GB2588447A

GB2588447A - Chair

Info

Publication number: GB2588447A
Application number: GB1915470.7A
Authority: GB
Inventors: Tierney Martin
Original assignee: Seating Matters Ltd
Current assignee: Seating Matters Ltd
Priority date: 2019-10-24
Filing date: 2019-10-24
Publication date: 2021-04-28
Anticipated expiration: 2039-10-24
Also published as: GB2588447B; GB201915470D0

Abstract

A chair comprising a support frame 2, a seat base 6 pivotally mounted on the support frame to permit adjustment of the angle of the seat base with respect to the support frame. A seat back 8 mounted on the seat base and a footrest assembly 10 including a foot plate 12. Said foot rest assembly being coupled to the seat base using a slotted coupling arrangement permitting limited upward and forward tilting of the foot rest assembly with respect to the seat base. Optionally the support frame is mounted on castor wheels 4, which can be locked to facilitate movement in a straight line.

Description

FIELD OF THE INVENTION

This invention relates to a chair, and in particular to a therapeutic chair suitable for healthcare use by adults and children with limited mobility and/or other health problems requiring advanced postural support, pressure management and enhanced comfort with increased safety.

BACKGROUND OF THE INVENTION

A chair is often considered furniture, but for those that spend a great deal of time sitting or in bed, a chair is a life-saving clinical aid. It can be argued that incorrect use of inappropriate seating has led to an increase in pressure injury incidence, preventable falls and has a detrimental effect on a persons' mobility. Many people who suffer from long term disabilities, who are elderly or lack mobility spend long periods of time sitting. Many chairs do not incorporate the necessary features for pressure management in seating. These include being able to adjust the chair to a person's individual size, provide postural support, repositioning for weight redistribution and appropriate cushion use.

It is known to provide therapeutic chairs specifically designed for healthcare applications which provide enhanced support and a much greater range of adjustability. Of particular importance is the provision of a foot plate upon which the user can place their feet when sitting. The ability to transfer weight to the user's feet when sitting is important for the patient's comfort and stability in the chair. Typically, such chairs provide adjustment for seat depth (distance between the front of the seat cushion and the backrest), angle of the seat back and foot plate and overall angle of tilt of the seat base and seat back (known as "tilt in space"). This tilt in space adjustment can vary between a posterior (rearward or reclined) tilt of to an anterior (forward) tilt to help the use to stand. However, such known chairs tend to be very expensive, heavy, complex and difficult to clean and great care must be taken in the adjustment of the chair to ensure that it remains stable and safe in all positions of adjustment. A particular area of concern is impact of the foot plate with the ground during an anterior tilt, which could tip the chair.

An object of the present invention is to provide a chair suitable for healthcare use 5 which overcomes these problems.

SUMMARY OF THE INVENTION

According to the present invention there is provided a chair comprising a support frame, a seat base pivotally mounted on the support frame to permit adjustment of the angle of the seat base with respect to the support frame, a seat back mounted on the seat base and a foot rest assembly including a foot plate upon which the user can rest their feet, said foot rest assembly being coupled to the seat base using a slotted coupling arrangement permitting limited upward and forward tilting of the foot rest assembly with respect to the seat base should the seat plate contact the ground during pivotal movement of the seat base with respect to the support frame.

In a preferred embodiment, the foot rest assembly is pivotally mounted on the seat base and a linkage member extends between the seat base and the foot rest assembly for retention of the foot rest assembly at a selected angle with respect to the seat base, said linkage member being pivotally coupled to the foot rest assembly at a first end and slidingly engaging a guide slot of the seat base at a second end thereof, opposite said first end, whereby said second end of the linkage may slide along said guide slot to permit upward pivotal movement of the foot rest assembly with respect to the seat base should the foot plate of the foot rest assembly contact the ground during pivotal movement of the seat base with respect to the support frame. Preferably said linkage member facilitates adjustment of the angle of the foot rest assembly with respect to the seat base by extension and retraction of the linkage member. The guide slot may include a downwardly and rearwardly facing end portion, at a bottom of which a pivot member of said second end of the linkage member rests during normal operation of the chair, and a forwardly extending substantially horizontal forward portion extending forwardly from an upper end of said end portion.

