Technical Terms

 Dot Density
Is the density of heater elements. It is shown either by [dot/mm] which means number of heater elements in 1mm, or by [dot/inch = dpi] which means number of heater elements in 1inch.

 Dot Pitch
Is the inverse number of dot density. Dot pitch is the distance between adjacent heater elements. For example, dot pitch of a 8dot/mm printhead is 0.125mm by 1/8mm. heater elements

 Heater Size
Each heater size is shown by W x L: Width in main-scanning direction x Length in sub-scanning direction.
In case of a typical 8dot/mm printhead, its heater size is shown as 0.125mm x 0.152mm.


 Resistance Value (= R-value)
resistance profile of non AD printhead
* Kyocera Internal data

Average resistance value (Rav) : Average of resistance value of all heater elements of a printhead (Shown in red line).
Resistance variation within a head : Maximum deviation of resistance value within a printhead in both +side and -side from the Rav of the printhead.
It is usually shown as +/-5%.
Resistance variation between two adjacent heater elements : Maximum difference of resistance value between two adjacent heater elements.
Kyocera is able to adjust the value to less than +/-1% when required.

 Applied Energy

equivalent circuit of driver IC and heater

Electric current per any one dot (I) can be calculated per the above formula, when R is the resistance value of the heater element and Ric is the driver IC's internal resistance.
Applied power is then calculated as above and is shown in (w/dot).
When one pulse time is shown as Ton(msec), applied energy (mJ/dot) can be calculated by the formula, P X Ton.


 Driving Method
DATA(IN) : On/Off data for all heater elements
CLOCK : A timing pulse to trigger the DATA transfer into the shift-register in driver IC.
LATCH : A timing pulse to forward DATA in the shift-register into output stage.
STROBE : ON time is controlled by STROBE time.

TIMING DIAGRAM
data input sequence

*A sequence of On/Off DATA is transferred by CLOCK (triggered by the signal edge upon start), and then is stored in the shift-register. The transfer speed is determined by the CLOCK frequency, which is 16MHz maximum depending on the driver IC.
DATA stored in the shift-register is transferred to the output stage by the LATCH signal (negative logic).
Only while STROBE signal (negative logic) is On (at GND voltage), heater elements are heated up by the current flow.
(Above Timing Diagram shows an example that makes 1 line print with 6 split strobes.)


 Thermistor

The temperature of a printhead rises as it continues to print, and the temperature has negative effects on driver IC. Moreover the heat accumulation in the printhead has a negative influence on the print quality. A thermistor, for monitoring the ambient temperature and the printhead temperature, is mounted on the printhead. A thermistor has a characteristic; the higher the temperature, the lower the resistance value from a reference resistance value at 25 degree C. Using this characteristic, temperature can be obtained by the following formula:


T = 1/(2.303/B x Log(R/R25)+1/298)-273

B : constant: a coefficient of the thermistor itself
R : resistance value at a temperature
R25 : a reference resistance value at 25 degree C
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