JP2007225325A - Magnetic sensor controller, magnetic measuring instrument, offset setting method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately set an offset without using statistical processing. <P>SOLUTION: This magnetic sensor controller comprises a means for inputting sequentially a plurality of magnetic data having three components or two components output sequentially from a magnetic sensor, a means for calculating a bisecting normal surface or a perpendicular bisector of two points corresponding to the two magnetic data, in every set comprising two combined according to an input order, and a means for repeating processing of updating a base point to a point on a line segment drawn perpendicularly to the bisecting normal surface or perpendicular bisector from the base point, as to the plurality of bisecting normal surfaces or perpendicular bisectors, and for setting the offset of the magnetic data, based on the updated base point. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, a three-dimensional magnetic sensor and a two-dimensional magnetic sensor that are mounted on a moving body and detect the direction of geomagnetism are known. In general, a three-dimensional magnetic sensor includes three magnetic sensor modules for detecting a scalar quantity by decomposing a magnetic field vector into three orthogonal components. The magnetic data that is the output of the three-dimensional magnetic sensor has three components because it consists of a combination of the outputs of such three magnetic sensor modules. The direction and magnitude of the vector having magnetic data as the component are the direction and magnitude of the magnetic field detected by the three-dimensional magnetic sensor. When the direction or magnitude of geomagnetism is specified based on the output of the three-dimensional magnetic sensor, the output includes the magnetization component of the moving body and the measurement error of the magnetic sensor itself. Therefore, a process for correcting the output of the three-dimensional magnetic sensor is necessary to cancel them. The operation value of this correction process is called offset. The offset represents a combined vector of a magnetic field vector due to magnetization of the moving body detected by the three-dimensional magnetic sensor and a measurement error vector of the magnetic sensor in a three-dimensional coordinate space, and is an output of the three-dimensional magnetic sensor. By subtracting the offset from the magnetic data, the magnetization component of the moving body and the measurement error of the magnetic sensor itself are canceled together. In the three-dimensional coordinate space, points having magnetic data as components are plotted along a predetermined spherical surface. The offset can be calculated by obtaining the center of the spherical surface. The process for obtaining the offset is called calibration.

  By the way, a set of points whose components are magnetic data is not a perfect sphere in reality. This is because the output of the three-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 three-dimensional magnetic sensor fluctuates during the period, and there is a calculation error until the output of the three-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. However, it is difficult to accurately determine the reliability of offset calculated by statistical processing and the suitability of magnetic data as a population element. Moreover, the amount of processing for obtaining the most probable spherical center by statistical processing is considerable, and it consumes a lot of time and resources.

  In addition, the 3D magnetic sensor can be calibrated without forcing the user to consciously rotate the moving object on a flat surface, so guidance on how to move the moving object during calibration is provided. There is no need to be a user. Therefore, it is fully foreseen that the strength of the magnetic field in which the moving body exists during calibration will fluctuate. However, when the component at the point where the variation in distance to the point having the magnetic data as a component is minimized as described in Patent Document 1, the magnetic data serving as a statistical processing population is accumulated. If the strength of the geomagnetism varies during the period, there is a problem that an accurate offset cannot be obtained. For example, when the magnetic sensor moves from indoor to outdoor, the geomagnetism detected by the magnetic sensor becomes stronger. Therefore, when the offset is obtained by the method described in Patent Document 1, the error increases.

International Publication No. 2004-003476 Pamphlet

  The present invention was created in view of the above-described problems, and an object thereof is to provide a magnetic sensor control device, an offset setting method and program, and a magnetic measurement device that can accurately set an offset without using statistical processing. And

