Abstract:
The present invention includes as one embodiment an inkjet printing method for decreasing print banding in a thermal inkjet printhead having a plurality of substrates with adjacent overlapping and non-overlapping regions between the substrates, the method comprising synchronizing a difference in time delay between ink ejected from the adjacent overlapping and non-overlapping regions of each substrate to reduce the difference.

Description:
BACKGROUND OF THE INVENTION 
     Multi-substrate modules are commonly used for high-resolution printheads or wide page array printheads and typically include plural substrates with adjacent overlapping and non-overlapping regions defining the area between adjacent substrates. One factor in assuring high print quality of inkjet printers with multi-substrate print modules is the control over the uniformity of ink drops ejected onto the print media. 
     In current systems, uniform printing is used from all columns of the multi-substrate module. However, this results in a large difference in the time delay for drops printed in the adjacent overlapping region versus the non-overlapping regions. As such, in the adjacent overlapping regions, ink is laid on ink rather than ink onto the print media, due to the adjacent overlapping substrates. 
     Consequently, ink laid on ink, in relation to drying time and image quality, can cause printed image quality problems due to the difference in the interaction between the ink and the media in the adjacent overlapping regions versus the non-overlapping regions. One of the image quality problems is print banding. Print banding is the appearance of repetitive horizontal bands within a printed image, which may appear as light or dark bands. Print banding is particularly undesirable in printers that require high quality printouts, such as images or photographs, where the effects of banding are more likely to be visible. 
     SUMMARY OF THE INVENTION 
     The present invention includes as one embodiment an inkjet printing method for decreasing print banding in a thermal inkjet printhead having a plurality of substrates with adjacent overlapping and non-overlapping regions between the substrates, the method comprising synchronizing a difference in time delay between ink ejected from the adjacent overlapping and non-overlapping regions of each substrate to reduce the difference. 
    
    
     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 embodiments. 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 one embodiment of the present invention. 
     FIG. 2 is an exemplary printer usable with the system of FIG. 1 that incorporates one embodiment of the invention and is shown for illustrative purposes only. 
     FIG. 3 shows for illustrative purposes only a perspective view of an exemplary print cartridge usable with the printer of FIG. 2 incorporating one embodiment of the printhead assembly of the present invention. 
     FIG. 4 is a schematic cross-sectional view taken through a portion of section line  4 — 4  of FIG. 3 showing a portion of the ink chamber arrangement of an exemplary printhead substrate in the print cartridge of FIGS. 1 and 3. 
     FIG. 5 is a flow diagram of the operation of a printhead assembly according to FIG. 3 that incorporates an embodiment of the present invention. 
     FIG. 6 is a block diagram of a printhead assembly according to FIG. 3 that incorporates an embodiment of the present invention. 
     FIGS. 7A-7B illustrate a working example of the operation of embodiments of the present invention. 
    
    
     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 as defined by the claims appended below. 
     I. General Overview 
     FIG. 1 shows a block diagram of an overall printing system incorporating one embodiment of the present invention. The printing system  100  of one embodiment of the present invention includes a printhead assembly  102 , ink supply or ink reservoir  104  and print media  106 . At least one printhead assembly  102  and ink reservoir  104  are typically included in a printer  101 . Input data  108  is sent to the printing system  100  and includes, among other things, information about the print job. 
     In addition, the printhead assembly  102  includes a timing controller  110 , which may be implemented as firmware and/or hardware incorporated into the printer in a master controller device (not shown), or physically integrated with the printhead assembly  102  as a printhead controller device. Also, the timing controller  110  can be implemented by a printer driver as software operating on a computer system (not shown) that is connected to the printer  101  or a processor (not shown) that is physically integrated with the printhead assembly  102 . 
     The printhead assembly  102  also includes plural substrates (not shown), such as plural semiconductor wafers or dies. The plural substrates may be in the form of a multi-substrate or multi-die module for a single printhead printer, as multiple single printhead modules for a wide page array printer or combination thereof. Each substrate or die includes ink ejection elements and associated ejection chambers for releasing the ink through corresponding nozzles or orifices in respective adjacent nozzle members. Also, each substrate can have its own controller disposed thereon that is synchronized with the other controllers. 
