Disc cartridge for accommodating recording discs

A disc cartridge comprising a casing designed to accommodate the disc and to allow the read-out and/or the recording of information while the disc is housed in said casing. The recording discs concerned may be of the type generally designated as "compact disc" or "CD", and more particularly information carrying discs called "CD ROM", although the invention is not limited to this type of disc.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to disc cartridges for accommodating recording discs 
capable of having information recorded thereon and read out by an 
appropriate reading apparatus. More particularly, the invention relates to 
a disc cartridge comprising a casing designed to accomodate the disc and 
to allow the read-out and/or the recording of information while the disc 
is housed in said casing. The recording discs concerned may be of the type 
generally designed as "compact disc" or "CD", and more particularly 
information carrying discs called "CD ROM", although the invention is in 
no way limited to this type of disc. 
2. Related Art 
Disc casings of the type referred to herein are being produced by various 
manufacturers according to a similar basic design in order to be usable in 
standardized reading apparatus, in which the disc is read while housed in 
the casing. Such known disc casings, also called cartridges, generally 
comprise a lower casing element designed to accomodate the disc, the 
bottom of this element comprising an opening, a first part of which is 
designed to provide a passage for a shaft for driving the disc in 
rotation, this shaft belonging to a disc-reading apparatus, and a second 
part of which is designed to provide access for a disc-reading device 
belonging to the same apparatus. The lower casing element is usually 
closed by a casing cover constructed in such a manner as to make possible 
the closing or the opening of the casing and provide a plane wall facing 
the bottom of the lower casing element. 
According to a known casing design, a movable shutter is provided on the 
casing for closing the opening in the bottom of the lower casing element 
to protect the disc against risk of mechanical damage and to limit the 
penetration of dust inside the casing when the disc is not used in the 
reading apparatus. This shutter is provided with a mechanical device for 
ensuring its automatic retraction and disengagement from said opening when 
the casing is introduced into the reading apparatus, and for ensuring its 
return to its closing position when the casing is withdrawn from the 
reading apparatus. Such a device generally includes actuating levers and 
at least one spring and is therefore relatively complicated, fragile and 
expensive. Hence the manufacturing cost of such a disc casing is rather 
high and there is further a non negligible risk of defective functioning, 
in particular when the casing reaches a more or less advanced state of 
wear. 
Prior art disc casings are usually provided with a disc clamping element 
comprising generally a circular part of a plastic material in which is 
housed a plate made of a magnetic material, this clamping element being 
designed to be attracted towards the surface of a frontal magnetized end 
of the driving shaft for rotating the disc, thereby ensuring the locking 
of the disc with this shaft. This clamping element is retained in a 
housing arranged in the cover of the casing opposite the bottom of the 
lower casing element, in such a manner as to provide for free rotation of 
this element in relation to the casing when the same is placed inside the 
reading apparatus and the driving shaft is locked with the disc. The 
presence of such a clamping element as a part of the disc casing also 
leads to increased costs for such a type of casing. 
In the prior art casings, a further major drawback results from a certain 
freedom of the disc to move within the casing when the same is not 
inserted in a reading or recording apparatus, in particular during 
transportation. Such a movement of the disc inside the casing produces 
frictional wear resulting in fine particles which can come to lie on the 
surface of the disc and create perturbations in the reading or recording 
process In the case of recordable discs, currently designated as CDR:s, it 
is particularly important that the surface of the disc remains free form 
dust or other contaminations before the disc is being recorded, which is 
not assured when the disc is housed in a prior art casing where it can 
move inside its compartment. 
SUMMARY OF THE INVENTION 
The present invention provides a disc cartridge which overcomes the 
drawbacks of the prior art casings In particular, the invention overcomes 
the drawbacks resulting from the presence of a shutter mechanism in the 
prior art casings and from the movability of the disc inside these casings 
by providing a cartridge comprising a removable protector member, said 
protector member comprising a bottom plate providing a wall closing the 
opening of the bottom of the lower casing element as well as engaging 
means for engaging the lower casing element so as to keep together the 
protector member and the lower casing element, said engaging means 
comprising locking means adapted to extend through the first part of said 
opening and to become engaged in the central hole of a recording disc 
placed in the lower casing element, so as to maintain the recording disc 
in a fixed position with respect to the lower casing element. 
