JPH0828946B2 - motor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor used in, for example, a laser printer, in which an air flow is generated between a fixed shaft and a rotor by a groove for dynamic pressure generation as the rotor rotates. And thus relates to a motor that constitutes an air bearing.

2. Description of the Related Art A conventional example of this type of motor is shown in FIG. 3 (see Japanese Patent Application No. 60-272915). Fixed base for housing 7
The fixed shaft 1 is erected on the 71. A rotor 2 is fitted onto the fixed shaft 1, and a drive magnet 3 is provided on the outer peripheral surface of the rotor 2. Grooves 12a and 12b for generating dynamic pressure are formed on the outer peripheral surface of the fixed shaft 1. A cap 6 is attached to the upper open end surface of the rotor 2. An air damper portion 4 is formed by sealing the space between the cap 6 and the upper end surface of the fixed shaft 1.

On the other hand, the stator 5 is attached to the inner peripheral surface of the housing. The drive magnet 3 is attached to a position slightly lower than the stator 5. Reference numeral 8 in the drawing denotes a sensor such as a Hall element for detecting the rotation speed of the rotor 2.

That is, when the motor is energized, the rotor 2 floats and rotates due to the magnetic action between the stator 5 and the driving magnet 3. Since the drive magnet 3 and the stator 5 are axially displaced from each other, the rotor 2 is levitated by the magnetic attraction force between the two and stands still at a position balanced with gravity. As the rotor 2 rotates, the dynamic pressure generating grooves 12a, 12b
As a result, an air flow is generated in the gap between the fixed shaft 1 and the rotor 2. This air flow constitutes an air bearing.

Further, the air damper portion 4 suppresses minute vibrations in the axial direction of the rotor 2 that periodically occur from immediately after the motor rotates until reaching the rated speed. That is, since the internal pressure of the air damper portion 4 acts on the rotor 2, the level of the minute vibration in the axial direction of the rotor 2 is small, and the rotor 2 is attenuated in a short time.

Since the dynamic pressure generating grooves 12a and 12b only need to function as air bearings, their axial widths are set to be the same. As a result, there is no air that greatly flows from the top to the bottom in the gap between the fixed shaft 1 and the rotor 2, and the air in the air damper portion 4 does not escape.

Problems to be Solved by the Invention However, in the case of the above conventional example, first of all,
Since the air damper part 4 has a closed structure, it is difficult to assemble. Secondly, when the rotor 2 rotates, the temperature of the gap between the rotary shaft 1 and the rotor 2 rises, and accordingly, the internal pressure of the air damper part 4 rises, and the position of the rotor 2 changes. Especially the rotor 2
When a polygonal mirror for reflecting the laser beam is attached to the, if the position of the rotor 2 changes, the position of the polygonal mirror changes accordingly, and the irradiation position of the laser beam may deviate from the polygonal mirror. .

The present invention was created under the above-mentioned background, and an object thereof is to provide a motor without the above-mentioned drawbacks.

Means for Solving the Problems In order to achieve the above-mentioned object, a motor according to the present invention includes a fixed shaft that is erected on a fixed base, and a drive magnet that is externally fitted to the fixed shaft and is provided on the outer peripheral surface. A cylindrical rotor attached to the stator, a stator axially displaced from the drive magnet and attached to the inner surface of the housing, and an outer peripheral surface of the fixed shaft inclined with respect to the circumferential direction. A dynamic pressure generating groove having a plurality of grooves formed around the entire circumference thereof, and a cap that is attached to the upper open end surface of the rotor and seals between the upper end surface of the fixed shaft to form an air damper part. When the motor is energized, the rotor rotates while levitating due to the magnetic action between the stator and the drive magnet, and as the rotor rotates, the dynamic pressure generating groove causes a gap between the fixed shaft and the rotor. Qi In a motor that generates a body flow and thereby constitutes a gas bearing, a small hole portion that is formed on the surface of the cap and that allows gas to flow to the air damper portion is provided on the outer surface of the cap. And a filter for filtering moisture and dust contained in the gas that is about to flow into the air damper through the small hole portion, and the dynamic pressure generating groove is
An upper inclined groove group formed at an upper position on the outer peripheral surface of the fixed shaft, and a lower inclined groove group formed at an lower position on the outer peripheral surface of the fixed shaft in a direction opposite to the upper inclined groove group. It is characterized in that the width of the lower inclined groove group in the axial direction is set shorter than that of the upper inclined groove group.

