Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-10-18
2002-04-30
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C399S301000
Reexamination Certificate
active
06380960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color image forming apparatus for use in an electrophotographic electrostatic-type copying machine, printer, facsimile device, etc.
2. Discussion of the Background
FIG. 11
illustrates the structure of a color image forming apparatus of the tandem type in which the image forming sections are arranged along the conveying belt.
In
FIG. 11
, color image forming sections;
1
Y,
1
M,
1
C, and
1
K for forming the image of the respective different colors yellow Y, magenta M, cyan C and black K are arranged in a row along a conveying belt
3
for conveying a transfer paper
2
. The conveying belt
3
is suspended on a rotating driving roller (not shown) for driving the belt
3
, at one side thereof, and on the conveying rollers (driven rollers)
4
and
5
at another one side thereof. The conveying belt
3
is rotatably driven in the direction shown by an arrow by the action of the conveying rollers' rotation.
A paper feeding tray
6
containing therein the transfer papers
2
is provided below the conveying belt
3
. The transfer sheet situated on the uppermost position of the transfer papers
2
contained in the paper feeding tray
6
is fed at the time of forming the image. At this time, the transfer paper is electrostatically adhered onto the conveying belt
3
. The transfer paper
2
thus adhered is conveyed to the first image forming section (yellow)
1
Y and the yellow image formation is performed in the section
1
Y. The first image forming section
1
Y is constructed with a photosensitive drum
7
Y, a charging unit (charger)
8
Y, an exposing unit
9
Y, a developing unit
10
Y and a photosensitive body cleaner
11
Y.
The surface of the photosensitive body drum
7
Y, after being uniformly charged by the charging unit
8
Y, is exposed by laser light
12
Y corresponding to the yellow image by the exposing unit
9
Y, and thereby an electrostatic latent image is formed on the surface of the photosensitive body drum
7
Y. The electrostatic latent image thus formed is developed by the developing unit
10
Y. In such a way, the yellow toner image is formed on the photosensitive drum
7
Y. The toner image is transferred onto the transfer paper by the transferring unit
13
Y at a position (transfer position) where the photosensitive drum
7
Y is brought into contact with the transfer paper on the conveying belt
3
. At this time, a single color image (yellow) is formed on the transfer paper. On the transfer-finishing photosensitive drum
7
Y, the excess toner remaining on the surface of the drum is cleaned (removed) by the photosensitive body cleaner
11
Y before the next image formation.
The transfer paper
2
transferred with the single color image (yellow) formed by the first image forming section
1
Y is conveyed to the second image forming section (magenta)
1
M by the conveying belt
3
. The toner image (magenta) formed on the photosensitive drum
7
M is superposedly transferred onto the transfer paper
2
.
The transfer paper
2
is further conveyed in order to the third image forming section (cyan)
1
C and the fourth image forming section (black)
1
K, and toner images formed in the same way are transferred thereto. At this time, the color images are respectively formed thereon. The transfer paper
2
passing through the fourth image forming section
1
K and having the color image formed thereon is separated (peeled off) from the conveying belt
3
. After fixing the transfer paper
2
by use of the fixing unit
14
, the fixed paper is discharged.
In the tandem type image forming apparatus as shown in
FIG. 11
, the exact alignment of the respective colors is very important. The components (factors) affecting positional displacement are mainly as follows:
(1) skew;
(2) resist displacement in the sub-scanning direction;
(3) unevenness of pitch in the sub-scanning direction;
(4) magnification rate error in the main scanning direction; and
(5) resist displacement in the main scanning direction.
FIG. 12
is a perspective view illustrating the area around the positional displacement detecting section disclosed in the published specification of Japanese Laid-open Patent Publication No. 10-198110.
FIG. 13
is an enlarged view illustrating the positional displacement detecting section.
FIG. 14
is an enlarged view illustrating a slit shown in FIG.
13
. The detecting section is composed of a light emitting unit
15
, a slit
16
and a light receiving unit
17
. The detecting section detects a detection mark
18
for the positional displacement formed on the conveying belt
3
. The detecting section is disposed at both sides of the belt
3
in the main scanning direction. The detection marks
18
correspond to each of respective positions. The slit is composed of openings (having a width “a” and a length “b”) oriented for respectively detecting the parallel lines in the main scanning direction (hereinafter, called the “transverse line”) and the inclined parallel lines inclined from the above lines (hereinafter, called the “oblique line”).
FIG. 15
is an enlarged view showing the detection marks. The detection marks
18
are composed of the respective transverse and oblique lines for K, C, M and Y. The width of the respective lines is same as the width “a” of the slit opening portion. The length thereof is longer than the length b of the slit opening portion. In this background art embodiment, the positional displacement detection marks
18
are arranged in the order of K-C-M-Y. The four transverse lines and the four oblique lines form a pair of lines groups.
Furthermore, plural pairs of toner marks of same color and same shape exist at positions separated by half the circumferential length of the photosensitive body. The respective toner mark couples exist at positions separated by multiples of the half circumferential length of the photosensitive body, and the plural toner mark couples of same color and same shape exist at positions separated by the half circumferential length of the photosensitive body. Those marks form a pattern in which one or more toner marks exist in the (positional) interval of the toner marks couples. In this embodiment, four sets of marks are formed in the length of one circumferential circle of the photosensitive body.
The positional interval “d” between the respective lines is set so as not to cause any inversion of the respective line rows order even though a positional displacement occurs. In the way mentioned above, the detection signal at the time when the line arrives at the opening portion of the slit
16
has a waveform of a regular mountain or valley, and therefore the line center can be precisely obtained.
Employing those transverse lines and oblique lines, the detected time difference between the respective lines and the left-and-right detection results are compared with each other based on the standard of the K transverse line in the respective couples of marks, and then the average of the four couples is calculated. In such the way, the detection error due to the unevenness of the photosensitive body's rotation can be determined. Thereby, the compensation of the skew, the sub-scanning resist displacement, the main scanning resist displacement and the main scanning magnification error can be precisely performed.
FIG. 16
is a timing chart illustrating the timing at the time of compensating the timing of writing in the sub-scanning direction, and
FIG. 17
is a timing chart illustrating the timing at the time of compensating the timing of writing in the main scanning direction.
Referring to FIG.
16
and
FIG. 17
, the compensation of the positional displacement amount disclosed in the published specifications of Japanese Patent Nos. 2642351 and 2765626 are described hereinafter.
In
FIG. 16
, the compensation resolution is assumed to be 1 dot. The image area signal in the sub-scanning direction (writing enabling signal) adjusts the writing with the timing of the synchronized detection signal. As a result of the mark detection and a calculation, i
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pendegrass Joan
Ricoh & Company, Ltd.
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