JP2002202152A - Magnetic encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic encoder capable of obtaining a highly accurate output signal even in the case that the diameter of a magnetic drum is small and easily performing positioning. SOLUTION: In the magnetic encoder, a magnetic field generated from the magnetic drum is detected by MR elements provided for a magnetic sensor. The magnetic sensor is provided with a recessed part on a substrate for arranging a plurality of the MR elements. The magnetic encoder in which the MR elements are arranged along the curved surface of the magnetic drum is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder, and more particularly, to a reduction in size and an improvement for facilitating positioning of a magnetic sensor and a magnetic drum.

[0002]

2. Description of the Related Art FIG. 7 is a perspective view of a conventional magnetic encoder. The magnetic recording medium 102 of the magnetic encoder is fixed around the shaft 101 near the end of the rotating body. The rotation of the magnetic recording medium 102 is detected by a magnetic sensor. On the surface of the magnetic sensor 103, patterns of magnetoresistive elements, which are magneto-sensitive elements, are arranged at predetermined intervals. Here, illustration of the pattern is omitted. The magnetic sensor 103 is used in combination with a signal processing circuit 105 and a flexible cable 104 for connecting the signal processing circuit 105. The magnetic recording medium 102 has a so-called magnetic drum shape having substantially the same diameter as the shaft 101. An arrangement of magnetic signals formed by magnetizing the magnetic recording medium 102 is called a track 106. The track 106 is a magnetic recording medium written at a magnetization pitch λ. The magnetic sensor detects each magnetic signal (magnetic field generated from the magnetic recording medium).

[0003] Generally, the magnetization pitch λ is 0.7 to 0.8.
A magnetic sensor and a magnetic recording medium are provided with a gap approximately twice as large. When the pitch λ becomes narrow, the gap g (gap) between the magnetic sensor and the magnetic recording medium must be set to be narrow. Therefore, a method of sliding the magnetic sensor with a spacer material having a predetermined thickness interposed has been used. The magnetic sensor has a configuration in which a spacer material is attached to a side having a pattern of a plurality of magnetoresistive elements. A spacer material having a thickness corresponding to the gap g is brought into contact with the rotating magnetic recording medium. By doing so, it is possible to configure a magnetic encoder capable of easily obtaining a signal without adjusting the gap g.

A conventional magnetic encoder in which a spacer material is adhered to the surface of a magnetic sensor and slides on a magnetic recording medium (hereinafter referred to as a magnetic drum) has a pitch λ = 120.
μm and the outer diameter of the drum φ = 50 mm, and the outer diameter of the drum is large. Therefore, even if the magnetic sensor has a slight inclination with respect to the outer periphery of the drum, the influence on the signal is small. At this time, the difference (g2−g1) between the gap g1 between the pattern at the center and the drum and the gap g2 between the pattern at the end and the drum was as small as 6 μm, and the effect on the output signal was small. The present inventors are studying a magnetic encoder that combines a shaft-shaped magnetic drum having a smaller outer diameter than a conventional magnetic drum with a magnetic sensor. Next, the problem caused by downsizing the outer diameter will be described with reference to FIG.

[0005]

FIG. 6 shows a magnetic sensor 62 in which patterns 63 and 64 are arranged on a flat substrate.
FIG. 2 is a schematic sectional view of a small magnetic encoder facing a magnetic drum 61. When the drum diameter becomes smaller, the gap g1 between the pattern 63 at the center and the magnetic drum 61 becomes
Gap g2 between end pattern 64 and magnetic drum 61
The difference becomes large. Since the magnetic field received by each pattern is different, the smaller the outer diameter of the drum, the greater the effect of the difference between g1 and g2 on the output signal. That is, in the pattern 64 at the end, a sufficient output signal cannot be obtained, so that the accuracy of the output signal of the magnetic sensor obtained from the output signal of each pattern also decreases. The diameter of the drum (the diameter of the magnetic drum) examined by the inventors is about 15 mm, and g1
And g2 is as large as 21 μm, which greatly affects the output signal. Therefore, an object of the present invention is to provide a magnetic encoder that obtains a highly accurate output signal while suppressing the difference between g1 and g2.

In addition, when the diameter of the drum is reduced in a small magnetic encoder, if the displacement in the direction parallel to the rotation direction occurs, the difference between g1 and g2 is further increased.
The effect on the output signal is greater. Therefore, another object of the present invention is to easily suppress the displacement parallel to the rotation direction,
An object of the present invention is to provide a magnetic encoder capable of positioning a magnetic sensor and a magnetic drum.

