WO2009127863A2

WO2009127863A2 - Tilt limit and locking mechanism for a chair

Info

Publication number: WO2009127863A2
Application number: PCT/GB2009/050363
Authority: WO
Inventors: Simon Roberts; Mark Jones
Original assignee: Simclar Seating Technologies Limited
Priority date: 2008-04-17
Filing date: 2009-04-14
Publication date: 2009-10-22
Also published as: WO2009127863A3; WO2009127863A4

Abstract

A chair has a back (2) and a seat part (1), which are pivoted at an axis (8), and to a fixed body (5) at a main pivot (7). An arm (16) is connected to the axis (8) by a link which is displaced by pivoting of the back (2), thereby moving the (arm16) reciprocally. The other end of the arm (16) is connected to a secondary pivot (15), which orbits the main pivot (7) on a further link. Main pivot (7) carries a latch (14) which is adapted to engage withstepped detents (21) on the upper edge of arm (16), while secondary pivot (15) carries a second latch (13) which is adapted to engage with stepped detents (18) formed in the base of body (5). The (arm16) is displaced by rotation of the link to pivot (8) so that latch (14) can engage with different ones of the detents (21), and at the same time displaceable latch (13) to engage with different ones of the fixed detents (18). Respective pivoted bell-crank levers (11) and (12) are also pivoted on axis (8), and have first respective ends which bear on respective latches (13 and 14), and second ends which bear a (cam10) carried on an axis which can be turned by a handle, to engage or disengage the latches. A tilt limiting device is provided by latch (13,14) engaging with stepped detents (119).

Description

TILT LIMIT AND LOCKING MECHANISM FOR A CHAIR

The invention relates to chairs, in particular to chairs of the kind which have an underseat assembly which adjustably connects a seat part and a back part of the chair to a base and allows the movement of the parts relative to one another to obtain a seating position. More particularly, the invention is concerned with a locking mechanism for ensuring that moving parts in the underseat assembly are locked in place, preventing further movement when a desired seating position is obtained.

Conventional underseat assemblies enable the inclination of the seat to the horizontal and/or the back to the vertical to be varied.

Such assemblies often comprise a back part pivotally linked to a seat part and a main body part. A compression spring force is often used to provide adjustable resistance to the inclination movement. Therefore, as the back part is inclined backwards, the back part pivots simultaneously on the pivotal links with both the seat part and the main body part, the pivotal link with the main body part being pushed upwardly, thereby pushing a front region of the seat upwardly and a back region of the seat downwardly. The obtained seating position can be locked in position using a latch or bolt pivotally connected to the main body part which engages with one of a number of teeth or slots in the back part.

Such arrangements can be bulky where a reasonable number of locking positions are to be provided. Where compact assemblies have been provided they tend to provide a lower number of locking positions, or the assemblies are very complex and difficult to manufacture.

An object of the present invention is to provide a locking mechanism which can be used in an underseat assembly, which allows the assembly to be compact, whilst avoiding the difficulties in providing a useful number of locking positions. A further object of the invention is to provide a locking assembly which can be used in a compact underseat assembly, whilst providing a mechanism which is easy and cost effective to manufacture, and a tilt limiting mechanism for comfort.

According to a first aspect of the invention, a chair mechanism comprises a locking mechanism and a tilt limiting mechanism.

According to a second aspect of the invention, there is provided a locking mechanism for use in an underseat assembly of a chair, comprising an engaging device for engagement with a receiving means in response to the alteration of the inclination of a back part of the chair to establish a discrete range of seating positions, characterised in that the engaging device comprises two engaging members for engagement with sets of detents of the receiving means respectively and wherein the locking mechanism further comprises a lock device providing an unlocked condition allowing movement of each of the engaging members within the respective series of detents and a locked condition preventing substantial movement of each of the engaging members within the respective series of detents.

With this arrangement the locking mechanism is relatively easy and cheap to manufacture whilst the provision of only two conditions of the locking mechanism make operation of the mechanism easy and not susceptible to damage by abuse in addition to still providing the chair with a useful number of secure discrete seating positions.

