the new design approach allows above all for sufficient sliding movement , which can additionally be supported by the possibility of small lever movements to achieve the desired angle of the seat . the centre of gravity is thereby moved forward significantly , with the result that the chair would be in danger of tipping forward unless counteracted by additional structural elements . the possibility of employing a large support area on the floor cannot be considered , as potential users would not buy such chairs . the risk of tipping over could be prevented by heavy weights mounted movably or immovably on the chair , e . g . in the form of large , half - moon - shaped weights suspended underneath at the back on the lower pivot point of the backrest lever or the base , for instance between all or some of the foot segments . this solution would also be likely to prove unpopular as it would push up the costs for production and transport and the chair itself would be seen as a monstrosity . repositioning of the chair seat by weights would also mean a constant pulling force , contrary to the situation with return springs . ( fig5 ) a solution of the intended kind can also be achieved by one or more extending feet ( 7 ) which slide or fold out in the frontward direction . before movement of the seat ( 1 ), an additional foot ( 7 ) is positioned between the feet / legs of the user . a fold - out foot ( 7 )( 8 )( 9 ) ( all figs . except 3 ) has the advantage of being less problematic in terms of operation and durability as it is a mechanical system ; on the other hand , however , when the chair is not in use , it is visually less attractive . the fold - down movement can be either vertical or even diagonal , allowing a somewhat longer extension under the chair . a foot pedal is provided on the side of the fold - out foot to allow the foot to be extended by the occupant &# 39 ; s foot , as well as a lever for releasing this extended foot after use . the extended foot can either lock in place or be held down by a coupling . telescopic extension ( fig3 ) is a possibility in particular for motorised chairs . there are thereby two possibilities : an existing foot can be converted into a telescopic foot . the extending foot thereby always stays in the foot area of the occupant . or a telescopic supporting foot ( 7 )( 8 )( 34 ) and ( 35 ), as it is named in the following text , can be extended directly from under the seat diagonally to the floor as an extended foot ; this telescopic supporting foot , which rests on the ground approx . 20 - 35 cm in front of the chair like a 6th foot , must be extended and positioned before the chair can be adjusted from the normal position into the position with sharply tilted backrest . movement of the telescopic supporting foot could be operated and locked in position by the foot or by a hand lever or manual crank axle . in very expensive versions of the chair , this could also be done electrically , pneumatically or hydraulically , as also for the telescopes for the chair seat movement . when extended , the telescopic supporting foot ( 7 ) reaches diagonally from under the chair down to the floor , in the frontward direction ; therefore , in its extended position it is diagonally located between the legs or feet of the occupant , which would be seen as sub - optimal . an interlocking or linking device ensures that the tilt of the backrest and the position of the seat can only be changed , when this telescopic supporting foot exerts pressure on the floor ; swivel movement is then also prevented . but it would appear more acceptable for the occupant to have only an extending foot that lies underneath in the foot area . in connection with the problem of tipping over that arises in the case of movable chair seats , it is possible to distinguish 3 different situations , for which solution c appears to be the best : a ) the chair backrest ( and therefore also the seat ) can be fixed in any tilt position . this requires the greatest support area on the floor , as also in this position the occupant can lean his / her body forward , and hence shift the centre of gravity forward . the extending foot must rest on the floor about 35 cm in front of the chair . in the case of chairs without motorised operation , the fold - out foot offers a simple solution . the next solutions b and c require only a smaller support area , i . e . shorter extending feet . in these cases , the extending foot must rest on the floor only about 20 cm in front of the chair . b ) the chair backrest does not lock in position and is provided with a tension spring which exerts a forward force . this solution has the disadvantage that the spring force must be precisely regulated ( for any occupant weight ). the occupant has constantly to fight against the potential movement and does not have a genuine backrest but only a springing back support . c ) the chair backrest