Abstract: A chair system including a main unit and an untethered chair is provided. The main unit includes a wireless transmitter, a subwoofer, an audio stream receiver and a processor. The untethered chair includes a plurality of speakers, a power source and a wireless receiver for receiving a processed audio stream from the main unit.

Abstract: A chair is described herein. The chair includes a first back support coupled to a base of the chair using one or more first support arms. The chair also includes a second back support coupled to the base of the chair using one or more second support arms. The first and second back supports are independently rotatable.

Abstract: A chair system including a main unit and an untethered chair is provided. The main unit includes a wireless transmitter, a subwoofer, an audio stream receiver and a processor. The untethered chair includes a plurality of speakers, a power source and a wireless receiver for receiving a processed audio stream from the main unit.

Abstract: A flat plate based system for securing legs to a chair is provided wherein a chair support has two catches and two leg pieces each have a tab at one end, the tab configured to interact with one of the two catches, each leg piece including an opening through which a tension member passes. Anchor pieces are configured to secure to the tension member such that the tension member pulls the anchor pieces together. The leg pieces each have an edge such that the edges face each other and the tabs interact with the catches and the tension member is positioned in the opening and the anchor pieces and tension member pull the edges together to hold the tabs against the two catches.

Abstract: The invention relates to a backrest for devices driven by means of pedals comprising a holder for fastening to the device and a contact surface for supporting a person operating the device, wherein the contact surface has a base body, on which at least one spherical segment-shaped contact surface, a roller segment-shaped contact surface arranged parallel to the pedals when in use, and/or a contact surface, which can be moved relative to the base body, is arranged. The invention furthermore relates to a saddle comprising a backrest, in the case of which the backrest is arranged in an articulated manner relative to the saddle, preferably so as to lock in place, in order to form an essentially horizontal saddle extension.

Abstract: The present disclosure relates to a vehicle seat frame structure comprising a backrest frame part and a seat cushion frame part. The backrest frame part and the seat cushion frame part are supported by a pivot bearing for being pivoted about a pivot axis. A spring device is biased with the pivoting movement. The spring device is only effective in a comfort inclination angular region. If the backrest frame part is pivoted out of the comfort inclination angular region towards the front, the spring device is released from the force flow between the backrest frame part and the seat cushion frame part. The release is provided by a shaft-hub-connection between a coupling section of a shaft and a hub of a hub body, the shaft-hub-connection comprising an angular clearance.

Abstract: A back support structure includes a frame, a support, a fulcrum member, and an adjustment mechanism. The support includes an upright member having a lower end and an upper end. The lower end of the upright member is connected to the frame at a first location. A support pad is connected to the upper end of the upright member. The fulcrum member has an upper portion and a lower portion. The upper portion is connected to the frame at a second location spaced vertically above the first location. The fulcrum member includes a fulcrum engaging the upright member between the upper and lower ends. The fulcrum member is moveable between a plurality of fulcrum positions. The adjustment mechanism includes an adjustment member connected to the frame and the lower portion of the fulcrum member. The adjustment member is adjustable to move the fulcrum member to the plurality of fulcrum positions.

Abstract: A noise reduction device is used together with a shell which surrounds at least a part of the periphery of reclinable seat. The device includes a plurality of noise microphones, a noise controller, and control speakers. Control speakers output a sound based on a control-sound signal that is generated by the noise controller. Each of noise microphones is accommodated in back wall configuring the shell and is set back from a surface of the back wall.

Abstract: A seat assembly is provided with a seat bottom adapted to mount to a vehicle. The seat assembly further includes a first seat back pivotally attached to the seat bottom defining a recline angle relative to the seat bottom, and a second seat back pivotally attached to the seat bottom proximate to the first seat back defining a recline angle relative to the seat bottom. A pin is pivotally connected to the second seat back, is sized to be received within a latch mechanism on the first seat back, and is operably connected to the second seat back to pivot to a stowed position when the first seat back is pivoted to a recline angle that is less than the second seat back recline angle.

Abstract: An item of seating furniture (100), with backrest (101), seat surface (102), supporting structure and resetting mechanism (200), wherein the backrest (101) and the seat surface (102) are connected to the supporting structure. The backrest (101) is pivotable relative to the supporting structure about a pivot axis from a first position into a second position, and the backrest (101) is connected to the seat surface (102) via connector (103). The connector (103) is designed such that, when the backrest (101) pivots relative to the seat surface, the seat surface (102) is inclined relative to the supporting structure, wherein the resetting mechanism (200) are designed to exert a resetting force on the backrest (101) in the second position, the resetting force is directed in the direction of the first position, wherein the item of seating furniture (100) with setting mechanism (104) which is designed to set the resetting force.

