US 4,395,716 AGranted

Bipolar ink jet method and apparatus

AssigneeXerox Corporation

InventorsPeter A. Crean, John M. Schneider, Anthony F. Lipani

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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.

Claims4

Dependent claims

In an ink jet marking array having a plurality of ink jet column generators, each generator including means for directing a series of ink droplets in the direction of a recording medium, apparatus comprising:

spaced electrodes for creating regions of substantially uniform electric field strength through which said ink droplets travel in their trajectory toward said recording medium, said electrodes configured in relation to said generators such that each series of droplets from a given generator enter an associated region substantially midway between two electrodes, and alternate ones of said spaced electrodes being electrically grounded and other ones of said electrodes being maintained at a uniform electric potential with respect to electrical ground so that said electrodes, in combination, provide a series of regions along the array width having electric field strengths substantially the same in magnitude but opposite in direction;
means for inducing charge on said droplets prior to their travel to said associated region of substantially uniform electric field strengths thereby causing said droplets to strike a particular area of the recording medium or to travel to means for intercepting said droplets depending on the induced charge polarity and magnitude, said means for inducing charge being operative to spatially separate closely adjacent droplets to diminish electrostatic and aerodynamic interaction between said closely adjacent droplets in their path to the recording medium, and
said means for inducing charge comprising circuitry for causing droplets from a particular generator to scan across a portion of the array width and said spatial separation being performed by applying an interlace charging sequence to said droplets.

Dependencies are inferred from the claim text.