JP2006153674A - Direction sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in a direction sensor for determining a direction by detecting earth magnetism that accurate and stable calibration is not made since it is necessary to turn the direction sensor in its calibration. <P>SOLUTION: This direction sensor comprises a magnetic sensor 1 for detecting earth magnetism, a vibration means 2 for vibrating the magnetic sensor, an amplifier 3 for amplifying an output of the magnetic sensor, a first differentiator 4 for differentiating an output of the amplifier, a second differentiator 5 for differentiating an output of the first differentiator, and an arithmetic means 6 for performing calibration by arithmetical operation and calculation of a direction. This constitution makes it possible to perform accurate and stable calibration while dispensing with turning the magnetic sensor for calibration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an azimuth sensor that detects geomagnetism and identifies an azimuth, and particularly relates to an azimuth sensor that performs calibration to increase detection accuracy.

  2. Description of the Related Art Conventionally, in an apparatus having a navigation function such as an automobile or a portable device, an orientation sensor that detects a traveling direction, an orientation of the apparatus, and the like has been widely used. Such an azimuth sensor detects geomagnetism by a magnetic sensor and specifies the azimuth. By the way, the detected geomagnetism is not always constant, and the intensity and direction change depending on the presence of surrounding metal, temperature change, change with time, etc., and therefore calibration work is generally required. The calibration is generally performed from the output value of the magnetic sensor in all directions by rotating the apparatus once.

  However, as is often seen in mobile devices, when a person rotates the device, it can not be calibrated correctly because the rotation is too fast, the level cannot be maintained, or the operation is complicated. There was a problem. In order to solve this problem, an azimuth sensor that calibrates only from the output value at that time is considered by using an arithmetic operation without causing the apparatus to rotate once, and is proposed. (For example, refer to Patent Document 1).

A conventional azimuth sensor shown in Patent Document 1 will be described with reference to the drawings. FIG. 7 is a block diagram showing a conventional azimuth sensor shown in Patent Document 1. In FIG.
In FIG. 7, 80 is a 3-axis magnetic sensor, 81 is an x-axis hall element, 82 is a y-axis hall element, 83 is a z-axis hall element, 84 is a chopper section, 85 is a magnetic sensor drive power supply section, and 86 is a differential input. An amplifier 87 is an A / D conversion unit, 88 is a correction value update unit, 89 is a correction value storage unit, 90 is a correction calculation unit, and 91 is an azimuth calculation unit.

The principle of direction detection will be described below. The triaxial magnetic sensor 80 has an x axis hall element 81, a y axis hall element 82, and a z axis hall element 83. The x-axis hall element 81 and the y-axis hall element 82 are arranged so as to detect a rotation angle in a horizontal plane, and the z-axis hall element 83 is arranged so as to detect magnetism in the vertical direction.
The chopper section 84 is for switching terminals for driving the x-axis hall element 81, the y-axis hall element 82, and the z-axis hall element 83, and the drive voltage output from the magnetic sensor driving power supply section 85 is used as the x-axis hall element. 81, applied to the y-axis hall element 82 and the z-axis hall element 83, respectively.
The signals output from the x-axis hall element 81, the y-axis hall element 82, and the z-axis hall element 83 are respectively amplified by the differential input amplifier 86, and the amplified output values are amplified by the A / D converter 87. After being converted to a digital signal, it is input to the correction calculation unit 90.
The correction value storage unit 89 stores an offset value indicating the variation in output of the x-axis hall element 81, the y-axis hall element 82, and the z-axis hall element 83, and the amplification degree. By using these offset values and the degree of amplification, the output values of the x-axis hall element 81, the y-axis hall element 82, and the z-axis hall element 83 are corrected and converted into values proportional to each axis component of geomagnetism. Output. The azimuth angle calculation unit 91 calculates the azimuth using the output of the correction calculation unit 90.

The calibration will be described below. Calibration refers to updating the offset value and the amplification degree of the x-axis hall element 81, the y-axis hall element 82, and the z-axis hall element 83, which are stored in the correction value storage unit 89, to correct values.
In the calibration procedure, first, a signal from the Hall element is acquired by using a human operation such as a button input when rotating 90 degrees in the same plane. For example, a signal in a certain direction of the x-axis Hall element 81 is acquired as Xa, and signals in directions of 90 degrees and 180 degrees with respect to the direction are acquired as Xb and Xc, respectively. Next, the offset value and the amplification degree obtained by the following calculation are stored in the correction value storage unit 89.
The x-axis offset value Ox can be expressed by the following equation.
Ox = (Xa + Xc) / 2
The amplification factor Ax on the x axis can be expressed by the following equation.
Ax = {(Xa-Ox) ^ 2 + (Xb-Ox) ^ 2} ^ 2
Similarly, the offset values Oy and Oz and the amplification degrees Ay and Az are obtained for the y-axis and the z-axis.

