Printing – Multicolor
Reexamination Certificate
2001-09-12
2003-09-30
Nolan, Jr., Charles H. (Department: 2854)
Printing
Multicolor
C347S116000, C399S301000
Reexamination Certificate
active
06626101
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electro-photographic color-image forming apparatus having a plurality of photosensitive bodies. More specifically, the invention relates to technology that detects positional displacements in each toner image formed on the photosensitive bodies carrying each color toner and transfers them with accurate positioning onto a recording material.
BACKGROUND OF THE INVENTION
In the prior-art color-image forming apparatus employing electro-photography, an image has been typically formed through the following procedures. First, a photosensitive body is charged as an image-carrier by a charger. Second, the charged body is provided with light radiation according to image information to form an electrostatic latent image thereon. Third, the electrostatic latent image is developed into a visible toner image by a developing unit. Fourth, the visualized toner image is transferred onto recording materials such as a sheet of paper.
Some kinds of apparatuses employing tandem type color-image forming have been developed to respond to the need for color images. A tandem-type color-image forming apparatus has a plurality of image-forming stations—a plurality of image-carriers. Each carrier is responsible for carrying cyan-, magenta-, yellow-, and preferably independent black-image. The four individual images are formed on the respective carriers in the series of image-forming process steps described above. All of the separately carried images are overlapped at a proper position of each carrier and transferred onto a sheet-type material to form a full-color image. Such a tandem type apparatus contributes to high-speed image forming due to the structural merit of having each image-forming section associated with each color. On the other hand, careful positioning (i.e., registration) of each image formed at different image-forming sections is indispensable for successful full-color image forming. Poor-registration of the four colors results in displacement in the whole picture or undesired gradations in color in transferring the image onto a sheet of paper or other materials.
FIGS.
34
(
a
) through (
e
) illustrate typical displacements in transferred image. FIG.
34
(
a
) shows displacement in the moving direction—shown by arrow A in the figure—of the transferred material (hereinafter referred to as displacement in secondary scanning). FIG.
34
(
b
) shows displacement in the scanning direction—in a direction orthogonal to the direction indicated by arrow A—(hereinafter displacement in primary scanning). FIG.
34
(
c
) shows displacement in a slanting direction (hereinafter called skew error). FIG.
34
(
d
) shows scaling error, and FIG.
34
(
e
) shows bend error. In a real world image-forming process, displacement is produced, with patterns FIGS.
34
(
a
) through (
e
) complicatedly combined.
In the case of FIG.
34
(
a
) above (displacement in secondary scanning), the displacement is mainly caused from inaccurate mounting of the image-forming stations or the scanning optical system, or inaccurate setting of the lenses and mirrors of the scanning optical system. This is also true in the case FIG.
34
(
b
) (displacement in primary scanning).
The displacement described in FIG.
34
(
c
) is caused from inaccurate angle-setting of the axis of rotation of a photosensitive drum in an image-forming station, or from inaccurate angle-setting of the scanning optical system. The displacement in FIG.
34
(
d
) is mainly from inaccurate scanning length generated by the optical-path length from a scanning optical system to the corresponding photosensitive drum. The displacement in FIG.
34
(
e
) is due mainly to inaccurate assembling of lenses in a scanning optical system.
In order to correct the displacement categorized in the five patterns, a suggestion has been made. The suggestion includes the steps of, (i) forming in advance a registration reference pattern (hereinafter referred to as a reference pattern); (ii) detecting positional displacement (displacement-detection) by a plurality of sensors; and (iii) performing the registration of each image (displacement-correction) according to the amount of displacement calculated from the result obtained in (ii).
Conventional reference-pattern detecting and displacement-correcting procedures will now be described.
FIG. 35
illustrates the structure of a prior-art reference pattern-detector (hereinafter pattern detector).
FIG. 36
shows the layout of a reference-pattern formed on an inter-stage transfer belt and pattern detectors in the prior-art apparatus.
FIGS. 37 and 38
illustrate the layout of a reference-pattern formed on an inter-stage transfer belt and pattern-detectors, and signals fed from the pattern detectors in the prior-art apparatus.
As shown in
FIG. 35
, pattern detector
14
contains an image sensor (hereinafter CCD)
51
and lens array
53
focusing light source
52
including a lamp, and reflected light onto CCD
51
. This structured pattern detectors
14
a
and
14
b
are, as shown in
FIG. 36
, arranged so that a series of pixels in CCDs
51
a
and
51
b
are aligned in a line orthogonal to moving direction A of the inter-stage transfer belt (hereinafter simply referred to as belt)
12
. Belt
12
has two CCDs, and each CCD is disposed close to a respective end of the belt in its widthwise direction with respect to the moving direction A of belt
12
.
The reference pattern-detecting and displacement-correcting steps are performed based on a predetermined reference pattern formed of a line or figure pattern shown in FIG.
36
. For example, the reference pattern can be formed of differently colored toner-images
54
,
55
,
56
, and
57
at predetermined spaced intervals, and each toner image is disposed on a line orthogonal to the moving direction A of belt
12
. Pattern detectors
14
a
and
14
b
detect positional displacement (i.e., registration displacement) based on an individual toner-image reference pattern.
In
FIG. 37
(
a
), i) T
1
represents the time required for each of the reference patterns
54
,
55
56
, and
57
to reach CCD
51
a
in the pattern detector, ii) T represents the time predetermined as a design value, and iii) v represents the moving speed of belt
12
. Then, displacement in secondary scanning shown in FIG.
34
(
a
) is obtained by calculating displacement in individual color through the following equations:
&Dgr;
T
1
=
T−T
1
&Dgr;
Y
1
=&Dgr;
T
1
·
v
In FIG.
38
(
a
), when passing CCD
51
a
in the pattern detector, the scanning-start position of each of reference patterns
54
,
55
,
56
, and
57
on belt
12
has a difference in pixel position (represented by (X
1
). Displacement in primary scanning shown in FIG.
34
(
b
) is obtained by calculating the displacement of the individual color based on the difference in pixel position.
Belt
12
has the same colored reference patterns
54
,
55
,
56
, and
57
on both of its widthwise ends. A row of the reference pattern on one end passes CCD
51
a
, while the other row of the reference pattern in the other end passes CCD
51
b
. If the skew error (
FIG. 34
c
) occurs, there should be a difference between the passing time of each reference pattern detected by CCDs
51
a
and
51
b
, as shown in FIG.
37
(
b
). When the difference is represented by &Dgr;T
2
and the moving speed of belt
12
is represented by v, the skew error is obtained from the following equation: &Dgr;Y
2
=&Dgr;T
2
·v.
If there is scaling error shown in FIG.
34
(
d
), the scanning-start position and the scanning-end position of each of the reference patterns
54
,
55
,
56
, and
57
on belt
12
have differences in pixel position when the two positions pass CCD
51
a
and CCD
51
b
, respectively. The differences are represented by &Dgr;X
2
, &Dgr;X
1
. The scaling error shown in FIG.
34
(
c
) is obtained by calculation of the scaling error of each color based on &Dgr;X
1
, &Dgr;X
2
: &Dgr;X
3
=&Dgr;X
2
−&Dgr;X
1
.
After the four calculations described above, displacement correction is p
Kajiwara Tadayuki
Shimada Masaya
Tanizaki Jun-ichi
Matsushita Electric Industrial Co. Ltd
Nolan, Jr. Charles H.
Wenderoth , Lind & Ponack, L.L.P.
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