JPH11308844A - Motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical motor in which output is high, and ultra- miniaturization, smooth starting and low cost manufacturing are made possible. SOLUTION: A cylindrical member 11 made of a soft magnetic material is fixed to the inner diameter part of a rotor magnet 1, which is magnetized to alternately different poles in the peripheral direction. A coil 2 is arranged in the axial direction of the rotor magnet 1, outside magnetic pole parts 18a 18b of a cylindrical stator 18 excited by the coil 2 are made to face the outer peripheral surface of the magnet 1, and inside magnetic pole parts 18c, 18d of a stator 18 are made to face the inner peripheral surface of a cylindrical member 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small cylindrical motor.

[0002]

2. Description of the Related Art FIG. 12 is a longitudinal sectional view showing a configuration example of a conventional small step motor having a cylindrical shape. In FIG. 12, the illustrated motor includes two stators 102 arranged in the motor axial direction, and each of the stators 102 has two stator yokes 106 arranged to face each other in the axial direction. For each stator 102, the bobbin 101 held by the two stator yokes 106
, A stator coil 105 is wound concentrically. Each bobbin 1 on which the stator coil 105 is wound
Numeral 01 is sandwiched and fixed by the two stator yokes 106 in the axial direction. Each stator yoke 106, 1
In 06, stator teeth 106a and 106b alternately arranged in the circumferential direction of the inner diameter surface of the bobbin 101 are formed. On the other hand, a pair of stator yokes 106, 106 having the stator teeth 106a, 106b are fixed to the case 103 of each stator 102. Thus, the stator 102 is configured.

[0003] A flange 115 and a bearing 108 are fixed to one (left side in the figure) of the two cases 103, and an opposite bearing 108 is fixed to the other case 103 (right side in the figure). The rotor 109 has a structure in which a rotor magnet 111 is fixed to a rotor shaft 110. The rotor magnet 1
11 and the stator yoke 1 of the stator 102
An air gap (air gap) is formed between the inner diameter surface and the inner diameter surface 06. The rotor shaft 110 is connected to each of the cases 1
The two bearings 108 are rotatably supported by two bearings 108.

FIG. 14 is a plan view illustrating a stepping motor driven by one coil used in a timepiece or the like. In FIG. 14, reference numeral 201 denotes a rotor made of a permanent magnet, 202 and 203 denote stators, and 204 denotes a coil.

[0005]

However, FIG.
In the conventional small stepping motor shown in FIG. 1, the case 103, the bobbin 101, the stator coil 1
Since the stator 05 and the stator yoke 106 are arranged concentrically, there is a disadvantage that the outer dimensions of the motor become large. Further, the magnetic flux generated by energizing the stator coil 105, as shown in FIG. 13, primarily an end face 106a ₁ and the stator teeth 106 of the stator tooth 106a
to pass the end face 106b ₁ of b, the rotor magnet 11
1 has a problem to be solved in that it does not work effectively and the motor output does not increase. Further, even in the motor shown in FIG. 14, the magnetic flux generated by energizing the coil 204 concentrates on a small gap between the rotor 201 and the stator 202 and does not effectively act on the magnet 201. There are issues.

[0006] The present invention has been made in view of such technical problems, and an object of the present invention is to provide a high output, miniaturization, smooth start-up, and inexpensive manufacture. An object of the present invention is to provide a cylindrical motor.

[0007]

In order to achieve the above object, a motor according to the present invention comprises a rotatable rotor magnet which is alternately magnetized in a circumferential direction at different poles, and faces the rotor magnet with a gap. A cylindrical stator that
And a coil mounted inside the stator, and a cylindrical member made of a soft magnetic material is fixed to the inner diameter of the rotor magnet, and the coil is arranged in the axial direction of the rotor magnet, and is excited by the coil. The outer magnetic pole of the stator is opposed to the outer peripheral surface of the magnet, and the inner magnetic pole of the stator is opposed to the inner peripheral surface of the cylindrical member.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view of one embodiment of a motor to which the present invention is applied, and FIG. 2 is a longitudinal sectional view of one embodiment of a motor to which the present invention is applied. 1 and 2, a motor according to the present invention includes a rotatable rotor magnet 1 magnetized to different poles alternately in a circumferential direction;
The rotor magnet 1 includes a cylindrical stator 18 opposed to the rotor magnet 1 with an air gap, and a coil 2 mounted inside the stator 18. And the coil 2 is arranged in the axial direction of the rotor magnet 1,
The outer magnetic poles 18a and 18b of the stator 18 excited by the coil 2 face the outer circumferential surface of the magnet 1, and the inner magnetic poles 18c and 18d of the stator 18 face the inner circumferential surface of the cylindrical member 11. Have been.
In the following description, the present invention will be described using a case where the motor is a step motor as an example.