[0007]

A magnetic encoder according to the present invention is a magnetic encoder for detecting a magnetic field generated from a magnetic drum by a magnetoresistive element provided on a magnetic sensor, wherein the magnetic sensor is mounted on a substrate. It is characterized in that it has a stepped concave portion in which a plurality of magnetoresistive elements are arranged, and the magnetoresistive elements are arranged along a curved surface of a magnetic drum.

In the present invention, a plurality of magnetoresistive elements (hereinafter, referred to as MR elements) are arranged on a substrate. When viewed in a plane perpendicular to the rotation axis of the magnetic drum, the MR elements are arranged along an arc corresponding to the diameter of the magnetic drum. The arrangement along the curved surface of the magnetic drum referred to in the present application is included in the arrangement along the stepped concave portion as long as it compensates for the displacement of the gap between the MR element and the magnetic drum. The MR element may be an AMR or GMR (giant magnetoresistive element).

The stepped recess includes a recess having a plurality of surfaces formed in a step shape, a trapezoidal groove, and the like. In the present invention, it is preferable that the magnetic sensor has the step-shaped concave portion disposed on the substrate as a step-shaped thin film structure or a step-shaped concave portion formed directly on the substrate. The step-like thin film structure can be formed by a method in which thin films are stacked stepwise by photolithography technology, or a method in which the thin film is cut by etching, grinding of a grindstone, or the like. In addition, the step-shaped recess directly formed on the substrate can be formed by pressing the substrate, or by cutting the substrate with a rotating grindstone,
Alternatively, it can be formed by a method of directly etching the substrate.

The following method can be used to form an MR element. The first method is to form an MR element for each stage when laminating thin films. The second method is to form a concave portion after embedding an MR element between insulating layers in the same arrangement as the first method. The third method is to form an MR element at each stage after forming a step-shaped concave portion. Further, a step-shaped concave portion is formed by the third method, and then an MR element is arranged on each step surface, and a resin or the like is molded on the medium facing surface to form a curved medium facing surface. It may be. When each MR element is covered with a protective film, it is referred to as a concave part including a configuration in which the MR elements appear to be arranged inside the concave part instead of the surface of the concave part.

By disposing the MR element in a stepped recess along the curved surface of the magnetic drum, the opposing magnetic drum and M
The deviation of the distance (gap) between the R elements is corrected, and the sensitivity can be made uniform at the center and the end of the MR element array even with a magnetic drum having a small diameter. Here, glass, ceramics, or the like is used for the substrate on which the step-shaped concave portions are arranged. Further, it is desirable to use an insulating alumina film or a silicon oxide film as the base film of the MR element in order to eliminate the influence of the substrate surface on the electromagnetic characteristics of the MR element (the occurrence of insulation failure). MR in photolithography technology
An exposure step is used to pattern the device. In order to focus the exposure on the surface of the recess and accurately pattern the MR element, a step-like thin film structure having a flat surface for each step or a step-like structure formed directly on the substrate may be used as the recess. .

Further, a method may be used in which an MR element is formed on a substrate in which a concave portion is formed in advance by pressing a nonmagnetic metal substrate or molding a resin (such as injection molding). According to these methods, a concave surface that slides smoothly on the curved surface of the magnetic drum can be formed.

Another magnetic encoder according to the present invention is a magnetic encoder for detecting a magnetic field generated from a magnetic drum by an MR element provided on a magnetic sensor, wherein the magnetic sensor comprises a magnetic drum provided on a substrate provided with the MR element. Characterized by being bent to a curvature corresponding to the diameter of. The method of bending the substrate includes a method of providing a stress difference between the front and back of the substrate, a method of providing a member for maintaining the curvature in a state where the substrate is bent, a method of forming a surface on which an MR element is formed in a curved shape, and the like. Can be

To generate a difference in stress between the front surface and the back surface of the substrate, a laser is applied to the magnetically sensitive surface side (the surface of the flat substrate surface which is bent inside) or the magnetically sensitive surface is This is achieved by applying or contracting a resin (adhesive) to the magnetically sensitive surface side by applying and curing a resin (adhesive). Alternatively, the substrate may be bent by performing heat treatment while applying stress. In order to generate a larger stress difference, ceramic, resin, or non-magnetic metal can be used as the substrate in addition to glass. Among the methods of bending the substrate, the method using laser light is the magnetic sensor 1
Since the bending time for the individual piece is short, this is preferable in shortening the process. Also, a method of applying a resin (adhesive) to the magneto-sensitive surface and bending the substrate by contraction stress when the resin is cured can be performed together with the process of forming the protective film, so that the process is lengthened. Don't do it. In these methods, since the magnetic sensor is completed by forming the MR element on a flat substrate in advance and then bending the substrate, there is no need to divide the exposure into a plurality of times in the step of forming the MR element on the substrate. There is an advantage that the lengthening of the dividing process is not required.

