Variable configuration seating
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A variable chair (10) features variable displacement between a back-to-seat pivot or slide pivot interconnection (14) and a back sliding pivot (15), to compensate for occupant weight in tilt moment in a weight responsive action; a particular construction features opposed pairs of intercoupled seat and back crank arm frames (111, 113) mounted upon a carrier or ground frame (114) by which the chair is supported, to achieve a back tilt, seat slide action; with the option of frame flex for restorative action; and with combined back and seat action about a virtual pivot which can approximate to a natural occupant body spine lumbar pivot and associated pivot movement path.

Birkbeck, Hilary Rolf (Warwickshire, GB)
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Primary Examiner:
Attorney, Agent or Firm:
Danald N.MacIntosh (San Francisco, CA, US)
1. {Pivot Disposition} A variable configuration chair (10) or chair support assembly comprising a seat frame (11) a back frame (12) mounted upon a movable pivot or slide pivot (15), with seat and base frames interconnected by a variable disposition element and/or coupling (14), whereby spacing between back pivot axis and back-seat coupling reflects seat occupancy.

2. {Weight-Responsive Configuration} A chair of claim 1, with an intercoupled back (12) and seat (11) configured with variable spacing between a back to seat pivot or slide pivot coupling (14) and a back slide pivot axis (15) responsive to chair loading, such as occupant size and/or weight (W), whereby to vary occupant turning moment arm about a back pivot for back tilt or recline action adapted to seat occupancy.

3. {Back Tilt—Seat Slide Action} A chair of any preceding claim with a intercoupled back frame tilt and seat frame slide action, over a seat ramp inclination set upon occupancy, by downward movement of a seat frame rear coupling with a back frame so back tilt drives a seat up an incline reflecting occupancy.

4. {Carrier Frame Ground Support} A chair of any preceding claim comprising back (12) and seat (11) frames intercoupled to a carrier or ground frame connected to a chair base or chassis upon a ground support.

5. {Pivot+Locus} A chair of any preceding claim with an effective pivot and pivot locus representing a natural pivot and pivot locus of a chair occupant

6. {Seat+Back Cranked Frames} A chair of any preceding claim, with a seat frame (II) of cranked arm profile a back frame (12) of cranked arm profile corresponding arms (21, 22/23, 24) of seat and back and frames (11, 12) being intercoupled directly or indirectly by pivots and/or slides (25, 26).

7. {Variable Configuration} A chair of any preceding claim, with back and seat frame inter-couple, through relatively movable, cranked frames (111, 114); each frame having respective upper and lower arms; an upper arm of one frame (111) carrying a back rest (112), a lower arm of said one frame (111) also being captive with a corresponding lower arm of another frame (114) through sliding pivot interconnection; a seat (115) carried by said other frame (114) lower arm; said other frame (114) upper arm being captive with a corresponding upper arm of said one frame (111) through sliding pivot interconnection; an intermediate carrier or ground frame (113) captive by pivotal connection with said one frame (111) upper arm and said other frame (114) lower arm; and for mounting upon a support.

8. {Complementary Frames} A chair of any preceding claim, with a complementary pair of opposed frame assemblies at each side, each frame assembly with indirect back (112) and seat (115) inter-couple, through relatively movable cranked inner (114) and outer (111) frames; outer frame (111) upper arms being secured to opposite sides of a back (112), and outer frame (111) lower arms being captive with corresponding lower arms of an inner frame (114) through sliding pivot interconnection; a seat (115) with opposite sides carried by inner frame (114) lower arms; inner frame (114) upper arms being captive with corresponding outer frame (111) upper arms through sliding pivot interconnection; an intermediate carrier or ground frame (113), captive by pivotal connection with outer frame (111) upper arms and inner frame (114) lower arms; and for mounting upon a support.

9. {Flex Frame} A chair of any preceding claim with a flex frame to provide cushion and/or restorative action upon loading and deflection, such as by chair occupancy.

10. {Flex Carrier Frame} A chair of any preceding claim with a flex frame as a carrier or ground frame intercoupled to respective seat and back frames, to allow relative frame displacement through pivot and/or slide and/or flex.

11. {Resilient Slide Path} A chair of any preceding claim with a resiliently deformable element in a slide path between intercoupled frames.

12. {Support Frame+Capture Fittings} A chair of any preceding claim, mounted upon a support frame (60) between spaced bearing and/or capture fittings (65, 75) for relative back and/or seat movement

13. {Variable Profile Skeletal Frame} A chair of any preceding claim, mounted upon a skeletal support frame (31, 32, 33) of variable profile in response to chair occupancy

14. {Frame Hoop} A chair of any preceding claim with a support frame (19) configured as a hoop with one end supporting a back frame pivot and another end supporting a seat frame.

15. {Frame Splay} A chair of any preceding claim, configured for support frame splay between support frame bearing and/or capture fittings (13, 15) to supplement frame movement upon loading and provide cushion and/or restorative action by frame deflection and/or bending upon splay.

16. {Adjustable Friction Capture Fittings} A chair of any preceding claim, with adjustable friction capture fittings (28, 29) between back, seat and support frames, for supplemental control of chair action freedom.

17. {Crank Frame Intercouple} A variable configuration chair, with relatively movable, cranked back, seat and carrier frames (111, 113, 114), for a back-tilt or recline and seat-slide interaction, over a seat ramp inclination variable with occupancy; and a back pivot movable in relation to a back and seat coupling, whereby back tit resistance varies with back pivot disposition and/or seat ramp inclination.

18. {Chair as Described and Illustrated} A chair or chair support assembly substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.


This invention relates to seating and is particularly, but not exclusively, concerned with variable configuration seating—that is seating which will react and adapt to occupancy, in particular to imposed occupant weight and weight-shift, by a change in configuration, such as shape and/or relative disposition of elements. Movement, such as pivot and articulation, in relation to prescribed pivot points and movement paths are also embraced.

Problems attendant seating—or chair occupancy—and sitting are well recognised. Issues of posture or stance, profile, balance and movement arise. Fundamentally, sitting is neither a static nor natural state or one for which the body is well adapted. So an occupant tends to move continually and perceived seating comfort in part reflects seat compliance to such ‘shuffling’ or ‘fidget’. Thus a chair action and attendant mechanism reactive to continual change of occupant seating position or stance, without undue obstruction, by say frictional resistance, is desirable.

Prolonged sitting in awkward postures can provoke muscular-skeletal disorders and attendant back pain. Even the brio-dynamics of sitting, that is transitions between standing and being seated and over different seating positions, merit attention. Occupant weight creates vertebrae and intervening disc compaction, particularly at the lower spine. This is perceived as discomfort and even pain. In an upright stance, occupant weight or at least that of upper body or trunk, is imposed downwards through the spine to the pelvis. Even a modest tilt or lean transfers weight from the lower spine and pelvis.

Such compaction admits of periodic relief by (spine) stretching. Stretching is a rationale for chair back tilt and tilt variation—such as periodic rocking to and fro. Extreme movement range is not so critical as the nature and extent of mobility. Thus even limited mobility—such as tilt/recline—of the ‘right kind’ can prove worthwhile, particularly if driven passively by occupant body weight. Mobility over a prescribed movement path is desirable. Spine loading can be relieved by occupant weight transfer or (re-) distribution—such as taking some of a chair occupant weight by back tilt or recline and upon arm and/or foot rests. Some compliance or give upon occupancy loading can help create a perception of comfort.

Movement and associated spine loading variation can provide beneficial joint tissue massage and promotion of blood circulation. This relieves the harmful effects of constant pressure. Continual such so-called ‘Ergo-dynamic’ movement, rather than sporadic transition between static poses, is natural, healthy and desirable. Mere manual discrete incremental chair adjustment between fixed positions will not suffice. A chair should therefore provide for occupant movement—and weight shift.

A human frame bends in a subtle and complex way—reflecting spine flex and pelvic hip joint articulation. This might be approximated to, or encapsulated by, rotation about a notional body pivot. This may or may not coincide with a body centre of gravity. Translational movement of this body pivot—in sitting and in being seated and over varied back and/or seat recline—might also be encapsulated by a body pivot path or locus of movement. This represents an optimum or idealised locus—and which becomes a target reference for emulation by a chair action. Analysis could be undertaken with a map or model—say through a physical position plot or software graphical simulation. A mechanical chair action admits of corresponding analysis.

Such mechanism and body analysis—offer the prospect of emulating a body action in a chair action. This could be achieved by iterative comparative matching of respective maps or models. If a very precise match is sought, it is necessary to emulate or reflect the full subtlety and complexity of body movement in a chair action. This is challenging demand, even with a complex bespoke chair mechanism. All the more so with a simple mechanism, such as pivot motion. An idealised solution would be a simple mechanism with a simple action replicating a simplified natural body action. Achievement of action subtlety and complexity in a simple mechanism would seem counter-intuitive. The solution lies in careful geometry. A pragmatic compromise is to simplify the target action—in turn to allow simplification of a chair action and attendant mechanism. Thus, say, chair back and seat support could be inter-related and constrained to a prescribed path. It would be desirable to achieve a ‘target’ or ‘idealised’ chair action, or at least a reasonable compromise, without an unduly elaborate or intricate mechanism. Indeed, a simple, ‘elegant’ mechanism achieving a ‘sophisticated’ (in the sense of following an occupant or a virtual pivot path) target action would provide benefit without disproportionate cost.

Prior Art—Perspective

One approach to chair action is slightly to tilt a seat upon back tilt. That is marginally to lower a seat rear edge to create a fresh seat-to-back included angle. Seat tilt inclination variability is not admitted in that case, but rather seat slide occurs along a pre-set inclination—of some 10 degrees to the horizontal. The front seat edge is set higher than the rear, to tip, cant or tilt an occupant slightly backward and promote weight transfer and lean upon the back. Diverse linkages and movement actions have been proposed to this end.

US 2004/0155502 Johnson is one of a family of cases on coordinated chair seat slide and back tilt. A sliding back pivot is carried by a rearward arm extension from a base slide mechanism. A seat back brace wraps around the sides of the chair to link to arm pivots, also carried by stub arms from the seat base slide.

