JP3196102B2 - Small displacement detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the thickness of paper or sheet, the thickness of printing ink printed on paper or sheet, the vibration of the skin in response to the heartbeat, and the like. The present invention relates to a small displacement detector that detects displacement.

[0002]

2. Description of the Related Art As a method of measuring a change in the position of an object,
There is a method using a ferromagnetic magnetoresistive element. Here, the ferromagnetic magnetoresistive element changes its resistance value in accordance with a change in a magnetic field in a plane direction of a film of the ferromagnetic magnetoresistive element material.

To measure a change in the position of an object using the ferromagnetic magnetoresistive element, as shown in FIG. 9, a magnetoresistive element 401 having a ferromagnetic magnetoresistive element pattern formed on its surface is placed on a substrate 400. Attach, on the other hand, the DUT 40
5 is installed such that the lines of magnetic force enter the surface of the magnetoresistive element 401 almost horizontally.

When the object 405 is displaced in the direction of arrow b with respect to the substrate 400, the direction and strength of the magnetic field in the plane direction of the ferromagnetic element pattern film of the magnetoresistive element 401 change. With this, the displacement of the measured object 405 can be detected. The small displacement detector using the ferromagnetic magnetoresistive element has an advantage that the sensitivity (resistance change) per unit magnetic field is large.

[0005]

However, the magnet 4
03 must be shifted to a position other than immediately below the magnetoresistive element 401, so that not only is it difficult to determine its position, but also the position of the magnet 403 is in the left-right direction (the direction of the arrow c shown in FIG. 9) or on the paper surface. There is a drawback that the strength and direction of the magnetic field with respect to the magnetoresistive element 401 greatly change only by a slight shift in the front and rear directions, and the desired output cannot be obtained.

[0006] In order to solve this drawback, the applicant of the present application has disclosed in an earlier application (Japanese Patent Application No. 6-232361)
A small displacement detector having a structure as shown in FIG. 10 has been proposed.

In this minute displacement detector, a magnet 415 is mounted on a movable film 411 and a substrate 419 just above the magnet 415 is mounted.
A soft magnetic material 419 is mounted thereon, and magnetoresistive elements 421 and 421 are mounted on both left and right sides of the soft magnetic material 419.
23 and 423 are attached.

According to this minute displacement detector, the magnet 415
Are attracted to the soft magnetic body 419, and many of the attracted magnetic force lines are forcibly induced in the directions of the soft magnetic bodies 423 and 423, whereby a large number of magnetic force lines are applied to the magnetoresistive elements 421 and 421 located therebetween. Collected and incident almost parallel to it. Therefore, even if the magnet 415 changes slightly in the vertical direction, the number of lines of magnetic force also changes greatly, and the amount of positional displacement can be detected as a good signal with a large S / N ratio.

[0009] However, this micro-displacement detector can obtain the expected performance when it is used in a stationary state. However, when this detector is mounted on a moving body and used, vibration due to the movement is caused. In addition, there has been a problem that the reference line of the output signal itself moves irregularly with time, and an accurate output waveform cannot be obtained.

That is, the magnet 415 moves up and down due to the vibration of the movable film 411, but also swings in directions other than the up and down direction. Since the swing of the magnet 415 in a direction other than the up-down direction becomes a swing of the entire line of magnetic force emitted from the magnet 415,
The number and direction of the magnetic lines of force incident on the magnetoresistive elements 421 and 421 are immediately affected.

The applicant of the present application has proposed a minute displacement detector having a structure as shown in FIG. 11 in an earlier application (Japanese Patent Application No. 6-34076) in order to solve this drawback.

In this minute displacement detector, a soft magnetic body 515 serving as a magnetic path is attached to the movable film 513, and the soft magnetic body 515
The magnetoresistive element 523 is disposed at a position separated by a predetermined distance upward from a substantially center of the magnetoresistive element 523 so that its magnetoresistive surface 527 is parallel to the direction of displacement of the soft magnetic material 515. The magnet 525 is attached so that a part of the magnetic force lines pass through the soft magnetic material 515 and enter the magnetoresistive surface 527 of the magnetoresistive element 523 substantially in parallel.

