Arm assembly for a chair

Abstract: An arm assembly (24) is provided for a chair (12). The chair (12) has a forward direction and a rearward direction. The arm assembly (24) comprises an armrest (26) and a support structure (28). A mounting device movably mounts the armrest to the support structure. The mounting device constrains the movement of the armrest (26) relative to the support structure to movement in a substantially horizontal plane having two degrees of freedom defined by first and second transversely arranged axes lying within the substantially horizontal plane. The armrest (26) thus move in a substantially planar fashion without changing the orientation of the armrest (26).

Description: The present invention relates to an arm assembly. In particular, although not exclusively, the invention relates to an arm assembly for an office chair where the armrest is adjustable for the comfort of the occupant. The invention also relates to a detachable arm assembly enabling the arm of a chair to be removed or substituted for another type eg a writing tablet. While the invention is described herein in terms of an office chair, it will be understood that the invention can be implemented in any type of chair including a wheelchair. Moreover, the invention might also have application beyond chairs. Arm assemblies of the invention may be attachable to a table or workstation, for example to be used as typists' aids. Background to the Invention Human beings come in all different shapes and sizes. For this reason, office chairs generally allow for adjustment eg seat height, seat depth. It is also known to provide for adjustment of armrests. A known adjustment includes a twisting action about a vertical axis. Another known type permits a twisting action as well as sideways movement. Another known type permits motion of the armrest in a predetermined oval path within a horizontal plane. Seat depth adjustment is one of the major adjustments required by an occupant of a chair and is to be commonly found on commercial office chairs. As the occupant adjusts their seat depth, the positioning of the armrests relative to the seat will vary even to the extent that the positioning of the armrests may be totally inappropriate for the occupant. Known office chairs do not satisfactorily meet the requirement of being easily adjustable to accommodate the seat depth position. An adjustable armrest is described in DE29901666. Another shortcoming of known armrest adjustment mechanisms is that they are not easy to adjust. In some known types, the user must reach under the armrest to effect the adjustment or alternatively use the opposite hand to make the adjustment. Adjustment in this fashion is awkward and cumbersome. Yet another shortcoming of some of the known adjustable armrests is that they rely on force for adjustment. Therefore, while the occupant is using the chair in the normal fashion, the armrest will function as intended in the position selected by the user. However, if the user unintentionally bears considerable force against the armrests they can move. This often occurs when the occupant uses the armrests to lift himself out of the chair. This can be destabilising to the occupant and moreover, requires the occupant to re-adjust the armrests when he resumes occupancy of the chair. It is therefore an object of the present invention to provide an armrest assembly which overcomes or at least addresses some of the foregoing disadvantages. Summary of the Invention In accordance with a first aspect of the present invention there is provided an arm assembly for a chair, said arm assembly comprising: an armrest; a support structure; a mounting device movably mounting the armrest to the support structure, characterized in that the mounting device constrains the movement of the armrest relative to the support structure to movement in a substantially horizontal plane having two degrees of freedom defined by first and second transversely arranged axes lying within the substantially horizontal plane to move in a substantially planar fashion so as to constrain the armrest against any change in its predetermined orientation. It will be understood that the invention need not be limited to travel along the two predetermined axes. It will be understood that the invention includes within its scope that the armrest is moveable along paths parallel to the first axis and additionally along paths parallel to the second axis. Thus the armrest may be permitted to move in a grid pattern. Additionally, the armrest is moveable in any direction along the substantially horizontal plane incorporating both the first and second axes. Suitably, the movement along the plane is within predetermined limits. It is also preferred that the mounting device enables the armrest to adopt any one of a plurality of adoptable positions defined by the intersection of coordinate locations along the first and second axes. The term "adoptable positions" is thereby defined. In a most preferred form of the invention, the first axis is generally aligned with the forward direction of the chair. Furthermore, the armrest