GB2632110A

GB2632110A - Height adjustment mechanism for a chair

Info

Publication number: GB2632110A
Application number: GB2311304.6A
Authority: GB
Inventors: Marsh Fred
Original assignee: Accora Ltd
Current assignee: Accora Ltd
Priority date: 2023-07-24
Filing date: 2023-07-24
Publication date: 2025-01-29
Also published as: GB202311304D0; IE20240422A2

Abstract

A height adjustment mechanism 10 for a chair is arranged to raise and lower a seat platform 14 of the chair relative to a base 12 of the chair. The mechanism comprises a four-bar linkage 30 comprising a fixed base link 32 connectable to the base of the chair, a coupler 60, and first 44 and second 46 wishbone linkages pivotally connected between the base link and the coupler. The mechanism further comprises a front seat linkage 72 fixedly connected to said platform and pivotally connected at a first seat pivot 69 to an arm 48 of the first wishbone linkage extending from the four-bar linkage, and a rear seat linkage 74 fixedly connected to said seat platform and pivotally connected at a second seat pivot 71 to an arm 54 of the second wishbone linkage extending from the four-bar linkage. During movement, a plane containing the seat pivots remains parallel to an axis of the fixed base link such that, in use, an angle between a plane of the seat platform and the axis of the fixed base link does not change. A method of adjusting the height of a seat platform of a chair is also disclosed.

Description

Height Adjustment Mechanism for a Chair

FIELD OF THE INVENTION

This invention relates to a height adjustment mechanism for a chair, and to a chair including such a height adjustment mechanism. The invention relates in particular to a height adjustment mechanism that permits a continuous height adjustment rather than a discrete height adjustment. It is envisaged that the height adjustment mechanism of the present invention will be used in arm chairs and the like, and may be used in rise and recline chairs.

BACKGROUND TO THE INVENTION

Some less mobile people, such as the elderly and patients, spend a significant time in bed or in a chair. However, if a person is in bed or in a chair for prolonged periods of time there is a significant risk that they will develop pressure sores. These are wounds that develop over time due to constant pressure and friction against a person's skin. As such, it is important that a chair is comfortable and will not cause or aggravate any pressure sores. For this reason it is desirable to provide a chair that is of the correct size for the person.

It is important that a chair is of the correct height to allow a person sitting in the chair to place their feet on the ground in a comfortable seated position. Furthermore, the correct height of the chair should ensure that the backs of a user's legs do not rub uncomfortably on the front edge of the seat during use. Having a chair of the correct height also assists a person to get into and out of the chair more easily.

For these reasons, chairs may be manufactured in a range of sizes to allow the correct chair to be selected based on the size of the person. This, however, means that a care facility may have to purchase a number of different sizes of chair to be able to select the most appropriate chair for a particular person.

It is also known to provide chairs with height adjustment. However, typically this adjustment is in discrete steps. Because the seat platform of the chair must support the weight of a user, it is necessary for any adjustment mechanism to be able to support this weight during use. Accordingly, in many prior art chairs the height adjustment is limited to be able to securely lock the chair at the required height to prevent the chair moving under the weight of the user.

It is an aim of the present invention to provide a chair having an improved height adjustment that overcomes at least some of the disadvantages of known chairs.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a height adjustment mechanism for a chair arranged to raise and lower a seat platform of the chair relative to a base of the chair, the mechanism comprising: a four-bar linkage comprising: a fixed base link connectable to the base of the chair; a coupler; and first and second wishbone linkages pivotally connected between the base link and the coupler, a front seat linkage fixedly connected to said seat platform and pivotally connected at a first seat pivot to an arm of the first wishbone linkage extending from the four-bar linkage; and a rear seat linkage fixedly connected to said seat platform and pivotally 25 connected at a second seat pivot to an arm of the second wishbone linkage extending from the four-bar linkage, wherein, during use, a distance between a seat pivot plane containing the first and second seat pivots and the base link changes to adjust a height of said seat platform of the chair, and the seat pivot plane remains parallel to an axis of the fixed base link such that, in use, an angle between a plane of the seat platform and the axis of the fixed base link does not change during height adjustment of the chair. -3 -

In preferred embodiments each of the first and second wishbone linkages are generally Y-shaped.