In the case of this minute displacement detector, the lines of magnetic force of the magnet 525 are attracted to the soft magnetic material 515, and most of them enter the magnetic resistance forming surface 527 directly above, almost in parallel, so that the sensitivity of the output signal is reduced. improves

On the other hand, since a soft magnetic material 515 is attached to the movable film 513 instead of a magnet, it is possible to use this soft displacement material 515 by attaching this minute displacement detector to a moving body.
If the soft magnetic material 515 irregularly swings in the other direction along with the vertical movement, the magnetic force lines near the magnetoresistive element 523 hardly change due to the irregular movement of the soft magnetic body 515, and therefore, an accurate output waveform is obtained. can get.

However, in the case of this minute displacement detector,
A force attracted to the magnet 525 always acts on the soft magnetic material 515 attached to the movable film 513, but the attraction force is large when the soft magnetic material 515 approaches the magnet 525, small when the soft magnetic material 515 is away from the magnet 525, and squared with the distance. Changes in inverse proportion to.

Therefore, the soft magnetic body 515 does not directly follow the minute displacement of the movable film 513, and the output waveform is distorted. In particular, this distortion is caused by the soft magnetic material 515 and the magnet 5
The smaller the separation distance of 25, the larger.

On the other hand, in order to eliminate this distortion, the separation distance between the soft magnetic material 515 and the magnet 525 may be increased, but
If it is set too high, the output signal itself will become small and the sensitivity will deteriorate. That is, in the case of this minute displacement detector, there is a problem that the width of the optimum separation distance between the soft magnetic material 515 and the magnet 525 is narrow.

Therefore, for example, when trying to detect the heartbeat by pressing the human skin against the movable membrane 513, the amount of bending of the movable membrane 513 due to the elasticity of the skin or the subcutaneous fat varies depending on the individual, and therefore the human In some cases, the distance between the soft magnetic body 515 and the magnet 525 may be too small to obtain an accurate output.

The present invention has been made in view of the above points, and has as its object to reduce the position change amount by using the characteristics of the ferromagnetic magnetoresistive element, that is, the effect that the rate of change in resistance per magnetic field is large. The N ratio is large and can be detected as a good signal. In addition, even when vibration is applied to the detector itself due to movement or the like, a good output signal can be obtained. In addition, a displacement between a displaceable object such as a movable film and another magnet can be obtained. An object of the present invention is to provide a minute displacement detector which can take a large width of an optimum separation distance.

[0020]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a method for mounting a magnetoresistive element on a displaceable object.
On the other hand, a magnet and a soft magnetic material are directly placed near the magnetoresistive element.
Or indirectly fixed and installed via other members,
The soft magnetic material has one side directly or one side of the magnet.
Is connected indirectly through another member and the other end
Part so that it is located on the side of the other pole of the magnet.
It is formed in a bent shape and the other end is magnetic.
Immediately below the magnetoresistive surface of the resistive element and from the center
Introduced to the soft magnetic material by being installed in the shifted position
The lines of magnetic force are substantially opposite to the magnetoresistive surface of the magnetoresistive element.
Inject parallel and inject to the other pole of the magnet
A small displacement detector was constructed by being guided .

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing an example in which a minute displacement detector according to the present invention is used for heartbeat detection, wherein FIG. 1 (a) is a plan view and FIG. 1 (b) is A in FIG.
FIG. 2A is a schematic sectional view, and FIG. 2C is a schematic sectional view taken along the line BB of FIG.

As shown in FIG.
The body 11, the magnet 21 and the soft magnetic body 25 installed in the recess 13 of the body 11, a movable film 31 attached so as to cover the upper surface of the body 11, and a magnetoresistance attached to the center of the lower surface of the movable film 31 And an element 35. Hereinafter, each component will be described.

