JPH07274467A - Brushless motor - Google Patents

Abstract

PURPOSE:To reduce an energization frequency to improve driving efficiency of a control circuit by setting the number of poles of a magnet for magnetic field to 2P (P is a positive integer) and setting the number of coreless armature coils to 3P. CONSTITUTION:A rotor magnet 52 has 2P magnetic poles (P is a positive integer) and 3P useless armature coils 53a, 53b are arranged with equal intervals in opposition to such magnetic poles. With such a relationship between the number of poises of the rotor magnet and the number of coils, the energizing frequency can be reduced to a half in comparison with related arts. Therefore, motor loss (iron loss) can be reduced up to 1/(frequency)<2>. Moreover, the switching frequency is reduced to 1/2 and heat generation of driving circuit is reduced to raise the motor efficiency. A Hall element 54 is located between the armature coils 53a and 53b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor, and more particularly to a brushless motor used for a high speed polygon scanner for rotating a polygon mirror.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus such as a laser printer or a digital copying machine is provided with a polygon scanner for deflecting and scanning a beam. High-speed rotation is required to meet the demand, and a high-performance brushless motor is provided to achieve this rotation. Conventionally, as a polygon scanner provided with this type of brushless motor, for example, a plurality of irregularities for generating dynamic pressure (for example, herringbone grooves) are formed on the outer peripheral surface of a fixed shaft fixed to a metal housing.
And a cylindrical rotary shaft is provided on the fixed shaft at a predetermined bearing interval to form a radial bearing, and a polygon mirror is attached to the rotary shaft. In this type of polygon scanner, for example, a magnet having 2P (P is an integer of 1 or more) magnetic poles on one surface of the rotary polygonal mirror body and an axial gap type brushless with 3P / 2 armature coils. It constitutes a motor. The Hall element is provided in the cavity of the coreless armature coil (see JP-A-59-28757).

[0003]

However, in such a conventional brushless motor, when the number of poles of the magnet is 2P, the armature coil is configured to be 3P / 2. Japanese Patent Laid-Open No. 59-28757 shows P
= 4, that is, a brushless motor having 8 poles and 6 coils is disclosed.) The excitation frequency increases, the driving efficiency of the control circuit decreases, and the current increases.
There is a problem that iron loss is increased and temperature rise is increased. That is, when the number of poles of the magnet is 2P and the number of armature coils is 3P / 2, the excitation frequency becomes high because of the large number of poles, and the drive efficiency of the control circuit decreases. It ends up. Further, since the iron loss increases with the square of the excitation frequency, the iron loss increases with an increase in the excitation frequency, which causes a problem that the temperature of the motor rises.

Further, in the conventional brushless motor, the Hall element is provided in the hollow portion of the coreless armature coil (see FIG. 5). In this configuration, the output signal of the Hall element is affected by the magnetic field of the exciting current by the coreless armature coil in which the Hall element is provided in the cavity, and the S / N ratio is deteriorated, so that the proper excitation is achieved. There was a problem that switching could not be done. High rotation motor (generally assumed to be a motor of 20,000 rpm or more)
In particular, the output signal of the Hall element is particularly susceptible to the magnetic flux of the coil. That is, in order to realize high-speed rotation, it is necessary to reduce the magnetic flux of the rotor magnet and increase the number of coil turns in order to reduce iron loss. Therefore, the magnetic field of the coil increases as the number of turns of the coil increases, and the magnetic flux strongly affects the output signal of the Hall element.

Further, in the conventional brushless motor, since the Hall element is provided in the hollow portion of the coreless armature coil, it is necessary to secure the hollow portion for providing the Hall element. Therefore, it has been difficult to reduce the size of the coreless armature coil and thus the rotating body having the coreless armature coil. Therefore, there is a limit to cost reduction due to downsizing, and since the rotating body becomes large, centrifugal force at the time of rotation becomes large, and it is difficult to realize high-speed rotation. Furthermore, in the conventional coreless motor, when energizing the armature coil to the circuit board, both ends of the winding start and the winding end are drawn out of the coil and used as terminals, and the terminals are soldered to the circuit board. It was Therefore, when the coil is mounted on the circuit board, the terminal is easily moved, resulting in poor work efficiency.

Therefore, according to the first aspect of the invention, the excitation frequency can be reduced to improve the drive efficiency of the control circuit, the occurrence of iron loss can be suppressed, and the temperature rise can be suppressed. It is an object of the present invention to provide a brushless motor whose output signal is not easily affected by the magnetic flux of the coreless armature coil and which can further reduce the size of the rotating body.
Further, the invention according to claim 2 can reduce the cost by downsizing the rotating body having the coreless armature coil, and further the coreless armature coil, and can reduce the rotating body by downsizing the rotating body. It is an object of the present invention to provide a coreless motor capable of realizing high speed rotation by reducing the centrifugal force applied to the motor.

