JP2003194901A - Magnetic field sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic field sensor capable of achieving compactness and detecting the absolute location of a movable body with high resolution. <P>SOLUTION: The magnetic field sensor is provided with a polarized body 80 in which north and south magnetic poles are alternately polarized in the direction A of movement, a magneto-resistance effect element 90 which is provided with a magneto-resistance pattern 93 for its surface and of which the resistance value changes according to changes in a magnetic field inn the direction which intersects with the longitudinal direction of the magneto-resistance pattern 93 at right angles due to relative movement to the polarized body 80, and a bias magnetic 10 which impresses a bias magnetic field in parallel with the longitudinal direction of the magneto-resistance pattern 93. The bias magnet 10 moves with the movement of the polarized body 80, and the distance of separation of the bias magnet 10 from the magneto-resistance pattern 93 is changed in such a way that the intensity of the bias magnetic field to the magneto-resistance pattern 93 is changed according to its moving location. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field sensor for detecting a moving position and a rotation angle of a moving body by utilizing a resistance change of a magnetoresistive effect element.

[0002]

2. Description of the Related Art Conventionally, there is a stepping motor, for example, as a device which requires position detection with high resolution. Rotational position detection methods for stepping motors include a method of electrically counting the number of step pulses and indirectly detecting the rotational position, and a method of obtaining the rotational position of the stepping motor as a change in its resistance value with a potentiometer. .

On the other hand, as a non-contact type position detecting means instead of a contact type position detecting means such as a potentiometer, a light source and a light receiving element using a photo coupler are provided on both sides of a shield plate (rotating plate) attached to a stepping motor. Set up,
There is also a method of detecting the rotation position of the slit provided on the shield plate by the number of times the photocoupler detects the slit. Further, instead of the photocoupler, N and S magnetic poles are alternately magnetized around the outer circumference of the rotating body attached to the stepping motor,
There is also a method in which a magnetoresistive effect element is installed at a position facing the outer circumference, and an alternating signal generated in the magnetoresistive effect element by rotation of a rotating body is counted to detect the rotational position.

However, the position detecting method for counting the step pulse number of the stepping motor is affected by the inertia of the object to be moved, and therefore the actual motor rotation number and the step pulse number do not always match, and the step number once If it goes out of order, there is a problem that a detection error remains unless it is returned to the reference position again.

The position detection method using a potentiometer must be used after correcting because the resistance value of the potentiometer varies, and at the same time, a contact must be used in the output section, resulting in a problem of life and sliding noise. Poor resolution is a problem.

The position detection method using a photocoupler has good life characteristics because it is non-contact, but when the shielding plate is rotated at a high speed, the amount of light passing through the slit is extremely reduced and the resolution cannot be improved. There is a problem.

In contrast to each of the above position detecting methods, the position detecting method using a magnetoresistive effect element has good life characteristics because of non-contact, has less noise, and has a rotating body magnetized with N and S magnetic poles. Since the alternating signal can be easily counted even when rotating at high speed, the resolution is high, and from these points, it is suitable as the position detecting means. However, the conventional position detection method using the magnetoresistive effect element has only the function of counting alternating signals. Therefore, in order to obtain the absolute position of the rotating body, the reference point of the rotating body is detected separately and the position of the rotating body is determined. We must add a means to return to.

The means for detecting the reference point and returning the rotating body to that position is also necessary for the position detecting method by the photocoupler, but in the case of the position detecting method by the photocoupler, the slit pattern arrangement is devised. In addition, in the case of the method of detecting by adding, and the method of detecting the position by the magnetoresistive effect element, the reference point (absolute position) can be detected by a method of detecting by devising the pattern arrangement of the magnetoresistive effect element. However, in either case, there arises a problem that the shield plate becomes larger and the magnetoresistive effect element becomes larger.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to provide a magnetic field sensor which can be downsized and which can detect the absolute position of a moving body with high resolution. To do.

[0010]

In a general magnetic field sensor using a magnetoresistive effect element, for example, as shown in FIG. 1, N and S magnetic poles are alternately magnetized in a moving direction (linear direction) A. Bar-shaped magnetized body 80 and the magnetized body 80 of the substrate 91
And a magnetoresistive effect element 90 having a magnetoresistive pattern 93 provided on the surface opposite to. The gap between the magnetized body 80 and the magnetoresistive effect element 90 is equal to the magnetized body 8
It is almost half of the magnetization pitch λ of the N and S magnetic poles to 0.

