Abstract:
An ergonomical chair is provided, of the type which is adjustable in height, whose seat has a front portion with a slope automatically changeable as a function of the height adjustment. The seat rear portion remains substantially horizontal, irrespective of the height adjustment and the consequent tilting of the front portion, thus avoiding the downward sliding of the body which can stay in its erect or slightly backward bent position, while a correct leaning of the seat front portion of the lower region of the thighs is ensured without exerting any tiring action by the user. Another embodiment of the invention has armrests and backrest adjustable integrally with each other.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an ergonomic chair adjustable as to the height having a seat front portion tiltable as a function of said height adjustment. 
     It is known that chairs or armchairs for use in an office or the like are often provided with a function allowing 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. It is known as well that chairs having a swingable backrest exist in which a seat front portion can be tilted downwards, thus avoiding the raising of the user&#39;s legs, either in a suitable adjustable way, or because said portion is hinged freely with respect to the rest of the seat and it can be lowered by means of a certain pressure exerted by a lower region of the thighs of the user himself. There are also chairs in which a seat front portion is permanently tilted downwards with a fixed angle, but clearly without any utility, as it results in a shorter seat, i.e. lacking said front portion. 
     From WO-A-8906101 of the present applicant another ergonomic chair is known, adjustable in height, in which the tilting angle of the whole seat changes as a function of the seat height by swinging along an arc of circumference about a center of rotation substantially coincident with the center of gravity of a person sitting on the chair itself. In that case the effect is very comfortable, however the problem remains unsolved in that, as the slope of the whole seat with respect to the backrest is changed as a function of the height of the seat itself, the user is necessarily caused to exert, in case of considerable tilting angles, a certain force on the rest areas in order to avoid a downward sliding along an inclined plane formed by the seat itself, in spite of the fixed position of the center of gravity. Thus the user must exert a pressure both on the floor by his feet and on the seat rear portion by his ischial region in order to stay in a balanced position, which may involve some discomfort and a non-negligible fatigue. 
     U.S. Pat. No. 4,521,053 discloses a chair whose seat is adjustable as to the height and which is formed in two portions, the front portion of which is downwardly tiltable with respect to the rear portion to which it is hinged. However, the tilting angle is to be chosen at will by the user who has to exert a pressure on the front part of the seat with his thighs until finding the preferred, most comfortable tilting angle. 
     It is also known that a great number of chairs, especially for use in an office and particularly suitable for typists and computer operators, or also for meeting-rooms and the like, have a backrest adjustable as to the height to keep correct, in accordance with the user&#39;s stature, the resting of the back, which takes place in the lumbar vertebrae region. By means of ergonomic research it was found that such height corresponds to a third of the height of a sitting person&#39;s trunk. 
     It is also known that the armrests of the chairs having same are preferably adjustable in height, either integrally to each other or independently, in order to ensure a correct leaning of the sitting person&#39;s elbows. However, it is necessary, to the aim of reaching an ergonomically valid result and to avoid uncomfortable postures, which are tiring so as to cause, in time, physical malformations, that the armrests adjustment is combined with a backrest adjustment as a function of the stature of the chair user. Naturally it is not easy to adjust armrests and backrests separately, based on both the difficulty of the operation to be executed, and the uncertainty of the obtained result, which often can involve additional adjusting operations. 
     SUMMARY OF THE INVENTION 
     It is the main object of the present invention to provide a chair, of the type which is adjustable in height, and possibly having a swinging backrest, whose seat has a front portion with a slope automatically changeable as a function of the height adjustment, thereby overcoming the drawbacks which remain unsolved by means of the solutions given by the prior art, such that the seat rear portion remains substantially horizontal, irrespective of the height adjustment and the consequent tilting of the front portion. As a result, the downward sliding of the body is avoided, since the body can stay in its erect or slightly backward bent position, while a correct leaning of the seat front portion to the lower region of the thighs is ensured without exerting any tiring action by the user. 
     In particular, the tilting angle of the seat front portion may change with the height of the seat itself following a ratio that can be modified at will by an adjustment to be executed once and for all by the user in function of his height, or every time as it is required by particular circumstances to let the user assume a more comfortable position. 
     To solve this second problem the present invention intends to make use of the surprising observation made by the present inventor after various antropometric measurements, that the difference between the height of the lumbar leaning zone, equivalent to a third of the height of a sitting person&#39;s trunk, and the height of the elbow lower region or leaning region on the armrests, in the great majority of the cases is substantially constant for people having different stature. 
