WO1999021781A1

WO1999021781A1 - Apparatus for bulk loading and packing of bulk products from silos

Info

Publication number: WO1999021781A1
Application number: PCT/BE1998/000161
Authority: WO
Inventors: Fabian Leroy
Original assignee: Katoen Natie Bulk Terminals
Priority date: 1997-10-24
Filing date: 1998-10-26
Publication date: 1999-05-06
Also published as: AU9730898A; BE1011831A3

Abstract

Apparatus for transferring bulk products comprising a silo battery as a storage space (101) and a load transfer space (102). It (102) is divided into two subspaces (121, 122) per silo, in which the flow aperture (112) of the silos (110) issues directly. Said one subspace (121) is provided for an in situ packing of the bulkproducts. The other subspace (122) is provided for a transfer of the bulk product to a transportation unit (170) in bulk form in unpacked condition. Both subspaces (121, 122) are mutually locally separated by a partition wall (160). A movable connecting means (100) is provided for connecting selectively said flow aperture (112) of each silo (110) with the desired subspace (121 or 122), so that the thus selected subspace (121 or 122) is brought into active condition.

Description

APPARATUS FOR BULK LOADING AND

PACKING OF BULK PRODUCTS FROM SILOS

Background of the invention

This invention relates to a apparatus for bulk loading and packing granules and powders from silos and the packaging of dry, free-flowing bulk goods, in particular synthetic material granules and similar.

State-of-the-art

In classical installations the product is stored in production silos. From these silos, depending on the destination of the product, the product can then be sent by means of a pneumatic conveying system either to bulk loading silos for loading bulk vehicles through gravity of to one or several buffer silos that stand above one or more permanently installed packing machines.

In the above mentioned traditional installations the silos can only fulfil one function which is directed either at bulk loading, or at packing. This then has the disadvantage that the forwarding manner of the product has to be determined already in an early stage, and namely prior to transferring the product to the packing or bulk loading silos. This therefore also has the disadvantage that when the product is in a packing silo and nevertheless has to be delivered in bulk, the product must first be packed and subsequently the sacks must be emptied into a bulk vehicle.

This involves additional handling, and therefore also additional labour, packing and co-ordination costs.

Furthermore there is usually only one or a limited number of packing silo(s). Since various types of products have to be handled there is consequently a great risk of cross- contamination or there are additional cleaning costs for these silos. These then involve production idle times pertaining thereto, which form yet another disadvantage.

The use of pneumatic conveying systems, whereby the product is blown with air in a closed conduit, results in the formation of dust and also of so-called angel hair. These are wisps which develop as a result of a laminar product flow resulting in an increased friction of the product at high speed along the conduit wall. The latter then gives a serious quality problem.

In view of the investment cost there is furthermore usually only one pneumatic conveying system available for the various products. This too as a result carries an additional risk of so-called cross-contamination.

Moreover there is still a considerable operational cost in the form of energy required for operating a pneumatic conveying system, as well as an additional investment for the pneumatic conveying system. In the latter case there is still an additional maintenance cost. Also no packing activities can be effected in case of a mechanical defect of the pneumatic conveying system. This results in a loss of efficiency. Thus with the above mentioned traditional apparatus rather a lot of handling is required for the packaging of bulk products which come from a storage silo.

A more advanced embodiment is that in which the production silos and the bulk loading silos are identical. In this case the bulk vehicles and/or containers can be loaded directly rom these silos , The product can also be despatched from these silos to the packing silos by means of a pneumatic conveying system.

Purpose of the invention

The purpose of this invention is to remedy the above mentioned disadvantages . For this purpose a apparatus according to the invention is presented as specified in the attached claims.

Summary of the invention

The apparatus for transferring bulk products comprises a storage space for the aforementioned bulk products consisting of a silo battery, and a load transfer space which is provided downstream in relation to the aforementioned storage space, whereby the aforementioned load transfer space is almost completely closed. The aforementioned bulk products, which follow a flow direction F, are processed into a transportable and dischargeable form. The apparatus according to a principal embodiment of the invention is remarkable because of the fact that the aforementioned load transfer space forms a multipurpose working space which is divided into at least two subspaces per silo, whereby one subspace forms the bulk side, while the other subspace forms the packing side. One of the aforementioned subspaces is hereby provided for an in situ packing of the aforementioned bulk products into package units, of which the volume and/or weight is adjustable, by means of a packing means provided for this purpose, while the aforementioned other subspace is provided for a transfer of the bulk product to a further transport unit in bulk form in unpacked condition. Both subspaces are thus in each case utilised separately whereby the bulk vehicles or container vehicles move to the bulk side for bulk loading through gravity. On the packing side there are movable packing machines that are advantageously movable on air cushions. Alternatively the aforementioned movement can however also occur on wheels or rails.

