| 摘要 |
PURPOSE:To obtain uniform recording image density regardless of the change tendency of temp., by correcting the present temp. of a thermal head on the basis of the change quantity of the temp. of the thermal head. CONSTITUTION:The present temp. t2 of a thermal head 1 is measured by a thermistor 2 and converted to predetermined temp. data Dt2 in a temp. detection circuit 10. The temp. data Dt2 is compared with the temp. data Dt1 sampled previously by a comparing circuit 11 to calculate change quantity DELTA= Dt2-Dt1. The present temp. data Dt2 is corrected on the basis of the temp. data change quantity DELTAD, that is, the temp. data is set to Dt2-alphaDELTAD to select a gradation table. Gradation control data and the image data from a data line memory 15 are outputted to an intermediate control part 14 and these data are converted to the current supply pulse data to the heat generating element 1a of the thermal head 1 to be transmitted to a head driving circuit 16. The thermal head 1 is operated on the basis of the current supply pulse data to form a recording image on a recording sheet 7. |