This is embodied in a so-called REACT (Trade Mark) ‘Hip-Pivot_Glider’ chair action—per Leggett & Platt, the subject of U.S. Pat. No. 6,685,267B1, exhibits a certain weight-responsiveness. In this approach, occupant upper body or trunk lean is coupled to a seat under-slide mechanism which draws or drives forward upon rearward seat back tilt. The chair action seeks to complement natural trunk-hip skeletal frame pivot joint action. Pivotally connected stub arms extend respectively from a back and seat. Back tilt about a pivot between an arm bracket—set forward of the back and above the seat plane—is transferred to seat (forward) slide.

Grammar of Germany have devised ergodynamic seating—recognising the role of permanent motion, rather than sitting still and upright while working. Promotion of oxygen circulation, prevention of back pain and improved seating feel and thus work performance are objectives.

In another approach, seat tilt about a forward (eg front seat edge) axis is used to assist lean forward such as for a task and to preface standing upon exit.

In a conventional pedestal chair an action mechanism is located under the seat. This consumes critical depth which restricts chair height adjustment range, so a cumbersome mechanism is undesirable. Thus an action mechanism accommodation problem arises. A less compromised chair action—yet one more readily implemented without intrusion upon adjustment range—would be desirable. The Applicant envisages dispensing altogether with a conventional cumbersome ‘add-on’ mechanism—and substitution by integrated, embedded, or ‘distributed’ geometry. A design resolution could thus effectively ‘permeate’ and are embedded in or integrated with the structure.

The Applicant also foresees a ‘tool kit’ of chair frame elements and an organising scheme to be deployed to achieve a target chair action. The target action could be a compromise—say to meet economic constraints—or optimised, if not idealised, in situations where occupant health and comfort is an over-riding priority. An optimised chair action would be ‘responsive’ to occupancy—and empathetic to body posture. A prime example would be a ‘weight-responsive’ chair action. ‘Weight responsive’ signifies pro-active and coherent predictable response) —such as re-configuration action or movement—to (super) imposed weight. This as distinct from merely ad hoc passive or static load-bearing. So another term might be ‘weight compensating’. In this case, imposed occupant weight, or rather variations in weight, should not generate variation in perceived response. Put another way, heavyweight occupants cannot, whether intentional or inadvertent, use their mass or weight to dictate, dominate or override chair action. An example would be a heavyweight occupant finding back tilt disconcertingly easy simply by disposition of their body mass centre of gravity (c of g) in relation to a back pivot. Nor should a lightweight user be frustrated by chair resistance to desired movement.

A parallel consideration is that occupant size (especially height)—which impacts upon weight distribution—should not generate variation in perceived response. So occupants of different size and/or weight do not perceive a different chair behaviour or action. A weight and size consideration is occupant body mass or frame distribution—taking account of top or bottom heavy body forms. Thus, whilst occupant weight may be used to drive a chair action, its contribution is not perceived directly by an occupant. So different occupant weights are perceived similarly by the respective occupants. The chair may, indeed does, react differently—but a chair occupant does not necessarily perceive that difference—even though an outside observer might. Rather, an occupant experiences a weight or size neutral response, even though the chair action has adjusted to accommodate occupant weight and size. A corresponding issue arises for occupant size. Thus, say a taller occupant could exert more leverage over a back simply by sitting higher—with more back mass above a back pivot point.

A chair mechanism is envisaged which counters or compensates for occupant weight diversity. Thus a heavier or lighter occupant experiences similar ease or resistance to required movement. Parallel compensation for diversity in body shape or size is also envisaged, so again different occupants share similar perceived seating experiences. This without having to adjust frame proportions or settings of bias or recovery springs. It would be desirable to achieve a target chair action with a ‘compact’ mechanism—in particular one concentrated at a position between back and seat and/or ‘distributed’ unobtrusively over and/or between the back and seat support—rather than a cumbersome under-seat mechanism which characterises certain known chair actions.

Statement of Invention

A variable configuration chair (10) or chair support assembly

comprises a seat frame (12)
a back frame (11) mounted upon a movable pivot or slide pivot (15),
with seat and base frames being interconnected
by a variable disposition element and/or coupling, such as a pivot (14),
whereby spacing between back pivot axis and back-seat coupling
reflects seat occupancy.

A variable configuration chair can respond to loading, such as occupancy by a change in disposition. This to achieve a certain pivot action or pivot movement path. The pivot and pivot path may lie outside the physical elements, and as such is called a ‘virtual’ pivot. Moreover, a pivot approximate to that of a chair occupant body frame could be contrived.

An instance is a weight-shift chair which adjusts its configuration, such as seat and back disposition, inter-relationship and interaction, with occupant weight, to alter loading or moment for seat back tilt. In a particular construction, a chair comprises a pivotally interconnected back and seat, the back itself having a pivot axis variably spaced from said pivotal interconnection according to chair loading by occupant weight. Thus an element of chair back position or movement is coupled to seat squab movement—and vice-versa.

Factors include:

    • spacing between . . .
      • back pivot or slide pivot and
      • back-seat interconnection (eg pivot or slide pivot);
    • variability of such spacing;
    • variability with chair occupant weight.

Back and seat frame coupling can be through direct interconnection in a basis structure, or indirectly through an intermediate element, such as another frame, which may also serve as a reaction, reference, carrier or ground support frame.

Pivot Action Shift

Overall tilt action reflects:

    • back frame tilt about a back pivot or slide pivot;
    • seat frame tilt and/or slide about a pivotal connection with the back;
    • and another point of support of a seat frame.

Whether direct or indirect, pivotal interconnection between chair back and seat—shifts in response to occupant weight. A heavier occupant displaces a back-to-seat pivotal connection further than would a lighter occupant. if this displacement is away from a back pivot axis, restorative action of occupant weight borne upon a seat is afforded a greater moment about a back pivot mounting upon a chair frame. To counterbalance this, over a smaller moment arm, a greater bit force must be applied by a chair occupant leaning against a back above the back pivot. Occupant weight upon the seat counters occupant (rearward) tilt or lean against the back. A working assumption for chair action design is that a heavier occupant is more able and so likely (albeit inadvertently) to apply greater tilt force, and turning moment—in turn likely to induce excessive bit. A balance can be struck with an occupant feeling free to tilt or sit more upright without undue effort. This balance contributes to perceived comfort and compliance of seat action with occupant demands. There is a subtle interplay of forces, including occupant weight downward and turning moment attendant action of that weight about seat back pivot.

A chair, or key constituent chair elements, such as seat and back, can vary in configuration, disposition and/or orientation to reflects superimposed loads, in particular occupant weight if not an entire chair, certain elements might respond individually or collectively to superimposed weight loading—independently or interactively. The weight loading is essentially that of a chair occupant—or that proportion applied to the chair, if some other remaining proportion is otherwise supported or borne, say by foot to floor contact. Adoption of variable configuration geometry which reflects applied weight in a sense ‘stiffens’ or ‘braces’ the chair against over-reaction to occupancy. An example would be automatic compensation for the effect of applied weight upon occupant freedom of movement. Thus resistance to certain action could be adjusted—say increased—to counter greater mass or forces reflecting such mass, ie weight. Occupant ability to apply force to a chair action reflects their body size and mass or weight—and indeed weight distribution. Matching chair response action to applied weight impacts occupant perception of chair action. An occupant need not be aware of their own weight in dictating seat movement.

A weight-responsive chair can be achieved with a movable seat, a back connected to the seat for inter-related movement according to occupant weight and/or size and occupant movement. Weight embraces weight distribution—a shape and size related factor. A tilt and/or slide seat movement action could be employed. A rigid or movable back-seat interconnection could be used. A slide connection between back and back pivot would allow variation in disposition of back pivot in relation to back upper edge. In some variants, back and seat might be intercoupled for minimal or even no relative movement—reliance being placed upon seat mobility for corresponding back mobility. Indeed back and seat might be integrated as a unitary element. This is advantageous for common moulding. A resilient foam outer skin or shell could impart modest cushion absorbency around an otherwise hard, rigid inner core. Spine curvature could also be reflected in back shell and cushion liner. Variable back profile is possible, but not essential.

In a particular unitary construction, back and seat, or at least their respective frames, are formed as a one piece shell of ergonomic form, with certain freedoms of movement, vis:

    • seat frame pivot parallel with front edge;
    • spring-loaded pivot;
    • pivot (axis) movement (by recti- or curvi-linear translation or slide action) parallel to a support surface or ground and 90 degrees to pivot axis itself; and
    • back rotation (optionally along with seat about an axis through hip to lumber point
    • and parallel to seat front).


    • a seated occupant is able to push the top edge or at least upper part (above the back pivot axis) of the back, in order to rotate it into an inclined position;
    • the front spring-loaded axis takes up or ‘absorbs’ the attendant movement, so an occupant can recline.

The force required to move the back is determined by the required turning moment. That is, the distance of the applied force from the pivot axis. This reflects occupant personal thoracic (chest) weight acting on the chair back (times) the distance from hip-lumber through axis to back top. The heavier the occupant, the greater the force, so the easier it becomes to recline the chair shell.

Mobility of the hip-lumber through axis to move up and down at right angles to the floor allows the distance to the top of the back to vary. Thus a light-weight occupant will not move the pivot point significantly, so the distance from pivot point to the top of the back will remain largely unchanged. Generally, turning force can be expressed as . . .

Moment ‘M’=Force ‘F’ (times) Distance ‘d’

With a heavier chair occupant, the back-seat pivot point moves up relatively, as the seat drops down. Thus the (pivot or tilt action) moment will change. The back will recline only when a greater force ‘F+’ is applied, as action distance ‘d-’ has become smaller. Thus, overall, the effective back-seat pivot point moves in sympathy with occupant weight. Articulation of seat and back recline will follow.

Counterbalance Action can be summarised as . . .

(New) Moment Mn=(increased) Force ‘F+’ (times) (Reduced) distance ‘d-’

A discrete back and seat allows relative re-disposition and movement. Coupling between back and seat can be a pivot joint between rear seat and lower back edges. Alternatively, an under slung seat carriage could have a movable back support arm extending rearward and upward to reach mid-back. Back and seat could be rigid or semi-rigid shell mouldings, with upholstered cover sleeve. Support frame bearers for back or seat carry or transfer loads, but admit relative movement. Bearers may incorporate or be used in conjunction with bias springs. Bearers could be incorporated in or integrated with seat frame capture fittings. Such fittings could embody some inherent bias, resistance or damping action. A sliding seat bearer could be fitted at the front edge of a seat to allow fore- and-aft and swing movement of the seat upon set occupancy and tilt. A back bearer could carry a back pivot. In a swivel seat, splayed forward and rearward arms could support respective back and seat bearers. These arms could be set upon a stub pillar or stem fitted to a spider arm base with end castor wheels.