These machines are placed under the silo in question in order to enable the packing activities also to be effected through gravity. A bulk vehicle can hereby be immediately positioned under the silo from which it is to be loaded. Yet another movable connection means is hereby also provided in order to connect the discharge opening of each silo with the subspace desired.

According to an advantageous embodiment of the invention both the aforementioned subspaces are separated from one another by a partition wall.

Due to the apparatus according to the invention it is achieved that silos are multifunctional. Both bulk transfer and packing can be effected from the same silo. This results in operational planning being simpler. It is possible at any time to start every operation from each silo. In the traditional installations prior to being able to pack, the product first had to be transferred to a packing silo. Even if in the meantime an urgent packing order comes in, the product that is already in the packing silo has to be packed first, subsequently this silo then has to be cleaned before the desired product can be transferred to this packing silo in order to be packed.

The product can be held in bulk until the last moment, specifically until the delivery form to the final buyer is known. There are no additional costs for repacking of already packed product which has to be delivered in another form of packing.

Investment costs are also lower in comparison to the traditional installations.

From the storage silo these products can either be directly packed or immediately transferred in bulk, this without any additional handling. For this purpose the silos are placed in a supporting structure. An open working space is thereby created under the silos which is used both for bulk loading and for packing activity. Thus all operations can be effected in one location, namely in the aforementioned load transfer space, so that packing and bulk loading activity supervision and control is simpler. This further leads to a better occupation of the personnel.

The structure of the aforementioned working space is an open structure, at least in the driving direction of the means of transport. Here there are namely no wind and cross bracings in order thus to provide a free passage at least in the driving directions. Advantageously cross columns are however hereby provided with which the wind and cross bracings can be eliminated. This open structure offers a maximum flexibility and mobility for the packing machines and their handling. Pallet transporters can furthermore be used on the floor without problem.

More especially with the apparatus according to the invention there are the following further characteristics and properties.

The silo configuration is in block form. In other words the silos are compactly disposed according to a grid, The block form offers minimum distances to all sides and as spacious a working surface space as possible, which enables easy securing of the packing machines when moving them from under one silo to a farther silo. Due to the above mentioned embodiment work can furthermore be effected through gravity, which is ideal for maintaining product quality.

According to a preferred embodiment the packing machines are movable from one silo to another on air cushions, at least according to one and the same grid direction of the silo grid. Placing the machines on air cushions makes them more mobile in the aforementioned driving or grid directions, whereby these are easy to move by only two people with a minimum of physical effort. Only a manual guiding of the machine is indeed required hereby. Alternatively the movement can however also be effected on rails or wheels.

According to an advantageous embodiment of the invention each of the aforementioned partition walls has a relatively low height which is such that this enables a free movement of the aforementioned connection means from one subspace to another. In particular each of the aforementioned partition walls has a length which is such that this both exceeds the diameter of a silo and is also smaller than half of the grid direction length of the silo battery in question. Thus the packing machine can in certain locations cross over from one silo row to another row. Due to the thus formed cross-over locations between successive partition walls the packing machine can be used is different silo rows.

According to a further advantageous embodiment of the invention the surface of the floor of the packing side and cross-over locations is very flat and even. The aforementioned floor is preferably provided with a multilayer finishing layer in particular with an epoxy coating. This appears to work very well for the air cushion transport. The smooth floor in epoxy coating enables a very efficient cleaning and thus prevents the risk of contamination due to remaining granules. This indeed forms a particularly critical problem.

Advantageously the aforementioned connection means between both subspaces is formed by a preferably rotating loading tube, which is secured at a certain angle in relation to the vertical axis to the silo outlet, and which can thereby be utilised on the one hand for bulk loading and on the other hand for packing from every silo. Each silo is thus multifunctional. With this the ultimate destination of the product for forwarding in bulk or packed can be freely determined as long as the product is in the silos. This is especially useful in on-site logistic terminals which are linked up immediately after the production line and are directly connected to this. This is also particularly useful in so-called multicustomer installations which are fed by supply of the products.

