WO1996032813A1 - Systemes de traitement et de copie de photographies - Google Patents

Systemes de traitement et de copie de photographies Download PDF

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Publication number
WO1996032813A1
WO1996032813A1 PCT/US1996/004816 US9604816W WO9632813A1 WO 1996032813 A1 WO1996032813 A1 WO 1996032813A1 US 9604816 W US9604816 W US 9604816W WO 9632813 A1 WO9632813 A1 WO 9632813A1
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WO
WIPO (PCT)
Prior art keywords
ink
printing
nozzles
die
drop
Prior art date
Application number
PCT/US1996/004816
Other languages
English (en)
Inventor
Kia Silverbrook
Original Assignee
Eastman Kodak Company
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
Priority claimed from AUPN2334A external-priority patent/AUPN233495A0/en
Priority claimed from AUPN2337A external-priority patent/AUPN233795A0/en
Application filed by Eastman Kodak Company filed Critical Eastman Kodak Company
Priority to US08/765,756 priority Critical patent/US5909227A/en
Priority to EP96911640A priority patent/EP0765570A1/fr
Publication of WO1996032813A1 publication Critical patent/WO1996032813A1/fr

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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
    • 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
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07F—COIN-FREED OR LIKE APPARATUS
    • G07F17/00—Coin-freed apparatus for hiring articles; Coin-freed facilities or services
    • G07F17/26—Coin-freed apparatus for hiring articles; Coin-freed facilities or services for printing, stamping, franking, typing or teleprinting apparatus
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N1/34—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device for coin-freed systems ; Pay systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
    • H04N1/40031—Circuits exciting or modulating particular heads for reproducing continuous tone value scales for a plurality of reproducing elements simultaneously
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/46—Colour picture communication systems
    • H04N1/50—Picture reproducers
    • H04N1/504—Reproducing the colour component signals line-sequentially