Further, according to the third aspect of the invention, the excitation frequency can be reduced to improve the driving efficiency of the control circuit, the iron loss can be suppressed, and the temperature rise can be reduced, and the Hall element can be reduced. The output signal of is not easily affected by the magnetic flux of the coil, and further provides a polygon scanner equipped with a brushless motor that can downsize the rotating body. Further, it is an object of the present invention to provide a coreless motor that improves work efficiency when attaching an armature coil to a circuit board.

[0008]

In order to solve the above-mentioned problems, the invention according to claim 1 has a field magnet having a plurality of magnetic poles alternately magnetized at equal angles N and S, A plurality of coreless armature coils that are provided in the magnetic path of the field magnet so as to face the magnet and are provided at equal intervals without overlapping each other; and a hall element that detects a rotational position of the rotor magnet, Is a brushless motor having a magnetic field magnet with a pole number of 2P.
(P is a positive integer), 3P coreless armature coils are arranged, and the Hall element is arranged at a position between the coreless armatures forming the plurality of coreless armature coils. It is a feature.

In order to solve the above-mentioned problems, a second aspect of the present invention is a coreless motor having a plurality of coreless armatures, each armature constituting a plurality of coreless armature coils. Part of the outer circumference of the coil is curved,
It is characterized in that the Hall element is arranged in a portion formed by a curved portion on the outer circumference of the adjacent armature coils. In order to solve the above-mentioned problems, a third aspect of the present invention provides a polygon mirror fixed to the rotating shaft of the brushless motor according to the first aspect, and a magnetic bearing that supports the rotating shaft in the axial direction. And a dynamic pressure air bearing that supports the rotating shaft thereof in the radial direction, thereby forming a polygon scanner. In order to solve the above problems, the invention according to claim 4 is the brushless motor according to claim 1, wherein the winding of each armature coil constituting the plurality of coreless armature coils is wound. It is characterized in that the beginning end and the end end of the winding are projected to the coil substrate side.

[0010]

According to the first aspect of the invention, when the number of poles of the magnetic field magnet is set to 2P (P is a positive integer), 3P coreless armature coils are arranged, so that the excitation frequency is reduced. It is possible to improve the driving efficiency of the control circuit, and it is possible to suppress the occurrence of iron loss and reduce the temperature rise. Furthermore, in the invention according to claim 1,
Since the Hall element is placed between the coreless armatures that make up the multiple coreless armature coils, the output signal of the Hall element is not easily affected by the coil magnetic field, and the rotating body is made smaller. A brushless motor capable of being provided can be provided.

According to a second aspect of the present invention, a part of the outer circumference of each armature that constitutes a plurality of coreless armature coils is curved, and a curved portion of the outer circumference of the adjacent armature coils is formed. Since the hall element is disposed in the core, the coreless armature coil, and eventually the rotating body having the coreless armature coil, can be downsized to reduce the cost. Further, since the centrifugal force applied to the rotating body is reduced by downsizing the rotating body, it is possible to realize high-speed rotation of the coreless motor.

According to the third aspect of the invention, since the coreless motor according to the first aspect is provided, it is possible to reduce the excitation frequency and improve the drive efficiency of the control circuit. A polygon scanner equipped with a brushless motor that can suppress the generation and reduce the temperature rise, and that the output signal of the Hall element is not easily affected by the magnetic field of the coreless armature coil, and that the rotating body can be downsized. Can be provided. In the invention according to claim 4, since the winding start end and the winding end end of the winding of each armature coil constituting the plurality of coreless armature coils are projected toward the coil substrate side, the armature coil is configured as a circuit. It is possible to improve work efficiency when mounting on a substrate.

[0013]

EXAMPLES Examples will be described below based on examples of the present invention. 1 to 4 are views showing an embodiment of a brushless motor according to the present invention and a dynamic pressure air bearing type polygon scanner according to the present invention. First, the configuration will be described. In FIG. 1, a polygon mirror 25 is placed on the upper surface of a stepped portion 21 a formed on the hollow rotary shaft 21, and the polygon mirror 25 is pressed by a mirror presser 23 from above to be locked. The mirror retainer 23 holds the magnet 32 and also has a function as a magnet holder. In addition, the mirror holder 23
A vertical vibration damping communication hole 23a is formed so that the thrust bearing has damping characteristics. Further, the mirror presser 23 is formed with a balance correction groove 23b for correcting the imbalance of the rotating body.

