US3029763A - Thread break sensing device for sewing machines - Google Patents

Description

April 17, 1962 I E. P. TURNER ETAL 3,029,763

THREAD BREAK SENSING DEVICE FOR SEWING MACHINES Filed Aug. 3, 1959 2 Sheets-Sheet 1 IN VEN TOR. Edgar P. Turner and BY A/ber/ /V. 600k TTORNEY April 17, 1962 E. P. TURNER ETAL 3,029,763

THREAD BREAK SENSING DEVICE FOR SEWING MACHINES 2 Sheets-Sheet 2 Filed Aug. 3, 1959 INVENTOR. Edgar P. Turner and B Albert M Cook TTORWY United Edgar P. Turner, Watchung, and Albert N. Cook, Rernardsville, Ni, assignors to The Singer Manufacturing Company, Elizabeth, N.J., a corporation of New Jersey Filed Aug. 3, 1959, Ser. No. 831,299 Claims. (Cl. 112-419) The present invention relates to a device for sensing and responding to a break in or exhaustion of the supply of the thread in a sewing machine.

Prior thread break sensing devices have been objectionable in that they required a sensing device in continuous contact with and placing a drag on the thread at all times during the stitching cycle. It is desirable at certain times in the stitch forming cycle that a minimum of tension or drag be placed on the thread. Prior devices have not met this requirement.

An object of this invention is to provide a sensing device which places drag on the thread during that portion only of the stitching cycle at which it will not affect proper stitch formation.

It is a further object of this invention to provide a single sensing device to detect breakage or e" raustion of the supply of either the needle thread or the bobbin thread.

The aforementioned objects are accomplished by the present invention which is so arranged as to apply a drag on the thread in that portion only of the sewin cycle when the already formed stitch is being set and thread is being drawn from the thread supply. These two actions occur as the take-up arm approaches the top of its stroke. During this portion of the sewing cycle the thread is drawn tight by the take-up and additional drag does not adversely affect stitch formation.

Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations and arrangements of parts as illustrated in the presently preferred embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation and advantages of it when read in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of the head portion of a sewing machine bracket arm having the present thread "break sensing device applied thereto.

FIG. 2 is a front elevational view of the sewing machine face plate. a

FIG. 3 is a fragmentary top view of the bracket arm head showing the position of the thread break sensing member relative to the take-up arm when the thread is unbroken.

FIG. 4 is a view similar to FIG. 3, but showing the position of the thread break sensing member when the thread is broken or the thread supply is exhausted.

FIG. 5 is an enlarged side elevational view of the bracket arm head of the machine showing the relationship of the parts as the stitch is being set and new thread is being drawn from the thread supply.

FIG. 6 is similar to FIG. 5 but shows the relationship of the parts when the bobbin thread supply is exhausted.

Referring now to the drawings, the present invention is embodied in a sewing machine having a bracket arm 10 terminating m a head 11 in which there is mounted a reciprocating needle bar 12 carrying at its lower end a needle 13. While the application of the present invention is not restricted to any particular type of sewing machine the invention is incorporated for purposes of illustration in a cyclically operated sewing machine, as for atom ' quires.

(hice example a buttonhole sewing machine, wherein the machine sews a predetermined number of stitches after which the buttonhole is slit. To this end, there is mounted in the head 11, a slitting knife 14 actuated in the usual manner in timed sequence with the stitching cycle.

Also carried in the head 11 is the usual vertically movable take-up arm 15 the outer end of which is provided with a thread eye 16. Secured to the front of the head 11 is a face plate 17 on which is mounted a thread break sensing member 18 having an upper horizontal limb 19 extending through a slot 20 formed in the face plate 17 and being located at a point adjacent the topmost position of travel of the take-up arm 15, as shown in FIG. 1. Secured to the upper horizontal limb 19 is an insulating sleeve 21 carrying on its inner side a contact 22 adapted to engage the take-up arm 15 in a manner hereinafter to be described.

