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Claims  |
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What is claimed is:
1. An optical disc-unit adapted for the optical writing and/or reading of
high density information, said unit comprising:
(a) an optical disc including a flexible, disc-shaped support carrying a
record layer;
(b) a disc cover opposing said record layer and comprising a flexible,
disc-shaped sheet which is substantially transparent to writing and/or
reading wavelengths and which is generally coextensive with said optical
disc; and
(c) annular retaining means, engaging said support and said sheet
substantially continuously around annular peripheral regions, for
positioning the sheet and record portions of said layer in spaced
relation.
2. The invention defined in claim 1 wherein said retaining means is
constructed to hold said peripheral regions and to exert
generally-uniform, radially-outward force on central portions of said
support and sheet, whereby said support and said sheet are substantially
parallel in cylindrically-symmetric tension.
3. The invention defined in claim 1 or 2 wherein said support and said
cover sheet have continuous surfaces and said retaining means cooperates
with said engaged regions to substantially seal the space between said
continuous sheet and support with respect to the external atmosphere.
4. The invention defined in claim 1 or 2 wherein said support is engaged in
cylindrically-symmetric tension substantially below its elastic limit and
wherein said optical disc-unit further includes index surface means for
positioning a region of said support in an abutting relation with a
tensioning abutment surface of optical write and/or read apparatus,
whereby said optical disc-unit can be stored with said optical disc in
relatively lower tension and used in such apparatus in relatively higher
tension.
5. The invention defined in claim 1 or 2 wherein said retaining means
comprises a first member, an intermediate member and a third member
disposed in opposing relation with said peripheral regions of said sheet
and said support interleaved therebetween.
6. The invention defined in claim 5 wherein opposing surfaces of said first
member and said intermediate member have cooperative rib and groove
portions and opposing surfaces of said third member and said intermediate
member have cooperative rib and groove portions, said members being
disposed in inter-pressing relation with portions of said sheet and said
support deformed between interfitting rib and groove portions thereof.
7. The invention defined in claim 6 wherein said rib portions have a
generally convex profile and said groove portions have an angular profile
whereby the interfit between such portions provides space to accommodate
cold flow of interleaved sheet and support material.
8. For use with optical disc appartus of the kind adapted for the optical
writing and/or reading of high density information and including a
rotatable receiving means having a reference surface which is rotatable
about an axis in a first plane that is normal to said axis and lens means
for focusing write and/or read light at a focal plane parallel to said
first plane, an optical disc-unit comprising:
(a) an optical disc including a flexible, disc-shaped support carrying a
record layer;
(b) a disc cover opposing said record layer and comprising a flexible,
disc-shaped sheet which is substantially transparent to writing and/or
reading wavelengths and which is generally coextensive with said optical
disc; and
(c) annular retaining means, engaging said support and said sheet around
their peripheral regions, for positioning the sheet and the record area of
the support in spaced relation, said retaining means including an index
surface adapted to predeterminedly position said unit on the reference
surface of such apparatus receiving means with said record layer proximate
such apparatus focal plane.
9. The invention defined in claim 8 wherein said retaining means is
constructed to hold said peripheral regions and to exert
generally-uniform, radially-outward force on central portions of said
support and said sheet, whereby said support and said sheet are
substantially parallel in cylindrically-symmetric tension.
10. The invention defined in claim 8 or 9 wherein said support and said
cover sheet have continuous surfaces and said retaining means cooperates
with said engaged regions to substantially seal the space between said
continuous sheet and support with respect to the external atmosphere.
11. The invention defined in claim 8 or 9 wherein said support is engaged
in cylindrically-symmetric tension substantially below its elastic limit
and wherein said index surface means is constructed to position said
support in a predetermined tensioning relation with a tensioning abutment
surface of such optical write and/or read apparatus, whereby said optical
disc-unit can be stored with said optical disc in relatively lower tension
and used in the predetermined focal plane of such apparatus in relatively
higher tension.
12. The invention defined in claim 8 or 9 wherein said retaining means
comprises a first member, an intermediate member and a third member
disposed in opposing relation with said peripheral regions of said sheet
and said support interleaved therebetween.
13. The invention defined in claim 12 wherein opposing surfaces of said
first member and said intermediate member have cooperative rib and groove
portions and opposing surfaces of said third member and said intermediate
member have cooperative rib and groove portions, said members being
disposed in inter-pressing relation with portions of said sheet and said
support deformed between interfitting rib and groove portions thereof.
