JPH11289739A - Motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-output, small-sized, and inexpensive motor. SOLUTION: A motor is provided with such a magnet 1 that is formed into a cylindrical shape by injection molding a plastic magnet material and has an outer peripheral surface divided into parts, which are alternately magnetized in differing poles in the peripheral direction. A first coil 2, the magnet 1, and a second coil 3 are arranged in this order in the axial direction of the magnet 1, so that the first outer magnetic pole sections and first inner magnetic pole sections which are excited by means of the first coil 2 are made to face respectively the outer and inner peripheral surfaces of the magnet 1 and second outer magnetic pole sections and second inner magnetic pole sections, which are excited by means of the second coil 3 so that they are made to face respectively the outer and inner peripheral surfaces of a rotor. The front ends of the first and second outer magnetic pole sections are held by a holding member in such a way that the front ends face opposite to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art FIG. 4 shows a conventional small cylindrical step motor. A stator coil 105 is concentrically wound around the bobbin 101, and the bobbin 101 is sandwiched and fixed in the axial direction by two stator yokes 106, and the stator yoke 106 has stator teeth 106 a in the circumferential direction of the inner surface of the bobbin 101. And 106b are arranged alternately, and a stator 102 is formed by fixing a stator yoke 106 integral with the stator teeth 106a or 106b to the case 103.

[0003] A flange 11 is attached to one of two cases 103.
5 and the bearing 108 are fixed, and another bearing 108 is fixed to the other case 103. The rotor 109 includes a rotor magnet 111 fixed to a rotor shaft 110,
The rotor magnet 111 is the stator yoke 1 of the stator 102.
06a and a radial gap. The rotor shaft 110 is rotatably supported between the two bearings 108.

[0004]

However, the above-mentioned conventional small step motor has a case 10 on the outer periphery of the rotor.
3. Since the bobbin 101, the stator coil 105, and the stator yoke 106 are arranged concentrically, there is a disadvantage that the outer dimensions of the motor become large. Also, as shown in FIG. 5, the magnetic flux generated by energizing the stator coil 105 mainly passes through the end face 106a1 of the stator teeth 106a and the end face 106b1 of the stator teeth 106b, so that it does not effectively act on the rotor magnet 111. Has the drawback that the output does not increase.

The present applicant has proposed a motor which has solved such a problem as Japanese Patent Application Laid-Open No. 09-331666. In this proposed motor, a rotor composed of permanent magnets alternately magnetized to different poles is equally divided in a circumferential direction and formed into a cylindrical shape, and the rotor is axially divided into a first coil, a rotor and a second coil. Are arranged in order, the first outer magnetic pole and the first inner magnetic pole excited in the first coil are opposed to the outer peripheral surface and the inner peripheral surface of the rotor, and the second outer magnetic pole and the second inner magnetic pole are excited by the second coil.
The outer magnetic pole and the second inner magnetic pole are opposed to the outer peripheral surface and the inner peripheral surface of the rotor, and the rotating shaft as the rotor shaft is taken out from the cylindrical permanent magnet.

Although the motor having such a configuration has a high output and a small external dimension of the motor, it is desired that the joining between the rotor shaft and the permanent magnet be facilitated. Further, in the above configuration, the distance between the first outer magnetic pole and the first inner magnetic pole and the distance between the second outer magnetic pole and the second inner magnetic pole can be reduced by thinning the magnet, thereby reducing the magnetic circuit. The magnetic resistance can be reduced. According to this, a large amount of magnetic flux can be generated with a small amount of current flowing through the first coil and the second coil. In other words, it is desired to reduce the difference between the outer diameter and the inner diameter of the magnet, that is, to make the magnet thinner in order to further increase the output.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a small-sized and inexpensive motor with high output.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a cylindrical magnet made of a plastic magnet material and having at least an outer peripheral surface divided circumferentially and alternately magnetized to different poles. A first coil and a second coil are arranged in the axial direction of the magnet, and a first outer magnetic pole portion and a first inner magnetic pole portion excited by the first coil are provided on the magnet. The outer peripheral surface and the inner peripheral surface are opposed to each other, and the second outer magnetic pole portion and the second inner magnetic pole portion excited by the second coil are opposed to the outer peripheral surface and the inner peripheral surface of the rotor. It is characterized by being constituted.

