JP4899506B2 - Magnetic sensor control device, magnetic measurement device, offset setting method, and offset setting program - Google Patents

Description

  The present invention relates to a magnetic sensor control device, a magnetic measurement device, an offset setting method, and an offset setting program.

Conventionally, a two-dimensional magnetic sensor that is mounted on a moving body and detects the direction of geomagnetism is known. In general, a two-dimensional magnetic sensor includes two magnetic sensor modules for detecting a scalar quantity by decomposing a magnetic field vector into two orthogonal components. The magnetic data that is the output of the two-dimensional magnetic sensor has two components because it consists of a combination of the outputs of such two magnetic sensor modules. The direction and magnitude of the vector having magnetic data as the component is the direction and magnitude of the magnetic field detected by the two-dimensional magnetic sensor. When the direction or magnitude of geomagnetism is specified based on the output of the two-dimensional magnetic sensor, the output includes the magnetization component of the moving body and the measurement error of the magnetic sensor itself. Therefore, processing for correcting the output of the two-dimensional magnetic sensor is necessary to cancel them. The operation value of this correction process is called offset. The offset represents a magnetic field vector generated by the magnetization of the moving body detected by the two-dimensional magnetic sensor, including the measurement error of the magnetic sensor, and the offset is subtracted from the magnetic data that is the output of the two-dimensional magnetic sensor. This cancels the magnetization component of the moving body and the measurement error of the magnetic sensor all together. The offset can be calculated by obtaining the center of the circumference passing through the point having magnetic data as a component. The process for obtaining the offset is called calibration.
By the way, a set of points having magnetic data as a component is not a complete circumference in reality. This is because the output of the two-dimensional magnetic sensor itself has a measurement error according to a Gaussian distribution, and in reality there is no completely uniform magnetic field, so magnetic data necessary for calculating the offset is accumulated. This is because the magnetic field measured by the two-dimensional magnetic sensor fluctuates during the period, and there is a calculation error until the output of the two-dimensional magnetic sensor is extracted as a digital value.
The conventional offset calculation method of a magnetic sensor is to accumulate a large number of magnetic data and calculate the most probable offset by their statistical processing (see, for example, Patent Document 1). However, when statistical processing of a large number of magnetic data is performed, it is possible to calculate an accurate offset if the distribution of the magnetic data group as a population is uniformly wide and unique magnetic data is not excluded from the population. Can not. Therefore, it is necessary to select a population to some extent in order to calculate an accurate offset, and after all, it is not possible to calculate an accurate offset only by statistical processing. In addition, the amount of processing for obtaining the most probable circle center by statistical processing is considerable, and time and resource consumption are high.

International Publication No. 2004-003476 Pamphlet

  It is an object of the present invention to provide a magnetic sensor control device, a magnetic measurement device, an offset setting method, and an offset setting program that do not require statistical processing for offset calculation.

(1) A magnetic sensor control device for achieving the above object includes an input means for inputting a plurality of magnetic data having two components sequentially output from a two-dimensional magnetic sensor, and a plurality of the magnetic data input. A selection means for selecting three magnetic data satisfying a predetermined three-point selection condition, and a center point that is a point equidistant from the three points having the selected three magnetic data as components. Calculating means; and setting means for setting a component of the center point as an offset of the magnetic data.
Three magnetic data satisfying a predetermined three-point selection condition are selected from magnetic data sequentially output from the two-dimensional magnetic sensor, and the points are equidistant from the three points having the selected three magnetic data as components. By calculating the center point that is, it is not necessary to use statistical processing for calculating the offset, so that the offset can be calculated efficiently.

(2) The magnetic sensor control device for achieving the above object may further include a buffer for storing the plurality of input magnetic data. When the magnetic data is newly stored in the buffer, the selection unit is configured to store the magnetic data newly stored in the buffer among the three data structures for holding the three magnetic data as selection candidates. By updating the data, the chord length of the arc passing through the three points including the three magnetic data held in the three data structures is extended and at least not shortened at both ends of the arc. The data structure holding the magnetic data corresponding to one point may be selected, and the selected data structure may be updated with the magnetic data newly stored in the buffer.
A circle passing through three points having three magnetic data components is a circle centered on a point having an offset component. In order to make the circle closer to a circle centered on a point whose exact offset is a component, the area of the circle is large, and the three points that define the circle are evenly distributed over a wide range on the circumference. Is desirable. Accordingly, it is desirable that the length of the string passing through the three points having the three magnetic data components is longer. Therefore, when new magnetic data is input, the chord length of the arc passing through the three points having the three magnetic data stored in the three data structures as a component is increased by updating the data structure. In addition, it is desirable to select the data structure to be updated.

(3) When the magnetic data is newly stored in the buffer, the selection means acquires the magnetic data that has not been selected as selection candidates of the magnetic data at two points at both ends of the arc from the buffer. The magnetic data may be selected at the midpoint of the arc.
After the magnetic data at both ends of the arc are tentatively determined, the magnetic data stored in the buffer that is not selected as both ends of the arc are again selected as candidates for selection of the midpoint of the arc, so that it is necessary to calculate the offset. The number of magnetic data can be reduced. As a result, the amount of operation of the moving body equipped with the two-dimensional magnetic sensor required for collecting magnetic data necessary for calculating the offset of the magnetic data is reduced, and the offset calculation time is reduced. Shortened.

(4) The three-point selection condition may include a condition that correlates with a distortion with respect to an equilateral triangle having three points as vertices having three magnetic data components stored in the data structure.
A circle passing through three points having three magnetic data components is a circle centered on a point having an offset component. In order to bring the circle closer to a circle centered on a point having an accurate offset as a component, it is desirable that the three points defining the circle are dispersed at equal intervals on the circumference. Therefore, it is desirable to set a three-point selection condition for the distortion of a triangular triangle having three points with three magnetic data as components. When a triangle whose apex is three points having three magnetic data components is a regular triangle, the three points are distributed at equal intervals on the circumference.
The distortion of a triangle with respect to a regular triangle can be defined by paying attention to some attributes of the triangle.

