Abstract:
A chair of the tilting type which includes a base, a seat and back, with the base pivotally supporting the seat with two parallel links of a four-bar parallel linkage, with one of the links extending to support the back. The four-bar linkage is duplicated on each side of the chair by forming the two opposite parallel links or cranks from the upturned ends of the tubes which pass through the base in parallel but vertically offset fashion, the base thus forming the fixed bar of the linkage with its opposite bar or coupler being formed by the seat. A spring within the base is operative on one (of both) of the tubes to urge the chair to an upright position. The tubes are pivotally connected to the seat and one of the tubes extends and is fixedly connected to the back. As the back tilts, the four-bar mechanism is engaged and lifts the seat which thereby uses the occupant&#39;s weight to counteract the reclining. 
     Also disclosed is an adjustable armrest that can readily raised, or lowered, and optionally rotated in a horizontal plane. 
     A further aspect of the present disclosure is a headrest that is pushed into place when the chair is reclined and retracted when the chair returns to an upright position.

Description:
This application is a continuation-in-part of my earlier filed U.S. patent applications Ser. No. 29/103,157 filed Apr. 9, 1999, Ser. No. 29/103,158 filed Apr. 9, 1999, and Ser. No. 29/103,159 filed Apr. 9, 1999, each of which are hereby incorporated by reference as showing embodiments of my inventions. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to a device for supporting a user in a seated position, and in one preferred embodiment, to a chair of the reclining back type. In another preferred embodiment, this invention relates to a chair having automatically adjusting armrests. In a further prefer-red embodiment, this invention relates to a chair having an adjustable headrest. In a still further preferred embodiment, this invention relates to a chair having an automatically adjusting resistance to tilting that increases in proportion to the weight of the user and as the tilt angle is increased. In a yet further preferred embodiment, the chair has a tilting mechanism which changes the angle of the seat and its support and increases the chair&#39;s angle of maximum recline, as well as providing a forward tilting position. 
     2. Description of the Related Art 
     Reclining type chairs commonly used in offices usually provide for the back to recline alone, for the seat and back to recline as a unit, or the seat back may recline in a coordinated proportion with the seat. If the back alone pivots, it generally creates a problem known as “shirt tail pull.” This problem is particularly acute if the pivot of the chair back is not coordinated with the natural body action. This problem can also be accentuated by the tendency of the hips of the user to slide forward as the back tilts rearwardly. 
     In chairs where both the seat and back recline as a unit, in the reclined position there is a tendency to lift the legs of the user from the floor creating an undue pressure by the forward edge of the seat against the underside of the legs of the user immediately above the knee. To overcome this problem the pivot point of the reclining action may be moved forward sufficiently to permit the user&#39;s feet to stay on the floor. The undesirable effect of this arrangement is that the body angle between the user&#39;s torso and legs is unchanged and as a result, the user&#39;s eye level drops undesirably when the chair is reclined. 
     In any reclining chair, it is desirable that the recline pivot point be at the center of the body or where the user&#39;s back normally pivots (i.e., an axis through the user&#39;s hip joints). The pivot point of a reclining chair is normally displaced from the ideal pivot point. It is also desirable to have a chair wherein the angle between the user&#39;s torso and his legs opens up to relieve internal congestive body pressures. It is, of course, also desirable to provide a chair wherein the user&#39;s feet remain on the floor and the recline action parallels the natural body action closely enough to avoid the common shirt tail pull problem. 
     It is also desirable to provide a chair which is of simplified construction and yet of clean, pleasing appearance emphasizing the isolated and separate appearance of the seat and back with respect to the supporting frames. 
     My earlier U.S. Pat. No. 4,429,917 shows one approach to solving these problems. U.S. Pat. No. 4,943,114 to Piretti allegedly reports a chair with a compact backrest linkage mechanism that enables the chair backrest and seat to recline. U.S. Pat. No. 5,251,958 to Roericht et al. allegedly reports a chair with a synchronous adjusting device that uses the weight of the user to provide a restoring force to return the chair back to an upright position after a user has reclined in the chair. 
     U.S. Pat. No. 5,486,035 to Koepke, et al., asserts, without providing any showing, that “In such constructions, the difficulty of reclining the chair, i. e., generating the reclining force, increases the further the chair is reclined, and it is common to employ adjusting apparatus for increasing or decreasing the reclining tension of a chair, such adjusting apparatus changing the tension of a spring, or otherwise modifying the reclining mechanism.” Col. 1, 1. 29-34. 
     While chairs with arms are well known in the art, heretofore, the arms have been either fixed, or adjustable. If the arms were adjustable, any adjustments have been less than ideal and/or quite cumbersome. 
     Additionally, it was known in the art to put a headrest on a chair, including a reclinable chair. However, such headrests typically provided the chair occupant with very little support, i.e., when the chair is reclined, the headrest maintains its position relative to the back of the chair. Alternatively, if the headrest were to provide the chair occupant with substantial support, the headrest required awkward adjustments. 
     Moreover, while it is believed that some reclining chairs heretofore available have had a means to adjust their resistance to reclining, such adjustments have been less than ideal, and/or very cumbersome and not practicable. 
     Instead, rather than confront the processes necessary to adjust their chairs to fit the needs of their particular body build, most users of chairs use them without making any adjustments. Consequently, any ergometric advantages that might be delivered by the properly tuned chair are not achieved. Thus, there remains a need for a chair that is adjustable to the needs of the individual chair occupant without requiring any substantial effort on the occupant&#39;s part to effect the adjustments. In other words, a substantially self-adjusting ergometric chair. 
     OBJECTS OF THE INVENTION 
     It is an object of one embodiment of the present invention is to provide an occupant-weight-operated chair having a reclinable back wherein the chair is of a simple economical construction and lends itself to high production manufacturing and fabrication procedures. 
     A further object is the provision of a tilting chair wherein the frame supporting the seat and back are pivotally connected to the seat and fixedly connected to the back in a manner to emphasize the isolated and separate appearance of the seat and back. 
     An alternative object is to provide armrests that are readily adjusted. 
     These and other objects and advantages of the invention will become apparent as the following description proceeds. 
