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Патент USA US2124296

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July 19, 193s.
2,124,296 _
E. c. GUEDQN
TRANSDUCER
Filed July 31. 1935 `
EG. 1.
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, IN VEA/'ron
Emile C. Guedon
2,124,296
Patented July 19, ‘1938
PATENT OFFICE
UNITEDN STATES
2,124,296
TRANSDUGER
to
:Emile vC. Guedon, Audubon, N. J.,a assigner
corporation
Radio Corporation of America,
‘ of Ílela'ware
Y Appncatión july 31, 1935, serial No. 34,016V
10i Claims.
(c1. 17e-¿100.411
sidered in connection with the accompanying
The present invention relatesto transducers
drawing and its scope will be Vpointed ’out in the
or translating devices for converting or translat
appended claims.
ing electrical signal currents into corresponding
mechanical Vmovement of an armature member
greatly enlarged scale of an electro-magnetic
and for converting or translating mechanical
movement of saidarmature member into corre
sponding electrical currents.
.
More particularly, the invention relates to
pickup device or transducer embodying the in
vention, with a cover removed to expose the in
I terior mechanism;
transducersof the electromagnetic pickup type
employed in phonographrecording and repro
10
ducing systems and comprising a vibratory ar
mature adaptedto carry a stylus or needle, an
electric pickup coil surrounding the armature
and a permanent magnet associated with the
15 armature and the coil to provide exciting flux.
The invention has for its primary object to
provide an improved and simplified construction
in a transducer device of the character referred
*to> having operating elements which may be more
20 rapidly and easily assembled and adjusted in
predetermined relation to each other and which
may withstand more severe handling in shipment
land'in servicing than has heretofore been possi
l25
ble in like devices.
_.
,
,
It has been the practice heretofore in trans
ducers of the electric pickup type to provide a
pair of pole pieces for the permanent magnet
having an air gap maintained constant by a non
magnetic bridge piece connecting the pole pieces.
30 The magnet itself is usually removable from the
pole pieces, being held thereon merely'by aspring
tension or by magnetic attraction alone. Be
cause of this arrangement the magnetic circuit
wasoften momentarily broken when the magnet
35 was moved by vibration or by accident in servic~
ing the device, with the result that the magnetic
field thereafter was greatly reduced in strength
and required recharging of the magnet before
efñcient operation could be obtained.
40
It is, therefore, a further objectof the pres
ent invention to provide an improved magnet
and pole piece construction in a transducer de
vice of the electro-magnetic pickupI type, where~>
in the air gap is maintained at a permanent
45
predetermined width-by the magnet itself ¿acting
as a yoke, permanently welded to the pole piece.
It is also a still further object of the invention
to provide an arrangement of parts in a trans
ducer device of the electro-magnetic pickup type
50 which renders such a device compact in construc~
vtion and highly efficient electrically in producing
relatively high output potentials in response to
normal vibratory movement of the armature.
The invention will, however, be better under
stood from the following description when con
V
In the drawing, Fig. 1 is a front view on a
f Fig. 2 is a cross `sectional view of the device
shown in Fig. 1 and on the same scale, taken on
0
line 2-2 vand with the cover in place;
Fig. 3 is a bottom view of the device shown in
Fig..1 also on the same scale;
Figs. 4 and 5 are front views, substantially full 15
size and on a reduced scale from Figs. 1, 2 and
3, showing the magnet and pole piece assembly
before and after completion; and
Fig. 6 is a detail view, partly in cross section
vand on a greatly enlarged scale over that of
Figs. 1, 2 and 3, of the armature assembly of the
o
.
device of Figs. l, 2 and 3.
'
Referring to the drawing, 1 is a molded compo
sition base of insulated material adapted to re'
ceive front and rear cover plates 8 and 9 to
form therewith a housing or casing for the trans
5
ducer operating mechanism. The base plate vis
provided with a rear extension or shank I0 for
connection with a suitable tone arm (not shown),
and embedded therein are the usual electrical 30
The base is provided with two spaced depend
ing leg portions vI2 and each is provided with an
elongated slot or opening as indicated at I3 for"
receiving a clamping screw indicated at I4 for
terminal means II for the device.
the interior mechanism. The clamping bolts also
engage a portion of a rear cover I5forv the mech
anism to hold said cover in place.
On the interior face of the base,l a unitary mag
net structure is provided, comprising a U-shaped
permanent magnet I6> and a pole piece I1 as
shown more clearly in Fig. 4. The pole piece
Il is provided with welding points I8 for engag
ing the poles of the permanent magnet I6 and is
thereby spot welded as indicated in Fig. 5 to- pro
-vide a good magnetic joint at I9, that is, a tight
joint having low reluctance.
