Patent ID: 7271818

Claim:
An improvement in a method of controlling a thermal transfer printhead in cold environments, the printhead having a plurality of heater elements arranged in a linear alignment for printing a corresponding number of image dots on a line-by-line basis, a selected number of said plurality of heater elements being activated within each line in accordance with an image being printed, each of said selected number being activated by one of five control signals, said printhead including a history control mechanism that tracks which heater elements have been activated in two previous image printing lines, said previous line activation determining which of said five control signals is applied to each heater element being activated in a current line, a first control signal having a first reference pulse width of 180 μsec at a print speed of 300 mm/sec, said pulse width decreasing with increasing print speed to a pulse width of 153 μsec at a print speed of 430 mm/sec, a second control signal having a second reference pulse width less than said first reference pulse width, a third control signal having a third reference pulse width equal to said second reference pulse width, a fourth control signal having a fourth reference pulse width less than said third reference pulse width, and a fifth control signal having a fifth reference pulse width less than said fourth reference pulse width, the improvement comprising: increasing the first reference pulse width by about 6-8% to obtain a first control signal pulse width; substantially maintaining the second and third reference pulse widths to obtain second and third control signal pulse widths, respectively; increasing the fourth reference pulse width by about 3-5% to obtain a fourth control signal pulse width; and substantially maintaining the fifth reference pulse width to obtain a fifth control signal pulse width.