US2937605A

US2937605A - Thread tension devices

Info

Publication number: US2937605A
Application number: US715281A
Authority: US
Inventors: Earl F Dunn; Stanley M Sliva; Francis L Walling
Original assignee: Singer Co
Current assignee: Singer Co
Priority date: 1958-02-14
Filing date: 1958-02-14
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24
Also published as: DE1138610B; GB863696A

Description

May 24, 1960 E. F. DUNN ET AL 2,937,605

THREAD TENSION DEVICES Filed Feb. 14, 1958 42 W INVENTORS.

Earl F. Dunn, Flg. BY Stanley M. Sliva,

and Francis L. Walling.

ATTORNEY United States Patent 2,937,605 I THREAD TENSION DEVICES Earl F. Dunn, Monroe, and Stanley M. Sliva and Francis L. Walling, Trumbull, Conn., assignors to The Singer Manufacturing Company, Elizabeth, N.J., a corporation of New Jersey Filed Feb. 14, 1958, Ser. No. 715,281

4 Claims. (Cl. 112-254) This invention relates to thread tension devices for sewing machines.

It is an object of this invention to provide a novel thread tension device for a sewing machine and more particularly for use with a sewing machine employing a rotary thread take-up.

It is an object of this invention to provide a thread tensioning unit with an associated check spring which, when located advantageously on a sewing machine, may be properly threaded easily and quickly and without danger of fouling the thread.

The elements which control the needle thread of a lock stitch sewing machine from a thread supply to the needle include a thread tensioning device, a check spring and a take-up. The take-up serves to draw in and give out thread in accordance with the demands of the stitch forming instrumentalities; the tensioning device establishes the degree of tension in the thread when all the slack has been taken up, and the check spring serves as a small, quick acting auxiliary take-up in which capacity it cushions shock loading in the thread and tailors the action of the main take-up on the thread.

For the most accurate control of the thread the length of thread from the tensioning device to the needle should be held to a minimum for the reason that thread has certain inherent elastic properties and the amount that the thread will stretch when tensioned will increase as its length increases. The shorter the length of thread from the tensioning device to the needle, therefore, the more accurate and predictable will be the control exercized thereon by the take-up.

It is also advantageous in a needle thread control arrangement to attain the most direct thread path between the tensioning device and theneedle. Since each thread guide and the like, imparts an uncontrolled drag upon the thread and thus detracts from the effectiveness of the tensioning device, an absolute minimum of such thread guides is essential to the most accurate control of the thread tension.

The above considerations as applied to a sewing machine with a rotary take-up indicate the most advantageous location for the thread tensioning device to be beneath the take-up member, in which position a substantially complete loop of thread is presented to the take-up directly from the thread tensioning device and, therefore, the most direct and the shortest possible length of thread is attained in the system.

When a tensioning device is thus advantageously located beneath a rotary take-up, however, there arises a difficulty in threading the system. This difiiculty stems from the fact that the manipulations of the thread necessary to introduce the thread into the check spring from the tensioning unit are substantially identical to those manipulations which are necessary in order to introduce the thread into the rotary take-up. The thread is apt, therefore, to be engaged on the check spring twice in "ice which case the thread will be snubbed and broken as soon as stitching is attempted.

It is an object of this invention to provide guard means carried as a part of a thread tensioning unit for preventing the double threading of a check spring.

The above and other objects will be hereinafter more I Fig. 1 represents an end elevational view of a sewing machine bracket arm illustrating a rotary take-up mechanism partly broken away and having the thread tensioning unit of this invention applied thereto,

Fig. 2 is an enlarged cross-sectional view of the thread tensioning unit,

Fig. 3 represents an exploded perspective view of the thread tensioning unit, and

Fig. 4 represents a perspective view of the guard member of the thread tension-ing unit.

Referring particularly to Fig. 1 of the drawings a sewing machine bracket arm is indicated at 10 closed at the end by a cover plate 11. Extending outside the cover plate and carried for turning movement with an arm shaft 12 in the bracket arm is a rotary take-up member 13 shielded by a take-up guard 14 which extends in spaced relation to the cover plate to define therebetween a thread receiving slot through which a thread may be introduced to the take-up member.

Journaled for endwise reciprocation in the sewing machine bracket aim is a needle bar 15 carrying a needle 16. A presser bar 17 is also journaled for endwise movement in the bracket arm and has a presser foot 18 secured thereto. A thread guide 19 carried for movement with the presser bar extends through a slot 20 in the cover plate.