A particular chair action has a back sliding pivot connection to a (rearward and underneath) support frame, and pivot connection between seat (rear edge) and back (bottom edge), with (forward and underneath) frame support for the seat through a movable connection. This supersedes or obviates the need for an arm, or rather arm bracket interconnection of back and seat—such as in the Legget & Platt configuration. Occupant weight upon the seat moves the seat and back-seat pivot connection downwards, taking with it the back. That is the back moves downward in relation to a support frame, along with the seat. Such back movement changes the relative proportions of back depth above and below the back sliding pivot connection. In particular, less back depth lies above the back pivot so reducing the back tilt or recline moment arm or leverage of a seat occupant about the back pivot. The occupant thus experiences back tilt or recline resistance. Less occupant body mass lies above the back pivot. Indeed the overall occupant chair centre of gravity (c of g) sits lower in the chair frame. More occupant effort is required to compensate for the reduced moment arm. A heavier occupant displaces the back and reduces the tilt moment even more. Thus no back tilt advantage is experienced by a heavier over a lighter occupant.

An example of a pivot movable with weight is given in FIGS. 1A and 1B. A movable frame, such as relatively splayed front and rear arms or legs might be used for such a movable seat connection. A splayed support frame example is given in FIGS. 2A and 2B, described later. Alternatively, or additionally, a slide bearer might be employed between seat (front edge) and forward frame element. A counterbalance may be fitted to inhibit chair collapse upon loading. A restorative resilient spring bias may be fitted, both to control the rate of chair action under occupant weight and to promote return upon weight removal. Support frame flex and/or splay may contribute to such resilient spring bias. Thus, for example, seat depression upon occupancy must not lead to overall chair collapse, but must be resisted or countered. This applies to any chair movement or action—including back tilt or recline. Otherwise a movement once started may continue uncontrollably. This is a dynamic stability issue—addressed by chair geometry and inherent c of g disposition.

A hoop or open/closed loop profile support frame profile would lend itself to frame flex and splay. Thus, both a back and/or seat upper frame hoop (say, a ‘U’ profile), with support arm splay freedom, could sit upon an underpinning lower frame hoop (say an inverted ‘U’ profile) with leg splay freedom. The overall chair geometry must pay regard to this. Wider spacing of frame support points with the back and seat upon frame splay could also contribute stability—both fore and aft and side-to-side. Frame base footprint and relative frame and chair footprint are contributory factors. Thus the chair centre of gravity (c of g)—whether occupied or unoccupied and over maximum back tilt or recline and attendant seat slide excursion must remain within the frame footprint to obviate tipping.

Support or capture fittings could themselves feature pre-set or adjustable resistance, such as friction damping, to inhibit undue relative movement, or even inhibit outright collapse, of chair and frame. Generally, the nature and location of frame capture with chair back and seat affects the chair action. Thus which chair element moves about another, or frame capture, determines the nature of action.

A refinement of a simple pivot connection between back and seat is a displaced, offset, dog-leg, ‘L’-profile, elbow or crank arm pivot. That is a pivot offset or displaced from the seat plane. A twin (crank) arm seat frame—that is a generic ‘L’ shape frame with differential arm length or span—could be adopted.

The Applicant recognises considerable scope for variation in base and/or seat frame or arm profile. Thus, even an ‘L’ frame profile, admits variations such polygonal or curved arms, acute or obtuse included angle, asymmetry between arms and seat and back frames, along with pivot or slide pivot interconnection between such frames. A longer arm of an ‘L’ profile seat frame can be set in the seat plane and a shorter arm transverse thereto. A back frame could feature a longer ‘L’ frame arm in the back plane and a shorter arm transverse thereto and orientated towards the shorter arm of the seat frame, to allow inter-connection of back and seat frames by a pivot or slide pivot

The ‘included’ or internal angle between arms can be acute (<90), obtuse (>90) or 90 degrees for orthogonal relative arm orientation. Similarly with a back frame crank arm. That is, a back-seat pivot may also be offset or displaced from the back plane. With opposed or counterpoised ‘L’ profile crank arms respectively in back and seat frames, shorter back and seat frame arms can be orientated respectively backward/upward and rearward/upward. A pivot, set forward of the back and upward of the seat plane, could connect such short frame arms. Alternatively, for a more sophisticated relative back-seat frame articulation, respective short arms could be connected by slide pivots to the longer arms of the other frame.

Effectively, paired juxtaposed back and seat ‘L’ frames could enjoy a variable splay and included throat angle or embrace. Back tilt would be accommodated by shorter back frame arm transition along the longer seat frame arm. At the same time, the shorter seat arm would transition the longer back frame arm. Both transitions could be accommodated by pivot action—that is slide pivot connections at the outboard ends of shorter back and frame arms.

Differential arm spans, such as ‘L’ profiles, are more usable in this context, but equal length or span arms are not precluded for certain specialist applications. A primary back tilt or recline could remain about an intermediate back pivot or slide pivot connection to a rear support frame member. Back and seat frames are not restricted to rectilinear profiles, but curvilinear—either continuous or segmented—forms maybe employed. Curvilinear interacting forms could afford more scope for co-operative, ‘scissor’-action geometry. Thus opposed frames, or rather mutually overlaid or superimposed arms can both intersect or cross-over and slide relative to one another. A combination of rectilinear and curvilinear frames—or indeed frame arms—could be adopted. ‘Effective’ chair pivot action would close or separate back and seat frames, about a point or locus of points out of the seat and back planes. Thus, whilst an occupant trunk might move fore and aft with seat slide, at each point trunk pivot would be in close conformity with chair pivot. This point, path or locus of points, can be contrived closer to an occupant body natural pelvic hip pivot and/or spine vertebrae flex, bend or articulation locus. Shorter (or stub) arm length could be adjusted together or differentially for greater conformity to a target action path or locus.


FIGS. 1A through 2B explore a basic frame assembly with a single pivot connection between back and seat frames in conjunction with a slide pivot back to support frame connection.

FIGS. 4A through 11E explore an offset or crank arm back and seat frame profiles, with multiple slide pivot interconnection.

Consolidation of otherwise distributed pivot and/or slide points is envisaged within a common mechanism—in some variant constructions. A ‘virtual’ pivot could be contrived with such a consolidated mechanism—to replicate the combined action or effect of multiple distributed pivots. The path or locus of movement of this mechanism virtual pivot could be contrived to follow a target path or locus of movement. A target path could be the idealised path of the notional body pivot of a seated chair occupant over a range of back and/or seat tilt. An offset or crank arm pivot linkage could be employed between back and seat to contrive a movement locus or path more complex than that achievable with a simple pivot arc. Moreover, a crank arm pivot could itself be movable—in particular slidable along a seat plane. The seat plane could be horizontal or inclined (upwards from back to front) to promote occupant lean backward. A typical such seat inclination would be some 10 degrees to the horizontal.

FIG. 2A reflects an initial seat inclination. That said, seat inclination could be varied—as reflected in FIG. 2D in reaction to occupant weight. A particular consideration with the present invention is variability of seat inclination with occupant weight—to present a steeper incline for heavier occupant. With a back tilt or recline action coupled to a traveller along the seat plane incline, tilt resistance would increase for steeper seat incline. Thus a weight-responsive seat action would provide back tilt or recline response—and indeed seat incline response—in reaction to seat occupant weight.

Back tilt could be about a fixed or movable pivot, such as a slide pivot. That is the back span above and below a back pivot would vary inversely with back pivot slide. Or rather, the back would slide along in addition to tilting about a back pivot. Back slide arises in both FIGS. 2B and 2D. As reflected in FIGS. 4A and 4B, the lower end of such a tilt-slide back could be coupled by an offset or crank arm pivot linkage to a fixed (non-slidable) or movable (slidable) seat pivot. Another consideration is occupant weight and size (height) or rather to contrive a reaction or response which compensates for or neutralises their effects in the perception of the chair occupant.

Seat and back contours—whether rigid or deformable cushion layer, are another factor in promoting occupant comfort. FIGS. 11A through 11E reflect upholstered back and seat in a chair action. Anthropometric data can be used to generalise human dimensions to reflect statistical proportions of the population—albeit with less emphasis upon extreme variants, absent adjustment provision. Or indeed a bespoke geometry could be contrived for an individual occupant.

Some measure of self-adjustment for weight and/or size is envisaged in certain embodiments of the present invention. Thus variable frame profiles and interconnections could be adopted. A ‘self-setting’ or self-stabilising chair might be contemplated. Such a chair would automatically set itself to suit a particular occupant—by adjustment upon initial occupation and transition over movement range. Occupant perceptions and evaluation of comfort can vary with time and context—both task and environment related.

A twin crank arm frame is suitable for a tilt-slide chair action. That is back tilt causes seat slide. With a movable back pivot the moment arm of the back in relation to the coupled seat is changed (reduced) by seat depression with occupant weight. Commonly, a seat plane is set at a ramp inclination to throw some occupant weight backwards or to promote occupant lean against a back rest. A component of occupant weight applies down the seat ramp, tending to bias the seat backwards. Back tilt then drives seat slide along the ramp, introducing a certain resistance to tilt related to ramp steepness. A balance or accommodation between back tilt and seat slide can thus be achieved, with or without supplementary ‘restorative’ spring bias. In this way, a twin frame is capable of a weight responsive action according to the invention. This assumes the twin frame is carried by some appropriate support frame which contacts and reacts against a ground support.

A ‘triple frame’ elaboration of the basic twin inter-coupled back and seat frames features a carrier or ground frame, in relation to which back and seat frame move and by which the frame assembly is carried—either by a fixed or movable carrier frame mounting. With a fixed carrier frame mounting an initial back tilt angle and range of tilt, along with an initial seat ramp inclination and range of seat slide along that ramp, are pre-determined by frame profile, disposition and inter-coupling. With a movable carrier frame mounting seat ramp angle can change to reflect occupant imposed weight so seat slide is along a different ramp inclination.

