Field of the invention

[0001] The present invention is related to procedures applicable in construction of buildings, roadworks or landscaping, wherein construction elements are attached to a support surface. The main but not exclusive field of application is the procedure of tiling, wherein tiles or plates are mounted on a flat surface such as a floor or a wall. The invention is particularly related to tools for improving flatness of a tiled surface.

State of the art.

[0002] Tiles are attached to a base surface by cement or glue. Level differences between adjacent tiles need to be minimized before the cement or glue sets. Tilers usually apply any type of beam, often a wooden beam placed on two or more adjacent tiles, after which the levelling is achieved by impacting the beam with a hammer. A wooden or plastic beam is often not sufficiently strong to withstand a large number of impacts. When a metal beam is used, such a beam has inadequate force distributing properties so that the impact force is insufficiently distributed over the tile surface, thus requiring many impacts before satisfactory levelling is obtained, leading to a risk of damaging the tiles and/or the levelling tool. Summary of the invention

[0003] The invention is related to a levelling tool as disclosed in the appended claims. The invention is thus related to a device for levelling construction elements on a support surface, the device comprising a levelling body with an underside configured to be placed onto said construction elements when the elements are placed on the support surface, and provided on an upper surface of said levelling body with an impact receiving portion, said impact receiving portion being formed of an impact receiving material that is different from the material of the levelling body. According to specific embodiments, the levelling body is formed of a rigid material such as metal, preferably aluminium. The underside of the levelling body is flat when the device is configured for levelling flat construction elements, such as tiles or plates on a flat surface such as a wall or floor. The construction elements are placed side by side on the support surface and the levelling device is placed on top of at least two adjacent elements. The device is configured for levelling said construction elements by impacting the impact receiving portion when the underside of the levelling body is placed onto the at least two adjacent construction elements. 'Levelling' in the context of this description means bringing the upper surfaces of the construction elements at the same level defined by the underside of the levelling device. The device is portable and can be manually placed on top of the construction elements. According to an embodiment, the impact receiving portion is attached to the levelling body with a bonding force that is strong enough to prevent the two portions from being separated manually. Alternatively, the impact receiving portion is partially inserted in a cavity provided in the levelling body, so that separation of the two portions as a consequence of the impacting is prevented. According to all preferred embodiments, the impact receiving portion is connected to the levelling body in a sufficiently firm manner to prevent the impact portion being separated from the levelling body as a consequence of performing manual impacts.

[0004] The impact receiving portion is configured to receive the impacts and effectively transfer the force of the impact to the construction elements that need to be levelled, without damaging the levelling body, nor the impact receiving portion itself. The force that is transferred is the force required for levelling the construction elements, for example for levelling tiles placed on a support surface with mortar or glue between the tiles and the support surface. According to a preferred embodiment, the impact receiving material is a resilient material. Preferably the impact receiving material is of higher resilience than the levelling body. The impact receiving material may be rubber. The impact receiving material may alternatively be an impact resistant plastic. It may for example be polyamide (nylon plastic). The levelling body may be an elongate beam-shaped body.

[0005] According to an embodiment, the levelling body is a hollow casing provided with reinforcement means inside the casing. Said reinforcement means may comprise an undulating plate formed as a sequence of upward pointing and downward pointing portions, optionally with horizontal beams arranged in said upward and downward pointing portions.

[0006] In a levelling device according to the invention, the impact receiving portion may comprise an elongate strip of said impact receiving material mounted on said upper surface of the levelling body.

[0007] According to an embodiment, the levelling body is a hollow casing provided with separating platelets which divide the casing into partitions, said platelets comprising U-shaped openings, wherein support elements having a matching U- shaped recess are located in said partitions, so as to form a U-shaped groove along the entire length of the casing, and wherein a resilient piece is mounted in said groove, said piece having a T-shaped cross-section, said piece comprising a beam portion that fits in said groove and a top portion that covers the upper surface of the casing.