Abstract: A vehicle seat includes a side support structure supporting a body of a seated occupant in a lateral direction of the vehicle seat. The vehicle seat includes a seat pad; a support member that supports the seat pad from a rear face side; and a rear face material provided in an integrally impregnated and hardened state along a rear face shape of the seat pad. The seat pad includes a rear face-side support region. The rear face-side support region is provided with a recessed portion formed such that a region between two points in a circumferential direction of a transverse section is recessed toward a surface, the two points being supported by the support member via the rear face material. The side support structure is formed by a protruding rear face-side support structure in which a rear face of the recessed portion is hardened by the rear face material.

Abstract: A seating furniture product, with a support surface unit which forms a seat part and a backrest connected directly to the seat part, and with a frame, wherein the seat part is connected to the frame by means of a swivel joint allowing a rotation about a swivel axis aligned transversely to the seating furniture product and the backrest is connected to the frame by a fastening point, is characterized in that the distance between the fastening point and the swivel joint can be changed in terms of the vertical direction of the seating furniture product, such that changing this distance is accompanied by a change in the inclination alignment of the seat part.

Abstract: A spring back hinge interconnects a backrest frame to a chair seat frame or is mountable to just the chair base frame, the spring back hinge being optionally fittable with a lever actuated locking assembly and the spring back hinge being fittable on a single side or both sides, alternative back rest frames being fittable to the spring back hinge.

Abstract: A chair comprising: a base structure, a seat fixed to the base structure, a backrest, and a pair of oscillation joints which connect the backrest to the seat or to the base structure so as to allow tilting of the backrest around a transverse axis between a rest position and a backwardly tilted position, wherein each of said oscillation joints comprises: an essentially L-shaped rigid support a rigid lever articulated to the rigid support, and having a first and a second lever arm located on opposite sides with respect to the articulation axis, and an elastic device comprising a telescopic element and a compression spring, wherein the elastic device applies an elastic force between said rigid support and said first lever arm and wherein said second lever arm protrudes outwards from said rigid support and is fixed to a corresponding side edge of the backrest.

Abstract: The adjustment device includes a seat connected to a back by a first rod and an elasticity set. The elasticity has a base connected to the first rod. A pressing rod is connected to the base. A first spring is passed through by the pressing rod and stopped by the base. A pushing block is connected to the pressing rod and the first spring. A rotating rod passes through the seat. Two pressing blocks with a threaded hole are passed by the rotating rod and separately screwed with the rotating rod. Two second springs are passed through by the rotating rod and nipped between the pressing blocks and the edge plates.

Abstract: An adjusting apparatus for a comfort element swingable in relation to a support structure, in particular for an armrest of a vehicle, includes a latching device actuatable by adjusting the comfort element and having a latching arm connected to the comfort element and a latching lever interacting with the latching arm. A swing position of the comfort element is locked by providing a locking lever which is swingably articulated to the latching arm and has an engagement portion which locks the swing position by a spring force, when the engagement portion assumes an engagement position with a locking portion of a locking element that is fixed to the support structure, and the swing position of the comfort element is unlocked by an actuator by which the locking lever is disengageable from the engagement position with the locking element.

Abstract: The present invention provides methods and systems for a fitness device that includes a frame having a horizontal portion and a vertical portion that are hingedly connected, a back engaged to the vertical portion of the frame, a seat engaged to the horizontal portion of the frame, and two pairs of legs extending away from the horizontal portion of the frame for positioning the fitness device on a surface.

Abstract: A spring back hinge interconnects a backrest frame to a chair seat frame or is mountable to just the chair base frame, the spring back hinge being optionally fittable with a lever actuated locking assembly and the spring back hinge being fittable on a single side or both sides, alternative back rest frames being fittable to the spring back hinge.

Abstract: A chair having a fixed support structure including two side uprights, a backrest having two side portions, and a pair of elastic joints connecting said side portions of the backrest to said side uprights, wherein each of said elastic joints comprises: a bushing fixed to a respective side upright, a helical spring having a longitudinal axis, the helical spring having an upper end resting against a front wall of the bushing, a compression member resting against a lower end of the spring, an upper attachment fixed to a corresponding side portion of the backrest, and a rigid connecting rod having an upper end and a lower end.

