| 摘要 |
In a duplex printing integrity system for insuring that correctly matching pages are being printed by a duplex printer on the opposing first and second sides of the sheets, the duplex printer having a duplex loop path circulating sheets printed on one side back to be printed on their opposite side and an output path for feeding out the duplex sheets after they have been printed on both sides; the printer is operable to selectively print a few small, simple solid marks spaced along the sheets, specifically printing a sequence of sheets with correspondingly spaced and parallel print marks, with different spacings of the marks on the sheets for different sheets in the duplex loop. A first optical sensor in the output path line scan the first sides, and an adjacent second optical sensor scanning the second sides, and a comparison circuit continuously compares the sensor output signals to provide a duplex printing error signal when the first and second optical sensors provide different output signals at different times due to a duplex document sheet passing the sensors which is not printed on opposing sides with correspondingly spaced print marks. A time delay circuit may be connected between at least one of the first and second sensors and the comparison circuit to allow the sensors and/or the pattern of print marks to be offset from one another.
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