According to another embodiment, a cartridge overcoming said drawbacks 
comprises a removable locking member placed between the bottom plate and 
the bottom of the lower casing element, said locking member comprising 
locking means adapted to extend through the first part of said opening and 
to become engaged in the central hole of a recording disc placed in the 
lower casing element, so as to maintain the recording disc in a fixed 
position with respect to the lower casing element. 
According to another embodiment avoiding the use of a shutter mechanism, 
the disc cartridge comprises a protector member arranged for removably 
receiving at least said lower casing element, said protector member 
comprising a bottom plate and at least two wall portions, said bottom 
plate providing a wall closing at least that part of the opening of the 
bottom of the lower casing element which provides access for the 
disc-reading device when the latter is placed in said protector member, 
said wall portions being each provided with a ledge extending from the 
free edge of said wall portion over at least a portion of the length of 
said edge, so as to retain said lower casing element when the same is 
placed in said protector member. 
According to a particular embodiment of such a cartridge, the protector 
member forms a drawer wherein said bottom plate provides a wall entirely 
closing the opening of the bottom of the lower casing element when the 
latter is placed in said drawer, said wall portions including two 
side-wall portions and a back-wall portion, each of said wall portions 
being provided with said ledges, so as to retain said lower casing element 
when the same is placed in said drawer. 
The ledge of said back-wall can be arranged for retaining the cover of the 
lower casing element when the same is placed with its cover in the drawer. 
According to a preferred embodiment, the ledges of the wall portions are 
however dimensioned so as to make possible the closing or the opening of 
the casing when the lower casing element is placed in the drawer. 
According to a preferred embodiment of the invention, to overcome the 
drawback of the prior art casings resulting from the movability of the 
disc inside these casings, the cartridge further comprises a removable 
locking member, said locking member comprising at least a first portion 
arranged for fitting into the central part of the opening in the bottom of 
the casing, said locking member being arranged for being maintained in 
place when said first portion of the same is fitted into the central part 
of said opening and the lower casing element is placed inside the drawer, 
said first portion of said locking member comprising locking means adapted 
for becoming engaged in the central hole of the recording disc for 
maintaining said disc in a fixed position with respect to the bottom of 
the lower casing element. According to one embodiment, the locking member 
comprises a second portion extending across said second part of said 
opening in the bottom of the disc casing, up to the back-wall portion of 
the drawer. Preferably, in such an embodiment, at least a part of the 
second portion of the locking member is arranged for fitting into the 
outer part of the opening in the bottom of the lower casing element. 
According to another preferred embodiment, the bottom plate of the drawer 
comprises a central hole arranged for receiving a removable central 
locking member, said locking member being adapted to be fitted into said 
hole and to become engaged in the central hole of the recording disc, so 
as to maintain the disc in a fixed position with respect to the bottom of 
the lower casing element when the same is placed in the drawer. 
According to still another preferred embodiment of the invention, the 
protector member comprises a flexible bottom plate, a front-wall portion 
and a back-wall portion, said ledges, which extend from said side-wall 
portions, having a width allowing said lower casing element to be removed 
from the protector member when at least one of said front-wall and 
back-wall portions is being pressed manually so as to become separated 
from said casing element as a result of a bending of said bottom plate. 
Preferably, the bottom of said lower casing element having at least one 
hole, said bottom plate of said protector member comprises at least one 
protruding part adapted for fitting into said hole of the lower casing 
element. 
According to a particular embodiment of such a cartridge, the bottom plate 
of the protector member comprises a protruding locking portion arranged 
for fitting into at least said first part of the opening in the bottom of 
said lower casing element, said locking portion comprising locking 
elements adapted for becoming engaged in said central hole of said 
recording disc, so as to maintain the disc in a fixed position with 
respect to the bottom of the lower casing element when the same is placed 
in the protector member. 
According to another embodiment, such a cartridge comprises a removable 
locking member, said locking member comprising at least a first portion 
arranged for fitting into said first part of the opening in the bottom of 
the lower casing element, the locking member being arranged for being 
maintained in place when the first portion of the same is fitted into the 
first part of the opening of the lower casing element and the same is 
placed inside the protector member, said first portion of the locking 
member comprising locking elements adapted for becoming engaged in the 
central hole of the recording disc for maintaining the same in a fixed 
position with respect to the bottom of the lower casing element. 
According to a particular embodiment of such a cartridge, the locking 
member comprises a second portion extending across said second part of 
said opening up to the back-wall or the front-wall portion of the 
protector member. Furthermore, the bottom plate of the protector member 
preferably has protruding positioning portions arranged for cooperating 
with border portions of said removable locking member to define the 
position thereof with respect to the bottom plate. 
