JPH10501485A - Heater power compensation for thermal lag in thermal printing systems - Google Patents

Abstract

SUMMARY A method and apparatus for compensating a printhead operating in a thermal drop-on-demand print mode for the effects of thermal lag is disclosed. The apparatus includes a counter that generates a number representing the amount of elapsed time as a ratio of the total pulse duration during the heater excitation pulse. The output of this counter is connected to a device that determines the power supply voltage required for the elapsed time. This result is used to control a programmable power supply connected to the printhead heater power supply. The apparatus is preferably a look-up table stored in a digital memory containing pulse waveforms calculated using a iterative transient finite element analysis of the thermal state of the nozzle during simulated operation.

Description

DETAILED DESCRIPTION OF THE INVENTION Heater power compensation for thermal lag in thermal printing systems Field of the invention The present invention relates to the field of computer controlled printing devices, and more particularly to the field of thermally excited drop-on-demand (DOD) printing systems. Background of the Invention A variety of many types of digitally controlled printing systems have been invented, and many types are currently in production. These printing systems use various operating mechanisms, various marking agents, and various recording media. Examples of digital printing systems currently in use include: laser electrophotographic printers; LED electrophotographic printers; dot matrix impact printers; thermal paper printers; film recorders; Printer (dye diffusion thermal transfer printer); and inkjet printer. However, while the traditional schemes are enormously expensive to install and rarely become commercially viable unless thousands of copies of a particular page are printed, the aforementioned electronic printing systems are currently not It does not significantly replace the conventional method. Thus, there is a need for an improved digitally controlled printing system that can produce high quality color images at high speed and at low cost, for example, using plain paper. Ink-jet printing, for example, is not an impact type, has low noise, can print on plain paper, and does not need to transfer or fix toner, so it has been recognized as an outstanding competitive means in the field of digitally controlled electronic printing. It has been reached. Many types of inkjet printing mechanisms have been invented. They can be classified as either continuous inkjet (CIJ) or drop-on-demand (DOD) inkjets. Continuous inkjet printing dates back to at least 1929: Hansell, US Pat. No. 1,941,001. US Pat. No. 3,373,437, 1967 to Sweet et al. Discloses an array of continuous ink jet nozzles in which ink drops to be printed are selectively filled and deflected toward a recording medium. Have been. This technique is known as binary deflection CIJ and is used by several companies, including Elmjet and Scitex. US Pat. No. 3,416,153,1966 to Hertz et al. Describes a printing spot having various optical densities in CIJ printing by adjusting the number of droplets passing through a small aperture (opening) using electrostatic dispersion of a filled drop stream. Are disclosed. This technology is used in an ink jet printer manufactured by Iris Graphics. No. 3,946,398, 1970 by Kyser et al. Applies a high voltage to a piezo (piezoelectric) crystal to bend the crystal, apply pressure to the ink container, and eject drops on demand (on demand). A DOD inkjet printer is disclosed. Subsequently, many types of piezoelectric drop-on-demand printing presses utilizing piezo crystals in bending mode, push mode, shear mode, and draw mode were invented. Piezoelectric DOD presses have achieved commercial success using hot melt inks (eg, Tektronix and Dataproducts printers) and image resolutions of less than 720 dpi for home and office printers (Seiko Epson). . Piezoelectric DOD printing machines have the advantage of using a wide range of inks. However, piezoelectric printing mechanisms usually require complex high voltage drive circuits and large piezo crystal arrays, which are disadvantageous in terms of productivity and performance. GB Pat. No. 2,007,162,1979 by Endo et al. Discloses an electrothermal DOD ink jet printer that applies a power pulse to an electrothermal converter (heater) that is in thermal contact with the ink in the nozzles. The heater rapidly heats the water-based ink to a high temperature, causing a small amount of the ink to evaporate rapidly and create bubbles. The generation of these bubbles results in pressure waves that cause ink drops to be ejected from small apertures provided along the edges of the heater substrate. This technology, Bubblejet ^TM (Registered trademark of Canon Inc., Japan) and used in a wide range of printing systems commercially available from Canon, Xerox, and other manufacturers. US Pat. No. 4,490,728, 1982 to Vaught et al. Also discloses an electrothermal drop injection system that also operates with bubble generation. In this system, drops are ejected in a direction perpendicular to the plane of the heater substrate through nozzles made in an aperture plate above the heater. This system is known as Thermal Ink Jet (thermal ink jet) and is manufactured by Hewlett-Packard Company. As used herein, the term "Thermal Ink Jet" refers to Hewlett-Packard systems and generally Bubblejet. ^TM To both known systems. Thermal Ink Jet printing typically requires about 20 μJ during about 2 μs to eject each drop. A substantial power consumption of 10 watts for each heater is disadvantageous in itself, requires more specialized inks, complicates the drive electronics and causes degradation of the heater elements. Other ink jet printing systems are described in the technical literature, but are not currently used on a commercial scale. For example, US Pat.No.4,275,290 teaches that ink can flow freely under the printhead toward the paper spaced by spacers by matching the addresses of predetermined printhead nozzles with heat pulses and water pressure. It discloses a system that can do this. US Pat. Nos. 4,737,803; 4,737,803 and 4,748,458 disclose an ink jet recording system that causes ejection of an ink drop onto a print sheet by the address of a printhead nozzle ink coincident with a heat pulse and an electrostatic attraction field. I have. Each of the inkjet printing systems described above has advantages and disadvantages. However, it is widely known that there is still a need for improved inkjet printing methods that provide advantages, for example, in terms of cost, speed, quality, reliability, power usage, simplicity of construction and operation, durability and consumables. ing. Summary of the Invention In my co-filed application, titled "Liquid Ink Printing Apparatus and System" and "Coincident Drop-Selection, Drop-Separation Printing Method and System", there is a significant improvement over overcoming the above-mentioned problems of the prior art. A new method and apparatus that results is described. These inventions relate, for example, to drop size and placement accuracy, to achievable printing speed, to power usage, to durability and to the thermal stresses encountered during operation and to other printer performance characteristics, and to productivity. And provides important advantages in terms of useful ink properties. One important object of the present invention is to further improve the structure and method described in the above-mentioned application and thus contribute to the advancement of printing technology. Accordingly, it is an important object of the present invention to provide improvements for thermal drop-on-demand printing systems that provide more consistent print output. In one aspect, the present invention relates to a printing device of the type having a thermal print head and a heater device that produces heat in response to excitation power, wherein the improved power control system comprises: A programmable power source for exciting the heater device; (b) varying the power source applied to the heater device during the excitation pulse during the excitation pulse by controlling the power source as predetermined. Control device to do. In a further preferred embodiment of the invention, the required voltage of the power supply is calculated before the operation of the print head and stored as digital information in an electronic memory. In a further preferred embodiment of the invention, the voltage measuring unit of the power supply comprises a counting device for providing a number representing the amount of time elapsed during the heater excitation pulse as a ratio of the total pulse duration, the output of which is digital-analog. It forms part or all of the addresses of a digital electronic look-up table connected to the converter. A further preferred aspect of the invention is that the counter function includes a circuit that produces a non-linear display of elapsed time. A further preferred embodiment of the invention is that the voltage of the heater power supply is determined by the following equation: k (t) ≒ p (t) A further preferred embodiment of the invention is that the power supply voltage also compensates for the print density. A further preferred aspect of the invention is that the power supply voltage also compensates for the ambient temperature. A further preferred aspect of the invention is that the power supply voltage compensates for both print density and ambient temperature. In a further preferred aspect of the invention, the voltage of the heater power supply is determined by the following equation: BRIEF DESCRIPTION OF THE FIGURES FIG. 1 (a) is a simplified block diagram of one representative printing device according to the present invention. FIG. 1 (b) is a cross-sectional view of one variation of the nozzle tip according to the invention. 2 (a) to 2 (f) show hydrodynamic simulations of drop selection. FIG. 3 (a) shows a hydrodynamic simulation of a limiting element of a nozzle in operation according to an embodiment of the invention. FIG. 3 (b) shows the continuous meniscus position during drop selection and separation. FIG. 3 (c) shows the temperature at various points during the drop selection cycle. FIG. 3 (d) shows measured surface tension versus temperature curves for various ink additives. FIG. 3 (e) shows a power pulse applied to the heater of the nozzle to create the temperature curve of FIG. 3 (c). FIG. 4 shows a block diagram of a print head drive circuit for implementing the invention. FIG. 5 shows the expected production yields for an A4 page width color printhead embodying the features of the invention, with and without fault tolerance. 