Liquid Jet Recorder

Abstract

A liquid jet recording system in which an electrically conductive tracing fluid is pressure ejected through a capillary nozzle to form a jet directed toward a recording sheet. A hollow control electrode is disposed around the point of drop formation so that a large potential pulse imposed between the fluid and electrode will cause the jet to break up, thus permitting the jet to be intensity modulated. The jet nozzle is supported in an element which can be moved to vary the direction of the jet axis periodically. In one system, a group of such nozzles, mounted to provide a corresponding group of jets in a common plane, can be moved periodically together.

Description

This invention relates to graphic recording system and more particularly to a liquid jet recorder.

German Auslegeschrift DAS 1,271,754 U.S. Pat. No. 3,416,153 describes a method of intensity-modulating a tracing liquid jet and how this method is practiced. In that method, use is made as tracing element of a fine liquid jet which is formed by ink ejected under high pressure from a nozzle. Some millimetres in front of the nozzle, the jet spontaneously breaks up into droplets which are supplied to a record carrier following exactly along a line. If an electrode is disposed in the vicinity of this point of drop formation and a sufficiently high electrical voltage is applied between said electrode and the tracing liquid, it is observed that the liquid jet a short distance behind the point of drop formation dissolves into a diffuse cloud of droplets which produces only a very diffuse coloration of the record carrier. This coloration may finally be eliminated altogether by suitable means so that one obtains on the record carrier an ink trace which permits high-frequency electric modulation.

An essentially simplified electrode system which exploits the same physical phenomenon for modulating a liquid jet is disclosed in German Offenlegungsschrift 1,950,430 my copending U.S. application Ser. No. 861,743 filed Sept. 29, 1969 which, inter alia, also treats of printing of alpha-numerical characters. However, the system defined therein for printing such characters is relatively complicated and slow in mechanical respect, or requires a large number of liquid jets. Since the alphanumerical characters printed with such a system moreover permit only with difficulty a better character resolving power than a 5 .times. 7 matrix, it is not possible by such system to print characters of sufficiently high quality as may be required, for instance in typography and other graphic printing methods. Similar difficulties are met with in the use of the apparatus described in U. S. Pat. No. 3,298,030, which is based on a quite different physical principle for controlling the ink droplets, and therefore has to operate with considerably larger drops than does the present invention.

In contrast thereto, the present invention makes it possible to print alphanumerical characters of desirable quality with the aid of a simple apparatus. Moreover, the invention opens up avenues for arranging a large number of ink jets which can be electrically modulated independently of each other according to the above-mentioned principle, in substantially closer relation than that attainable in using the prior-art electrode systems.

The above and further features of the invention will become apparent from the following, reference being made to the accompanying drawings in which:

FIG. 1 shows the principle of a liquid jet recording system in a possible embodiment of the invention;

FIG. 2 shows two examples of characters printed by this system;

FIG. 3 shows a recorder having a plurality of recording systems as illustrated in FIG. 1;

FIG. 4 shows two superimposed recorders of the type illustrated in FIG. 3;

FIG. 5 shows a structural improvement of the recorder in FIG. 3;

FIG. 6 shows a recorder having considerably simplified control electrodes;

FIGS. 7 - 9 show alternative embodiments of the control electrode in the recorder shown in FIG. 6;

FIG. 10 shows a device that prevents the tracing liquid from drying in the nozzles.

An embodiment of the recording system which is the basis of the invention is illustrated in FIG. 1. Fine capillary tube 12 is fixedly mounted in holder 5 and extends through a hole in plate 6 towards control electrode 3. Plate 6 is secured to resilient means such as leaf spring 7, the other end of which is attached to a support or holder 10. Electromagnet 8, through which flows alternating current from a-c source 9, is attached to leaf spring 7 to cause the latter to oscillate so that plate 6 swings in the direction of the arrow. Thus, the nozzle 4 at the end of the capillary tube 12 will be caused to swing back and forth in a plane at right angles to the direction of motion of the record carrier 2. Means, not shown, are provided for supporting and moving record carrier 2, typically a paper strip. If s suitable tracing liquid is now forced under high pressure through capillary tube 12, a fine linear liquid jet 1 will emerge from nozzle 4, and in the same manner as capillary tube 12, the liquid jet will also swing back and forth and provide an approximately sine-shaped recording trace 18 on the moving record carrier 2.

