YARN ACCUMULATION DEVIqE AND YARN WINDING MACHINE TECHNICAL FIELD [0001] The present winding machine, and device for applying a device. invention relates to b yarn accumulation device included in a yarn more specifically rplates to a mechanism in a yarn accumulation tension to a yam that is unwound from the yarn accumulation IO BACKGROUND ART [0002] In a yarn winding machine such as a spinning machine, a yarn accumulation l5 20 device is known that temporarily u..urnhu,.s a yam by winding the yam on a yarn accumulation roller. t00031 In this type of yam accumrtu]ion device, the yarn is pulled out along an extension of the axis line of the yarn accupulation roller, and thereby the yarn wound on the yarn accumulation roller is unwound. Here, the yarn accumulated on the yarn accumulation roller is wound in a helical lhape on an outer circumferential surface of the yarn accumulation roller. Therefore, while the yarn pulled out from the yam accumulation roller is unwound, the yarn is thrown around on the circumference of the yarn accumulation roller. At this timo, the trajectory of the yarn being unwound expands outward due to a centrifugal fofce, and when the yarn is excessively thrown around, the unwinding of the yarn from the roller may be unstable. A portion in which the trajectory of the yarn being unwound efipands as described above is called a balloon. [0004] Ideally, when the yarn is pulled out from the yarn accumulation roller in this yarn accumulation device, the yarn *otrrd in a helical shape is orderly unwound 25 from the 10 3 end side. However, in a case where un "J.,r"-.ly small force is required for pulling out the yarn from the yarn accumulation roller (in a case where a resistance in pulling out the yarn is low), a mass of the yarn wholly fal]ls off from the yarn accumulation roller at one time only with slight pulling of the yarn e>iisting on the yarn accumulation device. This phenomenon in which a mass of yam falls off at one time is called slaffing. [0005] In this respect, in a fine spinnite machine disclosed in Patent Document l, a yarn accumulation device (yarn looseniirS removal device) includes a flyer that is rotatable relative to the yarn accumulation roller while being engaged in a yam. This flyer is configured to cause a torque in thp direction against the relative rotation. This can prevent excessive throwing-around pf the yarn that is unwound from the yarn accumulation roller while being engaged irr the flyer. Thus, occurrence of the balloon is suppressed, and unwinding of the yam can be stabilized. t00061 In the configuration shown in Pftent Document l, the yam unwound from the yarn accumulation roller causes the relative rotation of the flyer against the torque. Due to the reaction thereof, a force is receive{ from the flyer. The force received from the flyer causes a resistance in unwinding of ,n. yam from the yarn accumulation roller. Thus, the yarn receives the resistance whon being unwound from the yarn accumulation roller, which consequently makes it difficqlt that the yarn falls off at once. As a result, occurrence of the slaffing, in which u -{r, of yam existing on the yam accumulation 15 20 roller falls ofl can be prevented. [0007] Since the yarn receives the re$istance when being unwound from accumulation device in the above-descri[.4 ,nu*er, it is possible to keep the the yam yam tightened at a location between the flyer atrd a winding device that winds the yarn at the downstream of the flyer. Thus, an apprgpriate degree of tension can be applied to the 25 yarn that is wound in the winding device. Therefore, a package with a high quality can be formed. i 4 I 1t'r [0008] In the fine spinning machine sh$wn in Patent Document l, an increase in the winding speed in the winding device "u.r.!, an increase in the speed of unwinding of the yarn from the yarn accumulation device. |A,s a result, the speed of relative rotation of the flyer also increases. However, the speed !f relative rotation of the flyer has a limitation in its own. Therefore, when the speed of rfrnwinding of the yam exceeds the limitation in the speed of relative rotation of the fly.r, u]d.lay occurs in the rotation of the flyer. This may cause failures such as occurrence of the balloon and winding of the yarn onto the flyer. Accordingly, in a yarn winding mfichine including the yam accumulation device l" of Patent Document l, there is a limitationlin increasing the speed of winding of the yarn. Here, in a yam winding machine includirls the yam accumulation device with the flyer, the winding speed is limited to about 5OOnflmin. [0009] The fine spinning machine tur]u relatively low winding speed, and therefore can normally wind the yarn even in a casd of adopting the yam accumulation device with the flyer (the configuration shown in fatent Document l). On the other hand, for example, in an automatic winder havingl a relatively high winding speed, the winding speed exceeds the limitation in the speed of rotation of the flyer, and therefore using of the yam accumulation device with the Hyer is diffrcult. Additionally, the automatic winder winds the yarn onto a wound bopbin while traversing (cross-winding) the yarn. This traversing causes a periodic change in the speed. Moreover, the automatic winder performs a so-called disturb control in ryhich the winding speed is rapidly changed in order to break a ribbon winding of the yaln. Since the flyer has inertia, it is difficult that the rotation of the flyer follows such a chpnge in the winding speed. This also presents a problem in applying the yarn accumulatidn device with the flyer to the automatic winder. [0010] In this respect, a yarn joining lvinding device disclosed in Patent Document 2 10 l5 20 25 ,l I . ttl includes a yam accumulation device (lenreth-measurement/accumulation part) provided with no flyer. In such a configuration in which a member (flyer) that causes a relative rotation is not provided, the above-describ[d problem involved in the flyer does not occur even during a high-speed rotation of the yam accumulation device. The yarn accumulation device shown in Patent Docrlrment 2 includes, instead of the flyer, a stopper flange provided at the distal end of an acct]mulation drum part. Providing such a stopper flange can prevent occuffence of the phelomenon (slaffing) in which a mass of the yarn accumulated on the accumulation drum part falls off at one time. However, merely providing the stopper flange is not "norg[, to give an appropriate resistance to the yarn l0 that is unwound from the accumulation drlm part. Therefore, it is impossible to prevent occurrence of a balloon during a high-spe[d rotation. Thus, the configuration shown in Patent Document 2 carurctbe directly appt]iea to the automatic winder. [0011] Accordingly, the applicant has {iscussed a yam accumulation device including a rubber ring instead of the flyer. To be specific, as shown in FIG. 11, this yam 15 accumulation device 100 is configured slch that a rubber ring 102 is attached to an end portion, at the unwinding side, of a yam qccumulation roller 101 made of a metal, so that ayam 99 unwound from the yarn accumulation roller 101 passes through a space between a surface of the yarn accumulation roller 101 and the rubber ring 102. The diameter of the rubber ring 102 is set smaller than thd outer diameter of the yarn accumulation roller 20 101 under the condition that no load is {pplied thereto. This configuration causes the rubber ring 102 to squeeze an outer cirpumferential surface of the yarn accumulation roller 101. As a result, the yarn 99 c1n be nipped with a weak force in its portion passing through the space between the sulface of the yam accumulation roller l0l and the rubber ring 102. This enables an appropriate degree of resistance to be applied to the 25 yan99 when the yarn 99 is unwound frorir the yarn accumulation roller l0l. I r--llr-j.l- 5 l0 6 [0012] As described above, the yarn ac{umulation device 100 shown in FIG. ll has a very simple configuration in which the rubber ring 102 is attached to the yarn accumulation roller 101, but neverthelels is able to apply an appropriate degree of resistance to the yarn99 that is unwound from the yarn accumulation roller 101. This can prevent occurrence of a balloon, slaffing, and the like, and additionally can apply an appropriate degree of tension to a yam focated downstream of the yarn accumulation device 100. The configuration shown in fIG. 11, which does not include a movable part such as a flyer, is excellent in the followability to a rapid change in the winding speed. Moreover, the rubber ring 102 causes an Spropriate degree of frictional effect relative to the yarn 99 passing under the rubber rin{ 102, and rolls the yam in a twist direction to thereby twist fluff in. Therefore, the effect of reducing fluff of the ywn 99 is highly exerted, which is an excellent feature of tfre rubber ring 102. Particularly, NBR (nitrile rubber) with an excellent abrasion resistan]ce, or the like, is suitable for the material of the rubber ring 102. [0013] Patent Document 3 discloses a lonfiguration in which ayarr, is nipped between a finger that extends from a yarn accumul{tor and a ring that is ananged around the finger. Patent Document 3 states that this configdration exerts a higher yarn pull-out tension and accordingly a relatively balanced yarn p{ll-out tension. However, in the configuration shown in Patent Document 3, it is n.rfrrury to form a plurality of fingers that act elastically toward the outside of the yarn 4ccumulator. This increases the manufacturing cost. Additionally, in the configuration ghown in Patent Document 3, a jacket surface is discontinued in the finger portion with resfect to the circumferential direction. Thus, the yarn that is unwound while sliding at a position corresponding to this finger would be damaged. In this respect, the very simlle configuration shown in FIG. I I is achieved merely by providing the rubber ring. T{is enables a low manufacturing cost and small l5 20 25 - -l----.