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
• • 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
  • H04N1/23—Reproducing arrangements

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
• thermal printing which involves a thermal imaging bar which is in contact with paper coated with a substance which changes color when heated.
• This paper is commonly known as 'thermal paper'
• the printing mechanism is known as thermal printing.
• Thermal paper has significant disadvantages over 'plain paper' printing. Among these are that the tactile feel of the coated paper is unpopular, the image fades rapidly, and the paper has a strong tendency to curl.
• Thermal printers are also typically low resolution bi-level printers. Facsimile machines using 'plain paper' are also available. Some of these use laser electrophotographic print engines as the means of marking the paper.
• the personal computer must contain a modem.
• Computers are less portable than printed magazines.
• the establishment of search criteria can be complex, and the 'general public' is likely to have considerable resistance to learning the complex procedures involved.
• the textual information bandwidth from computer to human is lower than for printed magazines. Advantages of reading daily magazines on computer include interactivity, digital archiving, digital sorting and searching, and motion video capability.
• television sets are very low resolution, with typically no more than 40 characters readable across the screen 4)
• Television sets are overscanned, with part of the image of the screen.
• the amount of image which is not visible varies widely from television to television. This restricts the space for characters to the television 'safe area', further restricting the displayable text.
• the normal viewing distance of a television is greater than two meters. This also restricts the amount of text that is easily readable on screen.
• This patent relates to the use of facsimile machines for the delivery of personalized magazines.
• a system using low cost color facsimile machines utilizing print heads operating on the principle of concurrent drop selection and drop separation drop on demand printing is described.
• Facsimile transmission data formats are standard worldwide
• Facsimile machines are typically permanently connected to telephone lines, so the data can be sent at any time. Sending daily personalized magazines at night is convenient for the recipient, as well as reducing the peak telephone line usage.
• Standard telephone lines can be used, as there is no consumer expectauon of motion video or high speed interactivity
• the personalized magazines are printed on paper, which can be read anywhere 5)
• the printed pages are high resolution, with 600 dpi text and 600 dpi halftoned color images being readily achievable.
• Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact- low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing.
• ink jet printing mechanisms Many types have been invented. These can be categorized as either continuous ink jet (CIJ) or drop on demand (DOD) ink jet. Continuous ink jet printing dates back to at least 1929: Hansell, US
• 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. 3,416,153, 1966 discloses a method of achieving variable optical density of printed spots in CU printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture. This technique is used in ink jet printers manufactured by Iris Graphics.
• Kyser et al US Pat. No. 3,946,398, 1970 discloses a DOD ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand.
• Many types of piezoelectric drop on demand printers have subsequently been invented, which utilize piezoelectric crystals in bend mode, push mode, shear mode, and squeeze mode.
• Piezoelectric DOD printers have achieved commercial success using hot melt inks (for example, Tektronix and Dataproducts printers), and at image resolutions up to 720 dpi for home and office printers (Seiko Epson).
• Piezoelectric DOD printers have an advantage in being able to use a wide range of inks.
• piezoelectric printing mechanisms usually require complex high voltage drive circuitry and bulky piezoelectric crystal arrays, which are disadvantageous in regard to manufacturability and performance.
• Endo et al GB Pat. No. 2,007,162, 1979 discloses an electrothermal DOD ink jet printer which applies a power pulse to an electrothermal transducer (heater) which is in thermal contact with ink in a nozzle.
• the heater rapidly heats water based ink to a high temperature, whereupon a small quantity of ink rapidly evaporates, forming a bubble.
• the formation of these bubbles results in a pressure wave which cause drops of ink to be ejected from small apertures along the edge of the heater substrate.
• BubblejetTM trademark of Canon K.K. of Japan
• 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 facsimile machine using a printing head operating on the concurrent drop selection and drop separation printing principle.
• the invention further provides a periodical information providing system wherein information is transmitted from a data processing system via telephone or ISDN systems to a facsimile machine which uses a concurrent drop selection and drop separation printing mechanism.
• 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(0 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 plain paper facsimile using printing technology according to the present invention.
• Figure 7 shows a simplified schematic diagram of a plain paper facsimile using printing technology according to the present invention.
• Figure 8 shows a side view of major component placement in one configuration of the facsimile.
• Figure 9 shows a perspective view of one possible configuration of the facsimile.
• the invention is a plain paper facsimile machine which uses a concurrent drop selection and drop separation printing mechanism.
• a facsimile machine When used as a facsimile machine, two compatible machines are required. One acts as an image sending device, and the other acts as an image receiving device. The image to be sent is placed on the scanner of the image sending device.
