Abstract:
In a line type inkjet printer, a method to clean a nozzle effectively reducing the occurrence of clogging of nozzle is provided. In the method to clean a nozzle of a printing apparatus having a fixed print head of line type, the method to clean a nozzle includes the first process for counting the number of times of non-ink jet work operations of nozzle in each print head from image data for printing, the second process for operating period to flush based on the number of times of non-ink jet work operations, and the third process for producing control signal of printing including the period to flush.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method to clean a nozzle of printing apparatus, and more particularly relates to a method to clean a nozzle of line type inkjet printer.  
         [0003]     2. Description of the Related Art  
         [0004]     In an inkjet printer for color printing, nozzle arrays for ink ejection of each color; Y (yellow) color, M (magenta) color, C (cyan) color, and K (black) color, are provided. The number of times of ink jet work operations of each nozzle differs depending on patterns, hue, and density of a print image to be expressed. Accordingly, in a case of a nozzle whose number of times of ink jet work operations is few, the ink in a nozzle part is left in a stationary state for a long time, the ink is affected by a drying effect due to peripheral temperature and the ink agglutinates. As a result, in the worst case, the nozzle may be clogged with ink. Particularly, since the ink is not ejected from the clogged nozzle, non-printed line may be formed and such defective state (irreparable state) may extend to a large number of substrates.  
         [0005]     In inkjet printers, there are two types of inkjet printers; a serial type and a line type. In the serial type printer, all nozzles provided on a print head move on a main scanning line. Accordingly, it is possible to reduce unevenness of the number of times of ink jet work operations among each nozzle by changing combinations of the nozzles to be used in one printing. For example, in Japanese Unexamined Patent Application Publication No. 2002-240257, a method that a nozzle which does not eject ink at all is detected and in subsequent printing, in order to actively use the nozzle, combinations of nozzles to be used are changed, is disclosed.  
         [0006]     On the other hand, in the line type printer, print head of each color is fixed and printing is performed when a substrate passes right under print head of each color. Since each nozzle on print head of each color is in charge of one print line to be formed on the substrate which passes right under the nozzle, it is not possible to change to other nozzle. Accordingly, depending on a print image to be expressed, the number of times of ink jet work operations of each nozzle is fixed. As a result, unevenness of the number of times of ink jet work operations among each nozzle is not corrected and in the extreme case, a nozzle which does not eject ink at all can exist. In such a case, in the nozzle, the nozzle can be clogged with ink. Accordingly, particularly in the line type printer, it is necessary to frequently clean the nozzle during the processing.  
         [0007]     For example, in Japanese Unexamined Patent Application Publication No. 11-078055, a method to clean a nozzle of printer is disclosed. In the method, by using a non-printing period, to all nozzles, operation of flushing in which a printing operation of n dots and a subsequent non-printing operation of m dots are repeated a predetermined number of times is performed.  
         [0008]     As described above, in the line type printer, the possibility of clogging of nozzle is much higher than that in the serial type printer. Accordingly, by frequently cleaning the nozzle during the non-printing period, it can be possible to reduce the possibility of the clogging of nozzle.  
         [0009]     In the method to clean a nozzle of printing apparatus in the above patent literature 2, since the same operation of flushing is performed to all nozzles, it may be suitable for a case that the number of times of ink jet work operations among each of the nozzles is relatively even such as the serial type printer. However, in a case that the line type printer is used, when the number of times of ink jet work operations among each of the nozzles is extremely uneven, the ink may be consumed more than necessary for the processing of flushing, the expensive ink is consumed, and it is extremely wasteful.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, it is an object of the present invention to provide a method to clean a nozzle capable of effectively reducing the occurrence of clogging of nozzle without consuming ink more than needs when the line type inkjet printer is used.  
         [0011]     In one aspect of the present invention, a method to clean a nozzle for a printing apparatus having a fixed print head of line type, the method to clean a nozzle includes the first process for counting the number of times of non-ink jet work operations of nozzle in each print head from image data for printing, the second process for operating period to flush based on the number of times of non-ink jet work operations, and the third process for producing control signal of printing including the period to flush.  