6 (a) and 6 (b) show simplified block diagrams of a method for controlling printhead power in relation to a power function p (t) according to the invention. FIG. 7 shows a timing diagram of a four-phase print head for power function compensation according to the invention. Detailed description of the preferred embodiment In one general aspect, the present invention comprises a drop-on-demand printing mechanism, wherein the means for selecting a drop to be printed comprises a location between the selected drop and the unselected drop. Creates a difference, but it is not enough to cause the ink drop to overcome the surface tension of the ink and separate from the puddle, and the other means to separate the selected drop from the puddle. Is provided. Due to the separation of the drop selection means from the drop separation means, the energy required to select which ink drop is to be printed is significantly reduced. Only the drop selection means must be driven by individual signals to each nozzle. The drop separation means may be a field or state that is applied to all nozzles simultaneously. The drop selection means may be selected from, but is not limited to, the following list: 1) electrothermal reduction of the surface tension of the pressurized ink 2) electrothermal reduction of insufficient bubble volume to cause drop ejection Bubble generation 3) Piezoelectric means with insufficient volume change to cause drop ejection 4) Electrostatic attraction using one electrode per nozzle Drop separation means is not limited, but can be selected from the list below May be: 1) Proximity (the recording medium is very close to the printhead) 2) Proximity by vibrating ink pressure 3) Electrostatic attraction 4) Magnetic attraction It shows desirable characteristics. The table also lists some ways in which some embodiments described herein or in my other related applications achieve improvements over the prior art. "DOD printing technology goals" In thermal ink jet (TIJ) and piezo ink jet systems, approximately 10 meters / second is required to ensure that the selected ink drop overcomes the surface tension of the ink, separates from the ink pool, and strikes the recording medium. Drop speed is desired. In these systems, the efficiency of converting electrical energy to drop kinetic energy is very low. The efficiency of the TIJ system is almost 0.02%). This means that the high current must be switched in the drive circuit of the TIJ print head. The drive circuit of the piezoelectric ink jet head must switch high voltage or drive a high capacitive load. The total power consumption of the page width TIJ printhead is also very high. An 800 dpi A4 full color page width TIJ printhead that prints one 4-color black image per second consumes about 6 kW of power, most of which is converted to waste heat. This difficulty in removing heat hinders the production of low cost, high speed, high resolution, compact page width TIJ systems. One important feature of embodiments of the present invention is a means to significantly reduce the energy required to select which ink drop to print. This is achieved by separating the means for selecting the ink drop from the means for ensuring that the selected drop separates from the puddle and forms a dot on the recording medium. Only the drop selection means must be driven by individual signals to each nozzle. The drop separation means may be a field or state that is applied to all nozzles simultaneously. The table "Drop Selection Means" shows some possible drop selection means according to the invention. The drop selection means is only needed to create sufficient change in the location of the selected drop so that the drop separation means can distinguish between the selected drop and the unselected one. "Drop selection means" Other drop selection means may be used. A preferred means of drop selection of ink on hydrogen is Method 1: "Electrothermal reduction of surface tension of pressurized ink". This drop selection means offers many advantages over other systems, including the following features: low power operation (about 1% of TIJ), compatibility with CMOS VLSI chip assembly, low voltage operation (about 10V) ), High nozzle density, low temperature operation, and a wide range of compatible ink formulations. The ink must show a decrease in surface tension with increasing temperature. A preferred drop selection means for hot melt or oil based inks is Method 2: "Electrothermal reduction of ink viscosity in relation to oscillating ink pressure". This drop selection means is particularly suitable for use with inks that exhibit a large decrease in viscosity with increasing temperature, but exhibit only a small decrease in surface tension. This occurs especially with non-polar ink carriers having relatively high molecular weights. This is particularly applicable to hot melt and oil based inks. The table "Drop Separators" shows some possible ways to separate the selected drop from the puddle and to ensure that the selected drop forms a dot on the print media. The drop separating means distinguishes the selected drop from the non-selected drop to ensure that the non-selected drop does not form a dot on the print medium. "Drop separation means" Other drop separation means may be used. The preferred drop separation means will depend on the application. For most applications, Method 1: "electrostatic attraction" or Method 2: "AC field" is most suitable. For applications where a smooth coated paper or film is used and where ultra-high speed is not essential, Method 3: "Proximity" may be appropriate. For high speed, high quality systems, Method 4: "Transfer Proximity" may be used. Method 6: "Magnetic attraction" is suitable for portable printing systems where the print media is too coarse for proximity printing and where the high voltage required for electrostatic drop separation is undesirable. There is no clear "best" drop separation method that can be applied in all situations. Further details of various types of printing systems according to the present invention are described in the following Australian patent application, filed April 12, 1995, the disclosure of which is incorporated herein by reference: "Liquid Ink Fault Tolerant" (Fault tolerant) (LIFT) printing mechanism "(Application No .: PN2308);" Electrothermal drop selection in LIFT printing "(Application No .: PN2309);" Drop separation of LIFT printing by proximity of print media "(Application No .: PN2310); "Adjustment of Drop Size of Proximity LIFT Printing by Changing Head to Match Media Distance" (Application No .: PN2311); "Increasing Proximity LIFT Printing for Acoustic Ink Wave" (Application No .: PN2312); (Application number: PN2313); "Multiple simultaneous drop sizes in proximity LIFT printing" (Application number: PN2321); "Self cooling operation of thermally activated print head" (Application number: PN2322); Decrease LI FT printing "(application number: PN2323); FIG. 1 (a) shows a simplified schematic diagram of one preferred printing system according to the invention. 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 form of digital image display. This image data is converted by the image processing system 53 into a pixel-map page image. This may be a raster image processor (RIP) for PDL image data or a pixel image manipulation for raster image data. The continuous tone data produced by the image processing system 53 is halftoned. Halftoning is performed by the digital halftoning unit 54. The halftoned bitmap image data is stored in the image memory 72. Depending on the configuration of the printing press and system, the image memory 72 may be a full page memory or a band memory. The heater control circuit 71 reads data from the image memory 72, and applies a time-varying electric pulse to a nozzle heater (103 in FIG. 1B) which is a part of the print head 50. These pulses are applied to appropriate nozzles at appropriate times, so that the selected drop forms a spot on the recording medium 51 at an appropriate position specified by data in the image memory 72. The recording medium 51 is moved relative to the head 50 by a paper transport system 65, which is electrically controlled by a paper transport control system 66, which is in turn controlled by a microcontroller 315. Will be controlled. The paper transport system shown in FIG. 1 (a) is only an overview, and thus many different mechanical configurations are possible. In the case of a page width print head, it is most convenient to move the recording medium 51 past the stop head 50. However, in the case of a scanning printing system, moving the head 50 along one axis (in the sub-scanning direction) and the recording medium 51 along its orthogonal axis (in the main scanning direction) in a relative raster motion, Usually the most convenient. Microcontroller 315 may also control ink pressure regulator 63 and heater control circuit 71. In printing using surface tension reduction, ink is contained in the ink tank 64 under pressure. At rest (no ink drops fired), the ink pressure is insufficient to overcome surface tension and fire the drops. A constant ink pressure can be obtained by applying pressure to the ink tank 64 under the control of the ink pressure regulator 63. Alternatively, for larger printing systems, ink pressure can be generated and controlled very precisely by positioning the top surface of the ink in ink tank 64 at a suitable distance above head 50. This ink level is adjustable with a simple float valve (not shown). In printing using viscosity reduction, the ink is stored under pressure in the ink tank 64, causing the ink pressure to oscillate. The device that produces this vibration may be a piezoelectric actuator mounted on an ink channel (not shown). When properly processed using the drop separation means, selected drops begin to form spots on the recording medium 51, while non-selected drops remain in the ink pool. The ink is distributed on the back surface of the head 50 by the ink channel device 75. The ink preferably flows through the silicon substrate of the head 50 through etched slots and / or holes to the front where the nozzles and actuators are located. For heat selection, the nozzle actuator is an electric heater. Certain types of printing presses according to the present invention require an external field 74 to ensure that the selected drop separates from the ink reservoir and moves toward the recording medium 51. In a conventional external field 74, the ink is a constant electric field because the ink is easily made conductive. In this case, the paper guide or platen 67 may be made from a conductive material and used as one electrode for generating an electric field. The other electrode may be the head 50 itself. Another embodiment uses print media proximity as a means to distinguish between selected and unselected drops. With a small drop size, the gravity on the ink drop is very small; ^-Four Therefore, gravity is almost always negligible. Therefore, the print head 50 and the recording medium 51 can be arranged in any direction with respect to the local gravitational field. This is an important requirement for portable printers. FIG. 1 (b) is a close-up close-up view of a single microscopic nozzle tip embodiment of the invention assembled using an improved CMOS process. The nozzle etches into the substrate 101, which can be silicon, glass, metal, or any other suitable material. If a non-semiconductor substrate is used, a semiconductive material (such as amorphous silicon) may be deposited on the substrate, and integrated drive transistors and data distribution circuits may be formed in the surface semiconductive layer. Good. Single crystal silicon (SCS) substrates have several advantages, including: 1) High performance drive transistors and other circuits can be incorporated into the SCS; 2) Printheads are standard VLSI manufacturing equipment 3) SCS has high mechanical strength and rigidity; and 4) SCS has high thermal conductivity. In this embodiment, the nozzle is cylindrical with an annular heater 103. The nozzle tip 104 is formed from a layer 102 of silicon dioxide deposited during the assembly of a CMOS drive circuit. The nozzle tip is passivated with silicon nitride. The protruding nozzle tip controls the point of contact of the pressurized ink 100 on the print head surface. The printhead surface is also made hydrophobic to prevent accidental spread of ink across the front of the printhead. Many other configurations for the nozzle are possible, and embodiments of the inventive nozzle may vary in shape, dimensions, and materials used. The one-piece nozzle etched from the substrate on which the heater and drive circuitry are formed has the advantage of not requiring an orifice plate. Eliminating the orifice plate provides significant manufacturing and assembly cost savings. Recent methods of eliminating orifice plates are described in US Pat. Nos. 4,580,158, 1986 by Domoto et al. (Assigned to Xerox) and US Pat. Nos. 5,371,527, 1994 by Miller et al. (Assigned to Hewlett-Packard). Includes the use of "vortex" actuators as described. However, they are complex to operate and difficult to assemble. A preferred method of eliminating the orifice plate of the inventive printhead is to incorporate an orifice into the actuator substrate. Nozzles of this type may be used in printheads that use various techniques for drop separation. Operation using electrostatic drop separation As a first example, an operation utilizing thermal reduction of surface tension as well as electrostatic drop separation is shown in FIG. FIG. 2 shows the results of energy transfer and hydrodynamic simulations performed using FIDAP, a commercial hydrodynamic simulation software package commercially available from Fluid Dynamics, Illinois, USA. This simulation is for an embodiment of a thermal drop selection nozzle with an ambient temperature of 30 ° C. and a diameter of 8 μm. The total energy applied to the heater was 276 nJ, which was applied as 69 pulses every 4 nJ. The ink pressure is 10 kPa above ambient air pressure and the viscosity of the ink at 30 ° C. is 1.84 cPs. The ink is water-based and contains a sol of 0.1% palmitic acid, which achieves a significant decrease in surface tension with increasing temperature. 