Ink jet printhead for multi-level printing

An ink jet printer comprising:

• a printing assembly comprising a plurality of nozzles having a respective ink-ejection opening for ejecting ink therethrough and being arranged to form at least one nozzle group, wherein:
• the ink-ejection opening of each of the nozzles that form a nozzle group has a size essentially equal to a corresponding size of the ink-ejection openings of all other nozzles of the group, and
• each of the nozzles of a group are respectively adapted to produce a different print density when actuated only by a non-constant input signal to heat the ink, the non-constant input signal corresponding to each different print density and having a non-linear decaying portion to avoid boiling of the ink;
• a body of ink associated with said nozzles;
• pressure means for subjecting ink in said body of ink to a pressure of at least 2% above ambient pressure, at least during drop selection and separation;
• drop selection means for selecting predetermined nozzles and generating a difference in meniscus position between ink in selected and non-selected nozzles;
• and
• drop separating means for causing ink from selected nozzles to separate as drops from the body of ink, while allowing ink to be retained in non-selected nozzles.

An ink jet printer comprising:

• a printing assembly comprising a plurality of nozzles having a respective ink-ejection opening for ejecting ink therethrough and being arranged to form at least one nozzle group, wherein:
• the ink-ejection opening of each of the nozzles that form a nozzle group has a size essentially equal to a corresponding size of the ink-ejection openings of all other nozzles of the group, and
• each of the nozzles of a group are respectively adapted to produce a different print density when actuated only by a non-constant input signal to heat the ink, the non-constant input signal corresponding to each different print density and having a non-linear decaying portion to avoid boiling of the ink;
• a body of ink associated with said nozzles;
• drop selection means for selecting predetermined nozzles and generating a difference in meniscus position between ink in selected and non-selected nozzles;
• and
• drop separating means for causing ink from selected nozzles to separate as drops from the body of ink, while allowing ink to be retained in non-selected nozzles, said drop selecting means being capable of producing said difference in meniscus position in the absence of said drop separation means.

An ink jet printer comprising:

• a printing assembly comprising a plurality of nozzles having a respective ink-ejection opening for ejecting ink therethrough and being arranged to form at least one nozzle group, wherein:
• the ink-ejection opening of each of the nozzles that form a nozzle group has a size essentially equal to a corresponding size of the ink-ejection openings of all other nozzles of the group, and
• each of the nozzles of a group are respectively adapted to produce a different print density when actuated only by a non-constant input signal to heat the ink, the non-constant input signal corresponding to each different print density and having a non-linear decaying portion to avoid boiling of the ink;
• a body of ink associated with said nozzles, said ink exhibiting a surface tension decrease of at least 10 mN/m over a 30° C. temperature range;
• drop selection means for selecting predetermined nozzles and generating a difference in meniscus position between ink in selected and non-selected nozzles;
• and
• drop separating means for causing ink from selected nozzles to separate as drops from the body of ink, while allowing ink to be retained in non-selected nozzles.