The engaging members preferably comprise two latches. One latch is preferably disposed so as to be engagable with a first set of detents, the other latch being disposed so as to be engagable with a second set of detents. The engagement of a latch with one of the detents in a set is preferably provided by the dropping of the respective latch in a downward direction.

The latches are therefore capable of pivotal movement in a generally vertical plane. Most preferably, the latches are pivotally movable in a generally vertical plane about a point. Most preferably, each of the latches is pivotally movable about a different pivot point within a predetermined range.

The movement of the latches is preferably linked. The link may be provided by the provision of a primary and a secondary pivot point, such that one secondary pivot point and therefore the respective secondary latch, is pivotally movable about the primary pivot point, thereby indirectly linking the movement of the primary and secondary latches. The secondary pivot point preferably orbits the primary pivot point in a generally transverse direction, thereby providing limited movement of the secondary latch in a generally transverse direction. This movement may be limited to, for example a movement of 23°.

To achieve this arrangement, the latches are preferably disposed one above the other with said primary pivot point being disposed generally above the secondary pivot point in the underseat assembly.

The sets of detents are preferably provided so as to resist disengagement of the respective latch. The sets of detents are therefore preferably provided as a series of steps. The sets may be arranged to span across the full range of transverse movement of the respective latch and provide a number of discrete steps therebetween. There may therefore, for example be four steps, one step corresponding to a forward most position of the respective latch, another corresponding to a rearward most position of the respective latch and two separate positions therebetween. One or both sets of steps may be provided by a main housing of the underseat assembly. Alternatively or additionally, one set of steps may be provided by a plate mounted within the main housing. Most preferably, a lower set of steps is provided as part of the moulding of the main housing and an upper set of steps is provided in said plate. The plate may be static or may be movable and perform an additional function in the underseat assembly. Where the plate is movable, the secondary pivot point may be provided therein, the plate being movable with the secondary pivot point. Alternatively, the plate may be unaffected by the movement of the secondary pivot point, which may move within a guide channel provided by said plate.

The lock is preferably a manual lock operable by a user. The lock also preferably comprises a retaining means to retain the engagement of the latches with the detents. The manual lock preferably provides an actuating means which bears down on the latches to prevent upward disengagement. Most preferably, the manual lock provides two actuating members, each one corresponding to a latch. The actuating members are preferably spring-loaded so as to be biased towards an upward direction of movement. The manual lock preferably provides a means to force the actuating members towards the respective latch and retain said members in a locked condition. The locked condition is provided by a cam which is rotatable between said locked condition and an unlocked condition. The manual lock preferably therefore provides a user adjustable handle to move the cam between the two conditions.

The back part is preferably attached to both the primary and secondary pivot points via a back member, such that when the back part is reclined, forward movement of the back member effects forward movement of said pivot points, the primary pivot point travelling upwardly and forwardly, the secondary pivot point travelling in a generally transverse direction, the latches travelling therewith to finish above one of said detents.

The underseat assembly preferably provides a moulded housing to contain the locking mechanism. Furthermore, such an underseat assembly may be used in a chair such as an office chair, so as to be mounted upon a pedestal and support a seat part. The seat part may be movable so as to recline with the reclining back part.

According to a third aspect of the invention there is provided a tilt limiting mechanism for a chair mechanism comprising a latch device which is displaceable in response to the alteration of the inclination of a chair back by pivoting, a limit device for setting a maximum range of pivoting of the device back, a series of detent means for engaging the latch device in any one of a plurality of positions, and means adjustable by the user to vary the path of the latch device when displaced by pivoting to engage with an appropriate one of the detent means.

The detent means may comprise a stepped series of ledges or notches.

The user adjustable means may comprise an arm which displaces the latch means against a spring bias, the arm itself being displaceable by a member responsive to manipulation by the user, such as a cam which is displaceable by rotation of a shaft by use of a hand wheel or crank handle. The cam may bear on the arm so as to press it against the latch means, in the sense of a spring bias, and to raise the arm against the spring bias to allow the latch means to raise.

