the seating module — or seat — according to the invention essentially includes a structural framework 10 , a fork - shaped frame 12 , a hinge 14 connecting , in a jointed manner , structural framework 10 and fork 12 , and an elastic membrane 16 , visible only in fig3 and 4 . the seat has a symmetrical structure with reference to a vertical plane passing through lines ii - ii of fig1 and 3 . more specifically , structural framework 10 , in plane , has a t - shape the vertical bar 18 of which , placed in axis ii - ii , extends forwards and is bent upwards to end in a pommel element 20 . the ends 22 a of arms 22 of the t , perpendicular to the axis , are raised and pierced with a hole that is not visible in the drawing . structural framework 10 has a central portion 24 provided with holes 24 a allowing the seat to be fixed onto a support , as will be explained hereinafter . in plane , fork 12 has a u - shape of axis ii - ii . its cross bar 26 , which is slightly raised and bent , acts as cantle element and its two teeth 28 extend forwards substantially as far as pommel element 20 , a few centimeters underneath it . it will be noted that , in the seat rest position , shown in the drawing , the tip of cantle element 26 is located at substantially the same height as pommel element 20 , and that fork 12 is inclined forwards by an angle of approximately 10 ° in relation to the ground . teeth 28 of the fork are provided , substantially in their middle , with a lug 30 a extending downward , each adjacent to one end 22 a of the structural framework and provided with a coaxial hole . bearings engaged in these holes and rods , engaged in the bearings , form hinge 14 , which thus enables fork 12 to be pivoted in relation to structural framework 10 about an axis a - a . advantageously , structural framework 10 and fork 12 are respectively made of aluminum and steel . firstly , between pommel element 20 and cantle element 26 ; secondly , between the two teeth 28 of fork 12 ; and thirdly , between the ends of teeth 28 and pommel element 20 . membrane 16 can be made of any elastic material , for example pvc , in the form of a fabric , as shown in fig3 and 4 , or film , in one piece or in strips . in the latter case , a first set of strips 16 a connects pommel element 20 to cantle element 26 , a second set 16 b connects the two teeth 28 to each other , this second set covering the first , and a third set 16 c connects the ends of teeth 28 to pommel element 20 . because of the shape of fork 12 and the position of pommel element 20 , membrane 16 has a horse - saddle shape , with a concavity between cantle element 26 and pommel element 20 and a convexity between the two teeth 28 . owing to these features , the function of membrane 16 is to : define the rest position of fork 12 in relation to structural framework 10 , the position taken when no - one is sitting on the seat , and return fork 12 to this rest position when the person who has tilted the seat forwards or backwards leaves it . as can be seen in fig4 , the seat according to the invention can advantageously be completed by a padding member 32 , forming a cushion , totally covering membrane 16 and permanently or removably fixed to the latter . this padding member can be formed by a fabric envelope containing an elastic filling or formed of a gel . advantageously , it is provided with a longitudinal groove 34 extending over the entire length of the cushion . consequently , the coccyx of the person occupying the seat is not compressed , which improves comfort and prevents certain damage , particularly as regards the vertebral column . fig5 shows that the seating module previously described is for fitting to a chair formed of a support 36 , which includes , in a known manner , a telescopic central column 38 and feet 40 disposed radially , each provided with a roller 42 . column 38 has , at its top end , a seating module 44 according to the invention , which is fixed by its structural framework 10 . such a chair , thus forming a stool , can advantageously be used by people essentially working in an “ active ” position , for example a dentist or a watchmaker . it can be completed , as shown in this figure , by a backrest 46 fixed to cantle element 26 and allowing a “ passive ” position to be taken . when the user frequently works in the “ active ” position , it is advantageous to provide the chair with a transverse support bar 48 for the knees , advantageously padded and covered with a fabric or leather , so that contact is comfortable . this bar is fixed to support 36 , permanently or removably , by means of an arm 50 . the latter has a roller 42 and is advantageously connected to support 36 so as to pivot or slide , so that it can be removed when the user often has to leave his chair . it should be stressed that the pressure of the knees against bar 46 is slight . the latter thus barely participates in the seating of the user . however , it prevents him crossing his legs , and thus , certain annoyances associated with this habit . as can be seen in fig5 , arm 50 is fixed to support 36 in proximity to feet 40 , i . e . very close to the ground . consequently , it does not interfere , or barely interferes , with movement when the user occupies his chair or leaves it . finally , in a very advantageous manner , seating module 44 can be jointed on column 38 owing to a conventional adjustable chair tilting mechanism 52 provided with an armrest 54 . owing to the construction described , when the user sits down to get into the “ active ” position , he finds seat 44 automatically placed in the rest position corresponding to maximum comfort , i . e . with the femoral articulation at right angles to joint 14 . if the user leans forwards , fork 12 accompanies his movement , allowing him to adjust his posture in a self - supporting process , which contributes to reinforcing the supporting musculature and thus tends to reduce the risk of health problems , as mentioned hereinbefore . when , in order to think or make a telephone call , the user gets into a “ passive ” position against backrest 46 , fork 12 tilt backwards , such that he finds himself in a posture in which his entire musculature is resting . this automatic adjustment provides optimum comfort due to the fact that the user &# 39 ; s weight is distributed very uniformly over the buttocks and the back of the thighs . in other words , in the “ active ” position , the chair according to the invention allows adjustments in posture facilitating the work of the self - supporting muscles , whereas in the “ passive ” position , these muscles can relax . both the seating module and the chairs described hereinbefore can be subject to numerous variants . it is , for example , possible to provide adjusting members , and more particularly , stops ( not shown ) limiting , on both sides , the tilting movement of fork 12 on structural framework 10 . pommel element 20 can also be provided with means for altering its position with reference to structural framework 10 . an asymmetrical structure can also be envisaged , for a handicapped user , either at padding member 32 , or in the form of cantle element 26 . the hinged connection , via hinge 14 , between structural framework 10 and fork 12 , can be achieved by means of a ball joint . in this case , the self - supporting mechanism would operate both from front to back and from the side . the position of hinge 14 can also advantageously be adjustable in the forward - backward direction , such that it is perfectly aligned on the ischium when the user is seated . other adjusting means are possible for varying the distance between pommel element 20 and cantle element 26 , in order to adjust the tension of elastic membrane 16 . seat 44 is advantageously fixed to support 36 by its structural framework 10 . it is also possible to envisage fixing via cantle element 26 itself . the spring function performed by elastic membrane 16 can also be reinforced by springs especially arranged for this purpose , for example , torsion , traction or compression springs . it will be noted , finally , that it may be advantageous to provide backrest 46 with an independent permanent contact lumbar support zone that can be disconnected .
the incentive seating module comprises : a structural frame provided with a gaiter , a frame , disposed above said structural frame and provided with an arch , whereby the structural frame exhibits planar symmetry , means for connecting the frame to the structural frame comprising a joint enabling the frame to swivel in relation to the structural frame about an axis which is perpendicular to the symmetrical plane , and a seating element joining the frame to the gaiter , made of an elastic membrane which is used to define a rest position for the frame in relation to the structural frame and to return it towards said position when a user causes it to tilt in one direction or the other .