JP5435370B2 - Magnetic encoder - Google Patents

Description

  The present invention relates to a magnetic encoder capable of detecting the magnetism emitted from a magnetic medium by a magnetic sensor and obtaining the displacement or speed of a movable member.

  There are many mechanical devices that perform feedback control by accurately detecting the displacement and speed of a movable member. One example is a lens barrel for an autofocus camera. In the lens barrel, a focus mechanism is provided for moving the focusing lens back and forth with an electric motor or an ultrasonic motor. In order to detect the rotational displacement of the rotating cylinder constituting the focus mechanism, a magnetic encoder is used in order to detect the movement amount of the magnetic medium (that is, the advance / retreat amount of the focusing lens group) with high accuracy.

  In order to detect displacement with high accuracy, the magnetic encoder is required to have high resolution. The resolution can also be expressed by the magnetization pitch of the magnetic medium, and the magnetization pitch is conventionally 30 to 50 μm, but 10 to 20 μm and further 10 μm or less have been demanded. As the resolution increases, the influence on the output of the magnetic gap, which is the distance between the magnetic medium and the element of the magnetic sensor, increases, and it becomes necessary to eliminate the gap fluctuation. For this reason, a method in which the magnetic medium and the magnetic sensor are brought into contact with each other and slid is advantageous, and is often employed.

  In this specification, in order to make it easy to understand the positional relationship between the magnetic sensor and the magnetic medium, the direction of the relative movement of the magnetic medium with respect to the magnetic sensor is the X axis, and the curvature of the magnetic medium is perpendicular to the X axis. The direction crossing the center is defined as the Z axis, and the other as the Y axis. The Y axis corresponds to the direction along the rotation axis of the magnetic medium. Also, the point where the force that presses the magnetic sensor against the magnetic medium (pressurizing point) is located on the Z axis is defined as the origin of the X axis, and the position shift in the X direction from the X axis origin is defined as the X offset. To do. Furthermore, in order to make it easy to understand the relative orientation between the sliding surface of the magnetic sensor and the magnetic medium, the angle at which the sliding surface rotates about the X axis as the rotation axis is the pitch angle, and the angle at which the sliding surface rotates about the Y axis is the roll. When the sliding surface is parallel to the X axis, the roll angle is defined as 0 degree, and when the sliding surface is parallel to the Y axis, the pitch angle is defined as 0 degree.

  Patent Document 1 discloses that in a magnetic encoder that obtains an output signal by making a magnetic sensor face a magnetic drum as a medium, the recording pitch is magnetized by tilting with respect to the rotation direction of the magnetic drum ( (See paragraph 0018, FIG. 1).

  Patent Document 2 discloses a magnetic disk device in which an angle formed between a direction perpendicular to the track direction and a magnetization transition line is 25 to 75 ° (see paragraphs 0007, FIGS. 1 and 6).

JP 2002-228485 A JP-A-11-273001

  Paragraph 0018 of Patent Document 1 describes that “the magnetic field applied to the MR element caused a phase difference of λ / 4 between adjacent MR elements” as the reason for tilting the recording pitch. . This inclination is used to apply a magnetic field with a phase difference to a plurality of MR elements arranged in a straight line to make the magnetic gap uniform. The inclination of the magnetization pattern (that is, the magnetization pattern) formed on the surface of the magnetic drum by magnetization is limited to a large inclination that causes a phase difference of λ / 4. Patent Document 1 does not suggest that tilting the recording pitch itself contributes to improving the accuracy of the output signal. A magnetic encoder having a magnetic sensor in which a plurality of MR elements are arranged in parallel and a magnetic medium tilted with magnetization is not disclosed.

  Patent Document 2 aims to provide a “magnetic disk device capable of high density” (see the problem in paragraph 0006) in the field of magnetic recording and reproduction, and is a technology different from the field of a magnetic encoder. The effect of paragraph 0034 of Patent Document 2 describes that “the crosstalk can be greatly reduced by reducing the leakage magnetic field from the adjacent track during reproduction”. That is, noise reduction from adjacent tracks. Patent Document 2 does not suggest that tilting the recording pitch itself contributes to improving the accuracy of the output signal of the magnetic encoder.

  It is an object of the present invention to provide a magnetic encoder with improved output signal accuracy.

The magnetic encoder of the present invention comprises a magnetic sensor having a plurality of magnetoresistive elements arranged in parallel, and a magnetic medium that moves relative to the magnetic sensor,
The magnetic medium has a magnetization pattern that changes with a period of 2λm,
The plurality of magnetoresistive elements are configured as a bridge connection by at least four magnetoresistive elements arranged at a pitch λ.
Λ is greater than zero and less than λm;
The magnetoresistive element is a spin valve type giant magnetoresistive element,
The longitudinal direction of the magnetoresistive effect element is inclined by 1 to 3 ° with respect to the longitudinal direction of the magnetization pattern.

