JP2012073241A - Encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoder that has improved position detection accuracy while keeping a gap with a magnetic medium.SOLUTION: In the magnetic medium 2, magnetic medium elements which are magnetized in opposite directions to each other are arranged alternately in a line at a fixed pitch. A magnet sensor 3 is provided to face the magnetic medium 2 with a gap therebetween and which moves in a longitudinal direction of the magnetic medium 2. The magnet sensor 3 has position detection units 50 including a plurality of magnetic resistance elements 51 which are arranged in the moving direction and mutually connected in series, and includes a higher harmonic cancelling pattern 52 for cancelling higher harmonics occurring in the detection signal at at least one of the position detection units along the moving direction.

Description

  The present invention relates to a linear encoder and an encoder including a rotary encoder, and more particularly to improvement of detection accuracy thereof.

  A magnetic encoder that detects the amount of movement with respect to a magnetic medium by using a magnetic medium in which portions having different magnetization directions are alternately arranged, moving relative to the magnetic medium, and detecting a change in a magnetic field generated by the magnetic medium. Known (Patent Document 1).

  The detection accuracy of the magnetic encoder increases as the pitch λ that changes the magnetization direction decreases, but when the pitch λ is decreased, the magnetic field detection element on the magnetic encoder side contacts the magnetic medium and slides on the magnetic medium. If it is not close enough, the magnetic field cannot be detected.

  On the other hand, when an air gap is provided between the magnetic medium and the magnetic encoder, the output of the magnetic encoder is a signal as shown in FIG. When this signal is expressed in terms of frequency components, as shown in FIG. 16 (b), it is a signal that includes odd-order harmonics in addition to the primary signal that is originally obtained. The higher the frequency, the smaller the component of the harmonic, but the signal detection accuracy may deteriorate due to this harmonic. In one example, assuming that the intensity of the primary signal (desired signal) is 100%, the intensity of the third harmonic is 30%, the intensity of the fifth harmonic is 10% of the desired signal intensity, and the seventh harmonic signal. Is also 5%.

  Conventionally, in order to cancel such harmonics, as shown in FIG. 17, a predetermined distance from the magnetic field detection element (λ / (2n) in the case of the nth harmonic, where λ is the magnetization pitch of the magnetic medium ), A harmonic cancellation pattern for canceling the harmonics is provided at a position that is far away. Specifically, Reference 2 discloses a position detector that reads position information periodically changing at a fundamental wavelength λ written on a scale by a magnetic sensor head, and the magnetic sensor head converts the position information into a predetermined signal. In this example, the first and second magnetoresistive elements are output in series, and the second and third magnetoresistive elements are arranged on both sides of the first magnetoresistive element with an interval δ and connected in series. . In this example, when the ratio of the outputs of the first magnetoresistive element and the second and third magnetoresistive elements is r, the condition r + 2cos (2nπδ / λ) = 0 (n is an odd number of 3 or more) is satisfied. Thus, the output ratio r of each magnetoresistive element is adjusted on the assumption that the nth harmonic is removed.

  Further, in Patent Document 3, a magnetoresistive element group having a phase in which one harmonic component with respect to the output fundamental wave is canceled out with an opposite phase is provided, and in this magnetoresistive element group, the harmonic order is k, A device in which magnetoresistive elements are arranged at intervals of (n ± m / (2k)) × λ, where λ is the pitch of the signal magnetic field, n is an integer, and m is an odd number is disclosed.

JP 2007-121253 A JP-A-10-185507 JP 63-225124 A

  As described above, if the magnetic field detection element on the magnetic encoder side is brought close to slide on the magnetic medium as described above, the magnetic medium and the magnetic encoder are relatively moved by the frictional resistance between the magnetic medium and the magnetic field detection element. Extra force is required to move it. As an example, in a lens of a camera that performs focusing by moving the lens linearly, it is considered to detect the movement position of the lens using a magnetic encoder (linear encoder) that detects the linear movement amount. In such an application example, it is expected that an air gap (gap) should be provided between the magnetic medium and the linear encoder so that the lens can be moved with as little force as possible.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an encoder capable of improving the accuracy of position detection while leaving a gap with a magnetic medium.

