Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-01-30
2002-12-10
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S388000
Reexamination Certificate
active
06493534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotography type or electrostatic photography type image forming apparatus such as a copying apparatus, a laser beam printer and a facsimile, and a sheet conveying apparatus to be applied to such an image forming apparatus.
2. Related Background Art
A conventional image forming apparatus will be described with reference to FIG.
12
.
FIG. 12
is a configurational diagram of a laser beam printer configured as the conventional image forming apparatus. Description will be made of an overall configuration and functions of the laser beam printer.
In
FIG. 12
, a feed cassette
13
which contains loaded sheets S is disposed in a lower section of a main body of the laser beam printer. The feed cassette
13
is configured to be detachable from and attachable to the main body of the laser beam printer.
Reference numeral
14
denotes a feed roller which feeds the sheets S loaded in the above described feed cassette
13
one by one from an uppermost side. Reference numeral
15
denotes a guide member which guides the sheet S fed by the above described feed roller
14
.
Reference numeral
16
denotes a conveying roller and reference numeral
17
denotes a driven runner. The conveying roller
16
and the driven runner
17
constitute a conveying roller pair. Rollers
1
and
2
are a registration roller pair comprising an upper registration roller
1
and a lower registration roller
2
which correct a skew feed of the sheet S by allowing a leading end of the sheet S to strike against a nip portion of the registration roller pair in a stop condition to form a loop of the sheet S, and then rotate at a predetermined timing to convey the sheet S to image forming means.
A process cartridge
80
is detachably mounted in the main body of the printer. Mounted in the process cartridge
80
is a photosensitive drum
8
as well as a cleaner
81
, a developing device
82
, a primary charger (not shown) or the like which are disposed around the photosensitive drum
8
.
Reference numeral
18
denotes a laser scanner which scans a laser beam in correspondence to image information and performs write (electrostatic latent image formation) on the photosensitive drum
8
. A latent image formed on a circumferential surface of the photosensitive drum
8
is developed by the developing device
82
into a developer (toner) image. Reference numeral
9
denotes a transfer roller which is in pressure contact with the above described photosensitive drum
8
and transfers the developer (toner) image from the photosensitive drum
8
to the sheet S while the sheet S is passing between the transfer roller
9
and the photosensitive drum
8
. The process cartridge
80
, the transfer roller
9
, a fixing device or the like described later compose the image forming means for forming an image on the sheet.
Reference numeral
19
denotes a conveying guide which leads the sheet S to the fixing device after the image is transferred to the sheet S. The fixing device which functions to fix the image (toner image) transferred to the sheet S has a fixing roller
20
, a pressure roller
21
, a fixing discharge roller pair
22
or the like. The sheet S is conveyed to a discharge roller pair
24
by a conveying roller pair
23
and discharged outside the printer after image fixing with a surface of the sheet S on which the image is formed facing downward.
Reference numeral
25
denotes a discharge tray which is formed on a top surface of the main body of the printer for loading and holding the sheet S which is discharged outside the printer after the image fixing.
Description will be made of image forming operations of the laser beam printer configured as described above. When image formation is designated from a host computer (not shown), the feed roller
14
first rotates, and the sheets S are fed one by one from the uppermost sheet in the feed cassette
13
and guided by the guide member
15
to the conveying roller pair consisting of the conveying roller
16
and the driven runner
17
and the registration roller pair.
The registration roller pair conveys the sheet S between the photosensitive drum
8
and the transfer roller
9
at a timing registered with an image formed on the photosensitive drum
8
and an image (toner image) is transferred to the sheet S while the sheet S is passing between the photosensitive drum
8
and the transfer roller
9
.
After transferring the image, the sheet S is conveyed to the fixing device along a conveying guide
19
, and the transferred image is fixed by applying heat and a pressure while the sheet S is passing between the fixing roller
20
and the pressure roller
21
.
After fixing the image, the sheet S is conveyed by the fixing discharge roller
22
and further discharged and loaded into the discharge tray
25
by the discharge roller pair
24
.
A description will be made of a sheet conveying device in detail with reference to
FIGS. 12 and 13
.
FIG. 13
is a schematic diagram of an image forming station of the laser beam printer shown in FIG.
12
.
The sheet S which is fed from the feed cassette
13
by the feed roller
14
passes through the conveying roller pair consisting of the conveying roller
16
and the driven runner
17
, and is fed into the nip of the registration roller pair consisting of the upper registration roller
1
and the lower registration roller
2
in a stop state of rotating.
The registration roller pair is under a pressure and stops conveyance of the sheet S at an entrance of the nip, thereby allowing the sheet S to form a loop when a leading end of the sheet S is sent into the nip portion of the registration roller pair.
When the registration roller pair starts rotating once again, the sheet S passes between a first sheet guide member
6
and a second sheet guide member
7
and sent into a nip formed by the photosensitive drum
8
and the transfer roller
9
.
However, the above described conventional technique poses problems which are described below. That is, it has become general to print high quality images such as photographic images directly on a thick sheet of paper or the like with printers as laser beam printers are configured to operate at higher speeds and form images of higher qualities.
In
FIG. 13
, the sheet S which is advanced toward transferring means by the registration roller pair is led into the transferring means by the upper and lower sheet guide members
6
and
7
. When the sheet S is led into the transferring means, the leading end of the sheet S strikes against the photosensitive drum
8
and then the sheet S is led into a transfer nip.
When the sheet S is a thick sheet of paper in particular, a strong impact is imparted to the photosensitive drum
8
at a write time with a laser, thereby producing an adverse influence on an image. Furthermore, a halftone image may be disturbed due to vibrations of the drum at a developing position which is a position of a developing roller and the photosensitive drum at an instant at which a leading end of the sheet strikes against the photosensitive drum
8
, a position at which the photosensitive drum
8
is irradiated with the laser or a charging position at which the photosensitive drum is charged.
Furthermore, an influence on an image is more remarkable as the higher a speed of a printer, the higher a conveying speed of the sheet.
Furthermore, printers have nowadays high resolutions of 1200 dpi and 2400 dpi for enhancing image qualities. The influence on the image due to the impact is more remarkable at a higher resolution. Furthermore, a sheet which is not the thick sheet of paper may produce an influence on an image.
Furthermore, frequently used nowadays as means for transferring a toner image from a photosensitive drum to a sheet is transferring means which uses a contact rotating type transferring member, or the so-called transfer roller, which is brought into contact with a photosensitive drum, subjected to voltage application, and is used for sandwiching and conveying the sheet in a transfer po
Ando Masao
Kanari Kenji
Matsuguma Minoru
Noguchi Tomio
Sawanaka Kei
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Susan S. Y.
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