The construction shown further includes in
»the pole piece, two rectangular end portions in
5
dicated in Fig. 5 at Ila'. and Ilb providing a flat-
surface at 22 to permit themagnet unit to be 50
seated on a magnetized device (not shown) and
properly charged. The pole piece ends I'Ia and
I'Ib are substantially of the same cross sectional
area as the magnet I6 and between the ends the
pole‘piece is recessed as indicated at 23, Figs. 55
2
_
_
'
2,124,296
4 and 5 to provide a thin bridge portion 24
through which the air gap slot 2U is madel by
cutting or milling after welding the ends to the
magnet.
ber 4I serves to clamp the upper end of the damper
block, as indicated particularly in Fig. 2. A
cover screw 43 engaging the bracket 4| through
It will be seen that a unitary pole piece and
magnet structure is thus provided in which the
an opening in the outer cover member, as shown
in Fig. 2, serves to hold the cover in position.
In order that the damping block 39 may not
pole piece is welded to the magnet so as to insure
a good magnetic circuit at all timeseven when
be under tension or compression, the clamping
screwsV I4 are released slightly when the screw 40
the pickup device isgbeing serviced `in the field.
The magnet acts as a bridge or yoke to maintain Y is inserted through the block. The screws I4 are
a constant air gap between the severed portions
of the pole piece without utilizing a special con
necting link or bridge piece as has been neces
then tightened to hold the assembly on the base.
rThe damping block .is secured to the armature
shaft by frictionV and, to provide a tight joint, the
sary heretofore. 'I'he thin wall bridge portion of armature shaft end is slightly heated to cause the
.material to melt and How about the shaft when
the pole piece is furthermore reduced in cross sec
.
tion at the center on a taper forming the endV the armature ‘assembly is completed as shown in 15
sections toward the center whereby thelresulting Fig. 6. It will be seen that with this construc
pole tips 25, Fig. 5 are tapered. The air gapis, tion the armature spring and damping block together with the armature spacer cushions may be
therefore, substantially equal in length to the .A assembled
as a unit.
20 width of the armature tail or upper Yenol herein
after described.
"
"
'
The unitary pole piece and magnet structure is
provided with two tapped holes 26 to receive the
clamping screws I4 through the slots i3 and per
25 mits the magnet structure 'to be adjusted‘on the
base 'l‘ before ‘being finally clamped in position.
A pickup coil or `winding' 2l is mounted on a
flat strip of insulating material 28, which is
seated against the bottom or lower .ends of the
pole piece. ' The pole piece ends are also tapped to
receive armature clamping screws 29, which serve
to draw a clamping plate V3G against the mount
ing strip 28 as shown to return the latter in` a
seated position against'th’e'ends ’of the pole piece
and to clamp the ends 3|-,32 of the armature
pivot shaft. YThe plate orv armature Clamp 3G is
of non-magnetic material, preferably of Zinc
alloy.
,
.
.
`
'
' Thearmature pivot shaft is integral with the
armature`33 which 'extends through the coil 2l'
and the space or large airi'gap 23, into the main
or narrow air gap 20. ~ _The armature pivot shaft
is surrounded by a spacer cushion -preferably of
rubber in the> form of sleeves 34 whereby the
armature is resiliently mounted when the clampf
ing screws 22 are tightened as shown in'Fig. l.
The armature pivot shaft portion 32 is tapped to
receive aneedleV clamping screw 35 :and extends
frontly to receive the curled en_'d of a centering
50
The pickup coil or winding 21 is provided with
20
output leads 44 `which are connected to the
terminals Il, .as shown. The armature is pro
vided With an axially extending recess for re
ceiving a stylus or needle 45 of any suitable type
and the needle is retained therein by the needle
25
screw 35 as indicated in Fig. 2.
A'second unit of the construction comprises
the coil 27 and mounting strip 28 therefor
which'may be assembled with the magnet and
pole piece structure and as a completed unit is »
entirely removable from the base -lwvithout dis
turbing the relation between the magnet and its
pole piece and without disturbing the air gap and
the flux existing in the magnetic circuit. It
will' be seen that the magnetic circuit may not be
broken by accidental separation of the parts and
that the air gap is permanently fixed to a pre
determined width.
It will further be seen that with the construc
tion shown, the pickup coil or winding lies within
a rela'tivelyrwide air‘gap between magnetic poles
40
and theV armature extends through the coil into
a relatively narrow thin air gap forming the onlylow reluctance path for the flux since the arma
ture clamping plate is of non-magneticrmaterial.
