CONTINUOUS INKJET PRINTHEAD

Abstract: A multi-nozzle CIJ printhead has a number of ink streams (5) issuing from a droplet generator (3) in a plane (5'). A pair of deflection electrodes (7, 7') are disposed one on each side of the plane (5') of the ink streams issuing from the nozzles. One of the deflection electrodes (7') is mounted on an intermediate element (40) secured to the droplet generator support (10) for adjustment on the droplet generator, the intermediate element being movable so as to adjust the position of the deflection electrode (7') towards and away from the plane (5') of the ink streams and to adjust the angle of the deflection electrode (7') relative to the plane of the ink streams (5).

Description: CONTINUOUS INKJET PRINTHEAD The present invention relates to continuous inkjet (CIJ) printers and, more particularly, to printheads of the multi-nozzle type. Multi-nozzle continuous inkjet printers have been developed in order to provide high quality, high speed printing. A row of inkjet nozzles at very close spacings are provided and individual streams of ink issue from each of the nozzles continuously in use, being broken up into individual droplets automatically. The individual droplets are charged appropriately to cause them to be printed or else deflected into a gutter. Printers of this type are described, for example, in US-A-4613871 and US-A-4427986. The printers described in these specifications are of the type generally known as binary continuous multi-jet. Multi-jet printers of this type have alignment and set-up requirements which are additional to those of single jet printers, it being necessary to ensure that the rows of nozzles or jets are all accurately aligned with the gutter, that each stream of droplets is accurately aligned with a respective charge electrode and that the charge electrodes are uniformly spaced from the respective droplet streams, ie. that the plane of the droplet streams and the row of charge electrodes are parallel to one another. These issues are addressed in US-A-5477254. Achieving accurate alignment between the individual droplets streams and their respective charge electrodes is a particularly critical requirement in order to avoid inappropriate charges being applied to droplets and this problem is addressed in our British Patent Application no. 9626683.8 and our co-pending International Patent Application reference MJB05545 O. However, it is also important to ensure that the deflection electrode is correctly positioned with respect to the multiple streams of droplets issuing from the nozzles. In our British Patent Application no. 9525970.1 we describe a printhead for a continuous ink jet printer, the printhead having ink supply means for supplying ink under pressure to a nozzle through which ink is emitted in use and broken up into droplets by the action of a piezoelectric oscillator, a charge electrode for applying electrostatic charge to selected droplets in use, a deflection electrode for deflecting the path of charged droplets, and a gutter for collecting droplets not required for printing, wherein the charge electrode and/or the gutter are movable in a direction transverse to the path of the droplets, the movement being controlled by the action of pressurised fluid selectively supplied to a hydraulic actuator or actuators coupled to the charge electrode and/ or the gutter. We also describe how the deflection electrode immediately below the charge electrodes is moved with them. According to the present invention, a multi-nozzle CIJ printhead having a droplet generator, has a pair of deflection electrodes, one disposed on each side of the plane of the ink streams issuing from the nozzles, one of the deflection electrodes being mounted for adjustment on a support for the droplet generator by means of an intermediate element secured to the support, the intermediate element being movable so as to adjust the position of the deflection electrode towards and away from the plane of the ink streams and the angle of the plane of the deflection electrode relative to the plane of the ink streams . Preferably, the intermediate element is adjustable about three axes defined by three adjustable stops arranged triangularly. The stops may be formed by screw-threaded bolts extending through the intermediate element and bearing on opposed portions of the support. The intermediate element is preferably secured to the support by a mounting screw which allows adjustment of the adjustable stops without distortion of the intermediate element. Suitable helical springs or similar may be used to bias the intermediate element against the stops. Advantageously, the intermediate element is also pivotally mounted on the support so that the deflection electrode can be swung away from the ink streams. One example of a flexure constructed in accordance with the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side view of a printhead of a multi- nozzle CIJ printer of the type described in our EP-A- 0780231; Figures 2A to 2D are inner and outer face views, a top plan view, and a side cross-sectional view respectively of a droplet generator support of the type described in our British Patent Application no. 9626683.8; and Figures 3A to 3E are inner and outer face views, a pair of cross-sectional views, and a bottom plan view of the intermediate element used in accordance with the present invention. Figures 4A & 4B show an alternative construction in views similar to Figures 1 and 2B. The printhead shown in Figure 1 is described in more detail in our EP-A-0780231. Since not all the features shown in Figure 1 are relevant for a description of the present invention only the primary features will be referenced and described. The printhead has an electronics sub-system 1 by means of which are controlled the piezoelectric oscillator 2 forming part of a droplet generator 3 which has a nozzle plate 4 from which, in use, issue plural streams 5 of ink. The closely spaced nozzles are arranged in a row normal to the plane of the drawing. The streams of ink break up into individual droplets which pass respective charge electrodes 6 also arranged in a row in the same direction, where they are selectively charged and then passed between a pair of deflection electrodes 7, 7' which establish, in use, an electric field by means of which charged droplets are deflected from their straight-line path into a gutter 8. Figure 2A to 3E illustrate the deflection electrode 7 1 mounting components. The droplet generator 3 is supported on a frame 9 by a flexure-type support 10 embodying the principles of the invention described in our British Patent Application no. 9626683.8. The flexure 10 has top and bottom end portions 12, 12' which are interconnected by integral thin flexible parallel beam portions 14 and is formed of stainless steel or a similar material. The lower end portion 12' is provided with a pair of mounting apertures 16 for the gun body or droplet generator 3. Extending from the centre of the end portion 12 ' is a central protrusion 15 which is disposed between the ends 18 of a yoke-like protrusion 19 extending inwardly of the flexure from the upper (as seen in the Figures) end portion 12. The upper end portion 12 has a mounting aperture 20 and (on the side opposite that which is seen in the Figures) a flange 21 which is also used for mounting the flexure to a supporting frame as described in our British Patent application no. 9626704.2 and our co-pending International Patent application reference MJB05497WO. A pair of adjusting screws (not shown) are located in corresponding screw-threaded bores 23 in the end portions 18 of the yoke-like projection 19 and each of the screws has an end which engages in a corresponding socket 25 in the protrusion 15. As described in our co-pending application, the screws thus control the relative positions of the projections 15, 18 and thus of the end portions 12, 12' in the direction generally perpendicular to the parallel beam portions 14 and allow adjustment from the neutral position to a flexed position (not shown) by appropriate rotation of the screws in opposite directions. The inner side or face of the upper end portion 12 has a transverse 22 slot which intersects a longitudinal groove 26 and which also includes, one at each end, a pair of screw-threaded bores 27. The lower portion 12' has a longitudinal central groove 28 (in extension of the groove 26) which has a screw-threaded bore 30 and a recessed cup 29. Figures 3A to 3E show an intermediate support element 40 in the shape of an inverted T, has a first, longitudinal limb 41 and a second, transverse limb 42. A mounting flange 43 for the deflection electrode 7' extends from the inner face of the transverse limb 42. The longitudinal limb 41 is a loose fit within the grooves 26,28 and the intermediate element 40 is held in position on the support 10 by a cross-pin 44 fitted in a cross bore 45 at the top of the limb 41 and the ends of which are trapped below the heads of screws fitted in the bores 27. This allows the element 40 to pivot but also allows the cross pin to float, in turn allowing adjustment of the position of the element 40 by means of adjustment stops in the form of screws (not shown) held in screw- threaded bores 46,47 located respectively at the ends of the transverse limb 42 and towards the top end of the longitudinal limb 41 and bearing in cups 31 & 29 respectively. A further screw (not shown) fits within a stepped bore 48 at the junction of the limbs 41 & 42 and screws into the screw-threaded bore 30 in the support 10 in order to hold the element 40 on the support 10. When it is removed, the element 40 can be pivoted to allow the deflection electrode 7' to be moved away from its normal position. The screws fitted into the bores 46, 47 and bearing against the cups 31,29 allow the fine adjustment of the position of the element 40 on the support 10. Springs (not shown) fit in cups 49 adjacent the adjusting screws in the limb 42 and bear against the outer face of the support 10 to ensure that the element 40 is biassed into the adjusted position. An alternative construction is shown in assembled condition in figures 4A & 4B. This example, which is only very slightly modified from the previous example (and which carries corresponding reference numerals for corresponding features) , shows fine adjustment of the angle of the deflection electrode 7' (and hence of the spacing of its ends relative to the plane of the droplets) to be achieved in the same manner as the previous example by use of the adjusting screws 50 in their respective bores 46.

