GB2096966A - Improvements in or relating to driving endless flexible belts - Google Patents

Abstract

A flexible belt e.g. a conveyor belt transmission belt or moving handrail is driven by linear induction motors positioned a predetermined distance from the lower portion of the belt and opposite a laminated section included in the belt and extending longitudinally thereof, said laminated section consisting of an upper layer of a standard belt construction and preferably including a plurality of textile yarns embedded in rubber, a second layer of magnetic material e.g. iron particles embedded in rubber, a third layer of non-magnetic material e.g. aluminium particles embedded in rubber, and fourth protective lower layer e.g. of rubber. The laminated section may be in the middle of the belt or may be located in the wing portions of the belt when the belt is to be used in a troughed configuration. A plurality of linear induction motors encapsulated in rubber are employed to provide the motive force for driving a conveying leg of the conveyor belt and a reduced number employed to provide the motive power on the return leg of the conveyor.

Description

SPECIFICATION Improvements in or relating to driving endless flexible belts The present invention relates to improvements in methods and apparatus used in driving endless flexible belt systems in which linear motors are used as the driving means.

The invention is especially concerned with the construction of the endless belt used in such systems, more especially the construction of conveyor belts.

It is known that linear induction motors can be utilised as a direct drive for endless flexible belts such as conveyor belts. However to date this method of driving conveyor belts has not been successfully used on a commercial scale. One of the reasons for this lack of commercial success has been the low electrical efficiency of the system resulting from, inter alia, unsuitable belt constructions.

Numerous attempts have been made to overcome this problem. Thus in British patent specification 1,317,944 there is described a belt including longitudinally developed squirrel cage inserts formed from two longitudinal braides of a non-metallic conducting metal, such as copper, and extending along each side of the belt and joined by transverse members which may be of the same construction. Additionally longitudinal support members having a lower extensibility than the braids are included in order to reduce the tendancy of the braids to fracture in use.

British patent specification 1,419,358 discloses a conveyor belt which includes insert portions extending longitudinally on the edges thereof and which are in the form of flattened wire mesh tubes having a core portion of rubber or plastics material.

We have now found that a particularly useful form of belt construction capable of being driven by a linear motor includes a portion extending longitudinally of the length of the belt and having a laminated structure comprising a first upper layer forming the load carrying surface of the belt, a second layer of a magnetic material, a third layer of a non-magnetic material and a fourth bottom layer of a material to protect the said nonmagnetic material and which may be the same as the material from which the first top layer is formed.

The invention also includes a transmission system comprising a belt and at least one linear motor positioned adjacent the said lower layer of said laminated portion to define an air gap therebetween and to provide, in co-operation with the said laminated portion, the motive power to drive the belt.

When the structure is a conveyor belt, for example, a plurality of linear motors will normally be spaced along the conveying leg below the belt with a reduced number along the return leg normally being positioned above the belt.

The top layer may be of a conventional belt construction, that is a rubber base in which plies of textile or steel wires are embedded to provide tensile strength. The second and third layers are preferably encapsulated in an insulating material which may be the same as the material used in the top layer, e.g. rubber, the second layer of magnetic material may be formed, for example, from iron particles embedded in rubber and the third layer of non-magnetic material may be formed for example from a metallic material such as aluminium based particles or wire embedded in rubber, or similar materials based on copper.

Whilst it is desirable that the insulating material in the second and third layers may be the same as the material from which the belt itself is formed, it may be of any suitable material, e.g. plastics material, provided that the individual layers are compatible with adjacent layers in order that successful lamination may be achieved with minimal risk of delamination during use.

It is also required that the laminated construction be capable of longitudinal and radial movement in order to traverse the head and tail drums of a conveyor assembly and remain sufficiently rigid in the transverse and longitudinal direction to prevent deflection by the attraction forces of a linear motor used to drive the belt. The belt must also be permitted to conform to a troughing configuration, thus the second and third layers, which together constitute a belt armature, will normally only appear in portions of the belt which may be kept flat in a transverse direction.

Therefore in troughing belts the armature may be installed singly at the centre underside or in pairs located in the outer wings or again, of course, in both the centre underside and outer wings, using appropriately positioned linear induction motors in each instance to provide the drive.

The linear motors, e.g. linear induction motors, used to drive structures of the present invention are preferably totally encapsulated to prevent damage from dust, such as is encountered in conveyor systems used in coal mines or quarries.

In order to achieve maximum driving force from the linear induction motors it is necessary that the gap between the belt and the motors be maintained at a critical dimension. This may be achieved by the use of narrow rollers in close pitch at both sides of the linear motor, the belt running on the peripheries of the rollers which are set the required distance above the upper surface of the linear motor. The use of such rollers effectively eliminates difficulties in respect of longitudinal belt sag resulting from both load being carried by the belt and the attraction forces of the linear motor itself. Alternatively, or in addition, idler rollers may be suitably positioned immediately in front and behind the linear induction motor.

