1. Field of the Invention
The present invention relates to an image forming apparatus which has a developing section in which single-component developing agent is caused to attach to the electrostatic latent image formed on an image carrier without the developing section and the image carrier contacting each other.
2. Description of the Related Art
In copying apparatus or laser printers which utilize the electrophotographic recording process such as shown in FIG. 1, the apparatus forms a copy image on copying paper 16 by devices such as a charging device 11, an exposure device 12, a developing device 13 and a image transferring device 14 being provided around a photosensitive drum 10. At the same time, this apparatus removes any residual toner on photosensitive drum 10 after image transferring by a contact type cleaning device 17 having of a cleaning blade 17a.
However, in image forming apparatuss such as this, apart from developing device 13, cleaning device 17 must also be provided in a position opposite to it. For this reason, from the viewpoint of the image forming process, restrictions will occur in the positions of installation of such other devices as exposure device 12 and image transferring device 14. Thus, the degree of freedom in design is reduced and, at the same time, there is the drawback that the surface of photosensitive drum 10 will be worn by friction with cleaning blade 17a when cleaning, causing deterioration of its properties and reducing its life. Moreover, ozone products are produced in charging device 11, when charging, and since deterioration occurs in negative polarity organic photoconductor (hereafter OPC) due to these ozone products, ozone products which are produced to excess must be instantly exhausted. However, there is a problem in that this exhaust route is blocked by cleaning device 17. Also, there are problems of disposal of toner collected in cleaning device 17 and of maintenance being difficult and, at the same time, of soiling occurring in the vicinity. For this reason, apparatus were developed which, after developing for the 1st revolution of the photosensitive drum using a developing device, would carry out cleaning on the 2nd revolution of the photosensitive drum using the same developing device. However, although a device exclusively for cleaning is not required in such apparatus, since the developing process and the cleaning process are carried out separately, a photosensitive drum is required of greater (longer) circumference than the length of the image to be formed. Thus, there is the drawback that miniaturisation of the photosensitive drum, and therefore of the apparatus as a whole, is prevented. Moreover, in recent years, apparatus have been developed such as U.S. patent application Ser. No. 571,800, now U.S. Pat. No. 4,664,504 (filed on Jan. 18, 1984) which carry out the developing process and the cleaning process simultaneously by a single developing device. However, this apparatus carry out developing and cleaning using a two-component developing agent having toner and carrier particles as the developing agent. Consequently, they have problems in that the developing device itself is both bulky and heavy, and also their cost rises because of the necessity of using the controller for automatic controlling the toner density. Furthermore, if the potential difference between the unexposed areas of the photosensitive body and the developing roller is increased too far when trying to ensure collection of the residual toner, since the carrier particles has the opposite potential to the toner it is liable to drawn from the developing roller to the photosensitive body. Also, since the resistance of carrier particles is lower than that of the toner, the carrier particles are liable to be charged with the opposite polarity charge to that of the toner by high electric fields. Consequently, there are such problems as deterioration of the photosensitive body and reduction of the image quality because of adherence of the carrier particles to the photosensitive body.