Patent Publication Number: US-2006017763-A1

Title: Method for inspecting whether a printhead of a printer conforms to a specification

Description:
BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to a method for inspecting whether a printhead of a printer conforms to a specification, and more particularly, to a method for inspecting, by a scanner or the naked eye, whether a printhead of a printer conforms to a specification.  
      2. Description of the Prior Art  
      In modern society, an inkjet printer has become the most popular form of printing equipment because of its fair price and outstanding printing qualities. Due to the demand for high resolution printing quality, the manufacturers have developed inkjet printers with high quality and high speed. Therefore, such a printer must have a printhead having properties of high resolution printing quality through the use of multi-nozzles. However, it is difficult to improve the yield of inkjet chips without damaged nozzles. Additionally, it has been proven that two damaged nozzles are tolerated for high resolution printing quality. However, it is insufficient to inspect whether the number of damaged nozzles is less than three for inspecting printheads.  
      Suppose that there are two damaged nozzles in a printhead. The positions of dots jetted by the two damaged nozzles are not adjacent on a print-medium. After printing a printing block, there are two blank lines within the printing block due to the two damaged nozzles with each blank line generated by one damaged nozzle. Therefore, the width of each blank line is so narrow that it has no effect on high resolution printing quality. However, if the positions of dots jetted by the two damaged nozzles were adjacent on the print-medium, the printing block would have a blank area, such as the blank area  8  of  FIG. 1 . The two damaged nozzles generate the blank area  8 . The width of the blank area  8  is wide and obvious. Therefore, printing quality is reduced. Consequently, for printheads having multi-nozzles and high resolution, it is insufficient to inspect whether the number of damaged nozzles is less than three for high resolution printing quality. Another method for inspecting printheads precisely and easily is needed.  
     SUMMARY OF INVENTION  
      It is therefore a primary objective of the claimed invention to provide a method for inspecting whether a printhead of a printer conforms to a specification to solve the above-mentioned problem.  
      The claimed invention provides a method for inspecting whether a printhead of a printer conforms to a specification. The method includes detecting if the number of damaged nozzles of the printhead is two. If the number of damaged nozzles of the printhead is two, it is determined whether the two damaged nozzles can be tolerated according to the specification.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is an image printed by an unqualified printhead according to the prior art.  
       FIG. 2  is a diagram of a first embodiment of the present invention for inspecting a printhead having two damaged nozzles.  
       FIG. 3  to  FIG. 6  are test patterns for a printhead having an even number of nozzles according to the present invention.  
       FIG. 7  is a diagram of a second embodiment of the present invention for inspecting a printhead having two damaged nozzles.  
       FIG. 8  to  FIG. 10  are test patterns for a printhead having an odd number of nozzles according to the present invention.  
       FIG. 11  is a diagram of the printer of the present invention.  
       FIG. 12  is a flowchart of inspecting whether a printhead having an odd number of nozzles conforms to the specification.  
       FIG. 13  is a flowchart of inspecting whether a printhead having an even number of nozzles conforms to the specification. 
    
    
     DETAILED DESCRIPTION  
      The present invention provides a method for inspecting high resolution printheads. The present invention determines if the number of damaged nozzles is equal to or less than two. When the number of damaged nozzles is two, an interpolation is used for inferring which positions of dots jetted by the two damaged nozzles can be tolerated for high resolution printing quality. Since two damaged nozzles are tolerated for multi-nozzled, high-resolution printheads, the present invention inspects the number of damaged nozzles in a printhead. If the number of damaged nozzles is greater than two, the printhead does not conform to the specification. If the number of damaged nozzles is less than two, the printhead conforms to the specification. If the number of damaged nozzles is two and the positions of dots jetted by the two damaged nozzles are not adjacent on a print-medium, the printhead conforms to the specification.  
