JP2014025715A - Magnetism measurement data calibration device and azimuth angle measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetism measurement data calibration device and azimuth angle measuring instrument for improving followability with respect to the change of an environment offset.SOLUTION: A device for correcting magnetism measurement data to be output from a magnetic element includes: an error function calculation unit for obtaining an error function on the basis of a difference between magnetic measurement data and a last offset; an offset residual calculation unit for calculating an offset residual on the basis of the error function and a last covariance matrix; an offset updating unit for adding the offset residual to an offset when last magnetism measurement data has been measured and calculating a new offset; a covariance matrix updating unit for updating the covariance matrix of magnetism measurement data where previously measured magnetism measurement data is defined as a parent population through the use of measured magnetism measurement data; an offset validity determination unit for calculating a first evaluation value that indicates an error between the updated offset and a true value; and an initialization determination unit for initializing offset processing when the first evaluation value exceeds a predetermined first threshold.

Description

  The present invention relates to a magnetic measurement data calibration apparatus and an azimuth measurement apparatus that calibrate a magnetic element mounted on a portable device.

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

Next, a magnetic field in the direction opposite to the reference magnetic measurement data is applied to the target magnetic element that is the target of offset adjustment by the three-axis Helmholtz coil.
Here, when the target magnetic element 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 element is measured as an offset of the target magnetic element itself, and the offset of the magnetic measurement data output from the magnetic element is adjusted based on the magnetic measurement data.
That is, the offset measured by the three-axis Helmholtz coil is subtracted from each magnetic measurement data from the magnetic measurement data output from the magnetic element, and the direction detection is performed as the measurement result of the magnetic element.

  However, even if the offset adjustment is performed for the magnetic element alone, many other parts are used in the portable device in addition to the magnetic element for detecting the orientation, and the magnetic field generated by these other parts is applied to the magnetic element. 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 element provided inside the portable device, and magnetic measurement data on which the environmental offset is superimposed is output from the single magnetic element subjected to the offset adjustment.
Therefore, after performing offset adjustment with a single magnetic element, the actual orientation that the mobile device is facing and the orientation obtained from the magnetic data output by the magnetic element due to the magnetic field generated by other components of the mounted mobile device In addition, a difference due to the environmental offset occurs.

Further, it is conceivable to perform offset adjustment including environmental offset by a three-axis Helmholtz coil in a state where the magnetic element 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 element 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 element is shifted from the true value due to the fluctuation of the environmental offset superimposed on the magnetic measurement data of the magnetic element.
For this reason, although it is necessary to perform offset again, the offset adjustment of the magnetic element mounted in the portable device cannot always be performed by the three-axis Helmholtz coil. Therefore, it is necessary for the portable device to have a function of adjusting the offset of the magnetic element.

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 elements of each of the three axes, and temporarily stores the measured magnetic measurement data in an internal data buffer.
There is a technique in which the offset adjustment unit obtains an offset that minimizes the distance (magnetic field strength) with respect to the magnetic measurement data stored in the data buffer (see, for example, Patent Document 1). In this method, as shown in the following equation, magnetic measurement data is substituted into a sphere equation, and an offset S _x is obtained by the least square method.
S _x = Σ {(X _i −X ₀ ) ² + (Y _i −Y ₀ ) ² + (Z _i −Z ₀ ) ² −R ² } = 0 (i)
X _i , Y _i and Z _i are magnetic measurement data, X ₀ , Y ₀ and Z ₀ are offset coordinates, and R is a constant.

In addition, the magnetic measurement data of each of the three-axis magnetic elements is set as one set, and four sets of magnetic measurement data are stored in the data buffer. As in Patent Document 1 described above, the offset is determined according to the distance from the magnetic measurement data. (For example, refer to Patent Document 2).
In Patent Document 2, when four sets of magnetic measurement data are extracted from measurement data measured in time series, extraction conditions for extraction are set as follows. That is, the following extraction conditions are set with the magnetic measurement data as coordinate points in a three-dimensional space constituted by three axes of magnetic elements.
When drawing (arranging) three-axis magnetic measurement data in a three-dimensional space (three-dimensional coordinate system),
a. The distance between the first set of magnetic measurement data and the second set of magnetic measurement data is sufficiently large b. The third set of magnetic measurement data is the apex of the obtuse angle of the obtuse triangle having the first and second sets of magnetic measurement data. C. The fourth set of magnetic measurement data is sufficiently separated from the plane formed by the first to third sets of magnetic measurement data.

And in patent document 2, the offset is calculated by solving simultaneous equations using the following spherical equations.
^{_{(X i -X 0) 2 +}} (Y i -Y 0) 2 + (Z i -Z 0) 2 -R 2 = 0 ... (ii)
X _i , Y _i and Z _i are magnetic measurement data, X ₀ , Y ₀ and Z ₀ are offset coordinates, and R is a constant.

Japanese Patent No. 4391416 Japanese Patent No. 4590511

  However, in Patent Document 1, a plurality of magnetic measurement data is accumulated in a data buffer, and an offset is calculated by the least square method using the equation (i) using the accumulated magnetic measurement data. Here, in Patent Document 1, after a large number of magnetic measurement data for the data buffer is measured, the offset is calculated. For this reason, Patent Document 1 requires time for accumulating a large number of magnetic measurement data, and the follow-up performance of the offset adjustment with respect to the change in the environmental offset is deteriorated.

Patent Document 2 calculates the magnetic noise due to the temporal variation factor of the characteristics of the magnetic element itself and the temporal variation factor of the external magnetic field by superimposing on the magnetic measurement data output from the magnetic element. Cannot be calculated accurately.
That is, when magnetic noise is superimposed on any of the four sets of magnetic measurement data, the offset calculated using these magnetic measurement data includes an error due to magnetic noise, and the actual offset and It will shift.

Furthermore, in both Patent Document 1 and Patent Document 2, it is assumed that the measurement point of the magnetic measurement data for obtaining the offset is measured on the surface of a certain sphere.
For this reason, the user needs to move the portable device so as to draw a circle, that is, along a certain spherical surface at the time of offset adjustment.
When this movement is performed, a large number of magnetic measurement data is acquired and stored in the buffer, and the magnetic measurement data used for the calculation described above is extracted.
Therefore, there are cases where the environmental offset cannot follow the change, and new magnetic measurement data must be acquired again and the offset adjustment must be repeated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetic measurement data calibration apparatus and an azimuth angle measurement apparatus that can improve the follow-up performance with respect to fluctuations in environmental offsets.