[0008] According to an embodiment, the impact receiving portion comprises one or more ball-shaped elements which are partly incorporated in said elongate beam-shaped body, so that part of the upper surface of said ball-shaped element extends above the upper surface of the elongate beam-shaped body.

[0009] According to a specific embodiment, said ball-shaped element is part of an impact receiving structure comprising said ball-shaped element, a shaft portion and a pedestal portion, the ball-shaped element being attached to the shaft portion, the shaft portion being mounted on the pedestal portion, the pedestal portion having a base surface that is at the same level as the flat underside of the device, the shaft portion and at least a part of the pedestal portion being mounted in the interior of the beam-shaped body.

[0010] The ball-shaped element may be a resilient element, comprising a hollow first ball attached to the shaft portion, a solid second ball attached to the upper surface of the interior of said first ball, so that an air-filled area is present between the first and second ball, wherein the pedestal portion comprises air pockets on either side of the shaft portion in the longitudinal direction of the beam-shaped body, and wherein the shaft portion comprises air tubes connecting the air-filled area with said air pockets. According to a further embodiment, a hollow third ball surrounds the first and second balls, said third ball being attached to the shaft portion.

[001 1] According to an embodiment, the levelling device further comprises one or more level indicators.

[0012] According to an embodiment, the levelling device according to the invention comprises a plurality of said levelling bodies wherein said levelling bodies are elongate beams and further comprising a central piece to which said beams are removably attached.

[0013] According to a preferred embodiment of the multi-beam device of the previous paragraph, the beams have a rectangular cross section, and the central piece comprises a plurality of sockets for receiving the ends of said beams, the sockets and the ends of the beams comprising side openings which match when the beams are inserted into the sockets, the central piece further comprising a securing mechanism between each pair of sockets, the securing mechanism comprising : • a push button connected to a spring-biased, radially arranged push beam so that actuation of the push button causes a forward motion of the push beam towards the centre of the central piece,

• a pair of spring-biased pivot plates, mounted so that the forward motion of the push beam causes pivoting of both pivot plates simultaneously about their respective vertically arranged pivot axes, the pivot plates having a first vertical edge in contact with the push beam and a second vertical edge that is inserted in one of said side openings of the sockets when the push button is not actuated, and that is pivoted out of said side opening by the push beam action, when the push button is actuated, so that insertion of a beam becomes possible by simultaneous actuation of two adjacent push buttons, and securing of said beam is obtained by releasing said button so that the second vertical edge of the pivot plates engages in the side openings of the socket and the beam, and wherein the second vertical edge of the pivot plates comprises a securing means for securing the beams in the sockets.

[0014] According to an embodiment, the device has a beam-shaped body having a trapezoidal cross-section as seen in a plane perpendicular to the longitudinal direction of the device with the side walls of the levelling body tapering downwards from a narrower top surface to a broader base surface of the levelling body.

[0015] According to an embodiment, the levelling body is an elongate beam-shaped body having an elongate strip of rigid material attached to the underside of the levelling body. Preferably the beam-shaped body in the latter embodiment is a flat, plank-shaped beam, with the impact portion and the rigid strip attached to opposing narrow surfaces of the beam. According to another embodiment of the latter type, the strip is replaced by an elongate groove running along the length of the beam.

These levelling devices are useful for levelling planks provided with a tongue-and- groove mechanism, but can also be used for levelling said planks on a support surface in the plane of the planks, or for levelling tiles on a flat surface.

[0016] According to an embodiment, the levelling body is a flat rigid body whereof one flat surface is to be placed on the construction elements that need to be levelled and with a recess in the opposite flat surface, into which recess a strip or layer of impact receiving material is fitted, thereby forming the impact receiving portion.

[0017] The invention is equally related to a method for levelling construction elements with a levelling device according to the invention, the method comprising the steps of :

- placing the construction elements on a support surface, - placing the levelling device on top of the construction elements, so that the device covers at least two adjacent elements,

- impacting the levelling device until the construction elements are at a desired common level.

