Label printers use media sensors to determine where the media (i.e., label/tag) begins and ends. This is needed so that the print can be accurately and consistently positioned on the label.
Label Printer Media types
As far as label printers are concerned there are 3 types of media:
- Continuous (e.g., lengths of card or satin/polyester tag rolls)
- Gaps/notches (e.g., die cut labels, or nursery tags)
- Black mark/eye-marks (e.g., clear die cut labels with marks on the backing paper).
Continuous Media
This is a label/tag/material that comes in a length without any die-cut, separation, gap or notch.
Examples include rolls of satin/polyester/card, which are printed and sometimes manually cut, or automatically cut using the printer’s built-in cutter.
When printing on continuous media the printer/driver should be set to continuous mode, so it is not using a sensor to determine the beginning/end of a printed area. In this instance the printer is only looking for the presence of the media, and not a specific position to begin printing.
Media with Gaps
This is the most common type of media and includes die-cut labels.
With die-cut labels the labels are lightly cut, and the unused label material is then removed. This allows for the labels to be peeled off easily. There is also a gap between each label.
The gap between the labels is what the printer uses to determine where each label begins and ends. Hence the printer can determine precisely where on the label it should print.
The printer uses a transmissive sensor to sense opacity changes between the areas with the label, and the area without. (I.e., the opacity of the backing paper with the label on it, is higher than the backing paper on its own – as it is more transparent).
Media with Notches, Slots, or Holes
Some synthetic media such as nursery plant tags have notches, slots or holes. These are a great way for a printer to determine the position of the media using a transmissive sensor.
It is worthwhile noting that not all printers have a movable sensor. If the notches/slots/holes are on the edge of the media, then the sensor would need to be moved to line up into the relative position in order to work.
Media with Black Marks or Eye-marks
Black Marks or Eye marks are usually used when printing on clear labels. Because there is very little if any difference in opacity between the transparent label and the label gap, the printer is unable to determine where the label begins/ends.
In these cases, a black mark or dark line is printed on the underside of the backing paper. The printer then uses a reflective sensor to work out where each label begins and ends. (i.e., the backing paper reflects more light than that of the eye-mark).
This method is also used for butt cut labels, where there is no gap between the labels. This minimises material waste, however the black marks are needed for the barcode label printer.
Printer Media Sensors
Label printers use media sensors to determine where the media (i.e., label/tag) begins and ends. This is needed so that the print can be accurately and consistently positioned on the label.
Most quality printer brands have both a gap (transmissive) sensor and a black mark (reflective) sensor. However not all media sensors are movable, this will depend on the individual printer model.
Transmissive media sensors are used to identify gaps, notches, holes or slots in the labels & tags.
Reflective media sensors are used to identify black marks, eye marks or other darker printed identifiers on the labels & tags.
