Printing apparatus and method of correcting step shift thereof

A printing apparatus configured to perform printing to a print medium, the printing apparatus comprising:

• a printer having at least two line heads spaced away in a transportation direction of the print medium, the line heads each having a plurality of recording modules with a train of recording devices arranged linearly in a width direction of the print medium;
• a scanner configured to scan an image printed with the printer to obtain a scanned image;
• a correcting-chart printing unit configured to cause a first line head of the printer to print a first correcting chart in a first line head printing area and cause a second line head to print a second correcting chart in a second line head printing area, away from the first line head printing area in the transportation direction;
• a scanned image collecting unit configured to operate the scanner to read the first line head printing area and the second line head printing area to collect a first scanned image and a second scanned image, respectively;
• a correction-data calculating device configured to calculate correction data, the correction-data calculating device regarding a line figure in the first scanned image formed with one of the plurality of recording modules as a reference line figure, and determining a difference in the transportation direction between the reference line figure and a line figure formed with the other recording module as a reference head difference, determining a difference in the transportation direction between a first line figure and a second line figure of the second scanned image as an individual head difference, the first line figure being formed with the first line head and the second line figure being formed with the second line head, and summing up the reference head difference and the individual head difference to obtain a total for every recording module, the reference head difference being regarded as the correction data in the transportation direction for every recording module in the first line head, and the total being regarded as the correction data for every recording module in the second line head;
• and
• an adjusting device configured to adjust a timing in accordance with the correction data upon printing with the printer;
• wherein the correcting-chart printing unit performs printing of the line figure of the first correcting chart for every recording module and the line figure of the second correcting chart for every recording module in the second line head printing area by a length in the width direction of the print medium such that the line figures printed at the same position in the transportation direction do not overlap each other;
• the correcting-chart printing unit prints the line figures of the first correcting chart and the second correcting chart in the second line head printing area so as to be spaced away from each other in the transportation direction with a portion other than the recording module used upon printing the line figures;
• and
• the correction-data calculating device calculates the individual head difference by averaging step shift, the step shift being determined from the line figures of the first and second correcting charts in the second line head printing area for every recording module.

A method of correcting step shift of a printing apparatus configured to perform printing to a print medium, the method comprising:

• a correcting-chart printing step of printing a first correcting chart with a first line head of a printer in a first line head printing area and printing in a second line head printing area, spaced away from the first line head printing area in a transportation direction, a second correcting chart with a second line head, the line heads each having a plurality of recording modules with a train of recording devices arranged linearly in a width direction of the print medium;
• said recording modules being arranged in a width direction of the print medium so that line figures printed by the recording modules of the first line head, and line figures printed by the recording modules of the second line head, that are printed at the same position in the transportation direction, do not overlap each other;
• a scanned-image collecting step of reading the first line head printing area and the second line head printing area to collect a first scanned image and a second scanned image, respectively;
• a correction-data calculating step of calculating correction data by regarding a line figure in the first scanned image formed with one of the plurality of recording modules as a reference line figure and determining a difference in the transportation direction between the reference line figure and another line figure formed with the other recording module as a reference head difference, determining a difference in the transportation direction between a first line figure and a second line figure of the second scanned image formed with the first line head and the second line head, respectively as an individual head difference, and summing up the reference head difference and the individual head difference to obtain a total for every recording module, the reference head difference being regarded as the correction data in the transportation direction for every recording module in the first line head, and the total being regarded as the correction data for every recording module in the second line head;
• and
• an adjusting step of adjusting a timing in accordance with the correction data upon printing with the printer.