Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1999-12-02
2001-03-06
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S140000, C399S044000
Reexamination Certificate
active
06198491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process.
2. Related Background Art
Recently, image forming apparatuses used as a hardware output machines for digital data information transmission via a data communication network and such information has been proposed like anything. As such image forming apparatuses, digital printers and digital copying machines are known.
Now, as an example of a conventional image forming apparatus, a digital printer will be schematically described with reference to FIG.
19
.
FIG. 19
is a constructural view showing main portions of the digital printer. In
FIG. 19
, a photosensitive drum
1
as an electrophotographic photosensitive member is constituted by coating a photoconductive layer on a cylindrical conductive substrate and is supported for rotation in a direction shown by the arrow R
1
. Around the photosensitive drum
1
, there are disposed, in order along a rotational direction thereof, a scorotron charger
2
for uniformly charging a surface of the photosensitive drum
1
, an exposure device for reading an original and for forming an electrostatic latent image by exposure the photosensitive drum
1
in accordance with an image signal proportional to image density, a developing device
4
for forming a toner image by adhering toner to the electrostatic latent image, a corona transfer charger (transfer charger)
8
for transferring the toner image formed on the photosensitive drum
1
onto a transfer sheet (transfer material) P, an electrostatic separating charger (separating charger)
9
for separating the transfer sheet P to which the toner image is transferred from the photosensitive drum
1
, a cleaning device
13
for removing residual toner from the photosensitive drum
1
after the toner image is transferred, and a pre-exposure (lamp)
30
for eliminating residual charge on the photosensitive drum
1
.
By the way, after separated from the photosensitive drum
1
the transfer sheet P to which the toner image is transferred is conveyed to a fixing device
12
, where the toner image is fixed to the transfer sheet to obtain a desired print image, and the transfer sheet P to which the toner image is fixed is discharged out of a main body of the image forming apparatus.
On the other hand, in a reader portion
18
, an original
15
rested on an original glass stand
14
is illuminated by an illumination lamp
16
, and light reflected from the original
15
is imaged on a photo-electric converting element (one-line CCD)
19
to convert the light into an electrical signal corresponding to image information. The light reflected from the original
15
illuminated by the illumination lamp
16
is imaged on the photo-electric converting element
19
through mirrors
17
a
,
17
b
,
17
c
and a lens
17
d
. The electrical signal outputted from the photo-electric converting element
19
is A/D-converted by an A/D-converter
21
into an 8-bit digital image data which is in turn logarithmically transformed in a black signal generating circuit
22
for changing luminance information to density information to obtain image density data.
The 8-bit digital image data signal formed in this way is inputted to a laser driving circuit
24
. The laser driving circuit
24
is a well-known PWM circuit which modulates a light emitting time for ON/OFF of a laser diode in accordance with magnitude of the image density signal inputted.
For example, when the image data per pixel is inputted in a laser scanning direction as shown in
FIG. 4A
, a driving signal for ON/OFF of the laser becomes as shown in FIG.
4
B. That is to say, ON duty of the laser driving signal when the image data is 00 hex is selected to 5% of one pixel scanning time, and ON duty of the laser driving signal when the image data is FF hex is selected to 85% of one pixel scanning time. A tone (dark/light) is achieved by effecting area-gradation within one pixel in this way.
Further,
FIG. 6
shows general I−L property (driving electric current−amount of light property) of the laser. Since driving currents used for ON and OFF of the laser are I
on
and I
off
, respectively, the laser driving signal for the image signal of
FIG. 4A
becomes as shown in
FIG. 4C
, which is current for driving the laser by the PWM circuit.
By the way, the laser driving circuits are generally divided into the above-mentioned PWM circuit and a binary value laser driving circuit. As mentioned above, the PWM circuit serves to modulate to a pulse width signal corresponding to the time for lighting the laser diode in accordance with the magnitude of the inputted image density signal; whereas, in the binarizing circuit, the signal is converted into a two-step signal including special ON light emitting signal and OFF signal in accordance with the pixel size, and the converted signal is inputted to the laser driving circuit
24
so that the laser diode element is turned ON/OFF. As a typical method for binarization, there is a method in which the binarization signal is formed by an error diffusion technique and a dither technique on the basis of the image data, and, fundamentally, the time for generating the laser light is constant regardless of density. The difference is that the laser is emitted at low frequency for the pixel having low density and is emitted at high frequency for the pixel having high density.
The laser light driven and emitted in accordance with the image signal in this way is written on the photosensitive drum
1
in raster scan manner through a high speed rotating polygon mirror scanner
28
and a mirror
17
f
(FIG.
19
), thereby forming the digital electrostatic latent image as image information.
Conventionally, many electrophotographic processes have been proposed as disclosed in U.S. Pat. No. 2,297,961, Japanese Patent Publication No. 42-23910 (1967) and Japanese Patent Publication No. 43-24748 (1968). In the general process, an electric latent image is formed on a photosensitive drum (recording member utilizing photo-electric material) by various means, and then the latent image is developed with toner (developer) to obtain a toner image which is in turn transferred onto a transfer material such as paper, and the toner image is fixed to the transfer material by heat or solvent vapor, thereby obtaining the copy image.
Further, various developing methods for visualizing the electric latent image by using the developer are already known. For example, there are magnetic brush development as disclosed in U.S. Pat. No. 2,874,063, powder cloud development as disclosed in U.S. Pat. No. 2,221,776, fur brush development and liquid electrophoretic development. Among such developments, particularly, although the magnetic brush development using two-component developer mainly including toner and carrier has widely been put to practice, this development can provide good image relatively stably, but has disadvantage inherent to the two-component developer such as deterioration of toner and change in mixing ratio between the toner and the carrier.
In order to eliminate the above disadvantages, various developments using one-component developer consisting of toner have been proposed. According to this development, since control of the mixing ratio of the toner to the carrier is not required, the apparatus can be made more simpler.
In the above-mentioned conventional examples, when a corona charger is used as means for uniformly charging the photosensitive member, ozone and nitrate (discharged substance) form a film on the photosensitive member. If the film absorbs moisture in the air, surface resistance of the photosensitive member is decreased not to hold the charges of the electrostatic latent image (after exposure) including the image information data, with the result that the image is flown along the surface to distort the image information partially or totally, thereby flowing the image as if aqueous ink is flown. Similarly, when a corona charger is also used as a post charger, the similar disadvantag
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Susan S. Y.
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