Sheet feeding or delivering – Delivering – To receiver for pack of sheets
Reexamination Certificate
2001-07-02
2002-12-17
Ellis, Christopher P. (Department: 3653)
Sheet feeding or delivering
Delivering
To receiver for pack of sheets
C271S217000, C270S058130
Reexamination Certificate
active
06494449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet stacking apparatus that is connected to a sheet discharge section of an image forming apparatus or the like.
2. Discussion of the Background
There is used a sheet stacking apparatus that includes a sheet discharge tray capable of raising and lowering in a vertical direction a stacking paper sheet (hereinafter referred to as a sheet) discharged from an image forming apparatus or the like and a sheet discharge roller, which is located at an upper part of the sheet discharge tray, for discharging the sheet to the sheet discharge tray. The sheet discharge tray of the sheet stacking apparatus receives the sheet from the sheet discharge roller at a standard sheet receiving position that is located at a predetermined downward distance away from the sheet discharge roller.
The aforementioned standard sheet receiving position is set in consideration of a normal sheet that is not stapled (hereinafter referred to as a non-stapled sheet) and is not curled, and even a stapled set of sheets having a mounded portion due to a thickness of staples is not apparently accounted for.
For example, as shown in
FIG. 10
, when a sheet discharge tray
12
stays at a standard sheet receiving position, the position of the sheet discharge tray
12
is at a predetermined distance L lower than a standard position relative to a sheet discharge roller
3
, such as measured at a nip portion of the sheet discharge roller
3
, for example. More particularly, the distance L is defined as a distance between the nip portion of the sheet discharge roller
3
and an upper surface of the sheet discharge tray
12
when the sheet discharge tray
12
is not loaded with the sheets, or between the nip portion of the sheet discharge roller
3
and an uppermost surface of the sheets on the sheet discharge tray
12
when the sheet discharge tray
12
is loaded with the sheets. Such a distance L is controlled to be constant by moving the sheet discharge tray
12
by a controller.
Actually, a height of the sheets stacked on the sheet discharge tray
12
is read by a sensor, and the distance L is controlled in accordance with the reading result by the sensor. The distance L accordingly may be within a certain range depending on an accuracy of the sensor.
When the sheet discharging tray
12
is not loaded with the sheets, the standard position for receiving the sheet is at the distance L beneath the nip portion of the sheet discharge roller
3
. The sheet discharge tray
12
receives a first sheet discharged from the sheet discharge roller
3
at the standard sheet receiving position. The sheet discharge tray
12
has an open end side (downstream relative to the sheet after being discharged), which is positioned higher than a base end side (upstream relative to the sheet after being discharged) in a vertical direction. The sheet discharge roller
3
conveys and discharges the sheet toward the sheet discharging tray
12
with a certain degree of momentum.
After being discharged out of the sheet discharge roller
3
onto the sheet discharge tray
12
, the sheet slides down along a slope of the sheet discharge tray
12
(to be more clear, the sheet slides down along the slope of the sheet stacked on the sheet discharge tray
12
in a switchback manner) by its own weight. The sheet is then stopped by a rear fence which is mounted on the base end side of the sheet discharge tray
12
.
As the sheets are successively stacked on the sheet discharge tray
12
, a height of a top surface of the sheets on the sheet discharge tray
12
increases. During this stacking operation, if the position of the sheet discharge tray
12
is not changed, a distance between the top surface of the stacked sheets and the sheet discharge roller
3
becomes smaller than the distance L which is made when the sheet discharge tray
12
is not loaded with the sheets. If such a distance becomes too small, the sheets discharged on the sheet discharge tray
12
can no longer be aligned properly. To avoid this problem, the sheet discharge tray
12
is controlled to lower each time when a sheet is stacked thereon so as to maintain the distance L within an appropriate range, and the sheets can be aligned.
Although an accurate and continuous control of the distance L is needed to be considered, the controller performs an intermittent control in which the sheet discharge tray
12
is lowered each time as part of the sheet stacking operation by an amount of distance so that the height of the top surface of the stacked sheets does not affect the alignment of the stacked sheets. The distance L is thus controlled to be constant within a predetermined allowance. The sheet discharge tray
12
repeats the above-described intermittent-lowering operation in accordance with a sheet stacking amount to receive the sheets. In such a case, the standard sheet receiving position is the top surface of the sheet discharge tray
12
(if the sheet discharge tray
12
is loaded with the sheets, the top surface of the sheets) which is positioned at the distance L, including the above-mentioned predetermined allowance, downward from the nip portion of the sheet discharge roller
3
.
When the sheet stacking apparatus is combined with a staple device, the sheet discharge tray
12
may receive various differently-formed sheets from the sheet discharge roller
3
. In some cases, the sheet discharge tray
12
may receive only non-stapled sheets or only a set of stapled sheets, or both non-stapled sheets and a set of the stapled sheets in a mixed fashion, depending upon the selected mode related to the sheets. In addition, such a sheet stacking status will be maintained until the sheets are removed from the sheet discharge tray
12
.
The sheet stacked on the sheet discharge tray
12
generally has a curl like a convex or concave shape, regardless of being stapled or not and of an amount of the sheets. For example, when the non-stapled sheet having a convex-shaped curl is stacked one after another on the sheet discharge tray
12
, the curls of the sheets are accumulated. This accumulation of curls causes the sheets to partly form a big mounded portion therein.
If such a situation arises, even though the height of the sheet discharge tray
12
is controlled around the standard sheet receiving position, the newly discharged sheet is caught at the aforementioned mounded portion of the previously stacked sheets on the sheet discharge tray
12
, and the trailing edge of the sheet cannot slide down toward the rear fence. Hence, the sheets will be improperly aligned on the sheet discharge tray
12
. Accordingly, the sheet that is caught on the mounded portion of the stacked sheets may be displaced at the leading edge side thereof toward the open end side of the sheet discharge tray
12
.
When the sheet discharge tray
12
is loaded with the thus-displaced sheets, assuming that the next sheet is further discharged from the sheet discharge roller
3
, the next sheet wraps over the aforementioned displaced sheets with the leading edge side thereof. Furthermore, the above-mentioned next sheet moves together with the displaced sheet by friction force. As a result, the misalignment of the stacked sheets occurs and, in an extreme case, the sheet may fall down from the sheet discharge tray
12
.
Such a misalignment of the sheets caused by the curl also occurs in a case of the stapled sheets. For example, when the stapled sheets are discharged, since the stapled sheets are formed in a set and have a larger rigidity than the non-stapled sheet, the stapled sheets set is stopped by another set of stapled sheets that are stuck over the mounded portion due to the curl and improperly aligned. The stapled sheets set then pushes other sets of stapled sheets to fall down from the sheet discharging tray
12
. In some cases, the leading edge of the next set of stapled sheets is stopped by the mounded portion of the stacked sets of the stapled sheets and convolve with the sheet discharge roller
3
nip or become misaligned.
The stand
Andoh Akihito
Iida Jun-ichi
Nakayama Yoshihiko
Nakazato Yukitaka
Tamura Masahiro
Bower Kenneth W.
Ellis Christopher P.
Ricoh & Company, Ltd.
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