Telescopically moving structures of this kind have an increasing importance as demands for compact and versatile telescopic structures are growing.

Structures of said kind can, as will appear later, be telescoped to essentially the triple length, which makes them very suitable for e. g. height-adjustment of tables, however, they are used in several connections.

For many purposes it is necessary or at least preferable that the means for rotation of the spindle tube, and thus for providing the telescopic movement, are situated at one end of the structure, and that the means for rotation of the spindle tube are stationary in relation to this end of the spindle tube. Further it is an advantage that the means for rotation of the spindle tube in the axial direction are connected in a slidable manner to the tube such that a load in the axial direction is not transferred to the driving mechanism. This means that gearwheels etc. do not have to be dimensioned in order to stand a blow in axial direction. If, for example, a height-adjustable table during transport or the like is dropped from a few centimeters, the driving mechanism can easily be

damaged, if this axial force is transmitted to gear wheels or the like. Therefor height-adjustable tables must be dimensioned to withstand a fall according to a so-called drop-test, but a telescopically moving structure connected in a slidable manner to the drive system merely has to be dimensioned to endure the forces at retracting or telescoping the structure, which means, for example, that the structure can be designed with nylon gearwheels which are much cheaper than steel gearwheel.

US patent no. 3404580 discloses an actuator in which a first threaded spindle tube is driven to rotate by a splined shaft slidably engaged in a splined hole in one end of the spindle tube. The spindle tube is engaged in a nonrotary nut, and a second, nonrotary spindle tube is threadably engaged in an internal thread of the first spindle tube, the internal and external threadings of the first spindle tube being of different directions.

A disadvantage of this actuator is that the spindle tube is driven by a small diameter splined shaft, which will not be able to transfer high torque because this may result in seizure so the splined shaft cannot slide in the splined hole.

Similarly DE 39 10 814 Al discloses a linear actuator in which a first, threaded spindle tube is driven to rotate by a splined shaft slidably engaged in a splined hole in one end of the spindle tube. The spindle tube is engaged in a nonrotary nut, and a second, nonrotary spindle tube is threadably engaged in an internal thread of the first spindle tube, the internal and external threadings of the first spindle tube being of different directions.

A disadvantage of this actuator is that a splined shaft of small diameter will not be able to transfer

high torque, because this may result in seizure so the splined shaft cannot slide in the splined hole.

US patent no. 1708450 discloses a dental chair having an adjustable support in which a first spindle tube is driven to rotate, so a nonrotary nut engaged thereon translates along the spindle tube. A nonrotary spindle is engaged in an internal thread of the first spindle, and a system of rollers prevents the dif- ferent nonrotary parts from rotating.

A disadvantage of this construction is that it is rather complicated and has large dimensions, so it is not suitable for being used as a telescopically moving structure in general, and further the drive means is not slidably connected to the spindle.

It is an object of the present invention to provide a telescopically moving structure of the above mentioned type, which is able to work even against a strong force, i. e. is able to transfer a large torque.

The telescopically moving structure according to the invention is characterized in that the driving shaft has an essentially polygonal cross section with a perimeter forming two opposite longitudinal tracks for engagement with torque-transferring rolling bodies which are journalled in a bushing fastened in the spindle tube. With transfer of the torque from the driving shaft to a bushing inserted in the spindle tube by means of opposite longitudinal tracks for engagement with torque-transferring rolling bodies, the axial friction will be minimized, and the struc- ture can therefore be used for movement of relatively heavy objects without risk of seizure.

According to an embodiment of the telescopically moving structure is characterized in that the driving shaft has an essentially rhombic cross section and is in engagement with rolling bodies in the form of two

sets of rollers arranged in pairs one opposite the other, where the two sets are mutually displaced in the longitudinal direction of the spindle. Due to the axial displacement of the roller pairs, this design is so compact that it is suitable for placement in the interior of the spindle tube.

An alternative embodiment of the telescopically moving structure according to the invention is characterized in that the driving shaft is designed as a polygonal tube freely surrounding the spindle tube, and where said tracks are formed by corners between internal adjacent sides. This design of the driving shaft enables transfer of a large torque as the diameter of the driving shaft is considerably enlarged, the force necessary to rotate the spindle therefor being considerably reduced. The tubular driving shaft can thus be designed with relatively thin walls, and the rollers and their bearings will be correspondingly simplified.

A further embodiment of the telescopically moving structure is characterized in that the rolling bodie. s are provided by ball or roller bearings, preferably deep groove ball bearings, which assure both a low friction and a sufficient wearing resistance.

An embodiment of the telescopically moving structure is characterized in that said tracks are provided with a flat bottom and sides extending perpendicularly to the bottom and a width which is a little larger than the diameter of a ball bearing fastened to a radially extending axle journal on said bushing.