might also be elongate in form with its longitudinal axis aligned with the forward direction of the chair. If the first axis is aligned with the forward direction of the chair then movement of the armrest along the second axis (or paths parallel thereto) will be in the sideways direction of the chair. The invention may be further provided with guides to guide the movement along the first/longitudinal and second/transverse axes. The first guide may be provided on part of the mounting device, to guide movement of the armrest relative thereto with a corresponding first guided portion on the armrest. A second guide may be provided in fixed relationship to the support structure with a corresponding second guided portion provided on said part of the mounting device. In a preferred form of the invention, the first guide is provided on a carrier having the second guided portion for engagement with the second guide secured relative to the support structure to allow movement of the carrier relative to the support structure. Preferably, the first guide is in the form of spaced tracks. Accordingly, there may be two corresponding first guided portions for engagement with the parallel spaced tracks. These may take the form of slots or channels provided on the armrest. Alternatively, the arrangement could be reversed with the first guide in the form of slots or channels with the first guided portions being in the form of one or more projections engageable in the slots or channels. Similarly, the second guide may be in the form of a pair of parallel spaced opposed edges forming a part fixed relative to the support structure. The second guided portion may simply comprise the carrier being shaped for sliding engagement with the opposed edges. Suitably, the length of the guides may determine the range of travel along the first and second axes. Stops may be provided to limit the range of travel along the first and second axes. As determined by the guides or by stops, the range of movement along the first axis may be larger than the range of movement along the second axis. For example, the range of movement in the forward/reverse direction may be greater than the range of movement permitted in the side to side direction. The mounting device may enable the armrest to adopt any one of a finite number of adoptable positions. However, within the scope of the invention is the provision that there may be in infinite number of adoptable positions. Where the mounting device enables the armrest to adopt any one of a plurality of adoptable positions defined by the intersection of coordinate locations of the first and second axes then it is preferred that there is a finite number of coordinate locations along the first and second axes with a resultant finite number of adoptable positions. This leads to a grid pattern of adoptable positions. With this in mind, there may be provided a fixed portion mounted in fixed disposition relative to at least the upper part of the support structure. This fixed portion could be part of the mounting device or alternatively an integral part of the support structure. The fixed portion may include a plurality of first engagement portions, there being a second engagement portion carried with the armrest for engagement with at least some of the first engagement portions. Alternatively, the plurality of first engagement portions may be carried with the armrest with the second engagement portion fixed relative to the support structure for engagement with at least some of the first engagement portions. In either case set out above, the arrangement of said some of the first engagement portions is such that each defines an adoptable position of the armrest when the second engagement portion is engaged therewith. In a preferred form of the invention, the arrangement of the first engagement portions may be in a grid pattern with the second engagement portion able to engage with at least some of the first engagement portions of the grid pattern. The first and second engagement portions are shaped to enable engagement therebetween. Accordingly, in a preferred form of the invention, the second engagement portion may take the form of a discrete engagement member or an engagement projection. The first engagement members may be correspondingly shaped recesses/slots/holes to engagingly receive the engagement member or the engagement projection. In a most preferred form of the invention, the second engagement member is in the form of a ball and the first engagement members are in the form of dimples, shaped to receive the ball. In a most preferred form of the invention, the ball is carried by the armrest and the dimples are provided on the fixed portion fixed relative to the support structure. Accordingly, the fixed portion may include a dimple pad. The recesses/slots/holes may have bevelled edges to enable the engagement members/engagement projections to be guided into position. Therefore, the ball and dimples arrangement is particularly preferred for the reason that the ball is easily locatable within any one of the dimples. Where the second engagement portion is provided