JPH0418511A - Mirror rotating motor - Google Patents

Abstract

PURPOSE:To suppress the inclination of a revolving shaft due to disturbance by storing a mirror, which controls the centroid position of a rotating system, in an annular recessed part of a bearing member. CONSTITUTION:An annular recessed part 40 where a polygon mirror 14 is stored is formed in the middle of a bearing member 4. This recessed part 40 is cut at a prescribed angle in the peripheral direction to pierce a motor outside part 12, and a scanning light passing hole 41 is formed where the scanning optical path through which the laser light emitted from a light source is made incident and the reflected light is scanned on a body to be scanned is secured. A rotating body 1 is provided with a step part 1b in a position corresponding to the annular recessed part 40 in the bearing member 4 to support the polygon mirror 14 in an about center, and dynamic pressure air bearings 7 and 7 are provided at least in two positions on both sides of the polygon mirror 14. Thus, the revolving shaft is not inclined regardless of disturbance (oscillation) in the transverse direction, and the scanning precision is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a motor whose rotor portion is supported by a hydrodynamic air bearing and which rotates an optical mirror, such as a polygon mirror.

More specifically, the present invention relates to a mirror rotation motor suitable for use in an optical scanning device using a polygon mirror.

(Prior Art) In optical scanning devices using polygon mirrors used in laser beam printers, facsimile machines, etc., a motor incorporating a hydrodynamic air bearing as shown in Fig. 5 is used to rotate the polygon mirror at high speed. is used.

This motor consists of a rotating body 10 to which a magnet 102 is attached.
1 and the inner circumferential surface 106 of a cylindrical bearing member 104 with a coil 105 arranged in the center.
07 to provide support in the radial direction,
A magnet 108.1 is placed between the rotating body 101 and the bearing member 104.
A thrust magnetic bearing 110 that utilizes the attraction force of 09 is constructed to provide support in the axial direction. In this motor, a mirror 114, which is an object to be rotated, is fixed to the upper end of the rotating body 101. In addition, 111 is inside the motor, 112 is outside the motor, 11
3 indicates a ventilation hole.

(Problem to be solved by the invention) However, the conventional polygon mirror rotation motor
Since a polygon mirror 114 is attached to the upper side of the rotating body 101 and its lower part is supported by a dynamic pressure air bearing 107, the center of gravity G of the rotating body 101 and the dynamic pressure are There is a possibility that the dynamic pressure center P of the air bearing 107 is separated in the axial direction, and the rotating body (rotor) 101 may be tilted due to disturbance (vibration) from the lateral direction. In particular, since the polygon mirror 114 has a relatively large mass, this tendency is remarkable.

If the movement of the hydrodynamic air bearing 107 increases and the tilt of the rotation axis of the polygon mirror 114 increases, for example in a laser beam printer, scanning lines will become uneven and the quality of the image formed will deteriorate. Improvement is desired. SUMMARY OF THE INVENTION An object of the present invention is to provide a mirror rotation motor that can suppress inclination of a rotation axis against disturbances such as lateral vibrations.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a rotating body that supports a mirror and a cylindrical bearing member that accommodates this rotating body, so that the outer peripheral surface of the rotating body is fitted. A dynamic pressure air bearing is configured between the inner circumferential surface of the bearing member and a stator side which is arranged at the center of the bearing member and fixed to the bearing member. In a mirror rotation motor that constitutes a motor with a coil, four annular portions are provided in the middle of the bearing member in the circumferential direction to accommodate the mirror, and a portion of the bearing member is cut out in the recess to transmit scanning light. While a passage opening is formed, at least two dynamic pressure air bearings are formed on both sides of the mirror.

(Function) Since the mirrors that control the center of gravity of the rotating system are housed in the four annular parts of the bearing member, the center of gravity of the rotating body is located inside the two hydrodynamic air bearings, and the center of gravity of the rotating body is The position and center of dynamic pressure almost coincide in the lateral direction.

(Example) Hereinafter, the configuration of the present invention will be described in detail based on an example shown in the drawings. This embodiment is applied to a rotation drive device for a polygon mirror used in an optical scanning device such as a laser printer or a facsimile machine.