  An encoder according to an aspect of the present invention is directed to a magnetic medium in which magnetic medium elements magnetized in opposite directions are alternately arranged in a line at a constant pitch λm, with a gap therebetween, and the magnetic medium An encoder including a magnetic sensor that relatively moves in the longitudinal direction, wherein the magnetic sensor is arranged along the moving direction and includes a plurality of magnetoresistive elements connected in series with each other, and the position detection A harmonic cancellation pattern that is connected in series to the magnetoresistive element of the unit and cancels the harmonics generated in the detection signal output by the position detection unit is provided on at least one side of the position detection unit along the moving direction. Is.

  Here, harmonic cancellation patterns that are connected in series to the magnetoresistive element of the position detection unit and cancel harmonics generated in the detection signal output by the position detection unit are provided on both sides of the position detection unit along the moving direction. May be.

  In addition, t position detection units are provided, t is an integer of 2 or more, and the magnetoresistive elements of the position detection units are respectively determined based on the pitch λm from predetermined detection positions of the position detection units. You may arrange | position to the position of the distance of (lambda) s / 2n using reference pitch (lambda) s. Here, n is an odd number of 3 or more. At this time, the plurality of magnetoresistive elements included in the position detection unit may be arranged at a distance of λs / (2n × k) from each other (k is an integer of 5 or more). Further, the magnetoresistive element of the position detecting unit may be a spin valve type giant magnetoresistive element, and the reference pitch λs may be set to λs = 2λm / t.

  Furthermore, the harmonic cancellation pattern that cancels the Nth-order harmonics may include a smaller number of magnetoresistive elements than the number of magnetoresistive elements included in the position detection unit.

  According to the present invention, a plurality of magnetoresistive elements in the position detection unit are provided, and the detection value is emphasized by increasing the resistance value compared to the magnetoresistive element of the harmonic cancellation pattern, thereby leaving a gap between the magnetic medium and the magnetic medium. , Position detection accuracy can be improved

It is explanatory drawing showing the outline | summary of the linear encoder which concerns on embodiment of this invention. It is a schematic diagram showing the structural example of the magnetic sensor of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing an example of the element shape in the magnetic sensor of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing another example of the element shape in the magnetic sensor of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of a pattern of the magnetic sensor of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing another example of a pattern of the magnetic sensor of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of the output signal of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of the output signal of the linear encoder of a comparative example. It is explanatory drawing showing the example of the output signal of the linear encoder of another comparative example. It is explanatory drawing showing the example of the output signal by an example of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of the output signal by another example of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of the output signal of the linear encoder of a comparative example. It is explanatory drawing showing the example of the output signal of the linear encoder of another comparative example. It is explanatory drawing showing the example of the output signal by an example of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of the output signal by another example of the linear encoder which concerns on embodiment of this invention. It is explanatory drawing showing the example of the output signal of the linear encoder containing a harmonic. It is explanatory drawing showing the element shape of the conventional linear encoder.

  The encoder according to the present embodiment is, for example, a linear encoder 1 and includes a magnetic medium 2 and a magnetic sensor 3 as illustrated in FIG. Further, the magnetic sensor 3 includes a base material 31 and a magnetic detection element 32 as illustrated in a cross section in FIG. The magnetic sensing element 32 is, for example, an AMR element, a stacked GMR element, or a spin valve (SV) type giant magnetoresistive (GMR) element. The spin valve type GMR element includes a tunnel junction type element (TMR element) having a nonmagnetic oxide layer between a fixed layer and a free layer and utilizing a tunnel current. The magnetoresistive element is also referred to as a magnetoresistive element. Hereinafter, a case where a spin valve type giant magnetoresistive (SVGMR) element is used will be described as an example. In this case, the magnetic detection element 32 includes a plurality of elements in which the fixed layer 41, the nonmagnetic conductor layer 42, and the free layer 43 are stacked in this order. Further, a protective layer (not shown) may be provided on the surface side of the free layer 43. In the present embodiment, the magnetic medium 2 and the magnetic sensor 3 are opposed to each other with a gap and linearly move in a predetermined direction. The magnetoresistive element is also called a magnetoresistive element.