(5-7) For example, the three-point selection condition may include that the variation in the inner angle of the triangle is within a predetermined range. Further, for example, the three-point selection condition may include that the variation in the length of the sides of the triangle is within a predetermined range. Further, for example, the three-point selection condition may include that a variation in distance from the center of gravity of the triangle to each vertex is within a predetermined range.
Variations in values can be arbitrarily defined mathematically, but in consideration of the amount of computation and processing time required for condition determination, and the possibility of reusing calculation results obtained in the condition determination process. It is desirable.

ただし、ｐ_i（ｉ＝０，１，２）は前記三角形の各頂点であり、ｄ₃は前記三角形の重心である。
この３点選抜条件の条件判定に必要な最大固有値及び最小固有値は、三角形の各頂点の座標値と三角形の重心の座標値から定義される２次方程式の解として求めることができるため、例えば、三角形の内角のばらつき、三角形の辺の長さのばらつき、三角形の重心から各頂点までの距離のばらつき等を３点選抜条件の条件判定に用いる場合と比較して計算量が軽減される。ばらつきの定義としては、例えば標準偏差が考えられる。 (8) Therefore, it is desirable that the three-point selection condition includes that the ratio of the minimum eigenvalue to the maximum eigenvalue of the following 2-by-2 symmetric matrix A is greater than or equal to a predetermined value.

Where p _i (i = 0, 1, 2) is each vertex of the triangle, and d ₃ is the center of gravity of the triangle.
The maximum eigenvalue and the minimum eigenvalue necessary for the condition determination of the three-point selection condition can be obtained as a solution of a quadratic equation defined from the coordinate value of each vertex of the triangle and the coordinate value of the center of gravity of the triangle. The amount of calculation is reduced as compared with the case of using the variation in the internal angle of the triangle, the variation in the length of the side of the triangle, the variation in the distance from the center of gravity of the triangle to each vertex, and the like for the condition determination of the three-point selection condition. As the definition of the variation, for example, a standard deviation can be considered.

(9) The three-point selection condition may include that the value of the ratio is the maximum.
By selecting the point at which the ratio of the minimum eigenvalue to the maximum eigenvalue of the symmetric matrix A is the maximum as the selection condition, the largest area among the plurality of magnetic data stored in the buffer and the distortion with respect to the equilateral triangle It is possible to select three points that are vertices forming a triangle with a small.

(10) A value indicating a progress situation from the start to the completion of selection of the three magnetic data satisfying the three-point selection condition, and a progress value derived based on the ratio value, or the ratio A progress value output means for outputting the value may be further provided.
The progress value indicating the progress of the three-point selection derived based on the value of the ratio of the minimum eigenvalue to the maximum eigenvalue of the symmetric matrix A or the ratio value itself is output from the magnetic sensor control device to obtain three points. The system outside the magnetic sensor control device can use information on the progress status from the start to the completion of selection.

  (11) The progress value may be an angle corresponding to a central angle of an arc passing through three points having the three magnetic data stored in the three data structures as components.

  (12) A magnetic measurement device for achieving the above object includes the magnetic sensor control device and a two-dimensional magnetic sensor.

(13) The magnetic measurement apparatus for achieving the above object further includes a notifying means for notifying a user of the progress status by emitting a sound of a different scale according to the progress value or the ratio value. Good.
The magnetic measuring device includes notifying means for emitting a sound of a different scale according to the progress value or the ratio value, so that the user can select the three magnetic data satisfying the three-point selection condition by the sound emitted by the notifying means. You can recognize the progress from the start to the completion.

(14) The magnetic measurement apparatus for achieving the above object may further include display means for allowing the user to visually recognize the progress status according to the progress value or the ratio value.
Since the magnetic measurement apparatus includes a display unit that displays the progress of the three-point selection according to the progress value or the ratio value, the user starts selecting the three magnetic data satisfying the three-point selection condition. You can see the progress until completion.

(15) An offset setting method for achieving the above object is to input a plurality of magnetic data having two components sequentially output from a two-dimensional magnetic sensor, and to determine in advance from the plurality of input magnetic data. The three magnetic data satisfying the three-point selection condition are selected, a central point that is equidistant from the three points having the selected three magnetic data as components is calculated, and the central point component is calculated. Setting as an offset of the magnetic data.
Three magnetic data satisfying a predetermined three-point selection condition are selected from magnetic data sequentially output from the two-dimensional magnetic sensor, and the points are equidistant from the three points having the selected three magnetic data as components. By calculating the center point that is, it is not necessary to use statistical processing for calculating the offset, so that the offset can be calculated efficiently.

(16) An offset setting program for achieving the above object includes an input means for inputting a plurality of magnetic data having two components sequentially output from a two-dimensional magnetic sensor, and a plurality of the input magnetic data. A selection means for selecting the three magnetic data satisfying a predetermined three-point selection condition, and a calculation for calculating a central point that is a point equidistant from the three points having the selected three magnetic data as components. The computer functions as means and setting means for setting the component of the center point as the offset of the magnetic data.
Three magnetic data satisfying a predetermined three-point selection condition are selected from magnetic data sequentially output from the two-dimensional magnetic sensor, and the points are equidistant from the three points having the selected three magnetic data as components. By calculating the center point that is, it is not necessary to use statistical processing for calculating the offset, so that the offset can be calculated efficiently.

  The functions of the plurality of means provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. The functions of the plurality of means are not limited to those realized by hardware resources that are physically independent of each other. The present invention can be specified not only as a magnetic sensor control device but also as a magnetic measurement device combining a magnetic sensor control device and a two-dimensional magnetic sensor, as a magnetic sensor control method, or as a magnetic sensor control program. is there.

