Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-10-25
2001-02-20
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S322000, C399S336000, C399S341000, C399S384000
Reexamination Certificate
active
06192213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a double-side printing apparatus for printing on double sides of a recording medium and, more particularly, to a double-side printing apparatus in which a plurality of electrophotographic recording units are disposed.
2. Related Background Art
A printing apparatus has been widely utilized as an output apparatus of a computer. An electrophotographic apparatus capable of printing on an ordinary sheet of paper has been utilized as the printing apparatus. In response to a demand for saving natural resources in recent years, a double-side printing apparatus for printing on double sides of the sheet has been required. Then, an apparatus provided with both a printing mechanism for printing on the right side of the recording medium and a printing mechanism for printing on the reverse side of the recording medium, is required for increasing printing speed.
FIG. 7
is an explanatory view showing the prior art.
The double-side printing apparatus includes an electrophotographic printing unit (a second image forming unit)
91
for printing on the right side of a sheet of recording paper P, and an electrophotographic printing unit (a first image forming unit)
92
for printing on the reverse side of the sheet P. The sheet P is classified as continuous paper perforated to delimit each page. The reverse side printing unit
92
has a photosensitive drum. The photosensitive drum is charged by a pre-charger and thereafter exposed to a light image by an exposing unit. An electrostatic latent image corresponding to the light image is thereby formed on the photosensitive drum. The latent image on the photosensitive drum is developed by a developing unit. Then, the developed image on the photosensitive drum is transferred onto the sheet P by a transferring unit. Thus, the image is printed on the reverse side of the sheet P.
The printing on the right side of the sheet P is likewise performed. To be specific, the right side printing unit
91
has a photosensitive drum. The photosensitive drum is charged by a pre-charger and thereafter exposed to a light image by an exposing unit. An electrostatic latent image corresponding to the light image is thereby formed on the photosensitive drum. The latent image on the photosensitive drum is developed by a developing unit. Subsequently, the developed image on the photosensitive drum is transferred onto the sheet P by a transferring unit. Thus, the image is printed on the right side of the sheet P.
Next, a toner image on the reverse side of the recording sheet P is fixed by a first fixing unit
93
. Then, a toner image on the right side of the recording sheet P is fixed by a second fixing unit
94
. Thus, according to the described double-side printing process, after the toner image has been formed on the right side, the toner image is formed on the reverse side. And then a fixing process is performed, thereby the double-side printing apparatus can be downsized. This type of double-side printing apparatus for printing on the continuous paper is disclosed in Japanese Patent Application Laid-Open Publication Nos.7-77851 and 8-211664.
There arise, however, the following problems inherent in the prior art.
First, if flash fixing units for fixing by a flash light are used as the fixing units
93
,
94
, the image can be fixed in a non-contact manner onto the sheet. Therefore, even when unfixed images are fixed by continuous feeding, it never happens that the unfixed images are disturbed. The flash has, however, a high intensity, and hence leaked flash beams strike upon the photosensitive drum of the electrophotographic printing unit, resulting in such a problem that the photosensitive drum might be deteriorated. Especially, the flash beams from the first fixing unit
93
impinge on the photo sensitive drum of the second electrophotographic printing unit
91
through the sheet P, and the problem is also the deterioration of this photosensitive drum.
Second, it is necessary for stabilizing the carry of the sheet that a guide member is provided between the first fixing unit and the second electrophotographic printing unit
91
. The guide member is, however, brought into contact with the unfixed image on the sheet, and consequently the toner image is offset by the guide member, with the result that the disturbance of the unfixed image on the sheet might occur as another problem.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a double-side printing apparatus capable of preventing a deteoritation of a photo conductive body of an image forming unit even when a fixing unit by a light is used as a fixing unit.
It is an another object of the present invention to provide a double-side printing apparatus capable of preventing a disturbance of an unfixed image even when providing a guide member.
To accomplish the above object, according to a first aspect of the present invention, a double-side printing apparatus for printing on double surfaces of a recording medium, comprises a first image forming unit for forming a toner image on one surface of the recording medium, a second image forming unit, provided downstream of the first image forming unit and including a photo conductive body for forming a toner image on the other surface of the recording medium, a first fixing unit for fixing the toner image on one surface of the recording medium by a light, a second fixing unit, provided downstream of the first fixing unit, for fixing the toner image on the other surface of the recording medium, and a preventing member, provided between the first fixing unit and the second image forming unit, for preventing the light of the first fixing unit from reaching the photo conductive body of the second image forming unit.
In the double-side printing apparatus according to the first aspect of the invention, the preventing member for cutting off the light from the first fixing unit is provided between the closest second image forming unit and the first fixing unit. Therefore, even when the first fixing unit is provided with the flash fixing unit for fixing by use of the flash, it is feasible to prevent the flash from impinging upon the photosensitive body of the second image forming unit. The photosensitive body of the image forming unit can be thereby prevented from being deteriorated.
According to a second aspect of the invention, the preventing member is constructed of a guide roller for guiding the recording medium. With this contrivance, the preventing member guides the recording medium, and hence the recording medium can be guided with a stability between the first fixing unit and the second image forming unit. Further, even when a non-contact type fixing unit is provided as the first fixing unit, the recording medium can be stably carried.
According to a third aspect of the invention, the guide roller contacts with the other surface of the recording medium.
According to a fourth aspect of the invention, the guide roller rotates at the same speed as a carrying speed of the recording medium.
According to a fifth aspect of the invention, the double-side printing apparatus further comprises a cleaning member for cleaning the guide roller.
According to a sixth aspect of the invention, a double-side printing apparatus comprises a first image forming unit for forming a toner image on one surface of the recording medium, a second image forming unit, provided downstream of the first image forming unit, for forming a toner image on the other surface of the recording medium, a first fixing unit for fixing the toner image on one surface of the recording medium, a second fixing unit, provided downstream of the first fixing unit, for fixing the toner image on the other surface of the recording medium, a guide member, provided between the first fixing unit and the second image forming unit, for guiding the recording medium, and a charger for charging the recording medium to prevent an offset of an unfixed image to the guide member.
In the double-side printing apparatus a
Adachi Katsumi
Wada Yoshinori
Armstrong, Westerman Hattori, McLeland, and Naughton, LLP
Chen Sophia S.
Fujitsu Limited
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