CA1145783A - Friction paper feeder - Google Patents

Abstract

Abstract of the Disclosure Apparatus for individually feeding sheets in which a friction feed roller positively driven in the direction of feed opposes a friction retarding roller biased in the reverse direction with a predetermined torque and urged against the feed roller with a predetermined force. The reverse bias torque is regulated by means of a spring and a controllable clutch which is disengaged in response to a predetermined strain in the spring. The spring and controllable clutch may comprise a helical spring clutch. In another aspect of the disclosure, the retarding roller is carried by an arm for rotation about a pivot center located such that the normal force urging the two rollers together is automatically suit-ably adjusted in response to changes in the biasing torque.

Description

11457~3 `~ ~
V' Titlc of the Invontion FI~ICTION Pt~Pl:.R FEEDER

Backqround of tho Invention This inven~ion rclatcs to friction paper feeders and, in particular, friction papcr feeders used to supply cithcr ori~inals or copy shocts to an olcctrostatic eopier.

Various arrangcments of friction rollers or belts have been used in an attompt to insure the reliable feeding of a shect from a stack whilc at thc same time preventing the feeding of more than onc sheet at a time. One type of paper feedcr of the prior art, opcrating on the differential friction principle, employs a driven feed roller opposing a retarding roller driven in an opposite direction at their point of contact. ~'hc feed roller surfacc rlaq a relatively high coefficient of friction with paper, while the retarding roller surracc has a cocfficicnL o~ friction with paper lcss than that of the foed rollor but groater than that between two succcssivo shcots of papcr.

In ordcr for fccdcrs of this typo to operate satis-factorily, the coofficicnt Or friction of the fecd roller withpaper must always cxccod that of thc rotarding roller, which in turn must always oxcced thc coofficient of friction between two 3heets of papor~ ~ftor somc pcriod of use, however, even . ~ ~

1145783 ` . ~-rollers h~ving a high initial coefficient of friction become coated with fibers from the paper and their coefficient of - friction drops down to about unity. Since the coefficient of friction between succcssive sheets of paper can be as high as --0.7, there is vcry littlc latitude for permissible variatic7n in tllc coefficient of Iriction of Lhc rctarding roller and unreliablo operation may rcsult.

In still another type of friction feeder known to the art, rather than having two rollers of different coeffi-cients of friction, opposin~ rollers both having high coeffi-cients of friction are used. The feed roller is positively driven in a forward direction, but the retarding roller, rather than being driven at a constant reverse velocity, is subjected to a prcdctcrmincd rcvcrsc torque. The retarding roller is free, however, to rotate in a forw,ard direction if thc externally applied torque is sufficient to overcome this prcdetermincd torquc. 'l~hc prcdctcrmincd torque applicd to thc retarding roller is selected so that it is sufficient to separatc two shcets of papcr in thc nip but is insufficicnt to overcome the frictional forcc between either roller and a contacting sheet of papcr. -Thus, if only a singlc shoet of paper is prcscnted to the roller nip, thc fccd rollcr not only advances the shoct of papor but also ovcrcomcs thc prcdctcrmined torque and causes the rctardim1 rollcr to rotatc in a forward dircction.

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1~5783 ` ~

If, however, two sheets of paper are presented to the roller-nip, the feed rollcr will conti:nuc to advance the first ~heet, but thc reverse tor~uc applied to the retarding roller sepa-rates the two sheets of papcr and~thereafter moves the second sheet rearwardly out of the nip. - ~~
l~S
A Osgood ct: allPatcnt 2,892,629 shows a fceder of this type using a torsion spring in combination with a friction clutch to bias the-retarding rollcr using energy derived from the feed roller through frictional enga~ement. Van Dalen et al U S. ~ .5, ~"s. --JPatent-3,272,~00;-BreucrsJPatent 3,044,770, and GibsonlPatent 4,060;232 show similar arrangements in which the retarding roller i9 driven from an independent energy source through a friction clutch whicll decouplcs at~thc desired level of torque.
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Fceders of tl-is type have the advantage over differential friction feedcrs that the coefficient of friction of the retarding roller can be as high as practical and need .. . ..
not be less than the friction of the feed roller. The only constraint on thc cocfficicnts of friction is that each roller have a coefficient of friction with papcr that is greater than the coefficicnt of friction between two sheets of paper.
Because of this rclaxcd rcquirement, thc reliability of feed is substantially incrcasod. -- - - - - -., .
Onc drawl)ack sharcd by fccdcrs of the typc discloscd in thc Osgood et al patent, in which a spring cocked by the ~14S783 ;~