The pickup winding, therefore-lies within the
normal flux path of the magnet and only the tip
ofV the armature liesY in the main or narrow air
gap.` lIthas Ybeen found that this arrangement
securedthereto as shown in Figs; l, 2Vand 6 ' provides high fidelity in the translation of sig 50
particularly. The centering spring is bent at an nals from and to a phonograph record in con
spring 36 which isV soldered'or otherwise suitably
angle to lie across one frontal face of the pole piece
to .be clamped’by a clamping piece 3l drawn in
wardly to 'grip it by af’bolt >38 which is threaded
intoi one of the tapped openings 25 in the pole
piece.
`
_
,.
SÃ;
.
.,
VIt will be noted thatl the Yarmature clamp 30
and the -coil mounting strip 28 are slotted about
60 the clamping screw 29- to permit adjustment of
nection with an audio frequency signal circuit.
It will further be seen that an'advantage in the
construction shown resides in the unitary magnet
and pole piece construction wherein the magnet
is U-shaped providing spaced poles and a pole
piece having end portions welded tothe poles of
the magnet to provide a low reluctance fiux path
throughthe joint.
'
the two members with the coil'Z'l and the arma
ture 33 to center the armature tail or free end
inthe fact that the magnet itself forms ayoke
later in the air gap 20 as shown, particularly in
for the pole pieces or pole pieceto maintain a
. A further advantage in this construction lies 60
Fig. l, before tightening the> clamping member Yfixed air ‘gap without additional bridge elements.
31 by meansv of the bolt 38f
»Y .
~
'I‘he opposite or rear end ofthe armature pivot
shaft *isY extended to receive a block or strip Vof
inertdamping material, such as Viscoloid-,a Du
Pont product, indicated at 39, one end of the strip
70 being .pressed on to the armature shaft as shown
more particula'rlyinFigs. 2 and 6, with the op
posite end extending upwardly to` a position
wherein it isY clamped> Vagainst thelbase member 7.
A vclamping screw 4l)Y extendingnfthroug‘h the
base into a combined bracketY and clamping mem'-V
The air gap is formed by cutting or slotting the
pole piece through the thin central web after
Welding to themagnet. In this manner the pole
piece is prevented from becoming separated from
the maghettov break the magnetic circuit, and the
air gap is maintained permanently at a desired
width.
`
‘
`
v
Y
The entire construction of the device is ar
ranged to facilitate _assembly inspection and ad
justment, and to lprevent impairment'of operation
inthe field.
75
3
2,124,296
net and pole piece structure, a flat plate of non
I claim as my invention:
-
»
‘
v
'
l. A‘magnet assembly for an electro-magnetic
transducer device comprising a magnet,- a pole
piece of magnetic material united therewith by
fusion of metal providing an air gap maintained
permanent wholly by said magnetv as a yoke, said
pole piece having a" thin bridge portion provided
with a slot to form said air gap, said bridge pore
magnetic material» engaging the pole piece ends in
spaced parallel relation to said central web, a coil
mounted on and secured to said plate between said
plate and said central web, a vibratory armature
extending through the coil and into the air gap,
means providing a pivot shaft for the armature
extending transversely of said coil support, a
tion providing the onlyv magnetic conductingpath
10 yexternal to the magnet'between vthe ends .of- said
pole piece, an electrical'winding within thefpole
piece adjacent to ` said bridge portion, and an
armature member extending through the winding
and into said air gap.
15
y
~
2. In an electro-magnetic pickup device, a uni
tary pole piece and magnet structure comprising
a U-shaped magnet, and a pole piece member of
magnetic material extending between and welded
to the poles of said magnet, said member having
20 a thin web between the poles and an air gap
therein maintained fixed in width wholly by said
¿magnet as yoke, and providing the only magnetic
conducting path external to the magnet between
the ends of the pole piece member.
3. In an electro-magnetic pickup device, the
25
, combination with a U-shaped magnet, of a uni
tary pole piece of magnetic material permanently
united therewith at the magnet pole faces, said
. pole piece providing a portion adjacent each pole
30 of the magnet of substantially the same cross
sectional area as'the magnet and a thin unitary
bridge portion therebetween of lesser cross-sec
35
clamping> plate of non-magnetic material for en- `
gaging the armature shaft, and means for adjust 10
ably-securing saidA clamping and- mounting plates
to said pole piece member.
