Optical deflector and optical scanner

Details Optical deflector and optical scanner Optical deflector and optical scanner

1999-12-06

2001-02-13

Schuberg, Darren (Department: 2872)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S198100, C359S216100, C310S090500

Reexamination Certificate

active

06188503

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical deflector and an optical scanner including the optical deflector, which are applied to, for example, image formation apparatuses such as a laser printer, a facsimile, and a copier.
2. Description of the Related Art
FIG. 15
shows an example of a conventional optical deflector
310
applied to an image formation apparatus (Japanese Published Unexamined Patent Application No. Sho 63-259510).
In the optical deflector
310
, a rotary axis
314
provided with a mirror
312
is fitted to a stationary axis
316
, and a thrust magnet
326
mounted on the top end of the rotary axis
314
is disposed between a thrust magnet
318
mounted on the top end of the stationary axis
316
and a top magnet
324
mounted on the top cover
322
of a case
320
. By repelling the thrust magnet
326
mutually by the thrust magnet
318
and the top magnet
324
, the rotor is floated to hold it at a predetermined position. Thereby, a so-called dynamic pressure air bearing is constituted, making it possible to rotate the rotor fast and stably. The thrust magnet
326
of the rotor
314
is opposite to the top magnet
324
of the top cover
322
with a small gap, with the result that disengagement of the rotor from the stationary axis
316
is prevented.
However, since three magnets are required to float the rotor, the number of parts of the optical deflector
310
itself increases, resulting in a higher cost. Also, the case
320
requires the top cover
322
to mount the top magnet
324
, boosting cost again. In addition, such a vertical placement of the three magnets in the vicinity of the top end of the stationary axis
316
makes it difficult to make the optical deflector
310
a flat construction, causing expansion of the optical deflector
310
itself in the axial direction.
On the other hand, in an optical deflector
340
shown in
FIG. 16
(see Japanese Published Unexamined Patent Application No. Hei 5-249398), a ring-shaped groove
346
is provided in the circumference of a rotor yoke
344
secured to a rotary axis
342
. By inserting, in the groove
346
in a not-contacted manner, one end of an anchoring member
350
provided in a housing
348
, disengagement of a rotary member is prevented.
In an optical deflector shown in
FIG. 17
(see Japanese Published Unexamined Patent Application No. Hei 6-165428), disengagement of a rotor is prevented by a disengagement prevention plate
386
mounted between a polygon mirror
382
and a rotor magnet
384
.
However, since these optical deflectors
340
and
380
rotatably hold a rotating member by a so-called dynamic fluid bearing, it is difficult to rotate a rotating member at high speed, in comparison with the optical deflector
310
employing a dynamic airbearing shown in FIG.
15
. In the case of the dynamic fluid bearing, when the optical deflectors
340
and
380
are, for example, horizontally, obliquely, or inversely placed, to prevent possible leak of lubricating fluid, the dynamic fluid bearing must be sealed in the circumference thereof, making the construction complicated.
Furthermore, since the dynamic fluid bearing constructionally requires that a mechanism for disengagement prevention be provided in the vicinity (a portion larger the diameter) of the outer circumference of a rotating member, contact between the anchoring member
350
and the ring-shaped groove
346
in the optical deflector
340
shown in
FIG. 16
might cause so-called rotation unbalance in the rotating member.
SUMMARY OF THE INVENTION
In view of such facts, present invention provides an optical deflector that enables a rotary polygon mirror to rotate at high speed with high reliability and a low noise level, and can prevent the rotary polygon mirror from disengaging from a stationary axis with a compact and simple construction, and an optical scanner including the optical deflector.
The optical deflector preferably comprises a stationary axis; a rotor including at least a rotary axis disposed with a predetermined gap from the stationary axis and capable of rotating about the stationary axis, a rotary polygon mirror rotating integrally with the rotary axis, and driving magnets attached to at least one of the rotary axis and the rotary polygon mirror; holding magnets for holding the rotor at a predetermined holding position in the axial direction of the stationary axis by magnetic force; and a disengagement prevention member, mounted in the vicinity of an end of the stationary axis in the axial direction with a predetermined gap in the axial direction from the rotor, coming into contact with the rotor moving in the axial direction and preventing the rotor from disengaging from the stationary axis.
Accordingly, magnetic force acting on the driving magnets acts on the rotor as rotation driving force, causing the rotor to rotate. Since the rotary polygon mirror making up the rotor also rotates, light irradiated on the rotary polygon mirror is subjected to main scanning.
A predetermined gap is maintained between the stationary axis and the rotary axis making up the rotor, which serves as so-called dynamic air bearing. The rotor is held at a predetermined position in the axial direction of the stationary axis by the magnetic force of the holding magnets. By virtue of this construction, the rotary polygon mirror can be rotated at high speed, and for example, if an optical scanner including the optical deflector is applied to an image formation apparatus, images of high quality can be formed at high speed. Also, no contact between the stationary axis and the rotary axis and the nonexistence of other members intervening therebetween cause no noise and vibration, increasing durability and reliability.
A disengagement prevention member is provided in the vicinity of an end of the stationary axis. Therefore, with a simple construction and at a low cost, the rotor can be prevented from disengaging from the stationary axis when moving in the axial direction with respect to the stationary axis. Since the disengagement prevention member is also provided with a predetermined gap from the rotor and is not in contact with the rotor, the rotor can be rotated at high speed. Also, since no noise or less noise and vibration occur, high durability and reliability are maintained.


REFERENCES:
patent: 5963353 (1999-10-01), Shibuya et al.
patent: 6031651 (2000-02-01), Nakasugi
patent: 6064130 (2000-05-01), Konno et al.
patent: 58-196564 (1983-12-01), None
patent: 63-259510 (1988-10-01), None
patent: 2-266856 (1990-10-01), None
patent: 3-249418 (1991-11-01), None
patent: 4-107313 (1992-04-01), None
patent: 5-249398 (1993-09-01), None
patent: 6-165428 (1994-06-01), None
patent: 6-186491 (1994-07-01), None

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