GB2294874A

GB2294874A - Support

Info

Publication number: GB2294874A
Application number: GB9522082A
Authority: GB
Inventors: Gary Johnson
Original assignee: GRORUD ENG Ltd
Current assignee: GRORUD ENG Ltd
Priority date: 1994-11-10
Filing date: 1995-10-27
Publication date: 1996-05-15
Anticipated expiration: 2015-10-27
Also published as: GB2320891B; GB9522082D0; GB2320891A; GB2294874B; GB9807347D0

Abstract

A support for a computer monitor or the like has a base 10, a lift arm 11 pivotally mounted on the base, and a support platform 12 pivotally mounted on the lift arm, the lift arm enclosing a linkage assembly in the form of a yoke (38) (Figure 1) having its lower end pivotally mounted to a crank 16 on the base at a position spaced from the pivotal connection of the lift arm to the base. A rotatable screw shaft 26 is threadedly engaged with a bush 31 engaged between the yoke sides (36), (37) (Figure 1) at the upper end of the yoke, and actuation of an operating knob 27 on the shaft 26 in one direction draws the bush and yoke towards it, thereby producing a turning moment on the lift arm 11 causing it to rise. The lift arm self locks at any selected height. Means are also provided for maintaining the attitude of the support platform 12 as the height of the lift arm is adjusted, and the linkage assembly is designed to be retained in position at the lift arm without fastening means. <IMAGE>

Description

SUPPORT This invention relates to a support, particularly in the form of a stand of adjustable height suitable for carrying a computer monitor or the like.

DE-B-2847135 discloses a support for a visual display unit, the support comprising a base and a boom pivotally mounted on the base. Torsion springs of large bulk are employed to support the VDU carried, in use.

No means are provided for locking the boom in its adjusted height position.

GB-B-2189210 also discloses a support for a VDU, this support being counterbalanced and incorporating a gas strut driving a lever system to raise a boom pivotally mounted on a base. A disadvantage of this support is that the inherent complexity of the internal linkages results in the boom and base unit of the support, especially widthwise, being relatively bulky. Additionally although the support has means which assists in keeping the boom in its set height position, said means does not hold down the boom when the supported equipment is removed or lifted upwards.

An object of the present invention is to provided a support which improves upon the prior art supports referred to.

According to a first aspect of the present invention, a support comprises a base, an arm, the base and arm being pivotally connected, the arm having means for carrying directly or indirectly an article to be supported, in use, the arm having adjustment means for effecting height adjustment movement of the arm between a fully lowered and a fully raised position, and the adjustment means self locking once a selected height of the arm is reached.

According to a second aspect of the present invention, a support comprises a base, an arm, the base and arm being pivotally connected, the arm having means for carrying directly or indirectly an article to be supported, in use, the arm also having adjustment means for effecting height adjustment movement of the arm between a fully lowered and a fully raised position by means of a linkage assembly fitted to the arm and translating actuation of the adjustment means, in use, into said height adjustment movement, said linkage assembly being retained in position without fastening means.

Preferably in both aspects of the invention said adjustment means is/are screw means.

Conveniently the linkage assembly comprises a yoke, opposite sides of which are retained in position in the arm for sliding movement by respective sidewalls, the sidewalls conveniently being integrally formed with the arm. By such means, fasteners are unnecessary to retain the yoke to a height adjuster pivot bush of the screw means and a hinge pin connected to lugs upstanding from the base.

Desirably said hinge pin is held captive by a shoulder thereof disposed between one of said lugs and one of the yoke sides.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a lift arm of a support of the invention, with a cover thereof removed; Figure 2 is a side view of the support, with the lift arm in cross-section and parts thereof removed for clarity, the lift arm being in a partly raised position; Figure 3 is a schematic, transverse cross-sectional view of the lift arm and its cover; Figure 4 is an exploded, perspective view of internal components of the lift arm for adjusting its height and counterbalancing the weight of an article carried by the support; Figure 5 is a perspective view of internal components of the lift arm together with a support platform of the support, the attitude of which is preserved throughout adjustment of the lift arm by said components;; Figures 6A to 6G show alternative forms of counterbalance within the lift arm; Figure 7 is a fragmentary, schematic plan view showing an alternative form of retainer of the lift arm adjustment means; Figure 8 is a fragmentary, schematic sectional side view of part of Figure 7; Figure 9 is a fragmentary, schematic plan view of alternative means of securing a hinge pin to a yolk of the lift arm; and Figures 10 to 12 show alternative forms of tie rod and crank lever of the lift arm.

