The present invention relates to a floor covering of electric conducting type for use in premises where it is desired to avoid static electricity by earthing. Such coverings have been developed in several types, e.g. so-called carbon mats, but a common feature for them all is that focus is on the earthing ability to such an extent that other qualities in exactly a floor covering have not been particularly considere It is presumed that the crucial point is the earthing ability in such a special floor covering as the appearance of major static charges, let alone even very small sparks , can have dire consequences; it is considered of secondary importance whether the floor covering is reasonably appropriate in all other respects, e.g. with regard to walking and standing comfort, cleanability, wear resistance etc. , even to a certai degree also regarding price.

The present invention breaks with this concept and its purpos is to provide a floor covering which, while fully allowing for the earthing ability, at the same time widely provides for all other requirements for floor covering in working premises.

The invention is based on the irecognition that exceedingly appropriate floor coverings have already been developed which, true enough, have not been provided with earthing qualities, but which may be easily modified to also show this capacity without such modification in any way harming the other good qualities as adapted to the purpose.

Reference is here made to floor coverings of plastic tiles of the type having principal dimensions of the magnitude 25 x 25 x 2 cm and being designed with an unbroken or per¬ forated top plate which is supported at a number of integral rib or stud parts protruding downwards therefrom; being

mutually spaced these parts can support the top plate on an underlying firm floor surface. Additionally the tiles are designed so that they can be laid closely against one another in a mutually interlocking fashion. It has been ascertained that floor coverings of this type have a multitude of advan¬ tages for a variety of reasons, regarding as well usability as maintenance and mounting. By the invention it is recognized that none of these good qualities will be sacrificed by the simple measure of manufacturing the tiles of a plastic material of the special kind having good electrical earthing abilities. Contradictory to the above view it could be said that such an intended ideal floor covering so far has been developed without consideration for the special quality that for cer¬ tain uses it is desirable that the covering is electrically groundable.

It is not immediately particularly conspicuous that a cover¬ ing built of relatively small, die-cast tile members can qualify as a groundable flooring, which in principle .ought to be spread over a large area, but it is realized by the invention that often only relatively restricted areas having earthing qualities are required, e.g. at permanent seats or standing room at existing worktables, and even though the tile elements in an electrically conducting version will be more expensive to produce than corresponding non-conducting elements, the_corresponding increase in cost can, however, be limited to the partial areas concerned, while the flooring as a whole can appear in a uniform way. Especially as die-cast, comparatively small covering elements are used, the employment of the more expensive, electrically conducting elements can easily be limited to precisely the actual walking or stand¬ ing areas.

In the light of this the covering according to the invention is characteristic in that it consists of modular elements

of intercoupled plastic tiles of the type being designed with an optionally perforated resilient stepping plate which at its bottom side has a number of mutually separated down- . ward projecting supports and along the edges is provided with coupling means enabling the tile to be interlocked with an adjacent tile, and that the entire floor covering is divid into two or more partial areas, viz. one or more relevant subareas with tiles having electrical conducting ability and one or more subareas with tiles having no such ability.

The type of tile elements considered here has the advantage that the resulting flooring can be adapted extensively to various or changed positions of machinery beds and other primary limitations to the floor space in that the tile elements conveninetly can be taken up and relaid anywhere, as they are stabilized only by their interlocking with other corresponding tile elements. Correspondingly any subarea consisting of conducting tiles may be established anywhere.

As another major advantage the tile elements of the considere type are "foot kind" in the sense that their top plates are resiliently flexible in the areas between the bracing support whereby a quite substantial therapeutical effect on the user' feet is achieved. This major advantage can be fully maintaine by the invention because the effect in question is not much influenced by the material being of electrically conducting or non-conducting plastic.

The said plastic tiles have the further advantage that they are easily cleaned, nor is this advantage jeopardized by using plastic of the electrically conductive type in the manufacture. The covering can simply appear exactly as before.

For the intended effect it obviously does not suffice that the tile elements themselves be electrically conductive, as

they should also be earthed effectively. When placed on a support floor which in itself has a sufficient earthing ability, the earthing can be effected immediately through the tiles where the relevant current path down through the support parts will be comparatively short, i.e. the tiles may or must have only a low conductivity,- whereby they can be correspondingly cheap. No improvement of the earthing will be obtained through the use of the tiles, but it is achieved that the walking or standing persons get a considerably im¬ proved floor surface to walk or stand on, viz. the same improved floor surface which is also found at the earthing- wise less critical subareas where it is advantageous and acceptable to place the cheaper, non-conductive tiles.

