JP2016114569A - Electronic apparatus, sensor calibration method, and sensor calibration program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calibrate the offset of a magnetic sensor satisfactorily without requiring a specific action, etc., by a user that accompanies a calibration process.SOLUTION: When a plurality of pieces of magnetic data acquired by a three-axis magnetic sensor 110 is plotted in a three-dimensional coordinate space where a plurality of axis directions of the magnetic sensor 110 constitute coordinate axes, a plurality of mutually different planes Feach including three or more coordinate points corresponding to first magnetic data are extracted. Second magnetic data corresponding to coordinate points that can be assumed to be present in the vicinity of each plane Fis extracted for each of the extracted planes F, a circumference Cformed on each plane Fin proximity to coordinate points corresponding to the first magnetic data and second magnetic data is estimated, and a vertical line Lpassing through the center coordinate Pof the circumference Cand orthogonal to the plane Fis calculated. Then, the coordinates of a point Pb where the vertical lines Lcalculated for each circumference Cintersect each other are calculated as the offset value of the magnetic sensor 110.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electronic device including a magnetic sensor for detecting geomagnetism, a sensor calibration method for a magnetic sensor applicable to the electronic device, and a sensor calibration program.

  In recent years, various services using location information and map information have been provided in the field of portable (or wearable) electronic devices such as mobile phones, smartphones (high-performance mobile phones), navigation terminals, and sports watches. . These electronic devices generally include a magnetic sensor (also referred to as an electronic compass), and a method of measuring the direction based on the geomagnetism detected by the magnetic sensor is employed.

  By the way, since such an electronic device is equipped with a speaker and various electronic components in addition to the magnetic sensor, magnetism leaking from the speaker or a metal package of the magnetized electronic component around the magnetic sensor. Existing. There may be a strong magnetic field around the electronic device. For this reason, a magnetic sensor mounted on an electronic device detects a magnetic field generated by combining a magnetic field generated from an electronic component inside the electronic device, a magnetic field around the electronic device, and a geomagnetism that is an original detection target. Become. Thereby, the azimuth | direction calculated based on the measured value of the geomagnetism detected by the magnetic sensor in the magnetized state differs from an actual (accurate) azimuth | direction. In order to solve such a problem, a calibration process is required to correct an azimuth error (= offset) due to a magnetic field generated from an electronic component or the like inside the electronic device.

  Conventionally, various offset correction methods by calibration of magnetic sensors have been proposed. For example, Patent Document 1 discloses that magnetic data acquired by a magnetic sensor is obtained by using magnetic data acquired by arbitrarily changing the direction of a magnetic sensor for detecting geomagnetism in three axial directions distributed on a spherical surface. A method is described in which the center coordinates of a specific sphere in which a spherical surface is located in the vicinity of each point of the group is estimated by a statistical method, and offset information (offset value) is calculated based on the center coordinates. Further, for example, in Patent Document 2, when magnetic data (magnetic field data) acquired by rotating a triaxial geomagnetic sensor in parallel with the ground surface in a tilted state exists in the same plane, the magnetic data A method is disclosed in which the center coordinates and radius of an arc serving as a distribution locus are obtained and calculated as a temporary offset value.

Japanese Patent No. 4391416 JP 2006-78474 A

  In the magnetic sensor offset value acquisition method disclosed in Patent Document 1 described above, it is necessary to arbitrarily change the orientation of the magnetic sensor during the magnetic data acquisition period. Here, if the orientation of the magnetic sensor does not change arbitrarily, and the orientation of the magnetic sensor changes while keeping the posture with respect to a specific axis (for example, the coordinate axis in the gravity direction) constant, the acquired magnetic data is It is distributed in a concentrated manner in a specific plane or locally distributed in a specific area of the spherical surface. Therefore, in such a case, there is a problem that the solution by the statistical method cannot be calculated or the calculation error becomes very large, and an incorrect solution (center coordinate and offset value) is calculated. doing.

  In addition, in the offset value acquisition method disclosed in Patent Document 2, for example, when the user looks at map information provided by an electronic device, for example, the user can change the direction while viewing the screen of the electronic device. Even when such an operation is performed, calibration (offset correction) can be performed. However, in this method, the center coordinates of an arc formed from the distribution locus of magnetic data existing on a specific plane is calculated as a temporary offset and used for azimuth calculation, as disclosed in Patent Document 1 The center coordinates (= offset) of the sphere on the three-dimensional coordinates are not calculated. Therefore, there is a problem that the original offset value cannot be calculated with high accuracy.

  Furthermore, when performing calibration processing of a magnetic sensor, as described in the above-mentioned patent documents, the user (device user) generally changes the direction with respect to the electronic device equipped with the magnetic sensor. It is necessary to perform an operation to be performed or a specific operation, and there is a problem that the operation is troublesome.

  Therefore, in view of the above-described problems, the present invention provides an electronic apparatus and a sensor calibration method that can satisfactorily perform offset correction of a magnetic sensor without requiring a specific operation associated with a calibration process by a user, An object is to provide a sensor calibration program.

The present invention
In electronic equipment,
A magnetic sensor that detects a magnetic field around the electronic device and outputs magnetic data in a plurality of axial directions;
Three or more different from each other in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes based on the plurality of magnetic data acquired from the magnetic sensor according to the movement of the magnetic sensor A plane extraction unit for extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. And a central coordinate calculation unit that estimates a circumference close to a coordinate point corresponding to the first magnetic data and the second magnetic data in each of the plurality of planes, and calculates a central coordinate of the circumference. When,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated, and a point closest to the plurality of vertical lines in the plurality of planes is calculated. An offset value calculation unit for calculating coordinates as an offset value of the magnetic sensor;
It is characterized by having.

