Multi-circuit rotary electrical conductor assembly

A full or partial rotational, substantially zero friction electrical conductor assembly conducts the electrical currents of a large number of electrical circuits between a pair of relatively rotatable members in a minimum axial length. A plurality of concentric, annular, radially spaced gaps are formed between corresponding concentric, concave surfaced, electrically conductive rings affixed to the members, such that a large number of circuits may be accommodated in a reduced axial length assembly. Resilient, filamentary conductor loops are disposed between the conductive rings, and the loops contact, roll on, and are captured by the concave surfaces of the conductive rings, thereby providing electrical continuity between the relatively rotatable members. The conductor loops are sealed within individual structural enclosures, thus, providing an environmentally clean and rugged assembly.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to improvements in the electrical 
current transfer device for transferring electrical current between 
relatively rotatable members, the broad class of such devices generally 
being referred to as slip rings. Specifically, the invention relates to an 
improved current transfer device for conducting currents between stator 
and rotor members, such as between the relatively rotatable members 
utilized in aerospace applications which require the reliable and long 
life expectancy transfer of electrical currents from a large number of 
circuits across a relatively short distance measured along the axial 
length of the relatively rotatable members. 
2. Description of the Prior Art 
Rolling electrical conductor assemblies are not broadly new and have 
heretofore been proposed for use in place of the more conventional slip 
ring and brush assemblies. For example, U.S. Pat. No. 4,098,546 issued to 
the Applicants' assignee, discloses a full rotational freedom, 
substantially zero friction electrical conductor assembly for conducting 
electrical currents between relatively rotatable members of sensitive 
instruments such as gyroscopic devices and the like. Each electrical 
transfer unit of the assembly comprises a pair of coaxial, concentric, 
coplanar continuous, concave conductor rings, one mounted on a relatively 
fixed member and the other mounted on a rotatable member, the relative 
diameters of the rings providing a substantial annular radial gap 
therebetween. A resilient electrically conducting continuous, filamentary 
loop is disposed in the radial gap such that its generally flat outside 
surface contacts and rolls on the concave surface of the conductor rings. 
The loop or conductor interface provices self-capturing and retaining 
forces to accommodate any misalignment between the rings and movements of 
the loops within the radial gap in a vibratory and/or shock environment, 
all without producing frictional torques on the rotatable member. 
The major disadvantage of the above described invention is that only a 
limited number of electrical currents can be transferred across a 
relatively short distance measured along the axial length of the 
relatively rotatable members. When the axial length is increased to 
accommodate a larger number of circuits that require electrical currents 
to be transferred between the relatively rotatable members, the increased 
length induces thermal and vibratory problems which result in a bulky, 
difficult to assemble, and possibly unstable structure unsuited for many 
environments. All known prior art attempts to solve the problem of the 
transfer of electrical current from high density electrical circuits 
between relatively rotatable members have been unsuccessful or have 
concentrated on increasing the axial length of the relatively rotatable 
members. In addition to the volumetric problems associated with the 
transfer of electrical current from high density electrical circuits 
between relatively rotatable members, there is also a need for an 
extremely dependable and an environmentally sound device which can operate 
efficiently under the adverse conditions which are common in aerospace and 
satellite applications. Facilitation of repairs as well as reliability are 
characteristics which are needed. Therefore, there is a need to provide 
the aerospace industry with a solution to the problem of the transfer of 
electrical currents from high density electrical circuits across 
relatively rotatable members such that efficient and reliable operation of 
satellite structures and/or sensitive instruments, such as gyroscopic 
devices may be provided under sometimes harsh environmental conditions 
characteristic of aerospace applications. The practice of the present 
invention can provide the aerospace industry with an environmentally 
rugged electrical conductor assembly which can efficiently transfer 
electrical currents from as many as 200 circuits across a distance of 13 
inches measured along the axial length of the relatively rotatable 
members. 
