JP3746354B2 - Magnetic field detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a device for detecting the azimuth and intensity of a parallel magnetic field such as geomagnetism, and a magnetic position detection device, and more particularly, to an improvement in detection accuracy, simplification of circuit configuration, and cost reduction. .
[0002]
[Prior art]
Conventionally, in a car navigation system or the like, as a device for detecting the direction and strength of a relatively weak parallel magnetic field such as geomagnetism, a magnetic modulator using a ring-shaped high permeability magnetic material (as a flux What is called a gate-type magnetic sensor is used.
[0003]
This flux gate type magnetic sensor is described in detail in Japanese Patent Application Laid-Open No. 54-21889 and Japanese Patent Application Laid-Open No. 61-83909. An example of the entire configuration is shown in FIG. is there.
[0004]
The magnetic path forming member 31 is made of a ring-shaped high magnetic permeability magnetic material.
An excitation coil 32 is uniformly wound on the magnetic path forming member 31 over the entire circumference of the ring. An excitation voltage having a frequency f is applied to the excitation coil 32 from the oscillator 34, whereby the magnetic path forming member 31 is excited to the saturation magnetic field.
[0005]
An output coil 33x is wound around the magnetic path forming member 31 so as to surround a portion of the X axis and the Y axis that are orthogonal to each other in the X axis direction. An output coil 33y is wound so as to surround the facing portion.
[0006]
A band pass filter 36x having a center frequency of 2f, a synchronous detection circuit 37x, and a smoothing circuit 38x are sequentially connected to the output coil 33x. A band pass filter 36y having a center frequency of 2f, a synchronous detection circuit 37y, and a smoothing circuit 38y are sequentially connected to the output coil 33y.
[0007]
The frequency multiplication circuit 35 generates a signal of frequency 2f from the signal of frequency f from the oscillator 34, and supplies this signal to the synchronous detection circuits 37x and 37y as a reference signal for synchronous detection.
[0008]
The detection method of the direction and intensity of the parallel magnetic field in this sensor is as follows.
When the sensor is not placed in a parallel magnetic field, the voltage induced in the output coils 33x and 33y is only based on the excitation voltage from the oscillator 34. However, the magnetic flux in the ring of the magnetic path forming member 31 due to the excitation voltage is in the opposite direction and equal in magnitude at both ends of the output coils 33x and 33y. Accordingly, in this case, no voltage is induced in the output coils 33x and 33y.
[0009]
On the other hand, when the sensor is placed in a parallel magnetic field H as shown in FIG. 11, for example, the magnetic flux in the ring of the magnetic path forming member 31 is changed at both ends of the output coils 33x and 33y. The size will be different. Therefore, the even-order harmonic components 2f, 4f, 6f,... Of the excitation frequency f that are proportional to the X-axis and Y-axis components Hx and Hy of the parallel magnetic field H are output from the output coils 33x and 33y, respectively. become.
[0010]
Of the even-order harmonic components, only the 2f component, the bandpass filter 36x, taken out by 36y, the synchronous detection circuit 37x, after being synchronous detection in 37y, smoothing circuit 38x, Through the 38y, Hx, Output signals Vx and Vy proportional to Hy are obtained.
[0011]
Here, assuming that the proportionality constant between Hx, Hy and Vx, Vy is K and the angle between the direction of the parallel magnetic field H and the X-axis direction is θ, Vx, Vy is
Vx = KHx = KHcosθ
Vy = KHy = KHsinθ
It becomes.
[0012]
Therefore, for example, when trying to obtain the orientation of the parallel magnetic field H using the output signals Vx and Vy,
Vy / Vx = KHsin θ / KH cos θ = tan θ
θ = tan ⁻¹ Vy / Vx
Can be obtained as
[0013]
[Problems to be solved by the invention]
However, the conventional flux gate type magnetic sensor as shown in FIG. 11 has the following disadvantages.