The rotor magnet assembly 50 includes a rotor flange 51 that also serves as a yoke and a rotor magnet 52.
The rotor magnet 52 is formed with a balance correction groove 52a for correcting the unbalance of the rotating body. Therefore, the polygon mirror 25 and the mirror holder 2
3. The hollow rotary shaft 21 to which the rotor magnet assembly 50 and the like are attached constitutes the rotary body 20 of the dynamic pressure air bearing type polygon scanner. The rotating body 20 has upper and lower balance correction grooves 23 in order to reduce vibration during rotation due to imbalance.
In b and 52a, the balance is corrected to an unbalanced amount of several mg or less.

Fixed shaft 1 to which hollow rotary shaft 21 is fitted
4, the magnet 33 is fixed to the upper end, and the lower end is firmly fixed to the housing 10 by a method such as press fitting and shrink fitting. Further, on the surface of the fixed shaft 14, herringbone grooves 14a, 14b for forming a dynamic pressure air bearing.
Have two pairs of upper and lower. When the rotating body starts to rotate, the pressure in the gap between the hollow rotating shaft 21 and the fixed shaft 14 increases to form a dynamic pressure bearing, which supports the rotating body in the radial direction without contact.

On the other hand, the axial bearing has magnets 31, 32, 33 fixed to the upper case 41, the upper end of the rotating body 20, and the upper end of the fixed shaft 14, and the vertical vibration damping communication hole 23a.
It is composed of. The magnetic poles of the magnets have the same poles facing each other, and the magnet 32 of the rotating body 20 is repulsed from above and below and floats and is supported in a non-contact manner. On the other hand, the motor is a brushless motor called an axial gap type, and includes a rotor magnet assembly 50 and a coreless armature coil 5.
3, Hall element 54 and the like. The hall element 54 detects the rotational position of the rotor magnet 52,
The rotor 20 is rotated by appropriately switching the excitation of the coreless armature coil 53 by a control circuit (not shown).

2 and 3 show the arrangement of the rotor magnet 52 and the coil 53 of this embodiment. Rotor magnet 5
2 has 2P (P is an integer of 1 or more) magnetic poles,
3P air-core armature coils 53 are arranged at equal intervals so as to face it. By setting the relationship between the number of rotor magnet poles and the number of coils as described above, the excitation frequency can be halved as compared with the conventional example, so that the motor loss (iron loss) can be reduced to the square of the frequency. It can be reduced. Further, the switching frequency becomes 1/2, the heat generation of the drive circuit is reduced, and the motor efficiency is increased (this embodiment shows the case of P = 2). Hall element 54
Are adjacent armature coils 53a and 53b.
It is placed in a position between and. Further, preferably, a part of the outer circumference of each armature coil 53 forming a plurality of coreless armature coils is formed into a curved shape, and the curved parts of the outer circumference of the adjacent armature coils 53a and 53b are formed. The Hall element 54 is arranged in the interval portion which is formed.

The position between the coreless armature coil 53a and the coreless armature coil 53b adjacent to each other where the hall element 54 is provided is, in other words, the position where the conventional hall element is provided (cavity of the armature coil). Therefore, it is located at a position rotated by (360 / 2P) ° at the mechanical angle around the rotation axis of the motor. Since P = 2 in this embodiment,
From the position of the conventional Hall element, centering around the rotation axis of the motor
The Hall element 54 is provided at a position rotated by 0 °.

Since the Hall element 54 is provided at this position, the Hall element 54 is not affected by the magnetic field generated by energizing the armature coil 54, and the rotor magnet 52 is not affected.
It is possible to accurately detect the position of. That is, when the hall element is provided in the cavity of the armature coil as in the conventional case, the hall element 54 is provided not only with the magnetic field from the rotor magnet 52 to be originally detected but also with the hall element in the cavity. It is also affected by the magnetic field generated by energizing the armature coil. Therefore, the position of the rotor magnet 52 cannot be accurately detected. On the other hand, if the Hall element 54 is arranged between the adjacent armature coils 53a and 53b as in the present application, the Hall element 5
4 is the magnetic field generated by the armature coil 53a and the armature coil 53
It will be affected by both the magnetic field due to b. Here, the current flowing through the armature coil 53a and the armature coil 5
The amount of the current flowing in the armature coil 3b is equal to that of the current flowing in the armature 3b and the direction thereof is opposite (in FIG. 4, I indicates the direction of the current in each armature coil). Therefore, the magnetic fields generated by the respective currents have the same magnitude and opposite directions. Therefore, the Hall element 54
Is equidistant from both armature coils 53a and 53b,
The magnetic flux generated by energizing the armature coil 53a and the magnetic flux generated by energizing the armature coil 53b are canceled at the position of the hall element 54. Therefore, the Hall element 54
Is not affected by the magnetic field generated by the energization of the armature coil, and should be detected by the rotor magnet 5
Since only the magnetic flux from 2 is detected, the position of the rotor magnet 52 can be detected accurately.

