JPH05223573A - Electronic azimuth meter - Google Patents

Abstract

PURPOSE:To reduce a measurement error in azimuth due to hysteresis of a magnet-sensitive element and/or that due to fluctuation of a bias magnetic field. CONSTITUTION:A bias magnetic field generation circuit 2 applies positive and negative bias magnetic fields to two magnetic resistance elements 1a and 1b which are laid out orthogonally. A detection circuit 3 is used to feed a constant current to the magnetic resistance elements 1a and 1b for picking up a change in magnetic resistance due to an external magnetic field as a voltage change. The detection circuit 3 is provided with a voltage difference detection circuit for detecting the difference between the output of the magnetic resistance elements 1a and 1b when the positive bias voltage is applied and that when the negative bias magnetic field is applied. The output voltage of the magnetic resistance elements 1a and 1b which is detected by the detection circuit 3 is converted to a digital value by an A/D converter 4, thus enabling an azimuth to be calculated according to the output voltage of two magnetic resistance elements 1a and 1b in an operation/control part 5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electronic compass.

[0002]

2. Description of the Related Art Conventionally, an electronic azimuth meter utilizing a change in magnetic characteristics of a ferromagnetic material or an electronic azimuth meter utilizing a hall element has been known.

Those utilizing these magnetic sensing elements are as follows:
All of them consume a large amount of electric power, and the one using the Hall element has a drawback that the shape becomes large because a magnetic flux concentrator is required.

Further, an electronic azimuth meter utilizing a magnetoresistive element whose resistance value changes with a magnetic field has been considered. The magnetoresistive element can obtain a larger output voltage than the Hall element, but since it has a hysteresis characteristic, the magnetoresistive value is different even in the same magnetic field, and the output voltage changes due to the fluctuation of the bias magnetic field. Therefore, there is a drawback that it is necessary to apply a stable bias magnetic field.

FIG. 9 is a diagram showing the relationship between the arrangement and orientation of the sensors of the electronic azimuth meter and the output of the magnetic sensor. The sensor A and the sensor B are arranged orthogonally to each other, and the detection voltages of the sensor A and the sensor B have a phase difference of 90 °. Geomagnetic X component detected by these two sensors A and B,
The direction and magnitude of geomagnetism can be obtained from the Y component.

[0006]

As described above, since the magnetoresistive element has the hysteresis characteristic, there are cases where the magnetic field applied to the magnetoresistive element is increased and when it is decreased. Then, even if the same magnetic field is applied, the value of magnetic resistance will differ.

FIG. 10 is a diagram showing the hysteresis characteristic of the magnetoresistive element. When the magnetic field applied to the magnetoresistive element is cyclically changed, the relationship between the magnetic resistance and the magnetic field is one as shown in FIG. It becomes a closed curve.

Now, with the bias magnetic field H _B applied to the magnetoresistive element, the geomagnetic strength when the magnetism detection direction of the magnetoresistive element is directed to the north is H _EN , and the geomagnetism strength when directed to the south. _Be H _ES .

When the azimuth meter is rotated, the angle formed by the direction of the earth's magnetism and the magnetic detection direction of the magnetoresistive element changes to change the resistance value. However, due to the hysteresis characteristic of the magnetoresistive element, the magnetic resistance and the magnetic field are changed. The relationship between and draws a hysteresis loop as shown in FIG.

Therefore, even when the same external magnetic field is applied to the azimuth meter in the same direction, the value of the magnetic resistance differs depending on which path of the hysteresis loop is followed, and an error occurs in the measurement of the azimuth. There was a point.

FIG. 12 shows a conventional electronic azimuth meter.
The bias magnetic field is H_BTo H _BWhen fluctuating to ′,
The output voltage of the magnetoresistive element is V due to the fluctuation of the bias magnetic field.
₀To V₀Problem that measurement error occurs due to fluctuation in
was there.

An object of the present invention is to reduce the measurement error due to the hysteresis of the magnetic sensing element and the measurement error due to the fluctuation of the bias magnetic field.

[0013]

In the first invention, the magnetic sensing means is means for detecting an external magnetic field, and is composed of, for example, a magnetoresistive element.

The bias magnetic field generating means alternately applies positive and negative bias magnetic fields to the magnetic sensing means. The azimuth calculating means calculates the azimuth from the output of the magnetic sensing means when positive and negative bias magnetic fields are applied to the magnetic sensing means.