According to a preferred embodiment for bulk loading telescopic connection tubes are inserted which are mounted on the silo outlet.

On the outside of the packing side in each silo row a fixed belt conveyor is mounted, which is only mobile at the crossover locations for the packing machine.

Specifically packing sacks are thrown off from the output belt of the packing machine on to a belt conveyor which is at a certain angle of e.g. approximately 90° to the axis of the output belt. For this purpose a specially formed turntable is provided. The belt conveyor in question is ascendingly mounted on the extremity of the silo row. At a height of minimum 4m it delivers the sacks on to some fixed belt conveyors which are placed on a platform transverse to the direction of motion.

These sacks further continue their way and successively go to a sack packaging unit, such as e.g. a metal detector, checkweigher, inkjet printer, and to a palletising machine and shrink-wrap or wind-wrapping machine, which are on the ground floor level in the packing shed next to the silo battery. Due to this advantageous further embodiment of the invention the problem that, with bulk loading and packing with packing machines on ordinary fixed tracks, the packing machine can only be easily moved in the axis direction, is remedied. Indeed, with this arrangement the packing machine has after all only a limited freedom of movement and this can only easily be moved in the axis direction of the tracks. For a movement of the machine to the tracks of another silo row use would in this case have to be made of a transfer station. The problem with this is that when different packing machines are deployed, as in the case that sacks of differing weight must be handled, and these have to be interchanged in the same row, one of the two first has to be transferred to the adjacent track. Subsequently this has to be moved to the transfer station at the other extremity of the track and transferred again to the first track prior to being able to be placed under the correct silo. With use of several machines much time is consequently lost with positioning of the machines.

The rails which are on the packing floor therefore form an obstacle for the operations. A pallet transporter can thus hardly if at all be used on the packing floor. Furthermore these tracks form an obstacle and a potential danger for personnel .

Also when the tracks are cast in the concrete floor there will be an agglomeration of residual granulate which is difficult to remove. Perfectly clean installations are very critical of handling synthetic materials. When a synthetic material granule with anomalous physical properties is in an homogeneous lot this can halt a whole production line. Modular belt conveyors according to the invention on the other hand provide a fast and easily manipulable connection between the location where the machine is disposed and the permanently disposed belt conveyors along one of the sides,

By placing the belt conveyors at the extremity of the silo rows at a height bulk vehicles can proceed in the extension of the roadways and it is possible to enable a through passage system. Furthermore forklifts or pallet transporters can at all times ride unhindered from one silo row to another row.

In relation to a rail system the air cushions offer the great advantage that no complex system is required for crossing over to another row. What is more if required two machines can cross each other in a cross-over location, which increases the flexibility of use.

Due to the fixed belt conveyors the installation time of the packing machine under the silos is reduced. The smooth floor in epoxy coating enables an efficient cleaning and prevents the risk of contamination through remaining granules .

Further characteristics and distinctive features of the apparatus according to the invention are specified in the further subclaims.

Further advantages and details of the apparatus according to the invention will appear from the following specification of an examplary embodiment of the apparatus according to the invention which isset out on the basis of the appended drawings .

Brief description of the drawings

Figure 1 is a schematic side view of the apparatus with a block disposition of the silos,

Figure 2 is a schematic representation in cross-section of a apparatus with a block disposition of silos according to the invention.

Figure 3 is a top view according to line I-I from figure 1.

Figures 4 and 5 are representations in greater detail of a detail of the apparatus according to the invention in front and side view respectively.

Figure 6 represents a top view of the part according to figures 3 and 4.

Figures 7 and 8 represent a variant of the apparatus according to the invention in side and respectively front view.

Figure 9 is a representation of the aforementioned variant analogous to figure 3 , Specification

Generally speaking this invention relates to a silo installation for processing bulk products during bulk loading and packing of bulk products, more specifically granules and powders . For clarity the following specification is directed at the example of handling synthetic material granules but this can among others also be applied to other types of granules, such as e.g. fertiliser pellets, or powders.

Figures 1 and 2 thus show a so-called block disposition 101 of silos 110 which are compactly disposed according to a grid which is also clearly represented in figure 3.