The body 11 is a columnar non-magnetic material (for example, aluminum, synthetic resin, rubber, etc.) and is provided with a circular recess 13 on its upper surface. On the bottom surface 15 of the concave portion 13 of the body 11, four terminals 51, 53, 55,
A through-hole 17 is provided to pass through the hole 57.

The magnet 21 is a columnar permanent magnet, and its two poles S and N are magnetized in the upper and lower directions.

The soft magnetic body 25 is formed by bending a flat plate made of nickel, cobalt, iron or the like into an L shape.

The movable film 31 is formed so as to cover the upper surface of the body 11, and is made of an elastic non-magnetic material (for example, a synthetic resin plate, a rubber plate, etc.).

The magnetoresistive element 35 has a magnetoresistive element pattern formed on one surface, that is, the surface on the side to be attached to the movable film 31 (the magnetoresistive forming surface 39), and has four terminals 51,5.
3, 55, 57 are projected. These terminals 51, 53, 55, and 57 are formed of a flexible soft copper wire that does not hinder the displacement movement of the movable film 31 and the magnetoresistive element 35. Note that a flexible flat cable may be used instead of the terminals 51, 53, 55, and 57.

FIG. 2 is a schematic plan view of the magnetoresistive element 35 on the magnetoresistive surface 39 side. As shown in the figure, the magnetoresistive element 35 is formed on a glass substrate 49 in a point-symmetric manner so that the zigzag directions of four zigzag magnetoresistive element patterns 41, 43, 45, and 47 are alternately orthogonal. And these magnetoresistive element patterns 41,
Four terminals 51, 53, 55, and 57 are drawn out from respective connection portions of 43, 45, and 47.

As shown in FIG. 1, the micro-displacement detector fixes a soft magnetic material 25 on the bottom surface 15 of the body 11 by bonding or the like, and fixes the magnet 21 on the upper surface of the soft magnetic material 25 by bonding or the like. Further, each terminal 51 of the magnetoresistive element 35 fixed to the center of the movable film 31 by bonding or the like,
53, 55, and 57 are passed through the through holes 17 provided in the body 11, and at the same time, the periphery of the movable film 31 is fixed to the upper surface of the body 11 by bonding or the like.
A lead wire 58 is attached to the tip of 57.

At this time, the upper end of the soft magnetic body 25 is located immediately below the magnetoresistive element 35 and slightly deviated from the center thereof, and is located at substantially the same height as the upper surface of the magnet 21.

FIG. 3 shows the magnet 21 and the soft magnetic material 25.
FIG. 6 is an enlarged sectional view of a main part showing a positional relationship between the magnetic field element and a magnetic resistance element 35 and a state of lines of magnetic force.

As shown in the figure, one of the soft magnetic members 25 is connected to one pole N of the magnet 21 and the other is connected to the magnet 21.
At the side of the other pole S of the
Lines of magnetic force induced from the poles into the soft magnetic body 25 are incident on the S pole of the magnet 21 after being incident substantially parallel to the magnetoresistive surface 39 of the magnetoresistive element 35.

That is, a large number of lines of magnetic force are
9, the sensitivity of the output signals of the magnetoresistive element patterns 41, 43, 45, 47 shown in FIG. 2 is improved.

The movable film 31 of the minute displacement detector
Is brought into close contact with a portion that vibrates due to the beating of the skin, the magnetoresistive element 35 moves up and down according to the vibration of the movable film 31,
Thereby, the magnetoresistive element patterns 41, 43, 45,
The output signal of 47 changes, and the vibration state is detected. More specifically, the magnetic flux density around the magnetoresistive element patterns 41, 43, 45, and 47 increases when the magnetoresistive element 35 approaches the soft magnetic body 25, and decreases when the magnetoresistive element pattern moves away from it. The change in magnetic flux density is substantially inversely proportional to the square of the distance.

