Patent Publication Number: US-6901776-B2

Title: Method of knitting an elastomeric yarn into a circularly knitted fabric

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 10/379,635 filed Mar. 5, 2003, now U.S. Pat. No. 6,810,694. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a method for knitting an elastomeric yarn into a circularly knitted fabric. 
     2. Description of Related Art 
     It is highly desirable to incorporate elastomeric yarns into knitted fabrics intended for the creation of garments. For example, the elastomeric yarn can provide a degree of elasticity to the knitted fabric, which is useful in many garments such as socks, brassieres, panties, underwear, bathing suits, leotards, and the like. 
     Generally, incorporating such yarns into a knitted structure as knitted stitches, as opposed to laying-in the yarn, is difficult due to the need to knit these yarns under tension. Further, incorporating such yarns into a knitted structure as knitted stitches is particularly difficult when using circular knitting machines such as those commercially available from Santoni S.p.A. (e.g., Santoni&#39;s SM8 knitting machine). 
     A prime difficulty arises at the start and finish of the knitting process when the elastomeric yarn is introduced and subsequently taken out of the knitting sequence. This difficulty arises from the fact that at the finish of a knitting sequence, the elastomeric yarn has to be severed, but held under tension in readiness for reintroduction at the start of the next knitting sequence. 
     Prior suction holding mechanisms for nonelastomeric yarns have not proven effective for elastomeric applications. In addition, prior mechanical clamping or holding systems for holding severed elastomeric yarns have proven to be overly expensive and complex. 
     Difficulties are also encountered in reliably introducing the elastic yarn into the needles for take-up at the start of a knitting sequence. In order to compensate for this difficulty, it is common to slow the speed of the knitting machine. Slowing the knitting machine allows the elastic yarn to be effectively incorporated into the fabric, which has not been possible at normal machine speeds where the elastic yarn tends to pull free from the fabric. 
     In view of these difficulties, it is common practice to either only introduce bare elastomeric yarn at the beginning of a knitting cycle and knit bare elastomeric yarn throughout the entire cycle, or to have reduced productivity as a result of the slowed machine speeds. 
     However, there is a continuing desire for apparatus and methods that can provide for the selective elastomeric yarn knitting, while addressing one or more of the aforementioned deficiencies of the prior art. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for introducing elastomeric yarns into a knitting cycle in a more reliable manner than previously possible. 
     It is another object to provide a method for selectively knitting elastic yarns during selected parts of a knitting cycle. 
     These and other objects of the present invention are provided by a method for circularly knitting an elastomeric yarn into a knitted fabric. The method includes: operating a circular knitting machine at a machine rate, retaining a free end of the elastomeric yarn in a substantially relaxed condition, and taking up the free end into the circular knitting machine while feeding the elastomeric yarn at a first feed rate. The first feed rate maintains the elastomeric yarn in the substantially relaxed condition. The circular knitting machine continues to operate at the machine rate during the taking up of the free end. 
     A method of knitting an elastomeric yarn with a circular knitting machine is also provided by the present invention. The method includes initiating a first and a second knitting stage. The first knitting stage maintains the elastomeric yarn in a substantially relaxed condition while maintaining a free end of the elastomeric yarn in a desired position. The second knitting stage causes the circular knitting machine to take up the elastomeric yarn in the substantially relaxed condition by positively feeding the elastomeric yarn at a first feed rate. The circular knitting machine maintains the desired machine rate during the take up of the elastomeric yarn. 
     It is a further object of the present invention to provide a method for knitting elastomeric yarn on a circular knitting machine to produce knitted stitches of the elastomeric yarn. The method includes: retaining a free end of the elastomeric yarn in a substantially relaxed condition in readiness for introduction to needles of the circular knitting machine; introducing the free end for take-up by the needles; feeding the elastomeric yarn at a first feed rate sufficient to maintain the substantially relaxed condition of the free end during take-up by the needles; feeding the elastomeric yarn at a second feed rate to cause tension in the elastomeric yarn to be raised to a desired level during continued knitting; feeding the elastomeric yarn at a third feed rate to cause the elastomeric yarn to be regain the substantially relaxed condition; severing the elastomeric yarn to define a new tail; and retaining the new tail in the relaxed condition. 
     The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of an exemplary embodiment of a circular knitting machine according to the present invention; 
         FIG. 2  is a first side view of the machine of  FIG. 1 ; 
         FIG. 3  is a second side view of the machine of  FIG. 1 ; and 
         FIGS. 4 through 8  schematically illustrate various stages of a knitting process according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to she drawings and in particular to  FIGS. 1 through 3 , a circular knitting machine generally indicated by reference numeral  10  is illustrated. Circular knitting machine  10  has a cylinder or base  12  with a plurality of needles  14  disposed about its periphery. Machine  10  rotates needles  14  about a central axis  16  while reciprocating the needles between an upper position  18  and a lower position  20  as illustrated in phantom in  FIGS. 2 and 3 . Thus, machine  10  moves and reciprocates needles  14  to perform a knitting operation according to known principles. 