Definitions

  • the present invention is in the field of computer controlled printing devices.
  • the field is thermally activated drop on demand (DOD) printing systems.
  • DOD drop on demand
  • the present invention is an apparatus for printing color photographs from negative strips.
  • the chemical printing process can produce high quality results at a low cost per photograph.
  • the equipment required is not ideal. Significant quantities of chemicals are required.
  • the color of the resultant print varies with temperature and 'age' of the chemicals used.
  • the images are not digitized, so digital image processing cannot be used to enhance the image.
  • the photograph processing equipment e.g. a 'mini-lab'
  • the photograph processing equipment is bulky and expensive.
  • a compact digital electronic mini-lab should be substantially lower in cost than chemical mini-labs.
  • Image quality should be equivalent to the consumer.
  • Processing speed should be equivalent or faster, with one second per photograph being a reasonable target.
  • Color correction should be automatic, and preferably should incorporate sophisticated techniques such as color histogram correction.
  • Processing costs should be no more than that of current chemical optical mini-labs.
  • the consumer requires an extra copy of one or more of the photographs. This requirement may occur at any time after the original photographs are taken. Extra copies are usually made in the following manner; the customer finds the negative strip with the required image, and identifies the correct image in the strip. The customer then takes the strip to the processing lab, which then does a special processing run printing only the requires image or images. Usually, the processing lab requires at least an hour to provide the service, as the processing machine may be busy with other jobs. The customer is required to return later to pick up the copies.
  • Negatives must be provided to the customer. These must be stored, and are often lost. The negatives must be handled carefully, as they are seriously degraded by fingerprints. The correct image must be identified by viewing a small negative image of the required photograph. The negative strips must then be taken to a processing lab, placed in a job queue, and the customer must either wait, or return later to collect the copies. The printing of a few copies is an interruption to the normal workflow of the processing lab, and therefore is usually charged at a premium rate. The duplication of instant print photographs such as 'Polaroids' is more difficult, usually requiring photographing of the original Polaroid print
  • 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 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.
  • 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.
  • 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
  • Each of the above-described inkjet printing systems has advantages and disadvantages.
  • there remains a widely recognized need for an improved inkjet printing approach providing advantages for example, as to cost speed, quality, reliability, power usage, simplicity of construction and operation, durability and consumables.
  • One object of the present invention is to provide liquid ink printing systems which afford significant advantages toward attaining the above-noted advantages.
  • the invention provides a color photograph printing apparatus comprising:
  • a digital halftoning unit which converts the continuous tone image data output by the scanner signal processing unit to bi-level image data
  • a data distribution and timing system which provides the bi-level image data to the printing head at the correct time during a printing operation
  • a bi-level color printing mechanism preferably operating on the concurrent drop selection and separation principle.
  • the bi-level printing mechanism is a single monolithic printing head which can print to the full width of the photographic print
  • bi-level printing mechanism is composed of a plurality of monolithic printing heads.
  • Another preferred feature of the invention is the inclusion of a digital color correction apparatus.
  • Another preferred feature of the invention is that the printing ink colors used are CC'MM * YK.
  • digital halftoning unit operates using vector error diffusion.
  • digital halftoning unit operates using independent error diffusion of each printing color.
  • digital halftoning unit operates using dithering.
  • the print paper is in the form of pre-cut sheets.
  • print paper is in the form of a continuous roll, and which incorporates an automatic paper cutter.
  • 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 simplified schematic diagram of a high performance color photograph printer using a printing mechanism according to the present invention.
  • Figure 7(a) shows a side view of major component placement in one possible configuration of the scanner section of the digital 'mini-lab' .
  • Figure 7(b) shows a side view of major component placement in one possible configuration of the printer section of the digital 'mini-lab' .
  • Figure 8 shows a perspective view of one possible configuration of the digital 'mini-lab'.
  • Figure 9 shows a simplified schematic diagram of a portable printer using LIFT printing technology.
  • Figure 10 shows a side view of major component placement in one possible configuration of the photograph copier.
  • Figure 11 (a) shows a perspective view of the photograph copier with the copy lid closed.
  • Figure 11(b) shows a perspective view of the photograph copier with the copy lid open.
  • One aspect of the invention is a high speed color photograph printing system (mini-lab) which uses a concurrent drop selection and drop separation printing mechanism.
  • the system consists of a color continuous tone scanner which is the width of the color negative transparency, a scanner signal conditioning unit a digital image processing unit, a digital halftoning unit a data phasing unit and a printing mechanism using liquid ink.
  • the printing head is the same width as the photograph to be printed.
  • continuous tone image information from the image scanner is digitally halftoned in real-time and printed by the printing head.
  • the system consists of a color continuous tone scanner the width of a photograph, a scanner signal conditioning unit, a digital halftoning unit (preferably using vector error diffusion), a data phasing unit and a printing mechanism using liquid ink.
  • the printing head is also the same width as the photograph.
  • continuous tone image information from the image scanner is digitally halftoned in real-time and printed by the printing head.
