CA2230107A1 - Swinging supporting frame for a chair seat and back - Google Patents

Abstract

A swinging supporting frame for a chair seat and back, comprising:
- a sustantially horizontal arm (1) for fastening a chair seat;
- a telescopic rod (2) supporting the chair back and being hinged to said arm (1);
- one or more springs (40) acting on said vertical rod to push the chair back forward;
- a spacer (44) inserted between the walls (5) of said horizontal arm; and - screw means (16) for pressing the walls of said telescopic rod (2) against the walls (5) of said arm (1) and against said spacer (44) to lock the chair back in position, wherein said springs (40) are helical springs inserted onto the hinge pin (6) which is fitted on said arm (1) and said telescopic rod (2), one of the ends of said springs acting directly against the wall of said arm (1) and the other spring end acting against said rod, in particular against said spacer (44) inserted on said clamping screw means.
A plurality of friction plates (1) are arranged between said spacer (44) and the walls of said arm (1), and in order to position and set up said plates (10), said frame includes a pair of teeth (8, 9) obtained in the walls (5) of said arm by blanking and drawing.

Description

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SWINGING SUPPORTING F;RAME FOR A C~IAI~ SEAT AND E~ACK

The ~r~aGnt In~ention pro~ldes ~ suppc.~lin~ frame for a chair seat ~nd back, comprisin~ a sv~st~tially l-ori~o~ l arm to whlch the chair ~eat i8 S faatoned and a substantially vL.lical rod on which the ch~ir back is fitted, said rod beTn~ hin~ed to sald arm and beln~ subJect to the action of elastic means whlch push it forward to keep the chair b~ck in CG~ Ct with the user.
Hln~ed su~J~.GIlill~ frames for a chair seat and back are known ~ener~l.y cG"I-J~ a 51'l~5~ y huri~Gnl,al arm, to which the chair seat 18 faat~..ed, and a te'sscopic rod bein~ hin~ed to ~Qid arrn at the back of the frame and subjoct to the action of a sprin~ which tends to push the chair back against the~ user.
This tel~c~pic rod usually Gonsists of a pair of ~6~ljGIIS~ for e~.nple C-15 shaped ~ecU0l)8, each slidin~ inside the other to allow the hei~ht of the chalr back to be ~djusted, and devices are provided which lock the tel~ rod in the Jeslred PO~IlIOn.
Genor~lly in prior art ~-~.-.e~ 21 pair of sicle walls are provlded ~t th~ base of the tolas~opic rod which fit around the hGr;~u~ l arrn and Y~herei n holes 20 are ~,r~Jvi~ed ~or a pin p~sslng therethrou~h, said pln forrninS7 the hin~e ~round which the t~les~ rod ro~ut~s, and for clampin~ screw means.
In the base arm of prlor art r~n,og a pin ~al~,l'eî to the hin~e pln i~
provided in front of said hinge pin.
On the hin~e pin a splral sprin~ is insorted, an end of which e"~a~oa th~
front pln in the i~GIi~G~ l arm and the othor end ~ a~s the lower edg~
of the l le~ lc rod, thus ex~ a forc~ which tends to rot~to the t6 1~ ~QOpiC rod forward. On the clalnph ,~ screw, inside the t-- ri~u, ~lal arm, a plurality of friction sheets are illse.l~d which are tiç~ e.l l~hve spacer, i, ~5E.l~.l on said screw, and the arm wall.