  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 geomagnetic measurement result for each measurement axis output from an element and correcting the magnetic measurement data, and for each measurement axis of the measured magnetic measurement data An error function calculation unit that calculates an error function from the difference between the magnetic data of and the previously determined offset, an offset residual calculation unit that calculates an offset residual from the error function and the previously determined covariance matrix, An offset update unit that calculates a new offset by adding the offset residual to the offset calculated when measuring the magnetic measurement data Using the measured magnetic measurement data, updating the covariance matrix of the magnetic measurement data with the previously measured magnetic measurement data as a population, and adding the measured magnetic measurement data to the population A covariance matrix updating unit for generating a new covariance matrix, an offset validity determining unit for calculating a first evaluation value indicating an error between the updated offset and the true value of the offset, and the first evaluation value Initialization is performed to determine whether or not a first threshold value set in advance is exceeded, and to perform processing for initializing the offset and the covariance matrix when the first evaluation value exceeds the first threshold value And a determination unit.

  In the magnetic measurement data calibration apparatus according to the present invention, the number of times that the initialization determination unit determines that the first difference exceeds the first threshold in the process of performing offset update is greater than or equal to a preset number. In some cases, the initialization process is performed.

  In the magnetic measurement data calibration apparatus of the present invention, the offset validity determination unit determines a first distance between each of the magnetic measurement data in the three-dimensional magnetic field space formed by the measurement axis of the magnetic element and the updated offset. A first difference between each of the first distances and the total magnetic force obtained from the magnetic measurement data is obtained, and the first difference corresponding to all the first distances is added to calculate the first evaluation value. It is characterized by that.

  The magnetic measurement data calibration device of the present invention is based on the measurement axis of the magnetic element, which is the magnetic measurement data used when obtaining the previously calculated offset and the new magnetic measurement data newly input from the magnetic element. When the second distance in the three-dimensional magnetic field space is obtained, the second distance is compared with a preset second threshold value, and the second distance exceeds the second threshold value, the offset update unit And a magnetic measurement data determination unit that performs control not to update the new offset when the second distance is equal to or smaller than the second threshold. To do.

  In the magnetic measurement data calibration apparatus of the present invention, the second threshold is determined as a distance between a measurement noise coordinate point in the measurement axis direction of the magnetic element in the three-dimensional magnetic field space and an origin of the three-dimensional magnetic field space. It is characterized by being.

  The magnetic measurement data calibration apparatus of the present invention is characterized in that geomagnetism is used as the first threshold value.

  The magnetic measurement data calibration apparatus of the present invention includes a buffer for storing the magnetic measurement data used when the offset has been calculated up to the present time in time series, each of the magnetic measurement data stored in the buffer, and the previous time Obtain a third distance from the offset, obtain a third difference between each of the third distances and the total magnetic force obtained from the magnetic measurement data when obtaining the previous offset, and correspond to all the third distances. A first evaluation value is added to calculate a second evaluation value, the second evaluation value and the first evaluation value are compared, and if the first evaluation value is less than the second evaluation value, a new value is obtained. If the first evaluation value is greater than or equal to the second evaluation value, the previously determined offset is used as the offset used for calibration of the magnetic measurement data. The features.

  In the magnetic measurement data calibration apparatus of the present invention, the error function calculation unit is configured to measure the data coordinates of the measured magnetic measurement data and the previous measurement of the magnetic measurement data in a three-dimensional coordinate system including the three measurement axes. The total magnetic force is obtained from the square of the distance of the offset calculated from time to time, the previous total magnetic force calculated last time is subtracted from the total magnetic force, and the subtraction result is used as the error function.

  The azimuth measuring device of the present invention has three measurement axes orthogonal to each other, and includes a magnetic element composed of an axis sensor that measures the geomagnetism in the measurement axis direction, and a geomagnetism for each measurement axis output from the magnetic element. A magnetic measurement data calibration unit for obtaining an offset of magnetic measurement data as a measurement result and correcting the magnetic measurement data, and an azimuth angle from the magnetic calibration data calibrated from the magnetic measurement data output from the magnetic measurement data calibration device An error angle calculation unit for calculating the error function calculation unit for obtaining an error function from the difference between the magnetic data for each measurement axis of the measured magnetic measurement data and the previously obtained offset, and the error function and An offset residual calculation unit that calculates an offset residual from the covariance matrix obtained last time, and the offset calculated during the previous measurement of the magnetic measurement data. The offset update unit that adds the offset residual and calculates a new offset, and the covariance of the magnetic measurement data using the measured magnetic measurement data and the previously measured magnetic measurement data as a population A covariance matrix updating unit for updating a matrix and adding the measured magnetic measurement data to the population to generate a new covariance matrix; and a first error indicating an error between the updated offset and the true value of the offset An offset validity determination unit that calculates one evaluation value, and determines whether or not the first evaluation value exceeds a preset first threshold, and the first evaluation value exceeds the first threshold An initialization determining unit that performs processing for initializing the offset and the covariance matrix.

  According to the present invention, an offset residual with respect to the previously calculated offset is obtained from the previously calculated offset and newly obtained magnetic measurement data, and this offset residual is added to the previously calculated offset to obtain a new offset. Since there is no delay time for calculating an offset after obtaining a plurality of magnetic measurement data as in the prior art, the offset can be calculated in real time, that is, at a high speed. Since the offset can be calculated from the initialization when it is larger than the geomagnetism, the followability with respect to the fluctuation of the environmental offset can be improved as compared with the conventional case.

It is a schematic block diagram which shows the structural example of the azimuth measuring device using the magnetic measurement data calibration apparatus by one Embodiment of invention. 5 is a flowchart showing an operation example of processing for calibrating magnetic measurement data M detected by a magnetic element 2; It is a table | surface which shows the offset estimation error (offset error) in the magnetic measurement data calibration apparatus 1, calibration apparatus # 1, and calibration apparatus # 2 by this embodiment. It is a figure which shows the experimental result until an offset approaches a true value when an offset changes rapidly. It is a figure which shows the experimental result until an offset approaches a true value when an offset changes rapidly. 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 element detects.

Hereinafter, an 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 apparatus using a magnetic measurement data calibration apparatus according to one embodiment of the present invention. This azimuth measuring device is mounted on a portable device or the like.
The azimuth measuring device of this embodiment is composed of a magnetic measurement data calibration device 1, a magnetic element 2, and an azimuth measuring unit 3.
The magnetic element 2, for example, X-axis direction of the X-axis direction magnetic detector unit 21 for measuring the magnetic data M _x indicating the strength of the magnetic field in the measurement axis, Y-axis magnetic data M _y indicating the strength of the magnetic field in the measurement axis X-axis, Y-axis, and Z-axis comprising a Y-axis direction magnetic detection unit 22 that measures the magnetic data M _z indicating the magnetic field strength on the measurement axis in the Z-axis direction, and a Z-axis direction magnetic detection unit 23 that measures the magnetic data M _z A magnetic element having three measurement axes. 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.

