Height adjustable underframe

Abstract

 This invention concerns a height-adjustable underframe for a table or a similar work platform, said underframe (1) comprising a cross-beam (10) with at least two telescopically adjustable legs (2), a mechanically-driven movement arrangement (20) to which cords are connected which run over cord pulleys in the underframe and the legs (2), and are arranged to work between a lower leg part (3) and at least one upper leg part (5).
According to the invention, the mechanically-driven movement arrangement (20) comprises a toothed wheel (25) in engagement with a toothed element (26), where a compression spring element (30) co-operates with the toothed element (26) for the displacement of this in the longitudinal direction of the cross-beam (10) for the adjustment of the height of the legs (2), in that a first and a second cord (40 and 41 respectively) are secured to an end (29) of the toothed element (26).

Description

Areas of application of the invention

[0001] The present invention concerns a height-adjustable underframe for a table or a similar work plafform, said underframe comprising a cross-beam with at least two telescopically adjustable legs, a mechanically-driven movement arrangement to which cords are connected and run over cord pulleys in the underframe and in the legs, and which are arranged to work between a lower leg part and at least one upper leg part.

Background of the invention

[0002] Height-adjustable underframes of this kind have been developed for places of work where height-adjustment of a table top or work plafform is expedient in order to achieve an ergonomically correct and individually adjusted working height in the working situation.

[0003] The concept places of work shall be understood in the broad sense and it comprises, for example, writing desks or tables at which the users shall sit or stand, where it can be desirable to adjust the height from approx. 60 to approx. 125 cm.

[0004] Other places of work can include assembly benches, welding tables and packing tables which are to be used by alternating operators, or be used during assembly operations where there is a need for an adjustment in height during the assembly work.

[0005] The expression platform shall also be taken in the broad sense, and in addition to actual table tops can thus include frames which are configured to support items which are to be worked with and/or assembled.

[0006] The displacement in height can be effected either manually or mechanically.

[0007] With a manual adjustment, time is of no significance for an adjustment from a low to a high position or vice versa, in that the operator is occupied herewith. However, the plafform is often of considerable weight, which makes it necessary to introduce weight-balancing elements in the construction so that it is at all possible for the operator to be able to adjust the plafform when it needs to be displaced upwards.

[0008] If, on the other hand, the displacement is to be effected mechanically, the adjustment time is often of considerable length, the reason being that the operator is not occupied during the process. Therefore, with a mechanical adjustment of the height, it is desirable that the time taken for the height adjustment is minimal, for example approx. 5 sec's.

[0009] A mechanical displacement of the height can be effected in several ways. For example, the displacement can be effected by means of screw spindles which by means of a motor are rotated inside nuts which are connected to the plafform, so that the plafform is hereby raised or lowered. However, this construction is slow, in that normally there can only be achieved a displacement of the plafform of approx. 1.5 to 3 cm during the course of 1 second. Moreover, there is great friction between the nuts and the screw spindles, so that great motor power is required and great wear takes place on the parts with subsequent frequent replacement, and a considerable emission of noise due to high speeds of rotation.

[0010] With mechanical displacement, it is also commonly known to introduce weight-balancing elements in order to be able to adjust the plafform when this needs to be raised, in that the motor must otherwise exercise a very great power.

The known technique

[0011] From SE-C2-502 504, a height-adjustable underframe is known for a table or similar work plafform and of the kind disclosed in the introduction. In the known construction, the mechanically-driven movement arrangement comprises a toothed wheel which on diametrically-opposing sides is in engagement with parallel toothed racks, so that rotation of the toothed wheel displaces the toothed racks in opposite directions. A first cord extends from the one end of the one toothed rack, further over a first cord pulley at the top of the one leg, and continues down in the leg around a second cord pulley, then upwards again over a third cord pulley and ends at the corresponding end on the second toothed rack. A corresponding cord extends in a similar manner from the opposite ends of the toothed racks and through the other leg. Both legs comprise a lower leg part, an upper leg part and an intermediate leg between the upper and the lower leg parts. The second cord pulley is arranged in a rotative manner lowermost in the intermediate leg, and each cord is additionally fastened to a driving pin in the upper leg part. In addition to the said two cords, a third and a fourth cord are provided in each of the two legs, all of which cords extend around a number of cord pulleys and are secured to fixture pins in the legs.