(1) A magnetic sensor control device for achieving the above object corresponds to means for sequentially inputting a plurality of magnetic data having three or two components, which are sequentially output from the magnetic sensor, and the two magnetic data. Means for calculating two sets of perpendicular bisectors or perpendicular bisectors for each set of the magnetic data combined in the order of input, and the vertical bisector or the vertical bisector from the base point The process of updating the base point to a point on the line segment perpendicular to the line is repeated for the plurality of vertical bisectors or the plurality of vertical bisectors, and based on the updated component of the base point Means for setting an offset of magnetic data.
Two perpendicular bisectors on the circumference pass through the center of the circle. When a large number of points whose components are magnetic data output from a two-dimensional magnetic sensor are distributed in a range from a specific circumference to a short distance, when these many points are grouped into two, The perpendicular bisector passes near the center of the circumference. Consider a number of straight lines extending radially from a plurality of points near the center of the circle. If the distance between these lines and the center of the circle is sufficiently close, find a point on a line segment that drops perpendicularly to the line from one point, and a point on a line segment that drops vertically from that point to another line By repeating the process of obtaining a point on a line segment that is perpendicular to another straight line from the newly obtained point, the obtained point converges near the center of the circle. Similarly, consider a number of planes that are not parallel to each other through multiple points near the center of the sphere, and if the distance between those planes and the center of the circle is close enough, they will be on the line down from one point to those Repeat the process of finding a point, finding a point on a line segment perpendicular to another plane from that point, and finding a point on the line segment perpendicular to another plane from that newly obtained point Thus, the obtained point converges near the center of the sphere. The present invention uses these phenomena to determine the offset of the magnetic sensor without using statistical processing.
Further, before and after only the strength of the geomagnetism detected by the magnetic sensor changes, the distance from the point corresponding to the true offset of the magnetic sensor to the point having magnetic data as a component changes. However, before the strength of geomagnetism changes, two perpendicular bisectors or perpendicular bisectors that have two magnetic data output from the magnetic sensor as components, and magnetism after the geomagnetism strength changes Two perpendicular bisectors or perpendicular bisectors that are composed of two magnetic data output from the sensor are in the case where the geomagnetic detection directions corresponding to the two points before and after the change coincide. Will match. Therefore, when the offset is obtained using two vertical bisectors or perpendicular bisectors having magnetic data as components, the accuracy of the obtained offset is not easily affected by changes in the strength of the geomagnetism. It can be said that. The present invention uses this phenomenon to improve the accuracy for obtaining the offset.

  (2) In the magnetic sensor control device for achieving the above object, the means for setting the offset performs a process of updating the base point on the plurality of vertical bisectors or the vertical bisectors. It may be repeated once each in the order of calculation of the bisector or the perpendicular bisector.

(3) In the magnetic sensor control apparatus for achieving the above object, the means for setting the offset performs the process of updating the base point a plurality of times for each vertical bisector or each vertical bisector. It may be repeated.
By updating the base point update process multiple times for each vertical bisector or each vertical bisector, the base point update process is performed even when there is little magnetic data used to obtain the offset. Allows the base point to converge near the point corresponding to the true offset.

(4) The magnetic sensor control device for achieving the above object may further comprise means for selecting two sets of the magnetic data corresponding to two points separated by a predetermined distance or more in the order of input. . The means for calculating the vertical bisector or the vertical bisector may calculate the vertical bisector or the vertical bisector for each selected set of magnetic data.
Focusing on the error of the magnetic data itself, 2 connecting the two points defining the vertical bisector or vertical bisector used for updating the base point corresponding to the offset and the point corresponding to the true offset. The smaller the angle formed by the straight line, the larger the distance between the two perpendicular bisectors or the perpendicular bisector and the point corresponding to the true offset. Therefore, the accuracy of obtaining the offset can be increased by selecting the magnetic data so that two points separated to a certain degree constitute one set, and obtaining the vertical bisector or the perpendicular bisector for each set. If attention is paid to the change in the strength of the geomagnetism, the smaller the difference in the timing of outputting the magnetic data corresponding to the two points as one set of elements, the smaller the vertical bisector or bisector of the two points. The distance between the line and the point corresponding to the true offset is reduced. Therefore, two sets of magnetic data that are components of two points separated by a predetermined distance or more are selected, and a perpendicular bisector or perpendicular bisector is calculated for each selected magnetic data set. By doing so, the accuracy of obtaining the offset can be increased.

(5) In the magnetic sensor control device for achieving the above object, all the angles formed by the already selected vertical bisector or the perpendicular bisector are equal to or larger than a predetermined angle. There may be further provided means for selecting a vertical bisector or the vertical bisector. The means for setting the offset may repeat the process of updating the base point for the selected vertical bisector or the vertical bisector.
The closer the two perpendicular bisectors or vertical bisectors used in succession to update the base point corresponding to the offset are in parallel, the line or point they intersect and the point corresponding to the true offset The distance increases. In the present invention, an algorithm for converging the base point near a line or a point at which the perpendicular bisector or the perpendicular bisector intersects is used, so that the base point is continuously used to update the base point corresponding to the offset. It is desirable that the angle formed by the two vertical bisectors or vertical bisectors is somewhat large. Therefore, a vertical bisector or vertical bisector where all the angles formed by the previously selected vertical bisector or vertical bisector are equal to or greater than a predetermined angle is selected and selected. It is desirable to repeat the process of updating the base point for the vertical bisector or vertical bisector.

