Spiral staircases are known in the art to comprise a central pillar onto which are successively mounted stair treads forming a spiral pattern as the staircase rises around the central pillar.

Various spiral staircase configurations have been developed in an effort to overcoming the traditional method of producing spiral staircases wherein stair treads are welded around the central pillar and the staircase has to be designed and constructed for each particular application.

In DE 19809248, AU 77237/87 and FR 2041584 spiral staircases are proposed wherein the central pillar is helicoidally perforated to provide slots adapted to receive the sequential stair treads and form the staircase around the central pillar.

Independently of the mode of mounting the stair treads onto the central pillar, such as wedging and gluing in AU 77237/87 or screwing via a bolt transversally through the central pillar as described in DE 19809248, or suspending the stair tread via a pair of hook extensions thereof and additionally screwing the same onto the central pillar as is the case in FR 2041584, the fact remains that such a staircase cannot be immediately delivered to suit specific customer requirements. Such a staircase is deliverable either with the angular rotation and rise of the stair treads and further the position where the stairway terminates being fixed by the manufacturer with the central pillar being perforated to comprise stair tread receiving slots in a standardized pattern thereby limiting consumer's choice or otherwise it might entail a possibility to vary angular rotation and rise of the stair treads to suit particular customer requirements, but then customized design of the central pillar prior to execution of each particular order of the spiral staircase has to be performed and the staircase is thus not deliverable on request.

In an effort to overcoming the above mentioned drawback of failing to render the staircase immediately deliverable yet with a certain degree of freedom of varying angular rotation and/or rise at the building site, US 5,088, 248 and GB 1,047, 846

have proposed spiral staircase designs wherein the central pillar is being divided in mating tubular portions, thereby allowing employment of alternatively dimensioned sets of such mating tubular portions to suit various individual applications. In both the above documents the stair treads are either incorporated in the mating tubular portions (US 5, 088, 248) or each one of the mating tubular portions extends into a tread-supporting fin (GB 1,047, 846) whereupon the treads are subsequently screwed.

Whilst allowing a freedom of setting the angular rotation of the stair treads at the building site, US 5, 088, 248 and GB 1,047, 846 do not provide for a variable rise in between stair treads and in this respect GB 1,047, 846 proposes the employment of collars in between the mating tubular portions to increase the rise between treads should the required height of the top stair tread from the base not be an exact multiple of the effective length of the mating tubular portions. It is noted that such collars if inserted in between successive tubular portions would render an aesthetically deteriorated result and would adversely affect the rigidity of the staircase. Moreover even the capacity of varying angular rotation of the stair treads is rather inadequate, since the tubular portions may be displaced by relatively sliding along their mating edges in GB 1,047, 847, whilst in US 5, 088, 248 the small diameter of the mating tubular portions of the stair treads does not allow for a fine adjustment of angular rotation. Most importantly if US 5, 088, 248 or GB 1,047, 846 would care to provide the spiral staircase being immediately deliverable for variable stair tread lengths and if the length was incremented by 5 cm from 50 to 100 cm, then a stock of 11 different combined tubular portions and associated treads or tread supporting fin extensions should be maintained. Assuming an average number of 20 stair treads for an average staircase, it follows that a total number of 20 x 11 = 220 items combining treads and tubular portions would be required to enable immediate delivery of a staircase within the above mentioned range of stair tread length variation. If furthermore it would be desirable to vary the length of the mating tubular portions, thereby allowing variation of the desired rise in between treads and if such tube length was incremented by 5 mm from 160 to 220 mm, this range covering most staircase requirements, an additional stock of 13 different combined

tubular portions and stair treads or stair tread supporting fin extensions for each one of the previously mentioned 11 different stair tread variations would be required, thereby leading to an overall stock requirement of 220il3 = 2860 items of stair treads and associated tube combinations to make the staircase immediately deliverable in accordance to customer requirements. If the awkward shape of tube- tread combination (US 5,088, 248) or tube-stair tread supporting fin combination (GB 1,047, 846) is taken into consideration, it follows that maintaining such a huge stock would be difficult and expensive.