Claims: CLAIMS 1. A multi-nozzle CIJ printhead having a plurality of nozzles for providing a corresponding number of ink streams in a plane; a droplet generator; a droplet generator support; a pair of deflection electrodes, one disposed on each side of the plane of the ink streams issuing from the nozzles; an intermediate element secured to the support, one of the deflection electrodes being mounted on the intermediate element for adjustment on the droplet generator, the intermediate element being movable so as to adjust the position of the deflection electrode towards and away from the plane of the ink streams and to adjust the angle of the plane of the deflection electrode relative to the plane of the ink streams. 2. A printhead according to claim 1, wherein the intermediate element is adjustable about three axes, the axes being defined by three adjustable stops arranged triangularly. 3. A printhead according to claim 2 , wherein the stops comprise screw-threaded bolts extending through the intermediate element and bearing on opposed portions of the support . 4. A printhead according to any of claims 1 to 3 , further including a mounting screw, wherein the intermediate element is secured to the support by the mounting screw to allow adjustment of the adjustable stops without distortion of the intermediate element. 5. A printhead according to claim 2, further including helical springs to bias the intermediate element against the stops. 6. A printhead according to any of claims 1 to 5, wherein the intermediate element is pivotally mounted on the droplet generator support so that the deflection electrode can be swung away from the ink streams.

Inventors: FOST IAN MICHAEL, ZABA JERZY MARCIN, FOST, IAN, MICHAEL, ZABA, JERZY, MARCIN
Applicants: DOMINO PRINTING SCIENCES PLC, FOST IAN MICHAEL, ZABA JERZY MARCIN, FOST, IAN, MICHAEL, ZABA, JERZY, MARCIN
Application year: 1997
Main classification: B41J2
IPC codes: B41J2