GB2514375A

GB2514375A - Apparatus for supporting a load

Info

Publication number: GB2514375A
Application number: GB1309161.6A
Authority: GB
Inventors: Alex Lau; Andrew Wills
Original assignee: Colebrook Bosson Saunders Products Ltd
Current assignee: Colebrook Bosson Saunders Products Ltd
Priority date: 2013-05-21
Filing date: 2013-05-21
Publication date: 2014-11-26
Anticipated expiration: 2033-05-21
Also published as: GB2514375B; GB201309161D0; WO2014188189A1; GB2514375B8; GB2514375A8

Abstract

The invention relates to an apparatus for supporting a load such as a display device. The load is supported by an extensible arm, which is an arm that may vary in length. An apparatus comprises an extensible arm having a pivot 120 and a first loading point 105, wherein the arm is extensible so as to allow the first loading point 105 to move relative to the pivot 120, wherein the arm comprises a second loading point 110. The apparatus comprises positioning means 200 arranged to set a distance between the second loading point 110 and the pivot 120 in dependence upon a distance between the first loading point 105 and the pivot 120 and loading means 150 for applying a counter-load to the second loading point 110. The loading means 150 may be a resilient member such as a spring and the positioning 200 means may comprise a first and second threaded members. In other embodiments the position means 200 may comprise a pneumatic and/or hydraulic linkage.

Description

Apparatus for Supporting a Load The invention reiates to an apparatus for supporting a load such as a display device. In particular, the load is supported by an extensible arm.

When a display devioe is supported at one end of an extensible arm, the moment caused by the mass of the computer monitor will vary in dependence upon the amount of extension. This requires adjustment of the force holding the display device in equilibrium. Typically, this must be done manually.

According to the invention, there is provided an apparatus defined by claim 1.

The invention can solve the problem of how to support a load using an extensible arm without having to manually adjust a supporting force when the arm is extended or shortened.

For a better understanding of the invention and to show how the same may be put into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1 shows a side view of a first embodiment of an apparatus for supporting a load; Figure 2 shows a perspective view of a second embodiment of an apparatus for supporting a load; Figures 3a to 3c show a side view of a positioning means for use in the invention; Figure 4 shows a perspective view of a third embodiment of an apparatus for supporting a ioad; Figure 5a shows components of a fourth embodiment of an apparatus for supporting a load; Figure Sb shows the components of Figure 5a when assembled; Figure 6 shows a diagrammatic representation useful for understanding the embodiment of Figure 5; Figure 7 shows an alternative arrangement of the first and second loading points and pivots of the disclosed embodiments; Figure 8 shows a cross-sectional view of a further embodiment of an apparatus for supporting a load; Figure 9a shows components of a bearing for use in the invention; and Figure Oh shows the components of Figure 9a when assembled.

A first embodiment of an apparatus for supporting a load is shown in Figure 1.

The apparatus comprises an extensible arm 100 having a pivot 120, a first loading point 105, and a second loading point 110.

The first loading point 105 may be configured for attachment to a load 50. Preferably, the load 50 is a display device.

The first loading point 105 may move relative to the pivot 120. The second loading point 110 may also move relative to the pivot 120.

The apparatus comprises positioning means 200 for setting the distance between the second loading point 110 and the pivot 120. Preferably, the positioning means moves the second loading point 110 relative to the pivot 120.

Specifically, the second loading point 110 may be positioned in dependence upon the distance between the first loading point 105 and the pivot 120.

Thus, a user can move the load 50, and this will automatically reposition the second loading point 110.

Loading means 150 may be provided for applying a counter-load to the second loading point 110. In various embodiments, the loading means 150 may be a simple counterweight. However, other loading means such as those described below can be used, for example a spring.

In the first embodiment, the positioning means 200 is a mechanical linkage. For illustrative purposes, a very simple linkage is shown in Figure 1. This linkage comprises a plurality of struts 201, 202, 203.

