JP2012112859A - Electronic compass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic compass capable of accurately calculating a central point of an azimuth sphere by a simple operation.SOLUTION: A plurality of detection values are acquired while performing a first operation in which a portable apparatus 2 is rotated, with a first axis of a triaxial rectangular coordinate system facing the direction orthogonal to the magnetic north direction, using the first axis defined as a central axis. Also, a plurality of detection values are acquired while performing a second operation in which the portable apparatus 2 is rotated, with a second axis facing the direction orthogonal to the magnetic north direction, using the second axis defined as a central axis. A central point O' of the azimuth sphere 7 is calculated using the acquired plurality of detection values. A detection value of a magnetic vector M by a triaxial magnetic sensor 3 is corrected based on a deviation between the central point O' of the azimuth sphere 7 and the original point O of the triaxial rectangular coordinate system. The azimuth of the portable apparatus 2 is calculated using the detection value after the correction.

Description

  The present invention relates to an electronic compass provided with a three-axis magnetic sensor.

  2. Description of the Related Art Conventionally, an electronic compass that obtains an orientation using a three-axis magnetic sensor provided in a portable device is known. The electronic compass detects a geomagnetic vector using a three-axis magnetic sensor, and calculates the orientation of the portable device based on the detected geomagnetic vector. Then, the direction is displayed on the display unit of the portable device.

  In addition to the three-axis magnetic sensor, many electronic components are mounted on the portable device. Therefore, a magnetic field (internal magnetic field) is generated inside the portable device by this electronic component, and the detection value of the geomagnetic vector by the three-axis magnetic sensor may be inaccurate. If the detection value of the three-axis magnetic sensor becomes inaccurate, it becomes impossible to accurately calculate the direction in which the mobile device is facing. In order to solve this problem, an electronic compass capable of correcting a detection error of a three-axis magnetic sensor caused by an internal magnetic field of a portable device has been developed (see Patent Documents 1 and 2 below).

In order to correct the influence of the internal magnetic field, for example, the following method is used.
When the attitude of the portable device is changed, the detected value of the geomagnetic vector by the three-axis magnetic sensor changes. As shown in FIG. 14, this detected value P indicates a sphere (hereinafter referred to as an azimuth sphere) on the three-axis orthogonal coordinate system (X, Y, Z) of the three-axis magnetic sensor as the posture of the portable device changes. Draw. When there is an influence of the internal magnetic field, the center point O ′ of the azimuth sphere 9 does not coincide with the origin O of the three-axis orthogonal coordinate system and is offset. When the coordinates of the center point O ′ of the azimuth sphere 9 are calculated, the deviation (OO ′ vector) between the origin O of the three-axis orthogonal coordinate system and the center point O ′ of the azimuth sphere is calculated from It is possible to correct the detection value (OP vector) of the magnetic sensor and obtain an accurate geomagnetic vector (O′P) that is not affected by the internal magnetic field. Thereby, it becomes possible to calculate an accurate orientation of the portable device.

  In order to accurately calculate the center point O ′ of the azimuth sphere 9, the detection value P of the three-axis magnetic sensor is acquired over a wide range on the azimuth sphere 9 by pointing the mobile device uniformly in all directions. It is preferable. In this way, the azimuth sphere 9 can be obtained accurately, and the center point O ′ of the azimuth sphere 9 can also be accurately calculated. On the contrary, if the detected value P of the three-axis magnetic sensor is biased to a part of the position on the azimuth sphere 9, it is difficult to accurately calculate the azimuth sphere 9 and its center point O '.

JP 2007-139715 A JP 2008-241675 A

  However, it is a heavy burden on the user to perform the operation of directing the portable device in all directions. In many cases, the detection value P of the three-axis magnetic sensor can be acquired only within a narrow range on the azimuth sphere 9 by simply performing a simple operation, and the azimuth sphere 9 and its center point O ′ are accurately calculated. It becomes difficult to do.

  That is, since the geomagnetism has a dip, the geomagnetic vector is inclined with respect to the horizontal plane except in the vicinity of the equator, and since it is inclined downward in the northern hemisphere, for example, as shown in FIG. When an operation of rotating the portable device in a plane parallel to the horizontal plane with the axis as the central axis is performed, the detection value P of the triaxial magnetic sensor can be acquired only within a narrow range below the azimuth sphere 9. Therefore, the plane including the circle of detection value groups that can be acquired by this operation not only does not include the center point O ′ of the azimuth sphere 9, but also becomes a plane far away from the center point O ′. Although it is possible to calculate the coordinates of the center point O ′ of the orientation sphere 9 from the data obtained by the operation, it is difficult to obtain the coordinates of the center point O ′ with a small calculation error and high accuracy.

  As described above, it is difficult to accurately calculate the center point O ′ of the azimuth sphere 9 by a simple operation, and the center point O ′ of the azimuth sphere 9 can be accurately determined by performing an operation of pointing the mobile device in all directions. However, there is a problem that the burden on the user is large.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an electronic compass capable of accurately calculating the center point of an azimuth sphere with a simple operation.

The present invention is an electronic compass that is provided in a mobile device and detects an orientation that the mobile device faces while correcting the influence of the internal magnetic field of the mobile device,
A three-axis magnetic sensor for detecting geomagnetism as a magnetic vector in a three-axis orthogonal coordinate system fixed to the portable device;
A center point calculating means for calculating a center point of an azimuth sphere drawn on the three-axis orthogonal coordinate system in accordance with a change in posture of the portable device, the detected value of the magnetic vector obtained by the three-axis magnetic sensor;
The detection value of the magnetic vector obtained by the three-axis magnetic sensor is corrected based on the deviation between the center point of the azimuth sphere and the origin of the three-axis orthogonal coordinate system, and the corrected detection value is used. Azimuth calculating means for calculating the azimuth facing the mobile device,
The center point calculation means is a state in which the first axis is oriented in a direction orthogonal to the magnetic north direction among the first axis, the second axis, and the third axis that are orthogonal to each other in the three-axis orthogonal coordinate system. Then, during the first operation of rotating the portable device with the first axis as the central axis, the plurality of detection values are acquired, and the second axis is set in a direction perpendicular to the magnetic north direction. While the second operation of rotating the portable device about the second axis as the central axis is performed, a plurality of the detection values are obtained, and the plurality of detection values obtained are obtained. To calculate the center point of the azimuth sphere,
The direction of the central axis in the first operation and the second operation is an electron whose orthogonal axis other than the central axis is directed in a direction parallel to the magnetic north direction during rotation. It is in the compass (claim 1).