The sensor calibration method according to the present invention includes:
Based on a plurality of magnetic data in a plurality of axial directions acquired from a moving magnetic sensor, in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes, three or more different from each other Extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. And
For each of the plurality of planes, estimate the circumference close to the coordinate point corresponding to the first magnetic data and the second magnetic data, calculate the center coordinates of the circumference,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated.
Calculating the coordinates of the point closest to the plurality of vertical lines in the plurality of planes as an offset value of the magnetic sensor;
It is characterized by.

The sensor calibration program according to the present invention includes:
On the computer,
Based on a plurality of magnetic data in a plurality of axial directions acquired from a moving magnetic sensor, in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes, three or more different from each other Extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. Let
In each of the plurality of planes, the circumference that is close to the first magnetic data and the second magnetic data is estimated, and the center coordinates of the circumference are calculated,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line passing through the central coordinates and orthogonal to the plane is calculated,
Calculating the coordinates of a point closest to the plurality of vertical lines in the plurality of planes as an offset value of the magnetic sensor;
It is characterized by.

  According to the present invention, it is possible to satisfactorily perform offset correction of a magnetic sensor without detecting a specific operation associated with a calibration process by a user, and to detect an accurate orientation.

It is a schematic block diagram which shows the some application example of the electronic device which concerns on this invention. It is a functional block diagram which shows one Embodiment of the electronic device which concerns on this invention. It is a flowchart which shows an example of the control method in the electronic device which concerns on one Embodiment. It is a conceptual diagram which shows the relationship between the output distribution example of a magnetic sensor, and offset correction. It is a conceptual diagram for demonstrating the calibration process which concerns on one Embodiment. It is a figure which shows the specific example (the 1) of the calibration process which concerns on one Embodiment. It is a figure which shows the specific example (the 2) of the calibration process which concerns on one Embodiment.

Hereinafter, an electronic device, a sensor calibration method, and a sensor calibration program according to the present invention will be described in detail with reference to embodiments.
<Electronic equipment>
FIG. 1 is a schematic configuration diagram showing a plurality of application examples of an electronic apparatus according to the present invention. FIG. 2 is a functional block diagram showing an embodiment of an electronic apparatus according to the present invention.

  The electronic device according to the present invention is applied to an electronic device having a function for providing a user with various services using position information and map information, for example. Specifically, the electronic device is, for example, a wristwatch-type or wristband-type sports watch 10 as shown in FIG. 1A, or an outdoor device such as mountaineering as shown in FIG. (Logger or navigation terminal) 20, smartphone 30 or tablet terminal as shown in FIG. Hereinafter, for convenience of explanation, these devices are collectively referred to as “electronic device 100”.

  For example, as shown in FIG. 2, the electronic device 100 according to the present embodiment includes a magnetic sensor 110, a motion sensor 120, a GPS receiving circuit 130, an input / output interface unit (hereinafter referred to as “input / output I / F unit”). 140, an input operation unit 150, an output unit 160, an arithmetic circuit unit 170, a memory unit 180, and a power supply unit 190. Here, the arithmetic circuit unit 170 corresponds to each configuration of a plane extraction unit, a center coordinate calculation unit, an offset value calculation unit, an offset value change determination unit, and an orientation calculation unit in the present invention. Further, in FIG. 2, when the present invention is applied to each electronic device shown in FIG. 1, various services using magnetic data or directions calculated based on the magnetic data are provided to the user. The configuration required at the time is also shown. In order to realize a sensor calibration method to be described later, it is sufficient that at least the magnetic sensor 110 is connected to the arithmetic circuit unit 170 among the configurations shown in FIG. The receiving circuit 130, the input / output I / F unit 140, and the output unit 160 may not be provided.

  The magnetic sensor 110 is a sensor that detects the magnitude and direction of the magnetic field around the electronic device 100, detects the magnitude of the magnetic field in three axial directions orthogonal to each other, and outputs the detected magnetic data. The magnetic field detected by the magnetic sensor 110 includes the geomagnetism at that location and the peripheral magnetic field generated by a magnet, a magnetic body, or the like existing in the vicinity of the magnetic sensor 110. This magnetic data is used, for example, when calculating an orientation based on the electronic device 100 in the arithmetic circuit unit 170 described later. Magnetic data acquired from the magnetic sensor 110 is associated with time data and stored in a predetermined storage area of the memory unit 180 described later.

  The motion sensor 120 includes an acceleration sensor 122, an angular velocity sensor (gyro sensor) 124, and the like, and detects a user's body movement and motion state, a force in a specific direction applied to the electronic device 100, and the like. The acceleration sensor 122 measures the rate of change (acceleration) in the movement speed that occurs in the electronic device 100 in accordance with the movement of the user's body. The acceleration sensor 122 includes, for example, a triaxial acceleration sensor, detects an acceleration component (acceleration signal) along each of the three axial directions orthogonal to each other, and outputs the acceleration data as sensor data. Further, the angular velocity sensor 124 measures a change (angular velocity) in the moving direction that occurs in the electronic device 100 in accordance with the movement of the user's body. The angular velocity sensor 124 includes, for example, a three-axis angular velocity sensor, and detects angular velocity components (angular velocity signals) generated in the rotational direction of the rotational movement along each axis for the three axes orthogonal to each other that define the acceleration data. And output as angular velocity data as sensor data. Sensor data (acceleration data, angular velocity data) acquired from the acceleration sensor 122 and the angular velocity sensor 124 is stored in a predetermined storage area of the memory unit 180 in association with time data.