In the above configuration, the diameter of the motor is determined by the first and second outer magnetic poles facing the outer peripheral surface of the magnet, and the axial length of the motor is determined by the first coil, the magnet, and the second coil. It is determined by arranging in order, and the motor can be made very small.

Also, the magnetic flux generated by the first coil crosses the magnet between the first outer magnetic pole and the first inner magnetic pole, so that it works effectively, and the magnetic flux generated by the second coil is It works effectively because it crosses the magnet between the second outer magnetic pole and the second inner magnetic pole, and increases the output of the motor.

Further, since the magnet is made of a plastic magnet material formed by injection molding, it can be formed in a thin cylindrical shape, whereby the distance between the first outer magnetic pole and the first inner magnetic pole and the second magnetic pole can be reduced. It is possible to reduce the distance between the outer magnetic pole and the second inner magnetic pole. As a result, since the magnetic resistance viewed from the coil side is configured to be small, a large amount of magnetic flux can be generated even with a small electric power, so that the output of the motor is increased. Furthermore, since the dimensional accuracy is enhanced by being formed of a plastic magnet material formed by injection molding, the structure of the present invention in which the magnetic pole portions face the outer peripheral surface and the inner peripheral surface, respectively, is suitable for reducing the gap, and the output is reduced. Enhanced.

In order to achieve the above object, the present invention provides a cylindrical member formed by injection molding, which is made of a plastic magnet material, and has a fitting portion having a small inner diameter at an axially central portion of the cylindrical shape. A magnet having a surface divided in a circumferential direction and alternately magnetized to different poles, and a rotor shaft fixed to a fitting portion of the magnet; a first coil, the magnet, and a A first outer magnetic pole portion and a first inner magnetic pole portion which are excited by the first coil are opposed to an outer peripheral surface and an inner peripheral surface of the magnet. The second outer magnetic pole portion and the second inner magnetic pole portion excited by the coil are configured to be opposed to the outer peripheral surface and the inner peripheral surface of the rotor, and the tip of the first outer magnetic pole portion and the second outer magnetic pole portion Magnetic pole Wherein the the tip of a structure that is held by the holding member facing.

In the above construction, the diameter of the motor is determined by the first and second outer magnetic poles facing the outer peripheral surface of the magnet, and the axial length of the motor is the first coil, the magnet, and the second coil. Are arranged in this order, and the motor can be extremely reduced in size.

Further, the magnetic flux generated by the first coil crosses the magnet between the first outer magnetic pole and the first inner magnetic pole, so that it works effectively, and the magnetic flux generated by the second coil is It works effectively because it crosses the magnet between the second outer magnetic pole and the second inner magnetic pole, and increases the output of the motor.

Further, since the magnet is made of a plastic magnet material formed by injection molding, the magnet can be formed in a thin cylindrical shape, whereby the distance between the first outer magnetic pole and the first inner magnetic pole and the second magnetic pole can be increased. It is possible to reduce the distance between the outer magnetic pole and the second inner magnetic pole. As a result, since the magnetic resistance viewed from the coil side is configured to be small, a large amount of magnetic flux can be generated even with a small electric power, so that the output of the motor is increased. Furthermore, since the dimensional accuracy is enhanced by being formed of a plastic magnet material formed by injection molding, the structure of the present invention in which the magnetic pole portions face the outer peripheral surface and the inner peripheral surface, respectively, is suitable for reducing the gap, and the output is reduced. Enhanced.

Further, a fitting portion having a small inner diameter is provided at a central portion in the axial direction, and at least the outer peripheral surface is divided in the circumferential direction and magnetized alternately with different poles, and is fixed to the fitting portion of the magnet. Although the rotor serving as the output shaft is constituted from the rotor shaft, the magnet and the rotor shaft can be fixed by press-fitting, and the assembly is simplified. Further, the shape of the rotor shaft is simplified, and the manufacturing cost of the rotor shaft can be reduced.