• a digital communications link is established over a communications network such as Integrated Services Digital Network (ISDN) or the Public Subscriber Telephone network (PSTN).
• ISDN Integrated Services Digital Network
• PSTN Public Subscriber Telephone network
• This data transmitted on this link is best transmitted in a facsimile transmission standard, such as G2, G3, or G4.
• the image is scanned and compressed using a facsimile compatible algorithm such as those standardized by the CCITT. This information is then sent via the communications link to the receiving device, which may be any compatible facsimile machine.
• the data is received from the communications network.
• This data is interpreted according to the appropriate facsimile transmission standard, and is expanded and stored in the bi-level page memory.
• the contents of the page memory are then printed using the printing head according to the present invention.
• a customized magazine and information distribution system which uses a color facsimile machine as the information delivery system.
• Daily news and other updated information is matched against a customers information request profiles on a daily basis. This information is transmitted overnight to the customers facsimile machine, which uses a drop on demand printing mechanism according to the present invention.
• 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 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.
• Monolithic A4 pagewidth print heads can be manufactured using standard 300 mm (12") silicon wafers
• 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 ⁇ J 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 ⁇ J printheads is also very high.
• An 800 dpi A4 full color pagewidth ⁇ J 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 imselected drops.
• Electrothermal Medium drop selection Requires ink pressure reduction of ink energy, suitable for hot oscillation mechanism. Ink viscosity, combined melt and oil based inks. must have a large decrease with oscillating ink Simple fabrication. in viscosity as temperature pressure CMOS drive circuits can increases be fabricated on same substrate
• Electrothermal Well known technology High drop selection energy, bubble generation, simple fabrication, requires water based ink, with insufficient bipolar drive circuits can problems with kogation, bubble volume to be fabricated on same cavitation, thermal stress cause drop ejection substrate
• Electrostatic Simple electrode Nozzle pitch must be attraction with one fabrication relatively large. Crosstalk electrode per nozzle between adjacent electric fields. Requires high voltage drive circuits
• drop selection means may also be used.
• the preferred drop selection means for water based inks is method
• the preferred drop selection means for hot melt or oil based inks is method 2: 'Electrothermal reduction of ink viscosity, combined with oscillating ink pressure".
• This drop selection means is particularly suited for use with inks which exhibit a large reduction of viscosity with increasing temperature, but only a small reduction in surface tension. This occurs particularly with non-polar ink carriers with relatively high molecular weight This is especially applicable to hot melt and oil based inks.
• 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.
• Transfer Very small spot sizes can Not compact due to size of Proximity (print be achieved, very low transfer roller or transfer head is in close power dissipation, high belt. proximity to a accuracy, can print on transfer roller or rough paper belt
• Proximity with Useful for hot melt inks Requires print medium to be oscillating ink using viscosity reduction very close to print head pressure drop selection method, surface, not suitable for reduces possibility of rough print media. Requires nozzle clogging, can use ink pressure oscillation pigments instead of dyes apparatus
• 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).
• 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 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).
• the ink is distributed to the back surface of the head 50 by an ink channel device 75.
• the ink preferably flows through slots and/or holes etched through the silicon substrate of the head 50 to the front surface, where the nozzles and actuators are situated.
• the nozzle actuators are electrothermal heaters.
• an external field 74 is required to ensure that the selected drop separates from the body of the ink and moves towards the recording medium 51.
• a convenient external field 74 is a constant electric field, as the ink is easily made to be electrically conductive.
• the paper guide or platen 67 can be made of electrically conductive material and used as one electrode generating the electric field.
• the other electrode can be the head 50 itself.
• Another embodiment uses proximity of the print medium as a means of discriminating between selected drops and unselected drops.
• Figure 1(b) is a detail enlargement of a cross section of a single microscopic nozzle tip embodiment of the invention, fabricated using a modified CMOS process.
• the nozzle is etched in a substrate 101, which may be silicon, glass, metal, or any other suitable material. If substrates which are not semiconductor materials are used, a semiconducting material (such as amorphous silicon) may be deposited on the substrate, and integrated drive transistors and data distribution circuitry may be formed in the surface semiconducting layer.
• Single crystal silicon (SCS) substrates have several advantages, including: 1 ) 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;
• nozzle embodiments of the invention may vary in shape, dimensions, and materials used.
• Monolithic nozzles etched from the substrate upon which the heater and drive electronics are formed have the advantage of not requiring an orifice plate.
• the elimination of the orifice plate has significant cost savings in manufacture and assembly.
• Recent methods for eliminating orifice plates include the use of 'vortex' actuators such as those described in Domoto et al US Pat. No. 4,580,158, 1986, assigned to Xerox, and Miller et al US Pat. No. 5,371,527, 1994 assigned to Hewlett-Packard. These, however are complex to actuate, and difficult to fabricate.