When the magnetic medium is a rotary magnetic drum, the plurality of magnetoresistive elements are arranged along the rotation direction of the magnetic drum.
By making λ smaller than λm, a multiplied output is obtained from a bridge circuit using at least four magnetoresistive elements.

The magnetic gap between the before and Symbol magnetoresistive element magnetic pattern is characterized in that it is in the range of 0～20Myuemu.

The magnetic medium is a magnetic drum, and a rotation axis is defined in a direction perpendicular to the rotation direction of the magnetic drum. When the longitudinal direction of the magnetoresistive element is parallel to the rotational axis of the magnetic drum, the longitudinal direction of the magnetization pattern is inclined with respect to the rotational axis.

  When the longitudinal direction of the magnetization pattern is parallel to the rotation axis of the magnetic drum, the longitudinal direction of the magnetoresistive element is inclined with respect to the rotation axis.

  The magnetic sensor is connected to the wiring board, a sensor board for sliding on a magnetic medium, a wiring board on which the sensor board is provided, a sensor holding plate that supports the sensor board via the wiring board. It is desirable to provide flexible printed wiring. By mounting the magnetic encoder of the present invention on a camera, the rotational displacement of the camera lens barrel can be detected.

  ADVANTAGE OF THE INVENTION According to this invention, the magnetic encoder which improved the precision of the output signal can be provided.

It is the schematic explaining the magnetic encoder of this invention. It is a top view of a sensor substrate. It is a circuit diagram which shows the connection of a spin valve type giant magnetoresistive effect element. FIG. 3 is an A-A ′ cross-sectional view of the sensor substrate of FIG. 2. It is a perspective view of a wiring board provided with a sensor board. It is the schematic of a magnetic encoder. It is a side view of the magnetic encoder of FIG. FIG. 8 is a schematic diagram supplementing FIG. 7. It is a perspective view of another magnetic encoder. It is the schematic of a spin valve type giant magnetoresistive effect element. It is the schematic explaining the magnetic encoder of a comparison form. It is the schematic for demonstrating a comparison form. It is a graph for demonstrating a comparison form. It is the schematic explaining the other magnetic encoder of this invention. It is the schematic explaining the other magnetic encoder of this invention. It is a graph which shows the output waveform of a comparative example. It is a graph which shows the output waveform of an Example. It is a graph which shows the output waveform of an Example. It is a graph which shows the output waveform of an Example. It is a graph which shows the output waveform of 16 multiplication of a comparative example. It is a graph which shows the output waveform of 16 multiplication of an Example. It is a graph which shows the Lissajous waveform of a comparative example. It is a graph which shows the Lissajous waveform of an Example.

  Hereinafter, embodiments will be described in detail with reference to the drawings. The present invention is not necessarily limited to these. For ease of understanding, the same reference numerals are used for the same parts or parts. In order to indicate the left or right side of the paired parts, an alphabet “a” or “b” is added after the reference numeral. For example, if the code is 50, 50a and 50b correspond.

(Embodiment 1)
FIG. 1 is a schematic diagram illustrating a magnetic encoder according to the present invention. The magnetic sheet 62 is shown in a state where it is developed on a plane. A magnetized pattern 62b is magnetized on the magnetic sheet 62 while alternately reversing the NS direction at a pitch λm. That is, it is magnetized in the direction of NS, SN, NS, SN along the moving direction. The longitudinal direction of each magnetized pattern 62b is inclined at an angle of θ with respect to the direction (Y-axis direction) orthogonal to the arrangement direction of the magnetized pattern (that is, the double arrow in FIG. 1). This θ is called an azimuth angle. By sticking the magnetic sheet 62 on the outer peripheral surface of the rotatable camera lens barrel and making the GMR sensor 2 formed on the sensor substrate 10 face the magnetic sheet 62 so as to have the positional relationship shown in FIG. A magnetic encoder using a magnetic drum is configured. The double arrows correspond to the direction of rotation of the magnetic drum. Although the GMR sensor 2 is hidden behind the sensor substrate on the side opposite to the magnetic sheet, the GMR sensor 2 is shown in a transparent manner for easy understanding of the positional relationship. As shown in FIG. 3, by using multiplication in the GMR sensor 2, the output of the GMR sensor can be made sinusoidal by tilting the longitudinal direction of the magnetized pattern 62b with respect to the arrangement direction of the magnetized pattern. The position detection accuracy can be increased.

