Patent ID: 7104634

Claim:
A method of printing a desired pattern on a substrate, comprising: discharging a continuous stream of liquid ink drops from a nozzle along the nozzle axis towards the substrate; selectively charging said liquid ink drops with multi-level charges for selectively deflecting them different amounts with respect to the nozzle axis to thereby direct some of the liquid ink drops to different locations on the substrate for printing said desired pattern thereon, while other liquid ink drops not to be printed are intercepted by a gutter before reaching the substrate; dividing the stream of ink drops produced from the nozzle into two streams by charging pulses of two charging levels and of appropriate phases; optically sensing the two streams of ink drops for determining velocity errors and/or charge phasing errors between the respective charging pulses and the physical drop separation in the stream exiting from the nozzle; and controlling the charging pulses and/or the drop formation timing pulses to correct said errors.