Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1997-10-07
2002-09-10
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S261000, C347S243000, C359S882000, C359S855000
Reexamination Certificate
active
06449000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a deflection scanning apparatus used in a laser beam printer or the like, and more particularly to a deflection scanning apparatus which can prevent noise generation or performance degradation due to vibration during rotation of a rotary polygon mirror therein.
2. Related Background Art
Laser beam printers and laser facsimile machines employ a deflection scanning apparatus, in which a photosensitive drum is scanned with a beam deflected and scanned by a deflector to form an electrostatic latent image thereon. This electrostatic latent image is visualized as a toner image by a developing device and the toner image is transferred onto a record sheet. Subsequently, the record sheet with the transferred toner image is guided through a fixing device to heat-fix the toner on the sheet to complete printing.
FIG. 1
is a plan view to illustrate the structure of a deflection scanning apparatus used in a laser beam printer for scanning a photosensitive member with a beam.
A deflection scanning apparatus
151
is enclosed in a housing
152
.
FIG. 1
is a plan view of the apparatus in housing
152
, a cover of which is removed. The scanning optical apparatus
151
is constituted by a light source
153
including a semiconductor laser device and a collimator lens system, a cylindrical lens
154
for condensing light emitted from the light source
153
into a linear beam, a rotary polygon mirror
155
having a deflection-reflecting surface
155
a
in the vicinity of a linear image of the beam condensed by the cylindrical lens
154
, and an f&thgr; lens
156
. The deflection-reflecting surface
155
a
deflects or reflects the beam. The thus deflected or reflected beam passes through the f&thgr; lens
156
then to impinge on a reflecting mirror
157
. The reflecting mirror
157
reflects the beam so that it irradiates a photosensitive drum
158
which is a recording medium.
The rotary polygon mirror
155
has a cross section of a regular hexagon perpendicular to the axis and uniform in the axial direction and has side faces of a reflecting mirror, which constitute the deflection-reflecting surface
155
a
. The rotary polygon mirror
155
is driven by a motor
159
to rotate at constant speed in the direction of arrow
171
about the axis. The rotation changes with time an angle between an optical path of the beam generated from the light source
153
and then passing through the cylindrical lens
154
and the normal line to the deflection-reflecting surface
155
a
, which is an incident angle of beam into the deflection-reflecting surface
155
a
. Since an angle of reflection changes with the change of incident angle, the beam forms a spot on the photosensitive drum
158
, moving in the direction of arrow
160
in FIG.
1
.
The f&thgr; lens
156
is so designed that the beam reflected on the deflection-reflecting surface
155
a
is focused to form a spot on the photosensitive drum
158
and that the scanning speed of the spot is kept uniform in the direction of arrow
160
. To obtain such characteristics of f&thgr; lens
156
, the f&thgr; lens
156
is composed of two lens systems, which are a first f&thgr; lens element
161
and a second f&thgr; lens element
162
.
The rotation of rotary polygon mirror
155
in the direction of arrow
171
effects the main scan of beam on the photosensitive drum
158
, while the sub-scan is carried out by rotating the photosensitive drum
158
around the axis thereof. An electrostatic latent image is thus formed on the surface of photosensitive drum
158
.
Arranged around the photosensitive drum
158
are a corona discharger for uniformly charging the surface of photosensitive drum
158
, a developing device for developing the electrostatic latent image formed on the surface of photosensitive drum
158
to form a visual toner image, and a transfer corona discharger for transferring the toner image onto a recording sheet, which are not shown. They work to print the record information according to the beam emitted from the light source
153
on the recording sheet.
A reflecting mirror
173
is provided between the first f&thgr; lens element
161
in f&thgr; lens
156
and the deflection-reflecting surface
155
a
of rotary polygon mirror
155
and on an optical path L
2
in which a beam passes on a more upstream side in the direction of arrow
160
in
FIG. 1
than an optical path L
1
of a beam reaching a write start position
172
of record information on the surface of photosensitive drum
158
. The beam reflected by the reflecting mirror
173
is guided through a condenser lens
174
onto a light receiving surface
175
a
of light receiving element
175
arranged to include, for example, a photodiode. When the condenser lens
174
focuses the beam deflected and scanned by the rotary polygon mirror
155
such that the beam irradiates the light receiving surface
175
a
, the light receiving element
175
outputs a signal for detecting a position where the beam is scanned.
The condenser lens
174
and the light receiving element
175
are disposed between the first f&thgr; lens element
161
in f&thgr; lens
156
and the rotary polygon mirror
155
, so that an optical path L
3
between the reflecting mirror
173
and the condenser lens
174
is located between the first f&thgr; lens element
161
and the rotary polygon mirror
155
.
The light source
153
emits a beam in accordance with a signal given from a processing circuit
181
for processing information from a host computer. The signal given to the light source
153
corresponds to information to be written on the photosensitive drum
158
, and therefore an electrostatic latent image corresponding to the desired information is formed thereby on the photosensitive drum
158
. The processing circuit
181
supplies to the light source
153
a unit of signal representing information corresponding to a scanning line which is a locus of the spot formed by the beam on the surface of photosensitive drum
158
. The signal is output in synchronism with the signal given from the light receiving element
175
through a line
176
.
A motor
159
is mounted on the bottom of housing
152
and the rotary polygon mirror
155
is attached to a drive shaft
159
b
of the motor
159
. The f&thgr; lens
156
is also mounted on the bottom of housing
152
, and the light receiving means arranged to include the reflecting mirror
173
, the condenser lens
174
and the light receiving element
175
as described above is set between the rotary polygon mirror
155
and the f&thgr; lens
156
.
A conventional deflection scanning apparatus of this type includes a rotary polygon mirror and its driving portion, as shown in
FIG. 2
, which comprise a base
102
set in a box
101
similar to the above-described housing
152
, bearings
103
supported in the base
102
, and a shaft
104
rotatably supported by the bearings
103
and in which a drive motor M
0
is constituted by a rotor
106
fixed to a flange
105
incorporated with the shaft
104
, and a stator
107
fixed to the base
102
.
The rotary polygon mirror
108
is urged against the flange
105
by a keep plate
109
screwed on the upper end of shaft
104
, a clamping washer
113
and a tension plate
112
, as shown in
FIG. 2
, whereby the rotary polygon mirror
118
is united with the rotor
106
so as to rotate with the shaft
104
. The upper opening of box
101
in
FIG. 2
is closed by a cover
110
.
A light source (not shown), similar to the above-described light source
153
, emits a laser beam irradiating the rotary polygon mirror
108
and the laser beam is deflected and scanned with rotation of rotary polygon mirror
108
to advance toward a photosensitive drum (not shown) similar to the above-described photosensitive drum
158
. The rotor
106
is provided with a recess
111
for relieving dynamic unbalance caused on the shaft
104
during rotation of the rotary polygon mirror
108
. The recess
111
is formed by cutting a part of the surface of rotor
106
before assembling.
T
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Le N.
Pham Hai C.
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