  As shown in FIG. 1, the magnetic medium 2 has magnetic medium elements 20 arranged in a line. The magnetic medium element 20 is magnetized so that the relative movement direction (hereinafter simply referred to as the movement direction) and the magnetization direction are parallel to each other. That is, the magnetization direction is the magnetization direction. The magnetic media 2 are arranged in a row so that the same poles face each other in adjacent magnetic media elements 20. That is, the magnetic medium elements 20 adjacent to each other are magnetized in opposite directions, and are arranged in the moving direction so as to become NS, SN, NS as a whole. That is, in the magnetic medium 2 of the present embodiment, magnetic medium elements magnetized in opposite directions are alternately arranged in a line at a constant pitch λm. The pitch λm is set larger than that when the magnetic medium 2 and the magnetic sensor 3 are in contact with each other.

The base 31 of the magnetic sensor 3 is formed using a non-magnetic material (for example, aluminosilicate glass having a thermal expansion coefficient α = 38 × 10 ⁻⁷ (deg ⁻¹ )). The fixed layer 41 is a ferromagnetic layer, and for example, a material having a composition of Co ₉₀ Fe ₁₀ (atm%) having a thickness of 5 nm is used. The fixed layer 41 has a magnetization direction fixed in a predetermined direction. In the present embodiment, it is assumed that the magnetic medium 2 is magnetized in the relative movement direction (hereinafter referred to as the movement direction).

The nonmagnetic conductor layer 42 can be formed of Cu having a thickness of 3 nm, for example. The free layer 43 is a ferromagnetic layer and may be a two-layer film of Ni ₈₅ Fe ₁₅ and Co ₉₀ Fe ₁₀ which are ferromagnetic materials. The film thickness ratio between Ni ₈₅ Fe ₁₅ and Co ₉₀ Fe ₁₀ is about 3: 1 to 5: 1, and the total thickness of the free layer 43 is 5 nm. In addition, since the method for fixing the magnetization direction of the fixed layer 41 and the method for improving the magnetic characteristics by adding anisotropy to NiFe in the free layer 43 are well known, detailed description thereof is omitted here.

  In the present embodiment, the following is performed in order to obtain the magnetic sensor 3. First, the fixed layer 41, the nonmagnetic conductor layer 42, and the free layer 43 are laminated on the base material 31 as described above, and then a resist mask having a desired element shape is formed on the laminated film by photolithography. Then, ion milling using argon ions or the like is performed to form a pattern of the magnetic sensor 3. In the pattern of the magnetic sensor 3, the wiring portion (portion that does not operate as a magnetoresistive element) is also formed in the same manner as the magnetoresistive element. However, by making the line width larger than that of the magnetoresistive element, it acts as a wiring without acting as a resistance.

  An example of the pattern (basic pattern) of the magnetic sensor 3 of the present embodiment has a meander shape as shown in FIG. Specifically, the position detection unit 50 includes a plurality of t magnetoresistive elements 51a, b,... Extending in a direction orthogonal to the moving direction, and includes a detection element pattern in which the magnetoresistive elements 51a, b,. And harmonic cancellation patterns 52a, 52,... Connected in series with each other.

  Here, the magnetoresistive elements 51a, b... Included in the position detection unit 50 are directly connected in series without placing the harmonic cancellation pattern 52 therebetween.

  The harmonic cancellation pattern 52 is also configured to include a magnetoresistive element. The magnetoresistive element of the harmonic cancellation pattern 52 is also formed in the same manner as the magnetoresistive element 51 of the position detection unit 50. One of the characteristic features of the present embodiment is that the plurality of magnetoresistive elements 51a, b,... Included in the position detector 50 have substantially the same length, width, and thickness (that is, variations). In such a manner that the range is within the range defined in advance). Thereby, the anisotropic magnetic field Hk of each of the magnetoresistive elements 51a, b... Is made uniform. Furthermore, in this example of the present embodiment, the length, width, and the like between the magnetoresistive element 51 included in the position detection unit 50 and the magnetoresistive element included in each harmonic cancellation pattern 52 are as follows. The thicknesses of the magnetoresistive elements are made uniform so that the thicknesses are substantially the same (that is, the variation range is within a predetermined range).