According to yet another embodiment of the invention, the disc cartridge 
further comprises a removable central locking member and the bottom plate 
of the protector member comprises a central hole arranged for receiving 
said removable central locking member, said locking member being adapted 
for fitting into said hole and for becoming engaged in the central hole of 
the recording disc, so as to maintain said disc in a fixed position with 
respect to the bottom of the lower casing element when the same is placed 
in the protector member. 
It is to be noted that the various embodiments of the invention which 
include a locking member or locking portion all overcome the drawback of 
the prior art casings resulting from the movability of the disc inside 
these casings in addition to the fact that they avoid the use of a shutter 
mechanism.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The cartridge according to the embodiment shown in FIG. 1 comprises a lower 
casing element 1, a casing cover 2 and a protector member in the form of a 
drawer 3. 
The lower casing element 1 includes a compartment 4 for receiving a disc, 
not shown, this compartment being defined by three arcuate wall portions 
5a, 5b, 5c. 
The bottom 6 of the lower casing element 1 has an opening 7, one part 7a of 
which as defined by an arcuate edge 7'a, is arranged in the central part 
of the bottom 6 and is designed to provide a passage for a shaft for 
driving the disc in rotation when the casing formed of parts 1 and 2 is 
placed inside an apparatus for reading the disc in a manner known per se. 
The remaining of the opening 7 is a part 7b , as defined by two edges 7'b, 
arranged to provide access for a disc reading device, for example an 
optical laser reading device, not shown, belonging to the reading 
apparatus. 
The position, the dimensions and the shape of the opening 7 as well as more 
generally the shape and the outer dimensions of the lower casing element 1 
correspond to those of the casings currently available on the market for 
discs of the CD-ROM type. The casing cover 2 is designed so that it may be 
fastened removably to the lower casing element 1 after insertion of a 
disc, not shown, in the compartment 4. The fastening of the cover 2 on 
element 1 is ensured by four hooked retaining fingers 8 consisting of thin 
strips protruding from the bottom 6 and inwards of element 1 in the 
vicinity of each one of its corners and running parallel to side-walls 9 
of element 1. As shown in FIG. 2, the end of each one of these fingers 8 
is provided with a hook 10 arranged so as to snap back on a ledge 11 
protruding inside an opening 12 arranged adjacent each one of the corners 
of the cover 2. For separating the cover 2 from the lower element 1, each 
hook 10 can be released from the ledge 11 by a slight flexion of the 
corresponding finger 8. 
A circle shown in phantom in FIG. 1 indicates the location of an optional 
housing 13 on the lower face 2b of cover 2. This housing 13, when 
provided, is designed for retaining a rotatory disc clamping element 
similar to that of conventional casings. 
The front-wall 9' of the lower casing element 1 has a recessed portion 14 
which is used in particular for the correct insertion of the casing into a 
disc reading apparatus. 
The drawer 3 is arranged for receiving, by a translatory movement as 
illustrated in FIG. 1, the casing assembly comprised of the lower casing 
element 1 closed by its cover 2. The drawer has a bottom 15, two 
side-walls 16 and a back-wall 17. The drawer 3 is shown in FIG. 1 to have 
the full depth of the casing 1, i.e. its bottom 15 and side-walls 16 cover 
at least approximately the entire bottom 6 and side-walls 9 of the lower 
casing element. In this case, preferably an arcuate cut-out 18 is provided 
in the frontal edge of bottom 15, which makes it easier to grip the casing 
with the hand when removing it from the drawer 3. 
According to similar embodiment, the drawer may have a lesser depth than 
the casing 1, but it must cover at least the opening 7 when the casing 1 
is placed in the drawer. 
Two side-ledges 19 extending from the free edges of the side-walls 16 over 
a portion of the length of these edges and an end-ledge 20 extending from 
the free end of the front-wall 17 are arranged for retaining the assembly 
formed by the casing element 1 and its cover 2 when the same is placed in 
the drawer 3. In that position, the drawer 3 completely closes the opening 
7, thereby ensuring an efficient protection of a disc, placed in the 
compartment 4. 
It will be seen that the parts 1, 2 and 3 of the cartridge are of very 
simple shape and can therefore be produced by molding from a plastic 
material at a low cost. The cartridge shown in FIG. 3 is similar to that 
of FIG. 1 and differs from the same mainly in that the cover 2' is 
attached to the lower casing element 1' by means of a hinge. FIG. 4 shows 
this hinge being formed by a constricted wall section 21 between the 
back-wall 22 of the casing element 1' and the cover 2', both elements 1' 
and 2' being advantageously moulded from a plastic material as one part. 
