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

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.

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.

DETAILED DESCRIPTION OF THE DRAWINGS

InFIG. 1, an exemplary sewing system is shown at10, representing an exemplary environment for the present invention. The sewing system10consists of a thread supply12, with the thread pulled out by a thread drawing assembly14from the thread supply12. The drawn thread is processed conventionally using one or more stitching components16to generate a desired stitching pattern. The nature of the stitching is not critical to the present invention. The invention is focused on a tensioning element18which cooperates with thread from the supply12to produce a frictional force that resists drawing of thread from the supply12. 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 assembly14. Further details of an exemplary sewing system10are shown in FIG.2.

InFIG. 2, the thread supply12is provided within a bobbin case assembly at20. The bobbin case assembly20consists of a bobbin basket assembly at22, which has a bottom wall24and an annular, peripheral wall26extending upwardly therefrom, and defining in conjunction therewith, a receptacle28for a bobbin30. A cylindrical post32projects upwardly from the bottom wall24and through a core34on the bobbin30around which thread36from the supply12is wrapped. The post32guides movement of the bobbin30in rotation around an axis38. Axially spaced flanges40,42, at the end of the core34, cooperatively bound a storage space at44for the thread supply12.

A bobbin case46has a peripheral wall at48which surrounds the bobbin30. A latch50on the bobbin case46releasably connects to the end52of the post32portion that is exposed through the bobbin30, to releasably connect the bobbin case46to the bobbin basket assembly22.

The bobbin case46and bobbin basket assembly22cooperatively define a wall structure at54that is mounted conventionally upon a support56. With the wall structure54suitably mounted, the thread36from the supply12is directed through the wall structure54to be engaged by the thread drawing assembly14. The thread36from the supply12is directed radially outwardly through an opening58in the wall structure54to be exposed for engagement by the thread drawing assembly14. A thread tensioning assembly at60, incorporating the tensioning element18, is interposed between the supply12and thread drawing assembly14to variably control the operative thread draw tension.

The tensioning element18has a mounting end62which is captively maintained on the wall structure54through a mounting plate64. The mounting plate64is maintained in place on the wall structure54through spaced fasteners66. The thread tensioning element18has an elongate body68, as seen also in FIG.3. The body68has a peripheral surface70against which the thread36is 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 thread36will be wrapped to produce at least a portion of a spiral which bears upon the surface70. As shown inFIGS. 2 and 3, the thread36is wrapped to extend completely around the peripheral surface70of the body60in a spiral pattern. The thread path on the tensioning element18inFIG. 3is indicated by dotted lines. To avoid shifting of the spiral thread portions lengthwise of the body68, projections72,74are provided and extend away from the peripheral surface70. In this case, each projection72,74is substantially cylindrical in shape with an axis that projects orthogonally to the length of the body68. As seen more clearly inFIG. 3, the projection72defines an edge76to which a spiral portion of the thread36abuts to limit lengthwise shifting of the spiral portion of the thread36thereat. The other projection74provides a like thread controlling edge76′ to engage another spiral portion of the thread36spaced lengthwise from the portion which engages the edge76. The projections72,74are preferably spaced lengthwise of the body68to correspond to the desired “rise” of the spirally wrapped thread36, to engage preferably adjacent wrapped turns thereof. Accordingly, a spiral thread arrangement can be consistently maintained with respect to the length of the body68as the thread36continues to be drawn off of the supply12.

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 projections72,74can be circumferentially offset so as not to reside in a line, as shown inFIGS. 2 and 3.

InFIG. 4, a modified tensioning element18′ is shown wherein three projections72′,74′,78from the peripheral surface70′ of the body68are utilized. This produces three spaced edges76′,76″,80against which spiral portions can abut.

InFIG. 5, a modified form of tensioning element is shown at18″ with an elongate body68″ having an offset end82defining a thread engaging/controlling edge84. The edge84serves the same purpose as the edges76,76′,76″,76′″. The angled end82may be formed by bending or preformed in the configuration shown.

A modification of theFIG. 5design is shown on a tensioning element18″ inFIG. 6wherein a body68′″ has a return bend86with a bight portion88defining a thread engaging edge84′.

InFIG. 7, a modified form of thread tensioning element is shown at18″″. The tensioning element18″″ has a body68″″ that is angled/bent or preformed in a zig-zag manner to produce edges90,92,94, to bear against the thread36to maintain the controlled spiral wrapping pattern therefor.

InFIGS. 8 and 9, a modified form of tensioning element185′is shown with a body685′with an undercut, spiral groove96corresponding to the intended spiral path for the thread36. A continuous edge97bounding the groove96limits lengthwise shifting of the spiral turns of the thread36.

InFIGS. 10 and 11, a modified form of tensioning element is shown at186′with a stepped diameter body686′. Thread engaging edges98,100are defined respectively at the junctures between a) a first diameter portion102and a larger diameter portion104and b) the larger diameter portion104and a third portion106having a diameter larger than the portion104. The thread36will hang up on the edges98,100, 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 portions102,104,106.

InFIG. 12, a further modified form of tensioning element is shown at187′. The tensioning element187′has a body687′with curved projections108, defining thread engaging edges110,112. Alternatively, the projections108can be close enough together so that they cooperatively define a receptacle at114that is slightly larger than the diameter of the thread36for purposes of consistently maintaining the thread36in a spiral pattern around the body687′.

InFIG. 13, individual projections116are regularly or randomly provided on a body688′of a tensioning element188′to produce edges118associated with the projections116. The projections116may be formed by a texturing process that produces a roughened surface with significant contour on the body688′.

While most of the embodiments for the tensioning element18-188′, described above, have shown bodies68-688′with cylindrical cross sections, taken transversely to their lengths, other cross-sectional configurations are contemplated. As just an example, inFIG. 14, a tensioning element189′is shown with a body689′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.

InFIG. 15, a tensioning element1810′is shown with the body6810′that is generally squared with a continuous groove96′, corresponding to the groove96shown inFIGS. 8 and 9. The groove96′ defines a continuous thread engaging edge97′.

InFIG. 16, a further modified form of tensioning element1811′, according to the present invention, shown with a body6811′. The body6811′has a peripheral surface7011′, with a diameter D at one location120and a diameter D1at a spaced location122. The diameter D1is greater than the diameter D. The diameter may increase progressively between the locations120,122. As a result, the thread spirals are limited in lengthwise shifting by reason of the increasing diameter of the peripheral surface7011′. As the thread36wraps and is tightened towards the one location120, 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 inFIG. 17, a tensioning element1812′, 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 end124that is attached to the wall structure54. The end126opposite to the end124is likewise attached to the wall structure54. In other words, a cantilever mounting of the tensioning element1812′is not required to practice the present invention.