Patent Publication Number: US-6901871-B1

Title: Bobbin case assembly with thread tensioning element and method of drawing thread from a thread supply

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to stitching systems utilizing a bobbin case assembly from which a stored supply of thread is drawn and, more particularly, to a bobbin case assembly having an associated thread tensioning element against which the thread paying off of the supply acts to produce controlled resistance to the payout of thread from the supply. 
   2. Background Art 
   In sewing/stitching operations, and particularly in embroidery operations, the tension of two source components forming the lockstitch needle thread and bobbin thread must balance to achieve a high quality stitch. If the tension in the needle thread is significantly greater than the bobbin thread tension, the bobbin thread can be pulled from through the underside of the fabric and show at the top side of the fabric being sewn. This condition can cause puckering of the fabric or disfigured sewing to occur. If the needle thread tension is significantly less than the bobbin thread tension, loops can form on either side of the fabric and the stitching formation can appear loose or distortedly large. 
   A primary job of a sewing equipment operator is to keep bobbin and needle thread tensions as close as possible to balanced. The method of balancing thread tension has historically been carried out by having the sewing operator observe the pattern after stitches are laid down. Good sewing operators constantly adjust the tension of both needle and bobbin threads to maintain the proper balance. Less skilled operators may not consistently maintain this balance as a result of which poor quality stitch formation may result. 
   The assignee herein is the owner of U.S. Pat. No. 6,152,057, which is directed to a bobbin case assembly with an associated tensioning element having a circumferential surface about which thread is wrapped to controllably increase thread draw tension. During setup, the sewing equipment operator can control the degree of wrapping of the thread around the tensioning element to thereby select the desired thread draw tension associated with that bobbin case assembly. This potentially obviates complex and time consuming adjustment procedures used in conventional sewing systems, which may incorporate a large number of sewing “heads”. While the system disclosed in U.S. Pat. No. 6,152,057 represents a tremendous contribution to the industry, there are some inherent limitations associated therewith. 
   First of all, in the event that a significant increase in draw tension is required, multiple wraps of the thread around the tensioning element may be required. This results in a spiral arrangement of the thread around the tensioning element. The spiral pattern of the wrapped thread may shift during operation relative to the tensioning element, which may result in an appreciable draw tension variation. 
   The industry continues to seek out ways to predictably select draw tensions, maintainable at or close to a desired value, without complicated setup procedures or excessive adjustment as the system is monitored both at start-up and during use. 
   SUMMARY OF THE INVENTION 
   In one form, the invention is directed to a bobbin case assembly having a wall structure mountable upon a support, a bobbin for a supply of thread, and a tensioning element for engaging thread projecting from a supply of thread on the bobbin. The tensioning element has a length and a circumferential surface against which thread can be wrapped so that a frictional resistance force can be generated between the thread and circumferential surface that resists drawing of thread off of the supply. The tensioning element has a configuration that limits lengthwise shifting of a spirally wrapped portion of thread wrapped against the circumferential surface. 
   In one form, the tensioning element has an edge to which thread can abut to limit lengthwise shifting of a spirally wrapped portion of thread wrapped around the circumferential surface. 
   In one form, the tensioning element has an elongate body and the edge is defined by a bend in the elongate body. 
   In one form, the edge is defined by a projection from the circumferential surface. 
   The edge may be defined by an undercut in the circumferential surface. 
   In one form, the body has a diameter and a first diameter portion and a second diameter portion. The edge is defined at a juncture between the first diameter portion and the second diameter portion. 
   In another form, the body has an angled portion at which the edge is defined. 
   The edge may alternatively be defined by texturing the circumferential surface. 
   In one form, the circumferential surface is defined on a body portion having a length with a diameter, a first end, and a second end. The diameter of the body portion increases between the first end and the second end so that thread is spirally wrapped against the circumferential surface is limited against lengthwise shifting between the first and second ends of the body portion. 
   In one form, the tensioning element has a plurality of edges to which thread can abut to limit lengthwise shifting of thread spirally wrapped against the circumferential surface. 
   The invention is further directed to the combination of a) a bobbin case assembly having a wall structure mountable upon a support, a bobbin, and a supply of thread wrapped on the bobbin, and b) a thread drawing assembly for exerting a tension on the thread to draw the thread from the supply. The bobbin case assembly further has a tensioning element with a length and a circumferential surface. The thread extends from the supply and is wrapped against and at least partially around the circumferential surface so that a frictional resistance force is generated between the thread and circumferential surface that resists drawing of the thread off of the supply. The tensioning element has a configuration that limits lengthwise shifting of a spirally wrapped portion of thread wrapped against the circumferential surface. 
