Optical disk cassette

A cassette for storing and handling optical disks without touching them, including in particular video disks recorded on both sides, the cassette comprising a plate contained in a plastic envelope. The plate comprises a first cavity in which the disk to be protected is positioned. An additional annular cavity is provided in the bottom surface of the plate. The cover of the envelope comprises a cavity of shape matching that of the additional annular cavity such that the recorded areas of both sides of the disk are protected. Additional conical surfaces bearing one on the other are provided in the cover and plate around the edge of the first cavity. Means for locking the plate in the envelope are also provided.

The present invention relates to optical disk cassettes for storing and 
handling such disks whilst protecting them from various types of damage, 
and in particular to video-disk cassettes. 
These cassettes are known under various names, such as container, 
protective cover, package, cartridge and also "caddy". 
The generic name video-disk covers physical supports of high-density 
information allowing the recording and reading, generally by optical 
means, of signals more often representing television images. In the more 
general case of an optical data support, it can cover digital data 
intended for data processing systems used in informatics. 
The data bits on the disk are in the form of disturbances which may be 
detected optically for example, having dimensions of the order of one 
micron. 
It is therefore essential to avoid as far as possible the rubbing of 
objects on the surface or surfaces of the disk carrying data, and even any 
contact likely to apply pressure to these surfaces or deposit foreign 
matter, such as dust. 
In the case of a flexible disk, it is moreover not possible to handle this 
disk by its edge as in the case of rigid disks. It is therefore necessary 
to design a cassette system which, in addition to storing the disk, allows 
its automatic reading in a reader, i.e. without operator intervention. 
Many cassette systems have been proposed. The earlier systems are in forms 
similar to those of audio disk envelopes. In a system, which is presently 
on the market and uses mechanical reading devices, the disk is contained 
in a flexible paper envelope contained in a cardboard envelope. This 
envelope is inserted in a reader, where a mechanism consisting of rollers 
extracts the disk and transfers it to a play turntable. The flexible 
envelope provides poor protection of the disk and the extraction mechanism 
bears on the recorded surface, which may in time damage the disk. In 
addition, the paper envelope may be accidentally folded when being 
extracted manually from the cardboard envelope. 
Other more recent systems comprise a drawer on the floor of which the disk 
rests. A first system proposed and described by the French patent 
application No. 75 27 928, filed on Sept. 11, 1975, and granted under the 
No. 2,324,089 (U.S. Pat. No. 4,084,694), is for a rigid cassette 
containing a rigid drawer itself carrying the video-disk. The cassette is 
inserted in the reader, where studs lock the unit. The envelope is then 
withdrawn and the unit remains held in the reader. During this last stage, 
the disk is drawn towards a plate possessing a prestabilization and 
rotation device. The disk is read optically through a slot in the plate. 
A variant of this system is described in the French patent application No. 
76 17 077, filed on June 4, 1976, and granted under No. 2,253,924. The 
cassette described in this patent application comprises a flexible 
envelope and a rigid plate. The envelope is drawn into the body of the 
reader, where it remains whilst being read. 
The reader comprises a prestabilizer. Any contact between the disk and 
prestabilizer, which is fixed, can thus cause serious damage to the 
recorded surface. Moreover, the disk is not held in the unit and can move 
freely in the cassette. Finally, if the top lip of the cassette is 
distorted, it can rub on the disk when inserting into or taken out of the 
reader. 
In order to prevent the recorded surface from rubbing on the plate fitted 
with a prestabilizer, another cassette arrangement was proposed in the 
French patent application No. 77 20 275, filed on July 1, 1977, and 
granted under the No. 2,396,380. This cassette comprises a plate which 
prestabilizes the disk and on which the disk rests on its unrecorded side. 
This plate has a cover which presses on the disk by means of a guard ring. 
Finally, another French patent application No. 78 05 338, filed on Feb. 24, 
1978, and granted under the No. 2,418,519 (U.S. Pat. No. 4,320,833), 
relates to a cassette with a moulded plastic plate possessing a cavity in 
which the disk is centered, with its unrecorded side in contact with the 
plate, and a cardboard envelope. The disk is held in the cavity in a 
central area by the contact between a multipole magnet attached to the 
plate and metallic lands glued to paper attached to the disk. 
This latter approach, although it perfectly fulfills the functions of 
protecting and storing the disk, complicates the manufacture of this disk 
by the necessity of gluing paper with metallic lands on the plastic disk. 
Finally, none of the proposed systems allows the protection and storage of 
disks recorded on both sides, such disks being particularly advantageous, 
since they are the only disks allowing the recording of long-duration 
features on a single support, such as full-length films or high-density 
optical recording. 
