JPH04229060A - Brushless motor - Google Patents

Abstract

PURPOSE:To provide a brushless motor in which the rotor magnet is reduced in size and weight by reducing the axial length thereof, the cost is also reduced and ambient temperature rise is suppressed. CONSTITUTION:Axial length of a rotor magnet 21 is made shorter than the length of the end face, in predetermined direction, of a field generating means and a magnetism detecting element 24 is disposed in a gap within the length of the end face in the predetermined direction.

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 as a drive source for polygon scanners used in laser printers, digital copiers, and the like.

0002

[Prior Art] Conventionally, a polygon scanner has been used as a deflector in a laser printer, etc., but this polygon scanner uses a brushless motor called an inner rotor type to rotate a polygon mirror at a very high speed. There is. Conventionally, as a polygon scanner using this type of brushless motor, for example,
There is one described in Japanese Patent No. 184236. In this device, a hollow rotary shaft rotatably supported by a fixed shaft is supported in the radial and axial directions by hydrodynamic air bearings, and a hollow rotary shaft is provided at the bottom of the hollow rotary shaft that extends in the axial direction below the bearing. A DC brushless motor consists of a rotor magnet made of a manganese-aluminum or alnico magnet, and a stator and Hall element arranged around this magnet. The polygon mirror is designed to rotate at high speed.

[0003] Other polygon scanners have been proposed, such as those shown in FIGS. 3 and 4, for example. In FIG. 3, a pedestal 2 is fixed to a housing 1, and a fixed shaft 5 is formed on the pedestal 2 with two pairs of herringbone grooves 3a, 3b, 4a, 4b for generating dynamic pressure.
is firmly fixed by press-fitting or shrink-fitting. A hollow rotating shaft 6 is rotatably supported on the fixed shaft 5. A flange 6a is formed on the upper part of the rotating shaft 6, and a polygon mirror 7 is placed on the upper surface of the flange 6a. A mirror holding plate 8 is placed on the top surface of the polygon mirror 7.
is attached, and this presser plate 8 is formed with a hollow inner cylinder 7a of the polygon mirror 7 and an outer cylinder 8a that can be inserted into the hollow portion of the hollow rotating shaft 6. This holding plate 8 is attached to the flange 6a via the polygon mirror 7 by bolts 9.
The polygon mirror 7 is attached to the hollow rotating shaft 6 so that it is coaxial with the hollow rotating shaft 6 by the holding plate 8.
is fixed.

A magnet 10 is attached to the mirror holding plate 8, and a fine hole 8 for damping vertical vibration is provided in the center.
b is formed to provide damping characteristics to the thrust bearing described later. Further, a balance correction groove 8c is formed in this presser plate 8, and the imbalance of each rotating member when the hollow rotating shaft 6 etc. rotate is corrected by this groove 8c.

Further, a rotor magnet 11 made of a manganese-aluminum or alnico magnet is provided approximately at the center of the hollow rotating shaft 6.
A balance ring 12 in which a balance correction groove 12a is formed is provided at the lower part of the balance ring 12. The above-mentioned hollow rotating shaft 6, polygon mirror 7, mirror holding plate 8, rotor magnet 11, and balance ring 12 constitute a rotating body 13, and as the rotating body 13 rotates, the hollow rotating shaft 6
When the pressure in the gap formed between the fixed shaft 5 and the herringbone grooves 3a, 3b, 4a, and 4b increases, a dynamic air bearing is formed by the herringbone grooves 3a, 3b, 4a, and 4b, and the rotating body 13 is supported in the radial direction without contacting the fixed shaft 5. be done. In addition, the above-mentioned balance correction groove 8
c and 12a indicate the rotation of the rotating body 13 when the rotating body 13 rotates.
In order to reduce the vibration caused by the unbalance, the balance is corrected to an unbalance of several milligrams or less.

Further, magnets 15 and 16 are provided on the upper end of the fixed shaft 5 and the upper cover 14 attached to the housing 1.
0 are arranged with the magnetic poles of the surfaces facing each other having the same polarity. And these magnets 10, 15, 16 have fine holes 8b.
Together, they form a thrust magnetic bearing as an axial bearing, and as the magnet 10 is repelled by the magnets 15 and 16, the rotating body 13 is levitated and supported in a non-contact manner in the thrust direction.

