TECHNICAL FIELD

[0001] The present disclosure generally relates to an article of furniture, and more particularly, to a tiltable stool or chair.

BACKGROUND

[0002] Articles of furniture such as stools or chairs which allow a user to rock forward, backward and sideways are generally known. A tiltable stool is typically configured to be used on a generally horizontal surface such as a floor. The stool comprises a top portion providing a seat and a base portion comprising a bottom surface configured to support the stool on the floor.

[0003] An example of a tiltable stool is disclosed in the applicant's U.S. Patent No. 9,894,998 which is hereby incorporated by reference thereto in its entirety.

SUMMARY

[0004] A tiltable stool includes a seat, a base, and a body structure extending between the seat and the base. The base includes at least an inner base element and an outer base element. The outer base element extends outwardly around the inner base element. The body structure is firmly connected to a central portion of the inner base element. The outer base element has an annular upper end extending outwardly around the inner base element and a rotationally symmetrical outwardly convex and inwardly concave body extending from the annular upper end to an annular lower end. The outer base element or the inner base element is resiliently deformable, thereby allowing the body structure to pivot in any direction.

[0005] The inner base element and the outer base element may be connected to each other with a tongue and groove joint. In particular, the outer base element may have an inwardly facing tongue which engaged an outwardly open groove in the inner base element.

[0006] An upper surface of the inner base element and an upper surface of the outer base element may be arranged in a common plane. The upper surface of the inner base element and the upper surface of the outer base element may transition seamlessly into one another. [0007] The inner base element may have an outwardly facing cylindrical support surface which abuts a corresponding inwardly facing cylindrical support surface of the outer base element. The outer base element may have an inwardly facing tongue which engages an outwardly open groove in the inner base element. In this configuration the outwardly facing cylindrical support surface of the inner base element may be arranged above the groove and the inwardly facing cylindrical support surface of the outer base element may be arranged above the tongue.

[0008] The inner base element may be made of an inelastic material and the outer base element may be made of a resiliently deformable material. Alternatively, the inner base element may be made of a resiliently deformable material and the outer base element may be made of an inelastic material. In yet another alternative both the inner base element and the outer base element may be made of resiliently deformable material.

[0009] An adjustment disk may be arranged at a variable height below the inner base element. A maximum tilt angle of the body structure may then be limited by selecting the variable height of the adjustment disk below the inner base element. The body structure may extend through the inner base element and the adjustment disk may comprise an inner thread which engages a corresponding outer thread arranged at a lower end of the body structure. The adjustment disk may be configured to push against the outer base element when a maximum tilt angle of the body structure has been reached.

[0010] The outer base element may have a generally C-shaped cross section. The inner base element may be generally disk-shaped. The inner base element may be made of spring steel and include a plurality of circumferentially distributed slots extending outward away from its central portion.

[0011] The seat of the stool may be pivotally mounted to an upper end of the body structure.

[0012] In another example, a tiltable stool includes a seat, a resiliently deformable inner base element, and a resiliently deformable outer base element extending outwardly around the inner base element. A body structure extends between the seat and the inner base element. The body structure is firmly connected to a central portion of the inner base element. The inner base element and the outer base element each form a spring damper system, allowing the body structure to pivot in any direction by deforming the inner base element and the outer base element. A damping factor of the outer base element is larger than a damping factor of the inner base element.

[0013] In a different configuration, a tiltable stool has a seat, an upper base element, a lower base element, and a body structure extending between the seat and the upper base element. The body structure is firmly connected to a central portion of the upper base element. The lower base element has an annular upper end firmly connected to an annular outer portion of the upper base element. The upper base element is resiliently deformable.

[0014] The lower base element may be a rotationally symmetrical outwardly convex and inwardly concave body extending from the annular upper end to an annular lower end.

[0015] The lower base element and the upper base element may be connected to each other with a tongue and groove joint. In particular, the lower base element may comprise an upwardly facing tongue which engages a downwardly open groove in the upper base element.

[0016] An outer surface of the upper base element and an outer surface of the lower base element may seamlessly transition into one another.

[0017] The upper base element may be made of a resiliently deformable material and the lower base element may be made of an inelastic material. Alternatively, both the upper base element and the lower base element may be made of resiliently deformable material.

[0018] The upper base element may comprise an annular groove. The annular groove may be deeper than it is wide. The annular groove may have an inner side wall and an outer side wall. The inner side wall and the outer side wall may be arranged at an angle towards one another when the tiltable stool is in an upright position. The annular groove may be arranged concentrically around and proximal to the central portion.

