JPH08322192A - Polygon mirror - Google Patents

Abstract

PURPOSE: To prevent rotational fluctuation of a polygon mirror from increasing by specifying the clearance at the time of filling a magnetic fluid bearing with magnetic fluid. CONSTITUTION: A cup-like rotor 2 fixed with a polygon mirror 1 is supported rotatably by upper and lower radial plate bearings 5, 6 fitted in the tubular supporting wall 4a of a bearing unit 4 through a rotary shaft 3. The gap between the rotary shaft 3 and the inner wall face of the radial plate bearings 5, 6 and the tubular supporting wall 4a is filled with magnetic fluid 7 and a magnetic seal 8 is disposed, along with a dynamic pressure seal 9, at the upper end of tubular supporting wall 4a. Rotational fluctuation of the polygon mirror can be suppressed by setting the clearances between the rotary shaft 2 and the inner wall face of tubular supporting wall 4a, between the lower surface of radial plate bearing 5 and the stepped surface of tubular supporting wall 4a, and between the upper surface of radial plate bearing 5 and an oil surface cover plate at 0.15mm or less thereby suppressing fluctuation in the rotational load on the rotary shaft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polygon mirror device used in an optical writing device such as an image forming device such as a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art A polygon mirror device is generally used in a laser scanning device such as an image forming device or a copying machine. For example, a rotor of a brushless motor has a regular polygonal member such as a regular hexagon or a regular octagon. A polygon mirror having a mirror portion formed on the side surface of the mirror is attached to rotate, the laser beam is reflected by the mirror portion, and the laser beam is repeatedly deflected. The photosensitive body is exposed and scanned with the deflected laser beam. Used to write.

Therefore, in order to write an image with high precision and high definition, the laser beam must be accurately deflected, and the rotation irregularity of the polygon mirror must be minimized.

[0004]

One of the causes of uneven rotation of a polygon mirror mounted on a rotating shaft that rotates at high speed is supported by a bearing that uses a magnetic fluid that is a mixture of magnetic powder and lubricating oil as a lubricant. When the rotating shaft rotates at high speed, bubbles are mixed or generated in the magnetic fluid that is a lubricant and the magnetic fluid is turbulent. When the bubbles enter between the rotating shaft and the bearing surface, the rotating load of the rotating shaft is large. It is fluctuating.

An object of the present invention is to prevent bubbles from being mixed in or generated in the magnetic fluid to cause turbulent flow of the magnetic fluid even when the rotating shaft rotates at a high speed, and the bubbles also prevent the rotation shaft and the bearing. This is to prevent the rotation unevenness of the rotary shaft from becoming large due to the fluctuation of the rotation load of the rotary shaft entering between the surfaces to increase the rotation unevenness of the polygon mirror.

[0006]

In order to achieve this object, the present invention is provided with a polygonal mirror for reflecting and deflecting a laser beam incident from a laser device while rotating and supporting it by a magnetic fluid bearing. In the polygon mirror device having the above described rotating shaft, the clearance for filling the magnetic fluid in the magnetic fluid bearing is 0.15 mm or less.

A lid plate is provided for contacting the liquid surface of the magnetic fluid in the magnetic fluid bearing so as to cover the liquid surface, and the rotary shaft has a diameter of 4 mm to 5 mm.

Alternatively, in a polygon mirror device having a rotating shaft supported by a magnetic fluid bearing, the polygon mirror is provided with a polygon mirror for reflecting and deflecting a laser beam incident from a laser device while rotating. With respect to the clearance filled with the magnetic fluid, in the region where the rotation speed of the rotary shaft is 10,000 to 40,000 r / min, the short cycle rotation unevenness of the rotary shaft is 0.01% or less and the long cycle rotation unevenness is 0.015% or less. It is characterized by doing so.

The clearance is set to 0.15 mm.
Further, the diameter of the rotary shaft is set to 4 mm to 5 mm, and the clearance is set to 0.15 mm or less.

[0010]

When the clearance around the rotating shaft filled with the magnetic fluid is 0.15 mm or less, the movement of bubbles in the magnetic fluid is suppressed, and the fluctuation of the rotating load on the rotating shaft is reduced.

[0011]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a vertical cross-sectional side view of a polygon mirror device using a brushless motor using a magnetic fluid bearing as a drive source, and FIG. 2 is an enlarged view of a main part thereof.

A cup-shaped rotor 2 having a polygon mirror 1 attached thereto is rotatably supported by a rotary shaft 3 by two upper and lower radial surface bearings 5 and 6 mounted in a bearing supporting cylindrical wall 4a of a bearing unit 4. ing. The rotating shaft 3, the radial surface bearings 5, 6 and the bearing supporting cylindrical wall 4
A magnetic fluid (mixture of magnetic powder and lubricating oil) 7, which is a lubricant, is filled in the gap between the inner wall surfaces of a. The magnetic fluid 7 filled in the gap is formed on the upper end of the bearing supporting cylindrical wall 4a.
A magnet seal 8 and a dynamic pressure seal 9 are installed to prevent the oil from overflowing.

A main magnet 10 and a rotor thrust magnet 11 are adhered to the outer peripheral surface of the cup-shaped rotor 2, and a stator core 13 is housed in a stator case 12 connected to the outer peripheral edge of the end bracket disc 4b of the bearing unit 4. The status last magnet 14 faces the outer peripheral surfaces of the main magnet 10 and the rotor thrust magnet 11 with a minute gap. The winding 15 wound around the stator core 13 has the main magnet 1
An exciting current corresponding to the magnetic pole position of 0 is supplied to generate a rotating magnetic field, and a rotating torque is generated in the main magnet 10. The rotor thrust magnet 11 and the status thrust magnet 14 are opposed to each other with their centers displaced in the axial direction, and apply a thrust force in the levitation direction to the rotor 2.

