JPH08126287A - Brushless motor with slit magnet and magnetizing method for the magnet - Google Patents

Abstract

PURPOSE: To provide a brushless motor having a slit magnet in which the decrease of a magnetic field intensity at a boundary of rotor magnet poles is prevented, the torque characteristics of the motor are improved, the rotation control efficiency is improved, a processing cost is reduced and assembling properties are improved, and a method for magnetizing the magnet. CONSTITUTION: A plurality of slits 25 for slitting the circumference are provided at the boundary of the poles of a rotor magnet 2. A stepped part is formed at each boundary of the poles of the FG magnet 3 of the rotor magnet, the detection signal of a Hall element is deformed from a sine curve to improve the rotation control efficiency. Further, bent pieces 30, 31 are provided at the stator core of the lowermost layer of a stator 18, engaged with a circuit board 21 to position the height and the rotating direction of the stator 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor suitable for a drive motor for office automation equipment such as copying machines and a tape drive motor for magnetic tapes, and more particularly to a brushless motor having a slit magnet having a high magnetic field strength. And a method of magnetizing the same.

[0002]

2. Description of the Related Art FIG. 7 shows the main structure of a brushless motor 1a which has been conventionally generally used. Bearing holder 1 integrally formed in the center of bracket 9a
Outer rings of the bearings 11a and 12a are fitted on the inner surface of 0a. In addition, the shaft 13 is attached to the inner rings of the bearings 11a and 12a.
a is fitted. The shaft 13a has a retaining ring 14a.
Positioned and fixed by. The rotor holder 16a of the rotor 15a is fixed to the upper side of the shaft 13a in the figure via a spacer 17a. The rotor magnet 2a is fitted on the inner surface of the rotor holder 16a. On the other hand, the stator 18a is mounted on the outer periphery of the bearing holder 10a,
The stator 18a is fixed to a predetermined position of the bearing holder 10a by the pin 23a and the like. Also, as shown,
The lowermost layer of the stator 18a contacts the stepped portion 33 of the bearing holder 10a and is positioned in the vertical direction. The stator coil 20a is wound around the stator core 19a of the stator 18a. An FG magnet 3a is formed on the lower end side of the rotor magnet 12a in the figure. On the other hand, the circuit board 21a is fixed to the bracket 9a with screws 22a and the like, and a hall element 4a for position detection is provided at a position facing the FG magnet 3a on the upper surface side. Although not shown in the drawing, an FG pattern for speed detection is provided at a position facing the FG magnet 3a on the circuit board 21a. With the structure described above, when a current is passed through the stator coil 20a, the rotor 15a rotates together with the shaft 13a by the magnetic action of the stator 18a and the rotor magnet 2a, and functions as a motor.

FIG. 8 shows the rotor magnet 2a shown in FIG.
This shows the method of magnetization. The stator-shaped magnetizing yoke 5a around which the coil 7a is wound is surrounded by a ring-shaped magnetic yoke 6a with a gap 8 therebetween. The rotor magnet 2a that needs to be magnetized is inserted into the gap 8 and sandwiched between the magnetizing yoke 5a and the magnetic yoke 6a. By supplying a large current to the coil 7a, a strong magnetic field is generated between the magnetizing yoke 5a and the magnetic yoke 6a, and the rotor magnet 2
a is magnetized. In this case, in the central portion of each magnetic pole, magnetic fluxes are interlinked as shown by arrow A, and efficient magnetization is performed.
However, at the boundary between the wound magnetic poles of the coil 7a, the lines of magnetic force are blunted as shown by the arrow B, and a magnetic field component in the circumferential direction enters to weaken the magnetization.

On the other hand, various known techniques relating to the brushless motor include those disclosed in Japanese Patent Publication No. 2-57323 and Japanese Patent Publication No. 63-38948. The former "annular resin magnet" is on the printed circuit board (same as the circuit board 21a) side of the resin magnet corresponding to the above-mentioned conventional rotor magnet.
The first magnet portion and the second magnet portion are separately provided, and the stepped structure thereof is similar to the shape of the FG magnet of the rotor magnet of the present invention described later. The latter is characterized in that the FG magnet for the FG pattern on the substrate and the pole sensor and the motor driving magnet are integrally formed in an L-shape, and magnetic pole rows of n-pole and m-pole are provided respectively for magnetization. Is to have.

