Printing – Processes – Condition responsive
Reexamination Certificate
2000-02-04
2002-09-10
Yan, Ren (Department: 2854)
Printing
Processes
Condition responsive
C101S485000, C358S412000
Reexamination Certificate
active
06446556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a printer such as an electrophotographic printer in which a planetary gear for driving a printing mechanism is switched between two positions depending on the direction of rotation thereof. The present invention also relates to a method of controlling such a printer.
2. Description of the Related Art
FIG. 10
illustrates a conventional printer.
Referring to
FIG. 10
, a charging roller
12
rotates in contact with a photoconductive drum
11
. The charging roller
12
receives a negative voltage from a charging power supply
10
and charges the surface of the photoconductive drum
11
to a negative potential of about −800 V. White circles on the photoconductive drum
11
indicate negative charges. A light source
13
in the form of, for example, an LED head illuminates the charged surface of the photoconductive drum
11
to form an electrostatic latent image on the surface. A developing unit
14
has a roller unit
15
consisting of a plurality of rollers. The developing unit
14
supplies negatively charged toner to the electrostatic latent image formed on the photoconductive drum
11
to develop the electrostatic latent image into a toner image. Black circles indicate toner particles. A transfer roller
19
rotates in contact with the photoconductive drum
11
and receives a positive voltage from a transfer power supply
18
, thereby transferring the toner image formed on the photoconductive drum
11
to print paper
16
. A cleaning unit
17
removes residual toner that failed to be transferred to the print paper
16
and was left on the photoconductive drum
11
after the transfer operation. A fixing unit
23
includes a heat roller
23
a
and a pressure roller
23
b
, so that when the print paper is pulled in between the heat roller
23
a
and pressure roller
23
b
, the toner image on the print paper
16
is fused. The heat roller
23
a
and the pressure roller
23
b
discharge the print paper
16
to the outside of the printer.
When the toner image is being formed on the photoconductive drum
11
, the print paper
16
is fed from a paper tray
20
. A feed roller
21
feeds the top page of a stack of print paper held in the paper tray
20
to the transfer point between the photoconductive drum
11
and the transfer roller
19
. The pages of print paper are fed on a sheet-by-sheet basis. The print paper passes through a transport path in which a pair of registry rollers
22
a
and
22
b
is disposed.
The rollers of associated mechanisms are driven by the same motor via a plurality of gears. While some of these rollers may be driven to rotate and stop at the same timing, others may have to be controlled independently.
Immediately before a printing operation, a warm-up operation is performed in order to ensure stable printing operation. During the warm-up operation, the print paper should not be advanced and therefore if the print paper is to be fed from the paper tray
20
, the feed roller
21
is prevented from rotating during the warm-up operation. Thus, the feed roller
21
must be controlled independently of the other rollers.
When the print paper is fed from the paper tray
20
, the registry rollers
22
a
and
22
b
may be rotated and stopped at the same timing as the other rollers. However, when the user feeds the print paper
16
manually from the front side of the printer, the controller is unable to know the timing at which the print paper is actually fed. Thus, it is required that a paper sensor
24
accurately detects the position of the print paper so that the registry rollers
22
a
and
22
b
are driven into rotation at a proper timing independent of the other rollers. The print paper is accurately fed in this manner so that the printing is initiated at a specified location on the print paper.
As described above, if the rollers are necessary to be driven independently, they are usually driven by separate motors. However, small size, low price printers should be equipped with a minimum number of motors. Therefore, a desirable printing mechanism uses a planetary gear mechanism.
FIG. 11
illustrates a gear train used in a small printer and driven by a single motor, showing the meshing engagement among the gears during the warm-up operation.
The gear train is featured by a planetary gear
25
g
. The planetary gear
25
g
is in mesh with a gear
27
g
which in turn is in mesh with a gear
26
g
of a motor
26
. The planetary gear
25
g
rotates in the same direction as the motor
26
. The planetary gear
25
g
is movable about the gear
27
g
so that the position of the planetary gear
25
g
may be switched between two positions depending on the rotational direction of the planetary gear
25
g.
The operations of the gears during the warm-up operation will be described with respect to FIG.
11
.
During the warm-up operation, the motor
26
drives the motor gear
26
g
in rotation in a direction shown by arrow A
1
. Thus, the planetary gear
25
g
rotates in a direction shown by arrow A
2
so that the position of the planetary gear
25
g
is switched in a direction shown by arrow A
3
. The planetary gear
25
g
drives an idle gear
28
g
in rotation. Then, the idle gear
28
g
drives a triple gear
29
g
, which in turn drives a transfer roller gear
19
g
and a fixing roller gear
30
g
. The transfer roller gear
19
g
is mounted to the transfer roller
19
and drives the transfer roller
19
in rotation. The transfer roller gear
19
g
also drives the photoconductive drum
11
, not shown, in rotation. The photoconductive drum
11
has another gear that drives other associated rollers such as the charging roller
12
and developing roller
15
. A gear
30
g
drives rollers
23
a
and
23
b
of the fixing unit
23
in rotation.
In
FIG. 11
, the gear
31
g
is not in mesh with the planetary gear
25
g
, so that no drive force is transmitted to the feed roller gear
21
g
, gear
32
g
, and registry roller gear
22
g
. Thus, the print paper is not fed.
FIG. 12
illustrates the gear train during the printing operation. During the printing operation, the motor
26
rotates in a reverse direction, driving the motor gear
26
g
to rotate in a direction shown by arrow B
1
. Thus, the planetary gear
25
g
rotates in a direction shown by arrow B
2
, the position of the planetary gear
25
g
being switched in a direction shown by arrow B
3
. Then, the planetary gear
25
g
is brought into meshing engagement with the triple gear
29
g
and gear
31
g
, thereby driving the triple gear
29
g
and gear
31
g
in rotation.
The gear
31
g
drives the feed roller gear
21
g
. The feed roller gear
21
g
is operatively connected to the feed roller
21
through a clutch, not shown, so that the feed roller gear
21
g
drives the clutch to engage and disengage in accordance with a signal from a printer controller. The rotation of the feed roller gear
21
g
is transmitted through the gear
32
g
to the registry roller gear
22
g
so that the registry roller
22
g
causes the print paper to advance.
As mentioned above, the motor gear
26
g
is rotated in the direction shown by arrow B
1
during the printing operation, rollers associated with the printing operation, rollers associated with fixing operation, and registry rollers are simultaneously rotated. The clutch is controlled by the signal from the printer controller, thereby causing the feed roller
21
g
to rotate and stop as required.
As described above, the conventional printer is designed to reverse the direction of rotation of the motor
26
depending on whether the print paper
16
should be fed and should not be fed. Then, the planetary gear
25
g
was used to control the transmission of the drive force of the motor
26
.
In the manual feed mode, the user inserts the print paper from the front side of the printer. However, the printer controller does not know the timing at which the user inserts the print paper. Therefore, the warm-up operation cannot be performed immediately before the transport of the print paper. In other
Akin, Gump. Strauss, Hauer & Feld, L.L.P.
Oki Data Corporation
Yan Ren
LandOfFree
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