Patent Publication Number: US-6213419-B1

Title: Elastic anti-ballooning band on a yarn feeder

Description:
FIELD OF THE INVENTION 
     The present invention relates to a yarn feeder including a housing for a drive motor and a drive shaft, a yarn winding on element which rotates with the drive shaft, a stationary storage drum having a cylindrical, circumferentially closed section, and a stationarily held ring-shaped yarn control element surrounding the circumferential section between a yarn store section and a yarn withdrawal section of the storage drum. 
     BACKGROUND OF THE INVENTION 
     In a yarn feeder as known from GB-C-1355518 (FIG. 9) the yarn control element is formed as a stable hollow body supported separately from the storage drum and put over the withdrawal end at the front side of the storage drum. The yarn control element surrounds the cylindrical circumferential section of the storage drum with radial distance by its big diameter cylindrical end portion. In this case the yarn control element minimizes the formation of a balloon during withdrawal of the yarn from the yarn store on the storage drum overhead of the withdrawal region into a withdrawal eyelet positioned in front of and co-axially relative to the storage drum. Among other influences the yarn orbiting around the withdrawal region due to centrifugal force tends to separate in an arch shape from the circumference of the storage drum and to form a spiral shaped ballooning-configuration downstream into the withdrawal eyelet. This known phenomena of the balloon formation leads to strong mechanical loads in the yarn, to an increasing tension in the withdrawn yarn and to yarn breakages, respectively. These disadvantages are eliminated by suppressing the balloon formation by means of the yarn control element. However, due to its distance from the circumferential surface of the storage drum the yarn control element does not suffice to guarantee a uniform and pre-determined basic tension in the withdrawn yarn. For this reason and as mentioned in GB-1355518 in addition to and upstream of the yarn control element frequently a so called brush braking ring is installed at a bracket fixed to the housing, the bristles of which contact the drum and brake the yarn in order to guarantee the necessary yarn withdrawal tension. However, a brush braking ring has, for mechanical reasons, the disadvantage of a speed-dependent braking effect i.e. a braking effect raising the yarn tension with increasing speed. This is a disadvantage, since the withdrawal tension should remain approximately uniform within a broad speed range in order to achieve optimal insertion relations in the weaving machine. 
     It is an object of the present invention to create a yarn feeder of the kind as disclosed above in which in a structurally simple way an essentially constant yarn withdrawal tension can be achieved in conjunction with the balloon limiting function. This object can be achieved by providing a yarn control element configured as a finite band having a planar cross section, which band is laid on the cylindrical circumferential section with mutually aligned adjacent ends. The band is resistant against extension in circumferential direction of the storage drum and is yieldable in the radial direction of the storage drum, and an elastic tensioning device is provided which preloads the band against the circumferential section. 
     The yarn is pulled through between the lower side of the band and the cylindrical circumferential section of the storage drum and in addition orbits in the circumferential direction during its withdrawal movement. The mechanical obstacle of the band suppresses the balloon formation tendency of the yarn extremely effectively. Further, a uniform and precisely pre-determinable braking effect is exerted onto the yarn by the contact pressure of the band against the circumferential portion, which braking effect surprisingly remains constant with yarn speed variations. In this way the balloon formation is suppressed by the yarn control element and simultaneously an essentially constant yarn withdrawal tension is achieved. The yarn has to overcome the elastic pre-load spanning or forcing the band onto the circumferential section only at its passing location below the band which in the circumferential area of the passing location remains supported on the circumferential section. Thanks to the yieldability of the band in the radial direction the yarn is forming so to speak an orbiting wave in the band or a sickle shaped free space, respectively, such that at this deformation the deformation resistance of the band remains essentially constant and independent of the speed. Since the perpendicular force on the yarn resulting from the pre-load of the band against the circumferential section remains essentially constant and is independent of speed, and due to the constant friction coefficients between the yarn and the band and the circumferential section, respectively, the advantageous result is that the yarn withdrawal tension remains essentially constant. The reasons for this positive effect of the yarn control element cannot be judged precisely. However, the result of the co-operation between the yarn, the band and the circumferential section, namely an essentially constant yarn withdrawal tension, is convincing. Unexpectedly even the gap between the ends of the band does not disturb the uniform braking effect, apparently since due to the dynamic movement relations the yarn does not feel the circumferential interruption in the band, provided that the yarn direction is inclined in relation to the direction of the circumferential gap. 
     Suitably the band is of flexible metal or plastic. Furthermore the use of a compound-band is possible having a wear resistant layer and in connection therewith another layer with differing properties. 
     The band in one embodiment includes a circumferential interruption so that two terminal ends are formed. The terminal ends of the band are parallel to one another and inclined, and the circumferential interruption in the band is as small as possible. The direction of the ends of the band is selected such that the yarn never will pass across the circumferential interruption with parallel orientation. 
