Compound Lever and Armrest Mounting Assemblies

A) Field of Invention

The present invention relates to a variable posture work chair with a displaceable armrest assembly which maintains a constant user defined spatial relationship to a moveable seat pan and backrest.

B) Known Art

The proliferation of computer terminals at the modern workstation has spawned a variety of attempts to provide a more comfortable environment for seated workers. The general discomfort that afflicts the legs, lower back, neck, shoulders and wrists of seated workers can be partially offset by building better seating devices, particularly those that conveniently allow a wide range of posture changes. An in depth discussion of the advantages and disadvantages of various seating designs is contained in my previous patent.

The builders of work chairs face several key challenges in effecting their designs. Among the most important:

Comfort and utility. A work chair must be adaptable to a wide range of work place requirements while maintaining ergonomically correct comfort for a seated user.

Ease of use. A seated user should be able to transition smoothly from one position to another with a minimum of mechanical intervention. The most efficient way of achieving this is by building a chair mechanism that effects its changes through a controllable rocking movement.

Adjustability. A single design platform should be able to accommodate a wide range of human body sizes while easily adapting to the changing needs of the workplace.

Integration of components and their movements. Interconnecting a moveable seat pan, backrest and armrest assembly so that they function in a synergistic fashion while effecting utilitarian variable posture remains a key focus of invention in the field of work chair design.

Engineering and production costs. A design must be relatively simple to engineer and cost effective to build, or it stands no chance of succeeding in the marketplace.

In addition much design emphasis is now being placed on the aforementioned term "variable posture", and while the term is important in the ergonomic sense it lacks any mechanical definition. A simple way to measure the degree of variable posture in any chair design is to assess the useable range of seat pan tilt the design provides. The greater the range of useable tilt (up to a maximum) the greater the shift in body footprint and center of gravity, this being variable posture. By "useable" is here meant that a seated user should be able to tilt the seat pan to a chosen inclination/declination from the horizontal, lock that inclination/declination in place and work comfortably from that position for extended periods of time. Obviously, for this scenario to succeed the other elements of the chair design must function in harmony with the movement of the seat pan.

A detailed discussion of the variable posture issue and several relevant patented designs is contained in my aforementioned patent. Further, U.S. Pat. Nos. 5,577,802 to Cowan and Kmicikiewicz and 5,540,481 to Roossien et al show chair designs which attempt to effect easy adaptation to the movements of a seated user. While Cowan shows armrests they are not crucial to the central design; for Roosien et al the armrests are superfluous. U.S. Pat. No. 5,536,070 to Lemmen shows an ergonomic armrest assembly but attempts no real integration with the seat pan and backrest. U.S. Pat. No. 4,277,102 to Aaras et al describes a chair with individually supported armrests. Various armrest assemblies are described in U.S. Pat. Nos. 5,439,267 to Peterson et al, 5,407,249 to Bonutti, 5,393,124 to Neil, 5,380,065 to Rohrer, 5,369,805 to Bergsten et al, 5,366,276 to Hobson et al, 5,215,282 to Bonutti, 5,056,863 to DeKraker et al, 5,009,467 to McCoy, and 4,887,866 to Rusin.

Several observations come to light when examining the prior art in this field. First, and in general, when chair designers attempt to build a relationship between a seat pan and a backrest they fail to adequately integrate armrest assemblies into their designs. Even when the appearance of attention to detail is given, armrest assemblies are usually dispensable add-ons to the basic chair assembly. Conversely, the designers of armrest assemblies show little interest in integrating the functions of their designs with the movements of a variable posture seat pan and backrest. Armrests, whether built individually or interconnected on a frame, are designed to be added onto, and not integrated into, a pre-existing chair.

More specifically, current design practice almost always fixedly attaches armrest assemblies to a tiltable seat pan or its mount without adequately separating and then integrating the functions of the two assemblies. If one posits that the chief a function of a work chair armrest assembly is to align a user's forearms with a keyboard or other work surface it can be seen that this alignment is constantly being upset by the movements of the seat pan to which it is locked, movements which are necessary to effect variable posture. Further, if one attempts to lock the armrests into an aligned position the seat pan can only follow, thus affording a position which may not be the most comfortable for the user's needs.