The first wishbone linkage preferably comprises a main arm pivotally connected to the front seat linkage, a connecting arm pivotally connected to the base link and a coupling arm pivotally connected to the coupler. The second wishbone linkage preferably comprises a main arm pivotally connected to the rear seat linkage, a connecting arm pivotally connected to the base link and a coupling arm pivotally connected to the coupler. In preferred embodiments an axis of the main arm is generally perpendicular to a line extending between the pivotal connection between the connecting arm and the base link and the pivotal connection between the coupling arm and the coupler. The main arm is preferably longer than each of the connecting arm and the coupling arm.

In preferred embodiments the height adjustment mechanism further comprises a back rest linkage arrangement connecting the base link to a back rest member, the back rest member being part of or connectable to a back rest of said chair. The back rest linkage arrangement preferably comprises a back rest link pivotally connected to the back rest member and an intermediate link pivotally connected at a first end to the back rest link and pivotally connected at a second end to the base link. The intermediate link may have an arch shape. In some embodiments the back rest link comprises an annular end providing the pivotal connection between the back rest link and the back rest member.

In preferred embodiments the position of the back rest member relative to the rear seat linkage does not change during use of the height adjustment mechanism to raise and lower said seat platform.

In some embodiments the height adjustment mechanism further comprises an actuator arranged to apply a force to a part of the four-bar linkage to change the distance between the seat pivot plane and the base link to adjust a height of said seat platform of the chair. -4 -

In other embodiment the height adjustment further comprises an actuator arranged to apply a force to a part of the back rest linkage to increase and/or decrease a distance between the back rest member and the base link.

A second aspect of the invention provides a chair comprising: a seat platform; a base member; and a height adjustment mechanism according to the first aspect of the invention, 10 the base link being fixedly connected to the base member and the front and rear seat linkages being fixedly connected to the seat platform.

In preferred embodiments the chair includes two height adjustment mechanisms, each being according to the first aspect of the invention. The front and rear seat linkages of a first one of the height adjustment mechanisms are fixedly connected to a first side of the seat platform and the front and rear seat linkages of a second one of the height adjustment mechanisms are fixedly connected to a second side of the seat platform.

The height adjustment mechanism or each of the height adjustment mechanisms preferably includes a back rest linkage arrangement connecting the base link to a back rest member. The chair preferably further comprises a back rest connected to the back rest member or a back rest connected to both of the back rest members.

A third aspect of the invention provides a method of adjusting the height of a seat platform of a chair, the chair being according to the second aspect of the invention, and the method comprising: applying a force to the four-bar linkage to rotate each of the first and second wishbone linkages in a first direction about their respective pivotal connections with the base link to increase a distance between the seat pivot plane and the base link; and/or applying a force to the four-bar linkage to rotate each of the first and second -5 -wishbone linkages in a second direction about their respective pivotal connections with the base link to decrease a distance between the seat pivot plane and the base link.

In embodiments in which the height adjustment mechanism or each of the height adjustment mechanisms includes a back rest linkage arrangement connecting the base link to a back rest member, the method preferably comprises: applying a force to the back rest linkage arrangement in a first direction to increase a distance between the back rest member and the base link; and/or applying a force to the back rest linkage arrangement in a second direction to increase a distance between the back rest member and the base link.

In embodiments in which the back rest linkage arrangement comprises a back rest link pivotally connected to the back rest member and an intermediate link pivotally connected at a first end to the back rest link and pivotally connected at a second end to the base link, the method preferably further comprises: applying a force to the or each back rest link to rotate the back rest link in a first direction about the pivotal connection with the back rest member to increase a distance between the back rest member and the base link; and/or applying a force to the or each back rest link to rotate the back rest link in a second direction about the pivotal connection with the back rest member to increase a distance between the back rest member and the base link.

