Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2003-02-26
2004-12-07
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C359S206100
Reexamination Certificate
active
06829001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a digital copier, a printer, a facsimile and so on of an electric photographic type, provided with a writing device that performs image exposure on a photoconductive image carrier by deflecting a light beam emitted from a light source by a deflector.
2. Description of the Related Art
A brief description of the schematic configuration of such an image forming apparatus is given below by taking a digital copier as an example. The digital copier of an electric photographic type includes an automatic document feeder that feeds document sheets one by one from a pile of document sheets onto a contact glass and sets the document sheet thereon. The digital copier further includes an image reading unit that optically scans the document sheet on the contact glass and forms an image on a CCD sensor, and an optical scan unit that forms an (electrostatic latent) image on a photoconductive image carrier by deflecting a light beam emitted from a light-emitting semiconductor based on a digital image signal. The digital image signal is converted from an analog image signal that is obtained by photoelectrically transforming a reflective light image of the document sheet formed on the CCD sensor by an analog-to-digital converter. The digital copier further includes a transfer unit that transfers an image developed from the electrostatic latent image formed on the photoconductive image carrier onto a transfer paper and a feeder unit that feeds transfer papers to the transfer unit.
Among these components, the optical scan unit that configures a writing device may be exemplified by an optical scanning system shown in
FIG. 1. A
laser beam emitted from a semiconductor laser (LD)
1
a
, which is provided in the interior of a semiconductor laser unit (LD unit)
1
as a light source, become a substantially parallel-light beam by passing through a collimator lens
1
b
and become a chief ray L having a cross-section shaped as necessary for image formation by an aperture
2
. The chief ray is condensed in the sub-scanning direction by a cylindrical lens
3
and is reflected by a mirror
4
so as to enter a polygon mirror
5
, which serves as a deflector. The chief ray L entering the polygon mirror
5
is deflected by the reflective side surface of the polygon mirror
5
that rotates with a high velocity in the direction indicated by the arrow, and the deflected chief ray L enters an F&thgr; lens
6
. By entering the F&thgr; lens
6
, the constant angular velocity scanning with the chief ray is transformed into constant linear velocity scanning with the same. The chief ray exits to the exterior of the writing device and is focused on a photoconductor drum
7
, which includes the surface to be scanned and thus an electrostatic latent image is formed thereon. In
FIG. 1
, the numerical references
9
a
and
9
b
represent a synchronism detection mirror provided outside of the image region and a synchronism detection sensor that detects a reflection beam from the synchronism detection mirror, respectively. A synchronization signal as a reference for the beginning of scanning in the main scanning direction can be obtained from the output of the synchronism sensor
9
b
. In addition, the F&thgr; lens
6
has an optical face tangle correction function.
FIG.
2
and
FIG. 3
show a configuration of one example of the writing device
10
provided with the above-mentioned optical scanning system.
FIG. 2
is a top plan view of such a configuration and
FIG. 3
is a sectional side view of such a configuration. As is apparent from FIG.
2
and
FIG. 3
, in the actual writing device
10
, the polygon mirror
5
is rotationally driven by a polygon motor
8
. A soundproof glass
5
a
is fastened to a polygon cover
8
a
of the polygon motor
8
. The light beam entering the polygon mirror
5
from the mirror
4
and the light beam exiting the polygon mirror
5
to the F&thgr; lens
6
pass through the soundproof glass
5
a
. The rotational velocity of the polygon mirror
5
is determined based on the rotational velocity of the photoconductor drum
7
, the writing density of the writing device
10
, and the number of side surfaces on the polygon mirror
5
.
However, in such a writing device of the image forming apparatus according to the related art, some undesired light beam may occur from the LD unit
1
, which light beam is different from the chief ray L and does not contribute to the proper image formation, due to the side lobes occurring from the LD
1
a
and being reflected internally of the LD unit
1
, etc. The undesired light beam is represented as flare beams FL
1
, FL
2
in FIG.
2
. These flare beams appear on both sides of the traveling direction of the chief ray L.
FIG. 4
shows a magnified view of a part of the optical path of these flare beams. It is often the case that the energy of the first flare beam FL
1
and the energy of the second flare beam FL
2
are smaller than that of the chief ray L. However, if they travel at the same height as the chief ray L, the first flare beam FL
1
passes through the gap between one end of the mirror
4
and the cover
8
a
of the polygon motor
8
and the second flare beam FL
2
travels on the side of the chief ray L, which side is outer with respect to the other end of the mirror
4
as shown in FIG.
2
and FIG.
4
. Both flare beams pass through the F&thgr; lens
6
shown in FIG.
2
and become flare beams FL
1
a
, FL
2
a
that reach the photoconductor drum
7
. The flare beams FL
1
a
, FL
2
a
always expose themselves to the photoconductor drum
7
as a certain image height and these flare beams form on finally obtained image black lines or black bands in the sub-scanning direction, therefore the image quality is significantly degraded. These flare beams may also be generated at both the upper side and the under side of the chief ray; however, such flare beams are blocked by an optical housing or a cover member that accommodates most of the optical devices and therefore they do not reach the photoconductor drum
7
.
SUMMARY OF THE INVENTION
Accordingly, it is necessary to prevent the first flare beam and the second flare beam from reaching the photoconductor drum by blocking the relevant flare beams. However, when the first flare beam FL
1
and the second flare beam FL
2
are traveling on the same scanning plane as the chief ray L and the parts FL
1
a
, FL
2
a
of the first flare beam FL
1
and the second flare beam FL
2
enter the scan region of the chief ray L as shown in
FIG. 2
, it is difficult to separate the flare beams from the chief ray L. Accordingly, it is necessary to block the first flare beam FL
1
and the second flare beam FL
2
in the optical path between the LD unit
1
and the polygon mirror
5
.
In particular, for blocking the first flare beam FL
1
, it is necessary to arrange a blocking member between the polygon motor
8
and the mirror
4
avoiding obstructing the traveling of the chief ray L and this is spatially difficult. Further, the polygon motor
8
is removably mounted to the housing of the writing device
10
by screws threaded in the direction perpendicular to the plane of the figure so that the polygon motor can be replaced in case of a failure, etc. However, under a certain design condition, the blocking member may obstruct the removal of the polygon motor and thus may impede a smooth removal of the polygon motor. Therefore, it is extremely difficult to completely block the first flare beam FL
1
by providing a blocking member between the motor
8
and the mirror
4
leaving no space between them, while avoiding obstructing the removal of the motor
8
and blocking the chief ray L.
The present invention is proposed in view of the mentioned problems, and therefore, it is a general object of the present invention to provide an image forming apparatus provided with a writing device with a simple configuration, by means of which writing device the flare beams emitted from the LD unit
Ricoh & Company, Ltd.
Tran Huan
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