Further, in the above-mentioned invention, the magnet is constituted by a plastic magnet formed by injection molding a mixture of a Nd-Fe-B-based rare earth magnetic powder and a thermoplastic resin binder material. .

Thus, 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, the bending strength of 800 kgf / cm ² or more is obtained. It is possible to form a thin cylindrical shape that cannot be achieved by the above. Further, the shape can be made freely, the shape for fixing the rotor shaft, which cannot be obtained by compression molding, can be integrated, and sufficient rotor shaft fixing strength can be obtained.

Further, since the rotor shaft is excellent in strength, it does not break even when a method such as press fitting of the rotor shaft is used. at the same time,
The coaxial accuracy of the magnet part with respect to the rotor shaft part is improved due to the integral molding of the rotor shaft fixed part, and it is possible to reduce the runout and to reduce the gap distance between the magnet and the stator part. Although the magnetic characteristics of the injection-molded magnet are about 5 to 7 MGOe with respect to the magnetic properties of the compression magnet of 8 MGOe or more, a sufficient torque can be obtained. In addition, since the injection molded magnet has a thin resin film formed on its surface and thus generates much less rust than the compression magnet, rust prevention treatment such as painting can be eliminated. In addition, the quality can be improved without the adhesion of magnetic powder, which is a problem with the compression magnet, and the surface swelling that is likely to occur during rust prevention coating.

[0020]

1 to 3 show a step motor according to a first embodiment of the present invention. FIG. 1 is an exploded perspective view of the step motor, and FIG. 2 is a shaft after the step motor is assembled. 3 is a sectional view taken along line AA and a sectional view taken along line BB of FIG.

1 to 3, reference numeral 1 denotes a cylindrical magnet constituting a rotor. The magnet 1, which is a rotor, has its outer peripheral surface divided into n parts in the circumferential direction (in this embodiment, divided into four parts). Suppose that the magnetized portions 1a, 1b, 1c, and 1d in which the S pole and the N pole are magnetized alternately are:
a and 1c are magnetized to the S pole, and the magnetized parts 1b and 1d are magnetized to the N pole. The magnet 1 is made of a plastic magnet material formed by injection molding. Thus, the thickness of the cylindrical shape in the radial direction can be made very thin.

The magnet 1 has a fitting portion 1e having a small inner diameter at the center in the axial direction. Reference numeral 7 denotes an output shaft serving as a rotor shaft. The output shaft 7 is fixed to the fitting portion 1e of the magnet 1 serving as a rotor by press-fitting. Magnet 1
Is made of a plastic magnet molded by injection molding, so that cracking does not occur even when assembled by press-fitting, and it is easy to manufacture even a complicated shape having a fitting portion 1e having a small inner diameter at the center in the axial direction. . Also,
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. The output shaft 7 and the magnet 1 constitute a rotor.

In particular, Nd-
A plastic magnet formed by injection molding a mixture of an Fe-B-based rare earth magnetic powder and a thermoplastic resin binder material such as polyamide is used. Thereby, while the bending strength of the compression molded magnet is about 500 kgf / cm ² , for example, when the polyamide resin is used as the binder material,
A bending strength of at least Kgf / cm ² can be obtained, and a thin cylindrical shape that cannot be obtained by compression molding can be formed. The configuration of the thin cylindrical shape improves the performance of the motor as described later. Further, the shape can be made freely, the shape for fixing the rotor shaft, which cannot be obtained by compression molding, can be integrated, and sufficient rotor shaft fixing strength can be obtained.

