JP2009250851A - Magnetization method of encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a magnetization method of an encoder for converting a shape of a boundary between a S-pole and a N-pole provided on a to-be-detected surface of the completed encoder into a target shape in a state that the to-be-detected surface is assumed to be planarly developed. <P>SOLUTION: The problem is overcome by using magnetization heads 12a, 12a having planar shapes at both circumferential side edges on apical surfaces 13a, 13a as a curve slightly shifted from the target shape. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is, for example, an encoder used for measuring a state quantity such as an axial load acting on a wheel support bearing unit, that is, an S pole and an N pole are alternately arranged on the detected surface in the circumferential direction. In addition, the present invention relates to an encoder magnetization method and an improvement of a magnetization apparatus in which at least a part of the boundary between the S pole and the N pole is inclined with respect to the width direction of the detected surface.

  For example, a wheel of an automobile is rotatably supported by a rolling bearing unit such as a double-row angular type with respect to a suspension device. In addition, in order to ensure the running stability of automobiles, for example, anti-lock braking system (ABS), traction control system (TCS), and electronically controlled vehicle stability control system (ESC) etc. The device is in use. In order to control such various vehicle running stabilization devices, signals representing the rotational speed of the wheels, acceleration in each direction applied to the vehicle body, and the like are required. In order to perform higher-level control, it may be preferable to know the magnitude of a load (for example, one or both of a radial load and an axial load) applied to the rolling bearing unit via a wheel.

  In view of such circumstances, Patent Document 1 describes an invention in which a special encoder is used to measure the magnitude of a load applied to a rolling bearing unit. FIG. 2 shows an example of a conventional structure relating to a state quantity measuring device for a rolling bearing unit, which employs the same load measurement principle as the structure described in Patent Document 1. In this conventional structure, a hub 2 that rotates together with a wheel while supporting and fixing the wheel in use is fixed to a plurality of rolling elements 3 and 3 on the inner diameter side of the outer ring 1 that does not rotate while being coupled and fixed to a suspension device when used. It is rotatably supported via A preload is applied to each of the rolling elements 3 and 3 together with a contact angle of the rear combination type. In the illustrated example, balls are used as the rolling elements 3 and 3. However, in the case of an automobile bearing unit that is heavy, tapered rollers may be used instead of balls.

  The inner end of the hub 2 in the axial direction ("inside" in the axial direction means the center side in the width direction of the vehicle when assembled to the automobile, and is the right side of Fig. 2. Conversely, the outer side in the width direction of the vehicle. The left side of FIG. 2 is referred to as “outside” in the axial direction. The same applies throughout the present specification.) The cylindrical encoder 4 is supported and fixed concentrically with the hub 2. The encoder 4 includes a cylindrical metal core 5 made of a magnetic metal plate, and a cylindrical magnet body 6 made of a permanent magnet fixedly attached to the inner half of the outer peripheral surface of the metal core 5 in the axial direction. The encoder body 6 has a cylindrical magnetic member (permanent magnet material, high coercive force material), which is a material, attached and fixed to the inner half in the axial direction of the outer peripheral surface of the core metal 5 (adhesion fixing, fixing by mold, etc.). After that, the magnetic member is magnetized. On the outer peripheral surface of the encoder body 6 that is the detection surface, the S poles and the N poles are alternately arranged at equal intervals in the circumferential direction. The boundary between these S poles and N poles has a "<" shape with the central portion in the axial direction (width direction) of the detected surface protruding most in the circumferential direction. Although the measurement accuracy is inferior, only one of the half halves of the detected surface is inclined with respect to the axial direction, and the other half is parallel to the axial direction. It can also be made.

  Further, a pair of sensors 9a and 9b are supported and fixed inside a cover 7 made of a metal plate and having a bottomed cylindrical shape that closes the axial inner end opening of the outer ring 1 through a sensor holder 8 made of synthetic resin. is doing. In this state, the detection portions of both the sensors 9a and 9b are respectively placed close to and opposed to both halves in the axial direction of the detected surface of the encoder 4. In addition, magnetic detection elements such as a Hall IC, a Hall element, an MR element, and a GMR element are incorporated in the detection portions of both the sensors 9a and 9b.