Magnetic measurement data correcting device 1, calibration of the offset of the supplied from the magnetic element 2, the magnetic data _{M x,} magnetic measurements made of the magnetic data _{M y} and the magnetic data _{M z} data _M (M _x, M y, _{M z)} The magnetic calibration data M _f (M _fx , M _fy , M _fz ) is output.
The azimuth measuring unit 3 uses the magnetic calibration data M _f (M _fx , M _fy , M _fz ) calibrated by the magnetic measurement data calibration apparatus 1, and is a three-dimensional configuration composed of the X-axis direction, the Y-axis direction, and the Z-axis direction. Outputs the orientation of the azimuth measuring device in the magnetic field space.

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 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 (1) using the magnetic measurement data M _n (M _xn , M _yn , M _zn ) and the offset O (O _x , O _y , O _z ).

This relationship of formula (1) always holds. That is, when the user carrying the portable device moves, the magnetic 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 (1) always holds even if the magnetic data in each measurement axis direction in the magnetic measurement data changes.

In the above equation (1), 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 (2) is defined.

  By using the above equation (2) and changing the equation (1) into a matrix configuration, the following equation (3) is transformed.

By solving the above equation (3), 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 (3) 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 (3) may not be able to obtain accurate values.
Therefore, by using a statistical method, that is, RLS (Recursive Least Square) method, by reducing magnetic noise, an estimate of the offset components O _x , O _y , O _z , total magnetic force R ( Hereinafter, the 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.

Next, the magnetic measurement data calibration apparatus 1 includes an offset validity determination unit 10, a measurement data input unit 11, a covariance matrix calculation unit 12, a covariance matrix update unit 13, a storage unit 14, an error function calculation unit 15, an offset residual A difference calculation unit 16, an offset update unit 17, a magnetic measurement data processing unit 18, a magnetic measurement data determination unit 19, and an initialization determination unit 20 are provided.
The measurement data input unit 11 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 data.
The measurement data input unit 11 also converts analog magnetic data M (M _x , M _y , M _z ) into digital magnetic measurement data M (M _x , M _y , M _z ). In order to remove the offset value included in the magnetic data of the value, the offset adjustment may be performed on the magnetic element alone.

  The covariance matrix calculation unit 12 sets the initial value of the covariance matrix P used in the offset residual calculation unit 16 described later as shown in the following equation (4).

In the equation (4), the covariance matrix calculation unit 12 sets the constant α in a range from 1.000 to 100.000, for example.
Further, a column matrix indicating magnetic measurement data in a 4 × 4 matrix on the right side in the equation (4) is defined as a vector z _{n in} the following equation (5).

Further, a matrix of 4 rows × 1 column on the right side in the equation (5) is defined as an offset vector x _n in the following equation (6).

The above equation (6) is a matrix indicating a vector composed of an offset On (O _xn , O _yn , O _zn ) when updated using the n-th magnetic measurement data and a constant Q _n calculated from the total magnetic force. is there.

Error function calculation unit 15, using the following equation (7), calculates the error function e _n.

That is, the error function calculator 15 calculates the n-th measured magnetic measurement data M _n and the previously calculated offset On _-1 (the offset obtained using the (n-1) th measured magnetic data M _n-1 ). If, because the (total magnetic force were determined using n-1 th magnetometric data _{Mn -1)} total force _{R n-1} previously calculated, to calculate the error function _{e n.}
Here, the error function calculation unit 15, the distance between 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, placing the magnetic measurement data Mn and the offset O _n-1 Is the distance between the coordinate points of the magnetic measurement data M _n and the offset On ₋₁ .

Offset residual calculating section 16, and the error function e _n obtained error function calculation unit 15, using the covariance matrix P _n-1 obtained at the previous measurement, the following equation (8), offset residual η Is calculated.

  In this equation (8), 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 13 includes the covariance matrix P _n when the magnetic measurement data M _n is included in the covariance matrix population, the matrix z _{n in the} equation (1), and the transposed matrix z in the equation (1). 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, calculated by shown below formula (9).

The offset updating unit 17 obtains an offset vector x _n corresponding to the magnetic measurement data M _n from the offset vector x _n−1 obtained from the immediately preceding magnetic measurement data M _n−1 and the offset residual η as follows ( 10) Calculated by the equation.

The magnetic measurement data processing unit 18 subtracts O _xn , O _yn , and O _zn in the offset vector X _n from the magnetic data M _xn , M _yn , and M _zn of the magnetic measurement data M _n , respectively, and magnetic calibration data M _f ( _Mfx , _Mfy , _Mfz ) is calculated.
The storage unit 14 stores a covariance matrix P, an offset vector x, and a total magnetic force R. Each of the covariance matrix P, the offset vector x, and the total magnetic force R is the data immediately before used in the next calculation when written, respectively, the covariance matrix P _n−1 , the offset vector _n−1, and the total magnetic force R Written as Rn _-1 .
In addition, the storage unit 14 includes initial values of the covariance matrix P, a forgetting factor ρ, equations (5), (6), (7), (8), (9), and (10). Pre-written and stored.

The magnetic measurement data determination unit 19 calculates the distance d between the magnetic measurement data M _{n -1 for} which the previous offset On _-1 was calculated and the magnetic measurement data M _n measured at the present time. As already described, the distance d is obtained by measuring the magnetic measurement data M _n and M in a three-dimensional space (magnetic field three-dimensional space) constituted by the measurement axes in the X-axis, Y-axis, and Z-axis directions of the magnetic element 2. It is the distance of each coordinate value when _n-1 is arranged.
The magnetic measurement data determining section 19, if the calculated distance d does not exceed the threshold value d _s set in advance, the magnetic measurement data correcting device 1 does not perform the calculation of the offset O _n by new magnetometric data M _n Take control. In this case, the data stored in the storage unit 14 is stored as it is without rewriting the numerical value calculated in the magnetic measurement data M _n−1 .

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 element 2. When the measurement noise of each measurement axis in the X-axis, Y-axis, and Z-axis directions for measuring magnetic data is measurement noise v _x , v _y , z _v , the magnetic element 2 is measured in time series even in a stationary state. The distance between the magnetic measurement data to be performed 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 threshold value ds is obtained by the following equation (11). This threshold value d _s is written and stored in the storage unit 14 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 (three-dimensional magnetic field space) constituted by the measurement axes of the magnetic element 2, The measurement noise v _x , v _y , z is set by the distance from the coordinate value of _v .
For example, when a magnetic element 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 equation (11) is 4.5 μT at the maximum.
In this case, the threshold value d _s is set as 5 μT.
Further, after the offset On is obtained, the measurement data input unit 11 writes and stores the magnetic measurement data M _n in the storage unit 14.

Offset validity judging unit 10, a determination is offset O _n determined from magnetic measurement data Mn read from the magnetic element 2 or not valid or, if it is determined that the offset O _n is not valid, the offset O previously obtained the _n-1 is used as the new offset _{O n.}
The storage unit 14 is provided with a data buffer, and 16 to 32 sets of magnetic measurement data M are written and stored in the data buffer. For example, when 16 sets of magnetic measurement data are stored, the magnetic measurement data from the magnetic measurement data M ₁ to M ₁₆ are stored in the data buffer.

