Seat Tilting Mechanism

Abstract

A seat tilting mechanism comprising a main body, a seat support, a backrest support and an articulation mechanism comprising a lever, a first portion of which defines along with a first arm, the seat support and the main body a first quadrilateral hinge, and a second portion of which defines alone with a second arm, the backrest support and the main body a second quadrilateral hinge. Interior corner angles and lengths of each side of the first and second quadrilateral hinges are such that a predetermined angular displacement ratio of the backrest support in relation to the seat support is provided. An extension resistance device is mounted between the main body and the first portion to provide resistance to rotation of the lever. A first end of the extension resistance device is rotationally mounted to the lever at a first mounting point, which is located between the midpoint and upper point, and is angularly displaced from a line extending between the midpoint and the upper point.

Claims

1. A seat tilting mechanism comprising a main body, a seat support, a backrest support and an articulation mechanism, in which said articulation mechanism comprises a lever rotationally mounted at a midpoint thereof to said main body, and comprising a first portion rotationally mounted at an upper point of said lever to said seat support, and a second portion rotationally mounted at a lower point of said lever to said backrest support, in which said articulation mechanism comprises a first arm, a first end of which is rotationally mounted to said main body and a second end of which is rotationally mounted to said seat support, said first arm defining with said first portion, said seat support and said main body a first quadrilateral hinge, in which said articulation mechanism comprises a second arm, a first end of which is rotationally mounted to said main body and a second end of which is rotationally mounted to said backrest support, said second arm defining with said second portion, said backrest support and said main body a second quadrilateral hinge, in which interior corner angles and lengths of each side of said first quadrilateral hinge, and interior corner angles and lengths of each side of said second quadrilateral hinge are such that a predetermined angular displacement ratio of said backrest support in relation to said seat support is provided, in which an extension resistance device is mounted between said main body and said first portion to provide resistance to rotation of said lever, in which a first end of said extension resistance device is rotationally mounted to said lever at a first mounting point located between said midpoint and said upper point, and in which said first mounting point is angularly displaced from a line extending between said midpoint and said upper point.

2. A seat tilting mechanism as claimed in claim 1 in which said first quadrilateral hinge is movable between a rest position in which said seat support is substantially horizontal, and a fully tilted position in which said seat support is angularly displaced from horizontal, in which a second end of said extension resistance device is rotationally mounted to said main body at a second mounting point, in which said first mounting point is located such that a rotation angle between an axis of said extension resistance device and a line extending between said second mounting point and said upper point decreases as the first quadrilateral hinge moves from said rest position towards said fully tilted position.

3. A seat tilting mechanism as claimed in claim 2 in which said first mounting point is located such that said rotation angle is zero prior to said first quadrilateral hinge achieving said fully tilted position.

4. A seat tilting mechanism as claimed in claim 3 in which said interior corner angles and said lengths of each side of said first quadrilateral hinge, and said interior corner angles and said lengths of each side of said second quadrilateral hinge are such that said predetermined angular displacement ratio of said backrest support in relation to said seat support is greater than one to one.

5. A seat tilting mechanism as claimed in claim 4 in which said interior corner angles and said lengths of each side of said first quadrilateral hinge, and said interior corner angles and said lengths of each side of said second quadrilateral hinge are such that said predetermined angular displacement ratio of said backrest support in relation to said seat support is less than two to one.

6. A seat tilting mechanism as claimed in claim 5 in which said interior corner angles and said lengths of each side of said first quadrilateral hinge, and said interior corner angles and said lengths of each side of said second quadrilateral hinge are such that said predetermined angular displacement ratio of said backrest support in relation to said seat support is substantially 1.9 to one.

7. A seat tilting mechanism as claimed in claim 2 in which said first portion is substantially L shaped, with said first mounting point located at a corner of said L shape.