It is to the aforementioned issues that the substance of the current invention is therefore addressed.

Objects and Advantages

The objects and advantages of my previous patent are incorporated into the present invention.

Further, it is the general objective of the present invention to provide a variable posture chair assembly that integrates and synchronizes the functions and movements of a seat pan, a backrest, two armrests and, optionally, a leg-rest for a seated user. The chair will be adaptable to a wide variety of workplace requirements, comfortable in all positions, easy to use, adjust to varying body sizes and be relatively simple and cost effective to build.

Specifically

A significant advantage of the present invention is its implementation of a compound lever mounting assembly to effect a differential in tilt among an armrest assembly, a seat pan and a backrest. A seated user will enjoy several key benefits by effecting this differential tilt. Chief among these is the ability to vary the angle of the seat pan and backrest to the maximum practical extent while simultaneously keeping the armrests, and thus the forearms, aligned with a work surface such as a keyboard. Only a rocking motion and operation of a braking assembly are necessary to effect basic changes in alignment. Simple controls allow further manual adjustments that remain part of the configuration.

The compound lever mounting assembly consists in part of two upper and two lower side rails that act as two levers mounted to a central dual fulcrum. Other elements of the chair are a seat pan assembly, a backrest assembly, an armrest assembly and an appropriate base. Elements may be linked to one or both of the levers. The key functions of the assembly are summed up as follows and are detailed later in the specification:

Two upper and two lower side rails are connected by a plurality of axes so that the four tilt in tandem as one upper and one lower lever. The levers are mounted to a dual fulcrum positioned near their center; the fulcrum may be moved to the forward end of the lever assembly. A seat pan assembly is attached to one end of the lever assembly and the armrest and backrest assemblies are attached to the other. The lever assembly may rock freely or be locked down; its total range of tilt is herein referred to as "tilt range".

The dual axles of the seat pan mount are connected to the forward end of the compound lever so that the axles share the same constant vertical axis as that of the non-moving central dual fulcrum. The seat pan itself is hinged to the upper of the two axles and is loaded by a spring at a constant forward inclination that changes only when counter loaded by a seated user. The maximum range of seat pan tilt is herein shown to be 33-40 degrees. A forward stop and the available rearward tilt of the compound lever assembly limit this range. It is anticipated that most users of the chair will find approximately 18 degrees of loaded seat pan tilt and 15 degrees of free tilt to be adequate for daily use.

The armrest assembly is also referenced by the two levers to the non-moving vertical axis of the central dual fulcrum. The vertical axis of the armrest assembly mount may be referenced in the same fashion as that of the seat pan or it may be offset. offsetting the mount is the preferred embodiment of the present invention. The degree of armrest assembly fore-aft tilt created by the interaction of its mount with the compound lever is herein referred to as "linked tilt range". This range will be shown to be variable depending upon the method of mounting the armrest assembly to the lever assembly. The fore-aft tilt of the armrest assembly may also be manually adjusted, herein referred to as "positional displacement".

The adjustable backrest assembly is referenced to the upper of the two levers only. It tilts in tandem with a single, not a dual lever. Thus the variable movements of the backrest are synchronized with the tilt of the loaded seat pan.

The difference in the default range of tilt between the lever assembly and the armrest assembly is determined by subtracting the linked tilt range from the tilt range. The difference is herein referred to as "differential tilt". The differential tilt of the assembly is determined by the method of attaching the armrest assembly to the compound levers and the degree of tilt range.