2 shows a cross section of the nozzle tip up to a distance of 40 μm in the radial direction from the central axis of the nozzle. The heat flow in nozzles of various materials, including silicon (silicon), silicon dioxide, silicon nitride, amorphous silicon dioxide, crystalline silicon dioxide, and water-based inks provide the density, heat capacity, and heat of each material. Simulated using conductivity. The time step of the simulation is 0.1 μs. FIG. 2A shows a stationary state immediately before the heater is operated. By ensuring that the ink pressure plus the external electrostatic field is not enough to overcome the surface tension of the ambient temperature ink, an equilibrium is created where the ink does not leak from the stationary nozzles . At rest, the meniscus of the ink does not protrude significantly from the surface of the printhead, and thus the electrostatic field is not significantly concentrated on the meniscus. FIG. 2 (b) shows isotherms at 5 ° C. intervals of 5 μs after the start of the heater heating pulse supply. As the heater heats, the ink in contact with the nozzle tip heats up quickly. The reduced surface tension causes the heated portion of the meniscus to expand rapidly compared to the cold ink meniscus. This causes convection and rapidly transfers this heat over the portion of the free surface of the ink at the nozzle tip. Heat needs to be distributed throughout the ink surface, not just where the ink is in contact with the heater. This is because the viscous resistance to the solid heater does not move ink in direct contact with the heater. FIG. 2 (c) shows isotherms at 5 ° C. intervals 10 μs after the supply of the heater heating pulse is started. The increase in temperature causes a decrease in surface tension and disrupts the force balance. When the entire meniscus is heated, the ink starts to flow. FIG. 2D shows isotherms at 5 ° C. intervals 20 μs after the supply of the heater heating pulse is started. The ink pressure causes ink to flow to a new meniscus position and protrudes from the print head. The electrostatic field is compacted by the protruding conductive ink drops. FIG. 2 (e) shows isotherms at 5 ° C. intervals 30 μs after the supply of the heater heating pulse was started, which is also 6 μs after the end of the heater pulse because the duration of the heater pulse is 24 μs. . The nozzle tip is cooling rapidly due to conduction through the layer of oxide as well as into the flowing ink. The nozzle tip is effectively "water cooled" with the ink. Due to the electrostatic attraction, the ink drop starts to be accelerated toward the recording medium. If the heater pulse is too short (less than 16 μs in this case), the ink will not be accelerated toward the recording medium and will instead return to the nozzle. FIG. 2 (f) shows an isotherm at an interval of 5 ° C. after 26 μs from the end of the supply of the heater heating pulse. The temperature of the nozzle tip is now less than 5 ° C. above ambient temperature. This causes an increase in surface tension around the nozzle tip. When the speed at which ink is withdrawn from the nozzle exceeds the speed defined by the viscosity of the ink flow through the nozzle, the ink in the area of the nozzle tip "thinns" and the selected drops separate from the ink pool. Thereafter, the selected drop proceeds to the recording medium under the influence of an external electrostatic field. The meniscus of the ink at the nozzle tip then returns to its rest position and waits 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. Since the heat pulse is electrically controlled, a drop-on-demand type ink jet operation can be achieved. FIG. 3A shows the continuous meniscus position during a drop selection cycle at 5 μs intervals after the supply of the heater heating pulse is started. FIG. 3 (b) is a graph of meniscus position versus time, showing the movement of the center point of the meniscus. The heater pulse starts 10 μs after the simulation starts. FIG. 3 (c) shows a composite curve of temperature with respect to time at various points of the nozzle. The vertical axis of the graph is the temperature in units of 100 ° C. The horizontal axis of the graph is time in units of 10 μs. The temperature curve shown in FIG. 3 (b) was calculated by FIDAP using a 0.1 μs time step. The ambient temperature of the place is 30 ° C. Shows the temperature history at three points: A-Nozzle tip: This shows the temperature history of the contact area between the passivation layer, the ink and the air. B-Meniscus Midpoint: This is the range on the ink meniscus halfway between the nozzle tip and the center of the meniscus. C-Tip Surface: This is at a point on the printhead surface 20 μm from the center of the nozzle. The temperature rises only a few degrees. This indicates that the live circuit can be placed closest to the nozzle without suffering performance or life degradation due to high temperatures. FIG. 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 temperature slightly below the boiling point of the ink for the duration of the pulse, and a rapid fall at the end of the pulse. . This is accomplished by varying the average energy applied to the heater over the duration of the pulse. In this case, the change is achieved by pulse frequency modulation of 0.1 μs sub-pulses, each having an energy of 4 nJ. The beak 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 easily be changed without significantly affecting the operation of the print head. Using a relatively high sub-pulse frequency allows for finer control over the power applied to the heater. A sub-pulse frequency of 13.5 Mhz is appropriate because this frequency is also suitable for minimizing the effects of radio frequency interference (RFI). Ink with negative temperature coefficient surface tension The requirement for the surface tension of the ink to decrease with increasing temperature is not a major constraint, as most pure liquids and many mixtures have this attribute. The exact equation for temperature versus surface tension for any liquid is not available. However, the following empirical formula derived by Ramsay and Shields holds for many liquids: Where γ _T Is the surface tension at temperature T, k is a constant, T _c Is the critical temperature of the liquid, M is the molecular weight of the liquid, x is the degree of binding of the liquid, and ρ is the density of the liquid. This equation shows that the surface tension of most liquids drops to zero when its temperature reaches a critical temperature. For most liquids, the critical temperature is essentially above the boiling point at ambient pressure, and therefore, to obtain an ink whose surface tension changes significantly with small temperature changes near the practical jetting temperature, requires an interface The addition of an activator is recommended. The choice of surfactant is important. For example, water-based inks for thermal ink jet printing presses often contain isopropanol alcohol (2-propanol) to reduce surface tension and promote rapid drying. The boiling point of isopropyl alcohol is 82.4 ° C., which is lower than the boiling point of water. As the temperature increases, alcohol evaporates faster than water, reducing the concentration of alcohol and increasing surface tension. Detergents such as 1-Hexanol (bp 158 ° C.) can be used to reverse this effect and obtain a surface tension that decreases somewhat with temperature. However, a relatively large reduction in surface tension with temperature is desirable to maximize the operating range. A reduction in surface tension of 20 mN / m over a temperature range of 30 ° C. is preferred to achieve a large operating margin, while a reduction in the order of 10 mN / m is necessary to achieve operation of the printhead according to the invention. Can be used. Large- △ γ _T Ink with Several methods can be used to obtain a surface tension that has a large negative change with increasing temperature. The two methods are: 1) The ink is solid at ambient temperature, but may contain a low concentration of surfactant sol that melts at a threshold temperature. Particle sizes of less than 1,000 mm are desirable. Suitable surfactant melting points for water-based inks are between 50 ° C and 90 ° C, preferably between 60 ° C and 80 ° C. 2) The ink may contain an oil / water microemulsion having a phase inversion temperature (PIT) above the maximum ambient temperature but below the boiling point of the ink. For stability, the PIT of the microemulsion is preferably above 20 ° C. or the maximum non-operating temperature encountered by the ink. A PIT of approximately 80 ° C is appropriate. Ink with surfactant sol The ink may be made as a sol of small particles of a surfactant that melts in the desired operating temperature range. Examples of this surfactant include carboxylic acids having between 14 and 30 carbon atoms, as in the table below: Since the melting point of sols with small particle sizes is usually somewhat lower than that of bulk materials, it is desirable to select a carboxylic acid with a melting point slightly above the desired drop selection temperature. These carboxylic acids are available in high purity and low cost. The required amount of surfactants is very small and therefore the cost of adding them to the ink is insignificant. Mixtures of carboxylic acids with somewhat different chain lengths may be used to extend their melting points over the temperature range. These mixtures will typically be less costly than pure acids. There is no need to limit the choice of surfactant to simple unbranched carboxylic acids. Surfactants having a branched or phenyl group, or other hydrophobic moieties, may be used. Also, there is no need to use carboxylic acids. The majority of the high polarity half is suitable for the hydrophilic end of the surfactant. Desirably, the polar ends can be ionized in water, so that the surface of the surfactant particles can be charged, promoting dispersion and preventing aggregation. In the case of carboxylic acids, this can be achieved by adding an alkali such as sodium hydroxide or potassium hydroxide. Preparation of ink with surfactant sol The surfactant sol may be made separately at a high concentration and added to the ink at the required concentration. A typical process for making a surfactant sol is as follows: 1) Add carboxylic acid to purified water in an oxygen-free atmosphere. 2) Heat the mixture above the melting point of the carboxylic acid. The water may be brought to a boiling state. 3) Sonicate the mixture until the representative size of the carboxylic acid droplets is between 100Å and 1,000Å. 4) Allow the mixture to cool. 5) Decant the larger particles from the top of the mixture. 6) Add an alkali such as NaOH to ionize carboxylic acid molecules on the surface of the particles. A pH of about 8 is appropriate. This treatment is not necessary, but promotes sol stabilization. 7) Centrifuge the sol. Since the concentration of carboxylic acid is lower than water, relatively small particles accumulate outside the centrifuge and larger particles accumulate in the center. 