Patent ID: 7334860

Claim:
An image forming range varying system for an image forming apparatus which jets liquid ink to a conveyed image forming medium to form an image, and which includes an ink head unit comprising at least two ink head rows each including a plurality of ink heads extending in a direction substantially orthogonal to a conveyance direction of the image forming medium, wherein the ink heads of the at least two ink head rows are alternately arranged with a predetermined overlap between respective ink heads of the at least two ink head rows in the conveyance direction of the image forming medium, the image forming range varying system comprising: a first detection unit which is disposed on a supply side of the image forming medium and which detects a tip portion of the image forming medium; a conveying mechanism which conveys the image forming medium, and which outputs conveying information of the image forming medium; a second detection unit which detects both transversal side ends of the image forming medium; an image forming range production unit which produces/outputs information of an image forming range with respect to the image forming medium by determining a valid nozzle address and an invalid nozzle address for each ink head based on detection results output by the second detection unit and based on pre-stored image forming reference timing data corresponding to each ink head of the at least two ink head rows; and a control unit which varies/controls an image forming operation based on pre-stored appropriate image forming timing information and the image forming range information output by the image forming range production unit.