On the upper side of the upper radial surface bearing 5, an oil level holding cover plate 16 is provided via a clearance forming a flow path of the magnetic fluid 7 circulating on the upper surface of the radial surface bearing 5.

The clearance between the rotary shaft 3 and the inner wall surface of the bearing supporting cylindrical wall 4a is g ₁ , the clearance between the lower surface of the radial surface bearing 5 and the step surface of the bearing supporting cylindrical wall 4a is g ₂ , the radial surface bearing 5 When the clearance between the upper surface of the oil surface and the oil surface holding cover plate 16 is g ₃ , the size of each of these clearances is such that bubbles mixed or generated in the magnetic fluid 7 filled therein have the above-described rotation axis. 3 is one of the factors that cause the rotational load fluctuation.

According to experiments, in the case of the rotating shaft 3 having a diameter of 4 mm and 5 mm, the clearance g ₁ between the rotating shaft 3 and the inner wall surface of the bearing supporting cylindrical wall 4a is changed to change the rotating shaft 3
Observing the rotational unevenness (rotational fluctuation), it was found that the clearance g ₁ can satisfy the required specification value in the range of 0.15 mm or less, as shown in FIG. However, if the values of the clearances g _{1 to} g ₃ are made too small, the lubricity is lowered and the temperature rises. It was found that this tendency is the same for the other clearances g ₂ and g ₃ .

The magnetic fluid 7 is applied to the radial surface bearing 5 and the rotary shaft 3.
When the clearances g _{1 to} g ₃ around the rotor are filled with a lubricant, when the rotating shaft 3 is in a high-speed rotating state, the gas components mixed in the magnetic fluid 7 and the rotating shaft 3 and the bearing supporting cylindrical wall 4a at the time of assembly. Air adhering to the inner wall and the surface of the radial surface bearing 5 is deposited to generate bubbles in the magnetic fluid 7, and the bubbles move in the clearance. Since the movement of the bubbles is irregular, the magnetic fluid 7 is turbulent when combined and grows, and when it enters the clearance between the rotating shaft 3 and the bearing surface of the radial surface bearing 5, the rotating load of the rotating shaft 3 changes. Then, uneven rotation occurs. However, if the clearances g _{1 to} g ₃ are uniformly maintained at the above-mentioned values, the bubbles generated by the high speed rotation of the rotary shaft 3 have a narrow clearance and thus freely move and grow in the clearance. In other words, it is miniaturized, and the influence on the fluctuation of the rotational load of the rotary shaft 3 is reduced.

The liquid surface of the magnetic fluid 7 moving on the upper surface of the radial surface bearing 5 is rotated at a high speed and is deformed into a mortar shape. Thus, bubbles are generated in the magnetic fluid 7 to increase the rotational load fluctuation. The oil surface pressing lid plate 16
Covers the liquid surface of the magnetic fluid 7 so as to cover the liquid surface to prevent the liquid surface from changing into a mortar shape and prevent entrainment of air bubbles.

[0020]

According to the present invention, the clearance around the rotating shaft filled with the magnetic fluid is set to 0.15 mm or less to suppress the movement of bubbles in the magnetic fluid and reduce the fluctuation of the rotating load of the rotating shaft. It is possible to reduce fluctuations in the rotation load of the rotating shaft and reduce uneven rotation of the polygon mirror.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of a polygon mirror device according to the present invention.

FIG. 2 is an enlarged view of a main part of the polygon mirror device shown in FIG.

FIG. 3 is a rotation fluctuation characteristic diagram of the magnetic fluid bearing.

[Explanation of symbols]

 1 Polygon Mirror 2 Rotor 3 Rotating Shaft 4 Bearing Unit 4a Bearing Support Cylindrical Wall 5,6 Radial Surface Bearing 7 Magnetic Fluid

Claims (6)

[Claims] 1. A polygon mirror device having a rotating shaft supported by a magnetic fluid bearing, to which a polygon mirror for reflecting and deflecting a laser beam incident from a laser device while rotating is attached. A polygon mirror device characterized in that the clearance for filling the magnetic fluid is 0.15 mm or less. 2. The polygon mirror device according to claim 1, further comprising a cover plate that is in contact with the liquid surface of the magnetic fluid in the magnetic fluid bearing and covers the liquid surface. 3. The polygon mirror device according to claim 1, wherein the rotating shaft has a diameter of 4 mm to 5 mm. 4. A polygon mirror device having a rotating shaft supported by a magnetic fluid bearing, wherein a polygon mirror for reflecting and deflecting a laser beam incident from a laser device while rotating is attached to the polygon mirror device. The clearance that fills the magnetic fluid is set at the rotation speed of the rotating shaft of 10,000 to 40,000 r /
A polygon mirror device, characterized in that, in the region of min, the short cycle rotation unevenness of the rotary shaft is 0.01% or less and the long cycle rotation unevenness is 0.015% or less. 5. The polygon mirror device according to claim 4, wherein the clearance is 0.15 mm or less. 6. The diameter according to claim 4, wherein the rotating shaft has a diameter of 4 mm to 5 mm and the clearance is 0.1 mm.
A polygon mirror device characterized by being set to 5 mm or less.