JP2009288105A - Magnetically-detecting encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetically-detecting encoder for following a rotation of a rotating magnet, obtaining an accurate detection output, and reducing a thickness. <P>SOLUTION: The rotating magnet 16 is magnetized so as to alternately change magnetic poles on an outer circumference 16a in the rotational direction. A detecting element 19 faces the outer circumference 16a, and has a magnetoresistance effect element with a fixed magnetic layer and a free magnetic layer. A vector for indicating the direction (the P-direction) of a fixed magnetization in the fixed magnetic layer and a vector of a magnetization in the free magnetic layer are located in a plane orthogonal to a central axis O of the rotating magnet 16. When the rotating magnet 16 rotates, the detection output corresponding to a rotational angle of the vector of the magnetization in the free magnetic layer is obtained. Thereby, the accurate detection output can be obtained without being affected by the fluctuation in a strength of a leakage magnetic field from the rotating magnet 16. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic detection encoder that detects a leakage magnetic field from a rotating magnet with a magnetoresistive element and obtains a detection output corresponding to the rotation angle of the rotating magnet.

  As shown in FIG. 7, in the magnetic detection type encoder, a rotating magnet 3 is supported on a base 1 so as to be rotatable about an axis 2, and a detecting element 5 such as a Hall element faces the magnetized surface of the rotating magnet 3. The change in the leakage magnetic field when the rotating magnet 3 rotates is detected by the detection element 5.

  In the conventional magnetic detection type encoder, the upper surface 3a and the lower surface 3b, which are surfaces orthogonal to the rotation axis of the rotating magnet 3, are magnetized so that N and S poles are alternately arranged in the rotation direction. In general, the detection element 5 such as a Hall element is installed at a position (a) facing the upper surface 3a or a position (b) facing the lower surface 3b.

  However, in the above structure, since the detection element 5 is arranged at a position overlapping with the rotating magnet 3, the height dimension of the magnetic detection type encoder becomes large, and it is difficult to configure in a thin package.

  In Patent Document 1 below, the outer peripheral surface 3c of the rotating magnet 3 is magnetized so that N poles and S poles are alternately arranged in the rotation direction, and the detection element 5 faces the outer peripheral surface 3c. A magnetic detection type encoder installed at the position (c) is disclosed.

  Patent Document 1 describes that a Hall element or a magnetoresistive element is used as the detection element 5 and a change in the density of magnetic flux passing through the detection element 5 is detected when the rotating magnet 3 rotates. Has been. That is, the detection element 5 is arranged at the position (c), and the change in the magnetic flux density of the vector component directed in the normal direction out of the leakage magnetic field from the outer peripheral surface 3c of the rotating magnet 3 is detected.

  However, in the method of detecting the leakage flux density change, if the leakage magnetic flux density fluctuates due to changes in the usage environment, etc., the detection output level will fluctuate. When jitter is obtained, fluctuations in the jitter direction occur in the period of the rectangular wave. Therefore, when it is attempted to detect the rotation angle of the rotating magnet 3 with fine resolution, an error due to fluctuation of the period of the rectangular wave is likely to occur. In order to accurately detect the rotation angle with a fine resolution, it is necessary to magnetize the N pole and the S pole on the outer peripheral surface 3c at a finer pitch, and the rotating magnet 3 to be used is expensive. I can't avoid becoming.

In order to detect a change in magnetic flux density of a vector component directed in the normal direction of the leakage magnetic field from the outer peripheral surface 3c of the rotating magnet 3 by using a magnetoresistive element as the detecting element 5, as shown in FIG. Thus, it is necessary to mount the detection element 5 vertically from the base 1 so that the surface 5a of the magnetic film of the detection element 5 arranged at the position (c) faces the outer peripheral surface 3c. However, in such a mounting structure, since the height dimension of the detection element 5 from the surface of the base 1 becomes large, there is a limit to the reduction in thickness of the magnetic detection type encoder even if the thin rotary magnet 3 is used. .
Japanese Patent Laid-Open No. 2007-3514

  The present invention solves the above-described conventional problems, and uses a magnetoresistive effect element as a detection element, and does not detect a change in the magnetic flux density of the leakage magnetic field from the rotating magnet, but changes the direction of the leakage magnetic field to 360 degrees. It is an object of the present invention to provide a magnetic detection type encoder capable of accurately detecting a change in a magnetic field corresponding to the rotation angle of a rotating magnet.

  Another object of the present invention is to provide a magnetic detection type encoder that can be thinly formed as a whole when a thin rotating magnet is used.

