JPH0151127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a displacement detection device that can be used as a rotary encoder or a linear encoder;
In particular, the present invention relates to a displacement detection device that detects displacement of a magnetization pattern arranged along a magnetic recording track using a plurality of magnetoresistive elements and obtains a differential output.

For example, a magnetic signal recorded in the form of a magnetization pattern with equally spaced bit lengths on a disk or cylinder having a magnetic recording medium attached to a rotating shaft is transferred to a ferromagnetic magnetoresistive element (hereinafter abbreviated as MR element).
A so-called rotary encoder is known that detects the rotation angle of a rotating shaft by reading it with a magnetic sensor having a rotary shaft. In such a rotary encoder, a magnetic signal is basically detected using one MR element, and the amount of displacement can be determined.
Since the output voltage is small and the output voltage drifts due to temperature change, it is common to differentially couple two or more MR elements to obtain the output. For example, in Japanese Patent Publication No. 54-115257, 2
An angle detector is described in which MR elements are arranged at intervals equal to an integral multiple of the pitch of a magnetic pattern on a magnetic recording medium, and the difference in the outputs of these MR elements is determined using a differential amplifier. There is. Also, "Nikkei Electronics", June 22, 1981 issue, No. 88
Each page has four MRs as shown in Figure 1.
Two groups of magnetic sensors having elements A ₁ to A ₄ and B ₁ to _{B 4} are provided, and the MR elements of each group are arranged at a distance of 1/2 the pitch P of the magnetization pattern of the magnetic recording medium M. and the MR elements of one group are connected to the MR elements of the other group.
The four MR elements in each group are connected as a bridge circuit as shown in Figure 2, with the elements shifted by P/4, and the difference in output voltage appearing at the diagonal points of each bridge circuit is a differential amplifier respectively
An angle detection device is shown that detects the amount and direction of displacement by determining DA ₁ and DA ₂ . Adopting such a differential coupling method has the advantage of increasing the output amplitude and canceling out the effects of drift. However, in such a conventional angle detection device, two or more MR elements must be arranged in the displacement direction, that is, in the arrangement direction of the magnetization pattern, at intervals that are an integral multiple or a fraction of the pitch P of the magnetization pattern. Not,
Magnetic sensors having MR elements arranged at predetermined intervals must be prepared for magnetic recording media having magnetization patterns of various pitches,
The disadvantage is that the degree of freedom in design is limited. Also,
When installing a magnetic recording medium on a cylindrical surface, multiple
When MR elements are formed on a flat substrate, the distances between each MR element and the magnetic recording medium are not equal, and each
This has the disadvantage that the amplitude of the output signal of the MR element varies, causing errors in the differential output. In order to solve this problem, Japanese Patent Publication No. 56-35011 discloses changing the width of the MR element, but manufacturing such an MR element is troublesome and the distance mentioned above is changed. In this case, it is necessary to manufacture an MR element with a width corresponding to this width, which has the disadvantage of lacking in versatility. Furthermore, if two or more MR elements are shifted in the direction in which the magnetization pattern of the magnetic recording medium is arranged, the size of the magnetic sensor inevitably becomes larger, which also has the disadvantage that the entire detection device tends to become larger.

An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a displacement detection device that does not require MR elements to be spaced apart in the arrangement direction of the magnetization pattern of a magnetic recording medium, and that can provide a differential output. This is what I am trying to do.

The displacement detection device of the present invention includes at least two magnetoresistive elements facing a magnetic recording medium having a magnetization pattern formed in the same direction as the displacement direction, and at least two magnetoresistive elements arranged perpendicularly to the displacement direction of the magnetic recording medium. The magnetoresistance effect elements are arranged side by side in a direction, and are characterized by being provided with means for magnetically biasing these magnetoresistive elements in mutually opposite directions, and means for differentially detecting the outputs of these magnetoresistive elements. be.

The present invention will be described in detail below with reference to the drawings.

