Photocopying – Projection printing and copying cameras – Identifying – composing – or selecting
Reexamination Certificate
1999-01-22
2001-05-29
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Identifying, composing, or selecting
C355S035000, C250S578100, C250S236000
Reexamination Certificate
active
06239860
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an apparatus, method, and system for adjusting a vertical regist shift between lines, pages or colors in a multiple beam recording system, and more particularly is directed to controlling the writing of information from the multiple beams to limit the vertical regist shift.
2. Discussion of the Background Art
A multiple beam optical scanning system for writing information onto a photoconductive drum is shown in FIG.
1
. In this multiple beam optical system, two light sources
25
and
26
are provided for generating laser beams for effecting writing onto the photoconductive drum
14
. The laser beams output of the light sources
25
and
26
pass through a collimator lens
27
, reflect off a polygonal mirror
28
, pass through a further lens
29
, and then impinge on the photoconductive drum
14
. The polygonal mirror
28
is rotated by a motor
30
and the photoconductive drum
14
is rotated by a motor
32
. Further, a photodetector
31
is provided for detecting a synchronous signal to effect scanning across the photoconductive drum
14
in the scanning direction. With this structure, the light sources
25
and
26
generate laser beams which scan across the photoconductive drum
14
in a scanning direction, and which generate different lines of information in a sub-scanning direction (i.e. the direction of rotation of the photoconductive drum
14
).
This system shown in
FIG. 1
, however, may suffer from a problem of a vertical regist shift during the following situation. The detected signal from the photodetector
31
is utilized as a synchronizing signal for the scanning direction. An image forming start signal for the sub-scanning direction, to start rotation of the photoconductive of drum
14
, is also generated. Further, when the image forming start signal is output image data is read out from a memory (a RAM, ROM, etc.) or from a memory via registers and the image forming operation starts. However, the situation may arise that the image forming start signal is not synchronized with the detected signal from photodetector
31
. As a result, situations as shown in
FIGS. 2
a
and
2
b
arise in an image forming operation, and during a series of image forming operations. Certain kinds of vertical regist shifts may occur based on the above lack of synchronization between the image forming start signal and the detected signal from the photodetector
31
.
When the situations as shown in
FIGS. 2
a
and
2
b
exist in an image forming operation, a vertical regist shift may occur on output sheets of paper on which a same image is printed, on lines on a sheet of paper, or on colors on a sheet of paper. When the image forming device prints the same image on plural sheets of paper by plural image forming operations, a vertical regist shift may occur between the same position of each line of each paper. Also, when a color image forming device outputs color images on a single sheet of paper, a vertical regist shift may occur between each color image on the sheet. For example, a vertical regist shift may occur between a cyan color image and a magenta color image. A vertical regist shift may also occur between lines in a sheet of paper on a monochrome image forming device.
A normal operation and an operation which results in the vertical resist shift are explained in further detail with reference to
FIGS. 2
a
and
2
b
which show two cases in the operation of the system of FIG.
1
.
FIGS. 2
a
and
2
b
disclose a range of a vertical regist shift based upon a relation between the image forming start signal and the synchronous signal for the scanning direction (i.e., the detected signal from the photodetector
31
).
In the operation of the system of
FIG. 1
shown in the second case of
FIG. 2
b
, the synchronous signal for the scanning direction (as detected by photoconductor
31
) is generated just after the image forming start signal for the subscanning direction (which starts rotation of the photoconductive drum
14
). As a result, in this operation of
FIG. 2
b
the first and second lines of information are immediately written at their appropriate positions.
In this operation of the system of
FIG. 1
the writing on the photoconductive drum
14
is determined to start after a predetermined number of synchronous signals are detected (i.e., when a designated synchronous signal is detected) after the image forming start signal for the sub-scanning direction is detected. That is, in the operation of the system shown in
FIG. 1
the photodetector
31
detects a signal to start writing onto the photoconductive drum
14
, and thereby the photodetector
31
provides an image forming start signal for the scanning direction. Further, the system as shown in
FIG. 1
is designed so that a predetermined number of synchronous signals for the scanning direction are generated prior to writing of the first and second lines of information onto the photoconductive drum
14
. In the operation shown in
FIG. 2
b
such a predetermined number of synchronous signals prior to the designated synchronous signal for writing are not shown.
In this first case of
FIG. 2
a
a synchronous signal (to initiate writing by the laser beams output of light sources
25
and
26
onto the photoconductive drum
14
) for the scanning direction occurs just prior to the image forming start signal for the sub-scanning direction (which starts rotation of the photoconductive drum
14
). As a result, the designated synchronous signal for the scanning direction which is detected after the image forming start signal is a significant time tl after the image forming start signal. In this situation, the first and second lines are not written onto the photoconductive drum
14
until approximately one time cycle later than desired. This problem is significant in a multiple beam scanning system because each time cycle for writing corresponds to a shift of two lines if two light sources
25
,
26
are being used, or a shift of three lines if three light sources are being used, etc.
One system for addressing this vertical regist shift operation is disclosed in Japanese Laid-Open Patent Application 08-142412. A control operation executed in this Japanese Laid-Open Patent Application 08-142412 is described in
FIGS. 3
a
and
3
b
of the present specification.
In the system of this further background art a time interval detector for detecting a time from an image forming start signal for a sub-scanning direction and a synchronous signal for the scanning direction is measured, and a light source selector is provided to select between activating the light sources
25
and
26
based on this detected time interval.
More particularly, in this background art in a second case of
FIG. 3
b
if a certain time interval t2 occurs between the image forming start signal for the sub-scanning direction and the synchronous signal for the scanning direction (which time interval t2 is detected by a time interval detector), a first line is written by only one of the light sources, and then for subsequent lines both of the light sources operate to write lines simultaneously. In the example shown in
FIG. 3
b
, with the time interval t2 the first line is written onto the photoconductive drum
14
by the light source
26
, and then the second and third lines are simultaneously written by both the light sources
25
and
26
after a second synchronous signal is detected, and so on.
This operation disclosed in Japanese Laid-Open Patent Application No. 08-142412 provides a benefit that a vertical regist shift between lines, colors or pages can be decreased to one line. However, this reduction in the vertical regist shift may still be unacceptable in a multiple beam writing system, and particularly if the multiple beam writing system of
FIG. 1
is utilized in a color copier where different colors must be precisely superimposed upon one another. The contents of this reference, Japanese Laid-Open Patent Application No. 08-142,412, are incorporated herein by reference.
S
Adams Russell
Kim Peter B.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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