Indicated generally at 21 is a thread tensioning unit which includes a check spring 22. As illustrated in Fig. 1 the tensioning unit is carried on the sewing machine bracket arm beneath the rotary take-up member and at one side of the thread guide 19. In Fig. 1, a needle thread is illustrated in solid lines in the position it will occupy during stitching operations, and in phantom lines in two positions A and B that it will occupy when it is being threaded. The thread after passing through the tensioning unit and over the check spring leads through the thread guide 19, over the take-up member 13, through a thread guide 23 on the cover plate 11, through a wire thread guide 24 onthe needle bar, and then to the needle.

The constructive features of the sewing machine thus far generally described are conventional and need not be described in further detail for an understanding of the' present invention.

Referring to Figs. 2 and 3, the thread tensioning unit 21 comprises a stud 30 formed at one extremity with external threads 31 and an attenuated slot 32 and at its other extremity with a short slot 33. Secured to thestud 30 i by means of a set screw 34 is a collar 35 formed with an external annular groove 36 and with a counterbore 37.'

An opening 38 is formed through the side wall of the collar 35 near its free end which presents a flat circular.

art these details have not been included in the drawings. Disposed on the stud 30 flush against the circular face a 39 of the collar 35 is the disc-likeback portion 41 of a Since 1 guard member 42. Diametrically opposed lugs 43 struck out from the portion 41 of the guard member seat in the notches 40 of the collar and thus serve to lock the guard member against rotation with respect to the stud. The inside face of the back portion 41 of the guard memher is formed with a raised bearing ring 44 which is serrated. Approximately half of the periphery of the back portion 41 of the guard member is formed with a wide flange 45 which extends substantially parallel to the axis of the stud 30, the remaining half of the periphery of the back portion 41 of the guard may be considered as coinciding with a gap in the flange 45. A thread entrance slot 46 is formed in the flange 45 and at one end opens into the gap. At the other extremity of the flange adjacent the gap, the flange is formed with a finger 47 which projects outwardly substantially in continuation on the flange.

A disc 48 of frictioning material such as felt, leather, etc., is disposed on the stud against the bearing ring 44 of the guard member. A thread-engaging wheel 49 is loosely journaled on the stud against the disc 48. The periphery of the wheel is preferably formed with a plurality of radially extending fingers 50 which are bent outwardly alternately in opposite directions so as to provide a V-shaped thread-engaging rim for engagement with the thread. A second frictioning disc 51 identical with the disc 48 is disposed on the stud at the opposite side of the thread-engaging wheel.

A pressure disc 52 is disposed on the stud and formed on the inside face with a raised serrated bearing ring 53 which bears against the frictioning disc 51. A pin 54 driven into the pressure disc 52 extends into the attenuated slot 32 in the stud so as to prevent rotation of the pressure disc with respect to the stud. The periphery of the pressure disc is preferably formed with a continuous flange 54 externally tapered inwardly and disposed to overlie the rim of the thread-engaging wheel to cam a thread properly into engagement within the V-shaped rim of the wheel.

A beehive spring 55 is constrained on the stud between the pressure disc 52 and a knurled nut 56 on the threads 31 of the stud. The pressure exerted on the thread-engaging wheel between the

discs

48 and 51 of frictioning material may be adjusted by means of the knurled nut 56.

Since the guard member 42 and'the pressure disc 52 are both locked against rotation on the stud and the

bearing rings

44 and 53 thereon are; serrated, rotation of the frictioning

discs

48 and 51 will be prevented and as a result the frictional forces exerted upon the thread engaging wheel will occur from a single source, namely the friction between the

discs

48 and 51 and the threadengaging wheel 49. The frictioning forces and thus the tension applied to a thread will be highly consistent.

The check spring 22 comprises a series of coils 57 disposed about the stud 30 and within the counterbore 37. An inturned extremity 53 of the check spring extends into the short slot 33 of the stud and serves to anchor the check spring thereon. The opposite extremity of the check spring is formed with a radial arm 59 which extends through the opening 38 in the wall of the collar and is bent into a loop 60 which extends across the periphery of the guard member 42 in the gap of the flange 45 thereon and, therefore, also extends across the rim of the thread-engaging wheel 49. The free extremity 61 of the check spring loop 60 is bent to extend substantially parallel to the pressure disc 52 and to a position between the stud 30 and the finger 47 on the guard member.

As illustrated in Fig. l, the thread tensioning unit is preferably secured to the bracket arm of the sewing machine with the finger 47 of the guard member disposed substantially on a line between the stud 30 and the axis of turning movement of the rotary take-up member as indicated by the arm shaft 12.

