Typewriting machines – Means auxiliary to typewriting function – Indicator means
Reexamination Certificate
2003-03-21
2004-10-19
Hirshfeld, Andrew H. (Department: 2854)
Typewriting machines
Means auxiliary to typewriting function
Indicator means
C400S708000, C400S707100, C400S708100, C400S596000, C271S227000, C271S229000, C271S258050
Reexamination Certificate
active
06805509
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 2002-26566, filed May 14, 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 relates to an office machine, such as a laser printer and a copying machine, and more particularly, to a paper sensing apparatus of an office machine, which is capable of controlling a top margin of a printing paper effectively by exactly sensing a leading end of the printing paper picked up by a pickup roller and conveyed by conveying rollers.
2. Description of the Related Art
An input/output apparatus for performing printing on a medium of printing paper, for example, an office machine, such as an inkjet printer, a laser printer, or a facsimile, generally has a paper sensing apparatus for sensing a leading end of the printing paper to control a top margin of the printing paper.
For example, as shown in
FIG. 1
, a laser printer
10
includes a paper stacking unit
1
containing sheets of printing paper P therein, a paper conveying unit
2
conveying the printing paper P from the paper stacking unit
1
, an image forming unit
6
forming a toner image on the printing paper P conveyed by the paper conveying unit
2
, a paper sensing apparatus
30
disposed between the paper conveying unit
2
and the image forming unit
6
to sense a leading end of the printing paper P, a settling unit
7
settling the toner image formed on the printing paper P by applying certain heat and pressure to the toner image and the printing paper P, and a paper discharging unit
8
discharging the printing paper P having the settled toner image formed thereon.
The paper stacking unit
1
includes a paper cassette having a paper pressing plate supported by an elastic spring elastically urging (biasing) the printing paper P upward.
The paper conveying unit
2
includes a pick-up roller
9
feeding the printing paper P from the paper stacking unit
1
one by one, first and second paper conveying rollers
21
and
22
conveying the printing paper P fed by the pick-up roller
9
, and a register roller
23
and a back-up roller
25
aligning the leading end of the printing paper P conveyed from the first and the second paper conveying rollers
21
and
22
.
The paper sensing apparatus
30
sensing the leading end of the printing paper P is provided at a downstream side of the register roller
23
on a paper conveying path, which is disposed at a rear side of the register roller
23
.
As shown in
FIG. 2
, the paper sensing apparatus
30
includes a sensor actuator
31
installed on a paper guide frame
24
to be elastically rotated by the printing paper P when the printing paper P is conveyed through the register roller
23
and a photo sensor
33
sensing an end portion of the sensor actuator
31
in accordance with a rotation of the sensor actuator
31
and sending a paper sensing signal to a controlling unit (not shown). The photo sensor
33
includes a light emitting unit emitting light and a light receiving unit receiving the light emitted from the light emitting unit.
The image forming unit
6
includes a photo sensitive drum
3
, a developing roller
11
facing the photo sensitive drum
3
, a toner supplying roller
13
supplying toner to the developing roller
11
, a doctor blade
15
controlling an amount of the toner attached on the developing roller
11
, an agitator
17
supplying the toner to the toner supplying roller
13
, a toner container
19
storing the toner, and a case
18
provided for the above components to compose a single unit.
A transferring roller
5
is provided at a lower part of the photo sensitive drum
3
installed at the case
18
. The settling unit
7
includes a heating roller
26
applying heat to the toner image transferred to the printing paper P from the photo sensitive drum
3
by the transferring roller
5
, and a pressing roller
27
pressing the printing paper P against the heating roller
26
.
The paper discharging unit
8
includes a paper discharging roller
28
discharging the printing paper P that has been completed with a printing operation, and a paper holder
29
holding and stacking the discharged printing paper P.
An operation of the laser printer
10
having the above structure is as follows. Firstly, the printing paper P is picked up from the paper stacking unit
1
by the pick-up roller
9
and conveyed to the register roller
23
through the first and the second conveying rollers
21
and
22
.
The leading end of the printing paper P that has been conveyed to the register roller
23
is aligned by being pushed against a nip between the register roller
23
and the back-up roller
25
.
Then, as the printing paper P continues to pass through the nip between the register roller
23
and the back-up roller
25
, the leading end of the printing paper P pushes the sensor actuator
31
of the paper sensing apparatus
30
disposed between the register roller
23
and the transferring roller
5
. Accordingly, the end portion of the sensor actuator
31
is rotated to be off from the photo sensor
33
. As a result, the light receiving unit of the photo sensor
33
receives light from the light emitting unit and sends the paper sensing signal to the controlling unit (not shown).
The controlling unit counts time consumed for the printing paper P to be conveyed from the paper sensing apparatus
30
to the transferring roller
5
in accordance with the paper sensing signal, conveys the printing paper P for a predetermined time, i.e., until the printing paper P reaches a printing operation start position, and then operates the image forming unit
6
and the transferring roller
5
.
While the printing paper P is being conveyed to the printing operation starting position, an electrostatic latent image is formed on the photo sensitive drum
3
of the image forming unit
6
by a laser beam reflected through a LSU (laser scanning unit)
4
in accordance with an image signal. The electrostatic latent image formed on the photo sensitive drum
3
is developed to a visible toner image by the developing roller
11
.
Then, when the printing paper P reaches the photo sensitive drum
3
of the image forming unit
6
, the toner image formed on the photo sensitive drum
3
is transferred to a surface of the printing paper P by the transferring roller
5
in accordance with a control of the controlling unit.
The toner image that has been transferred to the surface of the printing paper P is settled on the surface of the printing paper P by the heat and pressure of the heating roller
26
and the pressing roller
27
as being passed through the settling unit
7
. The printing paper P having the toner image settled thereon is discharged to the paper holder
29
formed outside of the laser printer
10
by the paper discharging roller
28
of the paper discharging unit
8
.
However, in the above conventional laser printer
10
, as shown in
FIGS. 3A and 3B
, the leading end of the printing paper P is frequently bent due to a friction force or static electricity generated by a contact between the leading end of the printing paper P and the sensor actuator
31
of the paper sensing apparatus
30
, and thus there is a problem that a contact point of the sensor actuator
31
and the leading end of the printing paper P is not constantly maintained.
As described above, when the contact point between the sensor actuator
31
and the printing paper P is not regularly maintained, an operation starting time of the paper sensing apparatus
30
becomes unstable. Therefore, the top margin of the printing image printed on the printing paper P also becomes irregular, and as a result, reliability of the laser printer
10
is lowered.
In addition, as shown in
FIG. 2
, since a distance between an original position and a moving position in which the sensor actuator
31
moves and returns to its original position during sensing the leading end of the printing paper P, is extended, in ot
Ghatt Dave A.
Hirshfeld Andrew H.
Staas & Halsey , LLP
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