SUMMARY OF THE INVENTION 
In accordance with the invention, the aforementioned difficulties with 
respect to the transfer of electrical currents in high density electrical 
circuits between relatively rotatable members are to a great extent 
alleviated through the practice of this invention. The present invention 
provides an electrical conductor assembly having a plurality of annular, 
radially spaced gaps formed between concentric conductive rings affixed to 
the stator and the rotor members within annular, radially spaced openings 
formed in the members. Resilient, filamentary conductive loops with a free 
diameter greater than the width of the annular radial gaps are disposed 
within the gaps and contact and roll on juxtaposed surfaces of the 
electrical conductive rings. Unlike the prior art electrical conductor 
assemblies which have only one radial annular gap for the conductor loops, 
the present invention has a plurality of annular concentric radial gaps, 
and thus the increased number of annular radial gaps can accommodate a 
larger number of electrical circuits. More specifically, the annular 
radial gaps are defined by perpendicular walls that extend from the 
surfaces of the relatively rotatable members. These perpendicular walls 
may form sealed enclosures within which the electrical conductor loops may 
roll and contact the surfaces of the electrically conductive rings. The 
electrically conductive rings are coupled to electrical conductors, 
thereby establishing electrical continuity across the stator and rotor 
members for a larger number of electric circuits without inducing 
vibratory and thermal problems that are associated with an increased axial 
length otherwise required to accommodate large numbers of circuits.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, an enlarged partial section of a gyroscopic gimbal 
support bearing device is illustrated, specifically, and by way of 
example, a section of the electrical current transfer apparatus associated 
with the support between the gimbal 10, i.e., the rotary member, and a 
base or housing 11, i.e., the stationary member. As shown, the stationary 
housing 11 supports the gimbal 10 in precision ball bearings 12 through a 
trunnion 13 mounted on the gimbal 10 for rotation about the common axis 14 
and includes passageways for conductors 45 from stationary electrical 
apparatus to the conductor assembly of the invention. The trunnion 13 is 
cylindrical and provides passages for electrical leads 46 from the 
electrical conductor assembly of the invention to the electrical apparatus 
carried on the gimbal assembly. The trunnion 13 is secured to the gimbal 
10 by suitable means such as mounting bolts 15. A bearing retainer ring 
and clamping screws 16 serve to clamp the ball bearings 12 in place. Thus, 
the relatively rotatable members include a plurality of annular, radially 
spaced, overlapping walls 11', 11" and 13' extending parallel with common 
axis 14 which define a plurality of radially spaced, concentric openings 
36, 37 therebetween. It will be understood of course that the invention is 
also applicable in structures other than gyroscopes or the like; for 
example, it is highly applicable in transferring electrical current 
between the relatively rotatable structures of space vehicles such as 
between spun and de-spun structures of satellites and pointing system axes 
of satellites. 
The electrical conductor assembly of the present invention serves to 
transfer a plurality of electrical power and/or signals between the 
stationary housing 11 and the relatively rotatable gimbal 10 with 
substantially zero mechanical friction and coupling torques. Generally, 
the conductor assembly comprises a fixed outer cylindrical housing 11, and 
an integral inner reentrant cylindrical support 11' defining axially 
coextensive interior cylindrical surface 21 and exterior cylindrical 
surface 20 respectively. Evenly and axially distributed along the surface 
20 and 21 of the housing 11 are sets of coplanar, circular, concave-faced 
electrically conductive rings 22 and 23. Hereinafter the conductive rings 
22 will be referred to as the outer housing conductor rings and the 
conductive rings 23 will be referred to as the inner housing conductor 
rings. The housing rings 22, 23 as shown in more detail in FIG. 3, may be 
made from a suitable electrically conductive material and a gold alloy 
conventionally used for such applications is deposited on the concave 
surfaces of the housing rings as taught in the above referenced patent. 
The cylindrical trunnion member 13 has an outer surface 30 and an inner 
surface 31 each axially coextensive with corresponding surfaces 20 and 21. 
Evenly distributed along the inner surface 31 and the outer surface 30 of 
the trunnion 13 are similar sets of circular, concave-faced, electrically 
conductive rings 32 and 33. Hereinafter the conductive rings 32 will be 
referred to as the outer trunnion conductor rings and the conductive rings 
33 will be referred to as the inner trunnion conductor rings. The trunnion 
conductor rings 32, 33 may be fabricated like rings 22 and 23. The rings 
22, 23, 32 and 33 are separated from each other by suitable insulation 
wafers or spacers 40 made from plastic or some other suitable insulating 
material. Each inner housing conductor ring 23 is so located within the 
housing 11 that it is accurately and axially aligned so as to be coplanar 
with a corresponding inner trunnion conductive ring 33 associated with the 
trunnion 13. The radial dimensions of rings 23, 33 define a substantial 
annular radial gap 37. Similarly, each outer housing conductor ring 22 is 
so located within the housing 11 that it is accurately and axially aligned 
with a corresponding outer trunnion conductive ring 32 associated with the 
trunnion 13. The radial dimensions of rings 22, 32 define a substantial 
annular radial gap 36. Within each of these concentric, radially spaced 
gaps 36, 37 is located at least one resilient filamentary conductor loop 
which contacts and rolls on the concave contact surfaces of the conductor 
rings 22, 32 and 23, 33. The contact interfaces between the conductor 
rings and the filamentary conductor loops are the same, or substantially 
the same as taught in the referenced patent whereby the loops are self 
captured and self aligned between the rings. The separator walls 40 form 
individual enclosures that effectively seal each conductor loop from one 
another so that, in the unlikely event that any loop fractures, it will be 
isolated and will not destroy or short circuit another conductor. The 
walls 40 further protect the conductor loop from damage during module 
assembly. The spacers 40 have radii such that they extend into the annular 
radial gaps 36 and 37, and a small annular clearance is left between 
spacers to form sealed enclosures for each of said loops. Similarly, end 
caps 41, 42 extend radially across the gaps 36, 37 at each end and may be 
so configured to form a labyrinth seal for protecting the gap cavities 36 
and 37 from contaminants. 
