JP5241002B2 - Magnetic sensor and actuator using the magnetic sensor - Google Patents

Description

  The present invention relates to a magnetic sensor for detecting an external magnetic field and an actuator using the magnetic sensor.

  Conventionally, as this type of sensor, Patent Document 1 discloses a magnetic detection device that detects the proximity of a permanent magnet as an inductance change of a coil wound around a saturable magnetic core.

The magnetic detection device described in Patent Document 1 includes a saturable magnetic core, a coil wound around the saturable magnetic core, a transmission circuit that supplies an AC signal to the coil, and a bias current that is supplied to the coil. And a comparison circuit for comparing an AC signal generated in the coil with a reference signal.
JP 56-158967 A

The magnetic detection device described in Patent Document 1 generates a DC bias magnetic field in a saturable magnetic core by applying a positive or negative DC current to a coil from a bias power source, and the central axis of saturation characteristics is positive with respect to an external magnetic field. Or the characteristic which moved negatively is acquired.
For this reason, it is relatively easy to determine the polarity of the external magnetic field, but in order to determine the strength of the external magnetic field, including the case where there is no external magnetic field, it depends on the strength of the external magnetic field to be detected. The output current value of the bias power source needs to be set to an optimum value, and there is a problem that the sensor is not versatile.

  In addition, the above conventional magnetic detection device is sufficient when used simply to detect the presence or absence of an object, but since the detectable range is very narrow, the high assembly accuracy between the sensor and the detection object is high. There was also a problem that was required.

  Accordingly, an object of the present invention is to provide a more versatile magnetic sensor capable of discriminating the strength and polarity of an external magnetic field including the case where there is no external magnetic field.

  In order to achieve the above object, the present invention is a magnetic sensor comprising an excitation coil having a magnetic core inserted therein and a detection coil, wherein a low frequency is applied to the excitation coil, High frequency is applied and modulated by the magnetic core of the detection coil periodically repeating the magnetic saturation state and the magnetic unsaturation state by the magnetic flux of the excitation coil and the magnetic field of the external magnetic field linked to the magnetic core of the detection coil. The magnetic flux of the external magnetic field is detected based on the voltage across the detection coil.

The magnetic sensor of the present invention has as a further preferable feature,
“Detecting the magnetic flux of the external magnetic field based on the modulation rate of the amplitude of the voltage across the detection coil”,
“Having means for detecting a modulated wave of the amplitude of the voltage across the detection coil and a low-frequency phase difference applied to the excitation coil”;
“The magnetic core of the excitation coil is soft iron, and the magnetic core of the detection coil is a saturable magnetic core.”
Is included.

In addition, the present invention is an actuator using a magnetic sensor, and controls a motor having a rotating shaft, an output shaft that outputs driving force of the motor transmitted through a plurality of gears, and the motor. And a permanent magnet that generates the external magnetic field is provided in an output gear that rotates integrally with the output shaft, and the magnetic sensor is provided at a position facing the permanent magnet when the output gear rotates. It is characterized by that.

The magnetic sensor of the present invention has as a further preferable feature,
“When the power is turned on, the control unit drives the motor to rotate the output shaft in a predetermined direction, and when the magnetic sensor detects the external magnetic field, the rotation position of the output shaft is set to the initial position. To set ",
Is included.

According to the present invention, a predetermined amount of magnetic flux from an external magnetic field, which is linked to the magnetic core of the detection coil, and magnetic flux from the exciting coil that periodically varies, the magnetic core of the detection coil is periodically magnetically saturated and magnetic. When the desaturation is repeated, the inductance of the detection coil periodically varies, and a phenomenon occurs in which the amplitude of the output voltage (both ends voltage) of the detection coil is modulated.
For this reason, the intensity of the magnetic flux from the external magnetic field can be detected by detecting the modulation rate, and an output signal having a phase difference of 180 degrees depending on the polarity of the external magnetic field can be obtained, so that the polarity of the external magnetic field can also be detected.

  Hereinafter, embodiments of the present invention will be exemplarily described based on the drawings. However, the material, shape, relative arrangement, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

  First, the basic configuration of the magnetic sensor 1 of the present invention will be described with reference to FIG.

  The magnetic sensor 1 of the present invention has an excitation coil L1 and a detection coil L2 into which a magnetic core 2 is inserted. An oscillator F1 and a resistor R1 are connected to the excitation coil L1, and an oscillator F2 and a resistor R2 are connected to the detection coil L2. Is connected.

