EP0765242B1 - Cartouche d'encre liquide mise sous pression, destinee a des imprimantes a forces coincidentes - Google Patents

Cartouche d'encre liquide mise sous pression, destinee a des imprimantes a forces coincidentes Download PDF

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Publication number
EP0765242B1
EP0765242B1 EP96912692A EP96912692A EP0765242B1 EP 0765242 B1 EP0765242 B1 EP 0765242B1 EP 96912692 A EP96912692 A EP 96912692A EP 96912692 A EP96912692 A EP 96912692A EP 0765242 B1 EP0765242 B1 EP 0765242B1
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Prior art keywords
ink
drop
nozzles
printing
temperature
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German (de)
English (en)
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EP0765242A1 (fr
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Kia c/o Eastman Kodak Company SILVERBROOK
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Eastman Kodak Co
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Eastman Kodak Co
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/17—Ink jet characterised by ink handling
    • B41J2/175—Ink supply systems ; Circuit parts therefor
    • B41J2/17503—Ink cartridges
    • B41J2/17513—Inner structure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/17—Ink jet characterised by ink handling
    • B41J2/175—Ink supply systems ; Circuit parts therefor
    • B41J2/17503—Ink cartridges
    • B41J2/17556—Means for regulating the pressure in the cartridge

Definitions

  • the present invention is in the field of computer controlled printing devices.
  • the field is removable ink cartridges for DOD liquid ink printers which require a positive ink pressure.
  • Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing.
  • ink jet printing mechanisms Many types have been invented. These can be categorized as either continuous ink jet (CIJ) or drop on demand (DOD) ink jet. Continuous ink jet printing dates back to at least 1929: Hansell, US Pat. No. 1,941,001.
  • Sweet et al US Pat. No. 3,373,437, 1967 discloses an array of continuous ink jet nozzles where ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection CIJ, and is used by several manufacturers, including Elmjet and Scitex.
  • Hertz et al US Pat. No. 3,416,153, 1966 discloses a method of achieving variable optical density of printed spots in CIJ printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture. This technique is used in ink jet printers manufactured by Iris Graphics.
  • Kyser et al US Pat. No. 3,946,398, 1970 discloses a DOD ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand.
  • Many types of piezoelectric drop on demand printers have subsequently been invented, which utilize piezoelectric crystals in bend mode, push mode, shear mode, and squeeze mode.
  • Piezoelectric DOD printers have achieved commercial success using hot melt inks (for example, Tektronix and Dataproducts printers), and at image resolutions up to 720 dpi for home and office printers (Seiko Epson).
  • Piezoelectric DOD printers have an advantage in being able to use a wide range of inks.
  • piezoelectric printing mechanisms usually require complex high voltage drive circuitry and bulky piezoelectric crystal arrays, which are disadvantageous in regard to manufacturability and performance.
  • Endo et al GB Pat. No. 2,007,162, 1979 discloses an electrothermal DOD ink jet printer which applies a power pulse to an electrothermal transducer (heater) which is in thermal contact with ink in a nozzle.
  • the heater rapidly heats water based ink to a high temperature, whereupon a small quantity of ink rapidly evaporates, forming a bubble.
  • the formation of these bubbles results in a pressure wave which cause drops of ink to be ejected from small apertures along the edge of the heater substrate.
  • BubblejetTM trademark of Canon K.K. of Japan
  • Thermal Ink Jet printing typically requires approximately 20 ⁇ J over a period of approximately 2 ⁇ s to eject each drop.
  • the 10 Watt active power consumption of each heater is disadvantageous in itself and also necessitates special inks, complicates the driver electronics and precipitates deterioration of heater elements.
  • U.S. Patent No. 4,275,290 discloses a system wherein the coincident address of predetermined print head nozzles with heat pulses and hydrostatic pressure, allows ink to flow freely to spacer-separated paper, passing beneath the print head.
  • U.S. Patent Nos. 4,737,803; 4,737,803 and 4,748,458 disclose ink jet recording systems wherein the coincident address of ink in print head nozzles with heat pulses and an electrostatically attractive field cause ejection of ink drops to a print sheet.
  • the printing mechanism is based on a new printing principle called "Liquid Ink Fault Tolerant” (LIFI) Drop on Demand printing
  • Figure 1(a) shows a simplified block schematic diagram of one exemplary printing apparatus according to the present invention.
  • Figure 1(b) shows a cross section of one variety of nozzle tip in accordance with the invention.
  • Figures 2(a) to 2(f) show fluid dynamic simulations of drop selection.
  • Figure 3(a) shows a finite element fluid dynamic simulation of a nozzle in operation according to an embodiment of the invention.
  • Figure 3(b) shows successive meniscus positions during drop selection and separation.
  • Figure 3(c) shows the temperatures at various points during a drop selection cycle.
  • Figure 3(d) shows measured surface tension versus temperature curves for various ink additives.
  • Figure 3(e) shows the power pulses which are applied to the nozzle heater to generate the temperature curves of figure 3(c)
  • Figure 4 shows a block schematic diagram of print head drive circuitry for practice of the invention.
  • Figure 5 shows projected manufacturing yields for an A4 page width color print head embodying features of the invention, with and without fault tolerance.
  • Figure 6 shows a generalized block diagram of a printing system using a print head
  • Figure 7 shows a schematic view of an ink cartridge and receptacle.
  • Figure 8 shows an exploded perspective view of a four color ink cartridge.
  • Figure 9 shows an exploded view of an ink channel assembly for a four color print head.
  • Figure 10 shows an exploded perspective view of a four color ink and paper cartridge.
  • the invention constitutes a drop-on-demand printing mechanism wherein the means of selecting drops to be printed produces a difference in position between selected drops and drops which are not selected, but which is insufficient to cause the ink drops to overcome the ink surface tension and separate from the body of ink, and wherein an alternative means is provided to cause separation of the selected drops from the body of ink.
  • the separation of drop selection means from drop separation means significantly reduces the energy required to select which ink drops are to be printed. Only the drop selection means must be driven by individual signals to each nozzle.
  • the drop separation means can be a field or condition applied simultaneously to all nozzles.
  • the drop selection means may be chosen from, but is not limited to, the following list:
  • the drop separation means may be chosen from, but is not limited to, the following list:
  • DOD printing technology targets shows some desirable characteristics of drop on demand printing technology.
  • the table also lists some methods by which some embodiments described herein, or in other of my related applications, provide improvements over the prior art.
  • DOD printing technology targets Target Method of achieving improvement over prior art High speed operation Practical, low cost, pagewidth printing heads with more than 10,000 nozzles.
  • Monolithic A4 pagewidth print heads can be manufactured using standard 300 mm (12") silicon wafers High image quality High resolution (800 dpi is sufficient for most applications), six color process to reduce image noise Full color operation Halftoned process color at 800 dpi using stochastic screening Ink flexibility Low operating ink temperature and no requirement for bubble formation Low power requirements Low power operation results from drop selection means not being required to fully eject drop Low cost Monolithic print head without aperture plate, high manufacturing yield, small number of electrical connections, use of modified existing CMOS manufacturing facilities High manufacturing yield Integrated fault tolerance in printing head High reliability Integrated fault tolerance in printing head. Elimination of cavitation and kogation. Reduction of thermal shock.
  • Shift registers, control logic, and drive circuitry can be integrated on a monolithic print head using standard CMOS processes Use of existing VLSI manufacturing facilities CMOS compatibility. This can be achieved because the heater drive power is less is than 1% of Thermal Ink Jet heater drive power Electronic collation A new page compression system which can achieve 100:1 compression with insignificant image degradation, resulting in a compressed data rate low enough to allow real-time printing of any combination of thousands of pages stored on a low cost magnetic disk drive.
  • TIJ thermal ink jet
  • piezoelectric ink jet systems a drop velocity of approximately 10 meters per second is preferred to ensure that the selected ink drops overcome ink surface tension, separate from the body of the ink, and strike the recording medium.
  • These systems have a very low efficiency of conversion of electrical energy into drop kinetic energy.
  • the efficiency of TIJ systems is approximately 0.02%).
  • the drive circuits for piezoelectric ink jet heads must either switch high voltages, or drive highly capacitive loads.
  • the total power consumption of pagewidth TIJ printheads is also very high.
  • An 800 dpi A4 full color pagewidth TIJ print head printing a four color black image in one second would consume approximately 6 kW of electrical power, most of which is converted to waste heat. The difficulties of removal of this amount of heat precludes the production of low cost, high speed, high resolution compact pagewidth TIJ systems.
  • One important feature of embodiments of the invention is a means of significantly reducing the energy required to select which ink drops are to be printed. This is achieved by separating the means for selecting ink drops from the means for ensuring that selected drops separate from the body of ink and form dots on the recording medium. Only the drop selection means must be driven by individual signals to each nozzle.
  • the drop separation means can be a field or condition applied simultaneously to all nozzles.
  • Drop selection means shows some of the possible means for selecting drops in accordance with the invention.
  • the drop selection means is only required to create sufficient change in the position of selected drops that the drop separation means can discriminate between selected and unselected drops.
  • Drop selection means Method Advantage Limitation 1. Electrothermal reduction of surface tension of pressurized ink Low temperature increase and low drop selection energy. Can be used with many ink types. Simple fabrication. CMOS drive circuits can be fabricated on same substrate Requires ink pressure regulating mechanism. Ink surface tension must reduce substantially as temperature increases 2. Electrothermal reduction of ink viscosity, combined with oscillating ink pressure Medium drop selection energy, suitable for hot melt and oil based inks. Simple fabrication.
