JPH08160332A - Rotary polygon mirror driving device - Google Patents

Abstract

PURPOSE: To reduce the air resistance of the rotary polygon mirror without reducing the bearing load capacity. CONSTITUTION: The centrifugal impeller integrated with rotary polygon mirror 46 uniting the rotary polygon mirror and the centrifugal impeller, is arrange in the mirror casing 48 closely sealed by the magnetic fluid seal 52 or the sealing member 50, rotated together with the rotor 36 driven by the stator electric magnet 34. When the centrifugal impeller integrated with rotary polygon mirror 46 is rotated, the pump part 46a as the centrifugal impeller is functioned as the pump, and the air inside the mirror casing 48 is inhaled from the upper part and exhaled to the outer peripheral part as shown by the arrow mark. Thus, the air inside the mirror casing 48 is discharged outside through the exhaust pipe 54, and the pressure in the periphery of the centrifugal impeller integrated with rotary polygon mirror 46 is reduced. Namely, the air resistance with respect to the centrifugal impeller integrated with rotary polygon mirror 46 is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary polygon mirror driving device, and more particularly to a rotary polygon mirror driving device used in, for example, digital copying machines, laser printers, laser facsimiles and the like.

[0002]

2. Description of the Related Art In a recording apparatus such as a digital copying machine, a laser printer or a laser facsimile, printing is performed by scanning a laser beam using a rotating polygon mirror (rotating polygon mirror). Due to demands for color printing and high resolution, higher quality and higher speed printing are required.

In printing using a rotary polygon mirror, the rotational speed and rotational accuracy affect the printing speed and the quality of the printing.
A polygon mirror motor (rotating polygon mirror driving device) that rotationally drives a rotating polygon mirror is required to have high rotation and high accuracy.
However, since the rotary polygon mirror receives air resistance during rotation, a large load is applied to the rotary polygon mirror driving device when it is rotated at a high speed. Therefore, it has been necessary to increase the size of the motor and heat generation of the motor has become a problem. Further, due to the air resistance, the rotary polygon mirror may generate vibrations and noises, which may deteriorate the rotation accuracy.

Therefore, conventionally, in a rotary polygon mirror driving device using an air bearing, a herringbone groove is provided in the shaft portion of the bearing, and this shaft portion functions as a vacuum pump at the time of rotation, thereby surrounding the rotary polygon mirror. Some have been designed to reduce the pressure. FIG. 8 shows a conventional rotary polygon mirror driving device.

In the conventional rotary polygon mirror driving apparatus 10, a cylindrical shaft member 12 is fixed to the housing 14 side, and a rotary member 16 having a hollow cylindrical shape with an open lower end is provided so as to cover the shaft member 12. It is arranged. The rotary polygon mirror 18 is attached to the upper part of the rotating body 16.

Pump shaft herringbone grooves 18a and 18b are provided above and below the outer peripheral surface of the shaft member 12, and a bearing herringbone groove 20 is provided in the central portion. Further, an air flow passage 22 that opens to the lower end surface is provided on the central axis of the shaft member 12, and a plurality of air suction holes 24 that communicate with the air flow passage 22 are provided on the outer peripheral surface of the shaft member 12. It is provided.

When the rotating body 16 is rotated by the motor 26, the rotating body 16 is supported by the dynamic pressure generated in the bearing herringbone groove 20. The pumping herringbone grooves 18a and 18b function as a vacuum pump, and a pressure difference is generated between the outer side and the inner side of the rotating body 16, so that the air in the housing is compressed into a plurality of air suction holes 2 as shown by arrows.
4, and is discharged to the outside through the air flow passage 22. As a result, the pressure inside the housing 14 is reduced, and the air resistance of the rotary polygon mirror 18 is reduced.

[0008]

However, in the conventional rotary polygon mirror drive apparatus 10 shown in FIG. 8, the dynamic pressure generated in the bearing herringbone groove 20 is reduced as the pressure inside the housing 14 is reduced. The load capacity as an air bearing was reduced. Since the air bearing originally has a lower bearing load capacity than other bearings such as ball bearings and magnetic bearings, this reduction in bearing load capacity has been a very serious problem.

Further, since the structure is complicated, the manufacturing cost is high. Therefore, an object of the present invention is to provide a rotary polygon mirror driving device that can reduce the air resistance of the rotary polygon mirror without lowering the bearing load capacity.