In the second aspect of the invention, the magnetic sensing means is arranged so that the directions of magnetic detection are orthogonal to each other, and is composed of, for example, two magnetoresistive elements. The detection means detects an output difference of the magnetic sensing means when a positive bias magnetic field is applied and when a negative bias magnetic field is applied.

The azimuth calculation means is 2 detected by the detection means.
The azimuth is calculated from the outputs of the individual magnetic sensing means.

[0017]

In the first aspect of the invention, since the positive and negative bias magnetic fields are alternately applied to the magnetic sensing means, the external magnetic field can be detected through a constant hysteresis loop at all times. The measurement error of the direction can be reduced.

According to the second aspect of the invention, the output difference between the output of the magnetic sensing means when the positive bias magnetic field is applied and the output of the magnetic sensing means when the negative bias magnetic field is applied is detected. Since the azimuth is calculated from the output difference, the azimuth measurement error due to the fluctuation of the bias magnetic field can be reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of the electronic azimuth meter according to the embodiment.

The magnetoresistive elements (MR elements) 1a and 1b are
It is a magnetic sensing element whose resistance value changes according to the strength of the magnetic field applied in the magnetic detection direction.
Are arranged so that the magnetic detection directions are orthogonal to each other.

The bias magnetic field generating circuit 2 is a circuit for applying positive and negative bias magnetic fields to the magnetoresistive elements 1a and 1b. The detection circuit 3 is a circuit that causes a constant current to flow through the magnetoresistive elements 1a and 1b and extracts a change in magnetic resistance due to an external magnetic field as a voltage change. The output of this detection circuit 3 is A /
The digital value is converted by the D converter 4 and output to the arithmetic / control unit 5.

The calculation / control unit 5 calculates the azimuth from the output of the A / D converter 4, that is, the output voltage of the two magnetoresistive elements 1a and 1b, and displays the calculated azimuth on the display unit 6. Further, the arithmetic / control unit 5 outputs signals Φ _{1 to} Φ ₄ to the bias magnetic field generation circuit 2 and the detection circuit 3 for controlling the operation timing of each circuit.

Now, the relationship between the resistance value of the magnetoresistive elements 1a and 1b and the magnetic field will be described with reference to FIGS. FIG. 2 is a diagram showing a relationship between the resistance value of the magnetoresistive element and the magnetic field when the bias magnetic field is not applied.

The magnetoresistive element has a characteristic that the resistance value is the largest when the external magnetic field is "0", and the resistance value decreases as a positive or negative magnetic field is applied. In the figure, the magnetic field H _EN is the strength of the geomagnetism applied to the magnetoresistive element when the magnetic detection direction of the magnetoresistive element is oriented north, and the magnetic field H _ES is when the magnetic detection direction is oriented south. It is the strength of the earth's magnetism applied to the magnetoresistive element.

FIG. 3 is a diagram showing the relationship between the resistance value of the magnetoresistive element and the magnetic field when a positive bias magnetic field H _B is applied to the magnetoresistive element. In this case, the bias magnetic field H
The resistance value of the magnetoresistive element changes around the point _B due to a change in the external magnetic field. Bias magnetic field H _B
When the external magnetic field H _{EN in the} same direction is applied, the resistance value decreases, and when the external magnetic field H _{ES in the} opposite direction to the bias magnetic field H _B is applied, the resistance value increases.

Next, an example of a specific circuit of the bias magnetic field generating circuit 2 will be described with reference to FIG. Transistor T
A signal Φ ₁ is applied to the bases of R3 and TR4, and a signal obtained by inverting the signal Φ ₁ by the inverter IN1 is applied to the bases of the transistors TR1 and TR2.

The output a from the connection point of the collectors of the transistors TR1 and TR2 is changed to the transistors TR3 and T3.
The output b is taken out from the connection point of the collector of R4. The signal Φ ₁ is a pulse signal having a constant cycle as shown in FIG. 5, and while the signal Φ ₁ is at a high level, the transistors TR1 and TR3 of the bias magnetic field generation circuit 2 are on and the transistors TR2 and TR4 are off, Transistor TR
The positive voltage + V supplied to the emitter of No. 1 is output from the output terminal a of the bias magnetic field generating circuit 2 to the terminal a of the bias magnetic field coil L ₁ described later.