     To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed. 
     SUMMARY OF THE INVENTION 
     Among advantages, some embodiments of the present invention provide an occupant-weight-operated chair having a reclining back wherein the occupant&#39;s weight loads the chair mechanism and automatically adjusts the reclining tension or force to recline the chair back. In a further preferred version of such embodiments, this occupant-weight-operated chair provides a substantially uniform force opposing the reclining of the chair back throughout its range of movement. Moreover, while this mechanism includes a spring, it does not rely on a spring or other adjustment to increase or decrease the chair reclining force. Instead, the spring merely provides a secondary or auxiliary force to the force provided by the user&#39;s weight. The spring does not require any adjustment. 
     An occupant-weight-operated chair in accord with the inventive concepts includes a chair having a seat and a back mounted upon support structure, such as a caster-mounted pedestal. The back is reclinable with respect to the seat, and the structure of the chair, and the relationship of the components, is such that as the back is reclined the entire seat raises against the weight of the occupant. In this manner, the occupant&#39;s weight loads the chair mechanism, and the force required to recline the back is substantially uniform throughout the back-reclining range of movement, such force being regulated by the weight of the occupant upon the seat rear portion. In turn, through the connecting top links, lifts the entire seat a small amount, typically between about a quarter of an inch to an inch. Preferably, the seat is lifted by between about a half and three quarters of an inch. 
     Furthermore, the inventive occupant-weight-operated chair with a reclinable back attaches the back to the seat rear region so that reclining the back raises the elevation of the seat rear region against the occupant&#39;s weight. The combination of the upward movement of the chair seat in conjunction with the reclining rotation of the chair back simulates the movement of the user&#39;s torso about the user&#39;s hip joint as the user reclines. 
     Some other embodiments of the present invention provide a tilting chair wherein the back is theoretically pivoted relative to the seat at or in alignment with approximately the ideal pivot point of the body of a user (for reclining the back, the ideal pivot point corresponds to a horizontal axis through the user&#39;s hip joint). In addition, the seat lifting is coordinated with the back recline to simulate the natural action of the reclining body. 
     In another embodiment, the present invention provides a chair occupant with a headrest support that adjusts to provide the support when support is needed and to retract to an out of the way position when not needed. 
     In still further embodiments of the present invention provides a chair occupant with armrests that readily, and simply adjust to deliver support to the user through a greater range of useful positions than was available through the armrests that have been heretofore available. Such support should be provided when and as needed by the chair occupant. 
     A yet still further embodiment of this invention provides a variable resistance to recline of the back as the adjustable mechanism is tilted forward or rearward. In the forward tilted mode there is less resistance to recline and more resistance in the rearward tilted mode. These changes are effected automatically without adjustment being required by the user. 
     Some preferred embodiments of a tilting chair of the present invention have a base that pivotally supports a seat with opposite links of a two four-bar linkage mechanisms. Typically, in such embodiments, one set of the opposite links on each side of the chair extends to support the back. Additionally reclining chair embodiments of the present invention usually have a base that forms a fixed bar of the linkage. This linkage translates the actuation of the rear links into a change in the angle of the forward links. 
     Some of the reclining chairs of the present invention have a spring in the base which acts on one of the bars of the linkage is operative to urge the chair to an upright position. This spring also provides some assistance to counterbalance the user&#39;s recline force. 
     Desirably, the chair lift mechanism of a reclining chair of the present invention is not normally noticed by the user, nor does such a chair lift the user&#39;s feet off of the floor. 
     With the present invention, a tilting chair is provided wherein the seat back pivot is effectively at the ideal point and which obviates the problems of shirt tail pull and feet lift common in prior art chairs. The present invention provides a chair in which both the seat and back are supported from the base by a linkage mechanism which permits the tilting of the back to increase the angle of the user&#39;s torso to his legs. 
     This reclining of the seat and back can be achieved with a four-bar linkage. The four-bar linkage can be parallel or non-parallel. In one embodiment of the inventive chair, the seat is supported on each side by one of the links or cranks of the four-bar linkage. The base of the chair forms a second link, or crank. The third link, or crank, extends to support the chair back. The fourth link couples the forward portion of the base to the forward portion of the seat. 
     The linkage is duplicated on each side of the chair. 
     The pivots of the linkage are designed so that the body weight tends to balance the seat pivot and a spring within the base is operative on one of the bars of the linkage to urge the chair to an upright position, simply to overcome the weight of the chair and maintain an unoccupied chair in an upright position. 
     Typically, when the chair is reclined by a user, the spring adds a small amount of return force. However, as the body weight of the user determines the amount of force necessary to return the chair to the upright position, and thus this force will vary among users and the degree of recline, the chair of the present invention uses the body weight of the user to counter-act the user&#39;s recline. 
     The bars of the linkage on each side of the chair are pivotally connected to the seat and the extended bar is fixedly connected to the back in a manner to emphasize the isolated and separate appearance of the seat and back. 
     Typically, the base spaced below the seat is of relatively small clean and compact construction housing the lower journals for the above-noted third and fourth links. In addition, the base houses the spring and a vertical height adjustment mechanism. 
     The horizontal links above the base are rails on which the seat pan is supported within guide tracks so the seat may be slid back and forth to adjust seat depth. The position of the seat within the guide tracks is fixed by a conventional mechanism. 
     Preferably, the back and seat portions are formed of a molded, stiffly flexible and resilient, synthetic plastic material, such as a reinforced glass fiber or other high strength material capable of flexing. The seat includes an upper, underside, front, and rear portions. Likewise, the back has an upper, lower, front, and rear portions. The Upper portion of the seat and the front portion of the back are typically contour molded and covered by a conventional cushioning material. 
     The underside of the seat front region (typically at the front of the rails that support the seat pan or support) is connected to the base by a pivot, and the underside of the seat rear portion is connected via a link to the lower region of the back. 