[0019] The annular groove may have a generally V-shaped cross-sectional profile with a flat bottom.

[0020] The annular groove may have an inner side wall and an outer side wall.

Upper portions of the inner side wall and the outer side wall may be arranged at a distance from one another when the tiltable stool is in an upright position. The upper portions of the inner side wall and the outer side wall may touch when the tiltable stool is deflected and reaches a maximum tilt angle. [0021] The tiltable stool may include a tilt angle adjustment ring which is axially displaceable along a longitudinal axis of the body structure. The tilt angle adjustment ring may have a lower portion which engages the annular groove at a selectable depth. A maximum tilt angle of the body structure may be limited by selecting the selectable depth of the lower portion of the tilt angle adjustment ring in the annular groove.

[0022] The upper base element of the tiltable stool may include a plurality of concentric and radially spaced annular grooves. The annular grooves have a generally U-shaped cross-sectional profile. The annular grooves may be filled with a

compressible compound.

[0023] The annular grooves may be wider than they are deep.

[0024] The upper base element may be generally disk-shaped.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows a cross section of a first example of a base of a tiltable stool.

[0026] FIG. 2 shows a cross section of a second example of a base of a tiltable stool.

[0027] FIG. 3 shows a cross section of a third example of a base of a tiltable stool.

[0028] FIG. 4 shows a perspective cross section of a fourth example of a base of a tiltable stool.

[0029] FIG. 5 shows a cross section of a fifth example of a base of a tiltable stool.

[0030] FIG. 6 shows a cross section of a sixth example of a base of a tiltable stool.

[0031] FIG. 7 shows a cross section of a seventh example of a base of a tiltable stool in a normal state.

[0032] FIG. 8 shows the base of FIG. 7 in a deflected state.

[0033] FIG. 9 shows a cross section of an eighth example of a base of a tiltable stool in a normal state.

[0034] FIG. 10 shows the base of FIG. 9 in a deflected state.

[0035] FIG. 11 shows a cross section of a stool.

[0036] FIG. 12 is a diagram showing a mechanical spring and damper

configuration.

[0037] FIG. 13 is a cross sectional view of a stool base showing an inner base member with conical lower surface.

[0038] FIG. 14 is a cross sectional view of a stool base showing an inner base member with conical upper surface. [0039] FIGs. 15-17 show a cross sectional profile of a stool base with an annular groove.

[0040] FIGs. 18-20 show a cross sectional profile of a stool base with a plurality of annular grooves.

[0041] FIGs. 21 and 22 show a cross sectional profile of a stool base with a corrugated upper base element.

[0042] FIG. 23 is a partially cut perspective view of the stool base as in FIG. 22.

[0043] FIG. 24 is a partially cut perspective view of the stool base as in FIG. 19.

[0044] FIG. 25 is a cross sectional profile of a stool base with annular grooves and a cover.

[0045] FIG. 26 is a cross sectional profile of a stool base with annular grooves formed in an intermediate part.

[0046] FIG. 27 is a cross sectional profile of a stool base with annular grooves formed in an intermediate part.

[0047] FIG. 28 is a cross sectional profile of a stool base with annular grooves and rollers.

[0048] FIG. 29 is a cross sectional profile of a stool.

DETAILED DESCRIPTION

[0049] Referring to FIGS. 1 and 11, a tiltable stool 1 has a seat 2, a base 3, and an elongated body structure 4 between the base 3 and the seat 2. The stool 1 may comprise a height adjustment mechanism including an adjustment lever 7 to adjust the length of the body structure 4. The body structure 4 may comprise a pillar assembly and defines a vertical axis 5 of the stool 1.

[0050] The base 3 may include an inner base element 20 which is connected to an outer base element 10. The body structure 4 is firmly connected to a central portion 29 of the inner base element 20. The central portion 29 may include a receiving opening for a lower portion of the body structure 4. The outer base element 10 is configured to rest on a floor.

[0051] The outer base element 10 or the inner base element 20 is resiliently deformable. This allows the body structure 4 to pivot in any direction by deforming the resilient element of the base 3. Throughout this specification and the following claims, the coordinating conjunction "or" is not used to express exclusivity. That is, the outer base element or the inner base element being resiliently deformable means that either the outer base element alone is resiliently deformable, that the inner base element alone is resiliently deformable, or that both the outer base element and the inner base element are resiliently deformable.

[0052] When a tilting force is applied to the seat, the seat is moved from a normal position into a dynamic seating position. Typically, the normal position is upright. In the upright position, the vertical axis 5 of the stool 1 is perpendicular to the floor. In response to a tilting force, the resilient element of the base 3 is deformed, and the vertical axis 5 of the stool 1 is tilted by a tilt angle a out of the normal position.

