Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-05-27
2002-07-02
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S212100, C359S216100, C360S099080, C310S090500, C310S261100
Reexamination Certificate
active
06414777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical deflection/scanning apparatus used in an image forming apparatus such as a laser beam printer or a laser facsimile device.
2. Related Background Art
An optical deflection/scanning apparatus used in an image forming apparatus such as a laser beam printer or a laser facsimile apparatus irradiates a light beam such as a laser beam on a rotary polygon mirror, and deflects and scans the beam by high-speed rotation of the rotary polygon mirror. The scanning beam obtained in this manner is formed into an electrostatic latent image on a photosensitive body serving as a recording medium. on a rotary drum. The electrostatic latent image on the photosensitive body is visualized into a toner image by a developing unit. The toner image is transferred to a recording medium such as a recording paper sheet and sent to a fixing unit. The toner on the recording medium is heated and fixed to print the image.
In recent years, as the speed of the optical deflection/scanning apparatus increases, one with a rotary polygon mirror whose rotational speed exceeds 5,000 rpm is developed.
As shown in
FIG. 1
, a motor for rotating the rotary polygon mirror comprises a rotating shaft
103
supported by an optical box of the optical deflection/scanning apparatus via a ball bearing
102
, a rotor
105
made up of a rotor yoke
105
a
integrally coupled to a flange member
104
integral with the rotating shaft
103
and a rotor magnet
105
b
, and a stator
107
fixed to a motor board
106
. A rotary polygon mirror
101
is pressed against the flange member
104
by an elastic press mechanism
108
made up of a leaf spring
108
a
, a washer
108
b
, and a G-ring
108
c
, and is integrated with the rotating shaft
103
and the rotor
105
.
When the stator
107
is excited by a driving current supplied from a driving circuit on the motor board
106
, the rotor
105
rotates at a high speed together with the rotary polygon mirror
101
to deflect and scan a light beam irradiated on the rotary polygon mirror
101
.
The rotor
105
is constituted by the rotor yoke
105
a
for ensuring a necessary structure strength (to be described later), and the rotor magnet
105
b
with magnetic properties. A material for the rotor yoke
105
a
is generally a metal or a reinforced plastic. As the rotor magnet
105
b
, a ferrite magnet, or a plastic magnet or so-called rubbernet prepared by kneading a ferrite in a resin and integrally molding them is used. The assembly of the rotor magnet
105
b
in the rotor yoke
105
a
is performed by fixing the rotor magnet
105
b
to the inner circumferential surface of the rotor yoke
105
a
using an adhesive, or press-fitting the rotor magnet
105
b
inside the rotor yoke
105
a.
Upon rotating the motor at a high speed, a large centrifugal force is generated in the rotor. If the rotor does not have a strength large enough to stand this force, the rotor may fracture, be divided, and scatter during rotation. Since the rotor magnet made of a rubbernet, a plastic magnet, or the like cannot be expected to have such a large strength, the rotor magnet is attached to the inside of the rotor yoke having a sufficient strength to form a strong structure which can stand the centrifugal force.
According to the prior art, however, even if the rotor magnet is attached to the inside of the rotor yoke having a sufficient strength, the lower end of the rotor magnetic easily cracks. This may lead division and fracture of the rotor magnet.
More specifically, as shown in
FIG. 2A
, the rotor yoke
105
a
is generally made of a sheet metal. A curved portion R
0
is formed at the lower end of the rotor yoke
105
a
as a press sag in processing the sheet metal. The outer circumferential surface of the lower end of the rotor magnet
105
b
cannot tightly contact the rotor yoke
105
a
, and a gap is made between the rotor yoke
105
a
and the rotor magnet
105
b
. When the motor rotates in this state, a centrifugal force A directly acts on the lower end of the rotor magnet
105
b
. As shown in
FIG. 2B
, a tensile stress is generated on the inner circumferential surface of the rotor yoke
105
a
near the start of the curved portion R
0
of the rotor yoke
105
a
, i.e., at one end at a center angle &thgr;
0
. Such portions where the tensile stress is generated successively exist in the circumferential direction at the lower end of the rotor magnet
105
b
. If the tensile stress exceeds the allowable stress of a material for the rotor magnet
105
b
, a crack S
0
is formed. If the crack S
0
grows and reaches the outer circumferential surface of the rotor magnet
105
b
, the lower end of the rotor magnet
105
b
is divided and fractures. As a result, the lower end of the rotor magnet
105
b
is lost, the rotation unbalance of the rotor
105
becomes very large, and large vibrations and noise are generated upon high-speed rotation.
FIG. 3
shows the example wherein a flange portion F
0
is formed at the lower end of a rotor yoke
205
a
, and a balance weight W
0
is attached to the flange portion F
0
in order to correct the rotation unbalance of a rotor
205
(balance correction). In this case, since the lower end of the rotor yoke
205
a
is bent, a curved portion R
0
having a center angle &thgr;
0
larger than that in the example of
FIGS. 2A and 2B
is easily formed. Therefore, the lower end of a rotor magnet
205
b
cracks and fractures more easily.
FIGS. 4A and 4B
show the example using a rubbernet as a rotor magnet
305
b
. The rubbernet is rolled by a roller during the manufacturing process. Small antislip projections are formed on the surface of the roller, and dimples D
0
are formed on the surface of the rotor magnet
305
b
by rolling.
Since the dimple D
0
is a recess having a quadrangular pyramid shape. Upon generation of the above tensile stress, the stress concentrates at the dimple D
0
, and the crack S
0
is easily formed. Since the dimples D
0
are aligned near each other in the circumferential direction at an equal interval, a crack so growing from the edge of a dimple D
0
in the circumferential direction is connected to an adjacent crack. In this manner, the cracking and fracture of the lower end of the rotor magnet
305
b
progress at a breath.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems of the prior art, and has as its object to provide an optical deflection/scanning apparatus in which the speed of a rotary polygon mirror can be greatly increased while preventing troubles such as separation and fracture of the lower end of the rotor of a motor by a centrifugal force during the rotation of the rotary polygon mirror.
To achieve the above object, according to the present invention, there is provided an optical deflection/scanning apparatus comprising a rotary polygon mirror for reflecting a light beam, and a motor for rotating the rotary polygon mirror, the motor having a rotor yoke with a curved portion at one end, and a rotor magnet attached to an inside of the rotor yoke, wherein the curved portion of the rotor yoke projects from one end of the rotor magnet in a direction of height.
The optical deflection/scanning apparatus may comprise a rotary polygon mirror for reflecting a light beam, and a motor for rotating the rotary polygon mirror, the motor having a rotor yoke with a curved portion at one end, and a rotor magnet attached to an inside of the rotor yoke, wherein one end of the rotor magnet is made locally thin at the same level as the curved portion of the rotor yoke.
The optical deflection/scanning apparatus may comprise a rotary polygon mirror for reflecting a light beam, and a motor for rotating the rotary polygon mirror, the motor having a rotor yoke with a curved portion at one end, and a rotor magnet attached to an inside of the rotor yoke, wherein a gap between one end of the rotor magnet and the curved portion of the rotor yoke is filled with a filler.
The optical deflection/scanning apparatus may comprise a rotary polygon
Cherry Euncha
Spyrou Cassandra
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