(6) In the magnetic sensor control device for achieving the above object, the means for setting the offset updates the base point to a perpendicular foot extending from the base point to the vertical bisector or the vertical bisector. May be.
By updating the base point to the foot of the perpendicular line drawn from the base point to the vertical bisector or the vertical bisector, the number of times the base point is updated before the base point converges within a certain range can be reduced.

(7) In the magnetic sensor control device for achieving the above object, the means for setting the offset is an internal dividing point on a line segment that is perpendicular to the vertical bisector or the perpendicular bisector from a base point. The base point may be updated.
If a vertical bisector or a perpendicular bisector that is far from the point corresponding to the true offset is obtained due to a temporary disturbance, the offset of the offset due to the disturbance will be updated when the base point is updated using them. Calculation error occurs. Such an error can be reduced by updating the base point to the internal divide point on the vertical bisector or the perpendicular bisector line from the base point.

(8) In the magnetic sensor control device for achieving the above object, the means for setting the offset performs a process of updating the base point from the base point to the vertical bisector or the vertical bisector. The offset may be set based on the last component of the base point by repeating until the length of the line segment to be lowered to a predetermined value or less.
The width of the distribution range of the updated base point does not converge to 0 even if the update process is repeated infinitely. Therefore, in a situation where the geomagnetism is constant, if the base point update process is repeated a certain number of times, the further update process becomes useless. Therefore, it is reasonable to set the component of the last base point as the offset of the magnetic data by repeating until the length of the vertical bisector or the line segment perpendicular to the vertical bisector from the base point is less than the predetermined value. It is.

  Each function of the plurality of means provided in the present invention is 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. Further, 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 an apparatus invention but also as a program invention, a recording medium recording the program, and a method invention. It should be noted that the order of each operation of the method described in the claims is not limited to the order of description as long as there is no technical obstruction factor, and may be executed in any order, or may be executed simultaneously. Also good.

Embodiments of the present invention will be described below based on examples.
In the present embodiment, an offset for canceling the magnetization component of the moving body on which the three-dimensional magnetic sensor is mounted and the measurement error of the magnetic sensor itself is obtained. In order to obtain the offset, an infinite number of points in the vector space whose components are magnetic data that is the output of the three-dimensional magnetic sensor is approximated as a spherical surface. This spherical surface is referred to as an azimuth spherical surface. In addition, an infinite number of points in a vector space whose component is magnetic data that is an output of an ideal three-dimensional magnetic sensor having no measurement error is referred to as a spherical surface of a true azimuth sphere. In this embodiment, the component of the center point of the azimuth sphere is calculated as an offset.

1. Hardware Configuration FIG. 2 is a schematic diagram showing the appearance of a mobile phone 1 as an example of a mobile body to which the present invention is applied, and FIG. 3 is a block diagram of the mobile phone 1. The mobile phone 1 is equipped with a three-dimensional magnetic sensor 4. A three-dimensional magnetic sensor detects the direction and strength of a magnetic field by detecting vector components of magnetic fields in three directions of x, y, and z orthogonal to each other. Various information on characters and images is displayed on the display 5. For example, the display 5 displays a map and an arrow or character indicating the direction.