Since the small hole is formed in the air damper, the gas in the air damper escapes from the small hole when the rotor is fitted on the fixed shaft.

Further, the upper inclined groove group and the lower inclined groove group are formed so as to be inclined in mutually opposite directions, and the axial width of the lower inclined groove group is set shorter than that of the upper inclined groove group. The flow of gas generated by the upper tilted groove group is stronger than that of the lower tilted groove group, and as a result, the gas largely flows from the top to the bottom in the gap between the fixed shaft and the rotor. That is, the gas enters the air damper portion through the filter and the small hole portion, passes through the gap between the fixed shaft and the rotor, and is then discharged to the outside of the rotor. Due to this gas flow, the heat in the gap between the fixed shaft and the rotor is efficiently radiated to the outside of the rotor.

Furthermore, since moisture, dust, etc. contained in the gas are filtered by the filter, they do not enter between the fixed shaft and the rotor.

Embodiment Hereinafter, an example in which the first embodiment of the motor of the present invention is applied to a laser printer will be described with reference to the drawings. FIG. 1 is a vertical sectional view of a motor.

In the figure, 10 is a shaft hole 21 formed on the fixed base 71 of the housing 70.
It is a fixed shaft installed upright. A dynamic pressure generating groove 11 called a herringbone groove is formed on the outer peripheral surface of the fixed shaft 10.

The dynamic pressure generating grooves 11 are a plurality of grooves that are inclined with respect to the circumferential direction on the outer peripheral surface of the fixed shaft 10, and are formed over the entire circumference thereof. This is formed at the upper inclined groove group 11a formed at the upper position on the outer peripheral surface of the fixed shaft 10 and at the lower position on the outer peripheral surface of the fixed shaft 10 so as to be inclined in the opposite direction to the upper inclined groove group 11a. And the lower tilt groove group 11b, the axial width B of the lower tilt groove group 11b is set shorter than the axial width A of the lower tilt groove group 11a.

Reference numeral 30 in the figure denotes a tubular rotor fitted onto the fixed shaft 10.
The rotor 30 is composed of a rotary sleeve 31 rotatably fitted to the outer periphery of the fixed shaft 10 and an annular drive magnet 32 mounted around the lower side of the rotary sleeve 31.

A polygonal mirror 40 for reflecting the laser light incident through the opening window 51 of the housing 50 is attached to the outer edge of the rotary sleeve 31.

A cap 70 is attached to the upper open end surface of the rotor 30. An air damper portion 71 is formed by sealing the upper end surface of the fixed shaft 10 with the cap 70.

On the surface of the cap 70, a small hole portion 72 for allowing air to flow through the air damper portion 71 is formed. That is, the air damper portion 71 and the housing inner space 52 communicate with each other through the small hole portion 72.

A tubular portion 73 is provided on the outer surface of the cap 70 so as to surround the small hole portion 72 from the outside. A filter 74 is attached to the open end of the tubular portion 73. The filter 74 is provided to filter moisture, dust, and the like contained in the air that is about to flow into the air damper portion 71 from the inner space 52 of the housing through the small hole portion 72.

In the figure, reference numeral 60 denotes a stator that is paired with the rotor 30, and is attached to the inner peripheral surface of the housing 50 so as to surround the outer peripheral surface of the drive magnet 32. The stator 60 is arranged at a position slightly higher than the driving magnet 32 and displaced by Δh.