The support of the present invention is shown best in Figure 2, and it can be seen that it comprises a circular base assembly 10, a lift arm 11, which can be raised and lowered relative to the base assembly, and a support platform 12 carried on the lift arm at a position remote from the connection of the lift arm to the base assembly. The actual configuration of the support platform can be varied as required, for example to mount a spherical or radiused tilt platform which is especially suitable for attaching visual display units (VDU's) or similar monitors. However the support of the invention is not limited to use with a VDU. The support platform is formed with two downwardly facing integral lugs, one of which, 12a, is shown in Figure 5, and a pair of axially spaced, but colinear hinge pin receiving holes 12b.

As shown in Figure 2 the base assembly 10 comprises a lower platter 13 and a base 14, between which is provided a low friction slip ring 15 to permit rotation of the base 14, in use. Instead of using the ring, the platter 1 3 could be formed with an integral, upstanding circular projection of generally dome shape in cross-section, which permits rotation of the base.

At its periphery the base 14 is provided with a pair of spaced, upwardly extending lugs 16 through which, as shown in Figure 1, a plain hinge pin 1 7 extends. The lugs form a crank.

The lift arm 11, as shown in Figures 1 and 3, is of generally rectangular box form having an open top closed by a cover 18. The lift arm 11 has longer, opposite sides 19, 20 respectively and shorter opposite sides 21, 22 respectively, the lugs 16 of the base 14 extending through respective oversized slots 16a in the bottom of the lift arm 11 at a position adjacent the side 21. The underside of the lift arm is formed at its lower end with two downwardly depending integral lugs, one at each side of said lower end. One of these lugs, denoted by the numeral 23, is shown in Figure 2. These lugs pass through slots in the base 14 and are pivotally connected thereto by a hinge pin 24, or alternatively by a respective hinge pin for each lug 23. By this means the lift arm is hinged to the base about a substantially horizontal axis.It will be noted that the respective axes of pins 1 7 and 24 are spaced apart vertically and, in this example, also horizontally.

Extending inwardly from the centre of the inner surface of the side 22 is a projection 25 through which extends a threaded shaft 26. At the exterior of the side 22 the shaft 26 is formed with a manually operable adjustment knob 27. Between the knob and the side 22 is a front bearing 28. A rear bearing 29 is provided on the shaft 26 between the projection 25 and a retainer 30 which holds the shaft captive longitudinally. The end of the threaded shaft 26 is engaged in an internally threaded bore of a bush 31 which is of generally cylindrical formed but has stub shafts 32,33 respectively extending from its opposite ends. The retainer 30, shown schematically in Figure 1, is preferably a castle nut 30a (Figure 7), i.e. a nut with castellations at its end remote from the bearing 29. A countersunk-headed screw 30b has its shank passing through the castellated end, between a pair of castellations, and engaging in a bore through the shaft 26 (Figure 8).

The stub shafts 32, 33 engage in respective circular holes 34, 35 at the ends of spaced sides 36, 37 of a yoke 38 which constitutes a linkage assembly translating rotation of the knob 27 into raising or lowering movement of the lift arm, as will be described.

The yoke sides extend in parallel within the lift arm and at their opposite ends have further circular holes 39, 40 respectively in which opposite ends of the hinge pin 1 7 are received. As shown best in Figure 1, this hinge pin 17 is held captive by respective folded tabs 41, 42 at the ends of the yoke sides, these tabs preventing movement of the hinge pin 1 7 along its axis and thus withdrawal from the yoke sides and the lugs 16.

Alternatively, as shown in Figure 9, the hinge pin can be formed with a radial shoulder 1 7a disposed between one of the lugs 16 and an adjacent yoke side, in the example illustrated side 37, the shoulder being sized to engage said lug or said yoke side upon axial pin movement, and thus retain the pin in place. The tabs 41, 42 can thus be omitted. In either arrangement two pivot pins, one for each yoke side and lug, could instead be used.

