Non-contacting power transfer device

A transformer (20) for coupling AC electrical energy from a stationary element (22) to a rotating element (24) without the use of sliding contacts. The transformer (20) is of the rotary type and includes a ferrite core (39) and two primary windings (70 and 72) which are stationary with respect to a secondary winding (88) which rotates within an annular cavity (48) adjacent an axial bore (58) in the core. The core (39) is comprised of two cup type core halves (40 and 42). Electrical connection to the secondary winding (88) is made through a split bobbin assembly (89) which couples to a coaxial shaft assembly (59) located in the axial bore (58). The electrical coupling to the coaxial shaft assembly is made through a continuous transverse channel (68) connecting the axial bore (58) with the annular cavity (48). The transverse channel (68) forms a single air gap; however, it is not open directly to free space but is shielded by the magnetic permeable material of the core halves (40 and 42).

TECHNICAL FIELD 
The invention relates generally to electrical transformers and more 
particularly to transformers where there is relative motion between the 
primary and secondary winding. 
BACKGROUND ART 
The invention described herein has particular utility in applications where 
electrical power is coupled from a stationary location to a moving 
location with a minimum of radio frequency and electromagnetic 
interference. Such an environment is encountered in spacecraft containing 
extremely sensitive electronic components which are being fed power from 
an on-board source via a transformer. 
Known prior art apparatus for coupling electromagnetic energy across a 
moving boundary or interface consist of rotary transformers, close coupled 
antennas, and capacitive plates. The disadvantages of known prior art 
transformer apparatus include the presence of an external air gap 
separating the two moving elements from which electrical energy leaks or 
is radiated away. Additionally, rotary transformers are sensitive to 
translational and/or rotational motions and the lack of parallelism 
between opposing, although non-contacting, surfaces results in changes in 
the electromagnetic coupling between the elements. Capacitive devices are 
subject to changes in their operational medium such as humidity and have a 
tendency to arc. In addition, where mutual rotation between elements is 
required, sliding contacts are often used to couple energy from the moving 
member, particularly where a rotation of 360.degree. is provided. 
STATEMENT OF THE INVENTION 
Accordingly, it is an object of the invention to provide non-contacting 
means for coupling electromagnetic energy across a moving interface. 
It is another object of the invention to provide transformer means for 
coupling electromagnetic energy across a moving boundary without the use 
of sliding contacts. 
Another object of the invention is to provide a transformer having one 
winding which is adapted to rotate 360.degree. with respect to the other 
winding. 
Still another object of the invention is to provide a transformer having a 
relative rotation between windings while substantially minimizing 
electromagnetic flux leakage therefrom. 
Yet another object of the invention is to provide a rotary transformer 
wherein the flux coupling is substantially constant regardless of angular 
position or velocity of the moving winding. 
These and other objects are achieved by means of a transformer for coupling 
alternating electrical energy between a stationary winding and a moving 
winding via a magnetic circuit element which has a core of magnetically 
permeable material which is also stationary relative to the moving 
winding. The magnetic circuit element comprises a toroidal core assembly 
having an interior annular cavity for enveloping fixed and movable annular 
winding assemblies. The movable winding assembly is freely rotatable 
within the cavity and couples to the outside via a coaxial shaft assembly 
located in an axial bore through the toroidal core. The rotatable winding 
is wound on a split bobbin assembly which connects to electrically 
insulated inner and outer conductors of the shaft assembly. While an air 
gap is provided, it is not open directly to free space, but is located 
within the core so that the core itself provides a magnetic shield to 
minimize flux leakage. 