   In one form, the tensioning element has an edge to which the thread can abut to limit lengthwise shifting of the spirally wrapped portion of thread wrapped against the circumferential surface. 
   In one form, the tensioning element has an elongate body and the edge is defined by a bend in the elongate body. 
   The edge may be defined by a projection from the circumferential surface. 
   In another form, the edge is defined by an undercut in the circumferential surface. 
   In one form, the tensioning element has a body with a diameter and a first diameter portion and second diameter portion. The edge is defined at a juncture between the first diameter portion and the second diameter portion. 
   In one form, the body has an angled portion at which the edge is defined. 
   In another form, the edge is defined by texturing the circumferential surface. 
   In one form, the circumferential surface is defined on a body portion having a length with a diameter, a first end, and a second end. The diameter of the body portion increases between the first and the second ends so that thread spirally wrapped against the circumferential surface is limited against lengthwise shifting between the first and second ends of the body portion. 
   The combination may further include at least one component for stitching using thread drawn from the supply by a thread drawing assembly. 
   The combination may further include a support to which the wall structure is mounted. 
   In one form, the tensioning element has a plurality of edges to which the thread abuts to limit lengthwise shifting of thread spirally wrapped against the circumferential surface. 
   The invention is further directed to a method of drawing thread from a supply of the thread that is wrapped around a bobbin. The method includes the steps of: providing a tensioning element on a body having a portion with a length and a circumferential surface; wrapping the thread against the circumferential surface so as to form a spiral portion of thread that is wrapped against the circumferential surface so that a frictional resistance force is generated between the thread and circumferential surface that resists drawing of thread off of the supply; exerting a tensioning force on the thread to cause the thread to be drawn off of the bobbin; and causing the spirally wrapped portion to be limited in lengthwise shifting relative to the portion of the body as the thread is drawn off of the bobbin. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic representation of a sewing system with a tensioning element, according to the present invention, incorporated therein; 
       FIG. 2  is a partially schematic representation of the sewing system in FIG.  1  and with a perspective view of a bobbin case assembly incorporating one form of thread tensioning element, according to the present invention, and having a peripheral surface around which thread is spirally wrapped and limited in shifting lengthwise by edges defined by two spaced projections from the peripheral surface; 
       FIG. 3  is a partially schematic representation of the sewing system in  FIG. 1  with an enlarged, fragmentary, perspective view of the tensioning element in  FIG. 2 ; 
       FIG. 4  is a view as in  FIG. 3  with a modified form of tensioning element, according to the present invention, including three projections defining thread controlling edges; 
       FIG. 5  is a view as in  FIG. 3  of a further modified form of tensioning element, according to the present invention, with a thread controlling edge defined by a bent end; 
       FIG. 6  is a view as in  FIG. 3  of a further modified form of tensioning element, according to the present invention, with a thread controlling edge defined by a hooked end; 
       FIG. 7  is a view as in  FIG. 4  of a still further modified form of tensioning element, according to the present invention, with thread controlling edges defined by a plurality of bends in the tensioning element; 
       FIG. 8  is a fragmentary, perspective view of a still further modified form of tensioning element, according to the present invention, with a thread controlling edge defined by a spiral undercut; 
       FIG. 9  is a fragmentary, side elevation view of the tensioning element in  FIG. 8 ; 
       FIG. 10  is a view as in  FIG. 3  of yet a further modified form of tensioning element, according to the present invention, with spaced thread controlling edges defined at the juncture of portions having different diameters; 
       FIG. 11  is an enlarged, cross-sectional view of the tensioning element taken along line  11 — 11  of  FIG. 10 ; 
       FIG. 12  is a view as in  FIG. 9  of a further modified form of tensioning element, according to the present invention, with curved projections from the peripheral surfaces defining thread controlling edges; 
       FIG. 13  is a view as in  FIG. 12  of a still further modified form of tensioning element, according to the present invention, including texturing to define thread controlling edges; 
       FIG. 14  is an enlarged, cross-sectional view of another modified form of thread tensioning element, according to the present invention, and having a body with a non-circular cross-sectional configuration; 
       FIG. 15  is a view as in  FIG. 8  of a further modified form of tensioning element, according to the present invention, wherein a squared body has an undercut groove defining a thread controlling edge; 
       FIG. 16  is a partially schematic representation of the sewing system of  FIG. 1  with a fragmentary, side elevation view of a further modified form of tensioning element, according to the present invention, and including a varying diameter body which limits thread shifting lengthwise thereof; and 
       FIG. 17  is a schematic representation of a tensioning element, according to the present invention, mounted operably upon a wall structure. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
   In  FIG. 1 , an exemplary sewing system is shown at  10 , representing an exemplary environment for the present invention. The sewing system  10  consists of a thread supply  12 , with the thread pulled out by a thread drawing assembly  14  from the thread supply  12 . The drawn thread is processed conventionally using one or more stitching components  16  to generate a desired stitching pattern. The nature of the stitching is not critical to the present invention. The invention is focused on a tensioning element  18  which cooperates with thread from the supply  12  to produce a frictional force that resists drawing of thread from the supply  12 . The manner of storing the thread to allow its withdrawal is not critical to the present invention, nor is the manner in which the thread is tensioned and drawn off by the thread drawing assembly  14 . Further details of an exemplary sewing system  10  are shown in FIG.  2 . 
