EP0765225A1 - Doublement des buses pour obtenir une tolerance aux defauts dans les tetes d'impression integrees - Google Patents

Doublement des buses pour obtenir une tolerance aux defauts dans les tetes d'impression integrees

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Publication number
EP0765225A1
EP0765225A1 EP96912651A EP96912651A EP0765225A1 EP 0765225 A1 EP0765225 A1 EP 0765225A1 EP 96912651 A EP96912651 A EP 96912651A EP 96912651 A EP96912651 A EP 96912651A EP 0765225 A1 EP0765225 A1 EP 0765225A1
Authority
EP
European Patent Office
Prior art keywords
printing
ink
acmators
nozzles
drop
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96912651A
Other languages
German (de)
English (en)
Inventor
Kia Silverbrook
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eastman Kodak Co
Original Assignee
Eastman Kodak Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0765225A1 publication Critical patent/EP0765225A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14451—Structure of ink jet print heads discharging by lowering surface tension of meniscus

Definitions

  • the present invention is in the field of computer controlled printing devices.
  • the field is fault tolerance for drop on demand (DOD) printing systems.
  • DOD drop on demand
  • 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. Many types of ink jet printing mechanisms have been invented.
  • 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 CU, and is used by several manufacturers, including Elmjet and Scitex. Hertz et al US Pat. No.
  • 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.
  • DOD ink jet printer which applies a power pulse to an electrothermal transducer
  • 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
  • Method and System describe new methods and apparatus that afford significant improvements toward overcoming the prior art problems discussed above.
  • Those inventions offer important advantages, e.g., in regard to drop size and placement accuracy, as to printing speeds attainable, as to power usage, as to durability and operative thermal stresses encountered and as to other printer performance characteristics, as well as in regard to manufacturability and the characteristics of useful inks.
  • One important purpose of the present invention is to further enhance the structures and methods described in those applications and thereby contribute to the advancement of printing technology.
  • One important aspect of the invention is to provide a fault tolerant printing system which allows improved manufacture yield and improved operative performance.
  • the present invention constitutes a fault tolerant printing apparatus comprising (a) a plurality of normally active printing actuators;
  • a plurality of redundant printing actuators having print capability correspondence to said normally active actuators; and (d) a means, responsive to said signaling means, for energizing a redundant printing actuator that corresponds to an ineffective, normally active printing actuator, under the control of the same image data that would normally control the energizing of the faulty printing actuator.
  • the printing actuators are coincident forces printing heads.
  • the printing actuators are thermal ink jet nozzles.
  • a further alternative preferred aspect of the invention is that the printing actuators are thermal wax printer actuators.
  • a further alternative preferred aspect of the invention is that the printing actuators are dye sublimation printer actuators.
  • a further alternative preferred aspect of the invention is that the printing actuators are heater elements that are part of a heater bar of a thermal paper printer.
  • a further alternative preferred aspect of the invention is that the normally active printing actuators and the redundant printing actuators are fabricated on a single substrate.
  • a further preferred aspect of the invention is that the normally active printing actuators are fabricated on a different substrate than the redundant printing actuators.
  • a further preferred aspect of the invention is that the number of the redundant printing actuators is equal to or greater than the number of normally active printing actuators.
  • a further preferred aspect of the invention is that the redundant printing actuators are offset from the normally active printing actuators in the scan direction, and are not offset in the non-scan direction more than ten times the spacing between the printing actuators in the non-scan direction.
  • 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 block diagram of a large print head with integrated drive circuitry.
  • Figure 8 shows a block diagram of a fault tolerant printing system using redundant actuators.
  • 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.
  • the drop separation means can be a field or condition applied simultaneously to all nozzles. 6/32263
  • 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.
  • 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 TU 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 TU 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.
  • 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 TD), 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: ' ⁇ lectrothermal 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.