  FIG. 2 is a detailed top view of the sensor substrate 10 as viewed from the side facing the magnetic sheet. An R chamfered portion 7 is formed between the surface of the sensor substrate 10 facing the medium and the side surface formed by cutting. The R chamfered portion 7 is dry-etched with plasma to finish a smooth chamfered surface. In the GMR sensor 2, as shown in FIG. 3, a plurality of spin-valve giant magnetoresistive elements a to l and terminal portions m to x are connected to form a bridge circuit, and electrodes are connected via the wiring film 2b. It is connected to the pad 2c. Specifically, 2c1 to 2c4 are used as the electrode pad 2c. The width of the sensor substrate was 0.6 mm, and the length (longitudinal dimension) of the sensor substrate in the direction orthogonal to the width was 3.1 mm. The width is a dimension of the sensor substrate in the A-A ′ direction, that is, the sliding direction (the moving direction in FIG. 1).

  FIG. 3 is a circuit diagram showing a pattern of elements connected by bridge connection. Hereinafter, when simply described as “element”, it means a spin valve type giant magnetoresistive element. First, three elements a, b, and c arranged at a pitch λ are connected in series via a terminal part m and a terminal part n to constitute a first branch part. Three elements d, element e, and element f arranged at a pitch λ are connected in series via a terminal portion o and a terminal portion p to form a second branch portion. Three elements g, h and i arranged at a pitch λ are connected in series via a terminal part q and a terminal part r to form a third branch part. Three elements j, k, and l arranged at a pitch λ are connected in series via a terminal portion s and a terminal portion t to form a fourth branch portion. The first branch portion and the second branch portion are adjacent to each other at a pitch of 5λ / 4, the second branch portion and the third branch portion are adjacent to each other at a pitch of 3λ / 2, and the first branch portion and the fourth branch portion are adjacent to each other. Are adjacent to each other at a pitch of 15λ / 2. The terminal portion u connects the first and second branches to connect to the electrode pad 2c2 (that is, the power supply voltage Vcc), and the terminal portion v connects the third and fourth branches to the electrode pad 2c4 (that is, the power supply voltage Vcc). The terminal portion w connects the first and fourth branches and is connected to the electrode pad 2c1 (that is, the B-phase output) which is the first output terminal, and the terminal portion x is connected to the second and second terminals. 3 is connected to the electrode pad 2c3 (that is, the A-phase output) which is the second output terminal. With these connections, a bridge circuit corresponding to the GMR sensor 2 is configured. Long stripe-shaped elements are arranged in parallel to each other. λ = 20 μm. The longitudinal direction of the elements a to l corresponds to the Y-axis direction in FIG. In each branch, as will be described later with reference to FIG. 13, three elements arranged in parallel at a pitch of λ are connected in series, and by multiplication, an output with a pitch of λ smaller than λm is obtained as a combined output of the three elements. Can be obtained.

  As another example of the pattern shown in FIG. 3, the terminal portion may not be formed as a member different from the element, but the element and the terminal portion may be integrally formed by using the film configuration of the element. However, it is desirable to make the change in magnetoresistance sufficiently small by forming the terminal portion wide.

4 is a cross-sectional view of the sensor substrate 10 taken along the line AA ′ of FIG. The surface of the silicon substrate 1c on which the GMR sensor 2 is formed has R chamfered portions on the ridges on both sides. The end of the SiO ₂ coating 3 was formed to have a smooth taper. The coating thickness in the flat region was about 2 μm. Even if elements and wiring are included, the thickness is several μm, and the thickness of the sensor substrate can be regarded as the thickness of the wafer. The SiO ₂ film on the element forms a magnetic gap with the surface of the magnetic sheet 62 . The detection surface between the R chamfered surfaces is composed of a flat surface and a smooth convex curved surface. As shown in FIG. 4 except for the electrode pads, the GMR sensor 2 is covered with a coating 3 that is an oxide protective film, but the coating 3 is not shown in FIG. 4, the portion of the GMR sensor 2 is illustrated in a simplified manner as compared with FIG. When sliding against the magnetic sheet, the gap is zero, but the magnetic gap is 2 μm.

  FIG. 5 is a perspective view of the sensor substrate 10 of FIG. 2 and the wiring substrate 20 provided with the same. The wiring board 20 is a glass epoxy board in which a wiring circuit is formed, and the electrode pad 2 c of the sensor board and the wiring pad 21 of the wiring board are electrically connected via the bonding wire 23. The wiring pads 21 and the wiring terminals 22 are electrically connected within the wiring board. It is difficult to directly connect an FPC (Flexible Print Circuit) to the electrode pad 2c due to the difference in size. Therefore, a wiring board was provided. An FPC is connected to the wiring terminal via lead-free solder.