      Please refer to  FIG. 2 .  FIG. 2  is a diagram of the first embodiment of the present invention for inspecting a printhead having two damaged nozzles. In  FIG. 2 , the number N of nozzles of the printhead is eight (an even number). After the printhead completes a printing pass on a print-medium, the print-medium moves a distance d1 of 3.5 nozzles. After the printhead completes the next printing pass, the print-medium moves a distance d2 of 4.5 nozzles. Next, after the printhead completes another printing pass, the print-medium moves a distance d3 of 3.5 nozzles, prints, and then moves a distance d4 of 4.5 nozzles and completes another printing pass. The print-medium moves distances of 3.5 nozzles and 4.5 nozzles alternately. Suppose that one of the two damaged nozzles is the 2nd nozzle, marked with thick lines. In this case, the other damaged nozzle could not be the 5th, 6th, or 7th nozzle, marked with thin lines. If the other damaged nozzle is the 5th or 6th nozzle, when the print-medium moves a distance of 3.5 nozzles, the positions of the 2nd and the 5th or 6th nozzles are adjacent on the print-medium as the block m of  FIG. 2 . Therefore, after the printhead completes a printing pass, the blank area  8  of  FIG. 1  will occur. Similarly, if the other damaged nozzle is the 6th or 7th nozzle, when the print-medium moves a distance of 4.5 nozzles, the positions of the 2nd and the 6th or 7th nozzles are adjacent on the print-medium as the block n of  FIG. 2  and then the blank area  8  of  FIG. 1  will occur.  
      We can infer a conclusion from the above. The number of damaged nozzles of the printhead is two and the number of nozzles of the printhead is even. After the printhead completes a printing pass, the moving distance of the print-medium is equal to a distance from the first nozzle to the middle of the N/2 nozzle and the (N+2)/2 nozzle. After the next printing pass, the moving distance of the print-medium is equal to a distance from the first nozzle to the middle of the (N+2)/2 nozzle and the (N+4)/2 nozzle. That is, the print-medium moves two different distances alternately. Suppose that one of the two damaged nozzles is the n nozzle, if the other damaged nozzle conforms to one of the following three rules, the printhead is unqualified. 
          (a1) When n=1 to (N/2)−1, the other damaged nozzle is the (N/2)+n−1 nozzle, the (N/2)+n nozzle, or the (N/2)+n+1 nozzle;     (a2) When n=N/2, the other damaged nozzle is the (N−1) nozzle, or the N nozzle;     (a3) When n=(N/2)+1, the other damaged nozzle is the N nozzle.        

      Note that the conditions of n=(N/2)+2 to N are included in the three rules. For instance, from the three rules, if one of the two damaged nozzles is the N nozzle, the other damaged nozzle cannot be the (N/2)−1, N/2, or (N/2)+1 nozzle. If there are only two damaged nozzles, and the first to the (N/2)+1 nozzles are not damaged, the printhead must conform to the specification.  
      According to the three rules, the present invention designs test patterns for the printhead having an even number of nozzles. Please refer to  FIG. 3  to  FIG. 6 , which are test patterns for the printhead having an even number of nozzles according to the present invention. The number of nozzles of the printhead of  FIG. 3  to  FIG. 6  is 300.  FIG. 3  is the first test pattern. Each set prints a line by a nozzle. Thus, there are 300 sets in  FIG. 3 . The number of damaged nozzles can be inspected with the naked eye from  FIG. 3 . For example, the line is not complete in the 4th set of  FIG. 3 . In other words, the 4th nozzle is damaged. If the number of damaged nozzles is two from the inspection of  FIG. 3 . The test patterns of  FIG. 4  to  FIG. 6  must be printed for further inspection. In  FIG. 4  to  FIG. 6 , each set has two lines printed by two nozzles respectively. If one of the two damaged nozzles is the first nozzle (n=1), according to the rule (a1), the other damaged nozzle could not be the 150th, 151st, or 152nd nozzle. Therefore, the first and the 150th nozzles jet ink in the same set in  FIG. 4 ; the first and the 151st nozzles jet ink in the same set in  FIG. 5 ; and the first and the 152nd nozzles jet ink in the same set in  FIG. 6 . If one of the two damaged nozzles is the second nozzle (n=2), the other damaged nozzle could not be the 151st, 152nd, or 153rd nozzle, as shown in the second set of  FIG. 4  to  FIG. 6 . Thus, the test patterns of  FIG. 4  to  FIG. 6  can be designed according to the three rules. There are 151 sets in  FIG. 4  and  FIG. 6 , and there are 150 sets in  FIG. 5 . If two lines of any set of  FIG. 4  to  FIG. 6  are not complete, the printhead is unqualified. For instance, the two lines of the 4th set of  FIG. 4  are not complete. We can infer that the 4th and 153rd nozzles are damaged and the printhead is unqualified. The arrangement of each set of  FIG. 4  to  FIG. 6  is random. If two lines of any set are not complete, the printhead is unqualified.  
