GB1591550A

GB1591550A - Electrical contact assemblies

Info

Publication number: GB1591550A
Application number: GB635/78A
Authority: GB
Original assignee: Sperry Corp
Current assignee: Sperry Corp
Priority date: 1977-01-14
Filing date: 1978-01-09
Publication date: 1981-06-24
Also published as: FR2377718A1; IT1103596B; JPS5388478A; FR2377718B1; DE2801260C2; JPS6261886B2; DE2801260A1; IT7847638A0

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL CONTACT ASSEMBLIES (71) We, SPERRY CORPORATION (formerly Sperry Rand Corporation), a Corporation organised and existing under the laws of the State of Delaware, United States of America, of 1290 Avenue of the Americas, New York, New York 10019, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to electrical contact assemblies for conducting electrical energy between a pair of relatively rotatable members, and to methods of assembling such contact assemblies. The invention is particularly, but not exclusively, concerned with contact assemblies for conducting electrical currents between stator and rotor members of sensitive instruments, such as between the relatively rotatable gimbals of gyroscopic instruments.

Rolling electrical contact assemblies are not broadly new and have heretofore been proposed for use in place of the more conventional slip ring and brush assemblies. The applicants are aware of two such rolling type contact assemblies and these are disclosed in U.S. Patent Specfications Nos. 2,467,758 and 3,259,727.

The applicants are unaware of any adoption of the assemblies disclosed in these prior patent specifications by industry in general and particularly by manufacturers of sensitive precision instruments such as gyroscopic instruments. The probable reason is that neither of the contact assemblies disclosed in these patent specifications is suitable for such applications.

As is well known to those skilled in the gyroscopic arts, slip rings and "hair pin" brushes supported in brush blocks have been used for many years for conducting electrical power and signal currents across the relatively rotatable gimbal axes of gyroscopes. While these have been generally satisfactory, they have suffered from both manufacture and service problems, causing fairly high removal rates for repair and overhaul. These assemblies are extremely delicate and require high skill in assembling and time consuming adjustment to achieve a preload consistent with minimum sliding friction in a vibration and shock environment.

Also, since they are normally exposed during repair and overhaul of the gyroscope, they are subject to being damaged during handling. In service, especially aircraft service, such gyroscopic devices operate in a vibratory environment and since sliding contact exists between brushes and slip rings, friction polymers tend to build up causing electrical shorting and/or open circuits, thereby requiring removal for cleaning and/or replacement; again a delicate, timeconsuming and costly operation. More importantly, in autopilot systems which derive aircraft body rates from displacement gyroscopes by differentiation of the gyro displacements signals, electrical noise inherent in this type of slip ring assembly is effectively amplified, rendering the rate signal undesirably noise and requiring heavy filtering, thereby detracting from the rate signal quality. Also in digital encoders, for example, conventional slip rings can produce objectionable digital noise. In addition, as appreciated by those skilled in gyroscopics, slip ring and brush assemblies reduce the long term accuracy of gyroscopes because of the relatively high friction-induced torques produced by the usually large number of slip rings and brushes required in modern electrical gyroscopes.

With the foregoing in view, it will be appreciated that devices for conducting current between relatively rotating members of sensitive instruments, such as across the gimbal axes of gyroscopic instruments, should desirably exhibit the following desirable properties: substantially zero friction and coupling torque; relatively consistent current conduction even in a shock and vibratory environment; long reliable life; low cost of manufacture and assembly; and no vibratory sliding friction contact, thereby eliminating friction polymer build-up.

The rolling electrical current conducting devices as disclosed in the abovementioned prior patent specifications, while perhaps suitable for some applications, (although the applicants are unaware of any general application in industry of either of these patented devices) are unsuitable for use in apparatus requiring low friction and coupling torques and capable of producing self retention forces without introducing variable coupling torques between the two relatively rotating members.

For example, in the first of the above patent specifications, U.S. Specification No. 2,467,758, a roller band conductor is disclosed for application as a "slip ring" for an alternating current motor and as a rolling content for an electrical switch potentiometer or rheostat. It will be noted that in all applications suggested in this prior patent specification, friction or coupling torques imposed by the roller band itself together with its retaining mechanism is clearly not a design consideration at all since in all cases one contact member is driven from a mechanical power source.

In many applications, for example sensitive instruments such as gyroscopes, any friction imposed by the electrical contact devices results in undesired torque on the supported member, thereby producing undesired drift or precession and reducing the effectiveness of the gyroscopes as an accurate, long term reference. Also, in this prior patent specification, the roller band is not self-captured or self-retained in its orbital path between the conductor rings but requires retaining flanges or pin and hole retaining arrangements. Such flanges, pin-and-hole arrangements and the like are completely unsatisfactory in many applications because of the high friction torques and the variable coupling torque magnitude produced by the bands contacting or rubbing against the flanges or pin-and-hole surfaces as it rotates. If a number of circuits are involved, this high and variable torque is correspondingly multiplied making these configurations wholly unsuitable for low torque applications. Also, in this prior patent specification, the ratio of the free loop diameter to the radial distance between the inner and outer conductor members is very large so that when the loop is compressed into the radial gap, the loop is highly distorted which results in coupling torque hysteresis and premature metal fatigue and rupture. Also, such distortion may produce buckling and further non-uniform torque. Thus an assembled loop which is highly distorted is not suitable in applications where substantially zero coupling torque is desired or required.