Transverse sag of the belt may normally be effectively eliminated by providing the belt with an adequate degree of transverse strength.

The present invention is not, of course, limited to use in conveyor belts but may be employed wherever there is a need to drive endless belt-like structures, for example transmission belts, moving pavements and escalator hand rails. In addition to driving endless conveyor belts, the linear motors may also be employed to act as a brake, for example where the belt has a long down hill run.

The invention will now be more fully described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic illustration of an endless conveyor belt system embodying the present invention: Figure 2 is a cross section across A-A of figure 1; Figure 3 is a representation in cross section of the construction of a portion of the belt of figures 1 and 2 containing the belt armature; Figure 4 is a representation of a preferred embodiment of the invention in which the armature is located in a centre section of the belt, and Figure 5 is a representation of a preferred embodiment of the invention in which armatures are located along opposite sides of a belt.

Referring to figures 1 and 2 a conveyor belt 1 has an upper conveying leg 10 and a return leg 11. Conveying leg 10 of the belt 1 is troughed and has side walls 9, as shown particularly in figure 2, and is supported at intervals along its length by conventional idler rollers which include a lower roller 4 and side rollers 5. In the return leg 11 the belt is in the flat condition and is supported at spaced intervals by conventional idler rollers 6.

A belt armature runs along the centre flat portion of the belt and is of a construction as hereinafter described.

Encapsulated linear induction motors 7 and 8 drive the belt along both the conveying 10 and return legs 11 Each motor has individual thyristor speed control equipment and is capable of being driven from the available electrical supply.

Generally it will be sufficient if each motor is located at the base of the trough along the conveying leg in which case just the single armature running along that portion of the leg will be required. However in some circumstances, in order to apply sufficient power, it will be necessary for additional motors 12 and 1 3 to be employed along the wings of the troughed section, in which case of course, the belt will require additional armatures running along those two wing portions of the belt.

The portion of a belt containing an armature may be constructed as shown in figure 3. The belt 20 consists of four layers 21, 22, 23 and 24 forming a laminated construction. The upper layer 21 is of conventional belt construction and comprises synthetic rubber reinforced with conventional fabric plies. The second layer 22 consists of iron particles embedded in rubber and laminated to the upper layer, the third layer 23 consists of aluminium particles embedded in rubber and laminated to layer 22 whilst the fourth and lowermost layer is a relatively thin protective layer of rubber.

In an alternative construction shown in figure 4, the belt 30 has four layers, 31, 32, 33, and 34, in which layers 31, 32 and 34 are constructed as in figure 3. In layer 33, however the non-magnetic material comprises copper squirrel coils laid in overlapping relationship and again embedded in rubber.

In a preferred embodiment, illustrated in figure 4 a troughed belt 50 has a flat centre section 51 and wing portions 52 and 53, section 51 and portions 52 and 53 are supported along their length by conventional idler rollers, e.g. as illustrated in figure 1. The centre section 51 includes an armature 54. The belt is driven by a series of linear induction motors 56 and 57. The centre section 51 of the belt 50 is maintained a fixed distance from the upper surface of the linear induction motor 56 by means of two freely rotatable rollers 57 and 58 mounted adjacent the linear motor and having their peripheral surfaces the required distance above the surface of motor 56.

On the return leg, the belt now in a flat condition is maintained a fixed distance from the linear motor 57, which is now located-as shown, above the belt, by means of freely rotatable rollers 60 and 61, the belt being maintained in contact with those rollers by the action of pressure applied to the belt by the idler roller 62 which is arranged to be supported so that its peripheral surface is spaced from the peripheral surfaces of the guide rollers 60 and 61 by a distance equal to the total thickness of the belt 50.

In a typical system, belt 50 may have an overall width of 1400mm, the centre section 51 being 460 mm wide, and the armature 450mm wide.

The armature being wider than the induction motors 56 and 57. The construction of section 51 is similar to that described with reference to figure 3 except that the non-magnetic layer is formed from 3 x 1 mm thick sheets of aluminium laminated together by 0.4mm of rubber. The lower layer of rubber is 2mm thick. The upper layer consists of a thick layer of rubber containing layers of polyester yarn in a conventional construction and extends across the total width of the belt.

Tha overall thickness of the belt is 18mm. Wing section 52 and 53 are also 18mm thick.

Using a linear induction motor thrusts in excess of 27000 Newtons per linear motor have been achieved using a belt of the construction described with reference to figure 5.