For example, a first strut 201 may be pivotally connected at its first end 201a to the arm 100 to move with the first loading point 105. A third strut 203 may be pivotally connected at its second end 203b to the arm 100 to move with the second loading point 110.

A second strut 202 may be pivotally connected at its first end 202a to the second end 201b of the first strut 201. The second strut 202 may be pivotaily connected at its second end 202b to the first end 203a of the third strut 203.

The second strut 202 is pivotally connected at a rotation point 202c along its length to the arm 100. Preferably, the rotation point 202c is axially aligned with the pivot point 120. More preferably, the rotation point 2020 coincides with the pivot point 120.

Preferably, the length of the second strut 202 is equal to the sum of the lengths of the first strut 201 and the third strut 203, and the rotation point 202o is located a distance along the length of the second strut 202 from the first end 202a equal to the length of the first strut 201.

Thus, the ratio between the length of the first and third struts 201, 203 determines the ratio between the displacements of first and second loading points 105, 110 relative to the pivot 120.

In order that the apparatus may have a compact appearance, It is preferable that the counter-loading distance between the second loading point 110 and the pivot 120 is smaller than the loading distance between the first loading point and the pivot 120.

In which case, the counter-loading force applied to the second loading point 110 by the loading means 150 must be greater than the force applied by the load 50 to the first loading point 105.

In embodiments in which the loading means 150 applies a substantially constant counter-loading force (for example, when it is a simple counterweight), the positioning means will position the second loading point 110 relative to the pivot 120 such that the counter-loading distance is proportional to the loading distance.

In embodiments such as Figure 1, in which the positioning means 200 is a simple linkage formed of a plurality of struts 201, 202, 203 and the loading means applies a constant force, the length of the struts 201, 202, 203 and the location of the rotation point 202c can be chosen such that the ratio of the loading distance to the counter-loading distance is equal to the ratio of the mass of the counterweight 150 to the mass of the load 50.

When the first loading point 105 moves a first distance, the second loading point 110 is moved in the opposite direction by a fraction of the first distance. In the embodiment of Figure 1, the fraction is fixed and egual to the ratio of the mass of the load 50 to the mass of the counterweight 150.

The extensible arm 100 may comprise a central arm portion 102 having the pivot 120 located thereon, a first arm portion 101 having the first loading point 105 located thereon, and a second arm portion 103 having the second loading point 110 located thereon. The first and second arm portions 101, 103 may each be slidably mounted on the central arm portion 102 to allow the first and second mounting points 105, 110 to move relative to the pivot 120.

A second embodiment is shown in Figure 2. In the embodiment of Figure 2 a different mechanical linkage is used as the positioning means 200. The positioning means 200 in the second embodiment comprises a threaded member 250.

The threaded member 250 may have a first threaded section 250a and a second threaded section 250c. The threaded member 250 may be mounted so as to rotate freely but be prevented from moving axially within the arm 100. For this purpose, the threaded member 250 is preferably provided with an unthreaded section 250b, which is held within a bush 252 attached to the arm 100.

A driving connector 254 may be mounted on the arm 100 to move with the first loading point 105. A driven connector 256 may be mounted on the arm 100 to move with the second loading point 110.

The driving connector 254 may mesh with the first threaded section 250a. The driven connector 256 may mesh with the second threaded section 250c.

When the length of the arm 100 is varied, the first loading point 105 is moved towards or away from the pivot 120 so that the driving connector 254 thereby causes the threaded member 250 to rotate relative to the arm 100. Rotation of the threaded member 250 causes the driven connector 256 to move axially relative to the pivot 120. Thus, the second loading point 110 will move relative to the pivot 120.

In embodiments in which the arm 100 is formed as three slidable portions, the bush 252 may be attached to the central arm portion 102, the driving connector 254 may be attached to the first arm portion 101, and the driven connector 256 may be attached to the second arm portion 103.