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The ~riction ~heet~ are ~Iternativ~ly Inte~ral with the ho,l~,ol~tal arm and thetelescopic rod to h~c~ea~Q the fricUon area.
I low~vor, thls confi~uration haa various ~ aclcs, amo,.S~ which, prlm~rily, c~,nsi~rably difflcult ~ss~"~blin~.
S As a matter of fact, in order to ~83~3m~ the frame, it is 11eCeS31~ry to nt up fir~t the frlctlon ~heets, then the sprln~, the~n the two pins in the holi~entalarm and finally the clam,c Tn~ screw me~ns.
~ Ho~._v-.r, Tn orderto ~JosiliGIl the various cen~pone~t~ ~ con~idsr~ble force must be a~.,.~J to ali~n the holes for the clal ",~,ln~ 8CtQW In the arm and in the 1~ Irsc-J,~Jic rod, by ove~-;o,-,i"~ the force of the 8prln~ and keepln~ thev~rîou~ parts In poc'llen.
Another problem of prior art ~,.,es is the difficul~ in preventin~ the rot~tiG" of tho 3cr~w fe"-,i"~ the st~ady pin when th~ knob for ~Bt._.li th~ t919~ iC rod is li~,~l,t~r.PI.
For thls purpose In the W811 of the horicv~ arrn an eyelet With ~ubstantially parallel ~ides is provided, inside whlch the poly~onal end of the acrew shank 18 1, .~e. ~;d.
A ~auged hole housin~ the ~crew head is provided in the wall of the talec_ol.ic rod.
If, when li~hl~"ing the knob, the he~d ~cted directiy on the wall of the tElsecopic rod, due to the structural inaccuracies of thls klnd of ~lem~n~ it would be Impos61b,e to have the friction ~heets we,ix~n~ ~.r~,erly.
The result of this is a complex ~cco,~ llehm~l ~t.
In ordor to obviate the above~de~cribed drawlJ~3cks, the ,~ ro~eal inventlol-provide~ ~ swin~in~ 8uppo,lln~a fr~me for a chalr seat and back, v~l,er~l., ~ the elastic force pushing r.,~ the t~l~s~, ic rod which supporh the oh~lr ~3k Is ~upplled by a sprln~" whl~h 18 ~t on a pln In the l.Grl~o,.t~l arm and an end ofwhich aGtsdirectlyagah~alsald ~nn,~ the other end acts aE~ainst the clampin~ screw means.