fecd roller supplics thc rcvcrsc torque to the retarding roller, is the depcndcnce of the reverse torque on the degree - to which the spring is wound. Because of this dependence, which is generally lincar, some period will elapse following initial actuation of thc rollcrs before the spring is suffi- -ciently tensioned ~o supply the dcsired torque. If two or morc shccts enter thc rollcr nip bcfore this period has elapsed, unreliablc operation may result. ~ny attempt to shorten the initial period by lowering the spring compliance will effect a corresponding shortening of the "throw" of the retarding roller at the desired reverse torque, also leading to unreliable operation.

~nother drawback, shared by all of the feeders disclosed in the abovc-identificd patcnts, is the dependenco of the rcvor~e torque on the rictional cha~acteristics of the friction clutcllcs uscd. ~s ~hc working surfaccs becomc worn, their frictional characteristics may change, and operation may become unreliable.

Summary of the Invention One of thc objccts o my invention is to providc a shcet fcedcr which opcratcs rcliably cvcn aftcr a long period of U9C.

~nother objcct of my invontion is to provide a sheet ceder whic)l docs not rcquirc all CXCCS5iVC period to bccome ~ ' .
., ~

~' ' ' " ~

operative after initial actuation.
Still another object of my invention is to provide a sheet feeder which fully ejects a second sheet.
A further object of my invention is to provide a sheet feeder which does not rely on the characteristics of frictional surfaces for its operation.
A further object of my invention is to provide a sheet feeder using a reverse-biased retarding roller which is relatively insensitive to changes in the value of the reverse biasing torque.
Other and further obiects of my invention will be apparent from the following description.
The invention relates to apparatus for feeding sheets including in combination a feed roller, means for driving the feed roller in a certain direction of rotation, a retarding roller, an arm rotatably supporting the retarding roller, the arm being mounted on a pivot axis for movement of the retarding roller into and out of engagement with the feed roller, a rotary member disposed on the pivot axis, means carried by the arm for coupling the member to the retarding roller, and means for rotating the member in such a direction as to tend to rotate the retarding roller in the certain direction, one of the rotating means and the coupling means including means for limiting the torque transmitted to the retarding roller, the pivot axis being so located that the rotary member exerts a torque on the coupling means about the axis tending to urge the retarding roller into engagement with the feed roller.

mb/ - 5 -By adjllsting ~he normal nip force a significant amount in response to changes in the biasing torque, I
greatly increase the reliability of ~he roller assembly by decreasing its sensitivity to fluctuations in biasing torque such as the type described above. In assemblies of the prior art, by-contrast, any coupling between the nip force and biasing torque is unintentional and in any case insignificant, and such fluctuations may easily result in feeder malfunction.
Brief Description of the Drawings In the accompanying drawings to which reference is made in the instant specification and in which like reference characters are used to indicate like parts in the various views:
FIGURE la is a fragmentary top plan of the front portion of one embodiment of my feeder.
FIGURE lb is a fragmentary top plan of the rear portion of the feeder shown in FIGURE la~
FIGURE 2 is a fragmentary section of the feeder shown in FIGURES la and lb, taken along line 2-2.
FIGURE 3 is a fragmentary right side elevation of the tension pulley of the feeder shown in FIGURES la and lb.
FIGURE 4 is a fragmentary top plan of the retarding roller assembly oE the feeder shown in FIGURES la and lb.

mb/ - 6 -':' ' ' ' ~ :
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5~83 i~ .

FIGURE S is a ragmcntary top plan of an alternative retard.ing rollcr asscmbly for thc fccdcr shown in FIGURES la and lb, PIGURE 6 is a right side clevation of the assembly shown in FIGURE 5.

FIGURE 7 is a schematic diagram of the forccs acting on the lower of two sheets in the nip formed by the feed roller and retarding roller of the embodiment shown in FIGURE5 la to 4.

l~IGURE 8 is a schematic diagram of the forces acting on a single shcet in thc nip formed by the rollers shown in FIGURE 7.