Further, while the signal Φ ₁ is at a low level, the transistors TR2 and TR4 are on and the transistors TR1 and TR1 are
TR3 is turned off, and the positive voltage + V supplied to the emitter of the transistor TR4 is output from the output terminal b of the bias magnetic field generation circuit 2 to the terminal b of the bias magnetic field coil L ₂ described later.

That is, the bias magnetic field generating circuit 2 outputs a voltage whose polarity is alternately inverted in synchronization with the signal Φ ₁ . Next, an example of specific circuits of the magnetoresistive elements 1a and 1b and the detection circuit 3 will be described with reference to FIG.

Two magnetoresistive elements 1 arranged orthogonally
a and 1b are coils L ₁ and L ₂ for generating a bias magnetic field.
Are wound in series for the same number of turns, and this coil L ₁ ,
Outputs a and b of the bias magnetic field generating circuit 2 are connected to both ends a and b of L ₂ .

The voltage V _DD is supplied to the magnetoresistive elements 1a and 1b through the resistor R1, and the current flowing through the magnetoresistive elements 1a and 1b is controlled to a constant current by the operational amplifier 11.

One end of the magnetic resistance element 1a is connected to the + input terminal of the operational amplifier 16 via the analog switch 12, and the other end of the magnetic resistance element 1a, that is, the magnetic resistance element 1a.
The connection point with b is connected to the + input terminal of the operational amplifier 16 via the analog switch 13, and is further connected to the + input terminal of the operational amplifier 17 via the analog switch 14. The other end of the magnetic resistance element 1b is connected to the + input terminal of the operational amplifier 17 via the analog switch 15.

The signal Φ ₄ is input to the control terminals of the analog switches 12 and 14, and the analog switches 13 and 15
A signal obtained by inverting the signal Φ ₄ by the inverter 24 is input to the control terminal of.

The outputs of the operational amplifiers 16 and 17 are supplied to the negative input terminal of the operational amplifier 18 via resistors R2 and R3, respectively.
It is connected to the + input terminal and is also connected to the-input terminal via the resistors R4 and R5. The circuit including the operational amplifiers 16, 17, and 18 and the resistors R2 and R3 is a circuit that converts the output voltage across the magnetoresistive elements 1a and 1b into a voltage with the analog ground as a reference.

The output of the operational amplifier 18 is connected to the capacitor C ₁ via the analog switch 19 and is connected to the capacitor C ₂ via the analog switch 20.

[0036] The respective signals [Phi ₂ to the control terminal of the analog switches 19 and 20, [Phi ₃ are given, the signal [Phi _2, by [Phi ₃ by turning on or off the analog switches 19 and 20, an operational amplifier 18 The output voltage of the magnetoresistive elements 1a and 1b to be output is held in the capacitor C ₁ or C ₂ .

The connection point between the capacitor C ₁ and the analog switch 19 is connected to the + input terminal of the operational amplifier 21,
The connection point between the capacitor C ₂ and the analog switch 20 is connected to the + input terminal of the operational amplifier 22. Further, the outputs of the operational amplifiers 21 and 22 are connected to the + input terminal and the-input terminal of the operational amplifier 23, respectively.

Here, the operation of the circuit of FIG. 6 will be described with reference to the time chart of FIG. As described above, the signal Φ ₁
Is a signal for switching the polarity of the bias magnetic field,
The signals Φ ₂ and Φ ₃ are signals that are high level for a predetermined period when the signal Φ ₁ is high level or low bell, respectively, and are signals for holding the output of the operational amplifier 18 in the capacitor C ₁ or C ₂ .

Further, the signal Φ_FourIs the output of the magnetoresistive element 1a.
Force voltage is detected or output of magnetoresistive element 1b
This is a signal for switching whether to detect the voltage. First,
The operation when detecting the output voltage of the magnetoresistive element 1a is explained.
Reveal Signal Φ _FourIs high, the analog switch
Switches 12 and 14 turn on, and analog switches 13 and 15
Turns off, and the voltage across the magnetoresistive element 1a becomes
It is detected in the pages 16 and 17.

