GB1591461A

GB1591461A - Conyeyor arrangements

Info

Publication number: GB1591461A
Application number: GB13294/77A
Authority: GB
Original assignee: Cable Belt Ltd
Current assignee: Cable Belt Ltd
Priority date: 1977-03-30
Filing date: 1977-03-30
Publication date: 1981-06-24
Also published as: PL113386B1; AU3454478A; FR2385614B1; JPS6047167B2; IN149960B; SU820654A3; PL205694A1; CA1085338A; FR2385614A1; DE2813063C2; DE2813063A1; JPS53121382A; AU523046B2; ZA781834B; SE7803427L; SE435487B; ES468316A1; BE865524A

Description

(54) IMPROVEMENTS IN AND RELATING TO CONVEYOR ARRANGEMENTS (71) We, CABLE BELT LIMITED, a British Company, of 3 Glenfinlas Street, Edinburgh EH3 6YY, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to belt conveyor arrangements. M[ore particularly, the invention relates to belt conveyors in which the belt which is intended to carry the load is driven by frictional contact with a separate endless driving member or plurality of driving members, such member or each such member being, for example, a driving belt, cable or rope.

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 flexible linear member arranged to be movable along a path extending longitudinally of at least part of the belt, and in which one of the surfaces of the belt defines a pair of parallel and immediately adjacent formations which extend without interruption along the entire length of the belt and which are sized to receive and locate and make frictional contact with the flexible linear member, the arrangement being such that successively adjacent parts of the linear member frictionally contact different ones of the two formations 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.

According to the invention, there is also provided a belt conveyor arrangement, comprising a continuous conveyor belt, two driving cables for frictionally engaging one of the surfaces of one of the runs of the conveyor belt for driving the conveyor belt, and a plurality of driving means spaced apart at intervals along the length of the conveyor belt each for imparting drive to the driving cables, the said surface of the conveyor belt having first and second pairs of formations running without interruption along its entire length with each formation adapted to frictionally receive a said driving cable, the two pairs being spaced apart across the width of the conveyor belt but the two formations of each pair being side-by-side and immediately adjacent, and each said driving means being associated with guidance means for guiding part of one of the driving cables out of frictional contact with one of the formations of the first pair and for guiding part of the other of the driving cables out of frictional contact with one of the formations of the second pair, guiding the disengaged cable parts to the associated driving means for the imparting of drive thereto, 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 guidance means) as the position of disengagement of frictional contact, and guiding the said part of the other said cable back into frictional contact with the other formation of the second pair substantially at the same position (relative to the guidance means) as the position of disengagement of frictional contact, whereby there is no gap (measured along the length of the belt) between each position of re-engagement of frictional contact- and the preceding position of disengagement of frictional contact.

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 being taken on: the line I-I 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 shown in Figures 7 and 8.

As shown in Figures 1 and 2, 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 10A and 10B. 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 provided with formations integral with the belt to define channels or grooves 16, 17 running along the length of the belt. On the opposite surface of the belt, that is, the undersurface of the upper run 10A and the upper surface of the lower run 10B, formations 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.

The conveyor belt is constructed of suitably reinforced material so that it is longitudinally flexible (to enable it to run around the terminal drums) but is laterally stiff and of course the material is designed 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. Briefly, 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 being driven by suitable driving motors and pulleys. Such cables not only drive the belt but also support it.

It will be appreciated that an arrangement in which each driving cable was arranged in a continuous loop so as to provide a continuous upper run frictionally engaging in, say, groove 18 and with the driving cable being driven by means of a drive motor driving one of its terminal pulleys, would produce a situation in which the tension in the driving cable was a maximum at one end and progressively decreased to the other end. Correspondingly, 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 this 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 several 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 grooves 18,20 or 22,24.

This means, therefore, that not only is the carrier belt subjected to frictional drive along substantially the whole of its length but it is also mechanically supported throughout substantially the whole of its length.

One such arrangement is shown in Figures 2 and 3.

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 conveyor 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 innermost driving grooves, grooves 20 and 22 respectively, on the undersurface 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 tare disengaged from the grooves 20,22, as will now be described in detail with particular reference to the driv ing cable 42.

As shown particularly in Figure 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 below that of roller 50), and thence around a pulley 54 having a vertical axis. The cable then passes over a further set of rollers 56, 58, 60 and 62 whose respective axes are arranged so as to guide the cable through a slightly curved path and thence to the driving pulley 36 on the gear box 32.From the Batter 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 surfaces 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 df the upper run 10A of the conveyor belt. The 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 the cable 42, except of course that it takes place on the opposite side of the conveyor belt. Figure 3 shows pulleys 54A, 64A and 66A, corresponding respectively to the pulleys 54, 64 and 66.