8) Filter the sol using a pore filter to remove any particles greater than 5000mm. 9) Add surfactant sol to the ink formulation. Sols only need to be well diluted. The ink formulation also contains either dye (s) or pigment (s), germicides, agents that increase the conductivity of the ink when electrostatic drop separation is used, lubricants, and other necessary agents. . An antifoam will generally not be required because no foam is formed during the drop injection process. Cationic surfactant sol Inks made with anionic surfactant sols are generally not suitable for use with cationic dyes or pigments. This is because cationic dyes or pigments can precipitate or aggregate with anionic surfactants. To be able to use cationic dyes and pigments, a cationic surfactant sol is required. The alkali amine series is suitable for this purpose. Various suitable alkali amines are shown in the table below: The method of making the cationic surfactant sol is essentially the same as that of the anionic surfactant sol, except that an acid is used instead of an alkali to adjust the pH balance and increase the charge on the surfactant particles. is there. PH 6 is appropriate when using HCl. Microemulsion base ink An alternative to achieving a large decrease in surface tension with certain temperature thresholds is to base the microemulsion on ink. The microemulsion is selected for a phase inversion temperature (PIT) near the desired injection threshold temperature. Below the PIT, the microemulsion becomes oil in water (O / W), and above the PIT, the microemulsion becomes water in oil (W / O). At low temperatures, surfactants that produce microemulsions prefer a high bending surface around the oil, and at temperatures significantly above the PIT, surfactants prefer a high bending surface around the water. At temperatures close to PIT, microemulsions form a continuous "sponge" of water and oil that are topologically linked. There are two mechanisms by which this reduces surface tension. Near PIT, surfactants prefer surfaces with very low curvature. As a result, the surfactant molecules migrate to the ink / air interface, which has a much smaller curvature than the oil emulsion. This lowers the surface tension of water. Above the phase inversion temperature, the microemulsion changes from O / W to W / O, so the ink / air interface changes from water / air to oil / air. The oil / air interface has a lower surface tension. There are a wide range of possibilities for making microemulsion-based inks. For fast drop injection, it is desirable to select a low viscosity oil. In many cases, water is a suitable polar solvent. However, in some cases, another polar solvent may be required. In these cases, a polar solvent with a high surface tension should be selected so that a large reduction in surface tension is achieved. Surfactants may be selected to provide a desired range of phase inversion temperatures. For example, poly (oxyethylene) alkylphenyl ether (ethoxylated alkylphenol, general formula: C _n H _{2n + 1} C _Four H ₆ (CH _Two CH _Two O) _m Surfactants of the group OH) may be used. The hydrophilicity of the surfactant can be increased by increasing m, and the hydrophobicity can be increased by increasing n. A value of about 10 for m and a value of about 8 for n are suitable. Low cost commercial preparations are the result of the polymerization of various molar ratios of ethylene oxide and alkylphenol, with the exact number of oxyethylene groups varying around the selected average. These commercial preparations are suitable and do not require high purity surfactants having a specific number of oxyethylene groups. The formula for this surfactant is C ₈ H ₁₇ C _Four H ₆ (CH _Two CH _Two O) _n OH (average n = 10). Aliases are octoxynol-10, PEG-10 octyl phenyl ether and POE (10) octyl phenyl ether. HLB is 13.6, melting point is 7 ° C, and cloud point is 65 ° C. Commercial formulations of this surfactant are commercially available under various brand names. The following table lists suppliers and brand names: These are low cost, high volume (less than $ 1 per pound), less than 10 cents per liter for microemulsion inks formulated at 5% surfactant concentration. Other suitable ethoxylated alkyl phenols include those listed in the table below: Microemulsion-based inks have advantages other than controlling surface tension: 1) Microemulsions are thermodynamically stable and will not separate. Therefore, the storage time may be long enough. This is particularly important for office and portable printers that may be used sporadically. 2) Microemulsions are naturally formed with a specific drop size and do not require extensive agitation, centrifugation, or filtration to ensure a specific range of emulsified oil drop sizes. 3) The amount of oil contained in the ink can be high enough, so that dyes that are soluble in oil or water or both can be used. In order to obtain a special color, a mixture of dyes, one of which is soluble in water and the other in oil, can be used. 4) Oil-miscible pigments do not agglomerate because they are captured by oil microdrops. 5) The use of microemulsions can reduce the mixing of various dye colors on the surface of the print media. 6) The viscosity of microemulsion is extremely low. 7) The need for lubricants can be reduced or eliminated. Dyes and pigments in microemulsion based inks A mixture of oils in water has a high oil content, as high as 40%, and forms an O / W microemulsion. For this reason, high filling of the dye or pigment can be achieved. Mixtures of dyes and pigments may be used. Examples of microemulsion based inks having both dyes and pigments are as follows: 1) 70% water 2) 5% water soluble dye 3) 5% surfactant 4) 10% oil 5) 10% oil miscibility Pigments The following table shows the nine basic combinations of oil phase and water phase colorants of the microemulsions that can be used. The ninth combination without the colorant is useful for printing clear coatings, UV inks, and selective gloss highlights. Because many dyes are amphiphilic, large amounts of dye can also be solubilized in the oil-water interface layer when that layer has a very large surface area. It is also possible for each phase to contain multiple dyes or pigments, and for each phase to contain a mixture of dyes and pigments. When using multiple dyes or pigments, the absorption spectrum of the resulting ink will be a weighted average of the absorption spectra of the various colorants used. This raises two problems: 1) Since the absorption beaks of both colorants are averaged out, the absorption spectrum will tend to be wider. This tends to cloud the color. Obtaining a glossy color requires careful selection of dyes and pigments based on their absorption spectrum, as well as colors that are perceptible to humans. 2) The color of the ink may be different on each substrate. If a combination of dye and pigment is used, the color of the dye is unlikely to contribute to the color of the ink printed on more absorbent paper, since the dye will be absorbed by the paper, while The pigment tends to "stay on the top surface" of the paper. This can be an advantage in some situations. Surfactant with Kraft point in drop selection temperature range For ionic surfactants, the solubility is very low below which and the solution has an essentially micelle-free temperature (Kraft point). Above the kraft temperature, micelle formation becomes possible and a rapid increase in surfactant solubility occurs. If the critical micelle concentration (CMC) exceeds the solubility of the surfactant at a particular temperature, then a minimum surface tension will be obtained at the point of maximum solubility, not at CHC. Surfactants generally have a significant drop in efficiency below the Kraft point. This factor may be used to achieve a significant decrease in surface tension with increasing temperature. At ambient temperature, only a portion of the surfactant is in solution. When the nozzle heater is turned on, the temperature rises and most of the surfactant enters the solution, reducing its surface tension. The surfactant should be selected for the Kraft point near the top of the temperature range over which the ink can be raised. This gives maximum room between the concentration of surfactant in solution at ambient temperature and the concentration of surfactant in solution at drop selection temperature. The surfactant concentration should be approximately equal to the CHC at the Kraft point. In this way, the surface tension is reduced to a maximum at elevated temperatures and to a minimum at ambient temperature. The table below shows some commercially available surfactants having the desired range of Kraft points. Surfactant with cloud point in drop selection temperature range Nonionic surfactants using polyoxyethylene (POE) chains may be used to make inks whose surface tension decreases with increasing temperature. At low temperatures, the POE chains are hydrophilic and retain the surfactant in solution. As the temperature increases, the structural water around the POE portion of the molecule is disturbed and the POE portion becomes hydrophobic. Surfactants are increasingly rejected by the hotter water, resulting in increased surfactant concentrations at the air / ink interface, thereby reducing surface tension. The temperature at which the POE portion of a nonionic surfactant becomes hydrophilic is related to the cloud point of the surfactant. POE chains by themselves are not particularly suitable because of their cloud points generally above 100 ° C. Polyoxypropylene (POP) is combined with POE in the form of a POE / POP block copolymer and can lower the cloud point of the POE chain without inducing strong hydrophobicity at low temperatures. Two main configurations of symmetric POE / POP block copolymers are available. They are: 1) Surfactants with a POE segment at the end of the molecule and a POP segment at the center, such as poloxamer class surfactants (collectively CAS 9003-11-6) 2) meroxapol Surfactants with a POP segment at the end of the molecule and a POE segment at the center, such as the class of surfactants (also collectively CAS 9003-11-6). The following table lists some commercial poloxamers and meroxapol types that have cloud points between -100 ° C and 100 ° C: Other types of poloxamers and meroxapol can be easily synthesized using well-known techniques. The desired property is a surface tension as high as possible at room temperature and a cloud point between 40 ° C and 100 ° C, preferably between 60 ° C and 80 ° C. Meroxapol [HO (CHCH _Three CH _Two O) _x (CH _Two CH _Two O) _y (CHCH _Three CH _Two O) _z The type of [OH] would be optimal if the averages x and z are about 4, and the average y is about 15. If a salt is used to increase the conductivity of the ink, the effect of this salt on the cloud point of the surfactant must be considered. The cloud point of POE surfactants disrupts the structure of water (I ^- Increased by ions (like): because this allows more water molecules to be used to form hydrogen bonds with the isolated pairs of oxygen in the POE. The cloud point of the POE surfactant forms a water structure because relatively few water molecules are available to form hydrogen bonds (Cl ^- , OH ^- ). Bromide ions are relatively ineffective. The ink formulation is prepared by changing the length of the POE and POP chains in the block copolymer surfactant and by changing the choice of salts added to increase conductivity (e.g., Cl ^- , Br ^- , I ^- ), Can be "tuned" to the desired temperature range. NaCl appears to be the best choice of salt to increase the conductivity of the ink due to its low cost and non-toxicity. NaCl slightly reduces the cloud point of nonionic surfactants. Hot melt ink The ink need not be liquid at room temperature. Solid "hot melt" inks can be used by heating the printhead and ink tank above the melting point of the ink. Hot melt inks must be formulated so that the surface tension of the molten ink decreases with temperature. For many such formulations using waxes and other materials, a reduction of about 2 mN / m is typical. However, a reduction in surface tension of about 20 mN / m is desirable to obtain a good operating margin when based on a reduction in surface tension rather than a decrease in viscosity. The temperature difference between the resting temperature and the drop selection temperature may be greater for hot melt inks than for water-based inks, since water-based inks are held down to the boiling point of water. The ink must be liquid at resting temperature. The static temperature must be higher than the highest ambient temperature that the printed page is likely to encounter. The quiescent temperature must also be practically low to reduce the power required to heat the printhead and to provide the maximum margin between the quiescent temperature and the drop firing temperature. A resting temperature between 60 ° C and 90 ° C is generally suitable, although other temperatures may be used. Drop ejection temperatures between 160 ° C and 200 ° C are generally suitable. There are several ways to achieve high surface tension reduction with increasing temperature. 