Tilt control mechanism for chair

A chair back is supported on a rigid upright coupled to a horizontal tilt shaft disposed under the front of the chair seat and supported on a control housing fixed to a pedestal. A tension mechanism urges the upright into an upright position. The chair seat is movably supported on the upright by an arrangement which permits the seat to pivot about a transverse horizontal axis positioned adjacent the upper surface of the seat. A control link is pivoted at one end to the control housing, and the other end has lost-motion pivotal connections to the seat frame and the upright. The lost-motion pivotal connection to the seat frame including a spring cooperating between the upright and the seat frame to allow the seat to move relative to the upright.

FIELD OF THE INVENTION

This invention relates to an office-type chair, and more specifically relates to an improved synchrotilt mechanism coupled to the seat and back of the chair for providing improved seating comfort.

BACKGROUND OF THE INVENTION

Office chairs conventionally provide some type of rearward tilting movement. In its simplest variations, the rear tilting involves solely the back, or the seat and back as a unitary construction. To provide improved and more desirable tilting movement and seating comfort, however, many office-type chairs employ a synchrotilt mechanism coupled between the chair base and the seat-back assembly, for permitting the seat and back to simultaneously tilt at different rates, with the tilt rate and maximum tilt angle of the back typically being about twice the tilt rate and maximum tilt angle of the seat.

Chairs employing synchrotilt mechanisms for permitting simultaneous but relative tilting of the seat and back are well known, and numerous mechanisms have been developed for performing this function. Most of these mechanisms, however, have caused relative motion between the chair and the seated occupant which has interfered with occupant comfort. Such relative motion may involve relative sliding between the seat and the occupant's hips or thighs, and/or sliding between the chair back and the occupant's back, during the relative tilting between the seat and back. In an attempt to alleviate or at least partially compensate for this problem, several chair mechanisms have been developed which cause the seat, during rearward tilting of the seat-back arrangement, to tilt relative to the back about an axis located approximately at the hip axis of the seated occupant. This hip axis is disposed in upwardly spaced relation from the rear portion of the seat, and spaced forwardly from the lower portion of the chair back. While locating the relative tilt axis between the seat and back at the occupant's hip axis is believed to provide improved performance, particularly with respect to minimizing the relative sliding motion between the seated occupant and the seat/back, nevertheless many of these known mechanisms still fail to provide the degree of performance desired, particularly with respect to the desired comfort and ease of movement (often referred to as “ride”) associated with tilting of the chair.

Copending application Ser. No. 09/957,695 filed Sep. 20, 2001, now U.S. Pat. No. 6,644,741, owned by the Assignee hereof, discloses a chair with a synchrotilt mechanism which is believed to provide improved control over the relative but synchronized tilting of the back and seat so as to provide improved occupant comfort and ride while minimizing relative sliding movement between the seated occupant and the back and/or seat of the chair. The synchrotilt mechanism of this chair employs a seat cradle pivotally supported on a back upright, the latter being pivoted from the chair base, and a tilt control linkage cooperatively coupled between the base, seat cradle and upright so that seat tilting occurs generally about an axis disposed above the seat cradle but slightly below an upper surface of the unoccupied seat. The tilt control linkage includes a first lower link pivotally connected at a forward end to the base, a second upper link pivotally connected at a forward end to the seat cradle, and rearward ends of the first and second links pivotally joined to one another and carrying thereon a roller or slide movably captivated within an elongate slot formed within the upright. The forward end of the first link is also pivotally supported within an elongate slot formed in the base, and cooperates with a suitable spring device at this forward end to permit limited forward tilting of the seat cradle relative to the remainder of the chair in response to forward leaning of the chair occupant.

While the aforementioned chair provides desirable performance and seating comfort, nevertheless it has been observed that the synchrotilt mechanism and the tilt control linkage associated therewith require a significant number of parts as well as pivotal connections, which in turn increases the complexity of the chair assembly with respect to required manipulations and assembly time. This linkage also is more space-consuming, particularly in view of the limited available space, and this additionally increases the complexities associated with assembly of the chair.

