Arrangement Of Writing Mechanisms For Writing On Paper With A Colored Liquid

Abstract

An arrangement for applying droplets of a substance in liquid form to a surface. The arrangement includes a chamber which is divided into an outer chamber portion and an inner chamber portion with a channel connecting the outer and inner chamber portions. The inner chamber portion is provided with a device which produces short duration pressure increases in the fluid in the chamber. The outer chamber portion is provided with at least one intake channel for the supply of liquid from a supply container and a discharge channel through which the liquid is discharged for deposition on the surface. The discharge channel and the connecting channel are arranged so that they are axially aligned.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an arrangement for applying fluid droplets, i.e., matter in liquid form, to a surface, and more particularly to a mechanism for writing on paper with a colored liquid.

The speed of recording data on paper in, for example, a data processing machine is limited for one thing by the capability of the writing mechanism, which in many cases is substantially less than that of the data processing machine. Then, too, a substantial portion of the costs of the data processing machine can be attributable directly to the rapid writer of the writing mechanism. Furthermore, the mechanisms for these rapid writers are heavy, operate clumsily and produce annoying noise.

One type of writing mechanism is, for example, the so-called impact printer in which hammers print symbols on paper with the aid of printing type or a type head. Impact printers transfer 15 to 50 symbols per second to the writing unit. However, a complicated method is involved with the impact printer in which unnecessarily high energy losses occur.

A modification of this writing mechanism is the mosaic writer in which pins and striking tools are used to record a symbol on paper in the form of dots with the aid of a colored ribbon. An arrangement is also known in which electrodes act on a special heat sensitive paper. However, this paper is expensive.

Instead of a colored ribbon a liquid can be used which is applied in one manner or other to the area to be inscribed. An Example of such a writing mechanism is the "Inctronic" writer. This type of writing mechanism utilizes a stream of charged liquid droplets in which the stream is deflected by an electrical field. A writing mechanism of this type is usually equipped with a great many stream guns and can record about 120 symbols per second. Once again, however, the structure is complicated and requires, inter alia, an arrangement for producing excess pressure. Then too the stream consisting of droplets cannot be shut off but must be deflected in a collecting vessel when no writing is to take place. Moreover, in these types of writing mechanisms a principal problem is the occurrence of interference between the different electrical fields.

SUMMARY OF THE INVENTION

It is, therefore, a general object of the present invention to provide a writing mechanism which substantially overcomes the disadvantages mentioned above.

It is a more specific object of the present invention to provide an arrangement for applying fluid droplets to a surface, such an arrangement comprising, for example, an ink ejection writing mechanism.

It is an even more specific object of the present invention to provide an arrangement for applying liquid droplets to a surface having an improved chamber arrangement.

These and other objects are accomplished according to the present invention by an arrangement having an improved chamber which in one embodiment includes means dividing the chamber into an outer chamber portion, an inner chamber portion, a connecting channel formed in the dividing means for connecting the outer and inner chamber portions, at least one intake channel for the supply of liquid from a supply container which input channel opens into the outer chamber portion, and a discharge channel through which the fluid passes out of the chamber for deposition onto the surface. The discharge channel is adjacent to the outer chamber portion and aligned with the connecting channel, while the inner chamber portion contains or is in direct communication with a pressure producing means which produces preferably short duration pressure increases in the fluid within the chamber.

The cross-sectional areas of the discharge and intake channels of the chamber are selected to be of an order of magnitude such that significant capillary forces are produced in the discharge channel due to the surface tension associated with the flowing fluid.

Some of the advantages of the arrangement of the present invention lie, for example, in its extremely low energy consumption, in the order of milliwatts instead of watts, in the relatively small dimensions which are utilized, in the noiseless writing or printing and in the fact that relatively inexpensive paper can be used. Also, the writing speed can be increased by the arrangement of the present invention to more than 1,000 symbols per second which is significantly higher than the speed of the above-mentioned known writing mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a writing mechanism according to the present invention in its simplest form.

FIG. 2 is a cross-sectional view of one embodiment of a writing mechanism according to the present invention with a divided fluid chamber and fluid container.

FIG. 3 is a graphic representation of a suitable voltage pulse for activating a piezoelectric crystal contained in the writing mechanism.

FIGS. 4-6 schematically illustrate on an enlarged scale the discharge channel and the connecting channel of the writing mechanism according to the present invention with the fluid at rest, passing through the discharge channel, and passing through the connecting channel, respectively.

FIGS. 7-10 schematically illustrate different states of the fluid during the formation of a droplet from the capillary type discharge channel.

