Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-03-28
2001-09-11
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S131000, C399S049000, C399S072000
Reexamination Certificate
active
06288733
ABSTRACT:
The present invention relates to an image forming method and an image forming apparatus, and in particular, to an electrophotographic image forming method and an electrophotographic image forming apparatus.
There has been available an electrophotographic image forming apparatus wherein a latent image is formed on a photoreceptor by a laser beam and an image is formed by developing the latent image.
In the course of obtaining an image in the image forming apparatus of this kind, an image is determined by adjusting the power of a laser beam and the exposure time thereof. As a method for adjusting the exposure time of a laser beam, there has been known PWM (pulse width modulation) which adjusts a period of time for turning on a laser with a pulse width.
With regard to a multiple-valued image by a laser writing system, constant gradation has been obtained by conducting &ggr; curve correction based on laser power and a laser pulse width. Further, with regard to a binary image (one-bit image) based on data of 0 and 1 formed with one bit dot, its density level is stipulated by a halftone dot pattern, and when a diameter (an area) of each dot constituting halftone dots is changed, midscale density level as an image is changed.
FIG. 7
is an illustrative diagram showing that a character image formed by dots of the same pattern becomes a blurred image or a weak image, if a dot diameter is changed, and image quality is changed. As is apparent from the diagram, an amount of toner used for one character is changed even in the case of a binary image if a dot diameter is changed, resulting in a change of toner consumption per one image sheet.
A diameter of a dot of the one-bit image is changed by fluctuation factors such as deteriorated sensitivity caused by deterioration of a photoreceptor, a contaminated optical system and deterioration of developing agents. It is therefore necessary to stabilize midscale density level of the one-bit image and to make an amount of consumption of toner to be constant.
Examples in the prior art under the aforesaid situation are as follows.
The first example in the prior art is the invention disclosed in Japanese Patent No. 2746942, and in that invention, a ratio of a main scanning line image-visualizing pattern is compared for obtaining a difference from the standard value established in advance, and thereby, a width of one line of laser diode power is corrected based on the result of calculation.
The second example in the prior art is the invention disclosed in TOKKAIHEI No. 7-25063, and in that invention, each of plural lasers provided is driven independently to form stipulated image density level, and detection and comparison of the density level are conducted to adjust an output level of a laser diode.
The third example in the prior art is the invention disclosed in TOKKAISHO No. 61-189575, and in that invention, a midscale density level image is made and visualized, then, detected by a sensor so that light emission intensity may be controlled in accordance with detected density level.
However, when the correction is made by detecting the main scanning line as in the first example in the prior art stated above, there is a problem that the line width in the main scanning direction can not be detected, although the line width in the sub-scanning direction can be detected.
Further, in the second example in the prior art stated above, it is possible to make each image formed by each of the plural lasers provided to be of the same density level, but, it is not possible to correct the change with time for image density level.
In the third example in the prior art mentioned above, each dot of middle tone image to be made is formed through pulse width modulation, and its density level is adjusted through adjustment of power of a laser diode. In this case, it is possible to adjust density level on the highest density level portion by matching midscale density level, if a density level curve (so-called &ggr; curve) in the case of changing a pulse width is constant. However, the &ggr; curve varies to the extent where &ggr; correction needs to be conducted, and optimizing of density level on the halftone image formed by pulse width cannot necessarily make the density level of the highest portion (in the vicinity of the maximum value of pulse width) used on a one-bit image to be constant.
FIG. 8
is an illustrative diagram showing fluctuation of the maximum density level portion caused by dispersion of the &ggr; curve. For example, even when density level is optimized with m of PWM value, image density level is changed by dispersion of the y curve greatly on the maximum density level portion used by the one bit image.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the aforesaid points, and its object is to provide an image forming apparatus capable of correcting changes with time in image density level efficiently.
The above object can be attained by the following structures:
(1) An image forming apparatus is provided with a photoreceptor;
exposure means for exposing the photoreceptor with a laser beam dot by dot so as to form a dotted latent image on the photoreceptor corresponding to image information;
developing means for developing the dotted latent image with developer;
dot diameter correcting means for correcting a diameter of the dot formed on the photoreceptor, the dot diameter correcting means including,
image patch producing means for forming an image patch having a specific dot pattern with a laser beam having a predetermined power strength by the exposure means,
image patch detecting means for detecting a density level of the image patch formed on the photoreceptor, and
memory means for storing data of laser power strengths with correlation to the detected density levels; and
control means for controlling laser power strength of the exposure means based on the correlated data stored in the memory and the density level detected by the image patch detecting means.
(2) In the image forming apparatus of (1), the dot pattern of the image patch is arranged such that each dot is substantially isolated from other dots so as not to superimpose with other dots.
(3) In the image forming apparatus of (1), the dot pattern of the image patch is formed by one bit dot image with a predetermined number of dots.
(4) In the image forming apparatus of (2), the image patch is a half tone image having a reflection density level of 0.2 to 0.6.
(5) In the image forming apparatus of (2), the image patch detecting means comprises an image density level sensor to detect an average reflection density level of the image patch with diffused light.
(6) In the image forming apparatus of (1), the image patch producing means produces plural different image patches with plural different laser power strengths and the image patch detecting means detects a density level of each of the plural different image patches.
(7) In the image forming apparatus of (6), the memory stored the correlated data between the plural different image patches and the plural different laser power strengths and the control means obtains a relationship among the correlated data and obtains a laser power strength corresponding to a desired density level.
(8) In the image forming apparatus of (1), the image forming apparatus further comprises:
maximum density level correcting means for adjusting a developing ability of the developing means and for determining the maximum density,
wherein the control means conducts correction by the maximum density level correcting means based on the laser power strength corrected by the dot diameter correcting means.
(9) In the image forming-apparatus of (1), the image forming apparatus further comprises:
gradation correcting means for correcting gradation characteristic by changing a pulse width of the laser beam, wherein the control means conducts correction by the gradation correcting means based on the laser power strength corrected by the dot diameter correcting means.
(10) In the image forming apparatus of (1), the image patch detecting means compr
Gunji Koichi
Komatsu Toru
Koshimura Yasushi
Nakazawa Kazuhiro
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
Lee Susan S. Y.
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