Abstract: Chair comprising, a base structure bearing a seat, a tilting backrest, and at least one joint which connects the backrest to the base structure and allows a movement of the backrest between a rest position and a backward tilted position under a backwards push applied by the user, wherein said joint comprises a first and a second curved component with a circular profile coupled together in a telescopic manner and fixed to the base structure or to the seat and, respectively, to the backrest.

Abstract: An object of the present invention is to provide a spiral spring assembly that is capable of suppressing lateral force generated in a central shaft. A spiral spring assembly (1) includes a central shaft (2), a spiral spring (3) that is disposed on the periphery of the central shaft (2) and includes an outer end (3a), an inner end (3b), and a spiral portion (3c) that connects the outer end (3a) and the inner end (3b) in a spiral form; an inner end fixing member (4) to which the inner end (3b) is fixed so as to be capable of transmitting torque; and an outer end fixing member (5) to which the outer end (3a) is fixed, and which is capable of moving relative to the inner end fixing member (4) within a predetermined section extending from a first state to a second state. The outer end (3a) is fixed to the outer end fixing member (5) so as to be capable of transmitting torque and suppressing a lateral force that is generated in the central shaft (2) in a predetermined state within the predetermined section.

Abstract: A pivoting mechanism with gross and fine adjustment with a housing, an elongate shaft pivotally retained by the housing, resiliently deformable members retained by the housing, cam members coupled to the shaft wherein the cam members are disposed to deform the resiliently deformable members when the cam members are pivoted, and a locking slide bar for selectively causing the cam members to pivot with the shaft to produce gross adjustments in pivoting resistance. First and second ends of the shaft can act as an output interface for outputting the pivoting resistance exhibited by the shaft to a seat back structure, a seat bottom structure, or some other structure. A threaded rod rotated by a handle can adjust an initial deformation of the first resiliently deformable member for fine pivoting resistance adjustment.

Abstract: A mobile task chair with a control mechanism with adjustment mechanisms and setting indicators. The mobile task chair has a mobile base structure, a control mechanism supported by the base structure, a seat bottom structure supported by the base structure, a seat back structure supported by the base structure, a mechanism for adjusting a physical setting of the mobile task chair, such as the pivoting resistance of the back structure, and a mechanism for providing a visual indication of the pivoting resistance of the mobile task chair.

Abstract: A chair assembly including a first chair structure, a second chair structure, an actuator assembly coupled to the second chair structure to move the second chair structure between the first and second positions, a control input assembly coupled to the first chair structure, and a control link assembly coupling the control input assembly with the actuator assembly to move the second chair structure between first and second positions, and including a first shaft operably coupled to the control link, and rotatable about a second axis that is substantially orthogonal to the first axis and to the first direction, and first and second universal joint assemblies coupling the first shaft member to the second shaft, wherein actuation of the control input moves the second chair structure between the first and second positions.

Abstract: In a vehicle seat that includes a seat cushion, a seatback that is rotatably attached to the seat cushion, and a spring that urges the seatback to a raised upright position from a reclined position in which the seatback is tilted back behind the seat cushion, the spring is spiral shaped, with a center-side end portion that is arranged near the rotational center of the seatback hooked on a seatback-connected member and an outside end portion that is positioned on the outer peripheral side of the spring hooked on a seat cushion-connected member. A shield member that covers the spring is attached to the seat cushion.

Abstract: A vehicle seat spring assembly having an engagement post connected to one of a seat and a seat back. A coil spring includes an internal end and an external end. The external end is operably connected with the engagement post. An arcuate engagement bracket is connected to the other of the seat and the seat back. The engagement bracket includes an elongate slot adapted to operably engage the internal end of the coil spring. The internal end moves between a compression position in contact with a first end of the elongate slot corresponding to a first predetermined position of the seat back relative to the seat. A tension position is in contact with a second end of the elongate slot corresponding to a second predetermined position of the seat back relative to the seat.

Abstract: Chair comprising, a base structure bearing a seat, a tilting backrest, and at least one joint which connects the backrest to the base structure and allows a movement of the backrest between a rest position and a backward tilted position under a backwards push applied by the user, wherein said joint comprises a first and a second curved component with a circular profile coupled together in a telescopic manner and fixed to the base structure or to the seat and, respectively, to the backrest.