FIGURE 9 is a plot of thc various relationships between the normal nip force and the rcvorse tangential force cxert~d by the retarding rollcr of FIGURE 7.
f FIGURE 10 is a schematic diagram of the forces producing moments about the pivot axis of the retarding roller shown in FIGURE 7.

FIGURE 11 is a schcmatic diagram of the forcos ~roducing moments al)out thc rotation axis of the retarding roller shown in FIGIIRE 7.

, , 11~5783 ~
, FIGURE 12 is a schcmatic diagram of the force~
producin~ moments abou~ tho pivot and ro~ation axes of the retarding rollcr r.hown in I~IGURES 5 and 6.

Detailed Dcscription of ~he Prcferred Embodiments ~eferring now to EIGURES la to 4,a first embod~ment of my shcet feeder employs a ~orsion spring to bias the retarding roller in a reverse direction. The feeder, indi-cated generally by the refercnce numeral 10, includes respec-tive right and left sidcwalls 12 and 14 joined adjacent to front ends thereof by a front wall 16 and adjacent to the rear ends thereof by vertically spaced rods 1~ and 20. Feet 22 carricd at thc froll~ alld rcar cnds of cach of thc sidewalls 12 and 14 ~pace thc focdcr 10 slightly from the surface (not shown) on which it rcsts. ~ vcrtically movable sheet-receiving platform 24 cxtending generally between sidewalls 12 and 14 supports a stack S of shccts of paper or the liXe to be fed.
A lower sheet guide 15 extends forwardly from the front wall 16 at a level just bclow the top of the stack S. If desired, the platform 24 may includo a longitudinally extending edge guide 26 against which onc sillc of thc stack S may bc aligned.
Guide 26 may bo adjustably positioncd latcrally of the ecdcr 10 to accommoda~c shccts of diffcrcnt widths.

A transverscly spaced pair of front cams 28 and 30 carricd by a camshaft 36 support thc platform 24 adjacent to , :' ' ' , :

. ~ .

` 11~5783 its front cnd, whilc a similar pair of rcar cams 32 and 34 carried by a camshaft 38 support the platform 24 adjacentto its rear end. Shaft 3G is rotatably reccivcd by bearings 40 and 42 carricd rcspcctivcly by si~lcwalls 12 and 14. One end of shaft 4~ extcnds bcyond sidcwall 12 to receive a pulley 52.
One end of shaft 38 cxtcnds through a bearing 44 carried by sidewall 12 to reccivc a pullcy 54. A friction clutch 46 couples the other cnd of shaft 38 through a gear box 48 to a motor 50 mounted outboard of sidcwall 14. A belt 56 tensioned by a pullcy 58 couples pullcys 52 and 54. Tension pulley 58 is supportcd on a brackct 60 fonmcd with a vertical slot 62 which reccivcs a guidc pin 64 carried by sidewall 12 as well as a screw 66 threadably reccived by sidewall 12 to permit vertical adjustment of pullcy 58 and thus the tension in belt 56.

Bearings 70 and 72 carried respect~vely by sidewalls 12 and 14 rotatably support a fccd roller shaft 68 at a location near the front cnd of the fecder 10. Shaft 68 extends bcyond sidcwall 1~ to rcceivc a pullcy 74 coupled by a belt 76 to a sccond pullay 7B carriad by thc shaft of motor 80 mounted inbnard of sidcwall 14. Onc arm of a bcll crank 84 rotatably mounted on shaft 6B by a bcaring B2 rotatably supports a pick-off roller B6 havin~ a high-friction workin~ surface 88.
~ gear 90 rotatablc with pick-off roller 86 meshes with an intermediate gcar 92 carricd by b 11 crank 84. Gcar 92 meshes w~th a drive gcar 9~ which is carricd by a sleeve 96 rotatably mounted on shaft 68. Slccvc 96 carries a fced roller 98 having Y

~145783 .

... . . .
a friction surfacc lO(). ~ one-way clutch 102 couples shaft 6a to sl~evc 96 to drivc fccd rollcr 98 and gear 94 positively in a clockwisc direction as scen in ~I~URE 2, while at the same time permitting thcse members to be overdriven if the sheets are taken up by a subsequent pair of rollers (not shown).

