| 摘要 |
PURPOSE:To perform a noncontact and highly reliable pickup position detection, by providing a light source and an optical element on one side of a movable table and a photoelectric transfer element on the other side, and by using the output of the photoelectric transfer element as the reference voltage of the position detection voltage of a feed gear. CONSTITUTION:An LED or the rear output of a semiconductor laser is used for a light source 1. A cylindrical lens 2 is set on a movable table 3. The output of a photoelectric transfer element 4, which is fixed sufficiently away from the focusing position I of the lens 2, is picked up by an amplifier 5. By defining X as the distance from the position I to the element 4, theta as opening angle of the flux of light, L as the width of the flux of light at the position of the element 4, l as the length of receiving light and K as a constant, the output V0 of the amplifier 5 is expressed as V0approx.=l/Lapprox.=l/X.tanthetaapprox.=k.1/X, and it is in inverse proportion to the distance X. This fact can be used as a revolution reference when the revolution speed of the disk changes in inverse proportion to the distance from the center to the pickup position. |