   In  FIG. 2 , the thread supply  12  is provided within a bobbin case assembly at  20 . The bobbin case assembly  20  consists of a bobbin basket assembly at  22 , which has a bottom wall  24  and an annular, peripheral wall  26  extending upwardly therefrom, and defining in conjunction therewith, a receptacle  28  for a bobbin  30 . A cylindrical post  32  projects upwardly from the bottom wall  24  and through a core  34  on the bobbin  30  around which thread  36  from the supply  12  is wrapped. The post  32  guides movement of the bobbin  30  in rotation around an axis  38 . Axially spaced flanges  40 ,  42 , at the end of the core  34 , cooperatively bound a storage space at  44  for the thread supply  12 . 
   A bobbin case  46  has a peripheral wall at  48  which surrounds the bobbin  30 . A latch  50  on the bobbin case  46  releasably connects to the end  52  of the post  32  portion that is exposed through the bobbin  30 , to releasably connect the bobbin case  46  to the bobbin basket assembly  22 . 
   The bobbin case  46  and bobbin basket assembly  22  cooperatively define a wall structure at  54  that is mounted conventionally upon a support  56 . With the wall structure  54  suitably mounted, the thread  36  from the supply  12  is directed through the wall structure  54  to be engaged by the thread drawing assembly  14 . The thread  36  from the supply  12  is directed radially outwardly through an opening  58  in the wall structure  54  to be exposed for engagement by the thread drawing assembly  14 . A thread tensioning assembly at  60 , incorporating the tensioning element  18 , is interposed between the supply  12  and thread drawing assembly  14  to variably control the operative thread draw tension. 
   The tensioning element  18  has a mounting end  62  which is captively maintained on the wall structure  54  through a mounting plate  64 . The mounting plate  64  is maintained in place on the wall structure  54  through spaced fasteners  66 . The thread tensioning element  18  has an elongate body  68 , as seen also in FIG.  3 . The body  68  has a peripheral surface  70  against which the thread  36  is placed to produce a controlled frictional resistance force. The basic structure to accomplish this is shown in U.S. Pat. No. 6,152,057, which is incorporated herein by reference. 
   In a typical operation, the thread  36  will be wrapped to produce at least a portion of a spiral which bears upon the surface  70 . As shown in  FIGS. 2 and 3 , the thread  36  is wrapped to extend completely around the peripheral surface  70  of the body  60  in a spiral pattern. The thread path on the tensioning element  18  in  FIG. 3  is indicated by dotted lines. To avoid shifting of the spiral thread portions lengthwise of the body  68 , projections  72 ,  74  are provided and extend away from the peripheral surface  70 . In this case, each projection  72 ,  74  is substantially cylindrical in shape with an axis that projects orthogonally to the length of the body  68 . As seen more clearly in  FIG. 3 , the projection  72  defines an edge  76  to which a spiral portion of the thread  36  abuts to limit lengthwise shifting of the spiral portion of the thread  36  thereat. The other projection  74  provides a like thread controlling edge  76 ′ to engage another spiral portion of the thread  36  spaced lengthwise from the portion which engages the edge  76 . The projections  72 ,  74  are preferably spaced lengthwise of the body  68  to correspond to the desired “rise” of the spirally wrapped thread  36 , to engage preferably adjacent wrapped turns thereof. Accordingly, a spiral thread arrangement can be consistently maintained with respect to the length of the body  68  as the thread  36  continues to be drawn off of the supply  12 . 
   The invention contemplates many different ways to limit lengthwise shifting of spirally wrapped thread portions with respect to an elongate portion of a body. In one variation (not shown), the projections  72 ,  74  can be circumferentially offset so as not to reside in a line, as shown in  FIGS. 2 and 3 . 