  Specifically, the length difference between any pair of magnetoresistive elements 51 is ± 10%, the width difference is ± 10%, and the thickness difference is ± 5%.

  In the present embodiment, the detection position C is set within the range of the detection element pattern in which the plurality of magnetoresistive elements 51 of the position detection unit 50 are arranged. As an example, the detection position C is the position of any one of the plurality of magnetoresistive elements 51 or the center position of the range in which the plurality of magnetoresistive elements 51 are arranged. In the following description, one end of the range in which the plurality of magnetoresistive elements 51 are arranged (in the case where a harmonic cancellation pattern is arranged on either side of the moving direction of the position detection unit 50, it is opposite to the one side) The side end) is set as a detection position C.

  The magnetoresistive elements 51 are arranged at a pitch less than λs / 10 from the detection position C using a reference pitch λs determined based on the arrangement pitch λm of the magnetic medium elements.

  This λs differs depending on the type of the magnetic detection element 32. When the spin valve type is used as in the example here, the reference pitch λs is the position detection adjacent to the magnetoresistive element 51 in one position detection unit. This is the pitch with the magnetoresistive element 51 in the part, specifically, λs = 2λm / t (t is the number of the position detection parts 50). In the case of an AMR element, a multilayer giant magnetoresistive element or the like, the reference pitch λs is assumed to be equal to λm. Note that n is an odd number of 3 or more, and if λs / 2n <λs / 10, then n> 5. The plurality of magnetoresistive elements 51 included in the position detection unit 50 are arranged at a distance of λs / (2n × k) (k is an integer of 5 or more).

  In the example shown in FIG. 3, the left end of the magnetoresistive element 51a shown on the left side is the detection position C, and another magnetoresistive element 51b is located on one side along the moving direction with respect to the detection position. That is, an example is shown in which the above k = 5) is arranged (with the center of the magnetoresistive element 51 shifted by λs / 30).

  Furthermore, in the present embodiment, the two harmonic cancellation patterns 52a and 52b are moved from the detection position C to the same side as the magnetoresistive element 51b, λs / 10 and λs / 6 (5th harmonic and 3rd harmonic, respectively). It is arranged at a position separated by a distance (cancelling waves). Thus, the magnetoresistive element 52 (52a, 52b) corresponding to the harmonic cancellation pattern corresponding to the harmonic of the nth order (n is an odd number of 3 or more) is arranged at a position of λs / 2n from the detection position. To do. Here, λs is the pitch between the position detectors 50.

  According to this example of the present embodiment, the plurality of magnetoresistive elements 51 are sufficiently smaller in pitch than λs / 30 and the position where the harmonic cancellation pattern is to be arranged. This is equivalent to connecting the resistance components in series, and the resistance value of the element is doubled. As a result, the influence of harmonics becomes relatively small. Furthermore, in this example of the present embodiment, the harmonic cancellation pattern 52 is provided to further reduce the influence of the harmonics.

  Here, the two harmonic cancellation patterns 52a and 52b are detected from the detection position C on the same side as the magnetoresistive element 51b (that is, one side), λs / 10, and λs / 6 (each of which is a multiple of 5). (5th order, 15th order, ...) and multiple harmonics (3rd order, 9th order, 15th order ...) are arranged at positions separated by a distance of 4 harmonics. The wave canceling patterns 52a, b, c, and d are placed on both sides of the position detection unit 50 and from the detection position C, respectively, λs / 10 and λs / 6 (5th harmonic and 3th harmonic, respectively) It may be arranged at a position separated by a distance of. That is, in the example of the present embodiment, the magnetism included in the position detector 50 is located at a position where the 15th harmonic already canceled by the harmonic cancellation pattern 52 (52a, 52b, 52c, 52d) can be canceled. At least one of the resistance elements 51 is disposed.

  Further, in the position detection unit 50, three or more magnetoresistive elements 51 may be provided in the detection element pattern. As an example, in the example shown in FIG. 4, among the three magnetoresistive elements 51 constituting the position detection unit 50, the left end side of the magnetoresistive element 51 b illustrated in the center is set as a reference (detection position C), and the reference The two magnetoresistive elements 51b and 51c are arranged on both sides of the magnetoresistive element 51b along the moving direction with an interval of λs / 30 from each other (the center of the magnetoresistive element 51 is shifted by λs / 30). An example is shown.

