JP4590511B2 - Electronic compass - Google Patents

Description

The present invention relates to an electronic compass that measures orientation using a magnetic sensor.
More specifically, the present invention relates to a technique for performing calibration (offset correction) for azimuth measurement using azimuth measurement data. In particular, data obtained from a triaxial geomagnetic sensor can be obtained without performing a special procedure by the user. It relates to an electronic compass that uses the proper calibration method to measure the correct orientation.

  A portable terminal such as a mobile phone that includes a magnetic sensor that detects geomagnetism and performs azimuth measurement based on the geomagnetism detected by the magnetic sensor is known. The direction measured here is used, for example, for display of a map for navigation, and enables a function of displaying a map based on the current position in accordance with the direction (direction) of the mobile terminal.

  However, since a mobile terminal has magnetism leaking from a speaker and a microphone mounted on the mobile terminal and a metal package of a magnetized electronic component, the magnetic sensor mounted on the mobile terminal is an electronic device inside the mobile terminal. A magnetic field generated by combining a magnetic field generated from a component or the like with the geomagnetism is detected. Therefore, a calibration process for correcting an error (offset) due to a magnetic field generated from an electronic component or the like inside the portable terminal is necessary. Therefore, in a conventional mobile terminal equipped with a biaxial geomagnetic sensor, the user rotates the mobile terminal, for example, 360 degrees to perform calibration processing, and during this operation, the mobile terminal collects measurement data from the magnetic sensor and performs measurement. The offset was estimated based on the data.

  Specifically, the output of each axis component when the three-axis magnetic sensor is rotated in a constant geomagnetism is expressed as a space (the space in which the output of each axis component of the three-axis magnetic sensor is plotted is a third order. When plotted in the original direction space, the trajectory forms a sphere. This sphere is called an azimuth sphere, and the center of the azimuth sphere corresponds to the offset of the azimuth sensor. Therefore, the calibration of the offset is nothing but to obtain the center point of the azimuth sphere from the measured values of geomagnetism measured in various directions and postures and to adopt it as a new offset value. Here, the radius of the azimuth sphere corresponds to the strength of geomagnetism.

Regarding the calibration of the magnetic sensor mounted on such a portable terminal, for example, there is a technique disclosed in Patent Document 1. In this technique, the mobile terminal is rotated by a predetermined angle, and the offset is estimated based on data measured by the magnetic sensor at each angle, so that calibration can be performed without depending on the rotation speed.
However, this forces the user of the mobile terminal to rotate the mobile phone by a predetermined angle, increasing the burden on the user. In addition, depending on the user, there is a possibility that a predetermined calibration procedure may not be performed accurately, and as a result, calibration is not performed accurately and there is an error in the direction measurement result.

In the method disclosed in Patent Document 2, the calibration process is performed using the temporary offset value even if effective measurement data cannot be obtained at the time of calibration. This eliminates the need for the user to move the mobile phone or the like in a predetermined procedure with care to acquire the orientation data, thereby reducing the burden.
However, in the first place, the calibration work is completed even though a measurement value effective for calibration cannot be obtained. Therefore, accurate calibration cannot be performed depending on the situation, and there is a possibility that an error occurs in the subsequent orientation display. In addition, since the least square method is used for calculating the offset value, there is a disadvantage that a large number of measured values are required to ensure the accuracy of calibration.

JP 2004-12416 A JP 2006-78474 A

  In the conventional technology, in order to perform a calibration process for correcting an error (offset) due to a magnetic field generated from an electronic component or the like inside a portable terminal, a user needs to execute a complicated calibration procedure determined in advance. There is a heavy burden on the user. Further, even if a measurement value effective for calibration cannot be obtained in an attempt to reduce this burden, an error is mixed in the direction display as a result when the calibration operation is completed. Furthermore, since the least square method is used for calculating the offset value, there is a problem that a large number of measured values are required for accurate calibration.

  Accordingly, an object of the present invention is made in view of the above points, and the basic operation when using the mobile terminal device without performing the calibration procedure of the magnetic sensor itself determined in advance by the user. In particular, the present invention provides an electronic compass capable of always accurately correcting a change in magnetic field due to an offset.