14. The invention defined in claim 13 wherein said rib portions have a
generally convex profile and said groove portions have an angular profile
whereby the interfit between such portions provides space to accommodate
cold flow of interleaved sheet and support material.
15. In optical disc write and/or read apparatus of the kind including: (i)
optical disc-unit receiving means having a reference surface, which is
rotatable about an axis in a first plane that is substantially normal to
said axis, and (ii) lens means for focusing write and/or read light at a
focal zone generally parallel to said first plane, an improved optical
disc-unit comprising:
(a) an optical disc including a continuous, flexible, disc-shaped support
carrying a record layer;
(b) a disc cover opposing said record layer and comprising a continuous,
flexible, disc-shaped sheet which is optically transparent to such writing
and/or reading light and which is generally coextensive with said optical
disc; and
(c) annular retaining means having index surface means contacting said
reference surface and means, engaging each of said disc-shaped support and
said disc-shaped sheet substantially continuously around respective
annular peripheral regions, for positioning said sheet and the record
portion of said layer in a spaced relation;
said index surface means being predeterminedly located with respect to said
support and said reference surface being predeterminedly located relative
to said focal zone so that said record layer is proximate said focal zone.
16. The invention defined in claim 15 further including a tensioning
abutment surface which is generally concentric to said axis and radially
inward from said retaining means, said abutment surface being adapted for
rotation with said receiving means in a second plane substantially normal
to said axis and located with respect to first plane and said focal zone
so that said support is uniformly tensioned by said abutment surface with
the record layer substantially coinciding with said focal plane.
17. The invention defined in claim 15 wherein said reference surface and
said retaining means are precisely constructed so that said record layer
substantially coincides with said focal plane.
18. The invention defined in claim 15, 16 or 17 wherein said receiving
means further includes axial centering means for contacting the periphery
of said disc-unit and aligning the central axis of such unit on said axis
of rotation.
19. Optical disc write and/or read apparatus adapted for use with an
optical disc-unit of the kind including: (i) an optical disc having a
continuous, flexible, disc-shaped support carrying a record layer and (ii)
annular retaining means having index surface means and means for engaging
said support substantially continuously around an annular peripheral
region so as to urge said support into a generally flat condition, said
apparatus comprising:
(a) receiving means having a reference surface which is rotatable about an
axis generally within a first plane that is normal to said axis; and
(b) lens means for focusing write and/or read light generally at a focal
zone that is generally parallel to said first plane,
said first plane being predeterminedly located with respect to said focal
zone so that when the index surface means of a received disc-unit contacts
said reference surface, the support of such disc-unit is located proximate
the focal zone of said lens.
20. The invention defined in claim 19 wherein said receiving means further
includes a tensioning abutment surface which is generally concentric to
said axis and radially inward from said index surface, said abutment
surface being adapted to rotate in a second plane that is substantially
normal to said axis, said second plane being located relative to said
focal zone and said first plane so that the support of a disc-unit
received on said index surface is subjected to cylindrically symmetric
tension by said abutment surface and so that the record layer carried on
such tensioned support substantially coincides with said focal zone.
21. The invention defined in claim 19 wherein said first plane is located
with respect to said focal zone so that the record layer of such disc-unit
substantially coincides with said focal zone.
22. The invention defined in claim 19, 20 or 21 wherein said receiving
means further includes axial centering means for contacting the periphery
of a received disc-unit and aligning the central axis of such unit on said
axis of rotation.
23. The invention defined in claim 16 or 20 further including means for
positively urging said index surface of retaining means into contact with
said reference of said receiving means so as to positively tension said
disc-unit support via said abutment surface.
24. A method of fabricating an optical disc-unit adapted for optical
writing and/or reading of high density information, said method comprising
the steps of:
(a) forming an optical disc including a continuous, flexible, disc-shaped
support carrying a record layer;
(b) forming a disc cover including a continuous, flexible, disc-shaped
sheet which is substantially transparent to writing and/or reading
wavelengths and of diameter generally equal to said optical disc;
(c) forming first, intermediate and third annular retaining members of
diameter generally equal to said optical disc, said first and intermediate
members having cooperative rib and groove portions in radially inward
surfaces thereof and said intermediate and third members having
cooperative rib and groove portions in radially inward surfaces thereof;
(d) placing said first, intermediate and third members in opposing relation
with respective groove and rib portions aligned for interfitting
cooperation and with peripheral regions of said support and sheet
interleaved therebetween; and
(e) manipulating said members into interfitting relation so as to dispose
unretained portions of said support and said sheet in cylindrically
symmetric tension.
