GB2294632A

GB2294632A - Lift arms with gas struts

Info

Publication number: GB2294632A
Application number: GB9421186A
Authority: GB
Inventors: Peter Bosson
Original assignee: Colebrook Bosson Saunders Products Ltd
Current assignee: Colebrook Bosson Saunders Products Ltd
Priority date: 1994-10-20
Filing date: 1994-10-20
Publication date: 1996-05-08
Also published as: GB9421186D0

Abstract

Gas lift arms are provided in which the gas strut 14 is substantially uncompressed when the arm is at the fully raised position. The strut 14 is compressible by lowering of the arm. The arrangement permits ease of manufacture and ease of gas strut replacement because it is unnecessary to compress the gas strut 14 before attachment to the arm. Such gas lift arms are suitable for the support and movement of equipment, for example to hold computers or other office equipment clear of office desk surfaces. <IMAGE>

Description

IMPROVEMENTS TO GAS LIFT ARMS The invention relates to gas lift arms for the support and movement of heavy equipment or parts thereof and especially to arms for the support of computer and other desk equipment in the office environment.

It is known to provide platforms and movable arms for the support of computer monitors, keyboards etc. above a desk to free the desk working surface for other office equipment and papers. Such arms commonly have a desk fixing plate or base pivotably connected to the lower end of the movable arm which can be raised and lowered, commonly through about 450, between a substantially horizontal position and a raised position. The desk equipment is affixed to the other end of the raisable arm.

In order that the arm may be easily raised and lowered despite the weight of the desk equipment it carries, and that it may remain in stable equilibrium at any given point between the fully raised and fully lowered positions, such arms have commonly been fitted with a compressed gas strut, which is a piston movable in a sealed bore containing a pressurised gas.

Lowering the movable arm pushes the piston into the bore and further compresses the gas. This increases the resistance to further lowering of the arm.

Gas struts have been incorporated into other lifting apparatus in other manufactured products and throughout industry. A common example is the use in the support struts of the rear doors in estate and hatchback cars to ease the raising and lowering of the door.

Because of the highly pressurised gas in the gas struts, insertion and replacement of struts is a difficult task requiring compression of the struts by machine. The forces required to compress a strut for insertion into a lifting arm, by forcing the piston into the gas-containing bore, are such that the operation cannot be performed by hand.

According to the present invention, there is provided a gas lift arm comprising a gas strut compressable by lowering of the arm, wherein the gas strut is substantially uncompressed when the arm is at the fully raised position.

In a second aspect, the invention also provides a method of manufacturing a gas lift arm comprising placing the arm in the raised position and securing a substantially uncompressed gas strut to the arm such that lowering of the arm compresses the gas strut. In this method there is no need for the gas strut to be compressed by a machine, and held in a compressed state while being inserted into the structure of the arm, resulting in a much simplified manufacturing process.

In preferred embodiments, the end of the gas lift arm on which the equipment to be supported is mounted has a hinged portion which may be opened away from the main body of the arm to allow insertion and removal of the gas strut. In gas lift arms according to the invention, the gas strut is essentially uncompressed when the arm is at its fully raised position, but the arm can still support the weight of equipment mounted thereon.

Gas lift arms according to the invention have the further advantage that, should a gas strut need replacement, this can be done by raising the arm to the fully raised position, unhinging the top portion of the arm, removing the old strut and inserting a new one.

This operation can be performed simply and easily without having to return the arm to the factory, as is necessary with conventional arms which require mechanical compression of the new strut.

Embodiments of the invention will now be described in further detail, by way of example only, with reference to the following drawings in which: Fig 1(a) is a plan view of a gas lift arm embodying the invention; Fig l(b) is a side elevation of the arm of Fig 1 (a) Fig 2 is a cross-section taken along line A-A of Fig 1 (a) Fig 3 is an end elevation of the arm of Fig 1; Fig 4.is a cross-section taken along line B-B of Fig 2; Fig 5Fa) is a plan view of a second embodiment, to a reduced scale; Fig 5(b) is a side elevation of the embodiment of Fig 5(a); Fig 6 is a cross-section taken along line A-A of Fig 5(a); Fig 7 is an end elevation of the arm of Fig 5, to an increased scale;; Fig 8 'is a cross-section taken along line B-B of Fig 6; and Fig 9 shows the arm of Figs 1 to 4 in a raised position.