In the electronic compass, while the first operation and the second operation are performed, a plurality of magnetic vector detection values are acquired using a three-axis magnetic sensor. Then, the center point of the azimuth sphere is calculated using the obtained plurality of detection values.
In this way, the center point of the azimuth sphere can be accurately calculated with a simple operation. That is, in the electronic compass, first, the user confirms in advance in which direction the magnetic north is. This confirmation may be made such that magnetic north is automatically calculated and displayed on the screen using the detection value of the three-axis magnetic sensor in the electronic compass, and the screen may be confirmed by the user. Alternatively, the user may check the map or the azimuth magnetic needle prepared independently. In addition, the magnetic north direction said here is a direction which considered the dip angle. However, when confirming the magnetic north direction with a map or azimuth needle, etc., the dip angle is often not accurately known. In this case, either axis is oriented in the same direction as magnetic north on the horizontal plane and is perpendicular to the horizontal plane. It is only necessary to rotate in the direction. Thereby, substantially the same rotation operation can be performed. When checking magnetic north on a map, care must be taken because there is a deviation (deviation angle) from true north.

  When performing the first operation, the portable device is rotated with the first axis as a central axis in a state where the first axis is oriented in a direction orthogonal to the magnetic north direction. At this time, the first axis is orthogonal to the magnetic north direction, and the direction of the first axis is the direction in which the second axis and the third axis, which are orthogonal axes other than the central axis, are parallel to the magnetic north direction during the rotation. Since it is determined to be oriented in the same direction, that is, in the same direction as magnetic north, when the portable device is rotated around the first axis, the second axis and the third axis The detection value of the three-axis magnetic sensor can be acquired in a plane including Incidentally, passing through the same direction as the magnetic north described above naturally includes not only the case where it completely coincides with the magnetic north but also the case where it passes through a slightly shifted direction. In other words, it means that it is rotated so that it passes through the same direction as magnetic north as much as possible. In addition, there are always two directions perpendicular to magnetic north that satisfy the above-mentioned conditions, but since there is a dip, one direction is not parallel to the horizontal plane, and the other one direction is parallel to the horizontal plane. . Therefore, it is more preferable that the rotation operation is performed using the direction parallel to the horizontal plane as the rotation axis because the user can easily operate and a detection value with high accuracy is easily obtained. This also applies to the second operation and the third operation described later. Therefore, when displaying on the output means described later, it is preferable to display a direction parallel to the horizontal plane.

When performing the second operation, the second axis is orthogonal to the magnetic north direction, and the second axis is determined so that the first axis and the third axis pass in the same direction as the magnetic north during the rotation. Therefore, when the portable device is rotated about the second axis as the central axis, the detection value of the three-axis magnetic sensor can be acquired in a plane including the first axis and the third axis.
Since the plane including the second axis and the third axis and the plane including the first axis and the third axis are orthogonal to each other, the detection value of the three-axis magnetic sensor is acquired within these two planes. Thus, the plane consisting of the obtained detection value group is a plane including the center point O ′ of the azimuth sphere if the magnetic north direction can be confirmed accurately, and even if it is not accurate and slightly deviates from the true magnetic north The radius of the circle formed by the points formed from the obtained detection value group is a value that is very close to the radius of the azimuth sphere. Therefore, it is possible to obtain detection values on two orthogonal planes and passing through the center point of the azimuth sphere (or passing through a very close position if not), It becomes possible to easily obtain the detection value of the three-axis magnetic sensor composed of a combination of two points that are equal to or close to the diameter of the azimuth sphere. Therefore, it is possible to accurately calculate the azimuth sphere and its center point.

  Further, since the first operation and the second operation are relatively simple operations, even if the user of the portable device performs this operation, it does not cause a heavy burden on the user.

  As described above, according to the present invention, it is possible to provide an electronic compass that can accurately calculate the center point of an azimuth sphere with a simple operation.

1 is a conceptual diagram of an electronic compass in Embodiment 1. FIG. 1 is a partially transparent perspective view of a mobile device in Embodiment 1. FIG. 1 is a block diagram of an electronic compass in Embodiment 1. FIG. Explanatory drawing of 1st operation in Example 1. FIG. The figure following FIG. The figure following FIG. Explanatory drawing of 2nd operation in Example 1. FIG. The figure following FIG. The figure following FIG. The figure which represented the detection value of the magnetic vector at the time of performing 1st operation and 2nd operation in Example 1 on an azimuth | sphere. 2 is a flowchart of an electronic compass in the first embodiment. 1 is a perspective view of a triaxial magnetic sensor in Embodiment 1. FIG. FIG. 10 is a diagram for explaining an example of acquiring a detected magnetic vector value in the third embodiment. The figure which displayed the measured value of the magnetic vector on the azimuth | direction sphere at the time of rotating operation of the portable apparatus in a prior art example.