Further, since the rotor shaft is excellent in strength, it does not break even when a method such as press fitting of the rotor shaft is used. at the same time,
The coaxial accuracy of the magnet part with respect to the rotor shaft part is improved due to the integral molding of the rotor shaft fixed part, and it is possible to reduce the runout and to reduce the gap distance between the magnet and the stator part. Although the magnetic characteristics of the injection-molded magnet are about 5 to 7 MGOe with respect to the magnetic properties of the compression magnet of 8 MGOe or more, a sufficient torque can be obtained. In addition, since the injection molded magnet has a thin resin film formed on its surface and thus generates much less rust than the compression magnet, rust prevention treatment such as painting can be eliminated. In addition, the quality can be improved without the adhesion of magnetic powder, which is a problem with the compression magnet, and the surface swelling that is likely to occur during rust prevention coating.

Reference numerals 2 and 3 denote cylindrical coils. The coils 2 and 3 are concentric with the magnet (located on the same axis) and arranged at positions sandwiched in the axial direction. Are almost the same size as the outer diameter of the magnet 1.

Reference numerals 18 and 19 denote a first material made of a soft magnetic material.
And the second stator have a phase of 180 / n degrees, that is,
The first stator and the second stator are arranged at an angle of 45 °, and each of the first and second stators includes an outer cylinder and an inner cylinder.

The coil 2 is provided between the outer cylinder and the inner cylinder of the first stator 18, and when the coil is energized, the first stator is excited. First stator 18
The outer cylinder and the inner cylinder have outer poles 18a, 18
b and inner magnetic poles 18c and 18d are formed, and the phases of the inner magnetic pole 18c and the inner magnetic pole 18d are formed so as to be in phase with each other by 360 / (n / 2) degrees, that is, 180 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.

Outer magnetic poles 18a, 1 of the first stator 18
The outer magnetic poles 19a and 19b of the second stator 8b and the second stator are formed by notches and teeth extending parallel to the axis. This configuration allows the formation of magnetic poles while minimizing the diameter of the motor. In other words, if the outer magnetic pole is formed with irregularities extending in the radial direction, the diameter of the motor will increase accordingly, but in this embodiment, the outer magnetic pole is formed by the notch holes and the teeth extending parallel to the axis. With the configuration, the diameter of the motor can be minimized.

Outer magnetic poles 18a, 1 of the first stator 18
The magnet 8b and the inner magnetic poles 18c and 18d are provided so as to sandwich the one end of the magnet 1 in opposition to the outer peripheral surface and the inner peripheral surface at one end of the magnet 1. One end of the output shaft 7 is rotatably fitted in the hole 18e of the first stator 18.

The coil 3 is provided between the outer cylinder and the inner cylinder of the second stator 19, and when the coil 3 is energized, the second stator 19 is excited. The outer cylinder and the inner cylinder of the second stator 19 have the outer magnetic pole 19
a, 19b and the inner magnetic poles 19c, 19d are formed. The phases of the inner magnetic pole 19c and the inner magnetic pole 19d are 360 / (n / 2) degrees, that is, 18 degrees, so that they are in phase with each other.
The outer magnetic pole 19a is formed so as to be shifted by 0 degrees, and the outer magnetic pole 19a is opposed to the inner magnetic pole 19c, and the outer magnetic pole 19b is opposed to the inner magnetic pole 19d.

Outer magnetic poles 19a, 1a of the second stator 19
The magnet 9b and the inner magnetic poles 19c and 19d are provided so as to sandwich the other end of the magnet 1 in opposition to the outer peripheral surface and the inner peripheral surface of the other end of the magnet 1. The other end of the output shaft 7 is rotatably fitted in the hole 19 e of the second stator 19.

Therefore, the magnetic flux generated by the coil 2 is applied to the outer magnetic poles 19a, 19b and the inner magnetic poles 19c, 19c.
Since it crosses the magnet which is the rotor between d and d, it effectively acts on the magnet which is the rotor and increases the output of the motor.

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 extremely reduced. for that reason,
The distance between the outer magnetic poles 18a, 18b of the first 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 first stator can be made small. Similarly, the outer magnetic poles 19a and 19b and the inner magnetic poles 19c and 19
The distance to d can be made very small, and the magnetic resistance of the magnetic circuit formed by the coil 3 and the second stator can be made small. As a result, a large amount of magnetic flux can be generated with a small current, and an increase in the output of the motor, a reduction in power consumption, and a reduction in the size of the coil are achieved.

