PURPOSE: To eliminate malfunction of information along with fluctuations of the quantity of light beam scanning the targer and perform accurate information reading by compensating the fluctuations of information signal levels by the use of the diffracted light of the hologram which is not used for radiation of bar codes.
CONSTITUTION: Laser light of a laser light source 7 is radiated via lenses 2, 3 and reflecting mirror 4 to the holograms 6a... provided to a disc 5. The + 1st order light 8 out of the diffracted light separated by radiating the holograms is radiated and scanned to the label 10 which is used for optical scanning. A signal detector 11 converts the intensity change of the reflected light of the label 10 to the read signal and inputs the same to a decoder 15 by way of an amplifier 14. On the other hand, the-1st order light 9 is made to the electric signal of the amplitude corresponding to the quantity of input light by a photo detector 13 and this signal is inputted to a level fluctuation detector 17 through an amplifier 16. The pulse signal of the amplitude corresponding to the level fluctuation components is inputted to the foregoing amplifier 14. the amplifier 14 makes the information signal level outputted by its automatic gain control mechanism constant and sends the same to the decoder 15, thus accurate information reading is accomplished irrespective of the quantity of light scanning the label 10.
ANDOU SANETOSHI
MATSUMOTO SEIKICHI