[0018] In a preferred embodiment, the method is configured to level tiles on a flat surface, the tiles being placed on a support surface with cement or glue in between the tiles and the surface, and wherein the levelling device of the invention is used to level the tiles by impacting the device when it is placed on top of the tiles, before setting of the cement or glue. The support surface could also be a layer of still moldable material such as unset cement or concrete, onto which the construction elements are placed and subsequently levelled by a device of the invention.

[0019] According to a preferred embodiment, when the levelling device comprises an impact receiving portion formed of a resilient material, the impacting is done with an impact tool that is formed of a material having essentially the same resilience as the impact receiving portion.

[0020] The invention is equally related to a level measuring device having multiple beams which are removably attached to a central piece, each beam comprising one or more level indicators, wherein the beams have a rectangular cross section, and wherein the central piece comprises a plurality of sockets for receiving the ends of said beams, the sockets and the ends of the beams comprising side openings which match when the beams are inserted into the sockets, the central piece further comprising a securing mechanism between each pair of sockets, the securing mechanism comprising :

• a push button connected to a spring-biased, radially arranged push beam so that actuation of the push button causes a forward motion of the push beam towards the centre of the central piece,

• a pair of spring-biased pivot plates, mounted so that the forward motion of the push beam causes pivoting of both pivot plates simultaneously about their respective vertically arranged pivot axes, the pivot plates having a first vertical edge in contact with the push beam and a second vertical edge that is inserted in one of said side openings of the sockets when the push button is not actuated, and that is pivoted out of said side opening by the push beam action, when the push button is actuated, so that insertion of a beam becomes possible by simultaneous actuation of two adjacent push buttons, and securing of said beam is obtained by releasing said button so that the second vertical edge of the pivot plates engages in the side openings of the socket and the beam, and wherein the second vertical edge of the pivot plates comprises a securing means for securing the beams in the sockets.

Brief description of the figures

[0021] Figure 1 illustrates an elongate tool according to the invention.

[0022] Figure 2 illustrates an elongate tool according to the invention provided with a strengthening frame inside the casing that forms the body of the tool.

[0023] Figures 3a-3b illustrates another embodiment, wherein a resilient structure fills the larger part of a casing that forms the body of the tool.

[0024] Figure 4 shows an embodiment wherein the tool has a trapezoidal section.

[0025] Figure 5 shows an embodiment that may be provided with a nylon impact receiving portion.

[0026] Figure 6 shows an embodiment of a mat-shaped tool according to the invention.

[0027] Figures 7a and 7b show tools according to the invention that may be useful for placing wooden planks having a tongue and groove mechanism.

[0028] Figure 8 shows a tool according to the invention provided with ball- shaped impact portions.

[0029] Figures 9 and 10 illustrate an impact structure provided with a ball- shaped impact element at the top.

[0030] Figures 1 1 a and 1 1 b illustrate a specific embodiment of the impact structure of Figure 10.

[0031] Figure 12 illustrates a tool according to the invention that also serves as a level measurement tool.

[0032] Figure 13 illustrates a tool according to the invention that is provided with four arms that are releasably attached to a centre piece.

[0033] Figures 14a/14b show a preferred embodiment of the centre piece shown in Figure 13.

[0034] Figure 15 illustrates a tool provided with the same centre piece as shown in Figures 13 and 14 but without impact receiving portions.