1) A dispersion of fine particles of surfactant having a melting point substantially above the static temperature, but substantially below the drop injection temperature can be added to the hot melt ink while in the liquid phase. 2) Preferably, a polar / non-polar microemulsion having a PIT at least 20 ° C. above the melting point of both polar and non-polar compounds. To achieve a large surface tension reduction with temperature, the hot melt ink carrier desirably has a relatively high surface tension (at least 30 mN / m) when at rest temperature. This generally excludes alkanes such as waxes. Suitable materials generally have strong intermolecular attraction, which can be obtained by means of multiple hydrogen bonds, for example polyhydric alcohols such as Hexanetetrol (having a melting point of 88 ° C.). Surface tension of various solutions FIG. 3 (d) shows the calculated temperature effect on the surface tension of various aqueous formulations containing the following additives: 1) 0.1% sol of stearic acid 2) 0.1% sol of palmitic acid 3) 0.1% solution of Pluronic 10R5 (trademark: BASF) 4) 0.1% solution of Pluronic L35 (trademark: BASF) 5) 0.1% solution of Pluronic L44 (trademark: BASF) An ink suitable for the printing system of the present invention discloses its disclosure. It is described in the following Australian patent application, which is incorporated herein by reference: "Ink composition based on a microemulsion" (application number: PN5223, filed September 6, 1995); "Ink composition containing surfactant sol" (Application number: PN5224, filed September 6, 1995); "Ink composition for DOD printers with Krafft point near the drop selection temperature sol" (Application number: PN6240, filed October 30, 1995); and "Dye and pigment in a microemulsion based ink "(application number: PN6241, filed October 30, 1995). Actions using viscosity reduction As a second example, the operation of a specific example using thermal viscosity reduction and proximity drop separation in combination with a hot melt ink is as follows. Prior to the operation of the printing press, the solid ink is melted in the ink tank 64. The ink tank, the ink passage to the printhead, the ink channels 75, and the printhead 50 maintain a temperature at which the ink 100 is liquid at that temperature but exhibits a relatively high viscosity (eg, about 100 cP). The ink 100 is held at the nozzle by the surface tension of the ink. Ink 100 is formulated such that the viscosity of the ink decreases with increasing temperature. The ink pressure oscillates at a frequency that is an integral multiple of the number of times of drop ejection from the nozzle. The vibration of the ink pressure causes the ink meniscus of the nozzle tip to vibrate, but the vibration is small due to the high viscosity of the ink. At normal operating temperatures, these oscillations are of insufficient amplitude to cause drop separation. When the heater 103 is energized, the ink forming the selective drop is heated, resulting in a decrease in viscosity, preferably to a value below 5 cP. The reduced viscosity will cause the ink meniscus to move further during the high pressure portion of the ink pressure cycle. The print medium 51 is placed sufficiently close to the print head 50 so that the selected drops contact the print medium 51, but far enough away that non-selected drops do not contact the print medium 51. Upon contact with the print medium 51, the selected drop portion solidifies and adheres to the print medium. As the ink pressure drops, the ink begins to move backward into the nozzle. The ink body separates from the ink that is solidified on the print medium. Thereafter, the meniscus of the ink 100 at the nozzle tip returns to low amplitude vibration. The viscosity of the ink increases to its resting level as residual heat is dissipated to the ink body and printhead. One ink drop is selected for each heat pulse, separated and forms one spot on print media 51. Since the heat pulse is electrically controlled, a drop-on-demand type ink jet operation can be realized. Print head manufacturing The process for manufacturing an integrated printhead according to the present invention is described in the following Australian patent application filed April 12, 1995, the disclosure of which is incorporated herein by reference: "A monolithic LIFT printing head" ( "Application number: PN2301";"A manufacturing process for monolithic LIFT printing heads" (Application number: PN2302); "A self-aligned heater design for LIFT print heads" (Application number: PN2303); "Integrated four color LIFT print heads" (Application number: PN2304); "Power requirement reduction in monolithic LIFT printing heads" (Application number: PN2305); "A manufacturing process for monolithic LIFT print heads using anisotropic wet etching" (Application number: PN2306); "Nozzle placement in "monolithic drop-on-demand print heads" (Application number: P N2307); "Heater structure for monolithic LIFT print heads" (Application number: PN2346); "Power supply connection for monolithic LIFT print heads" (Application number: PN2 347) ; "External connection for Proximity LIFT print heads" (Application number: PN 2348); and "A self-aligned manufacturing process for monolithic LIFT print heads" (application number: PN2349); and "CMOS process compatible fabrication of LIFT print heads" (application number: PN5 222, filed September 6, 1995) "A manufacturing process for LIFT print heads with nozzle rim heaters" (application number: PN6238, filed October 30, 1995); "A modular LIFT print heads" (application number: PN6237, filed October 30, 1995) ; "Method of incrreasing packing density of printing nozzles" (application number: P N6236, filed October 30, 1995); "Nozzle dispersion for reduced electrostatic interaction between simul taneously printed droplets" (application number: PN6239, October 1995) 30-day application). Print head control An apparatus for providing page image data and controlling heater temperature in a printhead of the present invention is described in the following Australian patent application filed April 12, 1995, the disclosure of which is incorporated herein by reference: "Integrated drive circuitry in LIFT print heads" (application number: PN2295); "A nozzle clearing procedure for Liquid Ink Fault Tolerant (LIFT) printing" (application number: PN2294); "Heater power compensation for temperature in LIFT printing systems" (Application number: PN2314); "Heater power compensation for thermal lag in LIFT printing systems" (Application number: PN2315); "Heater power compensation for print density in LIFT printing systems" (Application number: PN2316); "Accurate control of temperature "Data distribution in monolithic LIFT print heads" (Application number: PN2318); "Page image and fault tolerance routing device for LIFT printing syste ms" (Application number: PN2319); "A removable pressurized liquid ink cartridge for LIFT printers "(application number: PN2320). Image processing of print head The aim of the printing system according to the invention is to obtain a print quality which is comparable to that familiarized in quality to color prints printed using offset printing. This can be achieved with a printing resolution of approximately 1600 dpi. However, printing at 1600 dpi is difficult and expensive to achieve. Similar results can be achieved using 800 dpi printing, using 2 bits per pixel for cyan and magenta and 1 bit per pixel for yellow and black. This color model is referred to herein as CC'HM'YK. Where high quality monochrome image printing is also required, 2 bits per pixel may be used for black. This color model is referred to herein as CC 'MM'YKK'. A color model, halftoning, data compression, and real-time expansion system suitable for use in the system of the present invention and other printing systems is described in U.S. Pat. It is described in the following Australian patent application: "Four level ink set for bi-level colorprinting" (application number: PN2339); "Compression system for page images" (application number: PN2340); "Real-time expansion apparatus for "Compressed page images" (application number: PN 2341); and "High capacity compressed document image storage for digital dolor printers" (application number: PN2342); "Improving JPEG compression in the presence of text" (application number: PN2343); "An expansion and halftoning device for compressed page images" (application number: PN2344); and "Improvements in image halftoning" (application number: PN2345). Applications using the print head according to the invention The printing apparatus and method of the present invention are suitable for a wide range of applications, including, but not limited to, color and monochrome office printing, short run digital printing, high speed digital printing, process color printing, spot color. Printing, offset press additional printing, low-cost printing machine using scanning print head, high-speed printing machine using purge width print head, portable color / monochrome printing machine, color / monochrome copying machine, color / monochrome facsimile machine, composite printing Machine, facsimile / copier, label printing, large format plotter, photocopying, digital photoprocessing printing press, portable printing press built into digital "instant" camera, video printing, photo CD image printing, "Personal Digital" Assistants "for portable printing, wallpaper printing, indoor sign printing, billboard printing, and textiles printing. A printing system according to the present invention is described in the following Australian patent application filed April 12, 1995, the disclosure of which is incorporated herein by reference: "A high speed color office printer with a high capacity digital page i mage store "(application number: PN2329);" A short run digital color printer with a high capacity digital page image store "(application number: PN2330);" A digital color printing press using LIFT printing technology "(application number) : PN2331); "A modular digital printing press" (application number: PN2332); "A high speed digital fabric printer" (application number: PN2333); "A color photograph copying system" (application number: PN2334); "A high "A portable color photocopier using LIFT printing technology" (Application number: PN2336); "A photograph processing system using LIFT printing technology" (Application number: PN2337); "A plain paper facsimile machine using a LIFT printing system" (application number: PN23 38); "A Photo CD system with integrated printer" (application number: PN2293); "A color plotter using LIFT printing technology" (application number: PN2291); "A notebook computer with integrated LIFT color printing system" (application number: PN2292); "A portable printer using LIFT printing system" (application number: PN2300); "Fax machine with on-line database interrogation and custoomized magazine printing" (application number: PN2299); "Miniature portable color printer" (application number) : PN2298); "A color video printer using a LIFT printing system" (application number: PN2296); and "An integrated printer, copier, scanner, and facsimile using a LIFT printing system" (application number: PN2297). Printhead compensation for environmental conditions It is desirable for a drop-on-demand printing system to have consistent and predictable ink drop sizes and locations. Unnecessary changes in ink drop size and position will change the optical density of the resulting print, reducing the perceived print quality. These changes should be limited to a small portion of the nominal ink drop volume and pixel spacing, respectively. There are many factors that can affect drop volume and location. In some cases, the change can be minimized by proper head design. In other cases, the change can be compensated for by an active circuit. 