EP0709193A1

EP0709193A1 - Ink jet printhead

Info

Publication number: EP0709193A1
Application number: EP95307232A
Authority: EP
Inventors: Colin Edward Chamberlain
Original assignee: Domino Printing Sciences PLC
Current assignee: Domino Printing Sciences PLC
Priority date: 1994-10-24
Filing date: 1995-10-12
Publication date: 1996-05-01
Also published as: JPH08207275A; GB9421388D0

Abstract

An ink jet printhead has a housing 1 defining an ink chamber 2 to which ink is supplied in use. The ink chamber has a uniform cross-section over its length, a sidewall 19, and end walls 5,6. A tubular piezoelectric or electrostrictive actuator 15 is disposed within and extending over the length of the chamber between its end walls, with the longitudinal axis L of the actuator being parallel to that L' of the chamber and capable of radial expansion and contraction. One or more orifices 9,20 in the sidewall 19 of the chamber emit ink droplets in use under the action of the tubular piezoelectric or electrostrictive actuator 15, either in a drop-on-demand printer or a continuous printer.

Description

The present invention relates to an ink jet printhead and, more particularly, an ink jet printer for printing through a row of orifices or an elongate slot-like orifice.
A printer of this type may be utilised specifically for printing bar codes or the like in a drop-on-demand method of operation, but, alternatively, a continuous ink jet printer may incorporate a printhead of this type for emitting plural streams of droplets which are selectively deflected onto a print substrate for printing characters or symbols other than bar codes or the like.
One of the problems with prior art printers of both types is achieving uniformity of printing, particularly in continuous ink jet printers where plural streams of droplets are produced by a pressure pulse within the marking fluid in a chamber which is closed by a nozzle plate carrying the orifices. Non-uniformity of droplet production and break-up length are known problems.
The problem of synchronism in droplet production has been addressed in EP-A-0 126 649 which proposes the use of an elongate transducer in a chamber, the transducer being separated into sections by slots extending alternately from opposite sides therethrough. A similar proposal is made in WO-A-91/09736.
According to the present invention an ink jet printhead comprises an ink chamber to which ink is supplied in use, the chamber having a uniform cross-section over its operative length and being closed at each end, one or more orifices being provided in a sidewall of the chamber for emitting ink droplets in use under the action of radial expansion and contraction of a tubular piezoelectric or electrostrictive actuator disposed within and extending over the full length of the chamber between its closed ends, with the longitudinal axis of the actuator being parallel to that of the chamber.
Preferably, the chamber and actuator each have a substantially circular cross-section and thereby define an annular space for ink within the chamber.
Plural orifices are provided along a line parallel to the longitudinal axes of the actuator and chamber so that the operative parts of the printhead are uniformly arranged in cross-section.
The chamber cross-section may be tear-drop shaped with orifices disposed at the apex of the tear-drop shape.
At each end, the chamber may be formed with a counterbore of larger cross-section than the chamber itself, end closures or seals being disposed in the counter bores to close the chamber ends and support the actuator as well as acting as electrical terminals to the actuator to enable an actuating current to be passed therethrough.
Although it is primarily intended that the printhead be used in a continuous ink jet printer, it is envisaged that it may be possible to use it in a drop-on-demand printer for printing bar codes, by operating the actuator 'on demand' to produce emission of ink through the orifice(s).
A printhead for an ink jet printer, constructed in accordance with the present invention, will now be described with reference to the accompanying drawings in which:-

Figure 1 is a plan view;
Figure 2 is an underneath plan;
Figure 3 is a cross section on the line 3-3 in Figure 5;
Figure 4 is a cross section on the line 4-4 in Figure 5;
Figure 5 is a longitudinal section; and
Figure 6 is an underneath plan of a modified printhead.

The printhead of Figures 1 to 5 has a generally rectangular cuboid form, comprising a body or housing 1 of stainless steel having a generally cylindrical chamber 2 which, in cross-section, as seen in Figures 3 and 4, has a uniform tear-drop shape. The body 1 has a pair of end recesses 3, 4 in which are disposed respective end plates 5, 6, each of which is sealed within its respective recess by an O-ring type seal 7,8.
The lower side of the body 1 is closed by a nozzle plate 19 with an elongate slit 9 which provides an elongate orifice through which a sheet of droplets can be emitted in use. On the other side of the body 1 provision is made, through an ante-chamber 10 for a supply of fluid ink.
Mounted within respective recesses 11, 12 in the end plates 5, 6 and sealed into the recesses by sealing rings 13, 14 is a cylindrical piezoelectric transducer 15, preferably of PZT4D. In order to actuate the transducer electrodes 16 are provided on the end faces of the transducer and connections are made to the electrodes through end apertures 17, 18 in the end- plates 5,6. The transducer 15 is poled axially so that applying a stimulating voltage across the end faces through the electrodes 16, results in radial expansion of the tubular transducer. This, in turn, in use, reduces the size of the cylindrical space around the transducer within the chamber 2 causing ink to be squeezed through the elongate slit 9.
It will readily be appreciated that the slit 9 may be replaced by a row of individual nozzles or orifices 20 as shown in Figure 6, and that the internal shape of the chamber 2 may be adjusted as required for a particular application.

Claims

An ink jet printhead comprising
a housing (1) defining an ink chamber (2) to which ink is supplied in use, the ink chamber having a uniform cross-section over its length, a sidewall (19), and end walls (5,6);

a tubular piezoelectric or electrostrictive actuator (15) disposed within and extending over the length of the chamber between its end walls, with the longitudinal axis of the actuator (L) being parallel to that of the chamber (L') and capable of radial expansion and contraction; and

one or more orifices (9,20) in the sidewall of the chamber for emitting ink droplets in use under the action of the tubular piezoelectric or electrostrictive actuator.
A printhead according to claim 1, wherein the chamber (2) and actuator (15) each have a substantially circular cross-section and thereby define an annular space for ink within the chamber.
A printhead according to claim 1 or claim 2, wherein plural orifices (20) are provided in the sidewall (19), along a line parallel to the longitudinal axes (L,L') of the actuator and chamber.
A printhead according to claim 1 or claim 2, wherein an elongate orifice (9) is provided in the sidewall (19), along a line parallel to the longitudinal axes (L,L') of the actuator and chamber.
A printhead according to any of claims 1 to 3, wherein the chamber cross-section is tear-drop shaped with orifices disposed at the apex of the tear-drop shape.
A printhead according to any of claims 1 to 5, wherein, at each end, the chamber is formed with a counterbore (11,12) of larger cross-section than the chamber itself, end closures or seals (7,8) being disposed in the counter bores to close the chamber ends and support the actuator (15).
A printhead according to any of claims 1 to 6, wherein the transducer (15) is axially poled.
A continuous ink jet printer having a printhead according to any of claims 1 to 7.
A drop-on-demand printer for printing bar codes, having a printhead according to any of claims 1 to 7.