Abstract:
A print alignment method comprises detecting a skew direction of the printhead, receiving column data, corresponding to columns of printhead nozzles, dividing column data into N sections, selecting individual N column data, when the skew is to the right, the printhead receives the first section of first column data, the second section of second column data, the third section of third column data and so on; and when the skew direction is to the left, the printhead receives the Nth section of the first column data, the (N-1)th section of the second column data, the (N-2)th section of the third column data, and so on.

Description:
BACKGROUND  
       [0001]     The invention relates to print devices and more particularly to a printhead with an alignment compensation method and system.  
         [0002]     In ink jet printers, ink is fed to an array of digitally controlled nozzles on a printhead. As the printhead passes over the media, ink is ejected from the array of nozzles to print on the media. Current design combines the printhead with a print cartridge. The print cartridge is then installed in the carriage of a printer, likely incurring undesirable rotation of the print cartridge which can normally skew printed lines. Correction of misalignment is thus required.  
         [0003]     A conventional alignment method first supplies printing instructions to a printhead to energize printing elements in various groups (primitives). The printed pattern is then detected by optical sensors in the printer. Based on the detection, a position offset error for each primitive is determined. These errors generate a separate time correction for each of the primitives such that, when the printing is executed, the time period for printing a dot is advanced or delayed for each primitive so as to align the dots.  
         [0004]     The conventional method, as described above utilizing software, can reduce print speed and require additional costs for optical sensors and other elements.  
       SUMMARY  
       [0005]     The present invention is generally directed to a print alignment method. According to one aspect of the invention, a method comprises detecting a skew direction of the printhead, receiving column data, corresponding to columns of printhead nozzles, dividing column data into N sections, selecting individual N column data, when the skew is to the right, the printhead receives the first section of first column data, the second section of second column data, the third section of third column data and so on; and when the skew direction is to the left, the printhead receives the Nth section of the first column data, the (N-1)th section of the second column data, the (N-2)th section of the third column data, and so on.  
         [0006]     The invention further provides a print alignment method comprising detecting a skew direction of the printhead, receiving column data, corresponding to columns of printhead nozzles, dividing column data into N sections, when the skew direction is to the right, the printhead receives the first section of the column data to print and then receives the second section of the column data to print and so on in a print period (t p ), and when the skew direction is the right, the printhead receives the Nth section of the column data to print and then receives the (N-1) th section of the column data to print and so on in a print period (t p ).  
         [0007]     The invention further provides a print alignment system for a printhead comprising a print module, a compensation module and a compensation print module. The print module receives print data and translates it into column data, corresponding to a plurality of columns of printhead nozzles. The compensation module receives a test pattern and outputs compensation data, comprising a skew direction and displacement offset. The compensation print module executes an alignment procedure, in accordance with the column data and the compensation data, comprising dividing column data into N sections, and selecting specific N column data, such that when the skew is to the right, the printhead receives the first section of first column data, the second section of second column data, the third section of third column and so on to print, and when the skew direction is to the left, the printhead receives the Nth section of first column, the (N-1)th section of the second column data, the (N-2)th section of third column data and so on to print.  
         [0008]     The invention further provides a print alignment system for a printhead comprising a print module, a compensation module and a compensation print module. The print module receives print data and translates it into column data, corresponding to a plurality of columns of printhead nozzles. The compensation module receives a test pattern and outputs compensation data, comprising a skew direction and displacement offset. The compensation print module executes an alignment procedure, in accordance with the column data and the compensation data, comprising dividing column data into N sections, when the skew direction is to the right, the printhead receives and prints the first section of the column data and then receives and prints the second section of the column data and so on in a print period (t p ), and when the skew direction is the right, the printhead receives and prints the Nth section of the column data and then receives and prints the (N-1)th section of the column data and so on in a print period (t p ).  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1   a  is a schematic diagram of printhead skew detection.  
         [0010]      FIG. 1   b  is a diagram of printhead nozzle arrangement.  
         [0011]      FIG. 1   c  shows printing when a printhead is perpendicular to a moving direction.  
         [0012]      FIG. 2  shows printing when a printhead skews to the left.  