is not fixable in terms of forward movement — i . e . the backrest moves forward as soon as the occupant bends forward — but is sprung with such low return force that it is just able to move the seat with the occupant , while the backrest is fixed by an additional lever only for leaning back . the occupant can therefore lean back relaxed , but the risk of tipping forward with the whole chair is reduced because the seat immediately moves backwards if the occupant bends forward and so shifts the centre of gravity . so whenever the occupant wishes to tilt the seatback further back , he / she has to operate a lever or such like in order to release the fixing mechanism . a free - wheel with hand - operated clutch would allow such free one - way movement . a ratchet mechanism could also be used , but is not continuously adjustable and causes noise . this lever could also take the form of a foot mechanism . it could also be integrated into the chair backrest and be operated by the head or special back pressure or arm pressure . consideration must also be given to the linkage between the extending foot on the base of the chair , the swivel movement of the chair and the tilting movement of the backrest ; as otherwise an extending foot would be needed in all directions , whereas in the present case it is only necessary at the front . when the additional extending foot has been folded out at the front , the swivel movement of the chair is blocked , and only then is substantial forward movement of the seat and substantial tilting of the backrest possible . the linkage can be easily effected by two cable pulls with locking pins for swiveling and sliding , or a cable pull ( 111 ) from the extending foot ( 7 ) to underneath the chair , with , perhaps , a folding lever mechanism ( 74 ) for the other purposes , since the height adjustability of the chair base must also be taken into account . in the case of chairs with electric motors , this can also be achieved by simple control logic . the extending foot can , however , also be swivel - mounted ( fig1 ) ( 110 ) on the top frame / seat with an extension piece ; in this case , the base need not be positioned before the foot is folded down / out . because of the need for height adjustability , however , this would be more difficult to design . in place of the cable pull , a lever mechanism could also be used , possibly with cardan universal joints . whatever system is used , however , height adjustability of the chair must be maintained . as shown in fig7 and 10 , the chair backrest itself can consist of 2 parts : the backrest ( 2 ) itself can have a second cushion element ( 71 ) or “ backrest parallel ” on the occupant side which is able to move slightly parallel to the backrest in sliding bearings ( 73 ) or by small levers ( 72 ); the chair backrest proper ( 2 ) is held up by springs with low force . the design of the backrest parallel ( 71 ) can be used in all of the following chairs . the purpose is to offset the compression - movement effect on the body of the occupant during tilting . the seat ( 1 ) should be easily movable . this can be achieved by mounting it on one or two parallel telescopes with double tubes / pullouts ( 15 ) which permit large horizontal movement of the seat , while the backrest ( 2 ) is fixed to the rear of the seat ( 1 ) with one or more swivel joints ( 10 ). a long spring ( 100 ) is provided inside the telescope ( s ) ( 15 ) to return the seat ( 1 ) to normal position . alternatively , return can be done by one or more springs mounted in one of the swivel joints ( 10 ) or ( 11 ). also conceivable for this purpose would be a weight ( 51 ) mounted on cable pulls ( 50 ) to pull the seat ( 1 ) backwards . in terms of linking the seat ( 1 ) and backrest ( 2 ) ( possibly with backrest parallel ( 71 )) and optional backrest lever with the base ( 3 )( 5 ), four different mechanical systems can be envisaged . a common factor to them all is that the seat ( 1 ) is linked to the bottom of the backrest ( 2 ) by a swivel joint ( 10 ), so as to allow movement / adjustment of the seat . this swivel joint ( 10 ) can naturally also be additionally provided with a clutch in order to give the chair the possibility of operating as a perfectly normal chair ; in other words , the backrest can be tilted without the seat sliding forward . the difference in a ) to d ) is the guidance of the top point of the backrest ( parallel ). the length and inclination of the levers / telescopes described below can be made adjustable so as to give the occupant various adjustment options . in the embodiment shown in fig1 and 9 , a further lever mechanism — the “ backrest lever ”— is mounted at the top of the backrest ( parallel ) with a swivel joint ( 11 ) and extends down to the base of the chair ( 14 )— i . e . in this case the part above the vertical gas spring ( 3 )— where it is also secured with a swivel joint ( 13 ). the