INK JET PRINTER AND METHOD OF START-UP AND SHUTDOWN THEREOF

An ink jet printer includes a print head (10) for producing at least one jet drop stream (12) from a fluid filament emerging therefrom, and a charge electrode arrangement (26, 28) for inducing electrical changes on drops formed from the fluid filament. The charge electrode arrangement is movable into and out of an operating position in which it is adjacent and at least partially surrounds the fluid filament. A deflection field is established prior to start-up in which the field has a non-zero electrical potential in the region of the fluid filament. At start-up and shutdown of the printer, the charge electrode arrangement (26, 28) is retracted from its normal operating position (as shown in Figure 1b) and drops are charged by the deflection field. As a consequence, the charge electrodes (28) are not contaminated by ink from the unstable jets. The drops in the jet drop streams are, however, charged and deflected to a catcher (33) by the deflection field. After stable operation is obtained, the charge electrode arrangement is moved into its normal operating position (as shown in Figure 1d). At shutdown of the printer, this sequence of steps is reversed.