US2512329A

US2512329A - Current collector

Info

Publication number: US2512329A
Application number: US640841A
Authority: US
Inventors: Robert O Heinemann; Bernard F Langer; Harry C Werner
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1946-01-12
Filing date: 1946-01-12
Publication date: 1950-06-20
Anticipated expiration: 1967-06-20
Also published as: FR954548A; GB619718A

Description

June 1950 R. o. HEINEMANN ETAL 2,512,329

CURRENT COLLECTOR Filed Jan. 12, 1946 2 Sheets-Sheet 1 WITNESSESZ INVENTORS J/ L ck/"f O, Heine/nan,

Y/ Bernardflanyer a df/arry (2 Werner; 4"-

ATTO Y June 20, 1950 R. o. HEINEMANPJ ETAL 2,512,329

CURRENT COLLECTOR I Filed Jan. 12, 1946. 2 Sheets-Sheet 2 :3 t nt l 97 95 29 We 94 94 a 9a ig a Q 0 92 mo 93 I00 WITNESSES: E b H |NVENTOR5 a er/O, e/nemann,

fiernardf'zanyarandl/arr C. Warner.

Patented June 20, 1950 CURRENT COLLECTOR Robert O. Heinemann, Bernard F. Langer, and Harry 0. Werner, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 12, 1946, Serial No. 640,841

.1 I Our invention relates, generally; to current collectors, and it has reference, in particular, to

' pantograph current collectors for electricall perated vehicles.

Tests which have made on pantograph current collectors of the usual type show that the stressin the trolley conductor is greatly affected by the type of pantograph shoe mounting which is used. A mounting which has no flexibility near the point of support of the shoe produces very high stresses in the conductor, particularly when the vehicle is operating at relatively high speeds. Similarly, a flexible mounting which binds due to friction or operates so as to engage a rigid stop is not very effective in reducing the conductor stress.

The double shoe mounting, now in common use, uses pivoted shoe levers inclined to the front and rear, and held up by springs for supporting the two shoes. The shoes are attached to the outer ends of the levers by pivoted connections and can thus rotate freely about the pins. With this type of mounting, aerodynamic lift, aerodynamic drag andwire friction all combine to rotate the support levers of the leading pantograph shoe so as to force the leading shoe upwardly against the conductor. Conversely, these forces act to rotate the support levers of the trailing shoe and force the trailing shoe away from the conductor. At high speeds, this action is so great that the leading shoe is often lifted to the limit of its upward travel and rides against a solid stop, thus losing all the benefits of spring mounting. The trailing shoe is forced away from the conductor and often leaves it entirely.

Since the pivot connection between the shoe and shoe levers is in the usual shoe mounting positioned below the conductor, the shoe has a center of rotation below the contact surface of the conductor. Thus wire'friction tends to rotate the shoe so that only the leading edge of the shoe is in contact with' the conductor thus increasing the angle of attack, so that the aerodynamic lift becomes relatively large. tion, with'a center of rotation belowthe conductor, an increase in friction rotates the shoe to a position where the frictional force is still greater, thus producing a -stubbing action, wherein the leading edge of the shoe tends to dig into the conductor. In addition, when the center of rotation of the shoe is below the conductor, and an aerodynamic flutter of the shoe commences, the frictional force appears to feed energy into the resulting oscillation, so that the flutter increases. Furthermore, the mounting system usually used with pantog'raph shoes con- .ztains-apluralityof pivot points each having a relatively large amount of friction which tends to bindthe pivot action and nullify the action of thesprings.

Generally stated, it is an obejct of our invention to providea current collector which is simple and inexpensive to-manufacturaand which More specifically, it is an object of our invention to :provide for resiliently mounting a pantograph shoe so that the. center ofrotation of the shoeisv above the contact surface with the trolley conductor.

. It is also an object of our invention to provide for reducing the-tendency of a pantograph shoe to tilt so that the leading edge produces a stubbing action with the conductor.

Another object of our invention is to provide a resilient, parallel motion support for a pantograph shoe. f

Yet-another object of our invention is to "provide for mounting a pantograph shoe on an elastic pivot structure.

