GB2255499A

GB2255499A - "chair back adjustment mechanism"

Info

Publication number: GB2255499A
Application number: GB9109983A
Authority: GB
Inventors: Gordon Dennis Hobb
Original assignee: NORTHEASTERN COMPONENTS
Current assignee: NORTHEASTERN COMPONENTS
Priority date: 1991-05-09
Filing date: 1991-05-09
Publication date: 1992-11-11
Anticipated expiration: 2011-05-09
Also published as: GB9109983D0; GB2255499B

Abstract

A mechanism for adjusting the height of a chairback (10) relative to the seat of the chair comprises friction plates (17) associated (a) with the seat frame and (b) with the chairback support (18), respectively. The friction plates are urged into mutual frictionai engagement by pressure from a spring (21) and are capable of linear movement relative to one another when they are disengaged. in a preferred form of the mechanism, the friction plates are disengaged by pressure of the user upon the chairback. <IMAGE>

Description

Chair Back Adjustment }behatism The present invention is an improved mechanism devised to enable adjustment of the vertical position of a chairback relative to the seat itself. It has primarily been devised for application to the types of chairs widely used in offices, in which chairs there is often provision for adjustment of the height of the seat above the ground, the inclination of the chairback and the height of the chairback above the seat, but it is also of value for chairs of other types used in other commercial, industrial or domestic settings.

Available chairback height adjustment mechanisa.s require a certain dexterity and ofter. also physical strength on the part of the user. Often it is intended that the user should adjust the chairback fram a position behind the chair and adjustment from a seated position may be difficult or impossible. Thus finding the correct setting for the chairback may be a matter of trial and error. A proposed EEC Standard envisages that all adjustments must be achievable fran a seated position.

By way of example, one type of available chairback height adjustment mechanism entails the loosening and tightening in turn of a heundwheel or eccentric cam mechanism which is located either at the base of the back support or at the rear of that support. While mechanisms of this type permit the chairback to be set in an infinite number of height positions over the available range of adjustment, they have the inconvenience that the initial loosening of the mechanism permits the chairback to drop initially to its lowest possible setting unless it is held in its original position while the mechanism is adjusted. The difficulty of attempting satisfactory adjustment from a seated position will be immediately apparent.

Another available type of chairback height adjustment mechanism allows the height to be set at a limited number of fixed positions (for example four or six positions) over the possible range, by means of a series of notches in which the locking mechanism must engage. Again it is necessary for the user to release and engage the locking mechanism fran a position located at the rear of the back support in order to adjust the chairback height. While adjustment from a seated position may in one respect be a little easier than with the foregoing mechanism, since the releasing may be achieved by means of a spring-loaded button or lever, there is the added problem that effective locking can only be achieved when the chairback is at one of the height positions at which the locking mechanism can engage a notch.If the chairback has not been adjusted to one of this limited number of predetermined positions, then it will not lock properly but will drop to at least the nearest lower locking position, and possibly further.

There remains the need for an improved adjustment mechanism for chairbacks, which permits continuous adjustment of the chairback height and is readily operable fran a seated position. It is an object of the present invention to provide such an improved mechanism.

The chairback height adjustment mechanism according to the present invention is characterised in that friction plates associated with the seat frame and with the chairback support respectively are urged into mutual frictional engagement by spring pressure and, when disengaged, are adapted for relative linear movement. Preferably that relative linear movement is between predetermined limits.

Thus the adjustment mechanism according to the invention, by virtue of the relative movement of the friction plates, allows the chairback on its support to be moved and fixed as desired in an infinite number of height positions relative to the seat on the seat frame and allows of the possibility of adjustment being achieved by simple pressure against that of the spring.

The release of the friction plates may if desired be achieved by operation of a simple push-button, which may be located in a position which is readily accessible to a person sitting upon the seat and may require very little manual pressure to operate it. For example such a pushbutton may be located below the chairback. Howerer, in a particularly preferred form of the present invention, the friction plates are disengaged by pressure upon the chairback itself, especially pressure in the opposite direction to that naturally applied by the user's back when the chair is in use.

Thus this particularly preferred form of the chairback height adjustment mechanism according to the present invention comprises at least one first friction plate fixed relative to the seat of the chair, at least one second friction plate fixed relative to a support for the chairback, said first and second friction plates being mounted for relative linear movement, spring means to urge said first and second friction plates into mutual frictional engagement, and a release mechanism operable to disengage said friction plates in response to pressure upon the chairback support.

Preferably there are two or more friction plates associated with each of the chairback support and the seat respectively, for example four pairs of friction plates.