1 and 2, reference numeral 1 denotes a magnet (rotor magnet) constituting a rotor. The rotor magnet 1 divides the outer peripheral surface into a plurality of portions in the circumferential direction (four in this embodiment). , And are alternately magnetized to the S pole and the N pole. Assuming that the magnetized portions are 1a, 1b, 1c and 1d, the magnetized portions 1a and 1c are magnetized to the S pole,
b and 1d are N-pole magnetized. In addition, magnet 1
Is made of a plastic magnet material formed by injection molding. By making the plastic magnet material in this way, the thickness of the rotor magnet 1 in the radial direction of the cylindrical shape can be made extremely thin.

An axial through hole is formed at the center of the rotor magnet 1, and a fitting portion 1e having a reduced inner diameter is formed at an axially intermediate portion of the through hole. An output shaft 7 serving as a rotor shaft is press-fitted into the fitting portion 1e of the rotor magnet 1 and is fixed to the magnet 1. Since the magnet 1 is made of a plastic magnet formed by injection molding, no crack is generated even by an assembling method such as press-fitting the rotor shaft 7.
Further, even if the magnet 1 has a complicated shape having a small inner diameter fitting portion 1e at the axial center of the through hole, the magnet 1 can be easily manufactured. Further, since the output shaft 7 and the magnet 1 are assembled and fixed by press-fitting, the assembling is facilitated and the manufacturing can be performed at low cost. The rotor (magnet rotor) 1 has the output shaft 7
And the magnet 1.

As a material of the magnet 1, for example, a plastic magnet formed by injection molding a mixture of Nd-Fe-B-based rare earth magnetic powder and a thermoplastic resin binder such as polyamide is used. Thereby, while the bending strength of the compression molded magnet is about 500 kgf / cm ² , for example, when a polyamide resin is used as a binder material, a bending strength of 800 kgf / cm ² or more can be obtained, Therefore, it is possible to form a thin cylindrical shape that cannot be realized by compression molding. The thin cylindrical shape enhances the performance of the motor as described later. Further, by using the plastic magnet, the shape of the magnet can be freely selected,
An effect which cannot be obtained by compression molding, that is, a shape for fixing the rotor shaft 7 can be integrated, and sufficient rotor shaft fixing strength can be obtained. In addition, since the rotor shaft 7 is excellent in strength, the rotor shaft is not damaged (broken) even when a method of press-fitting the rotor shaft 7 is used.

At the same time, since the fixed portion of the rotor shaft 7 is integrally formed, the coaxial accuracy of the magnet portion with respect to the rotor shaft portion is improved, and the run-out can be reduced.
The gap distance between the magnet 1 and the stator portion can be reduced, and the magnetic characteristics of the compression molded magnet 8MG
The magnetic properties of the injection molded magnet are 5 to Oe or more.
Although it is about 7MGOe, a sufficient output torque of the motor can be obtained. In addition, since a thin resin film is formed on the surface of the injection molded magnet, rust generation is significantly reduced as compared with the compression molded magnet, and rust prevention treatment such as painting can be eliminated. In addition, there is no adhesion of magnetic powder, which is a problem with the compression magnet, and there is no surface swelling that tends to occur during rust-proof coating, so that the quality can be improved.

In FIG. 1 and FIG. 2, the cylindrical member 11 fixed to the inner diameter of the magnet rotor 1 is made of a soft magnetic material such as electromagnetic soft iron or pure iron. for that reason,
The magnetic flux of the magnet rotor 1 does not leak into the inner diameter of the cylindrical member 11. FIG. 3 is a schematic diagram showing the state of the magnetic flux of the magnet rotor 1 to which the cylindrical member 11 is fixed, as viewed in a cross section perpendicular to the motor shaft.