Abstract: A multi-section angle adjusting structure for a chair back contains a supporting member axially connected to a base and axially inserted to a sliding groove through a shaft to slide in the sliding groove so that the chair back fixed to the supporting member is adjusted to a desired angle relative to the base. The shaft includes a slidable bar fitted thereon to be connected to a slot of the base. Another end of the slot pushes a toothed block biased against by a first spring which contacts with a stop plate so that the toothed block abuts against an end portion of the slidable bar. The slot includes a positioning structure mounted therein, and the positioning structure includes a toothed seat guided by a guiding line to engage with the toothed block.

Abstract: An apparatus for adjusting the seat back angle, and more particularly an adjuster inclinedly disposed at a lower position of the bottom of the seat back and the rear side of the seat portion, comprising a rotating sleeve, an L-shaped connection body, a large spring, a shift shaft, and a locking device. When the locking device is locked, the seat back is positioned at a desirable inclination angle. When the locking device is unlocked, the shift shaft is axially movable such that the seat back is resiliently supported. Moreover, the compression state of the large spring is adjustable by a to-and-fro rotation of the rotating sleeve. In this way, the operators may adjust the resilience of the seat back 200 according to their own needs for obtaining a greatest sitting comfort.

Abstract: A seat back frame includes: a base frame; a movable frame supported for movement in a frontward-rearward direction with respect to the base frame; and a biasing member biasing the movable frame frontwardly and permitting a rearward movement of the movable frame in response to a load having a given value or more. The base frame has an upper frame section supporting a headrest, and two side frame sections extending in an upward-downward direction on laterally opposite sides of the upper frame section. The movable frame has a back-receiving section located between the side frame sections, and two side support sections on laterally opposite sides of the back-receiving section to project forward from the side frame sections. Front ends of the side support sections are disposed to stop a rear surface of the pad that receives a rearward load from a back of an occupant.

Abstract: A chair is provided that is designed so that the angle of the seat surface portion and the angle of the back surface portion are independent of each other and change, and a user can always take the optimum seated posture. The chair includes a base portion, a first link fixed to a seat and rotatably connected to the base portion, and a second link fixed to a seat back rest and rotatably connected to the first link. The chair also includes a first torque-generating mechanism that generates torque in accordance with the angle of the first link relative to the base portion; and a second torque-generating mechanism that generates torque in accordance with the angle of the second link relative to the first link.

Abstract: An angle-adjusting structure for a backrest of a chair is mounted at a rear side of a butterfly-shaped mounting member of the chair. The angle-adjusting structure includes a main body and a rotating member jointly passed through by a shaft having external teeth. A resilient element is mounted around an end of the shaft. A cover is secured to the main body by threaded fasteners. A pressing member is mounted on the other end of the shaft. By pressing the pressing member inward, the external teeth of the shaft are disengaged from internal teeth of the rotating member, and the rotating member is allowed to rotate freely. When the pressing member is released, the resilient element mounted around the end of the shaft extends outward to re-engage the external teeth of the shaft with the internal teeth of the rotating member, thereby securing the rotating member in place.

Abstract: A chair according to embodiments of the present invention includes a base; a first linkage pivotably coupled to the base, a seat pivotably coupled to the first linkage, a second linkage pivotably coupled to the seat and pivotably coupled to the base, a back comprising a substantially upright portion and an attachment portion, the attachment portion pivotably coupled to the base at a first pivot point, and a third linkage pivotably coupled to the back at a second pivot point and pivotably coupled to the second linkage, wherein the second pivot point is on the attachment portion between the first pivot point and the substantially upright portion.

Abstract: There is provided a link mechanism for a chair that is a link mechanism that is used at a chair, the link mechanism for a chair having: a first link whose one end is connected to a bottom surface of a link that supports a seat surface portion of the chair; a second link whose one end is connected to another end of the first link; a first joint portion rotatably connecting the first link and the second link; a second joint portion provided at another end of the second link; and a first elastic resistance unit imparting elasticity in a rotating direction to the second joint portion.

