IMPROVEMENTS IN OR RELATING TO CHAIRS

Abstract: A chair which can support a person in both a seated and standing position comprises a tiltable seat the angle of which changes with the height of the chair.

Description: The present invention relates to chairs and more particularly to chair seats designed to support the body of a human being (the user) at variable heights. The present invention is particularly concerned with the design of a chair which can support a user at a height approximately equal to the normal standing height of the user. Since users vary in height over a wide range the chair must be capable of being adjustable in height over such a wide range and also be capable of supporting a user in both a normal (low) sitting position and in a sit/stand (high) position whereby the user stands at for example 90% of normal standing height. DE 2837558 discloses a chair, the seat height being adjustable relative to the base and includes co-operative means for adjusting, at any height at which the seat is set relative the base, the angle of tilt of the seat and a backrest for the seat to suit a particular user. According to the present invention there is provided a chair characterised as in claim 1. Preferably the angle of tilt of the seat is adjusted by the co-operative means comprising a lever system attached to a base portion of the seat. In a particular embodiment the lever system is active to adjust the position of a backrest relative to the seat as the seat is raised and lowered. The seat is preferably substantially a convex arcuate shape in side cross-sectional elevation and substantially rectangular in front cross-sectional elevation. The seat is preferably wider in cross-section at the rear most portion and narrower in cross-section at the front portion. In a preferred embodiment the upper surface of the seat comprises a convex curve having three different radii of curvature the longest being at the rear edge of the seat and the shortest being at the front edge of the seat. Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings, in which: Figure 1 shows a chair according to the present invention in front elevation; Figure 2 shows the chair of Figure 1 in side elevation; Figure 3 shows a further chair according to the present invention in front elevation; Figure 4 shows the chair of Figure 3 in side elevation; Figure 5 shows a perspective view of a seat suitable for the chairs of Figures 1 to 4; Figure 6 shows a plan view of one half of the seat of Figure 5; Figure 7 shows a cross-section of the seat of Figure 6 on line ′A-A′; and Figure 8 shows a part cross-sectional front elevation of the seat of Figure 5. With reference now to Figures 1 and 2 a first chair according to the present invention comprises a base 10, seat portion 20, a backrest 30 and a lifting and tilting mechanism 40. The base 10 may be of any conventional form, for example five star. The lifting mechanism may comprise two hydraulic cylinders 41, 42 which may be operated via a conventional lever (not shown) to raise the height of the seat 20. The tilting mechanism comprises two levers 43, 44 pivoted as shown and attached to the front of seat 20 as shown such that as the height of the seat increases the front edge of the seat is tilted downwards in a controlled manner as predetermined by the length of the levers 43, 44. In this design the backrest 30 remains in a relatively fixed position to the seat 20 as the seat is raised. With reference now to Figures 3 and 4 an alternative design of chair is shown again comprising a base 10 (as in Figures 1 and 2 and not shown) a seat 20 a raising and tilting mechanism 40 and a backrest 30. The lifting mechanism again includes hydraulic cylinders 41, 42 to raise and lower the seat 20 as in Figures 1 and 2. The tilting mechanism comprises levers 45 and 46 (which in this embodiment is cranked) and which again by their pivoted action cause the front edge of the seat to be lowered as the height of the seat increases. In this embodiment the lever 46 is attached to the underneath rear of seat 20 and the height of the backrest 30 is adjusted as the seat height is adjusted. The seat is specifically designed such that there is always a horizontal portion of the seat to be sat on by the user for support at all heights within the designed height range. The shape of seat 20 is shown in Figures 5 to 8 and with reference to Figure 7 the seat is contoured to provide an upper surface 21 the shape of which is dictacted by three arcs of radii R1, R2 and R3 as shown. The seat is shaped to be narrower at the front as indicated by the cross-sectional shapes A′-A′, B′-B′ and C′-C′ shown in Figure 8 and by the plan view of Figure 6. With respect to the cross-sections the upper surface 21 of the seat need not necessarily be flat but could be contoured to provide for example a domed shape which may be more comfortable or a seat contoured to accommodate the shape of the upper legs or thighs. The seat may be provided for example with a tensioned net or canvas sling stretched over a suitable frame. The tilting action may be brought about by a co-ordinated movement of control cylinders rather than a series of links or by an electrically driven motorised system. This would enable a more complex tilting sequential movement to be obtained if required. In a particular embodiment the dimensions of the radii R1, R2 and R3 are as follows: These dimensions are given only by way of example and may be varied to suit specific requirements.

Claims: 1. A chair having a seat and a base, means for adjusting the height of the seat as a whole relative to the base and means for adjusting the angle of tilt of the seat, characterised in that the chair comprises means (40) attached to the seat (20) for automatically adjusting the angle of tilt of the seat (20) as the height of the seat relative to the base (10) is adjusted. 2. A chair as claimed in Claim 1 characterised in that the angle of tilt of the seat is adjusted by the automatic adjustment means comprising a lever system (43, 44) attached to the seat. 3. A chair as claimed in Claim 2 characterised in that the lever system (45, 46) is active to adjust the position of a backrest relative the seat (20) as the seat (20) is raised and lowered. 4. A chair as claimed in any one of Claims 1 to 3 characterised in that the seat (20) is substantially a convex arcuate shape in side cross-sectional elevation and substantially rectangular in front cross-sectional elevation. 5. A chair as claimed in any one of Claims 1 to Claim 4 characterised in that the seat 20 is wider in cross-section at a rear most portion (A′-A′) and narrower in cross-section at a front portion (C′-C′). 6. A chair as claimed in any one of Claims 1 to 5 characterised in that an upper surface (21) of the seat comprises a convex curve having three different radii of curvature (R1, R2, R3) the longest being at the rear edge of the seat and the shortest being at the front edge of the seat. 7. A chair as claimed in Claim 1 characterised in that the angle of tilt of the seat is adjusted by control cylinders the movement of which is co-ordinated to provide the required variation. 8. A chair as claimed in Claim 1 characterised in that the angle of tilt of the seat is adjusted by electric motors driven at variable speeds to provide the required variation.

Inventors: CORLETT, ESMOND NIGEL
Applicants: NATIONAL RESEARCH DEVELOPMENT CORPORATION
Application year: 1988
Main classification: A47C9
IPC codes: A47C9, A47C3