The second of the above-mentioned prior patent specifications, U.S.

Specification No. 3,259,727, discloses a flexible, rolling element current transfer device in which current transfer characteristics are stated to be improved over that of the first prior patent specification. This improved current transfer characteristic is stated as being accomplished by making the conductor rings on the relatively movable members in the form of a deep or acute "V" whereby the rolling contact element wedges itself into the "V" groove providing a wiping action to assure good electrical contact. This prior patent specification employs a small diameter spring closed upon itself to form a torus, the diameter of which is very large compared with the radial distance between the "V" grooves and therefore, when assembled, forms a highly distorted or rolling element which wedges itself into the steep "V" walls hence producing high torque coupling. A flat band is disclosed as an alternative but, like the spring torus, wedges itself between the steep sidewalls of the "V" groove. It is quite evident that the device disclosed in this prior patent specification is entirely unsuitable for use in applications which require substantially zero friction and coupling torques to be imposed on the supported rotatable manner by the current transfer assembly because of the substantial wiping or rubbing friction and uncompensated bending movements generated as the coil or band enters and leaves the "V" grooves.

From the overall disclosures of the above prior patent specifications, neither of the rolling contact configurations can exhibit low friction and coupling torque.

Furthermore, the above prior patent specifications disclose no methods, techniques or apparatus for assembling the loops in the radial space between the conductor rings.

It is therefore an object of the present invention to provide an improved contact assembly for transferring electrical power and/or signals between a pair of relatively rotatable members, the improvement resulting in the effective and reliable transfer of electrical energy with substantially zero friction and coupling torques being imparted between the members.

According to one aspect of the invention there is provided an electrical contact assembly for conducting electrical energy between a pair of members which are included in the assembly and which are relatively rotatable about a common axis, comprising first and second circular, coplanar and coaxial electrically conductive rings, one of the rings being disposed on one of said members and the other of the rings on the other of said members for relative rotation about said axis, the respective diameters of the rings providing a relatively large radial gap therebetween and at least one of the facing surfaces of the rings presenting towards the gap a relatively shallow, arcuately concave configuration, in radial section and a resilient, filamentary, electrically conductive circular loop having a free diameter greater than the gap and presenting an outer surface which is substantially linear in radial section, the loop being compressed within the gap, whereby the loop rolls on the or each concave ring surface substantially without friction upon relative rotation between the members, the loop thereby producing preload forces, between the outer loop surface and the or each concave ring surface, having force components in directions to maintain the loop within the or each concave surface.

According to another aspect of the invention there is provided a method of assembling the electrical contact assembly of said one aspect of the invention, the method comprising mounting one of the rings on one of the members so that it may be moved from a normal coaxial position relative to the other of the rings to an eccentric position relative thereto, whereby to provide a larger gap on one side of said other ring greater than the free diameter of said loop and a smaller gap on the opposite side thereof, moving said one ring to said eccentric position, inserting said loop within said larger gap and aligning said loop so that it is substantially coplanar with said inner and outer rings, and moving said one ring to said normal coaxial position whereby to compress said loop between said inner and outer- rings.

An electrical contact assembly according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view (taken on line 1--1 of Figure 2) of the contact assembly incorporated at one of the gimbal axes of a gyroscopic device, Figure la is a schematic plan view of the typical gyroscopic device, Figure 2 is an end view of the assembly of Figure 1 with a protective cover removed, Figure 2a is an end view of the assembly which has been prepared for the assembly of the loops, Figure 3 is a sectional view taken on line 3-3 of Figure 2a, Figure 3a is a fragmentary view showing a portion of the assembly of Figure 3 as viewed from the right-hand end thereof, Figure 4 is a greatly enlarged view of typical conductor loop/conductor ring interfaces, Figure 4a is a diagram illustrating the generalized geometry of the loop/ring interfaces, Figures 5 to 8 are diagrams illustrating the force vectors and moments by which the conductor loop is self-aligning and self-captured, Figures 9 and 9a are diagrams useful in understanding the principles of the invention, and Figures 10 and 10a are further sectional views illustrating the method according to the invention.

Referring first to Figure la, there is schematically illustrated a vertical gyroscopic device 10 although it will be understood that the invention is applicable to any instrument wherein low torque electrical contacts between relatively rotatable members is desired. The gyroscopic device 10 comprises a rotor 11 journalled by means of suitable spin bearings (not shown) in a rotor case 12 for high speed spining about a normally vertical axis 13. The rotor 11 is in turn journalled in a normally horizontal gimbal ring 14 for rotation about a first normally horizontal axis 15 and the gimbal ring 14 is in turnjournalled in a fixed housing 16 for rotation about a second horizontal axis 17 normal to the first axis 15.

As is well known, if the rotor 11 is spun at high speed and the bearings supporting the case 12, the ring 14 and the electrical conducting arrangements present zero torque coupling, the rotor spin axis will maintain its position in space indefinitely. Signal generators are normally placed at the gimbal axes and signals proportional to the deviations of the housing 16, for example an aircraft, from a horizontal plane may be generated and used for aircraft control and/or indication purposes. Such generators are schematically illustrated at 18 and 19 in Figure la.

