SHELL CHAIR AND TILT MECHANISM

Abstract: A one-piece shell chair (l0) includes an uni­ tary integrally formed shell body (l2) having a flexurally supported seat pan (l4). The seat (l2) is mounted to a tilt mechanism (28) which pivots the seat (l2) about an axis forward and below the front edge (l4a) of the seat pan (l4) enabling the user's feet to remain stationary on the floor. The tilt mechanism (28) and the flexure axis (25) are so positioned with respect to each other such that any rise in the front portion (l4a) of the shell (l2) due to pivoting of the shell (l2) as a unit rearwardly about the flexural axis (25) is negated at least in part by relative downward movement of the front portion (l4a) of the shell (l2) due to rotation of the shell (l2) as a unit backwardly about the tilt axis (32) so that upward movement of the shell front portion (l4a) is minimized during backward tilting of the shell (l2) about the tilt axis (28). Accordingly, the seat (l2) and tilt mechanism (28) provide a comfortable, convenient and accommodating chair (l0).

Description: Technical Field The invention relates to a posture chair having a tilt mechanism which cooperates with an independent seat and backrest of a one-piece shell chair. Background Art Tilt mechanisms are well recognized in the chair art. Most of these mechanisms tilt about an axis near the center of the chair. When the user tilts in these chairs, it can result in the tilting off the center of gravity which results in an unnatural reaction by the user. Further, the front edge of the seat is lifted away from the floor which raises the user's legs vertically and frequently moves the feet off the floor. This action has a tendency to impair circulation in the legs of the user. The reaction of the user to this tilting applies stress and compression to portions of the body, resulting in fatigue. Some mechanisms are designed to tilt about an axis at the front of the seat. The reaction to the user is still believed to be somewhat unnatural with such a tilt mechanism. Representative of the art to accommodate move­ ments of users are U.S. Patent 3 982 785, issued September 28, l976, and U.S. Patent 4 084 850 issued April l8, l978. Both of these patents disclose chairs with seats which automatically slide backward and forward while the backs tilt backwardly independent of the movements of the seat. Disclosure of the Invention According to the invention, there is provided a chair including a seat and backrest adapted to provide postural support to a wide variety of people of different shapes and sizes through a variety of different seat po­ sitions. Means in the seat and backrest react to the shape and movements of the user to maintain appropriate support in the back and seat. A base is mounted to the seat and backrest and comprises a tilt mechanism adapted to permit rotation of the seat and backrest about an axis beneath the knee and forward of the center of gravity of a user. The seat and backrest form a relatively rigid shell. Flexu­ ral support means support the rigid shell in a cantilevered fashion for flexural pivoting of the shell as a unit about a flexure axis transversely of the shell. A support means for the shell comprises a tilt mechanism and lever exten­ ding downwardly from the shell to the tilt mechanism, the latter of which is adapted to permit resilient rotation of the shell with respect to the support means about a tilt axis beneath the knee and forwardly of the center of gravi­ ty of the user such that the shell pivots rearwardly and downwardly upon tilting. The tilt mechanism and the flexu­ re axis are also so positioned with respect to each other such that any rise in the front portion of the shell due to pivoting of the shell as the unit rearwardly about the fle­ xure axis is negated at least in part by relative downward movement of the front portion of the shell due to rotation of the shell as a unit backwardly about the tilt axis so that upward movement of the shell front portion is mini­ mized during backward tilting of the shell about the tilt axis. The tilt mechanism preferably has two frame members which are connected at one end to the shell near the fle­ xure axis. The other ends of the frame members are connec­ ted by a torsion bar or a bushed rubber spring. Brief Description of the Drawings The invention will be described with reference to the accompanying drawings in which: Figure l is a perspective view of the preferred embodiment of the invention; Figure 2 is a side sectional view of the inven­ tion taken along lines 2-2 of Figure l; Figure 3 is a plan view of the chair shown in Figures l and 2; Figure 4 is an enlarged cross-sectional view of the chair taken along lines 4-4 of Figure 3; Figure 5 is an enlarged sectional view taken along lines 5-5 of Figure 3. Best Mode for Carrying out the Invention Referring to the drawings where like numerals have been used to describe like parts and to Figures l-5 in particular, a chair l0 has a unitary shell body l2 supported on a tilt mechanism 28 which in turn is sup­ ported on a five-star roller base 22. The shell body l2 is generally configured to the correct postural shape of a human torso in an ordinary seated position and is adapted to accommodate different body shapes and sizes while