Integral with and vertically depending from the upper horizontal limb 19 (FIG. 2) is an upper vertical reach 23 disposed on the inside of the face plate 17 and journaled thereon by a pair of spaced bearing elements 24 fastened to the face plate by screws 25. Secured on the upper vertical reach 23 are spaced collars 26 and 27 engageable with the bearing elements 24 such that vertical movement of the thread break sensing member 18 is prevented. Depending from the upper vertical reach 23 and connected thereto by a laterally and forwardly bent portion 28 extending through a notch 29 in the face plate 17 is a lower vertical reach 30 having a lower horizontal limb or thread feeler finger 31 extending in the opposite direction from the upper horizontal limb 19 and lying in the path of movement of the needle thread 1 extending between the take-up arm 15 and the needle 13. A forwardly bent thread retaining limb 31a retains the thread t within the confines of the thread feeler finger 31.

Normally urging the contact 22 toward the take-up arm 15 and into the path of movement thereof is a spring 32 which encircles the upper reach section 23 adjacent to the portion 28. One end of the spring 32 is anchored on the face plate by the screw 25 and the other end encircles the lower reach section 30. Limiting the movement of the upper limb 19 toward the take-up arm '15 is a stop plate 34 fixed to the upper reach 23 and adjustable in response to turning of screw 33.

Electrical leads 35 and 35a, leading respectively from the contact 22 to the low voltage control unit 36 and from the control unit to the machine frame, form an open circuit which when closed by engagement of the contact 22 and take-up 15 is effective to energize the control unit 36. The control unit may then transmit a visual or audible signal indicating that the thread has broken or the thread supply is exhausted. The control unit may also provide for automatic stopping of the machine.

The operation of the thread break sensing arrangement is as follows:

When the needle thread I is unbroken and stitches are being formed in the conventional manner the needle thread travels from its source, over a guide member 37 through a thread tension 38, through the check spring through the eye 16 of the take-up arm 15, across the face plate 17, into a thread guiding slot 39 and thence through the eye of the needle 13. During normal stitch formation the take-up arm 15 travels in a vertical path alternately giving and taking up thread as the stitch formation re- During this giving and taking up of thread the length of thread t extending between the take-up arm 15 and the material being stitched is tightened across the front surface of the face plate 17 only when the take-up arm moves upwardly toward its top position where it exerts a maximum tension on the thread. Thus, when thread is eing given up the thread 1 merely slides or drops over the thread feeler finger 31 and the thread break sensing member 18 is urged clockwise, as viewed in FIGS. 3 and 4, by the spring 32 and positions the contact 22 on the upper limb 19 in the path of movement of the take-up arm 15. However, since the contact 22 is located adjacent to the topmost position of the take-up arm 15 during the downward movement of the take-up arm 15 the contact 22 will not be engaged during this period of stitch formation. As the take-up moves upwardly, particularly as it approaches the top of the stroke, the needle thread 1 is being drawn tight and when substantially at the top of its stroke it draws the previously formed stitch tight. Accordingly, at this time, as shown in FIGS. 1 and 3, the thread I is drawn upwardly in the thread guiding slot 39 and tightened across the outer surface of the face plate 17 whereupon the tightened thread t engages the thread feeler finger 31 adjacent the retaining limb 31a and is efiective to apply a turning movement on the thread sensing device 18 to turn the limb i9 counterclockwise against the action of the spring 32 and thereby prevent the contact 22 from engaging the take-up arm 15.

In the event that the needle thread t is broken, as shown in FIG. 4, this condition wiil be sensed by the thread feeler finger 31 since the thread merely drops slack and the thread break sensing member 18 is not turned. The contact 22 will then remain in its spring-urged position in the path of the take-up arm 15 which, when the latter reaches its topmost position, will engage the contact 22 and energize the control unit 36.

In FIG. there is illustrated the relative positions of the take-up arm and the contact 22 at stitch setting when the needle thread tis unbroken and there is a supply of bobbin thread 12 on the usual bobbin housed within the loop taking member 49. It is to be observed that as the threads t and b are being set to form the lock stitch in the work the bobbin thread b holds one end of the needle thread I fixed in the work whereby the latter is held tight and in engagement with the thread feeler finger 31,. Hence, as above described in connection with the sensing of a break in the needle thread 2, the tightening of the needle thread I applies a turning movement to the thread break sensing member 18 to move the contact 22 out of engagement with the take-up arm 15.

