US2862594A - Feed roll supporting structure for typewriters - Google Patents

Description

2,862,594 FEED Rom. SUPPORTING STRUCTURE FOR TYFEwRITERs Filed Oct. 21. 1953 L. E. PALMER Dec. 2, 1958 6 Sheets-Sheet 1 llllllllllfll PALMER ATTORNEY FEED ROLL SUPPORTING STRUCTURE FOR TYPEWRITERS I Filed Oct. 21. 1953 L. E. PALMER Dec. 2, 1958 6 Sheets-Sheet 2 INVENTOR. LEON E.PALMER B wfifzm ATTORNEY Dec. 2, 1958 L. 1%. PALMER 2,362,594

FEED ROLL SUPPORTING STRUCTURE FOR TYPEWRITERS Filed Oct. 21, 1953 6 Sheets-Sheet 3 INVENTOR.

LEON E.PAL.MER

B Q) oma ATTORNEY Dec. 2, 1958 2,862,594

FEED ROLL SUPPORTING'STRUCTURE FoR TYPEWRITERS Filed Oct. 21. 1953 L. E, PALMER 6 Sheets-Sheet 4 INVENTOR. LEO E. PALMER w liawv Yo-h.

ATTORNEY Dec. 2, 1958 1. E. PALMER v 2,362,594 I FEED ROLL SUPPORTING STRUCTURE FOR TYPEWRITERS Filed Oct. 21. 1953 6 Sheets-Shee'i' 5 JNVENTOR.

LEO E.PALMER @FIA 0%; mag;

ATTORN EY Dec. 2, 1958 L. E. PALMER 2,862,594

FEED ROLL SUPPORTING STRUCTURE FOR TYPEWRITERS Filed 001;. 21, 1953 6 Sheets-Sheet 6 o INVENTOR. LEON E. PALMER Ll- B J [1 mp ATTORNEY United States Patent" 2,862,594 FEED" ROLL SIJ- PORTING 'STRUCTUREiron TYPEWRITERS" Leon E. PaImer Wap ingers Falls, N. Y., assignor to liter-national: Business Machines- Corporation, New York'gr-NiY .a'=c0rporation 'of NEWP'ZYOIR" Applicatibn oc'toberll, 1953, Srifil'No. 387,416 3"Clain'1sr ct-19 7 138;

This inventiomrelates-to printing machines and more particularly to an improved 'carriage for a typewriter, orsirnilanmachine: 7

It isa firstobject of this'invention toprovide an improved "carriage wherein paper feed rollers are releasably ehga'geabl'e with the platen ofthe' carriage in such a manner that feed roller pressure 'isalways' normal to the peripheral surface of the platen.

It'is a'further object of this invention to provide an improved means for releasing and restoringthe feed roll pressure against the platen.

It is a still further object of this inveution'to provide an improved structure for mounting paperi'feed rolls on a niovable carriage.

Other. objects of the invention will be pointedout in the following. description and. claims and illustrated irithe accompanying drawings, which disclose, by: way of example; the principle of the invention and the best mode; which has: been contemplated, of applyingjthatprinciple.

. While the following description relates primarily to typewriters, it is to" be understood that such a machine is fno't' intended .asa limitation, but rather has it been chosen simply as an-example toiexplain more clearly the operating features and principles of this invention.

B'riefly,- this inventionrelates to an improved oflice machine carriage structure wherein the paper-feedrolls, when in drivingpo'sition, always-exert a force normal to the platen.- The pressurev of the feed'rollersagainst the platen may. be relieved throughv the operation of asingle ha'n'dle,and the pressure may be restoredby a'converse operation of the same handle. Further, thecarriage is provided with an improved paper bail .which cooperates withthe end covers of the carriage.in such--amanner that the bailcannot bepositioned inoperative arrangement with the platen except in such a manner that the work sheet tends to besmoothed onto-theplaten; This is accomplished throughian improved a-rrn construction for the bail'arranged to cooperate-with camsurfaceson the side covers of thecarriage. The improvedcarriage structure also includes a new line spacing mechanism which is so-pivotedonthe carriage end frames as to insure a positive-and unique=-relationshipxwiththeplaten ratchet when the-line spacinglink-is-operated in response to a .clutchcontrolled pull on a tape during a carriage return operation.