  Further, in the present embodiment, the four harmonic cancellation patterns 52a, b, c, d are detected from the detection position C to λs / 10 and λs / 6 on both sides in the moving direction (fifth harmonic and third order, respectively). They are arranged at positions separated by a distance of (to cancel harmonics).

  According to this example of the present embodiment, the position detection unit 50 includes a plurality of magnetoresistive elements 51, so that the pitch is λs / 30, and the harmonic cancellation pattern arranged farther from the detection position C. Harmonics such as positions where the harmonics already canceled by 52 can be canceled, or where higher order harmonics can be canceled where the components contained in the signal are so small that they do not affect detection. Since it is sufficiently smaller than the position where the cancellation pattern is to be arranged, at the detection position C, it is equivalent to connecting the resistance components of several magnetoresistive elements in series, and the resistance value is doubled. As a result, the influence of harmonics becomes relatively small. Further, in this example of the present embodiment, the harmonic cancellation pattern 52 is provided, thereby further reducing the influence of the harmonics. In the case of the example of FIG. 4, the magnetoresistive elements 51 constituting the position detector 50 are symmetrically arranged along the moving direction with respect to the magnetoresistive element 51b corresponding to the detection position C, and further cancel the harmonics. The pattern 52 is also arranged symmetrically with respect to the magnetoresistive element 51b along the moving direction. As a result, it is expected that the output signal of the position detector 50 during movement is also symmetric with respect to the position.

  In the description so far, the harmonic cancellation pattern has been exemplified for the case of canceling harmonics of multiples of 5 and harmonics of multiples of 3, respectively. This is because higher harmonics (7th order, 11th order, 13th order, etc.) exceeding the 5th order and not a multiple of 5 or 3 are often weak and do not need to be canceled. However, when it is desired to cancel the 7th and higher order n-order harmonics, the magnetoresistive element 52 as a harmonic cancellation pattern may be disposed at a distance of λs / 2n from a predetermined detection position of the position detection unit. .

  In the present embodiment, the number of magnetoresistive elements 52 included in each of the nth-order harmonic cancellation patterns (one in the example of FIG. 3 and two in the example of FIG. 4) is the position detection unit. The number is less than the number of magnetoresistive elements 51 included in 50. Thereby, the resistance value due to the magnetic field in the vicinity of the detection position C is emphasized, and the distortion of the output signal due to the influence of the harmonic cancellation pattern is reduced.

  In the present embodiment, the basic pattern illustrated in FIG. 3 or FIG. 4 is used as a repeating unit, and a plurality of basic patterns are provided at intervals of (m + 1/2) λs (where m is 0 or a positive integer). Patterns arranged and connected in series may be formed (FIG. 5).

  FIG. 5 shows an example using an AMR element or a multilayer giant magnetoresistive element (laminated GMR element). In the example of FIG. 5, the basic patterns 60a and 60b, which are the repeating units illustrated in FIG. 3, are spaced apart by λs / 2 and symmetrical with respect to the axis along the moving direction. It is arranged along. The terminal on one side (left side of the drawing) of the basic pattern 60a is connected to the power supply (Vcc), and the terminal on the other side (right side of the drawing) is connected to the terminal on one side (left side of the drawing) of the basic pattern 60b. Then, the terminal on the other side (right side of the drawing) of the basic pattern 60b is connected to the ground (GND). Further, a tap b is formed at the midpoint of this pattern (here, on the line connecting the other side terminal of the basic pattern 60a and the one side terminal of the basic pattern 60b).

  Further, in the example of FIG. 5, another basic unit pattern of another repeating unit at a position further spaced apart from each of the basic patterns 60a and 60b by (m + 1/4) λs (where m is 0 or a positive integer). 60c and 60d are arranged symmetrically with respect to the axis along the moving direction and are inverted with respect to each other. These basic patterns 60a, b, c, d are arranged in a line along the moving direction.