The foregoing as well as other objects, features and advantages of the 
present invention will become more apparent from the following detailed 
description taken in conjunction with the appended drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings and more particularly to FIG. 1, the 
apparatus disclosed therein is intended to illustrate a typical 
operational environment for the invention, the details of which are 
illustrated in FIGS. 4 through 6. Reference numeral 10 is intended to 
designate generally an orbital spacecraft, or the like, having one section 
12 rotatable with respect to a second section 14 along a common central 
longitudinal axis. Section 12, for example, may house an electronics 
surveillance or communications system coupled to a directable antenna 
system 16 while being powered from a power supply contained in the section 
14 having a solar powered array 18 peripherally located on its outer 
surface. To couple power from the section 14 to the section 12, some type 
of rotary transfer device is required. Accordingly, reference numeral 20 
designates a rotary transformer in accordance with the subject invention 
having a stationary portion 22 and a rotatable portion 24 coupled between 
the sections 14 and 12, respectively. 
Due to the relative sophistication and complexity of current spacecraft 
systems, the presence of undesired RF and electromagnetic interference 
greatly affects the performance sensitivity of the circuitry proximate to 
the transformer device 20. In an effort to illustrate the manner in which 
the aforesaid undesirable interference is generated in a rotary 
transformer typically illustrative of the prior art, reference is now made 
to FIG. 2. What is significant about the device shown in FIG. 2 is the 
requirement for outside air gaps 26 and 27 between a rotatable core member 
28 on which is wound a winding 29 and a stationary core member 30 on which 
is located a winding 32. The presence of the air gaps 26 and 27 provide 
flux leakage apertures of electromagnetic energy from the interior of the 
device to the outside, whereupon it can be radiated as a form of 
undesirable interference. 
To eliminate the problem of the air gap flux leakage in a transformer where 
relative movement between windings is desired, reference is now made to 
FIG. 3 which discloses an embodiment of such a device wherein a continuous 
magnetic circuit in the form of a toroidal core 34 remains fixed with a 
primary winding 36 firmly wound thereon. The secondary winding 38, 
however, while being wound around the toroidal core, is adapted to move in 
a circular or arcuate path around the core until it comes into contact 
with the primary winding 36. In such a configuration, no air gap leakage 
occurs, but movement of the secondary winding 38 has limited translation 
and/or rotation around the core 34 of less than 360.degree.. 
Referring now to one embodiment of the invention, reference is made 
collectively to FIGS. 4, 5 and 6. Shown is a rotary transformer wherein 
both the magnetic circuit in the form of a magnetizable core and one 
winding remains fixed while the other winding is movable, i.e. rotatable, 
relative thereto and is capable of continuous 360.degree. rotation. An air 
gap or discontinuity in the magnetic circuit does exist; however, it is 
not open directly to free space but is situated within the interior of the 
magnetic core which provides a self-shielding effect. Reference numeral 20 
generally designates the rotary transformer structure shown in FIG. 1 
including the fixed member 22 and a rotatable member 24. The transformer 
20 comprises, in addition to a winding to be described, a generally 
cylindrical or toroidal core 39 of magnetically permeable material, e.g. 
ferrite, comprised of two contiguous cup type core half sections 40 and 
42, the details of which are shown in FIG. 6. The core halves 40 and 42 
respectively include annular slots 44 and 46 which, when the core halves 
are joined together in a face-to-face relationship, define an annular 
cavity 48 shown in FIG. 4. The inner hub portions 50 and 52 of the core 
halves 40 and 42, respectively, contain axial bores 54 and 56 which define 
a central axial bore 58 adapted to accommodate a coaxial shaft assembly 
59. The respective inner surfaces 60 and 62 of the hub portions 50 and 52 
are recessed with respect to the respective outer ring surfaces 64 and 66 
of the core halves to provide an interior continuous transverse channel 68 
which forms a single internal air gap 68. No external air gap exists 
because the outer surfaces 64 and 66 are in contact with one another. 
Within the annular cavity 48 formed by the annular cores 40 and 42 there is 
located a pair of fixed toroidal windings 70 and 72 respectively wound on 
a pair of insulated bobbins 74 and 76 which are secured to the respective 
core halves 40 and 42 as shown in FIG. 4. Pairs of electrical leads 78 and 
80 for the windings 70 and 72, respectively, are adapted to be brought out 
through one of a pair of longitudinal slots 82 and 84, shown in FIG. 5, 
which are formed in the rim portion of the core halves 40 and 42. 