In the drawings:

Fig.. *1 is-a plan viewof the left half of a" typewriter.

carriage-W Fig. 2 is a plan view of the rightihalf ofthe typewriter carriage.

Fig. 3 :is a side elevation through -plane=3-''3of Fig-. 1 taken in the direction of the arrows;

Fig.4 isa side elevation throughtplane 4=4'o'f Fig? 1- taken in direction of the arrows.

Fig. 5, like Fig. 3 ,.is a side elevation through plane 3--3 of Fig. 1 takeniridirec'tiorf of arrows, but with some I (see Figs. 3, 4) which extend-fromttheend platesandthrough suitable corresponding elongatedslotsZS .inthe.

2,862,594 Patented Dec. 2, 1958 Fig; 6 is aperspectiveviewof the improved feed roll' support structure.

Fig. 7 is an exploded view of a portion of the feed roll supporting structure of Fig. 6.

For simplicity of description, thefollowing-specification will be broken into four parts, namely, (a) general structure, (b) supporting structure for feed roller; ('0) paper bail structure; (d) line-spacingmechanism.

(a)'- GENERAL STRUCTURE With'jparticularreference to Fig. 4'of thedrawin'gs,

a carriage 1 is shown supported by meansof suitableline.

The carriage frame is provided-with suitable end plates 7, 8 (Figs. 1,2) which support platen 9 (again Fig. 4), a paper bail-i10,-line spacingjmechanisrn 11 (Fig. 3), and the usual assemblage of conventional carriage parts.

Referring now to Figs. 1 and2, a platen suspension or slidable element 20 is shown as comprising a pair of slide plates 22,- 24Yinterconnected by'a pair. of. shafts 2 6, 28.

Plates Z2, 24 are mounted for sliding motion in planes parallel to end plates 7, 3 by-means of. rivetsor studs .23

side plates 22,.24.

In this manner theslideable. element-20Iis=mounted for movement in a direction.transverse tothe axis of: the

platen, andthe purpose of -thisistructure.is torprovidefrom the printing position as far as possible, whiletwhen just a single work-sheet or single. copy is-to be made,

the platen sh0uld-be movedforwardly'towards-the printing position, and in this manner, irrespective of the thickness of the work sheet pile, the first sheet can be-maintainedin an identical positionrelative to the print position.

The operating mechanism for this transverse movement will hereinafter be described.

The platen 9 'issupported -in -.'suitable bearing-like grooves or notches-34 (Fig.4).- formed in end plates 22,-

24. The notches-have'a width adequateto accommodate the shaft of the platenyand suitable bearinglocks are providedbyhooked brackets--'40-(see" Fig.-. 5) pivotedas at'42 on the'end plates. 7, 8 respectively.

Each bracket 40-has-a slot Mi -therein, while a suitable-crankarrn 46 is pivoted at 48 -on the end plates 7, 8. Eachcrank arm 46 has an-arm-50-which is slideably connected by'mean's of-pin=52wto 'the'bra'cket 40 at slot-- 44. In this'mann'er, rotatio'ri of' the: crank arm46-perrnits pin 52 to slide in the slot 44,--and thereby rotate bracket 40 about its axis 42 into and-out of 'tlieizplatemshaft' locking position (both positions are shown in Fig. 5'). When bracket" 40 is rotated "counterclockwise to' its phantom position shown in Fig; 5;; the platencan be readily removed from its supporting: plates.

Shaft-2810f suspension element'20l (Fig. 2 is furnished withinte'gialcams, 47, 49;"atits'po'int' of] engagement with the' pla'tes 7, fi respectivelyu With tliiss'tructure; the rotation of shaft 28; because of the cams, is arranged" to slide the suspension element 20 r'earwa'rdly'or forwardly to: increase or: decrease the efiective' p'latem diameter.

3 Shaft 28 (Fig. 2) has an extension 54 that protrudes through plate 8 to support a crank arm 56. A link 58 connects crank arm 56 to a pivot point 60 in an adjusting arm 62, whereby pivotal movement of arm 62 rotates shaft 28 and varies the position of the .cams in contact with plates 7, 8.

(b) FEED'ROLLER SUPPORTING STRUCTURE Referring now to Fig. 6, the feed roller structure is shown supported on shafts 26 and 28. Specifically, depending upon the length of the carriage, a plurality of bracket units 64 are suspended between the shafts 26 and 28. In the instant situation,.three of the bracket units are shown.

