Chair having an assisted scissor mechanism

Abstract: Chair (1) with adjustable seat (3) and simultaneously adjustable backrest (4). In a first use position the seat (3) is arranged sloping forwards at an angle of a few degrees with respect to the horizontal whilst the backrest (4) slopes backwards with respect to the vertical. In a second end position the seat (3) is sloping backwards at an angle of a few degrees with respect to the horizontal whilst the backrest (4) is then sloping forwards with respect to the vertical.

Description: The invention relates to a chair, the seat of which is adjustable between two end positions whilst the backrest is simultaneously adjustable relative to the adjustment of the seat in a relationship which can be preset. Chairs of which the seat and/or the backrest are adjustable are generally known (an example is described in DE-A-2 843 058). With these chairs the seat and the backrest can be adjusted and fixed in position in a specific relationship relative to one another, depending on the body dimensions and/or personal preferences of the user. A seated person is continually moving on his or her chair. On average a person remains seated in one specific position on his or her chair for at most about 15 minutes. He or she will continually change sitting position. In doing so, the relative angles of the following three parts of the human skeleton are always changing: thigh and pelvis; pelvis and lumbar region of the spinal column; lumbar region and chest and shoulder area. In order to follow these changes in angle, chairs which have an independent or flexible backrest and seat adjustment are known. With these chairs the seated person adjusts the relative positions of the backrest and the seat with respect to one another by exerting forces on said backrest and/or seat when sitting down. Chairs are known in which the seat slides a small distance forwards under the influence of the forces exerted by the person sitting down, the return (or backwards) movement of said seat being actuated by a spring. Said sliding movement ensures that the changing angle of all three above mentioned parts of the human skeleton is readily possible without the backrest or seat exerting a shear force on the back or the seat of the seated person after the latter has sat down. Continuous pelvic rotations are the cause of the change in the desired sitting position and angle of sitting. These rotations give rise to torsional forces in the lumbar-sacral transition (loin/sacrum). For normal use a chair is equipped with three parts, which together provide the optimum support herefor: the support for the lumbar region and of the rearmost part of the seat, so that the pelvis does not tilt backwards; a rounded front seat section, so that the blood circulation in the legs is not disturbed. The correct support is that which forces the spinal column into a balanced lordosis position. In the bent kyphosis position it would be possible, by sitting in a hunched position, to develop symptoms relating to organs which are pressed together. The chair must therefore follow the movements of the body. However, that alone is not sufficient. It must be possible for the positions of the supporting parts of the chair to be fixed in the optimum position for an optimum sitting posture. The seated person will then always be forced into the optimum seating posture, depending on his or her movements, and more than one posture must be possible. The aim of the invention is to provide a chair, the seat and backrest of which are adjustable, which chair can be fixed by the seated person in changing, predetermined, optimum sitting positions. Said aim is achieved in that, in the use position of the chair, the seat in the one end position is sloping forwards at an angle of a few degrees with respect to the horizontal whilst the backrest is sloping backwards with respect to the vertical, and the seat in the other end position is sloping backwards at an angle of a few degrees with respect to the horizontal whilst the backrest is then sloping forwards with respect to the vertical, the transition from the last-mentioned to the first-mentioned end position being assisted. The chair according to the invention has two optimum seating positions. A user can take position on this chair in an 'active seating position' or in a 'passive seating position'. 'Active seating position' denotes that the user takes up position at the front of the seat of the chair in an active posture in which he or she him- or herself assumes the optimum lordosis position with his or her back. In this sitting position, his or her back does not have to be supported by a backrest. 'Passive sitting position' denotes that the user takes up a position at the back of the seat in a less active or inactive posture, in which he or she has a tendency to assume the adverse kyphosis position with his or her back. In this sitting position the back of the user must be supported by a backrest. The chair according to the invention provides a scissor mechanism, by which means the backrest is moved backwards - away from the back of the user - during 'active sitting' and forwards - towards the back of the user - when the 'passive sitting' position is assumed. The user selects 'active sitting' or 'passive sitting' by taking position at the front or the rear part of the seat respectively. If he or she takes up position on the rear section, he or she operates the scissor mechanism, which then compresses, as a result of which the backrest is brought forwards. If the user moves from the 'passive sitting' to the 'active sitting' position, he or she shifts to the front part of the seat and the spring in the scissor mechanism relaxes, as a result of which the chair assumes the seating position which is optimum for the 'active sitting' posture of the user. The rest position of the scissor mechanism