In any one of the above-mentioned present invention, the diameter of the magnetic drum is 30 mm or less, and the magnetization pitch is 100 μm.
It is characterized by the following. For example, pitch 80 μm
When the diameter of the magnetic drum is smaller than 30 mm, the difference between the center and the end of the magnetic drum in the arrangement of the MR elements is 11 μm. When the magnetization pitch is larger than 100 μm as in the conventional magnetic encoder, even if the magnetic drum diameter is 30 mm, the influence on the output signal is small. In general, the magnetic signal generated from the magnetic drum becomes weaker as the magnetization pitch becomes smaller. Therefore, when the magnetization pitch becomes 100 μm or less, the influence on the output signal increases when the gap difference is 11 μm. On the other hand, in the configuration of the present application, the position of the arrangement of MR elements on the substrate is adjusted to the curved surface of the drum, so that the diameter of the magnetic drum is 30 mm or less and the magnetic pitch is 100 μm or less. The difference in sensitivity between the center and the end of the MR element array can be suppressed. This configuration is particularly suitable for a magnetic encoder for a printer having a small drum diameter.

As magnetic encoders become smaller,
A smaller magnetization pitch than before is required. When the magnetization pitch becomes smaller, the magnetic signal generated from the magnetic drum becomes weaker, and the signal output becomes smaller. According to the measurement by the present inventors, when the magnetic encoder having a magnetization pitch of 40 μm was compared with the magnetic encoder having a magnetization pitch of 80 μm, the former could obtain only about half the signal output of the latter. For this purpose, a method has conventionally been adopted in which the MR element is folded back to increase the element length (a zigzag type MR element). According to this method, the output signal can be increased, but the width of the magnetic sensing portion is increased, and as the diameter of the magnetic drum becomes smaller, the difference in sensitivity between the center and the end of the MR element array increases. There was a disadvantage. In the magnetic encoder according to the present invention, even if the number of folded elements of the MR element is increased and the width of the magnetic sensing part is increased, the difference in sensitivity between the center and the end of the MR element array can be suppressed. That is, a high output signal can be obtained even when the magnetization pitch is reduced.

Further, in the conventional structure, when the diameter of the magnetic drum becomes 30 mm or less, the influence of the displacement in the direction parallel to the rotation direction on the output signal increases. On the other hand, in the configuration of the present application, when the concave portion of the magnetic sensor and the magnetic drum are slid, the center line of the concave portion and the axis of the drum are always parallel to each other, so that a deviation in a direction parallel to the magnetization pitch is prevented. be able to. That is, in any one of the present invention, a support member for supporting the magnetic sensor is provided, and the magnetic sensor and the magnetic drum are slid by elasticity of the support member, and positioning in a direction parallel to the rotation direction of the magnetic drum is performed. Doing is advantageous in that it facilitates positioning and minimizes deviation.

Preferably, the support member is made of an elastic non-magnetic metal or ceramic. Also,
It is desirable to provide a sheet or a coating film or the like for providing abrasion resistance on the sliding surface of the magnetic sensor.

In the magnetic sensor, the substrate has an electrode in addition to the MR element. Furthermore, it is fixed by the support member, and an FPC (flexible printed circuit board) is provided as a lead wire on the electrode of the board. Here, the substrate is made of a material having a strength necessary for accurately defining the distance between the MR element and the magnetic drum. The FPC is a lead wire and is made of a flexible material.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is an exploded perspective view for explaining a magnetic encoder according to an example of the present invention. Here, the magnetic drum includes a rotating shaft (shaft) 1 and a magnetic body 2 provided around the rotating shaft.
Having. The magnetic body 2 was provided with a plurality of magnetic poles (units for outputting a magnetic signal) at a predetermined pitch λ. The diameter of the magnetic drum was 15 mm, the magnetization pitch was 100 μm, and the shaft was used as a paper feed roller of a printer. Magnetic sensor 3
Supported its back side by the arm 4. Further, the arm applies a force to press the magnetic sensor so as to slide without leaving the magnetic drum. By providing the concave portion 3a on the magneto-sensitive surface side of the magnetic sensor, the displacement in the direction parallel to the drum rotation direction is suppressed, and the positioning of the magnetic sensor and the magnetic drum is facilitated. Details of the MR sensor applied to this magnetic encoder will be described with reference to FIG.