1 and 2, reference numeral 2 denotes a cylindrical coil. The coil 2 is arranged concentrically with the magnet 1 and arranged in the axial direction of the magnet 1. The outer diameter of the coil 2 is substantially the same as the outer diameter of the magnet 1. Reference numeral 18 denotes a stator made of a soft magnetic material, and the stator 18 includes an outer cylindrical portion and an inner cylindrical portion. The coil 2 is mounted between the outer cylindrical portion and the inner cylindrical portion of the stator 18. When the coil 2 is energized, the stator 18 is excited. The distal ends of the outer cylindrical portion of the stator 18 form outer magnetic poles 18a and 18b, and the distal ends of the inner cylindrical portion of the stator 18 form inner magnetic poles 18c and 18d. The inner magnetic pole 18c and the inner magnetic pole 18d
Are 360 / 0.5n such that they are in phase with each other.
Degree, that is, 18 when the number of magnetic poles is 4 as in this embodiment.
It is formed shifted by 0 degrees. The outer magnetic pole 18a is arranged to face the inner magnetic pole 18c, and the outer magnetic pole 18b is arranged to face the inner magnetic pole 18d.

The outer magnetic poles 18a and 18b of the stator 18 are formed by notches and teeth extending in a direction parallel to the axis. This configuration allows the formation of magnetic poles while minimizing the motor diameter. In other words, if the outer magnetic poles are formed with irregularities extending in the radial direction, the diameter of the motor will increase accordingly, but in this embodiment, the outer magnetic poles are formed by the notch holes and the teeth extending in the direction parallel to the axis. Therefore, the diameter of the motor can be minimized.

Outer magnetic poles 18a, 18 of the stator 18
b and the inner magnetic poles 18c, 18d
The rotor magnet 1 is provided so as to sandwich one end of the rotor magnet 1 so as to face the outer peripheral surface and the inner peripheral surface of one end of the rotor magnet 1. The hole 18 e of the stator 18 has one end 7 of the output shaft 7.
b is rotatably fitted. Therefore, the magnetic flux generated by the coil 2 is generated by the magnet 1 which is a rotor between the outer magnetic poles 18a and 18b and the inner magnetic poles 18c and 18d.
So that it effectively acts on the magnet which is the rotor and increases the output of the motor. Further, the magnet 1 is made of a plastic magnet material formed by injection molding as described above, so that the thickness of the cylindrical shape in the radial direction can be made extremely thin. Therefore, the outer magnetic pole 18a of the stator 18
The distance between the inner pole 18b and the inner magnetic poles 18c and 18d can be made very small, and the magnetic resistance of the magnetic circuit formed by the coil 2 and the first stator can be made small. As a result, a large amount of magnetic flux can be generated with a small amount of current, so that the output of the motor can be increased, the power consumption can be reduced, and the size of the coil can be reduced.

Reference numeral 20 denotes a cover as a cylindrical member made of a non-magnetic material, and an outer diameter portion (a portion on which outer magnetic poles 18a and 18b are formed) of the stator 18 is fitted to an inner diameter portion 20a of the cover 20. It is fixed with an adhesive or the like. A fitting portion 7a of the output shaft 7 is rotatably fitted to a fitting hole 20b of the cover 20, and one end 7b is fitted to a fitting hole 18e of the stator 18.

FIGS. 4 to 9 are explanatory diagrams sequentially showing the operation of the motor shown in FIGS. 1 to 3 using a sectional view taken along line 4-4 in FIG. In FIGS 9, Q ₁ represents a center of the outer magnetic pole 18a of the stator 18, Q ₂ denotes the center of the outer magnetic pole 18b of the stator 18, Q ₃ is the rotor magnet 1
Shows the center of rotation of. 1 to 9, since the cylindrical member 11 made of a soft magnetic material is fixed to the inner diameter of the rotor magnet 1, the magnetic flux of the rotor magnet 1 is applied to the inner diameter of the cylindrical member 11 and the inner magnetic poles 18c and 18d. There is no leakage. Therefore, when the coil 2 is not energized, the stop position of the rotor magnet 1 is such that the center of each pole of the magnetized portion is the outer magnetic pole 18a, 18b
Are shifted from a straight line connecting the centers Q ₁ and Q ₂ of the magnets 1 and the rotation center Q _{3 of the} magnet 1. From this position coil 2
When power is supplied to the magnet 1, the force applied to the magnetized portion of the magnet 1 by the excited outer magnetic poles 18 a and 18 b
In the direction of rotation. Therefore, the magnet (rotor magnet) 1 is started smoothly.