The yoke is retained against lateral movement within the lift arm 11 by two parallel spaced retaining sides walls 43, 44 respectively closely alongside the yoke sides, the side walls preferably being integrally formed with the base of the lift arm 11 and being normal thereto as shown in Figure 3, each wall extending to lie substantially flush with the top of the yoke side, or at least extending above the stub shafts 32, 33.

As shown in Figure 1, each side wall can be formed with guide means 45 along its length, extending inwardly to guide sliding movement of the yoke sides as will be described. The number and arrangement of guide means can be varied as required. The side walls prevent the yoke sides disengaging from the stub shafts 32, 33.

Also upstanding from the base of the lift arm 11, and extending centrally between the side walls 43, 44, is a rib 46 which provides an upstanding pivot post 47 and, at its one end, a nest 48 for gas strut retention as will be described.

When equipment of appreciable weight is to be carried by the support, it is desirable to counterbalance this weight, to minimise the turning force required to rotate the height adjustment knob 27. A gas strut is a convenient space effective way of providing this counterbalancing force, and by careful calculation of the internal linkages of the apparatus, and knowing the mass and centre of gravity position of the equipment to be supported, a gas strut can in most applications be specified to match very closely the theoretical forces within a useful range of lift arm adjustment.

A gas strut is therefore preferable for the present invention, but this does not exclude the use of helical coil springs, spring washers, and the like, either in series with the gas strut or on their own, to provide the correct counterbalancing forces. Accordingly although one form of gas strut is shown in Figures 1, 2 and 4, any of the arrangements shown in Figures 6A to 6G could be satisfactorily used. With the correct provision of the counterbalancing force, the apparatus can be essentially in equilibrium when the equipment is attached to the apparatus.

Figure 1 shows a gas strut 49 with its rod 50 mounted to the nest 48, the body of the gas strut itself lying between the yoke sides and having its opposite end in the form of a threaded shaft 51 which engages in a complementarily threaded bore through a cylindrical bush 52 of identical form to the bush 31, stub shafts extending from the end of the cylindrical part of the bush 52 engaging in respective circular holes in the sides of the yoke in the same manner as described for the shafts 32, 33 and holes 34, 35. The side walls 43, 44 prevent the yolk sides disengaging from the stub shafts of bush 52.It will be appreciated that when the lift arm is moved from its fully raised to its fully lowered position, to be described, the yoke, which carries one end of the gas strut via the bush 52, travels towards the nest 48 so that there is further compression of the gas strut, since in this embodiment the gas is compressed even when the strut is in its fully extended state. As the force required to support the equipment increases as the lift arm is lowered, a gas strut or compression spring is ideal for this application. A skilled person can calculate the change in force, namely the 'spring rate' required over the whole range of lift arm adjustment and then specify the correct strut, spring or combination thereof.

In many applications using the support of the present invention, it is desirable to preserve the attitude of the attached equipment throughout the complete range of height adjustment. In the embodiment shown in the drawings, parallel motion of the support platform 12 is achieved by the use of a crank lever 53 as will now be described.

As shown in Figures 1 and 5, the crank lever 53 is pivoted at its centre on the pivot post 47, preferably by screw means. Extending outwardly from the top of the yoke side 37 is a horizontal lug 54 to which one end of the crank lever 53 is drivingly connected so that when the yoke slides, the crank lever 53 is pivoted on the post 47. The other end of the crank lever 53 is pivotally connected to a tie rod 55, which, as shown in Figure 1, extends parallel to the side wall 43 at the opposite thereof from the yoke side 36. This tie rod is formed at its end remote from the crank lever 53 with an upstanding hook 56 which is disposed between the lugs 12a, a connecting rod 57 extending through the lugs 12a and through the hook 56. An alternative form of tie rod and connection to platform 12 will be described in relation to Figure 10, hereinafter.

At its upper end, the lift arm has two upward facing lugs (one of which is shown at 58), which pass through slots (not shown) in the support platform 12. By means of these lugs the support platform is hinged to the lift arm about a pivot pin 59 through said lugs and holes 12b, the axis of the pin 59 being parallel to but spaced from the axis of rod 57. If the crank lever 53 is of symmetrical dimensions, then the distance between the hinge pins 17 and 24, and the distance between the rod 57 and pin 59 must be identical. Non-parallel motion could be provided by changing the dimensions previously described for parallel motion of the support platform.

Operation, in use of the various functions of the support will now be described.

