Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
1998-06-26
2001-01-09
Grainger, Quana (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C399S300000
Reexamination Certificate
active
06173141
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a color image forming apparatus in which a final image is obtained by forming an image at the image forming station and transferring the formed image onto a print media being conveyed to the image forming station by print media conveying means. More specifically, the present invention is directed to an image forming apparatus of an electrophotographic type for forming color images such as a color copier, color printer etc.
(2) Description of the Prior Art
In recent years, color copiers have been developed to meet the demands for color recordings for office use.
One mechanism for such color copiers is of a tandem type, which comprises four photoreceptor drums arranged in parallel to each other, each drum being provided with a charger device, writing unit such as a LSU or the like, developing unit, transfer device, cleaning device arranged therearound. In this configuration, light reflected from a color original is separated into color components, each different color beam being supplied to a corresponding photoreceptor drum so that a corresponding latent image is formed thereon. The thus formed latent images on the photoreceptors are developed with toners of yellow, magenta, cyan and black, respectively, and the developed images are transferred in a superimposed manner onto printing paper which is supported on a transfer conveyor belt, thus producing a copy of the color image. When full color image forming is not needed, for example, in the case where a black monochrome image is formed, no toner image will be formed with the three photoreceptor drums of yellow, magenta and cyan and the black toner image is formed alone and then is transferred to the printing paper, thus producing a black monochrome image.
The method of driving the photoreceptor drums is disclosed in Japanese Patent Application Laid-Open Sho 61 No.156,161, in which all the photoreceptor drums are driven by a single driver source.
Development of color copiers of the tandem type provides a copy speed in the color copying copier, comparable to that in B/W monochrome copiers, but the price is still considerably high. When black monochrome copying is performed with a color copier of this type, the photoreceptor drums for colors which will not be used for the image forming, also are driven and hence worn out unnecessarily by the cleaning blades and the transfer conveyer belt. Further, when a black monochrome image is formed, the photoreceptor drums for colors also operate in contact with the transfer conveyer belt, which stains the belt with toner, causing degradation of image quality. Further, if the process speed is designed to be faster in order to enhance the speed of black monochrome copying, a large increase in the driving force is needed since the driver drives the photoreceptor drums for colors as well.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a color image forming apparatus wherein the image support provided for forming black monochrome images only is operated without activating the image supports provided for forming color images so as to avoid the wear of the parts and degradation of the image quality and wherein black monochrome copying can be performed at a speed as fast as in conventional black monochrome copiers.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the invention, a color image forming apparatus comprises:
a plurality of image supports;
driving means for rotationally driving each of the image supports;
latent image forming means for forming a latent image on each of the image supports;
developing means for visualizing the latent image formed on the each of the image supports; and
transfer means for transferring the visualized image formed on each of the image supports to a recording medium to form a color image thereon, and is constructed such that the image supports include the first set of image supports on which color separated images are formed and the second image support on which a black monochrome image is formed; and the first set of image supports and the second image support are driven by individual driving means.
In accordance with the second aspect of the invention, a color image forming apparatus comprises:
a plurality of image supports;
driving means for rotationally driving each of the image supports;
latent image forming means for forming a latent image on each of the image supports;
developing means for visualizing the latent image formed on the each of the image supports;
transfer means for transferring the visualized images formed on the image supports onto a recording medium to form a color image thereon;
conveying means for conveying the recording medium to the transfer means; and
discharging means for discharging the recording medium with an image transferred thereon, and is constructed such that the image supports include the first set of image supports on which color separated images are formed and the second image support on which a black monochrome image is formed; the first set of image supports and the second image support are driven by individual driving means; and the driving means for driving the second image support also drives the conveying means.
In accordance with the third aspect of the invention, the color image forming apparatus having the above second feature is characterized in that the transfer means temporarily transfers the visualized images formed on the image supports onto an intermediate transfer medium so as to produce a color image in a superimposed manner and then transfers the color image to the recording medium; and the driving means for driving the second image support also drives the intermediate transfer medium.
In accordance with the fourth aspect of the invention, the color image forming apparatus having the above second feature is characterized in that the driving means for driving the second image support also drives both the conveying means and the discharging means.
In accordance with the fifth aspect of the invention, the color image forming apparatus having the above second feature is characterized in that for forming a color image, the operation of the driving means of the first set of image supports and the operation of the driving means of the second image support are started and stopped simultaneously.
In accordance with the sixth aspect of the invention, the color image forming apparatus having the above first feature is characterized in that when only black monochrome images are formed, the first set of image supports is separated from the medium to which the image is transferred by the transfer means and only the driving means of the second image support is operated.
In accordance with the seventh aspect of the invention, the color image forming apparatus having the above first feature is characterized in that the driving means of the first set of image supports is operated at a first speed and the driving means of the second image support can be operated at the first speed and at a second speed, the first speed being lower than the second speed.
In accordance with the eighth and ninth aspects of the invention, the color image forming apparatus having the above first or second feature is characterized in that the driving means of the first set of image supports and the driving means of the second image support are operated with their periodical drive variations synchronized in phase with each other.
From the above configurations, the following effects can be obtained:
In accordance with the first aspect of the invention, the first set of image supports and the second image support are driven by individual driving means. Therefore, when a black monochrome image is formed, only the second image support is driven while the first set of image supports for forming color images will not be operated. In this way, the first set of image supports is not driven, so that no unnecessary wear will occur due to contact against cle
Hirai Masashi
Kurishita Toshiro
Nakayama Osamu
Sakagami Hidekazu
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Grainger Quana
Sharp Kabushiki Kaisha
Tucker David A.
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