[0010]

According to a first aspect of the present invention, there is provided a rotary polygonal mirror, a centrifugal impeller integrated with the rotary polygonal mirror, and an accommodating member accommodating the centrifugal impeller and the rotary polygonal mirror. An exhaust passage provided on the outer peripheral portion of the centrifugal impeller for communicating the inside and the outside of the accommodating member, and a rotation part of which is integrated with the rotary polygon mirror and is partially disposed outside the accommodating member. A rotary polygon mirror driving device that includes a shaft, a sealing unit that maintains airtightness inside the housing member, a motor that rotates the rotary shaft, and a radial bearing that supports a portion of the rotary shaft arranged outside the housing member. In order to achieve the above object.

According to another aspect of the invention, there is provided a rotating polygon mirror,
A rotary shaft integrated with the rotary polygonal mirror, a motor for rotating the rotary shaft, an accommodating member accommodating the motor, the rotary shaft, and the rotary polygonal mirror, and a rotary shaft of the rotary shaft in the accommodating member. A pump mechanism for decompressing the space on the rotary polygon mirror side by a rotary motion and a radial bearing of at least one of a rolling bearing and a magnetic bearing for supporting the rotary shaft are provided in a rotary polygon mirror driving device to achieve the above object. .

According to a third aspect of the present invention, in the rotary polygon mirror driving device according to the first aspect, the pump mechanism is formed by a spiral thread groove provided in at least one of the rotor and the stator of the motor. By doing so, the above object is achieved. According to a fourth aspect of the present invention, in the rotary polygon mirror driving device according to the first or second aspect, the radial bearing is a rolling bearing in which a rolling element rolls with an outer peripheral surface of the rotating shaft as a raceway surface. To achieve.

[0013]

In the rotary polygon mirror driving device according to the first aspect of the present invention, when the rotating shaft is rotated by the motor, the centrifugal impeller integrated with the rotating shaft is rotated and the atmospheric pressure of the outer peripheral portion thereof is increased. Then, the compressed gas is exhausted to the outside of the housing member via the exhaust passage, so that the pressure around the rotary polygon mirror is reduced.

According to another aspect of the present invention, there is provided a rotary polygon mirror driving device.
When the rotary shaft is rotated by the motor, the pump mechanism reduces the pressure on the rotary polygon mirror side by the rotation of the rotary shaft. In the rotary polygon mirror driving device according to the third aspect, the rotary polygon mirror side is depressurized by the spiral thread groove.

According to another aspect of the present invention, there is provided a rotary polygon mirror driving device.
When the rotating shaft is rotated by the motor, the rolling elements roll on the outer peripheral surface of the rotating shaft.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Each embodiment of the rotary polygon mirror driving apparatus of the present invention will be described in detail below with reference to FIGS. FIG. 1 shows a rotary polygon mirror driving device 30 according to a first embodiment.

The rotary polygon mirror driving apparatus 30 of this embodiment includes a motor housing 32, a stator electromagnet 34 fixed to the motor housing 32, and the stator electromagnet 3.
And a rotor 36 that is rotated by the drive of No. 4 of FIG.
The rotor 36 includes a cylindrical rotor shaft 38.
On the outer periphery of the rotor shaft 38, a cylindrical bearing inner permanent magnet 40 is attached on the upper side, and a motor permanent magnet 42 is attached on the lower side. Protective covers 43 and 47 are attached to the outer peripheral surfaces of the permanent magnets 40 and 42 respectively to prevent damage due to centrifugal force during rotation. Further, the lower end portion 38 a of the rotor shaft 38 is supported by a pivot bearing 44 which is a hemispherical recess formed on the inner bottom surface of the motor housing 32.

On the side of the motor housing 32 located outside the bearing inner permanent magnet 40, the bearing inner permanent magnet 40 is provided.
The cylindrical outer permanent magnet 45 for a bearing is attached so as to surround it with a slight gap. The bearing inner permanent magnet 40 and the bearing outer permanent magnet 45 constitute a repulsive radial magnetic bearing that supports the rotor 36 in the radial direction. That is, the portions of the bearing inner permanent magnet 40 and the bearing outer permanent magnet 45 that are close to each other have the same pole, for example, in FIG. 1, the upper side is the S pole and the lower side is the N pole. By repulsing each other, the rotor 36 is held in a non-contact position at a position where the repulsive forces are balanced.

