Note: Descriptions are shown in the official language in which they were submitted.
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INDUCTIVE COUPLER
CROSS REFERENCE TO RELATED APPLICATIONS
......
This application i8 related in sub~ect matter to
Canadian Application Serial No. 359,150, flled August 27,
1980 and as~igned to the same assignee as the present
invention.
BACKGROUND OF THE INVENTION
.
Field oi the Invention:
The invention in general relate~ to signal
and/or power coupllng devices, and more particularly to
one of the inductive coupler var~ety.
Descr~ 5~L9~ L~ Ar~
Inductive couplers for coupllng power from a
sourae to a load are used in environments where the am-
bient medium dictates against normal exposed metal-to-
metal contact, For example, such couplers are utilized to
prevent sparks in an explosive atmosphere and flnd a wide
use in the off-shore oil industry or other underwater
op~rations for maklng circult-to-circuit connections
beneath the suriace of the water.
The inductive coupler device is based upon the
alternating current transiormer principle, that is, by
means of electromagnetic induction a voltage i8 induced
irom a primary wlnding to a ~econdary winding with the aid
of a magnetic circuit without m~king any physlcal electri-
cal connections. In its simplest form, one type of induc-
tive coupler utilizes two C cores representing a magnet$c
circuit each having a respective winding and when the
respective end sections oi the two C cores are brought
,.~
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~(?gether, cl ba~ic transformer is formed. With the appli-
(`.t~ iOll O~` proper electrical insulating and corrosiorl
protecting materials, the connector may be utiliæed as the
electrical interface between submerged components
When utilized for signal or data transfer, these
face-to-face couplers if separated by a relatively small
gap exhibit an unacceptable degradation of overall fre-
quency response.
Another type of coupler such as described in
British Patent 1366134 has been proposed for power trans-
fer and is made up of an outer magnetic section with a
winding, into which is coaxially located an inner magnetic
circuit with a winding. A source of electrical power is
connected to the outer winding, which constitutes a pri-
mary, and a load circuit is connected to the inner winding
constituting a secondary. With such arrangement, when the
inner winding is removed, the primary current increases to
such an extent that a plug part must be inserted into the
open socket from which the inner section was removed so as
to prevent the primary circuit from burning out. Alterna-
tively, it is proposed to provide a complete auxiliary
electric circuit comprised of a plurality of inductive and
capacitive elements so as to form a tuned circuit with the
primary winding. Thus when the secondary is removed upon
decoupling, the circuitry becomes detuned such that the
primary current is appreciably lowered.
The present invention is of this coaxial variety
and completely eliminates the need for auxiliary plugs or
auxiliary electrical circuit components required for a
tuned circuit.
Another type of coaxial coupler utilizes primary
and secondary coaxial windings inductively coupled to one
another without the benefit of a closed magnetic core
circuit. Although power in such couplers is provided to
the inner winding constituting a primary, there is very
poor coupling and the design is relatively inefficient.
Still other types of coaxial couplers which
include closed magnetic circuits have mating tapered
3 ~l8,417
surfaces. When utilized in an underwater environment,
where dirt, algae, and marine growth for example may
contact the surfaces of the mating parts, proper operation
is severely degraded due to axial misalignment.
The coaxial coupler of the present invention is
of such design to allow for a relatively high degree of
axial misalignment while still maintaining proper opera-
tion for no-t only power transfer but for data transfer.
Further, the structure of the coupler is such as to facil-
itate coupling and uncoupling even in an underwater en-
vironment where visibility may be impaired.
SUMMARY OF THE INVENTION
The inductive coupler of the present invention
includes a first magnetic flux supporting elongated core
member which extends along an axis and includes first and
second enlarged end portions. A first winding is posi-
tioned around this core member between the first and
second end portions. A second magnetic flux supporting
elongated core member extending along an axis is of a
generally hollow cylindrical shape and has first and
second end portions which extend inwardly toward the axis
and includes a second winding positioned around the inside
between the end portions. The first core member is in-
sertable within the second core member such that the first
and second end portions of the first core member are in
magnetic flux registration with respective first and
second end portions of the second core member. In order
to accommodate for axial misalignment, in one embodiment
the axial lengths of the end portions of the first core
member are different from the axial lengths of the end
portions of the second core member. With this construc-
tion the axial lengths of the respective primary and
secondary windings are also different.