The present invention has a rotating magnet having an outer peripheral surface in which N poles and S poles are alternately magnetized in the rotation direction, and a sensing element facing the outer peripheral surface of the rotating magnet,
The sensing element includes a fixed magnetic layer whose magnetization direction is fixed, and a free magnetic layer whose magnetization direction is determined by a leakage magnetic field from the rotating magnet, and the magnetization direction of the fixed magnetic layer and the free magnetic layer A magnetoresistive effect element whose electrical resistance changes in relation to the magnetization direction of the layer,
Each of the magnetization vector of the pinned magnetic layer and the magnetization vector of the free magnetic layer is located in a plane perpendicular to the rotation center axis of the rotating magnet.

  That is, according to the present invention, when the rotating magnet rotates by an angle corresponding to one pitch of the arrangement of N pole and S pole, the magnetization of the free magnetic layer rotates 360 degrees in the plane, A detection output corresponding to one period of a sine curve or cosine curve can be obtained by changing the electric resistance.

  Further, the present invention is provided with a detection circuit that shapes the detection output corresponding to a sine curve or cosine curve, and the rotating magnet rotates at an angle corresponding to one pitch of an array of N poles and S poles. A rectangular wave for one period is obtained.

  In the magnetic detection type encoder of the present invention, since the film surface of the free magnetic layer of the detection element, that is, the detection surface is located in a plane orthogonal to the rotation axis, free magnetic field is generated by the leakage magnetic field from the outer peripheral surface of the rotary magnet. The magnetization vector in the layer rotates in the range of 360 degrees as the rotating magnet rotates. Because the detection element does not detect the change in the magnetic flux density of the leakage magnetic field from the rotating magnet, but detects the rotation of the magnetization vector. However, it is possible to always obtain an accurate detection output corresponding to the rotation angle of the rotating magnet. Therefore, fluctuations and the like are less likely to occur in the period of the rectangular wave obtained by waveform-forming the detection output from the detection element, and the rotation angle of the rotating magnet can be accurately detected with fine resolution.

  Therefore, it is not necessary to set the magnetization pitch of the outer peripheral surface of the rotating magnet to a very short pitch, and the rotation angle can be easily detected with fine accuracy even when magnetized at a relatively large pitch. Therefore, it is not necessary to use an expensive magnet that is magnetized at a fine pitch.

  Further, according to the present invention, the rotating magnet is a disk having a thickness dimension along a rotation center axis smaller than a radius, and the free magnetic layer of the sensing element is located within the thickness dimension and the outer peripheral surface. It is preferable that it faces.

  In the magnetic detection type encoder of the present invention, since the magnetoresistive effect element can be arranged so that the detection surface thereof is parallel to the surface of the base, it can be easily mounted on the base, and the free magnetic layer can be rotated. By disposing within the range of the thickness of the magnet, it is easy to realize the overall thinning with the thinning of the rotating magnet.

  In the rotating magnet of the present invention, the outer peripheral surface, which is a magnetized surface, is along a cylindrical surface centered on the rotation center axis. However, the outer peripheral surface, which is a magnetized surface, does not necessarily exist on an accurate cylindrical surface, and may have a shape corresponding to a slightly polygonal cylindrical surface that is flat for each magnetic pole. That is, the rotating magnet in the present invention is a radial magnetized magnet.

  The present invention is less susceptible to fluctuations in the magnetic flux density of the leakage magnetic field from the rotating magnet, and can accurately obtain a detection output corresponding to the rotation angle of the rotating magnet. Moreover, it becomes easy to comprise the whole thinly by using a thin rotary magnet.

  FIG. 1 is a plan view showing the structure of a magnetic detection type encoder 10 according to an embodiment of the present invention, and FIG. 2 is a side view of the magnetic detection type encoder 10.

  As shown in FIG. 2, in the magnetic detection encoder 10, a bearing 12 made of a nonmagnetic material is fixed to a base 11 made of a nonmagnetic material such as a thin synthetic resin material. A rotating shaft 13 made of a nonmagnetic material is rotatably supported. A rotating body 14 is fixed to the rotating shaft 13. The rotary shaft 13 and the rotating body 14 are rotated by operating a rotation operation unit (not shown). Or the rotational force of a mechanism is transmitted to the rotating shaft 13, and the rotating shaft 13 and the rotary body 14 are rotated. A central axis O of the rotation shaft 13 is perpendicular to the surface of the base 11.

  The rotating body 14 is a thin disk whose thickness dimension W along the central axis O is sufficiently smaller than the radius, and the thickness dimension W is uniform throughout the rotating body 14.