The other arm of bell crank 84 carries a pin 104 which, in response to downward movement of pick-off roller 86, strikes the actuating mcmber of a microswitch 106. I mount microswitch 106 on spaccrs 110 carricd by a brackct 108 mounted on sidewall 14. rin 104 and mic-roswitch 106 form a part of a servo system for maintaining the top cnd of the stacX S at a proper level for fceding shccts thcrefrom. As sheets are fed from the top of tho stack, pick-off roller 86, under the influence of gravity, drops down to a level below the desired eguilibrium level. This in turn causes pin,104 to pivot clockwise around shaft 68 and actuate switch 106. Switch 106 in turn controls camshaft motor 50 whi~h, when energii~ed, rotates each of the camshafts 28, 30, 32 and 34 clockwise as shown in FIGURE 2 to raisc thc levelof stack S. When the stack S rises to tho prcdctcrmined equilibrium level, pin 104 moves away from switch 1()6, breakinc3 the circuit and deact-uating motor S0.

Rcferring now to FI~UJ~S 2 and 4, my feedcr 10 includcs a rotarding roller 11Z having a high-friction worX~ng ; 25 surfacc 114. Rollcr llZ--i3 ~rcc to rotate on an-axis defined , 1 ''-- .
, ' 11~5783 by end scrcws 116 and lln, whicII arc adjustably reccived in slots 124 formcd in anns of rcspcctivc bcll cranks 120 and 122.
pivot pin 126 supportcd by spaccd arm~ of a bracket 128 secured to wall 16 rotatably supports the bell cranks 120 and 122. Iielical tension springs 130 disposed between the other arms of bell cranks 120 and 1~2 and extensions 132 on the arms of bracket 128 bias the retarding roller 112 upwardly through a slot 17 formcd in (~uidc 15 into cnyagcmcnt with the drive roller ~8. Rctardin~ roller 112 carries for rotation there-with the driver mem~cr 136 of a sprina clutch indicated generally by the reference numcral 13~, The driven member 138 of the spring clutch 134 fixedly supports one end of a helical torsion sprinq 140, thc other cnd of which wraps around driver member 136 and has a radially outwardly directed extension 142.

Spring 1~0 is so wound as normally to wrap around the driver member 136 in a counterclockwise,direction as viewed in FIGURE 2 to couple the driver 136 to the driven member 138 when roller 112 rotates in a counterclockwise direction. When rctardinq roller 112 is driven in a clockwise dircction as vi~wcd in IICUI~ 2, clutch 134 is disengaged.

Driven mcm~cr 138 of sprin~ clutch 134 carries for rotation thcrcwiLh tIlo mandrcl 152 of a torsion spring assembly indicatcd gcncrally by thc rcference numeral 148.
A helical coil 150 surroundin~ mandrel 152 is attached to the mandrel at one cnd an~ to a stationary cylindrical member l5g ~ 7 , /~

1~45783 at the other end tl~crcof. ~s may be seen in FIGURE 4, coil 150 is larger in diamctcr than thc mandrel 152 to permit the coil to wind down in rcsponse to an externally applicd torque.

Stationary mcmber 154 carries a collar 158 having an axially extcnding ~ingcr 144. In assembling my device, I
prewind spring 15~ in a countcrclockwise dircction to provide an initial bias torquc. ~ lug 160 on mandrcl 152 engages finger 144 to hald the bias torque. Preferably, the collar 158 is adjustable around stationary member 154 to vary the amount of bias torquc.

In my systcm, the force with which sprlngs 130 urge roller 112 into engagement with roller 98 and the torque applied to shaft G8 are such that, with the rollers in diract engagement or with only a single sheet of paper between the lS rollers, rollcr 112 is driven in a counterclockwise direction as shown in I~IGUI~I, 2 with a torquc sufficient to overcome the initial ~iasing torquc in spring 150. When roller 112 is driven under these conditions, drivcr member 136 is clutched to driven mcmber 138 to drivc mandrel 152 in a counterclock~
wise direction as viowcd in I~IG~l~ 2 furthcr to wind spring 150 down on the mandrcl to increase the revcrsing torque.
After a predetermincd rotation of the engaged clutch in thq countcrclockwisc dircction such, for examplc, as three-quarters of a rcvolu~ion, cnd 1~2 of spring 150 strikcs fingor 144 and the clutch rclcascs, ,!J~ , ~1~5783 .

