Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2003-08-25
2004-12-28
Eickholt, Eugene H. (Department: 2854)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C399S049000, C399S160000, C399S167000, C399S165000, C399S126000, C347S116000
Reexamination Certificate
active
06836277
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensor attachment position determining method which can suitably be applied to a color image forming apparatus for forming a color image by scanning and exposing a photosensitive body with a light beam and overlaying colors, and an image forming apparatus and an image forming method.
2. Description of the Prior Art
In recent years, tandem-type color printers, copying machines, and composite machines thereof are widely used. In these color image forming apparatuses, scanning optical units, developing units, and photosensitive drums for yellow (Y), magenta (M), cyan (C), and black (BK), an intermediate transfer belt, and a fixing unit are prepared.
For example, in the Y-color scanning optical unit, an electrostatic latent image is formed on the photosensitive drum on the basis of arbitrary image information. The developing unit applies a Y-color toner to the electrostatic latent image formed on the photosensitive drum to form a color toner image. The photosensitive drum transfers the toner image to the intermediate transfer belt. The same process is performed for the remaining colors, i.e., M, C and BK. Color toner images transferred to the intermediate transfer belt are transferred to a paper sheet (transfer paper sheet) and fixed by the fixing unit.
According to a color image forming apparatus of this type, color toner images must be formed on the intermediate transfer belt without any color misregistration in order to transfer the color toner images having no color misregistration to a paper sheet. For this purpose, the positions and tilts of the scanning optical units described above are appropriately adjusted with respect to the photosensitive drums.
The intermediate transfer belt of the color image forming apparatus is subjected to a process called “color registration mark detection” periodically or irregularly before formation of a color image based on arbitrary image information. As shown in
FIG. 1A
, in this detection process, almost V-shaped color registration marks (to also be simply referred to as “registration marks” hereinafter) on an intermediate transfer belt
6
are detected by using reflection-type photosensors (to also be referred to as registration sensors hereinafter)
12
A and
12
B which are arranged above the two side edge portions of the intermediate transfer belt
6
.
As shown in
FIG. 1B
, the registration sensor
12
A comprises a light projecting element SS
1
formed from an LED that projects a light beam to the intermediate transfer belt
6
, a light receiving element SS
2
which receives reflected light from the intermediate transfer belt
6
, and lenses SS
3
. The registration sensor
12
B has the same structure as that of the registration sensor
12
A.
Light beams emitted from the registration sensors
12
A and
12
B are shielded by, e.g., registration marks on the intermediate transfer belt
6
. In this process, the registration marks are detected by detecting light reflected by the intermediate transfer belt
6
.
As shown in
FIG. 1A
, a positional shift in the sub scanning direction (bow) is detected on the basis of the timing of the detection signal of a line segment P that is parallel to the main scanning direction D
1
of the registration marks arrayed in the main scanning direction D
1
.
In addition, a partial lateral magnification difference “m” is detected on the basis of the difference between the timing of detection of the line segments P that are parallel to the main scanning direction D
1
of the registration marks and the timing of detection of line segments Q that have a tilt of 45° with respect to the main scanning direction D
1
of the registration marks. The partial lateral magnification difference “m” means a partial variation in magnification in the main scanning direction D
1
. The partial lateral magnification difference m has adverse effects such as a horizontal image write positional shift on the photosensitive body. On the basis of the pieces of information (detection signals) related to the partial lateral magnification difference “m” and positional shift in the sub scanning direction D
2
, which are detected by the registration sensors
12
A and
12
B, the position and tilt of each scanning optical unit are controlled to eliminate color misregistration between the respective color images.
According to the conventional “color registration mark detection”, the registration sensors
12
A and
12
B are arranged above the side edge portions of the intermediate transfer belt
6
to detect the partial lateral magnification difference “m” and/or positional shift in the sub scanning direction. On the basis of the detection signals, the position and tilt of each scanning optical unit are controlled.
However, the scanning accuracy may vary between the scanning optical units due to the assembly errors of the scanning optical units in the color image forming apparatus or the internal temperature distribution in the color image forming apparatus. Accordingly, at any portion except the side edge portions of the intermediate transfer belt
6
where the registration sensors
12
A and
12
B are arranged, a considerable difference in partial lateral magnification difference “m” and/or positional shift in the sub scanning direction may be generated between the scanning optical units.
If a large difference in partial lateral magnification difference “m” and/or color misregistration in the sub scanning direction over the main scanning direction, namely, a scanning line bend is generated between the scanning optical units, the overlay accuracy between Y, M, C and BK colors decreases. This causes conspicuous color misregistration in the color image.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problem in the prior art, and has as its object to provide a sensor attachment position determining method, an image forming apparatus, and an image forming method, which can minimize color misregistration on the entire color image formation surface and also form a high-quality color image with minimum color misregistration.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a sensor attachment position determining method of determining an attachment position of a color misregistration detection sensor of an image forming apparatus which overlays colors on the basis of arbitrary image information to form a color image on an endless-belt-shaped transfer body that is rotatable in a predetermined direction, comprising the steps, which are carried out in a stage of designing the image forming apparatus, of: checking a relationship between the attachment position of the sensor and a formation positional shift of the color image by moving the sensor along an attachment position candidate line that is defined in advance in another direction perpendicular to the rotational direction of the transfer body; finding a specific attachment position on the sensor attachment position candidate line, at which color misregistration of the color image at a side edge portion of the transfer body becomes equal to a maximum value of color misregistration at a portion except the side edge portion; and fixing the sensor at a position that satisfies the found specific attachment position and opposes a color image formation surface of the transfer body.
According to the sensor attachment position determining method, the image forming apparatus can be controlled to correct the color overlay on the basis of a reliable detection signal for which the color misregistration of the color image at the side edge portion of the transfer body becomes equal to the maximum value of color misregistration at a portion except the side edge portion. The color overlay for color image formation can be corrected to eliminate the absolute amount difference of the color misregistration between the central portion in the widthwise direction and the side edge portion of the transfer body.
In order to achieve the above ob
Cohen & Pontani, Lieberman & Pavane
Eickholt Eugene H.
Konica Corporation
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