JP2007068277A - Brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for optimally magnetizing a magnet used for an outer rotor brushless DC motor. <P>SOLUTION: A length of a main magnetization yoke in the direction of a motor shaft is slightly larger than a lower end face of a stator core. The main magnetization yoke is configured in the radial direction so as to substantially match the magnetic center of the stator core and the magnet. The magnetization for a hall element is implemented from an end face of the magnet in the direction impossible to be magnetized so as to align with a main magnetic pole in homopolarity from a lower end face of the magnet in the axial direction as the direction impossible to magnetize the magnet. The FG magnetization is implemented from the end face of the magnet in the direction impossible to be magnetized so as to align with the magnetization for the hall element in homopolarity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used in an office machine such as a laser beam printer (hereinafter referred to as LBP) provided with a frequency generator (hereinafter referred to as FG) for detecting the rotational speed of a brushless DC motor (hereinafter referred to as a motor). The present invention relates to a method for magnetizing a motor with an FG for driving a drum.

  As an LBP drum driving motor, it is often used particularly in fields that require rotational unevenness characteristics. In many cases, an FG is attached to this motor, and a speed control circuit for controlling the motor is added to a predetermined rotational speed.

  FIG. 9 shows a main structure of a motor generally used in the past. A bearing holder 7 is formed so as to project integrally from substantially the center of the bracket 6, and an outer ring of the bearing 8 is fitted to the inner surface thereof. The motor shaft 3 is fitted on the inner ring of the bearing 8. The motor shaft 3 is positioned and fixed by a retaining ring 9. The rotor yoke 2 is fixed to the upper side of the motor shaft 3 through the spacer 10. A magnet 4 is fitted on the inner surface of the rotor yoke 2. On the other hand, the stator core 1 is fixed to the outer periphery of the bearing holder 7. Further, as shown in the figure, the lowermost layer of the stator core 1 contacts the stepped portion 11 of the bearing holder 7 and is positioned in the motor axial direction. A winding 12 is wound around the stator core 1.

  The magnet 4 is radially anisotropically oriented toward the stator core 1 at the time of manufacture. A printed wiring board 5 is disposed on the lower end surface 14 of the magnet via an air gap, and a Hall element 13 for detecting the magnetic pole position of the magnet 4 is provided. A radial FG pattern 15 is provided on the printed wiring board 5 facing the lower end surface 14 of the magnet via an air gap. With the above structure, the position of the motor magnetic pole is detected by the Hall element 13, and the stator winding 12 is energized through a drive circuit (not shown), whereby the rotational torque is generated by the magnetic force of the magnet 4 and the stator core 1 and the rotor. The motor shaft 3 rotates between the two and functions as a motor. Further, the rotational speed fluctuation due to load fluctuation or the like is detected by FG, and the rotational speed of the motor is kept constant by the control circuit.

  As described above, the magnetic flux of the magnet is classified into three types, that is, a main magnetic flux that generates rotational torque, a magnetic flux for Hall element that detects the magnetic pole of the magnet, and a magnetic flux for FG power generation, and each needs an appropriate magnetic flux density. .

FIG. 10 is an enlarged view of the magnet 4 shown in FIG. Here, a conventional magnet magnetizing method will be described in detail.
The main magnetization 20 for rotating the motor is applied in the easy magnetization direction on the inner diameter side of the magnet to which the radial anisotropic magnetic field orientation 22 is applied. FG magnetization 21 is applied from the magnet lower end surface 14 toward the magnetization difficult direction (motor axial direction). Originally, it is difficult to magnetize in the direction in which the rear magnetization is difficult. However, if the main magnetization 20 for rotating the motor reaches the magnet end surface 14, the FG magnetization 21 is more difficult to enter.
FIG. 11 shows the relationship between the main magnetizing yoke 31 and the magnet 4 for implementing the conventional main magnetizing 20. In the figure, 32 is a winding of the magnetizing yoke, and 35 is a magnetizing yoke guide. Further, as shown in FIG. 9, the magnet is designed to be longer in the axial direction than the thickness of the stator core. Therefore, the main magnetizing yoke 31 is also in contact with the axial length of the inner peripheral surface of the magnet. Originally, it is economical that the thickness of the stator core and the length in the magnet axial direction are substantially matched. However, since FG exists on the lower end surface of the magnet, it is necessary to make it longer than the stator core in the lower direction. In that case, a deviation occurs in the magnetic center of the magnet and the stator core in the motor axial direction, and if the motor is energized and rotated, an electromagnetic excitation force is generated. In order to avoid this, the upper end face of the magnet is also long.

