Abstract:
An ergonomic chair includes a four-bar linkage arrangement wherein a lower frame member is provided with a rigid front support and a rigid rear support with a seat member pivotably connected to the front support. A back rest has an upper support pivotably connected at an upper end of the rear support of the lower frame member. A link member pivotably connects at a first end to a rear support of the seat member and at second end to a lower support of the back rest. This novel arrangement permits tilting movement of the backrest rearwardly relative to the lower frame member causing elevation of a rear portion of the seat member, permitting the feet to remain on the floor and alleviating pressure on the user&#39;s thighs.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a chair of the type suitable for use in an office environment and, more particularly, to a reclining office chair having several structural and operating features which offer a number of ergonomic advantages over the prior art. 
     2. Description of the Related Art 
     Over many years attempts have been made to design chairs for use in office environments which are comfortable to use and thereby avoid user fatigue over prolonged use. In one simple form a chair may be provided with a swivel base for ease of turning and include a control mechanism which permits the chair to rock. A disadvantage of these relatively simple chairs is that conjoint rocking motion of the chair seat and back naturally lifts the user&#39;s feet off the floor, which can create stability problems and place upward force on the front of the user&#39;s thighs which can reduce fluid circulation in the user&#39;s legs. 
     To improve on the foregoing chair construction, chair controls are known which provide for synchronous movement of the chair seat and back. Where office chairs are concerned, a “synchronous control” means the arrangement of a combined or dependent back adjustment and seat adjustment, that is to say the adjustment of the back inclination fundamentally also results in an adjustment of the sitting surface. An example of a synchronous chair control is disclosed in U.S. Pat. No. 5,318,345, issued to Olson and assigned to the common assignee herein. With the aforementioned Olson control, the chair back is designed to tilt at one predetermined rate of recline while the seat tilts synchronously at a much lesser rate. The result is that the user&#39;s feet are not lifted from the floor when the back is reclined. Also, fluid circulation in the user&#39;s legs is not interrupted by substantial upward movement of the forward end of the seat. Another advantage of this control is that undesirable “shirt pull” is minimized by the strategic location of the tilt axis. Other examples of synchronous chair controls are disclosed in U.S. Pat. Nos. 5,366,274 and 5,860,701 to name a few. 
     Another feature embodied in recently designed office chairs that offers considerable ergonomic advantages is a tilt limiter feature for the chair back. With such a mechanism built into the chair control, the user may selectively set the degree of back recline at a predetermined angle thereby adding to comfort as the chair is used. An example of such a tilt limiter mechanism is disclosed in U.S. Pat. No. 6,102,477 issued to Kurtz and assigned to the common assignee herein. This particular mechanism offers the advantage of providing for infinitely variable angles of tilt within a predetermined overall range. The mechanism is also highly cost-effective to construct. 
     Yet another feature of current ergonomically designed chairs is the provision of height and pivot adjustable arm pads. Such a feature is particularly advantageous in providing the user with additional support to the arms, forearms, wrists and shoulders in order to minimize repetitive stress injuries when the user is keyboarding, for example, while seated in the chair. An example of such an adjustable arm pad is disclosed in U.S. Pat. No. 5,908,221 issued to Neil. One advantage of the &#39;221 structure is that it uses gas cylinders for arm pad height adjustment and thus is easily adjusted with the push of a single button. 
     Yet another feature of current ergonomically designed office chairs includes an adjustable lumbar support mechanism for providing preselected chair back tension in the region of the user&#39;s lower back. An adjustable lumbar support allows the chair user to select a comfortable level of pressure on the lower back depending upon the specific office task being performed. Such a mechanism is disclosed, for example, in U.S. Pat. No. 5,797,652. 
     Still another feature of certain ergonomically designed office chairs, particularly of recent vintage, is the incorporation of fabric mesh into the construction of the chair seat, and/or back. While mesh materials are well-known in the construction of lawn furniture seating, it has only been relatively recently that such materials have been used successfully in office seating. These materials offer the advantage of enhanced air circulation for and consequent heat transfer from the chair user&#39;s body, which can improve the comfort of the chair. An example of the use of such fabric mesh in an office chair is disclosed in U.S. Pat. No. 6,125,521 issued to Stumpf et al. 
