Patent ID: 7413280

Claim:
A method for detecting a change of an interval of recorded positions recorded by a plurality of recording heads, each including an array of a plurality of recording elements, wherein the plurality of the recording heads are straightly aligned in direction of the array comprising the steps of: recording a first pattern group in such a way that the recording heads scan a recording medium so that the recording elements in the recording heads record a pattern having repeatedly dark dens it area and light density area pependicuiar to a scanning direction at the recording heads as a first recording operation; recording a second pattern group in such a way that after the recording medium is angled in the scanning direction after the first pattern group is recorded the recording heads scan the recording medium so that the recording elements record a pattern having repeatedly dark density area and light density area perpendicular to the scanning direction of the recording heads so that the second pattern group is overlapped on and angled to the first pattern group as a second recording operation; detecting interference fringes generated by an overlap of the first pattern group and the second pattern group; and detecting the change of the interval of the recorded positions via a positional deviation of the interference fringes.