Abstract:
A method for efficiently compensating for malfunctioning nozzles in a printhead. A print order is input, malfunctioning nozzles on a printhead are identified, and, in the case malfunctioning nozzles are present, compensation printing occurs to optimize print quality. The detecting of malfunctioning nozzles includes printing a test pattern, scanning the test pattern, comparing the scanned test pattern to an ideal test pattern, and then identifying the locations of malfunctioning nozzles. In the case that only one nozzle is malfunctioning, the number of nozzles used to scan a line of print is reduced by two so that compensation printing can correct two lines of print with one single swath.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from the application entitled Printing Quality Improving Method filed with the Korean Industrial Property Office on Dec. 19, 1997 and there duly assigned Serial No. P97-70918 by that Office. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method for improving printing quality, more particularly, to a method for improving printing quality by printing through functioning nozzles, and reprinting over areas of non-functioning nozzles when non-functioning nozzles are present. The detection of nonfunctioning nozzles is accomplished by printing and scanning a piece of printed material. 
     DISCUSSION OF RELATED ART 
     Generally, an inkjet printer prints by jetting ink on paper through a number of nozzles by activating a number of electrical signals being applied to a jetting part of an ink head. However, alien substances may be inserted into any nozzle among nozzles jetting ink or a certain nozzle may not be continuously utilized. In those cases, any nozzle among the nozzles can be stopped or an electrical signal needed for jetting ink cannot be applied to a certain nozzle. As a result, malfunctioning nozzles, through which ink cannot be jetted in printing, may be formed. In earlier techniques, when an inkjet printer has malfunctioning nozzles, the ink head cannot jet ink through the malfunctioning nozzles. Accordingly, white lines formed on printing paper in a horizontal direction, and so the printing quality falls off. 
     SUMMARY OF THE INVENTION 
     Accordingly, in order to overcome such drawbacks in the earlier art, it is an object of the present invention to provide a method for improving printing quality by printing over these white lines using functioning nozzles. A scanner is used to detect the presence and location of any non-functioning nozzles so that the functioning nozzles can make-up for the non-functioning nozzles. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a printing quality improving method comprising the steps of: inputting a printing order; detecting the presence and absence of malfunctioning nozzles among the nozzles of the jetting part in the inputting step and a position and number of malfunctioning nozzles in case malfunctioning nozzles are present; printing firstly as much as a width of a printing band having a reference line distance set by a line feed value in case of the absence of a malfunctioning nozzle in the detecting step; printing secondly a compensation letter line of one line for each of two lines by moving a normal nozzle to two malfunctioning nozzle positions of each two neighboring lines, after printing with a first printing band, which has a smaller first line distance than the reference line distance, in case of the presence of a single malfunctioning nozzle in the detecting step; and printing thirdly as much as a width of the printing band having the line distance by positioning a normal nozzle at a position of detected malfunctioning nozzles for every line having the reference line distance, printing as much as the width of the reference printing band having the reference line distance for every line in case of the presence of two or more malfunctioning nozzles in the detecting step. 
     Further, the detecting step comprises the steps of: printing a test printing pattern for detecting the presence or absence of malfunctioning nozzles; reading the printing pattern printed in the test printing step with a scanner; comparing the data read in the reading step with the printing data in the test printing step; and detecting the number and position of malfunctioning nozzles in the case malfunctioning nozzles are present, comparing whether the read data are accorded with the printed data in the comparing step. 
     Furthermore, the first printing band subtracts 2 from the number of nozzles. 