By selecting the pitches of the threads of the first and second threaded sections 250a, 250c to be different, the apparatus can be arranged such that the second loading point moves relative to the pivot 120 by a proportion of the distance moved by the first loading point 105 relative to the pivot 120.

This form of positioning means 200 could be used with any form of loading means 150. For example, a loading means 100 that applies constant force irrespective of its position/extension, such as a counterweight or constant force spring, could be used.

On the other hand, this form of positioning means 200 could also be used in embodiments in which the counter-loading force applied by the loading means 150 is not substantially constant irrespective of its position/extension (for example, when it is a resilient member, such as a simple spring, extending between the second loading point 110 and an anchoring point) . In such cases, the positioning means will position the second loading point 110 relative to the pivot 120 such that the counter-loading distance is a function of the loading distance. The particular function will be based upon the behaviour of the loading means 150 so that the torque applied to the arm 100 by the loading means is egual and opposite to the torque applied to the arm by the load 50. This can be achieved by varying the pitch of one or more of the threaded sections 250a, 250c in the longitudinal direction.

In this way, the torque applied about the pivot by the loading means 150 will vary in proportion to the extension of the arm 100.

For example, where the loading means 150 oomprises a resilient member, this can be achieved by varying the difference in pitch between the threaded sections 250a, 250c along their lengths (e.g., by varying the pitch of one or both of the threaded sections 250a, 25Cc) along the length of the threaded member 250 in relation to the function linking extension to force (e.g. the spring function, or stress-strain curve) of the resilient member.

In various embodiments, one cr both of the threaded sections 250a, 25Cc may be formed as a twisted beam of material.

Preferably, the first threaded section 250a is formed in this way. Such a threaded member can be manufactured more easily than by tapping a solid bar of material, In particular in embodiments In which the pitch of the thread varies along the length of the threaded member.

In preferred embodiments, one or both of the driving connector 254 and the driven connector 256 may be provided with bearings to allow the connector(s) 254, 256 to travel along the threaded member 250 with low friction. A preferred form of bearing 400 Is shown In Figures Ca and 9b.

Preferably, a bearing 400 comprises a cage 415 with a plurality of indentations 420 in which ball-bearings 410 are held. The plurality of IndentatIons 420 are arranged to extend along the direction of the thread which the bearing is to follow. The ball-bearings 410 are preferably sized to substantially fill the root of the thread.

Although in the above embodiment, the positioning means 200 in the second embodiment comprises a single threaded member 250, embodiments are envisaged in which the first and second threaded sections 250a, 250c are formed on separate rotatbly linked members. Gearing may be provided such that the first and second threaded sections 250a, 250c rotate at difterent rates.

In Figure 3 there can be seen a positioning means 200 comprising a more complicated linkage than that shown in Figure 1. Whilst this linkage has more components, the functionality of the linkage is substantially the same as that of Figure 1. The linkage may form an extensible cage around the extensible arm 100. Thus, it can be provided in a form that is very compact in a radial sense.

A third embodiment is shown in Figure 4. Figure 4 shows a cross-section of an apparatus for supporting a load which may have a similar positioning means to that shown in Figure 3.

As can be seen from Figure 4, the first loading point 105 may be provided by a D-ring, or the like, having an arcuate member 105a, which slides within a complementary channel 105b near the end of the arm 100. The arcuate member 105a is arranged such that its centre is a constant distance from the pivot irrespective of its orientation. Thus, a load mounted on the arm 100 may be tilted without varying the torgue applied about the pivot 120 thereby.

-10 -In the embodiment of Figure 4, the loading means 150 is provided at least partially within the arm 100.

For example, the loading means 150 may comprise a gas strut 151. The gas strut may provide a substantially constant force irrespective of its compression. The gas strut 151 may be located within the arm 100 such that it is free to move axially with respect to the first loading point 105 and the pivot 120. Preferably, a wheeled support 155 may be provided to support the gas strut 151 whilst allow relative axial movement. The gas strut 151 is fixed axially relative to the second ioading point 110.