One advantage of the support of the present invention over prior art arrangements is that the self locking screw system for height adjustment of the lift arm enables the support be shipped to users in the 'down' position, thereby enabling significantly lower transport costs to be achieved. Additionally when the support is installed on site, for example in office environment where a VDU is attached, the height adjustment can be set to the lowest position and the combination can be easily relocated to another office without the lift arm extending, and without the need for a special locking operation. It will be appreciated that in fact, in the described embodiment, the arm is effectively always in a 'locked' position, even during each part of its adjustment movement, by virtue of the interengagement of the complementary threads.

As briefly described above, raising and lowering of the lift arm is accomplished by manually rotating the adjustment knob 27. Since this knob is held captive longitudinally by the retainer 30, rotation of the knob in one direction draws the bush 31 along the threaded shaft 26 towards the retainer, this movement of the bush being transmitted to the yoke by virtue of the stub shafts 32, 33 engaging with the sides of the yoke. The rotation of the knob thus pulls the yoke towards it. As the centre of the hinge pin 1 7 is considerably offset (by distance "X") from the hinge pin 24, this movement of the yoke exerts a biasing force which causes a turning moment on the lift arm which forces it upwardly.

Reversing the direction of actuation of the adjustment knob 27 results in the lift arm being lowered. The maximum angle through which the lift arm can rise can be set as required, with a normal maximum being less than 90 .

The provision of the bearings 28 and 29 at opposite sides of the knob/shaft assembly significantly lowers the effort required by a user turning the knob where appreciable loads need to be supported by the lift arm. Similarly a low friction bearing material is beneficial, though not essential, as the material of the bush 31.

The counterbalancing effect of the gas strut 49 has already been referred to in detail and it thus suffices to say that when the yoke moves towards the retainer 30 as described, the bush 52 is also moved in that direction thereby moving the body of the gas strut 49 relative to its associated piston head inside it (Figure 6A) so that the gas strut is in an extended position. However as described when the knob is moved in the opposite direction to lower the lift arm, the body of the gas strut 49 moves in the opposite direction thereby further to compress gas between the piston head and its end adjacent the threaded shaft 51 so that the gas strut provides the necessary counterbalancing force.

Figure 6B shows a first alternative arrangement for providing a counterbalancing force, in the form of a gas strut with an internal helical spring. Figure 6C shows a second alternative in the form of a gas strut with internal disc springs, whilst Figure 6D shows an alternative in the form of a gas strut with an external helical spring, a gas strut with external disc springs being shown in Figure 6E. Finally Figure 6F shows the use of a helical spring only and Figure 6G shows the use of disc springs only. However as will be appreciated various other alternative arrangements for providing the counterbalancing force could be provided.

As far as the preservation of the attitude of the attached equipment throughout the complete range of height adjustment of the lift arm is concerned, this has also previously been referred to and again it thus suffices to mention that as the yoke slides in the lift arm upon actuation of the knob 27, the crank lever 53 is pivoted in either a clockwise or anti-clockwise direction thereby either pulling or pushing the tie rod 55 thereby tilting the support platform into the horizontal by virtue of hook 56 and pivot pin 57. Thus the platform remains parallel to the base regardless of the lift arm position.

As well as the advantage of the stand of the present invention over the prior art in relation to ease of transportation, it is noted that the screw system inherently provides self-locking for the height adjustment of the lift arm, by virtue of the engagement of the shaft 26 with the bush 31.

Accordingly the arm will not easily collapse when additional loads are applied to the attached equipment. As explained, the provision of the counterbalancing force is to minimise the turning force required to rotate the height adjustment knob and is not necessarily to prevent such collapse of the arm. Instead of screw means for effecting movement of the arm, any suitable alternative means could be used, for example linear movement devices. In all cases the means are preferably manually actuable by an operator, but they could be controlled automatically and/or remotely, for example by an electronic control.

The yoke provides a very compact way of linking the gas strut or equivalent counterbalancing means to the height and parallel motion linkage, thereby significantly reducing the external dimensions, and thus the cost, of the support. In particular the narrower lift arm possible with this yoke arrangement is superior to the wider arms of said prior art stands both in terms of appearance and manufacturing cost.

