Modified Diffused Ink Jet Printer

Abstract

A plurality of nozzles are connected to a common manifold supplying ink under pressure. Individual nozzle electrodes are either grounded or connected to a source of potential. A common loop electrode between the nozzles and a document is connected to a source of potential. Streams from grounded nozzles are dispersed into a mist which is blocked by a shield having orifices aligned with the nozzles so as to provide selective printing for a matrix type printer.

Description

FIELD OF THE INVENTION

The invention relates generally to ink jet printers and it has reference in particular to parallel nozzle constructions for ink jet matrix printing.

DESCRIPTION OF PRIOR ART

U.S. Pat. No. 3,416,153, entitled "Ink Jet Recorder," issued on Dec. 10, 1968, to C. H. Hertz et al, and describes an ink jet recorder in which an electrode positioned between a nozzle and a document disperses the ink jet from the nozzle to prevent the stream passing through a shield to mark a document.

SUMMARY OF THE INVENTION

Generally stated, it is an object of this invention to provide for selective printing from a row of closely-spaced nozzles in a matrix ink jet printer.

Another object of the invention is to provide for selectively controlling different ones of a plurality of closely-spaced ink jet nozzles for printing characters.

Yet another object of the invention is to provide for using a common loop electrode with a plurality of closely-spaced ink nozzles which are conductive and may be selectively grounded or connected to a voltage source.

It is also an object of the invention to provide for having a common manifold with a plurality of closely-spaced nozzles connected thereto which have grounded connections at the common manifold end and conductive portions at the other ends which are selectively connected to ground or to a source of potential for controlling the individual ink jet streams.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing.

DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a schematic isometric view in part of an ink jet printing system embodying the invention in one of its forms; and

FIG. 2 is a sectional view in part of the manifold of FIG. 1 taken along the line 2--2.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. 1, the reference numeral 10 denotes generally an ink jet matrix printer system which is shown schematically and comprises a manifold structure 12 having a plurality of closely-spaced nozzles 11a- for producing ink jet streams in response to the supply of ink under pressure to the manifold through a conduit 13. The streams are disposed to provide individual dots on a document 14, represented by the dots 14a, 14c, 14d, and 14e, in order to print characters thereon.

In order to provide for selectively controlling the ink jet streams for printing characters on the document 14, an electrode 16 is provided for effecting dispersal of unwanted streams. The electrode 16 may, for example, comprise parallel plates or a loop, as shown, connected to a source of electric potential on the order of 100-500 volts, for example. A mask or shield 15 is interposed between the electrode 16 and the document for preventing dispersed streams from marking the document. The mask may be provided with a plurality of openings 15a-15e aligned with the ink jets for permitting the passage of ink jet streams therethrough.

Referring to FIG. 2, it will be seen that the nozzles 11 may comprise relatively fine tubes or bores connecting with a common plenum chamber 17 and are represented by the tubes 11a-11c. The non-conducting tubes 11a-11c may be provided with conducting sleeves 22a-22c at the ends adjacent the plenum chamber, being either separate metal inserts or formed by internal plating of the tubes. These sleeves may be connected together and connected to ground. At the other ends of the tubes 11a-11c conducting sleeves represented by the sleeves 24a-24c may be provided, which may also be separately formed or by internal plating of the tubes and which may be selectively connected either to a source of potential or to ground, as by means of individual switches 28a-28e connected to the sleeves by means of conductors 26a-26e, as shown in FIG. 1. The tubes 11a-11 should be dimensioned so that with the ink used there is a resistance of 0.1 to 1 megohm between the sleeves 22 and the sleeves 24. With a charging potential of 500 volts the current drawn will be on the order of 1 to 1/10 milliampere and the energy dissipated 0.5 to 0.05 watts. Since the nozzles are at high potential only for printing, which is a small fraction of the time, the heat generated is within acceptable limits. While it is intended that the selectively-chargeable nozzles are set at ground potential if printing is not to occur, depending on the time constants of the system and the desired "time on" for printing, it may be possible to let the selectively chargeable nozzles float if printing is not to occur.

As shown in FIG. 1, the loop electrode 16 is connected to a source of potential on the order of 500 volts and if it is desired to print dots at 14a, 14c, 14d, 14e and 14f but not at 14b, the switch 28b may be connected to ground while the switches 28a and 28b-28f may be connected to the 500 volt source. Under these conditions the stream from the nozzle 11b will disperse in the area of the electrode 16, and the shield 15 will prevent this stream from marking the document 14. The streams from the nozzles 11a and 11c-11f will continue through the openings 15a and 15c-15f to mark the document 14, as shown at 14a and 14c-e.

As an alternate to this arrangement, the manifold 12 can be kept at the high potential and the loop electrode 16 at ground potential as shown by the dotted connection of electrode 16 in FIG. 1. Then if no printing is to occur, the nozzles 11a-11c are kept at the 500 volt potential so that the stream disintegrates at the loop electrode 16. For printing to occur an individual nozzle will be grounded so that the stream passes intact through the loop electrode 16 and impacts the document 14.

The above-described arrangement operates in accordance with the phenomenon described in the Hertz et al U.S. Pat. No. 3,416,153 and is due to the well-known property of a jet of liquid to part into droplets soon after leaving the nozzle due to action of surface tension. When an electrode is placed around the jet near the point of drop formation and a voltage is applied between the liquid and the electrode, the drops are electrically charged due to the influence of the field. This electric charge gives rise to an electric force on the drop surface having the opposite direction to the drop-conserving force of surface tension. If this electric force becomes larger than the force due to surface tension, the drops will explode into smaller drops. Since each of the droplets still are carrying a charge of equal sign, they will repel each other more or less perpendicularly to the original direction of the jet, thus forming a spray and causing dispersal of the jet stream.

As described in the Hertz patent, with a nozzle having an inner-diameter of 0.015 millimeters from which nozzle a jet of liquid is discharged under a pressure of about 20 kilograms per square centimeter with a velocity of about 1,000 centimeters per second, the point of drop formation is situated about 1 millimeter in front of the nozzle. Any voltage larger than 90 volts caused the drops to explode. A voltage range of from 100-500 volts was found to be satisfactory.

From the above description and the accompanying drawing it will be seen that there is provided an arrangement for selectively printing with a plurality of closely-spaced jets on a document. This lends itself readily to a matrix type of character printing, relative movement of the document and the nozzles providing the completion of the matrix in the other direction, in this case, in the horizontal direction.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. In an ink jet printer;

a common manifold structure having a common plenum chamber with means to supply ink thereto under pressure and having a plurality of passages defined by a plurality of non-conducting tubes each connected thereto at one end and having a nozzle at the other end to direct streams of ink toward a document,

common electrode means for each of said non-conducting tubes positioned at said common plenum end and connected together to one terminal of a source of electrical potential,

electrode means individual to each nozzle end comprising a conductive portion at the end of said nozzle away from said manifold and having switch means selectively operable to connect said individual electrode means to the other terminal of said electrical source and to said one terminal,

a single electrode means common to all of said nozzles positioned in spaced relation with said individual electrode means between said individual electrode means and said document and connected to said one terminal of said common source of electric potential to disperse the ink stream from an individual nozzle electrode means connected to said other terminal of said source of potential, and

a mask having openings aligned with said nozzles positioned between said single electrode means and said document to permit passage of a non-dispersed ink stream.