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l'hl~ a~d o~h~r fe~ur~s of ~he pr~sent iFlYe~tlon, ~s d~ined in the ~pF~andew~ claim~, will becom~ m or~ apparent frorn ~ followin~ detaiied ~es~ripti~n, provi~ied, ~y w ay of ~n r~strictive ex~n~ple, wlth referenGe to lhe a~co m panyin~ ~r~ win~s in w hi~h:
ure 1 1~ a ~ie Yi~!W of an ~ssernbled fr~ m e ~co~rdir1g to the invention, ~howin~ ~he t~le~opic rod in i~ v~ri~us po~ le positi~ns;
. figures ~ ~nci 3 3r~ respectively ~ top view ~nd a ide vievY oF th~
horizorlt~ rm in a ~r~rne a~orciing tc the in~ention;
~g~re 3a i5 a per~pe~tive view of a p~rti~uiar of the ori~ontal ~rm, irl a 0 further pre~l re~ embo~iment ~f the inventinn;
a figure 4 iliu~tr~tes the plat~ from whi~h the ~rm of the pre~edi~ fi~res i~ o~t~ine~ anci it ~h~ws the pl~te ~ankin~ elnd fol~in~ lines;
fig~res 5, 6 ~nd 7 are re~pectively a front view and t~o opp~ing ~ici~
views of the teles~pic roci in ~ fr~3me 3c~ ing to th~ invention;
1~ ~ fig~re ~ str~tes th~ pia~e fror~ which the p~rt$ ~orrnin~ the teie~ pic r~d ~re o~t~ined and it ~hows the pl~te blanking ar1~ folding lines;
figure ~ shows a fricti~n pl~ in a ~rarr ~ accc~rdiny tu th~ inv~ntion;
fi~ur~ 10 ~hows the ~l~mping screw ~r~d ~ sp~cer in~:rted thereon;
fi~ure 11 show~ the spring;
~o ., h~res ~ and ~ 3 ~re ~ front view and a side ~/iew oF the support f~r ~he ~hair b~kl o fi~ure ~4 shows a plate fc)r ~stenin~ th~ ch~ir back;
Rgure ~ 5 is ~ plan view of the plate of fi~ure 1~;
.~ ~igure 1~ is ~ tion~l view of th~ plate of figure 74.
t'~5 With re~erenc~ to fi~re 1, the frarne of the inv~ntion co~nprises a suybst~ntially hori~ont;~l arm, shown ~s ~ whoie by ~umeral 1, to b~
f~~tened hy me~n~; of a plate vr the 5ike to a c~hair sea~, and ~ teles~opic rod, shown as a whole by numeral ~, which i~ hin~e~ t~ the arm 1 ~n~ at the upper end of which a plat~ 3 is hinged to whiGh th~ ch~ir back is f~s~ened.
The ~rrn 1 is o~t~ine~ t~y blarlking ~n~ sh~pi~g a pl~te, ~or ex~npl~ a ~onv~ ntly tlhick ~teel pl~e, t~ provide a ~ntral ~tilT~nin~ rib 4 ~ee fiSJure~ ~ arld 3~ an~ ~ p~ir o~ side w;~lls ~.
5 ~he ~ide w~lls 5 h~ve ~ h~le for the in~er~lorl oF a hin~e pin ~ on whi~h one or rnore ~prin~s ~0 (sh~wn in flg. 11) ~r~ fit~ed ~p, ~tin~ on the tetesoopi~ rod 2.
Arl eyelet 7 is ellso pr~vicled in the ~i~e w~lls S, to l~t a s~rew pas~
~herethrou h to lock the t~l~scopi~ rod in the ~sir~d posi~ion.
10 Th~ ~y~l~t 7 h~ ~n el~ny~t~d &hape to all~ the sc:r~w tG ~hift and ~ll~w the ~wingin~ of the telescopic r~d ~.
A~OYe ~nd ~enea~h the ey~let~ 7 th~ side ~all~ o~ ~he ~rm 1 hav~ tw~
p~irs of teeth, sh4wn ~y nurn~r~l~ 8 ~r~d 9 respe~ti~ely, whioh ar~ ob~ained dire~tly ir~ th~ pl;ate wall b~ bianking and dra~in~. Th~se t~eth 8 and ~ act guide to position ~riGtion plate~ 10, whi~h ~re ~h~p~d ~s shown in figure ~, ~ith an ey~let which ~orr~ponds to eyelet 7 l~l walls ~ of arm ~1.
~wc wa~h~rs, not illu~tr~t*d in the dr~wings, ~r~ insertd on the ~ pln3 ~cr~w an~ ~perat~ in qon~t with g~i~ friction pla~s l 0 ~nd with ~h~ ~Ivall$
5, to d~velop ~ fri~tion that ~low~ th~ movement~ of tho rod ~.
~n When rod ~ o~cillat~, rot2in~ ~rour7cl the hin~e pin ~, the w~sher~ ~lide in cont~ct with the friction plates 1~ an~i with ~ualls 6, while pl~t~s ~0 are lock~d ~y teeth ~ ~n~ ~.
Th~ central rib 4 h~s~a thickene~ portion 11 whir~h i~ drill~d ~nd thre~e~
to all~lv a scr~w to ~e tighten~d for fastening the chair se~t and which h~s ~5 ~ hexa~on~l c;~ity for a nut or the like.
The fact th~t the rib 4 is rather deep, hesid~s ~ ing ~re~t~r stiffn~ to the arrn 1, ~l~o ~llow~ ~ shortef s~rew to be used for f~stenin~~ ~he ~hair seat.
The tele~copl~ r~ (fi~. 1) conlprises ~ base ~ ~n~ a bar 13 &uppc;rtin the chair ba~k, ~aid bar 13 ~lidiny in~i~e th~ bo~ 1Z.