  • the preferred drop separation means depends upon the intended use. For most applications, method 1: ' ⁇ lectrostatic 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
  • 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-vaiying electrical pulses to the nozzle heaters
  • 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 si con) may be deposited on the substrate, and integrated drive transistors and data distribution circuitry may be formed in the surface semiconducting layer.
  • Single crystal silicon (SCS) substrates have several advantages, including:
  • Print heads can be fabricated in existing facilities (fabs) using standard VLSI processing equipment;
  • SCS has high mechanical strength and rigidity
  • SCS has a high thermal conductivity.
  • 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.
  • Many other configurations of nozzles are possible, and 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. Operation with Electrostatic 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 extemal 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. 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.
  • 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 temperamre, 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: A - Nozzle tip: This shows the temperature history at the circle of contact between the passivation layer, the ink, and air.
  • C - Chip surface This is at a point on the print head surface 20 ⁇ m from the centre of the nozzle. The temperature only rises a few degrees. This indicates that active circuitry can be located very close to the nozzles without experiencing performance or lifetime degradation due to elevated temperatures.
  • 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 n__inimizing the effect of radio frequency interference (RFI).
  • ⁇ r is the surface tension at temperature T
  • k is a constant
  • 7. is the critical temperature of the liquid
  • M is the molar mass of the liquid
  • x is the degree of association of the liquid
  • p 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 temperamre 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 lOmN/m can be used to achieve operation of the print head according to the present invention.
  • the ink may contain a low concentration sol of a surfactant which is solid at ambient temperatures, but melts at a threshold temperamre. Particle sizes less than 1,000 A are desirable. Suitable surfactant melting points for a water based ink are between 50°C and 90°C, and preferably between 60°C and 80°C. 2)
  • the ink may contain an oil/water microemulsion with a phase inversion temperamre (PIT) which is above the maximum ambient temperature, but below the boiling point of the ink.
  • PIT phase inversion temperamre
  • the PIT of the microemulsion is preferably 20°C or more above the maximum non-operating temperamre encountered by the ink. A PIT of approximately 80°C is suitable.
  • Surfactant Sols 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:
  • 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 temperamre.
  • 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 mixmre of carboxylic acids with slightly varying chain lengths can be used to spread the melting points over a range of temperamres. Such mixmres will typically cost less than the pure acid.
  • surfactant it is not necessary to restrict the choice of surfactant to simple unbranched carboxyUc 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.
  • 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 HC1 is suitable.
  • a microemulsion is chosen with a phase inversion temperature (PIT) around the desired ejection threshold temperamre. 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 temperamres, the surfactant forming the microemulsion prefers a high curvamre surface around oil, and at temperamres significantly above the PIT, the surfactant prefers a high curvamre 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 curvamre which is much less than the curvamre 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.
  • microemulsion based inks There is a wide range of possibilities for the preparation of microemulsion based inks. For fast drop ejection, it is preferable to chose a low viscosity oil.
  • surfactant can be chosen to result in a phase inversion temperamre in the desired range.
  • surfactants of the group poly(oxyethylene)alkylphenyl ether ethoxylated alkyl phenols, general formula:
  • C n H 2n+ ⁇ C H6(CH 2 CH 2 O) m OH) can be used.
  • 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:
  • Microemulsions are thermodynamically stable, and will not separate. Therefore, the storage time can be very long. This is especially significant for office and portable printers, which may be used sporadically.
  • microemulsion will form spontaneously with a particular drop size, and does not require extensive stirring, centrifuging, or filtering to ensure a particular range of emulsified oil drop sizes.
  • the amount of oil contained in the ink can be quite high, so dyes which are soluble in oil or soluble in water, or both, can be used. It is also possible to use a mixture of dyes, one soluble in water, and the other soluble in oil, to obtain specific colors. 4) Oil miscible pigments are prevented from flocculating, as they are trapped in the oil microdroplets. 5) The use of a microemulsion can reduce the mixing of different dye colors on the surface of the print medium.
  • 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.
