Note: Descriptions are shown in the official language in which they were submitted.
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BACI<GROUND OF THE INVEMTION
1. Field o the Invention
The inv~ntion relates t'o stylus assemblies ~or
cartridges having movable ma~nets findiny particular use in
High Fidelity installations as well as cartridges generally.
,The invention further,relates to a process for making such
assemblies.
' 2. Description of Prior Art
~'~ According to-a known technique, the magnet containing
cartridge cornprises a Isnob, itself integral with a damper
which, is linked to a movable assernbly cornprisiny the stylus
assembly which itself comprises a magnet and a stylus
cantileverO A diamond, sapphire or like stylus is mounted on
~ the cantilever.
' It is well known to fashion such cantilevers out of a
metal tube, the magnet being attached to one end of this tube
"-~ while the diamond or th,e sapphire is set at the other end by
" glue.
~n such embodiments it is necessary that the magnet be
worked so as to permit its attachment. Thus it may be
provided with a ~r,c)ove, and a flat area along its longitudinal
dimension or with a hole extending along its axis.
Such techniclues suf~er from serious inconvelliences,
both ~i'ch ~espect to the manaufacture and the assembly cf ~he
magnet as well as to the formation of the tube itself and its
assembly. ~ further drawbacl~ is thé necessity o se~ting and
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P2316 PAG~ 2
qluing the o~ diamond or the sapphire to the stylus
cantilever.
Thus with respect to the magnet, the rnaynet rnust be
given a required shape while maintaining high machining
consistency, whlch is known to be difficult.
The assembly o~ the tube and of the maynet requires
great precautions. It is, in effect, very difficult to avoid
any deformation of the tube in the course of mounting as ~ell
~ as to maintain a rigid configuration.
The fragility of the asssembly results in great
difficulties hoth in the assembly of the magnet and the tube
as welI as in the attachment, by mounting and gluing of the
diamond or sapphire, to the other end of the tube.
SUMMARY OF THE INVENTION
The present invention has particularly as an object to
overcome these inconveniences and makes it possible to
` , ~ manufacture stylus assemblies o~ very high quality.
A preferred process according to the invention
comprises the steps of providing a mold ha~ing a free space
corresponding to the desired shape of the cantl]ever. The
mold further comprises a chamber adapted to receive the magnet
to be molded into the cantilever. The chamber comprises an
enlarged zone adjacerlt to the free space and a second zone
naving smaller dimensions than the enlarged zone. The second
2S zone has dimensions adapted to closely co;respond to the
magnet. rrhe pro-ess further comprises the step of placing ~he
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~agnet in t'ne enlarged and second zones and thereafter
inserting therrnoplastic material. into the free space and the
enlarged zone t~ produce the stylus assembly prior to removing
the for-m.ed assembly frorn the mold.
The invention provides r and this constitutes an
important characterist;.c of the invention, for fashioning the
body of the stylus cantilever out of a thermoplastic resin in
which the magnet is partially mountedO This resin is
(advantageously reinforced with mineral fibers, particularly
10 glass or carbon, in a proportion on the order of about 20~ to
. 30~. This ~ounting is carried out, according to the
invention, while leaving a sufficient portion of the magnet
exposed so as to allow for the damper, assuri`ng the connection
between the fixed portion and the movable portion of the
15cartridge. The exposed por~ion makes it possible to achieve
t}le desired flexibility and optimal osciilation of the magnet.
'.. 3 According to one embodiment of the invention, a
process of manufacturing such stylus assemblies comprises the
combination of the following steps:
20a~ producing a mold having a free space corresponding
to the desired shape for the stylus cantilever;
b\ providing a chamber in the mold adapted to receive
the ma~net, whose end, in a zone situated adjacent to the
flrst end of the free space is su~stan~ially enlarged, while
25the other end of the chamber is adapted to rigorously
correspond to the dimensioris of ~he magnet;
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P2316 PhGE 4
c~ placing the magnet in the chamber;
d) injecting into tr.e free space and chamber a
thermoplastic resin which fills the free space corresponding
to the cantilever while resùlting in a partial surrounding or
s overmolding of the magnet; and
e) removing the resulting stylus assembly from the
mold.