The magnetoresistive effect element 90 is shown in FIG. 2, but the magnetoresistive pattern 93 formed on the substrate 91 is
It is configured by providing a first pattern portion R1 and a second pattern portion R2. Both of the pattern portions R1 and R2 are formed by forming a nickel iron (permalloy) ferromagnetic alloy thin film so as to be elongated and linear and bent into a substantially U-shape, and the both pattern portions R1 and R2 are connected in series. Both pattern parts R1,
The connection point of R2 is the output signal terminal Vout, one end is the power supply voltage terminal Vcc, the other end is the ground terminal GND, and a DC voltage is applied between the power supply voltage terminal Vcc and the ground terminal.
The configuration is such that an output is obtained from the output signal terminal Vout.

On the other hand, FIG. 3 shows one pattern portion R1 (or R
It is a figure which shows (DELTA) R / R-H characteristic at the time of applying the magnetic field Hx of the direction orthogonal to the longitudinal direction of 2). As shown in the figure, when the input magnetic field waveform to the pattern portion R1 changes, the output resistance value change rate waveform of the pattern portion R1 changes at a predetermined change rate. The distance L between the pattern portions R1 and R2 shown in FIG. 2 is L = λ · (n + 1/2) times when the magnetic pole distance between the adjacent N and S magnetic poles of the magnetized body 80 shown in FIG. 1 is λ. [However, n is 0 or a positive integer]. Therefore, for example, one pattern portion R1 has the highest magnetic field Hx.
, The other pattern portion R2 is located at the position where the magnetic field Hx is weakest, and conversely one pattern portion R2 is located.
When 1 is at the position where the magnetic field Hx is the weakest, the other pattern portion R2 is located at the position where the magnetic field Hx is the strongest, and the difference between the resistance values of the pattern portions R1 and R2 changes and the output signal terminal The output voltage of Vout can have a substantially sine waveform as shown in FIG.

However, as described above, the absolute position of the magnetized body 80 with respect to the magnetoresistive effect element 90 cannot be detected only with the signal waveform. Therefore, the inventor of the present application pays attention to the fact that the ΔR / RH characteristic curve shown in FIG. 3 changes by changing the strength of the bias magnetic field applied to the magnetoresistive effect element 80, and utilizes this phenomenon. The absolute position of the magnetized body 80 with respect to the magnetoresistive effect element 90 is detected with high resolution.

FIG. 5 is a diagram showing ΔR / RH characteristics when a magnetic field Hy in the longitudinal direction of one pattern portion R1 (or R2) and a magnetic field Hx in a direction orthogonal to the magnetic field Hy are applied. . When the strength of the magnetic field Hy is changed as shown in FIG.
The ΔR / RH characteristic curve changes, and the resistance value change rate ΔR / R (%) decreases as the strength of the magnetic field Hy increases. That is, although the resistance value of the pattern portion R1 changes with respect to the change of the input magnetic field to the pattern portion R1, the change rate of the resistance value when the bias magnetic field Hy is strongly applied is smaller than the resistance value when the bias magnetic field Hy is weakly applied. Small compared to the rate of change. For example, as shown in the figure, even if the input magnetic field (input magnetic field waveform) to the pattern portion R1 has the same amplitude, the bias magnetic field Hy = 0 (Oe) and the bias magnetic field Hy.
= 30 (Oe), the amplitude of the output resistance value change rate waveform greatly changes. Then, for example, when moving the position of the magnetized body 80 with respect to the magnetoresistive effect element 90 shown in FIG. 1, the magnetoresistive effect element 90 is moved according to the position of the magnetized body 80.
The strength of the bias magnetic field Hy applied to the
If it changes in the range of (Oe), unlike the case of FIG. 4, the amplitude of the output voltage of the output signal terminal Vout of the magnetoresistive effect element 90 changes as shown in FIG.

Therefore, if the strength of the bias magnetic field Hy applied to the magnetoresistive effect element 90 is changed according to the position of the magnetized body 80 with respect to the magnetoresistive effect element 90, the output signal terminal Vout outputs the signal. The absolute position of the magnetized body 80 with respect to the magnetoresistive effect element 90 can be easily measured depending on the magnitude of the output voltage.

