US3902775A

US3902775A - Multiple radially resilient wheel contact assembly

Info

Publication number: US3902775A
Application number: US307240A
Authority: US
Inventors: Jack B Speller
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-03-29
Filing date: 1972-11-16
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02

Abstract

The specification and drawings disclose a plurality of thin, resilient wheels on a common axle for conducting low-noise electrical signals between relatively movable members.

Description

United States Patent Speller Sept. 2, 1975 [54] MULTIPLE RADIALLY RESILIENT WHEEL 2,818,479 12/1957 Volk 200/166 BB CONTACT ASSEMBLY 3,246,089 4/1966 Lieberman et a1 ZOO/166 BB 3,384,850 5/1968 Cameron et a1. 200/166 BB [76] Inventor: Jack B. Speller, 151 Second St.,

Huntington Station, 11746 FOREIGN PATENTS OR APPLICATIONS 22 Filed: Nov. 16, 1972 733,518

21 Appl. No.: 307,240

Related US. Application Data [63] Continuation of Ser. No. 128,819, March 29, 1971,

abandoned.

[52] US. Cl 339/5 P; 339/5 S; ZOO/277 [51] Int. Cl H01! 39/28 [58] Field of Search ZOO/166 BB, 166 ED,

166 BH, 200/166 D, 166 F, 166 C; 339/5 S, 5P,5R,5L,5M,8PB,8L,8R

[56] References Cited UNITED STATES PATENTS 2,297,772 10/1942 Johnson 200/166 C X 7/1955 United Kingdom 200/166 BB Primary Examiner-Robert K. Schaefer Assistant ExaminerWilliam J. Smith Attorney, Agent, or F irm-Shenier & OConnor ABSTRACT 21 Claims, 9 Drawing Figures PATH-MUSE? 2975 3,902,775

INVE TOR JAc/(B. P544532 ATTORN EY INVENTOR (Ma/(B. 63 54 L [Q ATTORN EY MULTIPLE RADIALLY RESILIENT WHEEL CONTACT ASSEMBLY This is a continuation of application Ser. No. 128,8 l9 filed Mar. 29, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to an improved contact for conducting electricity between relatively moving members, and more particularly to a low-noise contact which has a long operating life.

An electrical contact has been sought in the prior art for many years without complete success for conducting low level electrical signals between relatively moving members without introducing spurious signals due to variations in contact impedance. The operating life of prior art contacts is also inadequate for certain commutating applications and instrumentation applications such as encoders, potentiometers, and the like. Then, too, in instrumentation applications where the contact area is necessarily very small and where the contacts must be lightweight so that they do not materially increase the drag and inertia of the system, prior art contacts have been found lacking.

Rolling contacts have been proposed in the prior art for conducting electrical signals between moving members for extended periods of time without loss of contact resolution and have proved more satisfactory than sliding contacts. However, prior art rolling contacts have not proved entirely satisfactory either. For example, these contacts have been found to require an undesirably large force urging the contact against the relatively movable member in order to insure a reliable, low-noise electrically conducting path between the moving members. Such high forces result in excessively high pressures at the point of contact leading often to a failure of the contact material after short periods of operation.

A fundamental problem with prior art contacts is the inability of the contacts to make intimate contact over a substantial contacting area due to microscopic imperfections in the contacting surfaces and small deviations in the geometries of the contacts from their intended shape. This problem has resulted in noise in low level contacts as described above, and contact heating in contacts designed to carry larger currents.

An object of this invention, therefore, is the provision of a contact which provides a reliable, low-noise, highresolution contact which has an extremely long operating life.

Another object of the invention is the provision of such a contact which can operate satisfactorily with only relatively small forces urging it into contact with a relatively moving member.

One further object of the invention is the provision of a contact that provides intimate contact over a substantial contact area. Additional objects, features, and advantages of the novel contact will become readily apparent from the following description.

SUMMARY OF THE INVENTION Briefly, this invention contemplates the provision of an electrical contact formed of a plurality of relatively DESCRIPTION OF THE DRAWINGS Having briefly described this invention, it will be described in greater detail along with other objects and advantages in the following detailed description of a preferred embodiment which may be best understood by reference to the accompanying drawings. These drawings form part of the instant specification and are to be read in conjunction therewith. Like reference numerals are used to indicate like parts in the various views:

FIG. 1 is a front elevation of a preferred embodiment of a contact constructed in accordance with the teachings of this invention;

FIG. 2 is a side elevation of the conductor shown in FIG. 1;

FIG. 3 is a plan view of one conducting wheel of the type used in the contact shown in FIGS. 1 and 2;

FIG. 4 is a sectional view taken along the line 44 of FIG. 3; v

FIG. 5 is an elevation view, with parts broken away, of an encoder employing contacts constructed in accordance with the teachings of this invention;