A low frequency of 10 Hz to 1 kHz as shown in FIG. 2A is preferably applied to the exciting coil L1 so that a low frequency is applied from the oscillator F1 and the magnetic core 2 can be an electromagnet. .
On the other hand, a high frequency is applied to the detection coil L2 from the oscillator F2, and preferably a high frequency of 100 kHz to 1 MHz as shown in FIG.
In FIG. 2, the horizontal axis represents a time of 0.05 sec on a scale, and the vertical axis represents a voltage of 1.0 V on a scale for a low frequency and 0.05 V on a scale for a high frequency.

  The magnetic core 2 is not particularly limited as long as it is a material having a high magnetic permeability. For example, soft iron such as silicon steel, ferrite, sendust, permalloy, amorphous magnetic alloy, or the like can be used. It is particularly preferable to use soft iron having a small residual magnetization as the magnetic core of the exciting coil L1, and it is particularly preferable to use a saturable magnetic core such as ferrite having a high permeability as the magnetic core of the exciting coil L2.

  In the present invention, it is desirable to set the coupling coefficient of the excitation coil L1 and the detection coil L2 low so that the coils are less likely to interfere with each other. This coupling coefficient is preferably 0.4 or less, more preferably 0.2 or less, and particularly preferably 0.1 or less.

Next, the principle of the magnetic sensor of FIG. 1 will be described.
When the oscillator F1 and the oscillator F2 are oscillated, the output voltage 3 of the detection coil L2 appears in the same manner as the signal of the oscillator F2 (see FIG. 2 (a) 2). This is because the magnetic coupling between the excitation coil L1 and the detection coil L2 is low, and the induced voltage of the excitation coil L1 hardly appears in the detection coil L2.
At this time, the magnetic core 2 of the detection coil L2 is in a magnetically unsaturated state.

  Next, a case where the permanent magnet 4 is brought close to the magnetic sensor 1 in which the excitation coil L1 and the detection coil L2 are integrally fixed as an external magnetic field will be considered. 3 and 4 show a state in which the north pole of the permanent magnet 4 is close to the magnetic sensor. Here, r described in FIGS. 2, 3, and 4 represents the distance between the magnetic sensor 1 and the permanent magnet 4.

  When the N pole of the permanent magnet 4 is gradually brought closer to the magnetic sensor, the magnetic flux in a certain direction from the permanent magnet 4 linked to the magnetic core 2 of the detection coil L2 gradually increases. On the other hand, a sine wave as shown in FIG. 2A is input to the exciting coil L1, and the magnetic field fluctuates periodically. When the magnetic field of the exciting coil L1 at a certain moment becomes the magnetic field of the S pole on the permanent magnet side (see FIG. 3), the magnetic flux of the permanent magnet 4 and the magnetic flux of the exciting coil L1 are in the same direction, and the magnetic flux increases in the detection coil. When the magnetic core of the detection coil starts to be magnetically saturated, the inductance of the detection coil L2 decreases, and the output voltage 3 of the detection coil undergoes amplitude modulation (see FIG. 2B).

  Further, when the magnetic field of the exciting coil L1 at a certain moment becomes an N-pole magnetic field on the permanent magnet side (see FIG. 4), the magnetic flux of the permanent magnet 4 and the magnetic flux of the exciting coil L1 are opposite to each other. Since the magnetic core 2 of the detection coil L2 is not magnetically saturated and the inductance of the detection coil L2 does not change, the output voltage 3 of the detection coil L2 is the same as that without the permanent magnet 4 (FIG. 2B). reference).

  When the N pole of the permanent magnet 4 is further brought closer to the magnetic sensor, the magnetic flux from the permanent magnet 4 further increases in the detection coil L2, and the detection coil L2 is applied to the excitation coil L1 within one cycle of the low frequency applied to the excitation coil L1. The time during which the magnetic core is magnetically saturated becomes longer, and the modulation rate of the output voltage 3 of the detection coil L2 increases (see FIGS. 2C to 2E).

  Further, when the N pole of the permanent magnet 4 is further brought closer to the magnetic sensor, the magnetic flux from the permanent magnet 4 further increases in the detection coil L2, and when the magnetic field of the excitation coil L1 is the S pole on the permanent magnet side, it is complete. Even when the magnetic field of the exciting coil L1 is N pole on the permanent magnet side, the magnetic core 2 of the detecting coil L2 begins to be magnetically saturated, and the modulation factor of the output voltage 3 of the detecting coil L2 starts to decrease (see FIG. 2 (f) to FIG. 2 (i)).