In a motor having no cylindrical member 11,
The position at which the magnet 1 stably stops when the coil 2 is not energized is either the position shown in FIG. 10 or the position shown in FIG. FIG. 10 and FIG. 11 are schematic sectional views showing those two positions. Accordingly, in the stepping motor described with reference to FIGS. 1 to 9, if the cylindrical member 11 is not provided, the position where the magnet 1 stably stops when the coil 2 is not energized (when not energized) is as shown in FIGS. FIG.
Either one. If the state shown in FIG. 10 is obtained, the center of the magnetic pole of the magnetized portion is on a straight line connecting the center Q _{1 of the} outer magnetic pole and the rotation center Q _{3 of the} magnet 1. Since the electromagnetic force does not act in the direction in which the magnet 1 is rotated, it cannot be started.

Next, referring to FIGS. 4 to 9, FIGS.
The operation of the step motor to which the present invention described in the above is applied will be described. The coil 2 is energized from the state shown in FIG. 4 to make the outer magnetic poles 18a and 18b of the stator 18 N poles and the inner magnetic pole 1
When 8c and 18d are excited to the S pole, the magnet 1, which is a rotor, rotates 45 degrees counterclockwise in the drawing, becomes a state shown in FIG. 5, and further rotates to a position shown in FIG. 6 by inertia. In the state of FIG. 6, since the center of the pole of the magnetized portion is not on the straight line connecting the center of the outer magnetic pole and the rotation center of the magnet 1, the energization to the coil 2 is switched at the timing of FIG. The outer magnetic poles 18a and 18b of
The rotor magnet 1 is rotated by receiving a rotational driving force by exciting the inner magnetic poles 18c and 18d to be N poles.

As a result, the state shown in FIG. 7 elapses, and the magnet 1 further rotates counterclockwise, passes through the stable state in this energized state shown in FIG. 8 instantaneously, and further rotates due to inertia. Rotate to the position shown in FIG. In the state shown in FIG. 9, since the center of the pole of the magnetized portion is not on the straight line connecting the center of the outer magnetic pole and the rotation center of the magnet 1, the power supply to the coil 2 is switched at the timing shown in FIG. When the outer magnetic poles 18a and 18b of the magnetic pole 18 are excited in the direction of N pole and the inner magnetic poles 18c and 18d are excited in the direction of S pole, the rotor magnet 1 is rotated by receiving a rotational driving force. Thereafter, by repeating the energization as described with reference to FIGS. 4 to 9, the rotor magnet 1 rotates. That is, the motor rotates. When the power supply to the coil 2 is cut off while the motor is rotating, the stable state shown in FIG. 4 or FIG. In this state, as described above, when the coil 2 is energized, the electromagnetic force acts in the direction of rotating the magnet 1, so that when the coil 2 is started again, it can be started smoothly.

According to the embodiment described above, the diameter of the motor is equal to the outer magnetic pole 18 facing the outer peripheral surface of the rotor magnet 1.
The length of the motor in the axial direction is substantially determined by a and 18b, and the length of the motor in the axial direction is determined by arranging (arranging) the coil 2 and the rotor magnet 1 in the axial direction. Further, the magnetic flux generated by the coil 2 crosses the magnet between the outer magnetic pole and the inner magnetic pole, and thus works effectively. Further, the cylindrical member 11
The magnetic flux generated from the inner diameter of the rotor magnet 1 is prevented from turning to the inner magnetic poles 18c and 18d, and when the coil 2 is not energized, the rotor magnet 1 is displaced from a straight line connecting the center of the outer magnetic pole and the rotation center of the magnet. When the motor is stopped, the magnetic flux generated from the coil 2 acts on the magnet when the motor is stopped for the first time, so that the force acting on the magnet is not directed to the center of rotation of the magnet. Can be performed.