This assembly allows a seated user to precisely align his or her forearms with a keyboard or other work surface while simultaneously adjusting the angle of the seat pan and lock that alignment into position. Necessary height compensations can be achieved through central chair height adjustment, the armrests themselves or the use of a detached adjustable keyboard desk. If a desk assembly is mounted directly to the armrest assembly no height compensation is needed. Further, a user may set the horizontal tilt of the armrest assembly to satisfy a specific need; this preset (positional displacement) determines a resulting default range of armrest movement. If the user locks the mounting assembly into a specific position the armrests remain at a solidly fixed position while the user enters into and exits from the chair and the seat pan continues to tilt over its available range of movement. This facilitates entering into or exiting from a seated position, particularly one of reclining. The user can also effect a rocking and stretching motion consistent with variable posture, this because the seat pan and backrest are pivotally fixed to their mounts.

A further significant advantage of the present invention is the use of a single integrated armrest assembly to be used in conjunction with a seat pan, a backrest, and, optionally, a leg-rest. This assembly has the following advantages:

It synchronizes easy user effected lateral adjustment of two armrests from a single control, thereby accommodating a wide range of shoulder widths.

It synchronizes easy user effected fore and aft tilt of two armrests from a single control by mounting the assembly so that it pivots controllably on its long axis within the mounting frame.

It allows for simple height and horizontal adjustment of the armrests.

It is relatively easy to engineer and cost effective to build.

The advantages of using a keyboard desk or an abdominal rest when attached to an armrest assembly were thoroughly covered in my previous patent. The present design incorporates these advantages and facilitates the use of these accessories by providing for easy mounting to and removal from the assembly.

Further objects and advantages of the present invention will become apparent from a consideration of the drawings and ensuing description.

FIG. 1 shows a profile of the major elements of the preferred embodiment of the present invention, minus a base. The main elements of the backrest assembly are detailed.

FIG. 2 shows the main components of the compound lever assembly in cutaway.

FIG. 3 shows the compound lever assembly and seat pan in profile with the lever assembly at an angle of approximately 7 degrees rearward tilt and the seat pan at approximately 8 degrees forward tilt.

FIG. 4 shows the compound lever assembly and seat pan in profile with the lever assembly at an angle of approximately 25 degrees rearward tilt. The maximum range of movement of the seat pan from a constant fully unloaded position of approximately 8 degrees forward tilt to a fully loaded position of about 25 degrees rearward tilt (here 33 degrees) is also shown.

FIGS. 5-5a through 10-10a show some possible pivot mounting combinations for an armrest bracket mounted to the rear of the dual compound lever assembly. The tilt range, linked tilt range, and differential tilt for each configuration is given (see discussion below).

FIG. 11a-11c show an alternative embodiment of the compound lever assembly.

FIG. 12 shows a relational summary of the linked tilt ranges and differential tilts created by the interaction of assemblies 2 and 4 as shown in FIGS. 5-11c.

FIG. 13 shows an exploded view of a possible construction of the armrest assembly.

FIG. 14 shows the lateral movements of the armrest assembly.

FIG. 15 shows the user definable positional displacement of the armrest assembly and reiterates the range of possible movement of the seat pan.

FIG. 16 shows a keyboard or other desk attaching to the assembly.

FIG. 17 shows an abdominal rest attaching to the assembly.

FIG. 18 shows a possible base assembly for the invention.

The design advantages and practical use of a variable posture chair that might be called a synergistic hybrid were thoroughly expounded upon in my previous patent; those advantages and general methods of use are incorporated into the present text. In addition, the user of the present invention will enjoy the synchronized movements of a seat pan, backrest and two armrests in an assembly that allows for maximum ease of use and maximum control over the positioning of the armrests relative to a work surface.

FIG. 1 shows the preferred embodiment of the present assembly in an unloaded position. A chair assembly 1 comprising a compound lever assembly 2, a seat pan assembly 3, an armrest assembly 4 and a backrest assembly 5 is mounted to an appropriate base assembly 6 (see FIG. 18) and upright stem 6a. Backrest assembly 5 consists of a vertically adjustable backrest upright assembly 5A which mounts to backrest mount assembly 2R at coupler housing 2t (see FIG. 2), a backrest cushion 5b, a wedge and pivot assembly 5C and a vertically moveable cushion pivot assembly at 5D.