In particular, in the case of the present invention, the magnet 21 and the soft magnetic body 25 are fixed to keep the state of the magnetic field constant, and the magnetoresistive element 35 is displaced in the fixed magnetic field. .

Therefore, when the minute displacement detector is attached to a moving person or the like, the magnetoresistive element 35 swings irregularly not only in the vertical direction due to the heartbeat but also in other directions. Even in this case, the entire magnetic field does not fluctuate as described above,
The change of the line of magnetic force with respect to the swing other than the swing in the vertical direction becomes very small. That is, since the change in the magnetic flux density near the magnetoresistive element 35 is mainly caused only by the vertical displacement of the magnetoresistive element 35, an accurate detectable output waveform can be obtained.

In the case of the present invention, what is displaced is the magnetoresistive element 35, but since this magnetoresistive element 35 is formed of a glass substrate, it is not subjected to a force by the lines of magnetic force. That is, there is no danger of being attracted by the magnet 21. Therefore, the magnetoresistive element 35 is displaced minutely following the minute displacement of the movable film 31 without any change, and there is no possibility that the output waveform thereof is distorted. Therefore, the separation distance between the soft magnetic body 25 and the magnet 21 with respect to the magnetoresistive element 35 can be reduced so that they do not collide with each other, so that the output signal can be increased and the sensitivity can be improved. In other words, even if the distance fluctuates, the output does not change much,
A stable output is obtained (this point will also be described in FIG. 6 described below).

Therefore, when a human skin is pressed against the movable membrane 31 to detect a heartbeat, the amount of curvature of the movable membrane 31 differs depending on the human due to the elasticity of the skin and subcutaneous fat. A stable and accurate output can be obtained even when the distance from the magnetic body 25 or the like varies.

The reason why the zigzag direction of the pair of magnetoresistive element patterns 41 and 43 shown in FIG. When the resistance value r1 of one of the magnetoresistive element patterns 41 is MAX, by making the incident angles of the lines of magnetic force incident on the magnetoresistive element patterns 41 and 43 on the horizontal plane different from each other, the other magnetoresistive element This is because the resistance value r2 of the pattern 43 is set to MIN, whereby the change in the resistance values r1 and r2 can be maximized, and the output voltage can be changed to the maximum. This means that the other sets of magnetoresistive element patterns 45, 4
7 is the same.

FIG. 4 is a diagram showing an example of a signal detection circuit used in the above-mentioned minute displacement detector. As shown in the figure, the terminal 51 is connected to the power supply voltage Vcc, and the terminal 57 is grounded. The terminals 53 and 55 are drawn out and connected to RC circuits 59 and 61 for taking out an AC component, and these are connected to a differential amplifier 63. In addition, 67 and 69 are bias circuits.

Then, for example, the magnetoresistive element 35 shown in FIG.
Is displaced upward or downward by a very small distance, and the number and direction of the lines of magnetic force incident on the four magnetoresistive element patterns 41, 43, 45, 47 change by a minute amount. The resistance values r1 and r2 and the resistance values r3 and r4 of the magnetoresistive element patterns 45 and 47 change.
The AC components are taken out by C circuits 59 and 61, respectively.
Next, the difference between the two AC components is amplified by the differential amplifier 63 and output.

By the way, as shown in FIG. 2, the magnetoresistive element patterns 41, 43 and the magnetoresistive element patterns 45, 47 are formed point-symmetrically because the output signals output from the two midpoint terminals 53, 55 are This is to reverse. That is, by inverting the output signals output from the terminals 53 and 55, the differential amplification of the detection circuit shown in FIG. 4 becomes effective. If the output signal is not reversed, terminals 53,
Since the output of 55 has a signal waveform of substantially the same phase, an output change cannot be taken out.

FIG. 5 (a) shows a state in which the micro-displacement detector shown in FIG. 1 is mounted on the chest near the heart of the person, the movable film 31 is in close contact with the skin, and the person is walking. FIG. 5 is a diagram showing an output waveform measured using the signal detection circuit shown in FIG. FIG. 2B is a diagram showing a result of measuring a current generated by contraction of the heart using an electrocardiogram.