In this state, when the signal Φ ₁ becomes high level, a positive bias magnetic field is applied to the magnetoresistive element 1a, and the operational amplifier 18 outputs an output voltage corresponding to the positive bias magnetic field and the strength of the earth's magnetism. .. Further, when the signal Φ ₂ becomes high level, the analog switch 19 is turned on, and the output voltage of the operational amplifier 18, that is, the output voltage of the magnetoresistive element 1a is held in the capacitor C ₁ .

When the signal Φ ₁ becomes low level, a negative bias magnetic field is applied to the magnetoresistive element 1a, and the operational amplifier 18 outputs an output voltage corresponding to the negative bias magnetic field and the strength of the earth's magnetism. Further, when the signal Φ ₃ becomes high level, the analog switch 20 is turned on, and the output voltage of the operational amplifier 18, that is, the output voltage of the magnetoresistive element 1a is held in the capacitor C ₂ .

The voltage held in the capacitors C ₁ and C ₂ is detected by a circuit composed of operational amplifiers 21, 22, 23 and the like, and the voltage difference is amplified and output from the operational amplifier 23.

The same applies to the case of detecting the output voltage of the magnetoresistive element 1b. When the signal Φ ₄ is at the low level, the analog switches 13 and 15 are turned on and the analog switch 1 is turned on.
The transistors 2 and 14 are turned off, and the voltage across the magnetoresistive element 1b is detected by the operational amplifiers 16 and 17.

In this state, when the signal Φ ₁ goes high, a positive bias magnetic field is applied to the magnetoresistive element 1b, and when the signal Φ ₂ goes high, the output voltage of the magnetoresistive element 1b changes to the capacitor C. ₁ is held.

Similarly, when the signal Φ ₃ becomes high level, the output voltage of the magnetoresistive element 1b is held in the capacitor C ₂ . As described above, the detection circuit 3 obtains the difference between the output voltages when the positive bias magnetic field is applied to the two magnetoresistive elements 1a and 1b and when the negative bias magnetic field is applied, and the geomagnetic field is calculated from the voltage difference. The azimuth is calculated by obtaining the X component and the Y component of.

In this case, since the strength of the earth's magnetism can be measured through a constant hysteresis loop that circulates a predetermined positive bias magnetic field and a negative bias magnetic field, the magnetoresistive element 1
The azimuth measurement error caused by the hysteresis of a and 1b can be reduced.

Further, by obtaining the difference between the output voltages of the magnetoresistive elements 1a and 1b when the positive and negative bias magnetic fields are applied, the azimuth measurement error due to the fluctuation of the bias magnetic field can be eliminated.

Next, the polarity of the bias magnetic field is periodically inverted.
Of the output voltage of the magnetoresistive element and the strength of the magnetic field
The relationship will be described with reference to FIG. 7. Magnetoresistive element 1
positive bias magnetic field H to a and 1b_B ⁺And negative bias field
H _B ^-It is assumed that and are alternately applied. In this example,
Geomagnetism H detected by the magnetoresistive element 1a or 1b_EWho
Direction is a positive bias magnetic field H_B ⁺Is the same as the direction of
It

As shown in FIG. 7, a positive bias magnetic field H _B ⁺
Let H _{E be} the strength of the geomagnetism when is applied
The output voltage of the magnetoresistive elements 1a and 1b is the bias magnetic field H.
The output voltage V _a by the terrestrial magnetism H _E than the output voltage by _B ⁺
It was decreased by the negative bias magnetic field H _B ^- when is applied, the magnetoresistive element 1a, the output voltage of 1b is increased by the output voltage V _b fraction which is proportional to the geomagnetic H _E.

Therefore, by obtaining the difference between the two, the output voltages of the magnetoresistive elements 1a and 1b due to the bias magnetic field are canceled out, and a voltage approximately twice the output voltage of the magnetoresistive elements 1a and 1b due to the geomagnetism H _E is obtained. be able to.

In this case, the magnetoresistive elements 1a and 1b are bypassed.
As the as magnetic field is periodically inverted and applied,
Constant hysteresis loop, negative bias field
H_B ^-And positive bias magnetic field H_B ⁺Hysteresis connecting to
Since the strength of the geomagnetism is measured through the loop, the external magnetic field
The output voltage of the magnetoresistive elements 1a and 1b is
The hysteresis of the magnetoresistive elements 1a and 1b is determined positively.
The influence of the characteristic can be eliminated.

