Use of a chair seat cushion

Abstract: A chair seat cushion which is intended to be placed on the front part of a chair seat, is essentially non-compressible when subjected to load, has a length (L 1 ) which is substantially smaller than the effective length (L 0 ) of the seat (21), so as to enable the rear edge (4) of the cushion to be moved to a position essentially immediately beneath the hip joints of a seated person, at the same time as the front edge (3) of the cushion will be located essentially inwardly of the front edge of the seat (21). The seat cushion has an effective thickness (t 2 ) of from 25-45 mm between the generally flat bottom surface of the cushion and those parts (2) of the upper side of the cushion that support the thighs of the seated person.

Description: The present invention relates to a use of a chair seat cushion. US 3511537 reveals the use of a chair seat cushion for a chair having a backrest, wherein the cushion has a length of at most 40 cm, and the user's calves are out of contact with the front edge (3) of said cushion; and wherein the upper thigh-supporting surface of the cushion can be placed at a height of at least 15 mm above a chair seat surface between the cushion and the backrest. Other earlier technique concerning contoured and structured chair seats is represented in US-A 5,352,023, US-A 4,726,624 and WO-A 94/10878, all of which relate to wheelchairs and more specifically to wheelchair seats that are designed for a different purpose to that intended by the invention, namely primarily to prevent a person seated in a wheelchair from sliding forwards on or from the chair seat, for instance in the event of an abrupt stop. The wheelchair seat has a sunken rear part which receives the user's back to this end. The transition from the rear sunken part of the seat and the front raised part forms a barrier which functions to prevent the user from slipping forwards. A wheelchair -bound user will often lack the ability to feel or correct an unsuitable hip position in the wheelchair. The seat can be given the "right" length with respect to the horizontal distance between the user's back and his/her bent knees, by enabling the whole of the wheelchair seat to be moved longitudinally in relation to the wheelchair back rest. In order to enable the barrier to be positioned so that the user's back/hips lie more or less stably enclosed between the barrier and the wheelchair backrest, the use of narrow strap-like cushions which are supported across the seat and function to raise the front seat part have been proposed. These cushions can be arranged or removed to displace the effective position of the barrier along the seat. When applying the known technique, it has been noted that roughly 75% of the user's body weight is transferred to the seat over an area of about 25 square centimetres (corresponding to the leg sitting area). In order to distribute this load over a wider area, it has been proposed to raise the aforesaid narrow barrier cushions to a level in which they project up over the level defined by the front part of the seat, thereby forming a pivot ridge which enables the weight of the user's thighs and legs to establish a pivotal moment around this ridge which tends to reduce the surface pressure on the user's back. The aforesaid technique also proposes the use of a liquid-filled cushion placed on the wheelchair seat to reduce the otherwise local high external load pressure on the user, or patient In distinction, an object of the present invention is to provide a use of a chair seat cushion enabling people who are otherwise essentially healthy to adopt a sitting position in which the persons back is relieved of load and to reduce, when applicable, back pains which would otherwise occur when a person is seated, or to prevent the occurrence of back pains in sitting positions. The invention is defined in the independent use Claim. Further embodiments of the invention are defined in the dependent use Claims. An essentially rigid chair seat cushion is used whose width will at most correspond to the width of a conventional chair seat. The cushion will have an effective thickness of about 35 mm, for instance. The length of the cushion will be much shorter than the length extension of the chair seat, so as to enable the cushion to be moved to different 1 longitudinal positions on the chair seat without the front edge of the cushion protruding beyond the front edge of the chair seat in normally occurring use positions. The inventive cushion may therefore have a length of about 28 cm in one practical embodiment thereof. The cushion itself may be comprised of a generally flat rectangular plate having a thickness of about 40 mm, said plate having formed in the upper side thereof two shallow, basin-like recesses or indentations which are intended to receive the rear parts of the respective thighs of the user. The upper front edge of the