Means are provided for connecting a source of
electrical power to the first winding, the inserted wind-
ing, which then constitutes a primary winding and means
are provided for connecting a load means to the second
winding, constituting a secondary winding.
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The inductance of the first winding changes
depending upon whether the core member is in a mated or
nmated condition. In the present invention the ratio of
load current to magnetizing current is chosen to be less
than the ratio of the inductance of the primary winding in
a mated to unmated condition.
The inductive coupler may also be used in an
information transfer mode of operation by connecting a
sensor system to one of the windings and a data receiver
and utilization system to the other of the two windings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a view, partially in section, of a
prior art face-to-face inductive coupler;
Fig. 2 are curves illustrating the performance
of the coupler of Fig. l;
Fig. 3 is a view of another prior art inductive
coupler;
Fig. 4 is a simplified view of the coupler of
the present invention utilized in a power coupling situa-
tion;
Fig. 5 is a circuit to illustrate the currents
in ~he primary winding of the inductive coupler;
Fig. 6 is a vector diagram illustrating certain
current relationships;
Fig. 7 i.s an axial cross-sectional view of a
preferred embodiment of the present invention, the coupler
being in an unmated condition;
Fig. 8 is an axial cross-sectional view of a
preferred embodiment of the present invention, the coupler
being in a mated condition;
Figs. 9 and 10 are exploded isometric views,
with portions broken away, of the coupler of Figs. 7 and
8;
Fig. 11 is a circuit diagram of a data trans-
mission system utilizing the present invention;
Fig. 12 are curves illustrating the performanceof the circuitry of Fig. 11; and
Fig. 13 is an axial sectional view of another
.
5~8
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embodiment of the present invention.
DESCRIPTION_OF THF PREFERRED EMBODIMF.NTS
Rererring now to Fig. 1, there is shown a typi-
cal prior art face-to-face inductive coupler. The coupler
10 is comprised of two housing parts 12 and 13 each in-
cluding a respective C-shaped core member 15 and 16 having
respective windings 18 and 19. Stainless steel cover
plates 21 and 22 protect the core members from the ambient
- medium such as an underwater environment.
10Windings 18 and 19 are electrically connected to
respective cables 24 and 25 which in one typical use
convey data or information signals. Such couplers are
extremely sensitive to variations in frequency response
due to small separations of the two mating portions 12 and
1513. For example, in Fig. 2, curve 30 illustrates a typi-
cal frequency response with no gap between the mated
portions. Curve 31 illustrates the degraded response if
the housing parts are separated by a distance of 0.030
inch (0.0762 cm). The curves illustrate that at 100
kilohertz (kHz), there is an approximately 2 dB reduction
in response, however, at the lower frequencies, the dif-
ference is significantly greater.
Another type of prior art inductive coupler
which has been proposed for use in an explosive atmosphere
i.s illustrated in Fig. 3 in cross-section and includes an
outer cylindrical member 34 having radially inwardly-
extending flanges 35 and 36 at each end whereby a winding
38 is fixed in the interior of the cylinder. The other
core member 40 includes two end discs 41 and 42 joined by
a cylindrical center limb 43, the arrangement carrying
winding 45.
The coupler is used to transfer power from a
source 47 to a load 48, with the source being connected to
winding 38, constituting the primary, and the load being
connected to winding 45, constituting the secondary of the
inductive coupling arrangement.
With such arrangement, when the core member 40
is withdrawn from core member 34 to effect a disconnec-
6 ~g,~17
tion, there is an objectionable increase in t}le primaryc~ ell~ so .IS t-o re(luire inserlion of ~ln .luxiliary clemenl
~ I-el)la(~ .he removed core.
In lieu of the requirement for insertion of a
separate plug, the arrangement of Fig. 3 may include an
auxiliary circuit 50 comprised of an inductor 51 in series
with the parallel arrangement of inductor 52 and capacitor
53, inductor 52 being connected to the primary winding 38.