      Please refer to  FIG. 7 , which is a diagram of the second embodiment of the present invention for inspecting the printhead having two damaged nozzles. In the embodiment of  FIG. 7 , the number N of nozzles of the printhead is seven (an odd number). After the printhead completes a printing pass on a print-medium, the print-medium moves a distance d5 of 3.5 nozzles. Suppose that one of the two damaged nozzles is the 6th nozzle, marked with thick lines. In this case, the other damaged nozzle could not be the 2nd or 3rd nozzle, marked with thin lines. If the other damaged nozzle is the 2nd or 3rd nozzle, when the print-medium moves a distance of 3.5 nozzles, the positions of the 6th and the 2nd or 3rd nozzles are adjacent on the print-medium as the block p of  FIG. 7 . Therefore, the blank area  8  of  FIG. 1  will occur.  
      We can infer a conclusion from the above. The number of damaged nozzles of the printhead is two and the number of nozzles of the printhead is odd. After the printhead completes a printing pass, the moving distance of the print-medium is equal to a distance from the first nozzle to the middle of the (N+1)/2 nozzle and the (N+3)/2 nozzle. Suppose that one of the two damaged nozzles is the n nozzle. If the other damaged nozzle conforms to one of the following two rules, the printhead is unqualified. 
          (b1) When n=1 to (N−1)/2, the other damaged nozzle is the ((N−1)/2+n) nozzle, or the ((N+1)/2+n) nozzle;     (b2) When n=(N+1)/2, the other damaged nozzle is the N nozzle.        

      Note that the conditions of n=(N+1)/2+ to N are included in the two rules. For instance, from the two rules, if one of the two damaged nozzles is the N nozzle, the other damaged nozzle could not be the (N+1)/2, or (N−1)/2 nozzle. If there are only two damaged nozzles, and the first to the (N+1)/2 nozzles are not damaged, the printhead must conform to the specification.  
      According to the two rules, the present invention designs test patterns for the printhead having an odd number of nozzles. Please refer to  FIG. 8  to  FIG. 10 , which are test patterns according to the present invention for the printhead having an odd number of nozzles. The number of nozzles of the printhead of  FIG. 8  to  FIG. 10  is 301.  FIG. 8  is the first test pattern. Each set prints a line by a single nozzle. Thus, there are 301 sets in  FIG. 8 . The number of damaged nozzles can be inspected with the naked eye from  FIG. 8 . For example, the line is not complete in the 4th set of  FIG. 8 . In other words, the 4th nozzle is damaged. If the number of damaged nozzles is two from the inspection of  FIG. 8 . The test patterns of  FIG. 9  and  FIG. 10  must be printed for further inspection. In  FIG. 9  and  FIG. 10 , each set has two lines printed by two nozzles respectively. If one of the two damaged nozzles is the first nozzle (n=1), according to the rule (b1), the other damaged nozzle cannot be the 151st or 152nd nozzle. Therefore, the first and the 151st nozzles jet ink in the same set in  FIG. 9  and the first and the 152nd nozzles jet ink in the same set in  FIG. 10 . If one of the two damaged nozzles is the second nozzle (n=2), the other damaged nozzle could not be the 152nd or 153rd nozzle, as shown in the second set of  FIG. 9  and  FIG. 10 . Thus, the test patterns of  FIG. 9  and  FIG. 10  can be designed according to the two rules. There are 151 sets in  FIG. 9  and there are 150 sets in  FIG. 10 . If two lines of any set of  FIG. 9  and  FIG. 10  are not complete, the printhead is unqualified. For instance, the two lines of the 4th set of  FIG. 9  are not complete. We can infer that the 4th and 154th nozzles are damaged and the printhead is unqualified. The arrangement of each set of  FIG. 9  and  FIG. 10  is random. If two lines of any set are not complete, the printhead is unqualified.  
