JP2008298796A - Correction method of geomagnetic sensor, method of measuring offset of geomagnetic sensor, direction data arithmetic device, and portable information terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a correction method of a geomagnetic sensor correcting an offset due to magnetization, for example, by only shaking the geomagnetic sensor on a horizontal plane, and to provide a portable information terminal capable of simplifying operation of the offset correction of the geomagnetic sensor by the use of a direction data arithmetic device which corrects the geomagnetic sensor. <P>SOLUTION: A user pushes a correction button (trigger ON) (Step Sa1). Geomagnetic field measurements are directed. (Step Sa2). Measurement data are read (Step Sa3), and stored in RAM (Step Sa4). It is decided whether a predetermined number of pieces of data are stored in the RAM (Step Sa5). When the storage of the data is completed (Step Sa7) after waiting every 0.1 sec (Step Sa6), offset estimation is performed. It is decided whether an estimated offset amount is effective (Step Sa8), and the offset amount is updated when effective (Step Sa9). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a correction method for a geomagnetic sensor for correcting an offset of a geomagnetic sensor, a method for measuring an offset of a geomagnetic sensor, an azimuth data calculation device, and a portable information terminal using the same.

When a conventional geomagnetic sensor is mounted inside a mobile phone (portable information terminal), there is a magnetic field leaking from a speaker mounted on the mobile phone or a metal package of a magnetized electronic component. Will also be detected. As a result, in a mobile phone equipped with a geomagnetic sensor to detect geomagnetism, the orientation calculated based on the magnetic field existing inside the mobile phone may not show an accurate orientation.

For example, in a mobile phone having a sensitivity direction in two orthogonal axes (X-axis and Y-axis directions) and a geomagnetic sensor having the same sensitivity in each direction, the angle between the geomagnetism vector and the X-axis Assuming that θ, the detection value Vx of the geomagnetic sensor in the X-axis direction and the detection value Vy of the geomagnetic sensor in the Y-axis direction are expressed by (Equation 1) and (Equation 2) because of the magnetic field existing inside the mobile phone. As described above, the output is a state in which m and n corresponding to the magnetization amount in the X-axis direction or the Y-axis direction are added.
Vx = R × cos θ + m (Formula 1)
Vy = R × sin θ + n (Formula 2)
(However, R is a proportional constant)

In other words, in a situation where there is no geomagnetism fluctuation, that is, when a constant external magnetic field is applied, if a non-magnetized geomagnetic sensor placed in a fixed location makes one revolution, the detection value of the geomagnetic sensor will change to the center coordinate. Draw a perfect circle with (0,0). Hereinafter, a circle drawn by the detection value of the geomagnetic sensor is referred to as an azimuth circle. On the other hand, when the magnetized geomagnetic sensor makes one rotation, as shown in FIG. 21, the detection value of the geomagnetic sensor draws a perfect circle having the center coordinates (m, n).
By obtaining the center coordinates of the azimuth circle, the amount of magnetization magnetized in the geomagnetic sensor is obtained equivalently, and the detected value is obtained by subtracting the center coordinate value (correction value) from the detected value of the geomagnetic sensor. A method of correcting and obtaining the direction is used.

Specifically, first, the center coordinate value is obtained. For example, while rotating the geomagnetic sensor horizontally in a plane including the sensitivity direction, the detected values in the X-axis direction and the Y-axis direction of the geomagnetic sensor are obtained for all directions, and the maximum and minimum values for these detected values are obtained. Set the values to Xma
Assuming x, Ymax, Xmin, and Ymin, the center coordinates (m, n) can be obtained by the following equation.
m = (Xmax + Xmin) / 2 (Formula 3)
n = (Ymax + Ymin) / 2 (Formula 4)
Further, the detected value (X1, Y1) when the geomagnetic sensor is moved to a predetermined position A and the output value (X2, Y1) when moved to a position D in the opposite direction of 180 ° while keeping horizontal from there. Y2
) And the average value thereof, the center coordinates (m, n) can be obtained by the following equation.
m = (X1 + X2) / 2 (Formula 5)
n = (Y1 + Y2) / 2 (Formula 6)
Next, the center coordinate value is subtracted by calculation to perform correction. Based on the center coordinates (m, n) obtained as described above, the detected value Vx of the geomagnetic sensor in the X-axis direction, and the detected value Vy of the geomagnetic sensor in the Y-axis direction, the azimuth angle θ is expressed as follows: Ask for.
When | Vy−n | <| Vx−m |, Vx−m> 0,
θ = tan−1 ((Vy−n) / (Vx−m)) (Expression 7)
When | Vy−n |> | Vx−m |, Vy−n> 0,
θ = 90 [deg] −tan−1 ((Vx−m) / (Vy−n)) (Expression 8)
When | Vy−n | <| Vx−m |, Vx−m <0,
θ = 180 [deg] −tan−1 ((Vy−n) / (Vx−m)) (Equation 9)
When | Vy−n |> | Vx−m |, Vy−n <0,
θ = 270 [deg] −tan−1 ((Vx−m) / (Vy−n)) (Equation 10)

However, in the above-described conventional correction method of the geomagnetic sensor, the magnetized state of the geomagnetic sensor always fluctuates. Therefore, whenever the geomagnetic sensor is considered to be magnetized, the user must detect the maximum value of the detected value of the geomagnetic sensor, In order to obtain the minimum value, it is necessary to rotate the mobile phone one or more times. In particular, it is difficult to rotate the mobile phone more than one turn while keeping it horizontal, and sometimes it may be dropped, and even if it is not dropped, the acquired data will be coarse and dense, and the offset will not be required accurately There was a problem. Therefore, the conventional geomagnetic sensor correction method described above has a problem that it is not suitable for portable devices.

Corresponding to this, for example, in Patent Document 1, the magnetic field determination means determines whether or not the strength of the magnetic field detected by the magnetic sensor is out of a predetermined range. An electronic azimuth meter that demagnetizes the magnetized magnetic sensor by determining that the magnetic sensor is magnetized and applying an alternating attenuation magnetic field using a coil that applies a bias magnetic field to the magnetic sensor during measurement is described. ing. However, the invention according to the publication generates a magnetic field in a certain direction with respect to the direction of the electronic compass regardless of the direction of the geomagnetism, such as a permanent magnet, inside the electronic compass. The magnetic compass can be demagnetized, but when the electronic compass moves in the geomagnetism, a soft magnetic material, such as a lead of an electronic component, which is a ferromagnetic material that can be magnetized and demagnetized relatively easily Since the generated induced magnetic field cannot be demagnetized, the above-described problem cannot be solved.

