Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
1999-12-13
2001-06-05
Braun, Fred L (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C399S072000
Reexamination Certificate
active
06243542
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and its control method and, more particularly, to an image forming apparatus for performing density control upon forming an image and its control method.
In general, in an image forming apparatus that forms a full-color image, the density of the formed image may vary in accordance with various conditions such as its use environment, the accumulated number of prints, and the like and, in such case, correct tone color of the image itself cannot be obtained.
To solve this problem, in order to detect the current image forming state, a conventional image forming apparatus tentatively forms toner images for density detection (to be referred to as patches hereinafter) in units of colors on a photosensitive drum or intermediate transfer member at a predetermined timing (e.g., immediately after power ON or after a predetermined number of prints are formed), automatically detects their densities, and executes a color correction (calibration) process based on the image forming state, thus maintaining stable image quality and image accuracy.
For example, an apparatus for forming an image using an intermediate transfer member will be explained below. As shown in
FIG. 8
, color patch patterns based on the first developing bias are formed on a print region on the intermediate transfer member from an image write start position, and after that, color patch patterns are formed in turn up to those based on the N-th developing bias. The densities of the patch patterns are detected by a toner density sensor, and the detection results are fed back to image forming conditions such as an exposure amount, developing bias, and the like to execute density control so as to form a color image with an original density, thus obtaining a stable image.
In this manner, as one of methods for calibrating based on the actual measurement results of patch densities, a method of optimizing the developing bias is known. Normally, the relationship between the developing bias and density in an image forming apparatus is readily influenced by the number of prints, and environmental changes such as changes in temperature, humidity, and the like, and changes over time. For this reason, by forming a plurality of patches shown in
FIG. 8
while changing the developing bias and measuring the densities of the patches every predetermined number of prints, the developing bias value that can obtain a predetermined density in the current environment is estimated.
However, as is known, density control based on the toner density detected on a recording sheet after fixing can assure higher accuracy than that executed by detecting the toner densities of patches formed on a photosensitive drum or intermediate transfer member. That is, the toner density control of an output image itself after image formation can obtain higher image quality than that in the middle of image formation.
Hence, in order to detect the toner density on a recording sheet after fixing, patches may be transferred onto the recording sheet and fixed, and their toner densities may be detected at a paper exhaust unit. However, in this case, a recording sheet is wasted every time density control is done.
In addition to calibration by density control based on the detection result of patch densities, for example, the following calibration methods are known:
a method of forming patches while changing the laser exposure amount, and preparing a laser exposure amount correction table based on the detected densities;
a method of forming patches while changing process conditions such as a photosensitive drum potential and the like, and estimating optimal process conditions on the basis of the detected densities;
a method of forming position detection patches of individual colors on an intermediate transfer member, and correcting the image forming positions (registration) of the individual colors by detecting their positional relationship using a sensor; and
a method of uniformly charging the surface of a photosensitive drum by a charger or the like, detecting deterioration of the photosensitive drum by measuring the charged potential of the photosensitive drum at that time by a sensor, and adjusting the charging bias value.
The conventional image forming apparatus executes optimal calibration using one of the aforementioned methods or combining a plurality of ones of those methods.
However, upon examining images formed before and after the calibration, stable image quality and image accuracy can be obtained after the calibration, but the image quality such as the image density and image accuracy considerably differ immediately before and after the calibration.
Hence, when the calibration is executed every predetermined number of prints, it may be executed in the middle of a series of print processes for copying a single original in large quantity. In such case, print results considerably vary before and after the calibration process although similar print processes are made.
Also, a considerable processing time is required for executing the calibration. Hence, when the calibration is unconditionally executed at a predetermined timing (e.g., at the beginning of printing, every predetermined number of prints, or the like), the processing time is prolonged even when the current print process requires high processing speed rather than high image quality or image accuracy.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an image forming apparatus which can selectively execute density control that can save recording sheets, and more accurate density control using a recording sheet, and its control method.
According to the present invention, the foregoing object is attained by providing an image forming apparatus comprising:
image forming means for forming an image on an image carrier, and transferring the image onto a recording sheet;
test image forming means for making the image forming means form a test image;
first density detection means for detecting a density of the test image formed on the image carrier;
second density detection means for detecting a density of the test image formed on the recording sheet; and
control means for controlling an image forming condition in the image forming means, wherein the control means controls the image forming condition by selectively using the first and second density detection means in accordance with a control mode based on a user instruction.
In this manner, since a plurality of toner density measurement means are provided, density control that saves recording sheets, and more accurate density control that uses a recording sheet can be selectively executed.
It is another object of the present invention to provide an image forming apparatus which can arbitrarily control the execution timing of a calibration process, and its control method.
According to the present invention, the foregoing object is attained by providing an image forming apparatus comprising:
image forming means for forming an image on the basis of an image signal;
control means for controlling an image forming condition in the image forming means in a first mode; and
instruction input means for inputting a user instruction, wherein
the control means controls the image forming condition in a second mode when the instruction input means instructs to control the image forming condition.
Note that the first mode is a mode for automatically executing the image forming condition control at a predetermined timing, and the second mode is a mode for executing the image forming condition control at an instruction input timing by the instruction input means.
In this manner, since the execution timing of the calibration process can be arbitrarily controlled, the user can stably obtain a high-quality image at a desired timing.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts th
Fujimoto Akihiro
Yamaguchi Atsuhiko
Braun Fred L
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ngo Hoang
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