[0007] Also, a slotted iron core 17 is arranged around the rotor magnet 11, and this slotted iron core 1
7 are arranged so that the magnetic surface 17a faces the magnet 11, and are separated from each other via a gap 17b (see FIG. 4). In addition, a coil 18 is attached to the slot iron core 17.
is attached to the slotted iron core 17, and when the coil 18 is energized, the slotted iron core 17 generates a magnetic field to rotate the rotor magnet 11. Further, a Hall element 19 is provided above the gap 17b of the slotted iron core 17, and this Hall element 19 is attached to a printed circuit board 20, and detects the magnetic field generated from the slotted iron core 17. The rotor magnet 11 is rotated by controlling the excitation switching of the coil 18 based on . The axial length of the rotor magnet 11 described above is determined by the length H of the magnetic surface 17a of the slotted iron core 17, the length h of the Hall element 19, and the length for stably maintaining the axial position (of the Hall element 19). (approximately the same as the axial length h).

[0008]

However, in the brushless motor described in the former publication, the rotor magnet extends long in the axial direction.
4. In the brushless motor described above, the rotor magnet 11 has a length H of the magnetic surface 17a of the slotted iron core 17.
Because it extended in the axial direction by the sum of the axial length h of the Hall element 19 and the length for stably maintaining the axial position (approximately the same as the axial length h of the Hall element 19), In either case, the rotor magnet 11 becomes longer in the axial direction, which not only increases the size but also increases the weight. In addition to this, rotor magnet 11
The rotor magnet 1 is made of expensive materials such as manganese-aluminum or alnico-based magnets in order to be used for high-speed rotation.
There was a problem that the cost of 1 increased. In addition, the rotor magnet 11 shown in FIGS.
extends longer in the axial direction than the magnetic surface 17a of the slotted iron core 17, and since the Hall element 19 is disposed above the gap 17b, a complete closed magnetic path is formed at the upper and lower ends of the magnet 11. Therefore, there is a problem in that eddy current is generated due to leakage magnetic flux, and the temperature inside the housing 1 increases.

[0009] Therefore, the invention according to claim 1 shortens the axial length of the rotor magnet to make the magnet smaller and smaller.
It is an object of the present invention to provide a brushless motor that can be lightweight, reduce costs, and prevent an increase in ambient temperature.

0010

[Means for solving the problem] The invention according to claim 1 includes:
In order to achieve the above object, a rotor magnet is attached to the outer periphery of a rotating shaft and extends for a predetermined length in the axial direction, and a rotor magnet is disposed around the rotor magnet with its tip end facing the magnet, and the rotor magnet is installed in a gap between each other. and a magnetic detection element that detects the magnetic field generated from the magnetic field generation means, the magnetic detection element detects the magnetic field, and the excitation of the magnetic field generation means is switched based on the detection result. In a brushless motor in which a rotating shaft is rotated via a rotor magnet by controlling the rotor magnet, the axial length of the rotor magnet is shorter than the length in a predetermined direction of the tip surface of the magnetic field generating means, and a magnetic detection element is provided. The magnetically sensitive surface is disposed within the gap and within a predetermined length of the tip surface.

[0011]

[Operation] In the invention as claimed in claim 1, the axial length of the rotor magnet is shorter than the length in the predetermined direction of the tip surface of the magnetic field generating means, and the magnetic sensing surface of the magnetic detection element is located within the gap and at the tip. It is arranged so as to be within a predetermined direction length of the surface. Therefore, the axial length of the rotor magnet becomes shorter, making the rotor magnet smaller and lighter. As a result, the cost of the brushless motor is reduced. Also,
A closed magnetic path is formed between the rotor magnet and the upper and lower parts of the slotted iron core, so that no eddy current is generated due to leakage magnetic flux, and the surrounding temperature rise due to this is prevented.

0012

EXAMPLES The present invention will be explained below based on examples. 1 and 2 are diagrams showing an embodiment of a brushless motor according to the present invention. In this embodiment, the same components as those of the conventional example shown in FIGS. 3 and 4 are given the same reference numerals, and the explanation thereof will be omitted.

First, the configuration will be explained. 1 and 2, a rotor magnet 21 is attached to the outer periphery of the hollow rotating shaft 6, and this magnet 21 extends for a predetermined length in the axial direction of the rotating shaft 6. A plurality of slotted iron cores 22 are disposed around the rotor magnet 21, and the slotted iron cores 22 have their tip surfaces 22a facing the magnets 21 and are connected to the rotating shaft 6 through a gap 22b.
spaced apart circumferentially. This slotted iron core 22 is provided with a coil 23, and the slotted iron core 22 and the coil 23 constitute magnetic field generating means, and when the coil 23 is energized, a magnetic field is generated from the slotted iron core 22. Further, the axial length of the magnet 21 is formed to be shorter than the length H1 in a predetermined direction of the tip surface 22a of the slot iron core 22 (hereinafter, the length in the predetermined direction of the tip surface 22a is referred to as the lamination thickness), The rotating shaft 6 is rotated via a magnet 21 by a magnetic field generated from a slotted iron core 22.