The latch means may be raised to lengthen the stroke of the latch means, to for example, engage with a higher one of a series of stepped detents, and thereby increase the possible range of pivoting of the chair back towards the maximum range.

The latch means may advantageously be provided with a snib or nose, which can enter a latching means or notch and ensure that the latch is truly engaged, and does not for example rebound from contact with a step surface.

Each notch or detent may be in the form of a step, formed on a thickened part of a housing shell, and the edge of each step may be furnished with a strip of rubber or plastics material, which provides an inclined under surface which serves to guide the nose of the latch means into a gap between upper and lower steps.

The detents may be arranged so that the uppermost provides the maximum travel, and so that the latch will engage therewith in the uppermost position permitted by the user adjustable arm.

The cam which is rotatable by the user to adjust the arm may be provided with a plurality of facets or lands, each corresponding to a position of the latch adapted to engage one step of the detent array.

The chair mechanism according to the first aspect of the invention preferably comprises the locking mechanism according to the second aspect of the invention.

The chair mechanism according to the first aspect of the invention preferably comprises the tilt limiting mechanism according to the third aspect of the invention.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic side view of a chair having an underseat mechanism according to the invention with the back in an upright position;

Figure 2 is a diagrammatic side view of the chair with the seat and back in a fully reclined position;

Figure 3 is a diagrammatic view showing the locking mechanism in a first locked pre-positioning condition relating to an intermediate tilting position; Figure 4 is a diagrammatic view showing the locking mechanism of

Figure 3 in a second locked transitional condition; Figure 5 is a diagrammatic view showing the locking mechanism of

Figure 3 in a third locked condition; Figure 6 is a diagrammatic view showing the locking mechanism in a forward unlocked position; Figure 7 is a similar view showing the locking mechanism of Figure 6 in a forward locked position; Figure 8 is a similar view showing the locking mechanism of Figure 6 in a further locked position; Figure 9 is a diagrammatic view of a seat tilt mechanism in a first condition wherein the tilt mechanism is unlatched; and Figure 10 is a similar view to Figure 9, wherein the tilt mechanism is latched.

As shown in Figures 1 and 2, a chair has a seat part 1 and a back part 2 supported by a base part 3.

The seat part 1 and the back part 2 are supported and adjusted relative to one another by an underseat mechanism 4.

The underseat mechanism comprises a main body 5 and a back element 6 connected together via a main pivot point 7 which is a static pivot in a moulded housing 5 a of the main body.

The back element 6 is also connected to a lower pivot point 15 (Figures 3 to 8) which is attached to the main pivot 7 and is movable therearound in limited arc of approximately 23° in a generally transverse direction so as to allow the main body 5 and the back element 6 to be movable relative to one another. The back element 6 is further pivotally connected to the seat part 1 by a seat pivot point 8. The back element 6 and the back part 2 may be integrally formed or otherwise.

In a fully upright position, as shown in Figure 1 , the seat part 1 is substantially level and the back element 6 is slightly inclined from the main pivot point 7 to the seat pivot 8 so that the back part is substantially upright, a front part of the main body 5 supporting a front end of the seat part 1.

In a fully reclined position shown in Figure 2, the seat part 1 is reclined downwardly at a back end and the back element 6 is slightly inclined in reverse from the seat pivot 8 to the main pivot point 7 so that the back part is fully reclined, an upper face of the main body 5 supporting a portion of the seat part 1 from the front end. In this position, the main pivot 7 has moved in a forward direction towards the front end of the seat part 1.

A tilting mechanism within the underseat mechanism 4 allows many discrete reclined positions in between the two described extremes and locks each position.

The main body 5 of the invention as shown in Figures 3 to 8 comprises a user- operated locking handle (not shown) which operates the limited rotational movement of a cam 10 between a first locked position and a second unlocked position.

To effect the two positions, the cam 10 provides a part circular portion 10a and a projecting nib portion 10b.