The gas strut 151 comprises a piston 151a within a bore 151b. A tether 152 extends from the piston 151a to an anchor 153. The tether 152 passes around a shaft 156 located at the second loading point 110. Tension in the tether 152 is resisted by the compression of gas within the bore 151b. The cam 153 is rctatably attached to the second loading point 110 at a first pivot point i56a.

Since the tether 152 wraps around the shaft 156, a force in the direction of the anchor 153 will act on the second loading point 110.

It is preferable that the force applied to the second loading point 110 is directed verticaliy downwards. To achieve a vertical counter force, the anchor 153 may comprise a free-running wheel within a horizontal channel 154 of the loading means 150. Tension in the tether 152 will cause the wheel to be located substantially below the second loading point 110.

-11 -Similar arrangements may be provided in other embodiments to maintain a vertically aligned force. For example, if the loading means 150 is a simple spring, this may extend between the second loading point 110 and a carriage arranged to move freely along a track oriented in a substantially horizontal direction.

A fourth embodiment is shown in Figure 5. Figure 5 shows a plurality of interfitting tubes 262, 263, 264, 266. The tubes 262, 263, 264, 266 may be nested coaxially. The tubes 262, 263, 264, 266 may slide relative to each other in the axial direction. Some or all of the tubes 262, 263, 264, 266 may be provided with one or more protruding tabs or wheels 270 to followw ithin one or more axially extending tracks or spiral tracks 275 on other tubes to either maintain rotational alignment or to induce relative rotational movement when the tubes are displaced axially.

Whilst not essential, wheels are preferable to tabs in order to reduce friction.

Advantageously, in such an arrangement the tubes can provide the extensible arm 100 and the tabs and tracks 170 can form the positioning means 200, thus providing a very compact assembly. The innermost tube provides a passage, which may define a space for other components such as at least part ci the loading means 100 and/or cabling to provide power and/or data to a load 50 such as a computer monitor.

In Figure 5, a central tube 262 may provide the central arm portion 102, and may have the pivot 120. A first tube 264 may form the first arm portion 101, and may have the first -12 -loading point 105. A second tube 266 may form the second arm portion 103, and may have the second loading point 110.

The arrangement shown in Figure 5 allows relative axial movement between the first, central, and second arm portions 101, 102, 103, without relative rotation.

The central tube 262 is provided with a central spiral 175a and the first tube 264 is provided with a first spiral 275b oriented in the opposite direction to the central spiral 275c.

Preferably, the central spiral 275a has an equal and opposite pitch to the first spiral 275b. Such an arrangement allows the central tube 262 and first tube 264 to be nested in the shortest axial space.

A rotatable tube 263 Is provided with at least one first wheel (or tab) at one end which follows the central spiral 275a and at least one second wheel (or tab) 270 at the other end which follows the first spiral 275b.

As the first tube 264 moves axially away from the central tube 262, the rotatable tube 263 rotates as its second wheel follows the first spiral. The central tube is not rotated as the first wheel follows the central spiral. Thus, a large axial movement of the first tube 264 leads to a small rotation of the rotatable tube 263.

Relative rotation is prevented between the first tube 264 and the second tube 266. For example, the second tube 266 may have at least one straight groove and the first tube 264 -13 -may have one or more tabs or wheels which follow the straight groove.

The first set of wheels 270 of the rotatable tube 263 also follow a spiral 275o formed in the seoond tube 266, which is oriented in the same direction as the central spiral 275a, but has a slightly different pitch. Thus, as the rotatable tube 263 rotates, axial movement is induced in the second tube 266.

Figure 6 shows a diagrammatic representation of the three tubes. The first two diagrams show how the axial displacement of the central tube 262 relative to the first tube 264 determines rotation of the rotatable tube 263. The second two diagrams show how the rotation of the rotatable tube 263 determines the displacement of the second tube 266 relative to the central tube 262.