25. The method defined in claim 24 wherein said manipulating step includes
first engaging forcing outer peripheral portions of said members together
to engage outer peripheral regions of said sheet and support therebetween
and then forcing inner portions of said members together so as to deform
portions of said sheet and web into the grooves of such members and
thereby symmetrically tension inward portions of said sheet and support.
26. The invention defined in claim 1 or 8 further including a second record
layer opposite said first-mentioned record layer and a second disc cover
on the opposite side of said optical disc from said first-mentioned disc
cover, said second cover comprising a flexible disc-shaped sheet that is
substantially transparent to writing and/or reading wavelengths and which
is coextensive with said optical disc, and wherein said retaining means
engages said second disc cover substantially continuously around its
peripheral regions to position it in spaced relation to said optical disc.
27. The invention defined in claim 16 or 20 wherein said tensioning
abutment surface is annular and located to contact an annular region of
said support proximate said retaining means. |
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Claims |
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Description |
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CROSS-REFERENCE TO RELATED APPLICATIONS
Reference is made herein to U.S. patent application Ser. No. 023,434, filed
Mar. 23, 1979, in the names of Thomas and Wrobel, and U.S. patent
application Ser. No. 124,381, filed Feb. 25, 1980, in the names of Howe
and Wrobel.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to record medium and apparatus useful in
optical writing and/or reading of high density information and more
particularly to improved configurations for optical discs and cooperating
optical disc apparatus.
2. Description of the Prior Art
The currently preferred optical disc technology employs disc elements with
spiral or concentric tracks of minute (e.g., on the order of a micron or
less in size), optionally-detectable marks. One real-time mode of
recording (writing) such marks is by scanning tracks on the disc with an
equivalently small beam of radiation (e.g., from a laser) which is
modulated "off or on" according to an eletrical signal representative of
the information to be written. Information is recovered (read) by scanning
the tracks with a larger, but still very tightly focused radiation (e.g.
light) spot. The recovered information is in the form of a fluctuating
electrical signal obtained from a photodetector that senses the read-out
light reflected from the recorded disc. The benefits (e.g. high data
storage density) inuring to recording with such small marks are very
important; however, the problems encountered in precise implementation of
the approach are very difficult. For example, focus of the write or read
beam should be maintained with precision and the record surface should be
protected e.g. from dirt and scratches.
More specifically, in order to write and read information in the form of
such minute markings, optical systems of high numerical aperture are used
to focus light to equivalently minute spots. Such optical systems have
extremely small depths of focus and the proper positional relation between
the writing or reading optical system and the optical disc record surface
must be stringently maintained. Therefore it is highly desirable that the
record layer, and thus optical disc support surface underlying the record
layer, be smooth (relatively free of high-spatial-frequency variations
from a nominal plane, e.g. such as caused by minute pits or bumps) and
flat (relatively free of large amplitude, low spatial frequency variations
e.g. such as caused by undulating surface variation of the support).
Although complex focus-servo devices can effect lens adjustment to
compensate for imperfect smoothness and flatness, these devices add to the
cost and fragileness of the write/read apparatus. The degree of complexity
of the focus-servo devices is proportional to the degree of such disc
imperfections and the speed of operation.
One approach to achieve requisite smoothness and flatness has been to form
the disc substrate of glass with a ground and polished surface. This
requires a time consuming and costly fabrication procedure. Another
approach is to mold a plastic disc substrate with a highly finished
surface and apply a surface smoothing sub-layer. However, it is extremely
difficult to mold such plastic discs having adequate surface
characteristics with a good yield; and this support fabrication method is
also relatively costly.
Several different approaches have been suggested for protecting the disc
recording layer surface from dirt and scratches. One is to overcoat that
surface with a transparent protective layer of sufficient thickness to
locate the exterior protective surface out of the depth of focus of the
optical system. However, protective layers of this thickness require
complicated optical correction of aberrations and can present problems in
certain deformation recording processes for the recording layer. An
alternative approach described in U.S. Pat. No. 4,038,663 is to centrally
attach a flexible disc cover (n spaced relation to the record surface of a
rigid optical disc) and "fly" the cover sheet above the record layer
during write or read operations. Another approach disclosed in U.S. Pat.
No. 4,074,282 provides inner and outer coaxial spacers to support a
transparent cover plate in spaced relation from the record surface of a
rigid optical disc.
While the above-noted and other protective layer or protective cover member
approaches are useful to avoid scratch or dirt problems, they do not
simplify the above-noted problems in meeting precise smoothness and
flatness requirements.