FIG. 6 shows a schematic diagram of the magnetic encoder. The arrangement of the magnetic sheet 62 , which is a magnetic medium, the sensor substrate 10 having the GMR sensor 2, the glass epoxy wiring substrate 20, the sensor holding plate 30 and the mounting base 50 when viewed from the magnetic medium side is shown. For easy understanding, the see-through magnetic sheet 62 is indicated by a dotted line, and the mounting base 50 hidden behind the sensor holding plate 30 is indicated by a chain line. The mounting base corresponds to a part of the camera lens barrel.

In FIG. 6, the sensor holding plate 30 is fixed to the mounting bases 50 a and 50 b with screws using holes 39 a and 39 b formed in the fixing portion 37. By fixing the sensor holding plate 30 to the mounting base, the sensor substrate 10 is pressed against the magnetic sheet 62 at a predetermined position with a predetermined load. The sensor holding plate 30 is made of an integral metal thin plate, functions as a leaf spring, and includes a sensor holding portion 31 that holds the glass epoxy wiring board 20, two elastic arm portions, and one fixing portion 37. Yes.

  The sensor holding plate made of an integral leaf spring is made thinner compared to the case where the elastic arm portion is manufactured and assembled with another member having high rigidity or when the pivot is used together with the sensor holding plate. In addition, the sensor holding plate made of an integral leaf spring reduces the posture angle variation of the sensor substrate, contributing to a reduction in the number of components and assembly cost. When this sensor holding plate is used for a magnetic encoder, it is used in a flat state. In order to increase the spring property, bending it in advance and making it a three-dimensional structure in the Z direction (thickness direction) not only increases the processing cost, but also due to unexpected deformation due to the assembly process of the magnetic encoder This is not preferable because the spring load varies and the posture angle also varies.

The elastic arm portion includes an elastic deformation portion 32 and a support portion 33. The elastic deformation portion extends in the X-axis direction and has a zigzag shape. The rotation axis in the pitch direction is indicated by a one-dot chain line along the X axis . Elastic deformation portions 32 a and 32 b are connected to both sides of the sensor holding portion 31 so that the one-dot chain line serves as a rotation axis in the pitch direction of the sensor holding portion 31. The other end of each elastically deformable portion 32 is supported by a support portion 33 that functions as a cantilever, and the support portion is connected so as to be joined to a fixed portion 37. The boundary between the support portion 33 and the fixed portion 37 is on a wavy line connecting the space 36s and the dimension line of L4.

Elastically deformable portion 32, when pressed against the sensor substrate 10 to the magnetic sheet 62 becomes a site for generating a spring force, to stabilize the sliding of the magnetic sheet 62 and the sensor substrate 10. Moreover, since the elastic deformation part 32 can make pitch rigidity small, it can suppress the breadth of an air gap with respect to pitch angle fluctuation | variation.

The center of the GMR sensor 2 in the sensor substrate 10 (the intersection of the center line of the one-dot chain line and the two-dot chain line) is more magnetic than the rotational axis in the pitch direction of the elastic deformation portion 32 (one-dot chain line parallel to the Y axis). On the side of the edge 62a . By adopting this positional relationship, it is possible to suppress the influence of the pitch angle fluctuation in the GMR sensor 2 and to suppress the deformation of the support portion 33 when the sensor substrate is pressed against the magnetic sheet. . The center of gravity of the sensor holding portion 31 is slightly shifted from the rotational axis in the pitch direction of the elastic deformation portion 32 in the negative direction of the Y axis, but substantially above the “rotational axis in the pitch direction”. There is no problem.

  The ends of the pair of support portions 33 a and 33 b are connected to the fixed portion 37. And the support part 33 is comprised by the cross part 34 which supports an elastic deformation part, and the wide part 35 and the wide part 36 which exist between the cross part 34 and a fixing | fixed part. In the intersecting portion 34, slits are provided in the X-axis direction on both sides of the portion connected to the elastic deformation portion 32. In the region where the slit 33s is formed, the width M1 of the intersecting portion is smaller than the width M2 in the remaining portion of the intersecting portion. Providing the slits 33 s prevents stress from being concentrated at the connecting portion between the elastically deforming portion and the intersecting portion even when an external force such as an impact is applied. Since most of the intersecting portions are widened to be M2, the rigidity is enhanced as compared with a leaf spring manufactured so that the width of the support portion extends only by M1. In the wide width portion 36, the width M3 is widened toward the inside (center line side) to the extent that the wiring substrate 20 can be avoided in order to secure a space 36s when the wiring substrate 20 is inclined by an external force such as an impact. To increase the rigidity. In the wide portion 37, the width is further expanded to (M3 + M4) toward the outside, and the space between the fixed portion and the fixed portion is contributed to the improvement of rigidity. The smaller hole 38 provided in the wide portion 36 is used for temporarily fixing the sensor holding plate, and is not a hole for securely fixing.

