Thermal printing control system

Abstract

A control system for a thermal print head includes means for regulating the firing of the print elements with the proper pulse width to compensate for increasing substrate temperature. The control circuit is divided into two separate circuits--the driving circuit for turning the print elements on and off, and the decision-making circuit which executes the substrate temperature coding and control codes and sends control signals to the driving circuit. Three types of temperature compensation are utilized in the control program. A tailored pulse width is used for each bank of the print elements to compensate for various element resistances. As the print head shuttles across the record medium, the pulse width is reduced for each horizontal dot position. The pulse width also is reduced for each line printed in the format. The system may be used for either direct thermal or thermal transfer printing with both full and half dot spacing and single or double width characters.