The gate during injection molding of the magnet 1 is connected to the outer magnetic poles 18a and 18b of the first stator 18 and the second magnetic pole.
Are located between the outer magnetic poles 18a, 18b and 19a, 19b which are not opposed to the outer magnetic poles 19a, 19b of the stator 19 of FIG. The gate is indicated by G in FIG. In this position, the output characteristics of the motor are not affected even if magnetic imbalance or surface irregularities occur due to post-processing such as gate remaining after molding or gate remaining removal, so that a good motor can be obtained. can do.

Reference numeral 20 denotes a connecting ring as a cylindrical member made of a non-magnetic material. Grooves 20a and 20b are provided at one end inside the connecting ring 20, and grooves 20a and 20b are provided at the other end. The grooves 20c and 20d whose phases are shifted from each other by 180 / n degrees, that is, 45 degrees are provided.
a, 20b are the outer magnetic poles 18a, 1
8b, and the second stator 19 is inserted into the grooves 20c and 20d.
Outer magnetic poles 19a and 19b are fitted, and these members are fixed with an adhesive. The first stator 18 and the second stator 19 have the outer magnetic poles 18a and 18b and the inner magnetic poles 18c and 18d and the outer magnetic poles 19a and 19b and the inner magnetic poles 19c and 19d facing each other. It is fixed at a certain distance by the parts 20e and 20f.

That is, the outer magnetic pole 18 of the first stator 18
a, 18b and outer magnetic poles 19a, 1b of the second stator.
9b is arranged so as to face the front end. Since the connecting ring is made of a non-magnetic material, the first stator 18 and the second stator 19 can be separated from each other on a magnetic circuit, so that they do not influence each other, and the performance of the motor is stabilized.

FIG. 2 is a sectional view of the stepping motor, and FIGS. 3A, 3B, 3C and 3D are sectional views taken along line AA in FIG. ), (F), (g), (h)
Shows a cross-sectional view taken along line BB of FIG. FIG. 3 (a)
3E and 3E are sectional views at the same point, FIGS. 3B and 3F are sectional views at the same point, and FIGS. 3C and 3G are sectional views at the same point. It is sectional drawing, FIG.3 (d) and (h) are sectional views in the same point.

Next, the operation of the step motor will be described.
3A and 3E, the coils 2 and 3 are energized, and the outer magnetic poles 18a and 18b of the first stator 18 are set to N.
When the inner magnetic poles 18c and 18d are S poles, the outer magnetic poles 19a and 19b of the second stator 19 are N poles, and the inner magnetic poles 19c and 19d are excited to S poles, the magnet 1 as a rotor is counterclockwise. Rotated by 45 degrees, and FIG. 3 (b)
And (f).

Next, the power supply to the coil 2 is reversed,
The outer magnetic poles 18a and 18b of the stator 18 are S poles,
The inner stator poles 18c and 18d are set to the N pole, and the second stator 1
9, the outer magnetic poles 19a and 19b are N poles,
When c and 19d are excited to the south pole, the magnet 1, which is the rotor, further rotates counterclockwise by 45 degrees, resulting in the state shown in FIGS. 3 (c) and 3 (g).

Next, the power supply to the coil 3 is reversed,
The outer magnetic poles 18a and 18b of the stator 18 are S poles,
The inner stator poles 18c and 18d are set to the N pole, and the second stator 1
9, the outer magnetic poles 19a and 19b are S-poles, and the inner magnetic poles 19a and 19b are
When c and 19d are excited to the N pole, the magnet 1, which is the rotor, further rotates counterclockwise by 45 degrees, resulting in the state shown in FIGS. 3 (d) and 3 (h).

Thereafter, the coil 2 and the coil 3
By sequentially switching the energizing direction to the magnet, the magnet 1, which is a rotor, rotates to a position corresponding to the energizing phase.