The values of the inductances and capacitance are such
that when the core member 40 is inserted within core
member 34, the primary circuit is twned to the supply
-frequency and when the core member 40 is removed, the
circuit is no longer tuned so as to substantially reduce
and limit the current in the primary circuit.
The inductor of the present invention is of the
variety illustrated in Fig. 3, however, when used for such
power transfer it completely eliminates the requirement
for either a separate insertable plug or a separate auxil-
iary circuit to protect the primary.
Fig. 4 basically illustrates the concept of
power transfer with the present invention. The inductive
coupler of Fig. 4 includes an inner core member 60 having
enlarged end portions 61 and 62 each of an axial length W,
and a winding 63 of length ~ therebetween. Disposed
coaxially about the inner core member is a generally
cylindrical outer core member 67 having inwardly extending
end portions 68 and 69 each of an axial length W' contain-
ing a winding 70 of length Q' therebetween. The unequal
axial lengths of the end portions and windings will permit
limited relative axial movement of the inner and outer
core members in response to axial forces on the coupler
without any accompanying change in performance.
The end portions of members 60 and 67 are in
magnetic flux registration and means are provided for con-
necting the inner winding 63 to a source of electricalpower 74 and for connecting the outer winding 70 to a load
75. It is to be noted that this arrangement of connecting
the source to the inner winding and the load to the outer
.
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winding is in direct contrast to that proposed by the
prior art of Fig. 3.
A simp]ified equivalent circuit of the primary
winding is illustrated in Fig. 5 and includes the parallel
arrangement of an inductor L and resistor R. The primary
current i5 Ip, which is comprised of the magnetizing
current IL through inductor L, and the reflected ],oad
current IR through resistor R.
Fig. 6 illustrates a vector diagram of the
o currents illustrated in Fig. 5. Vector I~ represents the
reflected load current and vector ILl represents the
magnetizing current through inductor L. Ip therefore is
the resultant primary current. In a preferred embodiment,
the core members would be made of a ferrite and according-
ly any core loss current would be minimal and for clarity
has not been illustrated. When the coupler is umnated,
there is no reflected load current and the total primary
current is the current through the inductor L, designated
as vector IL2 in Fig. 6.
The inner or primary winding 63 has a certain
inductance LM when in a mated condition and a different
and much lower inductance LU when in an unmated condition.
If the ratio of reflected load current to magnetizing
current (IR/ILl) is designed to be the same as the ratio
of LM/LU, then the primary current will not significantly
change in amplitude, but will remain essentially constant
from the mated to the unmated condition of the inductive
coupler. Thus, in Fig. 6, the vector Ip when the coupler
is in a mated condition is approximately the same magni-
tude as vector IL2, which is the primary current when the
coupler is in an unmated condition. By way of example in
one test set-up, for a coupler with 40 turns of primary
and secondary winding, with a ferrite core member, the
inductance of the winding of the inner core when in a
mated condition was in the order of 4.8 millihenries, and
360 microhenries when in an unmated condition. These
values yield a ratio of LM/LU = 13.3/1.
As a practical matter, this ratio 13.3/1 would
~lt",`~ 8
8 4~3,417
be somewhat hi~her than desired for a ratio of ref1ected
load current to ma~netization current since it would
rcguire more primary turns thus causing an increase in
copper losses resulting in a somewhat more inefficient
unit. Accordingly, the ratio of reflected load current to
nagnetization current is chosen to be in the order of 5/1.
Since this is not the exact ratio of LM/LU, the current in
the primary will go up somewhat when the unit is un-
coupled, but it will go up only approximately 2 1/2 times
lo (13.3 . 5 = 2.6), which is more than acceptable, and in
fact an increase of primary current of approximately 5
times that in a mated condition would still give satis-
factory results.
Fig. 4 illustrated the principles of one embodi-
ment of the present invention for the simplistic showing
of a coaxial coupler. Another embodiment of an actual
co-upler is illustrated in the views of Figs. 7 through 10
to which reference is now made. The coupler 80 is com-
prise~ of two mating sections 82 and 83, the section 82
2n containing an inner core member 86 and section 83 contain-
ing an outer core member 87. An inner support assembly 90
includes an elongated rod portion 91 upon which is mounted
the inner core member 86. For ease of manufacture, the
inner core member, pre~erably of a magnetic flux support-
ing ferrite is comprised of three separate pieces, end
pieces 94 and 95 and a central piece 96 around which is
wound a number of turns of primary winding 97. The entire
assembly is maintained in position by means of a retaining
cap 104 affixed to rod portion 91 by means of screw 105.
