Patent ID: 8556361

Claim:
An image forming device comprising: an exchangeable cartridge; a first memory unit arranged in the cartridge to store a first conductivity indicating an electric conductivity of an ink contained in the cartridge; a subtank arranged to store an ink supplied from the cartridge; a conductivity detector arranged to detect a second conductivity indicating an electric conductivity of the ink stored in the subtank, via sensors provided in the subtank; a second memory unit arranged in the image forming device to store the second conductivity detected by the conductivity detector; a comparing unit arranged to compare the first conductivity from the first memory unit and the second conductivity from the second memory unit to obtain a first comparison result; a storage control unit arranged to store the first conductivity into the second memory unit when the first conductivity and the second conductivity differ from each other in the first comparison result; a discharging unit arranged to completely discharge the ink stored in the subtank when the first conductivity and the second conductivity differ from each other in the first comparison result; and a supplying unit arranged to supply the ink contained in the cartridge to the subtank after the ink stored in the subtank is completely discharged, wherein the comparing unit is further arranged to compare the first conductivity stored in the second memory unit with a third conductivity detected by the conductivity detector and indicating an electric conductivity of the ink supplied to the subtank by the supplying unit to obtain a second comparison result; and the supplying unit is configured to stop supplying of the ink from the cartridge to the subtank based on the second comparison result.