Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2002-07-24
2004-02-03
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C399S046000, C399S050000, C399S053000
Reexamination Certificate
active
06687470
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 2002-5649, filed Jan. 31, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of compensating for image quality of a printing machine, and more particularly, to a method of compensating for image quality to provide a high quality image by effectively controlling a toner reproduction curve (TRC) to cope with environmental changes.
2. Description of the Related Art
An electrophotographic process used in a printing machine generally includes an initial step of charging a surface of a photoconductor. The charged surface of the photoconductor is exposed to light to form a latent electrostatic image in a specific image area. A develop unit controls a developing solution to adhere to the latent electrostatic image to develop the latent electrostatic image. The developed image is transferred to paper. The transferred image is fixed on the paper by a fixing roller.
In the step of charging the surface of the photoconductor, the photoconductor is charged with a uniform (constant) charge voltage so as to improve the quality of a printed image. Thus, the charge voltage charged on the photoconductor needs to be controlled to be uniform (constant). If the charge voltage is low, pollutants may occur in a non-image area. If the charge voltage is high, developed mass of the developing solution is changed. If the charge voltage is excessive, the photoconductor can become permanently damaged.
The charge voltage of the photoconductor is strengthened (modified) to a predetermined voltage, so-called “exposure voltage,” to form the latent electrostatic image in the exposure step. The developer unit has a developer bias so that a development voltage of the developing solution is higher than the exposure voltage of a portion on which the latent electrostatic image is formed, and lower than a non-image voltage of another portion of a photosensitive belt on which the latent electrostatic image is not formed. Due to this, a development step of adsorbing the developing solution to the latent electrostatic image may further be performed.
The developed mass of the developing solution absorbed in the latent electrostatic image is affected due to the exposure voltage and a development voltage as well as the charge voltage as described above.
A deviation (difference) between the development voltage and the exposure voltage becomes too big when the exposure voltage is low even though the uniform development voltage is applied. As a result, the adsorption of the developing solution increases. In contrast, the deviation between the development voltage and the exposure voltage is small when the exposure voltage is high even though the uniform development voltage is applied, thereby decreasing the adsorption of the developing solution. As a result, the developed image fades.
According to the above-described principle, when the photoconductor, which is charged with a predetermined charge voltage and a predetermined exposure voltage, is overcharged with the development voltage, a big deviation between the development voltage and the exposure voltage causes the developing solution to be excessively adsorbed on (attached to) the surface of the photoconductor. In contrast, the photoconductor is undercharged with the development voltage, a small deviation between the development voltage and the exposure voltage causes a relatively small amount of the adsorption of the developing solution on the photoconductor. As a result, the developed image fades.
Accordingly, efforts to develop an algorithm for properly controlling the charge voltage, the exposure voltage, and the development voltage have been made to compensate for the image quality. There was proposed a conventional method of compensating for the image quality by measuring the developed mass of an image on a photosensitive belt to control the printing machine since the above-mentioned three voltages affect the developed mass of the image.
FIG. 1
is a block diagram illustrating a conventional printing machine performing a method of controlling developed mass per unit area (DMA) to compensate for image errors so as to obtain a high quality image, which is disclosed in U.S. Pat. No. 5,749,021. The method suggests controlling the charge voltage, the exposure voltage, and the developer bias from internal process parameters, i.e., a discharge ratio, a cleaning voltage, and a development voltage.
The method of controlling the DMA improves the print quality by keeping the DMA under control in process control loops. Areas on which images are formed on a photoconductor are called “image areas,” and test patches are generally prepared in a zone between the image areas of the photoconductor to be used for measuring the DMA. After the measured DMA is compared with a target value, errors are transmitted to a controller to control the internal process parameters so as to compensate for development errors. In other words, a grid voltage of a charger and an average beam power of an exposure system can be calculated from the internal process parameters to control subsystems of the printing machine.
Referring to
FIG. 1
, a level 1 controller
120
of a development system
140
transmits proper control signals U
g
and U
l
to an electrostatic charging and exposure system
122
.
An electrostatic voltage sensor (ESV) measures a voltage of the electrostatic charging and exposure system
122
to obtain electrostatic and exposure voltage values V
h
and V
l
124
, respectively. The comparators
126
a
and
126
b
compare ESV sensor values V
h
and V
l
124
with target values V
h
T
and V
l
T
128
of the electrostatic and exposure voltage values V
h
and V
l
124
to provide error signals E
h
and E
l
129
to the level 1 controller
120
. Gains of level 1 loops are obtained from the error signals E
h
and E
l
129
to converge the voltage of the photoconductor to the target values V
h
T
and V
l
T
128
.
A level 2 controller
130
generates the target values V
h
T
and V
l
T
128
to obtain the electrostatic and exposure voltage values V
h
and V
l
124
through the level 1 controller
1
and the electrostatic charging and exposure system
122
. Comparators
136
a
and
136
b
compare DMA sensor values D
l
, D
m
, and D
h
134
, which are measured by a color toner density (CTD) sensor from the test patches prepared according to a toner area coverage, with target values D
l
T
, D
m
T
, and D
h
T
138
, respectively, to provide error signals
139
to the level 2 controller
130
. The level 2 controller
130
also generates a signal V
T
d
to control a development system
132
.
In other words, in the method of controlling the DMA, the DMA sensor values D
l
, D
m
, and D
h
134
measured by the CTD sensor are compared with the target values D
l
T
, D
m
T
, and D
h
T
138
to calculate deviations (differences) thereof. Thereafter, the calculated deviations are provided to the level 2 controller
130
to make the deviations linear with respect to the internal process parameters, i.e., the discharge ratio, the cleaning voltage, and the developer bias. Control parameters, i.e., the target values of the charging voltage, the exposure voltage, and the developer bias, are extracted from the linear discharge ratio, the cleaning voltage, and the developer bias to control the level 1 controller
120
, the electrostatic charging and exposure system
122
, and the development system
132
. This control process will now be described with reference to FIG.
2
.
FIG. 2
is a flowchart explaining the method of controlling the DMA in the printing machine of FIG.
1
. Referring to
FIG. 2
, in the method of controlling the DMA, the DMA value is measured in step
101
. Next, the measured DMA value is compared with the target DMA value to calculate a deviation thereof in step
103
. If the deviation is smaller than a tolerance, a printing job is perfor
An Seung-deog
Shim Woo-jung
Grainger Quana M.
Staas & Halsey , LLP
LandOfFree
Method of compensating for image quality by controlling... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of compensating for image quality by controlling..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of compensating for image quality by controlling... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3322615