WO2009127862A1

WO2009127862A1 - Chair back tilt tensioning

Info

Publication number: WO2009127862A1
Application number: PCT/GB2009/050362
Authority: WO
Inventors: Simon Roberts
Original assignee: Simclar Seating Technologies Limited
Priority date: 2008-04-17
Filing date: 2009-04-14
Publication date: 2009-10-22
Also published as: GB0806958D0

Abstract

A Chair backtilttensioning arrangement includes a spring (20), between a part (12) which is displaceable by tilting of the seat back (11) and a fixed part (17) and provides resistance to tilting movement of the seat back (11), and is connected at one end to a part (31) which isdisplaceable by a cam to adjust the length of the spring.

Description

CHAIR BACK TILT TENSIONING

The invention relates to means for varying the tension acting on a tiltable back for an office or other chair, to resist tilting movement of the chair back.

It is important for safety reasons, with a tiltable chair back, to provide a force resisting tilting movement of the chair back, as otherwise any force applied, to the back in the tilting direction, whether intended or not would cause the back to tilt. It is thus necessary to build in a resistance to tilting movement which must be overcome, to ensure that only deliberate tilting will take place.

The resistance is usually provided by incorporating a tension or compression spring between a part displaceable with the tiltable back, and another part fixed to the body of the chair. The resistance of this spring is fixed, so that the same effort will always be required to tilt the back.

For various reasons, such as differences in the weight of chair occupants, it is desirable to enable the resistance of the spring to tilting movement of the chair back to be varied, and to have this controllable by the user of the seat.

According to the invention therefore, in a seat having a tiltable back, there is provided, between a part displaceable by tilting of the seat back, and a further part which is fixed with respect to the seat, a spring is connected to provide resistance to tilting movement of the seat back, the spring being connected at one end to means enabling the length of the spring to be adjusted.

The spring is preferably a compression spring, but may be a tension spring.

The adjusting means may include a rotary or linear cam which can be moved by operation of a manual control, to displace the said one end of the spring. The spring may be a coil spring, or a resilient body such as rubber, or a gas spring for example.

There may be an arm extending from the end of the spring connected to the tiltable back, to the shaft located adjacent the other end of the spring, which arm serves to displace a seat for one end of the spring, the other end of the arm being deflectable by a cam surface to pull the seat of the spring towards the other end, movement of the said other end of the arm being effected by the first mentioned cam.

Shortening of the spring length by pulling the end seat of the spring will increase tension, and reduce compression, while lengthening the spring will have the opposite effect.

A preferred embodiment of chair apparatus according to the invention will now be described by way of example with reference to the accompanying drawings, wherein :-

Figures 1 and 2 are diagrammatic side views of the main components of a chair apparatus, with the seat back upright, and partially reclined respectively;

Figure 3 is a cut away view of the underseat arrangement of a chair apparatus according to the invention;

Figure 4 is a view similar to Figure 3, showing some components of

Figure 3 removed to show further components which form part of the apparatus according to the invention;

Figure 5 is a half tone image showing essentially the same components as the line drawing of Figure 4, in a state of maximum compression of a spring component; and

Figure 6 is a halftone image showing the components shown in Figure 5 in a state of minimum compression of the spring component.

Figures 1 and 2 are diagrammatic views of a chair, which comprises a seat platform 10 and a back rest support 11. These are shown without the customary cushions or padding. The back rest support 11 is connected, by for example being integrally formed, to an arm 12, forming a generally L-shaped configuration with the back rest support. An arm 12 may be provided at each side of the support 11. The or each arm 12 is provided part way along with a stub 13 which is articulated at 14 to a leg 15 near the rear edge of the seat platform 10. The arm or arms 12 are also articulated at each side on an axis 16, to a respective forward underseat bracket 17 which is mounted on a seat pedestal 18 and forms a housing for a tilt mechanism which is fixed in position with respect to the pedestal 18, whilst the back rest support 11 and arm 12, and the seat platform 10 are pivotable on the axis 16 and the point 14 to effect tilting of the backrest and reclining of the seat.

Figure 1 shows the seat in an upright 'alert' condition, with the seat platform 10 generally horizontal, and the back rest support 11 substantially upright. Figure 2 shows the seat reclined, with the seat platform 10 sloped downwardly towards the rear of the seat, and the back rest support 11 inclined rearwards, to produce a 'resting' position. It will be noted that the arm 12 has also pivoted on axis 16 from an up-sloping condition in Figure 1, to a down-sloping condition in Figure 2. A bracket 17 is provided towards each side of the underseat space, and these define between them a volume which accommodates a tilt control mechanism, which features means whereby the range of tilt of the seat back may be limited, to for example a range of up to 23°, by means of an arcuate slot, not shown and for latching the seat to hold the tilt mechanism in intermediate positions. These features are described in more detail in copending patent applications.

