Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2000-04-27
2001-04-24
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C358S426010, C358S525000
Reexamination Certificate
active
06223007
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus employing an electrophotographic process, such as photocopying machines, laser beam printers, facsimile apparatuses.
2. Description of the Related Art
Generally, a typical image forming apparatus employing an electrophotographic process includes a rotatably-supported photoconductive drum
1
as shown in FIG.
2
. The photoconductive drum
1
is driven by drive means (not shown) to rotate in a direction S
1
. Around the periphery of the photoconductive drum
1
are disposed a charging device
2
, an exposing device
3
, a developing device
4
, a transferring device
5
, and a cleaning device
6
in sequential order from upstream of the rotational direction S
1
. A surface of the photoconductive drum
1
charged in a uniform manner by the charging device
2
is exposed to laser light by the exposing device
3
, thereby to form an electrostatic latent image. The electrostatic latent image is developed with toner by the developing device
4
to become a toner image. Then, the toner image is transferred onto a transfer material by the transferring device
5
. After the transfer process, the cleaning device
6
is disposed to remove residual toner present on the photoconductive drum
1
.
As shown in
FIG. 2
, the color image forming apparatus comprises serially-arranged four units each comprising the photoconductive drum
1
, the charging device
2
, the exposing device
3
, the developing device
4
, the transferring device
5
, and the cleaning device
6
, so that images of Y (yellow), M (magenta), C (cyan), and BK (black) are individually formed. The developing devices
4
of these four units have developer tanks for holding therein toner of Y, toner of M, toner of C, and toner of BK, respectively.
A transfer belt
7
forming the transferring device
5
of each unit is common to the four units. The transfer belt
7
composed of denatured polyimide or the like material is constructed such that it is stretched between a pulley
17
on the drive side and a pulley
18
on the driven side in order to be able to travel in a direction S
2
, and transfer material such as a sheet of paper is electrostatically adsorbed to the transfer belt
7
and held there. Inside the transfer belt
7
are disposed transfer chargers
8
for transferring a toner image formed on the photoconductive drum
1
to the transfer material, to face their corresponding photoconductive drums
1
, respectively. Moreover, a cleaning member for cleaning toner accumulated on the transfer belt
7
and an electric-charge eliminating member for discharging electric charge accumulated on the transfer belt
7
, which are not shown in the figure, are provided inside or outside the transfer belt
7
. Toner images of Y, M, C and BK transferred onto the transfer material are fixed by a fixing device
9
, whereby a color image is formed.
The density characteristics of the formed image will vary with, for example, surrounding temperature and humidity and time. In other words, under the influence of variation factors of each of image formation processes such as charging, exposing, developing, transferring and fixing, image density characteristics change. To cope with such variations and obtain a constant image density, a correction to the image density is made. The amount of correction in the image density correction is determined in such a manner that a toner pattern
15
composed of a plurality of toner patches is formed on the transfer belt
7
, the densities of the toner patches are detected by a density detecting sensor
10
, and detection values are compared with a predetermined reference value, whereby amounts of correction to be made are determined. Image recording apparatuses of the type in which such an image density correction is made are disclosed in, for example, Japanese Unexamined Patent Publications JP-A 8-289148 (1996), JP-A 8-289153 (1996), and JP-A 8-340448 (1996).
The image output starting point obtained by increasing the exposure width of the exposing device
3
from its minimum value, i.e., the tone rise point, varies with the surrounding environment and time, as mentioned above. Although it is essential to stably obtain an accurate tone rise point when performing a tone representation (particularly a light color tone representation), the amount of toner adhesion at a tone rise point is extremely small and the density is, therefore, considerably low. Consequently, there are some image densities in a low-density region, undetectable by the density detecting sensor
10
due to the level of sensitivity thereof. Therefore, in the case where an exposure width which was detected by the density detecting sensor is employed as the tone rise point, there occurs a disagreement in exposure width with an actual density. Moreover, there are some image densities in a high-density region that cannot be detected with high accuracy by the density detecting sensor
10
due to the level of sensitivity.
SUMMARY OF THE INVENTION
Hence, an object of the invention is to provide an image forming apparatus capable of obtaining, with high accuracy and in a stable manner, an image density of a tone rise point in a low-density region in order to form an image with a constant steady density. Moreover, another object of the invention is to provide an image forming apparatus capable of obtaining, with high accuracy and in a stable manner, an image density in from a low- to an intermediate-density region, in from a low- to a high-density region, or in a high-density region in order to form an image with a constant steady image.
The invention provides an image forming apparatus comprising:
image forming means for forming an image of an output image density value obtained by correcting an input image density value in accordance with a correction table of input image densities;
density detecting means for detecting a density of the formed image;
density interpolating means for interpolating the image density detected by the density detecting means; and
density correcting means for correcting the output image density value by making a comparison between the correction table and an interpolation result of the density interpolating means;
wherein the density interpolating means comprises low-density region interpolating means for finding a linear interpolation formula by linearly interpolating a plurality of image densities in a low-density region which were detected above a predetermined level of sensitivity, to interpolate an image density in the low-density region below the predetermined level of sensitivity, with the linear interpolation formula.
According to the invention, in the case where a correction in image density is carried out, a toner pattern composed of a plurality of toner patches is formed, for example, on a transfer belt by the image forming means. The toner patch is an image having an output image density value as a result of correcting an input image density value on the basis of a correction table. The density of the toner patch formed is detected by the density detection means. The density interpolating means interpolates the image density detected. Here, the low-density region interpolating means interpolates detected image densities in the low-density region. The density correcting means makes a comparison between the correction table of input image density values and an interpolation result of the density interpolating means, thereby correcting the output image density value.
The low-density region interpolating means first finds a linear interpolation formula for linearly interpolating image densities in the low-density region, which were obtained by the density detecting means having a sufficient level of sensitivity. More specifically, the low-density region interpolating means finds a linear interpolation formula for a plurality of points in a sufficient level of sensitivity region which sequentially increase in density from a certain density point. Second, by the use of the linear interpolation formula,
Kitagawa Takashi
Maeda Yasutaka
Nagayama Katsuhiro
Ohta Toshihiro
Uehara Makoto
Chen Sophia S.
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Sharp Kabushiki Kaisha
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