[0014]
(1) Since the exciting coil 32 must be wound over the entire circumference of the ring of the magnetic path forming member 31, the winding of the exciting coil 32 may be slightly non-uniform, but the magnetic path is formed accordingly. Since the magnetic field strength of the member 31 is not uniform, the voltage induced in the output coils 33x and 33y is unbalanced, so that the detection accuracy is deteriorated.
[0015]
(2) Since the output coils 33x and 33y intersect at the central portion of the magnetic path forming member 1, when all of one of them is completely wound and the remaining one is wound, the output coils 33x and 33y A difference occurs in resistance and inductance, and the number of magnetic fluxes passing through the output coil 33x is different from the number of magnetic fluxes passing through the output coil 33y. For this reason, since a difference is produced between the output signals Vx and Vy, the detection accuracy is deteriorated.
[0016]
As a countermeasure for solving this inconvenience, a method of alternately winding the output coils 33x and 33y one by one has been proposed (Japanese Patent Laid-Open No. 1-288718). However, this method has another inconvenience that it takes a lot of time to perform winding.
[0017]
(3) Since the magnetic modulation method is adopted as the detection principle, the bandpass filters 36x and 36y, the synchronous detection circuits 37x and 37y, and the frequency multiplication circuit 35 are required, so that the circuit configuration becomes complicated and the cost is increased. turn into.
[0018]
The present invention has been made in view of the above-described points, and makes it easy to uniformly coil coils, there is no difference in resistance, inductance, and number of magnetic flux between coils, and the circuit configuration is simple and low-cost magnetic field detection. The device is to be provided.
[0019]
[Means for Solving the Problems]
A magnetic field detection apparatus according to the present invention includes a magnetic path forming member having a closed magnetic path made of a high magnetic permeability magnetic material, and three coils wound respectively at different locations on the closed magnetic path, An excitation unit that applies excitation voltage to these coils and an output unit that detects and smoothes the excitation voltage applied to these coils and outputs them, and the direction of the magnetic field in the closed magnetic circuit by the excitation voltage is equal by the excitation unit. These coils are excited so that a three-phase output corresponding to the external magnetic field is obtained from the output unit.
[0020]
According to this magnetic field detection device, coils are individually wound at different locations on the closed magnetic path of the magnetic path forming member. Accordingly, unlike the exciting coil 2 shown in FIG. 11 which must be wound over the entire circumference of the ring (closed magnetic circuit), uniform winding is easy, so that the disadvantage (1) described above. Is resolved. Further, for example, by performing winding in a state where the magnetic path forming member is mounted on the bobbin, the coil can be positioned and wound at a predetermined position on the closed magnetic path accurately.
[0021]
And the coil wound by the mutually different location on a closed magnetic path does not cross | intersect like the output coils 33x and 33y shown in FIG. Therefore, even if all the one is wound and then the rest is wound, there is no difference in resistance, inductance, or number of magnetic fluxes between the coils due to that, so the above (2) The inconvenience is also eliminated.
[0022]
Further, a complicated circuit such as a detector or a smoothing circuit can be used without using complicated circuits such as the bandpass filters 36x and 36y, the synchronous detection circuits 37x and 37y, and the frequency multiplication circuit 35 shown in FIG. Since an output can be obtained, the above-mentioned inconvenience (3) is also eliminated.
[0023]
In this magnetic field detection device, for example, by arranging the magnetic path forming member so that the surface including the closed magnetic path is parallel to the parallel magnetic field such as the geomagnetism, the orientation of the parallel magnetic field is the same as the sensor shown in FIG. And can be used to detect intensity.
[0024]
However, as another application, for example, a magnetic generator (permanent magnet or the like) is attached to one of the two members that move relative to each other, and the magnetic field detection device is attached to the other member in proximity to the magnetic generator. Thus, it can also be used as a position detection device that obtains an output corresponding to the relative movement of these two members.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of the structure of a magnetic field detection unit of a magnetic field detection apparatus according to the present invention, in which A is a plan view and B is a cross-sectional view along line XX ′ along A's X axis.
[0026]
The magnetic field detector 1 includes a magnetic path forming member 2 and coils X1, X2, and Y1.