Preferred and/or optional features of each aspect and embodiment described above may also be used, alone or in appropriate combination, in the other aspects and embodiments also.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described by way of example only and with reference to the accompanying drawings, in which like reference signs are used for like features, and in which: -6 -Figure 1 is a perspective view of a part of a chair including a pair of height adjustment mechanisms, each mechanism being in a fully lowered position; Figure 2 is a perspective view of the part of the chair of Figure 1 with each height adjustment mechanism shown in a fully raised position; Figure 3 is a side view from a first side of one of the height adjustment mechanisms of Figure 1 in the fully lowered position; Figure 4 is a side view from a second side of one of the height adjustment mechanisms of Figure 1 in the fully lowered position; Figure 5 is a perspective view of one of the height adjustment mechanisms of Figure 1 in the fully lowered position; Figure 6 shows a linkage arrangement of one of the height adjustment mechanisms of Figure 1 in the fully lowered position; Figure 7 is a plan view from above of the linkage arrangement of Figure 6; Figure 8 is a side view from a first side of one of the height adjustment mechanisms of Figure 2 in the fully raised position; Figure 9 is a side view from a second side of one of the height adjustment mechanisms of Figure 2 in the fully raised position; Figure 10 is a perspective view of one of the height adjustment mechanisms of Figure 2 in the fully raised position; Figure 11 shows a linkage arrangement of one of the height adjustment mechanisms of Figure 2 in the fully raised position; and Figure 12 is a plan view from above of the linkage arrangement of Figure 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a height adjustment mechanism that permits continuous adjustment of the height of a seat of a chair. The chair may, for example, be an armchair or similar. The chair may be a rise and recline chair.

The height adjustment mechanism comprises a linkage arrangement that allows a seat platform or support of the chair to be raised and lowered while remaining parallel to a floor on which the chair is standing. The seat platform may be retained or held in any position between a fully lowered position and a fully raised position allowing the position of the seat platform to be tailored to a user of the seat to provide the most appropriate support.

In the following description, references to upwardly and in an upward direction refer to directions away from a surface or floor on which the chair 2 is standing in its usual orientation in use. References to rear or rearwardly refer to locations closer to and/or in a direction towards the back rest 6 of the chair 2. References to front or forwardly refer to locations further from and/or in a direction away from the back rest 6 of the chair 2. Accordingly, in normal use a user will sit on an upward facing surface of the seat of the chair and their back will rest against forward facing surfaces of the back rest of the chair. References to inner and outer are with reference to a centreline of the chair, so that inner is closer to or towards the centreline of the chair and outer is away from the centreline and towards sides of the chair. Furthermore, references to horizontal and vertical will be understood to refer to orientations when a chair is standing on a horizontal surface.

A preferred embodiment of a height adjustment mechanism 10 is illustrated in Figures 1 to 12. -8 -

In preferred embodiments a chair includes two height adjustment mechanisms 10, each height adjustment mechanism 10 extending between and connecting a respective base member 12 of the chair and a seat platform 14 of the chair. A chair preferably, therefore, includes two base members 12.

It will be understood that the base members 12 are connected to a base structure of the chair (not shown) that may include a base frame, legs, castors and/or other adjustment mechanisms of the chair. The base structure is configured to stand on a floor or other suitable surface and to support the chair.

In this embodiment the seat platform 14 comprises a perimeter seat frame 16 and seat panels 18 surrounded by the seat frame 16. In use, the seat panels 18 support one or more seat cushions on which a person may be seated. The seat platform 14 has a front edge 20, a rear edge 22 and opposite side edges 24.

In this embodiment each of the height adjustment mechanisms 10 extends between the seat platform, proximate one of the side edges 24 of the seat platform 14, and a respective one of the base members 12.

It will be appreciated that the chair also includes a back rest that extends generally upwardly from proximate the rear edge 22 of the seat platform 14. Figures 1 and 2 illustrate a back rest member 26 of the chair. The back rest member 26 is connected to the back rest and may permit adjustment of a position of the back rest relative to the seat platform 14. The back rest member 26 extends generally parallel to the rear edge 22 of the seat platform 14 between first and second bearing elements 28. Each of the bearing elements 28 is disposed proximate a respective one of the side edges 24 of the seat platform 14.

Each height adjustment mechanism 10 comprises linkage arrangement 30 30 comprising a base link 32 which is connected to the base member 12. The base link 32 is elongate and extends between a first, front end 34 and a second, rear end 36. In this embodiment, and as shown most clearly in Figure 9, a part of the base -9 -member 12 is connected to the base link 32 substantially midway between the first and second ends 34, 36. In this embodiment the base link 32 is crank-shaped, having first and second end regions 38, 40 lying in the same plane and a central region 42 (between the two end regions 38, 40) lying in an offset plane. The base link 32 is disposed such that the central region 42 lies inwardly of the first and second end regions 38, 40, i.e. closer to a centreline of the chair, in a generally horizontal plane.