A preferred embodiment of the present invention described above will be described.
Further, the center point calculation means performs a third operation of rotating the portable device about the third axis with the third axis directed in a direction orthogonal to the magnetic north direction. In the meantime, a plurality of the detected values are acquired, and the center point of the azimuth sphere is calculated using the detected values acquired by the first operation, the second operation, and the third operation, The direction of the central axis in the third operation is preferably an orientation in which an orthogonal axis other than the central axis is directed in a direction parallel to the magnetic north direction during rotation (Claim 2).
In this case, not only the detection value rotated on the two axes orthogonal to each other (the first axis and the second axis) but also the data obtained by rotating the other orthogonal axis (the third axis) as the rotation axis is acquired. Therefore, the calculation accuracy of the center point can be further improved.
In this case as well, the first and second axes, which are orthogonal axes other than the third axis serving as the rotation axis, are rotated so that the directions of the first and second axes pass through the same direction as the magnetic north direction. Same as 1.

In addition, the center point of the azimuth sphere can be calculated with a precision within a predetermined range after performing a rotation operation, which is an operation for rotating the portable device about the orthogonal axis directed in a direction orthogonal to the magnetic north direction. Rotation operation direction confirmation means for confirming whether or not the center point cannot be calculated with an accuracy within the range and that there is a possibility of re-operation guidance and / or a decrease in accuracy is provided. (Claim 3).
Here, the rotation operation means two rotation operations of the first operation and the second operation when rotating with two orthogonal axes, and when rotating with all three orthogonal axes, This means three rotation operations of the first operation, the second operation, and the third operation (the same applies to claims 5 to 7 described later).
In the present invention, since a person performs a rotation operation, even if the magnetic north direction can be accurately grasped, there is a possibility that the rotation cannot be performed in the correct direction during the operation. In addition, the confirmed magnetic north direction may be slightly different from the true magnetic north. Accordingly, after performing the rotation operation, it is confirmed whether or not the correct operation has been performed from the detected value. It is preferable to display that the accuracy may not be sufficiently secured.
As a method for confirming from the detected value, for example, in Example 3 and Example 4 to be described later, it is checked whether the distance of the data obtained by two points at each of the six locations is a predetermined value or less, There is a method of confirming whether the distance between the maximum detection value and the minimum detection value detected in claim 6 is about twice the value of geomagnetism.

In addition, the center point of the azimuth sphere is temporarily calculated from the detected value of the magnetic vector detected by the three-axis magnetic sensor, and the difference between the temporarily calculated center point and the origin of the three-axis orthogonal coordinate system is calculated. Based on this, it is preferable to provide a magnetic north direction provisional calculation means for correcting the detected value of the magnetic vector obtained by the three-axis magnetic sensor and outputting the corrected direction of the magnetic vector as the magnetic north direction. 4).
In this way, since the magnetic north direction can be confirmed using the electronic compass, the user does not need to prepare a map, a magnetic azimuth, or the like separately.
When calculating the center point of the azimuth sphere in the electronic compass of the present invention, first, the magnetic north direction temporary calculation means is used to confirm in advance which is the magnetic north direction. That is, the necessary rotation operation is performed after the user confirms the magnetic north direction using the magnetic north direction temporary calculation means.
The confirmation of the magnetic north direction, as described above, temporarily calculates the center point of the azimuth sphere from the detected value of the geomagnetic vector by the three-axis magnetic sensor in the portable device, and corrects the offset based on the temporarily calculated center point. It is also possible to use the magnetic north direction calculated as described above. The direction of magnetic north thus obtained is inferior in accuracy as compared with the center point of the azimuth sphere calculated by the center point calculation means, but at least accuracy within a certain error range is ensured. Therefore, by using the magnetic north direction obtained in this way, the user can grasp the magnetic north direction to some extent without relying on other information sources such as a map. By performing the first operation and the second operation or the third operation, the center point of the azimuth sphere can be calculated conveniently and accurately.

In this invention, it is preferable that the said rotation operation is operation which rotates the said portable apparatus 180 degrees or more respectively (Claim 5).
In this case, since the angle at which the portable device is rotated is large in the first operation to the third operation, it is easy to obtain the detection value of the three-axis magnetic sensor in a wide range on the azimuth sphere. In particular, by rotating each of them by 180 ° or more, two points of the intersection of the straight line passing through the center point of the azimuth sphere and the azimuth sphere, that is, a point that is a combination of two points separated from each other by the diameter of the azimuth sphere Is possible. Of course, the magnetic north direction temporarily calculated by the magnetic north direction temporary calculation means may include some errors, but at least a measurement point consisting of a combination of two points separated by a distance that is quite close to the diameter of the azimuth sphere is acquired. be able to. Therefore, it becomes possible to calculate the azimuth sphere and its center point more accurately.
Note that it is more preferable that the rotation angle be 270 ° or more because two sets of two points separated from each other by the diameter of the azimuth sphere can be acquired. Further, if one rotation is performed, it is possible to reliably acquire two combinations of the maximum detection value and the minimum detection value described in claim 6 described later.

In addition, the center point calculation means includes, in each of the rotation operations, a maximum detected value that maximizes the magnetic vector component on any one of two axes other than the axis that is the center axis, and It is preferable to use the minimum detection value that minimizes the component for the calculation of the center point.
In this way, since the maximum detection value and the minimum detection value are separated from each other by a distance substantially equal to the diameter of the azimuth sphere on the azimuth sphere, the center point of the azimuth sphere can be calculated more accurately. .

In the rotating operation, output means for displaying on the display unit of the portable device a direction perpendicular to the magnetic north direction as the central axis based on the magnetic north direction obtained by the magnetic north direction temporary calculation means. It is preferable to provide (Claim 7).
In this case, since the direction to be the central axis is displayed on the display unit, the user can easily point the first axis to the third axis in that direction. Therefore, the first operation to the third operation can be easily performed.
As described above, in this display, it is more preferable to display a direction parallel to the horizontal plane among the directions perpendicular to the magnetic north direction.

Example 1
An electronic compass according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 2, the electronic compass 1 of this example is provided in a portable device 2. The electronic compass 1 detects the direction in which the mobile device 2 faces while correcting the influence of the internal magnetic field of the mobile device 2.
As shown in FIG. 1, the electronic compass 1 includes a three-axis magnetic sensor 3, a center point calculation unit 4, an azimuth calculation unit 5, a magnetic north direction temporary calculation unit 8, and a rotation operation direction confirmation unit 19.