The cam operates against a first arm 11 and a second arm 12 to alter the condition of the locking mechanism. The first arm 11 lies substantially on top of the second arm 12. The arms 11, 12 comprise a first short limb 11a, 12a and a second long limb 1 Ib, 12b, both of which extend from a static pivot point l ie, 12c. Both the long limbs l ib, 12b and the short limbs 11a, 12a are biased downwardly at an approximate mid-point along the limbs 11a, 12a, 1 Ib, 12b. The first limb 11 is longer in dimension than the second limb 12 and provides a greater reach.

Each of the arms 11, 12 are associated with a spring force (not shown) which act on the arms 11, 12 in an downward direction such that the natural movement of each of the arms 11, 12 is in an downward direction, (i.e. clockwise as shown in Figures 3 to 8).

The operation of the cam 10 against the arms 11, 12 alters the condition of the locking mechanism between a first locked condition where the arms are prevented from moving despite the downward spring force, and a second unlocked condition where the arms are able to move upwardly in the direction of the spring force.

Each of the arms 11,12 operate on one of two latches 13, 14, with an upper latch 14, being disposed generally above a lower latch 13 in spaced relationship.

The lower latch 13 is pivotally connected to the lower pivot point 15 which is provided in a push plate 16. The latch 13 is able to pivot around the pivot point 15 upwardly and downwardly in a limited arc of movement. The push plate 16 and the latch 13 are moveable in a generally transverse direction with the lower pivot 15 around the main pivot 7.

The lower latch 13 provides a corner 17 for engagement with one of a first series of upwardly directed steps 18 steps. In this embodiment, the main body 5 comprises the first series of steps 18 on a lower inwardly directed surface 19 of the housing 5 a. The upper latch 14 is pivotally connected to the main pivot point 7. The upper latch 14 is able to pivot around the main pivot point 7 upwardly and downwardly in a limited arc of movement.

The upper latch 14 also provides a corner 20 for engagement with one of a second series of upwardly directed steps 21 (not shown). In this embodiment, the push plate 16 comprises the second series of steps 21 on an upper edge 22.

The lower latch 13 provides a slightly concave engaging face 13a on an upper edge of the lower latch for engagement with an engaging end 1 Id of the arm 11.

In use, the locking mechanism has a number of conditions.

Figures 3 to 5 show the locking mechanism in a series of conditions relating to an intermediate tilting position.

As is shown in Figure 3, when the handle is in a first position, the cam 10 is also in a first unlocked condition. In this condition, the seat part 1 and the back part 2 of the chair are movable by a person adjusting the pressure on each of the parts 1,2.

Where pressure is applied to the back part 2 of the chair, the back part 2 reclines. This reclining movement causes the back element 6 to move in a forward and upward direction, pivoting on the main pivot 7 and the lower pivot 15. The main body is pushed upwardly to push the front end of the seat part 1 upwardly and the lower pivot 15 is pushed forwardly within the main body 5 (seen in Figure 4). This movement causes the latch 13 to move forwardly towards the first series of steps 18.

When the required seating position is obtained the reclined position can be locked, by turning the handle in an anticlockwise direction to adjust the cam 10 to a locked position. The part circular portion 10a of the cam 10 forces both of the short limbs 11a, 12a to move upwardly causing arms 11, 12 to pivot at the points l ie, 12c so that the engaging end Hd, 12d of each arm 11, 12 moves, on turning anticlockwise from the circular part of the cam to the flat part, the arm is allowed to rotate clockwise with the spring pressure, thus forcing the ends Hd 12d down onto the latches. The engaging ends Hd, 12d push the respective latch 13, 14 downwardly to engage with the appropriate step of the respective series of steps. The latches 13, 14 are held in position until the cam 10 is moved in a clockwise direction to an unlocked position, releasing the arms 11, 12 against spring force to lift away from the latches 13, 14, thereby releasing them and allowing further movement of the seating position.

As shown in Figure 4, where the corner 17, 20 of the latches 13,14 does not initially engage fully with the respective step, when the pressure on the back part 2 is released slightly, this will cause the respective latch 13, 14 to drop to the next step to engage fully therewith (Figure 5). This adjusting is facilitated by the curved configuration of the engaging face 13a, 14a of each latch 13,14 which allows small movements of the engaging end 1 Id, 12d of the respective arm 11, 12 thereon.

