CA1085338A

CA1085338A - Conveyor arrangements

Info

Publication number: CA1085338A
Application number: CA299,585A
Authority: CA
Inventors: Ian M. Thomson; Charles Thomson
Original assignee: Cable Belt Ltd
Current assignee: Cable Belt Ltd
Priority date: 1977-03-30
Filing date: 1978-03-22
Publication date: 1980-09-09
Also published as: SE435487B; FR2385614A1; JPS53121382A; ES468316A1; AU523046B2; BE865524A; FR2385614B1; SE7803427L; DE2813063C2; SU820654A3; PL113386B1; JPS6047167B2; IN149960B; PL205694A1; AU3454478A; ZA781834B; DE2813063A1; GB1591461A

Abstract

ABSTRACT OF THE DISCLOSURE

A belt conveyor arrangement is disclosed in which the conveyor belt is driven by two drive cables which frictionally engage the undersurface of its upper run. The undersurface of the belt is provided with a first pair of immediately adjacent grooves near one belt edge and a second pair of similar grooves near the opposite belt edge, the grooves being arranged to frictionally receive the drive cables for driving the belt.
One drive cable is periodically led out of one groove of the first pair, trained round the drive pulley, and then led back into the other groove of the first pair at substantially the same position as the exit position. The other drive cable is similarly arranged in relation to the second pair of grooves.

Description

10~5338 BACKGROUND OF TH~ INVENTION
The invention relates to belt conveyor arrangements.
Belt conveyor arrangements are known in which the belt which is intended to carry a load to be conveyed is driven by fric-tional contact on its undersurface with a separate endlessdriving member or a plurality of driving members, such members or each such member being, for example, a driving belt.
A disadvantage of such prior arrangements is that, in order to impart drive to the driving member or members, it is necessary to lead it or them away from the conveyor belt and thence to a driving roller or the like and this removes the supporting action which it or they give or gives to the conveyor belt.
Thus, if there are a plurality of separate driving belts arranged successively along the length of the conveyor belt, inevitably there will be unsupported portions of the conveyor belt between the ends of adjacent driving belts.
If the driving member comprises a single driving belt, then this may peridoically be led away from the conveyor belt, passed round a drive roller, and then fed back into frictional engage-ment with the conveyor belt (it is normally not practicable todrive such a single driving belt from one end of the installation because this entails excessive tension at one end of the installation). Inevitably again, there is an unsupported region of the conveyor belt where the driving belt is led away from the conveyor belt.
These unsupported regions of the conveyor belt necessitate ~ .

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' . ' ~ ' " ' ', " ' ' " iO85338 extra idler pulley arrangements, or similar structures, for supporting the conveyor belt, and these are expensive and of course are subject to wear and necessitate extra maintenance.
It is an object of the invention to provide an improved belt conveyor arrangement.
BRIEF SUMMARY OF TliE INVENTION
According to the invention, there is provided a belt conveyor arrangement, comprising a conveyor belt which is adapted to be frictionally driven by means of at least one of a plurality of flexible linear member sections arranged successively along a path extending longitudinally of at least part of the belt, and in which one of the surfaces of the belt define a pair of parallel and immediately adjacent formations which extend along the belt and which are sized to receive and locate and make frictional contact with the flexible linear member sections, the arrangement being such that successively adjacent ones of the linear member sections frictionally contact different ones of the two formations.
The plurality of flexible linear member sections may comprise ~O sections of a single driving cable, for example.
In accordance with the invention, therefore, and in the case where the flexible linear member sections comprise individual sections of a continuous driving cable, the arrangement may be utilised with driving and guidance means for guiding the cable out of engagement with one said formation, imparting drive to it, and guiding it back into engagement with the adjacent said .: . - . . . .
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`- 1085338 formation at su~stantially the same position with respect to the driving and guidance means. In this way, the conveyor belt can be supported substantially along the entire length of its upper run.
BI~IEF D~SC~IPTION OF Tll~ DI~AWINGS
Belt conveyor arrangements embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which:
Figure 1 is a cross-section of a conveyor belt which may be used in the arrangements, the view bein~ taken on the line 1-1 of Figure 2;
Figure 2 is a diagrammatic side elevation of part of one of the belt conveyor arrangements;
Figure 3 is a diagrammatic plan view of the arrangement as shown in Figure 2;
Figure 4 is a diagrammatic side elevation of another one of the belt conveyor arrangements;
Figure 5 is a diagrammatic plan view of the arrangement as shown in Figure 4;
Figure 6 is a cross-section, corresponding to Figure 1, through a modified form of the conveyor belt;
Figure 7 is a diagrammatic side elevation of part of a further one of the arrangements;
Figure 8 is a diagrammatic plan view of the arrangement as shown in Figure 7; and Figure 9 is a perspective view of a modified version of the arrangement of Figures 7 and 8.