Still another object of our invention is to provide forresiliently mounting a" pantograph shoe for limitedresilient rotational movement on a vertically resilient support. I J

. It important object of our invention to pantograph shoe mountings.

provide for reducing the operating friction of ,A further object of our invention is'to provide a current collector wherein the conductor frictio'n and'aerodynamic lift do not tend to rotate'the collector support andforce the collector upwardlyagainst the conductor.

j Another important obj ect' of our invention is to provide a current collector ..which is relatively stable over a. wide range of operating speeds;

, Other objects-wilLdn part, be obvious and will,

In =accordance,.w ith one embodiment ofv our 7' invention-1 a pantograph shoe mounting is provided having spaced supportmembers withrelatively flat springsupports extending to the front and rearpn the-topand the bottom.-. The pro- 'jecting. ends of the spring supports are connected it o ;provide a vertically movable resilient parallel motion support. Elastic pivots-are provided ad- .jacent the ends of the supports at both thefront wan drear endsforso supporting a pair :of main pantograph shoesastoprovidecenters of rota- *ytioniabove the contact surfaces of the shoes. An auxiliary shoeisrigidly connected to the support ing, in side elevation, a mounting embodying the invention in one of its forms;

Fig. 3 is a partial end elevational" view, partly in section, of a pantograph current collector. showing a mounting embodying the invention in another of its forms;

Fig. 4 is an enlarged longitudinal cross-sectional view of a well known type of efastic shear bushing used in connection with the current collector mounting shown in Fig. 3;

Fig. 5 is a plan view of a pantograph collector showing a mounting embodying the invention in another ofits forms;

Fig, 6 is an enlarged partial plan view of a current collector showing the pantograph 'shoe mounting used on the current collector shown in Fig.

Fig. 7 is an enlarged partial sid elevational view of the mounting shown in Fig. 6; i

Fig. 8 is an enlarged partial end elevational view of the mounting shown in Figs. 6 and. 7

v Fig. 9 is a partial side elevational view of a mod-- ification of the mounting shown inFigs. '6' and '7 illustrating a method of mounting. the elastic pivot by means of an. elastic shear connection;

Fig. 10 is a plan view of the elasticpivot shown in Fig. 9, with parts removed to show details of the elastic shear connection;

Fig. 11 is an enlarged. plan view of the elastic shear connection used in the mounting or Figs. 9

and 10;

Fig. 12 is an enlarged end elevational view of the elastic shear connection; and v Fig. 13 is an enlarged plan view of the lower member of the elastic pivot shown in Figs. 9 and 10;

Referring to Fig. 1, the reference numeral 10 may denote, generally, a mounting for a pair of pantograph shoes H which are disposedto engage a trolley conductor I2. The mounting, which is typical of the type commonly us'ed,"c'om.- prises inclined front and rear arms l3' pivotally connected to a support member M which is mounted on a pantograph support structure l5 and pivotally connected to the leading and trailing shoes, respectively, by pins l6.

It will be observed from examination of this construction that since the pins l6 are necessarily below the trolley conductor I 2, the frictional force between the'leading shoe (which'may, for example, be assumed to be on theleft-hand side of the figure) and the trolley conductor, produces a moment tending torotate the shoe in a clockwise direction. Thisforces the'l'eading edge of the shoe upwardly against the conductor which increases the frictional force and tends to still further rotate the shoe. i

Upon further examination of this'type of coningon this shoe, also tendto=rotate the supportlever l3 of the shoe in a clockwise direction so 4 as to lift the trolley conductor. At high speeds, this action is so great that the leading shoe II is often lifted to the limit of its upward travel. This not only causes the support lever to ride solidly against the stop [1, but it also produces relatively high stresses in the trolley conductor. At the same time, these forces acting on the support lever of the trailing shoe, tend to rotate it in 5 a clockwise direction away from the conductor.

Referring to Fig. 2, the reference numeral may denote, generally, an improved form of pantograph shoe mounting, wherein relatively flat spring supports 2! and 22 may be secured to the upper and lower sides of a support member 23, which may be mounted on the pantograph structurev iii, in a manner similar to that usually used with the pantograph structures of the prior art.

The spring supports 2! and 22 may be connected adjacent their ends by spacing members 25, so as to provide a resilient parallel motion structure 25 which is movable in the vertical direction only.