  In the state measuring device for a rolling bearing unit configured as described above, when an axial load acts between the outer ring 1 and the hub 2, the outer ring 1 and the hub 2 are displaced relative to each other in the axial direction. Accordingly, the phase difference ratio (= phase difference / 1 period) existing between the output signals of the sensors 9a and 9b changes. This phase difference ratio takes a value commensurate with the action direction and magnitude of the axial load (the direction and magnitude of the relative displacement). Therefore, based on this phase difference ratio, the direction and magnitude of the axial load (the direction and magnitude of the relative displacement) can be determined. Note that the processing for obtaining these is performed by an arithmetic unit (not shown). For this reason, in the memory of this computing unit, an equation or a formula representing the relationship (zero point and gain) between the phase difference ratio and the relative displacement or load in the axial direction, which has been examined in advance by theoretical calculation or experiment. Remember the map.

  In the case of the above-described conventional structure, the number of sensors that make the detection portion face the detection surface of the encoder is two. On the other hand, although not shown in the drawings, Patent Documents 2 to 4 describe structures in which multidirectional displacement and external force are obtained by setting the number of sensors to three or more.

  Next, two examples of the magnetizing method of the encoder 4 constituting the state quantity measuring apparatus described above and described in Patent Document 5 will be described with reference to FIGS. Of these figures, FIG. 3 shows a diagram common to both examples, FIG. 4 shows a diagram related to the first example, and FIG. 5 shows a diagram related to the second example. In both cases, the encoder material 10 as shown in FIGS. 4 to 5 is made prior to performing the magnetizing operation. The encoder material 10 is formed by attaching and fixing a cylindrical magnetic member 11 {the material of the encoder body 6 (FIG. 2)} to the outer peripheral surface of the metal core 5. Further, when performing the magnetizing operation, a pair of magnetizing heads 12a and 12a (12a and 12b) are used. As shown in FIGS. 4 to 5, the tip surfaces 13 a and 13 b of both the magnetized heads 12 a and 12 b are partial cylindrical surfaces concentric with the outer peripheral surface of the encoder material 10, which are surfaces to be detected. . 3A shows the planar shape of the tip surface 13a (13b) of each of the magnetized heads 12a (12b) {the shape seen from the axial direction of each of the magnetized heads 12a (12b). The same shape as the cross-sectional shape of the magnetized head 12a (12b)}, (B) in the figure is a developed view of a part of the circumference of the detected surface of the encoder 4 to be completed (assumed developed in a plane) The figure which shows) is each shown. As shown in FIGS. 3A and 3B, the planar shapes of both side edges of the tip surface 13a (13b) of each of the magnetized heads 12a (12b) in the circumferential direction (left and right direction in FIG. 3) are respectively It has a “<” shape that is the same as the shape of the boundary between the S pole and the N pole that appears in the developed view of the detected surface.

First, in the case of the first example of the magnetizing method shown in FIG. 4, when performing the magnetizing operation, as shown in the drawing, two locations adjacent to each other in the circumferential direction on the outer peripheral surface of the magnetic member 11 are shown. The tip surfaces 13a and 13a of the two magnetized heads 12a and 12a are made to face each other in close proximity to each other. In this state, when a current is passed through a coil (not shown) wound around the two magnetized heads 12a and 12a, a magnetic circuit is formed between the front end surfaces 13a and 13a of the two magnetized heads 12a and 12a. The magnetic flux constituting this magnetic circuit penetrates the two portions. As a result, a pair of “<”-shaped S poles and N poles is magnetized at these two portions. Therefore, in the case of this example, the magnetic member 11 and the core metal 5 are rotated continuously (or intermittently at every predetermined angle), and the rotation speed is appropriate (or is rotated or stopped). At appropriate timing, the energization of the coil is alternately switched on and off. Thus, a pair of “<”-shaped S poles and N poles are sequentially magnetized and formed in the circumferential direction on the entire outer circumference of the magnetic member 11 to complete the encoder body 6.
In the example shown in the figure, the number of the magnetizing heads 12a used side by side in the circumferential direction is two, but the number may be three or more (for example, 3 to 5).