[0012] However, the known underframe has some disadvantages.

[0013] The construction is to a significant degree made considerably more expensive by the number of cords and cord pulleys, and the motor for the driving of the movement arrangement must be very powerful in order to raise and lower the plafform within a reasonable period of time. It is also difficult to tighten the many cords, so that these do not slide away from the cord pulleys when the underframe is raised, after which the underframe must be separated again in order to place the cords correctly in the cord pulleys.

The object of the invention

[0014] It is the object of the present invention to provide a height-adjustable underframe of such a configuration that the above-mentioned disadvantages are avoided.

[0015] This object is achieved with a height-adjustable underframe of the kind disclosed in the introduction, said underframe according to the invention being characterised in that the mechanically-driven movement arrangement comprises a toothed wheel in engagement with a toothed element, and a compression spring element co-operates with the toothed element for its displacement in the longitudinal direction of the cross-beam for adjustment of the height of the leg, in that a first and a second cord are secured to an end on the toothed element.

The special advantages achieved with the invention

[0016] There is hereby achieved a very fast adjustment in the height of the underframe, and this is effected without great wear on the component parts of the construction, and only a very small supply of energy is necessary to undertake the adjustment in height, which means that a very weak motor, such as a commercially-available electric-motor, can be used in the underframe. Moreover, use is made of fewer cords and cord pulleys than in the known constructions. The construction is hereby considerably less expensive when compared with the known constructions.

[0017] As characterised in claim 2, it can be expedient for the movement arrangement according to the invention to be provided with a drawing-down arrangement. It is hereby achieved that the relative movement between the upper leg parts and the lower leg parts will always be controlled in relation to each other, and that there will always be an active traction in both directions.

[0018] When the movement arrangement is used without a drawing-down arrangement as characterised in claim 2, for example, in the raising of the cross-beam, the support profiles or the plafform mounted hereon, it can happen that the lower leg parts will remain on the ground. The first and the second cord will hereby be slackened, which means that there will thus be a risk that the cords can come out of engagement with the various cord pulleys. This can be particularly troublesome during the assembly process, where the foot part and lower leg parts of the frame do not follow with the frame when this is raised from the floor, and where the cords must possibly be placed correctly in the respective cord pulleys again.

[0019] Moreover, upon activation of the movement arrangement for the lowering of the underframe when this is only slightly loaded, it can happen that the upper leg parts, among other things because of friction, do not move downwards in the lower leg parts, whereby there is again the risk that the cords can come out of engagement with the respective cord pulleys. Moreover, it can happen that the upper leg parts with associated cross-beam, support profiles, plafform and possible load will suddenly fall downwards, with possible subsequent damages.

[0020] All of these disadvantages are avoided with the embodiment of the height-adjustable underframe in accordance with claim 2.

[0021] The remaining dependent claims disclose other advantageous embodiments of the height-adjustable underframe according to the invention.

The drawing

[0022] In the following, the height-adjustable underframe according to the invention and embodiments hereof will be described in more detail with reference to the drawing, where

fig. 1

is a perspective view of a height-adjustable underframe according to the invention,

fig. 2

is a schematic view of a vertical section through a first embodiment of the movement arrangement in a height-adjustable underframe according to the invention seen in the lowered position, where the legs comprise two leg parts,

fig. 3

shows a section corresponding to fig. 2, where the underframe is in the raised position,

fig. 4

is a schematic view of a vertical section through the first embodiment of the movement arrangement according to the invention corresponding to fig. 2, where single parts are omitted, but where a drawing-down arrangement for the movement arrangement is shown,

fig. 5

shows a partly horizontal section through the drawing down arrangement of the embodiment of the movement arrangement shown in fig. 4,

fig. 6

is a schematic view of a vertical section through a leg which comprises three leg parts, where the underframe is in a lowered position,

fig. 7

is a section corresponding to fig. 6, where the underframe is in the raised position,

fig. 8

is a schematic view of a vertical section through a second embodiment of the movement arrangement in a height-adjustable underframe according to the invention in a partly raised position,

fig. 9

is a section corresponding to fig. 8 through a third embodiment of the movement arrangement in a height-adjustable underframe according to the invention, similarly seen in a partly raised position,

fig. 10

shows a horizontal section through the third embodiment of the movement arrangement shown in fig. 9 in a height-adjustable underframe according to the invention, and

fig. 11

is a perspective view of a height-adjustable underframe according to the invention, where there are four legs in all.

