written in a region corresponding to a combination of the pitch angle p and the roll angle r.

With the configuration described above, in the present embodiment, the same or similar magnetic measurement data, that is, magnetic measurement data with a short distance, is repeatedly estimated to calculate the offset by repeating the calculation to calculate the offset, that is, all the magnetic measurement data is It is possible to eliminate the disadvantage that it is determined that the offset.
Also in the first embodiment, the magnetic measurement data determination unit 12 may be configured to perform the selection process of the magnetic measurement data M used for the offset of the measurement data input unit 10 described above.

<Explanation that offset is obtained as maximum likelihood estimate by RLS method>
In the following, when the RLS method is used, the offset O is updated using the latest magnetic measurement data M using the covariance matrix, that is, the offset vector x is always updated, so that the maximum likelihood value of the offset O (maximum value) is always obtained. The likelihood that the likelihood estimate) can be obtained will be described.
First, the following equation (21) is defined from the magnetic measurement data M _n (M _xn , M _yn , M _zn ).

According to a general least square method, using the magnetic measurement data M ₁ to M _n measured up to the present time, the offset vector x that minimizes the evaluation function J ₁ of the following equation (22) is calculated. become.

Next, as shown in Expression (23), a column matrix Z _n whose elements are the transposed matrix z _n ^T of the vector z _n and a column matrix Y _n whose elements are the vectors y _n of Expression (21) are defined. To do.

By using the column matrices Z _n and Y _n of the above equation (23), the equation (22) can be transformed into the following equation (24).

Above (24), as seen from (23), the magnetic measurement data M ₁ to M _n, that is, contains elements of all magnetic measurement data measured so far.

  Next, a matrix having the weighting coefficient Wn as an element, that is, a weighting matrix Wn is defined as the following equation (25).

Then, using this weighting matrix W _n and the column matrices Y _n and Z _n , the evaluation function J ₂ is shown as the following expression (26).

As shown in the equation (25), the weighting matrix Wn is introduced in order to increase the influence when the magnetic measurement data M is used for calculation, that is, the influence of the specific magnetic measurement data M. If this weighting matrix W _n is a unit matrix, the evaluation function J ₂ is a least square method for obtaining the same evaluation value (J ₂ = J ₁ ) as the evaluation function J ₁ according to the equation (22) already shown.

  Here, the offset vector x that minimizes the evaluation function J2 of the equation (26) is expressed by the following equation (27).

When the above equation (27) is substituted into the equation (26), the evaluation function J _{2 of the} equation (26) is minimum, that is, J ₂ = 0. Therefore, the equation (27) indicates the vector x of the maximum likelihood estimated value. I know that.

Further, in order to represent the covariance matrix P _n used in the calculation, the matrix _Un is defined by the following equation (28).

  By substituting the equations (23) and (25) for the inverse matrix of the matrix Un of the equation (28), the following equation (29) is obtained.

  Here, in order to solve Equation (29) analytically, the inverse matrix theorem is used. That is, in the inverse matrix lemma, when the matrix A is an n × n matrix, the matrix b is an n × 1 vector, and the matrix c is an n × 1 vector, the relationship expressed by the following equation (30) is established. .

  Therefore, substituting equation (29) into equation (30) yields the following equation (31).

  Thereby, (29) Formula can be expressed as a recurrence formula of the following (32) Formula by calculating | requiring the inverse matrix of (31) Formula.

  Here, the weighting matrix in the equation (25) is set as the following equation (33).

In the above (33), when the forgetting factor ρ is set in the range of 0 to 1 (0 <ρ <1), the degree of influence (reflection) of the magnetic measurement data acquired in the past gradually decreases.
Further, the covariance matrix _{P n,} expressed in weighting coefficient _{w n} and the matrix _{U n,} and becomes less (34), thereby coinciding with the (32) equation (14) below.

Further, for the convenience of subsequent calculations, defined by the following expression (35) to k _n.

  Next, by substituting the equations (32) and (35) into the equation (27), the following equation (36) is obtained.

Further, the estimated value of the offset vector x _n−1 obtained from the magnetic measurement data M ₁ to M _n−1 , that is, the estimated value of the n−1th vector x _n−1 is the following (37). It is calculated by the formula.