Therefore, the magnetic field sensor according to the present invention is installed at a position facing a magnetized body in which N and S magnetic poles are alternately magnetized in the moving direction and a magnetized surface of the N and S magnetic poles of the magnetized body. And a magnetoresistive element whose resistance value changes in response to a change in the magnetic field in a direction orthogonal to the longitudinal direction of the magnetoresistive pattern due to relative movement with the magnetized body. In the magnetic field sensor
A bias magnet that applies a bias magnetic field parallel to the longitudinal direction of the magnetoresistive pattern and moves with the movement of the magnetized body to change the strength of the bias magnetic field to the magnetoresistive pattern according to the movement position is installed. Is characterized by.

The magnetizing directions of the N and S magnetic poles on the magnetized body may be linear or arcuate. When the magnetizing direction is linear, the relative movement direction between the magnetizing body and the magnetoresistive effect element is the linear direction, and when the magnetizing direction is arcuate, the relative moving direction between the magnetizing body and the magnetoresistive effect element is. It becomes the direction of rotation.

In order to change the strength of the bias magnetic field applied to the magnetic resistance pattern, the distance between the bias magnet and the magnetic resistance pattern may be changed according to the moving position of the magnetized body. That is, for example, when the relative movement direction between the magnetized body and the magnetoresistive effect element is a linear direction, a bias magnet formed and installed linearly in a long direction toward the straight direction of the magnetized body is used as the magnetoresistive effect element. It may be installed at an angle so that the separation distance of is gradually changed. For example, when the relative movement direction between the magnetized body and the magnetoresistive effect element is an arc direction, a bias magnet that is formed and installed in a long arc shape in the direction of rotation of the magnetized body is used as the center axis of rotation of the magnetized body. The distance between the magnetoresistive effect element and the magnetoresistive effect element may be changed by installing so as to be eccentrically rotated when the element rotates.

In order to change the strength of the bias magnetic field applied to the magnetoresistive pattern, the strength of the magnetic field of the bias magnet itself may be changed according to the location of the bias magnet. That is, for example, when the relative movement direction between the magnetized body and the magnetoresistive effect element is a linear direction, the width and thickness of the bias magnet formed and installed linearly in a long direction toward the straight direction of the magnetized body are By gradually changing in the longitudinal direction, the strength of the magnetic field of the bias magnet itself may be changed according to the location of the bias magnet. Also, for example, when the relative movement direction between the magnetized body and the magnetoresistive effect element is an arc direction,
By gradually changing the width and thickness of the bias magnet itself, which is formed and installed in an arc shape in the direction of rotation of the magnetized body, in the direction of rotation, the strength of the magnetic field of the bias magnet itself can be changed. It may be changed according to.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIG. 7 is a diagram showing a magnetic field sensor (straight line position detecting device) according to a first embodiment of the present invention. In this magnetic field sensor, the relative movement direction between the magnetized body 80 and the magnetoresistive effect element 90 is a linear direction, and the bias magnet 10 changes the distance from the magnetic resistance pattern 93 according to the moved position of the magnetized body 80. It is of structure.

That is, in the magnetic field sensor according to the first embodiment, a bias magnet is provided on the same back surface side of the magnetized body 80 as the magnetic field sensor shown in FIG. 1 (the opposite side of the magnetized body 80 on which the magnetoresistive effect element 90 is installed). 10 are installed and configured.
The bias magnet 10 is composed of a long rod-shaped body having substantially the same length as the rod-shaped magnetized body 80, and has an N pole on the upper surface and an S pole on the lower surface.
The magnetic poles are evenly magnetized over the entire length of their sides. As a result, the lines of magnetic force radiated from the N magnetic pole to the outside are generated by both pattern portions R1 and R2 of the magnetoresistive effect element 90 (see FIG. 2).
Is applied as a bias magnetic field parallel to its longitudinal direction.

At the same time, the bias magnet 10 is installed obliquely with respect to the magnetized body 80 so that the distance from the magnetoresistive effect element 90 gradually changes in the straight traveling direction of the magnetized body 80 (direction of arrow A). Has been done. That is, in FIG. 7, the distance between the magnetized body 80 and the bias magnet 10 is different on the left and right (K1 ≠ K2). Although the magnetized body 80 and the bias magnet 10 are shown separated from each other in the figure, in reality, both are fixed integrally at any place, and the bias magnet 10 also moves linearly with the linear movement of the magnetized body 80.

