GB2252722A

GB2252722A - Seat height adjustment

Info

Publication number: GB2252722A
Application number: GB9101414A
Authority: GB
Inventors: Michael Charles Dye
Original assignee: HILLE EXECUTIVE FURNITURE AND
Current assignee: HILLE EXECUTIVE FURNITURE AND
Priority date: 1991-01-22
Filing date: 1991-01-22
Publication date: 1992-08-19
Also published as: GB9101414D0

Abstract

Height adjustment apparatus suitable for a seat (2) comprises a seat support arm (3) mounted to be movable up or down a column (5) for seat height adjustment, and a locking means, to lock the seat support arm (3) to the column (5) under the action of the weight of a user on the seat (2). <IMAGE>

Description

Height Adjustment Apparatus The invention relates to height adjustment apparatus for a seat of e.g. a chair, stool or the like.

It has been proposed to provide a chair having a seat which can be moved up or down a column to a desired level and then locked in position by a locking mechanism. The locking mechanism is operated by a knob or lever provided on the outside of a locking mechanism housing, it being necessary first manually to actuate the knob or lever to release the locking mechanism, then to make the desired height adjustment and finally to actuate again the knob or lever to lock the seat in position. Thus a user is required to actuate the knob or lever to cause both unlocking and locking; furthermore, there is a risk that the user may forget to lock the mechanism after height adjustment.

According to the invention there is provided height adjustment apparatus for a seat, comprising a seat support arm mounted on a column, the seat support arm being movable up and down the column for height adjustment of the seat, and locking means arranged to lock the seat support arm to the column under the action of the weight of a user on the seat.

Since a user's weight causes locking of the seat at the desired height it is not necessary to have a manually operated knob or lever to lock the seat in position. Furthermore, because locking is automatically effected when the user sits on the seat there is no risk of forgetting to lock the seat prior to sitting on it.

The locking means will preferably be located in a housing from which the seat support arm projects, there being no need for an external control knob or lever which might affect the external appearance of the housing.

The arrangement will preferably be such that when the weight is removed from the seat the seat support arm remains in position, but can be released by upward tilting or pivoting of the seat support arm, whereafter height adjustment can be effected. Thus the seat arm itself provides control of the locking means, both for locking and unlocking thereof.

There may be a positive mechanical locking action but it is preferred for the locking means to act by friction. The column can then be formed without any locking holes or protuberances along its length, being for example generally smooth, and this may be desirable from an aesthetic point of view. Thus for example the seat support arm may be mounted on the column such that the weight of a user on the seat causes frictional locking engagement between the seat support arm and the column.

Preferably the seat support arm is mounted to pivot about a horizontal axis and is provided with frictional means to be urged into locking engagement with the column when the seat support arm is pivoted in a downward direction. The weight of a user on the seat may be amplified by leverage to provide a larger urging force for frictional locking engagement. By positioning the frictional means substantially closer to the pivot axis than the weight of a user on the seat a significant mechanical advantage is achieved. For example if the mean distance of the weight on the seat is 250mm from the pivot axis and the mean distance of the contact between the frictional means and the column is 12.5mm from the pivot axis, then a mechanical advantage of 20:1 can be achieved.Thus a person sitting on the seat may cause a frictional locking force twenty times as great to be applied; for example a person of mass 90kg corresponding to a weight or downward force of 0.89kN may produce a locking force of about 18kN. Although the precise mechanical advantage or leverage will depend on the direction in which the locking force is applied and the position of the user on the seat, it will be seen that a substantial and sufficient locking force can be obtained. When released by removal of the user's weight from the seat and preferably also by upward tilting or pivoting of the seat support arm, the frictional means will permit the seat support arm to move up or down the column for height adjustment.

The seat support arm may be provided with opposed frictional means arranged respectively to be urged against forward and rear facing surfaces of the column.

Preferably however first frictional means is provided on the seat support arm and is arranged to be urged against one surface, e.g. a forward facing surface, of the column, and second frictional means is fixed relative to the pivot axis, for example by being fixedly secured in the housing of the locking means, the second frictional means being arranged to be urged against an opposite surface, e.g. a rear facing surface, of the column.

Thus when the seat support arm is pivoted downwardly the column will be clamped between the first frictional means of the seat support arm and the second frictional means fixed relative to the pivot axis. In a preferred arrangement, the pivot axis is located forwardly of the column and the first frictional means of the seat support arm is located generally below the pivot axis such that downward pivotal movement causes the first frictional means to move rearwardly into locking engagement with the front of the column.

