Device for use with a bobbin-less coil of thread

A device, preferably of disc configuration, capable of being fastened to a bobbin-less coil of thread for indicating the non-rotation of the coil during a sewing operation. One side of the device includes indicating means enabling the optical detection of the rotation of the device. The opposite side of the device includes fastening means, such as pins or adhesive, for fastening the device to a coil of thread, the fastening means being capable of disengaging from the coil when a predetermined length of thread remains therein.

FIELD OF THE INVENTION 
The present invention relates to a device for monitoring the rotation of 
the bobbin thread of a sewing machine, particularly while using a 
pre-wound bobbin. 
BACKGROUND OF THE INVENTION 
The known sewing machines are provided with various means for feeding an 
upper thread to the sewing needle, and other means, including a bobbin, 
for feeding the lower thread to the sewing needle. Monitoring the 
condition, particularly breakage, of the upper thread is relatively 
simple, and several methods are in use today, as described for example in 
U.S. Pat. No. 3,843,883. However, monitoring the condition of the lower 
bobbin thread is somewhat more problematical, and although a number of 
systems have been devised for doing this, the known systems are still not 
entirely satisfactory. The main reason for this is because of the 
complexity of the path of the lower thread out of the bobbin, which 
enables very little room for detection. Various methods for detecting an 
empty bobbin condition using a light beam are known, for example as 
described in U.S. Pat. Nos. 4,237,807 and 4,212,257, and in British 
Patents 1,335,677 and 2,078,798. However, these known techniques are 
usually of complicated construction and generally do not detect all the 
conditions of the bobbin thread, including thread exhaustion and thread 
breakage. 
Our prior U.S. Pat. No. 4,934,292 disloses an arrangement for detecting 
when a bobbin stops rotating, e.g., because of an empty bobbin. The 
detection of this condition may be used for terminating the operation of 
the sewing machine to enable refilling or replacement of the empty bobbin 
and to continue with the stitching operations. 
Those specifications relate to a conventional bobbin on which the thread is 
wound. Recently, however, "pre-wound bobbins" have gained popularity. 
These are coils of thread without a bobbin, held together by a weak glue 
so as not to interfere with the release of the thread. By leaving out the 
bobbin, the need to rewind the thread on the sewing head is eliminated, 
thus saving time and trouble. This bobbin-less coil of thread, however, 
cannot be used with the detecting arrangements disclosed in the above 
patent specifications. 
Another problem with sewing machines arises when a stitching operation is 
terminated in the middle because of an empty bobbin and is then resumed 
with a new bobbin. This results in a break in the stitch and is 
particularly unsightly in "top stitchings", such as collars, cuffs, 
pockets, etc., viewable from the outside of the garment, as distinguished 
from "inside stitches" which are not viewable from the outside of the 
garment. 
Our prior U.S. Pat. No. 4,934,292 discloses a bobbin structure which 
permits the bobbin, even when it stops rotating, to nevertheless supply a 
sufficient length of thread in order to finish a stitching operation. 
However, this structure is also incompatible with the use of a bobbin-less 
coil of thread. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the invention to provide a device capable of adapting a 
bobbin-less coil of thread for use with the detecting apparatuses 
disclosed in our aforementioned patent specifications. 
It is a further object of the invention to permit a sewing operation using 
a bobbin-less coil of thread to be completed even when the coil stops 
rotating. 
In accordance with the present invention, there is provided an indicator 
device capable of being fastened to a bobbin-less coil of thread for 
indicating the non-rotation of the coil during a sewing operation, the 
thread of the bobbin-less coil being held together in a cylindrical coil 
form by weak glue which permits easy release and unwinding of the thread 
from the coil. The indicator device comprises a disc-shaped member having 
an inner face to face the end face of the coil when fastened thereto, and 
an outer face facing away from the coil. The outer face includes 
indicating means enabling the optical detection of the rotation of the 
device, and the inner face includes fastening means for fastening the 
device to the coil of thread. The fastening means is fastenable to the end 
face of the coil at a predetermined radial distance from the center of the 
coil so that the disc-shaped member is released from the coil when a 
predetermined length of thread remains in the coil. The arrangement is 
such that the disc-shaped member rotates with the coil as thread is 
unwound therefrom but ceases to rotate with the coil when only the 
predetermined length of thread remains in the coil. 
In accordance with the present invention there is also provided a sewing 
apparatus comprising a sewing head including a drive therefor; a 
bobbin-less coil of thread for feeding thread to the sewing head; the 
aforementioned device fastened to the coil for indicating its 
non-rotation; a bobbin case for holding the coil and the device; and an 
optical sensor for optically sensing the indicating means and for 
producing a train of pulses during the rotation of the coil, such that the 
termination of the train of pulses by the non-rotation of the coil 
indicates a break in, or the exhaustion of, the thread of the coil. 
By using the above device, bobbin-less coils of thread can be monitored for 
breakage and/or exhaustion of thread using the apparatuses described in 
our aforementioned patents. Additionally, the use of the device of the 
invention prevents the unsightly break which normally is produced in a 
stitch when interrupted in the middle of a stitching operation. 
Further features and advantages of the invention will be apparent from the 
description below.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is illustrated a sewing machine head, 
generally designated 2, including a reciprocating sewing needle 4, a spool 
6 for feeding an upper thread 8 to the sewing needle, and a lower thread 
unit 10 for feeding the lower thread 12 to the sewing needle. The lower 
thread unit 10 comprises a bobbin case 14; a conventional bobbin 16 
disposed within the case and on which is wound a supply of the lower 
thread 12; a bobbin case mounting axis 17 on which is mounted the bobbin; 
and a rotary housing 18 which is rotated in synchronism with the 
reciprocation of the sewing needle and the other components of the sewing 
machine, so as to form stitches with the upper thread 8. The general 
construction and mode of operation of such sewing machines are well-known, 
and therefore further details not essential to an understanding of the 
present invention are not set forth herein. 