On the contrary, the present invention, whilst retaining all the advantages 
including in particular those of the last patent application mentioned 
above, allows the protection and storage of disks recorded on both sides. 
It also simplifies these disks by eliminating a certain number of 
manufacturing parts and operations. 
The subject of the present invention is therefore an optical disk cassette 
of the type comprising a plate possessing a first circular cavity for 
taking an optical disk and an envelope for containing said plate, the 
envelope having an opening through which the plate may be inserted and the 
disk possessing at least one recording area defined by two concentric 
circles of given first and second diameters, and a cassette in which a 
second annular cavity is provided at the bottom of said first cavity of 
inner and outer diameters respectively less than and greater than those of 
the first and second given diameters, and in which a third cavity also of 
annular shape and of dimensions virtually equal to those of said second 
cavity is provided in the inner surface of the envelope cover, said second 
and third cavities being concentric when the plate is inserted in the 
envelope.

FIG. 1 illustrates a cassette of known art described in U.S. Pat. 
No.4,320,833. The cassette comprises a rectangular cardboard envelope with 
a paper liner (not shown) and a plate moulded in plastic least sensitive 
to electrostatic charges, such as 6.6 polyamide. 
This plate 1 is rectangular in shape and its thickness has been 
deliberately exaggerated in the figure for the sake of clarity. Its rear 
edge (at the rear in the figure) is terminated by a shoulder 11 whose 
thickness is virtually the same as that of the envelope material. This 
shoulder buts against the open edge of the envelope, preventing the plate 
from penetrating completely inside this envelope. This arrangement 
therefore leaves exposed a rounded tongue 110, whose bottom surface 
(hidden in the figure) has a triangular recess for hooking onto an 
extraction stud attached to the reader. The front edge of the plate is 
tapered to facilitate its insertion into the envelope. 
A circular cavity 15 is provided in the top surface of the plate to take 
the disk 3, whose recorded side faces upwards. The diameter of this cavity 
is slightly greater than that of the disk. A central hole 16 lets through 
the drive shaft of the disk 3 when the cassette is inserted in the reader. 
If the cassette were limited to the means described above, the disk would 
move freely in the cavity 15, since it is necessary to provide radial 
clearance, even small, and its recorded side would come into contact with 
the inside of the envelope and rub on the latter, which would result in 
serious damage to the recording. 
In order to avoid such rubbing, a circular groove is provided at the bottom 
of cavity 15 and concentric with this cavity, and a central hole in which 
a multipole magnet 100 in the form of a crown has been placed. This 
magnet, for example, is cut from a sheet of rubber loaded with magnetic 
particles which are then magnetized to produce a succession of alternating 
north and south poles. In order to ensure satisfactory attraction of the 
disk, it is advantageous for the magnet to be slightly proud with respect 
to the plane at the bottom of the cavity 15. 
Such a magnet can attract a disk only if the latter has magnetic 
properties. For this purpose, a conventional flexible video-disk is 
modified in the manner shown in FIG. 2. This disk 3 comprises a recorded 
area defined by circles 31 and 32 and a central hle 33 letting through the 
drive shaft of the reader. A label 34 is glued to the unrecorded side and 
shown by a dotted line in the figure, this label possessing a central hole 
35 of diameter slightly greater than that of hole 33, and whose outer edge 
is cut along a wavy line. This label 34 can bear an inscription and is 
used for carrying a number of magnetic lands 36. When the disk is placed 
in cavity 15 of plate 1, with its unrecorded side facing the surface of 
this cavity, the magnet 100 attracts the lands 36, holding the middle of 
the disk against this surface and thereby immobilizing it. The first 
result is that the unrecorded side can only touch the bottom of the 
cassette without relative movement with respect to the cassette, thereby 
considerably reducing the danger of damage due to such contact and 
eliminating in particular the danger of scratching. Next, when the 
cassette is turned over such that the opening of cavity 15 faces 
downwards, the recorded side of disk 3 tends to fall towards the envelope, 
and since it is held at its center, it curves in the form of a dish such 
that it touches the envelope on a circle defined by its outer edge and 
whose width depends on the weight of the disk, its stiffness, and the 
depth of cavity 15. With normal disks it is possible to obtain for a very 
shallow depth of the cavity a width of this bearing surface sufficiently 
small such that the recorded area does not touch the bottom of the cavity. 
The recorded side therefore cannot touch the envelope and therefore cannot 
be damaged by such contact. 
In a practical embodiment in accordance with known art, use was made of a 
conventional PVC video disk having a thickness of 0.15 mm, a diameter of 
300 mm, a central hole with a diameter of 15 mm and recorded on one side 
between two circles of diameters 296 mm and 120 mm. A label was glued as 
shown in FIG. 2, having a central hole of diameter 20 mm and possessing 
ten 10 mm diameter steel lands having a thickness of 0.06 mm and evenly 
distributed on a circle having a diameter of 90 mm. This label with its 
lands weighed approximately 5 g. 
