Method and apparatus for improving print quality of a thermal pr

Details Method and apparatus for improving print quality of a thermal pr Method and apparatus for improving print quality of a thermal pr

1979-01-02

1981-04-14

Albritton, C. L.

Electric heating

Heating devices

Combined with diverse-type art device

346 76PH, H05B 100

Patent

active

042621887

ABSTRACT:
The uniformity of density of characters printed by thermal printers upon thermally sensitive paper is enhanced by controlling the amount of energy supplied to the print head during subsequent printings before the print head has completely cooled to ambient temperature. To obtain the desired uniformity the energy supplied to the print head for subsequent printings is made proportional to the energy lost by cooling of the print head between printings. This results in the print head being reheated to substantially the same printing temperature for each printing of a character or character segment.
By using a dot driver having an R-C circuit that recharges the capacitor between print pulses at a rate that is proportional to the thermal time constant of the print head, the energy stored by the capacitor can then be used to re-heat, or control the re-heating, of the print head to substantially the same selected print temperature. By maintaining the R-C charging time constant substantially between 0.1.tau. and .tau. (.tau. is the thermal time constant of the print head) the resultant printed character segments have substantially uniform density.

REFERENCES:
patent: 3577137 (1971-05-01), Brennan, Jr.
patent: 3745304 (1973-07-01), Hutner
patent: 3916256 (1975-10-01), Kotani

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