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Thermal Printhead Drive Circuit for High Speed Printing

IP.com Disclosure Number: IPCOM000052603D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR

Abstract

A typical thermal printing system uses an electrically heated print element which is energized with current pulses. Since the duty cycle of the current pulse is relatively short, the actual temperature of the print element follows the curve shown in Fig. 1A when high speed printing is attempted. The first several current pulses gradually bring the temperature of the print element into the paper printing temperature range. Typically, the first current pulse does not raise the temperature into the print range. The second and third pulses extend partially into the print range. Not until the fourth or later pulse is the print head at the proper operating temperature. This causes a lack of definition in the printed character.

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Thermal Printhead Drive Circuit for High Speed Printing

A typical thermal printing system uses an electrically heated print element which is energized with current pulses. Since the duty cycle of the current pulse is relatively short, the actual temperature of the print element follows the curve shown in Fig. 1A when high speed printing is attempted. The first several current pulses gradually bring the temperature of the print element into the paper printing temperature range. Typically, the first current pulse does not raise the temperature into the print range. The second and third pulses extend partially into the print range. Not until the fourth or later pulse is the print head at the proper operating temperature. This causes a lack of definition in the printed character.

In this system, the temperature of the print element ranges from Tmax to Tmin, as shown in Fig. 1B. When a print operation is suspended, as between data characters or lines, the temperature is maintained at Tmin. This assures that the starting temperature of the print element is always the same, regardless of whether a dot has just been printed.

Fig. 2 is illustrative of the waveforms applied to the print element. The drive voltage is the sum of the print signal and the sustain signal. When a mark is to be made, the drive voltage is applied to the print element for a portion of each print cycle. When no drive voltage is to be applied to the print element, the sustain voltage is applied for the entire prin...