When building up the flooring on a non-earthed floor the problem is entirely different, as an earthing with compara¬ tively long current paths in the horizontal direction to a suitable ground connection is required. Underneath the tiles an earthed metal foil can be placed, but this solution is none too attractive. As the tile elements are joined by means of special interlocking means they could also hereby be electrically interconnected, but it is considered dubious to rely on the necessary perfect contact always being established hereby. Admittedly the engagement parts could be optimized from an electrical contact point of view, but the fact remains that for an efficient earthing from a single point of a large floor area an almost metallic conductivity in the material would be required, and it is a fact that the plastic material for the actual purpose is substantially more expensive, the higher the conductivity is to be.

According to the invention the low-cost of the material as well as a high earthing safety of even a large floor space are considered by producing as a standard the individual tile elements with an embedded, central contact member which

at the laying of the tile is suited to be directly wire con¬ nected with the contact members of the other elements, where¬ by it suffices to earth the net of highly conducting wire connections in question at a single spot or at several places where large areas are concerned. Hereby, irrespective of the area of the floor space, the individual tile elements only have to be made in such a way that with a required efficiency they can conduct electricity away from their own small area, even limited to the area parts between the edge and the centre of the element, which in practice means a maximum distance of some 20-30 cm; normally this will be possible by means of an only moderately conducting plastic material, i.e. a reasonably inexpensive material.

When using the wire connections mentioned, it is pertinent to lay out wires on the rigid floor space underneath the tile elements which, however, can be done without any special problems provided some lower recesses are provided in the edge ribs supporting the elements at the floor. It should be mentioned that the known tile elements are already provided with such recesses, as they are already prepared for use on floor spaces where either laid out wires occur, e.g. exhi¬ bition stand floors, or where water should be able to be drained off.

It should be noted that the plastics in question must neces¬ sarily be produced by die-casting from a basic material which in itself is pronouncedly electrically insulating, i.e. a conducting material must be incorporated which can create the required moderate conducting ability. In practice a con¬ ducting fibre material ought to be used, preferably carbon fibres, and practice has shown that when die-casting such a composite material, it is rather dubious whether the result¬ ing tile will attain the required conducting ability in the horizontal and/or vertical direction between different sur-

face parts thereof, because the fibres do not necessarily remain in a homogeneous admixture within the material by the injection thereof into the compact mould. Therefore it has been found necessary to subject every single tile member produced to a control measuring of the conductivity in the horizontal and vertical direction, respectively, and it has been found hereby that a considerable percentage of rejects may occur, which of course will contribute to the conducting tiles generally being appreciably more expensive than the pure plastic tiles.

The invention is explained in more detail below with reference to examples illustrated in the drawing, in which:-

Fig. 1 is a perspective view of a floor covering tile seen from below

Fig. 2 is a top view of a group of assembled tiles

Fig. 3 is a plan view of a floor covering performed with both earthed and non-earthed covering tiles

Fig. 4 is a lateral sectional view of a tile with associated electrical connection means

Fig. 5 is a corresponding perspective view of a number of tiles seen from below, and

Fig. 6 is a plan view illustrating the electrical connection between several tiles in a flooring area of earthed tiles.

The tile elements shown in Figs. 1 and 2 are of a known de¬ sign and will be described only briefly. They are die-cast in a semi-soft plastic material and have a top plate part 4 and along the circumference thereof a downwardly protruding

edge wall 6, in the free lower edge of which recesses 8 are formed. At its lower side the top plate 4 is provided with a number of downwards protruding support studs 10 in a regular pattern, these studs preferably having a cylindrica form that is open at the lower side. The top plate can be unbroken or be designed with large or small holes 12 in the areas between the support studs. The edge walls 6 are inte¬ grally shaped with locking members 14, by means of which the tile elements can be joined to form a large coherent flooring.

By the invention these tile elements are modified by being manufactured of an electrically conducting plastic or rather by manufacturing uniform tiles in a non-conducting as well as in a more expensive conducting plastic such that in a given flooring conducting tiles can be incorporated every¬ where this may be desired.