The pant'ograph shoes Il may be mounted on the parallel motion structure 26 by means of elastic pivot supports 2?, which may be disposed to provide an effective center of rotation of the shoes at points a above the surface of contact of the shoes I! with the conductor l2. These elastic pivot supports 21' may, for example, each comprise a substantially rigid lower member 29, which may be rigidly connected to the spacing member '25, and a substantially rigid upper member 30.to which the pantograph shoe H may be rigidly connected by means of a pin 3!. The

.upper.member 3110f the elastic pivot support may be somewhat shorter than the lower member 29 and the two members may be connected by relatively flat springs '32 and 33 which are inclined inwardly and upwardly so as to provide a trapezoidal closed support structure with the

spring members

32 and 33 having an effective point of intersection at the point a above the surface of the pantograph shoe l I.

With the current collector shown in Fig. 2, the pantograph shoes H are relatively free to move in a vertical direction under the action of the spring members 2i and 22. Since there are no sliding surfaces, the action of these spring members is substantially undamped, and the current collectors may thus move readil to follow irregularities in the trolley conductor I 2.

Since the pantograph'shoes l I are mounted on elastic pivot supports 21, whenever any force such as frictional drag, aerodynamic drag or aerodynamic lift operate to retard motion of the shoe along the conductor t2 in a direction from right to left, for example, the elastic pivot supports function to produce rotation of the shoe in a counterclockwise direction. This reaction prevents stubbing between the pantograph shoe and the conductor, reduces aerodynamic lift because it reduces the'angle of attack, and prevents lifting of the trolley conductor. In addition, since the elastic pivotsare mounted on a-parallel motion structure, none of these forces tend to produce a moment lifting the leading pantograph shoe against the conductor as was the case in'the usual construction shown in Fig. 1, or lowering the trailing shoe.

Referring to Fig. 3, the reference numeral 35 may denote, generally,a modified form ofpantograph shoe mounting, wherein a parallel motion structure 34 comprising rigid upper and lower links 36 and SI'connected to a support member 38 at one end and-by spacer 39 at the other end, is used to mount the pantograph shoe l I on a pantograph structure (not shown). The upper and lower links, support member and spacing member may be connected by means of elastic shear members 49 so as toprovide for resilient vertical movement of the spacing member 39.

The elastic shear members may be of any suitable construction comprising, for example, as shown in Fig. 4, a center pin or shaft 4| which may be firmly connected to the upper and lower link members by reason of a press fit, or the like, and a tubular sleeve 43 which may be firmly connected to the support member 38 or spacing member 39 in a like manner. The sleeve and shaft may be connected to each other by means of an interposed sleeve of natural or synthetic rubber which may be vulcanized thereto.

The pantog'raph shoe H may be mounted on the parallel motion structure 34 by means of an elastic pivot structure 41. This structure may comprise rigid lower and

upper link members

48 and 49 connected by means of inwardly and upwardly inclined rigid link members 5!) and 55! forming a closed force structure and having an effective point of intersection at a point b above the surface of contact of the shoe II with the conductor 12. The shoe Il may be rigidly connected to the upper member 43 by means of a bolt 53, and the lower member 48 comprising a bar, may be connected to the spacing member 39 on one side thereof, in any suitable manner such as by means of welds 54, extending along adjoining surfaces of the

members

43 and 39 where they overlap. The upper and lower members .3 and 49 and the connecting members 50 and 5! may be connected together by means of elastic shear members 4i! of a type similar to that described in connection with the parallel motion structure 34, so as to provide an effective elastic pivot structure with a point of rotation above the contact surface of the current collector ll.

Referring to Fig. 5, the reference numeral may denote, generally, a pantograph current collector having a pair of main pantograph shoes I] positioned in substantially parallel spaced relation for engaging a current collector 12. The pantov graph shoes ii may be resiliently supported on a pantograph structure It by resilient mounting means Eli and provided with a rigidly mounted auxiliary shoe .6! intermediate the main shoes for preventing excessive deformation of the resilient mounting means.

Referring to Figs. 6, '7 and 8 it will be seen that the resilient mounting means-6B may comprise support members 62, which may be secured'to the pantograph structure ill by pins 63, which pass through openings in lugs 64 on the pantograph structure and are positioned in elongated openings 65 at each side of the support member. Attached to the upper side of the support member 62 are spring members (it which may be fastened by means of a plate 61 and bolts 68 so as to extend to the front and rear of the support member. The spring members 66 may comprise relatively flat springs having elongated openings -69 therein adjacent each end so as to provide spaced spring arms 10 and II. Additional spring members 12 may be secured to the support member 62 on the lower side so as to extend to the front and rear of the support member in substantially parallel spaced relation with the upper spring members 66. Spacing means may be provided adjacent the ends of the spring members 56 and i2 comprisingfor example, a spacing block '14 to which the spring members may be secured by means of bolts 15 so as to provide a bars 83 :and '84.

resilient parallel motion structure which is movable in the vertical direction only.

