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Description  |
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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.
The invention may be more easily understood and other advantages appear
upon reading the description below, which refers to the following appended
figures:
FIG. 1 illustrates a cassette of known art;
FIG. 2 illustrates the disk-holding plate of a cassette in accordance with
the present invention;
FIG. 3 illustrates an envelope for the plate in FIG. 2;
FIGS. 4 to 10 illustrate in detail various aspects of the invention.
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<.phi.'.sub.e <294 mm
109<.phi.'.sub.i <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.
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