Fig. 3 shows an example where a floor area has a covering of tiles 2 , of which those marked in shading are of the conduct¬ ing type, these being placed solely in places where an elec¬ trostatic earthing is imperative, thus in the example shown at the working positions opposite a couple of assembly desks 16 as well as along a diagonal walking area 18. For such an oblique path tiles of identical appearance as the surrounding tiles can appropriately be used, while for marking of more regular areas such as straight paths and working positions tiles of a different appearance can be used.

If the conducting tiles shall merely be earthed to an earthed underlying floor space per se it suffices, as already men-... tioned, that the individual tiles in the area concerned are suitably conductive between their upper and lower sides while when laying the tiles on a non-earthed floor space it should be ensured that the tiles are in mutual conducting

connection and that they are all efficiently connected to an earthing wire. By the invention it is preferred that all individual tiles are in direct contact with the earthing wire as the individual tiles will then only require a com¬ paratively small conductivity in the horizontal direction.

Figs. 4 and 5 show that one of the cylinder studs 10, i.e. a stud in or near the centre of the tile, is provided with a brass block 20 pressed up from below, which is provided with four horizontal radial bores 22, which between their inner ends leave a central core part of the block, and the cylinder stud 10 concerned is provided with side holes 24 exactly opposite the respective four orifices of these bores. A set of connecting wire elements 26 belongs to the tiles; these elements each consist of a wire part 28 which is slight¬ ly longer than the centre distance between two adjoining tiles and at both ends is provided with a coupling 30 con¬ sisting of a brass bushing with a protruding thread part 32 and a handle part 34. On the corresponding end of the. wire 28 a terminal member 36 is wedged or soldered which by the screwing home of the coupling 30 into a radial bore 22 is brought to press against the bottom of the bore, i.e. against the said central core part of the block 20, whereby a safe electrical contact between the wire 28 and the block 20 is achieved. A wire element 26 can thus be used for mutual electrical connection of two adjoining tiles, and as the block 20 has four thread holes 24 each tile can thus be con¬ nected with up to four adjoining tiles.

At its cylindrical outer side the block 20 is provided with axially extending projections, which can press or carve them¬ selves slightly into the inner wall of the cylinder stud 10 and thereby act not only as an extra hold on the inserted block, but also to provide extra electrical contact, viz. by cutting the adjoining conductive fibres, preferably carbon

fibres that are incorporated in the plastic material.

Fig. 6 shows a section of a floor covering which is placed on a non-earthed underfloor and comprising a shaded area 40 with earthed tiles 2, partly surrounded by and coherent with corresponding plastic tiles of non-conductive type. The centre block 20 of the earthed tiles are mutually connected by the said wire elements 26, and as shown the preferred rule is to direct wire connect any or all adjoining tiles irrespective of extra connections occurring hereby which can seem superfluous. The reason for this rule is that the floor covering can be laid and assembled by non-professionals whereby a certain risk occurs that some of the electrical connections are not established quite to perfection, and it is consequently to be expected that a sufficiently safe connection will be achieved when a plurality of connections to the individual tiles is established.

The tiles shown in the area 40 are connected to an earth wire 42. This connection is established through a resistance unit 44 ensuring a suitably high earthing resistance, e.g. of the magnitude 1 M Ohm in order that earthing of static electricity is ensured when a person is standing in the area, but without the person being susceptible to immediate earthing which can cause sparks or shocks if live wire parts are touched.

As indicated in Fig. 6 and shown more detailed in Fig. 5 the said earthing resistance can be placed in a special resistance block 44 which is provided with engagement parts 46 for clamped fixture to two adjoining stud parts 10 of a tile 2. This block 44, which contains the said resistance, can at one of its sides be shaped with a threaded bore ac¬ commodating a standard coupling 30, whereas at its opposite side it has a differently shaped connection terminal, e.g. a

thread hole of a larger diameter for connecting the earthing wire 42.

It will be appreciated that the invention is not limited to the method of connecting the tiles and the connection wires described in detail as these connections obviously can be established in a multitude of different ways. The crucial point is that in the entire floor covering distinction is made between the groupings of joined and in principle iden¬ tical, earthed and non-earthed tile elements, respectively, whereby a high quality earthed flooring can be substantially reduced in price by establisheing earthed areas solely where really needed, while the entire flooring is of a kind that is especially easy on the feet and legs when walking and standing and having the possibility of easy shifting of partial areas of the covering with regard to the earthed and non-earthed areas in mutually mechanical, releasable engage¬ ment.

It should be noted that an especially appropriate embodiment of the connectable tile elements is defined in the Danish patent application No. 118/87.