  • the system may be operated by a human operator, or may be fully automatic, producing a copy of a photograph after sensing payment by coin, banknote, credit card, or other means.
  • 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:
  • Electrothermal reduction of surface tension of pressurized ink 2) Electrothermal bubble generation, with insufficient bubble volume to cause drop ejection
  • 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
  • TU 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 TD systems is approximately 0.02%).
  • This means that the drive circuits for TU print heads must switch high currents.
  • the drive circuits for piezoelectric ink jet heads must either switch high voltages, or drive highly capacitive loads.
  • the total power consumption of pagewidth TO ptintheads is also very high.
  • An 800 dpi A4 full color pagewidth TU 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.
  • the table “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 TU), 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.
  • the table “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 may also be used.
  • 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
  • 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.
  • the microcontroller 315 may also control the ink pressure regulator
  • ink is contained in an ink reservoir 64 under pressure.
  • 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 In some types of printers according to the invention, an external field
  • 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
  • High performance drive transistors and other circuitry can be fabricated in SCS;
  • 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
  • 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.
  • 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.
  • 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 Qess 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:
  • a - Nozzle tip This shows the temperature history at the circle of contact between the passivation layer, the ink, and air.
  • B - Meniscus midpoint This is at a circle on the ink meniscus midway between the nozzle tip and the centre of the meniscus.
  • 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 minimizing the effect of radio frequency interference (RFI).
  • RFID radio frequency
  • ⁇ r 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
  • p is the density of the Uquid.
  • 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 shghtly 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 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 temperature. Particle sizes less than 1,000 ⁇ 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 temperature (PIT) which is above the maximum ambient temperature, but below the boiling point of the ink.
  • PIT phase inversion temperature
  • the PIT of the microemulsion is preferably 20°C or more above the maximum non-operating temperature encountered by the ink. A PIT of approximately 80°C is suitable.
  • 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 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 die 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 witii 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 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 significandy 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. There are two mechanisms whereby this reduces the surface tension.
  • 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.
  • a low viscosity oil For fast drop ejection, it is preferable to chose a low viscosity oil.
  • 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+ ⁇ C H 6 (CH 2 CH 2 ⁇ ) 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.
  • Low cost commercial preparations are the result of a polymerization of various molar ratios of ethylene oxide and alkyl phenols, and the exact number of oxyethylene groups varies around the chosen mean. These commercial preparations are adequate, and highly pure surfactants with a specific number of oxyethylene groups are not required.
  • the formula for this surfactant is C 8 H ⁇ 7 C 4 H6(CH 2 CH 2 O)_OH
  • 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 foUowing table:
  • Microemulsions are thermodynamicaUy stable, and will not separate. Therefore, the storage time can be very long. This is especiaUy significant for office and portable printers, which may be used sporadically.
  • the microemulsion wiU 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 oU 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.
  • Oil miscible pigments are prevented from flocculating, as they are trapped in the oil microdroplets.
  • the use of a microemulsion can reduce the mixing of different dye colors on the surface of the print medium.
  • OU in water mixtures can have high oil contents - as high as 40% - and still form O/W microemulsions. This aUows a high dye or pigment loading.
  • the foUowing table shows the nine basic combinations of colorants in the oU and water phases of the microemulsion that may be used.
  • the ninth combination is useful for printing transparent coatings, UV ink, and selective gloss highUghts.
  • dyes are amphiphiUc, large quantities of dyes can also be solubilized in the oU-water boundary layer as this layer has a very large surface area.
  • 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 wiU tend to have a smaUer contribution to the printed ink color on more absorptive papers, as the dye will be absorbed into the paper, whUe the pigment wiU tend to 'sit on top' of the paper. This may be used as an advantage in some circumstances.
  • a surfactant should be chosen with a Krafft point which is near t e 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 faUs with increasing temperature.
  • the POE chain is hydrophiUc, and maintains the surfactant in solution.
  • the structured water around die 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_O) x (CH 2 CH 2 O) y (CHCH 3 CH 2 O)_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 Utde effect
  • the ink composition can be 'tuned' for a desired temperamre 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.
  • the ink need not be in a Uquid state at room temperature.
  • SoUd '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 wiU be typical of many such preparations using waxes and other substances.
  • 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 temperature 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 die boiling point of the water.
  • the ink must be Uquid at the quiescent temperature.
  • the quiescent temperature should be higher than the highest ambient temperature likely to be encountered by die printed page. T he quiescent temperature 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 temperatures.
  • a quiescent temperature between 60°C and 90°C is generaUy suitable, though other temperatures may be used.
