Printing apparatus, printing method, computer program, and computer system for detecting skew of printing medium

A printing method conducted by a printing apparatus for carrying out printing on a printing medium, said printing apparatus including a print head that is movable in a main scanning direction and that is for ejecting ink onto said printing medium, printing medium feeding section for feeding said printing medium, a sensor that can detect said printing medium, said sensor being movable in the main scanning direction, wherein said printing method comprises:

• (a) positioning said sensor in a first position that is at substantially a center of width of said printing medium in the main scanning direction;
• (b) feeding said printing medium with said printing medium feeding section;
• (c) detecting at said first position a leading edge of said printing medium with said sensor;
• (d) moving said sensor to a temporary position different from said first position;
• (e) when said printing medium has not been detected with said sensor at said temporary position, considering a predetermined position as a second position, said predetermined position being at a same side as said temporary position with respect to said first position, and
• when said printing medium has been detected with said sensor at said temporary position, moving said sensor to a second position that is a position at an opposite side to said temporary position with respect to said first position, said printing medium not being detected with said sensor at said second position,
• (f) feeding said printing medium with said printing medium feeding section;
• (g) detecting at said second position said leading edge of said printing medium with said sensor;
• (h) obtaining a skew of said printing medium by performing a calculation using numerical values that are based on detection results of said leading edge at said first position and said second position;
• and
• (i) changing at least one of a starting position, an ending position, and both of these for ejecting ink from said print head, which moves in the main scanning direction, according to said skew that has been obtained.