The bearing inner permanent magnet 40 is located slightly below the bearing outer permanent magnet 45. Due to the deviation of the same poles, a magnetic repulsive force is exerted between the two magnets 40, 45. It also occurs in the direction (downward in FIG. 1). Therefore, the rotor 36 receives a downward force, and the tip of the small diameter portion 38 a of the rotor shaft 38 is pressed against the pivot bearing 44.

On the other hand, the upper portion of the rotor shaft 38 in FIG. 1 projects from the upper surface of the motor housing 32, and the centrifugal impeller-integrated rotary polygon mirror 4 is projected on this projecting portion.
6 is attached. The centrifugal impeller-integrated rotary polygon mirror 46 is formed by integrally forming a centrifugal impeller and a rotary polygon mirror. In FIG. 1, the upper side in FIG. 1 is a pump portion 46a that functions as a centrifugal pump, and the lower side reflects laser light. The rotary polygon mirror portion 46b is composed of a plurality of (for example, 6 or 8) mirrors m. Each mirror m
Is formed by polishing the lower outer peripheral surface of the centrifugal impeller-integrated rotary polygon mirror 46 by polishing or the like.

FIG. 2 shows a rotary polygon mirror 46 integrated with a centrifugal impeller.
The pump portion 46a of FIG. As shown in this figure, the pump portion 46a is provided with a plurality of blades A,
By rotating this, as shown by the arrow, gas is made to flow from the intake port B opened upward to the discharge port C formed in the side portion.

As shown in FIG. 1, the motor housing 32
A mirror casing 48 is mounted on the upper surface of the so as to surround the centrifugal impeller-integrated rotary polygon mirror 46, and a seal member 50 is held at a narrow pressure at the mounting portion. A magnetic fluid seal 52 is provided in the portion of the motor housing 32 where the rotor shaft 38 penetrates. The mirror casing 48 is sealed by the magnetic fluid seal 52 and the sealing member 50.
The inner space is kept airtight.

As shown in FIG. 1, the mirror casing 48
The window 4 is made of glass or the like at the same height as the mirror m.
8a is provided, and the laser light for scanning enters and exits through this window 48a. A discharge pipe 54 is attached to the mirror casing 48 as an exhaust passage communicating with the outside.

Incidentally, the permanent magnet 4 for the motor of the rotor 36
In the portion where 2 is attached, a rotating torque is generated by the rotating magnetic field of the stator electromagnet 34 located on the outer periphery thereof. Next, the operation of the embodiment thus configured will be described.

First, by driving the stator electromagnet 34, the rotor 36 and the centrifugal impeller-integrated rotary polygon mirror 46 are rotated. When the centrifugal impeller-integrated rotary polygon mirror 46 rotates, its pump portion 46a functions as a centrifugal pump, and the air in the mirror casing 48 is sucked from the intake port B and discharged from the discharge port C as shown in FIG. It is discharged to the outer peripheral portion. Then, it is discharged to the outside through the exhaust pipe 54 located on the outer peripheral portion of the discharge port C.

In this embodiment, since the inner space of the mirror casing 48 is isolated from the outside by the magnetic fluid seal 52 and the seal member 50, the exhaust from the exhaust pipe 54 reduces the pressure inside the mirror casing 48. It
Therefore, the air resistance with respect to the centrifugal impeller-integrated rotary polygon mirror 46 is reduced, and the load on the motor is reduced. Particularly, in the rotary polygon mirror driving device 30, the centrifugal impeller-integrated rotary polygon mirror 46 is rotated at a speed of 10,000 rpm or more,
The effect of reducing the load by reducing the air resistance is great. Therefore, the heat generation of the stator electromagnet 34 is suppressed to a low level, and the centrifugal impeller-integrated rotary polygon mirror 46 can be rotated at high speed without increasing the size of the motor. Further, due to the reduction of the air resistance, the centrifugal polygonal wheel integrated rotary polygon mirror 46 at the time of high speed rotation is
Vibration is reduced and rotation accuracy is improved.