  These basic patterns 60c and 60d are also spaced apart by λs / 2. The terminal on one side (left side of the drawing) of the basic pattern 60c is connected to the power supply (Vcc), and the terminal on the other side (right side of the drawing) is connected to the terminal on one side (left side of the drawing) of the basic pattern 60d. The terminal on the other side (right side of the drawing) of the basic pattern 60d is connected to the ground (GND). A tap a is formed at the midpoint of this pattern (here, on the line connecting the other terminal of the basic pattern 60c and the one terminal of the basic pattern 60d).

  In the present embodiment having the configuration of FIG. 5, the position detection unit 50 includes a plurality of magnetoresistive elements (more than the number of magnetoresistive elements included in the harmonic cancellation pattern). As the resistance value at the detection position increases, the detection signal is emphasized, the influence of harmonics is reduced, and the output signal for the movement position becomes closer to a sine wave. This further improves the position detection accuracy.

  FIG. 6 shows an example using a spin valve type giant magnetoresistive element (SVGMR element). FIG. 6 shows an example in which the basic patterns 70a, b, c, d, e, and f, which are the repeating units illustrated in FIG. 4, are arranged along the moving direction with an interval of λs / 2. . In the example of FIG. 6, the terminal on one side (left side in the drawing) of the basic pattern 70a is connected to the power supply (Vcc), and the terminal on the other side (right side in the drawing) is separated from the basic pattern 70a by λs. It is connected to a terminal on one side (left side in the drawing) of the basic pattern 70c at a certain position. Further, the terminal on the other side (right side in the drawing) of the basic pattern 70c is connected to a terminal on one side (left side in the drawing) of the basic pattern 70e located at a position away from the basic pattern 70c by λs.

  The terminal on the other side (right side in the drawing) of the basic pattern 70e is connected to the terminal on the other side (right side in the drawing) of the basic pattern 70f located at a position away from the basic pattern 70e by λs / 2. A terminal on one side (left side in the drawing) of the basic pattern 70f is connected to a terminal on the other side (right side in the drawing) of the basic pattern 70d at a position separated from the basic pattern 70f by λs. Further, the terminal on one side (left side in the drawing) of the basic pattern 70d is connected to the terminal on the other side (right side in the drawing) of the basic pattern 70b at a position separated from the basic pattern 70d by λs. A terminal on one side (left in the drawing) of the basic pattern 70b is connected to the ground (GND). Further, a tap a is formed at the midpoint of this pattern (here, on the line connecting the other terminal of the basic pattern 70e and the other terminal of the basic pattern 70f).

  In the example of FIG. 6, in the basic patterns 70b to 70f, the basic patterns 70 that are adjacent to each other are arranged symmetrically with respect to the axis along the moving direction and reversed with respect to each other.

  In FIG. 6, another basic pattern 70a ', b', c in the direction orthogonal to the moving direction is compared with the pattern (first pattern) including the basic patterns 70a, b, c, d, e, f. A pattern (second pattern) including ', d', e ', f' may be arranged. Here, the basic pattern 70a and the basic pattern 70a ′ are arranged at positions shifted from each other by λs / 4 along the moving direction.

  Here, the effect of multiplication will be described. The SVGMR element is an element whose resistance value varies depending on the direction and strength of the leakage magnetic field from the magnetic medium. Specifically, the resistance value of the SVGMR element increases as the leakage magnetic field from one side in a specific direction becomes stronger. When a magnetic field above the magnetic saturation point of the SVGMR element is applied, the resistance value does not change. Also, as the leakage magnetic field on the other side becomes stronger, the resistance value of the SVGMR element decreases, and when a magnetic field higher than the magnetic saturation point is applied, the resistance value does not change (for AMR elements and stacked GMR elements). In this case, the resistance changes depending on the strength of the magnetic field without depending on the direction of the leakage magnetic field).

  Therefore, considering the case of relative movement with respect to the magnetic medium 2, the resistance value of the basic pattern 70 a changes in a cycle of 2λm. Specifically, the state of the change is a substantially rectangular wave as shown in FIG. 7A according to the distance of relative movement. Similarly, the resistance values of the basic patterns 70c and 70e change with a period of 2λm according to the relative movement distance, and the state is a substantially rectangular wave (FIGS. 7B and 7C). However, the change in the resistance value of the basic pattern 70c is shifted in phase by λs (= 2λm / 3) with respect to the change in the resistance value of the basic pattern 70a, and the change in the resistance value of the basic pattern 70e is the resistance value of the basic pattern 70a. It is shifted by 2λs (= 4λm / 3) with respect to the change of.