         [0013]      FIG. 3  is a schematic diagram of a method for alignment of the print in  FIG. 2  according to embodiments of the invention.  
         [0014]      FIG. 4  is a schematic diagram of another method for alignment of the print in  FIG. 2  according to embodiments of the invention.  
         [0015]      FIG. 5  is a schematic diagram of another method for alignment of the print in  FIG. 2  according to embodiments of the invention.  
         [0016]      FIG. 6  shows printing when a printhead skews to the right.  
         [0017]      FIG. 7  is a schematic diagram of a method for alignment of the print in  FIG. 6  according to embodiments of the invention.  
         [0018]      FIG. 8  is a schematic diagram of another method for alignment of the print in  FIG. 6  according to embodiments of the invention.  
         [0019]      FIG. 9  is a schematic diagram of another method for alignment of the print in  FIG. 6  according to another embodiment of the invention.  
         [0020]      FIG. 10  is a functional block diagram of a system for alignment of print.  
     
    
     DETAILED DESCRIPTION  
       [0021]      FIG. 1   a  is a schematic diagram of printhead skew detection. Area  10   a  shows printing when a printhead is perpendicular to a print bar and area lob shows printing when a printhead is not perpendicular to a print bar. Area I shows printing without any displacement offset and area II shows printing with displacement offset. In the present disclosure, the printhead receives one, two and three dpi to the right (marked as +1, +2 and +3), one, two and three dpi to the left (marked as −1, −2 and −3) and the line marked  0  represents zero displacement offset. In area  10   a , the printhead is perpendicular to the print bar when lines  0  in area I and area II connect. In area lob, the printhead has one dpi displacement to the left when lines +1 in area I and area II connect. The method demonstrates skew of the printhead and displacement offset.  
         [0022]      FIG. 1   b  is a diagram of printhead nozzle arrangement. 0˜3F represent nozzles. The printhead has two columns of nozzles driven by address signals A 1 ˜A 8  and primitive select signals PS 1 ˜PS 8 , where the first column of nozzles is driven by address signals A 1 ˜A 8  and primitive select signals PS 1 , PS 3 , PS 5  and PS 7 , and the second column of nozzles is driven by address signals A 1 ˜A 8  and primitive select signals PS 2 , PS 4 , PS 6  and PS 8 . In addition, the two columns of nozzles are further divided into banks of nozzles driven by address signals A 1 ˜A 8  and primitive a select signal. When the printhead starts to print, address signals A 1 ˜A 8  are sequentially asserted and the nozzle outputs ink if the corresponding primitive select signal is asserted.  
         [0023]      FIG. 1   c  shows printing when a printhead is perpendicular to a moving direction. When each nozzle outputs ink in a position pulse, the printing is a straight line, and each time period of one position pulse is t_p. The following embodiments illustrate printhead  11  using two columns of nozzles  12 .  
         [0024]      FIG. 2  shows printing when a printhead skews to the left. When each nozzle of column  12  outputs ink in a position pulse, the printing is a straight line skewed to the left.  
         [0025]      FIG. 3  is a schematic diagram of a method for alignment of the print in  FIG. 2  according to embodiments of the invention. The printhead skews to the left and the displacement offset is two dpi. Column data transmitted to the printhead  11  is divided into two sections, section I and section II. The present embodiment uses three successive column reading as an example. Compensable print module  34  receives column data  31 , column data  32  and column data  33  and rearranges them. Printhead  11  receives and prints section  32 _I of column data  32  and section  31 _II of column data  31  in a position pulse and receives and prints section  33 _I of column data  33  and section  32 _II of column data  32  in the next pulse. Compared with  FIG. 2 , print misalignment is reduced.  
         [0026]      FIG. 4  is a schematic diagram of another method for alignment of the print in  FIG. 2  according to embodiments of the invention. When printhead is skewed to the left and the displacement offset is three dpi, column data transmitted to the printhead  11  is divided into three sections, section I, section II and section III. The present embodiment uses four successive column reading as an example. Compensable print module  34  receives column data  41 , column data  42 , column data  43  and column data  44  and rearranges them. Printhead  11  receives and prints section  43 _I of column data  43 , section  42 _II of column data  42  and section  41 _m of column data  41  in a position pulse and receives and prints the section  44 _I of column data  44 , section  43 _II of column data  43  and section  42 _II of column data  42  in the next pulse. Compared with  FIG. 2 , print misalignment is reduced.  