As can be seen from Figure 6, the difference in pitch between the spiral 275o on the second tube 266 and the central spiral 275a can determine the ratio between the amount of movement of the first tube 264 relative to the pivot 120, and the amount of movement of the second tube 266 relative to the pivot 120.

In general, it is preferred that the apparatus has three slidable but not rotatable tubes, since these may form the central, first, and second portions 102, 101, 103 of the extensible arm 100. Such a positioning means 200 comprises three slidable tubes 262, 264, 266, arranged to slide axially relative to each other but to not rotate relative to -14 -each other, and at least one rotatable tube 263 arranged to rotate relative to the three slidable tubes 262, 264, 266.

Since the rotational tube rotates relative to the three siidable tubes 262, 264, 266, there can be three spirals 275. The use of three spirals 275 is advantageous, since the difference in pitoh between spirals 275 can be smaller than the difference in pitch between threads in the embodiment shown in Figure 2, and therefore the overall friction in the mechanism can be lower.

Although in the description above, the pivot 120 is located between the first and second loading points 105, 110, and the counter force applied to the second loading point 110 is directed vertically downwards, as can be seen from Figure 7, embodiments are considered in which the second loading point is on the same side of the pivot 120 as the first loading point 105 and the counter force is directed vertically upwards. In which case, the positioning means 200 moves the second loading point 110 in the same direction as the first loading point 105 (i.e. in the opposite direction to the embodiments above) , but imposes a ratio on the amount of movement.

Other mechanical linkages beyond those described above are possible for providing the positioning means 200. For example a system of linear gears and one or more pinions may be provided in which the size and number of teeth of the gears/pinions may be chosen to achieve a ratio between the amount of movement of the first loading point 105 relative to the pivot 120, and the amcunt of movement of the second loading point 110 relative to the pivot 120.

-15 -Indeed, the positioning means 200 can use any mechanical linkage kncwn in the art. In general, the positioning means may comprises one or more of: at least two threaded members of differing pitch; a plurality of pivotally connected struts; a system of interconnected chain gears; a system of linear rack gears interconnected by at least one pinion; and a system of three slidable tubes and a rotatable tube; a system of interlinked pulleys.

In the description above there is disclosed a number of meohanioal linkages suitable for forming a positioning means 200. However, the positioning means 200 need not be solely mechanical and could be provided with, or replaced by, other systems, such as by a pneumatic system and/or a hydraulic system and/or an eleotronic system.

For example, and as shown in Figure 8, an embodiment of an apparatus for supporting a load may comprise two pistons.

Extension of the arm 100 may move a first piston 310 within a first bore 312. A second piston 316 may be provided in a second bore 314 which is in communication with the first bore 312. Thus, when the first piston 310 moves in the first bore 312, fluid moves between the first and second bores 312, 314, and thereby moves the second piston 316. If the second bore 314 has a greater cross-sectional area than the first bore 312, then a ratio between the two motions can be created.

-16 -An electronic system may comprise a sensor for sensing the extension of the arm 100 and an eleotronio drive device for providing a torgue to oppose the torque of the load. For example, the electronic drive device may move the second loading point 110.

As explained above, it is not necessary for the loading means 150 to apply a constant force irrespective of the extension of the arm 100, since any divergence from such a constant force can be compensated for using the positioning means 200. However, loading means 150 that apply such constant counter forces are known, such as a counterweight, or a constant force spring.

In the above embodiments, the pivot 120 is preferably at a fixed location and the second loading point 110 is moved by the positioning means relative to this fixed location.

However, this is not essential, and embodiments are considered in which the second loading point 110 is in a fixed location and the pivot 120 moves. In such cases, the positioning means 200 may set the distance between the second loading point 110 and the pivot 120 by moving the pivot 120 using the mechanisms set out above. In such cases, the pivot 120 may be mounted on a carriage arranged to move freely along a track oriented in a substantially horizontal direction.