[0053] The outer base element 10 surrounds and is firmly connected to the inner base element 20. In particular, an upper annular end of the outer base element is connected to an outer rim of the inner base element. The inner base element 20 may be connected to the outer base element 10 by a tongue and groove joint. As shown in FIG. 1, the outer base element 10 may include an inwardly facing tongue 11 which engages an outwardly open groove 21 in the rim of the inner base element 20. The tongue-and-groove connection may also use an outwardly facing tongue arranged on the inner base element 20 and an inwardly open groove at the outer base element 10.

[0054] The inner base element 20 and the outer base element 10 preferably transition seamlessly, i.e. smoothly and without gaps, into one another. An upper surface 26 of the inner base element and an upper surface 16 of the outer base element may be arranged in a common plane. The upper surface 26 of the inner base element and the upper surface 16 of the outer base element thereby transition seamlessly into one another.

[0055] The inner base element may have an outwardly facing cylindrical support surface 27 at its outer rim. This outwardly facing cylindrical support surface 27 abuts a corresponding inwardly facing cylindrical support surface 17 of the outer base element. In combination with a tongue and groove joint the outwardly facing cylindrical support surface 27 of the inner base element 20 and the inwardly facing cylindrical support surface 17 of the outer base element 10 are arranged in a plane axially spaced above the tongue 11 and groove 21. The support surfaces 17, 27 are generally vertically oriented.

[0056] The inner base element 20 may be generally disc-shaped having a generally vertically oriented, i.e. cylindrical, outer rim. The outer rim may alternatively have a frustoconical shape, in which case the support surfaces between the inner base element and the outer base element may also be frustoconical. [0057] The desired tiltability of the stool can be achieved in that the inner base element is made of an inelastic material and the outer base element is made of a resiliently deformable material. Within the scope of this specification and the following claims, a material will be considered inelastic if a part made thereof, when the same is subjected to typical forces occurring in a stool, do not lead to a noticeable deformation of the part. An inelastic material may also be referred to as rigid. A material will be considered resiliently deformable, or simply resilient, if a part made thereof, when the same is subjected to typical forces occurring in a stool, does elastically deform and resume its original shape when no longer subjected to the typical forces. Within a stool forces up to 2500 N are typical.

[0058] The desired tiltability can also be achieved by making the inner base element from a resiliently deformable material and the outer base element from an inelastic material. In yet another variation both the inner base element and the outer base element may be made of resiliently deformable material. In that case, the inner base element and the outer base element are preferably made of different materials, and in particular of materials having different hardness.

[0059] The resilient element of the base 3 may be made of thermoplastic

polyurethane (TPU), rubber, thermoplastic polyolefin (TPO), fiberglass enforced polyamide (PA) or fiberglass enforced polyurethane (PU). The selection of material requires a trade-off decision between cost and functionality. Experiments including durability tests have shown, that a thermoplastic polyurethane with 90A Shore hardness provides the required robustness at an affordable price. An outer base element 10 made of softer TPU with 75A Shore hardness would require about twice the amount of material as one made of TPU with 90 A Shore hardness.

[0060] The inelastic element of the base 3 may be made of metal, e.g. aluminum, or steel, or be made of a hard plastic, e.g. a plastic with greater than 100 A Shore hardness.

[0061] Shown in FIG. 1 and 2 is a configuration in which the inner base element 20 is made of a rigid material and the outer base element 10 is made of a resilient material. In this configuration, the shape of the outer base element 10 primarily determines how sitting on the stool feels to a user. The user primarily observes how the stool moves downwardly in response to vertical forces. This characteristic may be expressed as a vertical spring constant of the stool. The user will also observe how easily the stool pivots, i.e. how strongly the stool pushes back against horizontal forces applied to the seat.

[0062] The shape of the outer base element 10 can be defined by several characteristic metrics as illustrated in FIG. 2. Among those characteristic metrics are the height h of the outer base element 10, its thickness t, the diameter D _u of its circular upper end, the diameter Db of its circular lower end, and its maximum diameter Dmax between the upper end and the lower end.