Detailed description of the invention

[0035] In this description the terms 'horizontal' and 'vertical' are used to refer respectively to the direction of the surface onto which the levelling tool is placed, and the direction perpendicular thereto. [0036] The invention is related to tools for levelling tiles or plates on a support surface, characterized in that the tool comprises a levelling body, which is preferably a rigid body, for example a metal body, having a preferably flat underside configured to be placed on at least two adjacent tiles or plates that need to be levelled before the cement or glue used to attach these tiles on the support surface sets. On an upper part of the tool, an impact receiving portion is further provided, i.e. a portion configured to receive an impact force executed by a hammer or the like, preferably a rubber hammer, and to distribute the impact force to the surface onto which the tool is placed without damaging the tool or the surface to be levelled. The impact receiving portion may be attached, for example glued to the levelling body, so as to form a strong bond between the two, strong enough to prevent the two portions from being separated manually. Alternatively, the impact receiving portion may be partially inserted in a recess provided in the levelling body so as to prevent separation of the impact receiving portion from the levelling body during impacts. It is also possible that a combination of the two alternatives takes place, i.e. impact receiving portion partially inserted in a recess and glued or otherwise attached to the levelling body. Another option is that the impact receiving portion is incorporated in the levelling body. Examples of these various possibilities will be described hereafter, but it is important to note that in all preferred embodiments, the impact receiving portion is firmly connected to the levelling body so that it cannot be removed from it by manually impacting the impact receiving portion when the device is placed on the construction elements.

[0037] The impact-receiving portion is formed of a material other than the material of the levelling body. The impact-receiving portion may be formed of a resilient material such as rubber or urethane or of a harder but impact resistant material such as polyamide (nylon plastic). The impact receiving portion distributes the forces of impacts through the levelling body, so that adequate levelling may be obtained after a limited number of impacts. At the same time, the impact receiving portion avoids damage to the levelling body of the tool, as well as to the impact receiving portion itself. For this reason, a tool as shown in document DE4036338A1 for example is distinct from the tool according to the invention. In the cited document, a device is described for use in the application of concrete or plaster slabs to a flat surface of a building. The device is attached to a sidewall or floor after which molten plaster or concrete is applied to the surface, until the device is submerged in the molten material. The device is a longitudinal T-profile with the horizontal leg of the T attached to the surface and the vertical leg sticking outward from the surface. A removable plastic ridge is provided on top of the vertical leg, and configured to scrape off molten material along said ridge. When the molten material has set, the plastic ridge is removed, leaving a gap between adjacent plaster slabs, with the T-profile remaining in the slab. The tool of DE4036338A1 is thus not placed on any construction elements such as tiles or plates for levelling these elements by impacting the tool, nor is the tool of DE4036338A1 suitable for this use. The plastic ridge is not configured to receive impacts, therefore DE4036338A1 does not disclose a tool with an impact receiving portion as defined above, i.e. resisting impacts without damage to the tool nor the impact receiving portion itself. It is very likely that the removable plastic portion in DE4036338A1 is formed of a hard and rigid material, suitable for forming a scraping edge, but which would not be able to resist impacts without breaking. Also, the central leg of the T-shaped portion is provided with openings so that the concrete or plaster on both sides are connected. When using such a tool for levelling tiles, these openings would be detrimental for the force transfer. Finally, the plastic ridge is not fixed strongly to the T-shaped portion in order to be able to remove it easily once the concrete has set. Therefore if the tool would be used for levelling tiles in the manner of the present invention, the plastic ridge would surely be loosened from the T-shaped body by the impacts. Levelling tools according to specific embodiments of the invention may be suitable also for levelling other types of construction elements, such as concrete blocks or wooden planks.