The carrier or ground frame represents a form of restraint, containment or reference—but one which allows a weight-responsive action. In particular, a back frame can pivot to allow back tilt and a seat frame can vary in inclination or ramp angle, with back and seat frames coupled so that back tilt ‘drives’ a seat slide up the seat ramp angle, both back tilt and seat slide being in relation to a carrier or ground frame.

As back and seat frames effectively ‘float’ individually and as a mobile pair upon the carrier frame, so their combined pivot describes a path or locus. The pivot location for any instant disposition reflects back and seat frame form and inter-connection and can be determined by geometrical construction, such as by CAD modelling software. The location may lie outside either frame itself as a ‘virtual’ pivot. That is a ‘point in space’. Desirably, the (virtual) pivot is contrived to coincide with the natural body pivot (or skeletal frame) of a seat occupant. Similarly, the path of pivot movement upon back and seat relative articulation follows that of an occupant's body. In this way, an occupant experiences a minimal change in posture upon back tilt or recline. It follows that continual positional adjustment, which typify sitting are accommodated without radical change in occupant position in relation to the back or seat. Occupant movement merely triggers a complementary or reflective back and seat movement. That is the back and seat move in harmony with the occupant.

An ‘L’ profile rectilinear frame with an included angle of some 90 degrees allows a natural transition between back and seat planes, which are generally mutually orthogonal in an upright chair configuration. Back and seat depth and attendant frame span are variable, but an asymmetric ‘L’ frame, with a greater upright than transverse or horizontal span, is suitable for a taller back chair. Back depth can reach an occupant neck and head. Seat depth is sufficient to support occupant thighs, without intrusion upon knee joint articulation.


There now follows a description of some particular embodiments of weight responsive and virtual pivot action chairs according to the invention, by way of example only, with reference to the accompanying diagrammatic and schematic drawings, in which:

NB For ease of illustration, relative frame disposition and changes in disposition may on occasion be exaggerated somewhat for clarity, and in that sense are indicative rather than literal representations.

FIGS. 1A and 1B show principal seat and back chair elements and their pivotal interconnection;

More specifically:

FIG. 1A shows a pivot between rear seat edge and lower back edge, along with a sliding back pivot, set intermediate the back depth—for an unloaded or unoccupied chair with certain back tilt moment arm;

FIG. 1B shows seat shift (depression) upon occupant weight loading and re-disposed back in relation to back pivot in the chair of FIG. 1A;

FIGS. 2A through 2G show fuller implementation of relatively movable chair back and seat of FIGS. 1A and 1B upon an underlying support frame;

More specifically:

FIG. 2A shows an unloaded or unoccupied chair, with a neutral supporting frame splay condition—in this case with upright front and rear frame legs (although slight initial frame leg splay could be adopted to direct onward splay direction);

FIG. 2B shows notional seat (occupant) loading of the chair of FIG. 1A, along with optional back tilt—either or both accommodated by (in this case outward) frame splay;

FIG. 2C shows back tilt for a given seat loading and attendant frame splay for the chair of FIG. 2A;

FIG. 2D shows back tilt for an increased seat (occupant weight) loading to that of FIG. 2C—again with attendant frame splay;

FIGS. 2E through 2G show enlarged detail of variant frame capture fitting options for the chair of FIGS. 2A through 2D;

More specifically:

FIG. 2E shows a slide mount of bearer for a seat front edge;

FIG. 2F shows a seat pivot slide;

FIG. 2G shows a an adjustable clamp action back pivot slide;

FIGS. 3A through 3F show variant back and seat frame configurations for back tilt recline and seat depression upon occupancy;

More specifically:

FIG. 3A depicts a continuous folded front frame profile in which an upright or slightly canted frame leg merges seamlessly into a horizontal or slightly inclined seat frame;

FIG. 3B depicts a variant frame profile with inward canted front and rear frame legs leading to inward frame splay;

FIG. 3C depicts a variant of FIG. 3A with offset or cranked back and seat frames coupled by a pivot set above both back and seat planes;

FIGS. 4A and 4B reflect an offset or crank arm back and seat frame variants of FIGS. 1A and 1B;

More specifically:

FIG. 4A shows in solid line interconnected back and seat frames, with overlying inboard crank arm ends and back tilt recline depicted in broken outline;

FIG. 4B shows the seat of FIG. 4A with relative back and seat articulation;

More particularly, in FIG. 4A, back tilt or recline is accompanied by:

    • slide movement in the seat plane of a back-seat pivot; and
    • pivot (and possibly slide) about a back pivot;

overall this represents a dual pivot, individual or dual slide, or dual slide-pivot action;

FIGS. 5A through 6D show the crank back and seat frame arm chair of FIGS. 4A an 4B with spring bias recovery;

More specifically:

FIGS. 5A and 5B show (coil) spring bias fitted or operative in the seat plane;

FIG. 5A shows a relaxed, neutral or compressed return bias spring with no back tilt or recline;

FIG. 5B shows back tilt or recline with a stretched bias return spring in the seat plane;

FIGS. 5C and 5D show the crank back and seat frame arm chair of FIGS. 4A and 4B with a spring slide return fitted or operable in the back plane;

More specifically:

FIG. 5C shows a relaxed, neutral or stretched return bias spring with no back tilt;

FIG. 5D shows back tilt or recline with stretched bias spring action in the back plane;

FIGS. 6A through 6D depict variant crank arm seat frame configurations and operability;

More specifically:

FIG. 6A depicts an obtuse (ie greater than 90 degree), included angle between relatively longer and shorter (stub) frame arms for both seat and back frames;

FIG. 6B depicts an acute (ie less than 90 degree) included angle between longer and shorter arms of both seat and back frames;

FIG. 6C depicts differential or asymmetric seat and back frames—specifically a back frame with short stub arm and a seat frame with long stub arm;

FIG. 6D depicts symmetry of back and seat frames—both with short stub arms;

FIGS. 7A through 8B reflect emulation of a target chair action by substitute geometry and/or pivot coupling of back and seat;

In particular a chair action using an arm pivot and a seat slide of FIGS. 7A and 7B is substituted by a chair action of FIGS. 8A and 8B using an offset or crank arm pivot between back and seat; FIGS. 7A and 7B reflect a target chair action geometry with a fixed incline seat with slide action, by back tilt or recline and seat slide intercoupling about an arm pivot;

More specifically:

FIG. 7A shows an inter-coupled back and seat with no back tilt or recline;

FIG. 7B shows back tilt or recline in the chair of FIG. 7A;

FIGS. 8A and 8B reflect emulation of the chair action of FIGS. 7A and 7B by means of a crank arm or offset pivot interconnection of the invention set between back and seat;

More specifically:

FIG. 8A shows no or minimal back tilt or recline with a crank arm back-seat interconnection;

FIG. 8B shows marked back tilt or recline of the chair action of FIG. 8A;

FIGS. 9A through 10B reflect a weight responsive tilt or recline chair action variant of FIGS. 8A and 8B, set upon an indicative opposed or counter posed upper and relatively inverted hoop frames. Such hoop frames allow upper and/or lower frame splay options—for resilient back recline and/or seat (occupant) weight response. Stacked hoop frames could be replaced by intersecting ‘S’ frames—in which flex is distributed through upper and lower legs.

FIGS. 9A through 9C depict an overall chair support frame for the crank arm or offset pivot action of FIGS. 8A and 8B;

More specifically:

FIG. 9A shows interconnected crank back and seat frame arms, at a given seat inclination, upon supporting counterpoised hoop frame arms with local pivot slide capture;

A back is in a neutral, non-reclined or default recline condition and seat in a neutral or default inclination—with overlaid respective inboard cranked frame ends;

FIG. 9B shows back tilt or recline for the chair of FIG. 9A with common seat inclination;

FIG. 9C shows chair occupant weight-responsive seat loading of the chair of FIG. 9A—seat depression to a steeper inclination, with unchanged back tilt or recline;

FIGS. 10A and 10B depict back tilt or recline action for the loaded chair of FIG. 9C at a steeper seat plane inclination than the chair of FIGS. 9A and 9B;

More specifically:

FIG. 10A shows steeper seat plane inclination with superimposed occupant weight—at a given back tilt;

FIG. 10B shows back tilt or recline with the steeper seat inclination of FIG. 10A—and back and seat frame inboard crank arm ends separated;

FIG. 10C shows a multi-mode chair variant of FIG. 110A capable of transition from full recline to canted somewhat forward of upright—in this case using superimposed roll over action of upper upon lower frame hoops;

FIGS. 11A through 11E show a sequence from and unoccupied chair with no tilt, followed by relatively lightweight then heavyweight occupant tilt-recline—with weight-responsive seat inclination; as with FIGS. 9A through 10B, back and seat crank arm frames are set upon counterpoised frame hoops;

More specifically:

FIG. 11A shows an unoccupied chair with a given initial seat inclination and no back tilt or recline—along with a comparative indication of steeper seat inclination (but still no back tit) upon occupation;

FIG. 11B shows a relatively lightweight occupant seated with no back tilt or recline beyond the initial reference position of FIG. 11A;

FIG. 11C shows back tilt recline for the chair with relatively lightweight occupant of FIG. 11B;

FIG. 11D shows a relatively heavyweight occupant seated with no back tilt or recline beyond the reference position of FIG. 1A;

FIG. 11E shows back tilt or recline for the relatively heavyweight occupied chair of FIG. 11D;

The following embodiments reflect a development of the basis twin coupled crank arm frame of the preceding embodiments into more elaborate frame assemblies, in particular featuring an intervening carrier or ground frame, in turn mounted upon a chair support frame.

FIGS. 12A through 12F show a tilt-slide chair action embodied in a minimal structure of spaced inter-coupled frames set on each side of a seat and back; this to convey fundamental working principles;

More specifically:

A variable configuration chair features some five inter-coupled frames 111, 113, 114, grouped in two opposed pairs on opposite sides of a common central carrier or ground frame 113. A back panel or (upholstered) squab 112 is secured to corresponding upper arms of an outer-most pair of back frames 111. A seat panel or upholstered squab 115 is secured to an intermediate pair of seat frames 114. An innermost carrier or ground frame 113 is secured to a base or chassis, (such as element 130 in FIG. 22 sequence).

Frames 111, 113, 114 are each configured with arms splayed at right angles or thereabouts and are inter-connected by pivot-slide couplings with respective pivot pins 116, 117, 118, 119, allowing tilt-rotation about a virtual pivot point (such as element 121 in FIG. 13 seq.).