Accordingly, it is an object of this invention to provide an improved synchrotilt mechanism for a chair which retains the desirable performance, both with respect to control and ride, associated with the chair of Assignee's aforementioned application, but which is able to provide this desirable performance while utilizing a simplified synchrotilt control mechanism which is structurally less complex, occupies less space, is easier to assemble, and is consequently less costly.

More specifically, in the improved chair of this invention, the synchrotilt mechanism employs a seat cradle pivotally supported on the back upright for relative pivoting about an axis typically disposed in the vicinity of the upper surface of the seat, with the relative motion between the seat cradle and back upright being controlled by a tilt control linkage which couples the seat cradle and back upright to the chair base. The tilt control linkage has an elongate control link which at a front end is pivoted to the chair base about a first transverse horizontal axis, which control link at its rearward end has a slide or roller movably engaged within an elongate slot associated with a base leg of the back upright. This control link, where it joins to the back upright, also has a bias or spring arrangement coupled between the seat cradle and the rearward end of the control link to provide a spring-controlled lost motion connection with the seat cradle whereby, during normal rearward tilting of the back upright, the seat cradle also tilts rearwardly but at a lesser rate as permitted by compression of the spring between the control link and the seat cradle. This same spring and the lost motion connection defined thereby also enables the seat cradle to tilt forwardly a limited extent in response to forward leaning of the chair occupant to provide a simple forward tilt function at least when the chair is in the normal upright position.

Other objects and purposes of the invention will be apparent to persons familiar with constructions of this general type upon reading the following specification and inspecting the accompanying drawings.

Certain terminology will be used in the following description for convenience in reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. These latter terms will also refer to the normal directions and positional orientations associated with a person sitting in the chair. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the chair and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.

DETAILED DESCRIPTION

Referring toFIG. 1, there is illustrated a chair11which incorporates therein the improved synchrotilt control according to the present invention. The chair11includes a base12provided with a plurality of legs14which radiate outwardly and are provided with casters for rolling support on a floor. The base12, centrally thereof, has a height-adjustable pedestal13which projects upwardly and, at the upper end thereof, couples to a chair control16, the latter in turn providing support for an L-shaped seat-back arrangement17which includes a seat assembly18and a back assembly19.

The seat assembly18includes a rigid seat frame or cradle21defined by a generally rectangular ring-shaped top frame22which, adjacent opposite sides, is provided with generally parallel side frame elements23. The elements23are generally U-shaped and protrude downwardly, with upper ends of the legs being rigidly joined adjacent the front and rear corners of the top frame22.

The seat assembly18also includes a thin sheetlike seat shell24stationarily positioned on the upper surface of the top frame22, and a compressible seat cushion25supported on and extending generally coextensively over the upper surface of the seat shell24. The cushion25terminates in respective front and rear edges26and27, the latter being defined in close proximity to the back assembly19. The seat cushion defines thereon an upper surface28disposed for contacting engagement with a chair occupant. The seat cushion25, when engaged with a seated occupant, resiliently deforms downwardly so that the upper surface28, at least in the main central region of the cushion where engaged with the occupant, is deflected downwardly from the nondeformed position indicated inFIGS. 6 and 7.

The back assembly19is supported on a generally rigid upright structure31which is defined by a pair of generally parallel and sidewardly positioned L-shaped side upright elements or members32, each of which has a lower lever arm portion33positioned below the seat shell24and which, at a rearward end, is joined through an integral bend to an upper arm portion34which is cantilevered upwardly and has the back assembly19mounted thereon. The sidewardly spaced uprights32are, adjacent the lower ends of the upper arm portions34, rigidly joined by a cross member35extending therebetween.

The forward ends of the lower lever arm portions33are nonrotatably connected to a tilt shaft42which defines a rotational axis43extending generally horizontally in transverse relationship relative to the seat assembly18. The tilt shaft42is rotatably supported within a housing or support arm41which is fixed to the upper end of the height-adjusting pedestal13, with the housing41being cantilevered forwardly from the pedestal so that the tilt shaft42is positioned under but more closely adjacent the front edge26of the seat cushion25.

The tilt shaft42projects outwardly through openings44formed in opposite sides of the housing41so that opposite end portions of the tilt shaft42are disposed on opposite sides of the housing41. The projecting end portions of the shaft42in turn project through openings45associated with the forward ends of the lower lever arm portions33, with these latter arm portions being keyed or otherwise suitably nonrotatably secured to the shaft42, whereby the rigid upright arrangement31is angularly movable about the horizontal axis43in correspondence with angular displacement of the tilt shaft42.