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108533~

D~SCI~IPTION OF P~F~ D EMBODIM~N'rS
As shown in Figure 1, the installation or arrangement has a conveyor belt 10. The belt 10 extends around drums (not shown) at each end of the installation to provide upper and lower runs lOA and lOB. Intermediate pulley sets 12 support the upper and lower runs of the belt at intervals.
The conveyor belt 10 has a load-carrying surface 14 which is provi~ed with formations integral with the belt to define channels or grooves 16, 18 running along the length of the belt. On the opposite surface oI the belt, that is, the undersurface of the upper run lOA and the lower surface of the lower run lOB, Iormations integral with the belt define two pairs of channels or grooves running longitudinally of the belt, channels 18 and 20 and channels 22 and 24. It will be noted that channels 18, 20 and 22, 24 are spaced inboard of the edges of the conveyor belt.

~, ' ' ' . . :
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~ ' ''. ' 108533~3 ` The conveyor belt is constructed of suitably reinforced m~terial so that it is longitudin~lly flexi~le (to enable it to run around tlle terminal drums) ~ut is laterally stiff and of course the material is desi~ned to be hard-wearing and capable of withstanding heavy loads and impacts.
The terminal drums (not shown) around which the conveyor belt 10 runs do not transmit drive to the conveyor belt. For driving the conveyor belt 10, separate driving cables are used as will now be explained. ~riefly, however, the driving cables locate in the grooves running longitudinally of the conveyor belt 10 (as is shown at X in groove 18) and drive the conveyor belt by friction, the cables themselves bein~ driven by suitable drivin~ motors and pulleys Such càbles not only drive the belt but also support it.
It will be appreciated that an arrangement in which each drivin~, cable was arranged in a continuous loop so as to provide a continuous upper run frictionally enga~ing in, say, groove 18 and with the driving oable being driven by means of a dri~e motor drivin~ one of its terminal pulleys, would produce a situation in which the tension in the drivin~ cable was a maximum at one end and ~rogressively decreased to the other end.