It is therefore an object of the present invention to provide a modular spiral staircase immediately deliverable to customer requirements, wherein such a capacity is obtained with a minimum stock, that is substantially diminished in relation to the prior art and is therefore economically feasible. In accordance to the invention the spiral staircase is designed to comprise a central pillar divided in a plurality of mating tubular portions and a plurality of independently provided stair treads suspendable and screwed thereupon. Due to such independency of the mating tubular portions and stair treads, a stock of 11 different stair tread sizes with a length varying from 50 to 100 cm, i. e. a total of 11 x20=220 stair treads would be required together with a stock of 13 different tubular portion sizes with lengths varying in 5 mm increments from 160 to 220 mm, i. e. a total of 13X20=260 tubular portions. Thus the overall number of items to be stocked arrives at the manageable number of 480 items, that is substantially lower, approximately 6 times less, the aforementioned number of 2860 pieces of stock requirements of the prior art. This substantial improvement is further emphasized if the awkward to store or carry tube-tread combination of the items of the prior art is taken into consideration and compared to the orderly storing or carrying of the separate cylindrical central pillar forming tubular portions and planar stair tread members of the present invention.

It is further noted that in both US-5,088, 248 and GB 1,047, 846 a supporting rod passing through the mating tubular portions is employed for providing rigidity and strength in the overall structure. However, it is obvious that such a result is obtained if a relatively tight fit of the supporting rod with the inner walls of the tubular

portions is possible, and that such requirement may often be impossible due to lack of commercially available proper tube diameters.

It is therefore a further object of the invention to provide for the desirable relatively tight fit of a supporting rod with the inner walls of the tubular portions independently of commercial availability of successfully interacting rod and tubular portions by providing each tubular portion with a pair of annular rings welded at the proximity of both basements of the tubular portion, said annular rings having a diameter such as to receive the supporting rod and ensure a relatively tight fit.

It is further noted that whilst FR-2,041, 584 proposes a stair tread being provided with a pair of hook extensions which are inserted into a corresponding pair of slots of the central pillar, so as to suspend the stair tread from the central pillar, it is however evident that due to the tolerances allowed in the slots to enable free insertion of the hook extensions therein, following its suspension, the stair tread might be laterally movable and therefore it may fail to provide a rigid, strong vibration free connection of the stair tread to the central pillar.

Furthermore, such tolerances of the slots in the central pillar relatively to the hook extensions of the stair treads may lead to stair tread levelling and regulating requirements during assembly of the spiral staircase.

It is therefore a further object of the invention to provide for a stair tread that is rigidly suspended from the central pillar and is automatically leveled and regulated eliminating the need of additional care of the installation technician, such rigid, strong and vibration free connection being achieved by means of a pair of guiding protrusions being provided onto the stair tread axially underneath a pair of hook extensions thereof and a corresponding pair of additional slots for receiving the pair of guiding protrusions onto the tubular portion, axially underneath the pair of hook extension receiving slots.

A further object of the invention is to provide for an improved capacity of varying angular rotation of the stair treads and in particular of a fine adjustment of the angular rotation, such capacity being obtained by machining the ends of the tubular portions to provide a gear engagement of adjacent tubular portions, wherein both

ends of each one of the plurality of mating tubular portions are provided with a plurality of teeth to ensure fine adjustment of angular rotation and thereby ensure desirable exit of the staircase, wherein the gear engagement of the tubular portions has the further advantage of eliminating any undesirable circumferential and/or centrifugal displacement of the mated tubular portions.

A further object of the invention is to propose a hand railing structure and supporting members thereof easily mounted at the outermost ends of the spiral pattern of stair treads, with a capacity of on site regulation.

It is therefore an overall object of the present invention to provide an inexpensively constructed, easily assembled, yet strong and rigid construction of a modular spiral staircase, with a capacity to selecting the rise between stair treads and finely adjusting the angular rotation thereof and further selectively regulating the position where the staircase terminates, wherein the modular spiral staircase of the invention is immediately deliverable to customer requirements.

The invention will hereinafter be made apparent to those skilled in the art by reference to the accompanying drawings in which: Fig. 1 shows a perspective view of a part of the assembled modular spiral staircase of the invention.

