Bipolar ink jet method and apparatus

Abstract

An improved ink jet marking architecture for enhancing ink droplet placing accuracy. The improved architecture combines a bipolar scanning arrangement with a drop interlace scheme. The preferred marking apparatus comprises an array of ink jet column generators which direct ink droplets to first a charging region and then through a deflection region. The droplets are charged either negatively or positively depending on a desired droplet trajectory; thus the bipolar designation. The deflection region has an electric field strength slightly less than the breakdown field strength of air for the environment in which the apparatus is to operate. The high field strength reduces the charge which must be applied to the droplets and therefore minimizes the drop to drop coulomb interaction. The interlace strategy causes sequential drops from a given generator to be printed in non-sequential locations on the paper. This strategy spreads out the ink droplets in space and results in a reduction of both aerodynamic and coulombic interaction between droplets. By reducing these interactions and minimizing the time of flight for the drops the placement accuracy is increased. The placement accuracy is further enhanced by utilizing a charging scheme which takes into account the charge induced on other droplets in close proximity of the droplet to correct for coulomb interactions even the bipolar plus interlace strategy cannot avoid.