| 摘要 |
PURPOSE:To supply a constant quantity of light to a photodetecting element and also to place the photodetecting element to an optional position, by installing a prism to a chassis instead of a turntable, and also providing a passive reflector. CONSTITUTION:Holes 7, 8 are provided a little inside of records of 30cm and 17cm in disk diameters on a turntable 3, and a prism 4 and a passive reflector 5 are installed onto a chassis 9. When a 30cm-disk is placed, both the holes 7, 8 are closed up, and no output is generated to a photodetecting element 6. In case of a 17cm- disk, the hole 7 is opened, a light beam of a light source 1 passes through a part of incidence 15 and the prism 4, reaches the photodetecting element 6, and one pulse is outputted. In case when there is no record on the table 3, the holes 7, 8 are opened, and two pulses are outputted through the passive reflector 5. In this way, size is detected by the number of pulses in a prescribed time. Also, a constant quantity of light is supplied to the photodetecting element 6 since it is not influenced by vibration of the table, and is possible to place an optional position. |
