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I would like to undestand how black mark works on thermal printers.. I'm usign a Zebra GK420 but I think this works like many others.

This is what I think it should do for NON-Continous media type:

  1. Print the label ignoring any black mark
  2. At the end of printing the label feed forward
  3. If a black mark is detected the label is stopped and optionally forwarded for an offset and a backfeed will rewind it in the next print.

Is it right?

I'm asking this because I tried to customize the back of labels but images between blackmarks seems to interfere with the detection...

labels example

I think this is a bit strange because if is it right what I wrote before the black sensor should not used until print ends (in the front), then it will forward to the first black mark. As you can in the image the customized picture is smaller than the front print.

However this doesn't work and at the middle of the first label the printer stops and start another label. With a white back label (black mark only) everything works.

I say all of this because I really can't understand how black mark works. Can you please tell me exactly how it works?

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Thermal printers are equipped with an optical reader used to read the black marks printed on the back of the stock, which help the printer determine the beginning and end of the ticket. The size and position of the black mark will depend on the printer model and manufacturer.

If you have other images or data on the back of the label then these can confuse the sensor.

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  • I belive other images can confuse the printer to reach the correct position, what I can not understand is why this sensor is used BEFORE the end of the print... The process should be: 1. print all data, 2. feed until the blackmark position (if the print is longer than 1 label should feed to the next one). In my case the print job is interrupted by the sensor.
    – Tobia
    Commented Sep 25, 2014 at 6:22
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    Well, it's not actually used before the end of the print. It's used "regardless" of printing. Essentially the printer can't print something larger (longer) than two consecutive black marks. I believe this is by design. You'll have to buy special label paper or thermal paper that has the black marks further apart. As far as I know there is no way to skip a black mark and tell it to stop at the next one, and then keep doing this. I agree this is rather counterintuitive but the black mark sensor is used mainly with label printers and labels have a fixed size.
    – unom
    Commented Sep 26, 2014 at 12:11

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