3 to 5A and 5B show the configuration of an example of the displacement detection device of the present invention. Magnetic recording medium 10 provided integrally with the member whose displacement is to be measured
A magnetization pattern is recorded at a predetermined pitch P in the displacement direction indicated by the arrow. A magnetic sensor 11 is placed opposite this recording medium 10. As shown in FIG. 4, this magnetic sensor 11 has a first
And second ferromagnetic magnetoresistive elements 13a and 13b are arranged side by side in a direction orthogonal to the displacement direction. In this example, these MR elements 13
Conductive films 15a and 15b are provided on MR elements 13a and 13b via insulating films 14a and 14b in order to magnetically bias elements a and 13b in opposite directions, and bias currents are passed through these conductive films in opposite directions. That is, as shown in the side view of FIG. 4, conductive films 15a and 15b are connected to DC power supply 16 so that bias currents flow in opposite directions as shown by arrows. Therefore, as shown in FIGS. 5A and 5B, which are cut along lines A-A and B-B in FIG. A bias magnetic field is generated in the clockwise direction as shown by the broken line arrow, a current flows through the other conductive film 15b from the back side of the page to the front side, and a bias magnetic field is generated in the counterclockwise direction as shown by the broken line arrow. become. In this way the first and second
Bias magnetic fields in opposite directions are applied to the MR elements 13a and 13b. Therefore, the first and second MR elements 13a respond to changes in the composite magnetic field of the magnetic field and the bias magnetic field ±H _B according to the magnetization pattern recorded on the magnetic recording medium 10 as shown by curves 17a and 17b in FIG. and the resistance value R of 13b is the curve 18 in FIG.
They will change as shown by a and 18b, respectively. Here, the magnitude of the bias magnetic field ±H _B is preferably set so that the operating points of the respective MR elements 13a and 13b are approximately at the center of the straight line portions on opposite sides of the magneto-resistance characteristic curves. In this way, the changes in the resistance values R of the first and second MR elements 13a and 13b in response to the displacement of the magnetic recording medium 10 are in opposite phases to each other, as shown by the curves 18a and 18b. Therefore these
By connecting the MR elements 13a and 13b in series as shown in FIG. 7, and connecting both ends to the positive and negative power supplies +E and -E, the connection point 19 of both MR elements has a curve 20 in FIG. A differential output as shown will be obtained.

As in this embodiment, the MR elements 13a and 13b
When the conductive films 15a and 15b are formed above and connected in series to the DC power supply 16 to generate a bias magnetic field, fluctuations in the DC power supply 16 act equally on both MR elements, so the differential There is an advantage that is canceled out in the output and does not appear in the output.

FIG. 9 is a perspective view showing another example of the magnetic sensor of the displacement detection device of the present invention. In this example, the substrate 22 of the magnetic sensor 21 placed above the magnetic recording medium 10 is placed perpendicularly to the recording medium 10 .
Further, on the substrate 22, MR elements 23a and 23b are arranged in a direction orthogonal to the displacement direction shown by the arrow.
MR element 2 is provided on top of these MR elements via thin insulating films 25a and 25b, respectively.
4a and 24b are provided, respectively. Furthermore, in order to apply a bias magnetic field, conductive films 27a and 27b are provided on MR elements 24a and 24b via thick insulating films 26a and 26b, respectively. These conductive films are connected in series to a DC power supply as in the previous example, and the MR elements 23a, 24a and 23
Bias magnetic fields in mutually opposite directions can be applied to b and 24b.

The four magnetic sensors 21 configured in this way
MR elements 23a, 23b, 24a and 24b are connected to a bridge circuit as shown in FIG.
That is, the connection point between MR elements 23a and 24b is connected to a positive voltage source +E, the connection point between MR elements 23b and 24a is connected to a negative voltage source -E, and the MR element 24
By connecting the connection point between a and 24b to the positive input terminal of the differential amplifier 28, and connecting the connection point between MR elements 23a and 23b to the negative input terminal, a differential output can be obtained at the output terminal 29. It turns out.