     As the seat reclines, and the rearward links (typically extensions of the back support) pivot about the rear pivot points on the chair base. As a result of the this pivoting, the pivot points under the seat support are raised slightly upwardly and rearwardly. The action of the seat support moving in this upward and rearward manner pulls the forward link (e.g., the upper horizontal seat support rails) so as to raise the forward portion of the seat. This lifting of the seat against the occupant&#39;s weight, accordingly, uses the occupant&#39;s weight to “load” the back to resist the reclining forces. As a result, a seat constructed in accordance with this aspect of the invention has a substantially uniform resistance to reclining due to the fact that it is the occupant&#39;s weight which produces such resistance. As the reclining tension is adjusted by the weight of the occupant, the greater the occupant&#39;s weight, the greater the force required to recline the seat back, and vice versa. 
     In some embodiments of the present invention, the chair has one or two adjustable armrests. The adjustable armrests are supported by a pair of rods the originate in the back of the chair. Preferably, the adjustable arm support rods originate from an “exoskeleton” that holds the back of the chair. While it is most preferred that the chair having the adjustable arms is the reclinable chair of this application, the adjustable arms of the present invention can be adapted to most any chair having a back. 
     In a particularly preferred embodiment, the arms are readily raised or lowered. To disengage an arm, and permit it to be repositioned, the distal end of the armrest is raised by a slight amount, say about a centimeter. Once the positioning mechanism is disengaged, the arm can be readily repositioned to any height. When positioned, the arm is released and it falls into place, re-engaging the positioning mechanism. In one embodiment of this adjustable arm invention, a chair has two arms that are independent of each other. In an alternative embodiment of the adjustable arm invention, the movement of one arm adjusts the second arm a corresponding amount in the same direction. 
     In a particularly preferred embodiment, the chair has a headrest that moves forward to support the chair occupant&#39;s head as the chair is reclined back and retracts as the chair returns to its upright resting position. In this manner, the chair occupant&#39;s head is supported when the support is most needed, i.e., during full recline when the occupant&#39;s head is not aligned with the occupant&#39;s back. However, when the support is not needed, i.e., in the upright position when the occupant&#39;s head is aligned with the occupant&#39;s back, the support is moved out of the way. It is preferred that the headrest moves on an arc that mimics the natural movement of the head. 
     While it is most preferred that the chair having the automatically adjusting headrest is the reclinable chair of this application, the automatically adjusting headrest of the present invention can be adapted to most any chair having a reclinable back. 
     In yet another particularly preferred embodiment, an alternate support mechanism may be used in the base or lower link position that allows the entire chair above the base to be tilted forward or to the rear and locked in any position, i.e., either extreme or at any position between these extremes. This alternate support mechanism provides forward tilt for seat and back for work positions, such as writing, and the rearward tilt provides additional recline to the backrest. 
     From time to time, the term “resting position” is used herein to refer to the upright or forward tilt position of the unoccupied chair. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of a reclining chair in accordance with the present invention illustrating the seat and back in upright position; 
     FIG. 2 is a side elevation of a reclining chair in accordance with the present invention illustrating the seat and back in tilted position; 
     FIG. 3 is a side elevation of a reclining chair having the automatically adjusting headrest and adjustable armrests in accordance with the present invention illustrating the seat and back in upright position; 
     FIG. 4 is a side elevation of a reclining chair having the automatically adjusting headrest and adjustable armrests in accordance with the present invention illustrating the seat and back in tilted position; 
     FIG. 5 is a side elevation of a reclining chair having the increased tilt mechanism in accordance with the present invention illustrating the seat and back in upright position; 
     FIG. 6 is a side elevation of a reclining chair having the increased tilt mechanism in accordance with the present invention illustrating the seat and back in tilted position; 
     FIG. 7 is a side elevation view of a chair base useful with the chair of the present invention; 
     FIG. 8 is a side elevation view of a chair base capable of providing extra tilt to a chair of the present invention in the resting position; 
     FIG. 8A is an exploded side elevation view of the chair base of FIG. 8; 
     FIG. 9 is a side elevation view of a chair base capable of providing extra tilt to a chair of the present invention in the increased tilt position; 
     FIG. 10 shows a top view of an embodiment of a chair base of the present invention; 
     FIG. 11 shows a side view of a preferred armrest including locking mechanism with the locking mechanism engaged; 
     FIG. 12 shows a side view of a preferred armrest including locking mechanism with the locking mechanism disengaged; 
     FIG. 13 shows a side view of an alternative armrest locking mechanism with the locking mechanism engaged; 
     FIG. 14 shows a side view of an alternative armrest locking mechanism with the locking mechanism disengaged; 
     FIG. 15 shows a side view of a further alternative armrest locking mechanism with the locking mechanism engaged; 
     FIG. 16 shows a side view of a further alternative armrest locking mechanism with the locking mechanism disengaged; 
     FIG. 17 shows an isometric side view of two interconnected armrest mechanisms; 
     FIG. 18 shows an isometric side view of two isolated armrest mechanisms; 
     FIG. 19 shows an isometric side view of two armrest mechanisms interconnected via the top support arm; 
     FIG. 19A is a cutaway view along line  19 A— 19 A showing the armrest locking mechanism; 
     FIG. 19B shows an exploded view of an armrest locking mechanism; 
     FIG. 20 shows a side view of a headrest mechanism of the present invention; 
     FIG. 20A shows a cut away view of the headrest mechanism of FIG. 20 taken along line  20 A— 20 A: 
     FIG. 20B shows a cut away view of the headrest mechanism of FIG. 20 taken along line  20 B— 20 B; 
     FIG. 20C shows a cut away view of the headrest mechanism of FIG. 20 taken along line  20 C— 20 C; 
     FIG. 21 shows a view of an embodiment of a mechanism according to the present invention for couplingly using the chair occupant&#39;s weight to counteract the reclining of the chair back isolation; 
     FIG. 21A shows an exploded view of a means for movably mounting a seat on the seat support embodiment of the present invention; 
     FIG. 22 shows a view of an exploded view of an automatically adjustable headrest; 
     FIG. 23 is a side cutaway view showing an embodiment of a supplemental backrest adjustment mechanism; 
     FIG. 23A is an exploded view of the embodiment of FIG. 23; 
     FIG. 24 is a top view of an embodiment of a chair having a pivotable armrest development; 
     FIG. 25 is a top view of a pivotable armrest with the armrest cushion removed; 
     FIG. 26 is a side view of a pivotable armrest; 
     FIG. 27 is a rear view of a pivotable armrest; 
     FIG. 28 is a sectional view of a pivotable armrest taken along line  28 — 28  in FIG. 26; 
     FIG. 29 is a sectional view of a pivotable armrest taken along line  29 — 29  in FIG. 26; 
     FIG. 30 is a sectional view of a pivotable armrest taken along line  30 — 30  in FIG. 26; 
     FIG. 31 is a sectional view of a pivotable armrest taken along line  31 — 31  in FIG. 26; 
     FIG. 32 is a sectional view of a pivotable armrest taken along line  32 — 32  in FIG. 26; 
     FIG. 33 is a sectional view of a pivotable armrest taken along line  33 — 33  in FIG. 26; 
     FIG. 34 is a side view of a preferred embodiment of the inventive chair incorporating the inventive armrest and the inventive headrest; 
     FIG. 34A is a sectional view of the back of the chair of FIG. 34 taken along line  34 A— 34 A in FIG. 34; and 
     FIG. 34B is a sectional view of the back of the chair of FIG. 34 taken along line  34 B— 34 B in FIG.  34 . 