Patent Document 2 discloses that the amount of magnetization of the geomagnetic sensor is large without being rotated by determining whether or not a signal input to the calculation means from the geomagnetic sensor is out of a predetermined determination area. An azimuth detection device that recognizes and warns about it is described.
However, the invention according to this publication is an invention that detects and warns that the amount of magnetization of the magnetic sensor is large, and does not disclose a specific method for correcting the output, thus solving the above-described problem. It is not possible.

Further, in Patent Document 3, the detection value of the magnetic sensor for a predetermined uniform magnetic field is adjusted to a constant value in a state where the above-described soft magnetic body is not in the vicinity, and then the soft magnetic body is in the vicinity. In the existing situation, find the correction coefficient from the detection value when there is a magnetic field from the sensitivity axis direction,
There is described a magnetic detection method for correcting the output by the above-described induced magnetic field by canceling out the induced magnetic field generated around the soft magnetic material by a predetermined calculation formula based on this. However, since the invention according to the publication does not disclose a specific method for when correction is necessary and at what timing, the above-described problem cannot be solved. Can not.

In Patent Document 4, a magnetic field generator that can generate a magnetic field stronger than the geomagnetism is used to generate a magnetic field for adjustment while changing the strength according to a predetermined sequence. An adjustment method for an electronic compass is described, in which adjustment data is acquired and adjusted by a sequence for acquiring. However, the invention according to the publication has a problem that a magnetic field generator for applying an external magnetic field is required separately from the electronic compass.
JP-A-6-174472 JP-A-6-249663 Japanese Patent Laid-Open No. 7-151842 JP 2002-48551 A

Accordingly, the present invention has been made in consideration of the above circumstances, and an object thereof is, for example, a correction method for a geomagnetic sensor that corrects an offset due to magnetization by simply shaking the geomagnetic sensor on a horizontal plane, and a geomagnetic sensor. It is an object of the present invention to provide a portable information terminal capable of simplifying an operation for correcting an offset of a geomagnetic sensor using an azimuth data calculation device that corrects the above.

In order to achieve the above object, the present invention proposes the following means.
The present invention provides a geomagnetic sensor having a biaxial or triaxial sensitivity direction, an inclination sensor, first storage means for storing measurement data of the geomagnetic sensor and inclination angle data of the inclination sensor, and the geomagnetic sensor. A correction method for a geomagnetic sensor in a portable information terminal equipped with a correction means for correcting an offset due to magnetization of the magnetic field, wherein the measurement data of the geomagnetic sensor and the tilt angle data of the tilt sensor are read at predetermined time intervals. 1 and when the difference value between the current inclination angle data at a certain time and the past inclination angle data stored in the first storage means immediately before the time is a predetermined value or more, A second step of storing current tilt angle data and measurement data of the geomagnetic sensor read simultaneously with the tilt angle data in the first storage means; Repeating the first and second steps, the measurement data storage step for storing the measurement data of the geomagnetic sensor and the inclination angle data of the tilt sensor, and the offset measurement value is estimated based on the stored measurement data of the geomagnetic sensor And a step of correcting the geomagnetic sensor.

  In the correction method for the geomagnetic sensor, the present invention calculates distances on the coordinates of the accumulated measurement data of the geomagnetic sensor and the estimated offset measurement value, and further calculates an average value of the calculated distances. Calculating the average value, calculating the standard deviation based on the calculated individual values of the distances and the average value of the distances, and the effectiveness of the offset measurement values based on the calculated standard deviations And an effectiveness determination step for determining.

  The present invention is characterized in that, in the correction method of the geomagnetic sensor, the offset measurement value is stored in a second storage means when the offset measurement value is determined to be valid in the validity determination step. And

  The present invention is characterized in that the method for correcting a geomagnetic sensor includes a step of notifying the user of the fact that the offset measurement value is determined to be invalid in the validity determination step.

  The present invention includes a step of asking whether the user wishes to correct the offset measurement value after notifying the user that the offset measurement value is not valid in the correction method for the geomagnetic sensor. The offset measurement value is estimated again after performing the above.

  The present invention is an azimuth data calculation device comprising a geomagnetic sensor having a biaxial or triaxial sensitivity direction, an inclination sensor, and a correction means for correcting an offset due to magnetization of the geomagnetic sensor, wherein the correction The means reads out the measurement data of the geomagnetic sensor and the inclination angle data of the inclination sensor at predetermined time intervals, and reads out the current inclination angle data read at a certain time and immediately before the time. A first value for storing the current inclination angle data and the measurement data of the geomagnetic sensor read simultaneously with the inclination angle data when a difference value from the previous inclination angle data is a predetermined value or more; Storage means, and offset estimation means for estimating an offset measurement value based on measurement data of the plurality of geomagnetic sensors stored in the first storage means. A direction data calculation unit to.

The present invention is an azimuth data calculation device comprising a geomagnetic sensor having a biaxial or triaxial sensitivity direction, an inclination sensor, and a correction means for correcting an offset due to magnetization of the geomagnetic sensor, wherein the correction The means reads out the measurement data of the geomagnetic sensor and the inclination angle data of the inclination sensor at predetermined time intervals, and reads out the current inclination angle data read at a certain time and immediately before the time. A first value for storing the current inclination angle data and the measurement data of the geomagnetic sensor read simultaneously with the inclination angle data when a difference value from the previous inclination angle data is a predetermined value or more; Storage means; offset estimation means for estimating an offset measurement value based on measurement data of the plurality of geomagnetic sensors stored in the first storage means; and Validity determination means for determining the validity of the set measurement value, wherein the validity determination means includes the measurement data of the plurality of geomagnetic sensors stored in the first storage means and the estimated offset measurement. A distance on a coordinate with each value, and further, an average value calculating means for calculating an average value of the calculated distances, an individual value of the calculated distances, and an average value of the distances A standard deviation calculating means for calculating the standard deviation
An azimuth data calculation device comprising: a determination unit that determines the validity of the offset measurement value based on the standard deviation calculated by the standard deviation calculation unit.

  According to the present invention, in the above azimuth data calculation device, the correction unit includes an offset storage unit that stores the offset measurement value when the validity determination unit determines that the offset measurement value is valid. And

  The present invention is a portable information terminal including any one of the above-described azimuth data calculation devices.