As shown in FIG. 6, when the bobbin thread b is exhausted the needle thread 2 is slack, since the increment of needle thread t drawn from its source during the feeding of the work in is no longer concatenated with the bobbin thread b. It is readily apparent that in a slack condition the needle thread t is incapable of applying a turning movement to the thread break sensing member 13 for moving the contact 22 out of its spring urged position and the latter will contact the take-up arm when it reaches its topmost position as shown in FIG. 6.

Having thus set forth the nature of the invention, what we claim herein is:

1. A device for use with a sewing machine for sensing a break in or exhaustion of the thread supply, comprising a. control device for indicating when said sewing thread supply is broken or exhausted, a pair of electrical contacts to complete a circuit to said control device when said thread supply is broken or exhausted, said pair of contacts meeting only when said thread supply is broken or exhausted, a first of said contacts being normally urged into the plane of travel of said second contact, and means to urge first contact out of said plane of travel of said second contact only during that portion of a sewing cycle when a stitch is being set.

2. In combination with a sewing machine comprising a frame having stitch forming instrumentalities supported thereon and including a vertically movable thread take-up device, an electrical control unit for indicating a break in or exhaustion of the thread supply, switch means for energizing said control unit when the thread supply is broken or exhausted, said switch means comprising two movable contacts, said vertically movable take-up device comprising one of said contacts, said switch means being operable only when said take-up device is at substantially the high point of its vertical travel.

3. In combination with a sewing machine comprising a frame having stitch forming instrumentalities supported thereon and including a vertically movable thread take-up device, an electrical control unit for indicating a break in or exhaustion of the thread supply, switch means for energizing said control unit when the thread supply is broken or exhausted, said switch means comprising two movable contacts, said vertically movable thread take-up device comprising a first of said contacts, said second contact being normally biased into the path of travel of said take-up device, and means operable when said thread supply is unbroken to urge said second contact from the path of travel of said take-up lever as it approaches the high point of its vertical path.

4. In combination with a sewing machine comprising a frame having stitch forming instrumentalities supported thereon and including a vertically movable thread take-up device, an electrical control unit for indicating a break in or exhaustion of the thread supply, switch means for energizing said control unit, said switch means comprising two movable contacts, said vertically movable thread take'up cor rprising a first of said contacts, a vertically disposed thread break sensing member carrying said second contact, said thread sensing member mounted for pivotal turning about its vertical axis; a spring normally biasing said thread break sensing member about its vertical axis to bring said second contact carried thereby into the path of travel of said thread take-up member, and means to urge said thread break sensing member about its vertical axis in opposition to said spring when said thread supply is unbroken.

5. In combination with a sewing machine comprising a frame having stitch forming instrumentalities supported thereon and including a vertically movable thread take-up device, an electrical control unit for indicating a break in or exhaustion of the thread supply, switch means for energizing said control unit, said switch means comprising two movable contacts, said vertically movable thread take-up comprising a first of said contacts, a vertically disposed thread sensing member carrying said second contact, said thread sensing member mounted for pivotal turning about its vertical axis, a spring normally biasing said thread sensing member about its vertical axis to bring said second contact carried thereby into the path of travel of said thread take-up member, and an arm integral with and extending laterally from said vertical thread sensing member in the path of the needle thread between the take-up and the needle responsive to the tightening of the needle thread at that point in the sewing cycle when the stitch is being set to urge said thread break sensing member out of the path of travel of said take-up member.

References Cited in the file of this patent UNITED STATES PATENTS 1,042,602 Roberts et al Oct. 29, 1912 1,738,142 Gail Dec. 3, 1929 1,742,953 Gahlert et al. Jan. 7, 1930 2,400,529 Behrens May 21, 1946 2,868,151 Winz Jan. 13, 1959

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