A row of silos one next to the other in one and the same direction forms a silo row. Under each silo row the space is divided into two subspaces 121, 122. One of the subspaces 121 is predestined for the packing machine 140 which is movable in the direction of the silo row to under a selectable silo. The other subspace 122 is predestined to enable a bulk vehicle 170 to drive herein 122 in the direction of the silo row and be positioned under any silo.

The moving of the packing machine 140 and the bulk vehicle 170 occurs in one direction, namely the direction of the silo row, next to one another. At certain locations 191 the packing machine 140 can cross over from one silo row to the other.

In the subspace 121 of the packing machine fixed and movable belt conveyors are also placed, in the latter case in the cross-over locations 191,

Each silo in principle comprises a specifically unique product. Each unique product is to be considered as different from another unique product. It is however quite possible that certain silos contain the same unique product.

The discharging of a specific silo either occurs through the packing machine, or through bulk loading of a bulk vehicle, but not simultaneously. A discharging of a specific silo does not occur through both bulk and packing. Furthermore one and the same bulk vehicle is not loaded simultaneously from different silos.

The grid structure of the silos is so designed that under two adjacent silos in one and the same silo row two packing machines can also be placed next to one another. For this purpose the structure of the silo support 125 is greater than the dimensions of the packing machines.

When a silo is discharged by bulk loading of a bulk vehicle this bulk vehicle, in view of its length, prevents any other silos from possibly being discharged at that time through bulk loading.

The minimum dimensions of the grid structure are therefore the following: in the direction of the silo row at least the length of the entire packing machine 140 increased by the column structure 125 and in the direction transverse to the silo row at least the sum of the dimensions of the roadway for the bulk vehicles, of the separation wall 190, of the width of the entire packing machine 140 with belt conveyor and of the column structure 125.

The grid of silos is incorporated into a structure of which the frame for example consists of a strong steel construction 125. The supporting structure 125 is surrounded by an enclosure wall 120 comprising for example a vertical boarding, through which the space 121 downstream from the silos is almost completed closed. The aforementioned space 121 has a small exit 129 in one of the sides of the enclosure 120. At the aforementioned exit 129 an external belt conveyor 133, 137 is provided on top of a laterally adjoining packaging shed 103 of the installation 101 whereby the belt conveyor advantageously has a certain incline.

The above mentioned steel construction belonging to the supporting structure 125 is permanently secured to the ground via foundations suitable for this purpose, preferably of reinforced concrete, which are equipped with deep pile foundations .

As appears from figure 2 the silos 110 are disposed according to rows and columns, in other words according to a grid disposition in rows and columns, whereby between each row and/or column the aforementioned steel construction has an upright column 125, whereby all columns are preferably interconnected into a connected bearing structure 125.

Advantageously the processing space 121 of the installation 101 has a ground floor working level which extends over almost the entire processing space, constructed almost parallel to the ground 105. The working space is of the open type such that a free passage is left in the entire working space. In other words almost no obstacle is present in this subspace 121 such that a great freedom of movement is available. This provides a considerable freedom of movement for the packing machines 140, at least according to one of the grid directions which corresponds to the driving direction of the means of transport, such as a bulk vehicle 170 or also wagon.

Furthermore cross-over locations 191 are provided between successive and adjacent longitudinal separation walls 190. This is particularly useful when the packing machine 140 has to be moved from one silo row 110 to another.

In order to improve the mobility of the aforementioned packing machines 140 still further these are provided movable on air cushions. With this an extremely flexible freedom of movement is achieved and the number of men required in order to manipulate the packing machines 140 is extremely small, in particular maximum two men per machine.

The combination of free subspace with mobility on air cushions makes the unit especially flexible and efficient when moving the packing machines from one silo to another for deployment, within one and the same silo row or from one silo row to the other via the cross-over locations 191 provided for this purpose.

In order to increase still further the efficiency of the operation of the packing machines which are movable on air cushions the floor of the packing side 121 in question is made especially flat. For this purpose the floor 123 is preferably provided with a finishing layer in particular with an epoxy coating. This finish works extremely well for the mobility on air cushions .

