Ink jet synchronization and failure detection system

Claim 1

An ink jet printing system for printing on a record medium by ink drop deposition, comprising: means for supporting said record medium at a printing station; means for forming and propelling ink drops toward said record medium; cyclically operable means operable in timed relation with said forming and propelling means for charging and deflecting a plurality of said drops on a selective basis to form visible indicia upon said record medium, said charging and deflecting means being operable to charge and deflect said drops in a range from a relatively low to high potential with the extremes of said range representing drops not required for printing; first gutter means positioned in the path of travel of a first type of unused drops charged at said relatively low potential to collect said first type of drops said first gutter means providing a relatively low synchronization current from charged drops travelling in said first gutter means; second gutter means positioned in the path of travel of a second type of unused drops charged at said relatively high potential to collect said second type of drops said second gutter means providing a relatively high checking current level; from charged drops travelling in said second gutter means; amplifier means interconnected with said first gutter means for providing a low synchronization potential responsive to the relatively low synchronization current provided by said first gutter means, and further interconnected with said second gutter means for providing a high checking potential responsive to the high checking current level from said second gutter means; character generating means for activating said charging and deflecting means in a printing range within but not including said relatively low and relatively high potentials in order to deflect selected ones of said drops within a printing range on said record medium; synchronization means operable to activate said charging and deflecting means at said relatively low potential in order that low synchronization potential is developed by said amplifier means; checking means operable to activate said charging and deflecting means at said relatively high potential in order that the high checking potential is developed by said amplifier means; comparing means for comparing said synchronization potential with predetermined reference levels representative of correct synchronization in said system; means controlled by said comparing means for maintaining correct phase between drop formation and charging; said comparing means comparing said checking potential with predetermined reference levels representative of correct operation of said system; and output means from said comparing means for indicating a failure of said system.