  The GPS receiving circuit 130 receives radio waves from a plurality of GPS satellites constituting a GPS (Global Positioning System) via a GPS antenna (not shown), and is based on latitude and longitude information. Obtain geographical location information and output it as positioning data. Here, when the electronic device 100 is pointed in an arbitrary direction, or when a user wearing or carrying the electronic device 100 is moving, the positioning data acquired from the GPS receiving circuit 130 is calculated by the arithmetic circuit unit 170. Is used when calculating the azimuth and moving direction in which the electronic device 100 is facing. The positioning data acquired from the GPS receiving circuit 130 is stored in a predetermined storage area of the memory unit 180 in association with the time data.

  The input / output I / F unit 140 communicates various data and signals with peripheral devices, information devices, communication networks, etc. (not shown) outside the electronic device 100 in a predetermined communication format using wired or wireless. I / O or send / receive. For example, the input / output I / F unit 140 transmits / receives biological information such as heartbeat data to / from a sensor device attached to another part of the body, or an information processing device such as a personal computer or a network server The acquired magnetic data, sensor data, and the like are transmitted and received, and map information and the like are acquired.

  The input operation unit 150 includes, for example, an operation switch 152, a touch panel 154, and the like provided in a housing of the electronic device 100 (sports watch 10, outdoor device 20, smartphone 30, etc.) shown in FIG. The input operation unit 150 is used for various input operations such as an operation power source of the electronic device 100 and a positioning operation on / off operation of the GPS reception circuit 130, an operation of application software, and a function setting in each configuration.

  The output unit 160 includes a display unit 162, an acoustic unit 164, a vibration unit (not shown), and the like provided in the casing of the electronic device 100. The output unit 160 includes at least an orientation based on magnetic data acquired from the magnetic sensor 110 described above, sensor data acquired from the motion sensor 120, position information and map information based on positioning data acquired from the GPS receiving circuit 130, Various types of information such as alarms are provided or notified to the user through vision, hearing, touch, or the like.

  The arithmetic circuit unit 170 is an arithmetic processing device such as a CPU (central processing unit) or MPU (microprocessor) having a timekeeping function, and executes a predetermined control program or algorithm program based on an operation clock. Thereby, the arithmetic circuit unit 170 performs a sensing operation in the magnetic sensor 110 and the motion sensor 120, a positioning operation in the GPS receiving circuit 130, a calibration process and a direction calculation process of the magnetic sensor 110 described later, and an information providing operation in the output unit 160. To control various operations. Note that the control method of the electronic device 100 including the calibration process of the magnetic sensor 110 will be described in detail later.

  The memory unit 180 associates magnetic data acquired from the magnetic sensor 110 described above, sensor data acquired from the motion sensor 120, positioning data acquired from the GPS receiving circuit 130, etc. with a predetermined storage area. Save to. The memory unit 180 also stores various data generated by the processing operation (sensor calibration operation) executed in the arithmetic circuit unit 170 and the offset value of the magnetic sensor 110 in a predetermined storage area. The memory unit 180 also performs a calibration process for the magnetic sensor 110 based on a control program for executing operations in each configuration, such as the magnetic sensor 110, the motion sensor 120, and the GPS receiving circuit 130, and the magnetic data. Save the algorithm program to execute. Note that these programs may be incorporated in the arithmetic circuit unit 170 in advance. Further, the memory unit 180 may be partly or wholly configured as a removable storage medium such as a memory card and configured to be detachable from the electronic device 100.

  The power supply unit 190 supplies driving power to each component inside the electronic device 100. When the electronic device 100 is a portable device, for example, a primary battery such as a commercially available button type battery or a secondary battery such as a lithium ion battery is applied to the power supply unit 190. In addition to the primary battery and secondary battery described above, the power supply unit 190 can be used alone or in combination with a power source using energy harvesting technology that generates power using energy such as vibration, light, heat, and electromagnetic waves. And may be applied.

<Control method of electronic equipment>
Next, a control method (sensor calibration method) in the electronic apparatus according to the present embodiment will be described with reference to the drawings. Here, the control method of the electronic device shown in the following flowchart is realized when the arithmetic circuit unit 170 described above executes processing according to a predetermined control program and algorithm program.

  FIG. 3 is a flowchart illustrating an example of a control method in the electronic apparatus according to the present embodiment. FIG. 4 is a conceptual diagram showing a relationship between an output distribution example of the magnetic sensor and offset correction. FIG. 5 is a conceptual diagram for explaining the calibration process according to the present embodiment, and FIGS. 6 and 7 are diagrams illustrating a specific example of the calibration process according to the present embodiment.

  In the method for controlling the electronic device 100 according to the present embodiment, a series of processes as shown in the flowchart of FIG. 3 are executed in the electronic device 100 including the magnetic sensor 110, the motion sensor 120, and the GPS receiving circuit 130, for example. . First, when the user operates the input operation unit 150, driving power is supplied from the power supply unit 190 to each component inside the electronic device 100, and the electronic device 100 is activated. Thereby, the arithmetic circuit unit 170 performs normal processing including sensing operation by the magnetic sensor 110 and the motion sensor 120 and positioning operation by the GPS receiving circuit 130 (step S102).