Since frictionless support of the gimbal rings is not possible, it is necessary to apply torques to the gimbal rings for erecting the rotor to gravity references and for other control purposes, such torques being applied by means of torquers 20 and 21 as schematically illustrated. Conventionally, the rotor case 12 is supported for rotation about the axes 15 and 17 by means of precision ball bearings 22 (Figure 1).

Since modern gyroscopes are usually electrical, that is, the rotor is driven by an electric motor and the signal generators 18 and 19 and the torquers 20 and 21 are usually electrical, means must be provided to transfer electrical power and electrical signals between the housing 16 and the relatively rotatable gimbal ring 14 and between the gimbal ring 14 and the relatively rotatable rotor case 12.

In the past this electrical energy transfer was accomplished by means of a plurality of insulated slip rings mounted on a trunnion shaft extending from the bearing support structure and a corresponding plurality of brushes fixed to a brush block secured to the support structure. Each of these brushes usually comprises a pair of very delicate, springy wires carefully bent so as to produce pressure contact (and hence a friction contact) with opposite sides of the slip ring. Since there are usually a great many circuits associated with the operation of the gyroscope which must be accommodated, there are a corresponding number of slip rings and brushes, thus multiplying the friction torques. As is well known, the spin axis of the gyroscope will tend to drift from its reference position at a rate determined to the greatest extent by the friction torques existing at the gimbal axes 15 and 17. The precision ball bearings contribute to some extent to the free gyro drift rate but the greater contributors are the slip rings and brushes.

If the coupling torque contributed by the electrical energy transfer devices could be reduced almost to zero, a significant improvement in gyroscope quality would be realised. This is one of the objects of the present embodiment. Also, since many gyroscopes are used for vehicle stabilization and control, they are subject to the shock and vibration environment of the vehicle. It has been found that in such an environment the brushes tend to slide on the surfaces of the slip rings with the result that friction polymers tend to build up on the contacting surfaces which, given time, will actually lift the brush from the slip ring causing an open circuit. The gyroscope must then be taken out of service periodically and overhauled, increasing the cost of ownership of the gyroscope. It is a further object of the present embodiment to provide a current transfer device which is free of this friction polymer problem.

As stated, the brush and slip ring assemblies are extremely delicate; they require great care in initial assembly, thereby adding to manufacturing and maintenance costs. Also, great care must be exercised in handling the assembled instrument so as not to damage the exposed delicate brushes. A further object of the present embodiment is to provide an electrical energy contact assembly which is easy to assemble and which is fully protected and shielded.

Referring now to Figure 1, an enlarged partial section of the gyroscope of Figure la is illustrated, and in particular the electrical energy transfer apparatus associated with the support between the gimbal ring 14 and the housing 16. As shown, the stationary gyro housing 16 supports the gimbal ring 14 in the precision ball bearing 22 through a trunnion 25 of the gimbal ring 14 for rotation about the axis 17. The trunnion 25 is hollow and provides a passage for electrical leads from the electrical contact assembly. An extension 28 of the trunnion 25 along the axis 17 provides a mounting structure for an inner circular conductor, as will be described. A pair of clamping nuts 29, 29' are threaded into the housing 16 and on to the extension 28, respectively, and serve to clamp the ball bearing 22 in place.

The electrical contact assembly 30 serves to transfer electrical power and/or signals between the stationary housing 16 and the relatively rotatable gimbal ring 14 with substantially zero friction and coupling torques being applied to the sensitive gimbal ring. The contact assembly 30 comprises an outer cylindrical housing 31, (preferably a moulded plastics insulating material) having a mounting flange 26 secured by screws 27, 27' through an adapter plate 24, to the outer end surface of the housing 16. Shims may be added as necessary for proper conductor ring alignment. Evenly distributed along the interior surface 32 of the housing 31 are a plurality of circular, concave, conductor rings 33 hereinafter referred to as the outer conductor rings. Each ring, as shown in more detail in Figure 4, may be of a gold alloy conventionally used for such applications, electro-deposited on concave grooves 33' of the housing 31 and through the plating process electrically connected to a corresponding electrical terminal post 34 moulded in the housing 31 to provide an external circuit connection.

An inner cylindrical member 36, also of a moulded plastics insulating material, is mounted (for example by epoxy cement) in the trunnion extension 28. Evenly distributed along the exterior surface 37 of the cylindrical member 36 are a corresponding plurality of circular, concave conductor rings 38, hereinafter referred to as the inner conductor rings. Each ring 38 is preferably of gold, electro-deposited on corresponding concave surfaces 38' of the member 36 and electrically connected to a corresponding electrical conductor (e.g. wire) 39 moulded into the member 36 for providing circuit connections to electrical components carried by the gimbal ring 14. Each inner conductor ring 38 is so located on the member 36 that it is accurately aligned with a corresponding outer conductor ring 33 on the housing 31, thereby forming a plurality of ring sets (33, 38), the two rings of each set being concentric and coplanar within machining tolerances, shims being fitted as necessary between the adapter plate 24 and the housing 16.

The relative diameters of the ring sets, that is, the internal diameter of the surface 32 relative to the external diameter of the surface 37, are selected so as to provide a relatively large radial gap 41 between the two concentric rings of each set. In order to seal the contact assembly 30 from dust and other contaminating material, and provide protection during handling, a plastics cover 43 is secured to the housing 31 by spring tabs 44 in the manner of the fastening of a hub cap.