Thepantograph shoe II, which is shown in outline, may be connected to the spring members by means of an elastic pivot structure designated generally by the numeral 11. The elastic pivot structure 1'! may, for example, comprise a lower rigid bar 18, which may be connected to the spacing block 74 by means of bolts 19, and an upper rigid member which may be rigidly connected to the shoe I l by means of 2. lug 8i and a bolt 82. The upper rigid member 80 may be substantially shorter than the lower member 18. These upperand lower members may-be operatively connected by means of

flat spring members

83 and 84 which may be secured to the ends of the upper and lower members by means of screws 85. Therelative lengths of the upper and lower members 18 and 88 may be 50 arranged that the

spring members

83 and 84 are inclined inwardly and upwardly so that if extended, they would intersectat a point e which is the effective pivot .point of the elastic pivot.

The

spring members

83 and 84 are preferably relatively flexible so as to provide relatively free rotation of the shoe about the pivot point 0. Vertically the pivot 17 acts asa rigid beam. The spring members 66 and '12 are relatively rigid. Vertically they act as an elastic parallel motion structure, while in the horizontal direction they act as a rigid beam. The spring members .83 and 84 may, for example, be of spring steel approximately 1 inch wide and .032 inch thick. The

spring members-6E and 12 may be of spring steel 5% inch thick and 3 to 4 inches wide. Thus, whenever frictional forcesor aerodynamic drag act on the ,pantograph shoe, the shoe tends to rotate in a counterclockwise direction about the pivot point c. This tends to reduce the frictional drag or aerodynamic drag since it reduces the angle of attack, and thus restores the shoe to its normal operating position.

The length of the spring members 83 and 8 1 may be so selected that the upper rigid member 8B of the. elastic pivot is only a relatively small predetermined distance above the upper spring member 65. Too great a deformation of the

elastic spring members

83 and 84 by rotation of the shoe ii is thus prevented since the rigid .znember til acts as a stop. Deformation of the upper and

lower spring members

66 and 12, beyond a predetermined amount, is prevented by reason .of the auxiliary panto'graph shoe 6] which is positioned intermediate the main pantograph shoes,.and which may be rigidly connected to the .support'member .62 by means of depending'ears Bl and'bolts 88.

Referring to Figs. 9 throughl3, it will be seen that the shoe i] may be connected to the upper member 86 of the elastic pivot structure 11 by means of screws .89, The structure l1 may be connected to the parallel .motion structure by means of an elastic shear device .90, shown. in Figs. 11 and 12. Resilient movement of the elastic pivot may thus be provided about an axis parallel-to the trolley conductor, thus permitting horizontal misalignment of the pantograph shoe whenone isin :an operating position lower than the other without deforming the pring mem- For example, the lower rigid member 92, of the elastic pivot may be provided with a'recess .93 intermediate the ends for receiving the elastic shear device 90. I

The elastic shear device 9|! may comprise a substantially rectangular late 94 having cylindrical projections 95 at the opposite ends and provided with openings 96 for receiving bolts whereby the device may be connected to the lower end of the spacing member 14. Mounting blocks 97 may be positioned about the cylindrical projections 9.5 and connected thereto by means of an elastic material such as natural or synthetic rubber which may be vulcanized to both the cylindrical projections and the mounting blocks.

The elastic shear device 90 may be positioned with the rectangular plate 94 loosely positioned in the central recess 93 in the lower member. The mounting blocks 91 may be positioned in the recesses 98 at either end of the central recess 93, and secured'in fixed relation to the lower member 92 by means of clamp blocks 99 and bolts Hill.

The operation of the mounting shown in Figs. 9 through 13 i substantially the same as that described in connection with the mounting of Figs. 6, '7 and 8 with the exception that resilient movement of the elastic pivot 11, relativeto the parallel motion structure, is provided by the elastic-shear means 90. Accordingly, lateral deformation of the spring members 83 and B4 is substantially prevented and movement of the ends of the pantograph shoe relative to each other in a vertical direction is thus provided for.

