Sewing machine with automatic latch back device and method of sewing a portion of a thread chain

A sewing machine comprising:

• advancing means for moving the work piece along a sewing path through and beyond a sewing area,
• sewing needles in the sewing area for sewing a continuous overlock stitch or the like in the work piece moved along the sewing path through the sewing area whereby excess thread chain is created and extends along the sewing path between a trailing edge of a previously sewn work piece and said sewing needles;
• said advancing means including means for applying tension to the excess thread chain;
• severing means positioned in the sewing path for cutting the excess thread chain with the excess thread chain stretched taut from the needles to the previously sewn work piece to create a severed leading thread chain of a predetermined length extending from said sewing needles;
• a chaining tongue positioned for receiving thereabout the overlock stitch formed by the sewing needles and including an open end at the position of 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
• detector means responsive to the trailing end of the work piece moving through the sewing area for actuating said severing means and for continuing the operation of the sewing machine to a time after the severing means cuts the thread chain to maintain the thread chain in motion at the opening of the chaining tongue;
• whereby the excess thread chain extending from the sewing needles to the work piece along the sewing path is stretched as it is cut and the cut end of the severed leading thread chain recoils toward the chaining tongue and is drawn into the open end of the chaining tongue by the stream of air.

Apparatus for use with a sewing machine including sewing needles in a sewing area for sewing an overlock stitch or the like about a chaining tongue and into a series of work pieces moving along a path through said sewing needles whereby a thread chain is created between a trailing edge of the previously sewn work piece and the sewing needles, said apparatus comprising:

• detector means for determining when the trailing edge of a work piece moves beyond the sewing needle,
• conveyor means responsive to said detector means for moving the previously sewn work piece away from the sewing needles at a velocity greater than the rate at which the stitch is formed for applying tension to the thread chain extending between the previously sewn work piece and said sewing needles to require the thread chain to extend along the path,
• severing means responsive to said detector means for cutting the thread chain extending along the path from the sewing needles 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 from the sewing needles and causing the severed leading thread chain to recoil toward the sewing needles, and
• means for drawing off the free end of the severed leading thread chain extending from the sewing needles 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 passage through said chaining tongue including an open end adjacent the sewing area, and air induction means responsive to said detector means for inducing a stream of air to flow into said open end of said chaining tongue passage in timed relationship with the cutting of the thread chain, when by the free end portion of the leading thread chain extending from the sewing needles recoils from the severing means toward the chaining tongue and is drawn into the passage through the 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 to a previously sewn work piece, to a second work piece to eliminate any significant knot or thread chain at the leading edge of the second work piece, said method comprising the steps of:

• moving a first work piece along a sewing path of the sewing machine;
• forming an overlock stitch about a hollow chaining tongue with the sewing needles of the sewing machine in the first work piece as the first work piece moves through the sewing path and sewing off the first work piece to form a thread chain extending from the first work piece to the sewing needles;
• sensing the completion of sewing of the first work piece which has moved along the sewing path of the sewing machine;
• in response to sensing the completion of sewing the first work piece, drawing taut the thread chain extending from the first work piece to the sewing needles;
• 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 that recoils toward the hollow chaining tongue;
• drawing off the free end of the leading thread chain extending from the sewing machine needles into the hollow chaining tongue in such a manner as to cause the excess thread chain to extend below the sewing path of the sewing machine;
• continuing to form an overlock stitch with the needles of the sewing machine about the chaining tongue as the thread chain is drawn into the hollow chaining tongue,
• advancing the second work piece along the sewing path toward the sewing machine needles while the leading thread chain is drawn into the hollow chaining tongue until the second work piece is engaged in the sewing needles;
• simultaneously forming an overlock stitch in the second work piece and progressively oversewing the drawn off leading thread chain in the overlock stitch.

A method of sewing a portion of a thread chain, extending from the sewing needles and the hollow chaining tongue of a chain stitch sewing machine toward a previously sewn first work piece, to a second on-coming work piece to eliminate any significant thread knot or thread chain protruding from the leading edge of the second work piece, comprising the steps of:

• forming a chain stitch in the first workpiece and forming a thread chain extending from the first workpiece,
• cutting the thread chain to a predetermined length extending from the chaining tongue,
• stretching the thread chain away from the chaining tongue to a predetermined extent before the thread chain is cut so as to create a recoil of the cut end portion of the thread chain back toward the opening of the chaining tongue,
• applying a vacuum at a predetermined pressure range to an opening of the chaining tongue so as to form a uniform air flow into and through the chaining tongue during each cycle of operation of the sewing machine, and
• continuing the formation of the chain stitch about the chaining tongue after the cutting step is performed so that the thread chain is in motion at the opening of the chaining tongue as the thread chain recoils toward the opening of the chaining tongue.