  The control unit 45 is a so-called computer including a CPU 40, a ROM 42, and a RAM 44, and constitutes a magnetic sensor control device. The CPU 40 is a processor that controls the entire mobile phone 1. 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 magnetic sensor control program is a program for providing azimuth data to a navigation program or the like based on the magnetic data output from the three-dimensional magnetic sensor 4. The azimuth data is two-dimensional vector data indicating the direction of geomagnetism. The azimuth data may be provided to the navigation program as three-dimensional vector data. The module group of the magnetic sensor control program includes an offset setting program. The offset setting program is a program for setting an offset for correcting magnetic data output from the three-dimensional magnetic sensor 4. When the CPU 40 executes the magnetic sensor control program, the CPU 40, the RAM 44, and the ROM 42 function as a magnetic sensor control device. The navigation program is a well-known program that displays a surrounding map from the current location to the destination. 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 1 rotates, the map displayed on the display 5 rotates relative to the display 5 so as not to rotate relative to the ground. Direction data is used for such map display processing. Of course, the azimuth data may be used only for displaying the azimuth by characters or arrows. The RAM 44 is a volatile storage medium that temporarily holds data to be processed by the CPU 40. Some or all of the various programs may be stored in the ROM 42 by communication via a network. The magnetic sensor control device and the three-dimensional magnetic sensor 4 can be configured as a one-chip magnetic measurement device.

The antenna 13, the RF unit 10, the modem unit 12, and the CDMA unit 14 are circuits for performing CDMA communication between the base station and the mobile phone 1.
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 20 is a circuit that processes GPS radio waves from GPS satellites received by the antenna 21 and outputs the latitude and longitude of the current position.
The key input unit 48 includes a dial key that also serves as a character input key, a cursor key, and the like.
The electronic imaging unit 52 includes an optical system (not shown), an imaging device, an AD converter, and the like.
The display unit 54 includes a display 5 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 1 on the display 5.
The notification unit 58 includes a sound source circuit, a ring tone speaker, a vibrator, an LED, and the like (not shown) and notifies the user of an incoming call.

  FIG. 4 is a schematic internal configuration diagram of the three-dimensional magnetic sensor 4. The three-dimensional magnetic sensor 4 includes an x-axis sensor 30, a y-axis sensor 32, and a z-axis sensor 34 for detecting an x-direction component, a y-direction component, and a z-direction component of a magnetic field vector due to geomagnetism. The x-axis sensor 30, the y-axis sensor 32, and the z-axis sensor 34 are all composed of giant magnetoresistive elements, Hall elements, etc., and any directivity one-dimensional magnetic sensor can be used. Good. The x-axis sensor 30, the y-axis sensor 32, and the z-axis sensor 34 are fixed so that their sensitivity directions are orthogonal to each other. Outputs of the x-axis sensor 30, the y-axis sensor 32, the z-axis sensor 34, and the temperature sensor 36 are alternatively selected by the switching unit 24, amplified by the amplifier 25, and then AD-converted by the A / D converter 26. . The x-axis magnetic data, y-axis magnetic data, z-axis magnetic data, and temperature data corresponding to the outputs of the x-axis sensor 30, the y-axis sensor 32, the z-axis sensor 34, and the temperature sensor 36 are sent to the bus 11 by the magnetic sensor I / F 27. Is output. The temperature data can be used for setting an offset or for correcting each temperature of x-axis magnetic data, y-axis magnetic data, and z-axis magnetic data. The output data of the three-dimensional magnetic sensor 4 composed of three components of x-axis magnetic data, y-axis magnetic data, and z-axis magnetic data is referred to as magnetic data.

2. First Offset Setting Method FIG. 1 is a flowchart showing a process flow in a first offset setting method to which the present invention is applied. The process shown in FIG. 1 proceeds when the control unit 45 executes an offset setting program that is activated when the navigation program is activated, when an incoming call is received, or at regular intervals.

  In step S100, the first base point is set. The base point is stored in the data structure as coordinates having three components of xyz, and indicates the position of a specific point in the vector space. The initial base point can be set arbitrarily, but for example, the offset set at the previous end of the navigation program may be set as the base point, or the offset measured at the time of factory shipment may be set as the first base point. it can. Data structures and variable values are stored in the RAM 44.

At step S102, is input to the magnetic data control unit 45, a magnetic data input is set to p _1. The magnetic data is stored in the data structure p ₁ as coordinates having three components of xyz, and indicates the position of a specific point in the vector space.
At step S104, is input to the magnetic data control unit 45, a magnetic data input is set to p _2. The time interval from the input of the magnetic data set at p ₁ to the input of the magnetic data set at p ₂ can be arbitrarily set. The magnetic data is stored in the data structure p ₂ as coordinates having three components of xyz and indicates the position of a specific point in the vector space.