The above embodiments are preferably used to support a load in the form of a display device such as a computer monitor or television, other loads 50 are considered. For example, the load may be one or more of: a display device; a -17 -work surface; a light; a tablet computer; a camera; a microphone; a keyboard; and/or a speaker.

It should be noted that any of the positioning means 200 described above may be used with any of the loading means described above.

Claims

-18 -CLAIJYIS: 1. Apparatus for supporting a load, comprising an extensible arm having a pivot and a first loading point, wherein the arm is extensible so as to allow the first loading point to move relative to the pivot, wherein the arm comprises a second loading point, the apparatus further comprising: positioning means arranged to set the distance between the second loading point and the pivot in dependence upon the distance between the first loading point and the pivot; and loading means for applying a counter-load to the second loading point. 3-5
2. The apparatus of claim 1, wherein the positioning means is arranged such that the torgue applied about the pivot by the loading means varies in proportion to the extension of the arm.
3. The apparatus of claim 1 or claim 2, wherein the positioning means is arranged such that the distance between the second loading point and the pivot is a function of the distance between the first loading point and the pivot.
4. The apparatus of claim 3, wherein the positioning means is arranged such that the distance between the second loading point and the pivot is proportional to the distance between the first loading point and the pivot.

-19 -
5. The apparatus of any preceding claim, wherein the loading means is arranged to apply a constant vertical counter-loading force to the second loading point.
6. The apparatus of claim 5, wherein: a load is mounted to the first loading point; and the linkage is arranged such that the ratio between the distance between the second loading point and the pivot and the distance between the first loading point and the pivot is egual to the ratio between the force on the first loading point due to the weight of the load and the constant vertical counter-loading force.
7. The apparatus of any preceding claim, wherein the loading means comprises a constant force spring.
8. The apparatus of claim 3, wherein: the loading means comprises a resilient member; and the positioning means is arranged such that the distance between the second loading point and the pivot is related to the distance between the first loading point and the pivot by a function based upon the material properties of the resilient member.
9. The apparatus of claim 8, wherein the resilient member is a spring, and the function is based upon the spring function of the spring.
10. The apparatus of any preceding claim, wherein: the positioning means comprises a first threaded section meshing with a driving connector and a second threaded section meshing with a driven connector; -20 -the apparatus is arranged such that extension or shortening of the arm moves the first ioading point thereby translating the driven connector along the first threaded section and causing the first threaded section to rotate; and rotation of the first threaded section causes the second threaded section to rctate and thereby drives the driven connector to translate along the length of the second threaded section thereby moving the second loading point.
11. The apparatus of claim 10, wherein the first and second threaded sections are formed on a single threaded member.
12. The apparatus of claim 10 or claim 11, wherein the pitch of the first threaded section differs from the pitch of the second threaded secticn.
13. The apparatus of one of claims 10 to 12, wherein: the first threaded section meshes with the driving connector via a first bearing; the first bearing comprises a cage holding a plurality of balls; and the balls are arranged along a helical path corresponding to the thread of the first threaded section.
14. The apparatus of one of claims 10 to 13, wherein: the second threaded section meshes with the driven connector via a second bearing; the second bearing comprises a cage holding a plurality of balls; and the balls are arranged along a helical path corresponding to the thread cf the second threaded section.

-21 -
15. The apparatus of one of claims 10 to 14, wherein the pitch of at least one of the first threaded section and the second threaded section varies along its length.
16. The apparatus of claim 15, wherein the pitch of at least one of the first threaded section and the second threaded section varies along its length so that the torque applied about the pivot by the loading means varies in proportion to the extension of the arm.
17. The apparatus of any preceding claim, wherein the positioning means comprises a mechanical linkage.
18. The apparatus of claim 17, wherein the mechanical linkage comprises one or more of: at least two threaded members of differing pitch; a plurality of pivotally connected struts; a system of interconnected chain gears; a system of linear rack gears interconnected by at least one pinion; a system of three slidable tubes and a rotatable tube; and a system of interlinked pulleys.
19. The apparatus of any one of claims 1 to 9, wherein the positioning means comprises a pneumatic and/or hydraulic linkage.
20. The apparatus of any one of claims 1 to 9, wherein the positioning means comprises a sensor and an electronic drive device for moving the second loading point.