Each height adjustment mechanism 10 further comprises a first, front wishbone (Y-shaped) linkage 44 and a second, rear wishbone (Y-shaped) linkage 46. The first wishbone linkage 44 has a main arm 48, a connecting arm 50 and a coupling arm 52. The main arm 48 is preferably longer than each of the connecting arm 50 and coupling arm 52. The connecting arm 50 and coupling arm 52 may be of equal lengths. The second wishbone linkage 46 has a main arm 54, a connecting arm 56 and a coupling arm 58. The main arm 54 is preferably longer than each of the connecting arm 56 and coupling arm 58. The connecting arm 56 and coupling arm 58 may be of equal lengths.

In preferred embodiments the main arm 48 of the first wishbone linkage 44 and the main arm 54 of the second wishbone linkage 46 are the same length. Similarly, the connecting arm 50 of the first wishbone linkage 44 and the connecting arm 56 of the second wishbone linkage 46 are preferably the same length, and the coupling arm 52 of the first wishbone linkage 44 and the coupling arm 58 of the second wishbone linkage 46 are preferably the same length. The second wishbone linkage 46 is, therefore, preferably, identical to the first wishbone linkage 44.

The connecting arm 50 of the first wishbone linkage 44 is rotatably or pivotally joined to the first, front end region 38 of the base link 32 at a first base pivot 61. The first wishbone linkage 44 may be joined to the first end region 38 of the base link 32 at a distal end of the connecting arm 50. Similarly, the connecting arm 56 of the second wishbone linkage 46 is rotatably or pivotally joined to the second, rear end region 40 of the base link 32 at a second base pivot 63. The second wishbone linkage 46 may be joined to the second end region 40 of the base link 32 at a distal end of the connecting arm 56.

A coupler 60 extends between and connects the coupling arm 52 of the first wishbone linkage 44 and the coupling arm 58 of the second wishbone linkage 46. In this embodiment a first end 62 of the coupler 60 is rotatably or pivotally joined to the coupling arm 52 of the first wishbone linkage 44 at a first coupling pivot 65 and a second end 64 of the coupler 60 is rotatably or pivotally joined to the coupling arm 58 of the second wishbone linkage 46 at a second coupling pivot 67. Preferably the first end 62 of the coupler 60 is rotatably or pivotally joined to a distal end of the coupling arm 52 of the first wishbone linkage 44 and the second end 64 of the coupler 60 is rotatably or pivotally joined to a distal end of the coupling arm 62 of the second wishbone linkage 46.

In this embodiment the coupler 60 comprises a planar wall portion 66 that extends between the first and second ends 62, 64 and a foot portion 68 that extends generally perpendicularly from a lower edge of the wall portion 66. The foot portion 68 does not extend all of the way to the first and second ends 62, 64, but only extends along a central region of the wall portion 66. In this central region, therefore, the coupler has a generally L-shaped cross-section.

The base link 32 is connected to the first and second wishbone linkages 44, 46 on a first, inner side of the wishbone linkages 44, 46 and the coupler 60 is connected to the first and second wishbone linkages 44, 46 on a second, outer side of the wishbone linkages 44, 46. Furthermore, the base link 32 is connected to the first and second wishbone linkages 44, 46 such that there is a greater distance between the central region 42 of the base link 32 and the coupler 60 than between the first and second end regions 38, 40 of the base link 32 and the coupler 60. The foot portion 68 of the coupler 60 extends in an outwards direction towards the base link 32.

The base link 32, coupler 60, and first and second wishbone linkages 44, 46, form a four-bar linkage mechanism. The rotatable connections between each of the connecting arms 50, 56 and the base link 32 form fixed pivots of the four-bar linkage. The rotatable connections between each of the coupling arms 52, 58 and the coupler 60 form moving pivots of the four-bar linkage.

Referring now to Figure 2, with the linkage arrangements 30 spaced apart across a width of the chair and each base link 32 connected to the respective base member 12, a support member 70 extends between the first end regions 38 of the base links 32. When the seat platform 14 of the chair is in a fully raised position, the foot portion 68 of each of the couplers 60 contacts the support member 70 to prevent further upward movement of the seat platform relative to the base link 32, as described further below.

The linkage arrangement 30 further comprises a front seat linkage 72 and a rear seat linkage 74. The front seat linkage 72 is rotatably or pivotally connected to the main arm 48 of the first wishbone linkage 44 at a first seat pivot 69. Preferably the front seat linkage 72 is rotatably or pivotally connected to a distal end of the main arm 48 of the first wishbone linkage 44. The rear seat linkage 74 is rotatably or pivotally connected to the main arm 54 of the second wishbone linkage 46 at a second seat pivot 71. Preferably the rear seat linkage 74 is rotatably or pivotally connected to a distal end of the main arm 54 of the second wishbone linkage 46.