    
    
     DETAILED DESCRIPTION 
     The present invention comprises several developments that can be incorporated singly, or in any combination, into conventional chair designs. For example, the method and mechanism of the present invention for reclining the back of a chair can be used alone, or it could be used with the method and mechanism of the adjustable armrest, the method and mechanism of the adjustable headrest and/or the method and mechanism of the tilt mechanism. FIG. 34 illustrates a chair that incorporates several aspects of the present invention into a chair design specifically including the method and mechanism of the present invention for reclining the back of a chair, the method and mechanism of the adjustable armrest, the method and mechanism of the adjustable headrest and the method and mechanism of the tilt mechanism. 
     To understand how the present invention operates, the several separate inventive aspects are described separately. To start with, the method and mechanism for reclining the back of the seat in a way that uses the seat occupant&#39;s weight to counteract the reclining force is described. Thereafter, other inventive aspects of the inventive chair design are described. 
     Referring first to FIG. 1, it will be seen that the chair comprises a base  110 , a seat  111  which is secured to seat support  119  and a back support  113  which supports back  112 . The base  110  is supported on pintle  114  projecting upwardly from the center of five-legged pedestal  115 , the ends of the legs accommodating casters  116  supporting the chair on floor  117 . 
     Seat  111  is supported by seat support  119 , which in turn is connected to base  110  rearwardly by back support extension  123  and forwardly by support arm  120 . Specifically, back support extension  123  is connected to base  110  by horizontal pivot point  124  and to seat support  119  by horizontal pivot point  122 . Correspondingly, support arm  120  is connected to base  110  by horizontal pivot point  121  and to seat support  119  by horizontal pivot point  118 . As a result, the combination of base  110 , support arm  120 , seat support  119 , back support extension  123  and horizontal pivot points  118 ,  121 ,  122  and  124  form a substantially parallelogram linkage that permits movement between the forward and downward position in one direction (shown in FIG. 1) and the rearward and upward position of seat  111  in the other direction (shown in FIG.  2 ). 
     An imaginary horizontal extension of base  110  and support arm  120  forms a forward facing acute angle  101 , which, when the chair is in its resting position, is of at least about 5°, preferably of at least about 10°, and most preferably of at least about 20°. Nonetheless, the forward facing acute angle  101 , when the chair is in its resting position, is normally less than about 45° and preferably less than about 40°. A highly preferred forward facing acute angle  101 , when the chair is in its resting position, is about 26°. 
     Correspondingly, base  110  and back support extension  123  form a forward facing acute angle  102  which is typically less than the forward facing acute angle  101 . The forward facing acute angle  102 , when the chair is in its resting position, is of at least about 5°, preferably of at least about 8°, and most preferably of at least about 15°. Nonetheless, the forward facing acute angle  102 , when the chair is in its resting position, is normally less than about 40° and preferably less than about 30°. A highly preferred forward facing acute angle  102 , when the chair is in its resting position, is about 18°. 
     It is preferred that the raising of seat  111  to counteract the reclining of back support  113  lifts seat  111  between about 0.2 and 2 inches. Its is further preferred that the seat is raised between about 0.4 and 1 inch. In a particularly useful embodiment of the present reclining chair invention, the seat is raised by about 0.6 inches in the front and by about 0.8 inches in the rear. 
     As is apparent from the above description, the pivot point for the recline of the back support  124  is not the chair occupant&#39;s hip joint. Consequently, the recline of the back circumscribes an arc that is displaced from the arc based on the user&#39;s hip joint. However, the concurrent action of the reclining mechanism described herein of raising the seat produces a net positioning of the user that is substantially the same as the positioning which would have been achieved if the center of the back recline arc were coextensive with the hip joint. 
     FIGS. 1 and 2 also show spring means  125  which acts to restore back support  113  to its resting position when the chair is unoccupied. 
     Typically, both seat  111  and back  112  have a rigid shell, such as an injection molded plastic. It is preferred that seat  111  has a layer of a non-compressible, displacing gel. For example, a polyurethane gel is useful. Typically the gel pad on seat  111  is about half an inch thick and is located on top of a one inch thick layer of a conventional soft foam. It is further preferred that the seat  111  is shaped to reduce pressure points at the thickest portion of the gel. 
     Typically the back  112  has an about ¾ inch thick layer of a conventional soft foam attached to the rigid shell. 
     FIG. 21 provides another view of the interaction of the parts of the mechanism that uses the chair occupant&#39;s weight to counteract the reclining forces to help return the chair back to its upright or resting position. Again, chair back  113  is pivotally linked to base  110  at pivot point  124 . Chair back extension  123  continues and is pivotally linked to seat support  119  at pivot point  122 . Similarly, the front of base  110  is linked to the front of seat support  119  by the operation of link  120  which is pivotally coupled to base  110  at pivot point  118  and it is pivotally connected to seat support  119  at pivot point  121 . 
