Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
1999-07-21
2001-06-12
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C358S504000, C399S072000
Reexamination Certificate
active
06246844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the control of image density in an image formation apparatus.
2. Related Background Art
As a conventional example, the structure of a multi-color image formation apparatus as well as its operation will be described with reference to FIG.
1
.
In
FIG. 1
, latent images formed every each of colors on an image support body (photosensitive drum)
100
by an optical unit
101
are developed and visualized using each of color toners of Y (yellow), M (magenta), C (cyan) and K (black) respectively supplied from color developing units of Dy, Dm, Dc and Dk. Then the developed and visualized images are plural times transferred on an external surface of a transfer belt
102
so as to form a multi-color image. In this condition, the toner is transferred to a surface of the transfer belt
102
by applying high voltage on the transfer belt
102
. Then a recording sheet (paper)
105
fed from a sheet feed unit
103
or a sheet feed toner
104
is conveyed through a sheet conveying path and the multi-color image is re-transferred from the transfer belt
102
.
Thereafter, the recording sheet
105
is conveyed by a conveying roller
106
and is fixed by a fixing unit
107
to be discharged to a discharge tray
108
or a discharge unit
109
. The each of color developing units, which has a rotation spindle at its both edges, capable of being rotated around the spindle is held in a developing mechanical unit
110
and is rotated to be selected. Numeral
111
denotes a cleaning unit for cleaning the toner on the transfer belt
102
. Numeral
112
denotes a discharged toner collection unit for collecting discharged toners from the image support body
100
. Numeral
113
denotes a density sensor for measuring density of a toner image formed on the photosensitive body
100
.
In the above-described structure, as shown in
FIG. 2
, a beam is radiated from a light emitting element
1
structured within the density sensor
113
, which is disposed in the vertical direction to a surface of the image support body
100
, to a toner image
20
(called as patch hereinafter) formed on the image support body
100
. Then a reflected light is detected by a light reception element
2
to realize such a structure as stabilizing image density by correcting a difference between the detected result and a predetermined detection level as a change quantity corresponding to a developing bias.
An example of the content concerning a density control will be described. The density control can be categorized into a developing bias control for obtaining a developing bias value treated as a maximum value of toner density and a halftone density control for controlling halftone density by varying image data upon fixing the developing bias value defined by the developing bias control. Hereinafter, the developing bias control will be described.
FIG. 3
is a block diagram of the structure concerning the developing bias control. In
FIG. 3
, numeral
3
denotes an A/D converter which converts an analog detection signal transferred from the density sensor (light reception element)
113
into a digital signal. Numeral
4
denotes a data comparison means which judges whether or not an output value of the density sensor for a surface ground of the image support body reaches a predetermined value. Numeral
5
denotes an LED light quantity setting unit which varies light quantity so as to secure an output range in case of measuring several kinds of patches.
Numeral
6
denotes a data storage means which interpolates detected data. Numeral
7
denotes a density calculation unit which changes a sensor output value of the measured patch in terms of a density value. Numeral
8
denotes a density/developing bias comparison unit which determines the density value changed by the density calculation unit
7
and the developing bias value corresponding to the density value.
Numeral
9
denotes a developing bias control unit which gives a command to a high-voltage output unit
10
so as to output the determined developing bias value. The high-voltage output unit
10
applies an output designated from the developing bias control unit
9
to the developing unit. Numeral
50
denotes a CPU within a DC controller (not shown) provided in an image formation apparatus main body. Depending on the structure, each of the blocks
3
,
4
,
5
,
6
,
7
,
8
and
9
provided in the CPU
50
may be provided in the DC controller (not shown) or the density sensor
113
.
FIG. 4
is an operational flow chart of the developing bias control. In
FIG. 4
, the ground of the image support body surface is measured in a step S
101
. A flow advances to a step S
102
, where if a read value of the ground of the image support body surface is lower than a predetermined density value, the flow advances to a step S
104
. If the read value of the ground of the image support body surface is higher than the predetermined density value because of dirt or an inferior change in time of the density sensor
113
, a density sensor output is corrected in a step S
103
.
The density sensor output is corrected by each block of the A/D converter
3
, data comparison means
4
, the LED light quantity setting unit
5
and the data storage means
6
shown in FIG.
3
. In the step S
104
, density of the ground surface on a position, where the patch on the image support body is to be printed, is measured. Then density of the patch is measured in a step S
105
. In this case, the density of the patch for the ground can be measured as contrast by measuring the density of the ground in the step S
104
. The flow advances to a step S
107
after converting the read value of the density sensor
113
into the density value in a step S
106
. A method for determining an optimum developing bias value performed in the step S
107
will be described hereinafter.
FIG. 5
shows examples of measured patches. A patch
20
-
a
is in the lowest density and a patch
20
-
e
is in the highest density. The density is schematically expressed by hatching lines. The number of patches is not limited to these examples but may be varied depending on a diameter of the image support body or time spend in controlling the density.
FIG. 6
shows the relationship between the density value being the measured result of patches
20
-
a
,
20
-
b
,
20
-
c
and
20
-
d
shown in
FIG. 5
by the density sensor
113
and the developing bias value when the patches are formed.
In
FIG. 6
, in a case where a target density value want to be obtained among the measured density of five patches exits on somewhere between two points, the optimum developing bias value for the target density can be obtained by performing a linear interpolation for the two points.
FIG. 7
indicates a case that all patches which are measured can not reach the target density. In this case, the linear interpolation is performed for the two patches of which density is closer to the target density so as to estimate the optimum developing bias value for the target density.
FIG. 8
indicates a case that all patches which are measured can not reach the target density and the density value reaches peak between the patches
20
-
b
and
20
-
d
. In this case, the developing bias value of the patch of which density is closest to the target density (patch reaches a peak of the density) is treated as the optimum developing bias value.
The halftone density control is performed after determining the optimum developing bias indicating a maximum density by the developing bias control. Also, in case of the halftone density control, a plurality of patches are printed on the image support body to measure the patches density by the density sensor
113
similar to the case of the developing bias control. The relationship between image data of the halftone density control patch and the density value is shown in FIG.
9
. On an image data/density characteristic curve shown in
FIG. 9
, since a raise of the density is remarkable in the vicinity of center position of the image data, a halftone correction c
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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