The front seat linkage 72 extends from the main arm 48 of the first wishbone linkage 44 and is connected to a part of the seat platform 14. In this embodiment the front seat linkage 72 is connected to one side of the seat frame 16. The front seat linkage 72 is preferably connected to a side member of the seat frame 16 closer to the front edge 20 of the seat platform 14 than to the rear edge 22. The connection between the front seat linkage 72 and the seat platform 14 is preferably a fixed connection.

The rear seat linkage 74 extends from the main arm 54 of the second wishbone linkage 46 and is connected to a part of the seat platform 14. In this embodiment the rear seat linkage 74 is connected to a rear facing edge of the seat platform 14.

The rear seat linkage 74 may be connected to a rear member of the seat frame 16. The connection between the rear seat linkage 74 and the seat platform 14 is preferably a fixed connection.

In this embodiment the linkage arrangement 30 further comprises a back rest coupling linkage. The back rest coupling linkage includes a back rest link 76 that is rotatably or pivotally connected at a first end 78 to the back rest member 26. The back rest link 76 may be rotatably connected to the back rest member 26 proximate one of the bearing elements 28. In this embodiment the back rest link 76 includes, at the first end 78 an annular end region 80 that is engaged with the back rest member 26. The back rest link 76 is able to rotate about an axis that extends through the annular end region 80. This rotational axis is, or may be, disposed in a fixed position relative to the rear seat linkage 74 during movement between the fully lowered position and the fully raised position. It will be understood that with the rotational axis disposed in a fixed position relative to the rear seat linkage 74 the back rest is in a fixed position relative to the seat platform 14.

The back rest coupling linkage further comprises an intermediate link 82 that extends between the second, rear end 36 of the base link 32 and the back rest link 76. In this embodiment the intermediate link 82 is an arched link 82. A first end 84 of the arched link 82 is rotatably or pivotally connected to the rear end 36 of the base link 32 at a lower back rest pivot 73 and a second end 86 of the arched link 82 is rotatably or pivotally connected to a second end 88 of the back rest link 76 at an upper back rest pivot 75. An arched region of the arched link 82, between the first and second ends 84, 86, forms a concave edge 90 and an opposite convex edge 92 of the arched link 82.

The pivotal connection between the first end 84 of the arched link 82 and the rear end 36 of the base link 32 (lower back rest pivot 73) is disposed rearward of the pivotal connection between the connecting arm 56 of the second wishbone linkage 46 and the second, rear end region 40 of the base link 32 (second base pivot 63). The concave edge 90 of the arched link 82 faces in a forward direction towards the second wishbone linkage 46.

An axis of each of the (i) lower back rest pivot 73, (ii) second base pivot 63, and (iii) first base pivot 61 preferably all lie in the same plane. This plane containing the axes of the three pivots 73, 63, 61 may be parallel to but offset from a longitudinal axis of the base link 32.

The height adjustment mechanism 10 is moveable between a fully lowered position (shown in Figures 1 and 3-7) and a fully raised position (shown in Figures 2 and 8- 12). The height adjustment mechanism 10 may further include an actuator arranged to apply a force to a part of the linkage arrangement 30 to move the height adjustment mechanism 10 between the fully lowered and the fully raised positions. The actuator may be connected to the back rest link 76 and may be arranged to rotate the back rest link about its rotational axis through the annular end region 80.

During movement between the fully lowered position and the fully raised position each of the first and second wishbone linkages 44, 46 rotates about the respective first and second base pivots 61, 63. In this embodiment, in the fully lowered position the first coupling pivot 65 is a first distance below the first base pivot 61. In the fully raised position the first coupling pivot 65 is a second distance below the first base pivot 61, the second distance being less than the first distance. Furthermore, in the fully lowered position the first coupling pivot 65 is further forwards than in the fully raised position. Accordingly, during movement between the fully lowered position and the fully raised position the first coupling pivot 65 moves in an arc about the first base pivot 61 in a generally forwards and upwards direction. Similarly, due to the connection to the coupler 60, the relative positions of the second coupling pivot 67 and the second base pivot 63 are the same as those of the first coupling pivot 65 and first base pivot 61 in the lowered and raised positions. In the fully lowered position the first coupling pivot 65 may be rearward of the first base pivot 61 and the second coupling pivot 67 may be rearward of the second base pivot 63.

