US3250415A

US3250415A - Turning roll assembly

Info

Publication number: US3250415A
Application number: US401468A
Authority: US
Inventors: Paul P Wuesthoff
Original assignee: PANDJIRIS WELDMENT Co
Current assignee: PANDJIRIS WELDMENT COMPANY; PANDJIRIS WELDMENT Co
Priority date: 1964-10-05
Filing date: 1964-10-05
Publication date: 1966-05-10
Anticipated expiration: 1983-05-10

Description

May 10, 1966 P. P. wuEsTHox-'F TURNING ROLL ASSEMBLY 4 Sheets-Sheet l Filed OCT.. 5, 1964 NVENTOR PAUL R WUESTHOFF BVM/1 Mm AT''Ol'W.YSI

P. P. wUEsTHor-F 3,250,415

TURNING ROLL ASSEMBLY 4 Sheets-Sheet 2 lllclxL May 10, 1966 Filed Oct. 5, 1964 May 10, 1966 P. P. wuEsTHoFF TURNING` ROLL ASSEMBLY 4 Sheets-Sheet 5 Filed Oct.

May 10, 1966 P. P. wUEsTHor-'F TURNING ROLL ASSEMBLY 4 Sheets-Sheet 4 Filed OCL. 5, 1964 United States Patent O jiris Weldmeut Co., St. Louis, Mo., a corporation of Missouri Filed Oct. 5, 1964, Ser. No. 401,468 12 Claims. (Cl. 214 340) This invention relates generally to improvements in a turning roll assembly, and more particularly to an improved roll assembly adapted to support and rotate a workpiece.

It is conventional to utilize turning rolls to support and turn a horizontally disposed cylindrical tank at a predetermined rate incident to welding of annular seams. Each roll assembly has a pair of wheels located onopposite sides of the rotative longitudinal axis of the tank, the wheels being adapted to support the load.

An important objective is achieved by the provision of a pair of roll frames pivotally mounted in side by side relation on a base, and of a wheel rotatively mounted on and carried by each roll frame, the roll frames being selectively movable about their pivot axes tto different pivotal positions to bring the Wheels toward or away from each other to accommodate workpieces of different sizes.

Another important advantage is aiorded by means pivotally interconnecting the roll frames to the base and retaining the roll frames in adjusted pivotal positions.

Still another important object is realized by the provision of a drive means that operatively interconnects the same power means to each wheel and maintains such eliective driving connection to rotate the wheels regardless of the adjusted pivotal connection of the roll frames.

An important object is attained by the provision of an idler drive element rotatively mounted at each of the pivot axes of the roll frames and operatively connected to a common input drive member and to the wheel carried by the associated roll frame to maintain effective driving connection between the input drive member and the wheels in all adjusted pivotal positions of the roll frames.

Another important object is provided by the structural arrangement in which each idler drive element is operatively connected to an output drive element drivingly connected to and rotatable with the Wheel of :the associated roll frame, in addition to being operatively connected with the common input drive member.

Yet another important object is achieved by the provision of a pair of drive trains, each of which operatively connects the input drive member to one of the wheels so as to turn such wheels in the same direction, and each of which includes an idler drive element rotatively mounted at the pivot axis of the associated roll frame of the wheel with which it is operatively connected.

An important object is realized in that each drive train includes a common input drive member, an output drive element drivingly connected to and rotatable with one of the wheels, and an idler drive element rotatively mounted at the pivot axis of the associated roll frame. This drive assembly will maintain effective drive connection and wheel rotation no matter what the relative adjusted pivotal position of the roll frames.

Another important objective is attained in that the roll frames can be pivoted a greater distance apart in order for the wheels to support larger and greater loads, and yet eiective drive connection is maintained by modifying the drive assembly to include a plurality of idler drive elements in each drive train intermediate the common input drive member and the output wheel drive element, one of the idler drive elements of each train being rotatively mounted at the pivot axis of the associated roll frame.

It is an important objective to provide a turning roll assembly 'including a novel drive mechanism which is simple and durable in construction, economical to manufacture and assemble, highly eiiicient in operation, and which can be utilized by anyone with little or noinstruction.

