Thermal gradation printing apparatus

A thermal gradation printing apparatus comprising:

• a thermal head including a body portion, a substrate formed on said body portion, and a plurality of heat elements arranged in a line on said substrate, said plurality of heat elements being divided into a plurality of groups;
• head temperature detecting means for detecting the temperature of said body portion;
• data generating means for generating a plurality of data units each having a pulse width depending on density data, the pulse width indicating a time period for which a predetermined voltage is applied to one of said plurality of heat elements;
• group division accumulated heat amount estimating means for estimating accumulated heat amounts of regions of said substrate for every one line, the regions corresponding to said plurality of groups, respectively;
• correction value calculating means for calculating correction values assigned to said plurality of heat elements, respectively, based on the estimated accumulated heat amounts for said respective groups, and the temperature of said body portion;
• pulse width correcting means for correcting the pulse width of each of the plurality of data units based on the correction values, and for generating a plurality of corrected data units each having the corrected pulse width;
• and
• head driving means for applying the predetermined voltage to said plurality of heat elements for a time period in accordance with the plurality of corrected data units,
• wherein said group division accumulated heat amount estimating means estimates the accumulated heat amounts of regions corresponding to said plurality of groups, respectively, based on an average of the plurality of corrected data units generated for an immediately preceding line in each of said plurality of groups, and the accumulated heat amount of each of said plurality of groups in the immediately preceding line.

A thermal gradation printing apparatus comprising:

• a thermal head including a body portion, a substrate formed on the body portion, and a plurality of heat elements arranged in a line on the substrate, the plurality of heat elements being divided into a plurality of groups;
• head temperature detecting means for detecting the temperature of the body portion;
• data generating means for generating a plurality of data units each having a pulse width depending on density data, the pulse width indicating a time period for which a predetermined voltage is applied to one of the plurality of heat elements;
• group division accumulated heat amount estimating means for estimating accumulated heat amounts of regions of the substrate for every one line, the regions corresponding to the plurality of groups, respectively;
• correction value calculating means for calculating correction values assigned to the plurality of groups, respectively, based on the estimated accumulated heat amounts for the respective groups and the temperature of the body portion, the correction values being represented by n bits;
• pulse width correcting means for correcting the pulse width of each of the plurality of data units and for generating a plurality of corrected data units each having the corrected pulse width, the pulse width being corrected based on the corrected values, or values represented by (n-m) bits of the correction values and values obtained by comparing values represented by lower m bits of the correction values with reference values which are set to be different values for 2.sup.m lines;
• and
• head driving means for applying the predetermined voltage to the plurality of heat elements for a time period in accordance with the plurality of corrected data units,
• wherein the group division accumulated heat amount estimating means estimates the accumulated heat amounts of regions corresponding to the plurality of groups, respectively, based on an average of the plurality of corrected data units generated for an immediately preceding line in each of the plurality of groups, and the accumulated heat amount of each of the plurality of groups in the immediately preceding line.