Further, the rotary polygon mirror driving device 30 of the present embodiment.
When used in a recording device such as a digital copying machine, extremely high quality and high speed printing can be performed by the high speed rotation and high accuracy rotation of the centrifugal impeller integrated rotary polygon mirror 46. As described above, in the rotary polygon mirror driving device 30 of the present embodiment, the bearing load capacity of the radial magnetic bearing configured by the bearing inner permanent magnet 40 and the bearing outer permanent magnet 45 does not decrease, and the mirror casing does not deteriorate. The pressure inside 48 can be reduced.

Note that other radial bearings may be used in place of the repulsive type magnetic bearing composed of the permanent magnets 40 and 45. For example, even when an air bearing is used as the radial bearing, in the present embodiment, the magnetic fluid seal 52 separates the inside of the mirror casing 48 from the inside of the motor housing 32, so that the bearing load capacity of the air bearing is reduced. It is possible to reduce the pressure around the rotary polygon mirror 46 integrated with the centrifugal impeller without doing so.

In the above embodiments, the centrifugal impeller-integrated rotary polygon mirror 46 is formed by integrally forming the centrifugal impeller and the rotary polygon mirror. However, the rotary polygon mirror and the centrifugal blade are separate bodies. The two may be integrated by assembling with the vehicle. In the present specification, “integrated” includes not only the case where the members are made of the same member, but also the case where a plurality of members that are separate from each other are integrally fixed by adhesion or bolts.

Further, the pump section 46a and the mirror m are
Other positional relationships may be possible. FIG. 3 shows a rotary polygon mirror driving device in which the pump portion and the mirror have another positional relationship. The rotary impeller 60 integrated with the centrifugal impeller of this example
Has a flat regular hexagonal prism or regular octagonal prism shape,
A rotary polygon mirror is provided above the centrifugal impeller. That is, a plurality of mirrors m'for reflecting laser light are formed on the upper side of the outer peripheral surface of the centrifugal impeller-integrated rotary polygon mirror 60. An intake port E for intake is formed on the upper surface of the centrifugal impeller-integrated rotary polygon mirror 60, and the discharge port F is formed on the lower outer peripheral surface of each mirror m.

At the time of rotation of the centrifugal impeller-integrated rotary polygon mirror 60, the air in the mirror casing 64 is sucked from the intake port E as shown by the arrow and discharged from the discharge port F to the outside via the exhaust pipe 54. Is discharged to. As a result, the pressure inside the mirror casing 64 is reduced.

The window 64a of the mirror casing 64
Is provided above the window 48a of the mirror casing 48 shown in FIG. 1 according to the position (height) of the mirror m '. Next, a second embodiment will be described. FIG.
7 illustrates a rotary polygon mirror driving device 70 according to a second embodiment.

The rotary polygon mirror driving device 70 of this embodiment includes a motor housing 72 and a stator electromagnet 74 as a stator of the motor fixed to the motor housing 72.
And a rotating portion 76 that is rotated by driving the stator electromagnet 74. The rotating unit 76 includes a rotating polygon mirror 78 having a flat hexagonal shape or a regular octagonal flat plate shape,
It has a cylindrical rotor shaft 80. In this embodiment, the rotary polygon mirror 78 and the rotor shaft 80 are integrally formed, and their central axes coincide with each other. As the rotating portion 76, for example, an aluminum alloy or the like is used, and the outer peripheral surface 78a of the rotating polygon mirror 78 is mirror-finished to form a plurality of, for example, six, or eight.
It is a mirror.

The lower end 80a of the rotor shaft 80 is supported by a pivot bearing 82, which is a hemispherical recess formed on the inner bottom surface of the motor housing 72, as in the first embodiment. Further, on the outer peripheral surface of the rotor shaft 80, a cylindrical bearing inner permanent magnet 84 is attached to the upper side in FIG. 4 and a motor permanent magnet 86 is attached to the lower side by adhesion or the like in FIG. A protective cover 85 for preventing damage is attached to the outer peripheral surface of the bearing inner permanent magnet 84.

The bearing inner permanent magnet 84 is provided on the motor housing 72 side located on the outer periphery of the bearing inner permanent magnet 84.
The cylindrical outer permanent magnet 90 for a bearing is attached so that it may surround. Also in this embodiment, as in the first embodiment, the permanent magnets 84 and 90 constitute a repulsive radial magnetic bearing.

