The present invention relates to a developing apparatus and, more particularly, to a developing apparatus for developing an electrostatic latent image formed on a photosensitive layer of an electronic copying machine.
In general, in a developing apparatus of an electronic copying machine, a developing apparatus of non-contact type which develops a latent image by flying toner particles without direct contact of a toner layer held on a toner holder with a photosensitive member is known.
The conventional developing apparatus of this non-contact type has had the following disadvantages due to the fact that toner is not sufficiently and uniformly charged:
For example, there is disclosed in Japanese Patent Publication No. 9475/1966 a developing apparatus which develops a latent image by approaching a toner holder to a photosensitive layer. In this developing apparatus, since the toner is not uniformly and sufficiently charged, the transfer of the toner from the toner holder to the photosensitive layer is largely affected by the gap between the photosensitive layer and the toner holder, and by the electrostatic force. In other words, when the electrostatic force is excessively strong, the background of a photosensitive layer is contaminated. When the gap is excessively wide, the density of the image on the copy sheet becomes insufficient, or the density of the developed picture is uneven.
Further, there is also disclosed in Japanese Utility Model Laid-Open No. 126856/1974 a developing apparatus which develops an electrostatic latent image by applying electric pulses to the developing space between a toner holder and a photosensitive layer. In this case, toner is not sufficiently and uniformly charged. Accordingly, toner is adhered to the background of a photosensitive layer, thereby contaminating the background of the photosensitive layer. Thus, it cannot obtain a clear image on the copy sheet, or the density of the developed image becomes uneven.