The foregoing and numerous other objects and advantages of the invention will more clearly appear from the following detailed description of a preferred embodiment, particularly when considered in connection with the accompanying drawings, in which:

FIG. 1 is a top plan view of the turning roll assembly showing the power roll assembly and the idler roll assembly supporting a workpiece;

FIG. 2 is an enlarged slight elevational view of the idler roll assembly as seen along line 2 2 of FIG. l;

FIG. 3 is an end elevational view of the idler roll assembly of FIG. 2;

FIG. 4 is a top plan view of the power roll assembly;

FIG. 5 is a side elevational view of the power roll assembly of FIG. 4, with various parts broken away to clearly illustrate the meshing of gears and with adjusted pivotal positions illustrated by broken lines;

FIG. 6 is an enlarged cross sectional view as seen along staggered line 6 6 of FIG. 5;

FIG. 7 is a top plan View of a modified power roll assembly;

FIG. 8 is a side elevational View of the modified power roll assembly of FIG. 7 with various parts broken away to show meshing of gears, `and with adjusted pivotal positions illustrated by broken lines, and

FIG. 9 is an enlarged cross sectional view as seen along staggered line 9 9 of FIG. 8.

Referring now by characters of reference to the drawings, and irst to FIG. l, it is seen that the turning roll assembly consists of a power roll assembly generally indicated at 10 and a cooperating idler roll assembly referred to at 11, These turning rolls are utilized to support and rotate a workpiece indicated by 12 such as a cylindrical tank incident to the welding of annular seams.

The construction of the idler roll assembly 11 is best shown in FIGS. 2 and 3. 'Ihe idler roll assembly' 11 includes a base consisting of a pair of vertically disposed and horizontally spaced

plates

13 and 14 secured together rigidly at their opposite ends by a pair of

transverse angles

15 and 16. The

base plates

13 and 14 are maintained in substantially parallel relation. An I-bar 17 constituting a transverse brace is disposed between the

base plates

13 and 14 substantially between their ends, the I-bar 17 assisting the

end angles

15 and 16 to provide a rigid, unitary construction for the base. The

end angles

15 and 16 provide a secure footing for the base on the subjacent supporting door.

A pair of

roll frames

20 and 21 are pivotally mounted to the base between the base plates 13 `and 14 by

shafts

22 and 23 respectively detining substantially parallel pivot axes. The

roll frames

20 and 21 are formed by a pair of spaced

plates

24 and 25 rigidly connected together by a transverse angle brace 26.

Rotatively mounted on and carried by each

roll frame

20 and 21 is a

wheel

27 and 28 respectively. The

wheels

27 and 28 are located between the spaced

frame plates

24 and 25. These

idler wheels

27 and 28 are provided with rubber tires to provide an efficient friction contact with the workpiece 12 supported thereon.

It will be importantly noted that the roll frames 2t) and 21 can be selectively swung to different relative angular positions about their pivot axes in order to bring the

idler Wheels

27 and 28 toward or away from each other in order to accommodate workpieces 12 of different sizes. Of course, the

roll frames

20 and 21 can be selectively latched in any adjusted position by the placement of locking pins 30 through aligned apertures formed in the

base plates

13 and 14 and in the roll frame plates 24l and 25'. As is best seen in FIG. 2, the

base plates

13 and 14 are provided with regularly spaced apertures 31 formed in an arc about each of the pivot axes provided by the

pivot shafts

22 and 23. When either

roll frame

20 or 21 is moved to an adjusted pivoted position in which a corresponding pin aperture formed in the

frame plates

24 and 25 is aligned with one of the apertures 31 formed in the

base plates

13 and 14, and it is desired to lock the roll frame in such adjusted position, the locking pin 30 is inserted. It will be readily understood that this pin 30 can be withdrawn to enable subsequent pivotal adjustment.

y One embodiment of the power roll assembly is shown clearly in FIGS. 4 and 5. This power roll assembly 1t) includes a at horizontal base 32. Attached to one end of the base 32 is the power unit that includes an electric motor 33, the drive shaft of which is connected to a speed-reducing mechanism 34 through a drive connection enclosed by housing 35. Adjusting wheel 36 is operatively connected to the drive connection between the motor 33 and the speed-reducing unit 34 so as to obtain an adjustment Iof the degree of speed step-down from motor 33 to the speed-reducing mechanism 34.

A gear box 37 is attached to the base 32, the single `stage worm-gear reducer 40 therein operatively interconnects the drive shaft 41 to the input shaft 42. The output shaft 43 of speed-reducing mechanism 34 is operatively interconnected to the input shaft 42 by an intermediate llexible shaft 44.