The magnetic path forming member 2 is made of permalloy, which is a kind of high permeability magnetic material, and has a ring-shaped closed magnetic path. The dimensions of this ring are, for example, an outer diameter of 10 mm, a ring cross-section width of 0.2 mm, and a ring cross-section thickness of 0.05 mm (however, other dimensions may be used).
[0027]
A pair of coils X1 and X2 are wound around the Y axis direction of two rings (X axis and Y axis in the figure) of the ring of the magnetic path forming member 2 that are orthogonal to each other. A coil Y1 is wound around one of the locations facing each other in the X-axis direction. The coils X1, X2, Y1 all have the same number of windings.
[0028]
As is apparent from the figure, the coils X1, X2, and Y1 are individually wound at different locations on the ring, so that it is easy to wind these coils uniformly.
[0029]
In addition, since these coils do not cross each other, even if any one of them is wound and then the rest is wound, this causes a difference in resistance and inductance between the coils. There is no difference in the number of magnetic fluxes penetrating these coils due to the excitation voltage described later.
[0030]
The magnetic path forming member 2 is mounted on the three bobbins 22a to 22c so as to expose only one of the two opposing locations in the Y-axis direction and the two opposing locations in the X-axis direction. In this state, the coils X1, X2, and Y1 are wound around the magnetic path forming member 2. As a result, the coils X1, X2, and Y1 can be accurately positioned and wound at locations on the ring in the Y-axis and X-axis directions, respectively.
For each of the coils X1, X2, and Y1, a terminal P1 connected to one end thereof and the remaining generally connected terminal P2 are attached to the bobbins 22a to 22c.
[0031]
FIG. 2 shows an example of the magnetic field-impedance characteristic of the magnetic field detector 1 (relationship between the direction and intensity of the magnetic field applied to the coils X1 to Y1 and the impedance of the coils X1 to Y1). Regardless of the direction of the magnetic field, when the magnetic field becomes stronger, the magnetic permeability of the magnetic path forming member 2 becomes smaller, thereby reducing the impedance of the coils X1 to Y1, and conversely, when the magnetic field becomes weaker, the magnetic path forming member 2 As the magnetic permeability increases, the impedance of the coils X1 to Y1 increases. Such an impedance change is generated almost linearly even by a weak magnetic field such as geomagnetism. When the magnetic field intensity changes by 1 Oe, the impedance changes by about 10%, and the impedance changes by about 50% as a whole.
[0032]
As a modification of the magnetic field detector, the magnetic path forming member may be made of a material having a high magnetic permeability other than permalloy (for example, ferrite or amorphous alloy). A shape having a closed magnetic circuit (for example, a rectangular shape or a triangular shape) may be used. FIG. 3 shows an example of using a magnetic path forming member 2 ′ having a rectangular closed magnetic path in the same manner as FIG.
[0033]
FIG. 4 shows an example of the entire circuit configuration of the magnetic field detection apparatus according to this embodiment (illustration of bobbins 22a to 22c is omitted in the figure).
The excitation unit 3 includes a high-frequency oscillator 4, an amplifier 5, and resistors R4, R5, and R6.
[0034]
The high-frequency oscillator 4 applies a multivibrator circuit and eliminates chattering by a Schmitt inverter IC1 having hysteresis. The high frequency oscillator 4 oscillates a pulse wave having a frequency in the range of several tens of kHz to several MHz (for example, about 1 MHz) and a duty ratio of about 1/10. By increasing the oscillation frequency in this way, output response can be improved.
[0035]
This pulse wave is amplified by the amplifier 5 and supplied to one end of each of the coils X1 to Y1 via the terminal P1 in FIG. On the other hand, the other ends of the coils X1, X2, and Y1 are connected to a common DC power source (not shown) (voltage B) via resistors P4, R6, and R5 having the same resistance value via the terminal P2 in FIG. Thus, an excitation voltage is applied to each of the coils X1, X2, and Y1.