The baso i8 suL~ ti~alîy a C-sh~ped sectio~. havin~ at its lower end a pair of side W~1115 14 which fit around thel walls 5 at the back of the hori,v"tal arrn 1.
In these wall~ a hole is provided, in ~ loc~lion co~ s~Gn~lin~ to the hole 13 in the arm 1, to let the hin~e pin pa83 therethrou~h.
The seat for the scre~w ff etenln~ the l~l~sc~;:lc rod, shown by numeral 1 in flS~ure 10, i8 l~lanlc~J in the walls 14.
Accordin~ to the l,)v_.,lTG." in the walls 14 a pair of w~shers 17 and 18 Are blanked, the former of whioh has a poly~on~l openlng 1~ and the l~tter 10 has a clrcular port 20 (see figs. 6, 7).
Th~ washers 17 and 18 are not blanked alon~ the whc~le circ~J.,.r~rQnce, but blanking i~ interrupted for a short l~n~th in order to form an extension 21 CG~ C~ n~ th~ ~ her~ tcl the wall 14.
Thls conflsluration avoid~ tho need to work this part of the frame l~re ~'6 61Y
15 and, ll-c~rafore, CO8tIY.
AB a matter of fact, once the screw 1~3 ha~ been Ina.~. t-_~l into the w~sl.ers,it 18 prevented from rotating by the en~a~ .,t ~ n the polygonal liull of the shank and the port 1~ of the washQr 18, wl,~r~ 5 the screw and its washer are prevented from moviny by the ex~,nei3n 21 connoctln~
20 the washers to the w~ll 14.
On tho other hand, since the wTdth of the exl~n~ion 21 i~ limitodt the force by which the ~crew 18 tl~hle"~e~J, ex~rted along a short len~th, cEIu~es a ht local Je~urllldli~" of the w~ll 14, In particular of the e~le,)si~. 21, thus on~bling the washers 17 and 18 to move ~,lr~ar~ with r_sp~t to the ~ 25 wall 14 to lean z~ t the wall 6 of tho h~,rl,u,-l&l arm, as shown in detail in fi~ure 5.
According to a further ~,rer~ 1 c..lLo~i,.,ant, the slde W~ 8 5 of arm 1 may have tvvo upwclrdly bent winç~s 45, each havin~ a ~lot 46 (fi~. 3a).
A was~er, ;.~rt~l on the screw 16, may then be posit70ned b6hrl~0 wall 6 .

~ 5 snd wing 45, to exert ~ r ;cti.,al ~orce which op,ooties to the movem~nts of rod ~.
In such a c;~, the plate~ 10 as well Q8 teeth 8 and 0 are no more s ~
The se~tion 13, to which the chair back is hin~ed or rl~tv.~ed, fits into the base 12 of the teloscopic rod 2, ~aid b~se 12 having su6~t~.,lially a C-shaped c,~ q~tlo".
The ~30lIG~I 13 has, at its lo~er end, ~ central 8iot 22, whl~h starts at the base and extends to a cert~ln hei~ht.
Preferably the ~aoin~ ed~es of the section 13 have a ~eries of teeth 42 which er"t6M3 one onothor, in order to prevent th~ two ed~es from slTdln~
durln~ work and provide ~reah_r structural ~tlrr,.oa~.
A ton~ue 23 with a lar~er upper end 24 18 blanked In the bas~ tjGn 12.
In thTs uppQr end or head 24 ~ threade~l hole 25 j9 pro~lded, whereas the tonç1ue Z3 i8 bent to ~orm one or more loops shown by num~ral 2~ In fi8ures 8 and 7 The ~hank of a knob ~or lochlny the s~:tlo" 13 z~t the desired height is ~ scrG~Jod into the th~ c_l hole 25 to adjust the hel~ht o~ the ch~ir b~ck~
As a matter of f~ct, the ~ection 13 i51n9 e. lecl into the base 12 by flttin~ tho 810t 22 on the U~r~aJ~d shank o~ the knob (not shown), whlch i8 SUn9!VJ~
into the head 24.
It is now -Qufri_-snl to ti~7hten the knob in order to p~88 the tongue head 24 inst the ~e~slion 13 and the wall o~ th~ base 12 to lock the a~sembly in position~

