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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of disk shaped information recording
media, and in particular to the field of providing protective covers for
such optical information disk-shaped recording media.
2. Description of the Prior Art
In optical disk information recording systems, the data is recorded on
radiation sensitive media. The disk is ordinarily comprised of a
disk-shaped substrate, usually aluminum, onto which a thin film of
radiation sensitive media is deposited. Because of the optical nature of
the surface of this disk, the surface ordinarily is in need of protection
from dust and dirt contamination as well as for providing a means of
defocusing such dust particles. In the prior art, this protection has been
provided by a radiation-transmissive protective covering, which is fixedly
secured to the disk surface above the media. The prior art has taught the
use of both "thin" media covers (on the order of approximately 0.005
inches thick) and "thick" media cover (on the order of approximately 0.040
inches. Thick protective covers or windows have been attractive because of
their ease of manufacture and relatively tighter mechanical tolerances,
thus allowing for repeatable and accurate optical qualities.
In the prior art in which a relatively thick protective cover is used, the
prior art has taught the bonding of inner and outer diameter spacers to
the disk substrate and thereafter bonding the protective window to the
inner and outer diameter spacers. However, because of the different
materials used to form the protective cover and the disk substrate, the
protective cover usually has a thermal expansion coefficient that is
different from that of the support substrate. It has been found that if
rigid adhesives are used to bond the protective cover the spacers and the
substrate together, a temperature change of 20.degree. F. can result in a
protective cover distortion of 5-10 mills, causing the protective cover to
bow or warp relative to the disk surface. Such distortion can cause the
aberration of the radiation beam, with resulting read and write errors,
and can also degrade the device performance by effecting the dynamic
stability of the rotating disk.
The prior art has addressed this problem by focusing on the proper
selection of adhesives and spacer material in order to achieve a strong,
but flexible bond. In U.S. Pat. No. 4,073,282, entitled
"Radiation-Sensitive Record With Protected Sensitive Surface", issued Feb.
14, 1978, to Balas, Jr., et al, and assigned to U.S. Philips Corp., a
transparent protective cover is disclosed for keeping dust away from the
active layer of the disk and for keeping ablated material from being
deposited upon the objective lens, wherein the protective cover is bonded
to the disk substrate by an inner and an outer spacer ring, as discussed
above. Work in the field of improving disk performance is predicated upon
this basic patent.
Another approach to this problem is taken in U.S. Pat. No. 4,353,767,
entitled "Method of Manufacturing An Optical Recording Disk", issued Oct.
12, 1982 to Wilkinson, and assigned to Discovision Associates, wherein a
disk assembly is disclosed comprising a pair of transparent disks, each
having a thicker inner and outer edge, such that when the thick edges are
placed together, an interior chamber is formed. In this patent, either one
or both of the inner disk surfaces can be coated with the active media
layer, thus having the "spacer" rings manufactured as an integral part of
the disk itself, eliminating the differential expansion problem. One
problem with this patent is that should either of the protective surfaces
be damaged, information recorded on the disk is effectively lost. An
additional problem is the development of a transparent disk substrate
which can meet the performance standards as found with aluminum
substrates.
The present invention is an improvement over the prior art in that a
mounting method is disclosed which will allow for the differential
expansion of the disk substrate without warping of the protective cover.
The disclosed invention is also an improvement in that the protective
cover is removable thereby allowing a damaged window to be replaced or
reused, as need be.
It is an object of the disclosed invention to provide a transparent
protective cover for optical information recording disks.
It is another object of the disclosed invention to provide a transparent,
low distortion, protective cover for optical information recording disks.
It is yet another object of the disclosed invention to provide a removable
transparent protective cover for an optical information recording disks.
It is still another object of the disclosed invention to provide a reusable
transparent protective cover for an optical information recording disks.
It is still yet a further object of the disclosed invention to provide an
inexpensive means for mounting a transparent protective cover to optical
information recording disks.
SUMMARY OF THE INVENTION
The disclosed invention, an unconstrained removable protective cover for
optical disks, is comprised of a disk-shaped transparent protective cover
which is fixed to the substrate of the optical recording disk by an inner
and an outer spacer, wherein the outer spacer has in its lower interior
perimeter, a U-shaped annular recess, in which is disposed the outer rim
of the optical disk. The closely fixed, but unbonded, outer spacer ring,
allows the transparent protective cover to expand or contract relative to
the disk, without causing the transparent protective cover to warp or
otherwise bend thereby minimizing optical wavefront distortion. The
disclosed invention contemplates a number of different arrangements for
attaching the protective cover to the outer spacer ring. In the specific
embodiments disclosed herein, the protective cover is mounted to the
spacer ring by bonding the protective cover to the upper surface of the
spacer ring, by locating the outer perimeter of the spacer ring on the
L-shaped shoulder on the upper portion of the spacer ring, by constructing
the spacer ring and the protective cover as a single unit, and by
providing for interlocking lips on the outer perimeter of the protective
cover and the upper inner portion of the spacer ring, such that when
inserted, the protective cover is locked into place in the spacer ring.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross section drawing of a prior art method of
attaching a transparent protective cover to an optical disk surface.
FIG. 2 is a partial cross section drawing of one embodiment of the
disclosed invention, wherein the transparent protective cover is bonded to
the upper surface of the outer spacer ring, and the inner spacer ring is
constructed as an integral part of the inner rim of the transparent cover.
