Mechanism for chair

Details Mechanism for chair Mechanism for chair

1999-02-03

2001-05-29

Barfield, Anthony D. (Department: 3624)

Chairs and seats

Back movement resiliently opposed in operating position

Back and seat adjust simultaneously

C297S300800, C297S303400

Reexamination Certificate

active

06238000

ABSTRACT:

This invention relates to a mechanism for a chair of the kind having a base part, and a seat part mounted on the base part so as to be of adjustable inclination against a spring force relative to the horizontal.
In the case of an office chair of the kind which is used for working at a desk in front of word processing or computer equipment, it is usual for provision to be made for adjustment of seat and back parts of the chair so that the user can attain a desired comfortable sitting position. In particular, the inclination to the horizontal of the seat may be adjustable against a spring force, by means of a mechanism, between forwardly and rearwardly inclined limits. Also, the back may be movable forwardly and rearwardly relative to the seat and it is known to use a so called synchro mechanism which synchronises adjustment of the vertical rake of the back with tilting of the seat, whereby the back moves through a greater angle than the seat, say in accordance with a ratio of 3:2.
Adjustment of the seat angle and the rake of the back is effected with the user seated on the chair. The user leans backwards to cause his of her weight to move the back and the seat against the resistance of the spring force. It is desirable that the spring resistance should be adequate to achieve slow controlled movement but without requiring excessive effort. It is therefore usual to provide an adjustment control to adjust the spring force to suit the weight of the user.
The problem arises, however, that an adjustment control which involves, for example, rotating a screw to tighten or loosen a spring by increasing or releasing compression forces directly along the spring axis may necessitate awkward or unduly strenuous user activity. Also, the problem can arise that increase in spring compression may give rise to accentuation of progressive increase in spring force to the extent that the spring force is not linear throughout the adjustment movement and increases significantly, in an uncomfortable and inconvenient manner, as the chair seat and back approaches the rearmost limits of their travel.
It is to be understood that these problems can be significant especially because it is important to avoid the user being exposed to strain or injury.
Accordingly, one object of the invention is to provide a mechanism for a chair which is simple and convenient to operate and comfortable in use.
According to one aspect of the invention therefore there is provided an adjustable mechanism for a chair, which chair has a base part, and a seat mounted on the base part so as to be of adjustable inclination relative to the horizontal, said mechanism including a spring arrangement disposed in compression to provide a spring force applied in a direction between the base part and the seat part so as to resist said adjustment movement of the seat part, and an adjustment control operable to adjust the disposition of the spring arrangement with reference to extent of compression thereof and also the said direction thereof.
With this arrangement, because the adjustment control moves the direction of spring force application as well as changing compression, a desired resistance characteristic over the path of adjustment movement of the seat part can be more readily attained. In particular, it is possible to maintain a substantially linear resistance characteristic to the user, involving no perceived change in resistance or at least only a slight linear increase in resistance, rather than a significant progressive increase.
Most preferably, adjustment of the disposition of the direction of spring force application involves a change in inclination thereof, and this may be attained by lateral movement of one end of the spring arrangement relative to an opposite end thereof.
Preferably the spring arrangement is mounted, or held captive, at said opposite ends thereof between pivotally interconnected upper and lower supports, said lateral movement being effected by adjustment of the relative angular disposition of the lower support relative to the upper support. Preferably also, the lower support has a free end region which is engageable with a fulcrum member about which the lower support pivots during movement of the upper and lower supports towards and away from each other, and the said adjustment of the relative angular disposition of the upper and lower supports is effected by adjustment of the position of the fulcrum member.
In a particularly preferred embodiment the fulcrum member comprises in combination at least one fixed fulcrum element and at least one positionally adjustable fulcrum element arranged such that the said free end region of the lower spring support engages the (or each) fixed element at an initial phase of movement and subsequently engages the (or each) positionally adjustable fulcrum element. With this arrangement, positional adjustment of the (or each) latter fulcrum element can be effected in an unloaded condition thereby permitting easy and convenient adjustment.
The fulcrum member and the coacting end region of the lower spring support may take any suitable form but are preferably shaped to accommodate easy, controlled relative movement. Thus, one or more shaped, e.g. curved projections or rollers or the like may be used for the fulcrum member, and the end region of the lower spring support may comprise one or more curved and/or angled faces.
The above mentioned arrangement whereby the lower spring support initially contacts one or more fixed fulcrum elements and then contacts one or more positionally adjustable fulcrum elements is preferably achieved by arranging the respective elements in mutually displaced positions and incorporating a linkage which effects movement of the fulcrum member relative to the coacting end region of the lower spring support. This linkage may incorporate a cam follower engageable with a cam slot. For example the cam follower may comprise an axle on the said base part, and the cam slot may be provided on the seat part, although other arrangements are also possible.
The said spring arrangement may comprise a helical coil spring or any other suitable spring arrangement including leaf springs, rubber springs, gas cylinders.
The chair may also include a back part and this may be connected to the mechanism so that it moves with tilting of the seat part in accordance with any suitable desired relationship. A synchro arrangement may be used whereby the back is capable of rearward movement through a greater angle than the seat in accordance with a predetermined ratio (say 3:2), although other arrangements are also possible.
The back part may be rigidly mounted on the above mentioned upper spring support. This may be achieved via a rigid L-shaped plate member and one limb of this may be firmly anchored within a slot or other means in the upper support.
Alternatively or additionally the upper spring support may comprise a body part with an attached rearwardly projecting rigid elongate support member which provides support for the back. With this arrangement the back can be adequately supported without requiring a massive structure for the said body part.
Thus and in accordance with a second aspect of the present invention there is provided a mechanism for a chair which has a base part, and a seat mounted on the base part so as to be of adjustable inclination relative to the horizontal, said mechanism including a spring arrangement disposed in compression between upper and lower spring supports respectively connected between the base part and the seat part, and a back part supported on the upper spring support, wherein the upper spring support comprises a body part with an attached rearwardly projecting rigid elongate support member which provides support for the back part.
The elongate support member may comprise a U-shaped steel bar.
A locking mechanism is preferably provided for holding the seat part relative to the base part in a selected angular relationship and this may comprise at least one tooth member engageable between teeth of a rack or ratchet member. A spring may be provi

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