| 摘要 |
PURPOSE:To detect abnormal printing of blank paper or a blank ticket, by a method wherein the current flowing to a thermal head is detected at every printing line, and compared with the reference value corresponding to the min. number of printing dots per line to judge how many lines exceeding the reference value are there. CONSTITUTION:When a thermal head 8 performs the printing of a certain line, the number of heat generating elements r1-rn corresponding to the number of printing dots generate heat. The current proportional to the number of the heat generating elements is outputted from a DC constant voltage power source 5 and the voltage Va at a point P1 drops in proportion to the number of the heat generating elements. When the value of the voltage Va is looked at, the number of dots printed are cleared. When the min. number of printing dots per line are set to n1, reference voltage Vref is set to the intermediate value of the values of Va corresponding to the number n1 of dots and the number (n1-1) of dots. As a result, the output signal of a voltage comparator 9 becomes '1' when the number of printing dots per line are n1 or more and becomes '0' when said number is (n1-1) or less. The output signal of the voltage comparator 9 becomes '0' when no printing is performed at all or printing is abnormal. |
