JPH07274450A - Motor field system and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a motor field system and manufacturing method at low cost with no fear of shortage or variation in surface flux density. CONSTITUTION:A manufacturing method comprises a step for holding an elastic non-magnetized magnet sheet 1 firmly on a flat magnetizing face of a magnetizing unit 2, a step for magnetizing the elastic magnet sheet 1 by the magnetizing unit 2 with an applied current, a step for joining both ends of the elastic magnetic sheet 1 into an annular shape, and a step for assembling the annular magnetic sheet into an inner peripheral face of a cylindrical motor case.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field magnet for a sheet-shaped flexible magnet and a method for manufacturing the same.

[0002]

2. Description of the Related Art For example, a flexible magnet is known as a magnet used for a small motor or the like. The field of such a flexible magnet to a small motor is generally made in the following procedure.

(1) As shown in FIG. 19 (a), a plate-shaped flexible magnetic material is cut into an appropriate size and formed into a band-like shape as indicated by reference numeral 21. (2) As shown in FIG. 19B, both ends of a belt-shaped and flexible magnetic material 21 in the longitudinal direction are joined to form an annular shape, and the magnetic material 21 is formed into an annular rounding jig 2.
It is press-fitted into the inner peripheral surface of 3 and shaped so as to have a substantially perfect circle shape. (3) As shown in FIG. 19C, on the inner peripheral surface of the magnetic material 21 held and shaped on the inner peripheral surface of the rounding jig 23, the outer periphery of the disk-shaped magnetizing jig 24 of the magnetizing device. Fit the faces together,
The flexible magnet 21 is formed by magnetizing the magnetic material 21. (4) After the magnetization, as shown in FIG. 19D, the flexible magnet 21 is rolled up from the inner peripheral surface of the jig 23 to the motor case 22.
And the assembly of the flexible magnet 21 to the motor case 22 is completed.

Further, the sheet-shaped and flexible magnetic material 21 is directly attached to the inner peripheral surface of the motor case 22, and the magnetic material 21 is held in the motor case 22 and is formed into a disk shape of the magnetizing device. There is also a method in which the inner peripheral surface of the magnetic material 21 is fitted into the magnetizing jig 24 and magnetized. With such a method, since the rounding jig 23 is not used, the process can be shortened and the cost can be reduced.

[0005]

The motor field and the method for manufacturing the same as described above make it possible to make the surface magnetic flux density and the central angle of the magnetic poles after the field uniform. Have some problems. (1) In order to facilitate attachment and detachment of the magnetic material 21 to and from the magnetizing device during the magnetizing work, the magnetic material 21 attached to the magnetizing jig and the magnetizing surface 24a may be slightly separated. It is preferable that a gap of 1 is generated. However, when magnetized in a state where there is a gap, the magnetic flux density of the flexible magnet 21 becomes insufficient, or the gap varies in the circumferential direction, which causes variations in the magnetic flux density. On the contrary, if the gap is extremely small, it becomes difficult to attach the magnetic material 21 to the magnetizing device and remove it after the magnetizing, and the workability is extremely deteriorated. (2) The magnetizing jig 24 has the strongest magnetizing force around the central portion in the thickness direction (axial direction). However, in the case where the magnetic material 21 set to have a small width dimension to accommodate a thin motor or the like is magnetized after being attached to the motor case 22, as shown in FIG.
1 may not reach the central part where the magnetic force is strongest,
Sufficient magnetization cannot be obtained and the surface magnetic flux density becomes insufficient. (3) Since the magnetizing device having the disk-shaped magnetizing portion 24 is expensive and can only support the flexible magnet 21 having a certain size, it is not versatile. Further, in the case where the magnetizing device 25 for skew magnetizing as shown in FIG. 21 is formed, the cost further increases and becomes expensive.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a motor field that is inexpensive and has no surface magnetic flux density deficiency or variation and a method for manufacturing the same. .

[0007]

The invention according to claim 1 is
A step of bringing a sheet-shaped flexible magnet in an unmagnetized state into close contact with a flat magnetized surface of a magnetizing device and sandwiching it, and a step of passing a current through the magnetizing device to magnetize the sheet-shaped flexible magnet. The method is characterized by including a step of abutting both ends of the sheet-like flexible magnet into an annular shape, and a step of incorporating the annular flexible magnet into the inner peripheral surface of the cylindrical portion of the motor case.