FIG. 11 is a plan view of a writing head according to one embodiment of the present invention with seven writing units, with the outer fluid system and partition having been removed for clarity.

FIG. 12 is a cross-sectional view through the writing head shown in FIG. 11 taken along the line 12--12.

FIG. 13 illustrates a line of writing heads in a parallel writer.

FIG. 14 illustrates in side elevation one of the writing heads shown in FIG. 13.

FIG. 15 illustrates in front elevation one of the writing heads shown in FIG. 13.

FIG. 16 is a cross-sectional view taken along the line 16--16 of FIG. 14.

FIG. 17 is a partial cross-sectional view through a special writing element according to the present invention used in a writing head shown in FIG. 14.

FIG. 18 is a cross-sectional view taken along line 18--18 of FIG. 19 illustrating a writing head having two writing units with discharge channels of different cross-sectional dimensions.

FIG. 19 is a plan view of the writing units shown in FIG. 18 with an outer fluid system and a partition having been removed for clarity.

FIG. 20 is a plan view of a writing head according to another embodiment of the present invention with seven writing units each having capillary openings.

FIG. 21 is a cross-sectional view through the writing head shown in FIG. 20 taken along the line 21--21.

FIG. 22 illustrates one possible construction of a copying arrangement with a writing head according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to the drawings, FIG. 1 illustrates a writing unit 1 in its simplest form. The writing unit 1 comprises a fluid chamber 2 provided at its one end with a discharge channel 3 and limited at its other end by a thin, circular metal plate 4 which is fastened to the unit 1 in any conventional manner. The fluid chamber 2 has an inlet 5 through which fluid passing through an intake channel 6 flows into the chamber 2. The channel 6 is formed in a plate 6' fitted within a counterbore 6" in the unit 1. A piezoelectric crystal 7 is attached to the metal plate 4 in any conventional manner. Conductive wires 8 are provided with one being electrically connected to the metal plate 4 and the other to the exterior of the crystal 7. The wires 8 supply the control pulses to the crystal 7. The cross-sectional area of the discharge channel 3 is substantially smaller than the fluid contact area 4' of the metal plate 4. The ratio between these areas lies preferably at 1 : 10,000.

When a suitable voltage pulse is applied, the crystal 7 radially contracts and since it is fastened to the metal plate 4, causes the plate 4 to be subjected to a bending moment. Consequently, the center portion of the plate 4 bulges into the fluid chamber 2. This reduces the volume of the chamber 2 and the pressure of the fluid therein increases. The amount of fluid which can no longer be accommodated in the chamber 2 is discharged through the discharge channel 3 (and to a lesser degree also through the intake channel 6). Since the cross-sectional areas of the channels 6 and 3 are substantially smaller than the contact area 4' of the metal plate 4, there results a substantial increase in the rate of fluid flow through the channels compared to that in the chamber 2, particularly in the discharge channel 3 which opens to the atmosphere. The rate of fluid flow in the discharge channel 3 is preferably about 10 m/s. In order to insure that no air enters the chamber 2 through the discharge channel 3, and since the only force counteracting such inflow of air is the weak capillary force in the channel 3, the applied voltage pulse is kept relatively flat during its return to zero. Through the use of such a voltage pulse the discharged fluid drop will instead be replaced through the inlet channel 6.

In the embodiment of FIG. 2 the writing unit is provided with a two-part fluid chamber, i.e., an outer chamber portion 9 and an inner chamber portion 10 which are in communication through a connecting channel 11 which is provided in a dividing plate 11' situated between and forming the separation of the chamber into the chamber portions 9 and 10. The connecting channel 11 is positioned in the dividing plate 11' so that it is directly opposite and axially aligned with the discharge channel 3 which opens to the air from the outer chamber portion 9. The metal plate 4 is fastened to the wall 10' of the inner chamber portion 10. The distance between the outer end of the connecting channel 11 and the inner end of the discharge channel 3, i.e., the width of outer chamber portion 9, is less or equal to the diameter of the discharge channel 3 which again is less or equal to the diameter of the connecting channel 11.

The dividing plate 11' is also provided with at least one and, preferably, as illustrated, a plurality of inlet capillary type channels 12. The inlet channels 12 open into the outer chamber portion 9. The inlet channels 12 are in communication with a fluid container 13 via a pipeline 14. The container 13 may be disposed at a lower level than the discharge channel 3 because of the capillary forces existing in the channels communicating with the chamber portions.

