Dover markem-imaje SmartDate 5 - Printhead Type Detection; Printhead Temperature Control; Printhead Voltage Control

SECTION 4 - TECHNICAL INFORMATION
4-17
SmartDate 5 08/08
4.5.1 Printhead Type Detection
The SmartDate 5 printer can support two different widths of printhead a 53 mm
wide printhead and a 128mm wide printhead.
Both printhead types have thermistors and these have separate inputs to the
printer board.
On power up the micro-controller samples the two printhead temperature sensors.
One will be reporting a temperature; the other will be at full-scale (maximum).
The micro-controller can use this information to determine the type of printhead
fitted.
If both sensors report full-scale, or if neither reports full-scale the micro-controller
must report a fault.
4.5.2 Printhead Temperature Control
The printhead's are fitted with thermistors and the temperature is constantly
monitored.
The Strobe and Cont pulse widths are adjusted by the firmware to compensate,
ensuring a consistent print darkness at varying temperatures.
4.5.3 Printhead Voltage Control
The printhead voltage is electronically adjusted under processor control.
A lookup table based on an spreadsheet based off the electrical data sheets
provides a means of determining the required voltage setting for a given printhead
resistance.
The table also provides a calculated value for the digital potentiometer used to set
the printhead voltage.
The resistance is provided by the controller, as a setting, to the printer.
To adjust the voltage the algorithm used first uses the lookup table to set the
potentiometer to the calculated setting.
Due to component tolerances this setting will not provide the correct voltage.
The algorithm then uses the ADC connected to the printhead voltage to fine adjust
the potentiometer.