Patent ID: 8596736

Claim:
An image forming apparatus comprising: a recording head to discharge liquid droplets; a head tank to contain a liquid to be supplied to the print head; a carriage mounting the recording head and the head tank thereon; a main tank to contain a liquid to be supplied to the head tank; a fluid conveyance pump to convey the liquid from the main tank to the head tank; a liquid supply control processor to control the liquid supply from the main tank to the head tank by driving the fluid conveyance pump; a displacing member disposed at the head tank and configured to displace depending on a remaining amount of the liquid inside the head tank; a first sensor disposed on the carriage and configured to detect the displacing member; and a second sensor disposed on the apparatus body and configured to detect the displacing member, wherein a first position is detected by the first sensor and a second position is detected by the second sensor and the remaining amount of the liquid in the head tank is smaller at the first position than at the second position; and wherein the liquid supply control processor is configured to: detect and store a difference amount corresponding to a displacement amount of the displacing member between the first position detected by the first sensor and the second position detected by the second sensor; measure a consumed liquid amount when the displacing member displaces from the first position detected by the first sensor in the direction in which the remaining liquid amount of the head tank is reducing when supplying the liquid from the main tank to the head tank without using the second sensor; start the liquid supply upon the consumed liquid amount reaching a predetermined threshold so as to supply the difference amount after the first sensor has detected the displacing member; and stop the liquid supply when the first sensor does not detect the displacing member before a preset predetermined time has passed after the start of the liquid supply, when the liquid supply is performed from the main tank to the head tank without using the second sensor, wherein the preset predetermined time includes a first predetermined threshold time and a second predetermined threshold time, the first threshold time is the time in which the liquid supply from the main tank to the head tank is performed while consuming the liquid in the head tank and the second threshold time is the time in which the liquid supply from the main tank to the head tank is performed without consuming the liquid in the head tank, and the first threshold time is set longer than the second threshold time.