Thermal head printer and printing method in thermal head printer

A line thermal head printer performing a printing operation by conveying a recording medium between a platen and a thermal head and heating a plurality of heating elements included in the thermal head on the basis of image data to be printed, the line thermal head printer comprising:

• the platen;
• the thermal head having the plurality of heating elements linearly arranged therein;
• a heating-value arithmetic unit that calculates heating values S(a,b) for printing pixel data items included in the image data and arranged in a matrix of in-rows by n-columns, each pixel data item disposed on a b-th row (1≦b≦m) to be printed using one of the heating elements that corresponds to an a-th column (1≦a≦n) of the pixel data items;
• a heating-value comparator that compares each calculated heating value S(a,b) for the a-th column and the b-th row with a reference heating value L of the heating elements;
• an excess-value counter that counts the number of calculated heating values S(a,b) that exceed the reference heating value L on the basis of the comparison result of the heating-value comparator so as to determine an excess-value number N(a) for the a-th column;
• a maximum-excess-value-number extractor that determines a maximum excess-value number N(max) on the basis of excess-value number N(1) to excess-value number N(n) for first to n-th columns determined by the excess-value counter;
• and
• a heating-value controller that limits the heating values of the heating elements if the maximum excess-value number N(max) exceeds a reference number M.

A printing method in a thermal head printer that performs a printing operation by conveying a recording medium between a platen and a thermal head and heating a heating element included in the thermal head on the basis of image data to be printed, the method comprising the steps of:

• calculating heating values S for the heating element corresponding to the image data;
• comparing each calculated heating value S with a reference heating value L of the heating element;
• counting the number of calculated heating values S that exceed the reference heating value L so as to determine an excess-value number N;
• and
• limiting the heating values of the heating element if the excess-value number N exceeds a reference number M.

A printing method in a line thermal head printer that performs a printing operation by conveying a recording medium between a platen and a thermal head and heating a plurality of heating elements linearly arranged in the thermal head on the basis of image data to be printed, the method comprising the steps of:

• calculating heating values S(a,b) for printing pixel data items included in the image data and arranged in a matrix of in-rows by n-columns, each pixel data item disposed on a b-th row (1≦b≦m) to be printed using one of the heating elements that corresponds to an a-th column (1≦b≦n) of the pixel data items;
• comparing each calculated heating value S(a,b) for the a-th column and the b-th row with a reference heating value L of the heating elements;
• counting the number of calculated heating values S(a,b) that exceed the reference heating value L so as to determine an excess-value number N(a) for the a-th column;
• determining a maximum excess-value number N(max) on the basis of excess-value number N(1) to excess-value number N(n) for first to n-th columns;
• and
• limiting the heating values of the heating elements if the maximum excess-value number N(max) exceeds a reference number M.