[0038] A number of different embodiments are described hereafter, with reference to the enclosed drawings. Figure 1 shows a first embodiment of a tool according to the invention. The tool comprises a rigid body 1 in the form of a rectangular hollow casing in the shape of a rectangular beam (for example 3.5 cm wide and 6 cm high), with a wall thickness a of for example 1 cm, with a resilient strip 2 attached, for example glued, to the top. The casing is preferably made of aluminium, the resilient strip may be rubber. The resilient strip has a rounded upper surface, for example with a maximum thickness in the middle of about 2 cm. The hardness of the resilient material is such as to allow an efficient force transfer between the impact tool (preferably a hammer) and the surface onto which the levelling tool of the invention is placed. Rubber hammers are known today in the art. The resilient strip may be a rubber strip with a similar hardness as the rubber applied in these hammers. These rubber hammers or equivalent impact tools with resilient impact portions are suitable for being used as impact tools in combination with a levelling tool of the invention. Preferably, the resilient material on the levelling tool has about the same hardness as the resilient material on the impact tool. [0039] The hollow casing 1 may be reinforced with strengthening elements inside the casing, which may also improve the force transfer and distribution of impact forces to the surface onto which the tool is placed. One embodiment of such reinforcement elements is shown in Figure 2. Inside the casing is a metal (preferably aluminium) frame formed of an undulating plate 4 whose width corresponds to the width of the interior of the casing 1 . In the longitudinal direction of the casing, the plate is shaped to form a periodic series of triangle shapes 5 whose height H corresponds to the height of the casing. Upward pointing triangles alternate with downward pointing triangles with each pair of adjacent upward and downward triangles having one leg in common. The legs of the triangles are furthermore connected by horizontal beams 6. The horizontal beams between legs of an upward pointing triangle are positioned lower than the horizontal beams between legs of a downward pointing triangle. The horizontal beams could be omitted. Instead of triangle shapes, other periodic shapes could be applied (rounded, sine-like shapes, rectangular shapes for example). This frame provides mechanical strength as well as excellent force transfer of impacts executed on the rubber strip 2 and distribution of said forces in the longitudinal direction of the tool.

[0040] Figure 3 shows another embodiment, wherein the casing 1 is provided as a hollow box with 4 partitions 10 along the length of the casing (Fig. 3a - front wall of the casing is not shown), each partition having the same length, for example about 30 cm in a tool of about 1 .2m in length. The partitions are separated by vertically placed platelets 1 1 which have a U-shaped open area 12 with the opening of the 'U' pointing upwards. The openings 12 of the various separation platelets 1 1 are aligned in the longitudinal direction of the tool. First resilient elements 13 are placed into the partitions (Fig. 3b), said first elements having a U-shaped recess that is aligned with the open areas 12, so that a long U-shaped groove 15 is formed in the interior of the casing when the first resilient elements 13 are in place. A resilient piece 16 is then provided having a rounded top portion 17, and a beam-shaped lower portion 18 that fits into the groove 15 (Fig. 3c). The piece 16 thus has a T-shaped cross-section that fits into the U-shaped groove 15. By inserting the piece 16 into the groove 15, the tool is assembled. This embodiment thus provides a tool of which the interior is almost entirely filled with resilient material. The T-shape of the resilient piece 16 provides excellent characteristics in terms of the transfer of impact forces executed on the rounded portion 17 of the strip. The partitioning of the casing 1 by the platelets 1 1 at the same time ensures a high mechanical strength of the tool. Also, the resilient elements 13 and the resilient strip 16 are easily replaceable. According to an alternative embodiment, the U-shaped elements 13 are replaced by rigid elements, for example aluminium elements. The platelets 1 1 may be omitted in that case, given that the aluminium elements themselves provide sufficient stiffness to the structure. Instead of 3 separate aluminium elements 13, one longer aluminium element could be used provided with a U-shaped groove extending along the full length of the tool.

[0041] A further embodiment is shown in Figure 4. Here the elongate casing 1 has a trapezoidal shape with the side walls 20/21 tapering downwards from a narrower top surface to a broader base surface of the casing. The casing 1 is once again preferably a hollow (preferably aluminium) casing. A resilient impact receiving strip 2 with a rounded surface is once again attached to the top surface of the casing. This shape of the casing 1 provides excellent force distribution in a direction perpendicular to the resilient strip 2 and parallel to the base surface. According to a preferred embodiment, a second rubber strip 23 (e.g. about 0.5cm) is attached to the bottom of the rigid body. The second strip is to be placed on the surface of the tiles or plates that are to be levelled. The tool according to this embodiment is most suitable for levelling small tiles on vertical walls, such as mosaic tiles or for levelling plasterboard panels used for lining a wall, such plasterboards being attached to a wall by a plaster adhesive. A resilient strip like the strip 23 in Figure 4 can equally be used in combination with any other of the described embodiments which have a flat underside. The resilient strip is beneficial in improving the force transfer and avoiding damage to the construction elements, allowing higher impact forces to be applied.

