Folding chair with continuously variable self-balanced tilting action
FIELD OF THE INVENTION 
     This invention relates to a folding chair especially intended for office use and designed for continuous tilt adjustment of the seat and backrest to assume continuously stable settings automatically balanced by the same action which has brought about such adjustment. 
     BACKGROUND OF THE INVENTION 
     It is known that there is an increasing need to alter the setting of chair, armchair and similar seats in relation to the various positions assumed by the user throughout the day. In the office environment particularly, following the widespread introduction of computer and word processing systems on desks, it is necessary to provide a chair enabling a comfortable and ergonomically correct position to be achieved both when writing normally at a table or desk and when using a computer keyboard. The keyboard usually is placed in a lower position relative to the desk top so that it is necessary to provide a slight backward tilt to the so-called active rest position. 
     OBJECTS OF THE INVENTION 
     It is, therefore, the principal object of the invention to provide a chair capable of allowing forward swivelling of the seating unit as well as controlling swivel of the backrest relative to the seat so that the user may assume either a more favorable position for writing and/or typing or a slight backward tilt to the rest position. 
     A further object of this invention is to provide an improved chair capable of allowing substantially continuous adjustment to the setting of the seat and backrest as a result of the different positions at various times. 
     Still another object of the invention is to provide a chair having extremely compact dimensions and comprising of a small number of parts capable of being easily assembled and dismantled and easily folded when not in use in order to reduce its overall dimensions and facilitate both storage in a folded position by the user and transportation by the manufacturer. 
     SUMMARY OF THE INVENTION 
     The objects are obtained according to the present invention, which provides for a chair of a type comprising a seating unit consisting of a seat, a backrest and of two pairs of legs. The seat and backrest are made rotationally integral with one another by means of hinges while pairs of legs and the seating unit are made slidingly integral with one another by means of couplings attached to the seating unit and designed to engage the relevant inserts located at the legs. The latter, in turn, slide in relation to one another by further couplings integral with the legs and designed to engage further inserts located in such legs. Means for guidance is provided for the sliding of the legs in relation to the seat. This means is located on a single axis and designed to allow substantially continuous tilting of both the seat and the backrest relative to the seat. As a result of the pushing action exerted by the user the opening and closing of the chair is significantly facilitated. 
     More particularly, provision is made for such coupling facilities to be substantially comprised of pins integral with the backrest and the seat and projecting therefrom in a substantially horizontal direction. At least one pair of such pins constitude also the swivel pin of the hinge, the upper arm of which has its end rotationally integral with the other pair of pins. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features and advantages of my invention will become more readily apparent from the following description, reference being made to the accompanying highly diagrammatic drawing in which: 
     FIG. 1 is a diagrammatic perspective view in oblique projection of the chair according to the invention; 
     FIG. 2 is a partial diagrammatic section on plane II--II in FIG. 1; 
     FIG. 3 is a side elevational view of the chair according to FIG. 1; 
     FIG. 4a is a side elevational view according to FIG. 1 of the chair tilted forward; 
     FIG. 4b is a side elevational view according to FIG. 1 with the backrest tilted rearward; 
     FIG. 5 is a diagrammatic side elevational view of the chair according to FIG. 1; with the various movements depicted by broken lines and dotted lines for seat and backrest tilt respectively; 
     FIG. 6 is a side elevational view of the chair mounted on wheels; 
     FIG. 7 is a side elevational view of another embodiment according to the invention; and 
     FIG. 8 is a perspective view of still another embodiment according to the present invention. 
    
    
     SPECIFIC DESCRIPTION 
     As shown in FIG. 1, the chair according to the invention is substantially comprised of a seating unit 1 consisting of a slablike member folded along a curved line 1c to provide a substantially vertical backrest 1a and a substantially horizontal plane of seat 1b. Such seat 1b and backrest 1a are made rotationally integral with one another by means of a pair of hinges 100 consisting of two arms 100a and 100b respectively attached to backrest 1a and seat 1b. 
     More particularly, the upper end of each arm 100a ends in a circular insert containing a pin 2 partly extending from the edge of backrest 1a, while the swivel pin 3 of hinge 100 protrudes from seat 1b. The swivel pin 3, in turn, extends from the respective hinge 100. 
     Such pins 2 and 3 are designed to be inserted in a known manner into the appropriate slots 4a and 4b of a first pair of legs 4, located at an angle relative to seating unit 1, so that the pair of legs which are thus made is mounted slidingly on both backrest 1a and seat 1b. The legs 4 are then connected together by a crossbar 4d to form a substantially H-shaped first frame. 
     Slots 4a and 4b are furthermore respectively located as follows: the first slat 4a is substantially inclined upward and rearward, and the second slat 4b is substantially vertical. 