( ? According to another important embocliment of the
( invention, the diamond or sapphire may be directly inserted
into an orifice provided at the free or second end of the
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stylus cantilever formed of the molded plastic material. Such
an inertion is effectuated, according to the invention,
without gluiny.
` As yet another significant aspect of the invention, it
has been observed that flexibility and satisfactory
oscillation of the magnet could be obtained as a result of the
'~ overmolding of the magnet over bet~Jeen about one quarter and
one half of its total length. Particularly advantageous
results may be obtained in perorming the overmolding over on
-20 the orc'er of one third of the magnet length.
The above objects are further fulfilled by means of
- the stylus assembly of the invention which comprises a movable
magnet. The assembly comprises a stylus cantilever having
irst an~ second erlds. The magnet is mounted on the first end
of the cantilever ancl the secolld en~ of thG cantilever is
adapted to have a stylus rnounted thereon. The cant:ilever is
P2316 1 ~L fi~ ~81 PAGE 5
formed of a thermoplastic material.
The process according to the invention exhibits
significant advantages when compared with previous techniques.
Specifically, by avoiding gluing and assem-bly, a
5 stron~er product is obtained, more rapidly than previously and
with less cost.
The invention further makes it possible to avoid a
difficult machining of the magnet since the shape of the
magnet is no longer as critical as as was previously the case.
- 10 Another particularly important advantage of.the
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invention resides in the great precision wh.ich can be
achieved in the contour of the molded portion. Thus
according to the process: of the invention it is possible
to assure a precise pos~tioning of the damper on the
magnet, at the edge of the overmolding, together with a
very precise centering thereby making possible a perfect
coincidence of the axis of the stylus cantilever and the
axis of the magnet and an exact coincidence of the
vertical planes of symmetry of the magnet and of the
stylus cantilever.
This great precision in the contour of the
molded portion equally makes possible to always assure a
constant length of the stylus and ashape which is always
perfectly defined across its transverse cross-section.
It is thus possible to create, this being an
important aspect of the invention, stylus shapes which
make it possible to achieve both a careful distribution
of the mass and increased resistance to the shocks and
flexion and thus obtain new articles having particularly
desirable characteristics, both with respect to the
qualities of mechanical resistance as with respect to
the improvement of the results obtained in sound repro-
duction.
As yet another important aspect of the invention,
the stylus cantilever may have a cross-section which
diminishes from the portion situated adjacent to the
magnet towards the portion supporting the diamond or the
sapphire.
The invention provides inparticular forgiving the
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P2316 P~GE 7
cantilever a generally converging outline and in particular
regularly converging.
It is thus that advantageous results may be obtained,
according to the inventionl by imparting a conical shape to
the cantilever (the term 'Iconical" being used in its broadest
sense to include all surfaces generated by the movement of
straight line passing throlugh a fixed vertex~, particularly a
cone (surface formed by the movement in a circle cf a straight
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~-' line passing through a vertex~, whose vertex angle is
preferably very small. Particularly fa~70rable results being
obtained for a vertex angle between about one and two degrees
and a preferred angle ~-f about one and one half degrees.
According to another embodiment of the invention, the
cantilever may have the form of a truncated cone with an
elliptical directrix.
According to another embodiment o the invention, the
C! stylus cantilever, having a generally converging outline,
preferably regularly converginq, from the portion adjacent the
magnet. towards the portion supporting the diamond or the
sapphire, has polygonal sections of diminishing surface areas.
As used herein the term polygonal is taken to mean those
polygons having no internal reflex angles.
Another significant feature of the invention provides,
Lor dlrectly mounting, without gluing7 ~he diamond or sapphire
in the plastic material. To this end, a flat portion can be
ashioned on the end of the cantilever in which is arranged
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P2316 P~GE 8
- the mounting orifice.