According to the present invention, since the user can correct the offset of the output of the geomagnetic sensor without rotating the portable information terminal, the geomagnetism can be performed by a simple operation without checking the manual of the portable information terminal. There is an effect that the offset of the output of the sensor can be corrected.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 2, the mobile phone having the configuration shown in FIG. 1 includes a casing 1 having operation keys and a casing 2 having a liquid crystal display unit. 2A shows a case 1 and a case 2 of the mobile phone.
FIG. 2B is a front view of the case 2 when the case 1 and case 2 of the mobile phone are closed, and FIG. In the same state, the housing 1 and the housing 2
FIG. 2D is a back view of the housing 1 in the same state. Note that FIG.
As shown to (a), the X-axis along the short side of the housing | casing 1 and the Y-axis along the long side of the housing | casing 1 are assumed. The X axis and the Y axis are orthogonal to each other.

Here, each surface of each housing of the mobile phone is defined as follows. That is, the surface having the operation keys of the housing 1 is defined as the operation surface, and the surface opposite to the operation surface is defined as the back surface. Moreover, let the surface in which the liquid crystal display part 18a is provided among the surfaces of the housing | casing 2 be a main display surface, and let the surface opposite to a main display surface be a front surface.

As shown in FIG. 1, the mobile phone includes an RF (Radio Frequency) antenna 8 and a control unit 1.
0 (control means), ROM (Read Only Memory) 12, RAM (Random Access Memory)
) 14 (first storage means) (second storage means), display units 18a and 18b, key input unit 20, changeover switch 21, modem unit 22, and CDMA (Code Division Multiplex)
Access) unit 23, RF unit 24, microphone 27, incoming call speaker 28, and voice processing unit 2
9, geomagnetic sensor 30, GPS (Global Positioning System) receiver 71, G
A PS antenna 72, an acceleration sensor 80 that detects acceleration applied to the mobile phone, and a bus line 90 are included.

The control unit 10 controls each unit of the mobile phone by executing a telephone function program and other programs. Further, the azimuth is calculated by inputting the measurement data of the geomagnetic sensor 30 (azimuth data calculation device). The ROM 12 stores various telephone function programs and control programs at the time of transmission and reception executed by the control unit 10 and other various fixed data. The RAM 14 is set with a work area for temporarily storing data and the like used during operation of the control unit 10.

The RF unit 24 performs frequency conversion of the signal received by the RF antenna 8. The modem unit 22 demodulates the output signal and outputs it to the CDMA unit 23. The CDMA unit 23 performs spread spectrum or despread as follows. That is, CDM
The A unit 23 despreads the output signal of the modulation / demodulation unit 22, extracts the signal before spreading, and outputs it to the audio processing unit 29. In addition, the CDMA unit 23 spreads the output signal of the audio processing unit 29 and outputs it to the modem unit 22. The modem unit 22 receives a signal to be transmitted to the outside from the CDMA unit 23, performs modulation, and outputs the modulated signal to the RF unit 24. The RF unit 24 converts the frequency of the signal and transmits it from the RF antenna 8.

As shown in FIG. 2A, the key input unit 20 has a start key 3 used when receiving a call.
, An end key 4 used for ending the telephone call, a numeric keypad 5 composed of numerical keys and code keys, a redial key 7 and a changeover switch 21.

The display units 18a and 18b are configured to display text information of text created when an e-mail is transmitted, various data including contents of various menus, and detailed contents thereof. The display unit 18 a is provided on the operation surface of the housing 1, and the display unit 18 b is provided on the front surface of the housing 2.
The audio processing unit 29 includes an encoding unit (CODER) as an encoding unit and a decoding unit (DECODER) as a decoding unit, and decodes the audio signal output from the CDMA unit 23, Output to the receiving speaker. Further, the audio signal for transmission input from the microphone 27 is compression-coded and output to the CDMA unit 23.

The GPS receiver 71 receives signals transmitted from a plurality of GPS satellites constituting the GPS by the connected GPS antenna 72, demodulates the signals received from the GPS satellites, and performs the navigation based on the demodulated signals. The current position of the apparatus is calculated, and the position information (latitude / longitude) is obtained and output to the control unit 10. The process for calculating the current position is the same as the process performed in a conventional car navigation system or the like.

As shown in FIG. 3, the geomagnetic sensor 30 is an LSI having a square shape having sides along the X axis and the Y axis orthogonal to each other and having a small thickness in the Z axis direction orthogonal to the X axis and the Y axis.
(Large Scale Integration) Si substrate 30a and substrate 3
A total of eight GMR (Giant Magnetoresistive) elements 31 to 38 formed on 0a, and coils 31 to 38 for initialization that apply an initialization magnetic field to GMR elements 31 to 38, respectively.
48 and drive circuits 51 to 58 that are connected to the coils 41 to 48 and apply a predetermined voltage to both ends of the coils 41 to 48, respectively. A temperature sensor 60 for monitoring the temperature of the geomagnetic sensor 30 is provided on the substrate 30a.

The first GMR element 31 in the X-axis direction is formed in the vicinity of the end in the negative direction of the X-axis below the center in the Y-axis direction of the substrate 30a, and the pinned layer in which the magnetization direction is fixed (pinned). In the (pinned layer), the direction of pinned magnetization is the negative direction of the X axis. G in the second X-axis direction
The MR element 32 is formed near the end of the negative direction of the X axis above the center in the Y axis direction of the substrate 30a, and the pinned magnetization direction is the negative direction of the X axis. The third XMR direction GMR element 33 is formed in the vicinity of the positive end of the X axis above the center in the Y axis direction of the substrate 30a, and the direction of magnetization pinned in the pinned layer is the X axis. It is the positive direction. The fourth GMR element 34 in the X-axis direction is formed in the vicinity of the positive end of the X-axis below the center in the Y-axis direction of the substrate 30a, and the direction of magnetization pinned in the pinned layer is the X-axis. It is the positive direction.

Also, the first Y-axis direction GMR element 35 is formed in the vicinity of the positive end of the Y-axis to the left of the central portion in the X-axis direction of the substrate 30a and pinned in the pinned layer. Is the positive direction of the Y axis. The second GMR element 36 in the Y-axis direction is formed near the end of the positive direction of the Y-axis to the right of the center in the X-axis direction of the substrate 30a, and the magnetization direction pinned in the pinned layer is Y The axis is in the positive direction. The third GMR element 37 in the Y-axis direction is formed near the end in the negative direction of the Y-axis to the right of the center in the X-axis direction of the substrate 30a, and the magnetization direction pinned in the pinned layer is Y The axis is in the negative direction. G in the fourth Y-axis direction
The MR element 38 is formed near the end of the negative direction of the Y axis to the left of the central portion in the X axis direction of the substrate 30a, and the direction of magnetization pinned in the pinned layer is the negative direction of the Y axis. Yes.