in the form of a discrete member eg ball, roller, the ball/roller may be normally biased into a position for engagement with one of the first engagement members. Conversely, the first engagement portions may comprise discrete engagement members or engagement projections such as nodules. Additionally, the second engagement portion may be formed as a recess/slot/hole to receive one of the first engagement members or projections. In another specific form of the invention, the first engagement members may be in the form of rollers with the second engagement portion being shaped as a trough-shaped recess to receive any one of at least some of the rollers. In a preferred form of the invention, the plurality of first engagement portions are provided on the fixed portion. The fixed portion may extend forwardly or rearwardly of the carrier. Alternatively, the fixed portion may extend out partly forwardly and partly rearwardly of the carrier. This is the preferred form because in this way, the two sides of the fixed portion define opposing guides for the carrier. Some of the first engagement portions eg dimples, may also be provided on the carrier. This is particularly preferred where the carrier is centrally located. Therefore, there may be more than one second engagement portions. Preferably, there are two engagement portions eg two balls, with the arrangement of corresponding first engagement portions eg dimples, on the carrier being such that both second engagement portions are not engageable with the carrier at the same time. Where it is desirable to lock the armrest into position, this arrangement will preclude the armrest from being locked to the moveable carrier which is essentially a non-locking configuration of the armrest. In a most preferred form of the invention, there are two balls carried by the armrest and two portions of the dimple pad are arranged forwardly and rearwardly respectively of a centrally disposed carrier with further dimples arranged on the carrier with three dimples extending across the width of the carrier wherein the spacing between the outermost dimples on the carrier is less than the spacing of the two balls such that with one of the balls engaging the carrier, the other ball engages with one or other of the portions of the dimple pad. The two balls could be discrete balls but alternatively could be joined. In an alternative less preferred form of the invention, there may be one or more balls disposed on the fixed portion with the armrest carrying the dimple pad such that the dimple pad can engage with the balls and adopt any one of the plurality of adoptable positions. It will be also appreciated that the invention is not limited to balls and a dimple pad. For example, the fixed portion may comprise one or more projections eg nodules. The arm portion may carry one or more dimple portions shaped for engagement with the nodules with the arrangement of nodules and dimples enabling the arm portion to adopt any one of the plurality of adoptable positions. The armrest may be lockable in any one of the adoptable positions. In this regard, the armrest may be selectively lockable. However, it is preferred that the armrest is normally locked in each of the adoptable positions with a release device being provided to unlock the armrest from its adopted position. As such, the release device may release the engagement between the first and second engagement portions. The release device may be in the form of a separator to separate the second engagement portion out of engagement with the first engagement portion. Preferably, the separator is in the form of a moveable slide having an engagement position whereby the first and second engagement portions are in engagement and a release position allowing disengagement of the first and second engagement portions. Where the first engagement portions are in the form of a recesses and the second engagement portion comprises discrete engagement members then the moveable slide may include a shaped recess of graduated or varying depth with a shallow part and a deep part, with the engagement position of the slide corresponding to the discrete engagement member being received in the shallow part and the release position of the slide corresponding to the discrete engagement member being received in the deep part. The slide may be biased towards the engagement position. In an alternative form of the invention where the first engagement portion comprises a plurality of projections eg nodules and the second engagement portion comprises a correspondingly shaped recess provided on the slide member, the slide may include an inclined surface opposite the recess which is in engagement with a ramped surface, whereby the slide is slidable along the ramped surface to allow the recess of the slide to lift out of engagement with the engaged nodule. The release device may be directly operable by the user. Alternatively, the release device may incorporate an actuator. Preferably, the actuator is disposed for easy reach of the hand of a user whose corresponding arm is supported by the armrest. The armrest may be elongate