Sheet feeding or delivering – Feeding – By means to convey sheet
Reexamination Certificate
2000-04-10
2002-01-22
Skaggs, H. Grant (Department: 3651)
Sheet feeding or delivering
Feeding
By means to convey sheet
C271S188000, C271S010100, C399S406000
Reexamination Certificate
active
06340156
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet-transporting device provided in various sheet-employing apparatuses, such as image-forming apparatuses and other office equipment. In such image-forming apparatuses, an appropriate transfer-type image-forming process (such as an electrophotographic-type image-forming process) or a direct-type image-forming process is used. Examples of the image-forming apparatus include printers, facsimile machines, and copying machines.
2. Description of the Related Art
FIG. 7
is a schematic structural view of a conventional image-forming apparatus comprising a sheet-feeding section and a register section which temporarily stops the leading edge of a recording sheet fed from the sheet-feeding section, forms a loop in the recording sheet to correct any oblique movement of the recording sheet, and sends the recording sheet to an image-forming section at a predetermined timing. The conventional image-forming apparatus roughly comprises an image-input section
90
R and an image-output section
90
P.
The image-input section
90
R is, for example, an image information photo-reader mechanism. Image information to be recorded is input to the image-input section
90
R, and variously processed. Then, an image signal carrying the image information is sent to the image-output section
90
P. The image-input section
90
R may be an optical device for exposing an image-carrying member of an image-forming section
91
of the image-output section
90
P with light carrying an image of an original by projecting and focusing the light thereon.
The image-output section
90
P is a transfer-type image-recording mechanism using a transfer drum
93
. It comprises the image-forming section
91
; first to third sheet-feeding units
92
A to
92
C, serving as sheet-feeding sections; a sheet-transporting section
97
disposed in front of a register roller pair
96
serving as a register section; a transfer drum
93
; a fixing unit
94
; and a control unit
95
. The image-forming section
91
is used to form a transferable image, such as a toner image, on an image-carrying member, such as a photoelectric member, a dielectric member, or a magnetic member, by a suitable image-forming process, such as the electrophotographic-type image-forming process, an electrostatic-recording process, or a magnetic-recording process, in accordance with the image information input to the image-output section
90
P. The sheet-transporting section
97
transports a recording sheet P fed from any one of the sheet-feeding units
92
A to
92
C to the register roller pair
96
. The transfer drum
93
holds the recording sheet P transported from the register roller pair
96
and transports it to a transfer section T of the image-forming section
91
. The fixing unit
94
fixes the image to the recording sheet P onto which the image has been transfer at the transfer section T of the image-forming section
91
. The control unit
95
controls all of the operations of the image-forming apparatus.
The first and the second sheet-feeding units
92
A and
92
B are incorporated in the image-output section
90
P as top and bottom mechanisms for automatically separating sheets one by one for feeding. Starting from the topmost recording sheet, the recording sheets P loaded in and held by a sheet-feed cassette are fed one sheet at a time as a result of cooperation of a corresponding sheet-feed roller and a corresponding separating member based on a sheet-feed start signal. The third sheet-feeding unit
92
C is a manual sheet-feeding device. When it is used, a recording sheet P is inserted into the image-forming apparatus from a manual sheet-feed table, and is drawn into the image-forming apparatus in order to be fed to transfer section T.
When the image-forming apparatus starts to operate, a recording sheet P is fed from any one of the first to third sheet-feeding units
92
A to
92
C, and transported to the register roller pair
96
through the transporting section
97
by transporting roller pairs
98
A,
98
B, and
98
C, and a curling roller set
99
. The transporting roller pairs
98
A to
98
C and the curling roller set
99
can rotate in two different of rotational modes, or at two transporting speeds. In one mode, they rotate at ordinary transporting speeds. In the other mode, they rotate at speeds greater than the ordinary transporting speeds.
At the moment the edge of the recording sheet P fed from any one of the sheet-feeding units
92
A to
92
C is nipped by the corresponding first transporting roller pair (the transporting roller pair
98
A if the sheet has been fed from the first sheet-feeding unit
92
A; the transporting roller pair
98
B if the sheet has been fed from the second sheet-feeding unit
92
B; and the curling roller set
99
if the sheet has been fed from the third sheet-feeding unit
92
C) rotating at the ordinary transporting speed, the ordinary transporting speeds of the pairs of transporting rollers
98
A and
98
B and the pair of curling rollers
99
are switched to the higher transporting speeds in order to transport the sheet to the register roller pair
96
at a high speed. By this speed-controlling operation, the time from the start of the sheet-feeding operation to the start of the image-forming operation can be reduced compared to that when the recording sheet is transported only at the ordinary transporting speed. The rotational speed of each roller is changed by switching the rotational speed of a corresponding motor (not shown), such as a stepping motor. Each motor is directly connected to its corresponding roller. For example, when the transporting speed is to be quadrupled from 150 mm/s to 600 mm/s, the number of rotations of the driving motor of each roller is increased by a factor of
4
. In order to reduce loss of transporting speed, the speed switching is carried out in a short time period, that is, a time period of the order of 100 ms.
FIG. 4
illustrates the curling roller set
99
in detail. The pair
99
comprises two upper rollers
99
A and
99
B and one lower roller
99
C. The two upper rollers
99
A and
99
B are pressed against the lower roller
99
C by a spring or other biasing means (not shown). As shown in
FIG. 4
, when the recording sheet P passes between the two upper rollers
99
A and
99
B and the lower roller
99
C, the recording sheet P is curled upward into a convex shape. When the recording sheet P is curled, the recording sheet P is more easily attracted to the transfer drum
93
.
However, since the one lower roller
99
C is pressed by the two upper rollers
99
A and
99
B, the driving torque of the curling roller set
99
is larger than those of the transporting roller pairs
98
A and
98
B. For example, while the driving torques of these transporting roller pairs
98
A and
98
B are of the order of 1 kgf·cm, the driving torque of the curling roller set
99
is of the order of 2.5 kgf·cm.
An image corresponding to relevant image information is formed on the image-carrying member in the image-forming section
91
. In synchronism with an image-recording start signal, the register roller pair
96
starts to rotate, and the transporting section
97
returns to its recording-sheet-transporting state. The recording sheet P is transported from the register roller pair
96
to the rotating transfer drum
93
, and held by the outer face of the rotating transfer drum
93
in order to be transported to the transfer section T. This causes the portions of the image formed on the image-carrying member of the image-forming section
91
to be successively transferred onto the recording sheet P.
There are several methods by which the recording sheet P can be held by the outer face of the transfer drum
93
. The methods include electrostatic suction and air suction, towards a transporting medium, such as a thin dielectric film.
The timing at which the recording sheet P is transported by the register roller pair
96
is controlled such that when an edge of the image carried by the image-carrying member of the image-f
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