Further, the difference between the output voltage of the magnetoresistive elements 1a and 1b when a positive bias magnetic field is applied and the output voltage of the magnetoresistive elements 1a and 1b when a negative bias magnetic field is applied is calculated. Therefore, it is possible to eliminate the error in the output voltage of the magnetoresistive elements 1a and 1b which is caused by the fluctuation of the bias magnetic field.

FIG. 8 shows the magnetic field when the bias magnetic field changes.
It is a figure which shows the change of the output voltage of a gas resistance element. here,
Bias magnetic field H_B ⁺, H_B ^-When fluctuates only by ΔH
The magnetic field of H_B ⁺′, H_B ^-'And a positive bias magnetic field H
_B ⁺Applied and negative bias magnetic field H_B ^-Apply
Output voltage difference of the magnetoresistive element when₀And the positive ba
Iias magnetic field H_B ⁺′ Applied and negative bias magnetic field
H_B ^-The output voltage difference of the magnetoresistive element when
V₀’

Assuming that the curve of FIG. 8 showing the relationship between the output voltage of the magnetoresistive element and the magnetic field has a substantially constant slope in the range of H _B ± H _E , the output voltages V ₀ and V ₀ ′ are almost equal. Become. Therefore, the magnetoresistive elements 1a and 1b when a positive bias magnetic field is applied and when a negative bias magnetic field is applied.
By obtaining the difference between the output voltages of the magnetic resistance elements 1a and 1b, it is possible to eliminate the error in the output voltage of the magnetoresistive elements 1a and 1b.

The present invention is not limited to the device exclusively used for the azimuth meter described in the embodiments, but can be incorporated in an electronic wrist watch, an altimeter, etc., and can also be applied to a navigation device such as an automobile.

[0056]

According to the present invention, bias magnetic fields having different polarities are alternately applied to the magnetic sensing means, so that the measurement error of the azimuth caused by the hysteresis characteristic of the magnetic sensing means can be reduced. Further, by obtaining the output difference of the magnetic sensing means when the positive and negative bias magnetic fields are applied, the measurement error due to the fluctuation of the bias magnetic field can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an electronic azimuth meter according to an embodiment.

FIG. 2 is a diagram showing a relationship between a resistance value of a magnetoresistive element and a magnetic field when a bias magnetic field is not applied.

FIG. 3 is a diagram showing a relationship between a resistance value of a magnetoresistive element and a magnetic field when a bias magnetic field is applied.

FIG. 4 is a circuit configuration diagram of a bias magnetic field generation circuit.

FIG. 5 is a diagram showing a time chart of signals Φ _{1 to} Φ ₄ .

FIG. 6 is a circuit configuration diagram of a magnetoresistive element and a detection circuit.

FIG. 7 is a diagram showing a relationship between a magnetic resistance and a magnetic field when positive and negative bias magnetic fields are applied.

FIG. 8 is a diagram illustrating the influence of fluctuations in the bias magnetic field.

FIG. 9 is an explanatory diagram of an electronic azimuth meter in which sensors are arranged orthogonally.

FIG. 10 is an explanatory diagram of a hysteresis characteristic of a magnetoresistive element.

FIG. 11 is an explanatory diagram of a hysteresis characteristic of a magnetoresistive element.

FIG. 12 is a diagram showing variations in output voltage of a magnetoresistive element due to variations in bias magnetic field.

[Explanation of symbols]

 1a, 1b Magnetoresistive element 2 Bias magnetic field generation circuit 3 Detection circuit 4 A / D converter 5 Arithmetic / control section 6 Display section

Claims (2)

[Claims] 1. A magnetic sensing means, a bias magnetic field generating means for alternately applying positive and negative bias magnetic fields to the magnetic sensing means, and a positive and negative bias magnetic field applied by the bias magnetic field generating means. An electronic azimuth meter, comprising: an azimuth calculating means for calculating an azimuth from the output of the magnetic sensing means. 2. At least two magnetic sensing means arranged orthogonally to each other, bias magnetic field generating means for alternately applying positive and negative bias magnetic fields to these two magnetic sensing means, and the bias magnetic field generating means. Detecting means for detecting the difference between the output of the magnetic sensing means when a positive bias magnetic field is applied and the output of the magnetic sensing means when a negative bias magnetic field is applied, and the detection means And an azimuth calculating means for calculating an azimuth based on the outputs of the two magnetic sensing means.