  In this way, by widening the support portion toward the base, the rigidity is increased, and the sensor substrate 10 is prevented from being inclined in the roll direction. Due to this rigidity improvement, even if it is used in the state of a flat plate spring, it can be used thin and pivotless. A one-dot chain line parallel to the Y-axis direction corresponds to a center line connecting the center of the sensor holding unit 31 and the center of the fixed unit 37. The elastic arm portions were formed symmetrically with respect to the center line.

In FIG. 6, an electrode pad is provided near the lower end of the sensor substrate 10, and is electrically connected to the wiring substrate 20 via wire wiring, and the wiring terminal of the wiring substrate 20 is electrically connected to FPC 40 via lead-free solder. (Lead-free solder is hidden on the opposite side of the FPC and is not shown). The FPC 40 is supported by the resin 51 at the lower end of the fixed portion 37. An electrical signal from the GMR sensor 2 is taken out through the wiring board 20 and the FPC 40. The FPC is narrow between the wiring board 20 and the resin 51. This narrowing does not hinder the operation of the sensor holding plate in the pitch direction. If an FPC having a large width is used, the contribution of rigidity of the FPC becomes too large. Then, the elastic deformation portion is bent so as Ru is faced to the sensor holding plate parallel to the magnetic sheet prevents the FPC large-width.

L0 is the distance between the rotational axis in the pitch direction of the elastic deformation portion and the center of the GMR element, and corresponds to the distance between the one-dot chain line and the two-dot chain line along the X direction. L1 corresponds to the distance from the rotational axis in the pitch direction of the elastically deforming portion to the edge 62a of the magnetic sheet (edge on the side close to the fixed portion). L2 is from the rotation axis in the pitch direction of the elastically deformable portion (one-dot chain line in the direction along the X axis) to the root of the support portion (intersection or intersection of the support portions) 34 (boundary with the wide width portion 35). Corresponds to the dimensions. L3 corresponds to the dimension from the rotation axis in the pitch direction of the elastic deformation portion to the root of the thick portion 35 (boundary with the wide portion 36). L4 corresponds to the dimension from the rotation axis in the pitch direction of the elastic deformation portion to the root of the wide portion 36 (boundary with the fixed portion 37).

FIG. 7 is a side view when viewed from the magnetic medium side along the negative direction of the Y-axis of FIG. In this state, the sensor substrate 10 is pressed against the magnetic sheet 62 and the elastic deformation portion is bent. When the position of the sensor substrate is displaced in the X-axis direction, the amount of the displacement is referred to as an offset amount.

The magnetic sheet 62 according to FIGS. 6 and 7 was produced by fixing a tape-like plastic film coated with a magnetic material to a nonmagnetic surface having a predetermined curvature with an adhesive. With the rotation of the nonmagnetic surface, the width Wb of the magnetic sheet in the direction intersecting the sensor substrate 10 was 2.5 mm, and the curvature radius of the magnetic sheet surface was 27.5 mm.

  FIG. 8 is a schematic diagram supplementing FIG. FIG. 8A shows a state in which the magnetic sheet 62 adhered and fixed to a part of the lens barrel 69 for the camera and the sensor substrate 10 slide. Illustration of the sensor holding plate and the like is omitted. An enlarged view of part of FIG. 8A corresponds to FIG. 8B to 8D are cross-sectional views seen from the direction along the X axis in FIG. FIG. 8B shows that in order to press the sensor substrate 10 against the magnetic sheet 62, the periphery of the sensor holding plate 30 is pushed down to the location indicated by the solid line, but the sensor holding portion 31 is located at the location indicated by the dotted line. ing. The difference between the positions of the dotted line and the solid line is referred to as “push amount”. FIG. 8 (c) shows that when the sensor substrate 10 is pressed against the magnetic sheet 62, the surface parallel to the surface of the sensor holding plate 30 before pressing and the surface 11 on the medium facing side of the sensor substrate after pressing. An angle to be made is shown, and this angle is referred to as a pitch angle. FIG. 8D shows the length of the region where the magnetic sheet 62 and the sensor substrate 10 overlap, and this length is referred to as the “overlap amount”.