In one embodiment a first adjustable length linkage member may extend between the support frame and the seat base for facilitating adjustment of the angle of the seat base with respect to the support frame and retention of the seat base at a 5 selected angle with respect to the support frame. Said first adjustable length linkage member may facilitate adjustment of the angle of the seat base with respect to the base frame by extension and retraction of the first adjustable length linkage member. The first adjustable length linkage member may be adapted to provide a tilt in space function between a posterior tilt of up to 450 to the horizontal (with 10 respect to the seat base) and an anterior tilt of up to 100 to help a user to stand from a seated position in the chair.

The seat back may be pivotally mounted on the seat base, a second adjustable length linkage member extending between the seat base and the seat back for facilitating adjustment of the angle (recline) of the seat back with respect to the seat base and retention of the seat back at a selected angle with respect to the seat base. The second adjustable length linkage member may facilitate adjustment of the angle of the seat back with respect to the seat base by extension and retraction of the second adjustable length linkage member.

In one embodiment said linkage member extending between the seat base and the foot rest assembly comprises a third adjustable length linkage member facilitating adjustment of angle of the foot rest assembly (elevation) with respect to the seat base and retention of the foot rest assembly at a selected angle with respect to the seat base, said third adjustable length linkage member facilitating adjustment of the angle of the foot rest assembly with respect to the seat base by extension and retraction of the third adjustable length linkage member.

One or more of the first, second and third adjustable length linkage members may 30 incorporate biasing means to bias the respective adjustable length linkage member towards an extended position to facilitate adjustment of the chair.

One or more of the first, second and third adjustable length linkage members may be driven to extend and retract the respective adjustable length linkage member under the control of a control device.

Preferably the foot plate is mounted such that the distance between the seat base and the foot plate is adjustable to suit the length of the user's legs.

The foot plate may be pivotally mounted on a body of the foot rest assembly such that the angle of the foot plate with respect to a body of the foot rest assembly is 112 adjustable to adjust the angle of the user's ankles when their feet are supported on the foot plate. The foot plate may be provided with an adjustable stop delimiting the rest position of the foot plate with respect to the body of the foot rest assembly. The foot plate may be folded upwardly to an upright out of use position when required, wherein the foot plate lies flat against the body of the foot rest assembly.

The support frame may be mounted on castor wheels for mobility. One or more of the castor wheels may be braked and/or may incorporate a directional lock to facilitate movement of the chair in a straight line.

The seat base may comprise a planar tray having upstanding lateral side portions extending upwardly from either side of the tray to which the seat back is pivotally coupled. Cut out portions adjacent either side of the tray may be folded downwardly and provided with apertures to which the support frame may be pivotally coupled.

The foot rest assembly may be pivotally coupled to a forward end of each side portion of the tray on a pivot axis arranged to be substantially coincident with the knee flexure of a patient, in use, when sat in the chair.

The back rest may be pivotally coupled to the seat base via arched guide slots formed in each side portion of the tray within which slots a pivot member of a respective side of the seat back is slidingly retained to permit adjustment of the distance between a lower edge of the seat back and a front edge of the seat base to facilitate adjustment of the seat depth of the chair. The arched guide slots may comprise one or more arched regions, whereby the seat back is retained in a selected position by retention of the pivot members in a lower end of a respective leg of said arched guide slots under gravity.

In a preferred embodiment the first, second and third adjustable length linkage 5 members may be coupled to the seat base via a mounting bracket attached to the underside of the seat base, preferably by releasable fasteners such as nuts and bolts, and extending rearwardly from a rear side of the seat base. The mounting bracket may comprise a pair of parallel side plates between which respective ends of the first, second and third adjustable length linkage members can be received 10 and the side plates may be provided with aligned pairs of mounting apertures and slots for receiving pivot pins or bolts for securing said respective ends of the first, second and third adjustable length linkage members to the seat base.

BRIEF DESCRIPTION OF THE DRAWINGS

A chair in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 is a perspective view of a chair in accordance with an embodiment of the present invention; Figure 2 is a perspective view of a chair of Figure 1 from the rear; Figure 3 is a detailed view of the underside of the chair of Figure 1; and Figure 4 is a detailed side view through the chair of Figure 1 with parts omitted for clarity.

DETAILED DESCRIPTION OF THE DRAWINGS

As illustrated in the drawings, a chair in accordance with an embodiment of the present invention comprises a support frame 2 mounted upon ground engaging castor wheels 4 for mobility, a seat base 6 pivotally mounted on the support frame 2 to permit adjustment of the angle of the seat base 2 with respect to the support frame 2, a seat back 8 pivotally mounted on the seat base 6 to permit adjustment of the angle of the seat back 8 with respect to the seat base 6 and a footrest assembly 10 including a foot plate 12 upon which the user can rest their feet, said footrest assembly 10 being pivotally mounted on the seat base 6 to permit adjustment of the angle of the footrest assembly 10 with respect to the seat base 6.