FIG. 2 shows the major components of compound lever assembly 2. A main mounting assembly 2a comprises a mounting plate 2b, an upper main axle 2c, a lower main axle 2d, a main return spring 2e and a tilt lock assembly 2f (such as a spring and clutch plate brake of known design). A front axle assembly 2g comprises a front axle mount 2h, an upper front axle 2i, a lower front axle 2j, a seat pan return spring 2k and a seat pan stop 21. An upper left side rail 2m, an upper right side rail 2n, a lower left side rail 2o and a lower right side rail 2p mount onto axles 2c, 2d, 2I and 2j. A top plate 2q (also FIGS. 3 and 4) binds upper rails 2m and 2n together and serves as one point of mounting for backrest mount assembly 2r (see FIGS. 1, 3 and 4). Assembly 2r comprises a mounting plate 2s, a coupler housing 2t, a braking assembly 2u (preferably a spring and clutch brake of known design), a mounting axle 2v, a tilt axle 2w, tilt adjust springs 2x (see FIGS. 1, 3 and 4), a main spring shaft 2y and a main return spring 2z (see FIGS. 1, 3 and 4). Assembly 2r mounts by means of axle 2v at left bearing 2vl and right bearing 2vr. Seat pan mount L 3a and seat pan mount R 3b mount to axle 2I on either side of assembly 2. Seat pan cushion 3c mounts to 3a and 3b (see FIGS. 1, 3 and 4). Main armrest assembly housing 4a mounts by means of a combination of pivot pairs AA, BB and CC to rails 2m, 2n, 2o and 2p.

FIG. 3 shows the main components of assembly 2 in a position of approximately 7 degrees rearward tilt or, conversely, its maximum forward tilt. The assembly is forced into this position by the counter load of spring 2e, mounted on axle 2c (see FIG. 2). The minimum and maximum angles of the assembly are determined by the range of tilt lock assembly 2f, preferably a spring and clutch plate brake of known design. Tilt lock 2f can lock assembly 2 down at any position over its tilt range, or it can be disengaged to allow assembly 2 to act as a rocker. Seat pan cushion 3c is mounted to 3a and 3b; the assembly 3 is mounted to axle assembly 2g. Return spring 2k, mounted on axle 2I (see FIG. 2), keeps assembly 3 in a constant unloaded position of approximately 8 degrees forward tilt limited by seat pan stop 21. Variations in the forward tilt of assembly 3 can be achieved by making the seat pan stop 21 adjustable or changing its manufacture. Backrest mount assembly 2r is mounted by means of axle 2v to upper side rails 2m and 2n and spring shaft 2y through top plate 2q. Thus it is apparent that assembly 2r is referenced to only the upper of the two levers of assembly 2; unlike the seat pan and armrest assemblies its basic movements are tied to a single, not a compound lever. The inclination of coupler housing 2t, to which back rest assembly 5 is attached, is determined by the range of braking assembly 2u, preferably a spring and clutch plate brake of known design. As the brake is released interior springs 2x force the assembly to tilt forward and into the back of a seated user, who then counter forces with his or her weight until the desired angle is achieved and the brake locked down. Once in the chair a user effects some backrest rocking motion by forcing the assembly against main return spring 2z.

FIG. 4 shows assembly 2 in a position of maximum rearward tilt of approximately 25 degrees. A tilt range for assembly 2 of about 18 degrees is thus established. The position is limited and can be locked by tilt lock 2f. The full possible range of motion of seat pan assembly 3 (3-3') is also shown. From a forward position of approximately 8 degrees the seat pan can travel to a potential maximum rearward tilt of 25 degrees, a range in this case of 33 degrees. This range of travel could be extended by either altering the limit of tilt lock 2f or altering the limit of seat pan stop 21; it is unlikely that the maximum useable range would exceed 40 degrees. Seat pan position 3 represents an assembly 2 that is locked down and unloaded. Position 3' represents an assembly 2 that is under load and may or may not be locked down. Note that while the angle of inclination of the compound lever has changed by approximately 18 degrees from the 7 degrees of FIG. 3 the angle of the unloaded seat pan at position 3 has remained constant at 8 degrees forward tilt. This is because the vertical positions of axles 2I and 2j are referenced by parallel levers to the fixed vertical positions of axles 2c and 2d. The relative positions of the two identical (equal and parallel) sets of axles can always be illustrated as a parallelogram. As the levers tilt in tandem from the fixed vertical positions of fulcrum axles 2c and 2d the identical vertical axis of axles 2I and 2j will be held constant.