[0042] Further embodiments are shown in Figures 5 and 6. Figures 5a/5b show a tool having a flat rigid body 25 formed of a solid metal (preferably aluminium) plate with a recess 26 in its upper surface. A piece of impact receiving material 27 is fitted into said recess. This material may be rubber or it may be a plastic material with less resilience than rubber but with a high impact resistance such as polyamide (nylon plastic). This tool is primarily useful for levelling large elements, for example concrete plates or blocks. This tool is preferably about 1 m long and about 12 cm wide.

[0043] Figure 6 shows a mat-shaped tool according to the invention, in the form of a square or rectangular mat (for example 20cm X 20cm) 30 of a resilient material, for example a rubber or urethane mat, again with a recess 31 in its upper surface. An impact receiving portion 32 is fitted in said recess 31 . The impact receiving portion may for example be a full rubber mat 32 with higher resilience than the rubber mat 30, or a rubber mat filled with a gel 33. This very resilient type of a levelling tool according to the invention can be used for levelling out very fragile surface materials. [0044] Figure 7 a shows an embodiment wherein the rigid body of the tool is a relatively narrow aluminium casing 1 provided with a resilient rounded strip 2 at the top, and with a narrow longitudinal strip 35 at the bottom, the strip being perpendicular to the surface of the casing.

The strip 35 is preferably made of a rigid material. It could be made for example of aluminium. This embodiment can be used for putting in place and levelling wooden planks provided with a groove and tongue system, wherein planks are vertically mounted and placed one on top of the other, or wherein planks are mounted on a floor. The thickness of the tool corresponds more or less with the thickness of the planks. When the planks are placed with the groove-side upwards or outwards, the strip 35 can be fitted into a groove of a plank before impacting the tool on the resilient strip 2. Instead of the strip 35, the tool may be provided with a groove 36, as shown in Figure 7b. This tool can be used for placing and levelling planks when the tongue-side of the planks is pointing upwards or outwards. The tools of Figure 7a/7b can be equally be used for levelling the planks in the plane of the planks themselves, for example after the tongue/groove systems have been assembled, so levelling can be performed in two directions : parallel to the plane of the planks and perpendicular to the plane of the planks. The tools of Figure 7a/7b, though not preferably used for this purpose, are equally suitable for levelling other flat construction elements on a flat surface such as tiles.

[0045] Figure 8 shows an embodiment, wherein the impact receiving portion has the form of one or more ball-shaped impact receiving elements 40 incorporated in the rigid body of the tool. Figures 8a/8b shows an embodiment of a beam-shaped tool having three such ball-shaped impact receiving elements 40 incorporated in a metal (preferably aluminium) casing 1 . The ball-shaped elements 40 have the shape of an ellipsoid (rugby-ball) with the long axis in the direction of the tool's longitudinal axis. Said longitudinal axis of the ball-shaped elements is at a lower level than the upper surface of the tool, in other words only a portion of the ball-shaped element's upper surface extends out from the casing's upper surface. The width of the ball-shaped elements 40 in the direction perpendicular to the tool is preferably higher than the width of the tool, in other words, the ball-shaped portions extend laterally from the body of the tool (as is the case in the drawings). The ball-shaped elements may be full rubber or hollow rubber with an air hole 42 placed centrally so that the element may resume its shape after an impact.

