Problem when printing with linkos

Hi everyone.

I'm developing a Windows application in WPF, which uses the "link-os" SKD to print a large amount of tickets over a USB connection with a GC420t. The latest problem, and this is what makes me lose sleep at night, is that during printing, the printer apparently loses the detection of the mark (or gap) and begins to print the content in a wrong position relative to the top of the ticket.

Important points:

- My software build a ZPL string in runtime and sends it to the printer;

- I'm using the "GC420t" driver (non EPL);

- The printer properties are correctly assigned: label size, media type, speed, darkness, etc;

- The printer is calibrated.

Below, attached ZPL sample code, and the link to a video that demonstrates exactly the moment the error happens. Every help is welcome. Thank you very much.

Zebra GC420t error while printing - YouTube

ZPL Sample code attached.

Gustavo Leao
Hi, Dmitry.Apparently, you're

Hi, Dmitry.

Apparently, you're right to suspect that some elements on back side of the labels are confusing the printer's sensors.

We are gradually migrating to a new type of ticket, with gap reading, and so far no error has been reported, with more than 5000 labels printed.

I will continue to observe for the next few days, until we are sure that the problem has been resolved.

Thank you!

Gustavo Leão

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Dmitry Prokhorov
Hello Gustavo,Could you

Hello Gustavo,

Could you please to execute following command and share results here:
! U1 getvar "allcv"

You can capture result following advice in this article: Using the SGD Allcv Command ! U1 getvar "allcv" <CR>

Dmitry Prokhorov

Software Engineer, Kutir Mobility

Posted on behalf of Zebra Technologies

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Dmitry Prokhorov
Hello Gustavo,Could you

Hello Gustavo,

Could you please to run ~JG command and share a photo of result?

Dmitry Prokhorov

Software Engineer, Kutir Mobility

Posted on behalf of Zebra Technologies

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Gustavo Leao
Hello Dmitry,In approximately

Hello Dmitry,

In approximately 4 weeks we will receive a new shipment with a different label template. The reading will be by gaps, which theoretically will eliminate the possibility of confusing the sensors with the layout of the back of our tickets. As soon as I test, I'll come back here to tell you.

Thanks again!

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Gustavo Leao
In fact, I do not send an

In fact, I do not send an image on each label. At the top of the ZPL I use the ~DYE: command to save the image to printer memory, and on each label I add this image with the ^IME: command.

Please, if possible, give me an example of how I could change my code to suit your suggestion. Thank you so much again.

~DYE:LOGO1,P,P,34149,,89504E470D0A1A0A0000000D49484452000001E0000000DC08020000002779(continues)...

^XA^LS0^LT0^XZ

^XA^FO70,0^IME:LOGO1.PNG^FS^XZ

^XA^FO70,0^IME:LOGO1.PNG^FS^XZ

^XA^FO70,0^IME:LOGO1.PNG^FS^XZ

^XA^FO70,0^IME:LOGO1.PNG^FS^XZ

^XA^FO70,0^IME:LOGO1.PNG^FS^XZ

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Dmitry Prokhorov
Hello Gustavo,Also possible

Hello Gustavo,

Also possible cause of your problem could be in image data that seems you transfer to printer in ZPL with each label. It may lead to buffer overflow problem in your printer and you may need to check printer readiness by reading printer status.

As a workaround for this problem it would be good to implement a template for your label. It could contain your image. Then you will need just to print that template with specific values assigned to template fields. It may be more optimal approach to print your labels.

Dmitry Prokhorov

Software Engineer, Kutir Mobility

Posted on behalf of Zebra Technologies

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Gustavo Leao
Hi, Dmitry. Thanks for

Hi, Dmitry. Thanks for answering.

The code I sent is slightly different from what was used in the video, but the template is the same and the error happens for both. Only the image and some other dynamic data are inserted into zpl at runtime by our system. All the images used in the tickets have the same dimensions. Thank you again.

Gustavo Leão

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Gustavo Leao
Hello Dmitry,​Please, see

Hello Dmitry,

Please, see attached file.

Thank you!

Gustavo Leão

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Gustavo Leao
Hello again, Dmitry.We reduce

Hello again, Dmitry.

We reduce the occurrence of the problem by setting exactly the height of the label, without rounding. Previously, our label, measuring 107mm high, was being set to 100mm.

However, even at a lower incidence, the problem persists.

We have 35 Zebra printers in production environment. I attached the result of the ~ JG command on two different printers, which presented the problem recently.

Thanks a lot for the help.

~JG Printer 1 (Shopping Recife) - YouTube

~JG Printer 2 (Rio Mar Shopping) - YouTube

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Dmitry Prokhorov
Hello Gustavo,I have checked

Hello Gustavo,

I have checked your attached ZPL sample code and it looks ok.

So far I can see (by field values) it is not exactly a code that is reproducing the issue on your video.

Would you please to provide a code that is reproducing your issue?

Dmitry Prokhorov

Software Engineer, Kutir Mobility

Posted on behalf of Zebra Technologies

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Gustavo Leao
Hi, Dmitry. I realize that my

Hi, Dmitry.

I realize that my earlier explanation of how our system handles the images has gotten a bit incomplete.

Therefore, I will give more details about its operation:

When the system is started and the first print is requested, before saving any image in the printer memory, we delete all the png files saved previously, with the command: ^IDE:*.

After this, whenever an image is sent to the printer, we record this information in a global variable so that we can reference it in the future without having to send anything else to the printer.

In other words, we only send images to the printer that are not already there.

Thank you again, Dmitry. Your help has been very important.

Gustavo Leão

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Dmitry Prokhorov
Hello Gustavo,There is a

Hello Gustavo,

There is a chance that printer sensors may be confused by those white areas on back side of your labels that I can see on your videos. Could you please to check if issue can be reproduced while printing on another type of media? Can you try to print it on media that have nothing on its back side?

In case this guess will be confirmed you may need to contact Zebra tech support​ so the might be able to provide you some technical advice on how to resolve issue with your media used.

Dmitry Prokhorov

Software Engineer, Kutir Mobility

Posted on behalf of Zebra Technologies

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Dmitry Prokhorov
Hello Gustavo,You are right,

Hello Gustavo,

You are right, currently you are sending image once in each print session. However, so far your image is stored on printer you don't need to send it with ^DY command each session. It is enough to send it there just one time and then to use it in all print sessions. It would make communication with printer more optimal.

Dmitry Prokhorov

Software Engineer, Kutir Mobility

Posted on behalf of Zebra Technologies

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