While travelling from nozzle 4 to record carrier 2, liquid jet 1 passes through control electrode 3 which is not shown in detail here because its construction is already described in German Offenlegungsschrift 1,950,430. In order not to impede the oscillations of the liquid jet, the control electrode may be given, for instance, a rectangular cross section. By means of control electrode 3, the shape of the liquid jet may be influenced in a known manner by application of a control voltage derived from electronic generator 11. The latter applies a potential between control electrode 3 and the tracing liquid in capillary tube 12. Because the liquid jet breaks up upon application of the potential as described in German Auslegeschrift DAS 1,271,754, in this manner there is provided intensity modulation of recording trace 18. By suitable selection of the time sequence of the voltage pulses produced by the generator 11, optional alphanumerical or other characters can be printed in this manner on the record carrier 2. An example is shown in FIG. 2 where the digit seven is reproduced in two different ways by this method, the broken line showing the path that the jet would be following if the droplets were not then being dispersed. The broader areas show where, the potential having been removed, the droplets have made a record.

An improvement of the quality of the characters printed in this way can be attained by controlling the drop formation process in the manner described in the above-mentioned German Offenlegungsschrift 1,950,430 by means of, for instance, mechanical high-frequency oscillations at the nozzle 4.

Capillary tube 12 in the apparatus illustrated in FIG. 1 is, for instance, a glass tube about 20 mm long and 0.1 mm thick, which at end 4 tapers into a nozzle of about 0.01 mm inner diameter. The tracing liquid is forced through capillary glass tube 12 under a pressure of 20 to 30 atm. gauge and forms a fine linearly collected liquid jet. Plate 6 causes capillary glass tube 12 to oscillate typically at a frequency of about 200 to 1,000 Hz. The record carrier travels past capillary tube 12 at a constant speed of 20 to 100 cm per second and is spaced approximately 25 mm from the nozzle 4.

The apparatus shown in FIG. 1, which causes the liquid jet mechanically to oscillate transversely, can also be realized in other ways. For instance, the liquid jet could also be translated in a periodically oscillating movement. Further, the desired periodical change in direction of the liquid jet could also be attained in another way, for instance by suitable application of an electrical alternating field perpendicularly to the direction of the liquid jet 1. Alternatively, this can be realized with the aid of an alternating air stream directed perpendicularly at the liquid jet, or by supplying high-frequency mechanical oscillations at a frequency of 100 kHz and more to the end 4 of the capillary glass tube 12.

It is advantageous for many purposes to arrange a plurality of the recording systems shown in FIG. 1 in juxtaposition. In that way, whole rows of alphanumerical characters can be traced simultaneously, as is the case for instance in the printing registers of electronic computers. FIG. 3 shows a plan view of such an arrangement. Here, five capillary tubes 12a thru 12e are arranged in juxtaposition so that their liquid jets 1a thru 1e are directed towards record carrier 2, which is movable in a plane normal to the common plane of the jets.

The liquid jets can be intensity-modulated individually by control electrodes 3a thru 3e, each control electrode being connected to its respective electronic control circuit (not shown). All capillary tubes 12a thru 12e are secured in holder 14 and each of them is passed through a hole in oscillating beam 13. The latter is secured to two leaf springs 7a and 7b and is caused to oscillate by electromagnet 8 in the manner previously described: The other ends of the leaf springs are connected to fixed support blocks 10a and 10b.

In this manner all liquid jets can be caused to oscillate synchronously with the aid of the electromagnet 8, the oscillatory movement corresponding to that described above with reference to FIG. 1. This will produce five juxtaposed sine-shaped recording traces on the record carrier 2. With the aid of control electrodes 3a thru 3e, liquid jets 1a thru 1e can be electrically influenced individually in a suitable way, which results in an intensity-modulation of the recording traces, as already described. If a suitable sequence of electrical pulses is applied to each of the control electrodes, five alphanumerical or other characters can thus be printed simultaneously and independently of each other on record carrier 2. Obviously, it is possible to trace in this way any desired number of character columns beside one another if a corresponding number of the recording systems shown in FIG. 1 is arranged in juxtaposition.