The housing41functions as an enclosure for a conventional biasing or spring mechanism for normally urging the back assembly19into an upright position. In the present invention, and as illustrated inFIGS. 11–12, the chair employs a biasing or spring mechanism81which is disposed within the interior of the control housing41and includes a spring82, namely an elongate bar-like torsion spring in the illustrated embodiment. This torsion spring82has an arm83anchored thereto substantially at the center of the spring, which arm at its other end is stationarily interconnected to the control housing41, typically through a manually-adjustable tensioning mechanism which permits limited swinging of the arm so as to adjust the initial torsion of the torsion spring82. This torsion spring82, as it projects outwardly from opposite sides of the mounting arm83, is telescoped within the interior of coaxially aligned shaft segments which define the main tilt shaft42, and the free ends of the torsion spring82are nonrotatably secured to the shaft segments defining the shaft42. The shaft segments also have stop members84fixed thereto and cooperating with opposed stops (not shown) associated with the control housing41for defining the permissible angle of movement of the shaft42and of the back arrangement as coupled thereto through the upright structure. While the biasing mechanism81as described above represents one arrangement for effecting biasing of the chair into its normal upright position, it will be recognized that numerous other biasing mechanisms employing other types of spring devices are well known and hence could be usable with the chair of the present invention.

To control tilting of the seat and back assemblies relative to the base, an improved control linkage51is operatively coupled between the base and the seat frame or cradle21, and is additionally coupled to the upright arrangement31, as explained below.

The tilt control linkage51according to this invention includes two substantially identical linkages which are effectively mirror images of one another and are disposed on opposite sides of the chair control housing41for cooperation with the respective lower upright arms33and cradle side frame elements23as associated with the same side of the chair, as described below. Only one of the linkages51is described, it being understood that both linkages cooperate and function simultaneously in the same manner as described.

More specifically, the control linkage51permits synchronized but relative tilting of the seat and back with respect to the base, and for this purpose includes a main control link or lever52which is elongated in the front-to-rear direction of the chair and which, at a forward end thereof, has a transverse pivot shaft53which is rotatably supported with an opening54associated with one side of the control housing41so as to define a transverse horizontal hinge axis55. The hinge axis55is generally parallel with but spaced rearwardly and downwardly from the main tilt axis43. The other or rearward end of the main control lever52also has a transversely projecting pivot shaft56mounting thereon a roller57rotatable about a transverse horizontal axis58which is generally parallel with but spaced rearwardly from the hinge axis55. The roller57is confined for movement within an elongate slot59as formed in the inner side wall of the adjacent lower lever arm portion33of the upright side member32. The slot59is elongated in the front-to-rear direction of the chair seat, and in the front-to-rear direction of the lower arm portion33, with the longitudinal direction of the slot extending at a significant acute angle relative to the lengthwise direction of the main control lever52as defined transversely between the hinge axes55and58.

The transverse shaft end56associated with the rearward end of control lever52, in the illustrated embodiment, passes through an enlarged and elongated clearance hole60formed in the side element23of the seat cradle so as to permit access to the control slot59formed in the adjacent lever arm portion33.

In addition to the control linkage51, the synchronized but differential tilting of the seat and back with respect to the base is further controlled by a pivotal support mechanism71which couples the seat cradle21to the upright arrangement31. The pivotal support mechanism71includes a pair of aligned front rollers72which are mounted on opposite sides of the seat cradle21and project outwardly from the outer side surfaces of the side frame elements23in the vicinity of the front ends thereof. The aligned front rollers72define a pivot or rotational axis73which extends transversely in horizontal orientation so as to be generally parallel with the tilt axis43. A further pair of rearward rollers74are similarly mounted on the outer sides of the cradle side frame elements23and are disposed in aligned relationship so as to be rotatable about a transverse horizontal axis75which is generally parallel with but spaced rearwardly a substantial distance from the front roller axis73. The rear rollers74are positioned adjacent the rearward ends of the cradle side frame elements23.