In step S106, a distance between p ₁ and p ₂ is calculated, and it is determined whether the distance is greater than a predetermined value. Calculated distance is input again the magnetic data by the processing in step S104 is equal to or less than a predetermined value, p ₂ is updated by the newly entered magnetic data.
If the distance between p ₁ and p ₂ is too close, the measurement error of the three-dimensional magnetic sensor 4 itself, the calculation error when extracting the output of the three-dimensional magnetic sensor 4 as a digital value, and the like will cause the p ₁ and p ₂ just leaves slightly p ₁ and perpendicular bisector of p ₂ and true for the distance between the point corresponding to the offset deviates greatly (see the one-dot chain lines in FIG. 5), the perpendicular bisector When the offset is calculated using the surface, an error between the calculated offset and the true offset increases. In the process of step S106, the input magnetic data is selected so that two perpendicular bisectors that are too close are not used for the offset setting. Further, in the process of step S106, magnetic data for calculating the vertical bisector is combined in the order of input, so the difference in magnetic field strength corresponding to a set of magnetic data for which one vertical bisector is obtained is reduced. be able to. Therefore, by calculating the offset using the vertical bisector thus obtained, it is less likely to be affected by fluctuations in the strength of the geomagnetism during measurement, so that the offset can be set with high accuracy. On the other hand, when calculating two vertical bisectors whose input order is too far, the geomagnetism strength of each magnetic data corresponding to the two points may be different during the measurement period. There is a risk of calculating a vertical bisector where the distance between the vertical bisector and the point corresponding to the true offset is large.

In step S108, a perpendicular bisector of p ₁ and p ₂ is calculated. Assuming that p ₁ is (x ₁ , y ₁ , z ₁ ) and p ₂ is (x ₂ , y ₂ , z ₂ ), the vertical bisector of p ₁ p ₂ is given by the following equation (1): Street.

In order to use the calculated vertical bisector in subsequent calculations, variables a, b, c, and d expressed by the following equation (2) are calculated and stored as constants of the plane equation ax + by + cz + d = 0. That's fine.

In the subsequent step S112, since processing is performed using the two planes continuously calculated in step S108, the variables a ₁ and b ₁ for storing the current plane equation and the previous plane equation separately are stored. , C ₁ , d ₁ , a ₂ , b ₂ , c ₂ , d _2, and the previous calculation stored in the variables a ₁ , b ₁ , c ₁ , d ₁ for storing the current plane equation It is necessary to store the constants of the plane equation thus stored in the variables a ₂ , b ₂ , c ₂ , and d ₂ for storing the previous plane equation.

  In steps S110 and 112, for the vertical bisector calculated after the second time, whether the angle θ formed by the currently calculated vertical bisector and the previously calculated vertical bisector is greater than a predetermined value α. Determined. If the angle θ formed by the two planes is less than or equal to the predetermined value α, the new magnetic data is updated until the vertical bisector where the angle θ formed with the previously calculated vertical bisector is greater than α is calculated. The input and vertical bisector calculations are repeated.

Finding the angle between the two planes is equivalent to finding the angle between the normal vectors of the respective planes. Therefore, the vertical bisector a ₁ x + b ₁ y + c ₁ z + d ₁ = 0 calculated this time, the previously calculated vertical bisector a ₂ x + b ₂ y + c ₂ z + d ₂ = 0, and the angle θ formed by them The relationship is as shown in the following formula (3).

Therefore, in order to determine whether the angle θ formed by the two planes is larger than the predetermined value α (α <π / 2), it is determined by calculation whether the relationship of the following equation (4) is established. Good.

  When the angle formed by the continuously calculated perpendicular bisectors is too small as shown in FIG. 6, even if the distance from the true offset of these two planes is close, the two planes intersect at a position far from the true offset. . The algorithm employed in the present embodiment has the property that the locus of the base point to be updated is directed to a straight line where the planes intersect, so that the intersecting straight lines use two planes that may be far from the point corresponding to the true offset. Updating the base point causes a decrease in the offset calculation accuracy. Further, even if the base point is updated using two substantially parallel planes, the base point may not easily move toward the true offset. In step S112, in order to solve such a problem, the calculated plane is selected.

In step S114, the coordinates of the foot of the perpendicular line drawn from the base point to the vertical bisector calculated this time are obtained, and the base point is updated to the foot. Assuming that the coordinates of the base point are (x ₀ , y ₀ , z ₀ ), the vertical foot coordinates (x _a) down from the base point to the vertical bisector a ₁ x + b ₁ y + c ₁ z + d ₁ = 0 calculated this time. , Y _a , z _a ) is obtained by the following equation (5).

