| 摘要 |
PURPOSE:To accurately perform the position detection of an optical system for a long time with simple constitution, by constituting a device in such a way that coils are provided on the optical system and a base substance respectively and the displacement of the optical system is detected by making use of the activating force of the coils. CONSTITUTION:An objective lens position detecting means is fixed at a position where the coil 13 is confronted with a cylindrical magnetic material 9 and the coil 14 with the supporting body 15 of the objective lens 2, respectively. Accordingly, when a distance between the coils 13 and 14 changes according to the up-and-down movement of the lens 2, a magnetic coupling coefficient between the coils 13 and 14 changes. When a current flows on the coil 13, a voltage proportional to the coupling coefficient between both coils is generated between the terminals of the coil 14. The voltage, after passing a sole frequency by a BPF, is detected by a detector, and next, at an LPF, a low frequency component can be obtained after the sole frequency component is eliminated. Thus, by detecting the displacement of the optical system by making use of the electromotive force of the coil, it is possible to perform the position detection of the optical system accurately extending over the long period.
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