As shown in the exploded view in Fig. 7, each bracket unitcomprises a pair of parallel support plates 66, 68, an actuated or rear support arm 70 and a follower or front support arm 72.

The shaft 26 is equipped with cammed surfaces 74 in alignment with each of the bracket units 64. Specifically, as more particularly shown in Fig. 7, the rear support arm 70 normally rides close to the fiat surface 76 of cam 74, and this is the relative position of the parts when the support arms 70 and 72 are applying pressure through the feed rollers to the platen 9.

Upon rotation of shaft 26, however, the cam portion 74 slides on the rear support arm 70 to rotate it clockwiserelative to its position shown in Fig. 7 to move it and its associated rollers, hereinafter described, out of engagement with platen 9.

It will be noted that the rear support 70 carries a tail 78 positioned for cooperation with a shoulder 80 on the front support 72. Accordingly (Fig. 7), when the rear support 70 is rotated clockwise about its support, the tail 78 engages the shoulder 80 to rotate the front support 72 counterclockwise.

In order to furnish suitable pivotal suspension for the rear and front supports 70 and 72, and simultaneously to bias them for holding the drive rollers into engagement With the platen 9, a unique support is provided for their mounting. Specifically, bushings 82 and 84 respectively are secured in some manner, as by welding, to the supports 70 and 72. Each bushing has a pair of collars that extend through apertures in the both plates 68 and 66, where they are held in place by rings 69 (Fig. 6) which slide into peripheral grooves in the bushings. In this manner, a bearing support is provided for both the rear support 70 and the front support 72, permitting them to rotate relative to plates 66, 68.

Each of the bushings 82 and 84 has centrally formed therein a slot 83, 85 (Fig. 7) for receiving a strip spring 86, 88 respectively.

It will be noticed from Fig. 6 that each of the strip springs 86. and 88 is twisted along its axial length. The purpose of the spring is to bias the rear and forward supports 70, 72 into engagement with the'platen. Accordingly, a pair of support brackets 90, 92 are supplied to lock the spring at predetermined positions along its length, and then the spring is twisted relative to these fixed positions. Since these springs fit through slotted apertures 83, 85 in the bushings 82, 84, it follows that with suitable clockwise and counterclockwise twists in the spring, the rear arms 70 will be urged normally counterclockwise and the forward support 72 clockwise into engagement with the platen.

In Fig. 6, screws 94 are employed to secure the springs 86 and 88 to the brackets 90 and 92. The purpose of the screws is to wedge the springs against associated ears 96 which are upstanding from the brackets 90 and 92. In this manner, by adjusting the turns of the screws 94, the amount of twist or tension in the springs 86 and 88 canbe controlled and consequently the tension on each of the supports 70 or 72 'can be regulated for uniform pressure between the feed rollers and the platen.

The supports 90 and 92 which regulate the twist in springs 86, 88, must be free of the carriage frame in order that they may move transversely with suspension element 20. Accordingly, the supports and 92 are: suspended in front by integral collars 98 which encircle: the forward shaft 28. Their only rear support is provided by the springs 86 and 88. That is, the springs 86 and 88 are relatively stifi and tend to restrain rotation of the supports 90 and 92 about the shaft 28.

Feed rollers Two sets of feed rollers are provided to hold a work sheet in driving relation with the platen, namely rear feed rolls 100 and the front feed rolls 102. In order to support them, a pair of shafts 104 and 106 are carried respectively in the outer tips of the arms 70 and 72. Specifically, the outer ends of the supports 70 and 72 are slotted or bifurcated (Fig. 7) at 109 and 111 (Fig. 7) so as to receive the shafts 104 and 106 respectively.

Since the rear shaft 26 simultaneously cams each of the rear brackets 70, which in turn control the position of the front brackets 72, it follows that shafts 104, 106 carried by brackets 70, 72 respectively will be maintained parallel to the axis of the platen. This is an important feature, since it prevents skewing of a work sheet. 7

To control endwise movement of the feed rolls, a pair of them are secured to a collar-like shaft 108 which in turn fits over the shafts 104 and 106 respectively and between a pair of thebracket members 64. This structure holds the feed rollers freely rotatable and yet limits their endwise or axial. movement.