A sensor such as a Hall element for detecting the rotation speed of the rotor 30 is attached to the inner peripheral surface of the housing 70 at a position closer to the bottom of the stator 60.

The operation of the motor configured as above will be described. First, when the motor is energized, the rotor 30 floats and rotates due to the magnetic action between the stator 60 and the driving magnet 32. The drive magnet 32 and the stator 60 are Δh
The rotor 30 is floated by the magnetic attraction force of both, and is stationary at a position balanced with the gravity acting on the rotor 30 and the air attraction force by the dynamic pressure generating groove 11 described later. . As the rotor 30 rotates, an air flow is generated between the fixed shaft 10 and the rotor 30 from the top to the bottom by the dynamic pressure generating grooves 11, 11. That is, the space inside the housing
The air in 52 passes through the filter 74 and the small hole 72, and the air damper
After entering 71, it passes through the gap between the fixed shaft 10 and the rotor 30, and is discharged to the outside of the rotor 30.

The above-described air flow from the top to the bottom is generated because the upper inclined groove group 11a and the lower inclined groove group 11b are formed so as to incline in mutually opposite directions, and the lower inclined groove group 11b is formed. Since the axial width B of the lower inclined groove group 11a is set to be shorter than the axial width A of the lower inclined groove group 11a, the flow of air generated by the upper inclined groove group 11a is smaller than that of the lower inclined groove group 11b. It is stronger than that. The dynamic pressure generating groove 11 plays a role as a pump that sucks air from the small hole portion 72, so to speak.

This air flow not only forms an air bearing between the fixed shaft 10 and the rotor 30, but also heat generated in this portion is efficiently radiated to the outside of the rotor 30. Therefore, the rotor 30
Even when the engine rotates for a long time, heat is not accumulated in the gap between the fixed shaft 10 and the rotor 30, and the internal pressure of the air damper 71 does not change. As a result, the position of the rotor 30 does not change, and the laser light incident through the opening window 51 of the housing 50 is always applied to the polygon mirror 40, so that the function as the laser printer is continuously exhibited. Further, since the moisture and dust contained in the air are filtered by the filter 74, they do not enter the gap between the fixed shaft 10 and the rotor 30. Even if it gets in, it will be cleaned by the flow of air, so it will not be clogged and will not adversely affect the bearing performance.

Further, the minute vibration in the axial direction of the rotor 30, which is periodically generated immediately after the motor starts to reach the rated speed, is suppressed by the air damper portion 71 as in the case of the conventional motor. However, although the damper effect obtained by the air damper unit 71 is slightly inferior to the motor described in the conventional example,
It has been confirmed that the level of microvibration is reduced to such an extent that it is not a problem.

That is, in the case of the motor having no air damper, the amplitude of the minute vibration of the rotor was about 90 μm. However, in the case of the motor of this embodiment, the inner surface of the cap 70 and the rotor 30 are kept in a state where the rotor 30 is floating and stationary. When the size of each part including the diameter of the small hole 72 is appropriately adjusted so that the gap l with the upper end surface is 1.5 mm, it is about 5 μ which is practically no problem.
It has been confirmed that the size can be reduced to m.

Although the gap between the fixed shaft 10 and the rotor 30 is extremely small, about 10's of μm, a small hole 72 is formed in the cap 70, so that the rotor 30 can be attached to the fixed shaft 10 at the assembly stage of the motor. At the time of fitting, the air in the air damper portion 71 is pushed out from the small hole portion 72 and escapes to the outside, which is advantageous in that the assembly is easy.

Next, a second embodiment of the motor of the present invention will be described with reference to the drawings by taking a laser printer as an example as in the above. FIG. 2 is a vertical sectional view of the motor. The same parts as those in the first embodiment are designated by the same part numbers.

