THE SPHERE OF THE INVENTION The present invention relates to a belt conveyor for carrying bulk cargo, e.g. ore, sand etc. The conveyor according to the invention is of the so-called cable operated type (Cable Belt) where a conveyor belt of reinforced rubber material or the like is carried by two or more driving cables. The said driving cables co-operate with the conveyor belt and contribute to the driving of the said belt. Usually, the cables engage in special grooves in the underside of the belt. The cables may also be adapted to carry the return portion of the belt, which is unloaded.

PRIOR ART A conveyor of this kind is known from e.g. the Swedish Patent Specification No. 172,557, which shows a conveyor wherein the cables carry both the useful portion and the return portion. Both at the unloading end and at the loading end of the conveyor the cables must be guided outside the belt and will then pass to a driving means of a suitable kind. In that case the cables are wound in one or more turns around driving drums in order to obtain a sufficiently large contact surface to be able to transmit the necessary driving power. The cables are then returned into co-operation with the belt by suitably disposed pulleys. It is evident that these pulleys and this construction in its entirety are expensive and comprise sensitive parts which are exposed to considerable stresses. There is, however, no other known solution today for achieving this driving of the cables. Furthermore, there are difficulties in achieving driving of the cables when the belt is in an intermediate position, which is highly desirable especially in long conveyors.

The Swedish Patent Specification No. 7803427-9 describes a solution permitting driving of the cables at positions located

between the two end stations. In that case the conveyor belt is provided with two grooves on its underside, the cables being caused to co-operate with one of the grooves during a first portion of the conveyor path. Thereupon, the cables are caused to be removed from the belt to a driving means and are then returned in a loop to the belt at approximately the same place but to the groove located beside it. In this way it is made possible that the belt is always carried by the cables along the entire length of the belt even if the cables are temporarily removed from the belt in order to have driving power imparted to them.

This solution is of course practical. However, also this solution requires the use of several drums and pulleys in order to guide the cables. These cables are mostly, subjected to a very powerful tension, which entails that the drums and the pulleys are exposed to powerful stress and wear.

As is shown by the above-mentioned patent specifications, the conveyor belt in its entirety is carried by the cables, which means that the belt has no ability of its own to carry the load longitudinally. The principle of the above-mentioned cable system cable (cable belt) aims at imparting to the belt a sufficient transversal rigidity (by means of reinforcements) in order to make it function as a beam between the cables and to transmit the load on the belt to the cables. Of course, the belt must also have a certain reinforcement in the longitudinal direction but only to the extent required in order that the belt may not rupture. In that connection it should be observed specifically that the cables achieve the entire driving of the belt and that the driving power is transmitted to the belt via friction in the point of engagement between the belt and the cable.

In later years it has also been suggested to provide the belt with a longitudinal rigidity of its own by giving to the longitudinally and transversely reinforced belt a construction which is shaped like a trough from the outset, so that the belt will always tend to assume this trough-like shape; confer the International Patent Application No. PCT/SE85/00409. As a result

of this there is imparted to the belt an ability of its own to carry part of the load in a longitudinal direction, and the belt can assist the cables in carrying the load between the bearing points. This means that the sagging between the bearing points may be minimized and that the number of bearing points may be reduced and that less driving power is consequently required. Furthermore, the belt is reinforced longitudinally, which means that the belt may be driven together with the cables.

In order to be able to construct conveyors of considerable length which are also economically viable it is, however, also required that the driving of the cables is improved in relation to prior art.

SUMMARY OF THE INVENTION The purpose of the present invention is to propose a driving means for such a conveyor belt which is carried by cables wherein the belt and the cables may be driven with a minimum of guiding of the cables.

This is achieved according to the invention by a driving means having the characteristics described in the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in greater detail with the aid of a preferred embodiment of the invention with reference to the accompanying drawings.

Fig. 1a is a diagrammatical elevation and Fig. 1b is a diagrammatical plan view of a belt conveyor of the type covered by the invention and according to prior art. Fig. 2 is a diagrammatical cross-sectional view which shows the problem according to prior art. Fig. 3a is a diagrammatic elevation of a first embodiment of the driving means according to the present invention. Figs. 3b and 3c are cross-sections along lines A-A and B-B in Fig. 3a. Fig. 4 is a diagrammatical elevation of the embodiment according to the present invention and showing the loading end. Figs. 5a and 5b are cross-sectional views showing the co-operation between the cables and the belt. Finally, Fig.

6a is a diagrammatical elevation and Fig. 6b is a diagrammatic¬ al cross-sectional view showing an intermediate driving means according to the invention.

9 DETAILED DESCRIPTION OF THE EMBODIMENT PREFERRED

Figs. 1a and 1b show diagrammatically how the cables are driven according to prior art. Fig. 1a shows a conveyor belt 1 which is carried by two cables 2. The belt is laid around a belt drum 3a in order to form the return portion. The cables 2 must be guided outwardly past the end of the belt in order to be able to reach driving cable sheaves 4. The driving cable sheave is of the type called "Koepe-Winders" in the mining industry Cdeep pits), the cables being wound in one or more turns around the sheaves in order to form the requisite friction surface. The belt is not driven but all driving power is imparted to it by the cables. As a rule, the return part of the belt is also carried by the cables, which in that case must be located beneath the return portion of the belt, as is also shown in Fig. 1a. If it is desired to avoid separate sheaves for the cables and the belt this is not possible according to prior art, as is shown in more detail in Fig. 2. If it is tried to wind the cable several turns around the cable drum 3b the cable will lie outside the carrying groove 5 in the belt and cannot co-operate with the belt in the manner intended. Furthermore, the cables and the belt will run over different diametres, which gives different peripheral speeds. Finally, the edges or margins of the groove will be affected by the adjacent turns and will cause serious wear. Fig. 3a shows an embodiment of the present invention where, in spite of what is shown in Fig. 2, the belt drum is used in order to drive both the belt and the cables. As is shown in greater detail in Fig. 3c, the conveyor belt which is used in the present invention is a belt having a construction which is trough-like from the outset and which therefore has a certain height in Fig. 3a. Approximately from cross-section B-B the trough shape is becoming reduced and the belt becomes more and