The forward and rear facing surfaces of the column may be substantially flat front and rear surfaces. The column may thus have a generally square or rectangular cross-section. In a preferred embodiment, the column comprises a pair of laterally spaced stems, in which case the seat support arm may be provided with frictional means in the form of correspondingly laterally spaced frictional members each to be urged against the front surface of a respective stem. There may then be second frictional means in the form of laterally spaced frictional members fixed relative to the pivot axis and each to be urged against the rear surface of a respective stem.

The frictional means may be formed of a compressible material such as PVC, nylon, solid neoprene, rubber or the like in order to avoid damage to the column during both locking and height adjustment.

The frictional means may be in the form of one or more studs or buttons each secured by its shank portion in a suitable hole with its head portion arranged for frictional engagement with the column.

The column may be vertical or at an angle to the vertical.

In certain embodiments of the invention there may be a problem in maintaining a sufficient locking force to lock the seat support arm in position, for example if the user's weight is applied relatively near to the locking means with a resulting reduction in the mechanical advantage. The height adjustment apparatus may therefore include first and second locking means each arranged to lock the seat support arm to the column under the action of the weight of a user on the seat.

The first locking means may be as described above. The second locking means may have a positive mechanical locking action but it is preferred for the locking means to act by friction. The second locking means may act in a direction substantially perpendicular to that of the first locking means, so that in the preferred arrangement in which the seat support arm is mounted to pivot about a horizontal axis, the second locking means may be arranged to act on one or more lateral surfaces of the column, for example one or more outwardly facing lateral surfaces. Preferably however the second locking means is arranged to act on a pair of opposed, inwardly facing, lateral surfaces. These may be the facing surfaces of an elongate slot formed in the column, but are preferably the facing surfaces of a pair of laterally spaced stems forming the column.

With the seat support mounted to pivot about a horizontal pivot axis, the second locking means preferably includes a camming arrangement so that vertical pivoting movement of the seat support arm causes a lateral locking force to be applied to the column. The camming arrangement may take the form of a surface of the seat support arm which is at a slant to a vertical plane, the slanted surface being arranged to cooperate with a friction element such that when the seat support arm moves in a vertical direction the slanted surface thereof urges the friction element against a lateral surface of the column. The vertical movement of the seat support arm will normally be caused by downward force on the seat, and the resulting movement of the slanted surface may be up or down, depending on whether the camming arrangement is disposed to the front or rear of the pivot axis.Preferably the camming arrangement is to the rear of the pivot axis, so that upward movement of the slanted surface causes the required urging of the friction element.

In the embodiment described above where the second locking means is arranged to act on a pair of opposed, inwardly facing, lateral surfaces of the column, the seat support arm is advantageously provided with a wedge portion having a pair of outwardly facing slanted surfaces, a friction element being provided on each side of the wedge portion to be urged against a respective lateral surface of the column. The or each friction element is preferably wedge-shaped with its narrow end located adjacent the wide end of the wedge portion of the seat support arm. The or each friction element will normally be fixed relative to the pivot axis, for example by being fixedly secured in the housing.

The second locking means is preferably such as to hold the seat support arm in a downward position when a user's weight is removed from the seat, so that the seat is ready to be used again. It will be seen that this is advantageously achieved by the camming arrangement of the second locking means described above. If the user's weight is applied relatively near to the pivot axis of the seat support arm, reducing the mechanical advantage necessary for locking engagement, the second locking means will normally prevent the seat support arm from sliding down the column. Like the first locking means, the second locking means will generally be releasable by upward tilting or pivoting of the seat support arm.If the seat support arm has a slanted surface as described above, upward tilting or pivoting of the seat support arm will operate to remove the force urging the friction element against the lateral surface of the column.

The friction element(s) of the second locking means may be formed of a compressible material such as PVC, nylon, solid neoprene, rubber or the like in order to avoid damage to the column during both locking and height adjustment.

The invention also extends to the combination of the height adjustment apparatus and the seat, and to a chair, stool or the like having such a combination.

Although the invention has been particularly described with reference to a seat, it may in its broadest sense or in its preferred forms be applicable to other items of furniture, such as shelving or supports for office equipment, e.g. visual display units or printers.