seat ( 1 ) therefore moves backwards and forwards with the telescope ( 15 ). this system therefore consists of three system components , a horizontal seat surface ( 1 ) on the telescopes ( 15 ), a backrest ( 2 ) ( and parallel ( 71 ))— which may also consist of only one or two bars — and one or two other vertically rotating bars or surfaces , the backrest lever ( 12 ), as support against it ; in reality , of course , several adjacent joints can be fitted for the three swivel points . the movement of the whole structure is similar to the movement of the piston rod in an engine , except that instead of a complete circular movement , only less than half a circle is performed . the backrest lever is made adjustable to the different needs of the occupant , e . g . through an adjustable coupling point on the backrest parallel . for safety reasons , the mechanics at the rear of the chair are housed in a bellows to prevent the risk of injury . this also gives the chair a more homogenous appearance . for the same reason , it is also better to use only one bar for the backrest lever . for noise reasons , the double - tube telescopes ( 15 ) could be mounted in plastic ball bearings . simple sliding bearings may also be sufficient , though in this case problems may be caused by friction . the movement of the seat ( 1 ) can be locked with one hand . in an embodiment shown in fig2 and 8 , the backrest ( 2 ) has a smaller lever ( 21 ) at the top of each side , linked by a swivel joint ( 20 ) and also connected by a swivel joint ( 22 ) to a vertical extension ( 23 ) from the base of the chair . however , this requires very high chairs . in the embodiment of fig3 the backrest ( 2 ) has a smaller lever ( 36 ) at the bottom of each side or in the middle , linked by a swivel joint ( 11 ) and also connected by a swivel joint ( 32 ) to a vertical extension ( 33 ) from the base of the chair . in the embodiment of fig4 the backrest ( 2 ) has a shorter ( double - tube ) telescopic extension ( 41 )( 42 ) at the top of each side or in the middle , running diagonally upwards at the back and connected to a vertical extension ( 40 ) from the base . the inclination of this telescope could possibly be made adjustable . a benefit of the invention is that the occupant is able to change his / her position on the chair by adjusting the backrest ( 2 ) from upright position to tilted position , and so lessen the risk of back problems . the chair nevertheless offers support for the body . the position of the extended hand relative to the work desk changes only slightly , while the seat ( 1 ) moves backwards and forwards when the tilt of the backrest ( 2 ) is changed . an electrically operated chair may be optically more attractive and more convenient to use . depending on the number of motors installed , the various components can be controlled separately . however , this renders the chair more complex , with a resulting decrease in reliability . and it produces the further disadvantage that the chair requires a cable connection or battery . on the other hand , it has the advantage of allowing the occupant to adjust the parameters extremely slowly and continuously within a given range . all these systems can naturally also be equipped with the customary adjustment possibilities for swinging , tilting , chair back adjustment and so on . in the basic version , armrests are not provided as the patented moveable armrests as per the present inventor &# 39 ; s u . s . pat . no . 6 , 267 , 336 are very well suited for combination with this chair as they allow movement of up to 1 m , so the movement of 35 cm intended by the present chair could easily be achieved . if these moveable armrests are not used , armrests are preferably mounted on the seat so that their position relative to the occupant remains more or less unchanged . by small levers , they can be made additionally adjustable with the movements of the occupant . it would also be conceivable to provide the chair as standard with somewhat lower support elements in place of the armrests ( 74 )( fig7 ), which would facilitate tilting backwards by giving points for support ; these could be upgraded to armrests if desired . accordingly , it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention . reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims , which themselves recite those features regarded as essential to the invention .
an ergonomic chair having an extending foot and the possibility of swiveling with tilting of the chair backrest synchronized with horizontal movement of the chair seat . it is intended for the linkage system to be installed on a swivel chair . with this chair , it is intended to synchronize the tilt of the backrest with the forward movement of the seat in such a way that the distance of the seat occupant &# 39 ; s hands relative to the work equipment on the desk top remains virtually constant at all times .