Next, in the case of the second example of the magnetizing method shown in FIG. 5, when performing the magnetizing work, as shown in the drawing, a part in the circumferential direction of the magnetic member 11 and the cored bar 5 from both sides in the radial direction. The front end surfaces 13a and 13b of the two magnetized heads 12a and 12b are opposed to each other in a non-contact state. In this state, when a current is passed through a coil (not shown) wound around the two magnetized heads 12a and 12b, a magnetic circuit is formed between the front end surfaces 13a and 13b of the two magnetized heads 12a and 12b. The magnetic flux constituting this magnetic circuit penetrates through the portion of the outer peripheral surface of the magnetic member 11 facing the distal end surface of the radially outer magnetized head 12a. As a result, one "<"-shaped S-pole or N-pole is magnetized in this penetrating portion. Therefore, in the case of this example, while rotating the magnetic member 11 continuously (or intermittently every predetermined angle), at an appropriate timing commensurate with this rotational speed (or rotation and stop), The ON / OFF of the energization to the coil and the direction of energization to the coil are alternately switched. As a result, "<"-shaped S poles and N poles are alternately magnetized one by one in the circumferential direction on the entire outer peripheral surface of the magnetic member 11 to complete the encoder body 6.
In the illustrated example, the number of pairs of magnetizing heads 12a and 12b to be used is 1, but the number of pairs can be 2 or more (for example, 2 to 5).

  However, in the case of each of the magnetization methods described above, the shape of the boundary between the S pole and the N pole used for detection in the detected surface of the encoder 4 after magnetization is slightly shifted from the target shape. Shape. This point will be described below with reference to FIGS. 6 to 9 in addition to FIGS.

  FIG. 6 shows the positional relationship between the encoder material 10 and the magnetizing head 12a when the above-described magnetization methods are performed. Actually, as shown in FIGS. 4 to 5, two magnetizing heads are used. In FIG. 6, only one of the magnetizing heads 12a is shown. For convenience of explanation, the dimensional relationship between the encoder material 10 and the magnetized head 12a is extremely changed as shown in FIG. The planar shape (the shape seen from right above in FIG. 7) of both circumferential edges of the front end surface 13a of the magnetized head 12a shown in FIG. 7 is “ku” as shown in the upper half of FIG. It has a letter shape. As described above, this "<" shape is the shape of the boundary that appears in the developed view of the detected surface of the encoder 4 to be completed shown in FIG. 3B (the desired "<" shape). And the same shape. However, when the front end surface 13a is viewed in a developed view, that is, the front end surface 13a has a plane coordinate {circumferential direction θ of the front end surface 13a (positions of points P and Q in FIG. 8). Is taken as the zero point.), And the shape of the both side edges in the circumferential direction of the tip surface 13a is respectively 9 does not have the above-mentioned target “<” shape as indicated by a broken line J in FIG. 9, and is slightly deviated from this target “<” shape as indicated by a solid line K in FIG. 9. Become.

The reason for this is that the above-mentioned “<” shape is defined as the planar shape of both side edges of the tip surface 13a in the circumferential direction. That is, in FIG. 8, when the target “<” shape is transferred to a virtual plane F orthogonal to the axial direction of the magnetizing head 12 a, each portion of the target “<” shape ( For example, the width in the Y-axis direction is ΔY and the width in the X-axis direction perpendicular to the Y-axis direction is ΔX) is transferred with the same shape and dimensions (ΔY, ΔX). The In the example shown in the figure, ΔX = ΔYtan α (α: the inclination angle of both half portions of the above-mentioned “<” shape with respect to the Y-axis direction, 45 degrees in the example shown) = ΔY ( The relationship of 度 tan 45 degrees = 1) is established. On the other hand, when the desired “<” shape is transferred to the virtual partial cylindrical surface G having the same shape as the tip surface 13 a, each of the desired “<” shape portions (ΔY, ΔX) ) is the concerning the width △ Y is transferred as it dimension, in regard to width △ X, in the circumferential direction of the virtual partially cylindrical surface G, are transferred a width △ X _c. In the example shown in the figure, ΔX _c = r · β {r: radius of curvature of the virtual partial cylindrical surface G (= radius of the outer peripheral surface of the encoder material 10 + radial direction of the outer peripheral surface and the tip end surface 13a. (Interval), β: center angle corresponding to the width ΔX _c } = r · sin ⁻¹ (ΔYtan α / r) = r · sin ⁻¹ (ΔY / r) (∵tan 45 degrees = 1) To establish. For this reason, as apparent from a comparison between the expression related to ΔX _c and the expression related to ΔX, the “<” shape transferred to the virtual partial cylindrical surface G is the target “<”. Compared to the letter shape, it is longer in the + θ direction on the left side than the PQ line (coordinate origin) and longer in the −θ direction on the right side than the PQ line. Therefore, the shape of both side edges in the circumferential direction of the tip end surface 13a shown by the solid line K in FIG. 9 corresponding to the “<” shape transferred to the virtual partial cylindrical surface G is indicated by a broken line J in FIG. The shape is slightly deviated from the above-described “<” shape.