FIG. 9 is a perspective view of another magnetic encoder, which is illustrated for explaining the magnetized state of the magnetic sheet. While the magnetic sheet 62 inverts the magnetic field direction of the magnetizing field to be applied, N-S, S-N , N-S, in the order of S-N, to form a magnetized pattern 62 b in which a magnetization direction is reversed ing. However, the case where the azimuth angle is 0 ° is illustrated. The magnetic sensor has a GMR sensor 2 on the sensor substrate 10, and the GMR sensor 2 is connected to the FPC 40 ′ via a wiring film (not shown). The physical distance between the magnetic sheet 62 and the GMR sensor 2 is zero if it is a sliding type. However, since there is a coating layer or the like between the GMR sensor 2 and the magnetized pattern, the magnetic distance (that is, the magnetic gap) is not zero. When the magnetic sheet 62 moves relative to the magnetic sensor in the movement direction indicated by the double arrows, the magnetic field strength applied to the spin valve giant magnetoresistive effect element changes, and the resistance of the element changes. In FIG. 9, unlike the first embodiment, the flexible printed wiring is provided on the sensor substrate on the side opposite to the medium facing surface side.

FIG. 10 is a schematic diagram showing an example of a spin valve type giant magnetoresistive element. On a silicon substrate 1c, the fixed layer 1 21, after film formation in the order of the non-magnetic conductive layer 1 22, and the free layer 1 23, a resist mask by a photolithography technique, and patterned by ion milling, longitudinal A stripe-shaped element having the above structure was manufactured. Fixed layer 1 21 is a laminated film of CoFe / Ru / CoFe, and a thickness of 5 (nm). A nonmagnetic conductive layer 1 22 is Cu, and a thickness of 2 (nm). Free layer 1 23 is a two-layer film of CoFe / NiFe, and a thickness of 3 (nm). In order to fix the magnetization direction of the fixed layer, the film was formed by sputtering in a magnetic field of about 2.4 kA / m. About 2.4 kA / m corresponds to about 30 Oe. The free layer was also formed by sputtering in a magnetic field in order to increase the magnetic properties by adding anisotropy to NiFe.
In the examples, a spin valve type giant magnetoresistive element of a type in which an antiferromagnetic layer is further provided between the substrate and the fixed layer is used.

Magnetization direction of the pinned layer 1 21 is indicated by solid arrows 26, the magnetic field direction of the external applied to the free layer 1 23 is indicated by arrow 27 and dashed arrows 28 in dashed line. When an external magnetic field is applied in the direction of the dashed-dotted arrow 27, the direction of magnetization is the same as the magnetization direction of the fixed layer, so that the electrical resistance of the spin-valve giant magnetoresistive element decreases as the magnetic field strength increases. Even when an external magnetic field is applied in the direction of the broken arrow 28, the electric resistance of the spin-valve giant magnetoresistive element does not change because the direction is opposite to the magnetization direction of the fixed layer.

(Comparative form 1)
FIG. 11 is a schematic diagram illustrating a magnetic encoder according to a comparative example. Longitudinal magnetization pattern 62 b of the magnetic sheet 62 is perpendicular to the moving direction of the magnetic sheet shown in both arrows. That is, the configuration other than the magnetic sheet, the sensor substrate 10 and the GMR sensor 2 is merely omitted, and the configuration is the same as that of the first embodiment except that the azimuth angle θ = 0 °.

  12 is an enlarged schematic view of a part of the comparative example 1 of FIG. 11 and viewed in the Y-axis direction. The elements a, b and c in the circuit (circuit of FIG. The relationship with a magnetic sheet is shown. FIG. 13 is a graph for explaining signal multiplication for the element a, the element b, and the element c. Focusing on the enlarged portion 10 ′ of the sensor substrate 10 in FIG. 12, each of the elements a, b, and c arranged at the pitch λ receives a leakage magnetic field from the relatively moving magnetic sheet. , The magnetic resistance changes. Each change is shown in FIG. 13 as an output waveform of an electric signal. In addition to the output waveforms of the elements a, b, and c, the sum of the three output waveforms is shown as a combined waveform of the element a + element b + element c. The pitch of this composite waveform is λ = 20 μm, which is smaller than the pitch λm = 30 μm of the magnetized pattern of the magnetic sheet. Thus, by connecting three elements arranged in parallel at a pitch of λ in series, and multiplying, an output with a pitch of λ smaller than λm can be obtained as a combined output of the three elements.

