Printhead - Intermec EasyCoder 601 XP Service Manual

8.7 Printhead

Intermec EasyCoder 601 XP – Service Manual Ed. 2
Description
The printing is produced by the thermal printhead, which consists
of a line of very small, closely spaced resistors on a ceramic tile
fitted across the paper web. When a current is led through the
resistors, commonly called "dots," these will be heated very
quickly. When the current is shut off, the dots cool down just as fast.
As the paper is fed past the dots, the hot dots will produce a number
of black spots on direct thermal paper, or on other face materials via
a thermal transfer ribbon. The spots can be combined into patterns,
which make up letters, bar codes or images.
The direct thermal printing method requires a special paper coated
with a thin layer of heat-sensitive chemicals. As the paper is fed past
the dots, the heat from the dots will make the chemicals react,
producing a dark salt, which makes up the imprint under each dot.
In the thermal transfer printing method, a special "ink"-coated
transfer ribbon is used. When the ribbon is heated by a dot on the
printhead, the "ink" melts and sticks to the receiving face material,
where the ink immediately becomes solid again, producing a black
spot. The transfer ribbon does not smear, neither before nor after
printing. Nor do the printed labels smear, even if the printout may
be smudged by extensive rubbing if an unfortunate combination of
ribbon and face material is used. The thermal transfer method
makes it possible to use a much wider range of face materials for
printing, e.g. papers, boards, plastics, foils etc. However, an original
transfer ribbon from Intermec must always be used.
Information on how to switch between direct thermal and thermal
transfer printing is provided in the Installation & Operation manual.
The basis for all measures and positioning in the Intermec Finger-
print programming language is the size of printhead dots. In an 12
dots/mm printhead, each dot has a nominal size of 0.083 mm (3.28
mils). This means that a heated dot under standardized conditions
will produce a black spot which has a diameter of 0.083 mm.
Depending on dot temperature, exposure time, paper and ribbon
characteristics etc., the spot may actually be somewhat smaller
(weak print) or larger (black print), but that does not affect the
calculation of distances, sizes and positions.
The printer auto-detects the printhead density as well as the head
resistance at startup. The printhead can also be checked using the
Fingerprint function HEAD.
Chapter 8 Print Unit
56