The electronic compass of the present invention has three-axis component data (x ₁ , y ₁ , z ₁ ), (x ₂ , y ₂ , z ₂ ), which are orthogonal to the three-axis components of the geomagnetic vector that changes as the electronic compass moves. An orthogonally arranged three-axis magnetic sensor detected as (x _i , y _i , z _i ), a calibration means for calibrating the offset of the three-axis magnetic sensor, and an offset obtained based on the calibration means An electronic compass comprising an azimuth calculation unit for calculating the azimuth by correcting the geomagnetic vector with a calibration value, wherein the calibration means uses at least four measurement points of the geomagnetic vector to calculate an offset of the magnetic sensor. Measurement point determination unit for offset calculation that determines whether or not the measurement can be adopted, and the measurement for offset calculation sequentially obtained based on the determination result of the measurement point for offset calculation Offset calculation measurement point storage unit that sequentially stores the geomagnetic vector, offset calculation unit that calibrates the offset of the magnetic sensor based on the four measurement points stored in the offset calculation measurement point storage unit, An offset calibration value storage unit that stores the offset calibration value calculated by the offset calculation unit , the measurement point determination unit for offset calculation is a first point of an arbitrary geomagnetic vector detected by the three-axis magnetic sensor eyes _{(x 1,} y 1, _{z 1)} and the first point determination means for determining as said defined by determination of the first point, the first point of the measurement point _{(x 1,} y 1, _{z 1} ) From the first component (x ₁ , y ₁ , z ₂ ) and at least one of the three component data of the second point (x ₂ , y ₂ , z ₂ ) . z ₁ A second point determining means for determining the difference between the same component whether the threshold M2 greater than the defined by the determination up to the second point, the first point (x _1, y ₁ , z ₁ ) and the measurement point of the second point (x ₂ , y ₂ , z ₂ ) exceeding the threshold value M1, and the third point (x ₃ , y ₃ , z ₃₎ ), Any one of the two components different from the component data employed in the second point determination means is the second measurement point (x ₂ , y ₂ , z _2). ) With the same component exceeding the threshold M2, and the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ) and wherein the third point _{(x 3, y 3, z} 3) third point determines the measurement point is whether the triangle formed by the coordinate space is obtuse triangle A constant section, the third defined by determination to goal, the first point _{(x 1,} y _{1, z} 1), the second point _{(x 2,} y 2, _{z 2)} and the It is a distance exceeding the threshold value M1 from the measurement point of the third point (x ₃ , y ₃ , z ₃ ), and the three component data of the fourth point (x ₄ , y ₄ , z ₄ ) Among them, the remaining one component different from the component data adopted in the second point determination unit and the third point determination unit is the same as at least one of the measurement points from the first point to the third point. Fourth point determination for determining whether the difference from the component is greater than the threshold value M2 and the distance from the plane forming the triangle defined by the third point determination means is greater than or equal to the threshold value M1 Means (claim 1).

Thereby, it is possible to calculate the offset calibration value of the magnetic sensor by collecting data of at least four measurement points of the geomagnetic vector that changes with the movement of the electronic compass.
Therefore, it is not necessary for the user to execute a predetermined complicated calibration procedure, so that the burden on the user is eliminated. Further, in order to reduce this burden, no error is mixed in the azimuth display as a result of completing the calibration work without obtaining data of measurement points effective for calibration. Furthermore, since only four data points are required for offset calculation, a large amount of data necessary for using the least square method is not necessary.
Therefore, it is possible to accurately calibrate the magnetic sensor without depending on calibration work and data on a large number of measurement points.

In addition, the triaxial magnetic sensor used in the electronic compass of the present invention preferably has a noise level of 5 mG or less in the magnetic sensor (claim 2).

  Thereby, the error of the offset calibration value calculated from the data of at least four measurement points of the geomagnetic vector is reduced, and the calibration of the magnetic sensor can be accurately performed.

Moreover, it is preferable that the triaxial magnetic sensor used for the electronic compass of the present invention has a linearity of the magnetic sensor of 0.8% or less (claim 3).

  Thereby, the output corresponding to the magnetism detected by the magnetic sensor becomes accurate, and calibration of the magnetic sensor can be performed accurately.

  In the measurement point determination unit for offset calculation of the electronic compass according to the present invention, the center point of the azimuth sphere is obtained and used as a new offset value. Therefore, the correlation between the four points scattered on the sphere of the azimuth sphere is predetermined. It is determined whether or not it is satisfied as a measurement point for offset calculation. The radius of the azimuth sphere is the strength of geomagnetism.

That is, a first point (x ₁ , y ₁ , z ₁ ) that is an arbitrary geomagnetic vector detected by a three-axis magnetic sensor and is scattered on the spherical surface of the azimuth sphere is collected, and the first point (x ₁ , y ₁ , z ₁ ), the subsequent second point (x ₂ , y ₂ , z ₂ ), the third point (x ₃ , y ₃ , z ₃ ), and the fourth point A total of four points consisting of (x ₄ , y ₄ , z ₄ ) are mutually related to the strength of the geomagnetic vector, for example, about 450 mG (the measured value on the earth varies depending on the location, so in the present invention, it is set as the threshold value M1. ) Need to be away.
As a result, a total of four points are separated from each other by the radius of the azimuth sphere, and the center point of the azimuth sphere can be obtained with high accuracy.

In addition, for the three component data constituting the magnetic data of the geomagnetic vector, the first point (x ₁ , y ₁ , z ₁ ) and the second point (x ₂ , y ₂ , z ₂ ), the second point In contrast to the third point (x ₃ , y ₃ , z ₃ ) and the fourth point (x ₄ , y ₄ , z ₄ ), the value of the difference between the same component data is about 400 mG, for example. (In the present invention, the threshold value M2 is taken into consideration from the above-mentioned threshold value M1 in consideration of the accuracy between the measurement points).
As a result, a total of four points are three-dimensionally separated from each other in the azimuth sphere, and the center point of the azimuth sphere can be accurately obtained.