FIG. 2 is a sectional view of a magnetic sensor according to the present invention. In this magnetic sensor, a substrate is formed in a stepwise manner in order to arrange the MR element in a sectional shape corresponding to the outer diameter of the magnetic drum. Therefore, M
An insulating film used as a base of the R element was formed in a predetermined pattern by using a photolithography technique to form a step-shaped base film.

A method for forming the above-described cross-sectional shape will be described.
The film was formed in the order of film formation and etching. First, the film formation will be described. After forming the first MR element and the wiring film 12 on the glass substrate 11, an alumina film 13 was formed as an intermediate insulating film to a thickness of 1.0 μm. Chrome film 13
After a was formed to a thickness of 0.05 μm, an alumina film 14 was further formed to a thickness of 1.4 μm. Next, after forming the second MR element and the wiring film 15, the alumina film 16 is 1.0 μm, the chromium film 16a is 0.05 μm, and the alumina film 17 is 3.2 μm.
Films were formed in the order of m. Finally, after forming the third MR element and the wiring film 18, the alumina film 19 is 1.0 μm, the chromium film 19a is 0.05 μm, and the alumina film 20 is 2.0 μm.
m.

Next, the etching will be described. First, a resist was formed by photolithography outside 370 μm from the center of the sensor, and dry etching using BCl ₃ and Cl ₂ as reaction gases was performed. Here, the chromium film 19a is made of alumina films 19 and 20.
Of these, only the surface layer of the 1.4 μm alumina film 20 is removed, and serves as an etching stopper for preventing the second-layer alumina film 19 from being etched. Further, since the chromium film is non-magnetic, it does not impair the magnetic signal emitted from the magnetic drum. After removing the exposed portion of the chromium film 19a by ion milling, 270 μm from the center of the sensor.
A resist is formed on the outer side and the same dry etching and ion milling are performed to form alumina films 19 and 17.
And the chromium film 16a was removed according to the resist pattern. Finally, a resist was formed outside of 120 μm from the center of the sensor, and the same dry etching and ion milling were performed to remove the alumina films 16 and 14 and the chromium film 13a in accordance with the resist pattern.
By the above steps, the concave portion 3 is formed on the magnetic sensing surface side of the magnetic sensor 3.
a was formed. In addition, the arrangement of the MR elements was along the recess. Connections connecting the MR element and the layers of the wiring films 12, 15 and 18 are made of alumina films 13, 14 and 1
Through-holes (through-holes) were provided in each of layers 6 and 17, and copper was sputtered there.

(Embodiment 2) Another magnetic sensor of the present invention is shown in a sectional view of FIG. In this magnetic sensor, in order to arrange the MR elements in a cross-sectional shape corresponding to the outer diameter of the magnetic drum, a magnetic sensor substrate in which MR elements 12, 15, and 18 are formed on the same surface on a flat substrate is used. It differs in the point of bending. After forming the magnetic sensor on the substrate in the form of a flat plate,
Laser light emitted from the laser oscillator 21 was condensed by a lens 22, and the surface of the magnetic sensor was irradiated with laser to generate contraction stress. The laser-irradiated part is 120, 270 and 370 μm from the center line of the magnetic sensor.
And a bending angle of 2 ° between the patterns of the MR element. Fig. 1
A magnetic encoder such as that described above was constructed. The diameter of the magnetic drum was 15 mm, and the magnetization pitch was 100 μm. Since each MR element has its surface (magnetically sensitive surface) oriented in the direction of the center axis of the magnetic drum and has the same gap length, position detection can be performed with higher precision as compared with the conventional structure. did it.

(Embodiment 3) Another magnetic sensor of the present invention will be described with reference to the manufacturing method of FIG. This magnetic sensor differs in that a nonmagnetic metal pressed in advance along the diameter of a magnetic drum is used as a substrate. A flat non-magnetic metal plate 31 was press-formed along the diameter of the magnetic drum, and an insulating glass glaze 32 was applied thereon to form a base film. After the MR element and the wiring film 33 were formed on the base film 32, they were covered with a protective film 34. The diameter of the magnetic drum was 15 mm, and the magnetization pitch was 100 μm.

