Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-09-05
2001-12-25
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S131000
Reexamination Certificate
active
06333755
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic apparatus, such as a printer, a copier or a facsimile machine, and relates in particular to an electrophotographic apparatus that includes exposure means for exposing a photosensitive body to digital light.
2. Description of the Related Background Art
Electrophotographic printers have been drawing attention because of the features, such as high image quality and high printing speeds, that they provide.
FIG. 21
is a diagram illustrating the schematic arrangement of an electrophotographic printer that employs light beams for scanning and for exposing.
An organic or inorganic electrophotographic photosensitive body
1
, a rotating drum, is a recording medium, and is rotated clockwise, as indicated by an arrow, at a predetermined peripheral speed.
Charging means
2
is a corona charging device or a contact charging roller, for example, that uses a predetermined polarity and potential to uniformly charge the external surface of the rotating photosensitive body
1
.
An optical scanning apparatus
3
is a laser scanner or an LED array apparatus (a light-emitting device array apparatus), for example, that serves as image forming light irradiation means. When a light beam L is modulated and is output, in consonance with image information, by the optical scanning apparatus
3
, it is used to scan and expose the charged face of the rotating photosensitive body
1
. Thereafter, on the portion of the bright face of the photosensitive body
1
that is exposed the potential is decayed, and due to the potential contrast subsequently established by the potential on the dark exposed portion, an electrostatic latent image is formed on the face of the photosensitive body in consonance with the image information pattern that is scanned and exposed.
Development means
4
uses a developer (toner) to develop normally or to develop reversely the latent electrostatic image on the photosensitive body
1
and to visualize it as a toner image.
Transfer means
5
is a transfer corona charging device or a transfer roller, for example. A transfer material (a recording medium) P is fed by a paper feeding mechanism (not shown) to a transfer portion between the transfer means and the photosensitive body
1
in consonance with a predetermined control timing. The transfer material P is conveyed while attached to the face of the photosensitive body
1
, while concurrently the toner image on the photosensitive body
1
is transferred to the face of the transfer material P.
Once the transfer material P has passed through the transfer portion it is separated from the photosensitive body
1
and is fed into fixing means
7
, wherein, the toner image is subjected to a fixing process and the transfer material P is printed out.
After the transfer material P has been separated from the photosensitive body
1
, residual toner is removed from the face of the body
1
by cleaning means
6
, such as a blade or a fur brush, and the cleaned face of the photosensitive body
1
is again employed for image formation.
The main light sources for the image forming light irradiation means
3
are a laser and an LED. The procedure performed to scan the photosensitive body
1
, which is a recording medium, greatly affects printer performance, including the quality of the images it provides and the printing speed. Mainly, an LED is employed for processing involving the use of a spatial installation and electric scanning combination, while a laser is employed for processing involving the use of an optical scanning and electric scanning combination.
Further, while taking the relationship between image information and an exposure portion into account, roughly two image forming methods are available for use with a digital electrophotographic apparatus.
One method is an image exposure method (hereinafter referred to as the IAE method) according to which an image portion is exposed, and the other method is a background exposure method (hereinafter referred to as the BAE method) according to which a non-image portion (the background) is exposed.
The BAE method is the same as the image forming method used for an analog electrophotographic apparatus, and as an advantage provides that development and cleaning properties and a developer can be used in common by an analog electrophotographic apparatus.
On the other hand, according to the IAE method, to obtain an image, reversal-developing using a developer having the opposite polarity must normally be performed.
In practice, both methods are used, but their use tends to be determined by the operating limitations imposed by the photosensitive body and the developer that are employed.
Various development methods, including one-component development and two-component brush development, have been proposed or adapted for use with the development means
4
in accordance with the needs for specific processing, such as monochromatic printing or color printing. Generally, the image reproduction property of two-component brush development is superior to that of one-component development. These methods possess unique properties.
The following is a listing of the properties possessed by the primary developing methods.
a) BMT method and FEED method
one-component, insulating, magnetic, contact
the FEED method especially has substantially the same image characteristics as the two-component brush development.
b) touch-down method
one-component, insulating, nonmagnetic, contact
the occurrence of fog due to contact development is a problem.
c) jumping method
one-component, insulating, magnetic, noncontact
because of noncontact, fog and scratches seldom occur.
d) projection method
one-component, insulating, nonmagnetic, noncontact
because of noncontact, fog and scratches seldom occur, and because this method is nonmagnetic, color printing is available.
e) magnedynamic method
one-component, conductive, magnetic, contact
induced charging using a latent image electric field, brush development
either a positive or a negative latent image can be developed, but image transfer is difficult.
f) IMB method
two-component, insulating, nonmagnetic, contact
since an insulating carrier is employed, electric charges of the opposite polarity are accumulated after image development.
reproduction of solid image portions is not especially notable, but reproduction of fine lines is superior.
g) CMB method
two-component, conductive, nonmagnetic, contact
since a conductive carrier is employed, electric charges of the opposite polarity are not accumulated after image development.
reproduction of solid image portions is superior, but reproduction of fine lines at a low density is not especially notable.
The transfer and separation performances are greatly affected by the transfer efficiency and the separation/re-transfer latitude. Since in the IAE method the potential of the non-image portion (the background) is higher than the potential of the image portion, the latitude for the BAE method is greater than that for the IAE method.
Further, since the potential of the photosensitive body has decayed by the time cleaning is initiated, according to the IAE method for the development of an image on a low potential portion, much developer tends to remain attached to the photosensitive body at the cleaning position, and as for the cleaning property, the latitude for the BAE method is also greater than that for the IAE method.
As is apparent from the above explanation, the BAE method is easier to design, and has the potential of providing a stable electrophotographic apparatus for which the latitude is large.
However, for image recording for which a light beam is used for scanning, the latitude for the BAE method is less than the latitude for the IAE method, as will be described below.
Specifically, according to the image recording technique for which light beam scanning is used, the size, the shape and strength of a light beam spot greatly affect image quality and stabilization. Especially with an electrophotographic apparatus, since the
Ehara Toshiyuki
Kawada Masaya
Ohwaki Hironori
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Susan S. Y.
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