METHOD FOR PREVENTING RAVELING OF DOUBLE CHAIN STITCH SEAM, DEVICE FOR PREVENTING RAVELING OF SEAM IN DOUBLE CHAIN STITCH SEWING MACHINE, AND DOUBLE CHAIN STITCH SEAM STRUCTURE

摘要

PROBLEM TO BE SOLVED: To provide a method and device for preventing raveling of a double chain stitch seam which can surely and strongly prevent the occurrence of raveling of a single needle double chain stitch seam irrespective of the magnitude of tension applied to a needle thread and a looper thread.SOLUTION: The method prevents raveling of a double chain stitch seam formed by catching a needle thread loop 20a, which is formed below a needle plate by a needle, through the advance of a looper operable to be advanced and retreated in a direction substantially orthogonal to the vertical movement path of the needle, and by interlooping the needle thread loop with a looper thread 10. The method includes: after a normal sewing is finished with the looper set in an advanced state, maintaining a state in which the needle thread loop caught by the looper is held at a position which is closer to the advanced end of the looper than a needle lowering position until the needle lowers through the needle thread loop caught by the looper; and intralooping the needle thread loop with a needle thread held by the needle by releasing the position holding of the needle thread loop and performing a sewing operation for at least one stitch.