  • 200°C is generaUy suitable. There are several methods of achieving an enhanced reduction in surface tension with increasing temperamre.
  • a dispersion of microfine particles of a surfactant with a melting point substantially above the quiescent temperature, but substantially below the drop ejection temperature, can be added to d e hot melt ink while in the Uquid 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 wiU generaUy 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 temperamre on the surface tension of various aqueous preparations containing the foUowing additives:
  • operation of an embodiment using thermal reduction of viscosity and proximity drop separation, in combination with hot melt ink is as foUows.
  • sohd ink Prior to operation of the printer, sohd 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 Uquid, 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 osciUates at a frequency which is an integral multiple of the drop ejection frequency from the nozzle.
  • the ink pressure osciUation causes osciUations of the ink meniscus at the nozzle tips, but this osciUation is smaU due to d e high ink viscosity. At the normal operating temperamre, these osciUations are of insufficient ampUtude to result in drop separation.
  • 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 sufficientiy close to the print head 50 so that the selected drops contact the recording medium 51, but sufficientiy far away that the unselected drops do not contact the recording medium 51.
  • part of d e selected drop freezes, and attaches to the recording medium.
  • die ink pressure faUs 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 osciUation.
  • the viscosity of the ink increases to its quiescent level as remaining heat is dissipated to die bulk ink and print head.
  • One ink drop is selected, separated and forms a spot on die recording medium 51 for each heat pulse. As the heat pulses are electricaUy controUed, drop on demand inkjet 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 pubhcations 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 yeUow and black. This color model is herein caUed CC'MM' YK. Where high quahty monochrome image printing is also required, two bits per pixel can also be used for black. This color model is herein caUed 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 foUowing AustraUan patent specifications filed on 12 April 1995, die disclosure of which are hereby inco ⁇ orated by reference:
  • Printing apparatus and methods of this invention are suitable for a wide range of appUcations, including (but not limited to) die foUowing: 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, facsimUe and copying machines, label printing, large format plotters, photographic dupUcation, printers for digital photographic processing, portable printers inco ⁇ orated into digital 'instant' cameras, video printing, printing of PhotoCD images, portable printers for 'Personal Digital Assistants', waUpaper printing, indoor sign printing, biUboard 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 d e resultant print, reducing the perceived print quaUty. These variations should be kept to a smaU 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 temperamre profile for one print head embodiment involves an instantaneous raising of the active region of die nozzle tip to die ejection temperamre, maintenance of this region at the ejection temperature for the duration of die pulse, and instantaneous cooling of die region to die ambient temperature.
  • 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 die 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 logicaUy anded widi phase enable signal by a nand gate 215.
  • the ou ⁇ ut 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 clock to the shift register is stopped die 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 weU known gUtch free clock control circuits. Stopping the clock of the shift register removes the requirement for a paraUel data latch in the print head, but adds some complexity to the control circuits in the Head Control ASIC 400. Data is routed to eitiier the main nozzles or the redundant nozzles by the data router 219 depending on d e 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 me apparatus disclosed herein.
  • Digital information representing patterns of dots to be printed on the recording medium is stored in die 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 me Page or Band memory 1513 using addresses selected by die address mux 417 and control signals generated by the Memory Interface 418.
  • Address generators 411 which forms part of the
  • the addresses are generated based on die positions of the nozzles in relation to the print medium. As die 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 d e position of the main nozzles. However, when faulty nozzles are present, locations of blocks of nozzles containing faults can be marked in die Fault Map RAM 412. The Fault Map RAM 412 is read as the page is printed.
  • the address is altered so that the Address generators 411 generate d e address corresponding to the position of the redundant nozzles.
  • Data read from me Page or Band memory 1513 is latched by die 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 tiien buffered by die 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 die 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 die data output of die FIFO 415, and buffered by die buffer 431 to form the fault status bus.
  • the programmable power supply 320 provides power for d e head 50.
  • the voltage of the power supply 320 is controUed by die 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 d e MicrocontroUer 315. Temperamre is compensated by changing the contents of the dual port RAM 317.
  • These values are calculated by d e microcontroUer 315 based on temperature sensed by a diermal sensor 300.
  • the thermal sensor 300 signal connects to the Analog to Digital Converter (ADC) 311.
  • the ADC 311 is preferably inco ⁇ orated in the MicrocontroUer 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 die DAC 313 based upon data read from me 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 d e period of one enable pulse. This synchronization is ensured, as d e counter 403 is clocked by die system clock 408, and die top count of die counter 403 is used to clock d e enable counter 404.
  • the count from the enable counter 404 is then decoded by die decoder 405 and buffered by die buffer 432 to produce die 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 die counter 403 and die dual port RAM 317. However, these sixteen states may not be linearly spaced in time. To aUow non-linear timing of tiiese states the counter 403 may also include a ROM or otiier device which causes die counter 403 to count in a non-linear fashion. Alternatively, fewer than sixteen states may be used.
