Arrangement of discharge openings in a printhead of a multi-color ink printer
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an arrangement of discharge openings in a printhead of a multi-color ink printer. 
     2. Description of the Prior Art 
     Printing terminals and output devices found in modern office communications or data processing systems are generally required to present both text and graphics. For text representation, a high output rate is frequently desired in circumstances where reduced print quality is acceptable. Such reduced print quality is referred to herein as draft quality (DQ). In addition, there should also be the possibility of presenting text of very good print quality. For such good print quality, a reduced output speed is often acceptable. Such good print quality is referred to herein as near-letter quality (NLQ). Multi-color representations are also increasingly demanded for graphic presentations. 
     So-called ink printers have proven suitable devices to meet these demands. The ink printer comprises an ink printhead for representing characters or graphics. As is generally known, an ink printhead has a plurality of discharge openings formed as nozzles from which discrete droplets are ejected under the influence of individually driveable piezo-electric drive elements. The discrete droplets form the desired characters or desired graphic patterns in a grid fashion on a recording medium, which is moved relative to the printhead. The known devices which address the above-mentioned demands suffer from a disadvantage in that only one of the requirements is fully met in each device and other requirements are only provided with a more or less pronounced sacrifice in quality. 
     SUMMARY OF THE PRESENT INVENTION 
     It is an object of the present invention to specify an arrangement of nozzle discharge openings of a printhead in an ink printer means with which text can be represented in both draft quality as well as near-letter quality, and with which multi-color text or high-quality graphics can also be represented. 
     This and other objects are achieved in an ink printer printhead having a nozzle discharge opening arrangement with a first vertical row of openings for ejecting black ink and furtner vertical rows of openings for ejecting respective ones of fundamental colors of ink. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a printhead for an ink printer, including an ink discharge opening arrangement according to the present invention; 
     FIG. 2 shows a character grid on a recording medium for representing text in draft quality using another embodiment of an ink discharge opening arrangement; and 
     FIG. 3 shows a character grid on a recording medium for representing text in near-letter quality using the arrangement shown in FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, an ink printer means for representing text and graphics includes a write head 1 in front of which is disposed a recording medium 2, such as paper. The write head 1 is essentially composed of an ink supply system 3 connected, on the one hand, to ink channels 8 extending inside the write head 1 and, on the other hand, to an assortment of ink reservoirs 10, 11, 12, and 13 containing inks of different colors. It is known to use inks having the colors black, cyan, magenta, and yellow for representing multi-colored characters in graphics. The write head 1 includes individually controllable drive elements 9, which are shown as piezo-electric transducers allocated to ones of the ink channels 8. The ink channels 8 end at a nozzle plate 14 disposed at a forward end of the write head 1 facing the recording medium 2. Individual ink droplets are ejected at relatively high speeds from discharge openings formed in the nozzle plate 14, as controlled by a transducer drive means (not shown), and are sprayed against the recording medium 2. 
     In accordance with the teachings of the present invention, the discharge openings of the write head 1 are arranged so that a first vertical row of n discharge openings 40 1  -40 n  are provided for ejecting ink droplets having a black color, such nozzles hereinafter being referred to as black nozzles. In the illustrated example of FIG. 1, n =7 discharge openings 40, although other numbers of openings 40 are also possible. 
     An additional plurality of discharge openings are provided in additional rows for ejecting ink droplets of different colors, m discharge openings being provided in each row. In the illustrated example of FIG. 1, m =5 for discharge openings 50 1  -50 m , 60 1  -60 m  and 70 1-70   m  of each respective row. Hereinafter, the discharge openings 50, 60, and 70 will be referred to as color nozzles. In one embodiment, the different colors for the color nozzles are the fundamental colors in what is referred to as the subtractive color mixing system, wherein the colors cyan, magenta, and yellow are used. 
