How does double-feed detection work on Canon CR-180s?

[ForumAdmin]

How does double-feed detection work on Canon CR-180s?

[Bryan Clark]

According to Canon USA, all 4 generations of the CR-180 support double feed detection.  The expected behavior for a generation 1, 2, or 3 CR-180, which do not have LED sensors, is the same as a generation 4 transport with LED sensors for double feed detection:

The first item fed into the track is used as a thickness reference for subsequent items in that same batch until the transport returned to the ready to feed state.  Scanning items thicker than the first one will cause a double feed detection to be reported.  Once the item that causes a double feed detection is removed from the track and scanned again as the first item of a new batch, the item will not cause a double feed detection. The above behavior should occur with the following settings, found in the CR180Options.ini, in place:

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[General]

DoubleFeedDetectThickness=true
DFDThicknessReference=0
DFDThicknessReferenceMin=0


However, if the behavior above is not seen, both DFDThicknessReference and DFDThicknessReferenceMin may have to be adjusted.  Based on internal testing, adjusting the DFDThicknessReference to 400 or higher can be used as a reference of thickness for personal checks.  However, this is simply a guideline.  According to the CR-180 API documentation, the thickness reference can range from 0 to 65535; there are no specified ranges.

Please note that by changing the reference from automatic detection, with the value set to 0, to manual, you may see a difference in double feeding detection performance.  By changing the value, any items scanned thicker than the reference set will be stopped; this applies to the first item in the batch as well as subsequent ones.

Furthermore, if the automatic setting, where both DFDThicknessReference and DFDThicknessReferenceMin are set to '0', does not provide any double feed detection, it may be possible that the transport(s) require maintenance.  The adjustment of these settings should only be temporary until a Canon representative is contacted because it is possible that a mechanical problem with the sensors exists.

According to the native Canon API documentation, the following document types may cause unexpected double feed detection results on transports equipped with LED sensors because the infrared beam cannot pass through them: thick, colored, and glossy documents.  If unexpected double feed detection occurs when scanning such documents, double feed detection may have to be turned off when re-scanning these documents.  This is the case if the unexpected behavior occurs frequently.  Furthermore, adjustments to the values of either the DFDThicknessReference setting or the DFDThicknessReferenceMin setting will not resolve the issue.

In regards to 'DoubleFeedDetectLength', the behavior is a little different than the one seen when detecting double feeds based on thickness.  When 'DoubleFeedDetectThickness' is used, the first item scanned is used as a reference for subsequent items as the thickest item allowed.  When 'DoubleFeedDetectLength' is used, the length of the first item is used as a reference to subsequent items where both shorter or longer items scanned after this item will trigger the double feed detection warning.  Unlike 'DoubleFeedDetectThickness', the double feed detection based on length does not have corresponding settings.

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