Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1999-09-14
2001-03-27
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S232000, C347S234000
Reexamination Certificate
active
06208363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multiple-image forming apparatus for forming a synthetic image by superimposing image information on a transfer material through the electrophotography or the like.
2. Description of the Related Art
In the case of an image forming apparatus using the electrophotography, it has been performed so far to electrify an electrophotographic photosensitive body serving as an image bearing body by an electrifier, irradiate the photosensitive body with light in accordance with image information to form a latent image, develop the latent image by a development device, transfer an actualized toner image to a sheet material or the like, and form an image.
Moreover, as the number of color images has been increased, a tandem-type image forming apparatus is also proposed which forms a full-color image by preparing a plurality of image bearing bodies in which a series of the above processes is developed, forming a cyanogen image, a magenta image, a yellow image, and preferably a black image on each image bearing body, superimposing the color images at the transfer position of each image bearing body, and transferring them to a sheet material.
The above tandem-type multiple-image forming apparatus is advantageous for speed-up because it has an image forming section for each color.
However, it is a technical problem how to smoothly perform the alignment (registration) of images formed in different image forming sections.
This is because shifts of image forming positions of four colors transferred to a sheet material finally appear as color shifts or a change of color tones.
FIGS. 5A
to
5
D show types of positional shifts of a transferred image.
As shown in
FIGS. 5A-5D
, types of positional shifts of a transferred image include a positional shift (top margin) in the scanning-line write direction (direction of the arrow A in
FIGS. 5A-5D
) against a transfer material
9
(FIG.
5
A), a positional shift (left margin) in the scanning direction (direction of the arrow B perpendicular to the direction of the arrow A in
FIG. 5B
, which is the scanning-line write direction) (FIG.
5
B), a positional shift in the diagonal direction (FIG.
5
C), and a shift of a magnification error (FIG.
5
D), and actually, a shift obtained by superimposing these four types of shifts appears.
Moreover, the main cause of an image shift is a shift of the image write out timing of each image-forming station in the case of the top margin shown in
FIG. 5A
, and a shift of each image write timing of each image-forming station, that is, a shift of the scanning-start timing in one scanning line in the case of the left margin shown in FIG.
5
B. Moreover, the inclination shift in the diagonal direction shown in
FIG. 5C
is a shift of a scanning-optical-system setting angle or a shift of the angle of the rotation axis of a photo-sensitive drum, and the shift due to a magnification error shown in
FIG. 5D
is a shift of a scanning-line length due to an error of the optical path length from the scanning optical system of each image-forming station up to the photosensitive drum.
To eliminate the above four types of shifts, the shifts are corrected by adjusting the scan timing of each color for the top margin and left margin. Moreover, the magnification error shift and inclination shift are corrected by the compensator of the conventional multiple-image forming apparatus shown in
FIG. 6
by adjusting a pair of mirrors
101
and
102
whose mirror surfaces are perpendicularly held to each other and arranged almost at an angle similar to that of the character ‘V’, among three turn-back mirrors
101
,
102
, and
105
disposed in the midst of the optical path of each image-forming station, toward arrows M and N from the apparatus body respectively independently using actuators
103
and
104
. In this case, a linear stepping actuator or the like provided with a stepping motor serving as a driving source linearly moving stepwise is used as actuators
103
and
104
for performing the above adjustment.
In the case of the above conventional multiple-image forming apparatus, however, because inclination-shift correction means is complex in configuration and uses many parts, vibrations easily occur. Therefore, the position of a scanning line irradiated onto a photosensitive body is moved to cause scanning irregularity and the scanning irregularity appears as the irregular density of an output image to extremely deteriorate the image quality.
Moreover, these problems greatly influence the formation of a high-quality image free from color shift by a digital color multiple-image forming apparatus.
Therefore, it is an object of the present invention to provide a multiple-image forming apparatus capable of preventing the image quality from deteriorating due to scanning irregularity caused by the inclination shift of a scanning line.
SUMMARY OF THE INVENTION
It is an object of the present invention to prevent the image quality of a multiple-image forming apparatus from deteriorating due to scanning irregularity caused by the inclination shift of a scanning line.
To achieve the above object, the present invention comprises electrification means for uniformly electrifying the surfaces of photosensitive drums
1
a
to
1
d
, exposure means
3
which irradiates a scanning line corresponding to image data for specific colors and is arranged so that latent-image lines formed on the photosensitive drums
1
a
to
1
d
have predetermined inclinations from rotation axes of the photosensitive drums
1
a
to
1
d
to form an electrostatic latent image on the photosensitive drums
1
a
to
1
d
while performing curve correction on the photosensitive drums
1
a
to
1
d
, development means
4
a
to
4
d
for actualizing electrostatic latent images, and transfer means for transferring monochromatic images formed on the photosensitive drums
1
a
to
1
d
by successively superimposing the images on an intermediate transfer belt, and controls the peripheral speed of the photosensitive drums
1
a
to
1
d
so that inclinations of toner images of a plurality of colors on the intermediate transfer belt become equal to each other.
REFERENCES:
patent: 5508789 (1996-04-01), Castelli et al.
patent: 5995802 (1999-11-01), Mori et al.
patent: 11-102100 (1999-04-01), None
Ijima Yoshiaki
Kawano Yuhzou
Shimada Masaya
Tanizaki Jun-ichi
Matsushita Electric - Industrial Co., Ltd.
Pendegrass Joan
Stevens Davis Miller & Mosher L.L.P.
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