GB2235370A - Height adjustment mechanism - Google Patents

Abstract

A height adjustment mechanism for an article of furniture, such as a chair, comprises two slidably engaged members (3, 4), one of which can be raised or lowered relative to the other in order to change the height of the article of furniture, such movement being controlled by means of a constant force spring (8) fixed at one end to one of the members and with the other member bearing on the coiled portion of the spring so that the spring can normally withstand the weight and bearing thereon but by the application of an external force can be forced to uncoil and thus alter the relative relationship of the two members. Means (12) are provided to enable the two members to be fixed at selected points in their slidable relationship. <IMAGE>

Description

Support Mechanism This invention relates to a support mechanism which is particularly adapted for use as the height adjustment mechanism of a variable height chair.

Variable height chairs are commonly used in offices and elsewhere. It is estimated that there are several million such chairs in the United Kingdom alone.

Conventionally, these chairs have a height adjusting mechanism which, for very many years, has depended on the use of a "gas spring". Such gas springs basically comprise a piston and pressurized gas contained within an outer cylinder. This is itself contained within a central pedestal portion of the chair. Height adjustment is achieved by operation of a laterally-extending adjustment lever which is located towards the top of the pedestal and which opens an overflow pressure valve inside the gas spring, thereby changing the position of the piston and consequently the position of the seat.

Such gas springs provide not only sufficient force to raise a chair seat (which may weigh for example from 5 to 15 kilograms) but also sufficient total force to support the combined weight of the chair seat and its occupant at the desired height. Such combined weight may be anything from 50 to 100 kilograms or even more. In order to fulfill these functions, such gas springs commonly contain a compressed gas (such as nitrogen) at a pressure of about 40 atmospheres.

In use, gas springs contained in chairs are subjected to a variety of forces in addition to the simple weight of the occupant. There are, for example, bending stresses resulting from the occupant tilting the chair in one direction or another.

In the course of time, the risk of damage to the gas cylinder increases and the mechanism may fail.

The very high pressure of the gas in the gas cylinder means that any failure is potentially very dangerous. It may lead to explosive decompression of the compressed gas, and this may cause part of the mechanism, for example the piston, to shoot out of the cylinder at high velocity. It is understood that there have been serious injuries and some fatalities resulting therefrom.

Attempts have been made to mitigate the problem, for example by providing safety clamps or other mechanisms to reduce the danger of destruction.

Alternative methods of adjusting chair seat heights have existed, including for example screw threads in a mechanism involving rotating the chair so that the seat rises or falls, and the use of powerful compressed springs.

These mechanisms have not been successful in the market place, and some of them are at least as dangerous as gas springs, while others are of a complex nature requiring high precision engineering resulting in substantial expense. For various reasons, no alternative has succeeded in competing with the gas spring in the market place, and, as previously mentioned, there are millions of chairs with such gas springs in use at present, and the great majority of new chairs having adjustable height mechanisms depend on the use of gas springs in spite of their disadvantages.

The present invention at last provides a mechanism which not only avoids the disadvantages of the gas spring but also has the required simplicity and elegance to produce a commercially acceptable alternative for the gas spring mechanism, leading at last to a real possibility of providing the public with a safe and attractive system.

Among the many advantages conferred by the invention, the following may particularly be stressed: (1) safety: unlike all mechanisms depending on gas springs, coil springs, etc., the present mechanism has no stored energy if for any reason the top is lifted off, and accordingly there is no danger to persons sitting on or near the chair.

(2) Appearance: the mechanism makes it possible to maintain a smooth pedestal style with no bulge anywhere in the pedestal.

(3) Range: the mechanism may be made suitable for all requirements of range of seat weights and range of lift needed in the market place.

(4) Simplicity of construction: the mechanism can readily be made from easily available parts and no difficult engineering operations or tolerances are required for an sufficient and long-lasting mechanism.

(5) Cost: the mechanism is relatively cheap to make and to install.

While the mechanism finds its most desirable use in chairs, where the safety factor is so important, it may also be used in other aspects of furniture construction. Thus, other items of furniture may be provided with the possibility of adjustment of height by means of the mechanism of the invention. For example, it could be incorporated in the central pedestal of a pedestal table, such that the table top may conveniently be lowered to serve as a coffee table or raised to serve as a dining table.

