US2895440A - Thread-controlled contact device for power driven sewing machines - Google Patents

Description

K. WINZ THREAD-CONTROLLED CONTACT DEVICE FOR POWER DRIVEN SEWING MACHINES July 21, 1959 Filed March 13, 1957 United States Patent MEAD-CONTROLLED CONTACT DEVICE FOR POWER DRIVEN SEWING MACHINES Karl Winz, Kaiserslautern-Pfalz, Germany, assignor to G. M. Pfalr A.G., Kaiserslautern-Pfalz, Germany, a corporation of Germany Application March 13, 1957, Serial No. 645,691 Claims priority, application Germany March 27, 1956 2 Claims. (Cl- 112-219) The present invention relates to thread-controlled electrical contact devices for power driven sewing machines, more particularly to contact devices actuated by the upper or needle thread on failure of the lower or bobbin thread, to effect the stoppage of the machine by disconnecting it from its power supply or de-clutching it'from its driving means, in an effort to avoid wasteful running and other defects.

A known arrangement of this type comprises an oscillating lever pivotally mounted upon a support secured to the presser foot bar of the machine. The lower end of the lever is bent at a right angle and extended to a point immediately behind the needle and transverse to the sewing direction. There is further secured to the lower end of said lever a frame or loop engaged by the end of a contact bar. The latter is pivotally supported by a bearing mounted upon the cloth plate or table top of the machine and cooperates with a fixed insulatingly mounted contact. Upon displacement of the needle thread due to failure or breakage of the lower thread, the lever is deflected in the sewing direction, whereby the contact arm being disengaged from said frame is caused to fall and close the contacts of the device. This, in turn, closes a relay circuit or the like effecting the stoppage of the machine.

Devices of this type have the disadvantage that, due to the arrangement of the lever with its thread-actuated part transverse to the sewing direction and above the presser foot, a substantial number of unbound or idle stitches are required, to cause a displacement of the upper thread suflicient to effect closing of the contacts. Furthermore, the parts being mounted upon the table top obstruct or otherwise interfere with the operation of the machine. For this reason, devices of this are only suitable practically for machines designed for edge seaming or binding purposes.

Other known contact devices of this type comprise a pivoted lever having a movable contact and cooperating with fixed contact arm, both mounted upon the presser foot of the machine. The contacts are normally urged to open position by a spring, the movable contact arm being arranged with its lower end extending to a point close to the needle thread above the presser foot. There is further provided an electromagnet upon the fixed contact arm becoming energized upon closing of the contact device and actuation of the stoppage means of the machine, to maintain the movable contact arm in closed position until a main control switch of the machine is closed after removal of the disturbance or thread failure.

Again, with contact devices of this type, the lower end of the movable contact arm controlled by the needle thread must be spaced by a certain distance from the presser foot, thus requiring a substantial number of unbound or idle stitches to initiate the closing of the contacts and, in turn, the stoppage of the machine. Furthermore, it is difiicult to mount a contact device of remaining parts or without interfering with the proper operation of the machine.

For practical purposes and in the interest of safety, not more than about two unbound stitches should occur. upon actuating of the contact device and prior to the stoppage of the machine, to prevent jamming threads.

and other defects. This aim could not be achieved by the known devices for the reasons as pointed out and being obvious from the foregoing.

Accordingly, an object of the present invention is the' provision of a simple and improved thread-actuated contact device to effect the automatic stoppage of a power driven sewing machine by which the above and related difiiculties and drawbacks are substantially overcome.

A more specific object of the invention is to provide a control device of this type which can be used in connection with any type of stitching material or sewing operation.

Still another object of the invention is the provision of a thread-controlled contact device of the type referred to for power driven sewing machines which can be structurally embodied in conventional sewing machines without essential changes in the design and construction of the machines and without interfering with the normal operation thereof.

Yet another object of the invention is the provision of a contact device actuated by the displacement of the upper or needle thread of a conventional sewing machine consequent on the breakage or failure of the lower or bobbin thread, whereby closing of the contacts of the device is effected substantially instantly on thread failure, that is, with a minimum of the idle or unbound stitches being effected during the interval between the thread failure and engagement of the contacts.

The invention, both as to its further objects as well as novel aspects, will be better understood from the following detailed description taken in reference to the accompanying drawing, forming part of this specification and showing a fractional perspective view of a conventional sewing machine embodying an improved contact device constructed in accordance with the principles of the invention.

With the foregoing objects in view, the invention involves generally the provision of an improved contact device of the type referred to suitable for structural embodi ment with the presser foot base of a power driven sewing normally out of contact therewith.

The presser foot base is provided with a recess close to the needle, further means being provided to cause said thread-controlled portion or extension of said lever to resiliently engage the sewing material by the action of a biasing spring normally urging the frame or lever in a this type upon the presser foot without obstructing the Q downward direction. Upon failure or breakage of the lower or bobbin thread, the upper thread no longer emerges directly or straight from the stitching material close to the needle, but assumes an oblique position or slack dragging and raising the contact frame and effecting engagement thereof with a cooperating contact fixedly mounted upon said presser foot. As a result, a relay or the like connected in a circuit including the contact device initiates the stoppage of the machine. Due to the provi sion of the recess in the presser foot base enabling the movable contact to be extended to a point close to the Patented July 21, 1959,

3 needle thread and into direct contact with the work or stitching material, actuation of the contact device is effected practically instantly and involving a minimum number of idle or unbound stitches on the failure or breakage of the lower thread. Furthermore, the contact device may be structurally embodied within the confines of the presser foot base of conventional machines, substantially i.e. without any projecting parts or without requiring changes in the design thereof, as will become further evident hereafter.