is the position in which the seating posture is that of the 'active sitting' position. The two positions of the scissor mechanism, the compressed position and the relaxed position, are end positions, so that the optimum sitting posture for the user corresponds to a fixed sitting posture. The front part of the seat of the chair according to the invention is provided with a relatively rough surface. This prevents a user who has assumed the 'active sitting' position on the chair from tending to slip off the chair. The rear part of the seat is provided with a relatively smooth surface. The user who assumes the 'passive sitting' position will consequently slide a little backwards against the upturned edge, as a result of which he or she will come into precisely that position on the seat which is important for the optimum sitting posture. The upturned edge prevents the user from sliding too far backwards. In the unloaded stage and when the user is in an 'active sitting' position, the scissor mechanism of the chair according to the invention is held in one specific position by one or more spring elements. The precise positioning of said spring elements with respect to the rods of the scissor mechanism is adjustable depending on the weight of the user. For a person whose weight, for example, is low, the adjusting knob associated with the spring elements must be placed in the position tight to the seat. In contrast, for a heavyweight person, the adjusting knob must be placed in the position tight to the sub-frame. The stroke length of the spring elements is adjustable on either side of the spring elements, so that both the forward and the return movement can be variably limited, within specific limits. The stroke length of the spring elements determines the angle which the seat makes with respect to the horizontal, both in the position of 'active sitting' and in the position of 'passive sitting'. The seat of the chair according to the invention is provided with bevelled surfaces on either side. These surfaces support the legs of the user during 'passive sitting' and prevent the blood vessels being pinched by a square edge of the seat. The invention will be illustrated in more detail below with reference to the appended drawing, in which one illustrative embodiment is shown in detail. Figure 1 shows a perspective view from above of the chair according to the invention; Figure 2 shows a perspective view from below of the chair according to Figure 1; Figure 3 shows a side view of the chair, the seat being shown in cross-section, in the one end position; and Figure 4 shows the chair in the other end position in a view corresponding to that in Figure 3. In Figure 1 the chair is indicated in its entirety by 1, the sub-frame by 2, the seat by 3, the front part of the seat 3 by 5, the rear part of the seat 3 by 6 and the backrest by 4. In Figure 1, by way of example, the sub-frame 2 is constructed as a foldable tripod. Any other sub-frame known from the prior art can be chosen equally well as sub-frame 2. The seat 3 comprises a front part 5 and a rear part 6. The front part 5 is made with a relatively rough surface in order to prevent the seated person from slipping off. The front part 5 is, for example, covered with a rough, ribbed fabric, the ribs of which are positioned transversely with respect to the sitting direction. The tendency of a seated person to slip off occurs when said person is sitting actively, that is to say when said person has taken up position on the front part 5 of the seat 3. In this position his or her back is not resting against the backrest 4. During active sitting the seat 3 is at an angle of 0 to 15 degrees with respect to the horizontal, and in the preferred embodiment according to Figure 1 is at an angle of about 8 degrees with respect to the horizontal, as a result of which the seated person has the tendency to slide down over the seat. This angle is indicated by α in Figure 3. The rear part 6 is constructed with a relatively smooth surface in order to slide the person who sits down on the chair in the passive sitting position into the position on the rear part 6 of the seat 3 against the upturned edge 28. In Figure 2, supplementing the reference numerals in Figure 1, the scissor mechanism is indicated by 7, an adjusting knob by 23, a bottom bar by 9 and a transverse connection by 11. Using the adjusting knob 23, twisting of scissor mechanism 7 with respect to the sub-frame 2 can be blocked or released. In Figure 3 the base of the scissor mechanism 7 is indicated by 8, the bottom bar by 9, a top bar by 12, a back rod by 13, pivot points by 14, 15, 16, 17 and 18, the rest rod by 19, the cushion by 20, adjusting knobs by 21, 22, and 24, blocks by 25 and 27 and the compression spring cylinders by 26. The scissor mechanism comprises a base 8 which is fixed to the sub-frame 2 and can be rotated about the longitudinal axis thereof, a bottom bar 9, which is connected to the base 8 via the pivot point 14, a top 12, which is connected to the base 8 via the pivot point 15, and a back rod 13, which is connected to the bottom bar via pivot point 16 and to the top bar via pivot point 17. The backrest 4 is at an angle γ of  to 15 degrees with respect to the vertical plane. According to the illustrative embodiment, the bottom bar comprises two rods 10 and a transverse connection 11 located between them. In the unloaded state and when the seated person has assumed an active sitting position, the scissor mechanism 7 is held in the position shown by means of one or more compression spring cylinders 26 which are mounted between the adjustable block 25 and the block 27, which is rigidly fixed on the top bar 12. The block 25 is adjustable along the base 8 by unscrewing the adjusting knob 24 and then moving the block in the slot in the base 8 and screwing the adjusting knob 24 tight again. In Figure 3 the