The GMR elements 31 to 38 have the same structure except for the position and orientation arranged on the substrate 30a. Therefore, in the following, the GMR element 31 in the first X-axis direction will be described as a representative example.

As shown in FIGS. 5 and 6, the first XMR direction GMR element 31 shown in FIG. 4 includes a plurality of narrow strips 31a made of a spin valve film SV and having a longitudinal direction in the Y-axis direction. 31a
And cobalt (Co) chromium (below the both ends in the Y-axis direction of each narrow strip portion 31a (
Cr) is a hard ferromagnetic material such as platinum (Pt), and includes bias magnet films (hard ferromagnetic thin film layers) 31b... 31b made of a material having a high coercive force and a high squareness ratio. Each narrow strip portion 31a extends in the X-axis direction on the upper surface of each bias magnet film 31b and is adjacent to the narrow strip portion 3a.
It is joined to 1a.

As shown in FIG. 7, the spin valve film SV of the GMR element 31 in the first X-axis direction includes a free layer (free layer, free magnetic layer) F, a film stacked in order on the substrate 30a. The thickness is 2.4
Conductive spacer layer S, pinned layer P and film thickness of 2 nm (24 cm) copper (Cu)
. A capping layer C made of 5 nm (25 cm) titanium (Ti) or tantalum (Ta) is included.

The free layer F is a layer whose magnetization direction changes according to the direction of the external magnetic field. The free layer F is formed on the substrate 30a and has a film thickness of 8 nm (80 cm), cobalt (Co) zirconium (Zr) niobium (Nb). The amorphous magnetic layer 31-1 and the nickel (Ni) iron (Fe) magnetic layer 31- having a thickness of 3.3 nm (33Å) formed on the CoZrNb amorphous magnetic layer 31-1.
2 and a CoFe layer 31-3 having a thickness of about 1 to 3 nm (10 to 30 mm) formed on the NiFe magnetic layer 31-2. CoZrNb amorphous magnetic layer 31-1 and N
The iFe magnetic layer 31-2 constitutes the soft ferromagnetic thin film layer described above. CoFe layer 31
-3 prevents diffusion of Ni in the NiFe layer 31-2 and Cu31-4 in the spacer layer S. In order to maintain the uniaxial anisotropy of the free layer F, the bias magnet film 31b... 31b is in the Y-axis direction (the Y-axis negative direction indicated by the wide arrow in FIGS. 4 and 5). Direction).

The pinned layer P includes a CoFe magnetic layer 31-5 with a film thickness of 2.2 nm (22 mm), and 45 Pt.
A film thickness of 24 nm (240 mm) formed from a Pt manganese (Mn) alloy containing ˜55 mol%
The antiferromagnetic films 31 to 36 are superposed. The CoFe magnetic layers 31 to 35 are back-coupled to the magnetized (magnetized) antiferromagnetic films 31 to 36 in an exchange coupling manner, so that the magnetization direction is pinned in the negative direction of the X axis as described above. ing.

As shown by the solid line in FIG. 8, the first XMR direction GMR element 31 configured in this way is external in the range of −Hc to + Hc with respect to the external magnetic field changing along the X axis. It exhibits a resistance value that varies substantially in proportion to the magnetic field, and exhibits a substantially constant resistance value with respect to an external magnetic field that varies along the Y axis, as indicated by a broken line in FIG.

In this geomagnetic sensor 30, as shown in FIG. 9, GM in the first to fourth X-axis directions.
By connecting the R elements 31 to 34 with a full bridge, a geomagnetic sensor in the X-axis direction that detects a magnetic field in the X-axis direction is configured. In FIG. 9, arrows attached to the GMR elements 31 to 34 indicate the magnetization directions in which the pinned layers of the GMR elements 31 to 34 are pinned. In such a configuration, the coupling point Va between the GMR element 32 in the second X-axis direction and the GMR element 33 in the third X-axis direction, the GMR element 31 in the first X-axis direction, and the fourth X-axis A constant potential difference is applied between the coupling point Vb with the GMR element 34 in the direction, and the GMR element 31 in the first X-axis direction and the third X
The coupling point Vc with the GMR element 33 in the axial direction, the GMR element 32 in the second X-axis direction, and the fourth X
A potential difference (Vc−Vd) between the coupling point Vd and the axial GMR element 34 is taken out as a sensor output Vout.

As a result, the geomagnetic sensor in the X-axis direction changes substantially in proportion to the external magnetic field in the range of −Hc to + Hc with respect to the external magnetic field changing along the X-axis, as shown by the solid line in FIG. As shown by the broken line in FIG. 10, the output voltage Vxout is substantially “0” for the external magnetic field changing along the Y axis.

The geomagnetic sensor in the Y-axis direction is configured by full-bridge connection of the GMR elements 35 to 39 in the first to fourth Y-axis directions, and changes along the Y-axis, like the geomagnetic sensor in the X-axis direction. In the range of −Hc to + Hc, an output voltage Vyout that changes substantially in proportion to the external magnetic field is shown, and an external magnetic field that changes along the X axis is substantially “0”.
"Indicates the output voltage. As described above, the geomagnetic sensor 30 detects an external magnetic field. The geomagnetic sensor 30 performs temperature compensation of magnetic characteristics based on temperature information obtained by the temperature sensor 60 using a temperature compensation circuit (not shown).

Next, the principle of the azimuth measuring method of the azimuth data calculation device of the mobile phone will be described on the assumption that the operation surface of the mobile phone is placed in a substantially horizontal state and the external magnetic field applied to the geomagnetic sensor 30 is only geomagnetism. Here, the orientation ang of the mobile phone is a vector from the front portion of the mobile phone operation surface (for example, the microphone 27) toward the center of the connection portion when the operation surface of the case 1 of the mobile phone is substantially horizontal. That is, the direction of the vector directed in the positive direction of the Y axis.
In the present specification, the reference (0 °) of the azimuth ang is west, and the azimuth ang is north,
It is defined as 90 °, 180 ° and 270 °, respectively, as it rotates in the order of East and South.

By the way, geomagnetism is a magnetic field from south to north. Therefore, when the operation surface of the casing 1 of the cellular phone is substantially horizontal, the outputs of the geomagnetic sensor 30 in the X-axis direction and the geomagnetic sensor in the Y-axis direction of the geomagnetic sensor 30 are as shown in FIG. It changes in a cosine wave shape and a sine wave shape with respect to 10 directions ang. It is assumed that the sensor outputs Sx and Sy in FIG. 11 are standardized. Normalization means that the actual output of the geomagnetic sensor in the X-axis direction is half of the difference between the maximum value and the minimum value when rotated 360 ° with the operation surface of the casing 1 of the mobile phone being almost horizontal. The value divided by is used as the normalized output Sx. Similarly, normalization refers to the maximum and minimum outputs when the actual output of the geomagnetic sensor in the Y-axis direction is rotated 360 ° with the operation surface of the casing 1 of the mobile phone being substantially horizontal. The value divided by half of the value difference is used as the normalized output Sy.