The aforementioned packing machines 140 enable the synthetic material granules to be packed in sacks destined for that purpose. The sacks filled with synthetic material granules via the packing machine are then transported via internal belt conveyors 151, 152 provided for this purpose. In addition to this a permanently disposed belt conveyor 151 is provided which extends along one of the sides of the processing space 121 and moreover leads to the above mentioned discharge opening 129. The transport between packing machine 140 and permanently disposed belt conveyor 151 is effected by providing further belt conveyors 152 which are installed perpendicular hereto, starting from the packing machine 140 up to the fixed belt conveyor 151. With the above described arrangement the silo can consequently operate extremely well in a packing scheme.

The high smoothness of the floor 123 with an epoxy coating enables a very efficient cleaning thereof, through which all possibility of contamination through remaining synthetic material granules is excluded.

A further possible function of the silo is notably described hereafter subject to inclusion of the aforementioned loading tube 100 which is movable at one extremity. For this purpose on the aforementioned ground floor level 105 the partition walls 190 are installed near each silo discharge opening 112.

In the farther subspace 122 located next to former subspace 121 external transport units 170, such as lorries and similar, can then be brought in whereby these external transport units 170 can be directly loaded from each silo 110. A silo battery 101 is thus obtained whereby each silo 10 is multifunctional. Indeed both direct bulk loading as such can take place as well as load transfer of previously and in situ packed bulk products and this from the same silo. This occurs simply subject to the deployment of the packing machine 140 with a suitable connection from the aforementioned rotating loading tube 100 or respectively by connecting this 100 differently and using it for loading a transport unit 170 directly from the silo 110. In this manner the load transfer product can be kept in bulk up to the last moment and this up to the point in time that the buyer of the product has made the desired form of delivery known to the operator of the silo installation 101. Furthermore this occurs without additional costs for further repacking of an already packed product. In other words a packing phase at another location is saved with this because of the fact that both shipment forms can be simultaneously effected here.

Figures 4 up to and including 6 represent the packing machine which is deployed in the silo installation described here.

The feed for the aforementioned packing machines 140 is provided at the different cross columns 125 which are also installed according to a grid structure which is complementary to the grid structure of the silos 110. The electric and/or pneumatic connection to the packing machine 140 is achieved by means of short flexible connections not represented. A short wire or cable connection can moreover suffice since a closed grid structure on cross columns 125 is present.

The operation of the above specified apparatus is briefly described as follows.

On the ground floor level 105 there is a half open space 121, 122 in which the bulk vehicles 170 or bulk containers move for bulk loading through gravity. Moreover the bulk vehicle is positioned directly under the silo 110 from which this has to be loaded. In the subspace 121 which the packing side forms there are movable packing machines 140. These machines are movable on air cushions and are placed under the silo in question in order to enable the packing activities also to proceed through gravity. For bulk loading use is made of a rotating loading tube 100 which is detachably mounted at one of its extremities. Each silo is therefore multifunctional and the final destination of the product consisting in a forwarding in bulk or packed, can be freely determined as long as the product is in the silos.

Such a system is especially effective in on-site logistic terminals which are linked up immediately after and are directly connected to the production line or also in multicustomer installations which are fed by the supply of the products.

A variant of the load transfer apparatus is represented in figures 7 to 9. Herein a classical shed 200 is represented which is provided with one silo row 211. The silo row 211 extends on a longitudinal side of the shed 200 over at least a part hereof as represented in figure 8. In this embodiment the packing machine is brought almost directly under the silo outlet, whereby the subspace 221 in question takes up almost the entire space which is located downstream from the silo row 211. The transport unit of the lorry type drives along the shed 200 in a loading zone reserved for this purpose which forms the subspace 222 in question and can be closed or otherwise. The load transfer zone 222 extends along the first subspace 221 as represented in figure 9, so that by means of a suitably movable loading tube it is possible to change over rather flexibly from one manner of packaging with the packing machine to the other with a transport unit and vice versa. The total load transfer space 202 then comprises both subspaces 221 and 222 in analogous manner as in the embodiment described above. In figure 9 an expansion zone 201 is provided in the extension of the silo row 211 so that additional silos 210 can be included in function of requirements . This variant offers the advantage of forming a relatively inexpensive alternative whose construction modularity contributes to a flexibility of installation of the apparatus.