In its broadest aspect, the invention provides a pair of slideably engaged members and a constant force spring fixed at its open end to one of the members so that the other member bears on the coiled portion of the spring, the force of the spring being such as to withstand the weight of the member bearing thereon and of any fixed load on such member, means being provided to enable the two members to be fixed at selected points in their slideable relationship.

The force exerted by the spring should normally be equal to the weight of the member bearing on it together with any fixed load on that member.

The invention provides an item of furniture comprising a foot and a load-bearing surface connected by the said mechanism, so that the height of the surface above the foot may be adjusted by means of the mechanism. Examples of such items of furniture include tables, beds and the like.

The benefits of the invention are most significantly associated with its use in a chair.

Accordingly, the invention provides a pedestal chair comprising a seat fixed on a first member and one or more feet supporting a second member, the two members being in slideable relationship, a constant force spring fixed to one member with the other member bearing on the spring whereby the spring is capable of supporting and raising the first member and the seat (and any fixed weight attached thereto) but is not capable of supporting the first member and the seat (and any fixed weight attached thereto) if an additional downward force exceeding is applied thereto, and means for releasably locking the two members in fixed relationship to each other at a plurality of relationships within the slideable range.

Constant force springs or tensators are well known and a spring of appropriate dimensions and force can readily be selected, depending on the dimensions of the pedestal, the range of relative movement of the members, and the weight of the first member, of the seat and of any fixed weight attached thereto, such as a back rest and/or arm rests.

The means for releasably locking the members may, for example, be or comprise ratchet means, with or without a dampener means. Other means, such as a Bowden cable may be used or an overcentering cam, desirably with a felt washer.

The members may be in the form of concentric tubes, one sliding inside the other.

The constant force spring may be located within one of the tubes. For example, it may be located against the inner surface of the outer tube. That tube may serve as the second member. The spring may then be arranged so that its relatively uncoiled end is fixed in the upper part of this tube, and the spring is arranged to uncoil downwardly within this tube. The first member may be located within the second so that its lower portion, for example its lower end, bears directly or indirectly against the coiled portion of the spring, which uncoils as the first member is forced down.

It may be convenient to make the tubes of rectangular cross section (for example square cross section), as this eliminates rotatory movement and also provides a convenient space for locating the constant force spring.

Further aspects of the invention will be evident from the following description of an embodiment which is illustrated in the drawings, in which: Figure 1 is a general view of a chair embodying the invention.

Figure 2 is an elevation of the upper end of the pedestal portion of the chair shown in Figure 1.

Figure 3 is a cross section of the pedestal portion shown in Figure 2.

Figure 4 is a vertical cross section of the support system of the chair of Figure 1.

Figure 5 is a diagrammatic representation of an alternative arrangement to part of that shown in Figure 4.

In Figures 1 to 4 of the drawings, a chair seat 1 carrying a seat back 2 is borne on a member 3 of rectangular cross-section slideable within a second member 4, also of rectangular cross-section, constituting part of a pedestal section (shown generally at 5) borne on legs 6 resting on caster feet 7.

Within the member 4 is a constant force spring 8 which is fixed (for example by being bolted) at its upper end to the inner surface of the member 4; the spring 8 depends within the member 4 so that its coiled end 10 moves down as the spring 8 is unwound. Bearing as shown on the coiled portion 10 is the bevelled lower end 11 of the member 3.

The relationship between the constant upward force exerted by the coiled portion 10 of the spring 8 and the weight of the member 3 and everything fixed thereto (including the seat 1 and the backrest 2 as well as the ratchet mechanism and associated handle to be described below) is such that the former exceeds the latter by an amount equal to The above-mentioned ratchet mechanism includes conventional ratchet means whereby a finger 12 protruding at a fixed place from the member 3 is adapted to engage one of a plurality of holes 13, 14, 15, 16 ... in the wall of member 4. The protrusion of the finger 12 is controlled by means of a spring link 17 extending to a handle 18 which pivots about a fixed point 19 near the top of member 3 so that, by raising and lowering the handle 18, the finger 12 may be disengaged or engaged in one of the holes 13, 14, 15, .6....