     FIG. 21 also shows spring  125  and telescoping spring guide  464  interacting through pillow block  715  with connecting element  350 , which is attached to back support arms  113 . 
     Also shown in FIG. 21 is a plurality of slots that permit the seat of the chair to be advanced forward or backward to alter the chair to better accommodate a user. In the embodiment shown in this figure, the slots anchor the seat in the appropriate position. 
     FIG. 21A shows a means to secure the movable seat in the desired position. In this embodiment, lifting lever  2100  causes lever  2100  to pivot about pivot joint  2110  and lift pin  2120  out of slot  2130 . When pin  2120  is out of slot  2130 , seat  111  can move along support  119 , while being attached by pin  2140  that has an enlarged head  2145  below support  119 . At its upper end, pin  2140  is attached to seat  111 . 
     An alternative mechanism for interconnecting the seat occupant&#39;s weight to the force to restore the chair to its upright position replaces support arm  120  with a mechanism that performs the same function as the four-bar mechanism described above can be substituted for the four-bar mechanism. For instance, support arm  120  could be replaced by a track mounted on base  110  and a traveler projecting downward from seat support  119 . When back support extension  123  is pivoted as back  112  is reclined, seat support  119  pulls the traveler up the track which is inclined in a backward direction. Desirably, the track or the traveler, or both, have a low friction surface such as polytetrafluoroethylene. 
     In the embodiments of the present invention having a headrest, it is preferred that the headrest has a layer of about one inch thick of a conventional soft foam. 
     A first embodiment of base  110  of the present invention is illustrated in FIG.  7 . As seen in this figure, base  110  is mounted on pintle  114  via piston  400 . Piston  400  is part of a conventional gas cylinder for raising or lowering the height of the chair. Base  110  has a forward pivot axis  121  and a rearward pivot axis  124 . In the reclining chair of the present invention, the pivot axes are connected to two links of the four-bar linkage that interconnects the reclining of the chair back with a raising of the seat. Base  110  also has a spring means  125  that applies a force to the chair so as to maintain the unoccupied chair in its upright position. Spring means  125  is mounted about cylinder  720 , which in turn is mounted on cylinder base  710  which is attached, preferably pivotably attached, to attachment point  700  which is an integral portion of base  110 . 
     Additionally, FIG. 7 also shows telescoping spring guide  464  (which is slidably mounted in spring cylinder  720 ). Pivotably seated on top of telescoping spring guide  464  is a top pillow block  715  which bears against connecting element  350  between back support arms  113 . 
     Desirably, the top pillow block  715  is made of a low friction material such as polytetrafluoroethylene commonly marketed under the Trade name TEFLON. 
     Also shown in FIG. 7 is extension  725 , attached to seat support or link  119 , which in automatically adjusting headrest embodiments can form an attachment platform for the rod that translates the recline of the chair back into a forward motion of the headrest. 
     In an alternative, preferred embodiment of the present invention, for purposes of tilting seat  111  and back  112 , base  110  has a somewhat inclined, two-part housing. For instance, as shown in FIGS. 8 and 10, top  320  of base  110  houses horizontal pivot points  121  and  124 . Also shown in FIG. 10 is housing  315  for a conventional mechanism (such as lever  317 ) for releasing a first conventional gas cylinder located in pintle  114  that controls the elevation of base  110 . This embodiment also has a second conventional gas cylinder, namely gas cylinder  300 . Gas cylinder  300  functions to tilt the portions of the chair above base  110  and all parts attached to top  320 . 
     FIG. 8 shows a side view of base  110  in the forward tilted position. In this view, base housing top  320  is substantially horizontal. Base housing top  320  is pivotally connected to base housing bottom  430  at horizontal pivot point  121 . Piston  420  of gas cylinder  300 , is pivotally connected to linkage  430  at pivot point  431 . In turn, linkage  430  is pivotally connected to linkage  433  at pivot point  432 , forming a crank, which is connected at pivot point  435  to linkage  437  which is secured to base housing top  320  at pivot point  439 . Through this linkage system, gas cylinder  300  applies a force to alter the tilting angle of the chair parts above it. 
     Also shown in FIG. 8 is a conventional linkage mechanism that operatively connects housing  315  (for lever  317 ) with a conventional release mechanism  405  for conventional gas cylinder  400  located in pintle  114  that controls the elevation of base  110 . 
     In a preferred embodiment of the mechanism of FIG. 8, the counterclockwise rotation of lever  317  activates conventional release mechanism  405 , whereas the clockwise rotation of lever  317  activates gas cylinder  300 . Concurrently, the clockwise rotation of lever  317 , because of slot  427 , permits the mechanism connecting lever  317  to gas cylinder  400  to “float” or slid in slot  427  and thereby not activate conventional release mechanism  405 . 
     FIG. 8 further shows the preferred spring mechanism that increases the tilt restoring force as the tilt angle is increased. Specifically, spring  125  is mounted on spring base  460  that is pivotally connected to mount  458  within chamber  456  of spring housing  450 . Arm  454  pivotally connects spring housing  450  to lower base housing part  408 . Mounted in spring  125  is spring piston  462 , the top of which, spring piston top (or telescoping spring guide)  464 , pushes against chamber  468  top  466 . 
     It is preferred that chamber  468  top  466  is an arc equidistant from spring base  460  mount  458  to chamber  468  top  466 . This arrangement allows spring  125  and piston assembly (or telescoping spring guide)  464  to move varying distances from pivot  124 , thereby increasing or reducing leverage force to back support  113 . 
