Printing apparatus

A printing apparatus for printing on a front surface of a printing medium, and thereafter printing on a back surface of the printing medium, the apparatus comprising:

• a front surface print head for printing, on the front surface of the printing medium transported in a predetermined transport direction, a cue mark indicating a printing start position in the transport direction of a front surface image, and printing the front surface image based on front surface image data with reference to the cue mark;
• a back surface image data corrector for creating corrected back surface image data by correcting an image size of back surface image data to be formed on the back surface of the printing medium, based on elasticity information obtained beforehand, wherein the elasticity information indicates how much the printing medium expands in the transport direction after printing of the front surface image;
• a detector for detecting the cue mark printed on the front surface of the printing medium;
• a back surface print head for printing a back surface image based on the corrected back surface image data on the back surface of the printing medium with reference to the cue mark detected by the detector;
• and
• a printing control unit for controlling the front surface print head, the back surface image data corrector, the detector, and the back surface print head to print images on both surfaces of the printing medium,
• wherein the printing control unit comprises:
• a page interval calculator for calculating as the elasticity information a page interval in the transport direction between the cue marks detected by the detector;
• a cut limiting value memory for storing beforehand:
• (1) a first limiting value indicating, when an image printed based on the corrected back surface image data exceeds the cue mark of an upstream side in the transport direction, a length from the cue mark to an edge of the image, wherein the edge of the image is present outside the page interval, and
• (2) a second limiting value indicating, when an image printed based on the corrected back surface image data does not reach the cue mark of the upstream side in the transport direction, a length from the cue mark to the edge of the image, wherein the edge of the image is present within the page interval,
• a cut amount arithmetic processor for calculating a difference between (1) the page interval and (2) a transport-direction length of an image printed based on the corrected back surface image data;
• and
• an error checker for determining that an error has occurred when the difference exceeds the first or second limiting value.