Attached to and extending vertically upward from the base 32 are a pair of parallel spaced

plates

45 and 46. The gear box 37 is disposed immediately in front of the base plate 45 so that the drive shaft 41 extends through an opening 47 (FIG. 6) in the base plate 45 and into the .space between the

base plates

45 and 46. Drivingly attached to the end of the drive shaft 41 is a drive pinion 59 constituting a drive member.

Pivotally mounted to and between the

base plates

45 and 46 are a pair

lof roll frames

51 and 52. The structures of the

roll frames

51 and 52 are identical so that a detailed description of one willsuftice for the other. In

this regard, reference is made to the enlarged crossy sectional view of FIG. 6.

It will be noted that the roll frame 51 includes a pair of parallel spaced plates S3 and 54 rotatively mounted on a transverse pivot shaft 55. The spaced

frame plates

53 and 54 are rigidly connected together by a transverse 'shield 49 extending therebetween, the additional purposes and functions of the shield 49 being explained later upon further description of parts. l

The pivot shafts 55 define the pivot axes for the r-

oll frames

51 and 52 which are substantially .parallel to each other and to the axis of the drive pinion 50.

Rotatively mounted to the roll frame 51 between the

frame plates

53 and 54 is a wheel 56, the wheel 56 having a hub 57 that is rotatively mounted on a transverse shaft 60 by bearing 61. The wheel 56 includes a rubber tire that is adapted to provide a more effective frictional contact with the workpiece 12 supported thereon.

The drive assembly for rotating the wheels 56 consists of a pair of gear trains each having a common input drive pinion 50. Each gear train includes an output gear 62 attached to one of the wheel hubs 57 lby a plurality of screws 63. The output gear 62 is connected to and rotatable with the wheel 56 about the shaft 6G. An idler gear 64 is rotatively mounted by bearing 65 on the pivot shaft 55, the idler gear 64 meshing. with the input drive pinion 50 and with the output gear 62. v

Thus it is seen that the input drive pinion 50 is operatively connected to each of the wheels 56 through a gear train and serves to rotate the wheels 56 is the same direction.

In order to accommodate workpieces 12 of different sizes, the roll frames 51 and 52 can be pivotally adjusted about the pivot axes defined by the pivot shafts 55, as is indicated by the broken lines in FIG. 5. Because the idler gear 64 of each gear train is rotatively mounted at and about the pivot axis of the associated

roll frame

51 or 52, it will be apparent that meshing engagement of such idler gear 64 with the common input drive pinion 50 and the associated output wheel gear 62 is maintained regardless of the pivotal position of the roll frame.

The shields 49 are cut away to expose the wheels 56 and to preclude interference therewith. However, the

' shields 49 do cover the periphery of the gearing for safety.

That shield portion 66 extending between the

frame plates

53 and 54 immediately above the idler gear 64 is of sufcient length to cooperate with the top transverse plate portion 67 extending between the

base plates

45 and 46 to provide a complete cover, yet is short enough so as not to interfere with or engage the input drive pinion 5t) when the

roll frame

51 or 52 is swung upwardly as indicated 4by br-oken line in FIG. 5.

Each of the roll frames 51 and 52 may be selectively latched in any adjusted pivotal position. As is best seen in FIG. 5, the

base plates

45 and 46 are provided with a plurality of apertures 70 along an arc about each of the pivot axes defined by the pivot shafts S5. As will be readily understood, each of the roll frames 51 and 52 is provided with a corresponding aperture that is alignable with any one of the base plate apertures 70 upon pivotal movement of the roll frames to adjusted positions. When the roll frames 51 and 52 are locatedin the desired position, they are locked in place bythe insertion of a pin 71 through the base plate apertures 70 and through the roll frames.

It is thought that the operation of this power roll assembly 10 has become fully apparent from the foregoing detailed description of parts, but for completeness of disclosure the usage will be briefly described.

It will be rst assumed that the roll frames Sil and 52 are in a position illustrated in FIG. 5 to support a rather large cylindrical workpiece 12 shown in broken line. Upon energization of the power unit, the input drive pinion 50 is rotated at a desired speed. Consequently, the wheels 56 supporting the workpiece 12 are rotated in the same direction through a pair of gear. trains each of which has the same input drive pinion 5t). lFor example, the ipput drive pinion 50 meshes with the two idler gears 64, which in turn mesh with the output wheel gears 62.