From the above description and the accompanying drawings, it will be apparent that we have provided a current collector and a current collector mounting structure which is simple and inexpensive to manufacture, and which provides radically new operating advantages. Since movement of the pantograph shoe is limited only by the spring members themselves, frictional forces are reduced to a minimum, thus providing for relatively free operation of the pantograph and enabling it to more readily follow deviations in the trolley conductor. By providing a mounting structure using a parallel motion construction, lift of the trolley conductor is substantially prevented since there is no resultant moment from frictional drag, aerodynamic drag, and aerodynamic lift which tends to rotate the mounting structure in a direction such as to force the leading pantograph shoe against the trolley conductor.

In addition, since the effective center of rotation of the pantograph shoe is raised to a point above the surface of contact with the trolley conductor, frictional drag and aerodynamic drag no longer operate to rotate the pantograph shoe so that the leading edge is forced against the conductor with its resultant stubbin'g action. Because the reaction of the pantograph shoe to these forces in a current collector embodying our invention, is such as to cause the pantograph shoe to rotate away from the trolley conductor instead of toward it thus decreasing the angle of attack, the stability of the pantograph shoe is greatly increased. Wire friction thus tends to damp any fluttering of the shoe which may commence at the high speeds, instead of increasing the fluttering, as in the mounting structures commonly in use. By elimmating all sliding surfaces in the mounting structure, wearis reduced to a minimum, and the shoe is permitted to follow and maintain contact with the conductor more readily. The conductor stresses and wear are therefore greatly decreased due to the actions of the elastic pivot and resilient parallel support which support the pantograph shoe.

Since certain changes may be made in the abovedescribed construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter containedin the above description and shown in the accompanying drawings shall be considered as illustrative and not in a limiting sense.

We claim as our invention:

1. A current collector comprising, a shoe having a contact surface disposed to engage a conductor, and an elastic pivot supporting the shoe comprising a closed force structure having front and back members inwardly inclined adjacent the shoe end and arranged to provide a pivot point above the contact surface of the shoe.

2. A current collector comprising, a shoe having a current collector engaging surface, and a trapezoidal elastic pivot supporting the shoe, said elastic pivot having fiat springs on the front and rear so inclined towards each other as to provide a pivot point above the surface of the shoe.

3. A current collector comprising, a shoe, a support member, and a parallel motion support connecting the shoe to the support member for resilient vertical movement including relatively flat springs spaced apart in the vertical direction, said springs being connected to the support in spaced relation at one end, and maintained in fixed spaced relation to each other at the other end.

4. A current collector support comprising, a parallel motion support having relatively fiat and elongated spring members connected in fixed spaced relation at spaced apart points, and an elastic pivot connected to the parallel motion support havin relatively flat spring members inclined towards each other in a direction longitudinally of and away from the parallel motion support.

5. A current collector comprising, a pair of spaced support members, elongated flat spring members connected intermediate their ends to each of the support members on the tops and bottoms and extending to the front and' rear thereof, means connecting the ends of the spring members on each side of the support members in fixed spatial relation, and elastic pivot structure supported by the spring members adjacent each end, and an elongated current collector shoe secured to the elastic pivot structures on the front and rear of the support members.

6. A current collector comprising, a shoe, and

'a closed link pivot structure supporting the shoe havin rigid link members connected by elastic points, said closed link pivot structure being so constructed and arranged as to provide a center of rotation for the shoe above the contact surface with the conductor.

'7. A current collector comprising, a shoe having a surface disposed to engage a conductor, and a trapezoidal elastic pivot structure supporting the shoe arranged to provide an elastic support having a pivot point above the conductor engaging surface.

8. A support for a current collector having a conductor engagin surface comprising, an elastic pivot for supporting the collector having an effective pivot point above the conductor engaging surface of the collector, and resilient parallel motion means rigidly connected to the elastic pivot.

9. A current collector comprising, a shoe having a conduct-or engaging surface, a parallel motion spring structure, an elastic pivot connected 9 to the shoe providing a center of rotation above the conductor engaging surface, and means including a rubber shear bushing connecting the elastic pivot and the parallel motion spring structure to provide resilient movement of the elastic pivot transversely of the conductor.