     The band can be elastically pre-loaded by a tensioning device and is positioned on the circumferential section exclusively by frictional contact. The friction at the circumferential section is used to suppress an axial wandering of the band under the drag of the yarn. 
     The band can be positioned on the storage drum by means of a circumferentially extending shoulder. In this way bands of random widths can be positioned safely and with low tension for sensitive yarn materials. 
     In one embodiment, the band together with the tensioning device is supported in a holder and is positioned on the circumferential section by means of the holder. The holder, which is oriented parallel to the axis of the storage drum, is adjustable and is mounted in a bracket which is fixed to the housing and extends along the circumference of the storage drum. Thus, the position of the band is assured by the holder, suitably allowing an adjustment of the band in the longitudinal direction of the storage drum, and the holder also takes up occurring axial forces. 
     At the yarn entrance side of the band, a circumferentially extending depression is provided in the storage drum circumference, or the cylindrical circumference section is configured to project outwardly beyond the storage drum circumference at the yarn entrance side. In accordance with this embodiment, a significantly gentle yarn entrance below the band is achieved. 
     The tensioning device is provided with a spring element which at least bridges the circumferential interruption between the ends of the band. The spring element is connected with the band at least locally, and preferably is constructed of a tensioned elastomeric material, rubber strip or a tension spring. In this embodiment, tension is brought into the band exclusively by the spring element which at least bridges the circumferential gap of the band and pulls both ends of the band towards each other and produces in this way radial contact pressure. 
     In the alternative embodiment, the tension and the contact pressure of the band can be varied by means of a tension adjustment device in order to adapt to different withdrawal conditions or different yarn materials 
     In yet another embodiment the tensioning device is an annular magnet provided in the storage drum. Thus, the band is radially pressed against the circumferential section by magnetic effects. 
     Alternatively a circumferentially closed tension ring serves to span the band. The tension ring suitably is made from a material which does not produce a significant resistance against the wave shaped deformation of the band due to the influence of the yarn. 
     In another embodiment, the tensioning ring is open and includes overlapping ends. The tension ring spanning the band uniformly about the circumferential section can thus be adjusted in its length in order to vary the tension. 
     The tension ring can be made of plastic foam material or rubber, or may be formed as a ring-shaped coil spring. This construction is particularly advantageous since plastic foam material, elastomeric material, or rubber or even a ring-shaped coil spring lead to constant spring properties for long durations, and are contamination-proof. Particularly, homogenous materials have a negligible resistance against the wave motion of the band. 
     In an alternative embodiment the tension ring is designed as an annular membrane of rubber or elastomeric material. 
     In yet another alternative embodiment, the tension ring is in the form of a ring body with spokes or teeth. This type of tension ring simultaneously can be used to position the band in the axial direction. 
     A particularly advantageous embodiment includes a tension ring configured as a hollow, tubular and inflatable ring. The ring tube per se is able to produce a circumferential tension. Depending upon the degree of inflation, the tension or the radial pressure, respectively, can be varied and adjusted precisely, even without a tension adjustment device. 
     In another embodiment the band is solely fixed by friction, namely with the counter pressure of the storage drum. 
     In still another alternative embodiment the band at least in sections is connected with the tension ring. This can be of advantage for mounting reasons. In case of foam material, rubber or elastomeric material the connection can be made by in-situ forming, vulcanisation or bonding and for that reason can be made very uniformly such that a completely uniform response behaviour of the band is achieved for the passage of the yarn. 
     The tension ring can be as broad as the band, in which case a uniform back-up contact is achieved over the width of the band. Since the band already is rigid against bending in lateral direction due to its shape and due to the contact with the storage drum the tension ring may even be made narrower than the band. 
     In another embodiment the band is supported in the holder via the tension ring or by means of a carrier ring surrounding the tension ring. No special positioning of the band on the storage drum is needed. 
     In yet another embodiment, the tension adjustment device is provided at the holder or at the carrier ring of the tension ring. The variation of the tension of the band is possible by increasing or reducing the circumferential length of the holder or the carrier ring of the tension ring such that the tension ring can be biased more or less. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described in conjunction with the drawings, in which: 
     FIG. 1 illustrates a schematic side view of a yarn feeder; 
     FIG. 1A illustrates a detail variation of the tension ring; 
     FIG. 2 illustrates a section of a modified embodiment; 
     FIG. 3 is a plan view of the FIG. 2 embodiment; 
     FIG. 4 illustrates a detail variation; 
     FIG. 5 illustrates a detail in a side view seen in the direction of the axis of the storage drum, which detail can be used in the embodiment of FIGS. 2 and 3; 
     FIGS. 6A,  6 B, and  6 C illustrate another variation in a section and in views according to the direction of the storage drum axis; 
     FIGS. 7 and 8 detail variations in sections, similar to FIG. 6A; 
     FIGS. 9 and 10 illustrate a further detail variation in a section and a side view; 
     FIG. 11 illustrates a further detail variation in a sectional view; and 
     FIG. 12 illustrates a further detail variation in schematical illustration. 