Claims

1.Apparatus for transferring bulk products comprising a storage space (101) for the aforementioned bulk products consisting of a silo battery, and a load transfer space (102) which is provided downstream in relation to the aforementioned storage space (101) , whereby the aforementioned load transfer space (102) is substantially completely closed by a wall (120) , and whereby the aforementioned bulk products, which follow a flow direction (F) , are processed into a transportable and dischargeable form, characterised in that the aforementioned load transfer space (102) is arranged on the ground (105) itself on which the silo battery (101) is placed and in that said load transfer space (102) is divided into two subspaces (121,122) per silo, in which the flow aperture (112) of the silos issues directly, in that said one subspace (121) is provided for an in situ packing of the aforementioned bulk products into package units (180) , of which the volume and/or weight is adjustable, by means of a packing machine (140) provided for this purpose and which is movable by means (142) provided therefor, while the aforementioned other subspace (122) is provided for a transfer of the bulk product to a transportation unit (170) in bulk form in unpacked condition and in that a movable connecting means (100) is provided for bringing selectively said flow aperture (112) of each silo (110) in a cooperating connection with said packing machine (140) or with said transportation unit (170) in the desired subspace (121) or (122), so that the thus selected subspace (121) or (122) is brought into active condition.

2,Load transfer apparatus according to the preceding claim, characterised in that said silo battery (101) is formed by a set of silos (110) arranged in an array.

3. Apparatus according to claim 1 or 2, characterised in that said connecting means (100) is controllable remotely selectively.

4. Apparatus according to one of the preceding claims, characterised in that said connecting means (100) is formed by a rotatable loading tube.

5. Apparatus according to the preceding claim, characterised in thatsaid connecting means (100) has a supple and/or a deformable wall.

6. Apparatus according to one of the preceding claims, characterised in that both said subspaces (121,122) are mutually separated by a partition means (160) provided therefor which is formed by a wall (190) .

7. Apparatus according to the preceding claim, characterised in that the partition wall (190) is arranged substantially upright in the moving direction (G) of said transportation unit (170), in particular according an array direction of said silo battery (101) .

8. Apparatus according to one of the claims 6 or 7, characterised in that each said partition wall (190) has a relatively small height which is such that it enables a free movement of said connecting means (100) of the one subspace (121) to the other (122) .

9. Apparatus according to one of the claims 6 to 8, characterised in that each said partition wall (190) has a length which is such that this both exceeds the diameter of a silo (110) and is smaller than half of the array direction length of the silo battery (101) in question.

10. Apparatus according to one of the preceding claims, characterised in that said load transfer space (102) is substantially free, wherein supporting columns (125) are provided for supporting the silo battery (101) .

11. Apparatus according to claim 10, characterised in that the supporting columns (125) are arranged in an array.

12. Apparatus according to one of the preceding claims, characterised in that said packing machine (140) is provided for being used on the ground floor (105) in the subspace (121) provided therefor in stream downwards connection (141) with any of the silos (110) for packing said bulk products in situ.

13. Apparatus according to one of the preceding claims, characterised in that means (142) are provided for making said packing machine (140) moveable on an air cushion (A) .

14. Apparatus according to one of the claims 12 or 13, characterised in that energy supply means are provided at said supporting columns (125) for supplying said processing machine (140) with electrical current and /or compressed air.

15. Apparatus according to one of the claims 12 to 14, characterised in that at least one fixed conveying belt

(151,154) is provided along at least one of the walls (120) of said strea upwards subspace (121) , with which said processing machine (140) is brought in cooperating connection (152) for conveying of the packs (180) produced therewith (180) .

16. Apparatus according to the preceding claim, characterised in that the cooperating connecting means is formed by at least one additional movable conveying belt (152), which puts the outlet (148) in cooperating connection with said at least one fixed conveying belt (151,154).

17. Apparatus according to the preceding claim, characterised in that said additional movable conveying belt

(152) is built up in a modular way so that the length thereof can be set according to the instantaneous distance between the packing machine (140) and the fixed conveying belt (151, 154).

18. Apparatus according to one of the preceding claims, characterised in that said ground floor (105) is covered with a flat floor with a high smoothness.

19. Apparatus according to the preceding claim, characterised in that said floor (105) is covered with a multilayer finishing layer.

20. Apparatus according to one of the two preceding claims, characterised in that a toplayer of the floor (105) consists in an epoxy layer.

21. Apparatus according to claims 1 to 12, characterised in that said moving means are formed by wheels, resp. moving rails.