The sitting furniture having a seat area being an object of the invention is intended for schools, offices, household, catering institutions, transport vehicles and special working places requiring a longlastirig sitting.

Known are solutions of chair seats with a compact area whose parts in the anal and genitals location are free and/or have a possibility of getting free by means of an inserted section having various thickness. In an alternative solution the inserted area is continually displaceable. Such solution is known from the utility model DE 9416674U it represents a solution of a seat area having a recess in the location of the anal outlet, genitals and tailbone, the femoral parts being stabilized by rotary areas serving for constriction of the movements of a physically disabled person.

The patent specification DE 441479 shows a solution of a seat area composed of two tilting planes. The solution according to US 4643 481 Patent is a seat area consisting of two channel-like sections for location of the thighs with the aim of their stabilization, while in the area of the anal outlet the seat has a mushroom-like throughgoing opening. The seat area can be tilted:

Another example of known sitting furniture is disclosed in GB699608A.

The solutions mentioned above are suitable only for physically disabled persons and their aim is constricting the movements of the sitting part of a sitting person. They do not solve the origin of the diseases, resulting above all from a longlasting sitting on seats of e.g. chairs, armchairs etc. Their limitation is a complicated structure, which also affects their overall appearance.

A considerable disadvantage of known solutions is in that the sitting area is designed as a rigid structure with no or with only an insufficient adaptability of its form to the forms and dimensions of the user. They bring no really complete solution of the essential problem, arising from a longlasting sitting because of the said lack of adaptability to the anatomic forms and dimensions

The limitations of known sitting furniture having a seat area as described, above; their utilization being limited mostly to physically disabled persons only, their complicated structure, a poor possibility of an aesthetical design generally insufficiently reflecting physiological marks of sitting persons are removed in a large extent by the sitting furniture having a seat area according to the invention of claim 1. Prefered features of the present invention are set out in the dependent claims below.

At least one sleeve is placed in the central part of the seat area and fitted with an element for a sliding fastening on a carrying structure. Side parts of the seat area are fitted by their ends on a level carrying tube of the carrying structure.

The element for sliding fastening on the carrying structure is equipped with a fitting allowing for rocking movements of the sleeve in all directions and is designed preferably by means of a knuckle joint.

A method of production of a sitting furniture consists in that the seat area is manufactured by means of an elastic deformation of a flat blank of elastic material. The flat blank has a form of annular segment limited by two arches with a central angle of α = 10° to 170°and surface straight lines. AB and A'B', and by two side parts limited by tangents t₁, t₂, t'₁, t'₂, surface straight lines AB, A'B' and terminal lines n, n'.

Should a change of the seat area width be required, the latter can be made of two sections of the flat blank with compatible flat blank ends fitted in the contact place with a mechanism for widening the seat area.

The flat blank can be manufactured of a an elastic single-layer or of a sandwich type material.

The flat blank edges can be borded, preferably by rims.

The seat area can be manufactured preferably by moulding.

The substance of the invention is explained more in detail in the enclosed drawings, in which Fig. 1 shows schematically the flat blank, Fig. 2 shows schematically the blank in its deformed condition, Fig. 3 is a side view of an armchair with a seat area, Fig. 4 is a plan view of an armchair with the seat area, Fig. 5 is the mechanism in its basic position and Fig. 6 shows the mechanism in a first increased spacing of the extremities of the seat area sections.

The example shows the seat area 1 as fastened on the carrying structure of an armchair 5. The basic dimensions of the seat area are:

• width of the seat area w = 450 mm
• spacing of inner tangents d = 110 mm
• depth of the seat area h = 450 mm
• central angle α = 90°
• angle of the intersection line β = 70°.

The carrying structure 5 consists of a level carrying tube 5.1, on both extremities of which is fastened a twin armchair footing 5.2. At the middle of the carrying tube 5.1 a carrying bracket 5.3 is fastened: The central part 1.1 of the seat area 1 is equipped with a sleeve 4, on which a fastening element 4.1 is situated. An elastic deformation of the flat blank 2 is obtained in fixing it at the place of its terminal lines n₁, n₂ on the carrying tube 5.1 and fastening at the point of annular segment 2.1 axis by means of the sleeve 4 with the fastening element 4.1 to the carrying bracket 5.3.

The fastening element 4.1 is suspended on the bracket 5.3 on a sliding joint with freedom of rocking movements. The implementation shows an angle of β = 70°. The terminal lines n, n' form with the horizontal plane an angle 0°. The seat area 1 is made of a single-layer elastic material.

The example shows an armchair with a carrying structure 5 and a seat area 1 of identical dimensions and forms of Example 1. The seat area 1 is made of a flat blank 2 composed of two compatible flat blank ends 2.3, 2.4, where a joint of the two flat blank ends 2.3, 2.4 is performed by means of a mechanism 6, permitting to change the spacing of the flat blank ends and consequently enabling a widening or narrowing of the seat area 1. The mechanism 6 is fastened with freedom of shifting on the carrying bracket 5.3 of the carrying structure 5, and it replaces the sleeve. 4. A simple implementation of the mechanism 6 is in that two openings 2.3.1, 2.3.2 and 2.4.1,2.4. 2 respectively with identical spacing are shaped on compatibly modified flat blank ends 2.3, 2.4. An overlapping sheet 6.1 is fastened to the bracket 5.3 by means of a nut 6.3 and a screw 6.2, the screw 6.2 being slung through suitably chosen openings 2.3.1 or 2.3.2 and 2.4.1 or 2.4.2 respectively.

Fig. 1

2 flat blank
2,1 annular segment
2.1.1 outer arch
2.1.2 inner arch
2.2, 2.2' side parts
α central angle
t₁, t₂, t₁', t₂' tangents
n, n' terminal lines
AB, A'B' straight lines

Fig.2

2 flat blank
d distance of inner tangents
s width of seat area
h depth of seat area

Fig.3

1 seat area
4 sleeve
4.1 element
5 carrying structure
5.1 carrying tube
5.2 armchair footing
5.3 carrying bracket
β angle of intersectional line of central part and symmetry axis with level plane
p surface straight line

Fig. 4

1.1 central part
1.2, 1.2' side parts
4 sleeve
4.1 fastening element
5.1 carrying tube
5.2 armchair footing
5.3 carrying bracket
p, p' surface straight lines
n, n' terminal lines
d distance between inner tangents
s width of seat area
h depth of seat area

Fig. 5

2.3, 2.4 compatible flat blank ends
2.3.1, 2.3.2 openings
2.4.1, 2.4.2 openings
5.3 carrying bracket
6 mechanism
6.1 splice overlap plate
6.2 screw
6.3 nut

Fig. 6

references see Fig. 5