US3599586A

US3599586A - Bobbin thread depletion detector for sewing machines

Info

Publication number: US3599586A
Application number: US45148A
Authority: US
Inventors: Albert L Newman
Original assignee: Singer Co
Current assignee: SSMC Inc
Priority date: 1970-06-10
Filing date: 1970-06-10
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

A beam from a light source is transmitted through a fiber optic bundle and is directed into the root region of a lockstitch sewing machine bobbin by a converging lens. A receiving fiber optic bundle receives the beam which passes through the root region of the bobbin when the thread on the bobbin is below a predetermined amount and directs the ray to a display screen in view of an operator to alert the operator that the thread remaining on the bobbin is near depletion.

Description

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Inventor Albert L. Newman Cleveland Heights, Ohio Appl. No. 45,148

Filed June 10, 1970 Patented Aug. 17, 1971 Assignee The Singer Company New York, N .Y.

BOBBIN THREAD DEPLETlON DETECTOR FOR SEWING MACHINES 11 Claims, 6 Drawing Figs.

U.S.Cl 112/218 R,

350/96 B, 242/36 Int. Cl B6Sd 63/00 Field of Search 1 12/2 18 R,

219 R, 350/96 B; 139/273 A; 224/36 References Cited UNlTED STATES PATENTS 2,647,482 8/1953 Campbell 112/218 R 2,910,555 10/1959 Tunstall 112/218 R X 3,120,125 2/1964 Vasel 350/96 B 3,459,240 8/1969 Erickson 139/273 A Primary Examiner-H. Hampton Hunter Attorneys-Marshall J. Breen, Chester A. Williams, Jr. and

Robert E. Smith ABSTRACT: A beam from a light source is transmitted through a fiber optic bundle and is directed into the root region of a lockstitch sewing machine bobbin by a converging lens. A receiving fiber optic bundle receives the beam which passes through the root region of the bobbin when the thread on the bobbin is below a predetermined amount and directs the ray to a display screen in view of an operator to alert the operator that the thread remaining on the bobbin is near depletion.

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SHEET 1 [IF 2 llll ll L 3 INVENTOR. Albert L. Newman BY W 9 ATTORNEY PATENTED AUG! 7 l97| SHEET 2 OF 2 k m E V m Albert L. Newman WITNESS;

ATTORNEY BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES BACKGROUND OF THIS INVENTION This invention relates to a bobbin-thread-depletion detecting apparatus and more particularly to apparatus for detecting when the bobbin thread of a lockstitch sewing machine is depleted below a predetermined amount.

It is desirable in sewing machines of the lockstitch type, that an operator know in advance when the bobbin thread is near depletion to permit completion of the sewing to the next convenient stopping point prior to rewinding the bobbin. In this manner expected depletions of bobbin thread can be prevented thereby improving the quality of the work by avoiding restitching over paths already perforated by the needle and improving the efficiency of the sewing operation.

A variety of devices have been proposed for indicating when the thread on a bobbin is nearly exhausted. 'Some devices utilize feelers of various types acting against the thread on the bobbin. An example of this is U.S. Pat. No. 2,760,024 by S. Tunstall dated Aug. 21, 1956. However, such devices have not been generally successful since they have involved difficulties in connection with their interference with the manipulation of the thread.

Other devices have been proposed which make use of magnetically actuated switches which respond to alterations of a magnetic field induced in the vicinity of the bobbin when thread depletion is imminent. See, for example, U.S. Pat. No. 3,129,680 by E. H. Doerner, dated Apr. 21, 1964.'However, such devices are cumbersome and expensive to fabricate. Hence they are not readily adaptable to sewing machines made for general home use which must be competitive in price as well as appearance with other sewing machines on the market. The invention herein disclosed provides apparatus for detecting when the bobbin thread depletion is imminent which is relatively inexpensive to fabricate and which involves no interference with thread manipulation.

Briefly stated, one aspect of the present invention resides in apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount including, a source of light disposed in the sewing machine, a bobbin rotatably mounted in the sewing machine upon which the thread is wound, and first light-directing means for directing a beam of light from the source to intersect the thread on the bobbin when the amount of the thread thereon is above the predetermined amount and for permitting the beam to pass when the amount of the thread on the bobbin is below the predetermined amount. The invention further includes second light directing means for receiving at least a detectable portion of the beam of light passing the thread on the bobbin when the thread is less than the predetermined amount, and display means optically coupled with the second light-directing means for displaying to the operator of the sewing machine the received detectable portion of light, thereby alerting the operator that the amount of thread remaining on the bobbin is less than the predetermined amount and near depletion.