  As a result, the shape of the boundary appearing in the developed view of the detected surface after magnetization is slightly deviated from the intended “<” shape indicated by the broken line J in FIG. 9 as indicated by the solid line K in FIG. Become a shape. Incidentally, the shape deviation caused in this way is shown in FIG. 7 in which the width dimension (the lateral dimension in FIGS. 6 to 7) of the tip surface 13a of the magnetized head 12a compared with the diameter dimension of the encoder material 10 is shown. As shown in FIG. 6, the value increases as the value increases, and the value decreases as the value decreases. Therefore, in the case of the actual dimensional relationship as shown in FIG. 6, the shape deviation generated as described above is relatively small. However, such a deviation in shape causes a decrease in the measurement accuracy of the state quantity, so it is desirable to eliminate it as much as possible.

  In addition, as an encoder made from a permanent magnet which comprises a state quantity measuring apparatus, when it sees with an expanded view other than the encoder 4 shown to the above-mentioned FIG.2 and FIG.3 (B), it shows in FIGS. Encoders 4a to 4b having various boundary shapes (see Japanese Patent Application No. 2007-181605), encoders 4c having boundary shapes as shown in FIG. 12 (see Japanese Patent Application No. 2007-69749), and boundary shapes as shown in FIG. There is an encoder 4d (see Patent Document 3) having In each of the encoders 4a to 4d, the boundary shape formed on the detected surface after magnetization is slightly deviated from the target shape for the same reason as in the encoder 4. Occurs. For this reason, it is desired that the above-described encoders 4a to 4d have the above-described shape shift as little as possible.

JP 2006-317420 A JP 2006-322928 A JP 2007-93580 A JP 2008-64731 A JP 2007-85761 A

  In view of the circumstances as described above, the present invention assumes that the shape of the boundary formed on the detected surface of the encoder after being magnetized by the magnetizing head is developed in a planar shape. The present invention was invented to realize a method of magnetizing an encoder that can have a desired shape.

The encoder to be magnetized by the magnetizing method of the present invention has a cylindrical detection surface made of a permanent magnet, and S poles and N poles are alternately arranged on the detection surface in the circumferential direction, At least a part of the boundary between the S pole and the N pole is inclined with respect to the axial direction.
In the magnetizing method of the present invention, in order to build the encoder, in a state where the tip surface of the magnetizing head is opposed to the peripheral surface to be the detected surface among the encoder materials that are unmagnetized magnetic materials, The encoder material is magnetized by causing a magnetic flux to flow from the magnetizing head to the encoder material.
In particular, in the method of magnetizing the encoder according to the present invention, the shape of the boundary of the inclined portion used for detection in the detected surface after the magnetization by the magnetizing head is defined by this shape. The tip surface of the magnetized head is a partial cylindrical surface concentric with the surface to be detected so that the detection surface is assumed to be flattened. The shape of the part which should form the said target shape in the circumferential direction both sides is different from the said target shape in the state which looked at this front end surface from the axial direction of the said magnetic head.

When the present invention as described above is implemented, for example, the entire detected surface of the encoders 4 and 4d shown in FIG. 3B and FIG. 13 or the encoder 4a shown in FIGS. 4b, when the target shape is a straight line as shown in the portion excluding the central portion in the width direction of the detected surface (vertical direction in FIGS. 10 to 11), Similarly, the shape of the portion where the target shape should be formed among the circumferential side edges of the front end surface of the magnetized head is a state in which the front end surface is viewed from the axial direction of the magnetized head. And let's assume a curve.
In addition, the target shape is a straight line, the inclination angle of the straight line with respect to the axial direction of the encoder is α among the detected surfaces, and the tip surface of the magnetized head is When the radius of curvature is r, specifically, as in the invention described in claim 3, the tip surface of the tip surface when the tip surface is viewed from the axial direction of the magnetizing head is used. An XY plane coordinate (this tip surface is defined as an axial direction) in which the axis in the direction corresponding to the rotation direction of the encoder is the X axis, and the axis in the direction corresponding to the axial direction of this encoder is the Y axis. The shape of the portion where the above-mentioned target shape is to be formed among the circumferential side edges of the tip surface within the plane coordinates as viewed from the X axis direction width X and the Y axis direction width respectively. △ between the Y, △ relationship ^{X = r · sin -1 (△} Ytanα / r) is satisfied To the line. Incidentally, this relation is a formula relating △ X described above, by considering the relationship between the expression for △ X _c described above are those derived so as to form a shape with the above-mentioned object.