-l-- I tl l damage to the yarn. PRIOR-ART DOCUMENTS PATENT DOCUMENTS [0014] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-77576 Patent Document 2: Japanese Pltent Application Laid-Open No. 2004-131276 Patent Document 3: Japanese patent Application Laid-Open No. 63-262376 (1e88) IO SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [0015] In the yam accumulation deyice 100 shown in FIG. 11, when the yarn accumulation roller 101 rotates, a centrifugal force acts on the rubber ring 102. The rubber ring 102 made of NBR has a low rate of elasticity of about 50Yo, and in other 15 words, does not have "viscosity (ela$ticity)". Therefore, upon reception of the centrifugal force, the rubber ring 102 is easily separated from the surface of the yam accumulation roller 101. Separation of dhe rubber ring 102 from the surface of the yam accumulation roller 101 results in a failurg to give an appropriate resistance to the yarn99 that is unwound from the yarn accumututfion roller l0l. Consequently, occurrence of a balloon and slaffing cannot be prevented. Moreover, an appropriate tension cannot be applied to the yarn located downstream oflthe yarn accumulation device 100. [0016] To deal with the above-describ{d nroblems, it is conceivable to adopt a rubber ring (a rubber ring having a smaller diameter) configured to exert such a squeezing force that is able to act against the centrifugal force exerted during a high-speed rotation of the yarn accumulation roller l0l. In this "uf., ho*"ver, during a low-speed rotation (when 20 25 -. I I I the centrifugal force is small), the rubber ring 102 squeezes the yarn accumulation roller 101 with an excessive force. Therefore, an excessive resistance is given when the yam 99 is pulled out from the yarn accumulati{n roller 101 during a low-speed rotation. This causes another problem that, during a lowfspeed rotation, the stretched yarn 99 is broken when the yarn 99 is pulled out from the yafn accumulation roller l0l. [0017] It is also conceivable to adopt a rubber ring (elastic band) made of natural rubber instead of the rubber ring made of [nn. The rubber ring made of natural rubber has a rate of elasticity of 500% to 900Yo, [nd in other words, has "viscosity (elasticity)". 10 kept in tight contact separation therefrom. f b 15 20 Therefore, even when the centrifugal forcf acts on the rubber ring, the rubber ring can be with with the ssuurrffaaccee pf tthhee yarn aaccccuummuulalatitoionn roller 101 without Thus, it is not.r""lsrary that the squeezing exerted by the rubber ring is made too strong so as to withstand the centrifugal force in a high-speed rotation. This can prevent the yarn from being str$tched and broken during a low-speed rotation. In a case where the yarn accumulation defice 100 shown in FIG. 1l adopts a rubber ring made of natural rubber, no problem o.frr.. in the accumulation of the yarn and an acceptable yarn winding speed ranges fr$tm' a low speed to a high speed (for example, 1200 m/min), as long as the rubber ring is [resh. [0018] However, a rubber ring made df natural rubber does not have durability, and involves a problem that a surface of the nfbber ring is shortly deteriorated due to friction with the yarn. Moreover, since the naturfal rubber has adhesion properties, fer example, a problem arises that fibers, cotton ny, utd the like, of the yam are entwined to form a lump. Furthermore, even though the ru![er ring made of natural rubber has a high rate of elasticity, a reduction in the resistance $ir"n to the yam during a high-speed rotation of the yarn accumulation roller l0l cannot !e avoided because the centrifugal force acts on 25 the side where the rubber ring is opened. I -1 =1-_r r r I Lltr.l, ItltllrLrrrrrr r' llrr I I I tr l0 9 [0019] The present invention has Ueen]made in view of the circumstances described above, and a primary object of the present invention is to provide a yarn accumulation device that is able to cover a wide ranle of winding from a low-speed winding to a high-speed winding. MEANS FOR SOLVING THE PROBLEMS AND EFFECTS THEREOF [0020] Problems to be solved by the pre$ent invention are as described above, and next, means for solving the problems and effect$ thereof will be described. [0021] In a first aspect of the present intvention, a yam accumulation device having the following configuration is provided. The yarn accumulation device is a yarn accumulation device configured to wind {nd accumulate a yarn on a yarn accumulation part that is formed on an outer circumferential surface of a rotating element, the yarn being unwound from the yarn accumulatiqn part in a direction along a rotation axis of the rotating element, the yarn accumulation $evice including a tension applying part. The tension applying part is arranged at an unWinding side of the yarn accumulation part, and configured to rotate in synchronization with the yam accumulation part and in this condition apply a tension to the yu- U"fg unwound from the yarn accumulation part. The tension applying part includes a ring rhember made of an expandable elastic material, and an enlarged/reduced portion provided radially inside the ring member and configured such that the yarn is nipped between the pnlareed/reduced portion and the ring member. The enlarged/reduced portion is confi[ured to enlarge or reduce its diameter in accordance with the speed of rotation of t\e rotating element. lOO22) Nipping the yarn between the ri]ng member made of the elastic material and the enlarged/reduced portion in this manner Qan apply a tension to the yarn being unwound from the yam accumulation part. The erflarged/reduced portion is configured to enlarge or reduce its diameter in accordurr"" *it{, the speed of rotation of the rotating element. l5 20 25 l0 l0 Accordingly, even in a case where the rin[ member expands outward due to a centrifugal force when the speed of rotation increasgs, the ring member and the enlarged/reduced portion can be kept in tight contact with e{ch other. Thereby, an appropriate tension can be applied to the yarn during rotations inpluding a low-speed rotation and a high-speed rotation. [0023] Preferably, the yarn accumulatipn device is configured as follows. A recess for restricting movement of the ring merhber in a direction of the rotation axis of the rotating element is provided in the enl{rged/reduced portion. Additionally, the ring member is attached in the recess of the enlarged/reduced portion. lOO24) This can prevent the ring memfer from being dragged by the yarn pulled out from the yam accumulation device and corrsequently detached. In the yarn accumulation devile, it is preferable that [002s] the enlarged/reduced portion has a recess maintaining mechauism for maintaining the recess irrespective of l5 enlargement and reduction in the diameter of the enlarged/reduced portion. 10026) Accordingly, detachment of the ping member from the enlarged/reduced portion can be prevented during both a high-speed rotation and a low-speed rotation. [0027] Preferably, the yarn accumulatipn device is configured as follows. An outer circumferential surface of the enlarged/rdduced portion is constituted of an elastic film made of a film-like elastic material. Jhe recess maintaining mechanism includes a concavity/convexity maintaining ring portion that is formed along a circumferential direction of the enlarged/reduced portiofi. The concavity/convexity maintaining ring portion is made of an elastic material, and arranged inside the elastic film. [0028] Thus, arranging the concavity/ponvexity maintaining ring portion having an appropriate diameter inside the elastic film can form a recess in an outer surface of the 20 25 elastic film (in the outer circumferential sfrrface of the enlarged/reduced portion). Since ll the concavity/convexity maintaining rin! portion is made of diameter of the concavity/convexity -ui.r,lining ring portion can the elastic material, the be enlarged and reduced. 