  • die 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 die On pixel counters 402.
  • the number of enable phases in a print head in accordance with the invention depend upon d e specific design. Four, eight, and sixteen are convenient numbers, though there is no requirement that me 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 die adder 421 and accumulator 422. A latch 423 holds die accumulated value vaUd for die 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 die 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 die four bits of print density compensation address means mat 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 temperamre of the head varies only slowly, the microcontroUer 315 has sufficient time to calculate a matrix of 256 numbers compensating for thermal lag and print density at die current temperamre. PeriodicaUy (for example, a few times a second), the microcontroUer senses the current head temperamre and calculates this matrix.
  • the clock to the print head 50 is generated from me system clock 408 by the Head clock generator 407, and buffered by die buffer 406. To faciUtate testing of the Head control ASIC, JTAG test circuits 499 may be included.
  • Invention compares the aspects of printing in accordance witii the present invention witii thermal inkjet printing technology.
  • Thermal ink jet printers use the foUowing fundamental operating principle.
  • a thermal impulse caused by electrical resistance heating results in the explosive formation of a bubble in Uquid ink. Rapid and consistent bubble formation can be achieved by superheating the ink, so that sufficient heat is transferred to die 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 tiien coUapses, drawing ink from the ink reservoir to re-fill die nozzle.
  • Thermal ink jet printing has been highly successful commerciaUy due to d e high nozzle packing density and d e use of weU 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, satelUte drop formation, thermal stress, differential thermal expansion, kogation, cavitation, rectified diffusion, and difficulties in ink formulation.
  • Printing in accordance with die present invention has many of the advantages of thermal ink jet printing, and completely or substantiaUy eliminates many of the inherent problems of thermal ink jet technology.
  • Figure 5 is a graph of wafer sort yield versus defect density for a monolid ⁇ c fuU widtii color A4 head embodiment of die invention.
  • the head is 215 mm long by 5 mm wide.
  • the non fault tolerant yield 198 is calculated according to Mu ⁇ hy's method, which is a widely used yield prediction method. Witii a defect density of one defect per square cm, Mu ⁇ hy's method predicts a yield less tiian 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. Mu ⁇ hy' s method approximates the effect of an uneven distribution of defects.
  • Figure 5 also includes a graph of non fault tolerant yield 197 which expUcidy 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 die manufacturing process.
  • the defect clustering factor for manufacturing processes can be expected to be approximately 2, in which case yield projections closely match Mu ⁇ hy's method.
  • a solution to die problem of low yield is to inco ⁇ orate fault tolerance by including redundant functional units on the chip which are used to replace faulty functional units.
  • redundant functional units on the chip which are used to replace faulty functional units.
  • the redundant sub-unit may contain one or more printing actuators. These must have a fixed spatial relationship to die page being printed.
  • faulty actuators can be replaced with redundant actuators which are displaced in the scan direction.
  • the data timing to the redimdant actuator can be altered to compensate for d e displacement in die scan direction.
  • the minimum physical dimensions of die head chip are determined by die width of die page being printed, the fragUity 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 widtii, fuU color head for printing A4 size paper is approximately 215 mm x 5 mm. This size aUows the inclusion of 100% redundancy without significandy increasing chip area, when using 1.5 ⁇ m CMOS fabrication technology. Therefore, a high level of fault tolerance can be included widiout significandy decreasing primary yield.
  • Figure 5 shows the fault tolerant sort yield 199 for a fuU 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 tiiat 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 reliabiUty of print heads containing thousands of printing nozzles, and thereby make pagewiddi printing heads practical.
  • fault tolerance is not to be taken as an essential part of the present invention.
  • Example product specifications shows die specifications of one possible configuration of a high quaUty color photograph processing system.
  • Figure 6 shows a schematic process diagram of a high speed color photograph printing system (mini-lab) using printing technology according to die present invention.
  • the blocks in this diagram represent discrete functions, irrespective of tiieir implementations.
  • Some of the blocks are electronic hardware, some are computer software, some are electromechanical units, and some are mechanical units.
  • Some of the blocks are subsystems, which may include electronic hardware, software, mechanics, and optics.
  • the operator places the strip of negative film 520 in the negative transport mechanism 521.
  • the negative transport mechanism 521 moves the negative strip 520 relative to the scanner 502.
  • This scanner can be composed of a color Unear CCD, one or more focusing lenses, a Ught source, and an optical patii.
  • a suitable configuration includes a monoUthic linear CCD sensor containing three lines of optical sensors. If these sensor lines are the same length as die width of the negative film to be scanned (approximately 25 mm for standard 35 mm film), then no reduction or enlargement optics are required.
  • the three sensor lines can be fabricated witii integral optical filters, one for each of the red, green, and blue additive primary colors. The technology required to manufacture such scanners is weU known.
  • a scanner resolution of 2400 dpi is adequate, as tiiis wiU provides a resolution approximately equivalent to the size of film grain in 35 mm film.
  • An array CCD may be used instead of a linear CCD, in which case no relative movement is required.
  • array CCD's of optimum resolution are currentiy too expensive to be practical.
  • This wUl change in the future, and an area scanning CCD element designed for high definition television is likely to be suitable.