The present invention, whilst retaining the advantages of the approach 
described above, proposes a cassette arrangement, also comprising a plate 
and envelope, which can also protect an optical disk recorded on both 
sides. The arrangement of this cassette is such that there is no rubbing 
against the areas of the disk carrying recorded information during 
handling, storage and transportation as well as during insertion of the 
disk into or removal of the disk from the reader. In the following text, 
the areas of the disk carrying information is referred to as the recorded 
areas, without limiting the present invention to a particular process of 
recording data on a disk. The cassette also protects the disk from dust 
during storage outside of the reader. 
A practical example of a plate in accordance with the invention is 
described with reference to FIG. 2. This plate is preferably an injection 
moulding in plastic. This plate 1 is generally rectangular in shape with 
recesses in certain parts, and whose average thickness is 1.2 to 1.4 mm. 
This plate possesses a shoulder 11 against which butts the open edge of 
the envelope as described later. This shoulder 11 possesses a triangular 
recess 12 in its bottom surface, allowing the plate to be hooked by a 
retractable stud attached to the reader. The thickness of this shoulder, 
which is referred to as the front part, is approximately 12 mm, this 
dimension having been adopted for reasons of compatibility with present 
readers. This parameter is no way limits the present invention. This 
thickness also determines the overall thickness of the cassette, but may 
be decreased by approximately 50% if it is required to reduce the volume 
taken by the cassette especially during storage when out of the reader. 
The rear part of the plate 13 has been tapered to facilitate insertion of 
the plate into the envelope. A cavity 14 is provided in the top surface of 
the plate to take the disk. The depth of this cavity should match the 
thickness of the disk inserted in the cassette. As a non-restrictive 
example certain flexible disks in present use have a thickness of 
approximately 150 microns. The depth of the cavity may also be increased 
for storing and protecting rigid disks recorded on both sides and whose 
thickness is considerably more than that of flexible disks. 
The disk is centered in cavity 14 which a clearance of approximately 0.5 
mm, and the edge of the cavity is cut at 20.degree. as shown in greater 
detail in FIG. 5 (detail of the section through BB in FIG. 2). In order to 
prevent the recorded area of the disk from rubbing on the plate, and this 
constitues one of the main features of the present invention, an annular 
recess 15 having a depth of 1 to 1.5 mm and internal and external 
diameters .phi..sub.i and .phi..sub.e compatible with those of the 
recorded area of the disk is provided at the bottom of cavity 14. 
As an example, known disks have an overall diameter of approximately 301 mm 
and the following characteristics: 
293&lt;.phi.'.sub.e &lt;294 mm 
109&lt;.phi.'.sub.i &lt;110 mm 
where diameter .phi.'.sub.e corresponds to the start of the recording and 
diameter .phi.'.sub.i corresponds to the end of the recording. 
The transition between the bottom of the cavity 14 and the bottom of the 
annular recess 15 has a gentle slope 150 on diameter .phi.'.sub.e of the 
disk to prevent disk 3 from catching on any asperity. 
In order to let through the shaft of the motor driving disk 3 in rotation 
when the plate is inserted into the reader, a central hole 16 (FIG. 2) is 
provided in the plate. 
Finally, a conical bearing surface 17 is provided around the edge of cavity 
14, on which presses a matching conical bearing surface moulded on one of 
the inside surfaces of the envelope, as described below. 
As mentioned above, plate 1 is recessed in all its non-functional areas in 
order to minimize its production cost. In addition, as a non-restrictive 
example, the material used for its manufacture may be selected amongst the 
following: polyamide, anti-static treated and shock-resistant ABS. 
The envelope 2 is described with reference to FIGS. 3 and 4 (sections 
through AA), representing an overall view and a half-section of the 
envelope 2 respectively. This envelope comprises a cover 20 of particular 
shape and comprising itself surfaces 21 and 22 constituting bearing planes 
for the disk when the cassette is turned over with respect to the position 
shown in FIG. 4, and an annular recess 23 corresponding to diameters 
.phi.'.sub.i and .phi.'.sub.e corresponding to the end and start 
respectively of the recording. The cassette also comprises a rear edge not 
shown, a bottom surface 25 and side walls (24, for example), the part 
opposite the bottom surface being left open to allow insertion of the 
plate into the envelope 2. 
On the front part of the cassette, the envelope also comprises a conical 
bearing surface 26 for bearing against the corresponding conical part 17 
of the plate as a result of additional shapes 18 and 27 in the front part 
of the plate and the front part of the envelope cover respectively, as 
illustrated by the detail in FIG. 6. This figure is a partial section 
through CC of FIG. 2. 