  When the N pole of the permanent magnet 3 is further brought closer to the magnetic sensor, the magnetic flux from the permanent magnet 3 further increases in the detection coil L2, and even when the magnetic field of the exciting coil L1 is the S pole on the permanent magnet side. Even at the pole, the magnetic saturation is complete, and the amplitude modulation of the output voltage 3 of the detection coil L2 is not observed (see FIG. 2 (j)).

  In this way, by a predetermined amount of magnetic flux from the permanent magnet 4 (external magnetic field) interlinked with the magnetic core of the detection coil L2 and magnetic flux from the exciting coil L1 that periodically varies in synchronization with the frequency of the oscillator F1, When the magnetic core of the detection coil L2 periodically repeats a magnetic saturation state and a magnetic unsaturation state, the inductance of the detection coil L2 periodically varies, and the amplitude of the output voltage 3 of the detection coil L2 connected in series with the resistor R2 Therefore, by detecting this modulation factor, it is possible to detect the position of the permanent magnet including the strength of the magnetic flux from the permanent magnet 4, in other words, the presence or absence of the proximity of the permanent magnet 4.

In the above description, the case where the north pole of the permanent magnet 4 is close to the magnetic sensor 1 has been described. Next, the case where the south pole of the permanent magnet 4 is close to the magnetic sensor 1 will be considered.
When the S pole of the permanent magnet 4 is gradually brought closer to the magnetic sensor, the magnetic flux in the direction opposite to the case where the N pole is brought closer is gradually increased. On the other hand, a low-frequency sine wave is input to the exciting coil L1, and the magnetic field fluctuates periodically. When the magnetic field of the exciting coil L1 at a certain moment becomes the south pole magnetic field on the permanent magnet side, the magnetic flux of the permanent magnet 4 and the magnetic flux of the exciting coil are opposite to each other. Since the magnetic saturation does not occur and the inductance of the detection coil L2 does not change, the output voltage 3 of the detection coil L2 is the same as when the permanent magnet 4 is not provided.

  Further, when the magnetic field of the exciting coil L1 at a certain moment becomes an N-pole magnetic field on the permanent magnet side, the magnetic flux of the permanent magnet 4 and the magnetic flux of the exciting coil L1 become the same direction, and the magnetic flux increases in the detecting coil L2, and the detecting coil When the magnetic core 2 of L2 begins to be magnetically saturated, the inductance of the detection coil L2 decreases, and the output voltage 3 of the detection coil L2 undergoes amplitude modulation.

  Thus, since the phase of the output signal of the detection coil L2 differs by 180 degrees between the case where the N pole of the permanent magnet is close to the magnetic sensor 1 and the case where the S pole is close, the input signal to the excitation coil L1. And the phase of the output signal of the detection coil L2, the polarity of the permanent magnet 4 as an external magnetic field can be determined.

Next, examples of the present invention will be described.
Example 1
In the present embodiment, the magnetic sensor 1 having the configuration of FIG. 1 is configured and the magnetism of the permanent magnet 4 is detected. In the magnetic sensor 1 of this embodiment, a wire bobbin Φ0.11 is wound around a coil bobbin (not shown) 100 times around the excitation coil L1 and 30 times around the detection coil L2, and arranged in a coaxial manner on the same axis. Are the same.

A magnetic core 2 is inserted into a coil bobbin around which the excitation coil L1 and the detection coil L2 are wound. Soft iron is inserted into the magnetic core 2 of the excitation coil L1, and ferrite is inserted into the magnetic core 2 of the detection coil L2. The soft iron and ferrite are arranged with a gap of 0.05 mm. R1 = 100Ω and R2 = 3.9Ω. The inductance when the magnetic core 2 is inserted is 54.2 μH for the exciting coil L1, 18.1 μH for the detecting coil L2, and 76.5 μH for the combined inductance L0.
Therefore, the mutual inductance M is
M = (L0− (L1 + L2)) / 2
= 2.1
It becomes.
The coupling coefficient k is
k = M / √ (L1 · L2)
≒ 0.067
It becomes.

  At this time, MSO 6034A (Agilent Technology Co., Ltd. trade name) was used as a measuring instrument, 1946 (Wave Factory Co., Ltd. trade name) was used as the oscillator F1, and LAG-120A (Leader Electronics Co., Ltd. trade name) was used as the oscillator F2.