Here, a description will be given of the fact that the stepping motor having such a configuration is the most suitable configuration for miniaturizing the motor. The basic configuration of the step motor is described as follows: (1) the magnet is formed in a hollow cylindrical shape; and (2) the outer peripheral surface of the magnet is divided into n parts in the circumferential direction and magnetized alternately at different poles. (3) the first coil, the magnet, and the second coil are sequentially arranged in the axial direction of the magnet; (4) the first and second stators excited by the first and second coils. (5) The outer magnetic pole is constituted by a notch hole and a tooth extending in a direction parallel to the axis.

The diameter of the step motor may be large enough to make the magnetic pole of the stator face the diameter of the magnet, and the length of the step motor is the length of the first coil and the second coil. All you have to do is add the length. For this reason, the size of the step motor is determined by the diameter and length of the magnet and coil. If the diameter and length of the magnet and coil are made extremely small, the step motor can be made very small. is there.

At this time, if the diameters and lengths of the magnet and the coil are made very small, it becomes difficult to maintain the accuracy of the stepping motor. First and second outer circumferential and inner circumferential surfaces of a cylindrical magnet are formed.
The simple structure in which the outer and inner magnetic poles of the second stator face each other solves the problem of the accuracy of the step motor. At this time, not only the outer peripheral surface of the magnet,
If the inner peripheral surface of the magnet is divided in the circumferential direction and magnetized,
The output of the motor can be further increased.

Further, the relative rotational positions of the first stator 18 and the second stator 19 are made exactly the same, and the magnetization phase of the magnetized portion of the magnet sandwiched between the outer magnetic pole and the inner magnetic pole of the first stator and The magnetized phase of the magnetized portion of the magnet sandwiched between the outer magnetic pole and the inner magnetic pole of the stator 2 is 180
/ N degrees, that is, 45 degrees.

[0046]

As described above in detail, according to the present invention,
A magnet formed in a cylindrical shape and having at least its outer peripheral surface divided into n parts in the circumferential direction and magnetized to different poles, and the first coil, the magnet, and the second coil are sequentially arranged in the axial direction of the magnet. A first outer magnetic pole and a first inner magnetic pole, which are arranged and excited by the first coil, are opposed to an outer peripheral surface and an inner peripheral surface on one end side of the magnet, and a second outer magnetic pole and a first inner magnetic pole are excited by the second coil. Since the outer magnetic pole and the second inner magnetic pole are opposed to the outer peripheral surface and the inner peripheral surface on the other end side of the magnet, the motor has a completely new configuration different from the conventional one. This is an optimal configuration for miniaturizing the motor.

Further, the magnet 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 very thin. Therefore, the distance between the outer magnetic pole and the inner magnetic pole of the first stator can be made extremely small, and the magnetic resistance of a magnetic circuit formed by one coil and the first stator can be reduced. Similarly, the distance between the outer magnetic pole and the inner magnetic pole of the second stator can be extremely reduced, and the magnetic resistance of the magnetic circuit formed by the other coil and the second stator can be reduced. As a result, a large amount of magnetic flux can be generated with a small current, and the output of the motor can be increased, the power consumption can be reduced, and the size of the coil can be reduced.

The output shaft is fixed to the fitting portion of the magnet as the rotor by press fitting. Since the magnet is made of a plastic magnet molded by injection molding, it does not crack even when assembled by press-fitting, and it can be easily manufactured even with a complicated shape that has a fitting part with a small inner diameter at the center in the axial direction. . Further, since the output shaft and the magnet are assembled and fixed by press-fitting, it is easy to assemble and can be manufactured at low cost.

In particular, Nd-Fe is used as a magnet material.
-A plastic magnet formed by injection molding a mixture of a B-based rare earth magnetic powder and a thermoplastic resin binder material such as polyamide is used. Thus, while the bending strength of the compression molded magnet is about 500 kgf / cm ² , for example, when the polyamide resin is used as the binder material, the bending strength is 800 Kgf / cm ^2.
A bending strength of at least gf / cm ² can be obtained, and a thin cylindrical shape that cannot be obtained by compression molding can be formed. The thin cylindrical shape can improve the performance of the motor.

