Facsimile and static presentation processing – Static presentation processing – Memory
Reexamination Certificate
1997-11-17
2001-11-27
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Memory
C358S001180, C358S001900, C348S144000, C347S178000, C347S177000, C347S264000, C347S262000
Reexamination Certificate
active
06323955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copier, a laser printer, an inkjet printer and the like. The present invention specifically relates to an image forming apparatus which forms an image by combining a plurality of images on a single transfer sheet.
2. Description of the Related Art
In recent years it has become important that image forming apparatuses can reproduce full color images without image dislocation (color drift). Specifically, digital methods use a plurality of image forming units corresponding to each color are installed with integrated elements such as photosensitive members, charging devices, and developing devices, and multiple transfers are accomplished for the image formed by each unit onto a single transfer member. Position error of images formed by each image forming unit can be detected and corrected, which is necessary to obtain high precision in image reproducibility. Therefore, a predetermined registration mark or pattern is formed on the transfer member by each image forming unit, and these marks or patterns are read by detection devices to accomplish positional alignments.
For example, Japanese Laid-Open Patent Application No. 1-141746 discloses a method wherein registration marks extending in a main scan direction and a subscan direction are detected by an inclined charge-coupled device (CCD). Japanese Laid-Open Patent Application No. 4-131750 discloses a method wherein registration marks comprising straight lines extending in a main scan direction and diagonal lines inclined relative to said straight lines and extending in the same direction are formed. These registration marks are detected by a single photosensor, and the amount of dislocation is calculated and corrected.
In the former method, because the registration marks are read by a charge storage type CCD, the sampling period is long and detection precision does not allow fine resolution, or the sampling data rate must increase to accomplish fine resolution, thereby enlarging the processing unit and greatly increasing cost. The latter method, on the other hand, uses a non-integrating sensor, and avoids the aforesaid disadvantages in conjunction with the sampling period, but because the registration mark is detected at one point in the main scan direction, there are reading position errors in the main scan direction when the transfer member travels at irregular speed in the subscan direction. Furthermore, there is the possibility of inadequate detection when the pattern, skips so as to leave out part of the pattern because a combination of horizontal and vertical lines, or diagonal lines are used as the registration pattern.
SUMMARY AND OBJECTS OF THE INVENTION
An object of the present invention is to provide an image forming apparatus capable of detecting a registration pattern with high precision by using an inexpensive detection means of non-integrating type utilizing simple controls and processes.
A further object of the present invention is to provide an image forming apparatus capable of detecting a registration pattern reliably and with precision even when the registration pattern is partial and incomplete, and which is further capable of suitably correcting dislocation of overlapped images.
The image forming apparatus of the present invention attains the aforesaid objects by providing a plurality of recording units to form images based on their respective image data, overlaying the images formed by the plurality of recording units on a single transfer member traveling in one direction, control means to sequentially cause registration patterns of predetermined shape to be formed by the plurality of recording units, and detecting means to detect each registration pattern received onto the transfer member at two locations in both the direction of travel of the transfer member and a direction perpendicular thereto (i.e., main scan direction), and output non-integrated detection values.
Since a non-integrated type detecting means is used as the registration pattern detecting means, timely and continuous detection output is possible, thereby increasing pattern detection resolution and providing for simple controls and processing of detection data at low cost. Since the registration pattern is detected at two locations in the main scan direction, the position of the registration pattern in the main scan direction can be accurately detected even when the transfer member is traveling at irregular speed by reading at two detection intervals in the subscan direction.
The image forming apparatus of the present invention is provided with a plurality of recording units to develop images based on their respective image data, overlaying the images developed by the plurality of recording units on a single transfer member traveling in one direction, control means to sequentially cause registration patterns of predetermined shape to be formed by the plurality of recording units, detecting means to detect each registration pattern received onto the transfer member, and correction control means to calculate the amount of dislocation of the registration patterns detected by the detecting means and correct the position of the images formed by the recording units based on the amount of dislocation, and wherein the registration pattern extends at an incline relative to the direction of travel of the transfer member and comprises two lines which intersect at a point.
Since the shape of the registration pattern comprises two lines inclined relative to the direction of travel, a plurality of position information can be detected by the detecting means, and the amount of position dislocation can be calculated by reliably and accurately detecting a center position by averaging the detected data even when the line is partially skipped and non-printing, such that position dislocation of an image can be accurately corrected.
These and other objects and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.
REFERENCES:
patent: 5396282 (1995-03-01), Ogikubo
patent: 5600408 (1997-02-01), Horiuchi et al.
patent: 5722009 (1998-02-01), Haneda et al.
patent: 5854958 (1998-12-01), Tanimoto et al.
patent: 1-141746 (1989-02-01), None
patent: 4-131750 (1992-05-01), None
patent: 1-112266 (1989-04-01), None
Kanai Nobuo
Kohsaka Jun
Takeshita Kenji
Coles Edward
Lamb Twyler
Minolta Co. , Ltd.
Sidley Austin Brown & Wood
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