In the embodiment shown, the support frame 2 comprises a pair of parallel side beams 14,16 extending along either side of the chair and to which the castor wheels 4 are attached at respective ends thereof, said side beams 14,16 being linked by one or more transverse frame members 18,20 extending between the side beams 14,16, at or adjacent a central region of each side beam to define a substantially H shaped base frame portion. Upright support members 22,24 extend vertically upwardly from each side beam 14,16, extending parallel to one another. The seat 16 base 6 is pivotally coupled to the upright support members 22,24 of the support frame 2 at or adjacent the upper ends thereof permitting the seat base 6 to be tilted with respect to the support frame 2 about a substantially horizontal pivot axis extending transverse to the seat base 6 across a central region of the seat base 6 to permit the angle of inclination of the seat base 6 with respect to a horizontal plane to be adjusted.

A first adjustable length linkage member 26 extends between the support frame 2 and the seat base 6 for facilitating adjustment of the angle of the seat base 6 with respect to the support frame 2 and retention of the seat base 6 at a selected angle with respect to the support frame 2. The first adjustable length linkage member 26 facilitates adjustment of the angle of the seat base 6 (as well as the seat back 8 and footrest assembly 10) with respect to the base frame 2 (and with respect to the horizontal) by extension and retraction of the first adjustable length linkage member 26, thereby providing a "tilt in space" function. Preferably the first adjustable length linkage member 26 is adapted to provide a tilt in space function between a posterior tilt of up to 45° to the horizontal (with respect to the seat base 6) and an anterior tilt of up to 100 to help a user to stand from a seated position in the chair.

A second adjustable length linkage member 28 extends between the seat base 6 and the seat back 8 for facilitating adjustment of the angle of recline of the seat back 8 with respect to the seat base 6 and retention of the seat back 8 at a selected angle with respect to the seat base 6 (for example between 90° and 130° to the seat base 6). The second adjustable length linkage member 28 facilitates adjustment of the angle of the seat back 8 with respect to the seat base 6 by extension and retraction of the second adjustable length linkage member 28.

A third adjustable length linkage member 30 extends between the seat base 6 and to the foot rest assembly 10 for facilitating adjustment of the angle of elevation of the foot rest assembly 10 with respect to the seat base 6 and retention of the foot rest assembly 10 at a selected angle with respect to the seat base 6. The third adjustable length linkage member 30 facilitates adjustment of the angle of the foot rest assembly 10 with respect to the seat base 6 by extension and retraction of the third adjustable length linkage member 30.

One or more of the first, second and third adjustable length linkage members 26,28,30 may incorporate biasing means, such as a spring or gas pressure, to bias the respective adjustable length linkage member towards an extended position to facilitate adjustment of the chair, and locking means for retaining the linkage member at a desired length. Alternatively, or additionally, one or more of the first, second and third adjustable length linkage members 26,28,30 may be powered or driven, for example by means of an electric motor and gearing, to extend and retract the respective adjustable length linkage member under the control of a suitable control device.

The foot plate 12 extends outwardly from a lower end of a body of the foot rest assembly 10 for supporting a user's feet thereon when seated in the chair. Preferably the distance between the seat base 6 and the foot plate 12 is adjustable to suit the length of the user's legs, for example by mounting the foot plate 12 to said body of the foot rest assembly 10 on a sliding coupling 15, as shown in Figure The angle of the foot plate 12 with respect to the body of the foot rest assembly 10 may be adjustable to adjust the angle of the user's ankles when their feet are supported on the foot plate 12. In one embodiment such angle adjustment may be provided by an adjustable stop delimiting the rest position of the foot plate 21 with respect to the body of the foot rest assembly 10, for example to give an ankle angle of 750, 900 or 1050 to the body of the foot rest assembly 10. Preferably the foot plate 12 can be folded upwardly to an upright out of use position when required, wherein the foot plate 12 lies flat against the body of the foot rest assembly 10.