A preferred embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side elevation of part of a chair including height adjustment apparatus in accordance with the invention; Figure 2 is an opposite side elevation, partly in section, of a mounting boss of the height adjustment apparatus; Figure 3 is a section on the lines III-III of Figure 2; and Figure 4 is a section on the lines IV-IV of Figure 2.

Referring to Fig. 1, a chair 1 is provided with a seat 2 supported by a seat support arm 3 which projects in cantilever fashion from a mounting boss 4 mounted to be movable up or down a column 5 for seat height adjustment. The column 5 and a brace 6 therefor extend downwardly to a base of the chair (not shown) and the column 5 extends upwardly to where it supports a seat back (not shown). The mounting boss 4 has a housing 7 through which the column 5 passes and from which the seat support arm 3 projects forwardly, there being no other members externally of the housing for control of height adjustment.

Fig. 2 shows a side elevation of the mounting boss 4 with a side plate of the housing 7 removed and with certain details shown in section. The seat support arm 3 is shown in solid lines in its downwardly pivoted, locked position and in dotted lines in its upwardly pivoted, unlocked position.

Referring to Figs. 2, 3 and 4, the seat support arm 3 is pivotally mounted to the mounting boss 4 on a pivot shaft 8. A pair of locking plates 9 are disposed one on each side of the seat support arm 3 with the pivot shaft 8 passing therethrough. In this embodiment, the locking plates 9 are secured to the seat support arm 3 by dowels 10 but it is envisaged that the plates could be formed integrally with the seat support arm 3. Each locking plate 9 is formed in the lower part of its front surface with a bore 11 in which is received a frictional member comprising a compressible button 12. The buttons 12 may be formed of PVC, rubber, nylon, solid neoprene or the like. The seat support arm 3 extends forwardly of the pivot shaft 8 and has a wedge portion 13 at its front end.The wedge portion has a pair of laterally outwardly facing surfaces 14 which are slanted to a vertical plane such that the narrow end of the wedge portion is at the top. In this embodiment the angle of slant is 5 .

The mounting boss 4 is provided at its rear with a pair of upper laterally spaced bores 15 and a pair of lower laterally spaced bores 16, in which are respectively received a pair of upper laterally spaced frictional members in the form of compressible buttons 17 and a pair of lower laterally spaced frictional members in the form of compressible buttons 18. The mounting boss 4 is also provided with a pair of pockets 19 in which are retained the upper portions 21 of a pair of friction elements each consisting of a compressible wedge 20. The wedges 20 have lower portions 22 with opposed facing surfaces 23 at a slant to a vertical plane. In this embodiment the surfaces 23 are at a slant of 5".

The column 5 is in the form of a pair of laterally spaced rectangular stems 24 each having a front surface 25, a rear surface 26 and an inwardly facing surface 27, the surfaces all being substantially flat.

In use, when the seat support arm 3 is in an upwardly pivoted position as shown in dotted lines in Fig. 2, the pair of buttons 12 are rearwardly spaced from the front surfaces 25 of the stems 24, rather than being urged thereagainst. The wedge portion 13 of the seat support arm 3 is in a lower position and does not therefore apply laterally outward forces to the pair of wedges 20 on each side of the wedge portion 13. Thus the mounting boss 4 is free to move up or down the column 5, for example being gripped and moved by a hand of a user.

The operation of the first locking means will now be described. When downward force is applied to the seat 2 the seat support arm 3 moves to its downwardly pivoted position shown in full lines in Fig. 2 and shown also in Figs. 3 and 4. The buttons 12 are moved forwardly into frictional engagement with the front surfaces 25 of the stems 24 of the column 5, and the reaction force on the pivot shaft 8 is transmitted via the body of, the mounting boss 4 to the upper and lower buttons 17 and 18 which are then urged against the rear faces 24 of the stems. Thus the stems are clamped between the buttons 12 of the seat support arm 3 and the buttons 17 and 18 of the mounting boss so that the mounting boss is frictionally locked to the stems.

Accordingly, the first locking means is in a locked condition.

