| 摘要 |
PURPOSE:To hold data precisely by detecting a change with the passage of time in the reflectance of a disk to detect the recording and reproducing ability of the disk at every time. CONSTITUTION:A laser light beam projected from a laser light source 1 is irradiated on a recording surface 9 of a rotating recording medium (disk) 8 through a tracking mirror 6 and an objective lens 7 under the state narrowed thinly down to 1mum diameter. Information is entered (written) in the disk 8 by connecting/disconnecting (turning on/off) the laser light beam and the information is recorded by the change of reflectance or the formation of pit holes. When the disk is replaced, output current from a photoelectric detection element 14 is converted from current to voltage by a current/voltage converter 17 and the voltage is compared with the reference voltage corresponding to the reflectance of a usable range limit by a comparator 18. When the voltage is less than the reference voltage, an alarm lamp 20 is turned on to specify so as to replace the information recorded in the disk 8 to a new disk. |