      Additionally, the present invention can use a scanner for the inspection. Please refer to  FIG. 11 , which is a diagram of a printer  10  of the present invention. The printer  10  includes a printhead  12  having N nozzles  13  and a logic unit  14 . The logic unit  14  inspects whether the printhead  12  conforms to the specification according to the rules mentioned above. The logic unit  14  draws a test pattern of  FIG. 3  or  FIG. 8  from a memory  18  and controls the printhead  12  to print the test pattern on a print-medium  20 . A scanner  16  scans the test pattern printed on the print-medium  20 . Then the logic unit  14  inspects whether the printhead  12  conforms to the specification according to the scan result of the scanner  16  and the rules mentioned above.  
      Before starting the flowchart of the present invention, whether the number of nozzles of the printhead  12  is odd or even must first be determined. The detailed steps are shown in  FIG. 12  and  FIG. 13 .  FIG. 12  and  FIG. 13  are respective flowcharts of inspecting whether a printhead having odd and even nozzles conforms to the specification, respectively.  
      Please refer to  FIG. 12  for the number of nozzles being odd.  
      Step  100 : Detect the number m of all damaged nozzles. If m is smaller than 2, go to step  104 . If m is greater than 2, go to step  106 . If m is equal to 2, go to step  102 .  
      Step  102 : If the two damaged nozzles conform to one of the rules (b1) and (b2), go to step  106 . Otherwise, go to step  104 .  
      Step  104 : The printhead is qualified.  
      Step  106 : The printhead is unqualified.  
      Next, refer to  FIG. 13  for the number of nozzles being even.  
      Step  200 : Detect the number m of all damaged nozzles. If m is smaller than 2, go to step  204 . If m is greater than 2, go to step  206 . If m is equal to 2, go to step  202 .  
      Step  202 : If the two damaged nozzles conform to one of the rules (a1) and (a3), go to step  206 . Otherwise, go to step  204 .  
      Step  204 : The printhead is qualified.  
      Step  206 : The printhead is unqualified.  
      Moreover, the present invention can be implemented in the printhead with a resolution equal to or greater than 600 dpi with the length of the chip being equal to or greater than a quarter inch, especially for inspecting the number of nozzles equal to or greater than 150. However, the present invention is not limited to the conditions mentioned above. The present invention can also be implemented in other printheads with lower resolutions, shorter lengths of chips, and less nozzles.  
      Compared to the prior art, the present invention inspects that the number of damaged nozzles is equal to or less than two for printheads of high resolution and uses an interpolation to infer the rules mentioned above to detect if positions of dots printed by the two damaged nozzles are adjacent on the print-medium. In other words, the present invention can avoid poor printing quality, such as the blank area  8  of  FIG. 1 . In addition, the present invention designs test patterns, such as  FIG. 3  to  FIG. 6  and  FIG. 8  to  FIG. 10 , for operators speedily and precisely to inspect printheads with the naked eye. A scanner may also used in the present invention to scan test patterns, such as  FIG. 3  and  FIG. 8 , for speedily inspecting printheads.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.