The first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), and the third point (x ₃ , y ₃ , z ₃ ) are in the coordinate space. It is necessary that the triangle formed by is not an obtuse triangle.
Thus, the error first point _{(x 1,} y _{1, z} 1), second point _{(x 2,} y 2, _{z 2)} and a third point _{(x 3,} y 3, _{z 3)} has It is possible to reduce the error in the estimation of the center point of the azimuth sphere due to the above, and to accurately determine the center point of the azimuth sphere.

The first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), and the third point (x ₃ , y ₃ , z ₃ ) are in the coordinate space. The distance between the plane of the triangle formed by ( ₄ ) and the fourth point (x ₄ , y ₄ , z ₄ ) is separated from the strength of the geomagnetic vector, for example, about 450 mG (referred to as threshold value M1 in the present invention). Cost.
As a result, a total of four points do not exist on the same plane, and the fourth point (x ₄ , y ₄ , z ₄ ) is separated from the plane of the triangle by a vertical distance from the radius of the azimuth sphere. The center point of the sphere can be obtained with high accuracy.

In addition, the electronic compass of the present invention is mounted on a mobile phone, and at least 4 for determining a measuring point for offset calculation during a basic operation of taking out the stored mobile phone for a call and then completing the call. it is preferable to perform the sampling of measurement points consisting of point (claim 4).

That is, a person with a mobile phone keeps the mobile phone in a pocket in his clothes or a bag held in his hand. When receiving or transmitting a call, first, the user keeps the stored state at hand and performs a preparation operation for responding to the reception / transmission by looking at the screen of the mobile phone. Next, after the preparatory operation, a moving operation is performed to move to the ear to have a conversation, and the conversation is started. After the conversation ends, return to hand and complete the reception / transmission end work (movement operation) by looking at the screen of the mobile phone as necessary. Then, it is placed in a storage state (end operation).
In the above basic operation, at least four measurement points are sampled.

  This eliminates the burden on the user because the user does not need to execute a predetermined complicated calibration procedure.

  In addition, as a basic operation, a conversation is performed from a preparation operation for holding at hand and responding to reception / transmission, and after the conversation is finished, it is returned to the hand and operation until the end of reception / transmission (movement operation) Good.

  According to the present invention, the natural motion of a person having an electronic compass or a person having a mobile phone equipped with an electronic compass, that is, the output of a magnetic vector detected by a three-axis magnetic sensor obtained from a basic operation is It is scattered on the spherical surface of an azimuth sphere having a radius of geomagnetism, and offset can be performed by estimating the center coordinates.

Therefore, it is not necessary for the user to execute a predetermined complicated calibration procedure, so that the burden on the user is eliminated. Further, in order to reduce this burden, no error is mixed in the azimuth display as a result of completing the calibration work without obtaining data of measurement points effective for calibration. Furthermore, since only four data points are required for offset calculation, a large amount of data necessary for using the least square method is not necessary.
Therefore, it is possible to accurately calibrate the magnetic sensor without depending on calibration work and data on a large number of measurement points.

Hereinafter, an electronic compass according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of an electronic compass according to the present invention.

  In FIG. 1, the electronic compass 10 includes a triaxial magnetic sensor 1, a calibration unit 20, a calibration value (sensitivity) storage unit 6, an azimuth calculation unit 7, and an azimuth display unit 8. Measurement point determination unit 2, offset calculation measurement point storage unit 3, offset calculation unit 4 and offset calibration value storage unit 5 are provided. The offset calculation measurement point storage unit 3 stores the first point, the second point, the third point, and the fourth point.

  Here, the three-axis magnetic sensor 1 includes an x-axis magnetic sensor element, a y-axis magnetic sensor element, and a z-axis magnetic sensor element arranged in a sensor module, and the x-axis magnetic sensor element and the y-axis magnetic sensor element. The z-axis magnetic sensor elements are arranged so as to detect magnetism in three perpendicular magnetic directions.

The magnetic sensor 1 is preferably a small magnetic sensor such as an MI sensor or a Hall element in order to be mounted in an electronic compass. In addition, since the electronic compass of the present invention detects at least four points of magnetic data and performs offset, the magnetic sensor preferably has a noise level of 5 mG or less. The linearity of the magnetic sensor is preferably 0.8% or less.
Furthermore, it is preferable that the MI sensor has a small size, a noise level of 5 mG or less, and a linearity of 0.8% or less.

Next, the magnetic data consisting of the three components detected by the three-axis magnetic sensor, when the offset calculation is started, acquires the three-component magnetic data of the new measurement point from the three-axis magnetic sensor 1, It is input to the offset calculation measurement point determination unit 2 of the calibration means 20, is determined as the first point, and is stored in the offset calculation measurement point storage unit 3.
When the first point is stored, the three-component magnetic data of the new measurement point is acquired from the three-axis magnetic sensor 1 and input to the offset calculation measurement point determination unit 2 to be adopted as the second point. Is determined, and when it is adopted, it is stored in the offset calculation measurement point storage unit 3.
Hereinafter, the third point and the fourth point are also determined by the same process and stored in the offset calculation measurement point storage unit 3.