From the above, the azimuth ang of the mobile phone can be obtained in the following cases (a) to (d).
(A) For Sx and Sy, if Sx> 0 and | Sx |> | Sy |
g = tan-1 (Sy / Sx).
(B) When Sx <0 and | Sx |> | Sy | are satisfied, ang = 180 ° + tan−
1 (Sy / Sx).
(C) If Sy> 0 and | Sx | <| Sy | is satisfied, ang = 90 ° −tan−1
(Sx / Sy).
(D) When Sy <0 and | Sx | <| Sy | is satisfied, ang = 270 ° −tan−
1 (Sx / Sy).
However, when the azimuth ang obtained by any one of the above (a) to (d) is negative, a value obtained by adding 360 ° to the same azimuth ang is defined as the azimuth ang. Further, the obtained bearing ang is 360.
If the angle is greater than or equal to °, the value obtained by subtracting 360 ° from the same direction ang is defined as the direction ang.

However, as described above, many permanent magnet parts are included in the mobile phone as represented by the speaker 28, and a magnetic field leaks from these parts. For this reason, the geomagnetic sensor 30 disposed at a predetermined location in the mobile phone has a leakage magnetic field (
An external magnetic field other than geomagnetism is added. As a result, the output of the geomagnetic sensor in the X-axis direction is shifted (translated) by an output corresponding to the X-axis component of the leakage magnetic field. Similarly, the output of the geomagnetic sensor in the Y-axis direction is the Y-axis component of the leakage magnetic field. The output is shifted according to. This output shift is called an offset, and the amount of shift in each of the X-axis direction and the Y-axis direction is used as an offset measurement value. Therefore, in order to measure an accurate azimuth in a cellular phone, it is necessary to perform output correction such as subtracting the offset measurement value described above from the output values of the X axis and the Y axis. Here, as described above, the offset measurement value is actually measured at each point because of the influence of the soft ferromagnet inside the mobile phone, and it is necessary to determine its effectiveness.

Next, the principle of the method for estimating the offset measurement value and determining the effectiveness as described above in the azimuth data calculation apparatus when the geomagnetism and the leakage magnetic field are applied to the geomagnetic sensor 30 as the external magnetic field will be described.
The mobile phone is configured to measure external magnetism at predetermined time intervals. Then, as shown in FIG. 12, the mobile phone is shaken on a single plane such as a horizontal plane including the X-axis and Y-axis sensitivity directions, and during that time, the external magnetism is measured at a plurality of measurement points. The effectiveness of the estimated offset measurement value is determined from the measurement data.

Here, if the offset measurement values to be obtained are Xo, Yo, and the radius of the azimuth circle drawn by plotting the values output by the geomagnetic sensor 30 is R, the following relationship is established.
(X-Xo) 2 + (Y-Yo) 2 = R2
∴R2 -Xo2 -Yo2 + 2XXo + 2YYo = X2 + Y2 (Formula 11)
)
In addition, the external magnetism measured at the measurement point is expressed by coordinate values (Xi, Yi) (i = 1, 2).
, 3,..., N), the least square error ε is defined as follows. Then, the offset measurement value is estimated by obtaining the origin of the azimuth circle of the geomagnetic sensor 30 by the least square method for calculating the coordinate value that minimizes the least square error ε (offset estimation step).
(Offset estimation means).

Here, ai = (Xi2 + Yi2), bi = -2Xi, ci = -2Yi, D = (Xo2)
If + Yo2) -R2, then [Equation 2] is obtained.

At this time, the condition for minimizing the least square error ε is expressed as [Equation 3] by making Xo, Yo, Zo and D independent variables of ε and differentiating ε with Xo, Yo, Zo and D.

Further, the offset measurement value X can be obtained by solving the following equation from (Expression 14) to (Expression 16).
o, Yo are required. The coordinates (Xo, Yo) obtained from Xo, Yo are the origin (center point) of the azimuth circle.

但し、［数4］において、［数5］に示した表記を用いている。

However, in [Formula 4], the notation shown in [Formula 5] is used.

Next, a method for obtaining the standard deviation σ will be described. Each measurement value mi that is offset measurement data and each measurement point data and the average value A for each measurement value mi that is the distance between the origin of the azimuth circle obtained from the offset measurement value are calculated (average value calculation step) (average Value calculation means) (standard deviation calculation means). First, each measurement value mi includes measurement data (Xi, Yi) indicating external magnetism measured at a measurement point, and an origin of an azimuth circle that is an offset measurement value (
(Center) (Xo, Yo).

  Next, an average value of the measured values mi is calculated.

Based on these, the standard deviation is expressed by the following formula by mi and A.

  In addition, the standard deviation is

Therefore, [Expression 6] is applied to this, and the standard deviation uses the radius of the azimuth circle obtained by using the estimated offset measurement value (Xo, Yo) and the measurement data (Xi, Yi). And
[Expression 10]

Next, the effectiveness of the estimated offset measurement values (Xo, Yo) is determined (determination means) (effectiveness determination step).

If many distributions of the measurement data constituting the azimuth circle output from the geomagnetic sensor 30 are large with respect to the average radius, the measurement data is invalid, and the standard deviation is determined by the following formula. The effectiveness of the offset measurement value is determined on condition that the value is smaller than the value.
σ <F (Formula 22)

At this time, in the geomagnetic sensor, since it is a normal requirement specification that 16 orientations can be discriminated, the error of the offset measurement value needs to be within an amount corresponding to 1/5 of the geomagnetism. Therefore, it is determined that the azimuth circle radius should be within 1/5 of the terrestrial magnetism when the azimuth radius is 2σ, and thus F corresponds to 0.03 Oe (Oersted), which is 1/10 of the terrestrial magnetism. The amount will be preferred.

Next, the offset calibration operation of the geomagnetic sensor 30 by the mobile phone orientation data calculation device according to the present embodiment will be described. Offset calibration refers to measuring external magnetism, calculating an offset value based on the obtained measurement data, and updating (setting) the calculated offset value as an offset of the geomagnetic sensor.
First, the power of the mobile phone is turned on, and the operation of the mobile phone starts. Hereinafter, the offset calibration operation of the geomagnetic sensor 30 of the mobile phone will be described with reference to the flowchart shown in FIG. Note that it is assumed that the offset measurement value obtained in the previous operation is stored in the RAM 14.

