Patent ID: 7971957

Claim:
An ink-jet line printer which, by spraying ink, performs in a single operation printing of an entire line of a printing medium crossing a conveyance direction of the printing medium, comprising: a plurality of ink-jet heads arranged to cover a plurality of printing regions divided in a line direction of the printing medium and having a plurality of ink spraying nozzles arranged in the line direction; a backup mechanism, arranged at a home position on a side of the printing medium, for protecting and recovering the nozzles of the plurality of ink-jet heads, wherein the backup mechanism has caps covering surfaces of the nozzles of the ink-jet heads, a purging mechanism which performs purging of the insides of the caps, covers covering the caps, and a drive mechanism that opens the covers when the ink-jet heads are located at positions of the caps; an actuator which moves the ink-jet heads in the line direction between home positions and predetermined printing positions in the line direction, wherein the actuator is constituted by a plurality of guide rails that guide each of the ink-jet heads, respectively, towards the line direction, and a plurality of stages that move the ink-jet heads along the guide rails of the ink-jet heads; and a controller which, when a printing operation is to be performed in the line direction, positions the ink-jet heads at predetermined print positions in the line direction, performs printing by ink jet printing while remaining stationary, and, at a time when a printing operation is not about to take place, moves the ink let heads to home positions, thus enabling the backup mechanism to protect and recover the nozzles, wherein the controller measures continuous printing times of the ink-jet heads at the predetermined printing positions, moves the ink-jet heads from the printing positions to the home positions when the continuous printing time is longer than apredetermined set time, recovers the nozzles by means of the backup mechanism, and restores the ink-jet heads to the printing positions, and the controller measures frequencies of ink spraying by the ink-jet heads and, based on the results obtained, alternates the printing positions of the ink-jet heads.