  Therefore, the estimated value of the n-th vector xn is expressed as the following equation (38) by substituting equation (37) into equation (36) and modifying equation (37).

  Then, the following equation (39) is obtained by modifying the equation (38).

  By using the above equation (39), the third term on the right side of the equation (38) can be simplified to kn × yn. Therefore, the recurrence equation of the vector x in the equation (40) shown below from the equation (38) Can lead.

  The equation (40) is an equation obtained by integrating the equations (13) and (15). Therefore, by updating the offset vector x using the latest magnetic measurement data M by the RLS method described above, the maximum likelihood estimated value of the vector x can always be obtained.

<Direction detection device>
Next, operations of the azimuth measuring apparatus using the magnetic measurement data calibration apparatus 1 of the first embodiment and the magnetic measurement data calibration apparatus 1A of the second embodiment will be described below.
The azimuth angle measuring device mounted on the portable device has a configuration in which the magnetic sensor 2 including the three-axis magnetic detection unit shown in FIG. 1 and the three-axis acceleration sensor 3 are combined.
That is, this azimuth measuring device detects gravity by the acceleration sensor 3, and calculates its own inclination angle from the degree of inclination of the detected gravity.
Then, in the magnetic measurement device, the magnetic measurement data measured by the magnetic sensor 2 generates magnetic calibration data _Mf with the offset calibrated by, for example, the magnetic measurement data calibration device 1 or the magnetic measurement data calibration device 1A.
The azimuth angle measuring apparatus calculates the azimuth angle from the magnetic calibration data _Mf output from the magnetic measurement data calibration apparatus 1 or the magnetic measurement data calibration apparatus 1A.

Hereinafter, the calculation of the azimuth angle by the magnetic calibration data _Mf performed by the azimuth angle measurement unit 4 will be described with reference to FIG.
FIG. 2 is a diagram for explaining the deviation of each axis between the absolute coordinate system obtained by the acceleration sensor 3 and the sensor coordinate system detected by the magnetic measuring device which is a three-axis magnetic sensor, as already described. Then, the azimuth measuring unit 4 reads the pitch angle p and the roll angle r calculated by the tilt angle calculating unit 11.

Further, when the portable device carried by the user is in an inclined state, if the magnetic calibration data M _f output from the magnetic measurement data calibration device 1 is the magnetic measurement data M (M _tx , M _ty , M _tz ), the inclination is The angle calculation unit 11 uses the pitch angle (p) and the roll angle (r) calculated from the expressions (3) and (4) to calculate the magnetic measurement data M (H in the horizontal state according to the following expression (41). _x , _Hy , V) is obtained.

Therefore, the azimuth measuring unit 4 uses the magnetic measurement data M (H _x , H _y , V) calculated by the above equation (41) to calculate the azimuth angle (θ) from the following equation (42).

  As described above, according to the present embodiment, the environmental offset is adjusted, and the magnetic measurement data M output from the magnetic sensor 2 is calibrated (that is, the magnetic measurement data in the zero magnetic field is adjusted). , And the azimuth angle can be obtained by correcting the tilt state with a three-axis magnetic sensor, and the plane formed by the X-axis direction and the Y-axis direction of the detection coordinate system of the azimuth angle measuring device is always the absolute coordinate system. Since the magnetic measurement data in which the ground surface is horizontal and the offset is calibrated can be used, it is possible to obtain the azimuth angle with high accuracy.

Next, a process for obtaining the azimuth angle θ from the magnetic measurement data in the azimuth measuring apparatus using the magnetic measurement data calibration apparatus 1 of the present embodiment will be described with reference to FIGS. 1 and 10. FIG. 10 is a flowchart illustrating an operation example of processing for obtaining the azimuth angle θ of the azimuth measuring apparatus using the offset calculation unit 14A of the first embodiment.
Step S21:
The magnetic measurement data determination unit 12 secures a number of areas in the magnetic measurement data buffer 13 corresponding to the number of combinations of the angle range of the pitch angle p and the roll angle r specified by the user.
The magnetic measurement data determination unit 12 acquires magnetic measurement data M (M _x , M _y , M _z ) from the magnetic sensor 2.
At this time, the magnetic measurement data determination unit 12 reads the inclination angle (pitch angle p and roll angle) from the inclination angle calculation unit 11 at the timing when the magnetic measurement data M (M _x , M _y , M _z ) is read. A control signal requesting to obtain r) is output.