  • CMOS drive circuits can be fabricated on same substrate Requires ink pressure oscillation mechanism. Ink must have a large decrease in viscosity as temperature increases 3. Electrothermal bubble generation, with insufficient bubble volume to cause drop ejection Well known technology, simple fabrication, bipolar drive circuits can be fabricated on same substrate High drop selection energy, requires water based ink, problems with kogation, cavitation, thermal stress 4. Piezoelectric, with insufficient volume change to cause drop ejection Many types of ink base can be used High manufacturing cost, incompatible with integrated circuit processes, high drive voltage, mechanical complexity, bulky 5. Electrostatic attraction with one electrode per nozzle Simple electrode fabrication Nozzle pitch must be relatively large. Crosstalk between adjacent electric fields. Requires high voltage drive circuits
  • the preferred drop selection means for water based inks is method 1: "Electrothermal reduction of surface tension of pressurized ink”.
  • This drop selection means provides many advantages over other systems, including; low power operation (approximately 1% of TIJ), compatibility with CMOS VLSI chip fabrication, low voltage operation (approx. 10 V), high nozzle density, low temperature operation, and wide range of suitable ink formulations.
  • the ink must exhibit a reduction in surface tension with increasing temperature.
  • the preferred drop selection means for hot melt or oil based inks is method 2: "Electrothermal reduction of ink viscosity, combined with oscillating ink pressure".
  • This drop selection means is particularly suited for use with inks which exhibit a large reduction of viscosity with increasing temperature, but only a small reduction in surface tension. This occurs particularly with non-polar ink carriers with relatively high molecular weight. This is especially applicable to hot melt and oil based inks.
  • Drop separation means shows some of the possible methods for separating selected drops from the body of ink, and ensuring that the selected drops form dots on the printing medium.
  • the drop separation means discriminates between selected drops and unselected drops to ensure that unselected drops do not form dots on the printing medium.
  • Drop separation means Means Advantage Limitation 1. Electrostatic attraction Can print on rough surfaces, simple implementation Requires high voltage power supply 2. AC electric field Higher field strength is possible than electrostatic, operating margins can be increased, ink pressure reduced, and dust accumulation is reduced Requires high voltage AC power supply synchronized to drop ejection phase. Multiple drop phase operation is difficult 3.
  • Proximity print head in close proximity to, but not touching, recording medium
  • Very small spot sizes can be achieved. Very low power dissipation.
  • Transfer Proximity print head is in dose proximity to a transfer roller or belt Very small spot sizes can be achieved, very low power dissipation, high accuracy, can print on rough paper Not compact due to size of transfer roller or transfer belt. 5.
  • Proximity with oscillating ink pressure Useful for hot melt inks using viscosity reduction drop selection method, reduces possibility of nozzle clogging, can use pigments instead of dyes Requires print medium to be very close to print head surface, not suitable for rough print media.
  • Requires ink pressure oscillation apparatus Magnetic attraction Can print on rough surfaces. Low power if permanent magnets are used Requires uniform high magnetic field strength, requires magnetic ink
  • the preferred drop separation means depends upon the intended use. For most applications, method 1: “Electrostatic attraction”, or method 2: “AC electric field” are most appropriate. For applications where smooth coated paper or film is used, and very high speed is not essential, method 3: “Proximity” may be appropriate. For high speed, high quality systems, method 4: “Transfer proximity” can be used. Method 6: “Magnetic attraction” is appropriate for portable printing systems where the print medium is too rough for proximity printing, and the high voltages required for electrostatic drop separation are undesirable. There is no clear 'best' drop separation means which is applicable to all circumstances.
  • FIG. 1 A simplified schematic diagram of one preferred printing system according to the invention appears in Figure 1(a).
  • An image source 52 may be raster image data from a scanner or computer, or outline image data in the form of a page description language (PDL), or other forms of digital image representation.
  • This image data is converted to a pixel-mapped page image by the image processing system 53.
  • This may be a raster image processor (RIP) in the case of PDL image data, or may be pixel image manipulation in the case of raster image data.
  • Continuous tone data produced by the image processing unit 53 is halftoned.
  • Halftoning is performed by the Digital Halftoning unit 54.
  • Halftoned bitmap image data is stored in the image memory 72.
  • the image memory 72 may be a full page memory, or a band memory.
  • Heater control circuits 71 read data from the image memory 72 and apply time-varying electrical pulses to the nozzle heaters (103 in figure 1(b)) that are part of the print head 50. These pulses are applied at an appropriate time, and to the appropriate nozzle, so that selected drops will form spots on the recording medium 51 in the appropriate position designated by the data in the image memory 72.
  • the recording medium 51 is moved relative to the head 50 by a paper transport system 65, which is electronically controlled by a paper transport control system 66, which in turn is controlled by a microcontroller 315.
  • the paper transport system shown in figure 1(a) is schematic only, and many different mechanical configurations are possible. In the case of pagewidth print heads, it is most convenient to move the recording medium 51 past a stationary head 50. However, in the case of scanning print systems, it is usually most convenient to move the head 50 along one axis (the sub-scanning direction) and the recording medium 51 along the orthogonal axis (the main scanning direction), in a relative raster motion.
  • the microcontroller 315 may also control the ink pressure regulator 63 and the heater control circuits 71.
  • ink is contained in an ink reservoir 64 under pressure.
  • the ink pressure In the quiescent state (with no ink drop ejected), the ink pressure is insufficient to overcome the ink surface tension and eject a drop.
  • a constant ink pressure can be achieved by applying pressure to the ink reservoir 64 under the control of an ink pressure regulator 63.
  • the ink pressure can be very accurately generated and controlled by situating the top surface of the ink in the reservoir 64 an appropriate distance above the head 50. This ink level can be regulated by a simple float valve (not shown).
  • ink is contained in an ink reservoir 64 under pressure, and the ink pressure is caused to oscillate.
  • the means of producing this oscillation may be a piezoelectric actuator mounted in the ink channels (not shown).
  • the ink is distributed to the back surface of the head 50 by an ink channel device 75.
  • the ink preferably flows through slots and/or holes etched through the silicon substrate of the head 50 to the front surface, where the nozzles and actuators are situated.
  • the nozzle actuators are electrothermal heaters.
  • an external field 74 is required to ensure that the selected drop separates from the body of the ink and moves towards the recording medium 51.
  • a convenient external field 74 is a constant electric field, as the ink is easily made to be electrically conductive.
  • the paper guide or platen 67 can be made of electrically conductive material and used as one electrode generating the electric field.
  • the other electrode can be the head 50 itself.
  • Another embodiment uses proximity of the print medium as a means of discriminating between selected drops and unselected drops.
  • Figure 1(b) is a detail enlargement of a cross section of a single microscopic nozzle tip embodiment of the invention, fabricated using a modified CMOS process.
  • the nozzle is etched in a substrate 101, which may be silicon, glass, metal, or any other suitable material. If substrates which are not semiconductor materials are used, a semiconducting material (such as amorphous silicon) may be deposited on the substrate, and integrated drive transistors and data distribution circuitry may be formed in the surface semiconducting layer.
  • a semiconducting material such as amorphous silicon
  • SCS Single crystal silicon
  • the nozzle is of cylindrical form, with the heater 103 forming an annulus.
  • the nozzle tip 104 is formed from silicon dioxide layers 102 deposited during the fabrication of the CMOS drive circuitry.
  • the nozzle tip is passivated with silicon nitride.
  • the protruding nozzle tip controls the contact point of the pressurized ink 100 on the print head surface.
  • the print head surface is also hydrophobized to prevent accidental spread of ink across the front of the print head.
  • nozzle embodiments of the invention may vary in shape, dimensions, and materials used.
  • Monolithic nozzles etched from the substrate upon which the heater and drive electronics are formed have the advantage of not requiring an orifice plate.
  • the elimination of the orifice plate has significant cost savings in manufacture and assembly.
  • Recent methods for eliminating orifice plates include the use of 'vortex' actuators such as those described in Domoto et al US Pat. No. 4,580,158, 1986, assigned to Xerox, and Miller et al US Pat. No. 5,371,527, 1994 assigned to Hewlett-Packard. These, however are complex to actuate, and difficult to fabricate.
  • the preferred method for elimination of orifice plates for print heads of the invention is incorporation of the orifice into the actuator substrate.
  • This type of nozzle may be used for print heads using various techniques for drop separation.
  • Figure 2 shows the results of energy transport and fluid dynamic simulations performed using FIDAP, a commercial fluid dynamic simulation software package available from Fluid Dynamics Inc., of Illinois, USA.
  • FIDAP Fluid Dynamics Inc.
  • This simulation is of a thermal drop selection nozzle embodiment with a diameter of 8 ⁇ m, at an ambient temperature of 30°C.
  • the total energy applied to the heater is 276 nJ, applied as 69 pulses of 4 nJ each.
  • the ink pressure is 10 kPa above ambient air pressure, and the ink viscosity at 30°C is 1.84 cPs.
  • the ink is water based, and includes a sol of 0.1% palmitic acid to achieve an enhanced decrease in surface tension with increasing temperature.
  • a cross section of the nozzle tip from the central axis of the nozzle to a radial distance of 40 ⁇ m is shown.
  • Heat flow in the various materials of the nozzle including silicon, silicon nitride, amorphous silicon dioxide, crystalline silicon dioxide, and water based ink are simulated using the respective densities, heat capacities, and thermal conductivities of the materials.
  • the time step of the simulation is 0.1 ⁇ s.
  • Figure 2(a) shows a quiescent state, just before the heater is actuated. An equilibrium is created whereby no ink escapes the nozzle in the quiescent state by ensuring that the ink pressure plus external electrostatic field is insufficient to overcome the surface tension of the ink at the ambient temperature. In the quiescent state, the meniscus of the ink does not protrude significantly from the print head surface, so the electrostatic field is not significantly concentrated at the meniscus.
  • Figure 2(b) shows thermal contours at 5°C intervals 5 ⁇ s after the start of the heater energizing pulse.