As shown in FIG. 2, the triaxial magnetic sensor 3 detects geomagnetism as a magnetic vector M in a triaxial orthogonal coordinate system fixed to the portable device 2.
The center point calculation means 4 is configured so that the detected value of the magnetic vector M obtained by the three-axis magnetic sensor 3 represents an azimuth sphere 7 (see FIG. 10) drawn on the three-axis orthogonal coordinate system as the posture of the portable device 2 changes. A center point O ′ is calculated.
The azimuth calculating means 5 uses the detected value (OP vector) of the magnetic vector M obtained by the three-axis magnetic sensor 3 as a deviation (OO ′) between the center point O ′ of the azimuth sphere 7 and the origin O of the three-axis orthogonal coordinate system. Vector). Then, using the corrected detection value (O′P vector), the direction in which the mobile device 2 faces is calculated.

As shown in FIGS. 4 to 6, the center point calculation means 4 includes a first axis (X axis), a second axis (Y axis), and a third axis (Z axis) that are orthogonal to each other in a three-axis orthogonal coordinate system. The first operation of rotating the portable device 2 around the first axis (X axis) in the state where the first axis (X axis) is oriented in the direction orthogonal to the magnetic north direction N is performed. In the meantime, a plurality of detection values are acquired. Further, as shown in FIGS. 7 to 9, the center point calculation means 4 has the second axis (Y axis) as the central axis in a state where the second axis (Y axis) is directed in a direction orthogonal to the magnetic north direction N. As the second operation for rotating the mobile device 2 is performed, a plurality of detection values are acquired. Then, the center point calculating means 4 calculates the center point O ′ of the azimuth sphere 7 using the obtained plurality of detection values.
Note that the rotation axes in the first operation and the second operation are adjusted so that orthogonal axes other than the rotation axis face the same direction as the magnetic north direction N during the rotation.
The magnetic north direction provisional calculation means 8 sets the magnetic north direction N to 3 in order to determine the direction in which the portable device is directed during the rotation operation before performing the first operation and the second operation performed by the center point calculation means 4. This is a means for calculating from the data group of magnetic vectors M obtained by the axial magnetic sensor, and the center point O ′ of the azimuth sphere 7 is provisionally calculated from the magnetic vector data group acquired from the three-axis magnetic sensor 3, and this temporarily calculated center Based on the deviation between the value of the point O ′ and the origin O of the three-axis orthogonal coordinate system, the detected value of the magnetic vector M is corrected, and the direction of the corrected magnetic vector M is output as the magnetic north direction N.
The rotating operation direction confirmation means 19 determines whether the rotating operation direction by the first operation and the second operation is rotating within the allowable deviation range from the plane including the magnetic north direction N. Confirmation is made from the magnetic vector M acquired by two operations, and re-operation is displayed as necessary.
The details will be described below.

As shown in FIG. 2, the mobile device 2 includes a three-axis magnetic sensor 3 and a microcomputer 100. In addition to these, a plurality of electronic components 200 are mounted. A magnetic field is generated inside the portable device 2 by the electronic component 200, and the triaxial magnetic sensor 3 is affected by this magnetic field.
The mobile device 2 includes a display unit 20. The direction is displayed on the display unit 20.

As shown in FIG. 3, the microcomputer 100 includes a CPU 10, a ROM 11, a RAM 12, an I / O 14, and a line 13 that connects them. The ROM 11 stores a program 11p. When the CPU 10 reads and executes the program 11p of the ROM 11, the center point calculation means 4, the azimuth calculation means 5, the output means 6, the magnetic north direction temporary calculation means 8, and the rotation operation direction confirmation means 19 of this example are realized.
Further, the microcomputer 100 is connected to the three-axis magnetic sensor 3 and the display unit 20. The triaxial magnetic sensor 3 detects a magnetic vector, for example, every several milliseconds, and transmits the detected value to the microcomputer 100.

  As shown in FIG. 12, the three-axis magnetic sensor 3 includes a magneto-impedance sensor element 30. That is, the three-axis magnetic sensor 3 causes the three magneto-impedance sensor elements 30 to be in three-axis directions (X-axis direction, Y-axis direction, and Z-axis direction) in which the respective magnetic sensing directions are orthogonal to each other. It is formed by arranging.

  On the other hand, since the triaxial magnetic sensor 3 is affected by the internal magnetic field of the mobile device 2, the center point O ′ of the azimuth sphere 7 of the triaxial magnetic sensor 3 is the origin O of the triaxial magnetic sensor 3 as shown in FIG. It is off. The azimuth sphere 7 is a locus drawn on the three-axis orthogonal coordinate system by the detection value P (Xi, Yi, Zi) of the three-axis magnetic sensor 3 as the posture of the mobile device 2 changes. The O′P vector shown in FIG. 10 represents an accurate geomagnetic vector that is not affected by the internal magnetic field. Although the magnitude | O'P | of the geomagnetic vector O'P varies depending on the location on the earth, it can be regarded as constant if it is used continuously within a range where it does not move greatly. Then, the locus drawn by the detection value P becomes a sphere.

  The OO ′ vector represents the deviation between the origin O of the three-axis orthogonal coordinate system and the center point O ′ of the azimuth sphere 7. If the center point O ′ of the azimuth sphere can be accurately calculated, the detection value (OP vector) of the three-axis magnetic sensor 3 affected by the internal magnetic field can be corrected using the following formula, and the influence of the internal magnetic field can be reduced. The detection value (O′P vector) of the three-axis magnetic sensor 3 that is not received can be obtained. This makes it possible to calculate an accurate azimuth.

