Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2002-08-09
2004-11-09
Lee, Susan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C399S227000, C399S302000
Reexamination Certificate
active
06816178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for color image forming, and more particularly to a method and apparatus for color image forming that is capable of performing a precise synchronization between a toner image forming per color and its overlaying with an improved optical synchronization mechanism.
2. Discussion of the Background
In recent years, a color document is a rapidly growing tendency in offices and as a consequence an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., is also needed to have a color function. In line with an increasing demand for a high quality and a fast speed in office work, the color image forming apparatus is required for a high image quality and a fast processing speed.
Conventionally, a color image forming apparatus in response to such requirements uses a transfer drum method. The color image forming apparatus is provided with a photosensitive drum for forming different color images thereon one by one, and a transfer drum for holding a transfer sheet and transferring the different color images onto the recording sheet in a form overlaying one to another. Another color image forming apparatus in response to such requirements uses a transfer belt method wherein the color image forming apparatus is provided with at least one photosensitive drum and a transfer belt in place of the transfer drum.
In the color image forming apparatus using the transfer drum method, one color image is formed on the photosensitive drum each time the photosensitive drum makes a turn, and different color images are sequentially formed on the photosensitive drum to sequentially transfer the different color images onto the transfer drum. Thereby, a composite color image is formed on the transfer drum and is then transferred onto a transfer sheet. This color image forming procedure not only takes a relatively long time, but it is complex to improve the process speed. Further, this color image forming has a drawback in which performance of the image transferring is varied depending upon a type of transfer sheets, thus, limiting the type of transfer sheets that are used.
In contrast to the above, the color image forming apparatus using the transfer belt method forms different color images on a plurality of photosensitive drums and transfers the different color images onto the transfer belt in an overlaying form to generate a composite color image on the transfer belt which is then transferred onto a transfer sheet. As an alternative, in the color image forming apparatus having an intermediate transfer belt, the different color images are tentatively transferred onto the intermediate transfer belt in an overlaying form to generate a composite color image which is then transferred onto a transfer sheet. It is possible to improve the process speed in these color image forming procedures using the transfer belt method. In addition, this color image forming method does not limit the type of transfer sheets.
FIG. 1
shows a background color image forming apparatus using the transfer belt method. As shown in
FIG. 1
, the color image forming apparatus includes a laser diode
100
, a laser light detector
101
, a polygon mirror
102
, a mirror
103
, a roller motor
104
, a driving roller
105
, an intermediate transfer belt
106
, a photosensitive drum
107
, a development unit
108
, a transfer roller
109
, supporting rollers
110
,
111
,
112
, and
113
, and a drum motor
114
.
The laser diode
100
emits a laser light beam L modulated in accordance with specific color image data. The polygon mirror
102
is rotated by a polygon motor (not shown) to deflect the laser light beam L. The laser light detector
101
detects the laser light as a scan sync signal each time the laser light beam L completes a line scanning motion. The mirror
103
deflects the laser light beam L towards the photosensitive drum
107
. The roller motor
104
drives the driving roller
105
to rotate the intermediate transfer belt
106
which is supported by the transfer roller
109
and the supporting rollers
110
-
113
to partly contact with the photosensitive drum
107
, as shown in FIG.
1
. The photosensitive drum
107
has a photosensitive surface and is driven by the drum motor
114
.
By exposure to the modulated laser light beam L, an electrostatic latent image for a specific color is formed on the photosensitive surface of the photosensitive drum
107
. The development unit
108
includes development assemblies
108
a
,
108
b
,
108
c
, and
108
d
for containing cyan (C), magenta (M), yellow (Y), and black (K) color toners and developing the electrostatic latent image with a corresponding color toner to form a specific color toner image on the photosensitive drum
107
. The transfer roller
109
receives a bias voltage from a power source (not shown) and transfers with the bias voltage the specific color toner image formed on the photosensitive drum
107
onto the intermediate transfer belt
106
. Formation of specific color toner image on the photosensitive drum
107
is repeated for the colors of C, M, Y, and B, and the formed color images are in turn transferred onto the intermediate transfer belt
106
in a form of overlaying one to another. Thereby, a composite color toner image is formed on the intermediate transfer belt
106
. The composite color toner image thus formed is transferred onto a recording sheet with a secondary transfer mechanism (not shown). Consequently, a final color image is formed on the recording sheet.
The above-described color image forming apparatus controls the drum motor
114
to drive the photosensitive drum
107
in a precise manner so as to control a position of toner image forming to be precisely constant on the surface of the photosensitive drum
107
. However, it is not easy to avoid variations in this position due to various factors such as, for example, a manufacturing error in the photosensitive drum itself, a displacement of a mounting position, and so on. As a result, the position of toner image forming is varied, and the background color image forming apparatus fails to form a high precision multi-color toner image.
Furthermore, a problem is encountered on the overlaying images on the intermediate transfer belt
106
. That is, the image transfer to the intermediate transfer belt
106
takes place one color image after another color image. Therefore, image transferring needs to be synchronized with the rotation of the photosensitive drum
107
, and the synchronization should be controlled in a precise manner. This synchronization is generally performed with a marking/marker provided to an edge of the intermediate transfer belt
106
. By reading this marking, a signal is generated to represent a timing that the intermediate transfer belt
106
starts its rotation. With this signal, the image forming on the photosensitive drum
107
is initiated so that the synchronization between the image forming on the photosensitive drum
107
and the rotation of the intermediate transfer belt
107
is obtained.
However, the above-described procedure for obtaining the synchronization has a drawback in which the synchronization is made in a relatively good condition at the leading side of the images but it is prone to be out of order. As a result, the resultant color toner image is distorted. This is due to the mechanism of the intermediate transfer belt
106
. That is, different from the photosensitive drum
107
, the intermediate transfer belt
106
receives varying loads of mechanisms for cleaning, discharging, and transferring during a rotation cycle. These mechanisms are switched between two positions to connect and disconnect the intermediate transfer belt
106
. In addition, the intermediate transfer belt
106
is supported with a plurality of rollers and each of which may have a manufacturing error and a center displacement. Accordingly, these undesirable factors may irregularly affect the rotation of the intermediate transfer belt
106
.
An exemplary
Kamiya Takuroh
Kamoshita Mikio
Kudo Koichi
Takahashi Mitsuru
Yamada Yasufumi
Lee Susan
Ricoh & Company, Ltd.
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