maintaining correct postural support. The shell body l2 reacts to the user's macro and micro-movements without the necessity of any adjustments to the chair l0. Accordingly, the chair l0 is both convenient and comfortable. The unitary shell l2 is formed by a seat pan l4 and a backrest l6 with a generally H-shaped opening 20 therebetween and joined by resilient webs l8. The H-­ shaped opening 20 has two leg slots l9a, l9b and 2la, 2lb which extend from a mid-back portion l7 of the back­ rest l6 to a mid-thigh portion l5 of the seat pan l4 near side edges of the seat pan l4 and backrest l6. The leg slots l9a, l9b and 2la, 2lb are coextensive with each other and are joined by a horizontal cross-slot 23. The slots l9b, 23 and 2lb define a cantilevered seat support l4b and the slots 2la, 23 and l9a define a cantilevered back support l6a. As used herein, the portions of the straps l8 adjacent the slots l9b and 2lb are called "seat web" and the portions of the straps l8 adjacent the slots l9a and 2la are called "back web." The seat straps and the back straps are joined by a "flexure web." The slots l9b and 2lb extend forwardly in the seat at least one-half of the back-to-front seat length thereof and preferably about two-thirds of the back-to-front length. The length of the slots l9b, 2lb is selected to provide a convenient flexure axis of the seat as a unit with respect to the straps l8 adjacent the slots l9b, 2lb. Typically the length of the slots will be in the range of ll to l5 inches measured from the end of lip l4c along the centerline of the seat support l4b. The flexure axis for the seat with respect to the straps l8 will generally be at the forwardmost point of slots l9b, 2lb. Thus, in the embodiment shown in the drawings, the flexure axis for the seat is indicated by the phantom line 25 in Figure 3. Thus, the entire seat pan l4, except for straps l8, including the seat support l4b and the front edge l4a, moves as a rigid unit about flexure axis 25 when the seat is occupied and shifts in weight distribution on various portions of the chair occur. The flexure movement of the chair seat l4 about the flexure axis 25 is illustrated in phantom lines in Figure 4. An upturned lip l4c is formed on the back por­ tion of the cantilevered seat support l4b to rigidify the seat support l4b and to form a positioning means for correct placement of the occupant in the seat. The cantilevered seat support l4b is generally concave in shape and defines a surface which is closely contoured to the human ischial tuberosities. In like manner, a flexure axis 26 results at the upper portion of the straps l8 adjacent the end of the slots l9a, 2la. The backrest l6, except for the back webs, moves as a unit, flexing about flexure axis 26. The slots l9a, 2la, which control the location of the flexure axis 26, extend up along the sides of the backrest to a point generally between a midpoint on an occupant's spine at the intersection of the thoracic curve and the lumbar curve. In terms of the backrest structure, the slots l9a, 2la extend up the backrest about half way between the seat and top of the backrest for a normal size backrest. The relative length would be different for a low-back chair or a high-back chair but the absolute length of the slots l9a, 2la from the bottom of the back support l6a would be about the same, eg. in the range of 6 to 8 inches. As illustrated in Figure 4, the backrest has a convex shape in vertical cross-section to conform with the shape of the spine of a human torso seated in the chair. The bottom portion of the back support l6a is turned outwardly at l6b to avoid pinching between the edges of the seat support l4b and back support l6a. In addition, the top portion of the backrest l6 has an outwardly turned rim l6c. Both the outwardly turned rim l6c and the outwardly turned bottom edge l6b provide rigidity to the backrest so that the backrest moves as a whole about the flexure axis 26. The movement of the backrest as a unit about flexure axis 26 is illustrated by phantom lines in Figure 4. The shell seat l2, including the seat pan l4 and backrest l6, may be covered with padding and/or a fabric material for the further comfort of the occupant or aesthetic reasons or may be used simply in the shell form. The padding can be formed in an in-situ molding process with the padding being molded to the chair through a well-known foam molding process. One or both sides of the shell can be covered so long as there is little or no restriction of the cantilevered supports l6a and l4b with respect to the straps l8. Conventional upholstery can also be used. The H-shaped opening 20 may also be viewed as two U-shaped slots joined at the bight portions thereof. It is conceivable that the bight portions of the U-shaped slot need not join and a portion of the shell could divide the two U-shaped slots. The shell seat l2 is supported at the sides l3 of the seat pan l4 by the tilt mechanism 28 which allows the seat l2 to pivot with respect to the base 22. The tilt mechanism 28 has two frame members 30 which are connected at one end thereof to the straps l8 adjacent the slots l9b and 2lb with conventional fasteners (not shown). Between the other ends of the frame members 30 is a torsion bar 32 which restrains the tilting of the