(1) Field of the Invention
The present technology relates to a toner supply device and a developing unit using the above mentioned device, in particular relating to a toner supply device and a developing unit using the above mentioned device for use in an image forming apparatus for performing image formation with toner.
(2) Related Art and Other Considerations
Conventionally, in image forming apparatuses using toner, such as copiers, facsimile machines, etc., a toner supply device such as a toner cartridge etc., is used to supply toner to the developing unit to thereby achieve continuous operation of image output.
There is a generally known method for supplying toner to the developing unit, in which toner stored in a toner cartridge is directly supplied to the developing unit (see patent document 1 (Japanese Patent Application Laid-open 2003-162143).
However, the conventional method of directly supplying toner from the toner cartridge to the developing unit suffers the problem that the fluidity of the supplied toner is prone to vary, consequently causing variation in image quality. Also, in a configuration where toner which has been degraded in fluidity (due to long-term inactivity or the like) is processed into high-fluidity toner so as to be supplied without hindrance, toner beyond a controlled amount may be supplied to the developing unit, causing the problem that the toner concentration in the developer rises, exerting influence on mage quality and color tones.
In particular, in a tandem-type color image forming apparatus that requires high image quality, four image forming process units corresponding to four colors, i.e., YMCK, need to be arranged. And yet the developing units are required to be miniaturized so as to meet the demand for a compact equipment configuration. As a result, miniaturization problem occur for the developing units. That is, it becomes difficult to ensure uniform properties of the toner attributed to fluidity, such as charge quantity, toner concentration and the like, by agitation, and it also becomes difficult to secure the capability of absorbing the variations in supply quantity.