         [0027]      FIG. 5  is a schematic diagram of another method for alignment of the print in  FIG. 2  according to embodiments of the invention. When printhead is skewed to the left and the displacement offset is two dpi, the column data transmitted to the printhead  11  is divided into two sections, section I and section II. Compensable print module  34  receives column data  51  and transmits the section  51 _I of column data  51  to printhead  11  to print first and then transmits the section  51 _II of column data  51  to print. To avoid increasing the total print time, the print time of each section should be equal to or less than (1/2t p ). Compared with  FIG. 2 , print misalignment is reduced.  
         [0028]      FIG. 6  shows printing when a printhead skews to the right. When each nozzle of column  12  outputs ink in a position pulse, the printing is a straight line skewed to the right.  
         [0029]      FIG. 7  is a schematic diagram of a method for alignment of the print in  FIG. 6  according to embodiments of the invention. The printhead is skewed to the right and the displacement offset is two dpi. The column data transmitted to the printhead  11  is divided into two sections, section I and section II. The present embodiment uses three successive column reading as an example. Compensable print module  34  receives column data  71 , column data  72  and column data  73  and rearranges them. Printhead  11  receives and prints section  71 _I of column data  71  and section  72 _II of column data  72  in a position pulse and receives and prints section  72 _I of column data  72  and section  73 _II of column data  73  in the next pulse. Compared with  FIG. 6 , print misalignment is reduced.  
         [0030]      FIG. 8  is a schematic diagram of another method for alignment of the print in  FIG. 6  according to embodiments of the invention. When printhead is skewed to the right and the displacement offset is three dpi, column data transmitted to the printhead  11  is divided into three sections, section I section II and section III. The present embodiment uses four successive column reading as an example. Compensable print module  34  receives column data  81 , column data  82 , column data  83  and column data  84  and rearranges them. Printhead  11  receives and prints section  81 _I of column data  81 , section  82 _II of column data  82  and section  83 _III of column data  83  in a position pulse and receives and prints section  82 _I of column data  82 , section  83 _II of column data  83  and section  84 _III of column data  84  in the next pulse. Compared with  FIG. 6 , print misalignment is reduced.  
         [0031]      FIG. 9  is a schematic diagram of another method for alignment of the print in  FIG. 6  according to another embodiment of the invention. The printhead  11  is skewed to the right and the displacement offset is two dpi. The column data transmitted to the printhead  11  is divided into two sections, section I and section II. Compensable print module  34  receives column data  91  and transmits section  91 _II of column data  91  to printhead  11  to print first and then transmits section  91 _I of column data  91  to print. To avoid increasing the total print time, the print time of each section should be equal to or less than  
         (       1   2     ⁢     t   p       )     .         
 Compared with  FIG. 6 , print misalignment is reduced. 
 
         [0032]      FIG. 10  is a functional block diagram of a system for alignment of print. The print module  101  receives and translates print data into column data. The compensation module  103  receives a test pattern and outputs compensation data, including a skew direction and a displacement offset N for printhead  104 . The compensable print module  102  receives and divides the column data from the print module  101  into N sections and executes an alignment procedure. When the printhead  104  is skewed to the right, printhead  104  receives the first section of the first column data, the second section of second column data, the third section of third column data and so on to print. Alternatively, the printhead  104  receives the Nth section of the column data to print and then receives the (N-1)th section of the column data to print and so on in a print period (t p ). When the printhead  104  is skewed to the left, the printhead  104  receives the Nth section of first column data, the (N-1)th section of second column data, the (N-2)th section of third column data and so on to print. Alternatively, the printhead  104  receives the Nth section of the column data to print and then receives the (N-1) th section of the column data to print and so on in a print period (t p ).  
         [0033]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.