According to a second aspect of the present invention, there is provided a magnetizing device comprising a pair of flat type magnetizing jigs, which magnetize by sandwiching sheet-like flexible magnets which are not magnetized by magnetizing surfaces facing each other. Is used.

According to a third aspect of the present invention, the sheet-shaped flexible member is composed of a flat magnetizing jig and a back yoke, and the magnetizing surface of the flat magnetizing jig and the back yoke which face each other are not magnetized. It is characterized by using a magnetizing device which holds a magnet and magnetizes it.

According to a fourth aspect of the present invention, when the number of magnetic poles magnetized to the sheet-shaped flexible magnet in the non-magnetized state is n, a magnetizing device having n + 1 salient poles on the magnetized surface is provided. It is characterized by being used.

A fifth aspect of the present invention is characterized by using a magnetizing device having salient poles on both sides of a salient pole which is in close contact with both ends of a sheet-shaped flexible magnet which is not magnetized.

The invention according to claim 6 is characterized in that a magnetizing device is used which has auxiliary poles on both sides of salient poles which are in close contact with both ends of a sheet-shaped flexible magnet which is not magnetized.

According to a seventh aspect of the present invention, a sheet-shaped flexible magnet having a plurality of poles magnetized is formed into an annular shape by abutting both ends thereof, and is incorporated in the inner peripheral surface of the cylindrical portion of the motor case. The magnetic field of the motor, the dimension of the sheet-shaped flexible magnet in the longitudinal direction is L, the thickness of the sheet-shaped flexible magnet is T, the inner diameter of the cylindrical portion of the motor case is D, and the pi is Is 0.98 ≦ L / (D−T) π ≦ 1.1
It is characterized by being 0.

The invention according to claim 8 is characterized in that the length of the magnetic poles of the sheet-shaped flexible magnet is varied according to the contraction rate.

[0015]

Function: The sheet-like flexible magnet in an unmagnetized state is brought into close contact with the magnetizing device having a flat magnetized surface for magnetizing. Since there is no gap between the unmagnetized sheet-shaped flexible magnet and the magnetized surface, strong and uniform magnetization can be performed and workability is good. After being magnetized, the sheet-shaped flexible magnet is shaped into an annular shape and incorporated into the inner peripheral surface of the motor case.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a motor field and a method of manufacturing the same according to the present invention will be described below with reference to the drawings. 1 and 2, the magnetizing device comprises a pair of flat type magnetizing jigs 2 and 2. Each flat magnetizing jig 2,
A plurality of salient poles 3 are formed in a comb shape in the longitudinal direction of 2, and a coil 2b is wound around each salient pole 3. The head end surface of each salient pole 3 has a quadrangular shape, and the quadrangular head end surface of the plurality of salient poles 3 constitutes the magnetized surface 2a of the planar magnetizing jig 2. The magnetized surfaces 2a, 2a of the two surface type magnetizing jigs 2, 2 face each other,
A sheet-shaped flexible magnet 1 in an unmagnetized state is sandwiched and held between the two magnetized surfaces 2a, 2a.

As described above, the sheet-shaped flexible magnets 1 in the unmagnetized state are held on the magnetized surfaces 2a, 2a of the flat magnetizing jigs 2, 2 and the sheet-shaped flexible magnets in the unmagnetized state are held. By energizing the coil 2b wound around the salient pole 3 in a state where both sides of the magnetic magnet 1 are in close contact with the magnetized surface 2a, the salient poles 3 are applied to the sheet-shaped flexible magnet 1 which is not magnetized. And magnetized, as shown in Fig. 3.
A sheet-shaped flexible magnet 1 as shown in is formed. The salient poles 3 and 3 of the pair of magnetizing jigs 2 and 2 facing each other have mutually different polarities when viewed from the magnetized surface, and the adjacent salient poles 3 have mutually different polarities. The coils 2b and 2b are energized.

The sheet-shaped flexible magnet 1 magnetized by the magnetizing device is shaped into an annular shape with both ends abutted as shown in FIG. 4) is attached to the inner peripheral surface of the motor case 4, and the field of the motor case is completed as shown in FIG. When the flexible magnet 1 is attached to the motor case 4, a tapered cylindrical jig 10 as shown in FIG. 5 is used, and the jig 10 is flexed from the large diameter portion toward the tip small diameter portion. The flexible magnet 1 is gradually shaped into a ring shape while pushing the flexible magnet 1, and the flexible magnet 1 having both ends butted into an annular shape is pushed out into the motor case 4 to be mounted. Good.