Detailed description of preferred embodiments

[0023] The height-adjustable underframe 1 comprises at least two telescopically adjustable legs 2a,2b, which are built up of an outer part in the form of a lower leg part 3 and at least one inner part in the form of an upper leg part 5. There can also be a centremost leg part 4. In the example shown, the lower leg part 3 and the upper leg part 5, and the possible centremost leg part 4, consist of rectangular tubes in which the leg parts 3,4,5 are engaged with one another in a sliding manner.

[0024] At its lower end, the lower leg part 3 has a foot part 6 which can be of any configuration. At its upper end, the upper leg part 5 has a support profile 7 for a table top or the like, and it will be understood that the support profile 7 can be of any configuration and can therefore be adapted to suit various purposes.

[0025] A cross-beam 10 extends between the upper leg parts 5 and is configured as a box which forms a housing for the movement arrangement 20, cords and cord pulleys.

[0026] The movement arrangement 20 comprises a reversible motor 21 which has a protruding axle with a worm 22 which is in engagement with a worm wheel 23, the axle 24 of which extends transversely to the longitudinal direction of the cross-beam 10 and is mounted in a rotational manner in suitable bearings.

[0027] On the axle 24, a toothed wheel 25 is mounted in a fixed manner, so that the toothed wheel 25 is rotated together with the worm wheel 23. The toothed wheel 25 is in engagement with a toothed element, such as a toothed belt or preferably a chain 26, which extends as a U-shaped first loop more or less over half the circumference of the toothed wheel 25, in that the one end 27 of the chain 26 is secured at a fixed point 28 inside the cross-beam 10, and the other end 29 of the chain 26 is secured to the ends of a first and a second cord 40 and 41 respectively.

[0028] Between the toothed wheel 25 and the fixture point 28, there is inserted a compression spring element 30 with a toothed roller 31 which is in engagement with the chain 26 in such a manner that the chain 26 also extends as a U-shaped second loop between the toothed wheel 25 and the point 28, where the opening in the U-shape faces towards the toothed wheel 25. The chain 26 thus extends snakelike in a Z- or S-shape.

[0029] The opposite second end of the compression spring element 30 is secured in a pivotal manner at fixture point 32 in the cross-beam 10.

[0030] The two cords 40, 41 extend under a first rotational cord pulley 42.

[0031] Thereafter, the first cord 40 continues over and partly around a second cord pulley 43a which is arranged in a rotational manner at the top of the leg 2a, which is to the right in fig. 2. The first cord 40 continues downwards in the leg 2a on the inside of the upper leg part 5a, around a third rotational cord pulley 44a lowermost in the upper leg part 5a, then extends further upwards between the upper leg part 5a and the lower leg part 3a and is finally secured to a fixture point 45a uppermost on the inside the lower leg part 3a.

[0032] The second cord 41, on the other hand, extends halfway around the first cord pulley 42 so that it changes direction towards the second leg 2b, which is to the left in fig. 2, where the second cord 41 extends in a corresponding manner around rotational cord pulleys 43b and 44b and ends at a fixture point 45b uppermost inside the lower leg part 3b.

[0033] When the motor 21 is activated for rotation in such a direction that the worm wheel 23, the axle 24 and the toothed wheel 25 rotate clockwise in figs. 2 and 3, the end 29 of the chain 26 will be drawn towards the left with a corresponding shortening of the cords 40, 41 in the upper leg parts 5a, 5b, whereby both the cross-beam 10 and the upper leg parts 5 are lifted for the raising of a plafform which is placed on the support profiles 7,

[0034] When the motor 21 is made to rotate in the opposite direction, the toothed wheel 25 will draw in the chain 26 and work against the influence of the compression spring element 30, so that the compression spring element 30 is shortened, while at the same time the weight of the construction contributes towards the lowering of the platform, in that the upper leg parts 5 are accommodated telescopically in the lower leg parts 3.

