Ink jet printer with secondary, cyclically varying deflection field

Claim 1

An ink jet printer for printing on a moving print-receiving medium, comprising: print head means for producing a plurality of jet drop streams directed at said medium, said streams being arranged in a row which is oblique with respect to the direction of movement of said medium, charging means for selectively inducing a first, non-zero charge level on drops which are to be deposited on said medium and for inducing a second charge level on drops which are not to be deposited on said medium, means for providing a static primary deflection field extending parallel to said medium and perpendicular to said row and positioned in the paths of said streams, said primary deflection field separating said drops into print trajectories and catch trajectories in dependence upon whether said drops carry said first or second charge levels, respectively, catcher means, extending parallel to said row of jet drop streams and positioned generally between said print head means and said medium, for catching drops in said catch trajectories, and means for providing a cyclically varying secondary deflection field extending parallel to said primary deflection field and positioned in the path of said streams, said secondary deflection field separating drops having said first non-zero charge level into varying trajectories in dependence upon the strength of the secondary deflection field at the time that the drops pass therethrough, whereby the drops from each jet drop stream may be deflected into at least two print trajectories for deposit at two positions on the print receiving medium.