In the embodiment shown in figure 5 a troughed belt 70 having a centre portion 71 and wing portions 72 and 73 is driven by linear motors located adjacent the wing portions 72 and 73 which portions include endless armatures 74 and 75 on the same construction described with reference to figure 5. On the conveying leg the belts are, again, supported a fixed distance from linear motors 80 and 81 by means of freely rotatable rollers 76,77,78 and 79. Afreely rotatable idler 72 supports the centre section of the belt between the linear motors 80, 81.

On the return leg belt 71 is in a flat condition and is driven by linear induction motors 90 and 91 located above the armatures 74, 75. Freely rotatable rollers 92 93 and 94, 95 position the armatures the required distance from the linear motors, the belt being maintained in contact with the rollers by means of idler roller 96 mounted such that the distance between its peripheral surface and that of the rollers 92, 93 and 94, 95 is equal to the belt thickness.

Whilst the invention has been described with particular reference to the use of linear induction motors to provide the drive, other forms of linear motor may of course, be utilised for that purpose, e.g. transverse flux motors.

Claims (25)

1. A belt having a construction enabling it to be driven by a linear motor including a portion extending longitudinally of the belt and having a laminated construction, said laminated construction comprising (i) a first upper layer forming the load carrying surface of the belt, (ii) a second layer of magnetic material, (iii) a third layer of a non-magnetic material and (iv) a fourth lower outer layer of a material to protect the said nonmagnetic material layer.

2. A belt according to claim 1 wherein the upper layer forming the load carrying surface comprises a natural or synthetic elastomer base having embedded therein a plurality of plies of textile or steel wires to provide tensile strength.

3. A belt according to claim 2 wherein the fourth lower layer is formed from the natural or synthetic elastomer used in the said upper layer.

4. A belt according to any one of the preceding claims wherein the magnetic and non-magnetic materials of the second and third layers are encapsulated in an insulating material compatible with the elastomeric material of claim 2.

5. A belt according to claim 4 wherein the insulating material is the natural or synthetic elastomer material used as the base for the upper layer.

6. A belt according to any one of the preceding claims wherein the layer of magnetic material is in the form of particles or wire embedded in an elastomeric material.

7. A belt according to claim 6 wherein the magnetic material is iron.

8. A belt according to any one of the preceding claims wherein the layer of non-magnetic material is in the form of particles or wire embedded in an elastomeric material.

9. A belt according to claim 8 wherein the non magnetic material is aluminium based.

1 0. A belt according to claim 8 wherein the non-magnetic material is copper based.

11. A belt according to any one of claims 2 to 10 wherein the elastomeric material is rubber.

12. A belt according to any one of claims 4 to 10 wherein the insulating material in which the metallic and non-metallic materials of layers three and four are embedded is a plastics material compatible with the material of the upper and lower layers.

13. A belt according to any one of the preceding claims wherein layers 2 and 3 occupy a longitudinally extending middle portion of the belt the outer side portions of the belt comprising layers 1 and 4 only.

14. A belt according to any one of claims 1 to 12 wherein a longitudinally extending middle portion of the belt comprises layers 1 and 4 only and the longitudinally extending outer portions of the belt include the magnetic and non-magnetic layers 2 and 3 respectively.

1 5. A belt according to any one of the preceding claims in the form of a transmission belt, a conveyor belt or a moving hand rail.

1 6. A belt having a construction enabling it to be driven by a linear motor substantially as hereinbefore described with reference to figure 3 of the drawings.

1 7. A transmission system comprising a belt according to any one of claims 1 to 1 6 and at least one linear motor positioned adjacent the said lower layer of said laminated portion to define an air gap therebetween and to provide, in cooperation with the said laminated portion, the motive power to drive the belt.

1 8. A transmission system according to claim 1 7 wherein the transmission system comprises an endless belt and there are provided a plurality of linear motors spaced along the load carrying portion of the system and a lesser number along the return leg of the system.

1 9. A system according to claims 1 7 or 18 being a conveyor system, a transmission belt or a moving hand rail.

20. A system according to claim 19 wherein the conveyor system includes a conveyor belt.

21. A system according to any one of claims 1 7 to 20 wherein the air gap between the belt and a linear motor is maintained at a predetermined dimension.

22. A system according to claim 21 wherein the dimension of the gap between the belt and a linear motor is maintained by the use of narrow rollers in close pitch located either side of said linear motor on which the belt runs.

23. A system according to claim 22 wherein the rollers are located in front and behind said linear motor.

24. A system according to any one of claims 1 7 to 23 wherein the linear motors are linear induction motors.

25. A conveyor system substantially as hereinbefore described with reference to figures 1, 2 and 4 or 1,2 and 5 of the drawings.