Patent ID: 7497177

Claim:
A seam ravel preventing apparatus for preventing raveling at a sewing end portion of a seam, provided in a sewing machine for forming the seam by passing a looper, which advances from a right side of a needle drop position toward a left side, into loops of needle threads formed on a rear side of the needle drop position and intertwining a looper thread held by the looper with the needle threads, comprising: a looper thread hanging hook arranged on a right rear side of the needle drop position so that it can advance and retreat for catching the looper thread near an advance end of the looper when advancing to a left forward direction, and holding the looper thread at a position behind the needle drop position when retreating to a right backward direction; a thread cutting hook arranged on a right side of the needle drop position so that it can advance and retreat, and be inserted into the loops of the needle threads where the looper is passed when advancing to a left direction; a first hook section, provided at a tip of the thread cutting hook, for catching the looper thread near a tip of the looper when retreating to a right direction; a second hook section, provided in a middle of the thread cutting hook, for catching the needle threads and the looper thread held by the looper thread hanging hook on the rear side of the needle drop position when retreating to the right direction; a thread cutting knife for cutting the looper thread caught by the first hook section, and the looper thread and needle threads caught by the second hook section by coming into slide-contact with the first and second hook sections near a retreat end of the thread cutting hook; and a control unit for performing a ravel prevention operation by bringing the looper into an advance state just before an end of sewing, advancing and retreating the looper thread hanging hook to catch the looper, performing sewing for at least one stitch in this state, and then advancing and retreating the thread cutting hook to catch the looper thread with the first hook section, catch the looper thread and needle threads with the second hook section, and cut the threads respectively.