     Thus according to a particular aspect of the present invention a chair having both armrests and backrest adjustable integrally to each other has been conceived, such to maintain constant the difference between the heights of respectively the armrest and the zone for the lumbar leaning, with respect to the seat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other objects, advantages and characteristics of the present invention will be .clearer from the following detailed description with reference to the annexed drawings in which: 
     FIGS. 1a and 1b represent respectively three people of different stature and sitting on a seat adjustable in height for maintaining optimum ergonomic conditions, and a diagram which represents, as the person&#39;s stature increases, the height of the lumbar leaning region, computed as a third of the trunk height, and the height at which the armrest must be adjusted for a correct posture of the sitting person; 
     FIG. 2 shows a schematic view of a chair having adjustable armrests and backrest according to the present invention; 
     FIG. 3 shows a schematic view of a different embodiment of the adjustable chair according to this invention; 
     FIGS. 4a and 4b show how the seat position of a chair adjustable as to the height is changed, according to the invention, when the seat is adjusted at different heights for either the same person or people having the same stature; 
     FIGS. 5a and 5b show the different positions that a seat can take on, according to an embodiment of the present invention, for two people having different height both sitting at the same height of the seat; and 
     FIGS. 6a, 6b and 6c show respectively three different examples of how a personalized modification of the seat front portion slope as a function of the height, according to FIGS. 5a, 5b, can be accomplished. 
     FIG. 7 shows an embodiment of the present invention in which the one piece portion is tiltable with respect to the vertical axis. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1a three people are shown, sitting on a seat of a chair adjustable in height, and respectively of a small, medium and great stature which may correspond to heights of about 150, 170 and 190 cm. It can be considered that only 5% of adult people have a stature lower than the considered minimum of 150 cm and likewise only 5% of them are taller than the considered maximum of 190 cm. For each of the three people represented, A denotes the height from the seat, i.e. from the respective ischiatic region leaning on the seat, of the respective lumbar region that leans on the backrest, which height, according to antropometric considerations, is assumed equivalent to a third of the full height of a sitting person&#39;s trunk. Furthermore B denotes the height of the elbow from the seat, corresponding to the height which the adjustable armrest should assume in accordance with the person&#39;s stature. 
     FIG. 1b shows the diagrams of the variation of values A and B as a function of a person&#39;s stature, valid at least within the above-cited limits of 150-190 cm, thus leaving out only the people having a percentile of less than 5% and higher than 95%. As it can be seen in FIG. 1b, the difference between the values A and B corresponding to a certain stature is always constant, at least within the above-mentioned limits. Therefore an adjustment which maintains constant this difference is perfectly consonant with the anthropometric data and ergonomic requirements of a sitting person and this can be carried out for instance by maintaining integral to each other the backrest and the armrests, which can be formed in a single piece as shown in FIG. 2. Referring to this figure, a chair 1 is shown having a supporting base 5 mounted on castors 5a, with respect to which the chair is adjustable in height by means of an adjustment post 4, a supporting structure 3 which bears a seat 2 and a backrest 6 with armrests 7. The seat 2 can be tiltable as a function of the adjustment height and backrest 6 can swing backwards but anyhow, according to the present invention, armrests 7 are formed in a single piece with backrest 6, and therefore an adjustment in height of the latter on supporting structure 3 involves the same variation in height for armrests 7 thus maintaining the relation required by the diagram in FIG. 1b. 
     The adjustment in height can be accomplished in any known way, for instance by a knob which blocks, at a desired height, the backrest 6 which can slide with respect to the vertical portion of supporting structure 3, but also providing an electric motor or a pump for a pressure adjustment. The embodiment in FIG. 2 is surely simple and practical, by allowing to adopt interesting solutions under the &#34;design&#34; view point, but anyway it remains an embodiment which involves a certain structural rigidity with a single piece having a certain encumbrance and intended to be replaced, when necessary, as a whole. 
     According to FIG. 3, wherein an adjustable chair is shown and components equal to those shown in FIG. 2 have been denoted by the same reference number, it is proposed an embodiment which provides a structural interface between backrest 6 and armrests 7, thus allowing the independence thereof. Such interface consists for instance of a sleeve 7a integral with backrest 6 and separately with supports 7b of the two armrests 7, whilst it is adjustable in height with respect to structure 3, against which it can slide and be blocked at a desired position. This allows to have the armrests independent from the backrest, and therefore a less bulky whole, as well as the possibility of separately inserting and removing them with the advantage of possibly replacing them irrespective of backrest 6. Obviously even this one could be possibly replaced, while maintaining the same armrests 7 after having removed sleeve 8 from structure 3. 