     FIG. 9 shows a side view of base  110  in its full rearward tilt position. In this view, base housing top  320  is substantially inclined. In particular, arm  454  and its pivotal connection  452 , in this figure, has slid radially along the under-surface of top  466  to its position furthest from the pivot axis at  124 . Top  466  has an under-surface which is angled in a curvilinear fashion such that arm  454  connected to spring base  460 , spring piston  462  and piston assembly (or telescoping spring guide)  464  is tilted to the rear moving the top of spring  125  further from pivot  124  thereby increasing leverage. The top of telescoping spring guide  464  is pivotally seated in pillow block  715  so that it will slide along the arcuate under-surface of top  466  without changing compression of spring  125 . As a result of this repositioning, spring piston top  464  now pushes against chamber  468  top  466  at a point that is further from horizontal pivot point  124 . In other words, as the tilt mechanism increases is rearward tilt, the centerline of spring  125  tilts rearwardly at an increased angle relative to a vertical plane. These changes increase the leverage on spring  125  in the rear tilted position, producing a recline compression in spring  125  that increases as the angle of the tilt of spring  125  from the vertical plane increases and decreases as the angle of the tilt of spring  125  from the vertical plane decreases. The net effect is to increase the resistance of spring  125  to any further incremental deformation. This increase in spring  125 &#39;s resistance to incremental deformation provides greater resistance to support the increased load on the backrest resulting from the occupant being at a greater recline angle with more load of the occupant&#39;s upper body transferred to the back rest. 
     Spring  125 &#39;s resistance to incremental deformation can be increased as the chair is reclined in other ways. For example, any mechanism that tilts spring  125  away from horizontal pivot point  124  could accomplish this end. In an alternative embodiment, spring  125  is mounted on a pivoting base from which arises a shield. A manually engaged bar pushes against the shield and thereby tilts spring  125 . This tilting increases the distance between the top of spring  125  and horizontal pivot point  124 , which increases spring  125 &#39;s resistance to incremental deformation. 
     The functioning of the additional tilt mechanism of the present invention incorporated into a reclining chair is illustrated in FIGS. 5 and 6. FIG. 5 shows the chair in a resting position. Not shown in the FIGS. is a forward tilt position that the additional tilt mechanism is able to achieve. FIG. 6 shows a reclining chair with the additional tilt mechanism in an enhanced tilt position. 
     More particularly, in FIG. 5, top  320  of base  110  is in a somewhat horizontal position. As top  320  is the fixed link in the four-bar linkage that raises seat  111 , when top  320  is horizontal, seat  111  is also largely horizontal. Lower base housing part  408  is pivotally connected to top  320  of base  110  at pivot point  121 . When the chair occupant reclines in the chair, the additional tilt mechanism lowers the rear portion of top  320  while the forward portion of top  320  remains in substantially the same position. This movement of top  320  moves  454  about pivot  452 , which in turn lowers spring housing  450  and increases the angle between the centerline of spring  12 S and a vertical line going through the base of the centerline of spring  125 . This movement also increases the distance between pivot point  124  and the point at which spring  350  contacts back support  113 . 
     As noted above, this rotation of spring  125  increases the distance of the center of spring pressure which in turn increases the force urging the chair back into its resting position. However, this spring force requires the additional force provided by the occupant&#39;s weight to return the chair to the upright position when the chair occupant reclines. 
     Desirably, the additional tilt mechanism adds up to between about 1° and 15° of a forward tilt (i.e., a tilt in which the rear end of the seat rises in relation to the front) and it is more preferred that the additional tilt mechanism adds up to between about 3° and 10° of a forward tilt. It is yet further preferred that the additional tilt mechanism adds up to between about 4° and 8° of forward tilt. In a particularly preferred embodiment, the additional tilt mechanism adds up to about 6° of a forward tilt. 
     As noted above, the additional tilt mechanism add up to between about 1° and 12° of a rearward tilt (i.e., a tilt in which the rear end of the seat is lowered in relation to the front). It is more preferred that the additional tilt mechanism adds up to between about 2° and 10° of a rearward tilt. It is yet further preferred that the additional tilt mechanism adds up to between about 3° and 7° of rearward tilt. In a particularly preferred embodiment, the additional tilt mechanism adds up to about 5° of a rearward tilt. In adding an additional rearward tilt, caution must be taken to prevent the chair from reclining to a position such that the center of gravity of the occupied chair is moved significantly behind pintle  114  to prevent the chair from tumbling over backwards. 
     In a further aspect of the present invention, the chair is provided with a headrest that is urged forward as the back of the chair is tilted. The more the chair is tilted, the more the headrest moves forward. A preferred embodiment of this automatic headrest adjustment mechanism in a chair that incorporates both the reclining back that is opposed by the weight of the user and the automatically adjusting headrest developments of the present invention is illustrated by FIGS. 3 and 4. 
     Specifically, in addition to the several elements discussed in connection with the reclining mechanism of the chair of FIG. 1, this embodiment also includes automatically adjusting headrest  370 . 
     Mounted to the back of headrest  370  (also illustrated in an enlarged form in FIG. 20) is vertical adjustment bar  380 . Typically, there are a pair of parallel vertical adjustment bars  380  mounted to the back of headrest  370 . It is preferred that vertical adjustment bars have an adjustment range of between about 2 and 10 inches, and it is more preferred that these bars have an adjustment range of between about 3 and 7 inches in length. A particularly preferred range of vertical adjustment bar is about 5 inches. 
     Vertical adjustment bar(s)  380  pass through mounting  390 . It is preferred that mounting  390  and vertical adjustment bar  380  interact in a manner that retains the position of the headrest  370  relative to mounting  390 . For example, vertical adjustment bar  380  might be maintained in position within mounting  390  by a conventional frictional engagement. Alternatively, vertical adjustment bar  380  might have a plurality of apertures through which a mounting bar might pass to anchor vertical adjustment bar  380  within mounting  390 . A further alternative might consist of a conventional ratchet mechanism or substantially any other conventional means for fixing the position of a bar within a mounting. 
     Mounting  390  is affixed to a carriage  385 . Carriage  385  travels along a track on the interior side of back support extension  375 . Back support extension  375 , and correspondingly the track along the interior side of back support  375 , is curved. The curve of back support extension  375  (and hence of the interior track) corresponds to the arc through which a user&#39;s head travels when it the head is tilted back and forth when the user is seated. Desirably, this arc has a centerpoint corresponding to an imaginary axis through the shoulder joint of the user and a radius corresponding to the distance from this centerpoint to the bottom of the user&#39;s ear. 