2~ The lOOp8 26 help to move the h~ad 24 dO~h"~ Is wlth l~p~ 1 to its initlal ~J~9i''~ n, In or~er to avold that, by usin~ a sm~ll knob, said knob conpass throu~h the hole wlth whlch the he~d 2~ was ~:o"nect~d.
If prJferl~.l, the slot 22 m~y be provlded in th~ ba~e 12. In such a ca~e, only ~ U,re~JeJ hob for the knob wTII be provided in the 513Ct;~ 13, and the knob will 8hlft tG~U-er wlth the ~-e~liull whQn adJu~tln~ the hei~ht of the seat back.
Finally, In vlew of the fact that on the upper portion of thel ba8~ 12 only the cenl,~l aro~ of the s~ctlon i8 subJect to 6tress, ~:I-or~;~s the wall ends do 5 not co-oiJGrale, accorcii.,~ to the In~/ention this end has been blanked so that the upper end of the 5c~liGII has slopinçl sid~s~
Thls allows the 8eclien to be made by simply ~ a plate ~cco~dinS~ to the shape shown in figure 8, so that the whole plate u~idth csn be ernployed.
10 Thuo~ cc,nlr~ly to prior art syOtems, the need is avoided to use a wider plate and to provide ~ side 6~Ctu~16iO11 with a plurallty of olen,~..la for the CGI 11 le~,diul I to the various se~tiGI ~s b~inçl blanked.
Preferably the lower end of the section 13 has two llttle pr~ . ~s or teeth 43 (flg. 12) which, though reslliently buckllng and allowin~ the 13G_~100 to be fitted onto the s~rew of the lochl."~ knob, prevent the ~e~70-1 13 from being In~dv~ .-lly drawn out of the b~se 12.
Finally, th~ upper end of the ~ct.-,n 13 may be ,~ r-,f~ra~.Iy folded to provide a ~ort of b~r or ~rm on which the platc for ~astenin~ the chair back may be ~et, wlthout any need to flt a small ba~ by weldinSI, as It occurs wlth ~O the prior art.
The ~s~n~ly of the above-dea~ ed devlce i8 COI~Id~r~bly 8i~ ir~J.
The l~les~lc rod 2 i5 fltted onto the arm 1, then the 8heets 1~ are ~ inserted i~étr/~G.. the-teeth 8 and Çl, a~er which the spa~er is l.os~Uu~.~J
insldQ the arm 5, and the screw 16 is ins~rtod with tho ~ -hers tl.~r~Gr., ~ 25 s~aid screw 1~ o6ill~ throu~h tha holes 1~, 7 and ~!O and tho ~pacer 30, wlth th~ shank polyS;lonal portion e. ,t~. in~ the port 10 of the w~sher 18.
Finally, the sprinçls 40 and the hln~e pln are po~ltioned into the holes 15 ~nd ~.
One of the ~prin~ ends leans açlainst the arm 1 and the other sprlng encl leans a~ainst the spacQr 30 i,.s~ l on the screw 16.
It 18 then sufri~l~nt to push the sprin~ slightly to posltlon It correctly In Col" ~L ~ion with the hoIes and Insert the hin~e pin.
This easy assembly ~110VI18 the whole apparatus to be au~on ~tica11y 5 ~ 5GI ~
At this point the ~BC~l;CJO 13 iS fltt~d into the basl~ 12, end a knob is s~r~ed into the ll-re~lad hole 25 of the head 24 of the ton~ue 23.
By li~ in~ the knob the head 24 is pr~sse:l a~alnst the 6~ 1iell 13 and a~ainst the wall of the base section 12, tnus lochi,.~ the ~upport 13 ~f the 10 chair b8ck tat the d~ l hel~ht.
The action exerted by the s~ri,-~s fitted on the hinge pin tends to push the t61e~c,~ic rod ~ forward, In order to koep the chalr back alw_ys in contact with the user.