1) Ambient temperature: Changes in ambient temperature can affect the static meniscus position and the temperature obtained with heater pulses. Changes in the stationary meniscus position can be compensated for by changing the ink pressure or the strength of the external electric or magnetic field. The change in temperature obtained with the heater pulse can be compensated for by changing the power supplied to the heater. 2) Nozzle temperature: It is not practical to compensate the temperature separately for each nozzle. Reliable head operation requires a small difference between the nozzle temperature and the ambient temperature measured at the substrate. This can be achieved by using a substrate having a high thermal conductivity and by taking an appropriate time between pulses so that waste heat is dissipated. 3) Nozzle radius: Since it is difficult to apply various electric field strengths or ink pressures to the nozzle based on the nozzle, the change in nozzle radius for nozzles coming from a single ink tank should be minimized. Fortunately, changes in nozzle radius can easily be maintained below 0.5 µm using modern semiconductor manufacturing equipment. 4) Print density: Various numbers of ink drops may be fired in each cycle. As a result, the load resistance of the head can vary widely and rapidly, causing voltage fluctuations due to the finite resistance of the power supply and wiring. This can be precisely compensated by a digital circuit that determines the number of drops to be fired in each cycle and changes the power supply voltage to compensate for the change in load resistance. 5) Ink Contaminants: The ink must be free of contaminants larger than approximately 5 μm, which may penetrate each other and clog the nozzles. This may be achieved by providing a 5 μm absolute filter between the ink container and the head. 6) Surface tension characteristics of the ink: The most important requirement of the ink is the surface tension characteristics. The ink must be formulated so that its surface tension is high enough to hold the ink in the nozzle at ambient temperature within design limits and drops below the firing threshold at the temperature reached by the heater. Many ink formulations can meet these criteria, but care must be taken to control contaminants that affect surface tension. 7) Ink Drying: If the time between drop ejections from the nozzles is too long, the ink at the exposed meniscus may dry out to the extent that the drop ejections are affected or impeded. This can be compensated for by firing one or more drops from each nozzle between each printed page and capping the print head during periods of inactivity. 8) Pulse width: The pulse width of the heater can be precisely controlled and set very close to the minimum pulse width. Higher reliability can be achieved by making the pulse width considerably longer than the minimum. For a 7 μm nozzle using a water-based ink as described herein, the minimum pulse width is approximately 10 μs. The apparent pulse width is set to 18 μs to give a wide operation margin. The pulse width has little effect on the drop size. 9) Clogged or defective nozzles: In many cases, clogged nozzles can be cleared by giving the heater a fast pulse sequence and raising the ink above its boiling point. The vapor bubbles thus generated can drive out "crust" from the dried ink. Persistent occlusion nozzles may be periodically cleaned using a solvent. Defective or permanently clogged nozzles can be automatically replaced with extra nozzles using built-in fault tolerance. 10) Print Media Roughness: This is especially noticeable in proximity printing where media roughness can be a significant part of the head-to-media distance. The fibers protruding in the paper medium cause the ink drop to repel the paper faster than intended, resulting in less ink being transferred to the paper and a smaller drop size. This can be compensated for by using coated paper, compressing the paper fibers with rollers prior to printing, and / or coating or moistening the paper just before printing. Nozzle temperature control Nozzle performance is sensitive to the temperature and heat pulse duration applied to the nozzle tip. If too little energy is supplied to the heater, the temperature of the nozzle tip will not rise fast enough to cause the drop to be fired at the allotted time, or the fired ink drop may be smaller than required. If too much energy is supplied to the heater, too much ink may be ejected, the ink may boil, and more energy will be used for the printhead than required. This energy can then exceed the limits of the self-cooling operation. The amount of energy required to activate the nozzle may be determined by dynamic finite element analysis of the nozzle. The method can determine the required firing energy of the nozzle under various static and dynamic environmental conditions. The optimum temperature distribution for the head involves an instantaneous rise to the firing temperature of the active area of the nozzle tip, maintenance of this area at the firing temperature for the duration of the pulse, and instantaneous cooling of the area to ambient temperature. This optimum is not achievable due to the storage heat capacity and thermal conductivity of the various materials used in nozzle assembly. However, performance improvements can be achieved by shaping the power pulses using curves that can be derived by iterative refinement of the finite element simulation of the printhead. To obtain accurate results, dynamic simulation of the transition fluid using free surface modeling is necessary because the convection of the ink and the ink flow significantly affect the temperature obtained at a particular power curve. Compensation technology Many environmental variables can be compensated to reduce their effects to meaningless levels. Activity compensation for several factors can be achieved by varying the power applied to the nozzle heater. The optimal temperature distribution for the printhead involves an instantaneous rise in the active area of the nozzle tip to the firing temperature, maintenance of this area at the firing temperature for the duration of the pulse, and instantaneous cooling of the area to ambient temperature. This optimum is not achievable due to the storage heat capacity and thermal conductivity of the various materials used in nozzle assembly. However, performance improvements can be achieved by shaping the power pulses using curves that can be derived by iterative refinement of the finite element simulation of the printhead. The power applied to the heater can be changed in a timely manner by a variety of techniques including, but not limited to: 1) changing the voltage applied to the heater 2) modulating the width of a series of short pulses (PWM) 3) Modulate the frequency of a series of short pulses (PFH) In order to obtain accurate results, the convection of the ink and the free flow of the ink can significantly affect the temperature obtained at the specified power curve. Dynamic simulation of transition fluids using surface modeling is needed. It is practical to individually control the power applied to each nozzle by incorporating appropriate digital circuitry into the printhead substrate. One way to accomplish this is to "scatter" a variety of different digital pulse trains across the printhead chip, and use a multiplexing circuit to select the appropriate pulse train for each nozzle. Examples of environmental factors that may be compensated are given in the table "Compensation for environmental factors". This table identifies which environmental factors are best compensated globally (for all printheads) and per chip (for each chip of a composite multichip printhead) and per nozzle. "Compensation for environmental factors" Most applications do not require compensation for all of these variables. Some variables are less effective, and compensation is only needed when very high image quality is required. Print head drive circuit FIG. 4 is a schematic block diagram showing the electronic operation of the print head drive circuit. FIG. 4 is a block diagram of an 800 dpi pagewidth printhead using system for printing process colors using the CC'MM'YK color model. The print head 50 has 39,744 main nozzles and 39,744 spare nozzles, for a total of 79,488 nozzles. The main and spare nozzles are divided into six colors, each of which is separated into eight drive phases. Each drive phase has a shift register, which converts serial data from the head control ASIC 400 to parallel data to enable the heater drive circuit. There are a total of 96 shift registers, each generating data for 828 nozzles. Each shift register consists of 828 shift register stages 217, the output of which is ANDed with the phase enable signal by NAND gate 215. The output of NAND gate 215 drives inverting buffer 216, which in turn controls drive transistor 201. The drive transistor 201 activates an electric heater 200 which may be the heater 103 as shown in FIG. 1 (b). During the enable pulse, the clock to the shift register is stopped to keep the shift data valid, and is shown as a single gate for simplicity, but is preferably within the range of known defect-free clock control circuits. The enable pulse is activated by the clock stopper 218, which can be either one. Stopping the shift register clock removes the requirement for a parallel data latch in the printhead, but adds some complexity to the control circuitry of the head control ASIC 400. Data is routed by the data router 219 to either the primary nozzle or the spare nozzle, depending on the state of the appropriate signal on the fault status bus. The printhead shown in FIG. 4 is simplified and does not show various means of increasing manufacturing yield, such as block fault tolerance. The drive circuitry for the various printhead configurations can be readily derived from the apparatus disclosed herein. Digital information representing a dot pattern to be printed on a recording medium is stored in a page or band memory 1513, which may be the same as the image memory 72 in FIG. The 32-bit word data representing one color dot is read from the page or band memory 1513 using the address selected by the address multiplexer 417 and the control signal generated by the memory interface 418. These addresses are generated by an address generator 411 which forms part of a "per color circuit" 410, one for each of the six color components. The address is generated based on the position of the nozzle associated with the print medium. The address generator 411 is preferably made programmable, as the relative positions of the nozzles may be different for different print heads. The address generator 411 normally generates an address corresponding to the position of the main nozzle. However, if there is a faulty nozzle, the block position of the nozzle containing the fault can be marked in the fault map RAM 412. The failure map RAM 412 is read as a page to be printed. If the memory indicates a nozzle block failure, the address is changed so that the address generator 411 generates an address corresponding to the location of the spare nozzle. Data read from page or band memory 1513 is latched by latch 413 and converted by multiplexer 414 into four sequential bytes. The timing of these bytes is adjusted by FIFO 415 to match that of the data representing the other colors. This data is then buffered in buffer 430 to form a 48-bit main data bus to print head 50. The data is buffered when the print head can be located at a relatively long distance from the head control ASIC. The data from fault map RAH 412 also makes an input to FIFO 416. The timing of this data is aligned with the data output of FIFO 415 and buffered in buffer 