An additional on/off stop for the seat pan (not shown) may be added to the present configuration. The stop would be designed to keep the forward tilt of the seat pan in place. The connection would be made between mounts 3a-3b and either the axle of tilt lock 2f or an auxiliary axle mounted to the upper lever of assembly 2 (2m and 2n). This would allow a seated worker to lean forward and into his or her work with forward seat pan support and would make the use of an abdominal rest easier.

Before examining the linkages illustrated in FIGS. 5-11c some terms need to be repeated. First, the use of numbers and degrees herein is intended to be approximate and has been rounded out for the sake of clarity. "Tilt range" refers to the range of tilt of compound lever assembly 2, here 18 degrees. "Linked tilt range" refers to the range of armrest tilt afforded by the mount of assembly 4 to assembly 2. "Differential tilt" is the difference in tilt between the lever assembly's tilt range and the armrest assembly's linked tilt range; it is determined by subtracting the linked tilt range from the tilt range for a given configuration. "Positional displacement" refers to the manual change in fore-aft position a user may effect on the arm rest assembly (see FIG. 15 et al). A change in positional displacement will not affect the linked tilt range or the differential tilt.

There are numerous ways to mount a seat pan, a backrest, and an armrest assembly to a compound lever in order to effect a differential in tilt among the components. Three different methods of fastening the pivot mount of an armrest assembly to a compound lever are illustrated in FIGS. 5-5a through 10-10a; the seat pan and backrest mounts do not change. FIGS. 11a-11c show an alternative embodiment. In each set of drawings assembly 2 is shown both at 7 and 25 degrees rearward tilt, a tilt range of 18 degrees. The "a" series of drawings 5 through 10 are enlarged views of the three possible mounting combinations of housing 4a to the upper and lower side rails 2m, 2n, 2o, and 2p. The dual letters AA, BB and CC designate a mount to both left and right side rails (see FIG. 2).

In FIGS. 5-5a and 6-6a the linked tilt range of the armrest assembly is 0 degrees and the differential tilt is 18 degrees. (18 degrees -0=18). There is no change in the vertical or horizontal tilt of assembly 4 as lever assembly 2 effects a tilt range of 18 degrees from FIG. 5 to FIG. 6. Here pivot pairs BB-CC, 2I-2j and fixed fulcrum pair 2c-2d are parallel and equal, thus forming the corners of one or two parallelograms. Pivot AA is unattached. The three pairs of pivots maintain identical vertical axes as assembly 2 tilts over its range of movement. Since armrest assembly 4 responds to the tilt of assembly 2 with a mostly vertical movement a seated user would experience armrest pads that maintain a constant user defined horizontal inclination (note positional displacement and see FIG. 15), no matter what the angle of assembly 2.

The illustrated movement of assembly 4 is not strictly vertical. Pivot pairs BB-CC and 2I-2j travel on the arc of a circle relative to fulcrum pair 2c-2d; thus the horizontal distance between the vertical axes of BB-CC, 2c-2d and 2I-2j fluctuates as the pivot pairs reach the upper and lower positions of their arc. This can be seen by the offset in positions of unfixed pivot AA holes from FIG. 5-5a to 6-6a, and by measuring the distance between the vertical axes of BB-CC and 2I-2l on FIG. 5 and FIG. 6. Because pivots BB-CC begin their transit below the horizontal axis of fulcrum 2c-2d they move downward and inward on their arc as assembly 2 tilts rearward. Thus an attached arm rest assembly would move down and slightly forward while a seated user is positioning him or herself rearward, creating a potential alignment problem between the forearm and armrest pad. The problem can be corrected for this configuration by offsetting the levers and moving pivots BB and CC upward on the arc referenced from the assembly fulcrum (see FIGS. 11a-11c).