SUMMARY OF THE INVENTION
One general purpose of the present invention is to provide improved optical
disc and cooperating apparatus configurations to cope with the problems
outlined above. Thus an important feature of the invention is to provide
improved configurations for meeting smoothness, flatness and protective
requirements in optical disc writing and/or reading.
One particularly desirable advantage of the present invention is that it
obviates the use of rigid supports. This attribute is of great
significance in fabrication, for the recording layer(s) can be applied to
flexible webs in a continuous run, with many discs subsequently being cut
from the web. Rigid disc formats are not readily susceptible to such
coating techniques. Another desirable attribute of certain embodiments of
the present invention is the enhancement of dimensional stability in the
face of environmental stresses. This relaxes design requirements for
cooperating apparatus, e.g. as tracking servo devices.
In one general aspect the present invention relates to an improved optical
disc-unit adapted for the writing and/or reading of high density
information and comprising (i) an optical disc including a flexible,
disc-shaped support carrying a record layer; (ii) a disc cover, opposing
the record layer, comprising a flexible, disc-shaped sheet which is
substantially transparent to such writing and/or reading wavelengths and
which is generally coextensive with the optical disc and (iii) annular
retaining means, engaging said support and said sheet around respective
annular peripheral regions, for positioning the sheet and record portions
of the opposing record layer in spaced relation. In particularly preferred
embodiments central portions of the flexible sheet and flexible support
are held in cylindrically-symmetric tension by said retaining means. In
other preferred embodiments the support and cover sheet are continuous
surfaces and the retaining means cooperates with the retained sheet and
support portions to substantially seal the space between the continuous
sheet and support. In other preferred embodiments the optical disc support
is held in a relatively lower tension by the retaining means, which
further includes index surface means for positioning said support in an
abutting relation with a tensioning and/or positioning surface of optical
disc write/read apparatus. Thus the optical disc-unit can be stored with
the optical disc in such relatively lower tension and used with the
optical disc in a relatively higher tension to enhance its flatness.
In a related aspect the present invention relates to optical disc
write/read apparatus adapted to receive, predeterminedly position and/or
tension such an optical disc-unit. In another related aspect the present
invention relates to improvements in optical disc apparatus comprising
such a disc-unit and cooperative receiving, positioning and/or tensioning
structure. In another aspect the present invention relates to improved
methods for fabricating optical disc units. Other improvements and
advantages of the present invention will become more evident in view of
the subsequent description of preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The description of preferred embodiments refers to the attached drawings
wherein:
FIG. 1 is a perspective view of one preferred optical disc-unit
configuration illustrating the general approach of the present invention;
FIG. 2 is a sectional view of the FIG. 1 disc-unit configuration;
FIG. 3 is a fragmented perspective view of a portion of one specific
disc-unit configuration in accord with the present invention;
FIG. 4 is a cross-sectional view of a portion of an alternative disc-unit
embodiment;
FIG. 5 is a cross-sectional view similar to FIG. 2 but of another
embodiment of the present invention;
FIGS. 6-A and 6-B are cross-sectional views of portions of another
alternative preferred disc-unit embodiment;
FIG. 7 is a schematic fragmented sectional view of an optical disc-unit and
cooperative optical disc apparatus in accordance with the present
invention;
FIG. 8 is a view like FIG. 7 but of an alternative embodiment of optical
disc-unit and cooperative optical disc apparatus;
FIG. 9 is a view similar to FIG. 7 but of another embodiment of optical
disc-unit and cooperative apparatus;
FIGS. 10 and 11 are views similar to FIG. 2 but of yet other embodiments of
disc-units according to the present invention; and
FIGS. 12-14 are schematic, fragmented sectional views illustrating other
alternative embodiments of optical disc-unit and cooperative apparatus in
accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 and 2, the general approach of optical disc-unit
configurations in accord with the present invention can be explained.
Thus, the optical disc-unit 10 includes an optical disc 11 in the form of
a continuous, flexible, disc-shaped support 12 having recording layer 13
(and other appropriate layers) formed on one major surface of the support.
The disc-unit also includes a disc cover in the form of a continuous,
flexible, disc-shaped sheet 14 which is substantially transparent with
respect to the write and/or read wavelength suitable for use with the
record layer 13. The diameter of the disc cover sheet 14 corresponds
generally to the diameter of the optical disc 11, and, as shown, both
elements are supported in spaced relation by support structure of the
disc-unit 10 which engages peripheral annular regions of those elements.