According to the motor field and the manufacturing method thereof as described above, the flat magnetizing jigs 2 and 2 facing each other are provided.
Since the sheet-like flexible magnet 1 is sandwiched between the magnetized surfaces 2a and magnetized, and then the magnetized surface 2a is shaped into an annular shape and incorporated into the motor case, the magnetized surface 2a is not deteriorated.
The sheet-shaped flexible magnet 1 can be magnetized in a state of being in close contact. Further, the magnetized surface 2a and the sheet-shaped flexible magnet 1
Are closely attached to each other, it is possible to eliminate shortage and variation of the surface magnetic flux, and it is possible to magnetize at a fine pitch.
Further, since the flat type magnetizing jigs 2 and 2 can be manufactured only by flattening, the magnetizing device can be obtained at low cost, and the salient poles 3 can be formed into various shapes. Therefore, a magnetizing device for skew magnetizing, which has been difficult in the past, can be manufactured at low cost. Further, since the sheet-shaped flexible magnet 1 is closely attached to the magnetized surface 2a of the flat magnetizing jig 2 to magnetize the sheet-shaped flexible magnet 1, the magnetism is strongest regardless of the size of the sheet-shaped flexible magnet 1. Because it can be magnetized at the location
The sheet-shaped flexible magnet 1 can be sufficiently magnetized, and the lack of surface magnetic flux density can be eliminated. Further, since the sheet-shaped flexible magnet 1 is magnetized by the flat type magnetizing jigs 2 and 2 facing each other, a jig for holding the flexible magnet during the magnetizing is separately prepared. This also reduces the manufacturing cost.

As the magnetizing device, as shown in FIG. 6, the sheet-shaped flexible magnet 1 which is not magnetized by the magnetizing surface 2a of the flat magnetizing jig 2 and the flat back yoke 5. Sandwich the
You may use what is magnetized. This also makes it possible to eliminate shortage and variations in the surface magnetic flux. Further, since only one flat magnetizing jig 2 is required, the cost of the magnetizing device can be further reduced.

By the way, when the sheet-like flexible magnet 1 magnetized by the magnetizing device as described above is used for a small motor, as shown in FIG. When the short sheet-shaped flexible magnet 1 is magnetized by the flat magnetizing jig 2, the magnetized state of the constituent magnetic poles shown by the solid line in FIG. 7B is different from the ideal magnetized state shown by the dotted line. It was found that the deviation, the surface magnetization density and the central angle became non-uniform, resulting in cogging.

Therefore, the lengthwise dimension of the sheet-shaped flexible magnet 1 is L, the thickness dimension of the sheet-shaped flexible magnet 1 is T, and the cylindrical portion of the motor case to which the sheet-shaped flexible magnet 1 is attached. When the inner diameter is D and the circular constant is π, these L,
When the optimum relationship between T and D was verified, a graph as shown in FIG. 8 was obtained. In FIG. 8, R = L / (D
-T) π, the cogging torque tends to increase when the value of R becomes smaller than 0.98, and when the value of R becomes larger than 0.10. It has been found that the excessive compression in the longitudinal direction of (1) deteriorates the roundness of the inner circumference of the field and increases the cogging torque. From the above results, L, T, D
The value of 0.98 ≦ L / (D−T) π ≦ 1.1
If the relationship of 0 is established, it is possible to prevent the surface magnetization density and the central angle from becoming nonuniform, and to obtain a small motor with a small cogging torque.

Further, as shown in FIG. 9 (a), the longitudinal position of the sheet-shaped flexible magnet 1 is displaced during magnetization,
When one end of the sheet-shaped flexible magnet 1 is out of the magnetized surface 2a, as shown in FIG. 9B, the magnetized state of the constituent magnetic poles shown by the solid line becomes the ideal magnetized state shown by the dotted line. On the other hand, the deviation, the surface magnetization density and the central angle become non-uniform, which causes the torque unevenness and cogging torque of the motor to increase. In order to solve such a problem, it is necessary to increase the positioning accuracy of the sheet-shaped flexible magnet 1 with respect to the magnetizing device. However, if the positioning accuracy of the sheet-shaped flexible magnet 1 is increased, the cost of the field manufacturing apparatus will increase, and
Further, there is a problem that the manufacturing time of the field becomes long.