Here, the offset validity determination unit 10 causes the magnetic measurement data determination unit 19 to write and store the magnetic measurement data M _{n in} which the distance d exceeds the preset threshold d _s in the above-described data buffer. At this time, the offset validity determination unit 10 overwrites the newest magnetic measurement data M _n on the oldest magnetic measurement data in the data buffer. That is, the offset validity determination unit 10 writes and stores only the magnetic measurement data determined to be updated by the magnetic measurement data determination unit 19 by calculating the offset. The distance in this embodiment is also a distance in a three-dimensional space constituted by the measurement axes in the X-axis, Y-axis, and Z-axis directions of the magnetic element 2 shown in the second embodiment.

Further, the offset validity judging unit 10 from the storage unit 14 and the offset _{O n-1,} reads out the total magnetic _{R n-1,} vector _O 1 of the offset _{(O 1x, O 1y, O} 1z) and, Let R ₁ be the total magnetic force.
The offset validity determination unit 10 calculates the distance d _1n corresponding to each of the magnetic measurement data M ₁ to M _n stored in the data buffer by the following equation (12).

That is, the offset validity judging unit 10, for each magnetic measuring data M, squares the result of subtracting the offset O _1x from the magnetic data M _x, squares the result of the offset O _1y subtracted from the magnetic data M _y, magnetic The result of subtracting the offset O _1z from the data M _z is squared. This evaluation value G1 (second evaluation value) is estimated as an error between On _-1 and the true value of the offset at the previous offset.
And the offset effectiveness determination part 10 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 10 corresponds the magnetometric data _{M 1} to each of the _{M n,} determined each _{d 1n} from the distance _{d 11.}
Moreover, the offset validity determination part 10 calculates evaluation value G1 by the following (13) Formula.

Here, the offset validity determination unit 10 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 square results are added, and the sum of the squares as the addition result is set as the evaluation value G1.
Further, the offset validity judging unit 10, the vector offset of the offset _{O n} determined from magnetic measurement data _{M n} read from the magnetic element _{2 O 2 (O 2x, O} 2y, O 2z) and, the vector _{O 2} A total magnetic force R ₂ is newly obtained from (O _2x , O _2y , O _2z ) and magnetic measurement data M _n .
Then, the offset validity determination unit 10 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 (14).

Here, the offset validity judging unit 10, for each magnetic measuring data M, squares the result of subtracting the offset O _2x from the magnetic data M _x, squares the result of the offset O _2y subtracted from the magnetic data M _y, The result of subtracting the offset O _2z from the magnetic data M _z is squared.
Then, the offset validity determination unit 10 adds the squared results and calculates the square root of the addition result to obtain the distance d _2n . Here, the offset validity judging section 10 corresponds the magnetometric data _{M 1} to each of the _{M n,} determined each _{d 2n} from the distance _{d 21.}
Further, the offset validity determination unit 10 calculates the evaluation value G2 by the following equation (15).

Here, the offset validity determination unit 10 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 square results are added, and the sum of the squares as the addition result is set as the evaluation value G2. The evaluation value G2 (first evaluation value) is estimated as an error between the true value of O _n and the offset in this offset.
When the evaluation values G1 and G2 are calculated, the offset validity determination unit 10 compares the evaluation value G1 and 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 10 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 10 calculates the offset O _n−1 calculated previously and the offset O newly calculated from 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 10, 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 18, indicating that updating the offset The control signal is output to the offset update unit 17.
When the offset update unit 17 is supplied with control information indicating that the previously calculated offset On _-1 is updated, the offset update unit 17 newly calculates the offset On _-1 stored in the storage unit 14. to override the O _n. Thus, the latest offset O _n is held in the storage unit 14.

Further, when G2 ≧ G1, the offset validity determination unit 10 outputs the offset value and the total magnetic force R stored in the storage unit 14 to the magnetic measurement data processing unit 18 and does not update the offset. Is output to the offset update unit 17.
Offset updating unit 17, 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, an offset O _n-1 previously calculated Do not update the value of. Thus, the storage unit 14, as the latest offset, the offset O _n of the same value is maintained offset O _n-1 previously calculated.

The initialization determination unit 20 determines whether or not the evaluation value G2 exceeds a preset threshold GS (G1> GS) after determining whether the evaluation value G2 is greater than the evaluation value G1.
This threshold value GS is determined based on a standard value of geomagnetism. For example, since the magnitude of geomagnetism in Japan is about 46 μT, this square 2116 is used. That is, in the present embodiment, a case is detected where an offset error exceeding (equal or greater) exceeding the geomagnetism remains.
Further, the threshold value GS may be set to an arbitrary value corresponding to the specification of the magnetic calibration process.

Further, when the evaluation value G2 exceeds the threshold value GS, the initialization determination unit 20 increments the counter value J of a counter provided therein (adds “1” to the count value J).
Then, the initialization determination unit 20 determines whether or not the counter value J of the counter is greater than or equal to a preset threshold value JS. Here, when the counter value J is equal to or greater than the threshold value JS, the initialization determination unit 20 has an offset error exceeding the threshold value GS, that is, an offset error exceeding the geomagnetism remains. And a process of initializing the covariance matrix P.

  Here, when the evaluation value G2 exceeds the threshold GS, as a reason for initializing the offset O, the total magnetic force R, and the covariance matrix P, even when the offset O changes suddenly, the new offset is gently approached. Therefore, it takes time to reach the true value of the offset (the number of times the offset is updated increases). In the present embodiment, the offset is estimated so that the influence of the measurement data after the offset change is maximized. However, although the offset is estimated by the least-squares method weighted with respect to time, since the influence of the measurement data before the offset change remains on the covariance matrix, it is estimated as the offset error increases. It takes time for the offset to approach the true value (the number of offset updates increases), and as described above, a large offset change cannot be handled quickly.

As a solution to this, when there is an offset error larger than the threshold value GS, the effect before the offset change can be completely removed by initialization, so that the time for approaching the true value of the offset can be shortened. .
On the other hand, when the evaluation value G2 is equal to or smaller than the threshold value GS, the initialization determination unit 20 performs a process of resetting a counter provided therein, that is, setting the count value J to “0”.
Further, although depending on the program configuration or the circuit configuration, a plurality of steps are required from the initialization of the offset O, the total magnetic force R, and the covariance matrix P until the offset estimation is completed. From this initialization to the end of the offset, there are cases where the evaluation value G2 exceeds the threshold GS. For this reason, the threshold value JS is set as the number of steps from the initialization to the end of the offset estimation, that is, the offset update count in the offset estimation process.

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. 2 is a flowchart showing an operation example of processing for calibrating the magnetic measurement data M detected by the magnetic element 2.
Step S1:
The covariance matrix calculator 12 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 element 2 is written and stored in the storage unit 14 in advance. In addition, as a value for initializing the total magnetic force R, geomagnetic reference values in a plurality of regions are written and stored in the storage unit 14 in advance.
Then, 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.
Thereby, the covariance matrix calculation unit 12 reads the initial value of the offset O from the storage unit 14 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 installed in a portable device, the covariance matrix calculation unit 12 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.
Then, the covariance matrix calculation unit 12 advances the process to step S2.

