iSys V8.5e Thermal Printer - Manual (Page 44)

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The thermal printhead is comprised of a row of 1728 heater elements (nibs). Each bit within a scan addresses an
individual nib. Plot patterns are generated one scan at a time, each scan consisting of a horizontal row of dots. A
nib produces a dot if the corresponding scan bit in the buffer is a logic level “1”. Nibs in the printhead are heated,
causing a thermo-chemical reaction with the coating on the media. The intensity or period for which the nib is
heated is called the burn strobe.
Automatic Head Temperature Feedback
The thermal printhead rises in temperature as it plots images on paper, thus, less energy is required to activate
each nib as the plot proceeds to create an image of the same intensity. A thermistor embedded in the head
measures the head temperature and provides feedback information to the main logic board. The main logic board
decreases the burn strobe accordingly to keep the contrast of the plotted image consistent as the plot proceeds. If
the printhead temperature reaches 60º C, the Automatic Head Temperature Feedback circuit stops the plotter in
order to let the head cool down. The control panel display reads hot (Ht) and the error light flashes. When the
thermistor measures that the printhead temperature has cooled to 45º C, the plot resumes with no loss of data.
Film media
When the plotter is set to film mode, the strobe length is increased to accommodate the thicker media. The plot
speed is set to 1.0 inch per second to allow the longer strobe length and to maintain plot quality.
5.5 MEDIA SENSORS
The top-of-form (also known as the “I-mark”) sensor and the media sensor are contained on a media sensor
board. The top-of-form sensor consists of a focused infrared beam and
receptor that reacts to black top-of-form marks. The receptor sends a “stop form feed” command to the logic
circuitry if a mark stops the beam from reflecting back into the receptor. The paper sensor consists of an
unfocused infrared beam and receptor. If the receptor receives enough reflected light, the receptor sends no
command. If the reflected light is below the required level the receptor sends a “media out” command to the logic
circuitry and plotting stops. The “no media” indicator is displayed on the control panel.