When the process of step S114 is repeated, the base points that are sequentially updated follow the locus shown in FIG. 5 and gradually converge to a narrow range. In FIG. 5, f ₁ to f ₄ indicate vertical bisectors with perpendicular lines, and the suffix “f” indicates the calculation order of the vertical bisectors. Moreover, the broken line has shown the update locus | trajectory of the base point. The vertical bisector after f ₅ is omitted. In the algorithm employed in the present embodiment, even if the number of population elements (number of magnetic data) for calculating the offset is small, the offset can be calculated with accuracy according to the number of population elements. In addition, in the algorithm employed in this embodiment, the offset is calculated using the vertical bisector, so that the offset calculation accuracy is unlikely to decrease due to a change in the strength of the geomagnetism. For example, assume that the strength of the geomagnetism changes and the spherical surface of the true azimuth sphere changes from S ₁ to S ₂ . The perpendicular bisector of p ₁ and p ₂ (points indicated by black circles in FIG. 5) corresponding to the magnetic data input when the spherical surface of the true azimuth sphere is S ₂ is the true azimuth sphere. When the spherical surface of S ₁ is S ₁ , it coincides with a perpendicular bisector of a point (point indicated by a triangle in FIG. 5) corresponding to magnetic data input with the same posture and timing. Therefore, in this embodiment, even if the strength of geomagnetism changes, the offset calculation accuracy is unlikely to drop.

In step S116, it is determined whether the number of base point updates has reached a predetermined number.
If the number of updates of the base point increases to some extent, the base point is considered to have converged in a narrow range close to the point corresponding to the true offset. Therefore, when the base point update count reaches a predetermined number, the base point component is set as an offset (step S118).

  The above process is repeated after the offset is set for the first time, and the offset is updated each time. The update of the offset may be repeated any number of times, and the update process may be cut off a predetermined number of times. Also, an offset may be set regardless of the number of base point updates. The offset set in this way is used at a timing required by a program that uses azimuth data. Note that the offset may be set only once as described above in accordance with the request of the program using the azimuth data. In any case, in this embodiment, since the offset is set based on the output of the three-dimensional magnetic sensor 4, the xy axis of the three-dimensional magnetic sensor 4 needs to be rotated on the horizontal plane during the calibration. Absent. Therefore, it is not necessary to force the user to perform a specific operation for calibration. For this reason, in the calibration of the three-dimensional magnetic sensor, it may take time for the calibration, and the calibration may be executed at any timing. When the operation method and timing in calibration are not guided to the user, it is assumed that the strength of the magnetic field fluctuates during calibration. In the present embodiment, since the offset is calculated using the vertical bisector, even if the magnetic field strength fluctuates during calibration, the offset calculation accuracy is unlikely to decrease as described above.

3. Second Offset Setting Method FIGS. 7 and 8 are flowcharts showing the flow of processing in the second offset setting method to which the present invention is applied. The main difference between the second offset setting method and the first offset setting method is that the base point is updated by repeatedly using one vertical bisector group consisting of a predetermined number (for example, five) of perpendicular bisectors. It is a point to do. The processing shown in FIGS. 7 and 8 proceeds when the offset setting program is executed by the control unit 45.

In step S200, the first base point is set and the counter i is set to 1. The counter i is the number of repetitions of the first loop processing for accumulating vertical bisector groups that are repeatedly used for updating the base point.
From step S202 to step S212, processing similar to the processing from step S102 to step S112 described in the first offset setting method is executed.

In step S214, the currently calculated vertical bisector is stored as f _i . That is, the vertical bisector calculated this time is stored as the i-th element of the vertical bisector group used repeatedly for the base point update. Specifically, each constant of the vertical bisector formula calculated this time is stored in each variable a _i , b _i , c _i , d _i .
While i is incremented in step S218 calculates the perpendicular bisector is repeated, (if an affirmative decision is made at step S216) n-th perpendicular bisector f _n is and stored, n-number of perpendicular double The base point update process is started for the equally divided plane as follows. n is a constant that defines the number of components of one vertical bisector group.

