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Printhead Operation
Precautions |
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When printing
continuously, the supply energy may need to be reduced
to ensure the substrate temperature, monitored by the
onboard thermistor, remains below the maximum
temperature shown in the detailed specification.
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The power “ON” and “OFF”
sequence must in the following order to avoid damage to
the heating elements:-
Turning on: Apply logic voltage Vdd and then apply
printhead supply voltage VH.
Turning off: Switch off supply voltage VH and then
switch off logic voltage Vdd.
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Interface each signal
input (CLK, LAT, STB, DI) with CMOS level (ex 74HC240).
Keep STB signal to “disable” during ON/OFF and no
printing conditions.
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Heat elements and IC’s
should be protected from static influence to avoid
electrostatic destruction.
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Do not touch the
connector pins.
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The printhead substrate
surface is coated with glass. Mechanical stress or shock
(including dust scratch damage) must be avoided.
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When printing is
complete, the printhead supply voltage VH (including any
stored capacitor charge) should be reduced to ground
until the next printing operation commences.
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The platen roller should
be composed of non-conductive materials.
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Condensation on the
printhead must be avoided. If condensation occurs,
ensure the printhead has fully dried before applying the
supply voltage VH. If using the printhead in outdoor
equipment in colder, damp climates, the use of a space
heater within the printer inclosure is recommended to
reduce the risk of condensation.
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Avoid undue stress when
plugging cables into the connector(s).
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Print quality will
degrade if paper, ink or dust residues stick to the
heating elements. Clean the heating elements regularly
with ethyl alcohol applied with a clean, lint free cloth
or use a proprietary thermal printhead cleaning pen. The
frequency of cleaning should be established case by
case. Do not use acid or alkali to clean the dot line
and tracks nor any kind of abrasive tool or cleaner.
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If a “sticking” sound is
heard during printing, a set-up adjustment will be
needed. Review and adjust where necessary the paper feed
mechanism, voltages and timings settings.
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Ensure any printhead
carrier is perfectly flat and will not cause the
printhead to warp when tightening the mounting screws.
The mounting design should allow the printhead to
“float” to find its own level.
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Only use the thermal
paper detailed in the printhead specification sheet or a
recognised equivalent. The use of an inferior paper may
result in poor print quality, increased head abrasion
and may jeopardise any warranty issues.
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When using pre-printed
thermal paper, for example, labels, ensure the printing
inks used are suitable for use with thermal printers.
Certain inks contain abrasive pigments that will cause
the printhead to suffer early failure through abrasion
of the protective coating over the printhead elements.
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In order to reduce
surges, VH and GND cable lengths should be less than
300mm. A 47mfd aluminium electrolytic capacitor is
required between VH and GND on the controller board side
and a 0.1mfd ceramic capacitor should be placed between
Vdd and GND.
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Design the mechanics in
such a way that the printing media (while printing) and
the paper guide do not contact the protective coating
over the IC’s or the through hole connector pins on the
pcb.
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A thermal printhead
generates heat and under severe abnormal conditions,
smoke or even combustion may occur. It is therefore
recommended to use the onboard thermistor to monitor the
temperature of the substrate and to design the software
to reduce or disconnect the power in the event of a
serious over temperature condition.
Design the power supply for the head voltage (VH,Vdd) to
be shut down when the temperature of the thermal head
exceeds the stated maximum while STB is “ON” or the
printing media has stopped moving. If the paper jams
while the head is still “ON”, the paper will stick to
the printhead and may catch fire.
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Store printing media in
a clean, cool environment. Using paper or label rolls
which have been stored in a dirty area, will allow grit
to be drawn across the printhead causing mechanical
damage to the protective material covering the printing
elements.
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