Referring more particularly to the drawing, the numeral 1 indicates the cloth plate of a conventional sewing machine connected with the overhanging arm 2 by an upright or standard (not shown), said arm terminating in a head 3 having mounted therein a reciprocating needle bar 5 carrying a needle 4 and presser foot bar 6, all of standard construction well known in the art. The lower end 7 of the presser foot bar 6 is of square shape to receive the presser foot 8 removably secured thereto by means of a screw 9. The presser foot, in a known manner, resiliently engages the stitching plate 10 or sewing material, respectively, in the operative position, said plate being mounted flush with the cloth plate 1 underneath which are arranged in known manner the cooperating stitch forming tools, such as the loop taker and feed dog mechanism, not shown in the drawing for simplicity and being unessential for the understanding of the invention.

The pressure foot, in the example shown, comprises a vertical shaft 11 and a horizontal base 12 having a pair of bearings 13 and 14 supporting a shaft 15 pivotally connecting the base 12 with the shaft 11 of the presser foot. The base 12 has an enlarged rear portion 16 provided with a bore 17, wherein is pivotally mounted the rear portion 18 of a contact frame or lever 19, portion 18 being surrounded by a spiral spring 20 within said recess. The spring 20 has one end secured to the rear portion 16 of the base 12 and has its opposite looped-shaped end 22 arranged to engage the intermediate portion 19 of the contact frame or lever, in such a manner that the front portion 23 of the frame will be resiliently urged in a downward direction upon the stitching plate 10 or the work passed therebetween and the presser foot by the feed mechanism during the operation of the machine.

For this purpose, the base 12 of the presser foot is provided with an oblong recess 24 close to the needle thread and at right angle to the'stitching direction, said recess adapted to receive the front part 23 of the contact frame 19. The latter thus extends to a point immediately adjac'ent to the point of emergance of the needle thread 31 from the work or stitching material. As a result, the frame will be deflected substantially instantly, that is, with a minimum number of unbound stitches being eifected, upon failure or breakage of the lower thread by the displacement or slack formed by the upper thread 31 being dragged over the base of the foot in the rearward direction, in a manner readily understood.

The end 25 of the part 23 constituting a 'movable contact cooperates with a fixed contact 26 insulatingly mounted upon the bearing 13 between a-pair of insulating sheets or layers 27 and secured by means of a screw 28 or in any other suitable manner. Contact 26 is connected to an electrical conductor 29 which may, in turn, be connected to one pole of a suitable current source through a relay or the like (not shown), the opposite pole of said source being connected to the metal parts of the machine to complete the electrical circuit of the contacts 25 and 2 6 of; the device, in a manner readily understood.

The lower end of the shaft 11 of the presser foot 8 is shown provided with a recess 30 to enable the upper thread 31 on failure of the lower thread to readily form a slack or assume an oblique position to insure safe and positive actuation of the contacts by the frame or lever 19 on the occurrence of a lower thread failure.

In the drawing, the contact frame and needle thread are shown in their position during operation; or normal stitch formation of the machine. In this case, the frame has its front portion 23 resiliently engaging the work or stitching material with a light pressure, acting, so to speak, as a feeler or probe of the seam being stitched. Upon failure of the lower thread, the upper thread will be extracted from the work to form an oblique slack in the rearward direction of the presser foot. As a result, the front portion 23 of the frame 19 being engaged by the thread is raised against the action of the spring 20 to effect closing of the contacts 25 and 26 and, in turn, to initiate the stoppage of the machine. The machine may be stopped in any known manner, such as by disconnecting it from its power supply or by de-clutching it from its driving means, or in any other suitable manner known in the art. At the same time upon stopping of the machine, a warning signal may be produced indicating the thread failure.

In the foregoing the invention has been described with reference to a specific illustrative device. It will be evident, however, that variations and modifications, as well as the substitution of equivalent elements for those shown for illustration, may be made without departing from the broader scope and spirit of the invention as set forth in the appended claims. The specification and drawing are accordingly to be regarded in an illustrative rather than in a restrictive sense.

1 A thread-controlled electrical contact device for lock-stitch sewing machines having a needle and a presser foot comprised of a vertical shaft and a horizontal base connected thereto and engaging a work piece in the lowered position, said device comprising a lever having a rear; portion pivotally mounted upon the rear portion of said base. behind said shaft, as viewed in the sewing direction, and about an axis transverse thereto, said lever extending in a direction opposite to the sewing direction above and substantially parallel to said base and having a front portion at right angle to the sewing direction, said front portion forming a first contact element movable substantially vertically within a corresponding recess in the front portion of said base close to the path of said needle, spring biasing means for said lever, to urge said contact element into continuous resilient engagement with said work piece in the lowered position of said presser foot, and a second, cooperating contact element mounted upon said base adjacent to said first contact element.

2. A thread-controlled electrical contact device for lock-stitch sewing machines having a needle and a presser foot comprised of a vertical shaft and a horizontal base connected thereto and engaging a work piece in the lowered position, said device comprising a lever having a rear portion at right angle to the sewing direction and pivotally mounted about its axis upon the rear portion of said base. behind said shaft, as viewed in the sewing direction, said lever extending in a direction opposite to the sewing direction laterally of said shaft and substantially parallel to said base and said lever having a front portion at right angle thereto forming a first contact element, saidfront portion located and movable substantially vertically within a recess in the front portion of said base close to the path of said needle, a coiled spring to bias saidlever concentric to the rear portion thereof, to urge said contact element into continuous resilient engagement'with said work piece in the lowered position of said presser foot, and a second cooperating contact element insulatingly mountedupon said base adjacent to said first contact element.

Vossen Oct. 30, 1945 Vossen May 22, 1956

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