Also, the number of parts is the same as the rotor magnet 1,
The motor can be configured with a very small number of components such as the coil 2, the stator 18, the output shaft 7, and the cylindrical member 11, and the cost can be reduced. Further, the rotor magnet 1 is formed in a hollow cylindrical shape, and the outer magnetic poles 18a and 18b and the inner magnetic poles 18c and 1c are formed on the outer peripheral surface and the inner peripheral surface of the hollow cylindrical rotor magnet 1.
By facing 8d, an effective output as a motor can be obtained. The output shaft (rotor shaft) 7 is
The magnet 1 as a rotor is fixed to the fitting portion 1e of the center hole of the magnet 1 by press fitting. Since the rotor magnet 1 is made of a plastic magnet formed by injection molding,
Even when the assembly is performed by press-fitting, the rotor magnet 1 is not cracked, and can be easily manufactured even with a complicated shape in which a fitting portion 1e having a small inner diameter is provided at the center in the axial direction. In addition, since the output shaft 7 and the magnet 1 are assembled and fixed by press-fitting, it is easy to assemble and can be manufactured at low cost.

Next, a detailed description will be given of the fact that the stepping motor having the structure described in the above embodiment has an optimum structure for miniaturizing the motor. That is, in the basic configuration of the stepping motor, first, the rotor magnet 1 is formed into a hollow cylindrical shape, and, second, the outer peripheral surface of the rotor magnet 1 is divided into a plurality in the circumferential direction and different poles are alternately arranged. Third, the coils 2 are arranged side by side in the axial direction of the rotor magnet 1. Fourth, the outer and inner magnetic poles of the stator 18 excited by the coil 2 are connected to the rotor magnet 1. Fifth, the outer magnetic poles 18a, 1
Sixth, 8b is formed by a notch and a tooth extending parallel to the axis. Sixth, a cylindrical member 11 made of a soft magnetic material is fixed to the inner diameter of the rotor magnet 1.

The diameter of this step motor (motor) should be large enough to allow the magnetic poles of the stator 18 to face the diameter of the rotor magnet 1. In addition, it is sufficient that the length is sufficient to add the length of the coil 2. Therefore, the size of the step motor is determined by the diameter and the length of the rotor magnet 1 and the coil 2. If the diameter and the length of the rotor magnet 1 and the coil 2 are made very small, the step motor becomes extremely small. Can be

At this time, the rotor magnet 1 and the coil 2
If the diameter and the length of the rotor are very small, it is difficult to maintain the accuracy as a step motor. However, in the above embodiment, the rotor magnet 1 is formed in a hollow cylindrical shape, and the hollow cylindrical shape is formed. The problem of the accuracy of the step motor is solved by a simple configuration in which the outer magnetic pole and the inner magnetic pole of the stator 18 face the outer peripheral surface and the inner peripheral surface of the formed rotor magnet 1. In that case,
If not only the outer peripheral surface of the rotor magnet 1 but also the inner peripheral surface of the rotor magnet 1 is divided into a plurality in the circumferential direction and magnetized, the motor output can be further increased.

Further, the cylindrical member 11 can prevent the magnetic flux of the rotor magnet 1 from leaking to the inner diameter portion of the cylindrical member 11 and the inner magnetic poles 18c and 18d. For this reason, as shown in FIG. 4, the stop position of the magnet 1 when the coil 2 is not energized is such that the center of each pole of the magnetized portion of the magnet is the center Q of the outer magnetic poles 18a and 18b of the stator 18.
_1, connecting, Q ₂ and the rotation center Q ₃ of the magnet 1 is set to a position displaced from the straight line. This position (shifted position)
When the coil 2 is energized from the outside, the excited outer magnetic pole 18
The forces that a and 18b act on the magnetized portion of the magnet 1 always point in the direction of rotation of the magnet 1. Therefore, the magnet 1 is started smoothly.

The rotor magnet 1 is made of a plastic magnet material formed by injection molding as described above, so that the thickness of the cylindrical shape in the radial direction can be made extremely thin. Therefore, the distance between the outer magnetic poles 18a, 18b of the stator 18 and the inner magnetic poles 18c, 18d can be made very small, and the magnetic resistance of the magnetic circuit formed by the coil 2 and the stator 18 can be made small. This allows
A large amount of magnetic flux can be generated with a small amount of current, so that it is possible to increase the output of the motor, reduce the power consumption, and reduce the size of the coil.

Further, the magnet 1 is formed by the cylindrical member 11.
Can increase the mechanical strength of the magnet 1
Can have a thinner structure. If the magnet 1 is made thinner, the gap (gap) between the outer magnetic pole and the inner magnetic pole of the stator 18 can be narrowed, and the magnetic resistance can be reduced accordingly. As a result, it is possible to drive with a small current.