  Further, for example, as shown in the center portion in the width direction of the detected surface of the encoder 4a shown in FIG. 10 and the entire detected surface of the encoder 4c shown in FIG. In the case of a curved line, as in the invention described in claim 4, the shape of the portion where the target shape should be formed among the circumferential side edges of the tip surface of the magnetized head, In a state where the front end surface is viewed from the axial direction of the magnetizing head, a curve having a curvature different from that of the curve (the target shape) is used.

  That is, the magnetizing method of the encoder of the present invention as described above will be described by changing the expression. In the magnetizing method of the encoder of the present invention, the magnetized method after the magnetizing by the magnetizing head is used. As the magnetizing head, the front end surface is connected to the detected surface so that the boundary shape formed on the detection surface becomes a target shape assuming that the detected surface is developed in a flat shape. A concentric partial cylindrical surface is used, and the shape of both side edges in the circumferential direction of the tip surface, assuming that the tip surface is flattened, is the same as the target shape. For example, when magnetizing the encoders 4, 4a to 4d as shown in FIG. 3B and FIGS. 10 to 13, the tip surface of each encoder 4, 4a serves as a magnetizing head. The shapes of the circumferential side edges of the tip surface in a state where the tip surface is assumed to have been developed in a flat shape are the partial cylindrical surfaces concentric with the surface to be detected of 4d. (B) and the same shape as each boundary shape shown in FIGS.

  According to the magnetizing method of the encoder of the present invention as described above, it is assumed that the boundary shape formed on the detected surface of the encoder after magnetization by the magnetizing head is developed into a flat surface. In this state, the desired shape can be obtained.

  An example of the embodiment of the present invention will be described with reference to FIG. The feature of this example is to make the encoder 4 shown in FIG. 2 and FIG. 3B, in which the shape of the boundary between the S pole and the N pole is a “<” shape (V shape). Both edges in the circumferential direction of the tip surfaces of the pair of magnetizing heads (partial cylindrical surfaces concentric with the outer peripheral surface of the encoder material 10) used when magnetizing the encoder material 10 as shown in FIGS. It is in the point which devised the shape. The structure and operation of the other parts are the same as those of the first example of the conventional magnetizing method shown in FIG. 4 or the second example of the conventional magnetizing method shown in FIG. . For this reason, overlapping illustrations and descriptions will be omitted, and the following description will focus on the features of this example. FIG. 1 is a plane coordinate of the tip surfaces of the magnetized heads viewed from the axial direction of the magnetized heads (the tip surfaces of the magnetized heads are viewed from the axial direction of the magnetized heads). Of these tip surfaces in the state, the axis in the direction corresponding to the rotation direction of the encoder 4 is defined as the X axis, and similarly, the direction corresponding to the width direction of each tip surface (the axial direction of the encoder 4). XY plane coordinates) where the axis is the Y axis.

In the case of this example, it is assumed that the shape of the boundary formed on the detected surface after magnetization by each of the magnetizing heads is the target shape { The shape of both side edges in the circumferential direction of the front end surface of each of the magnetizing heads is set as follows so as to have a “<” shape as shown in FIG. In other words, in the case of this example, the shape of both side edges in the circumferential direction of the tip surface of each of the magnetizing heads is not set to the target shape as indicated by the broken line J in the XY plane coordinates of FIG. , A curve as shown by a solid line L {between the width ΔX in the X-axis direction and the width ΔY in the Y-axis direction, ΔX = r · sin ⁻¹ (ΔYtanα / r) (r: A curve that satisfies the relationship of the radius of curvature of the tip surface of the magnetic head, α: the inclination angle of the target shape with respect to the axial direction of the detected surface). In other words, in the case of this example, it is assumed that the shape of both side edges in the circumferential direction of the tip surface of each of the magnetized heads is developed in a flat shape. In the state, the target shape is used.

  Therefore, according to the magnetizing method of the encoder of this example as described above, the shape of the boundary formed on the detected surface of the encoder 4 after magnetization by the pair of magnetizing heads is flattened. In the state assumed to have developed into a shape, it is possible to make the target shape {a “<” shape as shown in FIG. Other configurations and operations are the same as those of the first example of the conventional magnetizing method shown in FIG. 4 or the second example of the conventional magnetizing method shown in FIG.