  • the heater When the heater is energized, the ink in contact with the nozzle tip is rapidly heated. The reduction in surface tension causes the heated portion of the meniscus to rapidly expand relative to the cool ink meniscus. This drives a convective flow which rapidly transports this heat over part of the free surface of the ink at the nozzle tip. It is necessary for the heat to be distributed over the ink surface, and not just where the ink is in contact with the heater. This is because viscous drag against the solid heater prevents the ink directly in contact with the heater from moving.
  • Figure 2(c) shows thermal contours at 5°C intervals 10 ⁇ s after the start of the heater energizing pulse.
  • the increase in temperature causes a decrease in surface tension, disturbing the equilibrium of forces. As the entire meniscus has been heated, the ink begins to flow.
  • Figure 2(d) shows thermal contours at 5°C intervals 20 ⁇ s after the start of the heater energizing pulse.
  • the ink pressure has caused the ink to flow to a new meniscus position, which protrudes from the print head.
  • the electrostatic field becomes concentrated by the protruding conductive ink drop.
  • Figure 2(e) shows thermal contours at 5°C intervals 30 ⁇ s after the start of the heater energizing pulse, which is also 6 ⁇ s after the end of the heater pulse, as the heater pulse duration is 24 ⁇ s.
  • the nozzle tip has rapidly cooled due to conduction through the oxide layers, and conduction into the flowing ink.
  • the nozzle tip is effectively 'water cooled' by the ink. Electrostatic attraction causes the ink drop to begin to accelerate towards the recording medium. Were the heater pulse significantly shorter (less than 16 ⁇ s in this case) the ink would not accelerate towards the print medium, but would instead return to the nozzle.
  • Figure 2(f) shows thermal contours at 5°C intervals 26 ⁇ s after the end of the heater pulse.
  • the temperature at the nozzle tip is now less than 5°C above ambient temperature. This causes an increase in surface tension around the nozzle tip.
  • the rate at which the ink is drawn from the nozzle exceeds the viscously limited rate of ink flow through the nozzle, the ink in the region of the nozzle tip 'necks', and the selected drop separates from the body of ink.
  • the selected drop then travels to the recording medium under the influence of the external electrostatic field.
  • the meniscus of the ink at the nozzle tip then returns to its quiescent position, ready for the next heat pulse to select the next ink drop.
  • One ink drop is selected, separated and forms a spot on the recording medium for each heat pulse. As the heat pulses are electrically controlled, drop on demand ink jet operation can be achieved.
  • Figure 3(a) shows successive meniscus positions during the drop selection cycle at 5 ⁇ s intervals, starting at the beginning of the heater energizing pulse.
  • Figure 3(b) is a graph of meniscus position versus time, showing the movement of the point at the centre of the meniscus.
  • the heater pulse starts 10 ⁇ s into the simulation.
  • Figure 3(c) shows the resultant curve of temperature with respect to time at various points in the nozzle.
  • the vertical axis of the graph is temperature, in units of 100°C.
  • the horizontal axis of the graph is time, in units of 10 ⁇ s.
  • the temperature curve shown in figure 3(b) was calculated by FIDAP, using 0.1 ⁇ s time steps.
  • the local ambient temperature is 30 degrees C. Temperature histories at three points are shown:
  • Figure 3(e) shows the power applied to the heater.
  • Optimum operation requires a sharp rise in temperature at the start of the heater pulse, a maintenance of the temperature a little below the boiling point of the ink for the duration of the pulse, and a rapid fall in temperature at the end of the pulse.
  • the average energy applied to the heater is varied over the duration of the pulse.
  • the variation is achieved by pulse frequency modulation of 0.1 ⁇ s sub-pulses, each with an energy of 4 nJ.
  • the peak power applied to the heater is 40 mW, and the average power over the duration of the heater pulse is 11.5 mW.
  • the sub-pulse frequency in this case is 5 Mhz. This can readily be varied without significantly affecting the operation of the print head.
  • a higher sub-pulse frequency allows finer control over the power applied to the heater.
  • a sub-pulse frequency of 13.5 Mhz is suitable, as this frequency is also suitable for minimizing the effect of radio frequency interference (RFI).
  • RFID radio frequency
  • ⁇ T is the surface tension at temperature T
  • k is a constant
  • T c is the critical temperature of the liquid
  • M is the molar mass of the liquid
  • x is the degree of association of the liquid
  • ⁇ is the density of the liquid.
  • surfactant is important.
  • water based ink for thermal ink jet printers often contains isopropyl alcohol (2-propanol) to reduce the surface tension and promote rapid drying.
  • Isopropyl alcohol has a boiling point of 82.4°C, lower than that of water.
  • a surfactant such as 1-Hexanol (b.p. 158°C) can be used to reverse this effect, and achieve a surface tension which decreases slightly with temperature.
  • a relatively large decrease in surface tension with temperature is desirable to maximize operating latitude.
  • a surface tension decrease of 20 mN/m over a 30°C temperature range is preferred to achieve large operating margins, while as little as 10mN/m can be used to achieve operation of the print head according to the present invention.
  • Inks can be prepared as a sol of small particles of a surfactant which melts in the desired operating temperature range.
  • surfactants include carboxylic acids with between 14 and 30 carbon atoms, such as: Name Formula m.p. Synonym Tetradecanoic acid CH 3 (CH 2 ) 12 COOH 58°C Myristic acid Hexadecanoic acid CH 3 (CH 2 ) 14 COOH 63°C Palmitic acid Octadecanoic acid CH 3 (CH 2 ) 15 COOH 71°C Stearic acid Eicosanoic acid CH 3 (CH 2 ) 16 COOH 77°C Arachidic acid Docosanoic acid CH 3 (CH 2 ) 20 COOH 80°C Behenic acid
  • the melting point of sols with a small particle size is usually slightly less than of the bulk material, it is preferable to choose a carboxylic acid with a melting point slightly above the desired drop selection temperature.
  • a good example is Arachidic acid.
  • carboxylic acids are available in high purity and at low cost.
  • the amount of surfactant required is very small, so the cost of adding them to the ink is insignificant
  • a mixture of carboxylic acids with slightly varying chain lengths can be used to spread the melting points over a range of temperatures. Such mixtures will typically cost less than the pure acid.
  • surfactant it is not necessary to restrict the choice of surfactant to simple unbranched carboxylic acids.
  • Surfactants with branched chains or phenyl groups, or other hydrophobic moieties can be used. It is also not necessary to use a carboxylic acid.
  • Many highly polar moieties are suitable for the hydrophilic end of the surfactant. It is desirable that the polar end be ionizable in water, so that the surface of the surfactant particles can be charged to aid dispersion and prevent flocculation. In the case of carboxylic acids, this can be achieved by adding an alkali such as sodium hydroxide or potassium hydroxide.
  • the surfactant sol can be prepared separately at high concentration, and added to the ink in the required concentration.
  • An example process for creating the surfactant sol is as follows:
  • the ink preparation will also contain either dye(s) or pigment(s), bactericidal agents, agents to enhance the electrical conductivity of the ink if electrostatic drop separation is used, humectants, and other agents as required.
  • Anti-foaming agents will generally not be required, as there is no bubble formation during the drop ejection process.
  • Inks made with anionic surfactant sols are generally unsuitable for use with cationic dyes or pigments. This is because the cationic dye or pigment may precipitate or flocculate with the anionic surfactant. To allow the use of cationic dyes and pigments, a cationic surfactant sol is required. The family of alkylamines is suitable for this purpose.
  • alkylamines are shown in the following table: Name Formula Synonym Hexadecylamine CH 3 (CH 2 ) 14 CH 2 NH 2 Palmityl amine Octadecylamine CH 3 (CH 2 ) 16 CH 2 NH 2 Stearyl amine Eicosylamine CH 3 (CH 2 ) 18 CH 2 NH 2 Arachidyl amine Docosylamine CH 3 (CH 2 ) 20 CH 2 NH 2 Behenyl amine
  • the method of preparation of cationic surfactant sols is essentially similar to that of anionic surfactant sols, except that an acid instead of an alkali is used to adjust the pH balance and increase the charge on the surfactant particles.
  • a pH of 6 using HCl is suitable.
  • a microemulsion is chosen with a phase inversion temperature (PIT) around the desired ejection threshold temperature. Below the PIT, the microemulsion is oil in water (O/W), and above the PIT the microemulsion is water in oil (W/O). At low temperatures, the surfactant forming the microemulsion prefers a high curvature surface around oil, and at temperatures significantly above the PIT, the surfactant prefers a high curvature surface around water. At temperatures close to the PIT, the microemulsion forms a continuous 'sponge' of topologically connected water and oil.
  • PIT phase inversion temperature
  • the surfactant prefers surfaces with very low curvature.
  • surfactant molecules migrate to the ink/air interface, which has a curvature which is much less than the curvature of the oil emulsion. This lowers the surface tension of the water.
  • the microemulsion changes from O/W to W/O, and therefore the ink/air interface changes from water/air to oil/air.
  • the oil/air interface has a lower surface tension.
  • water is a suitable polar solvent.
  • different polar solvents may be required.
  • polar solvents with a high surface tension should be chosen, so that a large decrease in surface tension is achievable.
  • the surfactant can be chosen to result in a phase inversion temperature in the desired range.
  • surfactants of the group poly(oxyethylene)alkylphenyl ether ethoxylated alkyl phenols, general formula: C n H 2n+1 C 4 H 6 (CH 2 CH 2 O) m OH
  • the hydrophilicity of the surfactant can be increased by increasing m, and the hydrophobicity can be increased by increasing n. Values of m of approximately 10, and n of approximately 8 are suitable.
  • Synonyms include Octoxynol-10, PEG-10 octyl phenyl ether and POE (10) octyl phenyl ether
  • the HLB is 13.6, the melting point is 7°C, and the cloud point is 65°C.
  • ethoxylated alkyl phenols include those listed in the following table: Trivial name Formula HLB Cloud point Nonoxynol-9 C 9 H 19 C 4 H 6 (CH 2 CH 2 O) -9 OH 13 54°C Nonoxynol-10 C 9 H 19 C 4 H 6 (CH 2 CH 2 O) -10 OH 13.2 62°C Nonoxynol-11 C 9 H 19 C 4 H 6 (CH 2 CH 2 O) -11 OH 13.8 72°C Nonoxynol-12 C 9 H 19 C 4 H 6 (CH 2 CH 2 O) -12 OH 14.5 81°C Octoxynol-9 C 8 H 17 C 4 H 6 (CH 2 CH 2 O) -9 OH 12.1 61°C Octoxynol-10 C 8 H 17 C 4 H 6 (CH 2 CH 2 O) -10 OH 13.6 65°C Octoxynol-12 C 8 H 17 C 4 H 6 (CH 2 CH 2 O) -12 OH 14.6 88°C Dodoxynol-10 C 12 H 25
  • Microemulsion based inks have advantages other than surface tension control:
  • Oil in water mixtures can have high oil contents - as high as 40% - and still form O/W microemulsions. This allows a high dye or pigment loading.
  • the ninth combination is useful for printing transparent coatings, UV ink, and selective gloss highlights.
  • This factor can be used to achieve an increased reduction in surface tension with increasing temperature. At ambient temperatures, only a portion of the surfactant is in solution. When the nozzle heater is turned on, the temperature rises, and more of the surfactant goes into solution, decreasing the surface tension.
  • a surfactant should be chosen with a Krafft point which is near the top of the range of temperatures to which the ink is raised. This gives a maximum margin between the concentration of surfactant in solution at ambient temperatures, and the concentration of surfactant in solution at the drop selection temperature.
