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(11) | EP 0 302 759 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A chair |
| (57) A chair is provided comprising a frame (1), which may be made from tubular metal.
The frame has a seat (2) mounted thereon and at least one (generally two) back frame
member (5) extending upwards from the seat, at the back thereof. A back support member
(4) is mounted on the or each back frame member and a back (3) is mounted on the back
support member. The back support member is moulded from plastics material and comprises
one or more vertical webs, the or each web being substantially thinner than the overall
width of the back frame member (5). In this manner, the back can be moved backwards
and forwards relative to the seat, by flexing of the back support member. Resistance
to such flexing is primarily provided by the or each web. |
[0001] This invention relates to a chair, and in particular to aspects of a chair having a seat and a back mounted on a frame and a gas cylinder device for adjusting the height of the seat.
[0002] In the international application published under the PCT, No. WO 87/01018, a chair is described comprising a frame with a seat and a back mounted thereon, wherein the frame extends vertically upwards at the rear of the seat, on either side, and extends in an arch around the top of the back. Between the seat and the back, the frame is interrupted on either side by a flexible spring device, which is plugged into the hollow frame members above and below it, allowing the back to flex backwards when a user sits on the seat and leans backwards. The flexible device disclosed in that document is formed from a substantial thickness of moulded plastic and has a central axial cable to limit its flexibility. The moulding of such a device would be expensive, having an estimated cycle time in the mould of about four minutes or so. A suitable mould would probably require cooling galleries to cool the substantial thickness of plastic, thereby adding to manufacturing costs.
[0003] The chair shown in the above document is not very aesthetically attractive, due in part to the frame member extending in an arch around the top of the back. The present applicants have designed an attractive new range of chairs which have back frame members extending vertically upwards from the seat and these frame members are cropped to a shape which conforms to the profile of the side of the back. This cropping operation is a relatively expensive one in comparison with merely cutting the frame members square with a saw.
[0005] Chairs are known, particularly for office use, in which a gas cylinder device is used for adjusting the height of the chair. The user sits on the chair and operates a lever, which allows the cylinder and its associated piston to contract, the weight of the user pressurising the gas in the cylinder. This allows the seat to sink. To raise the seat again, the user stands up and operates the lever, whereupon the pressure built up in the cylinder during the contracting operation is able to expand the piston and cylinder to raise the seat again. The lever for operating the cylinder is frequently mounted protruding from the cylinder, beneath the seat. Such an arrangement can be found obtrusive and the lever can inconveniently become caught on clothes.
[0007] According to a first aspect of the invention, there is provided a chair comprising a frame having a seat mounted thereon, at least one back frame member extending upwards from the seat, at the back thereof, a back support member mounted on the back frame member and a back mounted on the back support member, wherein the back support member is moulded from plastics material and comprises one or more vertical webs, the or each web being substantially thinner than the overall width of the back frame member, whereby the back can be moved backwards and forwards relative to the seat, by flexing of the back support member, resistance to such flexing being primarily provided by the or each web.
[0009] Preferably there is a principal web extending in a vertical plane from front to back, such as in the form of a length of universal cross-beam arranged vertically on its end. There may be two, three or more parallel principal webs, or a principal web and parallel ancillary webs.
[0010] Alternatively, the webs may form front and rear flanges arranged in parallel vertical planes extending from side to side, joined by a central web, in the form of an elongate I-beam arranged vertically on its end.
[0011] Preferably no part of the back support member exceeds 4 mm in thickness, and more preferably no part exceeds 3.5 mm in thickness. Preferably the or each web offering primary resistance to flexing has a thickness from about 1.5 mm to about 3.8 mm. Preferably the total depth of the or each principal web from front to back is from about 20 mm to about 23 mm.
[0012] Because a back support member is provided having webs which provide the required rigidity, the thickness of the plastics material throughout the back support member can be kept low, and the cycle time in the mould can be kept correspondingly low.
[0013] Preferably the flexibilty/rigidity of the back support member is such that when a force of 500 N is applied perpendicularly and rearwardly to the back at a point 145 mm above the point of mounting of the back support member to the back frame member, the chair back undergoes flexing of between about zero degrees and about 35 degrees rearward, and preferably between about 5 degrees and about 26 degrees.
[0014] More preferably this flexing is between about 20 degrees and about 26 degrees under this test.
[0015] Preferably the chair can also withstand a force of at least 1000 N when applied to the same point, without failure of the back support members.
[0016] Projections may be provided around or between the or each web, which offer no resistance to flexing but which project outwards to a line which is a projection of the edge of the back frame member, thereby giving the back support member the appearance of being as thick as the back frame member.
[0017] According to a second aspect of the invention, a chair is provided comprising a frame having a seat mounted thereon, two elongate back frame members extending upwards from the seat, at the back thereof, a moulded back support member mounted on each back frame member, each back support member generally forming an extension of its respective back frame member, and a back mounted on the back support members, wherein each back support member has a profile corresponding to the profile of the back at the position where the back is mounted on that back support member, that profile being other than a straight line crossing the back support member perpendicularly.