Figures 6 to 8 show the movement of the components corresponding to an upright seating position is desired.

In Figure 6, the cam 10 is unlocked condition and the arms 11, 12 are essentially at rest, the latches 13,14 being out of engagement with the respective steps.

In Figure 7 the cam 10 has been locked as described above and the latches 13, 14 have been forced downwardly by spring force to engage with a lowermost step by the arms 11, 12.

Figure 8 shows the cam 10, once again in an unlocked condition, the arms 11, 12 having been lifted against the biasing spring into a resting position. The upper latch 14 has disengaged with the upper series of steps, the lower latch 13 still being engaged with the lowermost step of the series 18. As the latch 13 is no longer being held in place by the arm 11, the next movement of the seating position will allow the latch 13 to disengage with the step. The latches 13, 14 will only both be disengaged when the user applies slight pressure to the seat mechanism. This is a necessary safety feature to prevent release of the mechanism when the chair is unoccupied or the user is leaning back. This is due to friction and pressure at the interface of the latch and the step, and prevents sudden and possibly dangerous movement backwards. Rearward force allows the latch 14 to release but causes the bottom latch 13 to stay locked. Forward force allows latch 13 to release, but keeps latch 14 engaged. A momentary reversal of the force however enables the second latch to be released ensuring that full release can occur only due to deliberate manipulation.

With the underseat mechanism 4 described, the range of discrete seating positions is dictated by the number of steps provided for engagement and the number and position of the steps relative to one another can be adjusted to provide fewer or more discrete seating positions.

It should, however, be appreciated that the arrangement of the components may be such that the first series of steps 18 may be provided on a lower edge of a stationary plate for the latch 13 to engage with. Furthermore, the arms 11, 12 may not be spring loaded, but may be allowed to fall, by gravity towards the latches 13, 14 to hold them in place and are otherwise held away from the latches 13, 14 in an unlocked condition.

The apparatus of Figures 9 and 10 has a moulded shell 110 which contains and shields the tilt mechanism and other components of the chair. The shell 110 provides a series of moulded steps 119 on the inner face, which provide detents for latching of the tilt mechanism. A seat back is pivoted about a pivot shaft 112 through an intermediate element 111 which is restricted in its rotation to an arc of for example 23°. This is defined by movement of a shaft 116 in a slot 117 which is provided in a plate 118 which is fixed in position in relation to the shell 110. Figure 9 shows the position when the seat back is in its most upright position. When the seat back is released a lever (not shown) which is connected to the intermediate element 111 and pivoted on the shaft 112 pushes the shaft 116 to the left, towards the Figure 10 position, up to the limit defined by the length of slot 117. This motion also pushes a latch plate 114 to the left.

The upward pivoting of the latch plate 114 on the shaft 116 is limited by a stop (not shown), and in the uppermost position, which is shown in the drawings, the latch plate 114 will engage the uppermost step of the stepped detents 119 formed in the shell 10. The latch plate 114 can however be lowered by pressure of the end of an actuator arm 124 on an abutment 125 which is integral with the latch plate 114. Progressive lowering of the latch plate 114 means that the lower left hand corner of the latch plate will engage with a progressively lower one of the stepped detents 119. As the plate 114 is moved leftwards from the Figure 9 position, the lower left hand corner of the latch plate will also encounter the lower detents after a reduced travel, and thus limit the travel of the shaft 116 in slot 117, and thus the range of movement in the reclining direction of the chair back.

An important feature of the latch plate 114 is the provision at the lower left hand corner (as shown in the drawing) of a snib or nose 115. This engages with and enters a gap between an upper plastics or rubber guide member 130 and a lower rubber or plastics guide member 131, as shown in Figure 10, to ensure that the latch member is engaged. Which step the latch engages with depends upon the degree to which the arm 124 presses down on the abutment 125.