Further, since the bearing inner permanent magnet 84 is disposed slightly downward from the bearing outer permanent magnet 90, the magnetic repulsive force also acts downward as in the first embodiment. However, the lower end portion 80a of the rotor shaft 80 has the pivot bearing 8
Pressed against 2. A portion of the rotor shaft 80, to which the motor permanent magnet 86 is attached, generates a rotating torque as a rotor of the motor due to the rotating magnetic field of the stator electromagnet 74 located on the outer periphery thereof.

Further, in this embodiment, the permanent magnet 8 for the motor is used.
A substantially cylindrical threaded cover 92 is attached to the outer peripheral surface of 6. The threaded cover 92 has a spiral groove 92a (threaded groove) formed on the outer circumference thereof, and is a pump that transfers gas from above to below in FIG. 4 by rotating in a predetermined direction. It is supposed to work. The width and interval of the groove 92a in the threaded cover 92 are narrower toward the lower side in FIG. Further, the upper space and the lower space of the stator electromagnet 74 are communicated with each other through the gap between the threaded cover 92 and the stator electromagnet 74.

Flange portion 72a of the motor housing 72
Is attached with a mirror casing 94 having a window 94a through which laser light is incident. The seal member 9 is provided between the mirror casing 94 and the flange portion 72a.
6 is held at a narrow pressure. In addition, the motor housing 72
On the side part located below the stator electromagnet 74,
An exhaust pipe 98 is attached.

Next, the operation of the embodiment thus constructed will be described. In this embodiment, the stator electromagnet 74
When the rotating part 76 rotates in a predetermined direction by the drive of
By the rotation of the threaded cover 92, the gas is transferred from the upper side to the lower side in FIG. 4 and is exhausted to the outside through the exhaust pipe 98. Therefore, the pressure P1 in the space above the stator electromagnet 74 becomes lower than the pressure P2 below (P1 <P2). That is, the atmosphere on the rotary polygon mirror 78 side is depressurized.

Therefore, the air resistance to the rotary polygon mirror 78 is reduced, and the rotary polygon mirror 78 can be rotated at high speed and with high precision as in the first embodiment. As described above, in the rotary polygon mirror driving device 70 of the present embodiment, since the repulsive magnetic bearing composed of the permanent magnets 84 and 90 is used as the radial bearing of the rotating portion 76, the bearing load capacity is reduced. It is possible to reduce the pressure around the rotary polygon mirror 78 without causing it.

Further, in this embodiment, the rotary polygon mirror 78 and the rotor shaft 80 are integrally formed, and the rotating portion 76 is automatically driven by the magnetic repulsive force of the outer bearing permanent magnet 90 and the inner bearing permanent magnet 84. Since it has a bearing structure that is retained at the center of the shaft, the assembling of the rotating portion 76 to the motor housing 72 can be greatly simplified. That is,
By simply inserting the rotating portion 76 into the motor housing 72 from above via the inner peripheral hole of the bearing outer permanent magnet 90,
You can finish the assembly. Therefore, the assembly time can be shortened as compared with the conventional one, and the manufacturing cost can be reduced.

Further, by mounting the inner permanent magnet 84 for bearings, the permanent magnet 86 for motors, etc. on the rotor shaft 80, the rotating portion 76 is completed as a rotating body before being assembled to the motor housing 72, so that the motor housing is No assembly error will occur after assembly to 72. Therefore, if the rotation balance is adjusted before assembling, the rotation balance will not be lost after that, and vibration and noise at the time of rotation due to an assembly error will not occur, so that the rotary polygon mirror 78 can be operated at a higher speed. And it can be rotated with high precision.

The pressure around the rotary polygon mirror 78 may be reduced by using another pump mechanism. 5 and 6 show
These are modifications of the second embodiment. In the rotary polygon mirror driving device 100 shown in FIG. 5, a cylindrical protective cover 102 is attached to the outer periphery of the motor permanent magnet 86. On the other hand, inside the stator electromagnet 74,
A cylindrical electromagnet cover 104 having a thread groove 104a formed on its inner peripheral surface is attached.