Hereinafter, embodiments of the present invention will be described in the following order.
A. First embodiment [1. Overall explanation]
1-1. Basic principle 1-2. Hardware configuration 1-3. Software configuration [2. Process flow]
2-1. Buffer update 2-2.1 point selection candidate tentative decision 2-3. Second point selection candidate tentative decision 2-4.3 point selection ・ 3 point update ・ 3 point selection condition ・ Selection verification ・ Offset Setting B. Second embodiment

[1. Overall explanation]
1-1. Basic Principle First, the basic principle used by the present embodiment will be described.
In the present embodiment, an offset is set for canceling the magnetization component of the moving body on which the two-dimensional magnetic sensor is mounted and the measurement error of the magnetic sensor itself. In order to obtain the offset, a circle that approximates a set of points in a vector plane whose component is magnetic data that is the output of the two-dimensional magnetic sensor is specified. This circle is called an azimuth circle. The component of the center point of the azimuth circle is an offset, and the radius is the strength of the magnetic field. In calibration using a two-dimensional magnetic sensor, magnetism collected when the moving body rotates while the direction of the rotation axis of the moving body on which the two-dimensional magnetic sensor is mounted is kept constant in the vertical direction. Data is needed. Since there is a measurement error in the output of the two-dimensional magnetic sensor itself, the moving body on which the two-dimensional magnetic sensor is mounted rotates around the axis perpendicular to the sensitivity direction of both the x-axis sensor and the y-axis sensor with a constant magnetic field. However, the set of points whose components are magnetic data is not a circle. In the present embodiment, three points having magnetic data as components are selected, a center point and a radius of the circumference passing through the selected three points are obtained, and the obtained center of the circumference is set as an offset. In order to reduce the error due to the measurement error of the two-dimensional magnetic sensor itself included in the offset by this method, three points including three magnetic data including the measurement error of the two-dimensional magnetic sensor itself as components are used. It is important to select so that it is evenly distributed over a wide range on the circumference passing through the three points.

  FIG. 2 shows an azimuth circle (solid line) that passes through three points whose components are magnetic data, which is the output of a two-dimensional magnetic sensor, and an infinite number of points, whose components are magnetic data of an ideal two-dimensional magnetic sensor that has no measurement error. It shows the relationship with the true azimuth circle (dashed line). When the three points whose components are magnetic data of a two-dimensional magnetic sensor are distributed in a narrow range on the circumference passing through them, the center of the azimuth circle (×) obtained from these three points and the ideal two-dimensional to be obtained The distance from the center (+) of the true azimuth circle of the magnetic sensor increases as shown in FIG. On the other hand, when three points whose components are magnetic data of a two-dimensional magnetic sensor are evenly distributed over a wide range on the circumference passing through them, the center (×) of the azimuth circle obtained from those three points, The distance from the center (+) of the true azimuth circle of the ideal two-dimensional magnetic sensor to be obtained becomes small as shown in FIG. When the three points whose components are magnetic data of the two-dimensional magnetic sensor are distributed at equal intervals around the circumference passing through them, that is, when the triangle having the three points as vertices becomes an equilateral triangle, the offset error is the most. Can be small. Therefore, in the present embodiment, the three points having magnetic data as components are selected so that the distortion of the triangle having the vertex as a vertex is smaller than a specific threshold value.

  Here, three points are selected in advance, the circumference passing through the selected three points is obtained, and the method of this embodiment for obtaining an offset from the circumference, and the circumference approximate to a set of a large number of four or more points Is obtained by a statistical method and compared with a method for obtaining an offset from the circumference. In the method using the statistical method, if the points with magnetic data as components are unevenly distributed or the magnetic population includes unique magnetic data, the center of the azimuth circle obtained from these points is the true azimuth circle. Deviation from the center. Therefore, if an attempt is made to reduce the offset error by using a statistical method, it is necessary to verify the variation of the population for obtaining the azimuth circle by the statistical method, or to select the population. In the method of this embodiment, if appropriate three points can be selected, an offset with an accuracy comparable to the offset accuracy obtained by the method using the statistical method can be used without using a statistical method with a large amount of calculation. Can be requested.

1-2. Hardware Configuration FIG. 3 is a schematic diagram showing an appearance of a mobile phone 3 which is an example of a mobile body to which the present invention is applied. The mobile phone 3 is equipped with a two-dimensional magnetic sensor 4. A two-dimensional magnetic sensor detects the direction and strength of a magnetic field by detecting vector components of magnetic fields in two directions x and y orthogonal to each other. Various information such as characters and images is displayed on the display 2 of the mobile phone 3. For example, the display 2 displays a map and an arrow or character indicating the direction.

  FIG. 4 is a block diagram showing a hardware configuration of a mobile phone 3 equipped with a magnetic measurement device including the two-dimensional magnetic sensor 4 and the magnetic sensor control device 1 to which the present invention is applied. The two-dimensional magnetic sensor 4 is mounted on various moving bodies and includes an x-axis sensor 30 and a y-axis sensor 32 that respectively detect an x-direction component and a y-direction component of a magnetic field vector due to geomagnetism. The x-axis sensor 30 and the y-axis sensor 32 are both configured by magnetoresistive elements, Hall elements, etc., and may be any one as long as they are directional one-dimensional magnetic sensors. The x-axis sensor 30 and the y-axis sensor 32 are fixed so that their sensitivity directions are orthogonal to each other. The outputs of the x-axis sensor 30 and the y-axis sensor 32 are time-divisionally input to a magnetic sensor I / F (Inter Face) 22. In the magnetic sensor I / F 22, the inputs from the x-axis sensor 30 and the y-axis sensor 32 are amplified and then AD converted. Digital magnetic data output from the magnetic sensor I / F 22 is input to the magnetic sensor control device 1 via the bus 5.

  The magnetic sensor control device 1 is a so-called computer including a CPU 40, a ROM 42, and a RAM 44. The CPU 40 is a processor that controls the entire mobile body such as the mobile phone 3. The ROM 42 is a non-volatile storage medium that stores a magnetic sensor control program executed by the CPU 40 and various programs for realizing the function of the moving body, for example, a navigation program. The RAM 44 is a volatile storage medium that temporarily holds data to be processed by the CPU 40. The magnetic sensor control device 1 and the two-dimensional magnetic sensor 4 can be configured as a one-chip magnetic measurement device.

The antenna 13 and the communication unit 14 are circuits for performing communication between the base station and the mobile phone 3.
The audio processing unit 18 is a circuit that performs AD conversion of an analog audio signal input from the microphone 16 and DA conversion for outputting the analog audio signal to the speaker 50.
The GPS receiver 41 is a circuit that processes GPS radio waves from GPS satellites and outputs the latitude and longitude of the current position.
The operation unit 48 includes a dial key that also serves as a character input key, a cursor key, and the like.
The display unit 54 as a display means includes a display 2 such as an LCD, a display control circuit (not shown), and the like, and displays various screens according to the operation mode of the mobile phone 3 on the display 2.
The notification unit 58 as a notification unit includes a sound source circuit, a ring tone speaker 59, a vibrator, an LED, and the like (not shown), and notifies the user of the progress of incoming calls and calibration. The calibration progress may be configured such that the user can visually recognize the progress by displaying an angle or a progress bar on the display 2.