[0063] While experiments have been conducted with parts of certain dimensions, the absolute size of those parts may be scaled, leaving characteristic proportions that have been found to be beneficial:

• Dmax/Du: 1 .2

• D _max /h: 3— 10

• Dmax/Db: 1.05— 2

• t/h: 0.05 - 0.35

[0064] Generally, use of a thicker and software material (e.g. between 75-85A Shore) for the outer base element should be considered for high-end products where comfort and service life of the product are critical. For lower cost models it is desirable to reduce the mass of the outer base member to ideally less than 1 kg, which can be accomplished by using thinner and harder material (e.g. above 90A Shore).

[0065] The outer base element 10 may have a generally C-shaped cross section. As illustrated in FIG. 1, the outer base element 10 may be formed as one piece, but functionally divided into an upper section 12, a center section 13, and a lower section 14. As indicated by dotted lines the upper section 12 may extend from the upper end to a virtual line which cuts the outer surface of the outer base element perpendicularly at a 45° upward angle. The lower section 14 may extend from the lower end to a virtual line which cuts the outer surface of the outer base element perpendicularly at a 45° downward angle.

[0066] A differently shaped outer base element is illustrated in FIG. 5. Here, the lower section 54 of the outer base element is shaped as a generally flat ring. The center section 53 is generally cylindrical having vertical walls. The upper section 52 has a generally rounded circular cross section.

[0067] While the outer base element 10 will preferably be formed as one piece, it may also be formed in two pieces as shown in FIG. 3. For example, the outer base element may consist of an upper outer base element 32 that is joined to a lower outer base element 34 by a joint 35 The upper outer base element 32 and the lower outer base element 34 may be made of different hard materials.

[0068] FIG. 7 and 8 show a configuration in which the outer base element 72 is made of a rigid material which the inner base element 71 is made of a resilient material.

[0069] FIG. 4 shows a configuration in which both the outer base element and the inner base element 40 are made of resilient material. To improve its elasticity the inner base element 40 includes a plurality of circumferentially distributed slots 41 which extend outward away from the central portion. The slots 41 extend diagonally, i.e. with a radial and a circumferential component, from the central portion towards the rim of the inner base element. While diagonal slots have proven to be beneficial, in particular, if the inner base element is not completely flat, radially extending slots without a circumferential component can be used in flat parts.

[0070] It may be desirable to limit the tilt of the stool to a maximum tilt angle and to allow a user to adjust this maximum tilt angle. This can be accomplished by providing an adjustment disk 61 as shown in FIG. 6. The adjustment disk 61 is connected to the lower end of the body structure 4 A central axis of the adjustment disk 61 is concentric with the vertical axis 5 of the stool 1 As the stool 1 tilts, so does the adjustment disk 61

[0071] The adjustment disk 61 is wide, such that an outer rim of the adjustment disk, upon reaching the maximum tilt angle, pushes against an inner surface of the outer base element. The stool 1 can tilt no further than permitted by the height between the outer rim of the adjustment disk 61 and the inner surface of the outer base element underneath.

[0072] The position of the adjustment disk 61 within the base may be adjustable.

For example, a lower portion of the body structure 4 may extend through the inner base element with a threaded end. The threaded end of the body structure may be connected with a threaded central opening of the adjustment disk 61 By rotating the threaded adjustment disk 61 within the base it can thus move up and down as indicated by a lower position 61 in dotted line and an upper position of the adjustment disk 61 shown in solid line in FIG. 6. In the lower position 61 tilt of the stool is significantly limited. Here, the adjustment disk 61 leaves very little space for the stool to tilt until the adjustment disk pushes against the outer base element. [0073] The concept of limiting the maximum tilt angle of the stool by an adjustment disk can also be applied to the configuration with a resilient inner base element 71 and rigid outer base element 72 shown in FIGS. 7 and 8. Such a configuration is shown in FIGS. 9 and 10. Here, the adjustment disk 91 is also provided in a height-adjustable arrangement within the base. However, the maximum tilt of the stool is limited when the adjustment disk 91 pushes against an upper portion of the outer base element. As shown, the maximum tilt of the stool is very limited when the adjustment disk 91 is in an upper position 90, while the maximum pivot angle of the stool is larger when the adjustment disk is in a lower position 92.

[0074] In either configuration, the adjustment disk is arranged within the base at a variable height below the inner base element. A maximum tilt angle of the body structure is limited by selecting the variable height of the adjustment disk below the inner base element.

[0075] The stool shown in FIG. 11 uses the same general structure of an inner base element 20 and an outer base element 10. In this configuration both the inner base element 20 and the outer base element 10 are made of resilient material. The outer base element 10 may be made of a thermoplastic material having a hardness of about 80A-90A Shore. The inner base element 20 is preferably made of spring steel. As shown, the outer base element 10 overlaps the inner base element 20. The inner base element 20 is connected to the outer base element 10 in that the inner base element 20 engages an undercut of the outer base element 10. The relative softness of the outer base element 10, in particular if still warm after molding or if heated, allows sliding the outer base element 10 onto the inner base element 20 by stretching the outer base element 10 and allowing the inner base element 20 to engage the undercut of the outer base element.