To provide for the rotation of the rear shaft 26 for the camming action required to release the pressure on feed rollers, it is extended through the slide plate 24 where it is equipped with a link-like collar 114 (Fig. 6). An intermediate link 116 connects a crank pin 118 on collar 114 to a stud 120 carried by an operating arm 122, which in turn is supported on a pivot stud 124 carried by the slide plate 24.

With this structure, a forward pull on the upper end of operating arm 122 as viewed in Fig. 6 produces a counsupports 70 thereby locking the supports and their associated rollers 100 and 102 out of engagement with the platen. the feed rollers and the platen whereupon by restoring the arm 122 to its position as shown in Fig. 6, the feed rollers are again brought into driving contact with the platen.

In Fig. 6, the plates 68 are shown having upwardly extending arms 126 that are notched as at 128 and provided with fingers 130 for supporting springs 132. (Both of the plates 66 and 68 at the central bracket unit 64 are provided with this arrangement.)

The function of the upstanding arms 126 is to support a guide or feed plate 134 which, as shown in Fig. 6, is rotated clockwise from its normal position. The guide plates 134 have slots 136 for interlocking with the notches 128 thereby to provide a hinge-like relationship. Theplates 134 also have apertures 135 to accommodate the around the platen and past both sets of feed rollers 100 V and 102 respectively.

(0) PAPER BAIL It has been mentioned that one of the objects of this If the arm 122 is rotatedj far enough, then the high dwell portion 123 (Fig. 7) of the cams 74 will be in contact with each of the rear,

In this position, paper can be inserted between' invention is to provide an improved paperbail which is so constructed that it' tends to smeoth*" aperitontoi the platen to prevent rumplin'g' or crinklinglof the, worksheet. In order to accomplish this objective, thepap'er bail is mounted on a support rod 140 (Figs, 3, 5 )"1vv'hi'ch in turn is suspended in the two slide plates 22 an'd'24.

The paper bail comprises hinge. arin's' 142, extension arms 144, a crossb'ail 145, spring arms-I46 and suitable interconnecting structure.

Each hinge arm 142 is provided' with a bearing-like aperture.147 for mounting on the support rod 140' to which they arebrazed adjacent each of the'slide' plates 22, 24, respectively.

Each hinge arm is providedwith' a pin hinge 1'48for a hinged connection witheach extension arm 144'respectively. The pin hinge 1'48 simply extends through suitable apertures in the hinge arm and the extension arm so .as to interconnect the. two arms while permitting rotation of one relative to the other. The extension arms 144, however, are each'provide'd'with" a" lock-f150 which; in effect, is a bentfover ear that lies a'cr'oss'the plane. of the hinge arms 142 to limit the clockwise rotation (as seen in Fig. 5 of the extension arm about thehinge pin 143. V

Each extension arm 144 has a rearward extension 151 beyond the hinge pin 148"which'includes theemension arm bearing; 152 that is positioned for sliding contact with spring. arm 146' hereinafter described.

A pair of spring arms 146 aresupported forrotation in planes'adjacent and p'aralleltothe'slide plates" 22, 24, respectively by means of pivot studs 156 which extend outwardly from theslide plates 22, 24 respectively; A coil spring 158 is wrapped arou'ndfeachof the pivot'st'uds 156 with its end' 160 connectedto a slide plate'and its opposite end'162 connected to the-spring arm; In'this manner, the in Fig. 5. I

Eachof the spring armshasian up surface 164- and a pull. surface 166 which are'engageable withthe extension arm bean'ngs 152. Specifically, the extension arm. bearings overlie the plane of the spring arm 146' and because of thebias of springs 158; ,either'ithe" up surface 164 or the. pull? surface 166 isalways in co ntact.

with the spring ,arm' bearings In view of the fact that the extension arm"bearings 152 are mounted on aprotrusion of the'exten'sion arm 144, it canbe appreciated-that, as shownin-Fig; 3, the

tension in spring arm 146" acting on theextension armbearing 152 tends to rotate the'extension-a'rm counterclockwise and into'enga'gement with the platen. That is, the cross armor bail-145 carrying-suitable rollers 170 (a structure hereinafter to be described) is forced into engagement-- with the platen. Itcan be appreciated that since the pull--arm'166"( in -itssolidsline position shown in Fig. 3)-- has-the form of an-inclined-plane, andsince it is biased'cloekwise-by spring '158, the spring arm bearing 152- will-tend-to be forced down thisplane and thereby exerta rearwardpull on'theextension' arm's 144, which rearward pullcauses rollers 170 to smooth a Work sheet onto the platen. V