In a preferred embodiment the foot rest assembly 10 is coupled to the seat base using a slotted coupling arrangement which provides enhanced stability and safety by permitting upward tilting of the foot rest assembly 10 should the foot plate 12 contact the ground during adjustment of movement of the chair. The third adjustable length linkage member 30 may be pivotally coupled to the foot rest assembly 10 at a first end 32 of the linkage member 30 and may slidingly engage a guide slot 34 of the seat base 6 at a second end 36 thereof, opposite said first end 32. Preferably the guide slot 34 includes a downwardly and rearwardly facing end portion 38, at a bottom of which a pivot member of said second end 36 of the third adjustable length linkage member 30 rests during normal operation of the chair, and a forwardly extending substantially horizontal forward portion 40, extending forwardly from an upper end of said end portion 38. In normal use, the pivot member of the second end 36 of the third adjustable length linkage member 30 rests against the bottom of said end portion 38 of the guide slot 34, transferring the weight of the foot rest assembly 10, and any load applied thereto, to the seat base 6.

When the first adjustable length linkage member 26 is extended in tilt to tilt the seat base 6 forwardly with respect to the support frame 2 during a tilt in space operation, for example to bring the seat to an anterior tilt to assist a seated user to stand, there is a risk of the foot plate 12 striking the ground, potentially lifting the support frame 2 of the chair and creating an unstable and potentially dangerous situation, particularly where the distance between the foot plate 12 and the seat base 6 is at or close to a maximum to suit taller patients. The slotted coupling between the second end 36 of the third adjustable length linkage member 30 and the guide slot 34 of seat base 6 prevents this from happening, as will be described below.

Should the foot plate 12 contact the floor during anterior tilt of the seat base 6 with respect to the support frame 2, the pivot member of said second end 36 of the third adjustable length linkage member 30 will be lifted out of the end portion 38 of guide 5 slot 34 and is able to move along the forward portion 40 of the guide slot 38, thereby permitting the foot rest assembly 10 to pivot forwardly and upwardly with respect to the seat base 2. The pivot member of said second end 36 of the third adjustable length linkage member 30 will slide back to the bottom of the end portion 38 of the guide slot 34 under the weight of the foot rest assembly once chair is 10 adjusted or moved to a configuration where the foot plate 12 no longer engages the ground.

One or more of the castor wheels 4 may be provided with a selectively operable brake. One or more of the castor wheels 4 may have a directional lock to facilitate 15 movement of the chair in a straight line.

Preferably the seat base 2 comprises a smooth flat tray 42, preferably formed in a single piece from a sheet of suitable material, such as pressed metal, more preferably laser cut and pressed steel, the tray 42 having upstanding lateral side portions 44,46 extending upwardly from either side of the tray 42 to which the seat back 8 may be pivotally coupled. Such construction provides an easily cleaned and stable support for the chair cushion. Mounting points may be provided adjacent a rear side of the tray 42 for attaching seat belts. Said mounting points, comprising raised loops, may also serving as a back stop for the seat cushion. Cut out portions 45 (see Figure 3) adjacent either side of the tray 42 of the seat base 2 may be folded downwardly and provided with apertures to which the upright support members 22,24 of the support frame 2 may be pivotally coupled.

In the embodiment shown in the drawings the foot rest assembly 10 is pivotally 30 coupled to a forward end of each side portion 44,46 of the tray 42 on a pivot axis 80 arranged substantially coincident with the knee flexure of a patient when sat in the chair, as best shown in Figure 4.

In the embodiment shown in the drawings the pivotal couplings between the first, second and third adjustable length linkage members and the seat base 6 are provided on a mounting bracket 60 bolted to the underside tray 42 of the seat base 6 and extending rearwardly from a rear side of the seat base 6. The mounting bracket 60 preferably comprises a pressed steel plate folded to define a pair of parallel side plates 62,64 between which respective ends of the first, second and third adjustable length linkage members 26,28,30 can be received and having aligned pairs of mounting apertures 66 and slots 68 for receiving pivot pins or bolts for securing said respective ends of the first, second and third adjustable length linkage members 26,28,30 to the seat base 6. A rearmost portion of the mounting bracket 60, extending rearwardly from the seat base 6, includes a portion extending over the upper surface of the tray 42 of the seat base 6 to transfer any load applied to the mounting bracket 60 via the back rest 8 to the seat base 6 and to facilitate location of the mounting bracket 60 onto the seat base 6.

As shown in Figures 3 and 4, the guide slot 34 within which the second end 36 of the third adjustable linkage member 30 slides comprises a pair of aligned slots 68 formed in said side plates 62,64 of the mounting bracket 60, the second end 36 of the third adjustable length linkage member 30 being located between said side plates 62,64 of the mounting bracket 60 with its pivot member/bolt 70 passing through said aligned guide slots 68.

