1. Field of the Invention
The present invention relates to a developing unit comprising a developer container and a toner hopper for supplying the same with toner.
2. Description of Related Art
Recently, a unit is provided with a screw conveyer having a blade which is adapted to agitate a developer material in a developer container. This unit is provided as a system for agitating the developer in the developer container of an image forming apparatus. Additionally, the developer container of this type employs a so-called one-point drop system for feeding toner to the developer container. This system is arranged such that the screw conveyer is used to convey toner in a toner hopper while agitating it, and the toner thus conveyed is fed to the developer container thereunder through a toner drop port provided at the toner hopper. The toner drop port generally comprises small holes which are defined in a predetermined position of a lower wall, as running downward or sideward.
The toner hopper of the aforedescribed one-point drop system suffers from the following two problems (i) and (ii).
(i) When the main body of an image forming apparatus is inclined during installation or when a clam-shell type image forming apparatus is opened for jam recovery, a developing unit including the toner hopper may in some cases be inclined. In such a case, developer in the developer container flows back to the toner hopper side through the aforesaid toner drop port, which leads to a failure to maintain a constant supply of the toner.
(ii) Under the aforesaid toner drop port, there exists a strong flow of developer caused by a spiral shaft, adversely affecting a smooth downflow of toner from the toner hopper. This also results in a failure to maintain a constant supply of the toner.