broken lines show how the adjusting knob 24, the block 25 and the compression spring cylinders 26 can jointly be in another position. The position must be set depending on the weight of the person who takes position on the chair. For a lightweight person, the position must be adjusted to, for example, that shown by continuous lines in Figure 3. For a heavier person, the position must be adjusted, for example, to that shown by broken lines in Figure 3. The rest rod 19 is fitted on the back rod 13 of the scissor mechanism 7 via the pivot point 18. A cushion 20 is fitted on the rest rod 19 and can be moved in the longitudinal direction with respect to the rest rod 19. With this arrangement, the adjusting knob 21 is used to fix the cushion 20 with respect to the rest rod 19. In Figure 3 the cushion 20 is shown in a higher position by a broken line than the position shown by the continuous lines. The rest rod 19 can rotate about the pivot point 18, as a result of which the cushion 20 can be moved in the direction towards the front part 5 of the seat 3 and vice versa. This movement is effected by turning the adjusting knob 22. In Figure 4 the position in which the cushion 20 and the rest rod 19 are in a position sloping forwards in the direction of the front part 5 of the seat 3 is shown by a broken line. This position is achieved by tightening the adjusting knob 22 with respect to the position of the cushion 20 and the rest rod 19 shown by a continuous line. Figure 4 shows the situation in which a person has taken position on the chair 1 in the passive sitting position. Compared with the situation in the unloaded state or in the active sitting position, as shown in Figure 3, the scissor mechanism 7 is compressed against the pressure of the compression cylinders 26. In this position, the bottom bar 9 has been rotated about the pivot point 14 and the top bar 12 about the pivot point 15. The angle α which the top bar 12 makes with respect to the horizontal plane has as a result been changed to an angle β. Said angle is 0 to 15 degrees; about 8 degrees in the embodiment according to Figures 1 to 4. As a consequence of the rotation of the top bar 12 and the bottom bar 9, the back rod has also rotated via the pivot points 16, 17, specifically in a direction counter to the direction of rotation of the top and bottom bars 12, 9. Moreover, the back rod 13 has assumed a position somewhat further forwards, that is in the direction of the front part 5 of the seat 3. As soon as the rest rod 19 rotates, the back rod 13 rotates at the same time through the same angle as the rest rod 19. If the rest rod 19 rotates clockwise, the cushion 20, in the view according to Figure 4, will move forwards, and will come into contact with the back of the person who has assumed the passive sitting position. The situation which is shown in Figure 4 occurs when a passive sitting position is assumed and can also be used to adjust the cushion with respect to the back of the seated person as desired, by turning the adjusting knob 22. The situation which is shown in Figure 4 reverts to the situation which is shown in Figure 3 when the seated person gets off the chair 1 and leaves the chair 1 in the unloaded position or when the seated person changes from the passive sitting position to the active sitting position and therefore takes up a position on only the front part 5 of the seat 3. The bevelled surfaces 29 of the front part 5 of the seat 3 are clearly visible in Figures 1 and 2.

Claims: Chair (1), the seat (3) of which is adjustable between two end positions whilst the backrest (4) is simultaneously adjustable relative to the adjustment of the seat (3) in a relationship which can be preset, characterised in that, in the use position of the chair, the seat (3) in the one end position is sloping forwards at an angle of a few degrees with respect to the horizontal whilst the backrest (4) is sloping backwards with respect to the vertical, and the seat (3) in the other end position is sloping backwards at an angle of a few degrees with respect to the horizontal whilst the backrest (4) is then sloping forwards with respect to the vertical, the transition from the last-mentioned to the first-mentioned end position being assisted. Chair according to Claim 1, wherein the seat (3) comprises a front part (5), which is made relatively rough, and a rear part (6) which is relatively smooth. Chair according to Claim 2, wherein the seat (3) has an upturned edge (28). Chair according to one of the preceding claims, wherein, in the said end position, the angle of inclination α and β of the seat (3) with respect to the horizontal plane is 0 to 15 degrees. Chair according to Claim 4, wherein the angle of inclination α and β is about 8 degrees in the one end position and in the other end position respectively. Chair according to one of the preceding claims, wherein a scissor mechanism (7) is provided comprising a base (8), bottom bar (9), top bar (12) and a back bar (13), which together form a four-rod mechanism. Chair according to Claim 6, wherein at least one compression spring is fitted between the base and one of the rods of the four-rod mechanism. Chair according to Claims 6 and 7, wherein the compression spring is adjustable with regard to its position within the scissor mechanism (7), depending on the weight of the user. Chair according to Claims 6, 7 and 8, wherein the compression spring is adjustable at either end of the compression spring with regard to its stroke length, depending on the desired angles (α) and (β). Chair according to one of the preceding claims, wherein the backrest (4) is at an angle γ of 0 to 15 degrees with respect to the vertical plane.

Inventors: HAAKSMA ERNST, HOOYMANS CORNO, HAAKSMA, ERNST, HOOYMANS, CORNO
Applicants: BACKQUALITY EUROP, BACKQUALITY EUROPE
Application year: 1995
Main classification: A47C1
IPC codes: A47C1