FIG. 3 is a partial cross section drawing of another embodiment of the
disclosed invention wherein the inner spacer ring is bonded between the
disk substrate and the protective cover, and the outer perimeter of the
protective cover is bonded to an L-shaped shoulder on the upper portion of
the outer spacer ring.
FIG. 4 is yet another cross section drawing embodiment of the disclosed
invention wherein the outer spacer ring is formed as an integral portion
of the protective cover.
FIG. 5 is still yet another cross section drawing of another embodiment of
the disclosed invention wherein the outer rim of the protective cover has
a lip which is inserted into a second, U-shaped recess in the upper
portion of the outer spacer ring, such that when the perimeter of the
protective window is snapped into place, the protective cover and the
outer spacer ring are interlocked.
FIG. 6 is still yet another cross section drawing of yet another embodiment
of the disclosed invention wherein the outer rim of the protective cover
has a tongue which is inserted into a second, U-shaped recess in the upper
portion of the outer spacer ring and a downward projecting rib for support
which loosely rests on the disk substrate.
FIG. 7 shows a partial cross section drawing of the disclosed invention
wherein a stiffening band is disposed around the outer circumference of
the spacer ring to strengthen the lock between the spacer ring and the
protective covering.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows one of the most basic means in the prior art by which a disk
substrate 1, upon which optical media 2 is coated, has mounted thereon an
inner spacer ring 3, bonded with adhesive 4, and an outer spacer ring 5,
also bonded with adhesive material 4, and wherein said spacer rings 3 and
5 are bonded with adhesive material 4 to a transparent protective covering
6. In operation, a radiation beam is directed onto the media 2 passing
through transparent protective cover 6. One problem with this prior art is
that with variations in temperature, this inflexible method of mounting
will cause the transparent protective cover 6 to expand at a different
rate than the substrate 1, causing the transparent protective cover 6 to
bend or warp, thereby changing the optical path through which the
radiation source strikes the media. The change in optical path causes
read/write errors, as well as altering the dynamic characteristics of the
disk assembly, resulting in instability during disk rotation.
As shown in FIG. 2, the disclosed invention addresses this problem by
providing for an unconstrained method of mounting an unconstrained spacer
ring 7 to the outer perimeter of the disk 1. As shown in FIG. 2, the outer
spacer ring 7 has an U-shaped interior recess 8 into which the outer
perimeter of the disk 1 is inserted. This outer spacer ring 7 is not
bonded to the disk 1 substrate, thereby allowing for the lateral sliding
of the spacer ring 7 with respect to the disk 1. As shown in FIG. 2, in
the simplest embodiment of the disclosed invention, the protective
covering 6 is now bonded to the upper surface of the outer spacer ring 7
with adhesive 4. Also shown in FIG. 2, is an embodiment of the disclosed
invention wherein an inner spacer rim 9 is formed as an integral portion
of the transparent protective covering 6.
In FIG. 3, the outer spacer ring 10 is modified to have an upper interior
shoulder 11 onto which the transparent protective cover 6 is inserted and
bonded with adhesive 4. Also as shown in FIG. 3, the interior spacer ring
3 is bonded between the disk substrate 1 and the protective cover 6 with
adhesive 4.
As shown in FIG. 4, in another embodiment of the disclosed invention, the
protective cover 6 is modified as such that the outer perimeter of the
protective cover 6 is formed with an outer spacer rim 12 is formed as an
integral component of the transparent cover 6, with the U-shaped annular
channel 8 disposed around the outer perimeter of the disk substrate. The
inner spacer ring 3 is bonded to the disk substrate 1 and the protective
cover 6 with adhesive 4.
In FIG. 5, attachment of the spacer ring 13 to the disk 1 and the
protective cover 6 is achieved without adhesive bonding. In this
embodiment, the outer perimeter 14 of the transparent protective cover 6
is modified to have a notch and lip section 15 which is inserted into a
second U-shaped annular channel 16 in the upper portion of the spacer ring
13, said second U-shaped channel 16 also having a downward projecting lip
17 which cooperates with the notch 15 in the protective cover 6 to lock
the spacer ring 13 into the protective cover 6.
In FIG. 6 an embodiment is shown wherein the outer spacer ring 19 has a
second upper U-shaped annular recess 20 into which a tongue 21 on the
outer rim of the protective cover 6 is slidably inserted. The upper
surface of the protective cover 6 is coplanar with the upper surface of
the spacer ring 19. For added support, the protective cover 6 also has a
downward projecting rib 22 which sets on the substrate 1 surface for
support. As shown in FIG. 6, the outer rim of the disk substrate 1 is
inserted into the lower annular recess 8.
In FIG. 7, the locking embodiment of FIG. 5 is further modified by the
addition of a stiffening band 18 which reinforces the spacer ring in
retaining the protective cover 6 over the disk substrate 1. While this
stiffening band 18 is illustrated with regard to only embodiment in FIGS.
5 and 7, it is contemplated that the restraining band can be used with any
embodiment of this disclosed invention.
While a number of embodiments have been disclosed herein, it should be
recognized that a plurality of different methods exists for securing the
protective covering 6 to the basic outer spacer ring 7, and that basic
spacer rings 3 and 7, can be modified in a plurality of different methods
for said attachment.
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