[0036]
Specifically, the peak value of the excitation voltage is made substantially equal to the voltage B of the DC power supply, and the resistances of the resistors R4, R5, and R6 are set so that the magnetic field strength due to the excitation voltage of this peak value becomes Hd in the figure. A value shall be set.
[0037]
Note that an oscillation circuit that oscillates a sine wave may be provided in the excitation unit 3 instead of the high-frequency oscillator 4 that oscillates a pulse wave. However, it is more preferable to use a pulse wave rather than a sine wave from the viewpoint of saving current consumption and improving the sensitivity of the element.
[0038]
The output unit 6 includes a detector 7 and a smoothing circuit 8.
The detector 7 is connected to a connection midpoint a between the coil X1 and the resistor R4 and connected to a diode D1 for detecting the excitation voltage of the coil X1 and a connection midpoint c between the coil Y1 and the resistor R5. A diode D2 for detecting the excitation voltage of the coil Y1, and a diode D3 for detecting the excitation voltage of the coil X2 connected to the connection midpoint b between the coil X2 and the resistor R6.
[0039]
The smoothing circuit 8 includes resistors R7, R8, and R9, capacitors C2, C3, C4, C5, and C6, volumes VR1 and VR2 for adjusting the DC component of the output voltage, and volumes VR3 and VR3 for adjusting the gain of the output voltage. VR4, which has a time constant sufficiently larger than the excitation voltage period of the excitation unit 3, a voltage Vx1 obtained by smoothing the excitation voltage of the coil X1, a voltage Vy obtained by smoothing the excitation voltage of the coil Y1, and a coil X2. The voltage Vx2 obtained by smoothing the excitation voltage is output.
Thus, the output unit 6 has a simple configuration using a small number of diodes, resistors, capacitors, and volumes.
[0040]
A detection method when this magnetic field detection device is used as a device for detecting the direction and intensity of a parallel magnetic field is as follows.
As described above, the coils X1 to Y1 can be wound uniformly without crossing each other, the number of windings is all equal (thus, their resistance value and inductance are equal to each other), and the resistors R4 to R6 Since the resistance values are all equal, the excitation voltages applied to the coils X1 to Y1 are all equal when the magnetic field detection device is not placed in a parallel magnetic field.
Therefore, in this case, the output voltages Vx1, Vy, Vx2 of the smoothing circuit 8 are lower than the voltage of the DC power supply and equal to each other (referred to as voltage E).
[0041]
On the other hand, when the magnetic field detection device is placed in the parallel magnetic field H as shown in FIG. 4, the magnetic field strength of the coil X1 increases to Hd + Hx, so that the coil X1 as shown in FIG. The impedance of becomes smaller. Therefore, since the excitation voltage applied to the coil X1 becomes small, the output voltage Vx1 becomes smaller than E.
[0042]
On the other hand, in the coil X2, since the magnetic field intensity decreases to Hd−Hx, the impedance of the coil X1 increases. Accordingly, since the excitation voltage applied to the coil X2 becomes large, the output voltage Vx2 becomes larger than E.
[0043]
Further, when the orientation of the X-axis component Hx is opposite to that shown in FIG. 4, the output voltage Vx1 is larger than E and the output voltage Vx2 is smaller than E.
[0044]
As described above, the output voltages Vx1 and Vx2 are signals whose levels vary according to the strength of the X-axis component Hx with the voltage E as the center, and their phases are shifted from each other by 180 degrees.
[0045]
The same applies to the coil Y1, and the output voltage Vy is a signal whose level varies depending on the strength of the Y-axis component Hy with the voltage E as the center. However, the phase of this signal is shifted by 90 degrees with respect to the signals Vx1 and Vx2 because the X-axis component Hx and the Y-axis component Hy are orthogonal to each other.
As a result, three-phase signals Vx1, Vy, and Vx2 having a phase difference of 90 degrees are obtained. FIG. 5 shows the phase relationship of the three-phase signal as a vector.
