Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2003-11-12
2004-11-30
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S235000
Reexamination Certificate
active
06825869
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority of Korean Patent Application No. 2002-79034, filed Dec. 12, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a light scanning apparatus for use in an image forming apparatus such as a printer, a facsimile machine, a copier, etc., and more particularly, to an apparatus to detect a laser beam, and to produce a laser beam detect signal that may be used to synchronize scanning operation of the image forming apparatus, which is capable of minimizing the dimension of the components and reducing performance degradation caused by the assembly deviations introduced in the fabricating and assembling processes, thereby enhancing the printing quality.
2. Description of the Related Art
Generally, a light scanning apparatus of an image forming apparatus such as a printer, a facsimile machine or a copier uses a light source that generates a beam of light, such as a laser beam, in order to form an electrostatic latent image on a photosensitive body, such as a photosensitive drum or a photosensitive belt.
The light scanning apparatus forms the electrostatic latent image on the photosensitive body by converting the laser beam from the light source, such as a semiconductor laser, into a parallel ray of light of a predetermined size through a collimator lens, leading the laser beam to a light deflector that rotates at a high speed, deflecting the direction of the laser beam at the light deflector and emitting the laser beam along a scanning line on the photosensitive body through a scanning lens such as an f-&thgr; (f-theta) lens.
In order to precisely locate the starting location where the electrostatic latent image is to be first formed on the photosensitive body, i.e., the starting location of the laser beam scanning line, an apparatus to detect the laser beam at a certain predetermined location relative to the intended starting point of the scanning line is employed. The apparatus to detect the laser beam, generates a beam detect signal, which is used by the image forming apparatus to synchronize the timing of the laser beam firing, or the like, so that the scanning is started at the intended starting point.
FIG. 1
schematically shows a conventional light scanning apparatus
10
to form an electrostatic latent image on a photosensitive body.
Referring to
FIG. 1
, the light scanning apparatus
10
includes a semiconductor laser
1
emitting a laser beam
14
, a collimator lens
2
arranged in correspondence with the semiconductor laser
1
to form the laser beam
14
into a parallel ray of light, a slit
3
through which the laser beam
14
which has passed through the collimator lens
2
is converted into a predetermined form, a cylindrical lens
4
through which the laser beam which has passed through the slit
3
is transformed into a linear light, and a light deflector
5
to deflect the laser beam
14
. The light deflector
5
includes a rotary polygon mirror
5
a
supported on a spindle motor (not shown) to be rotatably driven at a given speed.
The light scanning apparatus
10
also includes an f-&thgr; lens
6
that compensates for the error included in the laser beam
14
deflected from the rotary polygon mirror
5
a
, thereby emitting the laser beam
14
to a photosensitive drum
20
. The beam detect signal generating part
30
generates a signal used by the image forming apparatus to correctly synchronize the formation location of the electrostatic latent image along a laser beam scanning line
20
a
, shown across the photosensitive drum
20
.
The beam detect signal generating part
30
includes a reflective mirror
8
secured on a spring
7
on a portion of the optical path of the laser beam
14
that would not interfere with the scanning of the laser beam
14
along the length of the laser beam scanning line
20
a
. The reflective mirror
8
deflects the laser beam
14
in the direction of a laser beam detecting lens
9
. The laser beam detecting lens
9
has an incident face and an emissive face which are spherical, cylindrical or plane surfaces to converge the laser beam
14
from the reflective mirror
8
onto a laser beam detecting sensor
11
. The laser beam detecting sensor
11
may be a photo diode sensor, and upon detection of the laser beam
14
, generates a beam detect signal. The laser beam detecting sensor
11
may be assembled either in a printed circuit board
12
(PCB), which also supports the semiconductor laser
1
, or in a separate printed circuit board (not shown).
The operation of the conventional light scanning apparatus
10
will now be described.
In accordance with the input image signals, the laser beam
14
is emitted from the semiconductor laser
1
, and converted into a parallel ray of light by the collimator lens
2
. Then, after passing through the slit
3
that shapes the laser beam
14
in a predetermined form, the laser beam
14
is passed through the cylindrical lens
4
, and then deflected by the deflecting faces of the polygon mirror
5
a
that is rotated at relatively high speed by the spindle motor.
Next, the laser beam
14
is made to selectively pass through the f-&thgr; lens
6
to be converged on the photosensitive drum
20
in the form of a light spot, thereby scanning the scanning line
20
a
of a predetermined, effective scanning width along a main scanning direction as shown in FIG.
1
. At this time, the photosensitive drum
20
is driven to rotate in a sub-scanning direction by a driving motor (not shown). Accordingly, as a result of the scanning movements of the light spots in the main scanning direction and the rotation of the photosensitive drum
20
in the sub-scanning direction, a predetermined electrostatic latent image is formed on the photosensitive drum
20
.
In order to start each of the scanning lines
20
a
at the correct starting point, the laser beam
14
deflected from the rotary polygon mirror
5
a
is detected at a predetermined location either prior to the start of or past the end of the effective scanning width of the laser beam scanning line
20
a
. In the embodiment shown in
FIG. 1
, the beam detection is shown to be made at a location prior to the start of the scanning line
20
a
. The laser beam
14
, which have passed through the f-&thgr; lens
6
, is deflected by the reflective mirror
8
placed at the predetermined location in the main scanning direction towards the laser beam detecting lens
9
. When the laser beam
14
deflected by the reflective mirror
14
is received by the laser beam detecting sensor
11
, the laser beam sensor
11
in response thereto produces a beam sensed signal. The beam sensed signal itself may be taken as the beam detect signal, or, in the alternative, is converted into suitable voltage and/or current, by a beam detect signal generation circuit (not shown), which may be disposed on the same PCB
12
, to generate the beam detect signal .
The beam detect signal so generated is input to a controller unit (not shown), which controls the timings of both the scanning start and image formation of the light spots on the photosensitive drum
20
. The controller uses the beam detect signal in order to determine the proper location for the scanning start.
However, the conventional light scanning apparatus
10
operated as above has a rather complex structure in which the reflective mirror
8
and the laser beam detecting lens
9
are separated by a relatively large distance in a narrow space in the light scanning apparatus
10
. In addition, dimension and assembly deviations or errors are frequently generated during the process of fabricating and assembling the parts such as the reflective mirror
8
, the laser beam detecting lens
9
, and the laser beam detecting sensor
11
.
When the errors occur during the fabrication and assembly, the center of the optical axis of the laser beam detecting lens
9
may not properly align with the reflective mirror
8
, r
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
Tran Huan
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