  • the concentration of surfactant should be approximately equal to the CMC at the Krafft point. In this manner, the surface tension is reduced to the maximum amount at elevated temperatures, and is reduced to a minimum amount at ambient temperatures.
  • Non-ionic surfactants using polyoxyethylene (POE) chains can be used to create an ink where the surface tension falls with increasing temperature.
  • the POE chain is hydrophilic, and maintains the surfactant in solution.
  • the structured water around the POE section of the molecule is disrupted, and the POE section becomes hydrophobic.
  • the surfactant is increasingly rejected by the water at higher temperatures, resulting in increasing concentration of surfactant at the air/ink interface, thereby lowering surface tension.
  • the temperature at which the POE section of a nonionic surfactant becomes hydrophilic is related to the cloud point of that surfactant POE chains by themselves are not particularly suitable, as the cloud point is generally above 100°C
  • Polyoxypropylene (POP) can be combined with POE in POE/POP block copolymers to lower the cloud point of POE chains without introducing a strong hydrophobicity at low temperatures.
  • Desirable characteristics are a room temperature surface tension which is as high as possible, and a cloud point between 40°C and 100°C, and preferably between 60°C and 80°C.
  • Meroxapol [HO(CHCH 3 CH 2 O) x (CH 2 CH 2 O) y (CHCH 3 CH 2 O) z OH] varieties where the average x and z are approximately 4, and the average y is approximately 15 may be suitable.
  • the cloud point of POE surfactants is increased by ions that disrupt water structure (such as I - ), as this makes more water molecules available to form hydrogen bonds with the POE oxygen lone pairs.
  • the cloud point of POE surfactants is decreased by ions that form water structure (such as Cl - , OH - ), as fewer water molecules are available to form hydrogen bonds. Bromide ions have relatively little effect.
  • the ink composition can be 'tuned' for a desired temperature range by altering the lengths of POE and POP chains in a block copolymer surfactant, and by changing the choice of salts (e.g Cl - to Br - to I - ) that are added to increase electrical conductivity. NaCl is likely to be the best choice of salts to increase ink conductivity, due to low cost and non-toxicity. NaCl slightly lowers the cloud point of nonionic surfactants.
  • Figure 3(d) shows the measured effect of temperature on the surface tension of various aqueous preparations containing the following additives:
  • operation of an embodiment using thermal reduction of viscosity and proximity drop separation, in combination with hot melt ink is as follows.
  • solid ink Prior to operation of the printer, solid ink is melted in the reservoir 64.
  • the reservoir, ink passage to the print head, ink channels 75, and print head 50 are maintained at a temperature at which the ink 100 is liquid, but exhibits a relatively high viscosity (for example, approximately 100 cP).
  • the Ink 100 is retained in the nozzle by the surface tension of the ink.
  • the ink 100 is formulated so that the viscosity of the ink reduces with increasing temperature.
  • the ink pressure oscillates at a frequency which is an integral multiple of the drop ejection frequency from the nozzle.
  • the ink pressure oscillation causes oscillations of the ink meniscus at the nozzle tips, but this oscillation is small due to the high ink viscosity. At the normal operating temperature, these oscillations are of insufficient amplitude to result in drop separation.
  • the heater 103 When the heater 103 is energized, the ink forming the selected drop is heated, causing a reduction in viscosity to a value which is preferably less than 5 cP. The reduced viscosity results in the ink meniscus moving further during the high pressure part of the ink pressure cycle.
  • the recording medium 51 is arranged sufficiently close to the print head 50 so that the selected drops contact the recording medium 51, but sufficiently far away that the unselected drops do not contact the recording medium 51.
  • part of the selected drop freezes, and attaches to the recording medium.
  • ink pressure falls, ink begins to move back into the nozzle.
  • the body of ink separates from the ink which is frozen onto the recording medium.
  • the meniscus of the ink 100 at the nozzle tip then returns to low amplitude oscillation.
  • the viscosity of the ink increases to its quiescent level as remaining heat is dissipated to the bulk ink and print head.
  • One ink drop is selected, separated and forms a spot on the recording medium 51 for each heat pulse. As the heat pulses are electrically controlled, drop on demand ink jet operation can be achieved.
  • An objective of printing systems according to the invention is to attain a print quality which is equal to that which people are accustomed to in quality color publications printed using offset printing. This can be achieved using a print resolution of approximately 1,600 dpi. However, 1,600 dpi printing is difficult and expensive to achieve. Similar results can be achieved using 800 dpi printing, with 2 bits per pixel for cyan and magenta, and one bit per pixel for yellow and black This color model is herein called CC'MM'YK. Where high quality monochrome image printing is also required, two bits per pixel can also be used for black. This color model is herein called CC'MM'YKK'. Color models, halftoning, data compression, and real-time expansion systems suitable for use in systems of this invention and other printing systems are described in the following Australian patent specifications filed on 12 April 1995:
  • Printing apparatus and methods of this invention are suitable for a wide range of applications, including (but not limited to) the following: color and monochrome office printing, short run digital printing, high speed digital printing, process color printing, spot color printing, offset press supplemental printing, low cost printers using scanning print heads, high speed printers using pagewidth print heads, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printing, large format plotters, photographic duplication, printers for digital photographic processing, portable printers incorporated into digital 'instant' cameras, video printing, printing of PhotoCD images, portable printers for 'Personal Digital Assistants', wallpaper printing, indoor sign printing, billboard printing, and fabric printing.
  • the variation can be minimized by appropriate head design. In other cases, the variation can compensated by active circuitry.
  • the performance of nozzles is sensitive to the temperature and duration of thermal pulses applied to the nozzle tip.
  • the temperature at the nozzle tip will not rise fast enough for a drop to be ejected in the allotted time, or the ejected ink drop may be smaller than required. If too much energy is supplied to the heater, too much ink may be ejected, the ink may boil, and the energy used by the print head will be greater than required. This energy may then exceed the limit for self-cooling operation.
  • the amount of energy required to activate a nozzle can be determined by dynamic finite element analysis of the nozzle. This method can determine the required ejection energy of the nozzle under various static and dynamic environmental circumstances.
  • An optimum temperature profile for a head involves an instantaneous raising of the active region of the nozzle tip to the ejection temperature, maintenance of this region at the ejection temperature for the duration of the pulse, and instantaneous cooling of the region to the ambient temperature.
  • An optimum temperature profile for a print head involves an instantaneous raising of the active region of the nozzle tip to the ejection temperature, maintenance of this region at the ejection temperature for the duration of the pulse, and instantaneous cooling of the region to the ambient temperature.
  • Figure 4 is a block schematic diagram showing electronic operation of the print head driver circuits.
  • Figure 4 shows a block diagram for a system using an 800 dpi pagewidth print head which prints process color using the CC'MM'YK color model.
  • the print head 50 has a total of 79,488 nozzles, with 39,744 main nozzles and 39,744 redundant nozzles.
  • the main and redundant nozzles are divided into six colors, and each color is divided into 8 drive phases.
  • Each drive phase has a shift register which converts the serial data from a head control ASIC 400 into parallel data for enabling heater drive circuits.
  • Each shift register is composed of 828 shift register stages 217, the outputs of which are logically anded with phase enable signal by a nand gate 215.
  • the output of the nand gate 215 drives an inverting buffer 216, which in turn controls the drive transistor 201.
  • the drive transistor 201 actuates the electrothermal heater 200, which may be a heater 103 as shown in figure 1(b).
  • the enable pulse is active by a clock stopper 218, which is shown as a single gate for clarity, but is preferably any of a range of well known glitch free clock control circuits.
  • Stopping the clock of the shift register removes the requirement for a parallel data latch in the print head, but adds some complexity to the control circuits in the Head Control ASIC 400.
  • Data is routed to either the main nozzles or the redundant nozzles by the data router 219 depending on the state of the appropriate signal of the fault status bus.
  • the print head shown in figure 4 is simplified, and does not show various means of improving manufacturing yield, such as block fault tolerance.
  • Drive circuits for different configurations of print head can readily be derived from the apparatus disclosed herein.
  • Digital information representing patterns of dots to be printed on the recording medium is stored in the Page or Band memory 1513, which may be the same as the Image memory 72 in figure 1(a).
  • Data in 32 bit words representing dots of one color is read from the Page or Band memory 1513 using addresses selected by the address mux 417 and control signals generated by the Memory Interface 418.
  • These addresses are generated by Address generators 411, which forms part of the 'Per color circuits' 410, for which there is one for each of the six color components.
  • the addresses are generated based on the positions of the nozzles in relation to the print medium. As the relative position of the nozzles may be different for different print heads, the Address generators 411 are preferably made programmable.
  • the Address generators 411 normally generate the address corresponding to the position of the main nozzles. However, when faulty nozzles are present, locations of blocks of nozzles containing faults can be marked in the Fault Map RAM 412. The Fault Map RAM 412 is read as the page is printed. If the memory indicates a fault in the block of nozzles, the address is altered so that the Address generators 411 generate the address corresponding to the position of the redundant nozzles. Data read from the Page or Band memory 1513 is latched by the latch 413 and converted to four sequential bytes by the multiplexer 414. Timing of these bytes is adjusted to match that of data representing other colors by the FIFO 415.
  • This data is then buffered by the buffer 430 to form the 48 bit main data bus to the print head 50.
  • the data is buffered as the print head may be located a relatively long distance from the head control ASIC.
  • Data from the Fault Map RAM 412 also forms the input to the FIFO 416. The timing of this data is matched to the data output of the FIFO 415, and buffered by the buffer 431 to form the fault status bus.
  • the programmable power supply 320 provides power for the head 50.