431 to form a fault status bus. Programmable power supply 320 provides power for head 50. The voltage of the power supply 320 is controlled by a DAC 313 which is part of a RAM and DAC combination (RAMDAC) 316. RAMDAC 316 includes dual port RAM 317. The contents of dual port RAM 317 are programmed by microcontroller 315. The temperature is compensated by changing the contents of dual port RAM 317. These values are calculated by microcontroller 315 based on the temperature sensed by thermal sensor 300. The signal of the thermal sensor 300 is connected to an analog-to-digital converter (ADC) 311. ADC 311 is preferably incorporated into microcontroller 315. The head control ASIC 400 includes control circuits for thermal lag compensation and print density. In the thermal delay compensation, the power supply voltage to the head 50 needs to be a rapidly time-varying voltage synchronized with the heater enable pulse. This is achieved by programming the programmable power supply 320 to produce this voltage. An analog time-varying program voltage is generated in DAC 313 based on data read from dual port RAH 317. This data is read according to the address generated by the counter 403. The counter 403 makes one complete cycle for the address during the period of the enable pulse. This synchronization is ensured when the counter 403 is clocked by the system clock 408 and the upper count of the counter 403 is used to clock the enable counter 404. The count from enable counter 404 is then decoded by decoder 405 and buffered in buffer 432 to create an enable pulse for head 50. The counter 403 may include a prescaler if the number of states of the count is less than the number of clock cycles of one enable pulse. Sixteen voltage states are appropriate to accurately compensate for the thermal lag of the heater. These 16 states can be specified by using a 4-bit connection between the counter 403 and the dual port RAM 317. However, these 16 states do not have to take a linear time interval. To enable non-linear timing of these states, counter 403 may include ROH or other devices that cause counter 403 to count in a non-linear manner. Alternatively, states below 16 may be used. With respect to print density compensation, print density is detected by counting the number of pixels ("on" pixels) at which a drop will be printed during each enable cycle. “On” pixels are counted by an on-pixel counter 402. There is one on-pixel counter 402 for each of the eight enable pulses. The number of phases in the head depends on the particular design. There is no requirement that the number of phases be a power of two, but 4, 8, and 16 are convenient numbers. The on-pixel counter 402 may comprise a combinatorial pixel counter 420 that determines how many bits of a nibble are on. This number is then accumulated by adder 421 and accumulator 422. Latch 423 holds the accumulated value in a valid state during the period of the enable pulse. The multiplexer 401 selects the output of the latch 423 corresponding to the current enable phase, as determined by the enable counter 404. The output of multiplexer 401 forms part of the address of dual port RAH 317. An exact count of the number of "on" pixels is not required, and the four most significant bits of this count are sufficient. Combining the four bits of the thermal delay compensation address with the four bits of the print density compensation address means that dual port RAM 317 has an eight bit address. This means that dual port RAM 317 contains 256 numbers in a two-dimensional array. These two dimensions are time and print density (for thermal lag compensation). It may include three dimensions-temperature-. When the ambient temperature of the head merely changes gradually, the microcontroller 315 has enough time to calculate a matrix of 256 numbers that compensates for the thermal lag and print density at the current temperature. Periodically (eg, on the order of a few seconds), the microcontroller senses the current head temperature and calculates this matrix. The following equation may be used to calculate the matrix of numbers to be stored in the dual port RAH 317: Where V _ps Is the voltage specified for the programmable power supply 320; R _OUT Is the output resistance of the programmable power supply 320, including the connection to the head 50; R _H Is the resistance of a single heater; p is a number representing the number of heaters to be turned on in the current enable period, as provided by multiplexer 401; n is the least significant bit of one of p A constant equal to the number of heaters represented; t is the time divided into a number of steps over the period of a single enable pulse; p (t) is the time required to achieve improved drop injection. A function that defines the required power input to a single heater. This function depends on the specific arrangement and material of the nozzles, as well as the characteristics of the ink. It is best determined by comprehensive computer simulation, combined with experimentation. T _E Is the temperature in ° C required for drop ejection; and T _A Is the “ambient” temperature of the head in ° C. as measured by a temperature sensor. To reduce execution time and simplify programming for the microcontroller, most or all of the factors may be pre-calculated and simply kept in a table stored in the microcontroller's ROH. Comparison with thermal inkjet technology The table "Comparison between thermal ink jet and the present invention" compares the printing mode and the thermal ink jet printing technique according to the present invention. Because both are drop-on-demand systems that operate using thermal actuators and liquid ink, a direct comparison is made between the present invention and thermal inkjet technology. Although they may seem similar, the two techniques operate on different principles. Thermal ink jet printers use the following basic operating principles. Thermal shock caused by electrical resistance heating results in explosive bubble formation in the liquid ink. Rapid and permanent bubble formation can occur by overheating the ink, so that enough heat is transferred to the ink before bubble nucleation is complete. For water-based inks, an ink temperature of approximately 280C to 400C is required. Bubble formation produces a pressure wave that pushes the ink drop out of the opening at high speed. The bubble then collides, drawing ink from the container and refilling the nozzle. Thermal ink jet printing has been commercially successful due to the high nozzle packing density and the use of well-established integrated circuit manufacturing techniques. However, thermal ink-jet printing technology uses multi-part precision assembly, equipment yield, image resolution, "pepper" noise, printing speed, drive transistor power, waste power consumption, satellite drop formation, thermal stress, differential thermal expansion, kogation, Significant technical problems are encountered, including cavitation, corrective diffusion, and difficulty in producing ink. Printing in accordance with the present invention has many of the advantages of thermal ink jet printing and completely and substantially eliminates many of the inherent problems of thermal ink jet technology. "Comparison between thermal inkjet and the present invention" Yield and fault tolerance In most cases, integrated integrated circuits are irreparable if they are not fully functional at the time of manufacture. The percentage of working devices manufactured by wafer implementation is known as yield. Yield has a direct impact on manufacturing costs. A 5% yield device is actually more than 10 times more expensive to manufacture than the same device with a 50% yield. There are three major yield measures: 1) Manufacturing yield 2) Wafer classification yield 3) Final test yield For large dies, this is typically the wafer classification yield, which has the most impact on overall yield. It is a serious restriction. The full page width color head of the present invention is much larger than a typical VLSI circuit. Good wafer classification yield is critical for the cost-effective manufacture of the aforementioned heads. FIG. 5 is a graph of wafer classification yield versus failure density for a specific example of the integrated full width color A4 head of the invention. The head is 215 mm long-5 mm wide. The non-fault-tolerant yield 198 is calculated according to Hurphy's method, which is a widely used yield prediction method. At a fault density of 1 fault per square centimeter, Murphy's method predicts less than 1% yield. This means that more than 99% of the assembled heads will be discarded. This low yield is highly undesirable because the manufacturing cost of the printhead is unacceptably high. Murphy's method approximates the effect of uneven fault distribution. FIG. 5 also includes a graph of the non-fault tolerable yield 197, which explicitly models fault clustering by introducing a fault clustering (aggregation) factor. The fault clustering factor is not a controllable parameter in manufacturing, but is a characteristic of the manufacturing process. The failure clustering factor for the manufacturing process can be expected to be approximately 2, where the yield projection closely matches Murphy's method. The solution to the low-yield problem is to incorporate fault-tolerant yield by including spare functional units on the chip that are used to replace the failed functional unit. For memory chips and most wafer scale integration (WSI) devices, the physical location of the spare subunit on the chip is not important. However, in a printhead, the spare subunit may include one or more print actuators. These must have a fixed spatial relationship with the page being printed. To be able to print dots at the same location as the defective actuator, the spare actuator must not be displaced in the non-scanning direction. However, the fault actuator can be replaced by a spare actuator displaced in the scanning direction. To ensure that the spare actuator prints dots at the same location as the failed actuator, the data timing for the spare actuator may be changed to compensate for the displacement in the scanning direction. To allow displacement of all nozzles, there must be a complete set of spare nozzles resulting in 100% redundancy. What is required for 100% redundancy is typically more than twice the chip area, dramatically reducing the primary yield before replacing the spare unit, thus reducing the benefits of fault-tolerant yield. Most will be eliminated. However, for the printhead embodiment according to the present invention, the minimum physical dimensions of the head chip are the page width during printing, the fragility of the head chip, and the assembly of the ink channel that supplies ink to the back side of the chip. Is determined by manufacturing constraints. The minimum working 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 μm CMOS assembly technology. Therefore, high levels of fault-tolerant yield can be included without significantly reducing primary yield. When fault-tolerant yield is included in the device, the standard yield equation cannot be used. Instead, the mechanism and degree of fault-tolerant yield must be clearly analyzed and included in the yield equation. FIG. 5 shows a fault-tolerant classification yield 199 for a full-width color A4 head, which encompasses various forms of fault-tolerant yield, the modeling of which is included in the yield equation. This graph shows projected yield as a function of both fault density and fault clustering. The yield projections shown in FIG. 5 show that a fully implemented fault-tolerant yield can increase wafer classification yield from less than 1% to more than 90% under the same manufacturing conditions. Thereby, the manufacturing cost can be reduced to 1/100. Fault-tolerant yield is highly recommended to improve the yield and reliability of printheads containing thousands of printing nozzles, and thus to implement a page-width printing head. However, fault tolerable yield should not be treated as an essential part of the present invention. Fault-tolerant yield in drop-on-demand