FOCUSING

A thick video disc with a thickness of 1.1 mm rotating in free air at 30 Hz is generally stable but not critically damped. In order to restrict the action of transverse waves in the frequency range 0–15 Hz and also to compensate for the “umbrella” form deflection of the disc under its own weight, a stablisation system has been incorporated. Stabilisation is achieved in the player by means of an air bearing, which is created by the centrifugal action of the rotating disc on the surrounding air.

A plate with a central hole is positioned in the vicinity of the rotating disc's surface. This creates an air bearing having both the desired damping and stiffness characteristic. Disc stabilisation obtained in this way is by no means sufficient ...

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