According to the magnetic field sensor provided with the bias magnet 10, as described above, the alternating magnetic field by the magnetized body 80 is applied to the magnetoresistive effect element 90, and at the same time, the bias magnetic field by the bias magnet 10 is applied. , As shown in FIG. 8, depending on the position of the magnetized body 80, the output signal terminal V
The amplitude of the output voltage of out changes. Therefore, the absolute position of the magnetized body 80 can be immediately and easily obtained.
Of course, the moving speed and the moving direction of the magnetized body 80 can also be obtained at the same time from the state where the frequency and amplitude of the output voltage of the output signal terminal Vout increase or decrease.

[Second Embodiment] FIG. 9 shows a second embodiment of the present invention.
It is a figure which shows the magnetic field sensor (linear position detection apparatus) concerning. In this magnetic field sensor, the relative movement direction between the magnetized body 80 and the magnetoresistive effect element 90 is a linear direction, and the strength of the magnetic field of the bias magnet 10 itself is changed according to the location of the bias magnet 10. Is.

The magnetic field sensor according to the second embodiment differs from the magnetic field sensor shown in FIG. 7 only in the shape of the bias magnet 10 and its installation position. That is, the bias magnet 10 is attached to the back surface side of the magnetized body 80 (opposite side of the magnetized body 80 on which the magnetoresistive effect element 90 is installed) so as to make surface contact in parallel with the magnetized body 80, but the shape thereof is rod-like. The magnetized body 80 is a long rod-shaped body having substantially the same length, and its thickness in the height direction gradually changes from one side to the other side. The magnetic pole is magnetized over its entire length. As a result, the magnetic field lines emitted from the N magnetic pole to the outside are applied as a bias magnetic field parallel to the longitudinal direction of the pattern portions R1 and R2 (see FIG. 2) of the magnetoresistive effect element 90. The strength of the magnetic field radiated from is stronger as the thickness in the height direction is thicker, and weaker as the thickness is thinner. Therefore, the strength of the bias magnetic field applied varies depending on the positions of the magnetized body 80 and the bias magnet 10.

In FIG. 9, the magnetized body 80 and the bias magnet 1
Although 0 and 0 are directly adhered and fixed, it is not necessary to adhere them to each other, and they may be installed separately. The point is that the bias magnet 10 may move linearly as the magnetized body 80 moves linearly.

Also in the case of the magnetic field sensor in which the bias magnet 10 is installed, the magnetized body 80 is attached to the magnetoresistive effect element 90.
At the same time as the application of the alternating magnetic field by the bias magnet 1
A bias magnetic field of 0 is applied, and the amplitude of the output voltage of the output signal terminal Vout changes depending on the position of the magnetized body 80, as shown in FIG. Therefore, the absolute position of the magnetized body 80 can be immediately and easily obtained. Of course, the moving speed and the moving direction of the magnetized body 80 can also be obtained at the same time from the state where the frequency and amplitude of the output voltage of the output signal terminal Vout increase or decrease.

By the way, as a method of identifying the moving directions of the magnetized body 80 and the bias magnet 10, as shown in FIG. 10B, first and second pattern portions R1 (R1-1, R2), R1 are formed.
Two pairs of 2 (R2-1, 2) are provided to output signal terminal Vout
Of the first and second pattern portions R1- so that the phase difference between the two phases A and B is 90 °.
1, R1-2, R2-1, R2-2 are arranged so that the A-phase output is generated when the magnetized body 80 is moved to the right and to the left as shown in FIG. It is also possible to use a method of measuring the moving direction by measuring the difference in the appearance timing of the peak value of the signal and the peak value of the B-phase output signal. It goes without saying that this method can be used in the first embodiment and also in the following third and fourth embodiments.

[Third Embodiment] FIG. 11 is a diagram showing a magnetic field sensor (rotational position detecting device) according to a third embodiment of the present invention. In this magnetic field sensor, the relative movement direction between the magnetized body 80 and the magnetoresistive effect element 90 is the rotation direction, and the separation distance between the bias magnet 10 and the magnetoresistive pattern 93 changes according to the moved position of the magnetized body 80. It is of structure.