When the crystal 7 is activated by a pulse, as described above, fluid is discharged from the inner chamber portion 10 through the connecting channel 11, through the fluid layer in the outer chamber portion 9 and further through the discharge channel 3 whereupon it is applied to a writing surface. FIG. 3 shows a suitably shaped pulse for the voltage to activate the crystal 7.

If the rate of fluid flow in the inner chamber portion 10 is slowed down, a pressure reduction is produced in the vicinity due to the inertial forces in the fluid stream in the discharge channel 3. During the time when the voltage pulse drops or returns to zero the direction of the fluid stream in the connecting channel 11 is reversed and fluid is now sucked in through the outer chamber portion 9, i.e., from the container 13, while at the same time the fluid stream in the discharge channel 3 is interrupted. The surface tension then produces a stabilization of the fluid surface in the discharge channel 3.

The different flow states produced during discharge, or intake of fluid are significant for the functioning of the invention, the various stationary states being illustrated in FIGS. 4 through 6. FIG. 4 illustrates the fluid condition when the arrangement is at rest prior to the application of a pulse. During the discharge of fluid there results an increased flow whose cross section substantially coincides with the cross section of the connecting channel 11 as shown by the arrows in FIG. 5. During intake, however, the fluid is sucked from a hemispherical area around the connecting channel 11 in such a way that the fluid stream is substantially constant in every spatial sector having the same angle, as is shown in FIG. 6 by the arrows and a circular arc shown in dashed lines. These two flow phenomena together with the inertial forces and the surface tension result in an arrangement in the discharge channel 3 which principally operates in the same manner as a pump without valves. The degree of suction is determined by the diameter of the discharge channel 3 and by the surface tension of the fluid.

FIGS. 7 through 10 show how the fluid behaves outside of the discharge channel 3. FIG. 7 shows the fluid surface before the pressure wave, produced as a result of the activation of the crystal 7, has reached it; FIG. 8 shows the discharge of the fluid due to the pressure wave; FIG. 9 shows the droplet formation and the slight sucking in of the fluid in the channel 3 after the fluid droplet has left the channel and fluid has been sucked into the inner chamber portion 10; and FIG. 10 shows the fluid after it returns to the same position as in FIG. 7.

For serially writing on a writing surface, the writing head 15 shown in FIGS. 11 and 12 is particularly suited. The writing head 15 is provided with seven writing units 15' each having a discharge channel 3. To write a symbol the difference in speed between the writing head 15 and the paper is kept constant. The inner fluid chamber portions 10 are formed by channels in a base plate 16. The construction is simplified in that a common outer fluid chamber portion 17 is provided for a plurality of inner chamber portions 10 each of which is associated with a separate crystal 7. The seven discharge channels 3 are disposed in a row, each opposite and axially aligned with a respective connecting channel 11 formed in plate 11', and the writing head 15 is so arranged that this row of channels 3 lies at a right angle to the writing direction (indicated by the arrow A in FIG. 11) and in a plane which is parallel to the plane of the writing surface. Due to the fact that the ratio of the center distance between adjacent capillary type discharge channels 3 to their diameter is large, no interference is produced between adjacent channels. To control the writing units 15' of the writing head 15 a known circuit, e.g., an LSI circuit [large scale integration] can be used which effects the conversion of binary signals into mosaic script signals with 7 .times. 5 dots for serial writers. Details of the exemplary circuit are not shown since it is well known in the art.

For a very rapid writing mechanism a plurality of writing heads 20 (FIG. 13) can be provided in succession in a direction transverse to the direction of movement of the writing paper 19. According to this arrangement, a writing head 20 can be provided for each position in a line. As can be seen in FIG. 14, such a writing head 20 comprises a special writing element 18. The writing element 18 as shown in FIG. 17 contains connecting channels 11, a common outer fluid chamber portion 17 and discharge channels 3. The connecting channels 11 and discharge channels 3 are arranged in a row (FIG. 15). According to this embodiment of the invention an inner fluid system is provided. In this case, the inner fluid system comprises five writing units. These writing units are in communication with their respective connecting channels 11 in the writing element 18 via narrow channels 21. In order to be able to accomodate the five units in the space allotted to one writing head 20, the base plate 22 of the writing head 20 is so arranged that its major plane is at a right angle to the writing surface of the paper 19. Consequently, all symbols in a row are written simultaneously, and with a movement of the writing paper 19 from top to bottom a mosaic script is produced with 7 .times. 5 dots. With a writing mechanism operating according to this system there can thus be written as many lines per second as a writing unit according to the present invention can write symbols. According to this embodiment of the invention, up to 1,000 lines per second can be written whereas with the presently known writing mechanisms only 10 to 20 lines per second can be written.

