Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-06-10
2001-04-10
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S248000, C399S049000
Reexamination Certificate
active
06215512
ABSTRACT:
This application is based on an application No. 10-163395/1998 filed in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus which forms a color image by superposing images of a plurality of colors formed by a plurality of print units.
2. Description of Prior Art
In a color image forming apparatus of tandem structure, an image of four colors is formed at the same time in a scan. In the color image forming apparatus, four print units including photoconductors for the four print colors are aligned, and images of the four colors are supplied to exposure positions for each color, by delaying in correspondence to the distances between the photoconductors. In a system wherein four beams are scanned with a polygon mirror, the direction of luster scan becomes reverse to each other between the former two colors and the latter two colors, and the data are corrected therefor. Further, color shifts are caused by various factors.
Print positions for the four colors may be shifted due to image delay by the memories and the shift of exposure positions. Then, color displacement occurs, and image is distorted. When such image distortion is prevented, an image of high quality can be obtained. Then, in order to correct the shift of print positions, it is proposed to detect image distortion quantities and to change the line address in the main scan direction for the colors for an address in the main scan direction according to the detection results.
However, the detection of the distortion quantities for distortion correction is complicated when the line address in the main scan direction for the colors for an address in the main scan direction is changed according to the detection results of image distortion. Further, in order to detect the image distortion quantity correctly, sensors therefor have to be set correctly, and it takes a long time to set the sensor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image forming apparatus having an image distortion correction system for forming a color image.
In one aspect of the invention, an image forming apparatus comprises an image forming unit having a plurality of print units each forming an image of one of a plurality of colors based on image data. A pattern generator generates image data of a predetermined pattern for the plurality of colors. A sensor detects images of the predetermined pattern of the plurality of colors formed by the print units according to the image data generated by the pattern generator, while a detector detects a setting error of a position of the sensor. A controller calculates correction data based on the setting error detected by the detector and image distortion determined from detection data detected by the sensor.
In another aspect of the invention, in an image forming apparatus wherein a plurality of print units form a color image according to image data, a pattern generator forms images of a predetermined pattern of the plurality of colors. A sensor detects the images of the predetermined pattern formed by the pattern generator, while a detector detects a setting error of a position of the sensor. A controller corrects print positions of the plurality of print units based on the setting error and shifts of the images of the plurality of colors obtained from the images detected by the sensor.
An advantage of the present invention is that image distortion can be corrected without using a complex structure because the position error of the sensor and image distortion quantities of each color can be obtained at the same time with one kind of sensor by detecting predetermined patterns of the colors.
Another advantage of the present invention is that a mechanical setup time can be shortened because the position adjustment of the sensor is not needed.
REFERENCES:
patent: 5448277 (1995-09-01), Long
patent: 5457518 (1995-10-01), Ashikaga et al.
patent: 5539522 (1996-07-01), Yoshida
patent: 5768671 (1998-06-01), Komiya et al.
patent: 07306624 (1995-11-01), None
patent: 08286523 (1996-01-01), None
patent: 09234905 (1997-09-01), None
Hirota Yoshihiko
Imaizumi Shoji
Sugiura Hiroshi
Le N.
McDermott & Will & Emery
Minolta Co. , Ltd.
Pham Hai C.
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