The shape of the boundary (broken line) that should appear in the developed view of the surface to be detected after magnetization, and the circle of this tip surface that appears in the plan view of the tip surface of the magnetizing head used in one example of the embodiment of the present invention The diagram which shows the shape (solid line) of the circumferential direction both-sides edge. Sectional drawing which shows one example of the conventional structure regarding the state quantity measuring apparatus of a rolling bearing unit. (A) is a figure which shows the planar shape of the front end surface of the magnetizing head used by two examples of the conventional magnetizing method, (B) is a development view of the circumferential direction part of the detected surface of the encoder to be completed. . The figure which looked at the implementation condition of the 1st example of the conventional magnetization method from the axial direction of the encoder. The figure which looked at the implementation condition of the 2nd example from the axial direction of the encoder. The figure which looked at the positional relationship of the encoder raw material at the time of implementing the conventional magnetization method and a magnetic head from the axial direction of this encoder raw material. FIG. 7 is a view similar to FIG. 6 in which the width of the magnetized head is increased. The diagram for demonstrating the difference in the shape at the time of transferring the shape of the boundary which should appear in the developed view of the to-be-detected surface after magnetization (the target "<" shape) shape to a plane and a partial cylindrical surface. The boundary shape (dashed line) that should appear in the developed view of the detected surface after magnetization, and both circumferential edges of this tip surface appearing in the developed view of the tip surface of the magnetizing head used in the conventional magnetizing method The figure which shows the shape (solid line). The figure similar to (B) of Drawing 3 showing the 1st example of other encoders which can become the object of implementation of the magnetization method of the present invention. The figure similar to FIG. 10 which shows the 2nd example. The figure similar to FIG. 10 which shows the 3rd example. The figure similar to FIG. 10 which shows the 4th example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Outer ring 2 Hub 3 Rolling element 4, 4a-4d Encoder 5 Core metal 6 Encoder main body 7 Cover 8 Sensor holder 9a, 9b Sensor 10 Encoder material 11 Magnetic member 12a, 12b Magnetization head 13a, 13b Tip surface

Claims (4)

  The detection surface is made of a permanent magnet and has a cylindrical detection surface. S poles and N poles are alternately arranged on the detection surface in the circumferential direction, and at least a part of the boundary between these S poles and N poles is provided. In order to build an encoder that is inclined with respect to the axial direction, the magnetic head is positioned in the state where the tip surface of the magnetizing head is opposed to the peripheral surface to be detected among the encoder materials that are unmagnetized magnetic materials. In a method of magnetizing an encoder that magnetizes the encoder material by flowing a magnetic flux from the magnetic head to the encoder material, it is used for detection among the detected surfaces that are magnetized by the magnetized head. The tip surface of the magnetized head is the same as the surface to be detected so that the shape of the boundary of the inclined portion becomes a target shape assuming that the surface to be detected is flattened. This concentric partial cylindrical surface and this tip surface Of the circumferential side edges, the shape of the portion where the target shape should be formed is different from the target shape when the tip surface is viewed from the axial direction of the magnetizing head. An encoder magnetizing method characterized by the above.   The target shape is a straight line, and the shape of the portion where the target shape is to be formed among the circumferential side edges of the tip surface of the magnetizing head is the axial direction of the magnetizing head. The method of magnetizing an encoder according to claim 1, wherein the method is a curved line as viewed from above. When the target shape is a straight line, the inclination angle of this straight line with respect to the axial direction of the encoder among the detected surfaces is α, and the radius of curvature of the front end surface of the magnetizing head is r, this front end surface is The X axis is the axis in the direction corresponding to the rotation direction of the encoder in the tip surface when viewed from the axial direction of the magnetizing head, and the axis direction of the encoder is also in the tip surface. In the XY plane coordinates where the axis in the direction to be moved is the Y axis, the shape of the portion that should form the target shape among the circumferential side edges of the tip surface is the width ΔX in the X axis direction. 3. The curve according to claim 1, wherein the curve is such that a relationship of ΔX = r · sin ⁻¹ (ΔYtan α / r) is established between Y and the width ΔY in the Y-axis direction. Magnetization method of the described encoder.   The target shape is a curve, and the shape of the portion of the circumferential side edge of the magnetized head that should form the target shape is the tip of the magnetized head in the axial direction of the magnetized head. 2. The method of magnetizing an encoder according to claim 1, wherein the curve has a curvature different from that of the curve as viewed from the above.

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