The arrangement of the present invention can also be used under different circumstances for producing pictures, for example. With an amplitude or width modulation of the voltage pulse fed to the piezoelectric crystal, the discharged amount of fluid can be influenced so that a high picture quality is obtained. In order to further extend the modulation range, one or a plurality of writing units with converging different sized connecting and discharge channels can be used as shown in FIGS. 18 and 19 where the smaller channels are marked 3' and 11', respectively.

It is also conceivable to provide parallel discharge channels and to delay the activation of the different units in such a way that the fluid droplets impinge on the writing surface at the desired place. With degrees of blackening beyond a certain level, the larger channel begins to function under the control of a modulator. A color system with different colors in a plurality of writing units is also possible where the color droplets are either mixed on the paper or are applied one next to the other.

A further advantageous embodiment of the present invention provides for capillary openings which are disposed in the area of the discharge channels. These openings connect the outer chamber with the atmosphere. With this feature, the formation of very uniform ink droplets in a writing head comprising a plurality of writing units is further improved. The capillary openings here serve as an intermediate reservoir for the ink, a portion of this ink being sucked from these capillary openings for the rapid pressure equalization of the pressure reduction caused by the discharge of an ink droplet. Due to the surface tension of the ink this again effects a stabilization of the ink level in the capillary openings, ink being sucked from the outer chamber and thus from the reservoir. The sizes of the capillary openings are so selected that the amount of ink contained in the capillary openings is greater than the amount of ink droplets to be ejected. This prevents air from being sucked into the chambers.

FIGS. 20 and 21 show a writing head 15 provided with seven writing units each having a discharge channel 3. The seven discharge channels being aligned in a row. The capillary openings here consist of bores 35 and 36 which are disposed on both sides and parallel to the discharge channels 3. The distance of the bores 35 and 36 from the discharge channels 3 is preferably greater than the distance between the discharge channels 3 themselves. It is also possible within the scope of the present invention to replace the bores 35 and 36 aligned in a row by a capillary gap common to all discharge channels 3. The important fact is only that capillary openings are disposed in the area of the individual discharge channels which connect the outer chamber with the atmosphere in such a manner that a pressure reduction resulting from the ejection of ink droplets is avoided in the chambers which are under atmospheric pressure. A writing head provided according to such a design also permits the ejection of uniform ink droplets at high ejection frequencies.

FIG. 22 shows the principal construction of a duplicating device which employs the present invention. The original 23 and the copy 24 are mounted on a rotating drum 25 and the rotating movements are translated to a screw 26 via a gear device (not shown). This screw moves a carriage 27 in the longitudinal direction of the drum 25. The carriage 27 supports a writing head 28 according to any of the various embodiments of the present invention as well as the, for example, optical scanning device required for scanning the picture or original 23. The scanning device may comprise, for example, a lamp 29 and a photocell 30. The viedo signal of the photocell 30, which is checked periodically with the aid of a clock 31, controls a pulse width modulator 32. The output voltage from the modulator 32 is amplified by the amplifier 32 and is then fed to a piezoelectric crystal located in the writing head with the effect described above.

As exemplary of one set of dimensions for the components of the inventive arrangement, the following have been found to be advantageous: the diameter of the discharge channel 3 can have a range up to 0.05 mm, and its length can have a range up to 0.1 mm; the distance between the discharge channel 3 and the connecting channel 11 can have a range up to 0.05 mm; the diameter of the piezoelectric crystal 7 can have a range up to 10 mm, and the thickness of the crystal can have a range up to 0.5 mm.

The present invention is not limited to the above described and illustrated embodiments. Rather, any number of modifications are conceivable within the scope of the following patent claims. For example, the piezoelectric crystal 7 may be replaced by a magnetic system even though this is a poorer solution of the problem. The metal plate 4 could be replaced by a piston which is displaceable within certain limits and which is provided with means for producing the required pressure changes in the chamber 2. The means for producing the pressure changes may also comprise an element enclosed in a chamber which element expands when it is heated electrically or it may be a heating spiral which directly heats the fluid so that vapor is produced which leads to an increase in pressure. Gas may be produced by electrolysis of the writing fluid -- with the aid of electrodes enclosed in the container -- so that a pressure increase is obtained. The dots in the mosaic script may be moved closer together in that the writing heads are provided with more writing units than described above, e.g., 24 .times. 24 dots may be provided.

