Electrophotography – Document handling – Copy
Reexamination Certificate
2002-03-21
2004-06-29
Braun, Fred L (Department: 2852)
Electrophotography
Document handling
Copy
C399S066000
Reexamination Certificate
active
06757515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that is capable of performing a stable sheet transfer operation.
2. Discussion of the Background
A typical background sheet transferring apparatus used in an image forming apparatus, such as a laser printer, a plain paper copying machine, a facsimile machine, etc., is illustrated in FIG.
1
. The background sheet transferring apparatus of
FIG. 1
has a sheet passage for a recording sheet traveling from a sheet container
1
through a photoconductive member
12
. In
FIG. 1
, a stack of recording sheets
2
stacked in the sheet container
1
are positioned such that leading edges of the recording sheets
2
are neatly aligned at an initial position A. When a sheet transfer operation is started, a sheet feed signal is turned on in an electrical control system (not shown) and is transmitted to the background sheet transferring apparatus. With the sheet feed signal, a pick-up roller
3
is lowered and is rotated so as to move the recording sheets
2
towards a position B where a sheet separation mechanism is provided. The sheet separation mechanism, namely, a friction reverse roller system includes a feed roller
4
for being rotated to limit and to move one recording sheet
2
forward and a reverse roller
5
for being rotated to move back the accompanying recording sheets
2
. The feed roller
4
and the reverse roller
5
are driven at the same time the pick-up roller
3
is driven so that a recording sheet
2
is separated and is transferred forward. In this example, the feed roller
4
, the reverse roller
5
, and the pick-up roller
3
are driven with a motor (not shown).
After being separated at the position B by the friction reverse roller system, the recording sheet
2
is moved such that the leading edge of the recording sheet
2
reaches a photo sensor
6
located at a position C. Then, the pick-up roller
3
is lifted and is stopped to be driven so that the pick-up roller
3
loses a sheet transfer power for moving the recording sheet
2
. After that, the recording sheet
2
is further moved to a transfer roller
7
located at a position E by a sheet transfer power of the feed roller
4
. The feed roller
4
is stopped to be driven in a time period t
1
(see
FIG. 2
) after having been driven so that the leading edge of the recording sheet
2
is moved to a position F downstream from the position E. After the feed roller
4
is stopped to be driven, the recording sheet
2
is further transferred by the transfer roller
7
. The leading edge of the recording sheet
2
is then brought to pass a photo sensor
8
located at a position H and then to reach a position I when the trailing edge of the recording sheet
2
is brought away from the sheet separation mechanism. After that, the leading edge of the recording sheet
2
is further moved to a transfer roller
9
located at a position E′. In the above operations, the transfer rollers
7
and
9
are driven with a transfer roller driving motor (not shown). The recording sheet
2
is then transferred to a photo sensor
10
(referred to as a registration sensor
10
) located at a position J and to a registration roller
11
located at a position K. Further, the recording sheet
2
is transferred to an image transfer section located at a position L and which is composed of the photoconductive member
12
and an image transfer roller
13
.
FIG. 2
is a convenient graph with respect to a sheet transferring performance of the background sheet transferring apparatus, which is composed of a performance characteristic graph
1
to a time chart
1
. The performance characteristic graph
1
demonstrates a characteristic of a sheet transfer operation of the background sheet transferring apparatus by showing successive positions of leading and trailing edges of a recording sheet in the sheet passage in response to a time parameter. The time chart
1
shows the sheet feed signal and the subsequent actions of the various components in connection with the movement of the recording sheets shown in the performance characteristic graph
1
. In the performance characteristic graph
1
, the vertical axis represents a distance from the initial position A to a position after the position K and the horizontal axis represents time. In the performance characteristic graph
1
, with a time parameter, solid lines represent actual positions of the leading edge of a recording sheet
2
and thick broken lines represent actual positions of the trailing edge of the recording sheet
2
. Thin two-dotted chain lines represent calculated positions of the leading edge of the recording sheet
2
without consideration of slippage of the recording sheets
2
relative to the rollers and wearing of the rollers. Thin broken lines represent calculated positions of the trailing edge of the recording sheet
2
without consideration of slippage of the recording sheets
2
relative to the rollers and wearing of the rollers. In this example, the recording sheet
2
has a letter size and is transferred in a direction of a short edge having a length of 216 mm.
In a time period t
2
after the leading edge of the recording sheet
2
is brought to reach the registration sensor
10
at the position J, the transfer roller driving motor is stopped so that the transfer rollers
7
and
9
lose sheet transfer powers for moving the recording sheet
2
. The time period t
2
is determined so that the leading edge of the recording sheet
2
is brought to reach the registration roller
11
. At this time, the registration roller
11
is not driven. With this determination of the time period t
2
, a skew correction is conducted. That is, the leading edge of the recording sheet
2
is brought to collide against the registration roller
11
so that the recording sheet
2
makes a slack before the registration roller
11
which corrects a skew if it exists. In this example, the time period t
2
is set to 37.5 ms.
After that, the transfer roller driving motor is driven at the same time the registration roller
11
is driven so that the rotations of the transfer rollers
7
and
9
are restarted. Consequently, the recording sheet
2
is further transferred to the image transfer section so that an image formed on the photoconductive member
12
is transferred onto the recording sheet
2
. The registration roller
11
is configured to turn on in a time period t
3
after the photo sensor
8
at the position H is turned on. In this example, the time period t
3
is set to 400 ms. With this time period t
3
, the movement of the recording sheet
2
is timed in synchronism with the rotation of the photoconductive member
12
so that the position of the image on the photoconductive member
12
matches the position of the recording sheet
2
.
In the performance characteristic graph
1
of
FIG. 2
, distances of the various positions with reference to the initial position A are set as follows:
28 mm between the positions A and B,
38 mm between the positions A and C,
123.4 mm between the positions A and E,
133.4 mm between the positions A and F,
231.9 mm between the positions A and H,
244 mm between the positions A and I,
344 mm between the positions A and J,
359 mm between the positions A and K, and
216 mm between the positions B and I.
With the arrangement above, the following time periods t
11
-t
16
are needed:
979.75 ms for the time period t
11
in which the transfer roller driving motor is driven in synchronism with a rise time of the sheet feed signal;
1048.5 ms for the time period t
12
from a rise time of the sheet feed signal to a time the registration roller
11
is turned on;
826.09 ms for the time period t
13
from a rise time to the next rise time of the registration roller
11
;
755 ms for the time period t
14
between calculated times the leading edges of a recording sheet and the next recording sheet are forwarded by the registration roller
11
;
252.5 ms for the time period t
15
between c
Braun Fred L
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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