That is, the magnetic field sensor according to the third embodiment has a magnetized body 80 in which N and S magnetic poles are alternately magnetized on the outer circumferential surface of the circumference in the moving direction (rotational direction) C, and the outer circumference of the magnetized body 80. The magnetoresistive effect element 90 arranged close to the surface side (magnetized surface side) and the inner surface side of the magnetized body 80 (opposite side of the magnetized body 80 where the magnetoresistive effect element 90 is installed). And a bias magnet 10. The bias magnet 10 is ring-shaped and has an N magnetic pole on its upper surface and an S magnetic pole on its lower surface, which are evenly magnetized over the entire length of its upper and lower sides. As a result, the magnetic field lines emitted from the N magnetic pole to the outside are applied to both pattern portions R1 and R2 of the magnetoresistive effect element 90 as a bias magnetic field parallel to the longitudinal direction thereof.

The bias magnet 10 is fixed to the magnetized body 80 by a fixing means (not shown) and rotates together with the magnetized body 80 about the rotation center axis L1 of the magnetized body 80.
Is a predetermined center L2 of the bias magnet 10 with respect to the rotation center axis L1 of the magnetized body 80 so that the separation distance from the magnetoresistive effect element 90 gradually changes in the rotation direction of the magnetized body 80 (direction of arrow C). The dimensions are eccentric.

According to the magnetic field sensor provided with the bias magnet 10, the magnetized body 80 is attached to the magnetoresistive effect element 90.
At the same time as the application of the alternating magnetic field by the rotation of the bias magnet 10, the bias magnetic field by the bias magnet 10 is applied, and as shown in FIG. 12, the output signal terminal Vou depends on the position of the magnetized body 80.
The amplitude of the output voltage of t changes in one rotation and one cycle. Therefore, the absolute position of the magnetized body 80 can be immediately and easily obtained. Of course, the rotation speed of the magnetized body 80 can also be obtained at the same time from the frequency of the output voltage of the output signal terminal Vout.

[Fourth Embodiment] FIG. 13 is a view showing a magnetic field sensor (rotational position detecting device) according to a fourth embodiment of the present invention. In this magnetic field sensor, the relative movement direction between the magnetized body 80 and the magnetoresistive effect element 90 is the rotation direction, and the strength of the magnetic field of the bias magnet 10 itself is changed according to the location of the bias magnet 10. Is.

That is, the magnetic field sensor according to the fourth embodiment has a magnetized body 80 in which N and S magnetic poles are alternately magnetized on the outer peripheral portion of the upper surface of the disk in the moving direction (rotational direction) C and the magnetized body 8.
0 and a magnetoresistive effect element 90 arranged close to the outer peripheral upper surface side (magnetized surface side) and the lower surface side of the magnetized body 80 (magnetized body 80).
And a bias magnet 10 installed on the side opposite to the side on which the magnetoresistive effect element 90 is installed.
The bias magnet 10 is ring-shaped and is magnetized over its entire circumference so that the outer circumferential side has an N magnetic pole and the inner circumferential side has an S magnetic pole from the inner circumferential side to the outer circumferential side. As a result, the magnetic field lines emitted from the N magnetic pole to the outside are applied to both pattern portions R1 and R2 of the magnetoresistive effect element 90 as a bias magnetic field parallel to the longitudinal direction thereof.

The bias magnet 10 is fixed to the magnetized body 80 via the fixing means 70 and rotates together with the magnetized body 80 about the rotation center axis L1 of the magnetized body 80, but the bias magnet 10 rotates the magnetized body 80. In the direction (arrow C direction), the strength of the magnetic field of the bias magnet 10 itself is changed.
The width of the bias magnet 10 from the inner circumference side to the outer circumference side is gradually changed so that the bias magnet 10 gradually changes depending on the location (t1 ≠ t2). That is, the strength of the magnetic field radiated from the bias magnet 10 is stronger as the width thereof is larger and weaker as the width thereof is smaller. Therefore, the strength of the bias magnetic field applied to the magnetoresistive effect element 90 depends on the rotational positions of the magnetized body 80 and the bias magnet 10. Change according to.

Also in the case of the magnetic field sensor in which the bias magnet 10 is installed, the magnetizing body 80 is attached to the magnetoresistive effect element 90.
At the same time as the application of the alternating magnetic field by the bias magnet 1
A bias magnetic field of 0 is applied, and as shown in FIG. 12, the amplitude of the output voltage of the output signal terminal Vout changes in one rotation and one cycle according to the position of the magnetized body 80. Therefore, the absolute position of the magnetized body 80 can be immediately and easily obtained. Of course, the rotation speed of the magnetized body 80 can also be obtained at the same time from the frequency of the output voltage of the output signal terminal Vout.