[0005]

As described above, as shown in FIG.
In the case of the conventional brushless motor 1a shown in, a part where the magnetizing strength of the rotor magnet 2a is weak occurs,
Since it is not possible to obtain uniform magnetizing strength, there is a problem that the characteristics during rotation of the rotor, especially the torque characteristics, deteriorate. Further, the gap between the FG magnet 3a formed on the side of the circuit board 21a of the rotor magnet 2a and the Hall element 4a is uniform, and the detection signal by the Hall element 4a is almost a sine wave as shown by the curve C shown by the dotted line in FIG. The shape of the Hall element 4a has a problem that the boundary between the magnetic poles becomes unclear due to variations in accuracy of parts of the Hall element 4a and variations due to temperature changes. Further, as described above, the stator 18a needs to be positioned in the height direction and the rotation direction with respect to the rotor magnet 2a and the circuit board 21a. Therefore, as shown in FIG. 7, it is necessary to provide the bearing holder 10a with the stepped portion 33 to determine the height position of the stator 18a and to position the stator 18a in the rotational direction, which increases the machining cost of the bracket 9a and assembling the motor. There was a problem that the cost was high.

On the other hand, the above-mentioned known Japanese Patent Publication No. 63-38.
The brushless motors disclosed in Japanese Patent Publication No. 948 and Japanese Patent Publication No. 2-57323 each have characteristics, but the slit shape of the rotor magnet of the present invention is not disclosed at all, and the shape of the FG magnet and the stator. As for the structure, nothing related to the present invention is disclosed.

The present invention has been made in view of the above circumstances, and enhances the magnetic field strength of the entire rotor magnet to prevent deterioration of the characteristics during rotation of the rotor, in particular, torque characteristics, and to reduce the magnetic poles of the Hall element. An object of the present invention is to provide a brushless motor having a magnet with a slit and a method of magnetizing the magnet, which can improve the detection accuracy of the boundary, reduce the processing cost, and improve the assemblability.

[0008]

In order to achieve the above object, the present invention provides a stator fixed to a bracket,
A rotor that holds a rotor magnet that forms a frequency generator magnet (referred to as an FG magnet) at a position that is pivotally supported by the bracket and faces the circuit board, and an FG pattern and a Hall element that engage with the FG magnet on the surface of the rotor magnet. A brushless motor including the circuit board and the like having the above, wherein the rotor magnet constitutes a brushless motor having a slit magnet that forms a slit of an appropriate depth that divides the circumference at each boundary of magnetic poles. . Further, a rotor magnet having a slit that divides a circumference at each boundary of magnetic poles is interposed between a stator-shaped magnetizing yoke and a ring-shaped magnetic yoke that surrounds the yoke, and between the magnetizing yoke and the magnetic yoke. A magnetizing method for magnetizing the rotor magnet by a magnetic force line generated in the magnet, characterized by a magnetizing method for a magnet with a slit in which a notch is provided in a portion of the magnetic yoke opposite to the slit. . Further, a stepped portion formed at each boundary of magnetic poles is provided on an end surface of the FG magnet facing the Hall element, and the stator lamination of the largest layer of the stator is brought into contact with the surface of the circuit board and / or. It is characterized in that a bent piece that fits into a predetermined hole of the circuit board is formed.

[0009]

By providing the rotor magnet with slits at the boundaries between the magnetic poles, the magnetic field acting at the boundaries between the magnetic poles advances in the radial direction, and the rounding of magnetic lines of force as in the prior art is reduced. Therefore, the magnetic field strength at the boundary of the magnetic poles increases,
The magnetic field strength of the entire rotor magnet is improved. Further, by providing the magnetic yoke with a notch, the magnetic field is further directed in the radial direction, and the magnetic field strength can be further improved. On the other hand, by making the FG magnet portion of the rotor magnet into a saw-tooth shape and providing a stepped portion at each boundary of the magnetic poles, the sinusoidal waveform is broken and the accuracy of detecting the boundary of the magnetic poles is improved.
Also, by integrally forming a bent piece that engages with the circuit board on the bottom layer of the stator, positioning of the stator in the height and rotation direction can be easily performed, and machining of the stepped portion of the bracket is not necessary. And assembly can be improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an axial sectional view showing an overall schematic structure of the brushless motor of the present embodiment, FIG. 2 is an explanatory sectional view for explaining a magnetizing method of a rotor magnet of the present embodiment, and FIG. 3 is a rotor of the present embodiment. FIG. 4 is a partial axial sectional view for explaining the structure of the magnet and its assembling method, FIG. 4 is a perspective view of the rotor magnet of this embodiment, and FIG. 5 is a development view showing an embodiment of the stepped portion of the FG magnet of the rotor magnet. 6 is a diagram showing a change in the detection signal of the Hall element by the FG magnet shown in FIG. 5, FIG. 7 is an axial sectional view showing an overall schematic structure of a conventional brushless motor, and FIG. 8 is a conventional magnetizing method for a rotor magnet. FIG. 5 is an explanatory cross-sectional view showing