  In this normal processing, a plurality of magnetic data acquired from the magnetic sensor 110 while rotating or moving the electronic device 100 including the magnetic sensor 110 in the first environment having a certain geomagnetism is converted into three axes of the magnetic sensor 110. Is plotted on a three-dimensional coordinate space having coordinate axes as shown in FIG. 4, for example, the coordinate points corresponding to each magnetic data are distributed almost on the spherical surface Sp. The center point Pa of the sphere defined by the spherical surface Sp indicates the reference point of the magnetic data group acquired from the magnetic sensor 110, and the radius r of the sphere corresponds to the magnitude (strength) of geomagnetism. Further, the center point Pa of the sphere is shifted (= offset) from the reference point (origin point) Pc in the three-dimensional coordinate space due to the magnetic sensor 110 being influenced (magnetized) by the peripheral magnetic field of the electronic device 100. ) Is generated. In this case, an offset value (denoted as “offset vector” in the figure) corresponding to the difference between the center point Pa of the sphere and the reference point Pc is calculated, and a magnetic data group acquired from the magnetic sensor 110 is calculated. By performing offset correction by subtracting the calculated offset value, it is possible to remove the influence of the magnetic field around the magnetic sensor 110 and calculate an accurate azimuth with the electronic device 100 as a reference.

  Here, when the environment around the electronic device 100 changes to, for example, the second environment in which the peripheral magnetic field is strengthened or the direction of the magnetic field changes, the magnetic field detected by the magnetic sensor 110 under the influence of the change in the peripheral magnetic field is also Will change. Therefore, the distribution in the three-dimensional coordinate space of the coordinate points corresponding to the magnetic data group (denoted as “magnetic data group after magnetization” in the figure) acquired from the magnetic sensor 110 in the second environment is shown in FIG. As shown in FIG. 3, the distribution of coordinate points (spherical surface Sp and the center point Pa of the sphere) corresponding to the initial magnetic data group for which the offset value is calculated is changed (moved) from the position in the three-dimensional coordinate space. (In the figure, the spherical surface Sp ′ and the center point Pa ′ of the sphere). For this reason, if correction using the initially calculated offset value is performed on the magnetic data group acquired in this environment, the calculated azimuth is different from the accurate azimuth. In this case, it is necessary to recalculate the offset value.

  Therefore, the arithmetic circuit unit 170 monitors a change in the offset value and executes a process for determining whether or not the offset value has changed (step S104). Specifically, when the arithmetic circuit unit 170 performs correction using the current offset value on the magnetic data group acquired by the magnetic sensor 110, the coordinate point corresponding to the corrected magnetic data group Is distributed on a spherical surface centered on the reference point (origin) Pc in the three-dimensional coordinate space. When the coordinate points corresponding to the corrected magnetic data group are not distributed on the spherical surface, that is, the center coordinates of the sphere in which the coordinate points corresponding to the corrected magnetic data group are distributed are in the three-dimensional coordinate space. When it is deviated from the coordinates of the reference point (origin) Pc, it is determined that the current offset value is not appropriate and the offset value has changed from the current offset value (Yes in step S104), and the calibration process is performed. Start (step S106).

  Alternatively, the arithmetic circuit unit 170 may determine the distance between the coordinate point corresponding to the magnetic data acquired for a certain period and the center point Pa (the radius r of the sphere, that is, the magnitude of the geomagnetism), or the corrected magnetic data and the reference point Pc. If there is a variation in the distance between and the offset value, it is determined that the offset value has changed, and the calibration process is started.

  On the other hand, the coordinate points corresponding to the corrected magnetic data group using the current offset value are distributed on a spherical surface centered on the reference point Pc in the three-dimensional coordinate space, and the magnetic data and the reference point Pc are related to each other. If there is no variation in distance, the arithmetic circuit unit 170 determines that the offset value has not changed from the current offset value (No in step S104), returns to step S102, and continues normal processing.

  Note that the process of determining whether or not the offset value needs to be calculated in step S104 is executed in the background without making the user particularly aware. In addition, the determination process of whether or not the offset value needs to be calculated is not limited to the above-described method. For example, the magnitude (strength) of the geomagnetism at the point derived based on the positioning data acquired by the GPS receiver circuit 130 and the magnetic sensor output vector calculated based on the magnetic data acquired by the magnetic sensor 110 If the difference is equal to or greater than a predetermined threshold, it may be determined that the offset value needs to be calculated.

In the calibration process applied to the present embodiment, the offset value of the magnetic sensor 110 is calculated by roughly executing the following series of processes by the arithmetic circuit unit 170. That is, as shown in FIG. 5, when the arithmetic circuit unit 170 plots the coordinate points corresponding to the magnetic data acquired from the magnetic sensor 110 on the three-dimensional coordinate space, the arithmetic circuit unit 170 uses the data group distributed on the spherical surface Sp. Using the statistical method, the respective circumferences C ₁ and C ₂ , which are cross-sectional shapes when the spherical surface Sp is cut by a plurality of (here, two) planes, are estimated. Next, the arithmetic circuit unit 170 calculates vertical lines L1 and L2 that pass through the centers of the estimated circumferences C ₁ and C ₂ and are perpendicular to the planes. Then, the arithmetic circuit unit 170 estimates the point at which the vertical lines L1 and L2 intersect each other or the point closest to the vertical lines L1 and L2 as the center coordinate Pb of the sphere. The center coordinate Pb of this sphere corresponds to the offset value of the magnetic sensor 110.

Hereinafter, the calibration process applied to this embodiment will be specifically described.
First, the arithmetic circuit unit 170 acquires a plurality of magnetic (magnetic data group) data over time from the magnetic sensor 110 of the moving electronic device 100 at a predetermined sampling frequency (step S106). The acquired magnetic data group is stored in a predetermined storage area of the memory unit 180.