     At carriage connection  365 , carriage  385  is pivotally connected to rod  360  at point  367 . Rod  360  is at its lower end, pivotally connected to seat support extension  725  at point  357 , which in turn is connected to seat support  119 . As the length of rod  360  is substantially fixed, the differential in arc between chair back  113  and lower rod pivot  725  combined with the additional lifting action of seat support  119  to which pivot  725  is a part results in an upward push on rod  360  which in turn moves head rest support carriage  385  in its track  375  to cause the desired upward and forward motion. This upward force causes carriage  385  to travel along the track that is on the interior side of back support  375  in an arcuate path. This movement of carriage  385  in turn, moves headrest from its position substantially aligned with back support  113  to a forward position shown in FIG.  4 . As a result of this motion, headrest  370  is positioned by the reclining of the chair into the position where it provides the head of the chair user the support needed when the user reclines. 
     Cut away view FIG. 20A shows a spring and piston mechanism that can be used to hold vertical adjustment bar(s)  380  in place in mounting  390 . 
     Cut away view FIG. 20B shows how tongue  387  of carriage  385  fits into track groove  377  of back support extension  375 . 
     Cut away view FIG. 20C shows how back support extension  375  is secured to back  113  by a conventional attachment means such as a screw. 
     FIGS. 20 and 22 provide alternative views of an embodiment of an automatically adjusting headrest according to the present invention. Upper and lower interior portions of headrest  370  are connected by vertical adjustment bars  380 . Vertical adjustment bars pass through mounting  390  as described above. 
     Mounting  390  is affixed to the upper portion of carriage  385 . Near the lower portion, rod  360  is connected to carriage at point  365 . 
     Carriage  385  travels along a track in back support extension  375  and is propelled by a force applied to carriage  385  by rod  360 . 
     Exploded view FIG. 22 shows an embodiment of the track in back support  375  along which carriage  385  travels. In this embodiment, the track is groove  377  which is in the interior side of each back support  375 . Complementarily, carriage  385  has a tongue  387  on each exterior side adapted to fit within grooves  377 . 
     Yet another aspect of the present invention is a mechanism for fixing the position of the adjustable arms which can be used in any chair, including the reclining chair of the present invention. FIGS. 11 and 12 illustrate a preferred embodiment of the mechanism for fixing the position of the adjustable arms. In FIG. 11, the mechanism is engaged and the arm is secured in its position. The same mechanism is shown in FIG. 12 where the mechanism is disengaged and the position of the arm can be readily changed. 
     More particularly, FIG. 11 shows armrest  600  in an in use (and locked) position. Armrest  600  is attached by a pair of pivot joints  615  and  620  to corresponding substantially parallel bars  625  and  630 . These bars  625  and  630  are connected to back  113 . In this embodiment, back  113  has at least two ratchet surfaces  640  and  650  located on opposite sides of the interior of back  113 . Secured to bar  625  by a connecting device  660  is locking bar  675  which has a ratchet face that is complementary to ratchet tooth  640 . Similarly, secured to bar  630  by a connecting device  665  is locking bar  670  which has a ratchet face that is complementary to ratchet tooth  650 . 
     When terminal end  610  of armrest  600  is gently raised, as shown in FIG. 12, bar  625  is pushed backward while concurrently bar  630  is pulled forward. This movement of bars  625  and  630  correspondingly cause complementary ratchet face  645  to disengage from ratchet tooth  640  and complementary ratchet face  655  to disengage from ratchet tooth  650 . In this disengaged condition, the armrests can be repositioned with very little effort. 
     To assist the engagement of the ratchet faces with the complementary ratchet teeth, the reverse side of the locking bars ( 670  and  675 ) can have a chamber into which a spring  34  can push against a piston  690  that in turn pushes against an interior wall of a chamber inside back support arms  113  to drive the ratchet teeth into the complementary ratchet faces. 
     Typically, the armrests are attached to the back of the chair about 6 to 12 inches above the rear portion of the seat. 
     Commonly when a chair has two armrests that are coupled together, the two armrests are linked by a pair of substantially “C” shaped rods. The locking mechanism interacts with these substantially “C” shaped rods at the points where the rods pass through the support for the chair&#39;s back, or a housing for this purpose mounted on the back of the chair. When the arms are not interconnected, the shape of the rods may be approximately quarter circle shaped. However, these shapes are general characterizations, any shape can be used provided the shape is effective to (i) position the two armrests substantially parallel to the sides of the seat (if the armrests incorporate the horizontal adjustment development of the present invention, then the armrests should be substantially parallel to the sides of the seat when the armrests are in a centered position) and (ii) not interfere with the user sitting back in the chair. 
     U.S. Pat. No. 5,292,097 to Russell discloses a variety of alternative locking mechanisms that can readily be adapted for use in support of the armrest of the present invention. This patent is hereby incorporated by reference. 
     FIGS. 13 and 14 illustrate an alternative embodiment of the mechanism for fixing the position of the adjustable arms. In this embodiment, only lower bar  630  has a ratchet face which engages with a ratchet tooth  650 . Correspondingly, FIGS. 15 and 16 illustrate a further embodiment of the mechanism for fixing the position of the adjustable arms in which only upper bar  625  is connected to a ratchet face  645  that engages a ratchet tooth  640 . 
     In a preferred embodiment of the mechanism for fixing the position of the adjustable arms, for a chair having a left and a right arm, the two arms are interconnected so that the adjustment of one arm adjusts the other. In such an embodiment, a preferred configuration is one in which only upper bar  625  on one arm, e.g., the right arm, has a ratchet face  645  and a corresponding ratchet tooth  640  and on the other are, the left arm in this example, only the lower bar  630  has a ratchet face  655  and a ratchet tooth  650 . In such embodiments, there are two ratchet mechanisms (one on an upper bar and one on a lower bar) between the two arms that cooperate to control the positioning of the arms. 
     FIG. 17 provides an isometric view of a pair of armrests in which the upper and the lower bars are interconnected. Specifically, armrests  600  are supported by upper bars  625  and lower bars  630 . Within back supports  113 , the upper bars  625  and lower bars  630  engage and disengage with the positioning mechanisms. Upper bars  625  are interconnected by connecting bar  637  and lower bars  630  are interconnected by connecting bar  633 . 
     FIG. 18 provides an isometric view of a pair of armrests in which the upper and lower bars are independent. In this embodiment, the repositioning of one arm does not effect the position of the other. 
