Optimizing Processes with RFID and Auto ID, 2009

3 Optical codes
good contrast between the covering layer and the base layer, an easily
readable marking is thereby created. This process is used on circuit
boards and special plastic labels that are suitable for use with this laser
process.
The color change to the material when heated is used by tempering
during heat treatment. Without too strong of an effect on the material,
the color change is utilized for marking, especially on metal. As
opposed to engraving, this process does not create any cavities in the
surface and is, therefore, well-suited for use with objects that must be
kept sterile. However, such marking only remains durable if the material
is not heated further because the marking can degenerate.
Especially all when working with plastics, a controlled color change is
desired. A suitable doping of the plastic material with the impact of
the laser can achieve targeted color combinations and high contrasts.
If plastic is prepared accordingly, the laser can also make an embossed
marking by foaming material fractions. However, this results
in fuzzy edges between the light and dark cells and can only be used
successfully for large format codes.
The flexibility and suitability of laser marking only has one disadvantage
– the purchase costs for a laser marking system are high compared
to other methods and only pay-off, if there are high quantities
of the products to be marked.
Pin marking
Pin marking technology, which is relatively stress-free for the material,
is also cheap to purchase as opposed to laser marking (Fig. 3.3).
This method strikes a hard metal pin against the material with an upwards
and downwards movement, providing a sequence of interconnected
craters. Dotpin marking can also be used for hard metals without
any problems. The low costs and speed are comparable to laser
marking, which make this marking technology for matrix codes highly
attractive. The craters created during pin marking are circularshaped
and the displaced material is deposited at the edge of the crater
in a small mound. This form leads to special challenges for reading
devices as the shadows cast by the craters can sometimes be seen
as rings (to their special form also known as “donuts”) and can, sometimes
be seen as half-moon-shaped crescents or if the base of the crater
is fully reflected, as small, bright dots in the image. Not all code
reading systems are capable of recognizing and decoding such codes
reliably.
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