1-3. Software Configuration FIG. 5 is a block diagram showing the configuration of the magnetic sensor control program 90. The magnetic sensor control program 90 is a program for providing azimuth data to the navigation program 98 and is stored in the ROM 42. The azimuth data is two-dimensional vector data indicating the direction of geomagnetism. When the CPU 40 executes the magnetic sensor control program 90, the CPU 40, the RAM 44, and the ROM 42 function as a magnetic sensor control device. The magnetic sensor control program 90 is composed of a module group such as a buffer management module 92, an offset setting module 94, and an azimuth calculation module 96.

  The buffer management module 92 is a program component that stores magnetic data sequentially input from the two-dimensional magnetic sensor 4 in a buffer for use in offset calculation, and causes the CPU 40 to function as input means. The magnetic data sequentially input from the magnetic sensor 4 can be sequentially selected, and the magnetic data that has not been selected can be discarded. However, if the selection conditions up to the second point are different from the selection conditions of the third point, even the magnetic data that was not selected as the points up to the second point can be selected as the third point. Therefore, the buffer managed by the buffer management module 92 is used not only for buffering the difference between the input timing and the processing timing but also for the purpose of making magnetic data that has not been selected once available again as a selection candidate. The buffer may be configured by hardware or software.

  The offset setting module 94 is a program component that selects three magnetic data from the magnetic data held by the buffer management module 92, calculates an offset from the selected three magnetic data, and sets the calculated offset. The CPU 40 functions as selection means, calculation means, setting means, and progress value output means.

  The azimuth calculation module 96 is a program component that generates azimuth data using magnetic data sequentially input from the magnetic sensor 4 and a set offset. Specifically, the azimuth calculation module 96 outputs two components obtained by subtracting each component of the offset data from each component of the magnetic data, which is two-dimensional vector data, as azimuth data.

  The navigation program 98 is a well-known program that searches for a guidance route to a destination and displays the guidance route on a map. For ease of map recognition, the map is displayed on the screen so that the orientation on the map matches the actual orientation. Therefore, for example, when the mobile phone 3 rotates, the map displayed on the display 2 rotates with respect to the display 2 so as not to rotate with respect to the ground. Direction data is used for such map display processing. Of course, the azimuth data may be used only for displaying east, west, south, and north with characters or arrows. When the navigation program 98 is activated, for example, the user is guided to rotate the mobile phone 3 while maintaining a horizontal posture for calibration, and calibration is started. When calibration is started, an offset update request is generated, and a buffer update process and an offset setting process described later are executed.

[Process flow]
2-1. Buffer Update FIG. 6 is a flowchart showing the flow of buffer update processing. The process shown in FIG. 6 proceeds when the CPU 40 executes the buffer management module 92 when an offset update request is generated.
In step S100, a buffer for storing a plurality of magnetic data used for offset calculation is initialized. Specifically, for example, data stored in the buffer area of the RAM 44 is deleted.

In step S102, input of new magnetic data from the magnetic sensor 4 is awaited.
When new magnetic data is input from the magnetic sensor 4, it is determined whether the buffer needs to be updated (step S104). In the situation where the mobile phone 3 is hardly moving, if there is an input from the magnetic sensor 4 sequentially at short time intervals, the distance between two points having two magnetic data that are continuously input as components becomes close. It is not desired that two points that are close to each other are included in the three points that are necessary for obtaining the offset. In addition, storing a plurality of magnetic data whose magnetic data components are close to each other in a buffer having a limited capacity is a waste of memory resources and causes unnecessary buffer update processing. . Therefore, the necessity for updating the buffer is determined as follows. For example, if the distance between the point having the magnetic data input immediately before and the point having the magnetic data input last as the component is smaller than a certain threshold value, it is determined that there is no need to update the buffer. The last input magnetic data is discarded without being stored in the buffer. Otherwise, it is determined that there is a need to update the buffer. As a result, for example, when magnetic data is input in the order shown in FIG. 7, the magnetic data represented by black circles is not stored in the buffer, and the magnetic data represented by white circles is stored in the buffer. In FIG. 7, the input order of magnetic data is represented by white circles and black circles.

If the following conditions are further added to the above determination conditions to determine whether or not the buffer needs to be updated, the probability of successful calibration can be increased. Here, N _qmax data strings stored in the buffer are q ₀ , q ₁ ,... Q _Nqmax−1 , and the set Q is Q = {q _i | 0 ≦ i ≦ N _qmax −1}. .
Additional update condition: When a point q having magnetic data as a component satisfies || qq _i || ₂ > q _min for all i satisfying i <N _qmax −1 for a certain threshold value q _min As long as the last magnetic data is stored, the buffer is updated.
If it is determined that there is a need to update the buffer, the buffer is updated (step S106). The update algorithm is, for example, FIFO (First In First Out).

FIG. 1 is a flowchart showing a flow of offset setting processing. The processing shown in FIG. 1 proceeds when the CPU 40 executes the offset setting module 94 when an offset update request is generated. When the processing described below is progressing by executing the offset setting module 94, the processing by the buffer management module 92 is proceeding in parallel in the multitasking environment.

In step S200, initialization for discarding all selection candidates is executed. Specifically, the three data structures p ₀ , p ₁ and p ₂ for storing selection candidates declared by the offset setting module 94 are reset and the buffer is also initialized. In the data structures p ₀ , p ₁ and p ₂ , as will be described later, magnetic data as selection candidates is stored until the third point is selected and an offset is set. Each data structure p ₀ , p ₁ , p ₂ is an array composed of two variables for storing two components of magnetic data.

In step S202, the above-described buffer update is awaited.
When the buffer is updated, the first selection candidate is provisionally determined (step S204). That is, the magnetic data input first after the buffer initialization (step S200) is the first selection candidate. The first selection candidate is stored in the data structure p ₀ . Since the data structure p ₀ in which the first selection candidate is stored may be updated as described later, the first selection candidate is provisionally determined in this process. Not too much.

2-3. Temporary Selection Candidate Selection for Second Point In step S206, buffer update is awaited again.
When the buffer is updated again, the second selection candidate is provisionally determined (step S208). That is, the second input magnetic data after buffer initialization (step S200) becomes the second selection candidate. The second selection candidate is stored in the data structure p ₁ . Since the data structure p _{1 in} which the second selection candidate is stored may be updated as described later, the second selection candidate is temporarily determined in this process. Not too much.