A corresponding plurality of resilient, electrically conducting, continuous filamentary loops 42 are disposed in the radial gap 41, there being one loop 42 per ring set 33, 38. The outer generally flat surfaces of the loops 42 contact and roll on the conductive concave surfaces of the concentric rings 33 and 38, thereby providing electrical continuity between the terminal posts 34 and the electrical components on the gimbal ring 14 through the conductors 39. The critical design parameters of the conductor ring surfaces and the loop characteristics will be discussed in detail below; the primary considerations governing the selection of these design parameters being to minimize any torques imposed on the gimbal ring 14 by the loop/conductor interface, maximizing the retention capability of the loop/conductor ring interface 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 assembly reliability and life.

Figure 2 is an end view of the contact assembly 30 illustrating the normal random disposition of the conductor loops 42 (after a time period of operation) within the radial space or gap 41. It will be noted from Figures 1 and 2 that the delicate loops 42 and rings 33, 38 are all inside the assembly housing 31 and are therefore not exposed to accidental contact or snagging during normal handling of the sensitive gyroscope instrument.

Referring now to Figure 4, there is shown a greatly enlarged detailed view of two typical loop/outer conductor ring interfaces; the loop/inner conductor ring interfaces may be substantially the same. The arcuate concave surfaces of the rings 33 provide a self-capturing and retention capability for the loops 42, the depth of the concavity being selectable depending upon the severity of the shock and vibratory environment in which the gyroscope is to be operated, as will be further described below. It will be understood that in some applications such arcuate surface may be need to be formed in but one of the concentric conductor members depending upon the severity of the environment. After the concave grooves 33' have been machined or otherwise formed to the desired radius and depth they are suitably masked and the gold alloy is electro-deposited on the groove or concave surface to the desired thickness, typically 80 millionths of an inch to form the rings 33. The terminal posts are cast into the housing mould and cleanly exposed by groove machining so that the gold is deposited thereon and provides external electrical connection for the gold rings 33. Alternatively, if desired, separate copper rings may be cast in the plastics housing 31, machined to the desired concave shape, and then nickel and gold (or other suitable combinations of material) successively flashed thereon to form the concave conductor rings 33.

Each conductor loop 42 is also gold plated as indicated in Figure 4 to enhance the electrical conductivity of the contact assembly.

The loop retention characteristics of the assembly may be readily adapted to a wide range of vibration and shock environments without any constraints by assembly considerations. For example, if the sensitive instrument incorporating the contact assembly is to operate in a quiet or benign environment, and depth of the grooves 33' may be quite shallow as indicated by the dotted line X-X of Figure 4, indicating a small arc length, while on the other hand, if the vibration and shock environment is severe, it may be necessary to increase the groove depth, that is, increase the arc length, as indicated by dot-dash line Y-Y to prevent loop ejection. Note however, that the relatively shallow radius of curvature remains the same for both cases. The full line illustration of Figure 4 is a typical design for a moderate shock and vibration environment such as might be expected in aircraft gyroscopic applications; for example in one airborne gyroscope application, the radius of each groove 33' was 0.025 in. and its depth (for a nickel alloy loop 0.190 in.

diameter, 0.020 in thickness and a preload of 0.020 Ibs.) was 0.008 in and one of the loops 42 was ejected when subjected to a random vibration of 0.2 g2/Hz amplitude.

While the preferred embodiment of the invention has been illustrated and described with respect to sensitive instruments such as gyroscopes in which, in most cases, the contact assemblies are quite small, there may be many other applications wherein the assemblies are required to be substantially larger and still provide the self-capture capability of the assembly. Therefore, the geometry of the ring concavity, loop dimensions and radial gap may be generalised for adaptation to a variety of applications as follows, reference being made to Figure 4a. In general, the radius of curvature of the conductor ring surface or groove R, should be equal to or less than one-half the radial gap dimension, that is, 1 R, --R,-R, (I) 2 wherein R0 is the radius of the point of contact of the loop with the outer ring as defined below, and Rl is the radius of the point of contact of the loop with the inner ring, as defined below.

The dimensions of R0 and Rl are complex functions of the groove radius and loop width as follows:

wherein RIG is the radius from the assembly axis 17 to the bottom of the inner ring groove, ROG is the radius from the assembly axis 17 to the bottom of the outer ring groove, and W is the width of the loop.

Furthermore, the axial restoring or self-capture forces FAR produced by the loop/ring interfaces may be expressed

Turning now to the design of the conductor loop 42, it will be recalled from the above that when assembled into the radial gap 41 the free diameter of the loop is larger than the radial space between the conductor rings, such free diameter-toradial space ratio determining the loop preloads. This ratio is chosen such that purely rolling and hence substantially frictionless contact of the loop with the conductor ring surfaces, upon relative rotation between the gimbal ring 14 and housing 16, is achieved. This criterion is illustrated in Figure 9 wherein the conductor loop 42 characteristics are selected such that it retains its purely rolling contact with the rings 33 and 38. As will be explained further below, it is recognized that in order for the loop surface to contact the ring surfaces and form point contacts, the loop diameter must be theory exactly equal the radial gap dimension; i.e. the asymptote of Figure 9. This is, of course, not practical especially in a shock and vibratory environment. There must therefore be a trade-off between the theoretical and the practical loop characteristics, as will be discussed below.