  The rotating body 14 is provided with a support disk 15 made of a nonmagnetic material at the center, and the support disk 15 is fixed to the rotating shaft 13. A rotating magnet 16 is fixed to the outer periphery of the support disk 15. The outer peripheral surface 16a of the rotary magnet 16 is located on a cylindrical surface centered on the central axis O.

  As shown in FIG. 1, the rotating magnet 16 is magnetized by being divided into 16 poles, and the outer peripheral surface 16a and the inner peripheral surface 16b are opposite magnetic poles. The outer peripheral surface 16a is alternately magnetized with N and S poles in the rotational direction, and the opening angle of the magnetized range of each of the N and S poles is 22.5 degrees.

  As shown in FIG. 2, a support base 18 is provided on the base 11, and a detection element 19 is mounted on the support base 18. The upper surface 19 a of the detection element 19 is disposed so as not to protrude upward from the upper surface 14 a of the rotating body 14. The detection element 19 faces the outer peripheral surface 16a of the rotating magnet 16.

  The detection element 19 includes the magnetoresistive effect element 20 shown in FIGS. 3 and 4, and the magnetoresistive effect element 20 is covered with a protective layer.

  FIG. 3 is a plan view showing the magnetoresistive effect element 20, and FIG. 4 is an enlarged view of a sectional view of the magnetoresistive effect element 20 shown in FIG.

  As shown in FIG. 3, the magnetoresistive effect element 20 has a plurality of element portions 21 formed in parallel with each other, and the front and rear end portions of each element portion 21 are connected to each other by connection electrodes 28a and 28b. . Furthermore, extraction electrodes 29a and 29b are connected to the element portions 21 located on both sides. Therefore, each element part 21 is connected in series and the meander type | mold pattern is comprised.

  The paper plane of FIG. 3 coincides with a plane orthogonal to the central axis O. In FIG. 3, the radius direction of the rotating magnet 16 is indicated by R. Each element portion 21 has a longitudinal direction orthogonal to the radial direction R, that is, the longitudinal direction of the element portion 21 is directed in the tangential direction of the outer peripheral surface 16 a of the rotating magnet 16.

  As shown in the sectional view of FIG. 4, each element portion 21 is laminated on an element substrate 22 in the order of an antiferromagnetic layer 23, a pinned magnetic layer 24, a nonmagnetic conductive layer 25, and a free magnetic layer 26. The surface of the free magnetic layer 26 is covered with a protective layer 27.

  The antiferromagnetic layer 23 is formed of an antiferromagnetic material such as an Ir—Mn alloy (iridium-manganese alloy). The pinned magnetic layer 24 is formed of a soft magnetic material such as a Co—Fe alloy (cobalt-iron alloy). The nonmagnetic conductive layer 25 is made of Cu (copper) or the like. The free magnetic layer 26 is made of a soft magnetic material such as a Ni—Fe alloy (nickel-iron alloy). The protective layer 27 is a Ta (tantalum) layer.

  The film surfaces of the pinned magnetic layer 24 and the free magnetic layer 26 are located in a plane orthogonal to the central axis O, respectively.

  In the element portion 21, the magnetization direction of the pinned magnetic layer 24 is fixed by antiferromagnetic coupling between the antiferromagnetic layer 23 and the pinned magnetic layer 24. As shown in FIGS. 1 and 3, the fixed magnetization direction (P direction) of the fixed magnetic layer 24 of each element portion 21 is a tangential direction of the outer peripheral surface 16 a of the rotating magnet 16. A vector indicating the direction of fixed magnetization (P direction) is in a plane orthogonal to the central axis O.

  The detection element 19 is disposed close to the outer peripheral surface 16a of the rotating magnet 16, and the magnetization of the free magnetic layer 26 of each element portion 21 is always saturated by the leakage magnetic field from the outer peripheral surface 16a of the rotating magnet 16. Further, the distance between the element portion 21 and the outer peripheral surface 16a is determined.

  As shown in FIG. 2, in the rotating magnet 16, the outer peripheral surface 16a and the inner peripheral surface 16b are magnetized to have opposite polarities. A magnetic flux φ extends above the upper surface 14a and below the lower surface 14b. Further, although the magnetic flux extends between the adjacent magnetic poles on the outer peripheral surface 16a, in FIG. 1, the magnetic flux component extending in the plane perpendicular to the central axis O among the magnetic fluxes extending between the adjacent magnetic poles on the outer peripheral surface 16a. Are denoted by φ1 and φ2. The magnetic flux component φ1 means a magnetic flux component extending clockwise in the plane, and the magnetic flux component φ2 means a magnetic flux component extending counterclockwise in the plane.