FIG. 6 is a schematic view illustrating an advantageous orientation of the conductors with respect to the direction of motion;

FIG. 7 is a plan view of a cylindrical, resilient conductor. I

FIG. 8 is a side elevation of the conductor shown in FIG. 7;

FIG. 9 is a side elevation of an alternate embodiment of the conductor shown in FIGS. 7 and 8; and

FIG. 10 is a frontal elevation of an alternate embodiment of a contact constructed in accordance with the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2 of the drawings, one embodiment of a contact constructed in accordance with the teachings of this invention is generally indicated by reference numeral 10 andhas eleven radiallyresilient conductive wheels 12 mounted on a common axle 14. The ends of the axle 14 are secured respectively to the legs of a U-shaped conductive contact holder 16. A slot 18 in each leg of the holder facilitates assembly of the contact.

The wheels 12 can be threaded first on the axle 14 and then inserted in the holder with the ends of the axle passing along the slots 18. The axle can then conveniently be spot welded to shoulders formed at the ends of the slots. A lug 22 on the holder 16 provides a convenient means for securing the contact to a fixture and provides a convenient location for affixing a suitable conductor to the contact.

The wheels 12 are in contact with conductive region 24 carried by a relatively movable support 26. The support 26 is relatively movable essentially tangentially to the periphery of the wheels 12 (as indicated by the arrow in FIG. 2) so that relative movement causes rotation of the wheels 12.

It should be noted that in this embodiment of the invention each of the wheels 12 is free to rotate independently on the axle 14. It is important, however, that the U-shaped holder 16, which may be made of any material having suitable structural and current conducting capabilities such as silver-plated brass, for example, laterally support the wheels 12 and that the wheels stay together tightly while retaining an ability to freely rotate. For example, in one successful embodiment of the invention employing eleven wheels 12, each about 0.001 inch thick and about 0.125 inch in diameter, the total accumulated clearance of between wheels themselves and between the outermost wheels and the legs of the contact holder 16 is on the order of 0.002 inch. The relative clearance between the wheels shown in the drawing is exaggerated and thusly illustrated merely for ease of pictorial presentation. In an actual contact constructed in accordance with this invention, adjacent wheels are in contact with one another. If desired, the wheel adjacent the contact holder on each end of the set of wheels can be made in the shape of a bell-shaped washer. In this manner, the wheels at each end urge the set together while making contact with the holder only in the region of the back of the wheel.

It should be clearly understood that a contact constructed in accordance with the teachings of this invention need not have eleven wheels. Contacts can be successfully made having fewer than or more than eleven wheels. Since each wheel is independently radially resilient, the use of a plurality (two or more) of radiallyresilient wheels provides a contact redundancy that insures multiple points of contact despite the imperfections that invariably exist in contact wheels, themselves, and imperfections in the member they contact. In general, for applications involving low-level signals, it is preferable to make the wheels as thin as practical consistent with structural and handling requirements and to use a relatively large number of wheels (between 6 and 15, for example).

Referring now to FIGS. 3 and 4, each of the contact wheels 12 has a hub 28 in which is formed a bore 32. Concentric circular bans 32a, 34b, and 340, respectively, of increasingly larger diameters and preferably of increasingly larger widths are joined to one another and to the hub 28 by a series of short, narrow tabs 36.

As can be seen clearly in FIG. 3, the inner ban 34a is secured to the hub 28 by four tabs 36 spaced approximately 90 apart from one another. Four tabs 36 disposed intermediate the tabs 36 which join the inner ring 34a to the hub 28 join the intermediate ring 34b to the inner ring 34a.

Similarly, four tabs 36 joined the outer ring 340 to the intermediate ring 3417. These tabs 36 are disposed intermediate the tabs joining the inner and intermediate rings and are in radial alignment with the tabs joining the inner ring to the hub 28. Although the wheel 12 shown in FIGS. 3 and 4 has three rings respectively joined to one another by four tabs, alternate configurations will be readily apparent to those skilled in the art. For example, more or fewer than four tabs can be used for joining the rings and two or more rings can be used. In general, a large number of rings results in a more resilient contact.

If desired, a coating 42 of gold or silver or other highly conductive materil can be formed on the periphery of the wheel 12 in order to enhance its current conducting characteristics.

A wheel 12 may be conveniently formed from a thin sheet of material having suitable mechanical and elec tric current conducting capabilities. The chosen material, in general, should have no resilient memory and have a high conductivity. Etching is a process suitable for forming the wheels, and Beryllium-copper is one suitable material, and a spring steel, which preferably is gold or silver plated, is another. In forming the wheel by etching, the hub 28, rings 34, and tabs 36 may be protected by a photo resist and the open areas 38 removed by the etchant in a manner well understood by those skilled in the art.