2-4.3 Selection of points-Update of 3 points In step S210, buffer update is awaited again.
When the buffer is updated again, in step S212, it is determined whether the end of the arc should be updated. In order to hold as a candidate to be selected according to the three-point selection condition, which of the selection candidates up to the third existing point is updated and held for the magnetic data last input and stored last in the buffer (If selection using the three-point selection condition has not been executed, only selection candidates up to the second point exist, but the processing content to be executed is the same). That is, it is determined in which data structure p ₀ , p ₁ , p ₂ the magnetic data last input and stored last in the buffer is stored. This is because the data structures p ₀ , p ₁ , and p ₂ have different meanings as follows.

The three points whose components are magnetic data stored in the data structures p ₀ , p ₁ , and p ₂ uniquely define an arc passing through them as long as they are not on the same straight line. The data structures p ₀ and p ₁ are meant as data structures that store magnetic data that are components of points at both ends of the arc. The data structure p ₂ is meant as a data structure that stores magnetic data that is a component at the midpoint of the arc. Therefore, until the third point is selected, in order to hold the selection candidates up to the third point, the magnetic data last input and stored last in the buffer is any data structure p ₀ , p ₁ , p Whether it is stored in ₂ must be determined.

By the way, the reason why the meaning is given to the data structures p ₀ , p ₁ and p ₂ is as follows. The three selection candidates are located on the circumference of the azimuth circle passing through the three selection candidates. As described above, the offset error becomes smaller as the three points used for obtaining the azimuth circle are evenly distributed over a wide range on the circumference passing through the three points. Accordingly, the longer the chord length of the arc passing through the three selection candidates is, the smaller the offset error becomes. If the chord length is too short, the offset error becomes larger. For this reason, it is desirable to update the selection candidates up to the third point each time the magnetic data is stored in the buffer so that the chord length of the arc passing through the three points that are selection candidates is increased to some extent. .

FIG. 8 is a schematic diagram for explaining the update of three selection candidates. Now, it is assumed that the magnetic data shown in FIG. 8B is stored in the data structures p ₀ , p ₁ and p ₂ . (The numbers 1, 4, 5, and 6 shown in FIG. 8 are numbers for managing the storage order in the buffer, and the magnetic data managed in the buffer by that number is stored in each data structure. Here, the magnetic data managed by each number is referred to as magnetic data 1, magnetic data 4, magnetic data 5, and magnetic data 6.) In this state, selection candidates The arc chord passing through the three points is a line segment (broken line) connecting a point having the magnetic data 1 as a component and a point having the magnetic data 5 as a component. Next, it is assumed that the magnetic data 6 is stored in the buffer. At this time, an arc chord through which three points having three magnetic data components pass is defined as p ₀ , p ₁ , and p ₂ , and a point having the magnetic data stored in p ₁ as a component and p It is calculated as a distance from a point having magnetic data stored in ₀ as a component. Therefore, if the positional relationship between the point having the magnetic data 6 as a component and the three points having the magnetic data 1, 4, and 5 as the components is in the state shown in FIG. 8A, it is stored in p _0. If the selected candidate is not updated, the calculation result that the chord of the arc has become long cannot be obtained. Also if, when the magnetic data 6 has a value which does not lengthen the arc chord, unless update the selection candidate stored in the p _2, to become shorter arc strings as the calculation result, the p ₂ The stored selection candidates need to be updated.

The condition that the chord of the circular arc passing through the three points having the three magnetic data components is expanded at least efficiently without being shortened at each update is derived as follows. Let q be the last magnetic data stored in the buffer. Here, p ₀ , p ₁ , and p ₂ are magnetic data stored in each data structure. In FIG. 9, points having q, p ₀ , p ₁ and p ₂ as components are represented by black circles, and azimuth circles passing through these three points are represented by solid lines. When the chord of the arc passing through the three points that are selection candidates becomes longer due to q, the following expressions (3) and (4) are established.

If equation (3) holds, the string can be extended by updating p ₁ with q. If equation (4) holds, the string can be extended by updating p ₀ with q. If none of these are present, the string is not extended.

In step S214, the selection candidate to be updated, determined as described above, is updated with the magnetic data stored last in the buffer. As a result, for example, the data structures p ₀ , p ₁ , and p ₂ storing the magnetic data shown in FIG. 8B are updated as shown in FIG. 8C.

-Three-point selection condition All the magnetic data stored in the buffer are tried to be selected as the third selection candidate. At this time, it is not always necessary that all the buffers are filled. When the third point is selected, as shown in FIG. 11, magnetic data that has not been determined as a selection candidate up to the second point (including data that was provisionally determined but subsequently rejected) is included. Sequentially selected as a third selection candidate. In FIG. 11, identifiers for managing the input order of magnetic data in the buffer are indicated by numbers from 0 to N _qmax −1. A smaller number represents a data structure in which previously inputted magnetic data is stored.

  In step S216, a third selection candidate is provisionally determined. Specifically, the third selection candidate is sequentially determined sequentially from the data stored in the buffer, and it is determined whether one of the three-point selection conditions is satisfied (step S218). The three selection conditions are derived from two viewpoints. The first point of view is that the three points whose components are magnetic data that are candidates for selection are sufficiently dispersed on the circumference passing through these three points, that is, the triangle having the three points as vertices is close to an equilateral triangle. This is the point of view. Therefore, when selection from the first viewpoint is executed, the distortion with respect to a regular triangle of three points having apexes of magnetic data as selection candidates as components is calculated. The second point of view is whether the area of a circle passing through the three points whose components are magnetic data that are selection candidates is sufficiently large. When the area of the circle that passes through these three points is small, an unexpected magnetic field is measured to calculate whether the three points are distributed within a narrow range on the circumference of the azimuth circle that passes through these three points. Will be. If the area of the circle passing through these three points is too large, an unexpected magnetic field is measured in calculating an accurate offset. Therefore, when selection is performed from the second viewpoint, the radius of a circle passing through three points whose components are magnetic data that are selection candidates is calculated. In the following description, the condition for determining whether a selection candidate should be selected from the first viewpoint is also simply referred to as a three-point selection condition, and it is determined whether the selection candidate should be selected from the second viewpoint. This is also referred to as verification of 3-point selection.

