Field of the Invention
The present invention relates to an image forming apparatus, a drum unit, and a developing unit. More specifically, the present invention relates to an image forming apparatus, a drum unit, and a developing unit to form a color image by toners of plural colors.
Description of Related Art
An image forming apparatus for forming a color image by a tandem electrophotographic color printer includes an image carrier and a developing roller for each color to form a toner image with the corresponding color. The image carrier is used up by image forming, and hence a drum unit including the thus consumed image carrier needs to be replaced. Further, when the drum units have different configurations for each color, some measures are required to prevent wrong insertion of a drum unit for different color for replacement.
For example, Japanese Patent Application Publication No. JP 2010-217658 teaches a technique of providing protrusions and recesses in a drum unit and in an attachment part of an image forming apparatus in which the drum unit is to be attached in order to prevent wrong attachment of the drum unit. Specifically, these protrusions and recesses are provided in different positions for each color, and thus any drum unit other than a correct drum unit for the corresponding color is not allowed to be attached to the attachment part.
However, some drum units are not so largely different in visual appearance among different colors. Therefore, there is a case that a user erroneously inserts a wrong drum unit into an attachment part for the different color.
Further, the protrusions and the recesses for preventing the wrong attachment are formed by resin molding, which is an inexpensive method in general, and they do not have much strength. As a result, when a user erroneously inserts the drum unit in the attachment part for wrong color, the protrusions and the recesses for preventing the wrong attachment may be broken.
The present invention has been made to solve the above problem of the conventional technique. To be specific, the present invention has objects of providing an image forming apparatus enabling to prevent wrong attachment of a drum unit without causing breakage when a replacement part has the wrong attachment, and further providing a drum unit and a developing unit which can be used as the replacement part of the image forming apparatus.