First, a calibration start button (trigger key) for instructing offset calibration is turned on in the mobile phone (step Sa1), and the control unit 10 instructs the geomagnetic sensor 30 to measure external magnetism (step Sa2). ). Next, the control unit 10
Reads the measurement data from the geomagnetic sensor 30 (step Sa3) and stores the data in the RAM1.
4 (step Sa4). Next, the control unit 10 determines whether or not the number of data stored in the RAM 14 has reached a predetermined number. If the determination is “NO”, the number of data stored in the RAM 14 has not yet reached the predetermined number.
. 1 sec. After waiting only (step Sa6), the process returns to step Sa2, and the control unit 10 repeats the operations of the following steps Sa2 to Sa5 (data storage means).

On the other hand, when the determination in step Sa5 is “YES”, the process proceeds to step Sa7, and the control unit 10 estimates the offset measurement value. Next, the control unit 10 calculates the standard deviation σ described above, and determines whether or not the estimated offset measurement value is valid (step Sa8) (validity determination step) (validity determination means). . Judgment is “Y
If it is “ES”, the offset measurement value is stored in the RAM 14 under the control of the control unit 10 (step Sa9) (offset storage means). The offset measurement value previously stored in the RAM 14 is updated to the offset measurement value calculated in step Sa9 under the control of the control unit 10.
Then, the offset calibration operation of the geomagnetic sensor 30 of the mobile phone ends. On the other hand, if the determination in step Sa8 is “NO”, the offset measurement value stored in the RAM 14 is not updated, and the geomagnetic sensor 30 of the cellular phone is updated.
This completes the offset calibration operation. At this time, the offset measurement value updated in the previous calibration operation and stored in the RAM 14 is used as the offset measurement value.

As described above, according to the present embodiment, the offset calibration of the geomagnetic sensor can be performed by a simple operation without referring to a detailed manual, and the mobile phone determines the success or failure of the offset calibration. Only when proper calibration is performed, the offset measurement value can be updated. For this reason, the measurement data can be reliably corrected by a simple operation.

In this embodiment, a biaxial geomagnetic sensor is assumed as the geomagnetic sensor.
A similar operation can be realized using an axial geomagnetic sensor. In this case, in the biaxial geomagnetic sensor, offset calibration can be performed by swinging left and right in a plane including two sensitivity directions, whereas in the three axes, as shown in FIG. The offset calibration can be performed by shaking in a plane including two sensitivity directions (for example, left and right) and in another plane including a sensitivity direction different from the above (for example, up and down).
As shown in FIG. 15, when the mobile phone is arranged on the paper surface, the direction is perpendicular to the paper surface when the geomagnetism is in a special positional relationship such as running in the lateral direction of the paper surface. Even if the mobile phone is shaken up and down (front and back), the relative relationship between the geomagnetic sensor and the geomagnetism does not change. In such a case, the offset can be calibrated by shaking in another direction. .

Further, even when the offset calibration described above is performed in the biaxial geomagnetic sensor, as shown in FIG. 16, when the geomagnetism runs in the direction perpendicular to the paper surface,
The relative positional relationship between the geomagnetic sensor and the geomagnetism does not change even if the sensor is shaken as illustrated. However, in this case as well, the offset is calculated and correctly obtained assuming that the geomagnetic sensor outputs an azimuth circle having a radius of zero.

In this embodiment, a GMR element is assumed as the geomagnetic sensor. However, the type of the geomagnetic sensor is not limited to this, but a TMR (Tunneling Magnetoresistive) element, MR
Magnetoresistive elements such as (Magnetoresistive) elements, Hall elements, MI (Magneto Impeda)
nce) Any element, flux gate sensor, etc. may be used.
In particular, an element such as a Hall element that has a severe temperature change can be used to correct an offset change due to temperature. An element that is easily magnetized, such as an MI element, is effective as means for removing the influence of the element itself.

Next, a second embodiment of the present invention will be described.
The block configuration of the mobile phone in the second embodiment is the same as that of the first embodiment, but the offset calibration process of the control unit 10 is different from that of the first embodiment. Hereinafter, this embodiment will be described with reference to the drawings.

As shown in FIG. 17, first, steps Sb1 and Sb2 are performed. This process is
This is the same as the processing of steps Sa1 to Sa2 shown in FIG. Next, the control part 10 reads measurement data from the geomagnetic sensor 30 (step Sb3) (data reading means). (Step Sb3) (data reading means). Next, in Step Sb3, the geomagnetic sensor 30
The data to be stored in the RAM 14 by determining whether the distance on the coordinates between the current measurement data read from the previous measurement data and the previous measurement data already read is greater than or equal to a predetermined value. Is determined (step Sb4) (data storage determination means). The determination method will be described later. If the determination is “YES”, the process proceeds to step Sb5, and the current data is stored in the RAM 14 (step Sb6) (data storage means). And R
It is determined whether the number of data stored in the AM 14 has reached a predetermined number. If the determination is “NO”, since the number of data stored in the RAM 14 has not yet reached a predetermined number, 0.1 sec. After waiting (step Sb7)
Returning to b2, the operations of the following steps Sb2 to Sb6 are repeated.

On the other hand, if the determination in step Sb4 is “NO”, the process proceeds to step Sb7, and 0.1 sec. After waiting for only step Sb2, the following steps Sb2 to Sb are performed.
Repeat the operation of b6.

On the other hand, if the determination in step Sb6 is “YES”, the process proceeds to step Sb8, and steps Sb8 to Sb10 are performed. This process is performed in step S shown in FIG.
This is the same as the processing of a7 to Sa9. With the above processing, the offset calibration operation of the geomagnetic sensor 30 of the mobile phone is completed.

Next, the data read from the geomagnetic sensor 30 in step Sb3 is stored in the RAM 14.
A method for determining whether or not the data is to be stored in step Sb4 will be described. Here, the RAM 14 immediately before collecting the data to be stored as X, Y and data X, Y.
The data X and Y are stored in the RAM 14 only when the following conditions are satisfied, with the data stored in X being Xp and Yp.

As described above, according to the present embodiment, the following problems can be avoided. That is, in the first embodiment, when the user hardly moves the mobile phone, the data is concentrated near one point where the data is taken in, the speed at which the user moves the mobile phone is not uniform, and the data density The problem of unevenness can be avoided.