    
    
     DETAILED DESCRIPTION 
     A yarn feeder F in FIG. 1, typically used to feed a weaving machine with a weft yarn, includes in a stationary housing  1  a drive motor M for a driveshaft  2  shown by its axis. A winding on element  3  is connected to driveshaft  2  for co-rotation. On driveshaft  2  co-axially a storage drum T is rotatably supported, and is not allowed to rotate with driveshaft  2 . The yarn Y enters housing  1  in FIG. 1 from the left side, is then wound onto a circumferential surface  6  of storage drum T in subsequent windings into a yarn store  4  by the rotating winding on element  3  and finally, is withdrawn overhead of the storage drum by the weaving machine depending on consumption, either directly by means of a not shown insertion device and without using a yarn eyelet, or through a yarn eyelet  10  provided co-axially with the storage drum T on a bracket  9  of housing  1 . The circumferential surface  6  of the storage drum forms a yarn storing section  5  and a withdrawal section  7 , respectively. Between both sections  5 ,  7  a circumferentially continuous cylindrical section  8  is provided. 
     Said circumferential section  8  is surrounded by a yarn control element S with the form of a thin walled band B with a planar cross-section, extending in the circumferential direction. The band B does not form a closed ring but is finite with its ends,  16 ,  17  facing each other in the region of a gap  18 . Said gap  18  may run axially or as shown at  18 ′ obliquely in relation to the axis of storage drum T. Suitably said gap is oriented such that the yarn Y withdrawn from the yarn store  4  during its passage underneath band B passes the gap  18  with an inclined orientation and never parallel to gap  18 . 
     Said band B either consists of metal, a metal alloy or of plastic material, or is a compound band, is resistant against extension in longitudinal direction but flexible such that it can be deformed easily in the radial direction of the storage drum. Said band B surrounds the circumferential section  8  with direct contact and essentially uniform contact pressure which is produced by means of a tensioning device acting on the band B. 
     In the simplest form (FIG. 4) the tensioning device is a finite strip  30  made of plastic material, e.g. plastic foam material, rubber or elastomeric material, which bridges the circumferential gap  18  and is bonded to the band B in the areas  31 , e.g. by gluing, vulcanisation or the like. The band B should be homogenous over its length. A positive connection between the strip  30  and band B might be possible but is not suitable. The length of band B is adapted to the circumferential length of circumferential section  8  such that the ends defining circumferential gap  18  are as close as possible to each other without contacting or overlapping each other. As soon as band B is brought onto circumferential section  8  strip  30  or the tensioning device is under tension by which the band becomes spanned and is pressed with uniform contact pressure onto circumferential section  8 . 
     In the embodiments of FIG. 1 the tensioning device consists of a circumferentially closed tension ring  15  which e.g. consists of plastic foam material, plastic, rubber or elastomeric material. Tension ring  15  is dimensioned such that it at least presses the band in the radial direction against the circumferential section and, preferably, generates a tension in the circumferential direction. The tension ring  15  in FIG. 1 is a foam material ring having essentially the same width as the band. The plastic foam material ring  15  can be surrounded by a closed carrier ring in which the pre-loaded plastic foam material ring  15  is supported. 
     The band could be positioned on the circumferential section together with its tensioning device solely by friction contact. In FIG. 1 another kind of positioning is selected, since the carrier ring  20  is supported in a ring shaped holder  13  which itself is held by a sleigh  11  mounted in bracket  9 . Said sleigh  11  suitably can be shifted by means of a longitudinal adjustment device  12  in order to hold the band B at an axial optimal position were the balloon formation of the yarn Y is considerably suppressed and a uniform braking effect can be achieved. 
     FIG. 1A illustrates the tension ring  15  as an annular rubber- or elastomeric membrane  19  either only lying on the band B or connected within separate distinct regions (e.g. by vulcanisation). Said membrane  19  is held by a surrounding carrier ring  20  supported by holder  13 . 
     In FIG. 2 another embodiment is indicated in a sectional view. In this embodiment the storage drum is built with axial rods being moveable in relation to another in order to separate the yarn windings in said yarn store  4 , such that said rods define the circumferential surface  6  of the storage drum. In withdrawal direction of the yarn downstream of yarn storing section  5  and in front of withdrawal region  7  the cylindrical circumferential section  8  is situated such that it protrudes outwardly relative to circumferential surface  6 . At the entrance side of the yarn a circumferentially continuous depression  21 , e.g. a conical chamfer, is formed above which the band B with one edge is freely projecting. By said structural measure the yarn Y will find a suitable gradually tapering entrance gap. The tension ring  14  is a rubber- or elastomeric band  23  generating the contact pressure for the band B. In addition according to FIG. 2 a circumferentially continuous shoulder  22  can be provided in the withdrawal direction behind said circumferential section  8  in order to position band B. 
