GB2193884A

GB2193884A - A tilting mechanism for a chair

Info

Publication number: GB2193884A
Application number: GB08619986A
Authority: GB
Inventors: William John Hancock; Brian Charles Parker
Original assignee: CHAIR MECHANISMS Ltd
Current assignee: CHAIR MECHANISMS Ltd
Priority date: 1986-08-16
Filing date: 1986-08-16
Publication date: 1988-02-24
Also published as: GB8619986D0; GB2193884B

Abstract

A tilting mechanism, for the backrest of a chair having two relatively pivotable parts 10, 11 for connection to the backrest and chair seat respectively, comprises a number of friction leaves 17 movable with one part 10 and interleaved with friction leaves 18 movable with the other part 11. A rotatable cam 23 is mounted on one of the parts 10 and is rotatable between a clamping position where it clamps the friction leaves 17, 18 together and against an abutment 14 to retain the two parts of the mechanism in a required angular position and an inoperative position where it permits relative movement between the friction leaves. A spring 29 urges the cam towards the clamping position with a pre-determined adjustable force, and a manually operable lever 27 is connected to the cam for moving it towards the inoperative position, against the action of the spring, to permit adjustment of the angle of the backrest. <IMAGE>

Description

SPECIFICATION A tilting mechanism for a chair The invention relates to tilting mechanisms for chairs, of the kind comprising two parts, for connection to the chair seat and chair back respectively, pivotally connected together for relative pivotal movement about a horizontal axis, means being provided for securing the two parts of the mechanism in a required angular position, whereby the angle of the chair back with respect to the chair seat can be adjusted. Such a mechanism is frequently used in what are commonly referred to as "typists' chairs".

In one known form of mechanism of this type, the two parts of the mechanism are provided with interleaved friction plates, the pivot pin providing the pivotal connection between the parts passing through the interleaved plates and being provided at one end with a clamping knob which is in threaded engagement with the pivot pin. By screwing up the clamping knob after the back rest of the chair has been adjusted to a required position, the interleaved friction plates are clamped tightly into engagement with one another to prevent further relative pivoting movement between the two parts of the mechanism.

Such mechanisms suffer from significant disadvantages. For example, since the frictionally engaged surfaces closely encircle the pivot pin, any force applied to the chair back rest acts on the frictional surfaces with substantial mechanical advantage.

Consequently, the clamping knob must be screwed up very tightly to ensure that there is no risk of slip between the friction elements which could result in sudden and dangerous pivoting of the back rest. Not only may it be difficult for a user of the chair to screw the clamping knob up sufficiently tightly, it is also often difficult or impossible for a user to unscrew the knob should it become necessary to readjust the back rest angle.

The present invention sets out to provide a chair tilting mechanism in which the above mentioned disadvantages may be overcome.

According to the invention a tilting mechanism for a chair comprises two parts, for connection to the chair seat and chair back respectively, pivotally connected together for relative movement about a horizontal axis, at least one friction element movable with one part and overlying at least one friction element movable with the other part, a clamping element mounted on one of said parts and movable between a clamping position where it clamps said friction elements together to retain said two parts of the mechanism in a required angular position, and an inoperative position where it permits relative movement between said elements, spring means urging the clamping members towards the clamping position, and a manually operable member connected to the clamping element for moving it towards the inoperative position against the action of said spring means.

Since the friction elements are clamped together by spring means, the clamping force is predetermined by the strength of the spring means and it is not necessary for the user to exert the required clamping force, for example by screwing up a clamping knob. Furthermore, the mechanism is readily released by moving the manually operable member against the action of the spring means. The force necessary to release the mechanism is predetermined by the strength of the spring means and does not depend, as in the above described known construction, on the strength with which the mechanism was last clamped. The manually operable member may be so constructed as to provide a substantial mechanical advantage in overcoming the action of the spring means.

Preferably the friction elements are mounted on the two parts of the mechanism separately from the pivotal connection between the two parts, and spaced from that pivotal connection. With such an arrangement, due to the spacing of the frictional elements from the pivotal connection, the mechanical advantage is reduced so that a given force on the chair back rest results in a much lesser force acting on the friction elements than is the case hitherto, where the friction elements closely surround the pivotal connection. The clamping force between the friction elements can therefore be less than in the known arrangement.