An outer protective shell 110 is threadedly
engaged at 111 with the inner support assembly 90 to which
end cap 114 is also connected, by means of screws 113.
End cap 114 in conjunction with the inner support assembly
90 defines an internal cavity 118 in which is located an
ancllor member 120 preferably held in position by filling
the internal cavity 118 with a resin such as polyurethane.
The electrical cable 122 is of the coaxial
variety which is brought through the end cap 114, and
illc~ iw~
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thereafter the outer shield 123 and inner conductor 124
<lre connected to respective stand^offs 125 and 126, with
Ihe inn~r cond~lctor 124 passing through the anchor member
120. One end of winding 97 is connected to stand-off 125
by the path which includes groove 130 in ferrite piece 97,
through groove 131 in end piece 94 and through aperture
132 in inner support assembly 90. The other end of wind-
ing 97 is connected to the other stand-off 126 by the path
which includes groove 130' and 131' and aperture 132'.
Mating section 83 includes an end cap 150 to
which is connected, by means of screws 152, an inner
cylinder 154 made of a plastic material such as delring
and having a groove 155 on the inner surface thereof
designed to accommodate the outer magnetic core member 87
and limit its degree of insertion.
For ease of manufacture, the outer magnetic core
member 87 is fabricated in three pieces, two end pieces
160 and 161 having end portions which extend radially in
toward the center of the unit, and a central portion 162,
with winding 165 being contained between end sections 160
and 161. The magnetic section is held in position by
means of a large guide member 168 threadedly engaged to
the end of the inner cylinder 154 and having a generally
tapered and rounded end portion 169 for ease of insertion
into the outer protective shell 110 and to limit movement
oE the outer core member 87.
In a manner similar to cable 122, cable 170 has
its outer shield 171 connected to a stand-off 172 while
its inner conductor 174 passes through an anchor member
175 and is connected to stand-off 176. Anchor member 175
is held in position by means of a potting material 178,
such as polyurethane. One end of winding 165 is then
connected to stand-off 172 while the other end of the
winding is connected to stand-off 176.
In order to maintain sections 82 and 83 in a
locked condition when they are mated, there is provided a
plurality of latches 18~ disposed within recesses in end
cap 150. As seen in ~ig. 8, the projection portion 185 of
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latch 184 sits wlthin a groove 186 on the inside of thc
outer protective shell 110, and ls maintained ln that
position ~nder the action of spr~ng 188. With this ar-
r~ngement, the two mating portions will not become un-
coupled merely by pulling on respecti~e cables 122 and17G. In order to decouple the mating sections, there is
provided a releas~ cup 190 to which is connected a plur-
ality of release rods 191 passing through respective
apertures in end cap 150. The release rods include an
indented or cam surface 195 and when the relea~e cup 190
i~ pulled, the camming action o~ the surface of latch
member 184 which engages the cam surface 195 causes the
1 tch member 184 to be withdrawn further into its recess
thus pulling the projection 185 out of engagement with
groove 186 to thereby effect a decoupling of the mating
sections 82 and 83. Movement of the release cup 190 is
limlted by means of the pro~ection 197 at the end of
release rod 191. If the release cup 190 is maintained in
its extended position, then latch 184 is maintained in its
recessed condition 50 that the two sections may be mated,
after which release cup 190 ls moved to the position illu-
strated in Fig~ 8 to effect a locking of the two pieces.
If, on the other hand, while in an unmated
conditlon, release cup 190 is pushed forward so that latch
184 seats on the sloping surface 195 of release rod 191,
then coupling and locking may still be effected by virtue
of the sloping surface 200 on the inner surface of outer
protective shell 110 which forms a camming surface for
pro~ection 185 of latch 184 to force it into its recess so
that the coupler may assume th~ relationship of Figure 8.