When the waveforms shown in FIGS. 5A and 5B are compared, it can be seen that the waveforms are very similar and that an accurate waveform is obtained. Moreover, the reference line does not fluctuate constantly. In other words, even if the person is moving, the heartbeat can be measured with good reproducibility.

FIGS. 6A and 6B show a measurement test of the output of the signal detection circuit shown in FIG. 4 when the positions of the soft magnetic body 25 and the magnet 21 are shifted with respect to the magnetoresistive element 35. FIG. 3A shows the test method, and FIG. 3B shows the test results.

That is, as shown in FIG. 3 (a), the distance between the upper surface of the magnet 21 and the surface of the magnetoresistive element 35 is set to the gap X, and the center of the soft magnetic body 25 And the stay 65 to which the magnetoresistive element 35 is attached is moved up and down by 1 Hz.
The center value (reference value) of the output amplitude when vibrating at a constant amplitude is measured.

As a result, as shown in FIG. 5B, the output is at least in a wide range between the gap X = 0.35 mm to 0.76 mm and the lateral displacement Y = 0.2 mm to 1.2 mm. It turns out that it is flat, that is, stable. Therefore, the magnet 21, the soft magnetic body 25, and the magnetoresistive element 35
As long as the mutual positions are within the wide range of X and Y, a stable output can be obtained.

In other words, even if the dimensions of the gap X and the lateral deviation Y change relatively large, the output does not change much and is stable. Therefore, for example, when an attempt is made to detect the beating of the heart by pressing the human skin against the movable membrane 31 of the minute displacement detector shown in FIG. 1, the amount of bending of the movable membrane 31 due to the elasticity of the skin or the subcutaneous fat by the human. Is different from the magnetoresistive element 35
An accurate output can be obtained even if the separation distance of the magnet 21 and the like from the reference fluctuates more than the standard.

FIG. 7 is a schematic side sectional view showing another example in which the minute displacement detector according to the present invention is used for heartbeat detection. 1 is different from the embodiment shown in FIG. 1 in that a ring-shaped support member 71 is mounted around the body 11 and the upper end of the support member 71 is positioned at a predetermined distance from the surface of the body 11 on which the movable film 31 is mounted. The point is that it protrudes in height.

With this configuration, when the minute displacement detector is pressed against human skin, the skin is supported by the end of the support member 71 as shown by the dotted line in FIG. Therefore, the pressure with which the skin presses the movable film 31 can be made relatively uniform even if the elasticity of the skin or the like varies from person to person. Therefore, in addition to the effect of the present invention described above, that is, an accurate output can be obtained even if the amount of bending of the movable film 31 is different and the separation distance of the magnet 21 and the like to the magnetoresistive element 35 fluctuates more than the standard.
By making the distance itself uniform, more accurate output can be obtained.

Next, FIG. 8 is a schematic side view showing an example in which the minute displacement detector according to the present invention is used for detecting the paper thickness. As shown in the figure, this minute displacement detector has a support base 77 fixed in a substantially U-shaped frame 75, and an arm 79 at the upper end thereof.
Are pivotally supported, and a detection head 81 is attached to the tip of the arm 79. A roller 83 is attached to a lower end of the detection head 81, and a magnetoresistive element 35 is attached to an upper end thereof.

The magnet 21 and the soft magnetic body 25 are attached to the upper end of the frame 75. The structure and arrangement of the magnet 21, the soft magnetic body 25, and the magnetoresistive element 35 are the same as the structure and arrangement of each member shown in FIG.

When a paper 85 of, for example, 100 μm is inserted under the roller 83, the detection head 81 is pushed up and the magnetoresistive element 35 is displaced by a very small amount.
The magnetic field near 5 changes, and the paper thickness is detected from the change in the resistance value.

The roller 83 is attached so as to make the paper 85 move smoothly. When the insertion speed of the paper 85 is low, a contact needle type head that does not use the roller 83 may be used.