The correction calculation in the correction calculation unit 90 will be described below. When the output values of the x-axis hall element 81, the y-axis hall element 82, and the z-axis hall element 83 are X, Y, and Z, respectively, the corrected x-axis signal α can be expressed by the following equation.
α = (X−Ox) / Ax
The corrected y-axis signal β can be expressed by the following equation.
β = (Y−Oy) / Ay
The corrected z-axis signal γ can be expressed by the following equation.
γ = (Z−Oz) / Az

The azimuth calculation in the azimuth calculation unit 91 will be described below. The azimuth calculation unit 91 calculates the azimuth using the signals α, β, and γ corrected by the correction calculation unit 90. For example, when the X-axis and the Y-axis are in the horizontal plane, the azimuth calculation unit 91 uses α and β, which are values proportional to the geomagnetic axis components, to calculate the azimuth θ based on the following equation: To calculate.
θ = tan ⁻¹ (β / α)
When the X and Y axes are tilted from the horizontal plane, the azimuth angle θ is calculated after correcting the tilt angles using α, β, and γ, which are values proportional to the geomagnetic axis components. You can also.

  The direction can be specified by detecting the geomagnetism based on the principle as described above.

JP 2004-12416 A (page 8-11, FIG. 1)

  Since the azimuth sensor of the prior art shown in Patent Document 1 can be calibrated by using computation only from output signals in several directions, it is not necessary to rotate the device equipped with the azimuth sensor once. However, since it is necessary to orient the device in several orientations, for example, it is difficult to change the orientation by 90 degrees accurately, and it is also difficult to keep the device horizontal while changing the orientation. Therefore, there is a drawback that accurate and stable calibration cannot be performed. Furthermore, even in some orientations, it is necessary to move the device, which limits the size of the device that can be moved. That is, the conventional orientation sensor has a drawback that it cannot be mounted on a large apparatus.

  An object of the present invention is to solve the above-described problems, and to provide an orientation sensor that performs accurate and stable calibration and does not limit the size of a device to be mounted.

  In order to achieve the above object, the orientation sensor of the present invention employs the structure shown below.

An orientation sensor that detects geomagnetism and identifies the orientation,
Magnetic sensor for detecting geomagnetism, vibration means for vibrating the magnetic sensor, amplifier for amplifying the output of the magnetic sensor, first differentiator for differentiating the output of the amplifier, and differentiating the output of the first differentiator It has the 2nd differentiator and the calculating means which performs a calibration and the calculation of an azimuth | direction by a calculation.

  The vibrating means vibrates the magnetic sensor at a constant angular velocity.

  The vibration means has a shape memory alloy, and generates vibrations using a phase transformation of the shape memory alloy.

The azimuth sensor of the present invention is provided with vibration means for vibrating the magnetic sensor, and includes an amplifier that amplifies the output of the magnetic sensor and a differentiator that differentiates the output of the amplifier. This differentiator comprises a first differentiator and a second differentiator, and the second differentiator differentiates the output of the first differentiator.
The azimuth sensor of the present invention can perform calibration and azimuth calculation because the amplification degree and the offset can be obtained by calculation by vibrating the magnetic sensor at a constant angular velocity.
In addition, since there is no need for a human to touch for calibration, there is an effect that stable calibration can be performed with high accuracy. Moreover, since it is not necessary to move the apparatus which mounts the direction sensor of this invention, the magnitude | size of an apparatus is not restrict | limited. Therefore, there is an effect that the azimuth sensor of the present invention can be mounted on any device.

  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 block diagram showing the magnetic sensor and the vibration means of the direction sensor of the present invention. FIG. 3 is a shape diagram of the shape memory alloy of the azimuth sensor of the present invention, FIG. 3 (a) is a diagram showing the first shape, and FIG. 3 (b) is a diagram showing the second shape. is there. FIG. 4 is a diagram for explaining an ideal output waveform of the magnetic sensor of the azimuth sensor according to the present invention. FIG. 5 is a diagram for explaining an actual output waveform of the magnetic sensor of the azimuth sensor according to the present invention. FIG. 6 is a circuit diagram of the differentiator of the azimuth sensor of the present invention.

