WO2011031767A1

WO2011031767A1 - Device for regulating the tension of a chair back, in particular for chairs

Info

Publication number: WO2011031767A1
Application number: PCT/US2010/048140
Authority: WO
Inventors: Giampietro Tosato; Massimo Costaglia
Original assignee: L & P Property Management Company
Priority date: 2009-09-09
Filing date: 2010-09-08
Publication date: 2011-03-17
Also published as: CN102018383A; CN102018383B; ITTV20090173A1

Abstract

The subject of this application is a device to regulate the tension of a seat back, particularly for chairs, comprising a box-like structure to which are articulated a first support element for a chair and a second support element for a chair back. A knob (6), which can be grasped by the user, is rotatively connected to and protrudes from the first support element for a chair; this knob is connected to means for the selective setting of the position of an arm (17) capable of limiting, through a leaf-spring element (14), the travel of the second support element for a chair back. Finally, means are provided to selectively preload the leaf-spring element.

Description

DEVICE FOR REGULATING THE TENSION OF A CHAIR BACK, IN

PARTICULAR FOR CHAIRS

SPECIFICATION

This application relates to a device for the adjustment of the tension of a back, particularly a back for chairs.

Today, devices are known which are able to predetermine the obtaining of a desired angle between the chair and the back of a chair or small chair.

We know, then, patent DE 4.318.516 Al which illustrates a device to modify the reciprocal positioning between two movable components of a chair, such a device comprising a bolt (2) which engages gear teeth (1) fixed to the body of a chair to lock it in various positions.

The device can be defined as bistable in the sense that it makes it possible to define two distinct stable positions of the bolt.

The movements of the bolt (2) are in fact controlled by a device housed in a container (4), the bolt (2) having fixed to it an arm (7) to which are fixed a pair of pins (8) and (9), offset with respect to each other, a first spring (5) acting between the arm (7) and the container (4), whereas a second spring (6), stronger than the first one, acts between the container (4) and an enlarged head (10) of the pin (9).

The device is actuated by the user exerting a rotation to a lever or cam (3), which presses on the head (10) of the pin (9); such rotation is exerted along an axis perpendicular to that of the pin (9); the lever (3) has a given, but not discrete, length to allow the user to exert, due to the effort exerted to obtain rotation, a sufficient axial thrust on the head (10), this constituting a disadvantage for the resulting spatial arrangement which is imposed by the various elements.

Such a known solution involves many other disadvantages, in addition to the structural complexity of the arrangement and the volume occupied by the individual components, such as the need to act with a given rotational force on the lever to bring out the movements in the desired amount; such a lever is also not easy to actuate, as it has to convert a rotational force exerted on the lever (3) into an axial thrust for the pin (9). Finally, there is possible sticking in the mechanical interaction between the bolt (2) and the gear (lb).

Also known is the patent for Utility Model No. 2251165, filed on July 12, 1991, relating to a swiveling set for chairs with a device locking in various positions which describes a device (21) designed to interact with the lever arm (15) in order to lock or unlock it in various positions, respectively, to allow or not allow changes in the swiveling support (11), and with it the chair elements, with respect to the box body.

The device (21) comprises a knob lever (22) prone to rotating around its own axis, to which is roughly radially connected a rigid rod (23) with one end connected to said lever (22), and a lock element (24) connected to the other end of the rod (23).

The lock element (24) revolves in turn on a vertical axis (25) and is designed to move to and from the lever arm (15) due to the rotation of the knob lever (22).

There exist springs (26, 27) which make the device essentially bistable, in the sense that due to subsequent actuations of the knob lever (22) it is able to insure two corresponding stable positions.

However, the device entails certain disadvantages: above all, it is comprised of a large number of components, variously provided in the seat and interconnected, which make it expensive to manufacture and assemble.

In addition, actuation of the lock element is done by turning the lever, though this transmits the motion by interposing the rigid rod (23), which can release or deform due to the forces exerted on it.

