The present invention relates to an ergonomic chair the seat port on of which can change its position for a better adaptation to the users' height and the level of the work table in front of which the user is seating.

It is known that some types of chair for use in an office or the like have a function which allows the height of a seat portion to be freely changed in accordance with the physique of a sitting person, the height of a desk employed and so forth.

Another type of chair is also known in which the angle of its seat portion can be ti lted in a certain range toward the front and rear side of the seat portion in accordance with the intention of a sitting person. The function which allows adjustment of the height of a seat portion and the mechanism causing the seat portion to swing in a plane perpendicular to the work surface were devised as a result of a pursuit of a chair which allows a person to sit thereon at a height matching the height of the top plate of a desk or table employed, as well as on which a person can sit comfortably from the viewpoints of ergono ics and hence without experiencing fatigue or assuming any unnatural posture even if he continues to sir for a long time.

Chairs of almost all the conventional types each having a seat portion of different height

can only be used n combination with desks having a top plate provided at substantially the same height. Conventionally, the top plates of tables or the like with substantially the same height have been used as working surfaces and therefore the height of cha rs for use with such top plates have been limited to a certa n range.

On the other hand the rap d introduction of so-called office automation on the basis of the recent development of electronic techniques and computers compels off ces to introduce various desks or the like in which each of the work ng surfaces or top plates greatly differ from one another, with the working place being now characteriz¬ ed by volumes having different vertical extens ons, instead of a simple horizontal surface. In this situation, it has been desired to provide a chair having the function which allows the height of a seat portion to be adjusted in accordance with various top plates which greatly differ from one another n height.

In other words, in an office in which advanced office automation has been introduced, but also in different situations such as at a doctor's or dentist's surgery, or in any case when a person must perform a variety of tasks in front .of work surfaces having different heights, it will be neces¬ sary to introduce a chair which can be easily adapted to the user's requirements according to the various working surfaces (or top plates) which greatly differ from one another in height.

However, in a conventional type of chair which allows adjustment of the height of a seat portion or has a seat portion swingable back and forth, the he ght of the seat portion can only be adjusted in a state wherein the seat portion is aLlowed to swing back and forth within a limited range. Accordingly, if the height of the seat portion of such a seat is greatly changed and the seat is comb ned with desks having top plates which greatly differ from one another in height, a sitting person cannot assume a posture which is desirable from the viewpoints of ergonomics. Accordingly, a . chair on wh ch a person can sit comfortably wi ll have to be found out among the conventional chairs and giving up the ad ustabi lity in height. As a matter of fact the swinging axis about which the seat portion swings back and forth is located below the seat portion in any position. Therefore, since the center of gra ity of a person sitting on the chair is shifted up and down or back and forth by the swinging motion, it is impossible to avoid changes in position energy and there is a risk of compelling the s tting person to assume an unnatural posture wh ch is not only tiring but also unstable and dangerous. It is an object of the present invention to pro ide a chair having a seat adjustable so as to overcome the above-mentioned inconveniences and drawbacks of the prior art and in particular such as to keep the center of gravity of a person sitting thereon as much as possible along a vertical axis

w thin the base polygon upon variation of the seat height and tilt ng angle.

To this aim the chair according to the present invent on, comprising a seat portion wh ch is ad ustable in height, is characterized in that, when the height of the seat portion is changed, its tilting angle changes in accordance with changes in the height of the seat portion by swinging the same along an arc of circumference about a center of rotat on substantially coincident with the center of gravity of a person sitting on the chair.

According to a preferred embodiment of the invention, said swinging movement of the seat is accompanied by the rotation of a lever arm pivotedly mounted at an end to the stationary part of a support of said seat and at the other end to the front side of the seat, wherein the length of said lever arm, or the point at which it s p voted to the chair, can be changed according to the user's height and wi L I .

Thereby when the height of seat of the chair according to the invention is changed not only the t lting angle of the seat is modified as a consequence of a swinging movement about the center of gravity of the s tting person, but the latter can adapt the variation of such an angle as a function of the seat height, accord ng to his own height or however his willing so as to assume the mostly desirable posture, whichever the seat height may be.