     The plural substrates are located adjacent to one another with adjacent overlapping and non-overlapping regions existing between each adjacent substrate (discussed in detail below). The timing controller  110  is operatively connected to the ink ejection elements of each substrate and receives and processes input data  108  to create a consistent time delay difference between ink ejected from the adjacent overlapping and non-overlapping regions of the ink ejection elements of each substrate. 
     The timing controller  110  decreases print banding by creating a consistent difference in the time delay between ink ejected from the adjacent overlapping and non-overlapping regions of each substrate. For multi-die modules, this is achieved by controlled print distribution. Each die has inner and outer printing areas, such as inner and outer trenches. Inner trenches face opposing inner trenches of multiple dies, while outer trenches are located on opposite sides of the inner trenches of each die (the inner and outer trenches will be discussed in detail below with reference to FIGS.  7 A and  7 B). In non-overlap region, the ink is evenly printed in each trench of each die (half in the inner trench and the other half in the outer trench of each die to create an even distribution of ink between the trenches in each die). However, in the adjacent overlap region, although the same amount of ink is printed, the inner trenches of each die receive ink but the outer trenches of each die do not receive ink. This reduces artifacts and allows a smoother transition from the non-overlap to the adjacent overlap areas. Consequently, this reduces the difference in the time delay between the adjacent overlapping and non-overlapping regions to produce more consistent ink and print media  108  interactions and to help improve image quality. 
     II. Exemplary Printing System 
     FIG. 2 is an exemplary embodiment of a printer that incorporates a multi-substrate or multi-die module for a single printhead assembly according to an embodiment of the invention and is shown for illustrative purposes only. As discussed above, other printers, such as a wide page array printer with multiple single substrate printhead assemblies can incorporate embodiments of the present invention. 
     Generally, printer  200 , which is shown in FIG. 2 as one type of printer  101  of FIG. 1, can incorporate the printhead assembly  102  of FIG. 1  and further include a tray  222  for holding print media. When a printing operation is initiated, print media, such as paper, is fed into printer  200  from tray  222  preferably using sheet feeder  226 . The sheet is brought around in a U direction and then travels in an opposite direction toward output tray  228 . Other paper paths, such as a straight paper path, can also be used. 
     The sheet is stopped in a print zone  230 , and a scanning carriage  234 , supporting one or more printhead assemblies  236 , is scanned across the sheet for printing a swath of ink thereon. After a single scan or multiple scans, the sheet is then incrementally shifted using, for example a stepper motor or feed rollers to a next position within the print zone  230 . Carriage  234  again scans across the sheet for printing a next swath of ink. The process repeats until the entire sheet has been printed, at which point it is ejected into the output tray  228 . 
     The print assemblies  236  can be removeably mounted or permanently mounted to the scanning carriage  234 . Also, the printhead assemblies  236  can have self-contained ink reservoirs which provide the ink supply  104  of FIG.  1 . Alternatively, each print cartridge  236  can be 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  of FIG.  1 . 
     FIG. 3 shows for illustrative purposes only a perspective view of an exemplary print cartridge  300  (an example of the printhead assembly  102  of FIG. 1) that incorporates one embodiment of the invention and is shown for illustrative purposes only. A detailed description of one embodiment of the present invention follows with reference to a typical print cartridge used with a typical printer, such as printer  200  of FIG.  2 . However, embodiments of the present invention can be incorporated in any printhead and printer configuration. 
     Referring to FIGS. 1 and 2 along with FIG. 3, the print cartridge  300  is comprised of a thermal head assembly  302  and a 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  contains a nozzle member  306  to which the plural substrates are attached to form the printhead assembly  102 . 
