Ink jet printing apparatus

Abstract

An ink jet is ejected from an ink jet head (1.sub.1) at a constant frequency of pressure oscillation and separates into ink droplets at a certain position. A pulsating electric field is applied to the droplets at the separation position to charge the same where it is desired to print a dot on a sheet (PR), the charged droplets being electrostatically deflected onto the sheet (PR), whereas uncharged droplets are trapped by a gutter (GA). The phase of the pressure oscillation is initially progressively shifted until a charge detector (21) detects a charged condition of the droplets and then latched at that phase. A single charging electrode (41) and a single charge detecting electrode (21) may be used for several ink jet heads (1.sub.1, 1.sub.2, 1.sub.3) if a separate phase of charging voltage is provided for each respective ink jet head (1.sub.1, 1.sub.2, 1.sub.3) and the phases are alternatingly applied. A plurality of the latter described units may be provided in a row with ink jet heads in corresponding positions all being operated with the same charging voltage phase.

Dependencies are inferred from the claim text.