Electrophotography – Internal machine environment – Forced air circulation
Reexamination Certificate
2000-09-21
2002-07-02
Chen, Sophia S. (Department: 2852)
Electrophotography
Internal machine environment
Forced air circulation
C347S170000, C399S107000
Reexamination Certificate
active
06415118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a sheet, such as a copying machine, a printer or a facsimile apparatus.
2. Related Background Art
In the field of image forming apparatus such as a copying machine, a printer or a facsimile apparatus, there have been proposed various configurations on the arrangement of a sheet cassette or a sheet tray for containing and supporting sheets for image formation, image forming means for forming an image on a sheet, fixing means for semi-permanently fixing an image transferred onto a sheet, and control means for controlling the operation of the apparatus and the image forming process. The following explanation will be given on a laser beam printer (hereinafter simply represented as printer) as an example.
The principal configuration of a conventional printer is shown in
FIGS. 4 and 5
.
A printer, constituting an image forming apparatus, is provided with a sheet supplying portion, including a sheet cassette
101
serving as sheet supporting means for supporting and containing sheets for image formation, and sheet supplying means
102
for feeding the sheet supported by the sheet cassette.
Also an image forming portion is composed of a process cartridge
103
integrally formed of a photosensitive drum
104
for image formation, a charger for uniformly charging the photosensitive drum, a developing device for forming a toner image on the photosensitive drum and a toner container, and a laser scanner
105
for writing image information by a light beam onto the photosensitive drum charged by the charger.
In a position opposed to the photosensitive drum across the conveying path of the sheet, there is provided a transfer charger
106
constituting transfer means for transferring the toner image, formed on the photosensitive drum, onto a sheet. Also in a downstream position of the transfer means, there are provided paired fixing rollers
107
serving as fixing means for semi-permanently fixing the toner image transferred onto the sheet, and the sheet on which the image is fixed by the paired fixing rollers is thereafter discharged onto a sheet discharge tray
108
provided outside the apparatus.
Such sequence of image forming operations onto the sheet is more or less same in any printer, but the features of the printer vary according to the arrangement of the sheet conveying path within the apparatus.
In the printer shown in
FIG. 4
, the above-described sheet conveying path is provided approximately horizontally in the apparatus. In
FIG. 4
, a sheet cassette
101
is provided in an inclined position, with respect to the horizontal plane, at the right-hand end portion of the apparatus, and sheet supplying means
102
is provided at an end portion of the sheet cassette. The sheet conveying plane is provided substantially horizontally toward paired fixing rollers
107
, while image forming means such as a process cartridge
103
is provided above the conveying path and a transfer charger
106
is provided in an position opposed thereto. The sheet bearing the transferred image is discharged onto a sheet discharge tray
108
positioned approximately parallel to the sheet cassette
101
.
Also a printer shown in
FIG. 5
has a configuration obtained by rotating, by 90°, the image forming apparatus shown in FIG.
4
. More specifically, in this type of the apparatus, the sheet cassette
101
and the sheet discharge tray
108
are provided substantially horizontally, and a sheet fed by the sheet supplying means
102
from the sheet cassette
101
at the lowermost part of the apparatus is conveyed in a substantially vertical direction, with respect to the horizontal plane, for performing image forming and fixing operations.
As explained in the foregoing, the sheet conveying path in the recent printers is often formed linearly and substantially horizontally or vertically from the sheet supply means
102
to the fixing means
107
, and, in such configuration, the position of the fixing means
107
becomes a problem.
The fixing means
107
achieves fixation of the toner onto the sheet by fusing the toner deposited on the sheet, by heat generated by heating of the fixing roller and by a pressure generated at the nip of the paired rollers. Consequently the fixing means
107
generates a large amount of heat at the image formation, thereby elevating the temperature in the apparatus.
In the image forming apparatus of a type in which the sheet is conveyed substantially horizontally as shown in
FIG. 4
, the process cartridge
103
and the laser scanner
105
are positioned at the side of and above the fixing means
107
constituting the source of heat, so that the heat generated by the fixing means
107
may result in inconveniences such as fusion and solidification of the toner contained in the process cartridge
103
or a change in the refractive index of optical lenses provided in the laser scanner
105
.
Also circuit boards of the control means
109
, such as an electric supply portion or a driving portion for controlling the apparatus are to be provided in a space available substantially parallel to the sheet conveying path. Since such electric supply portion and driving portion also generate heat, there is required, in order that the process cartridge
103
and the laser scanner
105
are not affected by such generated heat, means for preventing the temperature increase in the apparatus as well as for dissipating the heat generated by the fixing means
107
. This has been achieved by providing a plurality of heat insulating members for preventing the temperature increase in the apparatus or providing a fan for air cooling the interior of the apparatus, but such means results in an increase in the cost and dimension of the apparatus.
Also in the sheet supplying operation, the leading end of a sheet fed by the sheet supply means
102
reaches the image forming portion so that the image forming operation is started, before the trailing end of the sheet comes out of the sheet supply means
102
. Therefore, when the trailing end of the sheet comes out of the sheet supply means
102
, a vibration is generated in the sheet by a large diversion in the direction thereof, and such vibration is transmitted to the image forming portion to perturb the image formed on the sheet.
Also in the apparatus of a type in which the sheet is conveyed substantially vertically as shown in
FIG. 5
, the process cartridge
103
and the laser scanner
105
are relieved from the influence of heat since the fixing means
107
is provided in the uppermost position of the apparatus, but a higher precision is required for such conveying control and image forming operation because the sheet is conveyed substantially vertically against the force of gravity. Such higher precision has been achieved by providing sheet conveying guide members and paired conveying rollers in a number larger than in the apparatus in which the sheet is conveyed horizontally, but such measure results in an increase in cost and dimension of the apparatus.
Also the mounting angle of the laser scanner becomes larger than in the horizontally conveying type (cf.
FIG. 4
) to result in a larger load on the bearing of a scanner motor, whereby the bearing becomes deteriorated sooner to shorten the service life of the apparatus.
Also a large diversion in the direction of the sheet, as in the case of the type shown in
FIG. 4
, results in drawbacks such as vibration noise and a perturbation in the image.
In order to resolve the above-mentioned drawbacks, the apparatus has been so designed as to increase the dimension of the entire apparatus thereby separating the heat-generating fixing means from components susceptible to heat or as to adopt a layout allowing horizontal positioning of the laser scanner, but such measure does not lead to fundamental resolution of these drawbacks but results in other drawbacks such as an increase in dimension or manufacturing cost of the apparatus.
SUMMARY OF THE INVENTION
In consideration of the for
Ikuma Susumu
Setoriyama Takeshi
Suzuki Hidenobu
Tomoyuki Yoji
Chen Sophia S.
Tran Hoan
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