[0076] While a force fit connection between the inner base element and the outer base element is preferred for recyclability, the inner base element may also be welded

(e.g. by ultrasonic welding) or glued to the outer base element. The outer base element may also be overmolded onto the inner base element. The inner base element and the outer base element may also be produced by multi -material injection molding.

[0077] Since both the inner base element 20 and the outer base element 10 are resiliently deformable, both deform when the stool is tilted. Surprisingly though, the dynamic response of the inner base element 20 and the outer base element 10 to a sudden lateral movement of the seat 2 can be quite different. Both the inner base element 20 and the outer base element 10 can be considered damped spring systems. The damping factor of the outer base element 10 is significantly larger than the damping factor of the inner base element 20. The different damping factors are attributed to the choice of materials (spring steel vs. thermoplastic) and their relative sizes.

[0078] The different damping characteristics of the inner base element and the outer base element support a desirable use of the stool: The inner base element allows small, high-frequency movements of a user, which stimulates the user's muscular system. The user may constantly make micro-adjustments to her position on the stool while maintain balance, and thereby exercising her muscles. Intentional larger movements of the stool, i.e. larger pivot angles when reaching for a distant object, are possible and supported by deformation of the outer base element. However, such larger movements are significantly more dampened than small and fast movements. This provides a sense of stability to the user and avoids a risk of accidental fall.

[0079] FIG. 11 illustrates this general concept of the base 3 schematically. The body structure 4 can pivot relative to the floor in response to a lateral force F by resiliently deforming the inner base element 20 or the outer base element 10. Each of the base elements is a mechanical spring damper system. The inner base element is preferably underdamped, i.e. its damping ratio is smaller than one. The outer base element is preferably overdamped, i.e. its damping ratio is greater than one. The stool 1 so achieves a dynamic behavior that previously could only be accomplished with pressurized components, but without using any such pressurized components.

[0080] As shown in FIG. 11, the seat 2 may be pivotably mounted to an upper end of the body structure 4. The seat 2 may include an upper seat member 111 which is firmly attached to a lower seat member 112. The connection between the upper seat member 111 and the lower seat member 112 resembles the connection between the inner base element 20 and the outer base element 10. The lower seat member 112 may be made of a resiliently deformable material. The lower seat member 112 may be a radially or diagonally slotted spring steel disk, which may be identical to the inner base element 20. When in use, the seat 2 may move horizontally in any direction while staying in a generally horizontal orientation. That is, while the body structure 4 pivots about the base 3, the seat 2 can pivot in opposite direction relative to the body structure and thereby maintain a generally horizontal orientation. [0081] FIG. 13 shows a configuration of a resiliently deformable inner base element 20 having a frustoconical lower surface 131 which faces a correspondingly shaped conical surface of an adjustment member 132. The adjustment member 132 is height- adjustably attached to the body structure 4. The adjustment member 132 limits how far the inner base element 20 can deform downwardly. Deformation of the inner base element 20 is limited to an adjustment space 133 between the inner base element 20 and the adjustment member 132. The adjustment member is arranged within the outer base element 10 and below the inner base element 20.

[0082] An alternative configuration of an adjustment member 142 is shown in FIG. 14. Here, the resiliently deformable inner base element 20 has a frustoconical upper surface 141 which faces a correspondingly shaped conical surface of an adjustment member 142. In this configuration the upward movement of the inner base element 20 is upwardly limited to a space 143 above the inner base element 20 and below the adjustment member 142. As indicated by dotted lines the position of the adjustment member 142 can be adjusted.

[0083] A differently configured stool is shown in FIG. 15-17. The tiltable stool 1 has a base 3 and an elongated body structure 4 between the base 3 and a seat 2. The base 3 includes an upper base element 150 which is firmly connected to a lower base element 160. The body structure 4 is firmly connected to a central portion 29 of the upper base element 150. The central portion 29 includes a receiving opening for a lower portion of the body structure 4. The lower base element 160 is configured to rest on a floor.