Here, the number of measurement points is desirably 20 points or more when the measurement range (rotation angle of the geomagnetic sensor) is 90 °. Therefore, the distance between the measurement points on the coordinates is the azimuth radius. It is necessary to be smaller than 1/10. As described above, the process of reading data from the geomagnetic sensor 30 is not performed every certain time interval, and the geomagnetic sensor 30 is rotated at such a rotation angle that the distance between measurement points is made smaller than 1/10 of the azimuth radius. It may be done by turning.

Next, a third embodiment of the present invention will be described.
The block configuration of the mobile phone in the second embodiment is the same as that in the first to second embodiments, but the offset calibration processing of the control unit 10 is a combination of the first and second embodiments. It has become. Hereinafter, this embodiment will be described. In addition, about a flowchart, FIG. 13 and FIG. 17 shall be combined and illustration is abbreviate | omitted.

At this time, steps Sa2 to Sa6 in FIG. 13 and step S in FIG.
When the process from b2 to Sb7 is performed in parallel and the number of data stored in the RAM 14 by any one process exceeds a predetermined number, step Sa7 or step Sb8 is performed.
Perform offset estimation at. However, the predetermined number is the number of data obtained by the processing of FIG.
It is necessary to increase the number of data by the processing of No. 7. For example, it is desirable to take the former 10 times the latter.

As described above, according to the present embodiment, the following problems can be avoided. That is, in the second embodiment, as shown in FIG. 16, when a mobile phone having a biaxial geomagnetic sensor is shaken perpendicular to the geomagnetism, the measured value of the geomagnetic sensor does not change more than a certain value. In addition, it is not possible to capture that the mobile phone is being shaken, and the problem that data is not stored in the RAM 14 can be avoided.

Next, a fourth embodiment of the present invention will be described.
The block configuration (FIG. 18) and operation of the mobile phone according to the fourth embodiment are as follows.
Although similar to the third embodiment, a tilt sensor 81 is added as a component. Further, the offset calibration process of the control unit 10 is partially different from that of the second embodiment. Hereinafter, this embodiment will be described with reference to the drawings.

As shown in FIG. 19, a tilt sensor 81 is attached to the mobile phone according to the present embodiment. As an example of the tilt sensor 81, for example, it is attached adjacent to the geomagnetic sensor 30, the fixed electrode and the movable electrode face each other with a certain interval, and the tilt sensor 81 is tilted so that the distance between the movable electrode and the fixed electrode is increased. There is a capacitance change type sensor in which the capacitance value formed by these changes.

Next, the offset calibration operation of the geomagnetic sensor 30 of the mobile phone according to the present embodiment will be described with reference to the flowchart shown in FIG. Note that the offset calibration operation of the geomagnetic sensor 30 of the mobile phone in this embodiment is performed in step S
Since steps other than c3 (steps Sc1 to Sc2, steps Sc4 to Sc10) are the same as steps Sb1 to Sb2 and steps Sb4 to Sb10 in the second embodiment, only the differences will be described.

That is, in step Sc3, the control unit 10 inputs not only the geomagnetism detection result by the geomagnetic sensor 30 but also the tilt detection result by the tilt sensor 81 at a certain time, and the tilt detected by the tilt sensor 81 is input. A difference value between the data and the previously detected inclination data is calculated, and if the calculated difference value is equal to or greater than a predetermined value, the current measurement data is stored in the RAM 14.
Into.

As described above, according to the present embodiment, the following problems can be avoided. In other words, except when the geomagnetism runs perpendicular to the ground, in the second embodiment, when the mobile phone equipped with the biaxial geomagnetic sensor is shaken perpendicular to the geomagnetism, the measurement of the geomagnetic sensor is performed. Since the value does not change more than a certain value, it cannot be recognized that the mobile phone is being shaken, and the problem that the data is not stored in the RAM 14 indefinitely is that the mobile phone is being shaken by the tilt sensor 81. It can be avoided by recognizing. Also,
The data density can also be made uniform in the range swung by the user without depending on the speed swung by the user. The detection result of the tilt sensor 81 can also be used for tilt correction in the azimuth display.

In the present embodiment, a capacitance change type sensor is assumed as the tilt sensor 81.
The type of tilt sensor is not limited to this, and any type may be used.

When it is determined that the estimated offset is not valid, the display unit 18a or 1
You may make it display that in 8b.

Further, after displaying that it is determined that the estimated offset is not valid, the offset calibration may be performed again by a specific key operation.

Further, when the offset calibration is performed again, the newly measured measurement data is compared with the measurement data stored in the RAM 14, and only proper data is stored in the RAM 14.
It is desirable to store in. For example, the newly measured measurement data and the RAM 14
It is desirable to obtain the distance between the measured data stored in each of the measured data and the offset measurement value, and store the data having the distance closer to the average radius of the azimuth circle in the RAM 14.

As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change in the range which does not deviate from the summary of this invention is also included.

It is a block diagram which shows the structure of the mobile telephone in the 1st Embodiment of this invention. It is a figure which shows the external appearance of the mobile telephone in the 1st-3rd embodiment of this invention. It is a schematic plan view of the geomagnetic sensor 30 in the 1st-4th embodiment of this invention. FIG. 4 is a partially enlarged plan view of a GMR element 31 and a coil 41 of the geomagnetic sensor 30 in FIG. 3. FIG. 4 is a plan view of the GMR element 31 in FIG. 3. It is the schematic sectional drawing which cut | disconnected the GMR element 31 and the coil 41 in the plane along the 3-3 line of FIG. FIG. 5 is a diagram showing a spin valve film configuration of the GMR element 31 in FIG. 4. It is the graph which showed the change of the resistance value with respect to the external magnetic field of the GMR element 31 in FIG. FIG. 5 is an equivalent circuit diagram of a geomagnetic sensor in the X-axis direction including the GMR element 31 in FIG. 4 and GMR elements 32 to 34 having the same structure. 10 is a graph showing changes in output voltage with respect to an external magnetic field changing in the X axis direction and a magnetic field changing in the Y axis direction of the geomagnetic sensor in the X axis direction in FIG. 9. It is the graph which showed the output with respect to the direction of the geomagnetic sensor of the X-axis direction in the same embodiment, and the geomagnetic sensor of the Y-axis direction. It is the figure which showed a mode that the mobile telephone in the embodiment was shaken on a single surface like a horizontal surface, for example. 6 is a flowchart showing an offset calibration operation of the geomagnetic sensor 30 in the mobile phone according to the embodiment. It is the figure which showed a mode that the mobile telephone provided with the triaxial geomagnetic sensor in the same embodiment was shaken back and forth. It is the figure which showed a mode that the mobile telephone provided with the triaxial geomagnetic sensor in the same embodiment was shaken perpendicularly to geomagnetism. It is the figure which showed a mode that the mobile telephone provided with the biaxial geomagnetic sensor in the same embodiment was shaken perpendicularly to geomagnetism. It is a flowchart which shows the operation | movement of the calibration of the offset of the geomagnetic sensor 30 in the mobile telephone in the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the mobile telephone in the 4th Embodiment of this invention. It is a figure which shows the external appearance of the mobile telephone in the same embodiment. 6 is a flowchart showing an offset calibration operation of the geomagnetic sensor 30 in the mobile phone according to the embodiment. It is a figure which shows the azimuth | direction circle drawn by the detection value of the conventional geomagnetic sensor.