As can be appreciated from Figures 1 and 4, the yoke is retained onto the bushes 31 and 52 and the hinge pin 17 and base lugs 16 merely by the provision of the two sides walls 43, 44, which can, as stated, be an integral part of the lift arm. The result is that there is no need for any fasteners, such as clips, screws, etc., in that the means for translating the actuation of the knob into adjustment movement of the lift arm is a selfcontained unit retained in position only by said side walls. It can be seen that the hinge pin 1 7 connecting the yoke to the lugs 1 6 is held captive by the two folded over tabs 41, 42 incorporated in the yoke sides, or by the use of the shoulder 1 7a on the hinge pin 17, with any fastening elements thus being eliminated.

It will be appreciated that although a balanced mechanism is provided by two links forming the yoke, a single link could instead be used, thereby also obviating the need for two side walls upstanding from the base of the lift arm. Moreover it will be appreciated that the support need not have any counterbalancing means, and/or any means for keeping the support platform parallel to the base. Instead of the support platform being a separate component attached to the lift arm for receiving the article to be supported, it could be an integral part of the housing of the article, so that, in use, the article is connected directly to the lift arm.

An alternative to the base assembly 10 is a base in the form of a fixed clamp for attachment to a desk or similar worktable. The clamp would function in the same manner as the base by providing lugs 16, and hinge points 17 and 24.

Figures 10 to 12 illustrate the use of possible alternative forms of tie rod 55 and crank lever 53.

As shown in Figure 10, the alternative tie rod 55a is twisted through 90" approximately half way along its length. In this way its ends for connection to the support platform lugs 12a and crank lever respectively are in the correct orientations. The hook 56 is thus eliminated, being replaced by the connecting rod 57 merely passing through a circular hole 56a in the tie rod end.

The crank lever 53 can be replaced by an alternative form of crank lever 53a. The end of the crank lever 53a adjacent side wall 43 is still pivotally connected to the tie rod by a screw, denoted by reference numeral 60, and the crank lever is still pivoted on post 47 by a screw, denoted by reference numeral 61. The other end of the crank lever 53a has a rectangular crank slot 62 therein, extending lengthwise of the lever.

The lug 54 is enlarged to form a platform 54a. The driving connection from the yoke to the crank lever 53a is provided by a stud 63 upstanding through a hole in the platform 54a and held by a lockwasher 64 and nut 65 on its lower threaded end.

A slider bush 66 is a close fit on the stud 63. The bush has a short cylindrical base part on the platform 54a, with parallel flats 67 being formed on opposite sides of the bush over the remainder of its length.

The flats are spaced apart by a distance just less than the width of the crank slot 62, so that flanges 68 formed by the base part outward of the flats prevent the bush from rising through the crank slot when the part of the bush with the flats thereon is received in the slot 62 as a sliding fit along the length of the slot. By virtue of the bush sliding along the slot 62, yoke movement is converted, in use, into crank angular movement and thus into pushing or pulling movement on the tie rod to retain the support platform in a horizontal orientation.

Claims

1. A support comprising a base, an arm, the base and arm being pivotally connected, the arm having means for carrying directly or indirectly an article to be supported, in use, the arm having adjustment means for effecting height adjustment movement of the arm between a fully lowered and a fully raised position, and the adjustment means self locking once a selected height of the arm is reached.

2. A support as claimed in Claim 1, wherein a linkage assembly fitted to the arm translates actuation of the adjustment means, in use, into said height adjustment movement.

3. A support as claimed in Claim 2, wherein said arm is connected to said base at a first pivot, and said linkage is connected to said base at a second pivot, the first and second pivots being parallel, but spaced apart.

4. A support as claimed in Claim 3, wherein the first and second pivots are relatively offset both vertically and horizontally, when said base is in a horizontal plane.

5. A support as claimed in Claim 3 or Claim 4, wherein the second pivot is formed by a crank extending from the base.

6. A support as claimed in any one of Claims 3 to 5, wherein the linkage includes an element having a first end connected to said second pivot, which second pivot is at the lower end of the arm when it raised, in use, and a second end which is connected to said adjustment means, which extend to the upper end of the arm, the spacing apart of the first and second pivots being such that actuation of the adjustment means pulls or pushes said element, thereby exerting a biasing force which causes a turning movement on the arm to raise or lower the arm respectively.