[0084] The upper base element 150 is resiliently deformable. The lower base element 160 may be resiliently deformable and may in particular be the annular elastic base disclosed in the applicant’s U.S. Pat. No. 9,894,998. The lower base element 160 may however be inelastic and may e.g. include roller wheels 281 attached to a rigid support structure 282 as shown in FIG. 28. At least the resiliently deformable upper base element 150 allows the body structure 4 to pivot in any direction. Even more preferably, both the upper base element 150 and the lower base element 160 are resiliently deformable and complement each other with different frequency responses to a deflective force.

[0085] When a tilting force is applied to the seat, the seat is moved from a normal position as illustrated in FIG. 16 into a dynamic seating position as shown in FIG. 15.

Tiltability of the upper base element is enhanced by an annular groove 151 which is arranged concentrically around and proximal to the central portion 29. The annular groove may have a generally V-shaped profile with an inner side wall 153 and an outer side wall 152. Both side walls 152, 153 extend from an upper end of the groove to a bottom 154 of the groove 151. The inner side wall 153 and the outer side wall 152 may be slanted at an angle towards one another. This causes a downwardly diminishing width of the groove. The bottom 154 of the groove may be generally flat.

[0086] The annular groove 151 is relatively deep, i.e. a depth of the groove is greater than a width of the groove. As illustrated, the groove is about three times deeper than it is wide.

[0087] The annular groove 151 allows use of relatively hard materials having a hardness greater than 90 Shore. Elasticity is primarily achieved through the shape of the groove, not the softness of the material used. Use of a relatively hard material is desirable, especially when using TPU which tends to become harder and brittle over time. This is true especially in areas where the TPU is frequently deformed. The structural elasticity afforded by the annular groove provides a longer life than elasticity obtained from use of softer material.

[0088] A tilt angle adjustment ring 170 may be provided. The tilt angle adjustment ring 170 as shown in FIG. 17 is axially displaceable along the longitudinal axis of the body structure 4. For example, a lower portion of the body structure 4 may have an outer thread 171 which meshes with an inner thread 172 of the adjustment ring. The axial position of the adjustment ring 170 can then be selected by rotating the adjustment ring relative to the body structure 4.

[0089] A lower portion 173 of the adjustment ring is configured to engage the annular groove 151 at a selectable depth. In a lowermost position of the adjustment ring 170 the lower portion 173 protrudes completely into and fills the space within the groove 151. Thereby, the deformability of the upper base member 150 in the area of the groove 151 is substantially reduced.

[0090] By raising the adjustment ring, a maximum tilt angle a of the stool can be controlled. The stool can tilt only until the upper end of the outer wall 152 touches the lower portion 173 of the adjustment ring 170.

[0091] The lower base element 160 is arranged entirely below and firmly connected to the upper base element 150. In particular, an upper annular end of the lower base element is connected to an outer end of the upper base element. The upper base element 150 may be connected to the lower base element 160 by a tongue and groove joint. As shown in FIGs. 15-17, the lower base element 160 may include an upwardly facing tongue 161 which engages a downwardly open groove 155 in the outer end of the upper base element 150.

[0092] The upper base element 150 and the lower base element 160 preferably transition seamlessly, i.e. smoothly and without gaps, into one another.

[0093] An alternative configuration of an upper base element 180 is shown in FIGs. 18-20 and FIG. 24. The upper base element 180 has two radially spaced concentric grooves 181,182. This includes an outer groove 181 and an inner groove 182. In the illustrated configuration the grooves 181,182 have a generally U-shaped profile with parallel side walls. The side walls include an outer side wall 183 and a parallel inner side wall 184. The U-shaped profile of the grooves 181,182 allows the body structure 4 to pivot in any direction about a pivot point P. The pivot point P is arranged along a central axis of the upper base element 180 within the base.

[0094] A total width of upper ends of the inner groove 182 and the outer groove 181 determines a maximum tilt angle a of the body structure 4 relative to the base 3. As shown in FIGs. 18 and 19, the maximum tilt angle a is reached when the grooves 181,182 have been fully deformed such that upper ends of their respective inner side walls 184 and outer side walls 183 touch. The maximum tilt angle a is preferably about 10 degrees.

[0095] The width of the grooves 181,182 should be selected to meet pinch test standards and is preferably less than 8 mm or wider than 23 mm. The grooves 181,

182 may be filled with a compressible material 185, for example a rubber compound.

[0096] Alternatively, the grooves 181, 182 may be covered with an annular cover 251 as shown in FIG. 25. The annular cover 251 is made of a compressible material such as a rubber compound or a resiliently deformable foam. The annular cover may have a ring-shaped body 254 which extends from the inner wall of the innermost groove to the outer wall of the outermost groove. Thereby, the ring-shaped body 254 covers upper ends of the grooves 181, 182. Extending downwardly from the ring- shaped body 254 are legs 252, 253 which extend into the grooves 181, 182. The legs 252, 253 may be held in the grooves 181, 182 by a form-fit connection.