If it is desired to support and rotate a much smaller workpiece 1i2 such as that indicated by broken lines in FIG. 5, the wheels 56 must be brought closer together. Therefore, the locking pins 71 are withdrawn to release the roll frames 51 and 52. The roll frames l51 and 52 are then swung upwardly about their pivot axes defined by the pivot shafts 55. When the rol-l frames 51 and 52, and hence the wheels 56 are located in the desired positions, the locking pins 71 are replaced through the aligned apertures formed in the

base plates

45 and 46 and in the roll frames. -It will be importantly noted that in any pivotal position of the roll frames 5-1 and 52, effective driving connection is maintained at all times in each of the gear trains in view of the fact that the idler gear 64 of each -gear train is rotatively mounted .at and about the pivot axis of the associated roll frame, thereby enabling such idler gear 64 to maintain meshing engagement with both the input drive pinion 50 and the output Wheel gear 62.

Under some circumstances, it is desirable for the power roll assembly l to support heavier and larger loads than that suggested in FIG. 5. To provide for this contingency, a modied embodiment is illustrated in FIGS. 7-9 inclusive. `In this modification, the parts corresponding to those previously described with respect to the embodiment of FIGS. 4-6 inclusive will be given corresponding reference numerals wherever possible. The only change of any consequence appears in the drive assembly operatively interconnecting the wheels 56 with the input drive pinion 50. This structure is perhaps best shown by the large cross sectional view of FIG. 9.

The main distinction in the drive assembly, as seen in FIG. 9, is that each gear train is provided with an additional intervening idler gear '72 rotatively mounted by bearing 73 on a transverse shaft 74 extending between and fixed to the spaced

base plates

45 and 46. This idler gear 72 is disposed to mesh with the input drive pinion 50 and to mesh-with the cooperating idler gear 64.

Of course, any convenient number of intervening idler gears may be utilized between the input drive pinion 59 and the idler gears 64 rotatively mounted at the pivot l axes of the roll frames 51 and 52. It will be understood that because the idler gears 64 are mounted rotatively at these pivot axes of .-the roll frames 51 and 52, effective driving connection is maintained at all times between all of the component parts of each gear train in all adjusted pivotal positions of the roll frames 5'1 and 52.

A s is best seen in FIGS. 7 and 8, that shield portion 7S isdetachably connected to the upper margin of the

base plates

45 and 46 so as to be selectively removed to enable the roll frames 51 and 52 to be swung upwardly to the position illustrated in broken lines in FIG. 8. When the shield portion 75 is in place, as is illustrated in FIG-S. 7 and 8, i-t cooperates with the transverse top plate portion 76 and the peripheral shield 49 on the roll frame to fully protect and cover the gearing from the top.

The usage of the power roll assembly disclosed in FIGS. 7-9, and its operation and function is identical to that previously described with respect to the embodiment of FIGS. 4 6 inclusive, so it is not believed that such descrip- -tion need be repeated.

Although the invention has been described by making detailed reference to several embodiments, such detail is to be understood in an instructive, rather than in any restrictive sense, any variants being possible within the scope of t-he claims hereunto appended.

I claim as my invention:

1. In a turning roll assembly for supporting and rotating a workpiece:

(a) a base,

(b) a pair of roll frames pivotally mounted in side by side relation to the base on spaced, substantially parallel pivot axes,

(c) a wheel rotatively mounted on each ro-lfl frame, the wheels being adapted to support a workpiece therebetween,

(d) the roll -frames being selectively movable to different pivotal positions to bring the wheels .toward or Aaway from each other to accommodate workpieces of diterent sizes,

(e) an input drive member rotatively mounted on an axis parallel to and between the spaced pivot axes of `the roll frames, and

(f) an idler drive element rotatively mounted at each of the pivot axes of the roll frames and operatively connected to the input drive member and to the wheel carried by the associated roll frame to maintain eiiective driving connection between Vthe input drive member and the wheelsregardless of the adjusted pivotal position of the roll frames.

2. yIn a turning roll assembly for supporting and rotating a workpiece:

(a) a base,

(b) a pair of roll frames pivotal-ly mounted in side by side relation to the base on spaced, substantially parallel pivot axes,

(c) a wheel rotatively mounted on each roll frame, the

wheels being adapted to support a workpiece therebetween,

(d) the roll frames being selectively movable to diierent pivotal positions to bring the wheels toward or away from each other to accommodate workpieces of dilicerent sizes,

(e) an input drive member rotatively mounted on an axis parallel to and between the pivot axes of the roll frames,

(t) a rst drive element rotatively mounted at each of the pivot axes of the roll frames and operatively connected to the input drive member, and

(g) a second drive element drivingly connected to and .rotatable with each Wheel and operatively connected to the first drive element of the associated roll frame to maintain effective driving connection between the input drive member and the wheels regardless of the adjusted pivotal position of the roll frames.