[0030]

As is apparent from the above description, according to the motor of the present invention, a rotatable rotor magnet which is alternately magnetized to different poles in the circumferential direction faces the rotor magnet with a gap. A cylindrical stator, and a coil mounted inside the stator; a cylindrical member made of a soft magnetic material fixed to an inner diameter portion of the rotor magnet; and the coil arranged in an axial direction of the rotor magnet. The outer magnetic pole of the stator excited by the coil is arranged to face the outer peripheral surface of the magnet, and the inner magnetic pole of the stator is opposed to the inner peripheral surface of the cylindrical member. It is sufficient that the diameter of the magnet is large enough to make the magnetic poles of the stator face each other, and the length of the motor is the length of the rotor magnet and the length of the coil. From the sufficient if the length of the just added can the diameter and length of the rotor magnet and the coil very small to the motor a tiny, also,
By preventing the magnetic flux of the rotor magnet from leaking to the inner diameter portion of the cylindrical member and the inner magnetic pole of the stator by the cylindrical member, the stop position of the rotor magnet when the coil is not energized is determined by the position of the rotor magnet. The center of each pole of the magnetic part is shifted from a straight line connecting the center of the outer magnetic pole and the rotation center of the rotor magnet, and by energizing the coil from this position, the excited outer magnetic pole becomes the rotor magnet. The force acting on the magnetized part is always directed to the rotation direction of the rotor magnet, thereby providing a motor that can start the rotor magnet smoothly.

[Brief description of the drawings]

FIG. 1 is a schematic exploded perspective view of an embodiment of a motor to which the present invention is applied.

FIG. 2 is a longitudinal sectional view of one embodiment of a motor to which the present invention is applied.

FIG. 3 is a schematic diagram showing a state of a magnetic flux of a magnet rotor to which a cylindrical member is fixed, as viewed in a cross section perpendicular to a motor axis.

FIG. 4 is an explanatory diagram showing an operation of the motor using a cross-sectional view taken along line 4-4 in FIG. 2;

FIG. 5 is an explanatory diagram showing an operation of the motor using a cross-sectional view taken along line 4-4 in FIG. 2;

FIG. 6 is an explanatory diagram showing an operation of the motor using a cross-sectional view taken along line 4-4 in FIG. 2;

FIG. 7 is an explanatory diagram showing the operation of the motor using a cross-sectional view taken along line 4-4 in FIG. 2;

FIG. 8 is an explanatory diagram showing an operation of the motor using a cross-sectional view taken along line 4-4 in FIG. 2;

FIG. 9 is an explanatory diagram showing an operation of the motor using a cross-sectional view taken along line 4-4 in FIG. 2;

FIG. 10 is a diagram illustrating one stable stop state of a magnet when a coil is not energized in a motor having no cylindrical member.

FIG. 11 is a view illustrating another stable stop state of the magnet when the coil is not energized in the motor having no cylindrical member.

FIG. 12 is a longitudinal sectional view showing a configuration example of a conventional small step motor having a cylindrical shape.

FIG. 13 is a partial sectional view showing a state of a stator of the motor of FIG.

FIG. 14 is a plan view illustrating a step motor driven by one coil used in a timepiece or the like.

[Explanation of symbols]

 Reference Signs List 1 rotor magnet 2 coil 7 output shaft (rotor shaft) 11 cylindrical member 18 stator 18a outer magnetic pole 18b outer magnetic pole 18c inner magnetic pole 18d inner magnetic pole 20 cover

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02K 1/27 502 H02K 1/27 502A 21/12 21/12 M

Claims (1)

[Claims] A rotatable rotor magnet alternately magnetized to different poles in a circumferential direction, a cylindrical stator opposed to the rotor magnet with a gap, and a coil mounted inside the stator. A cylindrical member made of a soft magnetic material is fixed to the inner diameter portion of the rotor magnet, the coil is arranged in the axial direction of the rotor magnet, and the outer magnetic pole of the stator excited by the coil is formed of the magnet. A motor, wherein an inner magnetic pole of the stator is opposed to an inner peripheral surface of the cylindrical member so as to face an outer peripheral surface.