Incremental printing of symbolic information – Ink jet – Ejector mechanism
Patent
1992-07-02
1995-04-25
Moses, R. L.
Incremental printing of symbolic information
Ink jet
Ejector mechanism
347 73, G01D 1518
Patent
active
054103428
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to ink jet printers and, more particularly, to the printhead of a so-called continuous ink jet printer.
Printers of this type have a printhead with one or more nozzles connected to a supply of ink, a string of droplets being caused to flow from the nozzle or nozzles by means of an oscillator, usually a piezoelectric transducer. The row of droplets is directed towards a gutter, but selective droplets can be charged as they leave the nozzle and then deflected in an electric field in order to impinge on a substrate, individual droplets being charged appropriately in order to print at the correct position.
In order to print multiple lines of print from a single nozzle, it is known to provide an array of nozzles and associated piezoelectric transducers arranged closely adjacent to one another, but a problem with this type of printer is that the height of the lines of print is limited by the pitch of the nozzles. Such printers also require the nozzles to be carefully matched in terms of size and directional uniformity as well as positioning relative to one another.
It is known to print multiple lines of print from a single nozzle (see for example our EP-B-0206614), but although this technique is capable of providing multiple lines of print at high speed, the number of lines that can be printed is relatively small.
EP-A-0084891 discloses an ink jet printer which has a pair of nozzles which eject ink droplets which are selectively oppositely charged. The ink droplets then pass between a single pair of deflector plates, the arrangement being that the two streams of droplets converge.
There is a need therefore for a printer capable of printing several lines of print without the complexity of an array of nozzles.
According to the invention therefore, there is provided a printhead for a continuous ink jet printer, comprising a single pair of nozzles; one or more oscillators for vibrating the ink to provide twin streams of droplets from the nozzles in use; a pair of charging gates for applying, selectively and respectively, a charge to droplets in the two streams; a pair of deflector means for applying respective electric fields across the streams to deflect the droplets individually in accordance with the charge thereon; and, a gutter or pair of gutters into which droplets from the respective streams may pass if they are not charged, characterised in that the arrangement is such that the two streams of droplets are deflected in opposite directions away from each other so as to be printed.
By providing only two nozzles and by deflecting the two streams in opposite directions, the height of the two lines of print is not restricted by the pitch of the nozzles.
Furthermore, the printhead may be arranged so that the nozzles are substantially aligned in the direction in which the substrate to be printed moves relative to the printhead, whereby continuous columns of droplets can be printed over the full printing width of the printhead so as to allow printing of large characters, bar codes, etc., as well as multiple lines of characters. The known offset between the nozzles can be taken into account by suitable control electronics in order to allow the printed droplets from each nozzle to be aligned to produce single, full height columns of printed dots.
In such an arrangement the charging gates preferably comprise a single assembly providing two charging paths for the respective droplet streams and the deflector means comprises three deflector plates, the central one of which is at a first voltage and the outer ones of which are at a second voltage. The central deflector plate is also preferably of a lazy-Z shape, whereby the two streams of droplets pass on opposite sides of the centre web of the `Z` in order to be able to be aligned in the direction of movement of the substrate. The gutter assembly may also have a lazy-Z shape when viewed in cross section, one gutter inlet being provided in each flange of the `Z`.
The nozzles may have respective oscillators, or may be vibrated by a single oscill
REFERENCES:
patent: 4194210 (1980-03-01), Krause
patent: 4374387 (1983-02-01), Iyoda et al.
patent: 4596990 (1986-06-01), Hou
patent: 4604547 (1986-08-01), Saito et al.
Patent Abstracts Of Japan, vol. 4, No. 171 (M-44 (653) 26 Nov. 1980, & JP-A-55 123480 (Y.EBI) 22 Sep. 1980 (see the whole document).
Lecheheb Ammar
Mitchell Richard F.
Domino Printing Sciences Plc of Bar Hill
Moses R. L.
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