| 摘要 |
PURPOSE:To prevent sufficiently the resonance of a pickup arm by placing a pickup and a record disk in invariably constant relative position relation on the basis of a signal corresponding to the phase difference between a transmission wave sent from a transmitter to the record disk and a reception wave which is reflected by the record disk and received by a receiver. CONSTITUTION:The phase difference between the transmission wave and reception wave is assumed to be zero when the height H from the transmission surface of the transmitter 1 and the reception surface of the receiver 2 is larger than specific reference height H1. When the height H becomes slightly larger than the reference height H1, a positive or negative phase difference corresponding to the variation in height is made. A phase comparator 12 outputs a zero- level phase difference signal when the height H is equal to the reference height H1 and outputs a positive or negative phase difference signal corresponding to the height between the transmission wave and reception wave. This phase difference signal is supplied to a vertical driving control part 14 which controls the motion of the pickup arm 7 in a vertical plane by controlling the driving of a vertical driving part 13. |