    
    
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols represent the same or similar components, wherein: 
     FIG. 1 is a flow view illustrating a method for improving printing quality according to the present invention; 
     FIG. 2 is a printing status view according to the present invention in case of the presence of a malfunctioning nozzle; and 
     FIG. 3 is a printing status view according to the present invention in case of the presence of two or more malfunctioning nozzles. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a flow chart illustrating a method for improving printing quality. A printing quality improving method for printing as much as a width of a printing band, which has a reference line distance set by a line feed value, by jetting ink through a number of nozzles of the jetting part, being provided with a jetting part having a number of nozzles, the method comprises the steps of: inputting S 10  a printing order; detecting S 20  the presence or absence of malfunctioning nozzles among the nozzles of the jetting part in the inputting step, and the position and number of malfunctioning nozzles in case of the presence of malfunctioning nozzles; printing S 30  firstly as much as a width of a printing band having a reference line distance set by a line feed value in case of the absence of a malfunctioning nozzle in the detecting step; printing S 40  secondly a compensation letter line of one line for each of two lines, by printing a first printing band, which has a smaller first line distance than the reference line distance, moving a functioning nozzle to two malfunctioning nozzle positions of every two neighboring lines in case of a single malfunctioning nozzle discovered in the detecting step; and printing S 50  thirdly as much as a width of the printing band having the line distance for every line by positioning a functioning nozzle at a position of first malfunctioning nozzle (DOT β1) of detected malfunctioning nozzles having the reference line distance, printing as much as the width of the reference printing band having the reference line distance for every line in case of two or more malfunctioning nozzles in the detecting step. 
     Here, line does not mean a line of printed letters from the viewpoint of a user, but a line formed by each nozzle forms by the movement of a head in the printing operation. 
     The detecting step S 20  comprises the steps of printing S 21  a test printing pattern for detecting the presence or absence of malfunctioning nozzles; reading S 22  the printing pattern printed in the test printing step S 21  with a scanner; comparing S 23  the data scanned in the reading step S 22  with the printing data in the test printing step S 21 ; and detecting S 24  the number and position of malfunctioning nozzles when malfunctioning nozzles are present, comparing whether the scanned data agree with the printed data in the comparing step S 23 . 
     The test printing step S 21  gets ink jetted through all the nozzles, activating electrical signals for determining the functionality for each of the nozzles. 
     The first printing band has a width two less than the total number of nozzles present The operation of the present invention according to the above-described construction can be described as follows. FIG. 2 is a printing status view according to the present invention in case of the presence of a single malfunctioning nozzle, and FIG. 3 is a printing status view according to the present invention in case of the presence of two or more malfunctioning nozzles. 
     The inputting step S 10  starts printing by inputting a printing order. The detecting step S 20  detects the presence or absence of malfunctioning nozzles among a number of nozzles of an ink head, as well as the position and number of the malfunctioning nozzles in case that malfunctioning nozzles are present, and therefor comprises the test printing step S 21 , the reading step S 22 , the comparing step S 23 , and the detecting step S 24 . The test printing step S 21  prints a test printing pattern by getting ink jetted through all nozzles, activating electrical signals for determining the functionality for the number of nozzles respectively. The reading step S 22  reads the printing pattern printed in the test printing step S 21  with a scanner. The comparing step S 23  compares the data read in the reading step S 22  with the printing data in the test printing step S 21  and the detecting step S 24  detects the number and position of malfunctioning nozzles when malfunctioning nozzles are present, comparing whether the read data agree with the printed data in the comparing step S 23 . 
     For example, let us assume, when electrical signals for determining the functionality of each of the nozzles are activated to jet ink through the nozzles, bits of data corresponding to the nozzles come to have high logical value in binary, whereas when electrical signals are inactivated not to jet ink through the nozzles, bits of data corresponding to the nozzles come to have low logical value in binary. Then, as the test printing step S 21  in the detecting step S 20  applies activated electrical signals to each of all nozzles, all the printed data are composed of bits having high logical value. The reading step S 22  reads the printing pattern printed in the test printing step S 21  with the scanner. The comparing step S 23  compares the printed data, composed of bits having high logical value, with the read data having low logical value owing to the malfunctioning nozzles in case of the presence of malfunctioning nozzles. The detecting step S 24  rotates the line feed motor and prints on the paper for every line as much as the width of the printing band having the reference line distance set by the line feed value in the first printing operation S 30  when the data read in the comparing step S 23  is the same as the printed data, that is, in case of the absence of a malfunctioning nozzle. 
