Incremental printing of symbolic information – Ink jet – Ejector mechanism
Patent
1995-07-07
1998-07-21
Malley, Daniel P.
Incremental printing of symbolic information
Ink jet
Ejector mechanism
G01D 1518
Patent
active
057840830
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to ink jet printers of the drop-on-demand type and, more particularly, to printheads for printers of this type.
In our GB-B-2134452, there is shown and described, a printhead in which a plurality of orifices are individually opened and closed by solenoid-actuated, wire-pulled closures. Locating the solenoids remote from the closures enables a fairly close spacing of the nozzles to be achieved. In the type of printhead shown in GB-B-2192590 (amongst others), which is a development of this system, individual nozzles are opened and closed by closure members on the end of rod-like magnetic armatures which are directly driven by respective coils. A problem with this design is that of nozzle spacing, resulting from the diameter of the coils/solenoids used to drive the armatures. If the solenoids are to be sufficiently strong and quick in pulling open the nozzles (hence of significant diameter) and if significant solenoid crosstalk is to be avoided (hence spaced well apart), then the nozzles cannot be located as closely as desired.
The present has the object, amongst others, of enabling a very close nozzle spacing to be achieved, without loss of opening power/speed.
According to the present invention there is provided a printhead for an ink jet printer, the printhead including a chamber for containing marking fluid fed to the head in use; a plurality of orifices opening from the chamber and through which a marking fluid can be emitted in use; and a corresponding plurality of actuators having means for selectively opening and closing a respective orifice, a magnetic circuit, and one or more coils for selectively inducing a magnetic flux in the circuit in order open the respective orifice, characterised in that opening and closing a respective orifice, the arm forming a side of the magnetic circuit, and the arm being moved between a position in which it closes and a position in which it opens the orifice.
The arm is moved by the induction of the magnetic flux between a position in which a gap is formed between part of the arm and the magnetic circuit and a position in which it closes the magnetic circuit.
Preferably, the arm is formed from spring steel and is mounted in cantilever fashion, flexing under the influence of the applied magnetic flux to open the orifice. The rest of the magnetic circuit is preferably substantially U-shaped.
The arm may vary in width, having a relatively narrow portion in order to provide suitable flexing characteristics, and a relatively wider portion in order to provide a low reluctance path in order to produce the desired degree of flux linking to the part of the circuit on the side of the arm adjacent the gap. A magnetic plate forming part of the magnetic circuit may extend over the narrower portion of the arm where the flexing chiefly occurs and partially over the wider portion in order to enable the required degree of flux linking between the portion of the circuit adjacent the fixed end of the arm and the wider portion of the arm.
In an alternative construction, the arm carries a magnetic plate which is attracted to the adjacent portions of the magnetic circuit on application of current to the coil or coils.
Preferably, the U-shaped portion of the circuit has a pair of coils, one mounted on each leg of the U. This enables adjacent actuators to be more closely spaced as each coil can be smaller in diameter than would be the case if a single coil were to be used and thus maximises copper volume thereby minimising copper losses.
The closeness of the orifices (which is dependent on the coil spacing) can also be improved by having the portion of the arm which closes the orifice extend beyond the leg of the U, so that, if adjacent actuators extend on opposite sides of the line of nozzles, the nozzles can be more closely located as the coils will be staggered and thus more closely "packed". The actuators may also be flared out from the nozzles to allow maximisation of coil diameter and to minimise spacing.
It is advantageous if the size of the gap between th
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Dot printer and Printing Method Thereof, vol. 8, No. 270 (M-344) (1707) Dec. 11, 1984.
Miller Anne Tregoning
Schumann Matthew Alexander
Teape John William
Domino Printing Sciences, Plc
Malley Daniel P.
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