The pivotal support mechanism71also includes a pair of elongate front slots76and a further pair of elongate rear slots77which are formed in the lower lever arms33for individually movably accommodating therein a respective said front or rear roller72or74. More specifically, the pair of front slots76open inwardly in opposed relationship to one another from the inner side surface of the lower lever arms33, and in similar fashion the pair of rear slots77are disposed in opposed relationship to one another and open inwardly into the respective lower lever arms33from the inner side surface thereof. The front slots76are positioned between the tilt shaft42and the elongate slots59in the front-to-rear direction of the chair seat, and the rear slots77are positioned rearwardly of the slots59but somewhat forwardly from the upper upright arms34.

The front slots76and the rear slots77are both of an upwardly-facing arcuate configuration in that they are each generated on a uniform radius generated about a common center point or axis78which, as illustrated inFIG. 6, is positioned at an elevation whereby this center point or axis78is preferably a small distance below the upper surface28of the seat cushion23when the seat cushion is not deformed, i.e., the seat is not occupied. The center point or axis78, however, is disposed more closely adjacent the rear edge27of the seat cushion but is spaced forwardly therefrom so as to be, when viewed horizontally, spaced forwardly a small distance from the back36. The center point or axis78is preferably oriented so as to be generally aligned with but spaced vertically downwardly from the hip point or hip axis79associated with the hips of the chair occupant, which hip axis79is always spaced upwardly a small distance above the chair seat and is always spaced forwardly a small distance (i.e., several inches) from the chair back.

In the construction of the present invention, however, the center point or axis78used for generating the curvature of the slots76and77is typically spaced downwardly a small distance below the upper surface28of the nondeformed seat cushion23such that, when the seat cushion23and the upper surface28thereof are deformed downwardly due to an occupant seated thereon, the upper surface28of the seat cushion at least in the center portion thereof directly under the occupant's hips is deformed downwardly so that the generating axis78for the slots76–77is preferably disposed at and more preferably slightly above the upper surface28of the occupant-deformed cushion25, whereby the axis78will more closely be positioned for substantially tangential contact with the outer periphery of the occupant's hip bones. With this relationship, the occupant's hips where they contact the deformed chair seat thus remain stationary during synchronized rearward tilting of the seat and back with respect to the chair base.

In the arrangement of the present invention, the center point or axis78will typically be in the range of about one-half to about one inch below the upper surface28of the seat cushion25when the latter is unoccupied and hence not compressed or externally deformed.

The overall construction of the chair and the structural and functional relationships associated with the components thereof, as described above, generally correspond to the construction of the chair disclosed in Assignee's copending application Ser. No. 09/957,695, now U.S. Pat. No. 6,644,741.

According to the present invention, the control linkage51includes a lost motion connection61cooperating between the seat cradle21and the control lever52for permitting limited relative motion therebetween, such as during tilting of the seat-back arrangement17. This lost motion connection61includes a spring or biasing arrangement62associated therewith for creating a controlled restraint against relative tilting between the seat cradle21and the back upright structure31during rearward tilting of the seat-back arrangement17.

The lost motion connection includes the clearance opening60which opens sidewardly through the base leg of the seat cradle. The opening60is positioned approximately midway between the front and rear cradle rollers72and74respectively, and as illustrated is formed generally as a slot which is elongated generally in a front-to-back direction. The transversely projecting pivot shaft56as provided at the rearward end of the control lever52projects sidewardly through the opening60so that the end of the pivot shaft56remote from the control lever52can be provided with the roller57thereon, the latter being engaged in the elongate slot59associated with the lower arm portion of the upright back structure. The lost motion connection61defined by the opening60and its cooperation with the transverse pivot shaft56hence permits a limited amount of relative movement, principally in a front-to-back direction, between the control lever52and the seat cradle21.

The spring or biasing connection62also cooperates between the seat cradle21and the rearward end of control lever52to restrain relative movement of the pivot pin56within the opening60and at the same time provide control over the positioning of the seat cradle21relative to the back upright structure31.