     Machine  10  can also receive one or more elastomeric yarns  22  from a feeding system  24 . For purposes of clarity, machine  10  is illustrated receiving only one elastomeric yarn  22  from one feeding system  24 . Of course, it is contemplated for machine  10  to have more than one feeding system, and for at least some of the feeding systems to feed more than one yarn to machine  10 . 
     Feeding system  24  has a guide  26 , a drive  28 , a spool or supply of yarn  30  (hereinafter “supply”), and a suction hood  32 . 
     Drive  28  pulls yarn  22  from supply  30 , and feeds the yarn to guide  26 . For example, drive  28  can be a servo-motor, a stepper motor, or any such motor. Preferably, drive  28  is an Elan2 (RTM). Drive  28  can be controlled by a programmable controller (not shown) of machine  10 . Alternately, drive  28  can be controlled by a programmable controller separate from, but in communication with, the controller of machine  10 . 
     Guide  26  is movable by machine  10  between a first position  34  ( FIG. 2 ) and a second position  36  (FIG.  3 ). When guide  26  is in first position  34 , it prevents yarn  22  from being taken-up by needle  14 . First position  34  of guide  26  holds yarn  22  out of reach of needle  14 , regardless of whether the needle is in its upper or lower position  18 ,  20 , respectively. For example, first position  34  of guide  26  can hold yarn  22  above needle  14  as illustrated. 
     However, guide  26  moves yarn  22  into the path of needle  14  when the guide is in its second position  36 , which allows the yarn to be taken-up by the needle. Second position  36  of guide  26  holds yarn  22  such that needle  14  takes-up the yarn when the needle is in its upper position  18 . For example, second position  36  of guide  26  can hold yarn  22  at or below needle  14  in its upper position  18  as illustrated. 
     Movement of guide  26  between first and second positions  34 ,  36  is illustrated by way of example only as being parallel to central axis  16 . Of course, it is contemplated by the present invention that guide  26  be movable either normal to central axis  16  or a combination of both parallel and normal to the central axis. 
     Suction hood  32  is disposed on base  12  in a position opposed to guide  26 . Suction hood  32  has a suction port  38 , which pulls a free end  40  of yarn  18  into the hood through the suction port. For example, suction hood  32  can evacuate air  42  to cause a negative pressure condition within the hood. The negative pressure within suction hood  32  draws air  44  into the hood at suction port  38 . The flow of air  44  into suction hood  32  pulls free end  40  into suction port  38  and, thus, maintains the free end in a desired location on base  12 . 
     Preferably, suction port  38  and guide  26  are radially aligned with respect to one another. In this configuration, free end  40  of yarn  22  is maintained in an optimal position with respect to needles  14  to ensure reliable introduction into the needles, when required. Preferably, suction hood  32  maintains free end  40  radially aligned with respect to the central axis  16  and perpendicular to the direction of travel of needles  14 . 
     The interaction of feeding system  24  with machine  10  is described in its various stages with reference to  FIGS. 4 through 8 . 
     In  FIG. 4 , machine  10  is performing a first stage  46  of a knitting process, which does not include the knitting of elastomeric yarn  22 . Here, base  12  is rotating and needles  14  are reciprocating such that other yarns (not shown for purposed of clarity) are being knitted in a known manner. Thus, machine  10  is operating at a desired machine rate. 
     During first stage  46 , drive  28  is not pulling yarn  22  from supply  30 . Free end  40  of the yarn is held in the desired position by suction hood  32 , while guide  26  is at its first position  34  such that yarn  22  is maintained out of reach of needles  14 . Accordingly, yarn  22  between drive  28  and free end  40  is in a substantially relaxed or slack condition, with the only tension being applied by the degree of suction applied by suction hood  32 . However, the amount of tension applied by suction hood  32  is sufficient to maintain free end  40  in the desired position relative to base  12 . Thus, feeding system  24  maintains yarn  22  for introduction into the knitting process, when desired. 
     First stage  46  outlined above may be considered to be a passive phase of the process, i.e. during this phase the elastomeric yarn is static and held in readiness for introduction into the knitting process. 
     A second stage  48  of the knitting process is illustrated in FIG.  5 . This is the beginning of the active phase of the process, i.e. the phase during which actual knitting of elastomeric yarn  22  is performed. 
     In second stage  48 , elastomeric yarn  22  is introduced to needle  14  for knitting, i.e. the second stage is the initial take-up of elastomeric yarn. In the second stage  22 , guide  26  is moved to its second position  36  to bring yarn  22  into the path of needles  14 . 
     Prior to free end  40  being taken-up by needle  14 , drive  28  is controlled to positively feed yarn  22  at a first feed rate. Preferably, drive  28  is controlled to begin positively feeding yarn  22  before or as guide  26  is moved to its second position  36 . 