Explanation of symbols

1, 2 ... casing, 3 ... start key, 4 ... end key, 5 ... numeric keypad, 7 ...
Redial key, 8 ... RF (Radio Frequency) antenna, 10 ... Control unit (azimuth data calculation device), 12 ... ROM (Read Only Memory), 14 ... RAM (Random)
(Access Memory) (first storage means) (second storage means), 18a, 18b ... display section, 20 ... key input section, 21 ... changeover switch, 22 ... modulation / demodulation section, 23 ... C
DMA (Code Division Multiple Access) section, 24... RF section, 27... Microphone, 28... Incoming call speaker, 29.
... Substrate, 31-38 ... GMR (Giant Magneto Resistive) element, 31a
Narrow strip portion 31b Bias magnet film (hard ferromagnetic thin film layer) 31-1 Cobalt (Co) zirconium (Zr) niobium (Nb) amorphous magnetic layer 31-2
Nickel (Ni) iron (Fe) magnetic layer, 31-3, 5 ... CoFe magnetic layer, 31-4
..Copper (Cu) layer, 31-6... Antiferromagnetic film ((Pt) manganese (Mn) layer), 31-
7 ... Titanium (Ti) layer, 41-48 ... coil, 51-58 ... drive circuit, 60
... Temperature sensor, 71 ... GPS (Global Positioning System) receiver, 72
..GPS antenna, 80 ... acceleration sensor, 81 ... tilt sensor, 90 ... bus line, C ... capping layer, F ... free layer (free layer, free magnetic layer), P・ ・
Pinned layer (fixed layer), S ... spacer layer, SV ... spin valve film

Claims (9)

By a geomagnetic sensor having a biaxial or triaxial sensitivity direction, an inclination sensor, first storage means for storing measurement data of the geomagnetic sensor and inclination angle data of the inclination sensor, and magnetization of the geomagnetic sensor A correction method for a geomagnetic sensor in a portable information terminal equipped with a correction means for correcting an offset,
A first step of reading measurement data of the geomagnetic sensor and tilt angle data of the tilt sensor at predetermined time intervals;
When the difference value between the current inclination angle data at a certain time and the previous inclination angle data stored in the first storage means immediately before the time is a predetermined value or more, the current inclination angle data And a second step of storing the measurement data of the geomagnetic sensor read simultaneously with the tilt angle data in the first storage means,
A measurement data storage step of repeating the first and second steps to store the measurement data of the geomagnetic sensor and the tilt angle data of the tilt sensor;
Estimating an offset measurement value based on the accumulated measurement data of the geomagnetic sensor;
A correction method for a geomagnetic sensor, comprising: Calculating a distance on the coordinates of the accumulated measurement data of the geomagnetic sensor and the estimated offset measurement value, and further calculating an average value calculating an average value of each calculated distance;
Calculating a standard deviation based on the calculated individual value of each distance and the average value of each distance;
An effectiveness determination step of determining the effectiveness of the offset measurement value based on the calculated standard deviation;
The correction method of the geomagnetic sensor of Claim 1 characterized by the above-mentioned.   3. The method of correcting a geomagnetic sensor according to claim 2, further comprising a step of storing the offset measurement value in a second storage means when the offset measurement value is determined to be valid in the validity determination step. .   4. The method of correcting a geomagnetic sensor according to claim 2, further comprising a step of notifying a user of the fact that the offset measurement value is determined to be invalid in the validity determination step. After the user is notified that the offset measurement value is not valid, the user asks whether the user wishes to correct the offset measurement value;
The method for correcting a geomagnetic sensor according to claim 4, wherein the offset measurement value is estimated again after performing this step. A azimuth data calculation device comprising a geomagnetic sensor having a biaxial or triaxial sensitivity direction, an inclination sensor, and a correction means for correcting an offset due to magnetization of the geomagnetic sensor,
The correction means is
Means for reading measurement data of the geomagnetic sensor and inclination angle data of the inclination sensor at predetermined time intervals;
When the difference value between the current inclination angle data read at a certain time and the past inclination angle data read immediately before the time is a predetermined value or more, the current inclination angle data and the First storage means for storing measurement data of the geomagnetic sensor read simultaneously with the tilt angle data;
Offset estimation means for estimating an offset measurement value based on measurement data of the plurality of geomagnetic sensors stored in the first storage means;
An azimuth data calculation device comprising: A azimuth data calculation device comprising a geomagnetic sensor having a biaxial or triaxial sensitivity direction, an inclination sensor, and a correction means for correcting an offset due to magnetization of the geomagnetic sensor,
The correction means is
Means for reading measurement data of the geomagnetic sensor and inclination angle data of the inclination sensor at predetermined time intervals;
When the difference value between the current inclination angle data read at a certain time and the past inclination angle data read immediately before the time is a predetermined value or more, the current inclination angle data and the First storage means for storing measurement data of the geomagnetic sensor read simultaneously with the tilt angle data;
Offset estimation means for estimating an offset measurement value based on measurement data of the plurality of geomagnetic sensors stored in the first storage means;
Effectiveness determining means for determining the effectiveness of the estimated offset measurement value;
With
The effectiveness determining means is
A distance on the coordinates between the measurement data of the plurality of geomagnetic sensors stored in the first storage means and the estimated offset measurement value is calculated, and an average value of the calculated distances is calculated. An average value calculating means;
A standard deviation calculating means for calculating a standard deviation based on the calculated individual value of each distance and the average value of each distance;
Determining means for determining the effectiveness of the offset measurement value based on the standard deviation calculated by the standard deviation calculating means;
An azimuth data calculation device comprising:   8. The azimuth data calculation apparatus according to claim 7, wherein the correction unit includes an offset storage unit that stores the offset measurement value when the validity determination unit determines that the offset measurement value is valid. .   A portable information terminal comprising the azimuth data calculation device according to any one of claims 6 to 8.

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