The spring unit62in the illustrated embodiment includes a coil spring63, specifically a compression-type coil spring which is elongated generally in a front-to-back direction and is substantially carried on the lower arm of the seat cradle. The elongate coil spring63has one end thereof, namely the forward end in the illustrated embodiment, seated generally on a nib or projection64defined on the seat cradle. The elongate spring projects rearwardly from the nib64dominantly in a horizontal direction and the rearward end of the spring63is seated on an end plate65, the latter having a short cantilevered guide pin66protruding centrally forwardly thereof for guiding confinement within the interior of the coil spring63adjacent the rearward end thereof. The end plate65also mounts thereon a rearwardly projecting clevis67which projects at least partially around and rotatably embraces the transversely projecting pivot shaft56. The clevis67can be constructed of a suitable plastics material having sufficient resiliency to enable the split forklike construction thereof to be resiliently snapped into engagement with the pivot shaft56.

The spring63is positioned generally within an elongate opening or cavity formed within a small housing69, the latter being at least partially seated within a shallow recess70defined on one side of the base member of the seat cradle, with the housing69being suitably fixed to the seat cradle in any conventional manner, such as by screws or by any type of suitable engagement which enables the seat cradle21and housing69to be fixedly and reliably joined while permitting separation for maintenance purposes if necessary.

The housing69also has a transverse slot68therethrough which effectively sidewardly aligns with the clearance slot60defined in the base leg of the seat cradle21so as to permit the pivot shaft56to project therethrough while permitting relative movement therebetween.

When the seat-back arrangement is in the normal upright position, the spring63and the engagement of the front end thereof on the seat cradle21causes a forwardly-directed biasing force to be exerted on the seat cradle which tends to move the bottom portion of the seat cradle forwardly, hence causing the seat cradle to rotate in a clockwise direction (FIG. 6) relative to the upright back structure31, thereby maintaining the pivot shaft56generally adjacent the rearward closed end of the clearance opening60. This defines the normal position of the seat cradle21relative to the upright back structure31when the latter is in its normal upright position and the chair is not occupied. The springs63, however, undergo compression during rearward tilting of the rigid upright back structure31so as to permit the seat cradle21to hence tilt relative to the seat back structure to provide synchronous but differential tilting of the seat and back. In addition, when the chair is in its normal upright position and is initially occupied, the weight of the occupant may cause the seat cradle21to slightly rotate downwardly and rearwardly (counter-clockwise inFIG. 6) about the axis78so as to effect partial compression of springs63and movement of the rear ends of openings60rearwardly away from the pivot shafts56. Further, the springs63also undergo compression and permit relative tilting between the seat cradle21and back structure31, specifically forward tilting of the seat cradle, in response to forward shifting of an occupant's weight on the seat member to hence permit the seat member to undergo a limited forward tilt (counter-clockwise inFIG. 6) from its normal position. These functions, which occur as a result of the lost motion connections61and the associated spring connections62, as provided on opposite sides of the chair, are explained in greater detail below.

When the chair is in an unoccupied condition, the seat-back arrangement17will be maintained in its generally upright or forward position due to the resilient urging of the spring or biasing mechanism81associated with the control assembly, which biasing mechanism always urges the seat-back assembly in a generally vertical direction about the tilt axis43(counter-clockwise inFIGS. 6 and 7A) into engagement with a suitable stop which defines the upright position, as shown inFIG. 7A. In this disposition, the springs63urge the seat cradle21in the opposite (i.e. clockwise inFIG. 6) direction so that rollers72,74are generally engaged with the forward ends of slots76,77, and pivot shafts54are positioned adjacent the rearward ends of clearance slots61A. When the chair in the upright position is occupied, however, the occupant's weight may cause the seat cradle21to slightly rotate (counterclockwise inFIG. 6) a small extent in opposition to the urging of the springs63. In this latter position, the occupant may elect to tilt rearwardly by applying suitable backward pressure against the chair back, causing the upright back structure31to tilt rearwardly (clockwise inFIGS. 6 and 7) about the tilt axis43against the urging of the biasing or spring device81. This rearward tilting of the upright arrangement31about tilt axis43causes the lower upright arms33to vertically swing downwardly about axis43, which causes the main control lever52to also swing downwardly (FIG. 7B), and simultaneously causes the roller57to move rearwardly along the slot59defined in the lower upright arm33. The downward swinging of upright lower arms33also causes the seat cradle21to be swung downwardly therewith due to the engagement of the rollers72and74within the respective slots76and77. This connection tends to tilt the seat cradle21downwardly at the same rate as the back upright arrangement31. Simultaneous with this latter movement, however, the pivot shaft56tends to move toward the rearward closed end of the clearance slot60and the downward load on the seat cradle caused by the seated occupant causes the seat cradle rollers72and74to move rearwardly along the respective slots76and77. Due to the arcuate curvature of the slots76–77as generated about the axis78, this causes the seat cradle21to effectively rotate about the axis78relative to the lower upright lever arms33as the latter swing downwardly about axis43. This relative rotation of the seat cradle21, however, is in the opposite rotational direction to that of the lower upright arms33, although at a lesser rate, so that the overall net effect is that the seat cradle21also effectively tilts rearwardly simultaneous with the rearward tilting of the back upright arrangement31, except that the rearward tilting of the seat cradle21occurs at a lesser rate of movement.