In practice, the electrical conductor generally described above is built up 
from separate components and secured together with suitable fasteners, 
such as bolts, to form annular module assemblies as hereinafter described. 
The modules are then inserted and fastened into the housing and trunnion 
annular spaces to produce the overall conductor assembly. For example, the 
concentric modules are held in place by a threaded portion 34 of the 
housing reentrant cylinder portion and nut 35 and by the suitable ring 
retainers 29 attached to the cylindrical trunnion 13 and housing 11. Of 
course, the electrical conductor assembly may be constructed using the 
molded plastic techniques disclosed in the above U.S. Pat. No. 4,098,546. 
It should also be noted that holes are drilled through the gimbal or rotor 
element 10 to provide passage for the electrical conductors 46, 47 which 
extend to electrical components carried by the gimbal, and similar holes 
are drilled into the housing 11 for passage of electrical conductors 45, 
48 which extend to fixed electrical components associated with the 
housing. It can be seen from the embodiment of FIG. 1, that there is a 
total of 16 separate circuits which can be accommodated by the electrical 
conductor assembly depicted therein. However, if extremely high 
reliability is desired, the conductor leads may be cross-strapped to 
provide two conductor/loop contacts per circuit. For example, electrical 
leads 47, 48, FIG. 2, which are coupled to one set of conductor rings 32, 
22 may be connected to electrical leads 46, 45 respectively, which are 
coupled to a corresponding set of conductive rings 33, 23 to provide 
parallel or redundant conductor/loop circuits between the rotor and stator 
members. This redundant circuit arrangement may be very advantageous in 
space applications, such that if one of the filamentary conductor loops 
should fail, the other conductor loop will maintain electrical continuity. 
Alternatively, the conductor rings 32, 33 may be formed as an integral 
ring rather than separate rings for this purpose. 
Referring now to FIG. 2, an end view of the folded contact assembly of the 
present invention illustrates a typical random disposition of circular 
filamentary conductor loops 44 within the annular radial gaps 36 and 37. 
As taught in the referenced patent, electrically conducting, continuous 
filamentary loops 44, disposed in the annular radial gap 36, at least one 
loop per ring set, have a generally rectangular cross section such that 
their outer edge surfaces, which may preferably include a rounded chamfer 
to enhance electrical conductivity, contact and roll on the facing concave 
surfaces of the concentric rings 22 and 32 thereby providing 
loop-retaining mechanical forces and electrical continuity between the 
leads 48, 47. Likewise, a plurality of resilient, electrically conductive, 
continuous filamentary loops 44 are disposed in the annular radial gap 37, 
that is, one loop 44 per ring set 23, 33, such that their outer generally 
flat surfaces contact and roll on the concave surfaces of the concentric 
rings 23, 33. 
The primary consideration governing the selection of design parameters for 
the resilient, filamentary, conductor loops are minimizing the effective 
contact resistance, over a given operational life, at the loop conductor 
interface, maximizing the self-retention capability of the loops between 
the rings in a shock and vibratory environment without contributing 
significant coupling torques, maximizing the current conduction capability 
of the loop/conductor ring interface, and maximizing the reliability and 
life of the assembly. It should be noted from FIG. 2, that the conductor 
loops 44 and the conductive rings 22, 23, 32 and 33 are all interior of 
the assembly housing 11, and they are therefore, protected from 
neighboring apparatus in use and are not exposed to accidental contact or 
snagging during normal handling. 
