Chair back adjustment mechanism

Details Chair back adjustment mechanism Chair back adjustment mechanism

1999-05-21

2001-08-14

King, Anita M. (Department: 3632)

Supports

Brackets

Adjustable

C297S353000, C297S411360

Reexamination Certificate

active

06273384

ABSTRACT:

This invention relates to a slider mechanism particularly although not exclusively for adjusting the height of the back part of a chair, especially an office chair, or typist's chair, of the kind which is used for working at a desk in front of word processing or computer equipment.
A conventional office or typist's chair has a wheeled base which supports a seat part and an upstanding rigid flat bar or elongate plate on which a back part is mounted. Typically the back part is movable longitudinally of the bar or plate for height adjustment purposes.
The back part may be movably mounted via a slider in the form of a sleeve which wraps around edges of the bar or plate, a mechanism of the nature of a ratchet having a pawl engageable with a toothed rack being provided to hold the sleeve relative to the bar or plate at a selected position along its length.
With this known arrangement the requirement is that the slider should move easily along the bar or plate but without undue transverse movement or play. This can be achieved by use of precision engineering to produce a slider having dimensions, particularly the separation between face parts, and between edge parts of the slider, which have close predetermined tolerances in relation to the corresponding dimensions of the bar or plate.
However, this is an expensive solution from the manufacturing point of view.
One object of the present invention is to attain the requirements for easy sliding and minimal play with a construction which can be manufactured relatively easily and inexpensively.
According to one aspect of the invention therefore there is provided an adjustment mechanism for adjusting the height of a back part of a chair comprising an elongate rigid support member having a longitudinally extending guide face bounded by edges, a slider for attachment to the back part mounted on the member so as to be slidable longitudinally thereof, said slider having a face part overlying the guide face and edge parts which locate around said edges of the member, and selectively interengageable parts on the slider and the member to releasably retain the slider and member in a selected position longitudinally of the member, characterised by the provision of a guide arrangement comprising at least one groove provided on one of the member and the slider and extending longitudinally of the member, and at least one projection slidably engageable with the groove and provided on the other of the member and the slider.
With this arrangement it is possible to attain precise guiding with a construction which can be easily and inexpensively manufactured in so far as precision formation of the (or each) groove can be more readily achieved than precision control of lateral dimensions of the slider.
Most preferably the (or each) groove is provided in the elongate member. Any suitable manufacturing process may be used although stamping or pressing is preferred since this is a convenient means of ensuring precise location and dimensions. The or each groove may be of V-shaped formation.
In practice, the transverse position and dimensions of the (or each) groove are selected, in relation to the (or each) projection, to maintain a desired positioning of the slider transversely (i.e. between the said edges) on the elongate member.
Also, the depth of the (or each) groove may be selected with precision, in relation to the (or each) projection, to maintain a desired positioning of the slider laterally (i.e. perpendicularly to the said guide face). In this case the slider and the elongate member will have confronting surfaces at an opposite side of the guide member to the guide face and the arrangement may be such that the (or each) groove and the (or each) projection are provided between the said guide face and face part, and a further guide arrangement is provided between the said confronting faces.
This further guide arrangement may be of like form to the first said guide arrangement i.e. comprising at least one further said groove interengageable with at least one further said projection. Most preferably the grooves of both guide arrangements are provided in the elongate member and the (or each) groove of the first said guide arrangement is superimposed with the (or a respective) groove of the further guide arrangement. With this latter construction, particularly using a stamping or pressing technique, it can be ensured that the bottoms of opposed superimposed grooves have an accurately predetermined separation which helps maintain location of the slider perpendicularly to the guide face.
There may be any number of grooves, preferably two or more at spaced apart positions for the (or each) said guide arrangement. In a particularly preferred embodiment there are two parallel straight grooves for the (or each) said guide arrangement.
Most preferably the member is a flat bar or elongate plate and has a further face opposite to the said guide face also bounded by the said edges. This further face and the guide face may be flat and parallel to each other. The edges of the elongate member may be straight and parallel to each other.
The slider may be in the form of a sleeve having a further part linking the said edge part and overlying the further face of the elongate member. Alternatively, the slider may be C-shaped having edge parts which are inturned over the further face of the elongate member but are not linked.
With regard to the (or each) projection this may take any suitable form capable of ensuring good sliding location in the respective groove. Preferably the (or each) projection is of elongate form.
In accordance with one embodiment the (or each) projection may be formed by a projecting length of strong cord or filamentary material, such as high strength, low-extension nylon filament, such material being fixed in position at its ends so that the body of the material extends into and runs along the respective groove.
Alternatively the (or each) projection may comprise a suitably shaped elongate body formed from plastics or any other suitable material.
With regard to the said selectively interengageable parts between the slider and the elongate member, these may take any suitable form.
In one preferred embodiment, these parts comprise respectively a longitudinally extending rack of teeth and a pawl member, the pawl member being slidably located within an inclined guide slot so that it is movable between the retracted position at which the rack is free to move relative to the pawl member, and an engaged position at which the pawl member engages the rack, at a selected position between adjacent teeth thereof, to hold the slider relative to the elongate member.
The arrangement may be such that the interengagement of the pawl member with the rack prevents downward movement of the rack but permits upward movement whereby when the pawl member is engaged with the uppermost end of the rack it is possible to move the rack upwardly relative to the pawl member to select a lower position on the rack for engagement with the pawl member. A deflecting structure may be provided at the bottom of the rack so that on reaching the lowermost position the pawl member is deflected out of engagement with the rack whereby the rack can be moved fully downwardly relative to the pawl member to return the pawl member to the uppermost position on the rack.
This arrangement is described in U.S. Pat. No. 4,749,230.
As an alternative to this arrangement, and to avoid the need to move the rack fully upwardly relative to the pawl member before the full range of height adjustment is available, the interengageable parts may comprise a longitudinally extending rack of teeth and a pawl member with a manual operating device, such as a lever for moving the pawl member along a guide slot out of engagement with the rack when adjustment is required, the pawl member being movable back into engagement with the rack by gravity or a spring or otherwise as desired.
The above two mentioned rack and pawl-member arrangements may be provided together so that the mechanism may be set up for use with

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