FIG. 12 is a diagram in which the magnetization state of the surface of the magnet end face 14 with only the main magnetization 20 is observed with a magnet viewer. When observed with a magnet viewer, a line 25 appears on the boundary line of the magnetic pole. The main magnetization is in the radial direction, and since the observation with the magnet viewer is in the direction of the motor axis, the boundary between the poles is not clear and is expanding toward the inner diameter of the magnet. In the figure, the number of magnetic poles of the main magnetization 20 is represented as four poles for simplification.
FIG. 13 shows an FG magnetized yoke 33 for performing FG magnetization, a winding 34 of the FG magnetized yoke, and 30 a magnetized guide. FIG. 14 is a diagram in which the magnetization state of the magnet lower end surface 14 after FG magnetization is observed with a magnet viewer. The number of magnetic poles of the FG magnetization 21 is 20, and the main magnetization magnetic pole and the FG magnetization. Magnetization is performed by matching the pole switching positions of the magnetic poles. The magnetic pole boundary 26 of FG magnetization that is originally magnetized in a radial pattern is greatly inclined. This is a phenomenon that occurs because the main magnetic pole is strong and the FG magnetization is weak, so that the FG magnetization does not reach the back. Further, the boundary 27 of the main magnetic pole is magnetized in the motor axial direction by FG magnetization, and is slightly sharper than that in FIG. However, as a result, the FG output voltage cannot be increased. If there is no main magnetization and only FG magnetization, the magnetization is weak due to magnetization in the difficult magnetization direction, but the magnetic pole boundary 28 appears linearly in the radial direction as shown in FIG. 15, and a sufficient FG output voltage is obtained. It is done.

  Further, in the surface mount Hall element 13 as shown in FIG. 9, there is a problem in the amount of magnetic flux and directivity from the magnet, and the magnetic pole position of the magnet may not be detected accurately. FIG. 16 shows an example in which a vertical Hall element 17 is used as a countermeasure. However, if a vertical Hall element is used, it is difficult to mount it, which causes a cost increase.

  Known techniques relating to the magnetization of brushless motors relating to these problems include those disclosed in Japanese Patent Publication No. 63-38948 and those disclosed in Japanese Patent Laid-Open No. 62-45008.

  Japanese Examined Patent Publication No. Sho 63-38948 discloses that the above-described prior art magnet is formed in a ring shape having a L-shaped cross section and having a flange at the tip, and the rotor yoke is also formed in a pan shape having a flange at the tip of the cylindrical portion. ing. The main magnetization for the motor is magnetized in the radial direction facing the stator core, the magnetization for the Hall element is magnetized on the inner periphery of the collar, and the FG magnetization for FG is magnetized on the outer periphery of the collar.

  In Japanese Patent Laid-Open No. 62-45008, a ring-shaped main magnet that is magnetically oriented in the motor radial direction and an FG magnet that projects from the outer circumferential surface and is magnetically oriented in the motor axial direction are integrated. Molded and magnetized in the direction of magnetic field orientation.

  In addition, if the center position in the thickness direction of the stator core of the motor in FIG. 9 is shifted from the center position in the motor axis direction of the magnet, an electromagnetic force is generated in the motor axis direction during motor rotation, and the motor vibration and noise are reduced. It is known to cause. For this reason, the axial length of the magnet of the motor is extended close to the upper surface of the rotor in order to match the length in the FG direction.

Further, according to the publication of Japanese Patent Application Laid-Open No. 2004-340751, the present inventors have provided a main magnetic pole for driving a motor, a plurality of magnetic poles for frequency generators at an equal pitch on the end surface in the motor axial direction, The frequency power generating coil pattern composed of a plurality of power generating line elements so as to face each other with a gap is an odd multiple of the number of magnetic poles for driving the motor, and both ends of the main magnetic pole for driving the motor are the same as the magnetic poles. It discloses disposing magnetic poles for frequency generators to be poles and improving the SN ratio of the output voltage of the frequency generators.
Japanese Patent Publication No. 63-38948 JP 62-45008 A Japanese Patent Laid-Open No. 2004-340751

  All of the conventional examples described above are resin magnets, and the thickness of the ring-shaped magnet is partially changed depending on the shape of the mold. In addition, anisotropic magnetic field orientation can be freely determined to some extent during magnet molding. However, there is no need for a mold such as molding, and in the method of punching a rubber sheet magnet, which can be obtained at low cost, and rolling it into the inner diameter of the rotor yoke, the magnet thickness is uniform and anisotropic magnetic orientation Is limited to the magnet thickness direction.