Ilaving thc opcration just described in mind, and assuming that two shccts of papcr cnter thc nip between rollcrs 98 and 112 at the same time, the paper-to-paper friction betwecn hc two shccts will be much less than the roller-to-paper fricLion bctwccn the uppcr and lower rollers and the respective upper and lower shcets. ~s a resultD the torque tending to drivc roller 112 in a counterclockwisc or feedin~3 direction will bc lcss than the torquc stored in spring 150. ~s a result, undcr the action of spring 150, the roller 112 will reverse its direction of rotatien and rotate in a clockwise direction as viewed in FIGURE 2 to drive the lower of the doublc fcd sheets out of the nip between rollers 98 and 112. When that is done, normal operation is restored.

IJ1 1'IGU~ S 5 and G, I show a modified version of my feeder in which thc rcLardin~3 rollcr clerives its reverse bia~ing torque from a continuously opcratint; power source.
In my modified fccdcr, indicatcd gcnerally by the reference numeral 162, a brackct 174 mounted on the front wall of the feeder 162 rotatably sl1pports one end of a shaft 186, the other end of which is rotatably supported in a bearing 188 on sidewall 14. Shaft 186 extcnds bcyond sidcwall 14 to receive a pullcy 190 coupled by drivc bclt 192 to a suitable rotary power sourcc (not shown) which drives shaft 186 in a counter-clockwise direction as sccn in l'IGUI~', G. ~uch a power source may comprise an addi~iollal pnllcy carricd by fced roller shaft 68 or, if desired~ a ~scparatc motor.

.

` ll~S783 ~ bcll cranX 170 rotatably supported by ~haft 186 and axially spacod from bracket 174 by a spacer 172 carries a shaft 168 at the cnd of onc arm thereof. Shaft 168 supports a retarding roller 164 having a high-friction working surface 166 and a roller gcar 176 rot~table with roller 164. A helical tension spring 202 coupled bctwcen the other arm of bell crank 170 and a post 20~ carriod by bracket 17~ biases rct~rding roller 164 upwardly against fecd roller 98 with a predetermined biasing forcc.

Roller gear 176 meshes with a drive gear 178 rotat-ably supported by shaft 186. Drive gcar 178 carries for rotation therewith thc drivcr member 182 of a spring clutch indicated generally by the reference numeral 180. The driven member 184 of clutch 180 is carricd by shaft 186 ~or rotation l; therewith ~nd i9 spaccd somcwhat from thc driver member 182 by a reduccd portion 183 of cither thc driver member 182 or the driven membcr 184. ~ clutch spring 194 fixcdly attachcd to the driven membcr 184 of spring clutch 180 extends around the driver mc3mbcr 182 in such ~ dircction that countercloc~wisc rotation of the drivc shaft 186 causes spring 194 to wrap around member 182 and to coil down along thc reduced portion 183.
When clutch sprincJ 194 wraps around driver member 182 a prede-termined extcnt, a pin 198 carried by a collar 200 fixedly carricd by drivc shaL~ 18G abuts a radially outwardly directed extension 196 oL tho frcc cnd o spring 194 to cause it to rcloa~c from mcm~cr IU2 a~ ~ proclcLc~linod desirod levcl of , ~ .
....
: . ~_ .
~:; 14 .` ~
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11~5783 torque. Collar 200 is prcfcrably adjustably mounted on cluteh portion 184 to pen~it variation of the biasing foree.

Spring clutch 180 thus servcs to couple the counterclockwise-rotatinc3 shaft 186 to drive gear 178 to urge retarding roller clockwise up ~o ~ prcdetermined torgue determined by thc angular position of pin 198 on drive shaft 186. Whcn no shcct or only a !;inglc shcct i9 in the nip between drive rollcr 98 and retarding roller 164, this pre-dctcnnined torquc i5 insufficicnt to ovcrcome the torquo supplied from the fccd rollcr 98, and roller 98 frictionally drives roller 164 in a countcrclockwise direction. When, however,two or more sheets enter the roller nip, the torque transmitted through the paper-to-paper interEace is insuffi-cient to ovarcome thc predctcrmined biasing torque, and roller 164 rotatcs cloc~wisc to drivc thc sccond shcet rearwardly out of the nip. -, FIGUI~ 7 shows thc forccs acting on the second, or lower, sheet when thcrc arc two shcets in thc nip fonned by rollcrs ga and 112, and rollcr ll2 is driving thc lower sheet rearwardly out of the nip. ~t the nip itself, the lower roller 112 excrts a rcvcrsc tan(3cntial forco T on the lower side of thc shcet; the uppcr shcct cxcr~s an oppositely directed shear force upN, whcrc up iY tile papcr-to-papcr cocfficient of friction and N is thc nonnal force urging rollers 98 and 112 togothor. At thc st.ick ~, ~hc nppcr facc of thc sccond sheat is subjected to a forwar(lly dircctcd shcar force of up(M ~ m), ~S~
.