   In  FIG. 4 , a modified tensioning element  18 ′ is shown wherein three projections  72 ′,  74 ′,  78  from the peripheral surface  70 ′ of the body  68  are utilized. This produces three spaced edges  76 ′,  76 ″,  80  against which spiral portions can abut. 
   In  FIG. 5 , a modified form of tensioning element is shown at  18 ″ with an elongate body  68 ″ having an offset end  82  defining a thread engaging/controlling edge  84 . The edge  84  serves the same purpose as the edges  76 ,  76 ′,  76 ″,  76 ′″. The angled end  82  may be formed by bending or preformed in the configuration shown. 
   A modification of the  FIG. 5  design is shown on a tensioning element  18 ″ in  FIG. 6  wherein a body  68 ′″ has a return bend  86  with a bight portion  88  defining a thread engaging edge  84 ′. 
   In  FIG. 7 , a modified form of thread tensioning element is shown at  18 ″″. The tensioning element  18 ″″ has a body  68 ″″ that is angled/bent or preformed in a zig-zag manner to produce edges  90 ,  92 ,  94 , to bear against the thread  36  to maintain the controlled spiral wrapping pattern therefor. 
   In  FIGS. 8 and 9 , a modified form of tensioning element  18   5′  is shown with a body  68   5′  with an undercut, spiral groove  96  corresponding to the intended spiral path for the thread  36 . A continuous edge  97  bounding the groove  96  limits lengthwise shifting of the spiral turns of the thread  36 . 
   In  FIGS. 10 and 11 , a modified form of tensioning element is shown at  18   6′  with a stepped diameter body  68   6′ . Thread engaging edges  98 ,  100  are defined respectively at the junctures between a) a first diameter portion  102  and a larger diameter portion  104  and b) the larger diameter portion  104  and a third portion  106  having a diameter larger than the portion  104 . The thread  36  will hang up on the edges  98 ,  100 , but is not as positively limited against lengthwise shifting by reason of the fact that the thread must cross over the edges in transitioning between the body portions  102 ,  104 ,  106 . 
   In  FIG. 12 , a further modified form of tensioning element is shown at  18   7′ . The tensioning element  18   7′  has a body  68   7′  with curved projections  108 , defining thread engaging edges  110 ,  112 . Alternatively, the projections  108  can be close enough together so that they cooperatively define a receptacle at  114  that is slightly larger than the diameter of the thread  36  for purposes of consistently maintaining the thread  36  in a spiral pattern around the body  68   7′ . 
   In  FIG. 13 , individual projections  116  are regularly or randomly provided on a body  68   8′  of a tensioning element  18   8′  to produce edges  118  associated with the projections  116 . The projections  116  may be formed by a texturing process that produces a roughened surface with significant contour on the body  68   8′ . 
   While most of the embodiments for the tensioning element  18 - 18   8′ , described above, have shown bodies  68 - 68   8′  with cylindrical cross sections, taken transversely to their lengths, other cross-sectional configurations are contemplated. As just an example, in  FIG. 14 , a tensioning element  18   9′  is shown with a body  68   9′  having an elliptical cross-sectional shape. Virtually any shape that defines a circumferential surface against which a spirally wrapped thread portion can be urged will suffice for purposes of the present invention. 
   In  FIG. 15 , a tensioning element  18   10′  is shown with the body  68   10′  that is generally squared with a continuous groove  96 ′, corresponding to the groove  96  shown in  FIGS. 8 and 9 . The groove  96 ′ defines a continuous thread engaging edge  97 ′. 
   In  FIG. 16 , a further modified form of tensioning element  18   11′ , according to the present invention, shown with a body  68   11′ . The body  68   11′  has a peripheral surface  70   11′ , with a diameter D at one location  120  and a diameter D 1  at a spaced location  122 . The diameter D 1  is greater than the diameter D. The diameter may increase progressively between the locations  120 ,  122 . As a result, the thread spirals are limited in lengthwise shifting by reason of the increasing diameter of the peripheral surface  70   11′ . As the thread  36  wraps and is tightened towards the one location  120 , the diameter of the spirals will not pass over the increasing diameter. Thus, the effect of a fixed edge is realized without any discrete edge formation. 
   The invention contemplates other variations. As shown in  FIG. 17 , a tensioning element  18   12′ , representative of all of the tensioning elements heretofore described, as well as others that could be devised by those skilled in the art with the present teachings in hand, is shown with a mounting end  124  that is attached to the wall structure  54 . The end  126  opposite to the end  124  is likewise attached to the wall structure  54 . In other words, a cantilever mounting of the tensioning element  18   12′  is not required to practice the present invention. 
   The foregoing disclosure of specific embodiments is intended to be illustrative of the broad concepts comprehended by the invention.