42 Intermec EasyCoder PD4—Service Manual
Chapter 7—Print Mechanism
7.7 Printhead Module
Description
The printing is produced by the thermal printhead, which consists of a
line of very small, closely spaced resistors on a ceramic tile fi tted across the
media path. 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 media is fed past the dots, the hot dots will produce a number of
black spots on heat sensitive (direct thermal) media, or on other face mate-
rials via a thermal transfer ribbon. The spots can be combined into bitmap
patterns, which make up characters, bar codes, images, lines, and boxes.
The direct thermal printing method requires special media coated with a
thin layer of heat-sensitive chemicals. As the media 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 immedi-
ately becomes solid again, producing a black spot. Transfer ribbons nor-
mally do not smear at room temperature, 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 mate-
rial is used. The thermal transfer method makes it possible to use a wide
range of face materials for printing, for example papers, boards, plastics,
foils, etc. However, an original transfer ribbon from Intermec should
always be used.
Information on how to switch between direct thermal and thermal transfer
printing is provided in the User’s Guide.
The EasyCoder PD4 comes with two printhead densities, 203.2 dpi (8
dots/mm) and 300 dpi (11.81 dots/mm). The 300 dpi printhead is only
available for printer models with displays.
In a 203.2 dpi printhead, each dot under standardized conditions will pro-
duce a black spot which has a diameter of 4.92 mils (0.125 mm).
In a 300 dpi printhead, each dot under standardized conditions will pro-
duce a black spot which has a diameter of 3.33 mils (0.086 mm).
Depending on dot temperature, exposure time, media and ribbon charac-
teristics, 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.
Note that there are different main boards, pulleys, and belts for each
printhead density.
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