20 [0032] portion. member that cooperates with the enlargedfreduced portion to nip the yarn therebetween is formed as a plane-shaped portion. This can prevent the ring memfer from being twisted on the enlarged/reduced Thus, a stable tension can be anfllied to the yarn. [0033] In the yarn accumulation devicp, it is preferable that a drive part for enlarging or reducing the diameter of the enlarged/r{duced portion is provided. [0034] This enables a tension applied io the yarn to be not only kept constant but also Therefore, the diameter of the enlarged/feduced portion can be enlarged and reduced while the shape of the recess is maintainedf 5 [0029] Preferably, the yarn accumulat]on device is configured as follows. A disk member is provided in an end portion of tle rotating element at the unwinding side. The disk member has a diameter larger than aq outer diameter of the enlarged/reduced portion under a state where the rotating element, is stopped. The enlarged/reduced portion is provided between the yarn accumulatior r[n and the disk member. l0 t0030] Accordingly, the yiun unwounJ ,ro- the yarn accumulation part comes into contact with the enlarged/reduced po(ion, and then is separated away from the enlarged./reduced portion, to travel while $eing guided by the disk member. Guiding the yarn in this manner can reduce the arel over which the yarn is in contact with the enlarged/reduced portion. This can prevgnt fluffing of the yarn and a deterioration in the 15 physical properties of the yarn. Thls can also prevent a situation where the enlarged/reduced portion is rubbed by the larn and damaged when the yarn is pulled out. t003ll In the yam accumulation deui[e, it is preferable that a portion of the ring 25 increased or reduced. j.-L-&-*Ll - , I I - --_LrrJrlaJ--t1 I If,rrrrrrru|| ilr rr r r,1l__tr_.J.rJr.|EJ!*_ 10 l2 [0035] In a second aspect of the presenl invention, ayarn accumulation device having the following configuration is providedf The yarn accumulation device is a yarn accumulation device configured to wind dnd accumulate a yarn on a yarn accumulation part that is formed on an outer circumfefential surface of a rotating element, the yarn being unwound from the yarn accumulatioflr part in a direction along a rotation axis of the rotating element, the yarn accumulation device including a tension applying part. The tension applying part is arranged at an unlirinding side of the yarn accumulation part, and configured to rotate in synchronization lwith the yam accumulation part and in this condition apply a tension to the yarn beifig unwound from the yarn accumulation part. The tension applying part includes a fir$ ring-shaped elastic material, a synchronized rotation member, a second ring-shaped el{stic material, and a cylindrical member. The first ring-shaped elastic material is mounled on a surface of the rotating element. The synchronized rotation member is arrangfd radially outside the rotating element, and configured to rotate in synchronizatiori with the rotating element. The second ring-shaped elastic material is provided to the synchronized rotation member. The cylindrical member is provided to the pynchronized rotation member such that the cylindrical member is opposed, from the fadially outside, to the first ring-shaped elastic material. Under a state where the rota(ing element is stopped, the first ring-shaped elastic material is not in contact wittrl the cylindrical member while the second ring-shaped elastic material is in contact qith the surface of the rotating element. When the yarn accumulated on the yarn accumulation part is unwound, the yarn passes through a space between the first ring-shaped ela$tic material and the cylindrical member and a space between the second ring-shaped elastic material and the sur ce of the rotating element. 25 t0036] In this configuration, during a low-speed rotation of the rotating element, a 15 20 I I i , I I l-r I I ----+-- r1---r.rI-l-.raJLUIlLl,tlrr"ir rr I rrr ' I tension is applied to the yarn by the lsurface of the rotating element and the second ring-shaped elastic material. In a higfr-speed rotation of the rotating element, a force acting in a direction that separates the $econd ring-shaped elastic material away from the l rotating element is caused by a centrifugal force, and therefore the second ring-shaped i elastic material can no longer apply a4t appropriate tension to the yarn. However, in a l range of the high-speed rotation, the first ring-shaped elastic material is pressed to the cylindrical member due to a centrifugal force. Accordingly, during a high-speed rotation, a tension is applied to the y4rn by the first ring-shaped elastic material and the l cylindrical member. Thus, an approflriate tension can be applied to the yarn during both l a low-speed rotation and a high-speedlrotation. l [0037] In a third aspect of the presdnt invention, a yarn winding machine including the above-mentioned yam accumulation jdevice and having the following configuration is l provided. The yarn winding machide includes ayarn supply part that supplies ayam, a yarn joining device that joins yapn ends that have been disconnected, the yarn l accumulation device, a tension applying device that applies a tension to the yam, and a winding part that winds the yam supplied from the yam supply part and forms a package. The yarn supply part, the yam joinilrg device, the yarn accumulation device, the tension l applying device, and the winding fart are arranged in this order along a direction of 20 traveling of the yarn. Even while lthe yarn joining device is performing a yam joining l operation, the winding part is able to continue winding with the tension applying device applying a tension to the yarn unwopnd from the yam accumulation device. [0038] That is, the yarn accumulation device is able to apply a constant tension to the yarn that is being unwound during both a low-speed rotation and a high-speed rotation. This facilitates a tension control pefformed by the tension applying device that is arranged l downstream of the yarn accumulation device. Additionally, since the winding part l l3 l0 15 25 winds the yarn accumulated on the yam accumulation device, the winding operation can be continued without receivinp any influence of the yarn joining operation and a , fluctuation in the unwinding tengion in the yam supply part. 5 BRIEF DESCRIPTION OF THd DRAWINGS t00391 [FIG. 1] A side vie* of a winder unit provided in an automatic winder according to an embodiment of the present invention. [FIG. 2] A side view oha yarn accumulation device. IFIG. 3] A cross-sectio[al view of the yam accumulation device. l0 [FIG. 4] A perspective view showing an external appearance of a tension applying part. [FIG. 5] A cross-sectiopal view of the tension applying part during a low-speed rotation. [FIG. 6] A cross-sectio{ral view of the tension applying part during a high-speed l5 rotation. [FIG. 7] A cross-secti(nal view of ayam accumulation device according to a second embodiment. [FIG. 8] A cross-secti{nal view of a yat:i. accumulation device according to a third embodiment. 20 IFIG. 9l A cross-sectioJal view of a tension applying part according to the third embodiment during a low-speeO r[tution. [FIG. 10] A cross-sectifnal view of the tension applying part according to the third embodiment during a high-speed rotation. [FIG. I l] A side view of a conventional yarn accumulation device. t4 25 l5 EMBODIMENT FOR CARRYTNG OUT THE INVENTION [0040] Next, embodiments oflthe present invention will be described. FIG. I is a side view showing an outline of a wipder unit 2 provided in an automatic winder that is ayam winding machine according td a first embodiment of the present invention. The 5 automatic winder of this "-Uofi-".rt is configured with a number of winder units 2 arranged side by side. This adtomatic winder includes a machine management device (not shown) and a blower bgx (not shown). The machine management device collectively manages the windef units 2. The blower box includes a compressed air source and a negative pressure ,lur... 10 [0041] As shown in FIG. 1, thb winder unit 2 mainly includes ayarnsupply partT and a winding part 8. The winder upit 2 is configured to unwind a yarn (spun yam) 20 from a yam supply bobbin 2l that is dupported on the yam supply part 7 and rewind the yarn 20 into a package 30. FIG. 1 thows a state of the winder unit 2 at a time of normal winding. In the description herdin, the "time of normal winding" indicates a state where the yarn is continuous between tfr" yu* supply bobbin 2l andthe package 30 and additionalty the yam is being untvound from the yarn supply bobbin 2l and wound into the package 30. IOO42| The yarn supply part 7 is configured to hold the yarn supply bobbin 21, which is for supplying a yam, in a subgtantially upright state. The yarn supply part 7 is also configured to discharge the yarn supply bobbin 2I that is empty. The winding part 8 includes a cradle 23 and a trave{se drum 24. The cradle 23 is configured such that a wound bobbin 22 is mounted thdreon. The traverse drum 24 is configured to traverse the yarn 20 and drive the wound bpbbin22. 