in shape to support a forearm of the chair occupant. A flat upper surface may be provided although a trough-shaped armrest is also possible. The preferred shape is convex both in X and Y planes. Preferably, the upper surface of the armrest is padded for comfort. The armrest assembly according to the foregoing aspect of the invention may be incorporated into a chair. Suitably two armrests will be incorporated into each chair. Preferably, the chair is an office chair. The armrest may also be incorporated into a wheelchair or used as a typist's aid at a workstation. The chair and arm assembly may be designed such that the support structure is detachable from the chair. The support structure may comprise a column-like portion supporting the mounting device at its upper end. The column-like portion may include a height adjustment mechanism to enable the height of the armrest to be adjusted to suit the chair occupant. The lower end of the column-like portion may be connected to an attachment portion for detachable connection of the arm assembly to the chair. The invention consists in the foregoing and also envisages constructions of which the following gives examples. Brief Description of the Drawings In order that the invention may be more fully understood, one embodiment will now be described by way of example with reference to the drawings in which: Figures 1 is an exploded perspective view illustratin a chair with two detachable arm assemblies according to a preferred embodiment of the present invention; Figures 2 to 5c show attachment of an arm assembly; Figure 6 is a perspective view of an upper portion of the arm assembly with parts removed for clarity; Figure 7 is a perspective view as per Figure 6 with additional parts shown; Figure 8a is a detailed view of the upper part of the arm assembly with the armrest pad removed for clarity; Figure 8b is a longitudinal sectional view through the upper part of the armrest assembly illustrated in Figure 8a; Figure 8c is a transverse sectional view through the upper part of the armrest assembly illustrated in Figure 8a; Figure 8d is a perspective view of an armrest pad of the armrest illustrated in Figure 1; Figure 9 is a perspective view of the armrests with a dependent upper column portion; Figure 10 is a perspective view of the armrest showing the internal detail of the upper column portion; Figure 11 is a detailed view of a lower part of the upper column portion 50 shown in Figure 9, from the rear; Figure 12 illustrates the detail of the lower part of the upper column portion as shown in Figure 11, received within a half portion of a stem liner; Figure 13 is a detailed view of the other half portion of the stem liner; Figure 14 is a perspective view of a modified form of an armrest in accordance with the present invention; Figure 15 is a view as per Figure 14 with the armrest pad removed; Figure 16 is a view as per Figure 15 with a further part removed; Figure 17 is an underside perspective view of a modified transom together with a lower part of a modified form of the arm assembly mounted to the transom; and Figure 18 is another underside perspective view as per Figure 17. Description of Preferred Embodiment Figure 1 illustrates two detachable arm assemblies 24. The arm assemblies 24 include an upper armrest 26 which is padded for user comfort. Each arm assembly also includes an upright support structure 28. The armrest 26 is mounted to the upper end of the upright support structure 28. The lower end of the upright support structure has an elongate attachment portion 30 extending inwardly therefrom in a downwardly inclined angle as shown in Figure 3. The elongate attachment portion 30 engages within one end of the main transom 22 in the manner illustrated in Figure 2. The manner of attachment is illustrated in more detail in Figures 4 and 5a-5c which are various views of the end of the transom 22 with the elongate attachment portion 30 engaged therein. As best shown in Figure 5a, elongate attachment portion 30 includes an outer male engagement surface 32 and an inner male engagement surface 34. The outer male engagement surface 32 is spaced from the inner male engagement surface 34 thereby defining an intermediate portion 36 of tapering configuration. As will be appreciated in connection with the drawings, "outer" and "inner" define the positioning of the engagement surfaces relative to the arm assembly. Each end of the main transom 22 includes an arm attachment portion in the form of a void to accommodate the elongate attachment portion 30. The void is not a fully sided hole but rather is defined only by an inner female engagement surface 38 and an outer female engagement surface 40 at the lower side thereof. It will be appreciated that the elongate attachment portion 30 will be supported on the inner and outer engagement surfaces 38, 40 of the main transom 22. Other surfaces of the elongate attachment portion 30 and the transom 22 are in contact. These are disposed at a clearance of 0.2 mm. The additional surfaces prevent side-to-side movement and up and down movement. It will be appreciated that in this