Browse Prior Art Database

Construction Method for a "Double Density" Compact Disk

IP.com Disclosure Number: IPCOM000114881D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Mar, RT: AUTHOR [+3]

Abstract

A double density Compact Disc (CD) can be constructed by connecting two CDs together. The CD player can be designed so that if the discs are not metalized, or partially metalized, the laser can focus on one disc or through the first disc to the second and thereby read either disc. This method of reading more than one optical surface has already been announced by IBM* as well as other companies. Constructing such a composite disc, however, poses several problems. First; some method must be provided to allow for equalization of atmospheric pressure changes. Secondly; temperature changes can result in moisture condensation in the area between the two discs which would render the data unreadable. A possible solution to this problem is to provide small openings in the spacer between the discs at the hub and rim.

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This is the abbreviated version, containing approximately 87% of the total text.

Construction Method for a "Double Density" Compact Disk

      A double density Compact Disc (CD) can be constructed by
connecting two CDs together.  The CD player can be designed so that
if the discs are not metalized, or partially metalized, the laser can
focus on one disc or through the first disc to the second and thereby
read either disc.  This method of reading more than one optical
surface has already been announced by IBM* as well as other
companies.  Constructing such a composite disc, however, poses
several problems.  First; some method must be provided to allow for
equalization of atmospheric pressure changes.  Secondly; temperature
changes can result in moisture condensation in the area between the
two discs which would render the data unreadable.  A possible
solution to this problem is to provide small openings in the spacer
between the discs at the hub and rim.  This idea is shown graphically
in fig's one and two.  As the disc rotates the linear velocity at the
rim V1 will be greater than the velocity at the hub V2.  This
difference in velocity will result in a difference in pressure
according to Daniel Bernoulli's principal.  Mathematically this can
be written as:
          P=K(V1*2 - V2*2)

Where P is the pressure difference and K is a constant.

The airflow between the discs due to this pressure difference will
then be:
          Flow=AK(V1*2 - V2*2)

Where A is the total area of the openings over which the pressure is
applied.

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