It has been found that when the maximum free diameter of the loop is exceeded, it becomes so deformed when assembled between the rings that the loop surfaces do not uniformly contact the conductor ring surfaces and the loop surfaces intermediate the loop ends tend to buckle or bulge away from their adjacent ring surfaces, resulting in positive loop contact at four places along the loop surface as indicated in the upper portion of Figure 9. By geometry, this means that there is not true rolling contact between the loop and the rings, and interface sliding will occur, thereby generating friction torques. This exaggerated "kidney" or "jelly-bean" shape also tends to overstress the loop material resulting in material fatigue and loop fracture after relatively few rotations resulting in unacceptable useful life.

More importantly, such exaggerated "kidney" or "jelly-bean" shape of the assembled loop will produce, upon rotation of the members, uncompensated bending moments in the loop with resultant increase in coupling torques. This may be referred to as torque sensitivity to loop angular position around the gap.

In most practical applications of the invention, and particularly in gyroscopic applications, absolute and continuous concentricity between the inner and outer conductor rings is not achievable due to the characteristics of the supporting ball bearing, machining tolerances and compliances produced by the instrument environment. Thus, the loop diameter is selected so that it provides the desired preload at the maximum eccentric gap position during such anomalies. This means that at the minimum eccentric gap position, the loop preload will be greater than desired. If the loop has too great a free diameter, the radii of the ends of the loop will not be equal and coupling torques will be produced by the loop on the rotatable member. This is illustrated at the top of Figure 9 by the dotted line position of the exaggerated kidney-shaped loop. Therefore, the desired free loop diameter is such that these loop end radii remain substantially equal even during operations wherein the conductor rings may not be precisely concentric.

In order to achieve the desired loop-ring contact preload without buckling, a number of interrelated loop parameters must be considered. Generally, the gap radial dimension (R0-R1), and the loop axial width W are pre-or present invention most of the loop and groove design parameters are not limited by mechanical assembly considerations or constraints.

The preload force FN in pounds may be approximated from the following relationship.

where Y=lOOp deflection E=modulus of ring material W,=loop width t=loop thickness R=lOOp free radius Figure 9 is a plot of loop thickness t against loop free radius RF (where loop width WF is a constant .02 in.; Ro-Rl is 0.150 in.; the loop elastic modulus is 30x 106 and yield stress is 200,000 psi) for a family of curves of constant preload FN. It is evident that the maximum preload is a function of the size of the loop and conductor ring diameters and that the maximum desirable preload occurs for a loop free radius of about 0.115 inches. Also, it will be noted that for loop free radii greater than the radius at the maximum desirable, preload will result in undesired contact characteristics, i.e. buckling, while for radii less than this, but of course greater than R,-R,, preload will provide the desired contact characteristic, i.e.

pure rolling contact. Thus, having the parameters R,-R, and W predetermined by basic design considerations, any desired preload FN may be determined; for example, see point B of Figure 9 given a loop thickness of say .0009 in., if a preload of .020 Ibs. is desired, the free loop radius must be 0.096 in. If a higher preload is desired, say .030 Ibs., the free radius may be maintained and the thickness increased to about .0013 in. It will be noted that for the selected thickness there are two free radii (A, B of Figure 9) which will provide the desired preload however, one (A) will be so large as to cause the undesired buckling when assembled in the gap. In general, it is best to maintain the loop deflection small by selecting the thickness to achieve a given preload so as to maintain optimum loop bending moment compensation resulting in minimum sensitivity of torque to radial gap changes.

Referring now to Figures 5 to 8 and recalling the groove geometry of Figure 4a, the self-capture and retention capability of the rolling loop conductor assembly will be described. As shown, this self-capture capability is achieved without the use of "V" grooves or vertical guide walls on each side of the conductor rings since in operation such walls would introduce substantial coupling torque. Concave, relatively shallow grooves on at least one of the relatively rotatable members in combination with a generally flat outer surface of the conductor loop 42 cooperate to generate force vectors (due to the preload) effective on the loop to maintain it within the grooves. These forces are generated during rolling contact and hence do not significantly contribute coupling torques between the members. Further, such self-retention of the loop is extremely advantageous should the grooves of one member not precisely line up with or be precisely coplanar with the grooves of the other, thereby reducing manufacturing costs. (As stated above, simple shims may be used to attain this alignment with a sufficeint degree of precision). Also, during operation, should normal motions of the gyro/aircraft tend to displace the loops axially relative to the groove center, the loops will be maintained within the grooves by these restoring faces.

Figures 5, 6, 7 and 8 illustrate three typical cases of loop misalignment or disturbance relative to the conductor rings. In Figure 5, a lateral or axial displacement of the loop (possibly due to a steady turn of the aircraft) is illustrated.

The force vector generated by FN under this situation will include lateral or axial components which create a restorting force and tend to return the loop to an equilibrium force position. In Figure 6, an axial misalignment (due for example to a non-planar condition between the inner and outer conductor rings) is illustrated.

Again, analysis of the force vectors involved shows the resultant force components are generated which tend to maintain the loop centred within the grooves. Lastly, in Figures 7 and 8 any twisting misalignment, 0 will result in the generation of restoring moments M due to the contact points of the flat surface of the loop with the concave surface of the conductor ring. Figure 7 illustrates a case wherein the loop has undergone an angular translation about a radius of the assembly while Figure 8 illustrates a case where the loop has undergone an angular translation out of the plane of the rotation axis.

