Patent ID: 7892330

Claim:
An image forming apparatus, comprising: a head which ejects droplets of liquid in accordance with an image signal; a sub tank which is integrated with the head; a liquid holding chamber which is arranged in the sub tank and has an intake port and an outflow port, the liquid being supplied to the liquid holding chamber through the intake port and supplied to the head through the outflow port; an air connection channel which is arranged in the sub tank above the liquid holding chamber and has a suction port through which air is sucked; a dividing plate which is arranged in the sub tank on an upper face of the liquid holding chamber and beneath the air connection channel, divides the liquid holding chamber from the air connection channel, and defines an upper limit of a surface of the liquid held in the liquid holding chamber; a gas/liquid separating member which is disposed in a portion of the dividing plate and allows only air to pass between the liquid holding chamber and the air connection channel, the surface of the liquid being in contact with the gas/liquid separating member when the sub tank is filled with the liquid; a supply connection device which is capable of connecting with the intake port and the suction port; a liquid holding tank which is connected to the supply connection device and capable of communicating with the liquid holding chamber through the intake port; a suction device which is connected to the supply connection device and capable of communicating with the air connection channel through the suction port; a measurement device which measures a sub tank full state duration as a duration of contact between the surface of the liquid and the gas/liquid separating member; and a judgment device which makes a judgment that replacement of the gas/liquid separating member is required in accordance with a comparison between a cumulative value of the duration of contact measured by the measurement device and a contact duration threshold value.