Sheet feeding or delivering – Feeding and delivering – Conveyor releases to subsequent conveyor
Reexamination Certificate
2000-01-28
2002-06-11
Skaggs, H. Grant (Department: 3651)
Sheet feeding or delivering
Feeding and delivering
Conveyor releases to subsequent conveyor
C271S265010, C271S265020, C271S270000, C271S291000, C271S301000, C271S186000
Reexamination Certificate
active
06402133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying a sheet and an image forming apparatus having such a sheet conveying apparatus.
2. Related Background Art
In the past, many sheet conveying apparatus have been incorporated, for example, in a main body of an image forming apparatus.
As shown in
FIG. 10
, such a sheet conveying apparatus is designed so that a (one-sided copying) sheet having one surface on which an image is formed by image forming means of an image forming apparatus (not shown) is discharged outside as it is or is reversed and then is discharged or is reversed and then is sent to the image forming means again in order to form an image on the other surface of the sheet (two-sided copying).
Now, an operation of a conventional sheet conveying apparatus
100
will be explained.
(Face-up sheet discharging mode in one-sided copying)
In the image forming apparatus, a sheet to which a toner image has been fixed is sent to an outer sheet discharge roller pair
27
by an inner sheet discharge roller pair
25
and then is discharged, by the outer sheet discharge roller pair
27
, onto a sheet discharge tray (not shown) of a main body
101
of the image forming apparatus with its image bearing surface facing upwardly. In this case, a flapper
26
disposed at a branched portion is switched to a position shown by the solid line.
(Face-down sheet discharging mode in one-sided copying)
By switching the flapper
26
to a position shown by the broken line, the sheet sent from the inner sheet discharge roller pair
25
is conveyed toward a conveying path
66
and then is sent in a direction indicated by the arrow A by a sheet discharge reverse roller pair
59
. At a time when a trailing end of the sheet reaches in a range L
a
, the sheet discharge reverse roller pair
59
reversely rotates to send the sheet to the outer sheet discharge roller pair
27
. Then, the sheet is discharged, by the outer sheet discharge roller pair
27
, onto the sheet discharge tray (not shown) of the main body
101
of the image forming apparatus with its image bearing surface facing downwardly.
(Two-sided copying mode)
Similar to the face-down sheet discharging mode, by switching the flapper
26
to the position shown by the broken line, the sheet sent from the inner sheet discharge roller pair
25
is conveyed toward the conveying path
66
and then is sent in the direction indicated by the arrow A by the sheet discharge reverse roller pair
59
and a two-sided reverse roller pair
60
. At a time when the trailing end of the sheet reaches in a range L
c
, the two-sided reverse roller pair
60
reversely rotates to sent the sheet to a sheet re-feeding path
50
with its image bearing surface facing upwardly.
By the way, in the two-sided copying mode, a sheet conveying sheet in such a sheet conveying apparatus is selected to be higher than a sheet conveying speed in the image forming apparatus in order to increase the image forming speed.
Now, a method of controlling the sheet conveying speed in this case will be briefly explained.
An inner sheet discharge sensor
62
is disposed downstream of the inner sheet discharge roller pair
25
. Fixing means
24
of the image forming apparatus and the inner sheet discharge roller pair
25
are rotated by a common motor M
3
. The sheet discharge reverse roller pair
59
also having a surface reverse function is rotated by a forward and reverse rotatable and speed-controllable pulse motor M
4
. Further, the two-sided reverse roller pair
60
also having a surface reverse function is rotated by a forward and reverse rotatable and speed-controllable pulse motor M
5
.
When a leading end of the sheet is detected by the inner sheet discharge sensor
62
, control means (not shown) calculates a time when the trailing end of the sheet surely leaves the inner sheet discharge roller pair
25
. At that time, motors M
4
, M
5
are brought to double speed. Thereafter, the two-sided reverse roller pair
60
reversely rotates so that the double speed control is continued until immediately before the sheet abuts against a second registration roller pair (not shown) disposed upstream of the image forming means of the image forming apparatus.
However, in the conventional sheet conveying apparatus
100
, the leading end of the sheet is detected by the inner sheet discharge sensor and the control means calculates the time taken till the trailing end of the sheet leaves, thereby determining the speed control and the stop point in the reverse rotation. Therefore, slip in the roller pairs due to change in a sheet surface characteristics caused by change in an environmental condition and sheet delay due to wear of the roller pairs must be taken into consideration.
Thus, the switching to the double speed must be set with some play, thereby the total processing speed in the two-sided copying mode is reduced.
Further, also regarding the reverse position, since the same factors must be taken into consideration, dispersion in the reverse position must be made allowance for. Thus, the excessive length including the dispersion amount and a (dimensions L
a
, L
c
in
FIG. 10
) must be reserved for the reverse position, thereby making the sheet conveying apparatus and the image forming apparatus having such a sheet conveying apparatus bulky.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a sheet conveying apparatus in which a length required for surface reverse is minimized by optimizing a timing for conveying a sheet at a high speed and by increasing a processing speed in a two-sided copying mode and by reducing dispersion in a reverse position, thereby making the sheet conveying apparatus compact without increasing a manufacturing cost, and an image forming apparatus having such a sheet conveying apparatus.
To achieve the above object, a sheet conveying apparatus according to the present invention comprises sheet constant speed conveying means for conveying a sheet at a predetermined speed, a sheet conveying path for guiding the sheet being conveyed by the sheet constant speed conveying means, a sheet reverse feeding rotary member pair for forwardly rotating to convey the sheet conveyed on the sheet conveying path downstream and then reversely rotating to feed the sheet reversely, a surface reverse conveying path branched from the sheet conveying path and for guiding the sheet reversely fed by the sheet reverse feeding rotary member pair, trailing end detecting means disposed between the sheet constant speed conveying means and the sheet reverse feeding rotary member pair and for detecting a trailing end of the sheet being conveyed on the sheet conveying path, and control means for controlling rotation of the sheet reverse feeding rotary member pair in such a manner that the sheet can be conveyed at a higher speed than the predetermined speed when the trailing end of the sheet is detected by the trailing end detecting means.
In the sheet conveying apparatus, the sheet is conveyed at the predetermined speed on the sheet conveying path by the sheet constant speed conveying means. The sheet is then conveyed by the sheet reverse feeding rotary member pair.
The control means serve to rotate the sheet reverse feeding rotary member pair at a high speed to convey the sheet at the higher speed than the predetermined speed when the trailing end of the sheet being conveyed on the sheet conveying path is detected by the trailing end detecting means. In the sheet conveying apparatus according to the present invention, the control means can store a time period from when the trailing end of the sheet is detected by the trailing end detecting means to when the sheet passes by a branched portion between the sheet conveying path and the surface reverse conveying path. The control means controls the reverse rotation of the sheet reverse feeding rotary member pair on the basis of the time period.
The image forming apparatus according to the present invention comprises the aforementioned sheet conveying appar
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