On the other hand, a Hall element 24 as a magnetic detection element is provided in the gap 22b, and the magnetically sensitive surface of the Hall element 24 is disposed within the laminated thickness H1 of the tip surface 22a, and the width W1 is It is formed shorter than the width W of the gap 22b. This Hall element 24 is connected to the printed circuit board 20, and by detecting the magnetic field generated from the slot iron core 22 with a magnetically sensitive surface, generates a voltage corresponding to the magnetic field, and generates a voltage corresponding to the magnetic field, and the slot iron core 22 Excitation switching control is performed. And the rotor magnet 21 mentioned above,
The slotted iron core 22, the coil 23, and the Hall element 24 constitute a brushless motor.

As described above, in this embodiment, the axial length of the rotor magnet 21 is determined by the tip surface 22a of the slot iron core 22.
is shorter than the stacking thickness H1 of the Hall element 2.
4 within the gap 22b and the tip surface 22a.
Since the rotor magnets 21 are arranged so that the lamination thickness H1 is within the axial direction length of the rotor magnets 21, the axial length of the rotor magnets 21 can be shortened. Therefore, the rotor magnet 21 can be made smaller and lighter, and the cost of the brushless motor can be reduced. In addition, the magnetically sensitive surface of the Hall element 24 is set to the tip surface 2.
2a, the upper and lower portions between the rotor magnet 21 and the tip surface 22a of the slotted iron core 22 can be made into a closed magnetic path, and eddy currents due to leakage magnetic flux are prevented. This can prevent the temperature inside the housing 1 from rising.

[0016]

According to the invention as claimed in claim 1, the axial length of the rotor magnet is made shorter than the predetermined length of the end face of the magnetic field generating means, and the magnetically sensitive surface of the magnetic sensing element is placed within the gap. In addition, since the rotor magnet is disposed within the predetermined length of the tip end surface, the axial length of the rotor magnet can be shortened. Therefore, the rotor magnet can be made smaller and lighter, and the cost of the brushless motor can be reduced. In addition, since the magnetically sensitive surface of the magnetic detection element is arranged within the predetermined length of the tip surface, a closed magnetic path can be created between the rotor magnet and the upper and lower portions of the tip surface of the magnetic field generating means. It is possible to prevent the generation of eddy currents due to leakage magnetic flux and to prevent the surrounding temperature from rising.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a polygon scanner motor equipped with a brushless motor according to the present invention.

FIG. 2 is a configuration diagram of a magnetic field generating means and a magnetic detection element in FIG. 1.

FIG. 3 is a cross-sectional view of a polygon scanner motor equipped with a conventional brushless motor.

FIG. 4 is a configuration diagram of a magnetic field generating means and a magnetic detection element in FIG. 3;

[Explanation of symbols]

6 Hollow rotating shaft (rotating shaft) 21 Rotor magnet 22 Slot iron core (magnetic field generating means) 22a
Tip surface 22b Gap 23 Coil (magnetic field generating means)

Claims (1)

[Claims] 1. A rotor magnet that is attached to the outer circumference of a rotating shaft and extends for a predetermined length in the axial direction; and a rotor magnet that is disposed around the rotor magnet so that its tip end face faces the magnet, and that the rotor magnet is disposed around the rotor magnet with a distal end facing the magnet, and that the rotor magnet is disposed around the rotor magnet with a distal end facing the magnet, and The magnetic field generating means is provided with a magnetic field generating means that is separated from the magnetic field generating means, and a magnetic detection element that detects the magnetic field generated from the magnetic field generating means, the magnetic field is detected by the magnetic detecting element, and excitation switching control of the magnetic field generating means is performed based on the detection result. In a brushless motor in which a rotary shaft is rotated via a rotor magnet, the length in the axial direction of the rotor magnet is shorter than the length in a predetermined direction of the tip surface of the magnetic field generating means, and the magnetic sensing element of the magnetic detection element is A brushless motor characterized in that the surface is disposed within the gap and within a predetermined direction length of the tip surface.