8. A seat tilting mechanism as claimed in claim 1 in which said extension resistance device is an extension coil spring.

9. A seat tilting mechanism substantially as described herein and as shown the accompanying drawings.

Description

[0024] An embodiment of the present invention will now be described by example, and with reference to the accompanying drawings in which:

[0025] FIG. 1 is a side view of a seat tilting mechanism according to the present invention in a rest position; and,

[0026] FIG. 2 is a side view of the seat tilting mechanism as shown in FIG. 1 in a fully tilted position.

[0027] Referring to FIG. 1, a seat tilting mechanism 1 comprises a main body 2, a seat support 3, a backrest support 4 and an articulation mechanism. The articulation mechanism comprises a lever 6 rotationally mounted at a midpoint 6 by annular hinge 7 to the main body 2, and comprising a first portion 8 rotationally mounted at an upper point 9 by annular hinge 10 to the seat support 3, and a second portion 11 rotationally mounted at a lower point 12 by annular hinge 13 to the backrest support 4.

[0028] The articulation mechanism further comprises a first arm 14, a first end 15 of which is rotationally mounted to the main body 2 by annular hinge 16, and a second end 17 of which is rotationally mounted to said seat support 3 by annular hinge 18. The first arm 14 defines with the first portion 8, the seat support 3 and the main body 2 a first quadrilateral hinge, indicated by hashed box 19. The articulation mechanism comprises a second arm 20, a first end 21 of which is rotationally mounted to the main body 2 by annular hinge 22, and a second end 23 of which is rotationally mounted to the backrest support 4 by annular hinge 24. The second arm 20 defines with the second portion 11, the backrest support 4 and the main body 2 a second quadrilateral hinge, indicated by hashed box 25.

[0029] As described further below, interior corner angles and lengths of each side of the first quadrilateral hinge 19, and interior corner angles and lengths of each side of the second quadrilateral hinge 25 are such that a predetermined angular displacement ratio of the backrest support 4 in relation to the seat support 3 is provided.

[0030] An extension resistance device, in the form of extension coil spring 26, is mounted between the main body 2 and the first portion 8 to provide resistance to rotation of the lever 5. A first end 27 of coil spring 26 is rotationally mounted to the lever 5 at a first mounting point 28 by annular hinge 29, which first mounting point 28 is located between the midpoint 6 and the upper point 9. As is clear from FIG. 1, the first mounting point 28 is angularly displaced from a line (the rightmost side of hashed box 19) extending between the midpoint 6 and the upper point 9.

[0031] The seat tilting mechanism 1 is adapted for use in an office chair, and provides a user-adjustable tilting movement thereto by virtue of being able to move between a rest position as shown in FIG. 1, in which the seat support 3 and the backrest support 4 are substantially horizontal, and a fully tilted position as shown in FIG. 2 in which the seat support 3 and the backrest support 4 are angularly displaced from horizontal. The main body 2 is adapted to rest atop an upright stanchion (not shown), the seat support 3 is adapted to support a seat (not shown) arranged generally horizontally above it, and the backrest support 4 is adapted to support a backrest (not shown) arranged generally vertically above it. The various components of the seat tilting mechanism 1 are constructed from metal. The various annular hinges are of a known construction, and allow the various components to freely rotate in relation to one another in either direction.

[0032] A second end 30 of the coil spring 26 is rotationally mounted to the main body 2 at a second mounting point 31 by annular hinge 32. In the rest position shown in FIG. 1 an axis 33 of the coil spring 26 is angularly displaced from a line 34 extending between the second mounting point 31 and the upper point 9, which is effectively the initial direction of extension which the coil spring 26 acts against. However, as will be appreciated from the Figures, the first mounting point 28 is located such that the rotation angle between the axis 33 and the line 34 decreases as the first quadrilateral hinge 19 moves from the rest position towards the fully tilted position. This is because the mounting point 28 has a different planetary movement path about the midpoint 6 to the upper point 9. The result achieved is that the increasing resistance provided by the coil spring 26 as it extends has an increasing impact on the first quadrilateral hinge 19 as it moves from the rest position as shown in FIG. 1 to the fully tilted position shown in FIG. 2. This is because the axis 33 of the coil spring 26 is brought closer and closer to the actual direction of extension. As such the resistance provided by the coil spring 6 increases as the first quadrilateral hinge 19 moves towards the fully tilted position to a greater extent that it would if axis 33 of the coil spring 26 were always aligned in the direction of extension.