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108~338 Correspondin~ly, there would be maximum tension in the conveyor belt 10 at one end, decreasing to a minimum at the other end.
In order to reduce thi~ maximum tension, and to provide more uniform tension along the length of the installation, each driving cable is, as will be explained in more detail below~
not driven at a single point only but driven at sever~l positions spaced apart along the length of the installation.
This necessitates guiding the driving cable out of its groove in the conveyor belt 10 at each such position, passing it round a driving pulley, and then directing it back into engagement with the conveyor belt 10. As will now be described in more detail, the installation to be described is such that it mitigates the effect at each such position of the removal of the support given to the conveyor belt 10 by the driving cables.
In a manner to be described, at each position where one of the driving cables has to be guided out of its driving groove in the conveyor belt, in order to direct it round a driving ` pulley, there is provided a suitable arrangement to be described which not only guides the driving cable around the driving pulley but re-directs it back into frictional contact with the carrier belt at substantially the same point (relative to the fixed part of the installation), the cable this time engaging the adjacent one of the particular pair of groo~es 18,20 or 22,24. ~his means, therefore, that not only is the carrier belt subjected to frictional drive along substantially the whole .,- . , , . . . . .. - :
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1~8S338 of its length but it is also mechanically supported throughout substantially the whole of its length.
One such arrangement is shown in Fi~ures 2 and 30 As shown in these Figures, a driving motor 30 is provided which drives a gear box 32 via a hydraulic coupling 34, the latter being adjustable ~in a manner to be described) to control the power supplied by the motor to the gear box, The gear box 32 drives a pulley 36 on one side of the con-veyor installation and a pulley 38 (Fig,3) on the other side of the installation, the pulleys being interconnected by a driving shaft 40 It is assumed that the upper run 10A of the conveyor belt is moving from left to right as viewed in Figures 2 and 3.
The driving cables 42,44 are assumed to be located in the inner-most driving grooves, grooves 20 and 22 respectively, on theundersurface of the upper run 10A of the conveyor belt in the left hand half of the two Figures, At the point Y, however, the driving cables are disengaged from the grooves 20,22, as will now be described in detail with particular reference to the driving cable 42, As shown particularly in ~'igure 2, a set of rollers 46, 48, 50 and 52 is provided and rotatably mounted between the runs 10A and 10B of the conveyor belt, The cable 42 is led out of the groove 20, over and in contact with the surfaces of the rollers 50 and 52 (the axis of the roller 52 being slightly ' '"" ~ ' .................... ' . ~ :
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' below that of roller 50), and thence around a pulley 54 having a vertical axis. ~he cable then passes over a further set of rollers 56, 5~, 60 and 62 who~e respective axes are arranged so as to guide the cable through a slig~ltly curved path and thence to the driving pulley 36 on the gear box ~2. From the latter pulley, the cable passes around a tension-detecting pulley 64 (whose operation will be described further below), and thence around a further vertical-axis pulley 66, Finally, the cable 42 passes over and in contact with the sur-faces of the rollers 46 and 48 (the axis of the roller 46 being slightly below that of roller 48) and thence into the outer driving groove 18 on the undersurface of the upper run 10A of the conveyor belt. ~he cable 42 enters the groove 18 alongside the position at which it left the groove 20, and thus there is substantially no part of the conveyor belt which is not supported and driven by the driving cable.
The path of the driving cable 44 exactly corresponds to that of t~le cable 42, except of course that it takes place on the opposite side of the conveyor belt. Figure 3 shows pulleys 20 54A, 64A and 66A, corresponding respectively to the pulleys 54, 64 and 66.
At a later point (not shown) along the conveyor instal-latlon, there will be a further driving motor, gearbox and driving pulley, corresponding to the driving motor 30, the gearbox 32, and the dri~ing pulley 36, together with ~urther .
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-sets of rollers and pulleys corresponding to the roller sets46 to 52, pulleys 54 to 66, 54A, 64A and 66A, and roller~ 56 to 62, and these pulleys and rollers will ~uide the cables out of tlle outermost driving grooves 18,24, around the driving pulleys driven by the gearbox, and then back to the conveyor belt at the same point where they left, except that they will now re-enter the inner driving grooves 20,22; and of course further similar installations may be provided at intervals along the entire len~th of the conveyor installation.
In this way, the driving cables are driven not by one but b~ several driving motors spaced apart at intervals along the conveyor installation ~thereby preventing an unacceptably high maximum tension in the driving cables), yet the conveyor belt is supported and driven b~ the driving cables along substan-tially its entire length, 5lhis is achieved by the provis.ion of the twin driving grooves along each edge region of the con-veyor belt, and the inevitable regions where a conveyor belt ` having only one driving groove along each edge region is unsupported and undriven by driving cables (because the latter have to be led away from the conve~or belt in these regions in order to feed them round driving pulleys before re-inserting them into the driving grooves) is avoided.
In order to control the tension in the driving cables, the pulleys 64 and 64A can be mounted so as to be bodily movable~
against a biasing force, in the directions of the arrows A and B.

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, . ~ . .. .. . ~ . --~35338 ~ny such movement which takes place will be dependent on thema~nitude of the tension in the driving cable passing round that pulley. This movement ean be transmit~ed by suitable link~e to the hydraulie eouplin~ 34 so as to eontrol the transmission of the power from the motor 30 to the gearbox 32.
In this way, the ~ension in the driving cables ean be controlled along th~ entire length of the in6tallation so as to prevent an unaeeeptable rise in tension (owing to non-uniform belt loading~
~or example) at any point. Such tension-eontrol mechanism ean be as diselosed in our British latents Nos. 1,0~2,240, 1~106,341 and 1~107,241. For example, such mechanism may comprise means associated with each of the motors for measuring and controlling the driving force which it imparts to the driving cables. Instead, i~ may comprise means associated with c each of the motors for measuring the driving force which it imparts to the driving cables and, in response thereto, to control the driving force which is imparted to the driving cables by the next motor in the direction of movement of the belt. In a further example, the tension controlling meehanism may comprise means for measuring the load on the belt at a predetermined point which is upstream of all the driving motors and for controlling the driving force imparted to the driving cables by each of the motors in dependence on the measured load, the application of the control to each motor being delayed by a time related to the distance between the predetermined point and the respective driving motor.