[0018] By use of a moulded back support member joining the back frame members and the back, the metal back frame members need not be cut to difficult shapes to fit the back, but they can each be cut in a straight line crossing the back frame member perpendicularly and the back support member can be moulded to fit the back, the moulding being a simpler operation.
[0019] In either embodiment of the invention described above, the or each back frame member is preferably hollow and the or each back support member has a lower end in the form of a plug which makes a press-fit into the back frame member.
[0020] According to a further aspect of the invention, there is provided a chair comprising: a frame having a seat mounted thereon; a gas cylinder device for adjusting the height of the seat, the gas cylinder having a gas release valve for the intake or outlet of air to adjust the height of the seat; and a control device mounted within the frame, connecting with the gas release valve to open and close the valve.
[0021] The frame preferably comprises tubular members and connecting means pass from the control device along the inside of a tubular member before connecting with the gas release valve. Preferably the control device is a knob or button forming an end cap for one such tubular member. That member may be one which extends from side to side underneath the seat, near the front thereof.
[0022] Preferably connecting means are provided between the control device and the gas release valve, which give a mechanical advantage greater than unity, whereby a lower force can be applied to the control device to release the valve than would be needed if applied directly to the valve.
[0023] The control device may be activated by rotary movement about the axis of the frame member within which it is mounted, by longitudinal movement along that axis, or by movement in other directions.
[0024] A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a perspective view of a chair, incorporating back support members, in accordance with the invention;
Figure 2 shows a back support member as shown in
Figure 1, with cross-sectional views thereof;
Figure 3 is a cross-sectional view of part of the frame of the chair shown in Figure 1, beneath the seat, and
Figure 4 is a section along the line X - X of Figure 3.
[0025] Referring to Figure 1, the chair has a frame 1 of tubular metal, on which is mounted a seat 2. A back 3 is mounted on the frame by means of two flexible back support members 4, which extend partially into two vertical back members 5 of the frame. The frame and seat are rotatably mounted on a lower frame comprising five radially projecting legs 6 and a gas cylinder 7.
[0026] Referring to Figure 2, the flexible back support member (FBM) 4 is moulded from Delrin 100 (trade mark) and comprises a back attachment part 10, a flexible part 11 and a plug part 12.
[0027] The back attachment part 10 has a profile shaped to correspond to the back of the chair 3. It has a U-shaped cross-section as shown and a screw-hole 13 for receiving a screw to attach the FBM to the chair back.
[0028] The flexible part 11 takes the form of a universal cross-beam and has a principal front-to-back web 15 and a transverse web 16.
[0029] Horizontal flanges 17 are provided for decorative purposes. The plug part 12 is designed to fit firmly within the vertical member 5 of the tubular frame 1 and for this purpose has a plurality of ribs 18, projecting horizontally on all sides, each being champfered on the underside for ease of insertion into the tubular frame member 5.
[0030] In use, with the plug part 12 firmly pressed into the tubular member 5 and the back attachment part 10 screwed onto the back 3, a person sitting on the chair and leaning backwards causes the flexible part 11 to flex, this flexing being resisted primarily by the principal web 15. To provide the desired degree of flexibility, the principal web 15 has a thickness of about 3.5 mm. With this construction, the FBM has no part with a thickness greater than 4mm, so can be moulded very quickly - ie. it has a low cooling time and the cycle time for moulding is reduced to about 1 minute. At thicknessess greater than 4 mm, the moulding cycle time is significantly increased.
[0031] For a more rigid FBM, the web 15 can be made deeper, though about 24 mm is an approximate upper limit. A further front-to-back web can be included on either side of the principal web 15, having a thickness of, say, 2 mm. The thickness of these webs can be chosen to give the desired degree of flexibility. Three such parallel webs can be used and the rigidity of the FBM decreased by using Delrin Supertough 100ST (Trade Mark) instead of Delrin 100 (Trade Mark).
[0032] The web 15 can effectively continue downwards (not shown) into the plug part 12 for greater rigidity at the interface between the parts 11 and 12.
[0033] Referring now to Figure 3, the part of the frame 1 beneath the seat 2 is shown, with the seat omitted. The upper end of a piston for the gas cylinder 7 is shown at 20 and a release valve 21 in the piston is shown. Above the valve 21 is a lever 22 which is loosely fastened to the frame by a bolt 23 on which is held a rubber bush 24 and a self-locking nut 25. The rubber bush 24 acts as a fulcrum for the lever 22.
[0034] The end of the lever 22 remote from the piston 20 passes inside a tubular cross member 26 forming part of the frame 1, protruding into that member through a hole in the wall thereof. Within the cross member 23 is a flap 27 mounted on flat bars 28 (Figure 4) extending to either end of the cross member 26, within that cross member.
[0035] As can be seen from Figure 4, a knob 30, 31 is located at the outer end of each of the bars 28. These knobs are rotatably mounted in the cross-member 26 and protrude out from underneath the seat 2, on either side thereof, as shown in Figure 1.