The rings 34, which comprise each wheel 12, are thin and flex along a radial line from the hub of the wheel. Because the tabs 36 joining adjacent rings are staggered with respect to one another, the wheel 12 is thusly radially resilient with an almost uniform spring constant around its entire periphery. Increasing the width of the outermost ring 34 of the contact increases the spring rate of the contact. The open construction of the wheel 12 also reduces its mass and hence contributes to the low inertia of the contact.

The diameter of the wheel 12 should be large compared to the diameter of the axle 14 so that the relative speed between the axle 14 and the wheel 12 is low even though the peripheral speed of the wheel is relatively high. This arrangement minimizes sliding friction which contributes to the long operating life of the contact. In addition, the axle 14 should closely fit the bores 32 in the wheels in order that the force between the axle and wheels be distributed over as large an area as possible. If desired, the axle can be plated with a hard gold or other suitable conducting material to further increase its operating life. The axle 14, itself, may be formed from any material having suitable structural and current conducting properties and is compatible with the material used for the wheels 12. Usually, it is preferable to make the axle of a hard gold alloy.

Since each of the rings 34 is flexible, the spring action of the wheel 12 is exerted right at the point where the wheel makes contact with the conductive member 24. This permits relatively high contact pressure without unduly loading the axle 14. The spring action tends to insure that at least some portion across the width of each wheel 12 makes contact with the conductor 24 so that with the redundancy resulting from using a number of wheels 12, the contact provides a uniform lowresistance, current conducting path between the relatively movable members with only relatively light loading of the contact.

FIG. 5 illustrates an example of a typical application in which the contact of this invention is used such as a shaft position encoder. The lug 22 of the contact is fixed to an insulating support 52 by means of an epoxy, for example. A lead 54 soldered to the lug 22 provides a means for coupling the contact to a suitable utilization device (not shown) A coded disk 56 is fixed to a rotatable shaft 58 which is journaled in a bearing 62 affixed to the support 52 and a bearing 64 secured in an opening in a housing 66. The coded disk 56 carries conducting regions 68 as is conventional in the art. It should be noted that the contact 10 should be positioned with respect to the code disk 56 to the end that good contact is achieved without overstressing the contact wheels. In the encoder shown in FIG. 5, the shaft 58 and housing 66 position the contact with respect to the housing; however, any suitable design known in the art may be used to achieve this end.

Referring now to FIG. 6 as well as FIG. 5, preferably the wheels 12 of the contact 10 are oriented at a small angle with respect to the direction of the relative motion. FIG. 6 illustrates this preferred relationship. The instantaneous velocity of the disk 56 is represented by the vector v and the orientation of the wheels 12 is represented by the vector 0. The skew angle between these two vectors is preferably on the order of one or two degrees and provides a wiping action for the contacts without materially increasing contact wear or the overall torque of the system. In addition, orientating the contacts with a slight skew tends to maintain the contacts tightly in contact with one another.

Resilient conductors having a substantially uniform spring constant all along their curvilinear surface can be advantageouslyemployed in applications other than the contact hereinabove described. For example, US. Pat. No. 3,534,194 discloses an encoder and other similar devices which employ a cylindrical conductor that is axially resilient, such as those shown in FIGS. 7 and 8 to which reference is now made. A cylindrical stack of concentric rings 72 joined by short, narrow tabs 74 offset from one another form a conductor that is substantially uniformly resilient all along its surface 76. This conductor may be etched from a single cylinder of suitable material such as Beryllium copper.

FIG. 9 shows a conductor similar to that shown in FIGS. 7 and 8. In the embodiment of FIG. 9, narrow, flexible tabs 84 in a generally herringbone pattern join an inner ring 78 to an outer ring 82 to provide an axially resilient contact which has a generally uniform spring constant along a circular path 86.

FIG. 10 shows an alternate embodiment of a conductor constructed in accordance with the teachings of this invention. In this embodiment, two sets of wheels 12 are fixedly secured to a conductive axle 14. The axle 14 is rotatably mounted in a pair of end bearings 104 and a central bearing 105. The contact holder 102, which may be of a nonconductive material, supports the

bearings

104 and 105. These bearings may be of any suitable type known in the art, such as ball bearings or jewel bearings.