Then, the arithmetic circuit 170, based on the distribution of coordinate points corresponding to the magnetic data group acquired in the three-dimensional coordinate space, for a predetermined number N or more different planes F _N of the three-dimensional coordinate space, each plane F determines whether or not to obtain the center coordinates _{P N} of the circumference _{C N,} which is formed on the _N (step S110). Here, the center coordinates P _N of the circumference C _N, which is formed on a plane F _N, the cross section of when the magnetic data group acquired from the magnetic sensor 110 is a spherical surface distribution, and cut by a specific plane F _N It is the center coordinate of the circumference which is a shape, and is an important parameter used for an offset value calculation process described later. Center coordinates _{P N} of the circumference _{C N} is calculated by a series of processes of steps S112~S120 to be described later. Therefore, immediately after starting the measurement of magnetic data by the magnetic sensor 110 or in a state where a sufficient number of magnetic data is not collected, the arithmetic circuit unit 170 determines “No” in step S110, and steps S112 to S112. A series of processing of S120 is executed.

That is, in step S110, when the center coordinates P _N of the circumference C _N equal to or greater than the predetermined number N have been acquired, the arithmetic circuit unit 170 executes an offset value calculation process described later (step S122).

On the other hand, when the number of center coordinates P _N of the acquired circumference C _N is less than the predetermined number N, the arithmetic circuit unit 170 has already extracted a specific plane F _N in the three-dimensional coordinate space. It is determined whether or not (step S112). In step S112, in a case (step S112, Yes) the particular plane _{F N} is already extracted, the arithmetic circuit 170, the magnetic data can be regarded as a magnetic data group is present on the plane _{F N} Obtain (step S116). On the other hand, in a case where the particular plane _{F N} is not extracted (step S112, No), the arithmetic circuit 170, after extracting the plane _{F N} (step S114), the plane _{F N} from the magnetic data group To obtain magnetic data that can be considered to exist.

Specifically, when the magnetic data is acquired as three-dimensional direction data (r, θ, φ), the arithmetic circuit unit 170 first obtains an angle component (θ, φ) from the magnetic data group. At least three different magnetic data (first magnetic data) are selected or extracted. Then, as shown in FIG. 6A, the arithmetic circuit unit 170 plots the coordinate points corresponding to the selected three pieces of magnetic data in the three-dimensional coordinate space of xyz (x ₁ , _{y 1, z 1), (} x 2, y 2, z 2), extracts the plane _{F N} that contains _{(x 3, y 3, z} 3). Then, the arithmetic circuit 170, to sift the obtained magnetic data group, magnetic data that can be regarded as being present on a plane F _N calculated above (the second magnetic data). Specifically, the arithmetic circuit 170, as shown in FIG. 6 (b), for each of the magnetic data by subtracting the normal to the plane F _N, the distance to the plane F _N (perpendicular distance) a predetermined threshold value Hth It is determined whether or not: The arithmetic circuit 170, when the perpendicular distance is less than the threshold value Hth may coordinate points corresponding to the magnetic data is regarded as being present on a plane F _N, acquires select the magnetic data. On the other hand, the coordinate point corresponding to the magnetic data when the perpendicular distance is greater than the threshold Hth is regarded as not present on a plane F _N. Here, the threshold value Hth, which is a reference for determining the perpendicular distance, is about 450 milligauss (mG) which is a general strength of geomagnetism in an environment where the electronic device 100 is used (for example, in Japan), It is set to an extremely small numerical value (for example, about ± 1 milligauss). Thus, be deemed to only the coordinate point of the magnetic data located in close proximity to the plane F _N is present on a plane F _N.

Then, the arithmetic circuit 170, the number of magnetic data acquired by selecting regarded as being present on said plane F _N (number of acquisition) is equal to or more than a predetermined number (step S118). Then, when the number of acquisition of the magnetic data is equal to or more than a predetermined number, the arithmetic circuit 170 estimates a circumference C _N which is formed to include a magnetic data distributed on the plane F _N, its circumference calculating the center coordinates _{P N} of C _N (step S120). On the other hand, when the acquisition number of magnetic data is less than the predetermined number, the arithmetic circuit unit 170 returns to step S108 and continues the process of acquiring magnetic data by the magnetic sensor 110. In step S118, the if the number of acquisition of the magnetic data is equal to or more than a predetermined number, the arithmetic circuit 170 executes the following series of processes, the circumference C which is formed on a plane F _N by the magnetic data calculating the center coordinates _{P N} of _N.

Specifically, the central coordinates _{P N} of the circumference _{C N (X N, Y N} , Z N), if the radius of the circle _{C N} was _{R N,} the center as shown in FIG. 6 (c) balls made of coordinates _{P N} and the radius _{R N} is expressed by the following equation (11).
(X−X _N ) ² + (y−Y _N ) ² + (z−Z _N ) ² = R _N ² (11)
The planar _{F N} extracted in step S114 described above is expressed by the equation of the following equation (12). Here, a, b, c, and d are coefficients.
ax + by + cz + d = 0 (12)

(12) In the formula, the central coordinates _{P N (X N, Y N} , Z N) Since a on the plane _{F N,} the following equation (13) holds.
aX _N + bY _N + cZ _N + d = 0
Z _N = − (aX _N + bY _N + d) / c (13)
Here, when A = −a / c, B = −b / c, and C = −d / c, the expression (13) is expressed by the following expression (14).
Z _N = AX _N + BY _N + C (14)

From the above, the following equation (15) holds.
(x−X _N ) ² + (y−Y _N ) ² + {z− (AX _N + BY _N + C)} ² = R _N ² (15)
Magnetic data distributed on a plane _{F N (x i, y i} , z i) from the circumference _{C N} center coordinates _P N of _{(X N, Y N, Z} N) distance _{d i} follows (16) to It is expressed by a formula.

