Thermal printer for providing printed characters with a uniform density

A thermal printer for providing printed characters with a uniform density and for constantly applying proper energy to dot heating elements either in a high-speed printing mode or in a low-speed printing mode, said thermal printer comprising:

• a high-speed printing table containing defined pulse widths respectively for a printing hysteresis of a current bit to an N-th previous bit, wherein N represents a positive integer;
• a low-speed printing table containing defined pulse widths respectively for a printing hysteresis of a current bit to an M-th previous bit, wherein M represents a positive integer which is smaller than said N;
• means connected to both said high-speed printing table and said low-speed printing table for selecting a printing mode of said thermal printer;
• means connected to said mode selecting means for selecting either said high-speed printing table or said low-speed printing table in response to a selected printing speed mode in accordance with said printing mode selecting means;
• means for determining a printing hysteresis of a current bit to said N-th or said M-th previous bit;
• means for selecting a pulse width at an address location on either said high-speed printing table or said low-speed printing table as selected by said table selecting means, said pulse width being selected in accordance with the printing hysteresis of said current bit of said selected printing table;
• and
• means for adjusting a time when a current flows through each of necessary dot heating elements to a time defined by said selected pulse width on either said high-speed printing table or said low-speed printing table as selected by said table selecting means.