Abstract:
The present invention is embodied in a system and method for optimizing ink drying time through the incorporation of a system of multiple spaced printheads. The printhead assembly includes connection and processing circuitry, multiple printhead bodies, ink channels, substrates, such as semiconductor wafers (commonly referred to as a die), and nozzle members. The printheads also include controllers for controlling printing on a print media and incorporating a programmable feedback loop. The loop activates the various printheads during printing so that the various data packets are added in a synchronized manner during the print swath. The present invention provides adequate drying time for inks produced in a printing swath on a wide array page. This will result in the use of water based inks compatible with ink jet materials in systems with fast raster scanning.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to inkjet printers and in particular to a system and method for optimizing ink drying time through the incorporation of a system of multiple spaced printheads. 
     BACKGROUND OF THE INVENTION 
     Inkjet printers are commonplace in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes a printing medium, such as paper. 
     An inkjet printer produces a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Pixels vary in size, the smaller the dot in the rectilinear array, means that more dots can be printed per inch of the printed medium. Smaller dots result in a more accurate rendition of the image and this in turn results in greater definition of the image. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink of specific size or from a combination of different sized dots. 
     Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with a nozzle member having ink ejecting nozzles. The carriage traverses over the surface of the print medium. The width of the carriage varies among the different printers. For any line of print, the carriage may make more than one traverse and utilize a varying number of nozzles. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed and to the physical properties of the ink and the print media. 
     In general, the ink is housed in a vaporization chamber with a tube leading to a nozzle exposed to the print media. Small drops of ink are ejected from the nozzles through orifices by rapidly heating a small volume of ink located in the vaporization chambers with small electric heaters, such as small thin film resistors. The small thin film resistors are usually located adjacent the vaporization chambers. Heating the ink causes the ink to vaporize and eject ink in the connecting tubing through the nozzle orifices. Specifically, for one dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor of a selected vaporization chamber. The resistor is then heated and in turn heats a thin layer of ink located within the selected vaporization chamber, causing explosive vaporization, and, consequently, a droplet of ink is ejected from the nozzle and onto a print media. The vacuum created as the ink droplet is ejected from the nozzle acts as a suction pump to draw more ink into the vaporization chamber. 
     The temperature will be high if the resistors fire a number of times in a short period of time. As the carriage traverses in a print swath, various heater elements in the array are activated. If the traverse is narrow, the mean temperature at the beginning of the traverse will be similar to the mean temperature at the conclusion, and the effect of temperature on the pass will be consistent for all ink droplets projected onto the print media. If the swath is wide more heater elements are activated. 
     Prior to page wide arrays, ink jet printing was limited in speed due to raster scanning of narrow printheads. This speed has now increased. With page wide arrays, the problem now is to have inks that dry with sufficient speed to allow for multiple passes without compromising the previously printed swaths. This means that either fast drying solvent based inks, which may not be compatible with ink jet material sets, must be used, or use water based ink at very slow speeds to allow for vehicle evaporation. 
     Therefore, what is needed is a system and method for optimizing ink drying time through the incorporation of a system of multiple spaced printheads. The system and method would divide data into packets to be processed by separate controllers in individual printheads. The printheads would be spaced on carriages along the long axis of the print media so that each printhead prints a portion of the same print swath. As the printed data from the first printhead reaches subsequent printheads, printed data to complete the swath would be added by successive printheads. By the time the printed data from the first printhead reached the second printhead the swath would have had time to dry 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a system and method optimizing ink drying time through the incorporation of a system of multiple spaced printheads. 
     The printhead assembly includes connection and processing circuitry, multiple printhead bodies, ink channels, substrates, such as semiconductor wafers (commonly referred to as a die), and nozzle members. The nozzle members have heating elements in arrays, as well as plural nozzles coupled to respective ink channels. The printheads also include controllers, which can be integrated circuit processors, printer drivers, firmware or the like for controlling printing on a print media and incorporating a programmable feedback loop. The loop activates the various printheads during printing so that the various data packets are added in a synchronized manner during the print swath. 
     The controller can be defined in the integrated circuit as receiving the location through an index sensor during the printing process, comparing this index with the set point for printing data packets, initiating various printheads in the printhead assembly, and by a forward communication loop initiate a stepper motor to keep the print media coordinated with the printing process. The controller can be created by any suitable integrated circuit manufacturing or programming process. 
     The present invention provides adequate drying time for inks produced in a printing swath on a wide array page. This will result in the use of water based inks compatible with ink jet materials in systems with fast raster scanning. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be further understood by reference to the following description and attached drawings that illustrate the preferred embodiment. Other features and advantages will be apparent from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     FIG. 1 shows a block diagram of an overall printing system incorporating the present invention. 
     FIG. 2 is an exemplary printer that incorporates the invention and is shown for illustrative purposes only. 
     FIG. 3 shows for illustrative purposes only a perspective view of an exemplary print cartridge incorporating the present invention. 
