Patent ID: 7780275
Filing Date: 2010-08-24
Classification: B41J

Abstract:
1. An image forming apparatus, comprising: a liquid ejection head having a plurality of ejection holes from which liquid droplets are ejected onto a recording medium; a recording medium conveyance device which causes the liquid ejection head and the recording medium to move relatively to each other, in one direction; a flight direction deflection device which is capable of deflecting directions of flight of the liquid droplets ejected from each of the ejection holes, in a direction including at least a component of a direction substantially parallel to a relative conveyance direction of the recording medium; and a deflection angle setting device which sets, with respect to each of the ejection holes, two or more angles of deflection with reference to a normal direction to a surface in which the ejection holes are formed and which is on an ejection side, in such a manner that when dots that are adjacent to each other in the direction substantially parallel to the relative conveyance direction of the recording medium are formed in an overlapping fashion, directions of flight of liquid droplets ejected consecutively from each of the ejection holes are deflected so that the directions of flight of the liquid droplets ejected consecutively from each of the ejection holes become different from each other, and a droplet landing time differential between a first liquid droplet and a second liquid droplet which form the dots that are adjacent to each other in the direction substantially parallel to the relative conveyance direction of the recording medium becomes equal to or greater than a quasi fixing time period from a landing time of the first liquid droplet until a time at which the first liquid droplet achieves a quasi fixed state, wherein: a relationship among a deflection distance y between dots formed on the recording medium by the liquid droplets ejected consecutively from each of the ejection holes, on a scanning plane in the direction substantially parallel to the relative conveyance direction of the recording medium, a minimum dot pitch Pt between dots formed on the recording medium in the direction substantially parallel to the relative conveyance direction of the recording medium, and a deflection shift amount k on the scanning plane of the liquid droplets ejected consecutively from each of the ejection holes (where k is an integer equal to or greater than 2), is expressed as y=k×Pt; and the deflection angle setting device determines the deflection shift amount k and sets the angles of deflection for the ejection holes on the basis of the deflection shift amount k, in such a manner that a relationship, on the scanning plane, among the deflection shift amount k, a droplet ejection cycle Tf of the liquid ejection head, and the quasi fixing time To, satisfies k≧(To/Tf)+1, and the angles of deflection for the ejection holes from which the liquid droplets are ejected to form the dots that are adjacent to each other in a direction substantially perpendicular to the relative conveyance direction of the recording medium, become different from each other.