The clamping element may be a rotatable cam member which is rotationally urged to the clamping position by said spring means. For example the spring means may be a torsion spring connected to rotate the cam.

The cam member may be mounted on, or integral with, a shaft rotatably mounted on said one part of the mechanism. For example, where the shaft is of circular cross section the cam member may be provided by a portion of the shaft formed with a flat. The spring means may comprise a helical spring encircling the shaft and secured between the shaft and said one part of the mechanism. The manually operable member may comprise a lever connected to the cam, or the shaft on which it is mounted, so that pivotal movement of the lever effects rotation of the cam.

Preferably said one part of the mechanism is provided with an abutment element mounted thereon, said friction elements being clamped between the clamping element and the abutment element. The cam may act on a thrust element, the friction elements being sandwiched between the thrust element and the abutment element.

Preferably the cam is adjustably mounted on said one part of the mechanism for movement towards and away from the abutment element. This permits adjustment of the clamping force exerted on the friction elements by the spring means through the cam.

The friction elements may be formed with apertures through which extends a shaft mounted on said one part of the mechanism, the aperture in each friction element on the other part of the mechanism being elongate so as to permit movement of the friction elements relatively to the shaft upon relative pivoting movement between the two parts ofthe mechanism.

In the case where said one part of the mechanism is for connection to the chair seat, it may include a main portion to which the other part of the mechanism is pivotally connected, and an adjustable tilting portion pivotally connected to the main portion and on which, in use, the seat is to be mounted.

In this case the friction element on said one part is preferably mounted on the tilting portion whereby clamping of the friction elements together secures the tilting portion at a required angle to the main portion, as well as securing the other part of the mechanism at a required angle to said main portion.

In any of the above arrangements there are preferably provided a plurality of friction elements on said one part interleaved with a plurality of friction elements on the other part.

The following is a more detailed description of embodiments of the invention reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic horizontal section through a tilting mechanism in accordance with the invention, Figure 2 is a diagrammatic vertical section through the mechanism of the Figure 1, Figure 3 is a side elevation of the cam/clamp bar of the mechanism of Figures 1 and 2, Figure 4 is a cross section through the mechanism along the line 4-4 of Figure 1, Figure 5 is a further cross section, along the line 5-5 of Figure 1, and Figures 6 to 10 are views, corresponding to Figures 1 to 5 respectively, of an alternative form of mechanism according to the invention.

Referring to Figure 1, the mechanism comprises a channel-sectioned part 10 for connection to the underside of a chair seat, and a generally U-shaped part 11 pivotally connected to the part 10 by means of a horizontal pivot pin 12 extending through registering holes in the side flanges of the part 10 and the part 11.

Between the flanges of the channel-sectioned part 10, adjacent the end remote from the part 11, is welded a socket member 9 in which the upper end of a support post for the chair seat is received in conventional manner.

The part 11 is shaped to receive a vertically slideable pillar 13 on the upper end of which is mounted the back rest (not shown) of the chair. Means (not shown) are provided on the part 11 for releasably locating the pillar 13 in a required vertical position.

As best seen in Figures 1 and 5, a tubular abutment sleeve 14 is welded to one side flange of the channel section part 10 and extends parallel to and spaced from the pivot pin 12. A circular cross section bar 15 is slideable within the sleeve 14. The end of the bar 15 remote from the sleeve 14 is formed with a circular boss 9 which is slideably located in a hole in the opposite side flange of the channel section part 10.

Adjacent the boss 9 the bar 15 is integrally formed with a larger diameter portion 21 to provide an annular shoulder 21a.

A thrust washer 16 abuts the shoulder 21a, and sandwiched between the thrust washer 16 and the end of the sleeve 14 are alternating washers 17 and friction leaves 18. The washers 17 encircle the bar 15 and, as best seen in Figure 2, the leaves 18 are formed with elongate apertures 19 through which the bar 15 extends. The leaves 18 are generally rectangular in shape and are mounted on a further pivot pin 20 which extends between the flanges of the U-shaped part 11 at a location spaced below the pivot pin 12.