Also the articulation of the lock element (24) contributes to defining additional disadvantages due to possible actuation problems involving both possible seizing or limitations in the efficiency between elements and the force necessary to exert to overcome both the resistance of a spring and the friction between the lever arm (15) and the lock element (24), all the greater friction because the user is seated during operation therefore increasing the connection between the lever arm (15) and the lock element (24).

Also know is Industrial Patent application MI98A000895 filed on April 27, 1919, concerning a support for a swiveling or synchronized chair equipped with a device for locking the chair in a position selected among a plurality of positions.

Such a lock device comprises at least two racks with staggered teeth, only one of said racks being able to engage with the said lock pin in a preselected position. Such a solution also entails disadvantages as the user must act on the operating lever (28) of the rod (22) to be able to change the interaction between the selector (16) on the racks (10) and (11) in such a fashion as to force the racks to lift, disengaging from the lock pin (9).

Such disengagement however can be limited by the fact that the racks are forced to engage the lock pin (9), under such conditions adding the friction between the mechanical components and the user's weight which is applied to the seat, including the back on which the arm (6) is pivoted presenting the lock pin (9).

Further, once the lock pin (9) is released from the racks, the swiveling of the chair is permitted and the new desired tilt must be obtained by the user, with the weight of his body, varying the tilt of the seat and back until a new tooth of the racks engages the lock pin (9) after the user has again moved the knob arm (22) in the initial condition.

Also known is Industrial Patent application MI2005A000751 filed on April 27, 2005, illustrating a mechanism for changing the tilt of the backs of chairs, especially office chairs, in which there are provided means to control the tilt of the back and spring mans to move the back toward the minimum tilt position.

Such means to control the tilt of the back comprise at least an incremental lock block, a step which is able to interfere with an element connected to the back in the course of its tilt movements, there being provided means to move in a number of discrete positions the lock block or the element connected to the back, with which to limit the travel of such an element between the minimum tilt position of the back and an interference position of the element connected to the back with one, preselected, steps of the block.

Such a solution also entails disadvantages in that the support (19) for the back is connected to a lever (18) which, having to move longitudinally to the mechanism (17) is subject to friction or sticking or deformation which could negatively impact its proper functioning; in addition, actuating the lever (18) using the cam (21) is not easy since the cam must have a rotational motion applied to it, which combined with the movement of the lever (18) itself must cause the pin (24) to interact with one of the gears of the fixed block (27), which can lead to further sticking and incorrect positioning.

Again, in the case that a toothed pinion (32) is used, it must interact with the rack (33) to obtain longitudinal movement which makes available one of the steps (34) for the end of the support (30): in this case as well there is friction present between the various surfaces which can make it difficult for the components to move. Also known is Utility Model patent No. 242153 filed on January 8, 1996 with application VE96U000001 in which a device for adjusting the tilt of the seat of chairs and small chairs in general is illustrated, which is characterized by the fact of comprising a bolt (26) belonging to a lock body (24) and fixed to one (2) of the two parts (2, 12) of the seat base, a plurality of holes (22) machined in the other part (12) of the seat base in positions which can be set by the bolt (26) and corresponding to the different reciprocal slants between the two parts (2, 12) of said base, an axial control rod (30) of said bolt (26), an axially bistable device (34) for the control of said rod (30), a pair of preloaded springs (50, 52) mounted between said rod (30) and said bistable device (34) and a knob button (46) for said bistable device (34).

Such a solution also entails many disadvantages: most of all the actuation of the device must be done using a button, which is typically placed near a knob connected below the seat; this button is not easy to operate.

Further, the bolt is placed in a remote location with respect to the button, requiring the presence of the interconnecting rod, housed in a provided sleeve, between the bolt itself and the button to actuate it.

Further, the presence of the sleeve can lead to a less than ideal actuation of the bolt, as when the button is actuated the rod may not move in an optimum fashion inside the sleeve or lead to a deformation of rod thwarting the thrust with respect to the bolt.

