System of controlling energization to thermal head in thermal printer

Abstract

An energization control system for controlling energization of a thermal head of a thermal printer, the thermal head being equipped with a plurality of heating elements successively arranged in line, which are energized to generate heat in response to supply of currents thereinto so as to thermally and gradationally print an image on a recording sheet with printing densities corresponding to the supplied currents. The system comprises a density correction data memory for storing density correction data corresponding to variations of resistances of the heating elements and a calculation circuit for correcting an image signal on the basis of the density correction data so as to produce image data. Also included is a data comparison circuit selectively coupled through a switching device to the density correction data memory and the calculation circuit for comparing first and second comparison signals with the density correction data and the image data. The data comparison circuit performs first energization so as to energize the heating elements in accordance with the comparison result between the first comparison signal and the density correction data and, after completion of the first energization, performs second energization so as to energize them in accordance with the comparison result between the second comparison signal and the image data.