1. Field of the Invention
The present invention relates to an image forming apparatus that includes a cleaning portion cleaning an image control toner image.
2. Description of the Related Art
When an image forming apparatus, which obtains an achievement by forming an image on a transfer material, outputs a plurality of same images, it is desirable that the first image to the final image are viewed with the same density and tone. U.S. Pat. No. 7,385,737 discloses an image forming apparatus which meets the requirement. The image forming apparatus disclosed in U.S. Pat. No. 7,385,737 first controls the density correction characteristic of the image forming apparatus based on an image characteristic of an image control toner image formed on a transfer material. Then, the image forming apparatus forms the image control toner image in a region other than an image formation region on a photosensitive drum by the use of an image characteristic of an image control toner image formed on the photosensitive drum as reference information, when forming a normal image, and corrects the density correction characteristic based on a difference between a reference characteristic and the image characteristic of the image control toner image. With such a configuration, it is possible to provide frequently executable image control with less time and effort.
On the other hand, as a known technique, there is known an image forming apparatus that includes an intermediate transfer belt. That is, there is known an image forming apparatus in which an image control toner image is allowed to be attached on the intermediate transfer belt and which includes a cleaning portion cleaning the image control toner image with a fur blush applied with an opposite-polarity bias of the polarity of a toner. It is known that the image forming apparatus of the known technique resolves the following problem with the image forming apparatus disclosed in U.S. Pat. No. 7,385,737. That is, the image forming apparatus disclosed in U.S. Pat. No. 7,385,737 forms the image control toner image at a position corresponding to a gap (gap between sheets) between transfer materials of a plurality of output image regions formed on the intermediate transfer belt, when continuously forming a plurality of images. In this way, the density of the image control toner image is corrected in parallel to formation of the output image. A transfer roller is separated from the intermediate transfer belt in the gap between the transfer materials and a cleaning device collects toner forming the image control toner image together with residual transfer toner so that the toner image on the surface of the intermediate transfer belt is not attached to the transfer material from the intermediate transfer belt. In recent years, a conveyance speed at which the intermediate transfer belt conveys the toner image is faster in order to meet a requirement for productivity improvement. For this reason, since a time is not sufficient to separate the transfer roller from the intermediate transfer belt in the gap between the transfer materials, there is a problem that the image control toner image may be attached to the transfer material. In order to resolve this problem, the image control toner image is allowed to be attached to the intermediate transfer belt and the image control toner image is cleaned electrostatically from the intermediate transfer belt by electrically conducting a fur brush.
In some cases, the image control toner images with a wide range of density gray scales are formed in image control regions near the image formation regions of an image bearing member in order to improve tone reproducibility of a color image. In this case, when the toner of the image control toner image attached to the intermediate transfer belt is cleaned with the fur brush under a constant conductivity condition of the fur brush, there is a problem that a part of the image control toner image with some density may not be cleaned and the rear surface of the transfer material is smeared.