~14S783 ,~

where M is the effoctivc woight of thc pic~-off roller 86 and .m is the efectivc woight of each sheet of paper in the stack S.
~ ~long its lower facc, ~he sccond shcct i9 subjected to a :~ forwardly diroctcd shc;lr forcc of up(M + 2m). The net reversc ; 5 tangential force acting on the sccond sheet is thus:
Pt = T - upN - u~ (2M + 3mj (1) l'o ensure reliablc opcration in this mode, then, roller 112 must be capable of cxcrting such a revcrse tangential force T
that:
T 2 upN ~ up(2M + 3m) (2) ~r, considering T as givcn, thc maximum permissible normal nip force N is given by the equation:
N ~ T/up - (2M ~ 3m) ~3) FIGURE 8 shows thc forcos actiny on a single sheet in the ~ ler nip in a modc of feedcr operation in which the feed roller 9~ is driving roller 112 ~orwardly aga,inst the action of its biasing torquo. In this casc, to avoid slippage between tho sheet of paper and cither of the rollcrs 98 and 112, the normal force N must be such that:
u~N ~ T (4) where Ur is the rollcr-to-papcr cocfficient of friction and urN
thc maximum sustainablo shcar forcc. In tcrms of N:
N ~ Ir/ur FIGURE 9 is a plo~, in which T is the x-coordinato and N thc y-coordinatc, showin~ thc various rclationship~

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1~45783 exi~ting bctwcen t~c normal nip forcc N and the reverse tangcntial forcc T cxortcd by ~hc rc~arding rollcr 112 shown in PIGURE 7. In this figure, exprossions (3) and ~5) abov~
define a shaded rcc3ion of permissiblc valucs of T and N. If the point (T,N) is to the ri~ht of a line Ll along which N = T/ur t6) then rollers 98 and 112 will slip with only one sheet there-between. Ir, on the other hand, the point (T,N) is to the left of a linc L2 alon~3 which N = T/up - (2M + 3m) ~7) the reversc tangcntial forcc T will bc insufficicnt to return ;~ the second sheet.

FIGVRE 10 is a force diagram of the moments acting about the pivot arm axis P2 of roller 112. In the diagram, a reprcscnts the spacin~J botwecn the roller axis Pl and pivot axis P2, r is the radius of rollcr 112, B is,the biasing force o spring 130, ~ i8 thc levcr arm of force B relative to axis P2, d is thc an(31c bctwccn thc line joining Pl and P2 and the plane of tangcncy of rollers 98 and 112, and w is the counterclocXwisc angular vclocity of rollcr 112.

To asccrtain thc dynamic rolation between N and T as detcrmincd by thorDllcr gcomctry, wo must consider the mo~t general situation in which rollcr 112 may be angularly accclerating. Tho an~3ular momcntum L of roller 112 about its 25 own axis Pl iso L = Iw ~8) , l?

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~1~5783 ~ ` .

wherc T is the momcnt of incrtia of rollcr 112. If Pl and P2 are fixed in space, i~ can bc shown that the angular momentum of roller 112 about axis P2 is also cqual to L.

