Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-10-30
2003-09-09
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C399S399000, C399S301000, C399S302000, C399S308000
Reexamination Certificate
active
06618064
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-33392, filed on Oct. 31, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a color image forming method and a color image forming apparatus and more particularly to a color image forming method and a color image forming apparatus for superimposing a plurality of images on an image forming unit and then transferring the color images onto a transfer medium in a batch.
(2) Description of the Related Art
In an image forming apparatus for forming a color image on an image transfer medium such as a recording form, there are various systems available. For example, one of them is a tandem system for arranging image forming units for forming a single-color toner image in correspondence to three colors of yellow, magenta, and cyan or four colors including black whenever necessary in the direction of recording-form transfer and sequentially superimposing a single-color image on a recording form so as to form a color image. The other one is a multiple-development system for installing an exposure means and developing units of three colors or four colors including black on one image forming unit and superimposing each single-color image on the image forming unit so as to form a color image.
Further, there are two multiple-development systems for superimposing and developing a plurality of images available as shown below. One of them is a system for installing one exposure means on an image forming unit, forming a latent image once every rotation of the image forming unit, developing one color, and superimposing each single-color image on the image forming unit by three rotations or four rotations including black so as to form a color image. The other one is a system for installing exposure means and developing units for three colors or four colors including black on an image forming unit, forming and developing a latent image of each color during one rotation, and superimposing each single-color image so as to form a color image.
In the aforementioned tandem system, the respective image forming units are generally arranged continuously in the direction of recording form transfer at an interval of a predetermined distance, so that a plurality of images cannot be printed at the same time and when an output image formed by a preceding image forming unit is transferred by the distance between the image forming units in the direction of recording form transfer from the preceding image forming unit, it is superimposed from above by the next image forming unit so as to form an image.
Therefore, depending on assembly precision and mounting position errors of each image forming unit, the respective single-color images may not be precisely formed and superimposed. Further, images may be shifted due to an uneven recording form transfer speed. Due to these causes, as one of the disadvantages of the tandem system, difficulty in keeping the image superimposition precision high may be cited.
In order to correct such a relative displacement of each single-color image, conventionally, for example, as described in Japanese Patent Application Laid-Open 8-278680, predetermined detection marks are formed on the recording form transfer belt so as to be shifted by a predetermined distance in the respective image forming units, and the variation of each detection mark from the predetermined distance is measured by a detector such as an optical fiber sensor or a line sensor, and the displacement is corrected by adjusting the image drawing timing of each image forming unit or controlling the recording form transfer speed.
On the other hand, in a multiple-development system having one exposure means, a latent image of the first color is formed on the image forming unit by the image exposure means and the latent image of the first color is developed by the development means installed on the downstream side thereof. When the image forming unit makes one rotation and reaches the position of the image exposure means again, a latent image of the second color is formed on the image forming unit and the latent image of the second color is developed in the same way. In the same way, images of three colors or four colors including black are developed every rotation. Thereafter, the color images are transferred onto the intermediate transfer medium or image transfer medium in a batch.
Since an image is formed on the image forming unit color by color ever rotation by one image exposure means like this, if a latent image is drawn on the same position on the image forming unit every rotation, no displacement of each color is generated. Therefore, to reduce the displacement of each color in this system, for example, as described in Japanese Patent Application Laid-Open 6-1002, a position detection mark is provided on an image forming unit and on the basis of a signal detecting the mark, each image is positioned by drawing each color every rotation. However, the image forming unit must make three rotations or four rotations including black so as to form one color image, so that the system is not suited to increase the color image forming speed.
On the other hand, in a multiple-development system having an image exposure means installed in each development means, a latent image is formed on the image forming unit by the image exposure means of the first color and developed by the development means of the first color installed just on the downstream side of the image exposure means. Thereafter, the image forming unit moves and after the time interval decided by the moving speed thereof and the interval between the first color and the second color, a latent image is formed by the image exposure means of the second color. In the same way, images of three colors or four colors including black are superimposed, thus a color image is formed and transferred onto the intermediate image medium or image transfer medium. In this system, a color image can be formed by one rotation, so that the image forming speed can be increased. Further, the image exposure means and development means can be arranged around the image forming unit, so that there is an advantage that the whole apparatus can be miniaturized.
However, in this system, in the same way as with the tandem system, a displacement of each color is caused by the assembly precision of each image exposure means, the mounting precision between the respective image exposure means, the thermal expansion, and errors with time and a deterioration of the image quality is caused. To reduce the displacement of each color in this system, conventionally, as described in Japanese Patent Application Laid-Open 8-240949, a method is used that a support member is provided around the image forming unit, thus the precision of relative position of each image exposure means is improved.
Further, the inventors proposed a method for developing a mark for detecting a superimposition displacement of images as disclosed in Japanese Patent Application Laid-Open 2000-137358 by a developer of a specific color, thereby improving the detection precision.
However, in the recent request for high speed and high resolution of a color image forming apparatus, a request for high precision for a displacement of each color is increased more and sufficient image superimposition precision cannot be obtained by the conventional proposed system aforementioned.
Furthermore, a detection mark formed on the image forming unit is unnecessary for an image output from the image forming apparatus and it is an image to be removed in the apparatus. Therefore, in Japanese Patent Application Laid-Open 2000-137358, the image transfer medium is separated from the image forming unit and the detection mark is not transferred onto the image transfer medium and removed by the image forming unit cleaner installed behind the transfer position in the rotational direction. The detection
Takahashi Masaki
Yokota Yasuhiro
Kabushiki Kaisha Toshiba
Lee Susan S. Y.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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