Incremental printing of symbolic information – Ink jet – Ejector mechanism
Patent
1994-12-20
1996-12-31
Barlow, Jr., John E.
Incremental printing of symbolic information
Ink jet
Ejector mechanism
B41J 202
Patent
active
055898637
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an Ink Jet Droplet Generator such as a droplet generator which is suitable for use in an ink jet printer.
In conventional continuous jet, multi-jet, ink jet printers, an array of jets is produced by forcing ink, under pressure, through closely spaced nozzles from a common ink-filled cavity behind the nozzles. These jets are caused to break up into uniform streams of drops by imposing a periodic disturbance on all of the jets.
it is advantageous if the time taken to form the drops from each continuous jet is as uniform as possible across the whole array of jets. It is also preferable that no small "satellite" drops are formed between the main drops.
Often, the disturbance is introduced by positioning a regularly vibrating element, such as a piezo crystal, somewhere in the print head structure so that the vibration is transmitted through the material used to construct the nozzle, the nozzle mounting, the ink supply manifold, and also (through the ink) to the jets.
Factors which affect the creation of "satellites" and the uniformity of drop formation across the array include the geometry of the cavity behind the nozzle, the acoustic properties of the materials used to construct the ink manifold and nozzle, and the way in which the separate components of the print head are connected together.
A known ink jet droplet generator comprises a print head structure, a cavity for ink, an ink nozzle element spaced from the print head structure by a spacing or sidewall element providing a sidewall for the cavity between the print head structure and the nozzle element. The spacing element is fixedly clamped between the print head structure and the ink nozzle element.
It is the purpose of the spacing element in the prior art to ensure that the distance from the print head structure, which includes a tuned piezo crystal, to the nozzle element is correct so that the shape and dimensions of the cavity behind the nozzle provide a disturbance at the jets which is of adequate magnitude and uniformity.
However, to ensure that a proper cavity geometry is provided and that the acoustic performance is as constant as possible, relatively large surfaces of the spacer have to make contact with the print head structure on one side and the nozzle element on the other side.
There are problems with this approach.
The performance of the ink jet generator varies merely by removing and replacing the nozzle or by slightly changing the tightness of the bolts. This is undesirable.
The present invention aims to at least alleviate these problems.
According to a first aspect of the present invention, there is provided an ink jet droplet generator comprising a print head structure, a cavity for ink, an ink nozzle element spaced from the print head structure, a cavity sidewall element providing a sidewall for the cavity between the print head structure and the nozzle element, characterised by coupling means for setting the distance between the print head structure and the nozzle element.
This provides a significantly improved droplet generator. The variation in a periodic disturbance transmitted through the structure is significantly reduced, yet the geometry of the ink cavity is maintained and acoustic energy is retained within the cavity.
Preferably, the droplet generator includes a layer of acoustically absorbent material located between the sidewall element and one of the print head structure and the nozzle element.
According to a second aspect of the present invention, there is provided an ink jet droplet generator comprising a print head structure, a cavity for ink, a nozzle element spaced from the print head structure, and a layer of acoustically absorbent material located adjacent to an internal surface of one of the nozzle element and the print head structure.
The layer of acoustically absorbent material has the advantage that the inherent acoustic decoupling across the layer improves the acoustic performance of the droplet generator.
Preferably, the droplet generator includes a cavity sidewall element provi
REFERENCES:
patent: 4779099 (1988-10-01), Lewis
Janse Van Rensburg Richard W.
Keep Peter R.
Barlow Jr. John E.
Casey Donald C.
Videojet Systems International Inc.
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