[0035] Figs. 4 and 5 show the system for the drawing-down of the upper leg parts 5 and the cross-beam 10 which is used in connection with the embodiment shown in figs. 2 and 3. For the sake of clarity, some of the components shown in figs. 2 and 3 have been omitted from figs. 4 and 5. There is thus seen the lower leg parts 3 and the upper leg parts 5 with the cross-beam 10 which extends between the upper leg parts. Mounted on the cross-beam 10 there is a reversible motor 21 with associated worm drive on which the toothed wheel 25 is mounted, which drives the toothed element 26, which in the example shown can be a chain or a toothed belt.

[0036] As described in connection with figs. 2 and 3, the one end 27 of the chain is secured inside the cross-beam 10 at the fixture point 28, in that the chain 26 extends around the sprocket 31 which is mounted on the end of the compression spring element 30. As described earlier, the other end of the chain is secured to the ends of the first and the second cord 40 and 41 respectively. For the sake of clarity, fig. 4 shows only the first part of these cords, the further extent of which will be as shown in figs. 2 and 3.

[0037] A third cord 46 and a fourth cord 47 are secured to the chain 26 at a point 48, which lies between the toothed wheel 25 and the sprocket 31. The third cord 46 extends down under a fourth rotational cord pulley 49 and from here up over the first cord pulley 42, as described in connection with figs. 2 and 3. From the first cord pulley 42, the third cord 46 extends over and partly around a fifth rotational cord pulley 50a which is placed at the side of the second cord pulley 43a uppermost in the leg 2a, which is to the right in figs. 4 and 5. From the fifth cord pulley 50a, the third cord 46 continues downwards inside the leg 2a to the lowermost end of the lower leg part 3a, where it is secured at fixture point 51a.

[0038] The fourth cord 47 extends halfway around the fourth cord pulley 49 so that it changes direction towards the second leg 2b, which is to the left in figs. 4 and 5, where it extends in a corresponding manner around a rotational cord pulley 50b which is placed at the side of the second cord pulley 43b, and ends at a fixture point 51b in the lowermost end of the lower leg part 3b.

[0039] When the motor 21 rotates in such a direction that the toothed wheel 25 rotates anticlockwise in fig. 4a, the fixture point 48 on the chain 26 for the third and fourth cord 46, 47 will be drawn towards the left, so that the cords 46, 47 give rise to traction between the lower leg parts 3 and the upper leg parts 5 and the cross-beam 10 associated herewith. The movement of the third and the fourth cord 46, 47, which will seek to draw the lower leg parts 3 and the upper leg parts 5 together, will be corresponded to by an equally great movement which is effected at the same time by the first and the second cord 40, 41, and this movement will allow the lower and the upper leg parts to draw closer to each other. Consequently, the uppermost part of the table will be lowered, partly due to the weight of the construction and partly due to the traction in the third and the fourth cord 46, 47.

[0040] Conversely, when the toothed wheel 25 rotates clockwise in fig. 4a, the fixture point 48 for the third and the fourth cord 46, 47 will be moved to the right, so that the cords 46, 47 will allow the lower leg parts 3 and the upper leg parts 5 to be drawn away from each other, corresponding precisely to the movement of the first and the second cord 40, 41, which lifts the upper leg parts 5 and the cross-beam 10 in relation to the lower leg parts 3.

[0041] By a suitable pre-stressing of the cords, the relative movement between the upper leg parts 5 and the lower leg parts 3 will thus always be controlled by the cords 40, 41 and 46, 47. When the movement arrangement is used without the drawing-down arrangement described above, it can happen, for example, when the cross-beam 10, the support profiles 7 or the platform mounted hereon are raised, that the lower leg parts 3 will remain on the ground, and there is thus a risk that the cords 40, 41 can come out of engagement with the various cord pulleys. Moreover, when the movement arrangement is activated for the lowering of the underframe when this is only slightly loaded, it can happen that the upper leg parts 5, due to friction, do not move downwards into the lower leg parts 3, whereby again there is a risk that the cords come out of engagement with the respective cord pulleys. Furthermore, it can happen that the upper leg parts 5 with associated cross-beam 10, support profiles 7, platform and possible load can suddenly fall downwards with possible subsequent damage. All of these disadvantages are avoided when use is made of the drawing-down system described.