When the upright arrangement31is returned toward its upright position (FIG. 7A), the swing of the upright31(counterclockwise inFIGS. 6 and 7B) causes the pivot shaft56to act against the coil springs63, which in turn act against the seat cradle21so that it angularly moves (clockwise inFIGS. 6 and 7B) relative to upright31so as to return to its normal position wherein the rollers72,74are positioned at or adjacent the forward ends of slots76,77.

During the aforementioned rearward tilting of the upright31, the tilting of the seat cradle21relative to the back assembly (i.e. upright31) occurs about the axis78which is approximately vertically aligned with but spaced downwardly below the occupant's hip axis79, with the center of relative tilting movement78being positioned adjacent and typically slightly above the deformed upper surface28of the seat cushion so that this tilt axis78is positioned to approximately transversely intersect the rounded exterior profile of the occupant's hip bones whereby, during the rearward flexing of the occupant's upper body portion about the hips relative to the lower body portion, the movement of the body closely conforms with the simultaneous but relative tilting movements of the back and seat so as to permit comfortable disposition of the occupant on the seat without undergoing significant relative sliding at the contact areas. At the same time the rearward tilting permits the occupant's knees to readily flex in an opening direction while the occupant's feet remain properly and comfortably engaged with the floor with overall rearward tilting of the occupant being permitted due to rearward flexing of the occupant's legs about the ankles.

The control linkage51of the present invention also permits the seat cradle21to rock or rotate through a small angle about the axis78in a direction which permits the front edge26of the seat cushion to be depressed, even though the upright structure31is maintained stationary.

More specifically, if the chair occupant leans forwardly in the chair or shifts his/her body weight onto the front portion of the chair seat, which force must be sufficient to overcome the biasing of the springs63, then the seat cradle21rotates about the axis78in a direction whereby the rollers72and74move rearwardly of their respective slots76,77(counterclockwise inFIG. 6), which pivoting of the seat cradle causes the springs63to be compressed a limited extent. Such tilting of the seat cradle and lowering of the front edge of the seat, as shown inFIG. 7C, can be accomplished wholly independently of the back and of the upright structure, the latter typically being maintained in the stationary position when the occupant effects forward tilting of the seat.

When the extra occupant-created downward force imposed on the front of the chair seat is relieved or shifted rearwardly, the compression force of the springs63acting against the seat cradle21is sufficient to effect reverse rotating of the seat cradle21back to its normal position with respect to the upright31.

With the structural arrangement of this invention as described above, the pivot shaft53is preferably formed as a short cantilevered stub shaft which is fixed to the forward end of the respective control link52so as to define the hinge axis55which is stationarily fixed relative to the upright pivot axis43due to the stub shafts53(FIG. 8) as disposed on opposite sides of the chair protruding inwardly in aligned relation for rotative support on opposite sides of the control housing41. Thus, there is no need for a separate cross shaft for defining the axis55and extending across the interior of the control housing, thereby providing additional space within the interior41A of the control housing41and thereby simplifying the structure interiorly thereof.

While the invention as described above illustrates the seat defined by a seat cushion25positioned on a seat shell, it will be appreciated that the seat may be defined by a sheet of flexible or elastic fabric (i.e. mesh or membrane) which, in a nonoccupied position of the chair, correspond generally to the upper surface of the cushion, with the fabric deforming and functioning in the same manner as the upper surface of the cushion when the chair is occupied.