  • the voltage of the power supply 320 is controlled by the DAC 313, which is part of a RAM and DAC combination (RAMDAC) 316.
  • the RAMDAC 316 contains a dual port RAM 317.
  • the contents of the dual port RAM 317 are programmed by the Microcontroller 315. Temperature is compensated by changing the contents of the dual port RAM 317. These values are calculated by the microcontroller 315 based on temperature sensed by a thermal sensor 300.
  • the thermal sensor 300 signal connects to the Analog to Digital Converter (ADC) 311.
  • ADC 311 is preferably incorporated in the Microcontroller 315.
  • the Head Control ASIC 400 contains control circuits for thermal lag compensation and print density.
  • Thermal lag compensation requires that the power supply voltage to the head 50 is a rapidly time-varying voltage which is synchronized with the enable pulse for the heater. This is achieved by programming the programmable power supply 320 to produce this voltage.
  • An analog time varying programming voltage is produced by the DAC 313 based upon data read from the dual port RAM 317. The data is read according to an address produced by the counter 403.
  • the counter 403 produces one complete cycle of addresses during the period of one enable pulse. This synchronization is ensured, as the counter 403 is clocked by the system clock 408, and the top count of the counter 403 is used to clock the enable counter 404.
  • the count from the enable counter 404 is then decoded by the decoder 405 and buffered by the buffer 432 to produce the enable pulses for the head 50.
  • the counter 403 may include a prescaler if the number of states in the count is less than the number of clock periods in one enable pulse. Sixteen voltage states are adequate to accurately compensate for the heater thermal lag. These sixteen states can be specified by using a four bit connection between the counter 403 and the dual port RAM 317. However, these sixteen states may not be linearly spaced in time. To allow non-linear timing of these states the counter 403 may also include a ROM or other device which causes the counter 403 to count in a non-linear fashion. Alternatively, fewer than sixteen states may be used.
  • the printing density is detected by counting the number of pixels to which a drop is to be printed ('on' pixels) in each enable period.
  • the 'on' pixels are counted by the On pixel counters 402.
  • the number of phases in a head depend upon the specific design. Four, eight, and sixteen are convenient numbers, though there is no requirement that the number of phases is a power of two.
  • the On Pixel Counters 402 can be composed of combinatorial logic pixel counters 420 which determine how many bits in a nibble of data are on. This number is then accumulated by the adder 421 and accumulator 422.
  • a latch 423 holds the accumulated value valid for the duration of the enable pulse.
  • the multiplexer 401 selects the output of the latch 423 which corresponds to the current enable phase, as determined by the enable counter 404.
  • the output of the multiplexer 401 forms part of the address of the dual port RAM 317. An exact count of the number of 'on' pixels is not necessary, and the most significant four bits of this count are adequate.
  • the dual port RAM 317 has an 8 bit address.
  • the dual port RAM 317 contains 256 numbers, which are in a two dimensional array. These two dimensions are time (for thermal lag compensation) and print density.
  • a third dimension - temperature - can be included.
  • the microcontroller 315 has sufficient time to calculate a matrix of 256 numbers compensating for thermal lag and print density at the current temperature. Periodically (for example, a few times a second), the microcontroller senses the current head temperature and calculates this matrix.
  • Thermal ink jet printers use the following fundamental operating principle.
  • a thermal impulse caused by electrical resistance heating results in the explosive formation of a bubble in liquid ink. Rapid and consistent bubble formation can be achieved by superheating the ink, so that sufficient heat is transferred to the ink before bubble nucleation is complete.
  • ink temperatures of approximately 280°C to 400°C are required.
  • the bubble formation causes a pressure wave which forces a drop of ink from the aperture with high velocity. The bubble then collapses, drawing ink from the ink reservoir to re-fill the nozzle.
  • Thermal ink jet printing has been highly successful commercially due to the high nozzle packing density and the use of well established integrated circuit manufacturing techniques.
  • thermal ink jet printing technology faces significant technical problems including multi-part precision fabrication, device yield, image resolution, 'pepper' noise, printing speed, drive transistor power, waste power dissipation, satellite drop formation, thermal stress, differential thermal expansion, kogation, cavitation, rectified diffusion, and difficulties in ink formulation.
  • Thermal ink jet printing has many of the advantages of thermal ink jet printing, and completely or substantially eliminates many of the inherent problems of thermal ink jet technology.
  • Thermal Ink-Jet Present Invention Drop selection mechanism Drop ejected by pressure wave caused by thermally induced bubble Choice of surface tension or viscosity reduction mechanisms Drop separation mechanism Same as drop selection mechanism Choice of proximity, electrostatic, magnetic, and other methods Basic ink carrier Water Water, microemulsion, alcohol, glycol, or hot melt Head construction Precision assembly of nozzle plate, ink channel, and substrate Monolithic Per copy printing cost Very high due to limited print head life and expensive inks Can be low due to permanent print heads and wide range of possible inks Satellite drop formation Significant problem which degrades image quality No satellite drop formation Operating ink temperature 280°C to 400°C (high temperature limits dye use and ink formulation) Approx.
  • yield The percentage of operational devices which are produced from a wafer run is known as the yield. Yield has a direct influence on manufacturing cost. A device with a yield of 5% is effectively ten times more expensive to manufacture than an identical device with a yield of 50%.
  • Figure 5 is a graph of wafer sort yield versus defect density for a monolithic full width color A4 head embodiment of the invention.
  • the head is 215 mm long by 5 mm wide.
  • the non fault tolerant yield 198 is calculated according to Murphy's method, which is a widely used yield prediction method. With a defect density of one defect per square cm, Murphy's method predicts a yield less than 1 %. This means that more than 99% of heads fabricated would have to be discarded. This low yield is highly undesirable, as the print head manufacturing cost becomes unacceptably high.
  • Figure 5 also includes a graph of non fault tolerant yield 197 which explicitly models the clustering of defects by introducing a defect clustering factor.
  • the defect clustering factor is not a controllable parameter in manufacturing, but is a characteristic of the manufacturing process.
  • the defect clustering factor for manufacturing processes can be expected to be approximately 2, in which case yield projections closely match Murphy's method.
  • a solution to the problem of low yield is to incorporate fault tolerance by including redundant functional units on the chip which are used to replace faulty functional units.
  • redundant sub-units In memory chips and most Wafer Scale Integration (WSI) devices, the physical location of redundant sub-units on the chip is not important. However, in printing heads the redundant sub-unit may contain one or more printing actuators. These must have a fixed spatial relationship to the page being printed. To be able to print a dot in the same position as a faulty actuator, redundant actuators must not be displaced in the non-scan direction. However, faulty actuators can be replaced with redundant actuators which are displaced in the scan direction. To ensure that the redundant actuator prints the dot in the same position as the faulty actuator, the data timing to the redundant actuator can be altered to compensate for the displacement in the scan direction.
  • the minimum physical dimensions of the head chip are determined by the width of the page being printed, the fragility of the head chip, and manufacturing constraints on fabrication of ink channels which supply ink to the back surface of the chip.
  • the minimum practical size for a full width, full color head for printing A4 size paper is approximately 215 mm x 5 mm. This size allows the inclusion of 100% redundancy without significantly increasing chip area, when using 1.5 ⁇ m CMOS fabrication technology. Therefore, a high level of fault tolerance can be included without significantly decreasing primary yield.
  • Figure 5 shows the fault tolerant sort yield 199 for a full width color A4 head which includes various forms of fault tolerance, the modeling of which has been included in the yield equation.
  • This graph shows projected yield as a function of both defect density and defect clustering. The yield projection shown in figure 5 indicates that thoroughly implemented fault tolerance can increase wafer sort yield from under 1% to more than 90% under identical manufacturing conditions. This can reduce the manufacturing cost by a factor of 100.
  • fault tolerance is highly recommended to improve yield and reliability of print heads containing thousands of printing nozzles, and thereby make pagewidth printing heads practical.
  • fault tolerance is not to be taken as an essential part of the present invention.
  • FIG. 6 A schematic diagram of a digital electronic printing system using a print head of this invention is shown in Figure 6.
  • This shows a monolithic printing head 50 printing an image 60 composed of a multitude of ink drops onto a recording medium 51.
  • This medium will typically be paper, but can also be overhead transparency film, cloth, or many other substantially flat surfaces which will accept ink drops.
  • the image to be printed is provided by an image source 52, which may be any image type which can be converted into a two dimensional array of pixels.
  • Typical image sources are image scanners, digitally stored images, images encoded in a page description language (PDL) such as Adobe Postscript, Adobe Postscript level 2, or Hewlett-Packard PCL 5, page images generated by a procedure-call based rasterizer, such as Apple QuickDraw, Apple Quickdraw GX, or Microsoft GDI, or text in an electronic form such as ASCII.
  • PDL page description language
  • This image data is then converted by an image processing system 53 into a two dimensional array of pixels suitable for the particular printing system. This may be color or monochrome, and the data will typically have between 1 and 32 bits per pixel, depending upon the image source and the specifications of the printing system.
  • the image processing system may be a raster image processor (RIP) if the source image is a page description, or may be a two dimensional image processing system if the source image is from a scanner.
  • RIP raster image processor
  • a halftoning system 54 is necessary. Suitable types of halftoning are based on dispersed dot ordered dither or error diffusion. Variations of these, commonly known as stochastic screening or frequency modulation screening are suitable.
  • the halftoning system commonly used for offset printing - clustered dot ordered dither - is not recommended, as effective image resolution is unnecessarily wasted using this technique.
  • the output of the halftoning system is a binary monochrome or color image at the resolution of the printing system according to the present invention.
