JP3865200B2 - Magnetic encoder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic encoder, and relates to an improvement in size reduction and easy positioning of a magnetic sensor and a magnetic drum.
[0002]
[Prior art]
A perspective view of a conventional magnetic encoder is shown in FIG . The magnetic recording medium 102 of the magnetic encoder is fixed around the end of the shaft 101 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 that are magnetosensitive elements are arranged at a predetermined interval. Here, the 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 shape of a so-called magnetic drum having substantially the same diameter as the shaft 101. A sequence of magnetic signals formed by magnetizing the magnetic recording medium 102 is referred to as a track 106. The track 106 is a magnetic recording medium written with a magnetization pitch λ. The magnetic sensor detects each magnetic signal (magnetic field generated from the magnetic recording medium).
[0003]
Generally, a magnetic sensor and a magnetic recording medium are installed with a gap of about 0.7 to 0.8 times the magnetization pitch λ. When the pitch λ is narrowed, the gap g (gap) between the magnetic sensor and the magnetic recording medium must be set narrow. Therefore, a method of sliding a magnetic sensor with a spacer material having a predetermined thickness has been used. The magnetic sensor has a configuration in which a spacer material is attached to the side having a plurality of magnetoresistive effect element patterns. A spacer material having a thickness corresponding to the gap g is brought into contact with the rotating magnetic recording medium. By doing in this way, the magnetic encoder which can obtain a signal simply, without adjusting the gap g can be comprised.
[0004]
A conventional magnetic encoder that affixes a spacer material on 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 an outer diameter φ = 50 mm of the drum. The diameter is large. For this reason, even if the magnetic sensor has a slight inclination with respect to the outer periphery of the drum, there is little influence on the signal. Further, the difference (g2−g1) between the central portion pattern and the gap g1 between the drum and the end portion pattern and the gap g2 between the drums was as small as 6 μm, and the influence on the output signal was small. The present inventors have studied 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 due to the reduction in the outer diameter will be described with reference to FIG .
[0005]
[Problem to be Solved by the Invention]
FIG. 3 is a schematic sectional view of a small magnetic encoder in which a magnetic sensor 62 having patterns 63 and 64 arranged on a flat substrate is opposed to the magnetic drum 61. As the drum diameter decreases, the difference between the gap g1 between the central pattern 63 and the magnetic drum 61 and the gap g2 between the end pattern 64 and the magnetic drum 61 increases. Since the magnetic field received by each pattern is different, the smaller the outer diameter of the drum, the greater the effect that the difference between g1 and g2 has on the output signal. That is, since the sufficient output signal cannot be obtained in the end pattern 64, the accuracy of the output signal of the magnetic sensor obtained from the output signal of each pattern also decreases. The drum diameter examined by the inventors (the diameter of the magnetic drum) is approximately 15 mm, and the difference between 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 by suppressing the difference between g1 and g2.
[0006]
Further, when the drum diameter is reduced in a small magnetic encoder, if a deviation in a direction parallel to the rotation direction occurs, the difference between g1 and g2 further increases, and the influence on the output signal is further increased. Accordingly, another object of the present invention is to provide a magnetic encoder capable of easily positioning a magnetic sensor and a magnetic drum while suppressing a shift parallel to the rotation direction.
[0007]
[Means for Solving the Problems]
The magnetic encoder of the present invention is a magnetic encoder that detects a magnetic field generated from a magnetic drum by a magnetoresistive effect element provided in a magnetic sensor, and the magnetic sensor has a plurality of magnetoresistive effect elements arranged on a substrate. A stepped recess is provided, and the magnetoresistive element is arranged along the curved surface of the magnetic drum.
[0008]
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. If the arrangement along the stepped concave portion corrects the gap deviation between the MR element and the magnetic drum, it is included in the arrangement along the curved surface of the magnetic drum referred to in the present application. The MR element may be an AMR or GMR (giant magnetoresistive element).
[0009]
The step-shaped 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 desirable that the magnetic sensor is configured such that the stepped recesses disposed on the substrate are stepped thin film structures or stepped recesses formed directly on the substrate. The stepped thin film structure can be formed by a method in which thin films are stacked stepwise by a photolithography technique, or a method in which the thin film is cut by etching, grinding of a grindstone, or the like. Further, the step-like recess formed directly on the substrate can be formed by a method of press molding the substrate, a method of cutting the substrate with a rotating grindstone, a method of directly etching the substrate, or the like.