Step S22:
Next, when the control signal is supplied from the magnetic measurement data determination unit 12, the tilt angle calculation unit 11 reads the acceleration data S (S _x , S _y , S _z ) from the acceleration sensor 3.
Step S23:
Then, the tilt angle calculation unit 11 obtains the tilt angle (pitch angle p and roll angle r) from the read acceleration data S (S _x , S _y , S _z ) by the processing already described.

Step S24:
Next, in the magnetic measurement data buffer 13, the magnetic measurement data determination unit 12 converts the magnetic measurement data M (M _x , M _y , M _z ) supplied from the magnetic sensor 2 into the magnetic measurement data M (M _x , (M _y , M _z ) is measured and written in the area corresponding to the pitch angle p and roll angle r at the time of measurement.

Step S25:
Then, the offset calculation unit 14 calculates the offset O as already described in the first embodiment.
Step S26:
Next, the offset validity judging unit 17, and the offset O _n the newly calculated, either an offset O _n-1 stored in the offset storage unit 16 determines whether close to the true value, rather closer Are stored in the offset storage unit 16.

Step S27:
The magnetic measurement data processing unit 15 subtracts the offset O from the magnetic measurement data M (M _x , M _y , M _z ) supplied from the magnetic sensor 2, and magnetic calibration data M _f (M _fx , M _fy , M _fz ) is output to the azimuth measuring unit 4.
Step S28:
When the magnetic calibration data M _f (M _fx , M _fy , M _fz ) supplied from the magnetic measurement data calibration device 1 is supplied, the azimuth measuring unit 4 receives the tilt angle (pitch angle p) from the tilt angle calculation unit 11. And the roll angle r) are read to determine the azimuth angle θ.

  Further, a program for realizing the functions of the magnetic measurement data calibration apparatus 1 in FIG. 1 and the magnetic measurement data calibration apparatus 1A in FIG. 7 is recorded on a computer-readable recording medium, and the program recorded on this recording medium is recorded. May be read into a computer system and executed to calibrate the magnetic measurement data M. Here, the “computer system” includes an OS and hardware such as peripheral devices.

Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within a scope not departing from the gist of the present invention.

  DESCRIPTION OF SYMBOLS 1,1A ... Magnetic measurement data calibration apparatus 2 ... Magnetic sensor 3 ... Acceleration sensor 4 ... Azimuth angle measurement part 10 ... Measurement data input part 11 ... Inclination angle calculation part 12 ... Magnetic measurement data determination part 13 ... Magnetic measurement data buffer 14, DESCRIPTION OF SYMBOLS 14A ... Offset calculation part 14A_1 ... Covariance matrix calculation part 14A_2 ... Covariance matrix update part 14A_3 ... Error function calculation part 14A_4 ... Offset residual calculation part 14A_5 ... Offset update part 14A_6 ... Storage part 15 ... Magnetic measurement data processing part 16 ... Offset storage unit 17 ... Offset validity determination unit 21 ... X-axis direction magnetic detection unit 22 ... Y-axis direction magnetic detection unit 23 ... Z-axis direction magnetic detection unit 31 ... X-axis acceleration detection unit 32 ... Y-axis acceleration detection unit 33 ... Z-axis acceleration detector

Claims (6)

