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Патент USA US2118608

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May 24, 1938.
J. M. KENDALL‘
, ELECTROMAGNETIC TRANVSLATING DEVJECE
:
Filed Feb. 8. 1955
2,118,608
Patented May 24, 1938
2,118,608
UNITED STATES PATENT OFFICE
2,118,608'
ELECTROMAGNETIC TRAN SLATING DEVICE
James M. Kendall, Tulsa, Okla, assignor to Radio
Corporation of America, a corporation of Del
aware
Application February 8, 1935, Serial No. 5,522
2 Claims. (Cl. 179-10041)
the two portions. A strip of spring material hav
My invention relates to electromagnetic trans
lating devices and more particularly to electrical
ing one end thereof fastened to the armature and
pickups of the type exempli?ed in the co-pending
the opposite end anchored in ?xed relationship
thereto functions to maintain the armature in
position after initial adjustment in the air gap.
The novel features that I consider character
istic of my invention are set forth with particu
larity in the appended claims. The invention
itself, however, both as to its organization and
method of operation, together with additional ob
application of Emile C. Guedon, Serial No.
"5 703,742, ?led December 23, 1933, and assigned to
the Radio Corporation of America.
In the aforementioned co-pending application,
substantially identical structure as that shown
and described in the present application is dis
110 closed.
Certain features shown and described
but not claimed in the co-pending application
constitute the subject-matter of my invention.
In prior art devices with which I am familiar,
satisfactory operating charactertistics are usually
1 attended by a multiplicity‘of parts. The produc
tion cost of electrical pickups of this character is,
of course, relatively high, and the time required
for the assembly and adjustment of the parts
thereof retards productionrate and further adds
~20 ‘to the cost of the pickups.
It is, accordingly, the primary object of my in
ventionto provide an electrical pickup which, al~
though having satisfactory operating charac
teristics, lends itself to cheap and speedy produc
es tlon.
A further object of my invention is to provide
an electrical pickup in which the design of the
parts thereof facilitates their assembly and ad
justment.
130
A still further object of my invention is to pro
vide in an electrical pickup improved means for
adjusting and maintaining the adjustment of an
armature in position in an air gap between two
jects and advantages thereof, will best be under
stood from the following description of a speci?c
embodiment when read in connection with the
accompanying drawing, in which
Figure 1 is a longitudinal section of an elec
trical pickup constructed in accordance with my
invention;
'
Fig. 2 is a view taken on the line II-~II of
Fig. 1;
Fig. 3 is a view taken on the line IlI--III of ‘V
Fig. 1;
Fig. 4 is a perspective view of an integral pole
piece structure comprising a part of my improved
electrical pickup;
Fig. 5 is a bottom view of the pole piece struc
ture shown in Fig. 4; and
25
Fig. 6 is a perspective view of a frame mem
ber which is utilized to support and maintain
various parts of my electrical pickup in position.
Referring to Figs. 1, 2 and 3, there is shown an
electrical pickup including a casing I which serves
to house the pickup unit proper. The various
parts of the pickup including a permanent mag
pole pieces thereof.
net 3 are mounted upon a frame member 5 of
In a preferred embodiment of my invention, I
employ an integral pole piece structure com
non-magnetic material, shown more clearly in 35
prising a plate of magnetic material having two
parallel spaced portions and. of substantially
U-shape con?guration. One of the portions of
:40 the‘structure is slotted whereby two pole pieces
having a non-adjustable air gap therebetween
are provided for a permanent magnet. The other
portion of the structure is provided with an open
ing opposite the air gap and a slot extending from
the opening and severing an ‘edge of the portion.
_ When positioned in the pickup, the portion of
the pole piece structure which‘ provides the pole
pieces is positioned above and being integral
therewith is supported by the other or lower por
550 tion of the structure.
. Passing through the opening in the lower por
tion of the pole piece structure and extending
into and positioned in the air gap in the upper
portion is an armature which is encircled by a
at '?xed‘ pickup coil which is sandwiched in between
Fig. 6, and the frame member and the pickup
parts mounted thereon are retained in position
within the casing l by screws 1, the heads of
which are counter-sunk in the face of the casing
and threaded into tapped openings 9 in the up
standing portions ll of the front of the frame
member 5. It will be noted that when the frame
member 5 and pickup unit are positioned within
the casing l, in the manner described above, the
bottom portion l3 of the frame member consti 4.6
tutes a cover plate for the open bottom of the
casing through which the frame member with the
various pickup parts mounted thereon is inserted
when assembling. Also, it will be noted from an
inspection of Figs. 1 and 3 that a panel [5 of
insulating material which functions as a termi
nal board and cover plate, is located within the
casing I at the rear of the pickup assembly.