[Description of structure: FIG. 1, FIG. 2, FIG. 4, FIG. 6]
First, the configuration of the azimuth sensor of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 4, and FIG.
In FIG. 1, 1 is a magnetic sensor, 2 is a vibration means, 3 is an amplifier, 4 is a first differentiator, 5 is a second differentiator, and 6 is an arithmetic means.
In the embodiment of the present invention, a case where a magnetoresistive element whose resistance value changes due to magnetism is used as the magnetic sensor 1 will be described as an example. However, the present invention is not limited to this, and a magnetic impedance element, a flux gate, etc. It may be a magnetic sensor. In the embodiment of the present invention, a case where a shape memory metal is used as the vibration means will be described as an example.
The calculation means 6 can use a microcontroller having a memory and an A / D converter.

In FIG. 2, 7 is a magnetoresistive element, 9a-9d are shape memory alloys, and 10 is an electrode.
As the shape memory alloys 9a to 9d, Ti—Ni alloys made of a compound of Ti (titanium) and Ni (nickel) can be used. FIG. 2 shows a case where there are four shape memory alloys 9a to 9d and eight electrodes 10.
The dotted arrow shown in the shape memory alloy 9b in FIG. 2 schematically shows the current flowing through the shape memory alloy 9b through the electrode 10.
The arc-shaped arrows shown in FIG. 1 and FIG. 2 schematically show the vibration of the magnetic sensor 1 by the vibration means 2.

  3, what is shown in FIGS. 3 (a) and 3 (b) is the shape stored in the shape memory alloys 9a to 9d shown in FIG. The shape memory alloys 9a to 9d memorize either the first shape shown in FIG. 3A or the second shape shown in FIG. 3B. The arc-shaped arrow shown in FIG. 3 schematically shows how the shape is deformed by heat generated by energizing the shape memory alloys 9a to 9d.

  In FIG. 4, 11 is an x-axis output and 12 is a y-axis output. Xa and Ya are respective axis outputs in a certain direction.

  In FIG. 5, Ax and Ay are amplification degrees, and Ox and Oy are offset values.

  In FIG. 6, 13 is an operational amplifier, 14 is a first resistor, 15 is a capacitor, and 16 is a second resistor.

  1 to 6, the same number is assigned to the same configuration.

[Description of orientation detection principle: Fig.1, Fig.2, Fig.4, Fig.5]
First, the azimuth detection principle of the azimuth sensor of the present invention will be described with reference to FIGS. 1, 2, 4, and 5. FIG.
The magnetic sensor 1 shown in FIG. 1 has a structure in which two magnetoresistive elements 7 are arranged at right angles as shown in FIG. 2 in order to detect geomagnetism in two directions of the x axis and the y axis. Each magnetoresistive element 7 outputs a signal corresponding to the geomagnetism. This signal is amplified by the amplifier 3 and then input to the arithmetic means 6. The calculating means 6 calculates an azimuth | direction using a calculation.
Since the resistance value of the magnetoresistive element 7 increases in proportion to the strength of the magnetism, the magnetoresistive element 7 shows the maximum resistance value when facing north-south, the output is maximized, and the direction is east-west. Output is 0 when That is, if the magnetic sensor 1 is vibrated at a constant angular velocity, a sine waveform as shown in FIG. 4 is ideally shown. The x-axis output 11 and the y-axis output 12 have waveforms that are 90 degrees out of phase because the magnetoresistive elements 7 are arranged at right angles. Now, assuming that the x-axis output in a certain direction is Xa and the y-axis output is Ya, the computing means 6 can calculate the azimuth angle θ based on the following equation.
θ = tan ⁻¹ (Ya / Xa)
However, the detected geomagnetism is not always constant and changes depending on the presence of surrounding metal, temperature change, change with time, etc., and therefore the waveform shown in FIG. 5 deviates from the ideal waveform shown in FIG. It becomes. In other words, a waveform including a phenomenon of variation in amplification in which the amplitudes of the x-axis output 11 and the y-axis output 12 are different, and a phenomenon in which an offset value is added because the center of the sine waveform is shifted from the point of the output 0. It becomes. Therefore, in order to perform correct measurement, a calibration operation is required to correctly detect the amplification degree and the offset value.