[0010]
The following method is mentioned as a method of forming the MR element. The first method is to form MR elements for each stage when thin films are stacked. The second method is to form a recess after embedding an MR element between insulating layers in the same arrangement as in the first method. In the third method, MR elements are formed in each step after the step-shaped recess is formed. Furthermore, after forming the step-like concave portion by the third method, the MR element is arranged on the surface of each step, and resin or the like is molded on the medium facing surface side to form a curved medium facing surface. It is good. By covering each MR element with a protective film, it is called a recess including a configuration in which the MR elements appear to be arranged inside the recess rather than on the surface of the recess.
[0011]
By disposing the MR element in a stepped recess along the curved surface of the magnetic drum, the deviation in the distance (gap) between the opposing magnetic drum and the MR element is corrected, and even if the magnetic drum has a small diameter, the MR elements are arranged. Sensitivity can be made uniform at the center and at the end. Here, glass, ceramics, or the like is used for the substrate on which the stepped recesses are arranged. Further, it is desirable to use an insulating alumina film or silicon oxide film for 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 (occurrence of insulation failure). In the photolithography technique, an exposure process is used to pattern the MR element. In order to focus the exposure focus on the surface of the recess and accurately pattern the MR element, a stepped thin film structure having a flat surface for each step or a stepped structure formed directly on the substrate may be used as the recess. .
[0012]
Alternatively, a method may be used in which an MR element is formed on a substrate on which a recess is formed in advance by pressing a nonmagnetic metal substrate or molding a resin (such as injection molding). According to these methods, the curved surface of the magnetic drum and the concave surface that slides smoothly can be formed.
[0013]
In the present invention, the magnetic drum has a diameter of 30 mm or less and a magnetization pitch of 100 μm or less. For example, when the pitch of the magnetic drum is smaller than 30 mm at a pitch of 80 μm, the difference in gap between the central portion and the end portion of the MR element in the MR element arrangement is 11 μm. When the magnetization pitch was larger than 100 μm as in the conventional magnetic encoder, the influence on the output signal was small even with a magnetic drum diameter of 30 mm. 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, the configuration of the present application adjusts the position of the arrangement of the MR elements on the substrate to the curved surface of the drum so that the magnetic drum has a diameter of 30 mm or less and a magnetization pitch of 100 μm or less. It is possible to suppress a difference in sensitivity between the central portion and the end portion of the MR element array. This configuration is particularly suitable for a magnetic encoder for a printer having a small drum diameter.
[0014]
As magnetic encoders become smaller, a smaller magnetization pitch is required than before. When the magnetization pitch becomes small, the magnetic signal generated from the magnetic drum becomes weak and the signal output becomes small. According to the measurement by the present inventors, when compared with a magnetic encoder with a magnetization pitch of 40 μm and a magnetic encoder with a magnetization pitch of 80 μm, the former only obtained about half the signal output of the latter. Therefore, conventionally, a method has been used in which the MR element is folded to increase the element length (i.e., a zigzag type MR element). With this method, the output signal can be increased, but when the width of the magnetic sensitive portion is increased and the diameter of the magnetic drum is reduced, the difference in sensitivity between the center and the end of the MR elements is increased. There was a drawback. In the magnetic encoder of the present invention, even if the number of turns of the MR element is increased and the width of the magnetic sensitive part is widened, a difference in sensitivity can be suppressed between the central part and the end part of the MR element arrangement. That is, a high output signal can be obtained even when the magnetization pitch is reduced.
[0015]
Further, in the conventional structure, when the diameter of the magnetic drum is 30 mm or less, the influence of the deviation in the direction parallel to the rotation direction on the output signal becomes large. 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 prevent the deviation in the direction parallel to the magnetization pitch. Can It includes a support member that supports the magnetic sensor, and sliding the magnetic sensor and the magnetic drum by the elasticity of the support member to perform positioning in a direction parallel to the rotation direction of the magnetic drum facilitates positioning. This is advantageous in that the deviation is kept small.
[0016]
The support member is preferably made of elastic nonmagnetic metal or ceramic. In addition, it is desirable to provide a sheet or a coating film that gives wear resistance to the sliding surface of the magnetic sensor.
[0017]
In the magnetic sensor, the substrate has electrodes in addition to the MR elements. Furthermore, it is fixed by the support member, and FPC (flexible printed circuit board) is provided as a lead wire on the electrode of the substrate. Here, the substrate is made of a material having a strength necessary to accurately define the distance between the MR element and the magnetic drum. FPC is a lead wire and is made of a flexible material.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is an exploded perspective view illustrating a magnetic encoder according to an example of the present invention. Here, the magnetic drum has a rotating shaft (shaft) 1 and a magnetic body 2 provided in the periphery thereof. The magnetic body 2 was provided with a plurality of magnetic poles (units for outputting magnetic signals) 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 for the printer. The magnetic sensor 3 was supported by the arm 4 on the back side. In addition, the arm applies a force to hold the magnetic sensor so that it slides without leaving the magnetic drum. By providing the concave portion 3a on the magnetic sensitive surface side of the magnetic sensor, the displacement in the direction parallel to the drum rotation direction is suppressed, and the magnetic sensor and the magnetic drum are easily positioned. Details of the MR sensor applied to this magnetic encoder will be described with reference to FIG.