First, the structure of the brushless motor 1 of this embodiment will be described with reference to FIG. A bearing holder 10 is integrally formed at the center of the bracket 9 so as to project. Outer rings of the bearings 11 and 12 are fitted in the bearing holder 10. The shaft 13 is fitted into the inner rings of the bearings 11 and 12 and fixed in place by a retaining ring 14. Shaft 1
A rotor holder 16 of the rotor 15 is fitted on the upper side of the rotor 3. A spacer 17 is provided between the rotor holder 16 and the bearing 11. The rotor magnet 2 is fitted on the inner circumference of the rotor holder 16. On the other hand, the stator core 19 of the stator 18 is mounted on the outer periphery of the bearing holder 10. A coil 20 is wound around the stator core 19. The circuit board 21 is fixed to the upper surface of the bracket 9 with screws 22 or the like. The stator 18 is fixed to the bracket 9 by a pin 23 penetrating the circuit board 21. The Hall element 4 is provided on the circuit board 21 at a position facing the FG magnet 3.

As shown in FIG. 4, the rotor magnet 2 is formed of a cylindrical body having a flange 24 on the lower end side, and a number of slits 25 are formed from the upper end surface along the axial direction.
In addition, the FG magnet 3 at the lower end of the rotor magnet 2
A large number of saw-toothed stepped portions 2 are provided in a part of the circumferential direction.
6 are formed. The slit 25 is formed by dividing the circumference at each boundary between the magnetic poles N and S, and as shown in FIGS. 3 and 4, extends from the upper end surface to the lower end surface at an appropriate depth (eg, total length) along the axial direction. (3/4 to 4/5) of the above. As shown in FIG. 3, the rotor magnet 2 has 1/4 to 1/1 of the entire length in which the slit 25 is not formed.
5 has a press-fitting margin formed on the outer periphery of the lower part thereof, and is inserted from the opening side of the rotor holder 16 as shown, and the rotor magnet 2 is fitted to the rotor holder 16 at the lower part having the press-fitting margin. Since the portion where the slit 25 is formed undergoes strong deformation, when the rotor magnet 2 is inserted into the rotor holder 16, the length is 3/4 to 4 /.
The range of 5 can be easily inserted with a light pressure. As a result, the assemblability can be improved. In addition, the rotation balance is better than when the rotor magnet 2 is fixed with an adhesive. That is, when an adhesive is used, a gap is apt to occur between the rotor holder 15 and the rotor magnet 2, and rotational imbalance is likely to occur. However, in the case of press fitting as in this embodiment, such imbalance is eliminated. To be done.

Next, a method of magnetizing the rotor magnet 2 will be described with reference to FIG. The magnetizing means comprises a magnetizing yoke 5 and a ring-shaped magnetic yoke 6 surrounding the magnetizing yoke 5 with a gap 8 interposed therebetween. The rotor magnet 2 is inserted in the gap 8 and is sandwiched between the magnetizing yoke 5 and the magnetic yoke 6. The coil 7 is wound around the magnetizing yoke. In addition, as shown in the figure, the slit 25 is formed by the magnetizing yoke 5.
The coil 7 is arranged at a position opposed to the intervening portion of the coil 7. On the other hand, a notch 27 is recessed at a position facing the slit 25 of the magnetic yoke 6. The notch 27 is not always necessary, but it is preferable to form the notch 27 because the notch 27 increases the effect of directing the magnetic field in the radial direction and increases the magnetizing strength. When a large current is passed through the coil 7 in the state shown in FIG. 2, the slit 25 and the notch 2
Due to the influence of 7, the magnetic force lines 28 are oriented in the radial direction as indicated by the arrow E even at the boundary between the magnetic poles. Of course, the magnetic lines of force are directed to the central portion of each magnetic pole in a substantially radial direction as shown by arrow F. As described above, the magnetic field strength of the rotor magnet can be improved.

As shown in FIGS. 4 and 5, the FG magnet 3 on the lower end surface of the rotor magnet 2 is arranged so as to face the Hall element 4 fixed on the circuit board 21, and as described above, the saw is used. A blade-shaped stepped portion 26 is formed.
The stepped portion 26 is formed at the same position as the boundary between the magnetic poles.
Therefore, the gap between the FG magnet 3 and the Hall element 4 changes periodically for each magnetic pole, and the waveform of the detection signal changes as indicated by the curve D shown by the solid line in FIG. That is, as shown in the figure, the position P at the boundary where the magnetic pole changes due to a sudden change in the stepped portion 26 is clarified, and the position where the magnetic pole changes can be detected accurately. Therefore, the efficiency of rotation control can be improved.