In order to accurately perform the center O ′ of the azimuth sphere 7, the first operation and the second operation described above are performed. To perform the first operation and the second operation, the magnetic north direction N is confirmed in advance. There is a need. In this example, the magnetic north direction N is confirmed using the magnetic north direction temporary calculation means 8.
The magnetic north direction temporary calculation means 8 uses the magnetic vector data group acquired by the three-axis magnetic sensor 3 detected within a predetermined time, and temporarily calculates the center point O ′ of the azimuth sphere 7 from this data group. Note that this magnetic vector data group may use data automatically obtained by using a change in posture when the user operates the mobile device 2 without requiring the user to perform a rotation operation. It may be obtained by performing the operation method of the mobile device 2 for acquiring offset correction data that has been proposed in the past, such as rotating at the same time.

  Then, the center point O ′ of the azimuth sphere 7 is temporarily calculated from the obtained magnetic vector data group. As a method of this provisional calculation, as already proposed, a method of selecting a point where the variation (standard deviation) in distance from each point of the magnetic vector data group is the smallest is selected from the data group. A method of selecting four or more points as far as possible on the azimuth sphere and calculating a center point from the selected points can be selected.

  The magnetic north direction N can be easily obtained by correcting the magnetic vector data group based on the temporarily calculated value of the center point O ′ of the azimuth sphere 7. The magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 is slightly inferior in accuracy to the magnetic north direction N calculated using the center point correction means 4, but a certain degree of accuracy is ensured. Therefore, in a first operation and a second operation described later, an extremely accurate offset correction can be performed by rotating the magnetic north direction N obtained here as a reference.

Next, when performing the first operation, as shown in FIG. 4, the user of the portable device 2 sets the first axis (X axis) in the magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 described above. Direct in the orthogonal direction. Thereafter, the portable device 2 is rotated about the first axis (X axis) as a central axis. Since the direction in which the first axis is directed is adjusted so that the other orthogonal axes are directed to the magnetic north direction during the rotation as described above, the third axis (Z-axis) as shown in FIG. Momentarily faces the same direction as the magnetic north direction N. The detection value of the triaxial magnetic sensor 3 at this time corresponds to the point A in FIG.
When further rotated with the first axis (X axis) as the central axis, the second axis (Y axis) instantaneously points in the same direction as the magnetic north direction N (point E), and is further centered on the first axis (X axis) When rotated as an axis, as shown in FIG. 6, the third axis (Z axis) is instantaneously opposite to the magnetic north direction N. The detection value of the triaxial magnetic sensor 3 at this time corresponds to the point B in FIG. Then, when further rotated, the second axis instantaneously opposes the magnetic north direction N (point F).
If the magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 is accurate, the points A and B, and the points E and F are points separated from each other on the azimuth sphere 7 by the diameter of the azimuth sphere 7. The middle point is the center point O ′ of the azimuth sphere 7. Further, even if the magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 is slightly deviated due to an error or the like during offset correction, the magnetic sphere 7 is separated from the azimuth sphere 7 by a distance substantially close to the diameter of the azimuth sphere 7. It becomes a measurement point.

When performing the second operation, the user of the portable device 2, as shown in FIG. 7, the direction orthogonal to the magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 with the second axis (Y axis) as described above. Turn to. Thereafter, the portable device 2 is rotated about the second axis (Y axis) as a central axis. In this way, for the same reason as the first operation, the first axis (X axis) instantaneously points in the same direction as the magnetic north direction N as shown in FIG. The detection value of the triaxial magnetic sensor 3 at this time corresponds to the point C in FIG.
When the second axis (Y-axis) is further rotated as the central axis, the third axis (Z-axis) is instantaneously oriented in the same direction as the magnetic north direction N (point A), and further centered on the second axis (Y-axis) When rotated as an axis, as shown in FIG. 9, the first axis (X axis) is instantaneously opposite to the magnetic north direction N. The detection value of the triaxial magnetic sensor 3 at this time corresponds to the point D in FIG. Then, when further rotated, the third axis instantaneously turns in the opposite direction to the magnetic north direction N (point B).
Similarly to the relationship between the points A and B and the points E and F, the points C and D are also measurement points that are separated from each other by a distance equal to or close to the diameter of the azimuth sphere 7 on the azimuth sphere 7. , The line connecting AB, the line connecting CD, and the line connecting EF are orthogonal to each other as shown in FIG.

  As described above, in this example, in the first operation and the second operation, the portable device 2 is separated from the azimuth sphere by a distance equal to or close to the diameter of the azimuth sphere, and the components on the axes other than the central axis are maximized and minimized. The angle necessary to acquire two sets of points (at least 270 ° or more) is rotated.

In this example, the center point O ′ of the azimuth sphere 7 is calculated using the points A to F. That is, in the first operation, the electronic compass 1 of the present example performs maximum detection in which the component of the magnetic vector M is maximized for each of two axes (Y axis, Z axis) other than the axis (X axis) as the central axis. The value (point A, point E) and the minimum detected value (point B, point F) that minimizes the component are used for calculating the center point O ′. In the second operation, the maximum detected value (C point, E point) at which the component of the magnetic vector M is maximum for each of two axes (X axis, Z axis) other than the axis (Y axis) as the central axis. The minimum detected value (D point, E point) that minimizes the component is used for calculating the center point O ′.
The six points A to F are not unevenly distributed in a part of the area on the azimuth sphere 7 of the measurement point as in the case of acquiring offset correction data by the conventional method, and Since B point, C point and D point, and E point and F point are the farthest points on the azimuth sphere 7, they are optimum measurement points for obtaining the center point O ′ of the azimuth sphere 7. Compared to offset correction, the correction error can be greatly reduced.

  Since the first operation and the second operation are manually operated by the user, there is a possibility that the first operation and the second operation may be rotated in a state where there is a deviation from a target direction. In such a case, if the center point of the azimuth sphere is obtained without performing any check as it is, the effects of the invention cannot be sufficiently obtained, and the offset correction accuracy cannot be kept small. Therefore, in the present invention, this is checked by the rotation operation direction confirmation means 19.