[0033] This is relevant in the context of seat tilting mechanism 1 because the force which moves it is provided by the user themselves. If they place all their weight on the seat support 3, the seat tilting mechanism 1 will assume the rest position shown in FIG. 1. This is because the upper point 9 is forward of the midpoint 6, and therefore weight applied to the upper point 9 serves to force it in a clockwise direction about the midpoint 6, thereby closing the first quadrilateral hinge 19. However, once the user starts to lean back and places some of their weight on the backrest support 4, a rotational force is applied to the lower point 12 to move it in an anti-clockwise direction about the midpoint 6. This force acts to open the first quadrilateral hinge 19 against the combined tensile force of the coil spring 26 and the rest of the user's weight bearing down on the upper point 9. The rotational force applied to the lower point 12 must reach a break out point at which it exceeds the combined tensile force of the coil spring 26 and the rest of the user's weight bearing down on the upper point 9, before the first quadrilateral hinge 19 will start to open. It will be appreciated that this will vary depending on the weight of the user.

[0034] What is relevant is that as the first quadrilateral hinge 19 opens up and moves from the rest position shown in FIG. 1 towards the fully tilted position shown in FIG. 2, the rotational force applied to the lower point 12 exponentially increases because the user is being rotated backwards, so their weight gradually shifts from acting on the seat support 3 to acting on the backrest support 4. The coil spring 26 compensates for this because the force required to extend it increases with the length of extension. In addition, the user can obviously compensate for this by adjusting their body position as the seat thing mechanism 1 moves, for example by leaning forward slightly when the seat tilting mechanism 1 reaches a desired angle. However, what also applies a further degree of compensation is the above described arrangement of the coil spring 26. As the axis 33 of the coil spring 26 moves closer to the line 34 it has a greater effect. As such the resistance provided by the coil spring 26 increases with an increasing angle of tilt more than in any prior art example, which makes for a more comfortable seating experience.

[0035] As will be appreciated from FIG. 2, the first mounting point 28 is located such that the axis 33 of the coil spring 26 aligns with the line 34 prior to the first quadrilateral hinge 19 achieving the fully tilted position. As such, in FIG. 2 the axis 33 is now angularly displaced from opposite side of the line 34. What this means is that the above described increase in resistance provided as the axis 33 of the coil spring 26 approaches and then meets the line 34 is beneficially located in a region of tile more likely to be used by a user, which is prior to the fully tilted position. This makes this increase in resistance more useful.

[0036] The first quadrilateral hinge 19 comprises four corners, namely midpoint 6, upper point 9, a centre 35 of the annular hinge 16, and a centre 36 of annular hinge 18, and it moves by virtue of the annular hinges 7, 10, 16 and 18 at those corners. The lengths of each side of the first quadrilateral hinge 19 are clear from the Figures, and the interior corner angles of the first quadrilateral hinge 19 when the seat tilting mechanism 1 is in the rest position are shown in FIG. 1. These interior corner angles change as the first quadrilateral hinge 19 moves, and FIG. 2 shows them when the seat tilting mechanism 1 is in the fully tilted position.

[0037] The important characteristics of the first quadrilateral hinge 19 in the context of the present invention are firstly the greater distance between centres 35 and 36, than between midpoint 6 and upper point 9. This means that as the first quadrilateral hinge 19 moves, a front 37 of the seat support 3 rises in relation to a rear 38 thereof, and hence the seat support 3 rotates. Secondly, throughout the entire movement range of the first quadrilateral hinge 1 the centre 36 is forward of the centre 35, which means that as the first quadrilateral hinge 19 moves from the rest position shown in FIG. 1 to the fully tilted position shown in FIG. 2, the front 37 of the seat support continuously rises as the centre 36 follows its planetary path about the centre 35. Thirdly, the planetary movement path the upper point 9 follows about the midpoint as the first quadrilateral hinge 19 moves from the rest position shown in FIG. 1 to the fully tilted position shown in FIG. 2 sees it initially rise, but then fall, as it passes over centre. This means that the rear 38 of the seat support 3 initially rises slightly, but then it fails. These different movements of the centre 36 and the upper point 9, mean that the rate at which the seat support 3 rotates increases the further the first quadrilateral hinge 19 moves from the rest position to the fully tilted position. This makes for a more comfortable seating experience for the user because the angle of tilt can be more precisely controlled at first.

