| 摘要 |
PURPOSE:To trace a position stably and automatically with high precision by using several photo detectors and a light beam position error information detecting method. CONSTITUTION:Over and under light source 1, a couple of photo detectors 11 and 12 consisting of photo diodes are arranged, and an alternating-current focus formed of capacity detector 5, servo-amplifier 17, adder 16, and driver 7, a direct-current focus formed of adder 13, multiplier 14, servo-amplifier 15, adder 16, and driver 7, and a tracking loop consisting of subtracter 18, multiplier amplifier 19 and driver 20 are provided. Consequently, outputs of photo detectors 11 and 12 are added together and multiplied by the output of capacity detector 5 and the multiplication output is added to the output of servo-amplifier 17 and inputted to driver 7. As a result, even if size distortion of an optical system occurs due to variation in ambient temperature, the position of lens 2 is shifted to compensate it, so that the position can be traced automatically and stably with high precision. |