  Accordingly, the change in the combined resistance value of the basic patterns 70a, 70c, and 70e connected in series is about 1/3 of the resistance value of each of the basic patterns 70a, 70c, and 70e, which is illustrated in FIG. Thus, the period is λs (= 2λm / 3). Similarly, the combined resistance value of the basic patterns 70b, 70d, and 70f connected in series is similar to the combined resistance value of the basic patterns 70a, 70c, and 70e, and the change in the resistance value is approximately the resistance value of each basic pattern 70. At 1/3, the period of the change is λs. However, the phase is shifted by λs / 2 with respect to the change in the combined resistance value of the basic patterns 70a, 70c, and 70e.

  From the above, the signal period of the output a of the bridge circuit composed of these two combined resistors is λs (= 2λm / 3), and the magnetization pitch λm of the magnetic medium is multiplied by 2/3.

  Next, examples of the present invention will be described. Here, the line width of the magnetization pitch λm = 600 μm of the magnetic medium 2, the magnetoresistive element 51 of the position detector 50, and the magnetoresistive element of the harmonic cancellation pattern are all 3 μm, and the wiring connecting the magnetoresistive elements With a line width of 30 μm, the patterns illustrated in FIG. 3 and FIG. 4 as examples (hereinafter referred to as patterns A and B, respectively), the pattern C of the conventional example shown in FIG. A pattern D having no wave canceling pattern was formed. The bridge circuit to which the pattern is applied is the one shown in FIG. Then, the gap (air gap) between the magnetic medium 2 and the magnetic sensor 3 is changed to 100 μm and 300 μm, and for each gap, the output waveform when the magnetic sensor 3 is moved by 1000 μm with respect to the magnetic medium 2. Got. A numerical value obtained by adding 100 μm to the air gap corresponds to the magnetic gap.

  FIG. 6 shows an example in which the pattern B is used. In this embodiment, the output of the bridge circuit is called the output of the pattern B. In the present embodiment, the case where each pattern B is replaced with the pattern A in FIG. In FIG. 6, the case where each pattern B is replaced with pattern C will be described later as the output of pattern C. In FIG. 6, a case where each pattern B is replaced with a pattern D (one element) will be described later as an output of the pattern D. When replacing the pattern, the detection positions C are arranged to be the same before and after replacement. Here, an example will be described in which a spin valve type giant magnetoresistive element in which an antiferromagnetic layer, a fixed layer, a nonmagnetic intermediate layer, and a free layer are stacked is used as the magnetoresistive element.

[Air gap 100μm]
FIG. 8 shows an output signal based on the pattern D and FIG. 9 shows an output signal based on the pattern C when the air gap is 100 μm. In the patterns of these comparative examples, when a harmonic cancellation pattern is not provided, a substantially rectangular waveform is formed as illustrated in FIG. 8 due to the influence of the harmonics.

  On the other hand, even if a harmonic cancellation pattern is provided, if the cancellation amount is too large, the output signal has a substantially triangular waveform as shown in FIG. Here, in view of the fact that the signal intensity of the third harmonic is smaller than the signal intensity of the fundamental frequency with respect to the output signal, and the signal intensity of the fifth harmonic is further smaller, the magnetoresistive element of the cancellation pattern of each harmonic. It is conceivable to adjust the resistance value of the magnetoresistive element by changing the length, width, and thickness, such as by shortening the length of the film, but in this case, the anisotropic magnetic field Hk of the magnetoresistive element film is reduced. The noise is generated in the output signal because the characteristics are changed and the characteristics are different.

