| 摘要 |
<p>A recording disc has a uniform spiral groove widening outwards in cross-section towards the surface of the disc and having a variable depth to record the desired information. The cross-section of the groove is tht of an inverted bell, varying with the depth at the centre of the groove, so that the width of the groove at the top or open end hardly varies with changes in its depth to suit the modulations. Pref. the cross-section of the groove is symmetrical about its centre line and the sides of the groove are defined by the equation dx = do.e-(x/w)2 (wher dx is the depth of the groove at centre line, w the half-width of the groove at hte surface of the disc and dx is the depth of groove at distnce x from the centre line). Used in particular for high speed discs intended for recording video signals, where the disc revolves at about 1800 rpm and therefore the groove pitch needs to be as small as 4 mu. The method ensured that, when a groove reaches its maximum penetration depth, it is not so widened out at the mouth that it runs into the neighbouring groove.</p> |