The operation of the second locking means will now be described. The downward pivoting of the main part of the seat support arm results in upward pivoting of its front wedge portion 13. The outer slanting faces 14 of the wedge portion 13 engage the opposed surfaces 23 of the compressible wedges 21 to urge them outwardly against the inner faces 27 of the stems 24. Thus the second locking means locks the mounting boss to the stems 24. The effect of the second locking means is that when the weight of a user is removed from the seat the seat support arm 3 is wedged in position and therefore stays in its lower pivoted position ready to be used again. Furthermore, if a person on the seat applies his or her weight towards the rear thereof the second locking means remains wedged even though the mechanical advantage for the first locking means may be reduced. In such circumstances, the combination of the first and second locking means should be sufficient to maintain the mounting boss in the locked position. Even if the first and second locking means do not perform properly, for example due to wear, providing the seat remains in its lower pivoted position, the wedging arrangement of the second locking means will normally ensure that the mounting boss 4 is able to slide only slowly, rather than catastrophically, down the column 5.

It will be seen that the first locking means and the second locking means are each arranged such that locking action is induced only by weight applied to the seat which tends to pivot the seat support arm.

Furthermore1 the locking action in each case is purely by friction, so that the column may have an outer surface or surfaces free of mechanical locking elements such as holes or protuberances.

Claims

1. Height adjustment apparatus for a seat, comprising a seat support arm mounted on a column, the seat support arm being movable up and down the column for height adjustment bf the seat, and locking means arranged to lock the seat support arm to the column under the action of the weight of a user on the seat.

2. Apparatus as claimed in claim 1, arranged such that when the weight is removed from the seat the seat support arm remains in position, but can be released by upward tilting or pivoting of the seat support arm.

3. Apparatus as claimed in claim 1 or 2, wherein the seat support arm is mounted on the column such that the weight of a user on the seat causes frictional locking engagement between the seat support arm and the column.

4. Apparatus as claimed in any of claims 1, 2 or 3, wherein the seat support arm is mounted to pivot about a horizontal axis and is provided with frictional means to be urged into locking engagement with the column when the seat support arm is pivoted in a downward direction.

5. Apparatus as claimed in claim 4, wherein the frictional means is positioned substantially closer to the pivot axis than the weight of a user on the seat.

6. Apparatus as claimed in claim 4 or 5, wherein the frictional means comprises first frictional means provided on the seat support arm arranged to be urged against a forward facing surface of the column, and second frictional means fixed relative to the pivot axis, the second frictional means being arranged to be urged against a rear facing surface of the column.

7. Apparatus as claimed in claim 6, wherein the pivot axis is located forwardly of the column, and the first frictional means of the seat support arm is located generally below the pivot axis such that downward pivotal movement causes the first frictional means to move rearwardly into locking engagement with the forward facing surface of the column.

8. Apparatus as claimed in claim 6 or 7, wherein the forward and rear facing surfaces of the column are substantially flat.

9. Apparatus as claimed in any of claims 6, 7 or 8, wherein the first and second frictional means are provided in the form of one or more studs or buttons each secured by a shank portion in a suitable hole with a head portion arranged for frictional engagement with the column.

10. Apparatus as claimed in any of claims 6 to 9, wherein the column comprises a pair of laterally spaced stems, the first frictional means being provided in the form of correspondingly laterally spaced frictional members each to be urged against a forward facing surface of a respective stem, the second frictional means being provided in the form of laterally spaced frictional members fixed relative to the pivot axis and each to be urged against a rear facing surface of a respective stem.

11. Apparatus as claimed in any preceding claim, wherein the locking means comprises first and second locking means, each being arranged to lock the seat support arm to the column under the action of the weight of a user on the seat.

12. Apparatus as claimed in claim 11, wherein the second locking means is arranged to act in a direction substantially perpendicular to that of the first locking means.

13. Apparatus as claimed in claim 11 or 12, wherein the second locking means includes a camming arrangement whereby vertical pivoting movement of the seat support arm causes a lateral locking force to be applied to the column.

14. Apparatus as claimed in claim 13, wherein the camming arrangement comprises a surface of the seat support arm, which is at a slant to a vertical plane, the slanted surface being arranged to cooperate with a friction element provided adjacent a lateral surface of the column such that when the seat support arm moves in a vertical direction the slanted surface thereof urges the friction element against the lateral surface of the column.

15. Apparatus as claimed in claim 10, wherein the seat support arm is provided with a wedge portion having a pair of outwardly facing slanted surfaces, a friction element being provided on each side of the wedge portion to be urged against a respective lateral surface of the column.

16. Apparatus substantially as hereinbefore described, with reference to Figures 1 to 4 of the accompanying drawings.