Patent ID: 6309058
Filing Date: 2001-10-30
Classification: B41J

Abstract:
A method of printing using a multi-nozzle ink jet print head having a pressure modulator for causing streams of ink emitted from the nozzles to be broken up into individual droplets, comprising:dividing the nozzles into a plurality of groups of nozzles with each group of nozzles having more than one nozzle,providing corresponding groups of charge electrodes, with each group of charge electrodes having a respective charge controller,generating a modulation waveform during the printing to operate the pressure modulator to cause droplets to be generated in each stream;operating the charge controllers during the printing to supply a signal waveform to the charge electrodes and charging droplets in the streams;during the printing setting the phase relationship of the charge signal waveform relative to the modulation waveform; and,adjusting the phase relationship of the charge signal waveform relative to the modulation waveform, during the printing process, when droplets do not require to be printed, independently for the charge controller of each group of charge electrodes, by carrying out the steps of:(A) operating the charge controller to apply a DC voltage simultaneously to all the charge electrodes in the group to charge all the droplets to prevent printing;(B) applying a pulse signal waveform to the charge electrode controller, to reduce the amplitude of the DC voltage periodically and temporarily to a level below that of the DC voltage but still sufficient to cause droplets to be deflected to avoid printing;(C) sensing the aggregate level of charge applied to the droplets and generating signals representative thereof;(D) determining the phase relationship of the pulse signal waveform relative to the modulation waveform from the signals generated in step (C); and,(E) if the pulse signal waveform is delayed relative to the modulation waveform, advancing the pulse signal waveform relative to the modulation waveform or, if the pulse signal waveform is advanced relative to the modulation waveform, delaying the pulse signal waveform relative to the modulation waveform, to reset the phase relationship of the pulse signal waveform relative to the modulation waveform.