  Further, in order to increase the FG magnetization and take out a large output voltage of the FG by the conventional magnet magnetization method described above, the following magnetization method is adopted. This is a method in which the main magnetizing yoke for rotating the motor is manufactured with a shorter length in the motor axial direction, and the main magnetizing is not performed on the lower end surface 14 of the magnet 4. Thereby, the main magnetic pole of the magnet lower end surface 14 becomes weak, and the FG is strongly magnetized.

  However, with this magnetizing method, the amount of magnetic flux to the Hall element 13 is reduced. Therefore, as shown in FIG. 16, it is necessary to devise such as mounting the Hall element 17 facing the inner circumference of the magnet and standing on the printed wiring board, which becomes an obstacle to automatic assembly.

Further, it is the magnetic balance between the stator core 1 and the magnet 4 that causes vibration noise during motor rotation. This requires that the centers of the lengths of the stator core 1 and the magnet 4 in the motor axial direction coincide with each other, that is, the magnetic balance must be matched. Generally, since the lower end surface of the magnet 4 extends to the vicinity of the FG 15 surface, the upper end surface of the magnet 4 needs to be greatly extended from the upper end surface of the stator core 1 in order to adjust the magnetic balance.
The extended upper end surface 16 of the magnet 4 has a low contribution rate to the motor torque, resulting in an increase in material costs.

  In the FG according to the method disclosed in Japanese Patent Application Laid-Open No. 2004-340751, the direction of the magnetic flux of the main magnetization is the radial direction, so the magnetic flux in the FG direction of the magnet end face is weak, and the FG generated voltage due to the main magnetization is small. .

The present invention pays attention to the above-mentioned conventional problems, effectively utilizes the entire magnetic flux of the magnet, secures a magnetic balance, applies main magnetization without deteriorating the motor rotational torque characteristics, An object of the present invention is to provide a low-priced and excellent motor by magnetizing Hall elements that are accurately detected and by applying FG magnetization to the magnet so as to extract the output voltage of the FG as much as possible.

  In order to achieve the above-mentioned purpose, the main magnetizing on the inner diameter side of the magnet is not magnetized up to the magnet end face, but limited to the position where the stator core and magnet can be magnetically balanced, and the magnetizing for the Hall element is performed from the magnet end face. Magnetization is performed in the magnetization difficult direction, and finally FG magnetization is performed in the magnetization difficult direction from the magnet end face.

Although the orientation of the end face of the magnet is difficult for FG magnetization, it has been experimentally found that magnetization can be facilitated by magnetizing the Hall element in advance. As a result, the effects of the present invention are listed as follows.
1. By increasing the magnetic flux density of the FG magnetization and increasing the magnetic flux density by magnetizing the Hall element, the FG output voltage can be greatly increased. As a result, the SN ratio is improved and the uneven rotation characteristic is improved.
2. The magnetic flux for the surface-mounting Hall element can be taken out sufficiently large even if it is attached to the back surface via the printed wiring board, and the Hall element can be mounted by an automatic machine.
3. Rubber magnets can also be used, and molds such as molding are not required.
4). Without extending the magnet in the direction of the motor shaft, the magnetic balance with the stator core can be secured, and the cost can be reduced.

  Prepare a radially oriented ring magnet, slightly longer than the upper end surface of the stator core, determine the length of the upper end surface of the magnet, extend the lower end surface of the magnet to near the FG surface, the length of the main magnetization in the motor axial direction is The main magnetizing yoke in the radial direction is set to be slightly longer than the lower end surface portion of the stator core so that the magnetic centers of the stator core and the magnet substantially coincide with each other. In addition, the position of the magnet is aligned with the main magnetic pole from the lower end surface of the magnet in the axial direction, which is the direction of hard magnetization of the magnet, and magnetization for the Hall element is performed in the direction of hard magnetization from the end surface of the magnet. Further, FG magnetization is magnetized in the direction in which magnetization is difficult from the magnet end face by combining the magnetization for the Hall element and the magnetic pole.

