| 摘要 |
PURPOSE:To simply and inexpensively keep a printing density of a thermal printer constant, by a method wherein a dummy resistance is mounted at a thermal head in a printing density control circuit. CONSTITUTION:If, for example, a printing signal PT is inputted, an expotential function waveform as shown in a signal Pa is obtained at a point (a) by means of a dummy resistance R0, a resistance r0, and a capacitor (c). If the signal Pa reaches a switching voltage V0 of a transistor TR1, the transistor TR1 closes and a signal having a signal width t0 as shown in a signal Pb is obtained at point (b). Furthermore, through the aid of a transistor TR2, a voltage value Vp as shown in a signal Pd and a thermal driving signal having the pulse width t0 are obtained. If each resistance value of the thermal head is higher than a standard, or a resistance value of the dummy resistance R0 is high, the waveform of the signal Pa inclines slowly, and the pulse width t0 is lengthened. A printing density is proportioned to the product of an applied power and a pulse width, and thereby a constant printing density can be obtained. |
