1. Field of the Invention
The present invention relates to an image forming apparatus for forming a toner image on a sheet by using an image carrier.
2. Description of Related Art
An image forming apparatus of an electrophotographic system, such as a copier and a printer and the like, forms a latent image on a photosensitive body (image carrier) which is uniformly charged, by performing a selective exposure of the photosensitive body, and visualizes the latent image with toner. The image forming apparatus then transfers the visualized image to a recording medium to perform image recording. The image forming apparatus then removes the toner remaining on the photosensitive body after the transfer with a cleaning blade, and performs the next image forming operation by the use of the photosensitive body, the surface of which is cleaned.
The image forming apparatus outputs not only a character image but also a high definition photographic image. Consequently, the image forming apparatus is required to form an image with a high accuracy and a high definition.
Under such a situation, the toner to be used for image formation has been shifting from mechanically pulverized non-uniform toner to spherical small particle diameter toner produced by a chemical reaction, such as a polymerization reaction and the like. However, in the case of the conventional cleaning method using only the cleaning blade, the spherical small particle diameter toner that remains on the photosensitive body after the transfer slips through the cleaning blade to produce defective cleaning.
Accordingly, a cleaning method of providing a brush on the upstream side of the cleaning blade for the purpose of assisting the cleaning blade to remove the toner remaining on the photosensitive body with the brush together with the cleaning blade was proposed.
By the method, even the spherical small particle diameter toner is efficiently removed from the photosensitive body, and the defective cleaning is decreased. However, when much toner adheres to the brush, the adhered toner is scrubbed by the brush and the photosensitive body to be broken to be smaller. When the broken toner is transferred onto the photosensitive body and reaches the cleaning blade, the method causes a problem that the broken toner is pressed by the cleaning blade to cause a fusion of the broken toner to the photosensitive body.
In consideration of this point, a technique for preventing the adherence of much toner to a brush was proposed.
A technique disclosed in Japanese Patent Application Laid-Open Publication No. 2001-158564 is the technique of applying a voltage for preventing the adherence of the toner having a negative polarity to a brush at the time of a toner consuming mode in which a great deal of toner is discharged.
The technique disclosed in Japanese Patent Application Laid-Open Publication No. 2001-158564 can prevent the adhesion of the toner having the negative polarity to the brush, but it is difficult for the technique to prevent the adhesion of the entire toner remaining on a photosensitive body to the brush because the toner remaining on the photosensitive body after transfer is not only the toner having the negative polarity, and the toner having a positive polarity also exists.