Patent ID: 7878608

Claim:
A liquid discharge apparatus, comprising: a discharge head which has a discharge port and discharges a liquid from the discharge port onto a recording medium to form an image thereon; a sub tank which is movable together with the discharge head and which stores the liquid to be supplied to the discharge head; a liquid supplement section which supplements the sub tank with the liquid; a purge section which performs a purge operation in which the liquid in the sub tank is pressurized to be fed to the discharge head, and the liquid in the discharge head is forcibly discharged from the discharge ports; a judging mechanism which judges whether or not an amount of the liquid in the sub tank is not more than a predetermined amount V 1 ; and a controller which controls the liquid supplement section and the purge section; wherein: when the purge operation is executed by the purge section, and when the judging mechanism judges that the amount of the liquid in the sub tank is not more than the predetermined amount V 1 , the controller controls, before the execution of the purge operation, the liquid supplement section to supplement the sub tank with the liquid until the amount of the liquid contained in the sub tank exceeds the predetermined amount V 1 ; wherein the purge section includes a charge tank which accumulates compressed air to be introduced into the sub tank, and an unoccupied volume V S of the sub tank, which is a volume of the sub tank, not occupied by the liquid after the sub tank is supplemented with the liquid from the liquid supplement section, satisfies the following expression: V S ≦{( P C −P S0 )/( P S0 −P 0 )}× V C ; and wherein P C represents a charge pressure of gas in the charge tank, P S0 represents a minimum pressure required to purge the sub tank P 0 represents atmospheric pressure, and V C represents a volume of the charge tank.