The enlarged portion 21 of the bar 15 is formed with a circular transverse bore 22 part of which extends into the central aperture in the thrust washer 16. Rotatable within the bore 22 is an end portion 23, formed with a flat 24, of a circular cross-section rod 25. The end of the rod 25 remote from the flat 24 is rotatably supported in a plate 26 extending transversely across the channel-sectioned part 10.

A release lever 27 is welded at one end to the rod 25 and extends transversely away from the rod 25 through a slot 28 in the adjacent side flange of the channel-sectioned part 10. A helical torsion spring 29 encircles the rod 25. One end 30 of the torsion spring bears against the bottom wall of the channelsectioned part 10 and the other end 31 is hooked over the release lever 27.

The mechanism operates as follows: Normally the torsion spring 29 urges the rod 25 in a clockwise direction (as seen in Figure 5) with the result that the cam provided by the flat 24 on the end portion 23 of the rod urges the thrust washer 16 to the left, as seen in Figure 5, compressing the washers 17 and leaves 18 together between the thrust washer 16 and the end of the abutment sleeve 14. This has the effect of tightly gripping the ends of the leaves 18 and preventing their movement relatively to the bar 15 and, as seen in Figure 2, this prevents pivotal movement of the U-shaped part 11, and hence of the back rest of the chair, relatively to the part 10 and the seat of the chair.

When it is required to adjust the angular position of the back rest, the release lever 27 is swung upwardly, rotating the rod 25 anti clockwise as seen in Figure 5. This brings the end portion 23 of the rod out of pressing engagement with the flange 16, releasing the frictional engagement between the leaves 18 and washers 17 and thus permitting pivoting of the part 11 relatively to the part 10. Movement of the leaves 18 relatively to the bar 15 is permitted by the elongate slots 19. When the back rest has been placed in the new desired position, the lever 27 is released and the spring 29 again rotates the rod 25 so that the cam portion 23 once again clamps the leaves 18 and washers 17 into frictional engagement.

The frictional pre-loading of the leaves and washers may be adjusted by means of an adjustment screw 32 which extends through the side flange of the part 10 and is in threaded engagement with the end of the bar 15. Adjustment of the screw 32 slides the bar 15 axially, together with the cam portion 23 of the rod 25, and thus adjusts the clamping pressure exerted on the leaves 18 and washers 17 by the cam portion.

It will thus be appreciated that the frictional restraint against pivoting of the back rest is provided solely by the torsional force applied to the rod 25 by the spring 29 and this may be predetermined, by adjustment of the screw 32, to provide adequate frictional restraint.

The force necessary to release the back rest is therefore constant, being the force necessary to overcome the torsional restraint of the spring 29, and the lever 27 may be of sufficient length to provide good mechanical advantage to enable a comparatively weak person to release the mechanism.

Furthermore, the area where the frictional engagement between the leaves 18 and washers 17 occurs is spaced from the pivot pin 12 so as to provide a greater mechanical advantage for the restraining force against forces applied to the back rest during normal use.

The compact and simple design of the mechanism is such that, unlike many known designs of mechanism, it is not necessary to provide for the movable components to project out of the channel 10 which houses the components. As a result, the channel 10 may be upwardly facing, as shown, so that the open side of the channel is covered by the seat on which it is mounted. The whole mechanism therefore presents a neat appearance on the underside of the seat, as well as being less liable to the ingress of dirt than known arrangements where the inside of the channel and the moving components are exposed.

Figures 6 to 10 show a modified arrangement where the part of the mechanism for attachment to the seat is formed in two portions, one of which is tiltable relatively to the other to provide adjustment of the angle of the seat. Figures 6 to 10 correspond to Figures 1 to 5 respectively, and corresponding parts in the two arrangements have the same reference numerals.