The spring means for urging the respective friction plates together may take any desired form, including compression springs, tension springs and one or more resilient sprung leaves, but it is particularly preferred to use one or more compression springs, extending between the chairback itself and its support. Advantageously the chairback is pivoted to its support about a horizontal pivot in the usual manner, with the ccmpression spring being disposed below the pivot so that normal user pressure on the chairback above the pivot tends to urge the chairback to move about the pivot in the opposite direction to that which would disengage the friction plates. Pressure exerted by the user on the chairback below the pivot, on the other hand, with the specific aim of adjusting the chairback height, may compress the spring between the chairback and its support and in doing so disengage the friction plates.

The invention will now be further described with reference to the acccaaanying drawings, which illustrate, by way of example only, one preferred embodiment of the chairback height adjustment device according to the invention and wherein: Fig. 1 is a vertical sectional view of the device from one side; Fig. 2 is a vertical sectional view of the device fram the rear, on the line II-II of Fig. 1; and Fig. 3 is a plan view of the device.

The chairback 10 in the drawings is pivoted in the region of its lower end upon pivot pins 11, 12. The pivot pins are mounted upon a spac-er tube 13 and downward extensions of the pivot pins are guided in bushes 14 within tubular guides 15.

By means of a rivet 16, the spacer tube 13 is rigidly secured to friction plates 17.

The friction plates 17 extend into a tubular back support 18, which is in turn connected to the seat of the chair, and linear vertical movement of the friction plates within the back support 18 allows the vertical position of the chairback 15 relative to the seat to be increased or decreased as required. A carriage bolt 19, secured by a locking nut 20, is encircled by a ccmpression spring 21 which, by applying spring pressure between the head of the bolt and the support 18, urges the friction plates 17 into mutual interengagenent and thereby holds the chairback 15 and back support 18 against relative movement.

Pivotally suspended from a bracket 22 which is mounted upon the back support 18 is an operating piece 23 which carries a roller 24 on a shaft 25. The operating piece 23 normally abuts the head of the bolt 19 and the roller 24 normally abuts, or lies close to, the rear of the chairback 10.

Operation of the adjustment mechanism is very simple.

Fram a seated position (that is, to the left of Fig. 1 as illustrated), the user pushes the chairback rearwardly at its lover end (that is, below its point of pivoting on the pins 11, 12) in the direction of the arrow 26. The chairback presses the roller 24 and the operating piece 23 is thereby caused to depress the bolt 19 against the pressure of the spring 21 and thus to allow the friction plates 17 to disengage. The chairback may therefore be adjusted vertically so long as the roller 24 is pressed by the chairback. When that pressure is removed, the spring 21 causes the friction plates to re-engage and thereby to secure the chairback 10 in its chosen vertical position.

In subsequent normal use of the chair, pressure of the usar's body against the chairback is naturally applied above the pivot pins 11, 12, so there is no tendency for any pressure to be applied to the roller 24, and therefore no tendency for the chairback to be inadvertently displaced in use.

Claims

1. A chairback height adjustment mechanism for a chair comprising a seat frame and a support for the chairback, characterised in that friction plates associated with the seat frame and with the chairback support respectively are urged into mutual frictional engagement by spring pressure and, when disengaged, are adapted for relative linear movement.

2. A chairback height adjustment mechanism as claimed in claim 1, wherein said relative linear movement is between predetermIned limits.

3. A chairback height adjustment mechanism as claimed in either of claims 1 and 2, wherein disengagement of the friction plates is by operation of a push-button.

4. l A chairback height adjustment mechanism as claimed in either of claims 1 and 2, wherein disengagement of the friction plates is by pressure upon the chairback.

5. A chairback height adjustment mechanism as claimed in claim 4, comprising at least one first friction plate fixed relative to the seat of the chair, at least one second friction plate fixed relative to a support for the chairback, said first and second friction plates being mounted for relative linear movement, spring means to urge said first and second friction plates into mutual frictional engagement, and a release mechanism operable to disengage said friction plates in response to pressure upon the chairback support.

6. A chairback height adjustment mechanism as claimed in claim 5, wherein said spring means comprises at least one compression spring extending between the chairback and its support.

7. A chairback height adjustement mechanism as claimed in claim 6, wherein said chairback is pivoted to its support about a horizontal pivot and the canpression spring is disposed below said pivot.

8. A chairback height adjustment mechanism as claimed in any of claims 1 to 5 wherein said spring pressure is provided by at least one tension spring or sprung leaf.

9. A chairback height adjustment mechanism as claimed in any of the preceding claims, having two or more friction plates associated with each of the chairback support and the seat frame.

10. A chairback height adjustment mechanism, substantially as hereinbefore described with reference to, and as illustrated in, the acccmpanying drawings.