The polygon mirror rotation drive device includes a rotating body (rotor) 1 that supports a polygon mirror 14 and rotates, and this rotating body 1.
and a cylindrical bearing member 4 that accommodates the polygon mirror 14 and constitutes a hydrodynamic air bearing 7.7 between it and the rotating body 1, and a center ball that is disposed at the center of this bearing member 4 and supports the coil 5. 15, a base member 16 that supports the center ball 15 and closes the bottom of the bearing member 4, and a bearing member 4 (
I! ! It mainly consists of a small control motor 17 constituted by a drive coil 5 fixed to I and a rotor magnet 2 fixed to the rotating body 1 side.

An annular recess 40 for accommodating the polygon mirror 14 is formed in the middle of the bearing member 4 . Furthermore, this recess 40 is notched in the circumferential direction at a predetermined angle, for example, in the range of 90 to 180 degrees, preferably in the range of 90 to 120 degrees, and penetrates into the motor exterior 12, so that laser light emitted from a light source (not shown) is incident thereon. In addition, a scanning light passage opening (1) is formed to ensure a scanning optical path for scanning the reflected light onto an object to be scanned (not shown). Further, a flange 32 is formed on the outer peripheral surface of the bearing member 4 for attaching the motor to a housing 31 of an optical scanning device such as a laser printer. still,
It is preferable that the inner circumferential surface 6 of the bearing member 4 be subjected to a surface treatment to improve its wear resistance. For example, it is provided with a wear-resistant coating or a lubricating coating as disclosed in JP-A-63-235749.

The rotary body 1 has a stepped portion 1b formed at a position corresponding to the annular recess 40 in the bearing member 4 to support the polygon mirror 14 approximately in the center, and at least two places on both sides of the polygon mirror 14 are provided with dynamic pressure air. For example, the rotating body 1 is composed of a large cylindrical portion 1b and a small cylindrical portion 1a, and a group 42 for generating dynamic pressure is etched on the outer circumferential surface 3 of each. Approximately 51111 ~
It is formed at a depth of 20IIfl. polygon mirror 1
4 is fitted into the small cylindrical portion 1a of the rotary body 1, for example, a wave spring 36 and a spring retainer 37 are placed thereon, and the plate 38 is fixed by press-fitting into the small cylindrical portion 1a. The polygon mirror 14 is pressed against the shoulder portion 1c of the rotating body 1 by the elastic force of the waveform spring 36, and is fixed at the same time as being positioned. Note that the rotating body 1 of the polygon mirror 14
The method of fixing is not particularly limited to the above-mentioned method, and for example, laser spot welding or the like may be used for fixing.

The hydrodynamic air bearings 7, 7 are not particularly limited in their structure or size. For example, as shown in FIG. 4(A), two pairs of herribone groups 42 are formed facing each other. Alternatively, as shown in FIG. 4(B), a pair of groups 42 are arranged facing each other with a polygon mirror 14 in between, and when the rotating body 1 is rotated in the direction of the arrow in the figure, the central scanning light passage opening 41 is opened. Group 42 by introducing air
The pressure may be formed so as to be discharged toward both ends of the bearing member 4 through the upper group 42. In this way, the pressure on the upper end side of the upper group 42 and the lower fIA 111I of the lower group 42 can be increased. . In the case of the configuration shown in FIG. 3 (A), if rotation #1 is rotated in the direction of the arrow in FIG. Dynamic pressure bearing action is maintained.

Further, on the outer peripheral surface 3 on which the group of rotating bodies 1 is formed,
Similar to the inner peripheral surface 6 of the bearing member 4, it is preferable to apply a surface treatment (Japanese Patent Application Laid-open No. 63-235719) to improve wear resistance. A yoke 35 is fixed thereto, and a cylindrical drive magnet 2 is fixed further inside the yoke 35.

Furthermore, due to machining errors in the rotating body 1 or installation errors when attaching the polygon mirror 14 to the rotating body 1, the center of gravity of the entire rotating system including the polygon mirror 14 may shift upward from the rotation axis, causing the rotational balance to be lost. In order to prevent vibration, a thick wall portion 1d is formed at the top of the top portion, and a hole is provided so that a blank hole can be drilled for balance adjustment if necessary.

Note that the internal space 11 formed by the fitting of the rotating body 1 and the bearing member 4 becomes a substantially sealed space when the rotating body 1 vibrates in the axial direction, and constitutes an air chamber. however,
This internal space 11 is exposed to the outside of the motor by a gap between the ventilation hole 3 and the dynamic pressure air bearing 7.

