Thermal head drive unit

A thermal head drive unit using recording paper for forming thereon an image through a color generation or ink transfer process comprising:

• electric power supply means for supplying electric power to heat-generating resistor elements arranged in a line in a thermal head;
• head drive means for electrically driving the heat-generating resistor elements in a lump by supplying electric power continuously variably in time to said heat-generating resistor elements depending on input gradation data;
• and
• head drive control means for controlling said head drive means so that, in a one-line recording time period composed of a power supply time during which electric power is supplied to said heat-generating resistor elements and an intermission time during which no electric power is supplied to said heat-generating resistor elements in disregard of the gradation data, the intermission time occupies a part not more than approximately 40% in the one-line recording time period,
• said head drive control means controls said head drive means so that substantially no intermission time is provided in a compensation time period for carrying out a compensation operation with maximum additional electric power supply necessary for compensating for recording density variance attributed to environmental temperature change and heat accumulation in the thermal head or for compensating for recording density variance attributed to deviation in resistance of the heat-generating resistor elements.

A thermal head drive unit using recording paper for forming thereon an image through a color generation or ink transfer process comprising:

• electric power supply means for supplying electric power to heat-generating resistor elements arranged in a line in a thermal head, wherein said electric power supply means supplies such maximum electric power that a temperature of said heat-generating resistor elements is maintained lower than a temperature at which deformation of the recording paper is caused;
• head drive means for electrically driving the heat-generating resistor elements in a lump by supplying electric power continuously variably in time to said heat-generating resistor elements depending on input gradation data;
• and
• head drive control means for controlling said head drive means so that, in a one-line recording time period composed of a power supply time during which electric power is supplied to said heat-generating resistor elements and an intermission time during which no electric power is supplied to said heat-generating resistor elements in disregard of the gradation data, the intermission time occupies a part not more than approximately 40% in the one-line recording time period,
• said head drive control means controls said head drive means so that substantially no intermission time is provided in a compensation time period for carrying out a compensation operation with maximum additional electric power supply necessary for compensating for recording density variance attributed to environmental temperature change and heat accumulation in the thermal head or for compensating for recording density variance attributed to deviation in resistance of the heat-generating resistor elements.