10. A current collector comprising, a shoe, a relatively rigid parallel motion spring structure movable in a vertical direction, and an elastic pivot connecting the shoe adjacent one end of the spring structure including a pair of upwardly and inwardly inclined relatively flexible spring members.

11. A current collector comprising, a pair of spaced supports, relatively flat spring members secured to the supports on the tops and bottoms thereof in parallel spaced relation and extending to the front and rear, means connecting the front ends and rear ends of the top and bottom springs respectively, an elastic pivot having a rigid lower member connected to the lower ends of each of said means and an upper rigid member positioned above and relatively close to the top spring member and connected to the lower rigid member by flat spring members connected to the ends of the rigid members, and an elongated collector shoe rigidly connected to the upper rigid members of the front ends and the rear ends.

12. A current collector comprising, a pair of spaced supports, an elongated auxiliary shoe rigidly connected adjacent its ends to said supports, a pair of main shoes positioned one on each side of the auxiliary shoe in substantially parallel relation, and means including relatively flat spring members connecting the main shoes to the supports for vertical resilient motion, said spring being positioned apart vertically and connected to each other at spaced apart points.

13. A current collector comprising, a pair of spaced supports, a pair of main shoes positioned on opposite sides of the supports, resilient parallel motion means connecting the main shoes to the supports for resilient motion in a predetermined direction including elongated relatively fiat springs positioned in spaced relation in the direction of motion and connected intermediate to their ends adjacent the tops and bottoms of the supportsand also connected adjacent their ends in spaced relation to the main shoes, and an auxiliary shoe rigidly connected to the supports intermediate said pair of shoes.

14. The combination with a pantograph support structure, of a support member connected adjacent the top of each side, a pair of main shoes positioned one each on opposite sides of the supports and having conductor engaging surfaces, an elastic pivot having inwardly and upwardly inclined flat spring members at the front and rear arranged to provide for pivotal movement of the shoes about axes transverse to the conductor and above the conductor engaging surfaces, an auxiliary shoe mounted rigidly 10D. the supports intermediate the main shoes, and means including relatively flat spring members connecting theelastic pivots to the supports on the top sides and spring members secured in fixed relation to the continuous spring members on the bottom sides of the supports.

15. A current collector comprising, a shoe having a conductor engaging surface on the upper side, and a support for the shoe comprisin an elastic pivot having a lower elongated rigid member and an upper relatively short member connected adjacent the ends by upwardly and inwardly inclined flat spring members to provide a center of rotation for the shoe above the conductor engaging surface.

16. A current collector comprising, a shoe, a trapezoidal shoe support having upper and lower links connected to inwardly inclined side links by elastic shear bushings, and a parallel motion support connected to the shoe support having upper and lower links connected in fixed spaced relation to substantially parallel end members by elastic shear bushings.

17. A current collector support comprising, an elastic pivot for supporting the collector having rigid upper and lower members connected by inclined link members, means pivotally connecting the link members to the upper member, and connecting means pivotally connecting the link members to the lower member including an elastic shear bushing connected to the lower rigid member and one of the links to provide limited movement thereof about an aXis normal of the lower member.

18. In combination with a current collector disposed for resilient movement in one direction relative to a support, a parallel motion support device connecting the shoe and the support comprising a pair of relatively flat elongated spring members positioned apart in the direction of motion and secured in fixed spacial relation to each other adjacent the support and the collector.

19. The combination with a current collector disposed for resilient linear movement relative to a support, of a parallel motion device connecting the shoe and the support, said device comprising elongated spring members positioned apart in the direction of resilient movement and secured in fixed spaced relation to each other at the support and at the collector.

20. The combination with a current collector disposed to be supported for resilient movement relative to a support, of a parallel motion support device comprising a pair of elongated links spaced apart in the direction of said resilient movement, spacing means disposed adjacent the collector, and resilient connecting means including elastic shear members connecting the links to the support and spacin means in predetermined spaced relation to each other to provide limited movement about axes normal to the link members.

ROBERT C. HEINEMANN. BERNARD F. LANGER. HARRY C. WERNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,261,578 McFarlane Apr. 2, 1918 2,057,994 Wylie et al Oct. 20, 1936 2,073,189 Williams Mar. 9, 1937 FOREIGN PATENTS Number Country Date 136,078 Austria Dec. 27, 1933 199,088 Great Britain June 21, 1923 646,292 Germany June 11, 1937