Disk unit with retaining ring

This disclosure relates to an optical disk unit with two states in which the web assembly is in different circumferentially-symmetric tensions. One tension is sufficiently great to provide the desired degree of planarity when used with write/read apparatus. The other tension is significantly reduced, keeping the web assembly materials well below their elastic limits to reduce tension and prolong product life. The optical disk unit includes a flexible disk-shaped web assembly including a support web and preferably an opposed cover sheet. An annular retaining ring engages the web assembly around its periphery. The support web carries a record layer with an information storage region. The annular retaining ring includes selectively operable means for changing the state of the disk unit to adjust the web assembly tension between the two tensions. In one embodiment, the state-changing means includes a bi-stable spring having a stable condition for each of the two web assembly tensions. In its high-tension state, the spring bears against the web assembly, deforming the web assembly to increase its tension.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a record medium and apparatus useful in 
high density storage of information by optical write and/or read 
(hereinafter referred to as write/read) methods, and more particularly to 
improved configurations of optical disk units for use with optical disk 
write/read apparatus. 
2. Description of the Prior Art 
Commonly-assigned U.S. Pat. No. 4,365,258, issued Dec. 21, 1982 to F. F. 
Geyer and E. M. Leonard discloses several optical disk units adapted for 
high density storage of information. One disclosed configuration comprises 
(i) a flexible, disk-shaped support web carrying a record layer; (ii) a 
transparent disk cover sheet opposing the record layer, and (iii) an 
annular retaining ring for holding the support web and cover sheet, 
collectively referred to as the web assembly, in a relatively low 
circumferentially-symmetric tension and tensioned to an operating tension 
when drawn over a rotatable annular locating surface on the disk unit 
receiving structure of the optical disk write/read apparatus. Thus the 
disk unit can normally be kept with the web assembly in low "storage" 
tension, and used with the web assembly in higher "operating" tension to 
enhance flatness. 
Preferred tensions for the disk-shaped support and cover sheet materials 
are from substantially zero to just below the elastic limit, or yield 
point, of those materials. More specifically, the preferred tension 
depends upon the desired degree of planarity for the particular member 
(i.e. size, composition, etc.) used. It is preferred that "storage" and 
"operating" support material tensions be below the elastic limit of the 
particular material; however, in certain applications some yield can be 
acceptable as long as surface planarity remains in the desired tolerance. 
In general, the tension (particularly storage tension) should be selected 
with respect to the support material so that the stressed material's 
continuous relaxation over time (i.e. material creep) is slow enough to 
ensure adequate spacing and planarizing tension throughout the expected 
product life period. 
The above-described disk unit configurations perform admirably. However, it 
is desirable in some applications to increase the difference between the 
"storage" tension and the "operating" tension beyond that obtainable by 
drawing the web assembly over an annular locating surface. Some web 
materials exhibit objectionably shortened expected product life when 
subjected to normal "storage" tensions, due to the material's continuous 
relaxation over time. Yet "storage" tension cannot be decreased without 
adversely affecting surface planarity at "operating" tension, because the 
write/read apparatus is capable of increasing tensions by only a 
predetermined amount. 
SUMMARY OF THE INVENTION 
The present invention is an improvement over the disk unit described in 
U.S. Pat. No. 4,365,258. It provides an optical disk unit with two states 
in which the web assembly is in different circumferentially-symmetric 
tensions. One tension is sufficiently great to provide the desired degree 
of planarity when used with write/read apparatus. The other tension is 
significantly reduced, keeping the web assembly materials well below their 
elastic limits to reduce relaxation and prolong product life. 
An optical disk unit according to the invention includes a flexible 
disk-shaped web assembly including a support web and preferably an opposed 
cover sheet. An annular retaining ring engages the web assembly around its 
periphery. The support web carries a record layer with an information 
storage resion. The annular retaining ring includes selectively operable 
means for changing the state of the disk unit to adjust the web assembly 
tension between the two tensions mentioned in the preceding paragraph. In 
the preferred embodiment, the state-changing means includes a bi-stable 
spring having a stable condition for each of the two web assembly 
tensions. In its high-tension state, the spring bears against the web 
assembly, deforming the web assembly to increase its tension. 