  The free magnetic layer 26 of each element portion 21 is in the range of the thickness dimension W of the rotating magnet 16, that is, the free magnetic layer 26 is above the lower surface 14b of the rotating body 14 and below the upper surface 14a. In the height position. Therefore, the magnetization of the free magnetic layer 26 is saturated with the magnetic flux component φ1 and the magnetic flux component φ2 whose directions change in a plane orthogonal to the central axis O. In FIG. 3, the magnetization vector of the free magnetic layer 26 saturated with the magnetic flux components φ1 and φ2 is denoted by F.

  When the rotating body 14 rotates and the outer peripheral surface 16a of the rotating magnet 16 moves to the side of the sensing element 19, the directions of the magnetic flux components φ1 and φ2 that saturate the free magnetic layer 26 change, so that the free magnetic layer 26 The magnetization vector F rotates in a plane orthogonal to the central axis O. In FIG. 1, when the rotating magnet 16 rotates clockwise, the vector F rotates counterclockwise in the plane, and when the rotating magnet 16 rotates counterclockwise, the vector F rotates clockwise in the plane. Rotate to. When the rotating magnet 16 is rotated clockwise or counterclockwise by an angle corresponding to one pitch of magnetization (45 degrees), that is, an angle corresponding to one cycle of alternating magnetization repeated with NSN, The magnetization vector F of the free magnetic layer 26 rotates 360 degrees.

  In the magnetoresistive effect element 20, the electric resistance changes depending on the relationship between the direction of the fixed magnetization (P direction) of the fixed magnetic layer 24 and the direction of the magnetization vector F of the free magnetic layer 26. When the magnetization vector F of the free magnetic layer 26 is parallel to the fixed magnetization direction (P direction), the electric resistance is minimized, and when the vector F is antiparallel to the fixed magnetization direction (P direction), the electric resistance is maximized. Become.

  FIG. 5 shows a detection circuit 30 that detects a change in electrical resistance of the magnetoresistive effect element 20.

  In the detection circuit 30, a power supply voltage Vdd having a predetermined voltage is applied intermittently by the switching circuit 31. The switching circuit 31 is intermittently opened and closed at a constant cycle by a timing circuit 32 including a clock. By supplying the power supply voltage Vdd intermittently, power consumption can be reduced.

  In the detection circuit 30, the magnetoresistive effect element 20 and the voltage dividing resistor 33 are connected in series, and the voltage Vdd is applied to the series voltage dividing resistor 33 and the magnetoresistive effect element 20. When the direction of the magnetization vector F of the free magnetic layer 26 is orthogonal to the direction of the fixed magnetization (P direction), the electric resistance value of the magnetoresistive effect element 20 is the same as the resistance value of the voltage dividing resistor 33. The voltage at the connection intermediate point 34 between the magnetoresistive effect element 20 and the voltage dividing resistor 33 becomes Vdd / 2.

  Further, the reference resistor 35 and the reference resistor 36 are connected in series, and the voltage Vdd acts on the reference resistor 35 and the reference resistor 36 connected in series. At this time, the voltage at the connection intermediate point 37 between the reference resistor 35 and the reference resistor 36 is set to Vdd / 2.

  The voltage at the connection intermediate point 34 and the voltage at the connection intermediate point 37 are applied to a differential amplifier 38, and the differential amplifier 38 outputs a difference between both voltages. That is, the differential amplifier 38 outputs the increment and decrement of the voltage at the connection intermediate point 34 with respect to the voltage at the connection intermediate point 37 and supplies it to the Schmitt trigger circuit 39. In the Schmitt trigger circuit 39, when the voltage difference detected by the differential amplifier 38 exceeds the first threshold value L1, a high output is given to the latch circuit 40, and the voltage difference is greater than the second threshold value L2. The output of the low level is applied to the latch circuit 40. In the latch circuit 40, the output switch circuit 41 is turned ON when a high output is obtained from the Schmitt trigger circuit 39, and the output switch circuit is turned OFF when the output from the Schmitt trigger circuit 39 is switched to low.

  An output waveform 45 of a cosine curve (or sine curve) shown in FIG. 6A shows a change in voltage at the connection intermediate point 34 when the rotating body 14 rotates. The horizontal axis in FIG. 6A is the rotation angle of the rotating body 14. While the rotating body 14 rotates 45 degrees, the magnetization vector F of the free magnetic layer 26 rotates 360 degrees. During this time, the output waveform 45 changes by one period T of the cosine curve. And while the rotary body 14 rotates 360 degree | times, the output waveform 45 changes by 8 periods.