Abstract: A chair has a coupling mechanism between a seat and a back, which includes a joining member, and a coupling member; the seat has two opposite front and two opposite rear ears on a bottom; the joining member is secured on a supporting tube for the seat, and has two opposite sloping slots on each end, and intermediate adjustment slots; the connecting member has a front fixing hole, and a rear sloping slot; the joining member, the connecting member, and the seat are joined together with a first shaft passed through the front ears and the front sloping slots, with a second shaft passed through the rear ears and all of the rear sloping slots; a third shaft is passed through the adjustment slots and the fixing hole; the connecting member is further pivoted to the joining member at a middle portion; the back is joined to the connecting member.

Abstract: An object of the present invention is to provide a spiral spring assembly that is capable of suppressing lateral force generated in a central shaft. A spiral spring assembly 1 includes a central shaft 2; a spiral spring 3 that is disposed on the periphery of the central shaft 2 and includes an outer end 3a, an inner end 3b, and a spiral portion 3c that connects the outer end 3a and the inner end 3b in a spiral form; an inner end fixing member 4 to which the inner end 3b is fixed so as to be capable of transmitting torque; and an outer end fixing member 5 to which the outer end 3a is fixed, and which is capable of moving relative to the inner end fixing member 4 within a predetermined section extending from a first state to a second state. The outer end 3a is fixed to the outer end fixing member 5 so as to be capable of transmitting torque and suppressing a lateral force that is generated in the central shaft 2 in a predetermined state within the predetermined section.

Abstract: A chair according to embodiments of the present invention includes a base; a first linkage pivotably coupled to the base, a seat pivotably coupled to the first linkage, a second linkage pivotably coupled to the seat and pivotably coupled to the base, a back comprising a substantially upright portion and an attachment portion, the attachment portion pivotably coupled to the base at a first pivot point, and a third linkage pivotably coupled to the back at a second pivot point and pivotably coupled to the second linkage, wherein the second pivot point is on the attachment portion between the first pivot point and the substantially upright portion.

Abstract: An apparatus for adjusting the angle of a seat back of an office chair includes: a supporting base; a seat body mounted on the supporting base; a seat back having a pair of elongated ears symmetrically parallel to each other and disposed at the bottom end of both sides thereof, the elongated ears each being pivotally connected to the rear side of the seat body; and an elastic support element slantly disposed at a lower location between the bottom end of the seat back and the rear end of the seat body. Based upon the above-mentioned configuration, a strong elastic supporting force is provided for the seat back. As a result, the inclination of the seat back can be automatically adjusted when the body of the user leans backward.

Abstract: A backpost for use in wooden dining chair. The backpost unit provides reclining movements for a wooden chair of the type having a stationary frame section within which the backpost unit is secured. The backpost unit consists of an interlocking mechanism with minimum components and requires minimum maintenance and provides a solid and reliable reclining mechanism. The chair enables the user to secure an accurate posture of sitting during eating and also enables the user to enjoy a relaxing posture while sitting on the same dining chair.

Abstract: The invention provides an improvement to a chair which has a tiltable seat carrier (1) and a tiltable backrest (2) on the backrest carrier (5) which are forcibly coupled to one another, and to an individual adjustment of the tilt of the seat carrier (1) in relation to the backrest carrier (5). The improvement consists in the fact that there is provided on the underside of the seat carrier (1) a bearing block (10) having a slideway contour (14) and a vertical slot (13) in which the flange (9) of a lifting element (7) is mounted vertically movably, and the lifting element (7) has a substantially triangular collar (12) which slides on the substantially rectangular slideway contour (14) when the flange (9) moves vertically. This means that the tilt of the seat carrier (1) can be adjusted to be steeper or flatter by turning the lifting element (7), and the limit positions are completely stable. The possibility of automatic unlocking is ruled out.

Abstract: A recliner assembly for a vehicle seat having a seat back movably mounted relative to a seat bottom includes first and second frame members. The first frame member supports the seat back. The second frame member supports the seat bottom. The first frame member is pivotally attached to the second frame member and is movable between an upright position and a storage position. In the upright position, the seat back is in a generally vertical position for supporting an occupant seated on the seat. In the storage position, the seat back is positioned above the seat bottom. A damper is operatively connected between the first and second frame members. The damper dampens the movement of the first frame member relative to the second frame member when the first frame member is pivoted from the upright position to the storage position.