FIGS. 7-7a and 8-8a illustrate the preferred embodiment of the present invention. Here the linked tilt range of the armrest assembly is 9 degrees and the differential tilt is 9 degrees. (18 degrees-9=9). Thus the differential tilt for this configuration is about half that of FIGS. 5-6a. Here pivots AA-CC, 2c-2d and 2I-2l are connected on upper and lower side rails 2m, 2n, 2o and 2p. Pivot BB is not connected. Pivot pairs 2c-2d and 2I-2l, which are parallel and equal, now define the four corners of a parallelogram and maintain identical vertical axes. The third (now offset) vertical axis formed by pivots AA and CC is of an arbitrary inclination. Pivot AA has been referenced to the armrest housing 4a so that a constant spatial relationship is maintained between 4a and the seat pan 3 at axle 2I (also see FIGS. 6-6a). While all aforementioned pivots have been circular because they need only rotate on the axes of a parallelogram, offset pivot AA must be able to move within a slot. If it were circular it would be a lock on the assembly due to its offset position. The length of slot AA in fact limits the tilt of assembly 2 (also limited by tilt lock 2f).

Pivot AA transits an arc that is referenced to and begins above the horizontal of the fulcrum at 2c. AA arcs downward and outward across the horizontal. AA is referenced to pivot CC, which is transiting downward and inward on the lower portion of a smaller arc referenced to 2d. These two intersecting and interconnected arcs restrict the linked tilt range of armrest assembly 4 to about half the tilt range of lever assembly 2 to which it is connected. Thus a seated user can employ a simple rocking motion to effect a change in tilt at the (loaded) seat pan of 18 degrees and a simultaneous change in tilt at the armrests of roughly half that, about 9 degrees. The user may effect a positional displacement of the armrests at any time (see FIG. 15).

Offsetting one of the compound lever pivots at AA and referencing it to CC thus has the following advantages over the configuration of FIGS. 5-6 (also see FIGS. 11a-11c):

a) It mitigates the potential problem of fluctuating distances between moving assembly components as previously described.

b) It allows a seated user to maintain a constant horizontal relationship between his or her forearms and the pads of the arm rest assembly while changing position and/or effecting a rocking motion.

c) While maintaining a constantly level armrest assembly may appear to be desirable for keyboard operation (FIGS. 5-6a and 11a-11b) many users will find the 9 degrees of armrest tilt afforded by this configuration more natural and thus more comfortable for general chair operation. A user can always manually override any degree of tilt the assembly is automatically delivering through positional displacement of the armrest assembly (see FIG. 15).

In FIGS. 9-9a and 10-10a the linked tilt range of the armrest assembly is 18 degrees and the differential tilt is 0 degrees. (18 degrees-18=0). Armrest assembly 4 is fixedly mounted to upper rails 2m and 2n by means of pivots AA and BB (which function here as arbitrary fastening points). Since the armrest assembly is here linked to the movements of a single, not a compound lever, its linked tilt range will equal that of the lever's tilt range. Thus there is no differential in tilt between assembly 4 and assembly 2 for this configuration. The movements of lower rails 2o and 2p here have no effect on the armrest assembly, and 2o and 2p have no function within the assembly rearward of their fulcrum at 2d. Since this mount creates no differential tilt a seated user must manually effect a positional displacement of the armrests (see FIG. 15).

FIGS. 11a-11c illustrate an alternative embodiment of the compound lever assembly. In FIGS. 11a-11c compound lever assembly 2' consists of the same elements (not shown) as compound lever assembly 2. (Certain elements may be refit as needed). Upper and lower right side offset rails 2m', 2n', 2o' and 2p' have been shaped to raise the positions of dual pivots xx and yy relative to their equivalent pivots bb and cc in FIGS. 5-6a. Raising the pivots on their arc of travel closer to the horizontal of fulcrums 2c and 2d diminishes the change in horizontal distance between the vertical axes formed by xx-yy, 2c-2d and 2I-2j (see the discussion of FIGS. 5-6a above).