[0046]
Here, in order to calculate the azimuth of the parallel magnetic field H, in principle, it is sufficient to have two-phase signals whose phases are shifted by 90 degrees from each other. Therefore, only Vx1 and Vy of the three-phase signals, or Only Vx2 and Vy need be used. However, each of the signals Vx1, Vy, and Vx2 includes a voltage E that is an offset voltage that is not related to the magnetic field. Since this voltage E fluctuates due to a drift due to a temperature difference, for example, when the magnetic field detection device is used in a severe environment such as a temperature change such as a car navigation system, the fluctuation amount becomes an error and the detection accuracy is increased. It gets worse.
[0047]
Therefore, the differential signal A (A = Vy−Vx1) between the signals Vx1 and Vy is obtained, and the differential signal B (B = Vy−Vx2) between the signals Vx2 and Vy is obtained. As shown in FIG. 5, the signals A and B are excluded from the offset voltage E and are out of phase with each other by 90 degrees. Therefore, the direction of the parallel magnetic field H can be detected with high accuracy by using the signals A and B.
[0048]
FIG. 6 shows the magnetic field detection apparatus in which the magnetic field detector 1 (here, the shape is schematically shown) is arranged in parallel to the ground surface as shown in FIG. 7 (that is, the XY plane in FIG. 1 is parallel to the ground surface). The measurement example of the rotation angle-output characteristics (relationship between the rotation angle and the signals A and B) when rotating around the Z axis perpendicular to the ground surface (and hence the XY plane) in the state is shown. As the signals A and B, it is shown that sine waves whose phases are shifted by 90 degrees can be obtained.
[0049]
Next, the detection method when this magnetic field detection device is used as a position detection device is as follows.
As shown in FIG. 8, a magnetism generator (permanent magnet or the like) 11 is attached to one member of two members (not shown) that relatively move in a machine tool or the like to be detected. Further, the magnetic field detection device having the configuration shown in FIG. 4 (here, the excitation unit 3 and the output unit 6 are shown in a simplified manner) is placed close to the magnet generator 11 on the remaining one of the two members. Let it attach. At this time, the positional relationship between the coils X1 to Y1 of the magnetic field detection unit 1 is such that the coils X1 and X2 are aligned on the relative movement direction (Y-axis direction in the figure) and that the coil Y1 faces the magnet generator 11. deep.
[0050]
Then, due to the magnetic field from the magnetism generator 11, in the coils X1 and X2, the strength of the magnetic field is Hd−Hs1 (where Hs1 is the X-axis component of the magnetic field from the magnetism generator 11 at the distance from the magnetism generator 11 to the coils X1 and X2). In the coil Y1, the magnetic field intensity is Hd + Hs2 (where Hs2 is the intensity of the Y-axis component of the magnetic field from the magnet generator 11 at the distance from the magnet generator 11 to the coil Y1).
[0051]
The strength Hs1 of the X-axis component is minimized at the central portion of the magnet generator 11 in the Y-axis direction, increases as it deviates from this central portion, and in the vicinity of the edge portion of the magnet generator 11 in the Y-axis direction. Become the maximum. In addition, the strength Hs2 of the Y-axis component becomes maximum at the central portion of the magnetic generator 11 in the Y-axis direction, and decreases as it deviates from this central portion, and in the vicinity of the edge portion of the magnetic generator 11 in the Y-axis direction. Be minimized.
[0052]
Accordingly, the output voltages Vx1, Vy, and Vx2 from the output unit 6 are three-phase signals having a phase difference of approximately 90 degrees as shown in FIG. 9 according to the relative positions of the magnetic field detection unit 1 and the magnet generator 11. It becomes. (Note that this phase difference varies depending on the size of the magnetism generator 11, the distance between the magnetism generator 11 and the magnetic field detector 1, etc., but by setting them appropriately, the phase difference can be made approximately 90 degrees. is there.)
[0053]
Here, the differential signal C between the signals Vx1 and Vx2 is obtained, and the relationship between the signal C and the signal Vy is shown in FIG. 10A. Therefore, for example, by obtaining a gate signal G as shown in FIG. 10B from the signal Vy and performing servo control using the signal C as a position detection signal within the operation range of the gate signal G, the linearity of the detection signal is good. The stable point of the servo can be positioned within a certain range.