FIG. 4 is a diagram of the coreless armature coil 53. For the coreless armature coil 53, in order to connect the coreless armature coil 53 to the coil substrate by soldering, extra windings are projected as terminals at the winding start and winding end portions to form winding start terminals 55 and winding terminators 56. There is. Here, the winding start terminals 55 and the winding terminator 56 both project toward the substrate in order to simplify the soldering process. Since the terminal is on the board side, the terminal portion does not move with the solder portion of the board when the armature coil is used, and the step of pressing the end portion during soldering can be omitted. In the description of the embodiments, the axial gap type brushless motor is used, but other outer rotor type and inner rotor type also have similar effects.

[0021]

According to the invention described in claim 1, when the number of poles of the magnetic field magnet is set to 2P (P is a positive integer), 3P coreless armature coils are arranged. It is possible to reduce the temperature and increase the driving efficiency of the control circuit, and it is possible to suppress the occurrence of iron loss and reduce the temperature rise. Further, in the invention according to claim 1, since the hall element is arranged at a position between the coreless armatures forming the plurality of coreless armature coils, the output signal of the hall element is influenced by the magnetic flux of the coil. It is possible to provide a brushless motor that is less likely to be affected and that can reduce the size of the rotating body. According to the second aspect of the present invention, a part of the outer circumference of each armature that constitutes the plurality of coreless armature coils is curved, and a curved portion of the outer circumference of the adjacent coreless armature coils is formed. Since the hall element is provided, the cost can be reduced by reducing the size of the coreless armature coil and the rotating body having the coreless armature coil. Further, since the centrifugal force applied to the rotating body is reduced by downsizing the rotating body, it is possible to realize high-speed rotation of the coreless motor.

According to the invention of claim 3, claim 1
Since the coreless motor described in (1) is provided, it is possible to reduce the excitation frequency and improve the drive efficiency of the control circuit, and it is also possible to suppress iron loss and reduce temperature rise. Further, the output signal of the Hall element is less likely to be affected by the magnetic flux of the coil, and it is possible to provide a polygon scanner equipped with a brushless motor that can downsize the rotating body. According to the invention of claim 4, since the winding start end and the winding end end of the winding of the armature coil 53 are projected toward the coil substrate side, when the armature coil is mounted on the substrate, the terminal portion is attached. Does not move at the solder portion of the board, and the step of pressing the end portion at the time of soldering can be omitted, so that the solder quality can be improved and the cost can be reduced.

[0023]

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a brushless motor and a polygon scanner according to the present invention, and a sectional view showing the overall configuration thereof.

FIG. 2 is a configuration diagram of a magnetic field rotor magnet of the brushless motor of the embodiment shown in FIG.

FIG. 3 is a configuration diagram of a coreless armature coil of the brushless motor of the embodiment shown in FIG.

4 is a configuration diagram showing windings of an armature coil of the brushless motor of the embodiment shown in FIG.

FIG. 5 is a configuration diagram of an armature coil of a conventional brushless motor.

[Explanation of symbols]

 10 Housing 14 Fixed Shaft 14a Herringbone Groove 14b Herringbone Groove 20 Rotating Body 21 Hollow Rotating Shaft 21a Step 23 Mirror Presser 23a Vertical Vibration Damping Communication Hole 23b Balance Correction Groove 25 Polygonal Mirror 31 Magnet 32 Magnet 33 Magnet 41 Upper Case 50 Rotor magnet assembly 51 Rotor flange 52 Rotor magnet 52a Balance correction groove 53 Coil 54 Hall element 55 Winding start terminal 56 Winding terminator 100 Coil 101 Hall element

Claims (4)

[Claims] 1. A field magnet having a plurality of magnetic poles alternately magnetized at equal angles N and S, and provided in the magnetic path of the field magnet so as to face the magnet and not to overlap each other. A brushless motor including a plurality of coreless armature coils provided at equal intervals, and a Hall element for detecting a rotational position of the rotor magnet,
When the number of poles of the magnetic field magnet is set to 2P (P is a positive integer), 3P coreless armature coils are arranged, and the hall elements constitute the coreless armature coils. A brushless motor, which is arranged at a position between the children. 2. The armature coils constituting the plurality of coreless armature coils are armature coils in which a part of the outer circumference is curved, and the curved parts of the outer circumference of the adjacent armature coils are The brushless motor according to claim 1, wherein the Hall element is disposed in a constituent portion. 3. A polygon mirror fixed to a rotating shaft of the brushless motor according to claim 1, a magnetic bearing for supporting the rotating shaft in an axial direction, and a dynamic pressure air bearing for supporting the rotating shaft in a radial direction. And a polygon scanner. 4. The brushless motor according to claim 1, wherein a winding start end and a winding end end of a winding of each armature coil forming the plurality of coreless armature coils are on the coil substrate side. A brushless motor characterized by being protruding.