In the embodiment shown in the drawings and as best illustrated in Figure 4, two sets of guide slots 34A,34B are provided in the mounting bracket 60 to which to the second end 36 of the third adjustable length linkage member 30 can be selectively coupled to provide different ranges of motion of the foot rest assembly 10 to suit different users of the chair. Similarly different sets of apertures 66 may be provided in the side plates 62,64 of the mounting bracket 60 which can be selected for coupling the first and/or second adjustable length linkage members 26,28, which may comprise manually operable gas struts or motorised linear actuators) to the mounting bracket 60 to provide different ranges of motion of the seat base 6 with respect to the support frame 2 and/or of the seat back 6 with respect to the seat base 6.

As best illustrated in Figure 4, preferably the back rest 8 is pivotally coupled to the seat base 6 via arched guide slots 48 formed in each side portion 44,46 of the seat base 6 within which a pivot member 50 (e.g. pivot pin) of a respective side of the seat back 8 may be slidingly retained to permit adjustment of the distance between a lower edge of the seat back 8 and a front edge of the seat base 6 to facilitate adjustment of the seat depth of the chair. Preferably said arched guide slots 48 comprise one or more arched regions, whereby the seat back 8 is retained in a selected position by retention of the pivot members 50 in a lower end of a respective leg of said arched guide slots 48 under gravity. In the embodiment shown in the drawings, each arched guide slot 40 comprises two arched regions providing three separate seat depth positions. Locking means (not shown) may be provided for retaining the pivot members 50 of the back rest 8 in selected positions in the arched guide slots 48 of the seat base 6.

Arm rests 52,54 are coupled to each side portion 44,46 of the seat base 6. Preferably the arms rests 52,54 are coupled to each side portion 44,46 of the seat base 6 via laterally extending slotted couplings permitting lateral adjustment of each arm rest 52,54 with respect to the seat base 6 and also angular adjustment of each arm rest with respect to the side portions 44,46 of the seat base 6 and one another.

The construction of the above described chair, using pressed steel folded plates and a bolted as opposed to welded construction, provides a strong, lightweight, easily cleaned and cost effective chair construction, the slotted coupling of the adjustment mechanism for the foot rest assembly alleviating the disadvantages of the prior art, while providing a highly cost effective and versatile chair suitable for a wide variety of patients with differing healthcare requirements.

The invention is not limited to the embodiment described herein but can be amended or modified without departing from the scope of the present invention as 30 defined by the appended claims.