The panel is retained in position by a screw II
which is threaded into a tapped opening 19 in‘
2
2,118,608
an upstanding portion 2i of the rear of the frame
member 5. Thus, it will be seen that the pickup
unit is completely enclosed within the casing |.
The various parts of the pickup unit which are
mounted upon the frame member 5, and housed
within the casing l, as described in the foregoing,
include the permanent U-shape magnet 3, an in
tegral pole piece structure 23 including pole
pieces 25 for the magnet, an armature 21 and a
10 pickup coil 29.
ber. Means of egress for the bottom end of the
armature 21 in which the stylus 31 is clamped
is provided by an opening 53 located about mid
way the length of the groove 5|.
The complete assembly of the various parts
of the pickup unit upon the frame member 5,
in their cooperative relationship and their order
of assembly, will now be described.
The pivot shaft 35 of the armature 21 is po
sitioned within the bearing groove 5| in the bot
10
The integral pole piece structure 23, the design
of which will be more clearly understood with
reference to Figs. 4 and 5, is constituted by the
bottom portion of the armature extending down
substantially U-shape member 23 of magnetic
material having two parallel spaced portions 24
up coil 29 which is in the form of a ?at torus is
positioned in between. the upper and lower por 15
tom portion I3 of the frame member 5 with the
wardly through the opening 53. Next, the pick
and 26 respectively. The upper portion 24 of the
member is provided with an air gap 30 which
extends transversely thereof and divides the por
tion into the two pole pieces 25 for the respective
pole faces of the U -magnet 3 which is positioned
tions of the U-shape pole piece structure 23 and
the cylindrical opening 55 in the coil is aligned
with the opening 4| in the lower porton 26 of the
pole piece structure and the air gap 30 in the
upper portion 24. The pickup coil 29 is retained 20
thereon. In order that the air gap 39 may be
of a suitable length for the ?attened end 3| of
the armature 21 which is centered therein, as
will be described later, the adjacent ends of the
lating material which extends below the pickup
pole pieces 25 are of reduced cross sectional area
as will be clearly seen in Fig. 4. Sandwiched in
between the lower and upper portions of the pole
piece structure 23 and encircling the armature
21 is the pickup coil 29.
The armature 21 is constituted by the ?attened
portion 3| which is positioned in the air gap 30,
a cylindrical portion 33 extending below the
flattened portion 3|, and a pivot shaft 35 ex
tending on either side and at right angles to the
cylindrical portion. The lower end of the cy
lindrical portion 33 is hollow to permit the in
sertion of a stylus 31 which is clamped in po
sition by means of a set screw 39 which is thread
ed into the forward end of the pivot shaft.
Directly below the air gap 3|] in the upper por
40
tion 24 is an opening 4| in the lower portion
26 of the pole piece member 23 through which the
cylindrical portion 33 of the armature 21 ex
tends. Extending from the opening 4| and sev
ering an edge 43 of the lower portion 26 of the
pole piece member is a slot 45, which serves to
prevent the said portion from acting as a “short
circuited turn” around the opening 4|. A short
circuited turn around the opening 4| would ma
terially reduce the efficiency of the pickup. It
will be seen, therefore, that the slot 45 consti
tutes an important feature of my invention.
A bearing for the pivot shaft 35 of the arma
ture 21 is provided by complementary grooves 46
and 5| in the bottom and top sides respectively
of the lower portion 26 of the pole piece struc
ture 23 and the bottom portion l3 of the frame
member 5. The bearing groove 46 runs along
the slot 45 from the severed edge 43 to the open
ing 4| and continues from the opposite side of
the opening to the farther side of the pole piece
structure as is clearly shown in Fig. 5.
The com
plementary bearing groove 5| is hereinafter de
scribed in connection with the frame member 5.
The aforementioned frame member 5 on which
the various parts of the pickup proper are mount
ed, and which is clearly illustrated in Fig. 6 of
the drawing, is constituted by the bottom por
tion l3, the upstanding and spaced front por
tions || connected at their tops by the portion
41, and the upstanding and spaced portions 2|
and 49 at the rear of the frame member. The
complementary bearing groove 5| for the arma
ture pivot shaft 35 extends along the upper sur
face of the bottom portion l3 of the frame mem
in position by means of a bushing 51 of insu
coil and fits tightly into the opening 4| in the
lower portion 26 of the pole piece structure 23.
The pole piece structure 23 including the pick
25
up coil 29 is positioned upon the bottom portion
l3 of the frame member with the bearing groove
46 in the lower portion 26 of the pole piece struc
ture enveloping the top half of the armature
pivot shaft 35. When the pole piece structure 23 30
is so positioned, the armature 21 extends up
wardly through the opening 4| and through the
bushing 51, the ?attened portion 3| of the arma
ture 21 extending into the air gap 30 between
the pole pieces 25. The pole piece structure 23 35
is retained ?rmly in position by screws 56 which
extend through openings 58 in the bottom portion
| 3 of the frame member 5 and threaded into
tapped openings 59 located on either side of the
opening 4| in the lower portion 26 of the pole 40
piece structure.
