Method and apparatus for preventing a seam from raveling in double chain stitch sewing machine

A method for preventing a seam from raveling in a double chain stitch sewing machine having at least one needle moving vertically through which a needle thread is passed, and a looper through which a looper thread is passed, for forming a double chain stitch by collaboration of the looper thread and the needle thread, while the looper moves forward and backward between a forward position and a backward position across the needle, said method comprising the steps of:

• hooking and engaging a looper thread consecutive to the looper from a cloth by an engaging means when the looper is in an advanced state relative to the forward position near the sewing end point;
• cutting off the looper thread hooked and engaged on the engaging means in a state when the looper is moved backward to the backward position from the forward position as the sewing machine is driven;
• and
• cutting off a needle thread loop consecutive to the needle from the cloth through the looper at a position between the cloth and the looper in a state when the looper is advanced again from the backward position to the forward position as the sewing machine is driven.

A method for preventing a seam from raveling in a double chain stitch sewing machine having at least one needle moving vertically through which a needle thread is passed, and a looper through which a looper thread is passed, for forming a double chain stitch by collaboration of the looper thread and the needle thread, while the looper moves forward and backward between a forward position and a backward position across the needle, said method comprising the steps of:

• moving an engaging means into a triangular space of threads formed by a looper thread loop consecutive to the looper from a cloth and a needle thread loop engaged with the looper when the looper is in an advanced state relative to the forward position near the sewing end point;
• engaging and holding the looper thread loop of said thread triangular space by the engaging means as the sewing machine is driven;
• cutting off the looper thread loop held in the engaging means;
• and
• cutting off a needle thread loop engaged with the looper in a state when the looper is advanced again to the forward position.

An apparatus for preventing a seam for raveling in a double chain stitch sewing machine having a needle drop point disposed in a sewing machine bed, at least one needle moving vertically through which a needle thread is passed, and a looper through which a looper thread is passed, for forming a double chain stitch by collaboration of the looper thread and the needle thread, while the looper moves forward and backward between a forward position and a backward position across the needle, said apparatus comprising:

• looper thread engaging means for engaging a looper thread between the needle drop point and a leading end of the looper at its forward position;
• a looper thread cutter for cutting off the looper thread engaged with the looper thread engaging means in its engaging portion;
• needle thread engaging means for engaging a needle thread loop consecutive to the needle from a cloth through the looper at a position between the cloth and the looper;
• a needle thread cutter for cutting off the needle thread engaged with the needle thread engaging means in its engaging portion;
• and
• looper thread pulling means for pulling out an end portion of a cut looper thread left over at the looper side from a final needle thread loop formed in the cloth.

An apparatus for preventing a seam from raveling in a double chain stitch sewing machine having at least one needle moving vertically through which a needle thread is passed, and a looper through which a looper thread is passed for forming a double chain stitch by collaboration of the looper thread and the needle thread, while the looper moves forward and backward between a forward position and a backward position across the needle, said apparatus comprising:

• looper thread engaging means for moving into a triangular space of threads formed by a looper thread loop consecutive to the looper from a cloth and a needle thread loop engaged with the looper when the looper is in an advanced state to the forward position, and for engaging and holding the looper thread loop of said thread triangular space by moving the looper to backward position;
• a looper thread cutter for cutting off the looper thread loop held in said engaging means;
• and
• a needle thread cutter for cutting off a needle thread loop engaged with the looper in a state when the looper is advanced again to the forward position.