When a total of four points from the first point to the fourth point are stored in the offset calculation measurement point storage unit 3, a total of four components of magnetic data are output to the offset calculation unit 4, and the offset calculation unit A new offset value is calculated at 4, and the new offset value is output to the offset calibration value storage unit 5, where it is replaced with the old offset calibration value and stored.
The offset calibration value storage unit 5 stores the first offset calibration value when the electronic compass (including portable electronic devices such as a mobile phone equipped with the electronic compass) is shipped from the factory or transferred to the user. Stored.

  With the above configuration, the new offset value stored in the offset calibration value storage unit 5 is output to the azimuth calculation unit 7 together with other calibration values stored in the other calibration value (sensitivity) storage unit 6 as necessary. Is done.

  The azimuth calculation unit 7 calibrates the magnetic data composed of the three components detected by the three-axis magnetic sensor based on the new offset value and other necessary calibration values and obtains and outputs an accurate azimuth. Displayed on the display unit 8.

Next, specific processing operations will be described with reference to the flowcharts of FIGS.
2 to 7 are flowcharts showing a calibration method of the three-axis magnetic sensor according to the embodiment of the present invention. FIG. 2 is a diagram showing a main flow of the calibration method, and FIGS. 3 to 7 are diagrams showing sub-flows in FIG.

In FIG. 2, a new measurement point (x, y, z) is obtained by a triaxial magnetic sensor (hereinafter referred to as a sensor in the flow diagram) that constantly acquires the triaxial magnetic data shown in FIG. 1 at predetermined time intervals. After the acquisition, the magnetic data is determined by the first point (x ₁ , y ₁ , z ₁ ) and the offset calculation measurement point determination unit 2 and stored in the offset calculation measurement point storage unit 3 (hereinafter, flow chart). Then, it is called storage.) (Steps S1 and S2).

The next new measurement point (x, y, z) is acquired by the sensor, and it is determined whether or not the magnetic data is adopted as the second point (x ₂ , y ₂ , z ₂ ) (steps S3 to S4). . When it is adopted, it is stored as the second point (x ₂ , y ₂ , z ₂ ) in the next step S5. If not adopted, the process returns to step S3 to acquire a new measurement point (x, y, z) by the sensor, and whether or not to adopt the magnetic data as the second point (x ₂ , y ₂ , z ₂ ). Is determined (step S4).

In FIG. 3, the determination of whether or not to adopt the new measurement point (x, y, z) in step S4 as the second point (x ₂ , y ₂ , z ₂ ) will be described.
First, the distance L _1-2 between the first point (x ₁ , y ₁ , z ₁ ) and the new measurement point (x, y, z) is compared with a predetermined threshold value M1. Next, with respect to the triaxial magnetic data of the first point (x ₁ , y ₁ , z ₁ ) and the new measurement point (x, y, z), the difference between the components is compared with a predetermined threshold value M2. Do.

That is, when the value L _{1-2 of} √ {(x ₁ −x) ² + (y ₁ −y) ² + (z ₁ −z) ² } is larger than the threshold value M1 in step S101 (Y) The process proceeds to step S102. When it is not larger than the threshold value M1 (N), the process proceeds to step S105, and it is determined that the second point (x ₂ , y ₂ , z ₂ ) is not adopted.

Next, when | x−x ₁ |> M 2 in step S102, it is determined that the second point (x ₂ , y ₂ , z ₂ ) is adopted (step S106). A flag of FLG1 = 0 is used as a determination marker in determining whether or not the point (x ₃ , y ₃ , z ₃ ) and the fourth point (x ₄ , y ₄ , z ₄ ) can be adopted.

If not | x−x ₁ |> M2, the process proceeds to step S103.

In the next step S103, when | y−y ₁ |> M2, it is labeled as FLG1 = 1, and it is determined to be adopted as the second point (x ₂ , y ₂ , z ₂ ) (step 106). If not | y−y ₁ |> M2, the process proceeds to step S104.

In the next step S104, if | z−z ₁ |> M2, it is marked as FLG1 = 2 and determined to be adopted as the second point (x ₂ , y ₂ , z ₂ ) (step S106). If | z−z ₁ |> M2 is not satisfied, it is determined that the second point (x ₂ , y ₂ , z ₂ ) is not adopted (step S105).

By the above steps S101-S106, it is determined to adopt as the second point _{(x 2,} y 2, _{z 2),} the second point in step _{S 5 (x 2, y 2} , z 2) is stored, the following The process proceeds to step S6.

The next new measurement point (x, y, z) is acquired by the sensor, and it is determined whether or not to adopt the magnetic data as the third point (x ₂ , y ₂ , z ₂ ) (steps S6 to S7). . When it is adopted, it is stored as the third point (x ₃ , y ₃ , z ₃ ) in the next step S8. If not adopted, the process returns to step S6 to obtain a new measurement point (x, y, z) by the sensor, and whether or not to adopt the magnetic data as the third point (x ₃ , y ₃ , z ₃ ). Is determined (step S7).

