An oscillation mechanism for chairs includes a support frame, a structure coupled to the support frame to rotate about a first axis, an elastic element interposed between the support frame and the structure and configured to oppose a reaction force to an oscillation of the structure. The reaction force generates a reaction moment acting on the structure with respect to the first axis. An oscillation adjustment system is able to vary the reaction moment with the oscillation being unchanged. The adjustment system includes a pin movably coupled to the structure and a movement system of the pin for varying the distance between the pin and the first axis. The elastic element is directly fastened to the pin so that the reaction force is transmitted to the structure with the application point corresponding to the pin and with direction and orientation unchanged.

A chair has a seat, a backrest, a lift structure, a back supporting structure, and a waist supporting structure. The backrest is deposited behind the seat. The lift structure is deposited on the backrest. The back supporting structure has a bending element and multiple supporting strips. The bending element is connected with the backrest and the lift structure, and is elastic and bendable to deform. The supporting strips are deposited on the bending element at spaced intervals from a top to a bottom of the bending element. The waist supporting structure is deposited in front of the back supporting structure. The waist supporting structure has two pivoting bases and a supporting plate. The pivoting bases are deposited on the seat. The supporting plate is pivoted between the two pivoting bases, abuts the back supporting structure, and selectively abuts the backrest.

A flexible support device for chair back tilting contains: a supporting frame, a seat mounting, and a base. The supporting frame includes a back portion, two peripheral extensions, two rotatable edges, two first coupling orifices, and two second coupling orifices. The seat mounting includes a first fixing portion, a second fixing portion, two connecting fences, two rotatable locating portions, two defining orifices, two joining elements, two slide orifices, and a drive protrusion. The base includes two locating fringes with two first positioning orifices, two second positioning orifices, a holder connected with a first end of a spring, and a second end of the spring is connected with a flexible sheet. The flexible sheet has two peripheral sections. The base further includes two connection segments, and the two connection segments have two openings. Two connectors are configured to accommodate the flexible sheet and have two pegs.

A chair comprises a leaf spring for biasing a seat towards the substantially horizontal position and an adjustment mechanism comprises a front and rear support configured to adjust a force curve of the leaf spring. The front support to enable (a) the front end portion of the leaf spring to deflect upwardly for relieving at least a portion of an increase in a spring reaction force induced by downward movement of the rear support as the seat moves in the rearward tilting direction through a range of rearwardly tilted positions, and (b) the front support to deflect the front end portion of the leaf spring downwardly for restoring at least a portion of a decrease in the spring reaction force induced by upward movement of the rear support as the seat moves in the forward tilting direction through the range of rearward tilted positions.

An adjustable support assembly for use in a chair has a mounting member 602, a support 605 for supporting part of the body of a chair occupant, and a carrier 611 slidably carrying the support 605. The support has a plurality of engagement features 621 and the carrier has an engagement member 615 that is selectively engageable with the engagement features to enable the support to be selectively positioned relative to the carrier at a plurality of positions. A biasing arrangement 607 operatively connects the carrier 611 to the mounting member 603 and forwardly biases the carrier 611 and support 605. The engagement between the engagement member 615 and an engaged engagement feature 621 increases upon application of rearward force to the support.

The chair is of the type with mutually synchronous adjustment between back inclination and seat inclination, namely via a region between a respective zero position of back inclination (R.sub.0) and seat inclination (S.sub.0) and a respective maximum back inclination and seat inclination. The chair has a substructure (1) which is intended for placing on the floor and on which a base (2) is fastened rigidly. A seat support (6) which has a seat region and a back region is connected to the base (2). Furthermore, the chair includes two backrest bows (3) which are deflectable differently with respect to each other and are fastened on one side to the base (2) and on the other side to the back region of the seat support (6). The two backrest bows (3) are coupled independently of each other to the base (2) on a stationary first axis of rotation (D1). The seat region of the seat support (6) is coupled to the base (2) on a stationary second axis of rotation (D2). The two backrest bows (3) are coupled independently of each other to the back region of the seat support (6) on an elastically deformable third axis of rotation (D3). The back region of the seat support (6) is twistable elastically. The seat support is covered with a cover. In the configuration as an office swivel chair, a height-adjustable pneumatic spring (12) on which the base (2) rests in order to adjust the seat support (6) to a height corresponding to a user's needs and in order to configure said seat support (6) to be rotatable about a vertical axis (V) is arranged in the substructure (1).

A tilt control system includes a spring adjuster and compression spring, which may be removed in an unstressed condition. The tilt control system may also include a variable back stop having curved transition surfaces between the stop surfaces. A lumbar compensator may be integrated into a backrest, which may be coupled with a quick release to the base and actuated by sliding engagement with the seat.

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.

A chair control assembly includes a base structure having first and second pivot points spaced from one another, a seat support structure coupled to the first pivot point, a back support structure coupled to the second pivot point and adapted to move between first and second positions, wherein the base structure does not move as the back support structure moves between the first and second positions, and a control link pivotably coupled to the seat support structure for rotation about a third pivot point and pivotably coupled to the back support structure for rotation about a fourth pivot point, wherein the third pivot point is rearward of the fourth pivot point when the back support structure is in the upright position, and the third pivot point moves forward relative to the fourth pivot point as the back support structure moves from the upright to reclined positions.

The invention is based on a mechanism (1) for a chair having a synchro mechanism by means of which a seat surface structure and a backrest structure are moved in a synchronized ratio relative to one another, wherein the mechanism (1) serves to adjust a restoring force of the synchro mechanism to a different body weight of a seat user by changing a working angle of a force accumulator, and the mechanism (1) includes a seat support (8) for the seat surface structure, a bearing yoke (5), the force accumulator unit (2) a backrest support (3) for supporting the backrest structure, and a translational bearing (16), wherein the mechanism (1) has a triangular steering block (21) and the force accumulator unit (2) is connected to the triangular steering block (21), and on a weight adjustment method for an improved dynamic sitting experience on the part of the seat user by means of a mechanism (1) for a chair with a synchro mechanism, in which the position of a first pivot point (31) of the force accumulator unit (2) is shifted by means of the adjuster (11) when the backrest support (3) is in a position (A), and a swivelling motion of the backrest support (3) into a second position (B) is not performed until the first step is completed.