Inkjet printer, gap detectable device, and a method to obtain fluctuation of gap levels

A method to obtain fluctuation of levels of a gap between an inkjet head and a recording medium along a first direction in an inkjet printer, which comprises an inkjet head configured to discharge ink droplets from nozzles formed in an ink discharging surface thereof and a head scanning unit configured to move the inkjet head facing the recording medium to reciprocate along a first direction, the first direction being parallel with the ink discharging surface of the inkjet head, comprising steps of:

• printing a gap level pattern, which is configured to exhibit fluctuation of levels of a gap between the ink discharging surface and the recording medium along the first direction to be detectable, on the recording medium;
• reading the gap level pattern printed on the recording medium;
• and
• obtaining fluctuation of the levels of the gap along the first direction from the gap level pattern read in the step of reading,
• wherein, in the step of printing, the gap level pattern including a plurality of unit patterns, in each of which a first linear pattern and a second linear pattern intersect each other, aligned along the first direction, is printed by:
• manipulating the inkjet head to move in a first orientation along the first direction and to discharge the ink from the plurality of nozzles to form a plurality of first linear patterns, which are formed to intersect the first direction, along the first direction while being moved;
• and
• manipulating the inkjet head to move in a second orientation along the first direction and to discharge the ink from the plurality of nozzles to form a plurality of second linear patterns, which are formed to intersect the first linear patterns respectively at a same angle, along the first direction while being moved, and
• wherein, in the step of obtaining, the fluctuation of levels of the gap between the ink discharging surface and the recording medium along the first direction is obtained by detecting the levels of the gap between the ink discharging surface and an area on the recording medium, in which the unit patterns in the gap level pattern are formed, based on positions of intersections, in which the second linear patterns intersect the first linear patterns within the respective unit patterns, along a second direction being orthogonal to the first direction.