Finally, in the known technique referenced above, the adjustment of the positioning of the different components appears to always be discrete and therefore the user may have to choose between two positions which do not correspond precisely to the desired position, but which only approximate it.

Also known in Italian Patent No. 1.306.230 filed on April 27, 1998, which illustrates a tiltable support for swiveling or synchronized chairs, which is provided with a swiveling spring (8) and a device to adjust the force necessary to tilt the set by calibrating the spring (8), which comprises a fixed part in contact with the support, a movable part (10) in contact with the end of the spring (8), at least a first surface (14, 15) tilted with respect to the axis of the spring (8) provided on the fixed part and/or on the movable part, at least one wedge (12) with at least a complementary second tilted surface and linked to the first tilted surface and to a screw (15) or to a similar means to drive said wedge on said first tilted surface. In such a solution, the user must grasp and turn a knob to which the screw (15) is connected, moving in opposite directions two wedges (12) adjust the movement of the movable part (10) by coming together or apart, according to a perpendicular axis, which more or less compresses the spring (8), which in turn interacts with a reaction pin (7) connected to a swiveling arm (6) rigidly connected to a pin (3) fixed to a mounting base (2) for a back.

Although such a solution permits a continuous adjustment of the force applied to the base (2), it fundamentally has the disadvantage of requiring the user to apply a high amount of effort to above all bring together the wedges (12) which load the spring (8), given that it is necessary to overcome the friction which is generated near the four tilted lateral surfaces of the two wedges (12) and the countermolded surfaces of the fixed part (13) and the movable part (10).

Other friction is present due to the presence of the pin (3) which, rigidly connected to the swiveling arm (6) controls the swiveling of the mounting base (2) of the back.

Further, the presence of the swiveling arm (6) increases the size of the device thus increasing its dimensions and weight, the device also being structurally comprised of a large number of components which augment overall production and maintenance costs.

The principal task of the subject of this invention is therefore to solve the technical problems indicated, eliminating the disadvantages of the cited state of the art and therefore to create an invention which makes it possible in a rapid, simple fashion and with reasonable effort to adjust the limits of the travel of the back in a number of positions.

Within the scope of the task set forth above, another important purpose of the invention is to realize a device which makes it possible to adjust, in a quick and easy fashion and according to pre-established conditions, the travel of the back.

Another purpose is to realize an invention that is structurally simple and compact, thus limiting the space it occupies.

A further purpose of the invention is to be able to be assembled quickly and to allow easy maintenance.

Another purpose is to provide an invention which allows the user to be provided with an aid that helps him when he gets up from the seat.

Last but not least of the purposes is to create a device which adds to the previous properties that of providing reasonable production costs and that the invention can be produced with normal known equipment and facilities. The task and the purposes referred to, as well as other which will be stated more clearly below, are achieved by a device to adjust the tension of a back, in particular for a chair, comprising a box-like structure, to which are articulated a first support element for a seat and a second support element for a seat, to which it is rotatively connected and a knob protrudes which can be gripped by the user characterized in that said knob is connected to means for the selective setting of the position of an arm capable of limiting, by a leaf-spring element, the travel of said second support element for a back, means being provided to selectively preload said leaf- spring element.

Additional properties and advantages of the invention will be shown in the detailed description of a specific, non-exclusive, embodiment, shown for illustrative and non exclusive purposes, in the attached figures, in which: Fig. 1 shows the device in a first axonometric view from above; Fig. 2 shows the device in a second axonometric view from below; Fig. 3 shows device in an exploded axonometric view; Figs. 4, 5 and 6 show the device in longitudinal section; Figs. 7, 8 and 9 show a detail of the knob; Fig. 10 shows the knob in an axonometric view; Fig. 11 shows the interconnection of the knob in a partial exploded axonometric view; Fig. 12 shows the means connected to the knob capable of limit the travel of the second support element; Figs. 13 and 14 show the device in an axonometric view in which the first support element for a chair has been omitted; Figs. 15 and 16 show the device in a longitudinal section of the leaf spring; Fig. 17 shows the device in a top axonometric view in which the first support element for a chair has been omitted; Fig. 18 shows a variant.