  The frequency of the oscillator F1 was 10 Hz, the voltage across the exciting coil L1 was adjusted to 0.8 Vp-p, the frequency of the oscillator F2 was 1 MHz, and the output voltage was adjusted to 0.2 Vp-p (see FIG. 2).

Next, as shown in FIG. 3, the N pole of the permanent magnet 4 was gradually brought closer to the detection coil L <b> 2 side of the magnetic sensor 1. The upper waveform in FIG. 2 is the output voltage waveform of the detection coil L2, and FIG. 5 summarizes the measurement results.
The modulation factor m (%) in FIG. 5 is given by assuming that the maximum amplitude appearing in the output signal of the detection coil L2 is A and the minimum amplitude is B
m = ((A−B) / (A + B)) × 100
It is said.

In FIG. 5, when the distance r between the permanent magnet 4 and the magnetic pole sensor 1 is 30 mm, amplitude modulation starts, the modulation rate becomes maximum at the distance r = 18, and then the modulation rate gradually decreases.
In order to obtain a useful signal by demodulating the modulated wave, it is required that the modulation rate be as large as possible. With the magnetic sensor of this example, a useful signal could be obtained when the modulation rate was 10% or more. .
That is, the magnetic sensor 1 of the present embodiment can detect the presence, strength, and polarity of the permanent magnet 4 when the distance r from the permanent magnet 4 is 20 mm to 15 mm.

(Example 2)
Except that an integral type ferrite was inserted as the magnetic core 2 of the excitation coil L2 and the detection coil L1, the magnetic sensor 1 was configured in the same manner as in Example 1, and the magnetism of the permanent magnet 4 was detected (see FIG. 6).
The inductance when the magnetic core 2 is inserted is 269.3 μH for the exciting coil L1, 25.5 μH for the detecting coil L2, and 358.7 μH for the combined inductance L0.
Therefore, the mutual inductance M is
M = (L0− (L1 + L2)) / 2
= 31.95
It becomes.
The coupling coefficient k is
k = M / √ (L1 · L2)
≒ 0.39
It becomes.

The waveform of FIG. 6 is an output voltage waveform of the detection coil when a permanent magnet is brought close to the detection coil side of the magnetic pole sensor. FIG. 7 summarizes the measurement results of FIG.
In FIG. 7, when the distance r between the magnetic pole sensor 1 and the permanent magnet 4 reaches 20 mm, amplitude modulation starts and the modulation factor increases up to the distance r = 16 mm. Thereafter, when the distance r = 15 mm, the modulation rate increases to 38.3%, but the waveform is distorted. This is presumably because the magnetic flux of the exciting coil L1 is weak and the detection coil L2 cannot faithfully reproduce the sine wave. Therefore, in the present embodiment, the presence / absence, strength and polarity of the permanent magnet 4 can be detected when the distance r = 16 mm to 17 mm.

  Thus, in Example 1, the range in which the presence / absence, strength, and polarity of the permanent magnet 4 can be detected is r = 15 mm to 20 mm, and in Example 2, r = 16 mm to 17 mm, which is detected from Example 2. I found that the range was wide.

(Example 3)
FIG. 8 is a block diagram of the first embodiment using the magnetic sensor 1.
In FIG. 8, reference numeral 60 denotes an envelope detection circuit that demodulates the amplitude-modulated wave generated by the detection coil L2. 61 is a phase comparator between the sine wave of the oscillator F1 and the sine wave of the output of the envelope detection circuit 60. Reference numeral 62 denotes an A / D converter which converts the amplitude of the output of the envelope detection circuit 60 into a digital signal and outputs a modulation rate signal to a control unit described later. Reference numeral 63 denotes a control unit that detects information related to the permanent magnet 4 based on information from the AD converter 62 and the phase comparator 61.

(Application examples)
FIG. 9 is an internal structure diagram of the actuator 55 incorporating the third embodiment.
In FIG. 9, reference numeral 50 denotes a motor having a rotation shaft 50 a, 51 denotes an output shaft that outputs the driving force of the motor 50 transmitted through a plurality of gears. Rotates together. The permanent magnet 4 is provided on an output gear 52 that rotates integrally with the output shaft 51, and the magnetic sensor 1 is provided on a substrate (not shown) at a position facing the permanent magnet 4 when the output gear 52 rotates. When the actuator is powered on, the control unit 63 drives the motor 50 to rotate the output shaft 51 in a predetermined direction, and the magnetic sensor 1 detects the magnetic field of the permanent magnet 4 attached to the output gear 52. Based on the information of the A-D converter 62 and the phase comparator 61, the rotational position of the output shaft 51 is set to the initial position.