In order to lock the 1~ ce,~ic rod in the desired posltion it i~ eufficient to 15 li~ n the knob which ~et8 ~srov.-~J on ~crew 16.
The ~ g~.n~.~t ~c~ on the poly~onal ,~Grlic", of the scr~w shank and the Cell~lS~Oi-dil~ hole in the wa~her 18, which 18 connoct~d to the wall 14 by means of tho extension 21, prevents the .ot~ l) of the screw, thus ~llow~n~ the knob to be liu~t~.~eJ with one hand only.
20 By tl~ erlln~ the knob the force axe, lec~ on the~ wa~ ra 17 and 18 causes a ~light ~uf~r~tlel~ of the waIIs 14 (exlension 21), enablln~ tho washers to move fo,.rvar~ with re~pect to the walls 14 and to lean a~ainst the wall5 5 of the arrn 1.
Thus, by conveni6..lIy li~I,t~nI~ J the knob, the t~'?'r8~0piC rod 2 can be 25 Iocke~d in position, .~heraa5, by Li~ the knob wlth Iess force the friction effect of tho plates 10 can be e,<~loll~d to ~Iow down the~
mov~ cnl~ c~ erl by tho sprin~.
Accor~JI,.u to an a",l.odl~"~ of the inventlon, the plato 3 has a centrai body 28 and a pair of nan~s 2~ which are cG"~,e ~i to the body 28 by ",et."s of a pair c~f ~lopln~ wall8 30 (fi~ure 16).
The sTde walls 30 have a pair of hol~8 31 Into which th~ arm 27 of the 8e.;tiGI ~ 13 iS i~ IS~t~. to provTde a hlnge 8upport for the plate.
At the uppor and lower sides of the piate 3 a palr of tab8 32 er~s also 5 provided by bl~nkinç~ and foldinç~ the plat~, whlch nt around the s~ctic~" 13 when the plate is set up in order to keep It cQol~d on the~ telescopic rod and the arm 27.
Tho l~n~th of tho arrn is sllghtly yre,~t~3r than the d;bt~~ e betw~en the hol~s 31 to allow the plate to be aet up flrmly when 1~ b c~ntred on its support and ~180 to allow the arms to be 81id from the pl~te by disen~aaç~in~
them from the holes 31 when the plQtl3 Ts pu~hed on one side or the other a~Qinstthe~s~;tiG.- 13.
Th7~ confi~ur~tion allows the plate to be easlly a~er,.blod with the chair back, without any need to u8e screws or the like.
1~ A~ ~ m~ffer of fact, it is Sum~lF nt to insert an end of the ann 27 Into one of tho hol~s 31, let then the plate ~lido ~lon~ tho arrn 27 untll the free hole ~e~t~ past the other end of said arm, and then In~ert the s~cc",d end of the arm Into th~ ~ocol-J hole 31.
By takin~ the plate to the central position a~ain, the arm ends wlll keep 20 on~ed in their seab.
In the worki"~ 05itiUIl the t~bs 32 enSaage th~ scctl~l- 13 to prevent the plate from slldlnç1 in one dil.,~lioll or the other, thu~ enablin~ said plate toswin~ with the ch~ir back, but not to slide from it~ support.
If, on the Co"tlt-,y, the chair b~ck has to be d ~ 5e~ J~ it is 8urrl~ t to ~5 rotate It to dlsens~6~ls th~ tabs 32 from the 3~ 1iol- 13, after which the chalr ~ back with the plate is pushed latorally ~nd the plate i~ d'~ od from the ~rrn 27.
Accordin~ to ~ further feature of the invsnl;on, a ~mall plate 33 made of a plastlc ~al6,;al, pref~rably a tender and cu"".r~sslLle pla~tic m~terial .