In FIG. 4, whether or not the magnetic data acquired by the sensor at the new measurement point (x, y, z) in step S6 is adopted as the third point (x ₃ , y ₃ , z ₃ ) in step S7. The determination will be described.

First, the distance L _1-3 between the first point (x ₁ , y ₁ , z ₁ ) and the new measurement point (x, y, z) and the second point (x ₂ , y ₂ , z ₂ ) And a predetermined threshold value M1 with respect to a distance L _2-3 between the new measurement point (x, y, z).
Next, the new measurement point (x, y, z) and the first point (x ₁ , y ₁ , z ₁ ) in step S4 are used as the second point (x ₂ , y ₂ , z ₂ ) by comparison. For the other two component data excluding any one of the three components of the first point (x ₁ , y ₁ , z ₁ ) that is the basis for the determination, the corresponding new measurement points (x, y , Z) is performed by comparing the difference of each component in the magnetic data component with a predetermined threshold value M2.
Finally, a triangle formed in a coordinate space consisting of a first point (x ₁ , y ₁ , z ₁ ), a second point (x ₂ , y ₂ , z ₂ ) and a new measurement point (x, y, z) It is determined whether or not is an obtuse triangle.

That is, in step S201, the values L _{1-3 of} √ {(x ₁ −x) ² + (y ₁ −y) ² + (z ₁ −z) ² } and √ {(x ₂ −x) ² + ( ^{_{y 2 -y) 2 + (z}} 2 -z) both values _{L 1-3} of ^2} is time larger than the threshold value M1 (Y), the process proceeds to step S202. When not greater than either or threshold M1 Both (N), the process proceeds to step S 2 05, it determines not to adopt a third point _{(x 3, y 3, z} 3).

  In step S202, the determination markers in FIG. 3, FLG1 = 0, FLG1 = 1, and FLG1 = 2, are performed for each case.

First, when FLG1 = 0, the process proceeds to step S203.
If | y−y ₁ |> M2 in step S203, it is labeled as FLG2 = 1 and the process proceeds to step S212. If not | y−y ₁ |> M2, the process proceeds to step S204.
If | z−z ₁ |> M2 in step S204, it is labeled as FLG2 = 2, and the process proceeds to step S212. If | z−z ₁ |> M2 is not satisfied, it is determined that the third point (x ₃ , y ₃ , z ₃ ) is not adopted (step S205).

Next, when FLG1 = 1, the process proceeds to step S206.
If | x−x ₁ |> M2 in step S206, it is labeled as FLG2 = 0 and the process proceeds to step 212. If not | x−x ₁ |> M2, the process proceeds to step S207.
If | z−z ₁ |> M2 in step S207, it is labeled as FLG2 = 2 and the process proceeds to step 212. If | z−z ₁ |> M2 is not satisfied, it is determined that the third point (x ₃ , y ₃ , z ₃ ) is not adopted (step S208).

Finally, if FLG1 = 2, the process proceeds to step S209.
If | x−x ₁ |> M2 in step S209, it is labeled as FLG2 = 0, and the process proceeds to step S212. If not | x−x ₁ |> M2, the process proceeds to step S210.
If | y−y ₁ |> M2 in step S210, then it is labeled as FLG2 = 1 and the process proceeds to step S212. If | y−y ₁ |> M2 is not satisfied, it is determined not to be adopted as the third point (x ₃ , y ₃ , z ₃ ) (step S211).

Step S20 3 and S20 4, steps S20 6 and S20 7, and steps S20 9 and S2 10 by a new measurement point has shifted to S212 and (x, y, z), first point _{(x 1, y 1, z} 1 ) And the second point (x ₂ , y ₂ , z ₂ ), it is determined whether or not the triangle formed by the three points is an obtuse triangle (step S212).

In step S212, the first point is A (x ₁ , y ₁ , z ₁ ), the second point is B (x ₂ , y ₂ , z ₂ ), and the new measurement point determined as the third point is C. As (x, y, z), the cos of A, B, and C is obtained using the cosine theorem.

  That is, if a, b, and c are calculated from (Equation 1) to (Equation 3), cosA, cosB, and cosC can be derived from (Equation 4) to (Equation 6).

  From the above calculation, when any of cosA, cosB, and cosC is a negative value, an obtuse triangle is obtained, and when all values are positive, a relationship that is not an obtuse triangle is obtained.

Therefore, when the triangle formed by the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ) and the new measurement point (x, y, z) is an obtuse angle triangle , It is determined that the third point (x ₃ , y ₃ , z ₃ ) is not adopted (step S213).

If the triangle formed by the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ) and the new measurement point (x, y, z) is not an obtuse triangle, the 3rd It determines to adopt as a point _{(x 3, y 3, z} 3) ( step S214).

If it is determined in steps S201 to S214 that the third point (x ₃ , y ₃ , z ₃ ) is adopted, the third point (x ₃ , y ₃ , z ₃ ) is stored in step 8, and the next step The process proceeds to S9.