[0042] With the embodiment shown in figs. 2, 3 and 4, where there is only one lower leg part 3 and an upper leg part 5 in each of the legs 2, it is difficult to achieve a desirable displacement in height from approx. 60 to approx. 125 cm, in that there will not be sufficient control of the upper leg parts 5 in relation to the lower leg parts 3.

[0043] Therefore, it is desirable to introduce centremost leg parts 4 between the lower leg parts 3 and the upper leg parts 5, as shown in figs. 4 and 5.

[0044] In the same way as with the embodiments in figs. 2 and 3, the cords 40, 41 in the upper leg parts 5 extend over cord pulleys 43 and 44 and end at fixture points 45. In figs. 6 and 7, which show only the right leg 2a, there is an additional cord 60a which, from a fixture point 61a inside the lowermost part of the upper leg part 5a, extends around a cord pulley 62a which is placed in a rotational manner in the centremost leg part 4a, and is finally secured at a fixture point 63a uppermost inside the lower leg part 3a.

[0045] An additional cord 60b extends in a corresponding manner in the left leg 2b.

[0046] With this arrangement, a good control is achieved mutually between the leg parts 3, 4 and 5, and at the same time also the desirable capability of adjustment in height from approx. 60 to 125 cm.

[0047] The drawing-down arrangement is not shown in figs. 6 and 7, but can be used in connection with legs consisting of upper, lower and centremost leg parts in the same way as described in connection with figs. 4 and 5, in that the third and fourth cord 46, 47 respectively from the fifth cord pulley 50 at the top of the upper leg part 5 will extend down through this, the centremost leg part 4 and down to the lowermost end of the lower leg part 3, where the cord is secured at fixture point 51.

[0048] A second embodiment of the movement arrangement according to the invention is shown in fig. 8.

[0049] Also here, the movement arrangement 20 comprises a reversible motor 21 which has a protruding axle with a worm 22 which is in engagement with a worm wheel 23, the axle 24 of which extends transversely to the longitudinal direction of the cross-beam 10 and is housed in a rotational manner in suitable bearings.

[0050] A toothed wheel 25 is mounted in a fixed manner on the axle 24, so that the toothed wheel 25 rotates together with the worm wheel 23. The toothed wheel 25 is in engagement with a toothed rack 26 which is housed in a displaceable manner in the longitudinal direction of the cross-beam in a way which is not shown in the drawing. The toothed element thus consists of the toothed rack 26, and a rotation of the toothed wheel 25 will displace the toothed rack 26 forwards and backwards in the cross-beam 10.

[0051] A compression spring element 30 is secured in a pivotal manner at a fixture point 32 inside the cross-beam 10, and the other end of the element is similarly secured in a pivotal manner to the end 29 of the toothed rack 26, to which cords 40, 41 are also secured.

[0052] When the motor 21 is activated for rotation in such a direction that the worm wheel 23, the axle 24 and the toothed wheel 25 rotate clockwise in fig. 8, the end 29 of the toothed rack 26 will be drawn towards the left with a corresponding shortening of the cords 40, 41 in the upper leg parts 5a, 5b, whereby both the cross-beam 10 and the upper leg parts 5 are lifted upwards for the raising of a platform which is placed on the support profiles 7.

[0053] The drawing-down arrangement described in connection with figs. 4 and 5 can also be used in connection with the second embodiment of the movement arrangement 20. This merely requires that the fourth cord pulley 49 is placed to the left of the toothed wheel 25 and the toothed rack 26 in fig. 8, in that the third and the fourth cord 46, 47 must be secured to that end of the toothed rack 26 which lies opposite the end 29. In such a case, the third cord 46 must extend halfway around the fourth cord pulley 49 before it continues over to the fifth cord pulley 50a, over this and down in the upper leg part 5a. The fourth cord must extend down under the fourth cord pulley 49 and up over the fifth cord pulley 50b, and hereafter down in the upper leg part 5b. This is not illustrated in fig. 8.