• the preferred method for elimination of orifice plates for print heads of the invention is incorporation of the orifice into the actuator substrate.
• This type of nozzle may be used for print heads using various techniques for drop separation.
• Figure 2 shows the results of energy transport and fluid dynamic simulations performed using FIDAP, a commercial fluid dynamic simulation software package available from Fluid Dynamics Inc., of Illinois, USA.
• FIDAP Fluid Dynamics Inc.
• This simulation is of a thermal drop selection nozzle embodiment with a diameter of 8 ⁇ m, at an ambient temperature of 30°C.
• the total energy applied to the heater is 276 nJ, applied as 69 pulses of 4 nJ each.
• the ink pressure is 10 kPa above ambient air pressure, and the ink viscosity at 30°C is 1.84 cPs.
• the ink is water based, and includes a sol of 0.1 % palmitic acid to achieve an enhanced decrease in surface tension with increasing temperature.
• Figure 2(b) shows thermal contours at 5°C intervals 5 ⁇ s after the start of the heater energizing pulse.
• the heater When the heater is energized, the ink in contact with the nozzle tip is rapidly heated. The reduction in surface tension causes the heated portion of the meniscus to rapidly expand relative to the cool ink meniscus. This drives a convective flow which rapidly transports this heat over part of the free surface of the ink at the nozzle tip. It is necessary for the heat to be distributed over the ink surface, and not just where the ink is in contact with the heater. This is because viscous drag against the solid heater prevents the ink directly in contact with the heater from moving.
• Figure 2(c) shows thermal contours at 5°C intervals 10 ⁇ s after the start of the heater energizing pulse.
• the increase in temperature causes a decrease in surface tension, disturbing the equilibrium of forces. As the entire meniscus has been heated, the ink begins to flow.
• Figure 2(d) shows thermal contours at 5°C intervals 20 ⁇ s after the start of the heater energizing pulse.
• the ink pressure has caused the ink to flow to a new meniscus position, which protrudes from the print head.
• the electrostatic field becomes concentrated by the protruding conductive ink drop.
• Figure 2(e) shows thermal contours at 5°C intervals 30 ⁇ s after the start of the heater energizing pulse, which is also 6 ⁇ s after the end of the heater pulse, as the heater pulse duration is 24 ⁇ s.
• the nozzle tip has rapidly cooled due to conduction through the oxide layers, and conduction into the flowing ink.
• the nozzle tip is effectively 'water cooled' by the ink. Electrostatic attraction causes the ink drop to begin to accelerate towards the recording medium. Were the heater pulse significantly shorter (less than 16 ⁇ s in this case) the ink would not accelerate towards the print medium, but would instead return to the nozzle.
• Figure 2(f) shows thermal contours at 5°C intervals 26 ⁇ s after the end of the heater pulse.
• the temperature at the nozzle tip is now less than 5°C above ambient temperature. This causes an increase in surface tension around the nozzle tip.
• the rate at which the ink is drawn from the nozzle exceeds the viscously limited rate of ink flow through the nozzle, the ink in the region of the nozzle tip 'necks', and the selected drop separates from the body of ink.
• the selected drop then travels to the recording medium under the influence of the external electrostatic field.
• the meniscus of the ink at the nozzle tip then returns to its quiescent position, ready for the next heat pulse to select the next ink drop.
• One ink drop is selected, separated and forms a spot on the recording medium for each heat pulse. As the heat pulses are electrically controlled, drop on demand ink jet operation can be achieved.
• Figure 3(a) shows successive meniscus positions during the drop selection cycle at 5 ⁇ s intervals, starting at the beginning of the heater energizing pulse.
• Figure 3(b) is a graph of meniscus position versus time, showing the movement of the point at the centre of the meniscus.
• the heater pulse starts 10 ⁇ s into the simulation.
• 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. To achieve this, the average energy applied to the heater is varied over the duration of the pulse. In this case, the variation is achieved by pulse frequency modulation of 0.1 ⁇ s sub-pulses, each with an energy of 4 nJ.
• 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 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.
• 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 carboxyhc acid with a melting point slightly above the desired drop selection temperature.
• a good example is Arachidic acid.
• An example process for creating the surfactant sol is as follows:
• the surfactant sol is required only in very dilute concentration.
• 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.
• 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.
• ethoxylated alkyl phenols include those listed in the following table:
• 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.
• a surfactant should be chosen with a Krafft point which is near the top of the range of temperatures to which the ink is raised. This gives a maximum margin between the concentration of surfactant in solution at ambient temperatures, and the concentration of surfactant in solution at the drop selection temperature.
