| 摘要 |
PROBLEM TO BE SOLVED: To prevent a printer from accidentally stopping during printing and to display a warning to allow previous measures. SOLUTION: A reflection-type optical sensor 6 for detecting existence of paper is disposed in a paper conveying passage. In a step D1 the paper 5 is fed, in steps D2 and D4 output voltages of the optical sensor 6 are respectively detected when the paper 5 exists and does not exist, and in step D5 difference between both output voltages is calculated. In a step D6, an error state is displayed when the voltage difference is lower than a limit voltage at which the existence of the paper 5 can be determined. In a step D7, the warning is displayed when the voltage difference is higher than the limit voltage and lower than a normal voltage.
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