100431 The traverse drum 24 is arranged opposed to the wound bobbin 22. The 25 traverse drum 24 is driven in rot{tion, and thereby the wound bobbin 22 is accordingly l5 20 l0 l6 rotated. This enables the yam120 accumulated on ayamaccumulation device l8 which will be described later to be wdund onto the wound bobbin 22. A traverse groove (not shown) is formed in an outer circumferential surface of the traverse drum 24. The traverse groove allows the yanr] 20 to be traversed (cross-wound) with a predetermined width. In the above-described bonfiguration, the yarn 20 is wound on the wound bobbin 22 whlle being traversed, to fortm the package 30 having a predetermined length and a predetermined shape. In the following description, the terms "upstream side" and "downstream side" mean the u{stream side and the downstream side with respect to a direction of traveling of the yarn. [0044] Each of the winder units 2 includes a control part 25. The control part 25 is composed of hardware such as + CPU, a ROM, and a RAM (not shown), and software such as a control program stored jin ttre RAM. The hardware and the software cooperate with each other, to control each donfiguration part of the winder unit 2. The control part 25 included in each winder unflt 2 is configured to communicate with the machine 15 management device. Accordingly, the machine management device can collectively manage operations of the pluralitj of winder units 2 included in the automatic winder. [0045] The winder unit 2 alsd includes various devices that are arranged in a yarn travel path between the yarn supply part 7 and the winding part 8. More specifically, in the yarn travel path, an unwinding assist device 10, a lower yarn blow-up part I l, a first 20 tension applying device 12, anrrP.. yarn catch part 13, a yarn joining device 14, ayam trap 15, a cutter 16, a clearer (yard defect detection device) 17, an upper yarn pull-out part 48, a yarn accumulation device I Q, and a second tension applying device 19, are arranged in this order from the yam supply i*, side toward the winding part 8 side. t00461 The unwinding assist delice 10 assists the unwinding of the ya.rr-20by bringing 25 a movable member 40 into contabt with a balloon, which is generated above the yarn t7 10 supply bobbin 2l as a result of fhe yam20 being unwound from the yarn supply bobbin 2l and,thrown around, and thereby appropriately controlling the size of the balloon. [0047] The lower yarn blow-[p part 11 is an air sucker device arranged immediately downstream of the unwinding pssist device 10. The lower yam blow-up part 11 is configured to blow up a lower fa.n of the yam supply bobbin 2l side toward the yarn joining device 14 side. When the yarn 20 is disconnected at a location between the yarn supply bobbin 21 andthe yarn {ccumulation device 18, the lower yarn blow-up part 1l can blow up the yarn of the yarq supply bobbin 2l and guide the yarn to the yarn joining device 14. [0048] The first tension applylng device 12 applies a predetermined tension to the yarn 20 that is traveling. In this embodiment, the first tension applying device 12 is configured as a gate type in whiqh a movable comb is arranged relative to a fixed comb. When a yam travels between th[ combs, a predetermined resistance is applied thereto. The movable comb is movable Uy means of a solenoid, which allows adjustment of the state of engagement between thel combs. The control part 25 controls the solenoid and thereby can adjust the tension thap the first tension applying device 12 applies to the yarn. However, a configuration of the first tension applying device 12 is not limited to this. For example, a disk type tension dpplying device is also adoptable. [0049] The upper yarn catch part 13 is arranged immediately upstream of the yarn joining device 14. The upper jarn catch part 13 is connected to a negative pressure source (not shown), and configurdd to generate a suction air stream to suck and catch the yarn of the yam accumulation device 18 side at a time of yarn joining (details will be given later). [0050] The yam trap 15 is ryanged upstream of the cutter 16 and immediately 25 downstream of the yarn joining ddvice 14. A distal end of the yam trap 15 is formed as 15 20 l8 10 a tube-like member, which is provided close to the travel path of the yarn 20 and connected to a negative pressurle source (not shown). In this configuration, the suction air stream is generated at the distal end of the yarn trap 15, and thereby dusts such as cotton fly adhering to the traveli[rg yam20can be sucked and removed. [0051] The clearer 17 is con{'lgured to detect a yam defect (yarn fault) such as a slub by, for example, monitoring ay4rn thickness of the yam20. When the clearer l7 detects ayam defect, the clearer 17 trar[smits a disconnection signal to, for example, the control part 25. The disconnection sipnal instructs to cut and remove the yarn defect. The cutter 16 is arranged near the cl$arer 17, for immediately cutting the yarn 20 in response to the disconnection signal. t00521 The upper yarn pull-o,f, run 48 is an air sucker device, and configured to, at a time of yarn joining, pull out a ypm accumulated on the yarn accumulation device l8 and blow off the yarn toward a yarn $uide member 60 (which will be described later). t00531 The yarn accumulatiori device 18 includes a yarn accumulation roller 32 having a substantially cylindrical shape, and a roller drive motor 33 configured to drive the yarn accumulation roller 32 in rotatiotr around the axis line thereof which serves as a rotation axis. The roller drive motor 33 is controlled by the control part 25. In this configuration, the yarn accumulaflion roller 32 is driven in rotation, and in this condition, the yarn 20 unwound from the yf,rn supply bobbin 2l is wound onto a circumference of the yam accumulation roller 32. I Thereby, the yam 20 can be temporarily accumulated on the yam accumulation roller 32. The yarn accumulated on the yarn accumulation roller 32 is pulled out in a directiqn along the axis line of the yam accumulation roller 32, and then wound by the windlng part 8. A detailed configuration of the yarn accumulation device l8 will be dJscribed later. [0054] The yarn joining devicg 14 performs yam joining between ayam of the yarn l5 20 25 l9 10 supply bobbin 21 side and a yarpr of the yarn accumulation device 18 side when the yarn is disconnected between the yarfr supply bobbin 2l andthe yarn accumulation device 18, which occurs, for exampl e, at ali." of ya* cutting in which the clearer l7 detects a yam defect so that the cutter 16 cutl the yarn, at a time of yarn breakage in which the yarn being unwound from the yam slrpply bobbin 21 is broken, or at a time of replacing the yarn supply bobbin 21. As the yarn joining device 14, one using fluid such as compressed air, mechanical one,lor the like, is adoptable. [0055] The second tension applying device 19 applies a predetermined tension to the yarn that has been pulled out frdm the yarn accumulation device 18, thereby controlling the tension of the yarn 20 at u Ji-e when the yam 20 is wound by the winding part 8. The second tension applying dgvice 19 is configured as a gate type tenser, which is similar to the first tension applyiirg device. The control part 25 appropriately controls a solenoid of the second tension afplying device 19, and thereby can adjust the tension that the second tension applying a.rif" 19 applies to the yam. However, a configuration of 15 the second tension applying device 19 is not limited to this. For example, a disk type tension applying device is also adbptable. [0056] A bobbin feeder 26 of lraeazine type is arranged at the front side of the winder luinit2. The bobbin feeder 26 ingludes a rotary magazine can27. The magazine can27 is configured to hold a plurality df extra yarn supply bobbins 21. The bobbin feeder 26 20 intermittently drives and rotates the magazine can 27, and thereby feeds a new yarn supply bobbin 21 to the yarn suqply part7. The bobbin feeder 26 includes a yarn end holder 28 for sucking and holdin[ a yam end of the yarn supply bobbin 21 held on the qperation performed in the automatic winder of this magazine can27. [0057] Next, a yarn joining embodiment will 25 be described. l0 20 [0058] The yarn joining devi0e 14 performs the yarn joining operation when the yarn of the yarn accumulation a"lric{ l8 side and the yarn of the yarn supply bobbin 21 side are disconnected from each othe[ because ofyarn breakage, yarn cutting by the cutter 16, replacement of the yarn supply {obbin 21, or the like. To be specific, firstly, the control part 25 causes the lower yarn blbw-up part I I to blow up the yam 20 of the yarn supply bobbin 2l side in an upward dirdction. The yam20 thus blown up is sucked and caught by the yarn trap 15. The yam trap 15 is movable by a yarn trap diver 47. When the yarn trap 15 is moved under u rtr[" where the yarn trap 15 sucks and catches ayamend of the yarn of the yarn supply bobbip 2l side, the yarn of the yarn supply bobbin 2l side can be introduced to the yarn joinine pevice 14. t00591 Around this time, the cbntrol part25 puts the yarn accumulation roller 32 of the yarn accumulation device 18 intd reverse rotation, and in this condition causes the upper yarn pull-out part 48 to blow off[he yam2lexisting on the yam accumulation roller 32. The direction in which the upper ia.n putl-out part 48 blows off the yarn2lis oriented to a position where a yarn guide -f*U". 