  • the binary image is processed by a data phasing circuit 55 (which may be incorporated in a Head Control ASIC 400 as shown in figure 4) which provides the pixel data in the correct sequence to the data shift registers 56. Data sequencing is required to compensate for the nozzle arrangement and the movement of the paper.
  • the driver circuits 57 When the data has been loaded into the shift registers 56, it is presented in parallel to the heater driver circuits 57. At the correct time, the driver circuits 57 will electronically connect the corresponding heaters 58 with the voltage pulse generated by the pulse shaper circuit 61 and the voltage regulator 62. The heaters 58 heat the tip of the nozzles 59, affecting the physical characteristics of the ink.
  • Ink drops 60 escape from the nozzles in a pattern which corresponds to the digital impulses which have been applied to the heater driver circuits.
  • the pressure of the ink in the ink reservoir 64 is regulated by the pressure regulator 63.
  • Selected drops of ink drops 60 are separated from the body of ink by the chosen drop separation means, and contact the recording medium 51.
  • the recording medium 51 is continually moved relative to the print head 50 by the paper transport system 65. If the print head 50 is the full width of the print region of the recording medium 51, it is only necessary to move the recording medium 51 in one direction, and the print head 50 can remain fixed. If a smaller print head 50 is used, it is necessary to implement a raster scan system. This is typically achieved by scanning the print head 50 along the short dimension of the recording medium 51, while moving the recording medium 51 along its long dimension.
  • the current invention is a removable ink cartridge and cartridge connection system suitable for use with full color printing heads requiring pressurized ink.
  • the ink cartridge comprises a rigid box containing vessels of ink which include at least one flexible surface. For a monochrome ink cartridge, one ink vessel is sufficient. For a full color 'process' printing head, four ink vessels are used. These vessels contain cyan, magenta, yellow, and black ink, respectively. There is no requirement that the ink vessels are of the same size. As more black ink is typically consumed than colored ink, the black ink vessel may be larger than the other vessels.
  • the ink vessels include a means by which ink can flow from the vessels to the printing head when the ink cartridge is installed in the printing device.
  • the current invention uses a single pressurizing system to provide identical pressure to all four of the ink colors. This is achieved by pressurizing the fluid surrounding the ink vessels inside the ink cartridge. As the ink vessels include a flexible membrane, the pressure inside the ink cartridge is transmitted to the ink.
  • a four color ink cartridge has five fluid ports in the rigid box. There is one outlet port for ink of each of the four colors, and one inlet port for the pressurizing fluid. The ink pressure may be maintained by a pump connected to the pressurizing fluid inlet port.
  • the drop size in coincident forces print heads can be affected by the ink pressure.
  • the pressure should be regulated. This can be achieved by any of many prior art means, such as mechanical regulation, analog electronic regulation, or digital electronic regulation.
  • FIG 8 shows a schematic representation of a removable ink cartridge 770.
  • This ink cartridge is shown 'plugged into' a receptacle 782.
  • the cartridge shown is for a four color printer, so there are four ink vessels.
  • the cartridge contains a cyan ink vessel 772, a magenta ink vessel 773, a yellow ink vessel 774, and a black ink vessel 775.
  • Each ink vessel may be a fully flexible 'bag' constructed from a thin plastic or rubber membrane, or may be a rigid box with one or more flexible or movable surfaces.
  • the ink vessels are contained in a rigid box 771.
  • the box 771 may be constructed of injection molded plastic, metal, or other materials.
  • the box 771 must be completely sealed except for the four ink outlet ports 776 and the pressurizing fluid inlet port 783.
  • the properties of the pressurizing fluid surrounding the ink vessels is not critical. Suitable fluids include air, water, and oil. If fully flexible ink vessels are used, it is recommended that these vessels be held in place by some means to prevent rupture during handling of the ink cartridge. This may be achieved by embedding the ink vessels in a rigid or semi-rigid 'sponge like' material 781, through which the pressurizing fluid may flow. Expanded plastic foams such as polyurethane foam are suitable. Alternatively, separate compartments can be injection molded for each ink color, as shown in figure 9.
  • the receptacle 782 contains five fluid connectors. There are four fluid connectors 786 for the ink outlets, and one fluid connector 787 for the pressurizing fluid inlet These fluid connectors may be constructed as simple metal tubes with tapered ends. When the ink cartridge is inserted into the receptacle, the ink outlet fluid connectors pierce a seal (which may be resealable) to open a path for the ink from the ink vessels to the print head. The ink may flow to the print head via hoses. For a full color process printing ink cartridge with four ink colors, four hoses are required. These are a cyan ink hose 777, a magenta ink hose 778, a yellow ink hose 779, and a black ink hose 780.
  • the pressurizing fluid inlet 783 is connected to the pump 784 by the pressurizing fluid connector 787 when the ink cartridge is inserted in the receptacle 782.
  • the pressure is regulated by the pressure regulator 785.
  • the pressure regulator may operate by mechanical or electronic means. There are many prior art means of regulating fluid pressure.
  • FIG 9 is an exploded perspective diagram of one possible physical configuration of a removable ink cartridge 770.
  • the cartridge shown is for a four color printer, so there are four ink vessels.
  • the cartridge contains a cyan ink vessel 772, a magenta ink vessel 773, a yellow ink vessel 774, and a black ink vessel 775.
  • the ink vessel movable surface is a membrane 765 which is vacuum formed from a thin flexible plastic or latex material.
  • the ink vessels are contained in a rigid injection molded plastic box, which is formed in two parts, a body 760 and a lid 761. During manufacture, the flexible membrane is placed in the body of the box, and filled with ink of the four colors. The lid 761 is then ultrasonically welded onto the body 760.
  • the box is completely sealed except for the four ink outlet ports 776 and the pressurizing fluid inlet port 783.
  • a channel 766 connects all four compartments to the one pressurizing fluid inlet port. Ridges 763 serve both to accurately locate the flexible membrane 765 and to provide contact between the box body 760 and box lid 761 for ultrasonic welding.
  • the box can also have 'polarizing' ridges 762 to prevent accidental insertion the wrong way around.
  • the four ink outlet ports 776 can have porous inserts to prevent ink escaping during handling.
  • the pressurizing fluid inlet port 783 does not require this porous insert.
  • This configuration can be manufactured at low cost with injection molded components. Machinery to manufacture these ink cartridges in high volume can readily be designed.
  • Figure 9 is an exploded mechanical diagram of one possible configuration of ink supply for a full color head.
  • the full color head 740 contains four bands of nozzles which print ink of the four process printing colors. In this diagram, the head 740 is facing downwards, and the back surface of the head is visible.
  • the recommended method of manufacturing large monolithic heads includes a process for etching ink nozzle 'barrels' directly through the silicon substrate, forming tapered cylindrical holes. In this case, the ink can be supplied from the back surface of the head.
  • the head includes a band of 'cyan nozzles' 741 for printing cyan ink. Another band of 'magenta nozzles' 742 is for printing magenta ink. Another band of 'yellow nozzles' 743 is for printing yellow ink. Another band of 'black nozzles' 744 is for printing black ink.
  • the ink must be filtered to prevent particulate contaminants from entering the head. If any particles larger than the nozzle tip diameter enter the head, a nozzle may be blocked.
  • a suitable filter type is a 10 micron absolute membrane filter 745, which may be assembled onto the back surface of the monolithic head 740.
  • An ink channel molding 750 is provided to direct ink of the appropriate color to all of the nozzles.
  • the spacing between nozzles of different colors is approximately 1 mm, so the ink channel molding 750 may be fabricated using precision injection molding of plastic materials.
  • Plastic inner wall thicknesses of 0.5 mm and dimensional tolerances of 0.1 mm are adequate for this design, and can be achieved using currently available injection molding processes.
  • the ink channel molding has four channels for liquid ink flow.
  • the channel 751 supplies cyan ink to the cyan nozzles 741.
  • the channel 752 supplies magenta ink to the magenta nozzles 742.
  • the channel 753 supplies yellow ink to the yellow nozzles 743.
  • the channel 754 supplies black ink to the black nozzles 744.
  • the ink channel molding 750 can be fabricated using a simple two part injection molding die with a vertical line of draw.
  • An ink hose attachment molding 760 is provided to connect ink hoses containing ink of the appropriate colors to the ink channel molding 750.
  • the ink hose attachment molding has four channels for liquid ink flow.
  • the hose attachment 761 supplies cyan ink to the cyan ink channel 751.
  • the hose attachment 762 supplies magenta ink to the magenta ink channel 752.
  • the hose attachment 763 supplies yellow ink to the yellow ink channel 753.
  • the hose attachment 764 supplies black ink to the black ink channel 754.
  • the ink hose attachment molding 760 can be fabricated using a simple three part injection molding die with a horizontal line of draw (out of the paper in this diagram) and a vertical mover.
  • the two part ink channel assembly is designed to allow easy fabrication using standard injection molding techniques.
  • the purpose of the ink channel assembly is to provide a simple connection of 'macroscopic' ink hoses to the 'microscopic' ink nozzles.
  • ink cartridge it may be advantageous to combine the ink cartridge with a paper cartridge. This is especially the case for printers which do not use standard letter size or A4 size 'plain paper'.
  • video and photograph printers which may be designed to print on glossy paper which is 'photograph' sized (approximately 100 mm x 150 mm).
  • Figure 10 shows an example of the physical configuration of a paper and ink cartridge designed for photograph printing.
  • the cartridge holds a plurality of sheets of paper (for example, 24), along with four ink compartments.
  • the ink compartments hold sufficient ink of each color to print all of the sheets.
  • FIG. 7 This is an exploded perspective diagram of one possible physical configuration of a removable ink cartridge 770 which includes paper 768.
  • the cartridge shown is for a four color printer, so there are four ink vessels.
  • the ink vessel movable surface is a membrane 765 which is vacuum formed from a thin flexible plastic or latex material.
  • the ink vessels are contained in a rigid injection molded plastic box, which is formed in two parts, a body 760 and a lid 761. During manufacture, the flexible membrane is placed in the body of the box, and filled with ink of the four colors. The lid 761 is then ultrasonically welded onto the body 760.
  • ink cartridge Some other configurations of ink cartridge are:

Claims (4)

  1. Système d'impression à encre liquide à gouttes à la demande à forces coïncidentes du type comportant : une tête d'impression (50) munie d'une pluralité de buses d'émission de gouttes (59), un collecteur d'alimentation en encre (750) comportant un orifice d'entrée d'encre et un orifice de sortie reliés auxdites buses, un dispositif de mise en pression (784, 785) conçu pour fournir une pression positive, un récipient d'encre étanche vis-à-vis de l'atmosphère et comportant un orifice de sortie d'encre relié au collecteur d'alimentation en encre (750) et un orifice d'entrée de pression de commande relié au dispositif de mise en pression (784, 785), une alimentation en encre à l'intérieur dudit récipient, d'où il résulte qu'une pression de commande peut être appliquée à l'encre dans ledit collecteur et aux buses d'émission de gouttes par l'intermédiaire dudit récipient d'encre et
       un dispositif de sélection de gouttes qui adresse l'encre dans lesdites buses avec une force de sélection de décalage de ménisque, caractérisé par un dispositif de séparation de gouttes qui amène des masses d'encre à ménisques décalés à se séparer sous forme de gouttes et à se déplacer vers une région d'impression.
  2. Invention selon la revendication 1, caractérisée en outre en ce que le dispositif de mise en pression est conçu pour soumettre une encre du collecteur à une pression d'au moins 2 % au-dessus de la pression ambiante, au moins durant une sélection et une séparation de gouttes afin de former un ménisque avec une interface air/encre, et que le dispositif de sélection de gouttes peut être mis en oeuvre sur l'interface air/encre pour sélectionner des buses prédéterminées et pour engendrer une différence de position de ménisque entre l'encre dans des buses sélectionnées et l'encre dans des buses non sélectionnées.
  3. Invention selon la revendication 1, caractérisée en outre par un corps d'encre associé auxdites buses et formant une interface air/encre à chaque buse, le dispositif de sélection de gouttes est mis en oeuvre sur l'interface air/encre afin de sélectionner des buses prédéterminées et pour engendrer une différence de position de ménisque entre l'encre dans les buses sélectionnées et l'encre dans les buses non sélectionnées, et le dispositif de séparation de gouttes est conçu pour amener l'encre provenant de buses sélectionnées à se séparer sous forme de gouttes depuis le corps de l'encre, tout en permettant que de l'encre soit retenue dans des buses non sélectionnées,
       ledit moyen de sélection de gouttes étant capable de produire ladite différence de position de ménisque en l'absence dudit moyen de séparation de gouttes.
  4. Invention selon la revendication 1, caractérisée en outre en ce que : ladite encre de collecteur présente une diminution de tension superficielle d'au moins 10 mN/m sur une plage de températures de 30 °C, et que le dispositif de sélection de gouttes peut être mis en oeuvre sur une interface air/encre afin de sélectionner des buses prédéterminées et d'engendrer une différence de position de ménisque entre l'encre dans les buses sélectionnées et l'encre dans les buses non sélectionnées.
EP96912692A 1995-04-12 1996-04-09 Cartouche d'encre liquide mise sous pression, destinee a des imprimantes a forces coincidentes Expired - Lifetime EP0765242B1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
AUPN2320/95 1995-04-12
AUPN232095 1995-04-12
AUPN2320A AUPN232095A0 (en) 1995-04-12 1995-04-12 A removable pressurised liquid ink cartridge for lift printers
PCT/US1996/005017 WO1996032287A1 (fr) 1995-04-12 1996-04-09 Cartouche d'encre liquide mise sous pression, destinee a des imprimantes a forces coincidentes