The position of the arm 124 is controlled by a cam 126 which is carried on a shaft which is arranged to be turned by a manual control (not shown) such as a hand wheel, or crank lever. In the position shown in the drawings, a nose 126a of the cam 126 pushes a tail end 124a of arm 124 as far to the right as it will go. The arm 124, pivoted on shaft 123, is held by the cam in its most anticlockwise position which raises the end of arm 124 which engages the abutment 125 of the latch plate 114 to its highest position, so that the latch plate will engage the uppermost and furthest left of the steps 119.

If the cam 116 is turned in an anticlockwise sense, the tail 124a of arm 124 will engage a succession of cam faces, each of which will allow the arm 124 to rotate slightly further in a clockwise direction, so that at each stage the latch plate 114 is pressed one stage further down, to lock with a lower step 119, and have a reduced possible travel in response to movement of the chair back, thus further restricting the scope for movement of the chair back as the cam 126 is turned further, to a minimum range when the latch engages with the bottommost step.

The latch plate 114 is biased upwardly by spring 113 to resist the pressure exerted by the end of lever 124 so that it will return to the higher position as the end is lifted. The arm 124 on the other hand is biased by a spring 127 to rotate in a clockwise sense about the shaft 123, so that arm 124 is biased to push the latch plate 114 downwardly.

The shaft 116 mounting the latch plate 114 is connected by an arm 120 at 122 to a further lever 121 which is also pivoted on shaft 123, and a spring 128 connects the lever 121 to a fixed abutment, and is connected to the lever by a connection 129 which is adjustable through a small range for varying the mechanical advantage of the lever. The operation of this feature is not connected with the present invention. The arm 120 displaces the lever 121 when the latch plate 14 is moved to the left.

Whilst the control lever may be actuated for release or adjustment whilst pressure is applied to the chair back in the reclined direction, the latch 114 will not release from the respective step, due to transferred pressure through the linkage, and friction. This operates to prevent sudden and possibly dangerous unexpected release of the latch.

The latch 114 is always activated indirectly. One spring 113 is biased to enable the latches to move out of engagement, whilst the spring 127 acts to load the latch 114 downwardly into engagement.

The apparatus according to the invention enables the range of adjustment of the position of a chair back to be varied under the control of the user, within a maximum range which is preset by the length of the slot 117 and the location of the uppermost step 119 for engagement with the latching device.

Variations may be made to the apparatus within the scope of the invention, for example whilst the nose 115 is desirable the corner of the lock may simply be configured as a right angle or other suitable shape to engage in the steps 119, which may be configured in turn as simple steps or notches.

It will be appreciated that in an alternative embodiment of a chair mechanism, the tilt limiting mechanism can be combined with the locking mechanism by replacing the cam 126 of the tilt limiting mechanism 4 with the cam 10 of the locking mechanism and adding arms 12 and 14 of the locking mechanism. It will of course be understood that the invention is not intended to be restricted to the details of the above embodiment which is described by way of example only.

Claims

1. A chair mechanism comprising a locking mechanism and a tilt limiting mechanism.

2. A locking mechanism for use in an underseat assembly of a chair comprising an engaging device for engagement with a receiving means in response to the alteration of the inclination of a back part of the chair to establish a discrete range of seating positions, characterised in that the engaging device comprises two engaging members for engagement with sets of detents of the retrieving means respectively, and wherein the locking mechanism further comprises a lock device providing an unlocked condition allowing movement of each of the engaging members with the respective series of detents and a locked condition preventing substantial movement of each of the engaging members within the respective series of detents.

3. A mechanism according to claim 2, wherein the engaging members comprise two latches, one of which latches being disposed so as to be engageable with a first set of detents and the other latch being disposed so as to be engageable with a second set of detents.

4. A mechanism according to claim 3, wherein each latch is adapted to drop in a downward direction to engage with one of the respective detents.

5. A mechanism according to claim 4, wherein the latches are each capable of pivotal movement in a generally vertical plane about a respective axis within a predetermined range.

6. A mechanism according to claim 5, wherein the latches are each contacted by an end of an arm of a respective pivoted lever, each lever having other arm which bears on an actuating cam; the pivoted levers sharing a common pivot axis on the seat pivot.