Further, the shape can be made freely, the shape for fixing the rotor shaft, which cannot be obtained by compression molding, can be integrated, and sufficient rotor shaft fixing strength can be obtained. Further, since it is excellent in strength, it does not break even when a method such as press-fitting the rotor shaft is used.

At the same time, since the rotor shaft fixing portion is integrally formed, the coaxial accuracy of the magnet portion with respect to the rotor shaft portion is improved, the runout can be reduced, and the gap distance between the magnet and the stator portion can be reduced. It is possible to reduce the size, the magnetic properties of the compression magnet 8MG
Although the magnetic properties of the injection molded magnet are about 5 to 7 MGOe for Oe or more, 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, the generation of rust is significantly less than that of a compression magnet, so that rust prevention treatment such as painting can be omitted. In addition, the quality can be improved without the adhesion of magnetic powder, which is a problem in the compression magnet, and the surface swelling which is likely to occur at the time of rust prevention coating.

The gate of the magnet 1 at the time of injection molding is formed by the outer magnetic poles 18a, 18b of the first stator 18 and the outer magnetic poles 18a, 18b, 19a not facing the outer magnetic poles 19a, 19b of the second stator 19. , 19b, the output characteristics of the motor are not affected even if a magnetic imbalance or surface irregularities occur due to post-processing such as gate residue after molding or gate residue removal. can do.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a step motor according to the present invention.

FIG. 2 is a sectional view of the step motor shown in FIG. 1 in an assembled state.

FIG. 3 is an explanatory view of a rotation operation of a rotor of the step motor shown in FIG. 2;

FIG. 4 is a sectional view of a conventional step motor.

FIG. 5 is a sectional view showing a state of a stator of a conventional step motor.

[Explanation of symbols]

 Reference Signs List 1 magnet 2 first coil 3 second coil 18 first stator 18a, 18b outer magnetic pole 18c, 18d inner magnetic pole 19 second stator 19a, 19b outer magnetic pole 19c, 19d inner magnetic pole 20 connecting ring

Claims (5)

[Claims] 1. A magnet formed in a cylindrical shape and made of a plastic magnet material and having at least an outer peripheral surface divided in a circumferential direction and alternately magnetized to different poles, and a first coil and an axial direction of the magnet. A second coil is arranged, and a first outer magnetic pole portion and a first inner magnetic pole portion excited by the first coil are opposed to the outer peripheral surface and the inner peripheral surface of the magnet, and A second outer magnetic pole portion and a second inner magnetic pole portion that are excited by the coils of the first and second coils are opposed to an outer peripheral surface and an inner peripheral surface of the rotor. 2. The motor according to claim 1, wherein the plastic magnet is formed into a cylindrical shape by injection molding. 3. The motor according to claim 1, wherein a tip of the first outer magnetic pole portion and a tip of the first outer magnetic pole portion face each other and are held by a holding member. 4. A cylindrically formed plastic magnet material formed by injection molding and having a fitting portion having a small inner diameter at a central portion in the axial direction of the cylindrical shape, and at least the outer peripheral surface is divided in the circumferential direction and alternately formed with different poles. And a rotor shaft fixed to a fitting portion of the magnet, and a first coil, the magnet, and a second coil are sequentially arranged in the axial direction of the magnet, and the first coil A first outer magnetic pole portion and a first inner magnetic pole portion which are excited by the first and second inner magnetic pole portions are opposed to the outer peripheral surface and the inner peripheral surface of the magnet, and a second outer magnetic pole portion which is excited by the second coil; The second inner magnetic pole portion is configured to face the outer peripheral surface and the inner peripheral surface of the rotor, and the distal end of the first outer magnetic pole portion and the distal end of the second outer magnetic pole portion face each other and are held by the holding member. Be done A motor having a structure. 5. The motor according to claim 1, wherein the magnet is formed by injection molding a mixture of a Nd—Fe—B rare earth magnetic powder and a thermoplastic resin binder material. A motor characterized in that it is a plastic magnet manufactured.