When the finger 12 is engaged in one of the said holes, this locks the two members 3 and 4, so that the member 3 is not supported only by the constant force spring 8, and weight may be placed on the member 3 (for example, by a person sitting on the chair seat 1) while the two members 3 and 4 are maintained in fixed relationship, in other words, the chair seat is maintained at a fixed height.

When it is desired to change the height of the chair seat, the handle 18 is operated so as to disengage the finger 12 from the hole in which it happens to be located, and the seat is either allowed to rise under the force of the spring 8, or it is pressed down with a force greater than that of the spring 8, and when the desired height change has been achieved, the handle 18 is moved so as to engage the finger 12 in the appropriate hole.

By appropriately selecting the constant force spring 8, the system may be arranged so that the upward force provided by the spring is only slightly greater than the downward force provided by the member 3, the seat 1, the backrest 2, the handle 18, the spring link 17, and the ratchet mechanism including the finger 12. As a result, disengagement of the finger 12 without application of an extra downward force, will lead to the seat slowly rising, whereas application of a small extra downward force to the seat will lead to the seat being slowly lowered.

The alternative arrangement shown in Figure 5 is generally similar to that of Figures 1 to 4, except that the member 3a carrying the seat back is slideable outside (rather than within) the second member 4a which is borne on the legs 6 (not shown in Figure 5). The constant force spring 8 is in effect inverted as compared with the spring shown in Figure 4, and it is fixed at its lower end to the inner surface of the member 3a. The coiled portion 10 of the spring 8 bears on the upper end 11a of the member 4a.

The situation is analogous in the system of Figure 5 to that in the system of Figure 4, except of course that instead of the spring directly pushing the seat up, it acts directly to push the legs down and by reaction to push the seat up.

While the invention has been particularly described in relation to a chair, and while it is in the field of chairs that the longest-felt and most serious want of such a mechanism has existed, so that the benefits provided by the invention are correspondingly greater, nevertheless it will be seen that the mechanism of the invention is adapted to be embodied in other items of furniture, as previously mentioned.

Claims (11)

1. A height adjustment mechanism for furniture comprising a pair of slidably engaged members and a constant force spring fixed at its open end to one of the members so that the other member bears on the coiled portion of the spring, the force of the spring being such as to withstand the . .

weight of the member bearing thereon--and of any fixed load on such member, means being provided to enable the two members to be fixed at selected points in their slidable relationship.

2. A mechanism according to Claim 1 in which the force exerted by the spring is equal to the weight of the member bearing on it together with any fixed load on that member.

3. An item of furniture comprising a foot and a loadbearing surface connected by a mechanism according to Claim 1 or 2, whereby the height of the surface above the foot may be adjusted by means of the said mechanism.

4. A pedestal chair comprising a seat fixed on a first member and one or more feet supporting a second member, the two members being in slidable relationship, a constant force spring fixed to one member with the other member bearing on the spring whereby the spring is capable of supporting and raising the first member and the seat (and any fixed weight attached thereto) but is not capable of supporting the first member and the seat (and any fixed weight attached thereto) if an additional downward force is applied thereto, and means for releasably locking the two members in fixed relationship to each other at a plurality of relationships within the slidable range.

5. A chair according to Claim 4 in which the means for releasably locking the members comprises ratchet means.

6. A chair according to Claim 4 or 5 in which the members are in the form of concentric tubes, one sliding inside the other.

7. A chair according to Claim 6 in which the constant force spring is located within one of the tubes.

8. A chair according to Claim 7 in which the constant force spring is located against the inner surface of the outer tube, that tube serving as the second member, and the spring is arranged so that its relatively uncoiled end is fixed in the upper part of the outer tube, the spring being arranged to uncoil downwardly within the outer tube, and the first member being located within the second so that its lower portion bears against the coiled portion of the spring which uncoils if the first member is forced down.

9. A chair according to Claim 7 or 8 in which the tubes are of rectangular cross section whereby relative rotatory movement is prevented.

10. A chair according to any of Claims 4-9 in which, attached to the seat, is a fixed weight comprising a backrest.

11. A chair having a height adjustment mechanism substantially as hereinbefore described with reference to Figures 1 to 3 and 5 of the drawings.

11. A chair having a height adjustment mechanism substantially as hereinbefore described with reference to Figures 1 to 4 of the drawings.