         [0012]     According to the present invention, in the line type inkjet printer, even if any image is to be printed, it is possible to adequately and effectively reduce the occurrence of clogging of nozzle. Accordingly, it can be possible to greatly increase printing quality without increasing printing costs. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  illustrates a structure of a print head in a printing apparatus according to an embodiment of the present invention;  
         [0014]      FIG. 2  illustrates a structure of a control unit in the printing apparatus according to an embodiment of the present invention;  
         [0015]      FIG. 3  is a view for explaining a method to produce a control signal of printing of each print head from image data for printing;  
         [0016]      FIG. 4  illustrates an example of data of flushing for cleaning nozzles of each print head;  
         [0017]      FIG. 5  illustrates an example of a control signal of printing of each print head; and  
         [0018]      FIG. 6  is a view for explaining an operation for cleaning nozzle according to an embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Hereinafter, a line type inkjet printer according to an embodiment of the present invention is described. In this embodiment, a case that printing is performed on a building board by using the inkjet printer is described. However, the present invention can be applied to print on other substrates than the building board.  
         [0020]      FIG. 1  schematically illustrates a structure of a print head in a line type inkjet printer. The print head includes four print heads; a print head  11  of Y (yellow) color, a print head  12  of M (magenta) color, a print head  13  of C (cyan) color, and a print head  14  of K (black) color. These print heads are arranged in line along a moving direction of a building board  100  with a predetermined space. On an under surface of each print head, nozzle arrays  11 A,  12 A,  13 A, and  14 A for ink ejection of each color are provided respectively.  
         [0021]     When the building board  100  is moved toward the print heads, first, a printing of Y color is performed. Then, a printing of M color is performed and further printings of C color and K color are performed. A width W of the nozzle array in each print head is wider than a print width H of the building board lo. Accordingly, by passing the building board  100  under each head once, the printing on the surface to be printed (surface design) of the building board  100  is completed. One nozzle on each print head prints on the opposite position on the surface to be printed on the building board  100  which moves right under the nozzle, and when the printing is completed, one print line is formed.  
         [0022]     With reference to  FIGS. 2 and 3 , a structure and operation of a control unit of the line type inkjet printer according to an embodiment of the present invention is described. A control unit  200  in this embodiment includes an extracting unit  201  for image data, a producing unit  202  for reversed image data, an arithmetic logical unit  203  for counting the number of times of non-ink jet work operations, an arithmetic logical unit  204  for operating period to flush, and a producing unit  205  for control signal of printing. The control device can be a computer which has a CPU, a RAM, a storage device, etc., and the operation of each part in the control device can be executed by software which is executed by the computer.  
         [0023]     In the extracting unit  201  for image data, when image data  300  for printing is input, extracts Y image data  301 , M image data  302 , C image data  303 , and K image data  304  as shown in  FIG. 3 . The image data  300  for printing represents a pattern and color of a surface design of a building board and includes a control signal of ink jet for each nozzle in all print heads. The control signal of ink jet is generally an on-off signal which has a predetermined cycle. That is, when ejecting ink, the signal becomes on and when not ejecting ink, the signal becomes off. The Y image data  301  includes a control signal of ink jet of each nozzle in the print head  11  of Y color. Similarly, the M image data  302  includes a control signal of ink jet of each nozzle in the print head  12  of M color. The C image data  303  includes a control signal of ink jet of each nozzle in the print head  13  of C color. The K image data  304  includes a control signal of ink jet of each nozzle in the print head  14  of K color.  
         [0024]     It is assumed that the number of on-signal included in the Y image data  301 , M image data  302 , C image data  303 , and K image data  304  is My, Mm, Mc, and Mk respectively. My, Mm, Mc, and Mk indicate the number of times of ink jet work operations, the total Mt=My+Mm+Mc+Mk indicates the number of total dots of an image to be printed by the image data  300  for printing.  
         [0025]     The producing unit  202  for reversed image data produces image data  311  of reversed Y image data, image data  312  of reversed M image data, image data  313  of reversed C image data, and image data  314  of reversed K image data from the Y image data  301 , M image data  302 , C image data  303 , and K image data  304  respectively. The reversed data is produced by reversing on and off of the original data. If printing is performed by using the reversed data, a reversed image of the image printed by using the original data is printed.  