Similarly, on the rear part of the cassette, illustrated by FIG. 7 (partial 
section through EE of FIG. 2), additional shapes 19 and 28 provided on the 
plate and envelope respectively ensure contact between the conical bearing 
surface 17 and the conical bearing surface 27. 
The following describes the interaction between the two main parts of the 
cassette: plate 1 and envelope 2, especially when inserting the cassette 
into or removing it from the disk reader. The envelope 2 slides on the two 
surfaces of plate 1, pinching the latter when closed. 
This action is facilitated by ramps 191 and 192 (FIG. 2) provided either 
side of the plate. Ramp 191 is illustrated in greater detail in FIG. 8. 
An additional groove, such as 201, is provided in the cover 20 of the 
envelope 2 and fits on the ramp 191. 
A clip arrangement then locks the envelope 2 and plate 1 to avoid 
accidental opening in the event of careless handling. For this purpose, 
protrusions 193 and 194 are provided on the sides of plate 1. 
Protrusion 193 is illustrated in greater detail in FIG. 9. Vertical 
grooves, such as 29 shown in FIG. 9, are provided in the side walls of the 
envelope 2. Locking then occurs by penetration of the protrusions into 
these vertical grooves. 
As indicated above, the internal surface 23 of the envelope facing the disk 
3 has the same shape as that of recess 15 in the thickness of the plate 
such that only the unrecorded parts of the disk 3 touch, independent of 
the orientation of the cassette in space. 
Depending on whether the cassette is inserted with one side or the other 
facing upwards, the disk 3 is centered in the cavity 14 of the plate 1 and 
rests either on the plate or on the internal surface of the envelope cover 
and, in both cases, there is no contact with recorded areas of the disk. 
When the envelope 2 is closed on plate 1, contact between the envelope and 
plate is ensured by the pressure of additional shapes 18 and 27 as 
described above with reference to FIG. 6. For this reason, the envelope 
and plate constitute a dustproof compartment. In addition, when the 
envelope 2 is closed on plate 1, the conical bearing surface 17 provided 
around cavity 14 of plate 1 bears on the conical surface 26 provided on 
the internal surface of the envelope 2. This contact creates a conical 
barrier preventing the disk 3 from sliding between the envelope 2 and 
plate 1, which would destroy the disk. The cone angle is such that the 
sliding of the envelope 2 on the plate when opening the cassette is 
accompanied by spreading of the two lips of the envelope, these lips being 
constituted by the cover 20 and the bottom surface 25, by distortion of 
the plastic by approximately 1 mm. This value is for a cassette whose 
other dimensions are those described above. 
When it is required to read the disk 3 contained in the cassette, the 
latter is inserted into a slot in the reader. A system specific to the 
reader extracts the plate 1 carrying the disk 3 from the envelope 2. The 
sliding of the two conical surfaces 17 and 26, one on the other, 
elastically distorts one of the surfaces of the envelope such that it does 
not rub on the surface of the disk 3 facing it. The sliding ramps 191 and 
192 provided on the plate also assist this function by transferring the 
clearance required for this sliding onto the side of the plate carrying 
the disk. During this phase, known as the envelope extraction-insertion 
movement, the elastic distortion increases the thickness of the cassette 
by approximately 1 mm, as mentioned above. Plate 1 is extracted in a known 
manner by means of a stud fitting into the triangular recess 12 described 
above with reference to FIG. 2. 
The disk reader, comprising in particular the mechanism mentioned above, 
does not come within the scope of the present invention and is not 
described. It is similar in every way to known readers. 
Finally, the stacking of cassettes one on top of another is achieved in a 
simple manner by means of two protrusions 30 and 31 (FIG. 3) provided on 
the cover of the envelope 2 and two recesses of matching shape in the 
bottom of this envelope 2. One of these protrusions 30 and one of these 
recesses 32 are shown in greater detail in FIG. 10 (section through DD). 
The two cassettes 2 and 2' are stacked one on top of the other by aligning 
the protrusions 30' with the corresponding recesses 32. 
The present invention is not limited to the practical embodiments described 
above. Summarizing, the cassette in accordance with the present invention 
provides protection against any damage to optical disks recorded on both 
sides. It also enables disks to be read in an entirely automatic manner 
without any handling other than insertion of the cassette into the reader. 
Finally, it is sufficiently sealed to avoid degradation of information 
recorded on a stored disk by the introduction of foreign matter, such as 
dust, into the cassette. 
Although particularly suitable for containing double-sided disks, this does 
not constitute a restriction to the invention, since all other types of 
disk, such as single-sided disks or multilayer disks may be kept in the 
cassettes described by the present invention. Such disks may also be ether 
flexible or rigid.