Rotation of the first and second wishbone linkages 44, 46 about the respective first and second base pivots 61, 63 from the fully lowered position to the fully raised position causes the first and second seat pivots 69, 71 to move in an upwards direction. Due to the fixed position of each of the first and second seat pivots 69, 71 relative to the respective first and second base pivots 61, 63, it will be appreciated that as the first and second seat pivots 69, 71 move in an upwards direction the first and second seat pivots 69, 71 also move in a forwards direction.

The main arms 48, 54 of the first and second wishbone linkages 44, 46 therefore effectively act as cranks. The front and rear seat linkages 72, 74 effectively act as rods connected to the cranks driving movement of the seat platform 14. Due to the arrangement of the four-bar linkage, the plane containing the first and second seat pivots 69, 71 remains parallel to the longitudinal axis of the base link 32 and a longitudinal axis of the coupler 60. This in turn means that an angle between a plane of the seat platform 14 and a plane of the base link 32 does not change during movement of the height adjustment mechanism 10 between the fully lowered and the fully raised positions.

As the seat platform 14 is raised and lowered, it will be appreciated that, due to the fixed position of the axis through the annular end region 80 of the back rest link 76 relative to the rear seat linkage 74, the back rest member 26 is also raised and lowered so that the back rest remains in a fixed position relative to the seat platform 14. The back rest coupling linkage accommodates this movement of the back rest member 26 relative to the base link 32.

As the height adjustment mechanism 10 moves from the fully lowered position to the fully raised position the back rest link 76 rotates about a rotational axis through the annular end region 80 of the back rest link 76. Accordingly, the upper back rest pivot 75 follows an arc. In the fully lowered position the upper back rest pivot 75 is disposed above the axis through the annular end region 80. In the fully raised position the upper backrest pivot 75 is disposed below the axis through the annular end region 80.

As shown most clearly in Figure 5, in the fully lowered position, the back rest member 26 and/or one of the bearing elements 28 is disposed at least partially in a recess defined by the concave edge 90 of the arched link 82. In the lowered position, while the upper back rest pivot 75 is disposed above the axis through the annular end region 80, the lower back rest pivot 73 remains in a position below the axis through the annular end region 80.

In the fully raised position, shown most clearly in Figures 10 and 11, the upper back rest pivot 75 and the lower back rest pivot 73 are both disposed below the axis 10 through the annular end region 80, such that the distance between the back rest member 26 and the base link 32 is increased.

It will be appreciated that the mechanism of the present invention permits a height of the seat platform 14 relative to a base of the chair to be altered in a continuous rather than discrete manner. The linkage mechanism may be used to set the height of the seat platform 14 to any position between the fully lowered position and the fully raised position described above. This allows a user to adapt dimensions of a chair to suit a particular user or patient to provide adequate support.

In embodiments of the mechanism including the back rest coupling linkage, this separate arrangement of the back rest coupling linkage and the connection to the seat platform means that, once the correct height of the seat platform 14 has been set as described above, the seat platform 14 and the back rest may be moved independently of each other using other adjustment mechanisms that may be provided on the chair. In particular, the back rest may be able to be reclined relative to the seat platform 14. In some embodiments a depth of the seat of the chair may be altered by moving the back rest forwards or rearwards relative to the rear edge of the seat platform. The back rest coupling linkage, however, ensures that the back rest remains at the current height relative to the seat platform.

Although in the above embodiment the first and second wishbone linkages are Y-shaped, in other embodiments the first and second wishbone linkages may be T-shaped. Importantly, in each wishbone linkage, the main arm extends in a direction generally transverse to a line extending between the base pivot and the coupling pivot. In some embodiments a longitudinal axis of the main arm may be perpendicular to the line extending between the base pivot and the coupling pivot.

