Method of adjusting image recording apparatus for correcting skew

A method of adjusting an image recording apparatus that comprises a recording material supply section for supplying sheets of recording material, a conveyer device for conveying the recording material along a transport path, a recording device for recording an image on the recording material as being conveyed, and a skew correction device for correcting skew of the recording material on said transport path so as to make a leading edge of each sheet of the recording material be parallel to a main scan direction that is a widthwise direction of said transport path, said method comprising steps of:

• supplying first and second sheets of recording material from said recording material supplying section, said first and second sheets being different in length in a sub scan direction that is a lengthwise direction of said transport path;
• recording a test pattern on said first and second sheets of recording material by said recording device, to produce first and second test prints, said test pattern having a first line that is defined to be parallel to said sub scan direction;
• measuring distances from one side of each of said test prints to two different points of said first line as recorded on each of said test prints;
• calculating a skew degree of each of said first and second test prints from said measured two distances;
• calculating skew characteristics of each of said first and second sheets of recording material from said skew degrees of said first and second test prints, said skew characteristics being dependent upon a location of said recording material supply section and the lengths in the sub scan direction of said first and second sheets;
• and
• adjusting, based on the calculated skew characteristics, correction parameters for said skew correction device to correct skew of recording materials supplied from said recording material supply section
• wherein said image recording apparatus comprises a second recording material supply section, said test pattern comprises a second line that is defined to be parallel to said main scan direction, a plural number of second lines defined to be parallel to the main scan direction, and a third line that is symmetrical to said first line about a referential line connecting center points of said second lines to each other, and said method further comprises steps of:
• supplying a third sheet of recording material from said second recording material supplying section, said third sheet being equal in length in the sub scan direction to said first sheet;
• recording a test pattern on said third sheet, to produce a third test print;
• measuring distances from one side of said third test print to two different points of said first line as recorded on said third test print;
• calculating a skew degree of said third test print from said measured two distances;
• calculating skew characteristics of said third sheet of recording material from said skew degrees of said first and third test prints, said skew characteristics being dependent upon a location of said second recording material supply section and the length in the sub scan direction of said third sheet;
• adjusting, based on the calculated skew characteristics of said third sheet, correction parameters for said skew correction device to correct skew of recording materials as supplied from said second recording material supply section;
• calculating a variation of a print starting position in the sub scan direction based on a distance from a leading end to said second line of either of said test prints;
• calculating a variation of a print starting position in the main scan direction based on a difference between a distance from the one side edge to said first line and a distance from opposite side edge to said third line with respect to each of said first and third test prints;
• adjusting the print starting positions in the main and sub scan directions by controlling said recording device based on the calculated variations of the print starting positions in the main and sub scan directions.