US3329923A

US3329923A - Multitrack slip-ring and brush assembly

Info

Publication number: US3329923A
Application number: US434976A
Authority: US
Inventors: Davis James Carl
Original assignee: Litton Precision Products Inc
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1965-02-24
Filing date: 1965-02-24
Publication date: 1967-07-04
Anticipated expiration: 1984-07-04
Also published as: GB1083564A; DE1564244B1; CH441496A

Description

' July 4, 1967 J. C DAVIS MULTITRACK SLIP-RING AND BRUSH ASSEMBLY fir/0r ,4/79

Filed Feb. 24, 1965 f ik w War/ray United States Patent 1 3,329,923 MULTITRACK SLIP-RING AND BRUSH ASSEMBLY James Carl Davis, Blacksburg, Va., assignor to Litton Precision Products, Inc, Beverly Hills, Calif.

Filed Feb. 24, 1965, Ser. No. 434,976 8 Claims. (Cl. 339-2) This invention relates to sliding or rotating contact assemblies. More particularly, it relates to brush and slipring assemblies suitable for transferring electrical signals or electrical power between relatively rotating or sliding components such as are employed in precision instruments, for example, in gyroscopic guidance systems.

Of major importance in precision instruments, such as the gyroscopic systems used to perform indicating or control functions on modern high speed aircraft or ships, is the low-noise transmission of low-level electrical signals to and from moving or rotating structures. A significant source of unwanted electrical fluctuations or noise in such apparatus is the variation of the resistance between the contacts in brush and slip ring assemblies. Related problems arise from inadequate contact life which necessitates frequent and expensive overhaul and repair to maintain critical operational tolerances.

Accordingly, it is among the objects of this invention to provide sliding electrical contact assemblies capable of reliable low-noise performance for relatively extended periods.

These and other objects of the invention are achieved in one particular illustrative embodiment which includes a longitudinally extending channel or groove having nonparallel conductive walls and a brush assembly having at least one brush mounted for movement relative to the walls of the groove. The longitudinal extent of the groove may be along a straight line, along a circle, or along a path of arbitrary curvature. A portion of the brush is positioned in the groove in sliding electrical contact with the conductive walls. The portion of the brush in the area of contact is characterized by an elongate cross-section, and the brush is aligned in the groove with the greater cross-sectional dimension extending thereacross.

In a preferred illustrative embodiment, the groove is V-shaped and the larger cross-sectional dimension of the brush in the contact area is greater than the width of the groove at its bottom but less than the width at its top. Thus, the brush rides in the groove somewhat above the bottom and contacts the side walls with a surface of relatively high curvature in a cross-sectional plane. It is considered most advantageous, in embodiments employing more than one brush in a groove, for the larger crosssectional dimension of each brush to differ from that of the others. Each brush, therefore, will ride in the groove at a difierent height above the bottom and each will contact the side walls along a separate set of traclm.

The objects, features and advantages of the invention will be fully understood from the following more detailed description taken in conjunction with the accompanying drawing, in which FIG. 1 depicts a slip-ring and brush assembly of the prior art;

FIG. 2 shows a sliding contact assembly embodying the principles of the invention; and

FIG. 3 illustrates a slip-ring and brush assembly in accordance with a preferred embodiment of the invention.

There is shown in FIG. 1 a typical prior art slip-ring and brush assembly comprising a slip-ring 11 having a V-shaped circumferential groove 12 with

conductive side Walls

13 and 14, and a wire type brush 15 of circular crosssection. The diameter of brush 15 is smaller than the width of the top but greater than the width of the bottom of groove 12 so that the brush rides in the groove somewhat above its bottom and in sliding conductive contact with

walls

13 and 14.

While the groove type slip-ring of FIG. 1 was a substantial improvement over earlier types in which the round brush rode on a single flat surface, it is still subject to difficulties which give rise to substantial and troublesome variations in the contact resistance at points 16 and 17, thereby causing undesirable noise in the electrical circuits associated with the precision instruments in which they are frequently used, such as gyroscopic instruments. For example, wear particles, dust and other foreign particles may accumulate in the bottom of the groove 12 to a depth sulficient to lift the brush intermittently out of contact with one or both of the groove walls.