     The first feed rate is selected to maintain yarn  22  at the substantially relaxed or slack condition as it is taken up by needle  14 . Thus, the first feed rate of drive  28  feeds yarn  22  at a rate substantially equal to the rate with which machine  10  is drawing the yarn into the machine. The rate with which machine  10  draws yarn  22  into the machine can depend on the machine rate and other factors, such as, but not limited to, the size and rate of rotation of base  12 , the number of needles  14 , and others. Moreover, the first feed rate of drive  28  compensates for the elastic properties of yarn  22  as it is taken up by needle  14 . 
     Drive  28  continues to feed yarn  22  at the first feed rate until at least one needle  14  descends to lower position  20 , allowing a knitted stitch  50  to be formed as illustrated in FIG.  8 . Knitted stitch  50  secures free end  40  in the resultant knitted fabric. For purposes of clarity, various components of feeding system have not been is illustrated in FIG.  8 . 
     A third stage  52  of the knitting process is illustrated in FIG.  6 . Third stage  52  represents the “normal” knitting phase of the process whereby yarn  22  is knitted into the resultant knitted fabric at a desired pretensioned or stretched condition. 
     In order to provide yarn  22  with the pretensioned condition in the resultant knitted fabric, drive  28  is controlled to positively feed yarn  22  at a second feed rate. The second feed rate is slower than the first feed rate and, thus, feeds yarn  22  at a rate slower than the rate with which machine  10  is drawing the yarn into the machine. In this manner, the second feed rate causes a rise in the tension of elastomeric yarn  22  between drive  28  and needles  14  to a desired “knitting” tension. 
     The knitting tension can be varied in yarn  22  by varying the second feed rate with respect to the rate with which machine  10  is drawing the yarn into the machine. Accordingly, the second feed rate can be a constant feed rate or can be a variable feed rate, to provide the desired knitting tension, which itself can be constant or variable within the garment. 
     Since third stage  52  increases the tension in yarn  22 , it is preferably initiated after the yarn has been knitted or trapped within a sufficient number of knitted stitches  50  so as to prevent free end  40  from being pulled from needles  14  upon application of the knitting tension. Thus, drive  28  is controlled to initiate third stage  52  after sufficient needles  14  have taken-up yarn  22  and moved to lower position  18 . This is indicated diagrammatically in  FIG. 5  as a distance  54 . Preferably, third stage  52  is initiated at a predetermined time delay from commencement of second stage  48 . 
     In order to stop knitting of elastomeric yarn  22 , it is necessary to sever the yarn with a cutter (not shown) of machine  10 . However, severance of yarn  22  can not be performed while the yarn is under its knitting tension; to do so would cause the yarn to elastically recover to its relaxed condition, causing the yarn to unthread from guide  26  so that it is not captured by suction hood  32 . Thus, a fourth stage  56  of the knitting process, illustrated in  FIG. 7 , is provided. 
     In fourth stage  56 , drive  28  is controlled to positively feed yarn  22  at a third feed rate. The third feed rate is chosen to maintain yarn  22  at the substantially relaxed or slack condition as it is taken up by needle  14 . Thus, the third feed rate of drive  28  feeds yarn  22  at a rate substantially equal to the rate with which machine  10  is drawing the yarn into the machine and at a rate that compensates for the knitting tension induced in the resultant fabric. 
     Accordingly, at the time when machine  10  severs yarn  22 , to create a new free end  40 , the yarn between drive  28  and suction hood  32  has already elastically recovered to its substantially relaxed state. Thus, due to its relaxed state, yarn  22  does not retract to unthread itself from guide  26  when severed, but instead is drawn into suction hood  32 . Substantially simultaneous with the severing of yarn  22 , fourth stage  56  controls drive  28  to stop positively feed yarn  22 , i.e. it is switched off, while guide  26  is moved back to its first position  34 . The knitting process has now progressed back into the passive phase (first stage  46 ) and is ready for the next knit or knitting cycle. 
     First through fourth stages  46 ,  48 ,  52 , and  56  can be repeated as desired within the same garment. Thus, a resultant garment can be provided by the method and apparatus of the present invention that has elastomeric yarns selectively incorporated therein. Importantly, positively feeding elastic yarn  22  into machine  10  allows the yarn to be incorporated into the resultant fabric while maintaining (e.g., without slowing) the machine rate of machine  10 . 
     The above method and apparatus are described by example only in relation to operation on an electronically controlled circular knitting machine having a plurality of yarn feeds around a needle cylinder. A suitable machine is a SM8 Santoni knitting machine; of course, other circular knitting machines are contemplated for use with the present invention. For such a machine, it is envisaged that each feed station would be provided with its own suction hood  32  and its own feeding system  24 . 
     It should also be noted that the terms “first”, “second”, “third”, “upper”, “lower”, and the like may be used herein to modify various elements. These modifiers do not imply a spatial, sequential, or hierarchical order to the modified elements unless specifically stated. 
     While the present invention has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this invention, but that the present invention will include all embodiments falling within the scope of the appended claims.