  The initial position of the output shaft 51 can be set by detecting the peak value of the magnetic field of the permanent magnet 4. Specifically, the control unit 63 sequentially stores the magnitude of the magnetic field, detects the change point of increase / decrease in the magnitude of the magnetic field, reverses the output gear 52, and sets the output shaft 51 to the initial position with the peak value of the magnetic field. Then, the output shaft 51 can be accurately set to the initial position.

The actuator 55 of this example can be used, for example, as a drive source for an airflow adjustment valve of a vehicle air conditioner.
In general, an airflow adjustment valve of an air conditioner for a vehicle stops at the same position when the power is turned off. For this reason, unless the airflow adjustment valve is reset to the initial position when the power is turned on, it cannot be adjusted to a predetermined opening degree.
By using the actuator 55 of this example as a drive source for the air flow regulating valve of such an air conditioning apparatus for a vehicle, the output shaft 51 is accurately set to the initial position as described above when the power is turned on. It is possible to accurately perform the initial setting of the airflow control valve operated in the above.

  Further, according to the magnetic sensor 1 of the present invention, since the detection range is wide, variations in assembly accuracy between the output gear 52 to which the external magnetic field (permanent magnet 4) is attached and the magnetic sensor 1 can be absorbed. The position can be reliably detected.

  Furthermore, according to the magnetic sensor 1 of the present invention, the variation in sensitivity is very small compared to the Hall element. In particular, when the actuator is installed in a vehicle or the like and used in a high temperature environment, the conventional Hall element is used. The actuator is more reliable than the actuator used as the magnetic sensor.

1 is a basic configuration diagram of a magnetic sensor according to an embodiment of the present invention. It is an output waveform of the magnetic sensor concerning the Example of this invention. It is a basic block diagram when the north pole of a permanent magnet adjoins the magnetic sensor concerning the Example of this invention. It is a basic block diagram when the north pole of a permanent magnet adjoins the magnetic sensor concerning the Example of this invention. The excitation coil according to the embodiment of the present invention is a measurement result when the iron core is inserted and the detection coil is ferrite. It is an output waveform of the magnetic sensor in FIG. The measurement result when ferrite is inserted into the exciting coil and the detecting coil according to the embodiment of the present invention is shown. It is a block diagram of the Example using the magnetic sensor of this invention. It is an internal structure figure of the actuator using the example of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic sensor 2 Magnetic core 3 Output voltage 4 Permanent magnet L1 Excitation coil L2 Detection coil r Distance 50 Motor 50a Rotating shaft 51 Output shaft 52 Output gear 55 Actuator 60 Envelope detection circuit 61 Phase comparator 62 AD converter 63 Control Part

Claims (6)

A magnetic sensor comprising an excitation coil and a detection coil with a magnetic core inserted therein,
A low frequency is applied to the excitation coil, a high frequency is applied to the detection coil,
The detection coil modulated by the magnetic core of the detection coil periodically repeating a magnetic saturation state and a magnetic unsaturation state by the magnetic flux of the excitation coil and the magnetic flux of the external magnetic field linked to the magnetic core of the detection coil A magnetic sensor for detecting a magnetic flux of the external magnetic field based on a voltage between both ends of the magnetic field.   The magnetic sensor according to claim 1, wherein the magnetic flux of the external magnetic field is detected based on a modulation factor of an amplitude of a voltage across the detection coil.   2. The magnetic sensor according to claim 1, further comprising means for detecting a phase difference between a modulated wave of amplitude of the voltage across the detection coil and a low frequency applied to the excitation coil.   The magnetic sensor according to claim 1, wherein the magnetic core of the exciting coil is soft iron, and the magnetic core of the detection coil is a saturable magnetic core. An actuator using the magnetic sensor according to any one of claims 1 to 4,
A permanent magnet having a motor having a rotating shaft, an output shaft for outputting the driving force of the motor transmitted through a plurality of gears, and a control unit for controlling the motor, and generating the external magnetic field ; The actuator is provided in an output gear that rotates integrally with the output shaft, and the magnetic sensor is provided at a position facing the permanent magnet when the output gear rotates.   When the power is turned on, the control unit drives the motor to rotate the output shaft in a predetermined direction. When the magnetic sensor detects the external magnetic field, the rotation position of the output shaft is set to an initial position. The actuator according to claim 5, wherein:

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