Ing C. Olivetti C., S.p.a.

Roberto Realis Luc

Alessandro Crotti

Pierangelo Berruti

Aquilino Barbero

Roberto Guelfo

Ennio A Pozzo

In an ink jet printing element in which the drop is expelled by generating a current pulse through the ink in the nozzle, in order to reduce the control voltage, a first pulse (Tr) for heating the ink is generated, followed by a vaporization pulse (Tv) with a delay such as to make the printing position independent of the direction of movement of the element with respect to the paper. The heating pulse (Tr) is generated by a circuit (31) controlled by a temperature sensor (34) so that the duration of the heating pulse has a negative temperature coefficient. The vaporization pulse (Tv) is generated by a circuit (32) manually controlled (potentiometer 39) to determine the pulse duration on the basis of the desired strength of the printing. The delay between the two pulses is controlled by a delay circuit (38), e.g. a monostable circuit. The two pulses are applied to a transformer (35) which generates the voltage between the electrodes. The two circuits (31, 32) may be constituted by one monostable circuit with separate RC networks sequentially enabled for determining the durations of the heating and vaporization pulses.

Control apparatus for an on-demand ink jet printing element

The head (12) comprises a closed container (14) carrying two electrodes (36, 62) and a nozzle (18) and mounted removably on a carriage (13). In order for the ink (16) always to be held at atmospheric pressure, the container (14) comprises an expansible space defined by a diaphragm (67) having a portion (74) aligned with an opening (73) in the container (14). The diaphragm (67) is of butyl rubber which can be pierced with a syringe to permit the container (14) to be refilled with ink (18). The container (14) is closed by an alumina plate (32) carrying the nozzle (18) and joined to a second plate (76) parallel thereto, and of a material which can be wetted by the ink (16). The second plate (76) constitutes a wall for resisting the pressure waves of an ink jet leaving the nozzle (18), and is immediately covered by the ink again.

Serial printhead ink supply

The printing head (12) comprises an insulating container (14) for conductive ink (16) which is expelled through a fine nozzle (18) when a voltage pulse is applied between an electrode (56, 57, 40) and a counter-electrode (22). Capillary passages (51, 50) lead to the nozzle (18) to allow formation of an ink meniscus (23) right up until exhaustion of the ink. A vent (69) keeps the pressure inside the container constant. The head (12) is snap fitted onto a carriage with a conductive plate abutted by the counter-electrode (20) and a spring contacting the external part (40) of the electrode. This plate and spring are fed by way of conductive elements sliding along conductive carriage guides.

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Roberto Realis Luc