First, the three-point selection condition will be described from the first viewpoint applied in step S218. In this embodiment, as shown in FIG. 10, the distortion with respect to the regular triangle of the triangle having three points as the vertices, the magnetic data of which is a candidate for selection, as the starting point, the centroid d ₃ of the triangle as the starting point, and each vertex as the ending point. It is evaluated by the eigenvalues of a 2-by-2 symmetric matrix expressed using the sum of vectors. The center of gravity d ₃ of the triangle is obtained by the following equation (5).

As the three-point selection condition derived from the first viewpoint, the ratio of the minimum eigenvalue λ _{A2 to} the maximum eigenvalue λ _A1 among the eigenvalues λ _A1 and λ _A2 of the symmetric matrix A defined by the following equation (6) is determined in advance. That is, it is not less than a predetermined threshold value E ₀ .

ただし、以下の通りである。

Equation (6) can also be written as Equation (7), where p _i = (p _ix , p _iy ), d3 = (d _3x , d _3y ).

However, it is as follows.

From the definition of the symmetric matrix A, all eigenvalues are non-negative real numbers. Calculates an evaluation quantity E _A of the magnetic data that has not been selected as the magnetic data of up to the second point, which is stored in the buffer is defined by the following equation (11), the evaluation quantity E _A is maximum p ₂ Search for. The three-point selection condition derived from the first viewpoint is that E _A satisfies E _A ≧ E ₀ with respect to the threshold value E ₀ . When the third point satisfying E _A ≧ E ₀ is found, it may be determined that the three-point selection condition is satisfied.

By the way, the distortion with respect to the regular triangle of the triangle whose vertex is the three points whose magnetic data is the candidate for selection is the variation of the internal angle of the triangle, the variation of the length of the side of the triangle, and the centroid of the triangle. It can be defined by the variation of the distance up to. Further, these variations can be defined by the evaluation amount E _A using the eigenvalues of the symmetric matrix A described above. Therefore, the three-point selection condition derived from the first point of view is a variation in the internal angle of a triangle whose apex is the three points whose components are magnetic data as selection candidates, or a variation in the length of the side of the triangle, or It can also be said that the variation in distance from the center of gravity of the triangle to each vertex is within a predetermined range. When the eigenvalues of the symmetric matrix A are used for the condition determination of the three-point selection condition, the maximum eigenvalue and the minimum eigenvalue of the symmetric matrix A are solutions of a quadratic equation defined by the coordinate values of the vertices of the triangle and the coordinate values of the centroid of the triangle. Since the value indicating the variation in the interior angle of the triangle, the variation in the length of the triangle, and the variation in the distance from the center of gravity of the triangle to each vertex is used for the condition determination of the three-point selection condition, In comparison, the amount of calculation is reduced.

  If the three-point selection condition derived from the first viewpoint is not satisfied, it is determined whether all the data stored in the buffer has been determined (step S220). Returning to the process of S216, the process of determining whether the data stored in the buffer satisfies the three-point selection condition derived from the first viewpoint is repeated. At this time, all the buffers need not be filled. The magnetic data stored in the buffer includes magnetic data that has not been provisionally determined as points at both ends of the arc. If all the data stored in the buffer does not satisfy the three-point selection condition, the points that satisfy the three-point selection condition have not yet been collected, and the process returns to step S210 to wait for the buffer update. .

Selection Verification When the three-point selection condition derived from the first viewpoint is satisfied, the magnetic data selected from the first viewpoint is verified from the second viewpoint (step S224). In this process, as described above, the radius of a circle passing through three points whose components are magnetic data that are selection candidates is calculated.

Assuming that the center point of the circle is c ₃ = (c _3x , c _3y ), a simultaneous linear equation for _obtaining the center point is the following equation (12).

c _3r is a value that does not need to be used later, but has been added to establish a ternary linear system. The radius r is finally obtained as the Euclidean distance between c ₃ and p ₀ calculated by the following equation (13).

If the radius of the circle that passes through the three points including the three magnetic data satisfying the three-point selection condition as determined above is within the range from the threshold value r _max to r _min , the test is accepted. . Otherwise, it is rejected and the process returns to step S210 to wait for buffer update.

Note that a step of determining whether the equation of the circle obtained as described above is valid may be further provided. Specifically, the validity of the azimuth circle is verified by statistical processing using not only the three selected magnetic data p ₀ , p ₁ and p ₂ but also part or all of the magnetic data stored in the buffer. Is done. This verification is effective to some extent in order to reduce the variation in offset error, but is not necessarily a necessary process. In this verification, prompted evaluation amount S by the following equation (14), adopted to predetermined threshold St, in the case of S> S _t is the center point of the calculated orientation circle as an offset Otherwise, it is determined that the calibration has failed.

-Offset setting If the selected three points pass as a result of the verification of the three-point selection, an offset is set in step S226. That is, each component at the center point of the calculated azimuth circle is set as each component of the offset.

Incidentally, while the process from step S210 to step S224 are repeated, the value of each time evaluation quantity E _A is calculated in step S218. _A table (see FIG. 12) in which the correspondence relationship between the angle corresponding to the center angle of the arc passing through the three points p ₀ , p ₁ , and p ₂ and the evaluation amount E _A is stored in the ROM 42 in advance. by deriving a corresponding angle with the value of the evaluation quantity E _a using the table, or two-dimensional magnetic sensor 4 portable telephone 3 which is mounted is rotated several times from the calibration start time, or several times after rotation Then, the user can recognize whether the calibration is completed. Derivation of an angle corresponding to the evaluation quantity E _A is evaluated amount E is performed by offset setting module according to the calculation of the _A, to the derived angle may be output to the navigation program 98, calculates the evaluation value E _A is is output to the evaluation value E _a itself is a navigation program 98 every time it is, the angle corresponding to the evaluation value E _a may be derived by the navigation program 98.