In accordance with another aspect of the invention a further improvement is provided to ensure that the operator's attention is directed to the display means when depletion is imminent. In accordance with this aspect of the invention there is provided in the root of the bobbin a radial protrusion with respect to the axis of rotation of the bobbin to provide for eccentric rotation of the root with the thread thereon. Thus when the amount of thread remaining on the bobbin is below the predetermined amount the beam is intermittently permitted to pass to the display means causing intermittent illumination thereof for attracting the operator's attention to the imminent depletion of the bobbin thread.

In accordance with yet another aspect of the invention, the apparatus is adapted to permit the sewing machine lamp to act as the aforementioned source of light by providing a first fiber optic bundle mounted with its input end in a position to receive a portion of light from the lamp. In this version of the invention the output end of the first fiber optic bundle is mounted in a position to provide a beam of light for a converging lens mounted between it and the bobbin. The converging lens is adapted to converge the light passing through the output end of the bundle to form a sufficiently narrow beam light in the vicinity of theroot of the bobbin. This version of the invention further includes a display screen mounted in a position viewable by the operator of the sewing machine and a second fiber optic bundle having an input end and an output end, the input end mounted in the vicinity of the bobbin in a position to receive at least a detectable portion of the beam of light passing the thread on the bobbin when the thread is less than the predetermined amount and the output e'nd'of the second fiber optic bundle being mounted in the vicinity of the display screen in a position to illuminate the display screen by the detectable portion of the beam. Thus, the same source of light can be used for signalling thread depletion and for illuminating the sewing workpiece; and the use of the aforementioned fiber optic device further provides a brilliantly illuminated screen when the thread is deleted below a predetermined amount.

In view of the foregoing, it is an object of the present invention to provide an apparatus for signalling when the bobbin thread of a sewing machine is near depletion.

It is another object of the present invention to provide a simple and relatively inexpensive apparatus for signalling when the bobbin thread of a sewing machine is near depletion.

It is a further object of the present invention to provide apparatus for signalling when the bobbin thread of a sewing machine is near depletion which involves no interference with the manipulation of the thread.

It is yet another object of the present invention to provide an apparatus for signalling when the bobbin thread of a sewing machine is near depletion in which relatively simple optical elements are used and which utilizes light provided by the sewing lamp.

These and other objects, advantages and features of the invention, will be more fully understood by referring to the-following description and claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a front elevation view, partly in section of a portion of a sewing machine illustrating features of the present invention.

FIG. 2 is a schematic illustration showing features of the present invention and the bobbin having a greater amount of thread than the predetermined minimum amount.

FIG. 3 is a schematic illustration showing features of another embodiment of the present invention and the bobbin having less thread thereon than the predetermined minimum amount.

FIG. 4 is an enlarged fragmentary top plan view partly in cross section of the bobbin and of the thread sensing elements of this invention in the same condition as shown in FIG. 2 and illustrating the preferred alignment of the first fiber optic bundle, the converging lens and the second fiber optic bundle with respect to the axis of the bobbin and a preferred design of the root region of the bobbin for practicing the invention.

FIG. 5 is an enlarged fragmentary top plan like FIG. 4 but showing the parts in the same condition as shown in FIG. 3.

FIG. 6 is a perspective view of the bobbin and bobbin case with an accompanying schematic representation of the preferred optical alignment for practicing the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sewing machine illustrated in the drawings, including the stitch-forming instrumentalities is similar to that disclosed in the U.S. Pat. OF W. J. Edwards et al., No. 3,154,035, Oct. 27, 1964 and the same is incorporated herein by reference.

The sewing machine frame comprises a bed 11, a standard 12 rising from the bed, a bracket arm 13 extending over the bed and a head 14 at the cantilevered end of the bracketarm 13. The head 14 carries a needle bar 15 and a needle 16 affixed thereto, the latter two parts being disposed for reciprocal vertical movement-and a presser bar 17 with a presser foot 18 depending therefrom, movable by means not shown to an upper and a lower fixed position. A bed shaft 19 conventionally rotated by an actuating mechanism described in the aforementioned incorporated U.S. Pat. is rotatably carried by a bed shaft support 20 and is operatively connected to a looptaker shaft 21 through meshing gears 22 therebetween to impart rotary motion to a loop-taker 23 secured on the looptaker shaft in timed relation with the needle reciprocation.