,
f
7. An electromagnetic pickup device comprising
a UÃ-shaped magnet, a pole piece member having
ends welded to the magnet poles and having a 15
thin central web slotted to provide a ñxed air gap,
said magnet and pole piece thereby providing a
unitary magnet and pole piece structure, a ñat
plate of non-magnetic material engaging the pole
piece ends in spaced parallel relation to said cen 20
tral web, a coil mounted on and secured to said
plate between said plate and said central web, a
vibratory armature extending through the coil
and into the air gap, means providing a pivot
shaft for the armature extending transversely of 25
said coil support, a centering spring for the arma
ture secured at one end to one end of said pivot
shaft, means for adjustably clamping the oppo
site end of the armature centering spring to one
end of the ypole piece, a block of vibration damp 30
ing material connected with the opposite end of
said pivot shaft, a base for said pickup device,
tional area, said bridge portion constituting the ' means for clamping said block of damping mate
rial to said base in spaced relation to its connec
only magnetic conducting element external to tion
with the pivot shaft, and means for adjust-` 35
the magnet betweenv the ends of said pole piece
and having a slot providing an air gap between
ably securing said unitary magnet and pole piece
said ends and said magnet thereby providing a
yoke to hold said pole piece permanently with
structure to said base member.
said air gap- fixed.
4. In an electro-magnetic pickup device, the
ing ends welded to- the magnet poles and having 40
combination with a magnet having poles in spaced
relation to each other, of a pole piece permanently
united with said poles and extending therebe
tween, said pole piece providing endportions of
relatively large cross-sectional area, one adja
45 cent to and contacting each of said poles, and a
thin unitary bridge portion of lesser cross-sec
tional area therebetween having a slot providing
an air gap between the magnet poles, said magnet
thereby providing a yoke to hold said pole piece
50 permanently with said air gap fixed, and said
bridge portion providing the only magnetic con
ducting member external to the magnet and be
tween the poles thereof.
8. An electromagnetic pickup device compris
ing a U-shaped magnet, a pole piece member hav
a thin central web slotted to provide a ñxed air
gap, said magnet and pole piece thereby providing
a unitary magnet and pole piece structure, a flat
plate of non-magnetic material engaging the
pole piece ends in spaced parallel relation to said 45
central web, a coil mounted on and secured to said
plate between said plate and said central web, al
vibratory armature extending through the coil
and into the air gap, means providing a pivot
shaft for the armature extending transversely of
said coil support, means providing a resilient
bearing for the pivot shaft on op-posite sides of
and adjacent to the armature, the ends of the
shaft projecting axially from said bearing means,
a centering spring for the armature secured to 55
5. An electro-mechanical translating device. one projecting end of said shaft, and a block of
55 comprising a magnet having poles aligned to pro
vide a gap between them, a pole piece member of
magnetic material bridging said gap and united
at its end >portions with the magnet poles by
fusion therewith, and said member having be
60
tween its end portions a thin bridge portion of
`relatively small cross-sectional area providing the
only magnetic circuit element external to the
65
magnet between said end and having an air gap
maintained constant in width by said magnet as
a yoke.
.
`
6. An electromagnetic pickup device comprising
posite projecting end of said shaft.
9. A transducer of the electromagnetic pickup
type comprising in combination a base member 60
of insulating material, a magnet and pole piece
structure comprising a U-shaped permanent
magnet and a rectangular pole piece bridge across
the ends of said `magnet and welded thereto to
provide a low reluctance magnetic circuit, said
pole piece being'recessed intermediate between '
its ends to receive a pickup winding and to pro»
to provide a fixed air gap maintained permanent
wholly by said magnet as a yoke and providing
the only magnetic conducting path external to the
vide a thin bridge between the ends of the magnet,
and said bridge portion having a transverse slot
and being tapered from the ends in the direction 70
of said slot to provide an air gap of predetermined
width and length, an armature having one end
positioned in said air gap and having an armature
magnet between the magnet poles, said magnet
versely on opposite sides thereof, means providing
a lU -shaped magnet, a pole piece .member of mag
netic material having ends welded to the magnet
~70 poles and having 'a thin intermediate web slotted
15
vibration damping material secured to the op
and pole piece thereby providing a unitary mag
pivot shaft integral therewith extending trans
4
2,124,296
a resilient pivot bearing for said armature shaft,
an armature centering spring secured to one end
of said pivot shaft, means for clamping _ said
spring to said pole piece, a block of vibration
damping material mounted 0n the oppositeend
of said armature, means for clamping said block
of damping material to the base member, and
means for adjustably clamping said magnet and
pole piece structure to said base member.
.
10. Inran electromagnetic transducer device, a
unitary magnet and pole piece structure having
an air gap maintained permanent in width bythe
magnet element thereof as a yoke and having a
thin severed- central web providing pole tips, said
web forming the only low reluctance flux path
between the magnet poles, an electrical pickup
winding lying within the normal ñux path of said
magnet and pole piece structure, and an armature
extending through the coil >and intothe air gap,
said armature having a pivot shaft, an armature
centering spring connected with one end of said
shaft anda block of vibration damping material 10
connected with the opposite end of said shaft.
EMILE C. GUEDON.
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