JP2008180673A - Azimuth sensor and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein the magnetometric sensor output trajectory is not a circle near a movable magnetic substance, so that offset of a magnetometric sensor cannot be determined and accurate azimuth cannot be calculated. <P>SOLUTION: A constitution is employed that comprises the magnetometric sensor 1 for detecting terrestrial magnetism of two or more axes and outputting a magnetometric sensor output, the movable magnetic substance 2 for making a magnetic flux generation source movable, a controlling means 3 for driving the movable magnetic substance and outputting attitude information on the movable magnetic substance, a memory 4 for previously storing the variation amount of the output of the magnetometric sensor varying dependently on the attitude of the movable magnetic substance, a correcting means 5 for correcting the magnetometric sensor output based on the attitude information and the variation amount of the output of the magnetometric sensor and outputting the magnetometric sensor output after the correction, an offset calculating means 6 for calculating the offset from the magnetometric sensor after the correction, and an azimuth calculating means 7 for calculating the azimuth based on the offset. Thus, the offset can be determined, and therefore the azimuth can be calculated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an azimuth sensor that detects geomagnetism and calculates an azimuth and an electronic apparatus including the azimuth sensor.

  In recent years, the practical use of travel navigation systems for automobiles and navigation systems for pedestrians using mobile phones has been accelerated. In such a system, it is essential to mount an orientation sensor that detects geomagnetism and determines the orientation. Since the error of the direction sensor that detects the direction of travel directly affects the performance of the navigation system, a high accuracy is required for the magnetic sensor in a system that uses the magnetic sensor as the direction sensor.

  In general, metal parts are mounted on a device such as a navigation system, but these parts may be magnetized by themselves due to the influence of passing through a strong magnetic field. Such a state is called magnetization.

  When the magnetic sensor detects geomagnetism, an output voltage centered on the reference voltage is obtained when there is no magnetization. However, if there are magnetized parts in the device, the output of the magnetic sensor is an output centered on a voltage obtained by adding an offset to the reference voltage. If the azimuth is calculated from the output including such an offset, it does not coincide with the actual azimuth.

  In order to correct this azimuth error, in the device equipped with the magnetic sensor, the entire device is rotated once, the average of the maximum value and the minimum value of the output voltage of the magnetic sensor is calculated, and a new reference voltage (correction value) May take a way to.

  However, there is a problem that the means for rotating and correcting the device each time the magnetization state changes is very troublesome for the user, so the offset can be calculated from the output value of the magnetic sensor multiple times without rotating the device. A method of obtaining was proposed (see, for example, Patent Document 1).

  The method described in Patent Document 1 is a method of obtaining an offset according to the magnetization of peripheral components by calculation and correcting the azimuth using the offset. Specifically, even after magnetization, an appropriate offset is calculated from a plurality of measurement points sampled while the magnetization state does not change, and an attempt is made to obtain a correct orientation using this offset. To do.

  This method will be described in more detail with reference to the drawings. FIG. 6 shows the relationship between the outputs of the X-axis and Y-axis magnetic sensors when a device including the azimuth sensor is rotated once in a horizontal state. The horizontal axis Vx shown in this figure is the X-axis magnetic sensor output, and the vertical axis Vy is the Y-axis magnetic sensor output. When a device equipped with these X-axis and Y-axis magnetic sensors is rotated once, these magnetic sensor outputs take a circular locus.

  In FIG. 6, the circle indicated by the solid line is the locus of the magnetic sensor output when there is no magnetization, and the center value of the circle coincides with the coordinate origin O.

  In FIG. 6, a circle indicated by a dotted line is a locus of the magnetic sensor output when magnetization is generated, and the center value of the circle moves from the coordinate origin to O ′.

The conventional azimuth sensor calculates the offset O ′, which is the center value of the circle of the magnetic sensor output locus, by the following method.

The output value of the magnetic sensor measured and acquired is (xn, yn) (n = 1, 2,...)
When the offset O ′ is (xo, yo), the following equation is established.
(Xn−xo) ² + (yn−yo) ² = R ² (1)
Where R is the radius of the circle.