     Referring now to FIGS. 4a and 4b, wherein the same numeral references are adopted for the same elements of FIGS. 1-3, a chair 1 is shown of the type adjustable as to the height and having a base 5 mounted on castors 5a and a vertical post 4 supporting a raisable portion 9 of the chair. The post 4 can be fixed in any known way, at different heights with respect to fixed base 5, thus causing to correspondingly raise and lower the portion 9 which consists of a backrest 6 and a seat rear portion 2a represented integral therewith, as well as a seat front portion 2b hinged to said portion 2a by a hinge element 11, thereby assuming a different slope with respect thereto. The chair seat 2 is comprised of said portions 2a, 2b. 
     As it is seen in FIGS. 4a and 4b, when the height of portion 9 increases, seat front portion 2b, initially horizontal or slightly tilted upwards in correspondence of the lowest position in FIG. 4a, tilts downwards, as shown in FIG. 4b, thus ensuring the feet to correctly rest on the floor and avoiding an excessive pressure of said portion 2b against the lower region of the user&#39;s thighs. Thus, when a person wants to take on a higher sitting posture, being for instance in front of a higher desk or work surface, he must only operate the usual height adjusting devices to obtain at the same time a correct tilting of the seat front portion 2b, as shown in FIG. 4b. At the same time the ischial region, on which a lot of the weight and the center of gravity itself of the person lean, will stay on the same vertical line of the seat rear side 2a, substantially horizontal or preferably integral with backrest 6, and then possibly with a slight backward tilting if the backrest can swing, anyhow without any downward and forward inclined component which would involve the sliding of the sitting person like on an inclined plane, thus forcing him to make an effort to balance himself. The automatic tilting of seat front portion 2b as a function of the height of portion 9 can occur in different ways, for instance simply by means of an arm hinged at one end on the fixed supporting base 5 and at the other end on the tiltable portion 2b itself. Therefore, as the height increases, e.g. from L1 to L2 (FIGS. 4a and 4b), the distance between said portion 2b and fixed base 5 would increase as well, whilst if these two portions are linked to each other by means of a rigid arm, the variation of the angle of the seat front side 2b with respect to the rear side 2a follows automatically. 
     Referring to FIGS. 5a and 5b, it is shown the possibility, according to the present invention, to obtain a different slope of seat portion 2b at the same height L for two people having different height. In fact, while for the person in FIG. 5b the seat front portion 2b is perfectly lined-up with the other portion 2a in correspondence with a height L of the seat, for the smaller person in FIG. 5a, the same height L involves a tilting of front portion 2b, thereby still ensuring to lean on the floor his feet, which otherwise would remain raised, and to have a correct sitting posture. This is obtained by providing the personalized adjustment of the slope of the seat mobile portion 2b, in practice the possibility to change at will the length of said link arm which connects base 5 and portion 2b (FIGS. 6a-6c). 
     At it is shown in FIGS. 6a-6c, the connecting means 10 may be provided with an adjusting device to make possible the modification of the degree of the tilting angle of seat portion 2b as a function of the height, whereby a greater or smaller tilting of front side 2b can correspond to the same height of the whole seat 2. For instance, according to FIG. 6a, the linked arm 10a has, at one end thereof, an articulated plate or link rod 8a which is fixable at different angles, thereby causing the length of arm 10a to correspondingly increase until a maximum length obtained by the alignment with plate 8a. In FIG. 6b such a changing is obtained by means of a pin fixable within a slot 8b of linked arm 10b, the length of which slot 8b corresponds to the maximum change obtainable. In FIG. 6c the arm is instead replaced in practice by a piston-cylinder system 10c wherein piston 8c can be made integral, by known means, with cylinder 7c, from a position in which it is fully retracted until a position of full projection corresponding to a maximum length. Now it is clear that a person of small height will adjust the length of connecting means 10 at the lower values thereof, thereby causing anyhow a greater donward tilting of front portion 2b to correspond to a changing in height of the seat, whereas the contrary will occur for a taller person. If the chair is always used by the same person an adjustment of this kind may be carried out once and for all, obviously without excluding that in particular circumstances the user can modify at his will the way in which the slope of the seat changes with the height thereof. 
     The chair 1 of FIGS. 4a-6C has been represented without armrests, but it is clear that armrests could be provided, possibly adjustable in height, as well as the backrest, according to the embodiments of FIGS. 2, 3, with the seat rear portion integral with the backrest, thus providing for a chair or armchair ergonomically improved also in this respect. Furthermore means different from those represented can be adopted to accomplish the automatic slope changing of a seat front portion as a function of the height thereof and to modify such a variation law, and/or for adjusting the height of the backrest together with the armrests.