To ensure that the pulse sequences delivered by the electronic voltage generator to the various control electrodes are in correct time relation to the oscillation phase of the liquid jets, slot 15 is preferably formed in beam 13. This slot partially shields a photoelectric sensor such as photodiode 17 from lamp 16. Upon oscillation of beam 13 by magnet 8, an electrical alternating signal will thus be obtained from the photodiode, and the phase of that alternating voltage is then synchronously associated with the phase of oscillation of beam 13. Such an alternating voltage can also be obtained in a known manner with the aid of other transducers, such as piezoelectrical, capacitive, inductive or resistive transducers in place of a photoelectric sensor.

It may be difficult to dispose the recording systems illustrated in FIG. 1 sufficiently close to one another so that character columns will not be too widely spaced apart. This difficulty can be overcome by the following system of which also two or more can be used concurrently.

To begin with, it is obviously possible to arrange the recording systems above each other with their nozzles in two or more planes, and the recording systems in each plane may be slightly staggered with respect to those in the other planes. FIG. 4 shows such an arrangement in side elevation. Additionally, the device shown in FIGS. 3 and 4 may be disposed on both sides of record carrier 2 so as to permit simultaneous tracing or printing on both sides of the record carrier, since the jets here described exert practically no force on the record carrier.

Furthermore, it is evident that the side walls of control electrodes 3a thru 3e are not absolutely necessary for the function of the device shown in FIG. 3, provided that a correct geometry is chosen for the control electrodes so as to insure that the electrical field at the point of drop formation of the individual liquid jets 1a thru 1e is determined only by the control electrode associated with the respective liquid jet. By this arrangement the recording systems can be arranged more closely together than what is possible with the recorder illustrated in FIG. 4.

FIG. 5 shows part of an exemplary construction of two juxtaposed recording systems in such an arrangement. With a distance of 4 mm separating the control electrodes, the spacing between each of the upper control electrode portions such as plates 3f and the corresponding lower control electrode portions such as plate 3g should typically amount to about 1 mm. The upper and lower portion or plates of each control electrode pair such as 3f and 3g, or 3h and 3i are conductively interconnected and coupled to a respective electronic voltage pulse generator such as 11f and 11h. In a known manner at least the surface of the control electrodes facing the liquid jet are electrically conductive and porous, and are connected to a suction means (not shown in FIG. 5) for sucking away any of the tracing liquid striking such porous surfaces. Alternatively, also each of the control electrode portions may be individually connected to a control pulse generator, which implies a more complex control with two independent signals per jet, one for each electrode plate or portion.

In the recorder shown in FIG. 5 all control electrode pairs have to be insulated from each other. With a large number of juxtaposed jets, this implies -- because of the suction means (not shown in FIG. 5) -- practical difficulties such that it is impossible to build a recorder according to FIG. 5 if the liquid jets have to be spaced less than some minimum distances apart. Therefore, alternatively, as shown in FIG. 6, a single control electrode 3j composed for instance, of two parallel plates can be substituted for the system of control electrodes of FIG. 5. When the control voltages produced by electronic voltage pulse generators shown as 11k and 11m are applied with the aid of respective electrodes 19k and 19m to the tracing liquid in capillary tubes 12k and 12m, the liquid jets can be modulated also in this way, since according to German Offenlegungsschrift 1,950,430, the electrical control of the jet is dependent only upon the voltage difference between the liquid jet emerging from the capillary tube and the control electrode. A prerequisite is that the flows of the tracing liquid in the various capillary tubes should be adequately electrically insulated from one another. This may be attained, for instance, in that the tracing liquid running from supply container 20a and pump 20b through supply conduit 21 to the capillary tubes 12k and 12m is to be supplied through relatively long and very narrow tubes 22k thru 22m. The electrical resistance in these latter capillary tubes will be high enough to constitute a buffer or open circuit approximation. Capillary tubes 12k and 12m are again secured like in FIG. 3 in holder 14 and are caused to oscillate by motion of beam 13. To avoid pollution of the tracing liquid by products of electrolysis, the electrodes 19k thru 19m may be enclosed within corresponding filters.