[0097] Stiffening ribs 186, 187 may be formed in the upper base element 180 radially outwardly of the grooves 181,182. Thereby, resilient deformation of the upper base element 180 is substantially limited to the area of the grooves 181,182. [0098] Another alternative configuration of an upper base element 210 is shown in FIGs. 21-23. In this configuration, five radially spaced grooves 211-215 are used. The grooves 211-215 are relatively shallow and resemble corrugations. The grooves 211- 215 have a generally sinusoidal profile of alternating ridges and valleys. Relatively shallow here refers to a depth of the grooves being smaller than a width of the grooves. The corrugated profile of the upper base element 210 extends substantially along its entire surface from its center 216 to its radially outer end 217.

[0099] Irrespective of a particular embodiment, the upper base element 150,180,210 is preferably an integrally molded single piece. In combination with a single-piece molded lower base element 160 the base 3 may thus consist essentially of only two parts. This allows for very cost effective manufacturing yet provides a desirable dynamic deformation. The utilization of grooves has proven beneficial to extend the useful life of the base.

[0100] In some configurations, it may be desirable not form the upper base element as a single part, but rather as an assembly of several pieces. One example of such a modular design is shown in FIG. 26. As shown, the body structure 4 of the stool is held in an inner base body 261. The inner base body is connected to an intermediate upper base body 260. The intermediate upper base body 260 is a resiliently deformable molded component. The intermediate upper base body 260 includes annual grooves 181, 182 which allows the body structure 4 to pivot in any direction. The intermediate upper base body 260 may overlap the inner base body 261 and extend to the body structure 4. That is, the inner base body 261 may be covered entirely by the intermediate upper base body 260. The intermediate upper base body 260 may be connected to the inner base body 261 with fasteners 265. An outer upper base body 262 may be arranged around the intermediate upper base body 260. The outer upper base body 262 may be generally disk-shaped and extend radially from the intermediate upper base body 260 at its inner end to a lower base body 263 at its outer end.

[0101] FIG. 27 shows an alternative configuration of an intermediate upper base body 270. As shown, the intermediate upper base body 270 is connected to the inner base body by an inner tongue-and-groove joint 272. The intermediate upper base body 270 is connected to the outer upper base body 275 by an outer tongue-and-groove joint 273. The intermediate upper base body 270 is covered by a cover 271 which reaches above the annular grooves formed in the intermediate upper base body 270. The cover 271 extends from the inner base body 261 to the outer upper base body 275. The cover 271 provides a seamlessly surface which hides the intermediate upper base body 270.

[0102] FIG. 29 shows a stool with a resiliently deformable base having an upper base member 292 which includes a plurality of two or more annual grooves 293. The grooves 293 are configured to deform under lateral load which allows the body structure 4 to pivot relative to the floor. The seat 2 is pivotably mounted to an upper end of the body structure 4. The seat 2 includes an upper seat member 111 which is firmly attached to a lower seat member 112. The lower seat member 112 mirrors the design of the upper base member 292 in that it has a plurality of two or more grooves 294. This allows the seat 2 to pivot relative to the body structure 4. The lower seat member 112 and the upper base member 292 may be so similar that they can be molded from a common tool.

[0103] Desirable configurations of a tiltable stool include: A tiltable stool, comprising: a seat; an inner base element; a body structure extending between the seat and the inner base element, the body structure being firmly connected to a central portion of the inner base element; and an outer base element, the outer base element having an annular upper end extending outwardly around the inner base element and a rotationally symmetrical outwardly convex and inwardly concave body extending from the annular upper end to an annular lower end, wherein the outer base element or the inner base element is resiliently deformable, thereby allowing the body structure to pivot in any direction.

[0104] The tiltable stool as described above, wherein the outer base element and the inner base element are connected to each other with a tongue and groove joint.

[0105] The tiltable stool as described above, wherein the outer base element comprises an inwardly facing tongue which engaged an outwardly open groove in the inner base element.

[0106] The tiltable stool as described above, wherein an upper surface of the inner base element and an upper surface of the outer base element are arranged in a common plane.

[0107] The tiltable stool as described above, wherein an upper surface of the inner base element and an upper surface of the outer base element transition seamlessly into one another. [0108] The tiltable stool as described above, wherein the inner base element comprises an outwardly facing cylindrical support surface which abuts a

corresponding inwardly facing cylindrical support surface of the outer base element.