  Here, if there is no problem in the rotation operation directions of the first operation and the second operation, the positions of the points A and B (maximum detection value and minimum detection value in the third axis direction) acquired by the first operation and the second operation. The positions of the points A and B acquired by the above should match or at least be close to each other, and if the deviation from the target rotational operation direction increases, the two points acquired by both operations The distance on the azimuth sphere between the points A and the distance on the azimuth sphere between the two points B increase. Therefore, in the first operation and the second operation, the detection value that maximizes the component in the third axis direction and the detection value that minimizes the component are acquired, and the distance between these points is calculated. When this distance exceeds a predetermined threshold, it is checked whether or not there is no problem in the direction of the rotation operation by displaying that re-operation is necessary. If it is determined by this check that there is no problem in the direction of the rotation operation, it is determined that the center point O ′ can be calculated with high accuracy.

  In addition, as shown in FIGS. 1 and 2, the electronic compass 1 of this example sets a direction R perpendicular to the magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 in the first operation and the second operation to the portable device 2. Output means 6 to be displayed on the display unit 20. For example, when performing the first operation, the user directs the first axis (X axis) in the displayed direction R, and then rotates the portable device 2 around the first axis (X axis) as a central axis. Similarly, when performing the second operation, the second axis (Y axis) is directed to the displayed direction R, and then the portable device 2 is rotated about the second axis (Y axis) as the central axis.

  Next, the program 11p shown in FIG. 3 will be described using the flowchart of FIG. First, the magnetic vector M is repeatedly acquired in advance by a three-axis magnetic sensor, and the detected value is stored (step S1). When the program 11p is started, the electronic compass 1 tentatively calculates the center point O ′ of the azimuth sphere 7 using the already acquired magnetic vector data group, and based on the tentatively calculated center point O ′. The offset is corrected and the magnetic north direction N is calculated (step S2). At this time, since the magnetic vector data group used may be unevenly distributed in a part of the area on the azimuth sphere 7, the accuracy is calculated when compared with the center point O ′ obtained in step S 7 described later. The magnetic north direction N, which is at least slightly inferior, but does not deviate at least, can be obtained. Then, the obtained direction R perpendicular to the magnetic north direction N is displayed on the display unit 20, and the user is notified to perform the first operation (step S3). At this time, although there are two directions perpendicular to the magnetic north direction N in the three-dimensional space, it is more preferable to display the direction parallel to the horizontal plane because the later rotation operation is easier. Thereafter, while the user performs the first operation, the magnetic vector M is detected using the triaxial magnetic sensor 3 (step S4).

  After step S4, the electronic compass 1 displays the direction R orthogonal to the magnetic north direction N on the display unit 20 and notifies the user to perform the second operation, similarly to step S3 (step S5). Thereafter, while the user performs the second operation, the magnetic vector M is detected using the triaxial magnetic sensor 3 (step S6).

  After step S6, it is checked whether or not there is no problem in the direction of the rotation operation by the first operation and the second operation (step S7). Specifically, the distance between two points, that is, the point that becomes the maximum detection value and the point that becomes the minimum detection value of the third axis (Z-axis) component that should be obtained in common in the first operation and the second operation is calculated. Then, the calculated distance is compared with a predetermined threshold value. If it is less than or equal to the threshold value, it is determined that there is no problem with the direction of rotation, and the process proceeds to step S9. If it exceeds the threshold value, it is determined that the rotational operation direction has deviated from the planned direction, and the process proceeds to step S8 to notify that the re-operation is necessary, and returns to step S3 again.

  If it is determined in step S7 that there is no problem in the direction of the rotation operation, the electronic compass 1 calculates the center point O 'of the azimuth sphere 7 using the plurality of acquired detection values (step S9). Thereafter, the detected magnetic vector OP (see FIG. 10) is corrected based on the deviation between the center point O ′ of the azimuth sphere 7 and the origin O of the three-axis orthogonal coordinate system, and the corrected magnetic vector O′P is obtained. Using, the azimuth | direction which the portable apparatus 2 faces is calculated (step S10).

  In the above description, the first axis is the X axis, the second axis is the Y axis, and the third axis is the Z axis, but the combination of these axes can be arbitrarily determined.

Next, the function and effect of this example will be described. As shown in FIGS. 4 to 9, in this example, a plurality of detected values of the geomagnetic vector are acquired using the triaxial magnetic sensor 3 while the first operation and the second operation are performed. Then, the center point O ′ of the azimuth sphere 7 is calculated using the plurality of detected values obtained.
In this way, the center point O ′ of the azimuth sphere 7 can be accurately calculated with a simple operation. That is, when performing the first operation, the first axis (X axis) is adjusted to be orthogonal to the magnetic north direction N, and the orthogonal axes other than the first axis are adjusted to face the magnetic north direction during rotation. When the portable device 2 is rotated about the first axis (X axis), a three-axis magnetic sensor in a plane (YZ plane) including the second axis (Y axis) and the third axis (Z axis) 3 detection values can be acquired.

Further, when performing the second operation, the second axis (Y axis) is adjusted to be orthogonal to the magnetic north direction N, and the orthogonal axes other than the second axis are adjusted so as to face the magnetic north direction during rotation. When the portable device 2 is rotated about the second axis (Y axis), a three-axis magnetic sensor in a plane (XZ plane) including the first axis (X axis) and the third axis (Z axis) 3 detection values can be acquired.
Since the YZ plane and the XZ plane are orthogonal to each other, acquiring the detection values of the triaxial magnetic sensor 3 in these two planes prevents the detection values from being unevenly distributed on the azimuth sphere 7. It becomes possible to acquire the detection value of the three-axis magnetic sensor 3 on the plane including the center point O ′ of the azimuth sphere 7 on the sphere 7. Therefore, the azimuth sphere 7 and its center point O ′ can be calculated more accurately than the conventional offset method.