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~OB5338 In the installation described with reference to Figures 2 and 3, altbou~h the motor 30 and the ~earbox 32 are mounted on one side of the installation, it is necessary for free space to be available on the other side of the installation to accommodate the pulleys 38, 54A, ~4A and 66A. In the arrangement disclosed with reference to Fi~ures 4 and 5, however, the cable trans-ferring mechanism is mounted on one side of the conveyor installation only and occupies substantially no space on ~he op~osite side. Such a modified form of the installation may be advanta~eous in certain applications, such as in mine tunnels because it avoids the necessity of providin~ recesses in t~e tunnel walls (for the cable driving mechanism) on both sides of the tunnel.
In other respects, however, the installation of Figures 4 . .~ . .
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lOB5338 and 5 is substantially the same as that oî l1'igures 2 and 3.
Motor 30 and hydraulic coupling 34 are not shown in Figures 4 and 5. As shown, however, the gearbox 32 has two driving pullcys 1~6 and 1~ mounted adJacent to each other on a short output shaft. ~`he driving cable 42 is led out of the inner driving groove 20, o~er two guide pulleys 150 and 152, thence around a pulley 154 having a vertical axis. From there it passes ~round the driving pulley 136, around idler pulley 164, and thence around vert;ical axis pulley 166 and back into the outer groove 1~3 of the conveyor belt 10 under guidance from idler rollers 146 and 148.
l'he other driving cable, cable 44, is guided out of the inner driving groove 22 by means of idler rollers 150A and 152A, around a vertical axis pulley 154A and thence around the driving pulley 138. It then passes around idler pulley 164A, around vertical axis pulley 16~A and bacl; into the outer driving ~;roove 24 under guidance from idler rollers 146A and 148A.
It will be noted that the vertical axis pulleys 154A and 166A
are of increased diameter to guide the driving cal~les 44 out of and into the driving grooves on the I`ar side of the conveyor installation.
The pulley and roller arrangements described with reference to ~i~;ures 2 to 5 are merely examples oï various arrangements that can be used with a conveyor belt of the form shown in Figure 1.

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. . - : .. : . -.. : , :. , . . ~. . : . : ., Figure 6 shows a modified form ~f the conveyor belt of Figure 1. In Figure 6, the inner driving grooves 20 and 22 of the belt of Figure 1 are removed, and replaced by wear pads 20A and 22A, and the driving cables therefore move between the grooves 18, 24 and the wear pads 20A and 22A. The position which the cable adopts when seated on one of the wear pads is shown by way of example at X'. It will be understood that the belt of Figure 6 does not ~ive such good cable location as the belt of Figure 1 but may suffice in certain circumstances.
It will also be understood that other formations for recei~ing the driving cables can be used.
Figures 7 and 8 show a further form of belt conveyor installation arrangement.
Figure 7 is a plan view of part of the installation and shows a motor and gearbox assembly indicated generally by the reference 200 and a belt-supporting and pulley arrangement indicated generally by the reference 202. In Figure 7, the conveyor belt itself is omitted for clarity.
Figure 8 is a side elevation corresponding to Figure 7 and showing the conveyor belt itself but omitting the motor and gearbox assembly 200.
The installation of Figures 7 and 8 comprises two side members 204 and 206 which are rigidly joined together by transverse members of which only some are visible, for example, 208, 210, 212, 214, 216, 218, 220, 224 and 226, The -- 1~ --';' , ~ ~ ' : .
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side member 204 carries a side plate 230, while the side member 206 carries a similar side plate 232 (see Fig.7). These side plates support bearings 234 and 236 in which run respective shaits 238 and 239. Shaft 238 carries a pulley 240, and shaft 239 carries a pulley 242. Between the pulleys is mounted a differential unit 244 which allows the pulleys to be driven at different speeds.
The motor and gearbox assembly 200 drives the shaft 238 and,through the differential unit 224, the shaft 239.
As shown in Figure 7, the assembly 200 comprises an electric motor 250 having an output shaft 252 driving a gearbox 254 through a fluid coupling 256 and a mechanical coupling 258.
The gearbox 254 has an output shaft 260 which is coupled to the shaft 238 through a mechanical coupling 262.
The fluid coupling 256 is adjustable for a purpose and in a manner to be explained, so as to vary the amount of motor torque which it transmits to the gearbox 254.
The side member 204 also carries a side plate 270, while the side member 206 carries a similar side plate 272. These side plates are rigidly interconnected by cross members 274 and 276. However, the assembly so formed is not rigidly connected to the side members 204 and 206 but is attached to those side members by pivotal connections (only one of which, referenced280, is visible) which allow the plates 270 and 272 to move angularly, through a relatively small angle, in the directions of the arrows C and D.

