Vacuum Thread Cutter for Use in an Automated Textile Sewing Operation

This invention relates generally to textile thread cutters, and more particularly to such cutters that utilize a vacuum source and that are employed as part of a continuous sewing operation immediately after stitching by a sewing machine.

Vacuum thread cutters are generally well known, as exemplified by U.S. Pat. Nos. 2,356,378 (Capolupo (1943); 2,607,101 -- Stout (1952); and 3,557,730 -- Armstead (1971). In this type of mechanism, a vacuum system is used to pull trailing chain stitch threads through a cutting element as the sewn cloth leaves a sewing machine. The vacuum both holds the thread in position for the cutters and removes the cut thread from the work station.

A problem common to most of such prior art trimmers when used with an automated sewing machine operation is that because the workpiece is removed automatically at a relatively rapid rate, the trailing chain stitch is drawn taut and passes over the cutting shears without being severed. The result is that the workpiece is still tethered to the sewing machine and is pulled free to the workpiece removal mechanism, thereby upsetting the sequence of operations of the entire automated system. One way to overcome this problem is to ensure that during removal of the workpiece from the sewing machine, slack is allowed to occur in the chain stitch. The slack in the chain stitch can then be sucked by a vacuum line into engagement with the cutting shears. This, however, necessitates that there be a pause in the removal operation which slows the severing operation.

It is a principal object of the present invention to provide an improved vacuum head thread cutter that positively severs a sewn workpiece from the sewing needle without the necessity of slowing the removal of the sewn workpiece from the sewing machine.

It is another object of the present invention to provide such an improved vacuum thread cutter that operates at increased rates of speed of cloth travel over the cutting station.

These and additional objects are accomplished by the structure of an improved vacuum head thread cutter according to the present invention wherein a trailing stitch chain from a sewn workpiece which is being automatically removed from a sewing machine is passed immediately over a vacuum throat and then over an upright thread cutter adjacent to the vacuum head, the cloth workpiece being held down against the cutting head by resilient elements on both sides thereof. The vacuum throat is shaped to provide a downward pull on threads from the cloth before they reach the cutting head, and after reaching the cutting head to pull the threads through the cutting head mechanism as well. The result is that threads to be cut are properly oriented long before reaching the cutting elements and are, once the threads reach the cutting elements, drawn therethrough, all resulting in short cuts of the thread. The cloth workpiece is permitted to move at high rates of speed because it is not necessary to allow slack to occur in the trailing stitch chain. The increased speed of cloth movement that is permitted increases the productivity of automatic sewing equipment.

Additional objects, advantages and features of the present invention are explained as part of the following detailed description which should be taken in conjunction with the accompanying drawings.

FIG. 1 is a plan view, with portions broken away, showing a preferred embodiment of a vacuum thread cutter according to the present invention utilized at the output of an automated sewing device;

FIG. 2 is a vertical, sectional view of the assembly of FIG. 1 taken at section 2--2 thereof;

FIG. 3 is a vertical view of a portion of the assembly of FIGS. 1 and 2 taken at section 3--3 of FIG. 2;

FIG. 4 is an enlarged vertical sectional view of the vacuum head thread cutter assembly of FIGS. 1-3 taken at section 4--4 of FIG. 1;

FIGS. 5 and 6 are enlarged views which illustrate the operation of the vacuum thread cutter of FIGS. 1-4 by showing different portions of cloth having trailing threads thereon in the view of FIG. 4;

FIG. 7 is an enlarged plan view of a vacuum head component of the assembly of FIGS. 1-6;

FIG. 8 is an enlarged end view of the vacuum head block of FIG. 7;

FIG. 9 is an enlarged perspective view of the vacuum head of FIGS. 7 and 8;

FIGS. 10 and 11 are enlarged, vertical sectional views of a portion of the vacuum head of FIGS. 7-9 taken at sections 10--10 and 11--11, respectively, of FIG. 9; and

FIGS. 12, 13, 14 and 15 depict a modified embodiment of the invention and correspond, respectively, to FIGS. 4, 3, 7 and 6.

Referring initially to FIG. 1, a vacuum head (trimmer block) 11 is positioned a few inches away from a standard sewing machine needle and presser foot assembly 13. The head 11 is positioned to receive a fabric piece 15, after it has first been stitched, a threaded stitch 17 being illustrated in FIG. 1.

A trailing stitch chain 19 extends from the needle of the sewing machine assembly 13 to the trailing edge of the fabric piece 15. The vacuum head 11 is furthermore positioned so that the trailing thread chain 19 from the sewing operation will tend to drop into channel shaped openings 21 and 23 of the head 11 under the influence of a reduced air pressure therein. Since the thread chain 19 is somewhat taut, however, it is necessary to provide means for mechanically forcing the thread chain 19 to travel into the channel shaped openings 21 and 23. This function is accomplished by a pair of leaf springs 51 and 53 (FIG. 2) as will be explained in greater detail further herein.

In this automatic sewing operation, the cloth is automatically moved from the sewing station to the vacuum thread cutter and thence on to its next operation along a work surface 25 by an overhead, motorized belt 27. The work surface 25 is generally flat except for the apertures 21 and 23 into which the trailing thread chain 19 is caused to drop. A pair of thread shearing elements 29 and 31 are positioned generally upright beneath the surface 25 in order to sever the thread chain 19 from the fabric 15 as it is passed thereover. After the thread chain 19 is severed from the fabric 15, the fabric proceeds onward to the next operation, in a manner such as shown by the fabric piece 15' being pulled by a movable fabric gripping element 33.