Further, the next new measurement point (x, y, z) is acquired by the sensor, and it is determined whether or not the magnetic data is adopted as the fourth point (x ₄ , y ₄ , z ₄ ) (steps S9 to S9). S10). When it is adopted, it is stored as the fourth point (x ₄ , y ₄ , z ₄ ) in the next step S11. If not adopted, the process returns to step S9 to obtain a new measurement point (x, y, z) by the sensor, and whether or not to adopt the magnetic data as the fourth point (x ₄ , y ₄ , z ₄ ). Is determined (step S10).

5 to 7, whether or not the magnetic data acquired by the sensor at the new measurement point (x, y, z) in step S9 is employed as the fourth point (x ₄ , y ₄ , z ₄ ) in step S10. This determination will be described.

First, the distance L _1-4 between the first point (x ₁ , y ₁ , z ₁ ) and the new measurement point (x, y, z) and the second point (x ₂ , y ₂ , z ₂ ) And the distance L _2-4 between the new measurement point (x, y, z) and the third point (x ₃ , y ₃ , z ₃ ) and the new measurement point (x, y, z) The distance L _3-4 is compared with a predetermined threshold value M1.

Next, the second point (x ₂ , y ₂ , z ₂ ) and the new measurement point (x, y, z) in step S4 and step S7 are compared with the first point (x ₁ , y ₁ , z ₁ ) and The remaining 1 except for the two components of the three components of the first point (x ₁ , y ₁ , z ₁ ) that became the basis for determination when adopting as the third point (x ₃ , y ₃ , z ₃ ) One component data is compared with a threshold M2 determined in advance with respect to a difference from the corresponding component in the magnetic data of the new measurement point (x, y, z) acquired in step S9.

Finally, a plane composed of three points: a first point (x ₁ , y ₁ , z ₁ ), a second point (x ₂ , y ₂ , z ₂ ), and a third point (x ₃ , y ₃ , z ₃ ). And a distance L ₁ , ₂ , _3-4 between the new measurement point (x, y, z) and a predetermined threshold value M2.

  That is, FIG. 5 (steps S301 to S303) and FIG. 6 (S301 to S303, FLG1 = 0, 1, and 2 in FIG. 3 and FLG2 = 0, 1, and 2 in FIG. S311-) and FIG. 7 (S301-S303, S318-) are performed for each case.

First, referring to FIG. 5, in step S301, the values L _{1-4 of} √ {(x ₁ −x) ² + (y ₁ −y) ² + (z ₁ −z) ² } , √ {(x ₂ −x ) ² + (y ₂ −y) ² + (z ₂ −z) ² } L ₂₋₄ and √ {(x ₃ −x) ² + (y ₃ −y) ² + (z ₃ −z ) when all values of L _3-4 of ^2} is greater than the threshold value M1 (Y), the process proceeds to step S302. When any one value is not greater than the threshold value M1 (N), the process proceeds to step S303, and it is determined that the fourth point (x ₄ , y ₄ , z ₄ ) is not adopted.

  In step S302, if FLG1 = 1 and FLG2 = 2, or if FLG1 = 2 and FLG2 = 1, the process proceeds to step S304.

If | x−x ₁ |> M2 in step S304, the process proceeds to step S308. If not | x−x ₁ |> M2, the process proceeds to step S305.
In step S305, when | x−x ₂ |> M2, the process proceeds to step S308. If not | x−x ₂ |> M2, the process proceeds to step S306.
In step S306, when | x−x ₃ |> M2, the process proceeds to step S308. If | x−x ₃ |> M2 is not satisfied, it is determined that the fourth point (x ₄ , y ₄ , z ₄ ) is not adopted (step S307).

In step S308 transferred from step S304 to step S306, the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), the third point (x ₃ , y ₃ , z ₃ ), and whether or not the distances L 1, 2, _3-4 between the plane consisting of three points and the new measurement point (x, y, z) are larger than a predetermined threshold value M1.

In step S308, A (x ₁ , y ₁ , z ₁ ) that is the first point, B (x ₂ , y ₂ , z ₂ ) that is the _second point, and C (x ₃ , y that is the third point. ₃ , z ₃ ) A method for calculating the distance L _1,2,3-4 between the surface defined by the three points and a new measurement point (x, y, z) that is a point outside the surface is as follows. It is.
That is, when the equation of the surface ABC is expressed by (Expression 7), the distance L can be calculated as (Expression 8).

The distance L 1, 2, _3-4 calculated by the above ( _Equation 8) is compared with a predetermined threshold value M1.

That is, a plane composed of three points of a first point (x ₁ , y ₁ , z ₁ ), a second point (x ₂ , y ₂ , z ₂ ), and a third point (x ₃ , y ₃ , z ₃ ) When the distance L 1, 2, _3-4 with the new measurement point (x, y, z) is not larger than the predetermined threshold value M1, it is not adopted as the fourth point (x ₄ , y ₄ , z ₄ ). Is determined (step S309).

On the other hand, a plane composed of three points: a first point (x ₁ , y ₁ , z ₁ ), a second point (x ₂ , y ₂ , z ₂ ), and a third point (x ₃ , y ₃ , z ₃ ) When the distance L 1, 2, _3-4 to the new measurement point (x, y, z) is larger than the predetermined threshold value M1, it is determined that the fourth point (x ₄ , y ₄ , z ₄ ) is adopted. (Step S310).

