| 摘要 |
An optical disc machine initially identifies a disc positioned in it by moving the focal point of its optical pick-up unit between an outer surface and an interior reflective data carrying surface. The time required for the focal point to travel between the two reflective layers, proportional to the distance between the layers, is compared with one or more thresholds to identify the type of disc present. Example types are CDs and DVDs that can be distinguished from each other because of different distances between their two layers. Variations in the velocity of a motive source that drive the focal point to traverse the disc are compensated in order to avoid erroneous measurements of the distance between reflective layers, and thus to avoid misidentifying the disc types. Different types of DVDs or CDs may also be identified by measurement of reflected light intensity with respect to a threshold that is updateable.
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