Abstract: A chair adjustable device includes a base with which a seat frame and a backrest frame are respectively and pivotably connected. A positioning mechanism is connected to the base and includes an operation handle which is able to shift a transmission frame and a positioning plate is movably connected to the transmission frame and biased by a spring, so that the positioning plate can be movably engaged with one of notches defined in a positioning member on the seat frame. The seat frame and the backrest frame are connected by a connection member so that the chair can be adjusted its tilt angle by operating the operation handle.

Abstract: A chair is provided with a base 6 fixed at an upper end of a leg pillar 5, a back support unit 13 attached to the base 6 so as to tilt backward, a backrest 3 attached to the back support unit 13, and a spring unit 14 supporting the backward tilt of the back support unit 13. The spring unit 14 is to expand and contract in a back and forth direction when viewed from above and arranged further behind than a tilt supporting point 16a of the back support unit 13. The back support unit 13, the spring unit 14, and the base 6 constitute a kind of link mechanism and the spring unit 14 will expand and contract mainly at the front end, while tilting backward.

Abstract: Cushioning device to cushion a backrest with respect to the seat of a chair or suchlike. The device comprises a first supporting element connected to the backrest, a second supporting element connected to the seat and pinned to the first supporting element, and a spring connected both to the first supporting element and to the second supporting element, to allow a reciprocal elastic oscillation, of a determined amplitude, between the backrest, which can oscillate, and the seat, which remain still. In a wall of the first supporting element a lodging seat is provided to lodge, at least partially, the spring in such a manner that the longitudinal axis of the spring is substantially aligned with respect to the first supporting element.

Abstract: A locking device in an office chair structure of the type with articulation permitting the movement of the adjustable seat and seat back, with a mobile base from which a column rises, which is adjustable in height, and which supports a seat plane and a hinged seat back. The structure of the office chair includes a seat, attached at the front to the corresponding front side of a central support body secured to the top of the adjustable column along the vertical axis; a central support body, which, at the back, keeps in place the lower ends of the two support uprights of the armrests and a seat back connected to the seat, swinging and linked, near to the back part, to the central support body by means of a compression spring; Coaxially to the compression spring, there is a rod, one side of which is integral with the back rest, while the other side is axially mobile with respect to a static connecting body linked to the central support body of the chair.

Abstract: A structure for an office chair with articulation by synchronized movement of the seat and the backrest of the adjustable type includes a swivel type movable base with a height adjustable column supporting a seat surface and a reciprocally hinged backrest. The seat surface is connected frontally by two braces to the corresponding anterior side of a central support body anchored on the top of the adjustable column along the vertical axis. The central support body supports with hinges the lower ends of two arm-rest stanchions provided with a device for the adjustment of the height of the seat and with an locking-unlocking device for the oscillation of the backrest and the chair. The frame of the backrest is hinged along the sides and in correspondence with the posterior part of the seat. A compressed spring is interposed between the central support body and the support frame of the backrest.

Abstract: A ball chair has a seat, a backrest assembly and a ball cushion. The seat has a top face, a passage defined in the top surface of the seat, at least three legs formed on the seat and each leg and a supporting base formed on seat. The backrest assembly mounted on the seat and has a bracket, an angle adjusting device, a locking device and a fixed arm. The bracket has two supporting tabs defined in the bottom of the bracket to abut against the supporting base. The ball cushion is mounted inside the passage in the seat. The ball chair provides functions as adjusting backrest angle and the backrest may be extended for convenient use.

Abstract: A chair comprising a support structure bearing a seat and a backrest, in which the backrest comprises a bearing portion and a connecting portion for connection to the support structure, in which the backrest is tiltable rearwards relative to a resting position under a rearwards thrust applied by the user and elastically returns to the resting position when the rearwards thrust ceases. The rearwards tilting of the backrest is formed in part by an elastic detonation of the bearing portion and in part by a displacement of at least a part of the connecting portion relative to the support structure.

Abstract: A chair comprises a frame, a chair back, and a chair back return device. The chair back is mounted to the frame for pivotable movement away from a home position. The chair back return device is arranged to return the chair back to the home position.

Abstract: A chair having a fixed support structure including two side uprights, a backrest having two side portions, and a pair of elastic joints connecting said side portions of the backrest to said side uprights, wherein each of said elastic joints comprises: a bushing fixed to a respective side upright, a helical spring having a longitudinal axis, the helical spring having an upper end resting against a front wall of the bushing, a compression member resting against a lower end of the spring, an upper attachment fixed to a corresponding side portion of the backrest, and a rigid connecting rod having an upper end and a lower end.