[0038] It will also be appreciated that the first quadrilateral hinge 1 moves from the rest position to the fully tilted position the seat support 3 moves rearwardly. This ensures that the seat and backrest parts (not shown) supported by the seat tilting mechanism 1 do not move laterally apart from one another as the user tilts the backrest back. Once again, this makes for a more comfortable seating experience.

[0039] The second quadrilateral hinge 25 comprises four corners, namely midpoint 6, lower point 12, a centre 39 of the annular hinge 22, and a centre 40 of the annular hinge 24, and it moves by virtue of the annular hinges 7, 13, 22 and 24 at those corners. The lengths of each side of the second quadrilateral hinge 25 are clear from the Figures, and the interior corner angles of the second quadrilateral hinge 25 when the seat tilting mechanism 1 is in the rest position are shown in FIG. 1. These interior corner angles change as the second quadrilateral hinge 25 moves, and FIG. 2 shows them when the seat tilting mechanism 1 is in the fully tilted position.

[0040] The second quadrilateral hinge 25 shares similar characteristics to the first quadrilateral hinge 19. It is inverted relative to the first quadrilateral hinge 19, but the spatial relationship between centres 40 and 39 is like that between centres 36 and 35, in that centre 40 is always rearward of centre 39, so it continuously falls during movement of the second quadrilateral hinge 25 from the rest position to the fully tilted position. Further, the spatial relationship between the midpoint 6 and the lower point 12 is like that between the midpoint 6 and the upper point 9, in that the lower point 12 initially falls as the second quadrilateral hinge 25 begins its movement from the rest position to the fully tilted position, but it then rises as its planetary movement path about the midpoint 6 passes over centre. As such, a front 41 of the backrest support 4 initially fails slightly, but then it rises. Once again, these different movements of the centre 40 and the lower point 12, mean that the rate at which the backrest support 4 rotates increases the further the second quadrilateral hinge 25 moves from the rest position to the fully tilted position. This works in conjunction with the similar rotation rate characteristic of the seat support 3 to make for a more comfortable seating experience for the user.

[0041] It will also be appreciated that as the second quadrilateral hinge 25 moves from the rest position to the fully tilted position the backrest support 4 moves forward. This also serves to ensure that the seat and backrest parts (not shown) supported by the seat tilting mechanism 1 do not move laterally apart from one another as the user tilts the backrest back.

[0042] However, the most important characteristic of the second quadrilateral hinge 25 in the context of the present invention is that it is configured to rotate the backrest support 4 more than the first quadrilateral hinge 13 is configured to rotate the seat support 3 The angular displacement ratio between the backrest support 4 and the seat support 3 is 1.9 to one. This is achieved because centre 39 is closer to midpoint 6 than it is to centre 40, which results in a greater angular change in the shape of the second quadrilateral hinge 25 than is achieved by the first quadrilateral hinge 25, where centre 35 is closer to centre 36 than it is to midpoint 6.

[0043] As is clear from the Figures, the first portion 8 of the lever 5 is L shaped, with the first mounting point 28 located at the corner of the L shape. This is a compact and efficient arrangement.

[0044] The seat tilting mechanism 1 operates as follows. When no user s seated on the office chair incorporating the seat tilting mechanism 1 it adopts the rest position shown in FIG. 1. This is due to the force of the coil spring 26 acting to rotate the first portion 8 of the lever 5 about the midpoint 6. The coil spring 28 comprises a sufficient tensile force to lift the backrest (not shown) back up into its generally vertical position by levering the lower point 12 clockwise about the midpoint 6.

