Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-07-13
2004-06-15
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S131000, C399S049000, C399S072000
Reexamination Certificate
active
06750892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a density correction method and an image forming apparatus, and particularly to an image forming apparatus, in which a latent image is formed by scanning a light beam on an image retaining member or by causing light from an array light source to be imaged on an image retaining member, and the latent image is subjected to development and transferred to an image recording medium, and an image is formed on the image recording medium, and to a density correction method in the image forming apparatus.
2. Description of the Related Art
There have spread image forming apparatuses, for example, an image forming apparatus such as a laser printer or an electrophotographic copying machine, in which an image is formed by irradiating a light beam on a photosensitive member while scanning the light beam thereon, or an image forming apparatus in which an image is formed by causing light from a light source formed by arrangement of a plurality of light emitting elements such as an LED array, that is, a plurality of light emission points (hereinafter referred to as an “array light source”), to be imaged on a photosensitive member by using a SELFOC lens or the like. In such image forming apparatuses, when an image is formed on an image recording medium such as paper, the density of coloring materials may become ununiform (density unevenness).
It has conventionally been known that, in a light scanning apparatus in which a light beam is scanned by using a deflector such as a polygon mirror, the intensity of a light beam is changed in order to correct uneven density caused by variation in irradiation energy in a region in which the light beam is scanned.
For example, in Japanese Patent Application Laid-Open (JP-A) No. 56-74275, the technique is proposed, wherein in order to prevent the light intensity per unit area of a light beam from decreasing as an angle of incidence &thgr; of the light beam on a photosensitive material drum 300 becomes large (see FIG.
23
), setting of driving current is carried out so that the output power level increases as the angle of incidence of the light beam on the photosensitive material drum
300
becomes larger (see
FIGS. 24A
to
24
C).
In JP-A No. 60-16058, the technique has been proposed, wherein in order to prevent a change in the beam intensity on a scanning surface by variation in the reflectance caused by the change in the angle of incidence of the light beam on a light deflector (see FIG.
25
), bias current I
1
is changed in accordance with an angle of incidence &PSgr; on the deflector.
Further, in JP-A No. 10-297017, the technique has been proposed, wherein in order to correct variations in the amount of light of an LED array, driving current of the LED is changed based on correction data of variations in the amount of light (see FIG.
26
).
Due to the variation in irradiation energy in a region in which a light beam is scanned, or the variation in the amount of light of the LED array being corrected as described above, uneven density in the direction in which a light beam is scanned, or a direction in which light emitting elements (light emission points) of the LED array are arranged (which both directions will be hereinafter generically referred to as a “scanning direction of a light beam”), that is, a direction perpendicular to a direction in which an image is formed on a photosensitive member or an image recording medium, is alleviated.
Uneven density in the scanning direction of a light beam on a light image recording medium, is not necessarily caused by only energy of a light beam irradiated on the photosensitive member or variation in the energy density (ununiform irradiation).
In addition to the above-described ununiform irradiation caused by a light beam, for example, ununiform charging caused by ununiformity of a corotoron or a charge roll for applying a charge to a photosensitive member (ununiformity of charging caused in the photosensitive member), variations in the amount of a toner in a development roll of a developing machine which supplies the toner to a latent image formed on the photosensitive member (variations in the density of toner), and an ununiform distance between the development roll and the photosensitive member (variations in the distance) each cause ununiform density of coloring materials at the time of forming a toner image on the photosensitive member. As a result, uneven density of coloring materials is caused on the image recording medium.
Further, even if uneven density of coloring materials occurs in the toner image formed on the photosensitive member, uneven density of coloring materials is also caused on the image recording medium due to ununiformity of charging by a transfer corotoron or a transfer roller for transferring, to a transfer printing medium (i.e., intermediate transfer material, paper, or the like), the toner image on the photosensitive member (ununiform charging caused in the transfer material) or due to ununiform nipping force (variations in the nipping force).
However, in the above-described conventional techniques, ununiform irradiation by a light beam is only corrected, and therefore, uneven density on an image recording medium with a final image formed thereon, cannot be corrected. Particularly, in a case of a full color image, there exists a problem in that if uneven density is not corrected, color hue varies and an image of high quality cannot be obtained.
SUMMARY OF THE INVENTION
The present invention has been devised in order to solve the above-described problems, and an object thereof is to provide a density correction method and an image forming apparatus, which allow reduction in the uneven density of an image in a main scan direction of a light beam, or a direction in which light emission points of an array light source are arranged.
In order to achieve the above-described object, according to a first aspect of the present invention, there is provided a density correction method in an image forming apparatus in which a planar latent image is formed by sub-scanning in which a main scanning position of a light beam is moved relatively to an image retaining member while main scanning of a light beam is being effected on the image retaining member, and the latent image is developed and transferred to an image recording medium, thereby forming an image on the image recording medium, the method comprising the step of: based on the density of an image on one of the image retaining member and the image recording medium, correcting an intensity of the light beam in an image region within a range of one main scan so as to allow correction of uniformity of the image density in the main scanning direction of the light beam.
In accordance with the first aspect of the present invention, based on the density of an image on the image retaining member or on the image recording medium, the intensity of the light beam in the image region is corrected within the range of one main scan so that ununiformity of the image density in the main scanning direction of the light beam is corrected. That is, unlike the conventional methods, the light beam is irradiated on the image retaining member while the intensity (amount of light) of the light beam is being corrected within one main scan based on the density of a formed image. Accordingly, any density unevenness caused by, not only ununiform irradiation, but also ununiformity of charging caused in the image retaining member, variations in the density of toner, variations in the distance, ununiform charging caused in the transfer material, variations in the nipping force, and the like is solved (reduced), and density unevenness in the image region can be reduced.
At this time, in accordance with a second aspect of the present invention, preferably, after the intensity of the light beam is in advance controlled automatically at a predetermined intensity level, based on the density of an image on one of the image retaining member and the image recording medium, the intensity of the l
Fuji 'Xerox Co., Ltd.
Lee Susan S. Y.
Morgan & Lewis & Bockius, LLP
LandOfFree
Density correction method and image forming apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Density correction method and image forming apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Density correction method and image forming apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3320609