Step S2:
Next, the covariance matrix calculation unit 12 initializes the covariance matrix P. That is, the covariance matrix calculation unit 12 reads the equation (4) previously written and stored in the storage unit 14, and sets the read equation (4) as the initial value of the covariance matrix.
Then, the covariance matrix calculation unit 12 advances the process to step S3.

Step S3:
The measurement data input unit 11 includes magnetic data M _xn , M as magnetic measurement data M _n from 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 element 2. _{Read yn} and _Mzn .
Then, the measurement data input unit 11 writes and stores the read magnetic measurement data M _n in the storage unit 14.
After reading the magnetic measurement data M _n , the measurement data input unit 11 advances the process to step S4.

Step S4:
Magnetic measurement data determining section 19, the magnetic measurement data M _n is supplied from the measurement data input unit 11, a threshold d _s, and a magnetic measurement data M _n-1 used to calculate the previous offset O _n-1 Read from the storage unit 14.
Next, the magnetic measurement data determination unit 19 calculates a distance d between the supplied magnetic measurement data M _n and the magnetic measurement data M _n−1 read from the storage unit 14 by Expression (11).
Then, the magnetic measurement data determination unit 19 compares the calculated distance d with the threshold value d _s read from the storage unit 14.
At this time, if the distance d is greater than or equal to the threshold value d _s , the magnetic measurement data determination unit 19 proceeds to step S5. If the distance d is less than the threshold value d _s , the process proceeds to step S6.

Step S5:
Then, the error function calculation unit 15, read from the storage unit 14 with respect to (7), magnetic data _M xn read from the magnetic element _2, and _{M yn} and _{M zn,} offset _{O n} read from the storage unit 14 _{-1 (O xn-1, O} yn-1, O zn-1) substituted and, to calculate the error function _{e n.}
That is, the error function calculation unit 15 squares the result of subtracting the offset O _xn-1 from the magnetic data M _xn , squares the result of subtracting the offset O _yn-1 from the magnetic data M _yn , and calculates the magnetic data M _zn from the magnetic data M _zn. The result of subtracting the offset O _zn−1 is squared.
The error function calculation unit 15 adds the results of the respective subtracted 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 15, the process proceeds to step S7.
In the loop (repetitive processing) from step S3 to step S17 in the flowchart of FIG. 2, 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 S6:
The magnetic measurement data determination unit 19 does not perform the process of calculating the offset On in the magnetic measurement data calibration apparatus 1, but keeps the numerical value stored in the storage unit 14 and advances the process to step S3.

Step S7:
The offset residual calculation unit 16 reads the expression (5), the expression (8), the forgetting factor ρ, and the covariance matrix P _n−1 obtained last time from the storage unit 14.
Next, the offset residual calculation unit 16 generates a matrix of the vector z _n by substituting the magnetic data M _n into the equation (5), and generates a transposed matrix z _n ^T of the generated vector z _n matrix. .
Then, the offset residual calculation unit 16 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 (8) to calculate the offset residual η, This offset residual η is output to the offset update unit 17.
After calculating the offset residual η, the offset residual calculation unit 16 advances the process to step S8.

Step S8:
The covariance matrix updating unit 13 reads the expression (5), the expression (9), the forgetting coefficient ρ, and the covariance matrix P _n−1 from the storage unit 14.
Next, the covariance matrix update unit 13 generates a matrix of the vector z _n by substituting the magnetic data M _n into the equation (5), and generates a transposed matrix z _n ^T of the generated matrix of the vector z _n. .
Then, the covariance matrix updating unit 13 substitutes the forgetting coefficient ρ, the covariance matrix P _n−1 , the vector z _n, and the transposed matrix z _n ^T into the equation (9), and creates a new covariance matrix. _Pn is generated and written into the storage unit 14 for storage. The covariance matrix P _n written by the covariance matrix update unit 13 in the storage unit 14 is used as the covariance matrix P _n−1 in the magnetic field loop.
Including the current magnetic data M _n, after all of the magnetic data M that were used to generate the covariance matrix P to generate the covariance matrix P _n to the population ever, the covariance matrix updater 13 Then, the process proceeds to step S9.

Step S9:
The offset update unit 17 reads the expressions (6) and (10) from the storage unit 14.
Next, the offset updating unit 17, (6) 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 17 substitutes the offset residual η supplied from the offset residual calculation unit 16 and the obtained vector into the equation (10), and measures the magnetic measurement data M _n (that is, the current time). An offset vector x _n indicating the offset On at is calculated. That is, the offset update unit 17 calculates a vector x _n indicating a new offset by adding the offset residual η to the vector x _n−1 .
After calculating the vector _xn , the offset updating unit 17 advances the process to step S10.

The magnetic measuring data processing unit 18, when the azimuth measuring unit 3 for calculating the azimuth angle, the offset O _n corresponding to the magnetic measurement data M _n for measurement data input unit 11 inputs, from the magnetic measurement data Mn Subtract.
The magnetic measurement data processing unit 18, the result of subtracting the offset _{O n} from magnetometric data _{M n,} calibrated magnetic calibration data _{M f (M fx, M fy} , M fz) as, the azimuth measuring part 3 Output.

Step S10:
Next, the offset validity determination unit 10 reads the magnetic measurement data M ₁ to M _n stored in the storage unit 14 and the offset O _n−1 (O ₁ ) calculated and stored last time, and stores the magnetic data. For each M, the distance d _1n is calculated by the above-described equation (12).
Then, the offset validity judging unit 10 reads out the magnetic measurement data _{M n-1} in the memory 14 is stored with offset _{O n-1,} it calculates the total magnetic _{R 1} by (1).
Thereby, the offset validity determination unit 10 calculates the evaluation value G1 from the calculated distance d _1n for each magnetic data and the total magnetic force R _{1 according} to the equation (13), and advances the processing to step S16.

Step S11:
Next, the offset validity judging unit 10, a M _n from magnetometric data M ₁ stored in the storage unit 14, reads the offset O _n stored is calculated this time _{(O 2),} each magnetic data M Then, the distance d _2n is calculated by the above-described equation (14).
Then, the offset validity judging unit 10 reads the magnetic measurement data M _n stored in the storage unit 14 and the offset O _n, calculates the total magnetic R2 by (1).
Thereby, the offset validity determination unit 10 calculates the evaluation value G2 from the calculated distance d _2n for each magnetic data and the total magnetic force R ₂ by the equation (15), and advances the processing to step S12.

Step S12:
Next, the offset validity determination unit 10 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, if the evaluation value G2 is less than the evaluation value G1, the offset validity determination unit 10 proceeds to step S13. If the evaluation value G2 is equal to or greater than the evaluation value G1, the offset validity determination unit 10 proceeds to step S14. .