Thc net countcrclockwisc torque about axis P2 is:
~ = B~ ~ T(r ~ a sin~ N(a cos ~ ) (9) Sinco ~ = dL/dt, cq~n~tions (8) and (9) yiold:
Idw/dt = s~ + T(r ~ a sin ~ ) - N(a cosd ) (10) FIGURE 11 is a forcc diagram of the moments acting about the axis Pl of rctarding roller 112. In this figure, spring clutch 134 is assumed to be exerting a clockwise tangential force Ts at a distance r from Pl to produce a torque of Tsr about axis Pl. Gcncralizing to the situation where the torque Tsr supplied by spring clutch 134 is not necessarily equal to Tr, we obtain ~ Pl = Idw/dt = Tr - Tsr (11) Equations (10) and (11) may in turn bc combined to yield:
E3~ + T(r + a sin ~) - N(a cos ~ ) = Tr - Tsr (12) Solving for N, wc obtain:
N = ~ + T~r.~ Ta sin ~)/a cos.t (13) The normal nip forcc N thus dcpcnds linearly on the spring force B, the supply torque Ts, and the instantaneous reverse tangcntial forc¢ T.

In thc spccial casc whcrc thc rollcr 112 is not accelcralillg angular~y, as whcn a sincJlo sllcot i5 bcing fed, , .' ' ' ~ ~
. . , 11~5783 I' , , .1 .
T may ~e equated with '1'5 and cquation ~13) simplified to:
Jl N = (B~ t Ts(r + a sin ~ ))/a eos ~ ~14) Sincc r ~ a sinl and a cos~- rcprcsent rcspcctively thc vertical displaccmcnl Y and thc hori7.0ntal displacement X of the nip point rclativc to the pivot ~xis P2, equation (14) may be rewritten as:
N = (B~ Y)/X - B~/X ~ TsY/~ (lS) rIGuRE ~ illustratcs the rclativc insensitivity of my roller assembly to chan~cs in the tangential force Ts exerted by the spring clutch 134. It will be assumcd that the spring force L is adjustcd to producc a normal force of N0 for a spring clutch forcc Ts(gencratintJ ~I torquc Tsr)of T0 and that roller llZ is not accclcratint3 so that Ts = T. In the non-aceclerating situation, if Ts varies, the point (T,N) will movc to a new point 1ying alon~ a line L3 passing through (TO,N0) and having a slopc ~ cqual to Y/X. Nore specifically, if the sprint3 clutch forco Ts increascs to a new levcl Tl, the normal foree N will increase compcnsatingly to a new level Nl in aceordancc with cquation (15), kceping the operating point (Tl,Nl) in the shadcd region. By contrast, if the assembly had provided no intcrdcpclldcncc betwccn T and N, thc new operatinq point (Tl,N0) wou1d be to the left of line Ll, rosultin~ in rollcr s]ippal1c in thc sinc~lc-shect modc. In a similar manncr, if thc sprin~J clutch forcc Ts decrcascs to a level T2, the normal forcc N will dccreasc in a compcnsating manner to a lcvcl N~ in accord~ncc with cquation (15) to kecp , ,, -- ' ~

- ~ /Y, ~, ~gL57~33 thc opcrating point ~T2,N2) in thc shadcd ro~ion. In this casc, if N had rcm~incd const~n~, the shiftcd operating point would bc to ~hc righL of linc L2 and the rcvcrsc torque T8r would bc insufficicnt to movc a sccond sheet out of the roller nip.

It is apparcnt from l'IGUR~ 9 that the scnsitivity of the asscmbly to changcs in Ts will be minimized if~ = Y/X is between approximately l/ur and l/up. In the embodiment shown - A in FIGURES la to 4, for ~ = 15, a = 20 mm, andl~= 13 mm, theslope~ is approximatDly 0.94. This constant of proportion-ality falls within these general limits, as in practice up is about 0.5 and ur is about 1Ø

Whcn two shccts arc bcing fcd, as in FIGURE 7, the operating point (T,N) is somawhat different, since roller 112 is at least initially accclcrating, In tl-is modo, tho rcverso tangontial forcc T drops to a valuc just equal to the drag forces in equation ~1) so that: :
T = upN + up(2M + 3m) (1~) In other words, tho doublc-shcct operating point (T3,N3) lies along line 1,2. ~t thc samo timc, T3 and N3 must satisfy equation (13). ~ccordingly, (T3,N3) lies on a line.segment L4 originating at (TO,N0) and having a slope ~J of tan ~ , as shown in FIGUI~ 9. It will be apparcnt that ~ is subject to the constraint:
tan A~ < l~up (17 - ~ .

. . .

114578~

Oth~rwise the line 1.2 and the line sogment L4 would not intersect and operation in this modc would be unstable.