Publications (2)

Publication Number Publication Date
EP0765242A1 EP0765242A1 (fr) 1997-04-02
EP0765242B1 true EP0765242B1 (fr) 2002-03-06

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EP96912692A Expired - Lifetime EP0765242B1 (fr) 1995-04-12 1996-04-09 Cartouche d'encre liquide mise sous pression, destinee a des imprimantes a forces coincidentes

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Country Link
EP (1) EP0765242B1 (fr)
JP (1) JPH10501770A (fr)
AU (1) AUPN232095A0 (fr)
DE (1) DE69619609T2 (fr)
WO (1) WO1996032287A1 (fr)

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* Cited by examiner, † Cited by third party
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US6036296A (en) * 1996-10-31 2000-03-14 Hewlett-Packard Company Fluid level detection apparatus and method for determining the volume of fluid in a container

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US4293865A (en) * 1978-04-10 1981-10-06 Ricoh Co., Ltd. Ink-jet recording apparatus
US4312009A (en) * 1979-02-16 1982-01-19 Smh-Adrex Device for projecting ink droplets onto a medium
JPS60210462A (ja) * 1984-04-05 1985-10-22 Fuji Xerox Co Ltd インクジエツト記録装置
US4737803A (en) * 1986-07-09 1988-04-12 Fuji Xerox Co., Ltd. Thermal electrostatic ink-jet recording apparatus
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JPS5945160A (ja) * 1982-09-07 1984-03-13 Konishiroku Photo Ind Co Ltd インクジエツト記録装置
JPS5959457A (ja) * 1982-09-29 1984-04-05 Konishiroku Photo Ind Co Ltd インクカ−トリツジおよび記録ヘツドの洗浄装置
JPS6027547A (ja) * 1983-07-26 1985-02-12 Canon Inc インクカ−トリツジ
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US4293865A (en) * 1978-04-10 1981-10-06 Ricoh Co., Ltd. Ink-jet recording apparatus
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WO1990014233A1 (fr) * 1989-05-26 1990-11-29 P.A. Consulting Services Limited Procede d'enregistrement a jet de liquide et appareil correspondant

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Also Published As

Publication number Publication date
AUPN232095A0 (en) 1995-05-04
EP0765242A1 (fr) 1997-04-02
DE69619609T2 (de) 2002-10-31
WO1996032287A1 (fr) 1996-10-17
DE69619609D1 (de) 2002-04-11
JPH10501770A (ja) 1998-02-17

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