Patent ID: 8660449

Claim:
A developer concentration adjustment apparatus for adjusting a toner concentration of liquid developer containing toner and carrier liquid to a predetermined concentration, the apparatus comprising: a concentration adjustment tank configured to store first liquid developer which is to be adjusted in concentration, and configured to discharge liquid stored therein, the first liquid developer containing toner and carrier liquid; a stirrer for stirring the first liquid developer stored in the concentration adjustment tank; a load detector configured to detect a stirring load of the stirrer while the stirrer is stirring the first liquid developer; a supplement section configured to supply the concentration adjustment tank with first supplemental developer having a concentration higher than the predetermined concentration, and carrier liquid or second supplemental developer containing second supplemental developer having a concentration lower than the predetermined concentration; a discharge section configured to discharge the first liquid developer from the concentration adjustment tank; and a controller configured to control the supplement section to supply the first supplemental developer, the second supplemental developer, or the carrier liquid so as to adjust a concentration of the first liquid developer to the predetermined concentration based on the stirring load detected by the load detector, wherein in a cleaning operation for the stirrer, the controller controls the discharge section concentration adjustment tank to discharge the concentration-adjusted first liquid developer from the concentration adjustment so as to empty the concentration adjustment tank, and then controls the supplement section to supply the concentration adjustment tank with the carrier liquid or the second supplemental developer, whereby the stirrer is cleaned with the carrier liquid or the second supplemental developer, and residue of toner in the first liquid developer attached to the stirrer is reduced.