Ink Distribution For Non-impact Printing Recorder

Abstract

A collapsible ink bag supplies ink at constant pressure through a manifold containing an air bubble trap, capable of venting, which manifold is connected in common to plural lines to a multiple orifice -- multiple transducer fluid wave printing head of a recorder. Constant static pressure in the ink supply is provided to avoid inadvertent ejection of ink through orifices of the nozzles. The manifold contains an air bubble and the manifold inlet line has a sufficiently low resistance to flow. Its source of ink supply is free to expand and contract, and the hydraulic resistance to fluid flow in the lines to the head is sufficiently high to eliminate cross talk of waves between separate orifices. Alternatively, a built in reservoir in the head has a single low resistance connection to the source of ink supply and high resistance lines connect it to the orifices.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to recorders and more particularly to markers having an ink supply to the markers. More particularly this invention relates to provision of a common ink supply for plural fluid wave markers with tapered cavities leading to their nozzles.

2. Description of the Prior Art

Prior matrix printers employing fluid pressure or shock waves to eject ink from selected ones of plural orifices in response to mechanical vibration of a diaphragm have employed central sources of ink with transducers located within the ink supply reservoir and with the orifices formed in the upper wall of the reservoir. Ejection of ink from a selected orifice is accomplished by placement of a transducer closely aligned with the corresponding orifice. Alternatively a separate ink supply is provided for a single orifice.

Patents considered include Hansell, U.S. Pat. No. 2,512,743; Welsh, U.S. Pat. No. 3,177,800; Naiman, U.S. Pat. No. 3,179,042; and Naiman, U.S. Pat. No. 3,211,088.

SUMMARY OF THE INVENTION

In accordance with this invention, a multiple orifice, fluid wave ink ejection recorder is provided. A printing head contains a plurality of tapered printing cavities. Each cavity has an orifice at the small end and a diaphragm actuator at the opposite end. A reservoir of ink is connected to each of said orifices by a passageway having a small diameter and a high impedance to fluid waves. The reservoir includes means for maintaining substantially constant fluid pressure in response to transmission of fluid waves through the passageways.

Preferably, the reservoir is connected to a substantially constant pressure source of ink.

Further, the means for maintaining substantially constant fluid pressure comprises a bubble chamber providing an air trap for absorbing pressure waves to reduce pressure fluctuations on the constant pressure source of ink.

In another aspect of this invention, the writing head includes a plurality of piezoelectric transducers secured to diaphragms and a plurality of tapered orifices having a diaphragm at one end and at the opposite end having a nozzle for writing. The head includes a plurality of high fluid-impedance passageways with each connected at one end to one of the orifices and coupled at the opposite end to the reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a plural orifice head recorder with a collapsible ink supply and manifold with additional elements omitted for convenience of illustration.

FIG. 2 is a partially sectional elevation of the recorder of FIG. 1, with elements sectioned along lines 2--2 in FIG. 1.

FIG. 3 is a sectional elevation of an alternative form of head with an internal manifold or reservoir.

FIG. 4 shows a sectional elevation of an alternative form of coupling between the ink cartridge and the ink supply line.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 an ink cartridge 10 is coupled through ink-supply line 11 to ink supply manifold 12 comprising a reservoir of ink for several nozzles 13 of a printing head 14.

PRINTING HEAD

The printing head 14 includes several piezoelectric crystal transducers 15, chambers 18, and passageways 19. Transducers 15 include ceramic crystals 20, diaphragms 17 and electrical leads 16 broken away for simplicity of illustration. Each crystal transducer 15, composed of a ceramic material, is affixed by cement to a brass disc diaphragm 17 to provide means for reducing the volume of chambers 18 in head 14 in response to application of direct current electrical energization pulses upon lines 16.

Each chamber 18 is part of a cavity 21 which tapers into a passageway 19 which terminates in a nozzle 13 with the nozzle 13 having the smallest inner diameter (I.D.). Preferably, about seven to 13 nozzles 13 spaced vertically and possibly staggered horizontally can be spaced within a 0.1 inch vertical spacing with slight lateral displacement and diameters of 0.001 - 0.006 inches.

The chambers 18 are supplied with ink via tubes 22 communicating from inside the head to the outside, connecting with lines 23 to the manifold 12. Lines 23 and manifold 12 provide clean, bubble free ink to the head 14.