It is clear that the control electrode 3j common to all liquid jets may be connected to ground or to a constant voltage. Alternatively, however, the control electrode 3j can also be connected to an electronic voltage pulse generator 23, which makes it possible collectively to influence all liquid jets. In this case, also, the control electrode 3j can be composed of two porous electrically conductive and electrically interconnected plates which are about 20 mm wide and are disposed about 0.5 mm above and beneath the plane defined by the plane of oscillation of the liquid jets. To such away scattered tracing liquid that is intercepted by the control electrode, the plates of the control electrode 3j may be provided with internal passageways connected to suction pump 24. Alternatively, these plates may be provided with a suction sleeve as in German Offenlegungsschrift 1,950,430.

It is obvious that the arrangement shown in FIG. 6 may also be provided with more than the two exemplary juxtaposed capillary tubes 12k and 12m. Also, control electrode 3j may be given other shapes, and, in particular, the distance between the plates of the control electrode may vary or be tapered in the direction of the jet. The two plates of the control electrode 3j may be provided with different potentials. Finally, control electrode 3j may be formed in a unitary structure which for each tracing jet has a tubular passage the axis of which coincides with the axis of the jet. FIG. 7 shows such an embodiment wherein the passages have rectangular cross sections. Moreover, a slot-shaped porous shutter may be interposed between control electrode 3j and the record carrier 2, and this shutter in turn may have applied to it a suitable constant voltage.

If capillary tubes 12 are arranged in vertical position, the recorder shown in FIG. 6 can be still further simplified. FIG. 8 shows an embodiment, chosen by way of example, of such a recorder in which the control electrode consists of two metal sheets 3k and 3m. The tracing liquid which has deposited on the inner side of the control electrode flows by gravity into grooves 25k and 25m and along said grooves to an outlet at the lateral end of the electrode, whereby the suction pump 24 shown in FIG. 6 can be dispensed with. By arranging also the recorder shown in FIGS. 3-5 and 6 in vertical position, gravity can be exploited to carry away the tracing liquid.

It is obvious that the arrangements shown in FIGS. 3 thru 8 inclusive permit an intensity modulation of the recording traces also in the case when the liquid jets are not caused to oscillate but are stationary. In this latter case, it may be advantageous if the line in which record carrier 2 intersects the plane formed by the liquid jets does not lie at right angles to the direction of motion of the record carrier but almost coincides with said direction. Furthermore, it is likewise not necessary that the liquid jets pass through control electrode 3j in parallel relation. It may rather be advantageous for certain uses if the jets are directed substantially concentrically in a common plane towards a point in the vicinity of the record carrier 2, as is shown in plane view in FIG. 9.

As already described in German Offenlegungsschrift 1,950,430, the part of the tracing liquid intercepted by control electrode 3 is sucked away and is thus lost. This can be prevented if, for instance, in FIG. 6, the tracing liquid sucked away by suction pump 24 is returned to the supply container 20a. In order that the tracing liquid may not lose solvent, such as water, and gradually thickens, fresh solvent can be added in correct amounts. This procedure may be automatized by running the tracing liquid through a semi-permeable tube surrounded by a solution of suitable osmotic pressure. The correct solvent concentration will thus be constantly adjusted in the tracing fluid by osmosis.

Mostly, relatively fine nozzles 4 are utilized at the ends of the capillary tubes 12 in the arrangements shown in FIGS. 1 thru 5. One should therefore retard or prevent, by selecting suitable tracing liquids, drying of the tracing liquid which would tend to clog nozzles 4 at shutdowns. This risk can be eliminated by covering nozzles 4 at shutdowns with a suitable liquid, whereby drying of the tracing liquid is prevented. To this end, oscillating beam 13 may be designed for instance as a hollow or double-walled structure (as shown in FIG. 10) into which capillary tubes 12 open through holes, as already hereinbefore described. In front of nozzles 4 at the ends of each of capillary tubes 12 there are arranged apertures 26, about 1 mm in diameter, through which the liquid jets can pass unobstructedly. If following shutdown beam 13 is filled with a protective liquid through flexible supply conduit 27 from closed supply container 28, the protective liquid will cover nozzles 4. The liquid level in the container should be so selected that the liquid certainly penetrates into beam 13 but is prevented by surface tension from escaping through apertures 26. If container 26 is also connected by appropriate valving (not shown) to suction pump 24 which, as shown in FIG. 6, is also utilized to suck away tracing liquid fron control electrode 3j, then automatically when the arrangement is made operative the liquid will immediately be sucked out of hollow beam 13. The arrangement illustrated in FIG. 10 has the further advantage that the front wall of beam 13 can serve to shield electrically nozzles 4 from each other, if that front wall is made from conductive material and is connected to a suitable voltage. Alternatively, however, other embodiments of beam 13 are conceivable. Thus, the double wall of the beam at each position of the capillary tubes can be replaced by a small vertical tube secured to beam 13 and so arranged as to convey protective liquid to each nozzle 4 of a respective capillary tube 12.