Other modifications and variations not explicitly disclosed above may also be contemplated without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. A height adjustment mechanism for a chair arranged to raise and lower a seat platform of the chair relative to a base of the chair, the mechanism comprising: a four-bar linkage comprising: a fixed base link connectable to the base of the chair; a coupler; and first and second wishbone linkages pivotally connected between the base link and the coupler, a front seat linkage fixedly connected to said seat platform and pivotally connected at a first seat pivot to an arm of the first wishbone linkage extending from the four-bar linkage; and a rear seat linkage fixedly connected to said seat platform and pivotally connected at a second seat pivot to an arm of the second wishbone linkage extending from the four-bar linkage, wherein, during use, a distance between a seat pivot plane containing the first and second seat pivots and the base link changes to adjust a height of said seat platform of the chair, and the seat pivot plane remains parallel to an axis of the fixed base link such that, in use, an angle between a plane of the seat platform and the axis of the fixed base link does not change during height adjustment of the chair.
2. The height adjustment mechanism of Claim 1, in which each of the first and second wishbone linkages are generally Y-shaped.
3. The height adjustment mechanism of Claim 1 or Claim 2, in which the first wishbone linkage comprises a main arm pivotally connected to the front seat linkage, a connecting arm pivotally connected to the base link and a coupling arm pivotally connected to the coupler, and the second wishbone linkage comprises a main arm pivotally connected to the rear seat linkage, a connecting arm pivotally connected to the base link and a coupling arm pivotally connected to the coupler.
The height adjustment mechanism of Claim 3, in which an axis of the main arm is generally perpendicular to a line extending between the pivotal connection between the connecting arm and the base link and the pivotal connection between the coupling arm and the coupler.
5. The height adjustment mechanism of Claim 3 or Claim 4, in which the main arm is longer than each of the connecting arm and the coupling arm.
6. The height adjustment mechanism of any one of Claims 1 to 5, further comprising a back rest linkage arrangement connecting the base link to a back rest 10 member, the back rest member being part of or connectable to a back rest of said chair.
7. The height adjustment mechanism of Claim 6, in which the back rest linkage arrangement comprises a back rest link pivotally connected to the back rest member and an intermediate link pivotally connected at a first end to the back rest link and pivotally connected at a second end to the base link.
8. The height adjustment mechanism of Claim 7, in which the intermediate link has an arch shape.
9. The height adjustment mechanism of Claim 7 or Claim 8, in which the back rest link comprises an annular end providing the pivotal connection between the back rest link and the back rest member.
10. The height adjustment mechanism of any one of Claims 6 to 9, in which the position of the back rest member relative to the rear seat linkage does not change during use of the height adjustment mechanism to raise and lower said seat platform.
11. The height adjustment mechanism of any one of Claims 1 to 10, further comprising an actuator arranged to apply a force to a part of the four-bar linkage to change the distance between the seat pivot plane and the base link to adjust a height of said seat platform of the chair.
12. The height adjustment mechanism of any one of Claims 6 to 10, further comprising an actuator arranged to apply a force to a part of the back rest linkage 5 to increase and/or decrease a distance between the back rest member and the base link.
13. A chair comprising: a seat platform; a base member; and a height adjustment mechanism according to any one of Claims 1 to 12, the base link being fixedly connected to the base member and the front and rear seat linkages being fixedly connected to the seat platform.
14. The chair of Claim 13 including two height adjustment mechanisms, each being according to any one of Claims 1 to 12, the front and rear seat linkages of a first one of the height adjustment mechanisms being fixedly connected to a first side of the seat platform and the front and rear seat linkages of a second one of the height adjustment mechanisms being fixedly connected to a second side of the seat platform.
15. The chair of Claim 13 or Claim 14, in which the or each of the height adjustment mechanisms is according to any one of Claims 6 to 10, and the chair further comprises a back rest connected to the back rest member or both of the back 25 rest members.
16. A method of adjusting the height of a seat platform of a chair, the chair being according to Claim 13 or Claim 14, and the method comprising: applying a force to the four-bar linkage to rotate each of the first and second wishbone linkages in a first direction about their respective pivotal connections with the base link to increase a distance between the seat pivot plane and the base link; and/or -20 -applying a force to the four-bar linkage to rotate each of the first and second wishbone linkages in a second direction about their respective pivotal connections with the base link to decrease a distance between the seat pivot plane and the base link.
17. A method of adjusting the height of a seat platform of a chair, the chair being according to Claim 15, and the method comprising: applying a force to the back rest linkage arrangement in a first direction to increase a distance between the back rest member and the base link; and/or applying a force to the back rest linkage arrangement in a second direction to increase a distance between the back rest member and the base link.
18. The method of Claim 17, in which the or each height adjustment mechanism is according to Claim 7, and the method comprises: applying a force to the or each back rest link to rotate the back rest link in a first direction about the pivotal connection with the back rest member to increase a distance between the back rest member and the base link; and/or applying a force to the or each back rest link to rotate the back rest link in a second direction about the pivotal connection with the back rest member to increase 20 a distance between the back rest member and the base link.