     Yet another feature of certain ergonomically designed chairs is the provision of a seat cushion having the capability of effecting heat transfer from the chair user&#39;s buttocks area while at the same time offering comfort to the user while seated, together with adequate support. Known seat cushions having such capability may involve a passive or active air flow circulation feature of the type disclosed, for example, in U.S. Pat. No. 6,179,706. 
     SUMMARY OF THE INVENTION 
     The present invention provides a totally redesigned ergonomic chair that incorporates improved functional aspects in all areas of a modular chair construction and in its use, including tilt limit control, seat adjustment, arm adjustment, lumbar support, cushion airflow, mesh attachment and modular base frame assembly. 
     The various subfeatures of these modular components are the subject of the following individual applications filed of even date herewith, all commonly assigned, the disclosures of which are incorporated in full by reference: 
     Multi-position Tilt Limiting Mechanism, application Ser. No. 09/882,500 
     Locking Device for Chair Seat Horizontal Adjustment Mechanism, application Ser. No. 09/881,896. 
     Height and Pivot Adjustable Chair Arm, application Ser. No. 09/881,818. 
     Lumbar Support for a Chair, application Ser. No. 09/881,795. 
     Body Support Member, application Ser. No. 09/882,503. 
     Chair Back Construction, application Ser. No. 09/882,237. 
     Chair of Modular Construction, application Ser. No. 09/881,897. 
     In each of these cases, features combine to provide an overall chair that is a significant improvement over the prior art. 
     Thus, for example, the present invention provides a reclining chair having a four bar linkage system that causes the rear of the seat to elevate as the back is reclined lending an unusual and comfortable balance during reclining. A tilt limit control conveniently and effectively limits the degree of chair back tilt to one of three reclined positions by manual movement of a simple lever. Horizontal positioning of the chair seat cushion is accomplished using a simple locking device that allows the chair user to simply lift up on the front of the cushion and select a preferred horizontal cushion position. Height and pivot adjustable chair arms are actuated with the push of a button by gas cylinders lending convenient adjustment to suit a specific work task. A lumbar support is easily height adjustable, by providing tension to the back frame and requires no screws or adjustment knobs in its adjustment mechanism. A modular cushion includes a comfortable heat absorbing gel layer and is vented uniquely for air circulation. The back of the chair is of fabric mesh construction and includes a novel attachment system for superior comfort. The base of the chair is of modular construction that provides for ease of assembly and lends rigidity to the chair construction. 
     The present invention improves over the prior art by providing an ergonomic chair having a four-bar linkage arrangement wherein a lower frame member is provided with a rigid front support and a rigid rear support with a seat member pivotably connected to the front support. A back rest has an upper support pivotably connected at an upper end of the rear support of the lower frame member. A link member pivotably connects at a first end to a rear support of the seat member and at second end to a lower support of the back rest. This novel arrangement permits tilting movement of the backrest rearwardly relative to the lower frame member causing elevation of a rear portion of the seat member, permitting the feet to remain on the floor and alleviating pressure on the user&#39;s thighs. This is accomplished by a linkage mechanism creating an instantaneous center of rotation of the chair seat and back that is approximately at the user&#39;s hip. A further advantage is that the movement of the seat and back reduces undesirable “shirt pull.” Still further, the user sitting in the chair will feel a weight reduction effect as a result of lift of the seat back during reclining. The apparent weight reduction will be sensed as lightness and give the feel of comfort. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other novel features and advantages of the invention will be better understood upon a reading of the following detailed description taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a left front perspective view of an ergonomic chair constructed in accordance with the principles of the invention and incorporating all of the improved modular components; 
     FIG. 2 is a right front perspective view thereof; 
     FIG. 2 a  is an exploded perspective view thereof; 
     FIG. 3 is a right side view thereof; 
     FIG. 4 is a left side view thereof; 
     FIG. 5 is a front view thereof; 
     FIG. 6 is a rear view thereof; 
     FIG. 7 is a top view thereof; 
     FIG. 8 is a bottom view thereof; 
     FIG. 9 is a bottom view thereof with the chair base removed; 
     FIG. 9 a  is a partial top view of the chair seat with the cushion removed; 
     FIG. 10 is a partial left side view illustrating the chair in a fully upright position; 
