Electrophotography – Machine operation – Job mode
Reexamination Certificate
2000-08-29
2002-06-18
Brase, Sandra (Department: 2852)
Electrophotography
Machine operation
Job mode
C271S207000, C399S405000
Reexamination Certificate
active
06408147
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a printer, a facsimile or the like, arranged to form an image on a sheet and to discharge the sheet onto a sheet stacking tray provided on the image forming apparatus.
2. Description of Related Art
An image forming apparatus, such as a copying machine, has heretofore been arranged to include a paper feed means for feeding a sheet of recording paper or the like, an image forming means for forming an image on the sheet supplied by the paper feed means, and a sheet discharging means for discharging, to the outside of the body of the apparatus, the sheet having an image formed thereon by the image forming means. Sheets thus discharged by the sheet discharging means are stacked one after another on a sheet stacking tray provided on the apparatus body.
In some of the image forming apparatuses of the above kind, an amount-of-stack detecting sensor for detecting an amount of stack (the height of stack) of sheets on the sheet stacking tray is provided at a sheet discharge port of the sheet discharging means. With the amount-of-stack detecting sensor arranged in this manner, the image forming apparatus can provide such control as to prevent an amount of sheets more than a predetermined amount from being stacked on the sheet stacking tray, thereby preventing jamming or fall of sheets due to excessive stacking of sheets.
It is also known that some of the conventional image forming apparatuses are provided with a plurality of sheet stacking trays (bin trays) for sorting a plurality of sheets having images formed thereon by an image forming means. The image forming apparatus having such a sorting function is arranged to control selection of use of trays for discharging the sheets.
FIG. 11
is a sectional view showing, by way of example, a conventional image forming apparatus having four sheet stacking trays vertically arranged in a four-step configuration which permits sorting sheets out. In the conventional image forming apparatus shown in
FIG. 11
, sheets P stacked within a paper feed cassette
201
are separated and conveyed one by one by a paper feed means
202
. After an image is formed on each sheet by an image forming part
263
, the image is fixed to the sheet by a fixing means
204
. Paper discharge roller pairs
205
a
,
205
b
,
205
c
and
205
d
are arranged as a sheet discharging means on one side of the body of the apparatus. Sheet stacking trays
206
a
,
206
b
,
206
c
and
206
d
are arranged in positions corresponding respectively to the paper discharge roller pairs
205
a
,
205
b
,
205
c
and
205
d.
A sheet to which an image has been fixed by the fixing means
204
is led to the paper discharge roller pair
205
a
,
205
b
,
205
c
or
205
d
selected, under the change-over control of conveying-path change-over means
207
a
,
207
b
and
207
c
, to be discharged onto the sheet stacking tray
206
a
,
206
b
,
206
c
or
206
d
corresponding to the paper discharge roller pair as selected. Amount-of-stack detecting sensors
208
,
209
,
210
and
211
are arranged to detect respectively the amounts of stack of sheets on the sheet stacking trays
206
a
,
206
b
,
206
c
and
206
d.
FIG. 12
shows the arrangement of the amount-of-stack detecting sensors in the conventional image forming apparatus. Referring to
FIG. 12
, an amount-of-stack detecting lever
208
is arranged to detect the height of stack of sheets stacked on the first sheet stacking tray
206
a
. The amount-of-stack detecting lever
208
is swingable around a swing shaft
208
a
disposed above a nip part of the first paper discharge roller pair
205
a
. A fore end part
208
b
of the amount-of-stack detecting lever
208
is located on the side of the sheet stacking tray
206
a
across the discharge path for sheets.
A photo-sensor
208
d
detects the arrival of the amount of stack of sheets at a predetermined height when the amount-of-stack detecting lever
208
swings to a predetermined position where an actuator
208
c
which swings integrally with the amount-of-stack detecting lever
208
comes to block the optical axis of the photo-sensor
208
d.
While the conventional image forming apparatus is in process of sorting sheets out, a control means (not shown) is arranged to cause the image forming means to suspend its image forming action on sheets when the amount-of-stack detecting sensor has detected that the sheet stacking tray has been brought into a maximum stacked state during the process of sorting the sheets.
In a case where no sheet sorting action is required, image-formed sheets are stacked, for example, only on the first sheet stacking tray
206
a
. When the amount-of-stack detecting sensor
208
has detected that the first sheet stacking tray
206
a
has been brought into a maximum stacked state, the sheet conveying path is changed, under the control of the control means, to the second paper discharge roller pair
205
b
to cause subsequent sheets to be discharged onto the second sheet stacking tray
206
b.
In the meantime, while image-formed sheets are in process of being continuously stacked on the sheet stacking tray, there is formed a very thin layer of air between one sheet and another. This air layer gradually disappears from between the sheets due to the weight of sheets accordingly as time elapses. Therefore, a stack of sheets generally settles on the tray after the lapse of several minutes from the completion of discharge. As a result, the height of stack of sheets stacked on the sheet stacking tray decreases by an amount corresponding to the thickness of several to ten-odd sheets.
Further, in a case where a sheet is curled (warped) by the fixing action of the fixing means
204
, the degree of the curl tends to decrease as the sheet heated by the fixing means
204
cools on the sheet stacking tray. In such a case, a stack of sheets on the tray also comes to settle several minutes after the discharge of sheets, and then the height of stack of sheets also comes to decrease from the height obtained immediately after the discharge of sheets.
Therefore, when the sheets are found by the first amount-of-stack detecting sensor
208
to be fully stacked on the tray while the sheets are in process of being discharged onto the first sheet stacking tray
206
a
, the control means causes use of the paper discharge port to be changed over to the second paper discharge port. The sheets then come to be discharged from the second paper discharge port onto the second sheet stacking tray
206
b
. However, while the sheets are being discharged onto the second sheet stacking tray
206
b
, the stack of sheets on the first sheet stacking tray
206
a
settles down and the height of stack of sheets stacked on the first sheet stacking tray
206
a
decrease, so that the detection of the maximum stacked state by the first amount-of-stack detecting sensor
208
comes to be canceled.
This misleads the control means to consider the first sheet stacking tray
206
a
to be vacant and causes the use of the sheet (paper) discharge port to be changed again to the first paper discharge port. As a result, the sheets cannot be correctly stacked on the trays as the paging sequence of sheets discharged on the trays is disrupted.
Further, even if, after the first sheet stacking tray
206
a
is brought into a maximum stacked state, the height of stack of sheets stacked on the first sheet stacking tray
206
a
comes to naturally decrease to cancel the maximum stacked state, the height of stack of sheets stacked on the first sheet stacking tray
206
a
is very close to the maximum stacked state. Therefore, when sheets of the next job come to be discharged onto the first sheet stacking tray
206
a
in which the maximum stacked state thereof has been canceled, several to ten-odd sheets are first stacked on the existing stack on the first sheet stacking tray
206
a
. However, after that, the use of one paper discharge port is soon changed over to another paper discharge port to cause
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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