Referring now to FIG. 3, there is shown an enlarged partial sectional view 
of the electrical conductor assembly of this invention and it illustrates 
in more detail a preferred configuration of the conductors/loop annular 
modules. Contained within the module 50 there is a typical loop 44/outer 
housing conductive ring 22 interface, as well as a typical loop 44/outer 
trunnion conductive ring 32 interface. The facing concave surfaces of the 
conductive rings 22, 32 provide self-capturing and retention forces for 
the loop 44 compressed therebetween, and the depth of the concavity is 
selected depending upon the severity of the shock and vibratory 
environment in which the gyroscope is to be operated, as taught in the 
referenced patent. Furthermore, the insulator spacers 40 disposed between 
adjacent rings of the ring set 22, 32 extend across the radial annular gap 
36 so as to leave a very small gap, preferably on the order of a few 
thousandths of an inch. The insulated spacers 40 form individual annular 
enclosures or chambers for each of the conductor loops 44, such that wear 
debris is prevented from fouling the other loops as described above. It 
can also be seen, that the end caps 41, 42 also extend across the annular 
radial gap 36 and are configured to provide labyrinth like seals 51. The 
outer labyrinth seals 51 define small gaps, preferably on the order of 
0.010 inch, between the end caps 41, 42 which prevent foreign objects from 
contaminating the interior of the assembly in use and also serve the 
additional function of maintaining the assembled components of the modules 
together for assembly into the housing and for protecting the conductor 
loop 44 from damage prior to and during such assembly. Particularly in 
space applications, it may be desirable to drill large holes in the end 
caps 41, 42 to facilitate evacuation during depressurization and while in 
orbit where contamination is not generally a severe problem. 
It should be understood that in some applications the arcuate surfaces of 
the conductive rings 22, 23 may need to be formed on only one of the 
conductive rings depending upon the severity of the environment. 
Preferably, the conductive rings 22, 23 are fabricated from copper alloy 
and machined to the desired concave shape, and then alloys of rhodium, 
nickel and gold, or other suitable material combinations are successively 
plated or deposited thereon to form the finished concave conductive rings. 
Alternatively, as taught in U.S. Pat. No. 4,098,546, concave grooves may 
be machined or otherwise formed on the surfaces of the plastic housing 11 
and the trunnion 13 to the desired radius and depth, after which they are 
suitably masked and a gold alloy is deposited on the groove or concave 
surface to the desired thickness. The conductor loops 44 are also plated 
to enhance the electrical conductivity characteristics of the conductor 
assembly. 
As shown in FIG. 3, the annular module assembly is built up by successively 
stacking the rings 32, 22 and insulation wafers 40 on insulation covered 
bolts 24 within the module walls 53, 54. The resulting module is installed 
in the annular spaces between the housing 11 and the gimbal 10 where it is 
secured in place, as described above. For example, holes are drilled in 
the lower flanges of the module wall 53, 54 to receive upstanding assembly 
bolts 26. The bolts are provided with an insulating sleeve 26'. A first 
set of insulated spacers 40 and conductive rings 22 and 32 are then placed 
on the insulated bolts 24 and the filamentary conductor loop 44 is then 
compressed between the rings 22, 32. The second layer of insulated spacers 
40 and conductive rings 22, 32 are placed over the first layer and 
conductor loop 44 compressed between the rings. This procedure is repeated 
until the module is filled. The end caps, 41, 42 are then placed over the 
top wafer 40. The fastening nuts 25 are then threaded onto the assembly 
bolts 26 to hold the module 50 together. Note that the labyrinth seal 
serves to maintain the integrity of the module during its assembly into 
the housing. 
Referring now to FIG. 4, an enlarged partial end view of the electrical 
conductor assembly illustrating further features is provided. The 
periphery of the rings are cut away to provide longitudinal channels 52 
extending from the end caps 41, 42 and along the interior surfaces of the 
module walls 53, 54, thereby providing passageways for the leads 47 and 
48. The portions of the outer trunnion conductive rings 32 which abut the 
module wall 53 and the portions of the outer housing conductive rings 22 
which abut the module wall 54 as well as the abutting spacers 40 are cut 
out so that the channels 52 extend from the bottom of the module walls to 
the end caps 41, 42. The conductors 47 and 48 are insulated wires which 
are soldered to holes drilled into the conductive rings 32 and 22, 
respectively. Preferably, the leads are soldered to the rings prior to 
their assembly to form the module. 
Referring now to FIG. 5, a partial sectional view of an electrical 
conductor assembly constituting a further preferred embodiment of the 
present invention is provided. This embodiment provides an even greater 
number of circuits in the same axial direction. Three angular radial gaps 
53, 54 and 55 are provided instead of the two annular radial gaps as 
depicted in the embodiment of FIGS. 1-4. Construction of the electrical 
conductor assembly having three annular radial gaps 53, 54, 55 is 
substantially the same as the construction of the FIGS. 1-4 embodiment. 
Note that an additional trunnion cylinder, an additional set of trunnion 
conductive rings 56 as well as housing conductor rings 57, and the 
components associated therewith are needed. Obviously, the radial 
expansion of conductor assemblies may be continued to any practical limit 
desired. 
While the invention has been described in its preferred embodiments, it is 
to be understood that the words which have been used are words of 
description rather than limitation and that changes may be made within the 
purview of the appended claims without departing from the true scope and 
spirit of the invention in its broader aspects.