7. A support as claimed in Claim 6, wherein the element is a yoke having opposite sides connected at their respective lower ends to said second pivot, and connected together at their respective upper ends by a bush disposed therebetween, the bush being engaged by a screw thread of said adjustment means, whereupon actuation of the adjustment means effects rotation of the screw thread to move the bush to pull or push the yoke, according to the direction of screw thread rotation.

8. A support as claimed in Claim 7, wherein an adjustment knob is disposed at an outer surface of the arm, the knob being on a shaft which provides said screw thread, said shaft having retaining means thereon to prevent axial movement of the shaft upon rotation of said adjustment knob, in use.

9. A support as claimed in Claim 7 or Claim 8, wherein counterbalancing means is connected to said yoke.

10. A support as claimed in Claim 9, wherein the counterbalancing means is a telescopic assembly having at one end a rod engaged against part of the arm and at its other end a relatively slidable part connected to the yoke, so that, in use, the counterbalancing force increases as the arm is lowered.

11. A support as claimed in Claim 9 or Claim 10, wherein the counterbalancing means is a gas strut.

12. A support as claimed in any one of Claims 7 to 11, wherein the arm has means for maintaining the attitude of said article, in use, throughout the range of height adjustment of the arm.

13. A support as claimed in Claim 12, wherein a support platform for said article is connected to said arm at a first pivot, and to a tie rod at a second pivot, the tie rod moving, in use, in response to movement of said yoke, and said first and second pivots for the support platform being parallel, but spaced apart.

14. A support as claimed in Claim 13, wherein the tie rod is pivotally connected at a position spaced from its connection to the support platform to one end of a lever pivotally mounted to the arm, the other end of the lever being pivotally mounted to a side of the yoke, so that pulling or pushing of the yoke is translated by said lever into movement of said the rod, such tie rod movement causing a pivoting of the support platform to maintain its attitude upon raising or lowering of the arm.

15. A support as claimed in Claim 13 or Claim 14, wherein the distance between the first and second pivots for the support platform is equal to the distance between the first and second pivots for the base.

16. A support as claimed in any one of Claims 7 to 15, wherein the yoke is retained against lateral movement by means of spaced retaining side walls at respective opposite sides of the yoke sides.

17. A support as claimed in Claim 16, wherein the retaining side walls have guide means to guide sliding movement of the yoke sides, in use.

18. A support comprising a base, an arm, the base and arm being pivotally connected, the arm having means for carrying directly or indirectly an article to be supported, in use, the arm also having adjustment means for effecting height adjustment movement of the arm between a fully lowered and a fully raised position by means of a linkage assembly fitted to the arm and translating actuation of the adjustment means, in use, into said height adjustment movement, said linkage assembly being retained in position without fastening means.

19. A support as claimed in Claim 18, wherein at the end of the arm which is lowermost, in use, when the arm is raised, said linkage is pivotally mounted to the base.

20. A support as claimed in Claim 19, wherein at a position remote from its connection to the base, the linkage is connected to said adjustment means, actuation of which effects pulling or pushing of said linkage.

21. A support as claimed in any one of Claims 18 to 20, wherein the linkage is a yoke having opposite sides pivotally connected at their respective lower ends to respective lugs upstanding from the base, a pivot pin extending through at least one of said lugs and its adjacent yoke side having an abutment thereon disposed between the one lug and adjacent yoke side, to retain the pivot pin captive with the lug and yoke side.

22. A support as claimed in Claim 21, wherein at a position remote from their respective lower ends, the yoke sides are connected together by a bush disposed therebetween, the bush having stub shafts at its respective opposite ends received through the respective yoke sides, respective retaining side walls being disposed at respective opposite ends of the stub shafts to prevent disengagement of the yoke sides therefrom.

23. A support as claimed in Claim 22, wherein the retaining side walls serve to guide movement of the yoke sides respectively when the arm is raised or lowered.

24. A support as claimed in Claim 22 or Claim 23, wherein said adjustment means includes a screw-threaded shaft engaged with a screw thread in a bore through the bush having said stub shafts.

25. A support as claimed in any one of Claims 22 to 24, wherein a further bush is connected between the yoke sides by respective further stub shafts at its respective opposite ends received through the yoke sides, the retaining side walls preventing disengagement of the yoke sides from said further stub shaft respectively, the further bush being connected to counterbalancing means received between the yoke sides, and having an end rod engaging part of the arm.

26. A support substantially as hereinbefore described, with reference to, and as shown in the accompanying drawings.