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(11) | EP 0 530 748 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Printer head modulation technique for thermal printers |
| (57) The present invention relates to a technique including method and apparatus for modulating
the power to thermal pixels of a thermal print head (18). The technique energizes
each thermal pixel with a plurality of N-M idle power modulating pulses and a plurality
of M print power modulating pulses during each line printing period. The idle power
modulating pulses are used for substantially maintaining the thermal pixel at a first
temperature which is (1) below a dye transfer temperature of a dye color on a dye
carrier member, and (2) above a base temperature of a material forming a heat sink
of the print head. The print power modulating pulses are used to raise the first temperature
of the thermal pixel to a second temperature above the dye transfer temperature of
the dye carrier member so as to cause an M dye color density level of N density levels
of the dye color to be transferred from the dye carrier member to a receiver member
engaging the dye carrier member opposite the thermal pixel, where M is a value between
0 and N. Alternatively, for modulating large area thermal pixels, two sequential sets
of N power modulating pulses can be generated, each plurality of N pulses having M/2
print power modulating pulses. During a first line printing period, after a cold start,
a plurality of idle power modulating pulses can initially be generated to raise each
thermal pixel from the base temperature to the first temperature. |