  In step S220, the counter j is set to 1. The counter j is a counter for limiting the number of times each of the n vertical bisectors is repeatedly used for the base point update. If n vertical bisectors do not intersect in a sufficiently close range, the base point is narrow and close to the point corresponding to the true offset even if the vertical bisector is used repeatedly to update the base point. Does not converge to the range. Therefore, in such a case, it is desirable to update the vertical bisector group used for obtaining the offset. This is the reason why the counter j is used.

In step S222, the coordinates of the current base point are set in g. Conceptually, g is the base point calculated second from the end when the end point of base point update is determined. Specifically, g is a data structure in which the coordinates of the current base point having three components are stored.
In step S224, the variable l _max is set to 0 and the counter i is set to 1. l _max is a variable in which a distance used for determining whether to update the base point is stored. i is a vertical bisector for which a vertical leg is sequentially obtained from the first vertical bisector to the n-th vertical bisector for one vertical bisector having n elements. It is a counter for specifying a surface.

In step S226, the coordinates of the perpendicular foot drawn from the base point to the vertical bisector f _i are obtained, and the base point is updated to the foot.
In step S228, the distance l between the updated base point and the base point g before the update is calculated, and it is determined whether or not the distance l is greater than l _max .
If this calculated distance l is greater than l _max, l _max is updated to l (step S30).

In step S232, it is determined whether the process of updating the base point using n vertical bisectors has been completed. Specifically, i and n match determination is performed.
When the process of updating the base point using one vertical bisector group consisting of n vertical bisectors while i is incremented in step S234 completes, the base point is determined using the vertical bisector group. The end determination of the update process is executed as follows.

In step S236, it is determined whether l _max is equal to or less than a predetermined value (for example, approximately 2 μT or less). In l _max , the maximum value of the distance between the two base points calculated in the course of the process of updating the base point using one vertical bisector group consisting of n vertical bisectors is stored. (See FIG. 9). If the maximum distance that the base point moves by one update in the process of updating the base point using one vertical bisector group is small, it is considered that the base point has converged in a narrow range. Therefore, it can be determined that a base point close to the point corresponding to the true offset has been obtained when l _max has decreased to some extent.

If l _max is less than or equal to a predetermined value, the last determined base point component is set as an offset (step S242).
If l _max is not less than a predetermined value, the base point is updated using one vertical bisector group consisting of n vertical bisectors while the counter j is incremented (step S240). The process is repeated (see FIG. 10).

Even if the process of updating the base point using one vertical bisector group is repeated for a predetermined number of times (for example, 20 times), l _max does not fall below a predetermined value (step S238). If the determination is affirmative), the stored one vertical bisector group is discarded and the process returns to step S202. Thereafter, as described above, the magnetic data input process and the n vertical bisectors are repeated, and when n vertical bisectors are newly accumulated, one newly accumulated one is stored. The base point update process is repeated for the vertical bisector group as described above.

3. Third Offset Setting Method FIG. 11 is a schematic diagram showing a third offset setting method to which the present invention is applied. The third offset setting method is different from the first offset setting method and the second offset setting method in that the base point is not updated with the foot of the vertical line that hangs down to the vertical bisector, but the vertical bisector from the base point. This is the point at which the base point is updated at the internal dividing point of the line segment drawn down perpendicular to the surface. The third offset setting method can be applied to both the first offset setting method and the second offset setting method.

In FIG. 11, in the second offset setting method, a locus traced by the base point when the base point is updated at the midpoint of the line segment extending vertically from the base point to the vertical bisector is indicated by a broken line. However, how to set the internal dividing point as 1: 2, 2: 1, 1: 3, 3: 1 is a design matter. As shown in FIG. 11, when the base point update process is performed using the vertical bisector f ₄ far from the true offset, the true point is updated when the base point is updated with a foot down to each vertical bisector. The base points (corresponding to the inflection points of the trajectory) are distributed in a range slightly distant from the point corresponding to the offset. On the other hand, when the base point is updated at the internal dividing point of the line segment perpendicular to the vertical bisector f ₄ far from the true offset, the base point is in a range closer to the point corresponding to the true offset. Distributed. Therefore, by updating the base point at the internal dividing point of the line segment extending vertically from the base point to the vertical bisector, it is possible to prevent the offset from being set by the component of the base point far from the point corresponding to the true offset.