It will be noted in Figs. 1 and 2 that the ar
mature pivot shaft 35 is provided with rubber
bushings or sleeves 6| which are slipped thereon
prior to assembly. The ?exible bushings 6| func
tion to permit movement of the armature 21
about its pivot shaft.
7 Clamped to the top portion 41 of the front of
the frame member 5 by the plate and screw 63
and 65 respectively and affixed to the forward
end of the pivot shaft 35 of the armature 21 is
a block 61 of the inert, damping material, such
as the composition commercially known as Visco
loid or the like. The damping block 61 functions
to level the frequency response of the pickup.
After the several parts of the pickup unit are
mounted upon the frame member 5 as described,
the ?attened portion 3| of the armature 21 is
centered in the air gap 30 by a centering spring
69. The spring 69, which has a sharp bend about
midway thereof, has an end attached to the rear
end of the armature pivot shaft 35 as by extend
ing into an opening therein and soldering, as is
clearly shown in Fig. 2. The other end of the
centering spring 69 is clamped between the up
standing portion 49 of the frame member 5 and
a washer 1| by the screw 13 after the armature
has been centered in the air gap 29. Should it
be necessary to reposition the armature in the
air gap, it is, of course, only necessary to release
50
65
65
70
the adjusting spring by loosening the screw 13.
In operation, it will be noted that the armature
centering spring 69 acts in bending rather than
in torsion, and it has been found that the spring
76
2,118,608
functions efficiently in this manner and lends
itself to easy adjustment.
After the adjustment of the armature 21 is
made, the magnet 3 is placed in position with its
respective pole faces in, contact with the pole
pieces 25, as clearly shown in Fig. 2. The as
sembly is then inserted through the bottom of
the casing I and fastened therein. by the screws
7, as previously described. From an inspection
of Fig. 2, it will be seen that the magnet 3 is
clamped between the pole pieces 25v and the in
wardly protruding portions 15 at the top of the
casing I. Also, in Figs. 1 and 3 it will be seen
that leads 11 for the pickup coil 29 are soldered
to suitable clips on the terminal board I5.
The integral pole piece structure 23 which is
an important part of my invention is preferably
constructed in the following manner. A plate of
magnetic material is bent substantially in the
shape of a U to provide the two spaced parallel
portions 24 and 26. Two semi-circular cuts are
then made in the opposite sides of the portion 24
whereby to reduce the width of the portion sub
stantially midway its length. A slot is then. cut
transversely of the reduced portion whereby the
air gap 30 and the pole pieces 25 are formed.
Next, the opposite portion 26 of the structure 23
is drilled opposite the air gap 30 to form the
opening 4| for the armature 21, and from the
opening to- the edge 43 of the structure the slot
45' is cut to- prevent the “short-circuited turn” as
heretofore described. The groove 46 for the ar
mature pivot shaft 35 is then cut on the under
side of the lower portion 26 of the structure and
the two openings 59 for fastening the structure
to the frame member 5 are tapped on opposite
sides of the opening 4|.
From the foregoing, it will be seen that I have
provided an electrical pickup, the various parts of
40 which are so designed that they lend themselves
3
to cheap and speedy production and facilitate the
assembly and adjustment of the pickup.
Although I have shown and described a pre
ferred embodiment of my invention, I am fully
aware that various modi?cations thereof may be
made. My invention, therefore, is not to be re
stricted except insofar as is necessitated by the
prior art and the spirit of the appended claims.
I claim as my invention:
1. In an electrical pickup, a frame member, a 10
permanent magnet, pol-e pieces therefor carried
by said frame member and having an air gap
therebetween, an armature having a shaft posi
tioned with its axis parallel with said air gap,
said armature having a portion extending into 15
said air gap, a translating coil for said armature
and means comprising a strip of spring material
having one end ?xed to one end of said shaft
and its other end adjustably secured to said frame
member, said strip extending approximately at 20
right angles to said axis for centering said por
tion in said air gap.
2. In an electrical pickup, a frame member, a
permanent magnet, pole pieces therefor carried
by said frame member and having an air gap
therebetween, an armature having a shaft posi
tioned with its axis parallel with said air gap, said
armature having a portion thereof extending into
said air gap, a translating coil for said armature
and means for centering said portion in said air 30
gap, said means comprising a strip of spring ma
terial having a portion thereof bent at an angle
with respect to the remaining portion and having
one of said portions fastened to said armature
shaft and the other portion adjustably secured 35
to said frame member, and said strip being posi
tioned in a plane substantially at right angles
to said armature shaft axis.
JAMES M. KENDALL.
40
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