In the embodiments that follow individual characteristics which are given for specific examples can be interchanges with other different characteristics which exist in other embodiments.

Further, it should be noted that everything is shown to be known during the patent granting process is understood not to be claimed and is the subject of a disclaimer from the claims.

With reference to the previously cited figures, number (101) indicates a device (not shown) to adjust the tension of a back, particularly for chairs, of the type comprising a box-like structure (102).

The box-like structure (102) is divided into an upper first shell (103), comprising a first support element for a chair, not shown, and into a lower second shell (104), to which can be connected a rod of a gas spring, also not shown. Both the first shell (103) and the second shell (104) are provided in a rectangular configuration from whose longitudinal edges there protrude a pair of first wings (105a, 105b) and a pair of second wings (106a, 106b).

Between the pair of first wings (105a, 105b) there are machined close to a rear third wing (107), a pair of first holes (108a, 108b) seats for a first pin (109) to which are rotatively connected, through first screws (110a, 110b) the ends of a part of fourth wings (111a, 111b) of a second support element (112) for a back, not shown, which has, in cross- section, an inverted C configuration and is placed outside said second shell (104).

The fourth wings (111a, 111b) are developed from the side opposed to said third wing (107) close to their terminal end being [which are] connected to provided second pins (113a, 113b) located near first seats (114a, 114b) machined beginning on the upper peripheral edge of said second wings (106a, 106b) of the second shell (104), and passing near a pair of second holes (115) having the same axis and machined on said first wings (105a, 105b) of said first shell (103), so as to define an end of travel for the rocking of said second support element (112) with respect to said second shell (104) and to transmit the motion to the first shell (103).

This motion is permitted with help of a pair of first levers (116a, 116b), whose ends are drilled to rotatively interconnect to a third pin (117) swiveled at the ends near a pair of provided third holes (118a, 118b) machined near the pair of first wings (105a, 105b) of the first shell (103) by/from? the side opposite to the third wing (107) of the second shell (104).

Said third pin (117) is also partially housable near the second seat (119a, 119b) machined beginning from the upper peripheral edge of the second shell (104).

At the other end, the pair of first levers (116a, 116b) is swiveled on a fourth pin (120) swiveled near four holes (121a, 121b) machined near the pair of second wings (106a, 106b) of the second shell (104), in an area facing the third wing (107).

The special geometry of the pair of first levers (116a, 116b) together with the presence of the second pins (113a, 113b) cause the movement of the first shall (103) with the rotating of the second support element (112) for the back.

To comprise the device (101) there is a knob (122) equipped with a first shaft (123) having at the terminal end a preferably circular third seat (124) and whose internal lateral surface has a profile consisting of a number of sequential arches (125) with a longitudinal axis parallel to that of the said first shaft (123). At the terminal end of the first shaft (123) there is limited a plate (126) from which there protrudes, in the direction opposite the knob (122) and according to an axis approximately parallel to that of the first shaft (123), a fifth pin (127) which is thus eccentric with respect to the axis of the first shaft (123).

This fifth shaft (127) is located near a provided first slot (128a) machined close to an end facing the direction of the fourth pin (120), of an arm (129) at the other end swiveled to a sixth pin (130).

The fifth pin (127) also slides guided within a second slot (128b), machined on the second wing (106a) and having an arched configuration with its center located roughly near the fourth hole ( 121 a) .

The sixth pin (130) is also fixed near to prepared fourth seats (131a, 131b) machined near the upper peripheral edge of the second wings (106a, 106b) of the second shell (104) close to the third rear wing (107).

The sixth pin (130) is also swiveled at its ends near the pair of first wings (105a, 105b) of the first shell (103), to which the seat is connectible.