[0036] When sitting on the seat 2, a user can rotate the right hand knob 30 clockwise (or the left-hand knob 31 anti-clockwise) and this turns the respective bar 28 and the flap 27 to the position 27′ shown by a dotted line in Figure 3. This lifts the front end of the lever 22 which pivots on the fulcrum 24 and the rear end depresses the valve 21, allowing the release of air from the cylinder 7 and allowing the piston 20 to sink, thus lowering the height of the seat 2. When a desired height is reached, the user releases the knob 30 and the valve springs upwards of its own accord, thus holding the seat at that height and returning the lever 22, the flap 27, the bars 28 and the knobs 30 and 31 to their original positions.
[0037] To raise the height of the seat again, the user merely stands up and turns one of the knobs 30 and 31. The valve 21 is again depressed and pressure in the cylinder 7, which has been built up by lowering the seat under the weight of the user, is now able to raise the seat.
[0038] In this way, a mechanism is provided, for operating the gas release valve and thereby adjusting the height of the seat, which is discreetly housed partially within the frame of the chair and the control means of which (the knob 30 or 31) is discreetly mounted within the frame of the chair, at a position easily accessible to the hand of the user when seated in a normal sitting position.
[0039] Other control means could be used instead of a rotating knob. For example, a push-button could be used, operating a wedge mounted within the transverse frame member 26, the wedge being positioned to raise the end of the lever 22. Other means of transferring the movement from the control means to the gas release valve could be used, such as cables and linkages, or a Bourdon cable. The arrangement shown in figure 3 has the advantage that the lever 22 provides a mechanical advantage to reduce the force required to depress the relatively stiff valve 21. If other suitable linkages were used, a mechanical advantage could be provided in a number of different ways.
1. A chair comprising a frame having a seat mounted thereon, at least one back frame
member extending upwards from the seat, at the back thereof, a back support member
mounted on the back frame member and a back mounted on the back support member, wherein
the back support member is moulded from plastics material and comprises one or more
vertical webs, the or each web being substantially thinner than the overall width
of the back frame member, whereby the back can be moved backwards and forwards relative
to the seat, by flexing of the back support member, resistance to such flexing being
primarily provided by the or each web.
2. A chair according to Claim 1, comprising two such back frame members and two such
back support members.
3. A chair according to either of Claims 1 and 2, having a principal web extending
in a vertical plane from front to back.
4. A chair according to Claim 2, wherein the back support member is in the form of
a length of universal cross-beam arranged vertically on its end.
5. A chair according to either of Claims 3 and 4, further comprising ancillary webs
parallel to the principal web.
6. A chair according to either of Claims 1 and 2, wherein the back support member
comprises webs in the form of front and rear flanges, arranged in parallel vertical
planes extending from side to side, joined by a central web, in the form of an elongate
I-beam arranged vertically on its end.
7. A chair according to any one of the preceding Claims, wherein no part of the back
support member exceeds 4 mm in thickness.
8. A chair according to Claim 7, wherein no part of the back support member exceeds
3.5 mm in thickness.
9. A chair according to any one of the preceding claims, wherein the or each web offering
primary resistance to flexing has a thickness from about 1.5 mm to about 3.8 mm.
10. A chair according to any one of Claims, 3, 4 and 5, wherein the total depth of
the principal web from front to back is from about 20 mm to about 23 mm.
11. A chair according to any one of the preceding Claims, wherein the flexibility/rigidity
of the back support member is such that when a force of 500 N is applied perpendicularly
and rearwardly to the back at a point 145 mm above the point of mounting of the back
support member to the back spring member, the chair back undergoes flexing of between
about 0° and about 35° rearward.
12. A chair according to Claim 10, wherein the chair back undergoes flexing of between
about 5° and about 26° under the said conditions.
13. A chair according to Claim 11, wherein the flexing is between about 20° and about
25° under the said conditions.
14. A chair according to any one of the preceding Claims, which can withstand a force
of at least 1000 N when applied perpendicularly and rearwardly to the back at a point
145 mm above the point of mounting of the back support member to the back frame member.
15. A chair according to any one of the preceding Claims, wherein the back support
member is provided with projections around or between the or each web, which offer
substantially no resistance to flexing, but which project upwards to a line which
is a projection of the edge of the back frame member.
16. A chair according to any one of the preceding Claims, comprising two elongate
back frame members extending upwards from the seat, at the back thereof, and a moulded
back support member mounted on each back frame member, each back support member generally
forming an extension of its respective back frame member, wherein each back support
member has a profile corresponding to the profile of the back at the position where
the back is mounted on that back support member, that profile being other than a straight
line crossing the back support member perpendicularly.
17. A chair according to any one of the preceding Claims, further comprising a gas
cylinder device for adjusting the height of the seat, the gas cylinder having a gas
release valve for the intake or outlet of air to adjust the height of the seat; and
a control device mounted within the frame, connecting with the gas release valve to
open and close the valve.