Patent ID: 7819491

Claim:
An ink jet head driver, which is adapted to discharge ink drops of a predetermined number and taking a maximum of discharged drops as a limit by each pixel data piece corresponding to a plurality of pixels for constituting an image to a transported paper sheet at desired timing to form the image on the paper sheet in driving an ink jet head including a piezoelectric element for pressurizing ink by displacement of a shear mode and a plurality of nozzles from which the ink is selectively discharged, the ink jet head driver comprising a control section that calculates a first head passing time required for the paper sheet from the leading edge to the tailing edge to pass the ink jet head, drives the piezoelectric element of the ink jet head for a predetermined time to perform precursor microvibration immediately before a leading edge of the paper sheet reaches right under the ink jet head and then drives the piezoelectric element according to the normal pixel data to form the image on the paper sheet when the first head passing time is shorter than deterioration time of the ink, and drives the piezoelectric element of the ink jet head for a predetermined time to perform precursor microvibration immediately before the leading edge of the paper sheet reaches right under the ink jet head and then drives the piezoelectric element according to the pixel data so as not discharge ink as many times as a difference between the maximum of discharged drops and a total number of ink drops to be discharged concerning the pixel in which the number of ink drops to be discharged is under the maximum of discharged drops to form the image on the paper sheet when the first head passing time is equal to or longer than the deterioration time of the ink.