Here, as in the following equation (17), the difference between the square of the square value and the radius R _N of the distance d _i is defined as the estimation error epsilon _{i.
^{ε i = d i 2 -R N}} 2 ··· (17)
Furthermore, the square sum value S of the estimation errors ε _i is defined as in the following equation (18). Then, the center coordinates P _N (X _N , Y _N , Z _N ) that minimize the square sum value S are calculated.
S = Σε _i ² (18)
The equation (18) representing the square sum value S can be rewritten as the following equation (19).

  By substituting the above equation (14) into the equation (19), the square sum value S is expressed by the following equation (20). Here, if it puts like (21) Formula, (20) Formula will be represented by the following (22) Formula.

(22) conditions for minimizing the square sum S expressed by the _formula, X _N, Y _N, as independent variables _{D N,} the S _{X N,} Y _N, follows by differentiating _{D N} ( 23).
Therefore, X _N , Y _N , and D _{N that} are independent variables are calculated by solving the following simultaneous equations (24). Here, the equation (24) is defined as the equation (25).

Then, in step S120, the arithmetic circuit 170, the center coordinates _P N of the circumference _{C N} which is formed by the magnetic data distributed on a specific plane _{F N (X N, Y N} , Z N) after calculating the Returning to step S110, it is determined again whether or not the center coordinates P _N of different circumferences C _N equal to or greater than the predetermined number _N have been acquired. In step S110, when the center coordinates P _N of a predetermined number N or more different circumferential C _N has been acquired, the arithmetic circuit 170 executes a series of offset value calculation process described below (step S122).

In the offset value calculation process, as shown in FIG. 5, the offset value of the magnetic sensor 110 is calculated by calculating the center coordinates Pb of the sphere defined by the spherical surface Sp on which the magnetic data group is distributed. That is, as shown in FIG. 7 (a), if the vertical line L _N passing through the center coordinate P _N of the circumference C _N on two different planes F _N intersect each other, the center coordinates Pb of the sphere, the above-described It passes through the center coordinate P _N of a series of circumferentially C _N estimated by the processing and present in the perpendicular on the vertical line L _N to the plane F _N. Therefore, by calculating the point at which the circumference C _N each vertical line L _N passing through the center coordinate P _N of the plurality of different planes F _N intersect each other, it obtains the offset value is a center coordinate Pb of the sphere.

Specifically, as illustrated in FIGS. 7B and 7C, first, the arithmetic circuit unit 170 determines the center coordinates P of the circumference C ₁ estimated based on the magnetic data distributed on the plane F _1. through _1, and calculates the vertical line _{L 1} perpendicular to the plane _{F 1.} The arithmetic circuit unit 170 through the center coordinates P ₂ of the circumference C ₂ which is estimated based on the magnetic data distributed on different planes F ₂ which is a plane F _1, and perpendicular to the plane F ₂ perpendicular to calculate the line _{L 2.} Then, when there is an intersection between the calculated vertical line L ₁ and the vertical line L ₂ , the arithmetic circuit unit 170 calculates the intersection as the center coordinate Pb (Cx, Cy, Cz) of the sphere, Calculate the offset value.

On the other hand, when there is no intersection between the calculated vertical line L ₁ and the vertical line L ₂ , the arithmetic circuit unit 170 determines the point closest to the vertical line L ₁ and the vertical line L ₂ as the center coordinate of the sphere. Calculated as Pb. That is, when the point on the vertical line L ₁ orthogonal to the plane F ₁ is P _L1 and the point on the vertical line L ₂ orthogonal to the plane F ₂ is P _L2 , each point with respect to the reference point Pc of the three-dimensional coordinates The positions of the points P _L1 and P _L2 are expressed by the following equation (26).

The distance between the vertical line L ₁ orthogonal to the plane F ₁ and the calculated center coordinate Pb (Cx, Cy, Cz) of the sphere is K _1, and the vertical line L ₂ orthogonal to the plane F ₂ is calculated. center coordinate Pb of the sphere to be (Cx, Cy, Cz) of the distance between the _{K 2.} Here, when I = K ₁ ² + K ₂ ² is defined as the error function I, it is expressed by the following equation (27).

Next, in this equation (27), a center coordinate Pb (Cx, Cy, Cz) that minimizes the error function I is obtained. Thus obtained center coordinates Pb (Cx, Cy, Cz) is estimated to be a point closest to the vertical line L ₁ and the vertical line L _2. Here, it is assumed that each derivative of I by Cx, Cy, Cz, p, q when the error function I is minimum is zero as shown in the following equation (28).

  By arranging the above equations (27) and (28), the following equation (29) is obtained.

As described above, when the number of the circumference C ₁ and the vertical line L ₂ used for calculating the center coordinate Pb of the sphere as the offset value is generalized as N (N ≧ 2), the following equation (30) It is represented by Here, in equation (30), A _i is defined as in equation (31).

  Therefore, Cx, Cy, and Cz indicating the center coordinates Pb of the sphere are calculated by solving the simultaneous equations shown in the following equation (32).

As described above, in the offset value calculation processing, the predetermined number N or more different planes F _N, passes through the center coordinate P _N of the circumference C _N, which is formed on each plane F _N, and the plane F _N By calculating the point at which the orthogonal vertical lines _LN intersect each other, the center coordinate Pb of the sphere defined by the spherical surface on which the magnetic data group is distributed is calculated. The central coordinate Pb is a new offset value (offset vector) of the magnetic sensor 110 that is affected by magnetization of an electronic component or the like disposed in the vicinity of the magnetic sensor 110. The offset value calculated in this way is stored in a predetermined storage area of the memory unit 180 by the arithmetic circuit unit 170, and the offset value is updated (step S124).