Step S13:
If the evaluation value G2 is smaller than the evaluation value G1, since the offset O _n the currently obtained is close to the true value than the offset O _n-1, which is stored is written as an offset to the previous memory section 14, an offset validity judging section 10 determines that you do not want to update the offset O _n found this time.
Then, the offset validity determination unit 10 outputs a control signal indicating that the offset value stored in the storage unit 14 is updated to the offset update unit 17.
When the control information indicating that performing this update is supplied, the offset updating unit 17, with respect to the offset stored in the storage unit 14 overwrites the offset O _n found this time to update the value of the offset .
And the offset update part 17 advances a process to step S15.

Step S14:
If the evaluation value G2 is rated value G1 or more, with respect to the offset O _n found this time, since towards the offset O _n-1 previously stored in the storage unit 14 is written as an offset is close to the true value, the offset The validity determination unit 10 outputs to the offset update unit 17 a control signal indicating that updating is performed while maintaining the previously written offset value.
When the control information indicating that this update is not performed is supplied, the offset updating unit 17 overwrites the offset O stored in the storage unit 14 while maintaining the previous offset On _-1 value. Update the offset value.
And the offset update part 17 advances a process to step S15.

Step S15:
Next, the initialization determination unit 20 determines whether or not the evaluation value G2 exceeds a threshold value GS that is previously written and stored in the internal storage unit.
At this time, if the evaluation value G2 exceeds the threshold value GS, the initialization determination unit 20 advances the process to step S16.
On the other hand, when the evaluation value G2 is equal to or less than the threshold value GS, the initialization determination unit 20 resets the counter value J of the internal counter, and then advances the process to step S3.

Step S16:
Next, the initialization determination unit 20 increments the counter value J of the counter provided therein, and then proceeds to step S17.

Step S17:
Next, the initialization determination unit 20 determines whether or not the counter value J of the counter is equal to or greater than a threshold value JS that is written and stored in advance in a storage unit provided therein.
At this time, if the counter value J is greater than or equal to the threshold value JS, the initialization determination unit 20 advances the processing to step S1 and sets the initial values of the offset O, the total magnetic force R, and the covariance matrix P to the covariance matrix calculation unit 12. Perform processing to make it.
On the other hand, if the counter value J is less than the threshold value JS, the initialization determination unit 20 advances the process to step S3 and continues the offset estimation process.

According to the embodiment described above, the 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, and calculates an offset residual η the order to calculate the offset O _n and offset residual η using the offset O _n-1 previously obtained, it is possible to also minimize magnetic noise superimposed on the magnetic measurement data M _n, as compared to conventional higher precision Te, it is possible to obtain the offset O _n of the magnetic measurement data M _n being measured.

Further, according to this embodiment, since the current of the magnetic measurement data M _n determine the offset O _n, when obtaining 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 Therefore, it is possible to improve the follow-up performance with respect to the fluctuation of the environmental offset.

  Further, according to 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, the magnetic measurement data are all offset. It is possible to eliminate the drawbacks of the first embodiment that are determined to be present.

Further, according to this embodiment, every time the magnetic measurement data M which has been determined to be used for the calculation of the offset O is supplied, calculates the offset O _n, is determined to the last valid in the memory unit 14 stores since the one the offset O _n-1, which is compared by the G2 and evaluation values G1 or close to the true value, and select the more offset close to the true value, for holding the offset selected in the storage unit 14, always The offset O estimated to be closest to the true value can be used for the calibration of the magnetic data M, and the magnetic data can be calibrated with high accuracy.

  Further, according to the present embodiment, when there is an offset error larger than the threshold GS, the influence of the measurement data before the offset change remaining in the covariance matrix is expressed as the offset O, the total magnetic force R, and the covariance matrix P. Therefore, even if the offset error becomes large, the time required for the estimated offset to approach the true value can be shortened.

Next, an error between the magnetic measurement data calibration apparatus 1 of the present embodiment, the true value of the offset On estimated by each of the first method of Patent Document 1 and the second method of Patent Document 2 was compared. The results will be explained.
A magnetic measurement apparatus equipped with each of the magnetic measurement data calibration apparatus 1 according to the present embodiment, the calibration apparatus # 1 using the algorithm of the first technique, and the calibration apparatus # 2 using the algorithm of the second technique. Prepared.
And each offset of a magnetic measuring device is measured with a triaxial Helmholtz coil, and it is set as the state which performed offset adjustment of the magnetic element in which each calibration apparatus was provided.

Next, each of the magnetic measurement data calibration apparatus 1, the calibration apparatus # 1 using the algorithm of the first technique, and the calibration apparatus # 2 using the algorithm of the second technique are each mounted. An offset calculation process was performed.
First, the magnetic measuring device to be measured is set stationary on the stage of the 3-axis Helmholtz coil with the offset calibrated.
Then, a magnetic field opposite to the geomagnetism is generated so that the magnetic field becomes zero, and a specific moving magnetic field that is a magnetic field applied to the magnetic element when the magnetic measuring device is moved in a specific direction in this state has three axes. Generate in Helmholtz coils.
That is, a magnetic field estimated to be detected by the magnetic element when the magnetic measuring device is moved is applied to the magnetic measuring device set stationary on the stage of the three-axis Helmholtz coil by the three-axis Helmholtz coil. Thereby, the state which moved the portable equipment carrying a magnetic measuring device is simulated.

In this embodiment, as a simulation of the movement of the portable device using the above-described three-axis Helmholtz coil, for example, a first simulation in which a movement for drawing a figure 8 is performed, and a second simulation in which the movement is performed in an oblique direction. And went. The oblique direction refers to a direction having an angle with respect to an axis perpendicular to the ground surface.
In this simulation, not only the magnetic field opposite to the geomagnetism and the specific moving magnetic field, but also a magnetic field having a specific direction of a certain direction in a certain direction as a virtual offset (as if an environmental offset exists) A combined magnetic field obtained by combining a magnetic field opposite to the geomagnetic field and a specific moving magnetic field.
And the synthetic magnetic field mentioned above was applied and the output of each magnetic measuring device was measured. At this time, when the magnetic field change of the synthetic magnetic field is detected and the calibration is normally performed, the calibration device in the magnetic measurement device determines the offset magnetic field as the offset inside the portable device. For this reason, the magnetic measurement device subtracts the offset magnetic field and the offset inside the portable device from the magnetic measurement data and outputs the result.