At this point it should be noted that a rectangular groove or a "V" groove, whether the latter groove is shallow or deep cannot produce the self-capture forces described above when the conductor rings are axially misaligned. Incidentally such axial misalignment may occur during the operation of an aircraft gyroscopic device in the presence of in-flight g-forces. A rectangular groove cannot produce such restoring forces, since the loop simply abuts the groove sidewalls, resulting in a distortion of the loop and the production of high friction torques. Likewise, with a "V" groove, even a shallow one, an axial misalignment of the conductor rings will result in forces which are actually divergent; that is, instead of tending to restore the loop into the groove, the forces tend to drive the loop out of the groove.

The combination of the concave groove and flat outside surface of the loop provides for redundant loop contact points thereby assuring reliable electrical continuity.

The rolling loop conductor assembly is designed so that the delicate loops 42 may be assembled within the radial space between the inner and outer concave conductor rings, 33, 38 without deforming, overstressing, marring or otherwise damaging the latter. This is extremely important since if the loop, in handling, such as with tweezers or the like, becomes scratched or nicked, even slightly, each loop surface imperfection becomes a source for torque changes as well as introducing the possibility of a fracture at that point after a short operating time.

Furthermore, without the present assembly method and apparatus, the loops would have to be deformed, using some sort of spreading tool in order to insert them into the gap 41. The spreading tool itself could mar or nick the loop.

Additionally, the use of such a tool would require a very skillful assembler to guide the loop into the gap and align the loop with the conductor rings, an extremely tedious and time consuming procedure. The presence assembly method and apparatus eliminates all of the foregoing assembly problems and may be accomplished by semi-skilled assemblers in a very short time, as will be described.

The present assembly method and apparatus also advantageously permit the assembly of loops having various free diameters or preloads, into concave inner and outer conductor ring having various depths depending upon the severity of the vibration and shock environment of the instrument in which it is installed.

The assembly method and apparatus will be described with reference to Figures 2, 2a, 3 and 3a. The method involves the use of the adapter plate 24 and an assembly tool or fixture 50 (Figure 3). As described above, the adapter plate 24 is fitted between the housing 31 and the instrument housing 16. A number of different adapter plates may be designed for different gyroscope configurations. The plate 24 is generally circular and includes an inner annular lip 51 which ultimately locates and concentrically aligns the conductor assembly with the gyro housing bearing and trunnion opening 52. The outer surface 53 of the adapter plate 24 includes an outer recess 54 which receives an inner shoulder 55 (Figure 1) of the housing 31, the shoulder 55 extending beyond the securing or mounting flange 26 to the depth of the adapter plate recess 54. The flat recess 54 defines a first substantially semicircular stop 56 (Figures 2a and 3) concentric with the lip 51 and the opening 52 and also concentric with the peripheral outer surface of the housing 31, thereby defining the normal assembled concentric position of the housing 31 with respect to the ring member 36. The flat recess 54 extends beyond the normal position of the housing 31 opposite the stop 56 and defines a second radially displaced substantially semi-circular stop 57 concentric with the peripheral outer surface of the housing and thereby defines a position for the housing 31 which is eccentric relative to the inner conductor 36. The overall shape of the recess 54 permits the outer conductor housing 31 to pivot or rotate about one of the assembly securing screws 27, 27', such as the screw 27, from a normal or closed position concentric with respect to the inner conductor member 36 to an open or "load" position eccentric with respect to the member 36. Thus, in the "load" or open position, a relatively large radial space is provided between one side of the inner and outer conductor rings of the contact assembly. This sarge radial space permits the assembly of various diameter loops 42. Actually, it can permit the assembly of loops of a diameter providing maximum preload (without buckling, as described above).

Alternatively, instead of pivoting the housing 31 about one of its mounting screws as illustrated in Figures 2, 2a and 3, the recess 54 of the adapter plate 24 as shown in Figures 10 and 10a, may be eccentric with respect to the trunnion 25 and the inner conductor member 36, and an extension 31' of the housing 31 may fit within the recess 54 and be correspondingly eccentrically located relative to the internal axis of symmetry of the housing 31, such that in its normal position its internal axis of symmetry is aligned with the axis of the inner member 36. Thus rotation of the adapter plate 24 (before the mounting screws 27, 27' are inserted) will eccentrically displace the housing 31, thereby providing the enlarged radial space for assembly of the loops as shown in Figure 10a.

The loop assembly apparatus of tool 50 is illustrated in Figures 2, 3 and 3a and in use permits the loops 42 to quickly assembled without handling with tweezers or other sharp objects which might mar or nick the loops. The tool 50 is preferably moulded from a suitable plastics materials and comprises a circular base flange portion 60 having a diameter larger than and adapted to bridge the internal diameter of the housing 31 so that the axial face of the housing 31 serves as an alignment stop for the tool when in use. An extension or hub 61 and a knob 62 on one side of the base flange permit the tool to be easily handled and manipulated.