However, if the extension "armis' pivoted clockwise about hinge 148 until the lock 150 prevents further rotation (see Fig. 5) and if the extension arm 144 and the hinge arm 142 arethen rotated as a unit about the axis of support rod 140, the spring arm bearing 152 will roll up the pull surface 166 towards the apex 172. At this stage, the spring arm 146 acting on the spring arm bearing 152 will tend to rotate the extension arm clockwise about the hinge pin 148, but since the two arms are locked relative to one another by the lock 150, the pull surface 166 simply maintains the extension arm rotated to that position shown in Fig. 5, wherein it is lifted out of the way of the platen.

To bring the bail rollers 170 into engagement with the platen, the cross arm 145 is pulled forwardly wherespring armsare biased clockwise'as viewed 6 upon the extension arm and the hinge arm rotate as a fixed unit-with support rod until a guide stud'1-74, carried by hinge arm 142- (shown in Fig.v 2)'I strikes the slide plate 24' thereby preventing further counterclockwise rotation of the hinge armunits.

At this point, since the rotation of I the hinge arm is blocked by the guide stud 7174, the extension arm will now rotate about hingepin-148 counterclockwise until thismotion is interrupted 'by the interaction of a cover bearing 176 (Fig. 3)- carried" by extension arm 144 with a cover guide cam 178 which is formed on a housing 179 that encloses carriage end plates 8, 22' and 9, 24' respectively At this step, the bail will stay in position' held by the up surface 164 of spring arm 146 until pushed by the operator pastpoint' 172' when pull surface 166 of the spring arms 146 will act'on extension arm bearing 152"to pulllthe rollers 170011 cross bail to the rear and into engagement with the platen; The motion of the cross bail 145 is guided, however, by the interaction of the cover bearing 176 with' the coverguide cam 178. That is, the cover guidec'am is 'so shaped that asthei cover bearin'g176' rides on it due to the rearward-pull exerted on the extension arm 144-15y the pull surface. 166 of spring arm 146, the-cross bail 145 moves upia' plane including the inelined surface surface'180 of the cover guide cam 178'; thus, the rollers tend to smooth the paper onto the platen to prevent any bulging or wrinkling of the work sheet.

In order to remove thebail fromthe' work sheet for erasures, the operator .simplypulls. cross arm 145 for- Wardly to expose thatipart of the work sheet which has just been printed. After. the erasure, the operator releases the cross: b'ail 145, and it will be pulled backwardly. by the interaction'of the spring arm 146' with the extension armbearing'lSZ, and'again the rollers tend to smooth the paper onto thework sheet; The. pulled out, or erasure position of' the bail is' shown in phantom' in Fig; 3 of thedrawings- In the erasure position of the bail, the up surface 166 of spring arm 146 bearingslides up surface 180*wherein rollers170 smooth the work sheet onto the platen, and then'the cam surface" fallsaway to permit roller 170 to engage the platen.

(d) LINE SPACING' MECHANISM Inthe prior art, and with particular reference to U. S.

Patent 1,957,322, Crumrine, the general principles of linespacing mechanisms are described. Specifically, Crumrines patent shows how a disc clutch is energized by applying. axialpressure between slipping discs, to ex? ert a pull on' a tape which tape performs two functions, namely, effecting a carriage return and the effecting of a line spacing mechanism. The present invention relates to an improvement of the line spacing mechanism as activated by a pull tape under the influence of a disc clutch such as that described in the aforementioned .patent.

Referring now to Fig. 3, a hook-shaped member 177 is suspended at one end for pivotal movement about a pin or stud 179 which in turn is mounted in the slide plate 22. The opposite end 181 of the hook member 177 is connected as at the pin 183 to tape 184. The latter tape is the one which brings about a carriage return upon the energization of the clutch as disclosed in U. S. Patent 1,957,322, Crumrine. In this invention,

however, a pull on tape 184 will rotate the hook member 177 clockwise about pin 179. The hook shape is provided in member 177 in order that it may partially encircle the platen shaft. In order to maintain hook member 177 in its normal or rest position as shown in Fig. 3, a roller bearing 185 is secured to the hook member 177 for contact with a dog 186. The latter is biased by a spring, not shown, but lying behind spring 188 which is supported about stud 190 along with the dog 186 to bias the dog 186 clockwise into engagement with the bearing 185 on the hook member 177.