Therefore, after the calibration process described above is performed on the magnetic measurement device, the magnetic measurement data M (Mx, My, and M) output from the magnetic measurement device in a state where a combined magnetic field of the magnetic field opposite to the geomagnetism and the offset magnetic field is applied. Mz) is zero.
In the experiment described above, 10 μT (micro Tesla) was used as the offset magnetic field for each measurement axis in the X, Y, and Z axis directions.
In addition, the square of the magnetic data of each measurement axis output from the magnetic measurement device in a state where a magnetic field opposite to the geomagnetism and the offset magnetic field is applied is added, and the square root of the addition result is calculated as an offset estimation error. The closer this offset estimation error is to 0, the closer the offset calculated by the calibration apparatus is to the true value.
FIG. 3 shows the result of the experiment in this embodiment. FIG. 3 shows a magnetic field opposite to magnetism and a specific moving magnetic field (eight-shaped movement and diagonal movement) with respect to the magnetic measurement data calibration apparatus 1, the calibration apparatus # 1, and the calibration apparatus # 2 according to the present embodiment. ) And an offset magnetic field applied to the offset magnetic field, and measured offset estimation error.

As shown in FIG. 3, the magnetic measurement data calibration in this embodiment is performed in either the first state where the portable device is moved in the shape of figure 8 or the second state where the portable device is moved in an oblique direction. The result that the offset by the apparatus 1 is close to the true value, that is, the calculated offset O is close to the actual offset was obtained.
In the case of the second state that is moved in the oblique direction, there is no difference from the case of the first state in the present embodiment, but in the calibration devices # 1 and # 2, the calculated offset is compared with the first state. Calculation accuracy is low. In particular, since calibration apparatus # 2 is 17.32 = (102 + 102 + 102) 1/2, it can be seen that the offset estimation itself is not performed.
From the result of FIG. 3 described above, according to the present embodiment, the movement of the portable device necessary for the calibration of the magnetic measurement data can be minimized, and the offset estimation accuracy is improved as compared with the conventional method. Can be made.

Next, FIGS. 4 and 5 are diagrams showing experimental results until the offset approaches a true value when the offset changes abruptly.
That is, in FIGS. 4 and 5, the horizontal axis indicates time, the vertical axis indicates the offset value, and the results of experiments for quantitatively evaluating the time required for offset estimation until the offset approaches the true value are shown. FIG. FIG. 4 shows the result of offset estimation by a magnetic calibration apparatus having a configuration without the initialization determination unit 20, while FIG. 5 shows the result of offset estimation by a magnetic calibration apparatus with a configuration of the initialization determination unit 20. Yes.

In this experiment, an offset of 100.0 μT is applied to the magnetic element 2 of both magnetic calibration apparatuses with a rotation of 20000 msec. In FIG. 4, even if 20000 milliseconds have elapsed since the application of the offset, the estimated offset is not 100.0 μT applied. On the other hand, in FIG. 5, when 3000 milliseconds have elapsed since the application of the offset, the estimated offset is close to the applied value of 100.0 μT and the true value.
As can be seen from the results of FIGS. 4 and 5, when the offset changes drastically and greatly, if the offset O, the total magnetic force R, and the covariance matrix P are not initialized, the offset becomes long until it approaches the true offset. It will take time. On the other hand, by performing initialization of the offset O, the total magnetic force R, and the covariance matrix P, it can be seen that even if the offset changes, the change in the offset can be followed more quickly than when initialization is not performed.

<Explanation that offset is obtained as maximum likelihood estimate by RLS method>
Hereinafter, 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 ( The maximum likelihood estimate) can be obtained.
First, the following expression (16) 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 (17) is calculated. become.

Next, as shown in the equation (18), 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 the equation (16) are defined. To do.

By using the column matrices Z _n and Y _n of the above equation (18), the equation (17) can be transformed into the following equation (19).

As can be seen from the equation (18), the above equation (19) includes elements of all the magnetic measurement data measured from the magnetic measurement data M ₁ to M _n , that is, the present.

Next, a matrix having the weighting coefficient W _n as an element, that is, a weighting matrix W _n is defined as the following equation (20).

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 equation (21).

(20) As shown in equation, the weighting matrix W _n is a weighting when used for the calculation of each magnetometric data M, that is introduced in order to increase the influence of a particular 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 (17) already shown.

Here, the vector x of the offset which minimizes the evaluation function J ₂ of (21) is as shown in the following equation (22).

When the above equation (22) is substituted into the equation (21), the evaluation function J _{2 of the} equation (21) is minimum, that is, J ₂ = 0, so that the equation (22) 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 (23).

To inverse matrix of the matrix _{U n} of the equation (23) by substituting the equation (18) and (20), shown below (24) is obtained.

  Here, in order to solve Equation (24) 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 (25) is established. .

  Therefore, when the equation (24) is substituted into the equation (25), the following equation (26) is obtained.

  Thereby, (24) Formula can be expressed as a recurrence formula of the following (27) Formula by calculating | requiring the inverse matrix of (26) Formula.

  Here, the weighting matrix in the equation (20) is set as the following equation (28).

In the above (28), 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 (29), thereby coinciding with the (27) equation (9) below.

Further, for the convenience of subsequent calculations, defined by the following equation (30) to k _n.

  Next, by substituting the equations (27) and (30) into the equation (22), the following equation (31) is obtained.

Further, the estimated value of the offset vector x _n−1 obtained from the magnetic measurement data M ₁ to Mn−1, that is, the estimated value of the n−1th vector x _n−1 is expressed by the following equation (32). Is required.

Therefore, the estimated value of the n-th vector _xn is expressed as the following equation (33) by substituting the equation (32) into the equation (31) and modifying the equation (31).

And the following (34) Formula is obtained by transforming this (33) Formula.

By using the above (34), (33) of the third term on the right side because it can _{k n} × _{y n} and simplified, (33) a recurrence of the vector x that shown below (35) from the equation An expression can be derived.

  The above expression (35) is an expression obtained by integrating the expressions (8) and (10). 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.

<Azimuth angle detection device>
Next, the operation of the azimuth angle measuring apparatus using the magnetic measurement data calibration apparatus 1 according to one embodiment of the present invention will be described below.
The azimuth measuring device mounted on the portable device has a configuration in which a magnetic element 2 including a magnetic detection unit having three measurement axes orthogonal to each other shown in FIG. 1 and a three-axis acceleration sensor (not shown) are combined. It is installed.
That is, this azimuth measuring device detects gravity by a triaxial acceleration sensor, and calculates its own inclination angle from the degree of inclination of the detected gravity.
Then, in the azimuth measuring device, the magnetic measurement data measured by the magnetic element 2 generates magnetic calibration data M _f with the offset calibrated by the magnetic measurement data calibration device 1.
The azimuth angle measuring device calculates the azimuth angle based on the magnetic calibration data M _f output from the magnetic measurement data calibration device 1.