Claims

CLAIMS1. A chair comprising a support frame, a seat base pivotally mounted on the support frame to permit adjustment of the angle of the seat base with respect to the 5 support frame, a seat back mounted on the seat base and a footrest assembly including a foot plate upon which the user can rest their feet, said foot rest assembly being coupled to the seat base using a slotted coupling arrangement permitting limited upward and forward tilting of the foot rest assembly with respect to the seat base should the seat plate contact the ground during pivotal movement of the seat 10 base with respect to the support frame.
2. A chair as claimed in claim 1, wherein the foot rest assembly is pivotally mounted on the seat base and a linkage member extends between the seat base and the foot rest assembly for retention of the foot rest assembly at a selected angle with respect to the seat base, said linkage member being pivotally coupled to the foot rest assembly at a first end and slidingly engaging a guide slot of the seat base at a second end thereof, opposite said first end, whereby said second end of the linkage may slide along said guide slot to permit upward pivotal movement of the foot rest assembly with respect to the seat base should the foot plate of the foot rest assembly contact the ground during pivotal movement of the seat base with respect to the support frame.
3. A chair as claimed in claim 2, wherein said length linkage member facilitates adjustment of the angle of the foot rest assembly with respect to the seat base by 25 extension and retraction of the linkage member.
4. A chair as claimed in claim 2 or claim 3, wherein the guide slot includes a downwardly and rearwardly facing end portion, at a bottom of which a pivot member of said second end of the linkage member rests during normal operation of the chair, and a forwardly extending substantially horizontal forward portion extending forwardly from an upper end of said end portion.
5. A chair as claimed in any of claims 2 to 4, wherein a first adjustable length linkage member extends between the support frame and the seat base for facilitating adjustment of the angle of the seat base with respect to the support frame and retention of the seat base at a selected angle with respect to the support frame.
6. A chair as claimed in claim 5, wherein said first adjustable length linkage member facilitates adjustment of the angle of the seat base with respect to the base frame by extension and retraction of the first adjustable length linkage member.
7. A chair as claimed in claim 6, wherein the first adjustable length linkage member 10 is adapted to provide a tilt in space function between a posterior tilt of up to 45° to the horizontal (with respect to the seat base) and an anterior tilt of up to 100 to help a user to stand from a seated position in the chair.
8. A chair as claimed in any of claims 5 to 7, wherein the seat back is pivotally mounted on the seat base, a second adjustable length linkage member extending between the seat base and the seat back for facilitating adjustment of the angle of the seat back with respect to the seat base and retention of the seat back at a selected angle with respect to the seat base.
9. A chair as claimed in claim 8, wherein the second adjustable length linkage member facilitates adjustment of the angle of the seat back with respect to the seat base by extension and retraction of the second adjustable length linkage member.
10. A chair as claimed in any of claim 9, wherein said linkage member extending between the seat base and the foot rest assembly comprises a third adjustable length linkage member facilitating adjustment of foot rest assembly with respect to the seat base and retention of the foot rest assembly at a selected angle with respect to the seat base, said third adjustable length linkage member facilitating adjustment of the angle of the foot rest assembly with respect to the seat base by extension and retraction of the third adjustable length linkage member.
11. A chair as claimed in claim 10, wherein one or more of the first, second and third adjustable length linkage members incorporates biasing means to bias the respective adjustable length linkage member towards an extended position to facilitate adjustment of the chair.
12. A chair as claimed in claim 10 or claim 11, wherein one or more of the first, 5 second and third adjustable length linkage members is driven to extend and retract the respective adjustable length linkage member under the control of a control device.
13. A chair as claimed in any preceding claim, wherein the foot plate is mounted 10 such that the distance between the seat base and the foot plate is adjustable to suit the length of the user's legs.
14. A chair as claimed in any preceding claim, wherein the foot plate is pivotally mounted on a body of the foot rest assembly such that the angle of the foot plate 15 with respect to a body of the foot rest assembly is adjustable to adjust the angle of the user's ankles when their feet are supported on the foot plate.
15. A chair as claimed in claim 14, wherein the foot plate is provided with an adjustable stop delimiting the rest position of the foot plate with respect to the body 20 of the foot rest assembly, and thereby the angle of the foot plate with respect to the body of the foot rest assembly.
16. A chair as claimed in claim 15, wherein the foot plate can be folded upwardly to an upright out of use position when required, wherein the foot plate lies flat against 25 the body of the foot rest assembly.
17. A chair as claimed in any preceding claim, wherein the support frame is mounted on castor wheels for mobility.
18. A chair as claimed in claim 17, wherein one or more of the castor wheels are braked and/or incorporate a directional lock to facilitate movement of the chair in a straight line.
19. A chair as claimed in any preceding claim, wherein the seat base comprises a planar tray having upstanding lateral side portions extending upwardly from either side of thereof to which the seat back is pivotally coupled.
20. A chair as claimed in claim 19, wherein cut out portions of the tray adjacent the side portions are folded downwardly and provided with apertures to which the support frame is pivotally coupled.
21. A chair as claimed in claim 19 or claim 20, wherein the foot rest assembly is 10 pivotally coupled to a forward end of each side portion of the tray on a pivot axis arranged to be substantially coincident with the knee flexure of a patient, in use, when sat in the chair.
22. A chair as claimed in any of claims 19 to 21, wherein the back rest is pivotally coupled to the seat base via arched guide slots formed in each side portion of the tray within which slots a pivot member of a respective side of the seat back is slidingly retained to permit adjustment of the distance between a lower edge of the seat back and a front edge of the seat base to facilitate adjustment of the seat depth of the chair.
23. A chair as claimed in claim 22, wherein said arched guide slots comprise one or more arched regions, whereby the seat back is retained in a selected position by retention of the pivot members in a lower end of a respective leg of said arched guide slots.
24. A chair as claimed in any of claims 10 to 23, when dependent upon claim 10, wherein the first, second and third adjustable length linkage members are coupled to the seat base via a mounting bracket bolted to the underside of the seat base and extending rearwardly from a rear side of the seat base, said mounting bracket comprising a pair of parallel side plates between which respective ends of the first, second and third adjustable length linkage members can be received and having aligned pairs of mounting apertures and slots for receiving pivot pins or bolts for securing said respective ends of the first, second and third adjustable length linkage members to the seat base, said guide slot of the seat base being defined by at least one pair of said slots.