3. In a turning roll assembly for supporting and rotating a workpiece:

(a) a base,

(b) a pair of roll frames pivotally mounted in side by side relation tothe base on spaced, substantially parallel pivot axes,

(c) a wheel rotatively mounted on each roll frame, the

wheels being adapted to support a workpiece therebetween,

(d) the roll frames being selectively movable to different pivotal positions to bring the wheels toward or away from each other to accommodate workpieces of different sizes,

(e) an input drive member rotatively mounted on an an axis parallel to and between the spaced pivot axes of the roll fra-mes, and

() a pair of drive trains, each of which operatively interconnects the com-mon input drive member to one of the wheels, each drive train including a drive element rota-tively mounted at the pivot axis of the associated roll frame of the wheel with which it is operatively connected to maintain effective driving connection between the input drive member and the wheel regardless of .the adjusted pivotal position of the rol-l frame.

4, In a turning roll assembly for supporting and rotating a workpiece:

(a) a base,

(c) a wheel rotatively mounted on each roll frame, the wheels being adapted to support a workpiece therebetween,

(d) the roll frames being selectively movable to different pivotal positions to bring the wheels toward or away from each other to accommodate workpieces of different sizes, and

(e) a pair of drive trains,

(f) each train including a common input drive member rotatively mounted on an axis parallel to and between the spaced pivot axes ofthe roll frames,

(g) an output drive element drivingly connected to and rotatable with one of the wheels, and

(h) an idler drive element rotatively mounted at the pivot axis of the associated roll frame and connected to the common input drive member and output drive element of the associated roll frame to maintain effective driving connection between the common input drive member and the wheel regardless of the adjusted pivotal position of the roll frame.

5. In a turning roll assembly for supporting and rotating a workpiece:

(a) a base including spaced plates,`

(b) a pair of roll frames pivotally mounted in side by side relation to and between the base plates on substantially parallel pivot axes, each roll frame including spaced plates,

(c) a wheel rotatively mounted on each roll frame between its frame plates, the wheels being adapted to support a workpiece therebetween,

(e) an'input drive member rotatively mounted on 'an axis parallel to and between the pivot axes of the roll frames, the input drive member being located between the base plates,

(f) a first drive element drivingly connected to and rotatable with each of the wheels, each first drive element being located between the associated roll frame plates, and l (g) a second drive element rotatively mounted at each of the pivot axes of the roll frames and between the roll frame plates and operatively connected to the input drive member and to the rst drive element of the associated roll frame to maintain effective driving connection between the input drive member and the wheel regardless of the adjusted pivotal position of the roll frame. A

6. In a turning roll assembly for supporting and rotating a workpiece:

(a) a base,

(b) a pair of roll frames pivotally mounted in side by side relation to the base on spaced, substantially parallel pivot axes, i

(c) a wheel rotatively mounted on each roll frame, the

wheels being adapted to support a workpiece therebetween, v

(e) an input drive pinion rotatively mounted on an axis parallel to and between the spaced pivot axes of the roll frames,

(f) an output drive gear drivingly connected to and rotatable with each of the wheels, and

(g) at least one idler gear operatively interconnecting the common input drive pinion with each output drive gear,

(h) one idler gear being rotatively mounted at each of the pivot axes of the roll frames to maintain eifective driving connection between the common input drive pinion and the output drive gear of the associated wheel regardless of the adjusted pivotal position of the roll frame.

7. In a turning roll assembly for supporting and rotating a workpiece:

(a) a base,

(d) the roll frames being selectively movable to dif' ferent pivotal positions to bring the wheels toward or away from each other to accommodate workpieces of different sizes,

(f) an outlet drive gear drivingly connected to and rotatable with each of the wheels,

(g) an idler gear rotatively mounted at each of the pivot axes of the roll frames, each idler gear meshing with the common drive pinion and with the output drive gear of the associated roll frame to maintain efective driving connection between the common input drive pinion and the wheel regardless of the adjusted pivotal position of the roll frame.