Referring to Figure 7, the channel-sectioned part 10 has pivotally mounted to it, by means of a pivot pin 33 remote from the pivot pin 12, a seat fixing channel 34 the flanges of which embrace the flanges of the part 10, as best seen in Figure 9.

In this arrangement, the washers 1 7 between the leaves 18 are replaced by further leaves 35, similar to the leaves 18, but pivoted on a pivot pin 36 extending between the side flanges of the seat fixing channel 34.

The cam clamping mechanism is otherwise the same as that in the arrangement of Figures 1 to 5. In the arrangement of Figures 6 to 10, however, when the release lever 27 is operated the leaves 35 are released as well as the leaves 18 so that the angular position of the seat fixing channel 34 with respect to the main channel 10 may be adjusted, as well as the angle of the back rest.

Claims

1. A tilting mechanism for a chair comprising two parts, for connection to the chair seat and chair back respectively, pivotally connected together for relative movement about a horizontal axis, at least one friction element movable with one part and overlying at least one friction element movable with the other part, a clamping element mounted on one of said parts and movable between a clamping position where it clamps said friction elements together to retain said two parts of the mechanism in a required angular position, and an inoperative position where it permits relative movement between said elements, spring means urging the clamping members towards the clamping position, and a manually operable member connected to the clamping element for moving it towards the inoperative position against the action of said spring means.

2. A mechanism according to Claim 1, wherein the manually operable member is so constructed as to provide a substantial mechanical advantage in overcoming the action of the spring means.

3. A mechanism according to Claim 1 or Claim 2, wherein the friction elements are mounted on the two parts of the mechanism separately from the pivotal connection between the two parts, and spaced from that pivotal connection.

4. A mechanism according to any of Claims 1 to 3, wherein the clamping element comprises a rotatable cam member which is rotationally urged to the clamping position by said spring means.

5. A mechanism according to Claim 4, wherein the spring means is a torsion spring connected to rotate the cam.

6. A mechanism according to Claim 4 or Claim 5, wherein the cam member is carried on a shaft rotatably mounted on said one part of the mechanism.

7. A mechanism according to Claim 6, wherein the shaft is of circular cross section and the cam member is provided by a portion of the shaft formed with a flat.

8. A mechanism according to Claim 6 or Claim 7, wherein the spring means comprise a helical spring encircling the shaft and secured between the shaft and said one part of the mechanism.

9. A mechanism according to any of Claims 4 to 8, wherein the manually operable member comprises a lever connected to the cam, so that pivotal movement of the lever effects rotation -of the cam.

10. A mechanism according to any of Claims 4 to 9, wherein said one part of the mechanism is provided with an abutment element mounted thereon, said friction elements being clamped between the clamping element and the abutment element.

11. A mechanism according to Claim 10, wherein the cam member acts on a thrust element, the friction elements being sandwiched between the thrust element and the abutment element.

12. A mechanism according to Claim 10 or Claim 11, wherein the cam member is adjustably mounted on said one part of the mechanism for movement towards and away from the abutment element.

13. A mechanism according to any of Claims 1 to 12, wherein the friction elements are formed with apertures through which extends a shaft mounted on said one part of the mechanism, the aperture in each friction element on the other part of the mechanism being elongate so as to permit movement of the friction elements relatively to the shaft upon relative pivoting movement between the two parts of the mechanism.

14. A mechanism according to any of Claims 1 to 13, wherein said one part of the mechanism is for connection to the chair seat, and includes a main portion to which the other part of the mechanism is pivotally connected, and an adjustable tilting portion pivotally connected to the main portion and on which, in use, the seat is to be mounted.

15. A mechanism according to Claim 14, wherein the friction element on said one part is mounted on the tilting portion whereby clamping of the friction elements together secures the tilting portion at a required angle to the main portion, as well as securing the other part of the mechanism at a required angle to said main portion.

1 6. A mechanism according to any of Claims 1 to 15, wherein there are provided a plurality of friction elements on said one part interleaved with a plurality of friction elements on the other part.

17. A tilting mechanism for a chair substantially as hereinbefore described with reference to Figures 1 to 5 or Figures 6 to 10 of the accompanying drawings.