IES81161B2 - A chair - Google Patents

Abstract

A chair (1) has a fixed support (10) pivotally connected to a seat (11) and to a backrest (12). Pivot axes (S.B) for the seat and the backrest are located to allow posture-responsive movement. The seat (11) can be tilted in the opposite direction to the backrest (12) to allow additional freedom of movement.

Description

“A Chair The invention relates to chairs, and more particularly chairs or seats of the type having a backrest and a seat which tilt.

In such chairs tilting of the backrest and of the seat is inter-related or synchronised at a fixed ratio. The ration may be 2.0:1.0 or 2.5:1.0 backrest to seat tilting ratio.

The facts that the seat and the backrest are constrained to tilt in the same direction and with a fixed angular relationship mean that the chair does not respond to the posture of the occupant. For example, if the occupant leans back, rearward tilting of the backrest causes rearward tilting of the seat, thus causing the occupant’s heel to lift and excess pressure to be applied to the occupant’s legs behind the knees.

Another problem with these chairs is that they need to be adjusted to suit the weight and size of the particular occupant. Such adjustment is, for example, performed by a large spring mounted at the front of the mechanism. This spring sets the tilting bias to home positions of the seat and backrest. The bias direction is typically forward.

To summarise, conventional tilting chairs have essentially been designed with the mechanical mechanism in mind, and not the occupant. This can cause pressure to be applied to parts of the occupant’s body in a manner which can cause repetitive stress, injury, or at least discomfort.

It is an object of the invention to provide a chair having a pivoted seat and a backrest and which reacts to posture of the occupant in an ergonomic manner.

Another object is that this is achieved in a simple manner. -2According to the invention, there is provided a chair having a tiltable seat and a tiltable backrest which respond to the posture of the occupant.

In one embodiment, the seat and backrest pivot axes are located in a region beneath the centre of gravity of an occupant.

In one embodiment, the pivot axes are located in a region beneath the centres of gravity of occupants having different sizes and weights sitting in a neutral position in the chair.

This location of the pivot axes obviates the need for adjustment to accommodate occupants with different weights and sizes. Stresses in the mechanisms are very low due to the low turning movements about the pivot axes.

In one embodiment, the seat pivot axis is forward of the backrest pivot axis.

Preferably, the seat and backrest pivot axes are less than 120mm apart.

In one embodiment, the seat and backrest pivot axes are approximately 90 mm apart.

Preferably, the seat and the backrest are pivotally connected to a fixed support.

In another embodiment, the backrest is independently pivotable.

Preferably, the seat is independently pivotable.

In another embodiment, the seat and the backrest comprise means for abutting against each other for part of their pivot ranges whereby tilting is inter-related.

Preferably, the abutment means engage at a rearward extremity of the seat tilt range. -3In another embodiment, the seat is biassed rearwardly to an abutment position.

Preferably, the backrest is biassed forwardly.

In another embodiment, the seat and the backrest each comprise a channel-shaped support in a mechanism.

Preferably, the supports are nested together.

In another embodiment, the supports are mutually inverted, and the abutment means comprise side walls of the supports.

In another embodiment, the seat comprises means for sliding to a set position.

According to another aspect, the invention provides a chair control mechanism comprising a seat support and a backrest support, wherein the supports are pivotally connected to allow posture-responsive action of a chair controlled by the mechanism.

Preferably, the mechanism comprises a fixed support to which the seat and backrest supports are pivotably connected.

In one embodiment, the seat support and the backrest support are both independently pivotable.

In another embodiment, the mechanism further comprises a bias means urging the seat support rearwardly and a bias means urging the backrest support forwardly.

Preferably, the seat support and the backrest support comprise means for abutment to set limit positions. -4The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which :Figs. 1 to 5 inclusive are diagrams illustrating operation of a chair of the invention; Fig. 6 is a diagram showing mutual positions of pivot axes and important points of movement of the chair; Fig. 7 is a set of side views showing parts of a control mechanism of the chair in detail; Figs. 8 to 10 are side views showing the chair mechanism in the positions of Figs. to 3 respectively.