     FIG. 19 provides an isometric view of a pair of armrests in which upper bars  625  are interconnected. In this embodiment, the repositioning of one arm is translated into the repositioning of the other arm by means of connecting bar  637 . 
     In an alternative embodiment, connecting bar  637  may include a conventional means to connect and disconnect the bar, such as a sliding bar or a set screw. In such an embodiment, the user can choose to have the adjustment of one armrest adjust the other when the connecting bar is used or the adjustment of one armrest becomes independent of the other when the connecting bar is disengaged. 
     FIG. 23 shows yet a still further aspect of the present invention that can be incorporated into the reclining chair of the present invention or any other chair having a back support  113  and a separate seat back  112 . In this embodiment, a track  900  mounted on the forward side of back support  113 . Seat back  112  has a pair of carriages adapted to travel on these tracks  900 . In addition, either track  900  or carriage  910  has a conventional locking mechanism for fixing the position of carriage  910  on track  900 . 
     Useful conventional locking mechanisms include ratchet mechanisms, levers that cause the carriage  910  to clamp onto track  900 , screw mechanisms, and mechanisms in which a pin is inserted to fix the carriage position. 
     In a particularly preferred embodiment of the track  900  and carriage  910  mechanism, carriage  910  also has a conventional pivot mechanism that permits seat back  112  to rotate somewhat about this pivot and provide a further adjustment to better support the chair occupant. Such an embodiment is illustrated in FIG.  23 A. To fix carriage  910  into the appropriate position, lever  920  is attached to carriage  910 . Mounted on lever  920  is pin  930  which when engaged fits into one of a plurality of slots  940 . Conversely, when lever  920  is pulled and pin  930  is withdrawn from slot  940 , carriage  910  can be moved up or down along track  900  and then when lever  920  is returned to its engagement position, pin  930  enters a new slot  940  and secures seat back  112  into position. A spring can be employed to urge lever  920  into engagement. 
     Additionally, seat  111 , or alternatively a conventional seat pan located directly under seat  111 , can be mounted on a pair of carriages that are adapted to travel along a track mounted on the top of seat supports  119 . Desirably such carriages would also have a conventional means for fixing the position of the carriages on the track. Additionally, it is also desirable that such tracks have stops on each end of the track to prevent the carriage from traveling beyond the end of the tracks. By putting seat  111  on such a track mechanism, the user is provided with yet another means of ensuring that the seat conforms the geometry of the user&#39;s body, and not vice versa. 
     A further development in armrests that can be incorporated into the adjustable armrests of the present invention, or into conventional armrests is a mechanism to permit pivotal horizontal repositioning of the armrests As illustrated in FIGS. 24 through 33. For instance, as shown in FIG. 24, armrest  600  can be pivoted either inward or outward. This additional pivoting of the armrest allows the user to position the armrest under the user&#39;s forearm when the user is performing a task such as typing on a keyboard. As a result, the chair provides more support to the user and as a result, it is believed that the user will be less worn as a result of using such support. 
     Turning now to FIG. 25, a top  800  view of an embodiment of a pivoting armrest taken without the cushioning. Starting at the back of armrest  600 , there is clevis base  810  which attaches to bars  625  and  630  to support armrest  600 . Within clevis base  810  there is a pivot pin that permits the rotation of armrest  600  about pin  805 . However, to restrict the range of rotation available in armrest  600 , attached to pivot pin  805  is index arm  820  whose motion is restricted by index arm limiters  815 . Additionally, to prevent free pivoting of armrest  600 , the armrest also has bar  825  with grooves into which index bar  820  can be secured. 
     In the embodiment of FIG. 25, bar  825  is locked into place (or permitted to swing freely) by the cooperative action of spring  830 , cam follower  840 , cam cut-out  845  and sliding lock-release control  835 . When sliding lock-release control  835  is in the position shown, spring  830  urges bar  825  towards index arm  820  so as to lock pivoting armrest  600  in place. However, when sliding lock-release control is slid into its alternate position, cam follower  840  is positioned in its alternate position in cam cut-out  845 , which releases the tension of spring  830  on bar  825  and thereby permitting index arm  820  to be moved into a different groove. If cam follower  840  is left in the detent position, lock bar  825  is disengaged so that armrest  600  can move freely. 
     In a further preferred embodiment of the pivoting armrest, the distance between adjacent grooves represents about  50  of pivoting. Thus, if there are six grooves, armrest  600  can be pivoted through about 30° of pivoting. 
     FIG. 26 shows a side view of a pivoting armrest embodiment. In this view, armrest  600  is attached to bars  625  and  630  by conventional fastening means  615  and  620 , respectively. Useful fastening means include nuts and bolts, and clevis pins. 
     Also in this view clevis base  810  is seen as is pivot pin  805 . Additionally, index arm limiter  815  is seen in the plane of index arm  820 . Spring  830  urges bar  825  into index arm  820 . Sliding lock-release control  835  projects out slightly from armrest  600 . Screws  850  attach the cushioning top to the armrest body. 
     It is particularly preferred that the sliding lock-release control  835  is positioned under the interior tip of the user&#39;s thumb on one side and the user&#39;s fingers on the other so that the user can readily adjust the pivot position of the armrest. 
     FIG. 27 shows a rear view of a pivoting armrest. In this view, clevis base  810  and sliding lock-release controller  835  are apparent. 
     FIG. 28 shows a sectional view of armrest  600  taken along line  28 — 28  in FIG.  26 . In this view, both the locked and released positions of sliding lock-release control  835  can be seen. 
     FIG. 29 shows a sectional view of armrest  600  taken along line  29 — 29  in FIG.  26 . 
     FIG. 30 shows a sectional view of armrest  600  taken along line  30 — 30  in FIG.  26 . 
     FIG. 31 shows a sectional view of armrest  600  taken along line  31 — 31  in FIG.  26 . 
     FIG. 32 shows a sectional view of armrest  600  taken along line  32 — 32  in FIG.  26 . 
     FIG. 33 shows a sectional view of armrest  600  taken along line  33 — 33  in FIG.  26 .