| 摘要 |
PURPOSE:To accurately detect the second and following sheets by comparing the voltage value of the quantity of light received by the first sheet with a reference voltage value and adding a light emitting quantity compensating current depending upon the count value corresponding to the pulse number of a comparator output to the initial current to decide the initial photo detecting quantity. CONSTITUTION:The photo detecting level which is lowered when a sheet 1 gets on a photo detecting portion 3, is amplified by an amplifier circuit 9, and an output signal is input to a comparator 10, a level change detection circuit 13 and a comparator 16. A set reference voltage E1 is input to the circuit 10, and while there is a difference between the inputs, a signal (b) is output from AND circuit 11 by a compensation designation signal from FF circuit 18 and a paper detection signal (c), thereby to set FF circuit 12. An output signal of the circuit 12 and a pulse signal from a pulse generation circuit 7 are input to AND circuit 8. A pulse signal (a) is output from the circuit 8 to be input to a counter circuit 6, and the number of pulses are counted to be input to a light emitting compensating current feed circuit group 5. A compensating current from the current feed circuit is added to the initial current, and when the photo detecting level reaches the reference voltage E1, it is regarded as the initial reference. |