The thickness of the ink (about 10 μm) printed on paper or a sheet can be detected by the same method as that of the minute displacement detector.

[0056]

As described in detail above, the present invention has the following excellent effects. Even if this minute displacement detector is used by attaching it to a moving body, a detectable and accurate output signal can be obtained.

Since the displaced magnetoresistive element is not subjected to the force of the magnet and is displaced minutely following the minute displacement of the displaced object as it is, there is no possibility that the output waveform is distorted. Even if the separation distance of the magnet fluctuates, its output does not change much, the width of the optimum separation distance can be widened, and a stable output can be obtained.

This small displacement detector fixes a magnet and a soft magnetic material directly or indirectly via another member, and moves a magnetoresistive element attached to a displaceable object in a direction displaced from the soft magnetic material or the like. It can be configured simply by fixing it to a position at a predetermined distance away, so that the positional relationship of each component can be simplified, the position can be easily set, and the design and manufacture of various devices using this minute displacement detector become easy. .

Since the ferromagnetic magnetoresistive element has the characteristic that the rate of change in resistance per magnetic field is large, the amount of change in position can be detected as a good signal with a large S / N ratio.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example in which a minute displacement detector according to the present invention is used for heartbeat detection, and FIG.
FIG. 2B is a schematic sectional view taken along the line AA of FIG. 2A, and FIG. 2C is a schematic sectional view taken along the line BB of FIG.

FIG. 2 is a schematic plan view of a magnetoresistive element 35 on a magnetoresistive surface 39 side.

FIG. 3 is an enlarged sectional view of a main part showing a positional relationship between a magnet 21, a soft magnetic body 25, and a magnetoresistive element 35 and a state of magnetic lines of force.

FIG. 4 is a diagram illustrating an example of a signal detection circuit of the minute displacement detector.

5A is a diagram showing an output waveform obtained by measuring the beating of a person's heart while the person is walking by using the small displacement detector shown in FIG. 1, and FIG. It is a figure showing the result of having measured the electric current generated by contraction of the heart using an electrocardiogram.

6 is a diagram illustrating a measurement test when the positions of the soft magnetic body 25 and the magnet 21 are shifted with respect to the magnetoresistive element 35. FIG.

FIG. 7 is a schematic sectional side view showing another example in which the minute displacement detector according to the present invention is used for heartbeat detection.

FIG. 8 is a schematic side view showing an example in which the minute displacement detector according to the present invention is used for paper thickness detection.

FIG. 9 is a diagram showing a conventional example using a ferromagnetic magnetoresistive element 401.

FIG. 10 is a schematic side sectional view showing a minute displacement detector proposed by the present applicant previously.

FIG. 11 is a schematic side sectional view showing a minute displacement detector previously proposed by the present applicant.

[Description of Signs] 21 Magnet 25 Soft magnetic body 31 Movable film (displaceable object) 35 Magnetoresistive element 39 Magnetoresistive surface

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-66504 (JP, A) JP-A-5-26604 (JP, A) JP-A-3-93705 (JP, U) JP-A 57- 29832 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 7/00-7/34 102 G01D 5/00-5/252 G01D 5/39-5/62 G01L 7 / 00-23/32 H01L 43/08

Claims (1)

(57) [Claims] 1. A magnetoresistive element is attached to an object to be displaced, and a magnet and a soft magnetic material are directly placed near the magnetoresistive element.
Or indirectly fixed and installed via another member, and one of the soft magnetic bodies is one of the poles of the magnet.
Connected directly or indirectly through other members
The other end is located on the side of the other pole of the magnet
And the other end
Part is just below the magnetoresistive surface of the magnetoresistive element
By being installed at a position shifted from the center, it is attracted to the soft magnetic material.
The guided lines of magnetic force are applied to the magnetoresistive surface of the magnetoresistive element.
Incident substantially parallel to the other pole of the magnet
Small displacement detector characterized by being guided as follows.