     FIG. 10 a  is a side schematic view showing the preferred dimensional relationships between the chair components with the chair back in a fully upright position; 
     FIG. 11 is a partial left side view of the chair shown in a partially reclined position; 
     FIG. 12 is a partial left side view of the chair shown in a fully reclined position; 
     FIG. 12 a  is a side schematic view showing the preferred dimensional relationships between the chair components when the chair back is in a fully reclined position; 
     FIG. 13 is a side schematic view showing the linkage arrangement of the chair; and 
     FIG. 14 is a side schematic view showing the kinematics of the chair. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, and initially to FIGS. 1,  2  and  2   a , an improved ergonomic chair constructed in accordance with the numerous principles of the invention is shown in front perspective and designated generally by the reference numeral  10 . The chair  10  comprises as its principal components a seat  12  and back  14 . Suitable arms  16  having upper pads  18  may be provided. The chair  10 , in a conventional manner, may be supported on a spider base  20  movable on casters  22 . 
     As shown in FIGS. 3-9, the chair  10  is so constructed as to have synchronous movement of the seat  12  and back  14 . To this end, a pair of main seat and back supports  24  are rigidly attached to a central support module  25  having a hub  26  for frictionally receiving the upper end of a gas cylinder  28 . The seat and back supports include first or front support portions  100  forming front pivots  101  and second or rear support portions  102  forming rear pivots  105 . The gas cylinder  28  is preferably a two-stage type available from Stablis GmbH of Germany. This cylinder  28  is operable by a manually pivotable lever  30  which activates the cylinder  28  for height and the adjustability of the chair  10  in a manner well-known in the art. The chair arms  16  are rigidly connected to the supports  24 . A seat pan  32  is pivotably connected at its front end portion  104  to the pivots  101  of the forward end portions  100  of the supports  24 . A back frame  34  is generally vertically disposed and includes a top part  120 , a bottom part  122  and a middle part  124 . The back  14  is connected to the top and middle parts of the back frame. The back frame is pivotably connected at its middle part to rear pivots  105  of the rear support portions  102  of the supports  24 . The chair back  14  in the preferred embodiment is of fabric mesh  36  construction supported around its periphery by a carrier  38 . An adjustable lumbar support member  40  slidably connects to the carrier  38  and bears against the back frame assembly  34 . 
     The relative positions of the seat  12  and back  14  of the chair  10  during reclining of the back  14 , can be seen in the side views of FIGS. 10-12. As illustrated in these views, the chair seat pan  32  is pivotably connected at its front end portion  104  to the pivots  101 , also known as pivot points P 12  of the supports  24 , (only one of which can be seen). At the rear  106  of the seat pan  32  another set of pivots  130  are formed, also known as rear pivots P 32 . These are connected to a pair of links  42  (only one of which can be seen). Each link  42  in turn is pivotably connected at pivots  132  (also known as pivot point P 34 ) to forward extensions of the bottom part  122  of the back frame assembly  34 . The back frame assembly is also pivotably connected through its middle part  124  at point P 14  (also known as pivots  105 ) to the two supports  24 . As shown in the dimensional schematic FIG. 10 a , when the chair back  14  is in a fully upright position the seat pan  32  in one preferred form is inclined to the rear and forms an angle of about 15.7 degrees from horizontal although this angle can be in a range of between about 10 and 20 degrees. The distance between pivot points P 12  and P 32  is about 12.889 inches and the distance between pivot points P 32  and P 34  of the links  42  is approximately 2.01 inches although these distances can be in ranges of between about 10 and 15 inches and about 1.5 to 2.5 inches, respectively. Further, the distance between pivot points P 14  and P 34  is approximately 4.71 inches while the horizontal distance between pivot points P 12  and P 14  may be in a range of between about 12 and 17 inches. As shown in the three stages of back tilt illustrated in FIGS. 10-12, as the back  14  reclines rearwardly, the link  42  moves in a counterclockwise direction of rotation causing the rear of the seat pan  32  to elevate relative to its front. In the fully reclined position of the back  14  as shown in the schematic of FIG. 12 a  the seat pan preferably reduces its angle of inclination with horizontal from 15.7 degrees (FIG. 10 a ) to 8.7 degrees while the afore-described distances between all pivot points remains constant. The reduced inclination angle may be in a range of between about 6 and 10 degrees. This synchronous motion of the seat pan  32  and back  14  provides for an exceptionally comfortable reclining motion of the chair  10  user to aid in avoiding fatigue as the user is performing various work-related tasks. 