When the coupler ls used in an underwater en-
vironment, there is a possibility that forelgn matter may
enter the cavities when in an unmated condition. Such
foreign matter, for example, may ~nclude dirt, sand,
algae, etc. Accordingly, provision is made for wlp~ng the
inner sur~ace of outer protective shell 110 and the sur-
faces of the exposed magnetic pieces. Thls is accom-
plished with the provision of washers or rlngs 204 and 205
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positioned between inner cylincler 154 and the large guide
member 168, as well as a similar washer 206 located around
rod 91 and held in position by means of retaining cap 104.
These washers preferably are made of a rubber material
which prevents fouling in the coupling, one example being
"NO FOUL", a product of the B. F. Goodrich Co. Since
washer 20~1 is in tight engagement with the inner surface
of outer shell 154, apertures 210 and 211 are provided in
the shell so as to provide bleed holes for water when the
mating sections are coupled and uncoupled, respectively.
Figure 11 illustrates an arrangement whereby the
coupler of the present invention is utilized for trans-
mitting information, as opposed to power, between two
different locations. The source of signals by way of
example is a rv camera 240 at one location, for providing
signals to be displayed on a monitor 241 at a remote
location, the signals being conducted over cable 243 and
cable 244 joined by coupler 245 previously illustrated in
Figures 7 through 10.
The TV signals are not coupled directly to
coupler 245 but are provided to a power emitter follower
driver stage 250 which presents an extremely low imped-
ance, for example less than 10 ohms, to the primary of
coupler 245. Where information signals rather than power
2rj is being transferred, either one of the windings of the
coupler may constitute the primary. If the coupler drives
a conventional 50 ohm cable, the cable is terminated by a
constant resistance equalizer 252 which functions to
elevate the high frequency response of the signal. This
equalization is then followed by an amplifier stage 254
and thereafter by a low frequency equalizer circuit 256.
Following amplifier stage 258, the signal is further
amplified in stage 260 and is given an additional high
frequency compensation by means of the feedback arrange-
3~ ment of the amplifier stage 260. The resultant signalsare then portrayed on monitor 241.
In Figure 12, wherein signal response is plotted
on the vertical axis and frequency on the horizontal axis,
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curve 264 illustrates the response if the TV signals were
fed directly to the TV monitor ~hrough the coupler. It is
seen that the response is objectionably degraded at the
lower and upper frequencies of about 500 ~Iz and two MHz
respectively. For good quality TV images, video frequen-
cies from around 60 Hz to at least three MHz must be
passed. Curve 265 illustrates the response with the
arrangement of Figure 11 and it is seen that the lower and
upper frequency respcnse is significantly improved by the
lo arrangement.
Figure 13 illustrates another embodiment of the
invention in which the mating and unmating of the cooper-
ating coaxial members effects a connection and disconnec-
tion of a plurality of circuits. A support assembly in
the form of a plunger 270 carries at one end thereof a
first inner core member 272 and adjacent thereto a second
inner core member 273. Core members 272 and 273 are
magnetically and electrically insulated from one another
by means of a plastic insert 274 and each core member
carries respective windings 276 and 277. In a similar
fashion, there is provided two outer core members 280 and
281 in respective magnetic registration with inner core
members 272 and 273 and including respective windings 282
and 283, with the members 280 and 281 being separated by a
plastic insert 285.
The outer core members are disposed within a
housing fixture 287 whereas the inner magnetic cores 272
and 273 are movable between fixture 287 and fixture 288 by
virtue of their connection to plunger 270.
30The other end of plunger 270 has an enlarged
section 290 which in the limit illustrated abuts against a
; shoulder portion 292 so as to ensure registration of the
magnetic circuits. Plunger 270 is movable in the direc-
tion of the double-ended arrow such as by mechanical or
3~ hydraulic means.
The arrangement illustrated in Figure 13 may
provide for multiple power sources supplying multiple
loads or may be utilized in a situation where a plurality
3~3
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of sensors are to provide signals to a plurali.ty of re-
(~eivers. A~terncltively, one pair of windi.ngs, for example
winclitlgs 276, 282, may be utilized for power transfer
while the other set of windings 277, 283 may be used for
signal transfer, both functions being terminated upon
removal of pl.unger 270 from fixture 287.