The cavities 21 comprising chambers 18, passageways 19, and nozzles 13 are filled with ink of appropriate viscosity, and surface tension which when maintained at such a constant low fluid pressure that when the transducers 15 are inactive, no ink will escape from nozzles 13. On the other hand, when a transducer 15 is energized electrically, it generates a fluid wave which is propagated through the cavity's chamber 18, its passageway 19, and its nozzle 13 as well as the tube 22 connected to the cavity 21. As a result, when a short electrical square wave signal energizes the transducer the resultant fluid wave ejects some ink from the nozzle 13. The ink is pushed against the printing medium which is in this case paper 25, thereby wetting the paper 25. Preferably, the paper is about 0.002 and 0.008 inches from the nozzles 113. When the energizing voltage pulse is removed from the crystal 20, the diaphragm 17 retracts to its normal shape, thereby increasing the volume of chamber 18 to its normal volume and sucking ink back towards chamber 18 from tube 22, passageway 19, and nozzle 13. The suction in nozzle 13 causes the ink droplet in contact with paper 25 to break off while the remainder of the ink retracts towards passageway 19. This droplet leaves a dot of ink deposited on paper 25. An array of such dots (e.g. seven nozzles) can be used for matrix dot printing. Alternatively, the ink can be propelled from the nozzle 13 to paper spaced farther away. In the latter case, higher momentum of the fluid must be provided.

Supply tube 22 replenishes the depleted supply of ink to cavity 21. Note that the passageways 19 are curved to converge in order to allow space for the transducers 15 at one end of the passageways 19 and to maintain a small distance between the nozzles 13.

INK DISTRIBUTION SYSTEM

While head 14 includes only two cavities 21 in the drawings, for simplicity and clarity of illustration, it is intended to be representative of a practical application in which seven or eight, more or less, cavities 21 are provided. In such case an ink distribution system which is shared by all of the cavities becomes a practical necessity.

However, we have found that a common ink supply for a fluid wave printer poses problems because the waves generated by transducers 15 are transmitted through tubes 22, lines 23 and tubes 24 into manifold 12. A straightforward ink supply system would serve to couple such waves occasionally through the lines 23, etc. to other cavities, which can cause ink to be ejected from a nozzle 13 whose transducer 15 is not actuated. Such undesirable or spurious operation is referred to herein as cross talk.

The system of FIGS. 1 and 2 includes long, thin I.D. lines 23, e.g. I.D. 0.020 or 0.060 inches, which inhibit the flow of significant volumes of ink through lines 23 to a small volume and tend to minimize the amount of wave energy transmitted into manifold 12. Tubes 24 have an I.D. of only about 0.012 to 0.030 inches which adds resistance to flow.

In addition, manifold 12 includes an air bubble trap 26 at the top which operates to regulate pressure fluctuations within manifold 12. Thus, incompressible liquid pressure waves can be absorbed by the compression of the volume of the air in trap 26. In addition line 45 has a relatively large I.D. of 0.125 and is connected to a relatively low impedance constant pressure source of ink in an expandable or collapsible plastic ink bag 30. Additional ink in bag 30 will not reflect waves back, but will simply expand its volume temporarily. Thus the liquid wave will be diminished in its intensity or amplitude upon reflection from the air bubble in trap 26 and upon flow of ink up into bag 30 so that less energy will flow back to the lines 23. In general, if the manifold 12 includes means providing space or freedom for excess ink to move up away from lines 23 without admitting air, waves will not cause cross talk.

As a result cross talk is effectively prevented without use of any check valves.

Another function of air trap 26 is to accumulate and trap bubbles of air and to prevent air bubbles in the ink or the lines and manifold from passing through the system and into the head 14. Air accumulated in the trap, when excessive can be vented manually by partially unscrewing the cap 27 threadably coupled at the trap end of manifold 12 and sealed by 0 ring 28 to close trap 26, normally. Alternatively a float valve could be employed to control the volume of air in the air bubble.

FIG. 3 shows an alternative form of ink distribution system in which a manifold 30 is contained within the head 114. The manifold 30 is connected through very thin 0.005 inches diameter tubes 160, which are 0.125 long or as long as convenient. Preferably, the diameter to length relationship should be k = (Diameter).sub.4 /(Length). Tubes 160 connect to chambers 118 of cavities 121 each of which includes an orifice 119 and a nozzle 113. At the large end of each chamber 118 is included a transducer 115. In addition the large 0.125 inch diameter, short tube 122 is to be connected from manifold 30 to a constant pressure ink supply cartridge 10 (not shown) which will provide pressure regulation. What is important is that the resistance to flow of lines 160 be relatively much greater than the resistance of tube 122.

The head 14 or 114 can move (i.e. traverse across the paper 25 in order to print) where the paper platen or roller does not reciprocate in front of the print head. Head 114 requires only one hose to be connected to tube 122 rather than several hoses 23 connected to several tubes 22 as in FIGS. 1 and 2.