     In order to allow the tension generated by tension ring  14  to vary, band  23  is designed finite with mutually overlapping ends  25  and  24  according to FIG. 3, such that pointed end  24  engages into bifurcated end  25 . As indicated in dotted lines at  28  the ends  24 ,  25  are connected with each other in order to transmit the tension of the tension ring  14  onto the band B. In region  26  and  27  tension ring  14  is connected with the band, e.g. by gluing points. Several gluing points or areas can be distributed along the circumference. It also is possible to connect the tension ring in its entire surface area with the band. In region  28  where ends  24 ,  25  are connected with each other, furthermore a tension adjustment device  29  could be provided in order to allow to vary the tension of tension ring  14 . 
     According to FIG. 5 a holder  32  for a tension roll  33  is provided as a tension adjustment device  29 . Holder  32  is designed with a curved lower side adapted to the curvature of band B. End  25  is secured to holder  32 . End  24  can be tightened or loosened by rotating the tension roll  33  in order to vary the tension of the tension ring  14  or the contact pressure of the band B, respectively. Holder  32  can be provided in a holder similar to holder  13  on bracket  9 . 
     According to FIG. 6A the tension ring  14  (FIG. 1) is as broad as band B. Tension ring  14  can be a plastic foam material ring  15  or the like. In dotted lines a conical entrance inclination  21  is indicated. When forming a plastic foam material ring  15  its inner circumference is measured such that it is suitably somewhat shorter than the circumferential extension of circumferential section  8  such that according to FIG. 6C the ends of band B overlap each other prior to installing the band B at the storage drum. In this overlapping-region a free space  34  can be provided in the plastic foam material ring  15 . If then the band B is installed on the circumferential section according to FIG. 6B then said ends will lie opposite to each other and the free space  34  will be enlarged. In this way the tension will be transmitted into the band B or the radial contact force will be generated uniformly, and the band can operate as intended. 
     In FIG. 6B a modified embodiment of the tension adjustment device  29  is illustrated. The carrier ring  20  of plastic foam material ring  15  is designed with a circumferential interaction in the region of which between two spaced apart flanges an adjustment device is engaging in order to enlarge or reduce the circumferential length of the carrier ring, respectively, and in order to vary the pre-load of the plastic foam material ring. With similar design said tension adjustment device could be integrated into the holder  13  according to FIG.  1 . 
     FIG. 7 shows that the tension ring  14 , e.g. a rubber- or plastic foam material ring  15 , is narrower than the band B. Suitably carrier ring  20  is provided in order to support tension ring  14 . In a case in which the band B with tension ring  14  is to be positioned on circumferential section  8  without external support by means of friction contact or with the help of the shoulder according to FIG. 2, carrier ring  20  also could be omitted. 
     In FIG. 8 a possible embodiment of tension ring  14  in the form of an annular rubber membrane  19  is indicated which is surrounded by a carrier ring  20  in order to allow to support the band B by means of the tension ring  14  in the not shown holder. 
     FIGS. 9 and 10 relate to an embodiment in which the tension ring  14  is designed as a ring body  20 ′ having inwardly protruding teeth or spokes  35  engaging at the band B and optionally even connected therewith. Said teeth or spokes  35  are elastic and are inclined in relation to the radial direction on the axis of the storage drum. At  36  connection zones could be provided. 
     In FIG. 11 tension ring  14  is defined by an annular tube  36  of elastic material, e.g. rubber or an elastomeric material, the inner hollow space of which can be inflated via a valve  37  by a suitable medium, e.g. air, in order to vary the tension of the band B. Tension ring  14  is supported by carrier ring  20 . Said tension ring  14  could, occasionally, be connected with band B at location  38 . However, it is possible, to position band B in tension ring  14  by friction contact only. 
     In FIG. 12 band B consisting of metal is pulled against the circumferential section  8  by means of an annular magnet arrangement  39  inside storage drum. The magnet arrangement  39  could consist of several separate magnets  39 ′ positioned in an array. In this case band B is not adjusted in the circumferential direction of circumferential section  8  but is only uniformly pressed on circumferential section  8  by radial magnetic forces. 
     The band B may have a thickness of about 0.2 mm and a width between 5 and 55 mm and may occasionally have an inner wear proof surface which is treated or coated. However, said band should be flexible enough so as to be deformable radially and only locally by the yarn in order to form a sickle shaped yarn passage opening with the circumferential section of the storage drum. 
     Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.