Referring to the drawings and initially to Figs. 1 to 5, there is shown a chair 1 of the invention. The chair 1 comprises a base 2 having a spindle 3 mounted on wheels 4.

The chair 1 also comprises a control mechanism having a fixed support 10 which is pivotally connected to a seat 11 and to a backrest 12. The pivot axes are through the fixed support 10, the seat pivot axis being indicated by the letter S and the backrest pivot axis by the letter B.

Fig. 1 shows home positions for the seat 11 and backrest 12. As shown in Fig. 1, the axes S and B are below the centres of gravity for a range of people having different weights and sizes. The axes S and B are spaced-apart by 90 mm as shown in Fig 6. The pivot axis B is directly below the centre of gravity as shown in fig. 1. However, the centre of gravity will be at different locations for different people and the important point is that -5the axes S and B are below a reasonable range for such centres of gravity. As shown in Fig. 6 the seat may slide to a set position to suit the occupant.

Referring to Fig. 2, a position is shown in which an occupant has leaned back, pushing the backrest rearwardly by 17°. This posture also causes the seat 11 to pivot rearwardly by 9°. Thus, the chair provides tilting in a conventional manner for a tilt range where the posture of the occupant requires such tilting. In this case, the occupant has lifted his legs to follow the movement.

However, referring now to Fig. 3, the chair 1 also allows the seat 11 to be tilted in the opposite direction to that of the backrest 12. In this illustration, seat 11 has pivoted forwardly by 9° whereas the backrest has tilted rearwardly by 17°. The seat is tilting independently of the backrest 12, as required by the posture of the occupant, who in this case has left his feet fully on the floor.

Referring now to Fig. 4, the backrest 12 is again at a rearward tilting angle of 17°. However, in this case the set is at the home position. Again, this is the particular relative positioning required by the posture of the occupant.

Referring now to Fig. 5, the backrest 12 is at its home position, however, the seat 11 has tilted forwardly by 9° to react to the posture of the occupant.

It will be seen for these examples that the chair provides a large degree of freedom of movement of the seat and backrest to respond to changes in posture of the occupant. This occurs for the occupants having different sizes and weights without readjustment. This has been achieved because of a number of features. The pivot axes S and B are below the range of centres of gravity for such occupants. If, for example, the backrest pivot axis were positioned rearwardly of this general area, there would be very different forces applied by the bias on the backrest at different positions, and there would be a sliding motion between the occupant’s back on the backrest. What the invention has achieved is -6to bring the seat and backrest axes close to the occupant’s hip axis so that there is compatible tilting with little or no relative movements between the occupant’s back and the backrest.

Also, the seat can be tilted in the rearward direction until a limit position set by the backrest is reached. This limit position is reached when the seat and the backrest abut against each other within the control mechanism.

There is a bias provided within the control mechanism to bias the seat rearwardly and the backrest forwardly. This brings the seat 11 and the backrest 12 to the home position of Fig. 1.

Referring now to Figs. 7 to 10, the manner in which this is achieved is described in more detail. A control mechanism under the seat of the chair 1 comprises the fixed support 10, which is a U-shaped channel having a socket 20 for receiving the spindle 3. The fixed support 10 also comprises a pair of seat pivot apertures 21 and a pair of backrest pivot apertures 22. A lip 23 extends from the rear of the fixed support 10, to act as a stop to limit rearward pivoting of the backrest 12. The mechanism also includes a seat support 25, which is an inverted U-shaped channel having a pair of pivot apertures 26 which are co-axial with the apertures 21. The seat support 25 also includes a pair of abutment surfaces 27 extending rearwardly and downwardly. The mechanism also includes a backrest support 30 which has a U-shaped configuration with a pair of aligned pivot apertures 31 and a pair of apertures 32 to receive a stop bar. The backrest support 30 also includes a pair of abutment surfaces 33.