[0054] A third embodiment of the movement arrangement according to the invention is shown in figs. 9 and 10.

[0055] Also here, the movement arrangement 20 comprises a reversible motor 21 which has a protruding axle with a worm 22 which is in engagement with a worm wheel 23, the axle 24 for which extends transversely to the longitudinal direction of the cross-beam 10 and is housed in a rotational manner in suitable bearings.

[0056] Two parallel toothed wheels 25 are mounted on the axle 24 in a fixed manner, so that the toothed wheels 25 rotate together with the worm wheel 23. The one toothed wheel 25 is in engagement with a toothed rack 26 which is housed in a displaceable manner (not shown) in the longitudinal direction of the cross-beam 10. By a rotation of the toothed wheels 25, the one toothed wheel will therefore displace the toothed rack 26 forwards and backwards inside the cross-beam 10. Cords 40, 41 are secured to the end 29 of the toothed rack 26.

[0057] The second of the two toothed wheels 25 is in engagement with a further toothed element in the form of an endless toothed belt or chain 80 which extends to and continuously around a further toothed wheel 81 at a distance from the axle 24. Mounted in a fixed manner on the axle for the further toothed wheel 81 there is a conical cord pulley 82, which thus rotates when the motor 21 is activated for rotation in one or the other direction.

[0058] A compression spring element 30 is secured in a pivotal manner to the inside of the cross-beam 10 at a fixture point 32, and the other end of the compression spring element 30 has a cord pulley 31. From a fixture point 28 in the cross-beam 10, a cord 83 extends in a U-shaped loop around the cord pulley 31 on the end of the compression spring element 30, runs for some turns around the conical cord pulley 81 and is secured hereto by its other end 85.

[0059] When the motor 21 is activated for rotation in such a direction that the worm wheel 23, the axle 24 and the toothed wheels 25 rotate clockwise in fig. 9, the end 29 of the toothed rack 26 will be drawn towards the left with a corresponding shortening of the cords 40, 41 in the upper leg parts 5a, 5b, whereby both the cross-beam 10 and the upper leg parts 5 are lifted for the raising of a platform which is placed on the support profiles 7.

[0060] The advantage with this embodiment is that the influence of the compression spring element 30 on the lifting force of the underframe 1 is compensated for by means of the conical cord pulley 82 shown in connection with the chain drive, so that the resulting influence can be held constant.

[0061] Moreover, by winding or unwinding the cord 83 on or off the conical cord pulley 82, it is possible to adjust the lifting force for specific loads, so that the motor power can be brought close to zero for given loads on the underframe 1.

[0062] The drawing-down arrangement described in connection with figs. 4 and 5 can also be used in connection with the third embodiment of the movement arrangement 20. The drawing-down arrangement must thus be modified in the same way as described in connection with the second embodiment of the movement arrangement shown in fig. 8, in that the fourth cord pulley 49 must be placed to the left of the toothed wheel 25 and the toothed rack 26 in fig. 9, and in that the third and fourth cord 46, 47 must be secured to that end of the toothed rack 26 which lies opposite the end 29. In such a case, the third cord 46 must extend halfway around the fourth cord pulley 49 before it continues over to the fifth cord pulley 50a, over this and down in the upper leg part 5a. The fourth cord must extend down under the fourth cord pulley 49 and up over the fifth cord pulley 50b, and hereafter down in the upper leg part 5b. This is not illustrated in fig. 9.

[0063] If the platform which is to be placed on the support frame 7 has a considerable extent at right-angles to the plane of the drawing, the underframe must be equipped with at least one extra set of legs, as shown in fig. 11. The extra legs 2c, 2d are provided on an additional cross-beam 10' parallel with the cross-beam 10 shown in figs. 2 and 3, and the two cross-beams 10, 10' are connected by longitudinal beams 90, 90' which consist of rectangular tubes. In such a case, all four legs 2a, 2b, 2c and 2d must naturally be adjusted in height simultaneously.