  • the output of the scanner 502 is connected to a scanner signal conditioning unit 503. This unit amplifies and filters the CCD analog signal, converts the signal to digital form, and provides CCD sensitivity compensation to adjust for differences in individual CCD sensors.
  • the analog ou ⁇ ut of the linear CCD should be converted to 12 bits per color component. Lower color resolution can be used, witii a subsequent reduction in color quaUty or color correction range.
  • the ou ⁇ ut of the scanner signal conditioning unit 503 is raster-ordered continuous tone image data, witii typically 36 bits per pixel.
  • the ou ⁇ ut of the scanner signal conditioning unit 503 is connected to a digital image processing unit 519.
  • the primary function of this unit is color correction, but the unit may also be used for digital special effects. Many digital effects can be performed, and many are weU known to the art.
  • the color correction process can be performed in real-time, and may inco ⁇ orate color look-up tables for each color as weU as matrix multiply operations. Alternatively, more general color correction techniques may be used, such as a subsampled color space look-up table with tri-linear inte ⁇ olation between the color samples.
  • the color correction process can include a conversion from the negative image of the negative film, to the positive image typically required for die photographic print.
  • the color correction process may also include gamma correction, and correction for film stock type.
  • the ou ⁇ ut of the digital image processing unit 519 is raster-ordered continuous tone image data, witii typicaUy 24 bits per pixel.
  • a vector error diffusion algorithm is used to achieve a high image quaUty. This operates by selecting die closest printable color in three dimensional color space to the desired color. The difference between the desired coior and tiiis printable Color is determined. This difference is then diffused to neighboring pixels.
  • the vector error diffusion unit 504 accepts a raster ordered continuous tone input image and generates a bi-level ou ⁇ ut with 7 bits per pixel (one bit for each of Cyan, Magenta, YeUow, and Black, as weU as quarter density inks of Cyan, Magenta, and Black).
  • the color components can be independenUy error diffused, although diis provides an image of substantiaUy lower quality. It is also possible to dither the continuous tone image to obtain a bi-level image. In this case, a computer optimized stochastic dispersed dot ordered dither is recommended.
  • This data is tiien processed by die data phasing and fault tolerance system 506.
  • This unit provides die appropriate delays to synchronize the print data witii the offset positions of the nozzle of the printing head. It also provides alternate data patiis for fault tolerance, to compensate for blocked nozzles, faulty nozzles or faulty circuits in the head.
  • the monoUthic printing head 50 prints the image 60 composed of a multimde of ink drops onto a recording medium 51.
  • This medium wUl typically be paper, but can also be overhead transparency film, cloth, or most other substantially flat surfaces which wiU accept ink drops.
  • the bi-level image processed by die data phasing and fault tolerance circuit 506 provides die pixel data in the correct sequence to the data shift registers 56. Data sequencing is required to compensate for the nozzle arrangement and die movement of the paper.
  • the heater driver circuits 57 When the data has been loaded into die shift registers, it is presented in parallel to the heater driver circuits 57. At the correct time, these driver circuits wiU electronically connect the corresponding heaters 58 witii the voltage pulse generated by die pulse shaper circuit 61 and d e voltage regulator 62. The heaters 58 heat the tip of die nozzles 59, reducing die attraction of the ink to the nozzle surface material.
  • Ink drops 60 escape from the nozzles in a pattem which corresponds to the digital impulses which have been appUed to the heater driver circuits.
  • the pressure of the ink in the nozzle is important, and die pressure in the ink reservoir 64 is regulated by die pressure regulator 63.
  • the ink drops 60 fall under die influence of gravity or another field type towards the paper 51.
  • the paper is continuaUy moved relative to the print head by die paper transport system 65. As the print head is the fuU widtii of die paper used, it is only necessary to move the paper in one direction, and die print head can remain fixed.
  • the paper may be suppUed as pre-cut sheets, in which case the paper transport mechanism must acquire and transport the sheets individually past the printing head.
  • die paper may be provided in rolls.
  • an automatic paper cutting blade is required.
  • the various subsystems are coordinated under die control of one or more control microcomputers 511, which also provide die user interface of the system.
  • Figure 7(a) shows a side view of die scanner section 628 of the digital 'mini-lab', showing possible placement of some of the major modules.
  • Strips of film negative 520 are inserted into the scanner unit and pass through a negative scanner 502.
  • the negative scanner consists of a Ught source, focusing optics, and an electronic image sensor, such as a linear CCD.
  • the signal from the scanner 502 is processed by control electronics 900.
  • Data representing the scanned images is transmitted to die printer section 629 of the digital 'mini-lab' shown in figure 7(b).
  • a cutting device 569 can be inco ⁇ orated to cut die fuU length negative (typicaUy 24 or 36 frames) into strips, as is conventional for photo processing.
  • Figure 7(b) shows a side view of die printer section 629 of the digital 'mini-lab', showing possible placement of some of the major modules.
  • Ink reservoirs 574 can be placed at die top of die printing unit, aUowing gravity feed of ink to the head 50 witii sufficient pressure to aUow operation of the nozzle. This depends upon nozzle diameter, but is approximately 11,200 Pa above ambient air pressure for an 11 mm nozzle. A drop of approximately 1.16 meters from the ink level in die reservoirs to the printing surface of the nozzle is required if gravity feed is to be used.
  • paper from die paper roll 575 is moved past die head 50 by paper transport mechanisms 65.
  • Data representing the scanned image is received from die scanner section 628 of the device and processed by an electronic subsystems 900.
  • This subsystem apphes any image enhancement and color correction required, then digitally halftones the image data.
  • This data is then used to control the pattern of dots printed by die head 50.
  • the printed photographs 51 are cut from the roll by the cutter 569.
  • Figure 8 shows a perspective view of the digital 'mini-lab'.