The normal or rest position of the hook member 177 is determined by a certain plate 192 (Fig. which is pivotally supported by pin 194 carried by slide plate 22. Specifically, a space determining arm 196 is mounted to be rocked about a stud 198. Arm 196 carries a pin 200 which inturn is engageable with a slotted aperture 202 in the plate 192. Consequently, clockwise rotation of the arm 196 about the pin 198 causes pin 200 to engage one of the hollows 204, 206, 208. A spring 210 biases the plate 192 clockwise about the support 194 and consequently, the position of the pin 200 in engagement with one of the hollows 204, 206, 208 limits the clockwise rotation of the plate 192 and thus determines the elevation of a pin 211 carried by plate 192. Pin 211 in turn determines the amount of line spacing in a manner that will be hereinafter described.

A pawl 212 (Fig. 3) is mounted on pin 214 which in turn is carried by the hook member 177. A spring 216 is wrapped around pin 214 and biases the pawl 212 normally clockwise about pin 214 and towards the teeth 218, of ratchet wheel 220, which in turn is mounted co-axially of and releasably secured to the platen in a well known manner. It will be seen that any pull on tape 184 will pull pin 183 down rotating hook member 177 clockwise about its support 179 thereby permitting spring 216 to bias pawl 212 clockwise about its support 214 and into engagement with the teeth 218 of the ratchet wheel 220. The extent of clockwise rotation of hook member 177, however (irrespective of the position of pin 200 and aperture 202), is determined by pawl 212 striking bracket 222. Subsequent release of tape 184 will permit the dog 186 to rotate arm 177 counterclockwise about its support pin 179 to restore it to its normal or rest position.

The pawl 212 has a shoulder 224 which is engageable with a tongue 226 of a U-shaped member 228, which in turn is supported at pin 183 with tape 184. The Uashaped member 228 is rotatable about pin 183 and it is also positioned for engagement with the pin 211 carried by plate 192. Consequently, as tension on tape 182 is released after a line spacing operation, the U-shaped member 228 strikes pin 211 and the outer extremity of tongue 226 strikes shoulder 224 of pawl 212, knocking it out of engagement with the teeth 218.

With this line spacing structure, single, double or triple line spacing is controlled by changing the position of pin 200 in aperture 202; i. e. as pin 200 is moved from hollow 204 to hollow 206, the elevation of pin 211 is increased and hence pawl 212 has a larger (double space) line spacing stroke. When in hollow 208, the line spacing stroke is again increased (triple space) since the elevation of pin 211 has been increased. Obviously, the hollows 206, 208 are positioned to effect the desired line spacing operation.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodimeng it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a typewriter having a platen, a structure supporting feed rollers for cooperation with said platen, said structure comprising, in combination, a pair of elongated torsion springs extending parallel to said platen, clamping means engaging said torsion springs at spaced points for holding said springs from turning about their axes at such points, support arms fixed to said torsion springs at points spaced from said clamping means, said support arms extending from said springs to opposite sides of said platen, feed rollers carried by said support arms and engageable with said platen, cam means engageable with one of said support arms for rocking it away from said platen against the action of the one of said springs towhich it is connected, and means interconnecting said support arms so that a rocking of said one of said support arms by said cam means causes a counter-rocking movement of another of said support arms extendings to the opposite side of said platen.

2. The structure of claim 1 in which said cam means is formed on a first shaft extending parallel to said platen at one side of said torsion springs, means including a lever fixed to one end of said shaft for rotating the latter, a second shaft extending parallel to said platen at the opposite side of said springs, support brackets extending between said first and second shafts and having openings through which said torsion springs extend, and bushings fixed to said support arms and rotatably received within said openings.

3. The structure of claim 2 in which said clamping means comprises a bracket fixed to said second shaft and having flange portions closely adjacent one side of each of said springs, and screws engaging the opposite sides of said springs for holding the latter in place and adjusting the spring action.

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