According to the present embodiment, even before the offset that is the center point of the azimuth circle is calculated, that is, even during a period in which the three points for which the offset can be obtained with high accuracy are not yet selected, the three points p ₀ and p ₁ , P ₂ , the central angle of the arc can be derived. For example, compared to the case of obtaining an offset using statistical processing, since the offset that is the center point of the azimuth circle is not obtained during a period when magnetic data as a population element used for statistical processing is not sufficiently collected, A rotation angle indicating how many times the type telephone 3 has rotated cannot be obtained. Even during a period when the magnetic data is not sufficiently collected, the rotation angle can be obtained using the temporarily set offset, but the accuracy may not be good. In the present embodiment, even in a period of three selection satisfies three points not yet selected, for deriving the rotational angle based on the evaluation value E _A, as described above, do not meet the three selection criteria Compared with the method of calculating the offset that may not be accurate from the three points, and calculating the rotation angle from the calculated offset and the positions of p ₀ and p ₁ , the calculation angle is small and the rotation angle is accurately calculated. Can be derived.

How to recognize progress to the user, for example, to the sound of the scale of do, re, mi, fa Sorashido according to the rotation angle may be generated by controlling the notification unit 58, the progress on the display 2 in accordance with the value of the evaluation quantity E _A The progress status may be recognized by the user by displaying a bar or the like. Since the value of the evaluation quantity E _A increases the rotation angle also in relation to increase, without conversion to an angle held in advance a correspondence table as shown in FIG. 12, according to the value itself of the evaluated amount E _A As described above, the user may be made to recognize the progress status.

  The offset setting method according to the present embodiment is more effective than the case of obtaining the offset using statistical processing in the following points. In places where the strength of the magnetic field is weak, the radius of the azimuth circle is smaller than in places where the strength of the magnetic field is strong. When collecting magnetic data as a population element of statistical processing, in order to avoid magnetic data distribution bias and duplication, for example, the previously used magnetic data as a component is used as a component as in the buffer update processing described above. If the distance from the point with the last input magnetic data as a component is smaller than a certain threshold value, the last input magnetic data is discarded without being stored in the buffer. When the mobile phone 3 is rotated by the same angle range in a weak place, the number of magnetic data stored in the buffer is smaller than in a place where the magnetic field strength is strong. That is, in order to collect a sufficient number of magnetic data as a statistical processing population, the mobile phone 3 must be rotated to a wider angle range. According to the present embodiment, even if the number of magnetic data stored in the buffer is small, it is only necessary to collect points that satisfy the above-described three-point selection condition. The amount of operation of the mobile phone 3 required for collecting magnetic data necessary for calculation is reduced, and the offset calculation time is shortened.

B. Second Embodiment FIG. 13 is a flowchart showing a flow of an offset setting process according to a second embodiment of the present invention. The process shown in FIG. 13 proceeds when the CPU 40 executes the offset setting module 94 when an offset update request is generated. As in the first embodiment, when the processing described below is progressing by executing the offset setting module 94, the processing by the buffer management module 92 is proceeding in parallel in the multitasking environment.

In step S300, initialization for discarding all selection candidates is executed. Specifically, the three data structures p ₀ , p ₁ and p ₂ for storing selection candidates declared by the offset setting module 94 are reset and the buffer is also initialized.
In step S302, buffer update is awaited.
When the buffer is updated, it is determined whether or not there is a vacancy in the buffer, that is, whether or not the number of data stored in the buffer is a predetermined N _qmax (step S304). The processes in steps S302 and S304 are repeated until the number of data stored in the buffer reaches N _qmax . As described above, in this embodiment, one point of magnetic data is not selected until N _qmax pieces of magnetic data are accumulated in the buffer.

When N _qmax pieces of magnetic data are accumulated in the buffer, the first and second magnetic data are selected (step S306). When N _qmax data strings stored in the buffer are q ₀ , q ₁ ,... Q _Nqmax-1 , and the set Q is Q = {qi | 0 ≤ i ≤ N _qmax -1}, q Each point having components ₀ , q ₁ ,..., Q _Nqmax-1 as data components q ₀ , q _{1 ,.} Similar to the first embodiment, magnetic data is stored so that the set Q does not become a multiple set.

  In order to accurately obtain an offset from the set Q, it is desirable that magnetic data corresponding to two points that are farthest in a specific direction are always selected. Even if two points that are farthest apart in a randomly determined direction are selected, there is an average effect. The specific selection method is as follows.

集合Ｑの要素を上式（１６）のｑ_iに順次代入してＤ_iを求め、Ｄ_iが最大となるデータ点ｑ_iをｐ₀とし、Ｄ_iが最小となるデータ点ｑ_iをｐ₁とすると、ベクトルａの向きと平行な直線に下ろした垂線の足が互いに最も離れる２つのデータ点が選抜される。そして本実施形態では、ここで選抜された２つのデータ点は、集合Ｑが破棄されない限り、他のデータ点に入れ替わることはない。すなわち、本実施形態でオフセットが設定される場合には、ここで選抜された２つの磁気データを必ず含む３つの磁気データに基づいて算出されたオフセットが設定される。

上述したある特定の向きと大きさを持つベクトルａは行列Ｃの最小固有値λ_C2に対する固有ベクトルであってもよい。 The inner product D of the vector a having a specific direction and size and the vector having the centroid d _N of the data points q ₀ , q _{1 ,.} the composed data points q _i and p _0, the data points q _i of the inner product D is minimized and p _1. The center of gravity d _N of the data points q ₀ , q ₁ ,... Q _Nqmax-1 is obtained by the following equation (15). An inner product D of a vector a and a vector starting from the center of gravity d _N of the data points q ₀ , q ₁ ,... Q _Nqmax-1 and ending at the data point q _i is obtained by the following equation (16).

Seeking D _i the elements of the set Q are sequentially substituted into q _i of Equation (16), the data points q _i where D _i is the largest and p _0, the data points q _i where D _i is the minimum p _{If it is 1} , two data points are selected where the legs of the perpendicular line drawn in a straight line parallel to the direction of the vector a are farthest from each other. In the present embodiment, the two data points selected here are not replaced with other data points unless the set Q is discarded. That is, when the offset is set in the present embodiment, the offset calculated based on the three magnetic data that always include the two magnetic data selected here is set.

The vector a having a specific direction and size described above may be an eigenvector for the minimum eigenvalue λ _C2 of the matrix C.

In step S308, the third selection candidate is provisionally determined as in step S216 of the first embodiment.
In step S310, it is determined whether or not the three-point selection condition is satisfied as in step S218 of the first embodiment.
In step S312, it is determined whether all the data stored in the buffer has been determined in the same manner as in step S220 of the first embodiment. If all the data has not been determined, the process returns to step S308.