  • dyes are amphiphilic, large quantities of dyes can also be solubilized in the oil-water boundary layer as this layer has a very large surface area. It is also possible to have multiple dyes or pigments in each phase, and to have a mixture of dyes and pigments in each phase.
  • the absorption spectrum will tend to become broader, as the absorption peaks of both colorants are averaged. This has a tendency to 'muddy' the colors. To obtain brilliant color, careful choice of dyes and pigments based on their absorption spectra, not just their human-perceptible color, needs to be made. 2)
  • the color of the ink may be different on different substrates. If a dye and a pigment are used in combination, the color of the dye will tend to have a smaller contribution to the printed ink color on more absorptive papers, as the dye will be absorbed into the paper, while the pigment will tend to 'sit on top' of the paper. This may be used as an advantage in some circumstances.
  • the Krafft point For ionic surfactants there is a temperature (the Krafft point) below which the solubility is quite low, and the solution contains essentially no micelles. Above the Krafft temperature micelle formation becomes possible and there is a rapid increase in solubility of the surfactant If the critical micelle concentration (CMC) exceeds the solubility of a surfactant at a particular temperature, then the minimum surface tension will be achieved at the point of maximum solubility, rather than at the CMC. Surfactants are usually much less effective below the Krafft point. This factor can be used to achieve an increased reduction in surface tension with increasing temperamre. At ambient temperatures, only a portion of the surfactant is in solution. When the nozzle heater is turned on, the temperamre rises, and more of the surfactant goes into solution, decreasing the surface tension.
  • CMC critical micelle concentration
  • 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 temperamres, and the concentration of surfactant in solution at the drop selection temperamre.
  • 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 temperamres, and is reduced to a rninimum 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 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 temperamre 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 temperamres.
  • 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. Hot Melt Inks
  • the ink need not be in a liquid state at room temperature.
  • Solid 'hot melt' inks can be used by heating the printing head and ink reservoir above the melting point of the ink.
  • the hot melt ink must be formulated so that the surface tension of the molten ink decreases with temperature. A decrease of approximately 2 mN/m will be typical of many such preparations using waxes and other substances. However, a reduction in surface tension of approximately 20 mN/m is desirable in order to achieve good operating margins when relying on a reduction in surface tension rather than a reduction in viscosity.
  • the temperature difference between quiescent temperamre and drop selection temperature may be greater for a hot melt ink than for a water based ink, as water based inks are constrained by the boiling point of the water.
  • the ink must be liquid at the quiescent temperature.
  • the quiescent temperature should be higher than the highest ambient temperature likely to be encountered by the printed page.
  • T he quiescent temperamre should also be as low as practical, to reduce the power needed to heat the print head, and to provide a maximum margin between the quiescent and the drop ejection temperamres.
  • a qmescent temperature between 60°C and 90°C is generally suitable, though other temperamres may be used.
  • a drop ejection temperamre of between 160°C and 200°C is generally suitable.
  • a dispersion of microfine particles of a surfactant with a melting point substantially above the quiescent temperamre, but substantially below the drop ejection temperamre, can be added to the hot melt ink while in the liquid phase.
  • a polar/non-polar microemulsion with a PIT which is preferably at least 20°C above the melting points of both the polar and non-polar compounds.
  • the hot melt ink carrier have a relatively large surface tension (above 30 mN/m) when at the quiescent temperamre. This generally excludes alkanes such as waxes. Suitable materials will generally have a strong intermolecular attraction, which may be achieved by multiple hydrogen bonds, for example, polyols, such as Hexanetetrol, which has a melting point of 88°C.
  • 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 temperamre 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 temperamre.
  • 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 temperamre, 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' .
  • 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.
  • drop on demand printing systems have consistent and predictable ink drop size and position. Unwanted variation in ink drop size and position causes variations in the optical density of the resultant print reducing the perceived print quality. These variations should be kept to a small proportion of the nominal ink drop volume and pixel spacing respectively. Many environmental variables can be compensated to reduce their effect to insignificant levels. Active compensation of some factors can be achieved by varying the power applied to the nozzle heaters.