[0019]
FIG. 2 is a cross-sectional view of a magnetic sensor according to the present invention. In this magnetic sensor, the substrate is formed in a staircase shape so that the MR elements are arranged in a cross-sectional shape corresponding to the outer diameter of the magnetic drum. Therefore, a step-like base film is formed by forming an insulating film used as a base of the MR element on a flat substrate in a predetermined pattern using a photolithography technique.
[0020]
A method for forming the cross-sectional shape will be described. The forming method was performed in the order of film formation and etching. First, film formation will be described. After the first MR element and the wiring film 12 were formed on the glass substrate 11, an alumina film 13 was formed to a thickness of 1.0 μm as an intermediate insulating film. After the chromium film 13a was formed to 0.05 μm, the alumina film 14 was further formed to 1.4 μm. Next, after the second MR element and the wiring film 15 were formed, an alumina film 16 was formed in an order of 1.0 μm, a chromium film 16a was formed in an order of 0.05 μm, and an alumina film 17 was formed in an order of 3.2 μm. Finally, after the third MR element and the wiring film 18 were formed, the alumina film 19 was formed in the order of 1.0 μm, the chromium film 19a was formed in the order of 0.05 μm, and the alumina film 20 was formed in the order of 2.0 μm.
[0021]
Next, etching will be described. First, a resist was formed by photolithography outside the center of the sensor from 370 μm, and dry etching using BCl ₃ and Cl ₂ as reaction gases was performed. Here, the chromium film 19a functions as an etching stopper for removing only the alumina film 20 having a surface layer of 1.4 μm from the alumina films 19 and 20, and preventing the second layer alumina film 19 from being etched. Further, since the chromium film is nonmagnetic, the magnetic signal emitted from the magnetic drum is not impaired. After removing the portion of the chromium film 19a exposed by ion milling, a resist is formed outside 270 μm from the center of the sensor, and the same dry etching and ion milling are performed to obtain the alumina films 19 and 17 and the chromium film 16a. It was removed according to the resist pattern. Finally, a resist was formed outside 120 μm from the sensor center, 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. Through the above steps, the recess 3 a was formed on the magnetic sensitive surface side of the magnetic sensor 3. In addition, the arrangement of the MR element is also along the recess. The connection for connecting each layer of the MR element and the wiring films 12, 15 and 18 was formed by forming through holes (through holes) in the layers of the alumina films 13, 14 and 16, 17 and sputtering copper therethrough. .
[0022]
【The invention's effect】
As described above, by using the magnetic encoder of the present invention, which has a recess for arranging a plurality of MR elements on a substrate, and the MR elements are arranged along the curved surface of the magnetic drum, the diameter of the magnetic drum can be reduced. Even if it becomes smaller, a highly accurate output signal can be obtained, and a magnetic encoder that does not cause positional deviation can be configured.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a magnetic encoder of the present invention.
FIG. 2 is a cross-sectional view of a magnetic sensor according to the present invention.
FIG. 3 is a schematic cross-sectional view illustrating a positional deviation of a conventional magnetic sensor.
FIG. 4 is a perspective view of a conventional magnetic encoder.
[Explanation of symbols]
1 rotating shaft, 2 magnetic material,
3 Magnetic sensor, 3a recess,
4 arms, 11 substrates,
12 first MR element and wiring film, 13 alumina film,
13a Chrome 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,
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 (5)

  A magnetic encoder for detecting a magnetic field generated from a magnetic drum by a magnetoresistive effect element provided in a magnetic sensor, wherein the magnetic sensor includes a stepped recess for arranging a plurality of magnetoresistive effect elements on a substrate, A magnetic encoder, wherein magnetoresistive elements are arranged along a curved surface of a magnetic drum. 2. The magnetic encoder according to claim 1, wherein the magnetic drum has a diameter of 30 mm or less and a magnetization pitch of 100 μm or less.   2. The magnetic encoder according to claim 1, wherein the magnetic sensor substrate has the stepped recess formed by a stepped thin film structure or a stepped recess formed directly on the substrate. .   2. The magnetic encoder according to claim 1, wherein the recess of the magnetic sensor substrate is formed by pressing a nonmagnetic metal substrate or molding a resin. 5. The magnetic encoder according to claim 1 , further comprising: a support member that supports the magnetic sensor, wherein the support member is elastic to slide the magnetic sensor and the magnetic drum. A magnetic encoder characterized by positioning in a direction parallel to the rotation direction of the drum.

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