Since there are three unknowns, xo, yo, and R, xo and yo can be obtained if there are at least three simultaneous equations. That is, xo and yo can be obtained by performing measurement three times or more. In particular,
(X1−xo) ² + (y1−yo) ² = R ²
(X2−xo) ² + (y2−yo) ² = R ²
(X3−xo) ² + (y3−yo) ² = R ² (2)
The following simultaneous equations are obtained, and the above equation (2) is expanded,
xo = {-(y3-y2) (y2-y1) (y1-y3) + x1 ² (y3-y2) + x2 ² (y1-y3) + x3 ² (y2-y1)} / {2 (x1 ( y3-y2) + x2 (y1-y3) + x3 (y2-y1))} (3)
yo = {-(x3-x2) (x2-x1) (x1-x3) + y1 ² (x3-x2) + y2 ² (x1-x3) + y3 ² (x2-x1)} / {2 (y1 ( x3-x2) + y2 (x1-x3) + y3 (x2-x1))} (4)
And the target offset (xo, yo) can be obtained using the equations (3) and (4).

Based on the offset (xo, yo) obtained in this way, the correct orientation θ can be calculated by obtaining the orientation from the magnetic sensor output (xn, yn) as follows.
θ = arctan {(yn−yo) / (xn−xo)} (5)

Japanese Patent Laid-Open No. 56-6169 (2nd page, FIG. 2)

  However, in the conventional azimuth sensor shown in Patent Document 1, when a movable magnetic body such as a motor is close, the magnetic field of the movable magnetic body fluctuates every moment. As a result, it is impossible to calculate the offset and to calculate the azimuth.

  In particular, in the case of an analog wristwatch, a step motor for driving a pointer that is a movable magnetic body is necessary, and the device itself is extremely small. Therefore, a magnetic sensor must be disposed very close to the step motor. It has been considered impossible to mount a magnetic sensor.

  Accordingly, an object of the present invention is to solve the above-described problems, and to provide an orientation sensor and an electronic device that can calculate a correct offset and obtain an orientation even when a movable magnetic body is in proximity. It is in.

  In order to achieve the above object, the azimuth sensor of the present invention and the electronic apparatus including the azimuth sensor basically adopt the following structure.

The azimuth sensor of the present invention is a azimuth sensor that detects geomagnetism and calculates azimuth, a magnetic sensor that detects geomagnetism of two or more axes and outputs a magnetic sensor output, and a movable magnetic that can move a magnetic flux generation source. Body, a control means for driving the movable magnetic body and outputting posture information of the movable magnetic body, a memory for storing in advance a change amount of the magnetic sensor output that changes depending on the posture of the movable magnetic body, and the control means Correction means for correcting the magnetic sensor output based on the posture information and the change amount of the magnetic sensor output stored in advance in the memory and outputting the corrected magnetic sensor output, and the center value of the corrected magnetic sensor output Offset calculating means for calculating and outputting an offset, and azimuth calculating means for calculating and outputting an orientation based on the offset output by the offset calculating means. It is an butterfly.

  The azimuth sensor of the present invention includes a magnetic core in which the above-described movable magnetic body is formed of a material having a high magnetic permeability, a conductive wire wound around the magnetic core, a stator magnetically connected to the magnetic core, , And a rotor magnet rotatably disposed in the center of the stator.

  An electronic apparatus according to the present invention includes the above-described azimuth sensor, and further includes azimuth display means for displaying the azimuth output by the azimuth calculation means.

  The azimuth sensor of the present invention and the electronic apparatus including the azimuth sensor include a control unit that drives the movable magnetic body and outputs posture information of the movable magnetic body, and a correction unit that corrects the magnetic sensor output based on the posture information. It is possible to always obtain a stable and correct offset, thereby obtaining a correct orientation.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an orientation sensor of the present invention. FIG. 2 is a configuration diagram showing a movable magnetic body of the direction sensor of the present invention. FIG. 3 is a diagram showing the magnetic sensor output of the direction sensor of the present invention. FIG. 4 is a diagram showing a difference table stored in the memory of the direction sensor of the present invention. FIG. 5 is a flowchart of the operation of the direction sensor of the present invention.