The main parts making up the telescopically moving structure, i. e. the spindle tube, the spindle and nuts may be ordinary threaded parts, but preferably one or more of these parts are produced by

hydroforming i. e. deforming a tube in a mould by a fluid under pressure. An actuator using elements manufactured by hydroforming is disclosed in WO 98/25051 Al. Although the cost of a device for manufacturing the parts by hydroforming is very high, this method is very cost effective when large quantities are produced as the cost per unit is very low compared to ordinary threaded spindles. Further the wave-shape of the walls forming rounded tracks or threads producible by hydroforming is very well suited for transfer of large torques without risk of jamming of the parts, so spindles having a high pitch can be used. This means that the structure can be driven from retracted to extended state in very few revolutions of the driving shaft, so noise related hereto and wear of the spindles will be minimized. With hydroforming it is possible to produce a telescopically moving structure of very small diameter as with this manufacturing process it is possible to produce spindles having a very small the thickness of the walls without sacrifice of strength. In fact a spindle having a 10 mm diameter and a wall thickness of 1 mm will be stronger than a corresponding massive rod because of the shape of the wall, i. e. corrugations or rounded tracks in the wall. Still a further advantage is that it is possible to produce spindles having changing cross section along the length, for example having integral"nuts"in the end of the spindle and/or formed with longitudinal tracks for rollers.

Furthermore, the invention relates to usage of a telescopically moving structure of the above type as a driving means in a height-adjustable table with tripartite telescopic legs, the elements of which are telescoped evenly when raising the table, and where the driving force to the driving means is supplied in

the area immediately under the tabletop. The fact is that this structure is particularly suitable to be built in a height-adjustable table, the driving means being positioned in a fixed position in the axial direction, which both provides a liberty of choice regarding the size of the motor as the motor need not be built in e. g. a table leg, and, at the same time, the driving means are arranged at one end of the structure, which permits to drive the telescopically moving structure over gearwheels or alike from a centrally situated driving arrangement, which may drive more telescopically moving structures.

Furthermore, the invention has the advantage that the even telescoping of the elements assures the largest possible stability of the structure in a partially telescoped condition, all elements being inserted approximately evenly in its adjacent element or elements.

In the following, the invention is explained in more detail with reference to the accompanying drawing, in which Fig. 1 shows a telescopically moving structure according to the invention where the structure is fully telescoped, Fig. 2 the structure according to Fig. 1 in a partially assembled condition, Fig. 3 the structure according to Fig. 1 in a completely assembled condition, Fig. 4 is an enlarged cross section of a driving shaft in a first embodiment, and Figs. 5a and 5b show axial and cross section, respectively, of an engagement between the driving shaft and a bushing of a spindle tube, Figs. 6a and 6b show axial and cross section, respectively, of an alternative embodiment of engage-

ment between a driving shaft and a bushing of the spindle tube, Figs. 7a and 7b show axial and cross section, respectively, of an alternative embodiment of engage- ment between the driving shaft and a bushing of the spindle tube, Figs. 8a and 8b show axial and cross section, respectively, of an alternative embodiment of engage- ment between the driving shaft and a bushing of the spindle tube, and Figs. 9a and 9b show axial and cross section, respectively, of an alternative embodiment of engage- ment between the driving shaft and a bushing of the spindle tube, The telescopically moving structure 1 comprises a spindle tube 3 with an external thread engaging a nut 2 mounted in a rotationally fixed manner. The spindle tube 3 can be turned with respect to the nut 2 by means of a drive shaft 6 connected with one end of the spindle tube 3 to be rotationally fixed with respect to the spindle tube, while allowing slidable displacement thereof in the axial direction. Thus, by rotation of the drive shaft 6 the spindle tube 3 will move linearly in the axial direction with respect to the nut 2. The spindle tube 3 is further provided with an internal thread 4 of opposite direction of inclination to that of the external thread, said internal thread 4 being engaged by a corresponding external thread on a non-rotating spindle 5 such that at the rotation of the spindle tube 3 the spindle 5 is displaced in the same axial direction as the spindle tube 3. The internal thread 4 can as shown be provided by a collar or nut mounted in a rotationally fixed manner to the spindle tube 3. Alternatively, the entire spindle tube 3 or a portion hereof can be

provided with an internal thread.

In this way, the structure can transform a rotational movement of the drive shaft 6 into a linear movement of spindle tube 3 and spindle 5 with respect to nut 2 as indicated by arrows in Fig. 1.

From Figs. 1 and 3 appears that the length of the structure 1 can change essentially by a factor three.