In order to solve the above problems, FIG.
As shown in 0, the flat type magnetizing jig 2 having the salient poles 3 more than the number of magnetic poles of the field magnet may be used for the magnetization. Even if the position of the sheet-shaped flexible magnet 1 attached to the magnetizing device is slightly displaced, if the sheet-shaped flexible magnet 1 is within the magnetized surface 2a, the sheet-shaped flexible magnet 1 is provided with a long side as shown in FIG. The magnetic poles 1a and 1b having different polarities with different directions are formed.
The magnetic poles 1a and 1b become a single magnetic pole by abutting the both ends of the sheet-shaped flexible magnet 1, and the longitudinal dimension of the magnetic pole composed of the magnetic poles 1a and 1b is the same as the longitudinal direction of other magnetic poles. The size of the magnetic pole is equal to the size of the magnetic pole, which is no different from another magnetic pole. Therefore, the surface magnetization density and center angle of the field will not be non-uniform, and during magnetization,
Since highly accurate positioning is unnecessary, the cost and manufacturing time of the manufacturing apparatus can be reduced.

Further, as shown by the solid line in FIG. 12, depending on the material of the sheet-shaped flexible magnet 1, the magnetic flux at both ends in the longitudinal direction becomes lower than the other magnetic poles and becomes non-uniform,
Torque unevenness and cogging torque may increase.
This is because when the flat magnetizing jig 2 as shown in FIG. 6 is used, the lines of magnetic force are reduced at the salient poles 3 at both ends.

In order to solve such a problem, FIG.
As shown in FIG. 3, dummy salient poles 6 that are not in close contact with the sheet-shaped flexible magnet 1 are provided on both sides of the salient poles 3 and 3 that are in close contact with both ends of the sheet-shaped flexible magnet 1 of the planar magnetizing jig 2. , 6 may be formed. By forming the dummy salient poles 6, 6, the salient poles 3 that are in close contact with both ends of the sheet-shaped flexible magnet 1,
Since the number of magnetic force lines of 3 is the same as the number of magnetic force lines of each of the other salient poles 3, it is possible to uniformly magnetize, and it is possible to suppress uneven torque of the small motor and increase of cogging torque.

Instead of the dummy salient poles 6 and 6, the auxiliary poles 7 and 7 which extend from the magnetized surface side to the back yoke side and are in close contact with the back yoke 5 are formed as shown in FIG. The salient poles 3 and 3 that are in close contact with both ends of the sheet-shaped flexible magnet 1.
The number of magnetic lines of force may be the same as that of each of the other salient poles 3. Unlike the salient poles 3, the auxiliary poles 7 and 7 do not have the coil 2b wound around them.

Further, depending on the material of the sheet-shaped flexible magnet 1, the contraction rate at the time of shaping into an annular shape is uneven, and torque unevenness and cogging torque tend to increase. For example, as shown in FIGS. 15 (a) and 15 (b), when the sheet-shaped flexible magnet 1 is rolled, the contraction rate is large at both ends in the longitudinal direction,
When the contraction rate is small in the central portion, if the lengthwise direction of the head of the salient pole 3 is uniform and magnetized, the central angle of the magnetic poles near the ends is small, and conversely, in the vicinity of the central portion. The central angle of the magnetic pole becomes large, and the torque unevenness and the cogging torque of the small motor increase.

In order to solve the above problems,
It suffices to change the longitudinal dimension of the salient pole head in accordance with the contraction rate and magnetize it. For example, as shown in FIG. 16, the sheet-shaped flexible magnet 1 having a contraction rate that is small in the central portion in the longitudinal direction and large on both end sides as shown in FIG. 15B has a long head portion of each salient pole 3 at both ends. It is sufficient to increase the directional dimension and reduce the longitudinal dimension of the head portion of each salient pole 3 in the central portion. In the state immediately after magnetization, the dimensions of the magnetic poles of the sheet-shaped flexible magnet 1 are not uniform, and as shown in FIG. 17, both ends are large and the central part is small. However, by rounding it into an annular shape, the eccentricity of the dimensions of the magnetic poles and the contraction rate are canceled out, and it is possible to obtain the field of a small motor in which the central angles of the constituent magnetic poles are uniform. The magnetized state is the ideal magnetized state,
Can be the same. Therefore, it is possible to reduce the torque unevenness and the cogging torque of the small motor.