  In the offset value calculation process described above, a case has been described in which the intersections of vertical lines passing through the center coordinates of the circumferences on two different planes including arbitrary magnetic data acquired from the magnetic sensor 110 are calculated. However, the present invention is not limited to this. That is, according to the present invention, center coordinates of a sphere defined by a spherical surface on which a magnetic data group is distributed may be obtained using a similar method for three or more planes. According to this, the calculation accuracy of the offset value that is the center coordinate of the sphere can be improved.

  Next, the arithmetic circuit unit 170 obtains magnetic data (a data group distributed on the spherical surface Sp ′ at the center point Pa ′ shown in FIG. 4 or the spherical surface Sp at the center coordinate Pb shown in FIG. 5) from the magnetic sensor 110. Is corrected using the updated offset value stored in the memory unit 180, thereby calculating an orientation based on the electronic device 100 (step S126). Here, the arithmetic circuit unit 170 may return to the normal process of step S102 and execute the azimuth calculation process as the normal process.

  Although not shown in the flowchart shown in FIG. 3, the arithmetic circuit unit 170 constantly monitors an input operation for interrupting or terminating the processing operation or a change in the operating state during the execution of the series of processing operations described above. When the input operation or state change is detected, the processing operation is forcibly terminated. Specifically, the arithmetic circuit unit 170 detects an operation power-off operation by the user, a decrease in the remaining battery level in the power supply unit 190, an abnormality in a function being executed or an application, and the like, and performs a series of processing operations. Forcibly interrupt and exit.

  In the series of processing operations described above, the control method is shown in which the calibration processing after step S106 is executed when it is determined in step S104 that the offset value needs to be calculated. However, the present invention is not limited to this. Is not to be done. For example, based on the acceleration signal output from the acceleration sensor 122 or the angular velocity sensor 124 included in the motion sensor 120 or the sensor data of the angular velocity signal, it is detected that the user carrying the electronic device has changed the moving direction by turning a corner or the like. The offset value of the magnetic sensor 110 is calculated by automatically executing the calibration process after step S106 described above and calculating the center coordinates of the sphere defined by the sphere on which the acquired magnetic data group is distributed. May be calculated.

As described above, in the present embodiment, when the coordinate points corresponding to the magnetic data acquired from the magnetic sensor 110 are plotted on the three-dimensional coordinates, the predetermined coordinate points including the coordinate points corresponding to arbitrary three magnetic data are included. calculating the equation number N or more different planes F _N. For each plane F _N calculated performs selection to extract only the coordinate point of the magnetic data that can be regarded as existing in the vicinity. The coordinate points corresponding to the extracted data group and estimating the circumference C _N, which is formed on each plane F _N, passes through the center coordinate P _N of the circumference C _N, and the vertical perpendicular line to the plane F _N L _N is calculated. By vertical line L _N calculated for each circumference C _N to calculate the point of intersection with each other, and calculates the coordinates of the intersection point as an offset value of the magnetic sensor. Further, the magnetic data acquired from the magnetic sensor is corrected by using the calculated offset value, thereby calculating an orientation based on the electronic device.

  That is, for example, when measuring an orientation while a user carries or wears an electronic device including a three-axis magnetic sensor, the orientation of the magnetic sensor does not change arbitrarily, and a specific axis (for example, a coordinate axis in the gravitational direction) ) When the orientation of the magnetic sensor changes while maintaining a constant attitude to the magnetic field, the magnetic data acquired from the magnetic sensor is concentrated and distributed in a specific plane, or locally in a specific area of the sphere Will be distributed. In such a case, in the offset value acquisition method disclosed in Patent Document 1 or the like shown in the background art, a solution by a statistical method becomes impossible to calculate or a calculation error becomes very large, and an incorrect solution is obtained. As a result, the offset value cannot be calculated correctly.

In contrast, in this embodiment, the circumference on the basis of the magnetic data of three arbitrary points distributed in a spherical to calculate the predetermined number N or more different planes F _N, it is formed on each plane F _N passes through the center coordinate P _N of C _N, and, by calculating the point at which the vertical line L _N perpendicular to the plane F _N cross each other, it is possible to accurately calculate the offset value of the magnetic sensor. Therefore, in this embodiment, the posture of the electronic device is changed, and the magnetic data acquired from the magnetic sensor is not widely distributed on the spherical surface. Even if the distribution is concentrated in the plane or locally distributed in a specific area of the spherical surface, the calibration process can be performed satisfactorily.

  Further, in the present embodiment, a series of processing operations including a determination process for determining whether to execute a calibration process by monitoring a change in an offset value, an offset value calculation process based on acquired magnetic data, and the like. Run in the background without any particular user awareness. Therefore, according to the electronic apparatus according to the present embodiment, the calibration process (offset correction) of the magnetic sensor is automatically performed without performing a specific operation or operation consciously by the user, and an accurate orientation is obtained. Can be calculated.

As mentioned above, although some embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It includes the invention described in the claim, and its equivalent range.
Hereinafter, the invention described in the scope of claims of the present application will be appended.

(Appendix)
[1]
In electronic equipment,
A magnetic sensor that detects a magnetic field around the electronic device and outputs magnetic data in a plurality of axial directions;
Three or more different from each other in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes based on the plurality of magnetic data acquired from the magnetic sensor according to the movement of the magnetic sensor A plane extraction unit for extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. And a central coordinate calculation unit that estimates a circumference close to a coordinate point corresponding to the first magnetic data and the second magnetic data in each of the plurality of planes, and calculates a central coordinate of the circumference. When,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated, and a point closest to the plurality of vertical lines in the plurality of planes is calculated. An offset value calculation unit for calculating coordinates as an offset value of the magnetic sensor;
An electronic device comprising:

[2]
The offset value calculation unit
When the plurality of vertical lines intersect with each other, the coordinates of the intersecting points of the plurality of vertical lines are calculated as the offset value,
The electron according to [1], wherein, when the plurality of vertical lines do not intersect each other, the coordinates of the point having the smallest distance from each of the plurality of vertical lines are calculated as the offset value. machine.