A shaft 284 extends fromthe side plate 270 and supports a pulley 286, while a shaft 287 extends from side plate 272 and supports a pulley 288, The shafts are rotatably supported in a block 289 which is connected to the cross member 276 by a bracket 290 (Fig.7). On its opposite side, the block 288 is attached to a bracket 294 which terminates in a plate 296. The plate 296 faces a plate 298 which is rigidly supported from the side plates 230 and 232 by inclined struts 300 and 302.
Between the plates 296 and 298 a load cell 304 is mounted, this load cell being of the type which produces an electrical output in dependence on the compression load to which it is subjected by the plates 296 and 298.
The electrical signal representing the value of the compression load is fed from the load cell by means of a cable 306 to a signal processing and amplifying unit 308. The amplified signal is then passed by a cable 310 to an electro-mechanical actuator 312. The actuator has a rotary output shaft 314 which is connected by a crank assembly 316 to an arm 318. The arm 318 is connected to the fluid coupling 256 so as to adjust the mount of motor torque which the fluid coupling transmits to the gearbox 254.
The pulleys 286 and 288 do not rotate in vertical planes but are slightly inclined tso that the parts of their peripheries which are for the time being uppermost are closer together than - lG -10853;~8 the lower parts of their peripheries).
The installation also includes idler pulleys.
At one end of the installation, an idler pulley assembly 320 is mounted. This assembly comprises two sets of freely rotatable pulleys 322 and 324. The set 322 is mounted between side members 326 and 328, and the set 324 is similarly mounted.
The side members are connected together by cross members 329 and 330, and the assembly is supported on the side members 204 and 206 by means of vertical stanchions 331, 332, 333 and 33~.
At the other end of the installation a similar idler pulley assembly 335 is mounted and will not be separately described.
A further pair of idler pulleys 336 is mounted on a platform 337 on the strut 300, and a corresponding pair of idler pulleys 338 is mounted on a platform 339 on the strut 302.
Finally, idler pulleys 340 and 341 are rotatably mounted in the side ~embers 204 and 206, respectively, approximately .. ..
below the idler pulleys 336 and 338.
The conveyor belt 10, in this example, takes the form shown in Figure 1 and has two pairs of drive grooves 18, 20 and 22, on one surface, and two, only, drive grooves 16 and 17 on its opposite surface. As with the installations of Figures

2 and 3, and Figures 4 and 5, the installation of Figures 7 and 8 has two drive cables 42 and 44.
As shown in Figure 6, the drive cable 42 is supported clear , .

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of the pulley 286 by the idler pulleys 321, and at this point, the drive cable is in the outermost one (18) of the two drive channels 18, 20 on the underside of the upper run lOA of the belt. The drive cable therefore passes over and makes contact with the outer one of the two idler pulleys 336 and is led from that idler pulley on to and partially arGund the drive pulley 240. Thence it passes to the lowermost part of the periphery of the pulley 286, and partially around that pulley.
Because of the tilted positioning of the pulley 286, the drive cable, at the uppermost part of the periphery of the pulley, is now immediately below the inner one (20) of the pair of drive channels 18, 20 and it is fed over and in contact with the inner one of the two idler pulleys 336 and at that point enters the drive channel 20. Finally, it leaves the installation, in the drive channel 20, passing over the idler pulley set 322. Figure 7 shows that the vertical plane of symmetry through these pulleys is offset (inwardly) from the corresponding vertical plane of the pulley 240.
The drive cable 44 on the opposite side of the installation follows a corresponding path. Thus, it passes above and clear of the drive pulley 288 in the drive channel 24 of the conveyor belt 10, over and in contact with the outer one of the two idler pulleys 33 where it leaves the drive channel 24, partially around and in contact with the drive pulley 242, onto the lowermost part of the periphery of the pulley 288, around that . .~ .