The needle passes endwise through a suitable needle aperture in a throat plate 25 carried on the sewing machine bed. In addition to having a needle accommodating aperture the throat plate may also be slotted in a conventional manner to accommodate a work-feeding dog '27 which is preferably driven in a conventional fashion from the actuating mechanism described in the aforementioned incorporated United States patent for the needle and loop-taker so as to cooperate with the needle and loop-taker in forming lockstitches in a workpiece (not shown) constrained on the throat plate 25 by presser foot 18 in the lower position.

The loop-taker 23 includes a cup-shaped body portion in which is journaled a bobbin case 31 which is conventionally restrained against rotation. A bobbin 32 is ordinarily free to turn in the bobbin case, being supported therein by a top flange 33 of the bobbin which rests on the bobbin case and is centered thereon by a spring biased arm 34 pivoted on a pin 35 in the bobbin case. The bobbin 32 also includes a bottom flange 36 somewhat smaller in diameter than the top flange 33. The arm 34 conventionally bears downward on the bobbin to provide a frictional force between the bobbin and the bobbin case which resists turning of the bobbin and provides during sewing operation a tension on the bobbin thread wound about a root or hub 37 of the bobbin.

A sewing machine lamp 40 is mounted below the bracket arm 13 to furnish illumination on and about the workpiece in the sewing machine. A fiber optic bundle 41 is arranged in the frame of the sewing machine with an input end 41a adjacent the sewing machine lamp 40 and an output end 41b held in an aligning passage 42 formed in the bedshaft' support 20. It is well known that a fiber optic bundle will direct received light through a nonlinear path with substantially no diminution of the luminosity thereof. The body of the fiber optic bundle 41 extends through the bracket arm 13, down through the standard 12 and through the bed 1 l.

A threaded ring 43 having a convergent or positive focal length lens 44 fastened therein is threadably engaged in the aligning passage 42 disposed in front of the output end 41b of the fiber optic bundle 41. The axes of the fiber optic bundle 41 at its output end 41b in the passage 42 and of the lens 44 are arranged to be in alignment and are selected to provide a beam of light B the axis of which passes radially outwardly of but closely adjacent to the root region 37 of the bobbin 32.

Cutout regions 31a and 31b (shown in FIG. 6) are provided in the upper portion of the bobbin case 31 and are aligned to provide free passage of the beam B, the cutout regions being larger in area than the narrow beam. The cutout region 31a is conventionally provided for finger access to the bobbin 32 in order to remove it from the bobbin case 31. As shown in FIG. 6, the cutout regions 31a and 31b are disposed opposite one another at the ends of a chord formed with respect to the axis of rotation of the bobbin.

A face 45a of the input end of a fiber optic bundle 45 is mounted in a manner to carry the light received thereon to the head 14. Thus fiber optic bundle 45 is fitted in a supporting passage 46 in a vertical end wall 47 below the passage 42, passes through the bed 11, up through the standard 12,

through the bracket arm 13 and down to the head 14. The support passage 46 is axially aligned with the cutout 31b. The output end of the fiber optic bundle 45 is mounted in the head 14 facing a display screen 48 fitted in an aperture 49 in the lower front portion of the head 14. The input face 45a is aligned and spaced away from the lens 44 by a distance equal to the image distance of the lens. The lens is also spaced from the output end 41b a distance equal to the object distance of the lens so that the beam B from the output end 41b is focused onto the input face 45a through the cutout region 31a, the root region 37 of the bobbin 32 and the cutout region 31b. This lens placement and design also results in substantially all of the light emerging from the fiber optic bundle 41 to be focused onto the input face 45a. As can be appreciated by those skilled in the art, the best illumination of the display screen 48 results when the lens 44 is placed in the aforementioned position. However, it is merely necessary that sufficient light be transmitted in the fiber optic bundle 45 from the beam B described to visibly illuminate the display screen.

The narrowness of the width and breadth of the beam in the root region of the bobbin 32 are such that if more than a predetermined small portion of the thread comprising a fully wound bobbin is present, the thread interferes with the beam and little or no light from the beam reaches the input face 45a. However, as the thread on the bobbin 32 is depleted to a predetermined level, illumination of the display screen 48 is started and maintained as an increasing proportion of the beam is unobstructed and is incident on the face of the fiber optic bundle 45. The embodiment of FIG. 1 provides for complete illumination of the display screen before the thread on the bobbin is depleted. However, a beam directed tangent to the root 37 will attract the attention of the operator to the depleting condition of the bobbin thread. The display screen 48 can be made from any material which is capable of being visibly illuminated for example, glass or plastic, and is preferably frosted to diffuse its incident light so that its illumination is readily visible. Any photosensitive device is usable in place of the display screen, however, the display screen in conjunction with the fiber optic bundle 45 is preferable due to its simplicity.