More particularly the disc-unit 10 includes annular retaining means,
denoted generally 20, which engage the optical disc support 12 and the
cover sheet 14 substantially continuously around respective annular
peripheral portions in a manner positioning central portions of those
elements into spaced relation. It is highly preferred that the cover sheet
14 and disc support be retained in cylindrically-symmetric tension, and in
the FIG. 1 and 2 embodiment this is accomplished by cooperating annular
ring members 21, 22 and 23. It is also highly preferred in accordance with
the present invention that the cooperative engagement between the disc
support 12, cover sheet 14 and retaining means 20 significantly seal the
space between the recording layer 13 (on support 12) and the inner surface
of the cover sheet 14. Various preferred specific retaining means
configurations for achieving these results will be described subsequently;
however first a brief description of useful and preferred characteristics
for the optical disc support and the cover sheet is appropriate.
Considering first the optical disc support, thickness uniformity, strength,
dimensional stability and surface quality are significant characteristics
to be considered in selecting a support material. In general, plastic
materials, e.g. extruded and biaxially oriented Estar polyethylene
terephthalate film base, provide desirable supports. However, other
materials, e.g. thin metal films are also useful.
Thickness uniformity is important in support selection to minimize large
amplitude, low spatial frequency vertical displacements of the supported
recording layer. In general, support thickness variation usually varies,
as a fixed percentage (e.g. 5%) with total support thickness. For this
reason supports with nominal thicknesses less than about 10 mils are
preferred.
With regard to strength, the supports preferably have a sufficiently high
Young's modulus to sustain utilized tension stresses with small strain.
This is particularly important when using recording layer susceptible to
fracture or similar distortion by support strains. The support also is
desirably highly stable dimensionally with respect to environmental
stresses resulting from excursions of relative humidity and/or
temperature. This characteristic has particular significance because
non-uniform dimensional changes could distort record information.
Additionally it is preferred that support materials have relatively high
dimensional stability (compared to other plastic materials) with regard to
loss of tension over time. Such loss of tension can cause support sag and
materials with relatively long relaxation times therefore are preferred.
Another preferred aspect for supports is a good surface quality compatible
with coating of a smoothing layer.
Now considering the cover sheet, it is important that it be highly
optically transparent at write and/or read wavelengths to be utilized. The
cover sheet also should be substantially non-birefringent, substantially
homogeneous and free from striae and occlusions of an extent that would
interfere with recording and reading. Also, it is desirable that thickness
variation of the cover sheet be sufficiently small to allow for simple
correction of aberrations incident to light passage therethrough. The
nominal thickness preferably is of a magnitude (e.g. less than about
300.mu.) where normal, high quality, high numerical aperture objectives
are available. The strength and dimensional stability characteristics of
the cover sheet desirable are like those described above with respect to
the optical disc supports.
A specific exemplary preferred optical disc support is biaxially oriented
Estar film base of 4 mil nominal thickness having a Young's modulus of
approximately 6.8.times.10.sup.5 psi. A specific exemplary preferred cover
sheet is solvent cast cellulose triacetate (such as the support of Eastman
Color Negative Film 5247) of 5.25 mil nominal thickness and having a
Young's modulus of approximately 6.times.10.sup.5 psi.
The preferred operative spacing between optical disc 11 and cover sheet 14
depends on the numerical aperture of the lens utilized, the thickness of
the cover sheet and the desired degree of protection from dirt and
scratches on the external cover sheet surface. For a cover sheet having a
refractive index of n=1.5, the table set forth below illustrates useful
minimum operative spacings "S" (i.e., between the recording surface and
the bottom of the disc cover in the utilized portion of the disc) that
will provide the same degree of protection from dust, scratches, etc., as
does a 1 mm thick, in situ, transparent overcoat of index n=1.5 used with
a 0.5 NA lens. The table lists S for various NA lenses and cover sheet
thicknesses of 100.mu., 133.4.mu. and 175.mu..
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NA S(100.mu.) S(133.4.mu.)
S(175.mu.)
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0.5 0.545mm 0.5246mm 0.4991mm
0.6 0.4085mm 0.3891mm 0.3648mm
0.65 0.353mm 0.3342mm 0.3108mm
0.7 0.3032mm 0.2853mm 0.2629mm
0.75 0.2578mm 0.2408mm 0.2196mm
0.8 0.2152mm 0.1994mm 0.1797mm
0.85 0.1743mm 0.1601mm 0.1423mm
0.9 0.1332mm 0.1211mm 0.1059mm
0.95 0.08814mm 0.0792mm 0.06797mm
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In view of the "S" values shown in the above table, it will be appreciated
by one skilled in the art, normal working distances (the value of S+0.001"
to 0.004" for clearance between the top of the cover and the lens)
pertain, thus biological objectives can be used.
