Sewing machine with latch back device

A sewing machine comprising:

• sewing needles in a sewing area for sewing a continuous overlock stitch or the like into a work piece moved through the sewing area whereby excess thread chain is created between a trailing edge of a previously sewn work piece and said sewing needles;
• means for applying tension to the excess thread chain;
• severing means for cutting the excess thread chain with the excess thread chain stretched taut to create a severed leading thread chain of a predetermined length extending from said sewing needle;
• a chaining tongue positioned for receiving thereabout the chain stitch formed by the sewing needles and including an open end adjacent said sewing needles for receiving a free end of the severed leading thread chain extending from said sewing needles;
• vacuum means for inducing a stream of air to flow into said chaining tongue and drawing the free end of the leading thread chain into said chaining tongue;
• and
• means for retaining one end of the excess leading thread chain about said chaining tongue after the severing means cuts the excess thread chain and as the excess thread chain is drawn into the chaining tongue.

An apparatus for use with a sewing machine, the sewing machine including sewing needles in a sewing area for sewing an overlock stitch or the like about a chaining tongue and into a work piece whereby a thread chain is created between a trailing edge of a previously sewn work piece and the sewing needles, said apparatus comprising;

• means for applying tension to the thread chain extending between the previously sewn work piece and said needle,
• severing means for cutting the thread chain extending from the sewing needle to the previously sewn work piece while tension is applied to the thread chain to create a severed trailing thread chain extending from the trailing edge of the previously sewn work piece and a severed leading thread chain of a predetermined length extending form the sewing needle, and
• means for drawing off the free end of the severed leading thread chain extending from the sewing needle and for positioning the free end of the leading thread chain in a position to be oversewn into the beginning of the stitching in a second work piece, comprising a hollow chaining tongue including an open end adjacent the sewing area and means for inducing a stream of air to flow into said open end of said hollow chaining tongue in timed relationship with the cutting of the thread chain, whereby the free end portion of the leading thread chain extending from the sewing needle recoils from the severing means toward the chaining tongue and is drawn into the hollow chaining tongue by the stream of air.

A method of sewing a portion of a thread chain extending from the sewing needles of a sewing machine from a previously sewn work piece to a second work piece for eliminating a knot or thread chain protruding from the leading edge of the second work piece, said method comprising the steps of:

• a. sensing the completion of sewing of the first work piece which has moved along a sewing path through the work area of the sewing machine as the sewing needles continue to operate to form the thread chain about a chaining tongue;
• b. drawing taut the thread chain extending from the chaining tongue as the sewing needles continue to operate;
• c. while the thread chain is taut, cutting the thread chain extending between the needles of the sewing machine and the first work piece in response to sensing the completion of sewing of the first work piece in a manner to create a leading thread chain of a predetermined length extending from the sewing needles;
• d. as the sewing needles continue to operate drawing off the free end of the leading thread chain extending from the sewing machine needles into a hollow chaining tongue in such a manner as to cause the excess thread chain to extend below the path of the second work piece;
• e. advancing the second work piece along the sewing path to the sewing machine needles as the sewing needles operate while the leading thread chain is drawn into the hollow chaining tongue until the second work piece is engaged by the sewing needles;
• f. simultaneously sewing the second work piece and progressively oversewing the drawn off free end of the thread chain to the second work piece.

A method of sewing excess thread chain extending from the sewing needles of a sewing machine to a work piece for eliminating a knot or thread chain protruding from the leading edge of the work piece, comprising the steps of:

• a. forming an overlock stitch or the like about a chaining tongue and into a series of work pieces with the operation of sewing needles as the work pieces move along a sewing path beneath the sewing needles of the sewing machine;
• b. sewing off a first one of the work prices to form a thread chain extending from a trailing edge of the first work piece to the sewing needles;
• c. drawing taut the thread chain extending from the trailing edge of the first work piece to the sewing needles;
• d. cutting the taut thread chain extending between the sewing needles and the previously sewn work piece at a predetermined distance from the sewing needles to create a predetermined length of leading thread chain extending from the sewing needles as the thread chain continues to be formed;
• e. simultaneously with the step of cutting the taut thread chain inducing a stream of air into the chaining tongue to draw off the free end of the leading thread chain extending from the sewing needles into the chaining tongue to cause the free end of the leading thread chain to extend along the sewing path;
• f. continuing the sewing action of the sewing needles and advancing a second work piece along the sewing path to the sewing machine while retaining the free end of the leading thread chain in the hollow chaining tongue until the second work piece is engaged in the sewing needles;
• and
• g. sewing the second work piece with the sewing needles while progressively pulling with the second work piece the free end of the leading thread chain from the chaining tongue and incorporating the leading thread chain into the chain stitch formed in the second work piece.

A sewing machine comprising:

• sewing needles in a sewing area for forming an overlock stitch or the like into a work piece moved in spaced series through the sewing area whereby excess thread chain is created between the trailing edge of a previously sewn work piece and the sewing needles;
• severing means for cutting the excess thread chain to form a severed leading thread chain of a predetermine length extending from the sewing needles;
• a chaining tongue in said sewing area positioned for receiving thereabout the chain stitch formed by the sewing needle and including an air passage therethrough and an open end adjacent said sewing needles for receiving a free end of a severed leading thread chain;
• vacuum means for inducing a stream of air to flow into the open end and through the air passage of said chaining tongue and drawing the free end of the leading thread chain into said chaining tongue;
• and
• control means responsive to the movement of a work piece beyond said sewing area for actuating said severing means to cut the excess thread chain and forming the severed leading thread chain, and for continuing the formation of the severed leading thread chain by the sewing needles about the chaining tongue until after the thread chain has been cut and as the vacuum means continues to induce a stream of air to flow into the open end of the chaining tongue.