  Embodiments according to claims 1 and 2 of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing magnetization in the direction of difficulty in magnetization from the magnet lower end surface 14 by using the magnetizing yoke 43 for the Hall element aligned so as to be the same polarity as the main magnetic pole on the inner diameter surface of the magnet. Since the main magnetic pole does not enter the magnet lower end surface 14, it can be magnetized relatively easily. When the lower end surface of the magnet is observed with a magnet viewer, the boundary 29 of the magnetic pole appears to be a straight line as shown in FIG.

  Fig. 3 shows the alignment of the magnetic poles for the Hall element with odd number of times of FG magnetization, and the magnetic poles for FG arranged so that both ends of one magnetic pole for the Hall element are the same as the magnetic poles. FIG. 3 is a diagram for magnetizing an FG magnetized yoke 46 from a magnet end face 14 in a direction in which magnetization is difficult. It has been experimentally confirmed that FG magnetization is relatively easy because it is magnetized in the direction of difficult magnetization by magnetization for the Hall element. In the figure, 47 is a winding for an FG magnetized yoke. When the magnet lower end surface 14 is observed with a magnet viewer, it can be seen that the inclination is improved as compared with the magnetic pole boundary 26 of FIG. 14 as shown in FIG.

  In addition, since the FG magnetic poles on the magnet end face are odd multiples of the number of magnetic poles for the Hall element and both ends of the one magnetic pole for the Hall element are the same as the magnetic poles, This power generation can contribute to power generation with many magnetic poles for the Hall element, and the output voltage of the FG can be increased almost twice as compared with the conventional method.

  The magnetic flux applied to the Hall element is as shown in FIG. 6 depending on the location of the Hall element. In FIG. 6, reference numeral 41 denotes a surface-mounted Hall element close to the magnet, and the influence of the magnetic flux of the FG is greatly related. 42 is an appropriate distance, as shown in FIG. 7 or FIG. The case where it arrange | positions is shown.

  FIG. 1 shows an embodiment according to claim 3 of the present invention, wherein 41 is a main magnetizing yoke, 42 is a winding of the main magnetizing yoke, and 40 is a magnetizing yoke guide. The axial position of the upper end portion of the stator core and the upper end surface 16 of the ring magnet is made substantially the same, the lower end surface 14 of the ring magnet extends to near the FG pattern, and the length h of the main magnetized yoke is made substantially the same as that of the stator yoke. No main magnetization is applied to the axial span portion facing the FG pattern from the lower end of the stator core. By performing magnetization in this way, the magnetic center position can be aligned, the excitation force in the motor axis direction can be reduced, the efficiency of use of the magnet can be increased, and cost dyne can be achieved.

  In addition, the magnetic pole is aligned with the main magnetic pole on the inner circumferential surface of the magnet, and magnetized for the Hall element, which is magnetized in the direction of magnetization difficult from the lower end of the magnet, and for the frequency generator that is an integral multiple of the Hall element magnetic pole. The magnetizing yoke having the form described in claim 4 is manufactured by aligning the magnetization so that the pole boundaries of the Hall element magnetic pole and the frequency generator magnetic pole coincide with each other, and integrally forming the magnetized yoke. Is possible.

  As described above, the embodiments of the present invention have been described with respect to the outer rotor type motor. However, it goes without saying that the present invention can be similarly applied to the inner rotor type motor.

Although the magnet end face is oriented in the direction of difficulty in magnetizing, magnetizing the Hall element to the main magnetizing area and the magnet end face has the effect of facilitating magnetization, increasing the FG output voltage. In addition, it is possible to improve the uneven rotation characteristics by increasing the magnetic pole detection accuracy in the surface mount Hall element. In addition, rubber-based anisotropic sheet magnets can be used, making it easy to mount surface-mounted hall elements and reducing the cost significantly by not extending the magnets in the direction of the motor shaft.
The basic technology of each element of the present invention has been established and can be said to be optimal for driving a drum used in an office machine such as a laser beam printer (hereinafter referred to as LBP).