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108S3~8 pulley, and onto the innermost one of the two idler pulleys 338 where it enters the drive channel 22 of the conveyor belt 10. Thence it leaves the installation via the pulley set 324.
As with the installations of Figures 2 and 3, and of Figures 4 and 5, the drive cables frictionally drive the conveyor belt and also support it, and the arrangement is such that the drive cables support the conveyor belt over substantially its whole length, there being no gap in this support where the drive cables are taken away from the belt for the imparting of drive to them.
It will be appreciated that several installations, each is shown in Figures 7 and 8, could be provided, at intervals along the length of the conveyor belt. At each end, rollers would be provided around which the conveyor belt passes to return along its lower run lOB which is visible in ~igure 8.
In addition, at each end the drive cables would be led out of their respective driving channels and fed back on the underside of the lower run lOB of the belt in the channels 16 and 17 (Fig.l) respectively. The idler pulleys 336 and 340 (Figs. -7 and 8) support the drive cables on the lower run.
In operation, the conveyor belt which may be of substantial length (several kilometres), may not be evenly loaded along its length and this may cause unequal tension to develop in the conveyor belt. In order to ensure that the tension in the belt does not become too great at any point and that the -- 1~ -- . .

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: . , , ' ~0~35338 driving mo~ors aloll~ the lell~tll of ~hc com~let~ run properly share the load tl~e load cell 304 (and the corresponding load cells in the other installations along the length of the conveyor belt) are provided.
Thtls the assc~bly comprising tlle plates 270 and 272 will tilt on its pivo~s 280 in the direction oI the arrow C or D
as the tension in ~he driving cables 42 and ~4 twhere they pass round tlle pulleys 286 and 288) varies. Tl~is tilting movement will ~e transmitted to tl~e load cell 304 as an increase or decrease of compression load. The resultant electrical signal will cause the actuator 312 to adjust the fluid coupling 256 (via the linlcage 318) so as to adjust the torque which the driving motor 250 applies to the pulleys 240 and 242. In this way the torquc which each motor applies to the driving cables can be controllcd in dependence on the tension of the driving cables at that point. The signal processing and amplifying units 308 of the various drive installations can be electrically interconnected so as to achieve a desired distribution of tension along the length of the conveyor belt so as to limit the tension that may be developed at any point in the driving cables and/or to tend to equalise the tension along the lengths of the cables.
The differelltial unit 224 allows the pulleys 240 and 242 to be driven at slightly different speeds to take account of wear and the like and any bends in the complete run. In addition it prevents any other cause from making the tension unequal between the driving cables on opposite sides of the conveyor belt.
It will be appreciated that many modifications may be made to the structures illustrated in Figs.7 and 8. In particular the load cell may be replaced by a linkage-connecting the , .
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lV85338 tiltable assembly of the plates 270 and Z72 directly to control the fluid coupling 256. In this case, the tiltable assembly could be biased in the direction of the arrow D
by a suitably mounted spring arrangement. However, other methods of measuring the reaction force exerted by the pulleys 286 and 288 against the tension in the driving cables (not necessarily involving displacement of the pulleys) may be usedO
Figure 9 is a perspective view of the mechanical layout of a slightly ~odified version of the arrangement of Figures 7 and 8 with part of the belt broken away for clarity. It is believed that the description already given will enable an understanding of this Figure without detailed descrlption.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A belt conveyor arrangement, comprising a flexible linear member, means mounting the flexible linear member to move along a longitudinally extending path, a conveyor belt having at least a portion supported by successive parts of the flexible linear member, one of the surfaces of the belt defining a pair of parallel and immediately adjacent formations which extend without interruption along the entire length of the said portion of the belt and which are sized to receive and locate and make frictional contact with the successive parts of the flexible linear member to enable them to frictionally drive the belt along the direction of the said path, a plurality of guiding means respectively guiding the successive parts of the flexible linear member away from the conveyor belt and them back to the conveyor belt such that success-ively adjacent ones of the said parts of the linear member fric-tionally make contact with different ones of the two said formations, and so that at any point along the said path, at least one of the said formations is frictionally contacted by one of the said parts of the linear member, a plurality of drive means, and means mounting each drive means in association with a respective one of the guiding means for imparting drive to the respective one of the said parts of the flexible linear member after it has been guided away from the conveyor belt and before it has been guided back to the conveyor belt.