  Therefore, by increasing the number of magnetoresistive elements in the position detection unit 50 from the number of magnetoresistive elements included in each harmonic cancellation pattern, a harmonic canceling action corresponding to the difference in signal intensity can be obtained. FIGS. 10 and 11 show examples in which the air gap is 100 μm by the patterns A and B. In the pattern A illustrated in FIG. 5, since the harmonic cancellation pattern 52 is only on one side of the detection position C, the corresponding output signal in FIG. 10 has a shape closer to a sine wave than the examples in FIGS. However, it has an asymmetric shape around the peak. On the other hand, the output signal of the pattern B illustrated in FIG. 6 forms a substantially sine wave as illustrated in FIG. 11, and its shape is symmetric about the peak.

[Air gap 300μm]
FIG. 12 shows an output signal based on the pattern D when the air gap is 300 μm, and FIG. 13 shows an output signal based on the pattern C. In the patterns of these comparative examples, when the harmonic cancellation pattern is not provided, the rectangular waveform is slightly dull as illustrated in FIG. 12 due to the influence of the harmonic. On the other hand, even if a harmonic cancellation pattern is provided as in pattern C, the amount of cancellation is too large in pattern C, so that the output signal has a substantially triangular waveform as shown in FIG. 13 as in the case where the air gap is 100 μm. .

  FIGS. 14 and 15 show examples in which patterns A and B are used as an embodiment of the present invention and the air gap is 300 μm. In the pattern A illustrated in FIG. 5, since the harmonic cancellation pattern 52 is only on one side of the detection position C, the corresponding output signal in FIG. 14 has a shape close to a sine wave, but has an asymmetric shape centered on the peak. It has become. On the other hand, the output signal of the pattern B illustrated in FIG. 6 forms a substantially sine wave as illustrated in FIG. 15, and its shape is symmetric about the peak.

  As described above, according to the linear encoder according to the present embodiment, an output signal having a shape close to a sine wave can be obtained even when the air gap is about 100 μm or 300 μm. Since the output signal is close, the accuracy of position detection can be improved.

  In the above description, the linear encoder has been described as an example. However, even if the linear encoder is not used, the magnetic medium 2 is wound in the circumferential direction along the outer circumference of the cylinder, By arranging the magnetic sensor 3 so as to move with a substantially constant magnetic gap, it can also be configured as a rotary encoder.

  DESCRIPTION OF SYMBOLS 1 Linear encoder, 2 Magnetic medium, 3 Magnetic sensor, 20 Magnetic medium element, 31 Base material, 32 Magnetic detection element, 41 Fixed layer, 42 Nonmagnetic conductor layer, 43 Free layer, 50 Position detection part, 51 Magnetoresistance element, 52 Harmonic cancellation pattern, 60, 70 Basic pattern

Claims (6)

A magnetic sensor that moves relative to each other in the longitudinal direction of the magnetic medium facing the magnetic medium in which magnetic medium elements magnetized in opposite directions are alternately arranged in a line at a constant pitch λm with a gap. An encoder with
The magnetic sensor is
A position detector including a plurality of magnetoresistive elements arranged along the moving direction and connected in series with each other;
A harmonic cancellation pattern that is connected in series to the magnetoresistive element of the position detection unit and cancels the harmonics generated in the detection signal output by the position detection unit, at least one side of the position detection unit along the moving direction The encoder provided in. The encoder according to claim 1, wherein
An encoder that is connected in series to the magnetoresistive element of the position detection unit and that has harmonic cancellation patterns that cancel harmonics generated in the detection signal output by the position detection unit on both sides of the position detection unit along the moving direction . The encoder according to claim 1 or 2,
T position detection units are provided, and t is an integer of 2 or more;
The magnetoresistive elements of the position detection unit are respectively arranged at a position of a distance of λs / 2n from a predetermined detection position of the position detection unit using a reference pitch λs determined based on the pitch λm. Is an odd number greater than or equal to 3. An encoder according to claim 3,
The plurality of magnetoresistive elements included in the position detection unit are arranged at a distance of λs / (2n × k) from each other, and k is an integer of 5 or more. The encoder according to claim 3 or 4, comprising:
The magnetoresistive element of the position detector is a spin valve type giant magnetoresistive element, and the reference pitch λs is λs = 2λm / t. The encoder according to any one of claims 1 to 5,
The harmonic cancellation pattern that cancels Nth-order harmonics is an encoder including a smaller number of magnetoresistive elements than the number of magnetoresistive elements included in the position detection unit.

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