Back frames 111 are coupled by respective sliding-pivots 117, 116 to seat frames 114 and carrier frame 113. Seat frames 114 have sliding pivot connections 117 to back frames 111 and slide pins 118 to carrier frame 113. Carrier frame 113 has sliding pivot connection to back frame 111 and slide pins 118 to seat frames 113.

More specifically:

FIG. 12A shows a front three-quarter perspective view of an indicative chair with a back in a generally upright stance or ‘rest’ position, with inter-coupled back, seat and carrier frames inter-nested within a minimal common side profile. Seat squab 115 is level, or at minimal ramp incline, and back rest squab 112 is almost upright

FIG. 12B shows a translucent or part cut-away side elevation of FIG. 12A revealing locations of pivot-slide connectors 116, 117, 118 and slide connectors 119 which are represented symbolically. Thus bi-directional slide action is represented by opposed linear arrows and bi-directional pivot rotation by opposed arcuate arrows. End or limit of travel is represented by a foreshortened arrow and/or cross-bar. A pair of pivot-slide connectors 116, such as pins and/or rollers, constrain and guide movement between carrier frame 113 and back frames 111. Two pairs of pivot-slide pins 117, 118 guide movement between back frames 111 and seat frames 114. Two slide pins 119 (FIGS. 12E and 12F) guide forward and backward translational movement of seat frame 114 relative to carrier frame 113.

FIG. 12C shows an articulated version of FIG. 12A with back squab 112 somewhat tilted or reclined and relative back and seat frame (111, 114) splay, along with seat squab 115 (forward) linear translational slide. Back frames 111 have rotated backwards and moved forward and down relative to ‘fixed’ common central carrier frame 113, allowing seat frames 114 and seat squab 115 to slide forward along guideways in lower arms of carrier frames 113.

In this variant, carrier frame 113 remains static, being rigidly mounted upon a base (such as 130), pedestal (such as 131) or chassis (such as 135, 136); whilst back and seat frames 111, 113 pivot and/or slide about it. However, carrier frame 113 mobility can be admitted, such as for a weight-responsive action. In either case, carrier frame 113 contacts and so is supported (directly or indirectly) a ground plane, represented by an ‘earth(ing)’ symbol—although the actual point of connection may vary.

FIG. 12D shows a side elevation of FIG. 12C revealing changed pivot-slide locations and relatively splayed or spread frame dispositions for a chair in a back recline or ‘tilt’ position. Frame splay can be seen in greater detail. Small or truncated arrows indicate slide movement of outer and intermediate frames. Small inset curved opposed arrows represent pivot angular rotation. Combined movement is indicated by a combination symbol with rotational arrows set within linear arrows on a common diameter span. A large arcuate arrow represents overall back tilt or recline through a tilt angle between inscribed chain dotted lines. For ease of illustration in FIGS. 12B and 12D carrier frame ‘earthing; or ground plane points are depicted near the transition between frame arms, but can be positioned differently, such as the cantilever offset mounting indicated in FIGS. 12E and 12F by reference to a base pedestal column.

FIGS. 12E shows an underside rear three-quarter view of FIGS. 12A and 12B with chair set in an upright rest position. Attachment of seat panel or squab 115 to inner seat frames 114, and back panel or squab 112 to outer back frames 111 is indicated by cross-hatching. Carrier frame 113 features a mounting aperture 110 to receive a column 131 of a pedestal base. A mounting axis is represented in FIGS. 12E and 12F by a broken line ** through a notional ground plane. Otherwise, any convenient point of attachment to carrier frame 113 may be used for a chair base or chassis. Positioning and action of pivot-slide and slide connectors 116, 117, 118, 119 are depicted symbolically. A T-section back frame 111 profile, allows for slide action between carrier frame 113 and back frame 112.

FIG. 12F shows an underside rear three-quarters view of FIGS. 12C and 12D with chair in a back ‘tilt’ seat forward slide position. Rotation and/or slide to a travel limit stop is indicated by cross-bars on foreshortened arrows,

FIGS. 13A and 13B show key geometry features of the inter-coupled frames of FIGS. 12A through 12F. This geometry is amplified later in FIGS. 26A and 26B. A chair occupant 120 and extended back and seat squabs 133, 134 are included. That is the included frame span or embrace is a lesser proportion of overall chair dimension than say in FIG. 12 seq.

More specifically:

FIG. 13A shows a locus or path of movement of a notional or virtual pivot action point of the inter-coupled frames, for given seat ramp inclination and range of back (rest) tilt angle; this for the chair frame such as of FIG. 12A, with the chair initially set in an upright configuration;

FIG. 13B shows the frame of FIG. 13A moved to an inclined back disposition, with attendant pivot path transition and seat forward slide movement upon back tilt;

Thus FIGS. 13A and 13B reflect occupant operation of the chair by a change in body posture and attendant weight-shift. In FIG. 13A an occupant is seated on chair in an upright ‘rest’ position. The starting seat incline 126, back tilt angle TR, and starting position of the seat front edge are indicated by a start position ‘S’ 123. Rotation and tilt of the chair and its occupant is about a virtual pivot point 121 which itself follows a pivot path 122. This approximates to a point in space in line with an occupant lower lumbar spine and pelvic articulation point. FIG. 13B shows the occupant seated with increased back tilt angle T1, so back squab 112 is now reclined to a backward ‘tilt’ position 128 and seat squab 115 is shifted forward to a position (‘F’) 124.

FIGS. 14A and 14B are paired views which compare ‘rest’ and ‘tilt’ positions of seat frames 114 and back frames 111 respectively, using differential cross-hatch shading for emphasis. Thus in FIG. 14A start and end sequence seat frame 114 is emphasised by cross-hatch shading in the upper and lower illustrations to the left of the page. Similarly, in the upper and lower right-hand pair of illustrations the seat frame 111 is emphasised by cross-hatch shading. Pivot-slide or slide action is represented symbolically by rotational and/or linear arrows.

More specifically:

FIG. 14A allows comparison of the position of the seat frame 114 in chair ‘rest’ and ‘tilt’ mode. Seat frame 114 is tilted and slides up the back frames 111 about pivot-slide 117, and seat squab 115 is moved forward from its ‘rest’ position 123 to its ‘tilt’ position 124.

FIG. 14B depicts the same scenario, this time highlighting the change in position of back frame 111—which moves about pivot-slides 116, 117, allowing back frame 111 to drop down at the rear and move forward and the front, resulting in a increase in the tilt angle of back squab 112.

FIGS. 15A through 15D show the effect of seat frame pivot location upon chair tilt-slide action and in particular the effect of moving seat pivot 117 down back frame 111, so that the corresponding arm of seat frame 114 is fore-shortened. For the same given back and back frame 111 tilt angle, greater seat frame 114 and seat squab 115 travel is achieved.

More specifically:

FIG. 15A shows a reference frame with relatively high set (seat) pivot between outer and inner frames, as in FIG. 12A;

FIG. 15B shows a variant of FIG. 15B with a lower set (seat) pivot point;

FIG. 15C shows articulation of the frame variant of FIG. 15B;

FIG. 15D shows, for the purposes of comparison, corresponding articulation of the original frame variant of FIG. 15A; the common carrier frame remains, but with greater displacement relative to side frames in FIG. 15C;

FIGS. 16A through 16C show the effect of back pivot point location upon chair action; in particular the effect of moving back rest pivot 118 so that back frame 111 lower arm is foreshortened, for greater leverage in relation to a back rest upper arm with greater back tilt for a given seat slide movement.

More specifically:

FIG. 16A shows a reference frame with forward-set back rest pivot between outer (back) and inner (seat) frames, as in FIG. 12A—and indeed FIG. 15A;

FIG. 16B shows a lower back rest pivot 118 relocated rearward in a seat frame 114;

FIG. 16C shows the revised back rest tilt action attendant the relocated forward lower pivot of FIG. 16B;

FIGS. 17A and 17B show a single-sided frame arrangement of paired inter-coupled crank arm frames 111, 114 mounted to one side of a common carrier frame 113;

More specifically:

FIG. 17A shows a three-quarter perspective view of an generally upright chair stance;

FIG. 17B shows a partially reclined chair stance;

FIG. 17C shows a front elevation of the chair of FIGS. 17A and 1B mounted upon a central pedestal 131 through an offset bracket; this bolsters lateral stability and keeps a combined chair and occupant CofG more central.

FIGS. 18A through 18C show the inter-coupled frame chair action incorporated in a diversity of chair configurations, from pedestal to stacking chair;

More specifically:

FIG. 18A shows a pedestal chair with a star base and optional side arms and castor wheels;

FIG. 18B shows a closed flex frame variant in which an external frame couples to opposite ends of a internal carrier frame;

FIG. 18C shows a stacking chair variant of FIG. 18B;

FIGS. 19A through 19D show detail of frame pivot slide coupling;

More specifically:

FIG. 19A shows a rear three-quarter view of a chair in a generally upright stance

FIG. 19B is a local enlargement part-sectional, part cut-away detail, taken along the line B-B′ in FIG. 19A, of a pivot slide coupling between outer back frame 111 and carrier frame 113;

FIG. 19C is a local enlargement part-sectional detail, taken along the line C-C′ in FIG. 19A, of a pivot slide coupling between outer back frame 111 and inner seat frame 114;

FIG. 19D is a local enlargement part-sectional, part cut-away detail, taken along the line D-D′ in FIG. 19A of a pivot slide coupling between inner seat frame 114, outer back frame 111 and carrier frame 113;

FIGS. 20A-20D show incorporation of intercoupled frame modules into upholstered furniture;

FIGS. 20A through 20C show a double-width chair,

More specifically:

FIG. 20A shows a wide-span, inter-coupled frame module configured as a tilt-slide bench assembly; such a arrangement might serve as a basis for public or common area seating;

FIG. 20B shows disposition of the wide span module of FIG. 20A within a two-seater sofa format;

FIG. 20C shows twin, independent, tilt-slide frame modules, set side-by-side for respective seat and back cushion halves, within the profile of a common two-seater sofa format; this might also be used in a exposed bench format, such as of FIG. 20A, and indeed continued by extrapolation through three or more chairs, set side-by-side upon a common chassis, but otherwise independently user-adjustable;

FIG. 20D depicts a motorised individual armchair variant, with back tilt actuation by an electric motor, powered by an external source, and controlled using a remote device;

FIGS. 21A through 21B show a vehicle chair variant with inter-coupled frames, for floor-mounted seat squab upon a ramp slide frame, fitted to runners mounted on a vehicle floor platform, and a tilt recline back rest; the frames extend over minor, albeit critical, parts inboard portions of larger upholstered seat and back squab. Back and seat cushions 133, 134 extend beyond the span beyond internal frame mechanism 111, 113, 114.