[0109] The tiltable stool as described above, wherein the outer base element comprises an inwardly facing tongue which engaged an outwardly open groove in the inner base element, and wherein the outwardly facing cylindrical support surface of the inner base element is arranged above the groove and the inwardly facing cylindrical support surface of the outer base element is arranged above the tongue.

[0110] The tiltable stool as described above, wherein the inner base element is made of an inelastic material and the outer base element is made of a resiliently deformable material.

[0111] The tiltable stool as described above, wherein the inner base element is made of a resiliently deformable material and the outer base element is made of an inelastic material.

[0112] The tiltable stool as described above, wherein both the inner base element and the outer base element are made of resiliently deformable material.

[0113] The tiltable stool as described above, further comprising an adjustment disk which is arranged at a variable height below the inner base element.

[0114] The tiltable stool as described above, wherein a maximum tilt angle of the body structure is limited by selecting the variable height of the adjustment disk below the inner base element.

[0115] The tiltable stool as described above, wherein the body structure extends through the inner base element and wherein the adjustment disk comprises an inner thread which engages a corresponding outer thread arranged at a lower end of the body structure.

[0116] The tiltable stool as described above, the adjustment disk is configured to push against the outer base element when a maximum tilt angle of the body structure has been reached.

[0117] The tiltable stool as described above, wherein the outer base element has a generally C-shaped cross section.

[0118] The tiltable stool as described above, wherein the inner base element is generally disk-shaped. [0119] The tiltable stool as described above, wherein the inner base element comprises a plurality of circumferentially distributed slots extending outward away from the central portion.

[0120] The tiltable stool as described above, wherein the seat is pivotally mounted to an upper end of the body structure.

[0121] A tiltable stool, comprising: a seat; a resiliently deformable inner base element; a body structure extending between the seat and the inner base element, the body structure being firmly connected to a central portion of the inner base element; and a resiliently deformable outer base element extending outwardly around the inner base element, wherein the inner base element and the outer base element each form a spring damper system, allowing the body structure to pivot in any direction by deforming the inner base element and the outer base element.

[0122] The tiltable stool as described above, wherein a damping factor of the outer base element is larger than a damping factor of the inner base element.

[0123] Various configurations of a tiltable stool are possible by combining any two or more of the following features: The structure of the lower base element being a rotationally symmetrical outwardly convex and inwardly concave body extending from the annular upper end to an annular lower end. The lower base element and the upper base element being connected to each other with a tongue and groove joint, in particular the lower base element having an upwardly facing tongue which engages a downwardly open groove in the upper base element. A seamless transition of an outer surface of the upper base element and an outer surface of the lower base element. A material selection of the upper base element being made of a resiliently deformable material and the lower base element being made of an inelastic material, or alternatively both the upper base element and the lower base element being made of resiliently deformable material. The upper base element having an annular groove, in particular an annular groove that is deeper than it is wide. The specific structure of the annular groove having an inner side wall and an outer side wall, the inner side wall and the outer side wall being arranged at an angle towards one another when the tiltable stool is in an upright position. The position of the annular groove being arranged concentrically around and proximal to the central portion. The shape of the annular groove having a generally V-shaped cross-sectional profile with a flat bottom.

The limitation of a maximum tilt angle when the upper portions of an inner side wall and outer side wall of an annular groove touch. The use of a tilt angle adjustment ring which is axially displaceable along a longitudinal axis of the body structure in which the tilt angle adjustment ring has a lower portion which engages the annular groove at a selectable depth. A maximum tilt angle of the body structure being limited by selecting the selectable depth of the lower portion of the tilt angle adjustment ring in the annular groove. The upper base element having a plurality of concentric and radially spaced annular grooves, in particular grooves having a generally U-shaped cross-sectional profile. Annular grooves being filled with a compressible compound or covered by a cover. The annular grooves being wider than they are deep. The upper base element being generally disk-shaped.

[0124] One skilled in the art will recognize that various additional configurations can be achieved by adding features not specifically listed above but generally described in this specification.

[0125] Within this specification the words“example” and“exemplary” are used herein to mean serving as an instance or illustration. Any embodiment or design described herein as“example” or“exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word example or exemplary is intended to present concepts in a concrete fashion. As used in this application and the following claims the term“or” is an inclusive“or” rather than an exclusive“or”. That is,“or” means“and/or” unless specified otherwise or clear from context. The articles“a” and“an” as used in this application and the appended claims should generally be construed to mean“one or more” unless specified otherwise or clear from context to be directed to a singular form.