Fig. 2 shows a perspective view of one from the central pillar forming tubular portions and associated stair tread suspended thereupon.

Fig. 3 shows a detailed enlarged view of the assembly of tubular portion and associated stair tread of Fig. 2.

Figs. 3a shows another detailed enlarged view of the assembly of tubular portion and associated stair tread of Fig. 2 with the tubular portion being partially cut to reveal the inner walls of the tubular portion at the region of connection to the stair tread, including the pair of annular rings delimiting the central supporting rod.

Figs. 3b and 3c show two successive phases of mounting the stair tread to the tubular portion.

Fig. 4 shows a frontal view of the tubular portion with the hook receiving slots and guide protrusions receiving slots and one hole for fixedly screwing the stair tread onto the tubular portion.

Figs. 5 and 6 show a cross sectional view of the stair tread approaching the tubular portion onto which it is mounted and assembled thereupon respectively.

Fig. 7 shows a planar view of the stair tread assembled with the tubular portion.

Fig. 8 shows an assembly of a tubular portion onto a stair tread including in perspective an optional stair tread bottom cover.

Fig. 9 shows the spiral staircase of the invention with a perimetrical hand railing.

Figs. 9a and 9b show in perspective alternative forms of the hand railing structure supporting members.

By reference to the drawings we will hereinafter present a preferred embodiment of the invention.

As depicted in Fig. 1, the staircase of the invention that is made from steel, stainless steel, aluminum or other suitable metal or other material comprises a central pillar 1 onto which are radially fitted stair treads 2 forming a spiral pattern. The central pillar 1 is being built by a plurality of identical mating tubular portions 4, each of which is machined at both ends thereof to form a plurality of teeth 8, whereby adjacent tubular portions are brought to a gear engagement when one sits above the other and a rigid mating thereof is obtained without circumferential or centrifugal displacement thereof being possible.

Each tubular portion 4 is adapted to receive one of the plurality of identical stair treads 2 and it is therefore, as shown in Fig. 4 perforated to form a pair of adjacent identical slots 4a onto its surface and a pair of adjacent identical slots 4b, axially underneath slots 4a.

Each stair tread 2 comprises a pair of identical rods 3 connected by means of rod 7 at the outermost end thereof, whilst rods 3 converge towards the tubular portion 4 and are connected by means of short length of sheet metal 17 that is curved at a curvature such as to fit around the tubular portion 4. Rods 3 extend beyond the

connecting sheet metal 17 to form a pair of upper identical hook extensions 3a and an underlying pair of guiding protrusions 3b, such hook extensions 3a and guiding protrusions 3b constituting the means of suspension of the stair tread 2 onto an associated tubular portion 4.

As depicted in Fig. 8, each stair tread 2 is provided with a sheet metal plate 21 welded along the inner walls of rods 3 and the inner wall of end connecting rod 7 to form a basement whereupon may be fitted tread items made from a variety of materials, such as wood, marble, glass, stainless steel or sheet metal grid, etc. In accordance with a preferred embodiment of the invention an additional sheet metal portion 20 formed in the configuration of the stair tread with side members 2a covering the pair of convergent rods 3 of the stair tread and further inwardly bent into extensions 2a that lock into longitudinally extending upper recessions 2a"of convergent rods 3, whereby sheet metal portion 20 with side members 2a thereof provides a bottom coverage of the stair tread 2 and substantially adds in the aesthetic result obtainable with the stair treads of the invention.

It is noted that longitudinal slots 7a are provided on either side of the outermost rod 7 of the stair tread to provide for connection of the supporting members of a hand railing structure.

It will be appreciated that as the diameter of the tubular portions is increased, a greater number of teeth can be cut along the perimeter of the edges of the tubular portions. The greater the number of teeth is the finest regulation of the angular displacement of the stair treads suspended from the tubular portions 4 is obtained together with an enhanced rigidity of the mating contact of adjacent tubular portions. Typically the number of teeth is selected to lie within a range of 140-400 teeth. Thus if 144 teeth are employed the relative circumferential displacement of a tubular portion against its adjacent ones by one tooth generates a change of 2. 5° in the angular rotation of correspondingly adjacent stair treads (360° : 144=2. 5°) whilst if the number of teeth 8 is doubled (288) a corresponding incremental change of 1. 25° (360° : 288=1. 25°) is obtained and if 400 teeth are employed incremental angular displacement changes of 0. 9° (360° : 400=0. 9°) are obtainable.