[0064] For this purpose, a fifth cord 70 is secured to the end 29 of the toothed element, the toothed belt, the toothed rack or the chain 26, as shown in figs. 2 and 8. This fifth cord 70 also extends halfway around the first cord pulley 42, and thereafter extends more or less parallel with the second cord 41. A sixth rotational cord pulley 71 is mounted at a suitable place in the cross-beam 10, the axle for this pulley extending more or less parallel with the legs 2. The fifth cord 70 extends a quarter of the way around the sixth cord pulley 71, and thereafter continues further at right-angles to the plane of the drawing through the one longitudinal beam 90 or 90' to the other cross-beam 10'.

[0065] The second cross-beam 10' is of the same construction as the cross-beam 10, but needs only to be provided with cord pulleys 71, 42, 43 and 44 and cords 40 and 41.

[0066] In the extra cross-beam 10' with the further set of legs 2c, 2d, there is thus no movement arrangement 20 with toothed wheel 25 and toothed element, toothed belt, toothed rack or chain 26. Therefore, in the second cross-beam 10' the fifth cord 70 must extend several times around the first cord pulley 42 in order to be able to be taken up with necessary length in the lowering of the platform, the weight of which contributes to the rolling-up of the third cord 50.

[0067] The electric motor discussed in the above can, for example, be an electric motor for the driving of windscreen wipers on a car, said motor 21 being made reversible by pole reversal. The motor can be designed for 24V operation, but with the normally brief operation times can be supplied with over-voltage. This over-voltage, which among other things for reasons of security must not exceed 50V, can e.g. lie in the range from 28V to 50V.

[0068] The compression spring element 30 serves as a weight-balancing device during the height adjustment of the underframe 1, and contributes in a positive manner to the raising of the platform, in that by its placing in all of the shown embodiments, the compression spring element 30 draws the toothed element, the toothed belt or the chain 26 in the desired direction around the toothed wheel 25.

[0069] The need for motor power for the raising of the platform is hereby reduced to a considerable degree, which means that at least with smaller platforms it is possible to use an electric motor which is commonly accessible within the trade and which is provided with a worm and worm wheel.

[0070] The compression spring element 30 preferably consists of a gas-pressure spring, but can also be a helical spring, which applies for the shown embodiments of the invention. In another embodiment of the movement arrangement in the underframe 1 according to the invention, the spring element can also be a tension spring.

[0071] At suitable places at the ends of the toothed element, the toothed belt or the chain 26, pins are provided which extend out to the side for the activation of switches in the cross-beam 10. These switches are used partly to disconnect the supply from the electric motor 21, and partly to effect a polarity reversal of the motor in relation to the state of the poles before the disconnection, so that upon a renewed supply of power the motor 21 will rotate in the opposite direction.

[0072] The cords described in the above consist, for example, of steel wire, carbon fibres, chains or similar materials.

Claims

1. Height-adjustable underframe for a table or a similar work plafform, said underframe (1) comprising a cross-beam (10) with at least two telescopically adjustable legs (2), a mechanically-driven movement arrangement (20) to which cords are connected and which run over cord pulleys in the underframe and in the legs (2) and which are arranged to work between a lower leg part (3) and at least one upper leg part (5), characterized in that the mechanically-driven movement arrangement (20) comprises a toothed wheel (25) in engagement with a toothed element (26), and that a compression spring element (30) co-operates with the toothed element (26) for the displacement of this in the longitudinal direction of the cross-beam (10) for the adjustment of the height of the legs (2), in that a first and a second cord (40 and 41 respectively) are secured to an end (29) of the toothed element (26).

2. Underframe according to claim 1, characterized in that a third and a fourth cord (46 and 47 respectively) are secured to the toothed element (26) in the vicinity of the other end of this element, and run over rotational cord pulleys (49, 50a, 50b) in the underframe to each their lower leg parts (3a, 3b), where the cords are secured to a fixture point (51a and 51b respectively).

3. Underframe according to claim 1 or 2, characterized in that the first and the second cord (40,41) extend under a first rotational cord pulley (42), that the first cord (41) continues over and partly around a second cord pulley (43a) which is placed in a rotational manner uppermost in the one leg (2a), and continues downwards in the leg (2a) inside the upper leg part (5a), around a third rotational cord pulley (44a) lowermost in the upper leg part (5a), extends further upwards between the upper leg part (5a) and the lower leg part (3a) and is secured at a fixture point (45a) uppermost inside the lower leg part (3a), and that the second cord (41) extends halfway around the first cord pulley (42) and towards the second leg (2b), and extends in a corresponding manner around rotational cord pulleys (43b, 44b) and ends at a fixture point (45b) uppermost inside the lower leg part (3b) (figs. 2 and 3).