  • An optimum temperature profile for one print head embodiment involves an instantaneous raising of the active region of the nozzle tip to the ejection temperamre, maintenance of this region at the ejection temperamre for the duration of the pulse, and instantaneous cooling of the region to the ambient temperamre.
  • Figure 4 is a block schematic diagram showing electronic operation of an example head driver circuit in accordance with this invention.
  • This control circuit uses analog modulation of the power supply voltage applied to the print head to achieve heater power modulation, and does not have individual control of the power applied to each nozzle.
  • 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 mm 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 clock to the shift register is stopped 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 cont ⁇ ning 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. Temperamre is compensated by changing the contents of the dual port RAM 317. These values are calculated by the microcontroller 315 based on temperamre 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 enable phases in a print head in accordance with the invention depend upon the specific design. Four, eight, and sixteen are convenient numbers, though there is no requirement that the number of enable phases is a power of two.
  • 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. Combining the four bits of thermal lag compensation address and the four bits of print density compensation address means that 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. As the ambient temperature of the head varies only slowly, the microcontroller 315 has sufficient time to calculate a matrix of 256 numbers compensating for thermal lag and print density at the current temperamre. Periodically (for example, a few times a second), the microcontroller senses the current head temperamre and calculates this matrix.
  • the clock to the print head 50 is generated from the system clock 408 by the Head clock generator 407, and buffered by the buffer 406.
  • JTAG test circuits 499 may be included.
  • Invention compares the aspects of printing in accordance with the present invention with thermal ink jet printing technology.
  • 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 temperamres 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 manufacmring 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.
  • Printing in accordance with the present invention 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.
  • Figure 5 shows the fault tolerant sort yield 199 for a full width color A4 print 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 fimction 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 manufacmring conditions. This can reduce the manufacturing cost by a factor of 100.
  • Fault tolerance approaches in drop-on-demand printing systems are described in the following Australian patent specifications filed on 12 April 1995, the disclosure of which are hereby incorporated by reference:
  • Yield has a direct influence on manufacmring cost
  • a device with a yield of 5% is effectively ten times more expensive to manufacture than a similar device with a manufacturing yield of 50%.
  • the semiconductor manufacturing industry has made significant improvements in device yield by establishing cleaner processing environments, purer substances, more accurate processes, and electronic designs more tolerant of processing variations.
  • Fab yield This is the percentage of the wafers which are started on the wafer fabrication line that reach the end of wafer fabrication. Causes for rejection during manufacmre include breakage, warping, incorrect processing order, process out of tolerance, and large area containination.
  • the fab yield Y F ⁇ k is typically low for a new process. However, with a mature process on an automated fab line, a fab yield of better than 90% can usually be achieved.
  • Wafer sort yield This is percentage of die which pass wafer test. Before the wafer is diced, the individual die are tested with a wafer probe.
  • the wafer sort yield Y ⁇ is usually affected primarily by the number of point defects caused by dust and other contaminants per unit area (the defect density, D), and the chip area, A. Only die which pass wafer sort are packaged.
  • Final test yield This is the percentage of packaged die which pass final functional and parametric tests.
  • Final test yield Y Tat is usually 95% or more in a mature process.
  • the total yield YTOUI is the percentage of functional dice (in this case, print heads) as compared with the number of whole dice on the starting wafers. This is calculated as:
  • Murphy's method which has proven to be a good predictor for LSI and VLSI circuits.
  • Murphy's method approximates the distribution of defect densities, calculating the yield as:
  • Figure 5 is a graph of wafer sort yield versus defect density for a monolithic f ull width color A4 print head. This graph compares the non fault- tolerant yield 198 with the fault tolerant yield 199.
  • the non fault tolerant yield is calculated according to Murphy's method.
  • the head is 215 mm long by 5 mm wide. It is possible to fabricate such print heads using current technology by using silicon wafers cut axially from the silicon crystal, rather than radial cut wafers.