As depicted in Fig. 4, each tubular portion is provided with a pair of equivalent longitudinal slots 4a with the appropriate dimensions and spacing for receiving the above mentioned hook extensions 3 a of the stair tread 2. A pair of further slots 4b is provided axially underneath the abovementioned hook extension receiving slots 4a, said slots 4b being adapted to receive the pair of guiding protrusions 3b of the stair tread accordingly. The process of suspending a stair tread 2 from a tubular portion 4 is depicted in Figs. 3b, 3c wherein it is shown that the stair tread 2 approaches tube portion 4 with a certain upward inclination to ensure inserting hook extensions 3a into hook receiving slots 4a and as the stair tread is lowered to horizontal orientation guiding protrusions 3b of the stair tread register into slots 4b of the tubular portion 4. Such 4-point connection of each stair tread to its associated tubular portion results in a rigid, self aligned connection that is obviously superior to the 2-point connection of the prior art. Prior to the installation of the upper and optional bottom tread cover, one or two bolts, passing though coincident holes 9, 9' or 9,9a and 9, 9a'of the curved connecting sheet metal 17 of the stair tread and of the tubular portion 4 respectively, are employed to fixedly connect the stair tread and tubular portion assembly of the invention. It is hereby noted that if a pair of holes 9,9a and 9', 9a'is employed, the bolt passing through 9a, 9a'might be elongated to reach the inner supporting rod 5 and thereby render a thoroughly fixed structure. Figs 3a-3c, 5-7 all present various views of the assembling process of one stair tread onto an associated tubular portion.

Each one of tubular portions 4 is provided with a pair of annular rings 6 welded around the inner walls of the same at the proximity of both basements thereof, such annular rings 6 having a diameter such as to receive the supporting rod 5 cut to a size corresponding to the overall height of the spiral staircase and fixedly mounted at ground level of the two floors being connected through the spiral staircase of the invention.

Fig. 9 shows a portion of the assembled staircase of the invention with a perimetrical hand railing structure mounted thereupon. The hand railing structure comprises a plurality of support members 10, each support member connecting a

pair of successive stair treads and comprising a pair of elongated holes 16 to allow adapting to a varied rise in between successive stair treads, wherein these elongated holes 16 become coincident with the elongated side holes 7a of the outer connecting rod 7 of the stair treads which allow applicability to variable angular rotation of the stair treads, whereby connection of support members 10 onto the stair treads 2 is effected by means of bolts passing through coinciding holes 16 and 7a. The upper end of support members 10 is shown to comprise a pivotally mounted basement 11 with a planar surface provided with holes 11 a onto which a desirable design of handrail (not shown) is being mounted.

Two alternative illustrative designs of the hand railing support members 10 are presented. Fig. 9 and the detail in Fig. 9b shows a support member 10 comprising a single sheet metal, whilst an alternative design of a double sheet metal structure with a pair of parallel bars 10a-lOb with the first support member being anchored onto ground level with plate 12 is shown in Fig. 9a. Lengthwise support members 10 are provided with an arrangement of equidistantly spaced pivotally mounted barrels 14a or 14b respectively, whereby a flexible railing 15 passing through successive barrels is connected in the perimeter of the staircase.

The modular spiral staircase described hereinabove defines a novel method to build spiral staircases in accordance with customer requirements and yet immediately executable following receipt of an order, since all that one has to do is, after being given the height in between floors to be connected by the spiral staircase as well as the orientation of entrance and exit therefrom, to select from stock, after defining the applicable rise and angular rotation of the particular staircase, an appropriate size and number of gearly engaged tubular portions 4 and a corresponding number of appropriately sized stair treads 2 which are immediately deliverable on site together with an appropriate length of the supporting rod 5, hand railing and miscellaneous connecting fixtures.