Abstract: A method of operating a continuous ink jet printing system which includes a nozzle arranged to be vibrated by a piezoelectric oscillator. The nozzle, in use, passes a stream of ink past a charging electrode. The continuity of charge detection is sensed by a charge detector disposed immediately downstream of the charging electrode. The amplitude of the stimulation voltage applied to the piezoelectric oscillator is set sufficiently low such that the level of charge detected by the charge detector is below a threshold value. The amplitude of the stimulation voltage is then increased in discrete steps until the charge detector detects intermittent and proper droplet charging. The amplitude of the stimulation voltage is then further increased from its level at the end of the second step by a predetermined amount.

Abstract: A method of and apparatus for controlling the velocity of a stream of droplets in a continuous ink jet printing system comprises controlling, from a system cabinet, the velocity of the stream expelled from the print head through a nozzle under pressure from a pressure source, in dependence upon a measured pressure of the ink in accordance with a predetermined relationship between the velocity and the pressure. On start up the system calibrates for the pressure differential P.sub.c due to the conduit length and the relative elevation of the print nozzle; and a determination of the ink viscosity in made at predetermined times. Thereafter the velocity is controlled in dependence upon a required pressure value P.sub.r in accordance with a stored look-up table, the required pressure value at any time being determined substantially by a given relationship.

Abstract: An ink jet printing head has a chamber for pressurized ink and a substantially linear array of outlet nozzles (5) leading from the chamber. A plurality of closure elements are selectively displaceable by respective actuators (13) to open and close respective ones of the nozzles. The closure elements are provided on respective flexible strips (7), each of which is fixed at one end and has the closure element at the other end and is displaceable by a respective actuator acting on the strip between its ends. At least some of the strips interdigitate with one another at their closure element-carrying ends from opposite sides of the substantially linear array of nozzles.

Abstract: A fluid jet marking apparatus comprises a housing (5) defining a chamber (6) for marking fluid. A plurality of outlet nozzles (8) allow ink to be ejected from the chamber and a corresponding plurality of closure elements (9) are selectively displaceable to open and close the nozzles. Springs (11) bias the elements to close the nozzles. A plurality of solenoids (14) are each connected to a respective closure element by means of a pulling element (12) slidable, under the action of the solenoid, in a respective tube (13,13') connecting the solenoid to the housing. A fluid supply (23) supplies fluid to the chamber and at least one liquid constituent part of the fluid is supplied to the chamber through the respective tubes (13') on which the solenoids are mounted.

Abstract: A piezo-electric ink jet droplet generator (1) has a body part (2) having a first ink supply passage (10/11) and a second ink supply passage (12) extending generally perpendicularly therefrom through a protrusion (20) of the body and opening at an end face (14) of the protrusion. A piezo-electric crystal (6) is attached to a surface of the body closely spaced from the first ink supply passage and adjacent the end of the second ink supply passage which connects with the first supply passage. A nozzle (17) is mounted in a cap (3) which is secured to the end of the protrusion (20), the nozzle being in alignment with the second supply passage (12). The inner surface (13) of the cap surrounding the nozzle is spaced from the end face (14) of the protrusion thereby forming, in use, a disk (21) of ink between the inner face of the cap and the end face of the protrusion. The cap is sealed to the protrusion by means of a flexible seal ( 16) and engaged with the protrusion by means of a quick-release coupling (9,19).

Abstract: In a continuous ink jet printing system a viscosity determining means (12) has a measuring tank (29). An inlet (32) to the tank is connected to the system ink circuit to receive ink under pressure and the inlet has a flow restriction. A vent/return pipe (34) vents the tank and enables ink to be returned to the reservoir. An outlet (33) drains ink from the tank and returns it to the pump, the outlet including a valve (13) to open and close the outlet. A level detector (30,31) in the tank is connected to a timer (38) to determine the time taken for the tank to fill from a first level to a second level detected by the level detector and hence to provide a representation of viscosity of the ink.

Abstract: In a continuous ink jet printing method for printing multiple lines of print (13-15), raster of drops is produced in which the differential charge between drops printed on opposite sides of an interline gap (17,18) is increased in comparison with that between adjacent drops to be printed within a line (13-15). At the same time the number of guard drops is maintained the same or is reduced between the printable drops immediately adjacent to the interline gap, so that the distance between printed drops immediately adjacent to the interline gap is increased without increasing the number of drops in the raster.

Abstract: A discharging head assembly for marking apparatus has a chamber for marking fluid with a plurality of fluid dispensing orifices which are closeable and openable by displaceable closure elements connected via flexible pulling means to respective actuators which are spaced from the chamber, and can therefore be relatively bulky, e.g. strong electromagnets.