Thermal line printer with staggered head segments and overlap compensation

A thermal line printer for line-sequentially printing dots on a recording medium in horizontal and vertical directions according to bit data, comprising:

• a line thermal head including a plurality of linear head segments arranged in a pair of parallel rows along the horizontal direction in staggered relation to each other such that the head segments partly overlap through different relative displacements with each other between the rows, each of the head segments having a plurality of heating elements disposed linearly along the segment, the heating elements being effective to print dots according to image bit data and being ineffective to print dots according to blank bit data;
• feeding means for line-sequentially feeding a recording medium relative to the line thermal head in the vertical direction;
• designating means operative according to the different relative displacements for designating effective and ineffective sections adjacently with each other to the respective head segments such that the designated effective sections are successively connected to each other in the horizontal direction without irregular overlapping and spacing, the designating means including detecting means operative during continuous printing operation for detecting the body temperature of the respective head segments, calculating means for calculating variation of the expansion of the head segments according to the detected body temperature thereof, and shifting means for shifting the designation of the effective and ineffective sections according to the calculation result so as to compensate for the variation of the relative displacements;
• and
• assigning means operative during each line-sequential printing for assigning image bit data to heating elements within the effective sections and blank bit data to heating elements within the ineffective sections to thereby effect regular dot printing along each line.