[0054]
In the above embodiment, the winding layer locations of the three coils on the closed magnetic path of the magnetic path forming member need not be limited to the locations shown in FIG. For example, depending on what phase relationship the three-phase signals Vx1, Vy, and Vx2 are desired to be made, the place where these three coils are wound may be determined (for example, the phases of the signals Vx1, Vy, and Vx2 are These three coils may be wound in places where they are shifted by 120 degrees). Or you may make it determine the location which winds these three coils according to convenience, such as the shape of a magnetic path formation member, and the space which winds a coil.
[0055]
Further, the present invention is not limited to the above-described embodiments, and various other configurations can be taken without departing from the gist of the present invention.
[0056]
【The invention's effect】
As described above, according to the magnetic field detection apparatus of the present invention, the following effects can be obtained.
(1) Uniform winding of the coil is easy. For example, the winding is performed with the magnetic path forming member mounted on the bobbin so that the coil is accurately positioned at a predetermined position on the closed magnetic path. Can be disguised. Therefore, it is possible to prevent the detection accuracy from being deteriorated due to non-uniform winding, and to improve the detection accuracy of the azimuth and strength of the parallel magnetic field and the detection accuracy of the position of the relative moving member.
[0057]
(2) Since the coils do not cross each other, there is no difference in the resistance and inductance between the coils, and no difference in the number of magnetic fluxes penetrating these coils due to the excitation voltage described later. Therefore, also in this respect, it is possible to improve the detection accuracy of the direction and intensity of the parallel magnetic field and the detection accuracy of the position of the relative moving member.
(3) Since the output can be obtained by a circuit having a relatively simple configuration such as a detector or a smoothing circuit, the circuit configuration is simplified and the cost of the apparatus can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a structure of a magnetic field detection unit.
FIG. 2 is a diagram illustrating an example of a magnetic field-impedance characteristic of a magnetic field detection unit.
FIG. 3 is a diagram illustrating a modification example of a magnetic field detection unit.
FIG. 4 is a diagram illustrating an example of an overall circuit configuration of a magnetic field detection device.
FIG. 5 is a diagram showing a phase relationship of a three-phase signal.
FIG. 6 is a diagram illustrating an example of a rotation angle-output characteristic of a magnetic field detection device.
FIG. 7 is a diagram illustrating an example of how the magnetic field detection apparatus is used.
FIG. 8 is a diagram illustrating an application example of a magnetic field detection device.
9 is a diagram showing a phase relationship of three-phase signals in the example of FIG.
10 is a diagram illustrating an example of a signal obtained from the three-phase signal of FIG.
FIG. 11 is a diagram illustrating an example of a configuration of a conventional magnetic field detection device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Magnetic field detection part, 2 Magnetic path formation member, 3 Excitation part, 4 High frequency oscillator, 5 Amplifier, 6 Output part, 7 Detector, 8 Smoothing circuit, 22a, 22b, 22c Bobbin, X1, X2, Y1 coil, R4 R5, R6 resistors

Claims (3)

A magnetic field detector including a magnetic path forming member having a closed magnetic path made of a high permeability magnetic material, and three coils respectively wound at different locations on the closed magnetic path;
An excitation unit for applying an excitation voltage to the coil;
An output unit that detects and smooths the excitation voltage applied to the coil and outputs the excitation voltage. A magnetic field detection device characterized in that a three-phase output corresponding to an external magnetic field is obtained from the unit. 2. The magnetic field detection apparatus according to claim 1, wherein a two-phase signal having a phase difference of 90 degrees is obtained from the three-phase output, and an external magnetic field is detected by the signal. 3. The magnetic field detection device according to claim 1, wherein the three coils are wound around a position on the closed magnetic path in such a positional relationship that a phase difference between the outputs of the three phases is 90 degrees. Magnetic field detection apparatus characterized by the above.

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