The actual thread cutting elements are preferably powered shears; that is, a set of stationary upright teeth 29 (see FIG. 3) has knife-like edges within its V-grooves. A cooperating element 31 is held for reciprocation back and forth in the direction shown by the arrow in FIG. 3 immediately against the stationary member 29. The plane where the principal cutting action occurs is the intersection of the stationary element 29 with the moving element 31, these elements being oriented so that the plane is substantially orthogonal to the plane of the work surface 25 and thus to the path taken by the fabric 15 as it is passed thereover. Reciprocal motion is provided to the moving element 31 of the cutting assembly, such as by a crank 35 and an eccentric 37 operably connected to an electric motor 39 and to each other in a manner to provide the desired rocking motion of the element 31.

The particular shape of the vacuum head 11 is shown in detail, particularly by FIGS. 7-11. The top elongated openings 21 and 23 are formed in a top, substantially planar surface 12 which is inclined upwardly from the work surface 25 in the direction of fabric travel, from left to right as viewed in the figures. The openings 21 and 23 are part of a vacuum throat 41 that opens downwardly. The throat 41 is connected with a vacuum chamber 43 (FIG. 4) from which a vacuum tube 45 extends for interconnection with a vacuum pump (not shown) of a standard type. By reducing the pressure in the chamber 43 and the throat 41 with the vacuum pump, the trailing thread chain 19 is drawn downwardly thereinto as the cloth passes over the vacuum thread cutter assembly 29 and 31. The vacuum is drawn through the top surface openings 21 and 23.

A cantilevered support element 47 separates the vacuum throat into the elongated openings 21 and 23 and helps support the fabric being drawing thereover.

Additional details of the shape of the vacuum head 11 as shown in FIGS. 7-11 can best be appreciated by reviewing its operation as shown in FIGS. 4-6. The top surface 12 of the block is oriented to provide a small acute angle with the work surface 25 in order to provide a ramp upon which the fabric 15 entering the thread cutting station can easily be accepted. A transparent plastic top guide 51 is provided to hold that portion of the fabric passing over the vacuum head 11 generally downward against the vacuum head 11 as well as to help direct the vacuum force.

Attached to this guide 51 are two leaf springs 53 and 55. They are attached at one end by an appropriate fastener 57 with the opposite ends of the leaf springs being free. The free end of the leaf spring 53 is shaped to depend downward on one side of the cutting blades while the free end of the leaf spring 55 is shaped to depend downwardly on an opposite side of the cutting assembly. The purpose of these leaf springs is to resiliently urge cloth passing through the cutting assembly downward on both sides of the cutting blade, as is best illustrated in FIG. 5, to thereby force the taut trailing stitch chain 19 to pass through the cutting blades 29 and 31.

The rest position of the leaf springs 53 and 55 is adjusted by an appropriate adjustable stop member 59. As is best shown in FIG. 1, the width of each of the leaf springs 53 and 55 is substantially the same as the width of the vacuum throat 41 and its upper surface thereof wherein it has the form of the openings 21 and 23.

Referring now more particularly to FIGS. 7-11, the initial portion of the vacuum throat openings 21 and 23 taken in the direction of travel of the cloth piece 15, are downwardly sloping depressions 61 and 63 on opposite sides of the elongated support 47. The beveled top edge shape of the divider 47 permits the threads 19 of a piece of cloth passing thereby to drop down into the openings 61 and 63. The depressions 61 and 63 slope downward in the direction of travel of the threads until joining the main throat area 41 at which point, as illustrated best in FIG. 5, the threads are permitted to drop downward through the throat 41 under the influence of gravity and the partial vacuum therein. The leaf springs 53 and 55 urge the cloth 15 downward against the cutting elements 29 and 31 in a manner to bow the cloth thereover. As shown best in FIG. 6, the trailing edge of the fabric 15 drops downward after passing through the cutting blades, thereby placing the undesired thread chain 19 squarely between cutting blade teeth. This cloth action is contributed to by the plastic guide member 51 whose lowest most edge is lower than the teeth of the cutting elements 29 and 31, as best shown in FIG. 6.

Referring now more particularly to FIGS. 12-15, a modified embodiment of the invention is disclosed. In this modified embodiment, the vacuum head 11 is spaced from the stationary cutting members 29 by a distance of from 0.2 to 0.3 inches. The outside edges of the vacuum head 11 which are immediately adjacent to the stationary cutting blade 29 are provided with a sponge rubber gasket 64 to prevent undue air leakage into the intervening space. The purpose of the gap is that if a thread passing through the middle of a workpiece is not in alignment with the openings 21 and 23 of the vacuum head, the gap between the vacuum head 11 and the stationary cutting blade 29 will allow the thread to move perpendicular to the direction of sewing and therefore will fall into the slot or gap between the vacuum head 11 and the stationary cutting blade 29. The thread will thereby be prevented from sliding over the top of the teeth in the stationary cutting blade 29.

Although the various aspects of the present invention have been described with respect to a preferred embodiment thereof, it will be understood that the invention is entitled to protection within the full scope of the appended claims.