It can be seen that the equal and parallel pivots in 11b now form a compound parallelogram, or two parallelograms with a common side at vertical axis 2c-2d. Armrest assembly 4 (not shown) mounted to 4a moves on a vertical axis as lever assembly 2' tilts from FIG. 11a to FIG. 11b. In FIGS. 11a-11b the linked tilt range of the armrest assembly is 0 degrees and the differential tilt is 18 degrees. (18 degrees-0=18). A seated user would thus experience no change in the horizontal inclination of the armrest pads as he or she reclined in the chair, and only a slight variation in the fore-aft positioning of the assembly. In all other respects the discussion of FIGS. 5-6a above applies to 11a-11b.

FIG. 11c shows the same mount as described in the discussion of FIGS. 7-8a above. Pivots xx/aa and zz/cc are equivalent, and the linked tilt range and differential tilt are identical to those of FIGS. 7-8a. It should be reiterated that this mount draws the armrest assembly rearward slightly more than the mount of FIG. 11b, possibly creating a preferable overall body to chair alignment for a seated user.

FIG. 12 shows a relational summary of the linked tilt ranges and differential tilts created by the interaction of assemblies 2 and 4 as shown in FIGS. 5-11c. This summary posits a compound lever assembly with a tilt range of 18 degrees. Double numbers (0-0, 9-0, 18-0) represent the beginning and ending inclinations from the horizontal of the armrest assemblies as the respective linked tilt ranges are effected. Numbers in parenthesis represent the differential tilt. The actual linked tilt ranges for each armrest configuration begin at the illustrated forward tilt and end at the horizontal. The horizontal is here represented as 0 degrees. The ending horizontal positions are not shown; see FIGS. 5a-11c. All numbers should be accepted as a close approximation.

0-0 degrees is the linked tilt range of armrest tilt and 18 degrees is the differential tilt created by the mount of FIGS. 5-6a and 11b.

9-0 degrees is the linked tilt range of armrest tilt and 9 degrees is the differential tilt created by the mount of FIGS. 7-8a and 11c.

18-0 degrees is the linked tilt range of armrest tilt and 0 degrees is the differential tilt created by the mount of FIGS. 9-10a.

FIG. 13 shows an exploded drawing of one possible embodiment of armrest assembly 4. Two left and right bushings 4j and 4k have oppositely threaded interiors (LH and RH); the bushings mate onto threaded rod 4m. The assembled rod and bushings mate into the interior of housing 4e where the rod is kept in place by keepers 4n and keeper screw 4f (4f sits flush with the surface of housing 4e when installed). The bushings are kept from rotating by the mating of their bushing exterior surface 41 to the inner housing's interior surface 4g; any equivalent method may be used. This assembly slides into main armrest assembly housing 4a where it may turn freely and is kept in place by a housing flange and limiter plate 4h. The rotation of the inner housing 4e inside outer housing 4a is limited by the mating of limiter plate 4h and striker plate 4b. A pin assembly 4c, fixed to 4b, injects a pin into a chosen hole of pinhole plate 4i, thus holding the housings in place; this adjustment configures the fore and aft tilt (positional displacement) of the armrest assembly. Any type of appropriate locking mechanism may be employed at this point. The assembled housing is mounted onto lever assembly 2 at pivots AA, BB, or CC (see FIG. 2). A spring 4d maintains forward rotational pressure between inner housing 15 and outer housing 16; thus when a user pulls the pin of assembly 4C the armrests tilt forward under spring pressure. Two left and right armrest upright assemblies, 4O and 4P are employed. Two left and right armrest uprights 4q and 4r are mounted onto the exposed ends of bushings 4j and 4k; their default orientation is determined by the positional displacement at 4C. Two left and right armrest extenders 4s and 4t are inserted into the uprights where their vertical height is limited by a mating of their teeth with a hammer pin contained in left and right hammer pin assemblies 4u and 4v. A left and right gear knob 4w and 4x is mounted to uprights 4q and 4r; its teeth mate with teeth on extenders 4s and 4t so that a seaed user may turn the knob to raise the elevation of the armrests. The rests are lowered by pulling out on hammer pin assemblies 4u and 4v; an alternate embodiment would raise and lower the extenders exclusively from 4v-4w. A pair of armrest pads and supports 4y and 4z is mounted onto upright extenders 4s and 4t so that they may rotate on the horizontal, shown by phantom position 4y-4z. Two accessory mounts 7a and 7b are fixed to the tops of extenders 4s and 14t.