  Next, according to FIG. 6, when all the values in step S301 in FIG. 5 are larger than the threshold value M1 (Y), the process proceeds to step S302, and if FLG1 = 2 and FLG2 = 0 by step S302, or FLG1 = When 0 and FLG2 = 2, the process proceeds to step S311.

If | y−y ₁ |> M2 in step S311, the process proceeds to step S315. If | y−y ₁ |> M2 is not satisfied, the process proceeds to step S312.
If | y−y ₂ |> M2 in step S312, the process proceeds to step S315. If not | y−y ₂ |> M2, the process proceeds to step S313.
If | y−y ₃ |> M2 in step S313, the process proceeds to step S315. If | y−y ₃ |> M2 is not satisfied, it is determined not to be adopted as the fourth point (x ₄ , y ₄ , z ₄ ) (step S314).

In step S315 transferred from step S311 to step S313, the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), the third point (x ₃ , y ₃ , z ₃ ) and whether or not the distance between the plane consisting of the three points and the new measurement point (x, y, z) is greater than a predetermined threshold value M1.

In step S315, the same processing as in step S308 is performed.
Therefore, a plane composed of three points of the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), and the third point (x ₃ , y ₃ , z ₃ ) When the distance to the new measurement point (x, y, z) is not greater than the predetermined threshold value M1, it is determined that the fourth point (x ₄ , y ₄ , z ₄ ) is not adopted (step S316).

A new plane with three planes: a first point (x ₁ , y ₁ , z ₁ ), a second point (x ₂ , y ₂ , z ₂ ), and a third point (x ₃ , y ₃ , z ₃ ) When the distance to the point (x, y, z) is larger than the predetermined threshold value M1, it is determined to be adopted as the fourth point (x ₄ , y ₄ , z ₄ ) (step S317).

  Next, according to FIG. 7, when all the values in step S301 in FIG. 5 are larger than the threshold value M1 (Y), the process proceeds to step S302, and if FLG1 = 1 and FLG2 = 0 by step S302, or FLG1 = If 0 and FLG2 = 1, the process proceeds to step S318.

If | z−z ₁ |> M2 in step S318, the process proceeds to step S322. If not | z−z ₁ |> M2, the process proceeds to step S319.
If | z−z ₂ |> M2 in step S319, the process proceeds to step S322. If not | z−z ₂ |> M2, the process proceeds to step S320.
If | z−z ₃ |> M2 in step S320, the process proceeds to step S322. If | z−z ₃ |> M2 is not satisfied, it is determined not to be adopted as the fourth point (x ₄ , y ₄ , z ₄ ) (step S321).

In step S322 transferred from step S318 to step S320, the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), the third point (x ₃ , y ₃ , z ₃ ) and whether or not the distance between the plane consisting of the three points and the new measurement point (x, y, z) is greater than a predetermined threshold value M1.

  In step S322, the same processing as in step S308 is performed.

Therefore, a plane composed of three points of the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), and the third point (x ₃ , y ₃ , z ₃ ) If the distance to the new measurement point (x, y, z) is not greater than the predetermined threshold value M1, it is determined not to be adopted as the fourth point (x ₄ , y ₄ , z ₄ ) (step S323).

A new plane with three planes: a first point (x ₁ , y ₁ , z ₁ ), a second point (x ₂ , y ₂ , z ₂ ), and a third point (x ₃ , y ₃ , z ₃ ) When the distance to the point (x, y, z) is larger than the predetermined threshold value M1, it is determined to be adopted as the fourth point (x ₄ , y ₄ , z ₄ ) (step S324).

If it is determined that the fourth point (x ₄ , y ₄ , z ₄ ) is adopted as the fourth point (x ₄ , y ₄ , z ₄ ) by the above steps S301 to S324, the fourth point (x ₄ , y ₄ , z ₄ ) is stored in step 11, and the next step The process proceeds to S12.

In step S12, the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), the third point (x ₃ , y ₃ , z ₃ ) and the fourth point (x ₄ , y ₄ , z ₄ ), a new offset value ((x ₀ , y ₀ , z ₀ ) is calculated.

The calculation method is as follows according to a ternary simultaneous equation.
The coordinates of the four points are
(X ₁ , y ₁ , z ₁ ), (x ₂ , y ₂ , z ₂ ), (x ₃ , y ₃ , z ₃ ), (x ₄ , y ₄ , z ₄ )
So if you move the origin to reduce the variable,
(X ₁ −x ₄ , y ₁ −y ₄ , z ₁ −z ₄ ), (x ₂ −x ₄ , y ₂ −y ₄ , z ₂ −z ₄ ), (x ₃ −x ₄ , y ₃ − _{y 4, z 3 -z 4)} , (0,0,0)
It becomes.
At this time, this coordinate is newly
(X1, y1, z1), (x2, y2, z2), (x3, y3, z3)
Redefine.
Extent towards sphere type may calculate organized by substituting the equation (9), the solution of simultaneous equations by matrix equation obtained (a, b, c).