     When only one nozzle is malfunctioning, that is to say, only one bit among the bits of data read in the reading step S 21  has low logical value, the detecting step S 24  detects the position of the one malfunctioning nozzle, as the bit having low logical value, among nozzles. For example, in case of the presence of one malfunctioning nozzle as shown in FIG. 2, assuming that the number of whole nozzles is N and a βth nozzle is malfunctioning, the second printing operation S 40  rotates the line feed motor as much as the width of the printing band having distance from dot 1 to dot N−2, which is the first line distance smaller than the line feed value, and prints as much as the width of the first printing band for every line (Band 1˜Band 4), and prints by inserting an inserting band (Irband 1, Irband 2), which rotates the line feed motor as much as the width of the printing band having the reference line distance from dot 1 to dot N, into the position (dot β) of the malfunctioning nozzle detected in the detecting step S 20  for every odd number of lines (band 1, band 3) among lines having the first line distance. Accordingly, in case of the presence of one malfunctioning nozzle, the operation S 40  prints the first line as much as the width of the printing band (band 1) having the first line distance from dot 1 to dot N−2. As the operation S 40  sets a variable of the movable step of the line feed motor so as to print from the malfunctioning nozzle position dot 1 and inserts the inserting band (Irband 1) and prints, ink is jetted into the dot β, which has not been printed in the first pass, through the normal nozzle, which is the first nozzle (dot 1) of the inserting band (Irband 1) and therefore the 13th dot occurred in the first line is finally printed. Further, as the position of the malfunctioning nozzle occurred in the second line (band 2) is normally printed by a N−1th nozzle (dot N−1) of the first inserting band (Irband 1), each inserting band (Irband) should be inserted into every odd number of lines (band 1, band 3) and printed. 
     FIG. 3 is a printing status view according to the present invention in case of the presence of two or more malfunctioning nozzles. The third printing operation S 50  has the same operation as the second printing step S 40  in case of the presence of one malfunctioning nozzle. However, the third printing step S 50  rotates the line feed motor as much as the width of the printing band having the reference line distance from dot 1 to dot N and prints for every line (band 1˜band 3), and prints by inserting each of inserting bands (Irband 1˜Irband 3) having the width of the printing band having the reference line distance beginning from the position dot β1 of a first malfunctioning nozzle among nozzles detected in the detecting step S 20  for every line. 
     For example, assuming that there are two malfunctioning nozzles and the malfunctioning nozzles are dot β1th nozzle and dot β2th nozzle respectively, the third printing operation S 50  prints the first line (band 1) having width from dot 1 to dot N, and prints by inserting the inserting band (Irband 1) having width from dot 1 to dot N, which begins to print from the first position (dot β1) of the malfunctioning nozzles detected in the detecting step S 20 . Accordingly, as the dots (dot β1, dot β2) of the two malfunctioning nozzles occurred in the first line, they are reprinted by the inserting band (Irband 1) so that the finished product shows no malfunctioning nozzles. The above description assumes that the normal nozzle is positioned in the first malfunctioning nozzle. However, when the normal nozzle is positioned in a position of malfunctioning nozzles irrespective of any malfunctioning nozzle, the operation according to the present invention can be expected to be performed. 
     As the inserting band is inserted and paper is printed by means of the above-described method also in case of the presence of a number of malfunctioning nozzles in the jetting part of the ink head, white dots do not occur on printing paper. Accordingly the printing quality can be improved. 
     As the present invention prints using only the nozzles with exception of malfunctioning nozzles, white lines being occurred by the malfunctioning nozzles do not occur. Therefore, the printing quality can be improved. 
     It will be apparent to those skilled in the art that various modifications can be made in the method for improving printing quality of the present invention, without departing from the spirit of the invention. Thus, it is intended that the present invention cover such modifications as well as variations thereof, within the scope of the appended claims and their equivalents.