| 摘要 |
PURPOSE:To enable to detect the presence of the record disc and the size of it with non-contact method, by using common ultrasonic speaker to a plurality of ultrasonic microphones and matching the resonant frequency of the both with a single frequency. CONSTITUTION:A pulrality of through-holes 24A to 24C are placed at the position different in radius respectively on the straight lines extended from the center of the turntable 23 radially which is mounted on the turn shaft 22 and turned unifiedly with the shaft 22. Ultrasonic microphones 26A to 26C are placed on the straight line of the player main body corresponding to the through-holes, common ultrasonic speaker 27 is provided by opposing to each microphone through the table 23, and the ultrasonic frequency signal in a single frequency is emitted to the microphones 26A to 26C. Further, the reflection plates 28A to 28C as the turntable position angle detector are provided corresponding to each through-hole inside the table external circumference, and the photo electric conversion element 29 is placed at the specific part of the main body 21. |