The arm (129) is permitted to assume a number of preset positions; in the specific illustrated embodiment the arm (129) is allowed three preset positions which are machined into the arm, in an intermediate area between the first slot (128a) and the swiveling area of the sixth pin (130), a milling (132) having an essentially rectangular triangular configuration with a cathetus pointed in the direction of the sixth pin (130) and the other in the direction of the bottom of the second shell (104), the hypotenuse thus being adjacent to the first slot (128a) and being machined in the same a number of fifth seats (133a, 133b, 133c), in sequence and configured in a circle.

Near these fifth seats (133a, 133b, 133c) there is a selectively movable seventh pin (134) that is fixed and attached to the second shell (104) and disposed along an axis almost parallel to that of the sixth pin (130) and the first pin (109).

The arm (129) can be made to rotate, with its axis centered in the sixth pin (130), by rotating the knob (122): In fact, the arm is used to limit the travel of the second support element (112) defining preset stable positions.

To obtain this function, the first shaft (123) is axially hollow, being positioned within it, when idle, an eighth pin (135).

To the second wing (106a), there is fixed by one or more screws (147), a selector/switch (136, which can be housed within the third seat (124), which has a diametrical cavity (137), the central part of which is occupied by the eighth pin (135), a seat for a pair of springs (138a, 138b) interacting at their free ends with respective sliders (139a, 139b), which are countermolded and interact selectively with one of the various arches (125) defined inside the third seat (124).

Thanks to the presence of the springs (138a, 138b), a rotation of the knob

(122) corresponds to a play of the sliders (139a, 139b) which. Working between the arches (125) in a ratcheting fashion, it thus permits the rotation of the plate (126) and the fifth pin (127) which, sliding inside the first slot (128a), controls the raising or the lowering of the arm (129).

The device (101) also comprises a leaf-spring element (140), which is used to cause a reaction during the thrust on the back by the user of the chair.

The leaf-spring element (140) is housed inside the box-like structure (102), which is placed between the ninth pin (141) at the ends supported by a pair of shoulders (142a, 142b), and the sixth pin (130) and the tenth pin (143) placed between the pair of second wings (106a, 106b) in an adjacent area, the third pin (117) in the direction of the third wing (107) of the second shell (104).

The device (101) further comprises a second lever (144) able to adjust the preloading intensity of the leaf-spring element (140), the second lever (144), being aligned with the terminal end of said eight pin (135) which protrudes beyond said second wing (106b).

The eighth pin (135) is rotatively connected eccentrically to a cylinder (146) placed facing/opposite and below the ninth pin (141) as well as to the leaf-spring element (140), this cylinder (146) being rotatively supported near a provided cradle (147) fixed to the second shell (104).

In Figures 1 and 17, the first lever (144) is positioned in the condition with the minimum preloading for the leaf- spring element (140), while Figure 14 shows, following a 180° rotation of the second lever (144), the maximum preloading condition for the leaf-spring element (140).

These two conditions are also found in the sections pertaining to Figures 15 and 16, respectively.

The cradle (147) is fixed to the pair of shoulders (142a, 142b) which in turn have a pair of appendices (148a, 148b), pointed from the opposite direction of the third wing 107) of the second shell (104), on each of which a third slot (149) is machined substantially perpendicular to the flat surface (150) of the first shell (103).

The fourth pin (120) is located close to the third slots (149).

Also, the eighth pin (135) is located near a pair of fourth slots (151a, 151b) machined near the shoulders (142a, 142b), these fourth slots being essentially vertical to allow movement of the cradle (147).

Coaxially to the eighth pin (135) there is a second lever (153) capable of controlling, with its rotation, a gear (153) capable of actuating the valve of a gas pump to adjust the height of the seat bottom, not shown.

The invention operates as follows: the second lever (144) allows the adjustment of the intensity of thrust in two distinct and defined positions, while the knob (122) determined the limitation of the play of the back in three or more positions.

During rotation, the second support element (112) transmits motion to the first semi-shell (103) through the second pins (113b) with the aid of the pair of first levers (116a, 116b).

On the other hand, the leaf- spring element (140) causes a reaction during the thrust on the back by the user of the chair.

