Winding – tensioning – or guiding – Tension control or brake – Supply controlled
Reexamination Certificate
2001-08-21
2003-12-09
Rivera, William A. (Department: 3653)
Winding, tensioning, or guiding
Tension control or brake
Supply controlled
C242S610400, C242S610500, C242S615000
Reexamination Certificate
active
06659384
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to bobbins for use in sewing machines, and relates more particularly to bobbins that are furnished with a quantity of sewing thread pre-wound thereon.
BACKGROUND OF THE INVENTION
In a typical lock-stitch sewing operation performed on an automatic sewing machine, a reciprocating needle carries a needle thread through a fabric from one side thereof through to the other side of the fabric, and the needle thread is looped around an under thread fed from a bobbin, such that the needle thread and the under thread form interlocking loops. The bobbin comprises a spool of thread rotatably mounted in a bobbin case located beneath the foot plate of the sewing machine over which the fabric travels.
A typical bobbin case
10
is shown in
FIG. 1
, along with a conventional single-flange bobbin
20
. The bobbin case comprises a cup-shaped housing formed of steel. A post
12
is mounted on an end wall
14
of the bobbin case and the bobbin
20
has a hollow cylindrical core
22
that fits over the post loosely enough so that the bobbin can freely rotate on the post. The bobbin thread
24
or under thread is wound about the core. A lock-stitch sewing machine includes mechanisms for guiding the bobbin thread out from the bobbin case and looping it in interlocking relation with the needle thread. During continuous lock stitching, the bobbin
20
rotates in the bobbin case
10
as a result of the bobbin thread being drawn out from the bobbin case by the various mechanisms.
When the sewing machine operator stops the machine, the various mechanisms of the machine tend to stop abruptly so that the tension on the bobbin thread suddenly ceases, but there is a tendency for the bobbin to continue to rotate in the bobbin case until frictional forces between the bobbin and the case bring the bobbin to a halt. This phenomenon is generally known as overspin. When the bobbin overspins, slack is created in the bobbin thread, and if the overspin is great enough, the slack thread can become looped around components in the bobbin case in an undesirable fashion, resulting in breakage of the thread when sewing is recommenced. Thus, it is desirable to minimize overspin as much as possible.
The draw-off tension, or amount of force required to draw the bobbin thread out from the bobbin case, is also an important parameter affecting the quality of stitching performed on lock stitch sewing machines. Bobbin assemblies typically include a tension adjustment spring for adjusting this draw-off tension to a desirable level for the particular type of bobbin thread being used and the sewing operation being performed. A typical amount of draw-off tension is about 30 to 35 grams. Although the tension adjustment spring can affect the average level of the draw-off tension, the draw-off tension can also be affected by interaction between the bobbin and the bobbin case. For example, in the case of bobbins of the type generally referred to as sidewall bobbins, having a circular sidewall or flange
26
attached to one or to each end of the core
22
such as in the single-flange bobbin
20
shown in
FIG. 1
, the outer periphery of the flange(s)
26
can rub against the inner surface of the bobbin case.
Such interference between the flange(s)
26
and the bobbin case is a potential problem particularly in sewing machines that employ automated bobbin changing devices, which automatically remove the bobbin case from the sewing machine when the bobbin thread is depleted and replace the bobbin case with another bobbin case containing a fully wound bobbin. During the automatic changing operation, the bobbin case can be subject to forces and accelerations that can tend to dislodge the bobbin from the case. To retain the bobbin in the case, conventional bobbin cases include a lever arm
16
pivotally mounted on the end wall of the bobbin case and connected with a movable finger
18
that can project through an opening in the side wall of the bobbin case and engage the flange of the bobbin contained therein, as shown in solid lines in FIG.
2
. The automatic bobbin changing apparatus A, schematically depicted in
FIG. 2
, is operable to actuate the lever arm
16
to cause the movable finger
18
to move into position engaging the flange
26
of the bobbin during the bobbin changing procedure. Once the bobbin case is installed in the sewing machine, the lever arm
16
is released so the finger
18
disengages the flange to allow the bobbin to rotate freely, as shown in phantom lines in FIG.
2
.
In order for the finger to be able to properly engage the flange
26
, the outer diameter of the flange must be only very slightly smaller than the inner diameter of the bobbin case. For instance, in prior single-flange bobbins made by the assignee of the present application, the flange has a nominal outer diameter of 0.865 inch, whereas the bobbin cases in which the bobbins are used have a nominal inner diameter of about 0.875 inch. Accordingly, if the flange
26
is mounted slightly eccentrically relative to the core
22
of the bobbin as a result of normal manufacturing tolerances during manufacture of the bobbin, the flange can rub against the inner surface of the bobbin case. This can cause the draw-off tension of the bobbin to be higher than optimal, and to vary to an undesirable extent.
Ideally, the draw-off tension should be constant and should be in an optimal range for the particular stitching operation being performed. Eliminating the flange(s) of the bobbin to create a so-called sideless bobbin would circumvent the problem of interference between the flange(s) and the bobbin case, but then another way of retaining the bobbin in the bobbin case during an automatic changing operation would have to be provided. Published International PCT Application WO 00/36201 describes a sideless bobbin that purports to solve this problem. The sideless bobbin comprises a hollow cylindrical core that is magnetized so that it is magnetically attracted to the steel post and end wall of the bobbin case, thus retaining the bobbin in the bobbin case during an automatic changing procedure. The sideless bobbin of WO 00/36201 is also said to reduce overspin of the bobbin and to improve the uniformity of draw-off tension as a result of the magnetic attraction force between the core and the bobbin case post and end wall.
It is believed the sideless bobbin in accordance with WO 00/36201 would have a number of drawbacks in practice. Because there must be a radial clearance between the core and the bobbin case post, the contact area between the inner surface of the core and the post must be quite small. More importantly, the contact between the core and the post can vary significantly and can even momentarily cease altogether as a result of wobbling or lateral movement of the bobbin on the post as the bobbin rotates, in which case the magnetic drag force between the bobbin and the post could momentarily drop to zero or a very low value, then jump up to a higher value when contact between the core and the post resumes. It is expected that this phenomenon would result in non-uniform draw-off tension.
A further drawback of the sideless bobbin of WO 00/36201 is that the magnetized core is magnetically attracted not only to the bobbin case, but also to the bobbin basket in which the bobbin case is installed in a sewing machine (for example, see the bobbin basket B schematically depicted in FIG.
2
). Thus, as stated in WO 00/36201, it is important to assure that the magnetic attraction force between the magnetized core and the bobbin case is greater than that between the magnetized core and the bobbin basket, so that the bobbin will be extracted along with the bobbin case during a bobbin changing procedure. Accordingly, use of the sideless bobbin necessitates special accommodations to assure that this is the case. In the case where the magnetized core has uniform magnetic strength over its entire length (which is the simplest form of the core to manufacture), the patent application suggests that a gap must be created betw
Milanese Dennis A.
Moennig Michael W.
Stuckey William C.
Alston & Bird LLP
J. & P. Coats Limited
Rivera William A.
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