[Calibration procedure explanation: Fig.1, Fig.2, Fig.3, Fig.5]
Next, the calibration procedure of the azimuth sensor of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, and FIG.
At the time of calibration, the vibrating means 2 shown in FIG. 1 vibrates the magnetic sensor 1 at a rotation angle of about 45 degrees and a constant angular velocity ω. At this time, the output of the magnetic sensor 1 shows a sine waveform as shown in FIG.
Considering the x-axis now, the x-axis output 11 can be expressed by the following equation.
X1 = Ax * sin (ωt + φ) + Ox (Expression 1)
Here, X1 is an x-axis output 11, Ax is an amplification factor, ω is a constant angular velocity, t is time, φ is an initial phase, and Ox is an offset value.
The first differentiator 4 differentiates the x-axis output 11. That is, since Expression 1 is differentiated, the output X2 of the first differentiator 4 can be expressed by the following expression.
X2 = Ax * ω * cos (ωt + φ) (Equation 2)
Since the second differentiator 5 further differentiates the output of the first differentiator 4, the output X3 can be expressed by the following equation.
X3 = −Ax * ω ^ 2 * sin (ωt + φ) (Equation 3)

The computing means 6 receives the signals represented by Equation 1, Equation 2, and Equation 3, and calculates the amplification degree Ax and the offset value Ox by the following equations. The offset value Ox is calculated by Equation 1 and Equation 3, and the amplification degree Ax is calculated by Equation 2 and Equation 3.
Ox = X1 + X3 / (ω ^ 2)
Ax = {(X2 / ω) ^ 2 + (X3 / ω ^ 2) ^ 2} ^ (1/2)

The above indicates that the amplitude Ax and the offset value Ox can be obtained by calculation from only the three outputs X1, X2, and X3 by vibrating the magnetic sensor 1 at a constant angular velocity ω.
Similarly, the amplification degree Ay and the offset value Oy are obtained for the y axis. The Ax and Ay and Ox and Oy thus obtained are stored in the memory in the calculation means 6 and used for correction calculation at the time of azimuth measurement.

[Explanation of correction calculation when measuring direction]
Next, correction calculation at the time of measuring the direction of the direction sensor of the present invention will be described. The x-axis output at the time of azimuth measurement is X, and the y-axis output is Y. The corrected x-axis output α, the corrected y-axis output β, and the azimuth angle θ corrected correctly using this can be expressed by the following equations.
α = (X−Ox) / Ax
β = (Y−Oy) / Ay
θ = tan ⁻¹ (β / α)

[Explanation of vibration means: FIGS. 2 and 3]
Next, the vibration means 2 of the direction sensor of the present invention will be described with reference to FIGS.
As shown in FIG. 2, the vibration means 2 includes shape memory alloys 9 a to 9 d and an electrode 10. As is generally known, the shape memory alloys 9a to 9d cause a phase transformation between the austenite phase and the martensite phase depending on the temperature. In the low temperature martensite phase, the shape memory alloys 9a to 9d are very soft and easily deformed. In the austenite phase, the memorized shape is restored.

In the azimuth sensor of the present invention, the shape memory alloys 9 a to 9 d are arranged around the magnetic sensor 1. In the example shown in FIG. 2, the shape memory alloys 9a to 9d sandwich the magnetic sensor 1, the shape memory alloys 9a and 9c face each other, and the shape memory alloys 9b and 9d face each other around the magnetic sensor 1. Provided.
The shape memory alloys that are placed opposite to each other with the magnetic sensor 1 in between store the same shape. For example, the shape memory alloys 9a and 9c store the first shape as shown in FIG. 3 (a), and the shape memory alloys 9b and 9d are the second as shown in FIG. 3 (b). Remember the shape. Therefore, when the number of shape memory alloys is four, adjacent shape memory alloys memorize different shapes.

The shape memory alloys 9a to 9d are heated by Joule heat when an electric current is applied through the electrode 10, but in the example shown in FIG. By alternately applying a current to the shape memory alloys 9a and 9c) and the shape memory alloys (for example, the shape memory alloys 9b and 9d) arranged opposite to each other, the magnetic sensor 1 is It can be vibrated as indicated by the arcuate arrow. Since Joule heat is proportional to the square of the current, it can be vibrated at a constant angular velocity by applying a constant current.

Of course, the method of vibrating the magnetic sensor 1 is not limited to this. In the example shown in FIG. 2, an example in which four shape memory alloys are used is shown. However, the number of shape memory alloys may not be four, and can be changed according to the size and shape of the magnetic sensor 1 to be vibrated. is there. For example, when the magnetic sensor 1 is large, the same shape is stored in several adjacent shape memory alloys, apparently grouped as one shape memory alloy, and a current is applied to the group. It doesn't matter.
Furthermore, although the example which alternately applies an electric current to the shape memory alloy arrange | positioned on both sides of the magnetic sensor 1 and the shape memory alloy arrange | positioned facing differently from it was demonstrated, It is limited to this. It is not a thing. In view of the deformation shape of the shape memory alloy, for example, if the shape memory alloys 9a and 9d and the shape memory alloys 9b and 9c are arranged to be deformed in the same direction, the shape memory alloys 9a and 9d and the shape memory If a current is alternately applied to the alloys 9b and 9c, the magnetic sensor 1 can be vibrated.
In the above description, heating to the shape memory alloys 9a to 9d is a case where Joule heat generated by current application is used, but is not limited thereto. The phase transformation may be caused by heating using a heater or the like.