     All of the discharge openings 40, 50, 60 and 70 are arranged in a vertical direction at a spacing &#34;a&#34;, whereby &#34;a&#34; is defined by the grid provided for the character representation and is selected such that individual ink dots applied in the grid correspond to draft quality representations or printing. At least the plurality n of black nozzles 40 is selected such that they cover the height of a write line provided by the character grid. 
     With the foregoing, a representation, or printing, in draft quality can be made in a single pass. The number of discharge openings 50 1  -50 m , 60 1  -60 m , and 70 1  -70 m  in each row of the color nozzles may be lower in number than the number of black nozzles 40 1  -40 n  (n&gt;m). However, the color nozzles 50, 60, and 70 are arranged at the same horizontal level as respective ones of the black nozzles 40. Thus, in multi-color printing, it is possible that printing points of black color ink are no longer formed by mixing the three fundamental colors of ink but, to the contrary, are formed by ink droplets having a black color. The present invention may be used to produce both draft quality and near-letter quality characters, as set forth hereinafter with reference to FIGS. 2 and 3. 
     In FIG. 2, a 9×10 character grid is defined for representing text in draft quality. For the sake of clarity, only black ink discharge openings 40 of the write head 1 are shown, the discharge openings 40 being shown in broken outline disposed behind the recording medium 2. The spacing &#34;a&#34; of the discharge openings 40 is equal to 1/60 inches in the illustrated example. The standard character height of 1/6 inches is, thus, covered by n=10 discharge openings. 
     During the printing of characters, the write head 1 in the example moves from the left to the right at a constant speed. Droplets are ejected from selected discharge openings 40 at predetermined printing times by a printer control (not shown). The printing times are defined here by the grid columns S1 through S9. In FIG. 2, the character &#34;A&#34; is formed in draft quality. The characters of a single print line are, thus, printed during one pass of the write head 1. Thereafter, the recording medium 2 is transported by one line height so that the next print line can be printed in the same way during a return pass of the write head 1. 
     The printing of colored characters fundamentally occurs in the same way, whereby the recording medium 2 is transported by half a line height after the conclusion of a single pass in the illustrated example, where m=1/2n. 
     For representing characters or graphics in the higher quality near-letter quality, a multi-pass mode is used. The multi-pass mode is a plurality of passes of the printhead per print line to represent the characters. The relative motion between the recording medium 2 and the write head 1 occurs in fine steps and a print clock portion of the printer control is emitted as a fine subdivision of the printing times defined by the grid S1-S9. The fine stepping of the relative motion between the write head 1 and the printing medium 2 is caused by a micro-line circuit. The subdivision of the printing times, or grid clock, is achieved in that the printer control generates character-augmenting printing pulses in half steps. 
     Referring now to FIG. 3, a 17×20 grid for representing a character in near-letter quality is shown. The printing of the character &#34;A&#34; occurs in that the write head 1 (shown in broken lines) is first moved in a direction 15 and the printer control emits print pulses at all respective horizontal print locations, the horizontal print locations being the grid columns S1-S9 and by the half-print step columns S&#39;1-S&#39;8 between S1 and S9. In this way, the horizontal cross-bar line of the character &#34;A&#34; is formed by a greater number of printing points from the discharge opening 40 5 . 
     After the end of the print line being printed has been reached, the printer control initiates a feed of the recording medium 2 corresponding to half the spacing &#34;a&#34; of the discharge openings 40. The write head 1 now assumes the position 16 shown in FIG. 3 relative to the recording medium 2. The write head 1 returns in a direction 17, thereby filling the vertical and oblique lines of the illustrated character &#34;A&#34; with ink dots intermediate those printed in the final pass. The ink dots in the near-letter quality, thus, have a double density as compared to the draft quality printed letter &#34;A&#34;. 
     It is also contemplated to divide the draft quality grid more finely than by half-steps. For example, a subdivision into thirds or quarters produces a very high quality result. 
     Although various alterations and modifications might be suggested by those skilled in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.