Hereinafter, the calculation of the azimuth angle by the magnetic calibration data _Mf performed by the azimuth angle measurement unit 3 will be described.
FIG. 6 is a diagram for explaining a shift of each axis between an absolute coordinate system obtained by a triaxial acceleration sensor and a sensor coordinate system detected by a magnetic measuring device which is a triaxial magnetic element.
In FIG. 6, 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 ).
The above and the absolute coordinate system, in the present embodiment, a plane formed by the X and Y axes relative to the gravity vector is vertical, magnetic measurement data M (M x measuring the magnetic element _2, M _y , M _z ) is a coordinate system with the origin O as the point where all of them are zero. The sensor coordinate system is a coordinate system formed by magnetic data M (M _x , M _y , M _z ) measured by the magnetic element 2. For this reason, the sensor coordinate system differs for each measurement point at which the magnetic element 2 measures the magnetic 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 elements, 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 element 2, the measurement axis (X-axis detection magnetic field) in the X direction in the sensor coordinate system of the magnetic element 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 element 2, that is, the azimuth measuring device can be accurately measured by the gravity vector.

At this time, when the azimuth measuring device is in a horizontal state with respect to the ground surface, the acceleration measurement data output from the triaxial acceleration sensor is _{defined as} 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 triaxial acceleration sensor is defined as 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 (36). .

When the portable device carried by the user is in an inclined state, the output of the triaxial acceleration sensor normalized by the gravitational acceleration in the inclined state is assumed to be 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 expression (36) is shown below ( 37).

Therefore, the azimuth measuring unit 3 uses the acceleration measurement data A (A _x , A _y , A _z ) output from the triaxial acceleration sensor, and the pitch angle (p) is expressed by the following equation (38): The roll angle (r) is calculated by the following equation (39).

Further, when the mobile device carried by the user is in an inclined state, 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 ). Based on the pitch angle (p) and the roll angle (r) calculated from each of the equations (38) and (39), the magnetic measurement data M (H _x , H _y in the horizontal state is obtained by the following equation (40). , V).

Therefore, the azimuth measuring unit 3 calculates the azimuth angle (θ) from the following equation (41) using the magnetic measurement data M (H _x , H _y , V) calculated by the above equation (40).

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

  Further, a program for realizing the function of the magnetic measurement data calibration apparatus 1 in FIG. 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. Calibration processing of the magnetic measurement data M may be performed. 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 ... Magnetic measurement data calibration apparatus 2 ... Magnetic element 3 ... Azimuth angle measurement part 10 ... Offset effectiveness determination part 11 ... Measurement data input part 12 ... Covariance matrix calculation part 13 ... Covariance matrix update part 14 ... Memory | storage part 15 ... Error function calculation unit 16 ... Offset residual calculation unit 17 ... Offset update unit 18 ... Magnetic measurement data processing unit 19 ... Magnetic measurement data determination unit 20 ... Initialization determination unit 21 ... X-axis direction magnetic detection unit 22 ... Y-axis direction magnetism Detection unit 23 ... Z-axis direction magnetic detection unit

Claims (9)

An offset of magnetic measurement data, which is a measurement result of geomagnetism for each measurement axis, is output from a magnetic element having three measurement axes orthogonal to each other and measuring the geomagnetism in the measurement axis direction, and the magnetism It is a magnetic measurement data calibration device that corrects measurement data,
An error function calculation unit for obtaining an error function from the difference between the magnetic 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 new offset by adding the offset residual to the offset calculated during 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 A covariance matrix updating unit for generating a covariance matrix,
An offset validity determination unit that calculates a first evaluation value indicating an error between the updated offset and the true value of the offset;
It is determined whether or not the first evaluation value exceeds a preset first threshold value, and when the first evaluation value exceeds the first threshold value, the offset and the covariance matrix are initialized. A magnetic measurement data calibration apparatus comprising: an initialization determination unit that performs a process for performing the process. The initialization determination unit
The initialization process is performed when the number of times the first difference is determined to exceed the first threshold in a process of performing offset update is equal to or greater than a preset number. The magnetic measurement data calibration apparatus according to 1. The offset validity determination unit
A first distance between each of the magnetic measurement data in the three-dimensional magnetic field space formed by the measurement axis of the magnetic element and the updated offset is obtained, and the total magnetic force obtained from each of the first distance and the magnetic measurement data. 3. The magnetic measurement data according to claim 1, wherein the first evaluation value is calculated by adding the first differences corresponding to all the first distances. Calibration device. The second distance in the three-dimensional magnetic field space consisting of the measurement axis of the magnetic element between the magnetic measurement data used when obtaining the previously calculated offset and the new magnetic measurement data newly input from the magnetic element. The second distance is compared with a preset second threshold, and if the second distance exceeds the second threshold, a new offset is updated to the offset update unit. On the other hand, when the second distance is less than or equal to the second threshold value, the magnetic measurement data determination unit further performs control not to update a new offset. The magnetic measurement data calibration device according to claim 1. The second threshold value is defined as a distance between a measurement noise coordinate point in each measurement axis direction of the magnetic element in the three-dimensional magnetic field space and an origin of the three-dimensional magnetic field space. 4. The magnetic measurement data calibration device according to 4.   6. The magnetic measurement data calibration apparatus according to claim 1, wherein geomagnetism is used as the first threshold value. A buffer for storing magnetic measurement data used in calculating the offset up to the present time in a time series;
A third distance between each of the magnetic measurement data stored in the buffer and the previous offset is obtained, and the total magnetic force obtained from the magnetic measurement data when each of the third distance and the previous offset is obtained; The third difference is calculated, the first difference corresponding to all the third distances is added to calculate a second evaluation value, the second evaluation value is compared with the first evaluation value, and the first difference is calculated. When the evaluation value is less than the second evaluation value, the newly obtained offset is used as an offset used for calibration of the magnetic measurement data. On the other hand, when the first evaluation value is greater than or equal to the second evaluation value, the previous calculation is performed. The magnetic measurement data calibration apparatus according to any one of claims 1 to 6, wherein the offset is an offset used for calibration of the magnetic measurement data. The error function calculator is
In a three-dimensional coordinate system composed of the three measurement axes, the total magnetic force is calculated from the square of the distance between the measured data coordinate of the magnetic measurement data and the offset coordinate of the offset calculated at the previous measurement of the magnetic measurement data. The magnetic measurement data calibration apparatus according to any one of claims 1 to 7, wherein the previous total magnetic force calculated last time is subtracted from the total magnetic force, and the subtraction result is used as the error function. . A magnetic element having three measurement axes orthogonal to each other and including an axis sensor for measuring geomagnetism in the measurement axis direction;
Obtaining a magnetic measurement data offset that is a geomagnetic measurement result for each measurement axis output from the magnetic element, 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 error function calculation unit for obtaining an error function from the difference between the magnetic 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 new offset by adding the offset residual to the offset calculated during 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 A covariance matrix updating unit for generating a covariance matrix,
An offset validity determination unit that calculates a first evaluation value indicating an error between the updated offset and the true value of the offset;
It is determined whether or not the first evaluation value exceeds a preset first threshold value, and when the first evaluation value exceeds the first threshold value, the offset and the covariance matrix are initialized. An azimuth angle measuring apparatus comprising: an initialization determination unit that performs processing to perform

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