In threading the needle thread control devices of this invention a thread limb leading from a supply is grasped by the machine operator and directed into the thread entrance slot 46 of the thread tensioning unit which delivers the thread directly to the rim of the thread engaging wheel. The operator then draws the limb of the thread once around the wheel and into the position marked A" in Fig. l in which the thread has been drawn under the finger 47 and under the free extremity 61 of the check spring. Then, holding the thread slightly upwardly inclined, the operator draws the limb of the thread back, i.e., to the right in Fig. 1, the thread being guided by the flange 45 over the check spring extremity 61 and under the finger 47. The thread is then drawn under the thread guide 19 after which the thread is drawn upwardly and to the left to the position marked B in preparation for threading the take up. Fig. 1 illustrates how close to the check spring the thread must be drawn in threading the take-up. In the position marked B, the grasped thread limb will extend over the finger 47 which will prevent the thread from passing around the free extremity 61 of the check spring a second time.

The operator then directs the thread into the space between the take-up guard member 14 and the end cover plate 11 to thread the take-up member and finally threads the guides 23 and 24.

The tensioning device of this invention may thus be threaded quickly and without special care on the part of the machine operator and the danger of fouling the thread by engagement twice with the check spring is minimized.

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

l. A thread tensioning device for a sewing machine comprising a stud adapted to be fixed in said sewing machine, thread tensioning means on said stud, a guard disc locked against turning movement on said stud at one side of said thread tensioning means, a laterally extending flange on the periphery of said guard disc arranged to span said thread tensioning means, said flange formed with a gap extending over a portion of the periphcry of said guard disc, a laterally projecting finger on said flange at the edge of said gap at check spring anchored on said stud and extending transversely across the periphery of said guard disc in said flange gap, a free extremity on said check spring formed to extend toward said flange and between said laterally extending finger and said stud.

2. A thread tensioning device for a sewing machine comprising a stud adapted to be fixed in said sewing machine, a thread engaging wheel journaled for turning movement on said stud, means on said stud for imparting a frictional resistance to turning movement of said wheel, a guard disc locked against turning movement on said stud at one side of said thread engaging wheel, a laterally extending flange on the periphery of said guard disc arranged to span said thread engaging wheel, said flange formed with a gap extending over a portion of the periphery of said guard disc, said flange formed with a thread receiving slot opening into said gap at one end of said flange and disposed substantially in the plane of said thread engaging wheel, a laterally extending finger formed on said flange adjacent said gap at the opposite end of said flange, a check spring anchored on said stud and extending transversely across the periphery of said guard disc in said flange gap, and a free extremity on said check spring formed to extend substantially parallel to said guard disc and between the laterally extending finger on said guard disc flange and said stud.

3. In a sewing machine having a single bracket arm, a rotary take-up in said bracket arm, a tensioning unit detachably secured to said sewing machine bracket arm beneath said rotary take-up member, a thread tensioning device associated with said tensioning unit for imparting frictional resistance to movement of a thread from a supply to the rotary take-up, a check spring anchored on said tensioning unit, a free extremity formed with a loop on said check spring for engagement with a thread extending from the thread tensioning device to said takeup, a thread guide, means supporting said thread guide on said sewing machine bracket arm for engagement with the thread extending from the check spring to the takeup, and a guard member fixedly secured to said tensioning unit, a finger formed on said guard member and disposed extending across the looped free extremity of said check spring and at a point substantially between the thread guide and the path of the periphery of said rotary takerup to prevent double threading of said check spring.

4. In a sewing machine having a bracket arm provided with an end cover plate, a rotary take-up member carried by said bracket arm for movement about an axis substantially perpendicular to said cover plate, a thread tensioning device comprising a stud fixed in said bracket arm substantially perpendicular to said end cover plate and beneath said rotary take-up member, a thread engaging wheel journaled for turning movement on said stud, means on said stud for imparting a frictional resistance to turning movement of said wheel, a guard member locked against turning movement on said stud between said thread engaging wheel and said end cover plate, a finger extending from said guard member outwardly away from said end cover plate, said finger arranged to span the periphery of said thread engaging wheel at a point between the stud of said thread tensioning device and the axis of movement of said rotary take-up member, a check spring anchored on said stud and extending transverselyacross the periphery of said thread engaging wheel, and a free extremity on said check spring formed to extend substantially parallel to said thread engaging wheel and between said stud and the finger of said guard member.

References Cited in the file of this patent UNITED STATES PATENTS 383,748 Melone May 29, 1888 413,657 Gibbs Oct. 29, 1889 875,610 Parkes Dec. 31, 1907 2,462,812 Parry et al. Feb. 22, 1949 2,810,532 Zeier et a1. Oct. 22, 1957 FOREIGN PATENTS 414,717 Italy Aug. 24, 1946