Optical: systems and elements – Deflection using a moving element
Reexamination Certificate
1998-06-16
2001-09-04
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
C359S197100, C359S212100, C359S216100
Reexamination Certificate
active
06285482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical deflecting-scanning apparatus used in such image forming apparatus as laser beam printers or digital copiers.
2. Related Background Art
The optical deflecting-scanning apparatus used in such image forming apparatus as laser beam printers or digital copiers is constructed to reflect a light beam such as a laser beam by a rotary polygon mirror and deflect the beam to scan with high-speed rotation of the rotary polygon mirror. The scanning light thus obtained is focused on a photosensitive member on a rotating drum to form an electrostatic latent image thereon. Then the electrostatic latent image on the photosensitive member is developed into a toner image by a developing device, this image is transferred onto a recording medium such as a recording sheet, then the sheet is sent to a fixing device, and the toner on the recording medium is heated to be fixed by the fixing device, thereby achieving printing (print).
With increase in speed of the digital copiers etc., there are recently developed machines with the rotating speed of the rotary polygon mirror being over 30,000 rpm.
FIGS. 1A and 1B
illustrate the main portion of an optical deflecting-scanning apparatus according to a conventional example, wherein the apparatus has a bearing
101
supported on an optical box (not illustrated) a motor
102
comprised of a rotor rotatably supported by the bearing
101
and a stator opposed thereto, and a rotary polygon mirror
103
integrated with the rotor by an elastic press mechanism or the like.
When the stator of the motor
102
is excited by driving current supplied from a driving circuit on a motor board, the rotor rotates the rotary polygon mirror
103
at high speed so as to deflect the light beam irradiating the rotary polygon mirror
103
to scan.
The rotary polygon mirror
103
is a polygonal member of a polygonal prism shape having a plurality of reflective surfaces, and the upper part of the rotary polygon mirror
103
and the motor is covered by a cover member
104
. As the rotary polygon mirror
103
rotates at high speed, the air around it flows to cause wind noise or the like. Therefore, the apparatus is designed so as to prevent the wind noise or the like from leaking to the outside of the apparatus, by covering the periphery of the rotary polygon mirror
103
by the cover member
104
.
The peripheral wall of the cover member
104
is provided with a window
104
a
opening so as not to intercept the light beam L
0
incident into and emergent from the rotary polygon mirror
103
. The window
104
a
is an aperture formed by removing a part in an arcuate shape from the peripheral wall of the cover member
104
, and a dustproof glass member
105
is attached to the window
104
a.
With a conventional technology described above, however, the pressure gradient occurs in the air in the cover member with rotation of the rotary polygon mirror, so as to increase vibration sound etc. of the motor, and there is an unsolved issue that the noise cannot be suppressed sufficiently by simply covering the periphery of the rotary polygon mirror by the cover member.
In general, the noise appearing with high-speed rotation of the rotary polygon mirror results from superposition of various types of noise, which can be roughly classified under three types. The first type is the wind noise (air sound) produced when the rotary polygon mirror causes the air in the cover member to flow with rotation thereof, and leaking from the optical box; the second type is the vibration sound caused in such a way that rotation of the rotary polygon mirror creates a pressure gradient in the air in the cover member and that the stator (coil) of the motor vibrates with receiving reaction force when the rotary polygon mirror is rotated at high speed against the load; the third type is great noise caused by resonance or forced excitation or the like when such vibration of the stator propagates to the cover member and the optical box.
The cover member of the conventional example is designed to focus on only the first wind noise and simply covers the periphery of the rotary polygon mirror so as to prevent the wind noise from leaking to the outside. As long as the rotating speed of the rotary polygon mirror is relatively low, the wind noise itself is small and is not so significant even with a little leakage thereof from the cover member. The wind noise leaking from the cover member, however, increases with increase in the speed of the optical deflecting-scanning apparatus, and the second and third vibration sound is added to this, thereby resulting in heavy noise.
FIG. 2
illustrates the air flow created in the cover member with rotation of the rotary polygon mirror, from which it is observed that the density of the air flow is small near the window of the cover member and as a consequence, the pressure of the air is locally decreased to create the pressure gradient.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the unsolved issue of the above conventional technology, and an object of the present invention is to provide an optical deflecting-scanning apparatus that can greatly decrease the noise caused with rotation of the rotary polygon mirror.
For accomplishing the above object, an optical deflecting-scanning apparatus of the present invention comprises a rotary polygon mirror for deflecting a light beam to scan, driving means for rotationally driving the rotary polygon mirror, and a cover having a cylindrical portion to cover the peripheral surface of the rotary polygon mirror, wherein the cylindrical portion of the cover comprises an annular slit extending in the circumferential direction of the rotary polygon mirror, said slit opening along the entire circumference of the rotary polygon mirror.
In a preferred embodiment, the cover comprises a first cylindrical member to cover a top half of the rotary polygon mirror, and a second cylindrical member to cover a bottom half of the rotary polygon mirror and the annular slit is formed between the first and second cylindrical members.
In the optical deflecting-scanning apparatus of the present invention, the annular slit extending in the circumferential direction of the rotary polygon mirror is formed in the cylindrical portion of the cover covering the peripheral surface of the rotary polygon mirror, and the light beam is incident or emergent through a portion of the slit. Since the uniform flow passage having the annular slit is formed along the peripheral surface of the rotary polygon mirror, the air flow generated with rotation of the rotary polygon mirror is uniform in the circumferential direction in the cover.
Accordingly, the present invention can prevent occurrence of the pressure gradient in the cover, which was seen in the case where the window for incidence and emergence of the light beam was made by removing a part of the cover in the arcuate shape, and hence the vibration noise etc. due to the pressure gradient can be reduced remarkably.
Since the light beam irradiating the rotary polygon mirror is a beam of a sheet shape with a small thickness as converged in the axial direction of the rotary polygon mirror, the width of the slit for incidence and emergence thereof can be set small. Use of the annular slit with the small width achieves the effect of greatly reducing an amount of input and output air through the cover with rotation of the rotary polygon mirror and the effect of reducing a trouble such as noise or pollution with input and output of the air.
REFERENCES:
patent: 4930869 (1990-06-01), Miyagawa et al.
patent: 4934836 (1990-06-01), Tanaka et al.
patent: 5046797 (1991-09-01), Kurisu et al.
patent: 0 618 469 (1994-10-01), None
patent: 0 692 726 (1996-01-01), None
patent: 61-97620 (1986-05-01), None
patent: 2-99910 (1990-04-01), None
patent: 7-64010 (1995-03-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Phan James
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