The advantages and features of the chair

according to the invention i ll become clearer on the ground of the following description given by way of a non-limiting example with reference to the drawings in which:

FIGURES_ a-lc are diagrammatic side elevation al views showing various postures taken by persons sitting on conventional chairs with a ti ltable seat, adjustable as to the height;

FIGURES_2a-2c are diagrammatic side views, simi lar to the preceding ones, of the positions taken by a chair provided with a seat according to the invention showing also the relationship ex sting between the seat height and the ti lting angle and at the same time the corresponding postures of a person sitting on said chair;

F GURE_3 shows the si lhouette of a person sitting on a chair according to the invention at various heights of the seat but with his feet at the same position;

FJ^JJJ? __4__^n_d___F_I_GjJJ5 __5 are diagrammatic side elevational views of two alternati e embodiments of the seat portion only of a chair according to the i nvent ion;

F 3JJJ_E_S__6a__aιjd__6b show two diagrammatic side views, at different heights of the seat, of a chair according to the invention in a preferred embodiment; and

FIGURES__7_a a_nd__7b are two diagrammatic side views of the seat portion only of a chair according to Figs. 6a and 6b, each of which shows a constructive possibi lity of a mostly preferred

embod ment of said seat.

W th reference to the dra ngs Figs. 1a, 1b and 1c are side views, taken from the left side of the posture assumed by a person sitting on a prior art chair being adjustable in height, the seat portion of wh ch is tiltable and respectively pos tioned at a low, average and a igher level from the floor. In the situation of F g. 1a it is seen that the femur is inclined along a frontally arising slope whereas the center of gravity of the sitting person, designated CG and substantially located in the vicinity of the navel, is shifted rearword to the vertical passing through the swinging center of the seat CR which is placed thereunder, substantially on the central upright supporting the same Cnot shown) .

Fig. 1b shows the position of a person who has adjusted a seat height to an average value: only in this case, with hor zontal seat, the center of gravity is along the vertical line passing through the point CR at a center position w th respect to the base polygon, whereby this person is in equili¬ brium. However it is an unstable equ librium because at a higher level (Fig. 1c) with the seat and there¬ fore the femur incl ned downwards, the center of gravity is dangerously shifted forward.

The center of gravity CG then moves along a l ne CGL, similar to an arc of circumference, when in a conventional adjustable chair the seat is changed as to the height and as a consequence also its tilting angle varies by swinging about a

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rotation center CR positioned thereunder. Therefore the human sitting ll be subject to a sensation of instability which he will unavoidably try to oppose by exerting some muscular force involving fatigue and discomfort with the passing of time.

For a person sitting on a chair according to the invention, Figs. 2a-2c show, respectively at the same heights of Figs. 1a-1c, that the center of gravity CG of this person in any case remains on the vertical axis of support di ag rammat i ca I ly indicated with a dashed and dotted line, even at considerable sloping angles of the seat, back or forth, with respect to the average position with hor zontal seat of Fig. 2b. This results apparently from Fig. 3 were the overlapping profiles of a person sitting at different heights on a chair according to the inven¬ tion have been shown with the feet coincident on the same posit on. The locus descr bed by the center of grav ty CG is a substantially vertical line CGI, without any forward or backward shifts. Every situation is therefore of stable equilibrium.

Turning now to Figs. 2a-2c the chair central support will have, as it is known, the function of freely allow ng the height to be ad usted, such as by means of gas under pressure, but however while allowing at the same time the rotation of the chair about its vertical ax s indicated ith a dashed and dotted line. Also a chair base, preferably with casters, has not been shown as it is of known type, which is provided at the lower end of the

vertical support. Reference character 3 denotes a support element of the seat 4 being prov ded at the upper end of the vertical support so as to extend rearwardly. The seat-portion supporting member 3 is formed as a surface having an arc-shape as viewed in side elevat on. From the rear end of its bottom portion 3a a backrest 3b extends upwardly. Reference numeral 4 denotes a seat portion which is carried on the upper surface of the bottom portion 3a of the above-mentioned support member 3 in such a manner that the seat portion can slide ith respect thereto back and forth.

As can be seen from Figs. 2a to 2c, one gist of the present invention is that, as the height of the seat portion 4 of the chair according to the present invention is increased or decreased, the tilting angle of the seat portion 4 is set by a rotation about a point substant ally coincident with the center of gravity of a person sitting on the chair.

The above-described ascending or descending of the seat portion and the setting of the tilting angle of the seat portion which varies in association with th s ascending or descending can be embodied ith a mechanism such as that schematically shown n Figs. 4 and 5 as an example. As the height of the seat portion 4 increases, this progressively inclines toward the front of the chair by a small amount, if the seat-portion height exceeds a certain value, such as about 60 cm, the weight which is applied to the legs of the person ncreases and

the we ght which is applied to the seat portion decreases. As a reaction, the seat portion is somewhat pushed toward the rear. Therefore, in the case of a chair with casters, it is desirable to provide a caster lock mechanism to be actuated according to the height of the seat.