Reference 6' designates the bottom of the casing element 1' and reference 
3' the drawer of the cartridge. 
FIG. 5 shows some further details of an embodiment of the cartridge of the 
present invention, similar to that of FIG. 1. It can in particular be seen 
that the lower casing element 1" has lateral recesses such as 23 which 
cooperate with tongue-like portions 24, 25 in the side walls 16" of the 
drawer 3" to retain the casing element 1" inside the drawer. 
FIG. 5 and the cross-sectional view of FIG. 6 show the bottom 26 of the 
casing element 1" being slightly reduced in height over an area 27 of that 
bottom indicated by a dotted line in FIG. 5. Furthermore, 
FIG. 5 shows the bottom 26 having a hole 28 which is one of a pair of holes 
provided symmetrically in the vicinity of opposite lateral walls 9". In 
FIGS. 5 and 6, the opening of the bottom 26 is designated by the reference 
7" and the cover of the casing element 1" by the reference 2". The 
reference 29 designates a front-wall portion of the lower casing element 
1" and the reference 14", the recessed portion of the front-wall. 
FIG. 7 shows an elongated locking member 30 which is a substantially flat 
part of plastic material adapted for being removably inserted into the 
opening 7" of the lower casing element 1" of FIG. 5, for example. The 
outer shape of locking member 30 therefore corresponds to that of the 
border of the opening 7" and its thickness is such that, when inserted, 
the upper surface 31 and the bottom surface 32 of its body portion 33 are 
flush, respectively, with the inner surface of the bottom 26 surrounding 
the opening 7" and with the outer surface of the bottom 26 where the same 
has the greatest thickness, i.e. outside the zone 27. The border of the 
locking member 30 has a step-shaped profile as shown at 34 in FIGS. 7 and 
8, for fitting into the opening 7". 
Furthermore, the locking member 30 further has two extensions 35, 36, the 
free ends of which are level with the front-wall portion 29 of the lower 
casing element 1" when the locking member 30 is fitted into the opening 
7". Accordingly, when the lower casing element 1" is inserted in the 
drawer 3", the locking member is maintained in a well determined fixed 
position with respect to the bottom 26 of the lower casing element. 
The locking member 30 is provided with a crown-shaped portion 37 which 
comprises protruding tongue-shaped locking elements 38 arranged for 
fitting into the central hole of a recording disc to hold the same in a 
fixed position with respect to the casing 1", 2", more particularly in a 
centered position with respect to the walls or wall portions of its 
compartment, such as the compartment 4. This is quite important in order 
to avoid frictional wear between the disc and the casing as it otherwise 
occurs, in particular during transportation and handling of the 
cartridges. 
FIGS. 9 and 10 show another embodiment of a protector member which can be 
used in place of the above described drawer in connection with a disc 
casing 1", 2" as shown in FIGS. 5 and 6. The protector member 39 comprises 
a bottom plate 40 and two wall-portions, namely front-wall and back-wall 
portions 41, 42. These wall portions are provided with respective ledge 
portions 43, 44 and 45, 46 which extend from the free edges of the wall 
portions and preferably have a width so as to overlap only the 
corresponding wall portions of the lower casing element 1", but not the 
cover 2". This makes it possible to open and close the disc casing even 
when the same is placed in its protector member 39. A ledge portion 47 
extending inwardly from the front-wall 41 has a length and width which are 
smaller than the length and depth of the recessed wall-portion 14" of the 
lower casing element and the length and depth of a corresponding cut-out 
of the cover 2" shown in FIG. 2. The bottom plate 40 of the protector 
member 39 is provided with two protruding parts 48, 49 having the form of 
short pins with a tapered or rounded end. These protruding parts extend 
from the bottom plate 40 at locations corresponding to the location of 
corresponding holes in the bottom of the lower casing element 1", one of 
which, 28, is shown in FIG. 5. 
The protector member 40 has no lateral walls and its width between its 
lateral edges 50, 51 is equal to that of the lower casing element 1". This 
makes it possible to insert the cartridge formed by the assembly of parts 
1", 2" and 39 into ususal storage means provided for storing conventional 
disc casings of standardized dimensions. 