chair l0 when occupied. The torque or resistance which is provided by the torsion bar 32 is adjusted by an adjusting handle 34 which tightens or loosens the stiffness of the torsion bar 32, affecting the resis­ tance of the tilt mechanism 28 to pivot. The tilt mechanism 28 is preferably made of cast aluminum. Torsion-bar tilt mechanisms are well known in the chair iron art and for that reason will not be further described herein. Alternatively, a bushed rubber spring can be used in lieu of the torsion bar 32. Preferably, the axis of the tilt mechanism is so positioned that the axis of rotation of the chair user will be forward of the user's center of gravity, preferably forwardly of the front of the chair and below knee level, preferably at ankle level. By this mechanism, the user can tilt back in the chair without increased pressure beneath the thighs and without a loss of a sense of balance. In this connection, it is seen in Figure 4 that the front edge l4a of the seat pan l4 rises slightly as the seat pan flexes about the flexure axis 25. This rise is compensated for by the pivoting of the chair about axis of rotation of the tilt mechanism. Thus on tilting of the chair and flexing of the seat pan l4, the front edge l4a will not rise with respect to the floor. The tilt mechanism 28 is supported by the pedestal base 22 which includes an adjustable height mechanism 27, a five-pronged frame 27 and five rollers 24. The adjustable height mechanism can be any conven­ tional height mechanism which allow height adjustment by rotation of the shell l2 about the base 22, thereby enabling one to select the vertical height at which the seat pan l4 is positioned. Mechanical height adjustment mechanisms are also well known in the chair base art and, for this reason, will not be further described herein. Each of the five rollers 24 is connected to a prong 3l of the frame 27 in conventional fashion. Although the base 22 is depicted as having wheels, a fixed wheelless base can alternatively be used. The tilt mechanism 28 enables the seat pan l4 and backrest l6 to pivot downwardly at an angle relative to the front edge l4a of the seat pan l4, as best seen in Figure 2. When an occupant sits back and reclines in the seat pocket l8, the seat pan l4 and backrest l6 will pivot below the knee or calf location of the user, thereby enabling the occupant's feet and ankles to remain stationary on the floor. Further, as the occu­ pant leans back and moves about the seat pocket l8, the seat and backrest will flex as independent units to accommodate the occupant's body movements. Although it is preferable to have the shell l2 connected to a tilt mechanism that tilts the shell seat l2 about an axis at the front edge l4a of the seat pan l4 or around the occupant's knee or calf location, other types of conven­ tional tilt mechanisms may be used such as that shown in U.S. patent 3,480,249, issued November 25, l969. In addition, the tilt mechanism can incorporate a rachet arrangement to permit forward tilting of the shell to enhance work postures in a work-surface chair embodi­ ment. The foregoing specification and drawings are merely illustrative of the invention and are not intended to limit the invention to the disclosed embodi­ ment. Reasonable variations and changes are possible within the scope and nature of tbe invention which is defined in the appended claims.

Claims: 1. A chair (l0), said chair (l0) comprising: a relatively rigid shell (l2) to support a user; flexural support means supporting said rigid shell (l2) in a cantilevered fashion for flexural pivoting of said shell (l2) as a unit about a flexure axis (25) transversely to said shell (l2) and support means (22) for said chair (l0),characterized in that said support means (22) comprise a tilt mechanism (28) and lever means (30) extending downwardly from said shell (l2) to said tilt mechanism (28) adapted to permit resi­ lient rotation of said shell (l2) with respect to said support means (22) about a tilt axis (32) beneath the knee and forwardly of the center of gravity of the user such that said shell (l2) pivots rearwardly and downwardly upon tilting; and said tilt mechanism (28) and said flexure axis (25) being so positioned with respect to each other such that any rise in the front portion (l4a) of the shell (l2) due to pivoting of the shell (l2) as a unit rearwardly about said flexural axis (25) is negated at least in part by relative downward movement of said front portion (l4a) of said shell (l2) due to rotation of said shell (l2) as a unit backwardly about said tilt axis (32) so that upward movement of said shell front portion (l4a) is minimized during backward tilting of said shell (l2) about said tilt axis (28). 2. A chair according to claim l wherein said flexural axis (25) is near the ankle of a user. 3. A chair according to claim l or 2,characterized in that the tilt mecha­ nism (28) has two frame members (30) which are connected at one end thereof to the shell (l2) near said flexure axis (25), the other ends of said frame members (30) being connected by a torsion bar (32) or a bushed rubber spring.

Inventors: CHADWICK, DONALD T., STUMPF, WILLIAM E.
Applicants: HERMAN MILLER, INC.
Application year: 1983
Main classification: A47C3
IPC codes: A47C3, A47C7, A47C1