Sheet feeding or delivering – Feeding – Separator and conveyor
Reexamination Certificate
2001-02-08
2003-03-18
Bollinger, David H. (Department: 3651)
Sheet feeding or delivering
Feeding
Separator and conveyor
C271S010030, C271S010110, C271S010130, C271S110000, C271S266000, C271S270000
Reexamination Certificate
active
06533263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying sheets one by one, and to an image forming apparatus or an image reading apparatus having such a sheet conveying apparatus, and more particularly, it relates to an arrangement for monitoring a conveying condition of sheets being continuously conveyed.
2. Related Background Art
As an example, a conventional image forming apparatus or image reading apparatus includes a sheet conveying apparatus comprising a sheet feeding portion for feeding out a sheet and a conveying portion for conveying the sheet fed out from the sheet feeding portion to an image forming portion or an image reading portion. In such a sheet conveying apparatus, it is required that a conveying condition of the sheet be monitored to ensure that the function of the image forming apparatus and the like having the sheet conveying apparatus is satisfied and that serious damage is avoided.
To this end, in the conventional sheet conveying apparatuses, for example, as shown in
FIG. 32
which is a schematic view of the conveying portion, there is provided a sensor
104
of flag type for detecting a sheet
105
being shifted in a conveying direction e to monitor a condition that the sheet
105
is being conveyed through a sheet conveying passage, and, sheets
105
being conveyed continuously with predetermined or more interval (sheet interval) are detected by the sensor
104
of flag type. In other words, by detecting the sheet interval by means of the sensor
104
of flag type, the conveying condition of the sheet
105
is monitored.
Incidentally,
FIG. 33
shows a construction of such a sensor
104
of flag type. In
FIG. 33
, the reference numeral
111
denotes a sensor flag;
112
denotes a photo-sensor ON/OFF of which is controlled as the sensor flag
111
is shifted; and
113
denotes a spring member. Incidentally, since the sensor flag
111
is biased by the spring member
113
, if the sheet does not exist in the sensor portion, a condition shown in
FIG. 33
is established.
When a sheet (not shown) conveyed in a direction shown by the arrow f between guide plates
115
abuts against the sensor flag
111
, the sensor flag
111
is pushed by the sheet to be rocked around a fulcrum
114
in a direction shown by the arrow g. If the sensor flag
111
is rotated down in the direction g in this way, a signal from the photo-sensor
112
is changed, for example, from OFF to ON, with the result that a controlling device (not shown) detects the passage of the sheet.
By the way, when sheets are conveyed continuously, an amount of the sheet interval required for detecting the sheet positively by the sensor
104
of flag type is determined by a time period during which the sensor flag
111
is returned by the spring member
113
when the sensor flag
111
is changed from a condition that the photo-sensor
112
is blocked by the sensor flag to a condition that the photo-sensor is not blocked by the sensor flag, a time period until the flag position is stabled, and a time period until potential of the photo-sensor
112
is stabled.
FIG. 34
is a view showing a construction of a sheet feeding portion
1000
of the conventional sheet conveying apparatus. Sheets S stacked on a sheet stacking portion
1101
are fed and conveyed one by one to a conveying path H
1100
by means of a pick-up roller
1102
which is started to be driven by sheet feeding command. The sheets S fed out by the pick-up roller
1102
enter into a nip portion between a retard roller
1103
and a sheet feeding roller
1104
which constitute separating means and feeding means, and, in the nip portion, only an uppermost sheet among the entered sheets is separated, and the separated sheet is conveyed to the downstream conveying path H
1100
.
When a plurality of sheets are conveyed, the retard roller
1103
is rotated in a direction opposite to the conveying direction by the action of a torque limiter (not shown) so that sheets other than the uppermost sheet are returned to the sheet stacking portion
1101
. Incidentally, in
FIG. 34
, the reference numeral
1105
denotes a sheet end detecting sensor; and
1106
denotes a pair of pull-out rollers.
After a leading end of the fed sheet S is detected by the sheet end detecting sensor
1105
, the sheet is transferred to the pair of pull-out rollers
1106
by which the sheet is pulled out from the nip portion between the sheet feeding roller
1104
and the retard roller
1103
and then is conveyed in the downstream direction.
In such a sheet feeding portion
1000
, the sheets S being conveyed continuously are conveyed in such a manner that a predetermined or more distance (sheet interval) between a trailing end of a preceding sheet and a leading end of a succeeding sheet is provided to meet sheet conveying requirement from the image forming apparatus thereby to prevent inconvenience due to conveying delay of the sheet S. By detecting such sheet interval by the sheet end detecting sensor
1105
, the conveying condition of the sheet S is monitored.
By the way, in some of sheet feeding portions
1000
, so-called speed increase control is effected for the purpose that conveying control timings for the sheet become the same at each of sheet feeding stages having different lengths of conveying paths and that an image forming timing for a first sheet (first copy time in a copying machine) is hastened.
In such speed increase control, the sheet end detecting sensor
1105
is used as a pre-registration sensor, and a sheet feeding speed (conveying speed of the sheet obtained by the pick-up roller
1102
and the sheet feeding roller
1104
) is maintained as it is, so that, after the sheet is detected by the pre-registration sensor, the sheet is temporarily stopped at a pre-registration stop position (which is effectively positioned behind the pair of pull-out rollers
1106
in order to stable the stop position) and then conveyance is re-started in a timed relationship thereby to realize stable conveyance, and, after the temporal stop, the re-conveying speed is made greater than the sheet feeding speed.
However, even when such control is effected, it is very important that the leading end of the sheet S is detected correctly by the sheet end detecting sensor
1105
, and, to this end, it is required that the sheet interval be provided similar to the conveying portion shown in FIG.
32
.
Further, in the sheet conveying apparatus, since skew-feed correction for aligning the posture and position of the sheet in front of the image forming portion or the image reading portion must be effected, in the past, various skew-feed correcting means (so-called registration means) have been proposed. Among them, there is means for effecting the skew-feed correction by temporarily stopping the sheet. In such skew-feed correction, greater sheet interval was required.
By the way, in a copying machine as an example of a conventional image forming apparatus of analogue type, even when continuous copying is effected after a single sheet (original) is read, an optical device for exposing the original must be reciprocated by times corresponding to the copy number, and, thus, the sheet interval is inevitably determined.
On the other hand, as image forming apparatuses and image reading apparatuses have been digitalized, by reducing the sheet interval to process the larger number of sheets within short time period, for example in case of image formation, substantial image forming speed has been enhanced without increasing a process speed of the image formation.
The reason is that, since the image reading and image formation are digitalized, after the original was once read, image information can be electrically coded and be stored in a memory, or, in the image formation, the information can be read out from the memory and an image corresponding to the image information of the original can be formed on a photosensitive member by means of an exposing apparatus such as a laser beam, an LED array or the like, with the result that, even
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