More specifically:

FIG. 21A shows a side elevation of a seat in a generally upright stance;

FIG. 21B shows a side elevation of the seat of FIG. 21A in a reclined stance, with rearward back tilt and seat advanced forward;

FIGS. 22A through 22C show bench sealing with multiple independent chairs 160 set side by side in a row upon a common chassis spine tube 130;

More specifically:

FIG. 22A shows a perspective view, with partly translucent detail, of a series of individual chairs 160;

FIG. 22B shows part cut-away side elevation of and individual chair of FIG. 22A with tilt-recline mode depicted in broken line;

FIG. 22C shows adjustable clamp mounting to vary individual chair disposition upon the mounting tube 130;

FIGS. 23A and 23B show an office chair variant set upon a splayed or spider leg pedestal base with a miniaturised variable configuration articulated frame coupling fitted as a hinge between back and seat cantilevered from a support pillar; variable configuration frame arms are foreshortened in relation to cantilevered seat and back cushions 133, 134; a bottom hinge arm is secured to a carrier frame to transmit support loads to ground through the base;

More specifically:

FIG. 23A shows a chair in a generally upright stance;

FIG. 23B shows the chair of FIG. 23A with back (rest) reclined and seat slid forward;

FIGS. 24A-E show a segmented frame variant with an adjustable connector plate or joint piece 143 interposed between respective upper and lower arms of each frame; plate perforations and removable fastenings allow arm ends to be secured in different positions, in order to vary relative arms dispositions, with changes in included angle, arm span and initial back or seat inclination. The arms of each frame could be connected by respective connector plates. Thus a five frame assembly would feature five discrete connector plates. Alternatively, a common connector could be differently coupled to an array of arms. With appropriately configured perforated arms ends, a separate connector could be dispensed with in favour of variable direct connection between arms.

More specifically:

FIG. 24A shows a part cut-way or translucent side elevation of a chair with fragmented upper and lower frames arms in a upright ‘rest’ position. T1 indicates the initial back tit angle and S1 an initial seat incline and slide disposition;

FIG. 24B shows the chair, of 24A in an ‘tilt’ position. T2 represents the additional tilt angle achievable by repositioning connector plate 145;

FIG. 24C shows a chair of with the lower arms a different fixing on the connector plate 145 giving an increased initial seat incline S2;

FIG. 24D gives an upper three-quarter perspective view of the chair of FIGS. 24A-C revealing some five juxtaposed individual connecting plates 145 for respective frames;

FIG. 24E shows a variant of FIG. 24D with a protective—say cushioned, sprung or compressible cover 161 over connector plates 145.

FIGS. 25A and 25B show centre of gravity excursion within a pedestal chair base footprint;

More specifically:

FIG. 25A shows a generally upright chair stance;

FIG. 25B shows the chair of FIG. 26A with a back rest reclined, but C of G remaining within a chair star base splayed leg footprint, as seat forward slide offsets the effect of back rest recline;

The resultant centre of gravity, represented by shading, remains directly over the pedestal or base of the chair, during tilt operation, ensuring safer operation of the chair.

FIGS. 26A and 26B show geometric detail for a variable configuration chair in ‘rest’ and ‘tilt’ positions.

More specifically:

FIG. 26A shows an upright chair stance;

FIG. 26B shows a reclined chair stance;

FIGS. 27A-27D show weight-responsive variable configuration seating—allowing for ‘weight-neutral’ operation;

Mores specifically:

FIG. 27A shows a pedestal style chair with variable seat inclination by a cantilever carrier frame pivot mounting upon a base pedestal; resilient spring restorative action is provided by (compression) coil spring 149 or a torsion spring 148, operative between carrier frame and pedestal 142;

Occupant weight is accommodated by deflection of responsive spring element(s); this steepens the seat inclination 126 creating a greater obstacle to back tilt;

FIG. 27B shows the chair and occupant of FIG. 27A in a ‘tilt’ position;

With an occupant of weight, W1 acting on the chair, a force of F1 is required in order to tilt the back 112 and move the seat 115 forward by M1.

In FIG. 27C an increased weight occupant 147 exerts a larger weight of W2 downwards on the chair of FIG. 27A. The increased force acts upon the hinge and gives a larger initial seat incline of b°;

FIG. 27D sees the increased weight occupant 147 in a ‘tilt’ position; A greater force, F2 is now required in order to move the seat 115 forward due to the increased incline, thus the occupant's increased weight is compensated for.

FIGS. 28A and 28B show a weight-responsive action achieved with a flex frame chair;

More specifically:

FIG. 28A shows a flexible (open or closed) loop frame chair chassis 135, 136 contiguous with a internal carrier frame. Inherent frame resilience replaces a discrete spring 146, 149 of FIG. 27 seq, again with an increased seat incline (b°) upon occupancy.

FIG. 28B shows a chair of FIG. 28A with increased downward force W2 exerted by a heavier weight occupant 147, leading to increased initial seat incline from a° to b°.

FIGS. 29A-29F portray evolution of chair design from simple paired arms, through inter-coupled crank arms, to a triple-frame.

More specifically:

FIG. 29A shows a single frame of intercoupled arms in a ‘rest’ position;

FIG. 29B shows the frame of FIG. 29A in ‘tilt’ position;

FIG. 29C shows dual intercoupled crank arms in a ‘rest’ position;

FIG. 29D shows the dual crank frames of FIG. 29C in a relatively articulated or splayed back ‘tilt’ position.

FIG. 29E shows triple intercoupled frame in a ‘rest’ position.

FIG. 29F shows the triple frame of FIG. 29E in a ‘tilt’ position.

FIGS. 30A through 30D shows chair pivot movement along with (minimal) occupant movement relative to a chair;

More specifically:

FIG. 30A shows a side elevation of an occupied chair in an upright position, along with locus or path of pivot movement upon chair (back) tilt (seat) slide; FIG. 30B is a local enlargement detail of pivot location at an initial fully-upright back position;

FIG. 30C is a local enlargement detail of pivot location at an intermediate recline position;

FIG. 30D is a local enlargement detail of pivot location at a fully reclined position.

Thus, in FIGS. 30B through 30D, an effective or virtual chair pivot starts its range of movement a nominal distance ‘X’ above a seat plane, then transitions forward and upward over a curved path to a distance ‘Y’, a continues forward but less steeply upward in a curved path, culminating in a distance ‘Z’.

A seat occupant moves with chair action, but about a body pivot which the chair pivot is intended to emulate, albeit may not do so precisely.

A lateral component of movement of a (virtual) pivot 121 is shared as an occupant moves forward along with the seat Modest vertical and rotational relative movement components remain. So an occupant experiences only a modest uplift and tipping disturbance relative to the chair.

Referring to the drawings . . .

FIGS. 1A and 1B reflect principal elements of a weight-responsive chair 10 with intercoupled seat 11 and back 12, with a tilt recline facility. A support frame is omitted for clarity, but is explored in later illustrations. Relative articulation of seat 11 and back 12 is accommodated by a pivot joint 14 between lower back and rear seat edges. Pivot 14 could be implemented in side frames (not shown) and/or as a continuous hinge between seat and back planes.

Pivot 14 is desirably closely juxtaposed with an occupant trunk-hip pivot axis. The embodiments explore geometry optimisation to this end. Mannequin (thick/thin) stick figures 40, 50 are used in FIGS. 11A through 11E to reflect this.

Back 12 is carried by a slide pivot 15, which allows variable spacing from back-seat pivot 14. Back pivot 15 is set movably intermediate back top and bottom edges through a slide pivot The distance ‘x’ between back 12 top edge and back pivot 15 represents an available moment arm for an occupant upper torso (at or above waist level up to shoulders, neck, or head, neck—according to back depth) of a seat occupant. The distance between back 12 lower edge—also the action point of back-seat pivot 14 and back pivot 15—represents an available counter moment arm for occupant weight applied to seat 11.

Occupant lean and weight moments thus act in opposition about back pivot 15—with relative effect determined by sliding displacement of back pivot 15 in relation to back 12 top or bottom edges. Although seat proportions and back depths can vary, generally a seat depth is less than back depth.

FIGS. 2A through 2D show a development of FIGS. 1A and 1B with intercoupled seat 11 and back 12 mounted upon a support frame 19, with front leg 31, rear leg 32 and intervening base spar 33. With a tubular or wire hoop construction, symmetrical side frames are linked by cross pieces (not shown). Back pivot 15 sits upon a rear bearer 18 at the upper end of rearward frame leg 22. Forward or leading edge of seat 11 sits upon a front bearer 17 at the upper end of forward frame leg 21. Bearers 17, 18 can vary in construction and in particular merged with pivot and or slide action.

FIGS. 2E through 2G depict variant formats.

FIG. 2G shows an integrated pivot and slide bearer in which a support frame carries an outer pivot mounting and inboard back frame carries an inner pivot mounting. Inner and outer mountings are damped together with pre-set or adjustable clamp compression, to allow seat frame slide in inboard mounting. Back-seat pivot 14 disposition is movable between frame bearers 17, 18. Thus, subject to wider constraints, such as bearers 17, 18 and inherent friction, pivot 14 can move fore and aft and/or up and down in response to occupant weight or weight shift. Were pivot 14 a solid or fixed brace—that is with back and seat mutually constrained in a unitary or integrated structure—residual shared back and seat mobility would rely upon bearers 17, 18.

FIG. 3A shows a variant with front bearers superseded by a continuous frame fold, with any movement reliant upon (resilient) frame flex. So occupant weight shift or displacement of trunk-hip (pivot) axis would still arise in relation to back pivot 15. However trunk-hip pivot would be translated to wholesale back and seat redisposition.

Frame Splay

Reliance may be placed upon modest bending, flex or splay of a supporting seat frame, to accommodate back and/or seat mobility or re-disposition. In principle, either inward or outward frame splay could be used—starting from a neutral upright or slight initial splay to direct onward splay. Splay may be symmetrical or asymmetrical as between forward and rearward legs. That is one frame portion may be deployed for more splay than another—which could in itself contribute some tilt or recline action.