The manner in which these parts are interconnected is shown in Figs. 8 to 10 inclusive. The apertures 21 and 26 are interconnected by a pivot pin to form a seat pivot joint 35. The apertures 22 and 31 are aligned by a pivot pin to form a backrest pivot joint 36. Thus the joints 35 and 36 provide the pivot axes S and B respectively. A stop bar 37 is inserted through the apertures 32. A seat bias spring 40 is mounted between the base of the fixed -7support 10 and the upper inner face of the seat support 25 and a backrest bias spring 45 is mounted between the base of the fixed support 10 and the base of the backrest support 30 via a bolt 46. The seat spring 40 urges the seat support 25 in a rearward, clockwise direction about the pivot joint 35 as viewed in the drawings. The backrest spring 45 urges the backrest support 30 in a forward anti-clockwise direction about the pivot joint 36.

The position of Fig. 8 corresponds to that of Fig. 1 in which the occupant is in a neutral position in with the backrest 12 and the seat 11 are at their home positions, as urged by the springs 40 and 45. In this position, the abutment surfaces 27 and 33 are in contact.

The position of Fig. 9 corresponds to that of Fig. 2. The occupant has pushed the backrest 12 rearwardly and so it has pivoted about the joint 36 against the action of the spring 45. The occupant has allowed the seat 11 to rotate under the bias of the spring 40 in a manner which tracks tilting of the backrest. Because the abutment surfaces abut at different positions the relative angular movement changes.

Fig. 10 shows a position whereby the backrest is still pushed rearwardly, however, the occupant has urged the seat 11 to tilt forwardly (anti-clockwise about the joint 35). This has been achieved because the seat is independently pivotable about the joint 35 between its extreme positions.

Because the turning moments of the backrest are greater than those of the seat, tilting of the backrest is only limited by the stop bar 37 abutting against the lip 23 at the rearward extremity, and by the base of the backrest support 30 abutting against the base of the fixed support 10 at the forward extremity. Tilting of the seat is limited in the rearward extremity by the extent of tilting of the backrest, and in the forward extremity by abutment of the seat support 25 with the base of the fixed support 10. -8The invention therefore allows the user to change posture at will while providing sitting comfort. The chair may therefore be regarded as posture-responsive. It will be suitable for occupants having a wide range of sizes and weights. For example, there is only a small difference in lower leg height for occupant’s of widely differing heights, and this difference is easily accommodated. Differences in torso height do not change action of the chair because the backrest rotation tracks that of the torso. There is no need for the occupant to adjust a bias spring to set the chair according to his or her weight. It is envisaged that the dramatically improved ergonomics will result in a much lower incidence of repetitive stress-type injuries.

The invention is not limited to the embodiments described but may be varied in construction and detail.

Claims (5)

Claims

1. A chair having a tiltable seat and a tiltable backrest which respond to the posture of the occupant.

2. A chair as claimed in claim 1, wherein the seat and backrest pivot axes are located in a region beneath the centre of gravity of an occupant, and wherein the pivot axes are located in a region beneath the centres of gravity of occupants having different sizes and weights sitting in a neutral position in the chair.

3. A chair as claimed in any preceding claim, wherein the seat and the backrest are pivotally connected to a fixed support, and wherein the backrest is independently pivotable, and wherein the seat and the backrest comprise means for abutting against each other, and wherein the abutment means engage at a rearward extremity of the seat tilt range, and wherein the seat is biassed rearwardly to an abutment position, and wherein the backrest is biassed forwardly, and wherein the seat and the backrest each comprise a channel-shaped support in a control mechanism.

4. A chair as claimed in claim 3, wherein the supports are nested together, and wherein the supports are mutually inverted, and the abutment means comprise support side walls, and wherein the seat comprises means for sliding to a set position.

5. A chair control mechanism comprising a seat support and a backrest support, wherein the supports are pivotally connected to allow posture-responsive action of a chair controlled by the mechanism, and comprising a fixed support to which the seat and backrest supports are pivotally connected, and wherein the seat support and the backrest support are both independently pivotable, and further comprising a bias means urging the seat support rearwardly and a bias means urging the -10backrest support forwardly, and wherein the seat support and the backrest support comprise means for abutment to set limit positions.