A chair back assembly includes a back shell member including laterally extending top, bottom and side portions cooperating to define an open space therebetween, where a portion of the back shell member is located in a lumbar region, a cover having a first surface and a second surface opposite the first surface, wherein the cover covers at least a portion of the open space, and a back frame assembly operably supporting the back shell member and movable between upright and reclined positions, wherein the back frame assembly causes the back shell to flex in a fore-to-aft direction as the back frame assembly is moved between the upright and reclined positions independent of an external force being exerted on the back shell member, and where the lumbar portion of the back shell member remains spaced from the back frame as the back frame is moved between the upright and reclined positions.

Disclosed is an underframe with an improved structure. The underframe includes an underframe body, an operating handle, a reclining pull rope and a gas spring pull rope, a cushion back-and-forth moving mechanism being installed on the outer side of the underframe body, the operating handle being installed through a left outer wall of the underframe body at a lower end of the cushion back-and-forth moving mechanism, a backrest installed on a rear end of the underframe body through a backrest connecting rod; and a reclining elastic adjusting mechanism is arranged at a front end of an inner wall of the underframe body, a backrest angle adjusting mechanism is arranged at the inner wall of the underframe body on a right side of the reclining elastic adjusting mechanism, a cushion height adjusting mechanism is fixedly connected in the underframe body.

A chair according to the present invention has a reference position P located midway in a front-back direction in a movable range of a seat 2. The chair includes a return force generation mechanism 4 configured to generate a return force in a direction to return the seat 2 moved from the reference position P at least in the front-back direction to the reference position P. The return force generation mechanism 4 includes an elastic member 40 configured to increase the return force in the direction to return the seat to the reference position P as the amount of movement of the seat from the reference position P increases.

An adjustable chair has a seat and a splat. The seat has a lower base, an upper base, a tilt adjusting device, a lower rotating shaft, and an upper rotating shaft. The lower base has an assembling space. The upper base is movably deposited on the lower base. The tilt adjusting device is deposited in the assembling space. The lower rotating shaft is rotatably deposited in the lower base and connected to the tilt adjusting device. The upper rotating shaft is deposited in the upper base. The splat is tiltably connected to the seat and has a backrest unit and two connecting legs. The backrest unit is deposited at a rear side of the seat. The connecting legs are connected to the backrest unit, are connected to the lower rotating shaft, and are pivotally connected to the upper rotating shaft.

A tilt-swivel chair employing a bearing base assembly in communication with connection plate or seat plate of the chair is provided. The tilting mechanism in forward and backward direction is provided by the spring which has a pushing and pulling action and the swiveling action is done along the side axis of the bearing base assembly, and the side axis is a cylindrical shape section with a bushing cap onto which a lever base is equipped and is connected to the connection plate or seat plate. The balance ball feeling is provided with the spring action. A cam and lever mechanism is provided at the base of the side axis in corporation with the base section of the assembly. The cam and lever mechanism provides a smooth swiveling action to the seat and to lock and shut down and take a break.

Disclosed herein is a chair that includes a backrest portion, a seat portion coupled with the backrest portion, a column portion coupled with the seat portion, a linkage coupled with the backrest portion, a leaf spring in direct contact with the linkage, an arc-shaped toothed structure fixed translationally relative to the column portion, and a different toothed structure in contact with the arc-shaped toothed structure. The chair is also configured such that when a weight is applied to the seat portion, a fulcrum point of the leaf spring moves as the different toothed structure moves along the arc-shaped toothed structure to thereby shorten a working length of the leaf spring and provide an increased resistance to tilting of the backrest portion relative to the column portion. A process for assembling the chair and a weight-based tilt-resistance assembly for use with the chair are also described herein.

A multifunctional swivel chair tray includes a main body. The main body is connected with a warping plate through a second rotating shaft. An ascending and descending block penetrates through the second rotating shaft. The ascending and descending block is connected with an ascending and descending driving mechanism. A first adjusting rod penetrates through one side of the main body. The first adjusting rod is connected with a multi-spring grouping adjusting mechanism. A second adjusting rod is arranged on another side of the main body. The second adjusting rod is connected with a gear adjusting mechanism. The warping plate is connected with a base plate through a third rotating shaft. A slide plate is slidably connected onto the base plate. A slide plate locking mechanism is arranged between the base plate and the slide plate.

Disclosed is an underframe with an improved structure. The underframe includes an underframe body, an operating handle, a reclining pull rope and a gas spring pull rope, a cushion back-and-forth moving mechanism being installed on the outer side of the underframe body, the operating handle being installed through a left outer wall of the underframe body at a lower end of the cushion back-and-forth moving mechanism, a backrest installed on a rear end of the underframe body through a backrest connecting rod; and a reclining elastic adjusting mechanism is arranged at a front end of an inner wall of the underframe body, a backrest angle adjusting mechanism is arranged at the inner wall of the underframe body on a right side of the reclining elastic adjusting mechanism, a cushion height adjusting mechanism is fixedly connected in the underframe body.

A seating arrangement includes a base, a seat assembly operably coupled to the base, and a back assembly that includes a substantially rigid back frame including a pair of side portions spaced from one another and extending upward from the base, and a substantially flexible back shell including a front surface and a rear surface opposite the front surface, a plurality of laterally-extending slots that extend between the front surface and the rear surface and that cooperate to define a plurality of laterally-extending ribs therebetween, where a pair of laterally-extending ribs of the plurality of laterally-extending ribs are connected to one another via a vertically-extending rib located at a substantial midpoint across a width of the back shell, and wherein the back shell is coupled to each of the side portions of the back frame at locations above the plurality of laterally-extending slots.

A chair that provides movement side-to-side about a first pivot axis positioned above the seat plane allows the user a wide range of dynamic movement, but does not require constant or excessive action on the part of the user to maintain a desired position. In addition and concurrently thereto, the structure may include a second pivot that is also positioned above the seat plane and that provides forward-and-back movement of the seat. The first and second pivot axes can be engaged synchronously or independently by the user as desired delivering infinite degrees of angles of movement. Said pivot axes are more closely adjacent to the human body pivot joints and axes. The seat and seat back may be joined together to a central spine frame that moves about the second pivot, thereby maintaining the seatback position and seat position relative to each other during forward-and-back movement of the spine along the second pivot. One or more biasing structures may be provided to urge the seat into forward-and-back and side-to-side neutral positions. If desired, the location of this forward-and-back neutral position can be statically adjusted by a user, and at least one of the biasing structures can hold this forward-and-back neutral position at a desired tension level thereby allowing a user to select the amount of force required to move the seat out of this defined forward-and-back neutral position. Moreover, an adjustment structure may be provided that allows for static adjustment of the seatback's position on the spine.