The Applicant envisages frame splay contributing—along with back and seat interconnection and mounting—to overall chair geometry adjustment with occupant seat loading and back tilt or recline. The intention is better to reflect body mus co-skeletal action and promote natural posture and continual posture adjustment for comfort.

For completeness, inward frame splay is reflected in FIG. 3B—albeit is perhaps less readily accommodated than, say, outward splay. Outward frame splay from a neutral upright front and rear stance is reflected in FIGS. 2A through 2D.

FIGS. 2A through 2D depict a folded wire or tube space frame construction with a seat and back set between spaced fore and aft bearers 17, 18. Forward bearer 17 could be a flex or knee joint, or a sliding, possibly spring biassed, coupling. Rear bearer 18 could be a carrier for back pivot 15. A plain-wall, impregnated or self-lubricating sleeve or bush might serve.

Somewhat Implicit in the albeit diagrammatic frame indications of FIGS. 2A through 3B are an upright chair stance, albeit with a back tilt recline facility. A minimal implementation might be, say, a canvas sling seat and back upon a skeletal frame, such as a collapse-fold director chair. If frame splay is foregone, more rigid chair profiles, such as upholstered cushion frame or moulded shells may be substituted for skeletal lattices.

FIGS. 1A and 1B along with FIGS. 4A through 6D are support frame ‘neutral’—in the sense that no specific structure or configuration is indicated. Indeed a similar consideration applies to the seat and back frames themselves. Rather attention is focussed upon back and seat frame geometry, intercoupling and interaction. That is support frame considerations are made subsidiary to chair action. So either fixed or splay frame variants are embraced. A splayed frame could also be adapted to suit a pedestal swivel chair configuration. Thus in FIGS. 9A through 11E an opposed hoop support frame configuration is depicted.

An upper frame hoop 60 carries an intercoupled back and seat and sits (indeterminately) upon a lower relatively inverted frame hoop 70. The form of, and interaction between, upper and lower frame hoops 60, 70 could be adapted for either a recliner or upright pedestal swivel desk chair. For a desk chair, upper frame hoop 60 could merge from spaced seat and back capture points 65, 75 into a pedestal stem or pillar (not shown). Similarly, lower frame hoop 70 could merge from a pedestal mounting, such as a stub collar, to spider legs with outboard castor wheels (not shown).

FIG. 10C depicts a counterpoised upper and lower hoop frame pair mounted for transition between full recline and canted forward from upright disposition.

Seat & Back Frame Profiles

FIG. 4A shows similar back and seat frame ‘L’-shape, offset or crank arm profiles. These are indicative evocations, rather than necessarily literal representations of actual frame sizes or proportions. A forward stub arm 22 of back frame 12 is coupled, by a slide pivot 26, to a longer seat frame arm 23, for linear (slide) translation in the seat plane 20 and pivot about any point in the locus of such slide movement. A rearward stub arm 21 of seat frame 11 is coupled by slide pivot 25 to a longer back frame arm 24, for linear (slide) translation in the back plane 30, and pivot about any point in the locus of such slide movement.

Thus both longer seat and back frame arms 23, 24 and shorter seat and back frame arms 21, 22 are intercoupled by slide pivots 25, 26—between which angular offset and relative displacement of arms 23, 24 and stub arms 21, 22 can arise. In itself, this seat 11 and back 12 intercouple is independent of support frame mounting and location of back pivot 15 and any seat bearer 13. That said, overall chair action reflects an interaction of all couplings, pivots and bearers. In a neutral or unloaded (unoccupied) chair condition, seat and back and frames 11, 12 are depicted as mutually overlaid. This helps illustration and contrast with relative frame movement upon loading. Nevertheless, an initial condition could be with frames relatively displaced.

A modest back frame 12 bit or recline and local separation from seat frame 11 is depicted in broken outline and equates to that shown in FIG. 4B. Relative displacement and separation of seat and back frames 11, 12 is more evident in FIG. 4B—as the back 12 reclines and respective frame arms adopt an angular offset and relative lateral displacement. Such local frame separation around the back-seat juncture could be accommodated by, say, a common upholstered back and seat overlay cover and/or upholstered cushion. Frame separation would more likely arise at the chair sides and could be concealed by modest profile side bolsters—or residual or formative arms, although fully developed arms are not essential. Pivot 25 undergoes linear translation in the back plane 30 through slide pivot action, just as slide pivot 26 transitions along the seat plane.

Restorative Action

The back and seat frame displacement reflected in back tilt or recline transition between FIGS. 1A and 1B, 4A and 4B has not automatic return action upon removal of the tilt force. Such a restorative bias can be provided by springs operative in the seat and/or back planes, as depicted respectively in FIGS. 5A, 5B and 5C, 5D. Thus in FIG. 5B a coil spring 48 set or operative in the seat plane 20 is compressed by back frame stub arm end pivot 26 transition in the seat plane 20 upon back tilt or recline. Spring 48 is in a neutral condition when the back 12 is in the default neutral condition of FIG. 5A.

Similarly, in FIG. 5D a coil spring 49 set or operative in the back plane 30 is compressed upon back tilt or recline from a neutral condition of FIG. 5C. In FIGS. 2A through 3B restorative tilt bias is contributed by resilient frame deflection and splay. Both discrete springs and inherent frame resilience may contribute to restorative action.

Frame Profile

Back and seat frame 11, 12 individual and relative profiles may be varied to achieve different movement action or locus of movement, as explored in FIGS. 6A through 6D. The overall included angle or ‘embrace’ between back and seat frames 11, 12, or rather longer frame arms 23, 24 affects:

    • start and end positions; and
    • rate of positional change
  • of seat-back connections 25, 26.

Obtuse Frame Angle

Obtuse (ie greater than 90 degree) angles 34, 35 between back and seat respective shorter and longer frame arms 21, 23 and 22, 24 is depicted in FIG. 6A.

Acute Frame Angle

Acute (ie less than 90 degree) angles 38, 39 between respective back and seat frame longer and shorter arms 21, 23 and 22, 24 is depicted in FIG. 6B. Asymmetry of back and seat frames is depicted in FIGS. 6C and 6D. In FIG. 6C a seat frame shorter (stub) arm 21 is longer than a corresponding back frame shorter (stub) arm 22. As indicated in broken outline, this creates relatively short seat displacement or throw in the seat plane for a given back tilt. In FIG. 6D a seat frame shorter (stub) arm 21 is shorter than a back frame shorter (stub) arm 22. This creates relatively long seat displacement of throw for a given back tilt. Any or all of frame included angle, frame arm lengths and differentiation or similarity between back and seat frame profiles may be employed.

Variables in geometry affect both back tilt or recline and seat depression under occupancy. Such considerations enable a complex chair action to be contrived from relatively simple elements—by careful attention to frame profiles, interconnection and support. That said, analysis of the combined effect of many variables is far from simple, and parametric computer modelling may be used to shorten the process of determining action of a given structure, or more challenging structure needed for a given action. Chair action can be expressed as locus of movement. Emulation of the locus of movement of a human frame is a prime target.

Chair Action Geometry

Chair Action Geometry is explored in FIGS. 7A through 8B. For demonstration purposes, although the invention allows improved actions, FIGS. 7A and 78 depict a target action, as achieved by the REACT chair of back-seat interconnection through reaction about an arm pivot to achieve seat slide upon back tilt. FIG. 7A depicts a neutral or unloaded back and seat disposition. FIG. 7B depicts back tilt or reline through an acute angle about pivot 44.

Whilst pivot 44 is offset from both back and seat planes 30, 20 and is intended to equate to a body pelvic joint it is in reality a constrained compromise. That is the chair action is reasonable, but could be improved, not least by a simplified mechanism.

FIGS. 8A and 8B show emulation by offset or crank arm intercouple according to the invention—that is a simplified frame structure and interconnection mechanism. FIG. 8A shows a neutral and dose to neutral chair condition. FIG. 8B shows back tilt or recline transition from FIG. 8A

FIGS. 9A and 9B transpose the offset or crank arm back and seat frame configuration of FIGS. 4A and 4B upon opposed upper and lower hoop frames. A rear capture fitting 75 is coincident with a back pivot and a front capture fitting 65 is forward of a pivot slide connection 25, 26 between back 12 and seat 11. FIG. 9B depicts back recline from a neutral chair condition or stance of FIG. 9A, with attendant slide movement of the seat 11 within a front capture fitting 65 of upper frame hoop 60. FIG. 9C depicts seat (notional occupant) loading, to a steeper depressed inclination, without back tilt and attendant seat slide in forward capture fitting 65. This is reproduced in FIG. 10A with emphasis upon depressed steeper seat inclination angle.

FIGS. 10A and 10B depict chair action in loaded depressed steeper seat inclination of FIG. 9C. Thus in FIG. 10B back 12 reclines, whilst seat 11 remains at a constant steeper angle of an initial condition of FIG. 10A Throughout, upper frame hoop 60 carries rear capture fitting 75 at the back pivot and front capture fitting 65 variably along the seat plane 20. With a rear capture fitting 75 coincident with a back pivot slide and a forward capture fitting 65 coincident with a rear pivot slide, the entire back and seat 12, 11 can move as an entity within upper hoop frame 60. Although not emphasised by Illustration, splay of upper frame hoop 60 can vary the relative disposition of front and rear frame capture fittings 65, 75 and thus promote further changes in chair geometry. In addition, upper—and indeed lower—frame hoop splay can impart a resilient cushion action and self-recovery from loaded or tilted to neutral condition.

FIG. 10C depicts a roll over upper and lower hoop frame interaction which allows extreme recline to bed configuration and continuous transition to an upright or slightly canted forward chair configuration. Forward chair cant or lean can prove helpful for VDU viewing and keyboard usage in computer at a desk situations. Transition between extreme positions can be effected by occupant weight shift and trunk lean—optionally using arms and legs as reaction points. Resilient frame flex and supplementary recovery springs can also assist configuration change.

Back, Seat and Support Frame Disposition

It is impractical exhaustively to describe or depict all possible combinations of back, seat and support frame disposition, within the scope of the appended claims, but key chair geometry and action variables include:

    • back disposition
    • back frame profile
    • seat disposition
    • seat frame profile
    • support frame disposition
    • support frame profile
    • frame capture fitting friction

Generally, a mutual sharing or transfer of positional adjustment between elements arises. Continual chair profile variability complements natural body shift not confined to a static pose. It is now recognised in ergodynamics that response to continual occupant posture and weight shift is important for long term occupancy comfort.