Furthermore, the angle between

walls

13 and 14 and the surface of the brush 15 adjacent to the contact areas 16 and 17, as measured in a cross-sectional plane, is extremely acute. Thus wear particles or dirt is easily trapped between the contacting surfaces and burnished into either the brush 15 or the ring 11, thereby causing troublesome variations in the electrical characteristics of the assembly. The space between the brush 15 and the bottom of the groove 12 could, of course, be increased by increasing the diameter of the brush but such a design has the disadvantage of extending the area of the acute angle intersection surrounding the contact areas so as to create a still larger trap for unwanted particles.

In accordance with one aspect of the invention, the sliding contact assembly 20 depicted in FIG. 2 comprises a brush 25 which is wider in one cross-sectional dimension than in the other. 'Brush 25 is positioned in groove 12 with the wider dimension of its cross-section extending thereacross. Thus, the edges or corners of the brush are in sliding electrical contact with the

walls

13 and 14 of the groove 12 at contact areas 26 and 27. Because of the elongate cross-section of brush 25, its surfaces in the contact areas 26 and 27 have a relatively high curvature in a cross-sectional plane. The radii of curvature of brush 25 in the contact areas is substantially less than one half the maximum cross-sectional dimension of the brush whereas, in the prior art embodiment of FIG. 1, the curvature of brush in the contact areas is equal to one half the maximum cross-sectional dimension, as can be seen from the circular cross-section of the brush 15.

By virtue of the relatively short radii of curvature of brush 25 at contact points 26 and 27, the angles between

conductive walls

13 and 14 of groove 12 on the one hand and the surface areas of the brush 25 adjacent the contact areas on the other hand are substantially less acute than in sliding contact arrangements of the prior art. Thus, the space between the brush and the walls of the groove, adjacent to the contact area, is less constricted. It has been found with this configuration that wear particles, dust and other foreign particles tend to be wiped away from the contact areas instead of being trapped under them and burnished into the contact surfaces.

The elongate cross-section of brushes employed in the illustrative embodiments offers an additional advantage over the round cross-section of prior art brushes in that a greater maximum cross-sectional dimension is achieved without adding significantly to the bulk, weight or stiffness of the brush. It is to be noted, moreover, that the relatively high curvature in the contact areas of brushes such as are shown in the drawing may result in a smaller area contact and consequently a greater contact pressure 'ice - with the same force applied to the brush. Alternatively,

tional dimension of brush 25, it will ride higher in groove 12 than does the round brush 15 illustrated in the embodiment 10 of FIG. 1. A larger space is therefore left at the bottom of groove 12 for the collection of wear particles and other undesirable materials which are wiped away from contact areas 26 and 27 by virtue of the improved contact configuration of the invention.

Although the invention is illustrated in the embodiment of FIG. 2 with a V-shaped groove or channel it will be appreciated that channels having other cross-sections which are wider at the top and narrower at the bottom may also be used. Yet other types of channels adapted to receive a brush in sliding conductive contact with the channel Walls may also be employed, such as channels which vary arbitrarily over their depth from a maximum to a minimum width.

It is a frequent practice in precision sliding contact assemblies to employ two or more brushes in sliding conductive contact with the walls of a single groove at areas spaced one from another. For example, a brush and slipring assembly of the type shown in FIG, 1 may employ two brushes of the same diameter positioned 180 apart in groove 12. While such a prior art arrangement has the benefit of four contact areas-two at each brush it is not free of problems since each brush rides on precisely the same tracks as the other.