The gas lift arms illustrated are intended for the mounting of a computer monitor and/or keyboard above a desk. They then extend horizontally over the desk and have a desk fixing, such as a screw-in base at one end of the lifting member 2. The lower surface 1 of a fixed support portion 3 is screw-fitted to a desk using threaded bore 5, and secured with a grub-screw 7.

The lifting member 2 is pivotably attached to an anchor block 9 rotatably mounted upon the fixed support portion 3 and, at its other end, the lifting member 2 is pivotably affixed to a platform 4 upon which e.g.

computer equipment may be mounted. In some embodiments, the fixed support portion 3 and the anchor block 9 may be separated by a pillar, to give increased height. The anchor block 9, rotatably mounted upon the fixed support portion 3, moves upon a swivel washer 29.

At the top end of the lifting member 2 an end member 8 is mounted upon a hinge pin 12 and rests upon pin 10, being held in place by screw 15. When screw 15 is unfastened, the end member 8 may be swung clear of the end of the lifting member 2, about the hinge 12, to allow access to the gas strut 14 within the lifting member 2.

The body of the lifting member 2 is closed by a face plate 24 which extends over most of the length of the lifting member 2. Inside the lifting member 2 and generally parallel to the face plate 24 is a link plate 26 which is pivotably affixed at either end 10,21 to provide one member of a parallelogram linkage, the four pivots of which are provided by the link plate pivots 21 and 10 and the two main pivot points of the lifting member 2 (pin 25 where the lifting member 2 is attached to the anchor block 9 and pin 12 by which the lifting member 2 is pivotably attached to the end member 8 of the arm).

The gas strut 14 is mounted at an angle within the lifting member 2. At the lower, piston end 16 of the strut 14, the open fork 20 is placed over bar 18, with no further means of fixing. The upper, bore end 22 of the gas strut 14 is fixed, by a pin 11 through a flange 13 attached to the strut, to the inside of the lifting member 2. The hinged member 8 is then closed back over the upper end of the lifting member 2 and secured by fixing 10. No pre-compression of the strut is required and, because of the simple fork 20 and bar 18 arrangement at the piston end 16, the strut 14 can simply be lifted clear of the lifting member 2 for replacement.

As the lifting member 2 is raised, pivoting on the anchor portion 9 at pin 25, the upper end of 22 of the gas strut 14 remains fixed to the lifting member 2, held by pin 11 about which the flange 13 pivots.

Because of the parallel linkage, the strut 14 is extended as the arm moves away from the horizontal, and compressed as it returns to the horizontal. The platform 4, fixed to the end member 8, remains horizontal as the lifting member 2 is raised and lowered, because of the parallel linkage. It pivots about fixing 12, the lower end of the end member 8 being pivotably affixed by pin 10, through link pin 37 to the link plate 26.

The lifting member 2, at its fully raised position, can take the weight of the computer equipment which is to be mounted on the platform by lowering slightly, so that the strut 14 is slightly compressed, increasing the pressure of the gas in the gas strut 14, and thereby increasing the resistance to lowering of the arm. Thus the fully raised position of the lifting member 2 bearing its load is slightly lower than the fully raised position in the unloaded state.

In order to compensate for different weights of equipment being placed on the platform, the position of the piston end 16 of the gas strut 14 is movable, vertically, by rotation of screw 30. The bar 18 which secures the piston end 16 of the gas strut 14 is affixed to a threaded collar 34 which surrounds the screw 30. Rotation of the screw moves the collar vertically by a worm gear action, to raise the bar 18 and therefore the piston end 16 of the gas strut 14.