         [0026]     The arithmetic logical unit  203  for counting the number of times of non-ink jet work operations counts the total of the number of times of non-ink jet work operations of all nozzles in each print head. On- signals in each reversed image data mean off-signals in image data, that is, non-ejection of ink. In order to count the number of times of non-ink jet work operations of each print head, on-signals included in each reversed image data are to be counted. It is assumed that the number of on-signals included in the image data  311  of reversed Y image data, image data  312  of reversed M image data, image data  313  of reversed C image data, and image data  314  of reversed K image data are Ny, Nm, Nc, and Nk respectively. Ny, Nm, Nc, and Nk indicate the number of times of non-ink jet work operations of each print head (in  FIG. 3, 321  to  324 ).  
         [0027]     The arithmetic logical unit  204  for operating period to flush operates a period to flush of each print head based on the number of times of non-ink jet work operations of each print head. Periods to flush of the print heads of four colors, tf 1 , tf 2 , tf 3 , and tf 4 , are operated based on the number of times of non-ink jet work operations of each print head, Ny, Nm, Nc, and Nk. Accordingly, tf 1 =tf(Ny), tf 2 =tf(Nm), tf 3 =tf(Nc), and tf 4 =tf(Nk). As the number of times of non-ink jet work operations increases, the possibility of clogging of nozzle increases. Accordingly, to the print head whose number of times of non-ink jet work operations is large, a long period to flush is set and to the print head whose number of times of non-ink jet work operations is small, a short period to flush is set. For example, by multiplying the number of times of non-ink jet work operations of each print head, Ny, Nm, Nc, and Nk, by a predetermined coefficient, the periods to flush tf 1 , tf 2 , tf 3 , and tf 4  can be operated. Based on the periods to flush tf 1 , tf 2 , tf 3 , and tf 4 , data of flushing is produced.  
         [0028]     With reference to  FIG. 4 , the data of flushing is described. The data of flushing is data of color bar of one color of Y color, M color, C color, or K color. The data of color bar is a signal for continuously ejecting ink without non-jet point.  FIG. 4  illustrates an image of one color which is printed by the data of color bar of one color. The longitudinal size of the data shows a width of flushing of print head and the horizontal size of the data shows a period to flush of the print head. For example, data  401  of flushing for print head of Y color has the same width as the print width H of the building board  100 , and has the period to flush tf 1 . As well as the data  401  of flushing, data  402  of flushing for print head of M color, data  403  of flushing for print head of C color, and data  404  of flushing for print head of K color have the same width as the print width H of the building board  100  respectively, and have the periods to flush tf 2 , tf 3 , and tf 4 , respectively.  
         [0029]     The producing unit  205  for control signal of printing produces print instructions to each print head, that is, produces control signals of printing by using the data  401  to  404  of flushing.  
         [0030]     With reference to  FIG. 5 , the control signal of printing is described. A control signal  500  of printing includes image data  501  for printing, a signal  502  of period to adjust, and data  503  for flushing. Each print head performs printing according to the image data  501  for printing, stops the printing in response to the next signal  502  of period to adjust, and performs flushing according to the next data  503  for flushing.  
         [0031]     The control signal of printing in which such data of flushing is inserted is provided to print heads every printing of a predetermined number of boards.  
         [0032]     In this embodiment, since the data of flushing is included in the data to control printing, cleaning the nozzle is performed without detecting the back end of the building board, that is, the printing end point.  
         [0033]     As described above, in the present invention, since each print head performs flushing corresponding to the number of times of non-ink jet work operations of each print head, Ny, Nm, Nc, and Nk, even if a nozzle whose number of times of non-ink jet work operations is much count exists, it is possible to reduce the clogging of nozzle with ink.  