In the embodiment of the invention illustrated in FIG. 3, a slip-ring 31 having a V-shaped circumferential groove 32 with

conductive side walls

13 and 14 is contacted by a pair of brushes 35 and 36 having the characteristics described above in connection with the brush of sliding contact assembly 20 shown in FIG. 2. In accordance with the principles of this invention, however, the longer crosssection dimension of each brush dilfers substantially from that of the other. As a result, each brush

contacts side walls

13 and 14 of groove 12 at a different height above the bottom of the groove. Each brush, therefore, rides along a separate set of tracks so that an accumulation of wear particles or other undesirable material which affects one brush will not affect the other.

Brush

contacts side walls

13 and 14 along

racks

33 and 34, while brush 36 is in contact along

tracks

37 and 38. Thus, variations between tracks and/or contacts as a result of variations in the finish, dimensions, compliance 7 or other structural characteristics of the brushes are offset as each brush creates its own independent set of tracks. Although the assembly of FIG. 3 has two brushes, it will be appreciated that the principle of the invention may be extended to a larger number without significant modification.

Miniature brushes of a type employing the invention may be fabricated by flattening the end portions of the round wire-type brushes used heretofore. Brushes having different maximum cross-sectional dimensions may be made by flattening each brush to a diiferent extent. Alternatively, brushes made from flat stock can be used.

It has been found that a brush and slip-ring assembly as shown in FIG. 3 operates with significantly less electrical noise caused by fluctuations in the contact resistance. Moreover, the amount of wear particles produced is substantially reduced, resulting in an extension of the useful life of the assembly, as well as an improvement of performance over a substantial portion of the useful life.

In one test, a brush block was fabricated and all brushes were flattened to give maximum width while keeping the brush thickness within allowable limits. The brush block was assembled with a slip-ring, subjected to an oil and chlorothene bath and tested for noise, which was found to average 26.7 milliohms. The part was then deliberately misaligned to cause wear particles to be produced of a type which, from experience, would increase the noise to a level between 60 and 600 milliohms. In this condition the part was rotated for 44 hours, after which the noise level was found to have decreased to 18.5 milliohms.

After an additional 24 hours the noise level decreased further to 16.5 milliohms. The assembly was then deliberately contaminated with foreign particles to an extent that could be expected to render the performance entirely unsatisfactory. The noise was found to have increased only to 40 milliohms, and, after 20 additional hours of running, this decreased to 8 milliohms.

Although the invention has been described with particular reference to a number of specific embodiments, these are for purposes of illustration only. Many variations and modifications in addition to those mentioned herein are possible and may be made by those skilled in this art without departing from the scope and spirit of the invention. For instance, brushes and grooves of various sizes and cross-sectional configurations may be employed to achieve multi-track-contact as taught herein by example.

What is claimed is:

1. Sliding contact assembly comprising, in combination,

an elongated channel with conductive side walls, said channel being substantially wider at its top than at its bottom, and

a plurality of brushes for engaging said side walls at longitudinally spaced points in longitudinally sliding conductive contact along a plurality of separate tracks spaced from one another on the walls of said channel, each of said brushes being wider than the bottom and narrower than the top of said channel.

2. Sliding contact assembly comprising, in combination,

an elongated channel with conductive side walls,

said channel being substantially wider at its top than at its bottom, and

at least a pair of brushes for engaging said side walls at longitudinally spaced points in longitudinally sliding conductive contact along at least four separate tracks spaced from one another on the walls of said channel,

each of said brushes being wider than the bottom and narrower than the top of said channel and engaging each of said walls along at least one track.

3. Sliding contact assembly comprising, in combination,

an elongated channel with conductive side walls,

said channel being substantially wider at its top than at its bottom, and

at least a pair of brushes each having at least a pair of conductive contact surfaces,

said pairs of surfaces being in longitudinally sliding conductive contact with said side walls along separate tracks and at longitudinally spaced points, said tracks being spaced apart on the walls of said channel.

4. Sliding contact assembly comprising, in combination,

an elongated channel with non-parallel conductive side walls, and

a plurality of brushes for engaging said side walls at longitudinally spaced points in longitudinally sliding conductive contact along a plurality of separate tracks spaced from one another on the walls of said channel,

each of said brushes having a cross-sectional dimension greater than the smallest and smaller than the greatest cross-sectional dimension of said channel and engaging each of said Walls along at least one track.