2. An arrangement according to claim 1, including means interconnecting the several drive means so that the driving tension in the belt is substantially uniform along the path.

3. An arrangement according to claim 1, in which the said surface of the conveyor belt defines a second pair of parallel and immediately adjacent said formations which extend without interruption along the entire length of the said portion of the belt, the two pairs of formations are respectively adjacent edge regions of the conveyor belt, a second flexible linear member is provided, means are provided which mount the second flexible linear member to move along a second path extending parallel to the first-mentioned path, the second pair of formations are sized to receive and locate and make frictional contact with successive parts of the second flexible linear member to enable them to frictionally drive the belt in the direction of the said path, and the said plurality of guiding means includes further guiding means respectively guiding the successive parts of the second flexible member away from the conveyor belt and then back to the conveyor belt such that successively adjacent ones of the said parts of the second flexible linear member frictionally make contact with different ones of the formations of the second pair, so that at any point along the second path at least one of the said second pair of formations is frictionally contacted by one of the said parts of the second linear member.

4. An arrangement according to claim 3, including mounting means mounting each drive means in association with a respective one of the further guiding means for imparting drive to the respetive one of the said parts of the second linear member after it has been guided away from the conveyor belt and before it has been guided back to the conveyor belt, and means interconnecting the several drive means so that the driving tension in the belt is substantially uniform along the two said paths.

5. An arrangement according to claim 4, in which the two linear member parts driven by each drive means are drivingly interconnected by a differential gear.

6. An arrangement according to claim 3, in which the belt has at least two said formations on its other surface.

7. An arrangement according to claim 1, in which each formation is a channel.

8. An arrangement according to claim 1, in which one of the said pair of formations comprises a ridge.

9. A belt conveyor arrangement, comprising two driving cables mounted substantially parallel to each other extending along a predetermined path, a plurality of driving means spaced apart at intervals along the said path for respectively imparting drive to different parts of the driving cables, a conveyor belt at least part of one run of which has its undersurface supported on the driving cables, the said surface of the conveyor belt defining first and second pairs of formations running without interruption along its entire length with each formation being sized to frictionally receive a said driving cable, the two pairs being spaced apart across the width of the conveyor belt but the formations of each pair being side-by-side and immediately adjacent, and guiding means associated with each driving means and supporting and guiding the driving cables, each guiding means comprising means guiding a part of one of the driving cables out of frictional contact with one of the formations of the first pair and guiding a part of the other of the driving cables out of frictional contact with one of the formations of the second pair, means guiding the disengaged cable parts to the associated driving means for the imparting of drive thereto, means guiding the said part of one cable back into frictional contact with the other formation of the said first pair substantially at the same position relative to the guiding means as the position of disengagement, and means guiding the said part of the other cable back into frictional contact with the other formation of the second pair substantially at the same position relative to the guiding means as the position of disengagement.

10. An arrangement according to claim 9, including control means for controlling the driving forces imparted to the driving cables by each of the plurality of driving means so that the tension in the belt is substantially uniform along the part of the said run of the belt which is frictionally engaged by the driving cables.

11. An arrangement according to claim 10, in which the control means comprises means associated with each of the driving means for measuring and controlling the driving force which it imparts to the driving cables.

12. An arrangement according to claim 11, in which each guidance means includes a rotatable pulley around at least part of which one of the driving cables passes, and in which the control means includes means for measuring the reaction force exerted by the pulley against the effect of the tension in the driving cable passing round it, and means responsive to the measured reaction force for controlling the driving force imparted to the driving cable by the associated driving means.

13. An arrangement according to claim 10, in which the control means comprises means associated with each of the driving means for measuring the driving force which it imparts to the driving cables and, in response thereto, to control the driving force which is imparted to the driving cables by the next driving means in the direction of movement of the belt.

14. An arrangement according to claim 10, in which the control means comprises means for measuring the load on the belt at a predetermined point which is upstream of all the driving means in the direction of movement of the belt and for controlling the driving force imparted to the driving cables by each of the driving means in dependence on the measured load, the application of the control to each driving means being delayed by a time related to the distance between the said predetermined point and the respective driving means.