     The lower surface of the front end of seat 1b is also supported on a crossbar 6&#39; for the attachment of a further pair of legs 6, the assembly of which forms a substantially &#34;inverted U&#34;-shaped second frame, linked in a sliding manner to seat 1b by means of a rail 5a as seen in FIG. 2 operatively connected with the lower surface of seat 1b and in which slides crossbar 6&#39;. 
     Legs 6 of the second pair are likewise linked in a sliding manner to the first pair of legs 4 by means of pins 7 inserted in a known manner into slots 4c which are provided in appropriate positions on legs 4. 
     As is apparent from FIGS. 1 and 2, the chair as used under normal conditions has its seat 1b located substantially horizontal, its backrest 1a substantially vertical and pins 2, 3 and 7 positioned respectively at the inner, lower and upper ends in slots 4a, 4b and 4c. 
     When the user wishes to change his position he shifts his own center of gravity so as to exert, with his own weight, a pushing action on the front end of seat 1b, thus bringing about a corresponding action on pins 7 which slide towards the lower end of slots 4c, while swivel pins 3, constituting the neutral axis, maintain their position relative to the lower end of slots 4b. On the other hand, should the user wish to assume an active rest position with the backrest tilted rearward, it will be sufficient to exert pushing action on backrest 1a which, rotating on pins 3 of hinge 100, will tilt rearward to shift pins 2 from the front end setting to the rear end setting of slats 4a and pins 3 themselves to the upper end, setting of slot 4b. 
     For a better understanding, FIGS. 3, 5 shows the various positions which may be assumed by the chair, namely: normal position with seat 1b horizontal and backrest 1a vertical, shown in FIG. 3 and indicated by a continuous line in FIGS. 5 and 6; working position with seat 1b tilted forward but no change in the relative position of backrest 1a and seat 1b, indicated by a broken line; rest position with seat 1b horizontal and backrest 1a tilted rearward, indicated by a dotted line. It is furthermore apparent that pins 2, 3 and 7 may be positioned, within the relevant slots 4a, 4b, 4c, in any intermediate setting between the two end settings, as a result of the pushing action exerted by the user; all the settings are stable since they are balanced by the user&#39;s own weight and by the position assumed by his center of gravity. 
     The chair according to the invention may also be folded after use, to be placed, for example, in a less conspicuous position or in a cupboard; in order to reduce its overall dimensions seat 1b is swivelled clockwise, whereupon it moves upward and causes pins 5 to slide within guides 5a toward backrest 1a, thus causing legs 6 to swivel on pins 7 and to close in a position parallel to legs 4, whilst seat 1b is folded onto the backrest thus substantially reducing the chair to a parallelepiped the thickness of which is substantially contained within the width of legs 4. 
     FIG. 6 also shows a first alternative version of the chair according to the invention in which the entire supporting structure is mounted on a column 8 which in turn is mounted on a star-like base (9) fitted with castors 10. In this case the lower ends of legs 4 and 6 are, in a known manner not described herein, made integral with column 8 by means of hinges 9a to enable backrest 1a and seat 1b to assume the same various positions previously described. 
     FIG. 7 shows, in turn, a second alternative version of the chair according to the invention in which legs 4 and 6 are replaced by a frame 104, substantially of channel section, with a first end still hinged at 105 and a second end extended upward and rearward to form an arm 110, which still includes slots 104a and 104b between which slide pins 2 and 3. In this case it is possible to adjust both the rake of backrest 1a rearward and, in a limited manner, the forward tilt of seat 1b by elastic deformation around link 107, the movement of the pins within the slots being entirely similar to that previously described for the chair in FIG. 1. The chair in FIG. 7 may also be provided with two flat members constituting the sides of an armchair still made connected with seating unit 1 by means of pins 2, 3 and slots 4a, 4b, the operation required for tilt adjustment remains unchanged. 
     FIG. 8 shows a further alternative version of the chair in which backrest 1a and seat 1b form a one-piece shell of suitable section to enable backrest 1a to swivel relative to seat 1b. In this case the chair can no longer be folded but, seat adjusting movements can still be carried out as shown in FIG. 5. It is therefore apparent that the chair according to the invention makes it possible to obtain different settings of the seat and of the backrest as a result of the different positions assumed by the user and that such settings, which can be substantially adjusted in a continuous manner, are all substantially stable because they are balanced by the action exerted by the actual user. 
     Many alternatives may be introduced in the technical development of the constructional details of the chair according to the invention without thereby departing from the scope thereof as far as its general features are concerned. In particular, it will be possible to altar the length and arrangement of the various slots in order to change the extent to which the seat and backrest can be moved from the rest position and/or the higher or lower sliding friction of the pins in the slots determining the dynamic characteristics of movement, i.e. the greater or lesser ability of the chair to adjust the settings of the seat and backrest.