     Thermal head assembly  302  also has interconnect contact pads (not shown) and is secured to the printhead assembly  300  with suitable adhesives. Contact pads  308  align with and electrically contact electrodes (not shown) on carriage  234 . The nozzle member  306  preferably contains plural parallel rows of offset nozzles  310  for each substrate through the thermal head assembly  306  created by, for example, laser ablation. 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 a portion of section line  4 — 4  of FIG. 3 of the print cartridge  300  utilizing one embodiment of the present invention. A detailed description of one embodiment of the present invention follows with reference to a typical print cartridge  300 . However, embodiments of 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, in general, the thermal head assembly  302  includes plural substrates  410  (only one substrate is shown in FIG. 4 for simplicity) and a barrier layer  412  located between the nozzle member  306  and each substrate  410  for insulating conductive elements from each substrate  410  and for forming a plurality of ink ejection chambers  418  (one of which is shown in FIG. 4, while both are shown as  614  and  616  in FIGS.  7 A and  7 B). The plural substrates are located adjacent to one another with adjacent overlapping and non-overlapping regions existing between each substrate. 
     Also included is a corresponding plurality of ink ejection elements  416  disposed on each substrate  410 . The timing controller  110  is operatively connected to the ink ejection elements  416 . Each chamber  418  is associated with a different one of the ink ejection elements  416 . The timing controller  110  receives print data and processes the print data to create a consistent time delay difference between ink ejected from the adjacent overlapping and non-overlapping regions of the ink ejection elements of each substrate. 
     An ink ejection or vaporization chamber  418  is adjacent each ink ejection element  416  of each substrate  410 , 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 . Thus, each ink ejection element  416  is associated with, and ejects ink from, a corresponding nozzle  420 . The nozzles  420  are shown in FIG. 4 to be located near an edge of the substrate  410  for illustrative purposes only. The nozzles  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 . 
     The ink ejection elements  416  may be resistor heater elements or piezoelectric elements, but for the purposes of the following description, the ink ejection elements may be referred to as resistor heater elements. In the case of resistor heater elements, 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 orifices  420  may be of any size, number, and pattern, and the various figures are designed to simply and clearly show the features of one embodiment of the invention. The relative dimensions of the various features have been greatly adjusted for the sake of clarity. 
     FIG. 5 is a flow diagram of the operation of a printhead assembly according to FIG. 3 that incorporates an embodiment of the present invention. First, adjacent overlapping and non-overlapping regions of adjacent substrates are determined (step  510 ). Second, the ink ejection elements that reside in the adjacent overlapping and non-overlapping regions of the adjacent substrates are determined (step  512 ). 
     Third, a difference in time delay between ink ejected from the adjacent overlapping and non-overlapping regions of each substrate is synchronized and programmed into synchronized firing signals (step  514 ) to create a consistent difference in time delay. Last, the synchronized firing signals are sent to the ink ejection elements of the plural substrates to create a consistent time delay difference between ink ejected from the adjacent overlapping and non-overlapping regions of the ink ejection elements of each substrate (step  516 ). 
     III. Working Example 
     FIG. 6 is a block diagram of a printhead assembly according to FIG. 3 that incorporates an embodiment of the present invention. Referring to FIGS. 1-5 along with FIG. 6, the printhead assembly  102  includes a timing controller  110 , a feedback processor  610  and plural substrates  614 ,  616  (only two substrates are shown for illustrative purposes), which can be in the form of a multi-substrate module. 
     Each substrate  614 ,  616  respectively includes non-overlapping nozzle arrangements  626 ,  628  and adjacent overlapping nozzle arrangements  630 ,  632 . The non-overlapping nozzle arrangements  626 ,  628  include ink ejection elements  640 ,  642  and the adjacent overlapping nozzle arrangements  630 ,  632  include ink ejection elements  644 ,  646 . The nozzles of the non-overlapping nozzle arrangement  626  are located in regions that do not overlap with nozzles of the non-overlapping nozzle arrangement  628 . The nozzles adjacent to each other of the overlapping nozzle arrangement  630  are located in regions that are adjacent to each other and overlap with nozzles of the overlapping nozzle arrangement  632 . 
     In operation, the feedback processor  610  receives feedback signals from the substrates  614  and  616 , such as position and timing signals, and determines the locations of the ink ejection elements and nozzles. In particular, feedback processor  610  determines the non-overlapping regions of the non-overlapping nozzles  626 ,  628  and the overlapping regions of the overlapping nozzles  630 ,  632  for electronically mapping the regions and the ink ejection elements associated with these regions. 