The advantage of this system is a reduction in the size and costs of the system compared to traditional steel helical springs.

The leaf- spring element (140), being placed between the ninth pin (141) on the one side and the sixth and the tenth pin (130, 143) on the opposite side, acts in such a way when the user pushes against the back of the seat that the second rotation element (112) rotates, which sets in motion the first semi-shell (103), which in turn moves upward the third and sixth pin (117, 130) connected to it.

The movement of the third and sixth pin (117, 130) is opposed by the non- movement of the ninth pin (141), which holds the leaf- spring element (140).

Alternatively, the leaf-spring element (140) is placed between the ninth pin (141) and only the third and sixth pins (117, 130).

The effect on the leaf-spring element (140) is a arched deformation which causes a reaction thrust on the third and sixth pins (117, 130), resulting in a thrust which causes balancing of the thrust on the user' s back creating a correct balance during the travel of the mechanism. The invention makes it possible to limit the travel via the arm (129), which is able to firmly maintain three or more preselected positions.

Basically, the invention is provided with a special geometry which causes a counterthrust against the back proportionate to the user' s weight.

The thrust on the back is in fact essentially provided by two factors and that is by the force exerted by the leaf- spring element (14) and by the reaction of the device to the user's weight.

Essentially, when the user pushes on the back to relax his back thanks for the system of fulcrums and levers the seat support moves upward; so when the user lifts his body there is an additional push on the back proportionate to his weight.

The component give by the leaf-spring element (140) is therefore constant, while the reaction generated by the weight is individual.

In practice it has been shown how the invention achieves its task and the purposes described above having obtained a device which makes it possible to achieve and adjust in a rapid and simple fashion and with modest effort, the limiting of the travel of the back in a number of positions; the invention is structurally simple and compact, thus limiting the space it occupies and thus permitting it to be assembled quickly and to allow easy maintenance.

The invention also allows the user to achieve an accommodation which helps him when he rises from the chair. Of course, the materials used as well as the dimensions of the individual components of the invention may be more relevant depending on specific needs. The different means to achieve different functions certainly do not have to coexist only in the embodiment shown, instead they can be present in many embodiments, also not shown. The characteristics indicated as advantageous, opportune or similar, can also be absent or be replaced by equivalent characteristics.

Thus, for example, as shown in Figure 18, the sixth pin (130) can be located at the adjacent ends of said pair of second wings (106a, 106b), on a provided pair of four slots (148a, 148b) machined near an appendix (149a, 149b) protruding toward said first upper shell (103); this solution makes the device more reliable in that it distributes the effort in the end travel phase of the second support element (102).

Claims

CLAIMS What is claimed is:

1. A device that is mountable to a seat bottom and that is usable to control movement of a seat back, the device comprising: an upper shell (103) that attaches to the seat bottom; a lower shell (104) that attaches underneath the upper shell, thereby forming a space therebetween; a seat-back support element (112) positioned toward rear portions of the upper shell and the lower shell, the seat-back support element pivotally connected to the lower shell by a first fastener (110b) that functions as a fulcrum and rotatably coupled to the upper shell by a second fastener (113b), such that, when the seat-back support element pivots on the first fastener, a front end of the upper shell is lifted and moved in a rearward direction; a first pin (130) fixed to the seat-back support element, wherein the first pin rotates when the seat-back support element pivots on the first fastener; and a motion-limiting arm (129) that is fixed to the first pin, such that a rotation of the first pin causes the motion-limiting arm to rotate, wherein the motion-limiting arm includes a first slot that receives a fixed pin, and wherein an interaction between the first slot and the fixed pin limits a range of motion in which the seat- back support element pivots on the first fastener.

2. The device of claim 1, wherein the motion-limiting arm (129) includes a second slot (128a) that receives another pin (127), wherein the other pin is operatively coupled to a knob (122), wherein moving the knob adjusts the other pin, thereby engaging the second slot, and wherein engaging the second slot pivots the motion-limiting arm on the first pin.