  • a defect clustering factor C can be introduced.
  • the defect clustering factor is a measure of the proportion that defects arc clustered (either by area on a wafer, or by wafer), thereby affecting fewer chips.
  • Defect clustering is advantageous for non-fault tolerant designs, but can adversely affect fault tolerance.
  • the yield for a non-fault tolerant device, with explicit modeling for clustering factor can be calculated as:
  • Figure 5 includes a graph of non fault tolerant yield with explicit clustering factor 197.
  • the defect clustering factor is not a controllable parameter in manufacmring, but is a characteristic of the manufacmring process.
  • the clustering factor for manufacmring 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.
  • Fault tolerance techniques have been used for some time in large memory chips and in wafer scale integration (WSI).
  • WMI wafer scale integration
  • Fault tolerance usually operates by providing redundancy. If some functional unit of the chip contains a defect, it is replaced by a 'redundant' or spare functional unit First, the faulty sub-units are determined (usually by external testing), then routing paths to connect redundant sub-units to replace the faulty sub-units are determined. Then the chip is programmed with these new connections. This programming may be achieved by various means, such as laser programming of connections, fused links, anti-fuses, or on-chip configuration registers.
  • redundant sub-units In memory chips and most WSI devices, the physical location of redundant sub-units has no intrinsic relevance. However, in printing heads the redundant sub-unit contains one or more printing acmators. These must have a fixed spatial relationship to the page being printed. In general, it is not effective to replace a faulty acmator with another acmator which is in a different position in the non-scan direction. Such an acmator cannot print a dot in the correct position to replace the faulty acmator. However, it is possible to replace faulty acmators with acmators which are displaced in the scan direction.
  • the data timing to the redundant acmator can be altered to compensate for the displacement in the scan direction.
  • the data timing to the redundant acmator can be altered to compensate for the displacement in the scan direction.
  • there must be a complete set of spare nozzles which results in 100% redundancy.
  • 100% redundancy is typically not required in memory chips or WSI devices, as a small number of redundant sub-units can be connected to faulty sub-units in many positions. The requirement for 100% redundancy would normally more than double the chip area, dramatically reducing the primary yield before fault tolerance progr ⁇ imming.
  • minimum physical dimensions of the head chip are set by the width of the page being printed, the fragility of the print head chip, and manufacmring 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 print head for printing A4 size paper is approximately 215 mm x 5 mm. This size allows the inclusion of 100% redundancy without increasing chip area, when using 1.5 micron CMOS fabrication technology. Therefore, a high level of fault tolerance can be included without decreasing primary yield.
  • This graph shows projected yield as a function of both defect density and defect clustering.
  • Defect clustering models the non-uniform distribution of defects. If a defect occurs at a particular location, the probability of another defect being nearby is typically higher than that implied by the defect density. This is because physical defects tend to cluster, both spatially and temporally.
  • a defect cluster factor of 1 is equivalent to a Boltzmann probability distribution.
  • sort YNozOeYsi aock*NF ⁇ Bus
  • YNo t ⁇ is the yield from defects in the nozzles and nozzle drive circuits. It models the fault tolerant simation where a fault must occur in both a nozzle or drive circuit and in the matching redundant nozzle or drive circuit before a system fault occurs. It is calculated according to the following equation:
  • D is the defect density
  • N is the number of main nozzles [19,840]
  • a N is the area of one main nozzle and drive circuit [8,400 ⁇ m 2 ]
  • C is the defect clustering factor (Values shown in square brackets [] are specific for the A4 full color
  • Ysn is the yield from defects in the shift register circuits.