The lefthand set of contacts 12 contact a conductor 106 and the righthand set contacts a conductor 108. The conductor 106 may be segmented as in an encoder, for example, and the conductor 108 continuous. An electrically conductive path is thusly provided between

conductors

106 and 108 via the two sets of wheels 12 and the axle 14. It should be noted that in this embodiment of the invention, all the contact members in the current conducting path are in rolling engagement with one another. It should be noted, also, that the outermost wheels 12 are bell-shape, as previously explained.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. The contacts of this invention have extremely good current conducting capabilities owing to the .very small contact resistance. This makes the contact extremely well suited for a large number of applications. These applications include contacts for relays and contacts for electrical motors and generators. In relay applications, the wheels can be skewed so that they rotate through a larger arc in one direction than in the other, presenting excessive wear on one spot on the contact. This is contemplated by and is within the scope of the claims. It is further obvious that various changes may be made in details within the scope of the claims without departing from the spirit of the invention. It is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

What is claimed is:

I. A contact for conducting electrical energy between relatively movable members comprising in combination:

a plurality of electric current conducting wheels mounted on an electric current conducting axle; each of said wheels comprising a plurality of concentric rings joined together by a plurality of sets of short, narrow tabs, two of said sets of tabs joining each ring of said plurality to two adjacent rings respectively, said two sets of tabs being radially offset with respect to one another whereby said wheels are substantially uniformly radially resilient; means supporting said axle; said support means coupled to a first member relatively movable with respect to a second electric current conducting member;

said second relatively movable electric current conducting member disposed to contact wheels and disposed for movement tangentially relatively thereto; and

said plurality of wheels acting in unison to make contact with said second member.

2. A contact for conducting electrical energy between relatively movable members, as in claim 1 wherein said wheels are in intimate contact with one another.

3. A contact for conducting electrical energy between relatively movable members, as in claim 1, wherein said wheels are rotatably mounted on said axle and said axle is affixed to said supporting means.

4. A contact for conducting electrical energy between relatively movable members, as in claim 2, wherein said wheels are rotatably mounted on said axle and said axle is affixed to said supporting means.

5. A contact for conducting electrical energy between relatively movable members, as in claim 1, wherein the peripheries of said wheels deflect slightly at the point of contact.

6. A contact for conducting electrical energy between relatively movable members, as in claim 2, wherein the peripheries of said wheels deflect slightly at the point of contact.

7. A contact for conducting electrical energy between relatively movable members, as in claim 3, wherein the periphery of said wheels deflect slightly at the point of contact.

8. A contact for conducting electrical energy between relatively movable members, as in claim 4, wherein the peripheries of said wheels deflect slightly at the point of contact.

9. A contact for conducting electrical energy between relatively movable members, as in claim 1, wherein said plurality of wheels comprises at least three wheels.

10. A contact for conducting electrical energy between relatively movable members, as in claim 2, wherein said plurality of wheels comprises at least three wheels.

11. A contact for conducting electrical energy between relatively movable members, as in claim 3, wherein said plurality of wheels comprises at least three wheels.

12. A contact for conducting electrical energy between relatively movable members, as in claim 4, wherein said plurality of wheels comprises at least three wheels.

13. A contact for conducting electrical energy between relatively movable members, as in claim 8, wherein said plurality of wheels comprises at least three wheels.

14. A contact assembly for conducting electrical energy between relatively movable members including in combination, an electrically conductive axle, a plurality of disk like metal wheels supported by said axle in closely spaced relationship, each of said wheels being formed with a plurality of openings between the circumference thereof and said axle to render said wheels radially resilient independent of each other, an electrically conductive member adapted to be contacted by said wheels, means for supporting said axle with the peripheries of said wheels in contact with said member and means for moving said supporting means and said member relative to each other to rotate said wheels.

15. A contact assembly as in claim 14, wherein said wheels are in intimate contact with one another.

16. A contact assembly as in claim 14, wherein said wheels are rotatably mounted on said axle and said axle is affixed to said supporting means.

17. A contact assembly as in claim 16, wherein said wheels are rotatably mounted on said axle and said axle is affixed to said supporting means.

18. A contact assembly as in claim 17, wherein the peripheries of said wheels deflect slightly at the point of contact.

19. A contact assembly as in claim 14, wherein said plurality of wheels comprises at least three wheels.

20. A contact for conducting electrical energy between relatively movable members, as in claim 1, wherein said wheels are affixed to said axle.

21. A contact assembly as in claim 14, wherein said wheels are affixed to said axle.

Claims

1. A contact for conducting electrical energy between relatively movable members comprising in combination: a plurality of electric current conducting wheels mounted on an electric current conducting axle; each of said wheels comprising a plurality of concentric rings joined together by a plurality of sets of short, narrow tabs, two of said sets of tabs joining each ring of said plurality to two adjacent rings respectively, said two sets of tabs being radially offset with respect to one another whereby said wheels are substantially uniformly radially resilient; means supporting said axle; said support means coupled to a first member relatively movable with respect to a second electric current conducting member; said second relatively movable electric current conducting member disposed to contact wheels and disposed for movement tangentially relatively thereto; and said plurality of wheels acting in unison to make contact with said second member.