(Embodiment 4) Another magnetic sensor of the present invention will be described with reference to the manufacturing method shown in FIG. In this magnetic sensor, an MR element and a wiring film 42 were formed on a flat substrate 41 and covered with a protective film 43 to constitute a magnetic sensor. Further, an adhesive resin 44 is applied to the surface of the magnetic sensor,
The substrate 41 was bent along the diameter of the magnetic drum by contraction stress when the adhesive resin 44 was cured. The diameter of the magnetic drum was 15 mm, and the magnetization pitch was 100 μm.

[0027]

As described above, by using the magnetic encoder of the present invention having the concave portion on which the plurality of MR elements are arranged on the substrate and the MR elements being arranged along the curved surface of the magnetic drum, Even if the diameter of the magnetic drum is reduced, a high-precision output signal can be obtained, and a magnetic encoder that does not cause positional displacement can be configured.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a magnetic encoder according to the present invention.

FIG. 2 is a sectional view of a magnetic sensor according to the present invention.

FIG. 3 is a sectional view of another magnetic sensor of the present invention.

FIG. 4 is a diagram for explaining a method for producing another magnetic sensor of the present invention.

FIG. 5 is a diagram illustrating a method for producing another magnetic sensor of the present invention.

FIG. 6 is a schematic cross-sectional view illustrating a positional shift of a conventional magnetic sensor.

FIG. 7 is a perspective view of a conventional magnetic encoder.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 rotating shaft, 2 magnetic body, 3 magnetic sensor, 3a recess, 4 arm, 11 substrate, 12 first MR element and wiring film, 13 alumina film, 13a chromium film, 14
Alumina film, 15 second MR element and wiring film, 16
Alumina film, 16a chromium film, 17 alumina film,
18 third MR element and wiring film, 19 alumina film,
19a chromium film, 20 alumina, 21 laser oscillator, 22 lens, 31 non-magnetic metal plate, 32 glass glaze, 33 MR element and wiring film, 34 protective film, 41 substrate, 42 MR element and wiring film, 43 protective film, 44 adhesive resin, 61 magnetic drum, 62 magnetic sensor, 63 patterns, 64 patterns, 101
Shaft, 102 magnetic recording medium, 103 magnetic sensor, 104 flexible cable, 105 signal processing circuit, 106 tracks

Claims (8)

[Claims] 1. A magnetic encoder for detecting a magnetic field generated from a magnetic drum by a magnetoresistive element provided on a magnetic sensor, wherein the magnetic sensor has a step-like shape in which a plurality of magnetoresistive elements are arranged on a substrate. A magnetic encoder comprising a concave portion, wherein the magnetoresistance effect element is arranged along a curved surface of a magnetic drum. 2. A magnetic encoder in which a magnetic field generated from a magnetic drum is detected by a magnetoresistive element provided in a magnetic sensor, wherein the magnetic sensor corresponds to a substrate provided with the magnetoresistive element corresponding to a diameter of the magnetic drum. Bend to the curvature
A magnetic encoder wherein the magnetoresistive element is arranged along a curved surface of a magnetic drum. 3. The magnetic drum has a diameter of 30 mm or less,
3. The magnetic encoder according to claim 1, wherein the magnetization pitch is 100 μm or less. 4. The magnetic encoder according to claim 1, wherein the substrate of the magnetic sensor comprises the step-shaped recess formed by a step-shaped thin film structure or a step-shaped recess formed directly on the substrate. And a magnetic encoder. 5. The magnetic encoder according to claim 1, wherein the substrate of the magnetic sensor has the recess formed by pressing a non-magnetic metal substrate or molding a resin. 6. The magnetic encoder according to claim 2, wherein a laser is applied to a surface of the flat substrate which is bent to be inward to bend the substrate. 7. The magnetic encoder according to claim 2, wherein a resin is applied to the magneto-sensitive surface side of the substrate, and the substrate is bent by a contraction stress when the resin is cured. . 8. The magnetic encoder according to claim 1, further comprising a support member for supporting the magnetic sensor, wherein the support member has elasticity to slide the magnetic sensor and the magnetic drum. The magnetic encoder performs positioning in a direction parallel to a rotation direction of the magnetic drum.