| 摘要 |
PURPOSE:To attain a stable focusing operation, to set a blind sector width to zero, and to raise the focusing accuracy by adjusting the gain of an amplifier in accordance with an output of a photodetector. CONSTITUTION:The reflected light of a light emitting diode 4 is converted by photodetectors 1, 2, and converting outputs I1, I2 are obtained by amplifiers 5, 6. After inputting the outputs I1, I2 to variable gain amplifiers 7, 8, an adding signal I1+I2 is made by a detector 9 in synchronization with an oscillator 3, as compared with reference voltage 11 by an operating device 10, the gain of the amplifiers 7, 8 is varied so that I1+I2 becomes constant, and thereafter, focusing is obtained by driving a motor 14 so as to become I1-I2=0 basing on an output I1-I2 of a synchronizing detector by an operating device 13, therefore, focusing which is stable and has high accuracy is obtained irrespective of a variation of an output level of the photodetectors 1, 2 in accordance with a distance of an object. |
