| 摘要 |
PURPOSE:To improve the reliability of detection by comparing a partial pressure voltage obtained by dividing a mark detection output of a photo sensor with a charge and discharge voltage of a charge and discharge circuit for charging and discharging in response to a detection output to fetch a mark detection signal. CONSTITUTION:While a black priming surface 1A of a belt 1 is detected by a photo sensor 2, a sensor voltage V is applied to + input terminal VA of a comparator IC, and partial pressure voltage by resistances R4, R5 is applied to - input terminal VB, so that a mark detection voltage Vout indicates H. When a mark 1B is detected, - input voltage VB increases with an increase of the sensor output VPE. R3 is selected to be VA<VB, so that mark detection signals can be put in the form of a panel for reliable discrimination. At the completion of mark detection, electric charges of a condenser C are discharged through a diode D and a resistance 2 to be on standby for the next detection. In this arrangement, a belt mark can be detected assuredly to improve the reliability of detection. |