[0045] When a user sits on the seat (not shown) mounted to the seat support 3, their weight acts to maintain the seat tilting mechanism 1 in the rest position, because the upper point 9 is forward of the midpoint 6, and therefore weight applied to the upper point 9 serves to force it in a clockwise direction about the midpoint 6, thereby closing the first quadrilateral hinge 19.

[0046] The user can lean back against the backrest (not shown) mounted to the backrest support 4 without the seat tilting mechanism 1 moving from the rest position as shown in FIG. 1, provided the force applied by the user is less than a break out point at which it exceeds the combined forces of the coil spring 26 and the rest of the user's weight bearing down on the upper point 9.

[0047] To force the office chair into a more relaxed seating position the user simply leans back against the backrest. Once the weight applied to the backrest exceeds the break out point, the first and second quadrilateral hinges 19 and 25 will start to move from the rest position to the fully tilted position. The rate at which this movement occurs will depend on the amount of force applied by the user, and they will be able to increase or decrease the rate by adjusting their body position accordingly.

[0048] As the angular displacement ratio between the seat support 3 and the backrest support 4 is 1.9 to one, the backrest will rotate more than the seat, creating a more relaxed relationship between backrest and seat the more the seat tilting mechanism 1 moves towards the fully tilted position.

[0049] Further, due to the relative positions of the upper point 9 and the lower point 12 about the midpoint 6, and in particular the fact that they initially travel upwards and downwards respectively, before travelling downwards and upwards respectively, the rate at which the seat and backrest rotate increases the further the seat tilting mechanism 1 moves towards the fully tilted position. This makes for a more comfortable seating experience.

[0050] In addition, due to the location of the first mounting point 28, the resistance to tilting increases the further the seat tilting mechanism 1 moves towards the fully tilted position, because the axis 33 of the coil spring 26 moves closer to the direction of extension. This compensates for the exponential increase in weight a user places on the backrest the further they tilt it back. Furthermore, this beneficial increase in resistance is applied in a middle region of tilt most used, which is prior to the fully tilted position.

[0051] If the user leans forward, and transfers their weight back again from the backrest to the seat, the seat tilting mechanism 1 will move back towards the rest position as shown in FIG. 1. If the user gets up from the office chair, the seat tilting mechanism 1 will return to the rest position as described above.

[0052] The seat tilting mechanism 1 shown in the figures can be used in isolation with an office chair or the like, but two can also be provided, one on either side of an office chair, to provide greater stability.

[0053] The present invention can be altered without departing from the scope of claim 1. For example in alternative embodiments (not shown) the extension resistance device is a pneumatic ram, a screw or a length of resilient material.

[0054] In further alternative embodiments (not shown) the interior corner angles and lengths of sides of the first and second quadrilateral hinges are configured to provide angular displacement ratios of the backrest support in relation to the seat support of which are different to 1.9 to one, for example 1.5 to one, two to one, three to one, four to one and five to one.

[0055] In further alternative embodiments (not shown) the seat tilting mechanism is adapted to be used with other kinds of chair, including an armchair, a garden chair and so on.

[0056] Thus, the present invention provides a seat tilting mechanism with a number of advantages over the prior art. Firstly, a more healthy angular displacement ratio of the backrest support in relation to the seat support of 1.9 to one is provided without any significant increase in the size of the mechanism. In particular, the coil spring 26 is actually shorter than in known examples. Secondly, a more user friendly and intuitive experience is provided by virtue of the increased resistance to tilt the further the seat tilting mechanism 1 is moved, and the increase in the rate of rotation the further the seat tilting mechanism 1 is moved. In combination this means that a seat to which the seat tilting mechanism 1 is applied can be moved from the rest position with less force and more precision initially. These advantageous features are provided by virtue of the location of the first mounting point 28 in relation to the upper point 9, and by the location of the upper point 9 and lower point 12 about the midpoint 6, which are all novel. Finally, the relocation of the first mounting point 28 to a dedicated site reduces the lateral loadings applied to the upper point 9 in use, which increases its operational life span.