| 摘要 |
PURPOSE:To enable to stably print with a predetermined density and unnecessitate maintenance, by such a control as to pass to a heating element a printing pulse current with a pulse width conforming to the resistance of the element, thereby operating the element to generate heat. CONSTITUTION:In response to a signal from a micro-computer 6, a power source controlling circuit 10 for the thermal head 5 turns ON a power source 9, and a head-driving circuit 7 drives thermal head 5 in response to a printing signal. To measure the resistance of the heating element of the thermal head 5, a small constant electric current is passed to the element from a constant current circuit 11 when the power source 9 is OFF, the driving circuit 7 divide the current for each of the heating elements in response to a driving signal from the micro-computer 6, the potential difference between both ends of each of the heating elements is detected by a detecting circuit 12, a detection signal is fed to the micro-computer 6 through an A-D converter 8, a pulse width of a printing pulse current conforming to the resistance thus detected is obtained, and thereafter, a printing current with the pulse width thus obtained is passed to the heating element, thereby operating the element to generate heat. Accordingly, it is enabled to print stably with a constant fixed density and to use the thermal head for a long period of time without requiring any maintenance. |