  In the field of magnetic encoders for cameras, higher resolution of sensor output signals is required. In order to achieve high resolution, it is necessary to stabilize the sensor output amplitude, increase the resolution of the output signal itself, and maintain the sensor output waveform as a sine wave so that the sensor output can be easily multiplied by the signal processing circuit. The inventors think that will be. The inventors examined a structure in which the magnetization pitch λm of the magnetic sheet was increased to 30 μm in the configuration of FIG. The reason why the intensity of the leakage magnetic field is increased by increasing the magnetization pitch is to stabilize the sensor output amplitude. However, increasing λm decreases the resolution of the sensor output signal itself. In order to improve the resolution, the bridge circuit of FIG. 3 is used to perform multiplication and obtain an output signal with λ smaller than the magnetization pitch λm, thereby improving the resolution. However, the leakage magnetic field exceeds the saturation magnetic field of the sensor, the harmonic component of the sensor output waveform increases, and the output waveform is distorted. Therefore, in order to reduce this distortion and cope with high resolution, the configuration of Embodiment 1 was produced. Specifically, it demonstrates using a graph with an Example and a comparative example.

(Embodiment 2)
FIG. 14 is a schematic diagram illustrating another magnetic encoder according to the present invention. Comparative Embodiment 1 differs, by GMR sensor 2 is a longitudinal direction of the element, to tilt by the same angle as the azimuth angle θ with respect to the longitudinal direction of the magnetization pattern 62 b, arranged a sensor substrate 10 is there. The effect by the azimuth angle is the same as that of the first embodiment. However, in the magnetic encoder, if the sensor substrate 10 is inclined at a minute angle in the moving direction of the medium, it is affected by an assembly error. Therefore, for industrial mass production, the first embodiment is more preferable than the second embodiment in terms of increasing the accuracy of the output signal.

(Embodiment 3)
FIG. 15 is a schematic diagram illustrating another magnetic encoder according to the present invention. The difference from the first comparative embodiment is that the element longitudinal direction of the GMR sensor 2 is inclined on the sensor substrate 10 with respect to the longitudinal direction of the sensor substrate. The angle of inclination, the longitudinal direction of the device is to make the azimuth angle θ with respect to the longitudinal direction of the magnetization pattern 62 b. The effect by the azimuth angle is the same as that of the first embodiment.

(Comparative Example 1)
FIG. 16 is a graph showing two output signals obtained from the bridge circuit of FIG. 3 when the azimuth angle θ = 0 ° in the configuration of the comparative example 1. The time on the horizontal axis is expressed in milliseconds, and the voltage on the vertical axis is expressed in arbitrary units. For both the A-phase output signal and the B-phase output signal, the waveform was saturated before and after the peak of the amplitude, and a trapezoidal output was obtained.

In the measurement of Comparative Example 1, the conditions according to FIG. 8 were set as follows.
In the GMR sensor, the spin valve type giant magnetoresistive element has a length = 225 μm, a width = 4 μm, and λ = 20 μm.
In the magnetic sheet, the magnetization pitch = λm / 2 = 30 μm.
The sensor substrate had an offset amount = 0 μm, a push-in amount = + 0.35 μm, a pitch angle = 0 °, and an overlap amount = 1.7 μm.

Example 1
FIG. 17 is a graph showing two output signals obtained from the bridge circuit of FIG. 3 when the azimuth angle θ = 1 ° in the configuration of the first embodiment. Conditions other than the azimuth angle were the same as in Comparative Example 1. In Example 1, by adding a minute azimuth angle, both the A-phase output signal and the B-phase output signal have clearer peaks than those in Comparative Example 1, and distortion is suppressed, resulting in a sinusoidal output. It was.

(Example 2)
18 is a graph showing two output signals obtained from the bridge circuit of FIG. 3 when the azimuth angle θ = 2 °. Other conditions were the same as in Example 1. Both the output signal of the A phase and the output signal of the B phase were clearer than those of Example 1, and an output having a sine wave shape with suppressed distortion was obtained.

(Example 3)
FIG. 19 is a graph showing two output signals obtained from the bridge circuit of FIG. 3 when the azimuth angle θ = 3 °. Other conditions were the same as in Example 1. Both the output signal of the A phase and the output signal of the B phase were clearer than those in Example 2, and an output having a sine wave shape with suppressed distortion was obtained. However, the amplitude of the output voltage was smaller than that in Example 2.

  When an experiment was performed with θ> 3 °, the amplitude of the output voltage decreased rapidly as the azimuth angle θ was increased.

(Comparative Example 2)
FIG. 20 shows a state in which a 16-phase signal is generated by phase inversion and waveform synthesis using an electronic circuit based on the output signals A and B of the output signal of Comparative Example 1 (multiplication by 16). It is a graph which shows. The length of the pitch between signals is shown in the upper left of the graph with double arrows. This pitch corresponds to the phase difference. Since the original waveform is distorted, the pitch between adjacent signals is not uniform.

