Electrophotography – Image formation – Transfer
Reexamination Certificate
2002-11-15
2004-05-18
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Transfer
C399S066000, C399S085000, C399S082000
Reexamination Certificate
active
06738594
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a tandem type color image forming apparatus and its control method wherein a multiple number of image forming devices for forming different colors of images are placed serially in the direction of conveyance of recording media. The present invention is particularly directed to a tandem type color image forming apparatus and its control method wherein different image forming modes are used for monochrome and multi-color image forming operations.
(2) Description of the Prior Art
Conventionally there have been known tandem type color image forming apparatuses, which are improved in throughput of image forming by serially arranging multiple, e.g., four image stations (image forming units or image forming devices) having image supports forming electrostatic latent images corresponding to multiple colors, e.g., four image colors K: black, C: cyan, M: magenta and Y: yellow, along the direction of conveyance of recording media.
In such a conventional tandem type color image forming apparatus, usually there is use of only one image forming station, with the others unused, when a monochrome image is formed. Therefore, in the monochrome image forming mode, the image supports of the image forming stations other than the one needed are adapted to stop rotating.
Since the image supports are stopped rotating by the above arrangement so that the image supports will not come into contact with the recording media, an intermediate transfer medium, or the like, more than needed, it is possible to avoid deterioration of the image supports due to abrasion and the like. Thus, this control leads to reduction in running cost.
In particular, in color image forming apparatuses, use of B/W (monochrome) image forming is made more frequently compared to use of full and mono color image forming operations. Therefore, the image forming stations other than that for K, or more explicitly, for C, M and Y are, in most cases, kept away from the recording media or the intermediate medium.
In this case, upon a mode change between monochrome image forming and color image forming, image supports to be non-rotated are separated from the transfer belt as a transfer support or image supports to be rotated are set into contact therewith. Therefore, with conventional typical technologies, the image supports are adapted to start rotating after discharge of the recording sheet from the transfer belt. Then, the image supports are shifted or the transfer belt or the transfer and conveyance support for supporting a transfer belt is shifted so that the supports to be rotated come into contact with the transfer belt while the image supports are stopped rotating after the transfer belt or the transfer and conveyance support for supporting a transfer belt is shifted so that the supports to be non-rotated are moved away from the transfer belt.
However, since the operation relating to the-separation and abutment of the image supports and the transfer belt needs a certain period of time, there has been a problem that it takes along time if a set of documents which contains monochrome pages without color images and multicolor pages with color images needs to be image formed.
In order to solve the above problem, a variety of technologies have been proposed.
For example, Japanese Patent Application Laid-open Hei 11 No. 133697 discloses a technology in which a rearrangement control means is provided in order to change the order of pages to be formed with images where the pages containing color and monochrome images are segregated into color page and monochrome page groups and reproduced separately one from the other. In this prior art, since it is possible to reduce the number times the transfer and conveyance support is shifted, it is not only possible to reduce the running cost but also to solve the above problem, or reduce the time for image forming of the whole images.
However, even though the method disclosed in Japanese Patent Application Laid-open Hei 11 No. 133697 is able to reduce the time for image forming, it entails new problems including increase in cost and lowering of user convenience.
More specifically, provision of the rearrangement control means increases the complexity of the control system of the color image forming apparatus hence increase the production cost of the machine and the cost for maintenance. Further, since the recording sheets with images formed using the rearrangement control means are not arranged in the correct order, the user has to rearrange them in the collated order.
In this case, an intermediate tray or the like which can temporarily hold the recording sheets may be provided in the color image forming apparatus so that the recording sheets printed out first and the recording sheets printed out later can be rearranged in the collated order. However, provision of the intermediate tray increases the number of parts of the color image forming apparatus and hence further increases the production cost, which results in an inefficient solution.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above problems, it is therefore an object of the present invention to provide a color image forming apparatus and its control method, wherein, when documents which include monochrome pages without color images and multicolor pages with color images are handled for image forming, the speed of image forming can be improved without any change of printed page order while degradation of the image supports can be prevented.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a color image forming apparatus includes: a plurality of image forming devices placed serially in the direction of conveyance of recording sheets; a transfer support which is arranged in abutment with image supports provided in the image forming devices and is separable therefrom, for transferring images from the image supports to a recording sheet; a mode switching means for making a changeover between the monochrome image forming mode for forming images using only one image forming device of the plural image forming devices and the multi-color image forming mode for forming images using the plural image forming devices; and a control means for governing the image forming devices, the image supports, the transfer support and the mode switching means, the control means making a control so that the transfer support can abut only the image forming devices which are actually engaged in image forming, among the plural image forming devices, and is characterized in that the mode switching means starts the changeover from the monochrome image forming mode to the multi-color image forming mode while the recording sheet remains on the transfer support.
In accordance with the second aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that the mode switching means starts the mode change immediately after the image has been transferred from the image support of the most upstream image forming device to the recording sheet.
In accordance with the third aspect of the present invention, the color image forming apparatus having the above first feature is characterized in that each of the image supports is comprised of a rotational photoreceptor drum and the control means makes a control so that the transfer support abuts the image supports after the image supports start rotating.
In accordance with the fourth aspect of the present invention, the color image forming apparatus having the above second feature is characterized in that each of the image supports is comprised of a rotational photoreceptor drum and the control means makes a control so that the transfer support abuts the image supports after the image supports start rotating.
In accordance with the fifth aspect of the present invention, the color image forming apparatus having the above third feature is characterized in that at lea
Fujimoto Osamu
Kobayashi Toshi-aki
Nakagawa Takashi
Oogita Kazuyuki
Takai Yasuhiro
Ngo Hoang
Sharp Kabushiki Kaisha
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