| 摘要 |
PURPOSE:To eliminate variation of the quantity of light, and to decrease the number of parts, and also not to damage a record, by using a turntable having a detecting hole and a passive reflector, without using a prism. CONSTITUTION:Holes 6, 7 are provided a little inside of records of 30cm and 17cm in disk diameters on a turntable 3, and a passive reflector 4 and a photodetecting element 5 are provided on a chassis 8. When a 30cm-disk has been placed, the hole parts 6, 7 are shielded, and an output of a photodetecting element becomes ''0''. In case of a 17cm-disk, the hole part 6 is opened, a light beam of a light source 1 is reflected by the passive reflector 4, and one pulse is outputted to the photodetecting element 5. In case when there is no record, the hole parts 6, 7 are opened, and two pulses are outputted. In this way, size of the record is detected by the number of pulses in a prescribed time. Also, the record is not damaged since it is not influenced by vibration of the table 3, the quantity of light is not varied, and also the number of parts as decreased is there is no projection on a sheet 2. |
