Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-02-03
2001-06-05
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S216100, C310S051000
Reexamination Certificate
active
06243187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polygonal mirror device for an optical scanning used in an image forming apparatus for optically forming an image, such as a laser printer.
2. Description of the Related Art
FIG. 2
is a cross sectional view showing a conventional polygonal mirror device.
As shown, a polygonal mirror
1
is formed around an outer peripheral surface of a rotor member
2
, and the rotor member
2
is rotatably fitted to a shaft
4
, which is mounted to a housing
3
a
. A specific groove is formed on the shaft
4
, to thereby form a hydrodynamic gas bearing which generates a dynamic pressure when the rotor member
2
rotates.
The rotor member
2
includes a motor magnet
5
. A stator core
6
, a coil
7
and a motor board
8
are mounted on the housing
3
a
to face the motor magnet
5
. The coil
7
is magnetically excited to rotate the rotor member
2
.
And a magnetic attraction force is generated between the motor magnet
5
and the stator core
6
. At this time, the rotor member
2
poises at a position where the attraction force balances a weight of the rotor member
2
. A dynamic unbalance of the rotor member is corrected by cutting a surface C and a surface D of the rotor member
2
, such as a small drill, whereby generation of mechanical vibration of the rotor member
2
is suppressed to maintain a stable rotation of the rotor member
2
. Holes
10
as cutting traces are left at specific positions on the surfaces C and D.
The rotor member
2
is covered with the housing
3
a
and a housing
3
b
as well, thereby preventing reflecting faces
1
a
of the polygonal mirror
1
from being soiled with dust and the like. A light beam goes into and out of the polygonal mirror device, through a window (not shown) formed in the housing
3
b
, in order to form a scan beam of light by the polygonal mirror
1
.
As described above, the conventional art corrects the dynamic unbalance of the rotor member by cutting the surface C and the surface D of the rotor member
2
as correcting portions by means of a drill, whereby generation of its mechanical vibration is suppressed to maintain a stable rotation of the rotor member
2
. Therefore, the holes
10
as cutting traces are left at specific positions on the surfaces C and D. Because of a centrifugal load generated by the rotation of the rotor member
2
, the rotor member
2
is deformed in the radial direction. When the holes
10
are nonuniformly present on the rotor member
2
, the rotor member
2
is also nonuniformly deformed in the radial direction. A height of the surface C is equal to that of the reflecting faces
1
a
of the polygonal mirror
1
measured from the same. Accordingly, the reflecting faces
1
a
of the polygonal mirror
1
formed on the outer peripheral surface of the rotor member
2
are also deformed nonuniformly, so that the reflecting faces
1
a
are strained by the centrifugal load. As a result, an accuracy of the light beam deflection for scanning is degraded, and when the polygonal mirror device is applied to, for example, a laser beam printer, this leads to a variation of a scanning angle by the rotation of the polygonal mirror device, and to deterioration of the print quality of the printer.
When the surface C is bored by the cutting means, the resultant hole
10
infrequently passes through the rotor member
2
and reaches the surface E located opposite to the surface C. When the through-hole reaches the surface E, the surface E is burred. The rotor member
2
is rotated at extremely high speed of 40,000 rpm. If the burr is left as it is, the burr is separated from the surface E by a centrifugal force, and will reach the reflecting faces
1
a
of the polygonal mirror
1
, thereby possibly damaging the reflecting faces
1
a
. This brings about degradation of an accuracy of the light beam deflection for scanning. When it is applied to a laser beam printer, for example, a problem of deterioration of the print quality of the printer arises. To cope with this, it is necessary to remove the burr of the surface E by use of a reamer or a drill bit of which the diameter is larger than the diameter of the through-hole.
In the structure of the polygonal mirror device, the motor magnet
5
, the stator core
6
and a ring portion (motor portion) including a coil are arrayed near the surface E. Accordingly, the surface E and its vicinal region are more complicated in configuration than the surface C and its vicinal region. This makes it difficult to remove the burr. For this reason, some of the burr remains on the surface E.
In
FIG. 2
, the diameter of the inner surface
11
of a portion of the rotor member
2
, which is located near the surface E and to be abutted against the motor magnet
5
, is larger than the inside diameter of the motor magnet
5
. Therefore, when after the boring, the surface E and its vicinal region are cleaned by use of a compressed-air blowing machine, such as an air gun, part of cutting particles produced when the rotor member
2
is cut remains on the surface E and its vicinal region. If the burr and the cutting particles remaining on the surface E and its vicinal region are left, the burr and the cutting particles are separated from the surface E by a centrifugal force, and will reach the reflecting faces
1
a
of the polygonal mirror
1
, thereby possibly damaging the reflecting faces
1
a
. This brings about degradation of an accuracy of the light beam deflection for scanning. When it is applied to a laser beam printer, for example, a problem of deterioration of the print quality of the printer arises.
Attempt to make it easy to remove the burr on the surface E will limit a freedom in designing the motor portion including the stator core
6
and the coil
7
. Further, when the work of correcting the dynamic unbalance is done on the surface C, and successively it is done on the surface D, it is required to invert the rotor member
2
or to use a couple of opposed cutting means. As a result, the number of manufacturing steps or cost of related equipment is increased.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a polygonal mirror which prevents the reflecting faces of the polygonal mirror from being strained by a centrifugal load applied thereto and heat thereof, makes it easy to remove burr and cutting particles, which are generated in the work of correcting a dynamic unbalance, and is excellent in a light-beam deflection for scanning accuracy, and further to provide a polygonal mirror device which reduces the number of manufacturing steps and cost of related equipment.
The present invention succeeds in solving the above problems in the following ways.
An annular groove is formed on the upper surface, or a surface C, of a rotor member. Execution of correcting means for correcting a dynamic unbalance of a rotor member is carried out at a portion closer to the center than an annular groove as radially viewed. When the portion closer to the center than an annular groove as radially viewed is cut by a cutting means, typically a small drill, the resultant hole
10
left in the rotor member is limited in location to the portion closer to the center than an annular groove as radially viewed. If a height of the potion where the hole
10
remains measured from the housing is equal to that of the reflecting faces of the polygonal mirror, as nonuniform deformation of the rotor member
2
in the radial direction, which is caused by the centrifugal load generated with the rotation of the rotor member
2
, reaches the wall of an annular groove which defines its inside diameter, but it does not reach the wall thereof which defines its outside meter since it is interrupted by the annular groove. Therefore, even if the rotor member
2
is rotated and a centrifugal load acts on the rotor member, the reflecting faces
1
a
of the polygonal mirror are not strained.
Similarly, a nonuniform thermal expansion of the rotor member
2
, which is caused by a temperature rise occurring by the rotation of
Inenaga Hiroshi
Sakamoto Junshin
Hitachi Koki Co,. Ltd.
Schuberg Darren
Sughrue Mion Zinn Macpeak & Seas, PLLC
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