Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1999-06-29
2001-09-18
Yockey, David F. (Department: 2861)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C358S001900, C358S300000
Reexamination Certificate
active
06292205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electrophotographic apparatus and method for use in a printer, a facsimile, etc., in which dot latent images in conformity with binarized image dot data are formed on a photosensitive drum through scanning of an LED array or a laser beam and in which after development of the latent images with toners the resultant dots are transferred onto record paper, and more particularly to an electrophotographic apparatus and method providing control of appropriate quantity of light emission taking into consideration the influence of light from lighting peripheral dots.
2. Description of the Related Arts
In the case of conventional electrophotographic apparatuses used for image printing in laser printers, facsimiles or the like, record paper is conveyed at a certain speed by a paper conveyance mechanism so that images are recorded on the record paper through the electrophotographic process executed by electrostatic recording units arranged in the record paper conveyance direction. The electrostatic recording unit forms latent images in conformity with image dot data by means of LED array line scanning or laser diode laser beam scanning on a photosensitive drum in rotation, and after development with toner components, transfers the developed images onto record paper. In recent years, color electrophotographic apparatuses for recording color images have also been put into practice. The color electrophotographic apparatus comprises four electrostatic recording units of black (K), cyan (C), magenta (M) and yellow (Y) in a tandem manner in the record paper conveyance direction. The electrostatic recording units for four colors optically scan the photosensitive drums on the basis of image data to form latent images, develop the latent images with color toners in developing vessels, transfer the developed images onto record paper being conveyed at a certain speed in a superposed manner in the order of yellow (Y), magenta (M), cyan (C) and black (K), and finally perform thermal fixing through a fixing device or other processes.
However, such conventional electrophotographic apparatuses have entailed the following problems since the LED array or the laser diode issues a uniform optical energy per dot to perform development and recording. Now assume that the optical energy has been determined so as to be able to develop isolated one dot on white background.
FIG. 1
shows a relationship between a latent image and a bias voltage in the case where the photosensitive drum has been subjected to optical energy capable of developing an isolated one dot in the electrophotographic process. A latent image
200
is not developed as a toner image at a specific bias voltage Vth or below, but it is developed as a toner image
202
at a voltage exceeding the bias voltage Vth, with the dot size of W
1
. However, in the case where the optical energy equal to
FIG. 1
is supplied to the adjoining two dot positions to develop two dot lines as shown in
FIG. 2
, latent images
204
and
206
indicated by broken lines are formed for respective dots, resulting in a combined latent image
208
indicated by solid line in its entirety, whereupon a toner image
210
is developed for broken line latent images exceeding the bias voltage Vth. Such a combination of the optical energy supplied to the adjoining dots leads to the dot size W
2
exceeding the original two dots. Alternatively, in cases where the optical energy equal to
FIG. 1
has been supplied to two dots with one dot space as shown in
FIG. 3
, combination of latent images
212
and
214
indicated by broken lines result in a latent image
216
indicated by a solid line, whereupon a toner image
218
comes to have three dot size W
3
with the crushed intermediate dot. In case of presence of another dot around the lighting dots in this manner, mutual influence will cause a crush of the isolated white point when the high-density pattern is printed, with another problem in that halftone pattern of the order of 50% will bring about saturation of density, leading to the density of solid print area.
On the contrary, if the optical energy per dot is determined as shown in
FIG. 4
so as to prevent the density of the high-density part from saturating, the latent image
220
may not reach the bias voltage Vth due to too small optical energy when the one dot isolated point is printed, which makes it impossible to develop the dots. For this reason, respective drawbacks lie in both the method of determining the optical energy so as to enable isolated one dot to be developed and the method of determining the optical energy so as to prevent the density of a high-density part from saturating, with the mutual trade-off relationship. Therefore, in reality, intermediate value of the two methods is employed with respective some problems unsolved.
Further, the drawbacks that the emission of light of a plurality of adjoining dots may cause too a large dot size and that no isolated dot may be formed by the high-density optical energy, will be attributable to the non-linear relationship as shown in
FIG. 5
, in which the relation between the developed dot diameter and the optical energy is not linear. That is, the dots are not formed with an optical energy L short of a certain threshold value Lth. Once the optical energy exceeds the threshold value Lth, the dot diameter W sharply increases in accordance with the increase of the optical energy P. Afterwards, increase of the dot diameter W become gradually gentle with respect to the increase of the optical energy P.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an electrophotographic apparatus and method capable of faithfully developing and recording dots irrespective of dot patterns, by appropriately controlling optical energy for light-emission taking into consideration the fact that optical energies mutually influence each other between adjacent dots.
The electrophotographic apparatus of the present invention comprises an electrostatic recording unit and a quantity-of-light control unit. The electrostatic recording unit forms a dot latent image in conformity with binarized image dot data through lighting of a scanning light on a latent image carrier in motion, e.g., a rotating photosensitive drum arranged in the record paper conveyance direction, and after development with a toner component, transfers dots onto record paper for development. The quantity-of-light control unit provides, for each lighting noticeable dot among the image dot data, a control of optical energy for use in formation of a latent image of the noticeable dot, on the basis of peripheral dots which may have influence on the size of the noticeable dot on the record paper. According to such an electrophotographic apparatus of the present invention, interpolation is made of non-linear characteristic upon the conversion of the optical energy into dot diameters in the electrophotographic process, thereby achieving a reproduction faithful to the image dot data. Further, there is no need for a technique such as edge recognition for dot pattern smoothing processing and the like, and letters, diagrams, images and their mixtures can faithfully be reproduced. For example, in the case of one dot isolated point, a developed dot of a normal size is obtained from the latent image. In the case of two dot lines, the optical energy is reduced in view of the mutual influence as in the latent image indicated broken line. Then from the combined latent image there is accurately obtained a developed dot having a dot size substantially double the size of one dot.
The quantity-of-light control unit provides a control of optical energy of the noticeable dot in response to the distance from the peripheral dots. For example, as shown by the optical energy arithmetic matrix, the quantity-of-light control unit defines, as a reference value, e.g., reference value 100% of optical energy of the noticeable dot, optical energy required for formation of a solid part of
Houki Youji
Kobayashi Kouichi
Nakayasu Hirofumi
Taira Yoshihiko
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Yockey David F.
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