[Description of structure: Fig. 1 and Fig. 2]
First, the configuration of the direction sensor 100 of the present invention will be described with reference to FIG.
As shown in FIG. 1, the azimuth sensor 100 of the present invention detects a magnetic field of two or more axes, and outputs a current magnetic sensor output 1a, a magnetoresistive element (MR element), or a fluxgate type magnetism. A magnetic sensor 1 comprising a sensor, and a magnetic flux generation source that has specific magnetism like a step motor and that can move the magnetic flux generation source, such as a magnetic flux generation source that repeatedly moves with two or more postures in a predetermined cycle, for example. The movable magnetic body 2 is configured. The configuration of the movable magnetic body 2 will be described in detail later.

  The azimuth sensor 100 takes two or more postures at a predetermined cycle, drives the movable magnetic body 2 so as to repeatedly move the magnetic flux generation source, and outputs the posture information 3b of the movable magnetic body 2. Control means 3 composed of a controller, memory 4 composed of EPROM or flash memory for storing in advance the amount of change in magnetic sensor output that varies depending on each posture of the magnetic flux generation source in the movable magnetic body 2, and posture information output by the control means 3. 3b and correction means 5 for correcting the current magnetic sensor output 1a output from the magnetic sensor 1 based on the information (difference 4a) in the memory 4 and outputting the corrected magnetic sensor output 5a.

  Further, the azimuth sensor 100 calculates an offset 6a that is the center value of the corrected magnetic sensor output 5a and outputs the offset 6a to the azimuth calculation means 7. The azimuth sensor 100 is based on the offset 6a output from the offset calculation means 6. and an azimuth calculating means 7 for calculating and outputting θ.

Next, the configuration of the above-described movable magnetic body 2 will be described with reference to FIG.
As shown in FIG. 2, the movable magnetic body 2 includes a magnetic core 10 made of a material having a high magnetic permeability, a lead wire 11 wound around a magnetic core for generating a magnetic field by passing an electric current, and a magnetic core. Are connected to each other and a rotor magnet 13 rotatably disposed at substantially the center of the stator 12. The rotor magnet 13 corresponds to the magnetic flux generation source described above.

[Description of operation: FIG. 1, FIG. 2, FIG. 3, FIG. 4]
Next, operation | movement of the movable magnetic body 2 in the direction sensor 100 of this invention is demonstrated using FIG.
First, the control means 3 causes a reverse magnetic field to be generated in the magnetic core 10 and the stator 12 every second by passing a current in the reverse direction through the conducting wire 11 in the movable magnetic body 2 every second.

  The rotor magnet 13 shown in the figure is a two-pole cylindrical permanent magnet (magnetic flux generation source), and rotates every 180 degrees in accordance with the reversal magnetic field per second. Although not shown, the analog wristwatch transmits a force by rotating the rotor magnet 13 using a gear wheel and drives a pointer including a second hand, a minute hand, an hour hand, etc., and displays a predetermined time. By mounting the above-mentioned direction sensor 100 on the analog electronic timepiece, the direction can be displayed by the direction display means together with the time display. Note that this direction display means displays the direction in which the device is facing by means of a liquid crystal panel or the like mounted on an analog electronic timepiece, or displays the direction of the device using a pointer that is different from the second, minute, and hour hands. Means.

  Next, the output of the magnetic sensor 1 arranged in the vicinity of the movable magnetic body 2 will be described with reference to FIG. FIG. 3 shows a relationship between magnetic sensor outputs of the X-axis and Y-axis magnetic sensors when the electronic device including the azimuth sensor 100 is rotated once in a horizontal state. The horizontal axis Vx shown in FIG. 3 is the X-axis magnetic sensor output, and the vertical axis Vy is the Y-axis magnetic sensor output.

  When an electronic device provided with these X-axis and Y-axis magnetic sensors is rotated once, these magnetic sensor outputs take a circular trajectory. However, as described above, the rotor magnet 13 rotates 180 degrees every second. That is, there are two postures of the rotor magnet 13, and as a result, the output of the magnetic sensor is on a circle C0 centered on the point P0 shown in FIG. 3 in one posture, and P1 in the other posture. Appears on a circle C1 centered at a point.