The present invention is suitable for use in, for example, positioning control of machine tools and arm angle control of robots that require high-resolution position detection and rotation angle detection.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the claims and the technical idea described in the specification and drawings. Can be modified. Note that any shape, structure, or material not directly described in the specification and drawings is within the scope of the technical idea of the present invention as long as the functions and effects of the present invention are exhibited. It goes without saying that various modifications can be made to the shape, structure, and arrangement structure of the magnetized body 80, the magnetoresistive effect element 90, and the bias magnet 10, for example. Further, the material of the magnetoresistive pattern 93 is the same as that of the above-mentioned embodiment as long as the ΔR / RH characteristic curve is changed by changing the bias magnetic field applied parallel to the longitudinal direction of the magnetoresistive pattern. It is not limited and various modifications are possible.

[0039]

As described in detail above, according to the present invention, a bias magnet is simply installed on a magnetic field sensor having a magnetized body and a magnetoresistive effect element, and a moving body with high resolution can be obtained. It is possible to provide a magnetic field sensor that can detect an absolute position and can be downsized.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration example of a general magnetic field sensor configured by using a magnetized body 80 and a magnetoresistive effect element 90.

FIG. 2 is a perspective view showing a magnetoresistive effect element 90.

FIG. 3 is a diagram showing ΔR / RH characteristics when a magnetic field Hx is applied to a pattern portion R1 (or R2).

4 is a magnetoresistive effect element 90 of the magnetic field sensor shown in FIG.
5 is a diagram showing the output voltage of the output signal terminal Vout of FIG.

FIG. 5 is a diagram showing ΔR / RH characteristics when a magnetic field Hy and a magnetic field Hx are applied to a pattern portion R1 (or R2).

FIG. 6 is a diagram showing an output voltage of an output signal terminal Vout of the magnetoresistive effect element 90 when the strengths of a magnetic field Hy and a magnetic field Hx applied to the magnetoresistive effect element 90 are simultaneously changed.

FIG. 7 is a perspective view showing a magnetic field sensor (straight line position detection device) according to the first embodiment of the present invention.

8 is a magnetoresistive effect element 90 of the magnetic field sensor shown in FIG.
5 is a diagram showing the output voltage of the output signal terminal Vout of FIG.

FIG. 9 is a perspective view showing a magnetic field sensor (straight line position detecting device) according to a second embodiment of the present invention.

10 is a diagram showing a method of identifying the moving directions of the magnetized body 80 and the bias magnet 10. FIG.

FIG. 11 is a perspective view showing a magnetic field sensor (rotational position detection device) according to a third embodiment of the present invention.

12 is a diagram showing an output voltage of an output signal terminal Vout of the magnetoresistive effect element 90 of the magnetic field sensor shown in FIG.

FIG. 13 is a perspective view showing a magnetic field sensor (rotational position detection device) according to a fourth embodiment of the present invention.

[Explanation of symbols]

10 Bias magnet 80 Magnetized body 90 Magnetoresistive effect element 91 substrate 93 Magnetic resistance pattern R1 First pattern part R2 second pattern part

Claims (3)

[Claims] 1. A magnetized body in which N and S magnetic poles are alternately magnetized in a moving direction, and a magnetoresistive pattern disposed on a surface of the magnetized body facing the magnetized surface of the N and S magnetic poles. And a magnetoresistive effect element whose resistance value changes in response to a change in the magnetic field in a direction orthogonal to the longitudinal direction of the magnetoresistive pattern due to relative movement with the magnetized body. A bias magnet parallel to the longitudinal direction of the resistance pattern is applied, and a bias magnet that moves with the movement of the magnetized body and changes the strength of the bias magnetic field to the magnetoresistive pattern according to the movement position is installed. And magnetic field sensor. 2. The bias magnet changes the strength of a bias magnetic field applied to the magnetoresistive pattern by changing the distance between the bias magnet and the magnetoresistive pattern according to the moving position of the magnetized body. Item 1. The magnetic field sensor according to item 1. 3. The bias magnet changes the strength of the magnetic field of the bias magnet itself according to the location of the bias magnet, thereby changing the strength of the bias magnetic field to the magnetoresistive pattern. Item 1. The magnetic field sensor according to item 1.