Incremental printing of symbolic information – Ink jet – Controller
Patent
1992-10-28
1995-10-17
Grimley, A. T.
Incremental printing of symbolic information
Ink jet
Controller
347 7, 347 89, B41J 2175
Patent
active
054594979
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to continuous ink jet printers of the kind in which ink under pressure is fed through a nozzle, the ink stream being broken up into small droplets which are then individually charged and deflected in order to print on a substrate moving relative to the nozzle.
BACKGROUND OF INVENTION
A number of problems arise with conventional ink supply systems. The inks that are generally used comprise a pigment and a solvent which tends to evaporate in air, so solvent has to be added continuously during printing. Most conventional systems also utilise a pair of pumps, a first pump being used to pressurise ink and supply it to the printhead, and a second pump being used to pump unused ink away from a gutter system into which uncharged and therefore unutilised droplets are directed. Ink supply systems for conventional printers are frequently complex.
SUMMARY OF THE INVENTION
According to the present invention there is provided an ink supply system for a continuous ink jet printer which includes a printhead having a gun body from which droplets are directed under pressure towards a gutter; the ink supply system includes a pressure above that required for ejection of the ink from the gun body; the first chamber, above the ink in the first chamber and for allowing excess air to vent from the first chamber; chamber, to pressurise the ink to the pressure required by the printhead; and,
Preferably, a solvent make-up reservoir is also provided.
In such a system, ink (together with air) entering the gutter is compressed by, for example, a two-stage pump into the first chamber at a pressure higher than that required in the gun body (printhead), the air and ink being separated in the first chamber. Ink from the first chamber can be arranged to pass through a valve and a restrictor to the second chamber substantially at gun body pressure and from the second chamber is fed to the gun body (printhead). The air above the ink in the second chamber is utilised to stabilise the ink feed pressure, this air being supplied from the first chamber via appropriate valving and being vented through a valve when desirable to reduce the pressure.
The system thus provided significantly reduces the amount of solvent lost by evaporation, due to the fact that air entering the gutter can be pressurised to a pressure above atmospheric pressure, for example, 4 bar.
The system has the advantage that a single pump may be provided, the output pressure of which is non-critical to the printing operation. The pump can be arranged to pressurise the ink to high pressure so that air entrained in the ink as it enters the gutter is compressed, thus condensing most of the solvent vapour out of the air and enabling it to be reconstituted in the ink and thus reducing the amount of solvent which needs to be added from time to time. The pump may be as described in our British application no. 9023552.4.
The crucial ink feed pressure can be determined by allowing compressed air to enter the second chamber from the first chamber, or venting air from the second chamber as necessary, or simply by the balance between the feeding of ink from the first chamber to the second chamber (which causes air in the second chamber to be compressed) and the flow of ink from the second chamber. The flow of ink into the second chamber can be determined by the pressure difference between the first and second chambers, a restriction between them and the duty cycle of a valve between the two chambers, and the flow out from the second chamber can be controlled by the air pressure in the second chamber, and the dimensions of the nozzle in the printhead and the pipe or conduit to the printhead. The balance of the flows in and out of the second chamber can be controlled by adjusting flow though the valve between the first and second chambers in accordance with the flow implied by the desired velocity of the jet of ink issuing from the printhead.
Other objects, advantages and novel aspects of the invention will become more apparent in the
REFERENCES:
patent: 3761953 (1973-09-01), Helgeson et al.
patent: 3929071 (1975-12-01), Cialone et al.
patent: 4555712 (1985-11-01), Arway et al.
Manning Howard J.
Reed David W.
Domino Printing Sciences PLC
Grimley A. T.
Ramirez Nestor R.
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