FIG. 2 illustrates the bobbin substantially fully wound with thread. The beam B from the output end 41b of the fiber optic bundle 41 is directed into the root region of the bobbin 32 by the lens 44 but is scattered by the thread occupying the space therein. As illustrated in FIG. 3 the bobbin thread is approaching depletion and the beam B is unobstructed and is thereby incident on the input face 45a and directed to the display screen 48, illuminating the latter to alert the operator.

A modified embodiment of the present invention is shown in FIG. 3 and includes an auxiliary lamp 50 which is electrically connected and mounted in the bed 11. The fiber optic bundle 41 is fitted between the auxiliary lamp and the lens 44 and is in alignment with the lens 44 and the input face 45a of the fiber optic bundle 45 to direct the beam of light B from the fiber optic bundle 41 to the input face 45a.

FIGS. 4 and 5 illustrate an embodiment utilizing the present invention with a radial protrusion 51 extending from a portion of the root 37 and providing a radial protrusion on the root and thread 52 wound thereabout with respect to the axis of rotation 53 of the bobbin, which as the bobbin turns will move alternately into and out of the beam of light. A similar result would be obtained if the root 37 were to be located eccentrically of the axis of rotation 37. The beam B emerging from the output end 41b of the fiber optic bundle 41 and directed by the lens 44, through the root region of the bobbin 32 and onto the input face 45a of the fiber optic bundle 45 held in the supporting passage 46 of the vertical end wall 47, is obstructed by the thread 52 in the root region of the bobbin 32 in FIG. 4 and is generally unobstructed in FIG. 5.

The radial protrusion 51 provides for intermittent obstruction of the beam B when the thread 52 approaches depletion during a portion of each revolution of the bobbin so that the display screen 48 shown in FIG. 1, is intermittently illuminated.

Although intermittent illumination of the display screen can be provided with a bobbin 32 having an eccentric axis of rotation, the radial protrusion 51 on the root 37 is preferred since such design requires the least modification of adjoining parts.

Fiber optic bundles are preferred in the practice of the present invention because of their simplicity and good function. However, when practicing the present invention in the form of an embodiment similar to that illustrated in FIG. 3 wherein a separate lamp is used in the vicinity of the bobbin 32, other optical designs can be incorporated.

In the practice of the present invention, a collimating lens or other compound lens system is not considered necessary as the simple convergent lens will be sufficient.

Although the present invention has been described in relation to particular illustrative embodiments thereof, these are not to be taken as limitations on the application of the underlying principles of the invention. These principles may be employed in many different forms and embodiments which will be obvious to those skilled in the art; and such variations are, of course, included within the spirit and scope of the invention.

Having thus set forth the nature of this invention, what I claim herein is: g

1. A bobbin-thread-depletion-detecting apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount, comprising:

a. a source of light disposed in said sewing machine;

b. a bobbin rotatably mounted in said sewing machine upon which said thread is wound;

c. first light-directing means disposed between said source of light and said bobbin for directing a beam of light from said source to intersect said thread on said bobbin when the amount of said thread thereon is above said predetermined amount and for permitting said beam to pass when the amount of said thread on said bobbin is below said predetermined amount;

d. second light-directing means for receiving at least a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount; and

e. display means optically coupled with said second lightdirecting means for displaying to the operator of said sewing machine said received detectable portion of light, whereby when the amount of said thread remaining on said bobbin is greater than said predetermined amount said beam is interrupted by said thread and .when said amount of thread is less than said predetermined amount said detectable portion of said beam is displayed to said operator alerting said operator that said thread remaining on said bobbin is near depletion.

2. A bobbin-thread-depletion-detecting apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount, comprising:

a. a source of light disposed in said sewing machine;

b. a bobbin rotatably mounted in said sewing machine upon which said thread is wound; first light-directing means disposed between said source of light and said bobbin for directing a beam of light into the root region of said bobbin, said beam being sufficiently narrow in width and breadth to be substantially prevented from passing through said root region when the amount of said thread remaining on said bobbin is above said predetermined amount and sufficiently narrow in width and breadth to permit at least a detectable portion of light from said beam to pass through said root region when the amount of said thread remaining on said bobbin is below said predetermined amount;

e. display means for displaying to the operator of said sewing machine said detectable portion of light, whereby when the amount of said thread remaining on said bobbin is greater than said predetermined amount said beam is interrupted by said thread and when said amount of thread is less than said predetermined amount at least a detectable portion of said beam is displayed to said operator alerting said operator that said thread remaining on said bobbin is near depletion.