  • the shift register circuits include redundant shift registers and data routing multiplexers. A fault in a shift register block will have no system level effect if there is no fault in either the matching redundant shift register, or any one of the nozzles driven by the matching redundant shift register. This case is described by the following equation:
  • NS K is the number of main shift register stages [19,840]
  • AS R is the area of one shift register stage [4,200 ⁇ m 2 ]
  • Lsn is the length of fault tolerant shift register blocks [64]
  • Yciock is the yield from defects in the fault tolerant clock circuits. This yield is described by the following equation Where:
  • Ao is the area of one clock generator [1,600 ⁇ m z ]
  • Y NF ⁇ is the yield from defects in the non fault tolerant input circuits. This does not include input pads, which usually have very low defect densities. This yield is described by the following equation:
  • i n p t is the area of non fault tolerant input circuits [80,000 ⁇ m 2 ]
  • Auw is the area of non fault tolerant multiplexer select controller circuits [1,600,000 ⁇ m 2 ]
  • YB I is the yield from defects in the non fault tolerant multiplexer control bus. While this is simply a 9 bit bus on one metal layer, it is not fault tolerant in the current design. The defect density is divided by three because only the top metal layer is defect sensitive. In a two level metal device, a single level of metal usually contributes less than 33% of the chip defects.
  • the multiplexer control bus can be made fault tolerant with a small increase chip complexity. This yield is described by the following equation: Where:
  • Lue d is the length of the print head [215 mm]
  • WBUI is width of the bus [108 ⁇ m]
  • the fault tolerant yield projection 199 shown in figure 5 is calculated according to this equation. It indicates that thoroughly implemented fault tolerance can increase wafer sort yield from under 1 % to more than 90% under identical manufacmring conditions. This can reduce the manufacturing cost by a factor of 100. Total practical yield for this device at a defect density of 1 defect per square cm can be calculated as:
  • 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.
  • Integrated Drive Circuitry Figure 7 shows one preferred embodiment of the invention comprising a print head with integrated drive circuitry.
  • This print head has 19,840 nozzles, which are connected using eight shift registers, each of which contains 2,480 drive modules 220.
  • 2,480 drive modules 220 in each shift register are shown.
  • only four of the eight shift registers are shown.
  • the preferred circuit for integrated nozzle drivers on large print heads incorporates fault tolerance. This is omitted from this diagram for simplicity.
  • the clock generation module 230 generates a gated two phase clock for the shift registers.
  • This gated two phase clock allows the elimination of the parallel registers that would otherwise be required to hold the data constant during the heater enable pulse.
  • the two clock phases allow the use of dynamic shift registers instead of static shift registers, further reducing the number of integrated transistors required for each nozzle driver.
  • the three EnPhase signals are the input of a three line to eight line decoder 260.
  • the Eight outputs of the decoder 260 are connected to the enable controls of the drive modules 220.
  • the output transistors of the decoder must be either very large, or buffered multiple times, to obtain fast switching.
  • the inclusion of the decoder 260 reduces the number of extemal connections required to control which of the eight groups is activated from eight to four.
  • the print head has only a small number of connections. There are:
  • V * which is the positive power connection to the heaters.
  • V which is the return power (ground) connection to the heater drive transistors.
  • V M which is the positive power connection to the shift registers and data enable circuits.
  • V View which is the return power (ground) connection for the shift registers and data enable circuits.
  • Clock which is the main system clock, used for clocking the shift registers.
  • Enable which is a global enable signal. If this signal is inactive, no printing can occur.
  • Data ⁇ 0-7> which are the eight serial data input signals which control which nozzles are to be energized.
  • Test which is an Or function of the data at the output of the shift registers. The eight outputs are wired to the inputs of a eight input Or gate 270. This output can be used for testing the integrity of the shift registers in the print head. Only one shift register can be tested at a time. More sophisticated test circuitry can be included on the print head using well known techniques.