4. Underframe according to claim 1, 2 or 3, where there are centremost leg parts (4) between the lower leg parts (3) and the upper leg parts (5), characterized in that in each leg part (2) there is provided a further cord (60) which extends from a fixture point (61) lowermost inside the upper leg part (5) and further around a cord pulley (62) which is placed in a rotational manner lowermost in the centremost leg part (4), and is secured to a fixture point (63) uppermost inside the lower leg part (3) (figs. 6 and 7).

5. Underframe according to one or more of the claims 1-4, characterized in that the toothed element is a chain (26) which extends snakelike in an S-shape in a first direction from a fixture point (28) in the cross-beam (10), around a sprocket (31) on the compression spring element (30), and in an opposite direction to and around the toothed wheel (25), and from here in the first direction towards the first and the second cord (40,41) to which the end (29) of the chain (26) is secured, and that the compression spring element (30) is secured in a pivotal manner to a fixture point (32) inside the cross-beam (10) (figs. 2 and 3).

6. Underframe according to one or more of the claims 1-4, characterized in that the toothed element is a toothed rack (26) which is housed in a displaceable manner in the longitudinal direction of the cross-beam (10), and that the compression spring element (30) extends substantially in the longitudinal direction of the cross-beam (10) away from the end (29) of the toothed rack (26), and is secured in a pivotal manner to a fixture point (32) inside the cross-beam (10) in a direction away from the toothed wheel (25) (fig. 8).

7. Underframe according to one or more of the claims 1-4, characterized in that the mechanically-driven movement arrangement (20) comprises two parallel toothed wheels (25a, 25b), where the one toothed wheel (25a) is in engagement with the toothed element in the form of a toothed rack (26) which is housed in a displaceable manner in the longitudinal direction of the cross-beam (10), and to the end (29) of which the first and the second cords (40, 41) are secured, and where the second toothed wheel (25b) is in engagement with an endless toothed belt or chain (80) which extends around a further toothed wheel (81) on which a conical cord pulley (82) is mounted in a fixed manner, that a cord (83) extends snakelike in an S-shape in a first direction from a fixture point (28) in the cross-beam (10), around a pulley (31) on the compression spring element (30), in an opposite second direction to and several times around the conical cord pulley (82) to which it is secured by its second end (85), and that the compression spring element (30) is secured in a pivotal manner inside the cross-beam (10) at a fixture point (32) which is placed between the fixture point (28) and the toothed wheels (25a, 25b) (figs. 9 and 10).

8. Underframe according to any of the claims 1-7, where the underframe has additional legs (2c, 2d) at a distance from the legs (2a, 2b), characterized in that a fifth cord (70) is secured to the end (29) of the toothed element (26), that the fifth cord (70) extends halfway around the first cord pulley (42), and thereafter extends more or less parallel with the second cord (41) to a sixth rotational cord pulley (71) inside the cross-beam (10), the axle of said cord pulley (71) extending more or less parallel with the legs (2), and extends a quarter of the way around the sixth cord pulley (71) and then continues at right-angles to the plane of the drawing to a corresponding construction of the underframe (1).

9. Underframe according to any of the claims 1-8, characterized in that the cords (40,41,46,47,60,70,83) consist of steel wire, carbon fibres, chains or similar materials.

10. Underframe according to any of the claims 1-9, characterized in that the motor is an electric motor (21) which is reversible by pole reversal and is supplied with a voltage which is less than 50V and preferably lying between 28V and 50V, and that the toothed element, toothed belt or chain (26) has pins which extend out to the side for the activation of switches arranged inside the cross-beam (10), said switches serving partly to disconnect the supply to the electric motor (21) and partly to effect a polarity reversal of the motor in relation to the state of the poles before the disconnection, so that upon a renewed supply of voltage the motor (21) rotates in the opposite direction.

Drawing