Example 4
FIG. 21 shows a state in which a 16-phase signal is generated by phase inversion and waveform synthesis using an electronic circuit based on the output signals of the output signals A-phase and B-phase in Example 2 (multiplication by 16). It is a graph which shows. The length of the pitch between signals is shown in the upper left of the graph with double arrows. This pitch corresponds to the phase difference. Since the distortion of the original waveform is suppressed, the pitch between the signals adjacent to each other is made more uniform than that of the comparative example 2, and the position detection accuracy can be improved as a magnetic encoder and high resolution can be supported. .

(Comparative Example 3)
FIG. 22 is a graph showing a Lissajous waveform obtained by synthesizing the sensor outputs of the output signals A phase and B phase of Comparative Example 1. Since the original waveform is distorted, the Lissajous is square. The Lissajous curve is wide due to the influence of noise. When the noise of these output signals is removed by a filter, a Lissajous figure that is narrow and close to a square with rounded corners can be obtained. It is difficult to accurately determine the rotation angle of the magnetic sheet using this Lissajous.

(Example 5)
FIG. 23 is a graph showing a Lissajous waveform obtained by synthesizing the sensor outputs of the output signals A phase and B phase in Example 2. Since distortion is suppressed in the original waveform, the Lissajous is circular. The Lissajous curve is wide due to the influence of noise. When the noise of these output signals is removed by a filter, it becomes narrow and a circle Lissajous can be obtained. When it is circular, the electric angle is converted into a position or distance by calculating the arc tangent using the sensor outputs of the A phase and the B phase of Example 2, and the magnetic sheet provided in the lens barrel The rotation angle can be obtained with high accuracy. When one of the sensor outputs is represented by a sine wave signal and the other of the sensor outputs is represented by a cosine wave signal, the rotation angle ψ can be obtained by the following equation.
ψ = arctan ((sine wave signal) / (cosine wave signal))

  The present invention can be applied as a magnetic encoder capable of detecting the magnetism emitted from the magnetic medium with a magnetic sensor and determining the displacement or speed of the movable member.

1: Magnetic encoder,
1c: silicon substrate,
2: GMR sensor,
a to l: Spin valve type giant magnetoresistive element,
mx: terminal part,
2b: wiring film,
2c: electrode pad,
3: coating,
7: R chamfer,
10: sensor substrate,
10 ': a part of the sensor substrate,
11: Surface facing the medium
20: wiring board,
21: Wiring pad,
22: Wiring terminal,
23: Bonding wire,
1 21: Fixed layer,
1 22: non-magnetic conductive layer,
1 23: Free layer,
26: magnetization direction of the fixed layer,
27, 28: Free layer magnetization direction,
30: sensor holding plate,
30 ': sensor holding plate,
30 ″: sensor holding plate,
31: Sensor holding part,
32a, 32b: elastic deformation part,
32e, 32f: elastic deformation part,
32d: elastic deformation part,
33a, 33b: support part,
33s: slit,
34a, 34b: intersection,
35a, 35b: thick part,
36a, 36b: wide part,
36s: space,
37: fixed part,
38: hole,
39a, 39b: holes,
40: FPC,
51: resin,
50a, 50b: mounting base ,
62 : Magnetic sheet
62b: magnetization pattern ,
6 9: Tube,
101: Magnetic encoder,
102: GMR sensor,
110: Sensor substrate

Claims (3)

A magnetic sensor having a plurality of magnetoresistive effect elements arranged in parallel, and a magnetic medium that moves relative to the magnetic sensor;
The magnetic medium has a magnetization pattern that changes with a period of 2λm,
The plurality of magnetoresistive elements are configured as a bridge connection by at least four magnetoresistive elements arranged at a pitch λ.
Λ is greater than zero and less than λm;
The magnetoresistive element is a spin valve type giant magnetoresistive element,
The magnetic encoder according to claim 1 , wherein a longitudinal direction of the magnetoresistive element is inclined by 1 to 3 degrees with respect to a longitudinal direction of the magnetization pattern.   The magnetic medium is a magnetic drum, wherein a longitudinal direction of the magnetoresistive element is parallel to a rotation axis of the magnetic drum, and a longitudinal direction of the magnetization pattern is inclined with respect to the rotation axis. Item 2. The magnetic encoder according to Item 1. The magnetic medium is a magnetic drum, a longitudinal direction of the magnetization pattern is parallel to a rotation axis of the magnetic drum, and a longitudinal direction of the magnetoresistive element is inclined with respect to the rotation axis. Item 2. The magnetic encoder according to Item 1.