5. Sliding contact assembly comprising,

an elongated V-shaped groove having conductive side walls, and

at least a pair of wire-type brushes mounted for relative movement longitudinally with respect to said groove,

a portion of each brush being in longitudinally sliding conductive contact with the side walls of said groove at points longitudinally spaced from the points of contact of the other brush,

each of said brush portions having an elongate crossscction with the longer dimension greater than the width of the bottom and smaller than the Width of the top of said groove and positioned in said groove with said longer dimension extending substantially across said groove,

the longer cross-section dimension of said brush portions differing substantially each from the other, each of said brushes being in longitudinally sliding conductive contact with the side walls of said groove along a separate pair of tracks, said pairs of tracks being spaced from one another on the walls of said grooves.

6. Brush and slip-ring assembly comprising, in combination,

a slip-ring having a brush-receiving circumferential groove,

said groove being substantially wider at its top than at its bottom and having conductive side walls, and

a pair of brushes in circumferentially sliding conductive contact with the conductive walls of said groove at circumferentially spaced points,

each of said brushes being wider in one cross-sectional dimension than in the other,

the Wider dimension of each brush being wider than the bottom and narrower than the top of said groove,

each of said brushes being positioned in said groove with its wider dimension of cross-section extending thereacross,

each of said brushes being in circumferentially sliding conductive contact with the walls of said groove along a separate pair of tracks,

said pairs of tracks being spaced apart on the walls of said groove.

7. Brush and slip-ring assembly comprising, in combination,

a slip-ring having a brush-receiving circumferential groove with conductive side walls,

the width of said groove varying over its depth from a maximum to a minimum, and

a pair of brushes in circumferentially sliding conductive contact with the side walls of said groove,

each of said brushes having an elongate cross-section with its wider dimension of cross-section being wider than the minimum and narrower than the maximum width of said groove,

each of said brushes being positioned in said groove with its wider dimension of cross-section extending between said walls,

said pairs of tracks being spaced apart on the walls of said groove.

8. Brush and slip-ring assembly comprising, in combination,

said groove being substantially wider at its top than at its bottom, and

a pair of brushes each having a pair of curved conductive contact surfaces,

the radii of curvature of said contact surfaces in a crosssectional plane being substantially smaller than onehalf the maximum cross-sectional dimension of the respective brush,

said contact surfaces being in circumferentially sliding conductive contact with separate tracks along the side walls of said groove,

the contact surfaces of one brush being in contact with the walls of said groove at points circumferentially spaced from the points of contact of the other brush,

each of said brushes being in circumferentially sliding conductive contact with each wall of said groove along separate tracks,

said tracks being spaced apart from one another on said walls.

References Cited UNITED STATES PATENTS 2,231,149 2/1941 Baum 3392 2,581,266 1/1952 Lum 3395 3,155,207 11/1964 Blemly et al. 191-23 3,259,727 7/1966 Casler 3392 X MARVIN A. CHAMPION, Primary Examiner.

ALFRED S. TRASK, Examiner.

P. TEITELBAUM, Assistant Examiner.

Claims

1. SLIDING CONTACT ASSEMBLY COMPRISING, IN COMBINATION, AN ELONGATED CHANNEL WITH CONDUCTIVE SIDE WALLS, SAID CHANNEL BEING SUBSTANTIALLY WIDER AT ITS TOP THAN AT ITS BOTTOM, AND A PLURALITY OF BRUSHES FOR ENGAGING SAID SIDE WALLS AT LONGITUDINALLY SPACED POINTS IN LONGITUDINALLY SLIDING CONDUCTIVE CONTACT ALONG A PLURALITY OF SEPARATE TRACKS SPACED FROM ONE ANOTHER ON THE WALLS OF SAID CHANNEL, EACH OF SAID BRUSHES BEING WIDER THAN THE BOTTOM AND NARROWER THAN THE TOP OF SAID CHANNEL.