Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2001-03-13
2001-12-18
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06331045
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to drop on demand ink jet printing apparatus and, in one example, to drop on demand ink jet printing apparatus having a two dimensional array of ink chambers.
Our co-pending PCT patent application no. PCT/GB98/01955 describes a drop on demand inkjet apparatus which utilises a piezoelectric actuating disc arranged so as to deflect in shear mode. The apparatus is formed of a plurality of laminated plates arranged so as to define an ink chamber. The actuator forms one side of the chamber and deflects towards a nozzle formed in a nozzle plate which provides the opposite side of the chamber. When a charge is applied between electrodes formed on the actuator, the piezoelectric disc deflects in shear mode towards the nozzle plate. An acoustic pressure wave travels radially within the chamber, is reflected from the side walls of the chamber to dissipate the energy stored in the ink and actuator, and converges again in the centre of the chamber to effect ejection of ink from the chamber. The volume strain or condensation as the pressure wave recedes from the nozzle develops a flow of ink from the nozzle outlet aperture for a period R/c, where c is the effective acoustic velocity of ink in the chamber and R is the radial distance to the walls of the chamber. A droplet of ink is expelled during this period. After time R/c the pressure becomes negative, ink emission ceases and the applied voltage can be removed. Subsequently, as the pressure wave is damped, ink ejected from the chamber is replenished and the droplet expulsion cycle can be repeated. By the application of a number of pulses in quick succession it is possible to increase the size of the droplet ejected and hence build up a number of grey levels.
SUMMARY OF THE INVENTION
The preferred embodiments of the present invention seek to extend this concept to provide further improvements in drop on demand ink jet printing.
In a first aspect, the present invention provides drop-on-demand ink jet printing apparatus comprising a nozzle on a nozzle axis; an ink chamber communicating with the nozzle; a piezoelectric actuating structure, said structure extending around the nozzle axis and extending in the direction of the nozzle axis; an actuating surface bounding the chamber and facing towards the nozzle, said structure being actuable to move said actuating surface in the direction of the nozzle axis to effect droplet ejection through the nozzle; and electrodes for applying an actuating electric field to the actuating structure.
Preferably, the electrodes comprise a first electrode on a face of the actuating structure abutting the ink chamber and a second electrode on an opposing face of the actuating structure isolated from the ink chamber.
In a second aspect, the present invention provides drop-on-demand ink jet printing apparatus comprising a nozzle on a nozzle axis; an ink chamber communicating with the nozzle; a piezoelectric actuating structure, said structure extending in the direction of the nozzle axis; an actuating surface bounding the chamber and facing towards the nozzle, said structure being actuable to move said actuating surface in the direction of the nozzle axis to effect droplet ejection through the nozzle; and electrodes for applying an actuating electric field to the actuating structure, said electrodes comprising a first electrode on a face of the actuating structure abutting the ink chamber and a second electrode on an opposing face of the actuating structure isolated from the ink chamber. The first electrode is preferably ground.
The ink chamber may extend radially about the nozzle axis, and the-actuating structure may be actuable to move the actuating surface in the direction of the nozzle axis to effect, through acoustic wave travel in the ink chamber radially of the axis of the nozzle, droplet deposition through the nozzle.
Preferably, the ink chamber extends a radial distance R from the nozzle axis and the actuating structure is actuable to move in the direction of the nozzle axis in a time which is at most half of the time R/c, where c is the speed of sound through ink in the ink chamber.
The ink chamber may be bounded by a generally circular structure providing a change in acoustic impedance serving to reflect acoustic waves travelling in the ink chamber radially of the nozzle axis. The change in acoustic impedance may be effected through a change in ink depth in the direction of the nozzle axis.
The circular structure may define an annulus of ink about the ink chamber which in the direction of the nozzle axis is of a depth different from the depth of the ink chamber.
Preferably, the apparatus further comprises ink supply means in fluid communication with the ink chamber for replenishment of the ink chamber following droplet ejection.
The ink supply means may be disposed at a plurality of locations disposed circumferentially about the ink chamber.
The ink supply means may serve to supply ink to the ink chamber around substantially the entire periphery of the ink chamber.
The actuating structure may taper towards the nozzle axis.
In one preferred embodiment, the actuating structure is homogeneous and so poled in relation to the actuating electric field as to deflect in direct mode. The actuating structure may be poled in a direction transverse to the faces thereof, the electric field being applied in a direction transverse to the faces of the actuating structure.
Alternatively, the actuating structure may be homogeneous and so poled in relation to the actuating electric field as to deflect in shear mode. The actuating structure may be poled in directions which converge towards the nozzle axis, the electric field being applied in a direction transverse to the faces of the actuating structure.
The actuating surface may comprise a disc of piezoelectric material, the piezoelectric disc being poled in the direction of the nozzle axis so as to deflect in direct mode upon actuation of the electric field.
The apparatus may comprise a plurality of said nozzles, each having a respective nozzle axis, said nozzle axes being provided in parallel; a plurality of said ink chambers, each extending about a respective nozzle axis; and a homogeneous piezoelectric sheet having a two dimensional array of said actuating structures, each actuating structure being associated with a respective ink chamber.
In a third aspect, the present invention provides a method of ink jet printing comprising the steps of establishing a planar body of ink in communication with a nozzle having a nozzle axis, the body of ink extending radially of the nozzle axis; providing in the body of ink an impedance boundary extending circumferentially of the nozzle axis; and selectively actuating a piezoelectric actuating structure extending in the direction of the nozzle axis and around the nozzle axis to move an actuating surface in the direction of the nozzle axis so as to establish an acoustic wave travelling radially of the nozzle axis in the ink chamber and reflected by the impedance boundary, thereby to effect ejection of an ink droplet through the nozzle.
In a fourth aspect, the present invention provides a method of manufacturing drop-on-demand ink jet printing apparatus, comprising the steps of forming a nozzle plate having a two dimensional array of nozzles each having a nozzle axis, said nozzle axes being in parallel; forming a two dimensional array of actuating structures on a substrate each extending in the direction of a respective nozzle axis and around the respective nozzle axis and being associated respectively with the nozzles, an actuating surface being provided for each actuating structure; applying electrodes on the actuating structures enabling selective actuation of each wall; and laminating the nozzle plate and the substrate; the laminated structure providing a plurality of disc-shaped ink chambers each extending about a respective nozzle axis and communicating with the respective nozzle, such that in the manufactured apparatus, actuation of a selected structure effects drop ejection fro
Harvey Robert A.
Temple Stephen
Gordon Raquel Yvette
Marshall Gerstein & Borun
Xaar Technology Limited
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