Patent ID: 8303094

Claim:
A liquid supply apparatus comprising: a main tank which stores liquid; a sub tank which is disposed vertically above a recording head configured to eject the liquid and which is not connected to atmosphere, the sub tank being composed of a deformable member so that a volume of the sub tank is changed depending on a volume of the liquid in the sub tank; a first flow channel which connects the main tank with the sub tank; a second flow channel which connects the sub tank with the recording head; a flow rate calculation device which calculates a flow rate of the liquid in the second flow channel; a liquid volume change calculation device which calculates an amount of change per unit time in the volume of the liquid in the sub tank, the calculated amount of change having a positive value when the liquid in the sub tank increases; a corrected flow rate calculation device which calculates a corrected flow rate of the liquid in the second flow channel by subtracting the calculated amount of change per unit time in the volume of the liquid in the sub tank obtained by the liquid volume change calculation device from the calculated flow rate of the liquid in the second flow channel obtained by the flow rate calculation device; a first pressure control device which controls an internal pressure of the main tank by applying pressure to the main tank according to the corrected flow rate calculated by the corrected flow rate calculation device so that a greater pressure is applied to the main tank when the corrected flow rate is greater; and a second pressure control device which controls an internal pressure of the sub tank so as to fall within a prescribed range.