plate is preferably gently bevelled down to half the plate thickness through, an angle of about 45 degrees. The rear edge of the plate is also preferably softly bevelled, wherein the angle between the bottom surface of the plate and the upwardly and forwardly sloping bevelled face is preferably about 30 degrees. The rear edge of the cushion has a slightly concave shape, wherein the concave rear edge extends essentially along an arcuate part whose pitch or height relative to a circle chord intersecting both rear comers of the cushion advantageously lies in the region of 10-25 mm in the case of a cushion whose width is approximately 400-450 mm. It has surprisingly been found that a cushion of the above kind can be moved on a chair seat with the front edge of the cushion generally parallel with the front edge of the chair seat to a position in which the user can sit comfortably on the cushion and, at the same time, feel relief in his/her lumbar region and/or obtain a comfortable curvature of the lumbar with the user's back in contact with the chair backrest. The rear edge of the cushion will then normally be located approximately in a vertical plane extending through the user's hip joints, wherein the user's back/hip region will be essentially relieved of load and, in principle, hang behind the rear, preferably concave edge of the cushion. The chair backrest supports the user in his/her lumbar region and the friction that is generated between the backrest and the user's back coacts to support the torso of the user. Since the vertical plane through the centre of gravity of the user's torso extends close to the rear edge of the cushion, the weight of the user will exert a small turning moment around the rear edge of the cushion. The user is therefore able to hold his/her hip part/back raised from the chair seat, or at least maintain a reduced load thereon quite easily with the aid of his/her own muscular force , so that the user's weight will also be favourably distributed over the backs of the user's thighs to the upper side of the cushion. This results in relieving the load on the user's lumbar region and also enables the user to readily curve the lumbar region in the median plane, therewith minimising back pains or minimising the risk of the occurrence of back pains in a person sining on the inventive cushion. The cushion is thus primarily intended for use by a person whose muscles are intact such as to enable the user to establish a comfortable sitting position on the cushion and chair after adjusting the inventive cushion to the best position in the forward/rearward direction of the cushion. Because the cushion has no rear side-edge parts which laterally support the user's hips, the inventive cushion has no parts which make it difficult for the user to change arching of his/her lumbar region in the forward/rearward direction of the chair, or prevent such changes. As indicated in the aforegoing, it is important that the rear edge of the cushion can be placed essentially in the vertical plane extending through the hip joints of a seated user with the user's back in comfortable contact with the chair backrest. In this way, the user's weight will be taken-up to a substantial degree or almost completely by the chair backrest and the cushion, i.e. the front part of the cushion, whereas the user's weight will only be taken-up by the rear part of the cushion to a small extent or essentially not at all. In conventional seating furniture, essentially all of the weight of a seated person is transferred to the rear part of the chair seat with the lumbar of the person being subjected to substantial compression forces. A person using the cushion such that the person's back will exert no load on the rear part of the chair seat, the lumbar region of the person concerned will instead be subjected to a tensile force, which is often desirable. The user can thus adjust the cushion position to obtain desired compression or tensile forces in the lumbar region within certain limits, by adjusting the level difference between the upper surface of the seat cushion (the front part of the cushion) and the rear part of the seat cushion. When effecting a change in level, it is important that the boundary or demarcation line between the front and the rear part of the cushion is located in the region of a vertical plane that extends through the user's hip joints with the user in good contact with the backrest. The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which Fig. 1 is a schematic side view of a chair provided with a chair seat cushion; Fig. 2 shows the chair seat cushion from above; Fig. 3 is a sectional view taken on lines III-III in Fig. 2; Fig. 4 illustrates a chair on which the cushion is fixedly mounted on the chair seat, which can be moved in the longitudinal direction thereof; It will be evident from Figs. 2 and 3 that the chair seat cushion 11 has a basic construction