| 摘要 |
The present invention relates to an electro-optical system for double document detection wherein an improved calibration is employed. To calibrate the system, a microcontroller generates a series of increasingly wider pulses, which are transformed into a series of respective increasingly higher ramp pulses to drive a light emitter (LED, a laser diode or fiber optic coupled laser) at gradually increased power until the predetermined value of an output signal of the light detector (photo-transistor) is achieved. Then the pulse width corresponding to the predetermined value of the output signal is fixed. This width becomes the drive for the light emitter until another calibration changes it. The microcontroller (with the software in it) monitors the output signal to determine a double-feed document condition if the output signal exceeds a predetermined value. The system is capable of "hands-off" calibration. To detect a "true" double-feed document condition, a software timer counts a prolongation of the alteration of the output signal. Also, in order not to miss a "true" double-feed document condition when the area of overlapping is small, the distance between a front edge of the first overlapped document and a rear edge of the last overlapped document is measured. The system also declares a double-feed document condition if a space between two fed documents is no greater than a predetermining value. The system is also capable of self compensating for component variations, component deterioration and voltage variation over time, slight misalignment, and accumulated paper dust, if any. The system also provides a safety circuit to protect the light emitter from excessive power dissipation. If the situation of power down in the system occurs, the recalibration is not needed, since the system is provided with the non-volatile memory to store the fixed width. Each stage of the system is indicated by LEDs. |