-22 -
21. The apparatus of any preceding claim, wherein the loading means comprises a gas strut.
22. The apparatus of any preceding claim, wherein the loading means comprises a counterweight.
23. The apparatus of any preceding claim, wherein the loading means is mounted on a carriage arranged to maintain vertical alignment between the loading means and the second loading point.
24. The apparatus of any preceding claim, wherein the extensible arm comprises: a central portion having the pivot; a first arm portion having the first loading point; and a second arm portion having the second loading point, wherein: the central portion is hollow and the first and second portions are slidable axially relative to the central portion; or the first and second portions are hollow and the central portion is slidable axially relative to the first and/or second portions.
25. The apparatus of ciaim 24, further comprising a rotatable tube, arranged to rotate relative to each of the first, second, and central portions, wherein: the rotatabie tube is arranged to slide axiaily relative to the central portion when rotated relative to the central portion; -23 -the rotatable tube is arranged to slide axially relative to the first portion when rotated relative to the first portion; and the rotatable tube is arranged to slide axially relative to the second portion when rotated relative to the second portion.
26. The apparatus of any preceding claim, wherein the pivot is located on the arm between the first and second loading points.
27. The apparatus of any preceding claim, wherein the seoond loading point is located on the arm between the pivot and the first loading point. :is
28. The apparatus of any preceding claim, further oomprising a load mounted to the first loading point, wherein the load is one or more of: a display devioe; a work surface; a light;a tablet computer;a camera; a microphone; a keyboard; and/or a speaker.
29. The apparatus of any preceding claim, wherein the positioning means is arranged to move the second loading point.