  What is important here is that the center coordinates P0 and P1 of the circle move due to the magnetization of the electronic device, but the relative difference (Δx1, Δy1) between P0 and P1 does not change. This is because (Δx1, Δy1) is a value that depends only on the magnetic force of the rotor magnet 13.

Next, the operation of the direction sensor 100 of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the magnetic sensor 1 detects geomagnetism and outputs the current magnetic sensor output 1a.

  Moreover, the control means 3 inputs the control signal 3a into the conducting wire 11 by a method such as passing a current through the conducting wire 11 (see FIG. 2), and causes the rotor magnet 13 in the movable magnetic body 2 to move at a predetermined cycle (every second). (Rotation of 180 degrees). Moreover, since the control means 3 can discriminate | determine the attitude | position of the rotor magnet 13 in the present movable magnetic body 2 with the drive state (direction of the electric current sent through the conducting wire 11) of the movable magnetic body 2, this is used as attitude | position information 3b, and the correction means 5 Output to.

In the memory 4, a difference in magnetic sensor output corresponding to the posture of the movable magnetic body 2 is stored in advance. For example, as shown in FIG. 3, when there are two postures of the rotor magnet 13, one posture (for example, the posture in which the output circle appears on C0) is set as the reference posture, and the other posture (the output circle is C1
The output difference (Δx1, Δy1) at the time of the (appearing posture) is stored as a lookup table as shown in FIG. In addition, when there are two or more postures of the rotor magnet 13, only the number of the postures, or when there are a plurality of rotor magnets 13, the number of combinations of the postures of the respective rotor magnets 13 is as shown in FIG. The lookup table is created as described above and the difference is stored.

  The correction unit 5 refers to the lookup table shown in FIG. 4A stored in the memory 4 based on the current posture information 3b output from the control unit 3, and the difference corresponding to the current posture. 4a is obtained, the difference 4a is subtracted from the current magnetic sensor output 1a which is the output of the magnetic sensor 1, the current magnetic sensor output 1a is corrected, and the offset calculating means 6 and the azimuth calculating means 7 The magnetic sensor output 5a is output. By correcting the current magnetic sensor output 1a in this way, the corrected magnetic sensor output 5a appears on the output circle of the reference posture. That is, in the case of FIG. 3, the current magnetic sensor output 1 a on the circle C <b> 1 is corrected, and all appear on C <b> 0 that is the output circle of the reference posture.

The offset calculation means 6 uses a generally well-known mathematical method, for example, the equations (1) to (4) shown in the prior art, so that a point on an arbitrary circle is selected from the corrected magnetic sensor output 5a. Is selected, and an offset 6a, which is the center coordinate of the circle, is calculated and output to the azimuth calculating means 7. The arbitrary circular point shown here is a point excluding the abnormal output value of the magnetic sensor output, and three or more points separated as much as possible are selected to calculate the offset 6a. It is desirable.
Note that the offset 6a may be obtained using not only a conventional technique using the above formulas (1) to (4) but also a numerical calculation technique such as the Newton-Raphson method.

Further, the azimuth calculating unit 7 calculates the azimuth θ from the offset 6a calculated by the offset calculating unit 6 and the corrected magnetic sensor output 5a output from the correcting unit 5 by the following formula and outputs the calculated value.
θ = arctan {(yn−yo) / (xn−xo)} (6)
However, (xo, yo) indicates the offset 6a, and (xn, yn) indicates the corrected magnetic sensor output 5a.

Next, an operation flow of the azimuth sensor 100 of the present invention will be described with reference to FIGS.
First, the movable magnetic body 2 is driven by the control means 3 (step S1).

  Next, after the movable magnetic body 2 is driven in step S1, it waits for the posture of the rotor magnet 13 to be stabilized (step S2). Specifically, after the control signal 3a is input to the movable magnetic body 2, the rotor magnet 13 is driven to rotate 180 degrees and waits for a moment. This is to avoid obtaining the magnetic sensor output from the magnetic sensor 1 while the posture of the rotor magnet 13 is not stable and performing the next calculation using the output value.

  After the posture of the rotor magnet 13 is stabilized in step S2, the posture information 3b of the rotor magnet 13 is obtained from the control means 3 (step S3), and further a difference 4a based on this posture information 3b is obtained from the memory 4 (step S3). S4).