When the collar 34 is at the upper extreme of its range (defined by cavity 32 in which it is retained), the gas strut 14 is compressed relative to when the collar 34 is at the lowest extreme of its range, and the arm is at the same angle (compare Figs 2 and 6). Also, the angle of the strut 14 to the lifting member 2 is increased as the collar 34 is lowered. Thus when the collar 34 is at its lowest position, the angle of the force transmitted through the strut is more nearly vertical, and the tendency to raise the arm to its fully raised position is greater. It follows that, by lowering the collar 34, the lifting member 2 can be made to support heavier weight than when the collar 34 is in the upper position.

Once the gas strut 14 has been inserted, the loaded arm may be raised and lowered to any position between horizontal and the fully raised position, and will be stable in any position between those two extremes. Travel beyond the horizontal can be prevented by a physical stop. The stability is ensured because the moment of the force from the weight of the arm and the load it bears is balanced by the force generated by the strut 14. Where the force profile of the strut is not constant throughout its stroke, the friction at the joints of the arm can be set to ensure stability at the intermediate positions.

Should any problem arise with the gas strut 14, replacement is simple and can be carried out by hand.

With the lifting member 2 unloaded and in the fully raised position, the hinged portion 8 is swung clear, the strut 14 removed and replaced with a new strut.

Re-fixing of the hinged portion 8 leaves the arm ready for loading and use.

The second illustrated embodiment of the invention (Figs 5 to 8) functions, as described above, in the same way as the first embodiment. The second embodiment differs, however, in having a further link 40,42,44 between the top of the lifting member 2 and the platform 4. This link allows movement of the platform 4 relative to the lifting member 2 in a horizontal plane, pivoted about pins 41 and 43. In both embodiments the platform is mounted upon a portion 8 or 44 having a cavity 45 in its underside, to reduce the weight of the overall structure. The size and shape etc of the platform can be varied depending on the equipment which is to be mounted thereon.

Claims

CLAIMS:

1. A gas lift arm comprising a gas strut compressible by lowering of the arm, wherein the gas strut is substantially uncompressed when the arm is in a fully raised position.

2. A gas lift arm according to claim 1 further comprising a hinged portion bearing an attachment site for equipment to be mounted upon the arm, wherein the arm is openable by movement of the hinged portion to allow insertion and removal of the gas strut.

3. A gas lift arm according to claim 2 wherein the hinged portion comprises a platform adapted and arranged to receive equipment to be supported on the gas lift arm.

4. A gas lift arm according to any preceding claim further comprising a fixing member by which the gas lift arm is anchorable.

5. A gas lift arm according to claim 4 wherein the fixing member is rotatably mounted upon the lower end of the lifting member of the arm.

6. A gas lift arm according to any preceding claim wherein a main lifting member of the arm comprises a parallel linkage to allow equipment mounted upon the arm to remain at a constant angle during raising and lowering of the arm.

7. A gas lift arm according to any preceding claim further comprising means to alter the compression of the gas strut for a given position of the arm to compensate for different loads.

8. A gas lift arm according to claim 7 wherein the means to alter the compression of the gas strut comprises a rotatable member in threaded engagement with a gas strut support member.

9. A gas lift arm for the support of equipment clear of a surface, the arm comprising a foot portion, a equipment support portion and a lifting member pivotally mounted upon the foot portion and upon the equipment support portion to provide a parallel linkage therebetween, wherein; the foot portion comprises a base by which the gas lift arm may be fixed to a surface and an anchor portion rotatably mounted upon the base to allow rotational movement of the gas lift arm; the lifting member comprises a gas strut; and the equipment support portion comprises means for attachment of equipment to be carried upon the gas lift arm; the arrangement being such that, when the gas lift arm is in a fully raised position, the gas strut is substantially uncompressed.

10. A method of manufacturing a gas lift arm comprising placing the arm in a raised position and securing a substantially uncompressed gas strut to the arm such that lowering of the arm compresses the gas strut.

11. A gas lift arm substantially as described herein with reference to and as illustrated in Figs. 1 to 4 or 5 to 9 of the accompanying drawings.