[0046] In a preferred embodiment, the ball-shaped element 40 is part of a larger impact receiving structure extending over the entire height of the tool. This is the case for the ball-shaped elements shown right and left on the tool of Figures 8a/8b, made better visible in Figure 9 which shows the shape of the impact receiving structures 45. A detail of the structure 45 as such is shown in Figure 10. The ball- shaped element 40 is fixed onto a shaft-like portion 46 that is itself fixed to a support portion 47 that forms a pedestal onto which the shaft portion 46 is mounted. The pedestal 47 has a downwardly and outwardly tapering side surface at least in the longitudinal direction of the tool, i.e. the length of a horizontal section of the pedestal becomes larger as you go down from line A to line B to line C. In the direction perpendicular to the casing, the pedestal 47 may also have a downwardly and outwardly tapering surface as shown in Figures 8a/8b, so that the base surface of the pedestal 47 is wider than the width of the casing 1 . The pedestal thereby becomes a stabilizing aid for the tool. The downward tapering shape of the pedestal in the longitudinal direction contributes to the efficient transfer and distribution of an impact force exerted on the ball-shaped element 40. The shaft 46 and pedestal 47 could be made of full rubber or hollow rubber. The ball-shaped element 40 can be full rubber or hollow rubber filled with air or a gel, or it may consist of multiple resilient balls one inside the other (one such embodiment is described in the next paragraph). The impact structure 45 could also be made of a harder impact receiving material than rubber, e.g. nylon plastic.

[0047] When the pedestal 47 is not wider than the casing 1 or when there is only a number of ball-shaped elements 40 and no shaft or pedestal, separate stabilization elements may be provided on the sides of the casing. This may be the case also for any other of the embodiments described above, e.g. the embodiment of Figure 1 having a continuous strip 2 of impact receiving material. The stabilization elements could look like the parts of the pedestal 47 that extend outward laterally from the side of the casing in Figure 8b.

[0048] Figure 1 1 a shows a specific embodiment of the resilient structure

45 comprising a ball-shaped element 40, shaft 46 and pedestal 47. In this case, a hollow resilient ball 50 is attached to the top of the shaft 46, with a smaller solid ball 51 attached inside the first ball 50, to the top of the first ball's interior surface, so that an air-filled area 52 is formed between the solid ball 51 and the interior of the hollow ball 50 underneath the solid ball. The hollow ball 50 is cut open in the drawing for the sake of clarifying the inner structure. Figure 1 1 b visualizes the shape of the air-filled area 52. Returning to Figure 1 1 a, a third hollow ball 53 surrounds the first hollow ball 50, and serves as the outer surface that receives the impacts. The area between the third ball 53 and the first ball 50 is equally filled with air. [0049] An air tube 60 is provided in the interior of the shaft 46, running vertically downward from the top of the shaft where it is in communication with the air- filled area 52 via hole 61 . Vertical tube 60 leads downward to a location centrally inside the shaft where it splits into two further air tubes 62/63, each leading to air pockets 64/65 on either side of the shaft in the longitudinal direction of the casing 1 , inside the downward tapering portions of the pedestal 47. Air transport is thus possible between said air pockets 64/65 in the pedestal and the air-filled area 52 between the first and second balls 50 and 51 . When the third ball 53 is impacted, the first ball 50 is compressed. The presence of the second ball 51 limits the compression of the first ball. The compression causes air to move downward through the air tubes 60/62/63, to the air pockets 64/65 in the pedestal. The air movement further enhances the lateral force transfer of the impact in the longitudinal direction of the tool. Without being bound by theory, it is thought that shock waves in the air tubes are beneficial for establishing said force transfer.

[0050] After the impact, the hollow ball 50 resumes its normal shape, and air is sucked back from the air pockets 64/65 in the pedestal to the area 52. Air present in the area between the first and third balls 50/53 can be released and reintroduced through side holes provided in the third ball 53 (see holes 42 in Figure 8b). The third ball 53 could be omitted and the first ball 50 could be dimensioned larger so that it acts as the impact receiving ball. The third ball 51 inside the first ball 50 could be omitted. The whole structure 45 as shown in Figure 1 1 a could be an integral rubber piece produced by known rubber production and forming techniques, possibly by producing rubber elements and assembling them together by a suitable welding technique. The structure could also be made of different materials, e.g. a harder material for the shaft and pedestal and a more resilient material for the ball structure

50/51 /53.

