| 摘要 |
PURPOSE:To eliminate an irregularity in a printing density by checking the resistance value of a thermal head before printing, and applying a value added to or subtracted from a print signal to a drive circuit at the time of actual printing. CONSTITUTION:A microprocessor 6 supplies a fine current of the degree that a thermal sensitive sheet does not color to thermal head resistors 11, 12..., and measured the resistance values of the resistors 11, 12.... Dummy resistance elements 31, 32... have a small resistance value, such as 0.1 ohm, a potential drop across the resistor is applied to a resistance value measuring circuit 4 to measure the resistance value. The resistance values of the resistors 11, 12... are stored in predetermined locations of a table 5, and the microprocessor 6 reads out the corresponding location of the table 5 before a normal print signal is applied to predetermined drive circuits 21, 22... when the printing operation is conducted by the signal. Resistance value data and an input signal are added by adding meats 7, the obtained signal is applied to the circuits 21, 22.... to control the heat generations of the resistors 11, 12..., thereby correcting the irregularity in a printing density on the basis of the intrinsic resistance values of the resistors 11, 12....
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