The present invention can also be used in other fields than in writing mechanisms; for example, it may be used to apply electrically conductive material, e.g., metal, onto plates in order to produce printed circuits.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

Claims

I claim:

1. In an arrangement for applying liquid droplets to a surface, e.g., an ink ejection writing mechanism, comprising at least one liquid applying unit including a chamber having an intake channel connected to a liquid supply container, and a discharge channel through which the liquid is discharged from said chamber, and means for producing short duration pressure increases in the liquid in the chamber, the imporvement wherein said chamber includes means dividing said chamber into an outer chamber portion adjacent to said discharge channel and an inner chamber portion, a connecting channel in said dividing means connecting the outer and inner chamber portions, said connecting channel being axially aligned with said discharge channel, and at least one said intake channel which opens into said outer chamber portion; and wherein said pressure producing means is in direct communication with and produces the desired pressure increases in said inner chamber portion.

2. An arrangement as defined in claim 1, wherein said liquid applying unit is a writing unit.

3. An arrangement as defined in claim 2, wherein the arrangement is constituted by a writing head which comprises at least seven writing units, wherein said writing units have a common outer liquid chamber portion, and wherein the discharge channels of said writing units are arranged in a row and parallel to one another.

4. An arrangement as defined in claim 3, wherein each writing unit further includes capillary openings provided in said unit in the area of said discharge channels, said capillary openings connecting the outer chamber portion with the atmosphere.

5. An arrangement as defined in claim 4, wherein the capillary openings consist of bores which are disposed on both sides of and parallel to the discharge channels.

6. An arrangement as defined in claim 5, wherein the distance of said bores from the discharge channels is greater than the distance of the discharge channels from one another.

7. An arrangement as defined in claim 2, wherein said arrangement is constituted by a plurality of writing heads provided in a row with each writing head including at least five writing units, each said writing unit including an extension means connecting the inner chamber portion to its connecting channel, wherein the connecting channels are arranged in a row and parallel to one another, said writing units have a common outer liquid chamber portion, and wherein said writing units lie in parallel rows perpendicular to said row of writing heads.

8. An arrangement as defined in claim 2, wherein the arrangement is constituted by a writing head which comprises two writing units, wherein said writing units have a common outer liquid chamber portion, and wherein the discharge channels of said writing units have different diameters.

9. An arrangement as defined in claim 8, wherein the discharge channels are oriented relative to each other to converge toward a common point.

10. An arrangement as defined in chaim 8, wherein the discharge channels are arranged parallel to one another.

11. An arrangement as defined in claim 2 wherein the arrangement is constituted by a writing head, and wherein said writing head comprises at least three writing units with fluid of different colors.

12. An arrangement as defined in claim 11, wherein the discharge channels of said writing units converge toward a common point.

13. An arrangement as defined in claim 11, wherein the discharge channels of said writing units lie in a row parallel to one another.

14. An arrangement as defined in claim 2, wherein the arrangement is constituted by a writing head; said arrangement further comprising a movable carriage, means mounting said writing head to said carriage, a paper bearing drum, said drum being so arranged that it rotates in front of said writing head, a picture bearing drum, a modulator, an amplifier and a photoscanner connected to said modulator, said writing head adapted to receive control signals via said modulator and said amplifier from said photoscanner which scans said picture from said picture bearing drum which rotates in synchronism with the respectuve position of the writing head on said paper bearing drum.

15. An arrangement as defined in claim 14, wherein said paper and said scanned picture are on a single drum, and wherein said writing head and photoscanner are disposed on the same carriage.

16. An arrangement as defined in claim 1, wherein the cross-sectional area of said discharge channel is so selected that the liquid is immediately stabilized therein when the fluid pressure in said chamber drops below a predetermined value due to the surface tension property of the liquid, and the direction of the liquid flow in the connecting channel is subsequently reversed, so that liquid is sucked in from said container through the outer chamber portion and said intake channel.

17. An arrangement as defined in claim 1, wherein the ratio of the diameter of said connecting channel to the diameter of said discharge channel lies between 1/4 and 4.

18. An arrangement as defined in claim 1, wherein the ratio of the distance between the two opposite ends of said discharge and connecting channels to the diameter of said discharge channel lies between 1/4 and 4.

19. An arrangement as defined in claim 1, wherein said pressure producing means comprises a movable membrane and a piezoelectric crystal, said movable membrane being adapted to be influenced by said crystal to produce a reduction in the volume of said chamber.