60 having a curved tube-like shape is arranged. The yam 20 thus blown off is ta{en into the yam guide member 60 from one end of the yarn guide member 60 and, alon! with an air stream, guided to the other end of the yam guide member 60. An exit froni the yarn guide member 60, which is provided at the other end thereof, is oriented to*ard a position where the upper yarn catch part 13 is arranged. In the above-describefl configuration, the yam 20 of the yarn accumulation roller 32 side, which has been bloYrn off by the upper yarn pull-out part 48, is sucked and caught by the upper yam catch pa{t 13. In the yarn guide member 60 having a tube-like shape, a slit extending in a longitfrdinal direction thereof is formed. Through this slit, the yarn 20 located in the yarn gulde member 60 can be drawn out to the outside. The yarn drawn out from the yarn guidb member 60 is further sucked by the upper yarn catch 15 20 25 2l l0 part 13,and thereby introduced [o the yam joining device 14. When the yarn of the yarn accumulation device 18 side is [ntroduced to the yarn joining device 14, the control part 25 stops the reverse rotation of tfre yam accumulation roller 32. t00601 Through the above-delcribed operation, the yarn of the yam supply bobbin 2l side and the yarn of the yu- u"[r*ulation device 18 side can be introduced to the yarn joining device 14. In this condlition, the control part25 actuates the yam joining device 14, to thereby join the yarn of {he yarn supply bobbin 21 side and the yarn of the yarn accumulation device 18 side. {fter the yarn joining operation is completed, the control part 25 restarts a normal rotatioh of the yarn accumulation device 18, to thereby restart the winding of the yarn onto the farn accumulation device 18. [0061] As described above, eqen when the yarn is disconnected at a location between the yarn supply bobbin 2l andt{e yu- accumulation device 18, the winding of the yarn 20 into the package 30 in the win[ing part 8 can be continued without intemrption. That is, in the automatic winder of this embodiment, as described above, the yarn accumulation certain amount of the yarn Therefore, even when the 20 15 device 18 is interposed between fhe yarn supply partT and the winding part 8, so that a ZO lis accumulated on the yarn accumulation device 18. supflly of the yarn from the yarn supply bobbin 2l is intemrpted for some reason (for qample, during the yarn joining operation), the winding part 8 is able to wind the yam tfr[t is accumulated on the yarn accumulation device 18. Thus, the winding of the yarn20 ihto the package 30 can be continued. 10062) Since a winding operatibn of the winding part 8 is not intemrpted by the yarn joining operation or the like, thelpackage 30 can be produced stably at a high speed. Additionally, since the yarn accfrmulation device 18 is interposed between the yarn supply bobbin 2l and the windiirg part 8, the winding in the winding part 8 can be performed without receiving an iffluence of a fluctuation in the tension occurring 25 at a 22 t0 time of unwinding the yarn fronJ the yarn supply bobbin 21. t00631 Next, the yarn accumulation device 18 will be described with reference to FIGS. 2 and 3. As mention"a uUori, the yarn accumulation device 18 includes the yarn accumulation roller 32. t00641 The yarn accumulatiorf roller (rotating element) 32 is a roller member having a substantially cylindrical shape, hnd includes a yarn accumulation part 37 and a tension applying part 38. The yarn acgumulation part 37 is formed on an outer circumferential surface of the yarn accumulatiof roller 32. As shown in FIG. 2, the yam 20 unwound from the yarn supply bobbin 2l is introduced on one end of the yarn accumulation roller 32 to the outer circumferential srlrface of the yarn accumulation roller 32, and wound onto the yam accumulation part 37. lrn"rr, the yam 20 is pulled out through the other end of the yam accumulation roller 32trand fed to the winding part 8 side. In the following description, with respect to the direction extending along the central axis of the yam accumulation roller 32, the side of the yarn accumulation roller 32 (shown in the lower left in FIG.2) on which the yaq of the yam supply bobbin 21 is introduced to the yam accumulation roller 32 will b{ called a base end side, and the side of the yarn accumulation roller 32 (shown ir[ the upper right in FIG. 2) on which the yam is pulled out from the yarn accumulation r$ller 32 will be called an unwinding side. [0065] As shown in FIG. 3, the yiun accumulation part 37 includes a 20 portion 37a and a tapered porti{n 37b. An outer circumferential surface accumulation part 37 is made of d metal. [0066] The cylindrical portion3Ta is configured such that a certain amount of the yarn 20 canbe wound and accumulatqd on the outer circumferential surface of the cylindrical portion 37a. More specifically, the yarn of the yarn supply bobbin 2l is introduced to the outer circumferential surface df the cylindrical portion 37a from an end portion of the l5 cylindrical of the yam 25 23 l0 cylindrical portion 37a atthe bfse end side thereof, and wound in a helical shape on the outer circumferential surface. The roller drive motor 33 drives the yarn accumulation roller 32 into rotation under u ,f,. where the yarn 20 is wound on the cylindrical portion 37a, andthereby the yarn 20 cdn be sequentially wound on a surface of the cylindrical portion 37a. When the yam fO ,"*tf coming to the end portion of the cylindrical portion 37a at the base end sidb is wound, the newly coming yarn 20 pushes away the yam2lthat is already wound orlthe cylindrical portion 37a toward the end portion of the cylindrical portion 37a at the unwinding side thereof. Accordingly, the yalr- 20 accumulated on the surface of tff. cylindrical portion 37a sequentially moves toward the end portion at the unwinding si[e. The diameter of the cylindrical portion 37a is not completely constant, but the cyfindrical portion 37a has a small taper whose diameter gradually decreases toward the lunwinding side. This facilitates the movement of the yarn wound on the cylindrical poFtion 37a toward the end portion at the unwinding side. t0067] The tapered portion l?U is formed continuous with the end portion of the 15 cylindrical portion 37aat the basg end side. The tapered portion 37b has a tapered shape whose diameter increases towarh the side (base end side) opposite to the cylindrical portion 37a. Since the tapered flortion 37b is formed in this manner, the yarn 20 wound on the tapered portion 37b moveJ from the tapered portion 37b to the cylindrical portion 37a due to the tension applied pt a time of the winding. Accordingly, the yarn 20 previously wound on the cylindribd portion 37a is pushed up by the newly wound yarn 20. The yarn 20 sequentially r{roves from the tapered portion 37b to the cylindrical portion 37a inthe above-mentionLd manner, and thereby the yarn 20 is regularly wound in a helical shape on the cylindric{l portion 37a. t0068] The yam 20 accumulatJd on the yarn accumulation part 37 is unwound toward the unwinding side. At this time;the tension applying part 38 arranged at the unwinding 20 25 24 side of the yarn accumulation pprt 37 gives a predetermined resistance to the yarn being unwound (details will be given lpter). t0069] As shown in FIG. 2, atlyarnguide 29 forguiding a yarn is arranged ahead of the end portion of the tension applying part 38 at the unwinding side. The yam guide 29 is configured to guide ayam in a pledetermined position on an extension of the rotation axis of the yarn accumulation roller 32. This enables the yam 20 wound in a helical shape on the yarn accumulation roller 32 p be pulled out in the direction along the axis line of the yarn accumulation roller 32 whgn the yam 20 is unwound from the yarn accumulation roller 32. The yarn 20, to whic{r a tension has been applied by the tension applying part l0 38, is wound up to the downstreain side (winding part 8 side) via the yam guide 29. t0070] As shown in FIG. 2, ah upper limit sensor 36 and a lower limit sensor 35 are arranged near the yarn accumulation roller 32. The