FIGURE 12 shows the forees acting on the roller asscmbly embodiment shown in 1`IGUR~S 5 and 6. The analysis of forees in this situation is simiIar to the above analysi~
(wiLh d = 0) excep~ Lhat thc external origin of the spring elutch torquc Tsr must be taken in account. This torque may be considercd as bein~3 applicd at a point between the roller axis P3 and the pivot axis P4 at a distance b from P3 equal to the radius of g~ar 176. With this assumption, the net counter-elockwise torque about r4 is:
= Idw/dt = B~ ~ Tr - Na + Tsr(a - b)~b (18) Similarly, the net eountcrelockwise torque about P3 is:
~ = Idw/dt = Tr - Tsr (19) Combining equations (18) and ~19) and solving for N:
N = (B~ + Tsr a/b)/a , (20) Or, in inercmental terms:
~N/.~Ts = r/b (21) . ~ssuming that r = 13 mm, a = 16 mm, and b = 7 mm, we obtain ~ N/~Ts = 1.86 ~22) ~gain, this constant ~[ proportioo.lity falls within the limits referred to above.

It will be soen th.t I have accompli3hed the objeets of my invcntion. My shQet feodcr operates rcliably even after . i , ~_ G~ ~

.. ' i~Lq~5q83 ' ,~ ~

r, ?

a long period o~ use and docs not rcly on the chasacteristics of frictional surfaces for its opcration. My sheet feeder can fully cject a second shect without rcquiring an excessive period to become opcrative after initial actuation. Finally, my sheet fecder uses a rcvcrse-biased retarding roller wh~ch is relatively insensitive to changes in the value of the reverse biasing torquc.

It will be undcrstood that ccrtain features and subcombinations are of utility and may be cmployed without reference to other featurcs and subcombinations, This is contemplated by and is within thc scope of my claims. It i5 further obvious that various changcs may be made in details within the scope of my claims without departing from the ~pirit of my invcntion. It is, thcrefore, to be understood that my invention is not to bc limitcd to the specific details shown and described.

llaving thus described my invention, what I
claim is:

_~_ -

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for feeding sheets including in combination a feed roller, means for driving said feed roller in a certain direction of rotation, a retarding roller, an arm rotatably supporting said retarding roller, said arm being mounted on a pivot axis for movement of said retarding roller into and out of engagement with said feed roller, a rotary member disposed on said pivot axis, means carried by said arm for coupling said member to said retarding roller, and means for rotating said member in such a direction as to tend to rotate said retarding roller in said certain direction, one of said rotating means and said coupling means including means for limiting the torque transmitted to said retarding roller, said pivot axis being so located that said rotary member exerts a torque on said coupling means about said axis tending to urge said retarding roller into engagement with said feed roller.

2. Apparatus for feeding sheets including in combination a feed roller, means for driving said feed roller in a certain direction of rotation, a retarding roller, an arm rotatably supporting said retarding roller, said arm being mounted on a pivot axis for movement of said retarding roller into and out of engagement with said feed roller, a first gear mounted for rotation on said pivot axis, means including a second gear carried by said arm and engaging said first gear for coupling said first gear to said retarding roller, and means for rotating said first gear in such a direction as to tend to rotate said retarding roller in said certain direction, one of said rotating means and said coupling means including means for limiting the torque transmitted to said retarding roller, said pivot axis being so located that said first gear exerts a torque on said second gear about said axis tending to urge said retarding roller into engagement with said feed roller.

3. Apparatus for feeding sheets along a path including in combination a feed roller disposed on one side of said path, means for driving said feed roller in a certain direction of rotation, a retarding roller, an arm rotatably supporting said retarding roller, said arm being mounted on a pivot axis for movement of said retarding roller into and out of engagement with said feed roller on the other side of said path, a first gear mounted for rotation on said pivot axis, means including a second gear carried by said arm coaxially with said retarding roller and engaging said first gear for coupling said first gear to said retarding roller, and means for rotating said first gear in such a direction as to tend to rotate said retarding roller in said certain direction, one of said rotating means and said coupling means including means for limiting the torque transmitted to said retarding roller, said pivot axis being disposed at a location along said path downstream from said feed roller whereby said first gear exerts a torque on said second gear about said axis tending to urge said retarding roller into engagement with said feed roller.