Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2000-02-22
2002-07-09
Beatty, Robert (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C358S519000, C358S300000
Reexamination Certificate
active
06418281
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image processing apparatus for forming an image on a recording medium and its control method.
BACKGROUND OF THE INVENTION
Conventionally, in order to improve the stability of image quality, an image processing apparatus of this type prints a specific pattern such as a gray scale pattern or the like on a recording medium such as a paper sheet upon completion of a warm-up process upon startup, reads the printed gray scale pattern using an image reader such as a scanner or the like, and feeds back that information to image forming conditions such as &ggr; correction and the like.
However, when the image processing apparatus has been used for a long period of time, the fed-back &ggr; correction characteristics alone often fail to obtain an optimal image.
For example, in an image processing apparatus using electrophotography, even when image forming conditions such as &ggr; correction and the like are optimally adjusted, the attachment characteristics of the toner with respect to the photosensitive drum charge change over long-term use, and consequently optimal image forming conditions cannot be assured.
To solve such problems, a method of making correction using the relationship between the potential data and density has been proposed. However, since the relationship between the potential data and density cannot be determined uniquely, such correction is insufficient. Also, a method of forming a developing patch on, e.g., the surface of a photosensitive drum, converting the output from a photosensor into a density using a density conversion table which is determined in advance, and making &ggr; correction using the converted value is also available. However, since this method detects the density of toner attached onto the surface of the photosensitive drum, the detected density does not always match the final image density. Furthermore, the sensor normally used in this method has insufficient resolution for the attached toner density, and has insufficient performance as an absolute density sensor.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the conventional problems, and has as its object to provide an image processing apparatus which reads a specific pattern such as a gray scale pattern, and can maintain given image density characteristics by feeding back the read information to image forming conditions such as &ggr; correction and the like, even when the apparatus has been used for a long period of time, and its control method.
In order to achieve the above object, an image processing apparatus according to the present invention, comprises:
forming means for forming a gray scale pattern on an image carrier, and forming a gray scale pattern image by transferring an image corresponding to the gray scale pattern onto a recording sheet;
determination means for reading the gray scale pattern image formed on the recording sheet, and determining density correction characteristics of the forming means;
holding means for holding the density correction characteristics determined by the determination means;
storage means for storing a density of an image formed on the image carrier using the density correction characteristics; and
adjustment means for adjusting the density correction characteristics held by the holding means in accordance with a relationship between the density stored in the storage means, and the density of an image formed on the image carrier at a predetermined timing.
Also, an image processing apparatus which forms an electrostatic latent image on an image carrier by an image exposure output corresponding to an image signal, develops the electrostatic latent image with toner, and transfers the developed toner image on the image carrier onto a recording medium, comprises:
pattern forming means for forming a gray scale pattern based on a predetermined image signal on the recording medium;
reading means for reading the gray scale pattern formed by the pattern forming means;
first control means for controlling the image exposure output corresponding to the image signal to match the tone of the image signal with the tone of an image recorded on the recording medium by comparing the gray scale pattern read by the reading means with the predetermined image signal;
storage means for storing a density value of a toner image formed on the image carrier by the image exposure output controlled by the first control means as a reference density value immediately after the control of the first control means;
detection means for detecting a density value of a toner image formed on the image carrier by the image exposure output controlled by the first control means; and
second control means for controlling the image exposure output corresponding to the image signal to match the density value detected by the detection means with the reference density value stored in the storage means.
The first control means comprises:
first table generation means for generating a first table for storing a correspondence between the image signal and image exposure output; and
table storage means for storing the first table,
the second control means comprises:
correction table generation means for generating a correction table for correcting the image signal to match the density value detected by the detection means with the reference density value stored in the storage means; and
second table generation means for generating a second table by combining the first table stored in the table storage means with the correction table, and
image forming means for forming an image by using the second table.
Detection by the detection means and control by the second control means are automatically done at a predetermined timing.
A method of controlling an image processing apparatus according to the present invention, comprises:
a forming step of forming a gray scale pattern on an image carrier, and forming a gray scale pattern image by transferring an image corresponding to the gray scale pattern onto a recording sheet;
a determination step of reading the gray scale pattern image formed on the recording sheet, and determining density correction characteristics of the forming step;
a holding step of holding the density correction characteristics determined in the determination step;
a storage step of storing a density of an image formed on the image carrier using the density correction characteristics; and
an adjustment step of adjusting the density correction characteristics held in the holding step in accordance with a relationship between the density stored in the storage step, and the density of an image formed on the image carrier at a predetermined timing.
An method of controlling an image processing apparatus which forms an electrostatic latent image on an image carrier by an image exposure output corresponding to an image signal, develops the electrostatic latent image with toner, and transfers the developed toner image on the image carrier onto a recording medium, comprises:
a first control step of controlling the image exposure output corresponding to the image signal to match the tone of the image signal with the tone of an image recorded on the recording medium by reading an image on the recording medium on which a predetermined image is recorded by the image processing apparatus;
an storage step of storing a density value of a toner image formed on the image carrier by the image exposure output controlled in the first control step as a reference density value immediately after the first control step;
a detection step of inputting the predetermined image signal at a predetermined timing and detecting a density value of a toner image formed on the image carrier at that time; and
a second control step of controlling the image exposure output corresponding to the image signal to match the density value detected in the detection step with the reference density value stored in the storage step.
The first control step comprises:
a first table generation step of generating a first table for storing a correspondence
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