• the concentration of surfactant should be approximately equal to the CMC at the Krafft point. In this manner, the surface tension is reduced to the maximum amount at elevated temperatures, and is reduced to a minimum amount at ambient temperatures.
• 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.
• POP Polyoxypropylene
• Two main configurations of symmetrical POE/POP block copolymers are available. These are:
• 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 reducuon m 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 the boiling point of the water.
• operation of an embodiment using thermal reduction of viscosity and proximity drop separation, in combination with hot melt ink is as follows.
• solid ink Prior to operation of the printer, solid ink is melted in the reservoir 64.
• the reservoir, ink passage to the print head, ink channels 75, and print head 50 are maintained at a temperature at which the ink 100 is liquid, but exhibits a relatively high viscosity (for example, approximately 100 cP).
• the Ink 100 is retained in the nozzle by the surface tension of the ink
• the ink 100 is formulated so that the viscosity of the ink reduces with increasing temperature.
• the ink pressure oscillates at a frequency which is an integral multiple of the drop ejection frequency from the nozzle.
• Ink dye or pigment Global Ink cartridge sensor or Global PFM patterns concentration user selection
• 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
• 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 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 prograrnming 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.
• 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.
• Basic ink carrier Water Water, microemulsion, alcohol, glycol, or hot melt
• Figure 5 also includes a graph of non fault tolerant yield 197 which explicitly models the clustering of defects by introducing a defect clustering factor.
• the minimum physical dimensions of the head chip are determined by the width of the page being printed, the fragility of the head chip, and manufacturing constraints on fabrication of ink channels which supply ink to the back surface of the chip.
• the minimum practical size for a full width, full color head for printing A4 size paper is approximately 215 mm x 5 mm. This size allows the inclusion of 100% redundancy without significantly increasing chip area, when using 1.5 ⁇ m CMOS fabrication technology.
• the scanner 502 scans the image.
• the output of the scanner 502 is connected to a scanner signal conditioning unit 503.
• This unit amplifies and filters the analog signal of the image sensor (typically a linear CCD), and converts the signal to digital form.
• This digital image data is digitally compressed by the image compression unit 543.
• the image compression unit compresses the image data using bi-level compression techniques such as the CCiTT standard for facsimile transmission.
• the compressed image is buffered in the compressed image buffer memory 544. This may be implemented as a FIFO, or by using a part of the physical memory that is used for the bi-level page memory 505.
• the compressed data stored in the compressed image buffer 544 is encoded into G2, G3, or G4 facsimile format by the network interface 541 and transmitted on the network 540. This data may be sent to any G2, G3, or G4 compatible facsimile machine.
• Different communications networks can be used instead of ISDN or PSTN.
• digital satellite transmission systems may be used.
• the system can also be used over local area networks such as Ethernet or FDDI, or across wide area networks such as the Internet.
• the network interface 541 is replaced with a digital interface to the appropriate network system.
• This facsimile system has many advantages over prior-art systems.
• the Bi-level page memory 505 requires approximately 16 MBytes. This can be implemented in DRAM.
• the Bi-level page memory may be a section of the main system processor's memory. PDL interpreters which require random access to a page memory cannot use the data path described for PDL interpreters which are able to render a page in scan-line order.
• One alternative is to provide the PDL with a full frame continuous tone memory. However, for 600 dpi A4 images, this requires more than 100 MBytes of high speed memory. This is currently too expensive to include in low cost office automation equipment.
• An alternative is to render the image directly to the bi-level page memory 505.
• the color facsimile system should use whichever compression and encoding system actually becomes the world standard in color facsimile transmission.
• the compressed image is stored in the compressed image memory 544. This may be implemented using a part or all of the physical memory that is used for the bi-level page memory 505, thereby reducing manufacturing costs.
• the compressed data stored in the compressed image memory 544 is encoded as ISDN packets by the ISDN interface 541 and transmitted on the ISDN network 540.
• the digitally halftoned image data is stored in the bi-level image memory 505. If the compressed image memory 544 and the bi-level page memory 505 share the same physical memory, then care must be taken not to overwrite compressed image data with halftoned image data before it has been de-compressed and halftoned. When the image expansion and halftoning process is complete, the image is printed using the color printing head in the same manner as color images generated by the copier or printer functions are printed.
• Figure 8 shows a side view of the layout of major components for one possible configuration of the facsimile machine.
• the facsimile machine includes an ink cartridge 920, an ink pressure regulator 63, a circuit board containing the control electronics 900, a full width print head 50, an optional telephone handset 549, and various other units.

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