7. A mechanism according to claim 6, wherein one of the latches is pivoted about an upper axis, and the other is pivoted about a lower axis, and the latch having the lower pivot is adapted to engage with detents provided on the base of a main body, and the upper pivoted latch being adapted to engage with detents provided in a link member which is connected by a crank to the seat pivot.

8. A mechanism according to claim 7, wherein the detents are provided as respective series of steps, arranged to extend across the full range of pivotal movement of the respective latch and to provide a series of discrete intermediate steps.

9. A mechanism according to claim 8, wherein the detents in the base of the main body comprises a lower set of steps provided as part of a moulding of a main housing.

10. A mechanism according to claim 7, wherein the pivot axis for the lower latch is provided on the link member.

11. A mechanism according to any one of claims 2 to 10 preceding claim wherein the lock device comprises a manual lock which is operable by the user, and comprises a retaining means to maintain the engagement of the latches with the detents.

12. A mechanism according to claim 11, wherein the manual lock comprises an actuating means which bears down on the latches to prevent upward disengagement.

13. A mechanism according to claim 12, wherein two actuating members are provided one corresponding to each latch, and are spring-loaded so as to be biased to move upwardly.

14. A mechanism according to claim 13, wherein the manual lock means include a cam which is rotatable by a handle between a locked condition and an unlocked condition in which the cam acts to retain the latches in the detents.

15. A mechanism according to any one of claims 2 to 14, wherein the back part is attached to both of the pivot point via a back member, so that when the back part is reclined, forward movement of the back member effects forward movement of the pivot points, the primary pivot point moving upwardly and forwardly and the secondary pivot moving in a generally transverse direction, the latches travelling therewith to arrive above respective ones of the detents.

16. A mechanism according to any preceding claim wherein the underseat assembly provides a moulded housing to contain the locking mechanism, and is mounted upon a pedestal and supports a seat part.

17. A tilt limiting mechanism for a chair mechanism comprising a latch device which is displaceable in response to alteration of the inclination of a chair back by pivoting, a limit device for setting the maximum range of pivoting of the chair back, a series of detent means for engaging the latch device in any one of a plurality of positions, and means adjustable by the user to vary the path of the latch device when displaced by pivoting to engage with an appropriate one of the detent means.

18. A mechanism according to claim 17, wherein the detent means comprises a stepped series of ledges or notches.

19. A mechanism according to claim 17 or 18, wherein the user adjustable means comprises an arm which displaces the latch means against a spring bias, the arm itself being displaceable by a member responsive to manipulation by the user.

20. A mechanism according to claim 19, wherein the said member comprises a cam which is displaceable by rotation of a shaft by use of a handwheel or crank handle.

21. A mechanism according to claim 20, wherein the cam bears on the arm so as to press it against the latch means under a spring bias, and to raise the arm against the spring bias to allow the latch means to raise.

22. A mechanism according to claim 21 wherein the latch means can be raised to lengthen the stroke of the latch means, the engage with a higher one of a series of stepped detents and thereby increase the possible range of pivoting of the chair back towards the maximum range.

23. A mechanism according to claim 22, wherein the latch means is provided with a snib or nose, which can enter a latching means or notch and ensure that the latch is truly engaged.

24. A mechanism according to claim 23, wherein each notch or detent is in the form of a step, formed on a thickened part of a housing shell.

25. A mechanism according to claim 24, wherein the edge of each step is furnished with a strip of rubber or plastics material, which provides an inclined under surface which serves to guide the nose of the latch means into a gap between upper and lower steps.

26. A mechanism according to any one of claims 17 to 25, wherein the detents are arranged so that the uppermost detent provides the maximum travel, and so that the latches will engage therewith in the uppermost position permitted by the user adjustable arm.

27. A mechanism according to claim 20, wherein the cam which is rotatable by the user to adjust the arm is provided with a plurality of facets or lands, each corresponding to a position of the latch adapted to engage one step of the detent series.

28. A chair mechanism according to claim 1, comprising the locking mechanism according to any one of claims 2 to 16 and/or the tilt limiting mechanism according to any one of claims 17 to 27.

29. A chair comprising a chair mechanism according to claim 28.