| 摘要 |
PURPOSE:To generate a signal indicating the precise positional relation of a focusing lens to the case of an optical head by coupling the light focusing lens with a prism unitedly so as to be moved in parallel with the surface of an information recording medium and by detecting the movement by a two-divided optical sensor. CONSTITUTION:The focusing lens 23 and the prism 20 are fitted to a common arm 25 and moved by a lens actuator 12 unitedly. If the actuator 12 is driven so as to move the position of an optical beam spot 24 on the surface of the recording medium 6, the position of the incident surface 21 of the prism 20 to the case 1 of the optical head is changed, the incident light is reflected by the reflecting surface 21 and the position of the center axis of light flux to be made incident to the two-divided opitical sensor 22 is changed. Consequently, the quantity of light incident upon the divided two optical sensors is changed. The difference between the outputs of the two optical sensors can detect the positional shifting of the condensing lens 23 to the case 1 of the optical head. |