The magnetic sensor 21 shown in FIG. 9 includes, for example, a Fe-Ni alloy (permalloy) of about 500% on a glass substrate 22.
The MR elements 23a, 23b, 2 are formed by vapor deposition to a thickness of Å.
4a and 24b, and thin insulating films 25a and 25b interposed between them contain SiO ₂ of 1000 to 2000%.
A thick insulating film 26a,
26b is similarly formed by vapor-depositing SiO ₂ to a thickness of several microns, and conductive films 27a and 27b are made of Al, Au,
It can be easily manufactured by depositing non-magnetic metal such as Cu to a thickness of 1000 Å or more.

As described above, according to the present invention, since two MR elements are arranged side by side in a direction perpendicular to the displacement direction of the magnetic recording medium, the pitch P of the magnetization pattern is
will no longer be restricted by. Therefore, it is not necessary to use a magnetization pattern with the same pitch as in the past. For example, as shown in FIG. 11, the pitch is P ₁ ,
A magnetic recording medium 30 in which magnetization patterns different from P ₂ and P ₃ are recorded, or a magnetic recording medium 40 in which a magnetization pattern whose pitch changes continuously as shown in FIG. 12 can be used. A magnetic recording medium in which the pitch of the magnetization pattern changes in this way is effective when, for example, the detection accuracy is to be changed during displacement.

The present invention is not limited to the embodiments described above, and can be modified and modified in many ways. For example, in the above example, the magnetic recording medium is shown as being linear, but it may also be disk-shaped or cylindrical, as in the case of application to a rotary encoder. Furthermore, in the above example, a current was passed through the conductive film to generate a bias magnetic field, but
A bias magnetic field may be applied by placing a permanent magnet or an electromagnet near the MR element.

As described above, according to the displacement detection device of the present invention, since a plurality of MR elements are arranged in a direction perpendicular to the displacement direction of the magnetic recording medium, it is possible to determine the pitch of the magnetization pattern recorded on the magnetic recording medium. Even if the magnetic recording medium is replaced, the magnetic sensor can be used as is. In addition, when applied to a rotary encoder in which the magnetic recording medium is installed on the side of a disk or cylinder, the distance between all MR elements and the magnetic recording medium is equal, resulting in uniform output and accurate detection. is possible, and there is no need to change the width of the MR element. Furthermore, since the present invention can use existing magnetic recording media, it can be implemented easily and at low cost.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of an example of a conventional displacement detection device, FIG. 2 is a circuit diagram showing a bridge circuit made of the same magnetoresistive element, and FIG. 3 is a diagram of the displacement detection device of the present invention. A plan view showing the configuration of an example, FIG. 4 is a side view similarly seen from the displacement direction, and FIGS. 5A and B are sectional views taken along the line AA and line B-B in FIG. FIG. 6 is a waveform diagram for explaining the operation, FIG. 7 is a circuit diagram showing the connection of the two magnetoresistive elements, and FIG. 8 is a waveform diagram showing the differential output.
FIG. 9 is a perspective view showing the configuration of another example of the displacement detection device of the present invention, FIG. 10 is a circuit diagram showing the connection of four magnetoresistive elements, and FIGS. 11 and 12 are FIG. 7 is a plan view showing a modification of the magnetic recording medium used in the displacement detection device of the present invention. 10, 30, 40...magnetic recording medium, 11, 2
1... Magnetic sensor, 12, 22... Board, 13
a, 13b, 23a, 23b, 24a, 24b...
...Magnetoresistive element, 14a, 14b, 25a,
25b, 26a, 26b...Insulating film, 15a, 1
5b, 27a, 27b... conductive film, 16... DC power supply, 28... differential amplifier.

Claims (1)

[Claims] 1. At least two magnetoresistive elements facing a magnetic recording medium having a magnetization pattern formed in the same direction as the displacement direction, in a direction perpendicular to the displacement direction of the magnetic recording medium. A displacement detection device characterized by comprising means for magnetically biasing these magnetoresistive elements arranged side by side in mutually opposite directions, and means for differentially detecting the outputs of these magnetoresistive elements. . 2. A patent claim characterized in that a conductive film is formed on the magnetoresistive element via an insulating film, and the magnetoresistive element is magnetically biased by passing a current through the conductive film in a predetermined direction. The displacement amount detection device according to item 1.