In this example, when the rotating portion 106 is rotated by driving the stator electromagnet 74, the electromagnet cover 104 is rotated.
The gas is transferred from the upper side to the lower side by the screw groove 104a of 1, and the pressure around the rotary polygon mirror 78 is reduced. On the other hand, the rotary polygon mirror driving device 110 shown in FIG.
An impeller 112 is attached to the lower part of the lower part, and the gas between the protective cover 113 of the motor permanent magnet 86 and the stator electromagnet 74 is sucked by the rotation of the rotating part 114 as shown by the arrow in FIG. , And the exhaust pipe 98. Below the stator electromagnet 74,
A cover member 116 is attached to the blade 112a with a slight clearance in order to form a gas flow passage.

In each of the above embodiments, a repulsive type magnetic bearing is used as the radial bearing of the rotor 36, the rotating portion 76, etc., but other radial bearings such as a rolling bearing and a control type magnetic bearing are used. May be used. For example, as shown in FIG. 7, the raceway groove 1 is formed on the outer peripheral surface of the rotor shafts 38, 80, etc.
It is also possible to use a rolling bearing 126 which forms 20 and holds a ball 124 which is a rolling element between the raceway groove 120 and the outer ring 122.

In this rolling bearing 126, the balls 124 directly roll on the outer peripheral surfaces of the rotor shafts 38 and 80, so that there is little vibration, and since there is no inner ring, the shaft diameter can be made thicker, so the rigidity is increased. You can Therefore, the rotary polygon mirror driving device 30, 70 using this rolling bearing 126
Etc., the rotating polygon mirrors 46, 7 at higher speed and higher accuracy.
8 etc. can be rotated.

[0047]

According to the rotary polygon mirror driving apparatus of the present invention,
The air resistance of the rotary polygon mirror can be reduced without lowering the bearing load capacity.

[Brief description of drawings]

FIG. 1 is a sectional view showing a rotary polygon mirror driving device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a rotary polygon mirror integrated with a centrifugal impeller of the device.

FIG. 3 is a cross-sectional view showing a modified example of the device.

FIG. 4 is a sectional view showing a rotary polygon mirror driving device according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a modified example of the same device.

FIG. 6 is a sectional view showing another modification of the device.

FIG. 7 is an explanatory view showing another example of the radial bearing according to the first and second embodiments of the present invention.

FIG. 8 is a sectional view showing a conventional rotary polygon mirror driving device.

[Explanation of symbols]

 30, 70 Rotating polygon mirror driving device 32, 72 Motor housing 34, 74 Stator electromagnet 36 Rotor 38 Rotor shaft 40, 84 Bearing inner permanent magnet 42, 86 Motor permanent magnet 44, 82 Pivot bearing 45, 90 Bearing outer permanent Magnet 46 Centrifugal impeller integrated rotary polygon mirror 46a Pump portion 46b Rotation polygon mirror portion 48, 94 Mirror casing 50, 96 Seal member 52 Magnetic fluid seal 54, 98 Exhaust pipe 78 Rotating polygon mirror 76 Rotating portion 92 Threaded cover 92a Thread groove m, m'mirror

Claims (4)

[Claims] 1. A rotary polygonal mirror, a centrifugal impeller integrated with the rotary polygonal mirror, an accommodating member accommodating the centrifugal impeller and the rotary polygonal mirror, and an outer peripheral portion of the centrifugal impeller. An exhaust passage that communicates the inside and the outside of the housing member, a rotary shaft that is integrated with the rotary polygon mirror, and a part of which is disposed outside the housing member; A rotary polygon mirror driving device comprising: a sealing means for holding; a motor for rotating the rotating shaft; and a radial bearing for supporting a portion of the rotating shaft arranged outside the housing member. 2. A rotary polygonal mirror, a rotary shaft integrated with the rotary polygonal mirror, a motor for rotating the rotary shaft, and an accommodating member accommodating the motor, the rotary shaft, and the rotary polygonal mirror. In the housing member, a pump mechanism for decompressing the space on the rotary polygon mirror side by the rotary motion of the rotary shaft, and a radial bearing that supports the rotary shaft and is at least one of a rolling bearing and a magnetic bearing are provided. A rotary polygon mirror drive device characterized by the above. 3. The rotary polygon mirror driving device according to claim 1, wherein the pump mechanism is constituted by a spiral thread groove provided in at least one of a rotor and a stator of the motor. 4. The rotary polygon mirror driving device according to claim 1, wherein the radial bearing is a rolling bearing in which a rolling element rolls with an outer peripheral surface of the rotary shaft as a raceway surface.