3. A bobbin-thread-depletion-detecting apparatus as claimed in claim 2, wherein said first light-directing means includes a first fiber optic bundle having an input end mounted in the vicinity of said source of light in a position to receive a portion of light therefrom and having an output end mounted in the vicinity of said bobbin for providing said beam of light.

4. A bobbin-thread-depletion-detecting apparatus as claimed in claim 3, wherein said first light-directing means further includes a converging lens mounted between said output end of said first fiber optic bundle and said bobbin and adapted to converge the light passing through said output end of said bundle to form said sufficiently narrow beam of light in the vicinity of the root of said bobbin.

5. A bobbin-thread-depletion-detecting apparatus as claimed in claim 4, wherein said root of said bobbin includes a radial protrusion with respect to the axis of rotation of said bobbin to provide for eccentric rotation of said root with said thread thereon, whereby when said amount of thread remaining on said bobbin is below said predetermined amount said beam is intermittently permitted to pass to said display means causing intermittent illumination thereof for alerting said operator.

6. A bobbin-thread-depletion-detecting apparatus as claimed in claim 3, wherein said source of light is a sewing machine lamp for illuminating the workpiece in said sewing machine, and wherein said input end of said fiber optic bundle is mounted in the vicinity of said lamp to receive a portion of the light thereof.

7. A bobbin-thread-depletion-detecting apparatus as claimed in claim 4, wherein said root of said bobbin is eccentrically formed with respect to the axis of rotation thereof to provide for eccentric rotation of said root with said thread thereon, whereby when said amount of thread remaining on said bobbin is below said predetermined amount said beam is intermittently permitted to pass to said display means causing intermittent illumination thereof for alerting said operator.

8. A bobbin-thread-depletion-detecting apparatus as claimed in claim 3, wherein said second light-directing means includes a second fiber optic bundle having an input end mounted in a position to receive said detectable portion of light from said beam passing through said root region and having an output end optically coupled with said display means.

9. A bobbin-thread-depletion-detecting apparatus as claimed in claim 2, wherein said display means includes a display screen mounted in said sewing machine in a position viewable by said operator and wherein said output end of said second fiber optic bundle is mounted in a position to illuminate said screen by said received light.

10. A bobbin-thread-depletion-detecting apparatus as claimed in claim 3, wherein said display means includes a display screen mounted in a position viewable by the operator of said sewing machine wherein said second light-directing means includes a second fiber optic bundle having an input end and an output end, said input end being mounted in the vicinity of said bobbin in a position to receive at least a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount wherein said first light-directing means further includes a lens having a positive focal length, an object distance substantially equal to the distance from said lens to said output end of said first fiber optic bundle, and an image distance substantially equal to the distance from said lens to said input end of said second fiber optic bundle, said lens being mounted in a position to transmit said detectable portion of said beam from said output end of said first fiber optic bundle through said root region of said bobbin to, said input end of said second 7 fiber optic bundle, and wherein said output end of said second fiber optic bundle is mounted in the vicinity of said display screen in a position to illuminate said display screen by said detectable portion of said beam.

11. A bobbin-thread-depletion-detecting apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount wherein said sewing machine includes a sewing machine lamp mounted in a position to illuminate the workpiece:

a. a bobbin having a root upon which said thread is wound forming a root region thereof;

b. a first fiber optic bundle having an input end and an output-end, said input end being mounted in a position to receive a portion of the light provided by said lamp and said output end being mounted in the vicinity of said bobbin in a position to direct light emerging therefrom toward said root region;

0. a converging lens mounted between said output end of said first fiber optic bundle and said bobbin in a position to direct said light emerging therefrom into said root region in the form of a beam sufficiently narrow in width and breadth to be substantially prevented from passing through said root region when the amount of said bobbin thread remaining on said bobbin is above said predetermined amount and sufficiently narrow in width and breadth to permit at least a detectable portion of said beam to pass when the amount of said thread remaining on said bobbin is below said predetermined amount;

a second fiber optic bundle having an input end and an output end, said input end being mounted at least in the vicinity of said bobbin in a position to receive a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount;

. a display screen mounted in said sewing machine in a position viewable by the operator thereof; and

. means for mounting said output end of said second fiber optic bundle in a position to illuminate said display screen with said received detectable portion of light thereby alerting said operator that said thread remaining on said bobbin is below said predetermined amount.