~his ori~ice can advantageously be fashioned in the
course of molding, in part'icular by means of a point or other
projection integral with ~he mold.
SSince this orificle may be fashioned with the greatest
precision, it is possible,¦according to the invention, to give
it any shape necessary to assure the precise positioning of
' ( ~the diamond, whatever its shape.
( ~Thus the hole may have a slight conicity and the
10entrance cross-section may be sligh,ly smaller than that of
the diamond to be mounted.
`One can equally, depending upor. the particular shape
'Y of the diamond, fashion the holes to have a square, circular
~- or elliptical cross-section.
15The choice of the thermoplastic resin to be used is of
course a function of the mechanical qualities to be conferred
r`'~to the stylus assembly and also a function of the qualities of
sound reproduction which this stylus, thus constituted, makes
it possible to obtain.
20 .As yet a f'urther apect of the invention, particularly
advantageous results may be obtained by utilizing a resin
comprising a polypilenylene oxide, which may comprise mineral
fibers, particularly glass or carbon fibers, said fibers
preferably\comprising on the order of about 20 to 30% of the
25cantilever resin. Particualary advantageous ~esults may
equally be obtained, according to the inven(ion, hy utilizing
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; a resin comprising a polyethylene tetraphthalate, this
resin being able equally to be reinforced with fibers of
glass or carbon in the proportions indicated previously.
In all cases, besides its great acoustical
qualities, the stylus assembly exhibits an elevated
mechanical resistance, particularly a high resistance to
deformation, particularly those resulting from sticking
in the course of manipulation.
BRIEF DESCRIPTION OF THE DRA~INGS
10The following annexed drawings show, solely by
way of non-limiting example preferred embodiments of the
invention.
Figure 1 illustrates, a longitudinal cross-
sectional view of a stylus assembly fashioned according
to the invention;
Figure 2 illustrates, a cross-sectional view of
the damper and stylus assembly and the connection with
the fixed portion of the cartridge;
Figures 3-5 illustrate preferred embodiments of
the cross-sections of the cantilever of the stylus
assembly;
Figures 6-8 illustrate planar views relative to
the different shapes of the end of the stylus cantilever
comprising the orifice adapted to receive the diamond or
sapphire; and
Figure 9 illustrates in vertical cross~section,
a preferred embodiment of the orifice.
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f DESCRIPTION OF PREFERRED EM~ODIM~NTS
/ According to Figure 1, the magnet 1 is partially
; mounted in the end of the cantilever ~ rnade out of a
thermoplastic material alo`ng a length equal to one third of
its total length.
; The stylus cantilever has preferably been fashioned,
according to ~he invention, by molding the assembly and
overmolding the magnet as indicated above.
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~ The cantilever has a flattened portion 3 at its free
end, which comprises an orifice 4 in which a diamond or
sapphire may be directly mounted, without gluing~
Figure 2 illustrates, the same stylus asse~bly carrying
the diamond or the sapphire stylus 5, connected by means of
the damper 6 to the fixed equipment comprising the stylus knob
7.
Figures 3, 4 and 5 illustrate a perspective view, in
f ` transverse cross-section, of three preferred embodiments in
which the cantilevers 2, integral with the magnet 1, have
cross-sections 8a, 8b, and 8c which are respectively
triangular, pc,lygonal and elliptically shaped.
Figures 6-8, illustrate the pre~erred embodiments 4a,
4b and 4c of the orifices adapted for mounting the diamoncl or
sapphire to ~he end of the cantilever 3, as beiny
respect:ively, circular, polygonal or ~lliptical.
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Figure ~ illustrates a longitudinal cross-section of
th~ oriricr, havins a conical rhape 4d in vhirh the diamomi ~r
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-. sapphire is introduced by mounting withou'c glue.
Althou~h l:he invention ilas been described with respect
to particular means, materials and embodirnents, it is to be
understood that the invention is not limited to the .,
particulars disclosed and extends to encompass all equivalent
èmbodiments falling wi~hin the scope of ~he claims.
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