As an example of the flat magnetizing jig 2, a coil is wound around an iron core, but the present invention is not limited to this, and a flat magnet having another structure such as having no iron core. A magnetizing jig may be used. Further, the shape of the magnetic poles of the sheet-shaped flexible magnet 1 after magnetization is a rectangular shape, but the shape is not limited to this, and may be another shape such as a parallelogram or a trapezoid. Further, the field may be the rotor of a small motor or the stator.

[0031]

According to the first aspect of the present invention, in the field of the motor, the sheet-like flexible magnet in the non-magnetized state is brought into close contact with the flat magnetized surface of the magnetizing device to sandwich it. , A step of applying a current to the magnetizing device to magnetize the sheet-shaped flexible magnet, a step of abutting the both ends of the sheet-shaped flexible magnet into an annular shape, and an annular flexible magnet of the motor case. A low-cost motor that does not deteriorate workability because it is manufactured from the process of incorporating it into the inner peripheral surface of the cylindrical part, and it does not magnetize in the state where a flexible magnet is molded into an annular shape like in the past. Can be manufactured.

According to the second aspect of the present invention, it is composed of a pair of flat magnetizing jigs, and the sheet-like flexible magnets in the non-magnetized state are sandwiched between the magnetized surfaces facing each other, and magnetized. Therefore, it is possible to manufacture the field of the motor without lack or variation in the surface magnetic flux density.

According to a fourth aspect of the present invention, the magnetizing device has n + 1 protrusions on the magnetized surface, where n is the number of magnetic poles magnetized in the sheet-shaped flexible magnet that is not magnetized. Since it has a pole, high-precision positioning is unnecessary, workability can be improved, and manufacturing cost can be reduced.

According to the fifth aspect of the present invention, the magnetizing device has salient poles on both sides of the salient pole that is in close contact with both ends of the sheet-shaped flexible magnet that is not magnetized. The number of magnetic fluxes of the salient poles that are in close contact with the flexible magnet can be made uniform, and the field of the motor can be manufactured without lack or variation in surface magnetic flux density.

According to the sixth aspect of the invention, the magnetizing device has the supplementary poles on both sides of the salient poles that are in close contact with both ends of the sheet-shaped flexible magnet that is not magnetized. The number of magnetic fluxes of the salient poles that are in close contact with the flexible magnet can be made uniform, and the field of the motor can be manufactured without lack or variation in surface magnetic flux density.

According to the seventh aspect of the present invention, the sheet-like flexible magnet having a plurality of poles magnetized is formed into an annular shape by abutting both ends thereof, and the inner peripheral surface of the cylindrical portion of the motor case is formed. Which is a field of a motor incorporated into a sheet-shaped flexible magnet, a longitudinal dimension of the sheet-shaped flexible magnet is L, a thickness dimension of the sheet-shaped flexible magnet is T, an inner diameter of a cylindrical portion of the motor case is D, a circle. Pi is π
Then, 0.98 ≦ L / (D−T) π ≦
Since the dimensions are set so as to satisfy 1.10, the compressive force in the longitudinal direction of the flexible magnet when the flexible magnet is incorporated in the motor case becomes an appropriate value, and the circularity of the field is good. Therefore, it is possible to suppress the lack or variation of the surface magnetic flux density and reduce the cogging torque.

According to the eighth aspect of the invention, since the length of the magnetic poles of the sheet-shaped flexible magnet is varied according to the contraction rate, when the magnetic poles are formed into a cylindrical shape, the magnetic poles are eccentrically arranged and contracted. The ratios are offset, and the central angles of the constituent magnetic poles can be made uniform.

[Brief description of drawings]

FIG. 1 is a plan sectional view showing an embodiment of a magnetizing device used in a motor field and a method for manufacturing the same according to the present invention.

FIG. 2 is a perspective view of the same.

FIG. 3 is a plan view showing an embodiment of a sheet-like flexible magnet formed by the above magnetizing device.

FIG. 4 is a perspective view showing an embodiment of a method for manufacturing a motor field according to the present invention.

FIG. 5 is a cross-sectional view showing an embodiment of a jig used to manufacture the field of the same motor.

FIG. 6 is a plan sectional view showing another embodiment of the magnetizing device applied to the motor field and the manufacturing method thereof according to the present invention.

7A and 7B show an embodiment of a magnetizing device used in a motor field and a method of manufacturing the same according to the present invention. FIG. 7A is a plan sectional view of the magnetizing device and FIG. The graph which shows the magnetization state of a field.

FIG. 8 is a graph showing the relationship between the field size setting and the cogging torque of the motor according to the present invention.

