Patent ID: 7478894

Claim:
A method of calibrating a print alignment error between a first printhead of a first ink cartridge and a second printhead of a second ink cartridge installed in an inkjet printer, the method comprising: printing a first preset test pattern using the first printhead and a second preset test pattern using the second printhead, on a paper according to an input correction signal, the first and second test patterns having first and second starting points and first and second end points, respectively; scanning the printed first and second test patterns; measuring positions of the first and second starting points and the first and second end points of the scanned first and second test patterns; calculating a horizontal print alignment error between the first and second printheads from the positions of the first and second starting points of the scanned first and second test patterns; calculating a vertical print alignment error between the first and second printheads from a first distance between the positions of the first starting and end points of the first test pattern and a second distance between the positions of the second starting and end points of the second test pattern; and calibrating the calculated horizontal and vertical print alignment errors, wherein the operation of calculating the horizontal print alignment error comprises: subtracting the starting point of the first test pattern by the first ink cartridge from the starting point of the second test pattern printed by the second ink cartridge; and calculating the horizontal print alignment error from a difference between a value, which is calculated in the operation of subtracting the first starting point of the first test pattern printed by the first ink cartridge from the second starting point of the second test pattern printed by the second ink cartridge, and a preset distance between the first test pattern and the second test pattern, wherein the first and second test patterns comprise n units of first sub-test patterns and n units of second sub-test pattern, respectively, in the operation of printing preset test patterns printing the n units of the first sub-test patterns using the first printhead and then the n units of the second sub-test patterns using the second printhead on the same swath of the paper, and the operation of calculating the horizontal print alignment error comprises calculating an average horizontal print alignment error with respect to n pairs of the first and second sub-test patterns by repeating the operations of subtracting the first starting point of each first sub-test pattern from the second starting point of each second sub-test pattern corresponding to the first sub-test pattern to calculate the horizontal print alignment error.