In addition, since the first operation and the second operation are relatively simple operations, unlike the case where data on the azimuth sphere 7 is to be acquired all over, the user of the portable device 2 performs this operation. However, this is not a heavy burden on the user.
Further, in this example, after performing the first operation and the second operation, it is confirmed whether or not the rotation operation is performed in the target direction by the rotation operation direction confirmation unit 19 before calculating the center point. As a result, it is checked whether data capable of accurately calculating the center point O ′ can be acquired, so that the accuracy of offset correction can be reliably increased.

In the first operation and the second operation in this example, the portable device 2 is rotated at least 270 ° or more.
In this way, by the first operation and the second operation, points that are diametrically opposite to each other about the center point O ′ of the azimuth sphere 7 (points at which the mutual distance is substantially equal to the diameter of the azimuth sphere 7) are acquired. be able to. Therefore, it becomes possible to calculate the azimuth sphere 7 and its center point O ′ more accurately.

In this example, the center point calculating means 4 in particular in each of the two axes other than the axis as the central axis in each of the first operation and the second operation is rotated by 270 ° or more. Two sets of maximum detection values (points A, C, and E in FIG. 10) that maximize the component of M and minimum detection values (points B, D, and E in FIG. 10) that minimize the component Acquired and used to calculate the center point O ′.
In this way, the combination of the maximum detection value and the minimum detection value (A point and B point, C point and D point, E point and F point) of each axis component is mutually on the azimuth sphere 7. Since the center point is the position of the center point O ′ of the azimuth sphere 7, the center point O ′ of the azimuth sphere 7 can be calculated more accurately. In addition, if it is decided to rotate 360 ° instead of 270 ° or more, two sets of maximum detected values can be reliably obtained by one rotation operation regardless of the direction of the rotation start position of the first operation and the second operation. The minimum detection value can be acquired.

In this example, as shown in FIGS. 1 and 2, in the first operation and the second operation, the direction R perpendicular to the magnetic north direction N obtained by the magnetic north direction temporary calculation means 8 is displayed on the display unit 20 of the portable device 2. Output means 6 for displaying is provided.
In this way, since the direction R perpendicular to the magnetic north direction N is displayed on the display unit 20, the user easily points the first axis (X axis) or the second axis (Y axis) in the direction R. be able to. Therefore, the first operation and the second operation can be easily performed.

  As described above, according to this example, it is possible to provide an electronic compass that can accurately calculate the center point of the azimuth sphere with a simple operation.

(Example 2)
In Example 1, the first operation for rotating the first axis in the direction R orthogonal to the magnetic north direction N and the second operation for rotating the second axis in the same manner were performed. A third operation for rotating the axis (Z axis) in the direction R may be performed. Further, in the third operation, the third axis is rotated by 270 ° or more, and the maximum detected value 2 points at which the component of the magnetic vector M becomes the maximum in the two axes of the first axis (X axis) and the second axis (Y axis) It is also possible to detect (C point, E point) and two minimum detection values (D point, F point) that minimize the component.
Thus, by performing three rotation operations, the calculation accuracy of the coordinates of the center point O ′ of the azimuth sphere 7 can be further improved.
In addition, the configuration and operational effects similar to those of the first embodiment are provided.

(Example 3)
Next, a method for processing the data of the detected magnetic vector M will be described.
As described above, the first operation to the third operation are performed, and when the maximum detection value at which the components of the orthogonal axes are maximum and the minimum detection value at which the minimum is minimum are acquired, this point is illustrated in FIG. Although there are 6 points as described above, 4 points can be obtained by one rotation operation, and therefore, a total of 12 points of data can be obtained, 2 points for each point. Hereinafter, an embodiment relating to a data processing method when data of the maximum detection value and the minimum detection value is acquired will be described.

First, it is checked whether the distance between the two points is not more than a predetermined value, and it is confirmed that there is no problem in the rotation operation direction. When it is confirmed that there is no problem, the center point O ′ of the azimuth sphere 7 can be obtained by calculating with four points. Therefore, first, the average value of the two points obtained for each point is obtained.
As a result, 6 points of data can be acquired. Of these, 4 points of data are selected, and the coordinates of these 4 points are substituted into a spherical equation and arranged, and the solution of the simultaneous equations is calculated. The coordinates of O ′ can be calculated.
The sphere equation is
(X−a) ² + (Y−b) ² + (Z−c) ² = r ²
(R = radius of the sphere = absolute value of the magnitude of the geomagnetic vector).

Here, there are ₆ C ₄ = 15 combinations for selecting data from 6 points to 4 points. However, when obtaining the center point O ′ of the azimuth sphere 7, the accuracy can be improved by selecting 4 points existing on the same plane. Since there is no improvement, there are 12 selection methods except for the three cases of selecting four points on the same plane.
Therefore, for all 12 selections, the center coordinates are obtained by the above method, the average value thereof is calculated, and this is used as the center coordinates of the sphere, thereby making it possible to perform highly accurate offset correction.

  Here, when only the first operation and the second operation are performed without performing the third operation, data of 8 points instead of 12 points is obtained. Of the 6 points shown in FIG. Two points are acquired in duplicate in only two places. Therefore, in this case, an average value is obtained only for the two overlapping points. The subsequent processing is exactly the same as described above.

Example 4
Next, an embodiment using a method different from the data processing described in the third embodiment will be described. In this case as well, it is the same as in the third embodiment in that it is first checked whether the distance between the two points is a predetermined value or more. In the third embodiment, since data can be acquired at two points for each of six points at the beginning, a process for obtaining an average value of these two points was performed. However, this process is not performed in the present embodiment. . Then, four detection values are selected on the condition that all four points are not on the same plane from the acquired detection values of twelve points. This selection is in when selecting the four points of a combination of 12 kinds in Example 3, since the may be considered two cases are present in each point, there is a combination of 192 kinds = 12 ways × 2 ⁴ . When the solution of the simultaneous equations is calculated from the four points selected in each case in the same manner as in the third embodiment, 192 kinds of center coordinates are calculated.
Thereafter, an average value of the 192 kinds of center coordinates is calculated and set as the center point O ′ of the azimuth sphere 7.