DISPOSABLE INK RESERVOIR

In the above system it is necessary that the static ink supply pressure be maintained close to a constant value in spite of the variation in the quantity of ink available from the source of supply so that the static pressure at nozzle 13 will be independent of the quantity of ink available.

In FIGS. 1 and 2, a disposable cartridge 10 includes a flexible ink bag 30 completely filled with ink hermetically sealed to protect the ink from air and dirt.

A central core or support 31 is contained within bag 30 and includes, extending below its base 32, a threaded coupling 33 passing through the bag 30. The base 32 of the support 31 comprises an annular flange which cooperates with gasket 34, below bag 30 and plate 35 below gasket 34, as well as cap 36 which threads onto coupling 33 and presses plate 35 up against base 32 to seal the flange, bag, gasket, and plate together. Coupling 33 extends through a hole in bag 30. The support 31 is generally cylindrical and hollow at 40 to provide a passageway for ink and needle 41. Vertical slots 37 permit ink between bag 30 and support 31 to reach hollow 40, even after bag 30 has emptied substantially and has collapsed upon the external walls of support 31.

The support 31 is provided for the purpose of preventing the bag 30 from collapsing vertically, in order to maintain a constant head of pressure of the ink in the manifold 12 as well as the rest of the system.

Between cap 36 and the bottom edge of coupling 33 is a medical or pharmaceutical elastomeric sealing membrane 42 adapted for self-sealing use with a hypodermic type of cannular needle 41 which is carried in base 38 upon which the cartridge is supported, with cap 36 inserted into receptacle hole 43 in base 38. Needle 41 extends through cylindrical coupling tube 44. A tubular line 45 is connected over the end of coupling tube 44 in sealed relationship therewith. Tubular line 45 is connected at its opposite end with its inner surface extending over the outer surface of the inlet tube 46 of manifold 12.

The upper end 47 of cannular needle 41 extends up into receptacle hole 43, but it is recessed sufficiently to minimize the probability of inadvertent injury to fingers of operatives employing these instrumentalities, when installing or removing a cartridge 10 or when a cartridge is absent from base 38 during machine maintenance, etc.

Manifestly, with this system, maintaining constant static ink supply pressure requires use of no moving parts other than the replaceable bag, subsequent to installation of the cartridge 10.

A transparent case 48 (with an air vent 49 for pressure equalization within the case) permits visual determination of the necessity for replacement of the cartridge 10.

A filter material can be placed over the support 31 or cage 31 to provide filtration before ink enters the hollow 40. Alternatively, the support 31 can be replaced by a filter material.

A cap is placed over the needle 47 when the cartridge 10 is removed for more than a short time to prevent air or dirt from entering the needle.

FIG. 4 shows an alternative way of providing coupling. Support 131 carries needle 141 with it base 50 within the hollow 140 of coupling 133 and the needles point extending down for insertion within the flexible, self-sealing connector on the end of flexible tubing 145.

Preferably a water base ink is employed, which is of medium surface tension, about 30-35 dynes/cm. The viscosity is low, in the order of 1-2 centipoise.

Example

The case 48 is rigid, plexiglass. Bag 30 is thin mylar of low permeability and high flexibility. The needle is stainless steel. The manifold and cap are plastic. The flexible hoses 23 are plasticized polyvinyl fluoride. The top of the ink bag 30 is about 1 1/2 inches higher than the nozzle.

Claims

What is claimed is:

1. A multiple orifice, multiple transducer, fluid wave ink ejection recorder including

a printing head with a plurality of tapered printing cavities,

each of said cavities having an orifice at the smaller end and a diaphragm actuator at the opposite end,

a reservoir of ink,

said reservoir being connected to each of said orifices by a passageway having a small diameter and a high impedance to fluid waves, said reservoir including means for maintaining substantially constant fluid pressure in response to transmission of fluid waves through said passageways.

2. Apparatus in accordance with claim 1 wherein said reservoir is connected to a substantially constant pressure source of ink.

3. Apparatus in accordance with claim 1 wherein said means for maintaining substantially constant fluid pressure comprises a bubble chamber providing an air trap for absorbing pressure waves to reduce pressure fluctuations.

4. A multiple orifice, multiple transducer, fluid wave ink ejection recorder including

a source of ink at a substantially constant pressure,

a reservoir of ink connected to said source of ink and including an air chamber providing pneumatic pressure regulation,

a writing head including a plurality of piezoelectric transducers secured to diaphragms, a plurality of tapered orifices having a said diaphragm at one end and at the opposite end having a nozzle for writing,

said head including a plurality of high fluid-impedance passageways each connected at one end to one of said orifices and coupled at the opposite end to said reservoir whereby cross talk of waves between orifices is substantially eliminated.