  • the negative fUm 520 is shown inserted into die scanner section 628 which is connected by a cable 627 to the printer section 629.
  • the amount of paper left on the paper roll 575 can be seen through a window in the printer section.
  • Figure 9 shows a schematic process diagram of a high speed color photograph copier using LIFT printing technology.
  • the operator places the photograph 516 in the photograph transport mechanism 517.
  • This system has a means of signaUng the control microcomputer 511 that a photograph is ready to be scanned.
  • This may be an optical sensor, a mechanical sensor, a push-button, or other means.
  • a payment detection mechanism 518 is required. This mechanism signals the microcomputer 511 with the payment amount every time payment is inserted.
  • a coin detection unit, a bank-note detection system, credit card system, or other automatic payment system may be used. Such mechanisms are weU known.
  • die system is ready to print a photograph copy.
  • the photograph transport mechanism 517 moves the photograph
  • This scanner can be composed of a color linear CCD, one or more focusing lenses, an optical path, and a means of scanning the optical path of the CCD relative to d e object being scanned.
  • a suitable configuration includes a monoUthic linear CCD sensor containing three lines of optical sensors. If these sensor lines are the same length as the width of the largest photograph to be scanned, tiien no reduction optics are required.
  • the tiiree sensor lines can be fabricated with integral optical filters, one for each of the red, green, and blue additive primary colors. The technology required to manufacture such scanners is weU known.
  • a scanner resolution of 400 dpi is adequate, and eliminates the need for complex sampUng rate conversions to match the 800 dpi resolution of the printer.
  • An array CCD may be used instead of a Unear CCD, in which case no relative movement is required.
  • array CCD's of optimum resolution are currendy too expensive to be practical. This will change in the future, and an area scanning CCD element designed for high definition television is likely to be suitable.
  • the ou ⁇ ut of the scanner 502 is connected to a scanner signal conditioning unit 503.
  • This unit amplifies and filters the CCD analog signal, converts the signal to digital form, provides CCD sensitivity compensation to adjust for differences in individual CCD sensors, and provides image processing functions such as color correction.
  • the ou ⁇ ut of the Scanner signal conditioning unit 503 is raster-ordered continuous tone image data, with typicaUy 24 bits per pixel.
  • a vector error diffusion algorithm is used to achieve a high image quaUty. This operates by selecting the closest printable color in three dimensional color space to the desired color. The difference between die desired color and tiiis printable color is determined. This difference is then diffused to neighboring pixels.
  • the vector error diffusion unit 504 accepts a raster ordered continuous tone input image and generates a bi-level ou ⁇ ut witii 6 bits per pixel (one bit for each of C,C',M,M',Y and K). Alternatively, the color components can be independendy error diffused, although tiiis provides an image of substantiaUy lower quaUty. It is also possible tc dither die continuous tone image to obtain a bi-level image. In this case, a computer optimized stochastic dispersed dot ordered dither is recommended.
  • This data is then processed by die data phasing and fault tolerance system 506.
  • This unit provides the appropriate delays to synchronize the print data with the offset positions of the nozzle of the printing head. It also provides alternate data patiis for fault tolerance, to compensate for blocked nozzles, faulty nozzles or faulty circuits in the head.
  • the monoUthic printing head 50 prints the image 60 composed of a multimde of ink drops onto a recording medium 51.
  • This medium wUl typically be paper, but can also be overhead transparency film, cloth, or most other substantiaUy flat surfaces which wiU accept ink drops.
  • the bi-level image processed by the data phasing and fault tolerance circuit 506 provides die pixel data in the correct sequence to the data shift registers 56. Data sequencing is required to compensate for the nozzle arrangement and die movement of the paper.
  • the heater driver circuits 57 When the data has been loaded into the shift registers, it is presented in parallel to the heater driver circuits 57. At the correct time, these driver circuits will electronically connect the corresponding heaters 58 with the voltage pulse generated by die pulse shaper circuit 61 and die voltage regulator 62.
  • the heaters 58 heat the tip of the nozzles 59, reducing the attraction of the ink to the nozzle surface material. Ink drops 60 escape from the nozzles in a pattern which corresponds to the digital impulses which have been appUed to the heater driver circuits.
  • the pressure of the ink in the nozzle is important and d e pressure in die ink reservoir 64 is regulated by d e pressure regulator 63.
  • the ink drops 60 fall under the influence of gravity or another field type towards die paper 51.
  • the paper is continuaUy moved relative to the print head by the paper transport system 65. As the print head is the full width of the paper used, it is only necessary to move the paper in one direction, and die print head can remain fixed.
  • the various subsystems are coordinated under die control of one or more control microcomputers 511, which also provide die user interface of the system.
  • Figure 10 shows a side view of die photograph copier, showing possible placement of some of the major modules.
  • the original photograph 516 is placed on the copy glass 519.
  • the image of one line of the photograph at a time is presented via three scanning mirrors forming part the photograph transport system 517 and a lens to the linear CCD scanner 502.
  • the signal from the CCD 502 is processed by control electronics 900.
  • Bi-level image data derived from die photograph image is used to control activation of the ink nozzles in the head 50.
  • Sheets of recording material 51 are picked up by the paper pick-up roUer 912 from the paper and ink cartridge 910 and passed through die paper transport roUers 65 and under die head 50, whereupon die ejected ink drops form an image related to die original photograph image.
  • Figure 11 (a) shows a perspective view of the photograph copier with the paper and ink cartridge 910 inserted, and die copy lid down. Visible are the printed paper 51, die ou ⁇ ut paper tray 911, and die user interface control buttons 901.
  • Figure 11(b) shows a perspective view of the photograph copier with the paper and ink cartridge 910 removed, and the copy lid up, exposing the copy glass 519.