         [0034]     With reference to  FIG. 6 , a case in which when printing on a building board by using the printing apparatus according to the present invention, the flushing for cleaning the nozzle according to the present invention is performed is described. After the time point that the back end of a previous building board  101  passed right under the nozzle array  11 A of the print head  11  of Y color, that is, after the time point that printing on the previous building board  101  by the Y color finished, at the time point that the period of adjustment tc has passed, flushing  601  of print head  11  of Y color is performed. The period to flush is tf 1 . After the flushing of the print head  11  of Y color finished, when time tr passes, printing on a next building board  102  by Y color is started.  
         [0035]     If it is assumed that the time from the back end of the previous building board  101  passed the nozzle array  11 A of Y color to the time the front end of the next building board  102  arrives to the nozzle array  11 A of Y color is tg, tg=G/v. In this case, the distance between the building board  101  and the building board  102  is G, and the moving velocity of the building board is v. Further, the period of adjustment is tc=ΔL/v. In this case, ΔL is the distance that the building board  101  moves during the time from the back end of the building board  101  passed right under the nozzle array  11 A until the flushing is started.  
         [0036]     Then, tg=tc+tf 1 +tr. The sum of the period of adjustment tc and the period to flush tf, that is, tc+tf, should be smaller than the moving time tg.  
         [0037]     Similarly, after the time point that printing on the previous building board  101  by M color finished, at the time point that the period of adjustment tc=ΔL/v has passed, flushing  602  of print head  12  of M color is performed. The period to flush of the print head  12  of M color is tf 2 . After the time point that the printing on the previous building board  101  by C color is finished and the period of adjustment tc has passed, flushing  603  of print head  13  of C color is performed. The period to flush of the print head  13  of C color is tf 3 . Finally, after the time point that the printing on the previous building board  101  by K color is finished and the period of adjustment tc has passed, flushing  604  of print head  14  of K color is performed. The period to flush of the print head  14  of K color is tf 4 . Right under each print head, an ink receiving part (not shown) is provided to collect the flushed ink by using the receiving part and the collected ink is returned to an ink tank.  
         [0038]     While the present invention has been described with reference to exemplary embodiment, it is to be understood that the invention is not limited to the disclosed exemplary embodiment and various modifications of the present invention can be made without departing from the spirit and scope of the present invention as defined in the appended claims.  
       Drawings  
       [0039]    
       FIG. 2 
       
           300 : IMAGE DATA FOR PRINTING  
           200 : CONTROL UNIT  
           201 : EXTRACTING UNIT FOR IMAGE DATA  
           202 : PRODUCING UNIT FOR REVERSED IMAGE DATA  
           203 : ARITHMETIC LOGICAL UNIT FOR COUNTING THE NUMBER OF TIMES OF NON-INK JET WORK OPERATIONS  
           204 : ARITHMETIC LOGICAL UNIT FOR OPERATING PERIOD TO FLUSH  
           205 : PRODUCING UNIT FOR CONTROL SIGNAL OF PRINTING          : CONTROL SIGNAL OF PRINTING  
           11 ˜ 14 : PRINT HEAD  
       
     
         [0048]    
       FIG. 3 
       
           300 : IMAGE DATA FOR PRINTING  
           301 : Y IMAGE DATA  
           302 : M IMAGE DATA  
           303 : C IMAGE DATA  
           304 : K IMAGE DATA  
           311 : IMAGE DATA OF REVERSED Y IMAGE DATA  
           312 : IMAGE DATA OF REVERSED M IMAGE DATA  
           313 : IMAGE DATA OF REVERSED C IMAGE DATA  
           314 : IMAGE DATA OF REVERSED K IMAGE DATA  
           321 : THE NUMBER OF TIMES OF NON-INK JET WORK OPERATIONS OF Y COLOR INK Ny  
           322 : THE NUMBER OF TIMES OF NON-INK JET WORK OPERATIONS OF M COLOR INK Nm  
           323 : THE NUMBER OF TIMES OF NON-INK JET WORK OPERATIONS OF C COLOR INK Nc  
           324 : THE NUMBER OF TIMES OF NON-INK JET WORK OPERATIONS OF K COLOR INK Nk  
       
     
         [0062]    
       FIG. 5 
       
           501 : IMAGE DATA FOR PRINTING  
           502 : SIGNAL OF PERIOD TO ADJUST  
           503 : DATA FOR FLUSHING