In step S314, three-point selection verification is performed in the same manner as in step S224 of the first embodiment. As a result of the verification of the three-point selection, if the result is unsuccessful, the process returns to step S300 and the buffer is reset.
In step S316, an offset is set in the same manner as in step S226 of the first embodiment.

  The present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

The flowchart which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The block diagram which concerns on embodiment of this invention. The block diagram which concerns on embodiment of this invention. The flowchart which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The correspondence figure concerning an embodiment of the invention. The flowchart which concerns on embodiment of this invention.

Explanation of symbols

1: magnetic sensor control device, 2: display, 3: mobile phone, 4: two-dimensional magnetic sensor, 13: antenna, 14: communication unit, 16: microphone, 18: audio processing unit, 30: x-axis sensor, 32 : Y-axis sensor, 41: GPS receiving unit, 40: CPU, 42: ROM, 44: RAM, 48: operation unit, 50: speaker, 54: display unit, 58: notification unit, 59: ringing tone speaker, 90: Magnetic sensor control program, 92: buffer management module, 94: offset setting module, 96: azimuth calculation module, 98: navigation program

Claims (16)

Input means for inputting a plurality of magnetic data having two components sequentially output from the two-dimensional magnetic sensor;
A buffer for storing a plurality of input magnetic data;
A selection unit that has a data structure that holds the three magnetic data as selection candidates, and that satisfies the predetermined three-point selection condition and selects the three magnetic data including the selection candidates ;
A calculating means for calculating a center point from the three points to the selected been three magnetic data components is a point equidistant,
Setting means for setting the component of the center point as an offset of the magnetic data;
With
In the selection means, when the magnetic data is newly stored in the buffer, the chord length of the arc passing through the three selection candidates and having the two selection candidates as end points corresponds to the end points of the arc. When the chord length of the arc is extended by updating the selection candidate with the magnetic data newly stored in the buffer, the selection candidate corresponding to the end point of the arc is newly stored in the buffer. Update with magnetic data,
Magnetic sensor control device. Said selection means, when the new the magnetic data is stored in the buffer, the said magnetic data has not been a corresponding selection candidate end point of the circular arc is obtained from the buffer at the midpoint of the circular arc As a selection candidate for magnetic data,
The magnetic sensor control apparatus according to claim 1 . The three-point selection condition includes a condition that correlates with a distortion with respect to a regular triangle of a triangle having three points as vertices having three magnetic data stored in the data structure as components.
The magnetic sensor control apparatus according to claim 2 . The three-point selection condition includes that the variation in the inner angle of the triangle is within a predetermined range,
The magnetic sensor control apparatus according to claim 3 . The three-point selection condition includes that the variation in the length of the side of the triangle is within a predetermined range,
The magnetic sensor control apparatus according to claim 3 . The three-point selection condition includes that the variation in distance from the center of gravity of the triangle to each vertex is within a predetermined range.
The magnetic sensor control apparatus according to claim 3 . The three-point selection condition includes that the ratio of the minimum eigenvalue to the maximum eigenvalue of the following 2-by-2 symmetric matrix A is greater than or equal to a predetermined value.
The magnetic sensor control apparatus according to any one of claims 3 to 6 .

However,
pi (i = 0, 1, 2) is each vertex of the triangle, and d3 is the center of gravity of the triangle. The three-point selection condition includes that the value of the ratio is maximum.
The magnetic sensor control apparatus according to claim 7 . A value indicating a progress status from the start to the completion of selection of the three magnetic data satisfying the three-point selection condition, and a progress value derived based on the ratio value, or the ratio value It further comprises a progress value output means for outputting,
The magnetic sensor control apparatus according to claim 7 or 8 . The progress value is an angle corresponding to a central angle of an arc passing through three points including three magnetic data stored in three data structures as components.
The magnetic sensor control apparatus according to claim 9 . A magnetic sensor control device according to any one of claims 1 to 10 ,
The two-dimensional magnetic sensor;
A magnetic measuring device comprising: A magnetic sensor control device according to claim 9 or 10,
The two-dimensional magnetic sensor;
Informing means for informing the user of the progress situation by emitting a sound of a different scale according to the progress value or the value of the ratio ,
Magnetic measuring device. A magnetic sensor control device according to claim 9 or 10,
The two-dimensional magnetic sensor;
Display means for allowing the user to visually recognize the progress status according to the progress value or the ratio value ;
Magnetic measuring device. Input a plurality of magnetic data having two components sequentially output from a two-dimensional magnetic sensor,
Storing a plurality of input magnetic data in a buffer;
When the magnetic data is newly stored in the buffer while holding the three magnetic data as selection candidates in the data structure, the chord of the arc passing through the three selection candidates and having the two selection candidates as endpoints Corresponds to the end point of the arc when the chord length of the arc is extended by updating the selection candidate corresponding to the end point of the arc with the magnetic data newly stored in the buffer. Updating the selection candidates with the magnetic data newly stored in the buffer, selecting the three magnetic data including the selection candidates while satisfying a predetermined three-point selection condition,
Calculate a center point that is a point equidistant from the three points having the three selected magnetic data as components,
Setting the center point component as an offset of the magnetic data;
Magnetic sensor offset setting method. Input means for inputting a plurality of magnetic data having two components sequentially output from the two-dimensional magnetic sensor;
A buffer for storing a plurality of input magnetic data;
A selection unit that has a data structure that holds the three magnetic data as selection candidates, and that satisfies the predetermined three-point selection condition and selects the three magnetic data including the selection candidates ;
A calculating means for calculating a center point from the three points to the selected been three magnetic data components is a point equidistant,
Setting means for setting the component of the center point as an offset of the magnetic data;
Make your computer work,
In the selection means, when the magnetic data is newly stored in the buffer, the chord length of the arc passing through the three selection candidates and having the two selection candidates as end points corresponds to the end points of the arc. When the chord length of the arc is extended by updating the selection candidate with the magnetic data newly stored in the buffer, the selection candidate corresponding to the end point of the arc is newly stored in the buffer. Update with magnetic data,
Magnetic sensor offset setting program. A computer-readable recording medium in which the offset setting program according to claim 15 is stored.

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