Multi-feed judging device, image forming apparatus, multi-feed judging method and multi-feed judging program

A multi-feed judging method comprising:

• a transporting step for holding a recording medium between a driving roller and a driven roller, which is driven by the driving roller, and for transporting the recording medium by rotating the driving roller;
• a detecting step for detecting a position of the driven roller when the recording medium is transported, and a position of the driven roller when the recording medium is not transported;
• a calculating step for calculating a thickness of the recording medium based on a position of the driven roller when the recording medium is transported and a position of the driven roller when the recording medium is not transported;
• a reference value updating step for updating a reference value for the thickness by using the thickness calculated in the calculating step;
• and
• a judging step for judging, using the reference value updated in the reference value updating step, whether recording media, which are transported after the reference value was updated, are transported while overlapping each other or not, wherein
• in the calculating step the thickness is calculated by using the position detected in the detecting step, when the position detected in the detecting step is within a predetermined range.

A non-transitory computer-readable storage medium storing a program for causing a computer to perform a process of judging a multi-feed, the process comprising:

• a step of holding a recording medium between a driving roller and a driven roller, which is driven by the driving roller, and transporting the recording medium by rotating the driving roller;
• a step of detecting a position of the driven roller when the recording medium is transported, and a position of the driven roller when the recording medium is not transported;
• a step of calculating a thickness of the recording medium based on a position of the driven roller when the recording medium is transported and a position of the driven roller when the recording medium is not transported;
• a step of updating a reference value for the thickness by using the thickness calculated in the step of calculating the thickness;
• and
• a step of judging, using the reference value updated in the step of updating the reference value, whether recording media, which are transported after the reference value was updated, are transported while overlapping each other or not, wherein
• in the step of calculating the thickness, the thickness is calculated by using the position detected in the step of detecting the position, when the position detected is within a predetermined range.