Image forming apparatus and color-shift control method

#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.

#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.

#FIG. 1 is a diagram for indicating an image forming apparatus to which an embodiment of the present invention is applied.

#FIG. 2 is a block diagram used to explain a function of a control unit.

#FIG. 3 is a flow chart for describing a color-shift control process operation executed in the control unit.

#The present invention will now be described in detail based upon embodiments shown in the accompanying drawings.

#FIG. 1 is a diagram for schematically indicating an image forming apparatus to which this embodiment of the present invention is applied. This image forming apparatus is a so-called “tandem type digital color electrophotographic machine”, which employs an electronic photographic system. This tandem type digital color electrophotographic machine has an image forming unit 11 containing a specific-color image for forming unit 11S and commonly-used color image for forming units 11Y, 11M, 11C, 11K, an exposing device 13, and a transfer belt 21. The commonly-used color image forming units 11Y, 11M, 11C, and 11K form respective color images such as a yellow (Y) image, a magenta (M) image, a cyan (C) image, and a black (K) image. The specific-color image forming unit 11S forms a specific-color image. The exposing device 13 forms electrostatic latent images with respect to these image forming units 11 (namely, 11Y, 11M, 11C, 11K, and 11S). The transfer belt 21 functions as an intermediate transfer member, which is made in contact with, for instance, the image forming units 11, and transfers images formed by these image forming units 11 by overlapping these images with each other. Also, a drive roller 22 for driving this transfer belt 21, a plurality of primary transfer rollers 23, a secondary transfer roller 24, and a back-up roller 25 are provided inside the transfer belt 21. The plurality of primary transfer rollers 23 are provided opposite to photosensitive members of the image forming unit 11, and form images on the transfer belt 21. The secondary transfer roller 24 transfers a color image formed on the transfer belt 21 to a recording medium such as paper (recording sheet). Each of the primary transfer rollers 23 specifies a primary position with respect to the transfer belt 21. The back-up roller 25 then positions the transfer belt 21 in the primary travel direction (shown as ) that is substantially parallel to the exposing device 13. Also, this image forming apparatus has a control unit 31, and a pattern detecting sensor 32. The control unit 31 supplies such a color-shift detecting pattern information to the exposing device 13 and the image forming unit 11. The pattern detecting sensor 32 reads a color-shift detecting pattern which is formed in a predetermined area of the transfer belt 21.

#The image-forming unit 11 has a developing device, a paper transferring member or an intermediate transfer member, a charging device, a photosensitive drum and an exposure device. The developing device forms images using different color toners on the commonly-used color image forming unit 11Y, 11M, 11C, 11K and the specific-color image forming unit 11S, respectively. The image carrying bodies such as photosensitive drums carry the images formed with the toners supplied from the developing device. The charging device charges the photosensitive drums. The various sorts of image forming units such as a cleaner for removing remaining toners. In this case, it is assumed that colors frequently used in normal color representations such as yellow (Y), magenta (M), cyan (C), and black (K), are defined as commonly-used colors. The specific-color image forming unit 11S can form an image having a specific-color (namely, specific image forming material), while the specific image forming material is not the commonly-used colors, but is not employed to form the normal color image. As this specific-color (specific image forming material), for instance, there are a corporate color, which is exclusively used by a specific user (for example, a green color of a specific film company and a red color of a specific beverage company), a foaming toner for braille, a fluorescent color and toners capable of improving a gloss. A predetermined specific-color toner is stored in the developing device of the specific-color image forming unit 11S. It should be noted that alternatively, as the commonly-used colors, six colors, or more colors including a dark yellow color in addition to the above-explained four colors Y, M, C, K may be employed. Also, as apparent from the above-explained example, the expression “specific-color” implies not only that color is limited to only the specific-color, but also specific image forming material having a material and/or a characteristic other than a material and a characteristic used for the normal color image formation as the commonly-used color. In other words, the specific-color image forming unit 11S maybe referred to as an “optional image forming unit 11” with respect to the image forming unit 11 used for the normal color.