An offset of magnetic measurement data, which is a measurement result of the geomagnetism for each of the measurement axes, is output from a magnetic sensor having three measurement axes orthogonal to each other and measuring the geomagnetism in the measurement axis direction. It is a magnetic measurement data calibration device that corrects measurement data,
An inclination angle calculation unit for obtaining a roll angle and a pitch angle from acceleration data supplied from an acceleration sensor;
A magnetic measurement data buffer provided with an area for storing magnetic measurement data corresponding to the combination of the angular range of the roll angle and the angular range of the pitch angle;
Magnetic measurement data determination unit for writing and storing magnetic measurement data supplied from a magnetic sensor in the region corresponding to the roll angle and the pitch angle detected when measuring the magnetic measurement data;
An offset calculating unit for obtaining the offset from the magnetic measurement data by a predetermined calculation;
Using the magnetic data stored in the magnetic measurement data buffer, it is determined whether the calculated offset, which is the offset obtained by the offset calculation unit, or the set offset, which is the currently used offset, is likely. And an offset validity determination unit that uses the determined offset as a new set offset. The offset calculation unit
An error function calculation unit for obtaining an error function from the difference between the magnetic measurement data for each measurement axis of the measured magnetic measurement data and the previously obtained offset;
An offset residual calculation unit for calculating an offset residual from the error function and the previously obtained covariance matrix;
An offset update unit that calculates the calculated offset by adding the offset residual to the set offset set at the time of the previous measurement of the magnetic measurement data;
Using the measured magnetic measurement data, update the covariance matrix of the magnetic measurement data with the previously measured magnetic measurement data as a population, and add the measured magnetic measurement data to the population to newly The magnetic measurement data calibration device according to claim 1, further comprising: a covariance matrix updating unit that generates a covariance matrix. The offset calculation unit
The difference between the magnetic measurement data written in the area and the temporary offset is calculated for each measurement axis, squared, added for each area, and the addition result is stored in the magnetic measurement data buffer. 2. The magnetic measurement data calibration apparatus according to claim 1, wherein addition is performed in all the stored areas, and the temporary offset that minimizes the addition result is used as the calculated offset. The offset validity determination unit
A first standard deviation which is a standard deviation of a difference between the calculated offset calculated from the magnetic measurement data and the magnetic data stored in the magnetic measurement data buffer is obtained, and the currently used set offset A second standard deviation which is a standard deviation of the difference from the magnetic data stored in the magnetic measurement data buffer is obtained, the first standard deviation is compared with the second standard deviation, and the comparison result is obtained. 4. The magnetic measurement data calibration apparatus according to claim 1, wherein a determination is made as to which of the calculated offset and the set offset is a new set offset. 5. A magnetic sensor having three measurement axes orthogonal to each other and including an axis sensor for measuring geomagnetism in the measurement axis direction;
An acceleration sensor having three measurement axes orthogonal to each other and measuring acceleration in the measurement axis direction;
Obtaining a magnetic measurement data offset that is a measurement result of the geomagnetism for each measurement axis output from the magnetic sensor, and correcting the magnetic measurement data;
An azimuth measuring unit that calculates an azimuth from magnetic calibration data calibrated from the magnetic measurement data output from the magnetic measurement data calibration device, and
An inclination angle calculation unit for obtaining a roll angle and a pitch angle from acceleration data supplied from an acceleration sensor;
A magnetic measurement data buffer provided with an area for storing magnetic measurement data corresponding to each combination of the roll angle angle range and the pitch angle angle range;
Magnetic measurement data determination unit for writing and storing magnetic measurement data supplied from a magnetic sensor in the region corresponding to the roll angle and the pitch angle detected when measuring the magnetic measurement data;
An offset calculating unit for obtaining the offset from the magnetic measurement data by a predetermined calculation;
Using the magnetic data stored in the magnetic measurement data buffer, it is determined whether the calculated offset, which is the offset obtained by the offset calculation unit, or the set offset, which is the currently used offset, is likely. An azimuth angle measuring apparatus comprising: an offset validity determining unit that sets the determined offset as a new set offset. An offset of magnetic measurement data, which is a measurement result of the geomagnetism for each of the measurement axes, is output from a magnetic sensor having three measurement axes orthogonal to each other and measuring the geomagnetism in the measurement axis direction. An inclination calculation unit that corrects measurement data, obtains a roll angle and a pitch angle from acceleration data supplied from an acceleration sensor, an offset calculation unit that obtains the offset from the magnetic measurement data by a predetermined calculation, and an offset calculation unit It is determined by using the magnetic data stored in the magnetic measurement data buffer whether the calculated offset that is the calculated offset or the set offset that is currently used is likely, and the magnetic measurement data is New magnetic measurement data determination unit to be acquired from sensor and offset determined to be probable A buffer for use in a magnetic measurement data correcting device comprising the offset validity judging unit to set offset,
For each combination of the angle range of the roll angle and the angle range of the pitch angle, an area for storing the magnetic measurement data corresponding to the combination is provided, and the magnetism supplied from the magnetic sensor by the magnetic measurement data determination unit Measurement data is written to the area corresponding to the roll angle and the pitch angle detected when measuring the magnetic measurement data.

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