3. The device of claim 2, wherein the first slot of the motion-limiting arm includes a plurality of seats configured to engage the fixed pin, wherein engaging the second slot to pivot the motion-limiting arm changes a seat with which the fixed pin is engaged.

4. The device of claim 3, wherein the motion-limiting arm includes three seats that are configured to engage the fixed pin, thereby providing three preset positions, each of which limits to a different degree the range of motion in which the seat-back support element pivots on the first fastener.

5. A device that is mountable to a seat bottom and that is usable to control movement of a seat back, the device comprising: an upper shell (103) that attaches to the seat bottom; a lower shell (104) that attaches underneath the upper shell, thereby forming a space therebetween; a seat-back support element (112) positioned toward rear portions of the upper shell and the lower shell, the seat-back support element pivotally connected to the lower shell and rotatably coupled to the upper shell, such that, when the seat-back support element pivots, a front end of the upper shell is lifted and moved in a rearward direction; a lever (116a) that is fixed between respective front portions of the upper shell and the lower shell, wherein a front end of the lever is rotatably coupled to the upper shell and a rear end of the lever is rotatably coupled to the lower shell, wherein when the front end of the upper shell is lifted, the front end of the lever is lifted and the rear end fixedly pivots; a leaf- spring element (140) positioned between the upper shell and the lever, wherein a front end of the leaf-spring element provides a tension that opposes lifting of the front end of the lever; and a pin (141) that is movable to engage the leaf-spring element, wherein, when the pin engages the leaf- spring element, a magnitude of the tension increases.

6. The device of claim 5 further comprising, another pin (130) fixed to the seat-back support element, wherein the other pin rotates when the seat-back support element pivots on the first fastener.

7. The device of claim 6, wherein the leaf-spring element is positioned between the pin and the other pin.

8. The device of claim 5, wherein the pin is operatively coupled to a user- operated lever (144) that, when rotated, positions the pin relative to the leaf-spring element to control the tension.

9. A device that is mountable to a seat bottom and that is usable to control movement of a seat back, the device comprising: an upper shell (103) that attaches to the seat bottom; a lower shell (104) that attaches underneath the upper shell, thereby forming a space therebetween; a seat-back support element (112) positioned toward rear portions of the upper shell and the lower shell, the seat-back support element pivotally connected to the lower shell and rotatably coupled to the upper shell, such that, when the seat-back support element pivots, a front end of the upper shell is lifted and moved in a rearward direction; a first pin (130) fixed to the seat-back support element, wherein the first pin rotates when the seat-back support element pivots; a motion-limiting arm (129) that is fixed to the first pin, wherein an operation of the motion-limiting arm limits a range of motion in which the seat-back support element pivots; a lever (116a) that is fixed between respective front portions of the upper shell and the lower shell, wherein, when the front end of the upper shell is lifted, a front end of the lever is lifted and a rear end of the lever fixedly pivots; a leaf- spring element (140) positioned between the upper shell and the lever, wherein a front end of the leaf-spring element provides a tension that opposes lifting of the front end of the lever; and another pin (141) that is movable to engage the leaf-spring element, wherein, when the other pin engages the leaf- spring element, a magnitude of the tension increases.

10. The device of claim 9, wherein a front end of the lever is rotatably coupled to the upper shell and a rear end of the lever is rotatably coupled to the lower shell.

11. The device of claim 9, wherein the motion-limiting arm includes a first slot that receives a fixed pin, and wherein an interaction between the first slot and the fixed pin limits the range of motion in which the seat-back support element pivots on the first fastener.

12. The device of claim 11, wherein the motion-limiting arm (129) includes a second slot (128a) that receives another pin (127), wherein the other pin is operatively coupled to a knob (122), wherein moving the knob adjusts the other pin, thereby engaging the second slot, and wherein engaging the second slot pivots the motion-limiting arm on the first pin.

13. The device of claim 9, wherein the other pin (141) is operatively coupled to a user-operated lever (144) that, when rotated, positions the other pin relative to the leaf- spring element to control the tension.