The invention and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiment presented below.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to schematic FIGS. 1 and 2, an optical disk unit 10 web assembly 
which includes a flexible, disk-shaped support web 12 having a heat 
deformable, dye binder record layer (and other appropriate layers) 
overlying a reflective surface of the support. The web assembly preferably 
also includes a continuous, flexible, disk-shaped cover sheet 14 which is 
substantially transparent with respect to the write and/or read optical 
wavelength suitable for use with the record layer. The diameter of cover 
sheet 14 corresponds generally to the diameter of support web 12. 
Cover sheet 14 and disk-shaped support web 12 are retained in 
circumferentially-symmetric tension by an annular retaining ring having 
inner and outer members 16 and 18, respectively, which engage support web 
12 and cover sheet 14 substantially continuously around their respective 
annular peripheral portions. The support web and the cover sheet are held 
apart by an annular spacer 20. The record layer on support web 12 has a 
predetermined annular information storage region radially inwardly of the 
spacer. Reference is made to aforementioned U.S. Pat. No. 4,365,258 for a 
description of useful and preferred materials and characteristics for the 
support web and the cover sheet. 
It is preferred that the cooperative engagement between disk-shaped support 
12, cover sheet 14, and the retaining ring (including spacer 20) 
significantly seal the space between the record layer on support web 12 
and the opposed surface of cover sheet 14. Although not included in the 
illustrated embodiment, the optical disk unit may have a central right hub 
including spacer means for maintaining proper spacing between the record 
layer and the cover sheet. 
Referring more specifically to the retaining ring, inner ring member 16 is 
an annual steel washer which has been conically deformed, and which is 
restrained from returning to its flat configuration by outer ring member 
18. The material of which inner ring member 16 is made is preferably cold 
rolled high-grade steel (approximately 0.8% carbon content). Spring metal 
may be used, but is not believed necessary because the expected number of 
flexures during product life will be relatively small. 
The preferred assembly operation, or manufacturing method, is schematically 
illustrated in FIGS. 3-7. A composite 30 is held above an annular clamping 
ring 36, as shown in FIG. 3, in circumferentially-symmetric tension. 
Composite 30 includes a web 32 from which support web 12 (FIG. 2) is cut, 
a web 34 from which cover sheet 14 (also FIG. 2) is cut, and an 
intermediate annular spacer 20. Webs 32 and 34 are illustrated in FIGS. 
3-8 by single lines because of space limitations and for clarity. 
Referring to FIG. 4, an inner ring member 16 is aligned with clamping ring 
36, with composite 30 therebetween. Ring member 16 has been pressed upon a 
plug 38 to conically deform the ring member, reducing its outer diameter. 
The plug and ring member are lowered into clamping ring 36 as shown in 
FIG. 5, and then the plug is removed, FIG. 6. 
Removal of plug 38 from inner ring member 16 permits the ring member to 
spring back towards its flat, undeformed configuration until restrained by 
the upturned flange of clamp ring 36. Web composite 30 is captured between 
ring member 16 and clamp ring 36, and can be trimmed without losing its 
tension. 
Crimping the clamp ring to form outer ring member 18, FIG. 7, completes the 
assembly process. The disk unit is in a state of significantly reduced web 
assembly tension with the web assembly tensions well below their elastic 
limits. 
To increase web assembly tension, inner ring member 16 is pushed "through" 
outer ring member 18. The inner ring member snaps to its second stable 
condition shown in FIG. 8, and pushes on the web assembly. This increases 
the web assembly tension sufficiently to provide the desired degree of 
planarity when the disk unit is used with write/read apparatus. 
The invention has been described in detail with particular reference to a 
preferred embodiment thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention. For example, although the invention has been described in an 
embodiment wherein the web assembly includes both a support web and a 
cover sheet, the invention is useful with optical disk units which have 
only an edge constrained support web and no cover sheet.