Such a leg device may comprise a holder which is adapted to be fixed to the underside of a table-top; first, second and third elongate supporting elements which are directed away from the holder and cooperate by threading engagement, one of the first and third supporting elements being mounted turnably but axially immovably in the holder, the second supporting element being arranged between the first and third supporting elements; and means for turning the supporting element mounted in the holder.

Vertically adjustable tables are used, for instance, as computer table, drawing table and treatment table in physiotherapy. This adjustability in the vertical direc- tion is achieved by means of adjustable legs, which can be controlled in pairs or fully synchronously with the aid of one or more drive means, such as an electric motor and selectively activatable connections with each of the legs.

Prior art leg devices are of the telescopic type with two or three screw elements, three screw elements being required to provide a sufficiently great setting range. Such a known leg device is disclosed in US-A-5 282 593 and has, in addition to the three screw/ supporting elements, a central, telescopic device which prevents turning and connects the holder with the third supporting element, and an external bellows device, in which the remaining parts of the leg device are con- tained. Thus, this known leg device is quite complicated.

Moreover FR 2 747 280 discloses a leg device of the type stated by way of introduction, in which besides the first supporting element has an external thread and a

widened portion at an end located in the second sup- porting element, the second supporting element is a tube with an external thread, with an internal threaded por- tion at an end enclosing the first supporting element, threadingly engaged with the external thread of the first supporting element, and with a widened portion at an end located in the third supporting element, the third sup- porting element consists of a tubular element with an internal threaded portion at an end enclosing the second supporting element, threadingly engaged with the external thread of the second supporting element, means for turn- ing the supporting element mounted in the holder; and three telescopingly displaceable tubular elements, in which the three supporting elements are arranged. Admit- tedly, this leg device is relatively simple in terms of function but complicated in terms of manufacture and does not satisfy requirements as to the greatest pos- sible ratio of maximum length to minimum length of the leg device.

Therefore the object of the present invention is to provide a lengthwise adjustable leg device of the type stated by way of introduction, which in terms of manu- facture is a simple construction and thus economically advantageous and which besides has the greatest possible ratio of maximum length to minimum length.

This object is achieved by the lengthwise adjustable leg device being given the features that are evident from claim 1. Preferred embodiments are defined by the depend- ent claims.

According to the invention, a lengthwise adjustable leg device is thus characterised in that the external thread of the second supporting element extends over essentially the entire internal threaded portion of the same supporting element. As a result, the entire length of the second supporting element is fully enclosed in the third supporting element, which gives the smallest pos- sible minimum length of the leg device and, thus, the

greatest possible ratio of maximum length to minimum length.

The internal threaded portion of the second and third supporting elements suitably consists of a nut which is non-turnably fixed relative to the respective supporting elements and which can advantageously be made of plastic, e. g. polyamide.

The other of the first and third supporting ele- ments is in one embodiment arranged non-turnably relative to the holder. This can be achieved by the telescopingly displaceable tubular elements being non-turnable relative to each other as well as relative to the holder and the other of the first and third supporting elements.

Alternatively, the other of the first and third supporting elements can be arranged non-turnably relative to the corresponding one of the telescopingly displace- able elements.

The first supporting element is advantageously ar- ranged closest to the holder.

The means for turning the supporting element located closest to the holder may comprise a bevel gear, such as a worm wheel coupling.

The three telescopingly displaceable tubular ele- ments can have gradually increasing diameters seen from the holder.

An embodiment of the lengthwise adjustable leg de- vice according to the invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1 is a side view, partly in cross-section, of an embodiment of a lengthwise adjustable leg device ac- cording to the invention, in a retracted state.

Fig. 2 is a side view, partly in cross-section, of the lengthwise adjustable leg device in Fig. 1, in an extended state.

The leg device shown in the drawings comprises a holder 1, which is fixed to the underside of a table-top 2. Moreover three elongate supporting elements 3,4 and 5

are arranged under the holder 1 and are extended verti- cally downwards or away from the holder. The supporting elements 3,4 and 5 each comprise a tube 6,7 and 8, re- spectively. The tube 6 is at its upper end mounted turn- ably, but axially immovably in the holder 1, and more specifically connected to the output shaft of a bevel gear 9, such as a worm gear, whose input shaft is con- nected directly or, by the intermediary of a connection shared by a plurality of leg devices, to an electric motor 10 or another driving device. The electric motor 10 and the bevel gear 9 suitably consist of a conventionally assembled unit.

The tube 6 has an external thread along essentially its entire length and a widened portion in the form of a collar 11 at its lower end, i. e. the end facing away from the holder 1.

The tube 7 has a larger diameter than the tube 6 and, at its upper end, i. e. at its end closest to the holder 1, a nut 12, which is fixed inside the tube end and has an internal thread for engaging the external thread of the tube 6. Like the tube 6, also the tube 7 has an external thread along essentially its entire length and a widened portion in the form of a collar 13 at its lower end, i. e. the end facing away from the holder 1.

The tube 8 has in turn a larger diameter than the tube 7 and has at its upper end, i. e. at its end closest to the holder 1, a nut 14 which is fixed inside the tube end and has an internal thread for engaging the external thread of the tube 7. Like the nut 12, the nut 14 can advantageously be made of plastic, e. g. polyamide. The tube 8 has no external thread and no widened portion at its lower end, where it is instead non-turnably fixed at the lower end of one of three telescopingly displaceable tubes 15,16 and 17, which enclose the tubes 6, 7 and 8.

The three tubes 15,16 and 17 can be non-turnable rela- tive to each other, e. g. with the aid of suitable axial

control means, and relative to the holder 1 to which the tube 17 is attached. The axial control means (not shown) may consist of at least two slide strips which are re- ceived in opposite axial grooves in the tubes 15 and 16 and, respectively, 16 and 17. Thus the tubes 15, 16 and 17 are movable coaxially and non-turnably relative to each other. The property of being non-turnable can also be achieved with a non-circular profile of the tubes 15, 16 and 17.

It will be appreciated that the tube 8 is non- turnable relative to the holder 1 owing to the described connection between the tubes 15, 16 and 17 as well as between the tubes 8 and 15 and between the tube 17 and the holder 1.

However, alternatively the tubes 15,16 and 17 need not be non-turnable relative to each other. For example, only the tubes 15 and 8 can be non-turnable relative to each other since the friction between the base and the lower end of these tubes is in most cases sufficient to hold the tube 8 immovable when turning at least one of the tubes 6 and 7.

By the tube 7 having the external thread along es- sentially its entire length, this tube and, thus, the second supporting element 4 can be completely enclosed in the tube 8 and the third supporting element 5, respec- tively. This results in the smallest possible minimum length of the leg device in its retracted state and, thus, the greatest possible ratio of maximum length to minimum length of the leg device.

When extending the leg device from the state shown in Fig. 1 to the one in Fig. 2, the tube 6 is made to turn, moving upwards in the tube 7 until the collar 11 abuts against the nut 12. Then the tube 7 begins to turn together with the tube 6, the tube 7 moving upwards in the tube 8 until the collar 13 abuts against the nut 14.

Depending on the friction, the order of the movement of the tube 6 up from the tube 7 and the movement of the

tube 7 up from the tube 8 can be different or even al- ternate.

This also applies when shortening the leg device from the state shown in Fig. 2 to the state shown in Fig. 1, in which the upper end of the tube 8 is on a level with the upper end of the tube 7 and also the upper end of the tube 6.

It is also obvious that the supporting elements 3 and 5 can change places, like the tubes 15 and 17.

Further modifications of the above embodiment of a leg device are feasible within the scope of the invention as defined by the appended claims.