The tracing speed of the recorders illustrated in FIGS. 3 to 8 inclusive can be in the order of 20 to 100 lines per second, and therefore it is not necessary to associate with each character position a separate electronic coding unit which produces the correct voltage pulse sequences for the tracing of the characters. If a shift register is associated with each character position, it is in fact, possible to carry out recording of all characters in a line during the time it takes the paper advance mechanism to provide the necessary line spacing. During this time, for instance, digital information delivered in series form by an electronic computer can be recoded digit by digit in a central coding unit and be stored in the shift registers in such a way that a parallel relatively slow reading of all shift registers simultaneously supplies to the control electrodes in each tracing position precisely the pulse sequence that is necessary to trace the character read into the respective shift register. It may be desirable to connect a voltage amplifier between the shift register and control electrode 3 or the electrodes such as 19k. It is obvious that reading of the information from the shift registers must take place in correct time relation with the mechanical oscillations of beam 13. Such synchronization may be realized by means of the electrical signal from photodiode 17 or in another manner.

Claims

What is claimed is:

1. A liquid jet recorder for writing with an electrically conductive marking fluid on a receiving surface movable along a first path, said recorder comprising in combination,

a plurality of capillary nozzles juxtaposed so that a corresponding plurality of jets of said fluid can be pressure ejected therefrom toward said receiving surface, said nozzles being at corresponding ends of a like plurality of capillary tubes mechanically coupled to one another,

control electrodes disposed adjacent the point of drop formation of each of said jets for applying a respective control voltage so as to intensity modulate each of said jets independently of one another,

means for periodically and simultaneously in tandem moving said capillary tubes with respect to said electrode means substantially along a common path substantially transverse to both the path of motion of said receiving surface and the axes of said jets.

2. A recorder as defined in claim 1, including transducer means for converting the periodic movement of said tubes into alternating electrical synchronizing signals substantially throughout each period of movement.

3. A recorder as defined in claim 2 wherein said tubes are flexible and said means for moving is connected for applying bending forces transverse to the longitudinal axes of said tubes.

4. A recorder as defined in claim 1 including a common control electrode for at least one group of said jets.

5. A recorder as defined in claim 1 including individual sources of supply of said tracing fluid for each of said jets, individual electrodes each associated with a corresponding one of said sources for imposing a potential on the fluid in said source.

6. A recorder as defined in claim 1 wherein all of the axes of said jets are in approximately parallel relationship in a substantially common plane.

7. A recorder as defined in claim 1 wherein all of the axes of said jets are in approximately convergent relationship to a common point in a substantially common plane.

8. A recorder as defined in claim 1 including means for covering the opening in said nozzles with a protective liquid during a period when said fluid is not being ejected.

9. A recorder as defined in claim 8 including pump means for removing said liquid prior to ejection of said fluid from said nozzles.

10. In a liquid jet recorder for pressure ejecting toward a recording surface a plurality of jets of an electrically conductive tracing fluid from corresponding nozzles, and including means for periodically varying the direction of said jets along paths substantially normal to the jet axes, electrical means for applying electrical potentials for each of said jets, and means for supplying said fluid to said nozzles from a common fluid source, the improvement wherein said means for supplying comprises a plurality of tubes each connecting a corresponding one of said nozzles to said common source, each of said tubes being dimensioned in length and cross-section so that the electrical resistivity of said fluid in each of said tubes is sufficiently high to constitute an electrical buffer between said nozzles with respect to said potentials.