The assembly and disassembly of the disc casing 1", 2" and the protector 
member 39 make use of the inherent flexibility of the bottom plate 40 
which allows resilient bending to separate the opposite wall portions 41, 
42 by the small distance necessary for placing the lower casing element 1" 
between the same. This bending can easily be effected by pressing on the 
ledge portion 47 while holding the member 39 on the opposite side. The 
protruding parts 48, 49 cooperate with the corresponding holes in the 
bottom 26 of the lower casing element to position and maintain the same on 
the bottom plate 40. 
FIGS. 11 and 12 show a protector member similar to the one of FIGS. 9 and 
10. In this embodiment, the bottom plate 40' of the protector member is 
provided with a protruding locking portion 52 comprising a peripheral 
ridge 53 having the shape of the border of the opening 7" in the bottom of 
the lower casing element 1". The locking portion 52 is thus arranged to 
fit into the opening 7". This provides an improved closure of this opening 
and also maintains the lower casing element in its position. This latter 
function can replace that of the protruding parts 48, 49 of FIGS. 9 and 
10, but such protruding parts are preferably provided in addition. The 
locking portion further comprises a crown-shaped portion including 
resilient locking elements 54 projecting from the bottom 40' for becoming 
engaged in the central hole of a recording disc placed inside the casing 
1", 2". The function of these locking elements is the same as that of the 
locking elements of the removable locking member 30 described in relation 
with FIGS. 7 and 8. 
FIGS. 11 and 12 further show the bottom plate 40' having a cut-out portion 
55 which makes it possible to hold the disc casing 1", 2" when assembling 
the same with the protector member or disassembling the same therefrom. 
FIGS. 13 and 14 show another embodiment of a protector member similar to 
those of FIGS. 9 to 12 In this embodiment, the bottom plate 40" is 
provided with protruding positioning portions 56, 57 and 58 which are 
formed as ridges projecting from the bottom plate. The arrangement of 
these ridges is such that it provides for a precise positioning of a 
removable locking member as described in relation with FIGS. 7 and 8. More 
particularly, the ridges 56 and 57 are arranged to be placed on either 
side of the body part 33 of that locking member and ridge 58, having for 
example a circular shape, is placed so that it penetrates into a 
corresponding circular recess in the bottom surface 32 of the locking 
member when that member is placed on the bottom plate 40". This ensures in 
particular that the central, crown-shaped portion 37 of the locking member 
is well centered with respect to the disc compartment. 
The protector member of FIG. 13 is thus designed for use with a removable 
locking member, the structure and the function of which have been 
described in relation with FIGS. 7 and 8. It is to be mentioned that such 
a separable locking member can also be used in connection with a protector 
member as shown in FIGS. 9 and 10, although the presence of positioning 
means, as provided by the ridges 56, 57 and 58, is preferred. 
FIGS. 15 to 17 illustrate an alternative solution for providing a locking 
function to fixedly maintain a recording disc in the cartridge, by means 
of a removable locking member. In this embodiment, the protector member of 
FIG. 15 is provided with a central hole 59 through its bottom plate 40'". 
The outer surface of the bottom plate 40'" has a small circular recess 60 
surrounding the hole 59. 
FIGS. 16 and 17 represent a removable locking member 61 of circular shape 
adapted for fitting into the hole 59 and recess 60 from the outer or 
bottom side of the plate 40'", so that the lower surface of the member 61 
is flush with the outer surface of the protector member. In a similar way 
as the crown-shaped locking portion described in relation with FIGS. 11 
and 12, the locking member 61 has a series of tongue-shaped locking 
elements 62 which are arranged for penetrating into the central hole of a 
recording disc placed inside a casing 1", 2". While the locking function 
of the locking member 61 is similar to that of the removable locking 
member 30 of FIG. 7, the embodiment of a cartridge of FIG. 15 
automatically provides for removal of the locking member when the disc 
casing 1", 2" is separated from the protector member. 
A similar central locking member adapted for insertion through a central 
hole in the protector member can also be used in a structure where the 
disc casing is arranged for being placed in the protector member by a 
translatory movement. In such a case, the locking member will have to be 
removed from the bottom plate of the protector member from the outside 
thereof. 
It is further to be noted that the locking elements of the locking member 
can have various appropriate shapes to fulfill their locking/clamping 
function for holding the disc in a well-defined fixed position inside its 
casing when they are engaged in the central hole of the disc. 