FIG. 1 also illustrates an optical sensor 20 aligned with an opening 22 in 
the end wall of the bobbin case 14 for monitoring the rotation of the 
bobbin. The pulses generated by the optical sensor 20 are fed into a 
control and indicating unit 24. The operation of the sensor and unit with 
a conventional bobbin were previously described in our prior U.S. Pat. No. 
4,934,292, hereby incorporated by reference. 
A bobbin-less coil of thread 26 is illustrated in FIG. 2 together with one 
embodiment of the device of the invention in the form of a thin, flat 
disc-shaped member or disc 28. The coil 26 has a cylindrical shape and is 
wholly composed of threads 30 held together by a weak glue which permits 
easy release and unwinding of the thread from the coil. An axial bore 32 
traverses the center of the coil to enable it to be mounted on the bobbin 
case mounting axis 17 (FIG. 1). As the thread 30 is fed to the needle, the 
coil rotates on the mounting axis until the supply of thread has been 
completely exhausted. A new coil is then inserted in its place, 
eliminating the need for rewinding the bobbin. 
The disc 28 will usually have a diameter similar to the diameter of the new 
bobbin-less coil, and an axial bore 34 traversing its center to allow the 
disc to be mounted on the bobbin case mounting axis. The disc has an inner 
face (41, FIG. 2) facing the end face of the coil 26 when fastened 
thereto, and an outer face (36, FIG. 3) facing away from the coil. Disc 28 
is preferably exceedingly thin, with a thickness 35 in the range of 
0.15-0.25 mm, so as to be insertable into the bobbin case without 
interferring with the rotation of the coil. Due to its thinness, the disc 
will usually be made from a rigid material such as a metal, preferably 
steel, so as to impart strength to the disc. However, a disposable disc 
made from a lightweight, inexpensive material such as cardboard is also 
contemplated. 
FIG. 3 illustrates the outer or `indicating` face 36 of the disc 28 which 
is coated with alternate reflecting 38a and non-reflecting 38b 
circumferentially spaced strips extending radially from the center of the 
disc. The strips can be of different colors (e.g. black and white) or of 
different optically-sensible materials. The only condition is that one of 
the strips be sensed by the optical sensor 20 (FIG. 1) during the rotation 
of the disc, as described in our aforementioned patent specifications in 
relation to the outer face of the end wall of the bobbin. An alternate 
embodiment is illustrated in FIG. 5 wherein the `indicating` face 36 of 
the disc has circumferentially spaced holes 39 cut out of a reflecting 
background 40. 
The opposite face 41 of the disc 28, illustrated in FIG. 2, contains 
fastening means in the form of three pointed pins 42 circumferentially 
arranged around the axial bore 34. The tips of the pins project outwardly 
from the surface of face 41 in order to engage the threads of the coil 26. 
FIGS. 4a-4c illustrate the mounting of the disc 28 on the coil 26 and its 
operation. The disc 28 is mounted concentrically onto the coil 26 with the 
pins 42 engaging the threads of the coil. As the thread is fed to the 
needle, the coil rotates around its axis 32 and the disc rotates 
concurrently. The optical sensor senses the alternate strips 38 (FIG. 3) 
and generates pulses which are fed to the control unit 24 (FIG. 1). When 
the thread supply has been exhausted, the pins 42 will no longer engage 
the thread 30 (FIG. 4c) causing the disc to release or disengage from the 
coil. The disc will then cease to rotate, and the non-rotation will be 
sensed by the optical sensor, which will feed the information to the 
control unit. The control unit can then inform the operator of the 
situation and/or automatically stop the sewing machine. In a similar 
manner, if the thread breaks during the sewing process, the coil will 
cease to rotate, and the resulting non-rotation of the disc will likewise 
be sensed by the sensor. 
In the case of thread exhaustion, the position of the pins on the disc will 
determine how much thread remains in the coil when the disc ceases to 
rotate. Referring to FIG. 2, if the location of the pins 42 borders on the 
bore 34, a minimal amount of threads 30 will remain in the coil on release 
of the disc from the coil. As the distance of the pins from the bore 
increases, a longer length of thread will remain in the coil. This is 
advantageous for avoiding a break in the stitch which results when a 
bobbin is depleted in the middle of a sewing operation. By positioning the 
pins a predetermined radial distance from the axial bore at the center of 
the disc, a predetermined length of thread will remain in the coil on 
release of the disc, as is illustrated in FIG. 4c. This remaining length 
of thread will permit the coil, even when it stops rotating, to 
nevertheless supply a sufficient length of thread in order to finish a 
stitching operation. 
FIG. 6 illustrates an alternate embodiment to the pin-mounted disc, in the 
form of an adhesive coating 44 on the `fastening` face 41 of the disc. The 
adhesive fulfills the same fastening function as the pins, and the width 
of an adhesive-less ring 46 surrounding the axial bore 34 determines the 
length of thread which will remain in the coil on release of the disc from 
the coil. 
The disc described above can be fastened to the coil externally of the 
bobbin case and the disc-coil combination can then be inserted into the 
case. FIG. 7 illustrates an alternate embodiment in which the disc 28 is 
permanently held in the bobbin case 14 by a recess 48 on the case shaft 
which, however, allows the disc to freely rotate inside the case. The coil 
26 is inserted into the case 14 and pressed against the pins 42 of the 
disc so as to be engaged by the disc. This embodiment eliminates the need 
to accurately position the disk on the coil prior to inserting the coil 
into the bobbin case. 
While the invention has been described with respect to several preferred 
embodiments, it will be appreciated that many other variations, 
modifications and applications of the invention may be made.