A center ball 15 disposed at the center of the bearing member 4 is fixed to the base 5 member 16 with a screw or the like. A stator core 21 is fitted onto the outer peripheral surface of the center ball 15, and the coil 5 is wound between coil plates 19 fitted into the stator core 21. The coil plate 19 has a shape or T to prevent the coil 5 from coming off.
shaped claw portions 20 protrude in the radial direction at regular intervals,
The coil 5 is wound using the claw portion 20 and then fixed with synthetic resin. The coil plate 19 is made of a non-magnetic material such as plastic or ceramics.

A pair of ring-shaped magnets 8 and 9 constituting the thrust l-magnetic bearing 10 are fixed to the center ball 15 on the stator side and on the rotating body 1 side so as to face each other.

These magnets 8 and 9 are magnetized in the axial direction so that their opposing surfaces or poles attract each other, thereby causing the entire rotating body 1 including the polygon mirror 14 etc. to levitate. .

Further, although not shown, a frequency power generation magnet for rotational speed detection and a detection circuit board are installed between the center ball 15 and the rotating body 1 as necessary. Further, a driving circuit board 22 for the motor 17 is screwed under the base member 16, and together with the base member 16, it closes the bottom of the bearing member 4 and creates a gap between the inside 11 and the outside 12 of the motor. Block the air circulation. Incidentally, the base member 16 is appropriately formed with a draw-out hole for drawing out the lead wires connected to the drive coil 5 and the circuit board 22 to the outside as necessary. Furthermore, although not shown, a protective cover may be attached as necessary.

According to the mirror rotation motor of the present invention configured as described above, a dynamic pressure distribution as shown in FIG. The tilt of the tilted rotation axis placed at the position is approximately O. On the other hand, in a conventional mirror rotation motor, the center P of pressure distribution and the center of gravity G are far apart, so when lateral acceleration is applied to the rotor, the rotation axis is tilted by an angle θ as shown in the figure.

It should be noted that although the above-described embodiment is an example of a preferred embodiment of the present invention, the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

(Effects of the Invention) As is clear from the above description, the mirror rotation motor of the present invention provides a circumferential annular recess in the middle of the bearing member to accommodate the mirror and ensure a scanning optical path. At least two dynamic pressure air bearings are formed on both sides of the mirror to ensure that the center of pressure distribution and the center of gravity of the rotating body are at approximately the same location, so even if lateral disturbances (vibrations) are applied, the rotation will not occur. The axis does not tilt, improving scanning accuracy.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an example in which the present invention is implemented as a motor for rotating a polygon mirror. Figure 2 shows U-It I! of Figure 1. FIG. 2 is a sectional view showing only the bearing member along . FIGS. 3A and 3B are explanatory diagrams illustrating an example of a dynamic pressure air bearing in a group formed as a rotating body. FIG. 4 is an explanatory diagram showing the position of the center of gravity of the rotating body and the pressure distribution state of the hydrodynamic air bearing, where (A) is for a conventional mirror rotation motor, and (B) is for the mirror rotation motor of the present invention. It is. FIG. 5 is a central vertical sectional view schematically showing a conventional mirror rotation motor. DESCRIPTION OF SYMBOLS 1... Rotating body, 2... Magnet, 3... Outer peripheral surface of rotating body, 4... Bearing member, 5... Coil, 6...
・Inner peripheral surface of bearing member, 7...Dynamic pressure air bearing, 14...
- Polygon mirror, 40... annular recess, 41... scanning light passage port. Patent applicant Sant! Co., Ltd. Precision equipment factory fee
Attorney Patent Attorney Murase -Bi Figure Figure (A) Figure (B) Figure (A) Figure (B) Figure B

Claims (1)

[Claims] A rotating body supporting the mirror and a cylindrical bearing member housing the rotating body are fitted to form a hydrodynamic air bearing between the outer circumferential surface of the rotating body and the inner circumferential surface of the bearing member. In a mirror rotation motor in which a motor is configured between a magnet attached inside a rotating body and a stator-side coil arranged at the center of the bearing member and fixed to the bearing member, a circle is formed in the middle of the bearing member. A circumferential annular recess is provided to accommodate the mirror, and a part of the bearing member is cut out in the recess to form a scanning light passage opening, while at least two hydrodynamic air bearings are provided on both sides of the mirror. A mirror rotation motor characterized by forming a part.