[Description of differentiator: Fig. 6]
Next, the differentiator of the azimuth sensor of the present invention will be described with reference to FIG.
The circuits constituting the first differentiator 4 and the second differentiator 5 shown in FIG. 1 can have the same configuration, and generally use a differentiator having a well-known operational amplifier, resistor, and capacitor. be able to. An example of such a differentiator is shown in FIG.
The differentiator shown in FIG. 6 includes an operational amplifier 13, a first resistor 14, a capacitor 15, and a second resistor 16. A capacitor 15 and a second resistor 16 are connected in series between the input of the differentiator and the negative input of the operational amplifier 13, and a first resistor 14 is connected between the output of the differentiator and the negative input of the operational amplifier 13. To do. The positive input of the operational amplifier is connected to ground or a constant potential.
The second resistor 16 is a resistor for preventing oscillation and has a resistance value of about 1/100 to 1/1000 of the first resistor 14.
Further, when the calculation means 6 has a high calculation capability, a differentiator may be realized by the calculation of the calculation means 6.

  In order to simplify the description of the azimuth sensor according to the embodiment of the present invention, the two-axis azimuth sensor of the x-axis and the y-axis has been described as an example. The azimuth sensor can also be configured.

  The azimuth sensor of the present invention can be calibrated simply by placing it on a horizontal desk or the like by providing the vibration means, the first differentiator, and the second differentiator, and it is necessary to touch the human at all. And accurate and stable calibration.

Since the direction sensor of the present invention uses a shape memory alloy for the vibration means, the structure is simplified and the size can be reduced. In particular, the MEMS (Micro Electro-Mechanical System) technology that has been put into practical use in recent years, that is, the technology of downsizing the mechanical parts using semiconductor manufacturing technology, makes it possible to provide a whole orientation sensor including a magnetic sensor and vibration means. Can be reduced to, for example, 5 mm square or less.
Of course, it is not necessary that all the vibration means be made of a shape memory alloy, and the shape memory alloy and a member that expands and contracts like a spring may be combined.
In addition, a shape memory alloy may not be used, and in that case, a member that expands and contracts by an electric signal can be used. For example, a polymer actuator whose shape is displaced by a voltage change is used.

  The direction sensor of the present invention can be applied to a device having a navigation function such as an automobile or a portable device. In particular, since calibration can be performed without any human touch, it is suitable for electronic devices that require accuracy and stable calibration.

It is a block diagram which shows the direction sensor of this invention. It is a block diagram which shows the magnetic sensor and vibration means of the direction sensor of this invention. It is a shape figure of the shape memory alloy of the direction sensor of this invention. It is a figure explaining the ideal output waveform of the magnetic sensor of the azimuth | direction sensor of this invention. It is a figure explaining the actual output waveform of the magnetic sensor of the azimuth | direction sensor of this invention. It is a circuit diagram of the differentiator of the azimuth sensor of the present invention. It is a block diagram which shows the direction sensor of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic sensor 2 Vibrating means 3 Amplifier 4 1st differentiator 5 2nd differentiator 6 Arithmetic means 7 Magnetoresistive element 9 Shape memory alloy 10 Electrode 11 X-axis output 12 Y-axis output 13 Operational amplifier 14 1st resistance 15 Capacitor 16 Second resistor 80 3-axis magnetic sensor 81 x-axis hall element 82 y-axis hall element 83 z-axis hall element 84 chopper section 85 magnetic sensor drive power supply section 86 differential input amplifier 87 A / D conversion section 88 correction value update section 89 Correction value storage unit 90 Correction calculation unit 91 Azimuth angle calculation unit

Claims (3)

An orientation sensor that detects geomagnetism and identifies the orientation,
A magnetic sensor for detecting geomagnetism, vibration means for vibrating the magnetic sensor, an amplifier for amplifying the output of the magnetic sensor, a first differentiator for differentiating the output of the amplifier, and the first differentiator. An azimuth sensor comprising: a second differentiator for differentiating an output; and arithmetic means for performing calibration and calculating an azimuth by calculation.   The direction sensor according to claim 1, wherein the vibration unit vibrates the magnetic sensor at a constant angular velocity.   3. The direction sensor according to claim 1, wherein the vibration unit includes a shape memory alloy, and generates vibration using a phase transformation of the shape memory alloy. 4.

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