FIG. 14 shows an assembled version of armrest assembly 4. By turning the knob of threaded rod 4m its mounted bushings 4j and 4k move laterally and in opposite directions, thus effecting the lateral adjustments of armrest upright assemblies 4O and 4P, movements represented by positions 4O-x and 4P-x. While the movements are not shown it is understood that upright extenders 4s and 4t move vertically within uprights 4q and 4r, thus effecting height adjustment of the armrest assemblies.

FIG. 15 shows a possible range of user effected tilt of the armrest assembly (positional displacement). By unlocking the assembly at 4C a user may then cause the assembly to rotate within its housing to the desired inclination, whereupon 4C is released and the assembly is locked down again. This new position becomes the default for all further armrest movements referenced to lever assembly 2. The actual degree of positional displacement will run at about 8 degrees. The potential range of motion of the seat pan 3-3' is here reiterated.

FIG. 16 shows armrest assembly 4 with a desk assembly 8 mounted to either of accessory mounts 7a or 7b.

FIG. 17 shows armrest assembly 4 with an abdominal rest assembly 9 mounted to either of accessory mounts 7a or 7b.

FIG. 18 shows a possible base configuration for the chair herein described. Compound lever assembly mounts to upright stem 6a; a seated user may employ the legrest assembly 6B.

AA Dual pivot, upper

BB Dual pivot, mid

CC Dual pivot, lower

XX Dual pivot, upper

YY Dual pivot, mid

ZZ Dual pivot, lower

1 Chair assembly

2 Compound lever assembly

2' Compound lever assembly, alternate

2a Main mounting assembly

2b Mounting plate

2c Upper main axle

2d Lower main axle

2e Main return spring

2f Tilt lock assembly

2g Front axle assembly

2h Front axle mount

2i Upper front axle

2j Lower front axle

2k Seat pan return spring

2l Seat pan stop

2m Upper left side rail

2n Upper right side rail

2o Lower left side rail

2p Lower right side rail

2m' Upper left side rail, offset

2n' Upper right side rail, offset

20' Lower left side rail, offset

2p' Lower right side rail, offset

2q Top plate

2r Backrest mount assembly

2s Mounting plate

2t Coupler housing

2u Braking assembly

2v Mounting axle

2vl Left bearing

2vr Right bearing

2w Tilt axle

2x Tilt adjust springs

2y Main spring shaft

2z Main return spring

3 Seat pan assembly

3a Seat pan mount L

3b Seat pan mount R

3c Seat pan cushion

4 Armrest Assembly

4a Main armrest assembly housing

4b Striker plate

4c Pin assembly

4d Return spring

4e Inner housing

4f Keeper screw

4g Inner housing interior surface (representation)

4h Limiter plate

4i Pin hole plate

4j LH Bushing

4k RH Bushing

4l Bushing exterior surface (representation)

4m Threaded rod

4n Keepers

4o LH Armrest Upright Assembly

4p RH Armrest Upright Assembly

4q Armrest upright, L

4r Armrest upright, R

4s Armrest extender, L

4t Armrest extender, R

4u Pin assembly, L

4v Pin assembly, R

4w Gear knob, L

4x Gear knob, R

4y Armrest pad, L

4z Armrest pad, R

5 Backrest assembly

5A Backrest Upright Assembly

5b Backrest cushion

5C Wedge and Pivot Assembly

5d Cushion Pivot Assembly

6 Base assembly

6a Upright stem

6B Legrest assembly

7a Accessory mount, L

7b accessory mount, R

8 Desk Assembly

Abdominal Rest