  Next, the current magnetic sensor output 1a is obtained by obtaining the current magnetic sensor output 1a from the magnetic sensor 1 (step S5), and subtracting the difference 4a obtained in step S4 from the current magnetic sensor output 1a. Thus, the corrected magnetic sensor output 5a is obtained (step S6).

The offset 6a is calculated using the corrected magnetic sensor output 5a (step S7),
Finally, the azimuth θ is calculated from the offset 6a and the corrected magnetic sensor output 5a (step S7). Note that the order of steps S3, S4, and S5 may be changed.

  So far, in order to simplify the explanation, the configuration of the azimuth sensor 100 using the biaxial magnetic sensor, the calculation method, and the electronic apparatus including the azimuth sensor have been described. However, an XYZ triaxial magnetic sensor is provided, It is obvious that the configuration of the azimuth sensor 100 of the present invention can be easily expanded to three axes by storing the difference for three axes in the memory.

  Further, the configuration example in which the azimuth sensor 100 of the present invention is mounted on an analog wristwatch has been described so far. However, the present invention is not limited to this. For example, the magnetic flux generation source is in accordance with a constant cycle. There are two or more postures, and each of the two or more postures can be applied to all electronic devices that generate a predetermined magnetic field.

  In addition, when the magnetic flux generating source takes a different posture aperiodically, for example, in the case of an analog wristwatch having a rotor magnet in order to indicate the temperature and pressure that are aperiodic information with a pointer, A similar method can be applied.

  As described above, the azimuth sensor 100 of the present invention drives the movable magnetic body 2 and outputs the attitude information 3b of the magnetic flux generation source included in the movable magnetic body 2 and the current information based on the attitude information 3b. Since the correcting means 5 for correcting the magnetic sensor output 1a is provided, the correct offset 6a can be obtained, and thereby the correct azimuth θ can be obtained.

  The azimuth sensor 100 of the present invention can be applied to a device that requires a highly precise azimuth θ. In particular, it is suitable for mounting the orientation sensor 100 of the present invention on a small portable device.

It is a block diagram which shows the azimuth | direction sensor of this invention. It is a block diagram which shows the movable magnetic body of the direction sensor of this invention. It is a figure which shows the magnetic sensor output of the direction sensor of this invention. It is a figure which shows the table of the difference memorize | stored in memory of the direction sensor of this invention. It is a flowchart of operation | movement of the direction sensor of this invention. It is an output locus | trajectory figure which shows the conventional azimuth | direction sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic sensor 1a Current magnetic sensor output 2 Movable magnetic body 3 Control means 3a Control signal 3b Attitude information 4 Memory 4a Difference 5 Correction means 5a Magnetic sensor output after correction 6 Offset calculation means 6a Offset 7 Direction calculation means 10 Magnetic core 11 Conductor 12 Stator 13 Rotor magnet 100 Direction sensor

Claims (3)

An orientation sensor that detects geomagnetism and calculates an orientation,
A magnetic sensor that detects geomagnetism of two or more axes and outputs a magnetic sensor output;
A movable magnetic body capable of moving the magnetic flux generation source;
Control means for driving the movable magnetic body and outputting posture information of the magnetic flux generation source;
A memory that stores in advance a change amount of the magnetic sensor output that changes depending on the attitude of the magnetic flux generation source;
Correction means for correcting the magnetic sensor output based on the attitude information output by the control means and the change amount of the magnetic sensor output stored in advance in the memory and outputting the corrected magnetic sensor output; ,
Offset calculating means for calculating and outputting an offset that is a center value of the corrected magnetic sensor output;
An azimuth calculating means for calculating and outputting an azimuth based on the offset output by the offset calculating means;
An azimuth sensor comprising: The magnetic flux generation source is a rotor magnet,
The movable magnetic body is
A magnetic core made of a material with high magnetic permeability,
A conducting wire wound around the magnetic core;
A stator magnetically connected to the magnetic core;
The rotor magnet rotatably disposed substantially in the center of the stator;
The direction sensor according to claim 1, comprising: An electronic device comprising the azimuth sensor according to claim 1 or 2, and further comprising azimuth display means for displaying the azimuth output by the azimuth calculation means.

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