Claims

1. A bobbin-thread-depletion-detecting apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount, comprising: a. a source of light disposed in said sewing machine; b. a bobbin rotatably mounted in said sewing machine upon which said thread is wound; c. first light-directing means disposed between said source of light and said bobbin for directing a beam of light from said source to intersect said thread on said bobbin when the amount of said thread thereon is above said predetermined amount and for permitting said beam to pass when the amount of said thread on said bobbin is below said predetermined amount; d. second light-directing means for receiving at least a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount; and e. display means optically coupled witH said second lightdirecting means for displaying to the operator of said sewing machine said received detectable portion of light, whereby when the amount of said thread remaining on said bobbin is greater than said predetermined amount said beam is interrupted by said thread and when said amount of thread is less than said predetermined amount said detectable portion of said beam is displayed to said operator alerting said operator that said thread remaining on said bobbin is near depletion.

2. A bobbin-thread-depletion-detecting apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount, comprising: a. a source of light disposed in said sewing machine; b. a bobbin rotatably mounted in said sewing machine upon which said thread is wound; c. first light-directing means disposed between said source of light and said bobbin for directing a beam of light into the root region of said bobbin, said beam being sufficiently narrow in width and breadth to be substantially prevented from passing through said root region when the amount of said thread remaining on said bobbin is above said predetermined amount and sufficiently narrow in width and breadth to permit at least a detectable portion of light from said beam to pass through said root region when the amount of said thread remaining on said bobbin is below said predetermined amount; d. second light-directing means for receiving at least a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount; and e. display means for displaying to the operator of said sewing machine said detectable portion of light, whereby when the amount of said thread remaining on said bobbin is greater than said predetermined amount said beam is interrupted by said thread and when said amount of thread is less than said predetermined amount at least a detectable portion of said beam is displayed to said operator alerting said operator that said thread remaining on said bobbin is near depletion.

10. A bobbin-thread-depletion-detecting apparatus as claimed in claim 3, wherein said display means includes a display screen mounted in a position viewable by the operator of said sewing machine wherein said second light-directing means includes a second fiber optic bundle having an input end and an output end, said input end being mounted in the vicinity of said bobbin in a position to receive at least a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount wherein said first light-directing means further includes a lens having a positive focal length, an object distance substantially equal to the distance from said lens to said output end of said first fiber optic bundle, and an image distance substantially equal to the distance from said lens to said input end of said second fiber optic bundle, said lens being mounted in a position to transmit said detectable portion of said beam from said output end of said first fiber optic bundle through said root region of said bobbin to said input end of said second fiber optic bundle, and wherein said output end of said second fiber optic bundle is mounted in the vicinity of said display screen in a position to illuminate said display screen by said detectable portion of said beam.

11. A bobbin-thread-depletion-detecting apparatus for detecting when the bobbin thread of a sewing machine is depleted below a predetermined amount wherein said sewing machine includes a sewing machine lamp mounted in a position to illuminate the workpiece: a. a bobbin having a root upon which said thread is wound forming a root region thereof; b. a first fiber optic bundle having an input end and an output end, said input end being mounted in a position to receive a portion of the light provided by said lamp and said output end being mounted in the vicinity of said bobbin in a position to direct light emerging therefrom toward said root region; c. a converging lens mounted between said output end of said first fiber optic bundle and said bobbin in a position to direct said light emerging therefrom into said root region in the form of a beam sufficiently narrow in width and breadth to be substantially prevented from passing through said root region when the amount of said bobbin thread remaining on said bobbin is above said predetermined amount and sufficiently narrow in width and breadth to permit at least a detectable portion of said beam to pass when the amount of said thread remaining on said bobbin is below said predetermined amount; d. a second fiber optic bundle having an input end and an output end, said input end being mounted at least in the vicinity of said bobbin in a position to receive a detectable portion of said beam of light passing said thread on said bobbin when said thread is less than said predetermined amount; e. a display screen mounted in said sewing machine in a position viewable by the operator thereof; and f. means for mounting said output end of said second fiber optic bundle in a position to illuminate said display screen with said received detectable portion of light thereby alerting said operator that said thread rEmaining on said bobbin is below said predetermined amount.