  • Printing heads incorporating a multitude of printing actuators typically give degraded performance if one or more of these acmators fail, or are imperfectly fabricated. If some printing heads contain imperfectly fabricated acmators at the time of manufacture, the 'yield' is decreased. This is because the printing heads are typically not repairable. A reduction in yield increases the effective manufacturing cost of the printing head. If a printing actuator fails during use, the reliability and 'life' of the printing head is impaired. If a printing head contains many thousands of printing acmators, the probability of a single acmator failing is typically larger than the failure probability in a printing head containing a small number of printing acmators manufactured using the same techniques. The coincident forces printing approach described herein and in my above-noted applications allows the cost effective fabrication of printing heads containing many thousands of printing actuators.
  • An important basis of the current invention is the provision of fault tolerance using redundant printing acmators.
  • a basic principle is simple: when a printing acmator fails, it is automatically replaced with a spare printing acmator.
  • One method is to simply replace the entire printing head. However, this is of no assistance if the main problem is low manufacturing yield. Also, only one set of simultaneous acmator failures can be compensated for.
  • a more flexible system is to automatically replace individual failed actuators. Using this method, manufacturing yields can be dramatically improved, and many failures during use can be compensated.
  • the physical position of the printing actuator is important, as it typically prints a line of dots in the scan direction.
  • the acmator must be replaced with a spare acmator with a different spatial location. This is easiest if the spare actuator is simply translated in the scan direction. This requires one spare (redundant) acmator for every printing actuator on the print head.
  • the main and redundant printing acmators can be simultaneously fabricated on a single substrate. To compensate for the physical displacement of the replacement printing acmator, the timing of the data to the replacement actuator must be changed.
  • a printing head which provides redundant printing nozzles and redundant drive circuitry, allowing individual faulty nozzles to be electronically replaced.
  • the redundant acmators must be at physically different positions than the faulty acmators.
  • the system disclosed herein ensures that a dot is printed by a redundant acmator in the same location that the faulty acmator would have printed the dot This is achieved by providing an electronic signal delay, and arranging the acmators so that they are displaced in the scan direction only.
  • a memory containing a map of faulty acmators is also provided, along with a means of routing print data directed at a faulty acmator to the corresponding redundant acmator.
  • the invention is applicable to many types of printing mechanisms which consist of a plurality of dot marking means integrated into a single structure.
  • printing mechanisms include, but are not limited to, coincident forces liquid ink printing heads, thermal ink jet print heads, thermal wax printer heads, dye sublimation print heads, and thermal paper print heads.
  • the example given here is the application of the invention to coincident forces printing.
  • the coincident forces printing approach allows the practical fabrication of print heads containing many thousands of printing acmators. As the number of printing acmators fabricated on a printing head using a particular technology increases, so to does the benefit of incorporating fault tolerance using redundant printing acmators.
  • the table "LIFT head type A4-4-600” (see Appendix A) is a summary of some characteristics of an example full color monolithic printing head capable of printing an color A4 page at 600 dpi in approximately one second.
  • Figure 8 shows a block diagram of a system implementing fault tolerance using redundant printing acmators.
  • the image data 281 controls the drive circuit 282 which energizes the normally active (main) printing actuators 283.
  • the main printing acmators are energized with electrical pulses which are timed so that the recording medium is marked in the correct positions corresponding to the image data as the printing head containing the printing acmators scans the recording medium.
  • the design of the fault detection unit depends upon the circumstance in which the faults must be detected. Three major categories for fault detection are:
  • printing heads can be tested by especially constructed equipment which detects the presence of marks on a recording medium, or directly detects the presence of the ink or other marking material as it leaves the printing acmator. Such equipment may detect the marking material optically, electrically, or by other means.
  • the equipment containing the printing head by the 'end user' will typically include a scanner and a microprocessor.
  • one possible method is to print a test page which includes dots printed by all of the printing acmators. This page can then be scanned by the user in a special 'calibration' operating mode.
  • the microprocessor analyses the scanned data and calculates a 'map' of faulty printing acmators.
  • the unit is a printer, it will typically not incorporate a scanner. In this case, the printer may include a single photodetector which is scanned across the printed test page while in 'calibration' mode. Using this technique, a low cost detector can be constructed.