context "inner" and "outer" are used from the perspective of the main chair assembly 12. In order to assemble the arm assembly 24 with the main assembly 12, the elongate attachment portion 30 is inserted into the main transom until the outer male engagement surface 32 engages against the inner female engagement surface 38 and the inner male engagement surface 34 engages against the outer female engagement surface 40. The male engagement surfaces are formed on parts of the elongate attachment portion 30 which are non-tapering and of small length compared to the length of the elongate attachment portion 30. It can be seen that the elongate attachment portion 30 is downwardly inclined relative to the upright support structure 28. In this way, any downward force applied by the chair occupant to the armrest 26 will be resolved in the elongate attachment portion in a direction tending to push the elongate attachment portion into the arm attachment portion. A force in the upright direction applied to the armrest will also be resolved in the elongate attachment portion in the same manner due to a cantilever effect. Additionally, a clip is provided to secure the attachment of the arm assembly. As shown in Figure 5c, the clip includes a latch member 42 having a hook portion 44 engageable against a latch surface 45 (see Figure 5a) formed as part of the main transom 22. The latch member 42 has a first fulcrum 43 resting on pivot 48 and a second fulcrum 47 bearing against button 46. The latch member 42 is formed to include an integral spring with the second fulcrum 47 biasing the button 46 outwardly. As the button 46 is pushed inwardly, the latch member 42 pivots about fulcrum 43 to release the hook portion 44 from engagement with the latch surface 45 in order that the arm assembly 24 may be detached from the main chair assembly 12. As best shown in Figure 2, the support structure 28 includes an upper column member 50 telescopically received in a hollow lower column member 52. The upper column member 50 and the lower column member 52 are adjustable relative to one another to effect height adjustment in a manner which will be explained in more detail in connection with Figures 9 through 13. Extending at a downwardly inclined angle from a lower part of the lower member 52 is leg portion 54. The elongate attachment portion 30 is connected to the lower end of the leg portion 54. The upper column portion 50 supports a fixed portion 56 in normally fixed disposition thereto (given that the fixed portion 56 is height adjustable as will subsequently be explained). Referring now to Figure 6, the fixed portion can be seen to include two dimple pads 57 extending on either side of a transversely slidable carrier 58. The dimple pads 57 are two separate injection moulded components self locating into the fixed portion 56. As shown in Figure 8b, the fixed portion 56 defines transverse guides for the slidable carrier 58. The carrier 58 is thereby slidable back and forth in the sideways direction of the chair. In Figure 8c, it can be seen that sides of the fixed portion 56 define stops for side-ways movement of the carrier 58. The carrier 58 additionally includes two longitudinal guides 62. The guides 62 are each of T-shaped configuration as shown. As best shown in Figure 8a, the guides 62 extend through longitudinally extending slots 64 provided in a base portion 66 of the armrest, the ends of the slots defining stops for longitudinal movement. The base portion 66 of the armrest 26 is thereby slidable forward and backward by the sliding action of the longitudinal guides 62 within the slots 64. Since the longitudinal guides 62 are formed on the carrier 58, as the carrier 58 slides sideways, the base portion 66 of the armrest 26 will be likewise carried in the sideways direction. It will be understood that with the combined action of the longitudinal guides 62 and the transverse guides 60, the armrest will be able to move in any direction along the horizontal plane defined by the transverse guide and the longitudinal guide 62 within predetermined limits established by the stops. In order to establish a finite number of adoptable positions which the armrest 26 can adopt within the plane, the armrest carries a pair of metal balls 70 in fixed disposition relative to each other. Together, these balls can move across the carrier 58 and engage with respective ones of the dimples 72 provided on either of the dimple portions 57. Additionally, the carrier 58 also has dimples 74. These are arranged at a spacing whereby only one of the balls can engage with the carrier 58 at a time, with the other ball engaging with a dimple 72 from one or other of the dimple pads 56. The balls 70 are carried by the base portion 66 of the armrest 26 by way of slide 80 as shown in Figure 7. On the underside of slide 80 as shown in Figure 8b, two recesses 82 are provided, each for receiving one of the balls 70. Each recess is graduated to include a shallow part and deep part, the orientation of the shallow and deep parts being the same in each case. When the balls 70 are located in the shallow part of the recesses 