     Shown now in FIGS. 13 and 14 are schematic views of the synchronous seat and back tilt feature employing a four-bar mechanism which allows the rear of the seat to elevate as the backrest is reclined. The mechanism is designed to immediately respond to a user exerting a back force and/or self-weight on the seat. This function allows for reclining of the chair  10  about a rotation point C that is very closely coincident with the pivot axis of the user&#39;s hips and avoids undesirable “shirt pull” of the user. Because the rear of the seat is elevated during back reclining, excess pressure is relieved at the front underside of the user&#39;s thighs, and also a relatively constant gaze angle is maintained during reclining. This provides for adequate fluid circulation in the user&#39;s legs and avoids swelling. To accomplish the foregoing advantages, the chair  10  comprises four basic members and four rotationally-free pivots. The basic members include a floor supported member  60 , a seat rest  62 , a linking member  64  and a backrest  66 . The floor supported member  60  has an upwardly directed portion  68  that terminates at an end defining pivot point P 12  to which the seat rest  62  is pivotably connected at its forward portion. The member  60  also has an upwardly directed portion  70  which terminates at an end defining pivot point P 14  to which the backrest  66  is pivotably connected. A lower portion  72  of the back rest  66  is pivotably connected at point P 34  to the linking member  64  and a downwardly extending portion  74  of the seat rest  62  is pivotably connected at point P 32  to the other end of the linking member  64 . 
     The kinematics of the chair  10  are illustrated in FIG.  14 . As force F is applied on the backrest  66 , the back tilt angle β increases, eye location shifts backwards an amount ΔH 1 , and eye elevation decreases by an amount ΔV 3 . The change in back tilt angle β transmits motion by way of the upper and lower back pivots P 14  and P 34 , respectively, to the linking member  64 . As a result of motion set in linking member  64 , the rear seat pivot P 32  moves in coordination with pivot P 34  in a composite rotational and translation motion. As the seat rest  62  rotates about pivot P 12 , a lift ΔV 2  is caused in the rear part of the seat rest  62  relative to its front edge ΔV 1  in the amount ΔV 2 −ΔV 1 , therefore introducing a seat rest angle α. The user sitting in the chair will feel a weight reduction effect as a result of the lift. The apparent weight reduction will be sensed as lightness and give the feel of comfort. 
     In order to assist the chair linkage mechanism in allowing the back  14  to maintain a fully upright position when the chair  10  is not in use, as shown in FIG. 9 a  one or more extension springs  80  may be connected between pivot shaft  82  and a rear edge portion  84  of the seat pan  32 . The pivot shaft essentially defines pivot points P 34  and will cause a return force to be exerted on back frame assembly  34  by the springs  80 . 
     It can now be appreciated that a chair  10  constructed according to the invention offers considerable advantages in user comfort by virtue of its synchronous linkage construction particularly where it is used for prolonged periods of time. The chair  10  is also cost effective to manufacture and assemble. 
     While the present invention has been described in connection with a preferred embodiment, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the true spirit and scope of the present invention. Accordingly, it is intended by the appended claims to cover all such changes and modifications as come within the spirit and scope of the invention.