which can be said to include a generally rectangular and essentially rigid plate, i.e. the plate be compressed by the weight of people sitting thereon. The cushion I 1 may conveniently be comprised of Frigolite or some other expanded, relatively rigid plastic material. As will also be evident from Figs. 2 and 3, the cushion 11 has a generally flat under surface and a generally flat upper surface parallel therewith, wherein the cushion has a total thickness t 1 of 40 mm. In a horizontal position, the cushion has a generally straight front edge which is bevelled at 3 adjacent the upper surface of the cushion. Both side edges 5,6 of the cushion 11 are generally parallel with one another and extends at right angles to the front edge of the cushion. The rear edge of the cushion 11 extends along a circular arc c. A chord K of the arc c intersects the intersection of said arc c with the side edges 5, 6. The pitch P between the arc and the chord is about 25 mm. The rear edge has a bevel or chamfer 4. The front bevel 3 defines an angle α1 of about 45 degrees with the bottom plane. The rear bevel 4 defines an angle α2 of about 30°, wherein the bevel 4, at least in its longitudinal centre region, extends essentially down to the bottom plane. In a practical embodiment, the bevel surface 4 has a length of about 70 mm in the longitudinal centre region of the cushion 11, wherein the length of the bevel decreases continuously in a direction towards the side edges 5, 6 of the cushion 1, where the length of the bevelled surface is about 30 mm and said surface spreads from the upper surface of the cushion 11 down to a point corresponding to roughly half the thickness of the cushion. Provided in the upper side of the cushion 11 are two generally basin-shaped and generally mutually parallel recesses or indentations 2 that have a depth of about 5 mm from the top surface of the cushion 11 along the whole of their lengths. The recesses or indentations 2 thus open out in the front and rear bevelled surfaces 3, 4. The effective sitting height t 2 of the cushion 11 from the bottom plane is therewith about 35 mm; t 2 may be in the range of 25-45 mm and t 1 in the range of 20-50 mm. The cushion 11 need not necessarily include recesses 2, and if recesses are provided they will preferably have a depth of 5-15 mm, preferably about 5 mm. The cushion 11 of one preferred embodiment has a length l 1 of about 280 mm and a width B of about 400 mm. Fig. 1 illustrates a chair 20 having a seat 21 and a backrest 22. The cushion 1 is placed on the seat 21 with the front edge of the cushion generally parallel with the front edge of the seat 21. The cushion 11 can be moved in the longitudinal direction of the seat 21 to an approximate position in which the rear bevel surface 4 is located roughly beneath the hip joints 7 of a user whose lumbar region is in contact with the backrest 22 and is seated in a comfortable position. It will be seen that the user's thighs 8 rest on the cushion and that the underside 81 of the thighs are received in the recesses 2 in the cushion, and it will be understood that the friction generated between the backrest 22 and the user's back 10 will assist in supporting the torso of the user. This means that the user's hip region and back 9 are able to sink down in the sunken area defined beneath the upper surface of the cushion 1 behind said cushion and above the chair seat 21. The curvature and inclination of the user's back in the median plane can now be easily adjusted in an optimal fashion, since the surface pressure between the user's back 9 and the chair seat 21 has been reduced, and since the shape of the user's back 9 has a limited influence on the setting of optimal angles between the user's hips and thighs and between the user's hip region and lumbar region and curvature of the lumbar. Because the hip joints 7 are located in the region above the rear bevelled edge 4 of the cushion, the rotational moments of force established around an axis corresponding to the area of the bevelled surface 4 in contact with the user will be small, whereby the user is able to ensure that the pressure against his/her back 9 and the backs 81 of the thighs can be equalised without needing to strain the muscles to any appreciable extent, whereby the surface pressure on the rear bevelled surface 4 is also limited. Although the cushion I 1 is essentially rigid, i.e. is not compressed by the weight of the user, it will be understood that the actual cushion 1 may still be slightly flexible in order to conform to some extent to any contours in the chair seat 21, the length of which will normally be about 45 cm. In the Fig. 4 embodiment, the seat cushion 11 is, in principle, fixedly connected to or integrated with the chair seat 21, said seat being movable longitudinally in relation to the chair backrest 22. Mobility of the seat in its longitudinal direction can be achieved by conventional