When the structure is collapsed the spindle 5 is received in the spindle tube 3, which again is received in a rotationally fixed tubular element 7, with which the nut 2 is connected. The element 7 can have an internal thread in engagement with the spindle tube 3. This need not be the case, however, and the element 7 can be of any design and form part of a frame structure, and the element 7 may further function as a guidance for the spindle tube 3 during collapsing and telescoping.

A telescopically moving structure 1 of this type is particularly suitable for e. g. height-adjustable tables or the like, the structure 1 being activated for extension and collapse by rotation of the drive shaft 6 arranged at one end of the structure 1, in particular because the drive shaft 6,6'does not move in the axial direction.

In order to obtain a telescopically moving structure 1, which even under load can be driven by a relatively small force, it may be advantageous for the nuts 2 and 4 to be of the kind having circulating balls. It will be appropriate, however, that the threads have a certain friction or locking, such that the structure 1 is not retracted or telescoped when subject to a load in the axial direction. Another way of reducing friction between the elements is by using low friction materials for the nuts 2,4, and/or coating the threads of the spindles 3,3', 5 with a

low friction material.

An important aspect of the telescopically moving structure 1 according to the invention is to minimize the axial friction between the driving shaft 6,6'and the spindle tube 3,3'. Various designs of means for reduction of this friction are shown schematically in Figs. 5-8. In the embodiment shown in Figs. 5a and 5b, the drive shaft 6 has a cross section corresponding substantially to a diamond. Two sets of rollers 10 arranged in pairs one opposite the other are journalled in a bushing 11, which is inserted in the spindle tube 3. The two sets of rollers 10 are displaced axially with respect to the longitudinal direction of the spindle tube 3, whereby the diameter of the bushing 11 can be reduced so much that the bushing 11 can be accomodated in the fixed tube 7.

Further the spindle tube 3 may be journalled in an axial thrust bearing (not shown) in the nut 4 to minimize friction and wear of the structure.

In the embodiments shown in Figs. 6,7 and 8, the drive shaft 6'is designed as a tube surrounding the spindle tube 3', but placed inside the tubular element tube 7'. The drive shaft 6'has as shown in Figs. 6b, 7b and 8b a polygonal cross section in the form of an octagon. Four of the edges form tracks in which opposite roller pairs 10 can run and thus transfer a torque to the bushing 11 in which the rollers 10 are journalled. The octagonal form constitutes a com- promise permitting a secure guidance of the rollers 10 and limited space requirements between the fixed tube 7 and the spindle tube 3'. However, other designs of the tubular driving shaft 6'are possible within the scope of the invention, if only an appropriate longitudinal track is assured for the rollers 10 to follow. In the embodiments with the tubular shaft 6',

the bearing of the rollers 10 is particularly simple as they merely rest in grooves in the bushing 11. The tubular shaft 6'is at the end provided with a closing, in the centre of which a hexagonal shaft 6" is mounted and forms a part of the connection to a not-shown drive motor or transmission. An embodiment having only two rollers 10 is shown in Figs. 9a and 9b. The rollers 10 travel in a groove in the drive shaft 6'.

In a special embodiment, the rollers 10 are designed as deep groove ball bearings positioned on a bushing in the spindle tube 3'. The ball bearings abut on the bottom of a relatively flat track in the tubular drive shaft 6'as they rest at the side face against the bottom of the track. The outer ring of the ball bearing rolls along one or the other of the sides of the track, depending on which direction the tubular shaft 6'is to drive the spindle tube 3'. The ball bearing is mounted on an axle journal directed perpendicularly on the axis of the spindle tube 3'and axially out from this.

As mentioned earlier the spindles may be ordinary threaded spindles, but advantageously the threads of the spindles are manufactured by hydroforming, i. e. deforming a tube in a mould by a fluid under pressure.

The cost of a device for manufacturing the elements by hydroforming is very high, but this method is very cost effective when large quantities are produced as the cost per unit is very low compared to ordinary threaded spindles. Further the wave-shape of the walls forming rounded tracks or threads producible by hydroforming is very well suited for transfer of large torques without risk of jamming of the parts, so spindles having a high pitch can be used. This means that the structure can be driven from retracted to

extended state in very few revolutions of the driving shaft, so noise related hereto and wear of the spindles will be minimized. With hydroforming it is possible to produce a telescopically moving structure of very small diameter as with this manufacturing process it is possible to produce spindles having a very small the thickness of the walls without sacrifice of strength. In fact a spindle having a 10 mm diameter and a wall thickness of 1 mm will be stronger than a corresponding massive rod because of the shape of the wall, i. e. corrugations or rounded tracks in the wall. Still a further advantage is that it is possible to produce spindles having changing cross section along the length, for example having integral"nuts"in the end of the spindle and/or formed with longitudinal tracks for rollers. This means that the telescopically moving structure can be produced with few parts and with parts having a very small diameter making them ideal for build-in.