The underseat apparatus incorporates a compression spring 20, which is shown schematically in Figure 4, and pictorially in Figures 5 and 6. In the view of Figure 3, the spring 20 is concealed behind the arm 12, which is articulated to the seat base at 14 and to the frame at fixed axis 16, and also has a third articulation shaft 18 where it is connected to a pushing link 21 which is connected to its other end (leftward in Figure 3) by an articulation 22 to a lever 23. A pawl 24 is also displaceable leftward by the same movement, and this can be deflected downwardly by a pusher lever 25 so that a catch 26 on the lower free end of the pawl can engage with a selected one of an array of detents 27, to prevent further displacement of the pivot 18, and thus limit the range of pivoting of the chair back by limiting the arc of pivoting of the arm 12.

The spring 20, is seated at one end in a block 28 which engages with a pin 29 on a lever 30 which is rotatable on the third articulation shaft 18. The opposite end of the spring 20 is seated in a block 31 located in a bracket 32. A link arm 33 extends from the pin 29, within the spring 20, as is evident from Figures 5 and 6 and is seated at the leftward end as shown on a pin 34 in member 36, which acts as a cam follower on a curved or sloped surface 37, to thus be displaced as for example shown by comparison of Figures 5 and 6. The member 36 can, as shown in Figures 5 and 6 be displaced by rotation of a cam 38 on a shaft 39. The lever 23 is pivoted to the body 17 by a fixed pivot shaft 41, so that the lower articulation points 34 and 39 describe arcs about the shaft 41 as the lever 23 is pivoted by movement of the link 21. The pivot 34 is displaceable by the cam 38, and as it is moved downwardly, to for example the Figure 5 position, from the Figure 6 position the distance from 41 to 34 is increased and this increases the mechanical advantage of the spring 20, whilst conversely lifting the pivot 34 decreases this advantage. This varies the effect of pressure exerted on the seat back by say a change in the user's position.

An alternative embodiment of means for varying the distance between the pivots 34 and 39 from the shaft 41, which is not illustrated in the drawings, may comprise the use of a pair of cooperating cams, one connected to the pivot 34 and one to the pivot 39, and which feature at least one cooperative inclined cam surface, preferably two. One of the cams, say that associated with pivot 39, is displaceable by rotation of a worm drive, so that the inclined cam surfaces interact so as to increase or decrease the separation of the pivots 39, 34.

The worm drive and the cams are in line with the axes of the pivots, and thus extend perpendicularly to the plane of the Figures of the drawings.

Figure 6 shows the cam 38 rotated to allow the plate 36 to occupy the highest position, to which it is biased by the tension of spring 20, 'down' the slope of the surface 37. Rotation of the cam 38 into the Figure 5 position pushes the plate 36 'up' the slope of surface 37. This pushes the end of arm 33 down in Figure 5, and also displaces the arm to the left in Figure 5, which in turn moves the block 28 at the rightward end of the spring to shorten the spring 20. On the other hand, when the cam

38 pushes the plate 36 down to the Figure 5 position riding "up" the surface 37, the block 38 is pushed to the right, and the spring 20 is shortened thereby increasing the tension.

The shaft 39 is arranged to be operated by a manually actuable knob or lever, not shown, mounted on an extension of the shaft through a side member having the tilt mechanism. Alteration of the tension of the spring 20 varies the resistance of the chair back to tilting of the back, as the pushing link 21 pushes the lever 23 to the left, against the tension of the spring 20, the bracket 32 carrying the leftward end block 31 mounting the spring 20 being connected to a part 40 integral with the lever 23 so that the end of the spring is pulled to the left when the link 21 is displaced by backward tilting of the chair back. The main effect however is due to variation of the leverage of the lever 23 by displacement of the pivot 34.

The apparatus described enables the tension of the spring and the leverage effected to be adjusted, and thus the resistance of the chair back to tilting, to be varied in accordance with the needs or preferences of the user of the chair, and is under the user's control.

The apparatus may be adopted appropriately to use a compression spring rather than a tension spring as the variable resistance component.

Claims

1. A seat having a tiltable back, and comprising, between a part displaceable by tilting of the seat back and a further part which is fixed with respect to the seat, a spring connected to said parts to provide resistance to tilting movement of the seat back, the spring being connected at one end to adjusting means enabling the length of the spring to be adjusted.

2. A seat according to claim 1, wherein the adjusting means includes a rotary or linear cam which can be moved by operation of a manual control, to displace said one end of the spring.

3. A seat according to claim 2, wherein an arm extends from the end of the spring connected to the tiltable back, to a shaft located adjacent the other end of the spring, said arm serving to displace a seat for one end of the spring and the other end of the arm being deflectable by a cam surface to pull the seat of the spring towards the other end of the arm, movement of the said other end of the arm being effected by the first mentioned cam.

4. A seat according to any preceding claim wherein the spring is a compression spring.

5. A seat according to any of claims 1 to 3, wherein the spring is a tension spring.

6. A seat according to any preceding claim, wherein the spring is a coil spring or gas spring.

7. A seat according to any of claims 1 to 5, wherein the spring comprises a resilient body.