Extending from the centre of the opposite side of the base flange 60 is a hollow cylinder or guide member 62 having a internal diameter permitting a sliding fit over the inner conductor member 36 and of a sufficient length to extend beyond the innermost inner conductor 38 of the member 36. A portion of the side of the member 63 facing the enlarged gap 41 is cut away at 64 in Figure 2a permit engagement of the loops with the inner conductor rings 38. Laterally displaced from the member 63 and opposite the cut away portion thereof is a rod 65 of a plastics material, slidingly fitted in a mounting hole 66 in the extension of hub 61.

As shown, the rod 65 has a diameter substantially less than the normal gap 41 and at one end is provided with a plurality of recesses 67, spaced according to the ring spacing, and at its other end a knob 68, Suitable low pressure ball and detent arrangements 69 are provided for establishing positive rod positions in use. It will be understood, however, that the rod 65 alone may be used, the assembler manually guiding the rod into the widened gap 41.

In operation, the assembly, preferably in a clean room, scatters some loops from their containers onto a soft, lint-free surface (such as sponge rubber or sponge plastics material) and using the tool 50 with the rod 65 in its extended detent position, (which aligns the recesses 67 with the ring pairs during assembly, as described herein), picks up at least the number of loops to be loaded on the rod end and manipulates the tool, as by tapping, such that one loop hangs freely in each of the recesses 67. The end of cylinder 63 is placed on the outer end of inner member 36 with the axis of member 36 aligned horizontally, and rotated so that an arrow or marker 70 disposed on the plate 24 is aligned with an arrow or marker 71 disposed on the flange 60 (thereby assuring proper alignment of the rod 65 within the enlarged radial opening 41) and then fully advances the tool 50 until the inner surface of the flange 60 abuts the outer surface of the housing 31. Now, all of the loops are aligned coplanar with their corresponding inner and outer conductor rings 33, 38. The assembler then rotates the housing 31 on the screw 27 so that the shoulder 55 abuts the recess stop 56, thereby to compress the loops between the conductor rings and establish the designed preload. Then the screw 27' is inserted through the hole in the mounting flange 26 of the housing 31 and the hole in the adapter plate 24, and the screw 27' is lightly tightened. The assembler then withdraws the rod 65, with the tool still held in place, so as to ensure that the rod does not inadvertently contact any of the loops upon removal. Finally, the tool 50 is carefully removed without rotation so that the open walls of the member 63 do not contact the loops, and both the screws 27 and 27' are tightened to the desired torque. The protective cap 43 is snapped in place to seal the interior of the assembly from any foreign matter.

While in the foregoing there have been described specific embodiments of the present invention, it will be understood that other embodiments are possible. For example, in the assembly method and apparatus, the adapter plate 24 may be dispensed with if desired and the guide and stop means provided by the components 54, 56 and 57 may be incorporated directly in the support member.

Also, other guide and stop means or arrangements may be employed; for example, the plate 24 with its recess 54 and stops 56, 57 may be dispensed with and a simple pin and arcuate slot arrangement used. In this case, the pin may be secured in the support member 16 and extend through an arcuate slot in one of the flanges 26, the ends of the slot providing stops which determine the pivotal movement of the ring housing 31 between its normal coaxial position and its 'load' or eccentric position.

The preferred embodiment of the invention provides an electrical contact assembly adapted to operate in a vibratory and shock environment wherein the depth of the concave surfaces of the circular conductors is such that the current transfer loop is self-captured and maintains electrical continuity in such environment without imparting friction and coupling torques on the sensitive instrument due to the capture mechanism. The current transfer element is selfaligning in the presence of any axial and/or angular misalignment of the contact rings and/or loop, this being accomplished without imparting friction and coupling torques on the sensitive instrument. Further normal axial and radial misalignments of the two concave contact surfaces are automatically compensated by reason of the fact that the radii of the two concave surfaces is less than half the radial clearance and the fact that the loaded loop minor and major axes are approximately equal.

In the preferred method the conductor loops are assembled within the shoulders of the concave surfaces of the inner and outer circular conductors without deforming, stressing or marring the loops, which is important for assuring long reliable operation and smooth and consistent coupling torque.

WHAT WE CLAIM IS: 1. An electrical contact assembly for conducting electrical energy between a pair of members which are included in the assembly and which are relatively rotatable about a common axis, comprising first and second circular, coplanar and coaxial electrically conductive rings, one of the rings being disposed on one of said members and the other of the rings on the other of said members for relative rotation about said axis, the respective diameters of the rings provided a relatively large radial gap therebetween and at least one of the facing surfaces of the rings presenting towards the gap a relatively shallow, arcuately concave configuration in radial section, and a resilient, filamentary, electrically conductive circular loop having a free diameter greater than the gap and presenting an outer surface which is substantially linear in radial section generally, the loop being compressed within the gap, whereby the loop rolls on the or each concave ring surface substantially without friction upon relative rotation between the members, the loop thereby producing preload forces, between the outer loop surface and the or each concave ring surface, having force components in directions to maintain the loop within the or each concave surface.

2. A contact assembly according to Claim 1, wherein both of the rings present said relatively shallow, arcuately concave configuration towards the gap.

3. A contact assembly according to Claim 1 or 2, wherein the pair of members include inner and outer cylindrical members of insulating material having substantially cylindrical external and internal cylindrical walls respectively, at least one of the cylindrical members having an annular, relatively shallow, arcuately concave surface on its wall, the corresponding conductive ring comprising a thin metallic film deposited on the concave surface of said wall.