Fig. 4 is a side elevational schematic view of an example of the swinging mechanism for the seat relating to the chair of the present inven- tion, in which the same reference numerals of the other figures denote the same members, in particular the portion 3a of the supporting member 3 being formed as a portion of an arc which is drawn about a center of rotation ideally coincident with the average location of the center of gravity CG of the persons using the chair. Like in Figs. 2a-2c reference numeral 4 denotes a seat portion which is carried on said portion 3a of the supporting member 3 and the lower surface 4a of the seat portion is formed in accordance with a curvature which is equal to the curvature of the portion 3a of the supporting member 3. Specifically, the seat portion 4 is carried on the supporting member 3 like on an arc-shaped guide in such a manner that it can swing in the opposite directions indicated by arrows in the drawing. Also the vertical support 1 has been i llustrated here, which is provided with a vertical adjustment mechanism, although not shown, which allows adjustment of the height of the seat-portion supporting member 3 as it is known. This vertical support 1 is centrally mounted on a chair base 2,

e.g. having rad al arms with casters 2a.

Fig. 5 is a side elevational view, also schematic, of another example of the swinging mechanism In this example the seat portion 4 is pivotally supported at 4b on a seat-portion supporting member 31 which is formed like a piLlar extending up from a side of the support 1, and s suspended from the pivot axis 4b which substantially coincides with the center of gravity CG of a person of average height sitting thereon. In Fig. 5, 4c denotes a suspended arm which projects upwardly from both sides of the seat portion 4, which therefore hangs l ke a swing.

With solutions of this type the swinging motion of the seat 4 is completely free about the stationary center of rotation and a sitting person ilL automatically assume the tilting angle of the seat w ich is the most su table to the particular height chosen with an unavoidable instability due to the seat being brought to return always back to the horizontal orientation of equil br um.

With reference to Figs. 6a, 6b the chair according to the invention has been shown with the seat portion at two different heights, in a preferred embodiment in which to avoid the above-mentioned inconvenience, the swinging movement of the seat portion 4 is accompanied by the corresponding motion of a lever 6 pivotedly mounted at an end 6a to the seat support 1 and in particular to the stationary portion 1a of su._:h a support, also comprising a portion 1b adjustable in height as already indicated.

such as by being te les cop i ca I ly mounted for an axial movement within the stationary portion 1a to which it is lockable at each desired position in whichever known manner. The other end 6b of lever 6 is p.ivotedly mounted to the front portion of the seat 4. The user of the chair according to the invention provides for adjusting the height of seat 4 according to his own height and the level of the working surface in front of him, whi le at the same time the ti lting angle of the seat 4 is automatically adjusted to assume the most comfortable position at this given height of the seat and maintains this particular angle without further swinging movements . According to a more preferred embodiment of the present invention, with reference to Figs. 7a and 7b, the length of said lever 6 is not fixed but it is also adjustable for having more possibi lities of postures which the user can obtain for a maximum comfort. In the example of embodiment of Fig. 7a the lever 6 is connected to the seat portion 4 through an additional lever 7 to which it is hinged in 6b. As the angle comprised between levers 6 and 7 varies, such as in function of the user's height, or arbitrari ly, the practical consequence is that also the distance changes between the stationary pivot point 6a and the pivot point to the lower surface of the seat 4, in other words the ti lting angle of the seat whi le the height is the same. Fig. 7b schematically shows an alternative embodiment in which the different length of lever 6 is obtained

by providing the same with an elongated slot at the end opposite to p vot 6a and arranging the pivoting point 6b onto the seat 4 to be adjustable at will within said slot. Furthermore the lever 6 may be made, instead of metal, of a relatively resilient material, such as plastic reinforced with glass fibers, so that the seat can have a certain spring-like movement about the ilting angle determined as stated before without disadvantages as to the stability of sitting which results thereby less rigid only.

As results from the foregoing description of the present invention, as the tilting angle of the seat changes according to the seat height, the latter can be smoothly and continuously moved upon changement of the posture of a person sitting on the seat wh le, according to the prior art, upon changing the height of the seat its tilting angle remained the same or its variation caused a forward or rearward movement of the center of gravity of the si ting person, whereby his posture was unstable and dangerous in addition to be tiring. It should also be appreciated that the tilting angle varies in an extremely smooth way with the seat swinging about a point near or coincident with the center of gravity of a person sitting on the chair as a funct on of the seat height. Therefore even if a person is sitting for a long time on a chair according to the invention at whichever height of the seat portion, this occurs in a comfortably way_ and without experiencing substantial fatigue.

This in particular when adopting the preferred solution of rendering ad ustable at wi ll, especially according to the user's height, the way of varying the seat ti lting angle in function of the height thereof.

Possible additions and/or modifications can be made by those ski lled in the art to the above-described and i llustrated embodiments of the chair according to the invention without departing from the scope of the invention itself. In particular there could be provided changements relating to the backrest portion of the chair, such as to modify for example also its slope with respect to the seat support according to the height of the latter.