At this stage, it also should be noted that the optical disc-unit approach
of the present invention is useful with a wide variety of recording
systems (i.e. record stratum and cooperating write/read apparatus). In one
particularly preferred recording system the record stratum 13 includes a
deformable dye-binder layer with a reflective surface or reflective layer
between the dye-binder layer and the support 12. Such dye-binder layers
can be coated in continuous-runs on flexible webs and provide significant
fabrication advantages. U.S. patent application Ser. No. 023,434, filed
Mar. 23, 1979, in the names of Thomas and Wrobel, and U.S. patent
application Ser. No. 124,381, filed Feb. 25, 1980, in the names of Howe
and Wrobel, disclose preferred optical disc configurations. However, the
record stratum can be of many other kinds known in the art, the
significant aspect being that optical disc support 12 is flexible,
preferably continuous, and has, as appropriate for a particular
application, the other characteristics outlined above.
Referring now to FIG. 3, one preferred retaining means 30 for engaging and
urging support 12 and cover sheet 14 into spaced relation can be seen. In
general this embodiment comprises three cooperating annular rings, viz.,
upper ring 31, spacer ring 32 and lower ring 33. As shown, spacer ring 32
is located between annular peripheral portions of support 12 and cover
sheet 14 and has raised flanges extending from central portions of its
upper and lower surfaces at a location to cooperate in a fitting relation
with corresponding grooves formed respectively in the central portions of
upper and lower rings 31 and 33. When the sheet 14 and support 12 are
located respectively between rings 31-32 and 32-33 and the rings are
clamped together into fitting relation, both of those continuous,
flexible, disc-shaped members are drawn into cylindrically symmetrical
tension. This maintains the proper spaced relation between the members,
maintains a flat orientation of the members and provides an air seal of
the space between the members. REtaining clamps 35 are provided around the
retaining means periphery to retain the press-fit cooperation of the
rings.
FIG. 4 discloses another preferred embodiment for retaining means, denoted
generally 40. In this embodiment upper and lower annular retaining rings
41 and 42 respectively have a cooperating female groove and male flange or
rib extending around their opposing central surfaces. Spacer ring 43 is
located between recessed inner portions of the more radially inward
surfaces of rings 41 and 42. In fabrication of this disc-unit embodiment
the spacer ring 43 is placed between support 12 and cover sheet 14, and
adhesive 45 is provided between rings 41, 42 before they are clamped into
their interfitting relation, which tensions the cover sheet and support
and seals the space therebetween The upper and lower rings are held in
this interfitting relation until the adhesive is fixed.
FIG. 5 discloses another preferred embodiment of optical disc-unit 50 in
accord with the present invention. In this embodiment a central spacer
disc 51 is positioned (e.g. affixed to cover sheet 11) between the central
portions of the cover sheet and the optical disc. Also, an annular spacer
ring 52 is similarly positioned between outer regions of the cover sheet
and optical disc. Of course, elements 51 and 52 can be used in combination
or singly. The annular retaining means in this embodiment comprises
retaining rings 53, 54 and 55 having aligned, circumferentially spaced
holes adapted to receive bolts 56. In fabrication, the disc support and
cover sheet are of larger diameter than illustrated and are grasped
outside the retaining rings by means which appropriately tension them. The
retaining means are then secured by bolts 56 and the outer portions of the
support and cover sheet released and trimmed.
FIG. 6-A discloses another preferred embodiment of retaining means, denoted
generally 60. This preferred configuration is similar to the FIG. 3
embodiment except that the spacer ring 62 has a plurality of convex flange
portions or ribs which cooperate with angular "V-shape" grooves of upper
and lower rings 61, 63. Also, it will be noted that the outer sectors of
upper and lower rings 61, 63 have coupled portions which cooperate to
engage the retaining means portions in a tightly interfitting relation. In
this embodiment the engagement is a force fit, however, cooperative thread
portions or other means can be utilized. The engagement of the members 61,
62, 63 tensions the continuous, flexible cover sheet 14 and support 12 and
seals the space therebetween. The specific flange-groove construction of
this embodiment (see FIG. 6-B) provides space for cold flow of the sheet
and support regions engaged therebetween and thus enhances firm retention.
In a preferred mode of fabrication the cover sheet 14 and suppor | | |