more plane in order that it may be wound around the belt drum 3c. This planing is due to the fact that the cables are successively being led down to the diameter of the driving drums and cannot therefore carry the belt any longer. The trough-shape is formed by the belt having this shape imparted to it already when being manufactured. Furthermore, there are transverse reinforcements of considerable strength but which do not to any considerable extent prevent a certain planing of the belt when it passes the end drums. Fig. 3a shows a first pulley wheel 6 which constitutes the last support wheel for the cable before the driving end. Thereupon, the cables run obliquely downwardly towards the periphery of the drum, as is shown in more detail in Fig. 3a. It is shown in Fig. 3b that the cables are wound several turns around the drum and are located in special recesses or grooves 7a in the drum.

The driving drum is provided with a suitable cable guide 15, as is shown at the driving drum in Fig. 3a. 'The cable guide 15 ensures that the cable will run in the intended manner on the surface of the driving drum. If the cable should deviate from this path an electronic monitoring device will sound an alarm. The monitoring device simultaneously monitors cable ruptures, if any. The cable guide actuates the cables and is operated mechanically, hydraulically or pneumatically in a manner known per se.

The return portion of the belt is carried by special return pulleys 8 and the cable passes above the return path on pulley wheels 9, confer Fig. 3a. These wheels 8 and 9 are not exposed to any considerable load but are only meant to carry the weight of the belt and the cables in principle. As the longitudinal rigidity of the belt is relatively great, the return pulleys may be located rather sparsely and will not make the construction more expensive.

The return cables may also be adapted to carry the return portion of the belt, in which case the cables and the cable sheaves are guided outside and below the belt in order to engage with a special groove at the margins of the belt which are now

directed downwardly, as is described in more detail in the above ^' -mentioned International Patent Application No. PCT/SE85/00409.

Fig. 4 shows the corresponding construction at the loading end, where the cables run over individual cable tensioning end pulleys 10, whereas the belt has its own belt tensioning end pulley 11. It is necessary to tension each cable individually in order to compensate for curves in the conveyor etc.

Fig. 5a shows an enlargement and a cross-sectional view of how the principle according to the invention functions.

The belt is .carried along the length of the conveyor by the cables which are in turn carried by cable sheaves 6 disposed at suitable distances from each other, as is shown to the left in Fig. 5a. As the belt has a longitudinal rigidity of its own, fewer supporting cable sheaves may be used than according to prior art.

To the right in Fig. 5a there is shown the outline of the driving drum 3c with the groove 7a where the cable co-operates with the drum and is driven. Simultaneously it is shown. approximately how the belt planes out when it passes around the driving drum.

In order to be able to use a common driving drum for driving both the belt and the cables it is required that the average diameter around the driving drum is equally large for the cables and for the longitudinal reinforcement of the belt. If that is not the case, the reinforcement in the base portion of the belt will quickly destroy the belt.

According to the invention this is made possible by recessing the cables beneath the surface of the drum in the said recesses or grooves. In that case the cables extend such a distance up from the recesses that their centre or central point is located at the same height as the reinforcement in the belt, i.e. on a common average diameter on the driving drum, which is shown in Fig. 5a by means of a dashed line. As also appears from Fig. 5a, these cable turns will not affect the sides of the belt, since the cables are recessed in the said groove 7a.

As shown in Fig. 5b, the drum may alternatively be provided with a central groove which is meant to receive the central portion of the belt and simultaneously achieve a suitable centering and guiding of the belt. In that case, according to the invention, both the centre of the cables and the centre of the reinforcement in the belt shall still be located on the same level or average diameter on the driving drum 3c. This is achieved by a suitable relation between the depth of the grooves 7a and the groove 7b. This relation is of course dependent on the diameter of the cables and the thickness of the reinforcing wires of the reinforcement, and depends on whether several reinforced layers are used, etc.

Nothing prevents the same property of a common average diameter from being obtained by raising the driving drum at the base portion of the belt.

Finally, Fig. 6a shows an intermediate driving means where the cables are driven. In that case the cable passes over a first pulley wheel 12 and then around a driving drum 13 constructed in the same way as the driving drum 3c, and is then- guided by a second pulley wheel 14 into co-operation with the carrying groove of the belt. The belt rests on the upper surface of the driving drum which may be provided with the groove 7b. Due to the inherent longitudinal rigidity of the belt there is no need for the cables to have a carrying function at the distance between the pulley wheel 12 and the driving drum 3c or between the driving drum 3c and the pulley wheel 14, but the belt runs freely without any support here.

As is shown diagrammatically in Fig. 6b, one or both of the pulley wheels are inclined in relation to the vertical plane in order to guide the cable back into co-operation with the groove in the belt. Of course, an additional cable sheave having a vertical axis may be disposed immediately after the driving drum in order to achieve the guiding back to the groove (not shown in detail in the figure). The solution according to the present invention is especially suitable in connection with the belt shown in the figures but it is not excluded that the invention may also be

used in other types of belts having a certain longitudinal rigidity of their own.

The invention has been described above with reference to the accompanying drawings. A person skilled in the art will, however, realize that the invention may be modified in many ways within the scope of the invention. Such modifications as are obvious to a person skilled in the art who reads the specification are meant to be comprised by the scope of the invention. The invention is only limited by the following claims.