means, for instance by guiding the seat in guides fitted to the chair chassis 23, wherein conventional latching means 26 enable the seat to be locked or released for locking and moving the seat in the guide means. The chair may, in general, be any type of chair, for instance a working chair, such as an office chair having conventional degrees of freedom with regard to adjustability. Seen in a horizontal projection, the seat part 11 has a generally straight front edge having a bevelled surface 3 joining the upper surface 31. Both side edges 5, 6 of the seat part 11 are essentially parallel with one another and extend generally at right angles to the front edge. The rear edge of the seat part 11 extends in a circular arc C whose centre lies in the longitudinal centre plane of the part 11. A chord K to the arc C intersects the intersection of the arc C with the side edges 5, 6. The pitch P between the arc and the chord is about 25 mm in one preferred embodiment. The rear edge part of the seat part I 1 has a bevelled surface 4. The front bevel 3 defines an angle α1 with the upper surface 31, this angle reaching to about 45 °. The rear bevel 4 defines an angle α2 of about 30 ° relative to the surface 31, wherein the bevel 4 extends, at least in its length central region, substantially down to a level corresponding to the bottom most end position 12' of the upper surface 32 of the seat part 12. In one practical embodiment, the length of the bevelled surface 4 in the plane of the surface 31 is about 70 mm in the length centre region of the seat part 11, wherein the length of the bevelled surface 4 continuously decreases in a direction towards the side edges 5, 6, where the length of the bevelled surface 4 in the plane 31 is about 30 mm. In this case, the rear edge of the bevelled surface 4 lies at about 40 mm beneath the surface 31 in the length centre region of the seat part 11, and at a distance of about 20 mm beneath the plane 31 at the edges 5, 6. Formed in the upper side of the seat part 11 are two generally basin-like shallow recesses or indentations 2 which extend in the longitudinal direction of the chair and which have a depth of about 5 mm from the upper surface 31 along the full length of the seat part 11. The recesses 2 thus open out in the front rear bevelled surfaces 3, 4 and function to receive the backs of the user's thighs. In one optimal embodiment of the invention, the seat part 11 has a length L1 of about 280 mm. Its width B may be about 400 mm. In the case of chairs that have raised side supports, such as car seats for instance, the width B may be smaller and correspond to the free space between said raised supports. The distance between the front side of the backrest 22 and the front edge of the seat part 11 will normally be about 45 mm, but can be adjusted by virtue of the mobility of the plate 36 in relation to the chassis 37 and the backrest 22. The pitch P of the arcuate rear edge of the seat part 11 will generally lie in the region of 10-45 mm and preferably reaches to about 25 mm. The total length L 1 of the front seat 11 lies in the region of 24-30 cm, and is preferably about 28 cm.

Claims: Use of a chair seat cushion (11) for a chair (20) having a backrest (22), the cushion (11) having a length (L 1 ) of at most 40 cm, wherein the rear edge (4) of the cushion (11) is placed in a position essentially immediately beneath the hip joints (48) of a user with the user's calves out of contact with the front edge (3) of said cushion (11) and with the user's back resting on a chair back rest (22) and the upper thigh-supporting surface of the cushion (11) being placed at a height (t 2 ) of at least 15 mm above the chair seat surface (12) between the cushion (11) and the backrest (22), wherein the rear edge of the cushion (11) is concave and extends essentially around a circular arc (C) whose pitch (P) relative to a circle chord (K) that intersects the arc (C) at the plate side edges (5, 6) is in the region of 10-45 mm, and preferably about 25 mm. Use according to Claim 1 wherein the total length (L 1 ) of the cushion is in the region of 24-30 cm, preferably about 28 cm. Use according to Claim 1 or 2 wherein the rear edge is bevelled and slopes forwardly and upwardly and defines an angle (α2) with the bottom surface of about 30 °, wherein the bevelled surface (4) preferably widens to about 70 mm in the longitudinal direction of the cushion in the centre plane region thereof. Use according to any one of Claims 1-3, wherein the cushion (1) is integrated with or fixedly mounted on the upper side of the forward part of a chair seat (21) that can be moved forwards and backwards to a selected position in relation to the chair backrest (22).

Inventors: RINNE TOMMI, RINNE YRJOE, RINNE, TOMMI, RINNE, YRJOE, Rinne, Yrjö
Applicants: RINNE TOMMI, RINNE YRJOE, RINNE, TOMMI, RINNE, YRJOE
Application year: 1996
Main classification: A47C7
IPC codes: A47C7, B60N2