Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-06-08
2002-07-09
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S132000, C347S133000, C358S296000, C358S300000, C382S209000
Reexamination Certificate
active
06417876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image forming apparatuses and methods for forming an image based on a digital image. In particular, the invention relates to an image forming apparatus and an image forming method, for forming a high-quality image by controlling exposure energy density.
2. Description of the Background Art
With the advent of an age of digital information, demand is growing for printers, facsimiles, copiers and the like that are based on digital processing system. There is also a growing demand on these image forming apparatuses for enhanced image quality. Especially, development of copiers and printers is requested these days that are superior in reproducibility which enables high-definition images of various document fonts or photo level to be reproduced accurately.
However, it has been known the reproducibility varies depending on the type of images (difference of dot density) even if the condition of exposure is unchanged. A problem then arises that it is difficult to maintain a superior reproducibility for various images.
For example, suppose that the resolution of a line pattern consisting of lines on every second lines (hereinafter referred to as “periodic line pattern”) is ensured. Then, the diameter of a dot included in a one-dot pattern consisting of nonadjacent dots with a low dot density (hereinafter referred to as “isolated dot pattern”) would be smaller than a desired value, or the dot itself would not be formed in some cases. On the contrary, if the dot diameter of the isolated dot pattern is ensured, the width of a line of the line pattern would be greater than a desired value, or the lines disappear resulting in solid black image.
This phenomenon is now described in conjunction with the drawings.
FIG. 6
illustrates one example of digital image information. Here, the reference characters A to G and numerals
1
to
20
are applied for indicating dot positions.
Referring to
FIG. 6
, a virtual pattern in a memory space is shown consisting of rows (A, B, C, . . . ) and columns (
1
,
2
,
3
, . . . ). For example, the black portions represented by (row, column)=(A,
1
) and the like mean “print” (voltage level is high), while white portions represented by (row, column)=(B.
1
) and the like mean “non-print” (voltage level is low).
If data is read in one-dimensional manner from the memory storing the image information shown in
FIG. 6 and a
semiconductor laser is driven based on the read data, the laser is turned on (driven) when the read data is “pint” (voltage level is high) and the laser is not turned on (driven) when the read data is “non-print” (voltage level is low).
Specifically, “A” is first designated as a row address which is one of signals input to the memory and then “
1
,
2
,
3
, . . .” are designated in this order as a column address which is another input signal. Accordingly, row data in row A thus designated are successively read and a laser driver which receives the data controls turning on/off of the laser. In this way, an electrostatic latent image according to the image information regarding row A is formed on a photoreceptor.
Next, “B” is designated as a row address and “
1
,
2
,
3
, . . .” are successively designated as a column address. Then, the designated data regarding row B are also read and the laser driver controls turning on/off of the laser according to the data. An electrostatic latent image is thus formed based on the image information for row B as done for row A.
This operation is repeated to form on the photoreceptor a two-dimensional electrostatic latent image pattern corresponding to the image pattern shown in FIG.
6
.
FIGS. 11 and 12
respectively illustrate extreme results of development obtained by performing such a process of forming an electrostatic latent image for each of all image patterns shown in
FIG. 6
under the same exposure condition.
FIG. 12
shows a result obtained by forming an image under an exposure condition which enhances the reproducibility of the line pattern of the original image (FIG.
6
). Under this exposure condition, the line pattern is properly reproduced as shown in
FIG. 12
while the reproducibility of the isolated dot pattern is deteriorated. In an extreme case, the isolated dot disappears or the dot is not reproduced at all.
FIG. 11
shows a result obtained by forming an image under an exposure condition which ensures the dot diameter of the isolated dot pattern of the original image (FIG.
6
). Under this exposure condition, the isolated dot is appropriately reproduced with a desired dot diameter as shown in
FIG. 11
while the reproducibility of the line pattern is impaired. In an extreme case, the line width increases to cause non-print portions to disappear, resulting in a solid black image.
In order to solve this problem that a superior reproducibility cannot be ensured for images having different dot densities, Japanese Patent Laying-Open No. 63-64763 discloses a method according to which print data itself is corrected (related art
1
). Specifically, an isolated one-dot print data is detected from print data, and one bit preceding or following the detected one-dot print data is corrected as print data.
Japanese Patent Laying-Open No. 63-296069 discloses a method for solving that problem by changing the diameter of a beam spot on the photoreceptor (related art
2
). Specifically, an isolated one-dot print data is detected from print data, and the diameter of a beam spot for the detected one-dot print data is increased.
This problem that a superior reproducibility cannot be ensured for images having different dot densities should be considered together with an influence of change in the film thickness of the photoreceptor as time progresses. Reproducibility of an image is considerably affected by charging and light attenuation characteristics of the photoreceptor as well as modulation transfer function of electric field within the photoreceptor, and the like. These characteristics of the photoreceptor vary depending on the film thickness of the photoreceptor,
The film thickness of the photoreceptor decreases with time due to contact with a cleaning member for removing residual toner, friction with a paper for transfer, and the like. Therefore, the various characteristics of the photoreceptor change with time merely by using the image forming apparatus.
A problem then arises that the density of a black portion of a printed image or the brightness of the image changes from the initial setting, or the reproducibility of images having different dot densities cannot be maintained.
Various image formation techniques have been proposed in order to overcome this problem, considering the change with time in the film thickness of the photoreceptor. As representative approaches, Japanese Patent Laying-Open No. 8-95433 discloses a technique of ensuring the brightness of an image by sensing change in the film thickness of the photoreceptor to control the amount of exposure lamp (related art
3
), Japanese Patent Laying-Open No. 5-16533 discloses a technique of ensuring the density by measuring the optical density of a reference patch image formed on the photoreceptor to feed back the result of the measurement (related art
4
), and Japanese Patent Laying-Open No. 11-15214 discloses a technique of controlling the charging potential of the photoreceptor and controlling the development bias potential in consideration of variation in the image density due to change in the development electric field caused by change with time in the photoreceptor characteristics (related art
5
).
However, with the higher image resolution, it is more difficult to ensure a superior reproducibility for images having different dot densities. If an image having a resolution of 1200 dpi is to be formed by using a practically employed photoreceptor with a film thickness of 20 &mgr;m to 30 &mgr;m, for example, a superior reproducibility for images with different densities cannot be ensured by the techniques discussed above.
When the same
Azuma Nobuyuki
Iwamatsu Tadashi
Mutou Yoshinori
Nakajima Yoshinori
Toyoshima Tetsuro
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Hartnell, III George W.
Pendegrass Joan
Sharp Kabushiki Kaisha
LandOfFree
Apparatus and method for forming image with high image... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for forming image with high image..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for forming image with high image... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2865719