[0051] According to an advantageous embodiment, the tool of the invention is further provided with one or more level indicators, see for example Figure 12. In the embodiment illustrated in this figure, two ball-shaped impact elements 40 are provided on both outer ends of the tool, with a level indicator 70 in the middle for measuring the level of a horizontal surface onto which the tool is placed. A further level indicator 71 may be provided for vertical measurements. This tool advantageously combines the functions of a level measuring device and an impact levelling tool. The level indicators 70/71 are preferably embedded in a resilient material that may be similar to the resilient material used for the impact portions. This material protects and stabilizes the indicators during impacts and ensures that the indicators remain readable during or at least immediately after the impact.

[0052] Figure 13 shows a combined level measuring and impact levelling tool comprising four detachable arms 74 attached to a central piece 75, each arm provided with ball-shaped impact portions 40 according to one of the embodiments described above, and with level indicating elements 70 and 71 on each arm. The central piece 75 is preferably provided with an additional level indicator.

[0053] The mechanism for attaching the arms to the central piece 75 is shown in more detail in Figures 14a and 14b. The central piece 75 is cylindrical in shape and has four access openings 76 for receiving the arms 74 which have a rectangular cross-section. In the interior of the central piece 75 is a cross-shaped element 77 comprising four sockets 78 arranged at right angles to each other. The arms 74 can be inserted into these sockets. Between each pair of adjacent sockets is a securing mechanism that is activatable by a push button 80. Pressing a button causes a central push beam 81 oriented along a radius of the central piece 75, to be moved forward against a spring bias generated by linear springs 82. The push beam's forward movement causes pivoting of two pivot plates 83 about vertical axes. The pivot plates' rotation is equally spring biased by linear springs 84 (could also be by rotational springs). The pivot plates have two vertical side edges 85/86. When the pivot plates are not actuated by the push beams (which is the situation shown in Figures 14a/14b, the first of said edges 85 is lodged against the push beam 81 (as in Figure 15a), while the second edge 86 is fully or partially inserted in a side opening 87 of one of the sockets 78. Said second edge 86 is provided with a hook-shaped extension 88. Actuating one of the push beams 81 causes two pivot plates 83 to pivot around their pivot axis so that the second edge 86 and the hook-shaped extension 88 is pivoted out of the opening 87 in the side wall of the socket.

[0054] Each push button 80 thus actuates two pivot plates 83 simultaneously. In order to liberate access to one socket, two push buttons on either side of the socket need to be pushed simultaneously. The arms 74 which are to be inserted in the sockets are provided with side openings that match the side openings

87 in the sockets when the arms are fully inserted, so that the hook extensions 88 secure the beams 74 when said openings are aligned with the openings 87 in the sockets. Attachment of one arm 74 thus takes place by pushing two buttons 80, inserting the arm and releasing the buttons. The spring bias of the pivot plates ensures that the hook extensions 88 firmly grip the openings in the arms thereby securing the arms into the sockets. Guide rails 89 in the bottom and/or top surface of the sockets 78 may be provided for guiding the arms correctly into the sockets (the arms are then provided with corresponding grooves). A central magnet 90 may be provided for enhancing the attachment force with which the arms are held in the central piece (the arms in that case must be steel or comprise a steel portion on the inserted end). The number of arms attachable to the central piece is preferably 4, but the invention is not limited to that number.

[0055] Any of the tools described in this text can be produced in a size appropriate to the application and the ease of use. For example, a beam-shaped tool for levelling tiles as shown in Figures 1 and 2 could be made with a length of 0.5m up to 2.5m. None of the indicated dimensions form a limitation of the patent scope.

[0056] The invention is related to the above-described multi-armed level measuring device with detachable arms 74, wherein the arms are provided with impact receiving portions 40 according to any of the above described embodiments. The invention is also related to a multi-arm level measuring device with detachable arms as described above but without such impact receiving portions. This device is illustrated in Figure 15. The description of the central piece with reference to Figures 14a/14b is valid also for the embodiment of Figure 15.

[0057] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0058] The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.