At a later point (not shown) along the conveyor installation, there will be a further driving motor, gearbox and driving pulley, corresponding to the driving motor 30, the gearbox 32, and the driving pulley 36, together with further sets of rollers and pulleys corresponding to the roller sets 46 to 52, pulleys 54 to 66, 54A, 64A and 66A, and rollers 56 to62, and these pulleys and rollers will guide the cables out of the 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 length of the conveyor installation.

In this way, the driving cables are driven not by one but by 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 by the driving cables along substantially its entire length. 'This is -achieved by the provision of the twin driving grooves along each edge region of the conveyor 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 conveyor 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. Any such movement which takes place will be dependent on the magnitude of the tension in the driving cable passing round that pulley. This movement can be transmitted by suitable linkage to the hydraulic coupling 34 so as to control the transmission of the power from the motor 30 to the gearbox 32. In this way, the tension in the driving cables can be controlled along the entire length of the installation so as to prevent an unacceptable rise in tension (owing to nonuniform belt loading, for example) at any point.Such tension-control mechanism can be as disclosed in our British Patents Nos. 1,052,240, .I,106,341 and 1,107,241.

For example, such mechanism may comprise means associated with each of thl motors for measuring and controlling the driving force which it imparts to the driving cables. Instead, it may comprise means associated with 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 mechanism 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.

In -the installation described with refer ence .to Figures 2 and3, although the motor 30.and the gearbox 32 are mounted on one side of the installation, it is neces- sary for free space to be available on the other side of the installation to accommo- date the pulleys 38, 54A, 64A and 66A.

In the arrangement disclosed with reference to Figures 4 and 5, however, the cable transferring mechanism is mounted on one side of the conveyor installation only and occupies substantially no space on the opposite side. Such a modified form of the instalTation may be advantageous in certain applications, such as in mine tunnels because it avoids the necessity of providing recesses in the tunnel walls (for the cable driving mechanism) on both sides of the tunnel.

In other respects, however, the installation of Figures 4 and 5 is substantially the same as that of Figures 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 pulleys 136 and 138 mounted adjacent to each other on a short output shaft. The driving cable 42 is led out of the inner driving groove 20, over two guide pulleys 150 and 152, thence around a pulley 154 having a vertical axis. From there it passes around the driving pulley 136, around idler pulley 164, and thence around vertical axis pulley 166 and back into the outer groove 18 of the conveyor belt 10 under guidance from idler rollers '146 and 148.

The 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 166A and back into the outer driving groove 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 cables 44 out of and into the driving grooves on the far side of the conveyor installation.

The pulley and roller arrangements described with reference to Figures 2 to 5 are merely examples of various arrangements that can be used with a conveyor belt of the form shown in Figure 1.

Figure 6 shows a modified form of 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 Q2A, 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 give 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 receiving 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 Figure 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 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 shafts 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 244, 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, referenced 280, 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 from the 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 which is connected by a crank assembly 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 (so that the parts of their peripheries which are for the time being uppermost are closer together than 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 334.

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 30û, 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 members 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 ånd 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 of the pulley 286 by the idler pulleys 335, and at this point, the drive cable is in the outermost one (,18), bf the two drive channels 18, 20 on the underside of the upper run 10A of the bey'. 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 around 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 338 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 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 10B which is visible in Figure 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. 1) respectively. The idler pulleys 340 and 341 (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 driving motors along the length of the complete run properly share 'the load, the load cell 304 (and the corresponding load cells in the other installations along the length of the conveyor belt) are provided.

Thus, the assembly comprising the plates 270 and 272 will tilt on its pivots 280 in the direction of the arrow C or D, as the. tension in the driving cables 42 and 44 (where they pass round the pulleys 286 and 288)1 varies. This tilting movement will be transmitted to the 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 linkage 318) so as to adjust the torque which the driving motor 250 applies to the pulleys 240 and 242.

In this way, the torque which each motor applies to the driving cables can be controlled 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 differential unit 244 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 tiltable assembly of the plates 270 and 272 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 suita.bly 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 used.

Figure 9 is ,a perspective view of the mechanical layout of a slightly modified 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 descrintion.

WHAT WE CLAIM IS: 1. A belt conveyor arrangement, comprising a conveyor belt which is adapted to be frictionally driven by means of at least one flexible linear member arranged to be movable along a path extending longitudinally of at least part of the belt, and in which one of.the surfaces of the belt defines a pair of parallel and immediately adjacent formations which extend without interruption along the entire length of the belt and which are sized to receive and locate and make frictional contact with the flexible linear member, the arrangement being such that successively adjacent parts of the linear member frictionally contact different ones of the two formations 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.