The figure which shows implementation of the main magnetization by this invention The figure which shows implementation of the magnetization for Hall elements by this invention The figure which shows implementation of the magnetization for FG by this invention Magnet viewer observation diagram after magnetizing for Hall element according to the present invention Magnet viewer observation after FG magnetization according to the present invention Magnetic flux applied to the Hall element Hall element layout Hall element layout Structure of conventional brushless DC motor Diagram showing magnet orientation and magnetization Diagram showing the implementation of conventional main magnetization Magnet viewer observation figure after main magnetisation The figure which shows implementation of the conventional FG magnetization Magnet viewer observation diagram after conventional FG magnetization Magnet viewer observation after FG magnetization only Hall element layout

Explanation of symbols

1: Stator core 2: Rotor core 3: Motor shaft 4: Magnet 5: Printed wiring board 6: Bracket 7: Bearing holder 8: Bearing 10: Spacer 11: Stepped portion 12: Winding 13: Hall element 14: Magnet lower end surface 15 : FG pattern 16: Magnet upper end surface 17: Vertical Hall element 20: Main magnetization 21: FG magnetization 22: Radial anisotropic magnetic field orientation 24: FG magnetization magnetic pole boundary 25: Main magnetization magnetic pole boundary 26: FG magnetization magnetic pole boundary line 27: Main magnetization magnetic pole boundary line 29: Main magnetization magnetic pole boundary line 30: Magnetization yoke guide 31: Main magnetization yoke 32: Magnetization yoke winding 33: FG Magnetized yoke 34: Magnetized yoke winding 35: Magnetized yoke guide 40: Magnetized yoke guide 41: Main magnetized yoke 42: Magnetized yoke winding 43: For Hall element Magnetizing yoke 44: winding 45 for magnetizing yoke: magnetizing yoke guide 46: FG magnetizing yoke 46
47: Winding for magnetized yoke h: Main magnetized yoke length

Claims (4)

  A stator core having a ring-shaped magnet that rotates integrally with the motor shaft and is magnetized in multi-poles in the radial direction on the inner periphery, and has salient poles of the number of main poles facing the inner periphery of the magnet via a gap. A printed wiring board disposed so as to face the lower end surface of the magnet via a gap, and the printed wiring board has a rectangular wave shape formed of a plurality of radial power generation line elements on the magnet facing surface side. In a brushless DC motor in which a frequency generating coil pattern is arranged, and a Hall element for detecting the magnetic pole position of the magnet is arranged on the printed wiring board, the magnet has anisotropy of substantially radial orientation. Multi-pole main magnetization is performed in the radial direction from the inner diameter side, and then magnetization for the Hall element, which is aligned with the same polarity as the main magnetic pole, is performed as described above. The magnet is magnetized in the direction of magnetization difficult from the lower end face of the magnet facing the wiring board, and the frequency generator magnetization is multiplied by an integer multiple of the Hall element magnetic pole, and the Hall element magnetic pole and the frequency generator magnetic pole A brushless DC motor characterized by magnetizing magnetized in such a way that the polar boundaries of each of the magnets coincide with each other in the direction of difficulty in magnetization from the lower end surface of the magnet facing the printed wiring board.   With respect to the main magnetic pole for driving the motor and the magnetic pole for the Hall element, a plurality of frequency generator magnetic poles are arranged at an equal pitch on the lower end surface of the magnet, and the number of magnetic poles for driving the motor is an odd multiple, and 1 for the Hall element. 2. The brushless DC motor according to claim 1, wherein the magnetic pole for the frequency generator is arranged so that both ends of the magnetic pole are the same as the magnetic pole.   The axial position of the upper end of the stator core and the upper end of the ring magnet are substantially the same, the lower end of the ring magnet extends to the vicinity of the frequency generator pattern, and the axial portion opposite the frequency generator pattern from the lower end of the stator core The brushless DC motor according to claim 1 or 2, wherein main magnetizing is not performed.   Magnetization for Hall element magnetized in the direction of difficulty of magnetization from the lower end face of the magnet facing the printed circuit board, which is aligned with the same polarity as the main magnetic pole, and the magnetic pole for the Hall element and integer frequency multiples for frequency generator The magnets are aligned so that the pole boundaries of the Hall element magnetic pole and the frequency generator magnetic pole coincide with each other, and it is difficult to magnetize from the magnet bottom face facing the printed circuit board with the integrally formed magnetizing yoke 4. The brushless DC motor according to claim 1, wherein the magnet is magnetized in the direction.

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