  6A shows the first threshold value L1 and the second threshold value L2 set by the Schmitt trigger circuit 39. FIG. The final output from the detection circuit 30 shown in FIG. 5 is a rectangular wave output 46 shown in FIG. The rectangular wave output 46 is a waveform that rises when the output waveform 45 exceeds the first threshold value L1 and falls when the output waveform 45 becomes lower than the second threshold value L2. The period T of the rectangular wave output 46 is the same as the period of the output waveform 45, and eight rectangular wave outputs 46 are obtained while the rotating body 14 rotates 360 degrees.

  Here, the output waveform 45 shown in FIG. 6A is determined by the rotation angle of the magnetization vector F of the free magnetic layer 26 accompanying the rotation of the rotating magnet 16, and leaks from the outer peripheral surface 16 a of the rotating magnet 16. Even if the magnetic flux density of the magnetic field changes, the level of the output waveform 45 does not vary without depending on this. That is, even if the magnetic flux density of the leakage magnetic field fluctuates due to temperature changes or other environmental changes, the direction of the vector F does not fluctuate, and thus the level of the output waveform 45 does not fluctuate up and down. Will be. When the output waveform 45 shown in FIG. 6A is shaped using the constant threshold values L1 and L2, the output waveform 45 does not fluctuate. The timing is less likely to be shifted, and the rectangular wave output 46 can accurately follow the rotation angle of the rotating magnet 16.

  Therefore, by counting the rectangular wave output 46 shown in FIG. 6B, the rotation angle of the rotating body 14 can be accurately measured in units of 22.5 degrees, and when the rotating body 14 is rotating. The fluctuation of the rotation speed can be detected with high accuracy.

  Further, as shown in FIG. 2, the surface of each film of the magnetoresistive effect element 20 constituting the detection element 19 is located in a plane orthogonal to the central axis O, so that the installation work of the detection element 19 is easy. In addition, since the detection element 19 can be arranged at a height within the range of the thickness dimension W of the rotary magnet 16, the magnetic detection encoder 10 can be configured to be thin.

  In the embodiment shown in FIG. 1, the fixed magnetization direction (P direction) of the fixed magnetic layer 24 of the magnetoresistive effect element 20 is directed to the tangential direction of the outer peripheral surface 16 a of the rotating magnet 16. The direction of the vector in the direction (P direction) may be any direction as long as it is in a plane orthogonal to the central axis O.

The top view which shows the magnetic detection type encoder of embodiment of this invention, A side view of the magnetic detection type encoder shown in FIG. Plan view of magnetoresistive effect element used for sensing element, The expanded sectional view which cut | disconnected the magnetoresistive effect element shown in FIG. The circuit diagram of the detection circuit provided in the magnetic detection type encoder of the embodiment of the present invention, Waveform diagram of the detection circuit, Illustration of prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Magnetic detection type encoder 11 Base 12 Bearing 13 Rotating shaft 14 Rotating body 16 Rotating magnet 16a Outer peripheral surface 19 Sensing element 20 Magnetoresistive element 21 Element part 24 Fixed magnetic layer 26 Free magnetic layer P Direction of fixed magnetization of fixed magnetic layer F Vector of magnetization of free magnetic layer

Claims (4)

A rotating magnet having an outer peripheral surface in which N and S poles are alternately magnetized in the rotation direction; and a sensing element facing the outer peripheral surface of the rotating magnet;
The sensing element includes a fixed magnetic layer whose magnetization direction is fixed, and a free magnetic layer whose magnetization direction is determined by a leakage magnetic field from the rotating magnet, and the magnetization direction of the fixed magnetic layer and the free magnetic layer A magnetoresistive effect element whose electrical resistance changes in relation to the magnetization direction of the layer,
The magnetic detection type encoder, wherein each of the magnetization vector of the pinned magnetic layer and the magnetization vector of the free magnetic layer is located in a plane orthogonal to the rotation center axis of the rotating magnet.   When the rotating magnet rotates by an angle corresponding to one pitch of the arrangement of N pole and S pole, the magnetization of the free magnetic layer rotates 360 degrees in the plane, and during that time, due to the change of the electric resistance 2. A magnetic detection type encoder according to claim 1, wherein a detection output corresponding to one cycle of a sine curve or cosine curve is obtained.   A detection circuit for shaping the detection output corresponding to a sine curve or cosine curve is provided, and when the rotating magnet rotates at an angle corresponding to one pitch of an array of N poles and S poles, it is a rectangle for one cycle. The magnetic detection type encoder according to claim 2, wherein a wave is obtained.   The rotating magnet is a disk having a thickness dimension smaller than a radius along a rotation center axis, and the free magnetic layer of the sensing element is located within the thickness dimension and faces the outer peripheral surface. Item 4. The magnetic detection type encoder according to any one of Items 1 to 3.

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