printing systems is described in the following Australian Patent Application, filed April 12, 1995, the disclosure of which is incorporated herein by reference: "Integrated fault tolerance in printing mechanisms" ( "Application number: PN2324";"Block fault tolerance in integrated printing heads" (Application number: PN2325); "Nozzle duplication for fault tolerance in integrated printing heads" (Application number: PN2326); "Detection of faulty nozzole in printing heads" ( Application No .: PN2327); and "Fault tolerance in high volume printing presses" (Application No .: PN2328). The optimal amount of power required by the printhead heater varies over time over the course of the drop firing process. The optimal power requirement is referred to herein as a power function p (t). The present invention provides an apparatus that changes the energy of a heater over time during drop ejection. This is achieved as shown in FIG. The apparatus includes a counter (403) that provides a number representing the amount of elapsed time during the heater excitation pulse as a ratio of the total pulse duration. The output of the counter (403) is connected to a voltage calculation process 310 that determines the appropriate power supply voltage based on the current time for the start of the pulse. The result of this calculation is V ^- About V ⁺ Used to control a programmable power supply 320 that generates This voltage is connected to the print head 50 and is used to energize the heater. The actual calculation of the optimal supply voltage is complex and should take into account the following factors: 1) the required temperature distribution in the active part of the nozzle for optimal ink drop ejection 2) at the beginning of the heater energization cycle Heat distribution 3) Heat conduction from similarly energized adjacent heaters 4) The amount of heat that is dynamically transferred into the ink 5) Dimensions and shape of the material used for nozzle assembly 6) Material used for nozzle assembly 7) Specific heat capacity of the material used for nozzle assembly 8) Density of material used for nozzle assembly 9) Heater thin film resistance 10) Behavior of heater thin film resistance changing with temperature 11) Drive transistor ON ( on) resistor 12) transistor turn-on time 13) interconnect wire resistance 14) power supply rise time 15) slew rate limits required to avoid interfering with digital circuitry on the printhead 16) regulatory bodies such as FCC and VDE By Radio frequency interference limit computer simulation technology required to satisfy various criteria imposed can decide power function p (t) used. These include thermal finite element analysis (FEA), computational fluid dynamics (CFD), and analog circuit simulation (such as "Spice"). The results of these simulations may be demonstrated experimentally. Computer simulation eliminates perturbations due to measuring instruments, allows for higher measurement accuracy, allows measurements of otherwise inaccessible points in the system, and generally involves experimental assembly and printing of many shape variant printing nozzles. It is much lower cost than measurement. Many simulations should generally be performed only on the most promising configuration prototype builds. The heater power function p (t) may also be determined simply experimentally. However, this is not recommended since many experiments must be performed to approach the optimal solution. The actual calculations are complex and impractical to perform in real time when the heater is energized. Fortunately, the materials and shapes of the nozzles are fixed at the time of manufacture and can be assembled with high precision, so that complicated calculations need not be performed in real time. Therefore, most of these calculations only need to be performed once for each nozzle shape and are invariant within production tolerances. The results of these calculations may then be stored in table k [t] and "retrieved" when needed. k (t) ≒ p (t) where: p (t) is the optimal power function for the time needed for the heater, and k [t] is a sampling approximation of the power function suitable for storage in electronic memory It is. One exception to this is the heat distribution at the start of the pulse. This will have a significant effect on the optimal thermal calculation, but unfortunately is dynamic. The initial condition of any heat pulse depends on how recently the heater was pre-energized. This effect can be mitigated by leaving enough time for the heater area to "cool" during the duration that the heater is energized. It is possible to compensate for this factor electronically by providing another p (t) function that depends on when the heater was last activated. However, in most situations, adapting different simultaneous p (t) functions to different nozzles that are simultaneously energized would require multiple power supplies, making this impractical. Will. Another exception is heat transfer from adjacent heaters that are also energized. This effect can be mitigated during printhead design by maximizing the distance between simultaneously energized heaters. FIG. 6 (b) shows a system where information including the sampled power function k [t] is stored therein in an electronic memory 318 such as a ROM. This information is read from memory 318 by microcontroller 315 and written to dual port RAM 317. Counter 403 generates an address for dual port RAH 317 and yields information calculated by a method incorporating an approximation of the power function p (t) to be output. It is connected to a digital-to-analog converter (DAC) 313. The output of the DAC controls a programmable power supply 320 that excites the printhead 50. FIG. 7 shows a timing diagram for a print head with four phase interleaving. Voltage V supplied to heater _H Is V ⁺ And V ^- Is the difference between This voltage is modulated in a control manner that compensates for thermal lag and other factors. While this voltage is supplied to the common power supply of all heaters, when the data supplied to the heater driver indicates that a drop should be fired, and the corresponding enable control (E0-E3) is activated When activated, only any particular heater will be exposed to this voltage. Waveform V _H0 to V _H3 Is one in which the individual heaters in the four phases are energized by them when a drop will be fired from them. V shown in FIG. _H (And hence V _H0 to V _H3 The voltage curve in () is only an example, and the actual curve will depend on the dimensions and materials selected for the print nozzles and ink. The foregoing has described some preferred embodiments of the present invention. It will be apparent to those skilled in the art that various modifications may be made thereto without departing from the scope of the invention.

Claims (1)

[Claims] 1. In a printing apparatus of the type having a thermal print head and heater means for generating heat in response to excitation power, the improved power control system comprises: (a) a programmable power supply for exciting the heater means; (B) control means for controlling the power supply as predetermined in order to vary the power applied to the heater means as predetermined during the excitation pulse period. And the system. 2. The print head comprises: (a) a plurality of drop ejecting nozzles; (b) an ink body associated with the nozzle; and (c) at least 2% of ambient ink pressure during drop selection and separation during ink selection. (D) a drop selecting means for selecting a predetermined nozzle and causing a difference in the meniscus position between the inks in the selected nozzle and the non-selected nozzle; and (e) a non-selection. 2. The invention according to claim 1, further comprising drop separation means for separating the ink from the selected nozzle as a drop from the ink body while holding the ink in the nozzle. 3. 3. The invention according to claim 2, wherein said control means includes a counter means for generating a signal (group) during said pulse period and indicating a current elapsed time of said period. 4. 4. The invention according to claim 3, wherein said counter means generates a signal representing the amount of elapsed time as a ratio of the total pulse duration during the excitation pulse. 5. 4. The invention according to claim 3, wherein said control means includes a look-up means for outputting a signal indicating a required power level in response to an input signal from said counter means. 6. The apparatus of claim 1, wherein the printhead is used in a coincedent force printer. 7. 4. The apparatus of claim 3 wherein said counter function includes a circuit that produces a non-linear display of elapsed time. 8. The apparatus according to claim 1, wherein the heater power supply voltage is determined by the following equation: k (t) ≒ p (t). 9. The apparatus of claim 1, further comprising means for compensating the supply voltage of the power supply for print density. 10. The apparatus of claim 1, further comprising means for compensating a supply voltage of said power supply with respect to ambient temperature. 11. The apparatus of claim 1, further comprising means for compensating the supply voltage of the power supply for both print density and ambient temperature. 12. The heater power supply voltage is given by the following equation: The apparatus of claim 11, wherein the apparatus is defined by: 13. The print head includes: (a) a plurality of drop ejection nozzles; (b) an ink body coupled to the nozzles; and (c) a predetermined nozzle is selected, and a meniscus position is selected between inks of the selected nozzle and the non-selected nozzle. And (d) drop separating means for separating ink from the selected nozzle from the ink body as a drop while holding ink in the non-selected nozzle, 2. The invention according to claim 1, further comprising: a drop separating means capable of producing said difference in meniscus position when said selecting device is not provided with said drop separating device. 14． 14. The invention according to claim 13, wherein said control means includes a counter device which generates a signal (group) during said pulse period and indicates the elapsed time of said period. 15. 15. The invention according to claim 14, wherein said counter means generates a signal representing the amount of elapsed time as a ratio of the total pulse duration during the excitation pulse. 16. 15. The invention according to claim 14, wherein said control means includes a look-up means for outputting a signal indicating a required power level in response to an input signal from said counter means. 17． The apparatus of claim 14, wherein the counter function includes a circuit that produces a non-linear display of elapsed time. 18. The print head comprises: (a) a plurality of drop ejection nozzles; and (b) an ink body associated with the nozzles, wherein the ink exhibits a surface tension reduction of at least 10 mN / m over a temperature range of 30 ° C. (C) a drop selection device for selecting a predetermined nozzle and causing a difference in the meniscus position between the ink in the selected nozzle and the ink in the non-selected nozzle; and (d) while holding the ink in the non-selected nozzle, 2. The invention according to claim 1, further comprising: a drop separation device for separating ink from the selection nozzle as a drop from an ink body. 19. 20. The invention according to claim 19, wherein said control means includes a counter means for generating a signal (group) during said pulse period and indicating a current elapsed time of said period. 20. 20. The invention according to claim 19, wherein said counter means generates a signal representing the amount of elapsed time during the excitation pulse as a ratio of the total pulse duration. 21. 20. The invention according to claim 19, wherein said control means includes lookup means for outputting a signal indicating a required power level in response to an input signal from said counter means. 22. 20. The apparatus of claim 19, wherein the counter function includes a circuit that produces a non-linear display of elapsed time.