upper limit sensor 36 detects that the amount of the yam 20 on the yarh accumulation roller 32 reaches a predetermined upper limit amount or more. The low$r limit sensor 35 detects that the amount of the yam20 on the yarn accumulation rollerl 32 falls below a predetermined lower limit amount. Detection results of the lower limi[ sensor 35 and the upper limit senso r 36 aretransmitted to the control part25. t00711 When the control p*tZ.Sdetects that the upper limit sensor 36 is tumed off and the yarn on the yarn accumulatibn roller 32 falls below the upper limit amount, the control part 25 appropriately conffols the roller drive motor 33 to increase the speed of rotation of the yarn accumulationlroller 32. Accordingly, the speed of winding of the yam 20 onto the yarn accumulati{n roller 32 increases. As a result, the amount of the yarn2} accumulated on the yurn uf.r-ulation roller 32 canbe gradually increased. On the other hand, when the control pdrt25 detects that the upper limit sensor 36 is tumed on and the yarn on the yarn accumulaltion roller 32 reaches the upper limit amount or more, l5 20 25 25 10 the control part 25 appropriately controls the roller drive motor 33 to reduce the speed of rotation of the yarn accumulatibn roller 32. Accordingly, the speed of winding of the yarn 2|onto the yarn accumutulio, roller 32 decreases. As a result, the amount of the yarn 20 accumulated on the yar4 accumulation roller 32 can be gradually reduced. Such a control enables the amount of tn. yam20 accumulated on the yarn accumulation roller 32tobe kept at a substantially cdnstant value near the upper limit amount. [0072] Additionally, when thj control put 25detects that the lower limit sensor 35 is turned off and the amount of tn"l yam 20 accumulated on the yarn accumulation roller 32 falls below the lower limit amoui,t, the control part25 stops the winding of the yam20by the winding part 8. This prevdnts occurrence of a situation where the winding part 8 fully winds up the yarn existing qn the yam accumulation roller 32. [0073] Next, a configuration of the tension applying part 38 will be described in detail. t00741 The tension applying flart 38 is configured to rotate integrally with (rotate in synchronization with) the yam Eccumulation part 37. The tension applying part 38 includes an enlarged/reduced portion 50 and a rubber ring (ring member) 51. t0075] As shown in FIG. 3, a]r outer circumferential surface of the enlarged/reduced portion 50 is constituted of a rubber film 52 (elastic film) made of an elastic material (in this embodiment, made of NBR). I O -or" specific description thereof is as follows. As shown in FIGS. 3 and 4, the yafn accumulation roller 32 includes the rubber film 52 having a substantially cylindricallshape. Both end portions of the rubber film 52 with respect to the axial direction are frked to an outer circumference of the yarn accumulation roller 32 by appropriate me{ns. Therefore, an outer circumference of the enlarged,/reduced portion 50 has alsuUstantially cylindrical shape. The outer diameter of the enlarged/reduced portion Sd is not constant but has concavity and convexity constituted of a first protrusion 50a, a second protrusion 50b, and a recess 50c formed l5 20 25 l0 between the first protrusion 50aland the second protrusion 50b. [0076] The enlarged/reduced portion 50 has a recess maintaining mechanism 58 for maintaining the recess 50c. $s shown in FIGS. 3 and 4, the recess maintaining mechanism 58 includes a lPluralitr of concavity/convexity maintaining rings (concavity/convexity maintainin[ ring portion) 55, 56, and 57 that are arranged radially inside the rubber film 52. Each of the concavity/convexity maintaining rings 55, 56, and 57 is formed with a ,ing-tile shape along the circumferential direction. The concavity/convexity maintainine]rings 55, 56, and, 57 are made of an elastic material (in this embodiment, made of NBR)I [0077) The plurality of concar,]itylconvexity maintaining rings are arranged side by side in the axial direction of the lru- u""u-ulation roller 32. The first protrusion maintaining ring 55, the ,...f, maintaining ring 56, and the second protrusion maintaining ring 57 arc arranged in this order from the base end side. In a state where no load is applied (the rotatioq of the yam accumulation roller 32 is stopped), the diameter of the recess maintainin! nr, 56 is smaller than the diameters of r the protrusion maintaining rings 55 and 57. Id tnis configuration, an outer circumferential surface of the rubber film 52 (the outer circhmferential surface of the enlarged/reduced portion 50) has the first protrusion 50a cQrresponding to the diameter of the first protrusion maintaining ring 55, the ,"r.r{ 50c corresponding to the diameter of the recess maintaining ring 56,, land the secofrd protrusion 50b corresponding to the diameter of the second protrusion maintaining rin$ 57. [0078] On the other hand, the rubber ring 5l is a ring member made of an elastic material (in this embodiment, ,nfa" of NBR). The rubber ring 5l is provided in a position corresponding to the receds 50c ofthe enlarged/reduced portion 50, and arranged radially outside the recess 50c. Itr a state where no load is applied, the diameter of the l5 20 25 l0 rubber ring 5l is slightly smdller than the outer diameter of the recess 50c of the enlarged/reduced portion 50. fhis configuration causes the rubber ring 5l to squeeze, from the radially outside, u Oo.i,on of the enlarged/reduced portion 50 corresponding to the recess 50c. I t0079] As shown in FIGS. 2 and 5, when the yarn 20 unwound from the yarn accumulation part 37 is pulled out from the yarn accumulation roller 32, the yam 20 passes through a space between [he outer circumferential surface of the enlarged/reduced portion 50 and the rubber ring 5i in the tension applying part 38. Since the rubber ring 5l squeezes the enlarged/reducdd portion 50, the yam 20 passing through the tension applying part 38 is nipped between the outer circumferential surface of the enlarged/reduced portion 50 and ffre ruUUe. ring 51. This configuration is able to give an appropriate degree of resistance [o the yarn 20 when the yarn 20 is pulled out from the yarn accumulation roller 32. Ad a result, slaffing can be prevented. Additionally, since a resistance is given to the yaqn 20 when the yam 20 is pulled out from the yarn accumulation roller 32, a portiln of the yam 20 located downstream of the yarn accumulation roller 32 canbe kelt tightened. Thus, an appropriate degree of tension can be applied to a portion of the 1i;am 20 located downstream of the yarn accumulation device 18. This enables the *ifairg part 8 to wind up the yarn with an appropriate tension. 20 t0080] Moreover, the yarn 20 dccumulated on the yam accumulation part 37 is wound in a helical shape on the outer dircumferential surface of the cylindrical portion 37a. Therefore, when being unwound from the cylindrical portion 37a, the yam 20 is thrown around on the circumference of thi enlarged/reduced portion 50. In the configuration of this embodiment, the yam 20 ihat is thrown around is nipped between the outer circumferential surface of the enlaffged/reduced portion 50 and the rubber ring 51. This 15 25 can prevent the yam 20 from being excessively thrown around, and thus can prevent occurrence of a balloon. Sincf the yarn 20 is thrown around when being unwound, the position where the yarn 20 pas$es in the space between the outer circumferential surface of the enlarged/reduced portiorf 50 and the rubber ring 51 shifts in the circumferential direction. Such a configuratiol in which the position where the yam 20 passes shifts in the circumferential direction cafi prevent occurrence of a situation where only particular portions of the enlarged/reduced portion 50 and the rubber ring 5l are rubbed by the yarn 20 and worn out in a short time. [0081] As mentioned above, the rubber ring 5l is attached in the recess 50c of the l0 enlarged/reduced portion 50. fherefo.", even though the rubber ring 5l is forced to move in the axial direction of td" yurn accumulation roller 32 together with the yam 20 being unwound, the protrusions pOa and 50b hinder such movement. This configuration can prevent the rubber ring 5l frdm being detached from the enlarged/reduced portion 50. [0082] The yarn accumulatioJ, d"ri.. 18 of this embodiment has a disk member 39 15 provided in an end portion of the enlarged/reduced portion 50 at the unwinding side. The disk member 39 is configurpd to rotate integrally with the yarn accumulation roller 32. The diameter of the disk member 39 is larger than the outer diameter of the enlarged/reduced portion 50 un{er a state where the rotation of the yarn accumulation roller 32 is stopped. Accordi$ely, when the yam 20 is pulled out from the yarn 20 accumulation roller 32, the y*n bO is guided by the disk member 39. This can prevent the surface of the rubber film 52lof the enlarged/reduced portion 50 from being strongly rubbed by the yarn 20. As a refult, wear-out of the rubber film 52 is reduced, and the durability can be improved. A rlnore detailed description is as follows. As long as the yarn is wound on the ,u* u""*lulation roller 32, the yam 20 unwound from the yarn 25 accumulation roller 32 is thrown pound on the circumference of the rubber film 52 when t0 the yarn 20 is passing. Therefdre, a situation where only one portion of the mbber film 52 is strongly rubbed by the lam 20 does not occur. However, once the yam 20 accumulated on the yarn accumftution roller 32 is fully unwound, the yarn 20 that is not wound linearly passes through ulrpu.. between the rubber film 52 and the rubber ring 51. 