9A and 9B show an example of a magnetizing device used in a field of a motor and a method for manufacturing the same according to the present invention. FIG. 9A is a plan sectional view of the magnetizing device, and FIG. The graph which shows the magnetization state of a field.

FIG. 10 is a plan sectional view showing another embodiment of the magnetizing device used in the motor field and the method for manufacturing the same according to the present invention.

FIG. 11 is a plan view showing an example of a sheet-shaped flexible magnet formed by the above magnetizing device.

FIG. 12 is a graph showing a magnetized state of a field manufactured by the manufacturing method according to the present invention.

FIG. 13 is a plan sectional view showing still another embodiment of the magnetizing device used in the motor field and the method for manufacturing the same according to the present invention.

FIG. 14 is a plan sectional view showing yet another embodiment of the magnetizing device used in the motor field and the method for manufacturing the same according to the present invention.

FIG. 15 is used for a magnetic field of a motor according to the present invention,
(A) is a plan view showing an embodiment of a sheet-like flexible magnet,
(B) is a graph showing the relationship between the longitudinal position of the sheet-shaped flexible magnet and the contraction rate.

FIG. 16 is a plan sectional view showing yet another embodiment of the magnetizing device used in the motor field magnet and manufacturing method therefor according to the present invention.

FIG. 17 is a plan view showing an example of a sheet-shaped flexible magnet formed by the above magnetizing device.

FIG. 18 is a sectional view showing a magnetized state of a field using the sheet-shaped flexible magnet of the above.

FIG. 19 is a perspective view showing an example of a conventional motor field and its manufacturing method.

FIG. 20 is a front view showing an example of a conventional motor magnetizing method.

FIG. 21 is a perspective view showing an example of a conventional magnetizing device used for skew magnetizing.

[Explanation of symbols]

 1 flexible magnet 2 magnetizing device 2a magnetizing surface 3 salient pole 4 motor case 5 back yoke 7 auxiliary pole

Claims (8)

[Claims] 1. A method of manufacturing a field of a motor, comprising at least the following steps: (1) A sheet-shaped flexible magnet in an unmagnetized state is magnetized in a plane of a magnetizing device. (2) a step of passing an electric current through the magnetizing device to magnetize the sheet-like flexible magnet, and (3) abutting both ends of the sheet-like flexible magnet into a circle. Step of forming an annular shape, (4) Step of incorporating an annular flexible magnet into the inner peripheral surface of the cylindrical portion of the motor case. 2. A magnetizing device comprising a pair of flat type magnetizing jigs and magnetizing by sandwiching the sheet-like flexible magnet in the non-magnetized state with magnetizing surfaces facing each other. 1. The method for manufacturing a motor field according to 1. 3. A flat magnetizing jig and a back yoke, wherein the non-magnetized sheet-like flexible magnet is sandwiched between the magnetizing surface of the flat magnetizing jig and the back yoke facing each other. The method of manufacturing a field of a motor according to claim 1, wherein a magnetizing device for magnetizing is used. 4. A magnetizing device having n + 1 salient poles on the magnetized surface is used, where n is the number of magnetic poles magnetized to the sheet-shaped flexible magnet in the non-magnetized state. The method for manufacturing a field of a motor according to claim 2 or 3. 5. A magnetizing device having salient poles on both sides of a salient pole that is in close contact with both ends of the sheet-shaped flexible magnet in the non-magnetized state is used. A method for manufacturing a field of a motor as described. 6. The magnetizing device according to claim 2, wherein a magnetizing device is used, which has salient poles that are in close contact with both ends of the sheet-shaped flexible magnet in the non-magnetized state and further has supplementary poles on both sides. A method for manufacturing a field of a motor as described. 7. A field magnet for a motor, wherein a sheet-like flexible magnet having a plurality of poles magnetized is formed into an annular shape by abutting both ends thereof, and is incorporated in an inner peripheral surface of a cylindrical portion of a motor case. Where L is the longitudinal dimension of the sheet-shaped flexible magnet, T is the thickness dimension of the sheet-shaped flexible magnet, D is the inner diameter of the cylindrical portion of the motor case, and π is the circular constant. When it did, 0.98 <= L / (D-T) (pi) <= 1.10 The field of the motor characterized by the above-mentioned. 8. The magnetic field of a motor according to claim 7, wherein the length of the magnetic pole of the sheet-like flexible magnet is changed according to the contraction rate.