S. A turning roll assembly as defined in claim 7, in

which:

(h) a plurality of idler gears are operatively disposed and interconnect the common input drive pinion mounted on the base with each of the output drive gears connected to and rotatable with the wheels, one of the idler gears of the plurality of such idler gears interconnecting the common input drive pinion with each output drive gear being rotatively mounted at the pivot axis of the associated roll frame, any idler gears interconnecting the input drive pinion with the said idler gears mounted at the pivot axes of the roll frames being mounted to the base.

9. In a turning roll assembly for supporting and rotating a workpiece:

(a) a base including spaced plates, (b) a pair of roll frames pivotally mounted in side by side relation to and between the base plates on sub-` stantially parallel pivot axes,

(c) each roll frame including a pair of spaced plates,`

(d) a wheel rotatively mounted on each roll frame between its frame plates, the wheels being adapted to support a workpiece therebetween,

(e) the roll fra-mes being selectively movable to different pivotal positions to bring the wheels toward o r away from each other to accommodate workpieces of different sizes,

(f) a pin selectively interconnecting the base frame with the frame plates of each roll frame to retain the roll frame in adjusted pivotal position,

(g) an input drive member rotatively mounted on an axis parallel to and between the pivot axes of the roll frames, the input drive member being located between the base plates,

(h) an output drive element drivingly connected to and rotatable with each wheel, the output drive elements being located between the frame plates of the associated roll frames, and

(i) an idler drive element rotatively mounted at each of the pivot axes of the roll frames and between the frame plates, and operatively connected to the input drive member and to the output drive element of the associated roll frame to maintain effective driving connection between theinput drive member and the wheel regardless of the adjusted pivotal position of the roll frame.

10. A turning roll assembly as deiined in claim 9, in

which:

(j) the input drive member, idler drive elements, and output drive elements are gears meshing to provide a pair of gear trains having a common input drive gear.

l1. In a turning roll assembly as deined in claim 9,

in which:

(j) at least one additional idler drive element is rotatively mounted to the base and located between the base plates and is disposed between and operatively interconnects the input drive member with each idler drive element rotatively mounted at the pivot axes of References Cited by the Examiner the rou frames. 0 UNITED STATES PATENTS 12..A tum1ng roll assembly as defined 1n clalm 11, 2,701,648 2/1955 McBath 214 340 l Yhlch- 3,026,838 3/1962 Ander 214-340 (j) the input drive member, the output drlve elements 5 and the plurality of idler drive elements operatively FOREIGN PATENTS interconnecting the input drive member with each 622,160 6/ 1961 Canada.

output drive element are gears meshing to provide l a pair of gear traing- HUGO O. SCHULZ, Primary Examzner.

Claims

1. IN A TURNING ROLL ASSEMBLY FOR SUPPORTING AND ROTATING A WORKPIECE: (A) A BASE, (B) A PAIR OF ROLL FRAMES PIVOTALLY MOUNTED IN SIDE BY SIDE RELATION TO THE BASE ON SPACED, SUBSTANTIALLY PARALLEL PIVOT AXES, (C) A WHEEL ROTATIVELY MOUNTED ON EACH ROLL FRAME, THE WHEELS BEING ADAPTED TO SUPPORT A WORKPIECE THEREBETWEEN, (D) THE ROLL FRAMES BEING SELECTIVELY MOVABLE TO DIFFERENT PIVOTAL POSITIONS TO BRING THE WHEELS TOWARD OR AWAY FROM EACH OTHER TO ACCOMMODATE WORKPIECES OF DIFFERENT SIZES, (E) AN INPUT DRIVE MEMBER ROTATIVELY MOUNTED ON AN AXIS PARALLEL TO AND BETWEEN THE SPACED PIVOT AXES OF THE ROLL FRAMES, AND (F) AN IDLER DRIVE ELEMENT ROTATIVELY MOUNTED AT EACH OF THE PIVOT AXES OF THE ROLL FRAMES AND OPERATIVELY CONNECTED TO THE INPUT DRIVE MEMBER AND TO THE WHEEL CARRIED BY THE ASSOCIATED ROLL FRAME TO MAINTAIN EFFECTIVE DRIVING CONNECTION BETWEEN THE INPUT DRIVE MEMBER AND THE WHEELS REGARDLESS OF THE ADJUSTED PIVOTAL POSITION OF THE ROLL FRAMES.