Chair adapted to force a forward and downward movement of the seat with respect to a backward inclination imparted to the backrest

1. A chair, provided with a plate, to which a seat is freely articulated above, by way of at least one first linkage and a second pair of linkages in rear and front regions, a backrest being articulated laterally and freely to said seat, a first end of a pair of cams being pivoted to said plate at the rear, a second end being pivoted to said backrest, said pair of cams having arc-like guiding means for a sliding of at least one pivot which is integral with and protrudes from said backrest, said at least one first linkage and said second pair of linkages and said pair of cams being adapted to force a forward and downward movement of said seat with respect to a backward inclination that can be imparted to said backrest.

2. The chair according to claim 1 , wherein said seat has a sitting portion which has a substantially rectangular shape, with a front region slightly arc-shaped toward the ground and the rear region substantially flat, said sitting portion being freely articulated below, proximate to said rear region and said front region, to said underlying plate respectively by way of said first linkage and said second pair of linkages, said first linkage being arranged substantially along the longitudinal central axis of said sitting portion and being pivoted transversely freely at its ends, by way of a first pivot and a second pivot, respectively between a pair of shoulders which protrude to the rear from said plate toward said seat, and between a pair of first protrusions which protrude below said sitting portion of said seat.

3. The chair according to claim 2 , wherein each one of said second pair of linkages is pivoted transversely freely at its ends, by way of a third pivot and a fourth pivot, respectively to the terminal and front end of said plate that is directed toward said front region and between a pair of second protrusions which protrude below said sitting portion of said seat.

4. The chair according to claim 2 , wherein a pair of rods protrude laterally and slightly upward at a rear end of said plate, a backrest being freely articulated to free ends of said rods and being provided with a frame which is composed of two L-shaped arms so as to define a first wing and a second wing, which are vertical and are blended above by a crossmember, and a third wing and a fourth wing, which are substantially horizontal, a fifth pivot for pivoting to said free ends of said pair of rods being arranged transversely at the blending region between said first, second, third and fourth wings.

5. The chair according to claim 4 , wherein a sixth pivot is arranged transversely proximate to terminal ends of said third wing and said fourth wing, for pivoting to a pair of third protrusions which are integral with and protrude laterally and below from said seat.

6. The chair according to claim 4 , wherein a connection between said backrest and said pair of rods occurs by way of a pair of cams with a substantially rhomboid shape structure which are pivoted at a first end, by way of said fifth pivot, to said free ends of said pair of rods and are pivoted at a second end, which is opposite to said first end, by way of a sixth pivot, said pair of cams having arc-like guiding means for the sliding of at least one seventh pivot which is integral with and protrudes from said first wing and said second wing in a region that is adjacent to the region for blending with said third wing and said fourth wing, each said pivot, which is integral with and protrudes from said backrest, acting in an arc-like through seat provided in said pair of cams in an intermediate region between said fifth pivot and said sixth pivot, the shape structure of said seat being such as to have a curvature with a center directed toward said sixth pivot.

7. The chair according to claim 6 , wherein an arrangement of the various articulations among the various components of said chair is such that, with respect to a horizontal plane and in the condition in which said seat is in a horizontal position, there is a sequence, from the bottom upward, of planes of arrangement that pass between said first pivot, said third pivot, said second pivot, said fifth pivot, said fourth pivot and said sixth pivot, said arrangement, together with the arrangement assumed by said first linkage and said second pair of linkages and said pair of cams, being adapted to force the forward and downward movement of said seat with respect to a backward inclination that can be imparted to said backrest.

8. The chair according to claim 5 , wherein it is provided with a pair of leaf springs which are interposed between a lower surface of said seat and a lateral and free point of articulation of said seat to said backrest, each one of said pair of springs being, at its ends, on one side laterally integral with said pair of third protrusions and on the other side able to freely slide on abutments that protrude from said lower surface of said seat proximate to said front region of said seat and with the vertex directed downward.