82, the balls will be held into engagement with the engaged dimples. In order to release the balls 70 from engagement with the dimples 72 the slide 80 is slid in its lengthwise direction so that the deep part of the recess is engaged with the balls 70, thereby releasing the balls 70 from engagement with the dimples 72. As shown in Figure 8a, the slide 80 is slidably mounted within the base portion 66. A pivotable actuator 84 is pivoted to the base portion 66 about pivot 86. The pivotable actuator 84 is an L-shaped member with a depressor portion disposed conveniently on the armrest in the vicinity of the user's thumb. The slide 80 is biased by spring 88 towards an engagement position whereby the balls 70 reside in the shallow part of the recess in the slide. Therefore, the actuator 84 is operated against the bias of the spring 88. The end of the slide 80 opposite to the actuator 84 also incorporates an abutment projection 90 which in the release position of the slide member, engages against stop 92. In operation, the user depresses actuator 84 with his or her thumb thereby moving the slide 80 to the release position whereby the balls 70 are released from engagement with the dimples 72. With the user holding his thumb against actuator 84, the base portion 66 can be slid forwards and backwards along the longitudinal guides 62. Additionally, the base portion 66 can be moved from side to side by movement of the carrier 58 along the transverse guides. Additionally, synchronous movement of the base portion 66 on the guide 62 and the carrier 58 on the transverse guides is possible so that the base portion 66 can move in any direction along the plane within predetermined outer limits. When the user releases the actuator 84, the balls 70 will bear against the dimple pads 57 and/or against the central portion of carrier 58. A slight adjustment of the armrest 26 will then locate the balls 70 within the closest dimples. The armrest will then be locked into the adopted position until the user again depresses the actuator 84. Figure 9 illustrates the upper half of the armrest 26 with the upper column portion 50 removed from the lower column portion 52 within which it is normally telescopically received. The upper column portion 50 is a substantially solid column member. Figure 10 illustrates the internal components of the upper column portion 50 including a height adjustment actuator 101, a roller carriage 102 and connecting rod 103. As can be seen in Figure 10 and more clearly in Figure 13, the roller carriage 102 has a graduated recess 105 provided therein having a deep part and a shallow part. A roller 104 is received within the graduated recess 105. Referring to Figure 11, the roller carriage 102 is slidable within the lower end of the upper column portion 50 as defined by a locating receptacle 106 in which the roller carriage 102 is housed. The roller carriage 102 is moveable within the receptacle 106 as the actuator 101 is operated by the user. The roller carriage is normally biased by a spring (not shown) into the lower most position illustrated in Figure 11. As shown in Figure 12 and 13, the lower end of the upper column portion 50 is received within two half portions of a stem liner. One of the half portions 108 is illustrated in Figure 12. The other half portion 109 is illustrated in Figure 13. The two half portions 108, 109 together define a central conduit within which the lower part of the upper column portion 50 is telescopically received. The half portions of the stem liner 108, 109 fill part of the void within the hollow lower column portion 52. The ribs 110 assist with filling the void and also adds strength to the half portions of the stem liners. Additionally, one half portion of the stem liner has integrally formed leaf springs (not shown) to bias the stem liner towards one side of the lower column portion 52. Furthermore, one or both of the half portions of the stem liner have internal integrally formed leaf springs to reduce any slack between the upper column portion 50 and the stem liner. The half portion 108 illustrated in Figure 12 is provided with a series of spaced trough-like recesses 100. The roller 104 which in part protrudes through an opening 111 (See Figure 9) is shaped to engage with any one of the trough shaped recesses 100. As already explained, the roller carriage 102 is normally biased by a spring into a lowermost position illustrated in Figure 12. In this position, the roller 104 will be received in the shallow part of the graduated recess 105 while it is in engagement with one of the trough-like recesses 100. When it is desired to adjust the height of the armrest 26, the user operates the actuator 101 in order to move the roller carriage 102 upwardly. The roller 104 in effect is moved down the graduated recess 105 towards the deep part until it is no longer held between the base of the recess 105 and the trough shaped recess 100. Once engagement between the roller 104 and the trough shaped recesses 100 is released, the upper column portion 50 can be moved relative to the lower column portion 52. Once the height of the armrest