On the other hand, as shown in FIG. 1, in the present embodiment, the stator lamination 29, which is the lowermost layer of the stator core 19 of the stator 18, has several bending pieces 30 and bending pieces 31 bent downward in the drawing. Are integrally formed. The bent piece 30 is arranged with its bent end in contact with the surface of the circuit board 21. As a result, the stator 18
You can determine the height position of the. Further, the bent piece 31 is fitted into the positioning hole 32 of the circuit board 21. As a result, the stator 18 can be positioned in the rotational direction, and the relative position between the stator 18 and the Hall element 4, that is, the timing position can be easily determined.

In the above description, the rotor magnet 2
The shape of the slit 25 is a concave groove having the same width as shown in FIG. 4, but the width may be variable, for example, tapered. Further, the shape of the stepped portion 26 does not have to be a saw-toothed shape, as long as it clearly shows the boundary between magnetic poles. The shape of the notch 27 of the magnetic yoke 6 in the magnetizing means is not limited to the semicircular shape as shown in FIG.
Any shape such as a mold, a square shape, or a ladder shape is adopted.

[0017]

According to the present invention, the following remarkable effects are obtained. 1) By adopting a structure in which a slit is provided at each boundary of magnetic poles in the FG magnet portion of the rotor magnet, the line of magnetic force is not rounded and a magnetic field is formed in the radial direction. Therefore, the magnetic field strength of the rotor magnet as a whole can be increased. 2) By increasing the magnetic field strength, it is possible to improve the characteristics during rotation of the rotor, especially the torque characteristics. 3) Further, by providing the magnetic yoke as a magnetizing means of the rotor magnet with a notch at a position facing the slit, the direction of the magnetic field is directed more in the radial direction, so that the characteristics of the rotor can be further improved. . 4) The detection signal output from the Hall element changes from a sine shape by forming a stepped portion such as a saw blade at each boundary between the magnetic poles of the FG magnet on the lower end surface of the rotor magnet,
The switching of magnetic poles can be clearly detected. Therefore, the efficiency of rotation control can be improved. 5) A bent piece is provided in the lowermost layer of the stator, and the bent piece is brought into contact with the surface of the circuit board and fitted into the positioning hole of the circuit board. In addition to the positioning in the vertical direction, the positioning in the rotational direction of the stator with respect to the circuit board can be easily performed. As a result, the processing cost can be reduced and the assemblability can be improved.

[Brief description of drawings]

FIG. 1 is an axial sectional view showing an overall schematic structure of an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view for explaining a method of magnetizing a rotor magnet of this embodiment.

FIG. 3 is a partial axial cross-sectional view illustrating a method of assembling the rotor magnet of this embodiment.

FIG. 4 is a perspective view of a rotor magnet of this embodiment.

FIG. 5 is a development view showing an embodiment of a stepped portion of an FG magnet of a rotor magnet.

FIG. 6 is a diagram showing a comparison of detection signals of the FG magnet shown in FIG. 5 and a Hall element according to a conventional technique.

FIG. 7 is an axial sectional view showing an overall schematic structure of a conventional brushless motor.

FIG. 8 is an explanatory sectional view for explaining a conventional magnetizing method for a rotor magnet.

[Explanation of symbols]

 1 Brushless Motor 2 Rotor Magnet 3 FG Magnet 4 Hall Element 5 Magnetizing Yoke 6 Magnetic Yoke 7 Coil 9 Bracket 15 Rotor 18 Stator 19 Stator Core 21 Circuit Board 25 Slit 26 Stepped Section 27 Notch 29 Stator Lamination 30, 31 Bending Piece 32 Positioning hole

Claims (4)

[Claims] 1. A stator fixed to a bracket, a rotor holding a rotor magnet forming a frequency generator magnet (referred to as FG magnet) at a position pivotally supported by the bracket and facing a circuit board, and a surface thereof. A brushless motor including the circuit board and the like having an FG pattern engaging with an FG magnet and a Hall element on the rotor magnet, wherein the rotor magnet forms a slit of an appropriate depth that divides the circumference at each boundary of magnetic poles. A brushless motor having a slit magnet. 2. A rotor magnet having a slit dividing the circumference at each boundary of magnetic poles is interposed between a stator-shaped magnetizing yoke and a ring-shaped magnetic yoke surrounding the yoke, and the magnetizing yoke is provided. A magnetizing method for magnetizing the rotor magnet by magnetic lines of force generated between magnetic yokes, characterized in that a notch is provided at a portion of the magnetic yoke facing the slit. Method. 3. A brushless motor having a slit magnet according to claim 1, wherein a stepped portion formed at each boundary of magnetic poles is provided on an end face of the FG magnet facing the Hall element. 4. The magnet with slits according to claim 1, wherein a bent piece that abuts on the surface of the circuit board and / or fits into a predetermined hole of the circuit board is formed in the stator lamination of the lowermost layer of the stator. Brushless motor having.