Incremental Encoder counts at various speed

[horner_user]

Hello fellow members

We are trying to refresh an old production line in paper bag packaging industry. We are using Sick NT6 contrast sensor together with HENGSTLER RI58 encoder to count the distance (number of encoder pulses) between printed marks on the paper in order to keep cutting process correct.

What we observe is that while VFD works on lower speed (eg. JOG), encoder counts about 1500 pulses more between printed marks, than in situation when VFD works on higher speed?

Printed marks are printed at the same distance, so we would expect the same number of pulses counts between them regardless of the line speed?

I am not sure, if we are missing something, but if someone would like to comment or have word of advice, or is experienced with the subject, I would
really appreciate any suggestion very much.
Regards

 

[rdrast]

First question:
Has this system ever worked as it is currently configured?
Second:
Which is correct... Counts at lower speed? or higher? My first suspicion is that whatever is doing your counter can't keep up with a high count rate.