1. Field of Invention
This invention relates to a staggered full-width array printing system, and particularly to a set of staggered full-width array printbars comprised of die modules and more particularly to a first printbar comprised of a plurality of first die modules, for applying a first color, spaced substantially evenly apart so as to have gaps between each die module and located on a top surface of a first substrate, and a second printbar comprised of a plurality of second die modules, for applying a second color, different from the first color, spaced substantially evenly apart so as to have gaps between each die module and located on a bottom surface of the first substrate.
2. Description of Related Art
In an ink jet printing apparatus, individual drops of ink are ejected from a nozzle such that the droplet of ink travels under its own momentum towards a sheet of paper or other print medium on which drops of ink are intended to fall, with the impact areas overlapping so that they form characters or other marks of desired shape. In the ink jet printing apparatus, a printhead including a printbar with several die modules may be used with a plurality of individual nozzles in which to dispel the ink droplets. Such printheads are scanned across the medium to be marked in order to print the entire page.
Alternatively, with a page-width printhead, the printhead is stationary and dispels ink onto the medium from the top of the medium to the bottom. With a page-width printhead, the printhead will include a full-width printbar with several die modules accurately positioned with respect to each other so that the line of picture elements (pixels) produced by printed droplets from neighboring modules show no seams, and the pixels appear to be produced by one continuous line of uniformly spaced ink drop nozzles. An ink may be deposited onto the print medium one line at a time by the full-width printbar as the paper passes by until full-page images are completed. This type of ink jet printing process uses a single pass method and is known as a “full-width array” printer.
Various methods are known for fabricating full-width array printbars. One method is to form a linear pagewidth printbar by providing end-to-end abutment of fully functional printhead elements (die modules) on a substrate. This type of arrangement is termed buttable or butted. In other words, each of the die modules are positioned joined end to end with respect to each other such that the die modules together make up the print region of the print medium. The die modules are positioned end to end so that the pixels produced by from neighboring modules show no seams, and the pixels appear to be produced by one continuous line of uniformly spaced ink drop nozzles. U.S. Pat. Nos. 5,192,959, 4,999,077, and 5,198,054 disclose processes for forming linear printbars of butted subunits.
Because each of the die modules are positioned joined end to end with respect to each other on a single substrate such that the die modules together make up the print region of the print medium, only one full width printbar is necessary, for example, with a black ink only system. Additional full-width color printbars may be added to enable a highlight or full color printer.
In a multi-color ink jet printing process, several full-width array printbars are used in a printer to deposit different color inks onto a print medium to give full color images. The different color inks comprise, for example, black, cyan, magenta, and yellow inks.
U.S. Pat. Nos. 5,280,308, 5,343,227, and 5,270,738 disclose full color pagewidth printers with four printbars, black, cyan, magenta, and yellow; and U.S. Pat. Nos. 5,192,959, 4,999,077, and 5,198,054 disclose processes for forming linear printbars of butted subunits.
However, in a full-width array printbar with die modules abutted end to end, the joints between successive die modules make it difficult to accurately and precisely print on a print medium. For example, one configuration includes a number of die modules 12 butted together on a substrate 14, as shown in FIGS. 1 and 2. However, in a full-width array printbar with die modules butted end to end, the butting requires very tight tolerances in dicing at placing the die module on the substrate. If these tolerances are not met, streaks may result when printing. Further, in a full-width array printbar 10 with die modules 12 butted end to end, the end jets of the die modules tend to behave differently than those in the middle of the array. Specifically, streaks can result, even with perfect dicing and placement. Thus, butting of the die modules has the disadvantage of inducing end-jet defects.
Another method for fabricating a full-width printbar is to provide same color die modules as two separated printbars. This type of arrangement is referred to as nonbuttable as the die modules of the printbars are not abutting each other. Die modules of the first printbar are spaced substantially evenly apart, creating a gap between each of the die modules. Die modules of the same output color are then located on the second printbar in a spaced apart manner such that they align with the gaps between the die modules on the first printbar. The die modules of the two printbars thus overlap so that the die modules of the two printbars together make up the print region of the print medium, as shown in FIG. 3. The die modules 12 of the first printbar 16 are spaced substantially evenly apart on the first substrate 18 creating gaps 20 between each of the die modules 12. Die modules 12 of the second printbar 17 are also spaced substantially evenly apart on the second substrate 22, but are spaced such that they cover the gaps 20 between the die modules 12 on the first substrate 18. The die modules 12 of the two printbars 16 and 17 overlap.
In other words, the die modules 12 of the two printbars 16 and 17 are staggered to form a checker board pattern, but also overlap each other. For this arrangement, two printbars are required for each color to be printed. Thus, for a four-color printer, for example, eight printbars on eight substrates are required.
With respect to the configuration illustrated in FIG. 3, the problems associated with streaking and end-jet defects as discussed above is addressed. However, using two substrates 18 and 22 for each set of same color die modules 12 is space consuming.
Alternatively, in order to reduce the space required for the nonbuttable array that requires two printbars 16 and 17 for each color and uses two substrates 18 and 22 as in FIG. 3, the die modules of one color printbar may be mounted on one side of a substrate and one or more die modules of the associated same color printbar maybe be mounted on an opposite side of the substrate. The die modules of the same color output may thus be staggered on opposite sides of a single substrate as shown in FIG. 4. Here, die modules 26 are right side up on one surface 28 of a substrate 30 and die modules 32 are upside down on an opposite surface 34 of the substrate 30. Thus, fewer substrates, namely half (or four substrates for a four color printer) are required. Such an alternative is disclosed in U.S. Pat. No. 5,257,043 to Kneezel, which is hereby incorporated by reference in its entirety.
However, in the ink jet printer disclosed by Kneezel, as ink is dispersed from the right side up die modules and ink is also dispersed from the upside down die modules, different intensity, brightness, tone, volume, and/or the like of the color ink may result, leading to color distortion.
Thus, a more compact full-width array printer with improved print quality is needed.
A further consideration when designing a pagewidth color printer is the cost and maintenance of the full-width printbars. Reducing the number of required substrates in a printhead would result in fewer parts and less maintenance.
A more compact printer that does not detract from the integrity of the ink printout is needed.