5 Il at this time, the yarn20 is in {ontact with the rubber film 52,a portion of this contact is strongly rubbed by the yarn 20,lwnicn may damage the rubber film 52. In this respect, as described above, the disk merhber 39 is provided, to allow the passing yam20 to float above the rubber film 52. fhis lan prevent the yarn 20 from being in entangling contact with the rubber film 52. .Thus,!u-ur. to the rubber film 52 due to the yam 20 can be prevented. Additionally, the urfu ou.. which the yarn 20 is in contact with the rubber film 52 can be reduced. This dan consequently prevent fluffing ofthe yarn2} and a deterioration in the physical propbrties of the yam20. [0083] The rubber ring 51 had a plane-shaped portion as shown in FIG. 5. [n other words, when cut along a planp passing through the central axis line of the yarn accumulation roller 32, the rubbBr ring 51 has a substantially D-shaped (semicircular) cross-section. The rubberui.rg f f is, in the plane-shaped portion, in contact with the outer circumferential surface of tne enlarged/reduced portion 50. Although it is conceivable that the rubber ring 51 has a circular cross-section, a rubber ring having a circular cross-section is often twidted due to its shape. In this respect, the rubber ring 51 having a substantially D-shap.d .rorr-rrction as illustrated in this embodiment is not easily twisted. Even if the rubber ring 51 having such a D-shaped cross-section is twisted, the plane-shaped portion rfhereof tends to be in contact with the enlarged/reduced portion 50, and thereby recovery ff'om the twisting is achieved. Moreover, a rubber ring having a circular cross-sectiorr, *{i.n makes a point-contact with a yarn, may sometimes l5 20 25 cause a stick-slip phenomenon so that a yam breakage occurs due to a fluctuation in the tension. On the other hand, the rubber ring 51 having a substantially D-shaped cross-section, which makes a line-contact with a yaffi, achieves a stable tension application. As thus far descrlibed, a substantially D-shaped cross-section makes the rubber ring 5l difficult to be t*lirted, and additionally causes the rubber ring 5l to be in 5 line-contact with a yarn. Thergfore, a resistance given to the yam 20 passing under the rubber ring 5l is stabilized. This can prevent the yarn 20 from being stretched and broken, and also enables the winhin gpartS to wind up the yam2}with a stable tension. [0084] Next, an enlargement/rgduction function of the enlarged/reduced portion 50 will be described. t0085] As already described, the rotation of the yam accumulation roller causes a centrifugal force to act on the ru]ber ring, which enlarges the diameter of the rubber ring. Therefore, in the conventional ya[n accumulation device (the configuration shown in FIG. l1), it may be impossible to give an appropriate resistance to the yam passing through the space between the rubber ring ar{ the yam accumulation roller. 15 [0086] In the yarn accumulatign device 18 of this embodiment, on the other hand, the outer circumferential surface of Xhe enlarged/reduced portion 50 is formed of the rubber film 52. Thus, when a centrifulgal force acts on the enlarged/reduced portion 50, the outer diameter of the enlarged/refluced portion 50 is also enlarged, as shown in FIG. 6. That is, the diameter of the enlarped/reduced portion 50 can be enlarged and reduced in accordance with the speed of rolation of the yarn accumulation rcller 32. Therefore, with enlargement in the diameter fr,n. rubber ring 51 caused by the centrifugal force, the outer diameter of the enlarged/rpduced portion 50 will also be enlarged accordingly. This can prevent the rubber .idg 5l from being separated from the surface of the enlarged/reduced portion SO eveJ during a high-speed rotation. Accordingly, the yarn accumulation device l8 of this empodiment is able to give an appropriate resistance to the 30 t0 20 25 3l 10 yarn20 passing through the spafe between the surface of the enlarged/reduced portion 50 and the rubber ring 5l even durihg a high-speed rotation. [0087] Since separation of thg rubber ring 51 from the surface of the enlarged/reduced portion 50 can be preventeO Auhng a high-speed rotation as mentioned above, a rubber ring having a smaller squeezing horce 1a rubber ring having a relatively large diameter) as compared with the configuratio4 shown in FIG. I I is applicable. Adoption of a rubber ring having a relatively weak squeezing force can avoid a problem that the yarn 20 is stretched and broken due to un l"*""rrire increase in the resistance that is given to the yarnZ}during a low-speed rotatilon (at a time when the centrifugal force is small). [0088] Additionally, with enl{rgement or reduction in the diameter of the rubber ring 51, the outer diameter of the enlarged/reduced portion 50 is enlarged or reduced accordingly. Therefore, in the donfiguration of this embodiment, the squeezing force of the rubber ring 5l squeezing th{ enlarged/reduced portion 50 can be kept substantially constant irrespective of the spped of rotation of the yarn accumulation roller 32. 15 Moreover, the enlarged/reduce{ portion 50 is enlarged and reduced with a good responsiveness relative to a chan{e in the speed of the yarn accumulation roller 32. Due '1 to these characteristics, a certain type of a mechanical system, which can be called an automatic tension control ,yrt"-] is achieved. Therefore, a tension applied to a portion of the yam 20 located downstr{am of the yam accumulation device 18 can be kept substantially constant irrespectivel of the speed of rotation of the yarn accumulation roller 32. This makes it easy to contrbl the second tension applying device 19 such that the tension of the yam20 at the dow$stream side of the yam accumulation device l8 is kept within a desired range. As a resfrtt, the winding part 8 can form a package with a high quality. [0089] In this embodiment, the concavity/convexity maintaining rings 55, 56, and 57 20 25 l--_..- 32 included in the recess maintaini[rg mechanism 58 are made of an elastic material (made of rings 55, 56, and rotation of the enlarged/reduced l0 l5 20 NBR). This configuration ena]bles the diameters of the concavity/convexity maintaining 57, too, to bp enlarged and reduced in accordance with the speed of yarn accumglation roller 32. Therefore, the diameter of the portion 50 dan be enlarged and reduced while the concavity and convexity thereof are maintainep by the recess maintaining mechanism 58. Accordingly, irrespective of the speed of rotafion of the yarn accumulation roller 32,the concavity and convexity of the enlarged/reduced portion 50 can prevent the rubber ring 51 from being dragged by the yam2l*d.on$quently detached from the enlarged/reduced portion 50. t00901 In this embodiment, ttfe recess maintaining ring 56 is bonded to the rubber film 52 from the inner side of the lbber film 52, such that a portion of the rubber film 52 corresponding to the recess 50c does not expand and protrude outward due to a centrifugal force. On the othef hand, the protrusion maintaining rings 55 and 57 need not always be bonded in such h .u*.r. For example, in this embodiment, the first protrusion maintaining ring 55 if bonded to the rubber f:.Jm 52, and the second protrusion maintaining ring 57 is merely arranged inside the rubber film 52 and not bonded to the rubber film 52. This allow, thL ,""ond protrusion maintaining ring 57 to move with a certain amount of freedom in thd direction along the rotation axis. Therefore, when the rubber film 52 is deformed by tfhe centrifugal force, the second protrusion maintaining ring 57 can move to a natural position. [0091] As thus far described, the yarn accumulation device 18 of this embodiment is configured such that the yarn 20 ls wound and accumulated on the yarn accumulation part 37 that is provided on the outer circumferential surface of the yarn accumulation roller 32 and such that the yarn2O is unwqund from the yam accumulation part 37 in the direction along the rotation axis of the yarn accumulation roller 32, and the 25 yarn accumulation JJ 10 device 18 has the tension applling part 38. The tension applying part 38 is arranged at the unwinding side of the yarn accumulation part3T,and configured to rotate integrally with the yarn accumulation Va\ ll and in this condition apply a tension to the yam 20 being unwound from the yarrl accumulation part 37. The tension applying part 38 includes the rubber ring 5l andl the enlarged/reduced portion 50. The rubber ring 5l is made of an expandable elastic material. The enlarged/reduced portion 50 is provided radially inside the rubber ring 5[, and configured such that the yam20 is nipped between the enlarged/reduced portion 5Q and the rubber ring 51. The enlarged/reduced portion 50 enlarges or reduces its diambter in accordance with the speed of rotation of the yarn accumulation roller 32. 