  In the present invention, in order to obtain the center coordinates of the azimuth sphere 7, an offset error is reduced by obtaining a detection value that is considered to be optimal. However, the detection values of the three-axis magnetic sensor 3 always have measurement errors and variations, and this affects the accuracy of the obtained center coordinates. However, as in this example, by averaging a plurality of obtained points, even if there is an error or variation in each obtained value, the error or variation is canceled out by averaging. Therefore, more accurate center coordinates can be obtained.

  In the example described above, the case of using the maximum detection value and the minimum detection value of each axis component has been described, but the present invention is not limited to this case. Regardless of the maximum detection value and the minimum detection value, it is possible to obtain the same accuracy as described above by using the detection value acquired every 180 ° rotation, and from the detection values acquired at other angular intervals. It is also possible to obtain by calculating the point where the variation in distance is the smallest.

(Experimental example)
Next, experimental examples of the present invention will be described. As described above, conventionally, offset correction is performed by selecting, for example, four points that are as far as possible from the acquired data, for example, without forcing the user to perform a specific rotation operation (for example, Patent Document 2). It was. The error of the center coordinate by such a conventional method may reach 50 mG at the maximum, and as a result of being calculated in a state where the center coordinate varies at the maximum of 50 mG, the portable device 2 is directed to an arbitrary direction in the horizontal plane. As the azimuth error calculated at the time, an error of about 10 ° at the maximum could not be avoided.
On the other hand, when the experiment of the method of Example 4 according to the present invention was performed and the error of the center coordinate was confirmed, it was confirmed that the maximum error could be suppressed to about 1/5 compared with the conventional method, which is 10 mG or less at the maximum. It was. As a result, it was confirmed that the azimuth error when directed in an arbitrary direction in the horizontal plane can be suppressed to about 2 ° at the maximum.

DESCRIPTION OF SYMBOLS 1 Electronic compass 19 Rotation operation direction confirmation means 2 Portable apparatus 3 3-axis magnetic sensor 4 Center point calculation means 5 Direction calculation means 6 Output means 7 Azimuth sphere 8 Magnetic north direction temporary calculation means O Origin of 3-axis orthogonal coordinate system O 'Azimuth sphere Center point

Claims (7)

An electronic compass that is provided in a mobile device and detects the orientation of the mobile device while correcting the influence of the internal magnetic field of the mobile device,
A three-axis magnetic sensor for detecting geomagnetism as a magnetic vector in a three-axis orthogonal coordinate system fixed to the portable device;
A center point calculating means for calculating a center point of an azimuth sphere drawn on the three-axis orthogonal coordinate system in accordance with a change in posture of the portable device, the detected value of the magnetic vector obtained by the three-axis magnetic sensor;
The detection value of the magnetic vector obtained by the three-axis magnetic sensor is corrected based on the deviation between the center point of the azimuth sphere and the origin of the three-axis orthogonal coordinate system, and the corrected detection value is used. Azimuth calculating means for calculating the azimuth facing the mobile device,
The center point calculation means is a state in which the first axis is oriented in a direction orthogonal to the magnetic north direction among the first axis, the second axis, and the third axis that are orthogonal to each other in the three-axis orthogonal coordinate system. Then, during the first operation of rotating the portable device with the first axis as the central axis, the plurality of detection values are acquired, and the second axis is set in a direction perpendicular to the magnetic north direction. While the second operation of rotating the portable device about the second axis as the central axis is performed, a plurality of the detection values are obtained, and the plurality of detection values obtained are obtained. To calculate the center point of the azimuth sphere,
The direction of the central axis in the first operation and the second operation is an electron whose orthogonal axis other than the central axis is directed in a direction parallel to the magnetic north direction during rotation. compass.   2. The center point calculating means according to claim 1, wherein the center point calculating means performs a third operation of rotating the portable device about the third axis as a center axis in a state where the third axis is directed in a direction orthogonal to the magnetic north direction. During the period, a plurality of the detection values are acquired, and the center point of the azimuth sphere is determined using the detection values acquired by the first operation, the second operation, and the third operation. The electronic compass characterized in that the direction of the central axis in the third operation calculated is an orientation in which an orthogonal axis other than the central axis is directed in a direction parallel to the magnetic north direction during rotation.   3. The azimuth according to claim 1, wherein after performing a rotation operation, which is an operation of rotating the portable device about the orthogonal axis directed in a direction orthogonal to the magnetic north direction, as a central axis, the orientation is accurate within a predetermined range. Confirm whether or not the center point of the sphere can be calculated, and if it is determined that the center point cannot be calculated with accuracy within the range, a re-operation guidance and / or a possibility that accuracy may be reduced is displayed. An electronic compass provided with rotating operation direction confirmation means.   The center point of the azimuth sphere is temporarily calculated from the detected value of the magnetic vector detected by the three-axis magnetic sensor according to any one of claims 1 to 3, and the temporarily calculated center point Magnetic north that corrects the detected value of the magnetic vector obtained by the three-axis magnetic sensor based on the deviation from the origin of the three-axis orthogonal coordinate system and outputs the corrected magnetic vector direction as the magnetic north direction. An electronic compass comprising a temporary direction calculation means.   5. The electronic compass according to claim 1, wherein the rotation operation is an operation of rotating the portable device by 180 degrees or more.   The center point calculation means according to any one of claims 1 to 5, wherein, in each of the rotation operations, the magnetic force on one of two axes other than the axis that is the center axis. An electronic compass characterized in that a maximum detection value at which a vector component is maximum and a minimum detection value at which the component is minimum are used for calculation of the center point.   7. The output device according to claim 4, further comprising: an output unit configured to display, on the display unit of the portable device, a direction orthogonal to the magnetic north direction obtained by the magnetic north direction temporary calculation unit in the rotation operation. An electronic compass characterized by that.

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