| 摘要 |
PURPOSE:To obtain a stable printing operation, by a method wherein when a power source voltage is lowered below a preset level, driving timings of a dot-generating mechanism and a carriage-driving motor are lowered to preset values. CONSTITUTION:When a printing signal requiring a high dot density is outputted, electric power to be supplied to a printing head 3 is increased, and an output voltage of a power source circuit 1 is lowered. A driving circuit 5 for a dot- generating mechanism supplies the dot-generating mechanism 3 with a driving signal with a pulse width inversely proportional to the power source voltage, thereby preventing the printed density from being lowered. When the output voltage of the circuit 1 is further lowered to become lower than the preset level, a power source voltage detecting circuit 7 outputs a signal to a printing speed controlling circuit 8. On receiving the signal, the circuit 8 divides the frequency of the timing pulse from a timing pulse generating circuit 9 to 1/2 of the original value, and outputs the resultant timing pulse to the circuit 5 and a pulse motor driving circuit 10, whereby the dot-generating mechanism of a printing head 3 and the carriage-driving motor 2 are driven at a fixed speed corresponding to 1/2 of the printing timing. |