     The feedback processor  610  then sends the map of the regions to the timing controller  110 . The timing controller  110  uses the input print data  108  and the map of the regions to formulate a synchronized firing pattern for the ink ejection elements in both regions. The synchronization pattern synchronizes a difference in time delay between ink ejected from the adjacent overlapping and non-overlapping regions of each substrate  614 ,  616  to create a consistent time delay difference between the regions. 
     FIGS. 7A-7B illustrate a working example of the operation of embodiments of the present invention. Referring to FIG. 6 along with FIGS. 7A and 7B, each substrate  614 ,  616  is respectively defined by an outer trench  712 ,  714  of nozzles and an inner trench  716 ,  718  of nozzles. Each outer trench  712 ,  714  of nozzles is located on a respective outer edge of each substrate that is not adjacent to the other substrate. In contrast, each inner trench  716 ,  718  of nozzles is located on a respective inner edge of each substrate that is adjacent to the other substrate. As shown in FIGS. 7A and 7B, a portion of each trench  712 ,  714 ,  716 ,  718  is in respective adjacent overlapping regions  720 ,  722 , shown as the cross-hatched areas. 
     In one embodiment, as shown in FIG. 7A, the timing controller  110  formulates the synchronized firing pattern discussed above by sending firing signals to print in all trenches, both in the adjacent overlapping regions  720 ,  722  and the non-overlapping regions. Designated distribution of the ink can be used for each trench of nozzles. Namely, in this embodiment illustrated with two substrates, the ink ejection elements in the trenches in the non-overlapping regions are instructed by the timing controller  110  to print half of the ink drops  730  in the non-overlapping regions to create a first print zone represented by zone  740 . 
     The ink ejection elements for each trench in the overlapping regions  720 ,  722  are instructed to print one quarter of the ink drops  732  in the overlapping region  720 ,  722  to create a second print zone represented by zone  742 . With this arrangement, ink is deposited from all four trenches in the overlapping regions  720 ,  722  and two trenches in the non-overlapping regions. As a result, a certain delay time between ink lay down in the second print zone  742  as opposed to the first zone  740  is created. 
     In another embodiment, as shown in FIG. 7B, the timing controller  110  formulates the synchronized firing pattern discussed above by sending firing signals to print in some of the trenches that are in the overlapping regions  720 ,  722  and with all of the trenches in the non-overlapping regions. Specifically, in this embodiment illustrated with two substrates, the ink ejection elements of all trenches  712 ,  714 ,  716 ,  718  in the non-overlapping regions are instructed to print half of the ink drops  750  in the non-overlapping regions to create a first print zone  752 . 
     The ink ejection elements of the inner trenches  716 ,  718  are instructed to print half of the ink drops  754  in the overlapping regions  720 ,  722  to create a second print zone  756 . As such, each trench has half of the ink drops  750  printed in the first print zone  752  and the other half of the ink drops  754  in the second zone  756 . In contrast to the embodiment of FIG. 7A, the embodiment of FIG. 7B creates less variation in delay time between ink lay down in the second print zone  756  as opposed to the first print zone  752  due to ink lay down from two trenches in both the overlapping and non-overlapping regions. In the embodiment of FIG. 7B, the difference in time delay between the overlapping and non-overlapping regions is significantly reduced as compared to the embodiment of FIG.  7 A. 
     This is because the print zone  742  of FIG. 7A is greater than the print zone  752  of FIG.  7 B. The first print zone  752  of FIG. 7B has a length that is slightly larger than the length of the second print zone  756 . In contrast, the first print zone  740  of FIG. 7A is much smaller than the second print zone  742  of FIG.  7 A. As a result, the system of FIG. 7B will produce a more consistent time delay between ink lay down in the first and second print zones. This will result in a decrease in print banding and associated artifacts and more consistent ink to print media interaction, which will improve image quality. 
     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 workers may make variations in those embodiments skilled in the art without departing from the scope of the present invention as defined by the following claims.