Abstract

Cette invention concerne une imprimante photographique couleur numérique (mini-laboratoire) ainsi qu'un copieur de photographies faisant appel à un mécanisme d'impression du type gouttes à la demande et à sélection et séparation de gouttes simultanées. Ce système comprend un scanner couleur à tons continus, une unité de conditionnement des signaux scanner, une unité numérique de création de demi-tons, une unité de mise en phase des données, ainsi qu'un mécanisme d'impression utilisant de l'encre liquide. Lors de la copie, les informations relatives à une image à tons continus provenant du scanner d'image sont corrigées numériquement en couleurs, mises en demi-tons numériquement et en temps réel, puis imprimées par la tête d'impression. Ce système peut être actionné par un opérateur humain ou être entièrement automatique, et permet d'obtenir la copie d'une photographie après détection d'un paiement par pièces de monnaie, billets de banque, carte de crédit ou tout autre moyen.
PCT/US1996/004816 1995-04-12 1996-04-10 Systemes de traitement et de copie de photographies WO1996032813A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US08/765,756 US5909227A (en) 1995-04-12 1996-04-10 Photograph processing and copying system using coincident force drop-on-demand ink jet printing
EP96911640A EP0765570A1 (fr) 1995-04-12 1996-04-10 Systemes de traitement et de copie de photographies

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
AUPN2334A AUPN233495A0 (en) 1995-04-12 1995-04-12 A color photograph copying system
AUPN2337 1995-04-12
AUPN2337A AUPN233795A0 (en) 1995-04-12 1995-04-12 A photograph processing system using lift printing technology
AUPN2334 1995-04-12

Publications (1)

Publication Number Publication Date
WO1996032813A1 true WO1996032813A1 (fr) 1996-10-17

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Application Number Title Priority Date Filing Date
PCT/US1996/004816 WO1996032813A1 (fr) 1995-04-12 1996-04-10 Systemes de traitement et de copie de photographies

Country Status (2)

Country Link
EP (1) EP0765570A1 (fr)
WO (1) WO1996032813A1 (fr)

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GB2356278A (en) * 1999-11-12 2001-05-16 Alessio Falino Multi-functional file vending and printing machine
EP1117246A1 (fr) * 2000-01-11 2001-07-18 Eastman Kodak Company Production d'images à partir d'images digitales contenant les données d'accès de ces images
EP1117247A1 (fr) * 2000-01-11 2001-07-18 Eastman Kodak Company Alteration des propriétés d'images contenant les données d'accès à ces images
WO2001089838A1 (fr) * 2000-05-24 2001-11-29 Silverbrook Research Pty. Ltd. Codeur d'etiquettes pour pages imprimees
US7154638B1 (en) 2000-05-23 2006-12-26 Silverbrook Research Pty Ltd Printed page tag encoder

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2356278A (en) * 1999-11-12 2001-05-16 Alessio Falino Multi-functional file vending and printing machine
EP1117246A1 (fr) * 2000-01-11 2001-07-18 Eastman Kodak Company Production d'images à partir d'images digitales contenant les données d'accès de ces images
EP1117247A1 (fr) * 2000-01-11 2001-07-18 Eastman Kodak Company Alteration des propriétés d'images contenant les données d'accès à ces images
US7154638B1 (en) 2000-05-23 2006-12-26 Silverbrook Research Pty Ltd Printed page tag encoder
US7388689B2 (en) 2000-05-23 2008-06-17 Silverbrook Research Pty Ltd Printed page tag encoder for encoding fixed and variable data
WO2001089838A1 (fr) * 2000-05-24 2001-11-29 Silverbrook Research Pty. Ltd. Codeur d'etiquettes pour pages imprimees
US7070098B1 (en) 2000-05-24 2006-07-04 Silverbrook Res Pty Ltd Printed page tag encoder
US7222780B2 (en) 2000-05-24 2007-05-29 Silverbrook Research Pty Ltd Inline printer assembly
US7398916B2 (en) 2000-05-24 2008-07-15 Silverbrook Research Pty Ltd Printer having straight media path
US7575151B2 (en) 2000-05-24 2009-08-18 Silverbrook Research Pty Ltd Binding printer having straight media path
US7891548B2 (en) 2000-05-24 2011-02-22 Silverbrook Research Pty Ltd Printer having straight media path
US7959066B2 (en) 2000-05-24 2011-06-14 Silverbrook Research Pty Ltd Controller having tag encoder for printhead

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