| 摘要 |
PURPOSE:To enable an ink ribbon to be replaced according to the status of the density of printed characters, by providing a counter on which a predetermined value is set according to the density of characters read by an optical reader and which performs subtraction each time one line or one character is printed by a printer. CONSTITUTION:When a timing-generating circuit 7 so connected that timing data can be written through a printer controller 6 outputs a character density reading timing signal to an optical reader 1, the reader 1 reads the density of a character on a paper on which it is opposed, and inputs a signal to an A-D converting circuit 8 through an amplifier 9. An output signal from the A-D converting circuit 8 is read by the printer controller 6, and when the number of times of measurement reaches a prescribed value, a counter for counting the number of times of measurement is cleared to 0, and a number of residual printable characters is selected from a residual printable character number table on the basis of the character density detected. A counter for the number of residual printable characters is determined by 1 each time one character is printed, and when the count becomes 0, an ink ribbon replacement directing lamp 11 is turned ON through a driver 10, thereby urging the operator of the printer to replace the ribbon.
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