whlch i~ dlvide~ into two overlapping areQ~ of different ll ,Ichi~03~, is applied onto th~ pl~t~ 3.
The thichlle,ss of the small plate 33, whTch lean8 a~alnat the 8ection 13 of the ~ c~ p ic rod 2, .lefi,)e~ the incli. ~ of the chair bsck.
5 Since the holes 31 in the small plate are arran~ed ~t half hel~ht and the small pl~te i8 8y.,~ tlic to both axes, it i8 posalble to 81ide and 8et the ~mall plate up a~aln a~ter havin~ turned It upslde-down, ao a8 to lean against the ~ _'' .1 13 the more or less thick ~uvll;Gll of the amall plate 33 and chan~e the inclination of the chair back.
10 In order to fasten the chair back to the tele3CG~JiC rod it is s~ rr.le..l, as previously ,-,eatiu-.eJ, tc~ in~rt the arrns 27 into the plate holes 31 with thechair bsck in a substantially horizontal ,~.o~ilTo,-, after which, when tho:cha7r back i6 taken into an upri~ht poaltlon, the tabs 32 ~..Jn~e the s~ t' )~ 13 thu~ c~.,t~.;.,~ the plate and the chalr back.

Claims (10)

1. A swinging supporting frame for a chair seat and back, comprising:
- a sustantially horizontal arm (1) for fastening a chair seat;
- a telescopic rod (2) supporting the chair back and being hinged to said arm (1);
- one or more springs (40) acting on said vertical rod to push the chair back forward;
- a spacer (44) inserted between the walls (5) of said horizontal arm; and - screw means (16) for pressing the walls of said telescopic rod (2) against the walls (5) of said arm (1) and against said spacer (44) to lock the chair back in position, characterized in that said springs (40) are helical springs inserted onto the hinge pin (6) which is fitted on said arm (1) and said telescopic rod (2), one of the ends of said springs acting directly against the wall of said arm (1) and the other spring end acting against said rod, in particular against said spacer (44) inserted on said clamping screw means.

2. A frame according to claim 1, further comprising a plurality of friction plates (10) arranged between said spacer (44) and the walls of said arm (1), characterized in that, in order to position and set up said plates (10), said frame includes a pair of teeth (8, 9) obtained in the walls (5) of said arm banking and drawing.

3. A frame according to claim 2, characterized in that it comprises a pair of washers, inserted on said clamping screw means between said friction plates (10) and said wall (5) of said arm (1).

4. A frame according to any of the claims 1 to 3, characterized in that said telescopic rod (2) comprises a base section (12) hinged to said arm and a second section (13), sliding inside the first one and provided, at its lower end, with a longitudinal slot (22), said base section having a tongue, obtained preferably by banking, with a free and larger upper end (25), said tongue being bent so that said end or head (25) is in a position lower than its initial position and at a certain distance from the wall of said base section, said head (25) being threaded to allow the knob to be screwed, said knob pressing said head against said sliding section and said base section.

5. A frame according to claim 4, characterized in that said base section (12) has a substantially C-shaped cross-section, the upper end of said section having downward sloping upper edges.

6. A frame according to claim 5, characterized in that the upper end of said sliding section is shaped to define a bar (27) for setting a plate (3) for fastening the chair back.

7. A frame according to any of the preceding claims, characterized in that it further comprises a pair of washers (18) with holes to let the clamping screw (16) pass therethrough, wherein one of said holes (19) has a polygonal cross-section, said washers being provided in the walls of the telescopic rod or of the arm and being connected to said telescopic rod or to said arm by means of an extension (21) which prevents them from rotating.

8. A frame according to claim 1, characterized in that the chair back is fastened to a plate (3) having a pair of holes (31) for the insertion of arms (27) provided in said telescopic rod, said plate comprising pairs of tabs (32) for engaging said telescopic rod to keep said plate centred with respect to said telescopic rod.

9. A frame according to claim 8, characterized in that a further small plate (33) of soft material is applied onto said plate, said small plate being placed between said plate (3) and said telescopic rod (2), said small plate having an upper and a lower areas of different thickness.

10. A frame according to claim 1, characterized by the fact of providing, in the side walls (5) of arm (1), two upwardly bent wings (45), each having a slot (46), a washer inserted on the screw (16), being positioned between wall (5) and wing (45), to exert a frictinal force which opposes to the movements of rod (2).