Weight-Responsive Tilt Action

Implementation of weight-responsive chair action of the invention admits of variation in tilt action with occupant weight, through position shift of a back in relation to a back pivot. For an inter-coupled back and seat, back shift is transposed to a seat. Thus seat height, or at least seat-back connection height in relation to a supported front end is reduced, with attendant change in seat inclination. With a crank arm or offset pivot connection between back and seat—and suitable support, capture or restraint by an underpinning frame—such a change in seat inclination with occupant weight can impact upon back tilt resistance.

Weight-responsive action can be added to, a variable configuration seat, by allowing for a seat mount inclination variable with occupant weight, by say a movable carrier frame, in particular one which inclines or tilts more with increased occupant weight, say in the manner of FIG. 11 sequence. That is, initial occupancy is weight-responsive, so initial seat inclination is set by a occupant weight. Such weight responsive action can be disabled by adopting (or re-instating) a fixed carrier frame so seat inclination is also fixed.

Frame Splay

The frame itself may contribute to pivot slide action, to achieve a weight-responsive action, by undergoing some modest splay or spread between front and rear uprights respectively to seat and back capture and support fittings. The latter may be slide bearers or pivot slides. A wire, rod or tubular metal or plastics (say composite fibre reinforced) skeletal frame structure lends itself to a certain (end on) stiffness allied to controlled resiliently deformable (lateral) flex and splay under load. Thus the frame self-recovers elastically upon unloading. Such frame resilient flex bias could supplement or substitute for recovery springs.

Some restraint can be incorporated into the frame capture fittings, such as by pivot and/or slide friction. A clamp action with adjustable compression, such as by a screw damp and deformable or spring washer, could curtail combined pivot slide freedom. A smooth and progressive chair action could be promoted by careful attention to linkage geometry and adoption of low friction, self-lubricating bearing surfaces, such as nylon inserts.

Occupant size-responsive seat action is an option alongside or independent of weight. Size and weight may be inter-related and the impact of size is weight, or rather mass, distribution related. Thus location and transition of CoG merits consideration for stability.

FIGS. 12A through 12F develop a variable configuration chair with indirectly coupled (crank) frames, through an intermediate carrier (crank) frame, rather than the direct coupled dual crank arms of FIGS. 4 through 11. The carrier frame supplements the dual crank frames in a triple frame assembly and effectively provides an integral ‘reaction’ mounting reference which can be secured to a chair base or chassis and fixed or movable in a prescribed manner. A particular such carrier frame mobility is one which affords a weight-responsive chair action. That is a chair responsive to occupant imposed weight, to counter the effective of weight, so that a common chair action—or ease of mobility performance—is perceived by occupants of different weight. The qualifier term ‘carrier’ frame is used herein for convenience. An alternative would be ‘ground’ frame. An important point is that back and seat frames move primarily in relation thereto. This, even though the carrier or ground frame may itself be mobile, yet remains in ground contact, as indicated by ground or ‘earthing’ symbol 150,

Generally, frames 111, 113, configured as ‘L’-profile crank arms, are grouped in pairs on opposite sides of a (static or mobile), mid-set, carrier frame (114), itself secured to a seat base, such as a pedestal in the case of an office chair. In a particular construction, one frame of each pair is associated primarily with a back and the other a seat, with the frames inter-coupled and coupled individually to a carrier frame; in the particular example shown, an outer frame is associated with a back and an inner frame with a seat Back and seat frame pairs may be fitted to each side of a common central carrier frame, which is in turn secured either as a fixed or mobile reference to a base chassis resting upon a ground plane. In the case of an office chair, the mounting may be upon a pedestal with a central pillar.

Such a pillar mounting for a pedestal may incorporate an adjustable height strut, possibly with some fluid (say, pneumatic) cushion action. Such a pillar could penetrate a mounting aperture in a carrier frame forward lower arm. For an upholstered armchair, a cast or fabricated bearer frame could be secured to opposite ends of a wide transverse span carrier frame or for individual spaced bearers with a spacer.

Some form of resilience or spring action may be incorporated between frames or between frame and a base or chassis mounting. Thus, say, a frame could feature a base mounting damp to an intervening torsion bar, leaf or compression spring. Moreover, the frame arms themselves could allow some inherent flex, rather as stiff leaf springs. A spring operative between a carrier frame and a base chassis could also serve as the basis for a variable geometry with weight-responsive action. Thus a variable couple or turning moment upon occupant loading of a seat to set a seat ramp angle, against which back tilt would be applied, would provide an occupant weight-proportionate resistance to tilt-slide action. That is a greater occupant mass would provide no advantage in back bit freedom because back tilt requires seat slide up a steeper ramp angle set by that greater mass.

Inner and outer frames may share corresponding profiles, so that they match or overlap for compact superimposition (ie in side elevation) in what is effectively a non-articulated ‘rest’ condition. Otherwise, frames may exhibit a certain symmetry with arms of similar span, or be markedly asymmetric, with arms of quite different span. The crank arms allow differential span of action of pivotal interconnections, along with pivots sliding in tracks inset into the arms.

The arm span, pivot disposition and slide track admit of considerable variation, individually and collectively, as does the included angle between arms; thus, even a superficially simple combination, by pivot-slide inter-couple, of ‘L’ frame profiles, is capable of defining a diversity of predetermined movement action. All this can be achieved with a fixed crank or ‘included’ angle between arms; that said, a variable included angle might be contemplated, say through a quick-release and snap-lock pivot mechanism (not shown). Although a paired frame solution has been explored, more than two frame elements may be linked serially in a chain, in order to bridge between three primary chair elements, namely a seat, a back and a carrier.

Individual frames can be of unitary construction—say by pressing, stamping, casting or forging. Alternatively, a fabricated frame of multiple components can allow variations in overall frame profile by selection from a common component set. Whilst a generally rectilinear profile helps with ease of production, compactness of form and predictability of action, curvilinear or combination flat and curved shapes may be adopted.

An intermediate bracket option is envisaged between respective arms of back and/or seat frames, for ready adjustment of frame span, included angle between frames, and initial seat ramp inclination. A perforated plate to receive fixing bolts could be interposed between respective back and seat frames. Similarly, variations in frame profile could be achieved. An example would be an offset or step. With a multiple split or discrete element or fabricated frame construction resiliently deformable or cushion spring elements could be interposed between rigid elements.

An objective starting point for chair geometry is a target movement, which can be expressed as a pivot point and/or a path (locus) of movement of a notional or virtual pivot point of a back or between a back and seat. In one optimised solution, the virtual pivot point—and its movement—approximate to an idealised natural pivot action of a human frame, taking account of lower spine to pelvic joint. In any event, the (virtual) pivot movement path may be simple, such as a shallow continuous arc, or complex, such as an irregular, even discontinuous, form. A simplified interacting framework geometry can be contrived to replicate that action or path.

Mix ‘n’ Match

In the context of the overall disclosure—and consistent within the scope of the appended claims—and without need for further invention, features described may be variously mixed and matched to suit operational requirements. It is not feasible to show every such permutation or combination of features. This applies in particular to permutations and combinations of arm and support frame profiles. A given chair upper assembly may be fitted to different bases.

Those examples illustrated are indicative, not exhausted. Whilst not every such combination may work with equal effect—variations in useful performance are readily explored without exercise of inventive step. Thus differential arm spans and profiles for individual frames and different frame combinations, with appropriately adjusted pivot or pivot-slide couplings can readily be explored graphically and/or by empirical, trial and error fabrication and adjustment. More elaborate frame profiles, such as zig-zag or re-entrant folded frame forms could be tried, but it is generally desirable to achieve a desired action with minimal frame elaboration in a unitary element, both for ease of fabrication and robustness and certainty of action. That said, perforated bolted plates are useful for evaluating diverse frame formats.


Phrases bracketed—vis { . . . }—alongside claim numbering—are for ease of reference and as such form no part of claim interpretation or scope.

Component List

10 chair

11 seat

12 back

13 seat pivot slide

14 back-seat pivot interconnection

15 back (slide) pivot


17 (front) bearer

18 (rear) bearer

19 support frame

20 seat plane

21 seat frame (shorter) stub arm

22 back frame (shorter) stub arm

23 seat frame (longer) arm

24 back frame (longer) arm

25 seat (shorter) arm—back pivot

26 back (shorter) arm—seat pivot

27 seat slide

28 seat-frame capture fitting

29 frame-back capture fitting

30 back plane

31 front frame leg

32 back frame leg

33 frame base spar

34 (obtuse) seat frame included angle

35 (obtuse) back frame included angle


38 (acute) seat frame included angle

39 (acute) seat frame included angle

40 mannequin (thin)

41 back frame

42 seat frame


44 back-seat arm pivot

45 seat arm


47 back arm

48 seat spring

49 back spring

50 mannequin (thick)

51 seat arm

52 back arm



55 seat frame pivot

56 back frame pivot




60 upper hoop frame

65 front capture fitting

70 lower hoop frame

75 rear capture fitting

‘x’ distance between top of back+back pivot for unoccupied seat

‘b’ displacement of back-seat pivot upon seat occupancy

‘h’ seat height above floor

‘W’ occupant weight

110 aperture

111 back frames (outer)

112 back

113 carrier frame (inner)

114 seat frames (intermediate)

115 seat

116 pivot-sliding pin

117 pivot-sliding pin/seat pivot point

118 pivot-sliding pin/back rest pivot point

119 sliding pin

120 occupant

121 virtual pivot

122 virtual pivot movement

123 seat ‘rest’ position

124 seat ‘tilt’ position

125 seat forward movement

126 seat incline

127 back ‘rest’ position

128 back ‘tilt’ position

129 back incline

130 base

131 pedestal

132 arm rest

133 seat cushion

134 back cushion

135 open chair chassis

136 dosed chair chassis

137 remote (wired) control

138 motor

139 external power source

140 car

141 rotating element for adjustment of ‘rest’ position

142 gas strut

143 connecting plate

144 multiple fixings

145 centre of gravity

146 torsion spring

147 increased weight occupant

148 force due to user weight

149 spring

150 ground support

160 chair

161 covering

170 support axis

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