2. An arrangement according to claim 1, including a respective drive means associated with each of the said parts of the linear member for imparting drive to it, the drive means being so interconnected that the driving tension in the belt is substantially uniform along the said path.

3. An arrangement according to claim 1, in which the conveyor belt has a second pair of parallel and immediately adjacent said formations which extend without interruption along the entire length of the belt, the two pairs of formations being respectively adjacent edge regions of the belt, the second pair of formations being sized to receive and locate and make frictional contact with a second flexible linear member arranged to be movable along a second path extending parallel to the firstmentioned path so that the belt can be driven by the second linear member, the arrangement being such that successively adjacent parts of the second linear member frictionally contact 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 a respective drive means associated with each of the parts of the firstmentioned linear member for imparting drive to that part and also to the corresponding part of the second linear member, the drive means being so interconnected that the driving tension in the belt is substantially uniform along the two said paths.

5. An arrangement according to claim 4, in which each said drive means comprises two drive pulleys interconnected by a differential gear.

6. An arrangement according to any preceding claim, in which each formation is a channel or groove.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and that the driving motors along the length of the complete run properly share 'the load, the load cell 304 (and the corresponding load cells in the other installations along the length of the conveyor belt) are provided. Thus, the assembly comprising the plates 270 and 272 will tilt on its pivots 280 in the direction of the arrow C or D, as the. tension in the driving cables 42 and 44 (where they pass round the pulleys 286 and 288)1 varies. This tilting movement will be transmitted to the 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 linkage 318) so as to adjust the torque which the driving motor 250 applies to the pulleys 240 and 242. In this way, the torque which each motor applies to the driving cables can be controlled 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 differential unit 244 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 tiltable assembly of the plates 270 and 272 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 suita.bly 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 used. Figure 9 is ,a perspective view of the mechanical layout of a slightly modified 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 descrintion. WHAT WE CLAIM IS:

1. A belt conveyor arrangement, comprising a conveyor belt which is adapted to be frictionally driven by means of at least one flexible linear member arranged to be movable along a path extending longitudinally of at least part of the belt, and in which one of.the surfaces of the belt defines a pair of parallel and immediately adjacent formations which extend without interruption along the entire length of the belt and which are sized to receive and locate and make frictional contact with the flexible linear member, the arrangement being such that successively adjacent parts of the linear member frictionally contact different ones of the two formations 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.

7. An arrangement according to any one

of claims 1 to 5, in which one of the said pair of formations, or one of each pair of formations, comprises a ridge.

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

9. A ;belt ,conveyor arrangement, comprising a continuous conveyor belt, two driving cables for frictionally engaging one of the surfaces of one lof the runs of the conveyor belt for driving the conveyor belt, and a. plurality of driving means spaced apart at intervals along the length of the conveyor belt each for imparting drive to the driving cables, the said surface of the conveyor belt having first and second pairs of formations running without interruption along its entire length with each formation adapted to frictionally receive a said driving cable, the two pairs being spaced apart across the width of the conveyor belt but the two formations of each pair being sideby-side and immediately adjacent, and each said driving means being associated with guidance means for guiding part of one of the driving cables out of frictional contact with one of the formations of the first pair and for guiding part of the other of the driving cables out of frictional contact with one of the formations of the second pairs, guiding the disengaged cable parts to the associated driving means for the imparting of drive thereto, 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 guidance means) as the position of disengagement of frictional contact, and guiding the said part of the other said cable back into frictional contact with the other formation of the second pair substantially at the same position (relative to the guidance means) as the position of disengagement of frictional contact, whereby there is no gap (measured along the length of the belt) between each position of re-engagement of frictional contact and the preceding position of disengagement of frictional contact.

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 included 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.

15. A belt conveyor arrangement, substantially as described with reference to Figures 1, 2 and 3 of the accompanying drawings.

16. A belt conveyor arrangement, substantially as described with reference to Figures 1, 4 and 5 of the accompanying drawings.

17. A belt conveyor arrangement, substantially as described with reference to Figures 1, 7 and 8 of the accompanying drawings.

18. A belt conveyor arrangement, substantially as described with reference to Figures 2, 3 and 6 of the accompanying drawings.

19. A belt conveyor arrangement, substantially as described with reference to Figures 4, 5 and 6 of the accompanying drawings.

20. A belt conveyor arrangement, substantially as described with reference to Figures 6, 7 and 8 of the accompanying drawings.