FIGS. 5a, 7a and 8a illustrate a cartridge according to the invention which 
comprises a disc casing with a lower element 1'", similar to the one 
illustrated in FIG. 5 but adapted so that a protector and locking member 
30', as shown in FIGS. 7a and 8a, can be removably mounted thereon. The 
protector and locking member 30' is similar to the locking member 30 of 
FIGS. 7 and 8, but is provided with a nose 34' and a wall and ledge 
portion 35' bearing two protrusions 36', 36". The lower casing element 1'" 
has a notch 7c in its bottom 26 and its recessed front-wall portion 14" 
has two holes 29' and 29". The protrusions 36', 36" are adapted to be 
inserted, respectively, into the holes 29', 29" and the nose 34' is 
adapted to cooperate with a corresponding portion of the bottom 26 so that 
the member 30' can be clipped onto the lower casing element 1'". When 
mounted, the member 30' is fitted in and fully closes the opening 7", 
while its locking elements 38 are maintaining a disc, not shown, in a 
fixed position inside the disc casing, in a similar manner as in the case 
of the locking member of FIGS. 7 and 8. To remove the member 30', the same 
can be seized by the ledge portion of 35' and drawn out until the nose 34' 
can pass through the notch 7c, the central portion of the member 30' being 
then withdrawn from the hole of the disc and the whole member 30' removed 
FIG. 18 shows the position of the elements of a disc casing which have been 
designated by the same reference numerals as in FIG. 1, in relation with a 
shaft 63 of a disc reading apparatus. A disc 64 placed in a compartment 4 
of the casing is, in this embodiment, provided with a circular part having 
a central depression surrounded by a flat circular ledge 65a, the bottom 
65b of the part 65 consisting of a small plate of a non permanently 
magnetizable material, such as soft iron. The part 65 is concentrically 
fixed to the disc 64 so as to surround the central opening thereof. 
When the frontal surface 66 of the magnetized end of shaft 63 is placed in 
the central opening of the disc in a manner known per se, the portion 65b 
of part 65 is attracted by the shaft and rotatably locked therewith. In 
order to avoid excessive air pressure that could build up inside the 
central opening of the disc 64, a small opening 67 is provided in the 
center of part 65 to act as a vent. This prevents uncontrolled movement of 
the part 65 and avoids the rise of a suction effect when the end of shaft 
63 is pulled out from the disc hole. 
As shown in FIG. 18, the cover has no housing for retaining a disc clamping 
element at the location indicated by the circle 13 in FIGS. 1 and 3, but 
simply a thinner portion indicated by the numeral 13' which avoids 
friction from occurring between the clamping element 65 and the inner 
surface of the cover 2 when the cartridge is in the disc reading position. 
FIG. 19 shows a disc casing cover 2'" which is provided with a disc 
clamping element designated as a whole by 68. This clamping element 68 
comprises a ring-shaped part 69 in which a circular plate 70 of not 
permanently magnetizable material is mounted in a concentric position. The 
clamping element has a flexible peripheral edge 71 which makes it possible 
to insert the clamping element into a housing 13 of the cover plate 2'". 
FIG. 20 shows the position of a driving shaft inserted in the reading 
position in a disc casing, the cover 2.sup.IV of which comprises a 
clamping element 72 and a circular plate 70 ' similar to the elements 71 
and 70 of FIG. 19. 
As can be seen in FIG. 20, the clamping device is attracted by the frontal 
surface 66 of the shaft 63, whereby the surface 73 of the clamping device 
presses firmly against the upper surface of disc 74 around the central 
opening thereof, thus locking the disc with the shaft 63. In the 
embodiment of FIG. 20, the housing 13 is closed by a wall element 75, the 
clamping element being inserted into the housing through an opening then 
closed by the wall element 75. 
FIGS. 21 (a) and 21 (b) illustrate the mounting of a clamping device, such 
as 68, in a housing 13 of a cover 2'", as shown in FIG. 19. The 
magnetizable plate 70 is inserted in the member 68, which in turn is 
introduced into the housing 13 by momentarily deforming resilient 
retaining elements of this housing surrounding a central opening. 
FIG. 22 shows an embodiment of a disc 64', similar to the disc 64 of FIG. 
18, which is provided with a clamping element 76 fastened by a snap-on 
mechanism consisting of fingers 77 protruding from the upper surface of 
the disc around the central opening thereof. 
The cartridge according to the present invention can be used with standard 
disc casings or disc casings designed as described above. The standardized 
dimensions and arrangements of such casings allow, in each case, the 
assembly thereof with a protector member to form a cartridge in accordance 
with the present invention.