The windings 70 and 72 preferably act as a composite primary winding. As 
such the electrical lead pairs 78 and 80 are adapted to be connected 
together in parallel and upon coupling an electrical energizing potential 
to the windings 70 and 72, a magnetic flux will be generated which will 
travel in path 86 (FIG. 4) through the core assembly and across the air 
gap 68. Inasmuch as the longitudinal slots 82 and 84 are parallel to the 
flux direction, their presence is inconsequential to the behavior and 
operation of the transformer and can when desirable, be deleted. 
A particularly significant feature about the preferred embodiment of the 
invention is the inclusion of a rotatable secondary winding assembly 
including a annular winding 88 wound on a split bobbin assembly 89 
connected to a coaxial conductor type of shaft assembly 59 shown in FIG. 
4. The winding 88 is located in the annular cavity 48 between the windings 
70 and 72 and is connected to the coaxial shaft assembly 59 through the 
transverse air gap channel 68. As best shown in FIG. 6, the split bobbin 
89 is comprised of two opposing like half sections 90 and 92 formed of 
non-conducting material such as plastic. The two bobbin half sections 90 
and 92 correspond to the bobbins 74 and 76, but which have been separated 
in their mid-portions so that the bobbin half 90 comprises the left 
portion, while the bobbin half 92 comprises the right portion. 
The plastic bobbin half 90 includes a circular hub 94 which is adapted to 
interfit with the circular radial flange 96 of a first flanged shaft 
member 98 whose enlarged diameter portion 100 is adapted to pass through 
the bore section 54 of the core half 40. The smaller diameter portion 102 
extends inwardly to engage a circular insulator disk 104 and an elongated 
insulated sleeve 106 which passes through a second flanged shaft member 
107. The second shaft member 107 includes a circular radial flange portion 
108 and a protruding portion 110. The flange portion 108 is adapted to 
interfit with the circular hub portion 112 of the plastic bobbin half 92 
while the protruding portion is adapted to pass through the bore section 
56 of the core half 42. The inner and outer shaft portions 98 and 107 and 
their respective flange portions 96 and 108 are adapted to be electrically 
conductive. The opposite ends of the winding 88 are electrically connected 
thereto and accordingly electrical contact is made from the winding 88 to 
the coaxial inner shaft portion 102 and the outer shaft portion 110 as 
shown in FIG. 4. 
Accordingly, with split bobbin 89 joined to shaft assembly 59, the winding 
88 is adapted to rotate freely inside of the toroidal core 39 between the 
two fixed windings 70 and 72. Since the coaxial shaft portions 102 and 110 
pass through the axial bore portion 56 of the core, electrical leads 114 
and 116 can be connected thereto for coupling to apparatus, not shown. 
While the embodiment shown in FIG. 4 includes two stationary windings 70 
and 72 which are adapted to operate as a common primary winding, they are 
included merely for purposes of symmetry. Accordingly, when desirable, a 
single stationary winding may be employed. 
In operation, excitation of the windings 70 and 72 by AC currents applied 
to the leads 78 and 80 set up alternately reversing flux shown by the flux 
path 86 in the composite toroidal core consisting of the "cup core" 
members 40 and 42. Since the flux path completely surrounds the secondary 
winding 88, an induced voltage is provided in the winding 88 which is 
unaffected by its physical rotation provided by the shaft assembly 24. In 
contrast with the prior art apparatus which normally uses a pair of 
concentric magnetic elements, one carrying the primary coil and the other 
carrying the secondary coil, the subject invention eliminates magnetic 
force interaction between permeable ferrous surfaces because all of the 
ferrous material remains fixed. Thus what has been shown and described is 
an improvement in transformer apparatus which is adapted to transfer 
electrical power across a movable interface without the use of sliding 
contacts and in such a way that undesired electromagnetic emissions is 
substantially reduced by the single air gap 68 being inside the core 39. 
Having thus shown and described what is at present considered to be the 
preferred embodiment of the subject invention, modifications, alterations 
and changes may be resorted to without departing from the spirit or scope 
of the invention as set forth in the appended claims.