[3]
An offset value change determination unit for determining whether or not the offset value of the magnetic sensor has changed,
When it is determined that the offset value has changed in the offset value change determination unit, the extraction of the plurality of planes in the plane extraction unit, the calculation of the center coordinates of the circumference in the center coordinate calculation unit, The electronic device according to [1] or [2], wherein the offset value is calculated by the offset value calculation unit.

[4]
A motion sensor that detects a movement operation of the electronic device and outputs sensor data including acceleration data and angular velocity data based on the movement operation;
When it is detected that the moving direction of the electronic device has changed based on the sensor data, extraction of the plurality of planes in the plane extraction unit and calculation of center coordinates of the circumference in the center coordinate calculation unit The electronic device according to any one of [1] to [3], wherein the offset value is calculated by the offset value calculation unit.

[5]
Based on a plurality of magnetic data in a plurality of axial directions acquired from a moving magnetic sensor, in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes, three or more different from each other Extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. And
For each of the plurality of planes, estimate the circumference close to the coordinate point corresponding to the first magnetic data and the second magnetic data, calculate the center coordinates of the circumference,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated.
Calculating the coordinates of the point closest to the plurality of vertical lines in the plurality of planes as an offset value of the magnetic sensor;
A sensor calibration method characterized by the above.

[6]
On the computer,
Based on a plurality of magnetic data in a plurality of axial directions acquired from a moving magnetic sensor, in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes, three or more different from each other Extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. Let
In each of the plurality of planes, the circumference that is close to the first magnetic data and the second magnetic data is estimated, and the center coordinates of the circumference are calculated,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated.
Calculating the coordinates of a point closest to the plurality of vertical lines in the plurality of planes as an offset value of the magnetic sensor;
A sensor calibration program characterized by the above.

DESCRIPTION OF SYMBOLS 100 Electronic device 110 Magnetic sensor 120 Motion sensor 122 Acceleration sensor 124 Angular velocity sensor 130 GPS receiving circuit 140 Input / output I / F part 170 Arithmetic circuit part 180 Memory part

Claims (6)

In electronic equipment,
A magnetic sensor that detects a magnetic field around the electronic device and outputs magnetic data in a plurality of axial directions;
Three or more different from each other in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes based on the plurality of magnetic data acquired from the magnetic sensor according to the movement of the magnetic sensor A plane extraction unit for extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. And a central coordinate calculation unit that estimates a circumference close to a coordinate point corresponding to the first magnetic data and the second magnetic data in each of the plurality of planes, and calculates a central coordinate of the circumference. When,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated, and a point closest to the plurality of vertical lines in the plurality of planes is calculated. An offset value calculation unit for calculating coordinates as an offset value of the magnetic sensor;
An electronic device comprising: The offset value calculation unit
When the plurality of vertical lines intersect with each other, the coordinates of the intersecting points of the plurality of vertical lines are calculated as the offset value,
2. The electron according to claim 1, wherein, when the plurality of vertical lines do not intersect each other, the coordinates of the point having the smallest distance from each of the plurality of vertical lines are calculated as the offset value. machine. An offset value change determination unit for determining whether or not the offset value of the magnetic sensor has changed,
When it is determined that the offset value has changed in the offset value change determination unit, the extraction of the plurality of planes in the plane extraction unit, the calculation of the center coordinates of the circumference in the center coordinate calculation unit, The electronic device according to claim 1, wherein the offset value is calculated by an offset value calculation unit. A motion sensor that detects a movement operation of the electronic device and outputs sensor data including acceleration data and angular velocity data based on the movement operation;
When it is detected that the moving direction of the electronic device has changed based on the sensor data, extraction of the plurality of planes in the plane extraction unit and calculation of center coordinates of the circumference in the center coordinate calculation unit The electronic device according to claim 1, wherein the offset value is calculated by the offset value calculation unit. Based on a plurality of magnetic data in a plurality of axial directions acquired from a moving magnetic sensor, in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes, three or more different from each other Extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. And
For each of the plurality of planes, estimate the circumference close to the coordinate point corresponding to the first magnetic data and the second magnetic data, calculate the center coordinates of the circumference,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated.
Calculating the coordinates of the point closest to the plurality of vertical lines in the plurality of planes as an offset value of the magnetic sensor;
A sensor calibration method characterized by the above. On the computer,
Based on a plurality of magnetic data in a plurality of axial directions acquired from a moving magnetic sensor, in a three-dimensional coordinate space having the plurality of axial directions of the magnetic data as coordinate axes, three or more different from each other Extracting a plurality of different planes including coordinate points corresponding to the first magnetic data;
The magnetic data corresponding to the coordinate point whose distance from the plane is different from the first magnetic data in the three-dimensional coordinate space and whose distance from the plane is a predetermined threshold value or less is extracted as second magnetic data from the plurality of magnetic data. Let
In each of the plurality of planes, the circumference that is close to the first magnetic data and the second magnetic data is estimated, and the center coordinates of the circumference are calculated,
In the three-dimensional coordinate space, for each of the plurality of planes, a vertical line that passes through the central coordinates and is orthogonal to the plane is calculated.
Calculating the coordinates of a point closest to the plurality of vertical lines in the plurality of planes as an offset value of the magnetic sensor;
A sensor calibration program characterized by the above.

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