4. A contact assembly according to any of the preceding claims, wherein the maximum free diameter of the loop is such that when compressed within said gap, the loop surface contact with the ring surfaces is continuous, whereby no coupling torques are produced on the pair of members by loop buckling.

5. A contact assembly according to any of the preceding claims, wherein the or each concave ring surface has a predetermined radius of curvature and the width of the loop outer surface is less than the width of the or each ring concave surface, and wherein the preload force produces force vectors substantially parallel to the predetermined radius at the points of contact between the flat loop surface and the or each ring concave surface, the force vectors having unbalanced components when the loop is axially and/or angularly misaligned relative to the or each concave surface which are substantially parallel to the rotation axis and which tend to maintain said loop within the or each concave surface.

6. A contact assembly according to any of the preceding claims, wherein a plurality of said rings, axially spaced, is provided on each of the members, a corresponding loop being disposed between each pair of facing rings.

7. A contact assembly according to Claim 3, wherein one of the cylindrical members is radially fixedly mounted on one of said members relative to said axis, and mounting means for movably mounting the other cylindrical member on the other of said members between a normal coaxial position relative to said one support member and an eccentric position relative to said one support member, the amount of said movement providing an enlarged radial gap greater than the free diameter of said loop, whereby said loop may be assembled within said gap at said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. depth of the concave surfaces of the circular conductors is such that the current transfer loop is self-captured and maintains electrical continuity in such environment without imparting friction and coupling torques on the sensitive instrument due to the capture mechanism. The current transfer element is selfaligning in the presence of any axial and/or angular misalignment of the contact rings and/or loop, this being accomplished without imparting friction and coupling torques on the sensitive instrument. Further normal axial and radial misalignments of the two concave contact surfaces are automatically compensated by reason of the fact that the radii of the two concave surfaces is less than half the radial clearance and the fact that the loaded loop minor and major axes are approximately equal. In the preferred method the conductor loops are assembled within the shoulders of the concave surfaces of the inner and outer circular conductors without deforming, stressing or marring the loops, which is important for assuring long reliable operation and smooth and consistent coupling torque. WHAT WE CLAIM IS:

1. An electrical contact assembly for conducting electrical energy between a pair of members which are included in the assembly and which are relatively rotatable about a common axis, comprising first and second circular, coplanar and coaxial electrically conductive rings, one of the rings being disposed on one of said members and the other of the rings on the other of said members for relative rotation about said axis, the respective diameters of the rings provided a relatively large radial gap therebetween and at least one of the facing surfaces of the rings presenting towards the gap a relatively shallow, arcuately concave configuration in radial section, and a resilient, filamentary, electrically conductive circular loop having a free diameter greater than the gap and presenting an outer surface which is substantially linear in radial section generally, the loop being compressed within the gap, whereby the loop rolls on the or each concave ring surface substantially without friction upon relative rotation between the members, the loop thereby producing preload forces, between the outer loop surface and the or each concave ring surface, having force components in directions to maintain the loop within the or each concave surface.

eccentric position without distorting the same and is compressed between said rings at said normal position.

8. A contact assembly according to Claim 7, wherein the mounting means comprise adapter means between the outer ring cylindrical member and said member, guide means on said adapter means defining said normal position, and shoulder means on said outer ring cylindrical member engageable with said guide means for providing movement of said outer ring from said eccentric position to said normal position.

9. A contact assembly according to Claim 8, wherein the guide means comprise a channel in the adapter means for receiving the outer ring support member and including first stop means for positioning said outer ring cylindrical member in its normal coaxial position relative to said inner ring cylindrical member and a second stop means for positioning said outer ring member in said eccentric position relative to said inner ring support member, and pivot means on said outer ring support member for maintaining said outer ring support member in said channel and guiding the same between said first and second stop means.

10. A contact assembly according to Claim 9, wherein the outer ring cylindrical member includes flange means radially extending therefrom and screw means through said flange for mounting the same on said instrument member and wherein said pivot means comprises said screw means.

11. A method of assembling the electrical contact assembly of Claims 1 to 10, the method comprising mounting one of the rings on one of the members so that it may be moved from a normal coaxial position relative to the other of the rings to an eccentric position relative thereof, whereby to provide a larger gap on one side of said other ring greater than the free diameter of said loop and a smaller gap on the opposite side thereof, moving said one ring to said eccentric position, inserting said loop within said larger gap and aligning said loop so that it is substantially coplanar with said inner and outer rings, and moving said one ring to said normal coaxial position whereby to compress said loop between said inner and outer rings.

12. A method according to Claim 11, wherein the inserting and aligning steps include locating said loop on a rod having a diameter less than said normal gap, guiding said rod and loop into said larger gap and aligning said loop with said inner and outer rings, and removing said rod after said rings are in their normal coaxial position.

13. A method according to Claim 11 or 12, wherein the contact assembly comprises a plurality of ring and loop assemblies distributed along said axis and wherein said rod is elongate and includes a corresponding plurality of notches correspondingly distributed along its length, the method additionally comprising collecting a corresponding plurality of loops on said rod, manipulating said rod so that one loop hangs in each of said notches, guiding said rod into said larger gap, and aligning said rod so that each of said loops lies substantially in the plane of its corresponding rings.

14. A contact assembly constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.

15. A method of assembling an electrical contact assembly, substantially as herein particularly described with reference to the accompanying drawings.