-24 -
30. The apparatus of any preceding claim, wherein the positioning means is arranged to move the pivot.
31. An apparatus as hereinbefore described with reference to the drawings.Amendments to the claims have been filed as follows CLAIMS: 1. Apparatus for supporting a load, comprising an extensible arm having a pivot and a first loading point, wherein the arm is extensible so as to have a variable length, thereby allowing the first loading point to move relative to the pivot, wherein the arm comprises a second loading point, the apparatus further comprising: positioning means arranged to set a distance between the second loading point and the pivot in dependence upon a distance between the first loading point and the pivot; and loading means for applying a counter-load to the second loading point. L52. The apparatus of claim 1, wherein the positioning means is arranged such that the torgue applied about the pivot by O the loading means varies in proportion to an extension of the arm.3. The apparatus of claim 1 or claim 2, wherein the positioning means is arranged such that the distance between the second loading point and the pivot is a function of the distance between the first lcading point and the pivot.4. The apparatus of claim 3, wherein the positioning means is arranged such that the distance between the second loading point and the pivot is proportional to the distance between the first loading point and the pivot.5. The apparatus of any preoeding olaim, wherein the loading means Is arranged to apply a constant vertical counter-loading force to the second loading point.6. The apparatus of claim 5, wherein: a load is mounted to the first loading point; and the positioning means is arranged such that the ratio between the distance between the second loading point and the pivot and the distance between the first loading point and the pivot is egual to the ratio between the force on the first loading point due to the weight of the load and the constant vertical counter-loading force.7. The apparatus of any preceding claim, wherein the loading means comprises a constant force spring.8. The apparatus of claim 3, wherein: O the loading means comprises a resilient member; and the positioning means is arranged such that the distance between the second loading point and the pivot is related to the distance between the first loading point and the pivot by a function based upon material properties of the resilient member.9. The apparatus of claim 8, wherein the resilient member is a spring, and the function is based upon a spring function of the spring.10. The apparatus of any preceding claim, wherein: the positioning means comprises a first threaded section meshing with a driving connector and a second threaded section meshing with a driven connector; the apparatus is arranged such that extension or shortening of the arm moves the first loading point thereby translating the driven connector along the first threaded section and causing the first threaded section to rotate; and rotation of the first threaded section causes the second threaded section to rotate and thereby drives the driven connector to translate along the second threaded section thereby moving the second loading point.11. The apparatus of claim 10, wherein the first and second threaded sections are formed on a single threaded member.12. The apparatus of claim 10 or claim 11, wherein a pitch of the first threaded section differs from a pitch of the second threaded section.13. The apparatus of one of claims 10 to 12, wherein: the first threaded section meshes with the driving connector via a first bearing; the first bearing comprises a cage holding a plurality of balls; and the balls are arranged along a helical path corresponding to the thread of the first threaded section.14. The apparatus of one of claims 10 to 13, wherein: the second threaded seotion meshes with the driven connector via a second bearing; the second bearing comprises a cage holding a plurality of balls; and the balls are arranged along a helical path corresponding to the thread cf the second threaded section.15. The apparatus of one of claims 10 to 14, wherein a pitch of at least one of the first threaded section and the second threaded section varies along its length.16. The apparatus of claim 15, wherein the pitch of at least one of the first threaded section and the second threaded section varies along its length so that the torque applied about the pivot by the loading means varies in proportion to the extension of the arm.17. The apparatus of any preceding claim, wherein the positioning means comprises a mechanical linkage.18. The apparatus of claim 17, wherein the mechanical linkage comprises one or more of: at least two threaded members of differing pitch; Ca plurality of pivotally connected struts; a system of interconneoted chain gears; a system of linear rack gears interconnected by at least one pinion; a system of three slidable tubes and a rotatable tube; and a system of interlinked pulleys.19. The apparatus of any one of claims 1 to 9, wherein the positioning means comprises a pneumatic and/or hydraulic linkage.20. The apparatus of any one of claims 1 to 9, wherein the positioning means comprises a sensor and an electronic drive device for moving the second loading point.21. The apparatus of any preceding claim, wherein the loading means comprises a gas strut.22. The apparatus of any preceding claim, wherein the loading means comprises a counterweight.23. The apparatus of any preceding claim, wherein the loading means is mounted on a carriage arranged to maintain vertical alignment between the loading means and the second loading point.24. The apparatus of any preceding claim, wherein the extensible arm comprises: a central portion having the pivot; a first arm portion having the first loading point; and a second arm portion having the second loading point, O wherein: the central portion is hollow and the first and second portions are slidable axially relative to the central portion; or the first and second portions are hollow and the central portion is slidable axially relative to the first and/or second portions.25. The apparatus of claim 24, further comprising a rotatable tube, arranged to rotate relative to each of the first, second, and central portions, wherein: the rotatable tube is arranged to slide axially relative to the central portion when rotated relative to the central portion; the rotatable tube is arranged to slide axially relative to the first portion when rotated relative to the first portion; and the rotatable tube is arranged to slide axially relative to the second portion when rotated relative to the second portion.26. The apparatus of any preceding claim, wherein the pivot is located on the arm between the first and second loading points.27. The apparatus of any preceding claim, wherein the seoond loading point is located on the arm between the pivot and the first loading point.I'-:is 28. The apparatus of any preceding claim, further comprising a load mounted to the first loading point, wherein the load is one or more of: a display device; a work surface; a light;a tablet computer;a camera; a microphone; a keyboard; and/or a speaker.29. The apparatus of any preceding claim, wherein the positioning means is arranged to move the second loading point.30. The apparatus of any preoeding claim, wherein the positioning means is arranged to move the pivot.31. An apparatus as hereinbefore described with reference to the drawings.5sI2576 JAS NXP1