Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2002-08-27
2004-02-03
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C347S116000, C399S301000
Reexamination Certificate
active
06687472
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No.2002-128838 filed on Apr. 30, 2002, which are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to an image forming apparatus such as a printer and a copy machine. More specifically, the present invention is directed to an image forming apparatus and the like, which is equipped with a plurality of recording apparatus for forming respective color images.
2. Description of the Related Art
Conventionally, image forming apparatus such as color printers and color copy machines have been widely used in which images having various colors are overlapped with each other to be formed on a single recording medium such as paper. In these image forming apparatus, color shifts (positional shifts) of the respective colors which are formed by a plurality of image forming units may cause a problem. For instance, in the case that a so-called “tandem type image forming apparatus” is employed in which a plurality of image forming units provided with respect to the respective colors are arranged side by side opposite to a transfer belt, such a color shift (color deviation) may occur, because of errors contained in the respective mounting positions of these plural image forming units, errors contained in peripheral speeds of the respective image forming units, differences in exposure positions with respect to the transfer belt, changes contained in linear speeds of the transfer belt, and the like. In other words, for example, in the case of such an image forming apparatus which employs the so-called “tandem system”, the alignments of the image forming units provided with respect to the respective colors and the mechanical errors directly cause the color shifts on the recording medium (paper etc.). As a result, in the image forming apparatus employing such a tandem system, a color shift control (registration control) is necessarily required, by which amounts of these color shifts are measured, and occurrences of these color shifts may be suppressed.
As this color-shift control operation, for instance, JP-A-8-248721 discloses such a technique that while marks having Y(yellow) color, M(magenta) color, C(cyan) color, and K(black) color are drawn on a transfer belt, the positions of these marks are read by a sensor, and color shifts are calculated based on sensor readout results, by which an image writing unit is controlled.
On the other hand, as a trend in future's color printers, with respect to a full-color printer having the above-described four colors of Y, M, C, K corresponding to commonly-used colors (normal colors), an image using an image forming member such a specific-color which could not be represented, or could be hardly represented will be formed by this full-color printer. For instance, as this image forming member, there are corporate colors which are exclusively used by specific users, forming toners in braille, and toners capable of improving fluorescent colors and glosses. In the case that a printing operation is carried out by using these specific-colors with respect to these conventional four (Y, M, C, K) colors, a specific-color image forming unit for printing out this specific-color must be arranged side by side with respect to the image forming units for printing the normal colors.
In this case, even when the specific-color image forming unit for forming the image by employing the image forming member such as the specific-color is arranged, the above-described color-shift control operation is required. However, since the processing operation as to the specific-color is different from the processing operations as to the normal colors such as Y, M, C, K, such a simple color-shift control operation that the color is merely increased and the color-shift control operation is simply executed cannot be practically accepted. For instance, in such a case that a use frequency of an additionally provided specific-color is low, it is not preferable to execute a color-shift control operation as to this specific-color, which is similar to the color-shift control operation of the normal colors. In particular, generally speaking, since cost of toners (image forming members) of these specific-colors is high, if the color-shift control operation is higher frequently carried out, then cost-up aspects caused by useless consumption of these toners (image forming members) cannot be negligible.
Also, for instance, considering now such an example that a foaming toner in braille is employed as a specific-color, a requirement of positional precision as to a print out operation thereof by using this forming toner is lower than that required to print out the normal color. As a result, if the color-shift control operation similarly executed with respect to the normal color is carried out as to such a foaming toner (image forming member), the necessary positional precision of which is low, then this color-shift control operation becomes useless. Furthermore, there is such a case that a certain image formed by using a specific-color cannot be read by merely employing the conventionally-used sensor. Also, although a specific-color itself can be read, there is another case that for instance, after a pattern made of this specific-color has been formed on a transfer belt, this specific-colored pattern of the transfer belt cannot be read by employing the above-described sensor in relation to this transfer belt (namely, specific-color cannot be discriminated from color of transfer belt).
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-described problems of the conventional techniques, and therefore, has an object to execute a suitable color-shift control operation which is fitted to a feature of an image forming unit while color-shift control operations in a plurality of image forming units are carried out.
Another object of the present invention is to execute a suitable color-shift control operation in an image forming apparatus which mounts thereon an image forming unit for a specific-color other than image forming units for commonly-used colors.
To achieve the above-described objects, according to the present invention, in an image forming apparatus such as a full-color printing apparatus employing, for example, a tandem system, both a color-shift control operation as to commonly-used colors, e.g., Y, M, C, K, and another color-shift control operation as to all colors including a specific-color are carried out in a discriminative manner. In other words, in an image forming apparatus in which images are overlapped with each other by employing “a (symbol “a” being integer larger than, or equal to 3)” pieces of image forming units for forming images, and then the overlapped image is transferred, a first color-shift control means executes a color-shift control operation by employing “b (symbol “b” being integer larger than, or equal to 2, and being defined by b<a)” pieces of image forming units; and a second color-shift control means executes a color-shift control operation by employing either a partial or all of (a-b) pieces of the image forming units where a color-shift detection is not carried out in the first color-shift control means in accordance with a condition different from that of the first color-shift control means.
In this case, the second color-shift control means may execute the color-shift control operation based upon a job using (a-b) pieces of image forming units. For instance; in the case that (a-b) pieces of image forming units form an image having a specific-color, the second color-shift control means may execute the color-shift control operation before the job in which this specific-color is used, or before one time after the job using such a specific-color has been carried out several times.
Also, the image forming apparatus may be further comprised of a switching means for switching a detection level of a sensor and/or a color-shift detecting pattern by both the first colo
Ando Ryo
Tagawa Kozo
Udaka Tsutomu
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