has been satisfactorily adjusted, the user releases the actuator. With possibly some slight adjustment required, the roller 104 will locate within the closest trough shaped recess 100 and in doing so, the roller carriage 102 will move with the bias of a spring (not shown) into a locking configuration with the roller 104 located in the shallow part of the recess and in engagement with a recess 100. Figure 13 illustrates the other half portion 109 of the stem liner, the inner side having two spaced tracks in the form of elongate recesses 112. The roller carriage 102 has two spaced guides 114 which are configured to be slidingly received within the tracks 112. At the upper end of the half portion 109, the tracks terminate and accordingly, this termination point will define an upper limit beyond which the guides 114 cannot be upwardly moved. This prevents the upper column portion 50 being fully withdrawn from the lower column portion 52. Figure 14 illustrates a modified form of the armrest 26a. The upper portion of the armrest 26a which is padded for user comfort includes an opening 118 in which a slide 120 is received. Figure 15 is a view as per Figure 14 except with the padded part of the upper portion removed. The slide 120 is slidably received within a slide casing 125, mounted on the base portion 66. The slide 120 can clearly be seen in Figure 16. The slide includes a shallow rebate 127. An optical disk such as a CD (not shown) is received in the rebate 127. The CD is used with a computer to graphically illustrate the operating features of the chair 10. Figures 17 and 18 illustrate of modified form of the main transom 22a. Several of the features of the main transom 22a are not described in detail. The main transom 22a is supported from the base 18 by a pneumatic spring at central spring connection ring 23a. Only the lower part of the modified form of the arm assembly is shown in Figures 17 and 18. This includes a lower column member 52a and an attachment portion 130 extending inwardly therefrom. The upper part of the modified form of the arm assembly may be the same as shown in the preceding drawings with the lower column member 52a telescopingly receiving the upper column member 50. The attachment portion 130 is made up of two parts including an outer attachment section 130a which is integrally formed with the lower column portion 52a. Further, the attachment portion 130 includes an inner attachment section 130b which is bolted to the outer attachment section 130a by means of bolts 131 and 132. A further bolt 133 fastens the whole attachment portion 130 to the main transom 22a. The inner attachment section is provided mainly for aesthetic reasons. The foregoing describes only one embodiment of the present invention and modifications can be made thereto without departing from the scope of the invention, as defined in the appended claims.

Claims: An arm assembly (24) for a chair, said arm assembly comprising: an armrest (26); a support structure (28); a mounting device (58) movably mounting the armrest (26) to the support structure (28), characterised in that the mounting device constrains the movement of the armrest (26) relative to the support structure (28) to movement in a substantially horizontal plane having two degrees of freedom defined by first and second transversely arranged axes lying within the substantially horizontal plane to move in a substantially planar fashion, so as to constrain the armrest (26) against any change in its predetermined orientation. An assembly according to claim 1, characterised in that the arm assembly is adapted to be assembled with a chair with the first axis corresponding substantially to the forward direction of the chair and the second axis corresponds with the transverse direction of the chair. An assembly according to claim 1 or to claim 2, characterised by first and second guides (60, 62) to guide the movement of the armrest (26). An assembly according to claim 3, characterised in that the mounting device (58) incorporates a carrier and in that the first guide (62) is incorporated into the carrier to guide movement of the armrest (26) relative thereto with a corresponding first guided portion (64) on the armrest (26) and in that the second guide (60) is provided in fixed relationship to the support structure (28) with a corresponding second guided portion incorporated into the carrier (58). An assembly according to claim 3 or to claim 4, characterised in that the first guide (62) is in the form of spaced parallel tracks and the first guided portions are in the form of slots or channels provided on the armrest (26). An assembly according to claim 4, characterised in that the second guide (60) is in the form of a pair of parallel spaced opposed edges in fixed relationship to the support structure with the carrier being shaped for sliding engagement with the opposed edges. An assembly according to any preceding claim, characterised in that stops are provided to define a limit of movement along the first axis and along the second axis and the range of movement along the first axis is greater than the range of