If the movement of the coordinate origin is restored, the solution is
(A + x ₄ , b + y ₄ , c + z ₄ )
Thus, a new offset value (x ₀ , y ₀ , z ₀ ) can be calculated.

The new offset value (x ₀ , y ₀ , z ₀ ) calculated in step S12 is stored in step 13 and the process ends.

  It is a block diagram which shows schematic structure of the electronic compass concerning this invention.   It is a figure which shows the main flow of the calibration method concerning this invention. 3 to 7 are diagrams showing the sub-flow in FIG. FIG.   It is a figure which shows the subflow regarding the process of the 2nd point in the main flowchart of the calibration method concerning this invention.   It is a figure which shows the subflow regarding the process of the 3rd point in the main flow figure of the calibration method concerning this invention.   It is a figure which shows the subflow regarding the process of the 2nd point in the main flow figure of the calibration method concerning this invention.   It is a figure which shows the subflow regarding the process of the 2nd point in the main flow figure of the calibration method concerning this invention.   It is a figure which shows the subflow regarding the process of the 2nd point in the main flow figure of the calibration method concerning this invention.

Explanation of symbols

1 3-axis magnetic sensor 2 Offset calculation measurement point determination unit 3 Offset calculation measurement point storage unit 4 Offset calculation unit 5 Offset calibration value storage unit 6 Other calibration value (sensitivity) storage unit 7 Direction calculation unit 8 Direction display unit 10 electronic compass 20 calibration means 20

Claims (4)

Three-axis component data (x ₁ , y ₁ , z ₁ ), (x ₂ , y ₂ , z ₂ ) (x _i , y _i ) orthogonal to the three-axis components of the geomagnetic vector that changes with the movement of the electronic compass , Z _i ), orthogonally arranged three-axis magnetic sensors,
Calibration means for calibrating the offset of the three-axis magnetic sensor;
An electronic compass comprising an azimuth calculation unit that calculates the azimuth by correcting the geomagnetic vector with an offset calibration value obtained based on the calibration means,
The calibration means is
The measurement points comprising at least four of the geomagnetic vectors are sequentially obtained based on the determination points of the offset calculation measurement points and the offset calculation measurement points for determining whether or not the magnetic sensor can be adopted for offset calculation. A measurement point storage unit for offset calculation for sequentially storing geomagnetic vectors of the measurement points for offset calculation;
An offset calculator for calibrating the offset of the magnetic sensor based on the four measurement points stored in the offset calculation measurement point storage;
Ri Do from the offset calibration value storage for storing the offset calibration value calculated by the offset calculation section,
The offset calculation measurement point determination unit,
First point determination means for determining an arbitrary geomagnetic vector detected by the three-axis magnetic sensor as a first point (x ₁ , y ₁ , z ₁ );
The distance determined by the determination of the first point is a distance exceeding the threshold value M1 from the _first measurement point (x ₁ , y ₁ , z ₁ ), and the second point (x ₂ , Y ₂ , z ₂ ), at least one of the three component data indicates whether the difference between the _first component (x ₁ , y ₁ , z ₁ ) and the same component exceeds a threshold value M2. Second point determining means for determining;
The threshold is determined from the measurement points of the first point (x ₁ , y ₁ , z ₁ ) and the second point (x ₂ , y ₂ , z ₂ ) determined by the determination up to the second point. Of the three component data of the third point (x ₃ , y ₃ , z ₃ ) that are distances exceeding the value M1, the two component data different from the component data adopted in the second point determination means One of them is that the difference between the _second measurement point (x ₂ , y ₂ , z ₂ ) and the same component is greater than the threshold value M2, and the first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ), and the third point (x ₃ , y ₃ , z ₃ ) measurement points form a triangle formed in the coordinate space. Third point determination means for determining whether or not an obtuse triangle,
The first point (x ₁ , y ₁ , z ₁ ), the second point (x ₂ , y ₂ , z ₂ ) and the third point determined by the determination up to the third point Among the three component data of the fourth point (x ₄ , y ₄ , z ₄ ) that is a distance exceeding the threshold value M1 from the measurement point (x ₃ , y ₃ , z ₃ ), The remaining one component different from the component data adopted in the two-point determination means and the third point determination means is a difference from the same component at least one of the measurement points from the first point to the third point. And a fourth point determination means for determining whether or not the distance M2 is greater than the threshold M2 and the distance from the plane forming the triangle defined in the third point determination means is equal to or greater than the threshold M1. Tei electronic compass according to claim Rukoto.   The electronic compass according to claim 1, wherein the three-axis magnetic sensor has a noise level of 5 mG or less.   The electronic compass according to claim 1 or 2, wherein the three-axis magnetic sensor has a linearity of the magnetic sensor of 0.8% or less. The electronic compass is mounted on a mobile phone, and is a measurement consisting of at least four points for determining an offset calculation measurement point during a basic operation of taking out a stored mobile phone for a call and then completing the call. electronic compass according to claim 1 to 3, characterized in that the sampling point.

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