Electricity: electrical systems and devices – Electric charging of objects or materials
Reexamination Certificate
2000-09-29
2003-09-30
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Electric charging of objects or materials
C361S212000, C361S220000, C361S235000
Reexamination Certificate
active
06628499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charging apparatus of a printer, and more particularly, to a printer charging apparatus having a simplified voltage generating circuit for charging a photoreceptor medium to a predetermined electric potential.
2. Description of the Related Art
FIG. 1
is a view showing the structure of a typical liquid type electrophotographic color printer. Referring to the drawing, the printer includes a photoreceptor web
11
, a discharger
12
, a charging apparatus
20
, a surface electric potential sensor
13
, a plurality of laser scanning units
14
, a plurality of developing units
15
, a drying unit
16
, and a transfer unit
17
.
The developing units
15
supply developer for yellow (Y), magenta (M), cyan (C) and black (K) to the photoreceptor web
11
to develop an electrostatic latent image formed by the corresponding laser scanning units
14
. The drying unit
16
removes a liquid carrier component remaining on the photoreceptor web
11
. The transfer unit
17
transfers a toner image formed on the photoreceptor web
11
to a sheet of paper
18
. The discharger
12
removes the electrostatic latent image remaining on the photoreceptor web
11
by emitting light onto the photoreceptor web
11
. The surface electric potential sensor
13
detects the electric potential of the photoreceptor web
11
.
The charging apparatus
20
charges the photoreceptor web
11
to a predetermined electric potential so that a new electrostatic latent image can be written on the photoreceptor web
11
. The charging apparatus
20
includes a first electrode
21
and a second electrode
31
which are separated from each other. The first electrode
21
is typically referred to as a corona electrode and the second electrode
31
is referred to as a grid electrode.
To charge the photoreceptor web
11
in an electromagnetic induction method, the second electrode
31
maintains an electric potential level of the photoreceptor web
11
to be charged or an electric potential slightly greater than the electric potential level of the photoreceptor web
11
to be charged. An electric potential level much greater than that of the second electrode
31
is applied to the first electrode
21
. For example, when it is desired that the photoreceptor web
11
be charged to 600 volts, the first electrode
21
is maintained at 5 through 6 kilo-volts while the second electrode
31
is maintained at 600 through 800 volts.
Referring to
FIG. 2
, the conventional charging apparatus
20
includes a first high voltage generating unit
25
for generating a high voltage to the first electrode
21
and a second high voltage generating unit
35
for generating the second high voltage lower than that of the first electrode
21
to the second electrode
31
.
An engine controller
40
outputs information on the voltage level to be generated by the first and second high voltage generating units
25
and
35
, to the first and second high voltage generating units
25
and
35
. The first high voltage generating unit
25
includes a first PWM (pulse width modulation) controlling portion
22
, a first switch
23
, and a first transforming portion
24
. The second high voltage generating unit
35
includes a second PWM (pulse width modulation) controlling portion
32
, a second switch
33
, and a second transforming portion
34
. Here, voltage generating processes of the first and second high voltage generating units
25
and
35
are the same. The voltage generating process of the first high voltage generating unit
25
is described as follows.
When the engine controller
40
outputs information on a target voltage to be maintained at the first electrode
21
to the first PWM controlling portion
22
, the first PWM controlling portion
22
controls the first switch
23
to be turned on/off at a duty set corresponding to the target voltage. Here, the duty signifies a ratio of the time the first switch
23
is turned on during a set period.
When the first switch
23
is turned on/off at a set duty, a voltage increased as much as a coil turn ratio is induced by the first transforming portion
24
. The induced voltage is rectified by a capacitor. The voltage rectified by the smoothing capacitor varies depending upon the duty.
The second high voltage generating unit
35
generates a voltage of the second electrode
31
in the same way as that in the first high voltage generating unit
25
. However, since the conventional charging apparatus
20
adopts the two high voltage generating units
25
and
35
having different voltage levels to be generated, the structure of the printer is complicated.
SUMMARY OF THE INVENTION
To solve the above problem, it is an object of the present invention to provide a charging apparatus of a printer in which the structure of a circuit for charging the photoreceptor web to a predetermined electric potential is made simple.
Accordingly, to achieve the above object, there is provided a charging apparatus of a printer for charging a photoreceptor medium to a predetermined electric potential which includes a first electrode and a second electrode installed to be separated a predetermined distance from the first electrode and to face the photoreceptor medium, in which the charging apparatus comprises a high voltage generating unit for generating a voltage provided to the first electrode, a first varister connected to one end of the second electrode, a second varister having one end connected to the first varister in parallel and the other end connected to a ground terminal, a switching unit connected to the second varister in parallel, and an engine controller for controlling a switching operation of the switching unit to control a voltage maintained at the second electrode.
Also, to achieve the above object, there is provided a charging apparatus of a printer for charging a photoreceptor medium to a predetermined electric potential which includes a first electrode and a second electrode installed to be separated a predetermined distance from the first electrode and to face the photoreceptor medium, in which the charging apparatus comprises a high voltage generating unit for generating a voltage provided to the first electrode, a varister having one end connected to one end of the second electrode, a capacitor having one end connected to the other end of the varister and the other end connected to a ground terminal, a switching unit connected to the capacitor in parallel, and an engine controller for controlling a switching operation of the switching unit to control a voltage maintained at the second electrode.
REFERENCES:
patent: 5272507 (1993-12-01), Yoshida et al.
patent: 5287146 (1994-02-01), Uno et al.
Jackson Stephen W.
Sughrue & Mion, PLLC
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