movement along the second axis. An assembly according to any preceding claim, characterised in that the armrest is selectively positionable in any one of a plurality of adoptable positions in the horizontal plane. An assembly according to claim 8, characterised in that the mounting device (58) is such that there are a finite number of adoptable positions. An assembly according to claim 8, characterised by a locking device (70, 72) to releasably lock the armrest (26) in any one of said adoptable positions. An assembly according to claim 10, characterised in that the locking device (70, 72) includes a fixed portion mounted in fixed disposition relative to at least the upper part of the support structure (28) and either: the fixed portion including a plurality of first engagement portions, there being a second engagement portion carried by the armrest (26) for selective releasable engagement with at least some of the first engagement portions; or the armrest (26) having a plurality of first engagement portions with a second engagement portion fixed relative to the support structure for selective releasable engagement with at least some of the first engagement portions; in either case, the arrangement of said some of the first engagement portions being such that each defines an adoptable position of the armrest (26) when the second engagement portion is engaged therewith. An assembly according to claim 11, characterised in that the second engagement portion is in the form of a discrete engagement member or an engagement projection and wherein the first engagement members are correspondingly shaped recesses or slots or holes to engagingly receive the engagement member or the engagement projection. An assembly according to claim 12, characterised in that the discrete engagement member is normally biased into a position for engagement with one of the first engagement members. An assembly according to any one of claims 11 to 13, characterised in that the second engagement member is in the form of a ball. An assembly according to any one of claims 11 to 14, characterised in that the fixed portion is in the form of a pad having an engagement surface with a spaced array of dimples formed on the engagement surface. An assembly according to any one of claims 11 to 15, characterised by first and second guides (62, 60) to guide the movement along the longitudinal and transverse axes respectively the mounting device further including a carrier (58) wherein the first guide (62) is provided on the carrier (58) with a corresponding first guided portion on the armrest (26) to guide movement of the armrest (26) relative to the carrier (58) wherein the second guide (60) is incorporated into the fixed portion with a corresponding second guided portion incorporated into the carrier (58), wherein fixed portion extends forward and rearward of the carrier (58) and the plurality of first engagement portions are provided on the fixed portion. An assembly according to claim 16, characterised in that first engagement portions are provided on the carrier (58). An assembly according to claim 17, characterised in that there are two second engagement portions with the arrangement of corresponding first engagement portions on the carrier (58) being such that both second engagement portions are not engageable with the carrier at the same time. An assembly according to any one of claims 10 to 18, characterised in that the locking device is operable to normally lock the armrest (26) in each of the adoptable positions, the locking device being selectively releasable. An assembly according to any one of claims 11 to 19, characterised in that the locking device further includes a separator (80) to selectively separate the second engagement portion from engagement with the first engagement portion. An assembly according to claim 20, characterised in that the separator (80) is in the form of a moveable slide having an engagement position whereby the first and second engagement portions are in engagement and a release position allowing disengagement of the first and second engagement portions. An assembly according to claim 21, characterised in that the second engagement portion comprises one or more discrete engagement members, the moveable slide including one or more shaped recesses of graduated or varying depth with a shallow part and a deep part, with the engagement position of the slide corresponding to the discrete engagement members being received in the shallow part and the release position of the slide corresponding to the discrete engagement members being received in the deep part of respective recesses. An assembly according to any one of claims 10 to 22, characterised in that the locking device incorporates an actuator (84) which is disposed for operation by the hand of a user whose corresponding arm is supported by the armrest (26).

Inventors: PRINCE JONATHAN WILLIAM, WILKINSON PAUL MICHAEL, PRINCE, JONATHAN WILLIAM, WILKINSON, PAUL MICHAEL
Applicants: FORMWAY FURNITURE LTD, FORMWAY FURNITURE LIMITED
Application year: 2001
Main classification: A47C1
IPC codes: A47C1, A47C7, A47C5, A47C3