     FIG. 4 is a schematic cross-sectional view taken through section line  4 — 4  of FIG. 3 showing the ink chamber arrangement of the print cartridge of FIGS. 1 and 3. 
     FIG. 5 shows a block diagram of the temperature sensor layout on the printhead incorporated in the present invention. 
     FIG. 6 shows for illustrative purposes only a perspective of a page wide array of inkjet printheads 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description of the invention, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration a specific example in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     I. General Overview 
     FIG. 1 shows a block diagram of an overall printing system incorporating the present invention. The printing system  100  of the present invention includes a printhead assembly  102 , ink supply  104  and print media  106 . Input data to the printing system  100  comes from the input data channel  108 . A locator controller system  110  is included in the printhead assembly  102 . The controller system  110  can be an integrated circuit, firmware, a software printer driver or the like and controls the timing of the activation of the printheads. 
     II. Exemplary Printing System 
     FIG. 2 is a perspective view of an exemplary high-speed large format printing system  200  that incorporates the invention and is shown for illustrative purposes only. The printing system  200  includes a housing  210  mounted on a stand  220 . The housing  210  has a left media transport mechanism cover  225  and a right media transport mechanism cover  230  housing a left media transport mechanism (not shown) and a right media transport mechanism (not shown), respectively. A control panel  240  is mounted on the right media transport mechanism cover  230  and provides a user interface with the printing system  200 . 
     A printhead assembly  102  with print cartridges  236  is mounted on a carriage assembly  234 , all being shown under a transparent cover  260 . The carriage assembly  234  positions the printhead assembly  250  along a carriage bar  265  in a horizontal direction denoted by the “y” axis A print media  270  (such as paper) is positioned by the media transport mechanism (not shown) in a vertical direction denoted by the “x” axis. 
     The print cartridges  236  may be removeably mounted or permanently mounted to the scanning carriage  234 . Also, the print cartridges  236  can have self-contained ink reservoirs in the body of the printhead (shown in FIG. 3) as the ink supply  104  (shown in FIG.  1 ). The self-contained ink reservoirs can be refilled with ink for reusing the print cartridges  236 . Alternatively, the print cartridges  236  can be each fluidically coupled, via a flexible conduit  240 , to one of a plurality of fixed or removable ink containers  242  acting as the ink supply  104  (shown in FIG.  1 ). As a further alternative, ink supplies  104  can be one or more ink containers separate or separable from print cartridges  236  and removeably mountable to carriage  234 . 
     FIG. 3 shows for illustrative purposes only a perspective view of an exemplary printhead assembly  102  incorporating the present invention. A detailed description of the present invention follows with reference to a typical printhead assembly used with a typical printer, such as printer  200  of FIG.  2 . However, the present invention can be incorporated in any printhead and printer configuration. 
     Referring to FIGS. 1 and 2 along with FIG. 3, the printhead assembly  102  is comprised of a thermal head assembly  302  and a printhead body  304 . The thermal head assembly  302  can be a flexible material commonly referred to as a Tape Automated Bonding (TAB) assembly. The thermal head assembly  302  includes a nozzle system  306  and interconnect contact pads (not shown) and is secured to the printhead assembly  102 . The thermal head assembly  302  can be secured to the print cartridge  300  with suitable adhesives. An integrated circuit chip (not shown) provides feedback to the printer  200  regarding certain parameters of printhead assembly  102 . The contact pads  308  align with and electrically contact electrodes (not shown) on carriage  234 . The nozzle system  306  preferably contains plural parallel rows of offset nozzles  310  through the thermal head assembly  302  created by, for example, laser ablation. It should be noted that other nozzle arrangements can be used, such as non-offset parallel rows of nozzles. 
     III. Component Details 
     FIG. 4 is a cross-sectional schematic taken through section line  4 — 4  of FIG. 3 of the inkjet print cartridge  300  utilizing the present invention. A detailed description of the present invention follows with reference to a typical printhead used with print cartridge  300 . However, the present invention can be incorporated in any printhead configuration. Also, the elements of FIG. 4 are not to scale and are exaggerated for simplification. 
     Referring to FIGS. 1-3 along with FIG. 4, as discussed above, conductors (not shown) are formed on the back of thermal head assembly  302  and terminate in contact pads for contacting electrodes on carriage  234 . The other ends of the conductors are bonded to the printhead  300  via terminals or electrodes (not shown) of a substrate  410 , such as a semiconductor material, commonly referred to as a die. The substrate or die  410  has ink ejection elements  416  formed thereon and electrically coupled to the conductors. The integrated circuit chip provides the ink ejection elements  416  with operational electrical signals. A barrier layer  412  is located between the nozzle member  306  and the substrate  410  for insulating conductive elements from the substrate  410 . 
     An ink ejection or vaporization chamber  418  is adjacent to each ink ejection element  416 , as shown in FIG. 4, so that each ink ejection element  416  is located generally behind a single orifice or nozzle  420  of the nozzle member  306 . The nozzles  420  are shown in FIG. 4 to be located near an edge of the substrate  410  for illustrative purposes only. The nozzle  420  can be located in other areas of the nozzle member  306 , such as centered between an edge of the substrate  410  and an interior side of the body  304 . 