4). Other Embodiments Although an example in which the present invention is applied to a three-dimensional magnetic sensor has been described above, the present invention can also be applied to a two-dimensional magnetic sensor. Further, in order to increase the accuracy of offset, it is better to select magnetic data and vertical bisector, but it is not always necessary to select these, and the example described in this embodiment It is also possible to sort by another mathematical process. Moreover, although the end determination of calibration was illustrated in the second offset setting method, the described end determination can also be applied to the first offset setting method.

The flowchart 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 schematic diagram which concerns on embodiment of this invention. The schematic diagram which concerns on embodiment of this invention. The flowchart 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.

Explanation of symbols

1: mobile phone, 4: three-dimensional magnetic sensor, 24: switching unit, 25: amplifier, 26: A / D converter, 27: magnetic sensor I / F, 30: x-axis sensor, 32: y-axis sensor, 34: z-axis sensor, 40: CPU, 42: ROM, 44: RAM, 45: control unit (magnetic sensor control device)

Claims (12)

Means for sequentially inputting a plurality of magnetic data having three or two components sequentially output from the magnetic sensor;
Means for calculating two sets of perpendicular bisectors or perpendicular bisectors corresponding to the two magnetic data for each set of the magnetic data combined in the order of input;
A process of updating the base point from a base point to a point on the vertical bisector or a line segment perpendicular to the vertical bisector, the plurality of vertical bisectors or the plurality of vertical bisectors Means for setting an offset of the magnetic data based on the updated component of the base point;
A magnetic sensor control device comprising: The means for setting the offset performs the process of updating the base point once for a plurality of the vertical bisectors or the vertical bisectors in the calculation order of the vertical bisector or the vertical bisector. repeat,
The magnetic sensor control apparatus according to claim 1. The means for setting the offset repeats the process of updating the base point a plurality of times for each vertical bisector or each vertical bisector,
The magnetic sensor control apparatus according to claim 1. A means for selecting two sets of magnetic data corresponding to two points separated by a predetermined distance or more in order of input;
The means for calculating the vertical bisector or the vertical bisector calculates the vertical bisector or the vertical bisector for each selected set of magnetic data.
The magnetic sensor control apparatus as described in any one of Claims 1-3. Means for selecting the vertical bisector or the vertical bisector in which all the angles formed by the selected vertical bisector or the perpendicular bisector are equal to or greater than a predetermined angle. Further comprising
5. The magnetic sensor control according to claim 1, wherein the means for setting the offset repeats the process of updating the base point for the selected vertical bisector or the perpendicular bisector. apparatus.   The magnetic unit according to any one of claims 1 to 5, wherein the means for setting the offset updates the base point to a perpendicular foot extending from the base point to the vertical bisector or the vertical bisector. Sensor control device.   The means for setting the offset updates the base point to an internal dividing point on the vertical bisector or a line segment perpendicular to the vertical bisector from the base point. The magnetic sensor control device according to one item.   The means for setting the offset repeats the process of updating the base point until the length of a line segment extending vertically from the base point to the vertical bisector or the vertical bisector is equal to or less than a predetermined value, The magnetic sensor control device according to claim 3, wherein the offset is set based on a component of the last base point. The magnetic sensor control device according to any one of claims 1 to 8,
The magnetic sensor;
A magnetic measuring device comprising: A plurality of magnetic data having three components or two components sequentially output from the magnetic sensor are sequentially input,
Two vertical bisectors or vertical bisectors corresponding to the two magnetic data are calculated for each set of the magnetic data combined in the order of input,
A process of updating the base point from a base point to a point on the vertical bisector or a line segment perpendicular to the vertical bisector, the plurality of vertical bisectors or the plurality of vertical bisectors Repeat about the
Setting an offset of the magnetic data based on the updated component of the base point;
An offset setting method. Means for sequentially inputting a plurality of magnetic data having three or two components sequentially output from the magnetic sensor;
Means for calculating two sets of perpendicular bisectors or perpendicular bisectors corresponding to the two magnetic data for each set of the magnetic data combined in the order of input;
A process of updating the base point from a base point to a point on the vertical bisector or a line segment perpendicular to the vertical bisector, the plurality of vertical bisectors or the plurality of vertical bisectors Means for setting an offset of the magnetic data based on the updated component of the base point;
An offset setting program that allows the computer to function. A computer-readable recording medium in which the offset setting program according to claim 11 is stored.

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