Ink drop charging device

Claim 2

An ink droplet charging device comprising: a nozzle for jetting an ink stream, said ink stream being divided into ink droplets; a charging electrode disposed at a position where said ink stream divides into said ink droplets for controlling a charge condition of said ink droplets according to whether said ink droplets are utilized for printing; and means for successively applying positive, negative and ground voltage levels to said charging electrode in synchronization with the formation of said ink droplets to deposit a charge on at least some of said ink droplets so that said charged ink droplets have an indentical type charge deposited thereon.

Claim 3

The ink droplet charging device of claim 1 further comprising an insulating film disposed over said charging electrode.

Claim 4

The ink droplet charging device of claim 1 or 2 wherein said means for successively applying positive, negative and ground voltage levels to said charging electrode comprises a first NPN transistor having an emitter coupled to ground and a collector coupled to a first positive voltage source through a first resistor; a first PNP transistor having a base coupled through a second resistor to said collector of said first NPN transistor and to a second positive voltage source through a third resistor, an emitter coupled to said second positive voltage source and an emitter coupled to an output terminal; a second PNP transistor having a base coupled to said base of said first NPN transistor and to an input terminal, an emitter coupled to ground and a collector coupled through a fourth resistor to a first negative voltage source; a second NPN transistor having a base coupled through a fifth resistor to said collector of said second PNP transistor and to a second negative voltage source through a sixth resistor, an emitter coupled to said second negative voltage source and a collector coupled to said output terminal; and a seventh resistor coupled between said output terminal and ground.