     Each ink ejection element  416  acts as an ohmic heater when selectively energized by one or more pulses applied sequentially or simultaneously to one or more of the contact pads via the integrated circuit. The ink ejection elements  416  may be heater resistors or piezoelectric elements and for the purposes of the current invention will be heater resistors. The orifices  420  may be of any size, number, and pattern, and the various figures are designed to simply and clearly show the features of the invention. The relative dimensions of the various features have been greatly adjusted for the sake of clarity. 
     Referring to FIGS. 1-4, during a printing operation, ink stored in an ink reservoir  104  defined by the printhead body  304  generally flows around the edges of the substrate  410  and into the vaporization chamber  418 . Energization signals are sent to the ink ejection element  416  and are produced from the electrical connection between the print cartridges  236  and the printer  200 . Upon energization of the ink ejection element  416 , a thin layer of adjacent ink is superheated. The energized heater element causes explosive vaporization and, consequently, causes a droplet of ink to be ejected through the orifice or nozzle  420 . The vaporization chamber  418  is then refilled by capillary action. This process enables selective deposition of ink on print media  106  to thereby generate text and images. 
     Referring to FIG.  5  and FIGS. 1-4 a preferred embodiment of the present invention has multiple carriage bars  265  each supporting a carriage assembly  234  and a printhead assembly  102 , and inkjet printheads  304 . On the printhead assembly  1 ,  102 , is located an index creator  520 . The index creator  520  creates a locator index  510  on the print media  106 . In one embodiment, a locator index can be printed in the margins. In another example, the index creator  520  can create data representative of a pattern inherent in the print media, such as fiber patterns. The last carriage n,  234 , has a locator sensor  522  that scans for the locator index  510  on the print media. 
     FIG. 6 is a block diagram illustrating the operation and integration of the printhead assembly  102  of FIG.  1 . Referring to FIGS. 1-4 along with FIG. 5, during a printing operation, ink is provided from the ink reservoir  104  to an interior portion of the printhead body  1 - n ,  304 . The interior portion of the printhead body  1 - n ,  304  provides ink to the ink channels for allowing ejection of ink from the vaporization chambers  418  through adjacent nozzles  420 . 
     The printhead assembly  102  receives commands from the controller  110  to print ink based on the input data  108  and form a desired pattern for generating text and images on the print media  106 . The data  108  is stored in the data memory  610  and converted into data packets by the data packeting system  620 . The data packeting system  620  is a controller that divides the data into discrete swaths. These swaths are in turn divided into packets that are integral portions of the swath to be printed. Packets are distributed by the data distributor  622  to the relevant printhead  1 - n ,  304 , so that when the combined output of all printheads  1 - n ,  304  is printed on the print media  106 , the image will represent the original single swath. 
     At the time that printhead  1 ,  304  is initiating the nozzle system  1 ,  306  to print the portion of the swath distributed to it by the data distributor  622 , it simultaneously initiates the index creator  520 . The index creator  520  determines a line encoder to be printed on the print media  106 . In a preferred embodiment of the invention this encoder is the locator index  510 . 
     A locator sensor  522  on the carriage  234  optically scans the locator index and forwards the position to the printhead assembly  102 . The locator index  510  indicates the position of the print in relation to the nozzle system. With this positioning information the printhead assembly can determine to advance the print media by activating the stepper motor  630  which turns the drive rollers  530  and advances the print media  106 . 
     In addition the locator sensor  522  activates the printhead assembly  102  upon reading the locator index  510 . The locator index  510  indicates that the next swath of print needs to be initiated. Printhead  1 ,  304  forwards its portion of the next swath of data to nozzle system  1 , printhead n,  304  forwards data to nozzle system n,  304  and so on; and printhead  1 ,  304  initiates the index creator  520  to formulate the next locator index. 
     As the print media emerges from printhead  1 ,  304  one third of the print swath will be completed in an embodiment of three printheads. Before the print media reaches the second printhead  304 , the ink on the print media will be dry and the second third of the swath will be printed by the second printhead,  304 . Again before the print media reaches the third printhead,  304 , it will be dry and will have two thirds of the swath printed. The final third will be printed at the third printhead  304 . 
     IV. Conclusion 
     In conclusion, with the system and method of the present invention, a dynamic and proactive printhead assembly is established through the locator sensor  522  feedback system. This allows the printhead assembly  102  to coordinate the timing of printing of data at the various printhead  304  and nozzle systems  306 . The data to be printed is configured at the data packeting system  620  so that each printhead  304  only receives a partial swath. The part of the swath received by a printhead is such that when printed on the print media the ink will dry before the print media reaches the next nozzle system  306  in the printer array. The net effect of this invention is that a quality print will be produced within the time frame of normal raster scanning of narrow printheads. Thus it will accommodate water vehicle inks which are compatible with ink jet material sets. 
     The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. The above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.