100921 Nipping the yarn 20 between the rubber ring 5l and the enlarged/reduced portion 50 in this manner can apply a tension to the yarn20 being unwound from the yarn accumulation part 37. The erilarged/reduced portion 50 is configured to enlarge or reduce its diameter in accordar{ce with the speed of rotation of the yarn accumulation roller 32. Accordingly, even irf a case where the rubber ring 5l expands outward due to a centrifugal force when the speed of rotation increases, the rubber ring 5l and the enlarged/reduced portion 50 cari be kept in tight contact with each other. Thereby, an appropriate tension can be appflO to the yarn2l during rotations including a low-speed rotation and a high-speed rotatiofi. [0093] The yarn accumulatio4 device 18 of this embodiment is configured as follows. The enlarged/reduced portion 50lhas the recess 50c for restricting movement of the rubber ring 5l in the direction of the rotation axis of the yarn accumulation roller 32. The rubber ring 5l is attached in the {ecess 50c of the enlarged/reduced portion 50. [0094] This can prevent the rybber ring 51 from being dragged by the yam20 pulled out from the yam accumulation device 18 and consequently detached. l5 20 25 tl 34 t0095] In the yam accumulalion device 18 of this embodiment, the enlarged/reduced portion 50 has the recess mailrtaining mechanism 58 for maintaining the recess 50c irrespective of enlargement and feduction in the diameter of the enlarged/reduced portion 50. [00e6] Accordingly, detachnlent of the rubber ring 5l from the enlarged/reduced portion 50 can be prevented durifig both a high-speed rotation and a low-speed rotation. t0097] The yarn accumulatiorl device 18 of this embodiment is configured as follows. The outer circumferential surfale of the enlarged/reduced portion 50 is formed of the rubber film 52. The recess mailrtaining mechanism 58 includes the concavity/convexity 10 maintaining rings 55,56, and 57lhu, rr" formed along the circumferential direction of the enlarged/reduced portion 50. tfr. "on.urity/convexity maintaining rings 55,56, and 57 are made of an elastic material, a{rd ananged inside the rubber film 52. t0098] Thus, arranging concfvity/convexity maintaining rings having appropriate diameters inside a rubber fih cJn form the recess 50c in an outer surface of the rubber 15 f/rm 52 (in the outer circumferenltial surface of the enlarged/reduced portion 50). Since the concavity/convexity maintaining rings 55, 56, and 57 are made of an elastic material, the diameters of the concavity/coJrvexity maintaining rings 55, 56, and 57 can be enlarged and reduced. Therefore, the diarpeter of the enlarged/reduced portion 50 can be enlarged and reduced while the shape of thp recess 50c is maintained. t0099] The yarn accumulation device 18 of this embodiment is configured as follows. The yam accumulation roller 32 has, in its end portion at the unwinding side, the disk member 39 whose diameter is lfrger than the outer diameter of the enlarged/reduced portion 50 under a state where th{ rotation of the yam accumulation roller 32 is stopped. The enlarged/reduced portion 50 ls provided between the yarn accumulation part 37 and, 20 25 the disk member 39. 35 t0100] The yarn 20 unwound fro- the yarn accumulation part 37 comes into contact with the enlarged/reduced Rprtion 50, and then is separated away from the enlarged/reduced portion 50, tp travel while being guided by the disk member 39. Guiding the yarn 20 inthis m{nner can reduce the area over which the yarn 20 is in contact with the enlarged/reau.Ja portion 50. This can prevent fluffing of the yam 20 and a deterioration in the physibal properties of the yam 20. This can also prevent a situation where the enlarged/redilced portion 50 is rubbed by the yarn and damaged when the yarn is pulled out. , t010ll In the yarn accumulati$n device l8 of this embodiment, a portion of the rubber 10 ring 5l that cooperates with {he enlarged/reduced portion 50 to nip the yarn 20 therebetween is formed as a plang-shaped portion. [0102] This can prevent the rufber ring 5l from being twisted on the enlarged/reduced portion 50. Thus, a stable tensiofi can be applied to the yam20. t0l03l The automatic winder $f this embodiment includes the yam supply part 7, the yarn joining device 14, the yu*lu"".r-ulation device 18, the second tension applying device 19, and the winding part 8 that are arranged in this order along the direction of traveling of the yarn. The yarn lsupply part 7 supplies the yarn 20. The yarn joining device 14 joins the yam ends that irur. b.., disconnected. The second tension applying device 19 applies a tension to t{re yam 20. The winding part 8 winds the yarn 20 supplied from the yarn supply part 7 andforms a package. Even while the yarn joining device 14 is performing the yarn;fining operation, the winding part 8 is able to continue the winding with the second tensidn applying device 19 applying a tension to the yam20 unwound from the yam accumulatiln device 18. t0l04l That is, the yam u""u-Jhtion device l8 is able to apply a constant tension to l5 20 25 the yam that is being unwound dur{ng both a low-speed rotation and a high-speed rotation. 36 This facilitates a tension controllperformed by the second tension applying device l9 that is arranged downstream of the yam accumulation device 18. Additionally, since the winding part 8 winds the yam {O u..u-ulated on the yarn accumulation device 18, the winding operation can be contirfued without receiving any influence of the yarn joining operation and a fluctuation in th{ unwinding tension in the yarn supply part7. [0105] In a case where a yafir having less strength is mixed in a package, the yarn having less strength may cause { ,u.n breakage during a warper process that is a process subsequent to a rewinding operafion performed by the automatic winder. Occurrence of a yam breakage in the warper prpcess is not preferable, because it leads to a considerable 10 drop in the efficiency of proddction. Accordingly, it is preferable that such a yarn having less strength is remov$d during the rewinding operation performed by the automatic winder. [0106] The automatic winder jf this embodiment is able to apply a constant tension to a yarn that is being unwound durling both a low-speed rotation and a high-speed rotation. 15 Therefore, ayarn having less stre[rgth, which cannot withstand the constant tension, is cut at a location downstream of dhe yam path between the rubber ring 5l and the enlarged/reduced portion 50. Tfre yarn having been cut is held under a state of being nipped between the rubber ring Ct and the enlarged/reduced portion 50. This does not cause a situation where a failure in accumulation (such as slaffing or overflow) occurs because the yam end ramps arouird during a period from when the yam breakage occurs to when the yarn accumulation roller 32 is stopped. Accordingly, it is possible that, after the yam accumulation roller 32 i[ stopped, the yarn nipped between the rubber ring 5l and the enlarged/reduced portion p0 is joined with the yarn of the package side and thus the winding operation is continudd. Moreover, occurrence of a yam breakage due to a yarn having less strength during ttr{e warper process can be prevented. 20 25 .tt [0107] Next, a second embddiment of the present invention will be described with reference to FIG. 7. In the follpwing description, configuration parts identical or similar to those of the above-described]first embodiment will be denoted bythe same reference numerals on the drawings as thdse of the first embodiment, and descriptions thereof may be omitted. t0108] As shown in FIG. 7,, a yarrr accumulation roller 32 provided in a yarn accumulation device 182 of thfis embodiment includes a roller main part 61 and an extensible moving part 62ttrat islarranged at the unwinding side of the roller main part 61. The extensible moving part 62 ahd the roller main part 61 are coupled by a spline fitting 10 part 63. Thus, the roller main $art 6l and the extensible moving part 62 are configured to integrally rotate about the axis line of the yarn accumulation roller 32, and also to move relative to each other in the direcrlion of the axis line. 10109] The roller main part 6l includes the yarn accumulation part 37. One axial end portion of the rubber film 52 is fi]