Here, the permanent magnet 90a is attached to the upper side surface of the cap 70, while the permanent magnet 90b is attached to the inner surface of the housing 50 at a position facing the permanent magnet 90a. Each of the permanent magnets 90a and 90b has a ring shape,
A repulsive magnetic force acts between them. That is, the rotor 30 is urged downward in the axial direction by the repulsive magnetic force of the permanent magnets 90a and 90b. By the balance between this urging force and the magnetic attraction force between the stator 60 and the drive magnet 32,
The axial rigidity of the rotor 30 during rotation will increase. Even in the case of the second embodiment, the merits of the first embodiment can be obtained similarly.

As described above, in the motor according to the present invention, when the rotor is fitted on the fixed shaft, the gas in the air damper part escapes from the small hole part to the outside, so that the rotor is fitted smoothly on the fixed shaft. It has the advantage that it can be assembled easily. Further, since the heat in the gap between the fixed shaft and the rotor is efficiently radiated, even if the rotor rotates at high speed, the heat is not accumulated, and as a result, the internal pressure of the air damper part does not change, The position of the rotor does not change either.
Furthermore, since the moisture and dust contained in the gas do not enter the gap between the fixed shaft and the rotor, the moisture and dust contained in the gas do not adversely affect the bearing performance.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a first embodiment of the present invention, which is a longitudinal sectional view of a motor, and FIG. 2 is a diagram for explaining a second embodiment of the present invention. It is a longitudinal cross-sectional view of a motor. FIG. 3 is a view for explaining a conventional motor and is a vertical cross-sectional view of the motor. 10 …… Fixed shaft 11 …… Dynamic pressure generating groove 30 …… Rotor 32 …… Driving magnet 70 …… Cap 71 …… Air damper 72 …… Small hole 74 …… Filter 50 …… Housing 60 …… Stator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihiro Matsubara 501-12 Fujimi-cho, Iwata-shi, Shizuoka Prefecture (72) Inventor Natsuko Mori 1343-1 Ninomiya, Iwata-shi, Shizuoka Prefecture (72) Tatsuo Kawase Iwata, Shizuoka Prefecture 1368 Higashi-Kaizuka (72) Inventor Yoshihito Urata 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-59-32336 (JP, A) JP-A-59-164413 (JP, JP, 164413) A) Actual development Sho 59-141451 (JP, U) Actual development Sho 56-152559 (JP, U)

Claims (1)

[Claims] Claim: What is claimed is: 1. A fixed shaft erected on a fixed base, a cylindrical rotor fitted onto the fixed shaft and having a drive magnet mounted on the outer peripheral surface thereof, and a shaft for the drive magnet. A stator that is arranged offset in the direction and is attached to the inner surface of the housing, and a dynamic pressure generating groove in which a plurality of grooves that are inclined with respect to the circumferential direction are formed on the outer peripheral surface of the fixed shaft over the entire circumference. , A cap that is attached to the upper open end surface of the rotor and that seals between the rotor and the upper end surface of the fixed shaft to form an air damper part. When the motor is energized, the stator and the drive magnet are separated. Due to the magnetic action between the rotors, the rotors rotate while floating, and with the rotation of the rotors, a gas flow is generated between the fixed shaft and the rotors by the dynamic pressure generating grooves, and in the motor that constitutes the gas bearing, A small hole portion formed on the surface of the cap for allowing gas to flow to the air damper portion, and a gas provided on the outer surface of the cap and flowing into the air damper portion through the small hole portion. It is equipped with a filter for filtering contained moisture, dust, etc., and the dynamic pressure generation groove has an upper inclined groove group formed at an upper position on the outer peripheral surface of the fixed shaft, and a groove on the outer peripheral surface of the fixed shaft. The lower tilt groove group is formed at the lower position so as to be tilted in the opposite direction to the upper tilt groove group, and the axial width of the lower tilt groove group is set shorter than that of the upper tilt groove group. A motor characterized by being used.