  • a 'map' of faulty acmators is stored in the faulty acmator memory
  • a simple method is to use one bit of information to store the status of each acmator.
  • 19,840 bits (2,480 bytes) are required to independently store the status of each main nozzle.
  • This amount of memory can readily be provided using semiconductor memory of various types. It is convenient to store the fault map in a semiconductor memory which will not lose data when the power is turned off. Suitable memory devices are EEPROMs, EPROMs, battery- backed SRAMs, or FLASH memory devices. Other device types may also be used.
  • the 'map' of faulty printing acmators is used to control a gating circuit 284 which suppressed print data which is directed to functional main printing acmators, and allows print data directed towards faulty printing actuators to pass to the redimdant printing acmators.
  • the timing of the print data is adjusted by a timing adjustment circuit 285 so that a dot printed by the redundant printing acmator will be at the same location as the dot would have been had it been printed by the main printing actuator. In the printing head example described herein, the timing adjustment is a delay of two line periods.
  • the timing adjusted image data for the redundant printing actuators controls the drive circuit 286 which energizes the redundant printing acmators 287.

Landscapes

  • Ink Jet (AREA)

Abstract

La présente invention concerne une tête d'impression pourvue de buses redondantes et d'un câblage de commande redondant, ce qui permet de remplacer, par des moyens électroniques, des buses isolées défectueuses. Les actionneurs redondants doivent impérativement se trouver matériellement dans des positions différentes de celles des actionneurs défectueux. Avec le système selon l'invention, on est assuré qu'un point est imprimé, par un actionneur redondant, au même emplacement que si l'actionneur défectueux l'avait fait. Cela s'obtient en introduisant un retard électronique du signal et en disposant les actionneurs de telle façon qu'ils soient décalés dans la direction du balayage seulement. Le système comprend aussi une mémoire contenant un plan des actionneurs défectueux, et il comprend un moyen qui dirige les données d'impression adressées à un actionneur défectueux vers l'actionneur redondant correspondant.
EP96912651A 1995-04-12 1996-04-10 Doublement des buses pour obtenir une tolerance aux defauts dans les tetes d'impression integrees Withdrawn EP0765225A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
AUPN2326A AUPN232695A0 (en) 1995-04-12 1995-04-12 Nozzle duplication for fault tolerance in integrated printing heads
AUPN2326/95 1995-04-12
PCT/US1996/004894 WO1996032263A1 (fr) 1995-04-12 1996-04-10 Doublement des buses pour obtenir une tolerance aux defauts dans les tetes d'impression integrees

Publications (1)

Publication Number Publication Date
EP0765225A1 true EP0765225A1 (fr) 1997-04-02

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EP (1) EP0765225A1 (fr)
JP (1) JPH10501492A (fr)
AU (1) AUPN232695A0 (fr)
WO (1) WO1996032263A1 (fr)

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JP3640080B2 (ja) * 1997-05-28 2005-04-20 セイコーエプソン株式会社 シリアル記録装置及び方法
EP0999935B1 (fr) 1997-08-01 2003-11-05 Encad, Inc. Imprimante a jet d'encre, et procede et systeme permettant de compenser le non-fonctionnement de certains elements d'impression
US6076910A (en) * 1997-11-04 2000-06-20 Lexmark International, Inc. Ink jet printing apparatus having redundant nozzles
US6209203B1 (en) 1998-01-08 2001-04-03 Lexmark International, Inc. Method for making nozzle array for printhead
US6502920B1 (en) 2000-02-04 2003-01-07 Lexmark International, Inc Ink jet print head having offset nozzle arrays
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EP3137302B1 (fr) 2014-04-30 2020-02-12 Hewlett-Packard Development Company, L.P. Détermination d'un instant temporel pour une mesure d'impédance
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Publication number Publication date
AUPN232695A0 (en) 1995-05-04
WO1996032263A1 (fr) 1996-10-17
JPH10501492A (ja) 1998-02-10

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